Genetic variants of homocysteine/folate metabolism pathway and risk of inflammatory bowel disease: a synopsis and meta-analysis of genetic association studies

The Role of Methyl Donors of the Methionine Cycle in Gastrointestinal Infection and Inflammation

Vitamin deficiency is well known to contribute to disease development in both humans and other animals. Nonetheless, truly understanding the role of vitamins in human biology requires more than identifying their deficiencies. Discerning the mechanisms by which vitamins participate in health is necessary to assess risk factors, diagnostics, and treatment options for deficiency in a clinical setting. For researchers, the absence of a vitamin may be used as a tool to understand the importance of the metabolic pathways in which it participates. This review aims to explore the current understanding of the complex relationship between the methyl donating vitamins folate and cobalamin (B12), the universal methyl donor S-adenosyl-L-methionine (SAM), and inflammatory processes in human disease. First, it outlines the process of single-carbon metabolism in the generation of first methionine and subsequently SAM. Following this, established relationships between folate, B12, and SAM in varying bodily tissues are discussed, with special attention given to their effects on gut inflammation.

The methylenetetrahydrofolate reductase 1298 A>C polymorphism is associated with an increased risk of inflammatory bowel disease: evidence from a meta-analysis

OBJECTIVE

The association between genetic variants in methylenetetrahydrofolate reductase (MTHFR) and risk for inflammatory bowel disease (IBD) has been widely studied. However, the results are equivocal. In this meta-analysis, we aimed to determine the association between MTHFR polymorphisms and susceptibility to IBD.

METHODS

We retrieved studies from the PubMed, Web of Science, Ovid, and China National Knowledge Infrastructure databases. Data were analyzed using STATA software; odds ratios (OR) and confidence intervals (CI) were calculated using fixed or random effects models.

RESULTS

A marginally significant association of the MTHFR 677 C > T polymorphism and patients' IBD risk was observed in the overall analysis (OR = 1.11, 95% CI, 1.01-1.23), but not in the analysis of high-quality studies. However, for the MTHFR 1298 A > C polymorphism, a significant association was found between the MTHFR 1298 AC/CC genotypes and IBD risk in the overall analysis (OR = 1.26, 95% CI, 1.10-1.44), in the high-quality studies (OR = 1.20, 95% CI, 1.02-1.41), and in patients with ulcerative colitis (OR = 1.28, 95% CI, 1.10-1.48).

CONCLUSIONS

Evidence from this meta-analysis indicates that the MTHFR 1298 A > C polymorphism may be responsible for susceptibility to IBD and ulcerative colitis.

A food pyramid, based on a review of the emerging literature, for subjects with inflammatory bowel disease

Emerging literature suggests that diet plays an important modulatory role in inflammatory bowel disease (IBD) through the management of inflammation and oxidative stress. The aim of this narrative review is to evaluate the evidence collected up till now regarding optimum diet therapy for IBD and to design a food pyramid for these patients. The pyramid shows that carbohydrates should be consumed every day (3 portions), together with tolerated fruits and vegetables (5 portions), yogurt (125ml), and extra virgin olive oil; weekly, fish (4 portions), white meat (3 portions), eggs (3 portions), pureed legumes (2 portions), seasoned cheeses (2 portions), and red or processed meats (once a week). At the top of the pyramid, there are two pennants: the red one means that subjects with IBD need some personalized supplementation and the black one means that there are some foods that are banned. The food pyramid makes it easier for patients to decide what they should eat.

Gene interactions observed with the HDL-c blood lipid, intakes of protein, sugar and biotin in relation to circulating homocysteine concentrations in a group of black South Africans

Background

Elevated homocysteine (Hcy) is associated with several pathologies. Gene–diet interactions related to Hcy might be used to customize dietary advice to reduce disease incidence. To explore this possibility, we investigated interactions between anthropometry, biochemical markers and diet and single-nucleotide polymorphisms (SNPs) in relation to Hcy concentrations. Five SNPs of Hcy-metabolizing enzymes were analyzed in 2010 black South Africans.

