Functionally important role for arginase 1 in the airway hyperresponsiveness of asthma

Biochemistry, pharmacology, and in vivo function of arginases

The enzyme arginase catalyzes the hydrolysis of l-arginine into l-ornithine and urea. The 2 existing isoforms Arg1 and Arg2 exhibit different cellular localizations and metabolic functions. Arginase activity is crucial for nitrogen detoxification in the urea cycle, synthesis of polyamines, and control of l-arginine bioavailability and nitric oxide (NO) production. Despite significant progress in the understanding of the biochemistry and function of arginases, several open questions remain. Recent studies have revealed that the regulation and function of Arg1 and Arg2 are cell type-specific, species-specific, and profoundly different in mice and humans. The main differences are in the distribution and function of Arg1 and Arg2 in immune and erythroid cells. Contrary to what was previously thought, Arg1 activity appears to be only partially related to vascular NO signaling under homeostatic conditions in the vascular wall, but its expression is increased under disease conditions and may be targeted by treatment with arginase inhibitors. Arg2 appears to be mainly a catabolic enzyme involved in the synthesis of l-ornithine, polyamine, and l-proline but may play a putative role in blood pressure control, at least in mice. The immunosuppressive role of arginase-mediated arginine depletion is a promising target for cancer treatment. This review critically revises and discusses the biochemistry, pharmacology, and in vivo function of arginases, focusing on the insights gained from the analysis of cell-specific Arg1 and Arg2 knockout mice and human studies using arginase inhibitors or pegylated recombinant arginase. SIGNIFICANCE STATEMENT: Further basic and translational research is needed to deepen our understanding of the regulation of Arg1 and Arg2 in different cell types in consideration of their localization, species-specificity, and multiple biochemical and physiological roles. This will lead to better pharmacological strategies to target arginase activity in liver, cardiovascular, hematological, immune/infectious diseases, and cancer.

Comprehensive time-course gene expression evaluation of high-risk beef cattle to establish immunological characteristics associated with undifferentiated bovine respiratory disease

Bovine respiratory disease (BRD) remains the leading infectious disease in beef cattle production systems. Host gene expression upon facility arrival may indicate risk of BRD development and severity. However, a time-course approach would better define how BRD development influences immunological and inflammatory responses after disease occurrences. Here, we evaluated whole blood transcriptomes of high-risk beef cattle at three time points to elucidate BRD-associated host response. Sequenced jugular whole blood mRNA from 36 cattle (2015: n = 9; 2017: n = 27) across three time points (n = 100 samples; days [D]0, D28, and D63) were processed through ARS-UCD1.2 reference-guided assembly (HISAT2/Stringtie2). Samples were categorized into BRD-severity cohorts (Healthy, n = 14; Treated 1, n = 11; Treated 2+, n = 11) via frequency of antimicrobial clinical treatment. Assessment of gene expression patterns over time within each BRD cohort was modeled through an autoregressive hidden Markov model (EBSeq-HMM; posterior probability ≥ 0.5, FDR < 0.01). Mixed-effects negative binomial models (glmmSeq; FDR < 0.05) and edgeR (FDR < 0.10) identified differentially expressed genes between and across cohorts overtime. A total of 2,580, 2,216, and 2,381 genes were dynamically expressed across time in Healthy, Treated 1, and Treated 2+ cattle, respectively. Genes involved in the production of specialized resolving mediators (SPMs) decreased at D28 and then increased by D63 across all three cohorts. Accordingly, SPM production and alternative complement were differentially expressed between Healthy and Treated 2+ at D0, but not statistically different between the three groups by D63. Magnitude, but not directionality, of gene expression related to SPM production, alternative complement, and innate immune response signified Healthy and Treated 2+ cattle. Differences in gene expression at D63 across the three groups were related to oxygen binding and carrier activity, natural killer cell-mediated cytotoxicity, cathelicidin production, and neutrophil degranulation, possibly indicating prolonged airway pathology and inflammation weeks after clinical treatment for BRD. These findings indicate genomic mechanisms indicative of BRD development and severity over time.

Serotonin-2 Receptor Agonists Produce Anti-inflammatory Effects through Functionally Selective Mechanisms That Involve the Suppression of Disease-Induced Arginase 1 Expression

Functional selectivity in the context of serotonin 2A (5-HT2A) receptor agonists is often described as differences psychedelic compounds have in the activation of Gq vs β-arrestin signaling in the brain and how that may relate to inducing psychoactive and hallucinatory properties with respect to each other. However, the presence of 5-HT2A receptors throughout the body in several cell types, including endothelial, endocrine, and immune-related tissues, suggests that functional selectivity may exist in the periphery as well. Here, we examine functional selectivity between two 5-HT2A receptor agonists of the phenylalkylamine class: (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] and (R)-2,5-dimethoxy-4-trifluoromethylamphetamine [(R)-DOTFM]. Despite comparable in vitro activity at the 5-HT2A receptor as well as similar behavioral potency, (R)-DOTFM does not exhibit an ability to prevent inflammation or elevated airway hyperresponsiveness (AHR) in an acute murine ovalbumin-induced asthma model as does (R)-DOI. Furthermore, there are distinct differences between protein expression and inflammatory-related gene expression in pulmonary tissues between the two compounds. Using (R)-DOI and (R)-DOTFM as tools, we further elucidated the anti-inflammatory mechanisms underlying the powerful anti-inflammatory effects of certain psychedelics and identified key mechanistic components of the anti-inflammatory effects of psychedelics, including suppression of arginase 1 expression.

NOTCH4 potentiates the IL-13 induced genetic program in M2 alternative macrophages through the AP1 and IRF4-JMJD3 axis

IL-13 signaling polarizes macrophages to an M2 alternatively activated phenotype, which regulates tissue repair and anti-inflammatory responses. However, an excessive activation of this pathway leads to severe pathologies, such as allergic airway inflammation and asthma. In this work, we identified NOTCH4 receptor as an important modulator of M2 macrophage activation. We show that the expression of NOTCH4 is induced by IL-13, mediated by Janus kinases and AP1 activity, probably mediated by the IL-13Rα1 and IL-13Rα2 signaling pathway. Furthermore, we demonstrate an important role for NOTCH4 signaling in the IL-13 induced gene expression program in macrophages, including various genes that contribute to pathogenesis of the airways in asthma, such as ARG1, YM1, CCL24, IL-10, or CD-163. We also demonstrate that NOTCH4 signaling modulates IL-13-induced gene expression by increasing IRF4 activity, mediated, at least in part, by the expression of the histone H3K27me3 demethylase JMJD3, and by increasing AP1-dependent transcription. In summary, our results provide evidence for an important role of NOTCH4 signaling in alternative activation of macrophages by IL-13 and suggest that NOTCH4 may contribute to the increased severity of lesions in M2 inflammatory responses, such as allergic asthma, which points to NOTCH4 as a potential new target for the treatment of these pathologies.

Regulated Arginine Metabolism in Immunopathogenesis of a Wide Range of Diseases: Is There a Way to Pass between Scylla and Charybdis?

More than a century has passed since arginine was discovered, but the metabolism of the amino acid never ceases to amaze researchers. Being a conditionally essential amino acid, arginine performs many important homeostatic functions in the body; it is involved in the regulation of the cardiovascular system and regeneration processes. In recent years, more and more facts have been accumulating that demonstrate a close relationship between arginine metabolic pathways and immune responses. This opens new opportunities for the development of original ways to treat diseases associated with suppressed or increased activity of the immune system. In this review, we analyze the literature describing the role of arginine metabolism in the immunopathogenesis of a wide range of diseases, and discuss arginine-dependent processes as a possible target for therapeutic approaches.

Metabolomics in pediatric lower respiratory tract infections and sepsis: a literature review

Lower respiratory tract infections (LRTIs) are a leading cause of morbidity and mortality in children. The ability of healthcare providers to diagnose and prognose LRTIs in the pediatric population remains a challenge, as children can present with similar clinical features regardless of the underlying pathogen or ultimate severity. Metabolomics, the large-scale analysis of metabolites and metabolic pathways offers new tools and insights that may aid in diagnosing and predicting the outcomes of LRTIs in children. This review highlights the latest literature on the clinical utility of metabolomics in providing care for children with bronchiolitis, pneumonia, COVID-19, and sepsis. IMPACT: This article summarizes current metabolomics approaches to diagnosing and predicting the course of pediatric lower respiratory infections. This article highlights the limitations to current metabolomics research and highlights future directions for the field.

Differences in L-arginine metabolism and asthma morbidity among asthma patients with and without obstructive sleep apnea

BACKGROUND

Imbalance in L-arginine and nitric oxide (NO) metabolism has been implicated in the pathophysiology of asthma and obstructive sleep apnea (OSA), and both diseases impact the other's morbidity. We sought to determine whether L-arginine/NO metabolism differs between adults with asthma with or without comorbid OSA, and its association with asthma morbidity.

