Endocrine disruptors

[Spook]

Endocrine Disrupting Chemicals

Environmental estrogens. Endocrine-disrupters. Endocrine-modulators. Ecoestrogens. Environmental hormones. Xenoestrogens. Hormone-related toxicants. Endocrine-active compounds. Phytoestrogens.

These terms describe endocrine disrupters, the synthetic chemicals and natural plant compounds that may affect the endocrine system (the communication system of glands, hormones and cellular receptors that control the body's internal functions). Many of these substances have been associated with developmental, reproductive and other health problems in wildlife and laboratory animals. Some experts suggest these compounds may affect humans in similar ways.

Endocrine disrupters alter hormonal functions by several means.

Substances can:

· mimic or partly mimic the sex steroid hormones estrogens and androgens (the male sex hormone) by binding to hormone receptors or influencing cell signaling pathways. Those that act like estrogen are called environmental estrogens.

· block, prevent and alter hormonal binding to hormone receptors or influencing cell signaling pathways. Chemicals that block or antagonize hormones are labeled anti-estrogens or anti-androgens.

· alter production and breakdown of natural hormones.

· modify the making and function of hormone receptors.

Environmental estrogens are the most studied of all the endocrine disrupters. Natural compounds capable of producing estrogenic responses, such as the phytoestrogens, occur in a variety of plants and fungi. Many synthetic chemicals that also mimic estrogen are commercially manufactured for a specific purpose or produced as a byproduct.

Exposure to these substances occurs throughout our lives from food, air, water, soil, household products and probably through breast milk and during development in our mother's womb. The human health risks that may be associated with these low-level yet constant exposures are still largely unknown and highly controversial.

Modes of Action

The endocrine disrupter story gets more and more complicated as new research findings are revealed. One of the biggest, and probably most complex, mysteries is how substances with different shapes and structures produce similar physiological results.

The most well studied effects are of compounds that simply bind to a hormone receptor and mimic or block normal hormone responses. It now appears that some environmental
hormones produce their effects via elaborate signaling pathways and other complex modes of action that are independent of binding hormone receptors.


Receptor Binding

Certain substances can mimic hormones by binding to specific hormone receptors inside cells.

One way foreign substances can mimic hormones is by binding to specific estrogen receptors inside a cell.

Receptors are protein molecules that read and respond to hormone signals. o,p’-DDT, some PCBs and many phytoestrogens bind to estrogen receptors. The process works something like this:

1. Natural hormones, in this case, estrogens (brown in upper left), travel through the bloodstream and enter cells (green circles) looking for estrogen receptors (yellow and black triangles).

2. Once inside the cell, the hormone binds to a protein receptor (like a key fitting a lock) and forms what is known as a “ligand-hormone receptor complex.” (A ligand is any molecule that binds to a specific site on a protein or other molecule. In this case, the hormone.) Hormones and their receptors have compatible, interlocking shapes, something like two puzzle pieces or a lock and key.

3. The binding activates the hormone receptor, which triggers specific cellular processes (like turning a car key which begins the cascading signals necessary to start the engine). The activated hormone receptor then turns on specific genes, causing cellular changes that lead to responses typical of a ligand-hormone receptor complex. In the case of estrogen, these responses can include uterine growth in preparation for pregnancy or prevention of bone loss. One way foreign substances can mimic hormones is by binding to specific estrogen receptors inside a cell. At one point, scientists thought only a specific hormone could trigger a specific receptor into action, just like how only one key opens only one lock.

Endocrine disrupters proved otherwise.

Foreign compounds (the blue drops), although different in shape from natural hormones, can travel in the bloodstream, enter a cell, bind with a receptor and trigger gene expression. It is as if the imposters pick the lock, open the door and fool the receptor into letting them inside. Once bound with the receptor, the mimicker can produce a normal hormone response, cause an abnormal response or elicit no response as it blocks the receptor site and prevents natural hormones from binding.


Other Modes of Action

Not all endocrine disrupters alter hormonal action by binding to hormone receptors. Some relay molecular messages through a complex array of cellular proteins that indirectly turn genes on and alter cell growth and division.

For instance, beta-hexachlorocyclohexane (beta-HCH) produced estrogen-like responses (cell division and growth) at levels found in human breast cancer tissue (2). The compound, which does not bind the estrogen receptor (1, 2), may promote DNA transcription, and thus produce estrogenic responses, by passing signals through a highway of hormone and nonhormone response elements that turn genes on (2).

In another study, p,p’-DDT, at or below levels found in human breast fat tissue, bypassed the estrogen receptor and stimulated a complex mixture of cell signaling proteins (growth factor receptors) and processes that eventually led to cell division (3). But, p,p’-DDT can also bind the androgen receptor and inhibit androgen binding (4). These results suggest that the same chemical can influence the endocrine system in more than one way.

The multiple signaling pathways initiated by beta-HCH and p,p’-DDT can lead to cell division by influencing the estrogen receptor without binding to it. If understood, these complex modes of action may be able to answer the questions of how different molecules impact the endocrine system and how pollutants may form and feed some types of tumors.


Confounding Factors

Several factors confound how environmental estrogens affect the endocrine system.

1. Natural estrogen production varies with gender, age and reproductive cycles. For instance, women produce more estrogen than men, estrogen is abundant during fetal development and post-menopausal women have very little estrogen. Thus, environmental estrogens may have different influences (mimicking, blocking or cancelling out estrogen's effects) depending on present estrogen levels.

2 Natural hormones are more potent than any of the known synthetic environmental estrogens (except drugs such as diethylstilbestrol (DES) and birth control pills).

3. Phytoestrogens, the natural plant compounds capable of acting like estrogen hormones, may produce opposing effects. At very high amounts, some cause infertility in farm animals and wildlife. Others seem to protect against breast and reproductive cancers in humans.

4. Combinations of certain synthetic compounds may have a synergistic effect (5). Two weakly estrogenic compounds can be more potent, or produce more effect, than one compound by itself.

5. Synthetic estrogens may also antagonize each other's effects. That is, a weakly anti-estrogenic compound may cancel out a weakly estrogenic compound and produce no effect (6).


References

1. Coosen, R. and F.L. van Velson. 1989. Effects of the beta-isomer of hexacholocyclohexane on estrogen-sensitive human mammary tumor cells. Toxicol. Appl. Pharmacol., 101:310-318.

2. Steinmetz, R., P.C.M. Young, A. Caperell-Grant, E.A. Gize, B.V. Madhukar, N. Ben-Jonathan, and R.M. Bigsby. 1996. Novel estrogenic action of the pesticide residue beta-hexachlorocyclohexane in human breast cancer cells. Cancer Research, 56:5403-5409.

3. Shen, K. and R.F. Novak. 1997. DDT stimulates c-erbB2, c-met and STATS tyrosine phosphorylation, Grb2-Sos association, MAPK phosphorylation and proliferation of human breast epithelial cells. Biochemical and Biophysical Research Communications, 231:17-21.

4. Kelce, W.R., C.R. Stone, S.C. Laws, L.E. Gray, J.A. Kempainen, and E.M. Wilson. 1995. Persistent DDT metabolite p,p’-DDE is a potent androgen receptor antagonist. Nature, 375:581-585.

5. Bergeron, J.M., D. Crews and J.A. McLachlan. 1994. PCBs as environmental estrogens: turtle sex determination as a biomarker of environmental contamination. Environmental Health Perspectives, 102:780-781.

6. Safe, S. 1995. Environmental and dietary estrogens and human health. Environmental Health Perspectives, 103:346-51.


Environmental Estrogen Effects

Wildlife/Human Effects

Many widely-used synthetic chemicals and natural plant compounds can alter or interfere with the endocrine system. These foreign substances have been associated with health and reproductive problems in wildlife and laboratory animals. Some believe these environmental compounds can affect human health, development and reproduction in similar ways, although this has not yet been scientifically proven.

These substances can affect the endocrine system in many ways. For example, some compounds, referred to as environmental estrogens, can mimic or act like estrogens, the hormones that control female characteristics. Many can block or cancel out hormone actions and are called anti-estrogens or anti-androgens (the male hormones). Other compounds can both mimic and block hormones. Still others known as environmental disrupters or modulators can alter how natural hormones and their protein receptors are made, are broken down and perform. And to complicate matters even more, many chemicals have distinct effects in different species and organs and at different developmental stages.

The Past To The Present

The idea that human-made chemicals have adverse health effects, including endocrine disruption, is not entirely new. In fact, a 1938 study found that certain synthetic chemicals could mimic estrogens (1). And, more than 30 years ago, Rachel Carson's book Silent Spring described how some synthetic chemicals were collecting in and contaminating water, soil, wildlife and even humans. These chemicals, she warned, were causing severe health problems (egg shell thinning, cancer, die offs) in wildlife, especially in species at the top of the food chain that eat other contaminated animals and accumulate the most chemicals.

It was Rachel Carson that alerted the world to the adverse health effects from pollutants. And it has been the decades of scientific research since her warnings that has helped scientists begin to understand the processes of how these substances affect health. The research has:

· helped identify and restrict use of the most harmful chemicals,

· started to decipher how these substances can interfere with hormones and lead to health problems, and

· broadened the definition of toxic chemical exposure, measured mainly by their ability to cause cancer, to include reproductive and developmental health problems.

