Kupffer cells and activation of endothelial TLR4 coordinate neutrophil adhesion within liver sinusoids during endotoxemia

Endothelial dysfunction: Pathophysiology and therapeutic targets for sepsis-induced multiple organ dysfunction syndrome

Sepsis and septic shock are critical medical conditions characterized by a systemic inflammatory response to infection, significantly contributing to global mortality rates. The progression to multiple organ dysfunction syndrome (MODS) represents the most severe complication of sepsis and markedly increases clinical mortality. Central to the pathophysiology of sepsis, endothelial cells play a crucial role in regulating microcirculation and maintaining barrier integrity across various organs and tissues. Recent studies have underscored the pivotal role of endothelial function in the development of sepsis-induced MODS. This review aims to provide a comprehensive overview of the pathophysiology of sepsis-induced MODS, with a specific focus on endothelial dysfunction. It also compiles compelling evidence regarding potential small molecules that could attenuate sepsis and subsequent multi-organ damage by modulating endothelial function. Thus, this review serves as an essential resource for clinical practitioners involved in the diagnosing, managing, and providing intensive care for sepsis and associated multi-organ injuries, emphasizing the importance of targeting endothelial cells to enhance outcomes of the patients.

Dynamic Multiplex Tissue Imaging in Inflammation Research

Inflammation is a highly dynamic process with immune cells that continuously interact with each other and parenchymal components as they migrate through tissue. The dynamic cellular responses and interaction patterns are a function of the complex tissue environment that cannot be fully reconstructed ex vivo, making it necessary to assess cell dynamics and changing spatial patterning in vivo. These dynamics often play out deep within tissues, requiring the optical focus to be placed far below the surface of an opaque organ. With the emergence of commercially available two-photon excitation lasers that can be combined with existing imaging systems, new avenues for imaging deep tissues over long periods of time have become available. We discuss a selected subset of studies illustrating how two-photon microscopy (2PM) has helped to relate the dynamics of immune cells to their in situ function and to understand the molecular patterns that govern their behavior in vivo. We also review some key practical aspects of 2PM methods and point out issues that can confound the results, so that readers can better evaluate the reliability of conclusions drawn using this technology.

Genetic and immune determinants of E. coli liver abscess formation

Systemic infections can yield distinct outcomes in different tissues. In mice, intravenous inoculation of Escherichia coli leads to bacterial replication within liver abscesses, while other organs such as the spleen clear the pathogen. Abscesses are macroscopic necrotic regions that comprise the vast majority of the bacterial burden in the animal, yet little is known about the processes underlying their formation. Here, we characterize E. coli liver abscesses and identify host determinants of abscess susceptibility. Spatial transcriptomics revealed that liver abscesses are associated with heterogenous immune cell clusters comprised of macrophages, neutrophils, dendritic cells, innate lymphoid cells, and T-cells that surround necrotic regions of the liver. Abscess susceptibility is heightened in the C57BL lineage, particularly in C57BL/6N females. Backcross analyses demonstrated that abscess susceptibility is a polygenic trait inherited in a sex-dependent manner without direct linkage to sex chromosomes. As early as 1 d post infection, the magnitude of E. coli replication in the liver distinguishes abscess-susceptible and abscess-resistant strains of mice, suggesting that the immune pathways that regulate abscess formation are induced within hours. We characterized the early hepatic response with single-cell RNA sequencing and found that mice with reduced activation of early inflammatory responses, such as those lacking the LPS receptor TLR4 (Toll-like receptor 4), are resistant to abscess formation. Experiments with barcoded E. coli revealed that TLR4 mediates a tradeoff between abscess formation and bacterial clearance. Together, our findings define hallmarks of E. coli liver abscess formation and suggest that hyperactivation of the hepatic innate immune response drives liver abscess susceptibility.

Interorgan communication with the liver: novel mechanisms and therapeutic targets

The liver is a multifunctional organ that plays crucial roles in numerous physiological processes, such as production of bile and proteins for blood plasma, regulation of blood levels of amino acids, processing of hemoglobin, clearance of metabolic waste, maintenance of glucose, etc. Therefore, the liver is essential for the homeostasis of organisms. With the development of research on the liver, there is growing concern about its effect on immune cells of innate and adaptive immunity. For example, the liver regulates the proliferation, differentiation, and effector functions of immune cells through various secreted proteins (also known as "hepatokines"). As a result, the liver is identified as an important regulator of the immune system. Furthermore, many diseases resulting from immune disorders are thought to be related to the dysfunction of the liver, including systemic lupus erythematosus, multiple sclerosis, and heart failure. Thus, the liver plays a role in remote immune regulation and is intricately linked with systemic immunity. This review provides a comprehensive overview of the liver remote regulation of the body's innate and adaptive immunity regarding to main areas: immune-related molecules secreted by the liver and the liver-resident cells. Additionally, we assessed the influence of the liver on various facets of systemic immune-related diseases, offering insights into the clinical application of target therapies for liver immune regulation, as well as future developmental trends.

The bidirectional immune crosstalk in metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is an unabated risk factor for end-stage liver diseases with no available therapies. Dysregulated immune responses are critical culprits of MASLD pathogenesis. Independent contributions from either the innate or adaptive arms of the immune system or their unidirectional interplay are commonly studied in MASLD. However, the bidirectional communication between innate and adaptive immune systems and its impact on MASLD remain insufficiently understood. Given that both innate and adaptive immune cells are indispensable for the development and progression of inflammation in MASLD, elucidating pathogenic contributions stemming from the bidirectional interplay between these two arms holds potential for development of novel therapeutics for MASLD. Here, we review the immune cell types and bidirectional pathways that influence the pathogenesis of MASLD and highlight potential pharmacologic approaches to combat MASLD based on current knowledge of this bidirectional crosstalk.

Genetic and immune determinants of E. coli liver abscess formation

Systemic infections can yield distinct outcomes in different tissues. In mice, intravenous inoculation of E. coli leads to bacterial replication within liver abscesses while other organs such as the spleen largely clear the pathogen. Abscesses are macroscopic necrotic regions that comprise the vast majority of the bacterial burden in the animal, yet little is known about the processes underlying their formation. Here, we characterize E. coli liver abscesses and identify host determinants of abscess susceptibility. Spatial transcriptomics revealed that liver abscesses are associated with heterogenous immune cell clusters comprised of macrophages, neutrophils, dendritic cells, innate lymphoid cells, and T-cells that surround necrotic regions of the liver. Susceptibility to liver abscesses is heightened in the C57BL/6 lineage, particularly in C57BL/6N females. Backcross analyses demonstrated that abscess susceptibility is a polygenic trait inherited in a sex-dependent manner without direct linkage to sex chromosomes. As early as one day post infection, the magnitude of E. coli replication in the liver distinguishes abscess-susceptible and abscess-resistant strains of mice, suggesting that the immune pathways that regulate abscess formation are induced within hours. We characterized the early hepatic response with single-cell RNA sequencing and found that mice with reduced activation of early inflammatory responses, such as those lacking the LPS receptor TLR4, are resistant to abscess formation. Experiments with barcoded E. coli revealed that TLR4 mediates a tradeoff between abscess formation and bacterial clearance. Together, our findings define hallmarks of E. coli liver abscess formation and suggest that hyperactivation of the hepatic innate immune response drives liver abscess susceptibility.

Disseminated intravascular coagulation phenotype is regulated by the TRPM7 channel during sepsis

BACKGROUND

Sepsis is an uncontrolled inflammatory response against a systemic infection that results in elevated mortality, mainly induced by bacterial products known as endotoxins, producing endotoxemia. Disseminated intravascular coagulation (DIC) is frequently observed in septic patients and is associated with organ failure and death. Sepsis activates endothelial cells (ECs), promoting a prothrombotic phenotype contributing to DIC. Ion channel-mediated calcium permeability participates in coagulation. The transient reception potential melastatin 7 (TRPM7) non-selective divalent cation channel that also contains an α-kinase domain, which is permeable to divalent cations including Ca²⁺, regulates endotoxin-stimulated calcium permeability in ECs and is associated with increased mortality in septic patients. However, whether endothelial TRPM7 mediates endotoxemia-induced coagulation is not known. Therefore, our aim was to examine if TRPM7 mediates coagulation during endotoxemia.

