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T Variant Influences Plasma Total Homocysteine Concentrations in Young Women after Restricting Folate Intake1
Human Nutrition and Food Science Department,
* Animal and Veterinary Science Department, and
Biological Sciences Department, Cal Poly Pomona University, Pomona, CA 91768
2To whom correspondence should be addressed. E-mail: macaudill{at}csupomona.edu.
ABSTRACT
Glycine N-methyltransferase (GNMT) is a key regulatory protein in folate metabolism, methionine availability, and transmethylation reactions. Perturbations in GNMT may lead to aberrations in homocysteine metabolism, a marker of numerous pathologies. The primary objective of this study was to examine the influence of the GNMT 1289 C
T alone, and in combination with the methylenetetrahydrofolate reductase (MTHFR) 677 CT variant, on plasma total homocysteine concentrations in healthy young women (n = 114). Plasma total homocysteine was measured at baseline (wk 0) and after 2 wk of controlled folate restriction (135 µg/d as dietary folate equivalents). Plasma homocysteine concentrations did not differ among the GNMT C1289T genotypes at baseline. However, after folate restriction, women with the GNMT 1289 TT genotype (n = 16) had higher (P = 0.019) homocysteine concentrations than women with the CT (n = 51) or CC (n = 47) genotype. The influence of the GNMT 1289 CT variant on homocysteine was dependent on the MTHFR C677T genotype. In subjects with the MTHFR 677 CC genotype, homocysteine was greater (P 
0.05) for GNMT 1289 TT subjects relative to 1289 CT or CC subjects. However, in subjects with the MTHFR 677 TT genotype, plasma homocysteine concentrations did not differ among the GNMT C1289T genotypes. Overall, these data suggest that the GNMT 1289 CT polymorphism influences plasma homocysteine and is responsive to folate intake.
KEY WORDS: • glycine N-methyltransferase • methylenetetrahydrofolate reductase • methionine synthase reductase • homocysteine • folate • women
Glycine N-methyltransferase (GNMT)3 is a tetrameric protein (1), which is abundant in liver (2,3) and integrally linked to folate and methyl group metabolism (4–7), methionine availability (8–11), and transmethylation reactions (6,10,12,13). GNMT catalyzes the S-adenosylmethionine (SAM)-dependent methylation of glycine to generate S-adenosylhomocysteine (SAH) and a biologically inert compound, sarcosine (13). GNMT influences transmethylation reactions by regulating both hepatic SAM concentrations (6,14,15) and the SAM:SAH ratio (6,10,12), a key variable in transmethylation potential (16,17).
Regulation of SAM and the SAM:SAH ratio by GNMT is dependent upon 3 allosteric relations. First, SAM inhibits methylenetetrahydrofolate reductase (MTHFR), which catalyzes the formation of 5-methyl-tetrahydrofolate (THF) from 5,10-methylene-THF (18,19). Second, 5-methyl-THF, the product of MTHFR-catalyzed reactions and primary methyl donor for homocysteine remethylation, inhibits GNMT (14,20). Third, unlike most methyltransferases, GNMT possesses a high Ki value for SAH and is only weakly inhibited by SAH (21,22). Hence, when SAM is high, MTHFR is inhibited and 5-methyl-THF formation is reduced allowing for a more active GNMT to reduce excess SAM levels. In contrast, low SAM leads to an increase in 5-methyl-THF production, which inhibits GNMT and spares methyl-groups for transmethylation reactions (i.e., DNA methylation). The high concentrations of GNMT in the liver (1–3% of cytosolic protein), the production of an inert nontoxic compound, the high Km value for SAM (22), and its relative resistance to inhibition by SAH are characteristics that make GNMT an ideal regulator of the SAM:SAH ratio (13,22).
Homocysteine is a by-product and potential marker of transmethylation reactions (23). Elevations in homocysteine are associated with increased risk for cognitive disorders (24), cardiovascular disease (25), neural tube and other birth defects (26), and pregnancy complications (26). Several functional polymorphisms in key one-carbon metabolizing genes, including MTHFR 677 CT, MTHFR 1298 AC, methionine synthase 2756AG, methionine synthase reductase (MTRR) 66AG, and cystathionine ß-synthase 844ins68, either alone or in combination, influence plasma homocysteine and/or disease risk (27). However, many of these variants are diet responsive and should be studied within the context of the nutritional status of the host.
Homocysteine metabolism may also be influenced by GNMT. In murine models, GNMT induction is associated with decreased plasma tHcy concentrations (10,13,28). However, more data are required to ascertain whether an inverse relation exists between GNMT and homocysteine. Further, it is unclear whether the changes in plasma tHcy are a direct consequence of changes in GNMT activity. Factors that modulate GNMT may also influence other homocysteine metabolizing enzymes including cystathionine ß-synthase and betaine-homocysteine S-methyltransferase (28).
A recent study examining the role of GNMT in liver cancer progression in humans (29) identified 3 single nucleotide polymorphisms in the human GNMT gene. Of these polymorphisms, a 1289 CT polymorphism was associated with cancer risk. To date, the implications of the GNMT 1289 CT polymorphism upon GNMT activity and homocysteine metabolism have not been examined.
