Activation of lung macrophage subpopulations in experimental acute pancreatitis

Alveolar and Bone Marrow-derived Macrophages Differ in Metabolism and Glutamine Utilization

Changes in metabolic activity are key regulators of macrophage activity. Proinflammatory macrophages upregulate glycolysis, which promotes an inflammatory phenotype, whereas prorepair macrophages rely on oxidative metabolism and glutaminolysis to support their activity. Work to understand how metabolism regulates macrophage phenotype has been done primarily in macrophage cell lines and bone marrow-derived macrophages (BMDM). Our study sought to understand changes in metabolic activity of murine tissue-resident alveolar macrophages (AM) in response to LPS stimulation and to contrast them to BMDM. These studies also determined the contribution of glutamine metabolism using the glutamine inhibitor, 6-diazo-5-oxo-L-norleucine (DON). We found that compared with BMDM, AM have higher rates of oxygen consumption and contain a higher concentration of intracellular metabolites involved in fatty acid oxidation. In response to LPS, BMDM, but not AM, increased rates of glycolysis. Inhibition of glutamine metabolism using DON altered the metabolic activity of AM but not BMDM. Within AM, glutamine inhibition led to increases in intracellular metabolites involved in glycolysis, the tricarboxylic acid (TCA) cycle, fatty acid oxidation, and amino acid metabolism. Glutamine inhibition also altered the metabolic response to LPS within AM but not BMDM. Our data reveal striking differences in the metabolic activity of AM and BMDM.

Gene Regulation of Neutrophils Mediated Liver and Lung Injury through NETosis in Acute Pancreatitis

Acute pancreatitis (AP) is one of the most common gastrointestinal emergencies, often resulting in self-digestion, edema, hemorrhage, and even necrosis of pancreatic tissue. When AP progresses to severe acute pancreatitis (SAP), it often causes multi-organ damage, leading to a high mortality rate. However, the molecular mechanisms underlying SAP-mediated organ damage remain unclear. This study aims to systematically mine SAP data from public databases and combine experimental validation to identify key molecules involved in multi-organ damage caused by SAP. Retrieve transcriptomic data of mice pancreatic tissue for AP, lung and liver tissue for SAP, and corresponding normal tissue from the Gene Expression Omnibus (GEO) database. Conduct gene differential analysis using Limma and DEseq2 methods. Perform enrichment analysis using the clusterProfiler package in R software. Score immune cells and immune status in various organs using single-sample gene set enrichment analysis (ssGSEA). Evaluate mRNA expression levels of core genes using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. Validate serum amylase, TNF-α, IL-1β, and IL-6 levels in peripheral blood using enzyme-linked immunosorbent assay (ELISA), and detect the formation of neutrophil extracellular traps (NETs) in mice pancreatic, liver, and lung tissues using immunofluorescence. Differential analysis reveals that 46 genes exhibit expression dysregulation in mice pancreatic tissue for AP, liver and lung tissue for SAP, as well as peripheral blood in humans. Functional enrichment analysis indicates that these genes are primarily associated with neutrophil-related biological processes. ROC curve analysis indicates that 12 neutrophil-related genes have diagnostic potential for SAP. Immune infiltration analysis reveals high neutrophil infiltration in various organs affected by SAP. Single-cell sequencing analysis shows that these genes are predominantly expressed in neutrophils and macrophages. FPR1, ITGAM, and C5AR1 are identified as key genes involved in the formation of NETs and activation of neutrophils. qPCR and IHC results demonstrate upregulation of FPR1, ITGAM, and C5AR1 expression in pancreatic, liver, and lung tissues of mice with SAP. Immunofluorescence staining shows increased levels of neutrophils and NETs in SAP mice. Inhibition of NETs formation can alleviate the severity of SAP as well as the levels of inflammation in the liver and lung tissues. This study identified key genes involved in the formation of NETs, namely FPR1, ITGAM, and C5AR1, which are upregulated during multi-organ damage in SAP. Inhibition of NETs release effectively reduces the systemic inflammatory response and liver-lung damage in SAP. This research provides new therapeutic targets for the multi-organ damage associated with SAP.

Mitochondrial (mt)DNA-cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling promotes pyroptosis of macrophages via interferon regulatory factor (IRF)7/IRF3 activation to aggravate lung injury during severe acute pancreatitis

BACKGROUND

Macrophage proinflammatory activation contributes to the pathology of severe acute pancreatitis (SAP) and, simultaneously, macrophage functional changes, and increased pyroptosis/necrosis can further exacerbate the cellular immune suppression during the process of SAP, where cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) plays an important role. However, the function and mechanism of cGAS-STING in SAP-induced lung injury (LI) remains unknown.

METHODS

Lipopolysaccharide (LPS) was combined with caerulein-induced SAP in wild type, cGAS -/- and sting -/- mice. Primary macrophages were extracted via bronchoalveolar lavage and peritoneal lavage. Ana-1 cells were pretreated with LPS and stimulated with nigericin sodium salt to induce pyroptosis in vitro.

RESULTS

SAP triggered NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation-mediated pyroptosis of alveolar and peritoneal macrophages in mouse model. Knockout of cGAS/STING could ameliorate NLRP3 activation and macrophage pyroptosis. In addition, mitochondrial (mt)DNA released from damaged mitochondria further induced macrophage STING activation in a cGAS- and dose-dependent manner. Upregulated STING signal can promote NLRP3 inflammasome-mediated macrophage pyroptosis and increase serum interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α levels and, thus, exacerbate SAP-associated LI (SAP-ALI). Downstream molecules of STING, IRF7, and IRF3 connect the mtDNA-cGAS-STING axis and the NLRP3-pyroptosis axis.

CONCLUSIONS

Negative regulation of any molecule in the mtDNA-cGAS-STING-IRF7/IRF3 pathway can affect the activation of NLRP3 inflammasomes, thereby reducing macrophage pyroptosis and improving SAP-ALI in mouse model.

Intranasal delivery of macrophage cell membrane cloaked biomimetic drug-nanoparticle system attenuates acute lung injury

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), a life-threatening disease, is typically induced by uncontrolled inflammatory responses and excessive production of reactive oxygen species (ROS). Astaxanthin (Ast) is known for its powerful natural antioxidant properties, showcasing excellent antioxidant, anti-inflammatory, and immunomodulatory effects. However, its poor water solubility and bioavailability significantly limit its efficacy. Taking inspiration from biomimetic biology, this study developed a nasal drug delivery system comprising macrophage membrane (Mϕ)-encapsulated Ast-loaded nanoparticles (Mϕ@Ast-NPs) for the treatment of ALI. Mϕ@Ast-NPs retain the original homing properties of Mϕ, enabling targeted delivery to inflamed lungs and enhancing the anti-inflammatory effects of Astaxanthin (Ast). In vitro and in vivo, Mϕ@Ast-NPs demonstrated excellent biocompatibility and safety, as evidenced by no hemolysis of red blood cells and no significant toxic effects on cells and major organs. To determine the inflammation-targeting of Mϕ@Ast-NPs, both healthy and ALI mice were intranasally administered with Mϕ@Ast-NPs, the results demonstrated that highly targeting to inflamed lungs and endothelia, while with minimal accumulation in healthy lungs and endothelia. Mϕ@Ast-NPs effectively inhibited ROS production, enhanced Nrf2 expression and nucleus translocation, and reduced the levels of pro-inflammatory factors such as IL-1β, IL-6, and tumor necrosis factor-α (TNF-α) in LPS-induced RAW264.7 cells and ALI mice. Our study provided a safe and effective nasal delivery platform for pulmonary diseases, and this biomimetic nano-formulation of Ast could be as functional foods in the future.

