Therapeutic effects of Caspase-1 inhibitors on acute lung injury in experimental severe acute pancreatitis

Effect of luteolin on the gene level expression of apoptosis-associated speck-like protein containing a caspase recruitment domain of NLRP3 inflammasome and NF-κB in rats subjected to experimental pancreatitis - influence of HSP70

OBJECTIVES

Nod-like receptor pyrin domain containing 3 (NLRP3) is one of the well characterized inflammasome that controls the maturation of pro-inflammatory cytokines and thereby the inflammation in pancreas which could be a promising target for anti-inflammatory drugs. The present study is aimed to explore whether luteolin can target the NLRP3 inflammasome and modulate its activity through the signaling protein, HSP70 in the ethanol-cerulein model of experimental pancreatitis.

METHODS

Male albino Wistar rats were divided into four groups. Groups 1 and 2 rats received normal diet. Groups 3 and 4 rats received isocalorically adjusted diet containing ethanol for 5 weeks and cerulein (20 μg/kg body weight i.p., thrice weekly for the last 3 weeks of the experimental period). Additionally, group 2 and 4 rats received 2 mg/kg body weight of luteolin orally from third week.

RESULTS

Luteolin co-administration decreased the serum levels of HSP70, oxidative stress markers, myeloperoxidase, GSH/GSSG and GST with concomitant downregulation in the mRNA expression of HSP70, caspase-1, ASC-NLRP3 and NF-κB. Spearman's rank correlation test showed that serum HSP70 has positive correlation with the expression of ASC-NLRP3, caspase-1, NF-κB and 4-hydroxynonenal and negative correlation with GSH:GSSG ratio.

CONCLUSIONS

The modulating effect of luteolin on the expression of HSP70, NF-κB and thereby on ASC-NLRP3 complex may be claimed for its pancreato-protective activity.

NLRP3 Inflammasome-Mediated Inflammation in Acute Pancreatitis

The discovery of inflammasomes has enriched our knowledge in the pathogenesis of multiple inflammatory diseases. The NLR pyrin domain-containing protein 3 (NLRP3) has emerged as the most versatile and well-characterized inflammasome, consisting of an intracellular multi-protein complex that acts as a central driver of inflammation. Its activation depends on a tightly regulated two-step process, which includes a wide variety of unrelated stimuli. It is therefore not surprising that the specific regulatory mechanisms of NLRP3 inflammasome activation remain unclear. Inflammasome-mediated inflammation has become increasingly important in acute pancreatitis, an inflammatory disorder of the pancreas that is one of the fatal diseases of the gastrointestinal tract. This review presents an update on the progress of research into the contribution of the NLRP3 inflammasome to acute pancreatic injury, examining the mechanisms of NLRP3 activation by multiple signaling events, the downstream interleukin 1 family of cytokines involved and the current state of the literature on NLRP3 inflammasome-specific inhibitors.

Role of Inflammasomes in the Development of Gastrointestinal Diseases

Many diseases of the gastrointestinal tract have been attributed to chronic inflammation, and a few have identified the role of inflammasomes in their pathogenesis. Inflammasomes are a group of protein complexes comprising of several intracellular proteins that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines. Recent studies have implicated activation of several families of NOD-like receptors (NLRs) which are major components of inflammasomes in the development and exacerbation of many diseases of human systems. In this chapter, we discuss the role of inflammasomes in some of the most prevalent diseases of the gastrointestinal tract and highlight potential targets for treatment.

Emodin alleviates intestinal mucosal injury in rats with severe acute pancreatitis via the caspase-1 inhibition

BACKGROUND

Emodin, a traditional Chinese medicine, has a therapeutic effect on severe acute pancreatitis (SAP), whereas the underlying mechanism is still unclear. Studies showed that the intestinal mucosa impairment, and subsequent release of endotoxin and proinflammatory cytokines such as IL-1β, which further leads to the dysfunction of multiple organs, is the potentially lethal mechanism of SAP. Caspase-1, an IL-1β-converting enzyme, plays an important role in this cytokine cascade process. Investigation of the effect of emodin on regulating the caspase-1 expression and the release proinflammatory cytokines will help to reveal mechanism of emodin in treating SAP.

