Thiamine triphosphate synthesis in rat brain occurs in mitochondria and is coupled to the respiratory chain

The importance of thiamine (vitamin B1) in humans

Thiamine (thiamin, B1) is a vitamin necessary for proper cell function. It exists in a free form as a thiamine, or as a mono-, di- or triphosphate. Thiamine plays a special role in the body as a coenzyme necessary for the metabolism of carbohydrates, fats and proteins. In addition, it participates in the cellular respiration and oxidation of fatty acids: in malnourished people, high doses of glucose result in acute thiamine deficiency. It also participates in energy production in the mitochondria and protein synthesis. In addition, it is also needed to ensure the proper functioning of the central and peripheral nervous system, where it is involved in neurotransmitter synthesis. Its deficiency leads to mitochondrial dysfunction, lactate and pyruvate accumulation, and consequently to focal thalamic degeneration, manifested as Wernicke's encephalopathy or Wernicke-Korsakoff syndrome. It can also lead to severe or even fatal neurologic and cardiovascular complications, including heart failure, neuropathy leading to ataxia and paralysis, confusion, or delirium. The most common risk factor for thiamine deficiency is alcohol abuse. This paper presents current knowledge of the biological functions of thiamine, its antioxidant properties, and the effects of its deficiency in the body.

Synthetic Thioesters of Thiamine: Promising Tools for Slowing Progression of Neurodegenerative Diseases

Thiamine (vitamin B1) is essential for the brain. This is attributed to the coenzyme role of thiamine diphosphate (ThDP) in glucose and energy metabolism. The synthetic thiamine prodrug, the thioester benfotiamine (BFT), has been extensively studied and has beneficial effects both in rodent models of neurodegeneration and in human clinical studies. BFT has no known adverse effects and improves cognitive outcomes in patients with mild Alzheimer's disease. In cell culture and animal models, BFT has antioxidant and anti-inflammatory properties that seem to be mediated by a mechanism independent of the coenzyme function of ThDP. Recent in vitro studies show that another thiamine thioester, O,S-dibenzoylthiamine (DBT), is even more efficient than BFT, especially with respect to its anti-inflammatory potency, and is effective at lower concentrations. Thiamine thioesters have pleiotropic properties linked to an increase in circulating thiamine concentrations and possibly in hitherto unidentified open thiazole ring derivatives. The identification of the active neuroprotective metabolites and the clarification of their mechanism of action open extremely promising perspectives in the field of neurodegenerative, neurodevelopmental, and psychiatric conditions. The present review aims to summarize existing data on the neuroprotective effects of thiamine thioesters and give a comprehensive account.

Dietary thiamine modulates carbohydrate metabolism, antioxidant status, and alleviates hypoxia stress in oriental river prawn Macrobrachium nipponense (de Haan)

Hypoxia is one of the challenges in prawns aquaculture. However, the role of thiamine, which is a coenzyme in carbohydrate metabolism with antioxidant properties, in reducing hypoxia in prawns aquaculture is currently unknown. We investigated the effects of thiamine on antioxidant status, carbohydrate metabolism and acute hypoxia in oriental river prawn, Macrobrachium nipponense. One thousand eight hundred prawns (0.123 ± 0.003 g) were fed five diets (60 prawns each tank, six replicates per diet) supplemented with graded thiamine levels (5.69, 70.70, 133.67, 268.33 and 532.00 mg/kg dry mater) for eight weeks and then exposed to hypoxia stress for 12 h followed by reoxyegnation for 12 h. The results showed that, under normoxia, prawns fed the 133.67 or 268.33 mg/kg thiamine diet had significantly lower glucose 6-phosphatedehydrogenase, succinate dehydrogenase and phosphoenolpyruvate carboxykinase activities than those fed the other diets. Moreover, total antioxidant capacity (T-AOC) increased significantly when prawns were fed the 133.67 mg/kg thiamine diet. Superoxide dismutase (SOD) activity and malonaldehyde (MDA) content also increased significantly when prawns were fed the 268.33 or 532.00 mg/kg thiamine diet under hypoxia. And the significantly increased SOD activity and MDA level also observed in prawns fed 532.00 mg/kg thiamine under reoxygenation. Under normoxia, prawns fed the 70.70 or 133.67 mg/kg thiamine diet decreased the mRNA expressions of AMP-activated protein kinase-alpha (AMPK-α), pyruvate dehydrogenase-E1-α subunit (PDH-E1-α) and hypoxia-inducible factor-1s (HIF-1α, HIF-1β), but increased the mRNA expressions of phosphofructokinase (PFK) significantly. After 12 h of hypoxia, the energy metabolism related genes (AMPK-β, AMPK-γ, PFK, PDH-E1-α), hypoxia-inducible factor related genes (HIF-1α, HIF-1β) and thiamine transporter gene (SLC19A2) were up-regulated significantly in prawns fed the 133.67 or 268.33 mg/kg thiamine diets. After 12 h of reoxygenation, prawns fed the 133.67 or 268.33 mg/kg diet significantly decreased the SOD activity, MDA level and SLC19A2 mRNA expression compared with other diets. The optimum thiamine was 161.20 mg/kg for minimum MDA content and 143.17 mg/kg for maximum T-AOC activity based on cubic regression analysis. In summary, supplementing 143.17 to 161.20 mg/kg thiamine in the diets for M. nipponense improves the antioxidant capacity under normoxia and reduces the oxidative damage under hypoxia stress.

