TYROSINE KINASE INHIBITORS PREVENT CYTOKINE-INDUCED EXPRESSION OF INOS AND COX-2 BY HUMAN ISLETS

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease th at is characterized by selective destruction of insulin-secreting beta -cells. Cytokines have been implicated as effector molecules that part icipate in both islet inflammation and beta-cell destruction during th e development of IDDM. In this study, the effects of cytokines on the expression of inducible nitric oxide synthase (iNOS) and inducible cyc looxygenase (COX-2) by human islets were examined. In combination, the cytokines, human recombinant interleukin-1 beta (IL-1 beta), human re combinant tumor necrosis factor-alpha (TNF-alpha), and human recombina nt interferon-gamma (IFN-gamma), induce the time-dependent formation o f nitrite and prostaglandin E(2) (PGE(2)) by human islets. The nitric oxide synthase inhibitor N-G-monomethyl-L-arginine (L-NMMA) completely inhibits cytokine-induced nitrite formation and attenuates PGE(2) pro duction by human islets. L-NMMA does not inhibit cytokine-induced expr ession of COX-2 by human islets, suggesting that nitric oxide may dire ctly activate cyclooxygenase, an effect that has been previously demon strated for isolated rat islets. This combination of cytokines (IL-1 b eta, TNF-alpha, and IFN-gamma) also induces the expression of iNOS mRN A by human islets as demonstrated by both reverse transcriptase-polyme rase chain reaction and Northern blot analysis. We further show that t he tyrosine kinase inhibitors genistein and herbimycin A prevent IL-1 beta plus IFN-gamma-induced expression of COX-2 and iNOS and the produ ction of PGE(2) and nitric oxide by human islets. These results demons trate that cytokines induce the expression of iNOS and COX-2 by human islets and that cytokine-induced expression of both COX-2 and iNOS by human islets appears to require the activation of a tyrosine kinase(s) .