The arginine-arginase balance in asthma and lung inflammation

Calcium-Sensing Receptor as a Novel Target for the Treatment of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a disease with a poor prognosis and no curative therapies. Fibroblast activation by transforming growth factor β1 (TGFβ1) and disrupted metabolic pathways, including the arginine-polyamine pathway, play crucial roles in IPF development. Polyamines are agonists of the calcium/cation-sensing receptor (CaSR), activation of which is detrimental for asthma and pulmonary hypertension, but its role in IPF is unknown. To address this question, we evaluated polyamine abundance using metabolomic analysis of IPF patient saliva. Furthermore, we examined CaSR functional expression in human lung fibroblasts (HLFs), assessed the anti-fibrotic effects of a CaSR antagonist, NPS2143, in TGFβ1-activated normal and IPF HLFs by RNA sequencing and immunofluorescence imaging, respectively; and NPS2143 effects on polyamine synthesis in HLFs by immunoassays. Our results demonstrate that polyamine metabolites are increased in IPF patient saliva. Polyamines activate fibroblast CaSR in vitro, elevating intracellular calcium concentration. CaSR inhibition reduced TGFβ1-induced polyamine and pro-fibrotic factor expression in normal and IPF HLFs. TGFβ1 directly stimulated polyamine release by HLFs, an effect that was blocked by NPS2143. This suggests that TGFβ1 promotes CaSR activation through increased polyamine expression, driving a pro-fibrotic response. By halting some polyamine-induced pro-fibrotic changes, CaSR antagonists exhibit disease-modifying potential in IPF onset and development.

Integrating metabolomics and network pharmacology analysis to explore mechanism of Pueraria lobata against pulmonary fibrosis: Involvement of arginine metabolism pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Pueraria lobata (Willd.) Ohwi is a typical medicinal and edible plant with a long application history in China and Southeast Asia. As a widely used traditional medicine, P. lobata exhibits the properties of anti-inflammatory, antipyretic, antioxidant, relieving cough and asthma. Particularly, the increasing evidence indicates that the P. lobata has the therapeutic effect on fibrotic-related diseases in terms of metabolic regulation. However, the mechanisms of P. lobata on pulmonary fibrosis (PF) has not been thoroughly explored.

AIM OF THE STUDY

This study aimed to explore the effect of arginine metabolites of P. lobata against PF model by integrating metabolomics and network pharmacology analysis. It might provide a new idea for the target finding of P. lobata anti-pulmonary fibrosis.

MATERIALS AND METHODS

In this study, the Sprague Dawley (SD) rats were randomly divided into five experimental groups: saline-treated control group, bleomycin-induced fibrosis group, prednisolone acetate group, P. lobata 3.2 g/kg group and P. lobata 6.4 g/kg group. The therapeutic effect of P. lobata on bleomycin-induced PF in rats was evaluated by clinical symptoms such as lung function, body weight, hematoxylin eosin staining (HE), Masson staining and hydroxyproline assay. Next, the plasma metabolomics analysis was carried out by LC-MS to explore the pathological differences between the group of control, PF and P. lobata-treated rats. Then, the network pharmacology study coupled with experimental validation was conducted to analysis the results of metabolic research. We constructed the "component-target-disease" network of P. lobata in the treatment of PF. In addition, the molecular docking method was used to verify the interaction between potential active ingredients and core targets of P. lobata. Finally, we tested NOS2 and L-OT in arginine-related metabolic pathway in plasma of the rats by enzyme-linked immunosorbent assay (ELISA). Real-time PCR was performed to observe the level of TNF-α mRNA and MMP9 mRNA. And we tested the expression of TNF-α and MMP9 by Western blot analysis.

RESULTS

Our findings revealed that P. lobata improved lung function and ameliorated the pathological symptoms, such as pathological damage, collagen deposition, and body weight loss in PF rats. Otherwise, the plasma metabolomics were employed to screen the differential metabolites of amino acids, lipids, flavonoids, arachidonic acid metabolites, glycoside, etc. Finally, we found that the arginine metabolism signaling mainly involved in the regulating of P. lobata on the treatment of PF rats. Furtherly, the network pharmacology predicted that the arginine metabolism pathway was contained in the top 20 pathways. Next, we integrated metabolomics and network pharmacology that identified NOS2, MMP9 and TNF-α as the P. lobata regulated hub genes by molecular docking. Importantly, it indicated a strong affinity between the puerarin and the NOS2. P. lobata attenuated TNF-α, MMP-9 and NOS2 levels, suppressed TNF-α and MMP-9 protein expression, and decreased L-OT and NOS2 content in PF rats. These results indicated that the effects of P. lobata may ameliorated PF via the arginine metabolism pathway in rats. Therefore, P. lobata may be a potential therapeutic agent to ameliorated PF.

CONCLUSION

In this work, we used metabolomics and network pharmacology to explore the mechanisms of P. lobata in the treatment of PF. Finally, we confirmed that P. lobata alleviated BLM-induced PF in rats by regulating arginine metabolism pathway based on reducing the L-OT and NOS2-related signal molecular. The search for the biomarkers finding of arginine metabolism pathway revealed a new strategy for P. lobata in the treatment of PF.

Metabolite signatures associated with microRNA miR-143-3p serve as drivers of poor lung function trajectories in childhood asthma

BACKGROUND

Lung function trajectories (LFTs) have been shown to be an important measure of long-term health in asthma. While there is a growing body of metabolomic studies on asthma status and other phenotypes, there are no prospective studies of the relationship between metabolomics and LFTs or their genomic determinants.

METHODS

We utilized ordinal logistic regression to identify plasma metabolite principal components associated with four previously-published LFTs in children from the Childhood Asthma Management Program (CAMP) (n = 660). The top significant metabolite principal component (PCLF) was evaluated in an independent cross-sectional child cohort, the Genetic Epidemiology of Asthma in Costa Rica Study (GACRS) (n = 1151) and evaluated for association with spirometric measures. Using meta-analysis of CAMP and GACRS, we identified associations between PCLF and microRNA, and SNPs in their target genes. Statistical significance was determined using an false discovery rate-adjusted Q-value.

FINDINGS

The top metabolite principal component, PCLF, was significantly associated with better LFTs after multiple-testing correction (Q-value = 0.03). PCLF is composed of the urea cycle, caffeine, corticosteroid, carnitine, and potential microbial (secondary bile acid, tryptophan, linoleate, histidine metabolism) metabolites. Higher levels of PCLF were also associated with increases in lung function measures and decreased circulating neutrophil percentage in both CAMP and GACRS. PCLF was also significantly associated with microRNA miR-143-3p, and SNPs in three miR-143-3p target genes; CCZ1 (P-value = 2.6 × 10-5), SLC8A1 (P-value = 3.9 × 10-5); and TENM4 (P-value = 4.9 × 10-5).

INTERPRETATION

This study reveals associations between metabolites, miR-143-3p and LFTs in children with asthma, offering insights into asthma physiology and possible interventions to enhance lung function and long-term health.

FUNDING

Molecular data for CAMP and GACRS via the Trans-Omics in Precision Medicine (TOPMed) program was supported by the National Heart, Lung, and Blood Institute (NHLBI).

Metabolomics in Animal Models of Bronchial Asthma and Its Translational Importance for Clinics

Bronchial asthma is an extremely heterogenous chronic respiratory disorder with several distinct endotypes and phenotypes. These subtypes differ not only in the pathophysiological changes and/or clinical features but also in their response to the treatment. Therefore, precise diagnostics represent a fundamental condition for effective therapy. In the diagnostic process, metabolomic approaches have been increasingly used, providing detailed information on the metabolic alterations associated with human asthma. Further information is brought by metabolomic analysis of samples obtained from animal models. This article summarizes the current knowledge on metabolomic changes in human and animal studies of asthma and reveals that alterations in lipid metabolism, amino acid metabolism, purine metabolism, glycolysis and the tricarboxylic acid cycle found in the animal studies resemble, to a large extent, the changes found in human patients with asthma. The findings indicate that, despite the limitations of animal modeling in asthma, pre-clinical testing and metabolomic analysis of animal samples may, together with metabolomic analysis of human samples, contribute to a novel way of personalized treatment of asthma patients.

