Impaired oxidation of branched-chain amino acids in the medial thalamus of thiamine-deficient rats

Thiamine, in its diphosphate form, is a required cofactor for enzymes of glucose metabolism and branched-chain α-ketoacid dehydrogenase (BCKDH). Although metabolic impairments in glucose metabolism have been found to occur in selectively vulnerable brain regions of the thiamine-deficient (TD) brain, the effects of thiamine deficiency on BCKDH have not been studied. BCKDH activity was assayed radiochemically in brain extracts of vulnerable (medial thalamus; MT) versus non-vulnerable (frontal cortex; FC) brain regions of rats made TD by administration of the central thiamine antagonist, pyrithiamine. A significant regional variation in BCKDH within the TD rat brain was noted, with a higher capacity for branched-chain amino acid oxidation in FC compared to MT: BCKDH activity was significantly reduced in MT of TD rats, resulting in selective accumulation of BCAAs in this brain region. Leucine concentrations were elevated over fivefold in the MT of symptomatic TD rats, compared with pair-fed control (PFC) rats. Impaired branched-chain ketoacid metabolism in rats may contribute to the neuronal dysfunction and ultimate thalamic neuronal cell death observed in thiamine deficiency.     

Ethanol Promotes Thiamine Deficiency-Induced Neuronal Death: Involvement of Double-Stranded RNA-activated Protein Kinase

Background:  Heavy alcohol consumption causes cerebellar degeneration, and the underlying mechanism is unclear. Chronic alcoholism is usually associated with thiamine deficiency (TD) which is known to induce selective neurodegeneration in the brain. However, the role of TD in alcohol-induced cerebellar degeneration remains to be elucidated. The double-stranded RNA-activated protein kinase (PKR) is a potent antiviral protein. Viral infection or binding to dsRNA causes PKR autophosphorylation and subsequent phosphorylation of the α-subunit of eukaryotic translation factor-2α, leading to inhibition of translation or apoptosis. PKR can also be activated by cellular stresses.
Methods:  In this study, we used an in vitro model, cultured cerebellar granule neurons (CGNs), to investigate the interaction between TD and ethanol and evaluate the contribution of their interaction to neuronal loss. TD was induced by treatment with amprolium in association with ethanol. Cell viability was determined by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide assay. PKR expression/phosphorylation and subcellular distribution was analyzed with immunoblotting and immunocytochemistry.
Results:  Thiamine deficiency caused death of CGNs but ethanol did not. However, TD plus ethanol induced a much greater cell loss than TD alone. TD-induced PKR phosphorylation and ethanol exposure significantly promoted TD-induced PKR phosphorylation as well as its nuclear translocation. A selective PKR inhibitor not only protected CGNs against TD toxicity, but also abolished ethanol potentiation of TD-induced loss of CGNs.
Conclusions:  Ethanol promoted TD-induced PKR activation and neuronal death. PKR may be a convergent protein that mediates the interaction between TD and ethanol.     

Bidirectional modulation of spatial working memory by ethanol

BACKGROUND: It is common knowledge that ethanol causes cognitive and memory impairments. Although these deficits are attributed to its central depressant properties, ethanol has biphasic effects and at low doses can produce excitatory actions. METHODS: Here we examined whether ethanol could have biphasic effects on performance in a delayed alternation task in a T-maze, a behavioral test of working memory. RESULTS: A dose-response study showed that intermediate doses of ethanol (1 g/kg) were associated with impairments of working memory in rats, as assessed at short intertrial intervals (10 sec). In contrast, at longer delays (120 sec), when the delayed alternation performance was reduced markedly in controls, a lower dose of ethanol (0.5 g/kg) significantly improved working memory. CONCLUSIONS: These results demonstrate a dose-dependent, bidirectional effect of ethanol on working memory and implicate the prefrontal cortex, the site of working memory function, as a target of ethanol action. The cognitive improvements caused by low, excitatory doses of ethanol may be perceived as rewarding and could have relevance for chronic ethanol consumption in humans.     