In response to this research, some of the most dangerous chemicals, such as DDT and PCBs, have been banned in the U.S. and Europe. Chemical manufacturers continue to replace the more persistent chemicals with shorter-lived ones that will not accumulate in soil, water, wildlife or our bodies.

Wildlife Effects

1. Many different kinds of synthetic chemicals are found all over the world because they are widely used, do not easily breakdown and are carried to other places by air, water and animals. The chemicals, or sometimes their more harmful breakdown products, are found in soil, water, plants and animals everywhere from the South Pole to the North Pole.

2. Animals, including humans, can and do accumulate some of these chemicals in their fat and often pass them along to offspring and predators.

3. At high doses, some of these chemicals can affect an animal's endocrine system, especially during critical developmental stages. Studies of laboratory animals, cell cultures, wildlife and human's accidentally exposed show that these chemicals may in some cases cause reproductive and developmental problems. For instance:
· Male fish living near municipal sewage outlets in England had both male and female sex characteristics and their livers produced vitellogenin, a female egg-yolk protein not normally found in males (2). The fish living close to the sewage outlet had severe abnormalities while the fish living farther downstream had less severe symptoms. Several different chemicals, especially the alkylphenols, the breakdown products of chemicals found in detergents and plastics, are suspected of causing the feminizing effects.

· Alligators living in Florida's Lake Apopka were exposed to the estrogenic pollutants dicofol, DDT and its metabolites, DDD, DDE and chloro-DDT, when a nearby chemical plant had an extensive spill in 1980. Ten years later, researchers trying to find out why alligator populations were dropping in the Lake, found higher than normal mortality among eggs and newborn alligators. They also found that adolescent females had severe ovarian abnormalities and had blood estrogen levels two times higher than normal. The male juvenile alligators were feminized, that is, they had smaller than normal penises, had abnormal testes and had higher estrogen levels and lower testosterone levels in their blood than normal males of the same age. The researchers concluded that chemicals from the spill not only killed developing eggs outright but also altered the embryo's endocrine system (hormone levels and sexual development), which severely limited the alligator's ability to reproduce (3a, b).

· Daughters of mothers who took the synthetic estrogen DES (diethylstilbestrol) during pregnancy to prevent miscarriage have higher rates of reproductive problems, reproductive cancer (vagina, cervix) and malformed reproductive organs (uterus, cervix) (4). Sons may also face higher rates of malformed or small penises, undescended testicles and abnormal sperm (5). However, a recent study found no evidence of reduced fertility in DES sons (6).
· DES is not only a potent estrogen, similar in strength to the natural estrogen estradiol, but it also has the unique ability to concentrate in target tissues, such as the reproductive tracts of birds, reptiles and other animals, during development and cause abnormalities. This drug serves as an example of what potent estrogenic compounds can do and may illustrate the health effects that other environmental estrogens can produce.
· Considerable controversy surrounds a study that found that sperm counts in men were falling worldwide, that rates of testicular cancer were increasing and that environmental estrogens may be responsible for these trends (7). Other studies do not support all of these findings and suggest that lower fertility and high cancer rates may only occur in certain human populations. (8)

4. Fetuses and embryos, whose growth and development are highly controlled by the endocrine system, seem especially vulnerable to exposure, as detailed in the previous examples (9). Mothers can pass contaminants to their offspring prenatally in eggs (amphibians, reptiles, birds) or the womb (mammals) and after birth by breastfeeding newborns. So, even though adult animals exposed to contaminants may not show any ill effects, their offspring may have lifelong health and reproductive abnormalities including reduced fertility, altered sexual behavior, lowered immunity and even cancer.

Studies looking at mammals, reptiles, birds and fish, as well as laboratory studies using rodents, primates and cultured cells, have linked exposure of a developing embryo to environmental contaminants with many permanent health effects in the adult. These effects include:
· abnormal blood hormone levels;
· reduced fertility;
· altered sexual behavior
· modified immune system
· masculinization of females;
. feminization of males (reduced testes and penis size);
· undescended testicles;
· cancers of the female and male reproductive tract;
· malformed Fallopian tubes, uterus and cervix
· altered bone density and structure.

Uncertain Human Health Effects

Although no one knows exactly how or to what extent environmental estrogens affect human health, there is considerable concern because the endocrine system is so important to our well-being. The reproductive hormones, such as estrogens, regulate the growth, reproduction, metabolism and even immunity that guide physical development, maintain reproductive cycles and ensure balance of normal body systems.

Because many of these synthetic chemicals are suspected of acting like natural estrogens, the most likely health problems would be related to sexual development, reproduction, and breast and reproductive cancers. In females, estrogens, mainly the hormone estradiol, foster development of female characteristics (breasts, no facial hair, behavior), protect bone strength and the cardiovascular system, regulate liver metabolism, influence ovarian and menstrual cycles, stimulate uterine growth and maintain pregnancies. In males, estrogens play a secondary role to androgens, mainly the hormone testosterone, which defines male characteristics and aids sperm production. But, when the ratio of estrogen to testosterone is increased, feminization can occur.

Given all of this, human health effects associated with exposure to environmental estrogens are mostly unknown and highly controversial. Aside from the drug DES, environmental estrogens have never been proven to cause human health problems, so we can only speculate on possible human health effects documented from animal studies:

For women:

Breast and reproductive organ tissue cancers, fibrocystic disease of the breast, polycystic ovarian syndrome, endometriosis, uterine fibroids and pelvic inflammatory diseases. These may be influenced by developmental or chronic lifetime exposure to estrogen mimics.

For men:

Poor semen quality (low sperm counts, low ejaculate volume, high number of abnormal sperm, low number of motile sperm), testicular cancer, malformed reproductive tissue (undescended testes, small penis size), prostate disease and other recognized abnormalities of male reproductive tissues.

As with any potential health risk, many factors such as length of exposure, dose, age and individual differences will influence the kinds and severity of health problems experienced. That is, one person may experience many problems while another may experience none.

Future Research

We still don't know much about how environmental estrogens affect health in humans and other animals. More research is needed to learn what we don't know. For instance, we don't know:

1. How many synthetic chemicals act like natural hormones?

Certain chemicals have been identified as environmental estrogens through laboratory assays, but with virtually thousands of synthetic chemicals already introduced into the environment and many new ones developed yearly, most remain untested. There is a great need for rapid and reliable testing systems.

2. What levels of exposure over what time frames will cause adverse effects?

No one is even sure how much exposure each of us faces on a daily or lifetime basis. There is a need for biomarkers to evaluate human exposure.

3. What is the effect of exposure to multiple chemicals?

In other words, how do pollutants react with each other outside and inside the body? Does exposure to a range of chemicals at a low dose have the same or greater effects as exposure to one chemical at a high dose? Do chemical's in a mixture cancel out each other's effects? Are the effects additive or synergistic (greater than additive)? Recent research suggests synergistic effects (10) but more information is needed.

4. Are they sequential?

For example, does exposure to one chemical predispose, or make an animal more sensitive to, subsequent chemicals? In the case of diethylstilbestrol (DES), the drug predisposes animals to an altered response to endogenous estrogens that may contribute to the development of cancer.


References1. Dodds, E.C. and W. Lawson. 1938. Molecular structure in relation to oestrogenic activity. Compounds without a phenantrene nucleus. Proceedings of the Royal Society of London (Series B), 118:222-232. 2. Jobling J.S. and J.P. Sumpter. 1993. Detergent component in sewage effluent are weakly oestrogenic to fish: An invitro study using rainbow trout (Oncorynchus mykiss) hepatocyctes. Aquatic Toxicology. 27:361-72. 3. a. Guillette, L.H. Jr. 1995. Endocrine disrupting environmental contaminants and developmental abnormalities in embryos. Human and Ecological Risk Assessment 1(2):25-36. 3. b. Guillette, L.H. Jr., T.S. Gross, G.R. Masson, J.M. Matter, H.F. Percival and A.R. Woodward. 1994. Developmental abnormalitiies of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida. Environmental Health Perspectives 102(8):680-688. 4. Nollar, K.L., P.C. O'Brien, T. Colton, R. Kaufman and L.J. Melton. 1990. Medical and surgical diseases associated with in utero exposure to diethylstilbesterol. ed. K.L. Nollar. Clinical Practice of Gynocology. New York: Elsevier Science Publishing Co. Inc., pp 1-7. 5. Gill, W.B., G.F.B. Schumacher and M. Bibbo. 1976. Structural and functional abnormalities in the sex organs of male offspring of mothers treated with diethylstilbestrol (DES). Journal of Reproductive Medicine, 16:147-153. 6. Raloff, J. 1995. DES sons face no fertility problems. Science News 147:324. 7. Sharpe, R.M. and Shakkebaek. 1993. Are oestrogens involved in falling sperm counts and disorders of the male reproductive tract? Lancet 341:1392-1395. 8. Fisch, H. and Goluboff. 1996. Geographic variations in sperm counts: A potential cause of bias in studies of semen quality. Fertility and Sterility 65:1044-1046. 9. Bern, H. 1992. The fragile fetus. In: Chemically-induced Alterations in Sexual and Functional Development: The Wildife/Human Connection, pp. 9-15. Eds T. Colborn and C. Clement. Vol 21. Princeton. NJ:Princeton Scientific Publishing Co. 10. Bergeron, J.M., D. Crews and J.A. McLachlan. 1994. PCBs as environmental estrogens: turtle sex determination as a biomarker of environmental contamination. Environmental Health Perspectives, 102:780-781.


