Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal de Rio Grande do Sul, Porto Alegre, RS, Brazil.
Mol Genet Metab. 2012 Jan;105(1):84-90. doi: 10.1016/j.ymgme.2011.10.006. Epub 2011 Oct 19.
Tissue accumulation and high urinary excretion of ethylmalonic acid (EMA) occur in ethylmalonic encephalopathy (EE) and short chain acyl-CoA dehydrogenase deficiency (SCADD). Although these autosomal recessive disorders are clinically characterized by neurological abnormalities, the mechanisms underlying the brain damage are poorly known. Considering that little is known about the neurotoxicity of EMA and that hyperlacticacidemia occurs in EE and SCADD, we evaluated the effects of this metabolite on important parameters of oxidative metabolism in isolated rat brain mitochondria. EMA inhibited either ADP-stimulated or uncoupled mitochondrial respiration supported by succinate and malate, but not by glutamate plus malate. In addition, EMA mildly stimulated oxygen consumption by succinate-respiring mitochondria in resting state. Methylmalonic acid (MMA), malonic acid (MA) and butylmalonic acid (BtMA) had a similar effect on ADP-stimulated or uncoupled respiration. Furthermore, EMA-, MMA- and BtMA-induced inhibitory effects on succinate oxidation were significantly minimized by nonselective permeabilization of the mitochondrial membranes by alamethicin, whereas MA inhibitory effect was not altered. In addition, MA was the only tested compound that reduced succinate dehydrogenase activity. We also observed that EMA markedly inhibited succinate and malate transport through the mitochondrial dicarboxylate carrier. Mitochondrial membrane potential was also reduced by EMA and MA, but not by MMA, using succinate as electron donor, whereas none of these compounds was able to alter the membrane potential using glutamate plus malate as electron donors. Taken together, our results strongly indicate that EMA impairs succinate and malate uptake through the mitochondrial dicarboxylate carrier.
组织中乙基丙二酸（EMA）的蓄积和高排泄发生在乙基丙二酸脑病（EE）和短链酰基辅酶 A 脱氢酶缺乏症（SCADD）中。尽管这些常染色体隐性疾病在临床上以神经功能异常为特征，但脑损伤的机制知之甚少。鉴于对 EMA 的神经毒性知之甚少，并且 EE 和 SCADD 中存在高乳酸血症，我们评估了这种代谢物对分离的大鼠脑线粒体氧化代谢重要参数的影响。EMA 抑制了由琥珀酸和苹果酸支持的 ADP 刺激或解偶联的线粒体呼吸，但不抑制由谷氨酸加苹果酸支持的呼吸。此外，EMA 轻度刺激了处于静止状态的由琥珀酸呼吸的线粒体的耗氧量。甲基丙二酸（MMA）、丙二酸（MA）和正丁基丙二酸（BtMA）对 ADP 刺激或解偶联呼吸具有相似的作用。此外，通过 alamethicin 对线粒体膜进行非选择性通透，EMA、MMA 和 BtMA 引起的琥珀酸氧化抑制作用显著减小，而 MA 的抑制作用没有改变。此外，MA 是唯一一种被测试的可降低琥珀酸脱氢酶活性的化合物。我们还观察到，EMA 明显抑制了琥珀酸和苹果酸通过线粒体二羧酸载体的转运。使用琥珀酸作为电子供体时，EMA 和 MA 还降低了线粒体膜电位，但 MMA 没有改变，而这些化合物都不能使用谷氨酸加苹果酸作为电子供体来改变膜电位。综上所述，我们的研究结果强烈表明，EMA 通过线粒体二羧酸载体损害琥珀酸和苹果酸的摄取。
