Haeme-oxygenase 1 expression in rat pancreatic beta cells is stimulated by supraphysiological glucose concentrations and by cyclic AMP

Aim/hypothesis Increased expression of haeme-oxygenase 1 (HO1) and other antioxidant enzymes could improve pancreatic beta-cell survival under stressful conditions, including hyperglycaemia. However, how hyperglycaemia increases islet HO1 expression is not known.Methods Rat islets were pre-cultured for 1 week in RPMI medium containing 10 mmol·l^–1 glucose (G10), and further cultured overnight in G5-G30 plus various test substances. Islet HO1 mRNA and protein expression was measured by semiquantitative RT-PCR, western blot, and immunohistochemistry.Results Islet HO1 mRNA expression was minimal after overnight culture in G10, slightly increased in G5, and increased by five- to ten-fold in G30 in parallel with a heterogeneous increase in beta-cell HO1 protein expression. The effect of G30 was fully inhibited by agents decreasing cytosolic Ca²⁺ (diazoxide, nimodipine), but was only slightly reproduced by agents raising Ca²⁺ (tolbutamide, 30 mmol·l^–1 potassium). It was also suppressed by the ₂-adrenoceptor agonist clonidine, whereas dibutyryl-cyclic-AMP largely increased beta-cell HO1 expression. The induction of HO1 mRNA expression by G30 was independent from changes in medium insulin concentration, but was completely inhibited by a cocktail of antioxidants. In contrast to HO1, islet mRNA expression of glutathione peroxidase and constitutive haeme-oxygenase 2 were not affected by G30, nor by dibutyryl-cyclic-AMP.Conclusion/interpretation High glucose and dibutyryl-cyclic-AMP stimulate expression of HO1 in rat pancreatic beta cells. The inhibition of HO1 expression in G30 by nimodipine, clonidine, and antioxidants, suggests that Ca²⁺ influx and cyclic-AMP are necessary for the generation of oxidative stress by G30, or for the stimulation of beta-cell HO1 expression by increased oxidative stress.Abbreviations HO Heme oxygenase - GPx glutathione peroxidase - TBP TATA-box binding protein - Gn n mmol·l^–1 glucose - [Ca²⁺]_i intracellular Ca²⁺ concentration - cDNA complementary DNA - mRNA messenger ribonucleic acid - NF-B nuclear factor of BAn erratum to this article can be found at