Alan Hazell | Université de Montréal (original) (raw)

Papers by Alan Hazell

Research paper thumbnail of Hepatic Encephalopathy: An Update of Pathophysiologic Mechanisms (44433A)

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs in both acute and chronic ... more Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs in both acute and chronic liver failure. Although the precise pathophysiologic mecha- nisms responsible for HE are not completely understood, a deficit in neurotransmis- sion rather than a primary deficit in cerebral energy metabolism appears to be in- volved. The neural cell most vulnerable to liver failure is the astrocyte. In

Research paper thumbnail of Role of manganese in hepatic encephalopathy

Encephalopathy and Nitrogen Metabolism in Liver Failure, 2003

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

Addiction Biology

Wernicke encephalopathy is a neurological disorder commonly observed in chronic alcohol abuse, in... more 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, g...

Research paper thumbnail of Altered “peripheral-type” benzodiazepine receptor (PTBR) gene expression in brain and testis following end-to-side portacaval anastomosis

Research paper thumbnail of Increased expression and uptake activity of the glast transporter during thiamine deficiency in cultured astrocytes

Research paper thumbnail of Increased “peripheral-type” benzodiazepine receptor sites and mRNA in thalamus of thiamine-deficient rats

Neurochemistry International

“Peripheral-type” benzodiazepine receptors (PTBRs) are highly expressed on the outer mitochondria... more “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 ...

Research paper thumbnail of Primary cultures of rat astrocytes respond to thiamine deficiency-induced swelling by downregulating aquaporin-4 levels

Neuroscience Letters

Imaging studies indicate that cerebral edema is an important consequence of Wernicke's enceph... more Imaging studies indicate that cerebral edema is an important consequence of Wernicke's encephalopathy (WE), a disorder caused by thiamine deficiency (TD). We have investigated this problem using a recently developed in vitro astrocyte model of TD. Measurement of cell volume using the 3-O-methylglucose uptake method revealed a dose-dependent swelling of astrocytes during exposure to TD conditions. Time course studies indicated a progressive volume increase up to a maximum of 93% above controls after 4 days of treatment. This swelling then partially resolved, and remained stable for up to 10 days following commencement of TD treatment. Measurement of aquaporin-4 (AQP-4) levels showed a 44% loss after 10 days and a temporal profile consistent with an important role for this water channel protein in astrocyte cell volume changes during TD. Our findings of astrocyte swelling in TD are consistent with previous reports of focal brain edema in cases of WE, and indicate that AQP-4 may be...

Research paper thumbnail of eNOS gene deletion restores blood-brain barrier integrity and attenuates neurodegeneration in the thiamine-deficient mouse brain

Journal of Neurochemistry

Wernicke's encephalopathy is a cerebral disorder caused by thiamine (vitamin B(1)) deficiency... more Wernicke's encephalopathy is a cerebral disorder caused by thiamine (vitamin B(1)) deficiency (TD). Neuropathologic consequences of TD include region-selective neuronal cell loss and blood-brain barrier (BBB) breakdown. Early increased expression of the endothelial isoform of nitric oxide synthase (eNOS) occurs selectively in vulnerable brain regions in TD. We hypothesize that region-selective eNOS induction in TD leads to altered expression of tight junction proteins and BBB breakdown. In order to address this issue, TD was induced in C57BL/6 wild-type (WT) and eNOS(-/-) mice by feeding a thiamine-deficient diet and treatment with the thiamine antagonist pyrithiamine. Pair-fed control mice were fed the same diet with additional thiamine. In medial thalamus of TD-WT mice (vulnerable area), increased heme oxygenase-1 and S-nitrosocysteine immunostaining was observed in vessel walls, compared to pair-fed control-WT mice. Concomitant increases in IgG extravasation, decreases in exp...

Research paper thumbnail of Brain lactate synthesis in thiamine deficiency: a re-evaluation using 1H-13C nuclear magnetic resonance spectroscopy

Journal of Neuroscience Research

Region-selective accumulation of brain lactate occurs in TD; however, the mechanisms responsible ... more Region-selective accumulation of brain lactate occurs in TD; however, the mechanisms responsible have not been elucidated fully. (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy were therefore used to investigate de novo lactate synthesis from [1-(13)C]glucose in vulnerable (medial thalamus) and nonvulnerable (frontal cortex) brain regions of rats made thiamine deficient by administration of the central thiamine antagonist pyrithiamine. De novo synthesis of lactate was increased in the medial thalamus to 148% and 226% of pair-fed control values at presymptomatic and symptomatic stages of thiamine deficiency, respectively, whereas no such changes were observed in the frontal cortex. Administration of a glucose load selectively worsened the changes in medial thalamus. Pyruvate recycling and peripherally derived lactate did not contribute significantly to the lactate increase within the thiamine-deficient brain. Increases in immunolabeling of the lactate dehydrogenase isoen...

