Asymmetric dimethylarginine is increased in asthma

Arginine methylation and respiratory disease

Arginine methylation, a vital post-translational modification, plays a pivotal role in numerous cellular functions such as signal transduction, DNA damage response and repair, regulation of gene transcription, mRNA splicing, and protein interactions. Central to this modification is the role of protein arginine methyltransferases (PRMTs), which have been increasingly recognized for their involvement in the pathogenesis of various respiratory diseases. This review begins with an exploration of the biochemical underpinnings of arginine methylation, shedding light on the intricate molecular regulatory mechanisms governed by PRMTs. It then delves into the impact of arginine methylation and the dysregulation of arginine methyltransferases in diverse pulmonary disorders. Concluding with a focus on the therapeutic potential and recent advancements in PRMT inhibitors, this article aims to offer novel perspectives and therapeutic avenues for the management and treatment of respiratory diseases.

Impaired Nitric Oxide Synthetase Activity in Primary Ciliary Dyskinesia-Data-Driven Hypothesis

Low nasal nitric oxide (nNO) is a typical feature of Primary Ciliary Dyskinesia (PCD). nNO is part of the PCD diagnostic algorithm due to its discriminative power against other lung diseases, such as cystic fibrosis (CF). However, the underlying pathomechanisms are elusive. To better understand NO dysregulation in PCD, the L-arginine/NO (Arg/NO) pathway in patients with PCD (pwPCD) and CF (pwCF) and in healthy control (HC) subjects was investigated. In a prospective, controlled study, we measured in 24 pwPCD, 25 age-matched pwCF, and 14 HC the concentrations of the NO precursors Arg and homoarginine (hArg), the arginase metabolite ornithine (Orn), the NO inhibitor asymmetric dimethylarginine (ADMA), and the major NO metabolites (nitrate, nitrite) in sputum, plasma, and urine using validated methods. In comparison to HC, the sputum contents (in µmol/mg) of L-Arg (PCD 18.43 vs. CF 329.46 vs. HC 9.86, p < 0.001) and of ADMA (PCD 0.055 vs. CF 0.015 vs. HC 0.010, p < 0.001) were higher. In contrast, the sputum contents (in µmol/mg) of nitrate and nitrite were lower in PCD compared to HC (nitrite 4.54 vs. 9.26, p = 0.023; nitrate 12.86 vs. 40.33, p = 0.008), but higher in CF (nitrite 16.28, p < 0.001; nitrate 56.83, p = 0.002). The metabolite concentrations in urine and plasma were similar in all groups. The results of our study indicate that PCD, unlike CF, is associated with impaired NO synthesis in the lung, presumably due to mechano-chemical uncoupling.

Role of micro-RNAs 21, 124 and other novel biomarkers in distinguishing between group 1 WHO pulmonary hypertension and group 2, 3 WHO pulmonary hypertension

BACKGROUND

Pulmonary hypertension "PH" is considered a serious cardiovascular disease. World Health Organization divided PH into groups depending on many factors like pathological, hemodynamic, and clinical pictures. Lately, various micro-RNAs "miRNAs" and other novel biomarkers like endoglin and asymmetric dimethylarginine "ADMA" might have a role in diagnosis of PH and may differentiate between pulmonary arterial hypertension "PAH" and non-PAH. The purpose of the study is to show the role of miR-21, miR-124, endoglin and ADMA in the diagnosis of PH and distinguishing between WHO group 1 PH and WHO group 2 and 3 PH and to identify patients who might benefit from non-invasive and inexpensive tools to diagnose PAH.

RESULTS

miR-21 was upregulated in group 1 PH, and there was significant difference between group 1 PH as compared with group 2 PH, group 3 PH and control; miR-124 was down-regulated in group 1 PH with highly significant difference between group 1 and group 2 PH and control but no significant difference with group 3 PH, endoglin was elevated in group 1 PH with a significant difference as compared to group 2 PH, group 3 PH and control. ADMA was elevated in group 1 PH as compared to control; however, there was no significant difference between it and group 2, 3 PH.

CONCLUSIONS

miR-21, miR-124, endoglin and ADMA are good biomarkers to diagnose PH; however, only miR-21 and endoglin could distinguish group 1 PH from group 2 and 3 PH.

Phenotypic characteristics of asthma and morbidity are associated with distinct longitudinal changes in L-arginine metabolism

BACKGROUND

The L-arginine metabolome is dysregulated in asthma, though it is not understood how longitudinal changes in L-arginine metabolism differ among asthma phenotypes and relate to disease outcomes.

OBJECTIVES

To determine the longitudinal associations between phenotypic characteristics with L-arginine metabolites and their relationships with asthma morbidity.

METHODS

This is a prospective cohort study of 321 patients with asthma followed semiannually for over 18 months with assessments of plasma L-arginine metabolites, asthma control, spirometry, quality of life and exacerbations. Metabolite concentrations and ratios were transformed using the natural logarithm.

RESULTS

There were many differences in L-arginine metabolism among asthma phenotypes in the adjusted models. Increasing body mass index was associated with increased asymmetric dimethylarginine (ADMA) and depleted L-citrulline. Latinx was associated with increased metabolism via arginase, with higher L-ornithine, proline and L-ornithine/L-citrulline levels, and was found to have higher L-arginine availability compared with white race. With respect to asthma outcomes, increasing L-citrulline was associated with improved asthma control and increasing L-arginine and L-arginine/ADMA were associated with improved quality of life. Increased variability in L-arginine, L-arginine/ADMA, L-arginine/L-ornithine and L-arginine availability index over 12 months were associated with increased exacerbations, OR 4.70 (95% CI 1.35 to 16.37), OR 8.69 (95% CI 1.98 to 38.08), OR 4.17 (95% CI 1.40 to 12.41) and OR 4.95 (95% CI 1.42 to 17.16), respectively.

CONCLUSIONS

Our findings suggest that L-arginine metabolism is associated with multiple measures of asthma control and may explain, in part, the relationship between age, race/ethnicity and obesity with asthma outcomes.

Dimethylarginine dimethylaminohydrolase 1 protects PM2.5 exposure-induced lung injury in mice by repressing inflammation and oxidative stress

BACKGROUND

Airborne fine particulate matter with aerodynamic diameter ≤ 2.5 μm (PM_2.5) pollution is associated with the prevalence of respiratory diseases, including asthma, bronchitis and chronic obstructive pulmonary disease. In patients with those diseases, circulating asymmetric dimethylarginine (ADMA) levels are increased, which contributes to airway nitric oxide deficiency, oxidative stress and inflammation. Overexpression of dimethylarginine dimethylaminohydrolase 1 (DDAH1), an enzyme degrading ADMA, exerts protective effects in animal models. However, the impact of DDAH1/ADMA on PM_2.5-induced lung injury has not been investigated.

METHODS

Ddah1^-/- and DDAH1-transgenic mice, as well as their respective wild-type (WT) littermates, were exposed to either filtered air or airborne PM_2.5 (mean daily concentration ~ 50 µg/m³) for 6 months through a whole-body exposure system. Mice were also acutely exposed to 10 mg/kg PM_2.5 and/or exogenous ADMA (2 mg/kg) via intratracheal instillation every other day for 2 weeks. Inflammatory response, oxidative stress and related gene expressions in the lungs were examined. In addition, RAW264.7 cells were exposed to PM_2.5 and/or ADMA and the changes in intracellular oxidative stress and inflammatory response were determined.

