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PubMed1985

[Biosynthesis of thiamine triphosphate and identification of thiamine diphosphate-binding proteins in the rat liver hyaloplasm].

The nature of the thiamine diphosphate binding proteins from rat liver hyaloplasm was studied. When [14C]thiamine was used as a marker, a [14C]thiamine diphosphate-containing electrophoretically homogeneous protein preparation was isolated from the liver soluble fraction and classified as transketolase. No other non-enzymatic proteins which bind thiamine diphosphate and can serve as substrates in the reaction of thiamine diphosphate synthesis in the hyaloplasm were found. It was shown that the phosphate group is transferred by rat liver thiamine diphosphate kinase to the free (but not to the protein-bound) thiamine diphosphate as it was believed earlier.

Animals↗

PubMedDate not supplied

[Metabolism and toxicity of various xenobiotics in vitamin B1 deficiency and after administration of thiamine and thiamine diphosphate].

Metabolism of aminopyrine, sodium benzoate and toxicity of cyclophosphamide were studied in 185 male rats under conditions of various content of vitamin B1 in the animals. Deficiency of thiamin led to an increase in excretion of 4-aminoantipyrine and especially of its acetylated derivative. After administration of thiamin metabolism of aminopyrine was not distinctly altered, while thiamin diphosphate inhibited the drug biotransformation. In deficiency of vitamin B1 transformation of benzoic acid into hippuric acid was inhibited but formation of glucuronides was elevated. Administration of thiamin or thiamin diphosphate stimulated the benzoic acid conjugation and inhibited the glucuronides formation. Deficiency of vitamin B1 accelerated the cyclophosphamide toxicity. Preadministration of thiamin and especially of thiamin diphosphate decreased the toxic effect of cyclophosphamide.

Aminopyrine↗

PubMed1985

Activities of thiamine-dependent enzymes in two experimental models of thiamine-deficiency encephalopathy: 1. The pyruvate dehydrogenase complex.

Chronic thiamine deprivation in the rat leads to selective neuropathological damage in brainstem structures whereas treatment with the central thiamine antagonist, pyrithiamine, results in more widespread damage. In order to further elucidate the neurochemical mechanisms responsible for this selective damage, the thiamine-dependent enzyme complex pyruvate dehydrogenase (PDHC) was measured in 10 brain structures in the rat during progression of thiamine deficiency produced by chronic deprivation or by pyrithiamine treatment. Feeding of a thiamine-deficient diet to adult rats resulted in 5-7 weeks in ataxia and loss of righting reflex accompanied by decreased blood transketolase activities. PDHC activities were selectively decreased by 15-30% in midbrain and pons (lateral vestibular nucleus). Thiamine treatment of symptomatic rats led to reversal of neurological signs and to concomitant reductions of the cerebral PDHC abnormalities. Daily pyrithiamine treatment led within 3 weeks to loss of righting reflex and convulsions and to decreased blood transketolase of a comparable magnitude to that observed in chronic thiamine-deprived rats. No significant regional alterations of PDHC, however, were observed in pyrithiamine-treated rats.

Animals↗

PubMed1994

Thiamin status of the elderly: dietary intake and thiamin pyrophosphate response.

OBJECTIVE: The present study was undertaken to investigate the relationship between thiamin intake and its biochemical status in 60 free-living (30 male, 30 female) elderly subjects (> or = 65 years). DESIGN: Dietary intake was estimated using a 3-nonconsecutive-day food record. Biochemical status was assessed by measuring the stimulating effect of thiamin pyrophosphate (TPP) on transketolase activity (TPP effect) in hemolyzed erythrocytes, which is a functional test indicative of metabolic availability of thiamin. RESULTS: Average daily thiamin intake was above the recommended requirement (> 0.4 mg/1000 Kcal) for each gender; however, almost half of the total study population had TPP effect > 14%, suggesting thiamin deficiency. There was no correlation between thiamin intake and TPP effect. CONCLUSION: These findings raise questions about the reliability of dietary intake in assessing metabolic availability of thiamin in the elderly.

