Competitive metabolism of L-arginine: arginase as a therapeutic target in asthma

Consistent Multi-Omic Relationships Uncover Molecular Basis of Pediatric Asthma IgE Regulation

Serum total immunoglobulin E levels (total IgE) capture the state of the immune system in relation to allergic sensitization. High levels are associated with airway obstruction and poor clinical outcomes in pediatric asthma. Inconsistent patient response to anti-IgE therapies motivates discovery of molecular mechanisms underlying serum IgE level differences in children with asthma. To uncover these mechanisms using complementary metabolomic and transcriptomic data, abundance levels of 529 named metabolites and expression levels of 22,772 genes were measured among children with asthma in the Childhood Asthma Management Program (CAMP, N=564) and the Genetic Epidemiology of Asthma in Costa Rica Study (GACRS, N=309) via the TOPMed initiative. Gene-metabolite associations dependent on IgE were identified within each cohort using multivariate linear models and were interpreted in a biochemical context using network topology, pathway and chemical enrichment, and representation within reactions. A total of 1,617 total IgE-dependent gene-metabolite associations from GACRS and 29,885 from CAMP met significance cutoffs. Of these, glycine and guanidinoacetic acid (GAA) were associated with the most genes in both cohorts, and the associations represented reactions central to glycine, serine, and threonine metabolism and arginine and proline metabolism. Pathway and chemical enrichment analysis further highlighted additional related pathways of interest. The results of this study suggest that GAA may modulate total IgE levels in two independent pediatric asthma cohorts with different characteristics, supporting the use of L-Arginine as a potential therapeutic for asthma exacerbation. Other potentially new targetable pathways are also uncovered.

Stimulation of Formyl Peptide Receptor-2 by the New Agonist CMC23 Protects against Endotoxin-Induced Neuroinflammatory Response: A Study in Organotypic Hippocampal Cultures

A substantial body of evidence demonstrates an association between a malfunction in the resolution of acute inflammation and the development of chronic inflammation. Recently, in this context, the importance of formyl peptide receptor 2 (FPR2) has been underlined. FPR2 activity is modulated by a wide range of endogenous ligands, including specialized pro-resolving mediators (SPMs) (e.g., LXA4 and AT-LXA4) and synthetic ligands. Since SPMs have unfavorable pharmacokinetic properties, we aimed to evaluate the protective and pro-resolving effects of a new potent FPR2 agonist, compound CMC23, in organotypic hippocampal cultures (OHCs) stimulated with lipopolysaccharide (LPS). The protective activity of CMC23 limited the lactate dehydrogenase release in LPS-stimulated cultures. This activity was mediated by the interaction with FPR2 as pretreatment with the FPR2 selective antagonist WRW4 abolished CMC23-induced protection. Furthermore, decreased levels of pro-inflammatory IL-1β and IL-6 were observed after CMC23 administration in LPS-treated OHCs. CMC23 also diminished the LPS-induced increase in IL-17A and both IL-23 subunits p19 and p40 in OHCs. Finally, we demonstrated that CMC23 exerts its beneficial impact via the STAT3/SOCS3 signaling pathway since it attenuated the level of phospho-STAT3 and maintained the LPS-induced SOCS3 levels in OHCs. Collectively, our research implies that the new FPR2 agonist CMC23 has beneficial protective and anti-inflammatory properties in nanomolar doses and FPR2 represents a promising target for the enhancement of inflammation resolution.

To What Extent Does Arginine Reduce the Risk of Developing Necrotizing Enterocolitis?

Necrotizing enterocolitis (NEC) and neonatal sepsis are polar opposite diseases that are commonly encountered in the NICU. Concerning the frequency of these pathologies, NEC is regarded as being a much rarer condition, whereas neonatal sepsis is slightly more commonly encountered. However, neonatal sepsis can present with varying clinical presentations and, if caught late, can be detrimental to the patient. Many different modes of therapies have been studied for both conditions at different levels of pathologies, from a microscopic to a macroscopic level, leading to an assessment of treatment approaches. With the different ongoing treatment protocols being studied, one such therapy under investigation that does stand out is the use of L-arginine in both conditions. The L-arginine, being an essential amino acid, has many basic biological roles in developing neonates. It mainly involves the production of nitric oxide (NO), a potent vasodilator, which is particularly important in the development of vasculature in almost every organ. In premature infants, poorly developed vasculature makes them more susceptible to injury, therefore increasing the risk of diseases such as NEC and the severity of diseases such as neonatal sepsis. By assessing the uses of L-arginine and its application towards treating conditions like NEC and neonatal sepsis, we aim to identify its potential benefits as a treatment and its potential applications in clinical practice by understanding its basic functions and role in the pathophysiology of NEC and neonatal sepsis.

