Inhibition of 5-lipoxygenase-activating protein abrogates experimental liver injury: role of Kupffer cells

Differential impact of 5-lipoxygenase-activating protein antagonists on the biosynthesis of leukotrienes and of specialized pro-resolving mediators

Lipoxygenases (LOX) transform arachidonic acid (AA, C20:4) and docosahexaenoic acid (DHA, C22:6) into bioactive lipid mediators (LMs) that comprise not only pro-inflammatory leukotrienes (LTs) but also the specialized pro-resolving mediators (SPMs) that promote inflammation resolution and tissue regeneration. The 5-LOX-activating protein (FLAP) is known to provide AA as a substrate to 5-LOX for generating LTs, such as LTB4, a potent chemoattractant and activator of phagocytes. Notably, 5-LOX is also involved in the biosynthesis of certain SPMs, namely, lipoxins and D-resolvins, implying a role of FLAP in SPM formation. FLAP antagonists have been intensively developed as LT biosynthesis inhibitors, but how they impact SPM formation is a matter of debate. Here, we show that FLAP antagonism suppresses the conversion of AA by 5-LOX to LT and lipoxins, while the conversion of DHA to SPM is unaffected. Screening of multiple prominent FLAP antagonists for their effects on LM formation in human M1- and M2-monocyte-derived macrophages by comprehensive LM profiling showed that all nine compounds reduced the production of 5-LOX-derived LTs but increased the formation of SPMs from DHA, e.g., resolvin D5. Some FLAP antagonists, especially those that contain an indole or benzimidazole moiety, even elicited SPM formation in resting M2-monocyte-derived macrophages. Intriguingly, in coincubations of human neutrophils and platelets that produce substantial AA-derived lipoxin and DHA-derived RvD5, FLAP antagonism abolished lipoxin formation, but resolvin D5 levels remained unaffected. Conclusively, antagonism of FLAP suppresses the conversion of AA by 5-LOX to LTs and lipoxins but not the conversion of DHA by 5-LOX to SPM, which should be taken into account for the development of such compounds as anti-inflammatory drugs.

Eicosanoids and other oxylipins in liver injury, inflammation and liver cancer development

Liver cancer is a malignancy developed from underlying liver disease that encompasses liver injury and metabolic disorders. The progression from these underlying liver disease to cancer is accompanied by chronic inflammatory conditions in which liver macrophages play important roles in orchestrating the inflammatory response. During this process, bioactive lipids produced by hepatocytes and macrophages mediate the inflammatory responses by acting as pro-inflammatory factors, as well as, playing roles in the resolution of inflammation conditions. Here, we review the literature discussing the roles of bioactive lipids in acute and chronic hepatic inflammation and progression to cancer.

Five-lipoxygenase-activating protein-mediated CYLD attenuation is a candidate driver in hepatic malignant lesion

Hepatocellular carcinoma (HCC) is an inflammation-associated cancer. However, the lipid pro-inflammatory mediators have only been seldom investigated in HCC pathogenesis. Cylindromatosis (CYLD) attenuation is involved in hepatocarcinogenesis. Here, we aimed to evaluate the significance of hepatic lipid pro-inflammatory metabolites of arachidonate-affected CYLD expression via the 5-lipoxygenase (5-LO) pathway. Resection liver tissues from HCC patients or donors were evaluated for the correlation of 5-LO/cysteinyl leukotrienes (CysLTs) signaling to the expression of CYLD. The impact of functional components in 5-LO/CysLTs cascade on survival of HCC patients was subsequently assessed. Both livers from canines, a preponderant animal for cancer research, and genetic-modified human HCC cells treated with hepatocarcinogen aristolochic acid I (AAI) were further used to reveal the possible relevance between 5-LO pathway activation and CYLD suppression. Five-LO-activating protein (FLAP), an essential partner of 5-LO, was significantly overexpressed and was parallel to CYLD depression, CD34 neovascular localization, and high Ki-67 expression in the resection tissues from HCC patients. Importantly, high hepatic FLAP transcription markedly shortened the median survival time of HCC patients after surgical resection. In the livers of AAI-treated canines, FLAP overexpression was parallel to enhanced CysLTs contents and the simultaneous attenuation of CYLD. Moreover, knock-in FLAP significantly diminished the expression of CYLD in AAI-treated human HCC cells. In summary, the hepatic FLAP/CysLTs axis is a crucial suppressor of CYLD in HCC pathogenesis, which highlights a novel mechanism in hepatocarcinogenesis and progression. FLAP therefore can be explored for the early HCC detection and a target of anti-HCC therapy.

The Role of Macrophages in Liver Fibrosis: New Therapeutic Opportunities

Chronic inflammation is the hallmark of fibrotic disorders and is characterized by the activation of immune cells in the damaged tissues. Macrophages have emerged as central players in the fibrotic process since they initiate, sustain and amplify the inflammatory reaction. As regards the liver, distinct populations of phagocytic cells, like Kupffer cells and monocyte-derived macrophages, are indisputably key cells implicated in the pathogenesis of several chronic liver diseases. In this review, we summarize the current knowledge on the origin, role and functions of macrophages in fibrotic conditions, with a specific focus on liver fibrosis; then, we discuss some innovative therapeutic strategies targeting macrophages in fibrotic liver diseases.

Lipids in Liver Failure Syndromes: A Focus on Eicosanoids, Specialized Pro-Resolving Lipid Mediators and Lysophospholipids

Lipids are organic compounds insoluble in water with a variety of metabolic and non-metabolic functions. They not only represent an efficient energy substrate but can also act as key inflammatory and anti-inflammatory molecules as part of a network of soluble mediators at the interface of metabolism and the immune system. The role of endogenous bioactive lipid mediators has been demonstrated in several inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease, atherosclerosis, cancer). The liver is unique in providing balanced immunotolerance to the exposure of bacterial components from the gut transiting through the portal vein and the lymphatic system. This balance is abruptly deranged in liver failure syndromes such as acute liver failure and acute-on-chronic liver failure. In these syndromes, researchers have recently focused on bioactive lipid mediators by global metabonomic profiling and uncovered the pivotal role of these mediators in the immune dysfunction observed in liver failure syndromes explaining the high occurrence of sepsis and subsequent organ failure. Among endogenous bioactive lipids, the mechanistic actions of three classes (eicosanoids, pro-resolving lipid mediators and lysophospholipids) in the pathophysiological modulation of liver failure syndromes will be the topic of this narrative review. Furthermore, the therapeutic potential of lipid-immune pathways will be described.

Shifting the Biosynthesis of Leukotrienes Toward Specialized Pro-Resolving Mediators by the 5-Lipoxygenase-Activating Protein (FLAP) Antagonist BRP-201

Background and Purpose

Lipid mediators (LM) play crucial roles in the complex inflammation process with respect to initiation, maintenance, and resolution. Proinflammatory leukotrienes (LTs), generated by 5-lipoxygenase (LOX) and the 5-LOX-activating protein (FLAP), initiate and maintain inflammation while specialized pro-resolving mediators (SPMs) formed by various LOXs as key enzymes promote inflammation resolution and the return to homeostasis. Since 5-LOX also contributes to SPM biosynthesis, smart pharmacological manipulation of the 5-LOX pathway and accompanied activation of 12-/15-LOXs may accomplish suppression of LT formation but maintain or even elevate SPM formation. Here, we demonstrated that the FLAP antagonist BRP-201 possesses such pharmacological profile and causes a switch from LT toward SPM formation.

Methods and Results

Comprehensive LM metabololipidomics with activated human monocyte-derived macrophages (MDM) of M1 or M2 phenotype showed that BRP-201 strongly inhibits LT formation induced by bacterial exotoxins. In parallel, SPM levels and 12/15-LOX-derived products were markedly elevated, in particular in M2-MDM. Intriguingly, in unstimulated MDM, BRP-201 induced formation of 12/15-LOX products including SPM and caused 15-LOX-1 subcellular redistribution without affecting 5-LOX. Experiments with HEK293 cells stably expressing either 5-LOX with or without FLAP, 15-LOX-1 or 15-LOX-2 confirmed suppression of 5-LOX product formation due to FLAP antagonism by BRP-201 but activated 15-LOX-1 in the absence of FLAP. Finally, in zymosan-induced murine peritonitis, BRP-201 (2 mg/kg, ip) lowered LT levels but elevated 12/15-LOX products including SPMs.

