Paradoxical Role of Matrix Metalloproteinases in Liver Injury and Regeneration after Sterile Acute Hepatic Failure

Beyond host defense and tissue injury: the emerging role of neutrophils in tissue repair

Neutrophils, the most abundant immune cells in human blood, play a fundamental role in host defense against invading pathogens and tissue injury. Neutrophils carry potentially lethal weaponry to the affected site. Inadvertent and perpetual neutrophil activation could lead to nonresolving inflammation and tissue damage, a unifying mechanism of many common diseases. The prevailing view emphasizes the dichotomy of their function, host defense versus tissue damage. However, tissue injury may also persist during neutropenia, which is associated with disease severity and poor outcome. Numerous studies highlight neutrophil phenotypic heterogeneity and functional versatility, indicating that neutrophils play more complex roles than previously thought. Emerging evidence indicates that neutrophils actively orchestrate resolution of inflammation and tissue repair and facilitate return to homeostasis. Thus, neutrophils mobilize multiple mechanisms to limit the inflammatory reaction, assure debris removal, matrix remodeling, cytokine scavenging, macrophage reprogramming, and angiogenesis. In this review, we will summarize the homeostatic and tissue-reparative functions and mechanisms of neutrophils across organs. We will also discuss how the healing power of neutrophils might be harnessed to develop novel resolution and repair-promoting therapies while maintaining their defense functions.

Temporal analysis of paracetamol-induced hepatotoxicity

Paracetamol-induced hepatotoxicity (APAP) causes severe damage that may be irreversible. Understanding the evolution of liver injury caused by overdose of the drug is important to assist in the treatment. In the present study, we evaluated the acute intoxication by APAP (500 mg/kg) in periods of 3 and 12 hours in C57BL/6 mice through biochemical, histological, inflammatory parameters, and the redox status. The results showed that in the 3-hour period there was an increase in creatinine dosage and lipid peroxidation (TBARS) compared to the control group. In the period of 12 hours after APAP intoxication all parameters evaluated were altered; there was an increase of ALT, AST, and necrosis, besides the increase of redox status biomarkers as carbonylated protein, TBARS, and MMP-9. We also observed activation of the inflammasome pathway as well as a reduction in the regenerative capacity of hepatocytes with a decrease in binucleated liver cells. In cytochrome gene expression, the mRNA level increased in CYP2E1 isoenzyme and reduced CYP1A2 expression. This study indicated that early treatment is necessary to mitigate APAP-induced acute liver injury, and alternative therapies capable of controlling the progression of intoxication in the liver are needed.

Cathelicidin promotes liver repair after acetaminophen-induced liver injury in mice

Background & Aims

Acetaminophen (APAP)-induced acute liver injury (AILI) is a leading cause of acute liver failure (ALF). N-acetylcysteine (NAC) is only effective within 24 h after APAP intoxication, raising an urgent need for alternative approaches to treat this disease. This study aimed to test whether cathelicidin (Camp), which is a protective factor in chronic liver diseases, protects mice against APAP-induced liver injury and ALF.

Methods

A clinically relevant AILI model and an APAP-induced ALF model were generated in mice. Genetic and pharmacological approaches were used to interfere with the levels of cathelicidin in vivo.

Results

An increase in hepatic pro-CRAMP/CRAMP (the precursor and mature forms of mouse cathelicidin) was observed in APAP-intoxicated mice. Upregulated cathelicidin was derived from liver-infiltrating neutrophils. Compared with wild-type littermates, Camp knockout had no effect on hepatic injury but dampened hepatic repair in AILI and reduced survival in APAP-induced ALF. CRAMP administration reversed impaired liver recovery observed in APAP-challenged Camp knockout mice. Delayed CRAMP, CRAMP(1-39) (the extended form of CRAMP), or LL-37 (the mature form of human cathelicidin) treatment exhibited a therapeutic benefit for AILI. Co-treatment of cathelicidin and NAC in AILI displayed a stronger hepatoprotective effect than NAC alone. A similar additive effect of CRAMP(1-39)/LL-37 and NAC was observed in APAP-induced ALF. The pro-reparative role of cathelicidin in the APAP-damaged liver was attributed to an accelerated resolution of inflammation at the onset of liver repair, possibly through enhanced neutrophil phagocytosis of necrotic cell debris in an autocrine manner.

