Fibrinogen deficiency increases liver injury and early growth response-1 (Egr-1) expression in a model of chronic xenobiotic-induced cholestasis

S-Acetyl-Glutathione Attenuates Carbon Tetrachloride-Induced Liver Injury by Modulating Oxidative Imbalance and Inflammation

Liver fibrosis, depending on the stage of the disease, could lead to organ dysfunction and cirrhosis, and no effective treatment is actually available. Emergent proof supports a link between oxidative stress, liver fibrogenesis and mitochondrial dysfunction as molecular bases of the pathology. A valid approach to protect against the disease would be to replenish the endogenous antioxidants; thus, we investigated the protective mechanisms of the S-acetyl-glutathione (SAG), a glutathione (GSH) prodrug. Preliminary in vitro analyses were conducted on primary hepatic cells. SAG pre-treatment significantly protected against cytotoxicity induced by CCl4. Additionally, CCl4 induced a marked increase in AST and ALT levels, whereas SAG significantly reduced these levels, reaching values found in the control group. For the in vivo analyses, mice were administered twice a week with eight consecutive intraperitoneal injections of 1 mL/kg CCl4 (diluted at 1:10 in olive oil) to induce oxidative imbalance and liver inflammation. SAG (30 mg/kg) was administered orally for 8 weeks. SAG significantly restored SOD activity, GSH levels and GPx activity, while it strongly reduced GSSG levels, lipid peroxidation and H₂O₂ and ROS levels in the liver. Additionally, CCl4 induced a decrease in anti-oxidants, including Nrf2, HO-1 and NQO-1, which were restored by treatment with SAG. The increased oxidative stress characteristic on liver disfunction causes the impairment of mitophagy and accumulation of dysfunctional and damaged mitochondria. Our results showed the protective effect of SAG administration in restoring mitophagy, as shown by the increased PINK1 and Parkin expressions in livers exposed to CCl4 intoxication. Thus, the SAG administration showed anti-inflammatory effects decreasing pro-inflammatory cytokines TNF-α, IL-6, MCP-1 and IL-1β in both serum and liver, and suppressing the TLR4/NFkB pathway. SAG attenuated reduced fibrosis, collagen deposition, hepatocellular damage and organ dysfunction. In conclusion, our results suggest that SAG administration protects the liver from CCl4 intoxication by restoring the oxidative balance, ameliorating the impairment of mitophagy and leading to reduced inflammation.

Von Willebrand factor exerts hepatoprotective effects in acute but not chronic cholestatic liver injury in mice

Acute and chronic liver disease are associated with substantial alterations in the hemostatic system, including elevated levels of the platelet-adhesive protein von Willebrand factor (VWF). Carbon tetrachloride-induced liver fibrosis is reduced in VWF-deficient mice, but it is unclear if VWF plays a pathologic role in all settings of liver fibrosis. Indeed, several studies suggest an anti-fibrotic role for components of the hemostatic system, including platelets, in experimental settings of bile duct fibrosis. However, the role of VWF in this specific pathology has not been examined. We tested the hypothesis that VWF exerts hepatoprotective effects in experimental bile duct injury. Wild-type and VWF-deficient (VWF^-/-) mice were challenged with the bile duct toxicant alpha-naphthylisothiocyanate (ANIT) and the impact of VWF deficiency on acute cholestatic liver injury and chronic liver fibrosis was determined. Acute ANIT (60 mg/kg, po)-induced cholestatic liver injury was associated with increased VWF plasma antigen and activity levels. VWF deficiency enhanced ANIT-induced hepatocellular injury, evidenced by increased plasma ALT activity and area of hepatocellular necrosis. Surprisingly, platelet accumulation within necrotic areas was increased in ANIT-challenged VWF^-/- mice compared to wild-type mice. Compared to acute ANIT challenge, hepatic platelet accumulation was modest and appeared to be VWF-dependent in mice exposed to ANIT diet (0.05 %) for 6 weeks. However, contrasting the role of VWF after acute ANIT challenge, VWF deficiency did not impact biliary fibrosis induced by chronic ANIT exposure. The results suggest that VWF plays dichotomous roles in experimental acute and chronic ANIT-induced cholestatic liver injury.

