title: Identification of enzymes involved in oxidation of phenylbutyrate.
abstract: In recent years the short-chain fatty acid, 4-phenylbutyrate (PB), has emerged as a promising drug for various clinical conditions. In fact, PB has been Food and Drug Administration-approved for urea cycle disorders since 1996. PB is more potent and less toxic than its metabolite, phenylacetate (PA), and is not just a pro-drug for PA, as was initially assumed. The metabolic pathway of PB, however, has remained unclear. Therefore, we set out to identify the enzymes involved in the β-oxidation of PB. We used cells deficient in specific steps of fatty acid β-oxidation and ultra-HPLC to measure which enzymes were able to convert PB or its downstream products. We show that the first step in PB oxidation is catalyzed solely by the enzyme, medium-chain acyl-CoA dehydrogenase. The second (hydration) step can be catalyzed by all three mitochondrial enoyl-CoA hydratase enzymes, i.e., short-chain enoyl-CoA hydratase, long-chain enoyl-CoA hydratase, and 3-methylglutaconyl-CoA hydratase. Enzymes involved in the third step include both short- and long-chain 3-hydroxyacyl-CoA dehydrogenase. The oxidation of PB is completed by only one enzyme, i.e., long-chain 3-ketoacyl-CoA thiolase. Taken together, the enzymatic characteristics of the PB degradative pathway may lead to better dose finding and limiting the toxicity of this drug.
authors.affiliation: Laboratory Genetic Metabolic Diseases, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Neža
authors.initials: N
authors.lastname: Palir
authors.affiliation: Laboratory Genetic Metabolic Diseases, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Jos P N
authors.initials: JPN
authors.lastname: Ruiter
authors.affiliation: Laboratory Genetic Metabolic Diseases, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Ronald J A
authors.initials: RJA
authors.lastname: Wanders
authors.affiliation: Laboratory Genetic Metabolic Diseases, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands r.h.houtkooper@amc.nl.
authors.forename: Riekelt H
authors.initials: RH
authors.lastname: Houtkooper
mesh_terms: D057075:Enzyme Assays; D004798:Enzymes / Q000378:metabolism*; D010084:Oxidation-Reduction; D010654:Phenylbutyrates / Q000378:metabolism*
chemical_list: D004798:Enzymes; D010654:Phenylbutyrates; C075773:4-phenylbutyric acid
keywords: cell metabolism; cells and tissues; coenzyme A; dehydrogenases; enzymology; fatty acid/oxidation; lipid biochemistry; phenylacetate; β-oxidation