NITRIC-OXIDE MEDIATES CYTOKINE-INDUCED INHIBITION OF INSULIN-SECRETION BY HUMAN ISLETS OF LANGERHANS

Cytokines have been implicated as immunological effector molecules that mediate beta cell destruction associated with insulin-dependent diabetes mellitus. In this report we demonstrate that the cytokine combination of human recombinant interleukin 1beta (IL-1beta), tumor necrosis factor a (TNF-alpha), and interferon gamma (IFN-gamma) induces the formation of nitric oxide by human islets. This combination of cytokines stimulates both the formation of the nitric oxide derivative, nitrite, and the accumulation of cGMPby human islets. The nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine prevents formation of both cGMP and nitrite. IL-1beta and IFN-gamma are sufficient to induce nitric oxide formation by human islets, whereas TNF-alpha potentiates nitrite production. This combination of cytokines (IL-1beta, TNF-alpha, and IFN-gamma) also influences insulin secretion by human islets. Pretreatment of human islets with low concentrations of this cytokine combination (IL-1beta at 15 units/ml, 0.7 nM TNF-alpha, and IFN-gamma at 150 units/ml) appears to slightly stimulate insulin secretion. Higher concentrations (IL-1beta at 75 units/ml, 3.5 nM TNF-alpha, and IFN-gamma at 750 units/ml) inhibit insulin secretion from human islets, and the inhibitory effect is prevented by N(G)-Monomethyl-L-arginine. This higher concentration of cytokines also induces the formation of an electron paramagnetic resonance-detectable g = 2.04 axial feature by human islets that is characteristic of the formation of an iron-dithio-dinitrosyl complex. The formation of this complex is prevented by N(G)-Monomethyl-L-arginine, thus confirming that this cytokine combination induces the formation of nitric oxide by human islets. These results indicate that nitric oxide mediates the inhibitory effects of cytokines on glucose-stimulated insulin secretion by human islets and suggest that nitric oxide may participate in beta-cell dysfunction associated with insulin-dependent diabetes mellitus.