Biological Properties of a Citral-Enriched Fraction of Citrus limon Essential Oil

Lemon essential oil (LEO) is a well-known flavoring agent with versatile biological activities. In the present study, we have isolated and characterized four citral-enriched fractions of winter LEO. We reported that in murine and human macrophages the pre-treatment with a mix of these fractions (Cfr-LEO) reduces the expression of the pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 induced by LPS. In addition, Cfr-LEO counteracts LPS-induced oxidative stress, as shown by the increase in the GSH/GSSG ratio in comparison to cells treated with LPS alone. Overall, the results reported here encourage the application of EO fractions, enriched in citral, in the nutraceutical industry, not only for its organoleptic properties but also for its protective action against inflammation and oxidative stress.

Inflammation and Cell Death During Cholestasis: The Evolving Role of Bile Acids

Cholestasis results in blockage of bile flow whether the point of obstruction occurs extrahepatically or intrahepatically. Bile acids are a primary constituent of bile, and thus one of the primary outcomes is acute retention of bile acids in hepatocytes. Bile acids are normally secreted into the biliary tracts and then released into the small bowel before recirculating back to the liver. Retention of bile acids has long been hypothesized to be a primary cause of the associated liver injury that occurs during acute or chronic cholestasis. Despite this, a surge of papers in the last decade have reported a primary role for inflammation in the pathophysiology of cholestatic liver injury. Furthermore, it has increasingly been recognized that both the constituency of individual bile acids that make up the greater pool, as well as their conjugation status, is intimately involved in their toxicity, and this varies between species. Finally, the role of bile acids in drug-induced cholestatic liver injury remains an area of increasing interest. The purpose of this review is to critically evaluate current proposed mechanisms of cholestatic liver injury, with a focus on the evolving role of bile acids in cell death and inflammation.

The multifaceted role of fibrinogen in tissue injury and inflammation

The canonical role of the hemostatic and fibrinolytic systems is to maintain vascular integrity. Perturbations in either system can prompt primary pathological end points of hemorrhage or thrombosis with vessel occlusion. However, fibrin(ogen) and proteases controlling its deposition and clearance, including (pro)thrombin and plasmin(ogen), have powerful roles in driving acute and reparative inflammatory pathways that affect the spectrum of tissue injury, remodeling, and repair. Indeed, fibrin(ogen) deposits are a near-universal feature of tissue injury, regardless of the nature of the inciting event, including injuries driven by mechanical insult, infection, or immunological derangements. Fibrin can modify multiple aspects of inflammatory cell function by engaging leukocytes through a variety of cellular receptors and mechanisms. Studies on the role of coagulation system activation and fibrin(ogen) deposition in models of inflammatory disease and tissue injury have revealed points of commonality, as well as context-dependent contributions of coagulation and fibrinolytic factors. However, there remains a critical need to define the precise temporal and spatial mechanisms by which fibrinogen-directed inflammatory events may dictate the severity of tissue injury and coordinate the remodeling and repair events essential to restore normal organ function. Current research trends suggest that future studies will give way to the identification of novel hemostatic factor-targeted therapies for a range of tissue injuries and disease.

Breviscapine ameliorates CCl4‑induced liver injury in mice through inhibiting inflammatory apoptotic response and ROS generation

Acute liver injury is characterized by fibrosis, inflammation and apoptosis, leading to liver failure, cirrhosis or cancer and affecting the clinical outcome in the long term. However, no effective therapeutic strategy is currently available. Breviscapine, a mixture of flavonoid glycosides, has been reported to have multiple biological functions. The present study aimed to investigate the effects of breviscapine on acute liver injury induced by CCl4 in mice. C57BL/6 mice were subjected to intraperitoneal injection with CCl4 for 8 weeks with or without breviscapine (15 or 30 mg/kg). Mice treated with CCl4 developed acute liver injury, as evidenced by histological analysis, Masson trichrome and Sirius Red staining, accompanied with elevated levels of alanine aminotransferase and aspartate aminotransferase. Furthermore, increases in pro‑inflammatory cytokines, chemokines and apoptotic factors, including caspase‑3 and poly(ADP ribose) polymerase‑2 (PARP‑2), were observed. Breviscapine treatment significantly and dose‑dependently reduced collagen deposition and the fibrotic area. Inflammatory cytokines were downregulated by breviscapine through inactivating Toll‑like receptor 4/nuclear factor-κB signaling pathways. In addition, co‑administration of breviscapine with CCl4 decreased the apoptotic response by enhancing B‑cell lymphoma-2 (Bcl‑2) levels, while reducing Bcl‑2‑associated X protein, apoptotic protease activating factor 1, caspase‑3 and PARP activity. Furthermore, CCl4‑induced oxidative stress was blocked by breviscapine through improving anti‑oxidants and impeding mitogen‑activated protein kinase pathways. The present study highlighted that breviscapine exhibited liver‑protective effects against acute hepatic injury induced by CCl4 via suppressing inflammation and apoptosis.

