Phenylbutyrate therapy for maple syrup urine disease - PubMed
- ️Sat Jan 01 2011
Clinical Trial
. 2011 Feb 15;20(4):631-40.
doi: 10.1093/hmg/ddq507. Epub 2010 Nov 23.
Brendan Lanpher, Ayelet Erez, Elitsa A Ananieva, Mohammad Islam, Juan C Marini, Qin Sun, Chunli Yu, Madhuri Hegde, Jun Li, R Max Wynn, David T Chuang, Susan Hutson, Brendan Lee
Affiliations
- PMID: 21098507
- PMCID: PMC3024040
- DOI: 10.1093/hmg/ddq507
Clinical Trial
Phenylbutyrate therapy for maple syrup urine disease
Nicola Brunetti-Pierri et al. Hum Mol Genet. 2011.
Abstract
Therapy with sodium phenylacetate/benzoate or sodium phenylbutyrate in urea cycle disorder patients has been associated with a selective reduction in branched-chain amino acids (BCAA) in spite of adequate dietary protein intake. Based on this clinical observation, we investigated the potential of phenylbutyrate treatment to lower BCAA and their corresponding α-keto acids (BCKA) in patients with classic and variant late-onset forms of maple syrup urine disease (MSUD). We also performed in vitro and in vivo experiments to elucidate the mechanism for this effect. We found that BCAA and BCKA are both significantly reduced following phenylbutyrate therapy in control subjects and in patients with late-onset, intermediate MSUD. In vitro treatment with phenylbutyrate of control fibroblasts and lymphoblasts resulted in an increase in the residual enzyme activity, while treatment of MSUD cells resulted in the variable response which did not simply predict the biochemical response in the patients. In vivo phenylbutyrate increases the proportion of active hepatic enzyme and unphosphorylated form over the inactive phosphorylated form of the E1α subunit of the branched-chain α-keto acid dehydrogenase complex (BCKDC). Using recombinant enzymes, we show that phenylbutyrate prevents phosphorylation of E1α by inhibition of the BCKDC kinase to activate BCKDC overall activity, providing a molecular explanation for the effect of phenylbutyrate in a subset of MSUD patients. Phenylbutyrate treatment may be a valuable treatment for reducing the plasma levels of neurotoxic BCAA and their corresponding BCKA in a subset of MSUD patients and studies of its long-term efficacy are indicated.
Figures

BCAA metabolites in control subjects. (A) BCAA in healthy controls before and after phenylbutyrate treatment. ILE, isoleucine; LEU, leucine; VAL, valine. *P ≤ 0.05. (B) BCKA in healthy controls before and after phenylbutyrate treatment. KMV, α-keto-β-methylvalerate; KIC, α-ketoisocaproate; KIV, α-ketoisovalerate. *P ≤ 0.05.

BCAA metabolites in MSUD subjects. (A) BCAA in MSUD patients before and after phenylbutyrate treatment. ILE, isoleucine; LEU, leucine; VAL, valine. *P ≤ 0.05. (B) BCKA in MSUD patients before and after phenylbutyrate treatment. KMV, α-keto-β-methylvalerate; KIC, α-ketoisocaproate; KIV, α-ketoisovalerate. *P ≤ 0.05.

BCKDC activity and phosphorylation status in lymphoblasts. (A and B) BCKDC activity in lymphoblast cells from control subjects (C-660, C-661) and MSUD patients (P-1, -2, -3, -4, -5) untreated or treated with 1 m
mphenylbutyrate for 48 h. Leucine oxidation was measured by using radioactive assay as described in Materials and Methods. Rates are expressed as pmol of CO2 released/min/mg protein. Values are means ± SD (n= 3), * P ≤ 0.05, **P ≤ 0.01. (C) Western blotting of lymphoblast cell BCKDC enzymes (E1α- P, E1α and E2), BCATm and BCATc untreated or treated with 1 m
mphenylbutyrate (PB) for 48 h. β-Tubulin was used as an internal control. Images are representative of three independent experiments.

In vivo analysis of BCKDC phosphorylation status. Western blot analysis of liver extract using an antibody against the phosphorylated form of the E1α from three representative mice treated with phenylbutyrate or saline. Each lane corresponds to the liver extract from an independent mouse (from #1 to #3). The phosphorylated form of the E1α is significantly reduced in the phenylbutyrate treated mice when compared with the placebo group. The two groups showed similar amount of tubulin, E1 and E2 proteins.

The IC50 value for inhibition of BDK by phenylbutyrate. The 100% control activity represents BDK activity in the absence of phenylbutyrate.
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