METHODS

This is a cross-sectional study of 322 adults with asthma recruited in Denver, CO and New York City, NY. Data were collected on OSA status, spirometry, and metrics of asthma control and morbidity. L-Arginine metabolites were quantified in patient serum. Bivariate analyses and multiple regression were performed to determine differences between L-arginine metabolism, OSA and association with asthma morbidity.

RESULTS

Among the 322 participants, 92 (28.5%) had OSA. The cohort was 81.6% female, 23.4% identified as Black and 30.6% as Latino. Patients with asthma and OSA had significantly higher serum concentrations of NO synthase inhibitor asymmetric dimethylarginine (ADMA) (p-value = 0.019), lower L-arginine to ornithine ratios (p-value = 0.003), and increased ornithine (p-value = 0.001) and proline levels (p-value < 0.001) compared to those without OSA. In adjusted models, OSA was associated with worse asthma control, adjusted mean difference in asthma control questionnaire of 0.36 (95% confidence interval [CI]: 0.06 to 0.65), and asthma quality of life questionnaire, adjusted mean difference: - 0.53 (95% CI: - 0.85 to - 0.21), after adjusting for relevant covariates including body mass index and L-arginine metabolites.

CONCLUSIONS

Adults with asthma and OSA had increased ADMA, an inhibitor of nitric oxide synthase, and greater metabolism of L-arginine via the arginase pathway compared to those with asthma alone, indicating a possible shared pathophysiological mechanism of these diseases.

Peanut allergen induces more serious allergic reactions than other allergens involving MAPK signaling pathways

There is no universally accepted uniform research to classify the severity of allergic reactions triggered by different food allergens. We established a food allergy model based on repeated intragastric administrations of proteins from peanut, egg, milk, or soybean mixed with cholera toxin followed by oral food challenges with a high dose of the sensitizing proteins. Increased specific IgE, specific IgG1, allergic symptom scores, histamine, murine mast cell proteases-1, vascular leakage, Th2 cytokines, and mast cell infiltration in the lungs and intestine were found in the allergic groups via enzyme-linked immunosorbent assay, hematoxylin-eosin, and toluidine blue staining. Each sensitized group showed a decrease in body temperature and Th1 cytokines after oral food challenge. The increased levels of Th2 cytokines, IL-25, IL-33, and TSLP, and related asthma genes ARG1, DCN, LTB4R1 and NFKBIA as well as the activation of MAPK signaling pathways were also revealed by quantitative real-time PCR and western blotting. In terms of the severity of food allergies, peanut allergy was the most serious followed by egg and milk, and soybean allergy was the least severe. Compared to other allergic groups, asthma genes were regulated through the MAPK signaling pathways to produce related Th2 cytokines in peanut allergy; consequently, mice in the peanut group exhibited more severe allergic reactions. Comparison of the severity of food allergies is required for the development of milder prevention for severe food allergies.

An IL-9-pulmonary macrophage axis defines the allergic lung inflammatory environment

Despite IL-9 functioning as a pleiotropic cytokine in mucosal environments, the IL-9-responsive cell repertoire is still not well defined. Here, we found that IL-9 mediates proallergic activities in the lungs by targeting lung macrophages. IL-9 inhibits alveolar macrophage expansion and promotes recruitment of monocytes that develop into CD11c+ and CD11c- interstitial macrophage populations. Interstitial macrophages were required for IL-9-dependent allergic responses. Mechanistically, IL-9 affected the function of lung macrophages by inducing Arg1 activity. Compared with Arg1-deficient lung macrophages, Arg1-expressing macrophages expressed greater amounts of CCL5. Adoptive transfer of Arg1+ lung macrophages but not Arg1- lung macrophages promoted allergic inflammation that Il9r-/- mice were protected against. In parallel, the elevated expression of IL-9, IL-9R, Arg1, and CCL5 was correlated with disease in patients with asthma. Thus, our study uncovers an IL-9/macrophage/Arg1 axis as a potential therapeutic target for allergic airway inflammation.

Dysregulated Arginine Metabolism in Young Patients with Chronic Persistent Asthma and in Human Bronchial Epithelial Cells

Background: Recent metabolomics studies have found circulatory metabolism alterations in patients with asthma, indicating that altered metabolites played a significant role in asthma. However, the regulatory mechanisms in asthma, especially in young chronic persistent asthma remain underexplored. Methods: In this study, a prospective cohort of 162 patients diagnosed of asthma admitted to the First Affiliated Hospital of Xi’an Jiaotong University from January 2018 to December 2019 was used to perform a nested case-control study. Among them, we included 30 patients with chronic persistent asthma between 20 to 35 years old; 30 health control with evenly distributed age and sex were then recruited. Nontargeted metabolomics was applied to identify serum metabolic profiles and altered metabolic pathways. Results: In vitro, human bronchial epithelial cells (HBECs) line BEAS-2B with the addition of L-citrulline and/or asymmetric dimethylarginine (ADMA) model was utilized and the concentrations of nitric oxide (NO) metabolites were tested to evaluate the therapeutic potential of L-citrulline. The young patients with chronic persistent asthma displayed dysregulated serum metabolic profiles, especially enriched in arginine metabolism. The ratio of L-citrulline to ornithine is associated with blood eosinophil count. In vitro, adding L-citrulline could reverse ADMA-mediated reduction of NOx at lower L-arginine concentration (25 μM), but was ineffective in the higher L-arginine concentration (100 μM) media. Conclusions: The arginine metabolism balance is of vital importance during the pathogenesis and progression of chronic asthma. L-citrulline could be a powerful approach to restore airway NO production, potentially exhibiting therapeutic benefits among young patients with chronic asthma.

Mesenchymal stromal cell apoptosis is required for their therapeutic function

Multipotent mesenchymal stromal cells (MSCs) ameliorate a wide range of diseases in preclinical models, but the lack of clarity around their mechanisms of action has impeded their clinical utility. The therapeutic effects of MSCs are often attributed to bioactive molecules secreted by viable MSCs. However, we found that MSCs underwent apoptosis in the lung after intravenous administration, even in the absence of host cytotoxic or alloreactive cells. Deletion of the apoptotic effectors BAK and BAX prevented MSC death and attenuated their immunosuppressive effects in disease models used to define MSC potency. Mechanistically, apoptosis of MSCs and their efferocytosis induced changes in metabolic and inflammatory pathways in alveolar macrophages to effect immunosuppression and reduce disease severity. Our data reveal a mode of action whereby the host response to dying MSCs is key to their therapeutic effects; findings that have broad implications for the effective translation of cell-based therapies.

Mesenchymal stromal cells (MSCs) demonstrate therapeutic benefits in multiple diseases, but the mechanisms remain unclear as infused MSCs do not persist in the body. Here, the authors show that MSC apoptosis is an important mechanistic element, as MSCs rendered genetically incapable of apoptosis lose their ability to ameliorate disease.

Pediatric Obesity-Related Asthma: The Role of Nutrition and Nutrients in Prevention and Treatment

Childhood obesity rates have dramatically risen in numerous countries worldwide. Obesity is likely a factor in increased asthma risk, which is already one of the most widespread chronic respiratory pathologies. The pathogenic mechanism of asthma risk has still not yet been fully elucidated. Moreover, the role of obesity-related inflammation and pulmonary overreaction to environmental triggers, which ultimately result in asthma-like symptoms, and the importance of dietary characteristics is well recognized. Diet is an important adjustable element in the asthma development. Food-specific composition of the diet, in particular fat, sugar, and low-quality nutrients, is likely to promote the chronic inflammatory state seen in asthmatic patients with obesity. An unbalanced diet or supplementation as a way to control asthma more efficiently has been described. A personalized dietary intervention may improve respiratory symptoms and signs and therapeutic response. In this narrative review, we presented and discussed more recent literature on asthma associated with obesity among children, focusing on the risk of asthma among children with obesity, asthma as a result of obesity focusing on the role of adipose tissue as a mediator of systemic and local airway inflammation implicated in asthma regulation, and the impact of nutrition and nutrients in the development and treatment of asthma. Appropriate early nutritional intervention could possibly be critical in preventing and managing asthma associated with obesity among children.

Tranglutaminase 2 contributes to the asthmatic inflammation by modulating activation of alveolar macrophages

BACKGROUND

Transglutaminase 2 (TG2), a multifunctional calcium-dependent acyltransferase, is upregulated in asthmatic airways and reported to play a role in the pathogenesis of allergic asthma. However, the underlying mechanism is not fully understood.

OBJECTIVE

To investigate the role of TG2 in alternative activation of alveolar macrophages by using murine asthma model.

