Hepato-neuro lab

Abstracts/Meetings

Bookmark and Share

abstract
Abstracts accepted in international or national scientific meetings.

2009

  1. Synergistic effect of systemic oxidative stress and hyperammonemia leads to brain edema in rats with chronic liver failure. Cristina R Bosoi; Xiaoling Yang; Wenlei Jiang; Christian Parent-Robitaille; Mélanie Tremblay et Christopher F Rose, 5th Annual CASL Winter Meeting, February 27th - March 2nd, Banff (Alberta, Canada).
    [Official abstract] [Abstract↓]
    Background: Liver failure/disease leads to hyperammonemia which is central in the pathogenesis of hepatic encephalopathy. However, it is believed systemic oxidative/nitrosative stress may play an important role in exacerbating the neuropsychological effects of hyperammonemia observed in patients with liver disease. The present study aims to investigate the role of oxidative/nitrosative stress in 2 rat models of liver disease/hepatic encephalopathy; 1) portacaval anastomosis (PCA), and 2) bile-duct ligation (BDL). Methods: Rats were sacrificed 4 weeks following PCA and 6 weeks following BDL. Arterial plasma and cerebrospinal fluid (CSF) were collected to measure ammonia, reactive oxygen species (ROS), hydrogen peroxide (H2O2) (only measured in plasma) and nitric oxide (NO) using a commercially available kit, the DCFDA and Amplex Red fluorescent techniques and the Griess reaction respectively. S-nitrosylation of cystein thiols was measured in the frontal cortex and plasma proteins by immunoblotting. Brain water content was measured in the frontal cortex using a specific gravimetric technique. Results: Hyperammonemia developed in both PCA (PCA: 181.0 ± 8.5uM vs sham: 60.5 ± 7.0uM; p<0.0001) and BDL (BDL: 101.1 ± 11.0uM vs sham: 41.7 ± 9.2uM; p<0.05) rats with PCA rats being significantly higher compared to BDL rats (p<0.001). Consequently, ammonia increased in CSF in both PCA (PCA: 159.5 ± 15.8uM vs sham: 32.5 ± 3.7uM; p<0.0001) and BDL (BDL: 123.5 ± 21.7uM vs sham: 23.3 ± 6.1uM; p<0.05), but no significant change was observed between PCA and BDL. Only rats with BDL demonstrated an increase in plasma levels of ROS (5.8-fold increase vs sham; p<0.001), H2O2 (3.2-fold increase vs sham; p<0.05) and NO (2.9-fold increase vs sham; p<0.05). This was accompanied by an increase in S-nitrosylation of plasma proteins. No significant changes in CSF ROS and NO, nor in S-nitrosylation of frontal cortex proteins were found in BDL or PCA compared to their respective control groups. In addition, an increase in brain water content was observed in rats with BDL (BDL: 81.91 ± 0.19% vs sham: 81.23 ± 0.20, p<0.05). No significant change in brain water content was found in PCA rats vs sham-operated controls. Conclusion: Systemic oxidative stress together with hyperammonemia results in an increase in brain water in rats with BDL which is not demonstrated in PCA rats where only hyperammonemia is observed. Our findings suggest systemic oxidative stress is implicated in the pathogenesis of brain edema and its synergistic effect with ammonia may lead to progression of hepatic encephalopathy.

     