Results

Hcy was higher with each additional methylenetetrahydrofolate reductase (MTHFR) C677T minor allele copy, but was lower in methionine synthase (MTR) 2756AA homozygotes than heterozygotes. Individuals harboring cystathionine β synthase (CBS) 833 T/844ins68 had lower Hcy concentrations than others. No interactive effects were observed with any of the anthropometrical markers. MTHFR C677T and CBS T833C/844ins68 homozygote minor allele carriers presented with lower Hcy as high density lipoprotein cholesterol (HDL-c) increased. Hcy concentrations were negatively associated with dietary protein and animal protein intake in the TT and TC genotypes, but positively in the CC genotype of CBS T833C/844ins68. Hcy was markedly higher in TT homozygotes of MTHFR C677T as added sugar intake increased. In CBS T833C/844ins68 major allele carriers, biotin intake was negatively associated with Hcy; but positively in those harboring the homozygous minor allele.

Conclusions

The Hcy–SNP associations are modulated by diet and open up the possibility of invoking dietary interventions to treat hyperhomocysteinemia. Future intervention trials should further explore the observed gene–diet and gene–blood lipid interactions.

Correlation between serum homocysteine level and ulcerative colitis: A meta-analysis

Background: The aim of the present meta-analysis was to investigate the correlation of serum homocysteine (Hcy) concentration and ulcerative colitis (UC) through pooling all the relevant publications.

Methods The electronic databases of PubMed, EMBase, Web of Science, Google Scholar, CBM, and CNKI were systematic searched with the text words of homocysteine/Hcy, ulcerative colitis/UC, and inflammatory bowel disease. The correlation between serum Hcy and UC were demonstrated by stand mean difference (SMD) and corresponding 95% confidence interval (95% CI). The publication bias was evaluated by Egger’s line regression test and Begg’s funnel plot.

Results After systematic searching the related electronic databases of PubMed, EMBase, Web of Science, Google Scholar, CBM, and CNKI, eighteen publications relevant to serum Hcy and UC were included in the present meta-analysis. The serum Hcy leves were 14.01±2.76 and 10.31±1.59 μmol/L for UC groups and healthy controls respectively with statistical difference (p<0.05). Significant heterogeneity was found (I2=94.5%, p<0.001) among the included studies. Therefore, the SMD was pooled through the random effect model. The pooled SMD was 1.20 (95% CI: 0.89-1.51), indicating that serum Hcy levels were significant higher in UC groups compared to healthy controls with statistical difference (Z=7.52, P<0.001). Egger’s line regression test indicated no publications bias (t=1.45, p=0.17).

Conclusion: Serum Hcy levels were usually elevated in UC patients, which indicates that Hcy may play an important role in UC development and may be used as a serological biomarker for UC diagnosis.

The association of the MTHFR C677T polymorphism with inflammatory bowel diseases in the Israeli Jewish population: An example of genetic heterogeneity

MTHFR C677T is a common gene polymorphism that has been shown to be associated with hyperhomocysteinemia. Studies on the role of MTHFR in inflammatory bowel diseases (IBD) have yielded conflicting results, perhaps due in part to genetic heterogeneity. The prevalence of the MTHFR C677T variant allele varies according to Jewish subpopulations: Ashkenazi vs non-Ashkenazi. The aim of this study was to examine the association between MTHFR C677T genotype and IBD in the different Jewish populations.DNA samples were assessed for the presence of the MTHFR C677T variant allele in 445 Jewish Israeli IBD patients: 338 with Crohn's disease [CD] (214 Ashkenazi and 124 non-Ashkenazi Jews) and 107 with ulcerative colitis [UC] (73 Ashkenazi and 34 non-Ashkenazi Jews), and in 347 healthy controls: 173 Ashkenazi and 174 Non-Ashkenazi Jews. Possible genotype-phenotype associations were investigated.We showed a significantly higher frequency of MTHFR 677T variant genotypes in non-Ashkenazi CD patients: Odds ratio of 1.86 for heterozygotes (CT) and 2.89 for homozygotes (TT) compared to non-Ashkenazi healthy controls. No significant association was found for UC in non-Ashkenazi patients or for CD or UC in Ashkenazi patients.Our findings suggest that the MTHFR 677T variant may contribute to the risk of CD in non-Ashkenazi but not Ashkenazi Jews. This may result from genetic heterogeneity and highlights the complexity of the genetic etiology of IBD.

