-
Bosoi, C. R.; Yang, X.; Huynh, J.; Parent-Robitaille, C.; Jiang, W.; Tremblay, M. & Rose, C. F. (2012). Systemic oxidative stress is implicated in the pathogenesis of brain edema in rats with chronic liver failure. Free Radic Biol Med 52:1228-1235. doi:10.1016/j.freeradbiomed.2012.01.006
- 
- 
- [↓Résumé↓]
Chronic liver failure leads to hyperammonemia, a central component in the pathogenesis of hepatic encephalopathy (HE); however, a correlation between blood ammonia levels and HE severity remains controversial. It is believed oxidative stress plays a role in modulating the effects of hyperammonemia. This study aimed to determine the relationship between chronic hyperammonemia, oxidative stress, and brain edema (BE) in two rat models of HE: portacaval anastomosis (PCA) and bile-duct ligation (BDL). Ammonia and reactive oxygen species (ROS) levels, BE, oxidant and antioxidant enzyme activities, as well as lipid peroxidation were assessed both systemically and centrally in these two different animal models. Then, the effects of allopurinol (xanthine oxidase inhibitor, 100mg/kg for 10days) on ROS and BE and the temporal resolution of ammonia, ROS, and BE were evaluated only in BDL rats. Similar arterial and cerebrospinal fluid ammonia levels were found in PCA and BDL rats, both significantly higher compared to their respective sham-operated controls (p<0.05). BE was detected in BDL rats (p<0.05) but not in PCA rats. Evidence of oxidative stress was found systemically but not centrally in BDL rats: increased levels of ROS, increased activity of xanthine oxidase (oxidant enzyme), enhanced oxidative modifications on lipids, as well as decreased antioxidant defense. In PCA rats, a preserved oxidant/antioxidant balance was demonstrated. Treatment with allopurinol in BDL rats attenuated both ROS and BE, suggesting systemic oxidative stress is implicated in the pathogenesis of BE. Analysis of ROS and ammonia temporal resolution in the plasma of BDL rats suggests systemic oxidative stress might be an important "first hit", which, followed by increases in ammonia, leads to BE in chronic liver failure. In conclusion, chronic hyperammonemia and oxidative stress in combination lead to the onset of BE in rats with chronic liver failure.
-
Sharma, V.; Ten Have, G. A. M.; Ytrebo, L.; Sen, S.; Rose, C. F.; Dalton, R. N.; Turner, C.; Revhaug, A.; Van-Eijk, H. M. H.; Deutz, N. E. P.; Jalan, R.; Mookerjee, R. P. & Davies, N. A. (2012). Nitric Oxide and L-Arginine Metabolism in a Devascularized Porcine Model of Acute Liver Failure Am J Physiol Gastrointest Liver Physiol doi:10.1152/ajpgi.00268.2011
- -
- [↓Résumé↓]
In acute liver failure (ALF), the hyperdynamic circulation is believed to be the result of over production of nitric oxide (NO) in the splanchnic circulation. However, it has been suggested that arginine concentrations, (the substrate for NO) are believed to be decreased, limiting substrate availability for NO production. To characterize the metabolic fate of arginine in early phase ALF, we systematically assessed its interorgan transport and metabolism; and measured the endogenous NO synthase inhibitor asymmetric dimethylarginine (ADMA) in a porcine model of ALF. Female adult pigs (23-30Kg) were randomized to SHAM (N=8) or hepatic devascularisation ALF (N=8) procedure and followed for 6 hours. Measurements: plasma arginine, citrulline, ornithine levels; arginase activity; NO, ADMA. Whole body metabolic rates and interorgan flux measurements were calculated using stable isotope-labelled amino-acids. Plasma arginine decreased >85% of the basal level at T=6 hrs (p<0.001), whereas citrulline and ornithine progressively increased in ALF (p<0.001 and p<0.001, vs. SHAM respectively). No difference was found between the groups in the whole body rate of appearance of arginine or NO. However, ALF showed a significant increase in de novo arginine synthesis (p<0.05). Interorgan data showed citrulline net intestinal production and renal consumption that was related to net renal production of arginine and ornithine. Both plasma arginase activity and plasma ADMA levels significantly increased in ALF (p<0.001). In this model of early phase ALF, arginine deficiency or higher ADMA levels do not limit whole body NO production. Arginine deficiency is caused by arginase-related arginine clearance in which stimulated de novo arginine production.
