title: Utilization of tyrosine-containing dipeptides and N-acetyl-tyrosine in hepatic failure.
abstract: The impact of hepatic dysfunction on the elimination and hydrolysis of three potential tyrosine sources for total parenteral nutrition, the dipeptides L-alanyl-L-tyrosine (Ala-Tyr) and glycyl-L-tyrosine (Gly-Tyr), and N-acetyl-L-tyrosine (Nac-Tyr) were evaluated in six patients with hepatic failure (five chronic, one acute) and seven healthy subjects. In controls, whole-body clearance (Cltot) of Ala-Tyr was higher than of Gly-Tyr (3,169 +/- 214 vs. 1,780 +/- 199 mL/kg/min, P < .01), and both exceeded clearance of Nac-Tyr (309 +/- 29 mL/kg/min, P > .01). Both dipeptides were hydrolyzed and released tyrosine immediately. In hepatic failure, elimination and hydrolysis of Ala-Tyr and Gly-Tyr were comparable to controls, but Cltot of Nac-Tyr was reduced (236 +/- 26 mL/kg/min). Neither in controls nor in patients an increase in plasma tyrosine concentration was seen after Nac-Tyr, and the major part of Nac-Tyr infused was lost in urine. The Cltot of tyrosine as evaluated after Ala-Tyr infusion (with the immediate release of tyrosine) was severely reduced in hepatic failure (152.7 +/- 38.4 vs. 484.4 +/- 41.4 mL/kg/min, P < .001) and half-life (kle) was retarded from 14.4 +/- 1.4 to 90.2 +/- 32.2 minutes (P < .03). The authors conclude that acute and chronic hepatic dysfunction does not affect elimination and hydrolysis of the dipeptides Ala-Tyr and Gly-Tyr and the constituent amino acids are released immediately. Nac-Tyr elimination was not grossly affected by hepatic failure, but neither in healthy subjects nor in hepatic failure patients was an increase of tyrosine seen. Both dipeptides but not Nac-Tyr may serve as a tyrosine source in parenteral nutrition. Moreover, by its rapid hydrolysis, the use of Ala-Tyr, for the first time, enables a simple rapid nonisotope evaluation of tyrosine kinetics for assessment of liver function.
authors.affiliation: Department of Medicine III, Vienna General Hospital, Austria.
authors.forename: W
authors.initials: W
authors.lastname: Druml
authors.forename: W
authors.initials: W
authors.lastname: Hübl
authors.forename: E
authors.initials: E
authors.lastname: Roth
authors.forename: H
authors.initials: H
authors.lastname: Lochs
mesh_terms: D000328:Adult; D000368:Aged; D004151:Dipeptides / Q000378:metabolism*; D005260:Female; D006207:Half-Life; D006801:Humans; D017093:Liver Failure / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D004151:Dipeptides; C016968:alanyltyrosine; D014443:Tyrosine; C022013:glycyltyrosine; C025787:N-acetyltyrosine