Andreu Gilberto Lázaro Pardo, Delgado René, Velho Jesus Antonio, Curti Carlos, Vercesi Anibal E
Departamento de Patologia Clínica, Faculdade de Ciências Médicas, Universidade Estadual de Campinas 13083-970 Campinas, SP, Brazil.
Arch Biochem Biophys. 2005 Jul 15;439(2):184-93. doi: 10.1016/j.abb.2005.05.015.
Mitochondrial permeability transition (MPT) is a Ca(2+)-dependent, cyclosporine A-sensitive, non-selective inner membrane permeabilization induced by a wide range of agents or conditions, which has often been associated with necrotic or apoptotic cell death. When mitochondria isolated from livers of rats treated with the natural occurring glucosyl xanthone mangiferin (40 mg/kg body weight) were exposed in vitro to Ca(2+), they underwent CsA, NEM, and ADP-sensitive high amplitude swelling and associated membrane potential dissipation, release of pre-accumulated Ca(2+), oxidation of thiol groups, and depletion of GSH, without changes in the NAD(P)H redox state. The same treatment reduced the phosphorylation rate of mitochondria and the resting respiration by around 4 and 11%, respectively, as well as generation of reactive oxygen species (ROS) by organelle. The in vitro exposure of untreated mitochondria to mangiferin plus Ca(2+) also resulted in oxidation of thiol groups, in the same way that the compound inhibited the Ca(2+)-induced peroxidation of mitochondrial membrane lipids. The spectrum of mangiferin during its oxidation by the H(2)O(2)/HRP system showed a characteristic absorption peak at 380 nm, which decreased immediately after reaction was started; two isosbestic points at around 336 and 412 nm, with a blue shift in the position of the maxima absorption of mangiferin were observed, suggesting their conversion into one oxidation product. Glutathione abolished this decrease of absorbance, suggesting that the oxidation product of mangiferin forms adducts with GSH. We propose that Ca(2+) increases levels of mitochondria-generated ROS, which reacts with mangiferin producing quinoid derivatives, which in turn react with the most accessible mitochondrial thiol groups, thus triggering MPT. It seems probable that the free radical scavenging activity of mangiferin shifts its anti-oxidant protection to the thiol arylation. An interesting proposition is that accumulation of mangiferin quinoid products would take place in cells exposed to an overproduction of ROS, such as cancer cells, where the occurrence of MPT-mediated apoptosis may be a cellular defence mechanism against excessive ROS formation.
线粒体通透性转换（MPT）是一种由多种因素或条件诱导的、依赖钙离子、对环孢素A敏感的非选择性内膜通透性改变，常与坏死或凋亡性细胞死亡相关。当从用天然存在的葡糖基氧杂蒽酮芒果苷（40毫克/千克体重）处理的大鼠肝脏中分离出的线粒体在体外暴露于钙离子时，它们会发生对环孢素A、N-乙基马来酰胺（NEM）和二磷酸腺苷（ADP）敏感的高幅度肿胀以及相关的膜电位耗散、预积累钙离子的释放、巯基氧化和谷胱甘肽（GSH）耗竭，而烟酰胺腺嘌呤二核苷酸磷酸（NAD(P)H）氧化还原状态没有变化。相同处理分别使线粒体的磷酸化速率和静息呼吸降低约4%和11%，以及细胞器产生的活性氧（ROS）减少。未处理的线粒体在体外暴露于芒果苷加钙离子也导致巯基氧化，同样该化合物抑制钙离子诱导的线粒体膜脂质过氧化。芒果苷在被过氧化氢（H₂O₂）/辣根过氧化物酶（HRP）系统氧化过程中的光谱在380纳米处显示出一个特征吸收峰，反应开始后立即下降；观察到在约336和412纳米处有两个等吸收点，芒果苷最大吸收位置发生蓝移，表明它们转化为一种氧化产物。谷胱甘肽消除了这种吸光度降低，表明芒果苷的氧化产物与谷胱甘肽形成加合物。我们提出钙离子增加线粒体产生的ROS水平，其与芒果苷反应生成醌类衍生物，进而与最易接近的线粒体巯基反应，从而触发MPT。似乎芒果苷的自由基清除活性将其抗氧化保护作用转移到巯基芳基化。一个有趣的推测是，芒果苷醌类产物会在暴露于ROS过量产生的细胞如癌细胞中积累，在这些细胞中MPT介导的凋亡的发生可能是一种针对过量ROS形成的细胞防御机制。