Mitochondria signaling pathways in allergic asthma

Mitochondria, as the powerhouse organelle of cells, are greatly involved in regulating cell signaling pathways, including those related to the innate and acquired immune systems, cellular differentiation, growth, death, apoptosis, and autophagy as well as hypoxic stress responses in various diseases. Asthma is a chronic complicated airway disease characterized by airway hyperresponsiveness, eosinophilic inflammation, mucus hypersecretion, and remodeling of airway. The asthma mortality and morbidity rates have increased worldwide, so understanding the molecular mechanisms underlying asthma progression is necessary for new anti-asthma drug development. The lung is an oxygen-rich organ, and mitochondria, by sensing and processing O₂, contribute to the generation of ROS and activation of pro-inflammatory signaling pathways. Asthma pathophysiology has been tightly associated with mitochondrial dysfunction leading to reduced ATP synthase activity, increased oxidative stress, apoptosis induction, and abnormal calcium homeostasis. Defects of the mitochondrial play an essential role in the pro-remodeling mechanisms of lung fibrosis and airway cells’ apoptosis. Identification of mitochondrial therapeutic targets can help repair mitochondrial biogenesis and dysfunction and reverse related pathological changes and lung structural remodeling in asthma. Therefore, we here overviewed the relationship between mitochondrial signaling pathways and asthma pathogenic mechanisms.

Gene expression of oxidative stress markers and lung function: A CARDIA lung study

BACKGROUND

Circulating markers of oxidative stress have been associated with lower lung function. Our objective was to study the association of gene expression levels of oxidative stress pathway genes (ALOX12, ALOX15, ARG2, GSTT1, LPO, MPO, NDUFB3, PLA2G7, and SOD3) and lung function forced expiratory volume in one second (FEV1 ), forced vital capacity (FVC) in Coronary Artery Risk Development in Young Adults study.

METHODS

Lung function was measured using spirometry and the Nanostring platform was used to estimate gene expression levels. Linear regression models were used to study association of lung function measured at year 30, 10-year decline in lung function and gene expression after adjustment for center, smoking, and BMI, measured at year 25.

RESULTS

The 10-year decline of FEV1 was faster in highest NDUFB3 quartile compared to the lowest (difference = -2.09%; p = 0.001) after adjustment for multiple comparisons. The 10-year decline in FEV1 and FVC was nominally slower in highest versus lowest quartile of PLA2G7 (difference = 1.14%; p = 0.02, and difference = 1.06%; p = 0.005, respectively). The other genes in the study were not associated with FEV1 or FVC.

CONCLUSION

Higher gene expression levels in oxidative stress pathway genes are associated with faster 10-year FEV1 decline.

L-arginine as a potential GLP-1-mediated immunomodulator of Th17-related cytokines in people with obesity and asthma

Obesity is considered as a risk factor for COVID‐19 with insulin resistance and increased production of inflammatory cytokines as likely mechanisms. Glucagon‐like peptide‐1 (GLP‐1) agonists and inhaled nitric oxide are proposed therapeutic approaches to treat COVID‐19 because of their broad anti‐inflammatory effects. One approach that might augment GLP‐1 levels would be dietary supplementation with L‐arginine. Beyond cytokines, multiple studies have started to investigate the relationship between new‐onset diabetes and COVID‐19. In a posthoc analysis of a randomized, placebo‐controlled human clinical trial of L‐arginine supplementation in people with asthma and predominantly with obesity, the results showed that 12 weeks of continuous L‐arginine supplementation significantly decreased the level of IL‐21 (p = 0.02) and increased the level of insulin (p = 0.02). A high arginine level and arginine/ADMA ratio were significantly associated with lower CCL‐20 and TNF‐α levels. The study also showed that L‐arginine supplementation reduces cytokine levels and improves insulin deficiency or resistance, both are two big risk factors for COVID‐19 severity and mortality. Given its safety profile and ease of accessibility, L‐arginine is an attractive potential therapeutic option that allows for a cost‐effective way to improve outcomes in patients. An expedition of further investigation or clinical trials to test these hypotheses is needed.

