EFFECTS OF ASPIRIN ON NITRIC-OXIDE FORMATION AND DE-NOVO PROTEIN-SYNTHESIS BY RINM5F CELLS AND RAT ISLETS

Aspirin and aspirin-like drugs are the most commonly indicated agents for the treatment of inflammation. Mechanisms of action for these drug s, however, are not clearly understood. In this study, we examined the effects of aspirin on production of nitric oxide (NO), a proinflammat ory mediator, and show that aspirin inhibits NO production by transfor med pancreatic beta cells (RINm5F) and rat islets in a concentration-d ependent manner with an IC50 value of similar to 3 mM. Therapeutic con centrations of aspirin (1-5 mM) that block NO production affected neit her nuclear factor-kappa B activation nor inducible NO synthase (iNOS) mRNA transcription but potently inhibited iNOS protein expression by both RINm5F cells and rat islets. The effects of aspirin on islet func tion were examined by measuring glucose-stimulated insulin secretion i n the presence of various concentrations of aspirin. Aspirin (1-5 mM) did not affect insulin secretion at basal or glucose-stimulated condit ions, whereas higher concentrations of aspirin (10-20 mM) significantl y increased basal insulin secretion. Aspirin at high concentrations of 10 and 20 mM inhibited de novo protein synthesis as demonstrated by i nhibition of [S-35]methionine incorporation into total islet protein a nd by inhibition of rabbit reticulocyte expression by Brome mosaic vir us mRNA, suggesting that inhibition of iNOS expression at these high c oncentrations of aspirin may be due to the impairment of the translati onal machinery. These findings indicate that inhibition of iNOS expres sion and NO production may explain, in part, the beneficial effects of aspirin as an anti-inflammatory agent at therapeutic concentrations, whereas inhibition of de nova protein synthesis may possibly explain c linical and side effects of aspirin in the inflamed tissues and organs such as stomach and kidney that may accumulate high concentrations of aspirin.