Environmental Estrogen Sources

Where Are Environmental Estrogens Found? Substances that act like estrogen hormones in living organisms are called environmental estrogens. These compounds are found all around us. Some, called phytoestrogens, occur naturally in plants such as clover, soybeans and other legumes, whole grains and many fruits and vegetables. Others are synthetic chemicals made commercially for a specific purpose or produced as a byproduct of manufacturing processes. We eat them, drink them, breath them and use them at work, at home and in the garden. They are present in soil, water, air and food. And although environmental estrogens are everywhere, scientists aren't sure how much we are exposed to and how that exposure affects us. Humans and other animals have a long history with phytoestrogens but a very short one with human-made environmental estrogens. Since the turn of the century, manufacture and use of synthetic chemicals have rapidly increased. So too has our exposure to them. These estrogenic chemicals, which differ from phytoestrogens in many ways, are found in (1): · pesticides (insecticides such as o,p'-DDT, endosulfan, dieldrin, methoxychlor, kepone, dicofol, toxaphene, chlordane; herbicides such as alachlor, atrazine and nitrofen; fungicides such as benomyl, mancozeb and tributyl tin; nematocides such as aldicarb adn dibromochloropropane); · products associated with plastics (bisphenol A, phthalates); · pharmaceuticals (drug estrogens - birth control pills, DES, cimetidine); · ordinary household products (breakdowns products of detergents and associated surfactants, including nonylphenol and octylphenol); · industrial chemicals (polychlorinated biphenyls (PCBs), dioxin and benzo(a)pyrene); and · heavy metals (lead, mercury, and cadmium). Chemical Structures Environmental estrogens cannot be identified by structure alone because they come in all shapes and sizes. This makes it hard to predict which natural and synthetic chemicals will act like estrogenic hormones in living organisms. Identification is especially difficult because the chemicals' effects are so variable; they can either mimic estrogen, block estrogen or exhibit distinct estrogen-like behavior. Note the structural differences and similarities in the following examples of proven environmental estrogens.
17ß-EstradiolThe most potent natural estrogen hormone in humans and animals. Diethylstilbestrol (DES)A pharmaceutical estrogen banned from use in the 1970s.


CoumestrolA phytoestrogen - a natural plant compound with some estrogenic tendencies. o,p'-DDTA synthetic pesticide constituting between 10 and 25 percent of technical DDT. DDT is banned in many countries but is still used extensively in equatorial countries to control mosquitoes and malaria.


4-nonylphenol (NP)A breakdown product of detergents that are widely used in household products, in agricultural and industrial applications, and in plastics manufacturing. Nonylphenols are found in natural water bodies, sewage sludge and river sediments. Kepone (chlordecone)A synthetic pesticide banned in the U.S.

Chemical Exposure We are all directly exposed to some environmental estrogens through our diet and industrial and household products including detergents, drugs, lubricants, cosmetics, pesticides and plastics. Indirect exposure occurs when chemicals are released into the air and water. For instance, airborne ash from industry or hazardous waste incinerators can land on grass or hay, be eaten by livestock and passed along to humans (probably a minor source of contact). Drinking water may also be contaminated by chemicals and their breakdown products found in industrial discharge and sewage effluent. Some proven environmental estrogens used as pesticides, most notably o,p'-DDT, toxaphene and dicofol, have been banned from use in most western industrial countries but are still used in many developing nations. Other proven estrogenic compounds are still being used worldwide in plastics manufacturing (phthlates) and to combat "pest" plants and insects (endosulfan). Even though some of the more harmful substances have been banned in certain areas, we are all still vulnerable to their effects because they and their breakdown products remain in our environment. Our bodies carry some of these chemicals in fat and tissue and can pass them along to our children during pregnancy and breastfeeding. Soil, water and animals remain contaminated with some of these persistent pollutants. For instance, DDD and DDE, breakdown chemicals of the highly chlorinated organic compound DDT, are found worldwide. The air-born pollutant toxaphene, a pesticide banned in the U.S. since 1982, persists in soil, the fat tissue of seals and Baltic salmon and in places like the Artic and Scandinavia where it was never even used (2). There is no doubt we are all exposed to some environmental estrogens. Whether or not the accumulated amounts are enough to produce long-term health problems is still unknown. References1. DeRosa, C., P. Richter, H. Pohl, and D.E. Jones. 1998. Environmental exposures that affect the endocrine system: Public health implications. Journal of Toxicology and Environmental Health, Part B. 1:3-26.2. Zhu, J. and R.J. Norstrom. 1993. Identification of polychlorocamphenes (PCCs) in the polar bear (Ursus maritimus) food chain. Chemosphere 27:1923-36.


Environmental Estrogens Differ From Natural Hormones
Environmental Estrogens Differ From Natural Hormones"Environmental estrogens," the plant compounds and synthetic chemicals that can act like estrogen hormones differ from natural hormones, the messenger molecules secreted by the endocrine system. OriginAll animals (including humans) release messenger molecules called hormones into their bloodstream and into the fluid surrounding their cells. These potent molecules help regulate many immediate and long-term responses such as dealing with stress, growing taller or developing male or female characteristics. For example, estrogens (especially estradiol), the female sex hormones, bring out the feminine traits, control reproductive cycles and pregnancy, and influence skin, bone, the cardiovascular system, immunity and even the brain. Environmental estrogens are a diverse group of synthetic chemicals and natural plant compounds that may act like estrogen hormones in animals and humans. Although most are weaker than natural estrogens, some have been associated with reproductive and developmental problems in wildlife and laboratory animals. Many estrogenic contaminants are produced for specific purposes and are used in pesticides, plastics, electrical transformers and other products. Other substances are generated as a byproduct during manufacturing or are breakdown products of some other chemical. Some, like diethylstilbestrol (DES), are drugs, while others are natural plant compounds called phytoestrogens. BreakdownNatural hormones are short-lived, do not accumulate in tissue and are easily broken down by our bodies. Most natural estrogens stay in the bloodstream only minutes or at most a few hours (1). After that, enzymes in the liver break the hormones into pieces. These pieces are either flushed out as a waste product or reused to build other molecules. The same holds true for phytoestrogens: they are easily broken down by our bodies, they spend very little time in our system, and they are not stored in fat or tissue. When eaten, these plant compounds are either flushed out intact or after being broken apart or are further changed and absorbed into the body where they can act like estrogens. Although opinions vary about their benefits, the health effects associated with phytoestrogens are influenced by the age of the individual during exposure (for instance, fetus, child or adult) and the length and concentration of exposure. The estrogenic drugs, such as ethynylestradiol found in birth control pills, are more stable and remain in the body longer than natural estrogens, like estradiol. However, they are not nearly as persistent as pesticides and other environmental estrogens. In contrast to natural estrogens, phytoestrogens and estrogenic drugs, synthetic environmental estrogens: · are not easily or readily broken down. · are long-lived, remaining intact in the environment and in living organisms for many years. · can accumulate in the natural world and within the fat and tissue of animals and humans. Upon exposure, some of these estrogenic chemicals can be either flushed out of the animal or a portion can be absorbed into the body where they can collect (or bioaccumulate) in fat and muscle. Because most are lipophilic - meaning they "like" or prefer to be surrounded by fat molecules rather than water molecules - they tend to congregate in fatty tissue and stay there for years. As organisms age, they collect and store more and more of these synthetic compounds. During stress, pregnancy or breast feeding, these substances can be released from fat and redistributed or passed on to offspring. The compounds can also be passed on through the food chain, collecting in top of the chain predators like humans, eagles and panthers. Several recent studies clearly show the global distribution of these estrogen-like pollutants and demonstrate the ability of these chemicals to collect and persist in the environment. 1. Samples of wildlife blood contained total DDT concentrations of 1 ng per milliliter (2) - a level about 1,000 times higher than concentrations of free estradiol (a natural estrogen hormone) in blood (3). Such high levels of contaminants are frequently found in wildlife, documenting that living creatures do incorporate these substances. 2. More than one study has found that polar bears, seals and humans living away from industrialized areas in the relatively pristine Artic have significantly elevated levels of many different pesticides and industrial waste products (4). This demonstrates the global distribution and impact that these chemicals have. Molecular Structure In most cases, the chemical structures of natural hormones and the synthetic environmental estrogens are strikingly different. Chains of carbon rings form the backbone of the sex steroid hormones (estrogens, androgens, progestins). Each hormone differs only in the location and number of attachments to the main stem. 17ß-Estradiol, the molecule on the right, is the most potent natural estrogen hormone in humans and animals. Only a small amount is needed to produce female characteristics and maintain reproductive cycles. Environmental estrogens, on the other hand, come in all shapes and sizes. In fact, scientists cannot look at a structure and predict if that chemical will behave like an estrogen. Many of the compounds have carbon rings stacked in various ways (polycyclic or many rings). Some have chlorine atoms or other side chains extending off the main structure. Still others contain no rings or chlorine. To illustrate the variety, compare the structures of the hormone estradiol with the proven estrogenic substances DES, coumestrol, PCB, o,p'-DDT and nonylphenol. Note that many of the polychlorinated biphenyls (PCBs) look like eyeglasses. Two 6-sided carbon rings (the lenses) are joined by a bond (the nose bridge) that connects one carbon from each ring. Different PCBs vary in the placement and number of chlorine atoms attached to the basic eyeglass structure. PCBs were used for a variety of purposes including electrical transformers and capacitors. Although their use is now severely restricted, PCBs are still found in older electrical stations and other machinery. The 209 different PCBs differ greatly in their estrogenic potency. Most PCBs do not readily degrade, and they accumulate in marine animals, birds and mammals (5).
Diethylstilbestrol (DES)A potent pharmaceutical estrogen. CoumestrolA phytoestrogen - a natural plant compound with some estrogenic properties.


o,p'-DDTA synthetic pesticide constituting between 10 and 25 percent of manufactured DDT. DDT is banned in many countries but is still used extensively in some places, (mostly equatorial regions such as Mexico, China, South America, Africa, Indonesia), to reduce malaria by controlling mosquitoes. Where used, the pesticide is mostly applied to specific areas and in lower concentrations than in the past. PCBs4-hydroxy, 2', 4', 6'-trichloro biphenyl. The 209 different PCBs have varying levels of estrogenicity. PCBs were used in electrical transformers and cooling systems. Many countries have restricted their use.


