Role of thiamine thiol form in nitric oxide metabolism

Thiamine as a Possible Neuroprotective Strategy in Neonatal Hypoxic-Ischemic Encephalopathy

On the basis that similar biochemical and histological sequences of events occur in the brain during thiamine deficiency and hypoxia/ischemia related brain damage, we have planned this review to discuss the possible therapeutic role of thiamine and its derivatives in the management of neonatal hypoxic-ischemic encephalopathy (HIE). Among the many benefits, thiamine per se as antioxidant, given intravenously (IV) at high doses, defined as dosage greater than 100 mg IV daily, should counteract the damaging effects of reactive oxygen and nitrogen species in the brain, including the reaction of peroxynitrite with the tyrosine residues of the major enzymes involved in intracellular glucose metabolism, which plays a key pathophysiological role in HIE in neonates. Accordingly, it is conceivable that, in neonatal HIE, the blockade of intracellular progressive oxidative stress and the rescue of mitochondrial function mediated by thiamine and its derivatives can lead to a definite neuroprotective effect. Because therapeutic hypothermia and thiamine may both act on the latent period of HIE damage, a synergistic effect of these therapeutic strategies is likely. Thiamine treatment may be especially important in mild HIE and in areas of the world where there is limited access to expensive hypothermia equipment.

Thiamine and benfotiamine protect neuroblastoma cells against paraquat and β-amyloid toxicity by a coenzyme-independent mechanism

Background

Benfotiamine (BFT) is a synthetic thiamine precursor with high bioavailability. It is efficient in treating complications of type 2 diabetes and has beneficial effects in mouse models of neurodegenerative diseases. The mechanism of action of BFT remains unknown, though it is sometimes suggested that it may be linked to increased thiamine diphosphate (ThDP) coenzyme function.

Methods

We used a mouse neuroblastoma cell line (Neuro2a) grown in thiamine-restricted medium. The cells were stressed by exposure to paraquat (PQ) or amyloid β_1-42 peptide in the presence or absence of BFT and the cell survival was measured using the MTT method. In each case, BFT was compared with sulbutiamine (SuBT), an unrelated thiamine precursor, and thiamine. Metabolites of BFT were determined by HPLC and mass spectrometry.

Results

At 50 μM, BFT protects the cells against PQ and amyloid β_1-42 peptide-induced toxicity with the same efficacy. Protective effects were also observed with SuBT and with higher concentrations of thiamine. The main metabolites of BFT were thiamine and S-benzoylthiamine (S-BT). Treatment with both precursors induces a strong increase in intracellular content of thiamine. Protective effects of BFT and SuBT are directly related to thiamine (but not ThDP) levels in Neuro2a cells.

Conclusions

BFT, SuBT and thiamine all protect the cells against oxidative stress, suggesting an antioxidant effect of thiamine. Our results are not in favor of a direct ROS scavenging effect of thiamine but rather an indirect effect possibly mediated by some antioxidant signaling pathway. It is however not clear whether this effect is due to thiamine itself, its thiol form or an unknown metabolite.

General significance

Our results suggest a role of thiamine in protection against oxidative stress, independent of the coenzyme function of thiamine diphosphate.

Thiamine increases the resistance of baker's yeast Saccharomyces cerevisiae against oxidative, osmotic and thermal stress, through mechanisms partly independent of thiamine diphosphate-bound enzymes

Numerous recent studies have established a hypothesis that thiamine (vitamin B1 ) is involved in the responses of different organisms against stress, also suggesting that underlying mechanisms are not limited to the universal role of thiamine diphosphate (TDP) in the central cellular metabolism. The current work aimed at characterising the effect of exogenously added thiamine on the response of baker's yeast Saccharomyces cerevisiae to the oxidative (1 mM H2 O2 ), osmotic (1 M sorbitol) and thermal (42 °C) stress. As compared to the yeast culture in thiamine-free medium, in the presence of 1.4 μM external thiamine, (1) the relative mRNA levels of major TDP-dependent enzymes under stress conditions vs. unstressed control (the 'stress/control ratio') were moderately lower, (2) the stress/control ratio was strongly decreased for the transcript levels of several stress markers localised to the cytoplasm, peroxisomes, the cell wall and (with the strongest effect observed) the mitochondria (e.g. Mn-superoxide dismutase), (3) the production of reactive oxygen and nitrogen species under stress conditions was markedly decreased, with the significant alleviation of concomitant protein oxidation. The results obtained suggest the involvement of thiamine in the maintenance of redox balance in yeast cells under oxidative stress conditions, partly independent of the functions of TDP-dependent enzymes.

