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Thiamine (vitamin B1) is a precursor of the well-known coenzyme of central metabolic pathways thiamine diphosphate (ThDP). Highly intense glucose oxidation in the brain requires ThDP-dependent enzymes, which determines the critical significance of thiamine for neuronal functions. However, thiamine can also act through the non-coenzyme mechanisms. The well-known facilitation of acetylcholinergic neurotransmission upon the thiamine and acetylcholine co-release into the synaptic cleft has been supported by the discovery of thiamine triphosphate (ThTP)-dependent phosphorylation of the acetylcholine receptor-associated protein rapsyn, and thiamine interaction with the TAS2R1 receptor, resulting in the activation of synaptic ion currents. The non-coenzyme regulatory binding of thiamine compounds has been demonstrated for the transcriptional regulator p53, poly(ADP-ribose) polymerase, prion protein PRNP, and a number of key metabolic enzymes that do not use ThDP as a coenzyme. The accumulated data indicate that the molecular mechanisms of the neurotropic action of thiamine are far broader than it has been originally believed, and closely linked to the metabolism of thiamine and its derivatives in animals. The significance of this topic has been illustrated by the recently established competition between thiamine and the antidiabetic drug metformin for common transporters, which can be the reason for the thiamine deficiency underlying metformin side effects. Here, we also discuss the medical implications of the research on thiamine, including the role of thiaminases in thiamine reutilization and biosynthesis of thiamine antagonists; molecular mechanisms of action of natural and synthetic thiamine antagonists, and biotransformation of pharmacological forms of thiamine. Given the wide medical application of thiamine and its synthetic forms, these aspects are of high importance for medicine and pharmacology, including the therapy of neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Recent studies from our laboratory have demonstrated the presence of a pH-dependent, amiloride-sensitive, electroneutral carrier-mediated exchange for thiamine absorption in the human small intestinal brush-border membrane vesicles. However, the mechanism of thiamine transport across the human small intestinal basolateral membrane is not understood. The present study was aimed to characterize the mechanism of thiamine transport across the basolateral membranes of the human jejunum. Basolateral membrane vesicles (BLMV) were purified from mucosal scrapings of organ donors, utilizing a Percoll continuous density gradient centrifugation technique. The results showed [3H] thiamine uptake into BLMV to be: (1) markedly stimulated in the presence of an outwardly directed H+ gradient (pH 5.5in/7.5out); (2) significantly inhibited by amiloride in a dose-dependent manner; (3) sensitive to temperature and medium osmolarity and insensitive to changes in membrane potential; (4) not influenced by the addition of 1 mM Mg(2+)-ATP, inside and outside the vesicles in the presence of Na+ and K+; (5) inhibited by structural analogs-amprolium, oxythiamin, and unlabeled thiamine (100 microM); (6) not affected by organic cations, eg, TEA, N-methyl-nicotinamide (NMN), and choline; and (7) saturable as a function of concentration (apparent Km of 0.76 +/- 0.21 microM and a V(max) of 1.38 +/- 0.35 pmol/mg protein/10 sec). These results indicate the presence of a proton gradient-dependent specialized carrier-mediated exchange mechanism for thiamine transport across the human jejunum basolateral membranes. [ABSTRACT FROM AUTHOR]

We have investigated the thiamine metabolism in Schizosaccharomyces pombe and shown that: (1) Thiamine-repressible acid phosphate, coded for by the gene pho4, dephosphorylates thiamine phosphates indicating that the enzyme acts as a thiamine phosphate phosphatase. (2) In vivo synthesized thiamine is present intracellulary mainly as thiamine diphosphate. Starving cells for glucose decreases the intracellular thiamine pool. (3) The genes thi2, thi3 and thi4 control thiamine biosynthesis and probably code for thiamine biosynthetic enzymes. Thi3, which is involved in the synthesis of the pyrimidine moiety of the thiamine molecule, is allelic to the thiamine repressible gene nmt1. (4) Thiamine uptake is a thiamine regulated process, probably occurs by active transport and is controlled by the gene ptr1. [ABSTRACT FROM AUTHOR]