Trypsin and activation of circulating trypsinogen contribute to pancreatitis-associated lung injury

VMP1 Constitutive Expression in Mice Dampens Pancreatic and Systemic Histopathological Damage in an Experimental Model of Severe Acute Pancreatitis

Acute pancreatitis (AP) an inflammatory condition caused by the premature activation of pancreatic proteases, leads to organ damage, systemic inflammation, and multi-organ failure. Severe acute pancreatitis (SAP) has high morbidity and mortality, affecting the liver, kidneys, and lungs. Autophagy maintains pancreatic homeostasis, with VMP1-mediated selective autophagy (zymophagy) preventing intracellular zymogen activation and acinar cell death. This study examines the protective role of VMP1 (Vacuole Membrane Protein 1)-induced autophagy using ElaI-VMP1 transgenic mice in a necrohemorrhagic SAP model (Hartwig's model). ElaI-VMP1 mice show significantly reduced pancreatic injury, including lower necrosis, edema, and inflammation, compared to wild-type (WT) mice. Biochemical markers (lactate dehydrogenase-LDH-, amylase, and lipase) and histopathology confirm that VMP1 expression mitigates pancreatic damage. Increased zymophagy negatively correlates with acinar necrosis, reinforcing its protective role. Beyond the pancreas, ElaI-VMP1 mice exhibit preserved liver, kidney, and lung histology, indicating reduced systemic organ damage. The liver maintains normal architecture, kidneys show minimal tubular necrosis, and lung inflammation features are reduced compared to WT mice. Our results confirm that zymophagy functions as a protective pathophysiological mechanism against pancreatic and extrapancreatic tissue injury in SAP. Further studies on the mechanism of VMP1-mediated selective autophagy in AP are necessary to determine its relevance and possible modulation to prevent the severity of AP.

Disulfiram relieves severe acute pancreatitis by inhibiting GSDMD-dependent NETs formation

OBJECTIVES

Severe acute pancreatitis (SAP) is characterized by pancreatic and systemic inflammation and persistent organ failure. Neutrophil extracellular traps (NETs) are considered to play an important role in the development of SAP. We aimed to explore the effect of disulfiram (DSL), a newly developed anti-inflammatory drug, on NETs in SAP.

METHODS

A mouse model of SAP was induced by caerulein and lipopolysaccharide, and the mice were divided into the normal control group, the DSL group, the SAP group, and the SAP treated with 50 mg/kg (50DSLSAP) and 100 mg/kg DSL (100DSLSAP) groups, respectively. The severity of SAP was evaluated based on the morphological and biochemical changes. Gasdermin D (GSDMD) expression was evaluated in vivo and in vitro to verify the effect of DSL. Additionally, the expressions of NETs were also evaluated in vivo and in vitro in SAP with and without DSL treatment to explore the possible mechanism of DSL on SAP.

RESULTS

Pancreatic inflammatory injury increased in the SAP group, which was alleviated by DSL. GSDMD, a protein related to the formation of NETs, increased in SAP. Expressions of NETs were also promoted in the in vivo SAP model and by phorbol myristate acetate (PMA) in vitro. Moreover, DSL inhibited the expressions of GSDMD and NETs in vivo. The results were further confirmed in the in vitro experiment.

CONCLUSIONS

NETs are highly associated with inflammatory injury in SAP. DSL inhibits NETs formation by downregulating GSDMD, which in turn relieves the inflammation of SAP. Our study may provide a possible therapeutic target for SAP.

Central role of neutrophil in the pathogenesis of severe acute pancreatitis

Severe acute pancreatitis (SAP) is an acute abdominal disease with the strong systemic inflammatory response, and rapidly progresses from a local pancreatic damage into multiple organ dysfunction. For many decades, the contributions of neutrophils to the pathology of SAP were traditionally thought to be the chemokine and cytokine cascades that accompany inflammation. In this review, we focus mainly on those recently recognized aspects of neutrophils in SAP processes. First, emerging evidence suggests that therapeutic interventions targeting neutrophils significantly lower tissue damage and protect against the occurrence of pancreatitis. Second, trypsin activation promotes the initial neutrophils recruitment into local pancreas, and subsequently neutrophils infiltration in turn triggers trypsin production. Finally, neutrophils have the unique ability to release neutrophil extracellular traps even in the absence of pathogens.

