Coenzyme Q_1 as a probe for mitochondrial complex I activity in the intact perfused hyperoxia-exposed wild-type and Nqol-null mouse lung

摘要

Previous studies showed that coenzyme Q_1 (CoQ_1 reduction on passage through the rat pulmonary circulation was catalyzed by NAD(P)H: quinone oxidoreductase 1 (NQO1) and mitochondrial complex I, but that NQO1 genotype was not a factor in CoQ1 reduction on passage through the mouse lung. The aim of the present study was to evaluate the complex I contribution to CoQ_1 reduction in the isolated perfused wild-type (NQO1~(+/+)) and Nqol-null (NQOl~(-/-)) mouse lung. CoQ reduction was measured as the steady-state pulmonary venous CoQ_1 hydroquinone (CoQ_1H_2) efflux rate during infusion of CoQ_1 into the pulmonary arterial inflow. CoQ_1H_2 efflux rates during infusion of 50 μM CoQ_1 were not significantly different for NQO1~(+/+) and NQO1~(-/-) lungs (0.80 ± 0.03 and 0.68 ± 0.07μmol·min~(-1) lung dry wt~(-1), respectively, P >0.05). The mitochondrial complex I inhibitor rotenone depressed CoQ_1H_2 efflux rates for both genotypes (0.19 ± 0.08 and 0.08 ± 0.04 μmol·min~(-1) lung dry wt~(-1) for NQO1~(+/+) and NQO1~(-/-), respectively, P < 0.05). Exposure of mice to 100% O_2 for 48 h also depressed CoQ_1H_2 efflux rates in NQO1~(+/+) and NQO1~(-/-) lungs (0.43 ± 0.03 and 0.11 ± 0.04 μmol·min~(-1)·g lung dry wt~(-1), respectively, P < 0.05 by ANOVA). The impact of rotenone or hyperoxia on CoQ_1 redox metabolism could not be attributed to effects on lung wet-to-dry weight ratios, perfusion pressures, perfused surface areas, or total venous effluent CoQ_1 recoveries, the latter measured by spectrophotometry or mass spec-trometry. Complex I activity in mitochondria-enriched lung fractions was depressed in hyperoxia-exposed lungs for both genotypes. This study provides new evidence for the potential utility of CoQ_1 as a nondestructive indicator of the impact of pharmacological or pathological exposures on complex I activity in the intact perfused mouse lung.