METHODS

Eighty Sprague-Dawley rats were randomly divided into four groups (n=20 each group): SAP, sham-operated (SO), emodin-treated (EM) and caspase-1 inhibitor-treated (ICE-I) groups. SAP was induced by retrograde infusion of 3.5% sodium taurocholate into the pancreatic duct. Emodin and caspase-1 inhibitor were given 30 minutes before and 12 hours after SAP induction. Serum levels of IL-1β, IL-18 and endotoxin, histopathological alteration of pancreas tissues, intestinal mucosa, and the intestinal caspase-1 mRNA and protein expressions were assessed 24 hours after SAP induction.

RESULTS

Rats in the SAP group had higher serum levels of IL-1β and IL-18 (P<0.05), pancreatic and gut pathological scores (P<0.05), and caspase-1 mRNA and protein expressions (P<0.05) compared with the SO group. Compared with the SAP group, rats in the EM and ICE-I groups had lower IL-1β and IL-18 levels (P<0.05), lower pancreatic and gut pathological scores (P<0.05), and decreased expression of intestine caspase-1 mRNA (P<0.05). Ultrastructural analysis by transmission electron microscopy found that rats in the SAP group had vaguer epithelial junctions, more disappeared intercellular joints, and more damaged intracellular organelles compared with those in the SO group or the EM and ICE-I groups.

CONCLUSIONS

Emodin alleviated pancreatic and intestinal mucosa injury in experimental SAP. Its mechanism may partly be mediated by the inhibition of caspase-1 and its downstream inflammatory cytokines, including IL-1β and IL-18. Our animal data may be applicable in clinical practice.

Chronic Pancreatitis Associated Acute Respiratory Failure

Pancreatitis is a condition characterized by parenchymal inflammation of the pancreas, which is often associated with lung injury due to low level of oxygen and the condition is termed as acute pancreatitis-associated lung injury (APALI). Clinical reports indicated that ~ 20% to 50% of patients from low oxygen levels in blood with acute respiratory distress syndrome (ARDS). ARDS is a severe form of acute lung injury (ALI), a pulmonary disease with impaired airflow making patients difficult to breathe. ALI is frequently observed in patients with severe acute pancreatitis. Approximately one third of severe pancreatitis patients develop acute lung injury and acute respiratory distress syndrome that account for 60% of all deaths within the first week. The major causes of ALI and ARDS are sepsis, trauma, aspiration, multiple blood transfusion, and most importantly acute pancreatitis. The molecular mechanisms of ALI and ARDS are still not well explored, but available reports indicate the involvement of several pro-inflammatory mediators including cytokines (TNF-α, IL-1β, IL-6) and chemokines [like interleukin-8 (IL-8) and macrophage inhibitory factor (MIF)], as well as macrophage polarization regulating the migration and pulmonary infiltration of neutrophils into the pulmonary interstitial tissue, causing injury to the pulmonary parenchyma. Acute lung injury and acute respiratory distress syndrome in acute pancreatitis remains an unsolved issue and needs more research and resources to develop effective treatments and therapies. However, recent efforts have tested several molecules in an experimental model and showed promising results as a treatment option. The current review summarized the mechanism that is operational in pancreatitis-associated acute respiratory failure and respiratory distress syndrome in patients and current treatment options.

Asbestos-Induced Mesothelial to Fibroblastic Transition Is Modulated by the Inflammasome

Despite the causal relationship established between malignant mesothelioma (MM) and asbestos exposure, the exact mechanism by which asbestos induces this neoplasm and other asbestos-related diseases is still not well understood. MM is characterized by chronic inflammation, which is believed to play an intrinsic role in the origin of this disease. We recently found that asbestos activates the nod-like receptor family member containing a pyrin domain 3 (NLRP3) inflammasome in a protracted manner, leading to an up-regulation of IL-1β and IL-18 production in human mesothelial cells. Combined with biopersistence of asbestos fibers, we hypothesize that this creates an environment of chronic IL-1β signaling in human mesothelial cells, which may promote mesothelial to fibroblastic transition (MFT) in an NLRP3-dependent manner. Using a series of experiments, we found that asbestos induces a fibroblastic transition of mesothelial cells with a gain of mesenchymal markers (vimentin and N-cadherin), whereas epithelial markers, such as E-cadherin, are down-regulated. Use of siRNA against NLRP3, recombinant IL-1β, and IL-1 receptor antagonist confirmed the role of NLRP3 inflammasome-dependent IL-1β in the process. In vivo studies using wild-type and various inflammasome component knockout mice also revealed the process of asbestos-induced mesothelial to fibroblastic transition and its amelioration in caspase-1 knockout mice. Taken together, our data are the first to suggest that asbestos induces mesothelial to fibroblastic transition in an inflammasome-dependent manner.