RESULTS

The results showed that TRPM7 regulated endotoxin-induced platelet and neutrophil adhesion to ECs, dependent on the TRPM7 ion channel activity and by the α-kinase function. Endotoxic animals showed that TRPM7 mediated neutrophil rolling on blood vessels and intravascular coagulation. TRPM7 mediated the increased expression of the adhesion proteins, von Willebrand factor (vWF), intercellular adhesion molecule 1 (ICAM-1), and P-selectin, which were also mediated by the TRPM7 α-kinase function. Notably, endotoxin-induced expression of vWF, ICAM-1 and P-selectin were required for endotoxin-induced platelet and neutrophil adhesion to ECs. Endotoxemic rats showed increased endothelial TRPM7 expression associated with a procoagulant phenotype, liver and kidney dysfunction, increased death events and an increased relative risk of death. Interestingly, circulating ECs (CECs) from septic shock patients (SSPs) showed increased TRPM7 expression associated with increased DIC scores and decreased survival times. Additionally, SSPs with a high expression of TRPM7 in CECs showed increased mortality and relative risk of death. Notably, CECs from SSPs showed significant results from the AUROC analyses for predicting mortality in SSPs that were better than the Acute Physiology and Chronic Health Evaluation II (APACHE II) and the Sequential Organ Failure Assessment (SOFA) scores.

CONCLUSIONS

Our study demonstrates that sepsis-induced DIC is mediated by TRPM7 in ECs. TRPM7 ion channel activity and α-kinase function are required by DIC-mediated sepsis-induced organ dysfunction and its expression are associated with increased mortality during sepsis. TRPM7 appears as a new prognostic biomarker to predict mortality associated to DIC in SSPs, and as a novel target for drug development against DIC during infectious inflammatory diseases.

Resident macrophages of the lung and liver: The guardians of our tissues

Resident macrophages play a unique role in the maintenance of tissue function. As phagocytes, they are an essential first line defenders against pathogens and much of the initial characterization of these cells was focused on their interaction with viral and bacterial pathogens. However, these cells are increasingly recognized as contributing to more than just host defense. Through cytokine production, receptor engagement and gap junction communication resident macrophages tune tissue inflammatory tone, influence adaptive immune cell phenotype and regulate tissue structure and function. This review highlights resident macrophages in the liver and lung as they hold unique roles in the maintenance of the interface between the circulatory system and the external environment. As such, we detail the developmental origin of these cells, their contribution to host defense and the array of tools these cells use to regulate tissue homeostasis.

Uptake of Plasmodium chabaudi hemozoin drives Kupffer cell death and fuels superinfections

Kupffer cells (KCs) are self-maintained tissue-resident macrophages that line liver sinusoids and play an important role on host defense. It has been demonstrated that upon infection or intense liver inflammation, KCs might be severely depleted and replaced by immature monocytic cells; however, the mechanisms of cell death and the alterations on liver immunity against infections deserves further investigation. We explored the impact of acute Plasmodium infection on KC biology and on the hepatic immune response against secondary infections. Similar to patients, infection with Plasmodium chabaudi induced acute liver damage as determined by serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) elevation. This was associated with accumulation of hemozoin, increased of proinflammatory response and impaired bacterial and viral clearance, which led to pathogen spread to other organs. In line with this, mice infected with Plasmodium had enhanced mortality during secondary infections, which was associated with increased production of mitochondrial superoxide, lipid peroxidation and increased free iron within KCs-hallmarks of cell death by ferroptosis. Therefore, we revealed that accumulation of iron with KCs, triggered by uptake of circulating hemozoin, is a novel mechanism of macrophage depletion and liver inflammation during malaria, providing novel insights on host susceptibility to secondary infections. Malaria can cause severe liver damage, along with depletion of liver macrophages, which can predispose individuals to secondary infections and enhance the chances of death.

The Significance of Neutrophil Extracellular Traps in Colorectal Cancer and Beyond: From Bench to Bedside

Neutrophil extracellular traps (NETs), products of neutrophil death when exposed to certain stimuli, were first proposed as a type of response to bacterial infection in infectious diseases. Since then, extensive studies have discovered its involvement in other non-infectious inflammatory diseases including thromboembolism, autoimmune diseases, and cancer. Colorectal cancer (CRC) is one of the most common malignancies in the world. NET formation is closely associated with tumorigenesis, progression, and metastasis in CRC. Therefore, the application of NETs in clinical practice as diagnostic biomarkers, therapeutic targets, and prognostic predictors has a promising prospect. In addition, therapeutics targeting NETs are significantly efficient in halting tumor progression in preclinical cancer models, which further indicates its potential clinical utility in cancer treatment. This review focuses on the stimuli of NETosis, its pro-tumorigenic activity, and prospective clinical utility primarily in but not limited to CRC.

Gut-derived lipopolysaccharide promotes alcoholic hepatosteatosis and subsequent hepatocellular carcinoma by stimulating neutrophil extracellular traps through TLR4

Background/Aims

Binge drinking leads to many disorders, including alcoholic hepatosteatosis, which is characterized by intrahepatic neutrophil infiltration and increases the risk of hepatocellular carcinoma (HCC). Molecular mechanisms may involve the migration of bacterial metabolites from the gut to the liver and the activation of neutrophil extracellular traps (NETs).

Methods

Serum samples from both binge drinking and alcohol-avoiding patients were analyzed. Mouse models of chronic plus binge alcohol-induced hepatosteatosis and HCC models were used.

Results

A marker of NETs formation, lipopolysaccharide (LPS), was significantly higher in alcoholic hepatosteatosis and HCC patients and mice than in controls. Intrahepatic inflammation markers and HCC-related cytokines were decreased in mice with reduced NET formation due to neutrophil elastase (NE) deletion, and liver-related symptoms of alcohol were also alleviated in NE knockout mice. Removal of intestinal bacteria with antibiotics led to decreases in markers of NETs formation and inflammatory cytokines upon chronic alcohol consumption, and development of alcoholic hepatosteatosis and HCC was also attenuated. These functions were restored upon supplementation with the bacterial product LPS. When mice lacking toll-like receptor 4 (TLR4) received chronic alcohol feeding, intrahepatic markers of NETs formation decreased, and hepatosteatosis and HCC were alleviated.

Conclusions

Formation of NETs following LPS stimulation of TLR4 upon chronic alcohol use leads to increased alcoholic steatosis and subsequent HCC.

The Role of Myeloid Cells in Hepatotoxicity Related to Cancer Immunotherapy

Drug-related hepatotoxicity is an emerging clinical challenge with the widening use of immunotherapeutic agents in the field of oncology. This is an important complication to consider as more immune oncological targets are being identified to show promising results in clinical trials. The application of these therapeutics may be complicated by the development of immune-related adverse events (irAEs), a serious limitation often requiring high-dose immunosuppression and discontinuation of cancer therapy. Hepatoxicity presents one of the most frequently encountered irAEs and a better understanding of the underlying mechanism is crucial for the development of alternative therapeutic interventions. As a novel drug side effect, the immunopathogenesis of the condition is not completely understood. In the liver, myeloid cells play a central role in the maintenance of homeostasis and promotion of inflammation. Recent research has identified myeloid cells to be associated with hepatic adverse events of various immune modulatory monoclonal antibodies. In this review article, we provide an overview of the role of myeloid cells in the immune pathogenesis during hepatoxicity related to cancer immunotherapies and highlight potential treatment options.

Activation and Functional Priming of Blood Neutrophils in Non-Alcoholic Fatty Liver Disease Increases in Non-Alcoholic Steatohepatitis

Introduction

In non-alcoholic fatty liver disease (NAFLD), neutrophils in liver infiltrates are activated, which may contribute to disease progression towards non-alcoholic steatohepatitis (NASH). However, the functional status of the blood neutrophils remains unknown and their role in the disease mechanisms is thus uncertain. We therefore characterized activation and function of blood neutrophils in patients with NAFLD in relation to clinical disease markers and the NAFLD plasma milieu.