-
Bosoi, C. R.; Parent-Robitaille, C.; Anderson, K.; Tremblay, M. & Rose, C. F. (2011). AST-120 (spherical carbon adsorbent) lowers ammonia levels and attenuates brain edema in bile duct-ligated rats. Hepatology 53:1995-2002. doi:10.1002/hep.24273
- -
- [↓Résumé↓]
The pathogenesis of hepatic encephalopathy is multifactorial, involving gut-derived toxins such as ammonia, which has been demonstrated to induce oxidative stress. Therefore, a primary hepatic encephalopathy treatment target is reducing ammonia production in the gastrointestinal tract. AST-120, an oral adsorbent of engineered activated carbon microspheres with surface areas exceeding 1600 m(2) /g, acts as a sink for neurotoxins and hepatotoxins present in the gut. We evaluated the capacity of AST-120 to adsorb ammonia in vitro and to lower blood ammonia, oxidative stress and brain edema in cirrhotic rats. Cirrhosis was induced in rats by bile duct ligation for 6 weeks. AST-120 was administered by gavage preventively for 6 weeks (0.1, 1, and 4 g/kg/day). In addition, AST-120 was evaluated as a short-term treatment for 2 weeks and 3 days (1 g/kg/day) and as a sink to adsorb intravenously infused ammonium acetate. In vitro, AST-120 efficiently adsorbed ammonia. Ammonia levels significantly decreased in a dose-dependent manner for all AST-120-treated bile duct-ligated rats (nontreated: 177.3 ± 30.8 μM; AST-120, 0.1 g/kg/day: 121.9 ± 13.8 μM; AST-120, 1 g/kg/day: 80.9 ± 30.0 μM; AST-120, 4 g/kg/day: 48.8 ± 19.6 μM) and significantly correlated with doses of AST-120 (r = -0.6603). Brain water content and locomotor activity normalized after AST-120 treatments, whereas arterial reactive oxygen species levels remained unchanged. Furthermore, AST-120 significantly attenuated a rise in arterial ammonia after ammonium acetate administration (intravenously). Conclusion:AST-120 treatment decreased arterial ammonia levels, normalized brain water content and locomotor activity but did not demonstrate an effect on systemic oxidative stress. Also, AST-120 acts as an ammonia sink, efficiently removing blood-derived ammonia. Additional studies are warranted to evaluate the effects of AST-120 on hepatic encephalopathy in patients with advanced liver disease. (HEPATOLOGY 2011;).
-
Kristiansen, R. G.; Lindal, S.; Myreng, K.; Revhaug, A.; Ytrebø, L. M. & Rose, C. F. (2010). Neuropathological changes in the brain of pigs with acute liver failure. Scand J Gastroenterol 45:935-943. doi:10.3109/00365521003675047
- -
- [↓Résumé↓]
Abstract Objective. Cerebral edema is a serious complication of acute liver failure (ALF), which may lead to intracranial hypertension and death. An accepted tenet has been that the blood-brain barrier is intact and that brain edema is primarily caused by a cytotoxic etiology due to hyperammonemia. However, the neuropathological changes in ALF have been poorly studied. Using a well characterized porcine model we aimed to investigate ultrastructural changes in the brain from pigs suffering from ALF. Materials and methods. Sixteen female Norwegian Landrace pigs weighing 27-35 kg were randomised into two groups: ALF (n = 8) and sham operated controls (n = 8). ALF was induced with an end-to-side portacaval shunt followed by ligation of the hepatic arteries. Biopsies were harvested from three different areas of the brain (frontal lobe, cerebellum, and brain stem) following eight hours of ALF and analyzed using electron microscopy. Results. Profound perivascular and interstitial edema were found in all three areas. Disruption of pericytic and astrocytic processes were seen, reflecting breakdown/lesion of the blood-brain barrier in animals suffering from ALF. Furthermore, neurons and axons were edematous and surrounded by vesicles. Severe damage to Purkinje neuron (necrosis) and damaged myelin were seen in the cerebellum and brain stem, respectively. Biopsies from sham operated animals were normal. Conclusions. Our data support the concept that vasogenic brain edema plays an important role in the development of intracranial hypertension in pigs with ALF.
