Fibrin(ogen) drives repair after acetaminophen-induced liver injury via leukocyte αMβ2 integrin-dependent upregulation of Mmp12

Degradation rather than disassembly of necrotic debris is essential to enhance recovery after acute liver injury

Necrotic cell death causes loss of membrane integrity, release of intracellular contents and deposition of necrotic cell debris. Effective clearance of this debris is crucial for resolving inflammation and promoting tissue recovery. While leukocyte phagocytosis plays a major role, soluble factors in the bloodstream also contribute to debris removal. Our study examined whether enzymatic degradation or disassembly of necrotic debris enhances clearance and improves outcomes in a mouse model of drug-induced liver injury. Using intravital microscopy and on-tissue spatially-resolved microproteomics, we demonstrated that necrotic debris is more complex than anticipated, containing DNA, filamentous actin, histones, complement C3, fibrin(ogen) and plasmin(ogen), among many other components. DNase 1 treatment facilitated recovery significantly by enhancing the clearance of DNA from necrotic areas, reducing circulating nucleosomes and actin, and lowering the associated inflammatory response. However, its effect on actin and other damage-associated molecular patterns in necrotic regions was limited. Treatment with short synthetic peptides, specifically 20-amino acid-long positively charged poly L-lysine (PLK) and negatively charged poly L-glutamic acid (PLE), which displace histones from debris in vitro, did not inhibit liver injury or promote recovery. Moreover, activating plasmin to disrupt fibrin encapsulation via tissue plasminogen activator (tPa) led to increased circulating actin levels and worsening of injury parameters. These findings suggest that fibrin encapsulation is important for containing necrotic debris and that enzymatic degradation of necrotic debris is a more effective strategy to enhance tissue recovery than targeting debris disassembly.

Fibrin induces infiltration of macrophages and neutrophils via integrin αMβ2 and triggers aortic dissection

BACKGROUND AND PURPOSE

Infiltration of macrophages and neutrophils plays a crucial role in the occurrence of aortic dissection (AD), while the mechanism elucidating their infiltration remains unknown. The present study aimed to delineate the underlying mechanism and provide a potential therapeutic strategy to attenuate AD progression.

EXPERIMENTAL APPROACH

A model of AD was established in male mice using β-aminopropionitrile and angiotensin II. Proteomic analysis, histological evaluation, flow cytometry, western blot, multiple fluorescence staining and adhesion assays were used to evaluate fibrin and inflammatory cells during AD progression. Fibrinogen-lowering drugs and fibrinogen γ-chain knockout (Fgg+/-) mice were also used to evaluate the fibrin-integrin αMβ2 interaction.

KEY RESULTS

Fibrin deposition was confirmed by proteomic analysis and histological staining, accompanied by infiltration of macrophages and neutrophils detected by flow cytometry during the progression of AD. After confirming that macrophages and neutrophils infiltrated at the sites where fibrin was deposited by immunofluorescence, an association between fibrin and the integrin αMβ2 was disclosed using protein-protein interaction analysis and immunofluorescence. The pivotal role of interactions between fibrin and integrin αMβ2 in AD progression was confirmed by cell adhesion in vitro, down-regulation of fibrin using batroxobin and Fgg+/- mice in vivo. The relevance of fibrin and integrin αMβ2 was also found in patients with AD.

CONCLUSION AND IMPLICATIONS

Fibrin plays a crucial role in triggering AD through recruiting macrophages and neutrophils via integrin αMβ2. Regulation of fibrin deposition or inhibition of the interaction between fibrin and integrin αMβ2 provide a potential therapy against AD.

Prognostic nomogram based on coagulation for individualized prediction after radical resection of hepatocellular carcinoma

BACKGROUND

The prognosis of patients with hepatocellular carcinoma (HCC) following radical resection remains suboptimal. This study aimed to create a nomogram integrating clinicopathological parameters and coagulation indices to predict the recurrence-free survival (RFS) of these individuals.

METHODS

A total of 863 patients with hepatocellular carcinoma after radical resection were included (504 patients in the training cohort, 216 patients in the internal verification cohort and 142 patients in the external verification cohort). Cox regression analysis was used to determine the independent risk factors in the training cohort, and it was used to construct a prognostic nomogram. Calibration curves, decision curve analysis (DCA), the C index and the time-dependent area under the curve (td-AUC) were used to evaluate the performance of the nomogram, and the internal and external validation cohorts were used for verification. We also calculated total risk points to divide patients into high-, medium- and low-risk groups. The Kaplan-Meier methodology was used to analyze RFS, and differences were compared using the log-rank test.

RESULTS

Age, tumor size, tumor differentiation, microvascular invasion, INR and FIB for RFS were integrated into the nomogram. The calibration curves revealed a strong correlation between the predicted and actual results, and the nomogram's C-index and DCA demonstrated superior predictive performance compared with TNM, BCLC, CNLC, and CLIP. Additionally, the td-AUC revealed that the nomogram effectively predicted recurrence-free survival (RFS) at 1, 3, and 5 years. Moreover, significant differences in RFS were observed between the high-, medium-, and low-risk groups (P < 0.0001) after the effective cutoff values of the risk points were identified using the nomogram.

CONCLUSIONS

A nomogram model that is based on coagulation indices has high predictive efficacy for the recurrence of hepatocellular carcinoma in patients and significant clinical application value.

Complement activation drives the phagocytosis of necrotic cell debris and resolution of liver injury

Cells die by necrosis due to excessive chemical or thermal stress, leading to plasma membrane rupture, release of intracellular components and severe inflammation. The clearance of necrotic cell debris is crucial for tissue recovery and injury resolution, however, the underlying mechanisms are still poorly understood, especially in vivo. This study examined the role of complement proteins in promoting clearance of necrotic cell debris by leukocytes and their influence on liver regeneration. We found that independently of the type of necrotic liver injury, either acetaminophen (APAP) overdose or thermal injury, complement proteins C1q and (i)C3b were deposited specifically on necrotic lesions via the activation of the classical pathway. Importantly, C3 deficiency led to a significant accumulation of necrotic debris and impairment of liver recovery in mice, which was attributed to decreased phagocytosis of debris by recruited neutrophils in vivo. Monocytes and macrophages also took part in debris clearance, although the necessity of C3 and CD11b was dependent on the specific type of necrotic liver injury. Using human neutrophils, we showed that absence of C3 or C1q caused a reduction in the volume of necrotic debris that is phagocytosed, indicating that complement promotes effective debris uptake in mice and humans. Moreover, internalization of opsonized debris induced the expression of pro-resolving genes in a C3-dependent manner, supporting the notion that debris clearance favors the resolution of inflammation. In summary, complement activation at injury sites is a pivotal event for necrotic debris clearance by phagocytes and determinant for efficient recovery from tissue injury.

The Role of Fibrinogen in Mediating NGAL-Associated Neuronal Damage in Acute Ischemic Stroke: A Moderated Mediation Analysis

Background

Both neutrophil gelatinase-associated lipocalin (NGAL) and fibrinogen are involved in the inflammation in acute ischemic stroke (AIS), but the interaction among them is unknown. Clarifying this issue will contribute to a better understanding of the mechanisms of injury in AIS. This study aimed to explore the association between NGAL, fibrinogen and neuronal damage in AIS.

Methods

This study is a cross-section study. One hundred ninety-six successively hospitalized AIS patients in Renji Hospital in China between January 1, 2023, and May 31, 2023, were included. Circulating NGAL and fibrinogen were measured, and neuron-specific enolase (NSE) was detected to evaluate central neuronal damage. All data were analyzed by linear curve fitting analysis, multiple linear regression analysis, and moderated mediation analysis, respectively.

Results

There are linear relationships between log2-transformed NGAL, NSE, and fibrinogen, respectively. The β (95%) for the positive association between log2-transformed NGAL and NSE was 2.24 (1.15-3.32, p < 0.01), between log2-transformed NGAL and fibrinogen was 0.37 (0.19-0.56, p < 0.01), and between fibrinogen and NSE was 1.16 (0.48-1.85, p < 0.01) adjusting for potential confounders. These associations remained consistent in sensitivity analysis and hierarchical analysis. Increased fibrinogen significantly (p < 0.01) mediated 14.28% of log2-transformed NGAL-associated increased NSE risk.

Conclusion

The NGAL levels were associated with NSE, and the NGAL-associated neuronal damage might be partially mediated by fibrinogen, suggesting that the inflammatory response among NGAL, fibrinogen, and NSE should be intervened to reduce neuronal damage after ischemic stroke. Further animal experiments are needed to clarify their specific mechanisms and precise relationships.

FAK inhibition delays liver repair after acetaminophen-induced acute liver injury by suppressing hepatocyte proliferation and macrophage recruitment

BACKGROUND

Overdose of acetaminophen (APAP), a commonly used antipyretic analgesic, can lead to severe liver injury and failure. Current treatments are only effective in the early stages of APAP-induced acute liver injury (ALI). Therefore, a detailed examination of the mechanisms involved in liver repair following APAP-induced ALI could provide valuable insights for clinical interventions.

