Common genetic polymorphisms affect the human requirement for the nutrient choline

Gene response elements, genetic polymorphisms and epigenetics influence the human dietary requirement for choline

Recent progress in the understanding of the human dietary requirement for choline highlights the importance of genetic variation and epigenetics in human nutrient requirements. Choline is a major dietary source of methyl-groups (one of choline's metabolites, betaine, participates in the methylation of homocysteine to form methionine); also choline is needed for the biosynthesis of cell membranes, bioactive phospholipids and the neurotransmitter acetylcholine. A recommended dietary intake for choline in humans was set in 1998, and a portion of the choline requirement can be met via endogenous de novo synthesis of phosphatidylcholine catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT) in the liver. Though many foods contain choline, many humans do not get enough in their diets. When deprived of dietary choline, most adult men and postmenopausal women developed signs of organ dysfunction (fatty liver, liver or muscle cell damage, and reduces the capacity to handle a methionine load, resulting in elevated homocysteine). However, only a portion of premenopausal women developed such problems. The difference in requirement occurs because estrogen induces expression of the PEMT gene and allows premenopausal women to make more of their needed choline endogenously. In addition, there is significant variation in the dietary requirement for choline that can be explained by common polymorphisms in genes of choline and folate metabolism. Choline is critical during fetal development, when it alters DNA methylation and thereby influences neural precursor cell proliferation and apoptosis. This results in long term alterations in brain structure and function, specifically memory function.

Sex and menopausal status influence human dietary requirements for the nutrient choline

BACKGROUND

Although humans require dietary choline for methyl donation, membrane function, and neurotransmission, choline can also be derived from the de novo synthesis of phosphatidylcholine, which is up-regulated by estrogen. A recommended Adequate Intake (AI) exists for choline; however, an Estimated Average Requirement has not been set because of a lack of sufficient human data.

OBJECTIVE

The objective of the study was to evaluate the dietary requirements for choline in healthy men and women and to investigate the clinical sequelae of choline deficiency.

DESIGN

Fifty-seven adult subjects (26 men, 16 premenopausal women, 15 postmenopausal women) were fed a diet containing 550 mg choline x 70 kg(-1) x d(-1) for 10 d followed by <50 mg choline x 70 kg(-1) x d(-1) with or without a folic acid supplement (400 microg/d per randomization) for up to 42 d. Subjects who developed organ dysfunction during this diet had normal organ function restored after incremental amounts of choline were added back to the diet. Blood and urine were monitored for signs of toxicity and metabolite concentrations, and liver fat was assessed by using magnetic resonance imaging.

RESULTS

When deprived of dietary choline, 77% of men and 80% of postmenopausal women developed fatty liver or muscle damage, whereas only 44% of premenopausal women developed such signs of organ dysfunction. Moreover, 6 men developed these signs while consuming 550 mg choline x 70 kg(-1) x d(-1), the AI for choline. Folic acid supplementation did not alter the subjects' response.

CONCLUSION

Subject characteristics (eg, menopausal status) modulated the dietary requirement for choline, and a daily intake at the current AI was not sufficient to prevent organ dysfunction in 19 of the subjects.

The phosphatidylethanolamine N-methyltransferase gene V175M single nucleotide polymorphism confers the susceptibility to NASH in Japanese population

BACKGROUND/AIMS

The genetic predisposition on the development of nonalcoholic steatohepatitis (NASH) has been poorly understood. A functional polymorphism Val175Met was reported in phosphatidylethanolamine N-methyltransferase (PEMT) that catalyzes the conversion of phosphatidylethanolamine to phosphatidylcholine. The aim of this study was to investigate whether the carriers of Val175Met variant impaired in PEMT activity are more susceptible to NASH.

METHODS

Blood samples of 107 patients with biopsy-proven NASH and of 150 healthy volunteers were analyzed by the polymerase chain reaction (PCR) and restriction fragment length polymorphism.

RESULTS

Val175Met variant allele of the PEMT gene was significantly more frequent in NASH patients than in healthy volunteers (p<0.001), and carriers of Val175Met variant were significantly more frequent in NASH patients than in healthy volunteers (p<0.01). Among NASH patients, body mass index was significantly lower (p<0.05), and non-obese patients were significantly more frequent (p<0.001) in carriers of Val175Met variant than in homozygotes of wild type PEMT.

CONCLUSIONS

Val175Met variant of PEMT could be a candidate molecule that determines the susceptibility to NASH, because it is more frequently observed in NASH patients and non-obese persons with Val175Met variant of PEMT are facilitated to develop NASH.

Choline: Dietary Requirements and Role in Brain Development

Choline is needed for the maintenance of the structural integrity and signaling functions of cell membranes, for neurotransmission, and for transport of lipids and as a source of methyl groups. Choline can be made de novo in the body, but some individuals must also obtain choline in the diet to prevent deficiency symptoms. A number of environmental and genetic factors influence dietary requirements for choline, and average intakes in the population vary widely. Therefore, certain individuals may be at greater risk of choline deficiency. Choline is critical during fetal development, particularly during the development of the brain, where it can influence neural tube closure and lifelong memory and learning functions.