-
Yang, X.; Bosoi, C. R.; Jiang, W.; Tremblay, M. & Rose, C. F. (2010). Portacaval anastomosis-induced hyperammonemia does not lead to oxidative stress. Metab Brain Dis 25:11-15. doi:10.1007/s11011-010-9174-1
- -
- [↓Résumé↓]
Ammonia is neurotoxic and believed to play a major role in the pathogenesis of hepatic encephalopathy (HE). It has been demonstrated, in vitro and in vivo, that acute and high ammonia treatment induces oxidative stress. Reactive oxygen species (ROS) are highly reactive and can lead to oxidization of proteins resulting in protein damage. The present study was aimed to assess oxidative status of proteins in plasma and brain (frontal cortex) of rats with 4-week portacaval anastomosis (PCA). Markers of oxidative stress, 4-hydroxy-2-nonenal (HNE) and carbonylation were evaluated by immunoblotting in plasma and frontal cortex. Western blot analysis did not demonstrate a significant difference in either HNE-linked or carbonyl derivatives on proteins between PCA and sham-operated control rats in both plasma and frontal cortex. The present study suggests PCA-induced hyperammonemia does not lead to systemic or central oxidative stress.
-
Ytrebø, L. M.; Kristiansen, R. G.; Maehre, H.; Fuskevåg, O. M.; Kalstad, T.; Revhaug, A.; Cobos, M. J.; Jalan, R. & Rose, C. F. (2009). L-ornithine phenylacetate attenuates increased arterial and extracellular brain ammonia and prevents intracranial hypertension in pigs with acute liver failure. Hepatology 50:165-174. doi:10.1002/hep.22917
- -
- [↓Résumé↓]
Hyperammonemia is a feature of acute liver failure (ALF), which is associated with increased intracranial pressure (ICP) and brain herniation. We hypothesized that a combination of L-ornithine and phenylacetate (OP) would synergistically reduce toxic levels of ammonia by (1) L-ornithine increasing glutamine production (ammonia removal) through muscle glutamine synthetase and (2) phenylacetate conjugating with the ornithine-derived glutamine to form phenylacetylglutamine, which is excreted into the urine. The aims of this study were to determine the effect of OP on arterial and extracellular brain ammonia concentrations as well as ICP in pigs with ALF (induced by liver devascularization). ALF pigs were treated with OP (L-ornithine 0.07 g/kg/hour intravenously; phenylbutyrate, prodrug for phenylacetate; 0.05 g/kg/hour intraduodenally) for 8 hours following ALF induction. ICP was monitored throughout, and arterial and extracellular brain ammonia were measured along with phenylacetylglutamine in the urine. Compared with ALF + saline pigs, treatment with OP significantly attenuated concentrations of arterial ammonia (589.6 +/- 56.7 versus 365.2 +/- 60.4 mumol/L [mean +/- SEM], P= 0.002) and extracellular brain ammonia (P= 0.01). The ALF-induced increase in ICP was prevented in ALF + OP-treated pigs (18.3 +/- 1.3 mmHg in ALF + saline versus 10.3 +/- 1.1 mmHg in ALF + OP-treated pigs;P= 0.001). The value of ICP significantly correlated with the concentration of extracellular brain ammonia (r(2) = 0.36,P< 0.001). Urine phenylacetylglutamine levels increased to 4.9 +/- 0.6 micromol/L in ALF + OP-treated pigs versus 0.5 +/- 0.04 micromol/L in ALF + saline-treated pigs (P< 0.001).Conclusion:L-Ornithine and phenylacetate act synergistically to successfully attenuate increases in arterial ammonia, which is accompanied by a significant decrease in extracellular brain ammonia and prevention of intracranial hypertension in pigs with ALF.
-
Rose, C.; Ytrebø, L. M.; Davies, N. A.; Sen, S.; Nedredal, G. I.; Belanger, M.; Revhaug, A. & Jalan, R. (2007). Association of reduced extracellular brain ammonia, lactate, and intracranial pressure in pigs with acute liver failure. Hepatology 46:1883-1892. doi:10.1002/hep.21877
- -
- [↓Résumé↓]
We previously demonstrated in pigs with acute liver failure (ALF) that albumin dialysis using the molecular adsorbents recirculating system (MARS) attenuated a rise in intracranial pressure (ICP). This was independent of changes in arterial ammonia, cerebral blood flow and inflammation, allowing alternative hypotheses to be tested. The aims of the present study were to determine whether changes in cerebral extracellular ammonia, lactate, glutamine, glutamate, and energy metabolites were associated with the beneficial effects of MARS on ICP. Three randomized groups [sham, ALF (induced by portacaval anastomosis and hepatic artery ligation), and ALF+MARS] were studied over a 6-hour period with a 4-hour MARS treatment given beginning 2 hours after devascularization. Using cerebral microdialysis, the ALF-induced increase in extracellular brain ammonia, lactate, and glutamate was significantly attenuated in the ALF+MARS group as well as the increases in extracellular lactate/pyruvate and lactate/glucose ratios. The percent change in extracellular brain ammonia correlated with the percent change in ICP (r(2) = 0.511). Increases in brain lactate dehydrogenase activity and mitochondrial complex activity for complex IV were found in ALF compared with those in the sham, which was unaffected by MARS treatment. Brain oxygen consumption did not differ among the study groups. Conclusion: The observation that brain oxygen consumption and mitochondrial complex enzyme activity changed in parallel in both ALF- and MARS-treated animals indicates that the attenuation of increased extracellular brain ammonia (and extracellular brain glutamate) in the MARS-treated animals reduces energy demand and increases supply, resulting in attenuation of increased extracellular brain lactate. The mechanism of how MARS reduces extracellular brain ammonia requires further investigation.