Aged↗

PubMed1991

Thiamin status of incarcerated and nonincarcerated adolescent males: dietary intake and thiamin pyrophosphate response.

We measured thiamin status in 137 incarcerated and 42 nonincarcerated adolescent males by use of both dietary intake data and a standard biochemical assay, thiamin pyrophosphate (TPP) response. Average thiamin intake of the total group was greater than 120% of the age-specific recommended dietary allowance (RDA). Ninety-two percent of incarcerated subjects and 93% of nonincarcerated subjects were consuming greater than or equal to 70% of RDA. Although average daily thiamin intake of nonincarcerated subjects was significantly higher than that of incarcerated subjects, both groups appeared to be at minimal risk for marginal thiamin status. Comparison of TPP response values indicated that there was no significant difference between groups. However, approximately 24% of the total population appeared to have less than adequate RBC thiamin on the basis of current standards for TPP response. Neither dietary intake nor reported previous alcohol intake was correlated with TPP response. These discrepant findings raise questions about the usefulness of the TPP response as the sole indicator of marginal thiamin status.

Adolescent↗

PubMed1991

Influence of thiamin supplementation on the health and general well-being of an elderly Irish population with marginal thiamin deficiency.

The effect of thiamin supplementation on the health and general well-being of 80 randomly selected healthy elderly Irish women, from a population with marginal thiamin deficiency, was studied. Key variables affecting thiamin status were controlled. Weekly dietary intakes, subjective feelings, and activity assessments were measured during a 4-week baseline and 6-week double blind treatment period. Clinical assessments were performed during the last week of each period. For treatment, subjects were randomly assigned to either thiamin (10 mg daily) or placebo groups. Compared to baseline and placebo supplemented values, thiamin-supplemented women experienced significantly increased appetite, energy intake, body weight and general well-being, and decreased fatigue. Thiamin supplementation also tended to reduce daytime sleep time, improve sleep patterns, and increase activity. These data suggest that evaluation of thiamin status is indicated when nonspecific conditions such as anorexia, weight loss, fatigue, depression, and sleep disorders are present in elderly persons.

Activities of Daily Living↗

PubMed1988

Intestinal transport of thiamin and thiamin monophosphate in rat everted jejunal sacs: a comparative study using some potential inhibitors.

Rat everted jejunal sacs were incubated for 15 and 30 min at 37 degrees C in oxygenated Krebs-Henseleit buffer, pH 7.4, containing 0.2 microM [3H]-thiamin (3H-T) or [3H]-thiamin monophosphate (3H-TMP) with and without 10 mM 1-phenylalanine (PAL) or 2.5 mM levamisole (LEV). The concentrations of 3H-T and its phosphoesters in sac wall and serosal fluid were determined by a radiometric method after electrophoretic separation. In separate experiments, thiamin pyrophosphokinase (TPKase) and thiamin pyrophosphatase (TPPase) activities were determined in mucosal scrapings, with and without PAL or LEV, by using a radiometric and a colorimetric method, respectively. 3H-TMP was transported partly unchanged by an active mechanism similarly to 3H-T, but less efficiently. During transport, 3H-TMP was also enzymatically transformed to thiamin (T) and thiamin pyrophosphate, which accumulated in the tissue. In the serosal fluid, the concentration of 3H-TMP exceeded that of 3H-T. Presence of PAL or LEV with 3H-T or 3H-TMP in the incubation medium reduced the serosal transport and the tissue content of T compounds. LEV caused a dose-dependent inhibition of TPKase without affecting TPPase, whereas PAL inhibited both activities to about the same extent. These results indicate that the transport of TMP involves a number of different processes similar to those responsible for T transport. The effects of PAL and LEV underline the importance of phosphorylation-dephosphorylation coupling.

