Catabolism of tryptophan by Trypanosoma evansi

Trypanosoma brucei gambiense, which causes human African trypanosomiasis, catabolizes the aromatic amino acid tryptophan via an initial aminotransferase catalyzed reaction to form several indole end products, which have been suggested to contribute to the pathogenesis of trypanosomiasis. To determine if this same pathway exists in T. evansi, the closely related trypanosome pathogen of domestic animals, tryptophan catabolism was examined in vitro and in vivo. As is the case with human African trypanosomes, T. evansi catabolized tryptophan to form indole-3-pyruvic acid and smaller amounts of indole-3-acetic acid and indole-3-lactic acid. Large concentrations of indole-3-pyruvic acid are excreted in urine of trypanosome-infected mice. However, indole-3-ethanol could not be detected in incubates of T. evansi or T. b. gambiense, even though the latter species had previously been reported to form this neutral metabolite. A new, previously unreported tryptophan metabolite was isolated and partially characterized from incubates of T. evansi and T. b. gambiense. Although the functional significance of tryptophan catabolism to trypanosomatids remains obscure, the pathway is quantitatively significant in all species examined thus far.