Research paper thumbnail of Manganese induces cell swelling in cultured astrocytes

NeuroToxicology

Manganese in excess is neurotoxic and causes a CNS disorder that resembles Parkinson's diseas... more Manganese in excess is neurotoxic and causes a CNS disorder that resembles Parkinson's disease (manganism). Manganese highly accumulates in astrocytes, which renders these cells more vulnerable to its toxicity. Consistent with this vulnerability, manganese has been shown to cause histopathological changes in astrocytes (Alzheimer type II change), generates oxidative stress and bring about mitochondrial dysfunction, including the induction of the mitochondrial permeability transition (mPT) in astrocytes. In addition to manganism, increased brain levels of manganese have been found in hepatic encephalopathy, a chronic neurological condition associated with liver dysfunction, wherein Alzheimer type II astrocytic changes are also observed. As low-grade brain edema, possibly secondary to astrocyte swelling, has been reported in hepatic encephalopathy, we hypothesized that manganese may contribute to such edema. We therefore exposed cultured astrocytes to manganese (Mn(3+)) acetate (2...

Research paper thumbnail of Astrocytic Poly (ADP) ribose polymerase-1 regulates glutamate transporter expression via NF-kB mechanism in experimental Wernicke’s encephalopathy

Research paper thumbnail of Downregulation of the glutamate transporter and its prevention by ceftriaxone in TD

Research paper thumbnail of Pyrithiamine-induced thiamine deficiency alters proliferation and neurogenesis in both neurogenic and vulnerable areas of the rat brain

Metabolic Brain Disease

Thiamine deficiency (TD) leads to Wernicke's encephalopathy (WE), in which focal histological... more Thiamine deficiency (TD) leads to Wernicke's encephalopathy (WE), in which focal histological lesions occur in periventricular areas of the brain. Recently, impaired neurogenesis has been reported in the hippocampus during the dietary form of TD, and in pyrithiamine-induced TD (PTD), a well-characterized model of WE. To further characterize the consequences of PTD on neural stem/progenitor cell (NSPC) activity, we have examined the effect of this treatment in the rat on both the subventricular zone (SVZ) of the rostral lateral ventricle and subgranular layer (SGL) of the hippocampus, and in the thalamus and inferior colliculus, two vulnerable brain regions in this disorder. In both the SVZ and SGL, PTD led to a decrease in the numbers of bromodeoxyuridine-stained cells, indicating that proliferation of NSPCs destined for neurogenesis in these areas was reduced. Doublecortin (DCX) immunostaining in the SGL was decreased, indicating a reduction in neuroblast formation, consistent ...

Research paper thumbnail of Altered expression of tight junction proteins and matrix metalloproteinases in thiamine-deficient mouse brain

Neurochemistry International

Wernicke's encephalopathy (WE) in humans is a metabolic disorder caused by thiamine deficienc... more Wernicke's encephalopathy (WE) in humans is a metabolic disorder caused by thiamine deficiency (TD). In both humans and experimental animals, TD leads to selective neuronal cell death in diencephalic and brainstem structures. Neuropathologic features of WE include petechial hemorrhagic lesions, and blood-brain barrier (BBB) breakdown has been suggested to play an important role in the pathogenesis of TD. The goal of the present study was to examine expression of the tight junction (TJ) protein occludin, its associated scaffolding proteins zona occludens (ZO-1 and ZO-2), and to measure matrix metalloproteinase (MMP) levels as a function of regional BBB permeability changes in thiamine-deficient mice. TD was induced in 12-week-old male C57Bl/6 mice by feeding a thiamine-deficient diet and administration of the central thiamine antagonist pyrithiamine. BBB permeability was measured by IgG extravasation; expression of occludin, ZO-1 and ZO-2 was measured by Western blot analysis and...

