Jimmy Huynh

Bumetanide normalizes brain edema in rats with bile duct ligation: evidence for increased BBB permeability via NKCC1.

Jimmy Huynh, Cristina R. Bosoi, Christian Parent-Robitaille, Mélanie Tremblay, Christopher F. Rose.

Background: Brain edema is a serious complication associated with hepatic encephalopathy (HE) due to chronic liver disease (CLD). An increase in blood brain barrier (BBB) ion permeability can occur across an intact BBB through alterations in transport mechanisms. NH4+ has very similar ionic properties to K+ and can be transported through K+ channels and cotransporters, implying that hyperammonemia could result in BBB hyperpermeability. An increase in BBB permeability via transport Na+-K+-2Cl- (NKCC1) has shown to promote brain edema and astrocyte swelling under pathophysiological conditions such as ischemia. Aim: To study the BBB integrity (vasogenic vs cytotoxic) and the role of NKCC1 in the pathogenesis of brain edema in cirrhotic rats. Methods: Two distinct animal models of HE are used in the present study; 1) biliary cirrhosis model (6 weeks bile duct ligation (BDL)). 2) portacaval shunt model (4 weeks portacaval anastomosis (PCA)). Both models develop hyperammonemia however brain edema is only observed in BDL. BBB breakdown was assessed by measuring brain extravasation of Evans blue and sodium fluorescein (injected i.v). Expression of BBB tight junction proteins (occludin, claudin-5, ZO-1 and ZO-2) were assessed by Western blot. Bumetanide was administered (i.p) for 10 days in BDL and SHAM animals. Brain water content was measured in the frontal cortex using the specific gravimetric method. Levels of brain NKCC1 mRNA were evaluated by RT-PCR in cerebral microvessels. Results: Extravasation of Evans blue and sodium fluorescein was not detected and no significant change in all tight junction protein was observed in both BDL and PCA models. Brain water content was reduced in bumetanide-treated BDL rats compared to control (77.66±0.15% vs 78.12±0.21%). In brain microvessels, NKCC mRNA increased in BDL rats compared to BDL SHAM (0.78±0.09 vs. 1.92±0.42) whereas no change was found in PCA compared to PCA SHAM (1.72±0.52 vs. 1.53±0.23). Conclusions: BDL rats did not demonstrate a change in BBB integrity or expression of tight junction proteins concluding brain edema in BDL is not of vasogenic origin. Furthermore, since brain edema was only observed in BDL rats (vs PCA), this implies additional factors aside ammonia, are involved in the pathogenesis of brain edema. Moreover, an increase of NKCC1 mRNA and an attenuation of brain edema following bumetanide treatment were demonstrated in BDL rats suggesting NKCC1 plays a role in the development of brain edema in CLD. These results demonstrate the potential therapeutic use of bumetanide for the treatment of HE.

Bumetanide normalizes brain edema in rats with bile duct ligation: evidence for increased bbb permeability via NKCC1.

Jimmy Huynh, Cristina R. Bosoi, Christian Parent-Robitaille, Mélanie Tremblay, Christopher F. Rose.

