ENHANCED RELEASE OF NITRIC-OXIDE CAUSES INCREASED CYTOTOXICITY OF S-NITROSO-N-ACETYL-DL-PENICILLAMINE AND SODIUM-NITROPRUSSIDE UNDER HYPOXIC CONDITIONS

S-Nitroso-N-acetyl-DL-penicillamine (SNAP) and sodium nitroprusside (S NP), both of which are known to release nitric oxide ((NO)-N-.), exhib ited cytotoxicity against cultivated endothelial cells. Under hypoxic conditions 5 mM SNAP and 20 mM SNP induced a loss in cell viability of about 90% and 80% respectively, after an 8 h incubation. Under normox ic conditions, cell death was only 45% and 42% respectively within the same time period. Concentrations of (NO)-N-. liberated from SNAP and SNP were measured by the oxyhaemoglobin method and by two of the recen tly developed nitric oxide cheletropic traps (NOCTs). The (NO)-N-. con centrations from SNAP and SNP increased from 74 mu M and 28 mu M to 13 6 mu M and 66 mu M respectively within 15 min of hypoxic incubation, a nd then decreased to 36 mu M and 28 mu M. In the respective normoxic i ncubations the (NO)-N-. levels from SNAP and SNP remained in the regio n of about 30 mu M and 20 mu M respectively. In contrast, spermine/NO adduct (spermineNONOate) was shown to be more toxic under normoxic tha n under hypoxic conditions. Under either of these conditions, the conc entration of (NO)-N-. liberated from 2 mM spermineNONOate was about 20 mu M. The results demonstrate that the cytotoxicity of SNAP and SNP, but not of spermineNONOate, is significantly enhanced under hypoxic co mpared with normoxic incubations. Studies on the (NO)-N-.-releasing be haviour of these compounds indicate that the increased toxicity of SNA P and SNP under hypoxic conditions is related to the influence of O-2 on the chemical processes by which (NO)-N-. is produced from the precu rsors, rather than to an increased sensitivity of the hypoxic cells to wards (NO)-N-..