Inhibition of geranylgeranyltransferase attenuates neutrophil accumulation and tissue injury in severe acute pancreatitis

Podocyte Geranylgeranyl Transferase Type-I Is Essential for Maintenance of the Glomerular Filtration Barrier

SIGNIFICANCE STATEMENT

A tightly regulated actin cytoskeleton attained through balanced activity of RhoGTPases is crucial to maintaining podocyte function. However, how RhoGTPases are regulated by geranylgeranylation, a post-translational modification, has been unexplored. The authors found that loss of the geranylgeranylation enzyme geranylgeranyl transferase type-I (GGTase-I) in podocytes led to progressive albuminuria and foot process effacement in podocyte-specific GGTase-I knockout mice. In cultured podocytes, the absence of geranylgeranylation resulted in altered activity of its downstream substrates Rac1, RhoA, Cdc42, and Rap1, leading to alterations of β1-integrins and actin cytoskeleton structural changes. These findings highlight the importance of geranylgeranylation in the dynamic management of RhoGTPases and Rap1 to control podocyte function, providing new knowledge about podocyte biology and glomerular filtration barrier function.

BACKGROUND

Impairment of the glomerular filtration barrier is in part attributed to podocyte foot process effacement (FPE), entailing disruption of the actin cytoskeleton and the slit diaphragm. Maintenance of the actin cytoskeleton, which contains a complex signaling network through its connections to slit diaphragm and focal adhesion proteins, is thus considered crucial to preserving podocyte structure and function. A dynamic yet tightly regulated cytoskeleton is attained through balanced activity of RhoGTPases. Most RhoGTPases are post-translationally modified by the enzyme geranylgeranyl transferase type-I (GGTase-I). Although geranylgeranylation has been shown to regulate activities of RhoGTPases and RasGTPase Rap1, its significance in podocytes is unknown.

METHODS

We used immunofluorescence to localize GGTase-I, which was expressed mainly by podocytes in the glomeruli. To define geranylgeranylation's role in podocytes, we generated podocyte-specific GGTase-I knockout mice. We used transmission electron microscopy to evaluate FPE and measurements of urinary albumin excretion to analyze filtration barrier function. Geranylgeranylation's effects on RhoGTPases and Rap1 function were studied in vitro by knockdown or inhibition of GGTase-I. We used immunocytochemistry to study structural modifications of the actin cytoskeleton and β1 integrins.

RESULTS

Depletion of GGTase-I in podocytes in vivo resulted in FPE and concomitant early-onset progressive albuminuria. A reduction of GGTase-I activity in cultured podocytes disrupted RhoGTPase balance by markedly increasing activity of RhoA, Rac1, and Cdc42 together with Rap1, resulting in dysregulation of the actin cytoskeleton and altered distribution of β1 integrins.

CONCLUSIONS

These findings indicate that geranylgeranylation is of crucial importance for the maintenance of the delicate equilibrium of RhoGTPases and Rap1 in podocytes and consequently for the maintenance of glomerular integrity and function.

AXL and MERTK receptor tyrosine kinases inhibition protects against pancreatic necrosis via selectively limiting CXCL2-related neutrophil infiltration

BACKGROUND

Acute pancreatitis (AP) was initiated within pancreatic parenchymal cells and sustained by uncontrolled inflammatory responses. AXL and MERTK receptor tyrosine kinases play a crucial role in negatively regulating the innate immunity. Therefore, this study aimed to investigate the role and underlying mechanism of AXL and MERTK in AP.

METHODS

Experimental AP was induced by ten hourly intraperitoneal administration of caerulein in global, hematopoietic- and pancreas-specific Axl and Mertk deficient mice. Pancreatitis severity was assessed biochemically and histologically. Pancreatic transcriptomics and pancreatic infiltrating immune cells were profiled. Some mice were given R428, an antagonist of AXL and MERTK. AXL and MERTK in peripheral leukocytes were measured by flow cytometry.

