Blonde-Cynober F, Aussel C, Cynober L
Biochem Laboratory Emile Roux Hospital, INSERM U402, CHU St Antoine, Paris, France.
Clin Nutr. 1999 Feb;18(1):5-13. doi: 10.1016/s0261-5614(99)80043-0.
Plasma branched-chain amino acid (BCAA) levels are decreased in patients with liver cirrhosis, owing to an increase in BCAA tissue uptake and/or catabolism and a decrease in BCAA production from proteins. Non-specific factors such as malnutrition worsen this picture. Studies of BCAA fluxes and protein turnover in cirrhotic patients have given conflicting results due to patient heterogeneity, differences in method and bias in the expression of results. In well compensated cirrhosis, muscle wasting is moderate and probably due more to decreased protein synthesis than to increased protein catabolism. Hyperinsulinemia has been suggested as the main cause of decreased BCAA levels, by increasing BCAA uptake in muscle and additionally in adipose tissue. However, as depletion of fat stores is frequent in cirrhosis, this effect is certainly quantitatively weak. Also, there is no correlation between state of hyperinsulinemia and decrease in BCAA levels. An effect of cytokines (IL1 and TNF) on muscle BCAA catabolism is a possibility. Until recently, the contribution of the liver to abnormal BCAA metabolism has been underestimated. In cirrhotic liver an increase in liver transamination of branched-chain keto acids (BCKAs) has been suggested and may result from inhibition of liver BCKA dehydrogenase. A modification of protein turnover in cirrhotic liver must be also considered. Lastly, the contribution of non-hepatocyte liver cells, which are activated in cirrhosis, remains to be assessed.
肝硬化患者血浆支链氨基酸（BCAA）水平降低，这是由于BCAA组织摄取和/或分解代谢增加以及蛋白质产生的BCAA减少所致。营养不良等非特异性因素会使这种情况恶化。由于患者的异质性、方法差异以及结果表达的偏差，对肝硬化患者BCAA通量和蛋白质周转的研究得出了相互矛盾的结果。在代偿良好的肝硬化中，肌肉萎缩程度中等，可能更多是由于蛋白质合成减少而非蛋白质分解代谢增加所致。高胰岛素血症被认为是BCAA水平降低的主要原因，它通过增加肌肉以及脂肪组织对BCAA的摄取来实现。然而，由于肝硬化患者经常出现脂肪储备耗竭，这种作用在数量上肯定较弱。此外，高胰岛素血症状态与BCAA水平降低之间没有相关性。细胞因子（IL1和TNF）对肌肉BCAA分解代谢有影响是有可能的。直到最近，肝脏对异常BCAA代谢的作用一直被低估。在肝硬化肝脏中，有人提出支链酮酸（BCKA）的肝脏转氨作用增加，这可能是由于肝脏BCKA脱氢酶受到抑制所致。还必须考虑肝硬化肝脏中蛋白质周转的改变。最后，在肝硬化中被激活的非肝细胞对BCAA代谢的作用仍有待评估。