Effects of hypoxia-inducible factor-1α and matrix metalloproteinase-9 on alveolar-capillary barrier disruption and lung edema in rat models of severe acute pancreatitis-associated lung injury

The aim of this study was to investigate the effects of hypoxia-inducible factor-1α (HIF-1α) and matrix metalloproteinase-9 (MMP-9) on alveolar-capillary barrier disruption and lung edema in rat models of severe acute pancreatitis-associated lung injury (PALI). A total of 40 male Sprague-Dawley rats were randomly divided into a sham surgery group (n=10) and three PALI groups, in which acute pancreatitis was induced by the retrograde infusion of 5% sodium taurocholate (1 ml/kg). The PALI groups were as follows: i) Untreated PALI group (n=10); ii) 2-methoxyestradiol (2ME2) group (5 mg/kg body mass; n=10); and iii) 2ME2 group (15 mg/kg body mass; n=10). In the two 2ME2 groups, the HIF-1α inhibitor 2ME2 was administered intraperitoneally 1 h after the induction of AP. The severity of the pancreatitis was evaluated by the serum amylase levels and pathology. The severity of the lung injury was evaluated by the wet/dry ratio, blood gas analysis and pathology. The alveolar-capillary barrier disruption was assessed by Evans blue dye extravasation. The protein and mRNA expression levels of HIF-1α and MMP-9 were studied using enzyme-linked immunosorbent assays (ELISAs), western blot analysis and reverse transcription-polymerase chain reaction. The active tumor necrosis factor-α levels were measured using an ELISA. The HIF-1α inhibitor 2ME2 attenuated the severity of the pancreatitis and PALI, while the lung edema and alveolar-capillary barrier disruption were significantly ameliorated compared with those in the untreated PALI group. Administration of the higher dose of 2ME2 significantly suppressed the protein expression of MMP-9 in the lung tissues. The results indicate that HIF-1α has a major function in alveolar-capillary barrier disruption and lung edema in PALI via a molecular pathway cascade involving MMP-9. Inhibition of HIF-1α by 2ME2 attenuates alveolar-capillary barrier disruption and lung edema. Pharmacological blockade of this pathway in patients with PALI may provide a novel therapeutic strategy.

Rho-kinase signalling regulates trypsinogen activation and tissue damage in severe acute pancreatitis

BACKGROUND AND PURPOSE

Severe acute pancreatitis (SAP) is characterized by trypsinogen activation, infiltration of leucocytes and tissue necrosis but the intracellular signalling mechanisms regulating organ injury in the pancreas remain elusive. Rho-kinase is a potent regulator of specific cellular processes effecting several pro-inflammatory activities. Herein, we examined the role of Rho-kinase signalling in acute pancreatitis.

EXPERIMENTAL APPROACH

Pancreatitis was induced by infusion of taurocholate into the pancreatic duct in C57BL/6 mice. Animals were treated with a Rho-kinase inhibitor Y-27632 (0.5-5 mg·kg⁻¹) before induction of pancreatitis.

KEY RESULTS

Taurocholate infusion caused a clear-cut increase in blood amylase, pancreatic neutrophil infiltration, acinar cell necrosis and oedema formation in the pancreas. Levels of pancreatic myeloperoxidase (MPO), macrophage inflammatory protein-2 (MIP-2), trypsinogen activation peptide (TAP) and lung MPO were significantly increased, indicating local and systemic disease. Inhibition of Rho-kinase activity dose-dependently protected against pancreatitis. For example, 5 mg·kg⁻¹ Y-27632 reduced acinar cell necrosis, leucocyte infiltration and pancreatic oedema by 90%, 89% and 58%, respectively, as well as tissue levels of MPO by 75% and MIP-2 by 84%. Moreover, Rho-kinase inhibition decreased lung MPO by 75% and blood amylase by 83%. Pancreatitis-induced TAP levels were reduced by 61% in Y-27632-treated mice. Inhibition of Rho-kinase abolished secretagogue-induced activation of trypsinogen in pancreatic acinar cells in vitro.

