The role of the cholinergic system in thiamin deficiency

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.

Phosphonate Inhibitors of Pyruvate Dehydrogenase Perturb Homeostasis of Amino Acids and Protein Succinylation in the Brain

Mitochondrial pyruvate dehydrogenase complex (PDHC) is essential for brain glucose and neurotransmitter metabolism, which is dysregulated in many pathologies. Using specific inhibitors of PDHC in vivo, we determine biochemical and physiological responses to PDHC dysfunction. Dose dependence of the responses to membrane-permeable dimethyl acetylphosphonate (AcPMe2) is non-monotonous. Primary decreases in glutathione and its redox potential, methionine, and ethanolamine are alleviated with increasing PDHC inhibition, the alleviation accompanied by physiological changes. A comparison of 39 brain biochemical parameters after administration of four phosphinate and phosphonate analogs of pyruvate at a fixed dose of 0.1 mmol/kg reveals no primary, but secondary changes, such as activation of 2-oxoglutarate dehydrogenase complex (OGDHC) and decreased levels of glutamate, isoleucine and leucine. The accompanying decreases in freezing time are most pronounced after administration of methyl acetylphosphinate and dimethyl acetylphosphonate. The PDHC inhibitors do not significantly change the levels of PDHA1 expression and phosphorylation, sirtuin 3 and total protein acetylation, but increase total protein succinylation and glutarylation, affecting sirtuin 5 expression. Thus, decreased production of the tricarboxylic acid cycle substrate acetyl-CoA by inhibited PDHC is compensated by increased degradation of amino acids through the activated OGDHC, increasing total protein succinylation/glutarylation. Simultaneously, parasympathetic activity and anxiety indicators decrease.

Axonopathy Likely Initiates Neuropathological Processes Via a Mechanism of Axonal Leakage in Alzheimer's Mouse Models

BACKGROUND

The formation of hyperphosphorylated tau and the production of β-amyloid are thought to be critical steps contributing to the pathological mechanisms in Alzheimer's disease (AD). However, there has been a long-lasting debate over their importance in the onset of AD. Recent studies have demonstrated that axonopathy is considered as an early neuropathological change of AD. However, the exact relationship between the development of axonopathy and the classic neuropathological changes such as senile plaques (SPs) and neurofibrillary tangles (NFTs) is unclear.

OBJECTIVE

The aim of this study was to investigate whether the formation of SPs and NFTs is associated with the development of axonal leakage.

METHOD AND RESULTS

Here we show that the formation and development of axonal leakage - a novel axonopathy is an age-dependent process, accompanied by swellings of axons and varicosities and associated with chronic oxidative stress induced by thiamine deficient (TD) diet in Kunming mice. In an APP/PS1 transgenic mouse model of AD, axonal leakage appears at 3 months, becomes more obvious at 6 months and severe, beyond 1 year. We also show that slight axonal leakage is related to the formation of hyperphosphorylated tau, but not plaques, and that only severe axonal leakage accompanied by the extensive swollen axons and varicosities, and overproduction of β-amyloid leads to the formation of SPs and hyperphosphorylated tau.

CONCLUSION

These data provide an explanation of the common origin and development of SPs and NFTs, and suggest that axonal leakage might be a key event in the development of the neuropathological processes in AD.

Protective Effects of Citicoline and Benfotiamine Each Alone and in Combination on Streptozotocin-induced Memory Impairment in Mice

Objective

Diabetes mellitus is associated with cognitive disorders such as Alzheimer’s disease. Studies have shown that citicoline and benfotiamine can improve memory and learning through different mechanism of actions. The aim of this study was to compare the individual effects of benfotiamine (100, 200, 300 mg/kg) and citicoline (50, 100, 250, 500 mg/kg, gavage) and their co-administration on memory impairments in diabetic mice.

Methods

Diabetes was induced by a single dose of streptozotocin (STZ, 140 mg/kg, intraperitoneal) and benfotiamine and/or citicoline were administered for three weeks. Memory was evaluated using the object recognition task (ORT) and passive avoidance test (PAT).

Results

Results from ORT shows that citicoline at 50, 100, 250, and 500 mg/kg and benfotiamine at 100, 200, and 300 mg/kg and their combination (benfotiamine at 100 mg/kg added to citicoline at 50, 100, and 250 mg/kg) are equally effective in reversing the memory loss induced by STZ (p < 0.001). PAT results demonstrate that citicoline at 100, 250, and 500 mg/kg and benfotiamine at above doses did not improve the latency time when administered separately, but benfotiamine at a fixed dose of 100 mg/kg in the presence of citicoline at 50, 100, and 250 mg/kg increased the latency time and improved memory significantly.

Conclusion

In conclusion, in PAT, co-administration of benfotiamine and citicoline was more effective than either alone in improving memory. Regarding ORT, although benfotiamine added to citicoline improved memory notably, the difference between combination therapy and single-drug therapy was not considerable.

The Regulatory Effects of Acetyl-CoA Distribution in the Healthy and Diseased Brain