  2. Synergistic effect of systemic oxidative stress and hyperammonemia leads to brain edema in rats with chronic liver failure. Cristina R Bosoi; Xiaoling Yang; Wenlei Jiang; Christian Parent-Robitaille; Mélanie Tremblay et Christopher F Rose, 44th Annual Meeting of the European Association for the Study of the Liver, April 22nd - 26th, Copenhagen (Denmark).
    [Abstract↓]
    Background: Liver failure/disease leads to hyperammonemia, a central component in the pathogenesis of hepatic encephalopathy. However, it is believed systemic oxidative/nitrosative stress may exacerbate the neuropsychological effects of hyperammonemia observed in patients with liver disease. The present study aims to investigate the role of oxidative/nitrosative stress in 2 rat models of liver disease/hepatic encephalopathy; 1) portacaval anastomosis (PCA), and 2) bile-duct ligation (BDL). Methods: Rats were sacrificed 4 weeks following PCA and 6 weeks following BDL. Arterial plasma and cerebrospinal fluid (CSF) were collected to measure ammonia, reactive oxygen species (ROS), hydrogen peroxide (H2O2) and nitric oxide (NO). S-nitrosylation of cystein thiols was measured in the frontal cortex and plasma proteins by immunoblotting. Brain water content was measured in the frontal cortex using a specific gravimetric technique. Results: Hyperammonemia developed in both PCA (PCA: 181.0 ± 8.5uM vs sham: 60.5 ± 7.0uM; p< 0.0001) and BDL (BDL: 101.1 ± 11.0uM vs sham: 41.7 ± 9.2uM; p< 0.05) rats with PCA rats being significantly higher compared to BDL rats (p< 0.001). Consequently, ammonia increased in CSF in both PCA (PCA: 159.5 ± 15.8uM vs sham: 32.5 ± 3.7uM; p< 0.0001) and BDL (BDL: 123.5 ± 21.7uM vs sham: 23.3 ± 6.1uM; p< 0.05), but no significant change was observed between PCA and BDL. Only rats with BDL demonstrated an increase in plasma levels of ROS (5.8-fold increase vs sham; p< 0.001), H2O2 (3.2-fold increase vs sham; p< 0.05) and NO (2.9-fold increase vs sham; p< 0.05). This was accompanied by an increase in S-nitrosylation of plasma proteins. An increase in brain water content was observed in rats with BDL (BDL: 81.91 ± 0.19% vs sham: 81.23 ± 0.20, p< 0.05) whereas no significant change in brain water content was found in PCA vs sham-operated control rats. Conclusion: Hyperammonemia together with systemic oxidative stress are associated with brain edema in rats with BDL which is not demonstrated in PCA rats where only hyperammonemia is observed. Our findings suggest systemic oxidative stress is implicated in the pathogenesis of brain edema and its synergistic effect with ammonia may lead to progression of hepatic encephalopathy.

     

  3. AST-120 (spherical carbon adsorbent) lowers arterial ammonia and attenuates brain edema in bile-duct ligated rats. Cristina Bosoi; Christian Parent-Robitaille; Mélanie Tremblay & Christopher F. Rose, International Symposium on Hepatic Encephalopathy, September 17th-19th, Valencia, Spain.
    [Abstract↓]
    Background: The pathogenesis of hepatic encephalopathy (HE) is multifactorial involving gut-derived toxins such as ammonia. Liver disease leads to hyperammonemia and neurotoxic levels of ammonia which have been demonstrated to induce oxidative stress. Therefore a primary treatment target for HE is to decrease ammonia production in the gastrointestinal tract. AST-120 (spherical carbon adsorbent), an oral adsorbent of engineered activated carbon microspheres with surface areas exceeding 1600m2/g works as a sink for neuro- and hepato-toxins present in the gut. In this study, we evaluated the protective effect of AST-120 in attenuating brain edema and the capacity of AST-120 to lower arterial ammonia and oxidative stress in rats with cirrhosis. Methods: Secondary biliary cirrhosis was induced in rats by bile duct ligation (BDL) for 6 weeks. BDL and SHAM-operated rats received AST-120 by gavage in methylcellulose (MC) at a dose of 0.1 or 1g/kg/day for 6 weeks. Control BDL and SHAM-operated groups received MC only. AST and ALT were measured at the end of the treatment period to assess liver function. Ammonia and reactive oxygen species (ROS) were measured in arterial plasma using a commercially available kit and DCFDA-fluorescent technique respectively. Brain water content was measured in the frontal cortex using the specific gravimetric technique. Results: AST-120 was well-tolerated with no deaths in either of the treatment groups. Brain water content increased in BDL vs SHAM-operated rats (81.8 ± 0.1% vs 81.3 ± 0.2%, p<0.05). Both 0.1 and 1g/kg/day AST-120 treatments normalised brain water content in BDL rats. Arterial ammonia increased in the BDL control group vs SHAM-operated controls (175.5 ± 48.1uM vs 105.3 ± 27.3uM, p<0.05) and decreased significantly in BDL 0.1g/kg/day (118.0 ± 6.4uM, p<0.05) and BDL 1g/kg/day (75.4 ± 31.4uM, p<0.05). Circulating levels of ROS were significantly increased in BDL vs SHAM-operated rats (11 fold, p<0.001). AST-120 treatment did not attenuate arterial levels of ROS compared to respective SHAM-operated controls. Liver functions enzymes, AST and ALT, were increased in all BDL rats compared to their respective SHAM-operated controls (p<0.001). Conclusions: AST-120 treatment normalized brain water content and decreased arterial ammonia levels but did not demonstrate an effect on systemic ROS. Long-term treatment with AST-120 is a safe, non-antibiotic alternative demonstrating a significant ammonia-lowering effect, as well as a protective effect on the development of brain edema in rats with chronic liver failure. Additional studies are warranted to evaluate the effects of AST-120 on HE in patients with advanced liver disease.