Follow-up of the re-evaluation of sulfur dioxide (E 220), sodium sulfite (E 221), sodium bisulfite (E 222), sodium metabisulfite (E 223), potassium metabisulfite (E 224), calcium sulfite (E 226), calcium bisulfite (E 227) and potassium bisulfite (E 228)

Sulfur dioxide-sulfites (E 220-228) were re-evaluated in 2016, resulting in the setting of a temporary ADI of 0.7 mg SO2 equivalents/kg bw per day. Following a European Commission call for data, the present follow-up opinion assesses data provided by interested business operators (IBOs) and additional evidence identified in the publicly available literature. No new biological or toxicological data addressing the data gaps described in the re-evaluation were submitted by IBOs. Taking into account data identified from the literature search, the Panel concluded that there was no substantial reduction in the uncertainties previously identified in the re-evaluation. Therefore, the Panel considered that the available toxicity database was inadequate to derive an ADI and withdrew the current temporary group acceptable daily intake (ADI). A margin of exposure (MOE) approach was considered appropriate to assess the risk for these food additives. A lower confidence limit of the benchmark dose of 38 mg SO2 equivalents/kg bw per day, which is lower than the previous reference point of 70 mg SO2 equivalents/kg bw per day, was estimated based on prolonged visual evoked potential latency. An assessment factor of 80 was applied for the assessment of the MoE. At the estimated dietary exposures, when using a refined exposure scenario (Data set D), MOEs at the maximum of 95th percentile ranges were below 80 for all population groups except for adolescents. The dietary exposures estimated using the maximum permitted levels would result in MOEs below 80 in all population groups at the maximum of the ranges of the mean, and for most of the population groups at both minimum and maximum of the ranges at the 95th percentile. The Panel concluded that this raises a safety concern for both dietary exposure scenarios. The Panel also performed a risk assessment for toxic elements present in sulfur dioxide-sulfites (E 220-228), based on data submitted by IBOs, and concluded that the maximum limits in the EU specifications for arsenic, lead and mercury should be lowered and a maximum limit for cadmium should be introduced.

B vitamin supply in plants and humans: the importance of vitamer homeostasis

B vitamins are a group of water-soluble micronutrients that are required in all life forms. With the lack of biosynthetic pathways, humans depend on dietary uptake of these compounds, either directly or indirectly, from plant sources. B vitamins are frequently given little consideration beyond their role as enzyme accessory factors and are assumed not to limit metabolism. However, it should be recognized that each individual B vitamin is a family of compounds (vitamers), the regulation of which has dedicated pathways. Moreover, it is becoming increasingly evident that individual family members have physiological relevance and should not be sidelined. Here, we elaborate on the known forms of vitamins B₁ , B₆ and B₉ , their distinct functions and importance to metabolism, in both human and plant health, and highlight the relevance of vitamer homeostasis. Research on B vitamin metabolism over the past several years indicates that not only the total level of vitamins but also the oft-neglected homeostasis of the various vitamers of each B vitamin is essential to human and plant health. We briefly discuss the potential of plant biology studies in supporting human health regarding these B vitamins as essential micronutrients. Based on the findings of the past few years we conclude that research should focus on the significance of vitamer homeostasis - at the organ, tissue and subcellular levels - which could improve the health of not only humans but also plants, benefiting from cross-disciplinary approaches and novel technologies.

Product inhibition of mammalian thiamine pyrophosphokinase is an important mechanism for maintaining thiamine diphosphate homeostasis

BACKGROUND

Thiamine diphosphate (ThDP), an indispensable cofactor for oxidative energy metabolism, is synthesized through the reaction thiamine + ATP ⇆ ThDP + AMP, catalyzed by thiamine pyrophosphokinase 1 (TPK1), a cytosolic dimeric enzyme. It was claimed that the equilibrium of the reaction is in favor of the formation of thiamine and ATP, at odds with thermodynamic calculations. Here we show that this discrepancy is due to feedback inhibition by the product ThDP.

METHODS

We used a purified recombinant mouse TPK1 to study reaction kinetics in the forward (physiological) and for the first time also in the reverse direction.

RESULTS

Keq values reported previously are strongly underestimated, due to the fact the reaction in the forward direction rapidly slows down and reaches a pseudo-equilibrium as ThDP accumulates. We found that ThDP is a potent non-competitive inhibitor (Ki ≈ 0.4 μM) of the forward reaction. In the reverse direction, a true equilibrium is reached with a Keq of about 2 × 10-5, strongly in favor of ThDP formation. In the reverse direction, we found a very low Km for ThDP (0.05 μM), in agreement with a tight binding of ThDP to the enzyme.

GENERAL SIGNIFICANCE

Inhibition of TPK1 by ThDP explains why intracellular ThDP levels remain low after administration of even very high doses of thiamine. Understanding the consequences of this feedback inhibition is essential for developing reliable methods for measuring TPK activity in tissue extracts and for optimizing the therapeutic use of thiamine and its prodrugs with higher bioavailability under pathological conditions.

