Plasma-derived exosomes contribute to pancreatitis-associated lung injury by triggering NLRP3-dependent pyroptosis in alveolar macrophages

A narrative review of acute pancreatitis and its diagnosis, pathogenetic mechanism, and management

Acute pancreatitis (AP) is an inflammatory disease that can progress to severe acute pancreatitis (SAP), which increases the risk of death. AP is characterized by inappropriate activation of trypsinogen, infiltration of inflammatory cells, and destruction of secretory cells. Other contributing factors may include calcium (Ca²⁺) overload, mitochondrial dysfunction, impaired autophagy, and endoplasmic reticulum (ER) stress. In addition, exosomes are also associated with pathophysiological processes of many human diseases and may play a biological role in AP. However, the pathogenic mechanism has not been fully elucidated and needs to be further explored to inform treatment. Recently, the treatment guidelines have changed; minimally invasive therapy is advocated more as the core multidisciplinary participation and "step-up" approach. The surgical procedures have gradually changed from open surgery to minimally invasive surgery that primarily includes percutaneous catheter drainage (PCD), endoscopy, small incision surgery, and video-assisted surgery. The current guidelines for the management of AP have been updated and revised in many aspects. The type of fluid to be used, the timing, volume, and speed of administration for fluid resuscitation has been controversial. In addition, the timing and role of nutritional support and prophylactic antibiotic therapy, as well as the timing of the surgical or endoscopic intervention, and the management of complications still have many uncertainties that could negatively impact the prognosis and patients' quality of life. Consequently, to inform clinicians about optimal treatment, we aimed to review recent advances in the understanding of the pathogenesis of AP and its diagnosis and management.

Epigallocatechin-3-gallate attenuates acute pancreatitis induced lung injury by targeting mitochondrial reactive oxygen species triggered NLRP3 inflammasome activation

Green tea has been considered as a health-promoting beverage and is widely consumed worldwide. Epigallocatechin-3-gallate (EGCG), the most abundant polyphenol derived from green tea leaves with potent antioxidative and chemopreventive activities, has been reported to offer protection against inflammation-driven tissue damage. Here, we evaluated the protective effects of EGCG against lung injury during acute pancreatitis (AP) and further revealed the detailed mechanism. The results showed that EGCG significantly attenuated l-arginine-induced AP and the consequent pulmonary damage in mice. Moreover, EGCG substantially attenuated oxidative stress and concurrently suppressed NOD-like receptor protein 3 (NLRP3) inflammasome activation in the lung. In vitro, EGCG considerably reduced the production of mitochondrial reactive oxygen species (mtROS) and oxidized mitochondrial DNA (ox-mtDNA) in alveolar macrophages (AMs) challenged with AP-conditioned plasma. Meanwhile, the amount of ox-mtDNA bound to NLRP3 decreased significantly by the treatment with EGCG, resulting in impaired NLRP3 inflammasome activation. In addition, the antagonism of NLRP3 signaling by EGCG was affected in the presence of the mtROS stimulant rotenone or scavenger Mito-TEMPO. Altogether, EGCG possesses potent activity to attenuate lung injury during AP progression by inhibiting NLRP3 inflammasome activation. As for the mechanism, the EGCG-conferred restriction of NLRP3 inflammasome activation probably arises from the elimination of mtROS as well as its oxidative product ox-mtDNA, which consequently enables the protection against AP-associated lung injury.

Polyethylene Glycol 35 (PEG35) Modulates Exosomal Uptake and Function

Polyethylene glycols (PEGs) are neutral polymers widely used in biomedical applications due to its hydrophilicity and biocompatibility. Exosomes are small vesicles secreted by nearly all cell types and play an important role in normal and pathological conditions. The purpose of this study was to evaluate the role of a 35-kDa molecular weight PEG (PEG35) on the modulation of exosome-mediated inflammation. Human macrophage-like cells THP-1, epithelial BICR-18, and CAPAN-2 cells were exposed to PEG35 prior to incubation with exosomes of different cellular origins. Exosome internalization was evaluated by confocal microscopy and flow cytometry. In another set of experiments, macrophages were treated with increasing concentrations of PEG35 prior to exposure with the appropriate stimuli: lipopolysaccharide, BICR-18-derived exosomes, or exosomes from acute pancreatitis-induced rats. Nuclear Factor Kappa B (NFκB) and Signal transducer and activator of transcription 3 (STAT3) activation and the expression levels of pro-inflammatory Interleukin 1β (IL1β) were determined. PEG35 administration significantly enhanced the internalization of exosomes in both macrophages and epithelial cells. Further, PEG35 ameliorated the inflammatory response induced by acute pancreatitis-derived exosomes by reducing the expression of IL1β and p65 nuclear translocation. Our results revealed that PEG35 promotes the cellular uptake of exosomes and modulates the pro-inflammatory effect of acute pancreatitis-derived vesicles through inhibition of NFκB, thus emphasizing the potential value of PEG35 as an anti-inflammatory agent for biomedical purposes.

