Serum cytokeratins in alcoholic liver disease: contrasting levels of cytokeratin-18 and cytokeratin-19

Distinct patterns of auto-reactive antibodies associated with organ-specific immune-related adverse events

The roles of preexisting auto-reactive antibodies in immune-related adverse events (irAEs) associated with immune checkpoint inhibitor therapy are not well defined. Here, we analyzed plasma samples longitudinally collected at predefined time points and at the time of irAEs from 58 patients with immunotherapy naïve metastatic non-small cell lung cancer treated on clinical protocol with ipilimumab and nivolumab. We used a proteomic microarray system capable of assaying antibody reactivity for IgG and IgM fractions against 120 antigens for systemically evaluating the correlations between auto-reactive antibodies and certain organ-specific irAEs. We found that distinct patterns of auto-reactive antibodies at baseline were associated with the subsequent development of organ-specific irAEs. Notably, ACHRG IgM was associated with pneumonitis, anti-cytokeratin 19 IgM with dermatitis, and anti-thyroglobulin IgG with hepatitis. These antibodies merit further investigation as potential biomarkers for identifying high-risk populations for irAEs and/or monitoring irAEs during immunotherapy treatment.

Trial registration

ClinicalTrials.gov identifier: NCT03391869.

Acute alcohol-associated hepatitis: Latest findings in non-invasive biomarkers and treatment

Acute alcohol-associated hepatitis (AH) is a syndrome that occurs in heavy and long-term drinkers and results in severe jaundice and liver failure. The mortality rate in severe cases is 20%-50% at 28 days, and in cases that do not improve despite appropriately timed corticosteroid therapy, the mortality rate reaches 70% at 6 months. The only curative treatment is early liver transplantation, but less than 2% of patients with severe AH are eligible. In order to improve the prognosis, diagnostic tools are needed to detect appropriate cases at risk of severe conditions, and new therapies need to be developed that can replace corticosteroids. Recent research has revealed that the pathogenesis of AH involves a complex of factors, including changes in the gut microbiota, inflammatory and cytokine signalling, oxidative stress and mitochondrial dysfunction, and abnormalities in the hepatic regenerative capacity. Non-invasive diagnostic tools focusing on these specific pathologies have been reported in recent years. In addition, several novel agents targeting specific pathways are currently being developed and tested in clinical trials. This review will provide an overview of alcohol-associated hepatitis and focus on the latest diagnostic tools, particularly non-invasive biomarkers, and novel therapies.

Emerging Biomarkers in Alcohol-associated Hepatitis

Alcohol-associated hepatitis (AH) is a clinical syndrome of jaundice, abdominal pain, and anorexia due to prolonged heavy alcohol intake. AH is associated with changes in gene expression, cytokines, immune response, and the gut microbiome. There are limited biomarkers to diagnose and prognosticate in AH, but several non-invasive biomarkers are emerging. In this review, clinical risk-stratifying algorithms, promising AH biomarkers like cytokeratin-18 fragments, genetic polymorphisms, and microRNAs will be reviewed.

Current and Future Biomarkers in Alcoholic Hepatitis

Alcoholic hepatitis (AH) is a clinical syndrome of jaundice, abdominal pain, and anorexia due to prolonged heavy alcohol intake, and is associated with alterations in gene expression, cytokines, immune response, and the gut microbiome. Currently, we have limited biomarkers to diagnose and prognosticate in AH, but there are many novel noninvasive biomarkers under development. We evaluate the currently used algorithms to risk-stratify in AH (such as the Maddrey modified discriminant function), and discuss novel biomarkers in development, such as breath biomarkers, microRNAs, cytokeratin-18 fragments, and the AshTest. We also review the characteristics of an ideal biomarker in AH.

Alcohol-Related Liver Disease: Basic Mechanisms and Clinical Perspectives

Alcohol-related liver disease (ALD) refers to the liver damage occurring due to excessive alcohol consumption and involves a broad spectrum of diseases that includes liver steatosis, steatohepatitis, hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). The progression of ALD is mainly associated with the amount and duration of alcohol usage; however, it is also influenced by genetic, epigenetic, and environmental factors. The definite diagnosis of ALD is based on a liver biopsy, although several non-invasive diagnostic tools and serum biomarkers have emerging roles in the early detection of ALD. While alcohol abstinence and nutritional support remain the cornerstone of ALD treatment, growing evidence has revealed that the therapeutic agents that target oxidative stress or gut-liver axis, inflammatory response inhibition, and liver regeneration enhancement also play a role in ALD management. Furthermore, microRNAs modulation and mesenchymal stem cell-based therapy have emerging potential as ALD therapeutic options. This review summarizes the updated understanding of the pathophysiology, diagnosis, and novel therapeutic approaches for ALD.

Time-Course Changes of Serum Keratin Concentrations after Liver Transplantation: Contrasting Results of Keratin-18 and Keratin-19 Fragments

Objective

Under normal conditions, adult hepatocytes express only keratin-8 (K8) and keratin-18 (K18), whereas cholangiocytes also express K19. In this study, we delineate the pattern of normal time-course changes in serum K19 and K18 levels after liver transplantation. Patients and Methods. Serum levels of the K19 fragment CYFRA 21-1 and the K18 fragments tissue polypeptide specific antigen (TPS) and M30 (a neoepitope that is generated after caspase cleavage during apoptosis) were measured at baseline and at regular intervals (up to 6 months) after liver transplantation in 11 adult patients.

Results

There was a gradual decrease in serum K19 concentrations from baseline values after transplantation, following a time-course pattern similar to that of serum bilirubin. In contrast, serum concentrations of K18 fragments increased markedly shortly after transplantation and gradually decreased thereafter, following a time-course pattern similar to that of serum transaminases. The increase in TPS tended to occur earlier than that in M30, suggesting an initial predominance of hepatocyte necrosis followed by a predominance of apoptosis in the first days after transplantation. Five patients presented posttransplant complications (acute rejection in three cases and HCV recurrence in two cases). An early increase in serum K19 concentrations was observed in all cases. An increase in serum concentrations of K18 fragments (M30 and TPS) was observed in the two cases with HCV recurrence and was more variable in the three cases with acute rejection.