CONCLUSIONS AND IMPLICATIONS

Our novel data suggest that Rho-kinase signalling plays an important role in acute pancreatitis by regulating trypsinogen activation and subsequent CXC chemokine formation, neutrophil infiltration and tissue injury. Thus, these results indicate that Rho-kinase may constitute a novel target in the management of SAP.

PAR2 exerts local protection against acute pancreatitis via modulation of MAP kinase and MAP kinase phosphatase signaling

During acute pancreatitis, protease-activated receptor 2 (PAR2) can be activated by interstitially released trypsin. In the mild form of pancreatitis, PAR2 activation exerts local protection against intrapancreatic damage, whereas, in the severe form of pancreatitis, PAR2 activation mediates some systemic complications. This study aimed to identify the molecular mechanisms of PAR2-mediated protective effects against intrapancreatic damage. A mild form of acute pancreatitis was induced by an intraperitoneal injection of caerulein (40 microg/kg) in rats. Effects of PAR2 activation on intrapancreatic damage and on mitogen-activated protein (MAP) kinase signaling were assessed. Caerulein treatment activated extracellular signal-regulated kinase (ERK) and c-Jun NH(2)-terminal kinase (JNK) within 15 min and maintained phosphorylation of ERK and JNK for 2 h in the rat pancreas. Although PAR2 activation by the pretreatment with PAR2-activating peptide (AP) itself increased ERK phosphorylation in rat pancreas, the same treatment remarkably decreased caerulein-induced activation of ERK and JNK principally by accelerating their dephosphorylation. Inhibition of ERK and JNK phosphorylation by the pretreatment with MAP/ERK kinase (MEK) or JNK inhibitors decreased caerulein-induced pancreatic damage that was similar to the effect induced by PAR2-AP. Notably, in caerulein-treated rats, PAR2-AP cotreatment highly increased the expression of a group of MAP kinase phosphatases (MKPs) that deactivate ERK and JNK. The above results imply that downregulation of MAP kinase signaling by MKP induction is a key mechanism involved in the protective effects of PAR2 activation on caerulein-induced intrapancreatic damage.

Mitochondrial injury in pancreatitis

Pancreatitis is an increasingly common disease that carries a significant mortality and which lacks specific therapy. Pathological calcium signalling is an important contributor to the initiating cell injury, caused by or acting through mitochondrial inhibition. A principal effect of disordered cell signalling and impaired mitochondrial function is cell death, either by apoptosis that is primarily protective, or by necrosis that is deleterious, both locally and systemically. Mitochondrial calcium overload is particularly important in necrotic injury, which may include damage mediated by the mitochondrial permeability transition pore. The role of reactive oxygen species remains controversial. Present understanding of the part played by disordered pancreatic acinar calcium signalling and mitochondrial inhibition offers several new potential therapeutic targets.

Interaction of complement and leukocytes in severe acute pancreatitis: potential for therapeutic intervention

In acute pancreatitis, local as well as systemic organ complications are mediated by the activation of various inflammatory cascades. The role of complement in this setting is unclear. The aim of the present study was to determine the level of complement activation in experimental pancreatitis, to evaluate the interaction of complement and leukocyte-endothelium activation, and to assess the effects of complement inhibition by soluble complement receptor 1 (sCR1) in this setting. Necrotizing pancreatitis was induced in Wistar rats by the combination of intravenous cerulein and retrograde infusion of glycodeoxycholic acid into the biliopancreatic duct; edematous pancreatitis was induced by intravenous cerulein only. In control animals, a sham operation (midline laparotomy) was performed. Complement activation, leukocyte sequestration, and pancreatic as well as pulmonary injury were assessed in the presence/absence of sCR1. Increased levels of C3a were found in necrotizing but not in edematous pancreatitis. When complement activation in necrotizing pancreatitis was blocked by sCR1, levels of C3a and total hemolytic activity (CH50) were decreased. Leukocyte-endothelial interaction, as assessed by intravital microscopy, and pancreatic as well as pulmonary organ injury (wet-to-dry weight ratio, MPO activity, and histology) were ameliorated by sCR1. As a result of the present study, necrotizing but not edematous pancreatitis is characterized by significant and early complement activation. Based on the interaction of complement and leukocytes, complement inhibition by sCR1 may be a valuable option in the treatment of leukocyte-associated organ injury in severe pancreatitis.