Conclusions

Cathelicidin reduces APAP-induced liver injury and ALF in mice by promoting liver recovery via facilitating inflammation resolution, suggesting a therapeutic potential for late-presenting patients with AILI with or without ALF.

Impact and implications

Acetaminophen-induced acute liver injury is a leading cause of acute liver failure. The efficacy of N-acetylcysteine, the only clinically approved drug against acetaminophen-induced acute liver injury, is significantly reduced for late-presenting patients. We found that cathelicidin exhibits a great therapeutic potential in mice with acetaminophen-induced liver injury or acute liver failure, which makes up for the limitation of N-acetylcysteine therapy by specifically promoting liver repair after acetaminophen intoxication. The pro-reparative role of cathelicidin, as a key effector molecule of neutrophils, in the APAP-injured liver is attributed to an accelerated resolution of inflammation at the onset of liver repair, possibly through enhanced phagocytic function of neutrophils in an autocrine manner.

Neutrophils in host defense, healing, and hypersensitivity: Dynamic cells within a dynamic host

Neutrophils are cells of the innate immune system that are extremely abundant in vivo and respond quickly to infection, injury, and inflammation. Their constant circulation throughout the body makes them some of the first responders to infection, and indeed they play a critical role in host defense against bacterial and fungal pathogens. It is now appreciated that neutrophils also play an important role in tissue healing after injury. Their short life cycle, rapid response kinetics, and vast numbers make neutrophils a highly dynamic and potentially extremely influential cell population. It has become clear that they are highly integrated with other cells of the immune system and can thus exert critical effects on the course of an inflammatory response; they can further impact tissue homeostasis and recovery after challenge. In this review, we discuss the fundamentals of neutrophils in host defense and healing; we explore the relationship between neutrophils and the dynamic host environment, including circadian cycles and the microbiome; we survey the field of neutrophils in asthma and allergy; and we consider the question of neutrophil heterogeneity-namely, whether there could be specific subsets of neutrophils that perform different functions in vivo.

Piperine as Therapeutic Agent in Paracetamol-Induced Hepatotoxicity in Mice

High doses of paracetamol (APAP) can cause irreversible liver damage. Piperine (P) inhibits cytochrome P450, which is involved in the metabolism of various xenobiotics, including paracetamol. We evaluated the hepatoprotective effects of piperine with or without N-acetylcysteine (NAC) in APAP-induced hepatotoxicity. The mice were treated with two doses of piperine (P20 or P40) and/or NAC at 2 h after administration of APAP. The NAC+P20 and NAC+P40 groups showed a reduced area of necrosis, MMP-9 activity, and Casp-1 expression. Furthermore, the NAC+P20 group was the only treatment that reduced alanine aminotransferase (ALT) and increased the levels of sulfhydryl groups (-SH). In the NAC+P40 group, NLRP-3 expression was reduced. Aspartate aminotransferase (AST), thiobarbituric acid-reactive substances (TBARS), and IL-1β expression decreased in the NAC, NAC+P20, and NAC+P40 groups compared to the APAP group. The liver necrosis area, TNF levels, carbonylated protein, and IL-18 expression decreased in the P40, NAC, NAC+P20, and NAC+P40 groups compared to the APAP group. The cytokine IL-6 was reduced in all treatments. Piperine can be used in combination with NAC to treat APAP-induced hepatotoxicity.

