Coenzyme Q1as a probe for mitochondrial complex I activity in the intact perfused hyperoxia-exposed wild-type andNqo1-null mouse lung

Abstract

Previous studies showed that coenzyme Q1(CoQ1) 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 CoQ1reduction on passage through the mouse lung. The aim of the present study was to evaluate the complex I contribution to CoQ1reduction in the isolated perfused wild-type (NQO1+/+) and Nqo1-null (NQO1−/−) mouse lung. CoQ1reduction was measured as the steady-state pulmonary venous CoQ1hydroquinone (CoQ1H2) efflux rate during infusion of CoQ1into the pulmonary arterial inflow. CoQ1H2efflux rates during infusion of 50 μM CoQ1were not significantly different for NQO1+/+and NQO1−/−lungs (0.80 ± 0.03 and 0.68 ± 0.07 μmol·min−1·g lung dry wt−1, respectively, P > 0.05). The mitochondrial complex I inhibitor rotenone depressed CoQ1H2efflux rates for both genotypes (0.19 ± 0.08 and 0.08 ± 0.04 μmol·min−1·g lung dry wt−1for NQO1+/+and NQO1−/−, respectively, P < 0.05). Exposure of mice to 100% O2for 48 h also depressed CoQ1H2efflux 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 CoQ1redox metabolism could not be attributed to effects on lung wet-to-dry weight ratios, perfusion pressures, perfused surface areas, or total venous effluent CoQ1recoveries, the latter measured by spectrophotometry or mass spectrometry. 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 CoQ1as a nondestructive indicator of the impact of pharmacological or pathological exposures on complex I activity in the intact perfused mouse lung.