Relationship between tryptophan intake and urinary excretion of 3-hydroxy-kynurenine, 3-hydroxyanthranilic acid, xanthurenic acid and kynurenic acid.

Abstract

Some metabolites of tryptophan such as 3-hydroxyanthra-nilic acid (3-OHAA), 3-hydroxykynurenine (3-OHKY) and xanthurenic acid (XA) have been suspected of being carcinogenic, and the relationship between bladder cancer and the urinary excretion of these metabolites has been discussed. However, the relationship between the intake of tryptophan and the excretion of these metabolites has not yet been reported. In this work, the urinary excretion of 3-OHAA, 3-OHKY, XA and kynurenic acid (KA) was determined when an experimental diet containing 770 or 850mg/day of tryptophan was given to six normal female human subjects and when 900mg/day of tryptophan was added to the experimental diet. Under the experimental diet, 3-OHAA, 3-OHKY, XA and KA in urine (μmole/day) were 3.57±1.35, 1.95±1.11, 10.11±3.25 and 15.80±2.35, respectively. Under the additional intake of tryptophan, the values increased to 7.07±5.31, 3.90±2.44, 18.85±7.20 and 31.51±7.52, respectively. The averages of excretion were proportional to the tryptophan intake. Mean excretion ratios (%) of 3-OHAA, 3-OHKY, XA and KA Cumoles) to tryptophan intake (μumoles) were 0.086±0.056, 0.053±0.032, 0.245±0.085 and 0.390±0.084, respectively. However, individual differences and daily fluctuations were observed and it was especially remarkable in 3-OHAA in the period of additional tryptophan intake.