Cellular and molecular mechanisms of liver injury

Derangements in apoptosis of liver cells are mechanistically important in the pathogenesis of end-stage liver disease. Vulnerable hepatocytes can undergo apoptosis via an extrinsic, death receptor-mediated pathway, or alternatively intracellular stress can activate the intrinsic pathway of apoptosis. Both pathways converge on mitochondria, and mitochondrial dysfunction is a prerequisite for hepatocyte apoptosis. Persistent apoptosis is a feature of chronic liver diseases, and massive apoptosis is a feature of acute liver diseases. Fibrogenesis is stimulated by ongoing hepatocyte apoptosis, eventually resulting in cirrhosis of the liver in chronic liver diseases. Endothelial cell apoptosis occurs in ischemia-reperfusion injury. Natural killer and natural killer T cells remove virus-infected hepatocytes by death receptor-mediated fibrosis. Lastly, activated stellate cell apoptosis leads to slowing and resolution of apoptosis. This review summarizes recent cellular and molecular advances in the understanding of the injury mechanisms leading to end-stage liver disease.     

Ischaemia reperfusion injury in liver transplantation: Cellular and molecular mechanisms

Liver disease causing end organ failure is a growing cause of mortality. In most cases, the only therapy is liver transplantation. However, liver transplantation is a complex undertaking and its success is dependent on a number of factors. In particular, liver transplantation is subject to the risks of ischaemia‐reperfusion injury (IRI). Liver IRI has significant effects on the function of a liver after transplantation. The cellular and molecular mechanisms governing IRI in liver transplantation are numerous. They involve multiple cells types such as liver sinusoidal endothelial cells, hepatocytes, Kupffer cells, neutrophils and platelets acting via an interconnected network of molecular pathways such as activation of toll‐like receptor signalling, alterations in micro‐RNA expression, production of ROS, regulation of autophagy and activation of hypoxia‐inducible factors. Interestingly, the cellular and molecular events in liver IRI can be correlated with clinical risk factors for IRI in liver transplantation such as donor organ steatosis, ischaemic times, donor age, and donor and recipient coagulopathy. Thus, understanding the relationship of the clinical risk factors for liver IRI to the cellular and molecular mechanisms that govern it is critical to higher levels of success after liver transplantation. This in turn will help in the discovery of therapeutics for IRI in liver transplantation – a process that will lead to improved outcomes for patients suffering from end‐stage liver disease.     

多种细胞在肝纤维化逆转中的作用

在多种慢性肝损伤病因的作用下,肝星状细胞(HSC)等活化为肌成纤维细胞(MFB),迁移至损伤部位并大量分泌细胞外基质(ECM),ECM在肝内过度沉积,从而形成肝纤维化。当肝损伤病因被移除或经过有效治疗后,肝纤维化可发生逆转。介绍了多种细胞参与肝纤维化的逆转过程,MFB通过自身衰老、凋亡、失活,在肝纤维化逆转中发挥关键作用;巨噬细胞通过加快ECM降解和诱导MFB衰老等发挥抗肝纤维化功能;肝窦内皮细胞通过维持其正常表型阻断并逆转肝纤维化;自然杀伤细胞杀伤处于活化早期的HSC和衰老的MFB,参与肝纤维化逆转。     

Endotoxin-induced aggravation of preservation-reperfusion injury of rat liver and its modulation

BACKGROUND/AIMS: In clinical transplantation, exposure of donors to gut-derived endotoxin occurs frequently and may adversely affect liver transplantation therapy. The aim of this study was to investigate: 1) whether brief exposure of rats to endotoxin before liver procurement aggravates the early phase of reperfusion injury of hepatic explants; and if so 2) whether Kupffer cell activation is a contributing factor to liver injury; and 3) whether heparin and pentoxifylline could minimize this effect. METHODS: Male Wistar rats were injected with 0.2-4.0 mg/kg of Escherichia coli lipopolysaccharide 2 h prior to liver harvest. After preservation in University of Wisconsin cold-storage solution, the livers were reperfused using a blood-free perfusion model. To inactivate Kupffer cells, some rats were pretreated with gadolinium chloride or liposome-encapsulated dichloromethylene-diphosphonate before lipopolysaccharide administration. The other rats received lipopolysaccharide with heparin or pentoxifylline. RESULTS: In a dose-independent fashion, lipopolysaccharide impaired portal flow during graft reperfusion. In a dose-dependent way, lipopolysaccharide increased lactate dehydrogenase release into the perfusate and decreased bile flow and bromosulfophthalein excretion. Gadolinium chloride, liposomal dichloromethylene-diphosphonate, heparin, and pentoxifylline reduced lactate dehydrogenase release by 34%, 43%, 59%, and 64%, respectively, and improved functional parameters of the liver. A 52-fold increased neutrophil infiltration in the liver sinusoids after lipopolysaccharide exposure was not affected significantly by the drugs studied; however, heparin reduced markedly neutrophil activation. CONCLUSIONS: The results of this investigation provide direct evidence that aggravation of preservation-reperfusion injury of rat liver by endotoxin is mediated by Kupffer cell-dependent mechanism(s) and it can be minimized by heparin and pentoxifylline.     