Brain neurons, to support their neurotransmitter functions, require a several times higher supply of glucose than non-excitable cells. Pyruvate, the end product of glycolysis, through pyruvate dehydrogenase complex reaction, is a principal source of acetyl-CoA, which is a direct energy substrate in all brain cells. Several neurodegenerative conditions result in the inhibition of pyruvate dehydrogenase and decrease of acetyl-CoA synthesis in mitochondria. This attenuates metabolic flux through TCA in the mitochondria, yielding energy deficits and inhibition of diverse synthetic acetylation reactions in all neuronal sub-compartments. The acetyl-CoA concentrations in neuronal mitochondrial and cytoplasmic compartments are in the range of 10 and 7 μmol/L, respectively. They appear to be from 2 to 20 times lower than acetyl-CoA Km values for carnitine acetyltransferase, acetyl-CoA carboxylase, aspartate acetyltransferase, choline acetyltransferase, sphingosine kinase 1 acetyltransferase, acetyl-CoA hydrolase, and acetyl-CoA acetyltransferase, respectively. Therefore, alterations in acetyl-CoA levels alone may significantly change the rates of metabolic fluxes through multiple acetylation reactions in brain cells in different physiologic and pathologic conditions. Such substrate-dependent alterations in cytoplasmic, endoplasmic reticulum or nuclear acetylations may directly affect ACh synthesis, protein acetylations, and gene expression. Thereby, acetyl-CoA may regulate the functional and adaptative properties of neuronal and non-neuronal brain cells. The excitotoxicity-evoked intracellular zinc excess hits several intracellular targets, yielding the collapse of energy balance and impairment of the functional and structural integrity of postsynaptic cholinergic neurons. Acute disruption of brain energy homeostasis activates slow accumulation of amyloid-β_1-42 (Aβ). Extra and intracellular oligomeric deposits of Aβ affect diverse transporting and signaling pathways in neuronal cells. It may combine with multiple neurotoxic signals, aggravating their detrimental effects on neuronal cells. This review presents evidences that changes of intraneuronal levels and compartmentation of acetyl-CoA may contribute significantly to neurotoxic pathomechanisms of different neurodegenerative brain disorders.

A multibiomarker approach to the assessment of pollution impacts in two Baltic Sea coastal areas in Sweden using caged mussels (Mytilus trossulus)

Blue mussels (Mytilus trossulus) were transplanted in cages for three months in two Swedish coastal areas in the Bothnian Sea (northern Baltic Sea) to investigate the interactions between analysed environmental chemicals and biological responses. A wide array of biological parameters (biomarkers) including antioxidant and biotransformation activity, geno-, cyto- and neurotoxic effects, phagocytosis, bioenergetic status and heart rate were measured to detect the possible effects of contaminants. Integrated Biomarker Response index and Principal Component Analysis performed on the individual biological response data were able to discriminate between the two study areas as well as the contaminated sites from their respective local reference sites. The two contaminated sites outside the cities of Sundsvall (station S1) and Gävle (station G1) were characterised by different biomarker response patterns. Mussels at station S1 showed a low condition index, increased heart rate recovery time and phagocytosis activity coinciding with the highest tissue concentrations of some trace metals, polycyclic aromatic hydrocarbons and organotins. At station G1 the highest organochlorine pesticide concentration was recorded as well as elevations in glutathione S-transferase activity, thiamine content and low lysosomal membrane stability. Significant variability in the geno- and cytotoxic responses and bioenergetic status was also observed at the different caging stations. The results obtained suggest that different chemical mixtures present in the study areas cause variable biological response patterns in organisms.

Abnormal thiamine-dependent processes in Alzheimer's Disease. Lessons from diabetes

Reduced glucose metabolism is an invariant feature of Alzheimer's Disease (AD) and an outstanding biomarker of disease progression. Glucose metabolism may be an attractive therapeutic target, whether the decline initiates AD pathophysiology or is a critical component of a cascade. The cause of cerebral regional glucose hypometabolism remains unclear. Thiamine-dependent processes are critical in glucose metabolism and are diminished in brains of AD patients at autopsy. Further, the reductions in thiamine-dependent processes are highly correlated to the decline in clinical dementia rating scales. In animal models, thiamine deficiency exacerbates plaque formation, promotes phosphorylation of tau and impairs memory. In contrast, treatment of mouse models of AD with the thiamine derivative benfotiamine diminishes plaques, decreases phosphorylation of tau and reverses memory deficits. Diabetes predisposes to AD, which suggests they may share some common mechanisms. Benfotiamine diminishes peripheral neuropathy in diabetic humans and animals. In diabetes, benfotiamine induces key thiamine-dependent enzymes of the pentose shunt to reduce accumulation of toxic metabolites including advanced glycation end products (AGE). Related mechanisms may lead to reversal of plaque formation by benfotiamine in animals. If so, the use of benfotiamine could provide a safe intervention to reverse biological and clinical processes of AD progression. This article is part of a Special Issue entitled 'Mitochondrial function and dysfunction in neurodegeneration'.

Brain and behavioral pathology in an animal model of Wernicke's encephalopathy and Wernicke-Korsakoff Syndrome

Animal models provide the opportunity for in-depth and experimental investigation into the anatomical and physiological underpinnings of human neurological disorders. Rodent models of thiamine deficiency have yielded significant insight into the structural, neurochemical and cognitive deficits associated with thiamine deficiency as well as proven useful toward greater understanding of memory function in the intact brain. In this review, we discuss the anatomical, neurochemical and behavioral changes that occur during the acute and chronic phases of thiamine deficiency and describe how rodent models of Wernicke-Korsakoff Syndrome aid in developing a more detailed picture of brain structures involved in learning and memory.

Thiamin(e): the spark of life

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

Acetyl-CoA metabolism in amprolium-evoked thiamine pyrophosphate deficits in cholinergic SN56 neuroblastoma cells

Inhibition of pyruvate (PDHC) and ketoglutarate (KDHC) dehydrogenase complexes induced by thiamine pyrophosphate deficits is known cause of disturbances of cholinergic transmission in the brain, yielding clinical symptoms of cognitive, vegetative and motor deficits. However, particular alterations in distribution of key acetylcholine precursor, acetyl-CoA, in the cholinergic neuron compartment of thiamine pyrophosphate-deficient brain remain unknown. Therefore, the aim of our work was to find out how amprolium-induced thiamine pyrophosphate deficits (TD) affect distribution of acetyl-CoA in the compartment of pure cholinergic neuroblastoma SN56 cells originating from murine septum. Amprolium caused similar concentration-dependent decreases in thiamine pyrophosphate levels in nondifferentiated (NC) and differentiated (DC) cells cultured in low thiamine medium. In such conditions DC displayed significantly greater loss of viability than the NC ones, despite of lesser suppressions of PDHC activities and tetrazolium salt reduction rates in the former. On the other hand, intramitochondrial acetyl-CoA levels in DC were 73% lower than in NC, which explains their greater susceptibility to TD. Choline acetyltransferase activity and acetylcholine content in DC were two times higher than in NC. TD caused 50% decrease of cytoplasmic acetyl-CoA levels that correlated with losses of acetylcholine pool in DC but not in NC. These data indicate that particular sensitivity of DC to TD may result from relative shortage of acetyl-CoA due to its higher utilization in acetylcholine synthesis.

