Brain edema and intracranial hypertension: a focus for the use of liver support systems

Aquaporin-4 deletion in mice reduces encephalopathy and brain edema in experimental acute liver failure

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.

Brain aquaporin-4 in experimental acute liver failure

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.

Molecular Adsorbent Recirculating System: clinical experience in patients with liver failure based on hepatitis B in China

The aim of this study is to evaluate the effect of treatment with the Molecular Adsorbent Recirculating System (MARS) on liver failure based on HBV. In 25 patients (median age, 36.3 years, range, 22-67 years, bilirubin level > 255 micro mol/l) admitted with liver failure based on HBV, the 6-8h MARS intermittent treatments were performed without any adverse events, A significant decrease in bilirubin, ammonia and urea levels were observed (P < 0.05). All patients achieved a remarkable neurologic recovery, particularly 2 HE-III and 3 HE-IV patients regained normal consciousness, respectively. The survival rate for the patients whose treatments kept to the MARS art strategy was 76.9% (10/13), while the others only had the survival rate of 16.7% (2/12) due to their giving up sequential MARS treatments after the first time. The rebounding rate of the bilirubin level in the patients after a single MARS treatment was significantly lower than that of patients, who underwent a single plasma-exchange treatment (P < 0.01). It is concluded that MARS method can contribute to the optimistic treatment of liver failure patients based on HBV which being the major epidemic liver disease in China.

Role of the molecular adsorbent recycling system (MARS) in the treatment of patients with acute exacerbation of chronic liver failure

OBJECTIVE

To test the efficacy of the molecular adsorbent recycling system (MARS) in patients with acute exacerbation of chronic liver disease.

DESIGN

A prospective case analysis.

SETTING

A university-affiliated tertiary medical center.

PATIENTS AND METHODS

We applied MARS to treat a consecutive series of eight patients with acute exacerbation of chronic liver disease.

RESULTS

The overall survival rate was 62.5%. All patients demonstrated improvement with regard to their degree of encephalopathy. In three patients, intracranial pressure and jugular bulb oxygen saturation decreased and cerebral perfusion pressure increased after treatment institution. Patients' hyperdynamic state was attenuated, as demonstrated by elevation of systemic vascular resistance, mean arterial pressure, and parallel reduction in cardiac index. A prompt reduction in serum ammonia, bilirubin, and lactate levels was observed. There were no complications during the treatment period.

CONCLUSIONS

Applying MARS treatments to patients with acute exacerbation of chronic liver disease can detoxify blood, improve cerebral circulation, and reduce brain edema, as reflected by the reduction in intracranial pressure and jugular bulb oxygen saturation values in our patients. A partial reversal of the characteristic hyperdynamic circulation was also achieved. Despite our encouraging results, further testing is needed to determine the reliability of the system.

Current status of liver support systems

The search for a support system for liver failure has been intensified. Methods currently being tested include those based on artificial support, on biological approaches (including extracorporeal liver perfusion and transplanted hepatocytes) as well as hybrid devices that combine artificial aspects with biological systems. Each of these three areas is undergoing fast technological and conceptual development. Controlled clinical trials are also under way.

Protein S-100beta: a biochemical marker for increased intracranial pressure in pigs with acute hepatic failure

BACKGROUND

Acute hepatic failure (AHF) may cause encephalopathy. Intracranial pressure (ICP) is frequently monitored to guide therapy, but such monitoring may cause intracerebral haemorrhagic complications. We hypothesize that determination of serum levels of S-100beta, a protein synthesized in astroglial cells, will provide useful clinical information on the presence and extent of intracranial hypertension in AHF.

METHODS

Continuous intraparenchymatous ICP monitoring and serial S-100beta measurements in serum were performed in 11 Norwegian Landrace pigs with surgically induced AHF and in 4 sham-operated controls.

RESULTS

ICP increased hour by hour in the devascularized pigs in parallel with increased serum levels of protein S-100beta. In the sham-operated controls S-100beta was not detectable at any time point.

CONCLUSIONS

Serum levels of S-100beta are increased early in experimental AHF. Determination of protein S-100beta may provide useful information on the presence and extent of intracranial hypertension in AHF.