Role of the blood coagulation cascade in hepatic fibrosis

Liver is the primary source of numerous proteins that are critical for normal function of the blood coagulation cascade. Because of this, diseases of the liver, particularly when affiliated with severe complications like cirrhosis, are associated with abnormalities of blood clotting. Although conventional interpretation has inferred cirrhosis as a disorder of uniform bleeding risk, it is now increasingly appreciated as a disease wherein the coagulation cascade is precariously rebalanced. Moreover, prothrombotic risk factors are also associated with a more rapid progression of fibrosis in humans, suggesting that coagulation proteases participate in disease pathogenesis. Indeed, strong evidence drawn from experimental animal studies indicates that components of the coagulation cascade, particularly coagulation factor Xa and thrombin, drive profibrogenic events, leading to hepatic fibrosis. Here, we concisely review the evidence supporting a pathologic role for coagulation in the development of liver fibrosis and the potential mechanisms involved. Further, we highlight how studies in experimental animals may shed light on emerging clinical evidence, suggesting that beneficial effects of anticoagulation could extend beyond preventing thrombotic complications to include reducing pathologies like fibrosis.

Effects of human amnion-derived mesenchymal stem cells and conditioned medium in rats with sclerosing cholangitis

Mesenchymal stem cells (MSCs) represent a valuable cell source in regenerative medicine, and large numbers of MSCs can be isolated from the amnion noninvasively. Sclerosing cholangitis is a chronic cholestatic disease and characterized by progressive biliary destruction leading to cirrhosis. Many factors are involved in the development of sclerosing cholangitis; however, effective medical therapy is not established. We investigated the effects of human amnion-derived MSCs (hAMSCs) and conditioned medium (CM) obtained from hAMSC cultures in rats with sclerosing cholangitis. Sclerosing cholangitis was induced via the intragastric administration of 100 mg/kg alpha-naphthylisothiocyanate (ANIT) twice weekly for 4 weeks. One million hAMSCs or 200 μL of CM were intravenously administered on days 15 and 22. Rats were sacrificed on day 29 and evaluated via histological, immunohistochemical, and mRNA expression analyses. hAMSC transplantation and CM administration significantly improved the histological score. In addition, these two interventions significantly improved biliary hyperplasia, peribiliary fibrosis, and inflammation in Glisson's sheath. Accordingly, CK19, MMP-9, and TNF-α, and MCP-1 expression in the liver was also decreased by hAMSC and CM administration. In conclusion, hAMSC and CM administration ameliorated biliary hyperplasia, peribiliary fibrosis, and inflammation in a rat model of sclerosing cholangitis. hAMSCs and CM may represent new modalities for treating sclerosing cholangitis.

Yinchenhao Decoction Ameliorates Alpha-Naphthylisothiocyanate Induced Intrahepatic Cholestasis in Rats by Regulating Phase II Metabolic Enzymes and Transporters

Yinchenhao Decoction (YCHD), a famous traditional Chinese formula, has been used for treating cholestasis for 1000s of years. The cholagogic effect of YCHD has been widely reported, but its pharmacodynamic material and underlying therapeutic mechanism remain unclear. By using ultra-high-performance liquid chromatography (UHPLC)-quadrupole time-of-flight mass spectrometry, 11 original active components and eight phase II metabolites were detected in rats after oral administration of YCHD, including three new phase II metabolites. And it indicated that phase II metabolism was one of the major metabolic pathway for most active components in YCHD, which was similar to the metabolism process of bilirubin. It arouses our curiosity that whether the metabolism process of YCHD has any relationship with its cholagogic effects. So, a new method for simultaneous quantitation of eight active components and four phase II metabolites of rhein, emodin, genipin, and capillarisin has been developed and applied for their pharmacokinetic study in both normal and alpha-naphthylisothiocyanate (ANIT)-induced intrahepatic cholestasis rats. The results indicated the pharmacokinetic behaviors of most components of YCHD were inhibited, which was hypothesized to be related to different levels of metabolic enzymes and transporters in rat liver. So dynamic changes of intrahepatic enzyme expression in cholestasis and YCHD treated rats have been monitored by an UHPLC-tandem mass spectrometry method. The results showed expression levels of UDP-glucuronosyltransferase 1-1 (UGT1A1), organic anion-transporting polypeptide 1A4 (OATP1A4), multidrug resistance-associated protein 2 (MRP2), multidrug resistance protein 1, sodium-dependent taurocholate cotransporter, and organic anion-transporting polypeptide 1A2 were significantly inhibited in cholestasis rats, which would account for reducing the drug absorption and the metabolic process of YCHD in cholestatic rats. A high dose (12 g/kg) of YCHD remarkably increased the expression of UGT1A1, bile salt export pump, MRP2, OATP1A4 in cholestasis rats presented it exhibited the greatest ameliorative effect on cholestasis, also particularly in histopathological examination and reducing levels of alanine transaminase, aspartate transaminase, total bilirubin, direct bilirubin, and total bile acid. Considering the metabolic process of bilirubin in vivo, the choleretic effect of YCHD is proven to be related to its regulatory action on expression of metabolic enzymes and transporters in cholestatic liver.