The purpose of this study was to examine the influence of the GNMT 1289 CT polymorphism alone and in combination with the MTHFR 677 CT polymorphism on plasma total homocysteine and serum folate concentrations in young women before and after a 2-wk period of folate restriction. In addition, the influences of the MTRR 66AG and MTHFR 1298 AC variants alone and in combination with the MTHFR 677 CT variant on the response variables were assessed.
SUBJECTS AND METHODS
Subjects
The subjects were recruited from Cal Poly Pomona University and surrounding areas in Southern California between 1999 and 2003. All subjects were healthy women (n = 114) with no history of vascular, gastrointestinal, renal, or hepatic disease; normal blood glucose and lipid concentrations, normal blood chemistry; 18–46 y old; nonsmoker; not taking drugs known to interfere with folate metabolism; not a current user (within the past 3 mo) of supplemental vitamins and/or minerals; not pregnant or planning a pregnancy; not lactating; and possessed the appropriate MTHFR 677 CT genotype. The screening and experimental procedures for the previously conducted trials were reviewed and approved by the Institution Review Board of Cal Poly Pomona University, and informed consent was obtained from each participant.
Experimental design
We pooled data obtained from 114 young women who participated in 1 of 2 controlled folate feeding protocols conducted between 1999 and 2003 by our research group (30–32). Both protocols consisted of a folate restriction phase that provided 135 µg DFE/d and lasted a minimum of 2 wk. Both protocols also included measurements of plasma tHcy and serum folate at baseline (wk 0) and after 2 wk of folate restriction (wk 2). In addition, both protocols assessed the MTHFR 677 CT genotype.
The present study is an extension of our previous work. In addition to the MTHFR 677 CT genotype, the MTHFR 1298 CT, MTRR 66AG, and GNMT 1289 CT genetic polymorphisms were assayed. The influence of these genetic polymorphisms alone and in combination with the MTHFR 677 CT on plasma tHcy and serum folate were examined at baseline (wk 0) and after folate restriction with 135 µg DFE/d (wk 2).
Diet and supplements
The 5-d menu utilized during folate restriction provided 
135 µg DFE/d (30,32). Subjects consumed breakfast and dinner under the supervision of investigators at the Cal Poly Pomona Human Nutrition metabolic kitchen. Lunch and snacks as well as 14 breakfast or dinner meals of the subjects choosing were provided as "take-away" items and consumed off-site. The nutrient content (except folate) and energy provisions of the menus were analyzed with ESHA Food Processor Nutrient Data Base (version 7.81; ESHA Research). Dietary intakes of choline and betaine were estimated using recently published data (33,34). The menus provided an estimated 2000–2300 kcal (8375–9632 kJ/d) with 54–66% from carbohydrate, 10–14% from protein, and 21–30% from fat. For nutrients that were not provided in recommended amounts via the diet, supplements were administered to ensure that total intakes (menus plus supplements) were at least 85% of recommended amounts (30,32). The supplements included a multimineral (LifeTime, Nutritional Specialties), given every day; a multivitamin (Trader Darwin’s Stress Vitamin, Trader Joe’s), cut into thirds and given every 4 d; vitamin K (KAL, Nutraceutical), given every other day; choline (TwinLab, Twin Laboratories), given every other day; and iron (TwinLab, Twin Laboratories) given as needed (based on weekly hematocrit measures).
Sample collection and blood processing
Baseline and weekly venous blood samples were collected from subjects who had fasted for 10 h into serum separator gel and clot activator tubes and EDTA tubes. Serum, plasma, and peripheral leukocytes were obtained for serum folate, plasma total homocysteine, and genotype analyses, respectively.
Analytical methods
Folate content of diet. The folate content of the diets was determined before starting the study and twice during the study. Each meal, including the beverage, was blended with 150 mL of cold 0.1 potassium phosphate buffer/L (pH 6.3) containing 57 mmol ascorbic acid/L, dispensed into 50-mL conical tubes and stored at –20°C. Duplicates of the blended samples were thawed, homogenized, and subjected to trienzyme treatment (35) and double extraction (36). The total folate content of each meal was determined microbiologically (37).
Genotype determinations. DNA for genotyping was extracted from stored leukocytes (–80°C) using a commercially available kit (DNeasy Tissue Kit; Qiagen). MTHFR C677T variants were determined by the method of Frosst et al. (38). MTHFR A1298C variants were determined using the primer pairs and restriction enzymes described by van der Put and Blom (39) and the PCR conditions described by Friedman and colleagues (40). MTRR A66G variants were determined using the primer pairs and restriction enzymes described by Jacques et al. (41) and the PCR conditions described by Olteanu and Banjeree (42).
A novel RFLP was developed in our laboratory for the determination of GNMT C1289T variants. The primers for the PCR reaction were: 5'-TGCAGCTGGACAGACTCGGG-3' sense and 5'-TCCCCGTCCGCGTACTGGTC-3' antisense and were obtained commercially (Invitrogen). Amplification was performed using initial denaturation at 95°C for 2 min followed by 30 cycles of 95°C for 30 s, 58°C for 15 s, and 72°C for 15 s with a final extension of 72°C for 5 min. PCR supermix (Invitrogen) was used as the PCR buffer. The 229 bp PCR product was digested with Mwo I (Invitrogen) producing a 15-, 98-, and 116-bp band for the CC genotype, a 131-, 116-, and 98-bp band for the TT genotype, and a 131-, 98-, and 15-bp band for the CT genotype. The digested products (98,116,131 bp) were size-fractioned on a 3.0% agarose gel (Invitrogen) and viewed under UV light.
