Xenoestrogen

Xenoestrogens are a type of xenohormone that imitates estrogen. They can be either synthetic or natural chemical compounds. Synthetic xenoestrogens include some widely used industrial compounds, such as PCBs, BPA, and phthalates, which have estrogenic effects on a living organism even though they differ chemically from the estrogenic substances produced internally by the endocrine system of any organism. Natural xenoestrogens include phytoestrogens which are plant-derived xenoestrogens. Because the primary route of exposure to these compounds is by consumption of phytoestrogenic plants, they are sometimes called "dietary estrogens". Mycoestrogens, estrogenic substances from fungi, are another type of xenoestrogen that are also considered mycotoxins.

Xenoestrogens are clinically significant because they can mimic the effects of endogenous estrogen and thus have been implicated in precocious puberty and other disorders of the reproductive system.

Xenoestrogens include pharmacological estrogens (in which estrogenic action is an intended effect, as in the drug ethinylestradiol used in contraceptive pills), but other chemicals may also have estrogenic effects. Xenoestrogens have been introduced into the environment by industrial, agricultural and chemical companies and consumers only in the last 70 years or so, but archiestrogens exist naturally. Some plants (like the cereals and the legumes) are using estrogenic substances possibly as part of their natural defence against herbivore animals by controlling their fertility.

The potential ecological and human health impact of xenoestrogens is of growing concern. The word xenoestrogen is derived from the Greek words ξένο (xeno, meaning foreign), οἶστρος (estrus, meaning sexual desire) and γόνο (gene, meaning "to generate") and literally means "foreign estrogen". Xenoestrogens are also called "environmental hormones" or "EDC" (Endocrine Disrupting Compounds, or Endocrine disruptor for short). Most scientists that study xenoestrogens, including The Endocrine Society, regard them as serious environmental hazards that have hormone disruptive effects on both wildlife and humans.

The onset of puberty is characterized by increased levels of hypothalamic gonadotropin releasing hormone (GnRH). GnRH triggers the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary gland, which in turn causes the ovaries to respond and secrete estradiol. Increases in gonadal estrogen promote breast development, female fat distribution and skeletal growth. Adrenal androgen and gonadal androgen result in pubic and axillary hair. Peripheral precocious puberty caused by exogenous estrogens is evaluated by assessing decreased levels of gonadotrophins.

Xenoestrogens in plastics, packaged food, drink trays and containers, (more so, when they've been heated in the sun, or an oven), may interfere with pubertal development by actions at different levels – hypothalamic-pituitary axis, gonads, peripheral target organs such as the breast, hair follicles and genitals. Exogenous chemicals that mimic estrogen can alter the functions of the endocrine system and cause various health defects by interfering with synthesis, metabolism, binding or cellular responses of natural estrogens.

Although the physiology of the reproductive system is complex, the action of environmental exogenous estrogens is hypothesized to occur by two possible mechanisms. Xenoestrogens may temporarily or permanently alter the feedback loops in the brain, pituitary, gonads, and thyroid by mimicking the effects of estrogen and triggering their specific receptors or they may bind to hormone receptors and block the action of natural hormones. Thus it is plausible that environmental estrogens can accelerate sexual development if present in a sufficient concentration or with chronic exposure. The similarity in the structure of exogenous estrogens and the estrogens has changed the hormone balance within the body and resulted in various reproductive problems in females. The overall mechanism of action is binding of the exogenous compounds that mimic estrogen to the estrogen binding receptors and cause the determined action in the target organs.

Xenoestrogens have been implicated in a variety of medical problems, and during the last 10 years many scientific studies have found hard evidence of adverse effects on human and animal health.