Conclusion

BRP-201 acts as FLAP antagonist but also as 12/15-LOX activator switching formation of pro-inflammatory LTs toward inflammation-resolving SPM, which reflects a beneficial pharmacological profile for intervention in inflammation.

Untangling the web of 5-lipoxygenase-derived products from a molecular and structural perspective: The battle between pro- and anti-inflammatory lipid mediators

Arachidonic acid (AA) is the precursor to leukotrienes (LT), potent mediators of the inflammatory response. In the 35 + years since cysteinyl-LTs were reported to mediate antigen-induced constriction of bronchi in tissue from asthma patients, numerous cellular responses evoked by the LTs, such as chemoattraction and G protein-coupled receptor (GPCR) activation, have been elucidated and revealed a potential for 5-lipoxygenase (5-LOX) as a promising drug target that goes beyond asthma. We describe herein early work identifying 5-LOX as the key enzyme that initiates LT biosynthesis and the discovery of its membrane-embedded helper protein required to execute the two-step reaction that transforms AA to the progenitor leukotriene A4 (LTA4). 5-LOX must traffic to the nuclear membrane to interact with its partner and undergo a conformational change so that AA can enter the active site. Additionally, the enzyme must retain the hydroperoxy-reaction intermediate for its final transformation to LTA4. Each of these steps provide a unique target for inhibition. Next, we describe the recent structures of GPCRs that recognize metabolites of the 5-LOX pathway and thus provide target alternatives. We also highlight the role of 5-LOX in the biosynthesis of anti-inflammatory lipid mediators (LM), the so-called specialized pro-resolving mediators (SPM). The involvement of 5-LOX in the biosynthesis of LM with opposing functions undoubtedly complicates the continuing search for 5-LOX inhibitors as therapeutic leads. Finally, we address the recent discovery of how some allosteric 5-LOX inhibitors promote oxygenation at the 12/15 carbon on AA to generate mediators that resolve, rather than promote, inflammation.

Single Cell Gene Expression Analysis in a 3D Microtissue Liver Model Reveals Cell Type-Specific Responses to Pro-Fibrotic TGF-β1 Stimulation

3D cell culture systems are widely used to study disease mechanisms and therapeutic interventions. Multicellular liver microtissues (MTs) comprising HepaRG, hTERT-HSC and THP-1 maintain multicellular interactions and physiological properties required to mimic liver fibrosis. However, the inherent complexity of multicellular 3D-systems often hinders the discrimination of cell type specific responses. Here, we aimed at applying single cell sequencing (scRNA-seq) to discern the molecular responses of cells involved in the development of fibrosis elicited by TGF-β1. To obtain single cell suspensions from the MTs, an enzymatic dissociation method was optimized. Isolated cells showed good viability, could be re-plated and cultured in 2D, and expressed specific markers determined by scRNA-seq, qRT-PCR, ELISA and immunostaining. The three cell populations were successfully clustered using supervised and unsupervised methods based on scRNA-seq data. TGF-β1 led to a fibrotic phenotype in the MTs, detected as decreased albumin and increased αSMA expression. Cell-type specific responses to the treatment were identified for each of the three cell types. They included HepaRG damage characterized by a decrease in cellular metabolism, prototypical inflammatory responses in THP-1s and extracellular matrix remodeling in hTERT-HSCs. Furthermore, we identified novel cell-specific putative fibrosis markers in hTERT-HSC (COL15A1), and THP-1 (ALOX5AP and LAPTM5).

Gigantol ameliorates CCl4-induced liver injury via preventing activation of JNK/cPLA2/12-LOX inflammatory pathway

Arachidonic acid (AA) signaling pathway is an important constituent of inflammatory processes. In our previous study, it was found that dihydro-stilbene gigantol relieved hepatic inflammation in mice with CCl₄-induced acute liver injury. This study aimed to investigate the involvement of arachidonate metabolic cascade in this process. Our results showed CCl₄ activated AA metabolism with the evidence of cPLA2 phosphorylation, which was dependent on the MAPK/JNK activation. Pretreatment with JNK inhibitor SU3327 or gigantol abolished the cPLA2 activation, along with the attenuation of liver damage. Besides, gigantol markedly decreased immune cells activation. Metabolomic analysis revealed that gigantol universally reversed the upregulation of major AA metabolites in injured mouse livers induced by CCl₄, especially 12-hydroxyeicosatetraenoic acid (12-HETE). Gigantol also decreased the mRNA and protein expression of platelet-, and leukocyte-type 12-lipoxxygenase (LOX) in the liver. Furthermore, pan-LOX inhibitor nordihydroguaiaretic acid (NDGA) and specific 12-LOX inhibitors baicalein and ML351 attenuated the liver injury to the same extent as gigantol. Overall, our study elucidated a comprehensive profile of AA metabolites during hepatic inflammation caused by CCl₄, highlighting the role of 12-LOX-12-HETE pathway in this process. And gigantol alleviated liver inflammation partly through inhibiting the JNK/cPLA2/12-LOX pathway.

Targeting biosynthetic networks of the proinflammatory and proresolving lipid metabolome

Nonsteroidal anti-inflammatory drugs interfere with the metabolism of arachidonic acid to proinflammatory prostaglandins and leukotrienes by targeting cyclooxygenases (COXs), 5-lipoxygenase (LOX), or the 5-LOX-activating protein (FLAP). These and related enzymes act in conjunction with marked crosstalk within a complex lipid mediator (LM) network where also specialized proresolving LMs (SPMs) are formed. Here, we present how prominent LM pathways can be differentially modulated in human proinflammatory M1 and proresolving M2 macrophage phenotypes that, upon exposure to Escherichia coli, produce either abundant prostaglandins and leukotrienes (M1) or SPMs (M2). Targeted liquid chromatography-tandem mass spectrometry-based metabololipidomics was applied to analyze and quantify the specific LM profiles. Besides expected on-target actions, we found that: 1) COX or 15-LOX-1 inhibitors elevate inflammatory leukotriene levels, 2) FLAP and 5-LOX inhibitors reduce leukotrienes in M1 but less so in M2 macrophages, 3) zileuton blocks resolution-initiating SPM biosynthesis, whereas FLAP inhibition increases SPM levels, and 4) that the 15-LOX-1 inhibitor 3887 suppresses SPM formation in M2 macrophages. Conclusively, interference with discrete LM biosynthetic enzymes in different macrophage phenotypes considerably affects the LM metabolomes with potential consequences for inflammation-resolution pharmacotherapy. Our data may allow better appraisal of the therapeutic potential of these drugs to intervene with inflammatory disorders.-Werner, M., Jordan, P. M., Romp, E., Czapka, A., Rao, Z., Kretzer, C., Koeberle, A., Garscha, U., Pace, S., Claesson, H.-E., Serhan, C. N., Werz, O., Gerstmeier, J. Targeting biosynthetic networks of the proinflammatory and proresolving lipid metabolome.

The Eicosanoids, Redox-Regulated Lipid Mediators in Immunometabolic Disorders

SIGNIFICANCE

The oxidation of arachidonic acid via cyclooxygenase (COX) and lipoxygenase (LOX) activity to produce eicosanoids during inflammation is a well-known biosynthetic pathway. These lipid mediators are involved in fever, pain, and thrombosis and are produced from multiple cells as well as cell/cell interactions, for example, immune cells and epithelial/endothelial cells. Metabolic disorders, including hyperlipidemia, hypertension, and diabetes, are linked with chronic low-grade inflammation, impacting the immune system and promoting a variety of chronic diseases. Recent Advances: Multiple studies have corroborated the important function of eicosanoids and their receptors in (non)-inflammatory cells in immunometabolic disorders (e.g., insulin resistance, obesity, and cardiovascular and nonalcoholic fatty liver diseases). In this context, LOX and COX products are involved in both pro- and anti-inflammatory responses. In addition, recent work has elucidated the potent function of specialized proresolving mediators (i.e., lipoxins and resolvins) in resolving inflammation, protecting organs, and stimulating tissue repair and remodeling.