Fuzhengjiedu formula exerts protective effect against LPS-induced acute lung injury via gut-lung axis

BACKGROUND

Acute lung injury (ALI) is distinguished by rapid and severe respiratory distress and prolonged hypoxemia. A traditional Chinese medicine (TCM), known as the Fuzhengjiedu formula (FZJDF), has been shown to have anti-inflammatory benefits in both clinical and experimental studies. The precise underlying processes, nevertheless, are yet unclear.

PURPOSE

This study sought to enlighten the protective mechanism of FZJDF in ALI through the standpoint of the gut-lung crosstalk.

METHODS

The impact of FZJDF on lipopolysaccharide (LPS)-induced ALI murine model were investigated, and the lung injury score, serum interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) expression were measured to confirm its anti-inflammatory effects. Additionally, gut microbiota analysis and serum and fecal samples metabolomics were performed using metagenomic sequencing and high-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry, respectively.

RESULTS

FZJDF significantly induced histopathological changes caused by LPS-induced ALI as well as downregulated the serum concentration of IL-1β and TNF-α. Furthermore, FZJDF had an effect in gut microbiota disturbances, and linear discriminant effect size analysis identified signal transduction, cell motility, and amino acid metabolism as the potential mechanisms of action in the FZJDF-treated group. Several metabolites in the LPS and FZJDF groups were distinguished by untargeted metabolomic analysis. Correlations were observed between the relative abundance of microbiota and metabolic products. Comprehensive network analysis revealed connections among lung damage, gut microbes, and metabolites. The expression of glycine, serine, glutamate, cysteine, and methionine in the lung and colon tissues was dysregulated in LPS-induced ALI, and FZJDF reversed these trends.

CONCLUSION

This study revealed that FZJDF considerably protected against LPS-induced ALI in mice by regulating amino acid metabolism via the gut-microbiota-lung axis and offered thorough and in-depth knowledge of the multi-system linkages of systemic illnesses.

Inhibition of YAP1 activity ameliorates acute lung injury through promotion of M2 macrophage polarization

The balance of M1/M2 macrophage polarization plays an important role in regulating inflammation during acute lung injury (ALI). Yes-associated protein (YAP1) is a key protein in the Hippo-YAP1 signaling pathway and is involved in macrophage polarization. We aimed to determine the role of YAP1 in pulmonary inflammation following ALI and regulation of M1/M2 polarization. Pulmonary inflammation and injury with upregulation of YAP1 were observed in lipopolysaccharide (LPS)-induced ALI. The YAP1 inhibitor, verteporfin, attenuated pulmonary inflammation and improved lung function in ALI mice. Moreover, verteporfin promoted M2 polarization and inhibited M1 polarization in the lung tissues of ALI mice and LPS-treated bone marrow-derived macrophages (BMMs). Additionally, siRNA knockdown confirmed that silencing Yap1 decreased chemokine ligand 2 (CCL2) expression and promoted M2 polarization, whereas silencing large tumor suppressor 1 (Lats1) increased CCL2 expression and induced M1 polarization in LPS-treated BMMs. To investigate the role of inflammatory macrophages in ALI mice, we performed single-cell RNA sequencing of macrophages isolated from the lungs. Thus, verteporfin could activate the immune-inflammatory response, promote the potential of M2 macrophages, and alleviate LPS-induced ALI. Our results reveal a novel mechanism where YAP1-mediated M2 polarization alleviates ALI. Therefore, inhibition of YAP1 may be a target for the treatment of ALI.

Neutrophil Extracellular Traps Augmented Alveolar Macrophage Pyroptosis via AIM2 Inflammasome Activation in LPS-Induced ALI/ARDS

Background

Uncontrollable inflammation is a critical feature of gram-negative bacterial pneumonia-induced acute respiratory distress syndrome (ARDS). Both neutrophils and alveolar macrophages participate in inflammation, but how their interaction augments inflammation and triggers ARDS is unclear. The authors hypothesize that neutrophil extracellular traps (NETs), which are formed during neutrophil NETosis, partly cause alveolar macrophage pyroptosis and worsen the severity of ARDS.

Methods

The authors first analysed whether NETs and caspase-1 are involved in clinical cases of ARDS. Then, the authors employed a lipopolysaccharide (LPS)-induced ARDS model to investigate whether targeting NETs or alveolar macrophages is protective. The AIM2 sensor can bind to DNA to promote AIM2 inflammasome activation, so the authors studied whether degradation of NET DNA or silencing of the AIM2 gene could protect alveolar macrophages from pyroptosis in vitro.

Results

Analysis of aspirate supernatants from ARDS patients showed that NET and caspase-1 levels were correlated with the severity of ARDS and that the levels of NETs and caspase-1 were higher in nonsurvivors than in survivors. In vivo, the NET level and proportion of pyroptotic alveolar macrophages in bronchoalveolar lavage fluid (BALF) were obviously higher in LPS-challenged mice than in control mice 24 h after injury. Administration of DNase I (a NET DNA-degrading agent) and BB-Cl-amidine (a NET formation inhibitor) alleviated alveolar macrophage pyroptosis, and Ac-YVAD-cmk (a pyroptosis inhibitor) attenuated NET levels in BALF and neutrophil infiltration in alveoli. All treatments markedly attenuated the severity of ARDS. Notably, LPS causes NETs to induce alveolar macrophage pyroptosis, and degradation of NET DNA or silencing of the AIM2 gene protected against alveolar macrophage pyroptosis.

Conclusion

These findings shed light on the proinflammatory role of NETs in mediating the neutrophil-alveolar macrophage interaction, which influences the progression of ARDS.

