Mechanisms of protection by buthionine sulphoximine against gamma-ray-induced micronuclei in polychromatic erythrocytes of mouse bone marrow

Abstract

The effect of pretreatment with buthionine sulphoximine (BSO) on the radiosensitivity of mouse bone marrow cells was studied using the in vivo micronucleus test. Varying concentrations of BSO were injected into mice by intraperitoneal injection 2 h before irradiation, and the frequency of micronuclei in polychromatic erythrocytes (MnPCEs) of bone marrow were scored. Treatment with BSO resulted in a significant reduction (41% at 20 mg/kg body weight) in the frequency of micronuclei induced by 1 Gy γ-rays. Reduction was observed in cells sampled at 24, 30 and 48 h postirradiation with no apparent effect on the ratio of poly- to normochromatic erythrocytes in BSO-treated versus control groups. Glutathione levels in the bone marrow of BSO-treated animals 2 h after a single injection were found to be unaltered. The protective effect of BSO was not observed if it was given either immediately or 2h after irradiation. Based on these and earlier findings it seemed as if BSO molecules may be involved in physicochemical reactions with reactive species generated in the system by irradiation. BSO showed relatively high reaction rate constants with hydroxyl radical (. OH, 2.5 109 dm3 mol^{- 1} s1, calculated on the basis of competition kinetics) and with singlet oxygen (1O2, 4.3 107 dm3 mol^{- 1} s^{- 1} but a lower rate constant with hydrated electrons (5.0 106 dm³ mol^{- 1} s1). Based on halflife estimates, transients formed and potential for damage to biomolecules,. OH and 1O2 seemed to be the possible species responsible. In vitro studies reveal that BSO has significant abilities to protect DNA against single-strand breaks and lipid peroxidation induced by 1O2 in microsomal membranes. This supports our hypothesis that BSO may be involved in scavenging the reactive species generated and that besides. OH, 1O2 may also be a major player in radiation damage.