Plasma tHcy. Plasma tHcy was measured in duplicate at baseline and after folate restriction by use of a modified HPLC method with fluorometric detection (43,44). The intra-and interassay CV based on the positive control (e.g., pooled plasma analyzed in duplicate with every assay conducted) were 5 and 7%, respectively.
Serum folate. Serum folate was measured in duplicate microbiologically using Lactobacillus casei (37) at baseline and weekly thereafter. The intra-and interassay CV for the positive control (e.g., pooled serum analyzed in triplicate with every assay conducted) were 10 and 12%, respectively.
Statistical analysis.
All analyses were conducted with SPSS 11.0 (SPSS; Mac OS X version). All data summaries of plasma tHcy and serum folate are presented as means ± SD. The influence of individual genotypes for the 4 genes (GNMT C1289T, MTRR A66G, MTHFR A1298C, and MTHFR C677T) and genetic variants of 3 of these in combination with the MTHFR C677T genotypes were assessed using 1-way ANOVA. When this was significant, Tukey’s HSD procedure was used for mean separations. Differences were considered significant at P 0.05.
RESULTS
Subject characteristics and baseline measures
The final study group was comprised of 114 women with a median age of 22 y (range, 18–46 y) and a median BMI of 24.0 kg/m2 (range, 17.6–36.6 kg/m2). The racial/ethnic composition was 57 Mexican Americans, 21 Caucasians, 21 African Americans, 14 Asians, and 1 Arabian. At baseline, the plasma tHcy concentration of the entire group was 5.6 ± 1.1 µmol/L and the serum folate concentration was 29.9 ± 12.2 nmol/L.
Frequency of variant genotypes
The frequency of the genotypes (n = 114) was 41% CC, 45% CT, and 14% TT for GNMT C1289T; 64% CC, 11% CT and 25% TT for MTHFR C677T; 56% AA, 36% AC and 8% CC for the MTHFR A1298C; and 46% AA, 42% AG, and 12% GG for the MTRR A66G. Additionally, 3.5% of the subjects were MTHFR 677 TT/GNMT 1289 TT or MTHFR 677 TT/MTRR 66 GG. One subject had the MTHFR 677/1298 CT/CC genotype and none of the subjects had the TT/CC genotype. Because this was a nonrandom sample, these frequencies cannot be used to assess the prevalence of these genotypes.
Influence of individual genotypes
GNMT C1289T. At baseline, plasma tHcy and serum folate concentrations did not differ among the genotypes (Table 1). After folate restriction with 135 µg DFE/d, plasma tHcy was higher (P = 0.0019) for the TT genotype compared with the CC and CT genotypes (Table 1). Serum folate concentrations did not differ among the GNMT C1289T genotypes (Table 1).
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0.05) for the TT and CT genotypes compared with the CC genotype, whereas serum folate tended to be lower (P = 0.064) for the TT genotype than for the CC genotype (Table 1).
MTHFR A1298C.
At baseline, plasma tHcy concentrations did not differ among the genotypes (Table 1). However, serum folate was lower (P 0.01) for the AA genotype than for the AC genotype (Table 1). After folate restriction with 135 µg DFE/d group, plasma tHcy was greater (P 0.05) for the AA genotype compared with the AC genotype (Table 1). In addition, serum folate concentrations were lower (P 0.01) for the AA genotype than for the AC genotype.
MTRR A66G. At baseline, plasma tHcy and serum folate concentrations did not differ (P > 0.05) among the genotypes (Table 1). Following folate restriction with 135 µg DFE/d, serum folate tended to be higher (P = 0.061) for the GG genotype than for the AA genotype (Table 1).
Influence of the genetic variants in combination with the MTHFR C677T genotype
GNMT C1289T/MTHFR C677T.
At baseline, plasma tHcy and serum folate concentrations did not differ among the various allele combinations (data not shown). After folate restriction with 135 µg DFE/d, plasma tHcy was greater (P 0.05) for the TT/CC genotype compared with the CT/CC and CC/CC genotypes. In addition, plasma tHcy was greater (P 0.05) for the CC/TT genotype than for the CC/CC genotype (Table 2).
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0.05) for the AA/TT genotype than for the AC/CC genotype.
MTRR A66G/MTHFR C677T.
At baseline, plasma tHcy and serum folate concentrations did not differ among the various allele combinations (data not shown). After folate restriction with 135 µg DFE/d, plasma tHcy was higher (P 0.05) for the AG/TT genotype compared with the AA/CC genotype (Table 2). Also, serum folate was lower (P 0.05) for the AA/TT genotype than for the GG/CC genotype (Table 2).