Arginine deprivation as a treatment approach targeting cancer cell metabolism and survival: A review of the literature

Amino acid requirement of metabolically active cells is a key element in cellular survival. Of note, cancer cells were shown to have an abnormal metabolism and high-energy requirements including the high amino acid requirement needed for growth factor synthesis. Thus, amino acid deprivation is considered a novel approach to inhibit cancer cell proliferation and offer potential treatment prospects. Accordingly, arginine was proven to play a significant role in cancer cell metabolism and therapy. Arginine depletion induced cell death in various types of cancer cells. Also, the various mechanisms of arginine deprivation, e.g., apoptosis and autophagy were summarized. Finally, the adaptive mechanisms of arginine were also investigated. Several malignant tumors had high amino acid metabolic requirements to accommodate their rapid growth. Antimetabolites that prevent the production of amino acids were also developed as anticancer therapies and are currently under clinical investigation. The aim of this review is to provide a concise literature on arginine metabolism and deprivation, its effects in different tumors, its different modes of action, as well as the related cancerous escape mechanisms.

Exacerbation-prone pediatric asthma is associated with arginine, lysine, and methionine pathway alterations

BACKGROUND

The asthma of some children remains poorly controlled, with recurrent exacerbations despite treatment with inhaled corticosteroids. Aside from prior exacerbations, there are currently no reliable predictors of exacerbation-prone asthma in these children and only a limited understanding of the potential underlying mechanisms.

OBJECTIVE

We sought to quantify small molecules in the plasma of children with exacerbation-prone asthma through mass spectrometry-based metabolomics. We hypothesized that the plasma metabolome of these children would differ from that of children with non-exacerbation-prone asthma.

METHODS

Plasma metabolites were extracted from 4 pediatric asthma cohorts (215 total subjects, with 41 having exacerbation-prone asthma) and detected with a mass spectrometer. High-confidence annotations were retained for univariate analysis and were confirmed by a sensitivity analysis in subjects receiving high-dose inhaled corticosteroids. Metabolites that varied by cohort were excluded. MetaboAnalyst software was used to identify pathways of interest. Concentrations were calculated by reference standardization.

RESULTS

We identified 32 unique, cohort-independent metabolites that differed in children with exacerbation-prone asthma compared to children with non-exacerbation-prone asthma. Comparison of metabolite concentrations to literature-reported values for healthy children revealed that most metabolites were decreased in both asthma groups, but more so in exacerbation-prone asthma. Pathway analysis identified arginine, lysine, and methionine pathways as most impacted.

CONCLUSIONS

Several plasma metabolites are perturbed in children with exacerbation-prone asthma and are largely related to arginine, lysine, and methionine pathways. While validation is needed, plasma metabolites may be potential biomarkers for exacerbation-prone asthma in children.

High throughput virtual screening strategy to develop a potential treatment for bronchial asthma by targeting interleukin 13 cytokine signaling

Chronic inflammation in the airway passage leads to the clinical syndrome of pediatric asthma. Allergic reactions caused by bacterial, viral, and fungal infection lead to the immune dis-balance which primes T helper cells (Th2), a specific cluster of differentiation 4 (CD4) T cell differentiation. This favors the Th2-specific response by activating the inter-leukin 4/interleukin 13 (IL-4/IL-13) cytokine signaling and further activates the secretion of immunoglobulin E (IgE). IL-13 develops bronchial asthma by elevating bronchial hyperresponsiveness and enables production of immunoglobulin M (IgM) and IgE. The present study aims to target IL-13 signaling using molecular docking and understanding molecular dynamic simulation (MDS) to propose a compelling candidate to treat asthma. We developed a library of available allergic drugs (n=20) and checked the binding affinity against IL-13 protein (3BPN.pdb) through molecular docking and confirmed the best pose binding energy of -3.84 and -3.71 for epinephrine and guaifenesin, respectively. Studying the interaction of hydrogen bonds and Van der Walls, it is estimated that electrostatic energy is sufficient to interact with the active site of the IL-13 and has shown to inhibit inflammatory signaling. These computational results confirm epinephrine and guaifenesin as potential ligands showing potential inhibitory activity for IL-13 signaling. This study also suggests the designing of a new ligand and screening of a large cohort of drugs, in the future, to predict the exact mechanism to control the critical feature of asthma.

Local and Systemic Alterations of the L-Arginine/Nitric Oxide Pathway in Sputum, Blood, and Urine of Pediatric Cystic Fibrosis Patients and Effects of Antibiotic Treatment

Alterations in the L-arginine (Arg)/nitric oxide (NO) pathway have been reported in cystic fibrosis (CF; OMIM 219700) as the result of various factors including systemic and local inflammatory activity in the airways. The aim of the present study was to evaluate the Arg/NO metabolism in pediatric CF patients with special emphasis on lung impairment and antibiotic treatment. Seventy CF patients and 78 healthy controls were included in the study. CF patients (43% male, median age 11.8 years) showed moderately impaired lung functions (FEV1 90.5 ± 19.1% (mean ± SD); 21 (30%) had a chronic Pseudomonas aeruginosa (PSA) infection, and 24 (33%) had an acute exacerbation). Plasma, urinary, and sputum concentrations of the main Arg/NO metabolites, nitrate, nitrite, Arg, homoarginine (hArg), and asymmetric dimethylarginine (ADMA) were determined in pediatric CF patients and in healthy age-matched controls. Clinical parameters in CF patients included lung function and infection with PSA. Additionally, the Arg/NO pathway in sputum samples of five CF patients was analyzed before and after routine antibiotic therapy. CF patients with low fractionally exhaled NO (FENO) showed lower plasma Arg and nitrate concentrations. During acute exacerbation, sputum Arg and hArg levels were high and dropped after antibiotic treatment: Arg: pre-antibiotics: 4.14 nmol/25 mg sputum vs. post-antibiotics: 2.33 nmol/25 mg sputum, p = 0.008; hArg: pre-antibiotics: 0.042 nmol/25 mg sputum vs. post-antibiotics: 0.029 nmol/25 mg sputum, p = 0.035. The activated Arg/NO metabolism in stable CF patients may be a result of chronic inflammation. PSA infection did not play a major role regarding these differences. Exacerbation increased and antibiotic therapy decreased sputum Arg concentrations.

Alterations in Serum-Free Amino Acid Profiles in Childhood Asthma

Asthma often begins in childhood, although making an early diagnosis is difficult. Clinical manifestations, the exclusion of other causes of bronchial obstruction, and responsiveness to anti-inflammatory therapy are the main tool of diagnosis. However, novel, precise, and functional biochemical markers are needed in the differentiation of asthma phenotypes, endotypes, and creating personalized therapy. The aim of the study was to search for metabolomic-based asthma biomarkers among free amino acids (AAs). A wide panel of serum-free AAs in asthmatic children, covering both proteinogenic and non-proteinogenic AAs, were analyzed. The examination included two groups of individuals between 3 and 18 years old: asthmatic children and the control group consisted of children with neither asthma nor allergies. High-performance liquid chromatography combined with tandem mass spectrometry (LC-MS/MS technique) was used for AA measurements. The data were analyzed by applying uni- and multivariate statistical tests. The obtained results indicate the decreased serum concentration of taurine, L-valine, DL-β-aminoisobutyric acid, and increased levels of ƴ-amino-n-butyric acid and L-arginine in asthmatic children when compared to controls. The altered concentration of these AAs can testify to their role in the pathogenesis of childhood asthma. The authors' results should contribute to the future introduction of new diagnostic markers into clinical practice.

Arginase Isoform Expression in Chronic Rhinosinusitis

Nitric oxide (NO) has emerged as an important regulator of upper airway inflammation, mainly as part of the local naso-sinusal defense mechanisms. Increased arginase activity can reduce NO levels by decreasing the availability of its precursor, L-arginine. Chronic rhinosinusitis (CRS) has been associated with low levels of nasal nitric oxide (nNO). Thus, the present study investigates the activity of arginase I (ARG1) and II (ARG2) in CRS and its possible involvement in the pathogenesis of this disease. Under endoscopic view, tissue samples of pathologic (n = 36) and normal (n = 29) rhinosinusal mucosa were collected. Arginase I and II mRNA levels were measured using real-time PCR. Our results showed low arginase I activity in all samples. The levels of ARG2 were significantly higher in patients with chronic rhinosinusitis compared to the control group (fold regulation (FR) 2.22 ± 0.42 vs. 1.31 ± 0.21, p = 0.016). Increased ARG2 expression was found in patients with CRS without nasal polyposis (FR 3.14 ± 1.16 vs. 1.31 ± 0.21, p = 0.0175), in non-allergic CRS (FR 2.55 ± 0.52 vs. 1.31 ± 0.21, p = 0.005), and non-asthmatic CRS (FR 2.42 ± 0.57 vs. 1.31 ± 0.21, p = 0.028). These findings suggest that the upregulation of ARG2 may play a role in the pathology of a distinctive phenotype of CRS.