Acetyl-CoA deficit in brain mitochondria in experimental thiamine deficiency encephalopathy

Several pathologic conditions are known to cause thiamine deficiency, which induce energy shortages in all tissues, due to impairment of pyruvate decarboxylation. Brain is particularly susceptible to these conditions due to its high rate of glucose to pyruvate-driven energy metabolism. However, cellular compartmentalization of a key energy metabolite, acetyl-CoA, in this pathology remains unknown. Pyrithiamine-evoked thiamine deficiency caused no significant alteration in pyruvate dehydrogenase and 30% inhibition of α-ketoglutarate dehydrogenase activities in rat whole forebrain mitochondria. It also caused 50% reduction of the metabolic flux of pyruvate through pyruvate dehydrogenase, 78% inhibition of its flux through α-ketoglutarate dehydrogenase steps, and nearly 60% decrease of intramitochondrial acetyl-CoA content, irrespective of the metabolic state. State 3 caused a decrease in citrate and an increase in α-ketoglutarate accumulation. These alterations were more evident in thiamine-deficient mitochondria. Simultaneously thiamine deficiency caused no alteration of relative, state 3-induced increases in metabolic fluxes through pyruvate and α-ketoglutarate dehydrogenase steps. These data indicate that a shortage of acetyl-CoA in the mitochondrial compartment may be a primary signal inducing impairment of neuronal and glial cell functions and viability in the thiamine-deficient brain.

Acetyl-CoA and acetylcholine metabolism in nerve terminal compartment of thiamine deficient rat brain

The decrease of pyruvate and ketoglutarate dehydrogenase complex activities is the main cause of energy and acetyl-CoA deficits in thiamine deficiency-evoked cholinergic encephalopathies. However, disturbances in pathways of acetyl-CoA metabolism leading to appearance of cholinergic deficits remain unknown. Therefore, the aim of this work was to investigate alterations in concentration and distribution of acetyl-CoA and in acetylcholine metabolism in brain nerve terminals, caused by thiamine deficits. They were induced by the pyrithiamine, a potent inhibitor of thiamine pyrophosphokinase. The thiamine deficit reduced metabolic fluxes through pyruvate and ketoglutarate dehydrogenase steps, yielding deficits of acetyl-CoA in mitochondrial and cytoplasmic compartments of K-depolarized nerve terminals. It also inhibited indirect transport of acetyl-CoA though ATP-citrate lyase pathway being without effect on its direct Ca-dependent transport to synaptoplasm. Resulting suppression of synaptoplasmic acetyl-CoA correlated with inhibition of quantal acetylcholine release (r = 0.91, p = 0.012). On the other hand, thiamine deficiency activated non-quantal acetylcholine release that was independent of shifts in intraterminal distribution of acetyl-CoA. Choline acetyltransferase activity was not changed by these conditions. These data indicate that divergent alterations in the release of non-quantal and quantal acetylcholine pools from thiamine deficient nerve terminals could be caused by the inhibition of acetyl-CoA and citrate synthesis in their mitochondria. They in turn, caused inhibition of acetyl-CoA transport to the synaptoplasmic compartment through ATP-citrate lyase pathway yielding deficits of cholinergic functions.

Nutrition and alcoholic encephalopathies

An assessment has been made of metabolic factors possibly causing or contributing to the brain damage associated with chronic alcoholism, especially thiamin lack or disturbance of amino acid metabolism. Abnormalities in the thiamin-dependent enzyme, transketolase, provide evidence of a high incidence of thiamin deficiency as well as of disturbed thiamin metabolism in chronic alcoholics, which are likely to be caused by reduced vitamin intake as well as impaired absorption. A grossly disturbed pattern of amino acids in the blood of patients undergoing treatment for alcohol withdrawal syndromes is likely to be caused by loss of hepatic function and may well aggravate brain damage caused by B group vitamin deficiency. A hypothesis is proposed of how chronic thiamin lack can lead to brain damage.

Thiamine deficiency induces oxidative stress and exacerbates the plaque pathology in Alzheimer's mouse model

Mitochondrial dysfunction, oxidative stress and reductions in thiamine-dependent enzymes have been implicated in multiple neurological disorders including Alzheimer's disease (AD). Experimental thiamine deficiency (TD) is an established model for reducing the activities of thiamine-dependent enzymes in brain. TD diminishes thiamine-dependent enzymes throughout the brain, but produces a time-dependent selective neuronal loss, glial activation, inflammation, abnormalities in oxidative metabolism and clusters of degenerating neurites in only specific thalamic regions. The present studies tested how TD alters brain pathology in Tg19959 transgenic mice over expressing a double mutant form of the amyloid precursor protein (APP). TD exacerbated amyloid plaque pathology in transgenic mice and enlarged the area occupied by plaques in cortex, hippocampus and thalamus by 50%, 200% and 200%, respectively. TD increased Abeta(1-42) levels by about three fold, beta-CTF (C99) levels by 33% and beta-secretase (BACE1) protein levels by 43%. TD-induced inflammation in areas of plaque formation. Thus, the induction of mild impairment of oxidative metabolism, oxidative stress and inflammation induced by TD alters metabolism of APP and/or Abeta and promotes accumulation of plaques independent of neuron loss or neuritic clusters.

