thioacetamide and Brain-Edema

Brain edema and associated astrocyte swelling leading to increased intracranial pressure are hallmarks of acute liver failure (ALF). Elevated blood and brain levels of ammonia have been implicated in the development of brain edema in ALF. Cultured astrocytes treated with ammonia have been shown to undergo cell swelling and such swelling was associated with an increase in the plasma membrane expression of aquaporin-4 (AQP4) protein. Further, silencing the AQP4 gene in cultured astrocytes was shown to prevent the ammonia-induced cell swelling. Here, we examined the evolution of brain edema in AQP4-null mice and their wild type counterparts (WT-mice) in different models of ALF induced by thioacetamide (TAA) or acetaminophen (APAP). Induction of ALF with TAA or APAP significantly increased brain water content in WT mice (by 1.6% ± 0.3 and 2.3 ± 0.4%, respectively). AQP4 protein was significantly increased in brain plasma membranes of WT mice with ALF induced by either TAA or APAP. In contrast to WT-mice, brain water content did not increase in AQP4-null mice. Additionally, AQP4-null mice treated with either TAA or APAP showed a remarkably lesser degree of neurological deficits as compared to WT mice; the latter displayed an inability to maintain proper gait, and demonstrated a markedly reduced exploratory behavior, with the mice remaining in one corner of the cage with its head tilted downwards. These results support a central role of AQP4 in the brain edema associated with ALF.

Topics: Acetaminophen; Analysis of Variance; Animals; Aquaporin 4; Brain Diseases; Brain Edema; Disease Models, Animal; Gene Expression Regulation; Glucose Transporter Type 1; Liver Failure, Acute; Mice; Mice, Transgenic; Thioacetamide; Time Factors

Astrocyte swelling and brain edema associated with increased intracranial pressure are major complications of acute liver failure (ALF). The mechanism for such astrocyte swelling/brain edema, however, is not well understood. We recently found that ammonia, a key etiological factor in ALF, caused the activation of the Na-K-Cl cotransporter-1 (NKCC1) in cultured astrocytes, and that inhibition of such activation led to a reduction in astrocyte swelling, suggesting that NKCC1 activation may be an important factor in the mechanism of brain edema in ALF. To determine whether NKCC activation is also involved in brain edema in vivo, we examined whether NKCC activation occurs in the thioacetamide (TAA) rat model of ALF and determined whether treatment with the NKCC inhibitor bumetanide reduces the severity of brain edema in TAA-treated rats.. Brain water content was measured using the gravimetric method. NKCC1 phosphorylation and protein expression were measured by Western blots. NKCC activity was measured in brain cortical slices.. NKCC activity was elevated in brain cortical slices of TAA-treated rats as compared to sham animals. Western blot analysis showed significant increases in total as well as phosphorylated (activated) NKCC1 protein expression in the cortical tissue. These findings were associated with a significant increase in brain water content which was attenuated by treatment with the NKCC inhibitor bumetanide.. Our studies suggest the involvement of NKCC in the development of brain edema in experimental ALF, and that targeting NKCC may represent a useful therapeutic strategy in humans with ALF.

Topics: Animals; Brain Edema; Bumetanide; Liver Failure, Acute; Male; Phosphorylation; Rats; Rats, Wistar; Sodium-Potassium-Chloride Symporters; Solute Carrier Family 12, Member 2; Thioacetamide

To investigate the expression of aquaporin-4 (AQP4) during brain edema in rats with thioacetamide-induced acute liver failure and encephalopathy.. The rat model of acute hepatic failure and encephalopathy was induced by intraperitoneal injection of thioacetamide (TAA) at a 24-hour interval for 2 consecutive days. Thirty-two SD rats were randomly divided into the model group (n = 24) and the control group (normal saline, n = 8). And then the model group was further divided into 3 subgroups by the timepoint of decapitation: 24 h (n = 8), 48 h (n = 8) and 60 h (n = 8). Then we observed their clinical symptoms and stages of HE, indices of liver function and ammonia, liver histology and brain water content. The expression of AQP4 protein in brain tissues was measured with Western blot and the expression of AQP4mRNA with RT-PCR (reverse transcription-polymerase chain reaction).. Typical clinical manifestations of hepatic encephalopathy occurred in all TAA-administrated rats. The model rats showed the higher indices of ALT (alanine aminotransferase), AST (aspartate aminotransferase), TBIL (total bilirubin) and ammonia than the control rats (P < 0.05). The brain water content was significantly elevated in TAA-administrated rats compared with the control (P < 0.05). The expressions of AQP4 protein and mRNA in brain tissues significantly increased in TAA-administrated rats (P < 0.05). In addition, the expressions of AQP4 protein and mRNA were positively correlated with brain water content (r = 0.536, P < 0.01; r = 0.566, P = 0.01).. The high expression of AQP4 in rats with TAA-induced acute liver failure and encephalopathy plays a significant role during brain edema. AQP4 is one of the molecular mechanisms for the occurrence of brain edema in hepatic encephalopathy.