Research paper thumbnail of Poly(ADP)ribose polymerase-1 dependent regulation of glutamate transporter during thiamine deficiency

Research paper thumbnail of Astrocytic soluble factors disrupt mitochondrial membrane potential and downregulate GLT-1 in thiamine deficiency

Loss of astrocytic glutamate transporters is a major feature of both TD and human cases of Wernic... more Loss of astrocytic glutamate transporters is a major feature of both TD and human cases of Wernicke’s encephalopathy, in which cerebral energy metabolism is significantly affected. However, the underlying basis of this process remains unclear presently. Previous studies have reported evidence for the involvement of soluble neuronal factors that can regulate the levels of these glutamate transporters. In the present study we have investigated the possibility of release of astrocytic soluble factors that might be involved in the regulation of the glutamate transporter GLT-1 on these cells. Treatment of naïve astrocytes with conditioned media from astrocytes exposed toTD conditions resulted in a progressive decrease in glutamate uptake over 24h, along with increased release of glutamate. Immunoblotting and flow cytometry measurements indicated this was accompanied by a 20-40% loss of GLT-1 in these cells. Lactic acid, produced in astrocytes as a consequence of TD, was found to decrease...

Research paper thumbnail of Mechanisms of hepatic encephalopathy and thiamine deficiency

Metabolic Brain Disease, 2014

Research paper thumbnail of Reduced expression of astrocytic glycine transporter (Glyt-1) in acute liver failure

Metabolic brain disease, 2002

A growing body of evidence suggests that alterations in N-methyl-D-asparate NMDA-mediated excitat... more A growing body of evidence suggests that alterations in N-methyl-D-asparate NMDA-mediated excitatory neurotransmission may be involved in the pathophysiology of hepatic encephalopathy (HE) in acute liver failure (ALF). The NMDA receptor requires glycine as a positive allosteric modulator. One of the glycine transporters Glyt-1 is expressed primarily in astrocytes of the cerebral cortex in association with regions of high NMDA receptor expression. As astrocytic transporters regulate the amino acid concentrations within excitatory synapses, the expression of Glyt-1 was studied in cortical preparations from rats with ischemic liver failure induced by portacaval anastomosis followed 24 hr later by hepatic artery ligation and from appropriate sham-operated controls. Expression of Glyt-1 mRNA, studied by reverse transcriptase-polymerase chain reaction, was significantly decreased in the brain at coma stages of encephalopathy (to approximately 50% of control) concomitant with a significant...

Research paper thumbnail of Mechanisms of neuronal cell death in Wernicke's encephalopathy

Metabolic brain disease, 1998

Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine def... more Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine deficiency, encountered in chronic alcoholics and in patients with grossly impaired nutritional status. Neuropathologic studies as well as Magnetic Resonance Imaging reveal selective diencephalic and brainstem lesions in patients with WE. The last decade has witnessed major advances in the understanding of pathophysiologic mechanisms linking thiamine deficiency to the selective brain lesions characteristic of WE. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase, a rate-limiting tricarboxylic acid cycle enzyme are significantly reduced in autopsied brain tissue from patients with WE and from rats treated with the central thiamine antagonist, pyrithiamine. In the animal studies, evidence suggests that such enzyme deficits result in focal lactic acidosis, cerebral energy impairment and depolarization resulting from increased release of glutamate in vulnerable brain...

Research paper thumbnail of Ammonia and manganese increase arginine uptake in cultured astrocytes

Neurochemical research, 1998

Recent work has suggested a possible role for nitric oxide (NO) in the development of hepatic enc... more Recent work has suggested a possible role for nitric oxide (NO) in the development of hepatic encephalopathy (HE). In this study, we examined the effect of ammonia and manganese, factors implicated in the pathogenesis of HE, on the transport of arginine (a precursor of NO) into primary cultures of astrocytes. Treatment with 5 mM ammonia for 1-4 days produced a maximal (53%) increase in L-arginine uptake at 3 days when compared to untreated cells. Kinetic analysis following 4-day treatment with 5 mM ammonia revealed an 82% increase in the Vmax and a 61% increase in the Km value. Similar analysis with 100 microM manganese showed a 101% increase in Vmax and a 131% increase in the Km value. These results suggest that both manganese and ammonia alter L-arginine uptake by modifying the transporter for arginine. A decrease of 32% in the non-saturable component of L-arginine transport was also observed following treatment with ammonia. When cultures were treated separately with 5 mM ammonia...

