BML-11, a lipoxin receptor agonist, protected carbon tetrachloride-induced hepatic fibrosis in rats

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.

Role of eicosanoids in liver repair, regeneration and cancer

Eicosanoids are lipid signaling molecules derived from the oxidation of ω-6 fatty acids, usually arachidonic acid. There are three major pathways, including the cyclooxygenase (COX), lipoxygenase (LOX), and P450 cytochrome epoxygenase (CYP) pathway. Prostanoids, which include prostaglandins (PG) and thromboxanes (Tx), are formed via the COX pathway, leukotrienes (LT) and lipoxins (LX) by the action of 5-LOX, and hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs) by CYP. Although eicosanoids are usually associated with pro-inflammatory responses, non-classic eicosanoids, as LX, have anti-inflammatory and pro-resolving properties. Eicosanoids like PGE₂, LTB₄ and EETs have been involved in promoting liver regeneration after partial hepatectomy. PGE₂ and LTB₄ have also been reported to participate in the regenerative phase after ischemia and reperfusion (I/R), while cysteinyl leukotrienes (Cys-LT) contribute to the inflammatory process associated with I/R and are also involved in liver fibrosis and cirrhosis. However, LX, another product of 5-LOX, have the opposite effect, acting as pro-resolving mediators in these pathologies. In liver cancer, most studies show that eicosanoids, with the exception of LX, promote the proliferation of hepatocellular carcinoma cells and favor metastasis. This review summarizes the synthesis of different eicosanoids in the liver and discusses key findings from basic research linking eicosanoids to liver repair, regeneration and cancer and the impact of targeting eicosanoid cascade. In addition, studies in patients are presented that explore the potential use of eicosanoids as biomarkers and show correlations between eicosanoid production and the course and prognosis of liver disease.

Beneficial role of bioactive lipids in the pathobiology, prevention, and management of HBV, HCV and alcoholic hepatitis, NAFLD, and liver cirrhosis: A review

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HBV, HBC, and alcoholic and non-alcoholic fatty liver disease lead to liver cirrhosis.

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All these are inflammatory conditions with PUFA deficiency state.

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HBV, HCV, and alcohol inhibit PUFA metabolism.

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PUFAs and their metabolites have anti-viral and cytoprotective actions.

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PUFAs and vitamin C may be of benefit in NAFLD, AFLD, and liver cirrhosis.

It has been suggested that hepatitis B virus (HBV)- and hepatitis C virus (HCV)-induced hepatic damage and cirrhosis and associated hypoalbuminemia, non-alcoholic fatty liver disease (NAFLD), and alcoholic fatty liver disease (AFLD) are due to an imbalance between pro-inflammatory and anti-inflammatory bioactive lipids. Increased tumour necrosis factor (TNF)-α production induced by HBV and HCV leads to a polyunsaturated fatty acid (PUFA) deficiency and hypoalbuminemia. Albumin mobilizes PUFAs from the liver and other tissues and thus may aid in enhancing the formation of anti-inflammatory lipoxins, resolvins, protectins, maresins and prostaglandin E1 (PGE1) and suppressing the production of pro-inflammatory PGE2. As PUFAs exert anti-viral and anti-bacterial effects, the presence of adequate levels of PUFAs could inactivate HCV and HBV and prevent spontaneous bacterial peritonitis observed in cirrhosis. PUFAs, PGE1, lipoxins, resolvins, protectins, and maresins suppress TNF-α and other pro-inflammatory cytokines, exert cytoprotective effects, and modulate stem cell proliferation and differentiation to promote recovery following hepatitis, NAFLD and AFLD. Based on this evidence, it is proposed that the administration of albumin in conjunction with PUFAs and their anti-inflammatory products could be beneficial for the prevention of and recovery from NAFLD, hepatitis and cirrhosis of the liver. NAFLD is common in obesity, type 2 diabetes mellitus, and metabolic syndrome, suggesting that even these diseases could be due to alterations in the metabolism of PUFAs and other bioactive lipids. Hence, PUFAs and co-factors needed for their metabolism and albumin may be of benefit in the prevention and management of HBV, HCV, alcoholic hepatitis and NAFLD, and liver cirrhosis.

