London - A chemical widely used in plastic packaging and food containers may be toxic to the central nervous system by interfering with a key gene involved in the development of nerve cells, a study suggests.
Scientists have found that bisphenol A (BPA), which is used in a variety of consumer products ranging from fizzy-drink cans to food mixers, affects the function of a gene called Kcc2 which is involved in the growth of neurons, or nerve cells, in the brain and spinal cord.
The study, based on rats and human neurons grown in the laboratory, found female nerve cells more susceptible to BPA than male neurons. This might explain why certain neurodevelopmental disorders in humans are more common in females, such as Rett syndrome, a severe form of autism found only in girls, the scientists said.
“Our study found that BPA may impair the development of the central nervous system, and raises the question as to whether exposure could predispose animals and humans to neurodevelopmental disorders,” said Wolfgang Liedtke of Duke University Medical Centre in Durham, North Carolina.
“Our findings improve our understanding of how environmental exposure to BPA can affect the regulation of the Kcc2 gene. However, we expect future studies to focus on what targets aside from Kcc2 are affected by BPA,” said Professor Liedtke, who led the study published in the Proceedings of the National Academy of Sciences.
Other scientists have, however, criticised the study for exposing neurons to relatively high doses of BPA that would not normally be encountered by the human body. They believe that suggestions of a link between BPA and human disorders are not supported by the evidence when it comes to realistic exposure levels.
“Interesting though the effects are from a mechanistic point of view, they have no relevance to human health because the concentration of bisphenol A used exceeds human exposure by about 100,000 times - and this is probably a conservative estimate,” said Professor Richard Sharpe of Edinburgh University.
“This study is reminiscent of many similar studies with bisphenol A in vitro or in animal studies. Many show convincing effects on various biological processes relevant to human health, but they always involve doses that are in a different ballpark to human exposure,” he said.
Despite many scientists' claims that there is no evidence that BPA is toxic at low doses, the European Commission banned the chemical in baby bottles in 2011 and the US Food and Drug Adminstration followed suit last year.
BPA is known to mimic oestrogen, the female sex hormone, but fertility experts such as Professor Sharpe have dismissed suggestions that it could explain the rise in male infertility, along with many other disorders, because it is quickly broken down in the body.
“Although we are all exposed to BPA, the rapid inactivation of BPA in the gut and liver means that exposure elsewhere in the body is so low as to be immeasurable. So although it appears we're exposed, effectively we are not,” Professor Sharpe said.
Professor Andrew Bartholomaeus of the University of Canberra in Australia, said that any BPA consumed in food or drink is completely metabolised before it enters the blood stream, which means that cells within the body are not exposed to “free” BPA.
BISPHENOL A: WHAT IT’S USED IN
Food and drink containers: Many food and drink cans are lined with a BPA resin, some glass jars include the chemical inside their lids, and many plastic bottles use the substance too.
Electronics: BPA is in the casings of many products including CDs and DVDs, telephones, televisions, laptops and personal computers, printers, cameras, shavers, hairdryers, irons, food mixers, microwaves and kettles.
Sports equipment: Sports helmets, ski goggles, binocular housings and equipment used for golf and tennis can all contain BPA.
Till receipts: BPA is used to make ink visible on thermal till receipts. Some people have raised concerns about shoppers handling the paper and then touching their mouths or their food. - The Independent