METHODS

TG2 expression was assessed in induced sputum of 21 asthma patients and 19 healthy controls, and lung tissue of ovalbumin (OVA)-induced murine asthma model. To evaluate the role of TG2 in asthma, we developed an OVA asthma model in both TG2 null and wild-type mice. The expression of M2 macrophage markers was measured by fluorescence-activated cell sorting (FACS) after OVA sensitization and challenge. To evaluate the effect of TG2 inhibition in vitro, interleukin 4 (IL-4) or IL-13-stimulated expression of M2 macrophage markers was measured in CRL-2456 cells in the presence and absence of a TG2 inhibitor.

RESULTS

The expression of both TG2 and M2 markers was increased in the sputum of asthmatics compared with that of healthy controls. The expression of TG2 was increased in macrophages of OVA mice. Airway hyperresponsiveness, and the number of inflammatory cells, including eosinophils, was significantly reduced in TG2 null mice compared with wild-type mice. Enhanced expression of M2 markers in OVA mice was normalized by TG2 knockout. IL-4 or IL-13-stimulated expression of M2 markers in alveolar macrophages was also attenuated by TG2 inhibitor treatment in vitro.

CONCLUSION

Our results suggest that TG2-mediated modulation of alveolar macrophage polarization plays important roles in the pathogenesis of asthma.

Arginine Therapy for Lung Diseases

Nitric oxide (NO) is produced by a family of isoenzymes, nitric oxide synthases (NOSs), which all utilize L-arginine as substrate. The production of NO in the lung and airways can play a number of roles during lung development, regulates airway and vascular smooth muscle tone, and is involved in inflammatory processes and host defense. Altered L-arginine/NO homeostasis, due to the accumulation of endogenous NOS inhibitors and competition for substrate with the arginase enzymes, has been found to play a role in various conditions affecting the lung and in pulmonary diseases, such as asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), pulmonary hypertension, and bronchopulmonary dysplasia. Different therapeutic strategies to increase L-arginine levels or bioavailability are currently being explored in pre-clinical and clinical studies. These include supplementation of L-arginine or L-citrulline and inhibition of arginase.

Mini review: Neural mechanisms underlying airway hyperresponsiveness

Neural changes underly hyperresponsiveness in asthma and other airway diseases. Afferent sensory nerves, nerves within the brainstem, and efferent parasympathetic nerves all contribute to airway hyperresponsiveness. Inflammation plays a critical role in these nerve changes. Chronic inflammation and pre-natal exposures lead to increased airway innervation and structural changes. Acute inflammation leads to shifts in neurotransmitter expression of afferent nerves and dysfunction of M₂ muscarinic receptors on efferent nerve endings. Eosinophils and macrophages drive these changes through release of inflammatory mediators. Novel tools, including optogenetics, two photon microscopy, and optical clearing and whole mount microscopy, allow for improved studies of the structure and function of airway nerves and airway hyperresponsiveness.

Oxidative stress and obesity-related asthma

Obesity is an asthma comorbidity associated with poor control, increased exacerbation risk and reduced response to inhaled and systemic corticosteroids. It affects children and adults differentially. In those with early onset asthma, it associated with increased eosinophilic inflammation, whereas in late onset, it correlates with lower nitric oxide (NO) and predominantly non-T2 inflammation. There are probably multiple pathways by which obesity impacts asthma; airway and systemic oxidative stress has been proposed as a mechanism that could potentially explain the obesity mediated increased comorbidity and poor response to treatment. More likely than not, oxidative stress is an epiphenomenon of a very diverse set of processes driven by complex changes in airway and systemic metabolism. This article provides a comprehensive overview of the clinical, metabolic, pathophysiological and therapeutic aspects of oxidative stress in patients with obesity and asthma.

Early-pregnancy transcriptome signatures of preeclampsia: from peripheral blood to placenta

Several studies have linked maternal asthma, excess BMI, and low vitamin D status with increased risk of Preeclampsia (PE) development. Given prior evidence in the literature and our observations from the subjects in the Vitamin D Antenatal Asthma Reduction Trial (VDAART), we hypothesized that PE, maternal asthma, vitamin D insufficiency, and excess body mass index (BMI) might share both peripheral blood and placental gene signatures that link these conditions together. We used samples collected in the VDAART to investigate relationships between these four conditions and gene expression patterns in peripheral blood obtained at early pregnancy. We identified a core set of differentially expressed genes in all comparisons between women with and without these four conditions and confirmed them in two separate sets of samples. We confirmed the differential expression of the shared gene signatures in the placenta from an independent study of preeclampsia cases and controls and constructed the preeclampsia module using protein-protein interaction networks. CXC chemokine genes showed the highest degrees of connectivity and betweenness centrality in the peripheral blood and placental modules. The shared gene signatures demonstrate the biological pathways involved in preeclampsia at the pre-clinical stage and may be used for the prediction of preeclampsia.

Leonurus sibiricus root extracts decrease airway remodeling markers expression in fibroblasts

Bronchial asthma is believed to be provoked by the interaction between airway inflammation and remodeling. Airway remodeling is a complex and poorly understood process, and controlling it appears key for halting the progression of asthma and other obstructive lung diseases. Plants synthesize a number of valuable compounds as constitutive products and as secondary metabolites, many of which have curative properties. The aim of this study was to evaluate the anti-remodeling properties of extracts from transformed and transgenic Leonurus sibiricus roots with transformed L. sibiricus roots extract with transcriptional factor AtPAP1 overexpression (AtPAP1). Two fibroblast cell lines, Wistar Institute-38 (WI-38) and human fetal lung fibroblast (HFL1), were incubated with extracts from transformed L. sibiricus roots (TR) and roots with transcriptional factor AtPAP1 over-expression (AtPAP1 TR). Additionally, remodeling conditions were induced in the cultures with rhinovirus 16 (HRV16). The expressions of metalloproteinase 9 (MMP)-9, tissue inhibitor of metalloproteinases 1 (TIMP-1), arginase I and transforming growth factor (TGF)-β were determined by quantitative polymerase chain reaction (qPCR) and immunoblotting methods. AtPAP1 TR decreased arginase I and MMP-9 expression with no effect on TIMP-1 or TGF-β mRNA expression. This extract also inhibited HRV16-induced expression of arginase I, MMP-9 and TGF-β in both cell lines (P < 0·05) Our study shows for the first time to our knowledge, that transformed AtPAP1 TR extract from L. sibiricus root may affect the remodeling process. Its effect can be attributed an increased amount of phenolic acids such as: chlorogenic acid, caffeic acid or ferulic acid and demonstrates the value of biotechnology in medicinal research.

Pharmacological Screening Identifies SHK242 and SHK277 as Novel Arginase Inhibitors with Efficacy against Allergen-Induced Airway Narrowing In Vitro and In Vivo

Arginase is a potential target for asthma treatment. However, there are currently no arginase inhibitors available for clinical use. Here, a novel class of arginase inhibitors was synthesized, and their efficacy was pharmacologically evaluated. The reference compound 2(S)-amino-6-boronohexanoic acid (ABH) and >200 novel arginase inhibitors were tested for their ability to inhibit recombinant human arginase 1 and 2 in vitro. The most promising compounds were separated as enantiomers. Enantiomer pairs SHK242 and SHK243, and SHK277 and SHK278 were tested for functional efficacy by measuring their effect on allergen-induced airway narrowing in lung slices of ovalbumin-sensitized guinea pigs ex vivo. A guinea pig model of acute allergic asthma was used to examine the effect of the most efficacious enantiopure arginase inhibitors on allergen-induced airway hyper-responsiveness (AHR), early and late asthmatic reactions (EAR and LAR), and airway inflammation in vivo. The novel compounds were efficacious in inhibiting arginase 1 and 2 in vitro. The enantiopure SHK242 and SHK277 fully inhibited arginase activity, with IC50 values of 3.4 and 10.5 μM for arginase 1 and 2.9 and 4.0 µM for arginase 2, respectively. Treatment of slices with ABH or novel compounds resulted in decreased ovalbumin-induced airway narrowing compared with control, explained by increased local nitric oxide production in the airway. In vivo, ABH, SHK242, and SHK277 protected against allergen-induced EAR and LAR but not against AHR or lung inflammation. We have identified promising novel arginase inhibitors for the potential treatment of allergic asthma that were able to protect against allergen-induced early and late asthmatic reactions. SIGNIFICANCE STATEMENT: Arginase is a potential drug target for asthma treatment, but currently there are no arginase inhibitors available for clinical use. We have identified promising novel arginase inhibitors for the potential treatment of allergic asthma that were able to protect against allergen-induced early and late asthmatic reactions. Our new inhibitors show protective effects in reducing airway narrowing in response to allergens and reductions in the early and late asthmatic response.