RESULTS

Ddah1^-/- mice developed more severe lung injury than WT mice after long-term PM_2.5 exposure, which was associated with greater induction of pulmonary oxidative stress and inflammation. In the lungs of PM_2.5-exposed mice, Ddah1 deficiency increased protein expression of p-p65, iNOS and Bax, and decreased protein expression of Bcl-2, SOD1 and peroxiredoxin 4. Conversely, DDAH1 overexpression significantly alleviated lung injury, attenuated pulmonary oxidative stress and inflammation, and exerted opposite effects on those proteins in PM_2.5-exposed mice. In addition, exogenous ADMA administration could mimic the effect of Ddah1 deficiency on PM_2.5-induced lung injury, oxidative stress and inflammation. In PM_2.5-exposed macrophages, ADMA aggravated the inflammatory response and oxidative stress in an iNOS-dependent manner.

CONCLUSION

Our data revealed that DDAH1 has a marked protective effect on long-term PM_2.5 exposure-induced lung injury.

Sterols in asthma

While sterols regulate immune processes key to the pathogenesis of asthma, inhibition of sterols with statin drugs has shown conflicting results in human asthma. Here, a novel understanding of the impact of sterols on type 17 immune responses and asthma lead us to hypothesize that sterols and statins may be relevant to severe asthma endotypes with neutrophil infiltration.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

PRMT5 in T Cells Drives Th17 Responses, Mixed Granulocytic Inflammation, and Severe Allergic Airway Inflammation

Severe asthma is characterized by steroid insensitivity and poor symptom control and is responsible for most asthma-related hospital costs. Therapeutic options remain limited, in part due to limited understanding of mechanisms driving severe asthma. Increased arginine methylation, catalyzed by protein arginine methyltransferases (PRMTs), is increased in human asthmatic lungs. In this study, we show that PRMT5 drives allergic airway inflammation in a mouse model reproducing multiple aspects of human severe asthma. We find that PRMT5 is required in CD4⁺ T cells for chronic steroid-insensitive severe lung inflammation, with selective T cell deletion of PRMT5 robustly suppressing eosinophilic and neutrophilic lung inflammation, pathology, airway remodeling, and hyperresponsiveness. Mechanistically, we observed high pulmonary sterol metabolic activity, retinoic acid-related orphan receptor γt (RORγt), and Th17 responses, with PRMT5-dependent increases in RORγt's agonist desmosterol. Our work demonstrates that T cell PRMT5 drives severe allergic lung inflammation and has potential implications for the pathogenesis and therapeutic targeting of severe asthma.

Metabolites of L-ARG in Exhaled Breath Condensate and Serum Are Not Biomarkers of Bronchial Asthma in Children

(1) Background: L-arginine (L-ARG) and its metabolites are involved in some aspects of asthma pathogenesis (airway inflammation, oxidative stress, bronchial responsiveness, collagen deposition). Published data indicate that lungs are a critical organ for the regulation of L-ARG metabolism and that alterations in L-ARG metabolism may be significant for asthma. The aim of this study was to assess the levels of L-ARG and its metabolites in pediatric patients with asthma in serum and exhaled breath condensate (EBC) by mass spectrometric analysis and compare them with non-asthmatic children. (2) Methods: Sixty-five children (37 pediatric patients with bronchial asthma and 28 healthy control subjects) aged 6–17 participated in the study. All participants underwent a clinical visit, lung tests, allergy tests with common aeroallergens, and serum and EBC collection. The levels of biomarkers were determined in both serum and EBC. Analytical chromatography was conducted using an Acquity UPLC system equipped with a cooled autosampler and an Acquity HSS T3 column. Mass spectrometric analysis was conducted using the Xevo G2 QTOF MS with electrospray ionization (ESI) in positive ion mode. (3) Results: Asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) levels in serum and EBC did not differ significantly in asthmatic children and healthy control subjects. We found no correlation between forced expiratory volume in one second (FEV1) and L-ARG and its metabolites, as well as between interleukin-4 (IL-4) serum level and L-ARG and its metabolites. Concentrations of ADMA, SDMA, citrulline (CIT), and ornithine (ORN) were higher in serum than EBC in asthmatics and non-asthmatics. By contrast, concentrations of dimethylarginine (DMA) were higher in EBC than serum. ADMA/L-ARG, SDMA/L-ARG, and DMA/L-ARG ratios were significantly higher in EBC than in serum in asthmatics and in non-asthmatics. (4) Conclusions: Serum and EBC concentrations of L-ARG and its metabolites were not an indicator of pediatric bronchial asthma in our study.

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

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

Asthma and Three Colinear Comorbidities: Obesity, OSA, and GERD

Asthma is a complex disease with heterogeneous phenotypes and endotypes that are incompletely understood. Obesity, obstructive sleep apnea, and gastroesophageal reflux disease co-occur in patients with asthma at higher rates than in those without asthma. Although these diseases share risk factors, there are some data suggesting that these comorbidities have shared inflammatory pathways, drive the development of asthma, or worsen asthma control. This review discusses the epidemiology, pathophysiology, management recommendations, and key knowledge gaps of these common comorbidities.

Review - Nutraceuticals Can Target Asthmatic Bronchoconstriction: NADPH Oxidase-Dependent Oxidative Stress, RhoA and Calcium Dynamics

Activation of various isoforms of NADPH oxidase contributes to the pathogenesis of asthma at multiple levels: promoting hypercontractility, hypertrophy, and proliferation of airway smooth muscle; enabling lung influx of eosinophils via VCAM-1; and mediating allergen-induced mast cell activation. Free bilirubin, which functions physiologically within cells as a feedback inhibitor of NADPH oxidase complexes, has been shown to have a favorable impact on each of these phases of asthma pathogenesis. The spirulina chromophore phycocyanobilin (PhyCB), a homolog of bilirubin’s precursor biliverdin, can mimic the inhibitory impact of biliverdin/bilirubin on NADPH oxidase activity, and spirulina’s versatile and profound anti-inflammatory activity in rodent studies suggests that PhyCB may have potential as a clinical inhibitor of NADPH oxidase. Hence, spirulina or PhyCB-enriched spirulina extracts merit clinical evaluation in asthma. Promoting biosynthesis of glutathione and increasing the expression and activity of various antioxidant enzymes – as by supplementing with N-acetylcysteine, Phase 2 inducers (eg, lipoic acid), selenium, and zinc – may also blunt the contribution of oxidative stress to asthma pathogenesis. Nitric oxide (NO) and hydrogen sulfide (H₂S) work in various ways to oppose pathogenic mechanisms in asthma; supplemental citrulline and high-dose folate may aid NO synthesis, high-dose biotin may mimic and possibly potentiate NO’s activating impact on soluble guanylate cyclase, and NAC and taurine may boost H₂S synthesis. The amino acid glycine has a hyperpolarizing effect on airway smooth muscle that is bronchodilatory. Insuring optimal intracellular levels of magnesium may modestly blunt the stimulatory impact of intracellular free calcium on bronchoconstriction. Nutraceutical regimens or functional foods incorporating at least several of these agents may have utility as nutraceutical adjuvants to standard clinical management of asthma.

