Prevention of cardiolipin oxidation and fatty acid cycling as two antioxidant mechanisms of cationic derivatives of plastoquinone (SkQs) (original) (raw)
Related papers
Journal of Membrane Biology, 2008
The antioxidant activity of mitochondria-targeted small molecules, SkQ1 and MitoQ (conjugates of a lipophilic decyltriphenylphosphonium cation with an antioxidant moiety of a plastoquinone and ubiquinone, respectively), was studied in aqueous solution and in a lipid environment, i.e., micelles, liposomes and planar bilayer lipid membranes. Reactive oxygen species (ROS) were generated by azo initiators or ferrous ions with or without tert-butyl-hydroperoxide (t-BOOH). Chemiluminescence, fluorescence, oxygen consumption and inactivation of gramicidin peptide channels were measured to detect antioxidant activity. In all of the systems studied, SkQ1 was shown to effectively scavenge ROS. The scavenging was inherent to the reduced form of the quinone (SkQ1H 2). In the majority of the above model systems, SkQ1 exhibited higher antioxidant activity than MitoQ. It is concluded that SkQ1H 2 operates as a ROS scavenger in both aqueous and lipid environments, being effective at preventing ROSinduced damage to membrane lipids as well as membraneembedded peptides. Keywords SkQ Á MitoQ Á Mitochondria-targeted antioxidant Á Liposome Á Bilayer lipid membrane Á Reactive oxygen species Á Gramicidin Abbreviations MitoQ 10-(6 0-Ubiquinonyl)decyltriphenylphosphonium SkQ1 10-(6 0-Plastoquinonyl)decyltriphenylphosphonium CoQ1 Ubiquinone-1 BLM Bilayer lipid membrane ROS Reactive oxygen species ML Methyl ester of linoleate AAPH 2,2 0-Azobis(2-amidinopropane)dihydrochloride AlPcS3 Aluminum phthalocyanine trisulfonate BR Rose bengal MB Methylene blue DPhPC Diphytanoylglycerophosphocholine DPhPG Diphytanoylphosphatidylglycerol TBARS Thiobarbituric acid-reactive species t-BOOH Tert-butyl-hydroperoxide
Interaction of cytochrome c with cardiolipin converts this respiratory chain electron-transfer protein into a peroxidase, supposedly involved in mitochon-dria-mediated apoptosis initiation. Liposome membrane permeabilization provoked by peroxidase activity of the cytochrome c/cardiolipin complex has been previously shown to be suppressed by conventional antioxidants. Here, the mitochondria-targeted antioxidant SkQ1 (plastoquinonyl-decyl-triphenyl-phosphonium) was found to strongly inhibit both cytochrome c/cardiolipin peroxidase activity and the permeabilization of liposomes composed of phos-phatidylcholine and cardiolipin. A number of binding assays revealed a significant inhibiting effect of SkQ1 on cytochrome c binding to liposomes, thus suggesting that SkQ1-mediated protection of liposomes from the cytochrome c/H 2 O 2-induced permeabilization involved distortion of the cytochrome c-membrane binding. It is suggested that antioxidant and antiapoptotic effects of alkyltriphenylphosphonium cations can be related to the prevention of cyto-chrome c/cardiolipin interaction.
How cardiolipin peroxidation alters the properties of the inner mitochondrial membrane?
Chemistry and Physics of Lipids
Cardiolipins have multiple vital functions within biological cell membranes, most notably in the energy metabolism associated with the inner mitochondrial membrane. Considering their essential role, peroxidation of cardiolipins may plausibly have significant effects, as peroxidation is known to alter the functionality of lipid molecules. We used atomistic molecular dynamics simulations to study how peroxidation of cardiolipin affects the properties of the inner mitochondrial membrane. To this end, we explored what happens when varying fractions of fatty acid chains of cardiolipin are replaced by its four different oxidized products in systems modeling the inner mitochondrial membrane. We found that the oxidation of cardiolipin leads to a conformational change both in the backbone/head group and in chain regions of oxidized cardiolipin molecules. The oxidized groups were observed to shift closer to the membrane-water interface region, where they formed hydrogen bonds with several other groups. Additionally, the conformational change turned out to decrease bilayer thickness, and to increase the area per lipid chain, though these changes were minor. The acyl chain conformational order of unoxidized lipids exposed to interactions with oxidized cardiolipins was increased in carbons 3-5 and decreased in carbons 13-17 due to the structural reorganization of the cardiolipin molecules. Overall, the results bring up that the conformation of cardiolipin is altered upon oxidation, suggesting that its oxidation may interfere its interactions with mitochondrial proteins and thereby affect cardiolipin-dependent cellular processes such as electron and proton transport. A c c e p t e d M a n u s c r i p t unique among phospholipids. 1 Cells invest eminent amount of energy to synthesize different lipids, 4 and it has been established that lipids interact specifically with membrane proteins and regulate their function. 5-8 Cardiolipin is primarily localized to membranes that have coupled electron transport and phosphorylation: bacterial plasma membranes, chloroplasts, chromatophores, and mitochondria. 9 CL has several vital functions especially in the energy metabolism associated with the inner mitochondrial membrane (IM). 