Endocrine disrupting chemicals hormones

Mechanistic studies to identify how endocrine disrupting chemicals interact with hormone systems are required. Although population effects coupled with biomarkers of exposure are strongly suggestive of endocrine disruption, the effect could be secondary to metabolic toxicity. Establishing mechanisms may avoid the need to make decisions on a weight of evidence approach alone. 

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine system because of the abihty of these chemicals to mimic or block endogenous hormones, or otherwise interfere with the normal function of the endocrine system. Chemicals with this type of activity are most commonly referred to as endocrine disruptors. Some scientists believe that chemicals with the ability to disrupt the endocrine system are a potential threat to the health of humans, aquatic animals, and wildlife. Others believe that endocrine disrupting chemicals do not pose a significant health risk, particularly in light of the fact that hormone mimics exist in the natural environment. Examples of natural hormone mimics are the isoflavinoid phytoestrogens (Adlercreutz 1995 Livingston 1978 Mayr et al. 1992). 

Dr. G. A. LeBlanc of North Carolina State University is evaluating effects of potentially endocrine-disrupting chemicals, including endosulfan, on steroid hormone biotransformation/elimination processes in daphnids, fish, and mice, and is constructing models of the processes. The work is being funded by the U.S. Department of Agriculture. 

Depending upon the circumstance and desired effects, endocrine-disrupting chemicals can be either good or bad. The endocrine system is a finely balanced system responsible for fertility and many of the feminine and masculine traits we are all familiar with. Endocrine disruptors are used by millions of women in the form of the pill to control fertility. Chemicals in birth control pills subtly manipulate the endocrine system to reduce fertility. Unfortunately, we now know that many chemicals are capable of influencing the endocrine systems. When these chemicals, such as DDT and TCDD, are released into the environment, they reduce the fertility of wildlife. Exposure to endocrine disruptors is linked to decreased fertility in shellfish, fish, birds, and mammals. Endocrine disruptors such as nonylphenol have been shown to feminize male fish, interfering with reproduction. Some studies have also linked exposure to endocrine disruptors to decreases in human male sperm count. Ironically, urinary metabolites of the birth control pill as well as the female hormone estrogen pass through waste treatment plants and are released into the aquatic environment, where even small concentrations cause feminization of male fish. 

Estradiol is one of the main female sexual hormones it is also the structural backbone for the engineering of some synthetic estrogens, such as ethynyl estradiol or mestranol, used in human hormone treatments. Both natural and synthetic estrogens are classified as endocrine disrupting chemicals (EDCs).6,362 Many of these substances and their metabolites end up in the environment where... 

Tschmelak, J., G. Proll, and G. Gauglitz. 2005. Optical biosensor for pharmaceuticals, antibiotics, hormones, endocrine disrupting chemicals and pesticides in water Assay optimization process for estrone as example. Talanta 65 313-323. 

Most developmental neurotoxicity studies have focused on general impairment of behaviour, but some studies have also found evidence for effects on sexual dimorphic behaviour. Hormones play a central role in central nervous system development, including the sexual differentiation of the brain. Studies on hormones and various endocrine disrupting chemicals (particularly those with estrogenic or antiandrogenic effects) have shown that the developing brain may be susceptible to disturbances in sexual behaviour. Therefore, effects on one sex but not the other should not be dismissed, but must be evaluated in the context of effects on sexual differentiation of the brain. 

Mu X, LeBlanc GA. 2004. Synergistic interaction of endocrine-disrupting chemicals model development using an ecdysone receptor antagonist and a hormone synthesis inhibitor. Environ Toxicol Chem 23 1085-1091. 

All natural hormones, all synthetic hormones, and many endocrine-disrupting chemicals (EDCs) achieve their effects by binding to a receptor and/or hormone binding protein [108,109]. However, it should be noted that binding to the receptor is necessary, but not sufficient for activity. The activity of a hormone or EDC in an organism does not only depend on the binding behavior (strong or weak) of itself or a metabolite to the receptor but is affected by a variety of other factors [110] ... 

It is known that many environmental endocrine-disrupting chemicals have weak estrogenic or antiestrogenic activity [111], or they act as androgens (e.g. tributyltin) or possess antiandrogenic activities (e.g. linuron, 3,4-dichloro-acetanilide etc.). Some chemicals can block the effects of male sex hormones, the androgens [112, 113, 115f]. These special chemicals are described in the next sections. 

Endocrine disrupting chemicals can wreak havoc with the human reproductive process as well as with endocrine system homeostasis. Their introduction into the environment has had an enormous effect on wild life. Given the similarities between many of the hormones (particularly the sex hormones) that circulate in animal and human bodies, the wildlife impacts serve as models and predictors of the effects of EDCs on humans. 

Sanderson JT (2006) The steroid hormone biosynthesis pathway as a target for endocrine-disrupting chemicals. Toxicol Sci 94(1) 3-21... 

Knoebl, I. The use of molecular biological methods to assess the effects of endocrine disrupting chemicals and natural hormones on growth in the sheepshead minnow (Cyprinodon variegatus). PhD Thesis. Oregon State University, Corvallis, OR, 2002. 

---