DISCUSSION
This study was conducted after folic acid fortification of the food supply, which has had a dramatic effect on folate status in all segments of the U.S. population (45). Because high and/or varying folate intakes may modify the influence of genetic variants in genes involved in 1-carbon metabolism, we assessed the influence of the GNMT 1289 CT, MTHFR 677 CT, MTHFR 1298 AC, and MTRR 66 AG at baseline and after a 2-wk period of folate restriction. Throughout the restriction period, folate intake was controlled and provided 135 µg DFE/d.
For the GNMT 1289 CT polymorphism, plasma tHcy concentrations did not differ at baseline. However, after controlled folate restriction, plasma tHcy concentration was higher (P = 0.0019) in women with the GNMT 1289 TT genotype than in women with the CC or CT genotype. The influence of the GNMT C1289T polymorphism on plasma tHcy was dependent on the MTHFR C677T genotype. In subjects with the MTHFR 677 CC genotype, plasma tHcy was greater (P = 0.002) for GNMT 1289 TT subjects relative to 1289 CT or 1289 CC subjects (Table 2). In contrast, plasma tHcy concentrations did not differ among the GNMT C1289T genotypes in subjects with the MTHFR 677 TT genotype. Although our samples sizes are small, these initial data suggest that the GNMT 1289 CT and MTHFR 677 CT polymorphisms operate via similar mechanisms to affect plasma homocysteine.
GNMT is integrally linked to plasma homocysteine metabolism through its regulation of hepatic SAM concentrations and the SAM:SAH ratio. Hypothetically, a less active GNMT would lead to reductions in SAH and subsequently homocysteine production. However, a less active GNMT would also lead to increases in SAM, inhibition of MTHFR and decreases in 5-methyl-THF. Decreases in 5-methyl-THF, the predominant in vivo source of methyl groups for homocysteine remethylation to methionine, would subsequently contribute to increases in plasma homocysteine concentrations. In the present study, the higher (P 0.05) homocysteine concentrations in women with the GNMT 1289 TT genotype relative to the CC or CT genotype suggests that this variant reduces GNMT activity in humans. The1289T polymorphism is located in the 5' UTR region of the gene, an important translational regulatory site (46). Thus, translation and/or activity of the gene may be influenced by the C to T substitution. However, additional studies assessing the influence of this variant on GNMT enzyme activity are warranted to more fully understand the relations between the GNMT 1289 CT variant, enzyme activity and homocysteine.
As expected, the MTHFR 677 CT polymorphism influenced plasma tHcy and serum folate concentrations. Serum folate tended to be lower at baseline (P = 0.09) and after folate restriction (P = 0.08), whereas plasma tHcy was higher (P 0.05) after folate restriction in women with the MTHFR 677 TT genotype relative to the CC genotype. Because of the marked effect that the MTHFR 677 CT polymorphism has on 1-carbon metabolism, it is important to consider this variant when assessing the influence of other polymorphisms on plasma homocysteine and/or folate status.
The MTHFR 1298 AC polymorphism is associated with reduced enzyme activity in vitro (47,48); yet, it has no effect on catalytic function and thermostability (49). To date, most studies have not demonstrated an effect of the MTHFR 1298 CC genotype on homocysteine and/or serum folate concentrations (40,47,50–57). In the present study, plasma tHcy was higher (P 0.05) after folate restriction for the MTHFR 1298 AA genotype compared with the AC genotype and lower for serum folate at baseline (P 0.01) and after folate restriction. However, these data were highly influenced by the MTHFR 677 CT polymorphism (Table 2). Of women with the MTHFR 1298 AA genotype, 50% possessed the MTHFR 677 TT genotype, whereas only 0.03% of the women with the MTHFR 1298 AC genotype possessed the MTHFR 677 TT genotype (Table 2). Thus, the higher prevalence of the MTHFR 677 TT genotype among women with the MTHFR 1298 AA genotype relative to the MTHFR 1298 AC genotype contributed to the higher plasma homocysteine and lower serum folate. As shown in this study and others (47,50,52,58), plasma tHcy or blood folate concentrations did not differ between the MTHFR A1298C/MTHFR 677CC genotypes. The absence of the MTHFR 677 TT/1298 CC genotype due to linkage disequilibrium between the MTHFR C677T and A1298C genotypes prevents a conclusive assessment of the combined influence of the MTHFR homozygous variants.
MTRR catalyzes the SAM-dependent reductive methylation of inactive cob(II)alamin to methylcob(III)alamin, the required cofactor for methionine synthase (59). In a 5-methyl-THF–dependent reaction, methionine synthase remethylates homocysteine to methionine. To date, the majority of studies reported that the MTRR 66 AG variant has no influence on plasma tHcy and/or blood folate (41,50,53,57,59–63). In the present study, plasma tHcy and serum folate concentrations did not differ among women differing in the MTRR A66G genotype at baseline or after folate restriction. However, after folate restriction, the relation between the MTRR AG variant and the measured variables was influenced by the MTHFR 677 CT variant. This finding highlights the importance of considering the MTHFR C677T genotype when examining the influence of the MTRR A66G genotype on plasma tHcy.
