Carbon monoxide-based therapy ameliorates acute pancreatitis via TLR4 inhibition

Carbon monoxide-loaded red blood cells ameliorate metabolic dysfunction-associated steatohepatitis progression via enhancing AMP-activated protein kinase activity and inhibiting Kupffer cell activation

Metabolic dysfunction-associated steatohepatitis (MASH) is a progressive form of nonalcoholic fatty liver disease characterised by fat accumulation, inflammation, oxidative stress, fibrosis, and impaired liver regeneration. In this study, we found that heme oxygenase-1 (HO-1) is induced in both MASH patients and in a MASH mouse model. Further, hepatic carbon monoxide (CO) levels in MASH model mice were >2-fold higher than in healthy mice, suggesting that liver HO-1 is activated as MASH progresses. Based on these findings, we used CO-loaded red blood cells (CO-RBCs) as a CO donor in the liver, and evaluated their therapeutic effect in methionine-choline deficient diet (MCDD)-induced and high-fat-diet (HFD)-induced MASH model mice. Intravenously administered CO-RBCs effectively delivered CO to the MASH liver, where they prevented fat accumulation by promoting fatty acid oxidation via AMP-activated protein kinase (AMPK) activation and peroxisome proliferator-activated receptor induction. They also markedly suppressed Kupffer cell activation and their corresponding anti-inflammatory and antioxidative stress activities in MASH mice. CO-RBCs also helped to restore liver regeneration in mice with HFD-induced MASH by activating AMPK. We confirmed the underlying mechanisms by performing in vitro experiments in RAW264.7 cells and palmitate-stimulated HepG2 cells. Taken together, CO-RBCs show potential as a promising cellular treatment for MASH.

From pancreas to lungs: The role of immune cells in severe acute pancreatitis and acute lung injury

BACKGROUND

Severe acute pancreatitis (SAP) is a potentially lethal inflammatory pancreatitis condition that is usually linked to multiple organ failure. When it comes to SAP, the lung is the main organ that is frequently involved. Many SAP patients experience respiratory failure following an acute lung injury (ALI). Clinicians provide insufficient care for compounded ALI since the underlying pathophysiology is unknown. The mortality rate of SAP patients is severely impacted by it.

OBJECTIVE

The study aims to provide insight into immune cells, specifically their roles and modifications during SAP and ALI, through a comprehensive literature review. The emphasis is on immune cells as a therapeutic approach for treating SAP and ALI.

FINDINGS

Immune cells play an important role in the complicated pathophysiology ofSAP and ALI by maintaining the right balance of pro- and anti-inflammatory responses. Immunomodulatory drugs now in the market have low thepeutic efficacy because they selectively target one immune cell while ignoring immune cell interactions. Accurate management of dysregulated immune responses is necessary. A critical initial step is precisely characterizing the activity of the immune cells during SAP and ALI.

CONCLUSION

Given the increasing incidence of SAP, immunotherapy is emerging as a potential treatment option for these patients. Interactions among immune cells improve our understanding of the intricacy of concurrent ALI in SAP patients. Acquiring expertise in these domains will stimulate the development of innovative immunomodulation therapies that will improve the outlook for patients with SAP and ALI.

The Pathogenesis of Pancreatitis and the Role of Autophagy

The pathogenesis of acute and chronic pancreatitis has recently evolved as new findings demonstrate a complex mechanism operating through various pathways. In this review, the current evidence indicating that several mechanisms act in concert to induce and perpetuate pancreatitis were presented. As autophagy is now considered a fundamental mechanism in the pathophysiology of both acute and chronic pancreatitis, the fundamentals of the autophagy pathway were discussed to allow for a better understanding of the pathophysiological mechanisms of pancreatitis. The various aspects of pathogenesis, including trypsinogen activation, ER stress and mitochondrial dysfunction, the implications of inflammation, and macrophage involvement in innate immunity, as well as the significance of pancreatic stellate cells in the development of fibrosis, were also analyzed. Recent findings on exosomes and the miRNA regulatory role were also presented. Finally, the role of autophagy in the protection and aggravation of pancreatitis and possible therapeutic implications were reviewed.

Toll-like receptor 4 in pancreatic damage and immune infiltration in acute pancreatitis

Acute pancreatitis is a complex inflammatory disease resulting in extreme pain and can result in significant morbidity and mortality. It can be caused by several factors ranging from genetics, alcohol use, gall stones, and ductal obstruction caused by calcification or neutrophil extracellular traps. Acute pancreatitis is also characterized by immune cell infiltration of neutrophils and M1 macrophages. Toll-like receptor 4 (TLR4) is a pattern recognition receptor that has been noted to respond to endogenous ligands such as high mobility group box 1 (HMGB1) protein and or exogenous ligands such as lipopolysaccharide both of which can be present during the progression of acute pancreatitis. This receptor can be found on a variety of cell types from endothelial cells to resident and infiltrating immune cells leading to production of pro-inflammatory cytokines as well as immune cell activation and maturation resulting in the furthering of pancreatic damage during acute pancreatitis. In this review we will address the various mechanisms mediated by TLR4 in the advancement of acute pancreatitis and how targeting this receptor could lead to improved outcomes for patients suffering from this condition.

Nicotinamide adenine dinucleotide phosphate oxidase in pancreatic diseases: Mechanisms and future perspectives

Pancreatitis and pancreatic cancer (PC) stand as the most worrisome ailments affecting the pancreas. Researchers have dedicated efforts to unraveling the mechanisms underlying these diseases, yet their true nature continues to elude their grasp. Within this realm, oxidative stress is often believed to play a causal and contributory role in the development of pancreatitis and PC. Excessive accumulation of reactive oxygen species (ROS) can cause oxidative stress, and the key enzyme responsible for inducing ROS production in cells is nicotinamide adenine dinucleotide phosphate hydrogen oxides (NOX). NOX contribute to pancreatic fibrosis and inflammation by generating ROS that injure acinar cells, activate pancreatic stellate cells, and mediate macrophage polarization. Excessive ROS production occurs during malignant transformation and pancreatic carcinogenesis, creating an oxidative microenvironment that can cause abnormal apoptosis, epithelial to mesenchymal transition and genomic instability. Therefore, understanding the role of NOX in pancreatic diseases contributes to a more in-depth exploration of the exact pathogenesis of these diseases. In this review, we aim to summarize the potential roles of NOX and its mechanism in pancreatic disorders, aiming to provide novel insights into understanding the mechanisms underlying these diseases.

Radix Glycyrrhizae extract and licochalcone a exert an anti-inflammatory action by direct suppression of toll like receptor 4

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Glycyrrhizae (GL), a herbal medicine that is widely available, has shown advantages for a variety of inflammatory diseases. Toll like receptor 4 (TLR4) pathway has been shown to play a key role in the progression of inflammation.

AIM OF THE STUDY

The purpose of this study was to investigate the involvement of TLR4 in the anti-inflammatory mechanism of GL extract and its active constituent on acute lung injury (ALI).

MATERIALS AND METHODS

A model of inflammation produced by lipopolysaccharide (LPS) was established in C57BL/6 mice and macrophages derived from THP-1. To screen the active components of GL, molecular docking was used. Molecular dynamics and surface plasmon resonance imaging (SPRi) were used to study the interaction of a specific drug with the TLR4-MD2 complex. TLR4 was overexpressed by adenovirus to confirm TLR4 involvement in the anti-inflammatory activities of GL and the chosen chemical.

RESULTS

We observed that GL extract significantly reduced both LPS-induced ALI and the production of pro-inflammatory factors including TNF-α, IL-6 and IL-1β. Additionally, GL inhibited the binding of Alexa 488-labeled LPS (LPS-488) to the membrane of THP-1 derived macrophages. GL drastically reduce on the expression of TLR4 and the activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-B (NF-κB). Furthermore, molecular docking revealed that Licochalcone A (LicoA) docked into the LPS binding site of TLR4-MD2 complex. MD2-LicoA binding conformation was found to be stable using molecular dynamic simulations. SPRi indicated that LicoA bound to TLR4-MD2 recombinant protein with a KD of 3.87 × 10^-7 M. LicoA dose-dependently reduced LPS-488 binding to the cell membrane. LicoA was found to significantly inhibit LPS-induced lung damage and inflammation. Furthermore, LicoA inhibited TLR4 expression, MAPK and NF-κB activation in a dose-dependent manner. The inhibitory effects of GL and LicoA on LPS-induced inflammation and TLR4 signaling activation were partly eliminated by TLR4 overexpression.

CONCLUSION

Our findings imply that GL and LicoA exert inhibitory effects on inflammation by targeting the TLR4 directly.

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.

