Effects on Wildlife and Human Reproductive Systems

Endocrine Disruptors:

Effects on Wildlife and Human Reproductive Systems

Table of Contents

Introduction 3

Lab Procedure: Detection Assay 3

Role of Estrogens 3

-Figure 1 4

Endocrine Disruptors 4

Mechanisms 4

Estrogenic Compounds 5

Phytoestrogens 5

Organohalogens 5

-Figure 2 6

DDT 6

-Figure 3 6

DES 6

-Figure 4 6

Phthalates 7

Pros and Cons of Phytoestrogens 7

-Figure 5 7

Organochlorine Pesticide Case Study: Kepone 7

Research Dealing with DES 8

The Endocrine Disruptor Effects on Ecology 8

Wildlife Effects, Studies with animals 9

Birds 9

-Table 1 9

Turtles 9

Alligators 9

Rats 9

Fish 10

Polar Bears and Seals 10

Florida Panthers 10

Human Effects 10

Speculated Effects of Environmental Estrogens in Humans

Women 10

Men 11

Discussion 12

Appendix 13

References 14

Endocrine Disruptors:

Effects on Wildlife and Human Reproductive Systems

The environment is a myriad of elements which when put together in different combinations create living and non-living things. Besides the natural chemicals that are formed by these combinations, there are also xenobiotics, man made chemicals. There are different classifications for all sorts of families of compounds to describe how they function.

The endocrine system of living animals is very sensitive. Hormones are chemicals used for signaling in the endocrine system. It has been studied, by design and by accident, and found that there are many compounds which can mimic or interfere with natural hormones and influence the normal balance. This disturbance of balance has been shown to have detrimental effects on the reproductive systems of many organisms including fish, mammals, birds and humans. Most of the growth of structures starts in the early stages of development in the womb. Testes are one of the many structures that are sensitive during this time of development (15).

Through observations of nature and in laboratory studies on cell cultures and animals, a great deal of concern for the interactions has arisen. Laboratory studies have shown that some chemicals can cause endocrine disruption. Some examples of disruption include: lack of normal sexual differentiation, hermaphroditism, changes in ovarian function, sperm production, pregnancy, fertility and metabolism changes. There is still a need for more research in this area of environmental impacts. (13)

Assay development for the detection of Environmental Estrogens:

Some of the laboratory research involves some simple “on / off” testing. One such method is the Cellular Litmus Test Assay. The Cellular Litmus Test was developed as a test to determine the presence and strength of environmental estrogens. Yeast cells are used as a host for the estrogen receptor to be added to. The gene for the human estrogen receptor was added to the yeast. The transformed cell now can express the estrogen receptor. Also added to the yeast is a reporter gene, which will sense the action of estrogen in the cell and change colors to indicate the presence of estrogenic activity. If there is no activity, or the activity has been surpressed, then the cell will not change color, in this case stay white instead of turning blue. This assay is useful for detecting antiestrogens. If you first expose the cells to estradiol, the cell turns blue. Then you introduce a substance you suspect to be an antiestrogen, and if the cell turns white, you know that it is. If the cell does not change color, then it is not an antiestrogen. A simple system for understanding a complex activity in nature. This system is flexible and provides an approach for detecting biologically active chemicals. This system also allowed scientists to test the theory of synergism and how more than one chemical at once will effect the results or signals. (20)

ROLE OF ESTROGENS:

The endocrine system is an essential part of the life process. This makes the issue of endocrine disruptors so threatening. This places a lot of fear into humans about the certainty of the future.

Estrogens and androgens are the two types of families of reproductive hormones. They are responsible for many life functions of organisms. These sex hormones help with regulating growth, metabolism and maintenance of reproductive cycles. (30)

Estradiol is one of the main estrogens, and it controls the development of female sexual characteristics (breast formation, lack of facial hair, and feminine behaviors), ovarian and menstrual cycles, pregnancies. When the ratio of estrogen to testosterone is increased in a male, feminization can occur. This is what is believed to have caused many of the cases where the male animals have smaller penises and other feminine characteristics in nature. Some have been proven because of acute problems (like the spill in a lake directly) while others are just inferred from the data. (30)

Figure 1. Molecular Structure of Estradiol, a natural estrogen. (32)