FINDINGS

The levels of AXL and MERTK in pancreatic tissue and pancreatic CD45⁺ cells were dynamically altered at 6 h and 12 h after the 1st injection of caerulein. Global and hematopoietic-specific, but not pancreas-specific deletion of Axl and Mertk protected against pancreatic necrosis and trypsinogen activation. Pancreatic transcriptomic analysis revealed that differentially expressed gene signatures were mainly related to metabolic and inflammatory pathways. Furthermore, deletion or inhibition of Axl and Mertk selectively inhibited pancreatic neutrophil infiltration, which was primarily related to CXCL2 secreted by pro-inflammatory macrophages. Increased levels of MERTK in peripheral leukocytes were correlated with more severe form of AP.

INTERPRETATION

Our findings reveal that specific AXL/MERTK antagonist may be a novel and potential early treatment for AP and the levels of MERTK in peripheral leukocytes may be a promising biomarker for predicting pancreatic severity in patients with AP.

FUNDING

National Natural Science Foundation of China, Shanghai Natural Science Foundation, a Shanghai Young Talent Award and a Shanghai Young Orient Scholar Award.

RESEARCH IN CONTEXT

Evidence before this study Acute pancreatitis (AP) is a common inflammatory disorder of the exocrine pancreas, the severity of which was determined by the extent of pancreatic necrosis, with no targeted therapy. AP was initiated by signals within pancreatic parenchymal cells and sustained by uncontrolled innate immune responses. One of the three crucial regulatory roles for AXL and MERTK is to negatively regulate innate immune responses. Added value of this study Global and hematopoietic-, but not pancreas-specific Axl and Mertk deficiency protected against pancreatitis, primarily pancreatic necrosis. Deletion of Axl and Mertk selectively inhibited pancreatic neutrophil infiltration that was related to CXCL2 secreted by pro-inflammatory macrophages. AXL and MERTK antagonist similarly reduced pancreatitis severity via limiting CXCL2-mediated pancreatic neutrophil infiltration. Higher levels of MERTK, but not AXL in peripheral leukocytes were correlated with more severe form of acute pancreatitis. Implications of all the available evidence A specific AXL/MERTK antagonist may be a novel and potential early treatment for AP. The level of MERTK on peripheral leukocytes may be a promising biomarker for predicting disease severity in patients with AP.

Complement Component 3 Is Required for Tissue Damage, Neutrophil Infiltration, and Ensuring NET Formation in Acute Pancreatitis

BACKGROUND

Neutrophil extracellular traps (NETs) are known to play an important role in the pathophysiology of acute pancreatitis (AP). Activation of the complement cascade has been shown to occur in AP. The aim of this study was to examine whether complement component 3 is involved in the generation of NETs in AP.

METHODS

AP was induced in wild-type and C3-deficient mice by retrograde infusion of taurocholate into the pancreatic duct. Blood, lung, and pancreas tissue were collected and MPO activity was determined in lung and pancreas tissue. Histological examination of the inflamed pancreas was performed. Plasma levels of CXCL2, MMP-9, IL-6, and DNA-histone complexes as well as pancreatic levels of CXCL1 and CXCL2 were determined by use of enzyme-linked immunosorbent assay. NETs were detected in the pancreas by electron microscopy. The amount of MPO and citrullinated histone 3 in neutrophils isolated from bone marrow was examined using flow cytometry.

RESULTS

In C3-deficient mice, challenge with taurocholate yielded much fewer NETs in the pancreatic tissue compared with wild-type controls. Taurocholate-induced blood levels of amylase, tissue injury, and neutrophil recruitment in the pancreas were markedly reduced in the mice lacking C3. Furthermore, MPO levels in the lung, and plasma levels of IL-6, MMP-9, and CXCL2 were significantly lower in the C3-deficient mice compared to wild-type mice after the induction of AP. In vitro studies revealed that neutrophils from C3-deficient mice had normal NET-forming ability and recombinant C3a was not capable of directly inducing NETs formation in the wild-type neutrophils.

CONCLUSION

C3 plays an important role in the pathophysiology of AP as it is necessary for the recruitment of neutrophils into the pancreas and ensuring NETs formation. Targeting C3 could hence be a potential strategy to ameliorate local damage as well as remote organ dysfunction in AP.

