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Distribution of thiamine, thiamine phosphates, and thiamine metabolizing enzymes in neuronal and glial cell enriched fractions of rat brain.
Full text linkThe distribution of thiamine, thiamine phosphoesters, and the thiamine pyrophosphate synthetizing [thiamine-pyrophosphokinase (TPKase)] as well as hydrolyzing [thiamine pyrophosphatase (TPPase) and thiamine monophosphatase (TMPase)] enzymes was determined in neuronal and glial enriched fractions prepared from rat brain. Nucleoside diphosphatases [inosine diphosphatase (IDPase) and uridine diphosphatase (UDPase)] and nucleoside monophosphatases [uridine monophosphatase (UMPase) and inosine monophosphatase (IMPase)] were also determined. Thiamine and thiamine mono- and pyrophosphate were present in neuronal enriched fractions at concentrations 2.8, 3.6, and 4.6 times higher than in glial fractions. TMPase was found only in glial enriched fractions, whereas the levels of TPKase, UMPase, IMPase, IDPase, UDPase, and TPPase were 2.0-, 2.2-, 1.3-, 2.8-, 3.7-, and 20.8-fold higher in neuronal than in glial fractions
Three thiamine analogues differently alter thiamine transport and metabolism in nervous tissues: an in vivo kinetic study using rats
No full textEffects of acute and chronic ethanol administration on thiamine metabolizing enzymes in some brain areas and in other organs of the rat.
No full textThe effect of ethanol (4.7 g/kg body wt intragastrically as a single dose or once daily for 35 days) on the levels of the thiamine metabolizing enzymes (thiamine pyrophosphokinase, TPKase; thiamine pyrophosphatase, TPPase; and monophosphatase, TMPase) was studied in different organs (liver, kidney, small intestine, heart and skeletal muscle) and nervous regions (cerebral cortex, cerebellum, medulla oblongata, pons, corpus callosum, hypothalamus and sciatic nerve) of the rat. In order to evaluate the non-specific effects of the stress of gastric gavage and of the additional caloric intake, appropriate control groups of animals were treated intragastrically with water or with a saccharose solution isoenergetic with ethanol respectively. All animals were reared on a nutritionally adequate diet supplying amounts of thiamine higher than the recommended daily requirement. Enzymatic activities were determined quantitatively by biochemical methods. Tissue TPKase levels were generally reduced by both acute and chronic ethanol administration. TPPase levels were generally reduced after acute and increased after chronic ethanol treatment. Changes in brain TMPase levels were similar to those observed for TPPase. In visceral organs and skeletal muscle TMPase activity was increased by chronic ethanol treatment as compared to acute ethanol administration. In conclusion, ethanol exerts a marked influence on the tissue levels of the thiamine metabolizing enzymes: the activity of the enzymes dephosphorylating thiamine phosphates is increased whereas the activity of the thiamine pyrophosphate synthesizing enzyme is reduced. These changes may contribute to an important extent to the disturbances in thiamine cellular uptake and metabolism observed in alcoholism
Blood-brain transport of thiamine monophosphate in the rat: a kinetic study in vivo.