Conclusions

Serum concentrations of K19 and K18 fragments follow a dissimilar pattern of time-course changes after liver transplantation. The diagnostic value of variations in these normal patterns should be addressed in future studies.

Alcohol-Related Liver Disease: Areas of Consensus, Unmet Needs and Opportunities for Further Study

A joint meeting of the European Association for the Study of the Liver (EASL) and the American Association for the Study of Liver Diseases (AASLD) was held in London on September 30 and October 1, 2017. The goals of the meeting were to identify areas of broad agreement and disagreement, develop consensus, and determine future directions to ultimately reduce the burden, morbidity, and mortality of alcohol-related liver disease (previously termed alcoholic liver disease). The specific aims of the meeting were to identify unmet needs and areas for future investigation, in order to reduce alcohol consumption, develop markers for diagnosis and prognosis of disease, and create a framework to test novel pharmacological agents with pre-specified treatment endpoints. A table summary of these goals and aims is provided in the context of epidemiology, current management strategies, next steps for future trials and translational science.

Biomarkers of drug-induced liver injury

Drug-induced liver injury (DILI) is a major clinical and regulatory challenge. As a result, interest in DILI biomarkers is growing. So far, considerable progress has been made in identification of biomarkers for diagnosis (acetaminophen-cysteine protein adducts), prediction (genetic biomarkers), and prognosis (microRNA-122, high mobility group box 1 protein, keratin-18, glutamate dehydrogenase, mitochondrial DNA). Many of those biomarkers also provide mechanistic insight. The purpose of this chapter is to review major advances in DILI biomarker research over the last decade, and to highlight some of the challenges involved in implementation. Although much work has been done, more liver-specific biomarkers, more DILI-specific biomarkers, and better prognostic biomarkers for survival are all still needed. Furthermore, more work is needed to define reference intervals and medical decision limits.

Alcohol-related liver disease: Areas of consensus, unmet needs and opportunities for further study

A joint meeting of the European Association for the Study of the Liver (EASL) and the American Association for the Study of Liver Diseases (AASLD) was held in London on September 30 and October 1, 2017. The goals of the meeting were to identify areas of broad agreement and disagreement, develop consensus, and determine future directions to ultimately reduce the burden, morbidity, and mortality of alcohol-related liver disease (previously termed alcoholic liver disease). The specific aims of the meeting were to identify unmet needs and areas for future investigation, in order to reduce alcohol consumption, develop markers for diagnosis and prognosis of disease, and create a framework to test novel pharmacological agents with pre-specified treatment endpoints.

Non-invasive diagnosis and biomarkers in alcohol-related liver disease

Even though alcohol-related liver disease (ALD) is a major cause of severe liver disease worldwide, most patients with ALD are diagnosed at the decompensation stage. Liver biopsy is still considered the gold standard for establishing a definite diagnosis and assessing the fibrosis stage of ALD, but it is an invasive procedure, associated with significant morbidity. During the last decade, non-invasive tests have been developed to estimate the severity of liver fibrosis and steatosis. Measurement of liver stiffness by transient elastography has become the most commonly used non-invasive parameter to evaluate fibrosis. In ALD, transient elastography has been demonstrated to have an excellent performance to detect advanced fibrosis and cirrhosis. However, aspartate aminotransferase levels must be considered when interpreting liver stiffness cut-offs. Non-invasive biological tests have also been evaluated to assess liver fibrosis in ALD. The commercially available Enhanced Liver Fibrosis test and FibroTest have comparable performance for the diagnosis of advanced fibrosis in ALD, with studies suggesting that they are better than other biological tests (i.e. FIB-4 and APRI). Although ultrasound is still accepted as an initial screen for fatty liver diagnosis, new methods have recently been developed to detect steatosis. Magnetic resonance spectroscopy and magnetic resonance imaging techniques are highly accurate and reproducible, with superior sensitivities and specificities for detecting histological steatosis than ultrasound. However, low availability and high cost limit the use of magnetic resonance techniques in routine clinical practice. More recently, controlled attenuation parameter was developed as a novel tool to non-invasively assess liver steatosis; performed in combination with transient elastography, it was suggested to be superior to regular ultrasound for detecting steatosis and was shown to have acceptable diagnostic accuracy. New serum biomarkers are under investigation to non-invasively diagnose more severe forms of ALD and to predict prognosis of patients.

Cell Death and Prognosis of Mortality in Alcoholic Hepatitis Patients Using Plasma Keratin-18

Alcoholic liver disease encompasses the progressive stages of liver dysfunction that culminates in alcoholic cirrhosis (AC) and in severe cases alcoholic hepatitis (AH). Currently, prognostic scores have limited specificity and sensitivity. Plasma keratin-18 (K18) levels are elevated during liver disease and may be biomarkers of outcome. The objective of this study was to determine if total K18 (M65) or caspase-cleaved K18 (M30) levels were different between AC and AH patients. M65 and M30 levels were measured in the plasma of consented healthy controls and patients with AC and AH. Cell death was assessed by TUNEL staining and caspase activity. M65 and M30 values were significantly higher in AC patients compared to healthy controls and further increased in AH patients. The M65 values and the M30/M65 ratios of nonsurviving AH patients were significantly elevated above their surviving counterparts and healthy controls. Statistical analysis indicated that M30/M65 ratios outperformed current indices for accurately distinguishing the prognosis of AH patients. These scores occurred with minimal increase in plasma cell death markers such as ALT and AST. Serum caspase activity, TUNEL staining, and M30 immunohistochemistry in biopsies indicated that serum and tissue values may not correlate well with overall cell death. In conclusion, both M65 and M30 differentiate AH from AC patients, and M65 values and the M30/M65 ratio are capable of predicting early stage mortality; however, they may not accurately reflect pure hepatocyte cell death in these populations, as they do not strongly correlate with traditional cell death markers.