Animals↗

PubMed1978

Thiamine whole blood pharmackinetics in rats using both a specific S-thiamine liquid scintillation assay and the thiochrome fluorescence assay.

The study of factors altering the CNS and GI absorption of thiamine in rats required the development of a specific assay for thiamine from 100-microliter samples of blood and plasma and small quantities of tissue. The specific thiochrome fluorescence assay for thiamine was modified to handle microsamples and to use S-thiamine. This sensitive and specific radioassay using S-thiamine gave pharmacokinetic parameters for 4-mg/kg iv doses of thiamine in rats equivalent to those using the less sensitive thiochrome fluorescence assay. The new assay, because of its lower limit of detection, allowed the study of the time profile of thiamine after a 1-mg/kg iv dose in rats. Such a time profile could not have been followed using the standard thiochrome fluorescence assay.

Animals↗

PubMed1991

Uptake of thiamine by Schizosaccharomyces pombe and its effect as a transcriptional regulator of thiamine-sensitive genes.

Wild-type fission yeast, growing in minimal medium, actively synthesizes thiamine and maintains an internal concentration which we have measured to be around 10 pmoles/10(7) cells. If thiamine is added to such cultures it is rapidly sequestered by the cell, and if added in excess (20 microM) the internal concentration of thiamine rises almost 1000-fold to a maximum of around 9000 pmoles/10(7) cells before the transport mechanism is shut down. The kinetics of decay of intracellular thiamine to the basal level are consistent with simple dilution as the cell mass doubles. In parallel with this analysis, we have studied the transcriptional activity of the thiamine-sensitive gene nmt1 as a function of intracellular thiamine concentration. Transcription of this gene is rapidly repressed as the internal thiamine concentration rises and is only reactivated as the concentration falls to below about 50 pmoles/10(7) cells.

Culture Media↗

PubMed1987

Activities of thiamine-dependent enzymes in two experimental models of thiamine deficiency encephalopathy: 3. Transketolase.

Chronic thiamine deprivation in the rat leads to ataxia, loss of righting reflex and neuropathological damage to lateral vestibular nucleus. Before onset of neurological symptoms, transketolase (TK) activities were found to be selectively reduced by 25% in lateral vestibular nucleus and surrounding pons. Further progression of thiamine deprivation resulted in a generalized reduction in TK activity. Measurement of enzyme activity in the presence of added TPP cofactor in vitro did not lead to normalisation of enzyme activities suggesting loss of apoenzyme. Administration of thiamine to symptomatic thiamine-deprived rats resulted in reversal of neurological symptoms and to normalisation of defective TK activities in less vulnerable structures such as cerebral cortex, striatum and hippocampus; reduction of TK activity, however, persisted in brainstem and cerebellar regions. Pyrithiamine treatment results, within 3 weeks, in loss of righting reflex, convulsions and more widespread neuropathological damage compared to that observed following thiamine deprivation. TK activity was found to be significantly decreased before the onset of neurological symptoms in all brain regions and appearance of symptoms was accompanied by more severe reductions of TK. In contrast to chronic thiamine deprivation, TK activities following pyrithiamine treatment were: equally reduced in magnitude in vulnerable and non-vulnerable brain structures, unchanged following reversal of neurological abnormalities by thiamine administration.

Animals↗

PubMed1987

Nervous tissue thiamine metabolism in vivo. III. Influence of ethanol intake on the dynamics of thiamine and its phosphoesters in different brain regions and sciatic nerve of the rat.