Oxidation of thiamine on reaction with nitrogen dioxide generated by ferric myoglobin and hemoglobin in the presence of nitrite and hydrogen peroxide

It is shown that nitrogen dioxide oxidizes thiamine to thiamine disulfide, thiochrome, and oxodihydrothiochrome (ODTch). The latter is formed during oxidation of thiochrome by nitrogen dioxide. Nitrogen dioxide was produced by incubation of nitrite with horse ferric myoglobin and human hemoglobin in the presence of hydrogen peroxide. After addition of tyrosine or phenol to aqueous solutions containing oxoferryl forms of the hemoproteins, thiamine, and nitrite, the yield of thiochrome greatly increased, whereas the yield of ODTch decreased. In the presence of high concentrations of tyrosine or phenol compounds ODTch was not formed at all. The neutral form of thiamine with the closed thiazole cycle and minor tricyclic form of thiamine do not enter the heme pocket of the protein and do not interact with the oxoferryl heme complex Fe(IV=O) or porphyrin radical. The tricyclic form of thiamine is oxidized to thiochrome by tyrosyl radicals located on the surface of the hemoprotein. The thiol form of thiamine is oxidized to thiamine disulfide by both hemoprotein tyrosyl radicals and oxoferryl heme complexes. Nitrite and also tyrosine, tyramine, and phenol readily penetrate into the heme pocket of the protein and reduce the oxyferryl complex to ferric cation. These reactions yield nitrogen dioxide as well as tyrosyl and phenoxyl radicals of tyrosine molecules and phenol compounds, respectively. Tyrosyl and phenoxyl radicals of low molecular weight compounds oxidize thiamine only to thiochrome and thiamine disulfide. The effect of oxoferryl forms of myoglobin and hemoglobin, nitrogen dioxide, and phenol on thiamine oxidative transformation as well as antioxidant properties of the hydrophobic thiamine metabolites thiochrome and ODTch are discussed.

Thiamin(e): the spark of life

One of the earliest vitamins to be discovered and synthesized, thiamin was originally spelled with an "e". The terminal "e" was dropped when it was found that it was not an amine. It is still spelled with and without the "e" depending on the text. This chapter provides a brief historical review of the association of thiamin with the ancient scourge of beriberi. It emphasizes that beriberi is the model for high calorie malnutrition because of its occurrence in predominantly white rice consuming cultures. Some of the symptomatology of this ancient scourge is described, emphasizing the difference from that seen in starvation. High calorie malnutrition, due to excessive ingestion of simple carbohydrates, is widely encountered in the U.S.A. today. Thiamin deficiency is commonly associated with this, largely because of its cofactor status in the metabolism of glucose. The biochemistry of the three phosphorylated esters of thiamin and the transporters are discussed and the pathophysiology of thiamin deficiency reviewed. The role of thiamin, and particularly its synthetic derivatives as therapeutic agents, is not fully appreciated in Western civilization and a clinical section describes some of the unusual cases described in the scientific literature and some experienced by the author. The possible role of high calorie malnutrition and related thiamin deficiency in juvenile crime is hypothesized.

Bacitracin inhibits the reductive activity of protein disulfide isomerase by disulfide bond formation with free cysteines in the substrate-binding domain

The peptide antibiotic bacitracin is widely used as an inhibitor of protein disulfide isomerase (PDI) to demonstrate the role of the protein-folding catalyst in a variety of molecular pathways. Commercial bacitracin is a mixture of at least 22 structurally related peptides. The inhibitory activity of individual bacitracin analogs on PDI is unknown. For the present study, we purified the major bacitracin analogs, A, B, H, and F, and tested their ability to inhibit the reductive activity of PDI by use of an insulin aggregation assay. All analogs inhibited PDI, but the activity (IC(50) ) ranged from 20 μm for bacitracin F to 1050 μm for bacitracin B. The mechanism of PDI inhibition by bacitracin is unknown. Here, we show, by MALDI-TOF/TOF MS, a direct interaction of bacitracin with PDI, involving disulfide bond formation between an open thiol form of the bacitracin thiazoline ring and cysteines in the substrate-binding domain of PDI.