Synthesis, physico-chemical properties and effect of adenosine thiamine triphosphate on vitamin B1 metabolism in the liver of alloxan diabetic rats

BACKGROUND

Adenosine thiamine triphosphate (AThTP) is a nucleotide discovered in bacteria and some other living organisms more than a decade ago. No biochemical function for AThTP has been established yet, however, experimental data available indicate its possible involvement in metabolic regulation or cell signaling. Metabolism of AThTP in mammals, as well as the feasibility of its pharmacological application, is essentially unstudied.

METHODS

Preparative low-pressure chromatography was employed to purify chemically synthesized AThTP with its further analysis by mass spectrometry, HPLC, UV and fluorescence spectroscopy. Enzyme activity assays along with HPLC were used to examine the effects of AThTP and thiamine on vitamin B₁ metabolism in the liver of alloxan-induced diabetic rats.

RESULTS

An improved procedure for AThTP synthesis and purification is elaborated. Solution stability, optical spectral properties and the molar absorption coefficient for AThTP were determined. The levels of thiamine compounds were found to be increased in the liver of diabetic rats. Neither AThTP nor thiamine treatment affected hepatic vitamin B₁ metabolism. Fasting blood glucose concentration was also unchangeable after AThTP or thiamine administration.

GENERAL SIGNIFICANCE

Contrast to the widespread view about thiamine deficiency in diabetes, our results clearly shows an adaptive increase in the level of B₁ vitamers in the liver of alloxan diabetic rats with no further rising after AThTP or thiamine treatment at a moderate dose. Neither AThTP nor thiamine is effective in glycaemic control. These findings are to be considered in future studies dealing with thiamine or its analogues application to correct metabolic disturbances in diabetes.

Update on Thiamine Triphosphorylated Derivatives and Metabolizing Enzymatic Complexes

While the cellular functions of the coenzyme thiamine (vitamin B1) diphosphate (ThDP) are well characterized, the triphosphorylated thiamine derivatives, thiamine triphosphate (ThTP) and adenosine thiamine triphosphate (AThTP), still represent an intriguing mystery. They are present, generally in small amounts, in nearly all organisms, bacteria, fungi, plants, and animals. The synthesis of ThTP seems to require ATP synthase by a mechanism similar to ATP synthesis. In E. coli, ThTP is synthesized during amino acid starvation, while in plants, its synthesis is dependent on photosynthetic processes. In E. coli, ThTP synthesis probably requires oxidation of pyruvate and may play a role at the interface between energy and amino acid metabolism. In animal cells, no mechanism of regulation is known. Cytosolic ThTP levels are controlled by a highly specific cytosolic thiamine triphosphatase (ThTPase), coded by thtpa, and belonging to the ubiquitous family of the triphosphate tunnel metalloenzymes (TTMs). While members of this protein family are found in nearly all living organisms, where they bind organic and inorganic triphosphates, ThTPase activity seems to be restricted to animals. In mammals, THTPA is ubiquitously expressed with probable post-transcriptional regulation. Much less is known about the recently discovered AThTP. In E. coli, AThTP is synthesized by a high molecular weight protein complex from ThDP and ATP or ADP in response to energy stress. A better understanding of these two thiamine derivatives will require the use of transgenic models.

Interactions between dietary carbohydrate and thiamine: implications on the growth performance and intestinal mitochondrial biogenesis and function of Megalobrama amblycephala

A12-week experiment was conducted to evaluate the influences of thiamine ongrowth performance, and intestinal mitochondrial biogenesis and function of Megalobramaamblycephala fed a high-carbohydrate (HC) diet. Fish (24·73 (sem 0·45) g) were randomly assigned to one of four diets: two carbohydrate (CHO) levels (30 and 45 %) and two thiamine levels (0 and 1·5 mg/kg). HC diets significantly decreased DGC, GRMBW, FIMBW, intestinal activities of amylase, lipase, Na+, K+-ATPase, CK, complexes I, III and IV, intestinal ML, number of mitochondrial per field, ΔΨm, the P-AMPK: T-AMPK ratio, PGC-1β protein expression as well as the transcriptions of AMPKα1, AMPKα2, PGC-1β, mitochondrial transcription factor A, Opa-1, ND-1 and COX-1 and 2, while the opposite was true for ATP, AMP and reactive oxygen species, and the transcriptions of dynamin-related protein-1, fission-1 and mitochondrial fission factor. Dietarythiamine concentrations significantly increased DGC, GRMBW, intestinal activities of amylase, Na+, K+-ATPase, CK, complexes I and IV, intestinal ML, number of mitochondrial per field, ΔΨm, the P-AMPK:T-AMPK ratio, PGC-1β protein expression as well as the transcriptions of AMPKα1, AMPKα2, PGC-1β, Opa-1, ND-1, COX-1 and 2, SGLT-1 and GLUT-2. Furthermore, a significant interaction between dietary CHO and thiamine was observed in DGC, GRMBW, intestinal activities of amylase, CK, complexes I and IV, ΔΨm, the AMP:ATP ratio, the P-AMPK:T-AMPK ratio, PGC-1β protein expression as well as the transcriptions of AMPKα1, AMPKα2, PGC-1β, Opa-1, COX-1 and 2, SGLT-1 and GLUT-2. Overall, thiamine supplementation improved growth performance, and intestinal mitochondrial biogenesis and function of M. amblycephala fed HC diets.