Folate status modifies the influence of the MTHFR 677 CT polymorphism on plasma tHcy. Guinotte et al. (30) observed lower (P 0.05) blood folate and higher (P 0.05) plasma tHcy concentrations in young women with the TT genotype compared with the CC genotype with folate intakes of 135 and 400 µg DFE/d. These differences disappeared with folate intakes of 800 µg DFE/d. Similarly, Ashfield-Watt et al. (64) reported higher (P 0.05) plasma tHcy in participants with the TT genotype relative to the CC genotype with folate intakes of 282 and 660 but not 800 µg DFE/d. For the MTHFR 677 CT polymorphism, it was shown that the folate protects the human MTHFR gene, both wild type and mutant, from thermal inactivation (65). Folate status/intake may also influence GNMT activity (66). In rodents, folate deficiency was associated with an increase in GNMT activity (66), which is consistent with data reporting an inhibitory effect of 5-methyl-THF on GNMT (14,20). Data from the present study suggest that the influence of the GNMT 1289 CT polymorphism should be assessed in combination with data on folate status/intake and that this variant may be of greater importance in countries that have not implemented widespread folic acid fortification of stable food items.
Because the GNMT 1289 CT variant appears to influence plasma homocysteine, it may be an important modulator of diseases/conditions associated with perturbations in homocysteine metabolism. In the present study, plasma tHcy was 1 µmol/L higher in women with the GNMT 1289 TT genotype compared with women with the CC or CT genotypes. A similar difference in plasma tHcy was observed between women with the MTHFR 677 TT and CC genotypes. It is possible that larger differences in plasma tHcy concentrations between genotypes may occur in populations consuming less folate. In this regard, a meta-analysis including studies whose populations were not exposed to widespread folic acid fortification reported that persons with the MTHFR 677 TT genotype had plasma tHcy concentrations that were 2.5 µmol/L greater than the CC genotype and that their risk of developing cardiovascular disease was 16% higher (67). It is also possible that the influence of the GNMT 1289 CT polymorphism on plasma tHcy may be different in men and in older populations.
In summary, the GNMT 1289 TT genotype influenced plasma tHcy concentrations after a 2-wk period of controlled folate restriction, an effect that was most evident in women with the MTHFR 677 CC genotype. The MTHFR 677 CT polymorphism also influenced plasma tHcy and serum folate concentrations after restricted folate intake and contributed to the effects observed individually for the MTHFR 1298 AC polymorphism. The apparent influence of the GNMT 1289 CT variant on plasma tHcy concentrations is intriguing and should be reexamined in larger populations in combination with data on MTHFR C677T genotype and folate intake/status.
FOOTNOTES
1 Supported by the National Institutes of Health grant S06GM53933, the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, grant number 2001–35200-10678, and funds from the California Agricultural Research Initiative. 
3 Abbreviations used: DFE, dietary folate equivalents; GNMT, glycine-N-methyltransferase; MTHFR, methylenetetrahydrofolate reductase; MTRR, methionine synthase reductase; SAM, S-adenosylmethionine; SAH, S-adenosylhomocysteine; THF, tetrahydrofolate; tHcy, total homocysteine.
Manuscript received 25 July 2005. Initial review completed 16 August 2005. Revision accepted 31 August 2005.
LITERATURE CITED
1. Fu Z., Hu Y., Konishi K., Takata Y., Ogawa H., Gomi T., Fujioka M., Takusagawa F. Crystal structure of glycine N-methyltransferase from rat liver. Biochemistry. 1996;35:11985-11993.[Medline]
2. Ogawa H., Gomi T., Fujioka M. Mammalian glycine N-methyltransferases. Comparative kinetic and structural properties of the enzymes from human, rat, rabbit and pig livers. Comp. Biochem. Physiol. B. 1993;106:601-611.[Medline]
3. Chen Y. M., Chen L. Y., Wong F. H., Lee C. M., Chang T. J., Yang-Feng T. L. Genomic structure, expression, and chromosomal localization of the human glycine N-methyltransferase gene. Genomics. 2000;66:43-47.[Medline]
4. Kerr S. J. Competing methyltransferase systems. J. Biol. Chem. 1972;247:4248-4252.
5. Ogawa H., Fujioka M. Purification and properties of glycine N-methyltransferase from rat liver. J. Biol. Chem. 1982;257:3447-3452.
6. Stipanuk M. H. Metabolism of sulfur-containing amino acids. Annu. Rev. Nutr. 1986;6:179-209.[Medline]
7. Wagner C. Biochemical role of folate in cellular metabolism. Bailey L. B. eds. Biochemical role of folate in cellular metabolism. Folate in Health and Disease. :23-42 Marcel Dekker New York, NY.
8. Mudd S. H., Cerone R., Schiaffino M. C., Fantasia A. R., Minniti G., Caruso U., Lorini R., Watkins D., Matiaszuk N., et al. Glycine N-methyltransferase deficiency: a novel inborn error causing persistent isolated hypermethioninaemia. J. Inherit. Metab. Dis. 2001;24:448-464.[Medline]
9. Luka Z., Cerone R., Phillips J. A., 3rd, Mudd H. S., Wagner C. Mutations in human glycine N-methyltransferase give insights into its role in methionine metabolism. Hum. Genet. 2002;110:68-74.[Medline]
10. Ozias M. K., Schalinske K. L. All-trans-retinoic acid rapidly induces glycine N-methyltransferase in a dose-dependent manner and reduces circulating methionine and homocysteine levels in rats. J. Nutr. 2003;133:4090-4094.
