Takeuchi Y, Morii H, Tamura M, Hayaishi O, Watanabe Y
Department of Neuroscience, Osaka Bioscience Institute, Japan.
Arch Biochem Biophys. 1991 Aug 15;289(1):33-8. doi: 10.1016/0003-9861(91)90438-o.
The dramatic increase in the arachidonic acid (AA) level in the brain is a well-known molecular event during cerebral ischemia. As mitochondria are known to be one possible site of the cell damage, the effects of AA on the respiratory activity of rat brain mitochondria were investigated in vitro using an oxygen electrode. In NAD-linked respiration, respiratory control ratio was decreased significantly by AA, with an IC50 of 6.0 microM. AA had the dual effect on mitochondrial respiration, a decrease in state 3 and uncoupled state and an increase in state 4 (i.e., uncoupling) as reported by Hillered and Chan (J. Neurosci. Res. 19, 94-100, 1988). Furthermore, we found that other unsaturated long-chain free fatty acids (C18:1-C18:3, C20:1-C20:5) also showed such a dual effect. Cyclooxygenase metabolites of AA such as prostaglandins (D2, E2, F2 alpha, E1) and thromboxane B2, and lipoxygenase metabolites such as leukotrienes (D4, B4) and 5- or 12-hydroperoxyeicosatetraenoic acid had no significant effect. The inhibition of the uncoupled state by AA was more marked in NAD-linked than that in FAD-linked respiration, while the degree of uncoupling by AA were the same in both respirations. In spectrophotometrical measurement, the reduction of cytochromes and flavo-protein was markedly inhibited by AA in NAD-linked respiration, but not in the FAD-linked one. In addition, the activity of cytochrome c oxidase was scarcely inhibited by AA. These data suggest that AA itself, not its metabolites, may inhibit mitochondrial ATP production during brain ischemia and that AA may act on the site(s) closely related to NAD-linked respiration, but not the FAD-linked one, in addition to its uncoupling effect.
脑缺血期间，大脑中花生四烯酸（AA）水平急剧升高是一个众所周知的分子事件。由于线粒体是已知的细胞损伤可能位点之一，因此使用氧电极在体外研究了AA对大鼠脑线粒体呼吸活性的影响。在NAD连接的呼吸中，AA使呼吸控制率显著降低，IC50为6.0微摩尔。如Hillered和Chan（《神经科学研究杂志》19，94 - 100，1988）所报道，AA对线粒体呼吸有双重作用，即状态3和非偶联状态降低，状态4升高（即解偶联）。此外，我们发现其他不饱和长链游离脂肪酸（C18:1 - C18:3，C20:1 - C20:5）也表现出这种双重作用。AA的环氧化酶代谢产物如前列腺素（D2、E2、F2α、E1）和血栓素B2，以及脂氧化酶代谢产物如白三烯（D4、B4）和5 - 或12 - 氢过氧化二十碳四烯酸均无显著作用。AA对非偶联状态的抑制在NAD连接的呼吸中比在FAD连接的呼吸中更明显，而AA在两种呼吸中的解偶联程度相同。在分光光度测量中，AA在NAD连接的呼吸中显著抑制细胞色素和黄素蛋白的还原，但在FAD连接的呼吸中则不然。此外，细胞色素c氧化酶的活性几乎不受AA抑制。这些数据表明，在脑缺血期间，AA本身而非其代谢产物可能抑制线粒体ATP的产生，并且除了解偶联作用外，AA可能作用于与NAD连接的呼吸密切相关的位点，而不是FAD连接的呼吸位点。