Responses of the mitochondrial alpha-ketoglutarate dehydrogenase complex to thiamine deficiency may contribute to regional selective vulnerability

Thiamine-dependent enzymes are diminished in multiple neurodegenerative diseases. Thiamine deficiency (TD) reduces the activity of thiamine dependent-enzymes [e.g., the alpha-ketoglutarate dehydrogenase complex (KGDHC)], induces regional selective neurodegeneration and serves as a model of a mild impairment of oxidative metabolism. The current experiments tested whether changes in KGDHC protein subunits (E1k, E2k and E3) or activity or message levels underlie the selective loss of neurons in particular brain regions. Thus, TD-induced changes in these variables in the brain region most vulnerable to TD [the sub-medial thalamic nucleus (SmTN)] were compared to those in a region that is relatively resistant to TD (cortex) at stages of TD when the neuron loss in SmTN is not present, minimal or severe. Impaired motor performance on rotarod was apparent by 8 days of TD (-32%) and was severe by 10 days of TD (-97%). At TD10, the overall KGDHC activity measured by an in situ histochemical staining method declined 52% in SmTN but only 20% in cortex. Reductions in the E2k and E3 mRNA in SmTN occurred as early as TD6 (-28 and -18%, respectively) and were more severe by TD10 (-61 and -66%, respectively). On the other hand, the level of E1k mRNA did not decline in SmTN until TD10 (-48%). In contrast, TD did not alter mRNA levels of the subunits in cortex at late stages. Western blots and immunocytochemistry revealed different aspects of the changes in protein levels. In SmTN, the immunoreactivity of E1k and E3 by Western blotting increased 34 and 40%, respectively, only at TD8. In cortex, the immunoreactivity of the three subunits was not altered. Immunocytochemical staining of brain sections from TD10 mice indicated a reduction in the immunoreactivity of all subunits in SmTN, but not in cortex. These findings demonstrate that the response of the KGDHC activity, mRNA and immunoreactivity of E1k, E2k and E3 to TD is region and time dependent. Loss of KGDHC activity in cortex is likely related to post-translational modification rather than a loss of protein, whereas in SmTN transcriptional and post-translational modifications may account for diminished KGDHC activity. Moreover, the earlier detection in TD induced-changes of the transcripts of KGDHC indicates that transcriptional modification of the two subunits (E2k and E3) of KGDHC may be one of the early events in the cascade leading to selective neuronal death.

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

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

Selective response of various brain cell types during neurodegeneration induced by mild impairment of oxidative metabolism

Age-related neurodegenerative diseases are characterized by selective neuron loss, glial activation, inflammation and abnormalities in oxidative metabolism. Thiamine deficiency (TD) is a model of neurodegeneration induced by impairment of oxidative metabolism. TD produces a time-dependent, selective neuronal death in specific brain regions, while other cell types are either activated or unaffected. TD-induced neurodegeneration occurs first in a small, well-defined brain region, the submedial thalamic nucleus (SmTN). This discrete localization permits careful analysis of the relationship between neuronal loss and the response of other cell types. The temporal analysis of the changes in the region in combination with the use of transgenic mice permits testing of proposed mechanisms of how the interaction of neurons with other cell types produces neurodegeneration. Loss of neurons and elevation in markers of neurodegeneration are accompanied by changes in microglia including increased redox active iron, the induction of nitric oxide synthase (NOS) and hemeoxygenase-1, a marker of oxidative stress. Endothelial cells also show changes in early stages of TD including induction of intracellular adhesion molecule-1 (ICAM-1) and endothelial NOS. The number of degranulating mast cells also increases in early stages of TD. Alterations in astrocytes and neutrophils occur at later stages of TD. Studies with transgenic knockouts indicate that the endothelial cell changes are particularly important. We hypothesize that TD-induced abnormalities in oxidative metabolism promote release of neuronal inflammatory signals that activate microglia, astrocytes and endothelial cells. Although at early stages the responses of non-neuronal cells may be neuroprotective, at late phases they lead to entry of peripheral inflammatory cells into the brain and promote neurodegeneration.

Relationships between cholinergic phenotype and acetyl-CoA level in hybrid murine neuroblastoma cells of septal origin

High susceptibility of cholinergic neurons to neurotoxic signals may result from their utilization of acetyl-CoA for both energy production and acetylcholine synthesis. SN56 cholinergic cells were transfected stably with cDNA for choline acetyltransferase. Transfected cells (SN56ChAT2) expressed choline acetyltransferase activity and acetylcholine content, 17 times and 2 times higher, respectively, than did nontransfected cells. Transfection did not change pyruvate dehydrogenase but decreased the acetyl-CoA level by 62%. Differentiation by cAMP and retinoic acid caused an increase of choline acetyltransferase activity and decrease of acetyl-CoA levels in both cell lines. Negative correlation was found between choline acetyltransferase activity and acetyl-CoA level in these cells. SN56ChAT2 cells were more susceptible to excess NO than were native SN56 cells, as evidenced by the thiazolyl blue reduction assay. Thus, the sensitivity of cholinergic neurons to pathologic conditions may depend on the cholinergic phenotype-dependent availability of acetyl-CoA.