The antioxidant and antiapoptotic effect of boric acid on hepatoxicity in chronic alcohol-fed rats

The harmful use of alcohol is a worldwide problem involving all ages. This study aims to investigate chronic alcohol exposure related hepatotoxicity on the rat liver and possible hepatoprotective effects of boric acid. Rats were separated into 4 different groups: control, ethanol, ethanol+boric acid, and boric acid. We measured (i) malondialdehyde (MDA), total sialic acid (TSA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) levels, which are known to be the markers of alcohol damage; and also (ii) caspase-3, tumor necrosis factor-alpha (TNF-α), and the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) as the markers of apoptosis. In the ethanol group, MDA, TSA, and TNF-α levels increased whereas SOD and CAT levels decreased compared with the control group. Ethanol+boric acid group MDA, TSA, caspase-3, and TNF-α levels decreased whereas SOD and CAT levels increased compared with the ethanol group. Using histopathological evaluation of light microscope images, immunohistochemical caspase-3 and TNF-α activity in the ethanol+boric acid group were shown to be decreased compared with that in the ethanol group. Our results revealed that ethanol is capable of triggering oxidative stress and apoptosis in the rat liver. We propose that boric acid is an effective compound in protecting the rat liver against ethanol.

Caspase-cleaved keratin-18 fragments increase during alcohol withdrawal and predict liver-related death in patients with alcoholic liver disease

Noninvasive assessment of disease activity in patients with nonalcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) is still unsettled, but essential for the evaluation of disease progression. We here studied the association of total (M65) and caspase-cleaved (M30) serum keratin-18 fragments (n = 204) with histological parameters (n = 106) in heavy drinkers primarily admitted for alcohol withdrawal before and after alcohol detoxification. An age-, sex-, and fibrosis-stage matched NAFLD cohort (n = 30) was used for comparison. The prognostic value of M30 and M65 levels were assessed in an additional prospectively followed-up cohort of 230 patients with alcoholic cirrhosis (AC) using competing risk analyses. Among the histological parameters, both M30/65 correlated significantly and better than any other serum marker with apoptosis and liver damage, such as ballooning (r = 0.65; P < 0.001), followed by lobular inflammation (0.48; P < 0.001), steatosis (0.46; P < 0.001), but less with fibrosis (0.24; P < 0.001). Area under the receiver operating characteristics curves to detect ballooning, steatosis, or steatohepatitis (SH) were slightly better for M30 (P < 0.005). Optimal M30 cut-off values for mild and severe ballooning were 330 and 420 U/L, and 290 and 330 U/L for SH grades 1 and 2. No significant differences of M30/65 were found between the matched NAFLD and ALD cohort. In contrast to aspartate-amino-transferase and M65, M30 levels increased significantly from 391 to 518 U/L during alcohol detoxification. Moreover, levels of M30 and M65 predicted non-hepatocellular carcinoma liver-related mortality in patients with AC during a mean observation interval of 67.2 months.

CONCLUSION

Our data suggest M30 as highly specific marker of liver apoptosis both in ALD and NAFLD. In addition, hepatocellular apoptosis, as determined by M30 levels, occurs during alcohol withdrawal, and survival data point toward a novel underestimated role of apoptosis in patients with ALD. (Hepatology 2017;66:96-107).

Liver Injury and Endotoxemia in Male and Female Alcohol-Dependent Individuals Admitted to an Alcohol Treatment Program

BACKGROUND

Interactions between the liver, the gut, and the immune system are critical components of alcoholic liver disease (ALD). The aim of this study was to explore the associations between alcohol-induced liver injury, endotoxemia, and inflammation at admission and over time during abstinence, as well as to examine the sex-related differences in these parameters in alcohol-dependent individuals admitted to an alcohol treatment program.

METHODS

A cohort of 48 otherwise healthy participants with alcohol use disorder, but no clinical signs of alcoholic liver injury (34 males [M]/14 females [F]) admitted to an alcohol detoxification program, was stratified into 2 groups based on baseline plasma alanine aminotransferase (ALT) levels (as a marker of liver injury). Group 1 (ALT < 40 U/l, 7M/8F) and Group 2 (ALT ≥ 40 U/l, 27M/6F) were identified. Plasma biomarkers of liver damage, endotoxemia, and inflammation were examined at baseline, day 8, and day 15 of the admission. The drinking history was also evaluated.

RESULTS

Sixty-nine percent of patients had elevated ALT and other markers of liver damage, including aspartate aminotransferase and cytokeratin 18 (CK18 M65 and CK M30) at baseline, indicating the presence of mild ALD. Elevated CK18 M65:M30 ratio suggested a greater contribution of necrotic rather than apoptotic hepatocyte cell death in the liver injury observed in these individuals. Females showed greater elevations of liver injury markers compared to males, although they had fewer drinks per day and shorter lifetime duration of heavy drinking. Liver injury was associated with systemic inflammation, specifically, elevated plasma tumor necrosis factor-alpha levels. Compared to patients without liver injury, patients with mild ALD had greater endotoxemia (increased serum lipopolysaccharide levels), which decreased with abstinence and this decrease preceded the drop in CK18 M65 levels.

CONCLUSIONS

The study documented the association of mild alcohol-induced liver injury and endotoxemia, which improved with 2 weeks of abstinence, in a subset of individuals admitted to an alcohol detoxification program.