Background: Brain edema is a serious complication associated with hepatic encephalopathy (HE) due to chronic liver disease. An increase in BBB ion permeability (increase uptake of ions and accompanied by water fluxes towards the brain) can occur across an intact BBB through alterations in transport mechanisms. Endothelial cells that comprise the BBB secrete up to 40% of brain interstitial fluid as they transport Na+, K+ and 2 Cl- across the BBB. NH4+ has very similar ionic properties to K+ (similar ionic radius and diffusion coefficient) and can be transported through K+ channels and cotransporters, implying that hyperammonemia could result in BBB hyperpermeability. An increase in BBB permeability via transport Na+-K+-2Cl- (NKCC1) has shown to promote brain edema and astrocyte swelling under pathophysiological conditions such as ischemia. Aim: To study the BBB integrity (vasogenic vs cytotoxic) and the role of NKCC1 in the pathogenesis of brain edema in cirrhotic rats. Methods: Two distinct animal models of chronic liver failure and HE are used in the present study; 1) biliary cirrhosis model (6 weeks bile duct ligation (BDL)). 2) portacaval shunt model (4 weeks portacaval anastomosis (PCA)). Both models develop hyperammonemia however brain edema is only observed in BDL. BBB breakdown was assessed by measuring brain extravasation of Evans blue and sodium fluorescein (injected i.v). Expression of BBB tight junction proteins (occludin, claudin-5, ZO-1 and ZO-2) were assessed by Western blot. Bumetanide was administered (i.p) for 10 days in BDL and BDL SHAM. Brain water content was measured in the frontal cortex using the specific gravimetric method. Levels of brain NKCC1 mRNA were evaluated by RT-PCR in cerebral microvessels. Results: Extravasation of Evans blue and sodium fluorescein was not detected and there was no significant change in all tight junction protein levels measured in both BDL and PCA models. Brain water content was reduced in bumetanide-treated BDL rats compared to control (77.66±0.15% vs 78.12±0.21%). In brain microvessels, NKCC mRNA increased in BDL rats compared to BDL SHAM (0.78±0.09 vs. 1.92±0.42) whereas no change was found in PCA compared to PCA SHAM (1.72±0.52 vs. 1.53±0.23). Conclusions: BDL rats did not demonstrate a change in BBB integrity or in expression of BBB tight junction proteins. This suggests brain edema in BDL is not of vasogenic origin. Furthermore, since brain edema was only observed in BDL rats (vs PCA), this implies additional factors aside ammonia, are involved in the pathogenesis of brain edema. Moreover, an increase of NKCC1 mRNA and an attenuation of brain edema following bumetanide treatment were demonstrated in BDL rats suggesting NKCC1 plays a role in the development of brain edema in chronic liver disease. Furthermore, these results demonstrate the potential therapeutic use of bumetanide for the treatment of HE.

OpenAccess

Increased brain lactate is central to the development of brain edema in rats with chronic liver disease.

Cristina R. Bosoi, Claudia Zwingmann, Helen Marin, Christian Parent-Robitaille, Jimmy Huynh, Mélanie Tremblay, Christopher F. Rose.

OpenAccess

Systemic oxidative stress is implicated in the pathogenesis of brain edema in rats with chronic liver failure.

Cristina R. Bosoi, Xiaoling Yang, Jimmy Huynh, Christian Parent-Robitaille, Wenlei Jiang, Mélanie Tremblay, Christopher F. Rose.

Na-K-Cl cotransporter is implicated in the pathogenesis of brain edema in rats with bile duct ligation.

Jimmy Huynh, Cristina R. Bosoi, Christian Parent-Robitaille, Mélanie Tremblay, Christopher F. Rose.

Background: Brain edema is a serious complication associated with hepatic encephalopathy (HE) due to chronic liver failure (CLF) and its pathogenesis remains undefined. NKCC1, a Na-K-Cl cotransporter, located on the blood-brain barrier (BBB) has been demonstrated to be implicated in the pathogenesis of brain edema in experimental models of ischemia. Therefore, our aim was to 1) investigate the relationship of hyperammonemia, 2) study the integrity of the BBB and 3) determine the role of NKCC1, in association with brain edema in rats with CLF. Methods: Two distinct animal models of CLF and HE were used; i) biliary cirrhosis model (6 weeks bile duct ligation (BDL)) ii) portacaval shunt model (4 weeks portacaval anastomosis (PCA)). Brain water content was measured using the specific gravimetric method. BBB breakdown was assessed by measuring brain extravasation of injected BBB permeability tracers (Evans blue and sodium fluorescein). Expression of BBB tight junction proteins (occludin, claudin-5, ZO-1 and ZO-2) were assessed by immunoblot. Levels of brain NKCC1 mRNA were evaluated by RT-PCR in isolated cerebral microvessels. Rats were treated with bumetanide (an NKCC inhibitor; administered (i.p) for 10 days). Results: Similar degree of hyperammonemia was measured in both BDL and PCA rats however brain edema was only found in BDL rats. In brains of both BDL and PCA rats, extravasation of Evans blue and sodium fluorescein was not detected and no significant change in the levels of all tight junction proteins was found. Brain water content was reduced in bumetanide-treated BDL vs BDL-non treated (77.35±0.18% vs 78.89±0.25%). A 2.4 fold increase in NKCC1 mRNA was detected in BDL vs BDL-sham rats whereas no change was found in PCA vs PCA-sham rats. Conclusions: Chronic hyperammonemia independently does not lead to an increase in brain water. Brain edema, present in BDL rats, is not associated with a change in either BBB integrity or expression of BBB tight junction proteins and is therefore not of vasogenic origin. Furthermore, an increase in NKCC1 mRNA and attenuation of brain edema following bumetanide treatment, suggests NKCC1, independent of hyperammonemia, plays a role in the development of brain edema in CLF.

