Thursday 29 November 2007

Pesticides, Contaminants & Fertility

Methoxychlor (MXC), a common insect pesticide used on food crops, may interfere with proper development and function of the reproductive tract, leading to reduced fertility in women, researchers at Yale School of Medicine write in the journal Endocrinology. The researchers found that MXC, which was manufactured as a safer replacement for the now-banned DDT, alters the estrogen-regulated gene Hoxa10 in the reproductive tract and reduces the ability of the uterus to support embryo implantation. The researchers used mice and then human cell lines to confirm their findings. MXC is a man-made pesticide used to kill flies, mosquitoes, cockroaches and other insects, and is applied directly to food crops, livestock, home gardens and pets. It is one of a large number of chemicals that can mimic the action of hormones and in some instances interfere with endocrine function. Some of these endocrine disruptors bind estrogen receptors and adversely affect reproductive tract development, which is heavily influenced by estrogen. MXC and other chemicals like DDT have been shown in other studies to induce abnormalities in tissue development and function in the female reproductive tract. "MXC has an adverse effect on these mice similar to that of DES, a synthetic estrogen," said senior author Hugh S. Taylor, M.D., associate professor in the Division of Reproductive Endocrinology and Infertility in the Department of Obstetrics, Gynecology & Reproductive Sciences at Yale School of Medicine. "Female offspring of women exposed to DES were more likely to have an abnormally shaped cervix, were more prone to cancer of the vagina, miscarriages, early labor and other complications."
The contaminant bisphenol-A (BPA)--widely used to make many plastics found in food storage containers and dental products--can have long-term effects in female development, according to a recent study by Yale School of Medicine researchers. Lead investigator Hugh S. Taylor, said the study shows that BPA changes the expression of key developmental genes that form the uterus. Taylor explained that if pregnant women are exposed to the estrogen-like properties found in BPA, it may impact female reproductive tract development and the future fertility of female fetuses the mother is carrying. The study was conducted on pregnant female mice by administering a range of doses of BPA on days 9-16 of their pregnancies. The aim was to see what interaction BPA would have with the HOXA10 gene, which is necessary for uterine development.
Taylor and co-author Caroline C. Smith of the Department of Epidemiology and Public Health at Yale School of Medicine, found that BPA does, in fact, alter the expression of the HOXA 10 gene, implying that exposure to the popular plastics component may lead to infertility in humans. "The net effect is concerning," said Taylor. "We are all exposed to multiple estrogen-like chemicals in industrial products, food and pollutants." BPA is found in plastics, including baby bottles, epoxy resins used in canned goods and dental sealants. In addition to this new link to fertility and reproductive health, previous findings by Csaba Leranth, M.D., also in Yale Ob/Gyn, found that low doses of BPA in female rats inhibited estrogen induction in the brain. This can lead to learning impairment and, in old age, the onset of neurodegenerative disorders such as Alzheimer's disease.

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