CYTOKINES INDUCE DEOXYRIBONUCLEIC-ACID STRAND BREAKS AND APOPTOSIS INHUMAN PANCREATIC-ISLET CELLS

We have previously observed that a 6-day exposure of human pancreatic islets to a combination of cytokines (interleukin-1 beta 50 U/ml + tum our necrosis factor-alpha 1000 U/ml + interferon-gamma 1000 U/ml) seve rely impairs beta-cell functions. In the present study, we examined wh ether this condition affects DNA integrity and viability of human isle t cells. Cells were studied after 3, 6, and 9 days of cytokine treatme nt by both single cell gel electrophoresis (the ''comet assay,'' a sen sitive method for detection of DNA strand breaks) and by a cytotoxicit y assay using the DNA binding dyes Hoechst 33342 and propidium iodide as indices for the number of viable, necrotic, and apoptotic cells. Cy tokine treatment for 6 and 9 days resulted in a 50% increase in comet length (P < 0.01 vs. controls), indicating DNA strand breaks, as well as in a significant increase in the number of apoptotic cells (P < 0.0 2 vs. controls), but not in the number of necrotic cells. The arginine analogs N-G-nitro-L-arginine and N-G-monomethyl-L-arginine prevented nitric oxide formation by the cytokines but did not interfere with cyt okine-induced DNA strand breaks and apoptosis. The present data sugges t that prolonged (6-9 days) exposure of human pancreatic islets to a m ixture of cytokines induces DNA strand breaks and cell death by apopto sis. These deleterious effects of cytokines appear to be independent o f nitric oxide generation.