4-nonylphenol (NP)A breakdown product of some detergents that are widely used in household products and in agricultural and industrial applications, such as pesticides and plastics manufacturing. Nonylphenol is found in sewage sludge, stream sediments and some drinking water supplies.

FunctionThe structural differences between natural hormones and environmental estrogens may lead to functional differences. Natural sex hormones (estrogens or androgens) travel in the bloodstream searching out compatible receptor sites located in the nucleus of a cell. The hormones enter the cell, lock onto a specific receptor and turn on specific genes on the DNA. The genes tell the cell to make new proteins or other substances that can change cell functions (grow, divide or make more enzyme). Unlike some hormones that act in seconds or minutes, this process takes hours to complete. For example, in the days before a women ovulates (or releases an egg from an ovary), estrogen binds with specific receptor sites inside the cells of the uterus and turns on genes that cause the cells to grow thicker (proliferate). This process is the first step in preparing the uterus for pregnancy. Although natural steroid hormones generally function by binding to specific receptor sites, synthetic environmental estrogens can affect the hormonal system in a number of different ways. They can interact directly with hormone receptors where they can have some, little or very different effects than natural estrogens. The chemicals can even block normal hormone action. Current theories on how environmental estrogens interact with the endocrine system include: 1. Ecoestrogens can bind to specific receptor sites inside the nucleus of a cell and · mimic or evoke a proper hormone response, · block or inhibit a proper hormone response, · both mimic and block hormones (PCBs do both), · elicit a weaker or a stronger hormone response, or make a totally new response. 2. Ecoestrogens can bind to other receptors and create a novel reaction or interfere indirectly with normal hormonal action. 3. Ecoestrogens can alter production and breakdown of hormone receptors and natural hormones, which changes hormonal blood concentrations and endocrine responses. Both natural estrogens and environmental estrogens can bind to hormone receptors, something akin to a key fitting a lock or a hand slipping into a glove. As shown, several normal and abnormal responses can occur when an imposter binds with an estrogen receptor. References1. Tait, J.F. and S.A.S. Tait. 1991. The effect of plasma protein binding on the metabolism of steroid hormones. Journal of Endocrinology, 131:339-357. 2. Thomas, K.B. and Colborn. 1992. Organochlorine endocrine disrupters in human tissue. In T. Colborn and C. Clement (Eds.) Chemically-induced Alterations in Sexual and functional Development: The Wildlife/Human Connection (pp. 365-394) (Princeton Science Publishing Company Inc., Princeton, New Jersey, 1992). 3. Mendel, C.M. 1989. The free hormone hypothesis: A physiologically based mathematical model. Endocrine Review, 10:232-274. 4. Cameron, M7810. and I.M. Weis. 1993. Organochlorine in the country food diet of the Belcer Island Inuit, Northwest Territories, Canada. Artic 46:42-48. Zhu, J. and R.J. Norstrom. 1993. Identification of polychlorocamphenes (PCCs) in the polar bear (Ursus maritimus) food chain. Chemosphere 27:1923-36. 5. Male Reproductive Health and Environmental Chemicals with Estrogenic Effects. Miljoprojekt, 290. (Ministry of Environment and Energy, Danish Environmental Protection Agency, Copenhagen, 1995). ISBN: 87-7810-345-2.


Phytoestrogens
Phytoestrogens Many different plants produce compounds that may mimic or interact with estrogen hormones in animals. At least 20 compounds have been identified in at least 300 plants from more than 16 different plant families (1). Referred to as phytoestrogens, these compounds are weaker than natural estrogens and reside in herbs and seasonings (garlic, parsley), grains (soybeans, wheat, rice), vegetables (beans, carrots, potatoes), fruits (date, pomegranates, cherries, apples) and drink (coffee). Most of us are exposed to many of these natural compounds through food (fruits, vegetables, meat). The two most studied groups of phytoestrogens are the lignans (products of intestinal microbial breakdown of compounds found in whole grains, fibers, flax seeds and many fruits and vegetables) and the isoflavones (found in soybeans and other legumes). Because scientists have found phytoestrogens in human urine and blood samples, we know that these compounds can be absorbed into our bodies. In fact, phytoestrogens can have one of several fates after being eaten: they can be excreted; they can be absorbed into our bodies; or they can be broken down into other compounds that can also be potent phytoestrogens. Whatever their destiny, phytoestrogens differ remarkably from synthetic environmental estrogens in that they are easily broken down, are not stored in tissue and spend very little time in the body. All in all, there are differing opinions about phytoestrogens' role in health. When consumed as part of an ordinary diet, phytoestrogens are probably safe and may even be beneficial. In fact, some studies on cancer incidences in different countries suggest that phytoestrogens may help protect against certain cancers (breast, uterus and prostate) in humans. On the other hand, eating very high levels of some phytoestrogens may pose some health risks. Reproductive problems have been documented in laboratory animals, farm animals and wildlife that ate very high (up to 100% of their diet) amounts of phytoestrogen-rich plants. Even though humans almost never eat an exclusive diet of phytoestrogen-rich foods (even vegetarians), those who consume uncooked soy or pop photoestrogen pills as a natural therapy may be exposing themselves to some health risks. Many natural compounds, especially hormones, can be potent and can have both good and bad health affects, depending on how much of it is in the body. These substances should always be used in moderation to avoid any unintentional health consequences. Possible Health BenefitsRecent recearch (outlined in the article Phytoestrogens: Friends or foes? may help to identify potential health benefits and shed some light on how plant compounds protect against certain diseases. Phytoestrogens have been investigated as possible cancer preventatives and as treatments for menopause and osteoporosis (2). Laboratory animal experiments and comparisons of Asian and Western human populations suggest that diet has a large role in these types of health problems. One study found that Asian populations that eat large amounts of soy products - which contain high levels of phytoestrogens - have lower rates of hormone-dependent cancers (breast, endometrial) and a lower incidence of menopausal symptoms and osteoporsis than do Westerners, who don't traditionally eat these products. Asian immigrants to Western nations also increase their risks of these maladies as they Westernize their diets to include more protein and fat and reduce their fiber and soy (2). Even short-term exposure to phytoestrogens may offer some long-term protection against some cancers, including breast, colon, prostate, liver and leukemia. According to some animal studies, phytoestrogens (mostly the soy-based compounds) eaten as part of an adult diet can protect against some types of cancer and may even inhibit tumor growth. Another animal study found that newborn rats injected with genistein (an isoflavone found in soy products) and then exposed to a cancer-causing agent later in life developed fewer tumors and waited longer to develop them than the nonexposed rats (2). Gaining these possible benefits may involve more than just eating more soy products. Asians, for instance, have been eating these compounds for thousands of years and may have evolutionary adaptations that allow them to use phytoestrogens to their advantage. And, some plant and soy products contain other potential anti-cancer substances (such as protease inhibitors and antioxidants) that may also be responsible for some of the health benefits (3). Evaluating health effects of phytoestrogens is difficult and depends on: · the kind and dose (amount) of phytoestrogens eaten, and · the age, gender and health of the person. For instance, the very foods that may interfere with the endocrine messaging centers during a baby's development may help protect against breast and prostate cancer in adults. Why? There is strong evidence that a high lifetime exposure to natural estrogens, such as estradiol, increases the risk of certain kinds of cancer, such as uterine cancer. Phytoestrogens may help reduce that risk because they may lower a person's lifetime exposure to natural estrogens by competing for estrogen receptor sites or changing the way natural estrogens are broken down. These endocrine interferences can reduce a person's exposure to natural estrogens thus reducing the cancer risk to steroid hormone target tissues (mostly reproductive organs). Possible Health Risks As for adverse health effects, the most likely risks associated with phytoestrogens deal with infertility and developmental problems (2). However, it is thought that very large amounts of dietary phytoestrogens would be needed to realize these risks. Humans have used plants for medicinal and contraceptive purposes for eons. According to modern-day analyses, many of the plants historically noted for their ability to prevent pregnancies or cause abortions contain phytoestrogens and other hormonally-active substances. For instance, during the fourth century BC, Hippocrates noted that the wild carrot (now known as Queen Anne's lace) prevented pregnancies (4). Its seeds, we now know, contain a chemical that blocks progesterone, a hormone that is necessary for establishing and maintaining pregnancy. More recent research shows that phytoestrogens can affect the fertility of animals that eat them. This is especially true when phytoestrogens represent the bulk of the diet, but this rarely the case for humans. Some examples from the animal world follow. · Phytoestrogens in dry, summertime grasses reduced the number of offspring in wild populations of California quail (5) and deer mice (6). · Australian sheep suffered from reproductive problems and infertility after grazing in pastures with the phytoestrogen-containing clover Trifolium subterraneum (7). Two phytoestrogen compounds, equol and coumestrol, were identified as the culprits. Overall, there is little known about the developmental health effects of phytoestrogens. Some researchers express concerns about exposure of unborn fetuses to high levels of these compounds because development is highly controlled by the hormones of the endocrine system. Some animal studies, mostly using relatively high amounts of the compounds during critical times of development, do suggest adverse effects. · Rat pups, exposed to high doses of the plant estrogen coumestrol (found in sunflower seeds and oil and alfalfa spouts) through their mother's milk, suffered permanent reproductive problems: female pups when grown did not ovulate, and males had altered mounting behavior and fewer ejaculations (8). · Neonatal and immature rats exposed to coumestrol experienced estrogen-related responses, such as premature estrous cycles. Coumestrol also interrupted ovarian cycles in adult female rats (2). · Newborn rats exposed to the phytoestrogen genistein (a compound found in soy products), experienced altered hormone secretions and the onset of puberty may have been delayed because female rats were exposed to the compound as fetuses (2). Phytoestrogens behave like hormones, and like any hormone, too much or too little can alter hormone-dependent tissue functions. Taking too much of any hormone may not be good for a human or an animal. Similarily, too many phytoestrogens, at the wrong time, may have some adverse health effects. The studies listed above, which cannot be directly applied to humans, can help us to define what dietary levels are safe and clarify the possible reproductive and developmental risks associated with phytoestrogens. An Explanation Some scientists believe that plants make phytoestrogens as a defense mechanism to stop or limit predation by plant-eating animals (9, 10, 11). Instead of protecting themselves with thistles or thorns or tasting bad, these plants use chemicals that affect the predatory animal's fertility. Although using estrogen-mimicking compounds for protection may sound far-fetched, it makes sense from an evolutionary stance. Many real-life examples support the theory that plants and animals change together, or co-evolve, over time. The explanation goes something like this: to avoid predation, plants produce compounds (phytoestrogens) that limit a herbivores reproduction. Thus, the predator's population decreases and more plants prosper. But remember, because of genetic differences, not all species or individuals of a given species will react to the phytoestrogens in the same way. While some herbivores may show fertility problems, others may acquire resistance - like some insects are resistant to pesticides and some bacteria that can survive antibiotics. Likewise, some humans may be more susceptible to the benefits and risks of phytoestrogens than others would be. References1. T. Colborn, D. Dumanoski and J.P. Myers. 1996. Our Stolen Future, p. 76. New York: Penguin Books. 2. Barrett, J. 1996. Phytoestrogens: Friends or foes? Environmental Health Perspectives 104:478-82. 3. Makela, S., R. Santti, L. Salo and J.A. McLachlan. 1995. Phytoestrogens are partial estrogen agonists in the adult male mouse. In Estrogens in the Environment (Proceedings Estrogens in the Environment, III: Global Health Implications). Environmental Health Perspectives 103(Supplement 7):123-127. 4. Riddle, J.M. 1994. Contraception and Abortion from the Ancient World to the Renaissance. Boston: Harvard University Press. 5. Leopold, A.S., M. Erwin, J. Oh and B. Browning. 1976. Phytoestrogens: Adverse effects on reproduction in California quail. Science 191:98-100. 6. Berger, P.J., E.H. Sanders, P.D. Gardner and N.C. Negus. 1977. Phenolic plant compounds functioning as reproductive inhibitors in Microtus montanus. Science 195:575-577. 7. Bennetts, H.W., E.J. Underwood and F.L.A. Sheir. 1946. A specific breeding problem of sheep on subterranean clover pastures in Western Australia. Australian Veterinary Journal 22:2-12. 8. Whitten, P., C. Lewis and F. Naftolin. 1993. A Phytoestrogen diet induces the premature anovulatory syndrome in lactationally exposed female rats. Biology of Reproduction 49:1117-21. 9. Ehrlich, P. and P.H. Raven. 1964. Butterflies and plants: A study of coevolution. Evolution 18:586-608. 10. Guillette, L.J. Jr. 1995. Endocrine disrupting environmental contaminants and developmental abnormalities in embryos. Human and Ecological Risk Assessment 1(2):25-36. 11. Hughes, C. 1988. Phytochemical mimicry of reproductive hormones and modulation of herbivore fertility by phytoestrogens. Environmental Health Perspectives 78:171-75.


