Posted on 02/12/2003 10:06:00 AM PST by cogitator
Lead Levels Linked to Male Infertility
MANHASSET, New York, February 6, 2003 (ENS) - Fertility experts today published the first conclusive evidence that lead is linked to male infertility.
A report a European medicine journal, "Human Reproduction," concludes that exposure to lead damages sperm function and may be one cause of unexplained male infertility cases.
The findings have led principal investigator Dr. Susan Benoff to urge doctors to measure lead in semen samples when evaluating men from couples with unexplained fertility. She said she also believes there is a case for health and safety authorities to continue reevaluating environmental exposure safety limits for lead.
Benoff, director of the Fertility Research Laboratories at the North Shore-Long Island Jewish Research Institute in Manhasset, and colleagues from several other U.S. institutions, studied metal ion levels and sperm function in semen from the partners of 140 women undergoing their first attempts at in vitro fertilization (IVF).
They found that while lead levels in seminal plasma varied over a wide range, there was a strong association between high lead levels and low fertilization rates, with changes in lead levels accounting for a fifth of the variance in fertilization rates.
"From our tests on lead in the seminal plasma of the participants and control experiments on nine fertile donors, we have evidence that higher lead levels interfere both with the ability of the sperm to bind to the egg and with its ability to fertilize the egg," said Benoff.
In order to fertilize an egg, a sperm has first to bind to it. A sugar called mannose on the outer coating of the egg is crucial to binding. Mannose receptors located on the head of human sperm recognize the mannose on the coating of the egg and regulate the binding process.
Then the sperm has to penetrate the egg. Successful binding induces an event called mannose-induced acrosome reaction (MIAR) - the release of digestive enzymes from the sperm that ease its passage through the egg coating so that its nucleus can fertilize the egg.
The researchers found that in the 140 men whose partners were undergoing IVF, higher lead levels in the semen were correlated with low numbers of mannose receptors, and with an inability of sperm to undergo MIAR. Higher lead levels were also associated with a premature or spontaneous acrosome reaction that occurred before sperm-egg contact, which also blocks fertilization.
"To see whether this association between increased lead levels could be causal we exposed healthy sperm from nine fertile donors to increasing doses of exogenous lead to see what would happen. We got the same results," said Benoff.
"Our data suggest that lead is acting at multiple levels in testis and sperm to decrease human male fertility," she added. "Our data also confirm that increased seminal plasma lead levels can occur without any detectable effects on male reproductive hormone function and also that they are associated with decreased sperm concentration, sperm shape, form and movement, suggesting that lead also acts in the testis."
Benoff said previous studies have shown that elevated lead levels in rats' testes are associated with programmed cell death of sperm precursors. Studies of men with low or zero sperm counts that are not caused by a physical obstruction suggest that programmed cell death in the testes is a major determinant of sperm count in the ejaculate.
"This leads us to believe that lead is a contributory factor of declining sperm counts," she said. "In the light of these results, environmental exposure limits for lead might be reevaluated."
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