MALAT1 shuttled by extracellular vesicles promotes M1 polarization of macrophages to induce acute pancreatitis via miR-181a-5p/HMGB1 axis

Acute pancreatitis (AP) is a serious condition carrying a mortality of 25-40%. Extracellular vesicles (EVs) have reported to exert potential functions in cell-to-cell communication in diseases such as pancreatitis. Thus, we aimed at investigating the mechanisms by which EV-encapsulated metastasis-associated lung adenocarcinoma transcript-1 (MALAT1) might mediate the M1 polarization of macrophages in AP. Expression patterns of MALAT1, microRNA-181a-5p (miR-181a-5p) and high-mobility group box 1 protein (HMGB1) in serum of AP patients were determined. EVs were isolated from serum and pancreatic cells. The binding affinity among miR-181a-5p, MALAT1 and HMGB1 was identified. AP cells were co-cultured with EVs from caerulein-treated MPC-83 cells to determine the levels of M1/2 polarization markers and TLR4, NF-κB and IKBa. Finally, AP mouse models were established to study the effects of EV-encapsulated MALAT1 on the M1 polarization of macrophages in AP in vivo. MALAT1 was transferred into MPC-83 cells via EVs, which promoted M1 polarization of macrophages in AP. MALAT1 competitively bound to miR-181a-5p, which targeted HMGB1. Moreover, MALAT1 activated the TLR4 signalling pathway by regulating HMGB1. EV-encapsulated MALAT1 competitively bound to miR-181a-5p to upregulate the levels of IL-6 and TNF-α by regulating HMGB1 via activation of the TLR4 signalling pathway, thereby inducing M1 polarization of macrophages in AP. In vivo experimental results also confirmed that MALAT1 shuttled by EVs promoted M1 polarization of macrophages in AP via the miR-181a-5p/HMGB1/TLR4 axis. Overall, EV-loaded MALAT1 facilitated M1 polarization of macrophages in AP via miR-181a-5p/HMGB1/TLR4, highlighting a potential target for treating AP.

Emodin attenuates severe acute pancreatitis-associated acute lung injury by suppressing pancreatic exosome-mediated alveolar macrophage activation

Severe acute pancreatitis-associated acute lung injury (SAP-ALI) is a serious disease associated with high mortality. Emodin has been applied to alleviate SAP-ALI; however, the mechanism remains unclear. We report that the therapeutic role of emodin in attenuating SAP-ALI is partly dependent on an exosomal mechanism. SAP rats had increased levels of plasma exosomes with altered protein contents compared to the sham rats. These infused plasma exosomes tended to accumulate in the lungs and promoted the hyper-activation of alveolar macrophages and inflammatory damage. Conversely, emodin treatment decreased the plasma/pancreatic exosome levels in the SAP rats. Emodin-primed exosomes showed less pro-inflammatory effects in alveolar macrophages and lung tissues than SAP exosomes. In detail, emodin-primed exosomes suppressed the NF-κB pathway to reduce the activation of alveolar macrophage and ameliorate lung inflammation by regulating PPARγ pathway, while these effects were amplified/abolished by PPARγ agonist/antagonist. Blockage of pancreatic acinar cell exosome biogenesis also exhibited suppression of alveolar macrophage activation and reduction of lung inflammation. This study suggests a vital role of exosomes in participating inflammation-associated organ-injury, and indicates emodin can attenuate SAP-ALI by reducing the pancreatic exosome-mediated alveolar macrophage activation.

Wedelolactone alleviates acute pancreatitis and associated lung injury via GPX4 mediated suppression of pyroptosis and ferroptosis

Acute pancreatitis (AP) is an inflammatory disorder associated with multiple organ failure. Pyroptosis and ferroptosis are two newly recognized cell death, and whether pyroptosis and ferroptosis are involved in AP remain largely elusive. The nature compound Wedelolactone (Wed) exhibits strong anti-inflammatory and antioxidant activities, the present study aims to investigate the effect of Wed on AP and unravel whether Wed could protect against AP and relevant lung injury against pyroptosis and ferroptosis. Our results showed that the pyroptosis inhibitor disulfiram or ferroptosis inhibitor ferrostatin-1 significantly alleviated AP and associated lung injury in the taurocholate or caerulein-induced murine AP model. Administration with Wed ameliorated AP and lung injury as evidenced by improved pathological injuries, reduced serum pancreatic digestive enzymes, and proinflammatory cytokines. The in vivo and in vitro data demonstrated that Wed broadly inhibited caspase1/caspase11 activation, reduced mature interleukin-1β (IL-1β) and N-terminal domain of gasdermin D (GSDMD-N) level. The oxidative stress and lipid peroxidation were also suppressed along with the up-regulation of the ferroptosis antagonism marker glutathione peroxidase-4 (GPX4) in Wed treatment group. Wed promoted the transcriptional activity and the selenium sensitivity of GPX4. Moreover, the protective effects of Wed in caerulein-stimulated pancreatic acinar cells were markedly abrogated by the down-regulation of GPX4. Collectively, our data suggest that pyroptosis and ferroptosis play crucial roles in AP. Wed mitigated AP and associated lung injury via GPX4 mediated suppression of pyroptosis and ferroptosis.

Extracellular vesicle activities regulating macrophage- and tissue-mediated injury and repair responses

Macrophages are typically identified as classically activated (M1) macrophages and alternatively activated (M2) macrophages, which respectively exhibit pro- and anti-inflammatory phenotypes, and the balance between these two subtypes plays a critical role in the regulation of tissue inflammation, injury, and repair processes. Recent studies indicate that tissue cells and macrophages interact via the release of small extracellular vesicles (EVs) in processes where EVs released by stressed tissue cells can promote the activation and polarization of adjacent macrophages which can in turn release EVs and factors that can promote cell stress and tissue inflammation and injury, and vice versa. This review discusses the roles of such EVs in regulating such interactions to influence tissue inflammation and injury in a number of acute and chronic inflammatory disease conditions, and the potential applications, advantage and concerns for using EV-based therapeutic approaches to treat such conditions, including their potential role of drug carriers for the treatment of infectious diseases.

DOCK2 contributes to endotoxemia-induced acute lung injury in mice by activating proinflammatory macrophages

Dedicator of cytokinesis 2 (DOCK2), an atypical Rac activator, has important anti-inflammatory properties in blepharitis, enteric bacterial infection and colitis. However, the roles of DOCK2 in macrophage activation and acute lung injury (ALI) are still poorly elucidated. In vitro studies demonstrated that DOCK2 was essential for the nucleotide-sensing Toll-like receptor (TLR) 4-mediated inflammatory response in macrophages. We also confirmed that exposure of macrophages to LPS induced Rac activation through a TLR4-independent, DOCK2-dependent mechanism. Phosphorylation of IκB kinase (IKK) β and nuclear translocation of transcription factor nuclear factor kappa B (NF-κB) were impaired in Ad-shDOCK2-expressing macrophages, resulting in a decreased inflammatory response. Similar results were obtained when EHop-016 (a Rac inhibitor) was used to treat uninfected macrophages. In summary, these data indicate that the DOCK2-Rac signaling pathway acts in parallel with TLR4 engagement to control IKKβ activation for inflammatory cytokine release. Next, we investigated whether pharmacological inhibition of DOCK2 protects against endotoxemia-induced lung injury in mice. Treatment with 4-[3'-(2″-chlorophenyl)-2'-propen-1'-ylidene]-1-phenyl-3,5-pyrazolidinedione (CPYPP), a small-molecule inhibitor of DOCK2, reduced the severity of lung injury, as indicated by decreases in the lung injury score and myeloperoxidase (MPO) activity. Moreover, CPYPP attenuated LPS-induced proinflammatory cytokine release in mice. Our studies suggest that inhibition of DOCK2 may suppress LPS-induced macrophage activation and that DOCK2 may be a novel target for treating endotoxemia-related ALI.