CRITICAL ISSUES

Inhibiting/stimulating selected eicosanoid pathways may result in anti-inflammatory and proresolution responses leading to multiple beneficial effects, including the abrogation of reactive oxygen species production, increased speed of resolution, and overall improvement of diseases related to immunometabolic perturbations.

FUTURE DIRECTIONS

Despite many achievements, it is crucial to understand the molecular and cellular mechanisms underlying immunological/metabolic cross talk to offer substantial therapeutic promise. Antioxid. Redox Signal. 29, 275-296.

BML-111 equilibrated ACE-AngII-AT1R and ACE2-Ang-(1-7)-Mas axis to protect hepatic fibrosis in rats

BACKGROUND

It was recently reported Lipoxins (LXs) had protective effects on fibrous diseases, and renin-angiotensin-aldosterone system (RAAS) had played vital and bidirectional roles in hepatic fibrosis. In this paper, a hepatic fibrosis model, induced by carbon tetrachloride (CCL₄) in rats, was used to observe the relations between RAAS and LXs, as well as to further explore the alternative anti-fibrosis mechanisms of LXs.

METHODS

The model was evaluated by morphological observations and biochemical assays. The activities and contents of angiotensin converting enzyme (ACE) and angiotensin converting enzyme 2 (ACE2) were examined through assay kits and ELISA. The expression levels of angiotensinII (AngII), Angiotensin II type 1 receptor (AT1R), angiotensin-(1-7) (Ang-1-7), and Mas were all measured using real time PCR, ELISA, and Western blot.

RESULTS

The model was established successfully and BML-111 significantly ameliorated CCL₄-induced hepatic fibrosis, including reduction inflammation injury, decrease extracellular matrix deposition, and improvement hepatic functions. Furthermore, BML-111 could obviously decrease not only the activities of ACE but also the expression levels of ACE, AngII,and AT1R, which were induced by CCL₄. On the other hand, BML-111 could markedly increase the activities of ACE2, besides the expression levels of ACE2, Ang-(1-7) and Mas. More importantly, BOC-2, a lipoxin A₄ receptor blocker, could reverse all these phenomena.

CONCLUSIONS

Equilibrating ACE-AngII-AT1R axis and ACE2-Ang-(1-7)-Mas axis mediated the protective effect of BML-111 on hepatic fibrosis in rats.

How to Face Chronic Liver Disease: The Sinusoidal Perspective

Liver microcirculation plays an essential role in the progression and aggravation of chronic liver disease. Hepatic sinusoid environment, mainly composed by hepatocytes, liver sinusoidal endothelial cells, Kupffer cells, and hepatic stellate cells, intimately cooperate to maintain global liver function and specific phenotype of each cell type. However, continuous liver injury significantly deregulates liver cells protective phenotype, leading to parenchymal and non-parenchymal dysfunction. Recent data have enlightened the molecular processes that mediate hepatic microcirculatory injury, and consequently, opened the possibility to develop new therapeutic strategies to ameliorate liver circulation and viability. The present review summarizes the main cellular components of the hepatic sinusoid, to afterward focus on non-parenchymal cells phenotype deregulation due to chronic injury, in the specific clinical context of liver cirrhosis and derived portal hypertension. Finally, we herein detail new therapies developed at the bench-side with high potential to be translated to the bedside.

An imbalance between specialized pro-resolving lipid mediators and pro-inflammatory leukotrienes promotes instability of atherosclerotic plaques

Chronic unresolved inflammation plays a causal role in the development of advanced atherosclerosis, but the mechanisms that prevent resolution in atherosclerosis remain unclear. Here, we use targeted mass spectrometry to identify specialized pro-resolving lipid mediators (SPM) in histologically-defined stable and vulnerable regions of human carotid atherosclerotic plaques. The levels of SPMs, particularly resolvin D1 (RvD1), and the ratio of SPMs to pro-inflammatory leukotriene B₄ (LTB₄), are significantly decreased in the vulnerable regions. SPMs are also decreased in advanced plaques of fat-fed Ldlr^−/− mice. Administration of RvD1 to these mice during plaque progression restores the RvD1:LTB₄ ratio to that of less advanced lesions and promotes plaque stability, including decreased lesional oxidative stress and necrosis, improved lesional efferocytosis, and thicker fibrous caps. These findings provide molecular support for the concept that defective inflammation resolution contributes to the formation of clinically dangerous plaques and offer a mechanistic rationale for SPM therapy to promote plaque stability.

Atherosclerosis progression is linked to inflammatory processes in the blood vessel wall. Here, the authors show that, with the progression of atherosclerosis, the resolution of inflammation is impaired as the result of an imbalance between specialized pro-resolving lipid mediators and leukotrienes.

Resolvin D1 protects the liver from ischemia/reperfusion injury by enhancing M2 macrophage polarization and efferocytosis

Resolution of inflammation is an active process involving a novel category of lipid factors known as specialized pro-resolving lipid mediators, which includes Resolvin D1 (RvD1). While accumulating evidence suggests that RvD1 counteracts proinflammatory signaling and promotes resolution, the specific cellular targets and mechanisms of action of RvD1 remain largely unknown. In the present study, we investigated the role and molecular mechanisms of RvD1 in ischemia/reperfusion (IR)-induced sterile liver inflammation. Male C57BL/6 mice underwent 70% hepatic ischemia for 60min, followed by reperfusion. RvD1 (5, 10, and 15μg/kg, i.p.) was administered to the mice 1h before ischemia and then immediately prior to reperfusion. RvD1 attenuated IR-induced hepatocellular damage and the proinflammatory response. In purified Kupffer cells (KCs) from mice exposed to IR, the levels of M1 marker genes (Nos2a and Cd40) increased, while those of M2 marker genes (Arg1, Cd206, and Mst1r) decreased, demonstrating a proinflammatory shift. RvD1 markedly attenuated these changes. Depletion of KCs by liposome clodronate abrogated the effects of RvD1 on proinflammatory mediators and macrophage polarization. In addition, RvD1 attenuated increases in myeloperoxidase activity and Cxcl1 and Cxcl2 mRNA expression. RvD1 markedly augmented the efferocytic activity of KCs, as indicated by increases in F4/80(+)Gr-1(+) cells in the liver. However, antagonist pretreatment or gene silencing of the RvD1 receptor, ALX/FPR2, abrogated the anti-inflammatory and pro-resolving actions of RvD1. These data indicate that RvD1 ameliorates IR-induced liver injury, and this protection is associated with enhancement of M2 polarization and efferocytosis via ALX/FPR2 activation.

MicroRNA-674-5p/5-LO axis involved in autoimmune reaction of Concanavalin A-induced acute mouse liver injury

Autoimmune hepatitis is characterized, in part, by the pathways involving cysteinyl-leukotriene metabolites of arachidonic acid, the dynamics of which remain unclear. Here, we explored post-transcriptional regulation in the 5-lipoxygenase (5-LO) pathway of arachidonic acid in a Concanavalin A (Con A) induced mouse model. We found that Con A administration lead to 5-LO overexpression and cysteinyl-leukotriene release in early hepatic injury, which was attenuated by cyclosporin A pretreatment. Subsequent microarray and qRT-PCR analysis further showed that microRNA-674-5p (miR-674-5p) displayed a significant decrease in expression in Con A-damaged liver. Noting that miR-674-5p harbors a potential binding region for 5-LO, we further transfected hepatic cell lines with overexpressing miR-674-5p mimic and discovered a negative regulating effect of miR-674-5p on 5-LO expression in the presence of IL-6 or TNF-α. These findings suggest that miR-674-5p might be a negative regulator in 5-LO mediated autoimmune liver injury, representing a compelling avenue towards future therapeutic interventions.