The Role of Neutrophils and Neutrophil Extracellular Traps in Acute Pancreatitis

Leukocyte invasion (neutrophils and monocytes/macrophages) is closely related to the severity of acute pancreatitis (AP) and plays an important role in the systemic inflammatory response and other organ injuries secondary to AP. Increased and sustained activation of neutrophils are major determinants of pancreatic injury and inflammation. After the onset of AP, the arrival of the first wave of neutrophils occurs due to a variety of triggers and is critical for the exacerbation of inflammation. In this review, we summarize the functional characteristics of neutrophils, elastase, and heparin-binding proteins in granules, the mechanisms of neutrophil recruitment and the role of neutrophil extracellular traps (NETs) in AP.

c-Abl kinase regulates neutrophil extracellular trap formation, inflammation, and tissue damage in severe acute pancreatitis

Neutrophil extracellular traps (NETs) are involved in acute pancreatitis (AP) but mechanisms controlling NET expulsion in AP are incompletely understood. Herein, we examined the role of c-Abelson (c-Abl) kinase in NET formation and tissue damage in severe AP. AP was induced by taurocholate infusion into pancreatic duct or intraperitoneal administration of l-arginine in mice. Pancreatic, lung, and blood samples were collected and levels of phosphorylated c-Abl kinase, citrullinated histone 3, DNA-histone complexes, myeloperoxidase, amylase, cytokines, and CXC chemokines were quantified. Citrullinated histone 3, reactive oxygen species (ROS), and NET formation were determined in bone marrow neutrophils. Taurocholate challenge increased phosphorylation of c-Abl kinase and levels of citrullinated histone 3 in the pancreas as well as DNA-histone complexes in the plasma. Administration of the c-Abl kinase inhibitor GZD824 not only abolished activation of c-Abl kinase but also decreased levels of citrullinated histone 3 in the pancreas and DNA-histone complexes in the plasma of animals with AP. Moreover, GZD824 decreased plasma levels of amylase, IL-6, and MMP-9 as well as edema, acinar cell necrosis, hemorrhage, CXC chemokine formation, and neutrophil infiltration in the inflamed pancreas. A beneficial effect of c-Abl kinase inhibition was confirmed in l-arginine-induced pancreatitis. In vitro, inhibition of c-Abl kinase reduced TNF-α-induced formation of ROS, histone 3 citrullination, and NETs in isolated bone marrow neutrophils. Our findings demonstrate that c-Abl kinase regulates NET formation in the inflamed pancreas. In addition, inhibition of c-Abl kinase reduced pancreatic tissue inflammation, and damage in AP. Thus, targeting c-Abl kinase might be a useful way to protect the pancreas in severe AP.

Emodin alleviates severe acute pancreatitis-associated acute lung injury by decreasing pre-B-cell colony-enhancing factor expression and promoting polymorphonuclear neutrophil apoptosis