Exposure to traffic-related air pollution and changes in exhaled nitric oxide and DNA methylation in arginase and nitric oxide synthase in children with asthma

BACKGROUND

Traffic-related air pollution (TRAP) has been associated with increased risk of airway inflammation in children with asthma. While epigenetic changes could potentially modulate TRAP-induced inflammatory responses, few studies have assessed the temporal pattern of exposure to TRAP, epigenetic changes and inflammation in children with asthma. Our goal was to test the time-lag patterns of personal exposure to TRAP, airway inflammation (measured as fractional exhaled nitric oxide, FeNO), and DNA methylation in the promoter regions of genes involved in nitric oxide synthesis among children with asthma.

METHODS

We measured personal exposure to black carbon (BC) and FeNO for up to 30 days in a panel of children with asthma. We collected 90 buccal cell samples for DNA methylation analysis from 18 children (5 per child). Methylation in promoter regions of nitric oxide synthase (NOS1, NOS2A, NOS3) and arginase (ARG1, ARG2) was assessed by bisulfite pyrosequencing. Linear-mixed effect models were used to test the associations of BC at different lag periods, percent DNA methylation at each site and FeNO level.

RESULTS

Exposure to BC was positively associated with FeNO, and negatively associated with DNA methylation in NOS3. We found strongest association between FeNO and BC at lag 0-6 h while strongest associations between methylation at positions 1 and 2 in NOS3 and BC were at lag 13-24 h and lag 0-24 h, respectively. The strengths of associations were attenuated at longer lag periods. No significant associations between exposure to TRAP and methylation levels in other NOS and ARG isoforms were observed.

CONCLUSIONS

Exposure to TRAP was associated with higher levels of FeNO and lower levels of DNA methylation in the promoter regions of the NOS3 gene, indicating that DNA methylation of the NOS3 gene could be an important epigenetic mechanism in physiological responses to TRAP in children with asthma.

Lipid-mediated innate lymphoid cell recruitment and activation in aspirin-exacerbated respiratory disease

OBJECTIVE

To synthesize investigations into the role of lipid-mediated recruitment and activation of group 2 innate lymphoid cells (ILC2s) in aspirin-exacerbated respiratory disease (AERD).

DATA SOURCES

A comprehensive literature review of reports pertaining to cellular mechanisms, cytokine, and lipid mediators in AERD, as well as ILC2 activation and recruitment, was performed using PubMed and Google Scholar.

STUDY SELECTIONS

Selections of studies were based on reports of lipid mediators in AERD, cytokine mediators in AERD, type 2 effector cells in AERD, platelets in AERD, AERD treatment, ILC2s in allergic airway disease, and ILC2 activation, inhibition, and trafficking.

RESULTS

The precise mechanisms of AERD pathogenesis are not well understood. Greater levels of proinflammatory lipid mediators and type 2 cytokines are found in tissues derived from patients with AERD relative to controls. After pathognomonic cyclooxygenase-1 inhibitor reactions, proinflammatory mediator concentrations (prostaglandin D2 and cysteinyl leukotrienes) are rapidly increased, as are ILC2 levels in the nasal mucosa. The ILC2s, which potently generate type 2 cytokines in response to lipid mediator stimulation, may play a key role in AERD pathogenesis.

CONCLUSION

Although the literature suggests that lipid-mediated ILC2 activation may occur in AERD, there is a dearth of definitive evidence. Future investigations leveraging novel next-generation single-cell sequencing approaches along with recently developed AERD murine models will better define lipid mediator-induced ILC2 trafficking in patients with AERD.

Selective extracellular arginine deprivation by a single injection of cellular non-uptake arginine deiminase nanocapsules for sustained tumor inhibition