Lactic Acid Bacteria and Natural Product Complex Ameliorates Ovalbumin-Induced Airway Hyperresponsiveness in Mice

The incidence of respiratory diseases, such as asthma, has substantially increased in recent times owing to environmental changes, such as air pollution. Induction of a chronic inflammatory response begins with production of biologically active mediators from the airway epithelium, which attracts and recruits inflammatory cells into the lung airway. In our previous study, we confirmed that Lactobacillus casei HY2782 and Bifidobacterium animalis spp. lactis HY8002 could improve lung inflammation in the COPD animal model. In this study, we investigated the effect of the HY2782 complex against airway hyperresponsiveness by using an ovalbumin (OVA)-induced animal model. An orally administered HY2782 complex on OVA-induced allergic asthma in a BALB/c mouse model was used. The present results showed that the HY2782 complex suppressed total immunoglobulin E in serum and bronchoalveolar lavage fluid (BALF). The cytokine production profile in BALF and serum revealed that the HY2782 complex showed reduced levels of Th2 cytokines among immune factors released due to the elevated allergic response. Levels of inflammatory mediators in BALF, MCP-1, MIP-2, and CXCL-9 were decreased by oral administration of the HY2782 complex. Lower numbers of eosinophils and neutrophils in BALF suggested that inflammation was ameliorated by the HY2782 complex. Histological observation of lung sections also showed infiltration of fewer cells. From results, we suggested that the HY2782 complex effectively responds to improvement of the immune response and airway hypersensitivity reaction because of the anti-inflammatory effect of the Pueraria lobata root extract and antioxidant effect of HY2782.

Arginine Therapy for Lung Diseases

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

Obesity and asthma

Obesity has been well recognized as an important comorbidity in patients with asthma, representing a unique phenotype and endotype. This association indicates a close relationship between metabolic and inflammatory dysregulation. However, the detailed organ-organ, cellular, and molecular interactions are not completely resolved. Because of that, the relationship between obesity and asthma remains unclear. In this article, clinical and epidemiological studies, as well as data from experimental animal work, are being summarized to provide a state of the art update on this important topic. Much more work is needed, particularly mechanistic, to fully understand the interaction between obesity and asthma and to develop novel preventive and therapeutic strategies.

L-Citrulline increases nitric oxide and improves control in obese asthmatics

BACKGROUNDThe airways of obese asthmatics have been shown to be NO deficient, and this contributes to airway dysfunction and reduced response to inhaled corticosteroids. In cultured airway epithelial cells, L-citrulline, a precursor of L-arginine recycling and NO formation, has been shown to prevent asymmetric dimethyl arginine-mediated (ADMA-mediated) NO synthase (NOS2) uncoupling, restoring NO and reducing oxidative stress.METHODSIn a proof-of-concept, open-label pilot study in which participants were analyzed before and after treatment, we hypothesized that 15 g/d L-citrulline for 2 weeks would (a) increase the fractional excretion of NO (FeNO), (b) improve asthma control, and (c) improve lung function. To this end, we recruited obese (BMI >30) asthmatics on controller therapy, with a baseline FeNO of ≤30 ppb from the University of Colorado Medical Center and Duke University Health System.RESULTSA total of 41 subjects with an average FeNO of 17 ppb (95% CI, 15-19) and poorly controlled asthma (average asthma control questionnaire [ACQ] 1.5 [95% CI, 1.2-1.8]) completed the study. Compared with baseline, L-citrulline increased whereas ADMA and arginase concentration did not (values represent the mean Δ and 95% CI): plasma L-citrulline (190 μM, 84-297), plasma L-arginine (67 μM, 38-95), and plasma L-arginine/ADMA (ratio 117, 67-167). FeNO increased by 4.2 ppb (1.7-6.7 ppb); ACQ decreased by -0.46 (-0.67 to 0.27 points); the forced vital capacity and forced exhalation volume in 1 second, respectively, changed by 86 ml (10-161 ml) and 52 ml (-11 to 132 ml). In a secondary analysis, the greatest FEV1 increments occurred in those subjects with late-onset asthma (>12 years) (63 ml [95% CI, 1-137]), in females (80 ml [95% CI, 5-154]), with a greater change seen in late-onset females (100 ml, [95% CI, 2-177]). The changes in lung function or asthma control were not significantly associated with the changes before and after treatment in L-arginine/ADMA or FeNO.CONCLUSIONShort-term L-citrulline treatment improved asthma control and FeNO levels in obese asthmatics with low or normal FeNO. Larger FEV1 increments were observed in those with late-onset asthma and in females.TRIAL REGISTRATIONClinicalTrials.gov NCT01715844.FUNDINGNIH NHLBI R01 HL146542-01.

Plasma based targeted metabolomic analysis reveals alterations of phosphatidylcholines and oxidative stress markers in guinea pig model of allergic asthma

Bronchial asthma is one of the most common, chronic respiratory diseases, characterized by reversible airway obstruction, eosinophil and Th2 infiltration, airway hyperresponsiveness and airway remodelling; with many cells and mediators involved. Metabolomics is a relatively new field in "omics" sciences enabling the identification of metabolome for better diagnostics and studying of diseases phenotype. The aim of this study was to investigate the role of targeted metabolomics study for better understanding of the bronchial asthma pathophysiology and finding potential biomarkers in experimental models of eosinophilic inflammation. Plasma level of 185 metabolites was measured with the AbsoluteIDQ™ p180 kit in guinea pigs with experimentally-induced allergic inflammation (n = 15) compared to naïve non-sensitised and non-challenged controls (n = 18). Of the 185 metabolites identified in plasma, 22 were significantly different and changed in ovalbumin sensitised animals. Plasma level of 13 phosphatidylcholines with saturated and unsaturated long-chain fatty acids, total phosphatidylcholines count, carnitine, symmetric dimethylarginine and its ratio to total unmodified arginine, and kynurenine to tryptophan ratio were found to be decreased, while phospholipase A2 activity indicator, tryptophan, taurine and ratio of methionine sulfoxide to unmodified methionine were found to be increased in sensitised guinea pigs compared to naïve controls. Targeted metabolomic analysis revealed significant differences in plasma metabolome of sensitised guinea pigs. Our observations point to the activation of inflammatory and immune pathways, as well as the involvement of oxidative stress.

Corticosteroid Withdrawal-Induced Loss of Control in Mild to Moderate Asthma Is Independent of Classic Granulocyte Activation

BACKGROUND

Loss of asthma control and asthma exacerbations are associated with increased sputum eosinophil counts. However, whether eosinophils, or the also present neutrophils, actively contribute to the accompanying inflammation has not been extensively investigated.

METHODS

Twenty-three patients with mild to moderate asthma were included in a standardized prospective inhaled corticosteroid (ICS) withdrawal study; 22 of the patients experienced loss of asthma control. The study assessed various immune, inflammatory, and oxidative stress parameters, as well as markers of eosinophil and neutrophil activity, in exhaled breath condensate, plasma, and sputum collected at three phases (baseline, during loss of control, and following recovery).

RESULTS

Loss of asthma control was characterized by increased sputum eosinophils, whereas no differences were detected between the three phases for most inflammatory and oxidative stress responses. There were also no differences detected for markers of activated eosinophils (eosinophil cationic protein and bromotyrosine) and neutrophils (myeloperoxidase and chlorotyrosine). However, free eosinophilic granules and citrullinated histone H₃, suggestive of eosinophil cytolysis and potentially eosinophil extracellular trap formation, were enhanced. Baseline blood eosinophils and changes in asymmetric dimethylarginine (an inhibitor of nitric oxide synthase) in plasma were found to correlate with the decrease in FEV₁ percent predicted upon ICS withdrawal (both, r_s = 0.46; P = .03).