Modulatory Role of Carbon Monoxide on the Inflammatory Response and Oxidative Stress Linked to Gastrointestinal Disorders

Significance: Carbon monoxide (CO) is an endogenous gaseous mediator that plays an important role in maintaining gastrointestinal (GI) tract homeostasis, acting in mucosal defense, and providing negative modulation of pathophysiological markers of clinical conditions. Recent Advances: Preclinical studies using animal models and/or cell culture show that CO can modulate the inflammatory response and oxidative stress in GI mucosal injuries and pathological conditions, reducing proinflammatory cytokines and reactive oxygen species, while increasing antioxidant defense mechanisms. Critical Issues: CO has potent anti-inflammatory and antioxidant effects. The defense mechanisms of the GI tract are subject to aggression by different chemical agents (e.g., drugs and ethanol) as well as complex and multifactorial diseases, with inflammation and oxidative stress as strong triggers for the deleterious effects. Thus, it is possible that CO acts on a variety of molecules involved in the inflammatory and oxidative signaling cascades, as well as reinforcing several defense mechanisms that maintain GI homeostasis. Future Directions: CO-based therapies are promising tools for the treatment of GI disorders, such as gastric and intestinal injuries, inflammatory bowel disease, and pancreatitis. Therefore, it is necessary to develop safe and selective CO-releasing agents and/or donor drugs to facilitate effective treatments and methods for analysis of CO levels that are simple and inexpensive. Antioxid. Redox Signal. 37, 98-114.

Tuftsin ameliorates splenic inflammatory injury by promoting neuropilin-1 in severe acute pancreatitis

Severe acute pancreatitis (SAP)-associated spleen injury causing immune disturbances aggravates organs injuries, which contributes to higher mortality rate. However, there are no effective drugs to cure SAP-induced spleen injury. Here, we found that Tuftsin (TN) is effective for ameliorating SAP-induced pathological damage and inflammation of spleen, mainly via alleviating mitochondrial dysfunction, oxidative stress, ATP depletion and the expression of pro-inflammatory factors. We further found that TN promoted anti-inflammatory macrophage phenotype M2 via up-regulating NRP1 on macrophage in spleen during SAP. Meanwhile, EG00229 (an inhibitor of NRP1 bound to TN) weakened TN's therapeutic effect in SAP-associated spleen injury. And EG00229 also inhibited M2 macrophage, leading to increasing inflammasome formation. Additionally, EG00229 reduced the protective efficiency of TN on mitochondrial dysfunction, and inflammation injury via NRP1 in spleen caused by SAP. Similarly, siRNA-Nrp1 into macrophage also prevented TN's inhibition on apoptosis. These findings reveal that TN alleviates SAP-induced spleen injury by promoting NRP1.

Ketogenesis acts as an endogenous protective programme to restrain inflammatory macrophage activation during acute pancreatitis

Background

Innate immunity and metabolites link to the pathogenesis and severity of acute pancreatitis (AP). However, liver metabolism and its role in immune response and AP progression remain elusive. We investigated the function of liver metabolism in the pathogenesis of AP.

Methods

Circulating ketone body β-hydroxybutyrate (βOHB) levels were determined in AP clinical cohorts and caerulein-induced AP (CER-AP) mouse models receiving seven (Cer*7) or twelve (Cer*12) injection regimens at hourly intervals. Liver transcriptomics and metabolomics were compared between CER-AP (Cer*7) and CER-AP (Cer*12). Inhibition of fatty acid β-oxidation (FAO)-ketogenesis, or supplementation of βOHB was performed in mouse models of AP. The effect and mechanism of βOHB were examined in vitro.

Findings

Elevated circulating βOHB was observed in patients with non-severe AP (SAP) but not SAP. These findings were replicated in CER-AP (Cer*7) and CER-AP (Cer*12), which manifested as limited and hyperactive immune responses, respectively. FAO-ketogenesis was activated in CER-AP (Cer*7), while impaired long-chain FAO and mitochondrial function were observed in the liver of CER-AP (Cer*12). Blockage of FAO-ketogenesis (Cpt1a antagonism or Hmgcs2 knockdown) worsened, while supplementation of βOHB or its precursor 1,3-butanediol alleviated the severity of CER-AP. Mechanistically, βOHB had a discernible effect on pancreatic acinar cell damage, instead, it greatly attenuated the activation of pancreatic and systemic proinflammatory macrophages via class I histone deacetylases.

Interpretation

Our findings reveal that hepatic ketogenesis is activated as an endogenous protective programme to restrain AP progression, indicating its potential therapeutic value.

Funding

This work was supported by the National Natural Science Foundation of China, Shanghai Youth Talent Support Programme, and Shanghai Municipal Education Commission-Gaofeng Clinical Medicine Grant.

Therapeutic potential of carbon monoxide in hypertension-induced vascular smooth muscle cell damage revisited: from physiology and pharmacology

As a chronic and progressive disorder, hypertension remains to be a serious public health problem around the world. Among the different types of hypertension, pulmonary arterial hypertension (PAH) is a devastating disease associated with pulmonary arteriole remodeling, right ventricular failure and death. The contemporary management of systemic hypertension and PAH has substantially grown since more therapeutic targets and/or agents have been developed. Evolving treatment strategies targeting the vascular remodeling lead to improving outcomes in patients with hypertension, nevertheless, significant advancement opportunities for developing better antihypertensive drugs remain. Carbon monoxide (CO), an active endogenous gasotransmitter along with hydrogen sulfide (H₂S) and nitric oxide (NO), is primarily generated by heme oxygenase (HO). Cumulative evidence suggests that CO is considered as an important signaling molecule under both physiological and pathological conditions. Studies have shown that CO confers a number of biological and pharmacological properties, especially its involvement in the pathological process and treatment of hypertension-related vascular remodeling. This review will critically outline the roles of CO in hypertension-associated vascular remodeling and discuss the underlying mechanisms for the protective effects of CO against hypertension and vascular remodeling. In addition, we will propose the challenges and perspectives of CO in hypertensive vascular remodeling. It is expected that a comprehensive understanding of CO in the vasculature might be essential to translate CO to be a novel pharmacological agent for hypertension-induced vascular remodeling.

Immune Regulation of Heme Oxygenase-1 in Allergic Airway Inflammation

Heme oxygenase-1 (HO-1) is not only a rate-limiting enzyme in heme metabolism but is also regarded as a protective protein with an immunoregulation role in asthmatic airway inflammation. HO-1 exerts an anti-inflammation role in different stages of airway inflammation via regulating various immune cells, such as dendritic cells, mast cells, basophils, T cells, and macrophages. In addition, the immunoregulation role of HO-1 may differ according to subcellular locations.

Carbon Monoxide in Pancreatic Islet Transplantation: A New Therapeutic Alternative to Patients With Severe Type 1 Diabetes Mellitus

Pancreatic islet transplantation is a minimally invasive procedure to replace β-cells in a subset of patients with autoimmune type 1 diabetic mellitus, who are extremely sensitive to insulin and lack counter-regulatory measures, and thereby increasing their risk of neuroglycopenia and hypoglycemia unawareness. Thus, pancreatic islet transplantation restores normoglycemia and insulin independence, and prevents long-term surgical complications associated with whole-organ pancreas transplantation. Nonetheless, relative inefficiency of islet isolation and storage process as well as progressive loss of islet function after transplantation due to unvoidable islet inflammation and apoptosis, hinder a successful islet transplantation. Carbon monoxide (CO), a gas which was once feared for its toxicity and death at high concentrations, has recently emerged as a medical gas that seems to overcome the challenges in islet transplantation. This minireview discusses recent findings about CO in preclinical pancreatic islet transplantation and the underlying molecular mechanisms that ensure islet protection during isolation, islet culture, transplantation and post-transplant periods in type 1 diabetic transplant recipients. In addition, the review also discusses clinical translation of these promising experimental findings that serve to lay the foundation for CO in islet transplantation to replace the role of insulin therapy, and thus acting as a cure for type 1 diabetes mellitus and preventing long-term diabetic complications.

Carbon monoxide as an emerging pharmacological tool to improve lung and liver transplantation protocols

Carbon monoxide (CO) has long been considered purely as a toxic gas. It binds to hemoglobin at high concentrations and displaces oxygen from its binding site, resulting in carboxyhemoglobin formation, which reduces oxygen-carrying capacity of blood and culminates in tissue hypoxia and its associated complications. Recently, however, CO is quickly moving past its historic notorious tag as a poisonous gas to a physiological signaling molecule with therapeutic potentials in several clinical situations including transplant-induced injury. This review discusses current knowledge of CO gas and CO-releasing molecules (CO-RMs) in preclinical models of lung and liver transplantation, and underlying molecular mechanisms of cyto- and organ protection during organ procurement, preservation, implantation and post-transplant periods. In addition, a discussion of the future of CO in clinical organ transplantation is provided.

Carbon Monoxide Therapy Using Hybrid Carbon Monoxide-Releasing/Nrf2-Inducing Molecules through a Neuroprotective Lens

Carbon monoxide (CO) has long been known for its toxicity. However, in recent decades, new applications for CO as a therapeutic compound have been proposed, and multiple forms of CO therapy have since been developed and studied. Previous research has found that CO has a role as a gasotransmitter and promotes anti-inflammatory and antioxidant effects, making it an avenue of interest for medicine. Such effects are possible because of the Nrf2/HO1 pathway, which has become a target for therapy development because its activation also leads to CO release. Currently, different forms of treatment involving CO include inhaled CO (iCO), carbon monoxide-releasing molecules (CORMs), and hybrid carbon monoxide-releasing molecules (HYCOs). In this article, we review the progression of CO studies to develop possible therapies, the possible mechanisms involved in the effects of CO, and the current forms of therapy using CO.