Pathogenesis, prevention, and management of bleeding and thrombosis in patients with liver diseases

Patients with liver diseases may develop alterations in all components of the hemostatic system. Thrombocytopenia, low levels of coagulation factors and inhibitors, low levels of fibrinolytic proteins, and increased levels of endothelial-derived proteins such as von Willebrand factor are all part of the coagulopathy of liver disease. Due to concomitant changes in pro- and antihemostatic drivers, the net effects of these complex hemostatic changes have long been unclear. According to current concepts, the hemostatic system of patients with liver disease is in an unstable balance, which explains the occurrence of both bleeding and thrombotic complications. This review will discuss etiology and management of bleeding and thrombosis in liver disease and will outline unsolved clinical questions. In addition, we will discuss the role of intrahepatic activation of coagulation for progression of liver disease, a novel paradigm with potential consequences for the general management of patients with liver disease.

Lymphocytes contribute to biliary injury and fibrosis in experimental xenobiotic-induced cholestasis

The etiology of chronic bile duct injury and fibrosis in patients with autoimmune cholestatic liver diseases is complex, and likely involves immune cells such as lymphocytes. However, most models of biliary fibrosis are not autoimmune in nature. Biliary fibrosis can be induced experimentally by prolonged exposure of mice to the bile duct toxicant alpha-naphthylisothiocyanate (ANIT). We determined whether lymphocytes contributed to ANIT-mediated biliary hyperplasia and fibrosis in mice. Hepatic accumulation of T-lymphocytes and increased serum levels of anti-nuclear-autoantibodies were evident in wild-type mice exposed to ANIT (0.05% ANIT in chow). This occurred alongside bile duct hyperplasia and biliary fibrosis. To assess the role of lymphocytes in ANIT-induced biliary fibrosis, we utilized RAG1^-/- mice, which lack T- and B-lymphocytes. ANIT-induced bile duct injury, indicated by increased serum alkaline phosphatase activity, was reduced in ANIT-exposed RAG1^-/- mice compared to ANIT-exposed wild-type mice. Despite this reduction in biliary injury, ANIT-induced bile duct hyperplasia was similar in wild-type and RAG1^-/- mice. However, hepatic induction of profibrogenic genes including COL1A1, ITGβ6 and TGFβ2 was markedly attenuated in ANIT-exposed RAG1^-/- mice compared to ANIT-exposed wild-type mice. Peribiliary collagen deposition was also reduced in ANIT-exposed RAG1^-/- mice. The results indicate that lymphocytes exacerbate bile duct injury and fibrosis in ANIT-exposed mice without impacting bile duct hyperplasia.

Dose-dependent effects of alpha-naphthylisothiocyanate disconnect biliary fibrosis from hepatocellular necrosis

Exposure of rodents to the xenobiotic α-naphthylisothiocyanate (ANIT) is an established model of experimental intrahepatic bile duct injury. Administration of ANIT to mice causes neutrophil-mediated hepatocellular necrosis. Prolonged exposure of mice to ANIT also produces bile duct hyperplasia and liver fibrosis. However, the mechanistic connection between ANIT-induced hepatocellular necrosis and bile duct hyperplasia and fibrosis is not well characterized. We examined impact of two different doses of ANIT, by feeding chow containing ANIT (0.05%, 0.1%), on the severity of various liver pathologies in a model of chronic ANIT exposure. ANIT-elicited increases in liver inflammation and hepatocellular necrosis increased with dose. Remarkably, there was no connection between increased hepatocellular necrosis and bile duct hyperplasia and peribiliary fibrosis, as these pathologies increased similarly in mice exposed to either dose of ANIT. The results indicate that the severity of hepatocellular necrosis does not dictate the extent of bile duct hyperplasia/fibrosis in ANIT-exposed mice.