Wernicke's encephalopathy - from basic science to clinical practice. Part 1: Understanding the role of thiamine

Wernicke's encephalopathy (WE) is an acute neuropsychiatric state. Untreated, WE can lead to coma or death, or progress to Korsakoff syndrome (KS) - a dementia characterized by irreversible loss of anterograde memory. Thiamine (vitamin B1) deficiency lies at the heart of this condition. Yet, our understanding of thiamine regarding prophylaxis and treatment of WE remains limited. This may contribute to the current undertreatment of WE in clinical practice. The overall aim of this review is to identify the best strategies for prophylaxis and treatment of WE in regard to (a) dose of thiamine, (b) mode of administration, (c) timing of switch from one mode of administration to another, (d) duration of administration, and (e) use of magnesium along thiamine as an essential cofactor. Evidence from randomized controlled trials and other intervention studies is virtually absent. Therefore, we have to resort to basic science for proof of principle instead. Here, we present the first part of our clinical review, in which we explore the physiology of thiamine and the pathophysiology of thiamine deficiency. We first explore both of these in their historical context. We then review the pharmacodynamics and pharmacokinetics of thiamine, exploring the roles of the six currently known thiamine compounds, their transporters, and target enzymes. We also explore the significance of magnesium as a cofactor in thiamine-facilitated enzymatic reactions and thiamine transport. In the second (forthcoming) part of this review, we will use the findings of the current review to make evidence-based inferences about strategies for prophylaxis and treatment of WE.

Thiamine Deficiency Increases Intrinsic Excitability of Mouse Cerebellar Purkinje Cells

Thiamine deficiency is associated with cerebellar dysfunction; however, the consequences of thiamine deficiency on the electrophysiological properties of cerebellar Purkinje cells are poorly understood. Here, we evaluated these parameters in brain slices containing cerebellar vermis. Adult mice were maintained for 12-13 days on a thiamine-free diet coupled with daily injections of pyrithiamine, an inhibitor of thiamine phosphorylation. Morphological analysis revealed a 20% reduction in Purkinje cell and nuclear volume in thiamine-deficient animals compared to feeding-matched controls, with no reduction in cell count. Under whole-cell current clamp, thiamine-deficient Purkinje cells required significantly less current injection to fire an action potential. This reduction in rheobase was not due to a change in voltage threshold. Rather, thiamine-deficient neurons presented significantly higher input resistance specifically in the voltage range just below threshold, which increases their sensitivity to current at these critical membrane potentials. In addition, thiamine deficiency caused a significant decrease in the amplitude of the action potential afterhyperpolarization, broadened the action potential, and decreased the current threshold for depolarization block. When thiamine-deficient animals were allowed to recover for 1 week on a normal diet, rheobase, threshold, action potential half-width, and depolarization block threshold were no longer different from controls. We conclude that thiamine deficiency causes significant but reversible changes to the electrophysiology properties of Purkinje cells prior to pathological morphological alterations or cell loss. Thus, the data obtained in the present study indicate that increased excitability of Purkinje cells may represent a leading indicator of cerebellar dysfunction caused by lack of thiamine.

On the nature of thiamine triphosphate in Arabidopsis

Vitamin B1 is a family of molecules, the most renowned member of which is diphosphorylated thiamine (TDP)-a coenzyme vital for the activity of key enzymes of energy metabolism. Triphosphorylated thiamine derivatives also exist within this family, specifically thiamine triphosphate (TTP) and adenosine thiamine triphosphate (ATTP). They have been investigated primarily in mammalian cells and are thought to act as metabolic messengers but have not received much attention in plants. In this study, we set out to examine for the presence of these triphosphorylated thiamine derivatives in Arabidopsis. We could find TTP in Arabidopsis under standard growth conditions, but we could not detect ATTP. Interestingly, TTP is found primarily in shoot tissue. Drivers of TTP synthesis are light intensity, the proton motive force, as well as TDP content. In plants, TTP accumulates in the organellar powerhouses, the plastids, and mitochondria. Furthermore, in contrast to other B1 vitamers, there are strong oscillations in tissue levels of TTP levels over diel periods peaking early during the light period. The elevation of TTP levels during the day appears to be coupled to a photosynthesis-driven process. We propose that TTP may signify TDP sufficiency, particularly in the organellar powerhouses, and discuss our findings in relation to its role.

Role of the Synthetic B1 Vitamin Sulbutiamine on Health

Sulbutiamine is a thiamine derivative developed in Japan in the mid-60's as a beriberi treatment drug. Since then, different potential applications have been described. For instance, there is some evidence that sulbutiamine can have anti-fatigue, nootropic, and antioxidant effects, which led to its use as a sport supplement (although some authors argue it is actually a masking doping strategy). Moreover, this molecule has been proposed as a possible treatment for some microsporidial infections and even for certain types of cancer. Despite these potential effects, sulbutiamine is still a relatively unknown molecule, which justifies the present review, where we discuss its history and the existing literature on its health applications. We conclude that there is a great potential for sulbutiamine use, well beyond its first described function (to increase thiamine tissue concentration). Indeed, new mechanisms of action have been found, mainly associated with its derivatives. Nevertheless, and although the research on sulbutiamine started 50 years ago, only a limited number of studies were conducted during this time frame. As so, methodological concerns need to be addressed and new studies are necessary, especially randomized controlled trials. Only then will the full potential of this versatile molecule be identified.

