FOR IMMEDIATE RELEASE: September 2, 2003
Contact: At the University of Maryland School of Medicine
Bill Seiler email@example.com 410-328-8919
A study conducted at the University of Maryland School of Medicine finds that exposure to low levels of mercury can speed up and worsen the symptoms of an induced lupus-like disease in mice, even when the exposure occurs before the development of the disease. The researchers say if this relationship were shown to be true in humans, it would redefine the association between mercury exposure and the autoimmune disease lupus. Their study, the first to connect low-level mercury exposure to the severity of lupus in mice after they develop the disease, appears in the August 2003 edition of Environmental Health Perspectives, published by the National Institute of Environmental Health Sciences, part of the National Institutes of Health.
The lead investigator of the study, Charles S. Via, M.D., professor of medicine, microbiology and immunology at the University of Maryland School of Medicine, says previous studies have found that mercury exposure in animals can exacerbate pre-existing autoimmune disease and even induce autoimmune disease in susceptible animals.
"Our study takes the link further by demonstrating that exposure to mercury prior to the induction of an autoimmune disease in mice significantly worsens the severity of that disease after it develops," says Dr. Via, who is also a rheumatologist at the University of Maryland Medical Center.
Scientists are uncertain about the impact of mercury exposure on humans. "There is considerable concern over potential neurotoxic effects associated with current levels of human exposure to mercury," says study co-author, Ellen K. Silbergeld, Ph.D., a professor of Environmental Health Sciences at the Johns Hopkins Bloomberg School of Public Health, who formerly worked at the University of Maryland School of Medicine. "These results suggest that we should examine the immune system as a target of mercury toxicity in humans."
One step in that direction involves using special mouse strains to study the links between mercury and autoimmune disease. In one strain, the mice are susceptible to mercury-induced autoimmune disease. Another strain of mice develops an autoimmune disease that is similar to lupus.
In this study, healthy mice that were not genetically susceptible to mercury-induced autoimmune disease were given injections of low-dose inorganic mercury over the course of two weeks. The levels of mercury and the length of exposure chosen were much lower than the range commonly used in mouse studies of mercury toxicity. Five days later, the mice were given cells from the lupus-inclined mouse strain to induce lupus-like chronic graft-versus-host disease, a well-established mouse model of acquired autoimmunity.
Dr. Via says the results surprised him. Mercury exposure accelerated the deaths of the lupus-induced mice and sped up the course of a kidney disease associated with lupus. Further, antibodies, or markers characteristic of lupus-like autoimmunity were significantly elevated in the mice that had been pretreated with mercury.
"Our findings suggest that low-level mercury exposure does not cause lupus," says Dr. Via. "Lupus is clearly multifactorial. You have to have a susceptible individual who has the appropriate environmental exposure. But our study clearly shows that mercury can act as a disease modifier for lupus. Exposure to mercury might either lower the threshold of susceptibility, or increase the severity of the disease."
According to Dr. Via, the researchers have begun additional studies to determine whether subtle abnormalities remain after mercury clears from the body that may produce the modifications in lupus. "We can speculate about a lot of possible mechanisms, but we clearly need further study to determine exactly how mercury accelerates lupus," says Dr. Via.
Lupus is a chronic disease that causes inflammation of connective tissue. The most common form of lupus affects exposed areas of the skin, while the more serious and potentially fatal form can affect many systems of the body including the kidneys. It is an autoimmune disorder, in which the immune system for unknown reasons attacks connective tissue as though it were foreign.
Other members of the research team include Phuong Nguyen, B.S., Florin Niculescu, M.D., Ph.D., John C. Papadimitriou, M.D., Ph.D., and Dennis Hoover, Ph.D., all of the University of Maryland School of Medicine.
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