METHODS

4D-label-free proteomics analysis was used to identify dysregulated proteins in the liver of APAP-treated mice. RNA-Seq, hematoxylin-eosin staining, immunohistochemical staining, immunofluorescence staining, quantitative PCR, western blotting, transwell were used to explore the underlying mechanisms.

RESULTS

Utilizing high throughput 4D-label-free proteomics analysis, we observed a notable increase in proteins related to the "focal adhesion" pathway in the livers of APAP-treated mice. Inhibiting focal adhesion kinase (FAK) activation with a specific inhibitor, 1,2,4,5-Benzenetetraamine tetrahydrochloride (also called Y15), resulted in reduced macrophage numbers, delayed necrotic cell clearance, and inhibited liver cell proliferation in the necrotic regions of APAP-treated mice. RNA-Seq analysis demonstrated that Y15 downregulated genes associated with "cell cycle" and "phagosome" pathways in the livers of APAP-treated mice. Furthermore, blocking extracellular matrix (ECM)-integrin activation with a competitive peptide inhibitor, Gly-Arg-Gly-Asp-Ser (GRGDS), suppressed FAK activation and liver cell proliferation without affecting macrophage recruitment to necrotic areas. Mechanistically, ECM-induced FAK activation upregulated growth-promoting cell cycle genes, leading to hepatocyte proliferation, while CCL2 enhanced FAK activation and subsequent macrophage recruitment via F-actin rearrangement.

CONCLUSIONS

Overall, these findings underscore the pivotal role of FAK activation in liver repair post-APAP overdose by promoting liver cell proliferation and macrophage recruitment.

Regulation of fibrinogen synthesis

The plasma protein fibrinogen is encoded by 3 structural genes (FGA, FGB, and FGG) that are transcribed to mRNA, spliced, and translated to 3 polypeptide chains (Aα, Bβ, and γ, respectively). These chains are targeted for secretion, decorated with post-translational modifications, and assembled into a hexameric "dimer of trimers" (AαBβγ)2. Fully assembled fibrinogen is secreted into the blood as a 340 kDa glycoprotein. Fibrinogen is one of the most prevalent coagulation proteins in blood, and its expression is induced by inflammatory cytokines, wherein circulating fibrinogen levels may increase up to 3-fold during acute inflammatory events. Abnormal levels of circulating fibrinogen are associated with bleeding and thrombotic disorders, as well as several inflammatory diseases. Notably, therapeutic strategies to modulate fibrinogen levels have shown promise in experimental models of disease. Herein, we review pathways mediating fibrinogen synthesis, from gene expression to secretion. Knowledge of these mechanisms may lead to the identification of biomarkers and new therapeutic targets to modulate fibrinogen in health and disease.

Fibrinolysis-Mediated Pathways in Acute Liver Injury

Acute liver injury (ALI), that is, the development of reduced liver function in patients without preexisting liver disease, can result from a wide range of causes, such as viral or bacterial infection, autoimmune disease, or adverse reaction to prescription and over-the-counter medications. ALI patients present with a complex coagulopathy, characterized by both hypercoagulable and hypocoagulable features. Similarly, ALI patients display a profound dysregulation of the fibrinolytic system with the vast majority of patients presenting with a hypofibrinolytic phenotype. Decades of research in experimental acute liver injury in mice suggest that fibrinolytic proteins, including plasmin(ogen), plasminogen activators, fibrinolysis inhibitors, and fibrin(ogen), can contribute to initial hepatotoxicity and/or stimulate liver repair. This review summarizes major experimental findings regarding the role of fibrinolytic factors in ALI from the last approximately 30 years and identifies unanswered questions, as well as highlighting areas for future research.

Coagulation factor XIII is a critical driver of liver regeneration after partial hepatectomy

BACKGROUND

Activation of coagulation and fibrin deposition in the regenerating liver appears to promote adequate liver regeneration in mice. In humans, perioperative hepatic fibrin deposition is reduced in patients who develop liver dysfunction after partial hepatectomy (PHx), but the mechanism underlying reduced fibrin deposition in these patients is unclear.

METHODS AND RESULTS

Hepatic deposition of cross-linked (ie, stabilized) fibrin was evident in livers of mice after two-thirds PHx. Interestingly, hepatic fibrin cross-linking was dramatically reduced in mice after 90% PHx, an experimental setting of failed liver regeneration, despite similar activation of coagulation after two-thirds or 90% PHx. Likewise, intraoperative activation of coagulation was not reduced in patients who developed liver dysfunction after PHx. Preoperative fibrinogen plasma concentration was not connected to liver dysfunction after PHx in patients. Rather, preoperative and postoperative plasma activity of the transglutaminase coagulation factor (F)XIII, which cross-links fibrin, was lower in patients who developed liver dysfunction than in those who did not. PHx-induced hepatic fibrin cross-linking and hepatic platelet accumulation were significantly reduced in mice lacking the catalytic subunit of FXIII (FXIII-/- mice) after two-thirds PHx. This was coupled with a reduction in both hepatocyte proliferation and liver-to-body weight ratio as well as an apparent reduction in survival after two-thirds PHx in FXIII-/- mice.

CONCLUSION

The results indicate that FXIII is a critical driver of liver regeneration after PHx and suggest that perioperative plasma FXIII activity may predict posthepatectomy liver dysfunction. The results may inform strategies to stabilize proregenerative fibrin during liver resection.

GAS6/TAM Axis as Therapeutic Target in Liver Diseases

TAM (TYRO3, AXL, and MERTK) protein tyrosine kinase membrane receptors and their vitamin K-dependent ligands GAS6 and protein S (PROS) are well-known players in tumor biology and autoimmune diseases. In contrast, TAM regulation of fibrogenesis and the inflammation mechanisms underlying metabolic dysfunction-associated steatohepatitis (MASH), cirrhosis, and, ultimately, liver cancer has recently been revealed. GAS6 and PROS binding to phosphatidylserine exposed in outer membranes of apoptotic cells links TAMs, particularly MERTK, with hepatocellular damage. In addition, AXL and MERTK regulate the development of liver fibrosis and inflammation in chronic liver diseases. Acute hepatic injury is also mediated by the TAM system, as recent data regarding acetaminophen toxicity and acute-on-chronic liver failure have uncovered. Soluble TAM-related proteins, mainly released from activated macrophages and hepatic stellate cells after hepatic deterioration, are proposed as early serum markers for disease progression. In conclusion, the TAM system is becoming an interesting pharmacological target in liver pathology and a focus of future biomedical research in this field.

Early predictors of prolonged intensive care utilization following liver transplantation

INTRODUCTION

Creatinine, bilirubin, and fibrinolysis resistance are associated with multi-organ dysfunction and likely risk factors for prolonged intensive care unit (pICU) stay following liver transplantation (LT). We hypothesize postoperative day-1 (POD-1) labs will predict pICU.

METHODS

LT recipients had clinical laboratories and viscoelastic testing with tissue plasminogen activator thrombelastography (tPA TEG) to quantify fibrinolysis resistance (LY30) on POD-1. pICU was defined as one week or longer in the ICU. Logistic regression was used to identify the relationship between POD-1 labs and pICU.

RESULTS

Of 304 patients, 50% went to the ICU, with 15% experiencing pICU. Elevated creatinine (OR 6.6, P ​< ​0.001) and low tPA TEG LY30 (OR 3.7, P ​= ​0.004) were independent predictors of pICU after controlling for other risk factors. A 9-fold increase in the rate of 90-day graft loss (19% vs 2% p ​< ​0.001) was observed patients who had these risk factors for pICU.

CONCLUSION

Elevated creatine and fibrinolysis resistance are associated with pICU and poor outcomes following LT.

Monocyte-derived Kupffer cells dominate in the Kupffer cell pool during liver injury

Healthy Kupffer cell (KC) pool is dominated by embryonic KCs (EmKCs), preserving liver homeostasis. How the KC pool varies upon injury remains unclear. Using chimeric mice with bone marrow (BM) cells labeled with enhanced green fluorescent protein, we identify that BM monocyte-derived KCs (MoKCs) become dominant in cholestatic- or toxic-injured livers via immunofluorescence and mass cytometry. Single-cell RNA sequencing (scRNA-seq) unveils the enhanced proliferative, anti-apoptotic properties and repair potential of MoKCs compared with EmKCs, which are confirmed in vivo and ex vivo through flow cytometry, qPCR, Cell Counting Kit-8, and immunofluorescence. Furthermore, compared with EmKC-dominated livers, MoKC-dominated livers exhibit less functional damage, necrosis, and fibrosis under damage, as tested by serum alanine aminotransferase activity detection, H&E and Sirius red staining, qPCR, and western blot. Collectively, we highlight that MoKCs dominate the KC pool in injured livers and show enhanced proliferative and anti-apoptotic properties while also promoting repair and attenuating fibrosis.