Cell death mechanisms in human chronic liver diseases: a far cry from clinical applicability

The liver is constantly exposed to a host of injurious stimuli. This results in hepatocellular death mainly by apoptosis and necrosis, but also due to autophagy, necroptosis, pyroptosis and in some cases by an intricately balanced combination thereof. Overwhelming and continuous cell death in the liver leads to inflammation, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Although data from various disease models may suggest a specific (predominant) cell death mode for different aetiologies, the clinical reality is not as clear cut. Reliable and non-invasive cell death markers are not available in general practice and assessment of cell death mode to absolute certainty from liver biopsies does not seem feasible, yet. Various aetiologies probably induce different predominant cell death modes within the liver, although the death modes involved may change during disease progression. Moreover, current methods applicable in patients are limited to surrogate markers for apoptosis (M30), and possibly for pyroptosis (IL-1 family) and necro(pto)sis (HMGB1). Although markers for some death modes are not available at all (autophagy), others may not be specific for a cell death mode or might not always definitely indicate dying cells. Physicians need to take care in asserting the presence of cell death. Still the serum-derived markers are valuable tools to assess severity of chronic liver diseases. This review gives a short overview of known hepatocellular cell death modes in various aetiologies of chronic liver disease. Also the limitations of current knowledge in human settings and utilization of surrogate markers for disease assessment are summarized.

Keratins: Biomarkers and modulators of apoptotic and necrotic cell death in the liver

Keratins, formerly known as cytokeratins, are the major epithelial-specific subgroup of intermediate filament proteins. Adult hepatocytes express keratin polypeptides 8 and 18 (K8/K18), whereas cholangiocytes express K8/K18 and keratins 7 and 19 (K7/K19). Keratins function primarily to protect hepatocytes from apoptosis and necrosis, which was revealed using several genetic mouse models. This cytoprotective function was further clarified by the identification of natural human keratin variants that are normally silent, but become pathogenic by predisposing their carriers to apoptosis during acute or chronic liver injury mediated by toxins, virus infection, or metabolic stress. During apoptosis, caspases cleave K18 and K19 at conserved aspartates (human K18/K19: (235) Val-Glu-Val-Asp(↓) ) and K18 at a unique aspartate (human K18: (394) Asp-Ala-Leu-Asp(↓) ), with the latter exposed epitope becoming recognized by the M30 antibody in blood and tissues. Additional K18-containing protein backbone epitopes are detected using the M6 and M5 (termed M65) antibodies. Intact K18 and its associated fragments, which are released into blood during apoptosis and necrosis in various diseases, have been analyzed by enzyme-linked immunosorbent assay using the M30/M65 antibodies or their signal ratios. Furthermore, M30/M65 levels have been used as diagnostic and prognostic biomarkers in acute and chronic liver diseases, including nonalcoholic steatohepatitis and acute liver failure. Other keratin biomarkers include K8/K18/K19-related tissue polypeptide antigen, K18-related tissue polypeptide-specific antigen, and K19-related CYFRA-21-1, which have been evaluated mostly in patients with epithelial tumors.

CONCLUSION

Keratins and their fragments are released into blood during liver and other epithelial tissue injury. The epithelial specificity of K18/K19, epitope unmasking upon caspase digestion, keratin abundance, and relative keratin stability render them useful biomarkers for hepatocyte and cholangiocyte apoptosis and necrosis. However, the precise biochemical nature and release mechanism of circulating keratins remain unknown. (Hepatology 2016;64:966-976).

Alcoholic and non-alcoholic steatohepatitis

This paper is based upon the "Charles Lieber Satellite Symposia" organized by Manuela G. Neuman at the Research Society on Alcoholism (RSA) Annual Meetings, 2013 and 2014. The present review includes pre-clinical, translational and clinical research that characterize alcoholic liver disease (ALD) and non-alcoholic steatohepatitis (NASH). In addition, a literature search in the discussed area was performed. Strong clinical and experimental evidence lead to recognition of the key toxic role of alcohol in the pathogenesis of ALD. The liver biopsy can confirm the etiology of NASH or alcoholic steatohepatitis (ASH) and assess structural alterations of cells, their organelles, as well as inflammatory activity. Three histological stages of ALD are simple steatosis, ASH, and chronic hepatitis with hepatic fibrosis or cirrhosis. These latter stages may also be associated with a number of cellular and histological changes, including the presence of Mallory's hyaline, megamitochondria, or perivenular and perisinusoidal fibrosis. Genetic polymorphisms of ethanol metabolizing enzymes such as cytochrome p450 (CYP) 2E1 activation may change the severity of ASH and NASH. Alcohol mediated hepatocarcinogenesis, immune response to alcohol in ASH, as well as the role of other risk factors such as its co-morbidities with chronic viral hepatitis in the presence or absence of human immunodeficiency virus are discussed. Dysregulation of hepatic methylation, as result of ethanol exposure, in hepatocytes transfected with hepatitis C virus (HCV), illustrates an impaired interferon signaling. The hepatotoxic effects of ethanol undermine the contribution of malnutrition to the liver injury. Dietary interventions such as micro and macronutrients, as well as changes to the microbiota are suggested. The clinical aspects of NASH, as part of metabolic syndrome in the aging population, are offered. The integrative symposia investigate different aspects of alcohol-induced liver damage and possible repair. We aim to (1) determine the immuno-pathology of alcohol-induced liver damage, (2) examine the role of genetics in the development of ASH, (3) propose diagnostic markers of ASH and NASH, (4) examine age differences, (5) develop common research tools to study alcohol-induced effects in clinical and pre-clinical studies, and (6) focus on factors that aggravate severity of organ-damage. The intention of these symposia is to advance the international profile of the biological research on alcoholism. We also wish to further our mission of leading the forum to progress the science and practice of translational research in alcoholism.

