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Components of One-carbon Metabolism Other than Folate and Colorectal Cancer Risk
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Pharmacology.
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2016 (English)In: Epidemiology, ISSN 1044-3983, E-ISSN 1531-5487, Vol. 27, no 6, p. 787-796Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Despite extensive study, the role of folate in colorectal cancer remains unclear. Research has therefore begun to address the role of other elements of the folate-methionine metabolic cycles. This study investigated factors other than folate involved in one-carbon metabolism, i.e., choline, betaine, dimethylglycine, sarcosine, and methionine and relevant polymorphisms, in relation to the risk of colorectal cancer in a population with low intakes and circulating levels of folate.

METHODS: This was a prospective case-control study of 613 case subjects and 1,190 matched control subjects nested within the population-based Northern Sweden Health and Disease Study. We estimated odds ratios (OR) by conditional logistic regression, and marginal risk differences with weighted maximum likelihood estimation using incidence data from the study cohort.

RESULTS: Higher plasma concentrations of methionine and betaine were associated with modest colorectal cancer risk reductions (OR [95% confidence interval {CI}] for highest versus lowest tertile: 0.76 [0.57, 0.99] and 0.72 [0.55, 0.94], respectively). Estimated marginal risk differences corresponded to approximately 200 fewer colorectal cancer cases per 100,000 individuals on average. We observed no clear associations between choline, dimethylglycine, or sarcosine and colorectal cancer risk. The inverse association of methionine was modified by plasma folate concentrations (OR [95% CI] for highest/lowest versus lowest/lowest tertile of plasma methionine/folate concentrations 0.39 [0.24, 0.64], Pinteraction = 0.06).

CONCLUSIONS: In this population-based, nested case-control study with a long follow-up time from baseline to diagnosis (median: 8.2 years), higher plasma concentrations of methionine and betaine were associated with lower colorectal cancer risk. See Video Abstract at http://links.lww.com/EDE/B83.

Place, publisher, year, edition, pages
2016. Vol. 27, no 6, p. 787-796
National Category
Cancer and Oncology
Identifiers
URN: urn:nbn:se:umu:diva-129408DOI: 10.1097/EDE.0000000000000529ISI: 000390251500006PubMedID: 27367522OAI: oai:DiVA.org:umu-129408DiVA, id: diva2:1060031
Available from: 2016-12-27 Created: 2016-12-27 Last updated: 2018-09-12Bibliographically approved
In thesis
1. Biomarkers of one-carbon metabolism in colorectal cancer risk
Open this publication in new window or tab >>Biomarkers of one-carbon metabolism in colorectal cancer risk
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One-carbon metabolism, a network of enzymatic reactions involving the transfer of methyl groups, depends on B-vitamins as cofactors, folate as a methyl group carrier, and amino acids, betaine, and choline as methyl group donors. One-carbon metabolism influences many processes in cancer initiation and development such as DNA synthesis, genome stability, and histone and epigenetic methylation. To study markers of one-carbon metabolism and inflammation in relation to colorectal cancer (CRC) risk, we used prediagnostic plasma samples from over 600 case participants and 1200 matched control participants in the population-based Northern Sweden Health and Disease Study cohort.

This thesis studies CRC risk with respect to the following metabolites measured in pre-diagnostic plasma samples: 1) folate, vitamin B12, and homocysteine; 2) components of one-carbon metabolism (choline, betaine, dimethylglycine, sarcosine, and methionine); and 3) three markers of different aspects of vitamin B6 status. In addition, this thesis examines three homocysteine ratios as determinants of total B-vitamin status and their relation to CRC risk.

In two previous studies, we observed an association between low plasma concentrations of folate and a lower CRC risk, but we found no significant association between plasma concentrations of homocysteine and vitamin B12 with CRC risk. We have replicated these results in a study with a larger sample size and found that low folate can inhibit the growth of established pre-cancerous lesions.

Using the full study cohort of over 1800 participants, we found inverse associations between plasma concentrations of the methionine cycle metabolites betaine and methionine and CRC risk. This risk was especially low for participants with the combination of low folate and high methionine versus the combination of low folate and low methionine. Well-functioning methionine cycle lowers risk, while impaired DNA synthesis partly explains the previous results for folate.

