2Chemical Faculty, Lomonosov Moscow State University, 119991 Moscow, Russia
3Institute of Chemical Physics, ul. Kosygina 4, 119977 Moscow, Russia
4Institute of Experimental Cardiology, Cardiology Research Center, 3-ya Cherepkovskaya ul. 15A, 121552 Moscow, Russia
5Biological Faculty, Lomonosov Moscow State University, 119991 Moscow, Russia
6Mitoengineering Center, Lomonosov Moscow State University, 119991 Moscow, Russia
7Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, 119991 Moscow, Russia
* This and the following four articles were written by the request of the Editorial Board of Biochemistry (Moscow).
** To whom correspondence should be addressed.
Received December 29, 2007; Revision received August 14, 2008
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, C1/2 values for inhibition of the H2O2-induced apoptosis in fibroblasts appear to be as low as 1·10-11 and 8·10-13 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 Δψ 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 1.3·108 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.
KEY WORDS: SkQ1, penetrating cations, plastoquinone, antioxidants, mitochondria, apoptosis