Endocrine Disruptors

Environmental disruptors alter how natural hormones and their protein receptors are made, broken down and interact. These chemicals which agitate the natural processes of the endocrine system are adequately called endocrine disruptors. There are different types of these chemicals depending on their mechanisms. Environmental Estrogens in general can mimic or act like estrogens. Endocrine disrupting chemicals include man made chemicals that are persistent, bioaccumulative, halogenated compounds. Some examples are pesticides, industrial chemicals, synthetic products (plastics) and some metals (lead and mercury) (23). There are a diverse group of synthetic chemicals and natural plant compounds that may act like estrogens in animals and humans (32). Anti-androgens are chemicals that can bind to the Androgen Receptor (AR) without activating it, simultaneously preventing true androgens from being able to bind to the receptor. (11, 31) Agonists are chemicals that are not a hormone but mimic a natural hormone (23). Antagonists are chemicals which interfere with a natural hormone or its pathway or signal (23). Phytoestrogens are hormone mimicking substances that are naturally occurring in plants. Along with all of these individual chemicals having the potential to interact, there is also the chance they will react with each other, changing or amplifying the response. All of these raise important questions about the future of the environment.

Environmental estrogens are the most extensively studied component of all the endocrine disruptors.

Mechanisms

Natural hormones are short lived, have no bioaccumulation, and are easily broken down. Phytoestrogens resemble natural hormones in their activity and residence in the body. This contrasts from environmental estrogens which are basically the complete opposite. The environmental estrogens are not easily broken down, the are long lived, and bioaccumulate (32). There are gradients that exist for each parameter. Some stay in the environment and bodies longer than others. For example, DES will stay longer than natural hormones, but less than synthetic pesticides and chemicals.

Environmental estrogens can bind to specific receptor sites inside the nucleus and then: mimic or provoke a proper hormone response, block or inhibit that proper hormone response, do both of these (PCBs) cause a weaker or stronger hormone response than what is proper, or make a completely different signal or response all together. The environmental estrogens can also bind to different receptors and interfere indirectly with the normal hormone action. (32)

The estrogen receptor has two or more interactive binding sites, which allows for flexibility and control in the response system. Multiple binding sites on the receptor are important in the signaling pathways. (20) Which adds extra complexity of figuring out the full effects of external estrogens. This is said very well by Metzger as follows:

“As we delve into the complex actions of estrogens in animals and tissue culture models, it is becoming increasingly clear that not only are most tissues estrogen sensitive by virtue of the presence of specific gene-regulating receptors but that estrogens may regulate cellular function at alternative sites.” (21)

Many sex-related characteristics are determined hormonally during a window of time in development, and any disturbance of the endocrine system during that sensitive time can alter or effect the development of the organism (23).

ESTROGENIC COMPOUNDS

As said earlier, there are many compounds which fit into this category of chemicals. The following list is a summary of the most researched and understood that we know of now or that are suspected of being estrogenic.

Phytoestrogens

Phytoestrogens are the natural plant compounds that act like weak estrogens. Two classes exist that we know of so far, lignans and isoflavones. These compounds can be broken down in our bodies, absorbed, and excreted. They are not stored in tissues, and have a short-lived time frame but are capable of interfering with the endocrine system (11, 29). Some examples are: herbs and seasoning (garlic, parsley), grains (soybeans, wheat, and rice), vegetables (beans, carrots, potatoes), fruits (date, pomegranate, cherries, apples) and coffee (29).

Organohalogens

Organochlorine pesticides such as DDT, DDD, DDE, dicofol, perthane, chlordane, heptaclor, aldrin, dieldrin, hexachlorobenzene, lindane and toxephene all contain one or more chlorine molecule. This is not something that is found in nature, these are all man made complexes. (27)

Polychlorinated Biphenyls, abbreviated PCB’s, are very abundant since the industrial revolution. They have many properties which make them useful in the manufacture of some products. There are 200 PCB’s, common in plastics, insulation material, oils, parts of pesticides and some in nature. They can be by products of the breakdown of DDT. (9) These compounds are recognizable by their distinctive structure which always contains two 6 sided carbon rings with various other elements bonded to
them.

Figure 2. One of the 200+ PCB compounds. (32)

Dioxin is a common name for 75 different compounds (24). Dioxins result as byproducts from incinerators, paper making mills, metal smelters, and chemical manufacturing processes. One very important chemical property of Dioxins is that they are soluble in fats and oils. This allows them to bioaccumulate in the fat of animals.

