Dietary intake of B-vitamins, polymorphisms in thymidylate synthase and serine hydroxymethyltransferase 1, and colorectal adenoma risk: A Dutch case-control study

A meta-analysis of the C1420T polymorphism in cytosolic serine hydroxymethyltransferase (SHMT1) among Caucasian colorectal cancer populations

PURPOSE

Inconsistency of reported associations between the C1420T polymorphism in the cytosolic serine hydroxymethyltransferase (SHMT1) gene and colorectal cancer (CRC) prompted us to undertake a meta-analysis.

METHODS

We conducted searches of published literature in MEDLINE through PubMed up to April 2012. Individual data on 5,043 cases and 6,311 controls from 15 published case-control studies were evaluated. Meta-analyses were performed on the compiled dataset.

RESULTS

In the overall analysis, association was lacking between the C1420T polymorphism and CRC risk (odds ratio [OR] 0.96-1.04, p = 0.47-0.77), materially unchanged when reanalyzed without the Hardy-Weinberg equilibrium-deviating studies (OR 1.03-1.09, p = 0.22-0.55) or subjected to outlier treatment (OR 0.89-0.99, p = 0.10-0.8). In the ethnic subgroups, Europeans were susceptible (OR 1.11-1.17, p = 0.13-0.48) and Americans, slightly protected (OR 0.86-0.87, p = 0.49-0.61). The increased risk effects, however, became null following outlier treatment (OR 0.95-1.06). Test for interaction between decreased risk associations in the low-folate subgroup (OR 0.60-0.85, p = 0.009-0.03) with the susceptible effects in the high-folate category (OR 1.14-1.22, p = 0.19-0.32) was significant (p interaction = 0.004).

CONCLUSIONS

Overall summary estimates imply no associations but suggest geography-specific effects of the SHMT1 polymorphism that render Europeans susceptible, but not Americans. Folate status appears to show an inverse association of this polymorphism with CRC.

Folate-genetics and colorectal neoplasia: what we know and need to know next

SCOPE

The metabolism of folate involves a complex network of polymorphic enzymes that may explain a proportion of the risk associated with colorectal neoplasia. Over 60 observational studies primarily in non-Hispanic White populations have been conducted on selected genetic variants in specific genes, MTHFR, MTR, MTRR, CBS, TCNII, RFC, GCPII, SHMT, TYMS, and MTHFD1, including five meta-analyses on MTHFR 677C>T (rs1801133) and MTHFR 1298C>T (rs1801131); two meta-analyses on MTR-2756A>C (rs1805087); and one for MTRR 66A>G (rs1801394).

METHODS AND RESULTS

This systematic review synthesizes these data, highlighting the consistent inverse association between MTHFR 677TT genotype and risk of colorectal cancer (CRC) and its null association with adenoma risk. Results for other variants varied across individual studies; in our meta-analyses we observed some evidence for SHMT 1420C>T (rs1979277) ((odds ratio) OR = 0.85; 95% confidence interval (CI) = 0.73-1.00 for TT v. CC) and TYMS 5' 28 bp repeat (rs34743033) and CRC risk (OR = 0.84; 95% CI = 0.75-0.94 for 2R/3R v. 3R/3R and OR = 0.82; 95% CI = 0.69-0.98 for 2R/2R v. 3R/3R).

CONCLUSION

To gain further insight into the role of folate variants in colorectal neoplasia will require incorporating measures of the metabolites, including B-vitamin cofactors, homocysteine and S-adenosylmethionine, and innovative statistical methods to better approximate the folate one-carbon metabolism pathway.

Polymorphisms in serine hydroxymethyltransferase 1 and methylenetetrahydrofolate reductase interact to increase cardiovascular disease risk in humans