Correlation between oxidative stress and NF-κB signaling pathway in the obesity-asthma mice

In this study, a mice model of obesity-asthma was established. We investigated the correlation between oxidative stress and NF-κB signaling pathway in the lung tissues, together with the effects of acetylcysteine. The animals were fed on a high-fat diet, and then ovalbumin (OVA) sensitization was utilized to establish the obesity-asthma model. N-acetylcysteine was used to treat asthma, animals treated with budesonide served as control. The malondialdehyde (MDA) in the lung tissues was determined, together with the activity of glutathione (GSH). EMAS assay was utilized to measure the nuclear factor-κB-P65 (NF-κB-P65) in lung tissues. Western blot analysis was performed to determine the expression of inhibitor kappa B-α (IκB-α) and inhibitor kappa B kinase-β (IKK-β). The MDA in the asthma groups showed significantly elevation (P < 0.01), and the GSH showed significant decrease (P < 0.01), especially in the obesity-asthma group. The efficiency of N-acetylcysteine was superior to that of the budesonide in the decline of MDA and elevation of GSH (P < 0.01). In both asthma groups, the expression of IKK-β and transcription of NF-κB-P65 in the lung tissues showed significant elevation (P < 0.01), and IκB-α showed significant decline (P < 0.01), especially in the obesity-asthma group. There was decline of IKK-β and NF-κB-P65 and elevation of IκB-α in the N-acetylcysteine group, which was even significantly in the Budesonide group (P < 0.01). There was a positive correlation between MDA and NF-κB activation in the lung tissues in all the asthma groups and treatment groups (P < 0.05). Obesity-asthma mice showed higher oxidative stress and activation of NF-κB compared with that of the asthma mice. There was a positive correlation between MDA and NF-κB activation in the lung tissues in the asthma groups. N-acetylcysteine was more effective in reducing the oxidative stress compared to the budesonide.

Increased Arginase Expression and Decreased Nitric Oxide in Pig Donor Lungs after Normothermic Ex Vivo Lung Perfusion

An established pig lung transplantation model was used to study the effects of cold ischemia time, normothermic acellular ex vivo lung perfusion (EVLP) and reperfusion after lung transplantation on l-arginine/NO metabolism in lung tissue. Lung tissue homogenates were analyzed for NO metabolite (NOx) concentrations by chemiluminescent NO-analyzer technique, and l-arginine, l-ornithine, l-citrulline and asymmetric dimethylarginine (ADMA) quantified using liquid chromatography-mass spectrometry (LC-MS/MS). The expression of arginase and nitric oxide synthase (NOS) isoforms in lung was measured by real-time polymerase chain reaction. EVLP preservation resulted in a significant decrease in concentrations of NOx and l-citrulline, both products of NOS, at the end of EVLP and after reperfusion following transplantation, compared to control, respectively. The ratio of l-ornithine over l-citrulline, a marker of the balance between l-arginine metabolizing enzymes, was increased in the EVLP group prior to reperfusion. The expression of both arginase isoforms was increased from baseline 1 h post reperfusion in EVLP but not in the no-EVLP group. These data suggest that EVLP results in a shift of the l-arginine balance towards arginase, leading to NO deficiency in the lung. The arginase/NOS balance may, therefore, represent a therapeutic target to improve lung quality during EVLP and, subsequently, transplant outcomes.

Tobacco smoking aggravates airway inflammation by upregulating endothelin-2 and activating the c-Jun amino terminal kinase pathway in asthma

BACKGROUND

Asthma is closely associated with tobacco smoking (TS) and is more difficult to effectively treat after exposure to TS.

OBJECTIVE

To observe the effects of TS on the expression of endothelin-2 (ET-2) and airway inflammation in asthmatic rats and to explore the related mechanisms.

METHODS

We established an animal model of asthma with ovalbumin (OVA)/Al(OH)₃ and subjected different animal groups to TS and/or dexamethasone/bosentan. The differences in the inflammatory cell infiltration, the pathological changes to the bronchial wall and the bronchial smooth muscle thickness, and the expression of ET-2, c-Jun amino terminal kinase (JNK1/2), malondialdehyde (MDA), and glutathione peroxidase (GSH) in the lung tissue and of interleukin (IL)-7 in bronchoalveolar lavage fluid (BALF) were assessed.

RESULTS

Exposure to TS or OVA caused an obvious increase in the inflammatory cells in the BALF over what was observed in the control group. In asthma models, the expression of ET-1, JNK1/2, MDA, and GSH in the lung tissues, as well as that of IL-17 in the BALF, was increased. After treatment with dexamethasone/bosentan, the expression of IL-17, JNK1/2, MDA, and GSH decreased compared to the smoking group; airway inflammation and the staining intensity in the lung tissue were also reduced.

CONCLUSION

TS exposure can clearly exacerbate airway inflammation in asthmatic rats, while bosentan can alleviate airway inflammation through regulation of the ET-2/JNK1/2 signalling pathway.

Effects of epigallocatechin-3-gallate on the HMGB1/RAGE pathway in PM2.5-exposed asthmatic rats

Current studies have shown that long-term exposure to fine particulate matter (PM_2.5) can aggravate lung injury in asthmatic children. The HMGB1/RAGE pathway may play an important role, but few studies on the HMGB1/RAGE signaling pathway in PM_2.5-induced asthma have been performed. Epigallocatechin-3-gallate (EGCG), which has antioxidant, anti-inflammatory and immunomodulatory effects, has not been examined in studies at home and abroad. In this study, we established an animal model of asthma and observed that the lung tissue was damaged, inflammatory cells infiltrated, bronchial wall thickness (WTt) and bronchial smooth muscle thickness (WTm) increased and the HMGB1 and RAGE mRNA and protein expression increased. The asthmatic rats exposed to PM_2.5 showed significantly increased lung injury and inflammatory cell infiltration, WTt and WTm further increased, and HMGB1 and RAGE mRNA and protein levels were higher than those in the asthma group. The asthmatic rats exposed to PM_2.5 were treated with EGCG, which alleviated the lung injury, reduced the number of inflammatory cells, decreased WTt and WTm, and reduced the expression of HMGB1 and RAGE mRNA and protein. The high-dose group showed more significant effects than the other groups. In conclusion, our results suggest that HMGB1 and RAGE are involved in the pathogenesis of asthma. PM_2.5 exposure significantly aggravated airway inflammation injury in asthmatic rats. EGCG can reduce lung injury and airway remodeling in PM_2.5-exposed asthmatic rats and has lung protective effects. The mechanism may be related to regulation of the HMGB1/RAGE signaling pathway. Our results may provide new ideas and methods for the prevention and treatment of PM_2.5-induced asthma.

Association of increased risk of asthma with elevated arginase & interleukin-13 levels in serum & rs2781666 G/T genotype of arginase I

Background & objectives

High expression of arginase gene and its elevated level in serum and bronchial lavage reported in animal models indicated an association with the pathogenesis of asthma. This study was undertaken to assess the serum arginase activity in symptomatic asthma patients and healthy controls and to correlate it with cytokine levels [interleukin (IL)-4 and IL-13] and arginase I (ARG1) gene polymorphism.

Methods

Asthma was confirmed by lung function test according to the GINA guidelines in patients attending Allergy and Pulmonology Clinic, Bhagwan Mahavir Hospital and Research Centre, Hyderabad, India, a tertiary care centre, during 2013-2015. Serum arginase was analyzed using a biochemical assay, total IgE and cytokine levels by enzyme-linked immunosorbent assay and genotyping of ARG1 for single-nucleotide polymorphisms (SNPs) rs2781666 and rs60389358 using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

Results

There was a significant two-fold elevation in the arginase activity in asthmatics as compared to healthy controls which correlated with disease severity. Non-atopic asthmatics showed elevated activity of arginase compared to atopics, indicating its possible role in intrinsic asthma. Levels of serum IL-13 and IL-4 were significantly high in asthma group which correlated with disease severity that was assessed by spirometry. A positive correlation was observed between arginase activity and IL-13 concentration. Genetic analysis of ARG1 SNPs revealed that rs2781666 G/T genotype, T allele and C-T haplotype (rs60389358 and rs2781666) were associated with susceptibility to asthma.

Interpretation & conclusions

This study indicated that high arginase activity and IL-13 concentration in the serum and ARG1 rs2781666 G/T genotype might increase the risk of asthma in susceptible population. Further studies need to be done with a large sample to confirm these findings.

