Choline- and betaine-defined diets for use in clinical research and for the management of trimethylaminuria

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

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.

Elevated serum creatine phosphokinase in choline-deficient humans: mechanistic studies in C2C12 mouse myoblasts

BACKGROUND

Choline is a required nutrient, and humans deprived of choline develop liver damage.

OBJECTIVE

This study examined the effect of choline deficiency on muscle cells and the release of creatine phosphokinase (CPK) as a sequela of that deficiency.

DESIGN

Four men were fed diets containing adequate and deficient amounts of choline, and serum was collected at intervals for measurement of CPK. C2C12 mouse myoblasts were cultured in a defined medium containing 0 or 70 micromol choline/L for up to 96 h, and CPK was measured in the media; choline and metabolites were measured in cells. Apoptosis was assessed by using terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling and activated caspase-3 immunohistochemistry. Cell fragility in response to hypo-osmotic stress was also assessed.

RESULTS

Three of 4 humans fed a choline-deficient diet had significantly elevated serum CPK activity derived from skeletal muscle (up to 66-fold; P < 0.01) that resolved when choline was restored to their diets. Cells grown in choline-deficient medium for 72 h leaked 3.5-fold more CPK than did cells grown in medium with 70 micromol choline/L (control medium; P < 0.01). Apoptosis was induced in cells grown in choline-deficient medium. Phosphatidylcholine concentrations were diminished in choline-deficient cells (to 43% of concentrations in control cells at 72 h; P < 0.01), as were concentrations of intracellular choline, phosphocholine, and glycerophosphocholine. Cells grown in choline-deficient medium had greater membrane osmotic fragility than did cells grown in control medium.

CONCLUSIONS

Choline deficiency results in diminished concentrations of membrane phosphatidylcholine in myocytes, which makes them more fragile and results in increased leakage of CPK from cells. Serum CPK may be a useful clinical marker for choline deficiency in humans.