We used the full study cohort to study associations between CRC risk and the most common marker of vitamin B6 status, pyridoxal' 5-phosphate (PLP), and two metabolite ratios, PAr (4-pyridoxic acid/(PLP + pyridoxal)) estimating vitamin B6 related inflammatory processes and the functional vitamin B6 marker 3-hydroxykynurenine to xanthurenic acid (HK:XA). Increased vitamin B6-related inflammation and vitamin B6 deficiency increase CRC risk. Inflammation was not observed to initiate tumorigenesis.

Total B-vitamin status can be estimated by three different recently introduced homocysteine ratios. We used the full study cohort to relate the ratios as determinants of the total B-vitamin score in case and control participants and estimated the CRC risk for each marker. Sufficient B-vitamin status as estimated with homocysteine ratios was associated with a lower CRC risk.

These studies provide a deeper biochemical knowledge of the complexities inherent in the relationship between one-carbon metabolism and colorectal tumorigenesis. 

Place, publisher, year, edition, pages
Umeå: Umeå University, 2017. p. 68
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1935
Keywords
Colorectal cancer, one-carbon metabolism, biomarkers, folate, epidemiology
National Category
Cancer and Oncology
Research subject
Cancer Epidemiology
Identifiers
urn:nbn:se:umu:diva-142868 (URN)978-91-7601-804-0 (ISBN)
Public defence
2018-01-19, E04, Norrlands Universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2017-12-15 Created: 2017-12-13 Last updated: 2018-06-09Bibliographically approved
2. Metabolic Risk Factors and Molecular Subtypes of Colorectal Cancer
Open this publication in new window or tab >>Metabolic Risk Factors and Molecular Subtypes of Colorectal Cancer
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Metabola Riskfaktorer och Molekylära Subtyper av Kolorektalcancer
Abstract [en]

Background: Colorectal cancer (CRC) is a heterogeneous disease developing from distinct pathways, resulting in tumor subtypes with large differences in clinical and molecular characteristics. Molecular characteristics are increasingly being used clinically to guide therapy. However, whether molecular subtypes of CRC differ in etiology or risk factors is not clear. Clarifying such potential differences may lead to an improved understanding of CRC etiology, with implications for CRC prevention and screening.

Aim: The aim of this thesis was to investigate whether risk factors related to energy metabolism, such as body fatness, and one-carbon metabolism, such as circulating B-vitamin status, were associated with specific subtypes of CRC defined by molecular characteristics of the tumor. 

Methods: These prospective studies are based on data and blood samples from cohorts within the population-based Northern Sweden Health and Disease Study (NSHDS). Prospective CRC cases with available archived tumor tissue were analyzed for key molecular features (KRAS and BRAF mutation status, Microsatellite instability (MSI) status, and CpG Island Methylator Phenotype (CIMP) status). Paper I was a cohort study of metabolic factors related to the metabolic syndrome (117 687 participants). Paper II was a nested-case control study on circulating insulin resistance-markers and adipokines (1010 cases and 1010 matched controls). Papers III and IV were nested case-control studies of one-carbon metabolism biomarkers and genetic variants (613 cases and 1190 matched controls).

Results: In paper I, we observed associations between metabolic factors, such as BMI, blood pressure, and blood lipids, and CRC risk consistent with previous studies. These associations were similar regardless of tumor KRAS and BRAF mutation status. In paper II, circulating biomarkers of insulin resistance and adipokines were not associated with the risk of CRC or specific molecular subtypes of CRC defined by KRAS and BRAF mutation or MSI status. In paper III, higher circulating levels of metabolites involved in the methionine cycle (namely, betaine and methionine) were associated with a lower CRC risk. In paper IV, we found no support for clear subtype-specific roles of any circulating one-carbon metabolism biomarker or genetic variants in CRC development.

Conclusions: The result of these prospective studies suggests that metabolic factors related to energy metabolism and one-carbon metabolism are generally associated with the risk of CRC, regardless of major subtypes defined by key molecular tumor features. If causal, metabolic risk factors likely influence the risk of colorectal cancer through more than one carcinogenic pathway.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2018. p. 70
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1975
Keywords
Colorectal cancer, risk factors, metabolic syndrome, one-carbon metabolism, molecular subtypes, KRAS, BRAF, MSI, molecular pathological epidemiology
National Category
Cancer and Oncology
Research subject
Cancer Epidemiology
Identifiers
urn:nbn:se:umu:diva-151753 (URN)978-91-7601-939-9 (ISBN)
Public defence
2018-10-12, Sal 260, Norrlands Universitetssjukhus, Målpunkt A21, Byggnad 3A, vån 2., Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2018-09-21 Created: 2018-09-12 Last updated: 2018-09-14Bibliographically approved

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