Systemic oxidative stress followed by increases in ammonia and lactate is involved in the pathogenesis of brain edema in chronic liver failure.

Claudia Zwingmann, Jimmy Huynh, Cristina R. Bosoi, Christian Parent-Robitaille, Helen Marin, Mélanie Tremblay, Christopher F. Rose.

Aims: Brain edema represents a constant finding in patients with hepatic encephalopathy (HE) due to chronic liver failure; however its pathogenetic mechanisms are poorly described. Hyperammonemia is considered the central component in the pathogenesis of HE, but ammonia levels are not correlated with severity of HE. Other factors such as oxidative stress and impaired lactate metabolism are believed to be involved. Temporal resolution of these factors involved in the progression of the disease and brain edema might elucidate the relationship between these pathogenetic factors. The present study investigates temporal resolution of ammonia, oxidative stress and lactate in relation to the development of brain edema in bile-duct ligated rats (BDL), a widely used rat model of chronic liver failure and HE. Methods: Ammonia (commercial kit), reactive oxygen species (ROS) (DCFDA fluorescence), lactate (Amplex Red fluorescence) and brain edema (specific gravimetric technique) were measured in BDL rats vs sham operated controls at 2, 4 and 6 weeks after surgical intervention in plasma and cerebrospinal fluid or brain tissue. Results: See table.Conclusions: Following 2 weeks of BDL, an increase in plasma oxidative stress is observed with no appearance of hyperammonemia, hyperlactataemia, increased brain lactate and ammonia or brain edema. Following 4 weeks of BDL, in addition to an increase in systemic oxidative stress, an increase in plasma and brain ammonia and brain (not plasma) lactate is demonstrated but still no evidence of brain edema. Brain edema appears at 6 weeks, along with an increase in all 3 pathogenetic factors. The further increase in brain lactate and ammonia compared to 4 weeks, superimposed on systemic oxidative stress, may be responsible the development of brain edema in BDL rats. Our results support the multifactorial pathogenesis of brain edema in HE and suggests systemic oxidative stress might be an important “first hit”, followed by increases in ammonia and lactate, in the pathogenesis of brain edema in chronic liver failure.

Oral

Impaired lactate metabolism, not brain ammonia and glutamine, contributes to the pathogenesis of brain edema in minimal hepatic encephalopathy.

Christian Parent-Robitaille, Cristina R. Bosoi, Claudia Zwingmann, Jimmy Huynh, Helen Marin, Mélanie Tremblay, Christopher F. Rose.