Gathering Evidence Using The Scientific Process
The Scientific Process How do we know that certain synthetic chemicals, referred to as environmental estrogens, can disrupt human and animal endocrine functions and affect the health of living organisms? What methods are used to determine the health effects that environmental estrogens may have on wildlife and humans? Science provides a way to answer these and other mysteries of endocrine disrupting chemicals. The goal in science is to gather information or evidence that supports, explains or disproves an original prediction or hypothesis. Enough evidence may explain the biological or physical event in question. The science process, also known as the scientific method, formed from our ancient curiosity to understand ourselves, the world and the universe. Good science, though, is more than just curiosity about the natural world. Researchers depend on their interest, creativity, imagination and logic. They also use and rely on the scientific method, which involves: · developing an idea by questioning or wondering how something works, · forming a hypothesis (a prediction or an explanation that answers the question), · testing the prediction (designing and running experiments), and · forming a conclusion (analyzing and publishing results). For instance, James Watson, Francis Crick and Maurice Wilkins used the scientific method to piece together the chemical structure and double-helix shape (two spiral staircases twisted together) of DNA, or deoxyribonucleic acid. Studying earlier chromosomal and x-ray diffraction studies helped them form a hypothesis. Years of experiments tested and confirmed their double-helix prediction, which won the 1962 Nobel Prize for physiology and medicine and led to modern genetics. Skepticism Is Built-InSkepticism and flexibility are also part of the scientific process. The wrong conclusions may be drawn, vital information may be overlooked or experiments may be faulty. That's why researchers are usually skeptical of new findings and have several checks and balances to ensure that scientific quality prevails. Research findings are usually peer reviewed, or scrutinized by other experts in the field, before the results are published. Scientists also present data to other experts at scientific meetings where healthy skepticism abounds. Once the research is publicized, working scientists debate the data at scientific meetings, in scientific journals and through the media. Sometimes, other scientific groups repeat (replicate) the experiments to validate results. If the research holds up to scrutiny, the scientific process is flexible enough to embrace the new conclusions and modify or change theories to more accurately represent what is now known about the subject. This happens all the time. For example, the discovery of microscopic spores and eggs in the 17th century explained how maggots got into decaying flesh, putting an end to the theory of spontaneous generation (animals and plants emerge spontaneously from other matter). In the early 1970s, geologists replaced all other theories and embraced the theory of plate tectonics as a plausible explanation for continental drift and other seismic activity. The discovery that the chromosomes carried genetic information in the pattern of DNA's (deoxyribonucleic acid) nucleotide subunits (made up of sugars, phosphates and nitrogen-containing base rings) revolutionized the field of genetics and replaced the belief that chromosomes were made from protein. In some cases, the research doesn't hold up and ideas are abandoned. For instance, in 1989, two chemists declared they had done something that nobody thought was possible: successfully demonstrated fusion at room temperature. Fusion, the union of atom nuclei, usually only occurs at very high temperatures like those inside the sun or during an atomic explosion. Although the research received lots of attention from scientists and the public, the claims were eventually dismissed because no one could reproduce the original experiment's results. As nonscientists, it is sometimes difficult to understand how experts can disagree about what data mean. Or how one study can contradict another study's findings. But that is part of the scientific process. By letting others critique experiments, conclusions and implications, ideas are challenged, knowledge is gained and, hopefully, a better, more accurate understanding is reached. Sources Of Evidence Everything from ecosystems to molecules is studied to answer perplexing questions. The main kinds of research avenues are: · wildlife studies · human clinical and health trend data · laboratory experiments (cells, tissues and nonhuman animals) · observation In the case of environmental estrogens, evidence has been gathered through: 1. Wildlife studies and laboratory research. Some synthetic chemicals and natural compounds have been shown to interfere with the endocrine system. For instance, wildlife embryos exposed to estrogenic contaminants show lifetime health effects such as abnormal genitals, increased mortality and lower fertility (1). 2. Observations, anecdotal reports and clinical data of human and wildlife health problems. Recent studies using data gathered from clinics looked at male sperm health during the last 40 years. The data showed a statistically significant trend towards lower sperm quality (lower volume, numbers and motility) that some researchers think is related to environmental estrogens (2). On the other hand, other clinical data studies have found opposite findings and directly challenge the idea that declining sperm quality is pervasive in our modern world (3). While examining 20 years of scientific literature dealing with wildlife populations near the Great Lakes, a researcher noticed many physical abnormalities, higher death rates in the young and decreasing populations in many kinds of animals, especially top-of-the-food-chain predators. When tests showed that wildlife tissue samples contained high levels of synthetic chemicals, the researcher theorized that the increased health problems could be linked to human-made chemicals (4).3. Animal and cell culture studies. Laboratory tests, known as assays, and certain kinds of animal studies have been used to measure a chemical's estrogenicity, or ability to act like estrogen. Because estrogens have several important functions (namely, promoting cell division, cell enlargement and protein synthesis), there is no agreed upon standard that says a chemical should do one or all of these to be considered estrogenic. Several different laboratory tests are used to measure the many ways a compound can resemble a natural estrogen. These tests determine (5): o if environmental estrogens bind to the estrogen receptor site; o if they activate certain estrogen-specific genes that make proteins; o if they cause specific kinds of cells to divide and enlarge; o how much of the total amount of chemical in the culture is available for the cell to use (in other words, how much of the chemical can enter and influence a cell) No one assay can test all of the above criteria at the same time. However, many compounds (including DDT, polychlorinated biphenyls (PCBs) and nonylphenols) used in pesticides, as plasticizers and in pharmaceuticals have been identified as estrogenic based on one or more of the above tests. Some estrogenic chemicals are banned but still persist in the environment, while others are still widely used. The ControversyScientific evidence is not always straightforward, especially with complex biological systems. That's why skepticism and flexibility have been built into the scientific process. Once data are published, other scientists review the paper and agree with or challenge the author's conclusions. The review process leads to scientific and public debates that help to shape our understanding of science and interpret, apply and use scientific results. The issue of environmental estrogens is no exception. Its complexities lend itself to controversy. Currently, a debate is taking place as to which chemicals, in what doses, at what ages, cause what health problems. · Some believe that research studies prove there are real and dangerous health effects for wildlife and humans. · Others admit there may be health effects but think the results are only applicable to wildlife, and even then, only where high doses exist. They also acknowledge the need for further scientific verification. · Still others believe the results are sketchy, mainly correlative and without substance. The Future The realization that cancer may not be the only long-term health threat we face is modifying the way we define toxicity and determine public health risk. Finding answers to increasingly complicated and interrelated problems that have environmental, health, economic and political consequences is no easy matter. In response, regulatory agencies, industry and universities are devoting time, money and research to learn how environmental estrogens may affect wildlife and human health. In order to better understand the long-term health effects, more research is needed to : · discern the problems · identify the compounds and develop reliable and sensitive assay systems · determine the related health effects · understand how individual differences, like age, dose, length of exposure and genetics, determine health effects · find out how multiple synthetic chemicals react with each other in the body and the environment. References1. Guillette, L. 1995. Endocrine disrupting environmental contaminants and developmental abnormalities in embryos. Human and Ecological Risk Assessment 1:25-36. 2. Sharpe, R. and N.E. Skakkenbaek 1993. Are oestrogens involved in falling sperm counts and disorders of the male reproductive tract? Lancet 341:1392-95. 3. Safe, S. 1995. Do environmental estrogens play a role in development of breast cancer in women and male reproductive problems? Human and Ecological Risk Assessment 1(2):17-23. 4. Colborn, T., F.S. vom Saal, and A.M. Soto. 1993. Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environmental Health Perspectives 101:378-384. 5. Soto, A.M., C. Sonnenschein, K.L. Chung, M.F. Fernandez, N.Olea and F.O. Serrano. 1995. The E-SCREEN assay as a tool to identify estrogens: An update on estrogeinic environmental pollutants. In Estrogens in the Environment proceedings of the Estrogens in the Environment III: Global Health Implications conference. Environmental Health Perspectives 103(Supplement 7):113-122.