Calcium silicate bioactive ceramics induce osteogenesis through oncostatin M

Immune reactions are a key factor in determining the destiny of bone substitute materials after implantation. Macrophages, the most vital factor in the immune response affecting implants, are critical in bone formation, as well as bone biomaterial-mediated bone repair. Therefore, it is critical to design materials with osteoimmunomodulatory properties to reduce host-to-material inflammatory responses by inducing macrophage polarization. Our previous study showed that calcium silicate (CS) bioceramics could significantly promote osteogenesis. Herein, we further investigated the effects of CS on the behavior of macrophages and how macrophages regulated osteogenesis. Under CS extract stimulation, the macrophage phenotype was converted to the M2 extreme. Stimulation by a macrophage-conditioned medium that was pretreated by CS extracts resulted in a significant enhancement of osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), indicating the important role of macrophage polarization in biomaterial-induced osteogenesis. Mechanistically, oncostatin M (OSM) in the macrophage-conditioned medium promoted osteogenic differentiation of BMSCs through the ERK1/2 and JAK3 pathways. This in vivo study further demonstrated that CS bioceramics could stimulate osteogenesis better than β-TCP implants by accelerating new bone formation at defective sites in the femur. These findings improve our understanding of immune modulation of CS bioactive ceramics and facilitate strategies to improve the in vitro osteogenesis capability of bone substitute materials.

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Calcium silicate (CS) bioceramics significantly promoted osteogenesis by the regulating of macrophage polarization.

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ERK1/2 and JAK3 pathways mediated the osteogenic differentiation stimulated by CS.

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CS played a promising osteoimmunomodulatory agent for bone induction.

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.

Macrophage polarization and its role in the pathogenesis of acute lung injury/acute respiratory distress syndrome

PURPOSE

Macrophages are highly plastic cells. Under different stimuli, macrophages can be polarized into several different subsets. Two main macrophage subsets have been suggested: classically activated or inflammatory (M1) macrophages and alternatively activated or anti-inflammatory (M2) macrophages. Macrophage polarization is governed by a highly complex set of regulatory networks. Many recent studies have shown that macrophages are key orchestrators in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) and that regulation of macrophage polarization may improve the prognosis of ALI/ARDS. A further understanding of the mechanisms of macrophage polarization is expected to be helpful in the development of novel therapeutic targets to treat ALI/ARDS. Therefore, we performed a literature review to summarize the regulatory mechanisms of macrophage polarization and its role in the pathogenesis of ALI/ARDS.

METHODS

A computer-based online search was performed using the PubMed database and Web of Science database for published articles concerning macrophages, macrophage polarization, and ALI/ARDS.

RESULTS

In this review, we discuss the origin, polarization, and polarization regulation of macrophages as well as the role of macrophage polarization in various stages of ARDS. According to the current literature, regulating the polarized state of macrophages might be a potential therapeutic strategy against ALI/ARDS.

GTS-21 Reduces Inflammation in Acute Lung Injury by Regulating M1 Polarization and Function of Alveolar Macrophages

BACKGROUND

Acute lung injury (ALI) is a severe outcome of sepsis. Alveolar macrophages (AMs) play key roles in defense, resolution in ALI. The polarization of AMs is dependent on micro environmental stimuli and might influence the progression of ALI. Gainesville Tokushima scientists (GTS)-21, a selective α7 nicotinic acetylcholine receptor agonist of the cholinergic anti-inflammatory pathway (CAP), has recently been established to be promising in the treatment of ALI. However, the molecular mechanism underlying the GTS-21-mediated suppression of inflammatory responses has been explored only partially. In this study, we examined the relation between GTS-21 and AM polarization in ALI.

METHODS

The adoptive transfer of M1 (classically activated) and M2 (alternatively activated)-polarized AMs was performed to AM-depleted ALI mice, along with the administration of GTS-21 in a murine model of lipopolysaccharide (LPS)-induced ALI and in isolated AMs that had been stimulated by LPS in vitro.

RESULTS

The adoptive transfer of M1-polarized AMs aggravated the inflammatory response in the lung in contrast to the adoptive transfer of M2-polarized AMs. GTS-21 protected the lung from the effect of LPS, preventing injury and decreasing the number of AMs, AM-related pro-inflammatory cytokine levels, high mobility group box 1 expression levels in AMs. In addition, GTS-21 significantly diminished the number of M1-polarized AM and increased the number of M2-polarized AM, by flow cytometry, RT-PCR, enzyme-linked immunosorbent assay, and the Arg1 and iNOS activity assays.

CONCLUSION

The GTS-21 substantially ameliorates LPS-induced ALI. This protection is predominantly associated with the inhibition of pulmonary AM M1 polarization and alteration in AM function.

Efficacy of pulmonary transplantation of engineered macrophages secreting IL-4 on acute lung injury in C57BL/6J mice

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are major causes of respiratory failure, but currently, no effective pharmacotherapy exists for these disorders. Alveolar macrophages play a critical role in both the acute/initial phase and chronic/resolving phase of ALI, rendering them a potential therapeutic target. Interleukin-4 (IL-4), a Th2 cytokine, not only directly inhibits the secretion of pro-inflammatory factors from macrophages but also drives macrophages to the anti-inflammatory and tissue remodeling M2 type. However, the short half-life of IL-4 in vivo hampers its effect on disease treatment. In this study, macrophages secreting IL-4 (M-IL-4) were established and used to treat ALI through pulmonary macrophage transplantation (PMT). The results showed that highly sustained levels of IL-4 and M2 macrophage markers were detected in mice lungs following pulmonary M-IL-4 transplantation. Furthermore, PMT improved the therapeutic effect by reducing lung inflammation, alleviating tissue injury, reducing alveolar macrophages necrotic cell death, and decreasing mortality in mice with ALI. These results suggest an efficient macrophage-based protein drug delivery strategy, and for the first time, prove the feasibility and efficacy of PMT in ALI treatment.

