Acute liver failure: from bench to bedside

Liver support systems: will they ever reach prime time?

Liver support systems aim to provide temporary support of liver function while maintaining extra-hepatic function in patients with liver failure. Important advances have been achieved in the design of artificial and bio-artificial devices, but the current systems are far from meeting the ideal. Artificial devices provide detoxification through different dialysis procedures, whereas bio-artificial devices add synthetic functions by incorporating a cellular component into the system. Overall, liver support systems have consistently shown beneficial effects on the pathophysiology of liver failure, especially in acute-on-chronic liver failure. However, these beneficial effects have not been translated into an improvement of survival. Our review discusses the current evidence, paying special attention to the clinical aspects of (bio)-artificial liver support devices.

Hepatoprotective effects of cathepsin B inhibitor on acute hepatic failure induced by lipopolysaccharide/D-galactosamine in mice

BACKGROUND

Increasing evidence suggests that the inactivation of cathepsin B attenuates hepatocyte apoptosis and liver damage. This study aimed to investigate the protective effects of a cathepsin B inhibitor (CA-074me) on lipopolysaccharide (LPS)/D-galactosamine (D-GalN)-induced acute hepatic failure (AHF) in mice.

METHODS

Mice were intraperitoneally injected with a combination of LPS/D-GalN to induce AHF with or without CA-074me pretreatment. The cumulative survival rates were calculated 48 hours after the induction of AHF. As well as changes in biochemical indicators and liver histology, hepatocyte apoptosis was assessed using a TUNEL method. Serum tumor necrosis factor-alpha (TNF-alpha) production, caspase-3, caspase-8, and caspase-9 activity was evaluated. Cytosolic cytochrome c and Bcl-2 expression were measured by Western blotting.

RESULTS

The marked elevation in serum aminotransferase activity and prothrombin time found in LPS/D-GalN-treated mice was significantly improved by pretreatment with CA-074me. The efficacy of CA-074me was also confirmed by histological analysis and TUNEL assay. The survival rate significantly improved in LPS/D-GalN-induced mice given CA-074me compared with untreated mice. LPS/D-GalN-induced caspase-3 and caspase-9 activation was remarkably suppressed by CA-074me. However, the increased levels of serum TNF-alpha and elevated caspase-8 activity in AHF mice were not significantly reduced by CA-074me. Moreover, CA-074me sharply reduced the increased expression of cytosolic cytochrome c and markedly augmented Bcl-2 expression.

CONCLUSION

These results suggest that CA-074me has a protective effect in acute hepatic failure induced by LPS/D-GalN.

Rodent animal models for surrogate analysis of cell therapy in acute liver failure

Without therapeutic intervention acute liver failure (ALF) is the consequence of a progredient destruction of the liver parenchyma due to metabolic exhaustion of the hepatocytes. Perivenous hepatocytes are responsible for the detoxification of noxious compounds via the cytochrome P450 enzyme system. Liver transplantation is the only remaining therapeutic option in the end-stage of the disease. Assuming that metabolic capacity could be provided by healthy hepatocytes and thus substitute for the genuine parenchymal cells hepatocyte transplantation since quite some time is considered to be an alternative to whole liver transplantation. While this hypothesis achieved proof-of-concept in animal trials clinical breakthrough is still awaiting success, the reasons of which are ongoing matter of debate. In recent times mesenchymal stem cells (MSC) came into focus as a transplantable cell source to treat ALF. Interestingly, as demonstrated in various rodent animal models their mode of action is rather based on trophic support of hepatocytes remaining in the damaged host parenchyma rather than substitution of tissue loss. Mechanistically, either direct or indirect paracrine effects from the transplanted cells acting pro-proliferative, anti-apoptotic, and anti-inflammatory seem to trigger the regenerative response of the residual healthy hepatocytes in the otherwise lethally injured liver parenchyma. Thus, allogeneic MSC may be the best choice for the treatment of ALF taking advantage of their short-term benefit to sustain the critical phase of the acute insult avoiding long-term immunosuppression.