The effects of chronic ethanol administration on different steps of the metabolism of thiamine (T), thiamine mono- (TMP) and thiamine pyrophosphate (TPP) in the cerebellum, brainstem, cerebral cortex and sciatic nerve were evaluated in vivo. The radioactivity of T and its phosphoesters was determined in plasma and in the selected nervous structures under steady-state conditions and at fixed time intervals (0.5-192 h) after an i.p. injection of [14C]T (30 micrograms: 1.25 microCi) to rats chronically (35 days) ethanol-treated (daily dose of 4.7 g X kg-1 b.wt. by gastric gavage) and pair-fed controls similarly treated with a sucrose solution isoenergetic with ethanol. All rats were given a nutritionally adequate diet supplying an excess of thiamine, which produced a virtually steady content of thiamine compounds in the tissues. By using a compartmental mathematical model, fractional rate constants, turnover rates and turnover times were calculated. Ethanol caused a reduction of the rate of thiamine compound enzymatic transformations (T phosphorylation to TPP, TPP dephosphorylation to TMP and TMP to T), and a facilitation of the regional uptake of T and TMP, associated to a less relevant influence on their release. Isoenergetic sucrose prevailingly caused an increased rate of thiamine metabolic steps (except phosphorylation in the brainstem and cerebral cortex), with negligible modifications of T and TMP uptake and release. Thus the changes induced by ethanol were virtually opposite to those caused by sucrose.

Animals↗

PubMed1992

Mechanism of ligand-protein interaction in plant seed thiamin-binding proteins. Probing the binding site of protein isolated from buckwheat seeds with a series of thiamin-related compounds.

Affinities of 14 thiamin derivatives or antagonists to a thiamin-binding protein isolated from buckwheat seeds were determined. A competitive displacement of radiolabeled thiamin by unlabeled ligand was analysed by a computerized model-fitting procedure. The dissociation constant of the thiamin-protein complex was 0.93 microM. Most modifications in ligand chemical structure weakened the ligand-protein interaction. A model of the thiamin-binding site is suggested. The hydroxyethyl-chain of thiamin while protein-bound appears to be excluded from the binding region. A positively charged quaternary nitrogen atom of the thiazolium ring probably interacts with some negative group(s) of protein. The rest of the thiazolium ring as well as the amino group of the pyrimidine fragment serve as additional anchors. The three structural features of the thiamin molecule accounting for binding contribute equally to overall binding energy by about 11-12 kJ/mol.

Binding Sites↗

PubMed1993

Pharmacokinetics of thiamin after oral administration of thiamin tetrahydrofurfuryl disulfide to humans.

We performed a pharmacokinetic analysis of the blood thiamin profile after oral administration of thiamin tetrahydrofurfuryl disulfide (TTFD) to healthy adults. To distinguish between thiamin derived from TTFD ingestion and that from previous dietary intake, the baseline thiamin level was subtracted from the apparent blood vitamin levels measured after administration. Following administration of 100 mg of TTFD, the peak blood thiamin level was almost 10 times the baseline level and the blood thiamin profile could be simulated by a two-compartment model to obtain reasonable pharmacokinetic parameters. When the blood thiamin profile for a 10-mg dose of TTFD was estimated using scaled-down pharmacokinetic parameters derived at the 100-mg dose level, a reasonable fit for the raw data obtained at 10-mg dose was obtained. Therefore, the parameters derived from the data at a dose of 100 mg appeared to be reliable. Since even 180 mg of TTFD is completely absorbed and the absorption ratio is independent of the dose, it can be concluded that gastrointestinal absorption of TTFD is good within the dose range.

Administration, Oral↗

PubMedDate not supplied

[Thiamine triphosphate content of the liver of albino rats with different levels of thiamine].

Content of thiamine triphosphate (TTP) was studied in rat liver tissue under conditions of normal state, thiamine deficiency and after loading with thiamine. The concentration of TTP in hepatocytes of control animals was found to be 3.2-3.6 micrograms/g, corresponding to 40% of the total thiamine pool in the cells. The TTP appears to serve as a reserve of vitamin B1 deposited in mitochondria of the cells in which the biosynthesis of thiamine pyrophosphate of their own did not take place. Administration of thiamine did not induce the TTP overproduction in hepatocytes; the content of TTP was maintained in the mitochondria of the hepatocytes at the constant level.

Animals↗

PubMed1988

A th-1 Mutant of Arabidopsis thaliana Is Defective for a Thiamin-Phosphate-Synthesizing Enzyme: Thiamin Phosphate Pyrophosphorylase.

