Study of the intestinal tyrosine metabolism using stable isotopes and gas chromatography-mass spectrometry

Abstract

Deuterated tyrosine, 4-hydroxyphenyllactic acid, 4-hydroxyphenylpropionic acid, 4-hydroxyphenylacetic acid and 4-hydroxybenzoic acid were incubated under anaerobic conditions with human faecal specimens for the in vitro study of their respective metabolisms. After 1 week, aromatic acids and phenols were extracted and analyzed by gas chromatography-mass spectrometry. [3′,5′- 2H 2]Tyrosine produced 4-hydroxyphenyllactic acid, 4-hydroxyphenylpropionic acid and 4-hydroxyphenylacetic acid; [3′,5′- 2H 2]-4′-hydroxyphenyllactic acid produced 4-hydroxyphenylpropionic acid, 3-hydroxyphenylpropionic acid, 4-hydroxyphenylacetic acid and phenylpropionic acid; [3′,5′- 2H 2]-4′-hydroxyphenylpropionic acid produced 3-hydroxyphenylpropionic acid and phenylpropionic acid; [3′,5′,2,2- 2H 4]-4′-hydroxyphenylacetic acid produced p-cresol; and [3′,5′- 2H 2]-4′-hydroxybenzoic acid produced phenol. Thus the intestinal flora showed activities for decarboxylation leading to phenol and p-cresol, dehydroxylation leading to phenylpropionic acid and rearrangement leading to 3-hydroxyphenylpropionic acid. Retention of both deuterium labels was observed in the rearrangement reaction.