A hispanolone-derived diterpenoid inhibits M2-Macrophage polarization in vitro via JAK/STAT and attenuates chitin induced inflammation in vivo

Macrophages are highly plastic cells that adopt different functional phenotypes in response to environmental signals. Classically activated macrophages (M1) exhibit a pro-inflammatory role, mediating host defense against microorganisms or tumor cells; whereas alternatively activated macrophages (M2) perform a range of physiological processes, including inflammation, wound repair and tissue remodeling. Interestingly, M2 macrophages have been involved in pathological settings such as tumor progression, parasitic infection and respiratory disorders. Consequently, the search of new agents able to control macrophage polarization is on the basis of new therapeutic strategies. In the present study, we have evaluated the effect of the hispanolone derivative 8,9-dehydrohispanolone-15,16-lactol (DHHL) on M2 macrophage polarization. Our results reveal that DHHL significantly inhibited IL-4- or IL-13-stimulated M2 macrophage activation, as showed by reduced expression of M2 markers. In addition, DHHL suppressed IL-4-induced STAT-6 and JAK-1 tyrosine phosphorylation, suggesting that this compound inhibited M2 polarization by suppressing the JAK-STAT signaling pathway. Finally, DHHL prevented eosinophil recruitment and the presence of F4/80⁺-CD206⁺ M2-like macrophages in an in vivo model of M2 polarization via administration of chitin. Collectively, these results confirm DHHL as a novel regulator of macrophage polarization suitable to design future therapies towards M2-macrophages mediated pathologies.

Large-Scale Label-Free Quantitative Mapping of the Sputum Proteome

Analysis of induced sputum supernatant is a minimally invasive approach to study the epithelial lining fluid and, thereby, provide insight into normal lung biology and the pathobiology of lung diseases. We present here a novel proteomics approach to sputum analysis developed within the U-BIOPRED (unbiased biomarkers predictive of respiratory disease outcomes) international project. We present practical and analytical techniques to optimize the detection of robust biomarkers in proteomic studies. The normal sputum proteome was derived using data-independent HDMS^E applied to 40 healthy nonsmoking participants, which provides an essential baseline from which to compare modulation of protein expression in respiratory diseases. The "core" sputum proteome (proteins detected in ≥40% of participants) was composed of 284 proteins, and the extended proteome (proteins detected in ≥3 participants) contained 1666 proteins. Quality control procedures were developed to optimize the accuracy and consistency of measurement of sputum proteins and analyze the distribution of sputum proteins in the healthy population. The analysis showed that quantitation of proteins by HDMS^E is influenced by several factors, with some proteins being measured in all participants' samples and with low measurement variance between samples from the same patient. The measurement of some proteins is highly variable between repeat analyses, susceptible to sample processing effects, or difficult to accurately quantify by mass spectrometry. Other proteins show high interindividual variance. We also highlight that the sputum proteome of healthy individuals is related to sputum neutrophil levels, but not gender or allergic sensitization. We illustrate the importance of design and interpretation of disease biomarker studies considering such protein population and technical measurement variance.

Hypoargininemia exacerbates airway hyperresponsiveness in a mouse model of asthma

BACKGROUND

Asthma is a chronic respiratory condition, with airway hyperresponsiveness (AHR) and inflammation as hallmarks. The hypothesis that the substantially increased expression of arginase 1 in activated macrophages limits the availability of L-arginine for nitric oxide synthesis, and thus increases AHR in lungs of mice with experimentally induced allergic asthma was recently refuted by several studies. In the present study, we tested the hypothesis that, instead, a low circulating concentration of arginine aggravates AHR in the same murine asthma model. Female FVB F/A2 tg/tg transgenic mice, which overexpress rat arginase 1 in their enterocytes, exhibit a ~ 50% decrease of their plasma L-arginine concentration.

METHODS

Adult female F/A2 tg/tg mice and their wild-type littermates (F/A2 wt/wt ) were sensitized and challenged with ovalbumin (OVA/OVA). Lung function was assessed with the flexiVent™ system. Adaptive changes in the expression of arginine-metabolizing or -transporting enzymes, chemokines and cytokines, and lung histology were quantified with qPCR, ELISA, and immunohistochemistry, respectively.

RESULTS

Reduction of circulating L-arginine concentration significantly increased AHR in OVA/OVA-treated mice and, to a lesser extent, even in PBS/OVA-treated mice. The pulmonary inflammatory response in OVA/OVA-treated F/A2 tg/tg and F/A2 wt/wt mice was comparable. OVA/OVA-treated F/A2 tg/tg mice differed from similarly treated female mice, in which arginase 1 expression in lung macrophages was eliminated, by a complete absence of an adaptive increase in the expression of arginine-metabolizing or -transporting enzymes.

CONCLUSION

A reduction of the circulating L-arginine concentration rather than the macrophage-mediated increase of arginine catabolism worsens AHR.

Glucagon-like peptide 1: A potential anti-inflammatory pathway in obesity-related asthma

Alterations in arginine metabolism and accelerated formation of advanced glycation end-products (AGEs), crucial mechanisms in obesity-related asthma, can be modulated by glucagon-like peptide 1 (GLP-1). l-arginine dysregulation in obesity promotes inflammation and bronchoconstriction. Prolonged hyperglycemia, dyslipidemia, and oxidative stress leads to production of AGEs, that bind to their receptor (RAGE) further potentiating inflammation. By binding to its widely distributed receptor, GLP-1 blunts the effects of RAGE activation and arginine dysregulation. The GLP-1 pathway, while comprehensively studied in the endocrine and cardiovascular literature, is under-recognized in pulmonary research. Insights into GLP-1 and the lung may lead to novel treatments for obesity-related asthma.

Arginase 1 deletion in myeloid cells affects the inflammatory response in allergic asthma, but not lung mechanics, in female mice

BACKGROUND

(Over-)expression of arginase may limit local availability of arginine for nitric oxide synthesis. We investigated the significance of arginase1 (ARG1) for the development of airway hyperresponsiveness (AHR) and lung inflammation in female mice with ovalbumin (OVA)-induced allergic asthma.

METHODS

Arg1 was ablated in the lung by crossing Arg1 fl/fl and Tie2Cre tg/- mice. OVA sensitization and challenge were conducted, and AHR to methacholine was determined using the Flexivent system. Changes in gene expression, chemokine and cytokine secretion, plasma IgE, and lung histology were quantified using RT-qPCR, ELISA, and immunohistochemistry, respectively.

RESULTS

Arg1 ablation had no influence on the development of OVA-induced AHR, but attenuated OVA-induced increases in expression of Arg2 and Nos2, Slc7a1, Slc7a2, and Slc7a7 (arginine transporters), Il4, Il5 and Il13 (TH2-type cytokines), Ccl2 and Ccl11 (chemokines), Ifng (TH1-type cytokine), Clca3 and Muc5ac (goblet cell markers), and OVA-specific IgE. Pulmonary IL-10 protein content increased, but IL-4, IL-5, IL-13, TNFα and IFNγ content, and lung histopathology, were not affected. Arg1 elimination also decreased number and tightness of correlations between adaptive changes in lung function and inflammatory parameters in OVA/OVA-treated female mice. OVA/OVA-treated female mice mounted a higher OVA-IgE response than males, but the correlation between lung function and inflammation was lower. Arg1-deficient OVA/OVA-treated females differed from males in a more pronounced decline of arginine-metabolizing and -transporting genes, higher plasma arginine levels, a smaller OVA-specific IgE response, and no improvement of peripheral lung function.

CONCLUSION

Complete ablation of Arg1 in the lung affects mRNA abundance of arginine-transporting and -metabolizing genes, and pro-inflammatory genes, but not methacholine responsiveness or accumulation of inflammatory cells.

Healing of Preterm Ruptured Fetal Membranes

Preterm premature rupture of membrane (pPROM) is associated with 30–40% of preterm births. Infection is considered a leading cause of pPROM due to increased levels of proinflammatory cytokines in amniotic fluid. Only 30%, however, are positive for microbial organisms by amniotic fluid culture. Interestingly, in some pregnancies complicated by preterm premature rupture of membranes (pPROM), membranes heal spontaneously and pregnancy continues until term. Here, we investigated mechanisms of amnion healing. Using a preclinical mouse model, we found that small ruptures of the fetal membrane closed within 72 h whereas healing of large ruptures was only 40%. Small rupture induced transient upregulation of cytokines whereas large ruptures elicited sustained upregulation of proinflammatory cytokines in the fetal membranes. Fetal macrophages from amniotic fluid were recruited to the wounded amnion where macrophage adhesion molecules were highly expressed. Recruited macrophages released limited and well-localized amounts of IL-1β and TNF which facilitated epithelial-mesenchymal transition (EMT) and epithelial cell migration. Arg1 + macrophages dominated within 24 h. Migration and healing of the amnion mesenchymal compartment, however, remained compromised. These findings provide novel insights regarding unique healing mechanisms of amnion.

Pidotimod exacerbates allergic pulmonary infection in an OVA mouse model of asthma

Pidotimod is a synthetic dipeptide with biological and immuno‑modulatory properties. It has been widely used for treatment and prevention of recurrent respiratory infections. However, its impact on the regulation of allergic pulmonary inflammation is still not clear. In the current study, an ovalbumin (OVA)‑induced allergic asthma model was used to investigate the immune‑modulating effects of pidotimod on airway eosinophilia, mucus metaplasia and inflammatory factor expression compared with dexamethasone (positive control). The authors determined that treatment with pidotimod exacerbated pulmonary inflammation as demonstrated by significantly increased eosinophil infiltration, dramatically elevated immunoglobulin E production, and enhanced T helper 2 response. Moreover, treatment failed to attenuate mucus production in lung tissue, and did not reduce OVA‑induced high levels of FIZZ1 and Arg1 expression in asthmatic mice. In contrast, administration of dexamethasone was efficient in alleviating allergic airway inflammation in OVA‑induced asthmatic mice. These data indicated that pidotimod as an immunotherapeutic agent should be used cautiously and the effectiveness for controlling allergic asthma needs further evaluation and research.