CORM-2 inhibits intracerebral hemorrhage-mediated inflammation

Background and purpose: Low-dose of carbon monoxide delivered by CO-releasing molecule-2 (CORM-2) had been confirmed having anti-inflammatory efficacy in some inflammatory diseases. Herein, we assessed the usefulness of CORM-2 in correcting intracerebral hemorrhage (ICH)-mediated inflammation.Methods: Healthy male Sprague Dawley (SD) rats randomly entered into four groups: sham-ICH, ICH, ICH+CORM-2, and ICH+ inactive carbon monoxide releasing molecule 2 (iCORM-2). ICH was induced by 50 μl of autologous arterial blood injected in situ in the rat brain. Neuro-functions of the ICH rats were evaluated with Garcia 18 scores at the 6th, 24th , 48th hou, and the fifthh day post-ICH. And brain tissues surrounding the hematoma area were collected from all ICH rats and assayed with Western blot and immunofluoresence analysis.Results: Neuro-dysfunctions in ICH rats were very severe than those in ICH +CORM-2 rats. Compared to sham group, the levels of HO-1, IKKβ, NF-κB, and TNF-α in ICH group began to elevate at the 6th hour, and reached to peak at the 48th hour post-ICH, all p < 0.05. While in ICH +CORM-2 group, the expressions of IKKβ, NF-κB, and TNF-α were very weaker than that in ICH group at every time points mentioned above; however, this phenomenon was not reproduced in ICH + iCORM-2 group. HO-1 in ICH+CORM-2 group highlighted in perihematomal area with many activated microglia (Iba-1-positive cells) and co-expressed with TNF-α, all of which were diminished at the fifth day post-ICH.Conclusion: CORM-2 may attenuate ICH-mediated inflammation by inhibiting microglial activation, which may involve the IKK/NF-κB pathway.AbbreviationsICH: intracerebral hemorrhage; CO: carbon monoxide; CORM-2: carbon monoxide releasing molecule-2; iCORM-2: inactive carbon monoxide releasing molecule-2; HO-1: heme oxygenase 1; IKKβ: inhibitor of IκB kinases β; NF-κB: nuclear factor-κB; TNF-α: tumor necrosis factor-α; Iba-1: ionized calcium binding adaptor molecule-1; IκB: inhibitor of NF-κB; iNOS: inducible nitric oxide synthase; Keap1: Kelch-like ECH-associated protein 1; Nrf2: NF-E2-related factor 2; DMSO: dimethylsulfoxide.

Contributions of HO-1-Dependent MAPK to Regulating Intestinal Barrier Disruption

The mitogen-activated protein kinase (MAPK) pathway controls intestinal epithelial barrier permeability by regulating tight junctions (TJs) and epithelial cells damage. Heme oxygenase-1 (HO-1) and carbon monoxide (CO) protect the intestinal epithelial barrier function, but the molecular mechanism is not yet clarified. MAPK activation and barrier permeability were studied using monolayers of Caco-2 cells treated with tissue necrosis factor α (TNF-α) transfected with FUGW-HO-1 or pLKO.1-sh-HO-1 plasmid. Intestinal mucosal barrier permeability and MAPK activation were also investigated using carbon tetrachloride (CCl₄) administration with CoPP (a HO-1 inducer), ZnPP (a HO-1 inhibitor), CO releasing molecule 2 (CORM-2), or inactived-CORM-2-treated wild-type mice and mice with HO-1 deficiency in intestinal epithelial cells. TNF-α increased epithelial TJ disruption and cleaved caspase-3 expression, induced ERK, p38, and JNK phosphorylation. In addition, HO-1 blocked TNF-α-induced increase in epithelial TJs disruption, cleaved caspase-3 expression, as well as ERK, p38, and JNK phosphorylation in an HO-1-dependent manner. CoPP and CORM-2 directly ameliorated intestinal mucosal injury, attenuated TJ disruption and cleaved caspase-3 expression, and inhibited epithelial ERK, p38, and JNK phosphorylation after chronic CCl₄ injection. Conversely, ZnPP completely reversed these effects. Furthermore, mice with intestinal epithelial HO-1 deficient exhibited a robust increase in mucosal TJs disruption, cleaved caspase-3 expression, and MAPKs activation as compared to the control group mice. These data demonstrated that HO-1-dependent MAPK signaling inhibition preserves the intestinal mucosal barrier integrity by abrogating TJ dysregulation and epithelial cell damage. The differential targeting of gut HO-1-MAPK axis leads to improved intestinal disease therapy.

Heme oxygenase-1 (HO-1) assists inorganic arsenic-induced immune tolerance in murine dendritic cells

Inorganic arsenic, a well-known human carcinogen, poses a major threat to global health. Given the immunosuppressive potentials of inorganic arsenic as well as limited understanding of this metalloid on antigen-presenting dendritic cells (DCs), we systematically screened the immune targets in response to arsenic treatment, as well as its possible molecular mechanism in cultured murine DCs. Our results denoted that arsenite (As) significantly induced immune tolerance by down-regulating the expression of phenotypic molecules, pro-inflammatory factors and T-lymphocyte helper (Th)1/Th17-inducible cytokines in lipopolysaccharides (LPS)-stimulated myeloid-derived dendritic cells (BMDCs). Inconsistent with dampened phosphorylation of immune-related proteins (nuclear factor kappa-B) NF-κB, p38 and JNK, the metalloid drastically induced the expression of Heme oxygenase-1 (HO-1) protein, which enlightened us to continuously explore the possible roles of HO-1 pathway in As-induced immune tolerance in BMDCs. In this respect, immunosuppressive properties of HO-1 pathway in BMDCs were firstly confirmed through pharmacological overexpression of HO-1 by both CoPP and CORM-2. By contrast, limited HO-1 expression by HO-1 inhibitor ZnPP specifically alleviated As-mediated down-regulation of CD80, chemokine factor C-C chemokine receptor 7 (CCR7), tumor necrosis factor (TNF) -α, Interleukin (IL)-23 and IL-6, which reminds us the peculiarity of HO-1 in As-induced immune tolerance in murine DCs. Based on these experimental findings, we postulated the immunosuppressive property of inorganic arsenic might be mediated partially by HO-1 in DCs, thus contributing to the interactions of DCs-polarized differentiation of T-lymphocyte subtype as well as the development of infections and malignant diseases.

Docosahexaenoic Acid Induces Expression of NAD(P)H: Quinone Oxidoreductase and Heme Oxygenase-1 through Activation of Nrf2 in Cerulein-Stimulated Pancreatic Acinar Cells

Oxidative stress is a major risk factor for acute pancreatitis. Reactive oxygen species (ROS) mediate expression of inflammatory cytokines such as interleukin-6 (IL-6) which reflects the severity of acute pancreatitis. The nuclear factor erythroid-2-related factor 2 (Nrf2) pathway is activated to induce the expression of antioxidant enzymes such as NAD(P)H: quinone oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1) as a cytoprotective response to oxidative stress. In addition, binding of Kelch-like ECH-associated protein 1 (Keap1) to Nrf2 promotes degradation of Nrf2. Docosahexaenoic acid (DHA)—an omega-3 fatty acid—exerts anti-inflammatory and antioxidant effects. Oxidized omega-3 fatty acids react with Keap1 to induce Nrf2-regulated gene expression. In this study, we investigated whether DHA reduces ROS levels and inhibits IL-6 expression via Nrf2 signaling in pancreatic acinar (AR42J) cells stimulated with cerulein, as an in vitro model of acute pancreatitis. The cells were pretreated with or without DHA for 1 h and treated with cerulein (10⁻⁸ M) for 1 (ROS levels, protein levels of NQO1, HO-1, pNrf2, Nrf2, and Keap1), 6 (IL-6 mRNA expression), and 24 h (IL-6 protein level in the medium). Our results showed that DHA upregulates the expression of NQO1 and HO-1 in cerulein-stimulated AR42J cells by promoting phosphorylation and nuclear translocation of Nrf2. DHA increased interaction between Keap1 and Nrf2 in AR42J cells, which may increase Nrf2 activity by inhibiting Keap1-mediated sequestration of Nrf2. In addition, DHA-induced expression of NQO1 and HO-1 is related to reduction of ROS and IL-6 levels in cerulein-stimulated AR42J cells. In conclusion, DHA inhibits ROS-mediated IL-6 expression by upregulating Nrf2-mediated expression of NQO1 and HO-1 in cerulein-stimulated pancreatic acinar cells. DHA may exert positive modulatory effects on acute pancreatitis by inhibiting oxidative stress and inflammatory cytokine production by activating Nrf2 signaling in pancreatic acinar cells.