Chronic ethanol consumption impairs learning and memory after cessation of ethanol

Acute consumption of ethanol results in reversible changes in learning and memory whereas chronic ethanol consumption of six or more months produces permanent deficits and neural damage in rodents. The goal of the current paper was determine whether shorter durations of chronic ethanol ingestion in mice would produce long-term deficits in learning and memory after the cessation of ethanol. We first examined the effects of four and eight weeks of 20% ethanol followed by a three week withdrawal period on learning and memory in mice. We determined that three weeks after eight, but not four, weeks of 20% ethanol consumption resulted in deficits in learning and long-term memory (seven days) in T-maze footshock avoidance and Greek Cross brightness discrimination, step-down passive avoidance and shuttlebox active avoidance. Short-term memory (1 hr) was not affected. The deficit was not related to changes in thiamine status, caloric intake, or nonmnemonic factors, such as, activity or footshock sensitivity. Lastly, we examined if the mice recovered after longer durations of withdrawal. After eight weeks of ethanol, we compared mice after three and 12 weeks of withdrawal. Mice that had been off ethanol for both three and 12 weeks were impaired in T-maze footshock avoidance compared to the controls. The current results indicate that a duration of ethanol consumption as short as eight weeks produces deficits in learning and memory that are present 12 weeks after withdrawal.     

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 timeout cycle. Each group of rats demonstrated equivalent saline baseline operant performance and ED₅₀for 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 pyrithia-mine injections in a 2 × 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. The control group receiving regular rat chow diet and twice daily injections of saline and pyrithiamine failed to demonstrate overt signs of thiamine deficiency or significant shifts in the behavioral dose-effect functions. We suggest a possible interaction between a surfeit of extracellular thiamine levels, and a subsequent decrease in magnesium levels may be involved in the development of increases in ethanol sensitivity.     

Depletion of Brain Histamine Produces Regionally Selective Protection against Thiamine Deficiency-Induced Lesions in the Rat

Breakdown of the blood brain barrier and the subsequent accumulation of free radicals, lactate, and glutamate appear to be the immediate causes of thiamine deficiency (TD)-induced damage to thalamus. The mechanisms triggering these events are unknown but recent evidence suggests an important role of histamine. We therefore studied the effects of histamine depletion on thalamic lesions in the pyrithiamine-induced thiamine deficient (PTD) rat. Chronic intracerebroventricular (i.c.v., 7 days) infusion of -fluoromethylhistidine (FMH), combined with bilateral ibotenate destruction of the histamine-containing neurons in the tuberomammillary (TM) nucleus and bolus i.c.v. infusion of 48/80, a potent mast cell degranulating agent, was used to deplete brain histamine levels. PTD rats receiving combined FMH + 48/80 + TM lesions developed acute neurological symptoms, including spontaneous seizures, approximately 1 day earlier than PTD rats treated with i.c.v. infusion of vehicle and sham lesions of the TM. When examined 1 week after restoration of thiamine, the PTD vehicle + sham lesion animals contained severe neuronal loss and gliosis in midline, intralaminar, ventral, lateral, and posterior nuclei. PTD animals treated with FMH + 48/80 + TM lesions had little evidence of neuronal loss or microglial proliferation in thalamus except in the gelatinosus and anteroventral nuclei, in which there was complete neuronal loss. These data demonstrate a significant and regionally selective role of histamine in the development of thalamic lesions in a rat model of Wernicke's encephalopathy. Furthermore, these data suggest either a dissociation between seizures and thalamic lesions or a significant role of histamine in seizure-related damage to the thalamus.     

Neuropathology of thiamine deficiency: an update on the comparative analysis of human disorders and experimental models

This paper provides a re-examination of the neuroanatomical consequences of thiamine deficiency in light of more recent studies of human disorders and models of experimental thiamine deficiency. A major goal is to elucidate the relative roles of thiamine deficiency and chronic alcohol consumption in the pathogenesis of Wernicke-Korsakoff syndrome (WKS). Particular emphasis is placed on the role of thiamine deficiency in lesions to basal forebrain, raphe, locus coeruleus, white matter and cortex and their role in the cognitive and memory disturbances of human WKS and experimental models of thiamine deficiency.     