Non-invasive diagnosis of alcoholic liver disease

Alcoholic liver disease (ALD) is the most common liver disease in the Western world. For many reasons, it is underestimated and underdiagnosed. An early diagnosis is absolutely essential since it (1) helps to identify patients at genetic risk for ALD; (2) can trigger efficient abstinence namely in non-addicted patients; and (3) initiate screening programs to prevent life-threatening complications such as bleeding from varices, spontaneous bacterial peritonitis or hepatocellular cancer. The two major end points of ALD are alcoholic liver cirrhosis and the rare and clinically-defined alcoholic hepatitis (AH). The prediction and early diagnosis of both entities is still insufficiently solved and usually relies on a combination of laboratory, clinical and imaging findings. It is not widely conceived that conventional screening tools for ALD such as ultrasound imaging or routine laboratory testing can easily overlook ca. 40% of manifest alcoholic liver cirrhosis. Non-invasive methods such as transient elastography (Fibroscan), acoustic radiation force impulse imaging or shear wave elastography have significantly improved the early diagnosis of alcoholic cirrhosis. Present algorithms allow either the exclusion or the exact definition of advanced fibrosis stages in ca. 95% of patients. The correct interpretation of liver stiffness requires a timely abdominal ultrasound and actual transaminase levels. Other non-invasive methods such as controlled attenuation parameter, serum levels of M30 or M65, susceptometry or breath tests are under current evaluation to assess the degree of steatosis, apoptosis and iron overload in these patients. Liver biopsy still remains an important option to rule out comorbidities and to confirm the prognosis namely for patients with AH.

Biomarkers of liver cell death

Hepatocyte cell death during liver injury was classically viewed to occur by either programmed (apoptosis), or accidental, uncontrolled cell death (necrosis). Growing evidence from our increasing understanding of the biochemical and molecular mechanisms involved in cell demise has provided an expanding view of various modes of cell death that can be triggered during both acute and chronic liver damage such as necroptosis, pyroptosis, and autophagic cell death. The complexity of non-invasively assessing the predominant mode of cell death during a specific liver insult in either experimental in vivo models or in humans is highlighted by the fact that in many instances there is significant crosstalk and overlap between the different cell death pathways. Nevertheless, the realization that during cell demise triggered by a specific mode of cell death certain intracellular molecules such as proteins, newly generated protein fragments, or MicroRNAs are released from hepatocytes into the extracellular space and may appear in circulation have spurred a significant interest in the development of non-invasive markers to monitor liver cell death. This review focuses on some of the most promising markers, and their potential role in assessing the presence and severity of liver damage in humans.

Non-alcoholic steatohepatitis in morbidly obese patients

The hepatic complications of morbid obesity range from steatosis to steatohepatitis (Non-alcoholic steatohepatitis [NASH]), fibrosis, cirrhosis and finally hepatocellular carcinoma. The pathophysiological mechanisms of the progression of a normal liver to a liver showing steatosis and then steatohepatitis are complex, including, per se, insulin-resistance, iron accumulation, oxidative stress and hepatocyte death. An imbalance in anti- and pro-inflammatory factors may be the trigger. These factors can originate from intra- or extrahepatic sites, particularly the adipose tissue and the gut. This review will provide insight into the current diagnosis and understanding of hepatic inflammation including non-invasive markers of NASH (markers of hepatocyte death), intrahepatic mechanisms (regulation of the immune and inflammatory response, hepatocellular iron deposition, hepatocyte death) and extrahepatic factors (from adipose tissue and gut) in morbidly obese patients.

The importance of CYP2E1 in the pathogenesis of alcoholic liver disease and drug toxicity and the role of the proteasome

The chapter discusses about the critical role of CYP2E1 in ethanol mediated liver injury and its association with NASH. Ethanol metabolism by CYP2E1 generates hydroxyethyl radicals which promote ethanol hepatotoxicity. Greater induction of CYP2E1 and hence greater liver injury occurs with co-administration of ethanol and drugs. Induction of CYP2E1 leads to prominent epigenetic effects and CYP2E1 polymorphism may be associated with alcoholic liver disease. These are some aspects of CYP2E1, amongst many others which account for its importance in the context of drug metabolism and disease development and have been reviewed in the chapter.

A pilot study assessing the prognostic value of CK18 and nDNA biomarkers in severe sepsis patients

BACKGROUND AND OBJECTIVES

Severe sepsis and septic shock have posed significant treatment challenges for many years. Recently, a number of circulating apoptosis biomarkers have emerged, such as full-length and caspase-cleaved cytokeratin 18 (CK18) and nucleosomal DNA (nDNA), that may be predictive of likely outcome. This non-interventional study aimed to assess the ability of enzyme-linked immunosorbent assays (ELISAs) for these biomarkers to provide clinically useful information to guide the management of sepsis.

METHODS

This study was conducted in patients admitted to the intensive care unit with severe sepsis at five US centres. Blood samples for assessment of plasma levels of full-length CK18 (measured by the M65® ELISA) and caspase-cleaved CK18 (measured by the M30-Apoptosense® ELISA) and nDNA (measured by ELISA) were collected from patients within 2 hours of consent (baseline) and on days 2, 4 and 8. Blood samples from 17 healthy volunteers acted as controls. Levels of each biomarker were presented descriptively.

RESULTS

A total of 22 patients (mean age 60 [range, 24-83] years; 50% male) were included in the study. The mean APACHE II score was 24.4 (range 7-50). One-third of patients had three organ system failures and over one-half had septic shock. Three patients died during the study. Full-length and caspase-cleaved CK18 levels decreased within 48 hours following initiation of treatment of sepsis in patients who survived, whereas increases were observed in the same timeframe in patients who died within 28 days of admission. Baseline nDNA and total soluble CK18 levels (caspase-cleaved and total intact) were significantly (p ≤ 0.05) higher in patients who required renal support than those who did not.

CONCLUSIONS

Despite the small numbers of subjects assessed in the current study, these results confirm that measurement of apoptosis biomarkers may help to provide clinically useful information to manage sepsis and expedite development of novel therapeutics. However, further investigations to fully assess their prognostic value are required.

Cytokeratins in hepatitis

Experimental and clinical evidence suggests that cytokeratins (CK), among other physiological functions, are expressed in hepatocytes and can be released in the bloodstream after acute or chronic inflammatory liver injury. Interest in CK in viral and nonviral hepatitis has been rapidly increasing during the last years, especially as they have been proposed as circulating biomarkers of hepatocyte necrosis and apoptosis. In the present review, we sought to summarize and discuss the alterations in circulating CK levels in different form viral and nonviral hepatitis, as well as their potential relation with liver histology. Understanding the mechanisms of hepatitis impact on CK and vice versa is a promising area of research that will positively enhance our understanding of the complexity of acute and chronic inflammatory liver injury.

