Effect of chronic hyperoxic exposure on duroquinone reduction in adult rat lungs

Abstract

NAD(P)H:quinone oxidoreductase 1 (NQO1) plays a dominant role in the reduction of the quinone compound 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone, DQ) to durohydroquinone (DQH2) on passage through the rat lung. Exposure of adult rats to 85% O2 for > or =7 days stimulates adaptation to the otherwise lethal effects of >95% O2. The objective of this study was to examine whether exposure of adult rats to hyperoxia affected lung NQO1 activity as measured by the rate of DQ reduction on passage through the lung. We measured DQH2 appearance in the venous effluent during DQ infusion at different concentrations into the pulmonary artery of isolated perfused lungs from rats exposed to room air or to 85% O2. We also evaluated the effect of hyperoxia on vascular transit time distribution and measured NQO1 activity and protein in lung homogenate. The results demonstrate that exposure to 85% O2 for 21 days increases lung capacity to reduce DQ to DQH2 and that NQO1 is the dominant DQ reductase in normoxic and hyperoxic lungs. Kinetic analysis revealed that 21-day hyperoxia exposure increased the maximum rate of pulmonary DQ reduction, Vmax, and the apparent Michaelis-Menten constant for DQ reduction, Kma. The increase in Vmax suggests a hyperoxia-induced increase in NQO1 activity of lung cells accessible to DQ from the vascular region, consistent qualitatively but not quantitatively with an increase in lung homogenate NQO1 activity in 21-day hyperoxic lungs. The increase in Kma could be accounted for by approximately 40% increase in vascular transit time heterogeneity in 21-day hyperoxic lungs.

Quantifying mitochondrial and plasma membrane potentials in intact pulmonary arterial endothelial cells based on extracellular disposition of rhodamine dyes

“…It should be emphasized that the effect of hyperoxic exposure on pulmonary endothelial mitochondria would not have been revealed by measuring only the resting ⌬ m or using only a single commonly used CCCP concentration (5 M) to depolarize the mitochondria. Various indications of mitochondrial dysfunction have been reported by us and others in hyperoxiaexposed rat lung, pulmonary endothelial cells in culture, and other cell types (2,3,5,7,8,36,37,51,57). In this context, the present observations are consistent with a hyperoxia-induced mitochondrial deficiency.…”

Genetic evidence for NAD(P)H:quinone oxidoreductase 1-catalyzed quinone reduction on passage through the mouse pulmonary circulation

“…The lung and perfusion system were washed again with the NQO1 inhibitor dicumarol (250 M) in the perfusate, and the quinone perfusion study was carried out as described above, except 250 M dicumarol was in the perfusate with the quinone. This dicumarol concentration was selected because of the high degree of dicumarol binding to the perfusate BSA, which substantially lowers its free concentration (9). Then the lung and perfusion system were washed a final time with control perfusate, and the FAPGG infusion was repeated as described above.…”

“…Therefore, quinones are useful for probing lung redox processes that affect their disposition in the blood. We have used the amphipathic quinone duroquinone (DQ) as one model compound for studying quinone metabolism on passage through the pulmonary circulation of the isolated perfused rodent lung (4,9). DQ is advantageous because the quinone (DQ) and hydroquinone (DQH 2 ) forms are cell membranepermeable and, thus, freely enter and leave lung tissue from the pulmonary circulation (4).…”

“…DQ is advantageous because the quinone (DQ) and hydroquinone (DQH 2 ) forms are cell membranepermeable and, thus, freely enter and leave lung tissue from the pulmonary circulation (4). Earlier studies revealed that DQ is reduced to DQH 2 on passage through the rat and mouse lung (4,9). Inhibitor studies indicated that nearly all the DQ reduction in the rat lung was attributable to NAD(P)H:quinone oxidoreductase 1 (NQO1) (4,9).…”

“…Earlier studies revealed that DQ is reduced to DQH 2 on passage through the rat and mouse lung (4,9). Inhibitor studies indicated that nearly all the DQ reduction in the rat lung was attributable to NAD(P)H:quinone oxidoreductase 1 (NQO1) (4,9). The contribution of NQO1 to DQ reduction in the mouse lung was not specifically addressed (4).…”