PROTECTION FROM NICOTINAMIDE INHIBITION OF INTERLEUKIN-1-BETA-INDUCEDRIN CELL NITRIC-OXIDE FORMATION IS ASSOCIATED WITH INDUCTION OF MNSODENZYME-ACTIVITY

We have studied the long-term effects of nicotinamide (NIC) on the syn thesis of NO by insulin producing cells. NIC delays the formation of n itrite by interleukin (IL)-1 beta-(IL-1, 25 U/ml)-stimulated RINm5F ce lls, and previous exposure of cells to IL-1 for 15 h prevents this eff ect. The delay is associated with a lack of cytokine-induced inducible nitric oxide synthase (iNOS) enzyme activity in cell extracts. NIC (2 0 mM) inhibits NO synthase (NOS) activity in extracts from cells incub ated with IL-1 for 6 h and 24 h, and oxyhemoglobin counteracts this in hibition. Hence, NIC could scavenge O-2(-) and allow NO to inhibit the enzyme. The NO donor SIN-1 inhibits in a concentration-dependent mann er iNOS activity, and the effect is potentiated by NIC. In intact cell s, protection from NIC is associated with IL-1-induced expression of M nSOD activity, and reversible blockade of iNOS expression with pyrroli dine dithiocarbamate counteracts the NIC effect. We conclude that O-2( -) plays a role in preventing NO inhibition of iNOS. The loss of this action coincides with the induction of MnSOD enzyme activity. In addit ion, the stimulation by NIC of IL-1-induced nitrite production in pyrr olidine dithiocarbamate-treated cells is a novel action that should be considered when the drug is proposed as potential agent for the preve ntion of insulin-dependent diabetes mellitus.