The relationship between coagulation state and inflammatory bowel disease: current understanding and clinical implications

Inflammatory bowel disease (IBD) is associated with a hypercoagulable state and subsequently with an increased risk for venous thromboembolism (VTE). VTE in IBD is characterized by a high recurrence rate and is associated with the disease activity. Acquired endothelial dysfunction, abnormalities of platelets, activation of coagulation system and impaired fibrinolysis are the main changes in the coagulation state in IBD. The development of VTE in IBD has been considered to be the result of multiple interactions between acquired and inherited risk factors. The treatment of VTE in IBD patients is recommended to be similar and to follow the same protocols as for non-IBD patients. In the clinical practice, the management of IBD patients and especially the hospitalized patients should include thromboprophylaxis.

Hyperhomocysteinemia as a potential contributor of colorectal cancer development in inflammatory bowel diseases: A review

Homocysteine is an amino acid generated metabolically by the S-adenosylmethionine-dependent transmethylation pathway. In addition to being a well-known independent risk factor for coronary heart disease, is also a risk factor for cancer. Patients suffering from inflammatory bowel diseases (IBD) including ulcerative colitis and Crohn’s disease are at increased risk of developing colorectal cancer in comparison to healthy individuals. Furthermore, the risk of hyperhomocysteinaemia is significantly higher in IBD patients when compared with controls. In the present article, we review the mechanisms in which hyperhomocysteinemia may contribute to increased risk of colorectal cancer in IBD patients.

A meta-analysis of genotypes and haplotypes of methylenetetrahydrofolate reductase gene polymorphisms in breast cancer

The association between methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms and breast cancer risk has been extensively explored, but their results are conflicting rather than conclusive. To derive a more precise estimation, we carried out not only an updated meta-analysis but also a combined analysis based on all the available studies estimating the association between MTHFR C677T and/or A1298C and breast cancer risk. With respect to C677T polymorphism, the results suggested that 677T allele was associated with significantly elevated breast cancer risk in overall analysis (T vs. C: OR 1.073, 95 % CI 1.028-1.120; TT vs. CC: OR 1.177, 95 % CI 1.072-1.293; TT vs. CC + CT: OR 1.175, 95 % CI 1.073-1.288); Stratifying by ethnicity, significantly increased risk was only found in East Asians (T vs. C: OR 1.150, 95 % CI 1.039-1.273; TT vs. CC: OR 1.441, 95 % CI 1.145-1.814; TT vs. CC + CT: OR 1.413, 95 % CI 1.148-1.739); When stratified by menopausal status, statistically significant association was found for postmenopausal women (CT + TT vs. CC: OR 1.092, 95 % CI 1.011-1.179). In regard to A1298C polymorphism, no significant associations were found between the polymorphism and breast cancer risk. With respect to MTHFR haplotypes, significantly elevated breast cancer risk was associated with 677T-1298C for overall result (OR 1.498, 95 % CI 1.143-1.962) and for Caucasians (OR 2.088, 95 % CI 1.277-3.416) when compared with 677C-1298A; Haplotype 677C-1298C might provide higher protection than 677C-1298A in East Asians (OR 0.840, 95 % CI 0.742-0.949). The combined genotypes for C677T and A1298C produced a significant OR for the 677TT/1298AC relative to 677CC/1298AA in overall population (OR 2.047, 95 % CI 1.275-3.288); When stratified by ethnicity, significant ORs were only found for East Asians (677CC/1298CC vs. 677CC/1298AA: OR 0.686, 95 % CI 0.478-0.985; 677TT/1298AC vs. 677CC/1298AA: OR 2.181, 95 % CI 1.179-4.035). The findings suggest that the MTHFR C677T polymorphism but not A1298C, and some variants on their combined genotypes or haplotypes may be involved with the development of breast cancer.