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.

Effects of Hyperoxia on the Developing Airway and Pulmonary Vasculature

Although it is necessary and part of standard practice, supplemental oxygen (40-90% O₂) or hyperoxia is a significant contributing factor to development of bronchopulmonary dysplasia, persistent pulmonary hypertension, recurrent wheezing, and asthma in preterm infants. This chapter discusses hyperoxia and the role of redox signaling in the context of neonatal lung growth and disease. Here, we discuss how hyperoxia promotes dysfunction in the airway and the known redox-mediated mechanisms that are important for postnatal vascular and alveolar development. Whether in the airway or alveoli, redox pathways are important and greatly influence the neonatal lung.

Arginase Structure and Inhibition: Catalytic Site Plasticity Reveals New Modulation Possibilities

Metalloenzyme arginase is a therapeutically relevant target associated with tumor growth. To fight cancer immunosuppression, arginase activity can be modulated by small chemical inhibitors binding to its catalytic center. To better understand molecular mechanisms of arginase inhibition, a careful computer-aided mechanistic structural investigation of this enzyme was conducted. Using molecular dynamics (MD) simulations in the microsecond range, key regions of the protein active site were identified and their flexibility was evaluated and compared. A cavity opening phenomenon was observed, involving three loops directly interacting with all known ligands, while metal coordinating regions remained motionless. A novel dynamic 3D pharmacophore analysis method termed dynophores has been developed that allows for the construction of a single 3D-model comprising all ligand-enzyme interactions occurring throughout a complete MD trajectory. This new technique for the in silico study of intermolecular interactions allows for loop flexibility analysis coupled with movements and conformational changes of bound ligands. Presented MD studies highlight the plasticity of the size of the arginase active site, leading to the hypothesis that larger ligands can enter the cavity of arginase. Experimental testing of a targeted fragment library substituted by different aliphatic groups validates this hypothesis, paving the way for the design of arginase inhibitors with novel binding patterns.

Cloning and comparative analysis the proximal promoter activities of arginase and agmatinase genes in Apostichopus japonicus

Our previous work demonstrated that Apostichopus japonicus arginase and agmatinase from l-arginine metabolism synergistically compete with NOS under pathogens challenge. Here we conducted a study to further investigate the mechanism in the regulation of arginase and agmatinase genes in l-arginine metabolism using EPC cell system. Luciferase analysis and progressive 5' deletion analysis suggested that Ajagmatinase promoter was a very robust promoter for its transcription, and the core region of Ajarginase promoter was located within -277 bp to -157 bp. Besides, their promoter activities were significantly activated by LPS and l-arginine challenge both in a time- and dose-dependent manners in EPC cells. When different truncated reporter vector and expression vector co-transfection experiment revealed transcription factor NF-κB/Rel and STAT5 could significantly inhibited Ajarginase promoter activity, but not Ajagmatinase. Our findings were provided novel insights into the transcriptional regulation of Ajarginase and Ajagmatinase, and selectively change their expressions might prevent pathogens infection.

Boysenberry ingestion supports fibrolytic macrophages with the capacity to ameliorate chronic lung remodeling

Lung fibrosis negatively impacts on lung function in chronic asthma and is linked to the development of profibrotic macrophage phenotypes. Epidemiological studies have found that lung function benefits from increased consumption of fruit high in polyphenols. We investigated the effect of boysenberry consumption, in both therapeutic and prophylactic treatment strategies in a mouse model of chronic antigen-induced airway inflammation. Boysenberry consumption reduced collagen deposition and ameliorated tissue remodeling alongside an increase in the presence of CD68+CD206+arginase+ alternatively activated macrophages in the lung tissue. The decrease in tissue remodeling was associated with increased expression of profibrolytic matrix metalloproteinase-9 protein in total lung tissue. We identified alternatively activated macrophages in the mice that consumed boysenberry as a source of the matrix metalloproteinase-9. Oral boysenberry treatment may moderate chronic tissue remodeling by supporting the development of profibrolytic alternatively activated macrophages expressing matrix metalloproteinase-9. Regular boysenberry consumption therefore has the potential to moderate chronic lung remodeling and fibrosis in asthma and other chronic pulmonary diseases.

Expression of arginase I and inducible nitric oxide synthase in the peripheral blood and lymph nodes of HIV‑positive patients

Arginase I (Arg I) and inducible nitric oxide synthase (iNOS) are important in regulating immune functions through their metabolites. Previous studies have revealed that the expression of Arg I is increased and the expression of iNOS is reduced in the serum and peripheral blood mononuclear cells of human immunodeficiency virus (HIV)-infected patients. As one of the most important immune organs and HIV replication sites, whether similar changes are present in the lymph nodes following HIV infection remains to be elucidated. To investigate this, the present study collected lymph node and blood specimens from 52 HIV-infected patients to measure the expression levels of Arg I and iNOS by immunohistochemistry and fluoresence-based flow cytometry. Compared with control subjects without HIV infection, the patients with HIV had significantly higher expression levels of Arg I in the lymph nodes and higher frequencies of Arg I⁺ CD4⁺ T cells and CD8⁺ T cells in the blood and lymph nodes, and these results were contrary the those of iNOS in the corresponding compartments. The expression levels of Arg I in the lymph nodes and blood were negatively associated with peripheral CD4⁺ T cell count and positively associated with viral load. However, the expression levels of iNOS in the lymph nodes and blood were positively associated with peripheral CD4⁺ T cell count and negatively associated with viral load. These results showed that alterations in the expression levels of Arg I and iNOS in the peripheral T cells and peripheral nodes of HIV infected patients are associated with disease progression in these patients. These results indicate a potential to therapeutic strategy for delaying disease progression through regulating and manipulating the expression levels of Arg I and iNOS in patients infected with HIV.

Exposure to cigarette smoke impacts myeloid-derived regulatory cell function and exacerbates airway hyper-responsiveness

Cigarette smoking enhances oxidative stress and airway inflammation in asthma, the mechanisms of which are largely unknown. Myeloid-derived regulatory cells (MDRC) are free radical producing immature myeloid cells with immunoregulatory properties that have recently been demonstrated as critical regulators of allergic airway inflammation. NO (nitric oxide)-producing immunosuppressive MDRC suppress T-cell proliferation and airway-hyper responsiveness (AHR), while the O2(•-) (superoxide)-producing MDRC are proinflammatory. We hypothesized that cigarette smoke (CS) exposure may impact MDRC function and contribute to exacerbations in asthma. Exposure of bone marrow (BM)-derived NO-producing MDRC to CS reduced the production of NO and its metabolites and inhibited their potential to suppress T-cell proliferation. Production of immunoregulatory cytokine IL-10 was significantly inhibited, while proinflammatory cytokines IL-6, IL-1β, TNF-α and IL-33 were enhanced in CS-exposed BM-MDRC. Additionally, CS exposure increased NF-κB activation and induced BM-MDRC-mediated production of O2(•-), via NF-κB-dependent pathway. Intratracheal transfer of smoke-exposed MDRC-producing proinflammatory cytokines increased NF-κB activation, reactive oxygen species and mucin production in vivo and exacerbated AHR in C57BL/6 mice, mice deficient in Type I IFNR and MyD88, both with reduced numbers of endogenous MDRC. Thus CS exposure modulates MDRC function and contributes to asthma exacerbation and identifies MDRC as potential targets for asthma therapy.