The metabolic enzyme-based arginine deprivation represents a tremendous opportunity to treat argininosuccinate synthetase (ASS1)-deficient tumors. Arginine deiminase (ADI), a typical representative, has aroused great interest. To date, the functional modification of ADI, such as PEGylation, has been applied to improve its weakness significantly, reducing its immunogenicity and extending its blood circulation time. However, the advantages of ADI, such as the cellular non-uptake property, are often deprived by current modification methods. The cellular non-uptake property of ADI only renders extracellular arginine degradation that negligibly influences normal cells. However, current-functionalized ADIs can be readily phagocytized by cells, causing the imbalance of intracellular amino acids and the consequent damage to normal cells. Therefore, it is necessary to exploit a new method that can simultaneously improve the weakness of ADI and maintain its advantage of cellular non-uptake. Here, we utilized a kind of phosphorylcholine (PC)-rich nanocapsule to load ADI. These nanocapsules possessed extremely weak cellular interaction and could avoid uptake by endothelial cells (HUVEC), immune cells (RAW 264.7), and tumor cells (H22), selectively depriving extracellular arginine. Besides, these nanocapsules increased the blood half-life time of ADI from the initial 2 h to 90 h and efficiently avoided its immune or inflammatory responses. After a single injection of ADI nanocapsules into H22 tumor-bearing mice, tumors were stably suppressed for 25 d without any detectable side effects. This new strategy first realizes the selective extracellular arginine deprivation for the treatment of ASS1-deficient tumors, potentially promoting the clinical translation of metabolic enzyme-based amino acid deprivation therapy. Furthermore, the research reminds us that the functionalization of drugs can not only improve its weakness but also maintain its advantages.

Naringin attenuates Bisphenol-A mediated neurotoxicity in hypertensive rats by abrogation of cerebral nucleotide depletion, oxidative damage and neuroinflammation

We examined whether active fruit naringin can reduce the risk of BPA-mediated neurotoxicity in L-NAME induced hypertensive rats and whether the modulation could be linked to improvement of brain NO signaling. Male albino rats were randomly distributed into eight (n = 7) groups. Group I was control animals, Group II was orally-treated with L-NAME, Group III was orally treated with 100 mg/kg BPA, Group IV was orally-treated with L-NAME +100 mg/kg BPA. Group V was orally-administered with L-NAME +80 mg/kg NAR. Group VI was orally-administered with 100 mg/kg BPA +80 mg/kg NAR. Group VII was orally-administered with L-NAME+100 mg/kg BPA +80 mg/kg NAR. Lastly, group VIII was orally-treated with 80 mg/kg NAR. The treatment lasted for 14 days. Sub-acute exposure to L-NAME and BPA induced hypertension and mediated-neuroinflammation at CA-2 and CA-4 of hippocampus cells. It was evident by increase in PDE-5¹ and enzymes of ATP hydrolysis (ATPase, ADPase and AMPase) with corresponding upsurge in cholinergic (AChE and BuChE), dopaminergic (MAO-A) and adenosinergic (ADA) enzymes as well as movement disorder. The hypertensive-mediated neurotoxicity was related to alteration of NO signaling and higher release of pro-inflammatory cytokines (TNF-α and IL-1β), apoptotic proteins (P53 and caspace-9) and facilitated entry of T-lymphocytes (CD43⁺) into CNS through blood brain barrier potentiated by antigen presenting cells. Hence, these features of BPA-mediated neurotoxicity in L-NAME induced hypertensive rats were prohibited by co-administration of NAR through production of neuro-inflammatory mediators, stabilizing neurotransmitter enzymes, normalizing NO signaling and improving brain histology.

l-Arginine supplementation in severe asthma

BACKGROUNDDysregulation of l-arginine metabolism has been proposed to occur in patients with severe asthma. The effects of l-arginine supplementation on l-arginine metabolite profiles in these patients are unknown. We hypothesized that individuals with severe asthma with low fractional exhaled nitric oxide (FeNO) would have fewer exacerbations with the addition of l-arginine to their standard asthma medications compared with placebo and would demonstrate the greatest changes in metabolite profiles.METHODSParticipants were enrolled in a single-center, crossover, double-blind l-arginine intervention trial at UCD. Subjects received placebo or l-arginine, dosed orally at 0.05 mg/kg (ideal body weight) twice daily. The primary end point was moderate asthma exacerbations. Longitudinal plasma metabolite levels were measured using mass spectrometry. A linear mixed-effect model with subject-specific intercepts was used for testing treatment effects.RESULTSA cohort of 50 subjects was included in the final analysis. l-Arginine did not significantly decrease asthma exacerbations in the overall cohort. Higher citrulline levels and a lower arginine availability index (AAI) were associated with higher FeNO (P = 0.005 and P = 2.51 × 10-9, respectively). Higher AAI was associated with lower exacerbation events. The eicosanoid prostaglandin H2 (PGH2) and Nα-acetyl-l-arginine were found to be good predictors for differentiating clinical responders and nonresponders.CONCLUSIONSThere was no statistically significant decrease in asthma exacerbations in the overall cohort with l-arginine intervention. PGH2, Nα-acetyl-l-arginine, and the AAI could serve as predictive biomarkers in future clinical trials that intervene in the arginine metabolome.TRIAL REGISTRATIONClinicalTrials.gov NCT01841281.FUNDINGThis study was supported by NIH grants R01HL105573, DK097154, UL1 TR001861, and K08HL114882. Metabolomics analysis was supported in part by a grant from the University of California Tobacco-Related Disease Research Program program (TRDRP).