An orally deliverable ornithine-based self-assembling polymer nanomedicine ameliorates hyperammonemia in acetaminophen-induced acute liver injury

l-Ornithine (Orn) is a core amino acid responsible for ammonia detoxification in the body via the hepatic urea cycle. Clinical studies in Orn therapy have focused on interventions for hyperammonemia-associated diseases, such as hepatic encephalopathy (HE), a life-threatening neurological symptom affecting more than 80% of patients with liver cirrhosis. However, its low molecular weight (LMW) causes Orn to diffuse nonspecifically and be rapidly eliminated from the body after oral administration, resulting in unfavorable therapeutic efficacy. Hence, Orn is constantly supplied by intravenous infusion in many clinical settings; however, this treatment inevitably decreases patient compliance and limits its application in long-term management. To improve the performance of Orn, we designed self-assembling polyOrn-based nanoparticles for oral administration through ring-opening polymerization of Orn-N-carboxy anhydride initiated with amino-ended poly(ethylene glycol), followed by acylation of free amino groups in the main chain of the polyOrn segment. The obtained amphiphilic block copolymers, poly(ethylene glycol)-block-polyOrn(acyl) (PEG-block-POrn(acyl)), enabled the formation of stable nanoparticles (NanoOrn(acyl)) in aqueous media. We employed the isobutyryl (iBu) group for acyl derivatization in this study (NanoOrn(iBu)). In the healthy mice, daily oral administration of NanoOrn(iBu) for one week did not induce any abnormalities. In the mice exhibiting acetaminophen (APAP)-induced acute liver injury, oral pretreatment with NanoOrn(iBu) effectively reduced systemic ammonia and transaminases levels compared to the LMW Orn and untreated groups. The results suggest that the application of NanoOrn(iBu) is of significant clinical value with the feasibility of oral delivery and improvement in APAP-induced hepatic pathogenesis. STATEMENT OF SIGNIFICANCE: Liver injury is often accompanied by hyperammonemia, a life-threatening condition characterized by elevated blood ammonia levels. Current clinical treatments for reducing ammonia typically entail the invasive approach of intravenous infusion, involving the administration of l-ornithine (Orn) or a combination of Orn and L-aspartate. This method is employed due to the poor pharmacokinetics associated with these compounds. In our pursuit of enhancing therapy, we have developed an orally administrable nanomedicine based on Orn-based self-assembling nanoparticle (NanoOrn(iBu)), which provides sustained Orn supply to the injured liver. Oral administration of NanoOrn(iBu) to healthy mice did not cause any toxic effects. In a mouse model of acetaminophen-induced acute liver injury, oral administration of NanoOrn(iBu) surpassed Orn in reducing systemic ammonia levels and liver damage, thereby establishing NanoOrn(iBu) as a safe and effective therapeutic option.

Robust coagulation activation and coagulopathy in mice with experimental acetaminophen-induced liver failure

BACKGROUND

Patients with acetaminophen (APAP)-induced acute liver failure (ALF) display both hyper- and hypocoagulable changes not necessarily recapitulated by standard hepatotoxic doses of APAP used in mice (eg, 300 mg/kg).

OBJECTIVES

We sought to examine coagulation activation in vivo and plasma coagulation potential ex vivo in experimental settings of APAP-induced hepatotoxicity and repair (300-450 mg/kg) and APAP-induced ALF (600 mg/kg) in mice.

RESULTS

APAP-induced ALF was associated with increased plasma thrombin-antithrombin complexes, decreased plasma prothrombin, and a dramatic reduction in plasma fibrinogen compared with lower APAP doses. Hepatic fibrin(ogen) deposits increased independent of APAP dose, whereas plasma fibrin(ogen) degradation products markedly increased in mice with experimental ALF. Early pharmacologic anticoagulation (+2 hours after 600 mg/kg APAP) limited coagulation activation and reduced hepatic necrosis. The marked coagulation activation evident in mice with APAP-induced ALF was associated with a coagulopathy detectable ex vivo in plasma. Specifically, prolongation of the prothrombin time and inhibition of tissue factor-initiated clot formation were evident even after restoration of physiological fibrinogen concentrations. Plasma endogenous thrombin potential was similarly reduced at all APAP doses. Interestingly, in the presence of ample fibrinogen, ∼10 times more thrombin was required to clot plasma from mice with APAP-induced ALF compared with plasma from mice with simple hepatotoxicity.

CONCLUSION

The results indicate that robust pathologic coagulation cascade activation in vivo and suppressed coagulation ex vivo are evident in mice with APAP-induced ALF. This unique experimental setting may fill an unmet need as a model to uncover mechanistic aspects of the complex coagulopathy of ALF.

The Role of Immune Cells in Liver Regeneration

The liver is the only organ that can regenerate and regain its original tissue-to-body weight ratio within a short period of time after tissue loss. Insufficient liver regeneration in patients after partial hepatectomy or liver transplantation with partial liver grafts often leads to post-hepatectomy liver failure or small-for-size syndrome, respectively. Enhancing liver regeneration after liver injury might improve outcomes and increase patient survival. Liver regeneration comprises hepatocyte proliferation, and hepatic progenitor cell expansion and differentiation into hepatocytes. The immune system is intensively involved in liver regeneration. The current review provides a comprehensive overview of the diverse roles played by immune cells in liver regeneration. Macrophages, neutrophils, eosinophils, basophils, mast cells, platelets, dendritic cells, type 1 innate lymphoid cells, B cells, and T cells are implicated in promoting liver regeneration, while natural killer cells and overactivated natural killer T cells are supposed to inhibit hepatocyte proliferation. We also highlight the predominant underlying mechanisms mediated by immune cells, which may contribute to the development of novel strategies for promoting liver regeneration in patients with liver diseases.

Altered fibrinogen γ-chain cross-linking in mutant fibrinogen-γΔ5 mice drives acute liver injury

BACKGROUND

Hepatic deposition of cross-linked fibrin(ogen) occurs alongside platelet accumulation as a hallmark of acetaminophen (APAP)-induced liver injury.

OBJECTIVES

We sought to define the precise role of the fibrinogen γ-chain C-terminal integrin αIIbβ3 binding domain in APAP-induced liver injury.

METHODS

Mice expressing mutant fibrinogen incapable of engaging integrin αIIbβ3 due to a C-terminal fibrinogen γ-chain truncation (mutant fibrinogen-γΔ5 [FibγΔ5] mice) and wild-type mice were challenged with APAP (300 mg/kg, intraperitoneally).

RESULTS

We observed an altered pattern of fibrin(ogen) deposition in the livers of APAP-challenged FibγΔ5 mice. This led to the unexpected discovery that fibrinogen γ-chain cross-linking was altered in the livers of APAP-challenged FibγΔ5 mice compared with that in wild-type mice, including absence of γ-γ dimer and accumulation of larger molecular weight cross-linked γ-chain complexes. This finding was not unique to the injured liver because activation of coagulation did not produce γ-γ dimer in plasma from FibγΔ5 mice or purified FibγΔ5 fibrinogen. Sanger sequencing predicted that the fibrinogen-γΔ5 γ-polypeptide would terminate at lysine residue 406, but liquid chromatography tandem mass spectrometry analysis revealed that this critical lysine residue was absent in purified fibrinogen-γΔ5 protein. Interestingly, hepatic deposition of this uniquely aberrantly cross-linked fibrin(ogen) in FibγΔ5 mice was associated with exacerbated hepatic injury, an effect not recapitulated by pharmacologic inhibition of integrin αIIbβ3.

CONCLUSION

The results indicate that fibrinogen-γΔ5 lacks critical residues essential to form γ-γ dimer in response to thrombin and suggest that hepatic accumulation of abnormally cross-linked fibrin(ogen) can exacerbate hepatic injury.

Leukadherin-1 inhibits NLRP3 inflammasome by blocking inflammasome assembly

Aberrant activation of the NLRP3 inflammasome has been implicated in the occurrence and development of many inflammatory diseases, and thus potent inhibitors of the NLRP3 inflammasome should be explored. An antitumor agent, Leukadherin-1 (LA-1), tested in phase 1/2 clinical trials, has been reported to exert anti-inflammatory properties by blocking the NF-κB pathway. However, the effects of LA-1 on the NLRP3 inflammasome have not been conclusively determined. In this study, we found that at lower doses (below 1 μM) ex vivo, LA-1 blocked NLRP3 inflammasome activation without affecting NF-κB signaling. Accordingly, 1 mg/Kg LA-1 strongly inhibited the release of NLRP3-dependent cytokine, but only slightly inhibited NLRP3-independent-cytokines secretion in endotoxemia and alleviated NLRP3-dependent peritonitis in vivo. Mechanistically, LA-1 had no effects on ion flux or mitochondrial injury. Instead, it inhibited NLRP3 inflammasome assembly by suppressing ASC oligomerization, blocking NLRP3 self-assembly, and reducing interactions of NLRP3 with ASC and NEK7. Therefore, LA-1 inhibits NLRP3 inflammasome activation, implying that it is a potential treatment option for NLRP3-associated diseases.

Aging aggravates acetaminophen-induced acute liver injury and inflammation through inordinate C/EBPα-BMP9 crosstalk

BACKGROUND

Previous studies have shown that bone morphogenetic protein 9 (BMP9) is almost exclusively produced in the liver and reaches tissues throughout the body as a secreted protein. However, the mechanism of BMP9 action and its role in aging-associated liver injury and inflammation are still unclear.

