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One-carbon metabolite ratios as functional B-vitamin markers and in relation to colorectal cancer risk
Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
Bevital AS, Laboratory building, Bergen, Norway.
Department of Clinical Science, University of Bergen and Laboratory of Clinical Biochemistry, Haukeland University Hospital, Bergen, Norway.
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2017 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Background: One-carbon metabolism biomarker are easily measured in plasma, but analyzing them one at a time in relation to disease does not take into account the interdependence of the many factors involved. The relative dynamics of major one-carbon metabolism branches can be assessed by relating the functional B-vitamin marker total homocysteine (tHcy) to transsulfuration (total cysteine) and methylation (creatinine) outputs.

Objective: We validated the ratios of tHcy to total cysteine (Hcy:Cys), tHcy to creatinine (Hcy:Cre), and tHcy to cysteine to creatinine (Hcy:Cys:Cre) as functional markers of B-vitamin status. We also calculated the associations of these ratios to colorectal cancer (CRC) risk.

Design: The relative contribution of potential confounders to the variance of the ratio-based B-vitamin markers was calculated by linear regression in a nested case-control study of 613 CRC cases and 1211 matched controls. Total B-vitamin status was represented by a summary score comprising Z-standardized plasma concentrations of folate, cobalamin, betaine, pyridoxal 5´-phosphate, and riboflavin. Associations with CRC risk were estimated using conditional logistic regression.

Results: The ratio-based B-vitamin markers all outperformed tHcy as markers of total B-vitamin status, in both CRC cases and controls. Associations with CRC risk were similar for the ratio-based B-vitamin markers and total B-vitamin status (approximately 25% lower risk for high versus low B-vitamin status).

Conclusions: Ratio-based B-vitamin markers were good predictors of total B-vitamin status, and displayed similar associations with CRC risk. Since tHcy and creatinine are routinely clinically analyzed, Hcy:Cre could be easily implemented in clinical practice to aid interpretation of tHcy results.

Place, publisher, year, edition, pages
2017. , p. 68
Keywords [en]
Biomarkers, colorectal cancer, metabolite ratios, B-vitamins, one-carbon metabolism
National Category
Clinical Laboratory Medicine
Research subject
Cancer Epidemiology
Identifiers
URN: urn:nbn:se:umu:diva-142854OAI: oai:DiVA.org:umu-142854DiVA, id: diva2:1165237
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2018-06-09
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

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Gylling, Björn

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