BML-111, a lipoxin receptor agonist, protects against acute injury via regulating the renin angiotensin-aldosterone system

BACKGROUND

The renin angiotensin-aldosterone system (RAAS) and lipoxins (LXs) have similar roles in many processes. We previously reported that BML-111, a Lipoxin receptor agonist, inhibited chronic injury hepatic fibrosis by regulating RAAS, but whether LXs are involved in BML-111-mediated protection from acute injury is unclear still.

METHODS

We established models of acute liver/lung injury and confirmed them with histopathology and myeloperoxidase (MPO) measurements. BML-111, a lipoxin receptor agonist, was applied to mimic the effects of LXs. The contents and activities of angiotensin converting enzyme(ACE) and angiotensinconverting enzyme 2 (ACE2) were measured through ELISA and activity assay kits respectively. Angiotensin II (AngII), angiotensin-(1-7) (Ang-1-7), AngII type 1 receptor (AT1R), and Mas receptor were quantified with ELISA and Western blot.

RESULTS

Models of acute injury were established successfully and BML-111 protected LPS-induced acute lung injury and LPS/D-GalN-induced acute liver injury. BML-111 repressed the activity of ACE, but increased the activity of ACE2. BML-111 decreased the expression levels of ACE, AngII, and AT1R, meanwhile increased the levels of ACE2, Ang-(1-7), and Mas. Furthermore, BOC-2, an inhibitor of lipoxin receptor, reversed all the effects.

CONCLUSION

BML-111 could protect against acute injury via regulation RAAS.

BML-111 suppresses TGF-β1-induced lung fibroblast activation in vitro and decreases experimental pulmonary fibrosis in vivo

Pulmonary fibrosis is an aggressive end‑stage disease. Transforming growth factor‑β1 (TGF‑β1) mediates lung fibroblast activation and is essential for the progress of pulmonary fibrosis. BML‑111, a lipoxinA4 (LXA4) receptor (ALX) agonist, has been reported to possess anti‑fibrotic properties. The present study aimed to elucidate whether BML‑111 inhibits TGF‑β1‑induced mouse embryo lung fibroblast (NIH3T3 cell line) activation in vitro and bleomycin (BLM)‑induced pulmonary fibrosis in vivo. In vitro experiments demonstrated that BML‑111 treatment inhibits TGF‑β1‑induced NIH3T3 cell viability and the expression of smooth muscle α actin (α‑SMA), fibronectin and total collagen. Furthermore, this suppressive effect was associated with mothers against decapentaplegic homolog (Smad)2/3, extracellular signal‑regulated kinase (ERK) and Akt phosphorylation interference. In vivo experiments revealed that BML‑111 treatment markedly improved survival rate and ameliorated the destruction of lung tissue structure. It also reduced interleukin‑1β (IL‑1β), tumor necrosis factor‑α (TNF‑α) and TGF‑β1 expression in the BLM intratracheal mouse model. In addition, the expression ofα‑SMA and extracellular matrix (ECM) deposition (total collagen, hydroxyproline and fibronectin) were also suppressed following BML‑111 treatment. However, BOC‑2, an antagonist of ALX, partially weakened the effects of BML‑111. In conclusion, these results indicated that BML‑111 inhibits TGF‑β1‑induced fibroblasts activation and alleviates BLM‑induced pulmonary fibrosis. Therefore, BML‑111 may be used as a potential therapeutic agent for pulmonary fibrosis treatment.

Lipoxin A4 and its analog suppress hepatocarcinoma cell epithelial-mesenchymal transition, migration and metastasis via regulating integrin-linked kinase axis

Epithelial-mesenchymal Transition (EMT) and migration play an important role in tumor progression, and lipoxin (LX), the 'stop signal' for inflammation, has been studied in basic research for its anti-inflammatory or inflammatory pro-resolving properties. Here, in the in vitro experiment, we showed that LXA₄ could inhibit the EMT and migration in phorbol myristate acetate (PMA) or activated conditioned medium (ACM)-stimulated Hep3B cells by downregulation of integrin-linked kinase (ILK), a pseudokinase in cytoplasm and these effects were via inhibiting the phosphorylation of Akt and GSK3β. Morover, LXA₄ could not affect the EMT and migration of PMA-stimulated Hep3B cells by knockdown of ILK. In the in vivo experiment, BML-111 (the analog of LXA₄) could inhibit the EMT and metastasis of hepatocarcinoma cells. We also demonstrated that ILK siRNA inhibited phosphorylation of downstream signaling targets Akt and GSK3β, decreased expression of MMP-2 and MMP-9. These results showed that LXA₄ could be a possible candidate for liver cancer therapy, and blocking ILK axis would be an effective drug target.

