IL-1-BETA INDUCES THE COEXPRESSION OF BOTH NITRIC-OXIDE SYNTHASE AND CYCLOOXYGENASE BY ISLETS OF LANGERHANS - ACTIVATION OF CYCLOOXYGENASE BY NITRIC-OXIDE

Autoimmune diabetes is characterized by an early infiltration of lymphocytes into and around islets, which is followed by selective destruction of the insulin-secreting beta-cell. Cytokines released during this inflammatory reaction have been implicated as effector molecules which mediate beta-cell destruction. In vitro treatment of rat islets with the cytokine IL-1beta results in an inhibition of glucose-stimulated insulin secretion that is mediated by the overproduction of nitric oxide. IL-1beta also stimulates the production of the cyclooxygenase (COX) product prostaglandin E2 (PGE2). In this study we have examined the effects of IL-1beta on both inducible nitric oxide synthase (iNOS) and inducible cyclooxygenase (iCOX) expression, and the direct effects of nitric oxide on the activity of COX. Treatment of rat islets with 5 units/mL IL-1beta induces a similar time-dependent production of both nitrite and PGE2. IL-1beta-induced nitrite and PGE2 production is attenuated by the NOS inhibitor N(G)-monomethyl-L-arginine (NMMA), but NMMA has no inhibitory effect on the expression of either iCOX or iNOS as determined by immunoprecipitation. Actinomycin D prevents IL-1beta-induced iCOX and iNOS expression and the production of both nitrite and PGE2 by islets, suggesting that mRNA transcription is required for IL-1beta-induced expression of both iNOS and iCOX. The effects of exogenous arachidonic acid on both constitutive COX (cCOX) and iCOX activity were also investigated. Treatment of islets for 10 min with 50 muM arachidonic acid stimulated a approximately 10-fold increase in the production of PGE2 by islets cultured with IL-1beta before the arachidonic acid stimulation. NMMA significantly attenuated (70% inhibition) PGE2 production induced by arachidonic acid, providing additional evidence for a direct effect of nitric oxide on the activity of iCOX. Arachidonic acid induced accumulation of PGE2 by both untreated islets and islets treated with IL-1beta and actinomycin D was also inhibited by NMMA (60% inhibition), suggesting that nitric oxide may also stimulate the activity of cCOX. These results show that IL-1beta induces the coexpression of both iCOX and iNOS by islets and that nitric oxide stimulates the activity of both cCOX and iCOX, resulting in the overproduction of the inflammatory mediator PGE2.