-
Rose, C. F. (2010). Increase brain lactate in hepatic encephalopathy: Cause or consequence? Neurochem Int 57:389-394. doi:10.1016/j.neuint.2010.06.012
- -
- [↓Résumé↓]
Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome which develops as a result of liver failure or disease. Increased concentrations of brain lactate (microdialysate, cerebrospinal fluid, tissue) are commonly measured in patients with HE induced by either acute or chronic liver failure. Whether an increase in brain lactate is a cause or a consequence of HE remains undetermined. A rise in cerebral lactate may occur due to (1) blood-borne lactate (hyperlactataemia) crossing the blood-brain barrier, (2) increased glycolysis due to energy failure or impairment and (3) increased lactate production/release or decreased lactate utilization/uptake. This review explores the different reasons for lactate accumulation in the brain during liver failure and describes the possible roles of lactate in the pathogenesis of HE.
-
Bosoi, C. R. & Rose, C. F. (2009). Identifying the direct effects of ammonia on the brain. Metab Brain Dis 24:95-102. doi:10.1007/s11011-008-9112-7
- -
- [↓Résumé↓]
Elevated concentrations of ammonia in the brain as a result of hyperammonemia leads to cerebral dysfunction involving a spectrum of neuropsychiatric and neurological symptoms (impaired memory, shortened attention span, sleep-wake inversions, brain edema, intracranial hypertension, seizures, ataxia and coma). Many studies have demonstrated ammonia as a major player involved in the neuropathophysiology associated with liver failure and inherited urea cycle enzyme disorders. Ammonia in solution is composed of a gas (NH(3)) and an ionic (NH(4) (+)) component which are both capable of crossing plasma membranes through diffusion, channels and transport mechanisms and as a result have a direct effect on pH. Furthermore, NH(4) (+) has similar properties as K(+) and, therefore, competes with K(+) on K(+) transporters and channels resulting in a direct effect on membrane potential. Ammonia is also a product as well as a substrate for many different biochemical reactions and consequently, an increase in brain ammonia accompanies disturbances in cerebral metabolism. These direct effects of elevated ammonia concentrations on the brain will lead to a cascade of secondary effects and encephalopathy.
-
Rose, C. (2006). Effect of ammonia on astrocytic glutamate uptake/release mechanisms. J Neurochem 97 Suppl 1:11-15. doi:10.1111/j.1471-4159.2006.03796.x
- -
- [↓Résumé↓]
Hyperammonemic disorders such as acute liver failure (ALF) or urea cycle enzymopathies are associated with hyperexcitability, seizures, brain edema and increased extracellular brain glutamate. Mechanisms responsible for increased glutamate content in the extracellular space of the brain include decreased uptake by perineuronal astrocytes and/or increased release from neurons and/or astrocytes. Exposure of astrocytes to millimolar concentrations of ammonia results in cell swelling, loss of expression of the glutamate transporters excitatory amino acid transporter (EAAT-1) and EAAT-2 and increased release of glutamate. Three distinct mechanisms are theoretically possible to explain ammonia-induced glutamate release from astrocytes namely: release due to swelling; reversal of glutamate transporters and due to Ca2+-dependent vesicular release. Recent identification of vesicular docking and fusion proteins in astrocytes together with glutamate-release (due to intracellular alkanization and mobilization of intracellular Ca2+-stores) studies implies that vesicular release is a predominant mechanism responsible for ammonia-induced release of glutamate from astrocytes.
Liste des publications des dernières années. Pour une liste complète.