     

  4. Brain edema is associated with systemic and not central oxidative stress in rats with bile-duct ligation. Xiaoling Yang; Cristina Bosoi; Mélanie Tremblay & Christopher F. Rose, International Symposium on Hepatic Encephalopathy, September 17th-19th, Valencia, Spain.
    [Abstract↓]
    Background: Ammonia plays a major role in the pathogenesis of hepatic encephalopathy however oxidative stress is also believed to be involved. Two lines of evidence lead us to the following aim of our study: 1) neurotoxic levels of ammonia have demonstrated to induce oxidative stress in vitro and 2) systemic oxidative stress is believed to exacerbate the neuropsychological effects of hyperammonemia observed in patients with liver disease. Our aim was to measure oxidative stress markers systemically and centrally, in association with brain edema in rats with cirrhosis. Methods: Rats were sacrificed 6 weeks following bile-ligated induced cirrhosis. Arterial plasma and cerebrospinal fluid (CSF) were collected to measure ammonia (commercially available kit), reactive oxygen species (ROS) (DCFDA-fluorescent technique), nitric oxide (NO) (Griess method) and lipid peroxidation (malondialdehyde, MDA) (commercially available kit). Frontal cortex was dissected to measure antioxidant catalase activity (Amplex Red fluorescent technique), S-nitrosylation of cystein thiols (immunoblotting) and brain water content was determined using the specific gravimetric technique. Results: Brain water content increased in BDL rats vs SHAM-operated controls (81.91 ± 0.19% vs 81.23 ± 0.20%, p<0.05). BDL rats vs SHAM-operated controls developed an increase in plasma arterial levels of ammonia (91.8 ± 18.4uM vs 41.2 ± 13.2uM, p<0.05), ROS (4.9 fold increase), NO (2.9 fold increase), MDA (41.9 ± 7.4uM vs 9.9 ± 0.6uM, p<0.005), S-nitrosylated proteins and a decrease in catalase activity (1.3 ± 0.5U/ml vs 3.2 ± 1.4U/ml, p<0.05). Centrally, BDL rats vs SHAM-operated controls developed an increase in CSF ammonia (123.5 ± 21.7uM vs 23.3 ± 6.1uM, p<0.05) but did not develop an increase in CSF ROS and NO or in brain MDA and S-nitrosylation detection. Furthermore, catalase activity in the brain was unchanged in BDL vs SHAM-operated controls. Conclusions: Six weeks following BDL, rats developed brain edema. An increase in arterial ammonia was accompanied with an increase in lipid peroxidation, NO, ROS and S-nitrosylation with a decrease in catalase activity. However, a similar increase in ammonia levels in CSF lead to contrary results where no increase in oxidative stress markers was found in brain. Our findings suggest 1) ammonia does not induce oxidative stress in the brain, 2) systemic oxidative stress is related to a decrease in catalase activity and 3) brain edema in BDL rats is associated with systemic, and not central, oxidative stress.