Short-term Effect of Fine Particulate Matter on Children's Hospital Admissions and Emergency Department Visits for Asthma: A Systematic Review and Meta-analysis

OBJECTIVES

No children-specified review and meta-analysis paper about the short-term effect of fine particulate matter (PM2.5) on hospital admissions and emergency department visits for asthma has been published. We calculated more precise pooled effect estimates on this topic and evaluated the variation in effect size according to the differences in study characteristics not considered in previous studies.

METHODS

Two authors each independently searched PubMed and EMBASE for relevant studies in March, 2016. We conducted random effect meta-analyses and mixed-effect meta-regression analyses using retrieved summary effect estimates and 95% confidence intervals (CIs) and some characteristics of selected studies. The Egger's test and funnel plot were used to check publication bias. All analyses were done using R version 3.1.3.

RESULTS

We ultimately retrieved 26 time-series and case-crossover design studies about the short-term effect of PM2.5 on children's hospital admissions and emergency department visits for asthma. In the primary meta-analysis, children's hospital admissions and emergency department visits for asthma were positively associated with a short-term 10 μg/m3 increase in PM2.5 (relative risk, 1.048; 95% CI, 1.028 to 1.067; I2=95.7%). We also found different effect coefficients by region; the value in Asia was estimated to be lower than in North America or Europe.

CONCLUSIONS

We strengthened the evidence on the short-term effect of PM2.5 on children's hospital admissions and emergency department visits for asthma. Further studies from other regions outside North America and Europe regions are needed for more generalizable evidence.

Deficiency of α7 nicotinic acetylcholine receptor attenuates bleomycin-induced lung fibrosis in mice

α7 nicotinic acetylcholine receptor (α7 nAChR, coded by Chrna7) is indispensible in dampening proinflammatory responses. However, whether α7 nAChR would play a role in regulating bleomycin (BLM)-induced lung fibrosis is less investigated. Here, we intratracheally challenged wildtype and Chrna7^-/- mice with BLM to elicit lung fibrosis. Taken advantage of this model, we measured body weight loss, lung fibrogenic genes (Acta2, Col1a1, Fsp1, and Fstl1), histology, Masson's trichrome staining, hydroxyproline levels, and expression of α-SMA at protein levels in the BLM-challenged lung for evaluating severity of lung fibrosis. We also pretreated human fibroblasts (MRC5 cell line) and isolated mouse lung fibroblasts with GTS-21 (an α7 nAChR agonist) to study its effects on TGF-β-stimulated profibrotic profiles. We found that lung Chrna7 expression and CD4⁺CHAT⁺ (Choline acetyltransferase, an enzyme for local acetylcholine synthesis) cells were 12-fold and 4.5-fold respectively elevated in the early stage of lung fibrosis. Deletion of Chrna7 prevented body weight loss and reduced lung fibrogenic genes (Acta2, Col1a1, Fsp1, and Fstl1) and Arg 1 (coding arginase 1). Deletion of Chrna7 attenuated lung arginase 1⁺Ly6C⁺ cells, Masson's trichrome staining, hydroxyproline levels, and expression of α-SMA at protein levels in BLM-challenged mice. Mechanistically, activation of α7 nAChR in human fibroblasts increased TGF-β-induced phosphorylation of Smad2/3 and transcription of fibrogenic genes (Acta2, Col1a1). In isolated mouse lung fibroblasts, activation of α7 nAChR also enhanced TGF-β induced-transcription of fibrogenic genes; however, deletion of Chrna7 diminished these effects. Taken together, deficiency of α7 nAChR could suppress the development of BLM-induced lung fibrosis. Thus, α7 nAChR might be a novel therapeutic target for treating lung fibrosis.

Innate Immune Pathways Associated with Lung Radioprotection by Soy Isoflavones

Introduction

Radiation therapy for lung cancer causes pneumonitis and fibrosis. Soy isoflavones protect against radiation-induced lung injury, but the mediators of radioprotection remain unclear. We investigated the effect of radiation on myeloid-derived suppressor cells (MDSCs) in the lung and their modulation by soy isoflavones for a potential role in protection from radiation-induced lung injury.

Methods

BALB/c mice (5–6 weeks old) received a single 10 Gy dose of thoracic irradiation and soy isoflavones were orally administrated daily before and after radiation at 1 mg/day. Arginase-1 (Arg-1) and nuclear factor κB (NF-κB) p65 were detected in lung tissue by western blot analysis and immunohistochemistry. Lung MDSC subsets and their Arg-1 expression were analyzed by flow cytometry. Cytokine levels in the lungs were measured by ELISA.

Results

At 1 week after radiation, CD11b⁺ cells expressing Arg-1 were decreased by radiation in lung tissue yet maintained in the lungs treated with radiation and soy isoflavones. Arg-1 was predominantly expressed by CD11b⁺Ly6C^lowLy6G⁺ granulocytic MDSCs (gr-MDSCs). Arg-1 expression in gr-MDSCs was reduced by radiation and preserved by supplementation with soy isoflavones. A persistent increase in Arg-1⁺ cells was observed in lung tissue treated with combined radiation and soy isoflavones at early and late time points, compared to radiation alone. The increase in Arg-1 expression mediated by soy isoflavones could be associated with the inhibition of radiation-induced activation of NF-κB and the control of pro-inflammatory cytokine production demonstrated in this study.

Conclusion

A radioprotective mechanism of soy isoflavones may involve the promotion of Arg-1-expressing gr-MDSCs that could play a role in downregulation of inflammation and lung radioprotection.

Syk Regulates Neutrophilic Airway Hyper-Responsiveness in a Chronic Mouse Model of Allergic Airways Inflammation

Background

Asthma is a chronic inflammatory disease characterized by airways hyper-responsiveness (AHR), reversible airway obstruction, and airway inflammation and remodeling. We previously showed that Syk modulates methacholine-induced airways contractility in naïve mice and in mice with allergic airways inflammation. We hypothesize that Syk plays a role in the pathogenesis of AHR; this was evaluated in a chronic 8-week mouse model of house dust mite (HDM)-induced allergic airways inflammation.

Methods

We used the Syk^flox/flox//rosa26CreER^T2 conditional Syk knock-out mice to assess the role of Syk prior to HDM exposure, and treated HDM-sensitized mice with the Syk inhibitor, GSK143, to evaluate its role in established allergic airways inflammation. Respiratory mechanics and methacholine (MCh)-responsiveness were assessed using the flexiVent^® system. Lungs underwent bronchoalveolar lavage to isolate inflammatory cells or were frozen for determination of gene expression in tissues.

Results

MCh-induced AHR was observed following HDM sensitization in the Syk-intact (Syk^flox/flox) and vehicle-treated BALB/c mice. MCh responsiveness was reduced to control levels in HDM-sensitized Syk^del/del mice and in BALB/c and Syk^flox/flox mice treated with GSK143. Both Syk^del/del and GSK143-treated mice mounted appropriate immune responses to HDM, with HDM-specific IgE levels that were comparable to Syk^flox/flox and vehicle-treated BALB/c mice. HDM-induced increases in bronchoalveolar lavage cell counts were attenuated in both Syk^del/del and GSK143-treated mice, due primarily to decreased neutrophil recruitment. Gene expression analysis of lung tissues revealed that HDM-induced expression of IL-17 and CXCL-1 was significantly attenuated in both Syk^del/del and GSK143-treated mice.

Conclusion

Syk inhibitors may play a role in the management of neutrophilic asthma.