Role of hemostatic factors in hepatic injury and disease: animal models de-liver

Chronic liver damage is associated with unique changes in the hemostatic system. Patients with liver disease often show a precariously rebalanced hemostatic system, which is easily tipped towards bleeding or thrombotic complications by otherwise benign stimuli. In addition, some clinical studies have shown that hemostatic system components contribute to the progression of liver disease. There is a strong basic science foundation for clinical studies with this particular focus. Chronic and acute liver disease can be modeled in rodents and large animals with a variety of approaches, which span chronic exposure to toxic xenobiotics, diet-induced obesity, and surgical intervention. These experimental approaches have now provided strong evidence that, in addition to perturbations in hemostasis caused by liver disease, elements of the hemostatic system have powerful effects on the progression of experimental liver toxicity and disease. In this review, we cover the basis of the animal models that are most often utilized to assess the impact of the hemostatic system on liver disease, and highlight the role that coagulation proteases and their targets play in experimental liver toxicity and disease, emphasizing key similarities and differences between models. The need to characterize hemostatic changes in existing animal models and to develop novel animal models recapitulating the coagulopathy of chronic liver disease is highlighted. Finally, we emphasize the continued need to translate knowledge derived from highly applicable animal models to improve our understanding of the reciprocal interaction between liver disease and the hemostatic system in patients.

Role of Fibrin(ogen) in Progression of Liver Disease: Guilt by Association?

Strong experimental evidence indicates that components of the hemostatic system, including thrombin, exacerbate diverse features of experimental liver disease. Clinical studies have also begun to address this connection and some studies have suggested that anticoagulants can improve outcome in patients with liver disease. Among the evidence of coagulation cascade activation in models of liver injury and disease is the frequent observation of thrombin-driven hepatic fibrin(ogen) deposition. Indeed, hepatic fibrin(ogen) deposition has long been recognized as a consequence of hepatic injury. Although commonly inferred as pathologic due to protective effects of anticoagulants in mouse models, the role of fibrin(ogen) in acute liver injury and chronic liver disease may not be universally detrimental. The localization of hepatic fibrin(ogen) deposits within the liver is connected to the disease stimulus and in animal models of liver toxicity and chronic disease, fibrin(ogen) deposition may not always be synonymous with large vessel thrombosis. Here, we provide a balanced review of the experimental evidence supporting a direct connection between fibrin(ogen) and liver injury/disease pathogenesis, and suggest a path forward bridging experimental and clinical research to improve our knowledge on the nature and function of fibrin(ogen) in liver disease.

Fibrin deposition following bile duct injury limits fibrosis through an αMβ2-dependent mechanism

Coagulation cascade activation and fibrin deposits have been implicated or observed in diverse forms of liver damage. Given that fibrin amplifies pathological inflammation in several diseases through the integrin receptor αMβ2, we tested the hypothesis that disruption of the fibrin(ogen)-αMβ2 interaction in Fibγ(390-396A) mice would reduce hepatic inflammation and fibrosis in an experimental setting of chemical liver injury. Contrary to our hypothesis, α-naphthylisothiocyanate (ANIT)-induced liver fibrosis increased in Fibγ(390-396A) mice, whereas inflammatory cytokine expression and hepatic necrosis were similar to ANIT-challenged wild-type (WT) mice. Increased fibrosis in Fibγ(390-396A) mice appeared to be independent of coagulation factor 13 (FXIII) transglutaminase, as ANIT challenge in FXIII-deficient mice resulted in a distinct pathological phenotype characterized by increased hepatic necrosis. Rather, bile duct proliferation underpinned the increased fibrosis in ANIT-exposed Fibγ(390-396A) mice. The mechanism of fibrin-mediated fibrosis was linked to interferon (IFN)γ induction of inducible nitric oxide synthase (iNOS), a gene linked to bile duct hyperplasia and liver fibrosis. Expression of iNOS messenger RNA was significantly increased in livers of ANIT-exposed Fibγ(390-396A) mice. Fibrin(ogen)-αMβ2 interaction inhibited iNOS induction in macrophages stimulated with IFNγ in vitro and ANIT-challenged IFNγ-deficient mice had reduced iNOS induction, bile duct hyperplasia, and liver fibrosis. Further, ANIT-induced iNOS expression, liver fibrosis, and bile duct hyperplasia were significantly reduced in WT mice administered leukadherin-1, a small molecule that allosterically enhances αMβ2-dependent cell adhesion to fibrin. These studies characterize a novel mechanism whereby the fibrin(ogen)-integrin-αMβ2 interaction reduces biliary fibrosis and suggests a novel putative therapeutic target for this difficult-to-treat fibrotic disease.

