Monday, October 8, 2012
More than 90 percent of all Americans are believed to carry varying levels of BPA exposure. Increasing urine BPA (Bisphenol-A) level was significantly associated with decreased sperm concentration, decreased total sperm count, decreased sperm vitality and decreased sperm motility, according to a Kaiser Permanente study appearing in the journal of Fertility and Sterility.
While the industry claims that BPA exposure levels from their products are safe, that claim seems very shaky when you start adding up all of the places we come into contact with BPA. See 5 Best Ways to Avoid Toxic BPA
In recent years, numerous studies have reported alarming associations between BPA exposure and myriad adverse health and development effects, from cancer and neurological disorders to physiological defects and, perhaps, a cause of childhood obesity.
Of particular concern is that BPA exposure is correlated with disruption of estrogen signaling. The chemical's molecular structure is similar to that of estradiol, one of the human body's three main estrogens, suggesting that BPA binds to estrogen receptors. The estrogen receptor is designed to grab and hold estradiol and related estrogens. Disparate chemicals, however, can share some structures found in estrogens, enabling them to bind to the estrogen receptor. When that happens, problems can occur.
Researchers at Yale School of Medicine have discovered that exposure during pregnancy to BPA causes permanent abnormalities in the uterus of offspring, including alteration in their DNA.
In binding to the estrogen receptor, BPA can disrupt the body's endocrine or hormone system, with consequences especially worrisome for fetuses, infants and young children. Earlier this year, the U.S. Food and Drug Administration banned BPA in baby bottles and sippy cups. Its use is more broadly banned elsewhere in the world.
In new research published in the October 4 online issue of the journal PLOS ONE, two scientists at UC San Diego School of Medicine say three-dimensional modeling suggests a metabolite of BPA -- a molecule produced when BPA is metabolized or broken down by the body -- actually binds to the estrogen receptor much more strongly than BPA itself. The finding could point the way to development of a new class of drugs designed to specifically inhibit excessive estrogen activity linked to disease.
According to Michael E. Baker, PhD, UCSD professor of medicine, and Charlie Chandsawangbhuwana, a graduate student in the UCSD Department of Bioengineering, several research labs have reported that BPA binds weakly to the estrogen receptor, suggesting that something else is interacting with this receptor.
In 2004, Shin'ichi Yoshihara, PhD, and colleagues at Hiroshima International University, discovered that another compound, dubbed MBP, was produced when BPA was metabolized. MBP has a 100-fold to 1,000-fold stronger bond to the estrogen receptor than BPA. However, the structural basis for MBP's high affinity for the estrogen receptor was not investigated further.
In their PLOS ONE study, Baker and Chandsawangbhuwana revived Yoshihara's research by creating three-dimensional, molecular models of MBP and BPA in the estrogen receptor and matching it against the crystal structure of estradiol in the estrogen receptor. They found that MBP's longer structure allows both ends of the chemical to interact with the estrogen receptor in a way similar to estradiol. The shorter BPA molecule contacts the receptor at just one end, resulting in a weaker connection, providing an explanation for BPA's lower affinity for the estrogen receptor.
"In other words, MPB is basically grabbing onto the estrogen receptor with two hands compared to just one hand for BPA," said Baker. "Two contact points makes a much stronger connection."
Baker said the 3D modeling supports the idea "that BPA is not the endocrine disruptor culprit. Instead, MBP is one (of perhaps several BPA metabolites) that causes disruption of estrogen signaling in humans and other animals."
He said the research points to the need to measure MBP levels in urine and blood of patients suspected of BPA-mediated health effects, and may fuel development of a new therapeutic treatment for conditions linked to excessive estrogen levels and activity, such as some forms of breast and prostate cancers.
"One could use MBP, which has a novel structure, as a template to develop a new class of chemicals that could bind to the estrogen receptor with high affinity," Baker said. "The goal would be to have these chemicals inhibit the action of estradiol instead of activating the estrogen response. These chemicals could control unwanted growth of estrogen-dependent tumors."
Marco Torres is a research specialist, writer and consumer advocate for healthy lifestyles. He holds degrees in Public Health and Environmental Science and is a professional speaker on topics such as disease prevention, environmental toxins and health policy.