Pathophysiologic mechanisms responsible for the reversible (thiamine-responsive) and irreversible (thiamine non-responsive) neurological symptoms of Wernicke's encephalopathy

Region-selective permeability of the blood-brain barrier to α-aminoisobutyric acid during thiamine deficiency and following its reversal

Thiamine deficiency (TD) results in focal lesions in several regions of the rat brain including the thalamus and inferior colliculus. Since alterations in blood-brain barrier (BBB) integrity may play a role in this damage, we have examined the influence of TD on the unidirectional blood-to-brain transfer constant (K_i) of the low molecular weight species α-aminoisobutyric acid (AIB) in vulnerable and non-vulnerable brain regions at different stages during progression of the disorder, and following its reversal with thiamine. Analysis of the regional distribution of K_i values showed early (day 10) increased transfer of [¹⁴C]-AIB across the BBB in the vulnerable medial thalamus as well as the non-vulnerable caudate and hippocampus. At the acute symptomatic stage (day 14), more widespread BBB permeability changes were detected in most areas including the lateral thalamus, inferior colliculus, and non-vulnerable cerebellum and pons. Twenty-four hours following thiamine replenishment, a heterogeneous pattern of increased BBB permeability was observed in which many structures maintained increased uptake of [¹⁴C]-AIB. No increase in the [³H]-dextran space, a marker of intravascular volume, was detected in brain regions during the progress of TD, suggesting that BBB permeability to this large tracer was unaffected. These results indicate that BBB opening i) occurs early during TD, ii) is not restricted to vulnerable areas of the brain, iii) is progressive, iv) persists for at least 24 h following treatment with thiamine, and v) is likely selective in nature, depending on the molecular species being transported.

The Relevance of Thiamine Evaluation in a Practical Setting

Thiamine is a crucial cofactor involved in the maintenance of carbohydrate metabolism and participates in multiple cellular metabolic processes. Although thiamine can be obtained from various food sources, some common food groups are deficient in thiamine, and it can be denatured by high temperature and pH. Additionally, different drugs can alter thiamine metabolism. In addition, the half-life of thiamine in the body is between 1 and 3 weeks. All these factors could provide an explanation for the relatively short period needed to develop thiamine deficiency and observe the consequent clinical symptoms. Thiamine deficiency could lead to neurological and cardiological problems. These clinical conditions could be severe or even fatal. Marginal deficiency too may promote weaker symptoms that might be overlooked. Patients undergoing upper gastrointestinal or pancreatic surgery could have or develop thiamine deficiency for many different reasons. To achieve the best outcome for these patients, we strongly recommend the execution of both an adequate preoperative nutritional assessment, which includes thiamine evaluation, and a close nutritional follow up to avoid a nutrient deficit in the postoperative period.

Toward Eradication of B-Vitamin Deficiencies: Considerations for Crop Biofortification

'Hidden hunger' involves insufficient intake of micronutrients and is estimated to affect over two billion people on a global scale. Malnutrition of vitamins and minerals is known to cause an alarming number of casualties, even in the developed world. Many staple crops, although serving as the main dietary component for large population groups, deliver inadequate amounts of micronutrients. Biofortification, the augmentation of natural micronutrient levels in crop products through breeding or genetic engineering, is a pivotal tool in the fight against micronutrient malnutrition (MNM). Although these approaches have shown to be successful in several species, a more extensive knowledge of plant metabolism and function of these micronutrients is required to refine and improve biofortification strategies. This review focuses on the relevant B-vitamins (B1, B6, and B9). First, the role of these vitamins in plant physiology is elaborated, as well their biosynthesis. Second, the rationale behind vitamin biofortification is illustrated in view of pathophysiology and epidemiology of the deficiency. Furthermore, advances in biofortification, via metabolic engineering or breeding, are presented. Finally, considerations on B-vitamin multi-biofortified crops are raised, comprising the possible interplay of these vitamins in planta.