Synergistic effect of alcohol consumption and body mass on serum concentrations of cytokeratin-18

BACKGROUND

Cytokeratin-18 is an essential component of the cytoskeleton of epithelial cells (including hepatocytes). Serum concentrations of cytokeratin-18 (tissue polypeptide-specific antigen [TPS]) are used as a marker of epithelial neoplasms. Here, we investigated the potential interaction between alcohol and obesity in relation to serum TPS concentrations.

METHODS

Alcohol consumption, body mass index, and components of metabolic syndrome were measured in a random sample (n = 420) of the adult population (aged 18 to 92 years, 45% men) from a single municipality. Regular alcohol intake of >20 g/d (women) or >30 g/d (men) was considered risky drinking. Serum TPS was measured with a commercial immunoassay.

RESULTS

Risky drinking was associated with increased serum concentrations of TPS, which was particularly evident among obese individuals. Among individuals without risky drinking, TPS concentrations were similar for all levels of body mass. Conversely, among risky drinkers, serum TPS concentrations increased in parallel with body mass (p = 0.002). The odds ratio of a high (>100 U/l) TPS concentration for the combination of risky drinking and obesity was greater than the additive effect of the 2 separate factors, after adjusting for age and sex. A similar interaction was observed between risky drinking and abdominal adiposity, a major component of the metabolic syndrome. Serum TPS concentrations were correlated with markers of liver damage. Serum TPS was not superior to standard markers (gamma-glutamyl transferase and red blood cell mean volume) for the detection of risky drinking.

CONCLUSIONS

There is a synergism between risky alcohol consumption and common metabolic disorders (particularly obesity) in relation to serum concentrations of cytokeratin-18 (TPS), which probably reflect liver disease.

Serum markers of hepatocyte death and apoptosis are non invasive biomarkers of severe fibrosis in patients with alcoholic liver disease

Background

Quantification of hepatotocyte death is useful to evaluate the progression of alcoholic liver diseases. Our aims were to quantify and correlate the circulating levels of Cytokeratin 18 (CK18) and its caspases-generated fragment to disease severity in heavy alcoholics.

Methodology/Principal Findings

CK18 and CK18-fragment were evaluated in the serum of 143 heavy alcoholics. Serum levels of markers of hepatocyte death (CK18), apoptosis (CK18 fragment) and necrosis (CK18 -CK18 fragment) increased in patients with severe fibrosis compared to patients with mild fibrosis. These markers strongly correlated with Mallory-Denk bodies, hepatocyte ballooning, fibrosis and with hepatic TNFα and TGFβ assessed in the liver of 24 patients. Elevated levels of serum hepatocyte death and apoptotic markers were independent risk factors in predicting severe fibrosis in a model combining alkaline phosphatase, bilirubin, prothrombin index, hyaluronate, hepatocyte death and apoptotic markers. The level of markers of hepatocyte death and apoptosis had an area under the receiving operator curve that predicted severe fibrosis of 0.84 and 0.76, respectively.

Conclusion/Significance

Death of hepatocytes can be easily evaluated with serum markers and correlated with severe fibrosis in heavy alcohol drinkers. These biomarkers could be useful to rapidly evaluate liver injuries and the efficacy of therapies.

Systematic review: caspase-cleaved fragments of cytokeratin 18 - the promises and challenges of a biomarker for chronic liver disease

BACKGROUND

Biomarkers hold great promise for detecting chronic liver disease without the use of liver biopsy.

AIM

To review the usefulness of cytokeratin (CK) 18 fragments, a marker of hepatocyte apoptosis, to predict the presence of chronic liver injury.

METHODS

Available literature identified from PubMed was reviewed.

RESULTS

Levels of CK18 fragments have been shown to be elevated in hepatocellular carcinoma, viral hepatitis, alcoholic hepatitis, nonalcoholic fatty liver disease and cholestatic liver disease. In the setting of nonalcoholic fatty liver disease, CK18 fragments may distinguish nonalcoholic steatohepatitis from simple fatty liver.

CONCLUSIONS

Undoubtedly, the most promising application of CK18 fragments is currently in nonalcoholic fatty liver disease, and especially for distinguishing patients with nonalcoholic steatohepatitis vs. those with simple steatosis. Further investigations and technical improvements are required to cross the boundary from research to the clinical application of CK18 fragments as a marker of chronic liver disease.

The impact of CYP2E1 on the development of alcoholic liver disease as studied in a transgenic mouse model

BACKGROUND/AIMS

CYP2E1 metabolizes ethanol, generates reactive oxygen species, and is suggested to be important for development of alcoholic liver disease. The present study aims to evaluate the role of CYP2E1 in combination with ethanol for development of alcoholic liver disease using mice transgenic for the human CYP2E1 gene.

METHODS

Changes in hepatic gene expression were monitored in controls and mice transgenic for human CYP2E1, treated with ethanol or isocaloric dextrose intragastrically for 4 weeks, and related to pathology using Affymetrix microarrays and TaqMan RealTime PCR.

RESULTS

Presence of the CYP2E1 transgene increased liver injury and increased expression of stress related genes. Microarray analyses revealed the expression of structural genes, particularly cytokeratin 8 and 18, to be highly related to pathology.

CONCLUSIONS

This in vivo study confirms several findings regarding CYP2E1 and alcohol previously found only in vitro. These results provide in vivo evidence that CYP2E1 overexpression aggravates hepatic injury, and suggest that expression of cytokeratins 8 and 18 can be considered as biomakers for the progression of alcoholic liver disease.

