title: Phenylbutyrate increases pyruvate dehydrogenase complex activity in cells harboring a variety of defects.
abstract: OBJECTIVE
  Deficiency of pyruvate dehydrogenase complex (PDHC) is the most common genetic disorder leading to lactic acidosis. PDHC deficiency is genetically heterogenous and most patients have defects in the X-linked E1-α gene but defects in the other components of the complex encoded by PDHB, PDHX, DLAT, DLD genes or in the regulatory enzyme encoded by PDP1 have also been found. Phenylbutyrate enhances PDHC enzymatic activity in vitro and in vivo by increasing the proportion of unphosphorylated enzyme through inhibition of pyruvate dehydrogenase kinases and thus, has potential for therapy of patients with PDHC deficiency. In the present study, we investigated response to phenylbutyrate of multiple cell lines harboring all known gene defects resulting in PDHC deficiency.
  
  
  METHODS
  Fibroblasts of patients with PDHC deficiency were studied for their enzyme activity at baseline and following phenylbutyrate incubation. Drug responses were correlated with genotypes and protein levels by Western blotting.
  
  
  RESULTS
  Large deletions affecting PDHA1 that result in lack of detectable protein were unresponsive to phenylbutyrate, whereas increased PDHC activity was detected in most fibroblasts harboring PDHA1 missense mutations. Mutations affecting the R349-α residue were directed to proteasome degradation and were consistently unresponsive to short-time drug incubation but longer incubation resulted in increased levels of enzyme activity and protein that may be due to an additional effect of phenylbutyrate as a molecular chaperone.
  
  
  CONCLUSIONS
  PDHC enzyme activity was enhanced by phenylbutyrate in cells harboring missense mutations in PDHB, PDHX, DLAT, DLD, and PDP1 genes. In the prospect of a clinical trial, the results of this study may allow prediction of in vivo response in patients with PDHC deficiency harboring a wide spectrum of molecular defects.
authors.affiliation: Telethon Institute of Genetics and Medicine Naples, Italy.
authors.forename: Rosa
authors.initials: R
authors.lastname: Ferriero
authors.affiliation: Laboratoire de Biochimie, AP-HP Hôpital de Bicêtre Le Kremlin Bicêtre, France.
authors.forename: Audrey
authors.initials: A
authors.lastname: Boutron
authors.affiliation: Laboratoire de Biochimie, AP-HP Hôpital de Bicêtre Le Kremlin Bicêtre, France.
authors.forename: Michele
authors.initials: M
authors.lastname: Brivet
authors.affiliation: Center for Inherited Disorders of Energy Metabolism, Case Western Reserve University Cleveland, Ohio, USA.
authors.forename: Douglas
authors.initials: D
authors.lastname: Kerr
authors.affiliation: Hayward Genetics Center, Tulane University Medical School New Orleans, Louisiana, USA.
authors.forename: Eva
authors.initials: E
authors.lastname: Morava
authors.affiliation: Department of Pediatrics, Nijmegen Center for Mitochondrial Disorders, Radboud University Medical Center Nijmegen, The Netherlands.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Rodenburg
authors.affiliation: Center for Molecular Diseases, Lausanne University Hospital Lausanne, Switzerland.
authors.forename: Luisa
authors.initials: L
authors.lastname: Bonafé
authors.affiliation: Division for Metabolic Diseases and Children's Research Center, University Children's Hospital Zürich, Switzerland.
authors.forename: Matthias R
authors.initials: MR
authors.lastname: Baumgartner
authors.affiliation: Metabolic Disease Unit, Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Tel-Hashomer and Sackler School of Medicine, Tel Aviv University Tel Aviv, Israel.
authors.forename: Yair
authors.initials: Y
authors.lastname: Anikster
authors.affiliation: Department of Human Genetics, McGill University Montreal, Quebec, Canada ; Department of Pediatrics, Montreal Children's Hospital Montreal Montreal, Quebec, Canada.
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Braverman
authors.affiliation: Telethon Institute of Genetics and Medicine Naples, Italy ; Department of Translational Medicine, Federico II University of Naples Naples, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Brunetti-Pierri