Molecularly targeted therapies for asthma: Current development, challenges and potential clinical translation

Extensive research into the therapeutics of asthma has yielded numerous effective interventions over the past few decades. However, adverse effects and ineffectiveness of most of these medications especially in the management of steroid resistant severe asthma necessitate the development of better medications. Numerous drug targets with inherent airway smooth muscle tone modulatory role have been identified for asthma therapy. This article reviews the latest understanding of underlying molecular aetiology of asthma towards design and development of better antiasthma drugs. New drug candidates with their putative targets that have shown promising results in the preclinical and/or clinical trials are summarised. Examples of these interventions include restoration of Th1/Th2 balance by the use of newly developed immunomodulators such as toll-like receptor-9 activators (CYT003-QbG10 and QAX-935). Clinical trials revealed the safety and effectiveness of chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) antagonists such as OC0000459, BI-671800 and ARRY-502 in the restoration of Th1/Th2 balance. Regulation of cytokine activity by the use of newly developed biologics such as benralizumab, reslizumab, mepolizumab, lebrikizumab, tralokinumab, dupilumab and brodalumab are at the stage of clinical development. Transcription factors are potential targets for asthma therapy, for example SB010, a GATA-3 DNAzyme is at its early stage of clinical trial. Other candidates such as inhibitors of Rho kinases (Fasudil and Y-27632), phosphodiesterase inhibitors (GSK256066, CHF 6001, roflumilast, RPL 554) and proteinase of activated receptor-2 (ENMD-1068) are also discussed. Preclinical results of blockade of calcium sensing receptor by the use of calcilytics such as calcitriol abrogates cardinal signs of asthma. Nevertheless, successful translation of promising preclinical data into clinically viable interventions remains a major challenge to the development of novel anti-asthmatics.

Association of ADAM33 gene polymorphism and arginase activity with susceptibility to ventilatory impairment in wood dust-exposed workers

ADAM33 represents an important gene of susceptibility for lung function impairment. This work aimed to evaluate the association between genetic polymorphism of ADAM33 at four single nucleotide polymorphisms (T1, T2, S1, and Q1) and arginase activity with respiratory functions impairment in wood workers. The study was done to compare ventilatory functions and arginase activity of 82 wood workers and 81 controls. Genotyping was determined by using the polymerase chain restriction fragment length polymorphism method. Forced expiratory volume in the first second (FEV1), forced vital capacity (FVC), and peak expiratory flow rate (PEF) of the workers were significantly reduced compared with the controls. T1 single nucleotide polymorphism (SNP) was associated with obvious decline in the FEV1, FVC, and PEF in wood workers, while T2 SNP was associated with decline in FEV1 and PEF. A significant increase in arginase activity was found in T2 and S1 SNPs of the exposed workers. Increase in duration of exposure was correlated with the decline in ventilatory functions. This inverse correlation was significant for pulmonary function indices in AA and GG genotypes of T1 and T2, respectively. Moreover, significance was detected for FVC and FEV1 in AA and GA genotypes of S1 and Q1. A positive correlation between arginase activity and duration of exposure was found to be significant in GG genotype of S1 SNP. An association between ADAM33 gene polymorphism and impaired lung functions was detected in wood dust-exposed workers. Arginase activity may play an associated important role in increasing this impairment in wood workers.

The adaptor protein insulin receptor substrate 2 inhibits alternative macrophage activation and allergic lung inflammation

Insulin receptor substrate 2 (IRS2) is an adaptor protein that becomes tyrosine-phosphorylated in response to the cytokines interleukin-4 (IL-4) and IL-13, which results in activation of the phosphoinositide 3-kinase (PI3K)-Akt pathway. IL-4 and IL-13 contribute to allergic lung inflammation. To examine the role of IRS2 in allergic disease, we evaluated the responses of IRS2-deficient (IRS2(-/-)) mice. Unexpectedly, loss of IRS2 resulted in a substantial increase in the expression of a subset of genes associated with the generation of alternatively activated macrophages (AAMs) in response to IL-4 or IL-13 in vitro. AAMs secrete factors that enhance allergic responses and promote airway remodeling. Moreover, compared to IRS2(+/+) mice, IRS2(+/-) and IRS2(-/-) mice developed enhanced pulmonary inflammation, accumulated eosinophils and AAMs, and exhibited airway and vascular remodeling upon allergen stimulation, responses that partially depended on macrophage-intrinsic IRS2 signaling. Both in unstimulated and IL-4-stimulated macrophages, lack of IRS2 enhanced phosphorylation of Akt and ribosomal S6 protein. Thus, we identified a critical inhibitory loop downstream of IRS2, demonstrating an unanticipated and previously unrecognized role for IRS2 in suppressing allergic lung inflammation and remodeling.

Emerging Comorbidities in Adult Asthma: Risks, Clinical Associations, and Mechanisms

Asthma is a heterogeneous disease with many phenotypes, and age at disease onset is an important factor in separating the phenotypes. Most studies with asthma have been performed in patients being otherwise healthy. However, in real life, comorbid diseases are very common in adult patients. We review here the emerging comorbid conditions to asthma such as obesity, metabolic syndrome, diabetes mellitus type 2 (DM2), and cardiac and psychiatric diseases. Their role as risk factors for incident asthma and whether they affect clinical asthma are evaluated. Obesity, independently or as a part of metabolic syndrome, DM2, and depression are risk factors for incident asthma. In contrast, the effects of comorbidities on clinical asthma are less well-known and mostly studies are lacking. Cross-sectional studies in obese asthmatics suggest that they may have less well controlled asthma and worse lung function. However, no long-term clinical follow-up studies with these comorbidities and asthma were identified. These emerging comorbidities often occur in the same multimorbid adult patient and may have in common metabolic pathways and inflammatory or other alterations such as early life exposures, systemic inflammation, inflammasome, adipokines, hyperglycemia, hyperinsulinemia, lung mechanics, mitochondrial dysfunction, disturbed nitric oxide metabolism, and leukotrienes.

Arginase 1 is an innate lymphoid-cell-intrinsic metabolic checkpoint controlling type 2 inflammation

Group 2 innate lymphoid cells (ILC2s) regulate tissue inflammation and repair following activation by cell-extrinsic factors including host-derived cytokines. However, the cell-intrinsic metabolic pathways that control ILC2 function are undefined. Here we demonstrate that expression of the enzyme Arginase 1 (Arg1) is a conserved trait of murine and human ILC2s during acute or chronic lung inflammation. Deletion of murine ILC-intrinsic Arg1 abrogated type 2 lung inflammation by restraining ILC2 proliferation and dampening cytokine production. Mechanistically, inhibition of Arg1 enzymatic activity disrupted multiple components of ILC2 metabolic programming by altering arginine catabolism, impairing polyamine biosynthesis and reducing aerobic glycolysis. These data identify Arg1 as a key regulator of ILC2 bioenergetics, controlling proliferative capacity and pro-inflammatory functions that promote type 2 inflammation.

Arginase-1 deficiency

Arginase-1 (ARG1) deficiency is a rare autosomal recessive disorder that affects the liver-based urea cycle, leading to impaired ureagenesis. This genetic disorder is caused by 40+ mutations found fairly uniformly spread throughout the ARG1 gene, resulting in partial or complete loss of enzyme function, which catalyzes the hydrolysis of arginine to ornithine and urea. ARG1-deficient patients exhibit hyperargininemia with spastic paraparesis, progressive neurological and intellectual impairment, persistent growth retardation, and infrequent episodes of hyperammonemia, a clinical pattern that differs strikingly from other urea cycle disorders. This review briefly highlights the current understanding of the etiology and pathophysiology of ARG1 deficiency derived from clinical case reports and therapeutic strategies stretching over several decades and reports on several exciting new developments regarding the pathophysiology of the disorder using ARG1 global and inducible knockout mouse models. Gene transfer studies in these mice are revealing potential therapeutic options that can be exploited in the future. However, caution is advised in extrapolating results since the lethal disease phenotype in mice is much more severe than in humans indicating that the mouse models may not precisely recapitulate human disease etiology. Finally, some of the functions and implications of ARG1 in non-urea cycle activities are considered. Lingering questions and future areas to be addressed relating to the clinical manifestations of ARG1 deficiency in liver and brain are also presented. Hopefully, this review will spark invigorated research efforts that lead to treatments with better clinical outcomes.

Transgenic mice overexpressing arginase 1 in monocytic cell lineage are affected by lympho-myeloproliferative disorders and disseminated intravascular coagulation

Arginase (ARG) is a metabolic enzyme present in two isoforms that hydrolyze l-arginine to urea and ornithine. In humans, ARG isoform 1 is also expressed in cells of the myeloid lineage. ARG activity promotes tumour growth and inhibits T lymphocyte activation. However, the two ARG transgenic mouse lines produced so far failed to show such effects. We have generated, in two different genetic backgrounds, transgenic mice constitutively expressing ARG1 under the control of the CD68 promoter in macrophages and monocytes. Both heterozygous and homozygous transgenic mice showed a relevant increase in mortality at early age, compared with wild-type siblings (67/267 and 48/181 versus 8/149, respectively, both P < 0.005). This increase was due to high incidence of haematologic malignancies, in particular myeloid leukaemia, myeloid dysplasia, lymphomas and disseminated intravascular coagulation (DIC), diseases that were absent in wild-type mice. Atrophy of lymphoid organs due to reduction in T-cell compartment was also detected. Our results indicate that ARG activity may participate in the pathogenesis of lymphoproliferative and myeloproliferative disorders, suggest the involvement of alterations of L-arginine metabolism in the onset of DIC and confirm a role for the enzyme in regulating T-cell homeostasis.

