Probing endogenous coenzyme Q10 (CoQ10) redox status in intact pulmonary arterial endothelial cells using the CoQ10 homolog, coenzyme Q1 (CoQ1)

Abstract

The exogenous quinone, CoQ1, is reduced predominately via mitochondrial complex I (CI) in intact, cultured bovine pulmonary arterial endothelial cells (PAECs), wherein the hydroquinone (CoQ1H2) product can be oxidized at complex III or appear in the extracellular medium. We hypothesized that insofar as CoQ1 is a homolog of the endogenous CI electron acceptor, CoQ10, CoQ1 reduction kinetics might reflect competition with oxidized CoQ10 for reduction at CI and provide information regarding CoQ10 redox status. Cell‐mediated CoQ1 reduction rates vs CoQ1 concentration (1–50 μM) were obtained in the presence of cyanide to eliminate CoQ10 as a CoQ1 competitor. A CoQ10 competition model was fit to cell‐mediated CoQ1H2 oxidation and CoQ1 reduction vs time and CoQ1 reduction rates vs CoQ1 concentration curves in the absence of cyanide. The model fit was consistent with CoQ10 competing with CoQ1 for reducing equivalents at CI. The 95% nonlinear confidence region for CoQ10 participating in competition for reducing equivalents at CI was 7–31 mM. The nonlinear confidence region provides an estimate of CoQ10 redox poise, % CoQ10H2 / (CoQ10H2 + CoQ10) of 57–64%, which is consistent with values reported for total tissue CoQ10 in various organs. The study reveals the potential utility of CoQ1 as a probe of CoQ10 redox status, which may be altered in oxidative stress and lung disease, in PAECs. Funding: HL‐65537,‐24349 and Dept of Veterans Affairs.