Lung Neutrophilia in Myeloperoxidase Deficient Mice during the Course of Acute Pulmonary Inflammation

Investigating the link between miR-34a-5p and TLR6 signaling in sepsis-induced ARDS

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) are lung complications diagnosed by impaired gaseous exchanges leading to mortality. From the diverse etiologies, sepsis is a prominent contributor to ALI/ARDS. In the present study, we retrieved sepsis-induced ARDS mRNA expression profile and identified 883 differentially expressed genes (DEGs). Next, we established an ARDS-specific weighted gene co-expression network (WGCN) and picked the blue module as our hub module based on highly correlated network properties. Later we subjected all hub module DEGs to form an ARDS-specific 3-node feed-forward loop (FFL) whose highest-order subnetwork motif revealed one TF (STAT6), one miRNA (miR-34a-5p), and one mRNA (TLR6). Thereafter, we screened a natural product library and identified three lead molecules that showed promising binding affinity against TLR6. We then performed molecular dynamics simulations to evaluate the stability and binding free energy of the TLR6-lead molecule complexes. Our results suggest these lead molecules may be potential therapeutic candidates for treating sepsis-induced ALI/ARDS. In-silico studies on clinical datasets for sepsis-induced ARDS indicate a possible positive interaction between miR-34a and TLR6 and an antagonizing effect on STAT6 to promote inflammation. Also, the translational study on septic mice lungs by IHC staining reveals a hike in the expression of TLR6. We report here that miR-34a actively augments the effect of sepsis on lung epithelial cell apoptosis. This study suggests that miR-34a promotes TLR6 to heighten inflammation in sepsis-induced ALI/ARDS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03700-1.

Non-Canonical Functions of Myeloperoxidase in Immune Regulation, Tissue Inflammation and Cancer

Myeloperoxidase (MPO) is one of the most abundantly expressed proteins in neutrophils. It serves as a critical component of the antimicrobial defense system, facilitating microbial killing via generation of reactive oxygen species (ROS). Interestingly, emerging evidence indicates that in addition to the well-recognized canonical antimicrobial function of MPO, it can directly or indirectly impact immune cells and tissue responses in homeostatic and disease states. Here, we highlight the emerging non-canonical functions of MPO, including its impact on neutrophil longevity, activation and trafficking in inflammation, its interactions with other immune cells, and how these interactions shape disease outcomes. We further discuss MPO interactions with barrier forming endothelial and epithelial cells, specialized cells of the central nervous system (CNS) and its involvement in cancer progression. Such diverse function and the MPO association with numerous inflammatory disorders make it an attractive target for therapies aimed at resolving inflammation and limiting inflammation-associated tissue damage. However, while considering MPO inhibition as a potential therapy, one must account for the diverse impact of MPO activity on various cellular compartments both in health and disease.

Nanoparticles reduce monocytes within the lungs to improve outcomes after influenza virus infection in aged mice

Older people exhibit dysregulated innate immunity to respiratory viral infections, including influenza and SARS-CoV-2, and show an increase in morbidity and mortality. Nanoparticles are a potential practical therapeutic that could reduce exaggerated innate immune responses within the lungs during viral infection. However, such therapeutics have not been examined for effectiveness during respiratory viral infection, particular in aged hosts. Here, we employed a lethal model of influenza viral infection in vulnerable aged mice to examine the ability of biodegradable, cargo-free nanoparticles, designated ONP-302, to resolve innate immune dysfunction and improve outcomes during infection. We administered ONP-302 via i.v. injection to aged mice at day 3 after infection, when the hyperinflammatory innate immune response was already established. During infection, we found that ONP-302 treatment reduced the numbers of inflammatory monocytes within the lungs and increased their number in both the liver and spleen, without impacting viral clearance. Importantly, cargo-free nanoparticles reduced lung damage, reduced histological lung inflammation, and improved gas exchange and, ultimately, the clinical outcomes in influenza-infected aged mice. In conclusion, ONP-302 improves outcomes in influenza-infected aged mice. Thus, our study provides information concerning a practical therapeutic, which, if translated clinically, could improve disease outcomes for vulnerable older patients suffering from respiratory viral infections.

