Metabolite profile analysis reveals association of vitamin B-6 with metabolites related to one-carbon metabolism and tryptophan catabolism but not with biomarkers of inflammation in oral contraceptive users and reveals the effects of oral contraceptives on these processes

Abstract

Background: The use of oral contraceptives (OCs) has been associated with low plasma pyridoxal 5'-phosphate (PLP). The functional consequences are unclear.

Objectives: To determine whether functional vitamin B-6 insufficiency occurs in OC users and is attributable to OCs, we investigated the associations of PLP with metabolites of one-carbon metabolism, tryptophan catabolism, and inflammation in OC users, and evaluated the effects of OCs on these metabolites.

Methods: Plasma metabolite concentrations were measured in 157 OC users (20-40 y of age). Associations between PLP and the metabolites were analyzed through use of generalized additive models and partial least squares-discriminant analysis (PLS-DA). Additionally, data from 111 of the 157 OC users were compared to previously reported data from 11 nonusers, at adequate and low vitamin B-6 status, with use of multivariate ANOVA.

Results: PLP showed significant (P < 0.05) negative nonlinear association with homocysteine, glutathione, and ratios of asymmetric dimethylarginine to arginine, 3-hydroxykynurenine to 3-hydroxyanthranilic acid, and 3-hydroxykynurenine to kynurenic acid. PLS-DA supported these conclusions and identified 3-hydroxykynurenine and the 3-hydroxykynurenine-to-kynurenine ratio as discriminating biomarkers in women with PLP ≤30 nmol/L. Among the many differences, OC users had significantly higher plasma pyridoxal (157% at adequate and 195% at low vitamin B-6 status), 4-pyridoxic acid (154% at adequate and 300% at low vitamin B-6 status), xanthurenic acid (218% at low vitamin B-6 status), 3-hydroxyanthranilic acid (176% at adequate and 166% at low vitamin B-6 status), quinolinic acid (127% at low vitamin B-6 status), and nicotinamide (197% at low vitamin B-6 status). Biomarkers of inflammation were not associated with PLP, and no differences were found between the 2 groups.

Conclusions: PLP is associated with biomarkers of one-carbon metabolism and tryptophan catabolism but not with biomarkers of inflammation in OC users. Independent of vitamin B-6 status, OCs have effects on metabolites and ratios of one-carbon metabolism and tryptophan catabolism but not on biomarkers of inflammation. This study was registered at clinicaltrials.gov as NCT01128244. The study from which data for nonusers was derived was registered as NCT00877812.

Keywords: metabolite profile; one-carbon; oral contraceptives; tryptophan; vitamin B-6.

Conflict of interest statement

Author disclosures: L Rios-Avila, B Coats, Y-Y Chi, Ø Midttun, PM Ueland, PW Stacpoole, and JF Gregory III, no conflicts of interest.

© 2015 American Society for Nutrition.

Figures

FIGURE 1

CONSORT diagram of the oral contraceptive users included in the study. PLP, pyridoxal 5′-phosphate.

FIGURE 2

Associations (95%) of plasma PLP with one-carbon, tryptophan metabolites and ratios. Associations were modeled by GAMs with use of data from 157 oral contraceptive users. Shaded areas indicate 95% CIs. The significant metabolites, by χ-square test based on GAM, were (A) Hcy, (B) GSH, and the ratios (C) ADMA to Arg, (D) HK to KA, and (E) HK to HAA. ADMA:arg, asymmetric dimethylarginine-to-arginine ratio; GAM, generalized additive model; GSH, glutathione; Hcy, homocysteine; HK:HAA, 3-hydroxykynurenine–to–3-hydroxyanthranilic acid ratio; HK:KA, 3-hydroxykynurenine-to-kynurenic acid ratio; PLP, pyridoxal 5′-phosphate.

FIGURE 3

Score plot from partial least squares–discriminant analysis of overall data for one-carbon, tryptophan metabolites, ratios, and biomarkers of inflammation in OC users according to PLP concentrations. Low PLP: ≤30 nmol/L; mid PLP: 31–99 nmol/L; high PLP: ≥100 nmol/L. Each data point represents a function of a pooled metabolite profile of each participant. Pyridoxal, 4-pyridoxic acid, and pyridoxine were omitted for this analysis to focus the analysis on the non–vitamin B-6 patterns of metabolites. Cumulative R2Y values for components 1 and 2 were 0.187 and 0.292, respectively. OC, oral contraceptive; PLP, pyridoxal 5′-phosphate; R2Y, variation of all Y explained by the model.

FIGURE 4

VIP plots from partial least squares–discriminant analysis of overall data for one-carbon, tryptophan metabolites, ratios, and biomarkers of inflammation between low-, middle-, and high-plasma PLP concentration in OC users. (A) VIP [1], component 1; (B) VIP [2], component 2. The bars represent a weighted sum of squares with CIs. Variables in which the lower range of the CI exceed a VIP value of 1 are considered to be significant at the 95% level (white bars). AA, anthranilic acid; ADMA, asymmetric dimethylarginine; Bet, betaine; Chol, choline; Cre, creatine; Crn, creatinine; CRP, C-reactive protein; Csn, cystathionine; Cysgly, cysteinylglycine; DMG, dimethylglycine; GSH, glutathione; HAA, 3-hydroxyanthranilic acid; hArg, homoarginine; Hcy, homocysteine; HK, 3-hydroxykynurenine; KA, kynurenic acid; Kyn, kynurenine; mNAM, N1-methylnicotinamide; NAM, nicotinamide; Neopt, neopterin; OC, oral contraceptive; PLP, pyridoxal 5′-phosphate; QA, quinolinic acid; Ribo, riboflavin; SDMA, symmetric dimethylarginine; TMAO, trimethyl N-oxide; TML, trimethylysine; Var ID, variable identification; VIP, variable influence on projection; XA, xanthurenic acid.