New Data on Effects of SkQ1 and SkQT1 on Rat Liver Mitochondria and Yeast Cells.

Mitochondria are involved in many processes in eukaryotic cells. They play a central role in energy conservation and participate in cell metabolism and signaling pathways. Mitochondria are the main source of reactive oxygen species, excessive generation of which provokes numerous pathologies and cell death. One of the most promising approaches to the attenuation of oxidative stress in mitochondria is the use of targeted (i.e., transported exclusively into mitochondria) lipophilic cationic antioxidants. These compounds offer advantages over conventional water-soluble antioxidants because they induce the so-called "mild uncoupling" and can prevent collapse of the membrane potential in low, nontoxic concentrations. A novel mitochondria-targeted antioxidant, SkQT1, was synthesized and tested within the framework of the research project guided by V. P. Skulachev. The results of these experiments were initially reported in 2013; however, one publication was not able to accommodate all the data on the SkQT1 interactions with isolated mitochondria and cells. Here, we examined comparative effects of SkQT1 and SkQ1 on rat liver mitochondria (with broader spectrum of energy parameters being studied) and yeast cells. SkQT1 was found to be less effective uncoupler, depolarizing agent, inhibitor of respiration and ATP synthesis, and "opener" of a nonspecific pore compared to SkQ1. At the same time SkQ1 exhibited higher antioxidant activity. Both SkQT1 and SkQ1 prevented oxidative stress and mitochondria fragmentation in yeast cells exposed to t-butyl hydroperoxide and promoted cell survival, with SkQT1 being more efficient than SkQ1. Together with the results presented in 2013, our data suggest that SkQT1 is the most promising mitochondria-targeted antioxidant that can be used for preventing various pathologies associated with the oxidative stress in mitochondria.

Effect of prooxidants on yeast mitochondria.

Tightly coupled mitochondria from Yarrowia lipolytica and Dipodascus (Endomyces) magnusii yeasts were used in this study. The two yeasts are aerobes containing the fully competent respiratory chain with three energy conservation sites. Interaction of the yeast mitochondria with prooxidants (diamide, menadione, oxaloacetate, phenylarsine oxide, hydrogen peroxide, t-butyl peroxide, and ascorbate plus Fe(2+)) was studied. The prooxidants, depending on their chemical nature, either caused uncoupling (e.g., activated state 4 respiration) or inhibited oxidation of respiratory substrates. All of the agents dissipated the membrane potential without megachannel formation (no large-scale swelling of mitochondria was observed). Except for combined application of ascorbate and Fe(2+), the prooxidant-induced decrease in the membrane potential was specifically prevented by ATP, even in the cases when classic antioxidants, e.g., N-acetylcysteine, were ineffective. No permeabilization of yeast mitochondria was observed under concerted action of prooxidants and Ca(2+), suggesting that an mPTP-like pore, if it ever occurs in yeast mitochondria, is not coupled with Ca(2+) uptake.

Interaction of yeast mitochondria with fatty acids and mitochondria-targeted lipophilic cations.

The effect of fatty acids and mitochondria-targeted lipophilic cations (SkQ1, SkQ3, MitoQ, and C(12)TPP) on tightly-coupled mitochondria from yeasts Dipodascus (Endomyces) magnusii and Yarrowia lipolytica was investigated. Micromolar concentrations of saturated and unsaturated fatty acids were found to decrease the membrane potential, which was recovered almost totally by ATP and BSA. At low, micromolar concentrations, mitochondria-targeted lipophilic cations are "relatively weak, mild uncouplers", at higher concentrations they inhibit respiration in state 3, and at much higher concentrations they induce swelling of mitochondria, possibly due to their prooxidant and detergent action. At very low, not uncoupling concentrations, mitochondria-targeted lipophilic cations profoundly promote (potentiate) the uncoupling effect of fatty acids. It is conceivable that the observed uncoupling effect of lipophilic cations can be, at least partially, due to their interactions with the endogenous pool of fatty acids.