Association between plasma fibrinogen levels and mortality in acute-on-chronic hepatitis B liver failure

Acute-on-chronic liver failure (AoCLF) is the most common type of liver failure and is associated with high mortality. Fibrinogen is critical in maintaining primary and secondary hemostasis. Therefore, we prospectively analyzed the association between fibrinogen and outcomes in AoCLF patients. Plasma fibrinogen was measured in 169 AoCLF, 173 chronic hepatitis B (CHB), and 171 healthy patients using a coagulation method. The predictive ability of fibrinogen for 3-month mortality in AoCLF patients was assessed using receiver operating characteristic (ROC) curve and multivariable logistic regression analyses. Plasma fibrinogen was significantly lower in nonsurvivor AoCLF patients compared with survivor AoCLF, CHB, and control patients. The sensitivity, specificity, and area under the ROC curve of 1/fibrinogen predicting mortality in AoCLF patients were 66.7%, 72.5%, and 0.746 (95% confidence interval (CI): 0.672–0.820, P < 0.001), and the fibrinogen cutoff value was 0.90 g/L. On multivariate logistic regression analysis, low fibrinogen was an independent factor predicting mortality (odds ratio: 0.304; 95% CI: 0.094–0.983; P = 0.047). Nonsurvivor AoCLF patients had significantly decreased fibrinogen levels, suggesting that low plasma fibrinogen may be a useful predictor of poor prognosis in AoCLF patients.

Coagulation-driven platelet activation reduces cholestatic liver injury and fibrosis in mice

BACKGROUND

The coagulation cascade has been shown to participate in chronic liver injury and fibrosis, but the contribution of various thrombin targets, such as protease activated receptors (PARs) and fibrin(ogen), has not been fully described. Emerging evidence suggests that in some experimental settings of chronic liver injury, platelets can promote liver repair and inhibit liver fibrosis. However, the precise mechanisms linking coagulation and platelet function to hepatic tissue changes following injury remain poorly defined.

OBJECTIVES

To determine the role of PAR-4, a key thrombin receptor on mouse platelets, and fibrin(ogen) engagement of the platelet αII b β3 integrin (αIIb β3 ) in a model of cholestatic liver injury and fibrosis.

METHODS

Biliary and hepatic injury was characterized following 4 week administration of the bile duct toxicant α-naphthylisothiocyanate (ANIT) (0.025%) in PAR-4-deficient mice, mice expressing a mutant form of fibrin(ogen) incapable of binding integrin αII b β3 (Fibγ(Δ5) ), and wild-type mice.

RESULTS

Elevated plasma thrombin-antithrombin and serotonin levels, hepatic fibrin deposition, and platelet accumulation in liver accompanied hepatocellular injury and fibrosis in ANIT-treated wild-type mice. PAR-4 deficiency reduced plasma serotonin levels, increased serum bile acid concentration, and exacerbated ANIT-induced hepatocellular injury and peribiliary fibrosis. Compared with PAR-4-deficient mice, ANIT-treated Fibγ(Δ5) mice displayed more widespread hepatocellular necrosis accompanied by marked inflammation, robust fibroblast activation, and extensive liver fibrosis.

CONCLUSIONS

Collectively, the results indicate that PAR-4 and fibrin-αII b β3 integrin engagement, pathways coupling coagulation to platelet activation, each exert hepatoprotective effects during chronic cholestasis.

Pharmacological and genetic depletion of fibrinogen protects from kidney fibrosis

Fibrinogen (Fg) has been implicated in the pathogenesis of several fibrotic disorders by acting as a profibrotic ligand for a variety of cellular surface receptors and by modulating the provisional fibrin matrix formed after injury. We demonstrated increased renal Fg expression after unilateral ureteral obstruction and folic acid (FA) nephropathy in mice, respectively. Urinary Fg excretion was also increased in FA nephropathy. Using in vitro and in vivo approaches, our results suggested that IL-6 mediates STAT3 activation in kidney fibrosis and that phosphorylated (p)STAT3 binds to Fgα, Fgβ, and Fgγ promoters in the kidney to regulate their transcription. Genetically modified Fg heterozygous mice (∼75% of normal plasma Fg levels) exhibited only 3% kidney interstitial fibrosis and tubular atrophy after FA nephropathy compared with 24% for wild-type mice. Fibrinogenolysis through Ancrod administration after FA reduced interstitial fibrosis more than threefold compared with vehicle-treated control mice. Mechanistically, we show that Fg acts synergistically with transforming growth factor (TGF)-β1 to induce fibroblast proliferation and activates TGF-β1/pSMAD2 signaling. This study offers increased understanding of Fg expression and molecular interactions with TGF-β1 in the progression to kidney fibrosis and, importantly, indicates that fibrinogenolytics like Ancrod present a treatment opportunity for a yet intractable disease.