Time course of lung injury in rat acute pancreatitis

OBJECTIVE

Lung injury is a severe complication of acute pancreatitis that increases the mortality rate of the disease. The pathophysiology of acute pancreatitis has been studied in several experimental models, but the kinetics of pulmonary complications in relation to the pancreatic disease is not completely understood. We then studied the severity of acute pancreatitis-associated lung injury over 18h in rats that had taurocholic acid injection in the pancreatic duct and determined whether blood collected from rats with pancreatitis is toxic enough to induce injury in normal lungs.

DESIGN AND SETTING

Prospective, randomized, and controlled animal study in an animal research laboratory in a university hospital.

INTERVENTIONS

We isolated lungs from rats with acute pancreatitis 2, 6, and 18h after taurocholic acid injection in the biliopancreatic duct and perfused them with blood collected from the same rats. Additionally, blood collected from rats with acute pancreatitis (time-points: 2 and 6h) was perfused in normal lungs.

MEASUREMENTS AND RESULTS

Taurocholic acid injection induced a severe pancreatic injury that started as early as 2h after the injection and persisted without recovery over the 18-h study period. In contrast, the pulmonary injury was transient, appearing at the 6-h time point with recovery by the end of the study. Pulmonary injury was moderate and evidenced mostly during lung reperfusion. Interestingly, blood collected at the 2-h time point in pancreatic rats induced pulmonary injury in normal lungs while blood collected at the 6-h time-point was not toxic.

CONCLUSIONS

While pancreatic injury persists over the full experimental period, pulmonary injury is transient in our experimental model. The recovery of lung injury by 18h might be explained by a decrease in the overall toxicity of pancreatic blood over time.

Neutral Endopeptidase Determines the Severity of Pancreatitis-Associated Lung Injury1

BACKGROUND

Neutral endopeptidase (NEP) is a cell-surface metalloprotease that degrades proinflammatory peptides such as substance P, neurokinin A, and bradykinin. Inhibition of NEP exacerbates both experimental pancreatitis and the associated lung injury. It is unclear if worsened lung injury is the indirect result of more severe pancreatitis or if it is a direct effect of NEP inhibition in the lung.

MATERIALS AND METHODS

We used a model of pancreatitis-associated lung injury (PALI) to test the hypothesis that antagonism or genetic deletion of NEP augments PALI inflammation and pulmonary damage irregardless of the degree of pancreatitic inflammation.

RESULTS

In NEP(+/+) mice, intraperitoneal injection of porcine pancreatic elastase (elastase, 0.085 U/g at t = 0 h and t = 1 h) caused a 7-fold increase in lung myeloperoxidase (MPO) activity and marked pulmonary edema, neutrophil infiltration, and hemorrhage at 4 h as compared to control animals. The pattern of lung injury induced by elastase mimicked that observed among a separate group of animals with PALI induced by cerulein but was not associated with pancreatitis. Both NEP(-/-) mice and NEP(+/+) mice pretreated with the NEP antagonist phosphoramidon (10 mg/kg s.c.) had significant elevations of lung MPO and worsened lung histology compared to NEP(+/+) mice given elastase alone. Antagonism of either the vanilloid receptor transient receptor vanilloid 1 or the substance P receptor NK1-R had no effect on elastase-mediated lung injury in NEP-deficient mice.

CONCLUSIONS

NEP is an inhibitor of pancreatic elastase-induced lung injury, presumably via degradation of proinflammatory mediators.

