Redox regulation of mitochondrial functional activity by quinones.

Quinones are among the rare compounds successfully used as therapeutic agents to correct mitochondrial diseases and as specific regulators of mitochondrial function within cells. The aim of the present study was to elucidate the redox-dependent effects of quinones on mitochondrial function. The functional parameters [respiratory activity, membrane potential, and reactive oxygen species (ROS) generation] of isolated rat liver mitochondria and mitochondria in intact cells were measured in the presence of eight exogenously applied quinones that differ in lipophilicity and one-electron reduction potential. The quinones affected the respiratory parameters of mitochondria, and dissipated the mitochondrial membrane potential as well as influenced (either decreased or enhanced) ROS generation, and restored the electron flow during electron transport chain inhibition. The stimulation of ROS production by juglone and 2,5-di-tert-butyl-1,4-benzoquinone was accompanied by a decrease in the acceptor control and respiration control ratios, dissipation of the mitochondrial membrane potential and induction of the reverse electron flow under succinate oxidation in isolated mitochondria. Menadione and 2,3,5-trimethyl-1,4-benzoquinone, which decreased the mitochondrial ROS generation, did not affect the mitochondrial potential and, vice versa, were capable of restoring electron transport during Complex I inhibition. In intact C6 cells, all the quinones, except for coenzyme Q, decreased the mitochondrial membrane potential. Juglone, 1,4-benzoquinone, and menadione showed the most pronounced effects. These findings indicate that quinones with the reduction potential values E in the range from -99 to -260 mV were effective redox regulators of mitochondrial electron transport.