Lipoxin A4 reverses mesenchymal phenotypes to attenuate invasion and metastasis via the inhibition of autocrine TGF-β1 signaling in pancreatic cancer

Background

Pancreatic cancer is a lethal disease in part because of its potential for aggressive invasion and metastasis. Lipoxin A4 (LXA4) is one of the metabolites that is derived from arachidonic acid and that is catalyzed by 15-lipoxygenase (15-LOX), and it has recently been reported to exhibit anti-cancer effects. However, the role of LXA4 in pancreatic cancer remains to be elucidated.

Methods

Pancreatic cell lines were treated with vehicle or LXA4, and the invasive capacity was then assessed by Transwell assays. The expression of epithelial and mesenchymal markers was determined by western blotting and immunofluorescence. Anti-TGF-β1 neutralizing antibody and exogenous recombinant human TGF-β1 (rhTGF-β1) were used to study the effect of LXA4 on the TGF-β signaling. A liver metastasis model was applied to investigate the effect of LXA4 in vivo. The correlation between the Lipoxin effect score (LES) and the clinical-pathological features of pancreatic cancer was also analyzed.

Results

We found that in patients with pancreatic cancer, low LES was correlated with aggressive metastatic potential. The LXA4 activity, which was mediated by the LXA4 receptor FPRL1, could significantly suppress invasion capacity and mesenchymal phenotypes. The expression and autocrine signaling pathway activity of TGF-β1 were also downregulated by LXA4. In the liver metastasis model in nude mice, the stable analog of LXA4, BML-111, could inhibit the metastasis of pancreatic cancer cells.

Conclusion

Our results demonstrated that LXA4 could reverse mesenchymal phenotypes, which attenuated invasion and metastasis via the inhibition of autocrine TGF-β1 signaling in pancreatic cancer, which may provide a new strategy to prevent the metastasis of pancreatic cancer.

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.

BML-111 Protected LPS/D-GalN-Induced Acute Liver Injury in Rats

Lipoxins (LXs) display unique pro-resolving and anti-inflammatory functions in a variety of inflammatory conditions. The present study was undertaken to investigate the effects of BML-111 (5(S),6(R),7-trihydroxyheptanoic acid methyl ester), the agonist of lipoxin A₄ receptor, in a model of Lipopolysaccharides (LPS) and d-Galactosamine (d-GalN) induced acute liver injury, and to explore the mechanisms. Histopathological analyses were carried out to quantify liver injury degree. The activities of myeloperoxidase (MPO) were examined to evaluate the levels of neutrophil infiltration. The activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in serum were detected to evaluate the functions of the liver. The amounts of tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), and interleukin-1β (IL-1β) were measured using enzyme-linked immunosorbent assay (ELISA), and the expression levels of transforming growth factor-β1(TGF-β1) and cyclooxygenase-2 (COX-2) were examined using Western blotting. The antioxidant capacity, the activities of inducible nitric oxide synthase (iNOS), the contents of malondialdehyde (MDA) and nitric oxide (NO) were analyzed with the kits via biochemical analysis. We established the model of acute liver injury with lipopolysaccharide and d-Galactosamine (LPS/d-GalN): (1) histopathological results and MPO activities, with the activities of AST and ALT in serum, consistently demonstrated LPS and d-GalN challenge could cause severe liver damage, but BML-111 could prevent pathological changes, inhibit neutrophil infiltration, and improve the hepatic function; (2) LPS/d-GalN increased TNF-α, IL-1β, COX-2, and IL-10, while decreasing TGF-β1. However, BML-111 could repress LPS/d-GalN -induced TNF-α, IL-1β and COX-2, meanwhile increasing the expression levels of TGF-β1 and IL-10; (3) LPS/d-GalN inhibited the activities of superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (T-AOC), and hydroxyl radical-scavenging ability, simultaneously increasing the levels of MDA and NO, so also the activity of iNOS. Otherwise, BML-111 could reverse all the phenomena. In a word, BML-111 played a protective role in acute liver injury induced by LPS and d-GalN in rats, through improving antioxidant capacity and regulating the balance of inflammatory cytokines.