Pathophysiology of Portal Hypertension

The bases of our current knowledge on the physiology of the hepatic portal system are largely owed to the work of three pioneering vascular researchers from the sixteenth and the seventeenth centuries: A. Vesalius, W. Harvey, and F. Glisson. Vesalius is referred to as the founder of modern human anatomy, and in his influential book, De humani corporis fabrica libri septem, he elaborated the first anatomical atlas of the hepatic portal venous system (Vesalius 2013). Sir William Harvey laid the foundations of modern cardiovascular research with his Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (Harvey 1931) in which he established the nature of blood circulation. Finally, F. Glisson characterized the gastrointestinal-hepatic vascular system (Child 1955). These physiological descriptions were later complemented with clinical observations. In the eighteenth and nineteenth centuries, Morgagni, Puckelt, Cruveilhier, and Osler were the first to make the connection between common hepatic complications – ascites, splenomegaly, and gastrointestinal bleeding – and obstruction of the portal system (Sandblom 1993). These were the foundations that allowed Gilbert, Villaret, and Thompson to establish an early definition of portal hypertension at the beginning of the twentieth century. In this period, Thompson performed the first direct measurement of portal pressure by laparotomy in some patients (Gilbert and Villaret 1906; Thompson et al. 1937). Considering all these milestones, and paraphrasing Sir Isaac Newton, if hepatologists have seen further, it is by standing on the shoulders of giants.

Nowadays, our understanding of the pathogenesis of portal hypertension has largely improved thanks to the progress in preclinical and clinical research. However, this field is ever-changing and hepatologists are continually identifying novel pathological mechanisms and developing new therapeutic strategies for this clinical condition. Hence, the aim of this chapter is to summarize the current knowledge about this clinical condition.

Comparative analysis and modeling of the severity of steatohepatitis in DDC-treated mouse strains

Background

Non-alcoholic fatty liver disease (NAFLD) has a broad spectrum of disease states ranging from mild steatosis characterized by an abnormal retention of lipids within liver cells to steatohepatitis (NASH) showing fat accumulation, inflammation, ballooning and degradation of hepatocytes, and fibrosis. Ultimately, steatohepatitis can result in liver cirrhosis and hepatocellular carcinoma.

Methodology and Results

In this study we have analyzed three different mouse strains, A/J, C57BL/6J, and PWD/PhJ, that show different degrees of steatohepatitis when administered a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) containing diet. RNA-Seq gene expression analysis, protein analysis and metabolic profiling were applied to identify differentially expressed genes/proteins and perturbed metabolite levels of mouse liver samples upon DDC-treatment. Pathway analysis revealed alteration of arachidonic acid (AA) and S-adenosylmethionine (SAMe) metabolism upon other pathways. To understand metabolic changes of arachidonic acid metabolism in the light of disease expression profiles a kinetic model of this pathway was developed and optimized according to metabolite levels. Subsequently, the model was used to study in silico effects of potential drug targets for steatohepatitis.

Conclusions

We identified AA/eicosanoid metabolism as highly perturbed in DDC-induced mice using a combination of an experimental and in silico approach. Our analysis of the AA/eicosanoid metabolic pathway suggests that 5-hydroxyeicosatetraenoic acid (5-HETE), 15-hydroxyeicosatetraenoic acid (15-HETE) and prostaglandin D2 (PGD2) are perturbed in DDC mice. We further demonstrate that a dynamic model can be used for qualitative prediction of metabolic changes based on transcriptomics data in a disease-related context. Furthermore, SAMe metabolism was identified as being perturbed due to DDC treatment. Several genes as well as some metabolites of this module show differences between A/J and C57BL/6J on the one hand and PWD/PhJ on the other.

Inhibition of 5-lipoxygenase pathway attenuates acute liver failure by inhibiting macrophage activation

This study aimed to investigate the role of 5-lipoxygenase (5-LO) in acute liver failure (ALF) and changes in macrophage activation by blocking it. ALF was induced in rats by administration of D-galactosamine (D-GalN)/lipopolysaccharide (LPS). Rats were injected intraperitoneally with AA-861 (a specific 5-LO inhibitor), 24 hr before D-GalN/LPS administration. After D-GalN/LPS injection, the liver tissue was collected for assessment of histology, macrophage microstructure, macrophage counts, 5-LO mRNA formation, protein expression, and concentration of leukotrienes. Serum was collected for detecting alanine aminotransferase (ALT), aspartate transaminase (AST), total bilirubin (Tbil), and tumor necrosis factor- (TNF-) α . Twenty-four hours after injection, compared with controls, ALF rats were characterized by widespread hepatocyte necrosis and elevated ALT, AST, and Tbil, and 5-LO protein expression reached a peak. Liver leukotriene B4 was also significantly elevated. However, 5-LO mRNA reached a peak 8 hr after D-GalN/LPS injection. Simultaneously, the microstructure of macrophages was changed most significantly and macrophages counts were increased significantly. Moreover, serum TNF- α was also elevated. By contrast, AA-861 pretreatment significantly decreased liver necrosis as well as all of the parameters compared with the rats without pretreatment. Macrophages, via the 5-LO pathway, play a critical role in ALF, and 5-LO inhibitor significantly alleviates ALF, possibly related to macrophage inhibition.

Role of cysteinyl-leukotrienes for portal pressure regulation and liver damage in cholestatic rat livers

Kupffer cells (KCs) have a major role in liver injury, and cysteinyl-leukotrienes (Cys-LTs) are known to be involved as well. The KC-mediated pathways for the production and secretion of Cys-LT in cholestatic liver injury have not yet been elucidated. Here, we hypothesized that KC activation by Toll-like receptor ligands results in Cys-LT-mediated microcirculatory alterations and liver injury in acute cholestasis. We hypothesized further that this situation is associated with changes in the secretion and production of Cys-LT. One week after bile duct ligation (BDL), livers showed typical histological signs of cholestatic liver injury. Associated microcirculatory disturbances caused increased basal and maximal portal pressure following KC activation. These differences were determined in BDL livers compared with sham-operated livers in vivo (KC activation by LPS 4 mg/kg b.w.) and in isolated perfused organs (KC activation by Zymosan A, 150 μg/ml). Treatment with the 5-lipoxygenase inhibitor MK-886 alone did not alter portal perfusion pressure, lactate dehydrogenase (LDH) efflux, or bile duct proliferation in BDL animals. Following KC activation, portal perfusion pressure increased. The degree of cell injury was attenuated by MK-886 (3 μM) treatment as estimated by LDH efflux. In normal rats, a large amount of Cys-LT efflux was found in the bile. Only a minor amount was found in the effluent perfusate. In BDL livers, the KC-mediated Cys-LT efflux into the sinusoidal system increased, although the absolute Cys-LT level was still grossly lower than the biliary excretion in sham-operated livers. In conclusion, our results indicate that treatment with Cys-LT inhibitors might be a relevant target for attenuating cholestatic liver damage.

5-lipoxygenase deficiency reduces acetaminophen-induced hepatotoxicity and lethality

5-Lipoxygenase (5-LO) converts arachidonic acid into leukotrienes (LTs) and is involved in inflammation. At present, the participation of 5-LO in acetaminophen (APAP)-induced hepatotoxicity and liver damage has not been addressed. 5-LO deficient (5-LO⁻/⁻) mice and background wild type mice were challenged with APAP (0.3-6 g/kg) or saline. The lethality, liver damage, neutrophil and macrophage recruitment, LTB₄, cytokine production, and oxidative stress were assessed. APAP induced a dose-dependent mortality, and the dose of 3 g/kg was selected for next experiments. APAP induced LTB4 production in the liver, the primary target organ in APAP toxicity. Histopathological analysis revealed that 5-LO⁻/⁻ mice presented reduced APAP-induced liver necrosis and inflammation compared with WT mice. APAP-induced lethality, increase of plasma levels of aspartate aminotransferase and alanine aminotransferase, liver cytokine (IL-1β, TNF-α , IFN- γ, and IL-10), superoxide anion, and thiobarbituric acid reactive substances production, myeloperoxidase and N-acetyl-β-D-glucosaminidase activity, Nrf2 and gp91(phox) mRNA expression, and decrease of reduced glutathione and antioxidant capacity measured by 2,2'-azinobis(3-ethylbenzothiazoline 6-sulfonate) assay were prevented in 5-LO⁻/⁻ mice compared to WT mice. Therefore, 5-LO deficiency resulted in reduced mortality due to reduced liver inflammatory and oxidative damage, suggesting 5-LO is a promising target to reduce APAP-induced lethality and liver inflammatory/oxidative damage.

