Regulation of inducible nitric oxide synthase expression in β cells by environmental factors: heavy metals

摘要

pThe expression of inducible NO synthase (iNOS) in pancreatic islet β cells modulates endocrine cell functions and, at very high levels of NO production causes β-cell death. We tested the hypothesis that environmental factors such as heavy-metal salts modulate iNOS expression in β cells. A rat β-cell line (insulinoma RINm5F) was cultured in the presence of low-dose interleukin (IL)-1β for suboptimal induction of iNOS. PbClsub2/sub (0.1–10 iμ/iM) dose-dependently increased NO (measured as nitrite) formation (iP/i& 0.001). In contrast, HgClsub2/sub suppressed nitrite production (0.1–10 iμ/iM, iP/i& 0.05). Measurements of iNOS activity by determining citrulline levels confirmed the potentiating effect of PbClsub2/sub (iP/i& 0.05). There was a narrow time window of heavy-metal actions, ranging from -24 h (Hgsup2+/sup) or -3 h (Pbsup2+/sup) to +2 h, relative to the addition of IL-1β. By semi-quantitative reverse transcriptase-PCR, enhanced levels of iNOS mRNA were found in the presence of Pbsup2+/sup (iP/i& 0.05) and decreased levels in the presence of Hgsup2+/sup. The amount of iNOS protein as determined by Western blotting was increased in the presence of Pbsup2+/sup. We conclude that Pbsup2+/sup upregulates and Hgsup2+/sup suppresses iNOS gene expression at the level of transcription, probably by acting on the signalling pathway. These observations may have important implications for understanding pathological effects of environmental factors on endocrine organ functions./p