Lipoxin A4 exerts protective effects against experimental acute liver failure by inhibiting the NF-κB pathway

Although rare, acute liver failure (ALF) is associated with high levels of mortality, warranting the development of novel therapies. Nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) play roles in ALF. Lipoxin A4 (LXA4) has been shown to alleviate inflammation in non-hepatic tissues. In the present study, we explored whether LXA4 exerted hepatoprotective effects in a rat model of ALF. A rat model of ALF was generated by intraperitoneal injections of D-galactosamine (300 mg/kg) and lipopolysaccharide (50 µg/kg). Animals were randomly assigned to: control group (no ALF); model group (ALF); and the groups treated with a low dose (0.5 µg/kg), medium dose (1 µg/kg), and high dose (2 µg/kg) of LXA4 (all with ALF); and pyrrolidine dithiocarbamate (PDTC)-treated group (ALF and 100 mg/kg PDTC, an inhibitor of NF-κB). Liver histology was measured using H&E staining, serum levels by ELISA, and liver mRNA expression was measured by RT-PCR for the detection of the pro‑inflammatory cytokines TNF-α and IL-6. Liver cell apoptosis (as measured using the TUNEL method and examining caspase-3 activity), and Kupffer cell NF-κB activity [using an electrophoretic mobility shift assay (EMSA)] were examined. Serum levels of transaminases, TNF-α and interleukin-6 (IL-6) were substantially higher in the model group compared to controls. In the model group, significant increases in TNF-α and IL-6 mRNA expression, TUNEL‑positive cells, and caspase-3 activity in the liver tissue were noted. LXA4 improved liver pathology and significantly decreased the indicators of inflammatory response and apoptosis in a dose-dependent manner. High-dose LXA4 provided better protection than PDTC. LXA4 administration significantly decreased NF-κB expression in hepatocytes and Kupffer cells. These results indicated that LXA4 inhibited NF-κB activation, reduced the secretion of pro-inflammatory cytokines, and inhibited apoptosis of liver cells, thereby exerting protective effects against ALF.

Maresin 1, a Proresolving Lipid Mediator, Mitigates Carbon Tetrachloride-Induced Liver Injury in Mice

Maresin 1 (MaR 1) was recently reported to have protective properties in several different animal models of acute inflammation by inhibiting inflammatory response. However, its function in acute liver injury is still unknown. To address this question, we induced liver injury in BALB/c mice with intraperitoneal injection of carbon tetrachloride with or without treatment of MaR 1. Our data showed that MaR 1 attenuated hepatic injury, oxidative stress, and lipid peroxidation induced by carbon tetrachloride, as evidenced by increased thiobarbituric acid reactive substances and reactive oxygen species levels were inhibited by treatment of MaR 1. Furthermore, MaR 1 increased activities of antioxidative mediators in carbon tetrachloride-treated mice liver. MaR 1 decreased indices of inflammatory mediators such as tumor necrosis factor-α, interleukin-6, interleukin-1β, monocyte chemotactic protein 1, myeloperoxidase, cyclooxygenase-2, and inducible nitric oxide synthase. Administration of MaR 1 inhibited activation of nuclear factor kappa B (NF-κb) and mitogen-activated protein kinases (MAPKs) in the liver of CCl4 treated mice. In conclusion, these results suggested the antioxidative, anti-inflammatory properties of MaR 1 in CCl4 induced liver injury. The possible mechanism is partly implicated in its abilities to inhibit ROS generation and activation of NF-κb and MAPK pathway.