1,10 In energy production, CL affects, e.g., the stability of the involved enzymes and enzyme complexes. 1 Moreover, CL is important for the stability of biological membranes 11 and CL and its oxidation products are involved in signaling in mitochondria. 12,13 Considering the multitude of essential roles that CLs have in the human body, it is hardly surprising that derangements in its metabolism and composition have been associated with various pathological conditions, 14 such as aging, Barth syndrome, 15 ischemia, 16 and heart failure. 17 Previous studies have revealed that lipid oxidation affects the physiological functions of cell membranes and has a role in cellular membrane damage. 18-22 Lipid peroxidation is thought to be linked to cellular aging and various health issues such as Parkinson's and Alzheimer's disease, schizophrenia, atherosclerosis, and inflammatory diseases. 18,21,23 Several reactive oxygen species, such as hydroxyl radicals or hydrogen peroxides, are thought to be the main culprits. 21 The end-products of lipid peroxidation reactions can be perilous for the viability of cells. Due to the high content of unsaturated acyl chains 14 and the location of CL near the production site of reactive oxygen species, CL is known to be particularly susceptible to oxidation, 24 and indeed prevention of CL oxidation may be a promising target for new therapies. 25 Previous studies suggest that oxidation of lipids alters the properties of membranes for instance by changing membrane fluidity, thickness, lipid organization, and lipid-lipid interactions. 18,19,22,26 The oxidation of membrane lipids may even lead to formation of pores and membrane disruption. 27-31 According to simulation studies, the oxidation of membrane lipids
Biochemistry-moscow, 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, C 1/2 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.
Effect of the Lipophilic o-Naphthoquinone CG 10-248 on Rat Liver Mitochondria Structure and Function
BIOCELL, 2002
CG 10-248 (3,4-dihydro-2,2 dimethyl-9-chloro-2H-naphtho[1,2b]pyran-5,6-dione), a ßlapachone analogue, modified the ultrastructure of rat liver mitochondria in vitro, in the absence of added oxidizable substrates. The condensed mitochondrial state was replaced by the orthodox or swollen state to a significant degree. The number of modified mitochondria depended on incubation time and quinone concentration, in the 25-100 µM range. Under the same experimental conditions, mitochondrial respiration was uncoupled as indicated by the increase in the rate of succinate oxidation by controlled mitochondria in metabolic state "4" (not in state "3"), and by the activation of latent F 0 F 1-ATP synthase. Taking into account structural similarities, the results reported here may be valid for other o-naphthoquinones, such as ß-lapachone.
Archives of Biochemistry and Biophysics, 1998
The protonophoric (uncoupling) action of various long-chain fatty acids and their derivatives in mitochondria was investigated as related to their ability for rapid transbilayer movement in the inner mitochondrial membrane (flip-flop) and interaction with the ADP/ATP carrier (AAC). Flip-flop was assessed from a rapid decrease of internal mitochondrial pH. It was found that long-chain unsubstituted fatty acids (with the exception of very-long-chain unbranched homologs) and their thia and oxa analogs performed a rapid flip-flop, inhibited AAC activity and increased proton permeability of the inner mitochondrial membrane, resulting in dissipation of mitochondrial membrane potential and increased resting state respiration. Bipolar fatty acid analogs, i.e., those containing a second carboxylic group or OH group(s) at the hydrocarbon tail, phenyl-substituted fatty acid derivatives, and fatty acid analogs containing strongly ionized sulfonyl or sulfate groups instead of the carboxylic group, did not flip-flop and were not uncoupling, although some of them were weak inhibitors of AAC. These results provide further confirmation of the fatty acid cycling model (V. P. Skulachev, FEBS Lett. 294, 158-162, 1991) in which the protonophoric function of fatty acids is a result of the spontaneous transbilayer passage of undissociated (protonated) molecules of the fatty acid from the external side of the inner mitochondrial membrane to the matrix side and the AACmediated transport of the fatty acid anion in the opposite direction.
Journal of the …, 2009
Cytochrome c (cyt c), a mitochondrial intermembrane electron shuttle between complexes III and IV, can, upon binding with an anionic phospholipid, cardiolipin (CL), act as a peroxidase that catalyzes cardiolipin oxidation. H(2)O(2) was considered as a source of oxidative equivalents for this reaction, which is essential for programmed cell death. Here we report that peroxidase cyt c/CL complexes can utilize free fatty acid hydroperoxides (FFA-OOH) at exceptionally high rates that are approximately 3 orders of magnitude higher than for H(2)O(2). Similarly, peroxidase activity of murine liver mitochondria was high with FFA-OOH. Using EPR spin trapping and LC-MS techniques, we have demonstrated that cyt c/CL complexes split FFA-OOH predominantly via a heterolytic mechanism, yielding hydroxy-fatty acids, whereas H(2)O(2) (and tert-butyl hydroperoxide, t-BuOOH) undergo homolytic cleavage. Computer simulations have revealed that Arg(38) and His(33) are important for the heterolytic mechan...