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.

Impact of Arginine Nutrition and Metabolism during Pregnancy on Offspring Outcomes

By serving as a precursor for the synthesis of nitric oxide, polyamines, and other molecules with biological importance, arginine plays a key role in pregnancy and fetal development. Arginine supplementation is a potential therapy for treating many human diseases. An impaired arginine metabolic pathway during gestation might produce long-term morphological or functional changes in the offspring, namely, developmental programming to increase vulnerability to developing a variety of non-communicable diseases (NCDs) in later life. In contrast, reprogramming is a strategy that shifts therapeutic interventions from adulthood to early-life, in order to reverse the programming processes, which might counterbalance the rising epidemic of NCDs. This review presented the role of arginine synthesis and metabolism in pregnancy. We also provided evidence for the links between an impaired arginine metabolic pathway and the pathogenesis of compromised pregnancy and fetal programming. This was followed by reprogramming strategies targeting the arginine metabolic pathway, to prevent the developmental programming of NCDs. Despite emerging evidence from experimental studies showing that targeting the arginine metabolic pathway has promise as a reprogramming strategy in pregnancy to prevent NCDs in the offspring, these results need further clinical application.

Pulmonary group 2 innate lymphoid cells: surprises and challenges

Group 2 innate lymphoid cells (ILC2s) are a recently described subset of innate lymphocytes with important immune and homeostatic functions at multiple tissue sites, especially the lung. These cells expand locally after birth and during postnatal lung maturation and are present in the lung and other peripheral organs. They are modified by a variety of processes and mediate inflammatory responses to respiratory pathogens, inhaled allergens and noxious particles. Here, we review the emerging roles of ILC2s in pulmonary homeostasis and discuss recent and surprising advances in our understanding of how hormones, age, neurotransmitters, environmental challenges, and infection influence ILC2s. We also review how these responses may underpin the development, progression and severity of pulmonary inflammation and chronic lung diseases and highlight some of the remaining challenges for ILC2 biology.

Simvastatin and bone marrow-derived mesenchymal stem cells (BMSCs) affects serum IgE and lung cytokines levels in sensitized mice

INTRODUCTION

The effects of bone marrow-derived mesenchymal stem cells (BMSCs) and simvastatin combination therapy on serum total and specific IgE levels and lung IL-13 and TGF-β levels in sensitized mouse were examined.

MATERIAL AND METHODS

Control (n = 5), Sensitized (S), (n = 5), S + BMSC (n = 6), S + simvastatin (n = 6) and S + BMSC + simvastatin (n = 4) groups of BALB/c mice were studied. Mice were sensitized by ovalbumin. Sensitized mice were treated with a single intravenous injection of BMSCs (1 × 10⁶) or daily intraperitoneal injection of simvastatin (40 mg/kg) or both BMSCs and simvastatin on the last week of challenge. Serum total and ovalbumin specific IgE levels as well as IL-13 and TGF-β levels in broncho-alveolar lavage (BAL) fluid were evaluated.

RESULTS

Serum total and specific IgE levels as well as lung IL-13 and TGF-β levels were significantly increased in S group compared to control group (P < 0.001 for all cases). Treatment with BMSCs, simvastatin and their combination significantly decreased serum total and specific IgE levels (P < 0.05 to P < 0.01). However, IL-13 and TGF-β levels were significantly decreased by BMSCs and BMSC + simvastatin combination therapy (P < 0.05 for all cases). The effect of simvastatin and BMSCs combination therapy on serum specific IgE levels as well as lung IL-13 and TGF-β levels were significantly higher than the effect of BMSCs and simvastatin alone (P < 0.001 for IL-13 and P < 0.01 for other cases).