The antifibrinolytic drug tranexamic acid reduces liver injury and fibrosis in a mouse model of chronic bile duct injury

Hepatic fibrin deposition has been shown to inhibit hepatocellular injury in mice exposed to the bile duct toxicant α-naphthylisothiocyanate (ANIT). Degradation of fibrin clots by fibrinolysis controls the duration and extent of tissue fibrin deposition. Thus, we sought to determine the effect of treatment with the antifibrinolytic drug tranexamic acid (TA) and plasminogen activator inhibitor-1 (PAI-1) deficiency on ANIT-induced liver injury and fibrosis in mice. Plasmin-dependent lysis of fibrin clots was impaired in plasma from mice treated with TA (1200 mg/kg i.p., administered twice daily). Prophylactic TA administration reduced hepatic inflammation and hepatocellular necrosis in mice fed a diet containing 0.025% ANIT for 2 weeks. Hepatic type 1 collagen mRNA expression and deposition increased markedly in livers of mice fed ANIT diet for 4 weeks. To determine whether TA treatment could inhibit this progression of liver fibrosis, mice were fed ANIT diet for 4 weeks and treated with TA for the last 2 weeks. Interestingly, TA treatment largely prevented increased deposition of type 1 collagen in livers of mice fed ANIT diet for 4 weeks. In contrast, biliary hyperplasia/inflammation and liver fibrosis were significantly increased in PAI-1(-/-) mice fed ANIT diet for 4 weeks. Overall, the results indicate that fibrinolytic activity contributes to ANIT diet-induced liver injury and fibrosis in mice. In addition, these proof-of-principle studies suggest the possibility that therapeutic intervention with an antifibrinolytic drug could form a novel strategy to prevent or reduce liver injury and fibrosis in patients with liver disease.

Role of fibrinogen in acute ischemic kidney injury

Renal ischemia-reperfusion (I/R) is associated with activation of the coagulation system and accumulation of blood clotting factors in the kidney. The aim of the present study was to examine the functional impact of fibrinogen on renal inflammation, damage, and repair in the context of I/R injury. In this study, we found that I/R was associated with a significant increase in the renal deposition of circulating fibrinogen. In parallel, I/R stress induced the de novo expression of fibrinogen in tubular epithelial cells, as reflected by RT-PCR, immunofluorescence, and in situ hybridization. In vitro, fibrinogen expression was induced by oncostatin M and hyper-IL-6 in primary tubular epithelial cells, and fibrinogen-containing medium had an inhibitory effect on tubular epithelial cell adhesion and migration. Fibrinogen(+/-) mice showed similar survival as wild-type mice but better preservation in early postischemic renal function. In fibrinogen(-/-) mice, renal function and survival were significantly worse than in fibrinogen(+/-) mice. Renal transplant experiments revealed reduced expression of tubular damage markers and attenuated proinflammatory cytokine expression but increased inflammatory cell infiltrates and transforming growth factor-β expression in fibrinogen(-/-) isografts. These data point to heterogeneous effects of fibrinogen in renal I/R injury. While a complete lack of fibrinogen may be detrimental, partial reduction of fibrinogen in heterozygous mice can improve renal function and overall outcome.

Fibrin(ogen)-independent role of plasminogen activators in acetaminophen-induced liver injury

Hepatic fibrin(ogen) has been noted to occur after acetaminophen (APAP)-induced liver injury in mice. Deficiency in plasminogen activator inhibitor-1 (PAI-1), an endogenous inhibitor of fibrinolysis, increases APAP-induced liver injury in mice. However, the roles of fibrinogen and fibrinolysis in APAP-induced liver injury are not known. We tested the hypothesis that hepatic fibrin(ogen) deposition reduces severity of APAP-induced liver injury. APAP-induced (300 mg/kg) liver injury in mice was accompanied by thrombin generation, consumption of plasma fibrinogen, and deposition of hepatic fibrin. Neither fibrinogen depletion with ancrod nor complete fibrinogen deficiency [via knockout of the fibrinogen alpha chain gene (Fbg(-/-))] affected APAP-induced liver injury. PAI-1 deficiency (PAI-1(-/-)) increased APAP-induced liver injury and hepatic fibrin deposition 6 hours after APAP administration, which was followed by marked hemorrhage at 24 hours. As in PAI-1(-/-) mice, administration of recombinant tissue plasminogen activator (tenecteplase, 5 mg/kg) worsened APAP-induced liver injury and hemorrhage in wild-type mice. In contrast, APAP-induced liver injury was reduced in both plasminogen-deficient mice and in wild-type mice treated with tranexamic acid, an inhibitor of plasminogen activation. Activation of matrix metalloproteinase 9 (MMP-9) paralleled injury, but MMP-9 deficiency did not affect APAP-induced liver injury. The results indicate that fibrin(ogen) does not contribute to development of APAP-induced liver injury and suggest rather that plasminogen activation contributes to APAP-induced liver injury.