Thiamin in Clinical Practice

Thiamin is a water-soluble vitamin also known as vitamin B1. Its biologically active form, thiamin pyrophosphate (TPP), is a cofactor in macronutrient metabolism. In addition to its coenzyme roles, TPP plays a role in nerve structure and function as well as brain metabolism. Signs and symptoms of thiamin deficiency (TD) include lactic acidosis, peripheral neuropathy, ataxia, and ocular changes (eg, nystagmus). More advanced symptoms include confabulation and memory loss and/or psychosis, resulting in Wernicke's encephalopathy and/or Wernicke's Korsakoff syndrome, respectively. The nutrition support clinician should be aware of patients who may be at risk for TD. Risk factors include those patients with malnutrition due to 1 or more nutrition-related etiologies: decreased nutrient intake, increased nutrient losses, or impaired nutrient absorption. Clinical scenarios such as unexplained heart failure or lactic acidosis, renal failure with dialysis, alcoholism, starvation, hyperemesis gravidarum, or bariatric surgery may increase the risk for TD. Patients who are critically ill and require nutrition support may also be at risk for TD, especially those who are given intravenous dextrose void of thiamin repletion. Furthermore, understanding thiamin's role as a potential therapeutic agent for diabetes, some inborn errors of metabolism, and neurodegenerative diseases warrants further research. This tutorial describes the absorption, digestion, and metabolism of thiamin. Issues pertaining to thiamin in clinical practice will be described, and evidence-based practice suggestions for the prevention and treatment of TD will be discussed.

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.

How important are brain banks for alcohol research?

This article contains the proceedings of a symposium at the 2002 RSA/ISBRA Meeting in San Francisco, organized and chaired by Clive Harper and co-chaired by Izuru Matsumoto. The presentations were (1) Introduction, by Clive Harper; (2) The quality of tissue-a critical issue, by Therese Garrick; (3) The first systematic brain tissue donor program in Japan, by Izuru Matsumoto; (4) Brain scans after death-really! by Adolf Pfefferbaum, Elfar Adalsteinsson, and Edith Sullivan; (5) Capture that (genial) expression, by Joanne Lewohl and Peter Dodd; and (6) Neurochemical/pharmacological studies: experimental design and limitations, by Roger Butterworth.

Mechanisms of selective neuronal cell death due to thiamine deficiency

Multiple mechanisms contribute to the selective brain lesions observed in WKS and experimental thiamine deficiency. Recent evidence of early microglial activation and increased free radical production suggest that oxidative stress processes play an important early role in the brain damage associated with thiamine deficiency.

Quantitative alpha-ketoglutarate dehydrogenase activity staining in brain sections and in cultured cells

The activity of a key mitochondrial enzyme, the alpha-ketoglutarate dehydrogenase complex (KGDHC), declines in the brains of patients with neurodegenerative diseases such as Alzheimer's disease, as well as in thiamine-deficient (TD) animals. The decreased activity often occurs without a reduction in enzyme protein, which negates the use of immunocytochemistry to study cellular or regional changes in enzyme activity within the brain. To overcome this limitation, an activity staining method using nitroblue tetrazolium was developed. The histochemical activity staining was standardized in cultured cells. The assay was linear with time and was highly specific for KGDHC. The dark-blue reaction product (formazan) formed a pattern that was consistent with mitochondrial localization. Treatment of the cultured cells with both reversible and irreversible inhibitors decreased formazan production, whereas conventional enzyme assays on cell lysates only revealed loss of KGDHC activity with irreversible inhibitors. The activity staining was also linear with time and highly specific for KGDHC activity in mouse brain sections. Staining occurred throughout the brain, and discrete neuronal populations exhibited particularly intense staining. The pattern of staining differed markedly from the distribution of KGDHC protein by immunocytochemistry. Generalized decreases in the intensity of activity staining that occurred in the TD brains compared to controls were comparable with the loss of KGDHC activity by conventional enzyme assay. Thus, the present study introduces a new histochemical method to measure KGDHC activity at the cellular and regional level, which will be useful to determine changes of in situ enzyme activity.