CONCLUSIONS

Simvastatin and BMSCs combination therapy affects serum IgE as well as lung IL-13 and TGFβ levels more than BMSC therapy and simvastatin therapy alone which may be due to increased BMSCs migration into the lung tissue.

Transcriptomic profiling reveals gene expression kinetics in patients with hypoxia and high altitude pulmonary edema

OBJECTIVE

High altitude pulmonary edema (HAPE) is a life threatening condition occurring in otherwise healthy individuals who rapidly ascend to high altitude. However, the molecular mechanisms of its pathophysiology are not well understood. The objective of this study is to evaluate differential gene expression in patients with HAPE during acute illness and subsequent recovery.

METHODS

Twenty-one individuals who ascended to an altitude of 3780 m were studied, including 12 patients who developed HAPE and 9 matched controls without HAPE. Whole-blood samples were collected during acute illness and subsequent recovery for analysis of the expression of hypoxia-related genes, and physiologic and laboratory parameters, including mean pulmonary arterial pressure (mPAP), heart rate, blood pressure, and arterial oxygen saturation (SpO₂), were also measured.

RESULTS

Compared with control subjects, numerous hypoxia-related genes were up-regulated in patients with acute HAPE. Gene network analyses suggested that HIF-1α played a central role in acute HAPE by affecting a variety of hypoxia-related genes, including BNIP3L, VEGFA, ANGPTL4 and EGLN1. Transcriptomic profiling revealed the expression of most HAPE-induced genes was restored to a normal level during the recovery phase except some key hypoxia response factors, such asBNIP3L, EGR1, MMP9 and VEGF, which remained persistently elevated.

CONCLUSIONS

Differential expression analysis of hypoxia-related genes revealed distinct molecular signatures of HAPE during acute and recovery phases. This study may help us to better understand HAPE pathogenesis and putative targets for further investigation and therapeutic intervention.

Arginine metabolic endotypes related to asthma severity

Aims

Arginine metabolism via inducible nitric oxide synthase (iNOS) and arginase 2 (ARG2) is higher in asthmatics than in healthy individuals. We hypothesized that a sub-phenotype of asthma might be defined by the magnitude of arginine metabolism categorized on the basis of high and low fraction of exhaled nitric oxide (F_ENO).

Methods

To test this hypothesis, asthmatics (n = 52) were compared to healthy controls (n = 51) for levels of F_ENO, serum arginase activity, and airway epithelial expression of iNOS and ARG2 proteins, in relation to clinical parameters of asthma inflammation and airway reactivity. In parallel, bronchial epithelial cells were evaluated for metabolic effects of iNOS and ARG2 expression in vitro.

Results

Asthmatics with high F_ENO (≥ 35 ppb; 44% of asthmatics) had higher expression of iNOS (P = 0.04) and ARG2 (P = 0.05) in the airway, indicating F_ENO is a marker of the high arginine metabolic endotype. High F_ENO asthmatics had the lowest FEV₁% (P < 0.001), FEV₁/FVC (P = 0.0002) and PC₂₀ (P < 0.001) as compared to low F_ENO asthmatics or healthy controls. Low F_ENO asthmatics had near normal iNOS and ARG2 expression (both P > 0.05), and significantly higher PC₂₀ (P < 0.001) as compared to high F_ENO asthmatics. In vitro studies to evaluate metabolic effects showed that iNOS overexpression and iNOS+ARG2 co-expression in a human bronchial epithelial cell line led to greater reliance on glycolysis with higher rate of pyruvate going to lactate.

Conclusions

The high F_ENO phenotype represents a large portion of the asthma population, and is typified by greater arginine metabolism and more severe and reactive asthma.

Nitric Oxide Synthase Activity Correlates with OGG1 in Ozone-Induced Lung Injury Animal Models