Binge pattern ethanol exposure in adolescent and adult rats: differential impact on subsequent responsiveness to ethanol

BACKGROUND: Recent evidence indicates that adolescent animals are more sensitive than adults to the disruptive effects of acute ethanol exposure on spatial learning. It is not yet known whether adolescent animals are also more sensitive than adults to the enduring neurobehavioral effects of repeated ethanol exposure. In this study, animals were exposed to ethanol in a binge-pattern during either adolescence or adulthood. At a time when all subjects were adults, spatial working memory was examined in the absence and presence of an acute ethanol challenge. METHODS: Rats were exposed to ethanol (5.0 g/kg intraperitoneally) or isovolumetric saline at 48 hr intervals over 20 days. Exposure began on either postnatal day 30 (adolescent group) or 70 (adult group). Twenty days after the final injection, a time at which all animals were adults, the subjects were tested on an elevated plus maze and then were trained to perform a spatial working memory task on an eight-arm radial maze. At the beginning of each session of training on the working memory task, subjects retrieved food rewards on four of the eight arms. After a delay, subjects were placed on the maze and allowed to retrieve food from the remaining four arms. RESULTS: Prior exposure to ethanol did not influence behavior on the plus maze. Performance of the groups did not differ during acquisition of the spatial working memory task with a 5 min delay or during subsequent testing with a 1 hr delay. However, animals treated with ethanol during adolescence exhibited larger working memory impairments during an ethanol challenge (1.5 g/kg intraperitoneally) than subjects in the other three groups. CONCLUSIONS: The findings indicate that binge pattern exposure to ethanol during adolescence enhances responsiveness to the memory-impairing effects of ethanol in adulthood.     

Comparison of the impact of melatonin on chronic ethanol-induced learning and memory impairment between young and aged rats

Chronic alcohol exposure causes functional and structural changes in nervous system which have all been associated with learning and memory impairments. Furthermore, alcohol consumption has been shown to alter the pattern of neural cell adhesion molecules (NCAM) which are involved in memory processes. In the current work, we investigated the effects of melatonin on learning and memory deficits induced by alcohol exposure in young and aged rats. A group of young rats (3 months old) were administered ethanol for 45 days and half of them were co-treated with melatonin. Similar treatments were performed in the aged (19 months old) rats. Morris water maze test and passive avoidance task were used to assess cognitive performance. Lipid peroxidation (LPO) and glutathione (GSH) levels were determined to characterize the level of oxidative stress in the hippocampus and cortex. NCAM levels were determined by Western blotting in the hippocampal homogenates. There was a significant elevation in LPO levels and a reduction in GSH levels in aged and alcohol-exposed rats. Furthermore, both young and aged rats displayed some cognitive impairment when given with alcohol for 45 days. Co-administration of melatonin with ethanol significantly reduced LPO and elevated GSH levels while improving the learning and memory deficits induced by ethanol; the aged rats exhibited a greater response to melatonin supplementation. Moreover, melatonin modulated NCAM expression in hippocampus. Present findings indicate that exposure to ethanol induces learning and memory deficits probably by generating reactive oxygen species and downregulating NCAM 180 in hippocampus of aged rats. Melatonin improves learning and memory deficits and the behavioral responses of rats to melatonin supplementation are age dependent.     

A Retinoic Acid Receptor Antagonist Suppresses Brain Retinoic Acid Receptor Overexpression and Reverses a Working Memory Deficit Induced by Chronic Ethanol Consumption in Mice

BACKGROUND: Chronic ethanol consumption induces disorders in the biosynthesis of retinoic acid, an active derivative of vitamin A. Recent evidence suggests that an alteration in the retinoic acid signaling pathway leads to impairments in learning and memory in adult mice. We have previously shown that chronic ethanol consumption in mice produces an increased expression of the brain retinoic acid receptor beta (RARbeta) mRNA. These results prompted us to examine whether suppressing the overexpression of retinoid receptors in alcohol-treated mice by RAR antagonist administration would reverse their cognitive impairment. METHODS: After 10 months of ethanol consumption (12% v/v in drinking water), C57BL/6 mice were submitted to a working memory task in a T-maze. Then, mice of the control and the ethanol-treated groups received an RARbeta antagonist (CD2665 0.6 mg/kg) for 22 days. The behavioral effect of CD2665 administration was evaluated on a spontaneous alternation task and the neurochemical effect was measured by quantifying the mRNA expression of RARalpha, RARbeta, retinoid X receptor (RXRbeta/gamma) and tissue transglutaminase (tTG; a retinoic acid-target gene). RESULTS: Mice submitted to ethanol treatment exhibited a progressive decrease in spontaneous alternation rates over successive trials. Moreover, these mice displayed an increased expression of brain RARbeta and RXRbeta/gamma mRNA, together with an increased level of tTG mRNA and enzymatic activity. The administration of CD2665 to alcohol-treated mice totally reversed the working memory deficit and suppressed the overexpression of brain RARbeta, RXRbeta/gamma and tTG mRNA, whereas the same treatment in control mice decreased only the RARbeta mRNA level without affecting memory performance. CONCLUSION: These data point to the potential role of the retinoid signaling pathway in memory processes and suggest that the overexpression of brain RARbeta and RXRbeta/gamma could be responsible, at least in part, for some memory impairments observed during chronic ethanol consumption.     