Aims: Chronic liver failure leads to hyperammonemia, a central component in the pathogenesis of hepatic encephalopathy (HE). Neurotoxic effects of ammonia induce numerous metabolic alterations such as increased brain lactate (Lac) and glutamine (Gln) levels. Brain edema is present in patients with chronic liver failure however the pathophysiological mechanisms are not clearly understood. The present study investigates the role of brain ammonia, Lac and Gln in pathogenesis of brain edema in 2 different rat models of chronic liver failure/HE; 1) portacaval anastomosis (PCA), and 2) bile-duct ligation (BDL). Methods: Ammonia (commercial kit), brain edema (specific gravimetric technique) Lac (Amplex Red fluorescence) and Gln (1H nuclear magnetic spectroscopy) were measured in brain tissue of PCA and BDL rats vs sham operated controls. De novo synthesis of Lac and Gln was assessed in brain tissue by 13C nuclear magnetic resonance spectroscopy, after injecting PCA and BDL rats along with their respective sham operated controls with [U-13C] glucose (500 mg/kg, i.p) 30 minutes before sacrifice. Lac, Gln and brain edema were also investigated in BDL rats at 2, 4 and 6 weeks after surgery and after reducing ammonia levels with AST-120 (spherical carbon adsorbent), at 1g/kg/day for 6 weeks. Results: Hyperammonemia developed in both PCA (177.3±8.9μM vs sham: 52.1±11.3μM; p<0.0001) and BDL (155.0±8.9μM vs sham: 41.0±11.2μM; p<0.0001); with no significant difference between the groups. An increase in brain water content was observed in rats with BDL (81.88±0.12% vs sham: 81.13±0.15%, p<0.05), as well as total Lac levels; whereas no significant change in brain water and total Lac was found in PCA. Gln levels significantly increased in PCA rats and BDL rats vs respective sham-operated controls. A significant increase in de novo synthesis of 13C Lac and 13C Gln from 13C glucose was found in BDL rats, whereas in PCA rats only de novo synthesis of 13C Gln increased. In addition, total Lac levels were increased in BDL rats before the apparition of brain edema. Following AST-120 treatment, Lac levels and brain edema significantly decreased, while Gln levels remained unchanged. Conclusions: BDL and PCA rats both presented with similar levels of hyperammonemia and Gln, as well as increased de novo synthesis of Gln from glucose. However only BDL rats demonstrated an increase in brain water and Lac as well as increased de novo synthesis of Lac from glucose. Our findings suggest increased brain Lac, not increased brain Gln, is associated with brain edema. We conclude that impaired Lac metabolism may contribute to the pathogenesis of brain edema in HE.

Oral

Na-K-Cl cotransporter is implicated in the pathogenesis of brain edema in rats with bile duct ligation.

Jimmy Huynh, Cristina R. Bosoi, Christian Parent-Robitaille, Mélanie Tremblay, Christopher F. Rose.

Aims: Brain edema is a serious complication associated with hepatic encephalopathy (HE) due to chronic liver failure. It is unclear whether brain edema is of vasogenic (blood brain barrier (BBB) breakdown) or of cytotoxic (disturbance of neurocellular metabolism) origin. It has been demonstrated that the Na-K-Cl cotransporter (NKCC) located on the luminal side of the BBB is implicated in the pathogenesis of brain edema in different animal models of ischemia. Furthermore, following the administration of bumetanide, an inhibitor of NKCC, brain edema is attenuated. Therefore, our aim was to study the BBB integrity and the role of NKCC in the pathogenesis of brain edema in cirrhotic rats. Methods: Two distinct animal models of chronic liver failure and HE are used in the present study; 1) biliary cirrhosis model (6 weeks bile duct ligation (BDL)). 2) portacaval shunt model (4 weeks portacaval anastomosis (PCA)). Both models develop hyperammonemia however brain edema is only observed in BDL. BBB breakdown was assessed by measuring brain extravasation of BBB permeability tracers. Evans blue and sodium fluorescein were injected (i.v), brains were perfused and extravasation was determined by spectophotometry. Expression of BBB tight junction proteins (occludin, claudin-5, ZO-1 and ZO-2) were assessed by immunoblot. Bumetanide was administered (i.p) for 10 days in BDL and BDL SHAM. Brain water content was measured in the frontal cortex using the specific gravimetric method. Levels of brain NKCC mRNA were evaluated by RT-PCR in microvessels isolated using centrifugation methods. Results: Extravasation of Evans blue and sodium fluorescein was not detected and there was no significant change in all tight junction protein levels measured in both BDL and PCA (negative control) models. Brain water content was reduced in bumetanide-treated BDL rats compared to control (77.66±0.15% vs 78.12±0.21%). In brain microvessels, NKCC mRNA increased in BDL rats compared to BDL SHAM (0.78±0.09 vs. 1.92±0.42) whereas no change was found in PCA compared to PCA SHAM (1.72±0.52 vs. 1.53±0.23). Conclusions: BDL rats did not demonstrate a change in BBB integrity or a change in expression of BBB tight junction proteins. This suggests brain edema in BDL is not of vasogenic origin. Moreover, an increase of NKCC mRNA and an attenuation of brain edema following bumetanide treatment were demonstrated in BDL rats suggesting NKCC plays a role in the development of brain edema in chronic liver failure.

