Whole-brain glutamate metabolism evaluated by steady-state kinetics using a double-isotope procedure: effects of gabapentin.
Whole-brain glutamate metabolism evaluated by steady-state kinetics using a double-isotope procedure: effects of gabapentin.
复制标题
使用双同位素程序通过稳态动力学评估全脑谷氨酸代谢：加巴喷丁的作用。
DOI：
10.1111/j.1471-4159.2004.02576.x
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发表时间：
2004
影响因子：
4.7
通讯作者：
Hutson,SH
中科院分区：
文献类型：
--
作者：
Xu,Y;Oz,G;LaNoue,KF;Keiger,CJ;Berkich,DA;Gruetter,R;Hutson,SH
众所周知，大脑的回返率是显着的，但体内测量的回返率一直存在争议。为了追踪脑谷氨酸能神经元和脑神经胶质细胞中的谷氨酸代谢，首次对不受限制的清醒大鼠连续输注 H14CO3 和 [1−13C] 葡萄糖的组合，输注次数超过 50 次，输注时间为 5 至 60 分钟。在这些动物的全脑提取物中，测量脑谷氨酸和谷氨酰胺中 14 C 的出现以及谷氨酸和谷氨酰胺 C-4 位中 13 C 的出现作为时间的函数。获得了神经元谷氨酸总周转率、从 H14CO3- 合成谷氨酰胺和谷氨酸的回补率、谷氨酸/谷氨酰胺循环的通量以及全脑回补的最小估计值。从 H14CO3 合成 14C-谷氨酸的速率为 1.29 ± 0.11 nmoles/min/mg 蛋白质，而 14C-谷氨酰胺的合成速率为 1.48 ± 0.10 nmoles/min/mg 蛋白质，与总谷氨酸周转率相比9.39±0.73 纳摩尔/分钟/毫克蛋白质。根据谷氨酰胺的周转率，谷氨酸/谷氨酰胺循环的通量上限估计为 4.6 纳摩尔/分钟/毫克蛋白质。从 H14CO3 合成谷氨酰胺的量很大，占谷氨酸/谷氨酰胺循环的 32%。单次注射 100mg/kg 的抗癫痫药物加巴喷丁对这些比率没有显着影响。相比之下，急性给予加巴喷丁显着降低了离体大鼠视网膜中 H14CO3 与谷氨酸和谷氨酰胺的结合，这表明加巴喷丁的代谢作用可能需要长期治疗和/或仅限于富含靶酶（如胞质支链转氨酶）的大脑区域。我们得出的结论是，大脑具有高回补活性，两种示踪剂与不同前体的组合为脑代谢的划分提供了独特的见解。
Cerebral rates of anaplerosis are known to be significant, yet the rates measuredin vivohave been debated. In order to track glutamate metabolism in brain glutamatergic neurons and brain glia, for the first time unrestrained awake rats were continuously infused with a combination of H14CO3–and [1−13C]glucose in over 50 infusions ranging from 5 to 60 min. In whole‐brain extracts from these animals, the appearance of14C in brain glutamate and glutamine and appearance of13C in the C‐4 position of glutamate and glutamine were measured as a function of time. The rate of total neuronal glutamate turnover, the anaplerotic rate of synthesis of glutamine and glutamate from H14CO3–, flux through the glutamate/glutamine cycle, and a minimum estimate of whole‐brain anaplerosis was obtained. The rate of synthesis of14C‐glutamate from H14CO3–was 1.29 ± 0.11 nmoles/min/mg protein, whereas the rate of synthesis of14C‐glutamine was 1.48 ± 0.10 nmoles/min/mg protein compared to total glutamate turnover of 9.39 ± 0.73 nmoles/min/mg protein. From the turnover rate of glutamine, an upper limit for flux through the glutamate/glutamine cycle was estimated at 4.6 nmoles/min/mg protein. Synthesis of glutamine from H14CO3–was substantial, amounting to 32% of the glutamate/glutamine cycle. These rates were not significantly affected by a single injection of 100 mg/kg of the antiepileptic drug gabapentin. In contrast, acute administration of gabapentin significantly lowered incorporation of H14CO3–into glutamate and glutamine in excised rat retinas, suggesting metabolic effects of gabapentin may require chronic treatment and/or are restricted to brain areas enriched in target enzymes such as the cytosolic branched chain aminotransferase. We conclude that the brain has a high anaplerotic activity and that the combination of two tracers with different precursors affords unique insights into the compartmentation of cerebral metabolism.