Evidence for early blood-brain barrier breakdown in experimental thiamine deficiency in the mouse

In order to assess the involvement of blood-brain barrier (BBB) breakdown in the pathogenesis of thiamine deficiency encephalopathy, autologous albumin immunohistochemistry was performed in mice which were rendered thiamine-deficient by pyrithiamine, a BBB-permeant antagonist of thiamine. In the presymptomatic animals until day 8 of the treatment, histological lesions were not detected by H&E staining. However, localized staining of albumin was evident, suggesting an extravascular leakage of the endogenous intravascular protein. On day 10 of thiamine deficiency, when neurological signs appeared, both histological lesions and massive albumin extravasation were demonstrated in all the animals. The BBB breakdown was only occasionally observed in the brains of mice treated with oxythiamine, a BBB-impermeant antagonist or in control animals. These results suggest that BBB breakdown is not only a phenomenon secondary to tissue destruction, but it is more directly involved in the pathogenesis of thiamine deficiency encephalopathy.     

Acute neuromyocarditis secondary to diet-induced beriberi. Case report

INTRODUCTION: Thiamine deficiency can be determined by various clinical signs; some of these symptoms may be acute, and require an urgent diagnosis. In countries such as ours with a high standard of living, this disorder is more commonly observed in cases of severe alcoholism, and cases of diet-associated thiamine deficiency are rare, and therefore not easily recognized. The metabolic disorders resulting from vitamin B1 deficiency are responsible for the well-known central or peripheral neurological symptoms, and also for the less common and often more acute cardiovascular reactions. Immediate thiamine/vitamin B1 supplementation is of major importance. The rapid reversal of symptoms following this treatment is often considered as a diagnostic index. EXEGESIS: In this study, an original case of diet-associated thiamine deficiency has been reported, with clinical symptoms including myocarditis and subacute peripheral nerve involvement in a young adult. The disorder was the result of a thiamine deficiency in the diet, which was exclusively based on milled rice. CONCLUSION: The present report is interesting both as regards its clinical aspects and its etiology, and it emphasizes the importance in the differential diagnosis of a given case of taking the possibility of diet-related thiamine deficiency into account, although this is an uncommon etiology in developed countries.     

Acceleration of Ethanol Metabolism by Past Thiamine Deficiency

Six months after severe thiamine deficiency, when their body and liver weights had normalized, male Sprague-Dawley rats were exposed to constant ethanol vapor concentrations for 6 days in an inhalation chamber and Mood ethanol concentrations (BECs) were determined. Previously induced thiamine deficiency was associated with about a 50% reduction of BECs and a significant increase in liver alcohol dehydrogenase (ADH) activity suggesting a persistent acceleration of ethanol metabolism. No significant changes were found in liver aldehyde dehydrogenase activity, plasma levels of thyroxine, testosterone, or estradid, or brain or liver histology. Plasma growth hormone concentrations were about 60K lower in the experimental group than in controls, but this effect of previous thiamine deprivation did not correlate with changes in ADH activity. Therefore, it remains to be elucidated how thiamine deficiency-induced central nervous system alterations may contribute to the development of metabolic tolerance to ethanol.     

Effects of physical exercise on spatial memory and astroglial alterations in the hippocampus of diabetic rats