Neutrophil accumulation within tissues: A damage x healing dichotomy

The abundance of neutrophils in human circulation, their fast mobilization from blood to tissues, along with their alleged short life-span led to the image of neutrophils as a homogeneous cell type designed to fight infections and die in the process. Additionally, their granule content and capacity to produce molecules with considerable cytotoxic potential, lead to the general belief that neutrophil activation inexorably results in side effect of extensive tissue injury. Neutrophil activation in fact causes tissue injury as an adverse effect, but it seems that this is restricted to particular pathological situations and more of an "exception to the rule". Here we review evidences arising especially from intravital microscopy studies that demonstrate neutrophils as cells endowed with sophisticated mechanisms and able to engage in complex interactions as to minimize damage and optimize their effector functions. Moreover, neutrophil infiltration may even contribute to tissue healing and repair which may altogether demand a reexamination of current anti-inflammatory therapies that have neutrophil migration and activation as a target.

25-Hydroxycholesterol 3-Sulfate Recovers Acetaminophen Induced Acute Liver Injury via Stabilizing Mitochondria in Mouse Models

Acetaminophen (APAP) overdose is one of the most frequent causes of acute liver failure (ALF). N-acetylcysteine (NAC) is currently being used as part of the standard care in the clinic but its usage has been limited in severe cases, in which liver transplantation becomes the only treatment option. Therefore, there still is a need for a specific and effective therapy for APAP induced ALF. In the current study, we have demonstrated that treatment with 25-Hydroxycholesterol 3-Sulfate (25HC3S) not only significantly reduced mortality but also decreased the plasma levels of liver injury markers, including LDH, AST, and ALT, in APAP overdosed mouse models. 25HC3S also decreased the expression of those genes involved in cell apoptosis, stabilized mitochondrial polarization, and significantly decreased the levels of oxidants, malondialdehyde (MDA), and reactive oxygen species (ROS). Whole genome bisulfite sequencing analysis showed that 25HC3S increased demethylation of 5mCpG in key promoter regions and thereby increased the expression of those genes involved in MAPK-ERK and PI3K-Akt signaling pathways. We concluded that 25HC3S may alleviate APAP induced liver injury via up-regulating the master signaling pathways and maintaining mitochondrial membrane polarization. The results suggest that 25HC3S treatment facilitates the recovery and significantly decreases the mortality of APAP induced acute liver injury and has a synergistic effect with NAC in propylene glycol (PG) for the injury.

Inhibition of Drug-Induced Liver Injury in Mice Using a Positively Charged Peptide That Binds DNA

Hepatic cell death occurs in response to diverse stimuli such as chemical and physical damage. The exposure of intracellular contents such as DNA during necrosis induces a severe inflammatory response that has yet to be fully explored therapeutically. Here, we sought means to neutralize the ability of extracellular DNA to induce deleterious tissue inflammation when drug-induced liver injury had already ensued. DNA exposure and inflammation were investigated in vivo in drug-induced liver injury using intravital microscopy. The necrotic DNA debris was studied in murine livers in vivo and in DNA debris models in vitro by using a positively charged chemokine-derived peptide (MIG30; CXCL9[74-103]). Acetaminophen-induced liver necrosis was associated with massive DNA accumulation, production of CXC chemokines, and neutrophil activation inside the injured tissue. The MIG30 peptide bound the healthy liver vasculature and, to a much greater extent, to DNA-rich necrotic tissue. Moreover, MIG30 bound extracellular DNA directly in vivo in a charge-dependent manner and independently of glycosaminoglycans and chemokines. Post-treatment of mice with MIG30 reduced mortality, liver damage, and inflammation significantly. These effects were not observed with a control peptide that does not bind DNA. Mechanistically, MIG30 inhibited the interaction between DNA and histones, and promoted the dissociation of histones from necrotic debris. MIG30 also inhibited the pro-inflammatory effect of CpG DNA, as measured by a reduction in CXCL8 production, indicating that MIG30 disturbs the ability of DNA to induce hepatic inflammation. Conclusion: The use of DNA-binding peptides reduces necrotic liver injury and inflammation, even at late timepoints.

