Human biomarkers for measuring vitamin B6 intake and status
Vitamin B6 can be assessed by different methods, as shown in Table 1.
Table 1. Assessment methods for vitamin B6
| Biomarker | Analysis type | Sample | Benefits | Intricacies |
|---|
| B6 vitamers |
Direct analysis |
plasma |
Good single B6 indicator |
Slow response to intake |
|---|
| B6 vitamers |
Direct analysis |
RBC, WB |
Status indicator |
|
|---|
| Urinary B6 |
Direct analysis |
Urine |
Reflects dietary intake |
|
|---|
| Functional B6 |
Indirect analysis |
|
Enzyme activities |
Assays may be affected by external factors |
|---|
RBC: red blood cells; WB: whole blood
Direct analysis of vitamin B6
Direct analysis of B6 vitamers has been described in various matrices (1):
PLASMA, RBC, WB B6
Plasma B6 has been often measured by an apo-tryrosine decarboxylase assay. Chromatographic techniques have been used more recently for all type of blood samples.
URINE
Includes the analysis of metabolites such as 4-pyridoxic acid often measured using HPLC.
Method
For details on chromatographic techniques for blood, plasma, erythrocyte and urine, see methods in references (5-8):
5. Talwar et al. J Chromatogr B 2003;792:333-43.
6. Meisser Redeuil et al. J Chromatogr A 2015.
7. Yagi et al. J Nutr Sci Vitaminol 2009;56:157-63.
8. Sharma & Dakshinamurti. J Chromatogr Biomed Applic 1992;578:45-51.
Functional B6 assessment
Several PLP-dependent enzymatic processes have been used for vitamin B6 assessment (1):
ERYTHROCYTE ASPARTATE AMINOTRANSFERASE (Α-EAST) AND ALANINE AMINOTRANSFERASE (Α-EALT)
PLP-stimulation of α-EAST and α-EALT has been widely used to assess long-term B6 status
Method
For details on α-EAST and α-EALT activities, see method in reference (9): Sorbi et al. Am J Gastroenterol 1999;94:1018.
TRYPTOPHAN CATABOLITES
Urinary xanthurenic acid, normally a minor tryptophan catabolite increases under vitamin B6 depletion
Method
For details on Tryptophan catabolites, see method in reference (11): Liu et al. Clin Chem 1996;42:397-401.
PLASMA HOMOCYSTEINE
Homocysteine catabolism is a PLP-dependent process, thus homocysteine in plasma is related to vitamin B6 (and folate and B12)
Method
For details on measuring homocysteine in plasma, see method in reference (10): Oosterink et al. J Chromatogr B 2015;998:106-13.
Quality control and technical assistance
Laboratory accreditation and validation
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E.g. vitamin B6 (pyridoxal 5’-phosphate), serum
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Technical assistance
For questions on vitamin B6 methods or for technical assistance, please contact sophie.moore@kcl.ac.uk or write to:
Dr Daniela Hampel, PhD
Project Scientist
USDA/ARS Western Human Nutrition Research Center
Department of Nutrition, University of California Davis
Email: dhampel@ucdavis.edu or daniela.hampel@ars.usda.gov