Serum levels of keratin-18 fragments [tissue polypeptide-specific antigen (TPS)] are correlated with hepatocyte apoptosis in alcoholic hepatitis

Apoptosis is a major feature in alcoholic hepatitis. During apoptosis, the M30 neoepitope becomes exposed after keratin-18 cleavage. The tissue polypeptide-specific antigen (TPS) is a keratin-18 fragment that is routinely used as a tumor marker. Serum TPS levels are increased in patients with alcoholic hepatitis. The aim of this study was to investigate the possible relationship of TPS levels with hepatocyte apoptosis in alcoholic hepatitis. Thirty-one patients with alcoholic hepatitis and 22 with fatty liver were included. Hepatocyte apoptosis was evaluated by M30 immunostaining. Serum TPS levels were measured by a commercial immunoassay. The apoptotic score was higher in patients with alcoholic hepatitis than in patients with fatty liver. There was a significant correlation between the apoptotic score and TPS levels. The correlation of the apoptotic score with TPS levels was stronger than with standard liver tests. Serum TPS may be a marker of apoptosis in alcoholic hepatitis.

Identification of proteins to predict the molecular basis for the observed gender susceptibility in a rat model of alcoholic steatohepatitis by 2-D gel proteomics

Females are reported to be highly susceptible to alcoholic steatohepatitis (ASH) compared to the males. Although a variety of mechanisms have been proposed to explain this higher sensitivity of females, the precise mechanism is not well understood. The objective of this study was to identify changes in global protein expression in liver tissues of male and female rats with pathologically evident ASH by 2-DE (dimensional electrophoresis). ASH was induced in the SD (Sprague-Dawley) rats by feeding ethanol (EtOH) containing Lieber-DeCarli diet for 6 wk followed by a single injection of lipopolysaccharide (LPS, 10 mg/kg, i.p.). Higher liver injury in females in the ASH group as compared to the males was confirmed by HE stained liver sections. As identified by 2-DE, 22 protein-spots were differentially expressed in the females in the ASH group as compared to the males. Following identification of these proteins by MALDI-MS, they were mainly categorized into metabolism and oxidative stress-related proteins. The expression pattern of a few of these oxidative stress-related proteins like Ferritin Heavy chain (Ferritin-H chain), ER stress protein 60 (ER 60) and Heat-shock protein-60 (HSP 60) were verified by Western blotting. To conclude, the current study has identified a set of proteins that highlights potential novel mechanisms associated with higher liver injury noted in the female rat ASH model.

One-hit effects in cancer: altered proteome of morphologically normal colon crypts in familial adenomatous polyposis

We studied patients with Familial Adenomatous Polyposis (FAP) because they are virtually certain to develop colon cancer, and because much is known about the causative APC gene. We hypothesized that the inherited heterozygous mutation itself leads to changes in the proteome of morphologically normal crypts and the proteins that changed may represent targets for preventive and therapeutic agents. We determined the differential protein expression of morphologically normal colon crypts of FAP patients versus those of individuals without the mutation, using two-dimensional gel electrophoresis, mass spectrometry, and validation by two-dimensional gel Western blotting. Approximately 13% of 1,695 identified proteins were abnormally expressed in the morphologically normal crypts of APC mutation carriers, indicating that a colon crypt cell under the one-hit state is already abnormal. Many of the expression changes affect pathways consistent with the function of the APC protein, including apoptosis, cell adhesion, cell motility, cytoskeletal organization and biogenesis, mitosis, transcription, and oxidative stress response. Thus, heterozygosity for a mutant APC tumor suppressor gene alters the proteome of normal-appearing crypt cells in a gene-specific manner, consistent with a detectable one-hit event. These changes may represent the earliest biomarkers of colorectal cancer development, potentially leading to the identification of molecular targets for cancer prevention.

Intermediate filament cytoskeleton of the liver in health and disease

Intermediate filaments (IFs) represent the largest cytoskeletal gene family comprising approximately 70 genes expressed in tissue specific manner. In addition to scaffolding function, they form complex signaling platforms and interact with various kinases, adaptor, and apoptotic proteins. IFs are established cytoprotectants and IF variants are associated with >30 human diseases. Furthermore, IF-containing inclusion bodies are characteristic features of several neurodegenerative, muscular, and other disorders. Acidic (type I) and basic keratins (type II) build obligatory type I and type II heteropolymers and are expressed in epithelial cells. Adult hepatocytes contain K8 and K18 as their only cytoplasmic IF pair, whereas cholangiocytes express K7 and K19 in addition. K8/K18-deficient animals exhibit a marked susceptibility to various toxic agents and Fas-induced apoptosis. In humans, K8/K18 variants predispose to development of end-stage liver disease and acute liver failure (ALF). K8/K18 variants also associate with development of liver fibrosis in patients with chronic hepatitis C. Mallory-Denk bodies (MDBs) are protein aggregates consisting of ubiquitinated K8/K18, chaperones and sequestosome1/p62 (p62) as their major constituents. MDBs are found in various liver diseases including alcoholic and non-alcoholic steatohepatitis and can be formed in mice by feeding hepatotoxic substances griseofulvin and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). MDBs also arise in cell culture after transfection with K8/K18, ubiquitin, and p62. Major factors that determine MDB formation in vivo are the type of stress (with oxidative stress as a major player), the extent of stress-induced protein misfolding and resulting chaperone, proteasome and autophagy overload, keratin 8 excess, transglutaminase activation with transamidation of keratin 8 and p62 upregulation.

Optimisation of circulating biomarkers of cell death for routine clinical use

BACKGROUND

M30 and M65 enzyme-linked immunosorbent assays detect circulating cytokeratin 18 fragments released during caspase-dependent or total cell death, respectively, and have potential as biomarkers in epithelial cancers. While these assays have been validated, their robustness for routine clinical use is unknown.

PATIENTS AND METHODS

M30 and M65 were measured in matched serum and plasma samples from 31 lung cancer patients and 18 controls.

RESULTS

Time allowable between sample acquisition and processing is critical for assays in clinical use. A 4-h delay in processing at room temperature increased M30 (P < 0.0001), an effect minimised by incubation on ice. M30 and M65 in serum were resistant to processing variations including delays. Serum and plasma measurements correlated well although M30 but not M65 was lower in serum (P < 0.0005). Less variation between duplicate assays was observed in serum. Prolonged storage (-80 degrees C) led to increased M30 (12%, 6 months; 34%, 1 year). Sample dilution in the supplied assay diluent proved non-linear, whereas dilution in donor serum or porcine plasma restored linearity up to a ratio of 1 : 6.

