Mechanisms of cytokine-induced destruction of rat insulinoma cells: The role of nitric oxide

Abstract

Cytokines produced by immune system cells infiltrating pancreatic islets are candidate mediators of islet β-cell destruction in insulin-dependent diabetes mellitus. In this study, we examined the role of nitric oxide (NO) as a mediator of cytokine-induced islet β-cell destruction in a rat insulinoma cell line (RINm5F). The cytokine combination of interleukin-1β (IL-1β; 10 U/ml), tumor necrosis factor-α (103 U/ml), and interferon-γ (103 U/ml) induced DNA fragmentation (first detected at 6 h), mitochondrial damage (by 12 h), and death (by 24 h) of RIN cells, whereas the individual cytokines did not have these destructive effects. Also, the cytokine combination of IL-1β, tumor necrosis factor-α, and interferon-γ induced a 10-fold increase in NO production by RIN cells, and L-N(G)-monomethyl arginine, an inhibitor of NO synthase, produced a dose-dependent inhibition of cytokine-induced NO production, DNA fragmentation, and cell destruction. However, IL-1β, acting alone, induced a 7-fold increase in NO production without causing DNA fragmentation, mitochondrial damage, or cell destruction. In addition, nicotinamide, a known inhibitor of ADP ribosylation and scavenger of oxygen free radicals, inhibited cytokine-induced DNA fragmentation and cell destruction without affecting NO production. We conclude that stimulation of NO production may be a necessary, but not sufficient, condition for cytokine-induced destruction of islet β-cells.