The presence of a phagocyte-like NAD(P)H oxidase in pancreatic ␤-cells was investigated. Three NAD(P)H oxidase components were found in pancreatic islets by RT-PCR: gp91 PHOX , p22 PHOX , and p47 PHOX . The components p67PHOX and p47 PHOX were also demonstrated by Western blotting. Through immunohistochemistry, p47PHOX was mainly found in the central area of the islet, confirming the expression of this component by insulin-producing cells. Activation of NAD(P)H oxidase complex in the ␤-cells was also examined by immunohistochemistry. The pancreatic islets presented slower kinetics of superoxide production than HIT-T15 cells, neutrophils, and macrophages, but they reached 66% that of the neutrophil nitroblue tetrazolium (NBT) reduction after 2 h of incubation. Glucose (5.6 mmol/l) increased NBT reduction by 75% when compared with control. The involvement of protein kinase C (PKC) in the stimulatory effect of glucose was confirmed by incubation of islets with phorbol myristate acetate (a PKC activator) and bysindoylmaleimide (GF109203X) (a PKC-specific inhibitor). Diphenylene iodonium [an NAD(P)H oxidase inhibitor] abolished the increase of NBT reduction induced by glucose, confirming the NAD(P)H oxidase activity in pancreatic islets. Because reactive oxygen species are involved in intracellular signaling, the phagocyte-like NAD(P)H oxidase activation by glucose may play an important role for ␤-cell functioning.

The activity of superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSP) in isolated rat pancreatic islets exposed to high glucose concentration for a short period of time (60 min) was determined. High glucose concentration (16.7 mM) did not significantly alter catalase activity. GSP activity was increased by glucose at 5.6 mM, remaining elevated at higher concentrations up to 16.7 mM. However, the activity of SOD increased with glucose concentration, and this increment was closely correlated with the rate of insulin secretion ( r = 0.96). High potassium (30 mM) did not increase SOD activity, suggesting that the increase in intracellular ionic calcium concentration does not stimulate this enzyme activity. α-Ketoisocaproic acid and pyruvate, which are metabolized through the TCA cycle, did not increase SOD activity, indicating that the stimulation of SOD activity might be triggered by a factor produced through glycolysis or the pentose phosphate pathway.