Nitric oxide radical (. NO) and peroxynitrite anion (ONOO-) have been implicated in lung inflammation and may be important in pleural injury. The present study was undertaken to determine the effects of asbestos exposure and cytokine stimulation on . NO and ONOO- production by rat pleural mesothelial cells. Accordingly, rat parietal pleural mesothelial cells were cultured for 2 to 72 h with or without 50 ng/ml of recombinant interleukin-1 beta (IL-1 beta) in the presence (1.05 to 8.4 mu g/cm(2)) or absence of crocidolite or chrysotile asbestos fibers. The effects of asbestos were compared with those of carbonyl iron, a nonfibrogenic particulate. Mesothelial cell messenger RNA (mRNA) expression of the inducible form of . NO synthase (iNOS), assessed with the reverse transcription-polymerase chain reaction (RT-PCR), increased progressively from 2 to 12 h in IL-1 beta-containing cultures. Nitrite (NO2-), the stable oxidation product of . NO in mesothelial cell conditioned medium, was assayed through the Griess reaction. Both types of asbestos fibers (chrysotile > crocidolite) upregulated the formation of NO2- in mesothelial cells costimulated with IL-1 beta in a concentration-dependent and time-dependent fashion. In contrast, carbonyl iron did not upregulate NO2- formation in 1L-1 beta-stimulated cells. Both types of asbestos fibers also induced NOS protein expression and the formation of nitrotyrosine in mesothelial cells and greatly induced the formation of nitrate (NO3-), a surrogate marker of ONOO- formation, in IL-1 beta-stimulated cells. However, the effects of chrysotile were notably greater than those of crocidolite. These findings may have significance for the induction of pleural injury by asbestos fibers.