Research paper thumbnail of Hepatic Encephalopathy: An Update of Pathophysiologic Mechanisms (44433A)

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs in both acute and chronic ... more Hepatic encephalopathy (HE) is a neuropsychiatric disorder that occurs in both acute and chronic liver failure. Although the precise pathophysiologic mecha- nisms responsible for HE are not completely understood, a deficit in neurotransmis- sion rather than a primary deficit in cerebral energy metabolism appears to be in- volved. The neural cell most vulnerable to liver failure is the astrocyte. In

Research paper thumbnail of Role of manganese in hepatic encephalopathy

Encephalopathy and Nitrogen Metabolism in Liver Failure, 2003

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

Addiction Biology

Wernicke encephalopathy is a neurological disorder commonly observed in chronic alcohol abuse, in... more 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, g...

Research paper thumbnail of Altered “peripheral-type” benzodiazepine receptor (PTBR) gene expression in brain and testis following end-to-side portacaval anastomosis

Research paper thumbnail of Increased expression and uptake activity of the glast transporter during thiamine deficiency in cultured astrocytes

Research paper thumbnail of Increased “peripheral-type” benzodiazepine receptor sites and mRNA in thalamus of thiamine-deficient rats

Neurochemistry International

“Peripheral-type” benzodiazepine receptors (PTBRs) are highly expressed on the outer mitochondria... more “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 ...

Research paper thumbnail of Primary cultures of rat astrocytes respond to thiamine deficiency-induced swelling by downregulating aquaporin-4 levels

Neuroscience Letters

Imaging studies indicate that cerebral edema is an important consequence of Wernicke's enceph... more Imaging studies indicate that cerebral edema is an important consequence of Wernicke's encephalopathy (WE), a disorder caused by thiamine deficiency (TD). We have investigated this problem using a recently developed in vitro astrocyte model of TD. Measurement of cell volume using the 3-O-methylglucose uptake method revealed a dose-dependent swelling of astrocytes during exposure to TD conditions. Time course studies indicated a progressive volume increase up to a maximum of 93% above controls after 4 days of treatment. This swelling then partially resolved, and remained stable for up to 10 days following commencement of TD treatment. Measurement of aquaporin-4 (AQP-4) levels showed a 44% loss after 10 days and a temporal profile consistent with an important role for this water channel protein in astrocyte cell volume changes during TD. Our findings of astrocyte swelling in TD are consistent with previous reports of focal brain edema in cases of WE, and indicate that AQP-4 may be...

Research paper thumbnail of eNOS gene deletion restores blood-brain barrier integrity and attenuates neurodegeneration in the thiamine-deficient mouse brain

Journal of Neurochemistry

Wernicke's encephalopathy is a cerebral disorder caused by thiamine (vitamin B(1)) deficiency... more Wernicke's encephalopathy is a cerebral disorder caused by thiamine (vitamin B(1)) deficiency (TD). Neuropathologic consequences of TD include region-selective neuronal cell loss and blood-brain barrier (BBB) breakdown. Early increased expression of the endothelial isoform of nitric oxide synthase (eNOS) occurs selectively in vulnerable brain regions in TD. We hypothesize that region-selective eNOS induction in TD leads to altered expression of tight junction proteins and BBB breakdown. In order to address this issue, TD was induced in C57BL/6 wild-type (WT) and eNOS(-/-) mice by feeding a thiamine-deficient diet and treatment with the thiamine antagonist pyrithiamine. Pair-fed control mice were fed the same diet with additional thiamine. In medial thalamus of TD-WT mice (vulnerable area), increased heme oxygenase-1 and S-nitrosocysteine immunostaining was observed in vessel walls, compared to pair-fed control-WT mice. Concomitant increases in IgG extravasation, decreases in exp...

Research paper thumbnail of Brain lactate synthesis in thiamine deficiency: a re-evaluation using 1H-13C nuclear magnetic resonance spectroscopy

Journal of Neuroscience Research

Region-selective accumulation of brain lactate occurs in TD; however, the mechanisms responsible ... more Region-selective accumulation of brain lactate occurs in TD; however, the mechanisms responsible have not been elucidated fully. (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy were therefore used to investigate de novo lactate synthesis from [1-(13)C]glucose in vulnerable (medial thalamus) and nonvulnerable (frontal cortex) brain regions of rats made thiamine deficient by administration of the central thiamine antagonist pyrithiamine. De novo synthesis of lactate was increased in the medial thalamus to 148% and 226% of pair-fed control values at presymptomatic and symptomatic stages of thiamine deficiency, respectively, whereas no such changes were observed in the frontal cortex. Administration of a glucose load selectively worsened the changes in medial thalamus. Pyruvate recycling and peripherally derived lactate did not contribute significantly to the lactate increase within the thiamine-deficient brain. Increases in immunolabeling of the lactate dehydrogenase isoen...