Thiamine and oxidants interact to modify cellular calcium stores

Diminished thiamine (vitamin B1) dependent processes and oxidative stress accompany Alzheimer's disease (AD). Thiamine deficiency in animals leads to oxidative stress. These observations suggest that thiamin may act as an antioxidant. The current experiments first tested directly whether thiamin could act as an antioxidant, and then examined the physiological relevance of the antioxidant properties on oxidant sensitive, calcium dependent processes that are altered in AD. The first group of experiments examined whether thiamin could diminish reactive oxygen species (ROS) or reactive nitrogen species (RNS) produced by two very divergent paradigms. Dose response curves determined the concentrations of t-butyl-hydroperoxide (t-BHP) (ROS production) or 3-morpholinosydnonimine ((SIN-1) (RNS production) to induce oxidative stress within cells. Concentrations of thiamine that reduced the RNS in cells did not diminish the ROS. The second group of experiments tested whether thiamine alters oxidant sensitive aspects of calcium regulation including endoplasmic reticulum (ER) calcium stores and capacitative calcium entry (CCE). Thiamin diminished ER calcium considerably, but did not alter CCE. Thiamine did not alter the actions of ROS on ER calcium or CCE. On the other hand, thiamine diminished the effect of RNS on CCE. These data are consistent with thiamine diminishing the actions of the RNS, but not ROS, on physiological targets. Thus, both experimental approaches suggest that thiamine selectively alters RNS. Additional experiments are required to determine whether diminished thiamine availability promotes oxidative stress in AD or whether the oxidative stress in AD brain diminishes thiamine availability to thiamine dependent processes.

Thiamine-dependent processes and treatment strategies in neurodegeneration

Reductions in brain glucose metabolism and increased oxidative stress invariably occur in Alzheimer's disease (AD) and thiamine (vitamin B1) deficiency. Both conditions cause irreversible cognitive impairment; their behavioral consequences overlap but are not identical. Thiamine-dependent processes are critical in glucose metabolism, and recent studies implicate thiamine in oxidative stress, protein processing, peroxisomal function, and gene expression. The activities of thiamine-dependent enzymes are characteristically diminished in AD, and the reductions in autopsy AD brain correlate highly with the extent of dementia in the preagonal state. Abnormalities in thiamine-dependent processes can be plausibly linked to the pathology of AD. Seemingly paradoxical properties of thiamine-dependent processes may underlie their relation to the pathophysiology of AD: Reduction of thiamine-dependent processes increase oxidative stress. Thiamine can act as a free radical scavenger. Thiamine-dependent mitochondrial dehydrogenase complexes produce oxygen free radicals and are sensitive to oxidative stress. Genetic disorders of thiamine metabolism that lead to neurological disease can be treated with large doses of thiamine. Although thiamine itself has not shown dramatic benefits in AD patients, the available data is scanty. Adding thiamine or more absorbable forms of thiamine to tested treatments for the abnormality in glucose metabolism in AD may increase their efficacy.

A review of the biochemistry, metabolism and clinical benefits of thiamin(e) and its derivatives

Thiamin(e), also known as vitamin B1, is now known to play a fundamental role in energy metabolism. Its discovery followed from the original early research on the ‘anti-beriberi factor’ found in rice polishings. After its synthesis in 1936, it led to many years of research to find its action in treating beriberi, a lethal scourge known for thousands of years, particularly in cultures dependent on rice as a staple. This paper refers to the previously described symptomatology of beriberi, emphasizing that it differs from that in pure, experimentally induced thiamine deficiency in human subjects. Emphasis is placed on some of the more unusual manifestations of thiamine deficiency and its potential role in modern nutrition. Its biochemistry and pathophysiology are discussed and some of the less common conditions associated with thiamine deficiency are reviewed. An understanding of the role of thiamine in modern nutrition is crucial in the rapidly advancing knowledge applicable to Complementary Alternative Medicine. References are given that provide insight into the use of this vitamin in clinical conditions that are not usually associated with nutritional deficiency. The role of allithiamine and its synthetic derivatives is discussed. Thiamine plays a vital role in metabolism of glucose. Thus, emphasis is placed on the fact that ingestion of excessive simple carbohydrates automatically increases the need for this vitamin. This is referred to as high calorie malnutrition.