11. Rowling M. J., McMullen M. H., Chipman D. C., Schalinske K. L. Hepatic glycine N-methyltransferase is up-regulated by excess dietary methionine in rats. J. Nutr. 2002;132:2545-2550.
12. Rowling M. J., McMullen M. H., Schalinske K. L. Vitamin A and its derivatives induce hepatic glycine N-methyltransferase and hypomethylation of DNA in rats. J. Nutr. 2002;132:365-369.
13. Rowling M. J., Schalinske K. L. Retinoic acid and glucocorticoid treatment induce hepatic glycine N-methyltransferase and lower plasma homocysteine concentrations in rats and rat hepatoma cells. J. Nutr. 2003;133:3392-3398.
14. Wagner C., Briggs W. T., Cook R. J. Inhibition of glycine N-methyltransferase activity by folate derivatives: implications for regulation of methyl group metabolism. Biochem. Biophys. Res. Commun. 1985;127:746-752.[Medline]
15. Rowling M. J., Schalinske K. L. Retinoid compounds activate and induce hepatic glycine N-methyltransferase in rats. J. Nutr. 2001;131:1914-1917.
16. Cantoni G. L. The role of S-adenosylhomocysteine in the biological utilization of S-adenosylmethionine. Prog. Clin. Biol. Res. 1985;198:47-65.[Medline]
17. Hoffman D. R., Marion D. W., Cornatzer W. E., Duerre J. A. S-Adenosylmethionine and S-adenosylhomocystein metabolism in isolated rat liver. Effects of L-methionine, L-homocystein, and adenosine. J. Biol. Chem. 1980;255:10822-10827.
18. Kutzbach C., Stokstad E. L. Feedback inhibition of methylene-tetrahydrofolate reductase in rat liver by S-adenosylmethionine. Biochim Biophys Acta. 1967;139:217-220.[Medline]
19. Jencks D. A., Mathews R. G. Allosteric inhibition of methylenetetrahydrofolate reductase by adenosylmethionine. Effects of adenosylmethionine and NADPH on the equilibrium between active and inactive forms of the enzyme and on the kinetics of approach to equilibrium. J. Biol. Chem. 1987;262:2485-2493.
20. Yeo E. J., Briggs W. T., Wagner C. Inhibition of glycine N-methyltransferase by 5-methyltetrahydrofolate pentaglutamate. J. Biol. Chem. 1999;274:37559-37564.
21. Kerr S. J., Heady J. E. Modulation of tRNA methyltransferase activity by competing enzyme systems. Adv. Enzyme. Regul. 1974;12:103-117.[Medline]
22. Takata Y., Huang Y., Komoto J., Yamada T., Konishi K., Ogawa H., Gomi T., Fujioka M., Takusagawa F. Catalytic mechanism of glycine N-methyltransferase. Biochemistry. 2003;42:8394-8402.[Medline]
23. Yi P., Melnyk S., Pogribna M., Pogribny I. P., Hine R. J., James S. J. Increase in plasma homocysteine associated with parallel increases in plasma S-adenosylhomocysteine and lymphocyte DNA hypomethylation. J. Biol. Chem. 2000;275:29318-29323.
24. Miller J. W. Folate, cognition, and depression in the era of folic acid fortification. J. Food Sci. 2004;69:SNQ61-SNQ67.
25. Caudill M. A. The role of folate in reducing chronic and developmental disease risk: an overview. J. Food Sci. 2004;69:SNQ55-SNQ60.
26. Vollset S. E., Refsum H., Irgens L. M., Emblem B. M., Tverdal A., Gjessing H. K., Monsen A. L., Ueland P. M. Plasma total homocysteine, pregnancy complications, and adverse pregnancy outcomes: the Hordaland Homocysteine study. Am. J. Clin. Nutr. 2000;71:962-968.
27. McCabe D., Caudill M. A. DNA methylation, genomic silencing, and links to nutrition and cancer. Nutr. Rev. 2005;63:183-195.[Medline]
28. Nieman K. M., Rowling M. J., Garrow T. A., Schalinske K. L. Modulation of methyl group metabolism by streptozotocin-induced diabetes and all-trans-retinoic acid. J. Biol. Chem. 2004;279:45708-45712.
29. Tseng T. L., Shih Y. P., Huang Y. C., Wang C. K., Chen P. H., Chang J. G., Yeh K. T., Chen Y. M., Buetow K. H. Genotypic and phenotypic characterization of a putative tumor susceptibility gene, GNMT, in liver cancer. Cancer Res. 2003;63:647-654.
30. Guinotte C. L., Burns M. G., Axume J. A., Hata H., Urrutia T. F., Alamilla A., McCabe D., Singgih A., Cogger E. A., Caudill M. A. Methylenetetrahydrofolate reductase 677CT variant modulates folate status response to controlled folate intakes in young women. J. Nutr. 2003;133:1272-1280.
31. Perry C. A., Renna S. A., Khitun E., Ortiz M., Moriarty D. J., Caudill M. A. Ethnicity and race influence the folate status response to controlled folate intakes in young women. J. Nutr. 2004;134:1786-1792.
