DURHAM, N.C. -- A combination of chemicals given to protect Gulf War soldiers against deadly diseases and nerve gas may have inadvertently damaged their testes and sperm production, according to animal experiments at Duke University Medical Center.
The new study could explain why some veterans have experienced infertility, sexual dysfunction, and other genitourinary symptoms, said Mohamed Abou Donia, Ph.D., a Duke pharmacologist.
Three chemicals were given to soldiers to protect them against insect-borne diseases and nerve-gas poisoning: the insect repellent DEET, the insecticide permethrin, and the anti-nerve gas agent pyridostigmine bromide.
In a study designed to mimic those same conditions, Abou Donia and his colleagues gave rats equivalent doses to what the soldiers received. When given together, the chemicals caused extensive cell degeneration and cell death with various structures of the testes, he found. The damage was even more severe among rats that were exposed to moderately stressful situations in addition to the chemicals.
Results of the study, funded by the Department of Defense, are published in the Jan. 10, 2003 issue of The Journal ofToxicology and Environmental Health.
"It appears that moderate stress, combined with the three chemicals, caused the most severe deterioration in testicular structure and sperm production, and these conditions were likely experienced by some Gulf War soldiers in the combat environment," said Abou Donia, principal investigator of the study.
"Interestingly, the chemically-treated rats don't look or behave any differently than normal rats, just as the soldiers don't show any outward signs of disease," said Abou Donia. "But under a microscope, you can see clear and well-defined damage to a variety of testicular structures."
Abou Donia's team found the most pervasive cell damage within basal germ cells and spermatocytes, which give rise to mature sperm. The three chemicals combined with stress caused these cells to detach from one another, slough off, and develop holes known as "vacuoles." Such changes are well-known stages in the progression toward programmed cell death, known as apoptosis. The more cells that die, the greater the suppression of "spermatogenesis" or sperm production, said Abou Donia.
In fact, pathologic exams showed that most of the developing stages of sperm were interrupted, and some of the stages were absent altogether among rats treated with all three chemicals and stressful conditions.
Similar cell degeneration occurred in the seminiferous tubules, where developing sperm are produced, and Sertoli cells that support and nurture the developing germ cells.
"On every objective measure, the testes showed severe degeneration in the presence of multiple chemicals, suggesting that the chemicals have a synergistic or additive effect," said Abou Donia.
BRAIN DEFICITS COINCIDE WITH REPRODUCTIVE DAMAGE
The testicular damage corresponds to equally devastating brain changes in the same rats exposed to the chemicals plus stress, said Abou Donia. Findings from those experiments were published in the August 2002, issue of Neurobiology of Disease.
In that study, Abou Donia's team showed that chemicals and stress increased the permeability of the blood-brain barrier, allowing substances that would normally be blocked to enter the brain. Moreover, the researchers found large numbers of dead neurons, or nerve cells, in regions of the brain that control muscle strength and movement (cortex); balance and coordination (cerebellum); and memory, cognition and mood (hippocampus). Yet the animals appeared normal to the naked eye.
Similarly, Gulf War veterans have complained of deficits in these very functions for more than a decade, while clinical exams show no obvious signs of disease.
"The brain deficits we found in rats reside in specific areas of the brain that we can't measure in living humans," said Abou Donia. "This is why the deficits are so difficult to assess clinically and why animal studies are so critical to understanding the cellular damage."
Complicating the diagnostic process even further is the sheer volume of brain cells that must die before clinical deficits become obvious, he said. The human brain contains billions of nerve cells and supporting cells, so the loss of brain cells does not produce immediate and overt symptoms. Often, it takes repeated exposures to chemicals before the brain is depleted of enough neurons to trigger deficits, he said.
However, once the damage occurs, little can be done to repair it. Extensive nerve cell death causes "holes" in the brain and thus permanent deficits, because neurons cannot regenerate like other cells in the body.
"Many of the effects we see with chemical exposure are similar to those of aging, which is also associated with fewer neurons," said Abou Donia. He said his ongoing research should help prevent such debilitating conditions in the future.
"The military used these chemicals with the best of intentions, to protect soldiers from indigenous diseases in the Gulf War region," he said. "Without protection, there may have been thousands of deaths. But it appears that the precautions prevented one set of problems while creating another. Now, our task is to discern the mechanisms of illness in order to provide the soldiers with maximum protection and the least risk of chemically induced injury."
Duke colleagues Hagir B. Suliman, Ph.D., Wasiuddin A. Khan, Ph.D., and Ali A. Abdel-Rahman were co-authors of the paper.