Type 1 diabetes mellitus (T1DM) is associated with neurocognitive dysfunction and astrogliosis. Physical exercise prevents cognitive impairments and induces important brain modifications. The aim of our study was to investigate the effect of treadmill exercise on spatial memory and astrocytic function in the hippocampus of a T1DM model. Fifty-seven Wistar rats were divided into four groups: trained control (TC) (n = 15), non-trained control (NTC) (n = 13), trained diabetic (TD) (n = 14) and non-trained diabetic (NTD) (n = 15). One month after streptozotocin-induced diabetes, exercise groups were submitted to 5 weeks of physical training, and then, all groups were assessed in the novel object-placement recognition task. Locomotor activity was analyzed in the open field apparatus using Any-maze software. The expression of glial fibrillary acidic protein (GFAP) and S100B in hippocampus and cerebrospinal fluid were measured using ELISA assay, and hippocampal GFAP immunoreactivity was evaluated by means of immunohistochemistry and optical densitometry. The results showed that physical exercise prevents and/or reverts spatial memory impairments observed in NTD animals (P < 0.01). Decreased locomotor activity was observed in both the NTD and TD groups when compared with controls (P < 0.05). ELISA and immunohistochemistry analyzes showed there was a reduction in GFAP levels in the hippocampus of NTD animals, which was not found in TD group. ELISA also showed an increase in S100B levels in the cerebrospinal fluid from the NTD group (P < 0.01) and no such increase was found in the TD group. Our findings indicate that physical exercise prevents and/or reverts the cognitive deficits and astroglial alterations induced by T1DM.     

Downbeat nystagmus caused by thiamine deficiency: an unusual presentation of CNS localization of large cell anaplastic CD 30-positive non-Hodgkin's lymphoma

 A 24-year-old woman with a large cell anaplastic CD 30-positive T-cell non-Hodgkin's lymphoma (NHL) developed downbeat nystagmus, anisocoria, and oscillopsia. Prior to overt cerebral invasion by NHL, she had a thiamine deficiency with very low thiamine concentrations in the CSF, probably caused by protracted vomiting and increased vitamin B₁ consumption by intrathecal tumor cells. We believe that her neurologic symptoms were caused – at least partly – by thiamine deficiency, as she reacted well to thiamine supplementation at the beginning of treatment. Received: September 16, 1998 / Accepted: October 22, 1998     

Beriberi after bariatric surgery: not an unusual complication. Report of two cases and literature review

The number of patients submitted to bariatric surgery to treat morbid obesity is increasing, therefore, some nutritional deficiencies, with which many physicians are no longer familiarized, are reappearing. Postoperatively, many nutritional disorders may occur, one of them is thiamine deficiency (beriberi). The thiamine and/or vitamin B12 deficiency can correspond to 40% of the neuropathy cases after bariatric surgery. Two patients with the clinic of peripheral neuropathy and Wernicke-Korsakoff syndrome will be reported. Some months after the surgery, they presented prostration, depression, mental confusion and nystagmus, associated with pain and paresthesia in limbs (especially lower limbs). With the diagnostic hypothesis of beriberi, the treatment with thiamine started. One of the patients presented complete improvement of the neurological symptoms, however the other one remained with motor deficiency, exactly the one who spent a longer period of time between the symptoms appearance and the treatment beginning. These cases serve to alert us about the importance of nutritional vigilance after bariatric surgery.     

Ethanol Attenuates Spatial Memory Deficits and Increases mGlu1a Receptor Expression in the Hippocampus of Rats Exposed to Prenatal Stress

Background: Although it is generally believed that chronic ethanol consumption impairs learning and memory, results obtained in experimental animals are not univocal, and there are conditions in which ethanol paradoxically improves cognitive functions. In the present work, we investigated the effects of prenatal stress and of chronic ethanol exposure during adulthood on spatial memory in rats. Methods: Rats were subjected to a prenatal stress delivered as 3 daily 45‐minute sections of restraint stress to the mothers during the last 10 days of pregnancy (PRS rats). After 7 months of ethanol exposure (ethanol 10%, oral intake), memory performances were evaluated in a spatial discrimination test in control and PRS male rats. Then, the oxidative damages and the expression of metabotropic glutamate (mGlu) receptors were assessed in their hippocampus. Results: Chronic ethanol exposure resulted in a reduced performance in a spatial recognition task in control animals. Unexpectedly, however, the same treatment attenuated spatial memory deficits in rats that had been subjected to prenatal stress. This paradigm of ethanol administration did not produce detectable signs of oxidative damage in the hippocampus in either unstressed or PRS rats. Interestingly, ethanol intake resulted in differential effects in the expression of mGlu receptor subtypes implicated in mechanisms of learning and memory. In control rats, ethanol intake reduced mGlu2/3 and mGlu5 receptor levels in the hippocampus; in PRS rats, which exhibited a constitutive reduction in the levels of these mGlu receptor subtypes, ethanol increased the expression of mGlu1a receptors but did not change the expression of mGlu2/3 or mGlu5 receptors. Conclusion: Our findings support the idea that stress‐related events occurring before birth have long‐lasting effects on brain function and behavior, and suggest that the impact of ethanol on cognition is not only dose‐ and duration‐dependent, but also critically influenced by early life experiences.     

