Circulating folate levels and colorectal adenoma: a case-control study and a meta-analysis

Genetic prediction of micronutrient levels and the risk of colorectal polyps: A mendelian randomization study

OBJECTIVE

Previous epidemiological and experimental studies have yielded conflicting results regarding the influence of human micronutrient levels on the risk of colorectal polyps (CP). In our study, we conducted a two-sample Mendelian randomization (MR) investigation to probe the link between 13 human micronutrients (calcium, selenium, magnesium, phosphorus, folate, vitamins B-6, B-12, C, D, beta-carotene, iron, zinc, and copper) and the genetic susceptibility to CP.

METHODS

Summary statistics for CP (n = 463,010) were obtained from pan-European genome-wide association studies, and instrumental variables for 13 micronutrients were screened from published genome-wide association studies (GWAS). After selecting suitable instrumental variables, we performed a two-sample MR study, deploying sensitivity analyses to judge heterogeneity and pleiotropy, using inverse variance weighted methods as our primary estimation tool.

RESULTS

Our study identified that a genetic predisposition to elevated toenail and circulating selenium or serum β-carotene concentrations lowers the risk of CP occurrence. However, no statistically significant association was observed between the other 11 micronutrients and the risk of CP.

CONCLUSION

The study findings provide evidence that the micronutrient selenium and β-carotene may confer protective effects against the development of CP.

MTHFR Gene C677T Polymorphism (rs1801133) and Susceptibility to Colorectal Polyps in an Azerbaijani Population

BACKGROUND

Understanding the relationships between the methylenetetrahydrofolate reductase (MTHFR) gene polymorphism, colorectal polyps, and CRC risk can aid in advancing personalized medicine approaches in CRC prevention. The aim of the current study is to identify the association of C677T polymorphism of the MTHFR gene with the risk of colorectal polyps in the Azerbaijani population.

METHODS

This study included 125 patients with colon polyps and 155 healthy individuals as a control group. DNA was extracted from venous blood samples obtained from patients and healthy individuals, and the results were analyzed through polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and agarose gel electrophoresis.

RESULTS

Wild-type, heterozygote, and homozygous mutant were revealed within 69 (55.2%), 49 (39.2%), and 7 (5.6%) patients and within 100 (64.5%), 45 (29%), and 10 (6.5%) healthy controls, respectively. However, no significant statistical associations were observed between CT and TT genotypes, dominant (CC vs. CT + TT) and recessive (CC + CT vs. TT) models, and the mutant T allele and disease risk. There were also no significant differences between patients and controls regarding age, sex, smoking and alcohol use.

CONCLUSION

Our research did not reveal any significant association between the MTHFR C677T polymorphism and susceptibility to colorectal polyps in the Azerbaijan population.

Association Between Folate and Health Outcomes: An Umbrella Review of Meta-Analyses

Background: There is no study that has systematically investigated the breadth and validity of the associations of folate and multiple health outcomes. We aimed to evaluate the quantity, validity, and credibility of evidence regarding associations between folate and multiple health outcomes by using umbrella review of meta-analysis. Methods: We searched the MEDLINE, EMBASE, and Cochrane Library databases from inception to May 20, 2018, to identify potential meta-analyses that examined the association of folate with any health outcome. For each included meta-analysis, we estimated the summary effect size and their 95% confidence interval using the DerSimonian and Laird random-effects model. We used the AMSTAR 2 (A Measurement Tool to Assess Systematic Reviews) to assess methodological quality and the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation working group classification) to assess the quality of evidence for each outcome included in the umbrella review. Results: Overall, 108 articles reporting 133 meta-analyses of observational studies and 154 meta-analyses of randomized controlled trials (RCTs) were included in the study. Among them, 108 unique exposure-outcome-population triplets (referred to as unique meta-analyses hereafter) of RCTs and 87 unique meta-analyses of observational studies were reanalyzed. Beneficial effects of folate were observed in the all-cause mortality rate and in a number of chronic diseases, including several birth/pregnancy outcomes, several cancers, cardiovascular disease and metabolic-related outcomes, neurological conditions, and several other diseases. However, adverse effects of folate were observed for prostate cancer, colorectal adenomatous lesions, asthma or wheezing, and wheezing as an isolated symptom and depression. Conclusions: Current evidence allows for the conclusion that folate is associated with decreased risk of all-cause mortality and a wide range of chronic diseases. However, folate may be associated with an increased risk of prostate cancer. Further research is warranted to improve the certainty of the estimates.