Differential toxicity of nitric oxide, aluminum, and amyloid beta-peptide in SN56 cholinergic cells from mouse septum

A characteristic feature of several encephalopathies is preferential impairment of cholinergic neurons. Their particular susceptibility to cytotoxic insults may result from the fact that they utilise acetyl-CoA both for energy production and acetylcholine synthesis. In addition, phenotypic modifications of cholinergic neurons are likely to influence their susceptibility to specific harmful conditions. SN56 cholinergic cells were differentiated by the combination of dibutyryl cAMP and retinoic acid. Al and sodium nitroprusside (SNP, NO donor) exerted direct additive inhibitory effects on mitochondrial aconitase activity. However, NO, Al, or amyloid beta (Abeta)(25-35) caused none or only slight changes of choline O-acetyl transferase (ChAT) and pyruvate dehydrogenase (PDH) activity and relatively small loss of non-differentiated cells (NCs). On the other hand, in differentiated cells (DCs) these neurotoxins brought about marked decreases of these enzyme activities along with greater than in non-differentiated ones increase of cell-death rate. Abeta(35-25) had no effect on these cell parameters. NO and other compounds aggravated detrimental effect of each other particularly in differentiated cells. Thus, differential vulnerability of brain cholinergic neurons to various degenerative signals may result from their phenotype-dependent ratios of acetylcholine to acetyl-CoA synthesising capacities.

Aluminum, NO, and nerve growth factor neurotoxicity in cholinergic neurons

Several neurotoxic compounds, including Al, NO, and beta-amyloid may contribute to the impairment or loss of brain cholinergic neurons in the course of various neurodegenerative diseases. Genotype and phenotypic modifications of cholinergic neurons may determine their variable functional competency and susceptibility to reported neurotoxic insults. Hybrid, immortalized SN56 cholinergic cells from mouse septum may serve as a model for in vitro cholinotoxicity studies. Differentiation by various combinations of cAMP, retinoic acid, and nerve growth factor may provide cells of different morphologic maturity as well as activities of acetylcholine and acetyl-CoA metabolism. In general, differentiated cells appear to be more susceptible to neurotoxic signals than the non-differentiated ones, as evidenced by loss of sprouting and connectivity, decreases in choline acetyltransferase and pyruvate dehydrogenase activities, disturbances in acetyl-CoA compartmentation and metabolism, insufficient or excessive acetylcholine release, as well as increased expression of apoptosis markers. Each neurotoxin impaired both acetylcholine and acetyl-CoA metabolism of these cells. Activation of p75 or trkA receptors made either acetyl-CoA or cholinergic metabolism more susceptible to neurotoxic influences, respectively. Neurotoxins aggravated detrimental effects of each other, particularly in differentiated cells. Thus brain cholinergic neurons might display a differential susceptibility to Al and other neurotoxins depending on their genotype or phenotype-dependent variability of the cholinergic and acetyl-CoA metabolism.

The contribution of mild thiamine deficiency and ethanol consumption to central cholinergic parameter dysfunction and rats' open-field performance impairment

We studied at the biochemical, morphological, and behavioral levels the effect of chronic ethanol consumption, associated or not with a mild thiamine deficiency episode. We found that (i) thiamine deficiency induced a significant decrease of the acetylcholinesterase (AChE) activity both in cortex and hippocampus; (ii) chronic ethanol treatment has no effect on cortical AChE activity, but induced a significant decrease of hippocampal enzyme activity; (iii) the reduction in cortical and hippocampal AChE activity induced by chronic ethanol treatment associated with a 1-week thiamine deficiency was also significant and was greater than that induced by ethanol alone. Furthermore, either chronic ethanol or thiamine deficiency induced a significant decrease in the release of acetylcholine (ACh) in the stimulated condition using high potassium concentration; and when both treatments were associated the decrease was even greater. In the unstimulated condition, the reduction in the release of ACh was greater for ethanol treatment than for thiamine deficiency. Open-field tests showed that only in the "sniffing" category were there significant differences among the experimental groups. No morphological change was detected by optical microscopy, suggesting that the injury process was in its initial stages in which only functional and behavioral changes are displayed. In addition, our biochemical results indicate that cortical cholinergic susceptibilities to ethanol and thiamine deficiency are significantly different.

Oxidative stress and a key metabolic enzyme in Alzheimer brains, cultured cells, and an animal model of chronic oxidative deficits

Oxidative stress and diminished metabolism occur in several neurodegenerative disorders. Brains from Alzheimer's disease (AD) patients exhibit several indicators of oxidative stress and have reduced activities of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key mitochondrial enzyme. Whether these abnormalities are secondary to neurodegenerative processes or are inherent properties of the cells cannot be determined in autopsy brain. Studies in cultured fibroblasts suggest that AD-related differences in oxidative stress and KGDHC reflect inherent properties of AD cells. KGDHC is sensitive to oxidative stress whether the enzyme is studied in cells, in purified mitochondria, or as an isolated protein. Reductions of brain KGDHC in living rodents lead to oxidative stress and selective cell death. The results suggest that KGDHC participates in a deleterious cascade of events related to oxidative stress that are critical in selective neuronal loss in neurodegenerative diseases.

The alpha-ketoglutarate dehydrogenase complex in neurodegeneration

Altered energy metabolism is characteristic of many neurodegenerative disorders. Reductions in the key mitochondrial enzyme complex, the alpha-ketoglutarate dehydrogenase complex (KGDHC), occur in a number of neurodegenerative disorders including Alzheimer's Disease (AD). The reductions in KGDHC activity may be responsible for the decreases in brain metabolism, which occur in these disorders. KGDHC can be inactivated by several mechanisms, including the actions of free radicals (Reactive Oxygen Species, ROS). Other studies have associated specific forms of one of the genes encoding KGDHC (namely the DLST gene) with AD, Parkinson's disease, as well as other neurodegenerative diseases. Reductions in KGDHC activity can be plausibly linked to several aspects of brain dysfunction and neuropathology in a number of neurodegenerative diseases. Further studies are needed to assess mechanisms underlying the sensitivity of KGDHC to oxidative stress and the relation of KGDHC deficiency to selective vulnerability in neurodegenerative diseases.