RESULTS

Aging significantly aggravates acetaminophen (APAP)-induced acute liver injury (ALI). Increased expression of CCAAT/enhancer binding protein α (C/EBPα) and BMP9 was identified in aged livers and in hepatocytes and macrophages (MФs) isolated from aged mice. Further analysis revealed that excess BMP9 was directly related to APAP-induced hepatocyte injury and death, as evidenced by activated drosophila mothers against decapentaplegic protein 1/5/9 (SMAD1/5/9) signaling, an increased dead cell/total cell ratio, decreased levels of ATG3 and ATG7, blocked autophagy, increased senescence-associated beta-galactosidase (SA-β-Gal) activity, and a higher rate of senescence-associated secretory phenotype (SASP) acquisition. In contrast, Bmp9 knockout (Bmp9^-/-) partially alleviated the aforementioned manifestations of BMP9 overexpression. Moreover, BMP9 expression was found to be regulated by C/EBPα in vitro and in vivo. Notably, BMP9 also downregulated autophagy through its effect on autophagy-related genes (ATG3 and ATG7) in MΦs, which was associated with aggravated liver injury and SASP acquisition.

CONCLUSIONS

In summary, the present study highlights the crucial roles played by C/EBPα-BMP9 crosstalk and provides insights into the interrelationship between hepatocytes and MΦs during acute liver injury.

Novel genetic regulators of fibrinogen synthesis identified by an in vitro experimental platform

BACKGROUND

Fibrinogen has an established, essential role in both coagulation and inflammatory pathways, and these processes are deeply intertwined in the development of thrombotic and atherosclerotic diseases. Previous studies aimed to better understand the (patho) physiological actions of fibrinogen by characterizing the genomic contribution to circulating fibrinogen levels.

OBJECTIVES

Establish an in vitro approach to define functional roles between genes within these loci and fibrinogen synthesis.

METHODS

Candidate genes were selected on the basis of their proximity to genetic variants associated with fibrinogen levels and expression in hepatocytes and HepG2 cells. HepG2 cells were transfected with small interfering RNAs targeting candidate genes and cultured in the absence or presence of the proinflammatory cytokine interleukin-6. Effects on fibrinogen protein production, gene expression, and cell growth were assessed by immunoblotting, real-time polymerase chain reaction, and cell counts, respectively.

RESULTS

HepG2 cells secreted fibrinogen, and stimulation with interleukin-6 increased fibrinogen production by 3.4 ± 1.2 fold. In the absence of interleukin-6, small interfering RNA knockdown of FGA, IL6R, or EEPD1 decreased fibrinogen production, and knockdown of LEPR, PDIA5, PLEC, SHANK3, or CPS1 increased production. In the presence of interleukin-6, knockdown of FGA, IL6R, or ATXN2L decreased fibrinogen production. Knockdown of FGA, IL6R, EEPD1, LEPR, PDIA5, PLEC, or CPS1 altered transcription of one or more fibrinogen genes. Knocking down ATXN2L suppressed inducible but not basal fibrinogen production via a post-transcriptional mechanism.

CONCLUSIONS

We established an in vitro platform to define the impact of select gene products on fibrinogen production. Genes identified in our screen may reveal cellular mechanisms that drive fibrinogen production as well as fibrin(ogen)-mediated (patho)physiological mechanisms.

The molecular mechanisms of acetaminophen-induced hepatotoxicity and its potential therapeutic targets

Acetaminophen (APAP), a widely used antipyretic and analgesic drug in clinics, is relatively safe at therapeutic doses; however, APAP overdose may lead to fatal acute liver injury. Currently, N-acetylcysteine (NAC) is clinically used as the main antidote for APAP poisoning, but its therapeutic effect remains limited owing to rapid disease progression and the general diagnosis of advanced poisoning. As is well known, APAP-induced hepatotoxicity (AIH) is mainly caused by the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI), and the toxic mechanisms of AIH are complicated. Several cellular processes are involved in the pathogenesis of AIH, including liver metabolism, mitochondrial oxidative stress and dysfunction, sterile inflammation, endoplasmic reticulum stress, autophagy, and microcirculation dysfunction. Mitochondrial oxidative stress and dysfunction are the major cellular events associated with APAP-induced liver injury. Many biomolecules involved in these biological processes are potential therapeutic targets for AIH. Therefore, there is an urgent need to comprehensively clarify the molecular mechanisms underlying AIH and to explore novel therapeutic strategies. This review summarizes the various cellular events involved in AIH and discusses their potential therapeutic targets, with the aim of providing new ideas for the treatment of AIH.

Effect of TRPM8 Functional Loss on Corneal Epithelial Wound Healing in Mice

Purpose

To reveal the role of cold-sensing transient receptor potential melastatin 8 (TRPM8) channels in corneal epithelial wound healing.

Methods

Cold sensitivity, tear production, corneal thickness, and corneal opacity assessments were used to evaluate the effect of Trpm8 knockout on the ocular surface. A corneal epithelial wounding model was generated by scraping the corneal epithelium once or multiple times using C57BL/6J (wild-type [WT]) and Trpm8-/- mice. The processes of corneal epithelial repair and corneal epitheliopathy were observed and recorded. Corneas were collected for sequencing, immunofluorescence staining, hematoxylin and eosin staining, and quantitative PCR.

Results

The perception of coldness, basal tear secretion, and corneal thickness were decreased in young Trpm8-/- mice compared with those in WT mice, except for the corneal sensitivity. Corneal opacity and increased corneal thickness were observed in aged Trpm8-/- mice. TRPM8 deficiency promoted corneal epithelial wound closure, consistent with the observed increase in Ki67-positive epithelial cells, and the pharmacological activation of TRPM8 in WT mice delayed corneal re-epithelization. After subjecting mice to multiple injuries, squamous metaplasia emerged in Trpm8-/- corneas, as verified by cytokeratin-1 and small proline-rich protein 1B-positive staining. The IFN-β and IFN-γ signaling pathways were significantly activated in Trpm8-/- mice, which was confirmed based on the up-regulated expression of the key mediators, signal transducer and activator of transcription-1 and phosphor-signal transducer and activator of transcription-1, as well as the induction of IFN-stimulated genes, compared with levels in WT mice.

Conclusions

In corneal wound healing, the loss of TRPM8 function could promote epithelial repair, but predispose the cornea to epithelial lesions.

Circulating Leukocyte as an Inflammatory Biomarker: Association with Fibrinogen and Neuronal Damage in Acute Ischemic Stroke

Background and Purpose

Leukocytes and fibrinogen are inflammatory markers involved in circulating and central inflammatory response after ischemic stroke. However, the interaction between circulating leukocytes and serum fibrinogen and neuronal injury in acute ischemic stroke (AIS) patients is still unclear. The present study aimed to investigate the association between circulating leukocyte and serum fibrinogen and neuronal injury respectively in AIS.

Methods

A cross-section study with 431 hospitalized AIS patients from department of neurology was performed. Circulating leukocytes and fibrinogen were measured, and neuron-specific enolase (NSE) was detected to evaluate central neuronal damage. A propensity score matching method was used to minimize the effects of confounding factors. The relationship between leukocytes and NSE and fibrinogen was analyzed by linear curve fitting analysis and multiple logistic regression models respectively.

Results

The mean levels of NSE, leukocyte, and fibrinogen were significantly higher in the matched AIS group (n=89) than those of in the healthy control group (n=89) (all p<0.05). Both serum NSE and fibrinogen were increased with the increasing of leukocyte in AIS patients (both p<0.05). Smoothed plots suggested that there are linear relationships between leukocyte and NSE and fibrinogen respectively. Multiple logistic regression analysis showed the OR (95%) for the relationship between leukocyte and high NSE were 1.13 (1.01-1.26, p=0.031) and 1.13 (1.00-1.28, p=0.048), and between leukocyte and high fibrinogen were 1.40 (1.22-1.61, p<0.001) and 1.35 (1.15-1.58, p<0.001) in all AIS patients before and after adjusting for potential confounders.

Conclusion

Our study suggests that elevated circulating leukocyte was associated with high fibrinogen and neuronal injury in AIS. Therefore, there may be potential targets among circulating leukocyte, fibrinogen and NSE that should be intervened to reduce inflammatory reaction after ischemic stroke.

Elimination of fibrin polymer formation or crosslinking, but not fibrinogen deficiency, is protective against diet-induced obesity and associated pathologies

BACKGROUND

Obesity predisposes individuals to metabolic syndrome, which increases the risk of cardiovascular diseases, non-alcoholic fatty liver disease (NAFLD), and type 2 diabetes. A pathological manifestation of obesity is the activation of the coagulation system. In turn, extravascular fibrin(ogen) deposits accumulate in adipose tissues and liver. These deposits promote adiposity and downstream sequelae by driving pro-inflammatory macrophage function through binding the leukocyte integrin receptor αM β2 .

OBJECTIVES

An unresolved question is whether conversion of soluble fibrinogen to a crosslinked fibrin matrix is required to exacerbate obesity-driven diseases.