Inhibition of endoplasmic reticulum stress by 4-phenylbutyric acid prevents vital organ injury in rat acute pancreatitis

This study was conducted to investigate the effect of 4-phenylbutyric acid (4-PBA) on vital organ injury following sodium taurocholate-induced acute pancreatitis (AP) in rats and the pertinent mechanism. The serum biochemical indicators and key inflammatory cytokines, histopathological damage and apoptosis of vital organs in rat AP, were evaluated in the presence or absence of 4-PBA. Moreover, mRNA and protein levels of endoplasmic reticulum stress (ERS) markers were assessed. 4-PBA significantly attenuated the structural and functional damage of vital organs, including serum pancreatic enzymes, hepatic enzymes, creatinine, and urea. The morphological changes and infiltration of neutrophils and macrophages were reduced as well. These effects were accompanied by decreased serum levels of proinflammatory TNF-α and IL-1β. Furthermore, 4-PBA diminished the expression of ERS markers (glucose-regulated protein 78, CCAAT/enhancer-binding protein homologous protein, protein kinase R-like ER kinase, activated transcription factor 6, and type-1 inositol requiring enzyme) in vital organs of AP rats. 4-PBA also reduced AP-induced apoptosis in lung, liver, and kidney tissues as shown by TUNEL assay. The present study demonstrated that 4-PBA protected pancreas, lung, liver, and kidney from injury in rat AP by regulating ERS and mitigating inflammatory response to restrain cell death and further suggested that 4-PBA may have potential therapeutic implications in the disease. NEW & NOTEWORTHY In this study, we suggest that endoplasmic reticulum stress (ERS) is an important player in the development of acute pancreatitis-induced multiorgan injury, providing additional evidence for the proinflammatory role of ERS. Because 4-phenylbutyric acid has been suggested to inhibit ERS in many pathological conditions, it is possible that this effect can be involved in alleviating inflammatory response and cell death to ameliorate vital organ damage following acute pancreatitis induced by sodium taurocholate in rats.

Innate immunity as the orchestrator of allergic airway inflammation and resolution in asthma

The respiratory system is constantly in direct contact with the environment and, has therefore, developed strong innate and adaptive immune responses to combat pathogens. Unlike adaptive immunity which is mounted later in the course of the immune response and is naive at the outset, innate immunity provides the first line of defense against microbial agents, while also promoting resolution of inflammation. In the airways, innate immune effector cells mainly consist of eosinophils, neutrophils, mast cells, basophils, macrophages/monocytes, dendritic cells and innate lymphoid cells, which attack pathogens directly or indirectly through the release of inflammatory cytokines and antimicrobial peptides, and coordinate T and B cell-mediated adaptive immunity. Airway epithelial cells are also critically involved in shaping both the innate and adaptive arms of the immune response. Chronic allergic airway inflammation and linked asthmatic disease is often considered a result of aberrant activation of type 2 T helper cells (Th2) towards innocuous environmental allergens; however, innate immune cells are increasingly recognized as key players responsible for the initiation and the perpetuation of allergic responses. Moreover, innate cells participate in immune response regulation through the release of anti-inflammatory mediators, and guide tissue repair and the maintenance of airway homeostasis. The scope of this review is to outline existing knowledge on innate immune responses involved in allergic airway inflammation, highlight current gaps in our understanding of the underlying molecular and cellular mechanisms and discuss the potential use of innate effector cells in new therapeutic avenues.

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.

IRF5 regulates lung macrophages M2 polarization during severe acute pancreatitis in vitro

AIM

To investigate the role of interferon regulatory factor 5 (IRF5) in reversing polarization of lung macrophages during severe acute pancreatitis (SAP) in vitro.

METHODS

A mouse SAP model was established by intraperitoneal (ip) injections of 20 μg/kg body weight caerulein. Pathological changes in the lung were observed by hematoxylin and eosin staining. Lung macrophages were isolated from bronchoalveolar lavage fluid. The quantity and purity of lung macrophages were detected by fluorescence-activated cell sorting and evaluated by real-time polymerase chain reaction (RT-PCR). They were treated with IL-4/IRF5 specific siRNA (IRF5 siRNA) to reverse their polarization and were evaluated by detecting markers expression of M1/M2 using RT-PCR.

RESULTS

SAP associated acute lung injury (ALI) was induced successfully by ip injections of caerulein, which was confirmed by histopathology. Lung macrophages expressed high levels of IRF5 as M1 phenotype during the early acute pancreatitis stages. Reduction of IRF5 expression by IRF5 siRNA reversed the action of macrophages from M1 to M2 phenotype in vitro. The expressions of M1 markers, including IRF5 (S + IRF5 siRNA vs S + PBS, 0.013 ± 0.01 vs 0.054 ± 0.047, P < 0.01), TNF-α (S + IRF5 siRNA vs S + PBS, 0.0003 ± 0.0002 vs 0.019 ± 0.018, P < 0.001), iNOS (S + IRF5 siRNA vs S + PBS, 0.0003 ± 0.0002 vs 0.026 ± 0.018, P < 0.001) and IL-12 (S + IRF5 siRNA vs S + PBS, 0.000005 ± 0.00004 vs 0.024 ± 0.016, P < 0.001), were decreased. In contrast, the expressions of M2 markers, including IL-10 (S + IRF5 siRNA vs S + PBS, 0.060 ± 0.055 vs 0.0230 ± 0.018, P < 0.01) and Arg-1 (S + IRF5 siRNA vs S + PBS, 0.910 ± 0.788 vs 0.0036 ± 0.0025, P < 0.001), were increased. IRF5 siRNA could reverse the lung macrophage polarization more effectively than IL-4.

CONCLUSION

Treatment with IRF5 siRNA can reverse the pancreatitis-induced activation of lung macrophages from M1 phenotype to M2 phenotype in SAP associated with ALI.

Lung Inflammation Associated With Clinical Acute Necrotizing Pancreatitis in Dogs

Although dogs with acute necrotizing pancreatitis (ANP) can develop respiratory complications, there are no data describing lung injury in clinical cases of ANP in dogs. Therefore, we conducted a study to characterize lung injury and determine if pulmonary intravascular macrophages (PIMs) are induced in dogs with ANP ( n = 21) compared with control dogs ( n = 6). Two pathologists independently graded histologic sections of pancreas from clinical cases to characterize the severity of ANP (total scores of 3–10) compared with controls showing histologically normal pancreas (total scores of 0). Based on histological grading, lungs from dogs with ANP showed inflammation (median score, 1.5; range, 0–3), but the scores did not differ statistically from the control lungs (median score, 0.5; range, 0–2). A grid intersects-counting method showed an increase in the numbers of MAC387-positive alveolar septal mononuclear phagocyte profiles in lungs of dogs with ANP (ratio median, 0.0243; range, 0.0093–0.0734, with 2 outliers at 0.1523 and 0.1978) compared with controls (ratio median, 0.0019; range, 0.0017–0.0031; P < .0001). Only dogs with ANP showed labeling for von Willebrand factor in alveolar septal capillary endothelial cells, septal inflammatory cells, and alveolar macrophages. Toll-like receptor 4 and interleukin 6 were variably expressed in alveolar macrophages and septal inflammatory cells in lungs from both ANP and control dogs. Inducible nitric oxide synthase was detected in alveolar macrophages of dogs with ANP only. These data show that dogs with ANP have lung inflammation, including the recruitment of PIMs and expression of inflammatory mediators.