     

  5. AST-120 (spherical carbon adsorbent) attenuates brain edema and lowers arterial ammonia in bile duct ligated rats. Cristina Bosoi; Christian Parent-Robitaille; Mélanie Tremblay & Christopher F. Rose, The 60th Annual Meeting of the American Association for the Study of Liver Diseases, October 30th-November 3rd, Boston, USA.
    [Official abstract] in Hepatology 50:336A [Abstract↓]
    Background: The pathogenesis of hepatic encephalopathy (HE) is multifactorial involving gut-derived toxins such as ammonia. Liver disease leads to hyperammonemia and neurotoxic levels of ammonia which have been demonstrated to induce oxidative stress. Therefore a primary treatment target for HE is to decrease ammonia production in the gastrointestinal tract. AST-120 (spherical carbon adsorbent), an oral adsorbent of engineered activated carbon microspheres with surface areas exceeding 1600m2/g works as a sink for neuro- and hepato–toxins present in the gut. In this study, we evaluated the protective effect of AST-120 in attenuating brain edema and the capacity of AST-120 to lower arterial ammonia and oxidative stress in rats with cirrhosis. Methods: Secondary biliary cirrhosis was induced in rats by bile duct ligation (BDL) for 6 weeks. BDL and SHAM-operated rats received AST-120 by gavage in methylcellulose (MC) at a dose of 0.1 or 1g/kg/day for 6 weeks. Control BDL and SHAM-operated groups received MC only. AST and ALT were measured at the end of the treatment period to assess liver function. Ammonia and reactive oxygen species (ROS) were measured in arterial plasma using a commercially available kit and DCFDA-fluorescent technique respectively. Brain water content was measured in the frontal cortex using the specific gravimetric technique. Results: AST-120 was well-tolerated with no deaths in either of the treatment groups. Brain water content increased in BDL vs SHAM-operated rats (81.8 ± 0.1% vs 81.3 ± 0.2%, p<0.05). Both 0.1 and 1g/kg/day AST-120 treatments normalised brain water content in BDL rats. Arterial ammonia increased in the BDL control group vs SHAM-operated controls (175.5 ± 48.1uM vs 105.3 ± 27.3uM, p<0.05) and decreased significantly in BDL 0.1g/kg/day (118.0 ± 6.4uM, p<0.05) and BDL 1g/kg/day (75.4 ± 31.4uM, p<0.05). Circulating levels of ROS were significantly increased in BDL vs SHAM-operated rats (11 fold, p<0.001). AST-120 treatment did not attenuate arterial levels of ROS compared to respective SHAM-operated controls. Liver functions enzymes, AST and ALT, were increased in all BDL rats compared to their respective SHAM-operated controls (p<0.001). Conclusions: AST-120 treatment normalized brain water content and decreased arterial ammonia levels but did not demonstrate an effect on systemic ROS. Long-term treatment with AST-120 is a safe, non-antibiotic alternative demonstrating a significant ammonia-lowering effect, as well as a protective effect on the development of brain edema in rats with chronic liver failure. Additional studies are warranted to evaluate the effects of AST-120 on HE in patients with advanced liver disease.