Methods

We studied 20 patients with NAFLD, among these 6 patients with NASH, and 14 healthy persons. Neutrophil activation, interleukin (IL)-8 production and oxidative burst were measured by flow cytometry on participants´ neutrophils and on healthy neutrophils exposed in vitro to plasma from the study participants.

Results

Blood neutrophils from the NASH patients showed a doubling in their expression of the activation marker CD62L. Also, all NAFLD patients had 50–100% increased expression of CD11b. Functionally, NASH neutrophils had 30% elevated IL-8 production and more than doubled spontaneous oxidative burst. In all NAFLD patients, higher spontaneous oxidative burst was associated with worse liver function. Incubation of healthy neutrophils with NAFLD plasma paradoxically slightly reduced CD62L and CD11b expression, and NASH plasma also reduced the frequency of IL-8-producing neutrophils.

Conclusion

In NAFLD, blood neutrophils are activated, and in NASH also functionally primed. This suggests a progressive neutrophil aggressiveness already present with liver fat infiltration. However, NAFLD plasma in vitro, if anything, had the opposite effect on the healthy neutrophils so the NAFLD-related neutrophil activation cannot be attributed to humoral factors and remains unexplained.

Neutrophil-Induced Liver Injury and Interactions Between Neutrophils and Liver Sinusoidal Endothelial Cells

Neutrophils are the most abundant type of leukocytes with diverse functions in immune defense including production of reactive oxygen species, bacteriocidal proteins, neutrophil extracellular traps, and pro-inflammatory mediators. However, aberrant accumulation of neutrophils in host tissues and excessive release of bacteriocidal compounds can lead to unexpected injury to host organs. Neutrophil-mediated liver injury has been reported in various types of liver diseases including liver ischemia/reperfusion injury, nonalcoholic fatty liver disease, endotoxin-induced liver injury, alcoholic liver disease, and drug-induced liver injury. Yet the mechanisms of neutrophil-induced hepatotoxicity in different liver diseases are complicated. Current knowledge of these mechanisms are summarized in this review. In addition, a substantial body of evidence has emerged showing that liver sinusoidal endothelial cells (LSECs) participate in several key steps of neutrophil-mediated liver injury including neutrophil recruitment, adhesion, transmigration, and activation. This review also highlights the current understanding of the interactions between LSECs and neutrophils in liver injury. The future challenge is to explore new targets for selectively interfering neutrophil-induced liver injury without impairing host defense function against microbial infection. Further understanding the role of LSECs in neutrophil-induced hepatotoxicity would aid in developing more selective therapeutic approaches for liver disease.

Gut-Liver Axis: Liver Sinusoidal Endothelial Cells Function as the Hepatic Barrier in Colitis-Induced Liver Injury

Background

Based on the gut–liver axis theory, a leaky gut can aggravate liver injury. However, clinical studies suggest that although gut mucosa damage is commonly observed in inflammatory bowel disease (IBD), it seldom leads to severe liver injury. We hypothesize that there is a hepatic barrier in the gut–liver axis, which protects the liver against gut-derived invasive factors.

Methods

Colitis was induced by dextran sulfate sodium (DSS) in eight different liver injury models in Sprague–Dawley rats. Liver sinusoidal endothelial cell (LSEC) injury was evaluated by a scanning and transmission electron microscope. Neutrophils were depleted by injection of anti-rat polymorphonuclear serum. Two pneumonia models were also induced to investigate the mechanism of neutrophil recruitment and activation. LSECs isolated from rat liver were used to investigate the effect on neutrophil recruitment and activation.

Results

Among eight liver injury models, DSS colitis had no effect on liver injury in three models with normal LSECs. In the other five models with LSEC rupture, liver injury was significantly exacerbated by colitis, and increased hepatic neutrophil accumulation was observed. When neutrophils were depleted, colitis-induced liver injury was significantly attenuated. In pneumonia, liver injury, and colitis models, the level of CXCL1 correlated with the recruitment of neutrophils in different tissues, while DSS colitis and LSEC injury synergistically contributed to increased CXCL1 expression in the liver. In colitis-induced liver injury, neutrophils were activated in the liver. Injured LSECs showed both structural and functional changes, with significantly increased expression of CXCL1 and TNF-α under the stimulation of lipopolysaccharide (LPS). The combination of gut-derived LPS and LSEC-derived TNF-α led to the activation of neutrophils, characterized by enhanced production of reactive oxygen species, pro-inflammatory cytokines, and the formation of neutrophil extracellular traps.

Conclusion

LSECs constitute a vitally important barrier in the gut–liver axis, defending the liver against colitis-induced injury. When LSECs are damaged, they can turn into a pro-inflammatory pattern under the stimulation of LPS. LSEC injury and colitis-derived LPS synergistically contribute to the recruitment and activation of hepatic neutrophils. Neutrophils play a pivotal role as a downstream effector in colitis-induced liver injury.

Neutrophil: An emerging player in the occurrence and progression of metabolic associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is a common type of chronic liver disease characterized by excessive lipid accumulation in hepatocytes, but the pathogenesis is still unclear. Neutrophils, the most abundant immune cells in the human body, defend against pathogens and regulate the inflammatory response. Recent studies have indicated that excessive liver infiltration of neutrophils is a significant histological hallmark of MAFLD, and neutrophils and their derived granule proteins participate in different stages of MAFLD, including hepatic steatosis, inflammation, fibrosis, cirrhosis and hepatocellular carcinoma. Hence, in this review, we summarize the role of neutrophils in the occurrence and progression of MAFLD and provide a perspective for the clinical application of neutrophils in MAFLD diagnosis and treatment.

Neutrophil Extracellular Traps and Liver Disease

Neutrophil extracellular traps, or NETs, are heterogenous, filamentous structures which consist of extracellular DNA, granular proteins, and histones. NETs are extruded by a neutrophil in response to various stimuli. Although NETs were initially implicated in immune defense, subsequent studies have implicated NETs in a spectrum of disease processes, including autoimmune disease, thrombosis, and cancer. NETs also contribute to the pathogenesis of several common liver diseases, including alcohol-associated liver disease and portal hypertension. Although there is much interest in the therapeutic potential of NET inhibition, future clinical applications must be balanced against potential increased risk of infection.

Hepatic Macrophages in Liver Injury

Ample evidence suggests that hepatic macrophages play key roles in the injury and repair mechanisms during liver disease progression. There are two major populations of hepatic macrophages: the liver resident Kupffer cells and the monocyte-derived macrophages, which rapidly infiltrate the liver during injury. Under different disease conditions, the tissue microenvironmental cues of the liver critically influence the phenotypes and functions of hepatic macrophages. Furthermore, hepatic macrophages interact with multiple cells types in the liver, such as hepatocytes, neutrophils, endothelial cells, and platelets. These crosstalk interactions are of paramount importance in regulating the extents of liver injury, repair, and ultimately liver disease progression. In this review, we summarize the novel findings highlighting the impact of injury-induced microenvironmental signals that determine the phenotype and function of hepatic macrophages. Moreover, we discuss the role of hepatic macrophages in homeostasis and pathological conditions through crosstalk interactions with other cells of the liver.