Rare germline alterations of myeloperoxidase predispose to myeloid neoplasms

Myeloperoxidase (MPO) gene alterations with variable clinical penetrance have been found in hereditary MPO deficiency, but their leukemia association in patients and carriers has not been established. Germline MPO alterations were found to be significantly enriched in myeloid neoplasms: 28 pathogenic/likely pathogenic variants were identified in 100 patients. The most common alterations were c.2031-2 A > C, R569W, M519fs* and Y173C accounting for about half of the cases. While functional experiments showed that the marrow stem cell pool of Mpo^-/- mice was not increased, using competitive repopulation demonstrated that Mpo^-/- grafts gained growth advantage over MPO wild type cells. This finding also correlated with increased clonogenic potential after serial replating in the setting of H₂O₂-induced oxidative stress. Furthermore, we demonstrated that H₂O₂-induced DNA damage and activation of error-prone DNA repair may result in secondary genetic damage potentially predisposing to leukemia leukemic evolution. In conclusion, our study for the first time demonstrates that germline MPO variants may constitute risk alleles for MN evolution.

RG100204, A Novel Aquaporin-9 Inhibitor, Reduces Septic Cardiomyopathy and Multiple Organ Failure in Murine Sepsis

Sepsis is caused by systemic infection and is a major health concern as it is the primary cause of death from infection. It is the leading cause of mortality worldwide and there are no specific effective treatments for sepsis. Gene deletion of the neutral solute channel Aquaporin 9 (AQP9) normalizes oxidative stress and improves survival in a bacterial endotoxin induced mouse model of sepsis. In this study we described the initial characterization and effects of a novel small molecule AQP9 inhibitor, RG100204, in a cecal ligation and puncture (CLP) induced model of polymicrobial infection. In vitro, RG100204 blocked mouse AQP9 H2O2 permeability in an ectopic CHO cell expression system and abolished the LPS induced increase in superoxide anion and nitric oxide in FaO hepatoma cells. Pre-treatment of CLP-mice with RG100204 (25 mg/kg p.o. before CLP and then again at 8 h after CLP) attenuated the hypothermia, cardiac dysfunction (systolic and diastolic), renal dysfunction and hepatocellular injury caused by CLP-induced sepsis. Post-treatment of CLP-mice with RG100204 also attenuated the cardiac dysfunction (systolic and diastolic), the renal dysfunction caused by CLP-induced sepsis, but did not significantly reduce the liver injury or hypothermia. The most striking finding was that oral administration of RG100204 as late as 3 h after the onset of polymicrobial sepsis attenuated the cardiac and renal dysfunction caused by severe sepsis. Immunoblot quantification demonstrated that RG100204 reduced activation of the NLRP3 inflammasome pathway. Moreover, myeloperoxidase activity in RG100204 treated lung tissue was reduced. Together these results indicate that AQP9 may be a novel drug target in polymicrobial sepsis.

Myeloperoxidase Deficiency Alters the Process of the Regulated Cell Death of Polymorphonuclear Neutrophils

Polymorphonuclear neutrophils (PMNs) play a key role in host defense. However, their massive accumulation at the site of inflammation can delay regenerative healing processes and can initiate pathological inflammatory processes. Thus, the efficient clearance of PMNs mediated by the induction of regulated cell death is a key process preventing the development of these pathological conditions. Myeloperoxidase (MPO), a highly abundant enzyme in PMN granules, primarily connected with PMN defense machinery, is suggested to play a role in PMN-regulated cell death. However, the contribution of MPO to the mechanisms of PMN cell death remains incompletely characterized. Herein, the process of the cell death of mouse PMNs induced by three different stimuli – phorbol 12-myristate 13-acetate (PMA), opsonized streptococcus (OST), and N-formyl-met-leu-phe (fMLP) – was investigated. MPO-deficient PMNs revealed a significantly decreased rate of cell death characterized by phosphatidylserine surface exposure and cell membrane permeabilization. An inhibitor of MPO activity, 4-aminobenzoic acid hydrazide, did not exhibit a significant effect on PMA-induced cell death compared to MPO deficiency. Interestingly, only the limited activation of markers related to apoptotic cell death was observed (e.g. caspase 8 activation, Bax expression) and they mostly did not correspond to phosphatidylserine surface exposure. Furthermore, a marker characterizing autophagy, cleavage of LC3 protein, as well as histone H3 citrullination and its surface expression was observed. Collectively, the data show the ability of MPO to modulate the life span of PMNs primarily through the potentiation of cell membrane permeabilization and phosphatidylserine surface exposure.

