Genetic sensitivity to thiamine deficiency and development of alcoholic organic brain disease

Thiamin deficiency on fetal brain development with and without prenatal alcohol exposure

Adequate thiamin levels are crucial for optimal health through maintenance of homeostasis and viability of metabolic enzymes, which require thiamine as a co-factor. Thiamin deficiency occurs during pregnancy when the dietary intake is inadequate or excessive alcohol is consumed. Thiamin deficiency leads to brain dysfunction because thiamin is involved in the synthesis of myelin and neurotransmitters (e.g., acetylcholine, γ-aminobutyric acid, glutamate), and its deficiency increases oxidative stress by decreasing the production of reducing agents. Thiamin deficiency also leads to neural membrane dysfunction, because thiamin is a structural component of mitochondrial and synaptosomal membranes. Similarly, in-utero exposure to alcohol leads to fetal brain dysfunction, resulting in negative effects such as fetal alcohol spectrum disorder (FASD). Thiamin deficiency and prenatal exposure to alcohol could act synergistically to produce negative effects on fetal development; however, this area of research is currently under-studied. This minireview summarizes the evidence for the potential role of thiamin deficiency in fetal brain development, with or without prenatal exposure to alcohol. Such evidence may influence the development of new nutritional strategies for preventing or mitigating the symptoms of FASD.

Double-blind, randomized placebo-controlled clinical trial of benfotiamine for severe alcohol dependence

Alcohol dependence is associated with severe nutritional and vitamin deficiency. Vitamin B1 (thiamine) deficiency erodes neurological pathways that may influence the ability to drink in moderation. The present study examines tolerability of supplementation using the high-potency thiamine analog, benfotiamine (BF), and BF's effects on alcohol consumption in severely affected, self-identified, alcohol dependent subjects. A randomized, double-blind, placebo-controlled trial was conducted on 120 non-treatment seeking, actively drinking, alcohol dependent men and women volunteers (mean age=47 years) from the Kansas City area who met DSM-IV-TR criteria for current alcohol dependence. Subjects were randomized to receive 600 mg benfotiamine or placebo (PL) once daily by mouth for 24 weeks with 6 follow-up assessments scheduled at 4 week intervals. Side effects and daily alcohol consumption were recorded. Seventy (58%) subjects completed 24 weeks of study (N=21 women; N=49 men) with overall completion rates of 55% (N=33) for PL and 63% (N=37) for BF groups. No significant adverse events were noted and alcohol consumption decreased significantly for both treatment groups. Alcohol consumption decreased from baseline levels for 9 of 10 BF treated women after 1 month of treatment compared with 2 of 11 on PL. Reductions in total alcohol consumption over 6 months were significantly greater for BF treated women (BF: N=10, -611 ± 380 standard drinks; PL: N=11, -159 ± 562 standard drinks, p-value=0.02). BF supplementation of actively drinking alcohol dependent men and women was well-tolerated and may discourage alcohol consumption among women. The results do support expanded studies of BF treatment in alcoholism.

Interaction of thiamine deficiency and voluntary alcohol consumption disrupts rat corpus callosum ultrastructure

The relative roles of alcohol and thiamine deficiency in causing brain damage remain controversial in alcoholics without the Wernicke-Korsakoff syndrome. Experimental control over alcohol consumption and diet are impossible in humans but can be accomplished in animal models. This experiment was designed to differentiate the separate and combined effects on the macro- and ultrastructure of the corpus callosum of thiamine deficiency and voluntary alcohol consumption. Adult male alcohol-preferring (P) rats (9 chronically alcohol-exposed and 9 water controls) received a thiamine-deficient diet for 2 weeks. There were four groups: five rats previously exposed to alcohol were treated with pyrithiamine (a thiamine phosphorylation inhibitor); five rats never exposed to alcohol were treated with pyrithiamine; four alcohol-exposed rats were treated with thiamine; and four rats never exposed to alcohol were treated with thiamine. On day 14, thiamine was restored in all 18 rats; 2 weeks later the 10 pyrithiamine-treated rats received intraperitoneal thiamine. The rats were perfused 61 days post-pyrithiamine treatment at age 598 days. Brains were dissected and weight and volumes were calculated. Sagittal sections were stained to measure white matter structures. The corpus callosum was examined using transmission electron microscopy to determine density of myelinated fibers, fiber diameter, and myelin thickness. The corpus callosum in the alcohol/pyrithiamine group was significantly thinner, had greater fiber density, higher percentage of small fibers, and myelin thinning than in the alcohol/thiamine and water/thiamine groups. Several measures showed a graded effect, where the alcohol/pyrithiamine group had greater pathology than the water/pyrithiamine group, which had greater pathology than the two thiamine-replete groups. Across all 16 rats, thinner myelin sheaths correlated with higher percentage of small fibers. Myelin thickness and axon diameter together accounted for 71% of the variance associated with percentage of small fibers. Significant abnormalities in the alcohol/pyrithiamine group and lack of abnormality in the alcohol-exposed/thiamine-replete group indicate that thiamine deficiency caused white matter damage. The graded abnormalities across the dually to singly treated animals support a compounding effect of alcohol exposure and thiamine depletion, and indicate the potential for interaction between alcohol and thiamine deficiency in human alcohol-related brain damage.

