Pregnancy alters choline dynamics: results of a randomized trial using stable isotope methodology in pregnant and nonpregnant women

Abstract

Background: Although biomarkers of choline metabolism are altered by pregnancy, little is known about the influence of human pregnancy on the dynamics of choline-related metabolic processes.

Objective: This study used stable isotope methodology to examine the effects of pregnancy on choline partitioning and the metabolic activity of choline-related pathways.

Design: Healthy third-trimester pregnant (n = 26; initially week 27 of gestation) and nonpregnant (n = 21) women consumed 22% of their total choline intake (480 or 930 mg/d) as methyl-d9-choline for the final 6 wk of a 12-wk feeding study.

Results: Plasma d9-betaine:d9-phosphatidylcholine (PC) was lower (P ≤ 0.04) in pregnant than in nonpregnant women, suggesting greater partitioning of choline into the cytidine diphosphate-choline (CDP-choline) PC biosynthetic pathway relative to betaine synthesis during pregnancy. Pregnant women also used more choline-derived methyl groups for PC synthesis via phosphatidylethanolamine N-methyltransferase (PEMT) as indicated by comparable increases in PEMT-PC enrichment in pregnant and nonpregnant women despite unequal (pregnant > nonpregnant; P < 0.001) PC pool sizes. Pregnancy enhanced the hydrolysis of PEMT-PC to free choline as shown by greater (P < 0.001) plasma d3-choline:d3-PC. Notably, d3-PC enrichment increased (P ≤ 0.011) incrementally from maternal to placental to fetal compartments, signifying the selective transfer of PEMT-PC to the fetus.

Conclusions: The enhanced use of choline for PC production via both the CDP-choline and PEMT pathways shows the substantial demand for choline during late pregnancy. Selective partitioning of PEMT-PC to the fetal compartment may imply a unique requirement of PEMT-PC by the developing fetus.

Trial registration: ClinicalTrials.gov NCT01127022.

Figures

FIGURE 1.

Deuterium-labeled methyl-d9-choline traces the distribution of orally consumed choline and its methyl groups. Black circles indicate deuterium-labeled methyl groups; white circles indicate unlabeled methyl groups. The administered methyl-d9-choline can enter the CDP-choline pathway to produce d9-PC or it can be oxidized to d9-betaine, which donates a methyl group to homocysteine, producing d6-DMG and d3-methionine. d3-Methionine serves as a precursor to d3-SAM, which can be used by PEMT to sequentially methylate PE, forming d3-PC as well as smaller amounts of d6-PC (4). Hydrolysis of d3-PC will generate d3-choline as well as d3-betaine, d3-methinone, d3-DMG, and d3-sarcosine when d3-choline is used as a methyl donor. CDP-choline, cytidine diphosphate-choline; DMG, dimethylglycine; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PEMT, phosphatidylethanolamine N-methyltransferase; SAH, S-adenosylhomocysteine; SAM, S-adenosylmethionine; SAR, sarcosine; SM, sphingomyelin.

FIGURE 2.

Enrichment of plasma d9-betaine (A) and the enrichment ratio of plasma d9-betaine:d9-PC (B) in study-end (week 12) blood samples obtained from pregnant and nonpregnant women consuming 22% of 480 or 930 mg choline/d as methyl-d9-choline from study week 6 to week 12 (n = 10–13/group). Linear regression models including pregnancy, choline intake, and their interaction term (pregnancy × choline intake) were constructed to assess the effects of pregnancy on dependent variables. Pregnancy interacted with choline intake to affect the dependent variables [P = 0.05 for plasma betaine enrichment (panel A); P = 0.027 for plasma d9-betaine:d9-PC (panel B)], thus data were stratified by choline intake, and the effects of pregnancy on dependent variables were examined for women consuming 480 or 930 mg choline/d separately. The enrichment ratio of d9-betaine:d9-PC in pregnant women consuming 930 mg choline/d did not differ (P = 0.75) from that in nonpregnant women consuming 480 mg choline/d. Select genetic variants of one-carbon metabolic genes were included as covariates in the model if they were predictors of the dependent variable. Values are presented as pooled estimated marginal means ± SEMs from multiple imputation analyses. NP, nonpregnant women; P, pregnant women; PC, phosphatidylcholine.

FIGURE 3.

Choline metabolite enrichments in maternal delivery plasma, placental tissue, and fetal cord plasma obtained from pregnant women consuming 22% of 480 and 930 mg choline/d as methyl-d9-choline from study week 6 until delivery (n = 24; paired t tests). Dissimilar letters (a, b, c) indicate differences between compartments at P ≤ 0.011. A statistical analysis performed separately for each choline intake group yielded similar results. Values are presented as pooled estimated marginal means ± SEMs from multiple imputation analyses. DMG, dimethylglycine; PC, phosphatidylcholine; SM, sphingomyelin

FIGURE 4.

Proposed mechanisms through which pregnancy alters choline metabolism based on the isotopic enrichment of choline metabolites after oral consumption of d9-choline by pregnant and nonpregnant women. Pregnancy increases the use of orally consumed choline for PC synthesis through the CDP-choline and PEMT pathways. Pregnancy also increases the use of betaine for methionine synthesis and the hydrolysis of PEMT-PC to free choline. The reduced production of betaine from orally consumed choline (due to its increased use by the CDP-choline pathway), along with enhanced use of betaine as a methyl donor, may contribute to its depletion during the last trimester of human pregnancy. The increase in circulating free choline during this timeframe may stem from greater degradation of PEMT-PC. Thin arrows indicate that metabolic flux did not differ or was not compared between pregnant and nonpregnant women. Thick arrows indicate that metabolic flux was enhanced in third-trimester pregnant compared with nonpregnant women. The dashed arrow indicates that metabolic flux was attenuated in third-trimester pregnant compared with nonpregnant women. CDP-choline, cytidine diphosphate-choline; DMG, dimethylglycine; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PEMT, phosphatidylethanolamine N-methyltransferase; SAH, S-adenosylhomocysteine; SAM, S-adenosylmethionine; SAR, sarcosine; SM, sphingomyelin.