32. Yang T. L., Hung J., Caudill M. A., Urrutia T. F., Alamilla A., Perry C. A., Li R., Hata H., Cogger E. A. A long-term controlled folate feeding study in young women supports the validity of the 1.7 multiplier in the dietary folate equivalency equation. J. Nutr. 2005;135:1139-1145.
33. Zeisel S. H., Mar M. H., Howe J. C., Holden J. M. Concentrations of choline-containing compounds and betaine in common foods. J. Nutr. 2003;133:1302-1307.
34. Howe J. C., Williams J. R., Holden J. M., Zeisel S. H., Mar M. H. Concentrations of choline-containing compounds and betaine in common foods. USDA database for the choline content of common foods. United States Department of Agricultural http://www.nal.usda.gov/fnic/foodcomp/Data/Choline/Choline.html [accessed Sept 9, 2004].
35. Tamura T., Mizuno Y., Johnston K. E., Jacob R. A. Food folate assay with protease, alpha amylase, and folate conjugase treatments. J. Agric. Food Chem. 1997;45:135-139.
36. Gregory J. F., Engelhardt R., Bhandari S. D., Bustafson S. K. Adequacy of extraction techniques for determination of folates in foods and other biological materials. J. Food Compos. Anal. 1990;3:134-144.
37. Tamura T. Microbiological assay of folates. Picciano M. F. Stokstad E.L.R. Gregory J. F. eds. Microbiological assay of folates. Folic Acid Metabolism in Health and Disease. :121-137 John Wiley & Sons New York, NY.
38. Frosst P., Blom H. J., Milos R., Goyette P., Sheppard C. A., Matthews R. G., Boers G. J., den Heijer M., Kluijtmans L. A., et al. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat. Genet. 1995;10:111-113.[Medline]
39. van der Put N. J., Blom H. J. Reply to Donnelly (Letter). Am. J. Hum. Genet. 2000;66:744-745.[Medline]
40. Friedman G., Goldschmidt N., Friedlander Y., Ben-Yehuda A., Selhub J., Babaey S., Mendel M., Kidron M., Bar-On H. A common mutation A1298C in human methylenetetrahydrofolate reductase gene: association with plasma total homocysteine and folate concentrations. J. Nutr. 1999;129:1656-1661.
41. Jacques P. F., Bostom A. G., Selhub J., Rich S., Ellison R. C., Eckfeldt J. H., Gravel R. A., Rozen R. Effects of polymorphisms of methionine synthase and methionine synthase reductase on total plasma homocysteine in the NHLBI Family Heart Study. Atherosclerosis. 2003;166:49-55.[Medline]
42. Olteanu H., Banerjee R. Human methionine synthase reductase, a soluble P-450 reductase-like dual flavoprotein, is sufficient for NADPH-dependent methionine synthase activation. J. Biol. Chem. 2001;276:35558-35563.
43. Vester B., Rasmussen K. High performance liquid chromatograph method for rapid and accurate determination of homocysteine in plasma and serum. Eur. J. Clin. Chem. Clin. Biochem. 1991;29:549-554.[Medline]
44. Pfeiffer C. M., Huff D. L., Gunter E. W. Rapid and accurate HPLC assay for plasma total homocysteine and cysteine in a clinical laboratory setting. Clin. Chem. 1999;45:290-292.
45. Pfeiffer C. M., Caudill S. P., Gunter E. W., Osterloh J., Sampson E. J. Biochemical indicators of B vitamin status in the US population after folic acid fortification: results from the National Health and Nutrition Examination Survey 1999–2000. Am. J. Clin. Nutr. 2005;82:442-450.
46. Karp G. The cell nucleus and the control of gene expression. Rusiello B. eds. The cell nucleus and the control of gene expression. Cell and Molecular Biology: Concepts and Experiments. 3rd ed. :540-545 John Wiley and Sons Inc New York, NY.
47. Chango A., Boisson F., Barbé F., Quilliot D., Droesch S., Pfister M., Fillon-Emery N., Lambert D., Frémont S., et al. The effect of 677CT and 1298AC mutations on plasma homocysteine and 5,10-methylenetetrahydrofolate reductase activity in healthy subjects. Br. J. Nutr. 2000;83:593-596.[Medline]
48. Weisberg I., Tran P., Christensen B., Sibani S., Rozen R. A second genetic polymorphism in methylenetetrahydrofolate reductase (MTHFR) associated with decreased enzyme activity. Mol. Genet. Metab. 1998;64:169-172.[Medline]
49. Yamada K., Chen Z., Rozen R., Matthews R. G. Effects of common polymorphisms on the properties of recombinant human methylenetetrahydrofolate reductase. Proc. Natl. Acad. Sci. U.S.A. 2001;98:14853-14858.
