Homocysteine metabolism and the associations of global DNA methylation with selected gene polymorphisms and nutritional factors in patients with dementia.

2016 
Abstract Epigenetics (particularly DNA methylation) together with environmental and genetic factors, are key to understanding the pathogenesis of many diseases including dementia. Disturbances in DNA methylation have already been implicated in dementia. Homocysteine metabolism, with folate and vitamin B 12 as essential cofactors, is integral to methylation processes. We evaluated in a case-control study the association of global DNA methylation, homocysteine, folate and vitamin B 12 status with dementia. Selected polymorphisms of genes previously associated with dementia development and the influence of various factors on DNA methylation were also investigated. 102 patients with dementia (53 with Alzheimer's disease, 17 with vascular dementia and 32 with mixed dementia) were recruited. The non-demented controls consisted of 45 age-matched subjects without dementia and 47 individuals with mild cognitive impairment. Global DNA methylation was determined by Imprint Methylated DNA Quantification Kit MDQ1 (Sigma-Aldrich, Gillingham, Dorset, UK). Plasma homocysteine, serum folate and vitamin B 12 were determined by chemiluminescence. Plasma and erythrocyte 5-methyltetrahydrofolate and plasma methylmalonic acid (markers of folate and vitamin B 12 status) were measured by HPLC. APOE , PON1 p.Q192R, MTHFR 677C > T (c.665C > T) and IL1B -511C > T polymorphisms were identified using PCR-RFLP methods. Patients with dementia had significantly higher concentrations of homocysteine (p = 0.012) and methylmalonic acid (p = 0.016) and lower folate (p = 0.002) and plasma 5-methyltetrahydrofolate (p = 0.005) than non-demented subjects. There was no difference in DNA methylation between patients and controls. A non-significant tendency to higher DNA methylation in patients with vascular dementia (p = 0.061) was observed. Multivariate regression analysis of all recruited individuals demonstrated a significant positive association between DNA methylation and folate (p = 0.013), creatinine (p = 0.003) concentrations and IL1B -511 T (p = 0.002) and PON1 192R (p = 0.049) alleles and negative association with fasting glucose (p = 0.004). The biochemical results showed significantly lower folate and vitamin B 12 status in demented patients than controls. Global DNA methylation was associated with markers of folate status, creatinine, glucose and PON1 and IL1B polymorphisms.
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