Mon, 06 Jun 2005 16:50:37 GMT

Toxins harm descendant fertility. Epigenetic effects of endocrine disruptors pass down four generations in rats [News from The Scientist]

These epigenetic effects (essentially effects that alter the course of an animals genetic programming without actually changing the genes) have been known for some time. This shows the ‘permanency’ of the effects for so many generations. The ability to alter genetic expression by exposure to hormones at inappropriate times, changes that seem to then become permanent, is a chilling discovery. Because we have been exposing large numbers of animals and people to just such hormones.

A good example is bisphenol A. This is a major ingredient in polycarbonate materials, such as plastic bottles It turns out to act as an estrogen. It can produces all sorts of changes in mice if they are exposed to it at the right time.

Exposure to a Low Dose of Bisphenol A during Fetal Life or in Adulthood Alters Maternal Behavior in Mice

Estrogenic chemicals in plastic and oral contraceptives disrupt development of the fetal mouse prostate and urethra

It turns out that the plastic bottles used to give water to mice in thousands if not millions of cages are also made of polycarbonate. Although the standard wisdom was that the Bisphenol A was rendered inert by the manufacturing process, that turns out not to be the case. In fact, it leaches out at room temperature. This suggests that many experiments investigating a wide range of molecules could be wrong because the ‘control’ mice were actually on a pseudo-estrogen treatment due to leaching polycarbonate bottles.

But it is the possible exposure to such hormones in pregnant woman, and the possible permanent changes in both males and females, that is particularly worrisome. This newest paper, from Science, examines the effects of a fungicide and pesticide on generations of mice. They show that the effect of these chemicals is to reprogram methylation of the DNA, which is a biological process used to turn certain genes on and other off. By altering the methylation pattern seen, these chemicals alter the expression of genes, resulting in possible wholesale changes. In these experiments, male infertility went up, with about 20% of the male mice from exposed mice being infertile, out to at least 4 generations.

Now, the only saving grace so far from this study it that the doses used were much higher than would be expected in our current environment. So perhaps our actual exposure to these chemicals would be below some threshold. But, then again, maybe not. As this paper says, further research is needed. I do, however, really like the last sentence of their abstract. Classic scientific understatement:

The ability of an environmental factor (for example, endocrine disruptor) to reprogram the germ line and to promote a transgenerational disease state has significant implications for evolutionary biology and disease etiology.

Significant implications, indeed.