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Low-Level Toxicants Can Harm Brain

By Jamie Talan, Newsday, Melville, N.Y.
http://www.redorbit.com/news/health/...urce=r_health#

Feb. 6--Low levels of mercury and lead exposure can damage developing brain cells -- a finding that might help explain how these toxicants can lead to a host of mental and medical problems, a new study said.

"There is a huge problem in toxicology," said Mark Noble, a professor of biomedical genetics and neurobiology at the University of Rochester and senior author of the study in the journal PLoS Biology. "There are 80,000 to 150,000 environmental toxicants about which we know nothing. Nobody knows how to screen for them or even where to start."

His study could be a major step in identifying methods of prevention and treatment.

Noble and his colleagues conducted their work in the laboratory, where they subjected so-called glial progenitor stem cells in the brain to low levels of lead and mercury. They found that these brain cells stopped dividing. They simply shut down. The mercury levels previously were thought to be safe in humans, Noble said. "It turns out they are not."

"These levels -- 5 to 6 parts per billion -- have adverse effects on these progenitor stem cells," he said.

These cells are crucial in building the brain during infancy and beyond.

Noble said studies have shown that between 300,000 and 600,000 babies are born each year with fetal mercury levels in cord blood that are 5 to 6 parts per billion.

The researchers found that progenitor stem cells -- the brain's support cells that carry out a number of key housekeeping functions -- are extraordinarily vulnerable to low levels of toxicants. In the test tube, as many as 25 percent of the progenitor cells obtained from rats shut down when exposed to the low levels of lead or mercury.

When the researchers looked at the cellular pathways affected by these exposures, they found the toxicants were disrupting cell function by increasing oxidative stress. All the toxicants they've studied led to the same oxidative stress-producing pathway. If similar processes are taking place in the developing brain of the fetus and child, "this could certainly have adverse effects," Noble said.

Glial progenitor cells also are present in adult brains. Noble said they have no idea what effects low level environmental toxicants are having but he suspects they might be making these brain cells more vulnerable to damage and disease.

"This needs to be taken very seriously," he said. "Development is a cumulative process and the effects of even small changes in progenitor cell division and differentiation over multiple generations could have a substantial effect on an organism."

On the positive side, finding one targeted pathway provides hope for identifying a single treatment for many kinds of environmental exposures, he said. His laboratory is studying a chemical called n-acetyl-cysteine, a potent antioxidant, that works to protect this pathway and could prevent abnormal cell damage and its consequences.