Therapeutic Targeting of Neutrophil Granulocytes in Inflammatory Liver Disease

Neutrophil granulocytes are the most numerous type of leukocyte in humans bearing an enormous, yet largely unexplored therapeutic potential. Scientists have very recently increased their efforts to study and understand these cells which contribute to various types of inflammatory diseases and cancer. The mechanisms that regulate neutrophil recruitment to inflamed tissues and neutrophil cytotoxic activities against host tissues and pathogens require more attention. The reactive oxygen species (ROS) are a popular source of cellular stress and organ injury, and are critically expressed by neutrophils. By combating pathogens using molecular combat factors such as neutrophil extracellular traps (NETs), these are immobilized and killed i.e., by ROS. NETs and ROS are essential for the immune defense, but upon excessive activation, may also harm healthy tissue. Thus, exploring new routes for modulating their migration and activation is highly desired for creating novel anti-inflammatory treatment options. Leukocyte transmigration represents a key process for inflammatory cell infiltration to injury sites. In this review, we briefly summarize the differentiation and roles of neutrophils, with a spotlight on intravital imaging. We further discuss the potential of nanomedicines, i.e., selectin mimetics to target cell migration and influence liver disease outcome in animal models. Novel perspectives further arise from formulations of the wide array of options of small non-coding RNA such as small interfering RNA (siRNA) and micro-RNA (miR) which exhibit enzymatic functions: while siRNA binds and degrades a single mRNA based on full complementarity of binding, miR can up and down-regulate multiple targets in gene transcription and translation, mediated by partial complementarity of binding. Notably, miR is known to regulate at least 60% of the protein-coding genes and thus includes a potent strategy for a large number of targets in neutrophils. Nanomedicines can combine properties of different drugs in a single formulation, i.e., combining surface functionalization with ligands and drug delivery. Inevitably, nanomedicines accumulate in other phagocytes, a fact that should be controlled for every novel formulation to restrain activation of macrophages or modifications of the immunological synapse. Controlled drug release enabled by nanotechnological delivery systems may advance the options of modulating neutrophil activation and migration.

The Role of Myeloid-Derived Cells in the Progression of Liver Disease

Control of homeostasis and rapid response to tissue damage in the liver is orchestrated by crosstalk between resident and infiltrating inflammatory cells. A crucial role for myeloid cells during hepatic injury and repair has emerged where resident Kupffer cells, circulating monocytes, macrophages, dendritic cells and neutrophils control local tissue inflammation and regenerative function to maintain tissue architecture. Studies in humans and rodents have revealed a heterogeneous population of myeloid cells that respond to the local environment by either promoting regeneration or driving the inflammatory processes that can lead to hepatitis, fibrogenesis, and the development of cirrhosis and malignancy. Such plasticity of myeloid cell responses presents unique challenges for therapeutic intervention strategies and a greater understanding of the underlying mechanisms is needed. Here we review the role of myeloid cells in the establishment and progression of liver disease and highlight key pathways that have become the focus for current and future therapeutic strategies.

Baishouwu Extract Suppresses the Development of Hepatocellular Carcinoma via TLR4/MyD88/NF-κB Pathway

Purpose: The root of Cynanchum auriculatum Royle ex Wight, known as Baishouwu, has been widely used for a tonic supplement since ancient times. The current study was performed to explore the effect of Baishouwu extract on the development of experimental hepatocellular carcinoma (HCC) and the potential mechanism involved.

Methods: Rats were injected diethylnitrosamine (DEN) to initiate the multistep hepatocarcinogenesis. Animals were treated concurrently with Baishouwu extract given daily by oral gavage for 20 weeks to evaluate its protective effects. Time series sera and organ samples from each group were collected to evaluate the effect of Baishouwu extract on hepatic carcinogenesis.

Results: It was found that Baishouwu extract pretreatment successfully attenuated liver injury induced by DEN, as shown by decreased levels of serum biochemical indicators (AST, ALT, ALP, TP, and T-BIL). Administration of Baishouwu extract inhibited the fibrosis-related index in serum and live tissue, respectively from inflammation stage to HCC stage after DEN treatment. It significantly reduced the incidence and multiplicity of DEN-induced HCC development in a dose-dependent manner. Macroscopic and microscopic features suggested that pretreatment with Baishouwu extract for 20 weeks was effective in inhibiting DEN-induced inflammation, liver fibrosis, and HCC. Furthermore, TLR4 overexpression induced by DEN was decreased by Baishouwu extract, leading to the markedly down-regulated levels of MyD88, TRAF6, NF-κB p65, TGF-β1 and α-SMA in hepatitis, cirrhosis, and hepatocarcinoma.

Conclusion: In conclusion, Baishouwu extract exhibited potent effect on the development of HCC by altering TLR4/MyD88/ NF-κB signaling pathway in the sequence of hepatic inflammation-fibrosis-cancer, which provided novel insights into the mechanism of Baishouwu extract as a candidate for the pretreatment of HCC in the future.

Intravascular heavy chain-modification of hyaluronan during endotoxic shock

During inflammation, the covalent linking of the ubiquitous extracellular polysaccharide hyaluronan (HA) with the heavy chains (HC) of the serum protein inter alpha inhibitor (IαI) is exclusively mediated by the enzyme tumor necrosis factor α (TNFα)-stimulated-gene-6 (TSG-6). While significant advances have been made regarding how HC-modified HA (HC-HA) is an important regulator of inflammation, it remains unclear why HC-HA plays a critical role in promoting survival in intraperitoneal lipopolysaccharide (LPS)-induced endotoxemia while exerting only a modest role in the outcomes following intratracheal exposure to LPS. To address this gap, the two models of intraperitoneal LPS-induced endotoxic shock and intratracheal LPS-induced acute lung injury were directly compared in TSG-6 knockout mice and littermate controls. HC-HA formation, endogenous TSG-6 activity, and inflammatory markers were assessed in plasma and lung tissue. TSG-6 knockout mice exhibited accelerated mortality during endotoxic shock. While both intraperitoneal and intratracheal LPS induced HC-HA formation in lung parenchyma, only systemically-induced endotoxemia increased plasma TSG-6 levels and intravascular HC-HA formation. Cultured human lung microvascular endothelial cells secreted TSG-6 in response to both TNFα and IL1β stimulation, indicating that, in addition to inflammatory cells, the endothelium may secrete TSG-6 into circulation during systemic inflammation. These data show for the first time that LPS-induced systemic inflammation is uniquely characterized by significant vascular induction of TSG-6 and HC-HA, which may contribute to improved outcomes of endotoxemia.

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HC-HA deficiency accelerated mortality after IP LPS, but only modestly affected IT LPS outcomes.

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Both intratracheal (IT) and intraperitoneal (IP) LPS triggered lung HC-HA formation.

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IP LPS, but not IT LPS instillation induced intravascular TSG-6 and HC-HA.

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Intravascular HC-HA formation may be protective against LPS-induced injury.

Effects of different periods of gastric ischemia on liver as a remote organ1

PURPOSE

To evaluate the hepatic changes associated with gastric ischemia.

METHODS

Thirty male rabbits were studied, distributed in 3 groups (n=10). Group 1: ligature and section of the gastric vasculature and removal of the liver after three hours; Group 2: ligature and section of the gastric vasculature and removal of the liver after 6 hours; Group 3: ligature and section of the gastric vasculature and removal of the liver after 12 hours. Blood samples were collected immediately before surgery and after the determined time of ischemia in each group to evaluate the hepatic function. After the death of the rabbits, the liver was removed for macro and microscopic study.

RESULTS

An increase in aminotransferases and bilirubin occurred in groups 2 and 3. Total protein and albumin diminished in all of the animals. All of the rabbits from groups 2 and 3 presented hepatocellular necrosis.

CONCLUSION

The devascularization of the stomach for a period of above three hours is associated with hepatic morphological and functional disorders.

Organ-Specific Mechanisms of Transendothelial Neutrophil Migration in the Lung, Liver, Kidney, and Aorta

Immune responses are dependent on the recruitment of leukocytes to the site of inflammation. The classical leukocyte recruitment cascade, consisting of capture, rolling, arrest, adhesion, crawling, and transendothelial migration, is thoroughly studied but mostly in model systems, such as the cremasteric microcirculation. This cascade paradigm, which is widely accepted, might be applicable to many tissues, however recruitment mechanisms might substantially vary in different organs. Over the last decade, several studies shed light on organ-specific mechanisms of leukocyte recruitment. An improved awareness of this matter opens new therapeutic windows and allows targeting inflammation in a tissue-specific manner. The aim of this review is to summarize the current understanding of the leukocyte recruitment in general and how this varies in different organs. In particular we focus on neutrophils, as these are the first circulating leukocytes to reach the site of inflammation. Specifically, the recruitment mechanism in large arteries, as well as vessels in the lungs, liver, and kidney will be addressed.

