By Janet Raloff
An ingredient in plastics and food-can linings coaxes cells from the pancreas to inappropriately secrete the hormone insulin, a finding that bolsters earlier links between type 2 diabetes and low-dose exposure to the chemical.
Bisphenol-A, or BPA, can mimic the effects of estrogen, a hormone that is involved in regulating insulin production in the body. Although controversy persists over BPA’s potency as an estrogen mimic, the new study, published online February 8 in PLoS ONE, finds that the pollutant is every bit as potent as the body’s natural estrogen in terms of triggering insulin release.
“I don’t think that anyone can say now that low-dose effects don’t occur,” says endocrinologist Ana Soto of the Tufts University School of Medicine in Boston, who was not involved in the new work. “It shows that changes happen in human cells — and at concentrations comparable to current levels of human exposure.”
The new work shows that BPA stimulates insulin release through a hormone-activating protein called estrogen receptor beta, or ER-beta, says Angel Nadal of Miguel Hernández University in Elche, Spain, who led the new study. Tiny concentrations of either estrogen or BPA boost the release of insulin. When his group tested mice engineered to produce no ER-beta, the effect went away, demonstrating that the protein is integral to BPA’s perturbation of insulin secretion.
For people with diabetes, oversecretion of insulin might be viewed as a positive development, he says. But in healthy individuals, it could eventually desensitize tissues to the hormone, creating insulin resistance — a hallmark of type 2 diabetes.
“If this happens in people with a genetic predisposition to diabetes, it will accelerate the induction of that disease,” Nadal says. His team has shown that exposure to BPA elevates an animal’s risk of developing insulin resistance. And people with type 2 diabetes — the type caused by the body’s diminished sensitivity to insulin — tend to have elevated concentrations of BPA in urine, a 2008 study showed.
“I don’t think BPA alone will cause type 2 diabetes,” says Franck Mauvais-Jarvis of Northwestern University’s Feinberg School of Medicine in Chicago. Dozens of environmental chemicals can mimic hormones, he says, “and I suspect it’s a cocktail of these nasties that predisposes individuals to developing metabolic disease, whether its type 2 diabetes or obesity.”
