GENETIC EFFECTS-FOLATE-DEPENDENT ONE-CARBON METABOLISM
Principal Investigator: JESSE GREGORY
Abstract: DESCRIPTION: One-carbon (Cl) metabolism consists of the generation of carbon units for use in cellular processes including DNA synthesis, regeneration of methionine (Met) from homocysteine (Hcy), and methylation of many biological compounds. Conditions that impair one-carbon metabolism (e.g. folate deficiency) are associated with elevation in plasma Hcy and increased risk of vascular disease, certain cancers, and neural tube defects. A common mutation of methylene-tetrahydrofolate reductase (MTHFR), known as the "thermolabile" or C677T mutant, has been associated with elevations in plasma I-Icy (especially in low folate status), lower plasma folate, altered distribution of erythrocyte folate, potentially increased risk of vascular disease, and decreased risk of colon cancer. The in vivo metabolic effects of the C677T mutation have not been determined directly. Our overall hypothesis is that the rate of acquisition and generation of methyl groups from serine (primary source of C1 units) is reduced in individuals homozygous for the C677T mutation, and that the genotypic effect is greatest when folate nutriture is inadequate. We also hypothesize that the rate of folate-dependent synthesis of nucleotides (purines and thymidylate) will be reduced in folate deficiency but may be enhanced by the C677T mutation. The proposed studies will determine nutritional and genetic dependence of the flow of Cl units from serine (Ser) to Met and from Ser to nucleotides. This protocol also will allow measurement of the transsulfuration pathway of Hcy catabolism important in disposal of excess Hcy. Specific aims. To determine: (a) The kinetics by which Ser serves as a donor of Cl units for methyl group synthesis and nucleotide synthesis and the possible degree of impairment caused by the C677T mutation and/or low folate status. (b) The influence of the C677T mutation and folate status on cellular Cl status as reflected by the distribution of folate species in erythrocytes. (C) The influence of the C677T mutation and folate status on homocysteine catabolism. (d) The relative contributions of cytosolic and mitochondrial metabolism in the generation of Cl units for synthesis of methyl groups and nucleotides. (e) The significance of mitochondrial glycine cleavage in generation of Cl units. Protocol: In the main protocol, healthy adequately nourished human subjects (20-30 yr) will be classified by MTHFR genotype, (homozygous control and homozygous mutant). Subjects will be given infusions with 13C-serine as primary precursor initially and following 8-wk dietary depletion of 120 ugld folate to evaluate the effect of nutritional and genotypic effects on Cl kinetics. Two variations of this study will be conducted to determine the relative roles of mitochondrial and cytosolic routes of Cl generation from serine and the role of the mitochondrial glycine cleavage pathway. In total, these studies will yield new functional data regarding the effects of folate deficiency, and the influence of common polymorphism of MTHFR.
Funding Period: 2001-04-01 - 2005-12-31
more information: NIH RePORT
- Methylenetetrahydrofolate reductase 677C->T polymorphism and folate status affect one-carbon incorporation into human DNA deoxynucleosidesEoin P Quinlivan
Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, College of Medicine, University of Florida, Gainesville, FL 32611, USA
J Nutr 135:389-96. 2005..These findings support the feasibility of further assessment of factors affecting deoxynucleotide synthesis and DNA methylation in human 1-carbon metabolism...
- Dietary vitamin B-6 restriction does not alter rates of homocysteine remethylation or synthesis in healthy young women and menSteven R Davis
Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611 0370, USA
Am J Clin Nutr 81:648-55. 2005..The effects of vitamin B-6 status on steady-state kinetics of homocysteine metabolism in humans are unclear...
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Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, College of Medicine, University of Florida, Gainesville, FL 32611 0370, USA
J Nutr 135:1040-4. 2005....
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Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, College of Medicine, University of Florida, Gainesville 32611 0370, USA
J Nutr 135:1045-50. 2005..In conclusion, elevated homocysteine synthesis is a cause of mild hyperhomocysteinemia in women with marginal folate status, particularly those with the MTHFR 677 T/T genotype...
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Department of Food Science and Human Nutrition, University of Florida, Gainesville, FL 32611, USA
Anal Biochem 348:163-84. 2006
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Food Science andHuman Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611 0370, USA
J Nutr 136:373-8. 2006..These data indicate that glutathione homeostasis is altered by dietary vitamin B-6 deficiency and appears to be unrelated to cysteine flux under conditions of minimal amino acid intake as evaluated in this study...
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Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, USA
J Nutr 136:2141-7. 2006..In spite of these effects, hepatic glutathione concentration increased in vitamin B-6 deficiency. These results suggest that vitamin B-6-dependent changes in transsulfuration do not limit hepatic glutathione production...
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Biomedical Mass Spectrometry Laboratory, General Clinical Research Center, University of Florida, Gainesville, FL 32611, USA
Anal Biochem 373:383-5. 2008..The new protocol is fully compatible with LC-MS/MS and gives similar recoveries for all five major deoxyribonucleosides when compared to the older protocol...
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Biomedical Mass Spectrometry Laboratory, General Clinical Research Center, University of Florida, Gainesville, FL 32611 0370, USA
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