title: Pyridoxamine and pyridoxal are more effective than pyridoxine in rescuing folding-defective variants of human alanine:glyoxylate aminotransferase causing primary hyperoxaluria type I.
abstract: Vitamin B6 in the form of pyridoxine (PN) is one of the most widespread pharmacological therapies for inherited diseases involving pyridoxal phosphate (PLP)-dependent enzymes, including primary hyperoxaluria type I (PH1). PH1 is caused by a deficiency of liver-peroxisomal alanine: glyoxylate aminotransferase (AGT), which allows glyoxylate oxidation to oxalate leading to the deposition of insoluble calcium oxalate in the kidney. Only a minority of PH1 patients, mostly bearing the F152I and G170R mutations, respond to PN, the only pharmacological treatment currently available. Moreover, excessive doses of PN reduce the specific activity of AGT in a PH1 cellular model. Nevertheless, the possible effect(s) of other B6 vitamers has not been investigated previously. Here, we compared the ability of PN in rescuing the effects of the F152I and G170R mutations with that of pyridoxamine (PM) and PL. We found that supplementation with PN raises the intracellular concentration of PN phosphate (PNP), which competes with PLP for apoenzyme binding leading to the formation of an inactive AGT-PNP complex. In contrast, PNP does not accumulate in the cell upon PM or PL supplementation, but higher levels of PLP and PM phosphate (PMP), the two active forms of the AGT coenzyme, are found. This leads to an increased ability of PM and PL to rescue the effects of the F152I and G170R mutations compared with PN. A similar effect was also observed for other folding-defective AGT variants. Thus, PM and PL should be investigated as matter of importance as therapeutics for PH1 patients bearing folding mutations.
authors.affiliation: Department of Life and Reproduction Sciences, Section of Biological Chemistry, University of Verona, 37134 Verona, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Oppici
authors.affiliation: Department of Urology, University of Alabama at Birmingham, Birmingham, 35294 AL, USA.
authors.forename: Sonia
authors.initials: S
authors.lastname: Fargue
authors.affiliation: Genetics and Genomic Medicine, UCL Institute of Child Health, WC1N 1EH London, UK and.
authors.forename: Emma S
authors.initials: ES
authors.lastname: Reid
authors.affiliation: Genetics and Genomic Medicine, UCL Institute of Child Health, WC1N 1EH London, UK and.
authors.forename: Philippa B
authors.initials: PB
authors.lastname: Mills
authors.affiliation: Genetics and Genomic Medicine, UCL Institute of Child Health, WC1N 1EH London, UK and.
authors.forename: Peter T
authors.initials: PT
authors.lastname: Clayton
authors.affiliation: Department of Cell and Developmental Biology, Division of Biosciences, University College London, WC1E 6B London, UK.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Danpure
authors.affiliation: Department of Life and Reproduction Sciences, Section of Biological Chemistry, University of Verona, 37134 Verona, Italy, barbara.cellini@univr.it.
authors.forename: Barbara
authors.initials: B
authors.lastname: Cellini
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D006960:Hyperoxaluria, Primary / Q000188:drug therapy / Q000235:genetics*; D009154:Mutation / Q000187:drug effects; D017510:Protein Folding / Q000187:drug effects; D011730:Pyridoxal / Q000494:pharmacology*; D011733:Pyridoxamine / Q000494:pharmacology*; D011736:Pyridoxine / Q000494:pharmacology*; D000637:Transaminases / Q000737:chemistry* / Q000235:genetics; D014803:Vitamin B Complex / Q000494:pharmacology*
chemical_list: D014803:Vitamin B Complex; D011730:Pyridoxal; D011733:Pyridoxamine; D000637:Transaminases; C023067:glyoxylate aminotransferase; D011736:Pyridoxine