What Does It All Mean?
What Does It Mean?We really don't know very much about the how's and why's of endocrine disrupters, the synthetic chemicals capable of acting like natural hormones. What we do know is based on wildlife studies, laboratory experiments and human experiences. Unfortunately, no simple conclusions can be drawn from the evidence, making it impossible to predict what, if any, human and wildlife health risks exist from daily, low level exposure to natural and synthetic environmental hormones found in: · the natural environment (water, soil and air) · household products · pesticides · processed foods · plants (fruits, vegetables, beans, grasses and more contain natural compounds known as phytoestrogens) · pharmaceutical products · plastics · industrial chemicals Concerns stem from wildlife and laboratory studies associating reproductive and developmental problems in animals (such as feminization of males, lower fertility and higher infant mortality) with exposure to "high" concentrations of synthetic environmental estrogens. Many animals living in or near contaminated areas have these kinds of health problems: fish; frogs, salamanders and other amphibians; alligators, turtles and other reptiles; birds (especially fish-eating species like gulls, terns, ospreys, eagles, pelicans); and marine mammals (whales, sea otters). Laboratory experiments (using animals and cells) also point to an association between certain kinds of contaminants and endocrine disruption. Many studies using molecular biology are showing how the foreign substances interact with the endocrine system's hormones, target cells and receptor sites. Probably the most convincing evidence that synthetic chemicals can act like hormones comes from the DES experience. DES, a strong synthetic estrogen banned since the 1970s, serves as a model. The drug, which is far more potent than other environmental estrogens, was given to pregnant women during critical fetal development to prevent miscarriages and was used in cattle feed. Daughters and sons of women who took the drug have higher reproductive problems and cancer rates than those not exposed to DES in the womb. Laboratory studies confirmed that DES causes reproductive problems and cancer (including the rare rete-testicular cancer in males) in male and female mice. In general, no one really knows whether long-term exposure to low levels of environmental estrogens and other hormones causes health problems in adult wildlife and humans. It may be that developing fetuses and embryos, whose growth and development is highly controlled by the endocrine system, may be the most vulnerable to and may have the most lasting effects from environmental estrogens. Even Scientists DisagreeTo confuse matters more, scientists themselves disagree about research conclusions. And, as the issue leaves the realm of science and moves into public policy arenas, the debates will become even more heated and polarized. Right now, it seems, opinions fall into one of three camps: 1. Some strongly believe that wildlife and laboratory evidence show that synthetic chemicals that act like estrogens have the potential to cause - and may already have caused - severe health problems. To them, the only questions that remain are: o How many health problems are related to environmental estrogens? o How severe will those problems be? o What will the consequences be for future generations? o What should be done to reduce public and wildlife exposure? 2. Many believe there may be reason for concern but call for more research to clarify murky areas. They believe a better understanding of how environmental estrogens may impact the endocrine system will help identify the most harmful substances and lead to less human and wildlife exposure to these compounds.3. Others remain skeptical, believing that scientific data are inconclusive. Pointing to the lack of strong cause and effect evidence, they advocate more research and believe policy decisions should be put off until more is known about the subject. How can such different opinions be represented when science is involved? To better understand, think of the 30-year controversy surrounding cigarette smoking and human health or the disagreement about whether or not the ozone hole exists. Sound scientific data from both issues does not show absolute cause and effect: that one thing -like smoking - causes the other - lung cancer. Or that environmental hormones cause diverse health effects. In cases like environmental estrogens, which involve complex biological systems and diverse health responses, cause and effect data are impossible to find. But, even without certain scientific evidence, the potential health, social and economic risks are forcing government, organizations and the general public to take notice. In these cases, we rely on scientific, political and public debate to weigh the evidence and decide how to deal with the potential health problems. Governments around the world are taking action by gathering information, funding more research initiatives, developing screening and testing programs for synthetic chemicals and setting up new policies. Individuals are becoming informed through media articles, books, Web sites and grassroots organizations. Several actions, including banning chemicals and reducing pesticide use, have been recommended by advocacy groups. Staying informed and becoming involved in the debate can help you discern the issues and form an opinion on the best course of action. On a day-to-day level, reduce contact and risk by following the ten tips outlined in The World Wildlife Fund's online pamphlet Reducing your risk: A guide to avoiding hormone-disrupting chemicals. Remaining QuestionsMany questions, such as the following, remain unanswered and await further research. 1. Does exposure to minimal amounts (background levels that an average person would be exposed to on a daily basis) of synthetic chemicals that are known to act like estrogens cause reproductive, health and behavioral problems in wildlife and humans? 2. Does exposure to environmental estrogens pose a greater threat to developing embryos than to adults, thus impacting fertility and health of the future generation? 3. How do variables such as profession, age, dose of exposure, diet, genetics and other factors influence susceptibility to these foreign substances? And what about toxicity? Up until now, health risk has been defined as cancer. Government health agencies use cancer risk as a guide to decide safe doses and exposure. Now, we may need to look further and redefine toxicity to include long-term reproductive and developmental problems caused by endocrine modulating chemicals. And, if these substances do pose health threats, how do we accurately measure toxicity and evaluate the risk not only to adult human health but to our developing and growing offspring? The author's of Our Stolen Future describe it this way (1).Hormone-disrupting chemicals are not classical poisons or typical carcinogens. They play by different rules. They defy the linear logic of current testing protocols built on the assumption that higher doses do more damage. For this reason, contrary to our long-held assumptions, screening chemicals for cancer risk has not always protected us from other kinds of harm. Some hormonally active chemicals appear to pose little if any risk of cancer . . . such chemicals are typically not poisons in the normal sense. Until we recognize this, we will be looking in the wrong places, asking the wrong questions, and talking at cross purposes. To further understand how environmental estrogens work and if they threaten wildlife and human health, several questions focusing on research and toxicity need to be asked and answered. · Can wildlife and animal data be applied to humans, when it is clear that some of these compounds have different effects in different kinds of animals? · Can laboratory tests on cell cultures explain and predict how environmental estrogens interact with the endocrine system in living organisms especially since these chemicals can affect more than one endocrine organ in an animal? So, does the study of a single cell type provide a good, accurate picture of how hormone-like substances interact with a living organism? · How do mixtures of compounds (like the way they are found in the environment) react and interact with each other, the endocrine system and natural hormones? · How do such things as length of exposure, dose, route of exposure (ingested, inhaled), age and gender influence toxicity? · Which animals will the most vulnerable: insects, fish, amphibians, reptiles, mammals (including humans)? Which age will be the most vulnerable to potential effects: fetuses, newborns, children, adolescents or adults? References1. Colborn, T., D. Dumanoski and J.P. Myers. 1996. Our Stolen Future: Are we threatening our fertility, intelligence, and survival?: A scientific detective story. New York: Penguin
Estrogens and Estrogen-mimicking Compounds
Estrogens are steroid hormones made primarily in the female ovaries and the male testes in humans and other animals. Estrogens, known as the female hormones, are found in greater amounts in females than males.Phytoestrogens, which are estrogen-like compounds, are found in plants; in addition, there are compounds in the environment which can act with estrogen-like effects on plants and animals.
To see examples of estrogens, phytoestrogens,and synthetic estrogen-mimicking compounds,click on the "compounds" link on the left.
These essential molecules influence growth, development and behavior (puberty), regulate reproductive cycles (menstruation, pregnancy) and affect many other body parts (bones, skin, arteries, the brain, etc.). Estradiol is the most abundant and potent estrogen hormone. Estrone and estriol are other types of estrogens. OH and hydroxy groups extend off the carbon-based ring structures, which are referred to as "polycyclic" because they consist of several rings (cycles) attached together. Estrogen's actions were initially described by Stockard and Papanicolaou in 1917 with guinea pigs (1) and by Long and Evans in 1922 using rats (2). Both observed that pre-ovulatory follicle swelling was followed by uterine lining growth and ******* cell maturation. Later, Allen and Doisy isolated the responsible steroid, called it estrone and described a test to detect this estrogenic activity in biological samples (3). Since then, their test, or similar ones, has become the standard way to detect, identify and characterize natural and synthetic compounds with estrogenic activity (4). Estrogen is commonly defined as "any of a family of steroid hormones that regulate and sustain female sexual development and reproductive function" (5). In this same vein, modern scientists define estrogens as materials that stimulate tissue growth by (6): * promoting cell proliferation (DNA synthesis and cell division) in female sex organs (breasts, uterus), * promoting hypertrophy, or increasing a cell's size, such as occurs in female breast and male muscle during puberty and * initiating synthesis (making) of specific proteins. Under these guidelines, any natural steroids, plant compounds or synthetic chemicals that elicit these responses in laboratory tests are considered to be estrogenic. All are not satisfied with this interpretation, however. In a recent comment, Lieberman suggests that classifying a variety of compounds as estrogens is too broad and causes confusion (4). In a response, Hughes offers to define estrogens as compounds that produce the behavior estrus ("the portion or phase of the sexual cycle of female animals characterized by willingness to accept the male"). He argues that since only true steroid compounds produce estrus, the plant and synthetic compounds that mimic other estrogenic responses are not estrogens and should be classified as something else, such as phytochemicals or environmental estrogens. In his view, "the potential importance of phytoestrogens in human health and disease is certain to derive both from their mimicry of steroidal estrogens and their failure to closely mimic the actions of steroidal estrogens." (7)


