Phenylbutyrate improves nitrogen disposal via an alternative pathway without eliciting an increase in protein breakdown and catabolism in control and ornithine transcarbamylase-deficient patients
Abstract
Background: Phenylbutyrate is a drug used in patients with urea cycle disorder to elicit alternative pathways for nitrogen disposal. However, phenylbutyrate administration decreases plasma branched-chain amino acid (BCAA) concentrations, and previous research suggests that phenylbutyrate administration may increase leucine oxidation, which would indicate increased protein degradation and net protein loss.
Objective: We investigated the effects of phenylbutyrate administration on whole-body protein metabolism, glutamine, leucine, and urea kinetics in healthy and ornithine transcarbamylase-deficient (OTCD) subjects and the possible benefits of BCAA supplementation during phenylbutyrate therapy.
Design: Seven healthy control and 7 partial-OTCD subjects received either phenylbutyrate or no treatment in a crossover design. In addition, the partial-OTCD and 3 null-OTCD subjects received phenylbutyrate and phenylbutyrate plus BCAA supplementation. A multitracer protocol was used to determine the whole-body fluxes of urea and amino acids of interest.
Results: Phenylbutyrate administration reduced ureagenesis by ≈15% without affecting the fluxes of leucine, tyrosine, phenylalanine, or glutamine and the oxidation of leucine or phenylalanine. The transfer of (15)N from glutamine to urea was reduced by 35%. However, a reduction in plasma concentrations of BCAAs due to phenylbutyrate treatment was observed. BCAA supplementation did not alter the respective baseline fluxes.
Conclusions:…
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Evidence Hub reads this as a clinical trial, done in people. Its evidence level is 3 of 5 (Moderate · trial / cohort / secondary analysis). Trials without a large randomized design, cohorts and secondary analyses give moderate evidence.
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