Mechanisms of Non-coenzyme Action of Thiamine: Protein Targets and Medical Significance

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.

The prominent alteration in transcriptome and metabolome of Mycobacterium bovis BCG str. Tokyo 172 induced by vitamin B1

BACKGROUND

Vitamin B1 (VB1) is a crucial dietary nutrient and essential cofactor for several key enzymes in the regulation of cellular and metabolic processes, and more importantly in the activation of immune system. To date, the precise role of VB1 in Mycobacterium tuberculosis remains to be fully understood.

RESULTS

In this study, the transcriptional and metabolic profiles of VB1-treated Mycobacterium. bovis BCG were analyzed by RNA-sequencing and LC-MS (Liquid chromatography coupled to mass spectrometry). The selection of BCG strain was based on its common physiological features shared with M. tuberculosis. The results of cell growth assays demonstrated that VB1 inhibited the BCG growth rate in vitro. Transcriptomic analysis revealed that the expression levels of genes related to fatty acid metabolism, cholesterol metabolism, glycolipid catabolism, DNA replication, protein translation, cell division and cell wall formation were significantly downregulated in M. bovis BCG treated with VB1. In addition, the metabolomics LC-MS data indicated that most of the amino acids and adenosine diphosphate (ADP) were decreased in M. bovis BCG strain after VB1 treatment.

CONCLUSIONS

This study provides the molecular and metabolic bases to understand the impacts of VB1 on M.bovis BCG.

Pathway Editing Targets for Thiamine Biofortification in Rice Grains

Thiamine deficiency is common in populations consuming polished rice as a major source of carbohydrates. Thiamine is required to synthesize thiamine pyrophosphate (TPP), an essential cofactor of enzymes of central metabolism. Its biosynthesis pathway has been partially elucidated and the effect of overexpression of a few genes such as thi1 and thiC, on thiamine accumulation in rice has been reported. Based on current knowledge, this review focuses on the potential of gene editing in metabolic engineering of thiamine biosynthesis pathway to improve thiamine in rice grains. Candidate genes, suitable for modification of the structural part to evolve more efficient versions of enzymes in the pathway, are discussed. For example, adjacent cysteine residues may be introduced in the catalytic domain of thi4 to improve the turn over activity of thiamine thiazole synthase 2. Motif specific editing to modify promoter regulatory regions of genes is discussed to modulate gene expression. Editing cis acting regulatory elements in promoter region can shift the expression of transporters and thiamine binding proteins to endosperm. This can enhance dietary availability of thiamine from rice grains. Differential transcriptomics on rice varieties with contrasting grain thiamine and functional genomic studies will identify more strategic targets for editing in future. Developing functionally enhanced foods by biofortification is a sustainable approach to make diets wholesome.

Vitamin B1 diversity and characterization of biosynthesis genes in cassava

Vitamin B1, which consists of the vitamers thiamin and its phosphorylated derivatives, is an essential micronutrient for all living organisms because it is required as a metabolic cofactor in several enzymatic reactions. Genetic diversity of vitamin B1 biosynthesis and accumulation has not been investigated in major crop species other than rice and potato. We analyzed cassava germplasm for accumulation of B1 vitamers. Vitamin B1 content in leaves and roots of 41 cassava accessions showed significant variation between accessions. HPLC analyses of B1 vitamers revealed distinct profiles in cassava leaves and storage roots, with nearly equal relative levels of thiamin pyrophosphate and thiamin monophosphate in leaves, but mostly thiamin pyrophosphate in storage roots. Unusually, the cassava genome has two genes encoding the 4-amino-2-methyl-5-hydroxymethylpyrimidine phosphate synthase, THIC (MeTHIC1 and MeTHIC2), both of which carry a riboswitch in the 3'-UTR, as well as the adenylated thiazole synthase, THI1 (MeTHI1a and MeTHI1b). The THIC and THI1 genes are expressed at very low levels in storage roots compared with the accumulation of vitamin B1, indicating only limited biosynthesis de novo therein. In leaves, vitamin B1 content is negatively correlated with THIC and THI1 expression levels, suggesting post-transcriptional regulation of THIC by the riboswitch present in the 3'-UTR of the THIC mRNA and regulation of THI1 by promoter activity or alternative post-transcriptional mechanisms.

Impact of exercise and vitamin B1 intake on hippocampal brain-derived neurotrophic factor and spatial memory performance in a rat model of stress

Chronic stress affects brain areas involved in learning and emotional responses through modulation of neurotropic factors or neurotransmitters. Therefore, we investigated the role of exercise and thiamine supplementation on spatial memory and on brain-derived neurotrophic factor (BDNF) and acetylcholine (Ach) content in the hippocampus of the stressed animals. Male Wistar rats were randomly assigned to 4 groups (8 rats/group): control group; stress group; swimming and stress group; and thiamine and stress group. All animals were assessed by a T maze for spatial memory or open field test for locomotion and anxiety. BDNF and Ach were estimated in the hippocampus. Chronic immobilization stress resulted in a significant decrease in BDNF and Ach levels in the hippocampus and impairment in spatial memory functions and decreased basal activity. However, either swimming training or thiamine intake for 30 d was proved to induce a significant increase both in BDNF and Ach in conjunction with improved performance in the T maze, marked anxiolytic effect and enhanced ambulation in the open field test, as compared to the stress group. Interestingly, swimming-exercised rats showed significantly higher levels of BDNF versus thiamine-receiving rats, while thiamine-receiving rats showed higher locomotor activity and less freezing behavior in the open field test compared to the swimming group. It was concluded that decreased BDNF and Ach after stress exposure could be a mechanism for the deleterious actions of stress on memory function; swimming exercise or vitamin B1 supplementation for 30 d was a protective tool to improve coping with chronic stress by modulating BDNF and Ach content along with enhancement of memory functions and motor activities.