Susceptibility of the cerebellum to thiamine deficiency

Thiamine or vitamin B(1), an essential nutrient absorbed from the diet, is involved in vital brain metabolic and cellular functions, including carbohydrate metabolism and neurotransmitter production. Diencephalic regions and, in particular, the cerebellum demonstrate lesions in cases of prolonged thiamine deficiency, such as that observed in alcohol-dependent individuals or in patients with cancer or AIDS. The purpose of this review is to demonstrate recent evidence of cerebellar dysfunction resulting from thiamine deficiency and to assemble theories as to why the cerebellum may be sensitive to this type of insult. A brief outline on cerebellar structure and function, as well as a short discussion on thiamine and thiamine deficiency are provided before detailing the conditions and mechanisms underlying thiamine deficiency-induced cerebellar dysfunction. Although much is known regarding cell loss from a lack of thiamine, further work is still required to identify the sequelae of events leading to the susceptibility of the cerebellum to injury stemming from a thiamine deficient diet or impaired thiamine utilization.

Long-term effect of therapeutic laser photocoagulation on gene expression in the eye

Microarray-based gene expression analysis demonstrated that laser photocoagulation (LPC) of mouse eyes had a long-term effect on the expression of genes functionally related to tissue repair, cell migration, proliferation, ion, protein and nucleic acid metabolism, cell signaling, and angiogenesis. Six structural genes, including five crystallins (Cryaa, Cryba1, Crybb2, Crygc, Crygs) and keratin 1-12 (Krt1-12), the anti-angiogenic factor thrombospondin 1 (Tsp1), the retina- and brain-specific putative transcription factor tubby-like protein 1 (Tulp1), and transketolase (Tkt), a key enzyme in the pentose-phosphate pathway, were all shown to be up-regulated by real-time PCR and/or Western blotting. Immunohistochemistry localized five of these proteins to the laser lesions and surrounding tissue within the retina and pigmented epithelium. This is the first study demonstrating long-term changes in the expression of these genes associated with LPC. Therefore, it suggests that modulated gene expression might contribute to the long-term inhibitory effect of LPC. In addition, these genes present novel targets for gene-based therapies aimed at treating microangiopathies, especially diabetic retinopathy, a disease currently only treatable with LPC.

Thiamine deficiency in the pathogenesis of chronic ethanol-associated cerebellar damage in vitro

