Lipids generated during acute pancreatitis increase inflammatory status of macrophages by interfering with their M2 polarization

Proanthocyanidins suppress NLRP3 inflammasome and M1 macrophage polarization to alleviate severe acute pancreatitis in mice

The role of reactive oxygen species (ROS) is crucial for the pathogenesis of acute pancreatitis (AP). Proanthocyanidins (PAs) have been confirmed to exert antioxidant activity. Our study aimed to determine whether PAs alleviated SAP via reducing ROS, suppressing NLRP3 inflammasome, and inhibiting M1 macrophage polarization. Our study investigated the protective effects of PAs on pancreatic histopathological injury using SAP mice. The effects of PAs on macrophages were investigated in inflammatory RAW 264.7 cells or mouse bone marrow-derived macrophages (BMDMs) induced by lipopolysaccharide (LPS). Immunofluorescence staining and/or western blot assay were employed to evaluate NLRP3 inflammasome in macrophages and pancreatic tissue. Cell counting kit-8 (CCK-8) was used to access effects of PAs on cell viability and cytometry flow was used to determine the effects of the PAs on the ROS levels of the RAW 264.7 cells. Then, we evaluated M1 macrophage polarization using flow cytometry or real-time quantitative polymerase chain reaction (RT-qPCR). PAs administration alleviated pancreatic inflammation in SAP mice. The PAs depressed NLRP3 inflammasome and inhibited M1 macrophage polarization in pancreatic tissue. We also found that the PAs showed no cellular toxicity but decreased ROS levels in RAW 264.7 cells, downregulated the NLRP3 inflammasome in the macrophages, and inhibited cell M1 macrophage polarization. Our study indicates the anti-inflammatory properties of the PAs on SAP mice by decreasing ROS levels, suppressing NLRP3 inflammasome, and M1 macrophage polarization.

Circulating monocytes in acute pancreatitis

Acute pancreatitis is a common gastrointestinal disease characterized by inflammation of the exocrine pancreas and manifesting itself through acute onset of abdominal pain. It is frequently associated with organ failure, pancreatic necrosis, and death. Mounting evidence describes monocytes - phagocytic, antigen presenting, and regulatory cells of the innate immune system - as key contributors and regulators of the inflammatory response and subsequent organ failure in acute pancreatitis. This review highlights the recent advances of dynamic change of numbers, phenotypes, and functions of circulating monocytes as well as their underling regulatory mechanisms with a special focus on the role of lipid modulation during acute pancreatitis.

Macrophage Polarization and Reprogramming in Acute Inflammation: A Redox Perspective

Macrophage polarization refers to the process by which macrophages can produce two distinct functional phenotypes: M1 or M2. The balance between both strongly affects the progression of inflammatory disorders. Here, we review how redox signals regulate macrophage polarization and reprogramming during acute inflammation. In M1, macrophages augment NADPH oxidase isoform 2 (NOX2), inducible nitric oxide synthase (iNOS), synaptotagmin-binding cytoplasmic RNA interacting protein (SYNCRIP), and tumor necrosis factor receptor-associated factor 6 increase oxygen and nitrogen reactive species, which triggers inflammatory response, phagocytosis, and cytotoxicity. In M2, macrophages down-regulate NOX2, iNOS, SYNCRIP, and/or up-regulate arginase and superoxide dismutase type 1, counteract oxidative and nitrosative stress, and favor anti-inflammatory and tissue repair responses. M1 and M2 macrophages exhibit different metabolic profiles, which are tightly regulated by redox mechanisms. Oxidative and nitrosative stress sustain the M1 phenotype by activating glycolysis and lipid biosynthesis, but by inhibiting tricarboxylic acid cycle and oxidative phosphorylation. This metabolic profile is reversed in M2 macrophages because of changes in the redox state. Therefore, new therapies based on redox mechanisms have emerged to treat acute inflammation with positive results, which highlights the relevance of redox signaling as a master regulator of macrophage reprogramming.

Free Fatty Acid Increases the Expression of NLRP3-Caspase1 in Adipose Tissue Macrophages in Obese Severe Acute Pancreatitis

BACKGROUND AND AIMS

Obesity is an important risk factor for severe acute pancreatitis. The necrosis of epididymal adipose tissue occurs in severe acute pancreatitis. Adipose tissue macrophages play an important role in metabolic related inflammation. Therefore, we explored the potential mechanisms between adipose tissue macrophages and obesity-related severe acute pancreatitis.