Selective increase of neuronal cyclooxygenase-2 (COX-2) expression in vulnerable brain regions of rats with experimental Wernicke’s encephalopathy: effect of nimesulide

Thiamine deficiency (TD) in both humans and experimental animals results in severe mitochondrial dysfunction and leads to selective neuronal cell death in diencephalic and cerebellar structures. We have investigated cyclooxygenase-2 (COX-2) expression in vulnerable (medial thalamus, inferior colliculus) and spared (frontal cortex) regions of rats with thiamine deficiency. Expression of COX-2 mRNA was selectively increased (twofold, p < 0.001) in vulnerable regions at symptomatic stages of encephalopathy (14 days) of TD compared to pair-fed controls or presymptomatic (days 12) rats. Induction of COX-2 expression was accompanied by a significant increase (two- to threefold, p < 0.001) in prostanglandin E2 (PGE2) synthesis in vulnerable regions at symptomatic stages of TD. COX-2 immunolabeling revealed a neuronal localization and COX-2 immunoreactive neurons were significantly increased at symptomatic stages of encephalopathy. Administration of nimesulide, a highly specific COX-2 inhibitor, significantly reduced PGE-2 levels in vulnerable regions but, rather than being neuroprotective, precipitated encephalopathy and exacerbated neuronal cell death due to TD. These findings suggest that newly synthesized prostanoids exert a neuroprotective role in TD.     

The combined effects of protein deficiency and chronic ethanol administration on rat ethanol metabolism

This investigation was performed to examine the combined effects of protein deficiency and chronic ethanol consumption on ethanol clearance and hepatic ethanol metabolism of the rat. Protein deficiency alone was associated with reduced ethanol clearance and decreased activity of hepatic alcohol dehydrogenase and the microsomal ethanol-oxidizing system. However, when ethanol (as 36% of energy) was administered concurrently with protein-deficient diets, accelerated ethanol clearance and increased microsomal oxidation of ethanol was observed. Furthermore, in protein-deficient animals fed ethanol, liver alcohol dehydrogenase levels were less decreased when compared with values observed in animals fed protein-deficient diets without ethanol, and this effect was associated with markedly reduced serum testosterone levels in the former group.     

Thiamine status in liver and brain of rats genetically selected for different sensitivity to hypnotic effect of alcohol

BACKGROUND: The mechanisms of the different sensitivity or resistance of animals and humans to alcohol are still not completely understood. For further biochemical characterization of animals genetically selected for high-alcohol sensitivity (HAS) and low-alcohol sensitivity (LAS) with the hypnotic effect of alcohol, the thiamine status and thiamine metabolizing enzymes in these animals have been studied. METHODS: We investigated thiamine diphosphate and thiamine triphosphate levels as well as the activity of thiamine-dependent enzyme, transketolase, and thiamine-metabolizing enzymes, thiamine kinase, and thiamine triphosphatase in the liver and brain of HAS, LAS, and CAS (control) rats by standard biochemical techniques. RESULTS: It was found that the activity of transketolase, and the level of the coenzyme form of thiamine, thiamine diphosphate (TDP), were significantly lower in HAS versus LAS rats. The activation of transketolase by the exogenous TDP (TDP-effect) was significantly higher in the liver and brain regions of HAS rats compared with LAS rats. The level of TDP in the liver and cerebellum of HAS rats was significantly lower compared with LAS rats. These results indicate a severe deficiency of TDP in HAS rats. HAS rats have a significantly lower activity of thiamine triphosphatase, the additional source of TDP. Accordingly, HAS rats have much higher thiamine triphosphate levels in the liver and brain, compared with LAS rats. There were no significant differences between groups with respect to the thiamine diphosphatase and thiamine kinase activity. Most of the above parameters had the intermediate values in CAS rats, compared with LAS and HAS rats. These data indicate the possible role of the thiamine phosphate esters and related enzymes in the mechanisms that bring about the differential sensitivity to the hypnotic effect of alcohol. CONCLUSIONS: HAS rats have the genetically mediated thiamine diphosphate deficiency and increased thiamine triphosphate levels, probably due to reduced activity of thiamine triphosphatase in the liver and brain, compared with LAS rats. It can be related with the higher initial sensitivity of HAS rats to hypnotic effect of ethanol.