Epigenetic effects of riboflavin supplementation on hypertension in adults screened for the MTHFR C677T polymorphism

Abstract

Overcoming the challenges of age-related disease remains a significant problem and is a high research priority owing to the socioeconomic, medical and psychological burdens associated with a rapidly ageing population. This thesis focuses on how B-vitamins, in particular,riboflavin can regulate the epigenome and the role this may play in prolonging healthy lifespan through improved cardiovascular function. In studies previously conducted at this centre, riboflavin, a cofactor for the folate-metabolising enzyme MTHFR, was shown to lower blood pressure in individuals with the MTHFR 677TT genotype, which is strongly associated with hypertension and stroke. Building on these studies, this thesis was conducted to investigate potential mechanisms underlying the role of this gene nutrient reaction in blood pressure. The aims were to explore DNA methylation as a potential mechanism contributing to the blood pressure lowering effect of riboflavin in adults with the MTHFR 677TT genotype. A comprehensive literature review of current evidence as well as focused systematic review and meta-analysis were conducted to provide a new insight into the overall role of one-carbon metabolism nutrients in DNA methylation. The specific effects of riboflavin supplementation on DNA methylation were investigated using established robust methodologies.Findings from the systematic review and meta-analysis indicated a functional role for one-carbon metabolism nutrients in DNA methylation and demonstrated increased global methylation in response to supplementation with folic acid alone or in combination with vitamin B-12 in studies using standardised LC-MS/MS methods which had markedly lower heterogeneity (n = 3, Z = 3.31, P = 0.0009; I2 = 0%) compared to other methods. Pyrosequencing revealed that riboflavin supplementation in adults with the MTHFR 677TT genotype resulted in decreased LINE-1 (P < 0.018), MTHFR north shore (P = 0.001) and increased IGF2 (P = 0.019) methylation. When stratified by MTHFR C677T genotype, results indicated higher LINE-1 (P = 0.011), MTHFR south shelf (P < 0.001) and NOS3 (P = 0.044)methylation in adults with the variant TT compared to the CC genotype. Genome-wide DNA methylation analysis identified a significant differentially methylated region (Benjamini-Hochberg adjusted, P = 0.008) and several CpG sites altered by riboflavin supplementation.Pathway analysis highlighted role for genes annotated to these positions in several diseases including stroke. Overall, the findings presented in this thesis, based on analysis of samples from targeted observational and RCT studies, using highly reproducible and established methods provide the first evidence of a novel role of riboflavin in modulating DNA methylation and associated CVD risk. This work adds significantly to current knowledge on how nutritional modifications can impact the epigenome.

Date of Award	May 2020
Original language	English
Sponsors	Vice Chancellors Research Scholarship
Supervisor	Diane Lees-Murdock (Supervisor) & Mary Ward (Supervisor)