Preferential effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) on pulmonary glutathione reductase and glutathione/glutathione disulfide ratios: possible implications for lung toxicity.

Single doses (8-80 mg/kg) of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) inhibited lung glutathione disulfide (GSSG) reductase in a dose- and time-dependent manner. The loss of enzyme activity persisted up to 8 days after 20 mg of BCNU per kg. A multiple dosing regimen consisting of 5 mg of BCNU per kg/week for 6 weeks decreased lung reductase activity by at least 70%. Recovery was very slow, still remaining well below (68%) control activity for 2 weeks after cessation of BCNU treatment. In contrast, liver GSSG reductase was only slightly decreased by the multi-dose BCNU regimen and rapidly returned to control levels. Pulmonary GSSG concentrations were increased to about 300% of control. This elevation persisted up to 2 weeks after BCNU treatment was completed. There was no effect on total pulmonary glutathione levels during or after BCNU treatment. BCNU administration did not alter hepatic GSSG, although there was a delayed elevation of total liver glutathione. The multi-dose BCNU regimen used in this study leads to the delayed onset of striking pulmonary damage which develops in severity over several weeks after the BCNU treatment is completed. The present results, therefore, suggest that a relatively preferential destruction of lung GSSG reductase by BCNU may precede the development of severe lung toxicity. Considering the probable importance of GSSG reductase in maintaining normal lung homeostasis, this biochemical lesion merits further attention as to its possible role in the pathogenesis of BCNU-induced lung disease.