Metabolic impairment elicits brain cell type-selective changes in oxidative stress and cell death in culture

Abnormalities in oxidative metabolism and inflammation accompany many neurodegenerative diseases. Thiamine deficiency (TD) is an animal model in which chronic oxidative stress and inflammation lead to selective neuronal death, whereas other cell types show an inflammatory response. Therefore, the current studies determined the response of different brain cell types to TD and/or inflammation in vitro and tested whether their responses reflect inherent properties of the cells. The cells that have been implicated in TD-induced neurotoxicity, including neurons, microglia, astrocytes, and brain endothelial cells, as well as neuroblastoma and BV-2 microglial cell lines, were cultured in either thiamine-depleted media or in normal culture media with amprolium, a thiamine transport inhibitor. The activity levels of a key mitochondrial enzyme, alpha-ketoglutarate dehydrogenase complex (KGDHC), were uniquely distributed among different cell types: The highest activity was in the endothelial cells, and the lowest was in primary microglia and neurons. The unique distribution of the activity did not account for the selective response to TD. TD slightly inhibited general cellular dehydrogenases in all cell types, whereas it significantly reduced the activity of KGDHC exclusively in primary neurons and neuroblastoma cells. Among the cell types tested, only in neurons did TD induce apoptosis and cause the accumulation of 4-hydroxy-2-nonenal, a lipid peroxidation product. On the other hand, chronic lipopolysaccharide-induced inflammation significantly inhibited cellular dehydrogenase and KGDHC activities in microglia and astrocytes but not in neurons or endothelial cells. The results demonstrate that the selective cell changes during TD in vivo reflect inherent properties of the different brain cell types.

Increased "peripheral-type" benzodiazepine receptor sites and mRNA in thalamus of thiamine-deficient rats

"Peripheral-type" benzodiazepine receptors (PTBRs) are highly expressed on the outer mitochondrial membrane of several types of glial cells. In order to further elucidate the nature of the early glial cell changes in thiamine deficiency, PTBR sites and PTBR mRNA were measured in thalamus, a brain structure which is particularly vulnerable to thiamine deficiency, of thiamine-deficient rats at presymptomatic and symptomatic stages of deficiency. PTBR sites were measured using an in vitro binding technique and the selective radio ligand [3H]-PK11195. PTBR gene expression was measured by RT-PCR using oligonucleotide primers based upon the published sequence of the cloned rat PTBR. Microglial and astrocytic changes in thalamus due to thiamine deficiency were assessed using immunohistochemistry and antibodies to specific microglial (ED-1) and astrocytic (GFAP) proteins respectively. Significant increases of [3H]-PK11195 binding sites and concomitantly increased PTBR mRNA were observed in thalamus at the symptomatic stage of thiamine deficiency, coincident with severe neuronal cell loss and increased GFAP-immunolabelling (indicative of reactive gliosis). Positron Emission Tomography using 11C-PK11195 could provide a novel approach to the diagnosis and assessment of the extent of thalamic damage due to thiamine deficiency in humans with Wernicke's Encephalopathy.

Alcohol-thiamine interactions: an update on the pathogenesis of Wernicke encephalopathy

Wernicke encephalopathy is a neurological disorder commonly observed in chronic alcohol abuse, in patients with AIDS, and in other conditions of compromised nutritional status. The underlying cause of the disorder is thiamine deficiency. The present review highlights data focusing on alcohol-thiamine interactions and their relationship to the pathogenesis of Wernicke encephalopathy. Recent findings on the effects of alcohol on thiamine absorption and storage and on thiamine phosphorylation to the enzyme co-factor form (thiamine diphosphate) are discussed with regard to the postulated "biochemical lesion" of Wernicke encephalopathy. Also discussed are new findings on the molecular genetics of the thiamine-dependent enzyme transketolase in patients with Wernicke encephalopathy. A discussion of the hypotheses regarding the mechanisms underlying the phenomenon of selective neuronal cell death observed in this disorder including cerebral energy deficit, focal lactic acidosis, glutamate excitotoxicity, increased expression of immediate-early genes, free radicals and perturbations of the blood-brain barrier are presented. Finally, the possible role of thiamine deficiency in alcoholic peripheral neuropathy is reviewed.

