High glucose and hydrogen peroxide increase c-Myc and haeme-oxygenase 1 mRNA levels in rat pancreatic islets without activating NFκB

Aims/hypothesis: Hyperglycaemia and the pro-inflammatory cytokine IL-1 beta induce similar alterations of beta cell gene expression, including up-regulation of c-Myc and haeme-oxygenase 1. These effects of hyperglycaemia may result from nuclear factor-kappa B (NF kappa B) activation by oxidative stress. To test this hypothesis, we compared the effects of IL-1 beta, high glucose, and hydrogen peroxide, on NF kappa B DNA binding activity and target gene mRNA levels in cultured rat islets. Methods: Rat islets were pre-cultured for 1 week in serum-free RPMI medium containing 10 mmol/l glucose, and further cultured in glucose concentrations of 5-30 mmol/l plus various test substances. Islet NF kappa B activity was measured by ELISA and gene mRNA expression was measured by RT-PCR. Results: IL-1 beta consistently increased islet NF kappa B activity and c-Myc, haeme-oxygenase 1, inducible nitric oxide synthase (iNOS), Fas, and inhibitor of NF kappa B alpha (I kappa B alpha) mRNA levels. In comparison, 1- to 7-day culture in 30 mmol/l instead of 10 mmol/l glucose stimulated islet c-Myc and haeme-oxygenase 1 expression without affecting NF kappa B activity or iNOS and I kappa B alpha mRNA levels. Fas mRNA levels only increased after 1 week in 30 mmol/l glucose. Overnight exposure to hydrogen peroxide mimicked the effects of 30 mmol/l glucose on haeme-oxygenase 1 and c-Myc mRNA levels without activating NF kappa B. On the other hand, the antioxidant N-acetyl-L-cysteine inhibited the stimulation of haeme-oxygenase 1 and c-Myc expression by 30 mmol/l glucose and/or hydrogen peroxide. Conclusions/interpretation: In contrast to IL-1 beta, high glucose and hydrogen peroxide do not activate NF kappa B in cultured rat islets. It is suggested that the stimulation of islet c-Myc and haeme-oxygenase 1 expression by 30 mmol/l glucose results from activation of a distinct, probably oxidative-stress-dependent signalling pathway.