The present study aimed to evaluate the protective effects of emodin on severe acute pancreatitis (SAP)‑associated acute lung injury (ALI), and investigated the possible mechanism involved. SAP was induced in Sprague‑Dawley rats by retrograde infusion of 5% sodium taurocholate (1 ml/kg), after which, rats were divided into various groups and were administered emodin, FK866 [a competitive inhibitor of pre‑B‑cell colony‑enhancing factor (PBEF)] or dexamethasone (DEX). DEX was used as a positive control. Subsequently, PBEF expression was detected in polymorphonuclear neutrophils (PMNs) isolated from rat peripheral blood by reverse transcription‑quantitative polymerase chain reaction and western blotting. In addition, histological alterations, apoptosis in lung/pancreatic tissues, apoptosis of peripheral blood PMNs and alterations in the expression of apoptosis‑associated proteins were examined by hematoxylin and eosin staining, terminal deoxynucleotidyl‑transferase‑mediated dUTP nick end labeling assay, Annexin V/propidium iodide (PI) assay and western blotting, respectively. Serum amylase activity and wet/dry (W/D) weight ratios were also measured. An in vitro study was also conducted, in which PMNs were obtained from normal Sprague‑Dawley rats and were incubated with emodin, FK866 or DEX in the presence of lipopolysaccharide (LPS). Apoptosis of PMNs and the expression levels of apoptosis‑associated proteins were examined in cultured PMNs in vitro by Annexin V/PI assay and western blotting, respectively. The results demonstrated that emodin, FK866 and DEX significantly downregulated PBEF expression in peripheral blood PMNs. In addition, emodin, FK866 and DEX reduced serum amylase activity, decreased lung and pancreas W/D weight ratios, alleviated lung and pancreatic injuries, and promoted PMN apoptosis by regulating the expression of apoptosis‑associated proteins: Fas, Fas ligand, B‑cell lymphoma (Bcl)‑2‑associated X protein, cleaved caspase‑3 and Bcl‑extra‑large. In addition, the in vitro study demonstrated that emodin, FK866 and DEX significantly reversed the LPS‑induced decrease of apoptosis in PMNs by regulating the expression of apoptosis‑associated proteins. In conclusion, the present study demonstrated that emodin may protect against SAP‑associated ALI by decreasing PBEF expression, and promoting PMN apoptosis via the mitochondrial and death receptor apoptotic pathways.

Therapeutic implications of innate immune system in acute pancreatitis

INTRODUCTION

Acute pancreatitis (AP) is an inflammatory disorder of the pancreas encompassing a cascade of cellular and molecular events. It starts from premature activation of zymogens with the involvement of innate immune system to a potential systemic inflammatory response and multiple organ failure. Leukocytes are the major cell population that participate in the propagation of the disease. Current understanding of the course of AP is still far from complete, limiting treatment options mostly to conservative supportive care. Emerging evidence has pointed to modulation of the immune system for strategic therapeutic development, by mitigating the inflammatory response and severity of AP. In the current review, we have focused on the role of innate immunity in the condition and highlighted therapeutics targeting it for treatment of this challenging disease.

AREAS COVERED

The current review has aimed to elaborate in-depth understanding of specific roles of innate immune cells, derived mediators and inflammatory pathways that are involved in AP. Summarizing the recent therapeutics and approaches applied experimentally that target immune responses to attenuate AP.

EXPERT OPINION

The current state of knowledge on AP, limitations of presently available therapeutic approaches and the promise of therapeutic implications of innate immune system in AP are discussed.

Correlation between serum levels of interleukin-6 and severity of acute pancreatitis

AIM: To assess the correlation between serum levels of interleukin (IL-6) and the severity of acute pancreatitis (AP).

METHODS: This study included 138 patients with severe AP (SAP), 126 with mild AP (MAP), and 150 healthy volunteers who underwent physical examination (control group). Serum levels of IL-6 in each group were detected and compared. The complications were recorded. The correlation between serum levels of IL-6 and Ranson score was analyzed, and the risk factors for the severity of AP were analyzed.

RESULTS: IL-6 level and Ranson score in the SAP group were both significantly higher than those in the MAP group and control group. IL-6 level and Ranson score in SAP patients with complications were significantly higher than those in SAP patients without complications (P < 0.05). Spearman correlation analysis showed that serum levels of IL-6 had a positive correlation with Ranson score. Using the severity of AP as the dependent variable, and age, gender, high Ranson score and high IL-6 level as the independent variables, we performed Logistic regression analysis and found that high IL-6 level was a risk factor for the severity of AP.

CONCLUSION: IL-6 is closely linked to the AP severity.

Chitosan coated curcumin nanocrystals augment pharmacotherapy via improved pharmacokinetics and interplay of NFκB, Keap1 and Nrf2 expression in Gram negative sepsis

Chi-CUR-NC provides a viable approach for reducing mortality in cIAI associated Gram negative sepsis.

Optimization of novel tocopheryl acetate nanoemulsions for parenteral delivery of curcumin for therapeutic intervention of sepsis

OBJECTIVE

The objective of this study is to develop a nanostructured parenteral delivery system, laden with curcumin (CUR), for the therapeutic intervention of sepsis and associated pathologies.