Neutrophil function and bactericidal activity against Staphylococcus aureus after cardiac surgery with cardiopulmonary bypass

Staphylococcus aureus is the main bacterial pathogen encountered in mediastinitis after cardiac surgical procedures; it remains a devastating complication with a high mortality rate. As neutrophils have a primordial role in the defense against staphylococcus infection and cardiopulmonary bypass (CPB) is known to induce immunosuppression, the aim of this study was to investigate CPB impact on neutrophil functions. Patients without known immunosuppression scheduled for cardiac surgery with CPB were included. Bone marrow and blood samples were harvested before, during, and after surgery. Neutrophil phenotypic maturation and functions (migration, adhesion, neutrophil extracellular trap [NET] release, reactive oxygen species (ROS) production, phagocytosis, and bacteria killing) were investigated. Two types of Staphylococcus aureus strains (one from asymptomatic nasal carriage and another from mediastinitis infected tissues) were used to assess in vitro bacterial direct impact on neutrophils. We found that CPB induced a systemic inflammation with an increase in circulating mature neutrophils after surgery. Bone marrow sample analysis did not reveal any modification of neutrophil maturation during CPB. Neutrophil lifespan was significantly increased and functions such as NET release and ROS production were enhanced after CPB whereas bacteria killing and phagocytosis were not impacted. Results were similar with the two different isolates of Staphylococcus aureus. These data suggest that CPB induces a recruitment of mature neutrophils via a demargination process rather than impacting their maturation in the bone marrow. In addition, neutrophils are fully efficient after CPB and do not contribute to postoperative immunosuppression.

Two Faces of Neutrophils in Liver Disease Development and Progression

Neutrophils, the most abundant type of leukocyte in human blood, play a major role in host defense against invading pathogens and in sterile injury. Neutrophil infiltration is characteristic of inflammation because of its antimicrobial and cytotoxic activities. Neutrophils also actively participate in the resolution of inflammation and subsequent tissue repair by acting as a critical mediator between the inflammation and resolution phases of tissue damage. However, neutrophils that are consistently exposed to inflammatory conditions lose their self-resolving capabilities and maintain an inflammatory phenotype, further exacerbating tissue damage. The current review describes how neutrophils interact with tissue microenvironments and acquire disease-specific phenotypes under chronic inflammatory conditions. Here, we aim to provide a better understanding of neutrophil-mediated pathogenesis of various liver diseases.

Neutrophils in liver diseases: pathogenesis and therapeutic targets

Previously, it was assumed that peripheral neutrophils are a homogeneous population that displays antimicrobial functions. However, recent data have revealed that neutrophils are heterogeneous and are additionally involved in tissue damage and immune regulation. The phenotypic and functional plasticity of neutrophils has been identified in patients with cancer, inflammatory disorders, infections, and other diseases. Currently, neutrophils, with their autocrine, paracrine, and immune modulation functions, have been shown to be involved in liver diseases, including viral hepatitis, nonalcoholic steatohepatitis, alcoholic liver disease, liver fibrosis, cirrhosis, liver failure, and liver cancer. Accordingly, this review summarizes the role of neutrophils in liver diseases.

Imaging and immunometabolic phenotyping uncover changes in the hepatic immune response in the early phases of NAFLD

Background & Aims

The precise determination of non-alcoholic fatty liver disease (NAFLD) onset is challenging. Thus, the initial hepatic responses to fat accumulation, which may be fundamental to our understanding of NAFLD evolution and clinical outcomes, are largely unknown. Herein, we chronologically mapped the immunologic and metabolic changes in the liver during the early stages of fatty liver disease in mice and compared this with human NAFLD samples.

Methods

Liver biopsies from patients with NAFLD (NAFLD activity score [NAS] 2–3) were collected for gene expression profiling. Mice received a high-fat diet for short periods to mimic initial steatosis and the hepatic immune response was investigated using a combination of confocal intravital imaging, gene expression, cell isolation, flow cytometry and bone marrow transplantation assays.

Results

We observed major immunologic changes in patients with NAS 2–3 and in mice in the initial stages of NAFLD. In mice, these changes significantly increased mortality rates upon drug-induced liver injury, as well as predisposing mice to bacterial infections. Moreover, deletion of Toll-like receptor 4 in liver cells dampened tolerogenesis, particularly in Kupffer cells, in the initial stages of dietary insult.