Cellular signaling mechanisms in alcohol-induced liver damage

Chronic excessive alcohol intake is associated with multiple liver defects ranging from mild steatosis to advanced cirrhosis. However, the mechanisms by which chronic ethanol intake affects liver function remain a matter of intense debate and investigation. The liver is the major site of ethanol metabolism in the body, and a wide range of metabolic alterations is associated with ethanol intake. As a result, the liver is exposed to dramatic changes in redox state, transient hypoxia, episodes of oxidative stress, and the products of ethanol metabolism, such as acetaldehyde, acetate, and fatty acid ethyl esters. Chronic ethanol consumption is associated with increased levels of circulating endotoxins and proinflammatory cytokines that affect liver function. A major source of the increase in circulating proinflammatory cytokines is the Kupffer cells, which are sensitized to generate tumor necrosis factor alpha (TNF-alpha) through multiple mechanisms. In addition, the hepatocytes themselves are more susceptible to external stress. In isolated hepatocytes, this effect of chronic ethanol is evident in a greater sensitivity to proapoptotic challenges and, more specifically, to the cytotoxic actions of TNF-alpha. The mechanism by which hepatocytes are sensitized to external stress remains poorly characterized but may involve defects in mitochondrial function and oxidative defense mechanisms, the activation of death-promoting signaling pathways, and the inactivation of survival pathways. In this article, we emphasize the role of the stress-activated mitogen-activated protein kinase (MAPK) cascades in the onset of cell injury and their regulation by the phosphoinositide-3-kinase/Akt signaling cascade, which appears to function as the central integrating module of the stress-signaling machinery in the cell. We also discuss the complications and challenges of extrapolating these findings to the conditions in vivo and what we can learn from these studies regarding the nature of the liver defects associated with chronic alcohol consumption.     

In vivo regulation of inducible no synthase in immune-mediated liver injury in mice

Inducible nitric oxide synthase (iNOS) has been shown to play an important role in the development of liver injury. iNOS deficiency protects mice from hemorrhage/resuscitation as well as from cytokine-mediated liver injury, for example, after administration of concanavalin A (con A). Here we investigated the in vivo effects of tumor necrosis factor (TNF)-alpha and/or interferon (IFN)-gamma, two mediators of con A-induced liver injury, the TNF receptor (TNFR) usage leading to iNOS expression, and its connection with nuclear factor kappaB (NF-kappaB) activation. In conclusion, iNOS expression in vivo is dependent on both TNF-alpha and IFN-gamma. Although con A-induced liver injury depends on both TNFR1 and TNFR2, TNF-dependent iNOS expression is mediated exclusively by TNFR1 and requires NF-kappaB activation.     

Cellular and molecular mechanisms of sex differences in renal ischemia-reperfusion injury

Renal ischemia-reperfusion (I/R) is an important etiopathological mechanism of acute renal failure (ARF). Despite improvements in the treatment of ARF, it is associated with significant morbidity and mortality. I/R injury also occurs during renal transplantation and leads to reduced allograft survival. Sex differences have been found in I/R injury in many different organs including the kidney. Women have half the mortality of men in ARF. In animal models also, females are protected against renal I/R injury. The mechanisms by which sex affects the outcome to renal I/R injury are being actively investigated. This review will examine the evidence for gender differences in renal I/R injury and discuss the probable mechanisms by which sex affects the renal response to I/R injury.     