Full text linkTo calculate the kinetic parameters of thiamine monophosphate transport across the rat blood-brain barrier in vivo, different doses of a [35S]thiamine monophosphate preparation with a specific activity of 14.8 mCi.mmol-1 were injected in the femoral vein and the radioactivity was measured in arterial femoral blood and in the cerebellum, cerebral cortex, pons, and medulla 20 s after the injection. This short experimental time was used to prevent thiamine monophosphate hydrolysis. Thiamine monophosphate was transported into the nervous tissue by a saturable mechanism. The maximal transport rate (Jmax) and the half-saturation concentration (Km) equaled 27-39 pmol.g-1.min-1 and 2.6-4.8 microM, respectively. When compared with that of thiamine, thiamine monophosphate transport seemed to be characterized by a lower affinity and a lower maximal influx rate. At physiological plasma concentrations, thiamine monophosphate transport rate ranged from 2.06 to 4.90 pmol.g-1.min-1, thus representing a significant component of thiamine supply to nervous tissue
Effects of phenytoin on the in vivo kinetics of thiamine and its phosphoesters in rat nervous tissues
No full textThe in vivo effects of chronic (30 days) and subchronic (10 days) intragastric treatment with phenytoin (PHT) (500 mg/kg) b.wt., suspended in 10% arabic gum water solution) on the uptake and metabolism of thiamine (T), T monophosphate (TMP) and T pyrophosphate (TPP) were evaluated in rat nervous regions (cerebral cortex, brainstem, cerebellum and sciatic nerve) by determining the radioactivity of T and its phosphoesters in plasma and tissues at fixed time intervals (0.25-240 h) after an i.p. injection of thiazole-[2-14C]thiamine (30 micrograms: 1.25 microCi). A nutritionally adequate diet containing T in excess was given to the animals in order to produce a virtually stable content of T compounds in the tissues. Analytical data were processed by using a compartmental model which allowed the calculation of fractional rate constants (FRC), turnover rates (TR) and turnover times. Compared with vehicle-treated controls, animals treated chronically with PHT exhibited lower levels of radiolabelled T compounds in all nervous regions except for the cerebral cortex. These alterations were not found in animals receiving subchronic treatment. Evaluation of FRC values indicated that PHT-induced effects on T metabolism differed depending on the length of PHT treatment and the nervous region considered. Overall, PHT appeared to interfere mainly with T and TMP uptake, TPP dephosphorylation to TMP and TPP turnover times, these effects being particularly prominent in the cerebellum and in the brainstem of chronically treated animals. Since all changes in T uptake and metabolism were observed in the absence of overt behavioural toxicity, these findings may have potential clinical relevance in highlighting possible mechanisms by which PHT therapy can alter brain metabolism
Effect of ethanol on the in vivo kinetics of thiamine phosphorylation and dephosphorylation in different organs of rat--II. Acute effects.
No full textThe effects of acute ethanol administration on different steps of thiamine (T), thiamine monophosphate (TMP) and pyrosphosphate (TPP) metabolism were determined in vivo in nervous tissues (cerebral cortex, cerebellum, brain stem and sciatic nerve) and in other tissues (small intestinal mucosa, kidney, heart, skeletal muscle and liver) of rats. The radioactivity of T and its phosphoesters in plasma and tissues was determined under steady-state conditions and at fixed time intervals (0.25-24 hr) after an i.p. injection of Thiazole-[2-14C]-thiamine (30 micrograms: 1.25 microCi) in the presence of a constant plasma ethanol concentration (37 mM; 1.75 g.l-1) produced by repeated intragastric administration of ethanol. Control animals received water intragastrically. Ethanol-treated rats and controls were starved, with water ad libitum during the 24 hr study period. Data were evaluated by using appropriate compartmental models, which allowed calculation of fractional rate constants, turnover rates and turnover times. In nervous tissues ethanol enhanced TMP entry (without affecting T entry or T and TMP release), reduced turnover time of total T and TPP, caused an almost general enhancement of TPP dephosphorylation without affecting T pyrophosphorylation, and increased markedly T content in the mixture released by tissues. Overall, ethanol appeared to enhance exchanges of T compounds in nervous tissues. In other tissues, the effects of ethanol were less consistent. Ethanol increased T uptake in kidney and liver and T release in liver and heart, but had no effect on T exchanges in the small intestinal mucosa and in skeletal muscle. In the presence of ethanol, TMP uptake increased in heart and skeletal muscle and decreased in the small intestinal mucosa, while TMP release decreased in heart and remained unchanged in all other organs. Turnover times tended to increase for total T and to decrease for TPP. T pyrophosphorylation was generally reduced, and T phosphates dephosphorylation generally enhanced. T became the most abundant component in the mixture released from all tissues
Effect of ethanol administration on the in vivo kinetics of thiamine phosphorylation and dephosphorylation in different organs. I. Chronic effects.