     

  6. Brain edema is associated with systemic and not central oxidative stress in rats with bile-duct ligation. Xiaoling Yang; Cristina Bosoi; Mélanie Tremblay & Christopher F. Rose, The 60th Annual Meeting of the American Association for the Study of Liver Diseases, October 30th-November 3rd, Boston, USA.
    [Official abstract] in Hepatology 50:459A [Abstract↓]
    Background: Ammonia plays a major role in the pathogenesis of hepatic encephalopathy however oxidative stress is also believed to be involved. Two lines of evidence lead us to the following aim of our study: 1) neurotoxic levels of ammonia have demonstrated to induce oxidative stress in vitro and 2) systemic oxidative stress is believed to exacerbate the neuropsychological effects of hyperammonemia observed in patients with liver disease. Our aim was to measure oxidative stress markers systemically and centrally, in association with brain edema in rats with cirrhosis. Methods: Rats were sacrificed 6 weeks following bile-ligated induced cirrhosis. Arterial plasma and cerebrospinal fluid (CSF) were collected to measure ammonia (commercially available kit), reactive oxygen species (ROS) (DCFDA-fluorescent technique), nitric oxide (NO) (Griess method) and lipid peroxidation (malondialdehyde, MDA) (commercially available kit). Frontal cortex was dissected to measure antioxidant catalase activity (Amplex Red fluorescent technique), S-nitrosylation of cystein thiols (immunoblotting) and brain water content was determined using the specific gravimetric technique. Results: Brain water content increased in BDL rats vs SHAM-operated controls (81.91 ± 0.19% vs 81.23 ± 0.20%, p<0.05). BDL rats vs SHAM-operated controls developed an increase in plasma arterial levels of ammonia (91.8 ± 18.4uM vs 41.2 ± 13.2uM, p<0.05), ROS (4.9 fold increase), NO (2.9 fold increase), MDA (41.9 ± 7.4uM vs 9.9 ± 0.6uM, p<0.005), S-nitrosylated proteins and a decrease in catalase activity (1.3 ± 0.5U/ml vs 3.2 ± 1.4U/ml, p<0.05). Centrally, BDL rats vs SHAM-operated controls developed an increase in CSF ammonia (123.5 ± 21.7uM vs 23.3 ± 6.1uM, p<0.05) but did not develop an increase in CSF ROS and NO or in brain MDA and S-nitrosylation detection. Furthermore, catalase activity in the brain was unchanged in BDL vs SHAM-operated controls. Conclusions: Six weeks following BDL, rats developed brain edema. An increase in arterial ammonia was accompanied with an increase in lipid peroxidation, NO, ROS and S-nitrosylation with a decrease in catalase activity. However, a similar increase in ammonia levels in CSF lead to contrary results where no increase in oxidative stress markers was found in brain. Our findings suggest 1) ammonia does not induce oxidative stress in the brain, 2) systemic oxidative stress is related to a decrease in catalase activity and 3) brain edema in BDL rats is associated with systemic, and not central, oxidative stress.

     