Estrogens and Estrogen-Mimicking Compounds
Click on a chemical structure below to find out more about the compound’s estrogenic activity, therapeutic uses, side effects, etc. These pages were prepared by students in the 2002 Endocrine Pharmacology class at Tulane University, under the directorship of John McLachlan, Ph.D. and Barbara Beckman, Ph.D. Each student chose an “estrogen” from the categories below (endogenous, pharmaceutical, phytoestrogen, synthetic environmental estrogen) and prepared these pages with the assistance of Jude Bloom, Information Systems Coordinator at the CBR. As a measure of estrogenicity, we list the relative binding affinity (RBA) to the estrogen receptor compared to that of estradiol, the primary endogenous estrogen. For example, Raloxifene (a pharmaceutical estrogen) has an RBA for Era of 69, or 69% that of estradiol. This value tells you how strongly the compound binds the estrogen receptor compared to estradiol, but by itself does not tell you what effect this binding will have, which depends on factors in addition to binding affinity, such as recruitment of coactivators and corepressors. In most cases RBA information came from Kuiper et al. (1998).We are not physicians, nor should the information on these pages be used as a substitute for medical advice from your physician.
Endogenous (Animal) Estrogens


Estrone

Phytoestrogens (Plants)


Coumestrol Daidzein



Genistein Resveratrol



Zearalenone

Exogenous (Synthetic) Estrogens


Bisphenol-A Diethylstibestrol




Methoxychlor Raloxifene



Ortho-N-Nonylphenol Ethinyl Estradiol


Genes May Influence Environmental Hormone Effects
Karen Gray
Ares Advanced Technology Inc., Randolph, Massachusetts
Jimmy Spearow
University of California at Davis, Davis, California

November 23, 1999


Research Paper

Spearow, JL, P Doemeny, R Sera, R Leffler, and M Barkley. 1999. Genetic variation in susceptibility to endocrine disruption by estrogen in mice. Science. 285:1259-1261.


Significance of Research
Written by Karen Gray

Sensitivity to environmental hormone disruptors may be partly controlled by genetic predisposition, a recent study on mice suggests. The results, published in the journal Science, imply that product safety tests using more resistant strains of mice may underestimate estrogenic effects.

In their paper, Jimmy Spearow and coworkers at the University of California-Davis demonstrate that the reproductive tracts of males from different mouse strains show large differences in susceptibility after juveniles are exposed to high concentrations of the natural hormone 17-beta estradiol (E2).

Estrogen exposure during critical developmental periods can profoundly affect sexual differentiation, reproductive function, and behavior in diverse vertebrate species. For humans, decreased human sperm counts and increased incidence of hypospadias, cryptorchidism, and prostate, testicular, and breast cancers may be related to exposure to environmental chemicals that mimic estrogen. However, a definite correlation has not been established.

In mice, there is considerable genetic variation in reproduction associated with testis size, ovulation rate, and litter size. Most commercial "outbred" strains of laboratory animals used in studies of environmental chemicals have been selected for large litter size and vigor. Spearow and his coworkers hypothesized that these better reproducers could also be less sensitive to estrogen. If this were the case, then product-safety testing using mice selected for large litter size may underestimate the role of estrogenic agents in disrupting reproductive development.

The researchers found that male mice from better reproducing strains showed less sensitivity to estrogen-s adverse effects than did mice from poorer reproducing strains. In the study, testis weight was more affected by strain, or genetic composition (genotype), than dose of estrogen. Males from large litter size strains had heavier gonads and were found to be significantly more resistant to the adverse affects of estradiol (30% inhibition at the highest dose) than male mice with smaller gonads and from small litter size strains. As an example, low to moderate doses of E2 obliterated spermatogenesis in mice with poorer reproductive capacities (B6 and C17/Jls), whereas, in mice with better reproductive performance (CD-1), little inhibition of spermatogenesis occurred in response to estradiol. In fact the CD-1 strain was 46 times more resistant to inhibition of testis weight and 126 times more resistant to disruption of spermatogenesis than the sensitive strains B6 and C17/Jls.

The discovery that individuals have major genetic differences in sensitivity to estrogen could have widespread implications. Testing of environmental chemicals for estrogenic activity or "endocrine disruption" may now require using many, genetically different strains of mice in order to assess a chemical-s true ability to disrupt reproduction in different genetic backgrounds. If humans also show genetic sensitivity to estrogenic compounds, more rigid federal standards may need to be implemented to prevent exposure of sensitive individuals to environmental chemicals. This knowledge may one day be used to optimize estrogen therapies (birth control pills, HRT) to the "hormone response genotype" of each woman maximizing safety and reducing the risk of hormone dependent cancers.


Research Paper Summary
Written by Jimmy Spearow

Estrogens have dramatic effects on reproductive development, function, and behavior in a wide range of vertebrate species. Since many industrial, agricultural, household, and natural chemicals have estrogenic activity and can disrupt reproductive development, the U.S. Environmental Protection Agency (EPA) is preparing to screen thousands of chemicals for endocrine-disrupting effects. Considerable attention has been given to the effects and the mechanisms by which natural and environmental estrogens act to alter reproductive development within strains of laboratory animals. Unfortunately, the nature of the genetic variation in susceptibility to endocrine disruption by estrogenic agents was largely unknown.

Reproductive traits, including testis weight, sperm production, litter size, and natural and hormone induced ovulation rates, show a high degree of genetic variation in several different species and can be altered by selective breeding (1, 2, 3, 4, 5). For economic reasons, most commercially available, highly prolific "outbred" lines of laboratory animals were developed by conventional long-term selection for large litter size and vigor. Selection for large litter size also results in several correlated responses including increased testes weight in males (6). Furthermore, males of large litter size strains were more resistant to the inhibition of testes weight by increasing doses of estrogen (7).

Thus we hypothesized that: 1) susceptibility to endocrine disruption is genetically controlled and 2) the process of selective breeding for large litter size could also result in animals that are resistant to estrogen. To test these hypotheses, Spearow et al., (8) studied strain differences in the effects of estradiol on testes weight and spermatogenesis. The strains of mice examined included: 1) C57BL/6J (B6), a widely-used strain used in producing genetically customized mice for biomedical research; 2) CD-1 mice, a large litter size selected line frequently used in toxicological and pharmacology studies and; 3) two other strains of mice developed from the same base population, including the C17/Jls strain that was bred by random selection followed by inbreeding and S15 strain that was bred by selection for large litters followed by inbreeding.

