Dual Involvement of Coenzyme Q 10 in Redox Signaling and Inhibition of Death Signaling in the Rat Heart Mitochondria

Abstract

Coenzyme Q₁₀ (CoQ) has long been utilized as a cardioprotective agent in various heart diseases. One of the most important mechanisms by which CoQ exerts cardioprotection is aerobic ATP production as a mobile electron carrier in the mitochondrial electron transfer chain. The ability of CoQ to afford myocardial protection is also attributed to its antioxidant property. However, CoQ may also act as a pro-oxidant through the generation of reactive oxygen species. Although excess oxidative stress is known to induce death signaling via cytochrome c release from mitochondria, it is now apparent that a brief exposure to oxidative stress stimulates redox signaling for acquisition of tolerance to oxidative stress. Therefore, we have investigated dual involvement of CoQ in redox signaling generation through enhanced production of reactive oxygen species and death signaling inhibition through antioxidation. Mitochondria were isolated from the rat heart and incubated with CoQ (10 or 100 μM) or its vehicle HCO 60 for 1 h. H₂O₂ and cytochrome c release from respiring mitochondria were increased by antimycin A (2 μM), an inhibitor of complex III respiratory chain, or by high Ca²⁺ (10 μM). This enhanced release of H₂O₂ was associated with an increase in lipid peroxidation as measured with 4-hydroxy-2-nonenal-modified proteins and with large amplitude swelling of mitochondria. CoQ potentiated H₂O₂ release from antimycin A- or high Ca²⁺-treated mitochondria, but was capable of inhibiting lipid peroxidation and large amplitude swelling, and attenuated cytochrome c release from the mitochondria. In addition, CoQ increased ATP synthesis by mitochondria. These results suggest that CoQ plays dual roles in mitochondrial generation of intracellular signaling. CoQ acts as a pro-oxidant that participates in redox signaling. CoQ also acts as an antioxidant that inhibits permeability transition and cytochrome c release, and increases ATP synthesis, thereby attenuating death signaling toward apoptosis and necrosis.