Decoding cell death signals in liver inflammation

Inflammation can be either beneficial or detrimental to the liver, depending on multiple factors. Mild (i.e., limited in intensity and destined to resolve) inflammatory responses have indeed been shown to exert consistent hepatoprotective effects, contributing to tissue repair and promoting the re-establishment of homeostasis. Conversely, excessive (i.e., disproportionate in intensity and permanent) inflammation may induce a massive loss of hepatocytes and hence exacerbate the severity of various hepatic conditions, including ischemia-reperfusion injury, systemic metabolic alterations (e.g., obesity, diabetes, non-alcoholic fatty liver disorders), alcoholic hepatitis, intoxication by xenobiotics and infection, de facto being associated with irreversible liver damage, fibrosis, and carcinogenesis. Both liver-resident cells (e.g., Kupffer cells, hepatic stellate cells, sinusoidal endothelial cells) and cells that are recruited in response to injury (e.g., monocytes, macrophages, dendritic cells, natural killer cells) emit pro-inflammatory signals including - but not limited to - cytokines, chemokines, lipid messengers, and reactive oxygen species that contribute to the apoptotic or necrotic demise of hepatocytes. In turn, dying hepatocytes release damage-associated molecular patterns that-upon binding to evolutionary conserved pattern recognition receptors-activate cells of the innate immune system to further stimulate inflammatory responses, hence establishing a highly hepatotoxic feedforward cycle of inflammation and cell death. In this review, we discuss the cellular and molecular mechanisms that account for the most deleterious effect of hepatic inflammation at the cellular level, that is, the initiation of a massive cell death response among hepatocytes.

Molecular mechanism of the inhibition effect of Lipoxin A4 on corneal dissolving pathology process

AIM

Excessive dissolve of corneal tissue induced by MMPs which were activated by cytokins and chemokines will lead to corneal ulcer. The molecular mechanism of Lipoxin A4 (LXA4) on corneal collagen degradation in three dimensions was investigated.

METHODS

Rabbit corneal fibroblasts were harvested and suspended in serum-free MEM. Type I collagen, DMEM, collagen reconstitution buffer and corneal fibroblast suspension were mixed on ice. The resultant mixture solidified in an incubator, after which test reagents and plasminogen was overlaid and the cultures were returned to the incubator. The supernatants from collagen gel incubations were collected and the amount of hydroxyproline in the hydrolysate was measured. Immunoblot analysis of MMP-1, -3 and TMMP-1,-2 was performed. MMP-2,-9 was detected by the method of Gelatin zymography. Cytotoxicity assay was measured.

RESULTS

LXA4 inhibited corneal collagen degradation in a dose and time manner. LXA4 inhibited the IL-1β induced increases in the pro-MMP-1, -2, -3, -9 and active MMP-1, -2, -3, -9 in a concentration dependent manner. LXA4 could also inhibit the IL-1β induced increases in TIMP-1, -2.

CONCLUSION

As a potent anti-inflammation reagent, LXA4 can inhibit corneal collagen degradation induced by IL-1β in corneal fibroblasts thus inhibiting corneal dissolving pathology process.

Resolution of inflammation in obesity-induced liver disease

Low-grade inflammation in adipose tissue is recognized as a critical event in the development of obesity-related co-morbidities. This chronic inflammation is powerfully augmented through the infiltration of macrophages, which together with adipocytes, perpetuate a vicious cycle of inflammatory cell recruitment and secretion of free fatty acids and deleterious adipokines that predispose to greater incidence of metabolic complications. In the last decade, many factors have been identified to contribute to mounting unresolved inflammation in obese adipose tissue. Among them, pro-inflammatory lipid mediators (i.e., leukotrienes) derived from the omega-6 polyunsaturated arachidonic acid have been shown to play a prominent role. Of note, the same lipid mediators that initially trigger the inflammatory response also signal its termination by stimulating the formation of anti-inflammatory signals. Resolvins and protectins derived from the omega-3 polyunsaturated docosahexaenoic and eicosapentaenoic acids have emerged as a representative family of this novel class of autacoids with dual anti-inflammatory and pro-resolving properties that act as “stop-signals” of the inflammatory response. This review discusses the participation of these endogenous autacoids in the resolution of adipose tissue inflammation, with a special emphasis in the amelioration of obesity-related metabolic dysfunctions, namely insulin resistance and non-alcoholic fatty liver disease.

Lipidic last breath of life in patients with alcoholic liver disease

Alcoholic liver disease (ALD) begins with the accumulation of lipid droplets in the liver. Lipids which accumulate in the liver can stimulate inflammation, and the fatty acid derivatives, hydroxyeicosatetraenoic acids (HETEs) and hydroxyoctadecadienoic acids (HODEs), may play an important role in this process. We evaluated the concentrations of linoleic and arachidonic acid derivatives in the plasma of patients with ALD, non-alcoholic fatty liver disease (NAFLD) and healthy individuals. The groups consisted of 173 subjects: 63 patients with ALD, 90 with NAFLD and 20 healthy volunteers. Plasma 12-, 15-, and 5-HETE as well as 9- and 13-HODE were assessed using HPLC and isoprostane 8-epi-PGF 2α III was evaluated with an ELISA. In addition the mRNA expression of lipoxygenases (5-LOX, 15-LOX-1, 15-LOX-2) in the liver samples of patients with ALD cirrhosis was measured. A significant difference between the plasma concentrations of the analyzed derivatives was found when divided according to gender. The most significant differences were found between healthy individuals and ALD patients, as well as ALD and NAFLD individuals regardless of gender. The increased plasma HODEs and HETEs concentrations were in line with the increase in 5- and 15-LOX-1 and 15-LOX-2 mRNA in liver samples from ALD cirrhosis patients. LOXs expression and peroxidation of polyunsaturated fatty acids by free radical-propagated chemical oxidation may be contributing factors in liver necroinflammatory injury in ALD.

New insights into the role of macrophages in adipose tissue inflammation and Fatty liver disease: modulation by endogenous omega-3 Fatty Acid-derived lipid mediators

Obesity is causally linked to a chronic state of “low-grade” inflammation in adipose tissue. Prolonged, unremitting inflammation in this tissue has a direct impact on insulin-sensitive tissues (i.e., liver) and its timely resolution is a critical step toward reducing the prevalence of related co-morbidities such as insulin resistance and non-alcoholic fatty liver disease. This article describes the current state-of-the-art knowledge and novel insights into the role of macrophages in adipose tissue inflammation, with special emphasis on the progressive changes in macrophage polarization observed over the course of obesity. In addition, this article extends the discussion to the contribution of Kupffer cells, the liver resident macrophages, to metabolic liver disease. Special attention is given to the modulation of macrophage responses by omega-3-PUFAs, and more importantly by resolvins, which are potent anti-inflammatory and pro-resolving autacoids generated from docosahexaenoic and eicosapentaenoic acids. In fact, resolvins have been shown to work as endogenous “stop signals” in inflamed adipose tissue and to return this tissue to homeostasis by inducing a phenotypic switch in macrophage polarization toward a pro-resolving phenotype. Collectively, this article offers new views on the role of macrophages in metabolic disease and their modulation by endogenously generated omega-3-PUFA-derived lipid mediators.

Molecular regulators of resolution of inflammation: potential therapeutic targets in the reproductive system

Inflammatory processes are central to reproductive events including ovulation, menstruation, implantation and labour, while inflammatory dysregulation is a feature of numerous reproductive pathologies. In recent years, there has been much research into the endogenous mechanisms by which inflammatory reactions are terminated and tissue homoeostasis is restored, a process termed resolution. The identification and characterisation of naturally occurring pro-resolution mediators including lipoxins and annexin A1 has prompted a shift in the field of anti-inflammation whereby resolution is now observed as an active process, triggered as part of a normal inflammatory response. This review will address the process of resolution, discuss available evidence for expression of pro-resolution factors in the reproductive tract and explore possible roles for resolution in physiological reproductive processes and associated pathologies.

Macrophages and tissue injury: agents of defense or destruction?