Background: NO is an important cellular signaling molecule which is derived from L-arginine by nitric oxide synthase (NOS) and the effects of NOS signaling in lung injury is conflicting. The present study was designed to observe the effect of NOS and Arginase signaling in the occurrence and development of lung injury and its mechanism. Methods: An ozone-stressed lung injury animal model was established by exposure to 2.0 ppm O₃ for 30 min every day for consecutive 12 day with or without the administration of NO precursor L-arginine or non-selective NOS inhibitor N-nitro-L-arginine methyl ester (L-NAME). Then, the lung histopathology, the releases of inflammatory mediators and the production of ROS were assayed by immunohistochemistry, ELISA and flow cytometry respectively. The activities and expression of NOS and Arginase were assayed by biochemical methods and western blot. Correspondingly, the release of 8-oxoguanine glycosylase 1(8-OxoG) and 8-oxoguanine glycosylase 1 (OGG1) were assayed by ELISA and western blot. The correlation between NOS/Arginase signaling with 8-OxoG/ OGG1 was also analyzed by Pearson correlation coefficients and immunofluorescence in NOS deficient bronchial epithelial cells. Results: In ozone-induced rat lung injury models, lung inflammation as well as lung architecture was disrupted in a time dependent manner. Ozone treatment with L-arginine showed a substantial attenuation of adverse lung histopathological changes and treatment with L-NAME promoted the inflammation and remodeling. Importantly, the expression of NOS was promoted by L-arginine and inhibited by L-NAME and the expression of Arginase was promoted by L-NAME treatment. Further, we observed significantly higher levels of 8-OxoG and lower levels of OGG1 in ozone group which was reversed by L-arginine and promoted by L-NAME. The expression of NOS is closely related with 8-OxoG /OCG1. Conclusion: These findings give further evidence that the NOS signaling is related with base excise repair.

Distinct Metabolic Profile of Inhaled Budesonide and Salbutamol in Asthmatic Children during Acute Exacerbation

Inhaled budesonide and salbutamol represent the most important and frequently used drugs in asthmatic children during acute exacerbation. However, there is still no consensus about their resulting metabolic derangements; thus, this study was conducted to determine the distinct metabolic profiles of these two drugs. A total of 69 children with asthma during acute exacerbation were included, and their serum and urine were investigated using high-resolution nuclear magnetic resonance (NMR). A metabolomics analysis was performed using a principal component analysis and orthogonal signal correction-partial least squares using SIMCA-P. The different metabolites were identified, and the distinct metabolic profiles were analysed using MetPA. A high-resolution NMR-based serum and urine metabolomics approach was established to study the overall metabolic changes after inhaled budesonide and salbutamol in asthmatic children during acute exacerbation. The perturbed metabolites included 22 different metabolites in the serum and 21 metabolites in the urine. Based on an integrated analysis, the changed metabolites included the following: increased 4-hydroxybutyrate, lactate, cis-aconitate, 5-hydroxyindoleacetate, taurine, trans-4-hydroxy-l-proline, tiglylglycine, 3-hydroxybutyrate, 3-methylhistidine, glucose, cis-aconitate, 2-deoxyinosine and 2-aminoadipate; and decreased alanine, glycerol, arginine, glycylproline, 2-hydroxy-3-methylvalerate, creatine, citrulline, glutamate, asparagine, 2-hydroxyvalerate, citrate, homoserine, histamine, sn-glycero-3-phosphocholine, sarcosine, ornithine, creatinine, glycine, isoleucine and trimethylamine N-oxide. The MetPA analysis revealed seven involved metabolic pathways: arginine and proline metabolism; taurine and hypotaurine metabolism; glycine, serine and threonine metabolism; glyoxylate and dicarboxylate metabolism; methane metabolism; citrate cycle; and pyruvate metabolism. The perturbed metabolic profiles suggest potential metabolic reprogramming associated with a combination treatment of inhaled budesonide and salbutamol in asthmatic children.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.

Increased mitochondrial arginine metabolism supports bioenergetics in asthma

High levels of arginine metabolizing enzymes, including inducible nitric oxide synthase (iNOS) and arginase (ARG), are typical in asthmatic airway epithelium; however, little is known about the metabolic effects of enhanced arginine flux in asthma. Here, we demonstrated that increased metabolism sustains arginine availability in asthmatic airway epithelium with consequences for bioenergetics and inflammation. Expression of iNOS, ARG2, arginine synthetic enzymes, and mitochondrial respiratory complexes III and IV was elevated in asthmatic lung samples compared with healthy controls. ARG2 overexpression in a human bronchial epithelial cell line accelerated oxidative bioenergetic pathways and suppressed hypoxia-inducible factors (HIFs) and phosphorylation of the signal transducer for atopic Th2 inflammation STAT6 (pSTAT6), both of which are implicated in asthma etiology. Arg2-deficient mice had lower mitochondrial membrane potential and greater HIF-2α than WT animals. In an allergen-induced asthma model, mice lacking Arg2 had greater Th2 inflammation than WT mice, as indicated by higher levels of pSTAT6, IL-13, IL-17, eotaxin, and eosinophils and more mucus metaplasia. Bone marrow transplants from Arg2-deficient mice did not affect airway inflammation in recipient mice, supporting resident lung cells as the drivers of elevated Th2 inflammation. These data demonstrate that arginine flux preserves cellular respiration and suppresses pathological signaling events that promote inflammation in asthma.