Operational criteria for the classification of chronic alcoholics: identification of Wernicke's encephalopathy

OBJECTIVES

To establish better operational criteria for the diagnosis of Wernicke's encephalopathy. Current criteria for diagnosing Wernicke's encephalopathy require the presence of three clinical signs (oculomotor abnormalities, cerebellar dysfunction, and an altered mental state), although it has often been reported that most patients do not fulfil all these criteria.

METHODS

The clinical histories of 28 alcoholics with neurological and neuropsychological assessments and definitive neuropathological diagnoses were examined to determine clinical signs for use in a screening schedule. Operational criteria were then proposed for differentiating patients with Wernicke's encephalopathy alone or in combination with Korsakoff's psychosis or hepatic encephalopathy. The new criteria for Wernicke's encephalopathy require two of the following four signs; (1) dietary deficiencies, (2) oculomotor abnormalities, (3) cerebellar dysfunction, and (4) either an altered mental state or mild memory impairment. Reproducibility and validity testing of these criteria were performed on 106 alcoholics screened from a large necropsy sample.

RESULTS

Despite rater variability with regard to specific symptoms, within and between rater reliability for diagnostic classification using the criteria retrospectively on patient records was 100% for three independent raters. Validity testing showed that Wernicke's encephalopathy was underrecognized only when occurring with hepatic encephalopathy (50% sensitivity).

CONCLUSIONS

By contrast with current criteria, the proposed operational criteria show that the antemortem identification of Wernicke's encephalopathy can be achieved with a high degree of specificity.

A non-cofactor role of thiamine derivatives in excitable cells?

Thiamine diphosphate (TDP) is an important cofactor of pyruvate (PDH) and alpha-ketoglutarate (KGDH) dehydrogenases and transketolase. Thiamine deficiency leads to reversible and irreversible brain lesions due to impaired oxidative metabolism. A specific non-cofactor role for thiamine has also been proposed in excitable cells and thiamine triphosphate (TTP) might be involved in the regulation of ion channels. Thiamine is taken up by neuroblastoma cells through a high affinity transporter. Inside the cells, it is rapidly phosphorylated to TDP. This high turnover TDP pool is the precursor for TTP. Most of the TDP however has a low turnover and is associated with PDH and KGDH in mitochondria. In excised inside-out patches from neuroblastoma cells, TTP, at a concentration of 1 microM, activates chloride channels of large unitary conductance, the so-called maxi-Cl- channels. These channels are inhibited by oxythiamine from the outide. In addition to the role of TTP in the regulation of chloride channels, thiamine itself, or a presently unknown analog, may have trophic effects on neuronal cells.

Can megadoses of thiamine prevent ethanol-induced damages of rat hippocampal CA1 pyramidal neurones?

The specific aim of this study was to evaluate whether high doses of thiamine can compensate or prevent alcohol-induced damages of rat hippocampus CA1 pyramids. Twenty weeks of ethanol consumption together with a dose of thiamine in the range of 1.19 mg/100 mg food induced significant enlargement (parameters measured were length of the whole spine and diameter of the end-bulb) of dendritic spines. Hypertrophy can be interpreted as a compensation process due to alcohol-induced cell death because viable spines are in search of new synaptic contacts. In contrast, dendritic spines of the alcohol group fed at the same time with a high dose of thiamine (119 mg/ 100 g food = megavitamintherapy) showed normal data concerning these parameters. From these results it may be concluded that a megavitamin therapy supports a neuron's carbohydrate metabolism and therefore could be able to prevent or reduce alcohol-induced damages of hippocampal CA1 pyramidal cells in rat central nervous system.