CONCLUSIONS

The clinical effect in mild to moderate asthma upon interruption of ICS therapy is not related to the classic inflammatory activation of eosinophils and neutrophils. It may, however, reflect another pathway underlying the onset of loss of disease control and asthma exacerbations.

TRIAL REGISTRY

The Netherlands Trial Register; No.: NTR3316; URL: trialregister.nl/trial/3172.

Bioenergetic Differences in the Airway Epithelium of Lean Versus Obese Asthmatics Are Driven by Nitric Oxide and Reflected in Circulating Platelets

Aims: Asthma, characterized by airway obstruction and hyper-responsiveness, is more severe and less responsive to treatment in obese subjects. While alterations in mitochondrial function and redox signaling have been implicated in asthma pathogenesis, it is unclear whether these mechanisms differ in lean versus obese asthmatics. In addition, we previously demonstrated that circulating platelets from asthmatic individuals have altered bioenergetics; however, it is unknown whether platelet mitochondrial changes reflect those observed in airway epithelial cells. Herein we hypothesized that lean and obese asthmatics show differential bioenergetics and redox signaling in airway cells and that these alterations could be measured in platelets from the same individual. Results: Using freshly isolated bronchial airway epithelial cells and platelets from lean and obese asthmatics and healthy individuals, we show that both cell types from obese asthmatics have significantly increased glycolysis, basal and maximal respiration, and oxidative stress compared with lean asthmatics and healthy controls. This increased respiration was associated with enhanced arginine metabolism by arginase, which has previously been shown to drive respiration. Inducible nitric oxide synthase (iNOS) was also upregulated in cells from all asthmatics. However, due to nitric oxide synthase uncoupling in obese asthmatics, overall nitric oxide (NO) bioavailability was decreased, preventing NO-dependent inhibition in obese asthmatic cells that was observed in lean asthmatics. Innovation and Conclusion: These data demonstrate bioenergetic differences between lean and obese asthmatics that are, in part, due to differences in NO signaling. They also suggest that the platelet may serve as a useful surrogate to understand redox, oxidative stress and bioenergetic changes in the asthmatic airway.

Oxidative stress and macrophages: driving forces behind exacerbations of asthma and chronic obstructive pulmonary disease?

Oxidative stress is a common feature of obstructive airway diseases like asthma and chronic obstructive pulmonary disease (COPD). Lung macrophages are key innate immune cells that can generate oxidants and are known to display aberrant polarization patterns and defective phagocytic responses in these diseases. Whether these characteristics are linked in one way or another and whether they contribute to the onset and severity of exacerbations in asthma and COPD remain poorly understood. Insight into oxidative stress, macrophages, and their interactions may be important in fully understanding acute worsening of lung disease. This review therefore highlights the current state of the art regarding the role of oxidative stress and macrophages in exacerbations of asthma and COPD. It shows that oxidative stress can attenuate macrophage function, which may result in impaired responses toward exacerbating triggers and may contribute to exaggerated inflammation in the airways.

Targeting arginase and nitric oxide metabolism in chronic airway diseases and their co-morbidities

In the airways, arginase and NOS compete for the common substrate l-arginine. In chronic airway diseases, such as asthma and COPD, elevated arginase expression contributes to airway contractility, hyperresponsiveness, inflammation and remodeling. The disrupted l-arginine homeostasis, through changes in arginase and NOS expression and activity, does not only play a central role in the development of various airways diseases such as asthma or COPD. It possibly also affects l-arginine homeostasis throughout the body contributing to the emergence of co-morbidities. This review focusses on the role of arginase, NOS and ADMA in co-morbidities of asthma and COPD and speculates on their possible connection.

The role of metabolomic markers for patients with infectious diseases: implications for risk stratification and therapeutic modulation

INTRODUCTION

Metabolomics is a rapidly growing area of research. Metabolomic markers can provide information about the interaction of different organ systems, and thereby improve the understanding of physio-pathological processes, disease risk, prognosis and therapy responsiveness in a variety of diseases. Areas covered: In this narrative review of recent clinical studies investigating metabolomic markers in adult patients presenting with acute infectious disease, we mainly focused on patients with sepsis and lower respiratory tract infections. Currently, there is a growing body of literature showing that single metabolites from distinct metabolic pathways, as well as more complex metabolomic signatures are associated with disease severity and outcome in patients with systemic infections. These pathways include, among others, metabolomic markers of oxidative stress, steroid hormone and amino acid pathways, and nutritional markers. Expert commentary: Metabolic profiling has great potential to optimize patient management, to provide new targets for individual therapy and thereby improve survival of patients. At this stage, research mainly focused on the identification of new predictive signatures and less on metabolic determinants to predict treatment response. The transition from observational studies to implementation of novel markers into clinical practice is the next crucial step to prove the usefulness of metabolomic markers in patient care.

Treatment Responses of Cognitive Function and Plasma Asymmetric Dimethylarginine to Atypical Antipsychotic in Patients With Schizophrenia

Cognitive deficits represent a core feature of schizophrenia. Previous studies have demonstrated that plasma asymmetric dimethylarginine (ADMA) was increased in patients with schizophrenia and correlated with cognitive impairments. Atypical antipsychotics can produce cognitive benefits in schizophrenia patients. In this study, we conducted a prospective observation trial to explore whether plasma ADMA may serve as an indicator for evaluating cognitive improvements induced by atypical antipsychotics in patients with schizophrenia. A total of 41 schizophrenia patients with acute exacerbation were enrolled and 29 patients completed this study. These recruited patients were drug-naive or had no exposure to antipsychotics for at least 3 months. Thirty healthy individuals were recruited as a control group. Positive and Negative Syndrome Scale (PANSS) and a neuropsychological battery were used to evaluate schizophrenic symptoms and cognitive function, respectively. Plasma ADMA was measured by high-performance liquid chromatography (HPLC). We found that schizophrenia patients with acute exacerbation had significantly poorer cognitive performances and higher plasma ADMA levels than control individuals (p < 0.05). After 2 months of atypical antipsychotic treatment, patients showed significant improvements in processing speed, working memory, attention, and executive function (all p < 0.01). Plasma ADMA levels in patients after treatment were significantly decreased compared to baseline (2.42 ± 0.84 vs. 1.55 ± 0.34 μmol/L; t = 6.491, p < 0.001). Correlation analysis reveals that there is a significant correlation of the decrease in ADMA with improvements in working memory (r = -0.413, p = 0.026) and attention (r = -0.417, p = 0.025). Collectively, our results suggest that atypical antipsychotics improve cognitive function in schizophrenia patients with acute exacerbation, in parallel with decreased plasma ADMA levels. Plasma ADMA levels may be an indicator of cognitive recovery in schizophrenia.

Relationship of asymmetric dimethylarginine levels with disease severity and pulmonary hypertension in chronic obstructive pulmonary disease

Background:

Asymmetric dimethylarginine (ADMA) has emerged as a risk marker for many conditions related to pulmonary hypertension (PH); however, little is known about ADMA and symmetric dimethylarginine (SDMA) plasma concentrations in chronic obstructive pulmonary disease (COPD). Our interest centers on the role of ADMA in regulation of endothelial function in COPD and secondary PH. The aim of the present study was to evaluate the serum ADMA, SDMA, and L-arginine concentrations in COPD and its association with PH.

