Accepted abstract for CASL 2011

Accepted abstracts

Three abstracts will be presented to CASL 2011.

Three abstracts are accepted for presentation at CASL (Canadian Association for Liver Disease) held at Vancouver, Canada, February 26th-March 1st 2011.

Related Publications

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

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.

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.