The enzymes serine hydroxymethyltransferase 1 (gene name SHMT1) and methylenetetrahydrofolate reductase (gene name MTHFR) regulate key reactions in folate-mediated one-carbon metabolism. Common genetic variants with the potential to influence disease risk exist in both genes. A prior report from the Normative Aging Study indicated no association of the SHMT1 rs1979277 SNP with cardiovascular disease (CVD), but a strong gene-gene interaction was detected with MTHFR rs1801133. We investigated the effect of the SHMT1 rs1979277 SNP and the SHMT1 rs1979277-MTHFR rs1801133 interaction in 2 epidemiologic cohort studies. In the Nurses' Health Study (NHS), the MTHFR rs1801133 variant genotypes were associated with an increased CVD risk and there was an interaction between SHMT1 and MTHFR such that the association of the MTHFR rs1801133 CT genotype (vs. CC; the TT genotype could not be evaluated) was stronger in the presence of the SHMT1 rs1979277 TT genotype (OR = 4.34, 95% CI = 1.2, 16.2; P = 0.049). In the Health Professionals Follow-Up Study, the MTHFR rs1801133 genotype was not associated with CVD risk, nor was there an interaction with SHMT1 rs1979277. The association of genetic variation in the SHMT1 gene, alone and in interaction with MTHFR, in relation to CVD risk is relatively understudied at the population level and results in the NHS confirmed a past report of gene-gene interaction, which is consistent with mechanisms suggested by basic science studies.

SHMT1 1420 and MTHFR 677 variants are associated with rectal but not colon cancer

Background

Association between rectal or colon cancer risk and serine hydroxymethyltransferase 1 (SHMT1) C1420T or methylenetetrahydrofolate reductase (MTHFR) C677T polymorphisms was assessed. The serum total homocysteine (HCY), marker of folate metabolism was also investigated.

Methods

The SHMT1 and MTHFR genotypes were determined by real-time PCR and PCR-RFLP, respectively in 476 patients with rectal, 479 patients with colon cancer and in 461 and 478, respective controls matched for age and sex. Homocysteine levels were determined by HPLC kit. The association between polymorphisms and cancer risk was evaluated by logistic regression analysis adjusted for age, sex and body mass index. The population stratification bias was also estimated.

Results

There was no association of genotypes or diplotypes with colon cancer. The rectal cancer risk was significantly lower for SHMT1 TT (OR = 0.57, 95% confidence interval (CI) 0.36-0.89) and higher for MTHFR CT genotypes (OR = 1.4, 95%CI 1.06-1.84). A gene-dosage effect was observed for SHMT1 with progressively decreasing risk with increasing number of T allele (p = 0.014). The stratified analysis according to age and sex revealed that the association is mainly present in the younger (< 60 years) or male subgroup. As expected from genotype analysis, the SHMT1 T allele/MTHFR CC diplotype was associated with reduced rectal cancer risk (OR 0.56, 95%CI 0.42-0.77 vs all other diplotypes together). The above results are unlikely to suffer from population stratification bias. In controls HCY was influenced by SHMT1 polymorphism, while in patients it was affected only by Dukes' stage. In patients with Dukes' stage C or D HCY can be considered as a tumor marker only in case of SHMT1 1420CC genotypes.

Conclusions

A protective effect of SHMT1 1420T allele or SHMT1 1420 T allele/MTHFR 677 CC diplotype against rectal but not colon cancer risk was demonstrated. The presence of SHMT1 1420 T allele significantly increases the HCY levels in controls but not in patients. Homocysteine could be considered as a tumor marker in SHMT1 1420 wild-type (CC) CRC patients in Dukes' stage C and D. Further studies need to clarify why SHMT1 and MTHFR polymorphisms are associated only with rectal and not colon cancer risk.

Analysis of candidate genes in occurrence and growth of colorectal adenomas

Predisposition to sporadic colorectal tumours is influenced by genes with minor phenotypic effects. A case-control study was set up on 295 patients treated for a large adenoma matched with polyp-free individuals on gender, age, and geographic origin in a 1 : 2 proportion. A second group of 302 patients treated for a small adenoma was also characterized to distinguish effects on adenoma occurrence and growth. We focussed the study on 38 single nucleotide polymorphisms (SNPs) encompassing 14 genes involved in colorectal carcinogenesis. Effect of SNPs was tested using unconditional logistic regression. Comparisons were made for haplotypes within a given gene and for biologically relevant genes combinations using the combination test. The APC p.Glu1317Gly variant appeared to influence the adenoma growth (P = .04, exact test) but not its occurrence. This result needs to be replicated and genome-wide association studies may be necessary to fully identify low-penetrance alleles involved in early stages of colorectal tumorigenesis.