The Polarization of M2b Monocytes in Cultures of Burn Patient Peripheral CD14+ Cells Treated with a Selected Human CCL1 Antisense Oligodeoxynucleotide

M2b macrophages (Mφ) play a major role in the increased susceptibility of subacutely burned patients, to sepsis stemming from enterococcal translocation. Certain opportunistic infections in severely burned mice have been controlled by murine CCL1 antisense oligodeoxynucleotide (ODN), a specific polarizer of mouse M2bMφ. In the present study, we have screened CCL1 antisense ODN, which is active against human M2bMφ. Among the 20 CCL1 antisense ODNs synthesized in our laboratory, HCA-11 was shown to be the most active polarizer for human CCL1⁺CD163⁺CD14⁺ cells. Burn patient CCL1⁺CD163⁺CD14⁺ cells (3 × 10⁵ cells/mL) switched to quiescent CCL1^-CD163^-CD14⁺ cells within 48 h in cultures supplemented with 100 μg/mL of HCA-11. After treatment with a 25 μg/chimera dose of HCA-11, the bacterial growth was not observed in various organs of patient chimeras (γNSG mice inoculated with burn patient WBCs) infected with a lethal dose of Methicillin-resistant Staphylococcus aureus. The host antibacterial defenses against certain opportunistic pathogens should be improved in severely burned patients treated with a human CCL1 antisense ODN, HCA-11.

Absinthin attenuates LPS-induced ALI through MIP-1α-mediated inflammatory cell infiltration

Acute lung injury (ALI) is characterized by severe lung inflammation, and anti-inflammatory treatment is proposed to be a pertinent therapeutic strategy for the disease. Absinthin is a triterpene, extracted from a Chinese herb, with anti-inflammatory properties. The aim of this study was to evaluate whether absinthin can attenuate ALI in a mouse model of lung injury. Mice were treated with various concentrations (20 mg/kg, 40 mg/kg, and 80mg/kg) of absinthin, and lipopolysaccharide (LPS) to induce ALI. We found that the administration of absinthin relieved LPS-induced acute lung injury, as suggested by reduced histological scores, wet-to-dry ratio, myeloperoxidase activity, and accumulation of inflammatory cells in lung bronchoalveolar lavage fluid. Moreover, we demonstrated that absinthin significantly enhanced the expression of matrix metalloproteinase-8 (MMP-8); this effect could inhibit the accumulation of inflammatory cells in lung tissues through a mechanism dependent on MMP-8-mediated inactivation of macrophage inflammatory protein-1α. Therefore, we propose that absinthin is a promising novel therapeutic candidate for the treatment of ALI.

Pancreatic Acinar Cells Employ miRNAs as Mediators of Intercellular Communication to Participate in the Regulation of Pancreatitis-Associated Macrophage Activation

Macrophage activation plays an important role in the inflammatory response in acute pancreatitis. In the present study, the activation of AR42J pancreatic acinar cells was induced by taurolithocholate treatment. The results showed that the culture medium from the activated AR42J cells significantly enhanced NFκB activation in the macrophages compared to that without taurolithocholate treatment. Additionally, the precipitates obtained from ultracentrifugation of the culture media that were rich in exosomes were markedly more potent in activating macrophages compared with the supernatant fraction lacking exosomes. The results indicated that the mediators carried by the exosomes played important roles in macrophage activation. Exosomal miRNAs were extracted and examined using microarrays. A total of 115 differentially expressed miRNAs were identified, and 30 showed upregulated expression, while 85 displayed downregulated expression. Target genes of the differentially expressed miRNAs were predicted using TargetScan, MiRanda, and PicTar software programs. The putative target genes were subjected to KEGG functional analysis. The functions of the target genes were primarily enriched in MAPK pathways. Specifically, the target genes regulated macrophage activation through the TRAF6-TAB2-TAK1-NIK/IKK-NFκB pathway. As the mediators of signal transduction, miRNAs and their predicted target mRNAs regulate every step in the MAPK pathway.

Minocycline inhibits peritoneal macrophages but activates alveolar macrophages in acute pancreatitis

Minocycline is a tetracycline antibiotic that, in addition to its antimicrobial function, has been reported to possess a relevant anti-inflammatory activity. Its effects have been extensively evaluated in inflammatory-related neurological diseases. Here, we evaluate its effect on the systemic inflammatory response in a model of experimental acute pancreatitis. Minocycline treatment significantly reduced the inflammation in pancreas and mesenterium, had no effect on the adipose tissue inflammation, and increased the inflammatory response in the lung. These differences seem to be related with different effects exerted on peritoneal and alveolar macrophages. In vitro, minocycline reduced the expression of IL-1β and inhibit the activation of nuclear factor kappa B (NF-κB) on peritoneal macrophages, while it had no effect on alveolar macrophages. Our data indicates that although minocycline may be useful as a tool to control some inflammatory processes, differences on its effects depending on the population of macrophages involved in the process can be expected. In the particular case of acute pancreatitis, it could promote or potentiate inflammation in the lung so that its use does not appear to be recommended.

Macrophage activation syndrome: A severe and frequent manifestation of acute pancreatitis in 362 childhood-onset compared to 1830 adult-onset systemic lupus erythematosus patients

OBJECTIVE

We previously reported a case series of acute pancreatitis (AP) and macrophage activation syndrome (MAS) in childhood (cSLE) patients; however, there are no data regarding the comparison of AP and MAS in large populations of cSLE and adult SLE (aSLE).

METHODS

A study included 362 cSLE and 1830 aSLE patients. MAS was diagnosed according to preliminary diagnostic guidelines and AP according to the presence of abdominal pain or vomiting associated to an increase of pancreatic enzymes and/or pancreatic radiological abnormalities. Demographic data, clinical features, SLEDAI-2K, SLICC/ACR-DI, and treatment were assessed.

RESULTS

Age in MAS patients was significantly lower compared with those without this complication [15 (8.8-55) vs. 33.5 (10.2-45.7) years, p = 0.007]. The frequencies of fever (94% vs. 37%, p = 0.001), leucopenia (82% vs. 19%, p = 0.0001), thrombocytopenia (65% vs. 19%, p = 0.013), hypertriglyceridemia (87% vs. 42%, p = 0.037), and hyperferritinemia (93% vs. 37%, p = 0.011) were also more frequently observed in AP patients with MAS compared in AP patients without MAS. Fever and hyperferritinemia concomitantly were more frequent in the former group (86% vs. 12%, p = 0.0015). Higher and significant frequency of AP in cSLE compared to aSLE patients [12/362 (3.3%) vs. 20/1830 (1.1%), p = 0.003], with similar AP duration [22 (6-60) vs. 15 (4-90) days, p = 0.534]. MAS (85% vs. 30%, p = 0.003) and death by MAS complication (31% vs. 0%, p = 0.017) were significantly higher in children compared with aSLE.

CONCLUSIONS

This study provides novel data demonstrating that MAS occur in the majority of cSLE with AP with a higher mortality compared to aSLE. In addition, we identified in AP patients, a cluster of MAS clinical and laboratorial parameters more associated with this complication.