Mechanisms of neuronal cell death in Wernicke's encephalopathy

Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine deficiency, encountered in chronic alcoholics and in patients with grossly impaired nutritional status. Neuropathologic studies as well as Magnetic Resonance Imaging reveal selective diencephalic and brainstem lesions in patients with WE. The last decade has witnessed major advances in the understanding of pathophysiologic mechanisms linking thiamine deficiency to the selective brain lesions characteristic of WE. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase, a rate-limiting tricarboxylic acid cycle enzyme are significantly reduced in autopsied brain tissue from patients with WE and from rats treated with the central thiamine antagonist, pyrithiamine. In the animal studies, evidence suggests that such enzyme deficits result in focal lactic acidosis, cerebral energy impairment and depolarization resulting from increased release of glutamate in vulnerable brain structures. It has been proposed that this depolarization may result in N-Methyl-D-Aspartate receptor-mediated excitotoxicity as well as increased expression of immediate early genes such as c-fos and c-jun resulting in apoptotic cell death. Other mechanisms involved in thiamine deficiency-induced cell loss may involve free radicals and alterations of the blood-brain barrier. Additional studies are still required to identify the site of the initial cellular insult and to explain the predilection of diencephalic and brainstem structures due to thiamine deficiency.

The supply of glucose to the brain and cognitive functioning

Unlike other organs the energy requirement of the brain is met almost exclusively by aerobic glucose degradation (Siesjo, 1978). The energy requirement of the brain is 20–30% of the whole organism at rest, although its weight is only 2%. The energy stores in the brain are extremely small when compared with the high rate of glucose utilisation: thus the brain is reliant on a continuous glucose supply. Only about 30% of glucose is required for direct energy production; much of the remainder is used for the synthesis of amino acids, peptides, lipids and nucleic acids (Siebert, Gessner & Klasser, 1986). Thus a source of glucose is essential for the synthesis of physiologically active amines such as serotonin, noradrenaline and acetylcholine. Although it is well accepted that hypoglycaemia can result in the disruption of cognitive functioning, this is a rare phenomenon and it has usually been assumed that levels of blood glucose, within the normal range, do not influence intellectual functioning. This assumption is discussed in this paper.

Thiamine therapy in Alzheimer's disease

Fursultiamine (TTFD), a derivative of thiamine, at an oral dose of 100 mg/day had a mild beneficial effect in patients with Alzheimer's disease in a 12-week open trial. The improvement could be observed not only in their emotional or other mental symptoms but also in intellectual function. Only mildly impaired subjects showed cognitive improvement. Alzheimer patients' blood levels of thiamine before the trial were within the normal range. No adverse reactions were observed and all patients tolerated the trial well. TTFD could afford an alternate treatment to large doses of thiamine hydrochloride in Alzheimer patients. However, further investigations of the therapeutic implications of thiamine and its possible etiologic clues to Alzheimer's disease are necessary.

Synergistic anticholinergic and antiserotonergic effects in humans

Animal research suggests an important interactive role for ascending cholinergic and serotonergic systems in modulation of cerebral function. Employing a randomized, double-blind, crossover design, 11 healthy young adults were tested in each of four conditions: (1) placebo, (2) fenfluramine (a serotonin depleting agent), (3) scopolamine (a muscarinic antagonist), and (4) fenfluramine and scopolamine. P3 latency was slowed by the dual drug treatment to an extent greater than the sum of individual drug effects. EEG mean frequency was decreased by behavioral activation, and this decrease was reversed by the combined drug treatment but not by single drugs. In contrast, verbal memory, EEG alpha power, and P3 amplitude were significantly affected only by scopolamine. No drug effects were found for the N1 and P2 potentials. The results provide the first demonstration of combined anticholinergic and antiserotonergic effects in humans, and offer partial support to the concept of an interactive role of cholinergic and serotonergic systems in cerebral mechanisms.

Central neurotoxicity induced by subchronic exposure to 2,4-pentanedione vapour

1. Male and female Fischer 344 rats were exposed to 2,4-pentanedione (2,4-PD) vapour acutely (4 h) at 1265 or 1811 ppm, or for 6 h day-1, 5 days a week for 14 weeks to 0, 101, 307 or 650 ppm. 2. Mortality occurred during or within a few hours of the acute exposures (10% at 1265 ppm; 70% at 1811 ppm). No animal had gross or microscopic brain lesions. 3. All female rats (20) and 10 of 30 male rats exposed to 650 ppm 2,4-PD vapour died by the 38th study day (29 exposures); there were no subsequent male deaths. Twenty-five of the 30 animals that died, and seven of the 15 males that survived, had light microscopical evidence of degenerative lesions, principally within the caudate/putamen nuclei, nuclei of the cerebellar medulla, and vestibular nuclei. Less frequently involved, in animals that died, were various regions of the cerebral cortex. The early histopathological lesions, seen from the 16th study day (12 exposures) to the 38th study day (28 exposures) were characterised by malacia. When present, lesions in male rats surviving the 14-weeks of 650 ppm 2, 4-PD exposure were characterised by malacia and gliosis. No peripheral nerve lesions were seen by light or transmission electron microscopy. 4. Neither mortality nor neuropathology were seen in rats subchronically exposed to 101 or 307 ppm, 2,4-PD vapour.

Influence of thiamine on the behavioral sensitivity to ethanol

Changes in sensitivity to ethanol's rate-decreasing effects on operant performance were examined in control rats and cohorts that received diet-induced or diet+pyrithiamine-induced thiamine deficiency. Seven groups of male Sprague-Dawley rats (12 rats/group) were trained in a 5-cycle lever-press operant task under a fixed-ratio 30 schedule of food reinforcement. Once trained to maintain consistent operant performance across all 5 cycles, each rat was tested with various doses of ethanol injected at the beginning of each time-out cycle. Each group of rats demonstrated equivalent saline baseline operant performance and ED50 for ethanol's rate-suppressing effects. Training sessions were suspended and rats received either a short- (9 days) or long-term (5-week) exposure to regular rat chow diet or thiamine-deficient diet, and received either saline or pyrithiamine injections in a 2 x 2 design. Three additional control groups were maintained on a regular rat chow diet and received supplemental injections of either thiamine+pyrithiamine injections, thiamine+saline injections, or saline+pyrithiamine injections. The controlled diet phase continued until the development of overt signs of thiamine deficiency, at which time thiamine supplements were administered for 4 days. In phase 3, all rats were retrained in the operant task and a second ethanol dose-effect function was generated. A history of thiamine deficiency and recovery failed to shift the behavioral dose-effect functions significantly for ethanol and their associated blood alcohol curves. Most interestingly, significant behavioral sensitization to ethanol's rate suppressant effects was demonstrated in the two control groups of rats receiving regular rat chow diet in combination with supplemental injections of thiamine and either saline or pyrithiamine.(ABSTRACT TRUNCATED AT 250 WORDS)