Inflammasome activation in acute lung injury

Inflammasomes are multiprotein complexes tasked with sensing endogenous or exogenous inflammatory signals and integrating this signal into a downstream response. Inflammasome activation has been implicated in a variety of pulmonary diseases, including pulmonary hypertension, bacterial pneumonia, COPD, and asthma. Of increasing interest is the contribution of inflammasome activation in the context of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Inflammasome activation in both the lung parenchyma and resident immune cells generates intereukin-1β (IL-1β) and IL-18, both of which drive the cascade of lung inflammation forward. Blockade of these responses has been shown to be beneficial in animal models and is a focus of translational research in the field. In this review, we will discuss the assembly and regulation of inflammasomes during lung inflammation, highlighting therapeutically viable effector steps. We will examine the importance of IL-1β and IL-18, two key products of inflammasome activation, in ALI, as well as the contribution of the pulmonary endothelial cell to this process. Finally, we will explore translational research moving toward anti-inflammasome therapies for ALI/ARDS and speculate toward future directions for the field.

Intestinal barrier damage, systemic inflammatory response syndrome, and acute lung injury: A troublesome trio for acute pancreatitis

Severe acute pancreatitis (SAP), a serious inflammatory disease of the pancreas, can easily lead to systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndromes (MODS). Acute lung injury (ALI) is one of the most serious complications of SAP. However, the specific pathogenesis of SAP-associated ALI is not fully understood. Crosstalk and multi-mechanisms involving pancreatic necrosis, bacteremia, intestinal barrier failure, activation of inflammatory cascades and diffuse alveolar damage is the main reason for the unclear pathological mechanism of SAP-associated ALI. According to previous research on SAP-associated ALI in our laboratory and theories put forward by other scholars, we propose that the complex pattern of SAP-associated ALI is based on the "pancreas-intestine-inflammation/endotoxin-lung (P-I-I/E-L) pathway". In this review, we mainly concentrated on the specific details of the "P-I-I/E-L pathway" and the potential treatments or preventive measures for SAP-associated ALI.

The potential roles of exosomes in pancreatic cancer initiation and metastasis

Pancreatic cancer (PaCa) is an insidious and highly metastatic malignancy, with a 5-year survival rate of less than 5%. So far, the pathogenesis and progression mechanisms of PaCa have been poorly characterized. Exosomes correspond to a class of extracellular nanovesicles, produced by a broad range of human somatic and cancerous cells. These particular nanovesicles are mainly composed by proteins, genetic substances and lipids, which mediate signal transduction and material transport. A large number of studies have indicated that exosomes may play decisive roles in the occurrence and metastatic progression of PaCa. This article summarizes the specific functions of exosomes and their underlying molecular mechanisms in mediating the initiation and metastatic capability of PaCa.

Macrophages in pancreatitis: Mechanisms and therapeutic potential

Macrophages play a crucial role in the pathogenesis of pancreatitis that is a common gastrointestinal disease. Particularly, macrophages differentiate into different phenotypes and exert diverse functions in acute pancreatitis (AP) and chronic pancreatitis (CP), respectively. In AP, macrophages in the pancreas and other related organs are mainly activated and differentiated into a pro-inflammatory M1 phenotype, and furthermore secrete inflammatory cytokines and mediators, causing local inflammation of the pancreas, and even intractable systemic inflammatory response or multiple organ failure. In CP, macrophages often exhibit a M2 polarisation and interact with pancreatic stellate cells (PSCs) in an autocrine and paracrine cytokine-dependent manner to promote the progression of pancreatic fibrosis. As the severity of pancreatic fibrosis aggravates, the proportion of M2/M1 macrophage cytokines in the pancreas increases. The discovery of macrophages in the pathogenesis of pancreatitis has promoted the research of targeted drugs, which provides great potential for the effective treatment of pancreatitis. This paper provides an overview of the roles of various macrophages in the pathogenesis of pancreatitis and the current research status of pancreatitis immunotherapy targeting macrophages. The findings addressed in this review are of considerable significance for understanding the pivotal role of macrophages in pancreatitis.

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.

Emodin Protects Against Acute Pancreatitis-Associated Lung Injury by Inhibiting NLPR3 Inflammasome Activation via Nrf2/HO-1 Signaling

Aim

Lung injury is a common complication of acute pancreatitis (AP), which leads to the development of acute respiratory distress syndrome and causes high mortality. In the present study, we investigated the therapeutic effect of emodin on AP-induced lung injury and explored the molecular mechanisms involved.

Materials and Methods

Thirty male Sprague-Dawley rats were randomly divided into AP (n=24) and normal (n=6) groups. Rats in the AP group received a retrograde injection of 5% sodium taurocholate into the biliary-pancreatic duct and then randomly assigned to untreated, emodin, combined emodin and ML385, and dexamethasone (DEX) groups. Pancreatic and pulmonary injury was assessed using H&E staining. In in vitro study, rat alveolar epithelial cell line L2 cells were exposed to lipopolysaccharide and treated with emodin. Nrf2 siRNA pool was applied for the knockdown of Nrf2. The contents of the pro-inflammatory cytokines in the bronchoalveolar lavage fluid and lung were determined using enzyme-linked immunosorbent assay. The expressions of related mRNAs and proteins in the lung or L2 cells were detected using real-time polymerase chain reaction, Western blot, immunohistochemistry and immunofluorescence.

Key Findings

Emodin administration alleviated pancreatic and pulmonary injury of rats with AP. Emodin administration suppressed the production of proinflammatory cytokines, downregulated NLRP3, ASC and caspase-1 expressions and inhibited NF-κB nuclear accumulation in the lung. In addition, Emodin increased Nrf2 nuclear translocation and upregulated HO-1 expression. Moreover, the anti-inflammatory effect of emodin was blocked by Nrf2 inhibitor ML385.

Conclusion

Emodin effectively protects rats against AP-associated lung injury by inhibiting NLRP3 inflammasome activation via Nrf2/HO-1 signaling.