Conclusion

The hepatic immune system acts as a sentinel for early and minor changes in hepatic lipid content, mounting a biphasic response upon dietary insult. Priming of liver immune cells by gut-derived Toll-like receptor 4 ligands plays an important role in liver tolerance in initial phases, but continuous exposure to insults may lead to damage and reduced ability to control infections.

Lay summary

Fatty liver is a very common form of hepatic disease, leading to millions of cases of cirrhosis every year. Patients are often asymptomatic until becoming very sick. Therefore, it is important that we expand our knowledge of the early stages of disease pathogenesis, to enable early diagnosis. Herein, we show that even in the early stages of fatty liver disease, there are significant alterations in genes involved in the inflammatory response, suggesting that the hepatic immune system is disturbed even following minor and undetectable changes in liver fat content. This could have implications for the diagnosis and clinical management of fatty liver disease.

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Hepatic immune response is already altered in liver biopsies from patients with mild NAFLD.

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We designed a novel mouse model to mimic mild NAFLD, enabling the chronological mapping of liver changes.

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This revealed an increased mortality rate upon secondary liver damage and a window of increased susceptibility to infection.

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NAFLD diagnosis may be significantly improved by a more profound investigation of changes in hepatic immunology.

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These data could guide customized nutritional and therapeutic interventions at different stages of NAFLD.

Prolonged neutrophil survival at necrotic sites is a fundamental feature for tissue recovery and resolution of hepatic inflammation

Neutrophils were classically described as powerful effectors of acute inflammation, and their main purpose was assumed to be restricted to pathogen killing through production of oxidants. As consequence, neutrophils also may lead to significant collateral damage to the healthy tissues, and after performing these tasks, these leukocytes are supposed to die within tissues. However, there is a growing body of evidence showing that neutrophils also play a pivotal role in the resolution phases of inflammation, because they can modulate tissue environment due to secretion of different kind of cytokines. Drug-induced liver injury (DILI) is a worldwide concern being one of the most prevalent causes of liver transplantation, and is well established that there is an intense neutrophil recruitment into necrotic liver during DILI. However, information if such abundant granulocyte infiltration is also linked to the tissue repairing phase of hepatic injury is still largely elusive. Here, we investigated the dynamics of neutrophil trafficking within blood, bone marrow, and liver during hepatic inflammation, and how changes in their gene expression profile could drive the resolution events during acetaminophen (APAP)-induced liver injury. We found that neutrophils remained viable during longer periods following liver damage, because they avidly patrolled necrotic areas and up-regulated pro-resolutive genes, including Tgfb, Il1r2, and Fpr2. Adoptive transference of "resolutive neutrophils" harvested from livers at 72 h after injury to mice at the initial phases of injury (6 h after APAP) significantly rescued organ injury. Thus, we provide novel insights on the role of neutrophils not only in the injury amplification, but also in the resolution phases of inflammation.

Effect of Liposomal Curcumin on Acetaminophen Hepatotoxicity by Down-regulation of Oxidative Stress and Matrix Metalloproteinases

BACKGROUND/AIM

The hepatoprotective role of various molecules in drug-induced hepatotoxicity arouses great interest. We investigated the effect of liposomal curcumin (LCC) on experimental acetaminophen (APAP)-induced hepatotoxicity.

MATERIALS AND METHODS

Rats were randomly allocated into 5 groups, and the effect of two LCC concentrations was studied: group 1 - 1 ml intraperitoneal (i.p.) saline, group 2 - APAP pretreatment, group 3 - APAP+silymarin (extract of the silybum marianum with anti-inflammatory, anti-oxidant, and anti-fibrotic properties), group 4 - APAP+LCC1, group 5 - APAP+LCC2. The biomarkers of oxidative stress (nitric oxide and malondialdehyde) and antioxidant status of plasma (thiols and catalase), TNF-α, MMP-2 and MMP-9 serum levels were evaluated.

RESULTS

An improvement in oxidative stress, antioxidant status, and TNF-α, MMP-2 and MMP-9 levels was obtained in groups pretreated with LCC compared to silymarin treatment, in a dose-dependent manner. Histopathological examination reinforced the results.