Asymmetric dimethylarginine in chronic obstructive pulmonary disease (ADMA in COPD)

L-arginine metabolism including the nitric oxide (NO) synthase and arginase pathways is important in the maintenance of airways function. We have previously reported that accumulation of asymmetric dimethylarginine (ADMA) in airways, resulting in changes in L-arginine metabolism, contributes to airways obstruction in asthma and cystic fibrosis. Herein, we assessed L-arginine metabolism in airways of patients with chronic obstructive pulmonary disease (COPD). Lung function testing, measurement of fractional exhaled NO (FeNO) and sputum NO metabolites, as well as quantification of L-arginine metabolites (L-arginine, L-ornithine, L-citrulline, ADMA and symmetric dimethylarginine) using liquid chromatography-mass spectrometry (LC-MS) were performed. Concentrations of L-ornithine, the product of arginase activity, correlated directly with L-arginine and ADMA sputum concentrations. FeNO correlated directly with pre- and post-bronchodilator forced expiratory volume in one second (FEV1). Sputum arginase activity correlated inversely with total NO metabolite (NOx) and nitrite concentrations in sputum, and with pre- and post-bronchodilator FEV1. These findings suggest that ADMA in COPD airways results in a functionally relevant shift of L-arginine breakdown by the NO synthases towards the arginase pathway, which contributes to airway obstruction in these patients.

Overexpression of dimethylarginine dimethylaminohydrolase 1 attenuates airway inflammation in a mouse model of asthma

Levels of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, are increased in lung, sputum, exhaled breath condensate and plasma samples from asthma patients. ADMA is metabolized primarily by dimethylarginine dimethylaminohydrolase 1 (DDAH1) and DDAH2. We determined the effect of DDAH1 overexpression on development of allergic inflammation in a mouse model of asthma. The expression of DDAH1 and DDAH2 in mouse lungs was determined by RT-quantitative PCR (qPCR). ADMA levels in bronchoalveolar lavage fluid (BALF) and serum samples were determined by mass spectrometry. Wild type and DDAH1-transgenic mice were intratracheally challenged with PBS or house dust mite (HDM). Airway inflammation was assessed by bronchoalveolar lavage (BAL) total and differential cell counts. The levels of IgE and IgG1 in BALF and serum samples were determined by ELISA. Gene expression in lungs was determined by RNA-Seq and RT-qPCR. Our data showed that the expression of DDAH1 and DDAH2 was decreased in the lungs of mice following HDM exposure, which correlated with increased ADMA levels in BALF and serum. Transgenic overexpression of DDAH1 resulted in decreased BAL total cell and eosinophil numbers following HDM exposure. Total IgE levels in BALF and serum were decreased in HDM-exposed DDAH1-transgenic mice compared to HDM-exposed wild type mice. RNA-Seq results showed downregulation of genes in the inducible nitric oxide synthase (iNOS) signaling pathway in PBS-treated DDAH1-transgenic mice versus PBS-treated wild type mice and downregulation of genes in IL-13/FOXA2 signaling pathway in HDM-treated DDAH1-transgenic mice versus HDM-treated wild type mice. Our findings suggest that decreased expression of DDAH1 and DDAH2 in the lungs may contribute to allergic asthma and overexpression of DDAH1 attenuates allergen-induced airway inflammation through modulation of Th2 responses.

Oxidants and redox signaling in acute lung injury

Acute lung injury (ALI) and its more severe form of clinical manifestation, the acute respiratory distress syndrome is associated with significant dysfunction in air exchange due to inflammation of the lung parenchyma. Several factors contribute to the inflammatory process, including hypoxia (inadequate oxygen), hyperoxia (higher than normal partial pressure of oxygen), inflammatory mediators (such as cytokines), infections (viral and bacterial), and environmental conditions (such as cigarette smoke or noxious gases). However, studies over the past several decades suggest that oxidants formed in the various cells of the lung including endothelial, alveolar, and epithelial cells as well as lung macrophages and neutrophils in response to the factors mentioned above mediate the pathogenesis of ALI. Oxidants modify cellular proteins, lipids, carbohydrates, and DNA to cause their aberrant function. For example, oxidation of lipids changes membrane permeability. Interestingly, recent studies also suggest that spatially and temporally regulated production of oxidants plays an important role antimicrobial defense and immunomodulatory function (such as transcription factor activation). To counteract the oxidants an arsenal of antioxidants exists in the lung to maintain the redox status, but when overwhelmed tissue injury and exacerbation of inflammation occurs. We present below the current understanding of the pathogenesis of oxidant-mediated ALI.

Phospholipase A2 in experimental allergic bronchitis: a lesson from mouse and rat models

Background

Phospholipases A₂ (PLA₂) hydrolyzes phospholipids, initiating the production of inflammatory lipid mediators. We have previously shown that in rats, sPLA₂ and cPLA₂ play opposing roles in the pathophysiology of ovalbumin (OVA)-induced experimental allergic bronchitis (OVA-EAB), an asthma model: Upon disease induction sPLA₂ expression and production of the broncho-constricting CysLTs are elevated, whereas cPLA₂ expression and the broncho-dilating PGE₂ production are suppressed. These were reversed upon disease amelioration by treatment with an sPLA₂ inhibitor. However, studies in mice reported the involvement of both sPLA₂ and cPLA₂ in EAB induction.

Objectives

To examine the relevance of mouse and rat models to understanding asthma pathophysiology.

Methods

OVA-EAB was induced in mice using the same methodology applied in rats. Disease and biochemical markers in mice were compared with those in rats.

Results

As in rats, EAB in mice was associated with increased mRNA of sPLA₂, specifically sPLA₂gX, in the lungs, and production of the broncho-constricting eicosanoids CysLTs, PGD₂ and TBX₂ in bronchoalveolar lavage (BAL). In contrast, EAB in mice was associated also with elevated cPLA₂ mRNA and PGE₂ production. Yet, treatment with an sPLA₂ inhibitor ameliorated the EAB concomitantly with reverting the expression of both cPLA₂ and sPLA₂, and eicosanoid production.

Conclusions

In both mice and rats sPLA₂ is pivotal in OVA-induced EAB. Yet, amelioration of asthma markers in mouse models, and human tissues, was observed also upon cPLA₂ inhibition. It is plausible that airway conditions, involving multiple cell types and organs, require the combined action of more than one, essential, PLA₂s.

Comparative pharmacokinetics of N(ω)-hydroxy-nor-L-arginine, an arginase inhibitor, after single-dose intravenous, intraperitoneal and intratracheal administration to brown Norway rats

1.  Rodent studies have documented that N(ω)-hydroxy-nor-L-arginine (nor-NOHA), an arginase inhibitor, has therapeutic potential in the treatment of cardiovascular and obstructive airway diseases. However, its bioavailability and pharmacokinetics have not been described so far. 2.  Anesthetized brown Norway rats were administered single doses of nor-NOHA (10, 30 or 90 mg/kg) intravenously (i.v.), intraperitonealy (i.p.) or via intratracheal (i.t.) instillation of aerosol. Plasma nor-NOHA was assayed using a validated HPLC method. 3.  Upon i.v. administration, the mean concentration showed a biphasic decline and its value dropped below 10% of the maximum after 20 min. The pharmacokinetics were linear with the total and inter-compartmental clearances of 33 and 17 mL/min/kg, central and peripheral volumes of distribution of 0.19 and 0.43 L/kg and terminal half-life of 30 min. 4.  The average absolute bioavailability of nor-NOHA after i.p. and i.t. delivery was 98% and 53%, respectively. The absorption from the airways was rate-limiting and its extent decreased with the dose. 5.  In conclusion, nor-NOHA is rapidly cleared from the plasma in concordance with the short time window of its in vivo inhibitory activity reported in the literature. I.t. instillation of aerosol for topical effects of nor-NOHA in the airways is characterized with significant systemic availability.

Inhibition of arginase ameliorates experimental ulcerative colitis in mice

Nitric oxide (NO) is produced from the conversion of L-arginine by NO synthase (NOS) and regulates a variety of processes in the gastrointestinal tract. Considering the increased activity of arginase in colitis tissue, it is speculated that arginase could inhibit NO synthesis by competing for the same L-arginine substrate, resulting in the exacerbation of colitis. We examined the role of arginase and its relationship to NO metabolism in dextran sulfate sodium (DSS)-induced colitis. Experimental colitis was induced in mice by administration of 2.5% DSS in drinking water for 8 days. Treatment for arginase inhibition was done by once daily intraperitoneal injection of N(ω)-hydroxy-nor- arginine (nor-NOHA). On day 8, we evaluated clinical parameters (body weight, disease activity index, and colon length), histological features, the activity and expression of arginase, L-arginine content, the expression of NO synthase (NOS), and the concentration of NO end-product (NOx: nitrite + nitrate). Administration of nor-NOHA improved the worsened clinical parameters and histological features in DSS-induced colitis. Treatment with nor-NOHA attenuated the increased activity of arginase, upregulation of arginase Ι at both mRNA and protein levels, and decreased the content of L-arginine in colonic tissue in the DSS-treated mice. Conversely, despite the decreased expression of NOS2 mRNA, the decreased concentration of NOx in colonic tissues was restored to almost normal levels. The consumption of L-arginine by arginase could lead to decreased production of NO from NOS, contributing to the pathogenesis of the colonic inflammation; thus, arginase inhibition might be effective for improving colitis.

