Studies Investigate Significance of BPA Health Effects
A recent study funded by the U.S. Environmental Protection Agency (EPA)
has reportedly measured internal exposure to bisphenol A (BPA) from dietary sources, with results suggesting that the substance is, for the most part, metabolized and excreted by the body. Justin Teeguarden, et al., “Twenty-Four
Hour Human Urine and Serum Profiles of Bisphenol A during High-Dietary
Exposure,” Toxicological Sciences, September 2011. Scientists with the Centers
for Disease Control and Prevention, Food and Drug Administration, and
Northwest Pacific National Laboratory apparently profiled the urine and
blood serum of 20 healthy adults for 24 hours (24-h) after “high-dietary” BPA
exposure via meals enriched with canned foods.
“From a safety perspective, the most pressing fundamental question
regarding BPA is whether human blood/tissue concentrations of BPA
following typical daily exposures are similar to, above, or below blood/tissue
concentrations causing demonstrably adverse effects in animal models,”
wrote the authors. “The main objective of this study was to characterize
internal exposure to TOTBPA and BPA by concurrently determining the 24-h
urinary elimination profile of TOTBPA and the serum time course of TOTBPA
and BPA in a group of healthy human adults on a controlled diet enriched in
canned food items likely to be significant dietary sources of BPA.”
The results evidently indicated that, “during these high dietary exposures,”
the subjects’ average BPA consumption, “estimated from the urinary excretion
of total BPA (TOTBPA = conjugated BPA + BPA), was 0.27 µg/kg body weight
(range 0.03-0.86), 21% greater than the 95th percentile of aggregate exposure
in the adult U.S. adult population.” At the same time, however, “TOTBPA
concentrations in serum were undetectable in 83% of the 320 samples
collected and BPA concentrations were determined to be less than or equal to
LOD [limit of detection] in all samples.”
The researchers concluded that “attributions of high blood BPA concentrations
from oral exposure seem implausible,” with peak BPA serum
concentrations “1-3 orders of magnitude below levels recently associated
with histological changes in a sensitive experimental model of rat prostate
intraepithelial neoplasia.” Recommending that future studies rule out dermal
exposure or leaching from the plastic tubing used in field collection, the
authors also urged a “continued focus on concurrent collection of internal
exposure data for experimental models of toxicity,” as well as “additional
refinements in the ability to collect and interpret human BPA biomonitoring
data through improved survey data and use of pharmacokinetic and reverse
dosimetry models to calculate internal exposures where experimental
measures are not feasible.”
Meanwhile, a second study has suggested that BPA and other xenoestrogens
could inhibit the effectiveness of new breast cancer drugs, as well as cause healthy breast cells to behave like cancerous ones. William Goodson, et al., “Activation of the mTOR Pathway by Low Levels of Xenoestrogens in Breast Epithelial Cells from High-Risk Women,” Carcinogenesis, September 2011. Conducted by California Pacific Medical Center researchers, the study allegedly found that exposing “renewable, human, high-risk donor, breast epithelial cells (HRBECs)” to BPA and the beauty product ingredient methylparaben activated “mammalian target of rapamycin (mTOR) pathway genesets,” thereby triggering “prosurvival changes” in healthy cells.
According to a September 12, 2011, medical center press release, this study
“breaks new ground” by examining BPA’s effect on cells before they turned cancerous, while also raising questions about the impact on cancer drugs such as tamoxifen and rapamycin. “Not every cell exposed to BPA or methylparaben will become cancer, but anything—any chemical exposure—that ‘flips the switch’ and causes healthy cells to act like cancer is cause for concern,” the lead author was quoted as saying. “Healthy breast cells exposed to cancer preventing and cancer treating drug Tamoxifen should undergo ‘programmed cell death’ or apoptosis, but after BPA exposure they don’t. Having two breast cancer drugs rendered ineffective by BPA exposure is very concerning for women who are battling breast cancer.”
