Thiazolium salt mimics the non-coenzyme effects of vitamin B1 in rat synaptosomes.

Long-term studies have confirmed a causal relationship between the development of neurodegenerative processes and vitamin B1 (thiamine) deficiency. However, the biochemical mechanisms underlying the high neurotropic activity of thiamine are not fully understood. At the same time, there is increasing evidence that vitamin B1, in addition to its coenzyme functions, may have non-coenzyme activities that are particularly important for neurons. To elucidate which effects of vitamin B1 in neurons are due to its coenzyme function and which are due to its non-coenzyme activity, we conducted a comparative study of the effects of thiamine and its derivative, 3-decyloxycarbonylmethyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chloride (DMHT), on selected processes in synaptosomes. The ability of DMHT to effectively compete with thiamine for binding to thiamine-binding sites on the plasma membrane of synaptosomes and to participate as a substrate in the thiamine pyrophosphokinase reaction was demonstrated. In experiments with rat brain synaptosomes, unidirectional effects of DMHT and thiamine on the activity of the pyruvate dehydrogenase complex (PDC) and on the incorporation of radiolabeled [2-14C]pyruvate into acetylcholine were demonstrated. The observed effects of thiamine and DMHT on the modulation of acetylcholine synthesis can be explained by suggesting that both compounds, which interact in cells with enzymes of thiamine metabolism, are phosphorylated and exert an inhibitory/activating effect (concentration-dependent) on PDC activity by affecting the regulatory enzymes of the complex. Such effects were not observed in the presence of structural analogs of thiamine and DMHT without a 2-hydroxyethyl substituent at position 5 of the thiazolium cycle. The effect of DMHT on the plasma membrane Ca-ATPase was similar to that of thiamine. At the same time, DMHT showed high cytostatic activity against neuroblastoma cells.

[Interaction of rat brain thiamine kinase with thiamine and its derivatives]. / Vzaiemodiia tiaminkinazy mozku shchuriv iz tiaminov i ioho pokhidnymy.

Participation of the enzyme which provides the phosphorylation of thiamine to thiamindiphosphate (TDP) thiaminkinase (thiaminpyrophosphokinase, KF 2.7.6.2) of rat brain in the realization of thiamine action on the syntheses of acethylcholine (AC) was studied. The thiamine and its structure analogue, which differ the nature of the radicals in the 3-d and 5-e positions of the thiazollium cycle were used: 3-[(4-amino-2methylpyrimidinyl-5)methyl]-4-methylthiazolium chloride, 3-decyloxycarbonylmethyl-4-metyl-5-beta-hydrozyethylthiazolium chloride, 3-decyloxycarbonylmethyl-4-methylthiazolium chloride. All salts in the concentrations lower then Km render active influence on thiaminkinase. The analysis of data shows the presence of the regulation site on the enzyme distinguishing from the active enzyme centre and participating in the interaction with which the hydrophobic fragments of thiamine molecule participating. The comparative studies of thiamine and above mentioned derivatives influence on the inclusion of the labelled carbon with [2-(14)C] pyruvate in acethylcholine confirm an assumption about the key-role of the thiamine interaction with thiaminkinase (meaning its phosphorilation) regarding its action on the acethylcholine syntheses, and probably, on the function of the nervous cells as a whole.

[Interaction of thiamine with rat brain synaptosomes]. / Vzaimodeistvie tiamina s sinaptosomami mozga krys.

Thiamine has been shown to be bound specifically by a synaptosomal plasmatic membrane and transported inside to the nervous ending. Apparent K[symbol: see text] and Km for processes of binding and transport have been determined as equal 2.34 +/- 0.55 MKM and 3.92 +/- 1.3 MKM, respectively. The thiamine uptake by the isolated nervous endings (synaptosomes) at its physiological concentration is reduced in presence of metabolic inhibitors and partially depends on Mg2+ and Ca2+ ions, that can testify about the interrelation between endogenic thiamine phosphorilation and its transport through the membrane. Thiamine binding with synaptosomes is inhibited by ouabain and neurotoxins such as, latrotoxin and most significantly--with veratridin; tetrodotoxin fail to be efficient practically. In the conditions of synaptic membranes depolarisation their ability to bind thiamine is reduced and output of already uptaken with synaptosomes thiamine is observed.

[Inactivation of yeast pyruvate decarboxylase in the presence of substrate and quinone electron acceptors]. / Inaktivatsiia drozhzhevoi piruvatdekarboksilazy v prisutstvii substrata i khinonovykh aktseptorov élektronov.

The rate constants of paracatalytic inactivation of pyruvate decarboxylase in the presence of 1,4-naphthoquinones and 1,4-benzoquinones are determined by redox potentials of the oxidant. The logarithm of k2 depends hyperbolically on the redox potential of quinone E0(Q/Q-.) with the coefficient of proportionality which approximates 8.4, The absence of considerable deviations in this correlation for the oxidants of different structures with closed values Eo(Q/Q-.) indicates that the enzyme produces no additional steric barrier.

[The interaction of pyruvate decarboxylase with the quinone-ferricyanide oxidative system]. / Vzaimodeistvie piruvatdekarboksilazy s okislitel'noi sistemoi khinon--ferritsianid.