  7. AST-120 (adsorbant sphérique de charbon) atténue l'œdème cérébral et diminue le niveau artériel d'ammoniaque chez les rats avec ligature de voie biliaire. Cristina R. Bosoi; Christian Parent-Robitaille; Mélanie Tremblay & Christopher F. Rose, 12e congrès annuel des étudiants, stagiaires et résidents du CRCHUM, December 16th, Montréal, Canada.
    [Abstract↓]
    Introduction: La pathogénèse de l'encéphalopathie hépatique (EH) est multifactorielle et implique des toxines provenant des intestins, telle que l'ammoniaque. L'insuffisance hépatique mène à l'hyperammonémie et aux niveaux neurotoxiques d’ammoniaque qui peuvent induire le stress oxydatif. Ainsi, la première cible du traitement de l'EH est la diminution de la production intestinale d'ammoniaque. AST-120 (adsorbant sphérique de charbon), un adsorbant oral de microsphères activées par ingénierie ayant une surface de plus de 1600m2/g, adsorbe les neuro- et hépato-toxines présentes dans les intestins. Dans cette étude, nous avons évalué l'effet protecteur d'AST-120 sur l'œdème cérébral et sa capacité à diminuer l'ammoniaque artérielle et le stress oxydatif chez les rats cirrhotiques. Méthodes: La cirrhose a été induite par la ligature de la voie biliaire (BDL) pour 6 semaines. Les rats BDL et SHAM ont reçu durant 6 semaines une dose d'AST-120 de 0.1 et 1mg/kg/jour dispersé dans la méthylcellulose (MC) par gavage. Des rats contrôles BDL et SHAM ont reçu seulement le véhicule. L'AST et ALT ont été mesurés à la fin du traitement pour évaluer la fonction du foie. L'ammoniaque et les espèces réactives d'oxygène (ROS) ont été mesurées dans le plasma artériel par un kit commercial et une technique de fluorescence. Le contenu en eau du cerveau a été mesuré dans le cortex frontal par une technique spécifique gravimétrique. Résultats: Le traitement avec AST-120 a été bien toléré. Les marqueurs de la fonction hépatique, AST et ALT, étaient augmentés dans tous les groupes de rats BDL vs SHAM (p<0.001). Le contenu en eau du cerveau a augmenté dans les rats BDL (BDL: 81.8±0.1% vs SHAM: 81.3±0.2%, p<0.05). Les deux dosages d'AST-120 de 0.1 et 1mg/kg/jour ont normalisé le contenu en eau du cerveau dans les rats BDL. L'ammoniaque artérielle était augmentée chez les rats BDL (175.5± 48.1uM vs SHAM: 105.3±27.3uM, p<0.05) et diminuée significativement dans les BDL 0.1mg/kg/jour (118.0±6.4uM, p<0.05) et BDL 1mg/kg/jour (75.4±31.4uM, p<0.05). Les niveaux de ROS étaient augmentés chez les rats BDL vs SHAM (augmentation de 11 fois vs SHAM). AST-120 n'a pas diminué les niveaux plasmatiques de ROS comparativement aux SHAM. Conclusions: Le traitement avec AST-120 normalise le contenu en eau du cerveau et diminue les niveaux artériels d'ammoniaque, mais n'a pas d'effet sur les ROS systémiques. AST-120 administré à long terme a été prouvé une alternative sûre de traitement non-antibiotique pour l'EH, en démontrant un effet significatif sur la diminution de l'ammoniaque, en même temps qu'un effet protecteur sur l'œdème cérébral chez les rats avec ligature de voie biliaire. Projet subventionné par: Instituts de recherche en santé du Canada et Ocera Therapeutics Inc. (CA, USA)

     