In this study juvenile male mice were implanted with increasing doses of E2 implants in silastic tubing starting at 22 to 23 days of age. Three weeks later testes weight was measured and spermatogenesis was determined by histological analysis. Testis weight of mice receiving empty, control implants was significantly higher in both large litter size selected strains of mice (8).

More importantly, strains differed dramatically in their sensitivity to estradiol (8). C17/Jls and B6 strain mice were sensitive to estradiol, showing a near maximal suppression of testis weight even at the lowest dose of estradiol examined (2.5 µg E2 implant per mouse or 0.12 µg E2/gm body weight) (P⁢0.01). In contrast, testes weight of large litter size selected CD-1 strain mice was not significantly inhibited by 2.5 or 10 µg E2 implants. CD-1 required a dose of 20 µg E2 implants corresponding to 0.66 µg E2 implant/g body weight to significantly inhibit testes weight.

Histological evaluation of the percentage of seminiferous tubules with elongated spermatids showed that even the lowest doses of estradiol nearly eliminated, and higher doses totally eliminated, sperm maturation in B6 and in C17/Jls strain mice (8). Sperm maturation in CD-1 mice, however, showed little or no inhibition in response to 16-fold higher (the highest) dose of estradiol. This provided further evidence that juvenile males of the highly prolific CD-1 strain of mice were much more resistant to the endocrine-disrupting effects of estrogen.

These results showed that CD-1 mice were over 16-times more resistant than B6 or C17 strain mice to disruption of juvenile testes weight and spermatogenesis by estrogen. Furthermore, extrapolation of the CD-1 data suggested that this line of mice is about 100 times more resistant to endocrine disruption by estrogen than strain B6 or C17 mice (8).


Other studies draw similar conclusions

While further studies are clearly needed, this study-s findings show that strains of laboratory mice vary dramatically in their sensitivity to inhibit testes weight and spermatogenesis by estradiol. These findings are in agreement with previous studies showing genetic variation in sensitivity to estrogen. Indeed, other studies show that strains of mice differ in uterotrophic responses to estradiol, DES, and phytoestrogens (9, 10, 11, 12) and in serum lipoprotein responses to estrogen (13). In these studies, B6 mice and crosses tended to be more sensitive, while large litter size selected ICR and especially CD-1 line mice tended to be more resistant to estrogenic agents. Furthermore, the most favored EPA rodent model for endocrine disruptor testing, the Sprague Dawley rat, has also been reported to be more resistant than other strains examined to the inhibition of testis weight by DES (14) and female reproductive tract responses to Bisphenol A (15). While the genetic basis is unknown, variation in sensitivity to contraceptive steroids also exists in human populations (16).

While the nature of genetic differences in sensitivity to in-utero developmental exposure remains to be determined, the available evidence suggests that juvenile to adult large litter size line males and females tend to be more resistant to estrogenic agents. Nevertheless, many different reproductive, developmental, functional, and carcinogenicity traits potentially affected by estrogenic chemicals are under the control of a wide array of only partially overlapping signal transduction and genetic control mechanisms. Thus, until we understand the genetic mechanisms involved, the relative sensitivity of different strains to estrogenic agents needs to be determined on a trait by trait basis.

Many laboratory animal studies of endocrine disruptors to date have used large litter size selected animals such as CD-1 mice or Sprague Dawley rats. Even though these rodent strains appear to be more resistant than several other strains to the disruption of testicular developmental by estrogenic agents , studies with these strains have provided important information on the mechanisms by which estrogenic compounds cause reproductive tract and gonadal pathologies in humans and other species (17). Comparison of the mechanisms by which these estrogenic agents act in resistant strains versus insensitive strains should enable the elucidation of these critical genetic controls regulating sensitivity to endocrine disruption.


Importance of testing many genetic lines

The findings of Spearow et al., (1999) suggest that current laboratory-animal-based safety tests of estrogenic chemicals using large litter size selected "outbred" lines of laboratory animals may greatly underestimate effects on estrogen sensitive genotypes. These and other findings suggest that there is likely to be broad variation in sensitivity to estrogen in many vertebrate populations and species, including humans. Thus, monitoring endocrine disruption will require considering susceptibility genotype as well as environmental exposure to estrogenic agents.

The genetic sensitivity of the animal model used for testing estrogenic chemicals for endocrine disruptor activity is extremely important. Given the observed genetic variation in susceptibility to endocrine disruption by estrogens between strains of mice, and the high level of resistance of currently used models, care is needed to protect the average and the genetically most sensitive individuals, populations and species from harm by endocrine disrupting chemicals. If an estrogen resistant strain is used for product safety testing, the resulting much higher allowable environmental release rates could potentially disrupt the reproductive development and function of sensitive genotypes thereby resulting in the demise of sensitive individuals, populations and species.

Furthermore, the magnitude of genetic differences in sensitivity to estrogen observed in this and other studies suggest that an individual-s estrogen-response genotype should be considered when prescribing estrogenic compounds for contraceptives, hormone-replacement therapy, as well as prevention and treatment of cardiovascular disease, breast, and prostate cancer.

Finally, these and other studies have shown a high level of genetic variation in the component controls of reproduction. In addition to the over 16-fold genetic differences in susceptibility to endocrine disruption, strains of mice differ 5 to 6-fold in hormone-induced ovulation rate and about 20-fold in hormone-induced aromatase activity (18). A Quantitative Trait Loci (QTL) linkage analysis approach has been used to map genes controlling these major differences in ovarian response to gonadotropins (19) as well as genes controlling uterotrophic responses to estrogen (12). Similarly, the mapping of genes controlling the observed genetic differences in susceptibility to endocrine disruption by estrogen will enhance the identification of the genes controlling this trait.


Further Reading

1. Bradford, GE. 1969. Genetics. Princeton, 61:905.

2. Toelle, VD, BH Johnson and OW Robison. 1984. Genetic parameters for testes traits in swine. J Anim Sci, 59(4):967-973.

3. Bradford, GE, S. J.L. and H. J.P. Eds. 1991. Genetic variation and improvement in reproduction. New York:Academic Press.

4. Johnson, RK, GR Eckardt, TA Rathje, and DK Drudik. 1994. Ten generations of selection for predicted weight of testes in swine: Direct response and correlated response in body weight, backfat, age at puberty, and ovulation rate. J Anim Sci, 72(8):1978-1988.

5. Okwun, OE, G Igboeli, JJ Ford, DD Lunstra, and L Johnson. 1996. Number and function of Sertoli cells, number, and yield of spermatogonia, and daily sperm production in three breeds of boar. J Reprod Fertil, 107(1):137-49.

6. Eisen, EJ and BH Johnson. 1981. Correlated responses in male reproductive traits in mice selected for litter size and body weight. Genetics, 99(3-4):513-524.

7. Spearow JL, JT Turgai, FC Mao, PJ Smith, and BA Trost. 1987. J. Animal Sci., 65(Suppl. 1):399A.

8. Spearow, JL, P Doemeny, R Sera, R Leffler, and M Barkley. 1999. Genetic variation in susceptibility to endocrine disruption by estrogen in mice. Science, 285:1259-1261.

9. Silberberg, M and R Silberberg. 1951. Proc Soc. Exp. Bio. and Med., 78:161.

10. Farmakalidis, E and PA Murphy. 1984. Different oestrogenic responses of ICR, B6D2F1 and B6C3F1 mice given diethylstilbestrol orally. Food Chem. Tox., 22(8):681-682.

11. Farmakalidis, E and PA Murphy. 1984. Oestrogenic response of the CD-1 mouse to the soya-bean isoflavones genistein, genistin and daidzin. Food Chem. Toxic., 22(3):237-239.

12. Roper, RJ, JS Griffith, CR Lyttle, RW Doerge, AW McNabb, RE Broadbent, and C Teuscher. 1999. Interacting quantitative trait loci control phenotypic variation in murine estradiol-regulated responses. Endocrinology, 140(2):556-561.

13. Srivastava, RA, ES Krul, RC Lin, and G Schonfeld. 1997. Regulation of lipoprotein metabolism by estrogen in inbred strains of mice occurs primarily by posttranscriptional mechanisms. Molecular and Cellular Biochemistry, 173(1-2):161-168.

14. Inano, H, K Suzuki, M Onoda, and K Wakabayashi. 1996. Relationship between induction of mammary tumors and change of testicular functions in male rats following gamma-ray irradiation and/or diethylstilbestrol. Carcinogenesis, 17(2):355-360.

15. Steinmetz, R, NA Mitchner, A Grant, D L Allen, RM Bigsby, and N Ben-Jonathan. 1998. The xenoestrogen bisphenol A induces growth, differentiation, and c-fos gene expression in the female reproductive tract. Endocrinology, 139(6):2741-2747.

16. Behre, H, et al. 1995. Journal of Clinical Endocrinology and Metabolism, 80:2394.

17. Newbold, R. 1995. Cellular and molecular effects of developmental exposure to diethylstilbestrol: implications for other environmental estrogens. Environmental Health Perspectives, 10(Suppl 7):83-87.

18. Spearow JL and M Barkley. 1999. Genetic control of hormone-induced ovulation rate in mice. Biology of Reproduction, 61:851-856.

19. Spearow JL, PA Nutson, WS Mailliard, M Porter, and M Barkley. 1999. Mapping genes that control hormone-induced ovulation rate in mice. Biology of Reproduction, 61:857-872.