Single immunoglobulin and Toll‑interleukin‑1 receptor domain containing molecule protects against severe acute pancreatitis in vitro by negatively regulating the Toll‑like receptor‑4 signaling pathway: A clinical and experimental study

Single immunoglobulin and Toll-interleukin-1 receptor domain-containing molecule (SIGIRR) is a specific inhibitor of IL-1R and Toll-like receptor (TLR) signaling and considered a potential target for the treatment of inflammatory diseases. Pathogenic mechanisms associated with the TLR4 signaling pathway have a critical role in the development of severe acute pancreatitis (SAP). The aim of the present study was to determine the role of SIGIRR in the regulation of TLR4 signaling during the progression of SAP. Pancreatitis-associated ascitic fluid (PAAF) was collected from patients with SAP. Murine RAW264.7 macrophages were transfected with a SIGIRR overexpression plasmid and co-cultured with the PAAF from the donors in order to evaluate the effect of SIGIRR in vitro. The mRNA expression of TLR4, SIGIRR and other key downstream signaling molecules was quantified using semi-quantitative PCR with agarose gel electrophoresis. Furthermore, the levels of pro-inflammatory cytokines in the culture supernatant were detected using ELISA. In contrast to SIGIRR, the mRNA expression levels of TLR4, myeloid differentiation factor 88 (MyD88), IL-1R-associated kinase-1 (IRAK-1) and TNF receptor-associated factor-6 (TRAF-6) were significantly increased in RAW264.7 cells following treatment with PAAF. Furthermore, TLR4, MyD88, IRAK-1 and TRAF-6 mRNA levels were significantly downregulated following SIGIRR overexpression and PAAF treatment in RAW264.7 cells. The levels of IL-2, IL-12, IL-17 and IFN-γ in the culture supernatant were also significantly decreased, while IL-10 levels were increased. Overall, SIGIRR negatively regulated the TLR4 signaling pathway to protect against the development of SAP in an in vitro model. Therefore, SIGIRR may represent a promising therapeutic target for SAP.

Macrophage phenotypic switch orchestrates the inflammation and repair/regeneration following acute pancreatitis injury

Background

Impaired or hyperactive pancreas regeneration after injury would cause exocrine insufficiency or recurrent / chronic pancreatitis and potentially carcinogenesis. Macrophages are the most abundant immune cells in the regenerative pancreas, however their phenotype and role remain poorly defined.

Method

Using caerulein-induced acute pancreatitis (AP) model, we examined the dynamic landscape of pancreatic macrophages throughout the acute inflammation to regeneration phases by flow cytometric and RNA-seq analyses. Liposome depletion of macrophages, Il4ra^−/− mice as well as inhibitors were used to elucidate the role and regulatory mechanism of macrophages during pancreatic regeneration.

Findings

We found that M1 macrophages dominated in the pro-inflammatory phase of AP, while M2-like macrophages dominated during pancreas repair/regeneration. Depletion of macrophages at early or late regenerative stage dramatically blocked the acinar-ductal metaplasia (ADM) or delayed inflammation resolution, respectively. Moreover, alternative activation of macrophages was partially dependent on IL-4RA signaling, and ECM/AKT activation in pancreatic macrophages facilitated inflammation resolution during tissue regeneration.

Interpretation

Our findings illustrate a dynamic phenotype and function of macrophages during AP repair/regeneration, helping us better understand the mechanism of pancreatic regeneration and providing clues for novel therapeutic strategy.

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.

Release of endogenous hydrogen sulfide in enteric nerve cells suppresses intestinal motility during severe acute pancreatitis

Previous studies have shown that during severe acute pancreatitis (SAP) attacks, hydrogen sulfide (H2S) is released in the colon. However, the roles played by H2S in regulating enteric nerves remain unclear. In this study, we examined the association between SAP-induced H2S release and loss of intestinal motility, and also explored the relevant mechanism in enteric nerve cells. A rat SAP model was constructed and enteric nerve cells were prepared. Intestinal mobility was evaluated by measuring the number of bowel movements at indicated time points and by performing intestinal propulsion tests. The production of inflammatory cytokines during a SAP attack was quantified by ELISA, and the levels of cystathionine-γ-lyase (CSE) and cystathionine-β-synthase (CBS) were examined by immunohistochemistry and western blot analysis. In vivo studies showed that PI3K/Akt/Sp1 signaling in enteric nerve cells was blocked, confirming the mechanism of endogenous H2S formation by western blot analysis and immunofluorescence. Our results also showed that rats with SAP symptoms had reduced intestinal motility. Furthermore, PI3K/Akt/Sp1 signaling was triggered and CSE expression was up-regulated, and these changes were associated with H2S formation in the colon. In addition, propargylglycine reduced the levels of inflammatory cytokines and suppressed the release of H2S. Enteric nerve cells that were incubated with LY294002 and transfected with a Sp1-knockdown vector displayed decreased levels of CSE production, which led to a decrease in H2S production. These results suggest that SAP symptoms suppressed the intestinal motility of rats via the release of H2S in enteric nerve cells, which was dependent on the inflammation-induced PI3K/Akt/Sp1 signaling pathway.

Systemic vasoprotection by inhaled carbon monoxide is mediated through prolonged alterations in monocyte/macrophage function

Carbon monoxide (CO) is anti-inflammatory and protective in models of disease. Its actions in vitro are short-lived but are sustained in vivo. We hypothesize that systemic CO can mediate prolonged phenotype changes in vivo, with a focus on macrophages (Mφs). Mφs isolated from CO treated rats responded to lipopolysaccharide (LPS) with increased IL6, IL10 and iNOS expression but decreased TNF. Conditioned media (CM) collected from peritoneal Mφs isolated from CO treated rats stimulated endothelial cell (EC) proliferation versus CM from Mφs from air treated rats. This effect was mediated by Mφ released VEGF and HMGB1. Inhaled CO reduced LPS induced Mφ M1 inflammatory phenotype for up to 5 days. Mitochondrial oxygen consumption in LPS treated Mφs from CO treated mice was preserved compared to LPS treated Mφs from control mice. Finally, transient reduction of inflammatory cells at the time of inhaled CO treatment eliminated the vasoprotective effect of CO in a rodent carotid injury model. Thus, inhaled CO induces a prolonged mixed phenotype change in Mφs, and potentially other inflammatory cells, that contribute to vasoprotection. These findings demonstrate the ability of inhaled CO to modify Mφs in a sustained manner to mediate its therapeutic actions, supporting the translational potential of inhaled CO.

STING signalling protects against chronic pancreatitis by modulating Th17 response

OBJECTIVE

Chronic pancreatitis (CP) is an inflammatory disease with progressive fibrosis leading to exocrine and endocrine dysfunction. Currently, there are no approved effective therapies for CP. Stimulator of interferon genes (STING) signalling is a key innate immune sensor of DNA. In this study, we evaluated the role of STING signalling in CP.

DESIGN

We used an experimental model of CP to test the effect of STING signalling in STING wild-type and knockout mice as well as bone marrow chimaeras (BMCs). STING was activated using a pharmacological agent. Since we found changes in Th17 cells, we used neutralising and control antibodies to determine the role of IL-17A. The effect of STING signalling was further explored in IL-17A generation and we examined the effect of IL-17A on pancreatic stellate cells (PSCs). Human pancreas from patients with CP and without CP were also stained for IL-17A.

RESULTS

STING activation decreased CP-associated pancreatic inflammation and fibrosis, whereas absence of STING led to worsening of the disease. BMCs showed that leucocytes play an important role in STING signalling-mediated amelioration of experimental CP. STING deletion was associated with increased Th17 cell infiltration in the pancreas, whereas STING agonist limited this Th17 response. Importantly, anti-IL-17A antibody treatment mitigated the severity of CP in the absence of STING signalling. STING deficiency promoted Th17 polarisation and PSCs express functional IL-17 receptor by upregulating fibrosis genes. Compared with tumour margins, pancreas from patients with CP had significant increase in IL-17A+ cells.

CONCLUSION

Unlike acute pancreatitis, STING activation is protective in CP. STING signalling is important in regulating adaptive immune responses by diminishing generation of IL-17A during CP and presents a novel therapeutic target for CP.

Study on the Mechanism of Curcumin Regulating Lung Injury Induced by Outdoor Fine Particulate Matter (PM2.5)

Background

Epidemiological studies have shown that exposure to PM induces oxidative stress, leading to a variety of health problems. In particular, PM2.5 contains a lot of substances harmful to the human body and penetrates into the lungs to induce lung injury. At the same time, there is increasing evidence that oxidative stress also affects the severity of lung injury. However, there is still no good way to reduce or eliminate these hazards. In the future, more experimental research is needed to further confirm the mechanisms of these hazards and formulate effective preventive measures and treatment plans for their hazard mechanisms. Curcumin has been reported to reduce oxidative stress and inflammatory damage and protect organs.

Objective

To investigate whether curcumin can play a protective role against PM2.5-induced oxidative stress and inflammatory damage by inducing expression of the HO-1/CO/P38 MAPK pathway.