The past several years have seen the accumulation of evidence demonstrating that tissue injury induced by diverse toxicants is due not only to their direct effects on target tissues but also indirectly to the actions of resident and infiltrating macrophages. These cells release an array of mediators with cytotoxic, pro- and anti-inflammatory, angiogenic, fibrogenic, and mitogenic activity, which function to fight infections, limit tissue injury, and promote wound healing. However, following exposure to toxicants, macrophages can become hyperresponsive, resulting in uncontrolled or dysregulated release of mediators that exacerbate acute tissue injury and/or promote the development of chronic diseases such as fibrosis and cancer. Evidence suggests that the diverse activity of macrophages is mediated by distinct subpopulations that develop in response to signals within their microenvironment. Understanding the precise roles of these different macrophage populations in the pathogenic response to toxicants is key to designing effective treatments for minimizing tissue damage and chronic disease and for facilitating wound repair.

Interplay of cysteinyl leukotrienes and TGF-β in the activation of hepatic stellate cells from Schistosoma mansoni granulomas

Hepatic stellate cells (HSCs) have a critical role in liver physiology, and in the pathogenesis of liver inflammation and fibrosis. Here, we investigated the interplay between leukotrienes (LT) and TGF-β in the activation mechanisms of HSCs from schistosomal granulomas (GR-HSCs). First, we demonstrated that GR-HSCs express 5-lipoxygenase (5-LO), as detected by immunolocalization in whole cells and confirmed in cell lysates through western blotting and by mRNA expression through RT-PCR. Moreover, mRNA expression of 5-LO activating protein (FLAP) and LTC(4)-synthase was also documented, indicating that GR-HSCs have the molecular machinery required for LT synthesis. Morphological analysis of osmium and Oil-Red O-stained HSC revealed large numbers of small lipid droplets (also known as lipid bodies). We observed co-localization of lipid droplet protein marker (ADRP) and 5-LO by immunofluorescence microscopy. We demonstrated that GR-HSCs were able to spontaneously release cysteinyl-LTs (CysLTs), but not LTB(4,) into culture supernatants. CysLT production was highly enhanced after TGF-β-stimulation. Moreover, the 5-LO inhibitor zileuton and 5-LO gene deletion were able to inhibit the TGF-β-stimulated proliferation of GR-HSCs, suggesting a role for LTs in HSC activation. Here, we extend the immunoregulatory function of HSC by demonstrating that HSC from liver granulomas of schistosome-infected mouse are able to release Cys-LTs in a TGF-β-regulated manner, potentially impacting pathogenesis and liver fibrosis in schistosomiasis.

Protection from hepatic lipid accumulation and inflammation by genetic ablation of 5-lipoxygenase

Five-lipoxygenase (5-LO) has been postulated as a pathogenic factor in liver injury. Indeed, Alox5, the gene coding for 5-LO, is heavily over-expressed in experimental liver disease, in which 5-LO inhibition consistently ameliorates hepatic steatosis, inflammation and fibrosis. Herein, we report the findings in mice with targeted deletion of Alox5 as a proof of concept of the role of 5-LO in liver injury. Our findings demonstrate that ablation of Alox5 in mice confers protection against carbon tetrachloride-induced liver injury since hepatic necroinflammation, inflammatory infiltrate, hepatocyte ballooning and serum ALT levels were significantly reduced in Alox5-deficient mice. These mice also showed a lower degree of hepatic steatosis, which affected micro- and macrosteatosis to a similar extent. Moreover, microarray analysis revealed a differential profile of hepatic gene expression in Alox5-deficient mice, with a total of 117 genes differentially expressed in these animals. Functional grouping of these genes revealed that 28 (approximately 24% of total changes) were related to the category of lipid metabolism, including the lipogenic factors Lpin1, C/EBP, Fasn, Acly and Elovl6. Moreover, Ingenuity Pathway Analysis revealed lipid metabolism as the molecular/cellular function most affected by the loss of Alox5. These findings confirm at a genetic level that Alox5 plays a pathogenic role in the response of the liver to injury.

5-lipoxygenase deficiency reduces hepatic inflammation and tumor necrosis factor alpha-induced hepatocyte damage in hyperlipidemia-prone ApoE-null mice

The actual risk factors that drive hepatic inflammation during the transition from steatosis to steatohepatitis are unknown. We recently demonstrated that hyperlipidemia-prone apolipoprotein E-deficient (ApoE(-/-)) mice exhibit hepatic steatosis and increased susceptibility to hepatic inflammation and advanced fibrosis. Because the proinflammatory 5-lipoxygenase (5-LO) pathway was found to be up-regulated in these mice and given that 5-LO deficiency confers cardiovascular protection to ApoE(-/-) mice, we determined the extent to which the absence of 5-LO would alter liver injury in these mice. Compared with ApoE(-/-) mice, which showed expected hepatic steatosis and inflammation, ApoE/5-LO double-deficient (ApoE(-/-)/5-LO(-/-)) mice exhibited reduced hepatic inflammation, macrophage infiltration, tumor necrosis factor alpha (TNF-alpha), monocyte chemoattractant protein-1 (MCP-1) and interleukin (IL)-18 expression, caspase-3 and nuclear factor-kappaB (NF-kappaB) activities, and serum alanine aminotransferase levels in the absence of changes in hepatic steatosis. The lack of 5-LO produced a remarkable insulin-sensitizing effect in the adipose tissue because peroxisome proliferator-activated receptor gamma, insulin receptor substrate-1, and adiponectin were up-regulated, whereas c-Jun amino-terminal kinase phosphorylation and MCP-1 and IL-6 expression were down-regulated. On the other hand, hepatocytes isolated from ApoE(-/-)/5-LO(-/-) mice were more resistant to TNF-alpha-induced apoptosis. The 5-LO products leukotriene (LT) B(4), LTD(4), and 5-HETE consistently triggered TNF-alpha-induced apoptosis and compromised hepatocyte survival by suppressing NF-kappaB activity in the presence of actinomycin D. Moreover, ApoE(-/-)/5-LO(-/-) mice were protected against sustained high-fat diet (HFD)-induced liver injury and hepatic inflammation, macrophage infiltration and insulin resistance were significantly milder than those of ApoE(-/-) mice. Finally, pharmacological inhibition of 5-LO significantly reduced hepatic inflammatory infiltrate in the HFD and ob/ob models of fatty liver disease.

CONCLUSION

These combined data indicate that hyperlipidemic mice lacking 5-LO are protected against hepatic inflammatory injury, suggesting that 5-LO is involved in mounting hepatic inflammation in metabolic disease.

Nutrigenomic analysis of the protective effects of bilberry anthocyanin-rich extract in apo E-deficient mice

Intake of anthocyanin-rich foods has been associated with a reduced risk of cardiovascular diseases. Supplementation with anthocyanin-rich extracts from black rice or purple sweet potato was reported to attenuate atherosclerotic lesion development in apolipoprotein E-deficient (apo E(-/-)) mice. However, the mechanism(s) of their preventive action are not completely understood. Previous studies revealed that anthocyanins altered mRNA levels of genes related to atherosclerosis in cultured macrophages and endothelial cells, but in vivo studies remain scarce. The aim of the study was to investigate the impact of bilberry anthocyanin-rich extract (BE) supplementation on gene expression in the liver of apo E(-/-) mice, the widely used model of atherosclerosis. The liver was chosen because it is the main site of lipid metabolism. Apo E(-/-) mice received for 2 weeks a standard diet supplemented with a nutritional dose of BE (0.02%). This study focused on the early stage of atherosclerosis development for better assessment of anthocyanin action on initiation mechanisms of this pathology. The results showed that a 2-week supplementation significantly reduced plasmatic total cholesterol and hepatic triglyceride levels, whereas the plasmatic antioxidant status remained unchanged. Transcriptional analysis, using microarrays, revealed that the expression of 2,289 genes was significantly altered. BE over-expressed genes involved in bile acid synthesis and cholesterol uptake into the liver and down-regulated the expression of pro-inflammatory genes. These results suggest an anti-atherogenic effect of BE through the regulation of cholesterol metabolism and liver inflammation and provide a global integrated view of the mechanisms involved in the preventive action of this extract.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12263-010-0171-0) contains supplementary material, which is available to authorized users.