Sterically stable liposomes improve the therapeutic effect of hepatic stimulator substance on fulminant hepatic failure in rats

BACKGROUND AND AIMS

Few drugs have been confirmed to be effective for fulminant hepatic failure (FHF). The purpose of this study was to prepare sterically stable liposomes (SSL) encapsulating hepatic stimulator substance (HSS) and determine their therapeutic effect on FHF.

METHODS

HSS were encapsulated into SSL (HSS-SSL). FHF was induced in rats by thioacetamide (TAA) injection (400mg/kg, three times with a 24-h interval). The agents, including HSS-SSL, SSL, HSS, and sodium chloride (NS), were each injected intravenously 2h after the second and the third TAA injection.

RESULTS

Freshly prepared HSS-SSL had a mean size of 93.59nm and the average encapsulation efficiency was 37.20%. HSS encapsulated in SSL showed a longer half life and more potent target to injured livers than free HSS. Twenty-four hours after the third TAA-injection, the survival rate of HSS-SSL-treated rats (80%) was significantly higher than that of rats treated with NS (20%), SSL (25%), or HSS (50%). Histopathologic examination showed that there was the least necrosis and inflammation in the livers of HSS-SSL-treated rats. The incidence of stage 3 or 4 hepatic encephalopathy in HSS-SSL-treated rats was significantly lower than that in rats treated with other agents. The serum pro-inflammatory cytokine levels and hepatic lipid peroxidation levels were both markedly reduced, while hepatocyte proliferative rate was markedly increased after HSS-SSL treatment.

CONCLUSION

Encapsulation by SSL markedly improved the therapeutic effect of HSS on FHF in rats. Encapsulation by SSL may be an effective approach to enhance the therapeutic potency of drugs for FHF.

A Src family kinase inhibitor improves survival in experimental acute liver failure associated with elevated cerebral and circulating vascular endothelial growth factor levels

BACKGROUND AND AIMS

Acute liver failure (ALF) is frequently complicated by cerebral oedema, systemic inflammation and multiorgan dysfunction. Vascular endothelial growth factor (VEGF) may stimulate liver regeneration but it can also be pro-inflammatory, activating endothelial cells and increasing permeability, actions mediated through Src kinase signalling. We therefore examined whether a Src inhibitor could have therapeutic potential in ALF.

METHODS

Murine ALF was induced with azoxymethane. Liver pathology was graded by a blinded examiner and apoptosis quantified by immunohistochemistry. Cerebral VEGF expression was imaged using VEGF-green fluorescent protein transgenic mice. Circulating and macrophage-secreted VEGF levels were measured. Experimental animals received a Src inhibitor or vehicle controls.

RESULTS

VEGF was undetectable in normal plasma but reached a mean of 835 pg/ml at grade III encephalopathy (P<0.001). Ammonia, lipopolysaccharide and interferon-gamma acted synergistically to enhance VEGF secretion by macrophages. Production of VEGF by cerebral cortical astrocytes increased with disease progression. Late treatment with inhibitors of Src or VEGF did not improve liver histology, encephalopathy or survival. However, early use of a Src kinase inhibitor significantly reduced hepatic injury, delayed encephalopathy and allowed 25% of mice to survive an otherwise lethal insult.

CONCLUSION

Systemic and cerebral VEGF levels are significantly elevated during experimental ALF and may be exacerbated by hyperammonemia and macrophage activation. Early use of a Src inhibitor reduced hepatocellular injury and enabled survival, indicating such agents may have some promise in the treatment of ALF.

Selective blockade of mGlu5 metabotropic glutamate receptors is hepatoprotective against fulminant hepatic failure induced by lipopolysaccharide and D-galactosamine in mice