Methods

In this experiment, PM2.5 was dropped into the trachea to establish a lung injury model in mice. 28 SPF-grade male Kunming mice were randomly divided into 4 groups: normal control group, saline control group, PM2.5 treatment group, and curcumin intervention group. Albumin (ALB), lactate dehydrogenase (LDH), and alkaline phosphatase (ALP) were measured in alveolar lavage fluid (BALF) to assess lung tissue damage. Colorimetric detection of oxidative stress indicators such as MDA, GSH-PX, T-AOC, and CAT in the lung tissue was performed. The levels of IL-6 and TNF-α in the lung tissue were determined by ELISA. Histopathological examination was used for the assessment of alveolar epithelial damage. The protein expression of the HO-1/P38 MAPK pathway in the lung tissue was determined by Western blot and immunohistochemistry. Endogenous CO was detected by spectrophotometry. The results showed that the expression of the HO-1/CO/P38 MAPK protein in the lung tissue was significantly increased in the curcumin intervention group compared with the PM2.5 treatment group, and it was statistically significant (P < 0.05). Compared with the PM2.5 treatment group, the curcumin intervention group can reduce the amount of ALB, LDH, and ALP in BALF; reduce the levels of MDA, IL-1, and TNF-α in the lung tissue; and improve GSH-PX, T-AOC, and CAT levels, but there is no statistical difference (P > 0.05).

Conclusion

We found that PM2.5 can cause lung damage through oxidative stress and inflammatory responses. Oxidative stress and inflammatory responses increase the expression of HO-1/CO/P38 MAPK. The intervention of curcumin can further increase the expression of HO-1/CO/P38 MAPK.

Carbon Monoxide Releasing Molecule-2-Upregulated ROS-Dependent Heme Oxygenase-1 Axis Suppresses Lipopolysaccharide-Induced Airway Inflammation

The up-regulation of heme oxygenase-1 (HO-1) is mediated through nicotinamaide adenine dinucleotide phosphate (NADPH) oxidases (Nox) and reactive oxygen species (ROS) generation, which could provide cytoprotection against inflammation. However, the molecular mechanisms of carbon monoxide-releasing molecule (CORM)-2-induced HO-1 expression in human tracheal smooth muscle cells (HTSMCs) remain unknown. Here, we found that pretreatment with CORM-2 attenuated the lipopolysaccharide (LPS)-induced intercellular adhesion molecule (ICAM-1) expression and leukocyte count through the up-regulation of HO-1 in mice, which was revealed by immunohistochemistrical staining, Western blot, real-time PCR, and cell count. The inhibitory effects of HO-1 by CORM-2 were reversed by transfection with HO-1 siRNA. Next, Western blot, real-time PCR, and promoter activity assay were performed to examine the HO-1 induction in HTSMCs. We found that CORM-2 induced HO-1 expression via the activation of protein kinase C (PKC)α and proline-rich tyrosine kinase (Pyk2), which was mediated through Nox-derived ROS generation using pharmacological inhibitors or small interfering ribonucleic acids (siRNAs). CORM-2-induced HO-1 expression was mediated through Nox-(1, 2, 4) or p47^phox, which was confirmed by transfection with their own siRNAs. The Nox-derived ROS signals promoted the activities of extracellular signal-regulated kinase 1/2 (ERK1/2). Subsequently, c-Fos and c-Jun-activator protein-1 (AP-1) subunits-were up-regulated by activated ERK1/2, which turned on transcription of the HO-1 gene by regulating the HO-1 promoter. These results suggested that in HTSMCs, CORM-2 activates PKCα/Pyk2-dependent Nox/ROS/ERK1/2/AP-1, leading to HO-1 up-regulation, which suppresses the lipopolysaccharide (LPS)-induced airway inflammation.

Carbon monoxide releasing molecule‑2 (CORM‑2)‑liberated CO ameliorates acute pancreatitis

The purpose of the present study was to investigate the effect of carbon monoxide (CO) released from CO‑releasing molecule 2 (CORM‑2) on mice with acute pancreatitis (AP). To perform the investigation, a mouse AP model was established using caerulein. The mice were treated with or without CORM‑2. The survival rate of the mice in the different groups was analyzed, and serum amylase and lipase levels were measured to assess the degree of pancreatic injury. The severity of AP was also evaluated by histological examination, and histopathological scoring of the pancreatic damage was performed. Pancreatic cell apoptosis was analyzed using a terminal deoxynucleotidyl‑transferase‑mediated dUTP nick end labelling assay. The function of the lung and liver was also assessed in the present study. Furthermore, the role of CORM‑2 on oxidative stress, intercellular adhesion molecule 1 (ICAM‑1) and vascular cell adhesion molecule 1 (VCAM‑1) expression, pro‑inflammatory cytokine production, and nuclear factor (NF)‑κB activation in the pancreas of AP mice was determined. The results demonstrated that CORM‑2 reduced the mortality, pancreatic damage, and lung and liver injury of AP mice. CORM‑2 administration also reduced systemic and localized inflammatory cell factors. Furthermore, treatment with CORM‑2 inhibited the expression of ICAM‑1 and VCAM‑1, and the activation of NF‑κB and phosphorylated inhibitor of NF‑κB subunit α, in the pancreas of AP mice. These results indicated that CO released from CORM‑2 exerted protective effects on AP mice, and the beneficial effects were likely due to inhibition of NF‑κB pathway activation.

Carbon monoxide releasing molecule‑2 (CORM‑2)‑liberated CO ameliorates acute pancreatitis

The purpose of the present study was to investigate the effect of carbon monoxide (CO) released from CO-releasing molecule 2 (CORM-2) on mice with acute pancreatitis (AP). To perform the investigation, a mouse AP model was established using caerulein. The mice were treated with or without CORM-2. The survival rate of the mice in the different groups was analyzed, and serum amylase and lipase levels were measured to assess the degree of pancreatic injury. The severity of AP was also evaluated by histological examination, and histopathological scoring of the pancreatic damage was performed. Pancreatic cell apoptosis was analyzed using a terminal deoxynucleotidyl-transferase-mediated dUTP nick end labelling assay. The function of the lung and liver was also assessed in the present study. Furthermore, the role of CORM-2 on oxidative stress, intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) expression, pro-inflammatory cytokine production, and nuclear factor (NF)-κB activation in the pancreas of AP mice was determined. The results demonstrated that CORM-2 reduced the mortality, pancreatic damage, and lung and liver injury of AP mice. CORM-2 administration also reduced systemic and localized inflammatory cell factors. Furthermore, treatment with CORM-2 inhibited the expression of ICAM-1 and VCAM-1, and the activation of NF-κB and phosphorylated inhibitor of NF-κB subunit α, in the pancreas of AP mice. These results indicated that CO released from CORM-2 exerted protective effects on AP mice, and the beneficial effects were likely due to inhibition of NF-κB pathway activation.

CO-Releasing Molecule-2 Induces Nrf2/ARE-Dependent Heme Oxygenase-1 Expression Suppressing TNF-α-Induced Pulmonary Inflammation

The upregulation of heme oxygenase-1 (HO-1) by the carbon monoxide-releasing molecule (CORM)-2 may be mediated through the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases [Nox] and reactive oxygen species (ROS) generation, which could provide cytoprotection against various cellular injuries. However, the detailed mechanisms of CORM-2-induced HO-1 expression in human pulmonary alveolar epithelial cells (HPAEpiCs) remain largely unknown. Therefore, we dissected the mechanisms underlying CORM-2-induced HO-1 expression in HPAEpiCs. We found that the administration of mice with CORM-2 attenuated the tumor necrosis factor-alpha (TNF-α)-induced intercellular adhesion molecule-1 (ICAM-1) expression and leukocyte count as revealed by immunohistochemical staining, western blot, real-time polymerase chain reaction (PCR), and cell count. Furthermore, TNF-α-induced ICAM-1 expression associated with monocyte adhesion to HPAEpiCs was attenuated by infection with adenovirus (adv)-HO-1 or incubation with CORM-2. These inhibitory effects of HO-1 were reversed by pretreatment with hemoglobin (Hb). Moreover, CORM-2-induced HO-1 expression was mediated via the phosphorylation of p47^phox, c-Src, epidermal growth factor receptor (EGFR), Akt, and NF-E2-related factor 2 (Nrf2), which were inhibited by their pharmacological inhibitors, including diphenyleneiodonium (DPI) or apocynin (APO), ROS [N-acetyl-L-cysteine (NAC)], PP1, AG1478, PI3K (LY294002), or Akt (SH-5), and small interfering RNAs (siRNAs). CORM-2-enhanced Nrf2 expression, and anti-oxidant response element (ARE) promoter activity was also inhibited by these pharmacological inhibitors. The interaction between Nrf2 and AREs was confirmed with a chromatin immunoprecipitation (ChIP) assay. These findings suggest that CORM-2 increases the formation of the Nrf2 and AREs complex and binds with ARE-binding sites via Src, EGFR, and PI3K/Akt, which further induces HO-1 expression in HPAEpiCs. Thus, the HO-1/CO system might suppress TNF-α-mediated inflammatory responses and exert a potential therapeutic strategy in pulmonary diseases.

