By Janet Raloff
Several studies have implicated estrogen, the primary female sex hormone, in fostering a serious autoimmune disease called lupus. That’s why scientists had expected that bisphenol-A (BPA), an estrogen-mimicking ingredient of polycarbonate plastics and dental sealants, might also abet lupus. A Minnesota group’s rodent data now show just the opposite.
In laboratory animals, BPA can not only impair reproductive development but also cause female mice to produce eggs bearing abnormal numbers of chromosomes (SN: 4/5/03, p. 213: Available to subscribers at Wrong Number: Plastic ingredient spurs chromosomal defects). Suspecting that BPA exposures might underlie some share of the unexplained incidence of lupus in people, Debby Walser-Kuntz and her colleagues at Carleton College in Northfield, Minn., administered the pseudohormone for 1 week to female mice that had not yet entered puberty. The dose was similar to doses that people can acquire unintentionally, and the researchers used both normal mice and a strain that develops lupus. The researchers monitored markers of immunity for up to 8 months.
Lupus ordinarily creates aggressive, tissue-damaging inflammation (SN: 12/20&27/03, p. 387: Available to subscribers at Cardiac Connection: Lupus patients exhibit signs of heart disease). In the normal mice, BPA exposures suppressed the animals’ production of interferon-gamma, a master-control protein in the immune system. Such a change might leave the animals at higher risk of infection, Walser-Kuntz notes.
BPA-treated lupus-prone animals also produced less interferon-gamma than is normal for their strain. That deficiency may keep the immune system under better control. In the treated mice, lupus developed 7 weeks later and proved less aggressive than in their untreated, disease-prone kin. These findings appear in the December 2003 Environmental Health Perspectives.
Walser-Kuntz’s team now plans to identify how BPA and estrogen differ mechanistically. Their goal: clues for developing a therapeutic BPA-like compound without the original’s potential reproductive toxicity.
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