Coagulation, Microenvironment and Liver Fibrosis

Fibrosis is the main consequence of any kind of chronic liver damage. Coagulation and thrombin generation are crucial in the physiological response to tissue injury; however, the inappropriate and uncontrolled activation of coagulation cascade may lead to fibrosis development due to the involvement of several cellular types and biochemical pathways in response to thrombin generation. In the liver, hepatic stellate cells and sinusoidal endothelial cells orchestrate fibrogenic response to chronic damage. Thrombin interacts with these cytotypes mainly through protease-activated receptors (PARs), which are expressed by endothelium, platelets and hepatic stellate cells. This review focuses on the impact of coagulation in liver fibrogenesis, describes receptors and pathways involved and explores the potential antifibrotic properties of drugs active in hemostasis in studies with cells, animal models of liver damage and humans.

Rapid clearance of heavy chain-modified hyaluronan during resolving acute lung injury

BACKGROUND

Several inflammatory lung diseases display abundant presence of hyaluronic acid (HA) bound to heavy chains (HC) of serum protein inter-alpha-inhibitor (IαI) in the extracellular matrix. The HC-HA modification is critical to neutrophil sequestration in liver sinusoids and to survival during experimental lipopolysaccharide (LPS)-induced sepsis. Therefore, the covalent HC-HA binding, which is exclusively mediated by tumor necrosis factor α (TNFα)-stimulated-gene-6 (TSG-6), may play an important role in the onset or the resolution of lung inflammation in acute lung injury (ALI) induced by respiratory infection.

METHODS

Reversible ALI was induced by a single intratracheal instillation of LPS or Pseudomonas aeruginosa in mice and outcomes were studied for up to six days. We measured in the lung or the bronchoalveolar fluid HC-HA formation, HA immunostaining localization and roughness, HA fragment abundance, and markers of lung inflammation and lung injury. We also assessed TSG-6 secretion by TNFα- or LPS-stimulated human alveolar macrophages, lung fibroblast Wi38, and bronchial epithelial BEAS-2B cells.

RESULTS

Extensive HC-modification of lung HA, localized predominantly in the peri-broncho-vascular extracellular matrix, was notable early during the onset of inflammation and was markedly decreased during its resolution. Whereas human alveolar macrophages secreted functional TSG-6 following both TNFα and LPS stimulation, fibroblasts and bronchial epithelial cells responded to only TNFα. Compared to wild type, TSG-6-KO mice, which lacked HC-modified HA, exhibited modest increases in inflammatory cells in the lung, but no significant differences in markers of lung inflammation or injury, including histopathological lung injury scores.

CONCLUSIONS

Respiratory infection induces rapid HC modification of HA followed by fragmentation and clearance, with kinetics that parallel the onset and resolution phase of ALI, respectively. Alveolar macrophages may be an important source of pulmonary TSG-6 required for HA remodeling. The formation of HC-modified HA had a minor role in the onset, severity, or resolution of experimental reversible ALI induced by respiratory infection with gram-negative bacteria.

Methicillin-resistant Staphylococcus aureus bacteremia among liver transplant recipients: epidemiology and associated risk factors for morbidity and mortality

Bacteremia due to Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), complicates the clinical course of liver transplantation and is associated with high morbidity and mortality. Intravascular catheters had been reported to be the most frequent source of MRSA bacteremia. Among bacteremic liver recipients, 26.3%-100% of S. aureus were MRSA. Previous studies identified pre-transplant and post-transplant acquired S. aureus carriage, greater severity of liver disease, hepatocellular carcinoma and infection with immuno-modulatory viruses as predictors of S. aureus bacteremia in liver recipients. MRSA bacteremia accompanied by pneumonia and abdominal infections was related to mortality. Vancomycin, as well as daptomycin, is a first-line antibiotic for MRSA bacteremia. The purpose of this review is to better understand the characteristics of MRSA bacteremia by summarizing the epidemiology and antimicrobial resistance of S. aureus, the primary source, and related risk factors for morbidity and mortality of MRSA bacteremia. We have also explored the diagnostic, therapeutic and preventive measures for MRSA bacteremia to improve the outcomes of liver recipients.

Neutrophils and neutrophil extracellular traps in the liver and gastrointestinal system

Neutrophil extracellular traps (NETs) have an important role during infection by helping neutrophils to capture and kill pathogens. However, evidence is accumulating that uncontrolled or excessive production of NETs is related to the exacerbation of inflammation and the development of autoimmunity, cancer metastasis and inappropriate thrombosis. In this Review, we focus on the role of NETs in the liver and gastrointestinal system, outlining their protective and pathological effects. The latest mechanistic insights in NET formation, interactions between microorganisms and NETs and the relationship between neutrophil subtypes and their functions are also discussed. Additionally, we describe the potential importance of NET-related molecules, including cell-free DNA and hypercitrullinated histones, as biomarkers and targets for therapeutic intervention in gastrointestinal diseases.

Kukoamine B promotes TLR4-independent lipopolysaccharide uptake in murine hepatocytes

Free bacterial lipopolysaccharide (LPS) is generally removed from the bloodstream through hepatic uptake via TLR4, the LPS pattern recognition receptor, but mechanisms for internalization and clearance of conjugated LPS are less clear. Kukoamine B (KB) is a novel cationic alkaloid that interferes with LPS binding to TLR4. In this study, KB accelerated blood clearance of LPS. KB also enhanced LPS distribution in the hepatic tissues of C57 BL/6 mice, along with LPS uptake in primary hepatocytes and HepG2 cells. By contrast, KB inhibited LPS internalization in Kupffer and RAW 264.7 cells. Loss of TLR4 did not affect LPS uptake into KB-treated hepatocytes. We also detected selective upregulation of the asialoglycoprotein receptor (ASGPR) upon KB treatment, and ASGPR colocalized with KB in cultured hepatocytes. Molecular docking showed that KB bound to ASGPR in a manner similar to GalNAc, a known ASGPR agonist. GalNAc dose-dependently reduced KB internalization, suggesting it competes with KB for ASGPR binding, and ASGPR knockdown also impaired LPS uptake into hepatocytes. Finally, while KB enhanced LPS uptake, it was protective against LPS-induced inflammation and hepatocyte injury. Our study provides a new mechanism for conjugated LPS hepatic uptake induced by the LPS neutralizer KB and mediated by membrane ASGPR binding.

Delayed liver regeneration in C3H/HeJ mice: possible involvement of haemodynamic and structural changes in the hepatic microcirculation

NEW FINDINGS

What is the central question of this study? The liver regenerative process is complex and involves a sequence of signalling events, but the possible involvement of structural and haemodynamic changes in vivo during this process has never been explored. What is the main finding and its importance? Normal sinusoidal blood flow and velocity are crucial for a normal regenerative response, and delays in these haemodynamic events resulted in impaired liver regeneration in lipopolysaccharide-insensitive, C3H/HeJ mice. Toll-like receptor 4 signalling is required for restoration of normal liver architecture during the liver regenerative process. Liver regeneration is delayed in mice with a defective Toll-like receptor 4 (TLR4; C3H/HeJ mice) but is normal in TLR4 knockouts (TLR4^-/- ). Here, we investigated the possible involvement of structural and haemodynamic changes in vivo in the underlying mechanism. In lipopolysaccharide-sensitive (C3H/HeN and C57BL/6) and lipopolysaccharide-insensitive (C3H/HeJ and TLR4^-/- ) mice, a 70% partial hepatectomy (PH) was performed under inhalational anaesthesia. At days 3 and 7 after PH, the hepatic microcirculation was interrogated using intravital microscopy. Delayed liver regeneration was confirmed in C3H/HeJ, but not in C3H/HeN, C57BL/6 (WT) or TLR4^-/- mice by liver weight-to-body-weight ratio, the percentage of proliferating cell nuclear antigen (PCNA)-positive cells and mitotic index data. At day 3 after PH, sinusoidal red blood cell velocity increased by 100% in C3H/HeN mice, but by only 40% in C3H/HeJ mice. Estimated sinusoidal blood flow was significantly higher at day 7 after PH in C3H/HeN than in C3H/HeJ mice. The hepatic cord width was significantly larger in C3H/HeN than in C3H/HeJ mice at day 3 and it was significantly larger in TLR4^-/- than in C57BL/6 WT mice at day 7 after PH. Hepatocyte nucleus density and functional sinusoidal density was significantly reduced at days 3 and 7 after PH in all mouse strains compared with their zero-time controls. Functional sinusoidal density was significantly lower in C3H/HeJ compared with C3H/HeN mice at day 7 after PH. The present study indicates that altered sinusoidal blood flow and velocity in C3H/HeJ mice may contribute to the observed delay in the regenerative response in these mice. In addition, restoration of normal liver architecture may be delayed in TLR4^-/- mice.