Inactivation of yeast pyruvate decarboxylase in the presence of substrate and oxidative system containing substituted quinone and ferricyanide has been investigated. It was established that ferricyanide at pH 5.2-6.4 can prevent irreversible inactivation of the pyruvate decarboxylase caused by the concerted action of pyruvate and substituted quinone. The influence of ferricyanide which depends on the redox potential of the substituted quinone is decreasing in a series tetramethyl-p-benzoquinone, trimethyl-p-benzoquinone, 2-methyl-5-isopropyl-p-benzoquinone. It is supposed that the effect of the oxidative system partially converting the nonoxidative to oxidative function of pyruvate decarboxylase is attributed to the oxidation of active acetaldehyde by substituted quinone and reaction of resultant semiquinone radical with ferricyanide.

[The neural activity of thiamine: facts and hypotheses]. / Neiroaktivnost' tiamina: fakty i gipotezy.

A review of some experimental results as to identification of the specific role of thiamine in functioning of nerve cells is presented. Failure to attribute high neuroactivity of thiamine considering only its known biochemical function as a coenzyme precursor of some key Enzymes of the carbohydrate metabolism has formed conceptions existence of non-coenzyme functions in this vitamin which are realized in nerve cells. The Investigation of this thiamine function has been developing mainly in two principal directions the study of participation of biologically active thiamine derivatives is functioning of the excited membrane ion channels and the study of their role in the synthesis and metabolism of acetylcholine. Taking into account analysis of their own data and those available in literature, the authors formulate a hypothesis which attributes high neuroactivity of thiamine not to the existence of a certain function in the nerve cells new for this vitamin but only to the peculiarities of the structure-functional organization of the cells the existence of excited membrane, and interdependence between the cellular metabolism and transport of loss via the membrane, which underlies regulation of the synthesis, release, capture and catabolism of neurotransmitters.

[Increasing the effectiveness of thiamine by its administration together with methionine and vitamin E]. / Povyshenie éffektivnosti ispol'zovaniia tiamina pri vvedenii ego v organizm sovmestno s metioninom i vitaminom E.

The influence of methionine and vitamin E, compounds intensifying thiol metabolism, on thiamine-phosphate level and thiamine-dependent dehydrogenase activity was studied in the liver of rats with varying thiamine providing: in case of its alimentary deficiency, and intensified thiamine consumption due to rat feeding with high-carbohydrate food. Methionine administration to vitamin B1-deficient rats led to a significant rise in thiamine-phosphate content and normalized alpha-ketoacid dehydrogenase acidity and non-protein SH-group level. Combined administration of thiamine with methionine and vitamin E increased the level of parameters studied. Methionine and vitamin E administered with thiamine intensified the regulatory action of thiamine on pyruvate dehydrogenase activity in the animals fed high-carbohydrate ration.

[Interrelationship between the thiamine content, thiamine diphosphate-dependent enzyme activity and reduced glutathione level in the rat liver]. / Issledovanie vzaimosviazi mezhdu soderzheniem tiamina, aktivnost'iu tiamindifosfatzavisimykh fermentov i urovnem vosstanovlennogo glutationa v pecheni krys.

Changes in the amount of thiamine, reduced glutathione, thiamine diphosphate-dependent dehydrogenase activity has been traced after thiamine injection to thiamine-deficient rats and oxythiamine to normal rats. The obtained data show that a drop in reduced glutathione level was a primary reason of the alpha-keto-acid dehydrogenase activity reduction under conditions of the thiamine deficiency. The existence of immediate connection between thiamine and glutathione metabolism is supposed.

[Thiamine phosphates and regulation of the pyruvate dehydrogenase complex activity in rat liver mitochondria]. / Tiaminfosfaty i reguliatsiia aktivnosti piruvatdegidrogenaznogo kompleksa v mitokhondriiakh pecheni krys.

The possibility of thiamine phosphates to participate in the regulation of pyruvate dehydrogenase complex activity on the level of isolated mitochondria is studied. It is shown that an increase in the thiamine diphosphate concentration in incubation medium produces no significant changes in the pyruvate dehydrogenase activity of mitochondria. The pyruvate dehydrogenase activity decreases when mitochondria are incubated with thiamine triphosphate or ATP under different conditions. Thiamine triphosphate is not able to replace ATP in kinase reaction of the isolated complex, but it inhibits reactivation of the complex with exogenase phosphatase; under the same conditions thiamine diphosphate activates phosphatase. Analysis of these data leads to conclusion that under native conditions an increase of the intramitochondrial thiamine triphosphate concentration can produce a drop in the pyruvate dehydrogenase complex activity by inhibition of the phosphatase reaction.

[Effect of thiamine on the activity of the pyruvate dehydrogenase complex in rat liver following stimulation of lipogenesis]. / Vliianie tiamina na aktivnost' piruvatdegidrogenaznogo kompleksa pecheni krys pri intensifikatsii lipogeneza.

It is shown that thiamine administration to rats (250 micrograms per 100 g of mass) who were given high-carbohydrate diet (lipogenesis intensification) after fasting inhibits an increase in the pyruvate dehydrogenase activity in the liver homogenate and mitochondria usual under these conditions. This is observed when determining total activity of the pyruvate dehydrogenase complex and activity of its first component--pyruvate dehydrogenase estimated from the ferricyanide reduction and [1-14C] CO2 formation from [1-14C] pyruvate. Fasting animals and animals whom thiamine was administered against a background of lipogenesis intensification revealed a higher ability of the liver tissue to synthesize acetoin as compared with the control group and animals with the intensified lipogenesis without thiamine administration.