We have examined the activity of the thiamin phosphate pyrophosphorylase in Arabidopsis thaliana wild type and in a mutant (th-1) which requires exogenous thiamin for growth. Mutant and wild-type plants grown in 1 x 10(-7) molar thiamin were used for the examination of the production of thiamin and thiamin monophosphate (TMP) using 4-methyl-5-hydroxyethylthiazole phosphate and 2-methyl-4-amino-5-hydroxymethylpyrimidine pyrophosphate as substrates. While the wild-type strain formed both thiamin and TMP, the th-1 mutant did not. When TMP was added to the extracts, the th-1 mutant, as well as wild type, produced thiamin. Accordingly, it was concluded that the th-1 mutant was defective in the activity of TMP pyrophosphorylase. Some of the characteristics of the enzyme from the wild-type plant were examined. The optimum temperature for the reaction is 45 degrees C, and the K(m) values for the substrates are 2.7 x 10(-6) molar for 4-methyl-5-hydroxyethylthiazole phosphate and 1.8 x 10(-6) molar for 2-methyl-4-amino-5-hydroxymethylpyrimidine pyrophosphate.

Journal Article↗

PubMed1991

In thiamine deficiency, activation of erythrocyte transketolase by thiamine in vivo exceeds activation by cofactor in vitro.

In 60 thiamine deficient patients, the mean erythrocyte transketolase activity after activation by thiamine diphosphate cofactor in vitro, representing the apparent sum of holoenzyme and apoenzyme activities, was 0.609 (SD 0.166) U/g Hb before thiamine therapy and rose to 0.772 (SD 0.152) U/g Hb immediately after the administration of thiamine to the patients. The difference between these values, 0.163 (SD 0.130) U/g, is the mean activity of transketolase protein which can be activated by thiamine in vivo but not by thiamine diphosphate in vitro. This difference correlated with low initial erythrocyte transketolase activity in these patients, but not with their alcohol intake, liver function or diagnoses.

Alcoholism↗

PubMed1995

Thiamine deficiency--induced partial necrosis and mitochondrial uncoupling in neuroblastoma cells are rapidly reversed by addition of thiamine.

Culture of neuroblastoma cells in a medium of low-thiamine concentration (6 nM) and in the presence of the transport inhibitor amprolium leads to the appearance of overt signs of necrosis; i.e., the chromatin condenses in dark patches, the oxygen consumption decreases, mitochondria are uncoupled, and their cristae are disorganized. Glutamate formed from glutamine is no longer oxidized and accumulates, suggesting that the thiamine diphosphate-dependent alpha-ketoglutarate dehydrogenase activity is impaired. When thiamine (10 microM) is added to the cells, the O2 consumption increases, respiratory control is restored, and normal cell and mitochondrial morphology is recovered within 1 h. Succinate, which is oxidized via the thiamine diphosphate-independent succinate dehydrogenase, is also able to restore a normal O2 consumption (with respiratory control) in digitonin-permeabilized thiamine-deficient cells. Our results therefore suggest that the slowing of the citric acid cycle is the main cause of the biochemical lesion induced by thiamine deficiency as observed in Wernicke's encephalopathy.

Amprolium↗

PubMed1977

Milk composition and thiamine transfer in thiamine deficient rats.

Milk composition was determined in rats maintained on a thiamine deficient diet from the 10th day of pregnancy. Percentage of thiamine transfer was reduced after the 14th postpartum day. Milk composition of thiamine deficient dams 18 days postpartum revealed similar protein and amino acid levels in both thiamine deficient and control rats, whereas milk protein fractions showed some differences. Milk lactose levels were depressed in thiamine deficient rats. Fatty acid content was higher in milk of thiamine deficient than in pair fed and adlibitum controls. The supply of a larger proportion of calories from lipids rather than carbohydrates may have clinical significance.

Amino Acids↗