METHODS

Here, fibrinogen-deficient/depleted mice (Fib- or treated with siRNA against fibrinogen [siFga]), mice expressing fibrinogen that cannot polymerize to fibrin (FibAEK ), and mice deficient in the fibrin crosslinking transglutaminase factor XIII (FXIII-) were challenged with a high-fat diet (HFD) and compared to mice expressing a mutant form of fibrinogen lacking the αM β2 -binding domain (Fib𝛾390-396A ).

RESULTS AND CONCLUSIONS

Consistent with prior studies, Fib𝛾390-396A mice were significantly protected from increased adiposity, NAFLD, hypercholesterolemia, and diabetes while Fib- and siFga-treated mice gained as much weight and developed obesity-associated pathologies identical to wildtype mice. FibAEK and FXIII- mice displayed an intermediate phenotype with partial protection from some obesity-associated pathologies. Results here indicate that fibrin(ogen) lacking αM β2 binding function offers substantial protection from obesity and associated disease that is partially recapitulated by preventing fibrin polymer formation or crosslinking of the wildtype molecule, but not by reduction or complete elimination of fibrinogen. Finally, these findings support the concept that fibrin polymerization and crosslinking are required for the full implementation of fibrin-driven inflammation in obesity.

Heterogeneity and Function of Kupffer Cells in Liver Injury

Kupffer cells (KCs) are key regulators of liver immunity composing the principal part of hepatic macrophages even body tissue macrophages. They reside in liver sinusoids towards portal vein. The micro-environment shapes KCs unique immunosuppressive features and functions. KCs express specific surface markers that distinguish from other liver macrophages. By engulfing gut-derived foreign products and apoptotic cells without triggering excessive inflammation, KCs maintain homeostasis of liver and body. Heterogeneity of KCs has been identified in different studies. In terms of the origin, adult KCs are derived from progenitors of both embryo and adult bone marrow. Embryo-derived KCs compose the majority of KCs in healthy and maintain by self-renewal. Bone marrow monocytes replenish massively when embryo-derived KC proliferation are impaired. The phenotype of KCs is also beyond the traditional dogma of M1-M2. Functionally, KCs play central roles in pathogenesis of acute and chronic liver injury. They contribute to each pathological stage of liver disease. By initiating inflammation, regulating fibrosis, cirrhosis and tumor cell proliferation, KCs contribute to the resolution of liver injury and restoration of tissue architecture. The underlying mechanism varied by damage factors and pathology. Understanding the characteristics and functions of KCs may provide opportunities for the therapy of liver injury. Herein, we attempt to afford insights on heterogeneity and functions of KCs in liver injury using the existing findings.

Cross-linking by tissue transglutaminase-2 alters fibrinogen-directed macrophage proinflammatory activity

BACKGROUND

The blood coagulation factor fibrin(ogen) can modulate inflammation by altering leukocyte activity. Analyses of fibrin(ogen)-mediated proinflammatory activity have largely focused on leukocyte integrin binding activity revealed by conversion of fibrinogen to a stabilized fibrin polymer by blood coagulation enzymes. In addition to coagulation enzymes, fibrinogen is a substrate for tissue transglutaminase-2 (TG2), a widely expressed enzyme that produces unique fibrinogen Aα-γ chain cross-linked products.

OBJECTIVES

We tested the hypothesis that TG2 dependent cross-linking alters the proinflammatory activity of surface-adhered fibrinogen.

METHODS

Mouse bone marrow-derived macrophages (BMDMs) were cultured on tissue culture plates coated with fibrinogen or TG2-cross-linked fibrinogen (10 µg/ml) and then stimulated with lipopolysaccharide (LPS, 1 ng/ml) or vehicle for various times.

RESULTS

In the absence of LPS stimulation, TG2-cross-linked fibrin(ogen) enhanced inflammatory gene induction (e.g., Tnfα) compared with unmodified fibrinogen. LPS stimulation induced mitogen-activated protein kinase phosphorylation, IκBα degradation, and expression of proinflammatory cytokines (e.g., tumor necrosis factor α) within 60 min. This initial cellular activation was unaffected by unmodified or TG2-cross-linked fibrinogen. In contrast, LPS induction of interleukin-10 mRNA and protein and STAT3 phosphorylation was selectively attenuated by TG2-cross-linked fibrinogen, which was associated with enhanced proinflammatory cytokine secretion by LPS-stimulated BMDMs at later time points (6 and 24 h).

CONCLUSIONS

The results indicate that atypical cross-linking by TG2 imparts unique proinflammatory activity to surface-adhered fibrinogen. The results suggest a novel coagulation-independent mechanism controlling fibrinogen-directed macrophage activation.

3'mRNA sequencing reveals pro-regenerative properties of c5ar1 during resolution of murine acetaminophen-induced liver injury

Murine acetaminophen-induced acute liver injury (ALI) serves as paradigmatic model for drug-induced hepatic injury and regeneration. As major cause of ALI, acetaminophen overdosing is a persistent therapeutic challenge with N-acetylcysteine clinically used to ameliorate parenchymal necrosis. To identify further treatment strategies that serve patients with poor N-acetylcysteine responses, hepatic 3′mRNA sequencing was performed in the initial resolution phase at 24 h/48 h after sublethal overdosing. This approach disclosed 45 genes upregulated (≥5-fold) within this time frame. Focusing on C5aR1, we observed in C5aR1-deficient mice disease aggravation during resolution of intoxication as evidenced by increased liver necrosis and serum alanine aminotransferase. Moreover, decreased hepatocyte compensatory proliferation and increased caspase-3 activation at the surroundings of necrotic cores were detectable in C5aR1-deficient mice. Using a non-hypothesis-driven approach, herein pro-regenerative/-resolving effects of C5aR1 were identified during late acetaminophen-induced ALI. Data concur with protection by the C5a/C5aR1-axis during hepatectomy and emphasize the complex role of inflammation during hepatic regeneration and repair.

Trimethylamine N-oxide exacerbates acetaminophen-induced liver injury by interfering with macrophage-mediated liver regeneration

Acetaminophen (APAP)-induced acute liver injury (AILI) is the most frequent cause of acute liver failure in developed countries. Trimethylamine N-oxide (TMAO) is a metabolite derived from the gut microbiota and is relatively high in the circulation of the elderly, individuals with diabetes, and heart disease. Herein, we showed that TMAO exacerbates APAP hepatotoxicity. It is possible that delayed liver repair and regeneration that resulted from reduced macrophage accumulation was responsible for this combined hepatotoxicity. Moreover, matrix metalloproteinase 12 (Mmp12), expressed predominantly by macrophages, were reduced by TMAO in vitro and in vivo. This led to the inhibition of macrophage migration and a subsequent decrease in the recruitment of proresolving macrophages to the necrosis area. Furthermore, the administration of recombinant Mmp12 mitigated the enhanced hepatotoxicity in mice cotreated with TMAO and APAP. Overall, this study indicates that TMAO exacerbates APAP-induced hepatotoxicity by hindering macrophage-mediated liver repair, which might stem from the inhibition of Mmp12. These findings imply that liver damage in patients with high levels of circulating TMAO may be more severe in AILI and should exercise caution when treating with NAC.

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.

Fibrinogen activates focal adhesion kinase (FAK) promoting colorectal adenocarcinoma growth

BACKGROUND

We previously showed that fibrinogen is a major determinant of the growth of a murine model of colorectal cancer (CRC).

OBJECTIVE

Our aim was to define the mechanisms coupling fibrin(ogen) to CRC growth.

RESULTS

CRC tumors transplanted into the dorsal subcutis of Fib- mice were less proliferative and demonstrated increased senescence relative to those grown in Fib+ mice. RNA-seq analyses of Fib+ and Fib- tumors revealed 213 differentially regulated genes. One gene highly upregulated in tumors from Fib- mice was stratifin, encoding 14-3-3σ, a master regulator of proliferation/senescence. In a separate cohort, we observed significantly increased protein levels of 14-3-3σ and its upstream and downstream targets (i.e., p53 and p21) in tumors from Fib- mice. In vitro analyses demonstrated increased tumor cell proliferation in a fibrin printed three-dimensional environment compared with controls, suggesting that fibrin(ogen) in the tumor microenvironment promotes tumor growth in this context via a tumor cell intrinsic mechanism. In vivo analyses showed diminished activation of focal adhesion kinase (FAK), a key negative regulator of p53, in Fib- tumors. Furthermore, nuclear magnetic resonance-based metabolomics demonstrated significantly reduced metabolic activity in tumors from Fib- relative to Fib+ mice. Together, these findings suggest that fibrin(ogen)-mediated engagement of colon cancer cells activates FAK, which inhibits p53 and its downstream targets including 14-3-3σ and p21, thereby promoting cellular proliferation and preventing senescence.

CONCLUSIONS

These studies suggest that fibrin(ogen) is an important component of the colon cancer microenvironment and may be exploited as a potential therapeutic target.

