Choline deficiency in mice and humans is associated with increased plasma homocysteine concentration after a methionine load

Abstract

Background: Elevated concentrations of homocysteine in blood may be an independent risk factor for the development of atherosclerosis. Elevated homocysteine concentrations can be caused by decreased methylation of homocysteine to form methionine, as occurs in folate deficiency. A parallel pathway exists for methylation of homocysteine, in which choline, by way of betaine, is the methyl donor.

Objective: Our goal was to determine whether choline deficiency results in a decreased capacity to methylate homocysteine.

Design: C57BL/6J mice were fed diets containing 0, 10, or 35 mmol choline/kg diet for 3 wk. We then administered an oral methionine load to the animals and measured plasma homocysteine concentrations. Also, in a pilot study, we examined 8 men who were fed a diet providing 550 mg choline/d per 70 kg body weight for 10 d, followed by a diet providing almost no choline, until the subjects were clinically judged to be choline deficient or for <or=42 d. A methionine load was administered at the end of each dietary phase.

Results: Two hours after the methionine load, choline-deficient mice had plasma homocysteine concentrations twice those of choline-fed mice. Four hours after the methionine load, clinically choline-depleted men had plasma homocysteine concentrations that were 35% greater than those in men not choline depleted.

Conclusion: These results suggest that choline, like folate, plays an important role in the metabolism of homocysteine in humans and that response to a methionine load may be useful when assessing choline nutriture.

FIGURE 1

Mean (±SE) plasma homocysteine concentrations in mice fed AIN-93G diets containing 0 (choline deficient, CD), 10 (control, C), or 35 (choline supplemented, CS) mmol choline/kg diet for 3 wk followed by a methionine load (100 mg/kg body weight). Blood was collected, plasma was separated, and homocysteine concentrations were measured by HPLC before (cross-hatched bars) and 2 h after (solid bars) the methionine load; n = 5–7/group. There was a significant (P < 0.001) methionine-load status × diet interaction. ^*Significantly different from fasting (no methionine load), P < 0.01 (Student’s t test). ^#Significantly different from all other groups, P < 0.01 (ANOVA and Tukey-Kramer test).

FIGURE 2

Change (Δ) in plasma homocysteine (Hcy) concentrations in 8 healthy men fed a 550-mg choline baseline diet for 10 d, followed by a 50-mg choline depletion diet for ≤42 d, before and after a methionine load (100 mg/kg body weight). Subjects with hepatic steatosis (n = 4) were judged to be clinically choline depleted (D) and were offered a repletion diet until hepatic steatosis resolved. Subjects without hepatic steatosis at the end of the depletion phase (n = 4) were deemed not to be depleted (ND). Plasma Hcy was measured at the end of each phase before and 4 h after the methionine load. Hcy concentrations rose from 6.4 ± 0.6 μmol/L before the methionine load to 18.5 ± 2.4 μmol/L after the methionine load in men fed the 550-mg diet (n = 8; P < 0.001, paired t test). A significant (P < 0.05) interaction was observed between methionine load and clinical status. The change in Hcy concentration was calculated as follows: depletion diet – 550-mg diet. Brackets represent 95%CIs.