Methods:

Patients with diagnosis of COPD underwent pulmonary function tests, echocardiography, and laboratory investigations including ADMA, SDMA, and L-arginine.

Results:

Serum concentrations of ADMA, SDMA, and L-arginine tend to increase as COPD progresses. Patients with PH had higher concentrations of ADMA, SDMA, and L-arginine compared to cases with normal pulmonary arterial pressure (PAP); the difference was not statistically significant.

Conclusions:

Our results show that increased ADMA, SDMA, and L-arginine concentrations are associated with increased PAP measurements in patients with COPD, however, the relationship is not statistically significant.

Lipopolysaccharide modulates p300 and Sirt1 to promote PRMT1 stability via an SCFFbxl17-recognized acetyldegron

E3 ubiquitin ligase recognizes its protein substrates via specific molecular signatures for ubiquitin proteasomal degradation. However, the role of acetylation/deacetylation in the process of E3 ubiquitin ligase recognizing its protein substrates is not fully studied. Here, we report that a tandem IK motif in protein arginine methyltransferase 1 (PRMT1) forms an acetyldegron to recruit the F-box/LRR-repeat protein 17 (FBXL17), a component of the SKP1-CUL1-F-box protein (SCF)-type E3 ubiquitin ligase complex. PRMT1 is polyubiquitylated for proteasome degradation with a half-life of approximately 4 h in lung epithelial cells. SCF^Fbxl17 mediates PRMT1 polyubiquitylation at K117. SCF^Fbxl17 specifically binds PRMT1 via a unique motif IKxxxIK. Strikingly, the acetylation/deacetylation status of the lysine residues within the motif determines Fbxl17 binding. Deacetylation on both K200 and K205 by Sirtuin 1 (Sirt1) and acetylation of p300 (EP300) on K205 collaboratively prepare the motif for SCF^Fbxl17 binding thereby triggering PRMT1 protein degradation. Pathogen-derived lipopolysaccharide (LPS) downregulates Sirt1 and p300 to protect PRMT1 from degradation. This study demonstrates that LPS promotes PRMT1 stability by blockade of PRMT1 and SCF^Fbxl17 binding via an acetylation/deacetylation-modified acetyldegron; and LPS-elevated levels of PRMT1 lead to bronchial epithelial cell overgrowth in pulmonary inflammatory diseases.

Pathways to pulmonary hypertension in sickle cell disease: the search for prevention and early intervention

INTRODUCTION

Pulmonary hypertension (PH) develops in a significant number of patients with sickle cell disease (SCD), resulting in increased morbidity and mortality. This review focuses on PH pathophysiology, risk stratification, and new recommendations for screening and treatment for patients with SCD. Areas covered: An extensive PubMed literature search was performed. While the pathophysiology of PH in SCD is yet to be fully deciphered, it is known that the etiology is multifactorial; hemolysis, hypercoagulability, hypoxemia, ischemic-reperfusion injury, oxidative stress, and genetic susceptibility all contribute in varying degrees to endothelial dysfunction. Hemolysis, in particular, seems to play a key role by inciting an imbalance in the regulatory axis of nitric oxide and arginine metabolism. Systematic risk stratification starting in childhood based on clinical features and biomarkers that enable early detection is necessary. Multi-faceted, targeted interventions, before irreversible vasculopathy develops, will allow for improved patient outcomes and life expectancy. Expert commentary: Despite progress in our understanding of PH in SCD, clinically proven therapies remain elusive and additional controlled clinical trials are needed. Prevention of disease starts in childhood, a critical window for intervention. Given the complex and multifactorial nature of SCD, patients will ultimately benefit from combination therapies that simultaneously targets multiple mechanisms.

Relationship of Oxidant and Antioxidant Markers to Asthma Severity in Egyptian Asthmatic Children

BACKGROUND

Asthma is a chronic airway disease which is characterized by oxidant antioxidant imbalance with the generation of oxidative stress related mediators.

AIM

The study aimed to evaluate the role of asymmetric dimethylarginine, and malondialdehyde as oxidant markers and serum paraoxonase activity as an antioxidant marker in asthma, and to determine their relationship to the asthma severity and lung function among asthmatic children in Egypt.

PATIENTS AND METHODS

This case control study was conducted on sixty patients with asthma compared with sixty apparently healthy children of matched age and sex.

RESULTS

Serum concentrations of oxidant markers as asymmetric dimethylarginine and malondialdehyde were significantly increased in asthmatic patients while anti-oxidant marker as paraoxonase activity was significantly decreased compared to healthy controls (P < 0.05). ANOVA test revealed highly significant elevation of the serum concentrations of oxidant markers while anti-oxidant marker was significantly decreased in severe asthmatic patients (P < 0.001) compared to the patients with moderate and mild asthma respectively. Serum malondialdehyde concentration was a strong predictor of asthma severity by multiple regression analysis (P < 0.05).

CONCLUSION

The study revealed an imbalance between oxidative and antioxidant defence systems in asthmatic children. Serum concentration of malondialdehyde was the most predictive biomarker having a significant association with asthma severity.

Metabolomics analysis identifies sex-associated metabotypes of oxidative stress and the autotaxin-lysoPA axis in COPD

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease and a leading cause of mortality and morbidity worldwide. The aim of this study was to investigate the sex dependency of circulating metabolic profiles in COPD.

Serum from healthy never-smokers (healthy), smokers with normal lung function (smokers), and smokers with COPD (COPD; Global Initiative for Chronic Obstructive Lung Disease stages I–II/A–B) from the Karolinska COSMIC cohort (n=116) was analysed using our nontargeted liquid chromatography–high resolution mass spectrometry metabolomics platform.

Pathway analyses revealed that several altered metabolites are involved in oxidative stress. Supervised multivariate modelling showed significant classification of smokers from COPD (p=2.8×10⁻⁷). Sex stratification indicated that the separation was driven by females (p=2.4×10⁻⁷) relative to males (p=4.0×10⁻⁴). Significantly altered metabolites were confirmed quantitatively using targeted metabolomics. Multivariate modelling of targeted metabolomics data confirmed enhanced metabolic dysregulation in females with COPD (p=3.0×10⁻³) relative to males (p=0.10). The autotaxin products lysoPA (16:0) and lysoPA (18:2) correlated with lung function (forced expiratory volume in 1 s) in males with COPD (r=0.86; p<0.0001), but not females (r=0.44; p=0.15), potentially related to observed dysregulation of the miR-29 family in the lung.

These findings highlight the role of oxidative stress in COPD, and suggest that sex-enhanced dysregulation in oxidative stress, and potentially the autotaxin–lysoPA axis, are associated with disease mechanisms and/or prevalence.