Enzymes involved in folate metabolism and its implication for cancer treatment

BACKGROUND/OBJECTIVES

Folate plays a critical role in DNA synthesis and methylation. Intracellular folate homeostasis is maintained by the enzymes folylpolyglutamate synthase (FPGS) and γ-glutamyl hydrolase (GGH). FPGS adds glutamate residues to folate upon its entry into the cell through a process known as polyglutamylation to enhance folate retention in the cell and to maintain a steady supply of utilizable folate derivatives for folate-dependent enzyme reactions. Thereafter, GGH catalyzes the hydrolysis of polyglutamylated folate into monoglutamylated folate, which can subsequently be exported from the cell. The objective of this review is to summarize the scientific evidence available on the effects of intracellular folate homeostasis-associated enzymes on cancer chemotherapy.

METHODS

This review discusses the effects of FPGS and GGH on chemosensitivity to cancer chemotherapeutic agents such as antifolates, such as methotrexate, and 5-fluorouracil.

RESULTS AND DISCUSSION

Polyglutamylated (anti)folates are better substrates for intracellular folate-dependent enzymes and retained for longer within cells. In addition to polyglutamylation of (anti)folates, FPGS and GGH modulate intracellular folate concentrations, which are an important determinant of chemosensitivity of cancer cells toward chemotherapeutic agents. Therefore, FPGS and GGH affect chemosensitivity to antifolates and 5-fluorouracil by altering intracellular retention status of antifolates and folate cofactors such as 5,10-methylenetetrahydrofolate, subsequently influencing the cytotoxic effects of 5-fluorouracil, respectively. Generally, high FPGS and/or low GGH activity is associated with increased chemosensitivity of cancer cells to methotrexate and 5-fluorouracil, while low FPGS and/or high GGH activity seems to correspond to resistance to these drugs. Further preclinical and clinical studies elucidating the pharmocogenetic ramifications of these enzyme-induced changes are warranted to provide a framework for developing rational, effective, safe, and customized chemotherapeutic practices.

Association Between Risk Factors for Colorectal Cancer and Risk of Serrated Polyps and Conventional Adenomas

BACKGROUND & AIMS

Serrated polyps (SPs) and conventional adenomas are precursor lesions for colorectal cancer (CRC), but they are believed to arise via distinct pathways. We characterized risk factor profiles for SPs and conventional adenomas in a post hoc analysis of data from 3 large prospective studies.

METHODS

We collected data from the Nurses' Health Study, the Nurses' Health Study 2, and the Health Professionals Follow-up Study on subjects who developed SPs or conventional adenomas. Our analysis comprised 141,143 participants who had undergone lower gastrointestinal endoscopy, provided updated diet and lifestyle data every 2-4 years, and were followed until diagnosis of a first polyp. We assessed 13 risk factors for CRC in patients with SPs or conventional adenomas and examined the associations according to histopathology features.

RESULTS

We documented 7945 SPs, 9212 conventional adenomas, and 2382 synchronous SPs and conventional adenomas during 18-20 years of follow-up. Smoking, body mass index, alcohol intake, family history of CRC, and height were associated with higher risk of SPs and conventional adenomas, whereas higher intake of vitamin D and marine omega-3 fatty acid were associated with lower risk. The associations tended to be stronger for synchronous SPs and conventional adenomas. Smoking, body mass index, and alcohol intake were more strongly associated with SPs than conventional adenomas (P for heterogeneity <.05), whereas physical activity and intake of total folate and calcium were inversely associated with conventional adenomas but not SPs. For SPs and conventional adenomas, the associations tended to be stronger for polyps in the distal colon and rectum, of 10 mm or larger or with advanced histology.

CONCLUSIONS

In an analysis of data from 3 large prospective studies, we found that although SPs and conventional adenomas share many risk factors, some factors are more strongly associated with one type of lesion than the other. These findings provide support for the etiologic heterogeneity of colorectal neoplasia.