OXYGEN-DEPENDENT FRAGMENTATION OF CELLULAR DNA BY NITRIC-OXIDE

Although active oxygen species and related metabolites, such as nitric oxide (NO), have been postulated to play important roles in the apopt osis of various cells, a precise mechanism leading to cell death remai ns to be elucidated. Recently we found that the lifetime of NO depends greatly on the concentration of environmental oxygen and that NO reve rsibly inhibits mitochondrial respiration and ATP synthesis; the inhib itory effect is stronger at physiologically low oxygen tension than un der atmospheric: conditions (Arch. Biochem. Biophys. 323, 27-32, 1995) . The present work describes the effects of the NO-generating agent, 1 -hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC 18) and oxygen te nsion on the respiration, Am synthesis and apoptosis of HL-60 cells Wh en respiration was inhibited by NOC 18, cellular ATP levels decreased significantly and DNA fragmentation was elici\ted. Both events were en hanced by decreasing oxygen tension and suppressed by adding NO-trappi ng agents, such as nyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) and oxyhemoglobin. The fragmentation of cellular DNA wa s inhibited in a dose dependent manner by herbimycin A, a tyrosine kin ase inhibitor. Fragmentation of the DNA of HL-60 cells was also induce d either by peroxynitrite, superoxide or hydroxyl radical by some mech anism which was diminished by lowering the oxygen tension. These resul ts indicated that the decrease in cellular ATP and activation of tyros ine kinase might play important roles in NO-induced apoptosis particul arly under physiologically low oxygen tensions.