Protective effects of carbon monoxide releasing molecule‑2 on pancreatic function in septic mice

The present study aimed to investigate the effect of carbon monoxide (CO)‑releasing molecule‑2 (CORM‑2) on pancreatic function in sepsis‑model mice. To perform the present investigation, mice were rendered septic by cecal ligation and puncture (CLP). Then, mice were either treated with or without CORM‑2 (8 mg/kg, intravenous) for different durations (6, 12 and 24 h) immediately following CLP. The levels of serum amylase and lipase, tumor necrosis factor α, interleukin‑1β and interleukin‑6 in addition to myeloperoxidase (MPO) activity in pancreatic tissues were determined at 6, 12 and 24 h post‑CLP. Histological scores and the expression of intercellular adhesion molecule 1 (ICAM‑1), vascular cell adhesion molecule 1 (VCAM‑1), nuclear factor‑κB (NF‑κB) and phosphorylated inhibitor of κB (p‑IκB‑α) in the pancreas were also evaluated at 24 h post‑CLP. The results of the present study revealed that compared with CLP‑alone group, CORM‑2 treatment significantly (P<0.05) reduced the levels of serum amylase, lipase and pro‑inflammatory cytokines. In parallel, the severity of pancreatic histology, MPO activity and the expression levels of ICAM‑1 and VCAM‑1 in the pancreas of CORM‑2 treated CLP mice were substantially decreased compared with the untreated group. Furthermore, CORM‑2 treatment inhibited the expression levels of NF‑κB and P‑IκB‑α in the pancreas of mice following CLP compared with the untreated group. CORM‑2‑liberated CO exerted protective effects on the pancreatic function of septic mice, and the beneficial effects may be due to the suppression of NF‑κB activation and subsequent regulation of NF‑κB‑dependent expression of cytokines.

Biomimetic carbon monoxide delivery based on hemoglobin vesicles ameliorates acute pancreatitis in mice via the regulation of macrophage and neutrophil activity

Macrophages play a central role in various inflammatory disorders and are broadly divided into two subpopulations, M1 and M2 macrophage. In the healing process in acute inflammatory disorders, shifting the production of M1 macrophages to M2 macrophages is desirable, because M1 macrophages secrete pro-inflammatory cytokines, whilst the M2 variety secrete anti-inflammatory cytokines. Previous findings indicate that when macrophages are treated with carbon monoxide (CO), the secretion of anti-inflammatory cytokine is increased and the expression of pro-inflammatory cytokines is inhibited, indicating that CO may have a potential to modulate the production of macrophages toward the M2-like phenotype. In this study, we examined the issue of whether CO targeting macrophages using a nanotechnology-based CO donor, namely CO-bound hemoglobin vesicles (CO-HbV), modulates their polarization and show therapeutic effects against inflammatory disorders. The results showed that the CO-HbV treatment polarized a macrophage cell line toward an M2-like phenotype. Furthermore, in an in vivo study using acute pancreatitis model mice as a model of an inflammatory disease, a CO-HbV treatment also tended to polarize macrophages toward an M2-like phenotype and inhibited neutrophil infiltration in the pancreas, resulting in a significant inflammation. In addition to the suppression of acute pancreatitis, CO-HbV diminished a subsequent pancreatitis-associated acute lung injury. This could be due to the inhibition of the systemic inflammation, neutrophil infiltration in the lungs and the production of HMGB-1. These findings suggest that CO-HbV exerts superior anti-inflammatory effects against inflammatory disorders via the regulation of macrophage and neutrophil activity.

Gasotransmitters and the immune system: Mode of action and novel therapeutic targets

Gasotransmitters are a group of gaseous molecules, with pleiotropic biological functions. These molecules include nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). Abnormal production and metabolism of these molecules have been observed in several pathological conditions. The understanding of the role of gasotransmitters in the immune system has grown significantly in the past years, and independent studies have shed light on the effect of exogenous and endogenous gasotransmitters on immune responses. Moreover, encouraging results come from the efficacy of NO-, CO- and H₂S -donors in preclinical animal models of autoimmune, acute and chronic inflammatory diseases. To date, data on the influence of gasotransmitters in immunity and immunopathology are often scattered and partial, and the scarcity of clinical trials using NO-, CO- and H₂S -donors, reveals that more effort is warranted. This review focuses on the role of gasotransmitters in the immune system and covers the evidences on the possible use of gasotransmitters for the treatment of inflammatory conditions.

STING Signaling Promotes Inflammation in Experimental Acute Pancreatitis

BACKGROUND & AIMS

Acute pancreatitis (AP) is characterized by severe inflammation and acinar cell death. Transmembrane protein 173 (TMEM173 or STING) is a DNA sensor adaptor protein on immune cells that recognizes cytosolic nucleic acids and transmits signals that activate production of interferons and the innate immune response. We investigated whether leukocyte STING signaling mediates inflammation in mice with AP.

METHODS

We induced AP in C57BL/6J mice (control) and C57BL/6J-Tmem173gt/J mice (STING-knockout mice) by injection of cerulein or placement on choline-deficient DL-ethionine supplemented diet. In some mice, STING signaling was induced by administration of a pharmacologic agonist. AP was also induced in C57BL/6J mice with bone marrow transplants from control or STING-knockout mice and in mice with disruption of the cyclic GMP-AMP synthase (Cgas) gene. Pancreata were collected, analyzed by histology, and acini were isolated and analyzed by flow cytometry, quantitative polymerase chain reaction, immunoblots, and enzyme-linked immunosorbent assay. Bone-marrow-derived macrophages were collected from mice and tested for their ability to detect DNA from dying acinar cells in the presence and absence of deoxyribonuclease (DNaseI).

RESULTS

STING signaling was activated in pancreata from mice with AP but not mice without AP. STING-knockout mice developed less severe AP (less edema, inflammation, and markers of pancreatic injury) than control mice, whereas mice given a STING agonist developed more severe AP than controls. In immune cells collected from pancreata, STING was expressed predominantly in macrophages. Levels of cGAS were increased in mice with vs without AP, and cGAS-knockout mice had decreased edema, inflammation, and other markers of pancreatic injury upon induction of AP than control mice. Wild-type mice given bone marrow transplants from STING-knockout mice had less pancreatic injury and lower serum levels of lipase and pancreatic trypsin activity following induction of AP than mice given wild-type bone marrow. DNA from dying acinar cells activated STING signaling in macrophages, which was inhibited by addition of DNaseI.

CONCLUSIONS

In mice with AP, STING senses acinar cell death (by detecting DNA from dying acinar cells) and activates a signaling pathway that promotes inflammation. Macrophages express STING and activate pancreatic inflammation in AP.

Emerging role of carbon monoxide in regulation of cellular pathways and in the maintenance of gastric mucosal integrity

Heme oxygenase (HO) catalyzes the degradation of toxic free heme to the equimolar amounts of biliverdin, Fe2+ and concurrently releases of carbon monoxide (CO). CO is nowadays increasingly recognized as an important signaling molecule throughout the body that is involved in many physiological processes and shows multidirectional biological activity. Recent evidence indicates that CO exhibits the anti-inflammatory, anti-proliferative, anti-apoptotic, anti-aggregatory and vasodilatory properties. The cellular mechanisms underlying the activity of CO involve stimulation of cGMP-dependent signaling pathway and large conductance calcium activated K+ channels, the activation of mitogen-activated protein kinases and the nuclear factor k-light chain-enhancer of activated B cells transcription factor pathway. Stimulation of endogenous CO production by HO inducers or the inhalation of CO or the delivery of this gaseous molecule by novel pharmaceutical agents have been found in experimental animal models to be promising in the future therapy of various diseases. CO appears to act as a significant component of the complex mechanism of gastrointestinal (GI) mucosal defense. This gaseous molecule plays an important role in diabetic gastroparesis, prevention of the upper GI mucosal damage, post-operative ileus and the healing of ulcerative colitis. This review focuses on the better understanding mechanisms through which CO contributes to the mechanism of protection, resistance to injury and ulcer healing. It is becoming apparent that the pleiotropic effect of this molecule may increase clinical applicability of CO donors and their implementation in many pharmacological research areas, pharmaceutical industry and health-care system.

Role of eosinophils in the initiation and progression of pancreatitis pathogenesis

Eosinophilic pancreatitis (EP) is reported in humans; however, the etiology and role of eosinophils in EP pathogenesis are poorly understood and not well explored. Therefore, it is interesting to examine the role of eosinophils in the initiation and progression of pancreatitis pathogenesis. Accordingly, we performed anti-major basic protein immunostaining, chloroacetate esterase, and Masson's trichrome analyses to detect eosinophils, mast cells, and collagen in the tissue sections of mouse and human pancreas. Induced eosinophils accumulation and degranulation were observed in the tissue sections of human pancreatitis, compared with no eosinophils in the normal pancreatic tissue sections. Similarly, we observed induced tissue eosinophilia along with mast cells and acinar cells atrophy in cerulein-induced mouse model of chronic pancreatitis. Additionally, qPCR and ELISA analyses detected induced transcript and protein levels of proinflammatory and profibrotic cytokines, chemokines like IL 5, IL-18, eotaxin-1, eotaxin-2, TGF-β1, collagen-1, collagen-3, fibronectin, and α-SMA in experimental pancreatitis. Mechanistically, we show that eosinophil-deficient GATA1 and endogenous IL-5-deficient mice were protected from the induction of proinflammatory and profibrotic cytokines, chemokines, tissue eosinophilia, and mast cells in a cerulein-induced murine model of pancreatitis. These human and experimental data indicate that eosinophil accumulation and degranulation may have a critical role in promoting pancreatitis pathogenesis including fibrosis. Taken together, eosinophil tissue accumulation needs appropriate attention to understand and restrict the progression of pancreatitis pathogenesis in humans. NEW & NOTEWORTHY The present study for the first time shows that eosinophils accumulate in the pancreas and promote disease pathogenesis, including fibrosis in earlier reported cerulein-induced experimental models of pancreatitis. Importantly, we show that GATA-1 and IL-5 deficiency protects mice form the induction of eosinophil active chemokines, and profibrotic cytokines, including accumulation of tissue collagen in an experimental model of pancreatitis. Additionally, we state that cerulein-induced chronic pancreatitis is independent of blood eosinophilia.

