Do Branched-Chain Amino Acids Have a Role in the Treatment of Hepatic Encephalopathy?
The last decade has witnessed a dramatic growth of interest in the administration of branched-chain amino acids as a possible therapy in patients with liver cirrhosis and hepatic encephalopathy. These patients show elevated levels of the aromatic amino acids (tyrosine, phenylalanine and tryptophan) as well as methionine, while the concentrations of the branched-chain amino acids (BCAA) leucine, isoleucine and valine are decreased.1,2,3 The aromatic amino acids are of particular interest since they serve as precursors for the physiological neurotransmitters norepinephrine, dopamine and serotonin. Moreover, they compete with the BCAA for transport across the blood-brain barrier via the same transport system, the L-system.4 As a result of the increased availability of aromatic amino acids, the reduced levels of BCAA and probably also an augmented permeability of the blood-brain barrier,5 the brain uptake of aromatic amino acids may increase. This in turn has been suggested to result in the formation of “false” neurotransmitters such as octopamine and phenylethanolamine.6 These amines are less biologically active than the physiological neurotransmitters and are thought to accumulate and displace the latter, thereby causing cerebral dysfunction.
KeywordsHepatic Encephalopathy Aromatic Amino Acid Branch Chain Amino Acid Brain Uptake Plasma Amino Acid
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