Molecular mechanisms of the non-coenzyme action of thiamin in brain: biochemical, structural and pathway analysis

Thiamin (vitamin B1) is a pharmacological agent boosting central metabolism through the action of the coenzyme thiamin diphosphate (ThDP). However, positive effects, including improved cognition, of high thiamin doses in neurodegeneration may be observed without increased ThDP or ThDP-dependent enzymes in brain. Here, we determine protein partners and metabolic pathways where thiamin acts beyond its coenzyme role. Malate dehydrogenase, glutamate dehydrogenase and pyridoxal kinase were identified as abundant proteins binding to thiamin- or thiazolium-modified sorbents. Kinetic studies, supported by structural analysis, revealed allosteric regulation of these proteins by thiamin and/or its derivatives. Thiamin triphosphate and adenylated thiamin triphosphate activate glutamate dehydrogenase. Thiamin and ThDP regulate malate dehydrogenase isoforms and pyridoxal kinase. Thiamin regulation of enzymes related to malate-aspartate shuttle may impact on malate/citrate exchange, responsible for exporting acetyl residues from mitochondria. Indeed, bioinformatic analyses found an association between thiamin- and thiazolium-binding proteins and the term acetylation. Our interdisciplinary study shows that thiamin is not only a coenzyme for acetyl-CoA production, but also an allosteric regulator of acetyl-CoA metabolism including regulatory acetylation of proteins and acetylcholine biosynthesis. Moreover, thiamin action in neurodegeneration may also involve neurodegeneration-related 14-3-3, DJ-1 and β-amyloid precursor proteins identified among the thiamin- and/or thiazolium-binding proteins.

Thiamine triphosphate: a ubiquitous molecule in search of a physiological role

Thiamine triphosphate (ThTP) was discovered over 60 years ago and it was long thought to be a specifically neuroactive compound. Its presence in most cell types, from bacteria to mammals, would suggest a more general role but this remains undefined. In contrast to thiamine diphosphate (ThDP), ThTP is not a coenzyme. In E. coli cells, ThTP is transiently produced in response to amino acid starvation, while in mammalian cells, it is constitutively produced at a low rate. Though it was long thought that ThTP was synthesized by a ThDP:ATP phosphotransferase, more recent studies indicate that it can be synthesized by two different enzymes: (1) adenylate kinase 1 in the cytosol and (2) FoF1-ATP synthase in brain mitochondria. Both mechanisms are conserved from bacteria to mammals. Thus ThTP synthesis does not seem to require a specific enzyme. In contrast, its hydrolysis is catalyzed, at least in mammalian tissues, by a very specific cytosolic thiamine triphosphatase (ThTPase), controlling the steady-state cellular concentration of ThTP. In some tissues where adenylate kinase activity is high and ThTPase is absent, ThTP accumulates, reaching ≥ 70% of total thiamine, with no obvious physiological consequences. In some animal tissues, ThTP was able to phosphorylate proteins, and activate a high-conductance anion channel in vitro. These observations raise the possibility that ThTP is part of a still uncharacterized cellular signaling pathway. On the other hand, its synthesis by a chemiosmotic mechanism in mitochondria and respiring bacteria might suggest a role in cellular energetics.

Metabolite damage and its repair or pre-emption

It is increasingly evident that metabolites suffer various kinds of damage, that such damage happens in all organisms and that cells have dedicated systems for damage repair and containment. First, chemical biology is demonstrating that diverse metabolites are damaged by side reactions of 'promiscuous' enzymes or by spontaneous chemical reactions, that the products are useless or toxic and that the unchecked buildup of these products can be devastating. Second, genetic and genomic evidence from prokaryotes and eukaryotes is implicating a network of new, conserved enzymes that repair damaged metabolites or somehow pre-empt damage. Metabolite (that is, small-molecule) repair is analogous to macromolecule (DNA and protein) repair and seems from comparative genomic evidence to be equally widespread. Comparative genomics also implies that metabolite repair could be the function of many conserved protein families lacking known activities. How--and how well--cells deal with metabolite damage affects fields ranging from medical genetics to metabolic engineering.

An alternative role of FoF1-ATP synthase in Escherichia coli: synthesis of thiamine triphosphate

In E. coli, thiamine triphosphate (ThTP), a putative signaling molecule, transiently accumulates in response to amino acid starvation. This accumulation requires the presence of an energy substrate yielding pyruvate. Here we show that in intact bacteria ThTP is synthesized from free thiamine diphosphate (ThDP) and P_i, the reaction being energized by the proton-motive force (Δp) generated by the respiratory chain. ThTP production is suppressed in strains carrying mutations in F₁ or a deletion of the atp operon. Transformation with a plasmid encoding the whole atp operon fully restored ThTP production, highlighting the requirement for F_oF₁-ATP synthase in ThTP synthesis. Our results show that, under specific conditions of nutritional downshift, F_oF₁-ATP synthase catalyzes the synthesis of ThTP, rather than ATP, through a highly regulated process requiring pyruvate oxidation. Moreover, this chemiosmotic mechanism for ThTP production is conserved from E. coli to mammalian brain mitochondria.

