The role of vitamin B6 in one-carbon metabolism, oxidative stress, immune system regulation and carcinogenesis.

Abstract

Vitamin B6 is a well known cofactor in over 100 metabolic reactions, among which one-carbon metabolism, and is shown to play a role in oxidative stress, immune system regulation and carcinogenesis. In one-carbon metabolism, vitamin B6 is a co-factor for serine hydroxylmethyltransferase (SHMT), cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGL). One-carbon metabolism is important in DNA synthesis, DNA repair, DNA methylation, protection against oxidative stress and detoxification. Therefore, adequate levels of vitamin B6 are required for maintenance of these processes. Vitamin B6, especially the vitamer pyridoxamine, is shown to have anti-oxidative capacities by scavenging reactive oxygen species (ROS), reactive carbonyl species (RCS) and chelation of redox-active metal ions. In vitamin B6 deficiency, suppression of development of lymphoid organs, lymphocyte proliferation, cytotoxicity, delayed type hypersensitivity reaction, skin transplant rejection, antibody production and production of interleukins involved in a T-helper 1 response, are shown in in vitro and animal studies. The effects of vitamin B6 status on one-carbon metabolism are the most hypothesized mechanism of the aberration of the regulation of the immune system, found in vitamin B6 deficiency. Vitamin B6 is shown to protect against (colorectal) carcinogenesis. Several mechanisms are hypothesized, such as aberration of one-carbon metabolism, expression of genes involved in cell proliferation, detoxification of carcinogenic compounds, protection against oxidative stress and angiogenesis, oxidative stress, inflammation and nitric oxide synthesis.