Caspase activation is associated with spontaneous recovery from acute liver failure.

UNLABELLED: Acute liver failure (ALF) has various causes and is characterized by rapid hepatocyte dysfunction with development of encephalopathy in the absence of preexisting liver disease. Whereas most patients require liver transplantation to prevent the high mortality, some patients recover spontaneously and show complete liver regeneration. Because of the low incidence of ALF, however, the molecular mechanisms of liver dysfunction and regeneration are largely unknown. In this study, we investigated the role of apoptosis and caspases in 70 ALF patients using novel biomarkers that allow the detection of caspase activation in serum samples. Compared with healthy individuals, activation of caspases was strongly enhanced in ALF patients. Interestingly, patients with spontaneous recovery from ALF revealed a significantly higher activation of caspases than patients that required transplantation or died, although in the latter patients extensive DNA fragmentation and signs of nonapoptotic cell death were observed. In the spontaneous survivors, increased caspase activation was accompanied by elevated levels of tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6), important cytokines involved in liver regeneration. CONCLUSION: Our data suggest that caspase activation and apoptosis are involved in ALF of patients with spontaneous recovery, whereas caspase-independent cell death might be more relevant in irreversible forms of liver failure. These findings might be important for therapeutic options of ALF but also suggest that measurement of caspase activation might be of prognostic value to predict the outcome of acute liver failure.

Increased hepatotoxicity of tumor necrosis factor-related apoptosis-inducing ligand in diseased human liver.

UNLABELLED: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumor cells but not in most normal cells and has therefore been proposed as a promising antitumor agent. Recent experiments suggested that isolated primary human hepatocytes but not monkey liver cells are susceptible to certain TRAIL agonists, raising concerns about the use of TRAIL in cancer treatment. Whether TRAIL indeed exerts hepatotoxicity in vivo and how this is influenced by chemotherapeutic drugs or liver disease are completely unknown. Employing different forms of recombinant TRAIL, we found that the cytokine can induce proapoptotic caspase activity in isolated human hepatocytes. However in marked contrast, these different TRAIL preparations induced little or no cytotoxicity when incubated with tissue explants of fresh healthy liver, an experimental model that may more faithfully mimic the in vivo situation. In healthy liver, TRAIL induced apoptosis only when combined with histone deacetylase inhibitors. Strikingly, however, TRAIL alone triggered massive apoptosis accompanied by caspase activation in tissue explants from patients with liver steatosis or hepatitis C viral infection. This enhanced sensitivity of diseased liver was associated with an increased expression of TRAIL receptors and up-regulation of proapoptotic Bcl-2 proteins. CONCLUSION: These results suggest that clinical trials should be performed with great caution when TRAIL is combined with chemotherapy or administered to patients with inflammatory liver diseases.

Serum biomarkers of cell death for monitoring therapy response of gastrointestinal carcinomas.

PURPOSE: Antitumour treatments are thought to exert their therapeutic efficacy mainly by induction of apoptosis in tumour cells. In epithelial cells, caspases, the key enzymes of apoptosis, cleave the intermediate filament protein cytokeratin (CK)-18 into specific fragments that are released into circulating blood and can be detected by a specific ELISA. EXPERIMENTAL DESIGN: To investigate the use of CK-18 fragments as a potential biomarker for the treatment response, we examined the association of serum CK-18 levels and clinical response in 35 patients with gastrointestinal cancers. RESULTS: While both cleaved and total CK-18 levels were intrinsically elevated in tumour patients, they were further increased during 5-fluorouracil (5-FU)-based therapy. Importantly, the increased levels of CK-18 could discriminate between patients with different clinical response. Cancer patients with a partial response or stable disease revealed a significantly higher increase of cleaved CK-18 during chemotherapy as compared to patients with progressive disease. CONCLUSIONS: Our results suggest that detection of circulating caspase-cleaved CK-18 might be a useful serum biomarker for monitoring treatment response and should merit further evaluation in larger patient groups.

Caspase activation is required for antiviral treatment response in chronic hepatitis C virus infection.

Only half of patients with chronic hepatitis C virus (HCV) infection and genotype-1 show a sustained antiviral response to the current antiviral therapy. The reason this treatment fails is unclear, and no reliable marker exists that predicts the treatment outcome. In the present study, we investigated the apoptotic activation of caspases in HCV patients undergoing antiviral therapy with regard to the treatment outcome. We determined caspase activation in sera from patients who were either responding or nonresponding to antiviral therapy by using two novel caspase assays, an immunological and a luminometric enzyme test. We found that compared with nonresponding individuals, responding patients showed significantly (P < .05) increased caspase activity, which was closely correlated with virus elimination (r = 0.81). The cutoff value of serum caspase activity was determined, which correctly predicted the treatment outcome with a sensitivity of 70% and a specificity of 82% (area under the curve 0.845; 95% CI). In conclusion, hepatic caspase activity might play a role in HCV clearance and could also predict the efficacy of antiviral therapy.

The extent of liver steatosis in chronic hepatitis C virus infection is mirrored by caspase activity in serum.

Hepatic steatosis is a frequent histological alteration in chronic hepatitis C virus (HCV) infection that sensitizes the liver to cell injury, inflammation, and fibrosis via unclear mechanisms. Although apoptosis has been implicated in various liver diseases, its importance in HCV-associated steatosis is largely unknown. In this study, we investigated the role of caspases, the key regulators of apoptosis, and employed two novel caspase assays, an immunological and a luminometric enzyme test, to detect hepatic caspase activation in sera from HCV patients with different grades of steatosis. Our data show that increased caspase activation can be found not only in liver biopsies, but also in sera from HCV patients with liver steatosis. Patients with steatosis exhibited significantly higher serum levels of caspase activity compared with normal healthy individuals. Moreover, the extent of steatosis closely correlated with serum caspase activity, whereas in particular in cases of low or moderate steatosis, no correlation was found with aminotransferase levels. In conclusion, apoptotic caspase activation is considerably elevated in HCV-associated steatosis. More importantly, our data imply that measurement of caspase activation might be a sensitive serum biomarker to detect liver steatosis in patients with chronic HCV infection and other liver diseases.

Detection of apoptotic caspase activation in sera from patients with chronic HCV infection is associated with fibrotic liver injury.

Chronic hepatitis C virus (HCV) infection is characterized by inflammatory liver damage and is associated with a high risk of development of cirrhosis and hepatocellular carcinoma. Although histological examination of liver biopsies is currently the gold standard for the detection of early liver damage, there is a strong need for better noninvasive methods. We recently demonstrated that the proapoptotic activation of caspases is considerably enhanced in histological sections from HCV-infected liver tissue, suggesting an important role of apoptosis in liver damage. Here, we investigated whether caspase activation is detectable also in sera from patients with chronic HCV infection. Using a novel enzyme-linked immunosorbent assay that selectively recognizes a proteolytic neoepitope of the caspase substrate cytokeratin-18, we demonstrate that caspase activity is markedly increased in the sera of HCV patients. Interestingly, while 27% of patients with chronic HCV infection showed normal aminotransferase levels despite inflammatory and fibrotic liver damage, more than 50% of those patients exhibited already elevated serum caspase activity. Moreover, 30% of patients with normal aminotransferase but elevated caspase activity revealed higher stages of fibrosis. In conclusion, compared with conventional surrogate markers such as aminotransferases, detection of caspase activity in serum might be a more sensitive method of detecting early liver injury. Thus, measurement of caspase activity might provide a novel diagnostic tool, especially for patients with normal aminotransferases but otherwise undiagnosed histologically active hepatitis and progressive fibrosis.