Molecular and cellular effects of vitamin B12 in brain, myocardium and liver through its role as co-factor of methionine synthase.

Vitamin B12 (cobalamin, cbl) is a cofactor of methionine synthase (MTR) in the synthesis of methionine, the precursor of the universal methyl donor S-Adenosylmethionine (SAM), which is involved in epigenomic regulatory mechanisms. We have established a neuronal cell model with stable expression of a transcobalamin-oleosin chimer and subsequent decreased cellular availability of vitamin B12, which produces reduced proliferation, increased apoptosis and accelerated differentiation through PP2A, NGF and TACE pathways. Anti-transcobalamin antibody or impaired transcobalamin receptor expression produce also impaired proliferation in other cells.

Association of MTRRA66G polymorphism (but not of MTHFR C677T and A1298C, MTRA2756G, TCN C776G) with homocysteine and coronary artery disease in the French population.

Methylenetetrahydrofolate reductase polymorphism (MTHFR C677T) is an established determinant of homocysteine plasma level (t-Hcys) while its association with coronary artery disease (CAD) seems to be more limited. In contrast, the association of the substitutions A2756G of methionine synthase (MTR), A66G of methionine synthase reductase (MTRR) and C776G of transcobalamin (TCN) to both t-Hcys and CAD needs to be evaluated further. The objective was to evaluate the association of these polymorphisms with t-Hcys and CAD in a French population.

High prevalence of hyperhomocysteinemia related to folate deficiency and the 677C-->T mutation of the gene encoding methylenetetrahydrofolate reductase in coastal West Africa.

Background: Moderate hyperhomocysteinemia is a risk for neural tube defect and neurodegenerative and vascular diseases and has nutritional, metabolic, and genetic determinants. Its prevalence in sub-Saharan Africa remains unknown.

Objective: Our goal was to evaluate the prevalence of hyperhomocysteinemia and the influence of nutritional, metabolic, and genetic determinants in savanna and coastal regions of Togo and Benin.

Low frequency of mutated methylenetetrahydrofolate reductase 677C-->T and 1298A-->C genetics single nucleotide polymorphisms (SNPs) in Sub-Saharan populations.

5,10-Methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MTR) are two of the key enzymes in the folate/vitamin B12-dependent remethylation of homocysteine to methionine. The frequencies of MTHFR single nucleotide polymorphisms (SNPs), 677C-->T, 1298A-->C, 1317T-->C and of MTR, 2756A-->G, have been widely studied in Caucasians, but they have never been reported simultaneously in a large population from Sub-Saharan Africa. Presently, we report the prevalence of these SNPs and their relationship to homocysteine in 240 subjects recruited in West Africa.

Hyperhomocysteinemia is related to residual glomerular filtration and folate, but not to methylenetetrahydrofolate-reductase and methionine synthase polymorphisms, in supplemented end-stage renal disease patients undergoing hemodialysis.

Glomerular filtration is one of the major determinants of plasma total homocysteine (tHcy). To evaluate the respective roles of residual glomerular filtration (by measuring a specific protein marker, cystatin C), genetic polymorphisms and nutritional status in tHcy blood levels in end-stage renal disease patients (ESRD) under hemodialysis and supplemented with folate, we measured tHcy, folate, vitamin B12 (B12), creatinine, cystatin C, albumin and C-reactive protein and determined the polymorphism of methylenetetrahydrofolate reductase (MTHFR) (C677T and A1289C) and of methionine synthase (MS) (A2756G) in 114 ESRD patients before hemodialysis and 76 control subjects. All patients received a folate supplementation of 700 microg/day.

Overexpression of folate binding protein alpha is one of the mechanism explaining the adaptation of HT29 cells to high concentration of methotrexate.

The human colon adenocarcinoma cell line HT29 can be adapted to 10(-7)- 10(-4) M concentrations of methotrexate (MTX). Cells adapted to 10(-4) M MTX have an enterocyte-like phenotype with DHFR gene amplification. Presently, we hypothetized that an increased expression of folate binding protein (FBP) may participate to the MTX resistance of 10(-4) MTX HT29 cells.

Transcobalamin codon 259 polymorphism in HT-29 and Caco-2 cells and in Caucasians: relation to transcobalamin and homocysteine concentration in blood.

Transcobalamin (TC) is the plasma transporter that delivers vitamin B(12) to cells. We have already reported that HT-29 and Caco-2 cells secrete different TC variants. HT-29 secretes 2 TC isoproteins (codon 259-Pro/Arg [259-P/R]), exhibiting unequal concentrations (TC 259-P > TC 259-R), and Caco-2 cells only secrete the phenotype 259-R.

Seven novel mutations in mut methylmalonic aciduria.

Methylmalonic aciduria (MMA) is an autosomal recessive inborn error of metabolism that results from functional defects in methylmalonyl CoA mutase (MCM), a nuclear-encoded, mitochondrial enzyme that uses the vitamin B12 derivative, adenosylcobalamin (AdoCbl) as a cofactor. To date, 23 mutations have been identified at the MUT locus on the short arm of chromosome 6, causing the mut forms of MMA (mut complementation group; mut MMA, McKusick #251000). We now report seven novel mutations.

Home parenteral nutrition and vitamin B12 status.

The vitamin B12 status of 20 subjects who were on home parenteral nutrition after surgical or functional small bowel resection and were given 1000 micrograms cyanocobalamin every 3 mo was studied by comparing their plasma vitamin B12, homocysteine (HS), and methylmalonic acid (MMA) concentrations. The plasma vitamin B12 concentration (median 145 pmol/L, 95% confidence interval: 123-217) was subnormal in four cases and borderline in four others. In the "4low B12" group, the concentrations of the markers of vitamin B12 deficiency were in the normal range; HS 10.

Alcoholic cirrhosis and cobalamin metabolism.

The cobalamin status of 27 patients suffering from alcoholic cirrhosis and 20 control subjects was analyzed. Plasma cobalamin (p < 0.005), total corrinoids (p < 0.

Human methionine synthase: cDNA cloning and identification of mutations in patients of the cblG complementation group of folate/cobalamin disorders.

Methionine synthase catalyzes the remethylation of homocysteine to methionine in a methylcobalamin-dependent reaction. We used specific regions of homology within the methionine synthase sequences of several lower organisms to clone a human methionine synthase cDNA by a combination of RT-PCR and inverse PCR. The enzyme is 1265 amino acids in length and contains the seven residue structure-based sequence fingerprint identified for cobalamin-containing enzymes.

Crohn's disease and vitamin B12 metabolism.

The concentrations of vitamin B12, its analogs, and the haptocorrin and transcobalamin carriers in 21 patients suffering from Crohn's disease and a group of controls (20 adults) were measured. There were no significant differences in the mean values for vitamin B12, total corrinoids (vitamin B12 + analogs), or vitamin B12 or total corrinoids bound to haptocorrin or transcobalamin of the Crohn's and control patients. There was a significant increase in the binding capacity of transcobalamin in the Crohn's patients compared to the controls (P < 0.

Method for the direct specific measurement of vitamin B12 bound to transcobalamin II in plasma.

The concentration of plasma vitamin B12 bound to transcobalamin II was measured by two methods: QUSO and Heparin Sepharose (HS). The new HS procedure provided a specific, direct measurement of vitamin B12 bound to both R binder and transcobalamin II in plasma.