Pathophysiological mechanisms in acute pancreatitis: Current understanding

The precise mechanisms involved in the pathophysiology of acute pancreatitis (AP) are still far from clear. Several earlier studies have focused mainly on pancreatic enzyme activation as the key intracellular perturbation in the pancreatic acinar cells. For decades, the trypsin-centered hypothesis has remained the focus of the intra-acinar events in acute pancreatitis. Recent advances in basic science research have lead to the better understanding of various other mechanisms such as oxidative and endoplasmic stress, impaired autophagy, mitochondrial dysfunction, etc. in causing acinar cell injury. Despite all efforts, the clinical outcome of patients with AP has not changed significantly over the years. This suggests that the knowledge of the critical molecular pathways in the pathophysiology of AP is still limited. The mechanisms through which the acinar cell injury leads to local and systemic inflammation are not well understood. The role of inflammatory markers and immune system activation is an area of much relevance from the point of view of finding a target for therapeutic intervention. Some data are available from experimental animal models but not much is known in human pancreatitis. This review intends to highlight the current understanding in this area.

Targeting caspase-6 and caspase-8 to promote neuronal survival following ischemic stroke

Previous studies show that caspase-6 and caspase-8 are involved in neuronal apoptosis and regenerative failure after trauma of the adult central nervous system (CNS). In this study, we evaluated whether caspase-6 or -8 inhibitors can reduce cerebral or retinal injury after ischemia. Cerebral infarct volume, relative to appropriate controls, was significantly reduced in groups treated with caspase-6 or -8 inhibitors. Concomitantly, these treatments also reduced neurological deficits, reduced edema, increased cell proliferation, and increased neurofilament levels in the injured cerebrum. Caspase-6 and -8 inhibitors, or siRNAs, also increased retinal ganglion cell survival at 14 days after ischemic injury. Caspase-6 or -8 inhibition also decreased caspase-3, -6, and caspase-8 cleavage when assayed by western blot and reduced caspase-3 and -6 activities in colorimetric assays. We have shown that caspase-6 or caspase-8 inhibition decreases the neuropathological consequences of cerebral or retinal infarction, thereby emphasizing their importance in ischemic neuronal degeneration. As such, caspase-6 and -8 are potential targets for future therapies aimed at attenuating the devastating functional losses that result from retinal or cerebral stroke.

Caspase-1 is hepatoprotective during trauma and hemorrhagic shock by reducing liver injury and inflammation

Adaptive immune responses are induced in liver after major stresses such as hemorrhagic shock (HS) and trauma. There is emerging evidence that the inflammasome, the multiprotein platform that induces caspase-1 activation and promotes interleukin (IL)-1β and IL-18 processing, is activated in response to cellular oxidative stress, such as after hypoxia, ischemia and HS. Additionally, damage-associated molecular patterns, such as those released after injury, have been shown to activate the inflammasome and caspase-1 through the NOD-like receptor (NLR) NLRP3. However, the role of the inflammasome in organ injury after HS and trauma is unknown. We therefore investigated inflammatory responses and end-organ injury in wild-type (WT) and caspase-1(-/-)mice in our model of HS with bilateral femur fracture (HS/BFF). We found that caspase-1(-/-) mice had higher levels of systemic inflammatory cytokines than WT mice. This result corresponded to higher levels of liver damage, cell death and neutrophil influx in caspase-1(-/-) liver compared with WT, although there was no difference in lung damage between experimental groups. To determine if hepatoprotection also depended on NLRP3, we subjected NLRP3(-/-) mice to HS/BFF, but found inflammatory responses and liver damage in these mice was similar to WT. Hepatoprotection was also not due to caspase-1-dependent cytokines, IL-1β and IL-18. Altogether, these data suggest that caspase-1 is hepatoprotective, in part through regulation of cell death pathways in the liver after major trauma, and that caspase-1 activation after HS/BFF does not depend on NLRP3. These findings may have implications for the treatment of trauma patients and may lead to progress in prevention or treatment of multiple organ failure (MOF).

Delayed production of IL-18 in lungs and pancreas of rats with acute pancreatitis

BACKGROUND/AIMS

During acute pancreatitis, tumor necrosis factor (TNF)-α, interleukin (IL)-1 and IL-6 play a pivotal role in promoting injury in the pancreas and remote organs. IL- 18 is a more recently discovered proinflammatory cytokine whose expression is also increased in serum. However, the profile of IL-18 expression in the pancreas and lung is unknown, and the aim of our study was to investigate such expression in rats with pancreatitis.