DDT

DDT was used largely to control mosquito populations. It was widely used on agriculture and also as a pesticide. DDT is lipophilic (fat-soluble) and because of its widespread use, it was found in high levels as a contaminant in animals. Concentrations of DDT were found to be tens of thousands times higher in the fish than in the water they were living in (17, p.248). DDT can act in the body like endogenous estrogen. DDT has breakdown products that may be estrogens or a compound that blocks the effects of androgens (male sex hormones) (20). DDT turns into p p’- DDE. P, p’ DDE can cause the suppression of androgens or in other words it switches off the “masculine” signals in rats that have been exposed to it (16).

Figure 3. Example of a DDT Molecule (32)

DES

Diethylstilbestrol, DES, is another compound that has estrogenic qualities. It was used as a medicine for women while they were pregnant to prevent miscarriages simply because of the estrogenic effects of it. Later it was found that there were many other side effects of the drug, not on the mother, but on the offspring.

Figure 4. Structure of DES (32)

Phthalates

Phthalates are ester compounds which are a component of plastic products.

Pros and Cons of Phytoestrogens

Some phytoestrogens have been used for years because they are incorporated in medicinal plants used by people. For example, in the 4th century Hippocrates noted that wild carrot, also known as Queen Anne’s Lace) is good as a birth control. (26) This class of compounds have been investigated as possible preventors of cancers due to their weak estrogenic qualities. Due to this competition with the natural forms of estrogen for the receptor sites, phytoestrogens may help reduce the risks by lowering a person’s lifetime exposure to natural estrogens or even change the way natural estrogens are broken down. Factors affecting the effect of phytoestrogens are dose and the age sex and health of the person. Though there are these positive things, there are also risks of exposure to phytoestrogens like possible problems of infertility and development. (29)

Phytoestrogens can affect the fertility of the animals who eat the plants containing them. This has been shown in some studies. There are some studies showing phytoestrogen effect of plant foods for certain animals. Phytoestrogens in dry summertime grasses reduced the number of offspring in wild populations of California quail and deer mice (3, 18). Australian sheep suffered reproductive problems and infertility after grazing in pastures that contained clover Trifolium subterraneum. This clover contains the compounds Equol and Coumestrol which have both been shown to be phytoestrogens. (2)

Figure 5. Molecular Structure of Coumestrol (32)

Another study dealing with Coumestrol exposure dealt with rat pups, and it was found that the mature female pups did not ovulate when they matured. The male pups had altered sexual behavior and fewer ejaculations than those not exposed (33). Neonatal and immature rats that were exposed to Coumestrol experienced premature estrous cycles. Genistein, a different phytoestrogen compound, was introduced to newborn rats and caused delayed puberty development. (1)

Organochlorine Pesticide Case Study: Kepone

One of the best cases of a human effect is the accidental spill of the pesticide component, Kepone in 1975. The men exposed to the spill experienced reduced sperm counts. Kepone has been tested in labs since and proven that it has weak estrogenic qualities. The effect was not determined earlier because there was not a direct correlation between the structure of the molecule to the structure of the estrogen molecule. Never the less, it is one documented study where there was a defined cause and effect relationship between a chemical and a reproductive disorder which involved estrogenic effect, making Kepone yet another environmental estrogen. (20)

Research dealing with DES

DES was a drug given to pregnant women to prevent miscarriages from the late 1940’s to early 1970’s (28). The resulting side effect to the generations of offspring was something no one predicted. Sons born of mothers who took DES have a higher incidence of malformed or abnormally small penises, undescended testicles at birth, abnormal sperm, and/or genital tract abnormalities that can make the males sterile. (34) The most common effect, though not the only one, in the second generation females was a cancer known as Clear Cell Adenocarcinoma. The rate of occurrence of this cancer is about 1 in 1000 in women who were exposed to DES in the womb. (17, p 174) Evaluating a population of men whose mothers took DES and those who did not resulted in the abnormality of the reproductive tract in DES-exposed men to be 32% while it was only 8% in the control group (those mothers who did not take the DES during pregnancy). (11) The challenge in making correlations with all these chemicals is that the structures are so different from each other as well as natural estrogens. (20)