Influence of mast cells on the expression of adhesion molecules on circulating and migrating leukocytes in acute pancreatitis-associated lung injury

Pancreatitis-associated lung injury is an early-occurring and severe complication, still associated with substantial mortality. A number of inflammatory cells and their products are involved in the initiation and progress of the condition. In the present study, acute pancreatitis (AP) was induced by the intraductal infusion of 5% sodium taurodeoxycholate in the rat. Pulmonary endothelial barrier dysfunction was measured by plasma exudation of radiolabeled albumin. Expression of PECAM-1, ICAM-1, and L: -selectin on neutrophils (CD11b(+)) and monocytes/macrophages (CD11b/c(+)), obtained from circulation and lung tissue, was measured 1 and 6 hours after AP induction (n = 10 rats/time point/group). Plasma levels of histamine and serotonin were determined. The role of mast cells was evaluated by pretreatment with the mast cell stabilizer cromolyn. Intraperitoneal administration of cromolyn downregulated pancreatitis-induced systemic increase of histamine at 1 hour (513 +/- 82 vs. 309 +/- 50, p < 0.05). Cromolyn prevented a decreased expression of PECAM-1 on circulatory neutrophils and monocytes/macrophages and against an increased expression of ICAM-1 and PECAM-1 on pulmonary neutrophils and monocytes/macrophages 6 hours after AP induction (about 40% vs. 10%, p < 0.01). The mast cell stabilizer also prevented pancreatitis-induced pulmonary endothelial barrier dysfunction at 6 hours. Thus, our data indicate that mast cells may play a critical role in the activation of leukocytes during the initiation of pancreatitis-associated lung injury by altering phenotypes of adhesion molecules.

Membrane-bound ICAM-1 is upregulated by trypsin and contributes to leukocyte migration in acute pancreatitis

In acute pancreatitis, ICAM-1 is upregulated in various organs and contributes to the development of organ injury. To investigate the effects of pancreatic proteases on ICAM-1 expression and their role in the early process of leukocyte migration, human umbilical vein endothelial cells (HUVECs) were incubated with serum subjected to limited trypsin digestion and Wistar rats were injected with trypsin. Significant upregulation of membrane-bound ICAM-1 was seen on HUVECs incubated with trypsinated serum. Likewise, soluble ICAM-1 increased in the supernatant of HUVECs. Changes of membrane-bound ICAM-1 and soluble ICAM-1 were maximal with high concentrations of trypsin. HUVECs incubated with TNF-alpha (positive control) showed similar changes. In the pancreas and lungs of animals infused with trypsin, ICAM-1 and leukocyte sequestration were increased compared with controls. Reflecting the relevance of protease-induced ICAM-1 expression in leukocyte migration, leukocyte-endothelium interaction, as assessed by intravital microscopy, was markedly increased by trypsin. Inhibition of ICAM-1 ameliorated these changes significantly. In conclusion, trypsinated serum induces the upregulation of both membrane-bound ICAM-1 on endothelial cells and soluble ICAM-1. These changes contribute to the early steps of leukocyte migration in acute pancreatitis. The role of soluble ICAM-1 remains to be investigated.

Effects of inhaled thrombin receptor agonists in mice

Active thrombin is found in the airways of patients with a variety of inflammatory lung diseases. However, whether thrombin contributes to the pathologies of these diseases is unknown, although thrombin is a potent inflammatory mediator in other organ systems. In the present study we have assessed the acute inflammatory effect of inhaled thrombin and investigated the possible receptors mediating any effects in mice. Thrombin (200-2000 U kg(-1) intranasally), induced the recruitment of a small, but significant, number of neutrophils into the airways as assessed by differential counts of cells retrieved by bronchoalveolar lavage (BAL). This small response was mimicked by peptide agonists of proteinase-activated receptor-4 (PAR(4); GYPGKF, AYPGKF; 2-20 mg kg(-1)), but not PAR(1) (SFLLRN; 2-20 mg kg(-1)). By contrast, trypsin (200-2000 U kg(-1)) caused profound inflammation and lung damage. Concentrations of tumour necrosis factor-alpha (TNF-alpha) were elevated in BAL fluid from thrombin-treated mice, and a TNF-alpha-neutralising antibody inhibited the influx of neutrophils in response to thrombin. Although isolated alveolar macrophages appeared to express PAR(1)- and PAR(4)-immunoreactivity, these cells failed to release TNF-alpha above baseline levels in response to thrombin, trypsin or any of the peptide PAR agonists. Neither thrombin (2000 U kg(-1)) nor trypsin (200 U kg(-1)) modified the airway neutrophilia in response to intranasal bacterial lipopolysaccharide (LPS; 100 micrograms kg(-1)). In conclusion, exogenous thrombin has only a modest acute inflammatory action in the lung that appears to be mediated by PAR(4) and involve release of TNF-alpha from an unknown source.