L'augmentation de novo du lactate cérébral, indépendamment des niveaux d’ammoniaque et glutamine, est impliquée dans la pathogénèse de l’œdème cérébral dans l’insuffisance hépatique chronique.

Cristina R. Bosoi, Claudia Zwingmann, Jimmy Huynh, Helen Marin, Mélanie Tremblay, Christopher F. Rose.

Introduction: L’insuffisance hépatique mène à l’hyperammonémie, la composante centrale dans la pathogénèse de l’encéphalopathie hépatique (EH). Les niveaux neurotoxiques d’ammoniaque induisent des nombreuses altérations métaboliques telles que l’augmentation du lactate et glutamine au niveau cérébral. Des nouvelles techniques d’imagerie ont démontré que l’œdème cérébral est présent chez les patients avec insuffisance hépatique chronique, mais les mécanismes pathophysiologiques ne sont pas bien connus. Dans cette étude, nous avons investigué l’implication de la synthèse de novo du lactate et glutamine dans la pathogénèse de l’œdème cérébral en utilisant 2 modèles différents d’insuffisance hépatique chronique/EH chez le rat: 1) la dérivation portosystémique (PCA); et 2) la ligature de voie biliaire (BDL). Méthodes: Des rats PCA et BDL, ainsi que contrôles SHAM-opérés ont été injectés avec [U-13C] glucose (500 mg/kg, i.p) et sacrifiés après 30 minutes. Les niveaux totaux, ainsi que la synthèse de novo de glutamine et du lactate ont été mesurés dans le tissu cérébral par spectroscopie de résonance magnétique nucléaire 1H et 13C. L’ammoniaque a été mesurée dans le plasma artériel et le liquide céphalorachidien par un kit commercial. Le contenu en eau du cerveau a été mesuré dans le cortex frontal par une technique spécifique gravimétrique. Résultats: L’hyperammonémie s’est développée dans les deux groupes; PCA: 177.3 ± 8.9 μM vs SHAM: 52.1 ± 11.3 μM; p<0.001 et BDL: 155.0 ± 8.9 μM vs SHAM: 41.0 ± 11.2 μM; p<0.001, sans différence significative entre les 2 groupes. Des résultats similaires ont été observés dans le liquide céphalorachidien; PCA: 179.5 ± 10.3 μM vs SHAM: 34.9 ± 6.3 μM; p<0.001 et BDL: 142.6 ± 28.3 μM vs SHAM: 27.9 ± 4.9 μM; p<0.001. Le contenu en eau du cerveau a augmenté dans les rats BDL (BDL: 81.88 ± 0.12% vs SHAM: 81.13 ± 0.15%, p<0.05), par contre dans les rats PCA il n’y avait pas une différence significative comparativement au rats SHAM-opérés. Les niveaux de glutamine étaient augmentés 3 fois chez les rats PCA vs SHAM et 2 fois chez les rats BDL vs SHAM. Une augmentation significative de la synthèse de novo du 13C lactate et 13C glutamine provenant du 13C glucose administré a été observée chez les BDL (1.6 fois, respectivement 2 fois vs SHAM), tandis que chez les rats PCA seulement une augmentation de la synthèse de novo de 13C glutamine a été observée. Conclusions: Les rats PCA et BDL présentent des taux similaires d’ammoniaque plasmatique et cérébral et une augmentation de la synthèse de novo de glutamine cérébrale provenant du glucose, mais seulement les rats BDL présentent l’œdème cérébral ainsi qu’une augmentation de la synthèse de novo du lactate cérébral provenant du glucose. Nos résultats suggèrent que le lactate est un important facteur dans la pathogénèse de l’œdème cérébral dans l’insuffisance hépatique chronique. Projet subventionné par: Instituts de recherche en santé du Canada