Effect of Endotoxemia in Suckling Rats on Pancreatic Integrity and Exocrine Function in Adults: A Review Report

Background. Endotoxin (LPS), the component of Gram-negative bacteria, is responsible for sepsis and neonatal mortality, but low concentrations of LPS produced tissue protection in experimental studies. The effects of LPS applied to the suckling rats on the pancreas of adult animals have not been previously explored. We present the impact of neonatal endotoxemia on the pancreatic exocrine function and on the acute pancreatitis which has been investigated in the adult animals. Endotoxemia was induced in suckling rats by intraperitoneal application of LPS from Escherichia coli or Salmonella typhi. In the adult rats, pretreated in the early period of life with LPS, histological manifestations of acute pancreatitis have been reduced. Pancreatic weight and plasma lipase activity were decreased, and SOD concentration was reversed and accompanied by a significant reduction of lipid peroxidation products (MDA + 4 HNE) in the pancreatic tissue. In the pancreatic acini, the significant increases in protein signals for toll-like receptor 4 and for heat shock protein 60 were found. Signal for the CCK1 receptor was reduced and pancreatic secretory responses to caerulein were diminished, whereas basal enzyme secretion was unaffected. These pioneer studies have shown that exposition of suckling rats to endotoxin has an impact on the pancreas in the adult organism.

Angiotensin 1-7 ameliorates caerulein-induced inflammation in pancreatic acinar cells by downregulating Toll-like receptor 4/nuclear factor-κB expression

The present study aimed to investigate the effects of angiotensin (Ang) 1–7 on caerulein (CAE)-stimulated nuclear factor (NF)-κB, Toll-like receptor (TLR4) and cytokine expression using pancreatic acinar AR42J cells. AR42J cells were treated with 10 nmol/l CAE for various durations. In addition, cells were pretreated with various concentrations of Ang 1–7 or A779, a specific antagonist of Ang 1–7, and were stimulated with CAE for 12 h. Control cells were treated with vehicle (F-12K complete medium with 2% fetal bovine serum, 10 U/ml penicillin and 100 mg/ml streptomycin) alone. The mRNA and protein expression levels of TLR4, NF-κB, interleukin (IL)-6, IL-8, IL-10 and tumor necrosis factor-α (TNF-α) were determined by western blotting, immunofluorescence and reverse transcription-quantitative polymerase chain reaction. CAE treatment stimulated TLR4 and NF-κB expression within AR42J cells. Immunofluorescence indicated that TLR4 was expressed on the membranes and in the cytoplasm of AR42J cells, whereas NF-κB expression accumulated in the cytoplasm and nuclei. CAE-induced expression of TLR4 and NF-κB within AR42J cells was abrogated by 10⁻⁵ mmol/l Ang 1–7; however, TLR4 and NF-κB expression was enhanced with the addition of A779, particularly 10⁻⁵ mmol/l. In addition, treatment with 10⁻⁶ and 10⁻⁵ mmol/l Ang 1–7 significantly mitigated CAE-induced expression of IL-6, IL-8 and TNF-α, whereas it enhanced IL-10 expression. Conversely, A779 treatment enhanced the CAE-induced expression of IL-6, IL-8 and TNF-α, and reduced IL-10 expression in AR42J cells. In conclusion, these results suggested that Ang 1–7 may attenuate CAE-induced inflammation by downregulating TLR4, NF-κB and proinflammatory cytokine expression within AR42J cells. Therefore, Ang 1–7 may exert protective effects against the pathological progression of AP in a cell model of AP induced by CAE and may be considered in the development of treatments for this disease.

Autophagy, Inflammation, and Immune Dysfunction in the Pathogenesis of Pancreatitis

Pancreatitis is a common disorder with significant morbidity and mortality, yet little is known about its pathogenesis, and there is no specific or effective treatment. Its development involves dysregulated autophagy and unresolved inflammation, demonstrated by studies in genetic and experimental mouse models. Disease severity depends on whether the inflammatory response resolves or amplifies, leading to multi-organ failure. Dysregulated autophagy might promote the inflammatory response in the pancreas. We discuss the roles of autophagy and inflammation in pancreatitis, mechanisms of deregulation, and connections among disordered pathways. We identify gaps in our knowledge and delineate perspective directions for research. Elucidation of pathogenic mechanisms could lead to new targets for treating or reducing the severity of pancreatitis.

Interleukin-10 Attenuates Hypochlorous Acid-Mediated Cytotoxicity to HEI-OC1 Cochlear Cells

Inflammatory reaction plays a crucial role in the pathophysiology of acquired hearing loss such as ototoxicity and labyrinthitis. In our earlier work, we showed the pivotal role of otic fibrocytes in cochlear inflammation and the critical involvement of proinflammatory cytokines in cisplatin ototoxicity. We also demonstrated that otic fibrocytes inhibit monocyte chemoattractant protein 1 (CCL2) upregulation in response to interleukin-10 (IL-10) via heme oxygenase 1 (HMOX1) signaling, resulting in suppression of cochlear inflammation. However, it is still unclear how IL-10 affects inflammation-mediated cochlear injury. Here we aim to determine how hypochlorous acid, a model inflammation mediator affects cochlear cell viability and how IL-10 affects hypochlorous acid-mediated cochlear cell injury. NaOCl, a sodium salt of hypochlorous acid (HOCl) was found to induce cytotoxicity of HEI-OC1 cells in a dose-dependent manner. Combination of hydrogen peroxide and myeloperoxidase augmented cisplatin cytotoxicity, and this synergism was inhibited by N-Acetyl-L-cysteine and ML-171. The rat spiral ligament cell line (RSL) appeared to upregulate the antioxidant response element (ARE) activities upon exposure to IL-10. RSL cells upregulated the expression of NRF2 (an ARE ligand) and NR0B2 in response to CoPP (a HMOX1 inducer), but not to ZnPP (a HMOX1 inhibitor). Adenovirus-mediated overexpression of NR0B2 was found to suppress CCL2 upregulation. IL-10-positive cells appeared in the mouse stria vascularis 1 day after intraperitoneal injection of lipopolysaccharide (LPS). Five days after injection, IL-10-positive cells were observed in the spiral ligament, spiral limbus, spiral ganglia, and suprastrial area, but not in the stria vascularis. IL-10R1 appeared to be expressed in the mouse organ of Corti as well as HEI-OC1 cells. HEI-OC1 cells upregulated Bcl-xL expression in response to IL-10, and IL-10 was shown to attenuate NaOCl-induced cytotoxicity. In addition, HEI-OC1 cells upregulated IL-22RA upon exposure to cisplatin, and NaOCl cytotoxicity was inhibited by IL-22. Taken together, our findings suggest that hypochlorous acid is involved in cochlear injury and that IL-10 potentially reduces cochlear injury through not only inhibition of inflammation but also enhancement of cochlear cell viability. Further studies are needed to determine immunological characteristics of intracochlear IL-10-positive cells and elucidate molecular mechanisms involved in the otoprotective activity of IL-10.

Carbon monoxide protects against hepatic steatosis in mice by inducing sestrin-2 via the PERK-eIF2α-ATF4 pathway

Nonalcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, has emerged as one of the most common causes of chronic liver disease in developed countries over the last decade. NAFLD comprises a spectrum of pathological hepatic changes, including steatosis, steatohepatitis, advanced fibrosis, and cirrhosis. Autophagy, a homeostatic process for protein and organelle turnover, is decreased in the liver during the development of NAFLD. Previously, we have shown that carbon monoxide (CO), a reaction product of heme oxygenase (HO) activity, can confer protection in NAFLD, though the molecular mechanisms remain unclear. We therefore investigated the mechanisms underlying the protective effect of CO on methionine/choline-deficient (MCD) diet-induced hepatic steatosis. We found that CO induced sestrin-2 (SESN2) expression through enhanced mitochondrial ROS production and protected against MCD-induced NAFLD progression through activation of autophagy. SESN2 expression was increased by CO or CO-releasing molecule (CORM2), in a manner dependent on signaling through the protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor-2 alpha (eIF2α)/ activating transcription factor-4 (ATF4)-dependent pathway. CO-induced SESN2 upregulation in hepatocytes contributed to autophagy induction through activation of 5'-AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin (mTOR) complex I (mTORC1). Furthermore, we demonstrate that CO significantly induced the expression of SESN2 and enhanced autophagy in the livers of MCD-fed mice or in MCD-media treated hepatocytes. Conversely, knockdown of SESN2 abrogated autophagy activation and mTOR inhibition in response to CO. We conclude that CO ameliorates hepatic steatosis through the autophagy pathway induced by SESN2 upregulation.

