B6 Vitamers

The B6 vitamers include pyridoxal (PL), pyridoxamine (PM), pyridoxine (PN), and their respective phosphorylated forms pyridoxal 5′-phosphate (PLP), pyridoxamine 5′-phsophate (PMP), and pyridoxine 5′-phosphate (PNP). All B6 vitamers need to be converted into the active cofactor PLP to exert the physiological function of vitamin B6 in a variety of enzyme-catalyzed reactions, playing central roles in metabolism. The metabolite Pyridoxic Acid (PA) is excreted into the urine. Several acquired and genetic causes lead to vitamin B6 deficiency manifesting in several neurological symptoms including seizures. The determination of the B6 vitamers is especially important in the differential diagnosis of vitamin B6-dependent epilepsies that can be treated with pharmacological doses of PN or PLP. B6 vitamers are measured in plasma after acidic protein precipitation by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using reverse-phase chromatography and detection by multiple reaction monitoring in positive ion mode. Interpretation of the plasma profile of B6 vitamers is valuable for the diagnosis of pyridox(am)ine oxidase (PNPO) deficiency (elevated PM and PM/PA ratio), hypophosphatasia due to mutations in ALPL (elevated PLP and PLP/PL ratio), and to assess the vitamin B6 status in a variety of more common conditions (reduced PLP, PL, PLP + PL).