Mitochondria-targeted plastoquinone derivatives as tools to interrupt execution of the aging program. 1. Cationic plastoquinone derivatives: Synthesis and in vitro studies

Abstract

Synthesis of cationic plastoquinone derivatives (SkQs) containing positively charged phosphonium or rhodamine moieties connected to plastoquinone by decane or pentane linkers is described. It is shown that SkQs (i) easily penetrate through planar, mitochondrial, and outer cell membranes, (ii) at low (nanomolar) concentrations, posses strong antioxidant activity in aqueous solution, BLM, lipid micelles, liposomes, isolated mitochondria, and cells, (iii) at higher (micromolar) concentrations, show pronounced prooxidant activity, the "window" between anti- and prooxidant concentrations being very much larger than for MitoQ, a cationic ubiquinone derivative showing very much lower antioxidant activity and higher prooxidant activity, (iv) are reduced by the respiratory chain to SkQH2, the rate of oxidation of SkQH2 being lower than the rate of SkQ reduction, and (v) prevent oxidation of mitochondrial cardiolipin by OH*. In HeLa cells and human fibroblasts, SkQs operate as powerful inhibitors of the ROS-induced apoptosis and necrosis. For the two most active SkQs, namely SkQ1 and SkQR1, C(1/2) values for inhibition of the H2O2-induced apoptosis in fibroblasts appear to be as low as 1x10(-11) and 8x10(-13) M, respectively. SkQR1, a fluorescent representative of the SkQ family, specifically stains a single type of organelles in the living cell, i.e. energized mitochondria. Such specificity is explained by the fact that it is the mitochondrial matrix that is the only negatively-charged compartment inside the cell. Assuming that the Deltapsi values on the outer cell and inner mitochondrial membranes are about 60 and 180 mV, respectively, and taking into account distribution coefficient of SkQ1 between lipid and water (about 13,000 : 1), the SkQ1 concentration in the inner leaflet of the inner mitochondrial membrane should be 1.3x10(8) times higher than in the extracellular space. This explains the very high efficiency of such compounds in experiments on cell cultures. It is concluded that SkQs are rechargeable, mitochondria-targeted antioxidants of very high efficiency and specificity. Therefore, they might be used to effectively prevent ROS-induced oxidation of lipids and proteins in the inner mitochondrial membrane in vivo.

Targeting of mitochondrial reactive oxygen species production does not avert lipid-induced insulin resistance in muscle tissue from mice

“…SkQ treatment normalised H 2 O 2 levels in HF+SkQ mice to those of the LF controls (Fig. 2c), thus confirming the efficacy of the mitochondrial-specific ROS scavenger as shown above and previously reported [12][13][14]. In addition, SOD2 (the mitochondrial SOD) activity was significantly elevated in HF mice (twofold vs LF, p<0.01) (Fig.…”

“…SkQ is a small cationic molecule that targets and accumulates in the inner mitochondrial membrane [12]. SkQ mainly scavenges superoxide radicals arising from complex I, but can also sequester ROS generated from complex III [13], thus preventing excessive production of mitochondria-generated ROS. In vitro studies have shown that SkQ has a wide concentration range of antioxidant capacity [13], and in vivo studies have demonstrated that SkQ treatment effectively reduced oxidative damage in several models of oxidative stress [12][13][14].…”

Penetrating cation/fatty acid anion pair as a mitochondria-targeted protonophore

“…In studies with a fungus, a crustacean, a fly, a fish, and mice, SkQ1 was shown to increase median lifespan (2,14). This effect was accompanied by retardation of the development of many age-related diseases and traits (2,14,(18)(19)(20)(21).…”

“…Therefore, we searched for mitochondria-targeted antioxidants with wider antioxidant concentration "window" than that of MitoQ. Cationic derivatives of plastoquinone (SkQs) were found to have the desired property (2,14).…”

“…Moreover, an SkQ1 analog containing two methylene groups instead of plastoquinone (dodecyltriphenylphosphonium, C 12 TPP) was synthesized (14). (For formulas, see Supplemental Information, Fig.…”