29 July 2013. Many biochemical processes can go wrong when exposed to a toxic chemical. Although some of these deviations may be short-lasting, effects happening during rapid brain development could have consequences that are lasting. For example, if the migration of brain cells is halted, the brain architecture may become abnormal, even if the chemical interference is long gone. However, biochemical effects could be long-lasting if they interfere with the DNA in brain cells. Without causing mutations, some environmental chemicals are known to interfere with the methylation pattern of the DNA. Such changes can be critical, because methyl groups at important locations along the chromosome will determine if a gene is active or not.
DNA methylation is thought to be crucial both for brain development and for the plasticity that underlies learning and memory. An international research group has just reported details on DNA methylation in the frontal cortex of human brains and mouse brains. They showed that widespread rearrangement of the methyl group placements happens during development from fetal to young adult age. The methylation pattern in neurons differs from other cells, and the positioning of the methyl groups is probably important for brain functions.
These results are intriguing in regard to chemical brain drain. It has already been established that brain-toxic chemicals, such as lead and other metals, air pollutants, tobacco smoke, polycyclic aromatic hydrocarbons, and endocrine disruptors, can affect the DNA methylation in a variety of cell types. Could this be a mechanism by which the brain is drained by toxic chemicals? This question cannot be answered right now, as very little research has been carried out on human brains, in part because tissue samples are not easily available and must be obtained from tissue banks or autopsies.
But there is indirect evidence that supports this hypothesis. DNA chemistry has been examined in brains from 46 suicide completers and from 16 comparison subjects who died of other causes. In the hippocampus part of the brain, the researchers found a total of 366 important DNA sites – socalled promoters – that were differentially methylated in the two groups of subjects. About one-quarter of these sites had less methylation in the suicide completers, the rest were more methylated, thereby affecting genes involved in cognitive processes. These results suggest that the methylation changes that happen during early development can result in reprogramming of the DNA and thereby possibly also reprogramming of behavior, mood and suicide risk.
Unfortunately, DNA methylation changes cannot be easily undone, but this recent research suggests a mechanism by which chemical brain drainers may have crucial and lasting impact on brain development.