METHODS

Severe acute pancreatitis mice model was induced by caerulein with lipopolysaccharide. The severity of severe acute pancreatitis was evaluated according to the morphological, general, and biochemical change. We assessed the injury of epididymal white adipose tissue, pancreas, and adipose tissue macrophages in obese mice and lean mice with severe acute pancreatitis. Outcomes of caerulein-induced severe acute pancreatitis were studied in lean and obese mice with or without lipase inhibitor orlistat.

RESULTS

Fat necrosis and pancreatic injury increased in the SAP groups. High levels of serum free fatty acid and triglyceride were increased significantly in the SAP group. The NLRP3-caspase1 inflammasome signal pathway in adipose tissue macrophages markedly enhanced in the SAP groups compared with control group. Free fatty acid can trigger macrophages inflammation through NLRP3-caspase1. Lipase inhibited by orlistat remarkably decreased in adipose tissue necrosis, and the levels of serum lipase, amylase, and pancreatic tissue damage decreased in the orlistat group compared with the SAP group. The NLRP3-caspase1 inflammasome pathway in adipose tissue macrophages markedly decreased in the orlistat groups compared with SAP group. The levels of serum free fatty acid and triglyceride were decreased significantly in the orlistat group.

CONCLUSIONS

Inflammation increases in adipose tissue macrophages of obese mice with severe acute pancreatitis. Free fatty acid generated via adipocyte lipolysis worsens inflammation in adipose tissue macrophages and the outcome of severe acute pancreatitis in obese mice through the NLRP3-caspase1 inflammasome pathway.

Sodium Butyrate Attenuates Taurocholate-Induced Acute Pancreatitis by Maintaining Colonic Barrier and Regulating Gut Microorganisms in Mice

Background

Acute pancreatitis (AP) damages the intestinal barrier, which aggravates AP. Butyrate exhibits anti-inflammatory effects in AP, but it is unknown if such a protective effect is associated with the regulation of gut microorganisms. We aim to investigate the effects of sodium butyrate (SB) on pancreatic inflammation, colonic barrier, and gut microorganisms.

Methods

C57BL/6 mice were divided into groups of sham operation (Sham), AP, 200 mg/kg SB intervention (SB-200), and 500 mg/kg SB intervention group (SB-500). Samples were harvested 24 h after the model was established. The gut microbiota was analyzed using 16S rRNA gene sequencing.

Results

Pancreatic infiltration of neutrophils, macrophages, and M2-type macrophages was significantly reduced in the SB-500 intervention group. Supplementation of SB-500 improved colon mucosal histology and the expression of ZO-1 and occluding. The relative abundance of Alloprevotella and Muribaculaceae was increased and that of Akkermansia was decreased in the SB-500 group compared with the AP group. Ruminococcaceae was the most significantly increased species and Prevotellaceae was the most significantly decreased species in the SB-500 group compared with the AP group.

Conclusion

High dose of SB inhibits pancreatic inflammation probably by maintaining the intestinal barrier and regulating gut microbiota in mice with AP.

Tissue-Specific Hydrogels Ameliorate Hepatic Ischemia/Reperfusion Injury in Rats by Regulating Macrophage Polarization via TLR4/NF-κB Signaling

Injectable acellular matrix hydrogels are proven to be potential translational materials to facilitate the repairment in various tissues. However, their potential to repair hepatic ischemia/reperfusion injury (IRI) has not been explored. In this work, we made hepatic acellular matrix (HAM) hydrogels based on the decellularized process and evaluated the biocompatibility and hepatoprotective effects in a rat IRI model. HAM hydrogels supported viability, proliferation, and attachment of hepatocytes in vitro. Treatment with HAM hydrogels significantly attenuated hepatic damage caused by IRI, as evidenced by hepatic biochemistry, histology, and inflammatory responses. Importantly, HAM hydrogels inhibited macrophage M1 (CD68/CCR7) differentiation but promoted M2 (CD68/CD206) differentiation. Additionally, TLR4/NF-κB signaling was found to be involved in the hepatoprotective effect of HAM hydrogels. Collectively, our study reveals that HAM hydrogels ameliorate hepatic IRI by facilitating M2 polarization via TLR4/NF-κB signaling.

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.

Clostridium butyricum Strains Suppress Experimental Acute Pancreatitis by Maintaining Intestinal Homeostasis

SCOPE

Acute pancreatitis (AP) is a common abdominal inflammatory disease. Disturbed gut homeostasis secondary to pancreatic inflammation aggravates the condition retroactively. The current study investigates potential beneficial effects of Clostridium butyricum (C. butyricum) strains on AP and underlying mechanisms.