Vitamins B2, B6, and B12 and risk of new colorectal adenomas in a randomized trial of aspirin use and folic acid supplementation

BACKGROUND

Folate, other vitamin B cofactors, and genes involved in folate-mediated one-carbon metabolism all may play important roles in colorectal neoplasia. In this study, we examined the associations between dietary and circulating plasma levels of vitamins B(2), B(6), and B(12) and risk colorectal adenomas.

METHODS

The Aspirin/Folate Polyp Prevention Study is a randomized clinical trial of folic acid supplementation and incidence of new colorectal adenomas in individuals with a history of adenomas (n = 1,084). Diet and supplement use were ascertained through a food frequency questionnaire administered at baseline. Blood collected at baseline was used to determine plasma B-vitamin levels. We used generalized linear regression to estimate risk ratios (RR) and 95% confidence intervals (95% CI) as measures of association.

RESULTS

We found a borderline significant inverse association with plasma B(6) [pyridoxal 5'-phosphate (PLP)] and adenoma risk (adjusted RR Q4 versus Q1, 0.78; 95% CI, 0.61-1.00; P(trend) = 0.08). This association was not modified by folic acid supplementation or plasma folate. However, the protective association of PLP with adenoma risk was observed only among subjects who did not drink alcohol (P(interaction) = 0.03). Plasma B(2) (riboflavin) was inversely associated with risk of advanced lesions (adjusted RR Q4 versus Q1, 0.51; 95% CI, 0.26-0.99; P(trend) = 0.12). No significant associations were observed between adenoma risk and plasma vitamin B(12) or dietary intake of vitamin B(2) and B(6). When we examined specific gene-B-vitamin interactions, we observed a possible interaction between methylenetetrahydrofolate reductase -C677T and plasma B(2) on risk of all adenomas.

CONCLUSION

Our results suggest that high levels of PLP and B(2) may protect against colorectal adenomas.

Thymidylate synthase polymorphisms, folate and B-vitamin intake, and risk of colorectal adenoma

The effects of polymorphisms in genes coding for key folate metabolism enzymes such as thymidylate synthetase (TS) on colorectal neoplasia risk are likely to be influenced by gene–gene and gene–nutrient interactions. We investigated the combined effects of three polymorphisms in the TS gene region, TSER, TS 3R G>C, and TS 1494del6, dietary intakes of folate and other B vitamins, and genotype for other folate metabolism variants, in a colorectal adenoma (CRA) case–control study. Individuals homozygous for TS 1494del6 del/del were at significantly reduced CRA risk compared to those with either ins/del or ins/ins genotypes (odds ratio 0.52; 95% confidence interval: 0.31–0.85, P=0.009). We also observed evidence of interactions between TS 1494del6 genotype and intake of folate, and vitamins B₆ and B₁₂, and MTHFR C677T genotype, with the reduction in risk in del/del homozygotes being largely confined to individuals with high nutrient intakes and MTHFR 677CC genotype (P_interaction=0.01, 0.006, 0.03, and 0.07, respectively). TSER genotype, when considered either alone or in combination with TS 3R G>C genotype, did not significantly influence CRA risk. These findings support a role for TS in colorectal carcinogenesis, and provide further evidence that functional polymorphisms in folate metabolism genes act as low-risk alleles for colorectal neoplasia and participate in complex gene–gene and gene–nutrient interactions.

Magnifying endoscopic observation of the gastric mucosa, particularly in patients with atrophic gastritis

The gastric mucosal surface was observed using the magnifying fibergastroscope (FGS-ML), and the fine gastric mucosal patterns, which were even smaller than one unit of gastric area, were examined at a magnification of about 30. For simplicification, we classified these patterns by magnifying endoscopy in the following ways; FP, FIP, FSP, SP and MP, modifying Yoshii's classification under the dissecting microscope. The FIP, which was found to have round and long elliptical gastric pits, is a new addition to our endoscopic classification. The relationship between the FIP and the intermediate zone was evaluated by superficial and histological studies of surgical and biopsy specimens. The width of the band of FIP seems to be related to the severity of atrophic gastritis. Also, the transformation of FP to FIP was assessed by comparing specimens taken from the resected and residual parts of the stomach, respectively. Moreover, it appears that severe gastritis occurs in the gastric mucosa which shows a FIP. Therefore, we consider that the FIP indicates the position of the atrophic border.