IL-13 receptor α2-arginase 2 pathway mediates IL-13-induced pulmonary hypertension

Although previous literature suggests that interleukin (IL)-13, a T-helper type 2 cell effector cytokine, might be involved in the pathogenesis of pulmonary hypertension (PH), direct proof is lacking. Furthermore, a potential mechanism underlying IL-13-induced PH has never been explored. This study's goal was to investigate the role and mechanism of IL-13 in the pathogenesis of PH. Lung-specific IL-13-overexpressing transgenic (Tg) mice were examined for hemodynamic changes and pulmonary vascular remodeling. IL-13 Tg mice spontaneously developed PH phenotype by the age of 2 mo with increased expression and activity of arginase 2 (Arg2). The role of Arg2 in the development of IL-13-stimulated PH was further investigated using Arg2 and IL-13 receptor α2 (Rα2) null mutant mice and the small-interfering RNA (siRNA)-silencing approach in vivo and in vitro, respectively. IL-13-stimulated medial thickening of pulmonary arteries and right ventricle systolic pressure were significantly decreased in the IL-13 Tg mice with Arg2 null mutation. On the other hand, the production of nitric oxide was further increased in the lungs of these mice. In our in vitro evaluations, the recombinant IL-13 treatment significantly enhanced the proliferation of human pulmonary artery smooth muscle cells in an Arg2-dependent manner. The IL-13-stimulated cellular proliferation and the expression of Arg2 in hpaSMC were markedly decreased with IL-13Rα2 siRNA silencing. Our studies demonstrate that IL-13 contributes to the development of PH via an IL-13Rα2-Arg2-dependent pathway. The intervention of this pathway could be a potential therapeutic target in pulmonary arterial hypertension.

Role of arginase in asthma: potential clinical applications

Allergic asthma is a chronic disease with significant morbidity and mortality. It affects 300 million people worldwide and absorbs a significant amount of the healthcare budget. The predisposition to asthma is dictated by complex genetic regulation, and the asthmatic inflammation itself is characterized by the interplay of various local cells of the bronchial tree and invading inflammatory immune cells. The clinical problems of asthma are owing to intermittent airway hyper-responsiveness that can become chronic in the course of the disease. Histopathologically, infiltration with a variety of inflammatory cells, smooth muscle cell hyperplasia and hypertrophy, goblet cell hyperplasia and subepithelial fibrosis are found in asthmatic inflammatory tissue. This special report sets out to review data on the role of the enzyme arginase and L-arginine metabolism as a unifying element of asthma pathophysiology and as a potential target for future clinical asthma treatment.

Biomarkers in asthma: a real hope to better manage asthma

Diagnosis and treatment of asthma are currently based on assessment of patient symptoms and physiologic tests of airway reactivity. Research over the past decade has identified an array of biochemical and cellular biomarkers, which reflect the heterogeneous and multiple mechanistic pathways that may lead to asthma. These mechanistic biomarkers offer hope for optimal design of therapies targeting the specific pathways that lead to inflammation. This article provides an overview of blood, urine, and airway biomarkers; summarizes the pathologic pathways that they signify; and begins to describe the utility of biomarkers in the future care of patients with asthma.

Pollutant particles induce arginase II in human bronchial epithelial cells

Exposure to particulate matter (PM) is associated with adverse pulmonary effects, including induction and exacerbation of asthma. Recently arginase was shown to play an important role in the pathogenesis of asthma. In this study, it was postulated that PM exposure might induce arginase. Human bronchial epithelial cells (HBEC) obtained from normal individuals by endobronchial brushings cultured on an air-liquid interface were incubated with fine Chapel Hill particles (PM₂.₅, 100 μg/ml) for up to 72 h. Arginase activity, protein expression, and mRNA of arginase I and arginase II were measured. PM₂.₅ increased arginase activity in a time-dependent manner. The rise was primarily due to upregulation of arginase II. PD153035 (10 μM), an epidermal growth factor (EGF) receptor antagonist, attenuated the PM₂.₅-induced elevation in arginase activity and arginase II expression. Treatment of HBEC with human EGF increased arginase activity and arginase II expression. Pretreatment with catalase (200 U/ml), superoxide dismutase (100 U/ml), or apocynin (5 μg/ml), an NAD(P)H oxidase inhibitor, did not markedly affect arginase II expression. Treatment of HBEC with arginase II siRNA inhibited the expression of arginase II by 60% and increased IL-8 release induced by PM₂.₅. These results indicate that PM exposure upregulates arginase II activity and expression in human bronchial epithelial cells, in part via EGF-dependent mechanisms independent of oxidative stress. The elevated arginase II activity and expression may be a mechanism underlying adverse effects induced by PM exposure in asthma patients.

Nitric oxide and related enzymes in asthma: relation to severity, enzyme function and inflammation

BACKGROUND

Exhaled nitric oxide (FeNO) associates with asthma and eosinophilic inflammation. However, relationships between nitric oxide synthases, arginase, FeNO, asthma severity and inflammation remain poorly understood.

OBJECTIVES

To determine the relationships of iNOS expression/activation and arginase 2 expression with asthma severity, FeNO, nitrotyrosine (NT) and eosinophilic inflammation.

METHODS

Bronchial brushings and sputum were obtained from 25 normal controls, eight mild/no inhaled corticosteroids (ICS), 16 mild-moderate/with ICS and 35 severe asthmatics. The FeNO was measured the same day by ATS/ERS standards. The iNOS, arginase2 mRNA/protein and NT protein were measured in lysates from bronchial brushings by quantitative real-time PCR and Western blot. Induced sputum differentials were obtained.

RESULTS

Severe asthma was associated with the highest levels of iNOS protein and mRNA, although the index of iNOS mRNA to arginase2 mRNA most strongly differentiated severe from milder asthma. When evaluating NO-related enzyme functionality, iNOS mRNA/protein expression both strongly predicted FeNO (r = 0.61, P < 0.0001 for both). Only iNOS protein predicted NT levels (r = 0.48, P = 0.003) with the strongest relationship in severe asthma (r = 0.61, P = 0.009). The iNOS protein, FeNO and NT, all correlated with sputum eosinophils, but the relationships were again strongest in severe asthma. Controlling for arginase 2 mRNA/protein did not impact any functional outcome.

CONCLUSIONS AND CLINICAL RELEVANCE

These data suggest that while iNOS expression from epithelial brushings is highest in severe asthma, factors controlling arginase2 mRNA expression significantly improve differentiation of severity. In contrast, functionality of the NO pathway as measured by FeNO, NT and eosinophilic inflammation, is strongly associated with iNOS expression alone, particularly in severe asthma.

Free radical-producing myeloid-derived regulatory cells: potent activators and suppressors of lung inflammation and airway hyperresponsiveness

Levels of reactive free radicals are elevated in the airway during asthmatic exacerbations, but their roles in the pathophysiology of asthma remain unclear. We have identified subsets of myeloid-derived suppressor-like cells as key sources of nitric oxide and superoxide in the lungs of mice with evolving experimental allergic airway inflammation and established these cells as master regulators of the airway inflammatory response. The profiles of free radicals they produced depended on expression of inducible nitric oxide synthase (iNOS), arginase, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. These radicals controlled the pro- and anti-inflammatory potential of these cells, and also regulated the reciprocal pattern of their infiltration into the lung. The nitric oxide-producing cells were Ly-6C(+)Ly-6G(-) and they downmodulated T-cell activation, recruited T(reg) cells, and dramatically downregulated antigen-induced airway hyperresponsiveness. The superoxide-producing cells were Ly-6C(-)Ly-6G(+) and they expressed proinflammatory activities, exacerbating airway hyperresponsiveness in a superoxide-dependent fashion. A smaller population of Ly-6C(+)Ly-6G(+) cells also suppressed T-cell responses, but in an iNOS- and arginase-independent fashion. These regulatory myeloid cells represent important targets for asthma therapy.

