Effects of vitamin B6 on one‐carbon metabolism in oral contraceptive users

Abstract

Oral contraceptive (OC) usage is associated with low plasma pyridoxal phosphate (PLP) indicating low vitamin B6 status. PLP serves as a coenzyme in several steps in 1C metabolism, including the entry of 1C units from serine via the glycine‐cleavage system and serine hydroxymethyltransferase (SHMT), as well as the transsulfuration pathway in which cystathionine β‐synthase (CBS) catalyzes the condensation of homocysteine with serine to form cystathionine, and cystathionine γ‐lyase (CTGL) catalyzes the cleavage of cystathionine to form cysteine. Whether vitamin B6 deficiency in OC users functionally affects 1C metabolism is uncertain. Therefore, we examined PLP‐related 1C metabolism in healthy OC users (20–40y, with plasma PLP < 30 nmol/L) before and after 4 wk of supplementation with pyridoxine (10 mg/d). We used an intravenous primed, constant infusion of stable isotopically‐labeled [13C5]methionine, [3‐13C]serine and [2H3]leucine to determine the effect of vitamin B6 supplementation on homocysteine remethylation from serine, methionine and serine fluxes, and fractional cystathionine synthesis. Preliminary data showed an expected increase in plasma PLP and changes in PLP‐dependent aspects of 1C metabolism due to supplementation. In conclusion, these findings imply a functional effect of vitamin B6 supplementation on 1C metabolism. Supported by NIH Grant DK072398 and NIH CTSA grant 1UL1RR029890.