Folate deprivation reduces homocysteine remethylation in a human intestinal epithelial cell culture model: Role of serine in one-carbon donation

Justin H. Townsend, Steven R. Davis, Amy D. Mackey, Jesse F. Gregory

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Abstract

Little is known about homocysteine metabolism in intestine. To address this question, we investigated homocysteine metabolism under conditions of folate adequacy and folate deprivation in the Caco-2 cell line, a model of human intestinal mucosal cells. Caco-2 cells were cultured in media enriched with [3-13C]serine and [U-13C5]methionine tracers, and enrichments of intracellular free amino acid pools of these amino acids as well as homocysteine, cystathionine, and cysteine were measured by using gas chromatography/mass spectrometry. Homocysteine transsulfuration plus folate-dependent and total remethylation were quantified from these amino acid enrichments. Homocysteine remethylation accounted for 19% of the intracellular free methionine pool in cells cultured with supplemental folate, and nearly all one-carbon units used for remethylation originated from the three carbon of serine via folate-dependent remethylation. Labeling of cystathionine and cysteine indicated the presence of a complete transsulfuration pathway in Caco-2 cells, and this pathway produced 13% of the intracellular free cysteine pool. Appearance of labeled homocysteine and cystathionine in culture medium suggests export of these metabolites from intestinal cells. Remethylation was reduced by one-third in folate-restricted cell cultures (P < 0.001), and only -50% of the one-carbon units used for remethylation originated from the three carbon of serine under these conditions. In conclusion, the three carbon of serine is the primary source of one-carbon units used for homocysteine remethylation in folate-supplemented Caco-2 cell cultures. Remethylation is reduced as a result of folate restriction in this mucosal cell model, and one-carbon sources other than the three carbon of serine contribute to remethylation under this condition.

Original languageEnglish (US)
Pages (from-to)G588-G595
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume286
Issue number4 49-4
StatePublished - Apr 1 2004
Externally publishedYes

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Keywords

  • Caco-2
  • Methionine
  • Methylation
  • Serine
  • Transsulfuration

ASJC Scopus subject areas

  • Physiology
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

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