title: Direct and Functional Biomarkers of Vitamin B6 Status.
abstract: Measures of B6 status are categorized as direct biomarkers and as functional biomarkers. Direct biomarkers measure B6 vitamers in plasma/serum, urine and erythrocytes, and among these plasma pyridoxal 5'-phosphate (PLP) is most commonly used. Functional biomarkers include erythrocyte transaminase activities and, more recently, plasma levels of metabolites involved in PLP-dependent reactions, such as the kynurenine pathway, one-carbon metabolism, transsulfuration (cystathionine), and glycine decarboxylation (serine and glycine). Vitamin B6 status is best assessed by using a combination of biomarkers because of the influence of potential confounders, such as inflammation, alkaline phosphatase activity, low serum albumin, renal function, and inorganic phosphate. Ratios between substrate-products pairs have recently been investigated as a strategy to attenuate such influence. These efforts have provided promising new markers such as the PAr index, the 3-hydroxykynurenine:xanthurenic acid ratio, and the oxoglutarate:glutamate ratio. Targeted metabolic profiling or untargeted metabolomics based on mass spectrometry allow the simultaneous quantification of a large number of metabolites, which are currently evaluated as functional biomarkers, using data reduction statistics.
authors.affiliation: Department of Clinical Science, University of Bergen, and the Laboratory of Clinical Biochemistry, Haukeland University Hospital, 5021 Bergen, Norway; email: per.ueland@ikb.uib.no.
authors.forename: Per Magne
authors.initials: PM
authors.lastname: Ueland
authors.forename: Arve
authors.initials: A
authors.lastname: Ulvik
authors.forename: Luisa
authors.initials: L
authors.lastname: Rios-Avila
authors.forename: Øivind
authors.initials: Ø
authors.lastname: Midttun
authors.forename: Jesse F
authors.initials: JF
authors.lastname: Gregory
mesh_terms: D000596:Amino Acids / Q000097:blood; D015415:Biomarkers / Q000097:blood* / Q000652:urine; D015992:Body Mass Index; D005260:Female; D006304:Health Status; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007249:Inflammation; D007737:Kynurenine / Q000097:blood; D008019:Life Style; D008297:Male; D055442:Metabolome; D055432:Metabolomics; D009752:Nutritional Status; D011247:Pregnancy; D011730:Pyridoxal / Q000097:blood; D011732:Pyridoxal Phosphate / Q000097:blood; D011735:Pyridoxic Acid / Q000652:urine; D000637:Transaminases; D025101:Vitamin B 6 / Q000097:blood / Q000502:physiology / Q000652:urine; D026681:Vitamin B 6 Deficiency / Q000097:blood* / Q000652:urine
chemical_list: D000596:Amino Acids; D015415:Biomarkers; D007737:Kynurenine; D011730:Pyridoxal; D011735:Pyridoxic Acid; D011732:Pyridoxal Phosphate; D025101:Vitamin B 6; D000637:Transaminases
keywords: B6 vitamers; amino acids; direct biomarkers; functional biomarkers; kynurenines; metabolomics; one-carbon metabolites; targeted metabolic profiling; transaminase tests; transsulfuration metabolites