Le cotransporteur Na-K-Cl est impliqué dans la pathogénèse de l’œdème cérébral chez les rats avec une ligature de la voie biliaire.

Jimmy Huynh, Cristina Bosoi, Christian Parent-Robitaille, Mélanie Tremblay, Christopher F. Rose.

Objectif : L’œdème cérébral est un symptôme sévère de l’encéphalopathie hépatique (EH) lors d’une insuffisance hépatique chronique. La cause de l’œdème cérébral est ambigüe parce qu’elle peut être de type vasogénique, la rupture des jonctions serrées de la barrière hémato-encéphalique (BHE), ou de type cytotoxique, la perturbation du métabolisme neurocellulaire. Plusieurs recherches démontrent que le cotransporteur Na-K-Cl 1 (NKCC1) serait impliqué dans la pathogénèse de l’œdème cérébral dans différents modèles animaux d’ischémie cérébrale et qu’un traitement avec de la bumetanide, un inhibiteur de NKCC1, atténue l’augmentation d’eau dans le cerveau. Ainsi, notre objectif était d’étudier l’intégrité de la BHE et le rôle de NKCC1 dans la pathogénèse de l’œdème cérébral chez des rats cirrhotiques. Méthodes : Deux modèles animaux d’insuffisance hépatique chronique sont utilisés dans cette étude. Le premier modèle (cirrhose biliaire de 6 semaines (BDL)), est une ligature de la voie biliaire. Alors, la bile synthétisée par les hépatocytes s’accumule dans le foie et provoque la cirrhose du foie. Ce modèle présente une hyperammonémie et du stress oxydatif plasmatique ainsi que l’œdème cérébral. Le deuxième modèle (dérivation portocave de 4 semaines (PCA)), est une anastomose de la veine porte à la veine cave inférieure. Ainsi, le sang provenant du système digestif n’est pas filtré par le foie, ce qui provoque une hyperammonémie mais elle n'est pas accompagnée par une induction de stress oxydatif et d’œdème cérébral alors ce sera un contrôle négatif. Pour déterminer la perméabilité générale de la barrière hémato-encéphalique, l’extravasation de l’Evans blue, un colorant qui se lie aux protéines (dont l’albumine sérique), et du fluorophore, fluorescéine de sodium, a été évaluée par spectrophotométrie et l’expression des protéines des jonctions serrées (occludin, claudin-5, ZO-1, ZO-2) a été mesurée par immunobuvardage dans les deux modèles. La bumetanide a été administrée i.p pendant 10 jours chez les BDL et BDL SHAM. La quantité d’eau dans le cortex cérébral a été mesurée par gravimétrie. L’expression d’ARNm de NKCC1 a été mesurée dans les microvaisseaux sanguins isolés à partir de cerveaux des deux modèles à l’aide d’un protocole de centrifugation. Résultats : L’extravasation des colorants n’a pas été détectée et l’expression des protéines de jonctions serrées est demeurée inchangée dans les deux modèles. L’œdème cérébral a été atténué lorsque la bumetanide a été administrée chez les BDL comparé aux contrôles (77.66±0.15% vs 78.12±0.21%). Dans les microvaisseaux sanguins cérébraux, le niveau d’ARNm de NKCC1 était augmenté chez les BDL comparé aux BDL SHAM (1.92±0.42 vs. 0.78±0.09) tandis qu’il restait inchangé chez les PCA comparé aux PCA SHAM (1.72±0.52 vs. 1.53±0.23). Conclusion : L’extravasation est absente et l’expression des protéines de jonctions serrées est inchangée donc l’œdème cérébral n’est pas de type vasogénique. L’augmentation d’ARNm de NKCC1 et l’atténuation de l’œdème cérébral par la bumetanide suggèrent que l’œdème cérébral est de type cytotoxique chez les rats avec une insuffisance hépatique chronique.