This study was designed to investigate the influence of 2-methyl-6-phenylethynyl pyridine hydrochloride (MPEP), an antagonist of metabotropic glutamate receptor subtype 5, in lipopolysaccharide (LPS) and d-galactosamine (D-GalN)-induced fulminant hepatic failure in mice. Mice were given an intraperitoneal injection of 50 microg kg(-1) LPS and 500 mg kg(-1) D-GalN. MPEP (1, 5 and 25 mg kg(-1)) was administered intraperitoneally 1 h before LPS/D-GalN injection. Twenty-four hours after administration of LPS/D-GalN, plasma was collected and used for biochemical assays. Mice were euthanized and histological analysis and toxicological parameters were carried out in the liver. MPEP, at all doses tested, protected against the increase in aspartate and alanine aminotransferase activities induced by LPS/D-GalN exposure. Ascorbic acid levels were not altered in all experimental groups. Glutathione S-transferase activity was increased by administration of LPS/D-GalN and MPEP did not modify the enzyme activity in mice. MPEP, at the doses of 5 and 25 mg kg(-1), was effective in protecting against the decrease in catalase activity caused by LPS/D-GalN administration in mice. The histological data showed that sections of liver from LPS/D-GalN-exposed mice presented extensive injuries. MPEP, at all doses tested, reduced the scores of liver damage and markedly ameliorated the degree of liver damage. The hepatoprotective effect of MPEP on fulminant hepatic failure induced by LPS and D-GalN in mice was demonstrated.

Mild hypothermia does not affect liver regeneration after partial hepatectomy in mice

BACKGROUND

The use of mild hypothermia has been suggested to be therapeutically useful in treating acute liver failure. It is not known if hypothermia influences liver regeneration.

AIM

To assess the effect of hypothermia on liver regeneration in mice.

METHODS

After partial (70%) hepatectomy (PHx), C57BL6/J mice were randomly assigned to either a hypothermic group or a normothermic group. Controlled mild hypothermia was maintained for up to 3 h after surgery. In addition, assessment of liver mass restitution was examined by studying the induction of key cell cycle proteins (cyclin A, D1 and E) and hepatocyte proliferation [assessment of proliferating cell nuclear antigen (PCNA) protein expression] by Western blotting and DNA synthesis by measuring 5-bromo-2-deoxyuridine (BrdU) incorporation by immunohistochemical techniques 45 h after PHx.

RESULTS

Partial hepatectomy induced a vigorous proliferative response in the remnant livers of both groups of mice (normothermic and hypothermic groups), as evidenced by the induction of key cyclins, PCNA and incorporation of BrdU after PHx. The liver/body weight ratio and both cyclin and PCNA protein expression as well as BrdU incorporation did not differ between the regenerating livers of hypothermic and normothermic groups.

CONCLUSION

Mild hypothermia does not influence liver regeneration in mice.

Neutralization of CXCL10 accelerates liver regeneration in carbon tetrachloride-induced acute liver injury

Remodeling of hepatic tissue structure following injury requires the coordinated action of hepatocytes, hepatic stellate cells (HSCs), and endothelial cells. However, their in vivo properties are not fully understood. We report here that the chemokine CXCL10 regulates hepatic tissue remodeling in a carbon tetrachloride (CCl(4))-induced acute liver injury in mice. The production of CXCL10 was enhanced by hepatocytes after CCl(4) exposure. Neutralization of CXCL10 protected mice from acute liver dysfunction and diminished hepatocellular loss. The hepatoprotective effect was associated with increased numbers of 5'-bromo-2' deoxyuridine (BrdU)+ hepatocytes from day 1 and with accumulation of HSCs and endothelial cells within the injured zones from day 3. In vitro, recombinant CXCL10 directly inhibited the proliferation of hepatocytic cells, establishing a novel role of CXCL10 in modulating hepatocyte proliferation, in addition to a previously reported angiostatic role. In summary, neutralization of CXCL10 initially stimulates hepatocyte proliferation and, subsequently, HSC migration and angiogenesis to facilitate remodeling of hepatic cords. Thus, CXCL10 can be a novel therapeutic target for acute hepatocellular damage by regulating liver tissue remodeling.

A surgical model of fulminant hepatic failure in rabbits

AIM

Animal models of fulminant hepatic failure (FHF) have been developed for characterization of disease progression and to evaluate the effectiveness of liver-assist devices, some by treatment with hepatotoxic drugs, viral hepatitis or surgical procedures. We have developed a model in the rabbit by combining resection of the three anterior lobes with ligation of the pedicle of the right lateral lobes, resulting in liver necrosis; the remnant quadrate lobes are left intact.