Neutrophil biology within hepatic environment

Neutrophils are the most abundant leukocyte in the human circulation. These short-lived cells are constantly produced from hematopoietic stem cells (HSC) within the bone marrow from which they daily reach the blood and perform major roles in innate immunity. Neutrophils are the first cells to reach inflamed tissues and are armed with a plethora of enzymes that help both with their trafficking within tissues and the killing of pathogens. Damaged or infected organs are rapidly invaded by neutrophils. Their erroneous activation within parenchyma or the vasculature is involved in the pathogenesis of several inflammatory diseases including arthritis, colitis, sepsis, acute lung injury and liver failure. Despite the proposal of a canonical pathway that governs neutrophil migration into tissues, the liver has been extensively described as a unique environment for leukocyte recruitment. Since the control of inflammatory responses is considered one of the most promising avenues for novel therapeutics, the expansion of our understanding of the mechanisms behind neutrophil accumulation within injured liver might add to the development of specific and more efficacious treatments. In this review, we discuss the basic concepts of neutrophil ontogeny and biology, with a focus on the particularities and the molecular steps involved in neutrophil recruitment to the liver.

Screening Assays to Characterize Novel Endothelial Regulators Involved in the Inflammatory Response

The endothelial layer is essential for maintaining homeostasis in the body by controlling many different functions. Regulation of the inflammatory response by the endothelial layer is crucial to efficiently fight against harmful inputs and aid in the recovery of damaged areas. When the endothelial cells are exposed to an inflammatory environment, such as the outer component of gram-negative bacteria membrane, lipopolysaccharide (LPS), they express soluble pro-inflammatory cytokines, such as Ccl5, Cxcl1 and Cxcl10, and trigger the activation of circulating leukocytes. In addition, the expression of adhesion molecules E-selectin, VCAM-1 and ICAM-1 on the endothelial surface enables the interaction and adhesion of the activated leukocytes to the endothelial layer, and eventually the extravasation towards the inflamed tissue. In this scenario, the endothelial function must be tightly regulated because excessive or defective activation in the leukocyte recruitment could lead to inflammatory-related disorders. Since many of these disorders do not have an effective treatment, novel strategies with a focus on the vascular layer must be investigated. We propose comprehensive assays that are useful to the search of novel endothelial regulators that modify leukocyte function. We analyze endothelial activation by using specific expression targets involved in leukocyte recruitment (such as, cytokines, chemokines, and adhesion molecules) with several techniques, including: real-time quantitative polymerase chain reaction (RT-qPCR), western-blot, flow cytometry and adhesion assays. These approaches determine endothelial function in the inflammatory context and are very useful to perform screening assays to characterize novel endothelial inflammatory regulators that are potentially valuable for designing new therapeutic strategies.

Taurine alleviates lipopolysaccharide‑induced liver injury by anti‑inflammation and antioxidants in rats

The aim of the present study was to investigate the protective effect of taurine on lipopolysaccharide (LPS)-induced liver injury and its mechanisms. Male rats were randomly divided into three groups: Normal saline, LPS model and taurine treatment. Experimental animals were treated with saline or taurine (dissolved in saline, 200 mg/kg/day) via intravenous injection. After 2 h, saline or LPS (0.5 mg/kg) was administrated via intraperitoneal injection. Markers of liver injury, pro-inflammatory cytokines and superoxide dismutase (SOD) activity were determined in plasma. Liver tissues were removed for morphological analysis and determination by western blot analysis. Taurine significantly reduced the elevation in the levels of LPS-induced aspartate transaminase and alanine transaminase and decreased the concentrations of LPS-induced inflammatory factors including tumor necrosis factor-α and interleukin-6. Taurine also increased the activity of SOD in serum and the expression of heme oxygenase-1 protein in liver tissue. Taurine pretreatment also reduced the elevated expression levels of LPS-induced cyclooxygenase-2, nuclear factor κB and extracellular regulated protein kinase. The results from the present study demonstrated that taurine alleviates LPS-induced liver injury. The beneficial role of taurine may be associated with its reduction of pro-inflammatory response and oxidative stress.

Intravital Imaging of Myeloid Cells: Inflammatory Migration and Resident Patrolling

Myeloid cell recruitment to sites of infection and injury started out as a simple model that has been referred to as the universal concept of leukocyte recruitment. However, as we gain more insight into the different mechanisms, it is becoming clear that each organ and perhaps even each cell has its own unique mechanism of recruitment. Moreover, as the ability to visualize specific cell types in specific organs becomes more accessible, it is also becoming clear that there are resident populations of leukocytes, some within the tissues and others attached to the vasculature of tissues, the latter poised to affect the local environment. In this review, we will first highlight the imaging approaches that have allowed us to gain spectacular insight into locale and function of specific cell types, and then we will discuss what we have learned from this approach as far as myeloid cells are concerned. We will also highlight some of the gaps in our knowledge, which exist almost certainly because of the challenges of being able to visualize certain compartments of the body.

Deep insight into neutrophil trafficking in various organs

Neutrophils are professional phagocytes that constitute the first line of defense in humans. The primary function of neutrophils is to eliminate invading pathogens through oxidative and nonoxidative mechanisms. Because neutrophils rapidly migrate into inflammatory foci via diapedesis and chemotaxis, neutrophil recruitment has long been considered a hallmark of inflammation. Recent advances in intravital microscopic technologies using animal model systems have enabled researchers to directly visualize neutrophil trafficking. Consequently, the specific mechanisms of neutrophil transmigration have been identified, and even the reverse migration of neutrophils can be verified visually. Moreover, the detailed phenomena of neutrophil infiltration into various organs, such as the liver, lymphoid organs, and CNS have been identified. This progress in the study of neutrophil migration from the blood vessels to organs results in a deeper understanding of these immune cells' motility and morphology, which are closely related to the spatiotemporal regulation of the overall immune response. In this review, we discuss our current understanding of neutrophil trafficking in various organs.

Neutrophils Play a Crucial Role in the Early Stage of Nonalcoholic Steatohepatitis via Neutrophil Elastase in Mice

Neutrophils infiltration in liver is one of the typical histological characteristics of nonalcoholic steatohepatitis (NASH) in both animal models and human subjects. This study was aimed to investigate the role of neutrophils in the process of NASH and its underling mechanisms. C57BL/6J mice were fed with either standard chow (SC) or methionine/choline-deficient (MCD) diet for 1, 2, 4, 8 weeks, respectively. C57BL/6J APOE(-/-) mice were fed with SC or high-fat high-cholesterol (HFHC) diet. Anti-Ly6G antibody was employed to deplete neutrophils and sivelestat was used to inhibit neutrophil elastase (NE). MCD-diet-receiving mice with neutrophil depletion had much lower serum ALT activity, liver inflammation, and mRNA levels of proinflammatory genes in the early stage of NASH (1 and 2 weeks) when compared to non-neutrophil-depleted mice. NE inhibitor sivelestat could recapitulate the effects of neutrophil depletion in APOE(-/-) mice fed with HFHC diet. As the disease progressed (4 and 8 weeks), neutrophil depletion did not lower serum ALT levels and liver lesions due to activation of Kupffer cells. Finally, we found neutrophils also affected anti-inflammation cytokine interleukin-1 receptor antagonist mRNA expression. Neutrophils play a crucial role in the early stage of NASH via NE.

