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Last Updated: Dec 27th, 2006 - 19:07:47 |
Exposure to an extremely low dose of bisphenol-A (BPA) can disrupt the pancreatic beta-cell function in vivo inducing insulin resistance, according to a new study published in the Sept. 17-24 issue of Environmental Health Perspectives.
BPA is a well known endocrine disruptor. Due to its cross-linking properties, BPA was widely used by the chemical industry to produce plastic polymers. These polymers were mainly polycarbonates, which are often used to make transparent plastic bottles used to pack food and beverages. BPA is also used to make barrier coasting for the inner surface of food and beverage cans.
In previous studies, high concentrations of BPA have been detected in food and water extracted from autoclaved cans. BPA is also found in 95 percent of the urine and blood samples from Americans.
Previous studies found that much lower doses of BPA than the lowest adverse level (LOAEL) can affect sexual maturation, induce a decrease in daily sperm count, fertility, disrupts chromosome alignment and affects synaptogenesis.
In the study, researchers subcutaneously administered adult male mice with an extremely low dose (10 ug/kg) of either 17beta-estradiol (E2) or BPA, which was dissolved in tocopherol-stripped corn oil. The concentration is over a thousand times lower than the minimal concentration that the U.S. EPA believes has an adverse effect. E2 is a natural hormone. Both BPA and E2 are similar in chemistry.
The researchers found that E2 or BPA induces a rapid decrease in glycaemia that correlates with a rise of plasma insulin after two days of treatment with 10 ug/kg/day of E2 or BPA. The pancreatic beta-cell insulin content increased in an estrogen receptor-dependent manner. After four days of treatment, the mice developed chronic hyperinsulinaemia and their glucose and insulin tolerance were altered.
The researchers concluded that either abnormal levels of endogenous estrogen or environmental estrogen enhance the risk of developing type 2 diabetes mellitus, hypertension and dyslipidaemia.
The toxicity of BPA has been officially recognized, but there is a discrepancy among nations regarding the safe level of BPA. The European Commission's Scientific Committee of Food reported a Tolerable Daily Intake (TDI) of 10 ug/kg/day while the U.S. EPA considers 50 ug/kg/day as the reference dose based on the LOAEL of 50 mg/kg/day.
The findings of the current study show that exposure to a concentration of BPA 1000-times lower than the LOAEL used by the U.S. EPA can still alter blood glucose homeostasis in vivo. It rapidly increases plasma insulin altering blood glucose concentrations through a non-classical estrogen pathway, according to the authors.
The study was funded by the Spanish Ministry of Education and Science and Instituto de Salud Carlos III and conducted by Dr. Angel Nadal and colleagues at Universidad Miguel Hernandez de Elche in Spain and Instituto Nacional de Ciencias Medicas in Mexico.
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