METHODS

Acute pancreatitis was induced by taurocholic acid and endotoxin. Pulmonary and pancreatic injury was measured by biological and histological parameters. Lung injury was also evaluated in ex vivo lung preparations.

RESULTS

Pancreatic and pulmonary injury appeared within 2 h after pancreatitis induction and persisted until the end of the protocol (18 h). TNF-α, IL-1 and IL-6 expression increased early in the lungs and pancreas, with a partial recovery by the end of the study. In contrast, IL-18 increased mostly by the end of the protocol (18 h after pancreatitis induction).

CONCLUSION

IL-18 may serve as an additional marker to monitor the severity of inflammation during pancreatitis since its tissue production is delayed and appears after that of more commonly investigated cytokines. and IAP.

Huangqi Injection reduces NF-κB activity and down-regulates TNF-α mRNA expression in rats with acute pancreatitis

AIM: To investigate the effects of Huangqi Injection on nuclear factor-κB (NF-κB) activity and NF-κB and tumor necrosis factor-α (TNF-α) mRNA expression in rats with acute pancreatitis.

METHODS: Sixty male Sprague-Dawley rats were randomly divided into five groups: sham-operation group, model control group, and low- [0.10 mL/(100 g•d)], medium- [0.15 mL/(100 g•d)] and high-dose [0.20 mL/(100 g•d)] Huangqi Injection groups. Acute pancreatitis was induced by injection of 5% sodium taurocholate [0.10 mL/(100 g•d)] into the pancreatic duct of rats. Huangqi Injection was injected into the tail vein 30 min before sodium taurocholate injection in the three treatment groups. The rats were killed 6 h after sodium taurocholate injection. The histomorphologic structure of the pancreas was observed under an optical microscope, and the severity of pancreatitis was evaluated using a pathologic grading system. The NF-κB activity in pancreatic acinar cells was determined by immunohistochemistry. The expression of NF-κB and TNF-α mRNAs in the pancreas was measured by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS: Compared with the sham-operation group, the pathologic grading score, NF-κB activity and TNF-α mRNA expression level increased obviously in the model group (both P < 0.01). The pathologic grading score, NF-κB activity and TNF-α mRNA expression level were significantly lower in the treatment groups than in the model group (all P < 0.05 or 0.01). A positive correlation was noted between NF-κB activity and TNF-α mRNA expression level (r = 0.542, P < 0.05). No significant difference was noted in NF-κB mRNA expression level among each group (all P > 0.01).

CONCLUSION: NF-κB activity and TNF-α mRNA expression are closely related with the severity of acute pancreatitis. Active NF-κB may play an important role in the pathogenesis of acute pancreatitis by up-regulating TNF-α mRNA expression. Huangqi Injection can significantly decrease NF-κB activity and TNF-α mRNA expression and therefore alleviate pancreatic injury in rats with acute pancreatitis.

Caspase-1 inhibitor prevents neurogenic pulmonary edema after subarachnoid hemorrhage in mice

BACKGROUND AND PURPOSE

We examined the effects of a caspase-1 inhibitor, N-Ac-Tyr-Val-Ala-Asp-chloromethyl ketone (Ac-YVAD-CMK), on neurogenic pulmonary edema in the endovascular perforation model of subarachnoid hemorrhage (SAH) in mice.

METHODS

Ninety-seven mice were assigned to sham, SAH+vehicle, SAH+Ac-YVAD-CMK (6 or 10 mg/kg), and SAH+Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK, 6 mg/kg) groups. Drugs were intraperitoneally injected 1 hour post-SAH. Pulmonary edema measurements, Western blot for interleukin-1beta, interleukin-18, myeloperoxidase, matrix metalloproteinase (MMP)-2, MMP-9, cleaved caspase-3 and zona occludens-1, MMP zymography, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling staining, and immunostaining were performed on the lung at 24 hours post-SAH.

RESULTS

Ten- but not 6-mg/kg of Ac-YVAD-CMK significantly inhibited a post-SAH increase in the activation of interleukin-1beta and caspase-3 and the number of terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive pulmonary endothelial cells, preventing neurogenic pulmonary edema. Another antiapoptotic drug, Z-VAD-FMK, also reduced neurogenic pulmonary edema. SAH did not change interleukin-18, myeloperoxidase, MMP-2, MMP-9, zona occludens-1 levels, or MMP activity.