Nitric oxide metabolism in asthma pathophysiology

BACKGROUND

Asthma, a chronic inflammatory disease is typically characterized by bronchoconstriction and airway hyper-reactivity.

SCOPE OF REVIEW

A wealth of studies applying chemistry, molecular and cell biology to animal model systems and human asthma over the last decade has revealed that asthma is associated with increased synthesis of the gaseous molecule nitric oxide (NO).

MAJOR CONCLUSION

The high NO levels in the oxidative environment of the asthmatic airway lead to greater formation of reactive nitrogen species (RNS) and subsequent oxidation and nitration of proteins, which adversely affect protein functions that are biologically relevant to chronic inflammation. In contrast to the high levels of NO and nitrated products, there are lower levels of beneficial S-nitrosothiols (RSNO), which mediate bronchodilation, due to greater enzymatic catabolism of RSNO in the asthmatic airways.

GENERAL SIGNIFICANCE

This review discusses the rapidly accruing data linking metabolic products of NO as critical determinants in the chronic inflammation and airway reactivity of asthma. This article is part of a Special Issue entitled Biochemistry of Asthma.

TGF-β2 reduces nitric oxide synthase mRNA through a ROCK-dependent pathway in airway epithelial cells

Exhaled NO (eNO) is a potential noninvasive biomarker of inflammation in asthma. The significant intersubject variability of eNO within clinically similar patients has contributed to its limited clinical application. Arginase and NO synthase (NOS) utilize the same substrate (l-arginine) and contribute to the fibrotic and inflammatory features of asthma, respectively. Interestingly, TGF-β(2) can increase the expression of arginase, stimulates fibrosis, and is overexpressed in asthma. We hypothesized that TGF-β(2)-enhanced arginase activity would decrease gas phase NO release from lung epithelial cells by limiting l-arginine availability for NOS. Our results show that TGF-β(2) (5 ng/ml) significantly enhances total arginase activity up to two- to threefold in both primary small airway epithelial cells (SAECs) and the A549 cell line. Preincubation with TGF-β(2) prior to cytokine (IL-1β, TNF-α, and IFN-γ, 10 ng/ml each) stimulation decreases gas phase NO release to baseline levels (from 1.66 ± 0.52 to 0.30 ± 0.12 pl·s(-1)·cm(-2) and from 0.27 ± 0.03 pl·s(-1)·cm(-2) to near zero in SAEC and A549 cells, respectively). Addition of arginase inhibitor (N(ω)-hydroxy-nor-l-arginine) or small interfering RNA only partly reverses the reduction. In contrast, Rho-kinase (ROCK) pathway inhibitor (Y-27632) completely recovers the cytokine-induced NO flux in the present of TGF-β(2). Inducible NO synthase (iNOS) mRNA and protein levels change in a similar trend as NO release from the cells. We conclude that TGF-β(2) impacts cytokine-induced NO production in airway epithelial cells by reducing iNOS mRNA and protein levels through a ROCK-dependent pathway.

Modeling gas phase nitric oxide release in lung epithelial cells

Nitric oxide (NO) is present in exhaled breath and is generally considered to be a noninvasive marker of airway inflammation, and is thus of particular relevance to monitoring asthma. NO is produced when L-arginine is converted to L-citrulline by NO synthase (NOS); however, L-arginine is also the substrate for arginase and both enzymes are upregulated in asthma. Recent reports have speculated that enhanced expression of one or both enzymes could lead to a limitation in substrate availability, and hence impact downstream targets or markers such as exhaled NO. The non-linear nature and vastly different kinetics of the enzymes make predictions difficult, particularly over the wide range of enzyme activity between baseline and inflammation. In this study, we developed a steady state model of L-arginine transmembrane transport, NO production, diffusion, and gas phase NO release from lung epithelial cells. We validated our model with experimental results of gas phase NO release and intracellular l-arginine concentration in A549 cells, and then performed a sensitivity analysis to determine relative impact of each enzyme on NO production. Our model predicts intracellular L-arginine and gas phase NO release over a wide range of initial extracellular L-arginine concentrations following stimulation with cytomix (10ng/ml TNF-α, IL-1β, and INF-γ). Relative sensitivity analysis demonstrates that enhanced arginase activity has little impact on l-arginine bioavailability for NOS. In addition, NOS activity is the dominant parameter which impacts gas phase NO release.

DNA methylation in the arginase-nitric oxide synthase pathway is associated with exhaled nitric oxide in children with asthma

RATIONALE

Genetic variation in arginase (ARG) and nitric oxide synthase (NOS) has been associated with exhaled nitric oxide (FeNO) levels in children. Little is known about whether epigenetic variation in these genes modulates FeNO.

OBJECTIVES

To evaluate whether DNA methylation in ARG and NOS genes is associated with FeNO.

METHODS

A subset of 940 participants in the Children's Health Study were selected for this study. Children were eligible if they had FeNO measurements and buccal cells collected on the same day. CpG loci located in the promoter regions of NOS1, NOS2A, NOS3, ARG1, and ARG2 genes were analyzed. Multiple loci in each gene were evaluated individually and averaged together. DNA methylation was measured using a bisulfite-polymerase chain reaction pyrosequencing assay. Linear regression models were used to investigate the association between DNA methylation and FeNO and whether associations differed by asthma status.

MEASUREMENTS AND MAIN RESULTS

DNA methylation in ARG2 was significantly associated with FeNO. A 1% increase in average DNA methylation of ARG2 was associated with a 2.3% decrease in FeNO (95% confidence interval, -4 to -0.6). This association was significantly larger in children with asthma (%diff = -8.7%) than in children with no asthma (%diff = -1.6%; p(int) = 0.01). Differences in FeNO by asthma status were also observed for ARG1 (%diff(asthma) = -4.4%; %diff(non-asthma) = 0.3%; p(int) = 0.02). DNA methylation in NOS genes was not associated with FeNO.

CONCLUSIONS

DNA methylation in ARG1 and ARG2 is associated with FeNO in children with asthma and suggests a possible role for epigenetic regulation of nitric oxide production.

Asthma in sickle cell disease: implications for treatment

Objective. To review issues related to asthma in sickle cell disease and management strategies. Data Source. A systematic review of pertinent original research publications, reviews, and editorials was undertaken using MEDLlNE, the Cochrane Library databases, and CINAHL from 1947 to November 2010. Search terms were [asthma] and [sickle cell disease]. Additional publications considered relevant to the sickle cell disease population of patients were identified; search terms included [sickle cell disease] combined with [acetaminophen], [pain medications], [vitamin D], [beta agonists], [exhaled nitric oxide], and [corticosteroids]. Results. The reported prevalence of asthma in children with sickle cell disease varies from 2% to approximately 50%. Having asthma increases the risk for developing acute chest syndrome , death, or painful episodes compared to having sickle cell disease without asthma. Asthma and sickle cell may be linked by impaired nitric oxide regulation, excessive production of leukotrienes, insufficient levels of Vitamin D, and exposure to acetaminophen in early life. Treatment of sickle cell patients includes using commonly prescribed asthma medications; specific considerations are suggested to ensure safety in the sickle cell population. Conclusion. Prospective controlled trials of drug treatment for asthma in patients who have both sickle cell disease and asthma are urgently needed.

Increased expression of arginase I and II in allergic nasal mucosa

OBJECTIVES/HYPOTHESIS

It is known that arginase may be a regulator of diverse pathways, including production of nitric oxide (NO). Increased expression of arginase has been reported in several inflammatory lung diseases, including allergic asthma, suggesting that this may be a common feature underlying the pathophysiology of airway hyperreactivity. Thus, arginase I and II may play a role in the pathogenesis of allergic rhinitis. The distribution pattern and level of expression of arginase I and II were therefore determined in normal and allergic nasal mucosa.

STUDY DESIGN

Controlled, prospective study.

METHODS

The distribution pattern and level of expression of arginase I and II in normal and allergic nasal mucosa were evaluated using RT-PCR, immunohistochemistry, and Western blotting.

RESULTS

The level of expression of arginase I and II mRNA was increased in allergic nasal mucosa in comparison with normal nasal mucosa. In normal nasal mucosa, arginase I and II were expressed in the surface epithelium, submucosal glands, vascular endothelium, and fibroblasts. In allergic nasal mucosa, both enzymes were also localized to similar sites, in addition to inflammatory cells, and the level of expression were greatly increased compared with normal nasal mucosa. These findings were verified by Western blotting.

