F. Blonde-cynober et al., Abnormalities in branched-chain amino acid metabolism in cirrhosis: influence of hormonal and nutritional factors and directions for future research, CLIN NUTR, 18(1), 1999, pp. 5-13
Plasma branched-chain amino acid (BCAA) levels are decreased in patients wi
th liver cirrhosis, owing to an increase in BCAA tissue uptake and/or catab
olism and a decrease in BCAA production from proteins. Non-specific factors
such as malnutrition worsen this picture. Studies of BCAA fluxes and prote
in turnover in cirrhotic patients have given conflicting results due to pat
ient heterogeneity, differences in method and bias in the expression of res
ults. In well compensated cirrhosis, muscle wasting is moderate and probabl
y due more to decreased protein synthesis than to increased protein catabol
ism.
Hyperinsulinemia has been suggested as the main cause of decreased BCAA lev
els, 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 st
ate 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 h
as been underestimated. In cirrhotic liver an increase in liver transaminat
ion of branched-chain keto acids (BCKAs) has been suggested and may result
from inhibition of liver BCKA dehydrogenase. A modification of protein turn
over in cirrhotic liver must be also considered. Lastly, the contribution o
f non-hepatocyte liver cells, which are activated in cirrhosis, remains to
be assessed.