Neuronal cell death in Wernicke's encephalopathy: pathophysiologic mechanisms and implications for PET imaging

Thiamine deficiency in humans is associated with Wernicke's encephalopathy (WE) which is characterized neuropathologically by neuronal loss in selective brain regions. Pyrithiamine-induced thiamine-deficiency in the rat results in lesions which are similar in nature and distribution to those seen in human WE. Several mechanisms have been implicated in the pathogenesis of neuronal loss in thiamine deficiency including, (i) impaired cerebral energy metabolism, (ii) focal lactic acidosis, (iii) NMDA-receptor mediated excitotoxicity and (iv) blood-brain barrier breakdown. WE is difficult to diagnose during life and a large number of cases are missed by routine clinical neurological evaluation. Recently, non-invasive diagnostic procedures such as CT and MRI have been used for the evaluation of acute and chronic WE. Autoradiographic studies reveal that increased densities of binding sites for the astrocytic ligand 3H-PK11195 closely parallel the topographic distribution of reactive gliosis and neuronal loss in selective brain regions of pyrithiamine-induced thiamine-deficient rats. In contrast, binding sites for the neuronal ligand 3H-Ro15-1788 show poor regional correlation with neuronal loss in thiamine deficiency. Both of these ligands are available, and have been used in PET assessment of various disorders in humans. The results of autoradiographic studies suggest that 11C-PK11195 may offer a useful PET ligand for the assessment of brain damage in WE in humans.

The neurochemical pathology of thiamine deficiency: GABAA and glutamateNMDA receptor binding sites in a goat model

Synaptic plasma membranes were prepared from four cerebrocortical areas from six male Angora goats made chronically thiamine deficient (TD) by the administration of AmproliumTM (600-900 mg/kg daily for 38-44 d). Four male controls were matched for age (27-30 mo). Four different radioligands were used to characterise GABAA and Glu-RNMDA receptor binding sites. There were marked, localised and contrasting changes in motor cortex, with an increase in GABAA and a decrease in Glu-RNMDA binding site densities. Less clearcut changes of a similar nature were seen in visual cortex. There was no variation in the parameters of GABA-activated [3H]diazepam binding between cortical areas in control goats, but there was a reduction in the maximal response to GABA in all areas in TD goats. There were regional variations in glutamate-activated [3H]MK-801 binding in control goat brain, and a non-selectively reduced maximal response in TD. Alterations in these indices of GABA- and glutamate-mediated neurotransmission may underlie the neurological signs of acute thiamine deficiency in these animals.

In vivo localized proton NMR spectroscopy of thiamine-deficient rat brain

Thiamine deficiency (TD) in rats produces lesions similar to those found in humans suffering from Wernicke's encephalopathy, an organic mental disorder associated with alcoholism. Male Sprague-Dawley rats (n = 29) were deprived of thiamine via a regimen of thiamine-deficient chow and daily intraperitoneal injections of the thiamine antagonist pyrithiamine hydrobromide. Spectra were obtained by using the STEAM sequence. No significant change occurred in the ratio of Cr/NAA, while the ratio of Cho/NAA declined significantly (60 +/- 11%) on Day 14. Eleven rats received intraperitoneal injections of thiamine hydrochloride at the end of 12 days, and dose-dependent recovery in Cho/NAA was observed.

Thiamine phosphatases in human brain: regional alterations in patients with alcoholic cirrhosis

Activities of thiamine monophosphatase (TMPase) and thiamine diphosphatase (TDPase) were measured in homogenates of brain tissue obtained at autopsy from eight alcoholic cirrhotic patients who died in hepatic coma and nine controls matched for age and for postmortem delay interval and free from neurological or psychiatric disorders, hepatic disease, or other conditions of grossly impaired nutritional status. Enzyme activities were measured by standard spectrophotometric techniques. Both TMPase and TDPase were distributed unevenly in brain with highest activities being recorded in temporal cortex. Regional correlations between TMPase and TDPase, however, were poor. TDPase activities in brain tissue from alcoholic cirrhotic patients were significantly increased in 5 of 6 brain regions, by 26 to 153% (p < 0.05). TMPase activities in alcoholic cirrhotics, on the other hand, were unchanged in all brain regions, with the exception of caudate nucleus where they were increased by 70% (p < 0.05). These findings add to the substantial body of evidence suggesting that alcoholic liver disease is associated with abnormal thiamine status and with altered thiamine neurochemistry. Increased TDP degradation resulting from increased activities of TDPase could contribute to the pathophysiological mechanisms involved in alcohol-related brain dysfunction.

