THE toxic effects of lead could be more far-reaching than we thought. Monkeys exposed to the heavy metal during infancy may be predisposed to develop the equivalent of Alzheimer鈥檚 disease.
鈥淲e鈥檙e not saying that lead exposure causes Alzheimer鈥檚 disease, but it鈥檚 a risk factor,鈥� says Nasser Zawia of the University of Rhode Island in Kingston, whose team discovered the link.
Zawia鈥檚 team fed baby monkeys infant formula milk laced with low levels of lead, then followed their progress until the age of 23. While the adult monkeys did not show symptoms of Alzheimer鈥檚 per se, post-mortem analyses of their brains showed that the lead-fed monkeys had plaques and other abnormalities identical to those found in the brains of people with Alzheimer鈥檚.
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What鈥檚 more, comparative analysis of RNA in their brains showed three key genes linked with Alzheimer鈥檚 disease were 50 to 100 per cent more active in lead-fed monkeys than in those given uncontaminated milk as infants (The Journal of Neuroscience, ). The genes help generate the beta-amyloid protein found in brain plaques.
鈥淭hree key genes linked with Alzheimer鈥檚 disease were 50 to 100 per cent more active in lead-fed monkeys鈥�
Blood samples taken from the baby monkeys at 400 days and at regular intervals thereafter showed lead concentrations slightly above those considered safe in children by the US Centers for Disease Control and Prevention. Yet by the time the monkeys were three years old the lead had been excreted, leading Zawia to conclude the damage was done during the critical early period of life, rather than during adulthood.
Earlier experiments in rats and mice that did develop Alzheimer鈥檚-like symptoms after being exposed to lead as infants also suggested adult exposure did not put them at any increased risk of Alzheimer鈥檚.
Other researchers caution against overreacting to the findings. 鈥淭his study does not prove that exposure to lead in early life causes Alzheimer鈥檚 disease,鈥� says Susanne Sorensen, head of research at the UK鈥檚 Alzheimer鈥檚 Society. 鈥淟ead is well known to have a number of negative effects on cells, so it鈥檚 not surprising some of these occur in the brain.鈥� She says more research is needed to investigate whether early life events can lead to brain changes that increase the risk.
Zawia agrees there鈥檚 no cause for alarm, particularly as much lead has already been removed from paint, petrol and other environmental sources. However, he says the findings reinforce the need to limit lead exposure, and highlight an unexpected hazard. 鈥淲e want to raise awareness that some environmental exposures could have delayed or masked consequences that become apparent later in life,鈥� he says.
Jackie Hunter, head of GlaxoSmithKline鈥檚 centre for neurology drug discovery in Harlow, UK, said the findings reveal how environmental and genetic factors might combine to alter susceptibility to the disease.
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