Inflammatory disease and cancer with a decrease in Kupffer cell numbers in Nucling-knockout mice

Nucling is a stress-inducible protein associated with apoptosomes. The cytochrome c-triggered formation of apoptosomes represents a key-initiating event in apoptosis. We have recently reported that Nucling regulates the apoptotic pathway by controlling the activation of NF-kappaB as well. Here we show that hepatocellular carcinoma (HCC) arising spontaneously against a background of hepatitis occurred more frequently in Nucling-knockout (KO) mice than wild-type (WT) mice. Biochemical serum testing revealed potential liver dysfunction with hypercholesterolemia in Nucling-KO males. In the background of Nucling-KO mice, we observed the up-regulation of TNFalpha, spontaneous NF-kappaB-activation and the induction of galectin-3 expression in liver. In addition, we observed a decrease in the number of Kupffer cells (KCs) in the KO mice. KCs are important for the hepatic immune system, acting as phagocytes or antigen-presenting cells (APCs). We found that KCs in Nucling-KO mice were apoptotic possibly through the up-regulation of TNFalpha. These observations indicate that Nucling is important for the regulation of NF-kappaB signals in liver. We propose that Nucling deficiency could be a powerful tool to reveal the NF-kappaB-related molecular networks leading to hepatitis and HCC development.

Inhibition of soluble epoxide hydrolase enhances the anti-inflammatory effects of aspirin and 5-lipoxygenase activation protein inhibitor in a murine model

Inflammation is a multi-staged process whose expansive phase is thought to be driven by acutely released arachidonic acid (AA) and its metabolites. Inhibition of cyclooxygenase (COX), lipoxygenase (LOX), or soluble epoxide hydrolase (sEH) is known to be anti-inflammatory. Inhibition of sEH stabilizes the cytochrome P450 (CYP450) products epoxyeicosatrienoic acids (EETs). Here we used a non-selective COX inhibitor aspirin, a 5-lipoxygenase activation protein (FLAP) inhibitor MK886, and a sEH inhibitor t-AUCB to selectively modulate the branches of AA metabolism in a lipopolysaccharide (LPS)-challenged murine model. We used metabolomic profiling to simultaneously monitor representative AA metabolites of each branch. In addition to the significant crosstalk among branches of the AA cascade during selective modulation of COX, LOX, or sEH, we demonstrated that co-administration of t-AUCB enhanced the anti-inflammatory effects of aspirin or MK886, which was evidenced by the observations that co-administration resulted in favorable eicosanoid profiles and better control of LPS-mediated hypotension as well as hepatic protein expression of COX-2 and 5-LOX. Targeted disruption of the sEH gene displayed a parallel profile to that produced by t-AUCB. These observations demonstrate a significant level of crosstalk among the three major branches of the AA cascade and that they are not simply parallel pathways. These data illustrate that inhibition of sEH by both pharmacological intervention and gene knockout enhances the anti-inflammatory effects of aspirin and MK886, suggesting the possibility of modulating multiple branches to achieve better therapeutic effects.

Lipoxin A(4) inhibited hepatocyte growth factor-induced invasion of human hepatoma cells

AIM

Inflammation is a critical component of tumor progression. Lipoxin A(4) (LXA(4)) has been approved for potent anti-inflammatory properties. Recently, it was reported that LXA(4) repressed the expression and activity of cyclooxygenase-2 (COX-2), which is essential for invasion. However, there are few reports dealing with its effects on cancer. To explore whether LXA(4) regulate invasion, the effects of LXA(4) and its receptor agonist BML-111 on hepatocyte growth factor (HGF)-induced invasion of hepatoma cells and the possible mechanisms were researched.

METHODS

Lipoxin A(4) receptor (ALX) expression in HepG2 cells were measured through reverse transcription polymerase chain reaction and western blot. Cytotoxicity of LXA(4) and BML-111 to HepG2 cells was detected by MTT and ((3)H)-TdR incorporation assay. Cell migration and invasion assays were performed using a Boyden chemotaxis chamber. COX-2 expression was detected by real-time polymerase chain reaction and western blot, respectively. Moreover, the expressions of matrix metalloproteinases (MMP)-2, MMP-9, IkappaBalpha and nuclear factor-kappaB (NF-kappaB) p65 were observed via western blot, and NF-kappaB transcriptional activity was tested by transfections and luciferase activities assay.

RESULTS

ALX expression was detected in HepG2 cells, and suitable concentrations of LXA(4) and BML-111 had no cytotoxicity to cells. LXA(4) and BML-111 inhibited HGF-induced migration and invasion; downregulated COX-2, MMP-2 and -9; restrained HGF-induced IkappaBalpha degradation, NF-kappaB translocation and the transcriptional activity of NF-kappaB in HepG2 cells. Furthermore, exogenous PGE2 could reverse the inhibitory effects of LXA(4) also BML-111 on HGF-induced invasion and migration partially.

CONCLUSION

LXA(4) inhibited HGF-induced invasion of HepG2 cells through NF-kappaB/COX-2 signaling pathway partially.

[Basic mechanisms of hepatocellular injury. Role of inflammatory lipid mediators]

The presence of a lesion in the cellular parenchyma is common to a large number of chronic liver diseases, such as viral hepatitides, alcoholic hepatitis, chronic cholestasis and steatohepatitis. Although the pathogenesis may vary according to the etiological agent, a series of mechanisms is common to all. Notable among these mechanisms are Kupffer cell activation and inflammatory cell recruitment, free oxygen radical formation and the development of oxidative stress, cytokine production, mainly TNFa and TGFb, and inflammatory mediator release due to arachidonic acid oxidation through the COX-2 and 5-LO pathways.

The protective effect of montelukast sodium on carbon tetrachloride induced hepatopathy in rat

AIM

This study investigates the effects of montelukast sodium (MK) (CysLTLT1 receptor antagonist) on CCl(4)induced hepatopathy on rat.

MATERIAL AND METHODS

We worked on 4 groups of 10 Wistar male rats each. The groups received as follows: group I (control group) - saline, group II - MK 5mg/kg/day i.p. for 5 days, group III - MK 5mg/kg/day i.p., 1 day prior to and 4 days concomitantly with CCl(4) p.o., 0.3ml/Kg/day and group IV - CCl(4), p.o., 0.3ml/Kg/day for 4 days. One day after the last administration, samples of blood were taken and alanine aminotransferase (ALT), total bilirubin (TB), direct bilirubin (DB), malondialdehyde (MDA), catalase (CAT) as well as total antioxidant capacity (TAC) were determined. The histopathological exam was performed. We also determined superoxide dismutase (SOD), MDA, CAT and GSH in liver homogenate.

RESULTS

Compared to group IV, group III exhibited statistically significant lower levels of ALT (318+/-15.75 versus 203.14+/-10.28 UI, p<0.0001), TB (3.16+/-0.30 versus 1.99+/-0.08mg/dl, p<0.0001), MDA in blood and in liver homogenate (4.98+/-1.71 versus 2.15+/-1.18nmol/ml, p=0.0004) and higher levels of SOD and CAT. Histopathologically, group IV presented important macro- and micro-vesicular hepatic steatosis and group III preserved lobular histoarchitecture and had less severe cellular lesions.

CONCLUSION

MK exhibits a partial hepatoprotective effect on rats treated with CCl(4).

Regulatory effects of arachidonate 5-lipoxygenase on hepatic microsomal TG transfer protein activity and VLDL-triglyceride and apoB secretion in obese mice

As 5-lipoxygenase (5-LO) is an emerging target in obesity and insulin resistance, we have investigated whether this arachidonate pathway is also implicated in the progression of obesity-related fatty liver disease. Our results show that 5-LO activity and 5-LO-derived product levels are significantly elevated in the liver of obese ob/ob mice with respect to wild-type controls. Treatment of ob/ob mice with a selective 5-LO inhibitor exerted a remarkable protection from hepatic steatosis as revealed by decreased oil red-O staining and reduced hepatic triglyceride (TG) concentrations. In addition, 5-LO inhibition in ob/ob mice downregulated genes involved in hepatic fatty acid uptake (i.e., L-FABP and FAT/CD36) and normalized peroxisome proliferator-activated receptor alpha (PPARalpha) and acyl-CoA oxidase expression, whereas the expression of lipogenic genes [i.e., fatty acid synthase (FASN) and SREBP-1c] remained unaltered. Furthermore, 5-LO inhibition restored hepatic microsomal TG transfer protein (MTP) activity in parallel with a stimulation of hepatic VLDL-TG and apoB secretion in ob/ob mice. Consistent with these findings, 5-LO products directly inhibited MTP activity and triggered cytosolic TG accumulation in CC-1 cells, a murine hepatocyte cell line. Taken together, these findings identify a novel steatogenic role for 5-LO in the liver through mechanisms involving the regulation of hepatic MTP activity and VLDL-TG and apoB secretion.