Mechanisms of cell death in cholinergic basal forebrain neurons in chronic alcoholics

Tau immunoreactivity was examined in post mortem tissue from patients in three groups: neurologically-asymptomatic and neuropathologically normal alcoholics, alcoholics with Wernicke's Encephalopathy (WE) and age matched non-alcoholic controls. Tau-positive granular and fibrillary inclusions were frequently observed within the magnocellular neurons of the cholinergic nucleus basalis, within occasional nucleus basalis neurons in non-WE alcoholics, but not in controls. Tau immunoreactivity was not however observed in cortical, brainstem, diencephalic or non-cholinergic forebrain structures. Peroxidase activity was also examined within the nucleus basalis using diaminobenzidine as an indicator. The majority of neurons in the basal forebrain showed increased peroxidase activity in all WE alcoholics and in some nucleus basalis neurons of non-WE alcoholics, but was rarely seen in controls. Neighboring astrocytes also showed increased peroxidase activity. These results suggest a link between peroxidase activity and the abnormal accumulation of phosphorylated tau. The presence of tau in the nucleus basalis of alcoholics with WE suggests a thiamine-dependent mechanism in tau accumulation and cell death in the cholinergic basal forebrain.

Thiamine homeostasis in neuroblastoma cells

We recently showed that thiamine uptake by neuroblastoma cells is mediated by two saturable transport system: the first with high affinity for thiamine (Km = 35 nM) is blocked by veratridine; the other, with low affinity is blocked by Ca2+. The driving force for thiamine uptake is its phosphorylation to thiamine diphosphate (TDP) by thiamine pyrophosphokinase and subsequent binding of this cofactor to apoenzymes. Our results suggest that cells of neuronal origin possess mechanisms regulating the intracellular concentration of thiamine. At low external thiamine, the vitamin is taken up by a high-affinity transporter and pyrophosphorylated in thiamine diphosphate (TDP): this is the TDP pool of slow turnover. An intraover extracellular concentration gradient of free thiamine is observed at low external concentration of the vitamin. At higher external thiamine concentration, TDP accumulation is limited by the binding capacity to the apoenzymes and unbound TDP (i.e. a small pool of fast turnover) is quickly hydrolyzed. Thiamine is slowly released by the cells by at least two different mechanisms. The first, accounting for a maximum of 50% of total thiamine release, is stimulated by external thiamine and is blocked by veratridine, suggesting that it is a self-exchange mechanism catalyzed by the high affinity thiamine transporter. The remaining thiamine efflux is neither sensitive to veratridine nor to Ca2+ and its mechanism is unknown. About 25% of intracellular thiamine is not released, even after treatment of the cells with digitonin, thus maintaining an apparent gradient. This suggests a binding or sequestration in intracellular compartments.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional alterations of thiamine phosphate esters and of thiamine diphosphate-dependent enzymes in relation to function in experimental Wernicke's encephalopathy

Thiamine phosphate esters (thiamine monophosphate-TMP; thiamine diphosphate-TDP and thiamine triphosphate-TTP) were measured as their thiochrome derivatives by High Performance Liquid Chromatography in the brains of pyrithiamine-treated rats at various stages during the development of thiamine deficiency encephalopathy. Severe encephalopathy was accompanied by significant reductions of all three thiamine phosphate esters in brain. Neurological symptoms of thiamine deficiency appeared when brain levels of TMP and TDP fell below 15% of normal values. Activities of the TDP-dependent enzyme alpha-ketoglutarate dehydrogenase were more severely reduced in thalamus compared to cerebral cortex, a less vulnerable brain structure. On the other hand, reductions of TTP, the non-cofactor form of thiamine, occurred to a greater extent in cerebral cortex than thalamus. Early reductions of TDP-dependent enzymes and the ensuing metabolic pertubations such as lactic acidosis impaired brain energy metabolism, and NMDA-receptor mediated excitotoxicity offer rational explanations for the selective vulnerability of brain structures such as thalamus to the deleterious effects of thiamine deficiency.