CYCLIC-AMP MEDIATES ENDOTHELIAL PROTECTION BY NITRIC-OXIDE

Incubation with TNF-alpha (50 ng/ml) for 72 hours markedly reduced via bility of endothelial cells. A 6-hour preincubation with nitroso-N-ace tyl-D,L-penicillamine,L-penicillamine (SNAP, 3-100 mu M) protected cel ls in a concentration-dependent manner and decreased TNF-alpha-mediate d toxicity by up to 70%. Cytoprotection by SNAP was completely abolish ed by the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine and mimick ed by 8-bromo cyclic AMP or forskolin. SNAP produced significant incre ases in cyclic GMP and cyclic AMP, both being abrogated in the presenc e of the NO scavenger nyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxi de (PTIO). Moreover, no endothelial protection by SNAP was detected in the presence of the protein kinase A inhibitor KT5720, whereas the pr otein kinase G inhibitor KT5823 left cytoprotection virtually unaltere d. Our results demonstrate a crucial role for cyclic AMP in mediating NO-induced endothelial protection against TNF-alpha, possibly through cyclic GMP-dependent inhibition of cyclic AMP breakdown. NO-dependent endothelial protection mag ultimately result from cyclic AMP-induced u p-regulation of antioxidant proteins or down-regulation of cytotoxic p rocesses. (C) 1998 Academic Press.