Science Forums 2

[Michaelangelica]

Q: In the online audio presentation, Dr. Dana Dolinoy states that the epigenome is responsible for determination of cell type and activity. Does the bisphenol A finding suggest that fetal or environmental exposure to plastics could play a direct role in a genetic propensity toward obesity in humans?
Chantel Smith, Toronto, Canada

Q: Could there be a connection between the increase in plastics in our environment and rising obesity rates?
Randy Grenier, Waltham, Massachusetts

A: We have recently demonstrated that exposure of pregnant mice to bisphenol A (BPA), a building block of polycarbonate plastics and epoxy resins used to make consumer items ranging from water bottles to dental sealants, significantly reduces DNA methylation in Avy mice (Dolinoy et al., Proc. Natl. Acad. Sci. USA 104: 13056-13061, 2007). This results in the birth of more yellow offspring, mice that become obese and have a higher incidence of diabetes and cancer as adults. Thus, there could be a connection between the increase in plastics in our environment and the rising incidence of obesity in humans. However, such an association will not be able to be demonstrated unequivocally until the expression and function of genes involved in human obesity are shown to be altered by BPA.

[Editor's note: For more on the agouti mice, see A Tale of Two Mice.]

Q: If BPA has the same effect on humans as it did the mice in your study, why aren't all human babies born sick and obese?
Anonymous

A: BPA exposure during pregnancy increases the incidence of yellow offspring, but it does not result in all of the offspring having a yellow coat color and becoming obese. Therefore, if BPA has the same effect on humans as it does in mice, it would simply increase the percentage of humans who become obese as the BPA exposure increases. This happens to be the situation found in Western cultures, regardless of whether BPA is the culprit.

Q: How do the exposure levels of BPA in the agouti mice experiments compare to human exposure levels—especially exposure levels in pregnant women?
Dr. Gloria Jahnke, Chapel Hill, North Carolina

A: It is difficult to compare the BPA dose used in our mouse study with that to which humans are exposed, because in humans, the BPA is found in the plasma or excreted in the urine. We can't tell exactly how much of the chemical people ingest. The level of BPA that the pregnant mice were exposed to in our study was five times lower than the maximum nontoxic threshold dose in rodents (Dolinoy et al., Proc. Natl. Acad. Sci. USA 104: 13056-13061, 2007). Although this is likely higher than typical human exposure, it produced no significant effects on reproductive outcomes, litter size, or offspring health at birth. It did, however, markedly increase the incidence of mice born with a yellow coat color—animals that become obese and have higher incidences of diabetes and cancer as adults.

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