Comparison of anti-inflammatory effects of Lonicerae Japonicae Flos and Lonicerae Flos based on network pharmacology

Objective

Methods

Results

Conclusion

Ulinastatin ameliorates LPS‑induced pulmonary inflammation and injury by blocking the MAPK/NF‑κB signaling pathways in rats

Ulinastatin, a urinary trypsin inhibitor (UTI) is commonly used to treat patients with acute inflammatory disease. However, the underlying mechanisms of its anti‑inflammatory effect in acute lung injury (ALI) are not fully understood. The present study aimed to investigate the protective effect of UTI and explore its potential mechanisms by using a rat model of lipopolysaccharide (LPS)‑induced ALI. Rats were treated with 5 mg/kg LPS by intratracheal instillation. The histological changes in LPS‑induced ALI was evaluated using hematoxylin and eosin staining and the myeloperoxidase (MPO) activity was determined using ELISA. The wet/dry ratio (W/D ratio) of the lungs was used to assess the severity of pulmonary edema and Evans blue dye was used to evaluate the severity of lung vascular leakage. The results demonstrated that LPS administration induced histological changes and significantly increased the lung W/D ratio, MPO activity and Evans blue dye extravasation compared with the control group. However, treatment with UTI attenuated LPS‑induced ALI in rats by modifying histological changes and reducing the lung W/D ratio, MPO activity and Evans blue dye extravasation. In addition, LPS induced the secretion of numerous pro‑inflammatory cytokines in bronchoalveolar lavage fluid (BALF), including tumor necrosis factor‑α, interleukin (IL)‑6, IL‑1β and interferon‑γ; however, these cytokines were strongly reduced following treatment with UTI. In addition, UTI was able to reduce cellular counts in BALF, including neutrophils and leukocytes. Western blotting demonstrated that UTI significantly blocked the LPS‑stimulated MAPK and NF‑κB signaling pathways. The results of the present study indicated that UTI could exert an anti‑inflammatory effect on LPS‑induced ALI by inhibiting the MAPK and NF‑κB signaling pathways, which suggested that UTI may be considered as an effective drug in the treatment of ALI.

Intraperitoneal Injection of Acetate Protects Mice Against Lipopolysaccharide (LPS)‑Induced Acute Lung Injury Through Its Anti-Inflammatory and Anti-Oxidative Ability

BACKGROUND As a member of short-chain fatty acids, acetate exhibits anti-inflammatory capacity. The present study aimed to investigate the effect of acetate on lipopolysaccharide (LPS)-induced acute lung injury (ALI) and explored its underlying mechanism. MATERIAL AND METHODS Acetate (250 mM, 400 µL) was given intraperitoneally 30 minutes after LPS (5 mg/kg) intratracheal injection. Lung tissues and bronchoalveolar lavage fluid (BALF) were collected 6 hours after the challenge of LPS. The histopathology scores, wet-to-dry weight ratios, protein content, and cytokine levels in BALF were assessed. RESULTS The acetate treatment resulted in improved lung pathological score, alleviated LPS-induced microvascular permeability, and suppressed the production of reactive oxygen species. Furthermore, acetate decreased the level of pro-inflammatory cytokines and chemokines in the lungs and BALF, consistent with the declined immune cell counting found in BALF. In addition, phosphorylation levels of mitogen-activated protein kinase (MAPK) pathway in lung tissues were downregulated by acetate. CONCLUSIONS These results suggested that acetate exerts its protective effects via anti-inflammatory and anti-oxidant activities on LPS-induced ALI.

Transplantation of Endothelial Progenitor Cells Attenuates Lipopolysaccharide-Induced Lung Injury via Inhibiting the Inflammatory Secretion of Neutrophils in Rats

BACKGROUND

Endothelial progenitor cells (EPCs) are special types of stem cells and are a potential novel therapeutic approach in acute lung injury (ALI). Transplantation of EPCs can ameliorate the inflammatory state by reducing adhesion and exudation of inflammatory cells. However, the mechanism underlying the effect of EPCs on inflammatory response modulation remains unclear. The aim of the present study was to investigate the effect of EPCs on the modulation of neutrophils in vitro and in vivo.

MATERIALS AND METHODS

EPCs were cocultured with neutrophils after lipopolysaccharide stimulation in vitro or transplanted into ALI rats, and neutrophil inflammatory mediators including tumor necrosis factor-α, interleukin-1β, neutrophil elastase, myeloperoxidase and matrix metalloproteinases-9 were detected by enzyme-linked immunosorbent assay, an myeloperoxidase detection kits, reverse transcription-polymerase chain reaction and western blotting.

RESULTS

The results showed that EPCs significantly downregulated the expression of inflammatory mediators when cocultured with neutrophils in vitro or in vivo.

CONCLUSIONS

These findings demonstrated that EPCs contributed to lung injury in ALI rats by downregulating neutrophil inflammatory mediators.