50. Botto N., Andreassi M. G., Manfredi S., Masetti S., Cocci F., Colombo M. G., Storti S., Rizza A., Biagini A. Genetic polymorphisms in folate and homocysteine metabolism as risk factors for DNA damage. Eur. J. Hum. Genet. 2003;11:671-678.[Medline]
51. Chen J., Ma J., Stampfer M. J., Palomeque C., Selhub J., Hunter D. J. Linkage disequilibrium between the 677CT and 1298AC polymorphisms in human methylenetetrahydrofolate reductase gene and their contributions to risk of colorectal cancer. Pharmacogenetics. 2002;12:339-342.[Medline]
52. Hiraoka M., Kato K., Saito Y., Yasuda K., Kagawa Y. Gene-nutrient and gene-gene interactions of controlled folate intake by Japanese women. Biochem. Biophys. Res. Commun. 2004;316:1210-1216.[Medline]
53. Kluijtmans L. A., Young I. S., Boreham C. A., Murray L., McMaster D., McNulty H., Strain J. J., McPartlin J., Scott J. M., Whitehead A. S. Genetic and nutritional factors contributing to hyperhomocysteinemia in young adults. Blood. 2003;101:2483-2488.
54. Lievers K. J., Boers G. H., Verhoef P., den Heijer M., Kluijtmans L. A., van der Put N. M., Trijbels F. J., Blom H. J. A second common variant in the methylenetetrahydrofolate reductase (MTHFR) gene and its relationship to MTHFR enzyme activity, homocysteine, and cardiovascular disease risk. J. Mol. Med. 2001;79:522-528.[Medline]
55. Rozen R. Genetic modulation of homocysteinemia. Semin. Thromb. Hemost. 2000;26:255-261.[Medline]
56. van der Put N. M., Gabreels F., Stevens E. M., Smeitink J. A., Trijbels F. J., Eskes T. K., van den Heuvel L. P., Blom H. J. A second common mutation in the methylenetetrahydrofolate reductase gene: an additional risk factor for neural-tube defects? Am. J. Hum. Genet. 1998;62:1044-1051.
57. Vaughn J. D., Bailey L. B., Shelnutt K. P., Dunwoody K. M., Maneval D. R., Davis S. R., Quinlivan E. P., Gregory J. F., 3rd, Theriaque D. W., Kauwell G. P. Methionine synthase reductase 66AG polymorphism is associated with increased plasma homocysteine concentration when combined with the homozygous methylenetetrahydrofolate reductase 677CT variant. J. Nutr. 2004;134:2985-2990.
58. Bailey L. B., Duhaney R. L., Maneval D. R., Kauwell G. P., Quinlivan E. P., Davis S. R., Cuadras A., Hutson A. D., Gregory J. F., 3rd. Vitamin B-12 status is inversely associated with plasma homocysteine in young women with C677T and/or A1298C methylenetetrahydrofolate reductase polymorphisms. J. Nutr. 2002;132:1872-1878.
59. Gaughan D. J., Kluijtmans L. A., Barbaux S., McMaster D., Young I. S., Yarnell J. W., Evans A., Whitehead A. S. The methionine synthase reductase (MTRR) A66G polymorphism is a novel genetic determinant of plasma homocysteine concentrations. Atherosclerosis. 2001;157:451-456.[Medline]
60. Brilakis E. S., Berger P. B., Ballman K. V., Rozen R. Methylenetetrahydrofolate reductase (MTHFR) 677CT and methionine synthase reductase (MTRR) 66AG polymorphisms: association with serum homocysteine and angiographic coronary artery disease in the era of flour products fortified with folic acid. Atherosclerosis. 2003;168:315-322.[Medline]
61. Brown C. A., McKinney K. Q., Kaufman J. S., Gravel R. A., Rozen R. A common polymorphism in methionine synthase reductase increases risk of premature coronary artery disease. J. Cardiovasc. Risk. 2000;7:197-200.[Medline]
62. Wilson A., Platt R., Wu Q., Leclerc D., Christensen B., Yang H., Gravel R. A., Rozen R. A common variant in methionine synthase reductase combined with low cobalamin (vitamin B12) increases risk for spina bifida. Mol. Genet. Metab. 1999;67:317-323.[Medline]
63. Geisel J., Zimbelmann I., Schorr H., Knapp J. P., Bodis M., Hübner U., Herrmann W. Genetic defects as important factors for moderate hyperhomocysteinemia. Clin. Chem. Lab. Med. 2001;39:698-704.
64. Ashfield-Watt P. A., Pullin C. H., Whiting J. M., Clark Z. E., Moat S. J., Newcombe R. G., Burr M. L., Lewis M. J., Powers H. J., McDowell I. F. Methylenetetrahydrofolate reductase 677CT genotype modulates homocysteine responses to a folate-rich diet or a low-dose folic acid supplement: a randomized controlled trial. Am. J. Clin. Nutr. 2002;76:180-186.
65. Guenther B. D., Sheppard C. A., Tran P., Rozen R., Matthews R. G., Ludwig M. L. The structure and properties of methylenetetrahydrofolate reductase from Escherichia coli suggest how folate ameliorates human hyperhomocysteinemia. Nat. Struct. Biol. 1999;6:359-365.[Medline]
66. Balaghi M., Horne D. W., Wagner C. Hepatic one-carbon metabolism in early folate deficiency in rats. Biochem. J. 1993;291:145-149.[Medline]
67. Klerk M., Verhoef P., Clark R., Blom H. J., Kok F. J., Schouten E. G. MTHFR 677 CT polymorphism and risk of coronary heart disease. J. Am. Med. Assoc. 2002;288:2023-2031.
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