Nutritional deficiencies associated with long-term ethanol consumption may cause neuronal damage in ethanol-dependent individuals. Thiamine deficiency, in particular, is thought to contribute to ethanol-associated cerebellar degeneration, although damage may occur in adequately nourished alcoholics. Thus, the present study examined the effects of thiamine depletion and ethanol exposure on cytotoxicity in rat cerebellum. Organotypic cerebellar slice cultures were treated starting at 25 days in vitro with 100 mM ethanol for 11 days or 10 days followed by a 24-h withdrawal period. This exposure paradigm has previously been shown in hippocampal slice cultures to result in spontaneous cytotoxicity upon ethanol withdrawal. Additional cerebellar cultures were exposed to the thiamine depleting agent pyrithiamine (10-500 microM) for 10 or 11 days, some in the presence of ethanol exposure or withdrawal. Other cultures were co-exposed to thiamine (1-100 microM), 500 microM pyrithiamine, and ethanol for 10 or 11 days. The results demonstrated that neither 11-day ethanol treatment nor withdrawal from 10-day exposure significantly increased cerebellar cytotoxicity, as measured by propidium iodide fluorescence. The 11-day treatment with 100 or 500 microM pyrithiamine significantly increased propidium iodide fluorescence approximately 21% above levels observed in control tissue. Cultures treated with both ethanol (11 days or 10 days plus withdrawal) and 500 microM pyrithiamine displayed a marked increase in cytotoxicity approximately 60-90% above levels observed in control cultures. Pyrithiamine and ethanol-induced cytotoxicity was prevented in cultures co-exposed to thiamine (10-100 microM) for the duration of pyrithiamine treatment. Findings from this report suggest that the cerebellum may be more sensitive to the toxic effects of thiamine deficiency, as compared with alcohol withdrawal, associated with alcohol dependence.

Disruption of frontocerebellar circuitry and function in alcoholism

This article represents a symposium of the 2002 joint meeting of RSA and ISBRA held in San Francisco. Presentations were Neuropathology of alcohol-related cerebellar damage in humans, by Antony J. Harding; Neuropathological evidence of cerebellar damage in an animal model of alcoholism, by Roberta Pentney and Cynthia Dlugos; Understanding cortical-cerebellar circuits through neuroimaging study of chronic alcoholics, by Peter R. Martin and Mitchell H. Parks; and Functional reorganization of the brain in alcoholism: neuroimaging evidence, by John E. Desmond, S.H. Annabel Chen, Michelle R. Pryor, Eve De Rosa, Adolf Pfefferbaum, and Edith V. Sullivan.

Relation of Apo E and ACE genes to cognitive performance in chronic alcoholic patients

Apolipoprotein E epsilon4 and ACE genes have been related to several conditions involving cognitive impairment, including Alzheimer's disease, normal ageing and cerebrovascular disease. However, it has not been established whether their genotypes are associated with alcoholism or its cognitive functioning. Genotypic distributions of 140 chronic alcoholic patients were compared with a non-alcoholic sample, and the cognitive performance of a subsample of the alcoholic subjects was assessed with standard neuropsychological tests. No differences in allele or genotype distributions of Apo E or ACE genes were found when comparing controls and alcoholics (Apo E epsilon2/2; patients 1.4%, controls 0% p < 0.06; epsilon2/epsilon3; patients 9.3%, controls 6.6% p < 0.29; epsilon2/epsilon4; patients 0%, controls 1% p < 0.31; epsilon3/epsilon3 patients 71.4%, controls 72% p < 0.89; epsilon3/epsilon4; patients 15.7%, controls 19.2%, p < 0.36; epsilon4/epsilon4; patients 2.1%, controls 1.2% p < 0.44; ACE D/D; patients 35%, controls 28.5% p < 0.14; I/D; patients 47.5%, controls 51.1% p < 0.51; I/I; patients 14.5%, controls 20.4% p < 0.19). In terms of cognitive performance, epsilon4/epsilon3 patients did better on visuoconstructive (p < 0.001) and visual memory (p < 0.04) functions compared with epsilon2/epsilon3 bearers. Furthermore, ACE D/D patients performed better on a test of abstract reasoning (p < 0.03) compared with the ACE I/I homozygous group. The cognitive results suggest that Apo E or ACE genotypes may modify the effects of ethanol on cognitive deterioration in alcoholic patients. However, the data do not support an association between the Apo E epsilon4 allele and reduced cognitive performance in alcoholism.

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.

Ethanol inhibits G-protein-mediated glucose uptake by C6 glioma cells

The mechanism of ethanol inhibition of glucose uptake was investigated using C6 glioma cells. Basal [3H]2-deoxy-D-glucose (2DG) uptake by C6 cells was inhibited by ethanol in a concentration-dependent manner. Fifty, 75 and 100 mM ethanol significantly inhibited basal 2DG uptake by 12, 20 and 23%, respectively (p < 0.05). Carbachol (an agonist acting via G protein-coupled receptors) stimulated the uptake by 26% (p < 0.05). In the presence of 100 mM ethanol, the ability of carbachol to stimulate 2DG uptake was abolished. In contrast, ethanol did not inhibit the ability of insulin to stimulate 2DG uptake. These results suggest that ethanol inhibits 2DG uptake by selectively interfering with G protein-mediated signal transduction pathway.