Plasmin-mediated cleavage of high-molecular-weight kininogen contributes to acetaminophen-induced acute liver failure

Acetaminophen (APAP)-induced liver injury is associated with activation of coagulation and fibrinolysis. In mice, both tissue factor-dependent thrombin generation and plasmin activity have been shown to promote liver injury after APAP overdose. However, the contribution of the contact and intrinsic coagulation pathways has not been investigated in this model. Mice deficient in individual factors of the contact (factor XII [FXII] and prekallikrein) or intrinsic coagulation (FXI) pathway were administered a hepatotoxic dose of 400 mg/kg of APAP. Neither FXII, FXI, nor prekallikrein deficiency mitigated coagulation activation or hepatocellular injury. Interestingly, despite the lack of significant changes to APAP-induced coagulation activation, markers of liver injury and inflammation were significantly reduced in APAP-challenged high-molecular-weight kininogen-deficient (HK-/-) mice. Protective effects of HK deficiency were not reproduced by inhibition of bradykinin-mediated signaling, whereas reconstitution of circulating levels of HK in HK-/- mice restored hepatotoxicity. Fibrinolysis activation was observed in mice after APAP administration. Western blotting, enzyme-linked immunosorbent assay, and mass spectrometry analysis showed that plasmin efficiently cleaves HK into multiple fragments in buffer or plasma. Importantly, plasminogen deficiency attenuated APAP-induced liver injury and prevented HK cleavage in the injured liver. Finally, enhanced plasmin generation and HK cleavage, in the absence of contact pathway activation, were observed in plasma of patients with acute liver failure due to APAP overdose. In summary, extrinsic but not intrinsic pathway activation drives the thromboinflammatory pathology associated with APAP-induced liver injury in mice. Furthermore, plasmin-mediated cleavage of HK contributes to hepatotoxicity in APAP-challenged mice independently of thrombin generation or bradykinin signaling.

Factor XIII cross-links fibrin(ogen) independent of fibrin polymerization in experimental acute liver injury

Intravascular fibrin clot formation follows a well-ordered series of reactions catalyzed by thrombin cleavage of fibrinogen leading to fibrin polymerization and cross-linking by factor XIIIa (FXIIIa). Extravascular fibrin(ogen) deposits are observed in injured tissues; however, the mechanisms regulating fibrin(ogen) polymerization and cross-linking in this setting are unclear. The objective of this study was to determine the mechanisms of fibrin polymerization and cross-linking in acute liver injury induced by acetaminophen (APAP) overdose. Hepatic fibrin(ogen) deposition and cross-linking were measured following APAP overdose in wild-type mice, mice lacking the catalytic subunit of FXIII (FXIII-/-), and in FibAEK mice, which express mutant fibrinogen insensitive to thrombin-mediated fibrin polymer formation. Hepatic fibrin(ogen) deposition was similar in APAP-challenged wild-type and FXIII-/- mice, yet cross-linking of hepatic fibrin(ogen) was dramatically reduced (>90%) by FXIII deficiency. Surprisingly, hepatic fibrin(ogen) deposition and cross-linking were only modestly reduced in APAP-challenged FibAEK mice, suggesting that in the APAP-injured liver fibrin polymerization is not strictly required for the extravascular deposition of cross-linked fibrin(ogen). We hypothesized that the oxidative environment in the injured liver, containing high levels of reactive mediators (eg, peroxynitrite), modifies fibrin(ogen) such that fibrin polymerization is impaired without impacting FXIII-mediated cross-linking. Notably, fibrin(ogen) modified with 3-nitrotyrosine adducts was identified in the APAP-injured liver. In biochemical assays, peroxynitrite inhibited thrombin-mediated fibrin polymerization in a concentration-dependent manner without affecting fibrin(ogen) cross-linking over time. These studies depict a unique pathology wherein thrombin-catalyzed fibrin polymerization is circumvented to allow tissue deposition and FXIII-dependent fibrin(ogen) cross-linking.

Clinical significance and influencing factors of fibrinogen in ANCA-associated vasculitis: A single-center retrospective study from Southwest China

Hypercoagulable is an important pathological state in anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). Fibrinogen (FIB) is the main protein in coagulation process. In this study, we aimed to investigate the clinical significance and influencing factors of FIB in AAV from Southwest China.A retrospective study was performed on AAV patients from Peoples Hospital of Deyang City from January 2007 to December 2018. Demographic and clinical characteristics were collected.A total of 463 AAV patients were included. In Wilcoxon rank sum test, FIB was significantly higher in AAV active group than inactive group (P = .005). FIB was also higher in bacterial infection group than in non-infection group both in active group (P = .008) and inactive group (P = .017). In receiver operating characteristic (ROC) curve analysis, the critical value of FIB for diagnosis of bacterial infection between AAV active and inactive groups was 3.385 g/L (P = .030), with sensitivity of 70.2% and specificity of 52.9%. In the multivariate analysis of variance (MANOVA), estimated glomerular filtration rate (eGFR) was shown to be an independent factor for FIB (P = .001). Least-significant difference showed the concentration of FIB (P < .05) increased with renal impairment, especially in endstage kidney disease (ESKD).FIB identified a certain reference value in distinguishing AAV activity from bacterial infection. ESKD had a statistical effect on it. Influencing factors of FIB should be evaluated based on the renal function impairment of patients.

Differential regulation of hepatic physiology and injury by the TAM receptors Axl and Mer

Genome-wide association studies have implicated the TAM receptor tyrosine kinase (RTK) Mer in liver disease, yet our understanding of the role that Mer and its related RTKs Tyro3 and Axl play in liver homeostasis and the response to acute injury is limited. We find that Mer and Axl are most prominently expressed in hepatic Kupffer and endothelial cells and that as mice lacking these RTKs age, they develop profound liver disease characterized by apoptotic cell accumulation and immune activation. We further find that Mer is critical to the phagocytosis of apoptotic hepatocytes generated in settings of acute hepatic injury, and that Mer and Axl act in concert to inhibit cytokine production in these settings. In contrast, we find that Axl is uniquely important in mitigating liver damage during acetaminophen intoxication. Although Mer and Axl are protective in acute injury models, we find that Axl exacerbates fibrosis in a model of chronic injury. These divergent effects have important implications for the design and implementation of TAM-directed therapeutics that might target these RTKs in the liver.

Investigation of Extracellular Matrix Protein Expression Dynamics Using Murine Models of Systemic Inflammation

Extracellular matrix (ECM) proteins form the structural support for migration of leukocytes and provide multiple signals to assist in their functions during inflammatory conditions. Presence of pro-inflammatory mediators in the tissues results in the remodelling of matrices which could modify the functions of extravasated leukocytes. Previous reports have shown changes in the expression of ECM proteins during local inflammatory responses. In this study, we have investigated the time- and tissue-specific expression profile of key ECM proteins in systemic inflammation using lipopolysaccharide (LPS)-induced endotoxemia and cecal ligation and puncture (CLP) mouse models. The results show that compared to naïve tissues, within 12 h following CLP surgery, a 20-30-fold increase was observed in the expression of collagen-IV (Col-IV) transcripts in the mesentery tissues with a 2.4-fold increase in the protein by 24 h. However, Western blot band intensities indicated that vimentin and fibrinogen were remarkably expressed in more quantity compared to Col-IV. Secondly, in CLP group of mice, fibrinogen showed 6-40-fold increase in mRNA level in various tissues with about 2-fold increase in the protein level compared to respective naïve tissues. Similar studies in the LPS-injected mice showed up to 2-3 fold increase in the expression of Col-IV, fibrinogen and vimentin at protein level in the lungs. In such animals, although similar pattern was observed for fibrinogen in kidney and liver tissues, the mesentery showed prominent changes in Col-IV and vimentin mRNA compared to CLP. Further, bioinformatics analysis showed multiple pathways which could be associated with vimentin, Col-IV and fibrinogen under inflammatory conditions both in human and mouse. The current study will help in better understanding of possible signalling from ECM proteins in inflammatory microenvironment and may contribute in development of cell adhesion-based therapeutics.

Design of anti-inflammatory heparan sulfate to protect against acetaminophen-induced acute liver failure

Acetaminophen/paracetamol (APAP) overdose is the leading cause of drug-induced acute liver failure (ALF) in the United States and Europe. The progression of the disease is attributed to sterile inflammation induced by the release of high mobility group box 1 (HMGB1) and the interaction with receptor for advanced glycation end products (RAGE). A specific, effective, and safe approach to neutralize the proinflammatory activity of HMGB1 is highly desirable. Here, we found that a heparan sulfate (HS) octadecasaccharide (18-mer-HP or hepatoprotective 18-mer) displays potent hepatoprotection by targeting the HMGB1/RAGE axis. Endogenous HS proteoglycan, syndecan-1, is shed in response to APAP overdose in mice and humans. Furthermore, purified syndecan-1, but not syndecan-1 core protein, binds to HMGB1, suggesting that HMGB1 binds to HS polysaccharide side chains of syndecan-1. Last, we compared the protection effect between 18-mer-HP and N-acetyl cysteine, which is the standard of care to treat APAP overdose. We demonstrated that 18-mer-HP administered 3 hours after a lethal dose of APAP is fully protective; however, the treatment of N-acetyl cysteine loses protection. Therefore, 18-mer-HP may offer a potential therapeutic advantage over N-acetyl cysteine for late-presenting patients. Synthetic HS provides a potential approach for the treatment of APAP-induced ALF.

