Effect of alternative pathway therapy on branched chain amino acid metabolism in urea cycle disorder patients

• Published in: Molecular genetics and metabolism Vol. 81; pp. 79 - 85
• Main Authors: Scaglia, Fernando, Carter, Susan, O’Brien, William E, Lee, Brendan
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-04-2004
• Subjects: Adolescent; Adult; Amino Acid Metabolism, Inborn Errors - drug therapy; Amino Acids, Branched-Chain - metabolism; Branched chain amino acids; Citrullinemia - drug therapy; Drug Therapy, Combination; Female; Humans; Male; Ornithine Carbamoyltransferase Deficiency Disease - drug therapy; Phenylacetates - pharmacokinetics; Phenylacetates - therapeutic use; Phenylbutyrates - pharmacokinetics; Phenylbutyrates - therapeutic use; Retrospective Studies; Sodium Benzoate - pharmacokinetics; Sodium Benzoate - therapeutic use; Sodium phenylacetate; Sodium phenylbutyrate; Time Factors; Urea - metabolism; Urea cycle disorders; Sodium phenylbutyrate; Urea cycle disorders; Branched chain amino acids; Sodium phenylacetate
• ISSN: 1096-7192; 1096-7206
• DOI: 10.1016/j.ymgme.2003.11.017

Urea cycle disorders (UCDs) are a group of inborn errors of hepatic metabolism caused by the loss of enzymatic activities that mediate the transfer of nitrogen from ammonia to urea. These disorders often result in life-threatening hyperammonemia and hyperglutaminemia. A combination of sodium phenylbutyrate and sodium phenylacetate/benzoate is used in the clinical management of children with urea cycle defects as a glutamine trap, diverting nitrogen from urea synthesis to alternatives routes of excretion. We have observed that patients treated with these compounds have selective branched chain amino acid (BCAA) deficiency despite adequate dietary protein intake. However, the direct effect of alternative therapy on the steady state levels of plasma branched chain amino acids has not been well characterized. We have measured steady state plasma branched chain and other essential non-branched chain amino acids in control subjects, untreated ornithine transcarbamylase deficiency females and treated null activity urea cycle disorder patients in the fed steady state during the course of stable isotope studies. Steady-state leucine levels were noted to be significantly lower in treated urea cycle disorder patients when compared to either untreated ornithine transcarbamylase deficiency females or control subjects (
P<0.0001). This effect was reproduced in control subjects who had depressed leucine levels when treated with sodium phenylacetate/benzoate (
P<0.0001). Our studies suggest that this therapeutic modality has a substantial impact on the metabolism of branched chain amino acids in urea cycle disorder patients. These findings suggest that better titration of protein restriction could be achieved with branched chain amino acid supplementation in patients with UCDs who are on alternative route therapy.