Critical role of arg433 in rat transketolase activity as probed by site-directed mutagenesis

It has been shown that one arginine per monomer at an unknown position is essential for enzyme activity of the homodimeric transketolase (TK) [Kremer, Egan and Sable (1980) J. Biol. Chem. 255, 2405-2410]. To identify the critical arginine, four highly conserved arginine residues of rat TK (Arg102, Arg350, Arg433 and Arg506) were replaced with alanine by site-directed mutagenesis. Wild-type and mutant TK proteins were produced in Escherichia coli and characterized. The Arg102-->Ala mutant exhibited similar catalytic activity to the wild-type enzyme, whereas Arg350-->Ala, Arg506-->Ala and Arg433-->Ala mutants exhibited 36.7, 37.0 and 6.1% of the wild-type activity respectively. Three recombinant proteins (wild-type, Arg350-->Ala and Arg433-->Ala) were purified to apparent homogeneity using Ni2+-affinity chromatography and further characterized. All these proteins were able to form homodimers (148 kDa), as shown by immunoblot analysis subsequent to non-denaturing gel electrophoresis. The Arg433-->Ala mutant protein was less stable than the wild-type and Arg350-->Ala proteins at 55 degrees C. Kinetic analyses revealed that both Vmax and Km values were markedly affected in the Arg433-->Ala mutant. The Km values for two substrates xylulose 5-phosphate and ribose 5-phosphate were 11.5- and 24.3-fold higher respectively. The kcat/Km values of the Arg433-->Ala mutant for the two substrates were less than 1% of those of the wild-type protein. Molecular modelling of the rat TK revealed that Arg433 of one monomer has three potential hydrogen-bond interactions with the catalytically important highly conserved loop of the other monomer. Thus, our biochemical analyses and modelling data suggest the critical role of the previously uncharacterized Arg433 in TK activity.

Thiamine deficiency decreases steady-state transketolase and pyruvate dehydrogenase but not alpha-ketoglutarate dehydrogenase mRNA levels in three human cell types

Reductions in the levels and activities of enzymes that utilize thiamine diphosphate (ThDP) as a cofactor are thought to be responsible for the tissue damage suffered during thiamine deficiency. Although loss of cofactor can account in part for loss of enzyme activity, thiamine and its phosphorylated derivatives may also regulate the expression of the genes encoding these proteins. To examine this possibility, steady-state mRNA levels for three ThDP-dependent enzymes were measured in human fibroblasts, lymphoblasts and neuroblastoma cells cultured under conditions of thiamine sufficiency and deficiency. In all three cell types, the mRNA levels of transketolase and the E1beta subunit of pyruvate dehydrogenase complex were lower in thiamine-deficient cultures. In contrast, mRNA levels for a ThDP-binding subunit of alpha-ketoglutarate dehydrogenase, the E1 subunit did not differ. These results indicate that thiamine or a thiamine metabolite regulates the expression in humans of some, but not all, genes encoding ThDP-utilizing enzymes.

Identification and characterization of the thiamine transporter gene of Saccharomyces cerevisiae

A positive selection scheme is described that selects for thiamine transporter clones. The scheme is based on the rescue of lethality, under non-permissive conditions, of Saccharomyces cerevisiae strains that are conditional for thiamine biosynthesis and are defective in thiamine transport. Transport defective strains were generated by selection for resistance to the lethal thiamine analog, pyrithiamine. Pyrithiamine resistance was shown to be a recessive, single gene trait that resulted from the mutation of the thiamine transporter gene, as suggested by previous work. Conditional thiamine biosynthesis was generated by cloning THI4, a thiamine biosynthetic gene, into a URA3 containing plasmid and transforming a strain disrupted in THI4. Thus, plating on 5-fluoroorotic acid causes the loss of thiamine synthesis ability. The gene for the yeast thiamine transporter, THI7, was cloned using this scheme. The predicted 598 amino acid transporter is a member of the major facilitator superfamily of transporters and thus possesses 12 transmembrane spanning segments with amino and carboxy termini intracellularly located. Several alterations in the coding region were characterized that result in greatly reduced ability to transport thiamine. The level of transporter mRNA was found to be rapidly and dramatically reduced by the addition of thiamine to the growth medium.

