Department of Laboratory Medicine, Medical University of Gdańsk, Gdańsk, Poland.
J Neurochem. 2010 Oct;115(2):333-42. doi: 10.1111/j.1471-4159.2010.06919.x. Epub 2010 Aug 25.
The decrease of pyruvate and ketoglutarate dehydrogenase complex activities is the main cause of energy and acetyl-CoA deficits in thiamine deficiency-evoked cholinergic encephalopathies. However, disturbances in pathways of acetyl-CoA metabolism leading to appearance of cholinergic deficits remain unknown. Therefore, the aim of this work was to investigate alterations in concentration and distribution of acetyl-CoA and in acetylcholine metabolism in brain nerve terminals, caused by thiamine deficits. They were induced by the pyrithiamine, a potent inhibitor of thiamine pyrophosphokinase. The thiamine deficit reduced metabolic fluxes through pyruvate and ketoglutarate dehydrogenase steps, yielding deficits of acetyl-CoA in mitochondrial and cytoplasmic compartments of K-depolarized nerve terminals. It also inhibited indirect transport of acetyl-CoA though ATP-citrate lyase pathway being without effect on its direct Ca-dependent transport to synaptoplasm. Resulting suppression of synaptoplasmic acetyl-CoA correlated with inhibition of quantal acetylcholine release (r = 0.91, p = 0.012). On the other hand, thiamine deficiency activated non-quantal acetylcholine release that was independent of shifts in intraterminal distribution of acetyl-CoA. Choline acetyltransferase activity was not changed by these conditions. These data indicate that divergent alterations in the release of non-quantal and quantal acetylcholine pools from thiamine deficient nerve terminals could be caused by the inhibition of acetyl-CoA and citrate synthesis in their mitochondria. They in turn, caused inhibition of acetyl-CoA transport to the synaptoplasmic compartment through ATP-citrate lyase pathway yielding deficits of cholinergic functions.
丙酮酸和酮戊二酸脱氢酶复合体活性的降低是硫胺素缺乏引起的胆碱能脑病中能量和乙酰辅酶 A 缺乏的主要原因。然而，导致胆碱能缺陷出现的乙酰辅酶 A 代谢途径的紊乱仍然未知。因此，本工作的目的是研究硫胺素缺乏引起的脑神经末梢中乙酰辅酶 A 的浓度和分布以及乙酰胆碱代谢的变化。这些变化是由吡哆醇，一种强有力的硫胺素焦磷酸激酶抑制剂引起的。硫胺素缺乏降低了通过丙酮酸和酮戊二酸脱氢酶步骤的代谢通量，导致 K 去极化神经末梢的线粒体和细胞质隔间中乙酰辅酶 A 的缺乏。它还抑制了通过 ATP-柠檬酸裂合酶途径的间接乙酰辅酶 A 转运，而对其直接 Ca 依赖性转运到突触浆没有影响。由此产生的突触浆乙酰辅酶 A 的抑制与量子乙酰胆碱释放的抑制相关（r = 0.91，p = 0.012）。另一方面，硫胺素缺乏激活了非量子乙酰胆碱的释放，这与乙酰辅酶 A 在末梢内分布的变化无关。胆碱乙酰转移酶活性不受这些条件的影响。这些数据表明，从硫胺素缺乏的神经末梢中释放的非量子和量子乙酰胆碱池的发散变化可能是由于线粒体中乙酰辅酶 A 和柠檬酸的合成受到抑制所致。反过来，它们通过 ATP-柠檬酸裂合酶途径抑制乙酰辅酶 A 向突触浆隔间的转运，导致胆碱能功能的缺乏。