No full textThe effects of chronic ethanol administration on different steps in the metabolism of thiamine (T), thiamine mono- (TMP) and pyrophosphate (TPP) were determined in vivo in the liver, kidney, heart, skeletal muscle and small intestinal mucosa. The radioactivity of T and its phosphoesters was measured in plasma and in the selected organs under steady-state conditions and at fixed time intervals (0.25-240 hr) after an i.p. injection of Thiazole-[2-14C]-thiamine (30 micrograms: 1.25 microCi) in rats chronically (35 days) ethanol-treated (daily dose of 4.7 g kg-1 body wt by gastric gavage). Two types of controls were used: pair-fed rats treated with a sucrose solution isoenergetic with ethanol, and water-treated rats. A nutritionally adequate diet, which supplied an excess of thiamine, was given to the rats, producing a virtually steady content of thiamine compounds in the tissues. The analytical data obtained were elaborated using appropriate compartmental mathematical models, which allowed the fractional rate constants, turnover rates and turnover times to be calculated. Alterations in thiamine metabolism were modest and differed according to the organs. The most widespread modification was to facilitate the entry of T (small intestine, kidney and heart) or TMP (small intestine and kidney), while no significant change of T and TMP release was seen. Sucrose had minimal effect in both steps. Enzymatic transformations of thiamine were likewise marginally affected. A general trend toward a slower T pyrophosphorylation and a faster T phosphate dephosphorylation was observed in the small intestine, kidney, heart and liver. Skeletal muscle was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS
Effect of acute and chronic ethanol administration on the transport of thiamine from plasma to different brain regions of the rat.
No full textThe effect of ethanol (4.7 g/kg body wt intragastrically as a single dose or once daily for 35 days) on the transport of thiamine from plasma to four brain regions (cerebellum, cerebral cortex, pons and medulla) was studied in albino rats. Animals were given an intravenous injection of labelled thiamine with a sampling procedure which allowed the determination of regional blood flow and tissue thiamine uptake. Regional blood flow was found to be enhanced after acute, but non chronic, ethanol administration. The magnitude of increase ranged from 13 to 35% depending on the brain region being considered. Thiamine was transferred from plasma to cerebral tissue by a saturable process with a non-saturable component prevailing at thiamine concentrations above 10-15 microM. Three main modifications in the thiamine transport were found as a result of ethanol treatment: a reduction in affinity for the carrier (Km increased), an increase in maximal transport rate (Jmax) and an increase in non-saturable diffusion (KD constant increased). The effects were more pronounced after acute ethanol administration. As a consequence of these modifications both acute and chronic ethanol treatment caused an increase in thiamine transport rate at high plasma concentrations. On the contrary, at low (physiological) plasma concentrations, thiamine transport was little increased by acute ethanol administration and virtually unaffected by chronic ethanol intoxication
Thiamine uptake in human intestinal biopsy specimens, including observations from a patient with acute thiamine deficiency.
Full text linkMucosal biopsy specimens obtained by routine endoscopy from 108 human subjects, including one patient with thiamine deficiency, were incubated at 37 degrees C in oxygenated calcium-free Krebs-Ringer solution (pH 7.5) containing tritiated thiamine and [14C]dextran as a marker of adherent mucosal water. The amount of labeled thiamine taken up was measured radiometrically. In subjects with no clinical evidence of thiamine deficiency, 1) thiamine uptake by duodenal mucosa had a hyperbolic time course, reaching equilibrium at 10 min; 2) thiamine concentrations > colon > stomach); and 4) thiamine uptake was competitively inhibited in the duodenum by thiamine analogs, albeit with a different order of potency compared with rats, and was blocked by 2,4-dinitrophenol. In the thiamine-deficient patient, the duodenal saturable uptake was increased, with higher K(m) and Jmax values. In conclusion, physiologic concentrations of thiamine were transported in human small intestine by a specific mechanism dependent on cellular metabolism, whose transporters appear to be down-regulated
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