  8. L'œdème cérébral est associé avec le stress oxydatif systémique et non central dans les rats avec ligature de la voie biliaire. Xiaoling Yang; Cristina R. Bosoi; Mélanie Tremblay & Christopher F. Rose, 12e congrès annuel des étudiants, stagiaires et résidents du CRCHUM, December 16th, Montréal, Canada.
    [Abstract↓]
    Introduction: L'ammoniaque joue un rôle majeur dans la pathogénèse de l'encéphalopathie hépatique. Le stress oxydatif est toutefois également proposé d'être impliqué. Des études récentes sont à l'origine de notre projet : 1) la concentration neurotoxique d'ammoniaque induisant le stress oxydatif a été démontrée in vitro et 2) le stress oxydant systémique exacerbe les effets neuropsychologiques de l'hyperammonémie observée chez les patients atteints d’une maladie hépatique. Notre étude vise à mesurer le stress oxydant systémique et central en association avec l'œdème cérébral chez les rats atteints de cirrhose. Méthodes: Les rats ont été sacrifiés six semaines après la ligature de la voie biliaire (bile-duct ligation, BDL), induisant une cirrhose. Le plasma artériel et le liquide céphalo-rachidien (LCR) ont été prélevés afin de mesurer l'ammoniaque (kit commercial), les espèces réactives de l'oxygène (ROS, technique de fluorescence DCFDA), l'oxyde nitrique (NO, méthode de Griess) et la peroxydation lipidique (malondialdéhyde, MDA, kit commercial). Le cortex frontal a été disséqué pour mesurer l'activité de la catalase (antioxydant, technique de fluorescence avec l'Amplex Red) et les dérivés de S-nitrosylation du résidu cystéine (immunobuvardage). Le volume en eau du cerveau a été déterminé en utilisant la technique gravimétrique spécifique. Résultats: Le volume en eau du cerveau a augmenté dans les rats avec BDL vs sham-contrôles (81.91 ± 0.19% vs 81.23 ± 0.20%, p <0.05). Les rats avec BDL ont développé, vs les sham-contrôles, une augmentation plasmatique de concentration d'ammoniaque (91.8 µM ± 18.4 vs 41.2 µM ± 13.2, p<0.05), de NO (2.9 fois plus élevé), de ROS (4.9 fois plus élevé), de MDA (41.9 µM ± 7.4 vs 9.9 µM ± 0.6, p<0.005) et de dérivés de S-nitrosylation du résidu cystéine, ainsi qu'une diminution de l'activité de la catalase (1.3 U/ml ± 0.5 vs 3.2 U/ml ± 1.4, p<0.05). Dans le système nerveux central, les rats avec BDL (vs sham-contrôles) ont développé une augmentation de l'ammoniaque dans le LCR (123.5 µM ± 21.7 vs 23.3 µM ± 6.1, p<0.05) mais n'ont pas développé une augmentation de ROS et de NO dans le LCR ou une augmentation de MDA et de dérivés de S-nitrosylation du résidu cystéine dans le cerveau. En outre, l'activité de la catalase dans le cerveau est restée inchangée dans les rats avec BDL. Conclusions: Six semaines après la ligature de la voie biliaire, les rats ont développé un œdème cérébral. L'augmentation de l'ammoniaque artérielle a été accompagnée d'une élévation du NO, des ROS, de la peroxydation lipidique et de la S-nitrosylation, ainsi qu'une diminution de l'activité de la catalase. Toutefois, une hausse du niveau d'ammoniaque dans le LCR conduit à des résultats inverses dans le cerveau, où aucune augmentation des marqueurs du stress oxydatif n'a été trouvée. Nos résultats suggèrent que 1) l'ammoniaque n'induit pas le stress oxydatif dans le cerveau, 2) le stress oxydatif systémique est liée à une diminution de l'activité de la catalase et 3) l'œdème cérébral chez les rats avec BDL est associé à un stress oxydatif systémique, et non central.

     

2008

  1. Hyperammonemia does not induce oxidative/nitrosative stress in rats with portacaval anastomosis. Cristina Bosoi; Mélanie Tremblay et Christopher F Rose, The 59th Annual Meeting of the American Association for the Study of Liver Diseases, October 31st- November 4th, San Francisco (États-Unis).
    [Official abstract] [Abstract↓]
    Background: Ammonia is central in the pathogenesis of hepatic encephalopathy however it is believed systemic oxidative/nitrosative stress may play an important role in exacerbating the neuropsychological effects of hyperammonemia observed in patients with cirrhosis. Furthermore, it has recently been demonstrated in vitro that pathophysiological concentrations of ammonia induce oxidative/nitrosative stress in brain (cultured astrocytes), however this remains to be evaluated in vivo. The present study aims to investigate the role of oxidative/nitrosative stress in a well characterized hyperammonemic rat model of portacaval anastomosis (PCA). Methods: Rats were sacrificed 4 weeks following PCA or SHAM-operation. Ammonia, nitrate/nitrite, reactive oxygen species and total glutathione were measured in both plasma (arterial) and cerebrospinal fluid. Activities of antioxidant enzymes (catalase, superoxide dismutase and glutathione reductase/peroxidase) were measured in both plasma (arterial) and frontal cortex of the brain. Results: Ammonia concentrations were increased in both plasma (PCA: 173.7 ± 13.58uM vs SHAM: 77.8 ± 11.2uM; p<0.001) and cerebrospinal fluid (PCA: 146.6 ± 26.0uM vs SHAM: 31.5 ± 6.9uM; p<0.001) in PCA rats compared to SHAM operated controls. Furthermore, PCA rats showed a significant increase in catalase (PCA: 3.27 ± 0.03U/ml vs SHAM: 3.10 ± 0.05U/ml; p<0.05) and superoxide dismutase (PCA: 97.30 ± 0.47 vs SHAM: 95.57 ± 0.45 % inhibition; p<0.05) activities, but no significant differences were found in frontal cortex between the two groups. In addition, no significant changes in reactive oxygen species, nitrate/nitrite and total glutathione levels, nor in glutathione reductase and peroxidase activities were found in both plasma and brain tissue of PCA and SHAM rats. Conclusion: Rats with PCA develop hyperammonemia which leads to toxic levels of ammonia in the brain. This in turn does not induce oxidative/nitrosative stress systemically or centrally. Maintenance of systemic antioxidant activity in rats with PCA preserves a balanced redox status and prevents progression of encephalopathy.