CONCLUSION

We present recommendations that improve the reliability of these assays for clinical use and recommend serum as the preferred matrix with data more resistant to variations in collection.

Keratins let liver live: Mutations predispose to liver disease and crosslinking generates Mallory-Denk bodies

Keratin polypeptides 8 and 18 (K8/K18) are the cytoskeletal intermediate filament proteins of hepatocytes while K8/K18/K19 are the keratins of hepatobiliary ductal cells. Hepatocyte K8/K18 are highly abundant and behave as stress proteins with injury-inducible expression. Human association studies show that K8/K18 germline heterozygous mutations predispose to end-stage liver disease of multiple etiologies ( approximately 3 fold increased risk), and to liver disease progression in patients with chronic hepatitis C infection. These findings are supported by extensive transgenic mouse and ex vivo primary hepatocyte culture studies showing that K8 or K18 mutations predispose the liver to acute or subacute injury and promote apoptosis and fibrosis. Mutation-associated predisposition to liver injury is likely related to mechanical and nonmechanical keratin functions including maintenance of cell integrity, protection from apoptosis and oxidative injury, serving as a phosphate sponge, regulation of mitochondrial organization/function and protein targeting. These functions are altered by mutation-induced changes in keratin phosphorylation, solubility and filament organization/reorganization. Keratins are also the major constituents of Mallory-Denk bodies (MDBs). A toxin-induced K8>K18 ratio, and keratin crosslinking by transglutaminase-2 play essential roles in MDB formation. Furthermore, intracellular or cell-released K18 fragments, generated by caspase-mediated proteolysis during apoptosis serve as markers of liver injury. Therefore, K8 and K18 are cytoprotective stress proteins that play a central role in guarding hepatocytes from apoptosis. Keratin involvement in liver disease is multi-faceted and includes modulating disease progression upon mutation, formation of MDBs in response to unique forms of injury, and serving as markers of epithelial cell death.

Serum concentrations of the tissue polypeptide specific antigen in patients suffering from non-alcoholic steatohepatitis

BACKGROUND

Liver histology is the gold standard for diagnosis of non-alcoholic fatty liver disease. Ethical considerations and patient choice often preclude performing a liver biopsy, especially considering the rare but potential risk. Searching for a good serological marker substitute for the invasive procedure was the aim of our study. Keratins, mainly 8 and 18, play not only a mere structural role providing mechanical stability to hepatocytes, but also represent a target via toxic stress ultimately inducing apoptosis/necrosis. Tissue polypeptide-specific antigen (TPS), a serological mirror of keratin 18, is widely used as a marker for various cancers. This antigen was assessed in three different groups who were overweight or obese.

MATERIALS AND METHODS

In this cross-sectional case-control study, 48 cancer-free patients with non-alcoholic steatohepatitis (NASH, Group 1), 48 patients with pure fatty liver (FL, Group 2), and 47 volunteers (Group 3) were studied. All of them were referred to our metabolic unit for routine evaluation.

RESULTS

The median (range) TPS levels were 123 (56-286) ng mL(-1) in NASH patients. FL patients and volunteers had significantly lower TPS levels, 76 (38-98) ng mL(-1) and 64 (28-87) ng mL(-1), respectively (P = 0.0001). A value of 88 ng mL(-1) in patients with underlying bright liver was associated with a high probability of NASH (sensitivity and specificity = 92% and 96%, respectively). One patient (2.1%) with FL had a TPS value > 88 ng mL(-1), but in the same group, 29 FL patients (60.4%) had an alanine aminotransferase value > 40 U L(-1). Based on a recent classification of liver fibrosis, the median (range) TPS values were significantly different among the stages: F1 (n = 23) = 100 (76-264) ng mL(-1); F2 (n = 21) = 134 (56-276) ng mL(-1); and F3 (n = 4) = 199.5 (123-286) ng mL(-1), respectively (P = 0.014).

CONCLUSIONS

Our study shows that TPS is a better marker than alanine aminotransferase activity, ultrasonography or the combination of both parameters in differentiating NASH from FL.

Serum levels of cytokeratin-18 (tissue polypeptide-specific antigen) in liver diseases

OBJECTIVE

The tissue polypeptide-specific antigen (TPS, cytokeratin-18, a normal constituent of the hepatocyte cytoskeleton) is a standard tumour marker. This study aimed to evaluate serum TPS levels in patients with liver disease.

METHODS

Serum TPS was measured with a commercial immunoassay in 884 individuals (753 outpatients from a liver disease clinic, 131 patients admitted to the hospital with acute liver disease).

RESULTS

Abnormally high (> 80 U/l) TPS levels were found in 57.7% (95% CI 54.0-61.3%) of outpatients with liver disease. Elevated TPS levels were observed for all liver diseases, including fatty liver, alcoholic disease, chronic viral hepatitis, autoimmune hepatitis, cholestasis, transplantation, and hepatocarcinoma. TPS levels correlated with liver markers, particularly serum AST. In addition, TPS levels correlated with Knodell's score in patients with chronic hepatitis. TPS was increased in one-third of patients with normal liver enzyme values. Serum TPS levels decreased after specific therapy in patients with hepatitis C and autoimmune hepatitis. Abnormally high TPS levels were found in the vast majority of patients admitted to the hospital, with markedly high (> 800 U/l) values being observed in 47.5% (95% CI 36.1-55.7%) of patients with alcoholic liver disease and in 80.8% (95% CI 60.0-92.7%) of patients with acute hepatitis.

CONCLUSIONS

Serum TPS (cytokeratin-18) is elevated in patients with non-malignant liver diseases, particularly in those with prominent cytolysis. Further studies are needed to evaluate the use of TPS as a marker of liver disease.