Immunology of pancreatitis and environmental factors

PURPOSE OF REVIEW

This report reviews recent aspects of pancreatitis immunology and environmental factors that link to development and progression of disease.

RECENT FINDINGS

Limited human and animal model studies have recently attempted to understand immune mechanisms that lead to the pathogenesis of acute and chronic pancreatitis. Based on these studies innate immune responses emerge as critical elements in disease pathogenesis and severity of inflammation. The immune basis for environmental factors such as smoking, which are highly associated with disease progression highlight novel cross talk mechanisms between immune and nonimmune pancreatic cells such as the pancreatic stellate cells.

SUMMARY

Better understanding of immune responses and signaling pathways are emerging as important contributors in pancreatitis development and progression. Such mechanisms are likely to offer future targetable therapies that can either halt or reverse disease progression.

Carbon monoxide as a promising molecule to promote nerve regeneration after traumatic brain injury

Carbon monoxide (CO) is known as a toxic gas. Although there have been many studies on both toxic and protective effects of CO, most of these studies lack novelty, except for Eng H Lo team's study on the therapeutic effect of CO on brain injuries. In this commentary, we summarize the potential application value of CO in the treatment of some clinical diseases, especially its protective effect and nerve regeneration in brain injuries, hoping that our interest in CO could promote related clinical application studies.

The Heme Metabolite Carbon Monoxide Facilitates KSHV Infection by Inhibiting TLR4 Signaling in Endothelial Cells

Kaposi sarcoma herpesvirus (KSHV) is the etiologic agent of Kaposi sarcoma (KS) and certain rare B cell lymphoproliferative disorders. KSHV infection of endothelial cells (EC) in vitro increases expression of the inducible host-encoded enzyme heme oxygenase-1 (HO-1), which is also strongly expressed in KS tumors. HO-1 catalyzes the rate-limiting step in the conversion of heme into iron, biliverdin and the gasotransmitter carbon monoxide (CO), all of which share anti-apoptotic, anti-inflammatory, pro-survival, and tumorigenic activities. Our previous work has shown that HO-1 expression in KSHV-infected EC is characterized by a rapid yet transient induction at early times post-infection, followed by a sustained upregulation co-incident with establishment of viral latency. These two phases of expression are independently regulated, suggesting distinct roles for HO-1 in the virus life cycle. Here, we investigated the role of HO-1 during acute infection, prior to the onset of viral gene expression. The early infection phase involves a series of events that culminate in delivery of the viral genome to the nucleus. Primary infection also leads to activation of host innate immune effectors, including the pattern recognition receptor TLR4, to induce an antiviral response. It has been shown that TLR4-deficient EC are more susceptible to KSHV infection than wild-type controls, suggesting an important inhibitory role for TLR4 in the KSHV life cycle. TLR4 signaling is in turn subject to regulation by several virus-encoded immune evasion factors. In this report we identify HO-1 as a host protein co-opted by KSHV as part of a rapid immune evasion strategy. Specifically, we show that early HO-1 induction by KSHV results in increased levels of endogenous CO, which functions as a TLR4 signaling inhibitor. In addition, we show that CO-mediated inhibition of TLR4 signaling leads to reduced expression of TLR4-induced antiviral genes, thus dampening the host antiviral response and facilitating KSHV infection. Conversely, inhibition of HO-1 activity decreases intracellular CO, enhances the host antiviral response and inhibits KSHV infection. In conclusion, this study identifies HO-1 as a novel innate immune evasion factor in the context of KSHV infection and supports HO-1 inhibition as a viable therapeutic strategy for KS.

Modulation of antigen processing by haem-oxygenase 1. Implications on inflammation and tolerance

Haem-oxygenase-1 (HO-1) is an enzyme responsible for the degradation of haem that can suppress inflammation, through the production of carbon monoxide (CO). It has been shown in several experimental models that genetic and pharmacological induction of HO-1, as well as non-toxic administration of CO, can reduce inflammatory diseases, such as endotoxic shock, type 1 diabetes and graft rejection. Recently, it was shown that the HO-1/CO system can alter the function of antigen-presenting cells (APCs) and reduce T-cell priming, which can be beneficial during immune-driven inflammatory diseases. The molecular mechanisms by which the HO-1 and CO reduce both APC- and T-cell-driven immunity are just beginning to be elucidated. In this article we discuss recent findings related to the immune regulatory capacity of HO-1 and CO at the level of recognition of pathogen-associated molecular patterns and T-cell priming by APCs. Finally, we propose a possible regulatory role for HO-1 and CO over the recently described mitochondria-dependent immunity. These concepts could contribute to the design of new therapeutic tools for inflammation-based diseases.

CORM-2 inhibits TXNIP/NLRP3 inflammasome pathway in LPS-induced acute lung injury

OBJECTIVE

Accumulated studies suggest that exogenously administered carbon monoxide is beneficial for the resolution of acute lung inflammation. The present study aimed to examine the effects and the underlying mechanisms of CORM-2 on thioredoxin-interacting protein (TXNIP)/NLRP3 inflammasome pathway in lipopolysaccharide (LPS)-induced acute lung injury (ALI).

METHODS

ALI was intratracheally induced by LPS in C57BL6 mice. CORM-2 or iCORM-2 (30mg/kg i.p.) was administered immediately before LPS instillation. 6 h later, lung bronchoalveolar lavage (BAL) fluids were acquired for IL-18, IL-1β, and cell measurement, and lung issues were collected for histologic examination, wet/dry weight ratio, and determination of TXNIP/NLRP3 inflammasome expression, NLRP3 inflammasome and NF-ΚB activity, and reactive oxygen species (ROS) production.

RESULTS

LPS triggered significant lung edema, lung injury, and leukocyte infiltration, and elevated the levels of IL-1β and IL-18 in lung BAL fluids. CORM-2 pretreatment resulted in a marked amelioration of lung injury and reduced IL-1β and IL-18 secretion in BAL fluids. In lung tissues; CORM-2 down-regulated mRNA and protein level of TXNIP, NLRP3, ASC, and caspase-1. Furthermore, CORM-2 reduced ROS production, inhibited NLRP3 inflammasome and NF-κB activity, and interaction of TXNIP-NLRP3. However, no significant differences were detected between the LPS and iCORM-2 (an inactive variant of CORM-2) group.

CONCLUSION

CORM-2 suppresses TXNIP/NLRP3 inflammasome pathway and protects against LPS-induced lung injury.

Pulmonary Epithelial TLR4 Activation Leads to Lung Injury in Neonatal Necrotizing Enterocolitis

We seek to define the mechanisms leading to the development of lung disease in the setting of neonatal necrotizing enterocolitis (NEC), a life-threatening gastrointestinal disease of premature infants characterized by the sudden onset of intestinal necrosis. NEC development in mice requires activation of the LPS receptor TLR4 on the intestinal epithelium, through its effects on modulating epithelial injury and repair. Although NEC-associated lung injury is more severe than the lung injury that occurs in premature infants without NEC, the mechanisms leading to its development remain unknown. In this study, we now show that TLR4 expression in the lung gradually increases during postnatal development, and that mice and humans with NEC-associated lung inflammation express higher levels of pulmonary TLR4 than do age-matched controls. NEC in wild-type newborn mice resulted in significant pulmonary injury that was prevented by deletion of TLR4 from the pulmonary epithelium, indicating a role for pulmonary TLR4 in lung injury development. Mechanistically, intestinal epithelial TLR4 activation induced high-mobility group box 1 release from the intestine, which activated pulmonary epithelial TLR4, leading to the induction of the neutrophil recruiting CXCL5 and the influx of proinflammatory neutrophils to the lung. Strikingly, the aerosolized administration of a novel carbohydrate TLR4 inhibitor prevented CXCL5 upregulation and blocked NEC-induced lung injury in mice. These findings illustrate the critical role of pulmonary TLR4 in the development of NEC-associated lung injury, and they suggest that inhibition of this innate immune receptor in the neonatal lung may prevent this devastating complication of NEC.

Therapeutic implications of innate immune system in acute pancreatitis

INTRODUCTION

Acute pancreatitis (AP) is an inflammatory disorder of the pancreas encompassing a cascade of cellular and molecular events. It starts from premature activation of zymogens with the involvement of innate immune system to a potential systemic inflammatory response and multiple organ failure. Leukocytes are the major cell population that participate in the propagation of the disease. Current understanding of the course of AP is still far from complete, limiting treatment options mostly to conservative supportive care. Emerging evidence has pointed to modulation of the immune system for strategic therapeutic development, by mitigating the inflammatory response and severity of AP. In the current review, we have focused on the role of innate immunity in the condition and highlighted therapeutics targeting it for treatment of this challenging disease.

AREAS COVERED

The current review has aimed to elaborate in-depth understanding of specific roles of innate immune cells, derived mediators and inflammatory pathways that are involved in AP. Summarizing the recent therapeutics and approaches applied experimentally that target immune responses to attenuate AP.

EXPERT OPINION

The current state of knowledge on AP, limitations of presently available therapeutic approaches and the promise of therapeutic implications of innate immune system in AP are discussed.