Research paper thumbnail of Manganese induces cell swelling in cultured astrocytes

NeuroToxicology

Manganese in excess is neurotoxic and causes a CNS disorder that resembles Parkinson's diseas... more Manganese in excess is neurotoxic and causes a CNS disorder that resembles Parkinson's disease (manganism). Manganese highly accumulates in astrocytes, which renders these cells more vulnerable to its toxicity. Consistent with this vulnerability, manganese has been shown to cause histopathological changes in astrocytes (Alzheimer type II change), generates oxidative stress and bring about mitochondrial dysfunction, including the induction of the mitochondrial permeability transition (mPT) in astrocytes. In addition to manganism, increased brain levels of manganese have been found in hepatic encephalopathy, a chronic neurological condition associated with liver dysfunction, wherein Alzheimer type II astrocytic changes are also observed. As low-grade brain edema, possibly secondary to astrocyte swelling, has been reported in hepatic encephalopathy, we hypothesized that manganese may contribute to such edema. We therefore exposed cultured astrocytes to manganese (Mn(3+)) acetate (2...

Research paper thumbnail of Astrocytic Poly (ADP) ribose polymerase-1 regulates glutamate transporter expression via NF-kB mechanism in experimental Wernicke’s encephalopathy

Research paper thumbnail of Downregulation of the glutamate transporter and its prevention by ceftriaxone in TD

Research paper thumbnail of Pyrithiamine-induced thiamine deficiency alters proliferation and neurogenesis in both neurogenic and vulnerable areas of the rat brain

Metabolic Brain Disease

Thiamine deficiency (TD) leads to Wernicke's encephalopathy (WE), in which focal histological... more Thiamine deficiency (TD) leads to Wernicke's encephalopathy (WE), in which focal histological lesions occur in periventricular areas of the brain. Recently, impaired neurogenesis has been reported in the hippocampus during the dietary form of TD, and in pyrithiamine-induced TD (PTD), a well-characterized model of WE. To further characterize the consequences of PTD on neural stem/progenitor cell (NSPC) activity, we have examined the effect of this treatment in the rat on both the subventricular zone (SVZ) of the rostral lateral ventricle and subgranular layer (SGL) of the hippocampus, and in the thalamus and inferior colliculus, two vulnerable brain regions in this disorder. In both the SVZ and SGL, PTD led to a decrease in the numbers of bromodeoxyuridine-stained cells, indicating that proliferation of NSPCs destined for neurogenesis in these areas was reduced. Doublecortin (DCX) immunostaining in the SGL was decreased, indicating a reduction in neuroblast formation, consistent ...

Research paper thumbnail of Altered expression of tight junction proteins and matrix metalloproteinases in thiamine-deficient mouse brain

Neurochemistry International

Wernicke's encephalopathy (WE) in humans is a metabolic disorder caused by thiamine deficienc... more Wernicke's encephalopathy (WE) in humans is a metabolic disorder caused by thiamine deficiency (TD). In both humans and experimental animals, TD leads to selective neuronal cell death in diencephalic and brainstem structures. Neuropathologic features of WE include petechial hemorrhagic lesions, and blood-brain barrier (BBB) breakdown has been suggested to play an important role in the pathogenesis of TD. The goal of the present study was to examine expression of the tight junction (TJ) protein occludin, its associated scaffolding proteins zona occludens (ZO-1 and ZO-2), and to measure matrix metalloproteinase (MMP) levels as a function of regional BBB permeability changes in thiamine-deficient mice. TD was induced in 12-week-old male C57Bl/6 mice by feeding a thiamine-deficient diet and administration of the central thiamine antagonist pyrithiamine. BBB permeability was measured by IgG extravasation; expression of occludin, ZO-1 and ZO-2 was measured by Western blot analysis and...