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.

Macrophage polarization drives granuloma outcome during Mycobacterium tuberculosis infection

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), induces formation of granulomas, structures in which immune cells and bacteria colocalize. Macrophages are among the most abundant cell types in granulomas and have been shown to serve as both critical bactericidal cells and targets for M. tuberculosis infection and proliferation throughout the course of infection. Very little is known about how these processes are regulated, what controls macrophage microenvironment-specific polarization and plasticity, or why some granulomas control bacteria and others permit bacterial dissemination. We take a computational-biology approach to investigate mechanisms that drive macrophage polarization, function, and bacterial control in granulomas. We define a "macrophage polarization ratio" as a metric to understand how cytokine signaling translates into polarization of single macrophages in a granuloma, which in turn modulates cellular functions, including antimicrobial activity and cytokine production. Ultimately, we extend this macrophage ratio to the tissue scale and define a "granuloma polarization ratio" describing mean polarization measures for entire granulomas. Here we coupled experimental data from nonhuman primate TB granulomas to our computational model, and we predict two novel and testable hypotheses regarding macrophage profiles in TB outcomes. First, the temporal dynamics of granuloma polarization ratios are predictive of granuloma outcome. Second, stable necrotic granulomas with low CFU counts and limited inflammation are characterized by short NF-κB signal activation intervals. These results suggest that the dynamics of NF-κB signaling is a viable therapeutic target to promote M1 polarization early during infection and to improve outcome.

Targeting the mevalonate cascade as a new therapeutic approach in heart disease, cancer and pulmonary disease

The cholesterol biosynthesis pathway, also known as the mevalonate (MVA) pathway, is an essential cellular pathway that is involved in diverse cell functions. The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR) is the rate-limiting step in cholesterol biosynthesis and catalyzes the conversion of HMG-CoA to MVA. Given its role in cholesterol and isoprenoid biosynthesis, the regulation of HMGCR has been intensely investigated. Because all cells require a steady supply of MVA, both the sterol (i.e. cholesterol) and non-sterol (i.e. isoprenoid) products of MVA metabolism exert coordinated feedback regulation on HMGCR through different mechanisms. The proper functioning of HMGCR as the proximal enzyme in the MVA pathway is essential under both normal physiologic conditions and in many diseases given its role in cell cycle pathways and cell proliferation, cholesterol biosynthesis and metabolism, cell cytoskeletal dynamics and stability, cell membrane structure and fluidity, mitochondrial function, proliferation, and cell fate. The blockbuster statin drugs ('statins') directly bind to and inhibit HMGCR, and their use for the past thirty years has revolutionized the treatment of hypercholesterolemia and cardiovascular diseases, in particular coronary heart disease. Initially thought to exert their effects through cholesterol reduction, recent evidence indicates that statins also have pleiotropic immunomodulatory properties independent of cholesterol lowering. In this review we will focus on the therapeutic applications and mechanisms involved in the MVA cascade including Rho GTPase and Rho kinase (ROCK) signaling, statin inhibition of HMGCR, geranylgeranyltransferase (GGTase) inhibition, and farnesyltransferase (FTase) inhibition in cardiovascular disease, pulmonary diseases (e.g. asthma and chronic obstructive pulmonary disease (COPD)), and cancer.

Effect of substrate competition in kinetic models of metabolic networks

Substrate competition can be found in many types of biological processes, ranging from gene expression to signal transduction and metabolic pathways. Although several experimental and in silico studies have shown the impact of substrate competition on these processes, it is still often neglected, especially in modelling approaches. Using toy models that exemplify different metabolic pathway scenarios, we show that substrate competition can influence the dynamics and the steady state concentrations of a metabolic pathway. We have additionally derived rate laws for substrate competition in reversible reactions and summarise existing rate laws for substrate competition in irreversible reactions.