Stimulating early years environments can reverse damage caused by lead poisoning
Lead exposure in early childhood can lead to severe cognitive and behavioural impairments in children, lasting well into adulthood.
Children who live in housing stock built before 1978, the year in which lead was banned as an ingredient in paint, are at high risk of being exposed to lead from lead dust or chipping and peeling lead-containing paint in their homes, and although researchers have looked at effects of early life lead exposure on a small number of genes involved in learning, memory, and brain development, until now research was lacking as to the full extent of the toxicity.
New research from Thomas Jefferson University shows that over 3,500 genes in the hippocampus, a part of the brain involved in learning and memory, are affected by lead poisoning.
The work also shows that providing animals with stimulating environments early in life can reverse the large majority of these genetic changes, reinforcing the potentially important role of early-childhood education in combating the effects of lead poisoning.
Dr Jay Schneider, a senior author in the study explained that recent estimates suggest that there are at least a half million children in the U.S. with blood lead levels at or above amounts that can adversely affect cognitive function.
“Our work demonstrates that by providing an enriched early life environment, the adverse effects of lead on the brain may be minimised or potentially reversed, emphasizing how important early childhood interventions may be,” he continued.
Working with Dr Garima Singh, Dr Schneider looked at rats which were exposed to lead from birth to the time of weaning, at 21 days of age.
“Our experiments aimed to replicate conditions of human lead exposure,” says Dr. Singh. “21 days of age for rats is the equivalent to an age of about 2-3 years in humans, which is commonly when lead exposure occurs. That is because crawlers and toddlers are likely to put many things in their mouths including paint chips or toys covered in dust from deteriorating lead paint.”
From 21 days, the lead-exposed animals were separated into two different housing conditions: ones that were either enriched or ones that lacked stimulation. The so-called enriched cages had more social activity, with a total of six rats, together with chew toys and various things to climb on and burrow through that were changed twice every week for novelty.
The non-enriched cages were smaller, only held three animals and did not contain any additional stimulation.
“We now know that stimulating social environments are as important for rodents as they are for human children, in terms of cognitive and behavioral health and with effects on physical health as well,” Dr Singh explained.
The researchers looked at changes in expression of genes from the part of the brain involved in memory – the hippocampal region. They found that the expression levels of over 3,500 genes were affected by the lead exposure, either abnormally churning out more or less of their gene products.
In rats exposed to lead, the genes affected were amongst those involved in memory and nerve signaling pathways, and also those involved in brain development.
However, approximately 80 per cent of the gene expression changes induced by the lead exposure were reversed in the group of animals that lived in the stimulating environment until day 55, which is roughly equivalent to adolescence in humans.
Additionally, the animals living in the non-enriched environment had memory deficits while the animals living in the enriched environment did not.
“We know that there is no safe level of lead exposure for children,” Dr Schneider emphasised. “Lead can damage the brain and derail normal brain development. However, our work suggests that it may be possible to mitigate the wide-spread adverse effects of lead on the young brain by providing adequate access to stimulating, interesting environments and activities in early childhood and perhaps longer.”
“Unfortunately, these kinds of resources are often not available to the population most at risk for lead poisoning, that is, children who are growing up in impoverished or low socioeconomic environments.”
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