Examining strategies to facilitate vitamin B1 biofortification of plants by genetic engineering

Thiamin (vitamin B1) is made by plants and microorganisms but is an essential micronutrient in the human diet. All organisms require it as a cofactor in its form as thiamin pyrophosphate (TPP) for the activity of key enzymes of central metabolism. In humans, deficiency is widespread particularly in populations where polished rice is a major component of the diet. Considerable progress has been made on the elucidation of the biosynthesis pathway within the last few years enabling concrete strategies for biofortification purposes to be devised, with a particular focus here on genetic engineering. Furthermore, the vitamin has been shown to play a role in both abiotic and biotic stress responses. The precursors for de novo biosynthesis of thiamin differ between microorganisms and plants. Bacteria use intermediates derived from purine and isoprenoid biosynthesis, whereas the pathway in yeast involves the use of compounds from the vitamin B3 and B6 groups. Plants on the other hand use a combination of the bacterial and yeast pathways and there is subcellular partitioning of the biosynthesis steps. Specifically, thiamin biosynthesis occurs in the chloroplast of plants through the separate formation of the pyrimidine and thiazole moieties, which are then coupled to form thiamin monophosphate (TMP). Phosphorylation of thiamin to form TPP occurs in the cytosol. Therefore, thiamin (or TMP) must be exported from the chloroplast to the cytosol for the latter step to be executed. The regulation of biosynthesis is mediated through riboswitches, where binding of the product TPP to the pre-mRNA of a biosynthetic gene modulates expression. Here we examine and hypothesize on genetic engineering approaches attempting to increase the thiamin content employing knowledge gained with the model plant Arabidopsis thaliana. We will discuss the regulatory steps that need to be taken into consideration and can be used a prerequisite for devising such strategies in crop plants.

Overexpression of CD39 in mouse airways promotes bacteria-induced inflammation

In airways, the ecto-nucleoside triphosphate diphosphohydrolase CD39 plays a central role in the regulation of physiological mucosal nucleotide concentrations and likely contributes to the control of inflammation because accelerated ATP metabolism occurs in chronic inflammatory lung diseases. We sought to determine whether constant elevated CD39 activity in lung epithelia is sufficient to cause inflammation and whether this affects the response to acute LPS or Pseudomonas aeruginosa exposure. We generated transgenic mice overexpressing human CD39 under the control of the airway-specific Clara cell 10-kDa protein gene promoter. Transgenic mice did not develop any spontaneous lung inflammation. However, intratracheal instillation of LPS resulted in accelerated recruitment of neutrophils to the airways of transgenic mice. Macrophage clearance was delayed, and the amounts of CD8(+) T and B cells were augmented. Increased levels of keratinocyte chemoattractant, IL-6, and RANTES were produced in transgenic lungs. Similarly, higher numbers of neutrophils and macrophages were found in the lungs of transgenic mice infected with P. aeruginosa, which correlated with improved bacteria clearance. The transgenic phenotype was partially and differentially restored by coinstillation of P2X(1) or P2X(7) receptor antagonists or of caffeine with LPS. Thus, a chronic increase of epithelial CD39 expression and activity promotes airway inflammation in response to bacterial challenge by enhancing P1 and P2 receptor activation.

Thiamine deficiency related microstructural brain changes in acute and acute-on-chronic liver failure of non-alcoholic etiology

BACKGROUND & AIMS

Mammillary body atrophy in alcoholic liver disease usually indicates thiamine deficiency. The purpose of this study was to explore the relationship among blood thiamine, mammillary bodies, major fiber bundle fractional anisotropy, and volume changes with diffusion tensor tractography in patients with acute and acute-on-chronic liver failure of non-alcoholic etiology.

METHODS

Blood thiamine, mammillary bodies, fiber bundle fractional anisotropy and volume of major fiber tracts were quantified from acute and acute-on-chronic liver failure patients and compared with healthy controls. In 7 acute liver failure patients, follow-up study was done after clinical recovery at 5 weeks.

RESULTS

Blood thiamine, mammillary bodies and fornix volume, and fornix fiber bundle fractional anisotropy were significantly decreased as compared to controls. Blood thiamine showed significant positive correlation with mammillary bodies' volume only. On follow-up study, acute liver failure patients showed significant reversibility only in blood thiamine level and mammillary bodies' volume.

CONCLUSIONS

Mammillary bodies' volume changes are primarily a consequence of thiamine deficiency, which may secondarily result in microstructural changes in the fornix. These observable changes are known to be specific and may be reversible with restoration of blood thiamine level. These imaging changes may be used as imaging biomarker of thiamine deficiency in these patients in future.