Xenobiotic-induced liver injury and fibrosis

INTRODUCTION

Many different drugs and xenobiotics (chemical compounds foreign to an organism) can injure the bile duct epithelium and cause inflammatory bile duct diseases (cholangiopathies) ranging from transient cholestasis to vanishing bile duct syndrome, sclerosing cholangitis with development of biliary fibrosis and cirrhosis. Animal models of xenobiotic-induced liver injury have provided major mechanistic insights into the molecular mechanisms of xenobiotic-induced cholangiopathies and biliary fibrosis including primary biliary cirrhosis and primary sclerosing cholangitis.

AREAS COVERED

In this review, the authors discuss the basic principles of xenobiotic-induced liver and bile duct injury and biliary fibrosis with emphasis on animal models. A PubMed search was performed using the search terms "xenobiotic," "liver injury," "cholestasis," and "biliary fibrosis." Reference lists of retrieved articles were also searched for relevant literature.

EXPERT OPINION

Xenobiotic-induced cholangiopathies are underestimated and frequently overlooked medical conditions due to their often transient nature. However, biliary disease may progress to vanishing bile duct syndrome, biliary fibrosis, and cirrhosis. Moreover, xenobiotics may prime the liver for subsequent liver disease by other agents and may also contribute to the development of hepatobiliary cancer though interaction with resident stem cells.

Early growth response factor-1 limits biliary fibrosis in a model of xenobiotic-induced cholestasis in mice

Hepatic expression of the transcription factor early growth response-1 (Egr-1) is increased in livers of patients with cholestatic liver disease. Bile acid induction of inflammatory genes in hepatocytes is Egr-1 dependent, and Egr-1 expression is increased in livers of mice after bile duct ligation. Of importance, Egr-1 deficiency reduces liver inflammation and injury in that model. However, it is not known whether Egr-1 promotes inflammation in other models of cholestasis. We tested the hypothesis that Egr-1 contributes to liver inflammation in mice exposed chronically to the bile duct epithelial cell (BDEC) toxicant alpha-naphthylisothiocyanate (ANIT). Egr-1-knockout (Egr-1(-/-)) mice and wild-type mice were fed a diet containing 0.025% ANIT for 2 weeks. Expression of Egr-1 mRNA and protein was significantly increased in livers of mice fed ANIT diet. Egr-1 deficiency did not significantly affect ANIT diet-induced hepatocellular injury, inflammatory gene induction, BDEC hyperplasia, or hepatic neutrophil accumulation. In contrast, the deposition of Type 1 collagen was significantly increased in livers of Egr-1(-/-) mice fed ANIT diet compared with wild-type mice fed ANIT diet. Interestingly, this increase in liver fibrosis occurred in association with elevated expression of the β6 integrin (Itgb6) gene, suggesting the potential for increased local activation of transforming growth factor beta. Taken together, the results indicate that Egr-1 does not contribute to liver injury or inflammation in mice fed a diet containing ANIT. Rather, these studies indicate that Egr-1 deficiency worsens liver fibrosis in conjunction with enhanced expression of the profibrogenic Itgb6 gene.

Role of early growth response 1 in liver injury

Liver injury is a sophisticated pathophysiological process caused by many factors. Currently, the role of early growth response 1 (EGR1) in liver injury is still controversial. Some studies show that EGR1 can amplify the systemic inflammatory response and promote apoptosis in galactosamine/lipopolysaccharide-induced acute liver injury and alpha-naphthylisothiocyanate (ANIT)-induced intrahepatic cholestasis as well as other non-liver injuries, while some other studies indicate that EGR1 protects the liver from CCl₄ exposure by regulating the expression of inducible nitric oxide synthase, cyclooxygenase-2, and tumor necrosis factor-α-regulated genes that have hepatoprotective function.