Blood-borne phagocytes internalize urate microaggregates and prevent intravascular NETosis by urate crystals

Hyperuricemia is strongly linked to cardiovascular complications including atherosclerosis and thrombosis. In individuals with hyperuricemia, needle-shaped monosodium urate crystals (nsMSU) frequently form within joints or urine, giving rise to gouty arthritis or renal calculi, respectively. These nsMSU are potent instigators of neutrophil extracellular trap (NET) formation. Little is known on the mechanism(s) that prevent nsMSU formation within hyperuricemic blood, which would potentially cause detrimental consequences for the host. Here, we report that complement proteins and fetuins facilitate the continuous clearance by blood-borne phagocytes and resident macrophages of small urate microaggregates (UMA; <1 μm in size) that initially form in hyperuricemic blood. If this clearance fails, UMA exhibit bipolar growth to form typical full-sized nsMSU with a size up to 100 μm. In contrast to UMA, nsMSU stimulated neutrophils to release NETs. Under conditions of flow, nsMSU and NETs formed densely packed DNase I-resistant tophus-like structures with a high obstructive potential, highlighting the importance of an adequate and rapid removal of UMA from the circulation. Under pathological conditions, intravascularly formed nsMSU may hold the key to the incompletely understood association between NET-driven cardiovascular disease and hyperuricemia.

Angiocrine signaling in the hepatic sinusoids in health and disease

The capillary network irrigating the liver is important not only for nutrient and oxygen delivery, but also for the signals distributed to other hepatic cell types necessary to maintain liver homeostasis. During development, endothelial cells are a key component in liver zonation. In adulthood, they maintain hepatic stellate cells and hepatocytes in quiescence. Their importance in pathobiology is highlighted in liver regeneration and chronic liver diseases, where they coordinate paracrine cell behavior. During regeneration, liver sinusoidal endothelial cells induce hepatocyte proliferation and angiogenesis. During fibrogenesis, they undergo morphological and functional changes, which are reflected by their role in hepatic stellate cell activation, inflammation, and distorted sinusoidal structure. Therapeutic strategies to target angiocrine signaling are in progress but are in the early stages. Here, we offer a short synthesis of recent studies on angiocrine signaling in liver homeostasis, regeneration, and fibrogenesis.

Pathogenesis of Kupffer Cells in Cholestatic Liver Injury

Kupffer cells are the resident macrophages in the liver. They are located in hepatic sinusoid, which allows them to remove foreign materials, pathogens, and apoptotic cells efficiently. Activated Kupffer cells secrete various mediators, including cytokines and chemokines, to initiate immune responses, inflammation, or recruitment of other liver cells. Bile duct ligation (BDL) surgery in rodents is often studied as an animal model of cholestatic liver disease, characterized by obstruction of bile flow. BDL mice show altered functional activities of Kupffer cells compared with sham-operated mice, including elevated cytokine secretion and impaired bacterial clearance. Various mediators produced by other liver cells can regulate Kupffer cell activation, which suggest that Kupffer cells orchestrate with other liver cells to relay inflammatory signals and to maintain liver homeostasis during BDL-induced liver injury. Blocking or depletion of Kupffer cells, an approach for the treatment of liver diseases, has shown controversial implications. Procedures in Kupffer cell research have limitations and may produce various results in Kupffer cell research. It is important, however, to reveal underlying mechanisms of activation and functions of Kupffer cells, followed by hepatic inflammation and fibrosis. This review summarizes present Kupffer cell studies in cholestatic liver injury.

Modulation of liver tolerance by conventional and nonconventional antigen-presenting cells and regulatory immune cells

The liver is a tolerogenic organ with exquisite mechanisms of immune regulation that ensure upkeep of local and systemic immune tolerance to self and foreign antigens, but that is also able to mount effective immune responses against pathogens. The immune privilege of liver allografts was recognized first in pigs in spite of major histo-compatibility complex mismatch, and termed the "liver tolerance effect". Furthermore, liver transplants are spontaneously accepted with only low-dose immunosuppression, and induce tolerance for non-hepatic co-transplanted allografts of the same donor. Although this immunotolerogenic environment is favorable in the setting of organ transplantation, it is detrimental in chronic infectious liver diseases like hepatitis B or C, malaria, schistosomiasis or tumorigenesis, leading to pathogen persistence and weak anti-tumor effects. The liver is a primary site of T-cell activation, but it elicits poor or incomplete activation of T cells, leading to their abortive activation, exhaustion, suppression of their effector function and early death. This is exploited by pathogens and can impair pathogen control and clearance or allow tumor growth. Hepatic priming of T cells is mediated by a number of local conventional and nonconventional antigen-presenting cells (APCs), which promote tolerance by immune deviation, induction of T-cell anergy or apoptosis, and generating and expanding regulatory T cells. This review will focus on the communication between classical and nonclassical APCs and lymphocytes in the liver in tolerance induction and will discuss recent insights into the role of innate lymphocytes in this process.

Synergistic Action of Staphylococcus aureus α-Toxin on Platelets and Myeloid Lineage Cells Contributes to Lethal Sepsis

Multi-organ failure contributes to mortality in bacterial sepsis. Platelet and immune cell activation contribute to organ injury during sepsis, but the mechanisms by which bacterial virulence factors initiate these responses remain poorly defined. We demonstrate that during lethal sepsis, Staphylococcus aureus α-toxin simultaneously alters platelet activation and promotes neutrophil inflammatory signaling through interactions with its cellular receptor ADAM10. Platelet intoxication prevents endothelial barrier repair and facilitates formation of injurious platelet-neutrophil aggregates, contributing to lung and liver injury that is mitigated by ADAM10 deletion on platelets and myeloid lineage cells. While platelet- or myeloid-specific ADAM10 knockout does not alter sepsis mortality, double-knockout animals are highly protected. These results define a pathway by which a single bacterial toxin utilizes a widely expressed receptor to coordinate progressive, multi-organ disease in lethal sepsis. As an expression-enhancing ADAM10 polymorphism confers susceptibility to severe human sepsis, these studies highlight the importance of understanding molecular host-microbe interactions.

Significance of expression of mannose receptor in hepatocellular carcinoma

AIM: To detect the expression of mannose receptor (MR) in hepatocellular carcinoma tissues and hepatocellular carcinoma cell lines, and to analyze the relationship between MR expression and the occurrence, development and malignancy of hepatocellular carcinoma.

METHODS: Immunohistochemical method was used to detect the expression of MR in 50 hepatocellular carcinoma tissues, matched tumor adjacent tissues and 10 normal liver tissues. Immunofluorescence and Western blot were used to assay the expression of MR in hepatocellular carcinoma cell lines and a normal liver cell line.

RESULTS: By immunohistochemistry, it was found that MR expression was significantly higher in hepatocellular carcinoma tissues than in tumor adjacent tissues (86% vs 76%, P < 0.05) and normal liver tissues (86% vs 30%, P < 0.01). Immunofluorescence showed that MR was highly expressed in hepatocellular carcinoma cell lines BEL-7402 and HepG2, but lowly expressed in the human liver cell line HL-7702. Western blot analysis indicated that MR expression was significantly higher in BEL-7402 cells than in HepG2 cells (P < 0.01) and HL-7702 cells (P < 0.01).

CONCLUSION: MR is highly expressed in hepatocellular carcinoma tissues and hepatocellular carcinoma cell lines, and the expression of MR is significantly associated with the occurrence, development and malignancy of hepatocellular carcinoma.