Interleukin-18 binding protein attenuates lipopolysaccharide-induced acute lung injury in mice via suppression NF-κB and activation Nrf2 pathway

Interleukin (IL)-18 belongs to a rather large IL-1 gene family and is a proinflammatory cytokine. IL-18 plays important roles in lung injury. IL-18 binding protein (IL-18BP), a natural antagonist of IL-18, binds IL-18 with high affinity. IL-18BP is able to neutralize IL-18 biological activity and has a protective effect against renal fibrosis. The aim of this study was to evaluate the potential protective effect of IL-18BP on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice and to illuminate the underlying mechanisms. Results indicated that pretreatment with IL-18BP significantly attenuated LPS-induced pulmonary pathological injury. Meanwhile, IL-18BP pretreatment markedly inhibited infiltration of inflammatory cell and release of inflammatory factor in ALI mice in vivo and in primary macrophages after LPS insult in vitro. IL-18BP treatment dramatically reduced oxidative stress through increasing superoxide dismutase (SOD) and glutathione (GSH) contents, and decreasing the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) in LPS-induced ALI mice and primary macrophages. Additionally, IL-18BP was also observed to markedly decreased the activation of nuclear factor-kappa B (NF-κB) and upregulated the nuclear factor erythroid 2-related factor 2 (Nrf2). Taken together, IL-18BP possessed protective effect against LPS-induced ALI, which might be associated with its regulation of NF-κB and Nrf2 activities. The results rendered IL-18BP worthy of further development into a pharmaceutical drug for the treatment of ALI.

Childhood asthma clusters reveal neutrophil-predominant phenotype with distinct gene expression

BACKGROUND

Childhood asthma comprises different phenotypes with complex pathophysiology. Different asthma phenotypes evoke various clinical symptoms and vary in their responses to treatments.

METHODS

We applied k-means clustering algorithm of twelve objective laboratory tests among 351 asthmatic children enrolled in the Taiwanese Consortium of Childhood Asthma Study (TCCAS). We constructed gene expression profiles of peripheral blood mononuclear cells (PBMC) from children with different asthma phenotypes.

RESULTS

Five distinct phenotypes of childhood asthma were identified and can be characterized by either eosinophil-predominant or neutrophil-predominant inflammatory characteristics. In the gene expression profile analysis, significant differences were noted for neutrophil-predominant asthma, compared with samples from all the other asthma phenotypes. The vast majority of the differentially expressed genes in neutrophil-predominant asthma was associated with corticosteroid response. From an independent inhaled corticosteroid (ICS) response cohort, we also found neutrophils could be activated in this severe asthma phenotype and neutrophil-predominant asthma may be associated with corticosteroid nonresponsiveness.

CONCLUSION

Phenotype clustering of childhood asthma can be helpful to identify clinically relevant patients and reveal different inflammatory characteristics in asthmatic children. Neutrophil-predominant asthma is the most severe asthma phenotype with poor corticosteroid response. Gene expression profile of different asthma phenotypes not only improve our knowledge of childhood asthma, but also can guide asthma precision medicine.

Myeloperoxidase: Its role for host defense, inflammation, and neutrophil function

Myeloperoxidase (MPO) is a heme-containing peroxidase expressed mainly in neutrophils and to a lesser degree in monocytes. In the presence of hydrogen peroxide and halides, MPO catalyzes the formation of reactive oxygen intermediates, including hypochlorous acid (HOCl). The MPO/HOCl system plays an important role in microbial killing by neutrophils. In addition, MPO has been demonstrated to be a local mediator of tissue damage and the resulting inflammation in various inflammatory diseases. These findings have implicated MPO as an important therapeutic target in the treatment of inflammatory conditions. In contrast to its injurious effects at sites of inflammation, recent studies using animal models of various inflammatory diseases have demonstrated that MPO deficiency results in the exaggeration of inflammatory response, and that it affects neutrophil functions including cytokine production. Given these diverse effects, a growing interest has emerged in the role of this well-studied enzyme in health and disease.

Leukoreduction of packed red blood cells attenuates proinflammatory properties of storage-derived microvesicles

BACKGROUND

Leukoreduction prior to packed red blood cell (pRBC) storage is not a universally accepted practice. Our laboratory has previously shown that microvesicles (MVs) accumulate in pRBC units during storage and play an important role in lung injury after resuscitation. Currently, the effect of leukoreduction on MV formation in stored pRBC units is unknown. In the present study, we investigated the hypothesis that leukoreduction of pRBC units prior to storage would attenuate the production of MVs and decrease pulmonary inflammation after hemorrhage and resuscitation.