Dietary folate does not significantly affect the intestinal microbiome, inflammation or tumorigenesis in azoxymethane-dextran sodium sulphate-treated mice

Inflammatory bowel disease (IBD) is a risk factor for the development of colon cancer. Environmental factors including diet and the microflora influence disease outcome. Folate and homocysteine have been associated with IBD-mediated colon cancer but their roles remain unclear. We used a model of chemically induced ulcerative colitis (dextran sodium sulphate (DSS)) with or without the colon carcinogen azoxymethane (AOM) to determine the impact of dietary folic acid (FA) on colonic microflora and the development of colon tumours. Male mice (n 15 per group) were fed a FA-deficient (0 mg/kg), control (2 mg/kg) or FA-supplemented (8 mg/kg) diet for 12 weeks. Folate status was dependent on the diet (P< 0·001) and colitis-induced treatment (P= 0·04) such that mice with colitis had lower circulating folate. FA had a minimal effect on tumour initiation, growth and progression, although FA-containing diets tended to be associated with a higher tumour prevalence in DSS-treated mice (7-20 v. 0%, P= 0·08) and the development of more tumours in the distal colon of AOM-treated mice (13-83% increase, P= 0·09). Folate deficiency was associated with hyperhomocysteinaemia (P< 0·001) but homocysteine negatively correlated with tumour number (r - 0·58, P= 0·02) and load (r - 0·57, P= 0·02). FA had no effect on the intestinal microflora. The present data indicate that FA intake has no or little effect on IBD or IBD-mediated colon cancer in this model and that hyperhomocysteinaemia is a biomarker of dietary status and malabsorption rather than a cause of IBD-mediated colon cancer.

Potential value of nutrigenomics in Crohn's disease

Crohn's disease is a chronic relapsing condition that has no certain cure. Both genetic susceptibility and nutrition have key roles, but their level of involvement varies between patients. Interacting gene pathways influence the probability of disease development, but these are affected by stress and various environmental factors, including diet. In addition, the role of the gut microbiome must not be underestimated, as it is substantially altered in patients with Crohn's disease. Although an elemental diet might lead to disease remission, reintroducing real foods and sustainable diets in patients with Crohn's disease is currently difficult, and would benefit from the sensitivity and rapid feedback provided by the field of nutrigenomics. Nutrigenomics utilizes high-throughput genomics technologies to reveal changes in gene and protein expression that are modulated by the patient's nutrition. The most widely used technique thus far is transcriptomics, which permits measurement of changes in the expression of thousands of genes simultaneously in one sample. Given the volume of numbers generated in such studies, data-basing and bioinformatics are essential to ensure the correct application of nutrigenomics at the population level. These methods have been successfully applied to animal models of Crohn's disease, and the time is right to move them to human studies.

Is there evidence to claim or deny association between variants of the multidrug resistance gene (MDR1 or ABCB1) and inflammatory bowel disease?

BACKGROUND

Inflammatory bowel disease (IBD) is a complex disease with a genetic background. Crohn's disease (CD) and ulcerative colitis (UC) are the two main types of IBD. There is indication that variants in the MDR1 gene are associated with development of IBD. However, the 20 published genetic association studies (GAS) for the three most popular variants in the MDR1 gene (C3435T, G2677T/A, and C1236T) have produced inclusive results.

METHODS

In order to decrease the uncertainty of pooled risk effects and to explore the trend and stability of the risk effects, a meticulous meta-analysis, including cumulative and recursive cumulative meta-analysis, of the GAS related to the MDR1 gene with susceptibility to IBD was conducted. The risk effects were estimated based on the odds ratio (OR) of the allele contrast and the generalized odds ratio (OR(G) ).

RESULTS

The analysis showed marginal significant association for the C3435T variant in UC: the risk estimate for the allele contrast was OR = 1.11 (1.00-1.22) and OR(G) = 1.12 (1.01-1.27), indicating that a subject with high mutational load has a 12% higher probability of being diseased. The respective cumulative meta-analysis indicated a downward trend of association, as evidence accumulates with the association being significant during the whole published period. The cumulative meta-analysis for the other variants showed lack of any trend of association. However, the recursive cumulative meta-analysis showed that there is no sufficient evidence for denying or claiming an association for all variants.

CONCLUSIONS

More evidence is needed to draw safe conclusions regarding the association of MDR1 variants and development of IBD.

Variants of the MTHFR gene and susceptibility to acute lymphoblastic leukemia in children: a synthesis of genetic association studies

BACKGROUND

Acute lymphoblastic leukemia (ALL) is a complex disease with genetic background. The genetic association studies (GAS) that investigated the association between ALL and the MTHFR C677T and A1298C gene variants have produced contradictory or inconclusive results.