Immunologic mechanisms of alcoholic liver injury

Clinically, the association of alcoholic liver disease (ALD) with circulating autoantibodies, hypergammaglobulinemia, antibodies to unique hepatic proteins, and cytotoxic lymphocytes reacting against autologous hepatocytes strongly suggests altered immune regulation with an increased activity toward normal self-proteins (loss of tolerance). Experimentally, there are several immune responses generated specifically recognizing self-proteins that are modified by metabolites of alcohol. These data strongly suggest that immune reactions may play a significant role in inducing and sustaining an inflammatory cascade of tissue damage to the liver. Additional support for this comes from the observation that the histological appearance of livers with ALD is that of a chronic active hepatitis-like inflammatory disease. Therefore, the hypothesis that immune mechanisms are involved in recurrent alcoholic hepatitis, although not summarily proven, is reasonable, supported by clinical and experimental evidence, and the subject of this article.     

Influence of recombinant adenovirus on liver injury in endotoxicosis and its modulation by IL-10 expression

Adenovirus-based gene therapy offers a unique opportunity to target gene expression to the liver by systemic delivery. However, systemic administration of a first generation adenoviral construct elicits an inflammatory response leading to TNF-alpha-dependent liver injury. The aim of this study was to evaluate whether the systemic administration of recombinant adenovirus exacerbates a subsequent TNF-alpha-dependent liver injury induced by D-galactosamine and lipopolysaccharide. Surprisingly, low-dose adenovirus administration (10(5) particles) protects, while high-dose adenovirus (10(10) particles) is associated with an exaggerated hepatic inflammatory response from a subsequent D-galactosamine and lipopolysaccharide challenge. This exacerbation is TNF-alpha dependent, since treatment with a TNF inhibitor fully protects against the liver injury. Moreover, intravenous administration of an adenoviral construct expressing the anti-inflammatory protein interleukin-10 reduces TNF-alpha appearance and attenuates the increased hepatocyte injury. Taken together, this report demonstrates potential additive effects of TNF-alpha responses induced by adenovirus and other inflammatory signals, and suggests that the response can be mitigated by relative adenovirus particle dose or by inhibitors, such as TNF-binding protein or interleukin 10.     

Severe immune-mediated drug-induced liver injury linked to ibandronate: A case report

Ibandronate is a widely used bisphosphonate with no previously well documented hepatotoxicity. We report the first case of ibandronate-related hepatotoxicity and, to our knowledge, the first case of immune-mediated drug-induced liver injury (DILI) related to bisphosphonates.     

Crosstalk of liver immune cells and cell death mechanisms in different murine models of liver injury and its clinical relevance

BACKGROUND: Liver inflammation or hepatitis is a result of pluripotent interactions of cell death molecules, cytokines, chemokines and the resident immune cells collectively called as microenvironment. The interplay of these inflammatory mediators and switching of immune responses during hepatotoxic, viral, drug-induced and immune cell-mediated hepatitis decide the fate of liver pathology. The present review aimed to describe the mechanisms of liver injury, its relevance to human liver pathology and insights for the future therapeutic interventions.DATA SOURCES: The data of mouse hepatic models and relevant human liver diseases presented in this review are systematically collected from Pub Med, Science Direct and the Web of Science databases published in English. RESULTS: The hepatotoxic liver injury in mice induced by the metabolites of CCl4, acetaminophen or alcohol represent necrotic cell death with activation of cytochrome pathway, formation of reactive oxygen species(ROS) and mitochondrial damage. The Fas or TNF-α induced apoptotic liver injury was dependent on activation of caspases, release of cytochrome c and apoptosome formation. The Con A-hepatitis demonstrated the involvement of TRAIL-dependent necrotic/necroptotic cell death with activation of RIPK1/3. The α-Gal Cer-induced liver injury was mediated by TNF-α. The LPS-induced hepatitis involved TNF-α, Fas/Fas L, and perforin/granzyme cell death pathways. The MHV3 or Poly(I:C) induced liver injury was mediated by natural killer cells and TNF-α signaling. The necrotic ischemia-reperfusion liver injury was mediated byhypoxia, ROS, and pro-inflammatory cytokines; however, necroptotic cell death was found in partial hepatectomy. The crucial role of immune cells and cell death mediators in viral hepatitis(HBV, HCV), drug-induced liver injury, non-alcoholic fatty liver disease and alcoholic liver disease in human were discussed.CONCLUSIONS: The mouse animal models of hepatitis provide a parallel approach for the study of human liver pathology. Blocking or stimulating the pathways associated with liver cell death could unveil the novel therapeutic strategies in the management of liver diseases.     