CONCLUSIONS

These results indicate that arginase I and II may play a role in the pathophysiology of allergic rhinitis, and suggest the possible role of the L-arginine metabolic pathway through modulation of L-arginine availability as a substrate for nitric oxide synthase (NOS) and arginase in the pathogenesis of allergic rhinitis.

2-aminoimidazole amino acids as inhibitors of the binuclear manganese metalloenzyme human arginase I

Arginase, a key metalloenzyme of the urea cycle that converts L-arginine into L-ornithine and urea, is presently considered a pharmaceutical target for the management of diseases associated with aberrant l-arginine homeostasis, such as asthma, cardiovascular diseases, and erectile dysfunction. We now report the design, synthesis, and evaluation of a series of 2-aminoimidazole amino acid inhibitors in which the 2-aminoimidazole moiety serves as a guanidine mimetic. These compounds represent a new class of arginase inhibitors. The most potent inhibitor identified in this study, 2-(S)-amino-5-(2-aminoimidazol-1-yl)pentanoic acid (A1P, 10), binds to human arginase I with K(d) = 2 microM and significantly attenuates airways hyperresponsiveness in a murine model of allergic airways inflammation. These findings suggest that 2-aminoimidazole amino acids represent new leads for the development of arginase inhibitors with promising pharmacological profiles.

Exhaled nitric oxide in the diagnosis and management of childhood asthma

The management of asthma in children and adolescents is currently guided by assessment of clinical symptoms, exacerbation risk and spirometric measure of lung function. The use of biomarkers, an objective measure which indicates normal or pathophysiologic processes and/or the response to a treatment intervention, could greatly enhance the efficacy and safety of current algorithms. Measurement of the fraction of expired nitric oxide in exhaled air (FeNO) has been suggested as a readily determined biomarker that can aid in the diagnosis and management of asthma. FeNO has been used to identify steroid responsive patients, adjust the dose of controller medications, most notably inhaled corticosteroids, and predict relapse during medication taper. In spite of early enthusiasm for the utility of this measure, more recent data suggest a more limited role for FeNO. This review will focus on the use of FeNO in the diagnosis and management of asthma in children and adolescents.

Advancing from immunonutrition to a pharmaconutrition: a gigantic challenge

PURPOSE OF REVIEW

This review presents some difficulties encountered to develop and translate immunonutrition into clinical practice, and suggests moving forward to a pharmaconutrition approach.

RECENT FINDINGS

Immunonutrition suffers from inconclusive and contradictory data due to the design of many of experiments and clinical studies conducted so far. The concept of a single immunonutrient formula applicable to various types of patients has also contributed to leave the medical world in a state of uncertainty. We propose to move forward to the concept of pharmaconutrition where a disease-dedicated nutrition therapy is developed following a rigorous step-by-step procedure. Nutrients are selected according to their pharmacological properties and after an in-depth evaluation of their biological interactions when mixed together. The optimum administration schedule (i.e. dose, route, timing and duration) of the new formulae is then determined in well conducted projective clinical trials where it is administered apart from the standard nutrition to ensure full delivery of the expected doses.

SUMMARY

This review suggests moving forward to a pharmaconutrition approach where a rigorous step-by-step procedure would allow overcoming of the difficulties encountered to translate immunonutrition into clinical practice.

Mepacrine inhibits subepithelial fibrosis by reducing the expression of arginase and TGF-beta1 in an extended subacute mouse model of allergic asthma

Asthma is a dynamic disorder of airway inflammation and airway remodeling with an imbalance in T helper type 1 (Th(1))/Th(2) immune response. Increased Th(2) cytokines such as IL-4 and IL-13 induce arginase either directly or indirectly through transforming growth factor-beta(1) (TGF-beta(1)) and lead to subepithelial fibrosis, which is a crucial component of airway remodeling. Synthetic antimalarials have been reported to have immunomodulatory properties. Mepacrine is known for its reduction of airway inflammation in short-term allergen challenge model by reducing Th(2) cytokines and cysteinyl leukotrienes, which has an important role in the development of airway remodeling features. Therefore, we hypothesized that mepacrine may reduce airway remodeling. For this, extended subacute ovalbumin mice model of asthma was developed; these mice showed an increased expression of profibrotic mediators, subepithelial fibrosis, and goblet cell metaplasia along with airway inflammation, increased Th(2) cytokines, allergen-specific IgE, IgG(1), increased cytosolic PLA(2) (cPLA(2)), and airway hyperresponsiveness. Presence of intraepithelial eosinophils and significant TGF-beta(1) expression in subepithelial mesenchymal regions by repeated allergen exposures indicate that asthmatic mice of this study have developed human mimicking as well as late stages of asthma. However, mepacrine treatment decreased Th(2) cytokines and subepithelial fibrosis and alleviated asthma features. These reductions by mepacrine were associated with a decrease in levels and expression of TGF-beta(1) and the reduction in activity, expression of arginase in lung cytosol, and immunolocalization in inflammatory cells present in perivascular and peribronchial regions. These results suggest that mepacrine might reduce the development of subepithelial fibrosis by reducing the arginase and TGF-beta(1). These effects of mepacrine likely underlie its antiairway remodeling action in asthma.

Identification of gene biomarkers for respiratory syncytial virus infection in a bronchial epithelial cell line

Respiratory syncytial virus (RSV) infection involves complex virus-host interplay. In this study, we analyzed gene expression in RSV-infected BEAS-2B cells to discover novel signaling pathways and biomarkers. We hybridized RNAs from RSV- or vehicle-treated BEAS-2B to Affymetrix HU133 plus 2.0 microarrays (n = 4). At 4 and 24 h post-infection, 277 and 900 genes (RSV/control ratio >/=2.0 or </=0.5), and 1 and 12 pathways respectively were significantly altered. Twenty-three and 92 genes at 4 and 24 h respectively matched respiratory disease biomarkers with ARG2 flagged at 24 h and SCNN1G, EPB41L4B, CSF1, PTEN, TUBB1 and ESR2 at both time points. Hierachical clustering showed a cluster containing ARG2 and IL8. In human bronchial epithelial cells, RSV upregulated arginase II protein. Knockdown of ARG2 increased RSV-induced IL-8, LDH and histone release. With microarray, we identified novel proximal airway epithelial cell genes that may be tested in the sputum samples as biomarkers of RSV infection.

Animal models of airway inflammation and airway smooth muscle remodelling in asthma

Asthma is a complex disease that involves chronic inflammation and subsequent decline in airway function. The widespread use of animal models has greatly contributed to our understanding of the cellular and molecular pathways underlying human allergic asthma. Animal models of allergic asthma include smaller animal models which offer 'ease of use' and availability of reagents, and larger animal models that may be used to address aspects of allergic airways disease not possible in humans or smaller animal models. This review examines the application and suitability of various animal models for studying mechanisms of airway inflammation and tissue remodelling in allergic asthma, with a specific focus on airway smooth muscle.

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

l-Arginine metabolism by the arginase and nitric oxide (NO) synthase (NOS) families of enzymes is important in NO production, and imbalances between these pathways contribute to airway hyperresponsiveness (AHR) in asthma. To investigate the role of arginase isozymes (ARG1 and ARG2) in AHR, we determined the protein expression of ARG1, ARG2, the NOS isozymes, and other proteins involved in l-arginine metabolism in lung tissues from asthma patients and in acute (3-wk) and chronic (12-wk) murine models of ovalbumin-induced airway inflammation. Expression of ARG1 was increased in human asthma, whereas ARG2, NOS isoforms, and the other l-arginine-related proteins (i.e., cationic amino acid transporters 1 and 2, agmatinase, and ornithine decarboxylase) were unchanged. In the acute murine model of allergic airway inflammation, augmentation of ARG1 expression was similarly the most dramatic change in protein expression. However, ARG2, NOS1, NOS2, and agmatinase were also increased, whereas NOS3 expression was decreased. Arginase inhibition in vivo with nebulized S-(2-boronoethyl)-l-cysteine attenuated the methacholine responsiveness of the central airways in mice from the acute model. Further investigations in the chronic murine model revealed an expression profile that more closely paralleled the human asthma samples: only ARG1 expression was significantly increased. Interestingly, in the chronic mouse model, which generates a remodeling phenotype, arginase inhibition attenuated methacholine responsiveness of the central and peripheral airways. The similarity in arginase expression between human asthma and the chronic model and the attenuation of AHR after in vivo treatment with an arginase inhibitor suggest the potential for therapeutic modification of arginase activity in asthma.