Activation of annexin A1 signalling in renal fibroblasts exerts antifibrotic effects

AIM

The anti-inflammatory protein annexin A1 (AnxA1) and its formyl peptide receptor 2 (FPR2) have protective effects in organ fibrosis. Their role in chronic kidney disease (CKD) has not yet been elucidated. Our aim was to characterize the AnxA1/FPR2 system in models of renal fibrosis.

METHODS

Rats were treated with angiotensin receptor antagonist during the nephrogenic period (ARAnp) to induce late-onset hypertensive nephropathy and fibrosis. Localization and regulation of AnxA1 and FPR2 were studied by quantitative real-time PCR and double labelling immunofluorescence. Biological effects of AnxA1 were studied in cultured renal fibroblasts from AnxA1(-/-) and wild-type mice.

RESULTS

Angiotensin receptor antagonist during the nephrogenic period kidneys displayed matrix foci containing CD73(+) fibroblasts, alpha-smooth muscle actin (a-SMA)(+) myofibroblasts and CD68(+) macrophages. TGF-β and AnxA1 mRNAs were ~threefold higher than in controls. AnxA1 was localized to macrophages and fibroblasts; myofibroblasts were negative. FPR2 was localized to fibroblasts, myofibroblasts, macrophages and endothelial cells. AnxA1 and FPR2 immunoreactive signals were increased in the foci, with fibroblasts and macrophages expressing both proteins. AnxA1(-/-) fibroblasts revealed higher α-SMA (sevenfold) and collagen 1A1 (Col1A1; 144-fold) mRNA levels than controls. Treatment of murine WT fibroblasts with TGF-β (22.5 ng mL 24 h(-1)) increased mRNA levels of α-SMA (9.3-fold) and Col1A1 (fourfold). These increases were greatly attenuated upon overexpression of AnxA1 (1.5- and 1.7-fold, respectively; P < 0.05). Human fibroblasts reacted similarly when receiving the FPR2 inhibitor WRW4.

CONCLUSION

Our results demonstrate that AnxA1 and FPR2 are abundantly expressed in the renal interstitium and modulate fibroblast phenotype and extracellular matrix synthesis activity.

Dissecting fibrosis: therapeutic insights from the small-molecule toolbox

Fibrosis, which leads to progressive loss of tissue function and eventual organ failure, has been estimated to contribute to ~45% of deaths in the developed world, and so new therapeutics to modulate fibrosis are urgently needed. Major advances in our understanding of the mechanisms underlying pathological fibrosis are supporting the search for such therapeutics, and the recent approval of two anti-fibrotic drugs for idiopathic pulmonary fibrosis has demonstrated the tractability of this area for drug discovery. This Review examines the pharmacology and structural information for small molecules being evaluated for lung, liver, kidney and skin fibrosis. In particular, we discuss the insights gained from the use of these pharmacological tools, and how these entities can inform, and probe, emerging insights into disease mechanisms, including the potential for future drug combinations.

Lipoxin A4 inhibits NF-κB activation and cell cycle progression in RAW264.7 cells

Lipoxins (LXs), including lipoxin A4 (LXA4), etc., have been approved for potent anti-inflammatory and immunomodulatory properties. Based on the important roles of macrophages in inflammation and immunomodulation, we investigate the effects of LXA4 on lipopolysaccharide (LPS)-induced proliferation and the possible signal transduction pathways in RAW264.7 macrophages. RAW264.7 cells were treated in vitro with or without LPS in the absence or presence of LXA4. [(3)H]-TdR incorporation assay and flow cytometry were used for detecting cell proliferation and cycle, respectively. Moreover, Western blot was applied to evaluate the protein expression levels of Cyclin E, IκBα, nuclear factor-κB (NF-κB), and IκB kinase (IKK). Our research showed that LXA4 suppressed LPS-induced proliferation, increased the proportion of the G0/G1 phase, decreased the proportion of the S phase, and downregulated the expression of Cyclin E. Besides these, LXA4 suppressed LPS-induced IκBα degradation, NF-κB translocation, and the expression of IKK. The data suggested that LXA4 inhibited LPS-induced proliferation through the G0/G1 phase arrest in RAW264.7 macrophages, and the inhibitory effect might depend on NF-κB signaling transduction pathway.