Pulmonary trypsin-2 in the development of bronchopulmonary dysplasia in preterm infants

OBJECTIVES

In the preterm infant, lung injury can lead to irreversible tissue destruction and abnormal lung development. We examined whether pulmonary trypsin, a potent matrix-degrading serine proteinase and proteinase-cascade activator, is associated with the development of bronchopulmonary dysplasia (BPD) in preterm infants.

METHODS

Samples of tracheal aspirate fluid were collected from 32 intubated preterm infants during their first 2 postnatal weeks. The presence and molecular forms of trypsin in tracheal aspirate fluid samples were analyzed by zymography and Western blotting. The concentrations of trypsinogen-1 and -2 and tumor-associated trypsin inhibitor were measured by immunofluorometry. For examining the expression of trypsin-2 in lung tissue, immunohistochemistry was performed on autopsy specimens of fetuses, of preterm infants who died from respiratory distress syndrome or BPD, and of term infants without lung injury.

RESULTS

In infants who subsequently developed BPD (n = 18), we detected significantly higher concentrations of trypsinogen-2 during postnatal days 5 to 10 compared with those who survived without it. There was no difference in trypsinogen-1 concentrations. Tumor-associated trypsin inhibitor concentrations were significantly lower in infants who needed mechanical ventilation for >1 week. Immunohistochemistry demonstrated that trypsin-2 was predominantly expressed in bronchial and bronchiolar epithelium. In 2 preterm infants who died from prolonged respiratory distress syndrome, trypsin-2 was also expressed in vascular endothelium.

CONCLUSIONS

The levels of trypsinogen-2 are higher during postnatal days 5 to 10 in infants who subsequently develop BPD. The results suggest that high levels of pulmonary trypsin-2 may be associated with the development of BPD. This raises the possibility that therapy with exogenous proteinase inhibitors might prevent the development of BPD in preterm infants with respiratory distress.

Expression of the adhesion molecules Mac-1 and L-selectin on neutrophils in acute pancreatitis is protease- and complement-dependent

OBJECTIVE

To examine the effect of pancreatic proteases on the expression of the adhesion molecules Mac-1 and l-selectin on neutrophils, and the role of complement activation in this process.

SUMMARY BACKGROUND DATA

Sequestration of neutrophils in the pancreatic and pulmonary microvasculature characterizes acute pancreatitis.

METHODS

Serum was collected from inbred rats after induction of necrotizing pancreatitis; trypsinogen activation peptide was measured to quantify trypsin activation. Normal rat serum was also collected and subjected to limited trypsin digestion with and without the addition of complement inhibitor. Both groups of sera were incubated in vitro with healthy leukocytes. Expression of Mac-1 and L-selectin on neutrophils was measured quantitatively by flow cytometry. To assess the consequences of these events in vivo, trypsinated serum with or without complement inhibition or control serum was infused intravenous into rats. Soybean trypsin inhibitor was added to serum before injections to block residual trypsin activity. Pancreatic and pulmonary injury was quantitated by histology, measurement of edema, and myeloperoxidase activity.

RESULTS

Mac-1 expression on neutrophils incubated with pancreatitis serum was increased compared with controls, whereas L-selectin was decreased. Neutrophils incubated with trypsinated serum also showed upregulation of Mac-1 and downregulation of L-selectin, particularly with trypsin at 10(-4) mol/L. Addition of soluble complement receptor 1 abrogated both Mac-1 upregulation and L-selectin downregulation. Lungs of animals injected with trypsinated serum showed increased edema and myeloperoxidase activity, which were reduced by soluble complement receptor 1.

CONCLUSIONS

Trypsin-generated complement activation participates in the upregulation of Mac-1 and shedding of L-selectin on neutrophils in acute pancreatitis. Protease or complement inhibition may be effective in preventing leukocyte migration and subsequent local and remote organ injury.