METHODS AND RESULTS

C. butyricum strains MIYAIRI 588 (CBM588) and CGMCC0313.1 (CB0313.1) were supplemented to mice for three weeks before experimental AP or SAP induction. Both CBM588 and CB0313.1 protected against AP, as evidenced by reduced serum amylase and lipase levels, pancreatic edema, and myeloperoxidase activity. Amelioration of both experimental AP and SAP by CB0313.1 indicated a non-model-specific effect. Moreover, C. butyricum inhibited pancreatic neutrophil and dendritic cell infiltration, nucleotide-binding domain leucine-rich repeat-containing family, pyrin domain-containing 3 inflammasome activation, and pro-inflammatory pathways. Additionally in the gut, C. butyricum strains attenuated AP-associated intestinal inflammation and barrier dysfunction, accompanied with reduced pathogenic bacteria Escherichia coli and Enterococcus penetration into pancreas. Gut microbiome analyses further revealed that beneficial effects of C. butyricum on pancreatic-gut homeostasis were correlated with improved dysbiosis. In particular, relative abundance of Desulfovibrionaceae decreased, and Verrucomicrobiaceae Clostridiaceae and Lactobacillaceae increased.

CONCLUSIONS

For the first time, a protective effect of C. butyricum in AP by modulating intestinal homeostasis is demonstrated.

Dynamic Detection of Monocyte Subsets in Peripheral Blood of Patients with Acute Hypertriglyceridemic Pancreatitis

Aim

Monocytes play an important role in acute pancreatitis (AP). Hypertriglyceridemic pancreatitis (HTGP) is always more severe than normal lipid-AP, whether the mechanism of aggravation involves monocyte subsets remains unknown though. The present study was aimed to analyze changes of peripheral blood M1 and M2 monocytes in HTGP patients.

Methods

A total of 90 subjects were enrolled, among which 16 diagnosed with HTGP, 34 with acute biliary pancreatitis (ABP), 20 with hypertriglyceridemia (HTG), and 20 healthy controls (HC). Peripheral blood CD14+CD86+ M1 and CD14+CD206+ M2 monocytes were examined by flow cytometry on days 1, 3, and 7 after admission.

Results

We found a marked increase in total and M1 monocyte count in AP patients (P < 0.05). In HTGP, the percentage of M1 monocytes in white blood cells was significantly higher on days 1, 3, and 7, while M2 monocyte percentage was decreased on day 3, compared with ABP (P < 0.05). In mild HTGP, M1 monocyte count and percentage gradually decreased, while M2 monocyte percentage gradually increased from day 1 to 7. In severe HTGP, M1 monocyte count and percentage rose to the highest point while M2 were the lowest on day 3. Additionally, the level of M1 monocytes showed a positive correlation with plasma triglyceride and Ranson score of HTGP patients.

Conclusions

Peripheral blood M1 and M2 monocytes showed different dynamic changes in mild and severe HTGP. A more dominant role of CD14+CD86+ M1 monocytes may be involved in the pathogenesis of HTGP.

A Novel Derivative of the Natural Product Danshensu Suppresses Inflammatory Responses to Alleviate Caerulein-Induced Acute Pancreatitis

Acute pancreatitis (AP), a common abdominal inflammatory disorder, is characterized by premature intracellular activation of digestive proteases within pancreatic acini and a consecutive systemic inflammatory response. Although the mechanism remains to be fully understood, inflammation is the main cause of pancreatic damage in AP. A novel compound [4-(2-acetoxy-3-((R)-3-(benzylthio)-1-methoxy-1-oxopropan-2-ylamino)-3-oxopropyl)-1,2-phenylene diacetate (DSC)], derived from danshensu, exhibits anti-inflammatory and anti-apoptotic properties in vitro. However, its potential beneficial effect in AP has not been demonstrated. This study aimed to investigate the effects and underlying mechanisms of DSC in experimental AP in mice. We found that DSC suppressed inflammatory responses in AP by inhibiting the activation of nuclear factor-κB (NF-κB), signal transducer and activator of transcription 3 (STAT3) and nucleotide-binding domain leucine-rich repeat containing family, pyrin domain-containing 3 (NLRP3) inflammasome. Furthermore, treatment with DSC modulated the infiltration of neutrophils and the phenotypes of macrophages in mice induced with AP. Interestingly, we found that the expression of nuclear factor-erythroid 2 related factor 2 (Nrf2) and its regulated antioxidant enzyme heme oxygenase-1 (HO-1), which modulate inflammatory activities, was significantly increased in DSC-treated groups. Together, our findings demonstrate that DSC alleviates pancreatic inflammation and damage in AP by inhibiting the activation of NF-κB, STAT3, and NLRP3 inflammasome and modulating immune cell responses.

