Endocrine disrupting estrogens

Kumar AK, Mohan SV (2012) Removal of natural and synthetic endocrine disrupting estrogens by multi-walled carbon nanotubes (MWCNT) as adsorbent kinetic and mechanistic evaluation. Sep Purif Technol 87 22-30... 

Female sexual development and behaviour in mammals occurs by default and requires no ovarian secretion, and it is only in genetic males that the testis can secrete hormones which destroy this female pattern and superimpose that of the male. Sexual differentiation is not so well defined in fish, and larval exposure to both synthetic estrogens and androgens is widely used in aquaculture to produce monosex cultures. Endocrine disruption of sexual differentiation in fish may therefore reflect both the complexity and diversity of such processes between different species. Some care is required in use of the terms hermaphrodite and sex-reversal since a true hermaphrodite has both functional testes and ovaries and a sex-reversed fish is fully functional as its final sex—both produce the appropriate viable gametes. Such functional sex-reversal is not possible in mammals, but in some species of fish it is the normal developmental pattern. In most of the cases of hermaphroditism or sex-reversal reported in the non-scientific press, there is evidence only for a few ovarian follicles within a functional testis. This may be considered as feminisation or a form of intersex, and is very clearly endocrine disruption, but it is certainly neither sex-reversal nor hermaphroditism. In some cases the terms have even been used to infer induction of a single female characteristic such as production of yolk-protein by males. 

The liver plays an important role in the endocrine system. The concentrations of hormones in plasma, and the activity of the glands which secrete them, are determined by the rate at which they are deactivated by the liver. The liver also has a major function in female reproduction since it is the target tissue of ovarian estrogen, to which it responds by producing the yolk protein vitellogenin. " Xenobiotics that affect either of these functions can therefore be considered to be potential endocrine disrupters. 

Exposure to estrogenic compounds through diet will differ for herbivores and carnivores, the latter being most likely to encounter endogenous steroids in their prey. Efficient uptake of steroids in mammals is illustrated by the use of the contraceptive pill, but routes of absorption in invertebrates remain to be determined. The relationship between endocrine disruption and metabolic toxicity, with reduced reproductive viability a secondary consequence of metabolic disturbance, also merits further study in invertebrate species. 

In vivo studies in animals suggest that endosulfan may disrupt normal reproductive hormone levels in male animals, but that it is not an endocrine disrupter in females. Persistent depressed testicular testosterone was seen in male rats after intermediate duration oral exposures to endosulfan. In ovariectomized female rats, orally administered endosulfan did not induce normal development of female reproductive tissues, and in female mice and immature female rats, acute parenteral exposure to endosulfan did not affect several endocrine-related end points. In vitro studies have evaluated endosulfan for estrogen receptor (ER) and cytosolic protein binding affinity, ER-mediated reporter gene expression, estrogenic induction of cell proliferation, and alteration of relative abundance of active estradiol metabolites. Overall, in vitro evidence in favor of endosulfan estrogenicity indicates relatively weak potency compared to 17[3-estradiol. Apparently contradictory results were reported in different... 

In addition to the foregoing, three further examples in this list (numbers 5-7) deserve consideration. These are (5) interaction of endocrine disrupters with the estrogen receptor, (6) the action of uncouplers of oxidative phosphorylation, and (7) mechanisms of oxidative stress. Until now only the first is well represented by biomarker assays that have been employed in ecotoxicology. 

Endocrine disrupters Chemicals that cause disturbances of the endocrine system (e.g., by acting as agonists or antagonists of the estrogen receptor). 

In some animals, consumption of a phytoestrogen-rich diet can cause temporary infertility and reproductive system disorders (Irvine, 1999). In humans, lower testosterone levels and a decline in human semen quality over the past century have been luiked to increased exposure to environmental endocrine disrupters (EDCs) (Sharpe and Skakkebaek, 1993). Furthermore, cases of sexual impotence have been reported in males exposed to synthetic estrogens in the pharmaceutical industry (Mattison et al., 1990). If this might be the case, the fetal-prepubertal period and Sertoli cell development would be of critical importance (Sharpe and Skakkebaek, 1993). However, an adverse effect of phytoestrogens on male fertility has yet to be proven. Recent work (Mitchell et al., 2001) addressing this point led to the conclusion that up to 40 mg/day of isoflavones over a two-month period had no effects on gonadotrophin and... 

A general overview of endocrine disrupters and estrogens mechanism(s)... 

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