Transplantation of mesenchymal stem cells and their derivatives effectively promotes liver regeneration to attenuate acetaminophen-induced liver injury

Acetaminophen (APAP)-induced injury is a common clinical phenomenon that not only occurs in a dose-dependent manner but also occurs in some idiosyncratic individuals in a dose-independent manner. APAP overdose generally results in acute liver injury via the initiation of oxidative stress, endoplasmic reticulum (ER) stress, autophagy, liver inflammation, and microcirculatory dysfunction. Liver transplantation is the only effective strategy for treating APAP-induced liver failure, but liver transplantation is inhibited by scarce availability of donor liver grafts, acute graft rejection, lifelong immunosuppression, and unbearable costs. Currently, N-acetylcysteine (NAC) effectively restores liver functions early after APAP intake, but it does not protect against APAP-induced injury at the late stage. An increasing number of animal studies have demonstrated that mesenchymal stem cells (MSCs) significantly attenuate acute liver injury through their migratory capacity, hepatogenic differentiation, immunoregulatory capacity, and paracrine effects in acute liver failure (ALF). In this review, we comprehensively discuss the mechanisms of APAP overdose-induced liver injury and current therapies for treating APAP-induced liver injury. We then comprehensively summarize recent studies about transplantation of MSC and MSC derivatives for treating APAP-induced liver injury. We firmly believe that MSCs and their derivatives will effectively promote liver regeneration and liver injury repair in APAP overdose-treated animals and patients. To this end, MSC-based therapies may serve as an effective strategy for patients who are waiting for liver transplantation during the early and late stages of APAP-induced ALF in the near future.

Plant-derived oleanolic acid ameliorates markers of subclinical inflammation and innate immunity activation in diet-induced pre-diabetic rats

AIMS

Sub-clinical inflammation during pre-diabetes is one of the predisposing factors that facilitates the progression of pre-diabetes to type 2 diabetes. The administration of oleanolic acid (OA) with or without dietary intervention ameliorates the metabolic and cardiovascular complications in diet-induced pre-diabetes animal models of pre-diabetes. This study aimed to investigate whether OA can also suppress immune activation and ameliorate pro-inflammatory markers.

METHODS

Pre-diabetes was induced by feeding Sprague Dawley rats a high-fat high carbohydrate diet for 20 weeks. The pre-diabetic rats were then treated with OA (80 mg/kg) or metformin (500 mg/kg) in the presence or absence of dietary interventions for a period of 12 weeks. At the end of the treatment period, the animals were euthanised and whole blood was used for platelet and immune cell count while plasma was used for fibrinogen, cluster differentiation 40 ligand and pro-inflammatory cytokine evaluation.

RESULTS

The results of this study revealed that OA, with or without dietary intervention, improved lipid metabolism by restoring high-density lipoprotein (HDL) and low-density lipoproteins (LDLs) as well as reducing platelets and immune cell counts. Furthermore, OA also decreased plasma proinflammatory cytokines, including tumour necrosis factor-α and -1β. Markers of immune activation such as C-reactive protein, fibrinogen, and CD40L were also decreased upon administration of OA with or without dietary intervention.

CONCLUSION

The findings of this study suggest that OA may provide an alternative to prevent the progression of pre-diabetes to overt diabetes. This was evident by the reduction of differential white blood cell count and proinflammatory cytokines that exercebate insulin resistance. However, more studies are needed to elucidate the molecular mechanisms and to improve efficacy.

Von Willebrand factor delays liver repair after acetaminophen-induced acute liver injury in mice

BACKGROUND & AIM

Acetaminophen (APAP)-induced acute liver failure is associated with substantial alterations in the hemostatic system. In mice, platelets accumulate in the liver after APAP overdose and appear to promote liver injury. Interestingly, patients with acute liver injury have highly elevated levels of the platelet-adhesive protein von Willebrand factor (VWF), but a mechanistic connection between VWF and progression of liver injury has not been established. We tested the hypothesis that VWF contributes directly to experimental APAP-induced acute liver injury.

METHODS

Wild-type mice and VWF-deficient (Vwf^-/-) mice were given a hepatotoxic dose of APAP (300 mg/kg, i.p.) or vehicle (saline). VWF plasma levels were measured by ELISA, and liver necrosis or hepatocyte proliferation was measured by immunohistochemistry. Platelet and VWF deposition were measured by immunofluorescence.

RESULTS

In wild-type mice, VWF plasma levels, high molecular weight (HMW) VWF multimers, and VWF activity decreased 24 h after APAP challenge. These changes coupled to robust hepatic VWF and platelet deposition, although VWF deficiency had minimal effect on peak hepatic platelet accumulation or liver injury. VWF plasma levels were elevated 48 h after APAP challenge, but with relative reductions in HMW multimers and VWF activity. Whereas hepatic platelet aggregates persisted in livers of APAP-challenged wild-type mice, platelets were nearly absent in Vwf^-/- mice 48 h after APAP challenge. The absence of platelet aggregates was linked to dramatically accelerated repair of the injured liver. Complementing observations in Vwf^-/- mice, blocking VWF or the platelet integrin α_IIbβ₃ during development of injury significantly reduced hepatic platelet aggregation and accelerated liver repair in APAP-challenged wild-type mice.

CONCLUSION

These studies are the first to suggest a mechanistic link between VWF, hepatic platelet accumulation, and liver repair. Targeting VWF might provide a novel therapeutic approach to improve repair of the APAP-injured liver.

LAY SUMMARY

Patients with acute liver injury due to acetaminophen overdose have highly elevated levels of the platelet-adhesive protein von Willebrand factor. It is not known whether von Willebrand factor plays a direct role in the progression of acute liver injury. We discovered that von Willebrand factor delays repair of the acetaminophen-injured liver in mice and that targeting von Willebrand factor, even in mice with established liver injury, accelerates liver repair.

Liver-targeted delivery of TSG-6 by calcium phosphate nanoparticles for the management of liver fibrosis

Mesenchymal stem cells (MSCs) transplantation is a promising antifibrotic strategy but facing clinical controversies. Inspired by advances in nanomedicine, we aimed to bypass these clinical barriers of MSCs by identifying the key antifibrotic molecule of MSCs and developing a specific liver-targeting nanocarrier.

Methods: Cytokines secreted by MSCs were examined with serum stimulation of cirrhotic patients. Immunohistochemistry, microarray, immunoblotting, and quantitative real-time PCR (qRT-PCR) were applied to identify the critical antifibrotic cytokine and to discover its role in modulating antifibrotic effects. Biomineralization method was used to prepare calcium phosphate nanoparticles (NPs). The targeting and therapeutic efficiency of NPs were evaluated by in vivo imaging and biochemical studies on fibrotic mice induced by CCl₄.

Results: The stimulated MSCs exhibited high-level expression of Tumor necrosis factor (TNF)-stimulated gene 6 (TSG-6). On animal study, exogenous administration of TSG-6 alone can ameliorate liver fibrosis while TSG-6 knocked MSCs (Lv-TSG-6 MSCs) lost antifibrotic effects. Further studies verified the importance of TSG-6 and identified its antifibrotic mechanism by modulating M2 macrophages and increasing matrix metalloproteinase 12 (MMP12) expression. Additionally, we found a feedback loop between TSG-6, MMP12 and pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β), which may improve our understanding of the aggravating process of cirrhosis and antifibrotic mechanisms of TSG-6 and MSCs. Based on these findings, we developed calcium phosphate nanoparticles (CaP@BSA NPs) by biomineralization method using bovine serum albumin (BSA) as the biotemplate. Imaging tracking and drug loading studies showed specific liver targeting and high TSG-6 loading efficacy of as-prepared CaP@BSA NPs. In vivo therapeutic study further demonstrated the improved therapeutic effects of TSG-6 loaded CaP@BSA.

Conclusions: TSG-6 was a major antifibrotic cytokine of MSCs, TSG-6 loaded CaP@BSA NPs showed specific liver accumulation and improved therapeutic effects, which indicated translational potentials of CaP@BSA as a promising drug carrier for the liver disease management.

SPHK1 deficiency protects mice from acetaminophen-induced ER stress and mitochondrial permeability transition

Acetaminophen (APAP) is the leading cause of drug-induced acute liver failure. Sphingosine-1-phosphate (S1P), whose formation is catalyzed by sphingosine kinase (SPHK)-1 or -2, is a bioactive lipid implicated in human health and disease. Here, we show that APAP-treated sphK1-deficient (sphK1^-/-) mice exhibited markedly less liver damage and reduced inflammation compared with the wild-type mice. SPHK1 deficiency alleviated APAP-induced endoplasmic reticulum (ER) stress by affecting the phosphorylation of inositol-requiring enzyme 1α (IRE1α) and protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK)-eukaryotic translation initiation factor 2α (eIF2α), levels of activating transcription factor 4 (ATF4), and activation of activating transcription factor 6 (ATF6). SPHK1 deficiency also inhibited mitochondrial permeability transition (MPT), as evidenced by the impaired phosphorylation of JNK, apoptosis signal-regulated kinase 1 (ASK1), and glycogen synthase kinase 3β (GSK3β). In addition, SPHK1 deficiency reduced the levels of histone deacetylase and promoted the acetylation of p65 and STAT1, thereby impairing the transcription of inflammatory genes. Supplementation with exogenous S1P significantly reversed the activation of the PERK-eIF2α-ATF4 pathway and ATF6 during ER stress as well as the activation of GSK3β, ASK1, and JNK during MPT. Both FTY720, a functional S1P receptor antagonist, and PF543, an SPHK1 inhibitor, significantly ameliorated APAP-induced liver injury and improved animal survival. Our study reveals a critical role for SPHK1 in mediating APAP-induced hepatotoxicity by promoting ER stress and MPT.