Lactose Induces Phenotypic and Functional Changes of Neutrophils and Macrophages to Alleviate Acute Pancreatitis in Mice

Acute pancreatitis (AP) is one common clinical acute abdominal disease, for which specific pharmacological or nutritional therapies remain elusive. Lactose, a macronutrient and an inducer of host innate immune responses, possesses immune modulatory functions. The current study aimed to investigate potential modulatory effects of lactose and the interplay between the nutrient and pancreatic immunity during experimentally induced AP in mice. We found that either prophylactic or therapeutic treatment of lactose time-dependently reduced the severity of AP, as evidenced by reduced pancreatic edema, serum amylase levels, and pancreatic myeloperoxidase activities, as well as by histological examination of pancreatic damage. Overall, lactose promoted a regulatory cytokine milieu in the pancreas and reduced infiltration of inflammatory neutrophils and macrophages. On acinar cells, lactose was able to suppress caerulein-induced inflammatory signaling pathways and to suppress chemoattractant tumor necrosis factor (TNF)-α and monocyte chemotactic protein-1 production. Additionally, lactose acted on pancreas-infiltrated macrophages, increasing interleukin-10 and decreasing tumor necrosis factor alpha production. Notably, lactose treatment reversed AP-associated infiltration of activated neutrophils. Last, the effect of lactose on neutrophil infiltration was mimicked by a galectin-3 antagonist, suggesting a potential endogenous target of lactose. Together, the current study demonstrates an immune regulatory effect of lactose to alleviate AP and suggests its potential as a convenient, value-added therapeutic macronutrient to control AP, and lower the risk of its systemic complications.

Inulin-Type Fructans Modulates Pancreatic-Gut Innate Immune Responses and Gut Barrier Integrity during Experimental Acute Pancreatitis in a Chain Length-Dependent Manner

Acute pancreatitis (AP) is a common abdominal inflammatory disorder and one of the leading causes of hospital admission for gastrointestinal disorders. No specific pharmacological or nutritional therapy is available but highly needed. Inulin-type fructans (ITFs) are capable of modifying gut immune and barrier homeostasis in a chemistry-dependent manner and hence potentially applicable for managing AP, but their efficacy in AP has not been demonstrated yet. The current study aimed to examine and compare modulatory effects of ITFs with different degrees of fermentability on pancreatic-gut immunity and barrier function during experimentally induced AP in mice. BALB/c mice were fed short (I)- or long (IV)-chain ITFs supplemented diets for up to 3 days before AP induction by caerulein. Attenuating effects on AP development were stronger with ITF IV than with ITF I. We found that long-chain ITF IV attenuated the severity of AP, as evidenced by reduced serum amylase levels, lipase levels, pancreatic myeloperoxidase activity, pancreatic edema, and histological examination demonstrating reduced pancreatic damage. Short-chain ITF I demonstrated only partial protective effects. Both ITF IV and ITF I modulated AP-associated systemic cytokine levels. ITF IV but not ITF I restored AP-associated intestinal barrier dysfunction by upregulating colonic tight junction modulatory proteins, antimicrobial peptides, and improved general colonic histology. Additionally, differential modulatory effects of ITF IV and ITF I were observed on pancreatic and gut immunity: ITF IV supplementation prevented innate immune cell infiltration in the pancreas and colon and tissue cytokine production. Similar effects were only observed in the gut with ITF I and not in the pancreas. Lastly, ITF IV but not ITF I downregulated AP-triggered upregulation of IL-1 receptor-associated kinase 4 (IRAK-4) and phosphor-c-Jun N-terminal kinase (p-JNK), and a net decrease of phosphor-nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 (p-NF-κB p65) nuclear translocation and activation in the pancreas. Our findings demonstrate a clear chain length-dependent effect of inulin on AP. The attenuating effects are caused by modulating effects of long-chain inulin on the pancreatic-gut immunity via the pancreatic IRAK-4/p-JNK/p-NF-κBp65 signaling pathway and on prevention of disruption of the gut barrier.