Oxidative stress and the autotaxin–lysoPA axis evidence sex-associated metabotypes in the serum of COPD patientshttp://ow.ly/kAeE309MpdI

Long-Term Intermittent Exposure to High Altitude Elevates Asymmetric Dimethylarginine in First Exposed Young Adults

Lüneburg, Nicole, Patricia Siques, Julio Brito, Juan José De La Cruz, Fabiola León-Velarde, Juliane Hannemann, Cristian Ibanez, and Rainer Böger. Long-term intermittent exposure to high altitude elevates asymmetric dimethylarginine in first exposed young adults. High Alt Med Biol. 18:226–233, 2017.—Hypoxia-induced dysregulation of pulmonary and cerebral circulation may be related to an impaired nitric oxide (NO) pathway. We investigated the effect of chronic intermittent hypobaric hypoxia (CIH) on metabolites of the NO pathway. We measured asymmetric and symmetric dimethylarginine (ADMA and SDMA) and monomethyl-L-arginine (L-NMMA) and assessed their associations with acclimatization in male draftees (n = 72) undergoing CIH shifts at altitude (3550 m) during 3 months. Sixteen Andean natives living at altitude (3675 m) (chronic hypobaric hypoxia [CH]) were included for comparison. In CIH, ADMA and L-NMMA plasma concentrations increased from 1.14 ± 0.04 to 1.95 ± 0.09 μmol/L (mean ± SE) and from 0.22 ± 0.07 to 0.39 ± 0.03 μmol/L, respectively, (p < 0.001 for both) after 3 months, whereas SDMA did not change. The concentrations of ADMA and L-NMMA were higher in CH (3.48 ± 0.07, 0.53 ± 0.08 μmol/L; p < 0.001) as compared with CIH. In both CIH and CH, ADMA correlated with hematocrit (r² = 0.07, p < 0.05; r² = 0.26; p < 0.01). In CIH, an association of ADMA levels with poor acclimatization status was observed. We conclude that the endogenous NO synthase inhibitors, ADMA and L-NMMA, are elevated in hypoxia. This may contribute to impaired NO production at altitude and may also be predictive of altitude-associated health impairment.

Toxic Dimethylarginines: Asymmetric Dimethylarginine (ADMA) and Symmetric Dimethylarginine (SDMA)

Asymmetric and symmetric dimethylarginine (ADMA and SDMA, respectively) are toxic, non-proteinogenic amino acids formed by post-translational modification and are uremic toxins that inhibit nitric oxide (NO) production and play multifunctional roles in many human diseases. Both ADMA and SDMA have emerged as strong predictors of cardiovascular events and death in a range of illnesses. Major progress has been made in research on ADMA-lowering therapies in animal studies; however, further studies are required to fill the translational gap between animal models and clinical trials in order to treat human diseases related to elevated ADMA/SDMA levels. Here, we review the reported impacts of ADMA and SDMA on human health and disease, focusing on the synthesis and metabolism of ADMA and SDMA; the pathophysiological roles of these dimethylarginines; clinical conditions and animal models associated with elevated ADMA and SDMA levels; and potential therapies against ADMA and SDMA. There is currently no specific pharmacological therapy for lowering the levels and counteracting the deleterious effects of ADMA and SDMA. A better understanding of the mechanisms underlying the impact of ADMA and SDMA on a wide range of human diseases is essential to the development of specific therapies against diseases related to ADMA and SDMA.

Effects of fetal exposure to high-fat diet or maternal hyperglycemia on L-arginine and nitric oxide metabolism in lung

Background/Objectives:

Alterations in the L-arginine/nitric oxide (NO) metabolism contribute to diseases such as obesity, metabolic syndrome and airway dysfunction. The impact of early-life exposures on the L-arginine/NO metabolism in lung later in life is not well understood. The objective of this work was to study the effects of intrauterine exposures to maternal hyperglycemia and high-fat diet (HFD) on pulmonary L-arginine/NO metabolism in mice.

Methods:

We used two murine models of intrauterine exposures to maternal (a) hyperglycemia and (b) HFD to study the effects of these exposures on the L-arginine/NO metabolism in lung in normal chow-fed offspring.

Results:

Both intrauterine exposures resulted in NO deficiency in the lung of the offspring at 6 weeks of age. However, each of the exposures leading to different metabolic phenotypes caused a distinct alteration in the L-arginine/NO metabolism. Maternal hyperglycemia leading to impaired glucose tolerance but no obesity in the offspring resulted in increased levels of asymmetric dimethylarginine and impairment of NO synthases. Although maternal HFD led to obesity without impairment in glucose tolerance in the offspring, it resulted in increased expression and activity of arginase in the lung of the normal chow-fed offspring.

Conclusions:

These data suggest that maternal hyperglycemia and HFD can cause alterations in the pulmonary L-arginine/NO metabolism in offspring.

Admission levels of asymmetric and symmetric dimethylarginine predict long-term outcome in patients with community-acquired pneumonia

BACKGROUND

During infection, there is an activation of the L-arginine-nitric-oxide pathway, with a shift from nitric oxide synthesis to a degradation of L-arginine to its metabolites, asymmetric and symmetric dimethylarginine (ADMA and SDMA). However, the prognostic implications for short-term or long-term survival remains unclear. We investigated the association of L-arginine, ADMA, and SDMA with adverse clinical outcomes in a well-defined cohort of patients with community-acquired pneumonia (CAP).

METHODS

We measured L-arginine, ADMA, and SDMA in 268 CAP patients from a Swiss multicenter trial by mass spectrometry and used Cox regression models to investigate associations between blood marker levels and disease severity as well as mortality over a period of 6 years.

RESULTS

Six-year mortality was 44.8%. Admission levels of ADMA and SDMA (μmol/L) were correlated with CAP severity as assessed by the pneumonia severity index (r = 0.32, p < 0.001 and r = 0.56, p < 0.001 for ADMA and SDMA, respectively) and higher in 6-year non-survivors versus survivors (median 0.62 vs. 0.48; p < 0.001 and 1.01 vs. 0.85; p < 0.001 for ADMA and SDMA, respectively). Both ADMA and SDMA were significantly associated with long-term mortality (hazard ratios [HR] 4.44 [95% confidence intervals (CI) 1.84 to 10.74] and 2.81 [95% CI 1.45 to 5.48], respectively). The effects were no longer significant after multivariate adjustment for age and comorbidities. No association of L-arginine with severity and outcome was found.

CONCLUSIONS

Both ADMA and SDMA show a severity-dependent increase in patients with CAP and are strongly associated with mortality. This association is mainly explained by age and comorbidities.

TRIAL REGISTRATION

ISRCTN95122877 . Registered 31 July 2006.

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

Background

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

Methods

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

Results

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

Conclusion

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

l-citrulline prevents asymmetric dimethylarginine-mediated reductions in nitric oxide and nitrosative stress in primary human airway epithelial cells

BACKGROUND

Asthma is associated with reduced systemic levels of l-arginine and increased asymmetric dimethylarginine (ADMA). This imbalance leads to nitric oxide synthase (NOS) uncoupling with reduced nitric oxide (NO) formation and greater oxidative and nitrosative stress. Whether this imbalance also occurs in bronchial epitheliumof asthmatics is unknown.

OBJECTIVES

We used primary human bronchial epithelial cells (HBECs) from asthmatics and healthy controls to evaluate: (i) ADMA-mediated NOS uncoupling reduces epithelial production of NO and increases oxygen and nitrogen reactive species, and (ii) l-citrulline can reverse this mechanism by recoupling NOS, restoring NO production and reducing oxidative and nitrosative stress.

RESULTS

In HBECsIL-13 and INFγ stimulated NOS2 and increased NOx levels. The addition of ADMA reduced NOx and increased H₂ O₂ levels (p<0.001). Treatment with l-citrulline (800, 1600 μm) rescued NOx when the l-arginine media concentration was 25 μm but failed to do so with higher concentrations (100 μm). Under reduced l-arginine media conditions, HBECs treated with l-citrulline increased the levels of argininosuccinate, an enzyme that metabolizes l-citrulline to l-arginine. l-citrulline prevented the ADMA-mediated increase in nitrotyrosine in HBECs in cells from asthmatics and controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Increasing ADMA reduces NO formation and increases oxidative and nitrosative stress in airway epithelial cells. l-citrulline supplementation restores NO formation, while preventing nitrosative stress. These results, suggest that l-citrulline supplementation may indeed be a powerful approach to restore airway NO production and may have a therapeutic potential in diseases in which there is a defective production of NO.