     

  2. Synergistic effect of systemic oxidative stress and hyperammonemia leads to brain edema in rats with chronic liver failure. Cristina R Bosoi; Christian Parent-Robitaille; Mélanie Tremblay et Christopher F Rose, SFRBM's 15th Annual Meeting, November 19-23rd, Indianapolis (États-Unis).
    [Official abstract] [Abstract↓]
    Background: Liver failure/disease leads to hyperammonemia which is central in the pathogenesis of hepatic encephalopathy. However, it is believed systemic oxidative/nitrosative stress may play an important role in exacerbating the neuropsychological effects of hyperammonemia observed in patients with liver disease. The present study aims to investigate the role of oxidative/nitrosative stress in 2 rat models of liver disease/hepatic encephalopathy; 1) portacaval anastomosis (PCA), and 2) bile-duct ligation (BDL). Methods: Rats were sacrificed 4 weeks following PCA or 6 weeks following BDL. Ammonia, reactive oxygen species (ROS), H2O2 and nitric oxide (NO) were measured in plasma (arterial) and ammonia, ROS and NO were measured in cerebrospinal fluid (CSF) using respectively a commercially available kit, a fluorescent technique and the Griess reaction. Brain water was measured in the frontal cortex using a specific gravimetric technique. Results: Hyperammonemia developed in both PCA (PCA: 173.7 ± 13.6 uM vs sham: 77.8 ± 11.2 uM; p<0.001) and BDL (BDL: 114.1 ± 19.2 uM vs sham: 33.2 ± 4.7 uM; p<0.05) rats with PCA rats being significantly higher compared to BDL rats (p<0.05). Consequently, ammonia increased in CSF in both PCA (PCA: 146.6 ± 26.0 uM vs sham: 31.5 ± 6.9 uM; p<0.001) and BDL (BDL: 128.4 ± 36.7 uM vs sham: 23.3 ± 6.1 uM; p<0.05). No significant change was observed between PCA and BDL. Only rats with BDL demonstrated an increase in plasma levels of ROS (5.8-fold increase vs sham; p<0.001) and H2O2 (3.2-fold increase vs sham; p<0.05). No significant change in CSF ROS was found in BDL or PCA compared to their respective control groups. In addition, an increase in brain water content was only observed in rats with BDL (BDL: 81.52 ± 0.15% vs sham: 80.43 ± 0.21%, p<0.05). No significant change in plasma ROS, H2O2 or brain water was found in PCA rats vs sham-operated controls. Conclusion: Oxidative stress in addition to hyperammonemia results in an increase in brain water in rats with BDL which is not in PCA rats where only hyperammonemia is observed. Our findings suggest systemic oxidative stress is implicated in the pathogenesis of brain edema and its synergistic effect with ammonia may lead to progression of hepatic encephalopathy.