Heterogeneous expression of transketolase in ocular tissues

PURPOSE

Previous studies have shown that transketolase is preferentially expressed in the corneal epithelium and comprises up to 10% of the soluble protein of the mature mouse cornea. The aim of this study is to evaluate the expression and distribution of TKT in the different ocular tissues.

METHODS

We have used in situ hybridization and immunohistochemistry to localize TKT mRNA and protein in the developing and adult mouse eye.

RESULTS

TKT were found to be widely distributed throughout the adult mouse eye. Among the ocular tissues examined, the corneal epithelium exhibited the highest levels of TKT mRNA and protein. Within the epithelial layer, TKT mRNA and protein were differentially distributed with the highest expression occurring in basal cells and the lowest in apical cells, suggesting that TKT expression in the corneal epithelium may be differentiation-related. Enriched expression of TKT was also found in the cornea endothelium, lens epithelium, ciliary body, and iris. Low basal levels of expression were observed in the limbus and conjunctiva. In contrast to the adult eye, TKT expression in the one-day-old mouse eye was homogeneous at low, but detectable levels, suggesting that TKT expression is developmentally regulated in the cornea as well as in the other ocular tissues. In the healing corneal epithelium, TKT expression in the single cell layer of the leading edge was completely suppressed until the cells began to stratify, at which point TKT expression increased markedly.

CONCLUSIONS

The results presented here suggest that TKT is differentially expressed and developmentally regulated in the various tissues that comprise the eye.

The effects of single and repeated episodes of thiamin deficiency on memory in alcohol-consuming rats

The underlying pathogenesis of Korsakoff's syndrome, an amnesic disorder most commonly found in alcoholics, is not well understood. Chronic alcoholism is associated with thiamin deficiency and current thinking is that this may be the causal factor. In Experiment 1, rats were given a 20% (v/v) ethanol/water mix as their only source of fluid for 156 days. Three groups were made thiamin deficient through the combination of a thiamin-deficient diet and the centrally acting thiamin antagonist pyrithiamin hydrobromide, after 4, 15, and 26 weeks exposure to ethanol, respectively. The control group was given ad lib access to laboratory chow and water throughout this period. There were no differences between groups on either the working or reference versions of the Morris water tank paradigm. In Experiment 2, to test the hypothesis that a single bout of thiamin deficiency, with or without concurrent alcohol intake, is not sufficient to cause severe memory impairments, two groups of rats were subjected to three bouts of thiamin deficiency. One of these groups consumed an ethanol/water mix, the other tap water. A third group was made thiamin deficient on only one occasion. The control group was not made thiamin deficient and consumed lab chow and tap water throughout. Once again, there were no between-group differences in the data derived from testing in either the eight-arm radial maze or the Morris water tank task. These experiments indicate that the aetiology of Korsakoff's syndrome is more complex than previously thought.

Transketolase is a major protein in the mouse cornea

Earlier experiments in this laboratory identified a highly expressed 65-68-kDa protein in both mouse and human corneas (Cuthbertson, R. A. , Tomarev, S. I., and Piatigorsky J. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 4004-4008). Here, we demonstrate that this protein is transketolase (TKT; EC 2.2.1.1), an enzyme in the nonoxidative branch of the pentose-phosphate pathway, based on peptide and cDNA isolation and sequence analysis of mouse cornea protein and RNA samples, respectively. While expressed at low levels in a number of tissues, the 2.1-kilobase TKT mRNA was expressed at a 50-fold higher level in the adult mouse cornea. The area of most abundant expression was localized to the cornea epithelial cell layer by in situ hybridization. Western blot analysis confirmed TKT protein abundance in the cornea and indicated that TKT may comprise as much as 10% of the total soluble protein of the adult mouse cornea. Soluble cornea extracts exhibited a correspondingly high level of TKT enzymatic activity. TKT expression increased progressively through cornea maturation, as shown by Northern blot, in situ hybridization, Western blot, and enzymatic analyses. TKT mRNA and protein were expressed at low levels in the cornea prior to eye opening, while markedly increased levels were observed after eye opening. Taken together, these observations suggest that TKT may be a cornea enzyme-crystallin, and suggest that the crystallin paradigm and concept of gene sharing, once thought to be restricted to the lens, apply to other transparent ocular tissues.

