Urinary and faecal excretion of metabolizes of tyrosine and phenylalanine in a patient with cystic fibrosis and severely impaired amino acid absorption

Abstract

In a patient with severely impaired amino acid absorption and cystic fibrosis, the urinary excretion of metabolites of phenylalanine and tyrosine was found to be highly increased. Presumably, for the greater part, these metabolites are products of bacterial degradation of the amino acids in the intestinal lumen. The main urinary metabolites were phenylacetic (con j.+ free), benzoic (conj.+ free), p-hydroxyphenylacetic and p-hydroxybenzoic (conj.+ free) acids; the first two represent a considerable percentage of phenylalanine intake and the latter two that of tyrosine intake. Minor urinary metabolites, probably typical for tyrosine malabsorption, were p-hydroxyphenylpropionic and p-hydroxyphenylacrylic acids; the latter compound, however, occurs seldom or never. In the faeces were found small amounts of p-hydroxyphenylpropionic, p-hydroxyphenylacetic, p-hydroxybenzoic and p-hydroxyphenyllactic acids, all derived from tyrosine. Also small quantities of the phenylalanine metabolites phenylacetic and benzoic acid were present. Faecal excretion of the metabolites was clearly less than their urinary elimination. The analytical data obtained from urine and faeces indicate that the tyrosine ammonia-lyase pathway and possibly also the phenylalanine ammonia-lyase pathway are important metabolic routes of intestinal bacteria. The urinary excretion of phenyl acids and p-hydroxyphenyl acids may be an important parameter for phenylalanine and tyrosine malabsorption.