APOPTOTIC CELL-DEATH TRIGGERED BY NITRIC-OXIDE IN PANCREATIC BETA-CELLS

Nitric oxide (NO) is believed to be an effector molecule that mediates interleukin (IL)-1 beta-induced destruction and dysfunction of pancre atic beta-cells. We have demonstrated that both exogenous NO and NO ge nerated endogenously by IL-1 beta brought about apoptosis of isolated rat pancreatic islet cells as well as pancreatic beta-cell tumor-deriv ed cell Line HIT. This apoptosis was characterized by cleavage of DNA into nucleosomal fragments of 180-200 bp and morphologically by nuclea r shrinkage, chromatic condensation, and apoptotic body formation. The IL-1 beta-induced internucleosomal DNA cleavage occurred in a time- a nd dose-dependent manner. Actinomycin D, cycloheximide, and nitric oxi de synthase inhibitors inhibited the DNA cleavage, which was correlate d with the amount of NO produced, indicating that NO produced by HIT c ells themselves could mediate the apoptosis. Furthermore, in the prese nce of tumor necrosis factor (TNF)-alpha, large amounts of NO were pro duced by IL-1 beta and DNA cleavage occurred more noticeably, although TNF-alpha alone did not generate NO. Streptozotocin (STZ), a diabetog enic reagent containing a nitroso moiety, also released NO and induced internucleosomal DNA cleavage in HIT cells. These results suggest tha t NO-induced internucleosomal DNA cleavage is an important initial ste p in the destruction and dysfunction of pancreatic beta-ceLls induced by inflammatory stimulation or treatment with STZ.