Protective effect of selenium-enriched lactobacilluson CCI_4-induced liver injury in mice and its possible mechanisms

AIM: To study the protective effects and mechanisms of Se-enriched lactobacillus on liver injury caused by carbon tetrachloride(CCI_4) in mice. METHODS: Seventy-two ICR mice were randomly divided into four groups: normal group, CCl_4-induced model group, low Se-enriched lactobacillus treatment group(L-Se group), and high Se-enriched lactobacillus treatment group(H-Se group). During a 3-wk experimental period, the common complete diet was orally provided daily for normal group and model group, and the mice in L-Se and H-Se groups were given a diet with 2 and 4 mg of organoselenium from Se-enriched lactobacillus per kg feed, respectively. From the 2~(nd) wk of experiment, the model group, L-Se group, and H-Se group received abdominal cavity injection of olive oil solution containing 500 mL/L CCl_4(0.07 mL/100 g body mass) to induce liver injury, and the normal group was given olive oil on every other day for over 2 wk. In the first 2 wk post injection with CCl_4, mice in each group were killed. The specimens of blood, liver tissue, and macrophages in abdominal cavity fluid were taken. Then the activities of the following liver tissue injury-associated enzymes including glutathione peroxidase(GSH-Px), superoxide dismutase(SOD), alanine aminotransferase(ALT) and aspartate aminotransferase(AST) as well as malondialdehyde(MDA) content were assayed. Changes of phagocytic rate and phagocytic index in macrophages were observed with Wright-Giemsa stain. Plasma TNF-α level was measured by radioimmunoassay. The level of intracellular free Ca~(2+)([Ca~(2+)]_i) in hepatocytes was detected under a laser scanning confocal microscope. RESULTS: During the entire experimental period, the AST and ALT activities in liver were greatly enhanced by CCl_4 and completely blunted by both low and high doses of Se-enriched lactobacillus. The Se-enriched lactobacillusprotected liver homogenate GSH-Px and SOD activities were higher or significantly higher than those in model group and were close to those in normal group. CCl_4 significantly increased MDA content in liver homogenates, while administration of Se-enriched lactobacillus prevented MDA elevation. Phagocytic rate and phagocytic index of macrophages decreased after CCl_4 treatment compared to those in normal control, but they were dramatically rescued by Se-enriched lactobacillus, showing a greatly higher phagocytic function compared to model group. CCl_4 could significantly elevate plasma TNF-α and hepatocyte[Ca~(2+)]_i level, which were also obviously prevented by Se-enriched lactobacillus. CONCLUSION: Se-enriched lactobacillus can intervene in CCl_4-induced liver injury in mice by enhancing macrophage function activity to keep normal and beneficial effects, elevating antioxidant-enzyme activities and reducing lipid peroxidation reaction, inhibiting excessive release of TNF-α, preventing the dramatic elevation of [Ca~(2+)]_i in hepatocytes.     

Cellular and molecular mechanisms in the pathogenesis of liver fibrosis: An update

There have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying liver fibrogenesis. Recent data indicate that the termination of fibrogenic processes and the restoration of deficient fibrolytic pathways may allow the reversal of advanced fibrosis and even cirrhosis. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in liver fibrosis. Activation of hepatic stellate cells (HSCs) remains a central event in fibrosis, complemented by other sources of matrix-producing cells, including portal fibroblasts, fibrocytes and bone marrow-derived myofibroblasts. These cells converge in a complex interaction with neighboring cells to provoke scarring in response to persistent injury. Defining the interaction of different cell types, revealing the effects of cytokines on these cells and characterizing the regulatory mechanisms that control gene expression in activated HSCs will enable the discovery of new therapeutic targets. Moreover, the characterization of different pathways associated with different etiologies aid in the development of disease-specific therapies. This article outlines recent advances regarding the cellular and molecular mechanisms involved in liver fibrosis that may be translated into future therapies. The pathogenesis of liver fibrosis associated with alcoholic liver disease, non-alcoholic fatty liver disease and viral hepatitis are also discussed to emphasize the various mechanisms involved in liver fibrosis.