METHODS

Leukoreduced and nonleukoreduced pRBC units were prepared from human donors and C57/Bl6 mice and stored for up to 42 d and 14 d, respectively. At intervals during storage, MVs were isolated from pRBC units, quantified and characterized based on size, morphology, and levels of proinflammatory cytokines. In additional experiments, mice underwent controlled hemorrhage followed by resuscitation with normal saline (NS) with or without equal numbers of MVs isolated from leukoreduced or nonleukoreduced stored mouse pRBC. Histologic lung sections were evaluated for the presence of tissue edema and inflammatory cells.

RESULTS

For both human and mouse pRBCs, the number of MVs significantly increased throughout the storage period. There were significantly fewer MVs present in leukoreduced units. The average MV size significantly increased over time and was similar between groups. Levels of interleukin 1α (IL-1α), regulated on activation, normal T cell expressed and secreted (RANTES), and macrophage-derived chemokine (MDC) were lower in MVs from leukoreduced pRBC units as compared with MVs from nonleukoreduced units. Hemorrhaged mice resuscitated with NS with the addition of MV from leukoreduced pRBC demonstrated significantly less pulmonary edema and inflammatory cell recruitment as compared to those resuscitated with NS with the addition of MV from nonleukoreduced pRBC.

CONCLUSIONS

Prestorage leukoreduction of pRBC units reduces the formation and proinflammatory properties of MV, which in turn decreases lung injury secondary to MV from stored pRBC units after hemorrhage and resuscitation.

Myeloperoxidase targets oxidative host attacks to Salmonella and prevents collateral tissue damage

Host control of infections crucially depends on the capability to kill pathogens with reactive oxygen species (ROS). However, these toxic molecules can also readily damage host components and cause severe immunopathology. Here, we show that neutrophils use their most abundant granule protein, myeloperoxidase, to target ROS specifically to pathogens while minimizing collateral tissue damage. A computational model predicted that myeloperoxidase efficiently scavenges diffusible H₂O₂ at the surface of phagosomal Salmonella and converts it into highly reactive HOCl (bleach), which rapidly damages biomolecules within a radius of less than 0.1 μm. Myeloperoxidase-deficient neutrophils were predicted to accumulate large quantities of H₂O₂ that still effectively kill Salmonella, but most H₂O₂ would leak from the phagosome. Salmonella stimulation of neutrophils from normal and myeloperoxidase-deficient human donors experimentally confirmed an inverse relationship between myeloperoxidase activity and extracellular H₂O₂ release. Myeloperoxidase-deficient mice infected with Salmonella had elevated hydrogen peroxide tissue levels and exacerbated oxidative damage of host lipids and DNA, despite almost normal Salmonella control. These data show that myeloperoxidase has a major function in mitigating collateral tissue damage during antimicrobial oxidative bursts, by converting diffusible long-lived H₂O₂ into highly reactive, microbicidal and locally confined HOCl at pathogen surfaces.

Blocking triggering receptor expressed on myeloid cells-1 attenuates lipopolysaccharide-induced acute lung injury via inhibiting NLRP3 inflammasome activation

Acute lung injury (ALI) is associated with high mortality and uncontrolled inflammation plays a critical role in ALI. TREM-1 is an amplifier of inflammatory response, and is involved in the pathogenesis of many infectious diseases. NLRP3 inflammasome is a member of NLRs family that contributes to ALI. However, the effect of TREM-1 on NLRP3 inflammasome and ALI is still unknown. This study aimed to determine the effect of TREM-1 modulation on LPS-induced ALI and activation of the NLRP3 inflammasome. We showed that LR12, a TREM-1 antagonist peptide, significantly improved survival of mice after lethal doses of LPS. LR12 also attenuated inflammation and lung tissue damage by reducing histopathologic changes, infiltration of the macrophage and neutrophil into the lung, and production of the pro-inflammatory cytokine, and oxidative stress. LR12 decreased expression of the NLRP3, pro-caspase-1 and pro-IL-1β, and inhibited priming of the NLRP3 inflammasome by inhibiting NF-κB. LR12 also reduced the expression of NLRP3 and caspase-1 p10 protein, and secretion of the IL-1β, inhibited activation of the NLRP3 inflammasome by decreasing ROS. For the first time, these data show that TREM-1 aggravates inflammation in ALI by activating NLRP3 inflammasome, and blocking TREM-1 may be a potential therapeutic approach for ALI.