Griffin J L, Rae C, Dixon R M, Radda G K, Matthews P M
Department of Biochemistry, University of Oxford, England, UK.
J Neurochem. 1998 Dec;71(6):2477-86. doi: 10.1046/j.1471-4159.1998.71062477.x.
Excitatory amino acids are an important cause of cell death in the hypoxic and ischaemic brain. Neuronal glutamate stores are depleted rapidly in hypoxia, but alanine production rises under such conditions and has been suggested to be a potential precursor of glutamate. To test this hypothesis, we have investigated amino acid metabolism using 13C NMR with superfused guinea pig cortical slices subjected to varying degrees of hypoxia. During severe hypoxia, brain slices metabolising 5 mM [2-(13)C]pyruvate exported [2-(13)C]alanine into the superfusion fluid. The metabolic fate of alanine during normoxia and hypoxia was tested by superfusion of brain slices with 10 mM glucose and 2 mM [2-(13)C,15N]alanine. Metabolism of exogenous alanine leads to the release of aspartate into the superfusion fluid. The pattern of labelling of aspartate indicated that it was synthesised via the glial-specific enzyme pyruvate carboxylase. 13C-labelled glutamate was produced with both normoxia and hypoxia, but concentrations were 30-fold lower than for labelled aspartate. Thus, although substantial amounts of glutamate are not synthesised from alanine in hypoxia, there is significant production of aspartate, which also may have deleterious effects as an excitatory amino acid.
兴奋性氨基酸是缺氧和缺血性脑损伤中细胞死亡的重要原因。在缺氧状态下，神经元内的谷氨酸储备会迅速耗尽，但在此种情况下丙氨酸的生成会增加，有人认为丙氨酸可能是谷氨酸的潜在前体。为验证这一假说，我们利用13C核磁共振技术，对不同程度缺氧的豚鼠皮层脑片进行灌流，研究了氨基酸代谢情况。在严重缺氧期间，代谢5 mM [2-(13)C]丙酮酸的脑片将[2-(13)C]丙氨酸释放到灌流液中。通过用10 mM葡萄糖和2 mM [2-(13)C,15N]丙氨酸对脑片进行灌流，测试了常氧和缺氧状态下丙氨酸的代谢命运。外源性丙氨酸的代谢导致天冬氨酸释放到灌流液中。天冬氨酸的标记模式表明它是通过胶质细胞特异性酶丙酮酸羧化酶合成的。常氧和缺氧状态下均产生了13C标记的谷氨酸，但浓度比标记的天冬氨酸低30倍。因此，尽管在缺氧状态下大量谷氨酸并非由丙氨酸合成，但天冬氨酸的生成量可观，而天冬氨酸作为兴奋性氨基酸也可能产生有害影响。