Effects of ethanol on GLUT1 protein and gene expression in rat astrocytes

Effects of ethanol on glucose transporter gene expression were examined in cultured rat astrocytes. Exposure to 50 or 100 mM ethanol for 18 hours significantly inhibited hexose uptake and reduced the number of glucose transporters, as indicated by binding studies with cytochalasin B. Indirect immunofluorescence and immunoperoxidase staining showed marked reduction of the GLUT1 glucose transporter by exposure to 100 mM ethanol for 5 or 18 hours, but no obvious change in response to 50 mM ethanol. Western blot analysis showed GLUT1 protein levels to be decreased by 52 +/- 12% (p < 0.05) after exposure to 100 mM ethanol for 18 hours. In situ hybridization histochemistry indicated an increase in steady-state GLUT1 mRNA in astrocytes exposed to 50 or 100 mM ethanol for 5 or 18 hours. Quantitation of GLUT1 mRNA levels by northern blot analysis showed that GLUT1 mRNA levels were increased by 59 and 112% in cells treated for 5 h with 50 and 100 mM ethanol, respectively. A similar effect was observed after treatment for 18 hours, but ethanol did not alter actin gene expression. Experiments using actinomycin D to block RNA synthesis suggest that this increase in steady-state mRNA level results from increased message stability. These results suggest that ethanol acts on GLUT1 gene expression at the post-transcriptional level.

Neuronal degeneration in rat cerebrocortical and olfactory regions during subchronic "binge" intoxication with ethanol: possible explanation for olfactory deficits in alcoholics

Severe, repetitive ("binge") ethanol intoxication in adult rats (intragastric delivery 3 times daily for 4 days in a modification of the Majchrowicz method) precipitates neuronal degeneration in selected cerebral cortical regions involved in memory and olfaction, confirming the results of Switzer and colleagues (Anat. Rec. 202: 186a, 1982). Neuronal damage was visualized with the de Olmos cupric silver technique for degenerating neurons and processes (argyrophilia), and was quantitated by total counts and densities of argyrophilic cells/fields. The specificity of the degeneration provides a neuropathological basis for the olfactory memory deficits in chronic alcoholics. In highly intoxicated rats, argyrophilia was most extensive among hippocampal dentate gyrus granule cells, pyramidal neurons in layer 3 of the entorhinal cortex, and olfactory nerve terminals in the olfactory bulb. Degenerating pyramidal neurons were also consistently seen in the insular cortex and olfactory cortical regions, such as the piriform and perirhinal cortices. There were few argyrophilic neurons in the CA regions of the hippocampus and none in the cerebellum--regions generally shown to have cell loss in long-term ethanol feeding models--but degenerating mossy fibers in the CA2 region were observed. Degeneration was maximal before the peak period of abstinence symptoms in this model, because argyrophilic densities were no greater 36 hr, compared with 8 hr after the last ethanol dose. High blood ethanol levels were required, because argyrophilia, absent from isocaloric controls, also was only evident in ethanol-intoxicated rats with mean blood ethanol levels for days 2 to 4 above 300 mg/dl; however, it increased substantially between 350 and 550 mg/dl. The resemblance of the argyrophilic distribution to the regional neuropathology that occurs in experimental seizures indicates that the ethanol-induced degeneration may have an excitotoxic basis. Progressive reductions in the seizure threshold (e.g., kindling phenomena that have been documented during binge ethanol intoxication) might be associated with excitotoxic hyperactivity during the repetitive nadirs between high blood and brain ethanol peaks. However, direct toxic actions of ethanol or its metabolites could also be involved. Overall, the model should be useful for studying mechanisms of ethanol-induced selective cortical and olfactory brain damage.

