title: Effect of nitric oxide on gamma-ray-induced micronucleus frequency in RAW264.7 cells.
abstract: The effect of low-dose nitric oxide (NO) on gamma-ray-induced micronucleus (MN) frequency was investigated in RAW264.7 cells. Treatment of RAW264.7 cells with 0.25 mM sodium nitroprusside (SNP), a chemical NO donor, reduced the frequency of micronuclei induced by 5 Gy gamma rays by 43 to 45% between 3 and 12 h post-treatment. This effect was blocked by carboxy-PTIO, suggesting that NO may play a role in the reduction of radiation-induced MN frequency. To examine possible mechanisms underlying this effect, we first looked at changes in the antioxidant system after SNP treatment. A significant increase in intracellular glutathione (GSH) was seen in SNP-treated cells between 3 and 12 h post-treatment. Depletion of GSH with buthionine sulfoximine (BSO) increased the gamma-ray-induced increase in MN frequency. Detailed studies using various inducers of intracellular GSH suggested that GSH induction has a partial role in the reducing effect of NO on the gamma-ray-induced MN frequency. Next, the effect of NO on DNA repair and replication systems was examined. Wortmannin, an inhibitor of DNA-dependent protein kinase (DNA-PK), dose-dependently inhibited the reducing effect of NO, while caffeine, an inhibitor of ATM kinase and ATR kinase, did not. DNA-PK activity was increased by NO treatment. Etoposide, a topoisomerase II inhibitor, dose-dependently blocked the effect of NO in reducing the gamma-ray-induced MN frequency. These results suggest that the mechanisms of the effect of NO on the gamma-ray-induced MN frequency include elevation of GSH and up-regulation of DNA-PK activity for repairing double-strand breaks. NO may act as a signal for repair systems, e.g. for nonhomologous recombination and for the replication system in S phase, to reduce the MN frequency.
authors.affiliation: Department of Radiation Bioscience, Faculty of Pharmaceutical Sciences, Tokyo University of Science, Noda-shi, Chiba 278-8510, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tokuzumi
authors.forename: Mayumi
authors.initials: M
authors.lastname: Hori
authors.forename: Manami
authors.initials: M
authors.lastname: Monobe
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Hosoi
authors.forename: Shuji
authors.initials: S
authors.lastname: Kojima
mesh_terms: D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D005720:Gamma Rays; D007093:Imidazoles / Q000494:pharmacology; D051379:Mice; D048629:Micronuclei, Chromosome-Defective / Q000187:drug effects* / Q000528:radiation effects*; D015162:Micronucleus Tests; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects
chemical_list: D001565:Benzoates; D007093:Imidazoles; D020030:Nitric Oxide Donors; C079393:1,3-dihydroxy-4,4,5,5-tetramethyl-2-(4-carboxyphenyl)tetrahydroimidazole; D009599:Nitroprusside; D009569:Nitric Oxide; D019328:Buthionine Sulfoximine; D004247:DNA