Dysautonomia in autism spectrum disorder: case reports of a family with review of the literature

Case histories of a mother and her two children are reported. The mother was a recovered alcoholic. She and her two children, both of whom had symptoms that are typical of autistic spectrum disorder, had dysautonomia. All had intermittently abnormal erythrocyte transketolase studies indicating abnormal thiamine pyrophosphate homeostasis. Both children had unusual concentrations of urinary arsenic. All had symptomatic improvement with diet restriction and supplementary vitamin therapy but quickly relapsed after ingestion of sugar, milk, or wheat. The stress of a heavy metal burden, superimposed on existing genetic or epigenetic risk factors, may be important in the etiology of autism spectrum disorder when in combination. Dysautonomia has been associated with several diseases, including autism, without a common etiology. It is hypothesized that oxidative stress results in loss of cellular energy and causes retardation of hard wiring of the brain in infancy, affecting limbic system control of the autonomic nervous system.

Thiamine status in humans and content of phosphorylated thiamine derivatives in biopsies and cultured cells

Background

Thiamine (vitamin B1) is an essential molecule for all life forms because thiamine diphosphate (ThDP) is an indispensable cofactor for oxidative energy metabolism. The less abundant thiamine monophosphate (ThMP), thiamine triphosphate (ThTP) and adenosine thiamine triphosphate (AThTP), present in many organisms, may have still unidentified physiological functions. Diseases linked to thiamine deficiency (polyneuritis, Wernicke-Korsakoff syndrome) remain frequent among alcohol abusers and other risk populations. This is the first comprehensive study on the distribution of thiamine derivatives in human biopsies, body fluids and cell lines.

Methodology and Principal Findings

Thiamine derivatives were determined by HPLC. In human tissues, the total thiamine content is lower than in other animal species. ThDP is the major thiamine compound and tissue levels decrease at high age. In semen, ThDP content correlates with the concentration of spermatozoa but not with their motility. The proportion of ThTP is higher in humans than in rodents, probably because of a lower 25-kDa ThTPase activity. The expression and activity of this enzyme seems to correlate with the degree of cell differentiation. ThTP was present in nearly all brain and muscle samples and in ∼60% of other tissue samples, in particular fetal tissue and cultured cells. A low ([ThTP]+[ThMP])/([Thiamine]+[ThMP]) ratio was found in cardiovascular tissues of patients with cardiac insufficiency. AThTP was detected only sporadically in adult tissues but was found more consistently in fetal tissues and cell lines.

Conclusions and Significance

The high sensitivity of humans to thiamine deficiency is probably linked to low circulating thiamine concentrations and low ThDP tissue contents. ThTP levels are relatively high in many human tissues, as a result of low expression of the 25-kDa ThTPase. Another novel finding is the presence of ThTP and AThTP in poorly differentiated fast-growing cells, suggesting a hitherto unsuspected link between these compounds and cell division or differentiation.

Thiamine biosynthesis can be used to dissect metabolic integration

The emergence of systems biology has re-emphasized the advantages of understanding biological processes with a global perspective. One biological process amenable to global approaches is microbial metabolism. This review describes a model system that contributes to the goals of systems biology by experimentally defining metabolic integration found in a bacterial cell and thus providing data needed for implementation and interpretation of systems approaches. We have taken a largely unbiased in vivo approach centered on thiamine biosynthesis to identify new metabolic components and connections, and to explore uncharacterized paradigms of the integration between them. This article summarizes recent results from this approach that include the identification of the function of unknown genes, connections between cofactors biosynthesis and thiamine biosynthesis, and how metabolites from one biosynthetic pathway can be used in thiamine biosynthesis.

Adenosine thiamine triphosphate accumulates in Escherichia coli cells in response to specific conditions of metabolic stress

Background

E. coli cells are rich in thiamine, most of it in the form of the cofactor thiamine diphosphate (ThDP). Free ThDP is the precursor for two triphosphorylated derivatives, thiamine triphosphate (ThTP) and the newly discovered adenosine thiamine triphosphate (AThTP). While, ThTP accumulation requires oxidation of a carbon source, AThTP slowly accumulates in response to carbon starvation, reaching ~15% of total thiamine. Here, we address the question whether AThTP accumulation in E. coli is triggered by the absence of a carbon source in the medium, the resulting drop in energy charge or other forms of metabolic stress.

Results

In minimal M9 medium, E. coli cells produce AThTP not only when energy substrates are lacking but also when their metabolization is inhibited. Thus AThTP accumulates in the presence of glucose, when glycolysis is blocked by iodoacetate, or in the presence lactate, when respiration is blocked by cyanide or anoxia. In both cases, ATP synthesis is impaired, but AThTP accumulation does not appear to be a direct consequence of reduced ATP levels. Indeed, in the CV2 E. coli strain (containing a thermolabile adenylate kinase), the ATP content is very low at 37°C, even in the presence of metabolizable substrates (glucose or lactate) and under these conditions, the cells produce ThTP but not AThTP. Furthermore, we show that ThTP inhibits AThTP accumulation. Therefore, we conclude that a low energy charge is not sufficient to trigger AThTP accumulation and the latter can only accumulate under conditions where no ThTP is synthesized. We further show that AThTP production can also be induced by the uncoupler CCCP but, unexpectedly, this requires the presence of pyruvate or a substrate yielding pyruvate (such a D-glucose or L-lactate). Under the conditions described, AThTP production is not different when RelA or SpoT mutants are used.

Conclusions

In E. coli, AThTP accumulates in response to two different conditions of metabolic stress: lack of energy substrates (or inhibition of their metabolization) and uncoupled pyruvate oxidation. Both conditions prevent bacterial growth. There is no obvious link with the stringent response or catabolite repression.