Dichotomous Role of Plasmin in Regulation of Macrophage Function after Acetaminophen Overdose

Kupffer cells and monocyte-derived macrophages are critical for liver repair after acetaminophen (APAP) overdose. These cells produce promitogenic cytokines and growth factors, and they phagocytose dead cell debris, a process that is critical for resolution of inflammation. The factors that regulate these dynamic functions of macrophages after APAP overdose, however, are not fully understood. We tested the hypothesis that the fibrinolytic enzyme, plasmin, is a key regulator of macrophage function after APAP-induced liver injury. In these studies, inhibition of plasmin in mice with tranexamic acid delayed up-regulation of proinflammatory cytokines after APAP overdose. In culture, plasmin directly, and in synergy with high-mobility group B1, stimulated Kupffer cells and bone marrow-derived macrophages to produce cytokines by a mechanism that required NF-κB. Inhibition of plasmin in vivo also prevented trafficking of monocyte-derived macrophages into necrotic lesions after APAP overdose. This prevented phagocytic removal of dead cells, prevented maturation of monocyte-derived macrophages into F4/80-expressing macrophages, and prevented termination of proinflammatory cytokine production. Our studies reveal further that phagocytosis is an important stimulus for cessation of proinflammatory cytokine production as treatment of proinflammatory, monocyte-derived macrophages, isolated from APAP-treated mice, with necrotic hepatocytes decreased expression of proinflammatory cytokines. Collectively, these studies demonstrate that plasmin is an important regulator of macrophage function after APAP overdose.

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.

Intrahepatic fibrin(ogen) deposition drives liver regeneration after partial hepatectomy in mice and humans

Platelets play a pivotal role in stimulating liver regeneration after partial hepatectomy in rodents and humans. Liver regeneration in rodents is delayed when platelets are inhibited. However, the exact mechanisms whereby platelets accumulate and promote liver regeneration remain uncertain. Thrombin-dependent intrahepatic fibrin(ogen) deposition was recently reported after partial hepatectomy (PHx) in mice, but the role of fibrin(ogen) deposits in liver regeneration has not been investigated. We tested the hypothesis that fibrin(ogen) contributes to liver regeneration by promoting intrahepatic platelet accumulation and identified the trigger of rapid intrahepatic coagulation after PHx. PHx in wild-type mice triggered rapid intrahepatic coagulation, evidenced by intrahepatic fibrin(ogen) deposition. Intrahepatic fibrin(ogen) deposition was abolished in mice with liver-specific tissue factor deficiency, pinpointing the trigger of coagulation after PHx. Direct thrombin activation of platelets through protease-activated receptor-4 did not contribute to hepatocyte proliferation after PHx, indicating that thrombin contributes to liver regeneration primarily by driving intrahepatic fibrin(ogen) deposition. Fibrinogen depletion with ancrod reduced both intrahepatic platelet accumulation and hepatocyte proliferation after PHx, indicating that fibrin(ogen) contributes to liver regeneration after PHx by promoting intrahepatic platelet accumulation. Consistent with the protective function of fibrin(ogen) in mice, low postoperative plasma fibrinogen levels were associated with liver dysfunction and mortality in patients undergoing liver resection. Moreover, increased intrahepatic fibrin(ogen) deposition was evident in livers of patients after liver resection but was remarkably absent in patients displaying hepatic dysfunction postresection. The results suggest a novel mechanism whereby coagulation-dependent intrahepatic fibrin(ogen) deposition drives platelet accumulation and liver regeneration after PHx.

Diallyl sulfide treatment protects against acetaminophen-/carbon tetrachloride-induced acute liver injury by inhibiting oxidative stress, inflammation and apoptosis in mice

The purpose of the present study was to investigate the effects and underlying mechanisms of diallyl sulfide (DAS), an organosulfur compound extracted from garlic, on drug-induced or chemical-induced liver injury caused by acetaminophen (APAP) or carbon tetrachloride (CCl4) in mice. DAS (100, 200, or 400 μmol kg-1) was orally administered 1 hour before APAP or CCl4 intraperitoneal injection, and the serum and liver tissue were collected 24 hours after APAP or CCl4 exposure. The serum aminotransferase activities and liver histopathological examination showed that DAS exhibited obvious hepatoprotective effects against acute liver injury induced by APAP or CCl4. In addition, exposure to APAP or CCl4 resulted in an increased content of malonaldehyde as well as a decreased ratio of reduced to oxidized glutathione, and a decreased level of superoxide dismutase and catalase activity in the liver (p < 0.05); however, pretreatment with DAS restored the perturbations of the antioxidant system in the liver. Beyond that, DAS pretreatment reduced the APAP-/CCl4-induced increase in phosphorylation of inhibitor of kappa B alpha (IκBα) and p65 subunit of nuclear factor kappa B (NF-κB) expression in the cytoplasm and nucleus in the liver. DAS pretreatment also decreased the excessive level of TNF-α caused by APAP or CCl4 in serum (p < 0.05). Moreover, DAS pretreatment regulated the expression of cleaved caspase 3, Bax and Bcl-2 in the liver and suppressed APAP-/CCl4-induced hepatocyte apoptosis. In conclusion, DAS exhibits hepatoprotective effects against drug-induced and chemical-induced liver injuries induced by APAP or CCl4 in mice, probably due to its ability to reduce hepatic oxidative stress and inhibit inflammatory injury and hepatocyte apoptosis.

Chronic liver injury drives non-traditional intrahepatic fibrin(ogen) crosslinking via tissue transglutaminase

Essentials Fibrin clots are often implicated in the progression of liver fibrosis. Liver fibrosis was induced in transgenic mice with defects in clot formation or stabilization. Liver fibrosis and fibrin(ogen) deposition do not require fibrin polymerization or factor XIIIa. Fibrin(ogen) is an in vivo substrate of tissue transglutaminase in experimental liver fibrosis. SUMMARY: Background Intravascular fibrin clots and extravascular fibrin deposits are often implicated in the progression of liver fibrosis. However, evidence supporting a pathological role of fibrin in hepatic fibrosis is indirect and based largely on studies using anticoagulant drugs that inhibit activation of the coagulation protease thrombin, which has other downstream targets that promote fibrosis. Therefore, the goal of this study was to determine the precise role of fibrin deposits in experimental hepatic fibrosis. Methods Liver fibrosis was induced in mice expressing mutant fibrinogen insensitive to thrombin-mediated proteolysis (i.e. locked in the monomeric form), termed FibAEK mice, and factor XIII A2 subunit-deficient (FXIII-/- ) mice. Female wild-type mice, FXIII-/- mice and homozygous FibAEK mice were challenged with carbon tetrachloride (CCl4 ) twice weekly for 4 weeks or 6 weeks (1 mL kg-1 , intraperitoneal). Results Hepatic injury and fibrosis induced by CCl4 challenge were unaffected by FXIII deficiency or inhibition of thrombin-catalyzed fibrin polymer formation (in FibAEK mice). Surprisingly, hepatic deposition of crosslinked fibrin(ogen) was not reduced in CCl4 -challenged FXIII-/- mice or FibAEK mice as compared with wild-type mice. Rather, deposition of crosslinked hepatic fibrin(ogen) following CCl4 challenge was dramatically reduced in tissue transglutaminase-2 (TGM2)-deficient (TGM2-/- ) mice. However, the reduction in crosslinked fibrin(ogen) in TGM2-/- mice did not affect CCl4 -induced liver fibrosis. Conclusions These results indicate that neither traditional fibrin clots, formed by the thrombin-activated FXIII pathway nor atypical TGM2-crosslinked fibrin(ogen) contribute to experimental CCl4 -induced liver fibrosis. Collectively, the results indicate that liver fibrosis occurs independently of intrahepatic fibrin(ogen) deposition.

Matrix metalloproteinase-12 as an endogenous resolution promoting factor following myocardial infarction

Following myocardial infarction (MI), timely resolution of inflammation promotes wound healing and scar formation while limiting excessive tissue damage. Resolution promoting factors (RPFs) are agents that blunt leukocyte trafficking and inflammation, promote necrotic and apoptotic cell clearance, and stimulate scar formation. Previously identified RPFs include mediators derived from lipids (resolvins, lipoxins, protectins, and maresins), proteins (glucocorticoids, annexin A1, galectin 1, and melanocortins), or gases (CO, H₂S, and NO). Matrix metalloproteinase-12 (MMP-12; macrophage elastase) has shown promising RPF qualities in a variety of disease states. We review here the evidence that MMP-12 may serve as a novel RPF with potential therapeutic efficacy in the setting of MI.