Department No. 75, Institute of Physiology, Academy of Sciences, Vídeňská 1083, Prague 14220, Czech Republic.
Department No. 75, Institute of Physiology, Academy of Sciences, Vídeňská 1083, Prague 14220, Czech Republic.
Biochim Biophys Acta Bioenerg. 2017 Sep;1858(9):750-762. doi: 10.1016/j.bbabio.2017.05.005. Epub 2017 May 26.
Previously suggested antioxidant mechanisms for mitochondria-targeted plastoquinone SkQ1 included: i) ion-pairing of cationic SkQ1 with free fatty acid anions resulting in uncoupling; ii) SkQ1H ability to interact with lipoperoxyl radical; iii) interference with electron flow at the inner ubiquinone (Q) binding site of Complex III (Q), involving the reduction of SkQ1 to SkQ1H by ubiquinol. We elucidated SkQ1 antioxidant properties by confocal fluorescence semi-quantification of mitochondrial superoxide (J) and cytosolic HO (J) release rates in HepG2 cells. Only in glycolytic cells, SkQ1 prevented the rotenone-induced enhancement of J and J but not basal releases without rotenone. The effect ceased in glutaminolytic aglycemic cells, in which the redox parameter NAD(P)H/FAD increased after rotenone in contrast to its decrease in glycolytic cells. Autofluorescence decay indicated decreased NADPH/NADH ratios with rotenone in both metabolic modes. SkQ1 did not increase cell respiration and diminished J established high by antimycin or myxothiazol but not by stigmatellin. The revealed SkQ1 antioxidant modes reflect its reduction to SkQ1H at Complex I I or Complex III Q site. Both reductions diminish electron diversions to oxygen thus attenuating superoxide formation. Resulting SkQ1H oxidizes back to SkQ1at the second (flavin) Complex I site, previously indicated for MitoQ. Regeneration proceeds only at lower NAD(P)H/FAD in glycolytic cells. In contrast, cyclic SkQ1 reduction/SkQ1H oxidation does not substantiate antioxidant activity in intact cells in the absence of oxidative stress (neither pro-oxidant activity, representing a great advantage). A targeted delivery to oxidative-stressed tissues is suggested for the effective antioxidant therapy based on SkQ1.
先前提出的靶向线粒体质体醌 SkQ1 的抗氧化机制包括：i）带正电荷的 SkQ1 与游离脂肪酸阴离子形成离子对，导致解偶联；ii）SkQ1H 与脂氧自由基相互作用的能力；iii）干扰复合物 III（Q）的内泛醌（Q）结合位点的电子流，涉及泛醇还原 SkQ1 为 SkQ1H。我们通过 HepG2 细胞中线粒体超氧化物（J）和胞浆 HO（J）释放率的共聚焦荧光半定量阐明了 SkQ1 的抗氧化特性。只有在糖酵解细胞中，SkQ1 可防止鱼藤酮诱导的 J 和 J 的增强，但不能防止没有鱼藤酮的基础释放。在谷氨酰胺糖酵解无葡萄糖细胞中，该效应停止，其中氧化还原参数 NAD（P）H/FAD 在鱼藤酮后增加，而在糖酵解细胞中则减少。自荧光衰减表明，两种代谢模式下，鱼藤酮均降低了 NADPH/NADH 比值。SkQ1 不会增加细胞呼吸，并减弱由抗霉素或粘菌素建立的高 J，但不会减弱由 stigmatellin 建立的 J。所揭示的 SkQ1 抗氧化模式反映了其在复合物 II 或复合物 III Q 位点还原为 SkQ1H。两种还原均减少电子向氧气的转移，从而减弱超氧化物的形成。由此产生的 SkQ1H 在先前指示为 MitoQ 的第二个（黄素）复合物 I 位点氧化回 SkQ1。只有在 NAD（P）H/FAD 较低的情况下，再生才会在糖酵解细胞中进行。相比之下，在没有氧化应激（既没有代表巨大优势的促氧化剂活性）的情况下，完整细胞中的循环 SkQ1 还原/SkQ1H 氧化不能证明其抗氧化活性。建议将其靶向递送至氧化应激组织，以基于 SkQ1 进行有效的抗氧化治疗。