CONCLUSIONS

We report for the first time that Ac-YVAD-CMK prevents lung cell apoptosis and neurogenic pulmonary edema after SAH in mice.

Investigation of new dominant-negative inhibitors of anthrax protective antigen mutants for use in therapy and vaccination

The lethal toxin (LeTx) of Bacillus anthracis plays a key role in the pathogenesis of anthrax. The protective antigen (PA) is a primary part of the anthrax toxin and forms LeTx by combination with lethal factor (LF). Phenylalanine-427 (F427) is crucial for PA function. This study was designed to discover potential novel therapeutic agents and vaccines for anthrax. This was done by screening PA mutants that were mutated at the F427 residue for a dominant-negative inhibitory (DNI) phenotype which was nontoxic but inhibited the toxicity of the wild-type LeTx. For this, PA residue F427 was first mutated to each of the other 19 naturally occurring amino acids. The cytotoxicity and DNI phenotypes of the mutated PA proteins were tested in the presence of 1 microg/ml LF in RAW264.7 cells and were shown to be dependent on the individual amino acid replacements. A total of 16 nontoxic mutants with various levels of DNI activity were identified in vitro. Among them, F427D and F427N mutants had the highest DNI activities in RAW264.7 cells. Both mutants inhibited LeTx intoxication in mice in a dose-dependent way. Furthermore, they induced a Th2-predominant immune response and protected mice against a challenge with five 50% lethal doses of LeTx. The protection was correlated mainly with a low level of interleukin-1 beta (IL-1 beta) and with high levels of PA-specific immunoglobulin G1, IL-6, and tumor necrosis factor alpha. Thus, PA DNI mutants, such as F427D and F427N mutants, may serve in the development of novel therapeutic agents and vaccines to fight B. anthracis infections.

Sepsis: links between pathogen sensing and organ damage

The host's inflammatory response to sepsis can be divided into two phases, the initial detection and response to the pathogen initiated by the innate immune response, and the persistent inflammatory state characterized by multiple organ dysfunction syndrome (MODS). New therapies aimed at pathogen recognition receptors (PRRs) particularly the TLRs and the NOD-like receptors offer hope to suppress the initial inflammatory response in early sepsis and to bolster this response in late sepsis. The persistence of MODS after the initial inflammatory surge can also be a determining factor to host survival. MODS is due to the cellular damage and death induced by sepsis. The mechanism of this cell death depends in part upon mitochondrial dysfunction. Damaged mitochondria have increased membrane permeability prompting their autophagic removal if few mitochondria are involved but apoptotic cell death may occur if the mitochondrial losses are more extensive. In addition. severe loss of mitochondria results in low cell energy stores, necrotic cell death, and increased inflammation driven by the release of cell components such as HMGB1. Therapies, which aim at improving cellular energy reserves such as the promotion of mitochondrial biogenesis by insulin, may have a role in future sepsis therapies. Finally, both the inflammatory responses and the susceptibility to organ failure may be modulated by nutritional status and micronutrients, such as zinc, Therapies aimed at micronutrient repletion may further augment approaches targeting PRR function and mitochondrial viability.

Interleukin-18: a pro-inflammatory cytokine that plays an important role in acute pancreatitis

A large body of clinical and experimental evidence suggests that cytokines play a key role in the pathogenesis of local and systemic complications of acute pancreatitis. IL-18 is a pro-inflammatory cytokine that plays a key role in many human diseases, including acute pancreatitis. This review focuses on the present understanding in IL-18 and its potential role in acute pancreatitis. IL-18 levels reflect the severity of acute pancreatitis and display a significant negative correlation with the concentrations of antioxidative damage factors, serum selenium and glutathione peroxidases (GPx). The relationship between IL-18 and other pro-inflammatory cytokines shows that IL-18 is one of the key mediators of inflammation in the pathogenesis of acute pancreatitis. Elevation of serum IL-18 levels may mediate acute pancreatitis associated liver injury. The use of IL-18 antagonists as direct routes to block IL-18 activity and P2X7 receptor antagonists and interleukin-1beta-converting enzyme (ICE) inhibitors as indirect routes to block IL-18 activity suggest that specific therapeutic inhibition of IL-18 is a promising therapeutic approach for acute pancreatitis.