MATERIALS AND METHODS

In order to decrease the uncertainty of estimated genetic risk effects, a meticulous meta-analysis of published GAS related the variants in the MTFHR gene with susceptibility to ALL was conducted. The risk effects were estimated based on the odds ratio (OR) of the allele contrast and the generalized odds ratio (OR(G)). Cumulative and recursive cumulative meta-analyses were also performed.

RESULTS

The analysis showed marginal significant association for the C677T variant, overall [OR=0.91 (0.82-1.00) and OR(G)=0.89 (0.79-1.01)], and in Whites [OR=0.88 (0.77-0.99) and OR(G)=0.85 (0.73-0.99)]. The A1298C variant produced non-significant results. For both variants, the cumulative meta-analysis did not show a trend of association as evidence accumulates and the recursive cumulative meta-analysis indicated lack of sufficient evidence for denying or claiming an association.

CONCLUSION

The current evidence is not sufficient to draw definite conclusions regarding the association of MTHFR variants and development of ALL.

Meta-analysis: hyperhomocysteinaemia in inflammatory bowel diseases

BACKGROUND

The magnitude of association between homocysteine metabolism and inflammatory bowel diseases (IBD) remains unknown, whereas the association between hyperhomocysteinaemia and thrombosis remains controversial in IBD.

AIM

To conduct a systematic review and meta-analysis to examine these issues.

METHODS

The literature search was conducted using MEDLINE database and international conference abstracts from January 1966 to April 2011 and included all studies that evaluated plasma homocysteine level in IBD.

RESULTS

Twenty-eight studies evaluated the plasma homocysteine level and/or hyperhomocysteinaemia risk in IBD patients. Five studies assessed the association of hyperhomocysteinaemia with thrombosis. The mean plasma homocysteine level was significantly higher in IBD patients when compared with controls (weighted mean difference (WMD)=3.75 μmol/L; 95% CI, 2.23-5.26 μmol/L; P<0.0001; reference ranges for plasma homocysteine level: 5-12 μmol/L). The mean plasma homocysteine level did not differ between ulcerative colitis (UC) and Crohn's disease (CD) (WMD=0.41 μmol/L; 95% CI, -2.45 to 3.06 μmol/L; P=0.76). The risk of hyperhomocysteinaemia was significantly higher in IBD patients when compared with controls [odds ratio (OR)=4.65; 95% CI, 3.04-7.09; P<0.0001]. The risk of hyperhomocysteinaemia was not higher among IBD patients who experienced thromboembolic complications (OR=1.97; 95% CI, 0.83-4.67; P=0.12). Plasma folate level was inversely correlated with IBD risk associated with MTHFR C677T polymorphism (P=0.006).

CONCLUSIONS

The risk of hyperhomocysteinaemia is significantly higher in IBD patients when compared with controls. The risk assessment of hyperhomocysteinaemia-related thrombosis in IBD requires further investigation. Deficient folate status is associated with a higher impact of MTHFR C677T polymorphism on IBD risk.

Evidence of association between methylenetetrahydrofolate reductase gene and susceptibility to breast cancer: a candidate-gene association study in a South-eastern European population

The methylenetetrahydrofolate reductase (MTHFR) gene has been proposed as a candidate gene for breast cancer (BC). However, the specific role of MTHFR polymorphisms and haplotypes has not been fully clarified and replicated. We examined the association of two common MTHFR polymorphisms (C677T and A1298C) and their haplotypes in a candidate-gene association study, involving 300 female patients with BC and 283 healthy women. The single locus analysis for the two polymorphisms revealed an association only for the C677T polymorphism [odds ratio (95% confidence interval), OR=2.05 (1.21-3.48)], but adjustment for age diminished this association [OR=1.76 (0.92-3.42)]. The menopausal status showed no significant effect in the association between the MTHFR polymorphisms and BC. The analysis of haplotypes showed an association for the C677-A1298 haplotypes (p=0.04). The available evidence from our study may support a contributory role of MTHFR polymorphisms in BC development. Future larger studies may help in elucidating the genetics of BC further.