Effects of ethanol on glucose transporter expression in cultured hippocampal neurons

Glucose transport was studied in primary hippocampal neuron cultures exposed to ethanol. Immunofluorescent staining with antibodies against neuron-specific enolase and glial fibrillary acidic protein identified approximately 95% of the cultured cells as neurons. Western blot analysis was conducted with polyclonal antisera to glucose transporter isoforms GLUT1 and GLUT3. As previously seen in astrocytes, GLUT1 protein was regulated by the culture medium glucose content. Exposure to 50 and 100 mM of ethanol for 5 hr induced dose-dependent reductions in GLUT1 and GLUT3 protein. In contrast, GLUT1 mRNA abundance was increased relative to controls under the same conditions. Glucose uptake, measured with the nonmetabolized analog, 2-deoxy-D-glucose, was reduced by 50 and 100 mM of ethanol in four experiments. These results indicate a direct effect of ethanol on neuronal glucose transporter expression, which may play a role in the neurotoxic effects of alcohol.

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.

Molecular genetics of transketolase in the pathogenesis of the Wernicke-Korsakoff syndrome

Thiamine deficiency, a frequent complication of alcoholism, plays an important role in the pathogenesis of the Wernicke-Korsakoff syndrome [WKS]. Previous work by a number of investigators has implicated the thiamine-utilizing enzyme transketolase [Tk] as being involved mechanistically in the genetic predisposition to WKS. In particular, Tk derived from fibroblasts has been found to have an increased Km app for its cofactor thiamine pyrophosphate [TPP] and/or exist in different isoelectric forms in alcoholic patients with WKS as compared with unaffected individuals. We have demonstrated that these differences are not due to different Tk alleles, tissue-specific Tk isozymes, or differential mRNA splicing. These findings point to other mechanisms to explain the biochemical Tk variants, such as differences in assembly of the functional holoenzyme or differences in modification of the primary translation product. Tk assembly or modification, once biochemically characterized, may be found to be subject to genetic variation.

Pathophysiology of alcoholic brain damage: synergistic effects of ethanol, thiamine deficiency and alcoholic liver disease

Chronic alcoholism results in brain damage and dysfunction leading to a constellation of neuropsychiatric symptoms including cognitive dysfunction, the Wernicke-Korsakoff Syndrome, alcoholic cerebellar degeneration and alcoholic dementia. That these clinically-defined entities result from independent pathophysiologic mechanisms is unlikely. Alcohol and its metabolite acetaldehyde are directly neurotoxic. Alcoholics are thiamine deficient as a result of poor diet, gastrointestinal disorders and liver disease. In addition, both alcohol and acetaldehyde have direct toxic effects on thiamine-related enzymes in liver and brain. Alcoholics frequently develop severe liver disease and liver disease per se results in altered thiamine homeostasis, in cognitive dysfunction and in neuropathologic damage to astrocytes. The latter may result in the loss of neuron-astrocytic trafficking of neuroactive amino acids and thiamine esters, essential to CNS function. The present review article proposes mechanisms whereby the effects of alcohol, thiamine deficiency and liver disease combine synergistically to contribute to the phenomena of cognitive dysfunction and "alcoholic brain damage".

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)

Brain lesions in alcoholics

Brain lesions in alcoholics are multifactorial in origin. Ethanol neurotoxicity, Wernicke's encephalopathy, hepatocerebral degeneration, head trauma, central pontine myelinolysis, Marchiafava-Bignami syndrome, pellagra, and premorbid pathological conditions, such as fetal alcohol syndrome, may all contribute to cognitive dysfunction in alcoholics. With the exception of ethanol neurotoxicity, all of these conditions are associated with specific neuropathological lesions. Wernicke's encephalopathy, the neurological syndrome of thiamine deficiency, is frequently overlooked during life and may cause global dementia as well as the more familiar Korsakoff's amnestic syndrome. Distinguishing ethanol neurotoxicity from nutritional deficiency can be facilitated by magnetic resonance imaging, which can visualize some of the specific macroscopic lesions of Wernicke's encephalopathy, central pontine myelinolysis, cerebellar degeneration, and Marchiafava-Bignami syndrome. Computerized morphometric studies of alcoholic brains have revealed ventricular enlargement, selective loss of subcortical white matter, and alterations in neuronal size, number, architecture, and synaptic complexity. These lesions tend to be more severe when there is coexisting nutritional deficiency or liver disease, suggesting that ethanol neurotoxicity may not be the sole cause. A search for similar lesions in nonalcoholic Wernicke's encephalopathy and nonalcoholic liver disease will help determine the specificity of these lesions.