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Regulation of inducible nitric oxide synthase expression in beta cells by environmental factors: heavy metals
W Eckhardt1, K Bellmann, H Kolb
1Diabetes Research Institute at the University of Düsseldorf, Auf'm Hennekamp 65, D-40225 Düsseldorf, Germany.
Abstract:
The expression of inducible NO synthase (iNOS) in pancreatic islet beta cells modulates endocrine cell functions and, at very high levels of NO production causes beta-cell death. We tested the hypothesis that environmental factors such as heavy-metal salts modulate iNOS expression in beta cells. A rat beta-cell line (insulinoma RINm5F) was cultured in the presence of low-dose interleukin (IL)-1beta for suboptimal induction of iNOS. PbCl2 (0. 1-10 microM) dose-dependently increased NO (measured as nitrite) formation (P<0.001). In contrast, HgCl2 suppressed nitrite production (0.1-10 microM, P<0.05). Measurements of iNOS activity by determining citrulline levels confirmed the potentiating effect of PbCl2 (P<0.05). There was a narrow time window of heavy-metal actions, ranging from -24 h (Hg2+) or -3 h (Pb2+) to +2 h, relative to the addition of IL-1beta. By semi-quantitative reverse transcriptase-PCR, enhanced levels of iNOS mRNA were found in the presence of Pb2+ (P<0.05) and decreased levels in the presence of Hg2+. The amount of iNOS protein as determined by Western blotting was increased in the presence of Pb2+. We conclude that Pb2+ upregulates and Hg2+ 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.
Insights
Environmental heavy metals impact pancreatic beta cells. Lead (Pb2+) increases inducible NO synthase (iNOS) expression, while mercury (Hg2+) suppresses it, affecting endocrine function and potentially beta-cell survival.
Area of Science:
- Endocrinology
- Toxicology
- Molecular Biology
Background:
- Inducible NO synthase (iNOS) expression in pancreatic beta cells regulates endocrine function and can lead to cell death at high nitric oxide (NO) levels.
- Environmental factors may influence iNOS expression in beta cells.
Purpose of the Study:
- To investigate the effect of heavy-metal salts, specifically lead (PbCl2) and mercury (HgCl2), on iNOS expression in a rat beta-cell line.
Main Methods:
- Insulinoma RINm5F cells were cultured with low-dose interleukin (IL)-1beta for iNOS induction.
- Cells were treated with varying concentrations of PbCl2 and HgCl2.
- Nitrite formation (NO production), iNOS activity (citrulline levels), iNOS mRNA, and iNOS protein levels were measured.
Main Results:
- PbCl2 dose-dependently increased NO production and iNOS activity.
- HgCl2 suppressed nitrite production.
- PbCl2 increased iNOS mRNA and protein levels, while HgCl2 decreased iNOS mRNA levels.
- Heavy metal effects occurred within a specific time window relative to IL-1beta addition.
Conclusions:
- Pb2+ upregulates iNOS gene expression at the transcriptional level, whereas Hg2+ suppresses it.
- These heavy metals likely act on the iNOS signaling pathway.
- Findings suggest environmental heavy metals can pathologically affect endocrine organ function.