Determination of Free Tryptophan in Plasma and Its Clinical Applications

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Abstract
Free tryptophan in plasma was separated by centrifugation through an Amicon ultrafiltration membrane cone. The value obtained without control of pH was lower than that obtained with control of pH by an improved method. For determination of the total tryptophan concentration in the plasma, high performance liquid chromatography (HPLC) was better than the method of Denckla Dewey as modified by Bloxam and Warren (1974), as judged on the basis of sensitivity, recovery rate and coefficient of variance. The total tryptophan concentration in the plasma determined by HPLC was lower than that determined by the Bloxam and Warren method. The total tryptophan concentration (t-Trp), free tryptophan concentration (f-Trp) and f-Trp/t-Trp ratio were 55.8 .+-. 10.2 .mu.mol/l, 11.6 .+-. 1.5 .mu.mol/l and 0.211 .+-. 0.03 (mean .+-. 1 SD), respectively, in healthy subjects (controls). No significant difference was observed between the values of controls and those of patients with liver cirrhosis, hepatocellular carcinoma, liver cirrhosis with hepatocellular carcinoma and hepatic encephalopathy of liver cirrhosis without bleeding. But in liver cirrhosis with bleeding, free tryptophan concentration (f-Trp, 48.0 .+-. 23.3 .mu.mol/l, P < 0.001) and f-Trp/t-Trp ratio (0.645 .+-. 0.289, P < 0.001) were significantly higher than those of controls. In fulminant hepatitis free tryptophan concentration, (f-Trp, 106.6 .+-. 79.9 .mu.mol/l, P < 0.02) and f-Trp/t-Trp ratio (0.973 .+-. 0.017, P < 0.001) were significantly higher than those of controls, and free tryptophan concentration (f-Trp) and f-Trp/t-Trp ratio (P < 0.005) were significantly higher than in liver cirrhosis with bleeding. In other words, the increase of free tryptophan concentration in plasma may be related to the bleeding, and in fulminant hepatitis the binding ability of free tryptophan to albumin may decrease. In the examined cases of liver cirrhosis, the correlation of the concentration of plasma tryptophan with those of other amino acids and indicators of liver function was changed when hepatocellular carcinoma was also present.

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