noc-18 and peroxynitric-acid

We studied the mechanism of nitric oxide (NO) toxicity in cultured rat spinal motoneurons. Treatment with the NO donor NOC-18 (NOC) resulted in slow motoneuron death, ending in apoptosis. The observed motoneuron death was completely prevented by hemoglobin. Treatment with inhibitors of the known intracellular targets of NO, soluble guanylate cyclase, polyADP-ribose polymerase (PARP) and superoxide, did not result in any significant protection against NOC-induced motoneuron death. ATP levels were reduced as soon as 3 h after the start of NOC treatment, suggesting a direct inhibition of cellular energy production. NOC toxicity could be blocked by the general voltage-gated calcium channel blocker cobalt, but not by specific blockers of various subtypes of calcium channels.

Topics: Adenosine Triphosphate; Animals; Apoptosis; Calcium; Cells, Cultured; Cobalt; Cyclic GMP; Electrophysiology; Motor Neurons; Nerve Degeneration; Nitrates; Nitric Oxide; Nitric Oxide Donors; Nitroso Compounds; Poly (ADP-Ribose) Polymerase-1; Poly(ADP-ribose) Polymerases; Proteins; Rats

Although active oxygen species and related metabolites, such as nitric oxide (NO), have been postulated to play important roles in the apoptosis of various cells, a precise mechanism leading to cell death remains to be elucidated. Recently we found that the lifetime of NO depends greatly on the concentration of environmental oxygen and that NO reversibly inhibits mitochondrial respiration and ATP synthesis; the inhibitory effect is stronger at physiologically low oxygen tension than under 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 tension on the respiration, ATP synthesis and apoptosis of HL-60 cells. When respiration was inhibited by NOC 18, cellular ATP levels decreased significantly and DNA fragmentation was elicited. Both events were enhanced by decreasing oxygen tension and suppressed by adding NO-trapping agents, such as 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) and oxyhemoglobin. The fragmentation of cellular DNA was inhibited in a dose dependent manner by herbimycin A, a tyrosine kinase inhibitor. Fragmentation of the DNA of HL-60 cells was also induced either by peroxynitrite, superoxide or hydroxyl radical by some mechanism which was diminished by lowering the oxygen tension. These results indicated that the decrease in cellular ATP and activation of tyrosine kinase might play important roles in NO-induced apoptosis particularly under physiologically low oxygen tensions.

Topics: Adenosine Triphosphate; Apoptosis; Benzoates; Benzoquinones; DNA Fragmentation; Enzyme Inhibitors; Free Radicals; HL-60 Cells; Humans; Imidazoles; Lactams, Macrocyclic; Nitrates; Nitric Oxide; Nitrites; Nitroso Compounds; Oxygen; Quinones; Reactive Oxygen Species; Rifabutin