Research paper thumbnail of Poly(ADP)ribose polymerase-1 dependent regulation of glutamate transporter during thiamine deficiency

Research paper thumbnail of Astrocytic soluble factors disrupt mitochondrial membrane potential and downregulate GLT-1 in thiamine deficiency

Loss of astrocytic glutamate transporters is a major feature of both TD and human cases of Wernic... more Loss of astrocytic glutamate transporters is a major feature of both TD and human cases of Wernicke’s encephalopathy, in which cerebral energy metabolism is significantly affected. However, the underlying basis of this process remains unclear presently. Previous studies have reported evidence for the involvement of soluble neuronal factors that can regulate the levels of these glutamate transporters. In the present study we have investigated the possibility of release of astrocytic soluble factors that might be involved in the regulation of the glutamate transporter GLT-1 on these cells. Treatment of naïve astrocytes with conditioned media from astrocytes exposed toTD conditions resulted in a progressive decrease in glutamate uptake over 24h, along with increased release of glutamate. Immunoblotting and flow cytometry measurements indicated this was accompanied by a 20-40% loss of GLT-1 in these cells. Lactic acid, produced in astrocytes as a consequence of TD, was found to decrease...

Research paper thumbnail of Mechanisms of hepatic encephalopathy and thiamine deficiency

Metabolic Brain Disease, 2014

Research paper thumbnail of Reduced expression of astrocytic glycine transporter (Glyt-1) in acute liver failure

Metabolic brain disease, 2002

A growing body of evidence suggests that alterations in N-methyl-D-asparate NMDA-mediated excitat... more A growing body of evidence suggests that alterations in N-methyl-D-asparate NMDA-mediated excitatory neurotransmission may be involved in the pathophysiology of hepatic encephalopathy (HE) in acute liver failure (ALF). The NMDA receptor requires glycine as a positive allosteric modulator. One of the glycine transporters Glyt-1 is expressed primarily in astrocytes of the cerebral cortex in association with regions of high NMDA receptor expression. As astrocytic transporters regulate the amino acid concentrations within excitatory synapses, the expression of Glyt-1 was studied in cortical preparations from rats with ischemic liver failure induced by portacaval anastomosis followed 24 hr later by hepatic artery ligation and from appropriate sham-operated controls. Expression of Glyt-1 mRNA, studied by reverse transcriptase-polymerase chain reaction, was significantly decreased in the brain at coma stages of encephalopathy (to approximately 50% of control) concomitant with a significant...

Research paper thumbnail of Mechanisms of neuronal cell death in Wernicke's encephalopathy

Metabolic brain disease, 1998

Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine def... more Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine deficiency, encountered in chronic alcoholics and in patients with grossly impaired nutritional status. Neuropathologic studies as well as Magnetic Resonance Imaging reveal selective diencephalic and brainstem lesions in patients with WE. The last decade has witnessed major advances in the understanding of pathophysiologic mechanisms linking thiamine deficiency to the selective brain lesions characteristic of WE. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase, a rate-limiting tricarboxylic acid cycle enzyme are significantly reduced in autopsied brain tissue from patients with WE and from rats treated with the central thiamine antagonist, pyrithiamine. In the animal studies, evidence suggests that such enzyme deficits result in focal lactic acidosis, cerebral energy impairment and depolarization resulting from increased release of glutamate in vulnerable brain...

Research paper thumbnail of Ammonia and manganese increase arginine uptake in cultured astrocytes

Neurochemical research, 1998

Recent work has suggested a possible role for nitric oxide (NO) in the development of hepatic enc... more Recent work has suggested a possible role for nitric oxide (NO) in the development of hepatic encephalopathy (HE). In this study, we examined the effect of ammonia and manganese, factors implicated in the pathogenesis of HE, on the transport of arginine (a precursor of NO) into primary cultures of astrocytes. Treatment with 5 mM ammonia for 1-4 days produced a maximal (53%) increase in L-arginine uptake at 3 days when compared to untreated cells. Kinetic analysis following 4-day treatment with 5 mM ammonia revealed an 82% increase in the Vmax and a 61% increase in the Km value. Similar analysis with 100 microM manganese showed a 101% increase in Vmax and a 131% increase in the Km value. These results suggest that both manganese and ammonia alter L-arginine uptake by modifying the transporter for arginine. A decrease of 32% in the non-saturable component of L-arginine transport was also observed following treatment with ammonia. When cultures were treated separately with 5 mM ammonia...