Chilean Strawberry Consumption Protects against LPS-Induced Liver Injury by Anti-Inflammatory and Antioxidant Capability in Sprague-Dawley Rats

The Chilean strawberry fruit has high content of antioxidants and polyphenols. Previous studies evidenced antioxidant properties by in vitro methods. However, the antioxidant effect and its impact as functional food on animal health have not been evaluated. In this study, rats were fed with a Chilean strawberry aqueous extract (4 g/kg of animal per day) and then subjected to LPS-induced liver injury (5 mg/kg). Transaminases and histological studies revealed a reduction in liver injury in rats fed with strawberry aqueous extract compared with the control group. Additionally, white strawberry supplementation significantly reduced the serum levels and gene expression of TNF-α, IL-6, and IL-1β cytokines compared with nonsupplemented rats. The level of F2-isoprostanes and GSH/GSSG indicated a reduction in liver oxidative stress by the consumption of strawberry aqueous extract. Altogether, the evidence suggests that dietary supplementation of rats with a Chilean white strawberry aqueous extract favours the normalization of oxidative and inflammatory responses after a liver injury induced by LPS.

Acute and temporal expression of tumor necrosis factor (TNF)-α-stimulated gene 6 product, TSG6, in mesenchymal stem cells creates microenvironments required for their successful transplantation into muscle tissue

Previously, we demonstrated that when mesenchymal stem cells (MSCs) from mouse ES cells were transplanted into skeletal muscle, more than 60% of them differentiated into muscles in the crush-injured tibialis anterior muscle in vivo, although MSCs neither differentiated nor settled in the intact muscle. Microenvironments, including the extracellular matrix between the injured and intact muscle, were quite different. In the injured muscle, hyaluronan (HA), heavy chains of inter-α-inhibitor (IαI), CD44, and TNF-α-stimulated gene 6 product (TSG-6) increased 24-48 h after injury, although basement membrane components of differentiated muscle such as perlecan, laminin, and type IV collagen increased gradually 4 days after the crush. We then investigated the microenvironments crucial for cell transplantation, using the lysate of C2C12 myotubules for mimicking injured circumstances in vivo. MSCs settled in the intact muscle when they were transplanted together with the C2C12 lysate or TSG6. MSCs produced and released TSG6 when they were cultured with C2C12 lysates in vitro. MSCs pretreated with the lysate also settled in the intact muscle. Furthermore, MSCs whose TSG6 was knocked down by shRNA, even if transplanted or pretreated with the lysate, could not settle in the muscle. Immunofluorescent staining showed that HA and IαI always co-localized or were distributed closely, suggesting formation of covalent complexes, i.e. the SHAP-HA complex in the presence of TSG6. Thus, TSG6, HA, and IαI were crucial factors for the settlement and probably the subsequent differentiation of MSCs.

Role of Kupffer cells in hepatitis B/C viral hepatitis

Kupffer cells (KCs) are the largest group of tissue macrophages. KCs in the hepatic sinusoid contact with pathogens from circulation earliest. The quantity of KCs increases significantly in patients with viral hepatitis, suggesting that KCs play an important role in viral hepatitis related immunity. KCs can not only engulf virus particles, but also present antigens, secrete cytokines, and participate in a variety of inflammatory responses, immune tolerance and liver injury. In hepatitis B virus (HBV)/hepatitis C virus (HCV) infections, the diversity of KCs-related cytokines, the complexity of interactions of receptor signaling pathways as well as the duality of cytotoxic effect, indicate that KCs play a dual role in the immune response; the activation of KCs regulates the balance of inflammatory and anti-inflammatory mechanisms in viral hepatitis.

The where, when, how, and why of hyaluronan binding by immune cells

Hyaluronan is made and extruded from cells to form a pericellular or extracellular matrix (ECM) and is present in virtually all tissues in the body. The size and form of hyaluronan present in tissues are indicative of a healthy or inflamed tissue, and the interactions of hyaluronan with immune cells can influence their response. Thus, in order to understand how inflammation is regulated, it is necessary to understand these interactions and their consequences. Although there is a large turnover of hyaluronan in our bodies, the large molecular mass form of hyaluronan predominates in healthy tissues. Upon tissue damage and/or infection, the ECM and hyaluronan are broken down and an inflammatory response ensues. As inflammation is resolved, the ECM is restored, and high molecular mass hyaluronan predominates again. Immune cells encounter hyaluronan in the tissues and lymphoid organs and respond differently to high and low molecular mass forms. Immune cells differ in their ability to bind hyaluronan and this can vary with the cell type and their activation state. For example, peritoneal macrophages do not bind soluble hyaluronan but can be induced to bind after exposure to inflammatory stimuli. Likewise, naïve T cells, which typically express low levels of the hyaluronan receptor, CD44, do not bind hyaluronan until they undergo antigen-stimulated T cell proliferation and upregulate CD44. Despite substantial knowledge of where and when immune cells bind hyaluronan, why immune cells bind hyaluronan remains a major outstanding question. Here, we review what is currently known about the interactions of hyaluronan with immune cells in both healthy and inflamed tissues and discuss how hyaluronan binding by immune cells influences the inflammatory response.

Lipopolysaccharide-induced inflammatory liver injury in mice

The intraperitoneal application of lipopolysaccharide (LPS) alone or in combination with other hepatotoxins is an experimental model for inducing systemic and hepatic inflammation in rodents applied worldwide. The endotoxin is recognized by the LPS-binding protein. This complex binds together with the lymphocyte antigen 96 (MD2) and the pattern-recognition receptor CD14 to members of the toll-like receptor family. The activated receptor complex in turn transduces signals to well characterized intracellular cascades that result in a multifaceted network of intracellular responses ending in inflammation. The most prominent among these is the activation of the NF-κB pathway and the production of a multitude of inflammatory cytokines. Although the application of LPS is in general easy to perform, unintended variations in preparation of the injection solution or in handling of the animals might affect the reproducibility or the outcome of a specific experiment. Here, we present a well-standardized protocol that allows for an induction of highly reproducible acute hepatic inflammation in mice. Furthermore, examples of appropriate readouts for the resulting inflammatory response are given.

Chronic alcohol consumption potentiates the development of diabetes through pancreatic β-cell dysfunction

Chronic ethanol consumption is well established as a major risk factor for type-2 diabetes (T2D), which is evidenced by impaired glucose metabolism and insulin resistance. However, the relationships between alcohol consumption and the development of T2D remain controversial. In particular, the direct effects of ethanol consumption on proliferation of pancreatic β-cell and the exact mechanisms associated with ethanol-mediated β-cell dysfunction and apoptosis remain elusive. Although alcoholism and alcohol consumption are prevalent and represent crucial public health problems worldwide, many people believe that low-to-moderate ethanol consumption may protect against T2D and cardiovascular diseases. However, the J- or U-shaped curves obtained from cross-sectional and large prospective studies have not fully explained the relationship between alcohol consumption and T2D. This review provides evidence for the harmful effects of chronic ethanol consumption on the progressive development of T2D, particularly with respect to pancreatic β-cell mass and function in association with insulin synthesis and secretion. This review also discusses a conceptual framework for how ethanol-produced peroxynitrite contributes to pancreatic β-cell dysfunction and metabolic syndrome.

Interactions between CD44 and Hyaluronan in Leukocyte Trafficking

Recruitment of leukocytes from the bloodstream to inflamed tissues requires a carefully regulated cascade of binding interactions between adhesion molecules on leukocytes and endothelial cells. Adhesive interactions between CD44 and hyaluronan (HA) have been implicated in the regulation of immune cell trafficking within various tissues. In this review, the biology of CD44–HA interactions in cell trafficking is summarized, with special attention to neutrophil recruitment within the liver microcirculation. We describe the molecular mechanisms that regulate adhesion between neutrophil CD44 and endothelial HA, including recent evidence implicating serum-derived hyaluronan-associated protein as an important co-factor in the binding of HA to CD44 under flow conditions. CD44–HA-mediated neutrophil recruitment has been shown to contribute to innate immune responses to invading microbes, as well as to the pathogenesis of many inflammatory diseases, including various liver pathologies. As a result, blockade of neutrophil recruitment by targeting CD44–HA interactions has proven beneficial as an anti-inflammatory treatment strategy in a number of animal models of inflammatory diseases.