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

BACKGROUND

Necrosis of adipose tissue is a common complication of acute pancreatitis. The areas of steatonecrosis become a source of inflammatory mediators, including chemically modified fatty acids which could influence the progression of the systemic inflammation. In an experimental model of acute pancreatitis we analyzed the effects of lipids generated by two representative areas of adipose tissue on the switch to the M1 phenotype in macrophages.

METHODS

Pancreatitis was induced in rats by intraductal administration of 5% taurocholate and after 6 h, lipids from retroperitoneal, mesenteric or epididymal adipose tissues were collected. Lipid uptake, phenotype polarization and the activation of PPARγ and NFκB were evaluated in macrophages treated with these lipids.

RESULTS

After induction of pancreatitis, lipids from visceral adipose tissue promote the switch to an increased pro-inflammatory phenotype in macrophages. This effect is not related with a higher activation of NFκB but with an interfering effect on the activation of M2 phenotype.

CONCLUSIONS

During acute pancreatitis, lipids generated by some areas of adipose tissue interfere on the M2 polarization of macrophages, thus resulting in a more intense pro-inflammatory M1 response.

The ischemic environment drives microglia and macrophage function

Cells of myeloid origin, such as microglia and macrophages, act at the crossroads of several inflammatory mechanisms during pathophysiology. Besides pro-inflammatory activity (M1 polarization), myeloid cells acquire protective functions (M2) and participate in the neuroprotective innate mechanisms after brain injury. Experimental research is making considerable efforts to understand the rules that regulate the balance between toxic and protective brain innate immunity. Environmental changes affect microglia/macrophage functions. Hypoxia can affect myeloid cell distribution, activity, and phenotype. With their intrinsic differences, microglia and macrophages respond differently to hypoxia, the former depending on ATP to activate and the latter switching to anaerobic metabolism and adapting to hypoxia. Myeloid cell functions include homeostasis control, damage-sensing activity, chemotaxis, and phagocytosis, all distinctive features of these cells. Specific markers and morphologies enable to recognize each functional state. To ensure homeostasis and activate when needed, microglia/macrophage physiology is finely tuned. Microglia are controlled by several neuron-derived components, including contact-dependent inhibitory signals and soluble molecules. Changes in this control can cause chronic activation or priming with specific functional consequences. Strategies, such as stem cell treatment, may enhance microglia protective polarization. This review presents data from the literature that has greatly advanced our understanding of myeloid cell action in brain injury. We discuss the selective responses of microglia and macrophages to hypoxia after stroke and review relevant markers with the aim of defining the different subpopulations of myeloid cells that are recruited to the injured site. We also cover the functional consequences of chronically active microglia and review pivotal works on microglia regulation that offer new therapeutic possibilities for acute brain injury.

Are gastric mucosal macrophages responsible for gastric injury in acute pancreatitis?

AIM: To investigate the protective effect of clodronate-containing liposomes against severe acute pancreatitis (SAP)-triggered acute gastric mucosal injury (AGMI) in rats.

METHODS: Clodronate- and phosphate-buffered saline (PBS)-containing liposomes were prepared by reverse-phase evaporation. The SAP rat model was established by injecting sodium taurocholate into the pancreatic subcapsular space. Sprague-Dawley rats were randomly divided into three groups: control (C), SAP plus PBS-containing liposome (P) and SAP plus clodronate-containing liposome (T). Serum tumor necrosis factor (TNF)-α levels were estimated by ELISA. Pathological changes in the gastric mucosa and pancreas were observed by hematoxylin and eosin (HE) staining. Apoptotic cells were detected by terminal deoxynucleotidyl transferase dUTP nick end labeling staining. The numbers of macrophages in the gastric mucosa were analyzed by CD68 immunohistochemical staining.

RESULTS: The liposomes had a mean diameter of 150 ± 30 nm. The TNF-α levels were significantly higher in the P group than that in the C group (2 h, 145.13 ± 11.50 vs 23.2 ± 2.03; 6 h, 245.06 ± 12.11 vs 30.28 ± 6.07, P < 0.05), and they were significantly lower in the T group than that in the P group (2 h, 93.24 ± 23.11 vs 145.13 ± 11.50; 6 h, 135.18 ± 13.10 vs 245.06 ± 12.11, P < 0.05). The pathological scores of the pancreas were lower in the T group than in the P group (2 h, 1.88 ± 0.83 vs 4.13 ± 0.83; 6 h, 2.87 ± 0.64 vs 6.25 ± 0.88, P < 0.01). The pathological scores of the gastric mucosa were also lower in the T group than in the P group (2 h, 1.12 ± 0.64 vs 2 ± 0.75; 6 h, 1.58 ± 0.53 vs 3 ± 1.31, P < 0.05). In addition, increased CD68 levels were observed in the gastric mucosa of the P group compared with the C group. Clodronate-containing liposomes decreased the CD68 levels in the mucosa of the T group. The apoptotic indexes of the gastric mucosa were higher in the T group than in the P group (2 h, 15.7 ± 0.92 vs 11.5 ± 1.64; 6 h, 21.12 ± 1.06 vs 12.6 ± 2.44, P < 0.01).

CONCLUSION: Gastric macrophages contribute to the pathogenesis of gastric injury in SAP. Clodronate-containing liposomes have protective effects against AGMI in rats with SAP.

Akt2 deficiency protects from acute lung injury via alternative macrophage activation and miR-146a induction in mice

Acute respiratory distress syndrome (ARDS) is a major cause of respiratory failure, with limited effective treatments available. Alveolar macrophages participate in the pathogenesis of ARDS. To investigate the role of macrophage activation in aseptic lung injury and identify molecular mediators with therapeutic potential, lung injury was induced in wild-type (WT) and Akt2(-/-) mice by hydrochloric acid aspiration. Acid-induced lung injury in WT mice was characterized by decreased lung compliance and increased protein and cytokine concentration in bronchoalveolar lavage fluid. Alveolar macrophages acquired a classical activation (M1) phenotype. Acid-induced lung injury was less severe in Akt2(-/-) mice compared with WT mice. Alveolar macrophages from acid-injured Akt2(-/-) mice demonstrated the alternative activation phenotype (M2). Although M2 polarization suppressed aseptic lung injury, it resulted in increased lung bacterial load when Akt2(-/-) mice were infected with Pseudomonas aeruginosa. miR-146a, an anti-inflammatory microRNA targeting TLR4 signaling, was induced during the late phase of lung injury in WT mice, whereas it was increased early in Akt2(-/-) mice. Indeed, miR-146a overexpression in WT macrophages suppressed LPS-induced inducible NO synthase (iNOS) and promoted M2 polarization, whereas miR-146a inhibition in Akt2(-/-) macrophages restored iNOS expression. Furthermore, miR-146a delivery or Akt2 silencing in WT mice exposed to acid resulted in suppression of iNOS in alveolar macrophages. In conclusion, Akt2 suppression and miR-146a induction promote the M2 macrophage phenotype, resulting in amelioration of acid-induced lung injury. In vivo modulation of macrophage phenotype through Akt2 or miR-146a could provide a potential therapeutic approach for aseptic ARDS; however, it may be deleterious in septic ARDS because of impaired bacterial clearance.

