These findings highlight mechanisms that affect vitamin B6, vitamin B12 and homocysteine serum levels.AB - The B vitamins are components of one-carbon metabolism (OCM) that contribute to DNA synthesis and methylation.
The conversion of homocysteine back to methionine via donation of a methyl group from betaine and methyltetrahydrofolate are homocysteine salvage pathways. These pathways are vital because they allow continued methylation of DNA which modifies gene expression. In addition, these salvage pathways are also important because they reduce the accumulation of homocysteine in the blood. Homocysteine is now thought to be a driver of disease because it can induce oxidative stress and damage cellular components. High blood levels of homocysteine are independently associated with cardiovascular disease and dementia, brought about through homocysteine induced damage to blood vessels. Homocysteine may deplete nitric oxide from the endothelium of vessels via the generation of free radicals and this in turn leads to endothelial dysfunction which is a likely cause of vascular disease. The homocysteine salvage pathways are therefore important at reducing this process through the removal of homocysteine.
B12 and folate in DNA synthesis - UpToDate
Methyltetrahydrofolate is the biologically active form of folate and is therefore reliant on dietary intake of folic acid for synthesis. Betaine (N,N,N-trimethylglycine) is a metabolite of choline, a conditionally essential element considered part of the B vitamin group. Betaine synthesis therefore relies on an appropriate intake of dietary choline. Variations in the diet is able to cause alterations to the efficiency of the methionine pathway and homocysteine salvage pathways because dietary variation can alter the synthetic rates of the one carbon donors required for flux. In a study investigating the seasonal variation in dietary intakes of nutrients involved in one carbon metabolism in African women1, it was reported that dietary intake of these nutrients varied because of seasonal variation in food supply. The variation in these nutrients then caused a switch between the betaine and methyltetrahydrofolate salvage pathways, suggesting that natural food variation is able to alter pathway flux, and that the salvage pathways interact.