CONCLUSION

Liposomal curcumin improves the oxidative stress/antioxidant balance and alleviates inflammation in experimental APAP-induced hepatotoxicity.

Neutrophil Chemotaxis and NETosis in Murine Chronic Liver Injury via Cannabinoid Receptor 1/ Gαi/o/ ROS/ p38 MAPK Signaling Pathway

Neutrophils play an essential role in the control of inflammatory diseases. However, whether cannabinoid receptors (CBs) play a role in neutrophil chemotaxis and NETosis in sterile liver inflammation remains unknown. The expression of marker genes on neutrophils was characterized by FACS, immunofluorescence, qRT-PCR, and Western blot. The amount of neutrophils was significantly elevated from 7 days and reached the peak at 2 weeks in carbon tetrachloride (CCl₄)-treated mouse liver. The mRNA expression of neutrophil marker Ly6G had positive correlation with CB1 and CB2 expression in injured liver. In vitro CBs were abundantly expressed in isolated neutrophils and CB1 agonist ACEA promoted the chemotaxis and cytoskeletal remodeling, which can be suppressed by CB1 antagonist AM281. Moreover, ACEA induced NETosis, myeloperoxidase release from lysosome and ROS burst, indicating neutrophil activation, via Gα_i/o. Conversely, CB2 agonist JWH133 had no effect on neutrophil function. ROS and p38 MAPK signaling pathways were involved in CB1-mediated neutrophil function, and ROS was upstream of p38 MAPK. CB1 blockade in vivo significantly attenuated neutrophil infiltration and liver inflammation in CCl₄-treated mice. Taken together, CB1 mediates neutrophil chemotaxis and NETosis via Gα_i/o/ROS/p38 MAPK signaling pathway in liver inflammation, which represents an effective therapeutic strategy for liver diseases.

Therapeutic targets for liver regeneration after acute severe injury: a preclinical overview

Introduction: Liver transplantation is the only viable treatment with a proven survival benefit for acute liver failure (ALF). Donor organ shortage is, however, a major hurdle; hence, alternative approaches that enable liver regeneration and target acute severe hepatocellular damage are necessary.Areas covered: This article sheds light on therapeutic targets for liver regeneration and considers their therapeutic potential. ALF following extensive hepatocyte damage and small-for-size syndrome (SFSS) are illuminated for the reader while the molecular mechanisms of liver regeneration are assessed in accordance with relevant therapeutic strategies. Furthermore, liver background parameters and predictive biomarkers that might associate with liver regeneration are reviewed.Expert opinion: There are established and novel experimental strategies for liver regeneration to prevent ALF resulting from SFSS. Granulocyte-colony stimulating factor (G-CSF) is a promising agent targeting liver regeneration after acute severe injury. Autophagy and hepatocyte senescence represent attractive new targets for liver regeneration in acute severe hepatic injury. Liver support strategies, including tissue engineering, constitute novel regenerative means; the success of this is dependent on stem cell research advances. However, there is no firm clinical evidence that these supportive strategies may alleviate hepatocellular damage until liver transplantation becomes available or successful self-liver regeneration occurs.

More friend than foe: the emerging role of neutrophils in tissue repair

Neutrophils are the most abundant immune cells in humans and serve as first responders to a myriad of host perturbations. Equipped with a plethora of antimicrobial molecules, neutrophils invade sites of inflammation to eradicate pathogens and clear debris. Traditionally, neutrophils were thought to cause collateral tissue damage before dying at the site. However, the presence of neutrophil infiltration into sterile injuries (in the absence of infections) suggests additional roles for these cells. Now, the view of neutrophils as indiscriminate killers seems to be changing as evolving evidence suggests that neutrophils actively orchestrate resolution of inflammation and contribute to tissue repair. Novel concepts include the idea that neutrophils are key to revascularization and subsequently reverse-transmigrate back to the vasculature, actively leaving sites of tissue damage to re-home to functional niches in the lung and bone marrow. This Review scrutinizes the role of neutrophils in tissue damage and repair, discussing recent findings and raising unresolved questions around this intriguing immune cell.