The neuropathogenesis of delirium. A need to focus our research

Delirium symptoms suggest dysfunction of multiple brain regions. However, little is known about delirium's underlying neuropathogenesis. This article addresses the need for research on neuroanatomic and neuropathophysiologic underpinnings of delirium, analogous to that of schizophrenia and affective disorders. Electrophysiologic tests, structural and functional brain imaging, and neurotransmitter studies in delirium are critically reviewed. The importance of both cerebral cortical and subcortical areas is noted, with emphasis on frontal, right-hemisphere, and subcortical regions, including caudate and anteromedial thalamus. Each symptom of delirium can be viewed from a neuroanatomic and neurochemical perspective. Recommendations for research are made throughout the article.

Evidence for a central cholinergic effect of high-dose thiamine

In vitro animal studies have suggested that thiamine is involved in the presynaptic release of acetylcholine. Total thiamine content in cholinergic nerve terminals is comparable with that of acetylcholine, and the phosphorylation state of thiamine changes with release of acetylcholine. Thiamine binds to nicotinic receptors and may exhibit anticholinesterase activity. Based on these observations, we investigated the effects of pharmacological doses of thiamine on the cognitive deficits induced by the anticholinergic scopolamine in healthy young adults using a randomized, double-blind, placebo-controlled, double-crossover design. Drug effects were assessed by P3 event-related potential, quantitated electroencephalography, and free recall memory. Conditions included (1) baseline, (2) thiamine 5 gm p.o. and scopolamine 0.007 mg/kg IM, and (3) lactose PO and scopolamine 0.007 mg/kg IM. Thiamine significantly reduced adverse effects of scopolamine on P3 latency, spectral components of electroencephalography, and memory recall. The results are consistent with a cholinomimetic effect of thiamine in the central nervous system. Additional studies are needed to delineate the basic mechanisms and possible therapeutic efficacy of thiamine at pharmacological dosages.

Preliminary findings of high-dose thiamine in dementia of Alzheimer's type

Thiamine is important not only in the metabolism of acetylcholine but also in its release from the presynaptic neuron. Pathologic, clinical, and biochemical data suggest that thiamine deficiency is detrimental to the cholinergic system and that thiamine-dependent enzymes may be altered in Alzheimer's disease. Two previous studies reported contradictory results in patients with dementia of Alzheimer's type treated with 3 g/day of thiamine. In the present study, we examined the effects of 3 to 8 g/day thiamine administered orally. Our results suggest that thiamine at these pharmacologic dosages may have a mild beneficial effect in dementia of Alzheimer's type. The mechanism of the observed effect is unknown, but the findings warrant further investigation, not only for their therapeutic implications but for their possible etiologic clues. In addition, the results suggest long-term carry-over effects that should be considered in the design of future studies.

Decrease of high affinity ouabain binding in rat cerebellum and hypothalamus by thiamin deficiency

The effect of dietary thiamin deficiency on high affinity [3H]ouabain binding was examined in different regions of rat brain. The binding activity in the cerebellum and hypothalamus was significantly lower in the thiamin-deficient group than in the pair-fed control and freely fed control groups. The decrease was due to a change in Bmax but not in Kd. The results suggest a possible involvement of (Na+,K+)-ATPase in neurological manifestations of thiamin deficiency.

Muricidal suppression by chlorpheniramine and changes in brain levels following dietary-induced thiamine deficiency in rats

The effects of thiamine deficiency on pharmacological and pharmacokinetic activities of chlorpheniramine were investigated in rats. Chlorpheniramine (5-10 mg/kg) showed a dose-dependent suppressive effect on muricide induced by thiamine deficiency. The ED50 value for muricidal suppression at 1 hr was approximately 7.1 mg/kg (95% confidence limits, 5.4-9.3 mg/kg) after oral administration. Using a high-performance liquid chromatographic (HPLC) method, chlorpheniramine was detectable at 10 min in the blood and brain of rats. The present pharmacokinetic data suggest that chlorpheniramine can easily pass through the blood-brain barrier (B.B.B.) and enter the brain. It is stored therein and is later slowly released and excreted. In thiamine deficient rats, chlorpheniramine entered the brain in much higher concentrations than in normal and pair-fed rats, and significantly higher levels were maintained for a period of 1.5 hr. These results suggest that thiamine deficiency affects pharmacological and pharmacokinetic activities in rats, and support the view that there is a malfunction of the B.B.B. in thiamine deficient rats. These factors should be taken into consideration in clinical usage and dosage.

Chronic administration of sulbutiamine improves long term memory formation in mice: possible cholinergic mediation

Thiamine deficiency in both man and animals is known to produce memory dysfunction and cognitive disorders which have been related to an impairment of cholinergic activity. The present experiment was aimed at testing whether, inversely, chronic administration of large doses of sulbutiamine would have a facilitative effect on memory and would induce changes in central cholinergic activity. Accordingly mice received 300 mg/kg of sulbutiamine daily for 10 days. They were then submitted to an appetitive operant level press conditioning test. When compared to control subjects, sulbutiamine treated mice learned the task at the same rate in a single session but showed greatly improved performance when tested 24 hr after partial acquisition of the same task. Parallel neurochemical investigations showed that the treatment induced a slight (+ 10%) but significant increase in hippocampal sodium-dependent high affinity choline uptake. The present findings and previous results suggest that sulbutiamine improves memory formation and that this behavioral effect could be mediated by an increase in hippocampal cholinergic activity.