MATERIALS AND METHODS

Adult male New Zealand white rabbits (n=16) were used. Six animals were killed to measure the weight of the separate liver lobes. The others (n=10) underwent left neck central line placement to monitor continuous blood pressure and collect blood for laboratory analysis, and a burr hole on the right parietal bone to monitor the intracranial pressure (ICP). Blood laboratory analysis, clinical hepatic encephalopathy and ICP levels were measured in FHF animals (n=6). Animals (n=4) undergoing a sham operation served as controls.

RESULTS

All FHF animals died between 12 and 26 h after liver surgery from FHF characterized by a progressive increase in liver enzymes, ammonia, total bilirubin, coagulopathy, hepatic encephalopathy and intracranial hypertension. Histological features of the ischaemic lobes showed coagulative necrosis of hepatocytes with absence of nuclei and collapse of cell plates. Brain histology revealed hypoxic cell damage.

CONCLUSION

We have developed a simple, reproducible model of FHF in rabbits that has a number of features comparable with clinical FHF patients and is well suited for testing experimental bioartificial liver systems and investigating the pathogenesis of FHF.

Effects of free radical scavenger on acute liver injury induced by d-galactosamine and lipopolysaccharide in rats

AIM

Acute severe liver injury still has a high mortality rate. Acute liver injury induced by a coadministration of d-galactosamine (GalN) and lipopolysaccharide (LPS) is an experimental model of fulminant hepatitis in rats. Our aim is to investigate the effects of free radical scavenger on the injury induced by GalN/LPS in rats.

METHODS

Free radical scavenger edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) was twice injected into rats 5 min before and 60 min after the GalN/LPS injection. Liver injury was biochemically and histologically assessed. The survival rate was examined 72 h after the intoxication.

RESULTS

In the GalN/LPS-treated rats, a marked elevation in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels was observed. On the other hand, edaravone significantly inhibited the elevation in serum AST and ALT levels. The efficacy of edaravone was also confirmedby histological analysis. Edaravone lowered the levels of proinflammatory cytokines TNF-alpha mRNA and interleukin-6 mRNA expression, antioxidative enzyme heme oxygenase-1 protein and myeloperoxidase activity, a marker of neutrophil infiltration, in rat livers. In addition, edaravone reduced the mortality rate in GalN/LPS-treated rats as compared to the rats without edaravone treatment.

CONCLUSIONS

Free radical scavenger edaravone effectively ameliorated the liver injury induced by the GalN/LPS administration in rats, not only by attenuating oxidative stress, but also by reducing the expression of proinflammatory cytokines.

The activin axis in liver biology and disease

Activins are a closely related subgroup within the TGFbeta superfamily of growth and differentiation factors. They consist of two disulfide-linked beta subunits. Four mammalian activin beta subunits termed beta(A), beta(B), beta(C), and beta(E), respectively, have been identified. Activin A, the homodimer of two beta(A) subunits, has important regulatory functions in reproductive biology, embryonic development, inflammation, and tissue repair. Several intra- and extracellular antagonists, including the activin-binding proteins follistatin and follistatin-related protein, serve to fine-tune activin A activity. In the liver there is compelling evidence that activin A is involved in the regulation of cell number by inhibition of hepatocyte replication and induction of apoptosis. In addition, activin A stimulates extracellular matrix production in hepatic stellate cells and tubulogenesis of sinusoidal endothelial cells, and thus contributes to restoration of tissue architecture during liver regeneration. Accumulating evidence from animal models and from patient data suggests that deregulation of activin A signaling contributes to pathologic conditions such as hepatic inflammation and fibrosis, acute liver failure, and development of liver cancer. Increased production of activin A was suggested to be a contributing factor to impaired hepatocyte regeneration in acute liver failure and to overproduction of extracellular matrix in liver fibrosis. Recent evidence suggests that escape of (pre)neoplastic hepatocytes from growth control by activin A through overexpression of follistatin and reduced activin production contributes to hepatocarcinogenesis. The role of the activin subunits beta(C) and beta(E), which are both highly expressed in hepatocytes, is still quite incompletely understood. Down-regulation in liver tumors and a growth inhibitory function similar to that of beta(A) has been shown for beta(E). Contradictory results with regard to cell proliferation have been reported for beta(C). The profound involvement of the activin axis in liver biology and in the pathogenesis of severe hepatic diseases suggests activin as potential target for therapeutic interventions.