Arginines Plasma Concentration and Oxidative Stress in Mild to Moderate COPD

Background

Elevated plasma concentrations of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) have been observed in respiratory conditions such as asthma and cystic fibrosis. Since oxidative stress has been shown to increase the activity of arginine methylating enzymes, hence increased ADMA synthesis, and to reduce ADMA degrading enzymes, hence increased ADMA concentrations, we assessed methylated arginines concentrations in chronic obstructive pulmonary disease (COPD), a disease characterized by increased oxidative stress.

Methods

Plasma arginine, ADMA and symmetric dimethylarginine (SDMA), oxidative stress markers (thiobarbituric acid reactive substances, TBARS, and plasma proteins SH, PSH) and antioxidants (taurine and paraoxonase 1, PON1, activity) were measured in 43 COPD patients with mild (n = 29) or moderate (n = 14) disease and 43 age- and sex-matched controls.

Results

TBARS significantly increased with COPD presence and severity (median 2.93 vs 3.18 vs 3.64 μmol/L, respectively in controls, mild and moderate group, p<0.0001 by ANOVA) whereas PSH decreased (6.69±1.15 vs 6.04±0.85 vs 5.33±0.96 μmol/gr prot, p<0.0001 by ANOVA). Increased ADMA/arginine ratio, primarily due to reduced arginine concentrations, was also observed with COPD presence and severity (median 0.0067 vs 0.0075 vs 0.0100, p<0.0001 by ANOVA). In multiple logistic regression analysis, only TBARS (OR 0.44, 95% CI 0.25–0.77; p = 0.0045) and ADMA/Arginine ratio (OR 1.72, 95% CI 2.27–13.05; p = 0.02) were independently associated with COPD severity.

Conclusion

COPD presence and severity are associated with increased oxidative stress and alterations in arginine metabolism. The reduced arginine concentrations in COPD may offer a new target for therapeutic interventions increasing arginine availability.

Adipokines, asymmetrical dimethylarginine, and pulmonary function in adolescents with asthma and obesity

OBJECTIVE

This study was to investigate whether the metabolic abnormalities of adipokines and asymmetrical dimethylarginine (ADMA) associate with pulmonary function deficits in adolescents with obesity and asthma.

METHODS

This study enrolled 28 obese adolescents with asthma, 46 obese adolescents without asthma, 58 normal-weight adolescents with asthma, and 63 healthy control subjects. Serum levels of leptin, high-molecule-weight (HMW) adiponectin, retinol binding protein 4 (RBP4), asymmetrical dimethylarginine (ADMA), and pulmonary function were qualified.

RESULTS

The obese subjects had higher levels of leptin and ADMA but lower levels of HMW adiponectin than the normal-weight subjects with or without asthma. The subjects with asthma had higher levels of RBP4 than those without asthma. The obese adolescents with asthma had lowest forced expiratory lung volume in the first second (FEV₁)/forced vital capacity (FVC) ratio among the four study groups. In all the study subjects and in the subjects with asthma alone, the FEV₁/FVC ratio associated negatively with leptin, however, such association was rendered non-significant when adjusted for BMI. The pulmonary function deficits associated inversely with BMI percentile in the subjects with asthma. However, the decreased FEV₁/FVC ratio was not correlated with HMW adiponectin, RBP4 or ADMA.

CONCLUSIONS

Our present study confirmed obstructive pattern of pulmonary function characterized by the reduced FEV₁/FVC ratio in the obese adolescents with asthma. These pulmonary deficits were associated inversely with the increased BMI percentile.

Asymmetric dimethylarginine and related metabolites in exhaled breath condensate of children with cystic fibrosis

INTRODUCTION

Asymmetric dimethylarginine (ADMA) competitively inhibits nitric oxide synthase (NOS). Its levels in specimens from murine models and asthmatic patients are related to inflammation and oxidative stress. Patients with cystic fibrosis(CF) reportedly have higher arginase activity, lower NO production and NOS expression than healthy controls.

OBJECTIVE

The objective was to assess the role of ADMA and related metabolites as disease biomarkers in exhaled breath condensate (EBC) of pediatric CF patients, compared with age-matched healthy controls (HC).

METHODS

A longitudinal design was conceived and 34 CF patients (21 stable, 13 at the onset of exacerbation) and 16 HC were enrolled. All CF patients underwent clinical examination, spirometry and EBC collection at enrolment; the same tests were performed also after an antibiotic course in those patients with exacerbation. Metabolites levels in EBC were measured with an ultra-performance liquid chromatography and tandem mass spectrometry technique.

RESULTS

All CF patients had ADMA levels (expressed as ratio to tyrosine) similar to those in HC (median 0.0112, IQR 0.0103-0.0120 and median 0.0114, IQR 0.0090-0.0128, respectively; P = 0.983), while a significant increase in the citrulline/tyrosine ratio was found in CF patients (median 0.6419, IQR 0.5738-0.6899 in CF vs median 0.4176, IQR 0.2986-0.5082 in HC; P = 0.00003). No differences in ADMA levels emerged between stable patients and those with exacerbation.

CONCLUSION

ADMA and related aminoacids were measured simultaneously for the first time in EBC from CF patients. Higher citrulline/tyrosine ratios were found in CF children with normal ADMA levels, suggesting a dysregulated ADMA metabolism in these patients.

Soft TCPTP Agonism-Novel Target to Rescue Airway Epithelial Integrity by Exogenous Spermidine

A reparative approach of disrupted epithelium in obstructive airway diseases, namely asthma and chronic obstructive pulmonary disease (COPD), may afford protection and long-lasting results compared to conventional therapies, e.g., corticosteroids or immunosuppressant drugs. Here, we propose the polyamine spermidine as a novel therapeutic agent in airways diseases, based on a recently identified mode of action: T-cell protein tyrosine phosphatase (TCPTP) agonism. It may include and surpass single-inhibitors of stress and secondary growth factor pathway signaling, i.e., the new medicinal chemistry in lung diseases. Enhanced polyamine biosynthesis has been charged with aggravating prognosis by competing for L-arginine at detriment of nitric oxide (NO) synthesis with bronchoconstrictive effects. Although excess spermine, a higher polyamine, is harmful to airways physiology, spermidine can pivot the cell homeostasis during stress conditions by the activation of TCPTP. In fact, the dephosphorylating activity of TCPTP inhibits the signaling cascade that leads to the expression of genes involved in detachment and epithelial-to-mesenchymal transition (EMT), and increases the expression of adhesion and tight junction proteins, thereby enhancing the barrier functionality in inflammation-prone tissues. Moreover, a further beneficial effect of spermidine may derive from its ability to promote autophagy, possibly in a TCPTP-dependent way. Since doses of spermidine in the micromolar range are sufficient to activate TCPTP, low amounts of spermidine administered in sustained release modality may provide an optimal pharmacologic profile for the treatment of obstructive airway diseases.

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

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

Serum levels of homocysteine, asymmetric dimethylarginine and nitric oxide in patients with Parkinson's disease

OBJECTIVES

Endothelial dysfunction has been implicated as a crucial event in the development of several neurodegenerative diseases. The aim of this study was to investigate the serum homocysteine, asymmetric dimethylarginine (ADMA) and nitric oxide (NO) levels in patients with Parkinson's disease (PD) and to compare the results with data from healthy controls.