Endogenous lipid mediators in the resolution of airway inflammation

Acute inflammation in the lung is fundamentally important to host defence, but chronic or excessive inflammation leads to several common respiratory diseases, including asthma and acute respiratory distress syndrome. The resolution of inflammation is an active process. In health, events at the onset of acute inflammation establish biosynthetic circuits for specific chemical mediators that later serve as agonists to orchestrate a return to tissue homeostasis. In addition to an overabundance of pro-inflammatory stimuli, pathological inflammation can also result from defects in resolution signalling. The understanding of anti-inflammatory, pro-resolution molecules and their counter-regulatory signalling pathways is providing new insights into the molecular pathophysiology of lung disease and opportunities for the design of therapeutic strategies. In the present review, the growing family of lipid mediators of resolution is examined, including lipoxins, resolvins, protectins, cyclopentenones and presqualene diphosphate. Roles are uncovered for these compounds, or their structural analogues, in regulating airway inflammation.

Protective effects of BML-111, a lipoxin A(4) receptor agonist, on carbon tetrachloride-induced liver injury in mice

BACKGROUND

Lipoxins (LX) are trihydroxytetraene-containing eicosanoids that display unique anti-inflammatory and pro-resolving actions during various inflammatory conditions, but the pathophysiological significance of LX in liver disorders remains unknown.

METHODS

In the present study, we used a murine model of carbon tetrachloride (CCl(4))-induced acute liver injury to investigate the effects of LX on the progression of acute liver injury.

RESULTS

The results indicated that the lipoxin A(4) receptor (ALX) was upregulated after giving CCl(4). BML-111, a commercially available ALX agonist, effectively protected the liver from CCl(4)-induced injury as evidenced by decreased serum aminotransferase (ALT, AST) levels and improved histological damage. The dampened liver injury was accompanied byreduced malondialdehyde (MDA) content in liver homogenates and decreased concentration of tumor necrosis factor-alpha (TNF-alpha) in the serum. Most interestingly, BML-111 markedly upregulated hepatic heme oxygenase-1 (HO-1) expression in CCl(4)-treated mice, which might provide antioxidative activities in the liver.

CONCLUSION

These data indicate that ALX agonist BML-111 plays a critical protective role in CCl(4)-induced acute liver injury through limiting the inflammatory response and promoting antioxidative protein expression.

Role of TLR-4 in liver macrophage and endothelial cell responsiveness during acute endotoxemia

Liver macrophages and endothelial cells have been implicated in hepatotoxicity induced by endotoxin (ETX). In these studies, we analyzed the role of toll-like receptor 4 (TLR-4) in the response of these cells to acute endotoxemia. Treatment of control C3H/HeOuJ mice with ETX (3 mg/kg, i.p.) resulted in increased numbers of activated macrophages in the liver. This was associated with morphological changes in the cells and a rapid (within 3 h) induction of nitric oxide synthase-2, cyclooxygenase-2, microsomal PGE synthase-1, interleukin-1 beta and tumor necrosis factor alpha gene expression. In endothelial cells, acute endotoxemia led to increased expression of these genes, as well as 5-lipoxygenase. In contrast, liver sinusoidal cells from C3H/HeJ TLR-4 mutant mice were relatively unresponsive to ETX. Treatment of C3H/HeOuJ, but not C3H/HeJ mice with ETX, resulted in activation of transcription factors AP-1 and NF-kappaB in liver sinusoidal cells, which was evident within 3 h. Whereas in macrophages, transcription factor activation was transient, in endothelial cells, it persisted for 24 h. In C3H/HeOuJ mice treated with ETX, activation of p38 MAP kinase was also evident in macrophages and endothelial cells, and JNK kinase in macrophages. In contrast, reduced protein kinase B (AKT) was noted in macrophages. In C3H/HeJ mice, ETX administration also led to activation of p38 MAP kinase in macrophages with no effects on JNK, p44/42 MAP kinase or AKT. These studies demonstrate that liver macrophages and endothelial cells are highly responsive to acute endotoxemia. Moreover, this activity is largely dependent on TLR-4.

Comparative protection against liver inflammation and fibrosis by a selective cyclooxygenase-2 inhibitor and a nonredox-type 5-lipoxygenase inhibitor

In this study, we examined the relative contribution of cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LO), two major proinflammatory pathways up-regulated in liver disease, to the progression of hepatic inflammation and fibrosis. Separate administration of 4-[5-(4-chlorophenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide (SC-236), a selective COX-2 inhibitor, and CJ-13,610, a 5-LO inhibitor, to carbon tetrachloride-treated mice significantly reduced fibrosis as revealed by the analysis of Sirius Red-stained liver sections without affecting necroinflammation. Conversely, combined administration of SC-236 and 4-[3-[4-(2-methylimidazol-1-yl)-phenylthio]]phenyl-3,4,5,6-tetrahydro-2H-pyran-4-carboxamide (CJ-13,610) reduced both necroinflammation and fibrosis. These findings were confirmed in 5-LO-deficient mice receiving SC-236, which also showed reduced hepatic monocyte chemoattractant protein 1 expression. Interestingly, SC-236 and CJ-13,610 significantly increased the number of nonparenchymal liver cells with apoptotic nuclei (terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive). Additional pharmacological profiling of SC-236 and CJ-13,610 was performed in macrophages, the primary hepatic inflammatory cell type. In these cells, SC-236 inhibited prostaglandin (PG) E2 formation in a concentration-dependent manner, whereas CJ-13,610 blocked leukotriene B4 biosynthesis. Of note, the simultaneous addition of SC-236 and CJ-13,610 resulted in a higher inhibitory profile on PGE2 biosynthesis than the dual COX/5-LO inhibitor licofelone. These drugs differentially regulated interleukin-6 mRNA expression in macrophages. Taken together, these findings indicate that both COX-2 and 5-LO pathways are contributing factors to hepatic inflammation and fibrosis and that these two pathways of the arachidonic acid cascade represent potential targets for therapy.

Docosahexaenoic acid (DHA) blunts liver injury by conversion to protective lipid mediators: protectin D1 and 17S-hydroxy-DHA

Docosahexaenoic acid (DHA) is a omega-3 essential fatty acid that reduces the incidence and severity of a number of diseases. Recently, a novel series of DHA-derived lipid mediators with potent protective actions has been identified. In this study we demonstrate that dietary amplification of these DHA-derived products protects the liver from necroinflammatory injury. In vitro, supplementation of hepatocytes with DHA significantly reduced hydrogen peroxide-induced DNA damage, evaluated by the "comet assay," and oxidative stress, determined by measurement of malondialdehyde levels. In vivo, dietary supplementation of mice with DHA ameliorated carbon tetrachloride-induced necroinflammatory damage. In addition, hepatic cyclooxygenase-2 expression and PGE2 levels were significantly reduced in mice fed DHA-enriched diets. In these animals, increased hepatic formation of DHA-derived lipid mediators (i.e., 17S-hydroxy-DHA (17S-HDHA) and protectin D1) was detected by HPLC-gas chromatography/mass spectrometry analysis. Consistent with these findings, synthetic 17-HDHA abrogated genotoxic and oxidative damage in hepatocytes and decreased TNF-alpha release and 5-lipoxygenase expression in macrophages. In a transactivation assay, 17-HDHA acted in a concentration-dependent manner as a PPARgamma agonist. Taken together, these findings identify a potential role for DHA-derived products, specifically 17S-HDHA and protectin D1, in mediating the protective effects of dietary DHA in necroinflammatory liver injury.