Asymmetric dimethylarginine contributes to airway nitric oxide deficiency in patients with COPD

INTRODUCTION

Asymmetric dimethylarginine (ADMA) and nitric oxide (NO) show their mechanism of action reciprocally, the balance between these molecules contributes to the tight regulation of airways tone and function.

OBJECTIVES

The aim of this study to determine the serum levels of ADMA and NO in patients with chronic obstructive pulmonary disease (COPD) and establish whether their level vary in relation to forced expiratory volume in 1s (FEV₁ ), to assess their role in pathophysiology of COPD.

MATERIALS AND METHODS

This study consisted of 58 patients with COPD and 30 healthy subjects. Serum ADMA and NO levels were measured using enzyme-linked immunosorbent assay and the colorimetric method, respectively.

RESULTS

Serum ADMA levels were significantly higher, however, NO levels were lower in patients with COPD compared with controls. ADMA levels were inversely correlated with NO levels. Serum ADMA and NO were significantly correlated with FEV₁ . Multivariable logistic regression analysis revealed that serum ADMA and NO were independently and significantly associated with the presence of COPD. Multiple linear regression analysis showed that COPD was positively associated with ADMA, additionally COPD and ADMA were independently and inversely associated with NO. NO levels were decreased, ADMA levels were increased compliant with progression of COPD stages.

CONCLUSION

While circulating ADMA is higher, NO is lower in COPD and both show a strong correlation to the degree of airflow limitation. ADMA seems to be a possible new marker of prognosis of COPD and can be a novel therapeutic target for the treatment of COPD.

Thalidomide inhibits alternative activation of macrophages in vivo and in vitro: a potential mechanism of anti-asthmatic effect of thalidomide

Background

Thalidomide is known to have anti-inflammatory and immunomodulatory actions. However, the effect and the anti-asthmatic mechanism of thalidomide in the pathogenesis of asthmatic airways are not fully understood.

Objective

This study is designed to determine the effect and the potential mechanism of thalidomide in the pathogenesis of asthmatic airways using animal model of allergic asthma.

Methods

Six-week-old female BALB/C mice were sensitized with alum plus ovalbumin (OVA) and were exposed to OVA via intranasal route for 3 days for challenge. Thalidomide 200 mg/kg was given via gavage twice a day from a day before the challenge and airway hyperresponsivenss (AHR), airway inflammatory cells, and cytokines in bronchoalveolar lavage fluids (BALF) were evaluated. The expression levels of pro-inflammatory cytokines and other mediators were evaluated using ELISA, real time (RT)-qPCR, and flow cytometry. CRL-2456, alveolar macrophage cell line, was used to test the direct effect of thalidomide on the activation of macrophages in vitro.

Results

The mice with thalidomide treatment showed significantly reduced levels of allergen-induced BALF and lung inflammation, AHR, and the expression of a number of pro-inflammatory cytokines and mediators including Th2 related, IL-17 cytokines, and altered levels of allergen-specific IgG1/IgG2a. Of interesting note, thalidomide treatment significantly reduced expression levels of allergen- or Th2 cytokine-stimulated alternative activation of macrophages in vivo and in vitro.

Conclusion

These studies highlight a potential use of thalidomide in the treatment of allergic diseases including asthma. This study further identified a novel inhibitory effect of thalidomide on alternative activation of macrophages as a potential mechanism of anti-asthmatic effect of thalidomide.

Plasma arginine metabolites reflect airway dysfunction in a murine model of allergic airway inflammation

L-arginine metabolism is important in the maintenance of airway tone. Shift of metabolism from the nitric oxide synthase to arginase pathways contributes to the increased airway responsiveness in asthma. We tested the hypothesis that systemic levels of L-arginine metabolites are biomarkers reflective of airway dysfunction. We used a mouse model of acute allergic airway inflammation to OVA that manifests with significant airway hyperresponsiveness to methacholine. To determine tissue arginase activity in vivo, the isotopic enrichment of an infused L-arginine stable isotope and its product amino acid L-ornithine were measured in lung and airway homogenates using liquid chromatography-tandem mass spectrometry. Tissue and plasma concentrations of other L-arginine metabolites, including L-citrulline and symmetric and asymmetric dimethylarginine, were measured and correlated with lung arginase activity and methacholine responsiveness of the airways. The effectiveness of intratracheal instillation of an arginase inhibitor (boronoethylcysteine) on pulmonary arginase activity and circulating concentrations of L-arginine metabolites was also studied. We demonstrate that 1) plasma indexes of L-arginine bioavailability and impairment of nitric oxide synthase function correlate with airway responsiveness to methacholine; 2) plasma levels of L-ornithine predict in vivo pulmonary arginase activity and airway function; and 3) acute arginase inhibition reduces in vivo pulmonary arginase activity to control levels and normalizes plasma L-ornithine, but not L-arginine, bioavailability in this model. We conclude that plasma L-ornithine may be useful as a systemic biomarker to predict responses to therapeutic interventions targeting airway arginase in asthma.

Syk mediates airway contractility independent of leukocyte function

BACKGROUND

Syk, an immune regulatory tyrosine kinase, plays a role in inflammatory disease processes. We recently reported a role for epithelial expression of Syk in the airways hyper-responsiveness in response to air pollution in a mouse model of asthma. The aim of this study was to further investigate the role of Syk in airway contractility in response to methacholine (MCh) and particulate matter (PM) air pollutants, in the absence of underlying inflammation.

METHODS

We used Syk(flox/flox) //rosa26CreER(T) (2) conditional Syk knockout mice to evaluate respiratory mechanics and MCh responsiveness following PM exposure in vivo using the ventilator-based flexiVent system.

RESULTS

While total and differential cell counts in bronchoalveolar lavage fluid were similar between the Syk(flox/flox) and Syk(del/del) mice, central airways respiratory resistance (RN ) to MCh was significantly augmented following PM exposure between Syk-intact (Syk(flox/flox) ) and Syk-deficient (Syk(del/del) ) mice (RN (max) : 2.06 ± 0.29 vs. 1.29 ± 0.10, respectively; p < 0.05, n = 8-10/group). We employed live videomicroscopy to investigate changes in airway luminal diameter using ex vivo lung slices, which were devoid of circulating leukocytes. MCh reduced the airway luminal area of Syk(flox/flox) mice to 81.1 ± 1.4% of baseline, which was virtually abrogated in Syk(del/del) mice (luminal area = 93.2 ± 0.5%, n = 5/group, p < 0.05). In response to PM exposure, Syk(flox/flox) airways contracted to 73.8 ± 2.7% of baseline luminal diameter, whereas Syk(del/del) airways exhibited minimal contractility to PM and MCh (90.0 ± 1.3% of baseline, n = 5/group, p < 0.05).

CONCLUSIONS

These observations suggest that Syk mediates airway contractility in the normal and allergic airways, independent of its role and function in leukocytes, and supports a paracrine role for airway epithelial Syk in modulating airway smooth muscle activity.

l-Arginine administration attenuates airway inflammation by altering l-arginine metabolism in an NC/Nga mouse model of asthma

Changes in l-arginine metabolism, including increased arginase levels and decreased nitric oxide production, are involved in the pathophysiology of asthma. In this study, using an intranasal mite-induced NC/Nga mouse model of asthma, we examined whether administration of l-arginine ameliorated airway hyperresponsiveness and inflammation by altering l-arginine metabolism. Experimental asthma was induced in NC/Nga mice via intranasal administration of mite crude extract (50 µg/day) on 5 consecutive days (days 0-4, sensitization) and on day 11 (challenge). Oral administration of l-arginine (250 mg/kg) was performed twice daily on days 5-10 for prevention or on days 11-13 for therapy. On day 14, we evaluated the inflammatory airway response (airway hyperresponsiveness, the number of cells in the bronchoalveolar lavage fluid, and the changes in pathological inflammation of the lung), arginase expression and activity, l-arginine bioavailability, and the concentration of NOx, the end products of nitric oxide. Treatment with l-arginine ameliorated the mite-induced inflammatory airway response. Furthermore, l-arginine administration attenuated the increases in arginase expression and activity and elevated the NOx levels by enhancing l-arginine bioavailability. These findings indicate that l-arginine administration may contribute to the improvement of asthmatic symptoms by altering l-arginine metabolism.

Novel therapeutic strategies for adult obese asthmatics

Asthma is a complex syndrome that affects an estimated 26 million people in the United States but gaps exist in the recognition and management of asthmatic subgroups. This article proposes alternative approaches for future treatments of adult obese asthmatics who do not respond to standard controller therapies, drawing parallels between seemingly disparate therapeutics through their common signaling pathways. How metformin and statins can potentially improve airway inflammation is described and supplements are suggested. A move toward more targeted therapies for asthma subgroups is needed. These therapies address asthma and the comorbidities that accompany obesity and metabolic syndrome to provide the greatest therapeutic potential.