Protein kinase C and acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a major public health problem and a leading source of morbidity in intensive care units. Lung tissue in patients with ARDS is characterized by inflammation, with exuberant neutrophil infiltration, activation, and degranulation that is thought to initiate tissue injury through the release of proteases and oxygen radicals. Treatment of ARDS is supportive primarily because the underlying pathophysiology is poorly understood. This gap in knowledge must be addressed to identify urgently needed therapies. Recent research efforts in anti-inflammatory drug development have focused on identifying common control points in multiple signaling pathways. The protein kinase C (PKC) serine-threonine kinases are master regulators of proinflammatory signaling hubs, making them attractive therapeutic targets. Pharmacological inhibition of broad-spectrum PKC activity and, more importantly, of specific PKC isoforms (as well as deletion of PKCs in mice) exerts protective effects in various experimental models of lung injury. Furthermore, PKC isoforms have been implicated in inflammatory processes that may be involved in the pathophysiologic changes that result in ARDS, including activation of innate immune and endothelial cells, neutrophil trafficking to the lung, regulation of alveolar epithelial barrier functions, and control of neutrophil proinflammatory and prosurvival signaling. This review focuses on the mechanistic involvement of PKC isoforms in the pathogenesis of ARDS and highlights the potential of developing new therapeutic paradigms based on the selective inhibition (or activation) of specific PKC isoforms.

The role of macrophages in obstructive airways disease: chronic obstructive pulmonary disease and asthma

Macrophages are a major cellular component of the innate immune system, and play an important role in the recognition of microbes, particulates, and immunogens and to the regulation of inflammatory responses. In the lung, macrophages react with soluble proteins that bind microbial products in order to remove pathogens and particles and to maintain the sterility of the airway tract. Chronic obstructive pulmonary disease and asthma are both obstructive airway diseases that involve chronic inflammation of the respiratory tract which contributes to disease progression. In the case of COPD, there is increasing evidence that lung macrophages orchestrate inflammation through the release of chemokines that attract neutrophils, monocytes and T cells and the release of several proteases. On the other hand, in asthma, it seems that alveolar macrophages are inappropriately activated and are implicated in the development and progression of the disease. In this review we summarize the current basic and clinical research studies which highlight the role of macrophages in asthma and COPD.

Controversial role of toll-like receptors in acute pancreatitis

Acute pancreatitis (AP) is a common clinical condition with an incidence of about 300 or more patients per million annually. About 10%-15% of patients will develop severe acute pancreatitis (SAP) and of those, 10%-30% may die due to SAP-associated complications. Despite the improvements done in the diagnosis and management of AP, the mortality rate has not significantly declined during the last decades. Toll-like receptors (TLRs) are pattern-recognition receptors that seem to play a major role in the development of numerous diseases, which make these molecules attractive as potential therapeutic targets. TLRs are involved in the development of the systemic inflammatory response syndrome, a potentially lethal complication in SAP. In the present review, we explore the current knowledge about the role of different TLRs that have been described associated with AP. The main candidate for targeting seems to be TLR4, which recognizes numerous damage-associated molecular patterns related to AP. TLR2 has also been linked with AP, but there are only limited studies that exclusively studied its role in AP. There is also data suggesting that TLR9 may play a role in AP.

Acute lung injury in acute pancreatitis--awaiting the big leap

Acute lung injury is a severe complication to acute pancreatitis and a significant health problem associated with a considerable mortality. Underlying mechanisms are complex and poorly understood, although recent insights have identified several inflammatory profiles and cellular components involved to varying degrees during different phases of pancreatitis exacerbation and acute lung injury. This review aims to highlight the current understanding of the inflammatory and cellular components involved in and responsible for the associations of acute pancreatitis and acute lung injury, with the hope of thereby providing an increased understanding of the underlying mechanisms. In addition, novel experimental models of modulating the pancreatitis-associated acute lung injury are presented, interventions that may be of potential future clinical value.

Differences in the inflammatory response induced by acute pancreatitis in different white adipose tissue sites in the rat

BACKGROUND

There is increasing evidence of the role of adipose tissue on the systemic effects of acute pancreatitis. Patients with higher body mass index have increased risk of local and systemic complications and patients with android fat distribution and higher waist circumference are at greater risk for developing the severe form of the disease. Here we evaluated the changes on different areas of adipose tissue and its involvement on the inflammatory response in an experimental model of acute pancreatitis.

METHODS

Pancreatitis was induced in male Wistar rats by intraductal administration of sodium taurocholate. Orlistat was administered to inhibit lipase activity. Activation of peritoneal macrophages was evaluated by measuring IL1β and TNFα expression. Inflammation was evaluated by measuring myeloperoxidase activity in mesenteric, epididymal and retroperitoneal areas of adipose tissue. Changes in the expression of inflammatory mediator in these areas of adipose tissue were also evaluated by RT-PCR.

RESULTS

Pancreatitis induces the activation of peritoneal macrophages and a strong inflammatory response in mesenteric and epididymal sites of adipose tissue. By contrast, no changes were found in retroperitoneal adipose tissue. Inhibition of lipase prevented the activation of macrophages and the local inflammation in adipose tissue.

CONCLUSIONS

Our results confirm the involvement of adipose tissue on the progression of systemic inflammatory response during acute pancreatitis. However, there is a considerable diversity in different adipose tissue sites. These differences need to be taken into account in order to understand the progression from local pancreatic damage to systemic inflammation during acute pancreatitis.

Macrophages in allergic asthma: fine-tuning their pro- and anti-inflammatory actions for disease resolution

Macrophages exert prominent effects in the defense of the respiratory tract from airborne pathogens. These cells are specialized to recognize, phagocytose, and destroy these infectious agents and then promote appropriate tissue repair after successful pathogen clearance. For reasons that are not presently clear, macrophages appear to be inappropriately activated during asthma responses. Evidence stems from the appearance of either classically (or M1) and alternatively activated (or M2) cells in the alveolar compartment of asthmatic lung. Macrophages localized in the interstitial area of the lung appear to be less prone to polarization toward either the M1 or M2 phenotype as these cells predominately express interleukin-10 and exhibit immunoregulatory properties. Effective treatment of clinical asthma, regardless of severity, might depend on restoring an appropriate balance between M1, M2, and immunoregulatory macrophages in the lung.

Repertoire of microglial and macrophage responses after spinal cord injury

Macrophages from the peripheral circulation and those derived from resident microglia are among the main effector cells of the inflammatory response that follows spinal cord trauma. There has been considerable debate in the field as to whether the inflammatory response is good or bad for tissue protection and repair. Recent studies on macrophage polarization in non-neural tissues have shed much light on their changing functional states. In the context of this literature, we discuss the activation of macrophages and microglia following spinal cord injury, and their effects on repair. Harnessing their anti-inflammatory properties could pave the way for new therapeutic strategies for spinal cord trauma.