Background: Vitamin B-6 has attracted renewed interest because of its role in homocysteine metabolism and its possible relation to cardiovascular risk. We examined the plasma B-6 vitamers, pyridoxal 5'-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA) before and after vitamin B-6 supplementation. Methods: Patients (n=90; age range, 38-80 years) undergoing coronary angiography (part of the homocysteine-lowering Western Norway B-Vitamin Intervention Trial) were allocated to the following daily oral treatment groups: (A), vitamin B-12 (0.4 mg), folic acid (0.8 mg), and vitamin B-6 (40 mg); (B), vitamin B-12 and folic acid; (C), vitamin B-6; or (D), placebo. EDTA blood was obtained before treatment and 3, 14, 28, and 84 days thereafter. Results: Before treatment, PLP (range, 5-111 nmol/L) and 4-PA (6-93 nmol/L) were the predominant B-6 vitamers identified in plasma. During the 84-day study period, the intraindividual variation (CV) in patients not treated with vitamin B-6 (groups B and D) was 45% for PLP and 67% for 4-PA. Three days after the start of treatment, the increases in concentration were similar to10-, 50-, and 100-fold for PLP, 4-PA, and PL, respectively. No significant additional increase was observed at the later time points. The PLP concentration correlated to the concentrations of 4-PA and PL before treatment, but not after treatment. The PL concentration correlated with 4-PA before and after treatment. Conclusions: Vitamin B-6 treatment has an immediate effect on the concentrations and the forms of B-6 vitamers present in plasma, and the changes remain the same during prolonged treatment. Our results suggest that the B-6 vitamers in plasma reflect vitamin B-6 intake. (C) 2003 American Association for Clinical Chemistry.