New asthma biomarkers: lessons from murine models of acute and chronic asthma

Many patients suffering from asthma are not fully controlled by currently available treatments, and some of them display an airway remodeling leading to exaggerated lung function decline. The aim of the present study was to unveil new mediators in asthma to better understand pathophysiology and propose or validate new potential therapeutic targets. A mouse model of asthma mimicking acute or chronic asthma disease was used to select genes undergoing a modulation in both acute and chronic conditions. Mice were exposed to ovalbumin or PBS for 1, 5, and 10 wk [short-, intermediate-, and long-term model (ST, IT, and LT)], and gene expression in the lung was studied using an Affymetrix 430 2.0 genome-wide microarray and further confirmed by RT-PCR and immunohistochemistry for selected targets. We report that 598, 1,406, and 117 genes were upregulated and 490, 153, 321 downregulated at ST, IT, and LT, respectively. Genes related to mucous secretion displayed a progressively amplified expression during the allergen exposure protocol, whereas genes corresponding to growth and differentiation factors, matrix metalloproteinases, and collagens were mainly upregulated at IT. By contrast, genes related to cell division were upregulated at ST and IT and were downregulated at LT. In this study, besides confirming that Arg1, Slc26a4, Ear11, and Mmp12 genes are highly modulated throughout the asthma pathology, we show for the first time that Agr2, Scin, and Cd209e genes are overexpressed throughout the allergen exposure and might therefore be considered as suitable new potential targets for the treatment of asthma.

Inhibition of arginase activity enhances inflammation in mice with allergic airway disease, in association with increases in protein S-nitrosylation and tyrosine nitration

Pulmonary inflammation in asthma is orchestrated by the activity of NF-kappaB. NO and NO synthase (NOS) activity are important modulators of inflammation. The availability of the NOS substrate, l-arginine, is one of the mechanisms that controls the activity of NOS. Arginase also uses l-arginine as its substrate, and arginase-1 expression is highly induced in a murine model of asthma. Because we have previously described that arginase affects NOx content and interferes with the activation of NF-kappaB in lung epithelial cells, the goal of this study was to investigate the impact of arginase inhibition on the bioavailability of NO and the implications for NF-kappaB activation and inflammation in a mouse model of allergic airway disease. Administration of the arginase inhibitor BEC (S-(2-boronoethyl)-l-cysteine) decreased arginase activity and caused alterations in NO homeostasis, which were reflected by increases in S-nitrosylated and nitrated proteins in the lungs from inflamed mice. In contrast to our expectations, BEC enhanced perivascular and peribronchiolar lung inflammation, mucus metaplasia, NF-kappaB DNA binding, and mRNA expression of the NF-kappaB-driven chemokine genes CCL20 and KC, and lead to further increases in airways hyperresponsiveness. These results suggest that inhibition of arginase activity enhanced a variety of parameters relevant to allergic airways disease, possibly by altering NO homeostasis.

Alterations of the arginine metabolome in asthma

RATIONALE

As the sole nitrogen donor in nitric oxide (NO) synthesis and key intermediate in the urea cycle, arginine and its metabolic pathways are integrally linked to cellular respiration, metabolism, and inflammation.

OBJECTIVES

We hypothesized that arginine (Arg) bioavailability would be associated with airflow abnormalities and inflammation in subjects with asthma, and would be informative for asthma severity.

METHODS

Arg bioavailability was assessed in subjects with severe and nonsevere asthma and healthy control subjects by determination of plasma Arg relative to its metabolic products, ornithine and citrulline, and relative to methylarginine inhibitors of NO synthases, and by serum arginase activity. Inflammatory parameters, including fraction of exhaled NO (Fe(NO)), IgE, skin test positivity to allergens, bronchoalveolar lavage, and blood eosinophils, were also evaluated.

MEASUREMENTS AND MAIN RESULTS

Subjects with asthma had greater Arg bioavailability, but also increased Arg catabolism compared with healthy control subjects, as evidenced by higher levels of Fe(NO) and serum arginase activity. However, Arg bioavailability was positively associated with Fe(NO) only in healthy control subjects; Arg bioavailability was unrelated to Fe(NO) or other inflammatory parameters in severe or nonsevere asthma. Inflammatory parameters were related to airflow obstruction and reactivity in nonsevere asthma, but not in severe asthma. Conversely, Arg bioavailability was related to airflow obstruction in severe asthma, but not in nonsevere asthma. Modeling confirmed that measures of Arg bioavailabilty predict airflow obstruction only in severe asthma.

CONCLUSIONS

Unlike Fe(NO), Arg bioavailability is not a surrogate measure of inflammation; however, Arg bioavailability is strongly associated with airflow abnormalities in severe asthma.

ARG1 is a novel bronchodilator response gene: screening and replication in four asthma cohorts

RATIONALE

Inhaled beta-agonists are one of the most widely used classes of drugs for the treatment of asthma. However, a substantial proportion of patients with asthma do not have a favorable response to these drugs, and identifying genetic determinants of drug response may aid in tailoring treatment for individual patients.

OBJECTIVES

To screen variants in candidate genes in the steroid and beta-adrenergic pathways for association with response to inhaled beta-agonists.

METHODS

We genotyped 844 single nucleotide polymorphisms (SNPs) in 111 candidate genes in 209 children and their parents participating in the Childhood Asthma Management Program. We screened the association of these SNPs with acute response to inhaled beta-agonists (bronchodilator response [BDR]) using a novel algorithm implemented in a family-based association test that ranked SNPs in order of statistical power. Genes that had SNPs with median power in the highest quartile were then taken for replication analyses in three other asthma cohorts.

MEASUREMENTS AND MAIN RESULTS

We identified 17 genes from the screening algorithm and genotyped 99 SNPs from these genes in a second population of patients with asthma. We then genotyped 63 SNPs from four genes with significant associations with BDR, for replication in a third and fourth population of patients with asthma. Evidence for association from the four asthma cohorts was combined, and SNPs from ARG1 were significantly associated with BDR. SNP rs2781659 survived Bonferroni correction for multiple testing (combined P value = 0.00048, adjusted P value = 0.047).

CONCLUSIONS

These findings identify ARG1 as a novel gene for acute BDR in both children and adults with asthma.

BYK191023 (2-[2-(4-methoxy-pyridin-2-yl)-ethyl]-3h-imidazo[4,5-b]pyridine) is an NADPH- and time-dependent irreversible inhibitor of inducible nitric-oxide synthase

Imidazopyridine derivates were recently shown to be a novel class of selective and arginine-competitive inhibitors of inducible nitric-oxide synthase (iNOS), and 2-[2-(4-methoxypyridin-2-yl)-ethyl]-3H-imidazo[4,5-b]pyridine (BYK191023) was found to have very high selectivity in enzymatic and cellular models ( Mol Pharmacol 69: 328-337, 2006 ). Here, we show that BYK191023 irreversibly inactivates murine iNOS in an NADPH- and time-dependent manner, whereas it acts only as a reversible l-arginine-competitive inhibitor in the absence of NADPH or during anaerobic preincubation. Time-dependent irreversible inhibition by BYK191023 could also be demonstrated in intact cells using the RAW macrophage or iNOS-overexpressing human embryonic kidney 293 cell lines. The mechanism of BYK191023 inhibition in the presence of NADPH was studied using spectral, kinetic, chromatographic, and radioligand binding methods. BYK191023-bound iNOS was spectrally indistinguishable from l-arginine-bound iNOS, pointing to an interaction of BYK191023 with the catalytic center of the enzyme. [(3)H]BYK191023 was recovered quantitatively from irreversibly inactivated iNOS, and no inhibitor metabolite was detected by high-performance liquid chromatography (HPLC). Size exclusion chromatography revealed only about 20% iNOS dissociation into monomers. Furthermore, HPLC and spectrophotometric analysis showed that the irreversible inhibition was associated with loss of heme from iNOS and a reduced ability to form the distinctive ferrous heme-CO complex (cytochrome P450). Thus, enzyme inactivation is mainly caused by heme loss, and it occurs in the inhibitor-bound enzyme in the presence of electron flux from NADPH.