Thiamine deficiency and nervous system function disturbances

Thiamine is important for oxidative metabolism, and B1 deficiency is thought to give rise to polyneuropathies. A group of male Wistar rats (n = 15) received a vitamin B1 deficient diet (group-a), and the pair fed control group (n = 20, group-b) received a normal diet with no vitamin deficiency. A second control group (group-c) was fed unrestrictedly with a standard diet (n = 19). All animals were examined for 25 weeks. The sensory nerve conduction velocity, the compound radicular, spinal and brain stem responses and the SEP were derived for tail and hind paw stimulation. The examination was repeated at 6-week intervals. There was no difference in nerve conduction between group-a and -b, but for both groups the conduction velocity was significantly slower than in group-c. The SEP latencies were significantly increased in group-a compared with group-b and also with group-c. The spinal and cerebral latencies were delayed in group-a. The diameters of myelinated nerve fibres were decreased in group-a compared with group-b, and in group-b compared with group-c. The results indicate that a specific polyneuropathy exists as a result of B1 deficiency, and that the sequelae of the lack of thiamine are pronounced in the CNS.

Alterations in muscarinic cholinergic receptor densities induced by thiamine deficiency: autoradiographic detection of changes in high- and low-affinity agonist binding

Animals fed a diet deficient in thiamine or treated with a drug preventing the utilization of thiamine (thiamine antagonist) exhibited alterations in ligand binding to muscarinic receptors in several brain regions. Using quantitative techniques of receptor autoradiography, an increase in muscarinic receptor binding was demonstrated in such regions as the corpus callosum, lamina VI of the parietal cortex, caudate-putamen, ventral nucleus of the thalamus, stratum lacunosum moleculare and stratum oriens of the hippocampus, and the hilus of the area dentata. As a result of thiamine deficiency, this increase in muscarinic receptor populations was primarily due to an increase in the binding of the low-affinity agonist site. In the same experiment, a decrease in muscarinic receptor binding was found in the ventromedial region of the hypothalamus. Thiamine deficiency thus causes an up-regulation of muscarinic receptor binding in several regions of rat brain while causing a down-regulation of these same receptors in other brain areas.

The severe lacticacidosis of thiamine deficiency: acute pernicious or fulminating beriberi

Adults who had been drinking alcohol were admitted to hospital with severe lacticacidosis and died within two days. Empirical treatment with thiamine proved to be a cure for the disorder, for it was acute pernicious or fulminating beriberi. Thiamine deficiency is neglected as a cause of lacticacidosis.

Correlation of enzymatic, metabolic, and behavioral deficits in thiamin deficiency and its reversal

To clarify the enzymatic mechanisms of brain damage in thiamin deficiency, glucose oxidation, acetylcholine synthesis, and the activities of the three major thiamin pyrophosphate (TPP) dependent brain enzymes were compared in untreated controls, in symptomatic pyrithiamin-induced thiamin-deficient rats, and in animals in which the symptoms had been reversed by treatment with thiamin. Although brain slices from symptomatic animals produced 14CO2 and 14C-acetylcholine from [U-14C]glucose at rates similar to controls under resting conditions, their K+-induced-increase declined by 50 and 75%, respectively. In brain homogenates from these same animals, the activities of two TPP-dependent enzymes transketolase (EC 2.2.1.1) and 2-oxoglutarate dehydrogenase complex (EC 1.2.4.2, EC 2.3.1.61, EC 1.6.4.3) decreased 60-65% and 36%, respectively. The activity of the third TPP-dependent enzyme, pyruvate dehydrogenase complex (EC 1.2.4.1, EC 2.3.1.12, EC 1.6.4.3) did not change nor did the activity of its activator pyruvate dehydrogenase phosphate phosphatase (EC 3.1.3.43). Although treatment with thiamin for seven days reversed the neurological symptoms and restored glucose oxidation, acetylcholine synthesis and 2-oxoglutarate dehydrogenase activity to normal, transketolase activity remained 30-32% lower than controls. The activities of other TPP-independent enzymes (hexokinase, phosphofructokinase, and glutamate dehydrogenase) were normal in both deficient and reversed animals.

Impairment of acetylcholine synthesis in thiamine deficient rats developed by prolonged tea consumption

The synthesis of whole brain acetylcholine is reduced in thiamine deficient rats produced by prolonged administration of tea. In those rats fed a normal diet and given tea (1:50, w/v) instead of drinking water for 20 weeks, the conversion of [14C] pyruvate to [14C]acetylcholine decreased by 35%. However, no neurological symptoms were observed. Administration of tea to rats fed a thiamine half-deficient diet for 7-8 weeks caused not only 60% decrease in acetylcholine synthesis but also neurological symptoms. This decreased synthesis of acetylcholine is related to a decline in pyruvate dehydrogenase activity. The results suggest that prolonged administration of tea to rats cause an impairment of acetyl CoA production resulting in a deficit in acetylcholine synthesizing capacity.

Brain acetylcholine synthesis declines with senescence

The synthesis of whole brain acetylcholine is reduced in two strains (C57BL and BALB/c) of senescent mice. The incorporation of [U-14C]glucose into acetylcholine decreased in both strains by 40 +/- 4 per cent in 10-month-old mice and by 58 +/- 9 percent in 30-month-old mice compared with mice 3 months old. The incorporation of [2H4]choline into acetylcholine declined 60 and 73 percent in 10- and 30-month-old mice, respectively. Deficits in the cholinergic system may contribute to brain dysfunctions that complicate senescence.