METHODS

Nanoemulsions were fabricated using sonication and speed homogenization. Size and zeta potential were evaluated by dynamic light scattering and transmission electron microscopy analysis. Pharmacodynamic and pharmacokinetic studies were performed on a rat model of lipopolysaccharide (LPS)-induced sepsis.

RESULTS

The drug content of optimized nanoemulsion (F5) formulation (particle size 246 ± 08 nm, polydispersity index (PDI) of 0.120, zeta potential of -41.1 ± 1.2 mV) was found to be 1.25 mg/ml. In vitro release studies demonstrated that F5 was able to sustain the release of CUR for up to 24 h. Minimal hemolysis and cellular toxicity demonstrated its suitability for intravenous administration. Significant reduction of inflammatory mediator levels was mediated through enhanced uptake by in RAW 264.7 and THP-1 in absence/presence of LPS. Nanoemulsion resulted in an improvement of plasma concentration (AUCF5/AUC CUR = 8.80) and tissue distribution of CUR in rats leading to a reduction in LPS-induced lung and liver injury due to less neutrophil migration, reduced TNF-α levels and oxidative stress (demonstrated by levels of lipid peroxides as well as carbonylated proteins) as confirmed by histopathological studies.

CONCLUSION

The findings suggest that the therapeutic performance (i.e., reduction in oxidative damage in tissues) of CUR can be enhanced by employing tocol acetate nanoemulsions (via improving pharmacokinetics and tissue distribution) as a platform for drug delivery in sepsis-induced organ injury.

Recent advances in the investigation of pancreatic inflammation induced by large doses of basic amino acids in rodents

It has been known for approximately 30 years that large doses of the semi-essential basic amino acid L-arginine induce severe pancreatic inflammation in rats. Recently, it has been demonstrated that L-arginine can also induce pancreatitis in mice. Moreover, other basic amino acids like L-ornithine and L-lysine can cause exocrine pancreatic damage without affecting the endocrine parenchyma and the ducts in rats. The utilization of these noninvasive severe basic amino acid-induced pancreatitis models is becoming increasingly popular and appreciated as these models nicely reproduce most laboratory and morphological features of human pancreatitis. Consequently, the investigation of basic amino acid-induced pancreatitis may offer us a better understanding of the pathogenesis and possible treatment options of the human disease.

Liposomal clodronate reduces Akt and mitogen-activated protein kinase expression in the intestinal mucosa of rats with severe acute pancreatitis

AIM: To study the effect of liposomal clodronate on the expression of protein kinase B (Akt) and mitogen-activated protein kinase [MAPK (ERK1/2)] in the intestinal mucosa of rats with severe acute pancreatitis (SAP), and to investigate the mechanism behind the therapeutic effect of liposomal clodronate on SAP-associated intestinal mucosal injury.

METHODS: Liposomal clodronate was prepared by means of thin film. Forty-eight SD rats were randomly divided into a model control group (C), a liposome control group (P), and a liposomal clodronate group (T). SAP was induced in rats of groups P and T by injection of sodium taurocholate under the pancreatic capsule, while group C received equal volume of normal saline. Serum levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and AMS were measured 2 and 6 h after SAP induction. Pathological alterations in the intestinal mucosa were observed.

RESULTS: Serum levels of AMS, IL-6 and TNF-α were significantly elevated in group P compared to group C (all P < 0.01). Compared with group P, serum levels of AMS, IL-6 and TNF-α were significantly decreased in group T (all P < 0.01). Pathological alterations (scores) in the intestinal mucosa were significantly attenuated in group T compared to group P. The expression of Akt and MAPK (ERK1/2) was significantly decreased in group T compared to group P.

CONCLUSION: Macrophages play an important role in the pathogenesis of intestinal mucosal injury in SAP. Macrophages can be depleted via phagocytosis of liposome encapsulated clodronate. Liposomal clodronate alleviates intestinal mucosal injury in SAP rats possibly by decreasing the expression of Akt and MAPK (ERK1/2).