Increased de novo synthesis of brain lactate, independent of brain ammonia and glutamine, is implicated in the pathogenesis of brain edema in chronic liver failure.

Cristina R. Bosoi, Claudia Zwingmann, Jimmy Huynh, Helen Marin, Mélanie Tremblay, Christopher F. Rose.

Background: Chronic liver failure leads to hyperammonemia, a central component in the pathogenesis of hepatic encephalopathy. Neurotoxic effects of ammonia have been shown to induce numerous metabolic alterations such as increased brain lactate and glutamine levels. Newly developed imaging techniques have demonstrated brain edema is present in patients with chronic liver failure however the pathophysiological mechanisms are not clearly understood. The present study investigates the role of de novo synthesis of brain lactate and glutamine in pathogenesis of brain edema in 2 different rat models of chronic liver failure/hepatic encephalopathy; 1) portacaval anastomosis (PCA), and 2) bile-duct ligation (BDL). Methods: PCA and BDL rats along with their respective sham-operated controls were injected with [1-13C] glucose (500 mg/kg, i.p) and sacrificed 30 minutes later. Glutamine and lactate were assessed in brain tissue by 1H and 13C nuclear magnetic resonance spectroscopy. Ammonia levels were measured in arterial plasma and cerebrospinal fluid using a commercially available kit. Brain water content was measured in frontal cortex using a specific gravimetric technique. Results: Hyperammonemia developed in both PCA (177.3 ± 8.9μM vs sham: 52.1 ± 11.3μM; p< 0.0001) and BDL (155.0 ± 8.9μM vs sham: 41.0 ± 11.2μM; p< 0.0001); with no significant difference between the groups (p> 0.05). Similar results were found in cerebrospinal fluid (PCA: 179.5 ± 10.3μM vs sham: 34.9 ± 6.3μM; p< 0.0001 and BDL: 142.6 ± 28.3μM vs sham: 27.9 ± 4.9μM; p< 0.0001); with no significant difference between the groups (p> 0.05). An increase in brain water content was observed in rats with BDL (81.88 ± 0.12% vs sham: 81.13 ± 0.15%, p< 0.05) whereas no significant change in brain water content was found in PCA vs their respective sham-operated controls. Glutamine levels significantly increased 3 fold in PCA rats and 2 fold in BDL rats vs respective sham-operated controls. A significant increase in de novo synthesis of 13C lactate and 13C glutamine from 13C glucose was found in BDL rats (1.6 fold and 2 fold respectively vs sham), whereas in PCA rats only de novo synthesis of 13C glutamine increased. Conclusion: BDL and PCA rats both presented with similar levels of hyperammonemia and increased brain ammonia, increased de novo synthesis of glutamine from glucose however only BDL rats demonstrated an increase in brain water as well as an increase in de novo synthesis of lactate from glucose. Our findings suggest lactate is an important pathogenic factor implicated in the pathogenesis of brain edema in chronic liver failure.

Increased de novo synthesis of brain lactate, independent of brain ammonia and glutamine, is implicated in the pathogenesis of brain edema in chronic liver failure.

Cristina R. Bosoi, Claudia Zwingmann, Jimmy Huynh, Helen Marin, Mélanie Tremblay, Christopher F. Rose.

Jimmy Huynh, M.Sc.

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