METHODS

A total of 132 subjects, including 82 idiopathic PD patients who were newly diagnosed and untreated (47 males, 35 females, mean age of 60.8 ± 7.1 years) and 50 healthy controls (28 males, 22 females, mean age of 60.2 ± 6.7 years) were enrolled in this study. The serum ADMA and NO levels were determined using enzyme-linked immunosorbent assay (ELISA), while the homocysteine levels were determined by chemiluminescent microparticle immunoassay.

RESULTS

The ADMA and NO levels of the PD patients were significantly higher than those of the healthy controls. The serum ADMA levels were 0.70 ± 0.15 μmol/L in the PD patients and 0.50 ± 0.12 μmol/L in the healthy controls (p < 0.001). The serum NO levels were 78.7 ± 10.3 μmol/L in the PD patients and 59.9 ± 9.5 μmol/L in the healthy controls (p < 0.001). In addition, the ADMA and NO levels were significantly correlated with the serum homocysteine levels in patients with PD (r = 0.874, p < 0.001, r = 0.803, p = 0.005, respectively).

CONCLUSION

In our study, the high ADMA and NO levels of patients with PD indicate endothelial dysfunction, and this dysfunction may play a role in PD pathogenesis. Larger studies, including randomised clinical trials in humans and animal studies, are needed to validate our findings and help in developing a better understanding of the pathogenesis of PD.

Systematic review regarding metabolic profiling for improved pathophysiological understanding of disease and outcome prediction in respiratory infections

Metabolic profiling through targeted quantification of a predefined subset of metabolites, performed by mass spectrometric analytical techniques, allows detailed investigation of biological pathways and thus may provide information about the interaction of different organic systems, ultimately improving understanding of disease risk and prognosis in a variety of diseases. Early risk assessment, in turn, may improve patient management in regard to cite-of-care decisions and treatment modalities. Within this review, we focus on the potential of metabolic profiling to improve our pathophysiological understanding of disease and management of patients. We focus thereby on lower respiratory tract infections (LRTI) including community-acquired pneumonia (CAP) and chronic obstructive pulmonary disease (COPD), an important disease responsible for high mortality, morbidity and costs worldwide. Observational data from numerous clinical and experimental studies have provided convincing data linking metabolic blood biomarkers such as lactate, glucose or cortisol to patient outcomes. Also, identified through metabolomic studies, novel innovative metabolic markers such as steroid hormones, biogenic amines, members of the oxidative status, sphingo- and glycerophospholipids, and trimethylamine-N-oxide (TMAO) have shown promising results. Since many uncertainties remain in predicting mortality in these patients, further prospective and retrospective observational studies are needed to uncover metabolic pathways responsible for mortality associated with LRTI. Improved understanding of outcome-specific metabolite signatures in LRTIs may optimize patient management strategies, provide potential new targets for future individual therapy, and thereby improve patients' chances for survival.

Asthma and obesity: mechanisms and clinical implications

Obesity is the most common asthma co-morbidity; it has been associated with increased risk for asthma exacerbations, worse respiratory symptoms and poor control. The exact mechanisms remain elusive and are probably multifactorial, stemming from mechanical alterations of the airways and lung parenchyma, to systemic and airway inflammatory and metabolic dysregulation that adversely influences lung function and or response to therapy. However, the fact that not every obese asthmatic is equally affected by weight gain highlights the many challenges and complexities in understanding this association. The factors that determine susceptibility may not depend on being obese alone, but rather the interactions with other phenotypical characteristics, such as age of asthma onset, gender and race to name a few. Inability to account for asthma phenotypes that are differentially affected by increasing body mass index (BMI) may contribute to the lack of consistent results across studies. This review will provide a succinct summary of obesity-related mechanisms and the clinical impact on asthma including highlights on recent progress.

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

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

Metabolic origins of childhood asthma

Childhood obesity and incidence of asthma are increasing globally. The parallel increase of the two suggests that obesity and asthma may be related and that abnormalities in the lipid and/or glucose metabolism may contribute to the pathogenesis of asthma. The clinical presentation of obese asthma is distinct from other asthma phenotypes and depending on age of onset of symptoms. Asthma in obese people tends to be more severe, not typically associated with allergy, and less responsive to standard anti-inflammatory therapy, including corticosteroids. Obesity and obesity-related comorbidities may lead to asthma via a number of mechanisms including changes in lung mechanics, the nitric oxide metabolism, and by causing inflammation. Furthermore, evidence suggests that nutrition during pregnancy contributes to intrauterine immune and metabolic programming in the offspring, which may have major influences on predisposition to cardiovascular, metabolic, and allergic diseases, including asthma, later in life. This review will highlight some suggested mechanistic links between obesity and diabetes with asthma.

Alterations of the arginine metabolome in sickle cell disease: a growing rationale for arginine therapy

Low global arginine bioavailability (GAB) is associated with numerous complications of SCD including early mortality. Mechanisms of arginine dysregulation involve a complex paradigm of excess activity of the arginine-consuming enzyme arginase, elevated levels of asymmetric dimethylarginine, altered intracellular arginine transport, and nitric oxide synthase dysfunction. Restoration of GAB through exogenous supplementation is therefore, a promising therapeutic target. Studies of arginine therapy demonstrate efficacy in treating patients with leg ulcers, pulmonary hypertension risk, and pain. Co-administration with hydroxyurea increases levels of nitrite and fetal hemoglobin. Addressing the alterations in the arginine metabolome may result in new strategies for treatment of SCD.

Asymmetric dimethyl-arginine metabolism in a murine model of cigarette smoke-mediated lung inflammation

There is increasing evidence that the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethyl-arginine (ADMA) is involved in the pathogenesis of chronic lung diseases. One important regulator of this molecule is the ADMA-metabolizing enzyme dimethyl-arginine dimethyl-aminohydrolase (DDAH). The objective of this study was to determine whether perturbation of the ADMA-DDAH pathway contributes to lung inflammation following exposure to cigarette smoke (CS). For these studies, wild-type and DDAH transgenic mice were sham or CS-exposed. Serum ADMA levels were determined by mass spectrometry. ADMA content and DDAH expression were also visualized in mouse lung tissue by immunohistochemistry. DDAH expression was determined by real-time quantitative PCR (qPCR). Inflammation was assessed by H&E staining and analyses of total cell counts and fluid tumor necrosis factor (TNF)-α levels (using ELISA) in lung lavage fluid. NF-κB binding activity in mouse lung epithelial (LA-4) cells was assessed by a transcription factor-binding assay. The results indicated that the concentration of serum ADMA was increased following exposure to CS, and this corresponded with increased ADMA content in bronchial epithelial cells in lung tissue. Total lung DDAH expression was significantly decreased in lung tissue and cultured LA-4 cells following CS exposure. Addition of exogenous ADMA increased CSE-mediated NF-κB binding activity and TNFα production in LA-4 cells more than 2-fold compared to that in CSE-exposed controls. CS-mediated lung inflammation was significantly attenuated in DDAH transgenic mice compared to in wild-type controls. These findings demonstrated that lung ADMA metabolism was altered in mice following CS exposure and suggested that ADMA played a role in CS-mediated inflammation through increasing the presence of inflammatory mediators in lung epithelial cells.