Topics: Animals; Aquaporin 4; Brain Diseases; Brain Edema; Disease Models, Animal; Hepatic Encephalopathy; Rats; Rats, Sprague-Dawley; Thioacetamide

Intracranial hypertension caused by brain edema and associated astrocyte swelling is a potentially lethal complication of acute liver failure (ALF). Mechanisms of edema formation are not well understood, but elevated levels of blood and brain ammonia and its by-product glutamine have been implicated in this process. Since aquaporin-4 (AQP4) has been implicated in brain edema in other conditions, we examined its role in a rat model of ALF induced by the hepatotoxin thioacetamide. Rats with ALF showed increased AQP4 protein in the plasma membrane (PM). Total tissue levels of AQP4 protein and mRNA levels were not altered, indicating that increased AQP4 is not transcriptionally mediated but likely reflects a more stable anchoring of AQP4 to the PM and/or interference with its degradation. An increase inAQP4 immunoreactivity in thePM was observed in perivascular astrocytes in ALF. Rats with ALF also showed increased levels of α-syntrophin, a protein involved in anchoringAQP4 to perivascular astrocytic end-feet. Increased AQP4 andα-syntrophin levels were inhibited by L-histidine, an inhibitor of glutamine transport into mitochondria, suggesting a role for glutamine in the increase of PM levels of AQP4. These results indicate that increased AQP4 PM levels in perivascular astrocytic end-feet are likely critical to the development of brain edema in ALF.

Topics: Ammonia; Animals; Aquaporin 4; Astrocytes; Brain; Brain Edema; Calcium-Binding Proteins; Cell Membrane; Cells, Cultured; Histidine; Liver Failure, Acute; Membrane Proteins; Muscle Proteins; Rats; Rats, Inbred F344; RNA, Small Interfering; Thioacetamide

Brain edema in hepatic encephalopathy has been associated with circulating ammonia that is metabolized to glutamine. We measured alterations in blood chemistry and brain regional specific gravity and ion and amino acid contents in models of simple hyperammonemia and liver failure induced by daily administrations of ammonium acetate (AAc) or thioacetamide (TAA), respectively. Serum and brain ammonia increased to similar levels (200 and 170% of control, respectively) in both experimental groups. Serum transaminase activities increased 10-fold in animals injected with TAA but were unchanged in animals given AAc injections. In both experimental groups glutamine was elevated in cerebral white matter, cerebral gray matter, and basal ganglia, whereas brain tissue specific gravity decreased in all brain regions, indicating edema formation. In the AAc group, we observed a decrease in glutamate and taurine contents concomitant with the development of brain edema. In these animals, cerebral gray matter specific gravity and taurine contents returned to control levels 24 h after the third AAc injection. TAA-injected animals demonstrated similar decreases in brain tissue specific gravity, whereas glutamine, glutamate, and taurine contents were all elevated. During hepatic encephalopathy, ammonia-induced changes in brain amino acid content may contribute to brain edema development.

Topics: Acetates; Alanine Transaminase; Amino Acids; Ammonia; Animals; Aspartate Aminotransferases; Blood Proteins; Brain; Brain Edema; Hepatic Encephalopathy; Male; Potassium; Rats; Rats, Sprague-Dawley; Sodium; Thioacetamide

This contribution presents data from the literature as well as our own results concerning the mechanisms of hepatic encephalopathy (HE). 1. Blood chemistry: In patients with liver cirrhosis, the plasma levels of ammonia, phenylalanine, tyrosine, phenolic acids, and octopamine correlated with the stages of HE. Methionine and free tryptophan concentrations were increased only in stages 2-4. Further, branched chain amino acids were below the normal range. Experimental findings in animals elucidated some mechanisms of these changes. 2. Effects of administered substances: With ammonia, methionine, methanethiol, tryptophan, phenolic substances, and fatty acids central nervous disturbances were observed. 3. Interactions: Anemia, methanethiol, and fatty acids favored ammonia toxicity. Alkalosis diminished cerebral symptoms. 4. Neurotransmitters: HE was accompanied by an enhanced turnover of serotonin and by increased amounts of false neurotransmitters (like octopamine) in the brain. 5. Oxydative brain metabolism: Disorders of cerebral oxygen and glucose utilization were mainly documented in cases of long term HE with EEG alterations. 6. Structural changes of the brain: Most of them are irreversible.

Topics: Alkalosis; Amino Acids; Ammonia; Anemia; Animals; Brain; Brain Edema; Carbon Dioxide; Catecholamines; Cats; Demyelinating Diseases; Glucose; Hepatic Encephalopathy; Humans; Liver Diseases; Neurotransmitter Agents; Octopamine; Oxygen Consumption; Serotonin; Thioacetamide