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Tuesday, April 23, 2013

BPA levels in fetal livers higher than adult exposures.

Published Apr 18, 2013 in environmentalhealthnews.org

Nahar, MS, L Chunyang, K Kannan, DC Dolinoy. 2012. Fetal liver bisphenol A concentrations and biotransformation gene expression reveal variable exposure and altered capacity for metabolism in humans. Journal of Biochemical and Molecular Toxicology http://dx.doi.org/ 10.1002/jbt.21459.



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HoboMama/flickr

A new study shows bisphenol A can cross the placenta and get into the developing livers of fetuses. Even more importantly, 80 percent of the BPA measured in the fetal livers was the more active type of BPA -- free BPA -- which is thought to cause health effects. Results from one of the first studies of its kind show the fetal livers had higher levels than adult livers. The chemical is found in food can linings, some thermal paper receipts and polycarbonate plastics.

Context

Bisphenol A (BPA) is used in many industrial applications as components of polycarbonate plastics and epoxy resins. BPA is commonly found in consumer products, such as the linings of beverage and food cans, dental sealants and thermal receipt paper.

Because of its wide use, exposure is ubiquitous in people. The chemical has been measured in human urine, blood, placental tissue, amniotic fluid and breast milk.

Animal and human studies link BPA to cancer, cardiovascular disease, reproductive health problems and childhood behavior changes.

The U.S. National Toxicology Program and the Food and Drug Administration consider BPA as a chemical of some concern because of its possible effects on pregnant women, the fetus, infants and children. Last month, California announced its intent to list BPA as a reproductive toxin.

The total BPA level measured in urine or blood contains two important parts: free BPA and conjugated BPA. Free BPA is the part that is potentially harmful. It is biologically active and can mimic estrogen hormones.

Conjugated BPA is formed when the liver processes free BPA. This part is not active and is considered less likely to have health effects. It is excreted from the body in urine.

In adults, BPA is rapidly transformed – usually in less than a day – from free BPA to conjugated BPA and then excreted. Therefore, free BPA usually comprises a small fraction – about 10 to 30 percent – of the total BPA when measured in urine or blood.

BPA can pass from a mother into the developing fetus. Because of differences in the way fetal and adult livers process the chemical, the fetus may be exposed to higher doses of free BPA than adults.

Aside from one study that measured BPA in fetal livers, little is known about fetal exposure, including how well fetal livers can process free BPA and the resulting exposure levels.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

What did they do?

Researchers analyzed 50 liver samples from first- and second-trimester fetuses. Fetal tissues were collected with permission from women choosing to terminate pregnancies. Two adult liver samples from autopsies were used as controls.
Free and conjugated BPA levels were measured in each sample. Samples were also tested for four genes known to affect liver function. If the genes were "expressed," then they had been activated and were presumably performing the function of processing BPA.

What did they find?

BPA was detected in the fetal liver samples, and the majority found – close to 80 percent – was the more harmful free BPA. BPA levels in the adult liver controls were either very low or too low to measure.
Other studies that measure BPA in adult blood or urine report the proportion of free BPA typically as 10-20 percent – the opposite of what was found in the fetal livers.
Three of the four metabolism genes had reduced expression when compared to adults. The fourth gene was not different. This suggests that fetal livers are not functioning in the same way as adult livers would.
However, reduced gene expression was not directly associated with higher free BPA levels in the tissue samples, so more questions remain about how BPA is processed in fetal livers.

What does it mean?

Fetuses may be exposed to much higher doses of the more harmful free BPA variety than adults. This may be a result of differences in the way adult and fetal livers function.
The results are important because exposure to BPA during critical developmental stages may alter fetal development and have health effects later in life.
The study is the first attempt to identify possible mechanisms that may result in higher fetal exposures to BPA. Surprisingly, levels of free BPA were much higher in the fetal liver tissues than adult controls or what is typically measured in adult blood or urine.
It is possible that differential gene expression played a role in these differences. The results from this study did not provide a clear connection. One of the limitations of the study, acknowledged by the authors, is that only two adult livers were used for comparison.
This is one of only two studies to directly assess fetal exposures to BPA by measuring the two parts of the chemical in the livers. The results of this study are in line with the handful of other studies that measure BPA in the placenta and amniotic fluid.

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