Vitamin B6: a molecule for human health?

Washington State University, Abelson 435, P.O. Box 66224, Pullman, WA, USA.
Molecules (Impact Factor: 2.1). 01/2010; 15(1):442-59. DOI: 10.3390/molecules15010442
Source: PubMed

ABSTRACT Vitamin B6 is an intriguing molecule that is involved in a wide range of metabolic, physiological and developmental processes. Based on its water solubility and high reactivity when phosphorylated, it is a suitable co-factor for many biochemical processes. Furthermore the vitamin is a potent antioxidant, rivaling carotenoids or tocopherols in its ability to quench reactive oxygen species. It is therefore not surprising that the vitamin is essential and unquestionably important for the cellular metabolism and well-being of all living organisms. The review briefly summarizes the biosynthetic pathways of vitamin B6 in pro- and eukaryotes and its diverse roles in enzymatic reactions. Finally, because in recent years the vitamin has often been considered beneficial for human health, the review will also sum up and critically reflect on current knowledge how human health can profit from vitamin B6.

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    ABSTRACT: Pyridoxal 5'-phosphate (PLP; a B6 vitamer) serves as an important cofactor in a myriad of metabolic reactions, including the transsulfuration (TS) pathway, which converts homocysteine (Hcy) to cysteine. While overt vitamin B6 deficiency is rare, moderate deficiency is common and may be exacerbated by anti-pyridoxine factors in the food supply. To this end, we developed a model of moderate B6 deficiency and a study was conducted to examine the in vivo effect of 1-amino d-proline (1ADP), an anti-pyridoxine factor found in flaxseed, on indices of Hcy metabolism through the TS pathway in moderately B6 deficient rats. Male weaning rats received a semi-purified diet containing either 7mg/kg (control; CD) or 0.7mg/kg (moderately deficient; MD) diet of pyridoxine·hydrochloride (PN∙HCl), each with 1 of 4 levels of 1ADP, viz. 0, 0.1, 1 and 10mg/kg diet for 5weeks. Perturbations in vitamin B6 biomarkers were more pronounced in the MD group. Plasma PLP was significantly reduced, while plasma Hcy (8-fold) and cystathionine (11-fold) were increased in rats consuming the highest amount of 1ADP in the MD group. The activities of hepatic cystathionine β-synthase and cystathionine γ-lyase enzymes were significantly reduced in rats consuming the highest 1ADP compared to the lowest, for both levels of PN∙HCl. Dilation of hepatic central veins and sinusoids, mild steatosis and increased liver triglycerides were present in MD rats consuming the highest 1ADP level. The current data provide evidence that the consumption of an anti-pyridoxine factor linked to flaxseed may pose a risk for subjects who are moderate/severe vitamin B6 deficient. Copyright © 2014 Elsevier Inc. All rights reserved.
    The Journal of Nutritional Biochemistry 12/2014; 26(3). DOI:10.1016/j.jnutbio.2014.10.014 · 4.59 Impact Factor
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    ABSTRACT: Vitamin B6 (pyridoxal 5'-phosphate) is an essential cofactor of many metabolic enzymes. Plants biosynthesize the vitamin de novo employing two enzymes, PDX1 and PDX2. In Arabidopsis, there are two catalytically active paralogs of PDX1 (PDX1.1, PDX1.3) producing the vitamin at comparable rates. Since single mutants are viable but the pdx1.1 pdx1.3 double mutant is lethal, the corresponding enzymes seem redundant. However, the single mutants exhibit substantial phenotypic differences, particularly at the level of root development, with pdx1.3 being more impaired than pdx1.1. Here we investigate the differential regulation of PDX1.1 and PDX1.3 by identifying factors involved in their disparate phenotypes. Swapped promoter experiments clarify the presence of distinct regulatory elements in the upstream regions of both genes. Exogenous sucrose triggers impaired ethylene production in both mutants but is more severe in pdx1.3 than pdx1.1. Interestingly, sucrose specifically represses PDX1.1 expression, accounting for the stronger vitamin B6 deficit in pdx1.3 compared to pdx1.1. Surprisingly, sucrose enhances auxin levels in pdx1.1, whereas the levels are diminished in pdx1.3. In the case of pdx1.3, the previously reported reduced meristem activity combined with the impaired ethylene and auxin levels manifests the specific root developmental defects. Moreover, it is the deficit in ethylene production and/or signaling that triggers this outcome. On the other hand, we hypothesize that it is the increased auxin content of pdx1.1 that is responsible for root developmental defects observed therein. We conclude that PDX1.1 and PDX1.3 play partially non-redundant roles and are differentially regulated as manifested in disparate root growth impairment morphologies. Copyright © 2014, American Society of Plant Biologists.
    Plant physiology 01/2015; 167(1):102. DOI:10.1104/pp.114.247767 · 7.39 Impact Factor
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    ABSTRACT: Serine hydroxymethyltransferase isoforms (SHMT1 & SHMT2α), which serve as scaffold protein for the formation of a multi-enzyme complex and generate one-carbon unit for the de novo thymidylate biosynthesis pathway during DNA synthesis, are vitamin B6 (VB6)-dependent enzyme. Cancer cells with high proliferation intensity need increased SHMT activation which enforces the facilitated-diffusion of VB6 for the continuous functioning of thymidylate synthase cycle. Therefore, SHMT knockdown presents an alternative approach to prevent DNA synthesis in cancer cells; however, its potential to inhibit cancer growth remains unknown so far. Here we demonstrated that VB6 coupled to poly(ester amine) (VBPEA) enforces a high level of VTC (VB6-transporting membrane carriers)-mediated endocytosis of the complexed SHMT1 siRNA (siSHMT1) to interrupt the thymidylate biosynthesis pathway of cancer cells. The detrimental effect of SHMT1 knockdown on the disintegration of multi-enzyme complex resulted in cell cycle arrest and a decrease in cell's genomic DNA content, leading to enhanced apoptotic events in cancer cells. A reduction in tumor size was observed with constant SHMT1 suppression in xenograft mice. This study illustrates how silencing the SHMT1 expression inhibits cancer growth and the increased VB6 channeling for sustenance of cancer cells promotes VB6-coupled vector to elicit enhanced delivery of siSHMT1.
    Biomaterials 08/2014; DOI:10.1016/j.biomaterials.2014.07.045 · 8.31 Impact Factor


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