Elevated asymmetric dimethylarginine alters lung function and induces collagen deposition in mice

A mouse model of wildfire smoke-induced health effects: sex differences in acute and sustained effects of inhalation exposures

Due to climate change, wildfires have increased in intensity and duration. While wildfires threaten lives directly, the smoke has more far-reaching adverse health impacts. During an extreme 2017 wildfire event, residents of Seeley Lake, Montana were exposed to unusually high levels of wood smoke (WS) causing sustained effects on lung function (decreased FEV1/FVC). Objective: The present study utilized an animal model of WS exposure to research cellular and molecular mechanisms of the resulting health effects. Methods: Mice were exposed to inhaled WS utilizing locally harvested wood to recapitulate community exposures. WS was generated at a rate resulting in a 5 mg/m3 PM2.5 exposure for five days. Results: This exposure resulted in a similar 0.28 mg/m2 particle deposition (lung surface area) in mice that was calculated for human exposure. As with the community observations, there was a significant effect on lung function, increased resistance, and decreased compliance, that was more pronounced in males at an extended (2 months) timepoint and males were more affected than females: ex vivo assays illustrated changes to alveolar macrophage functions (increased TNFα secretion and decreased efferocytosis). Female mice had significantly elevated IL-33 levels in lungs, however, pretreatment of male mice with IL-33 resulted in an abrogation of the observed WS effects, suggesting a dose-dependent role of IL-33. Additionally, there were greater immunotoxic effects in male mice. Discussion: These findings replicated the outcomes in humans and suggest that IL-33 is involved in a mechanism of the adverse effects of WS exposures that inform on potential sex differences.

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.

The Association between Maternal Urinary Phthalate Concentrations and Blood Pressure in Pregnancy: A Systematic Review and Meta-Analysis

Phthalates are commonly found in a wide range of environments and have been linked to several negative health outcomes. While earlier research indicated a potential connection between phthalate exposure and blood pressure (BP) during pregnancy, the results of these studies remain inconclusive. The objective of this meta-analysis was to elucidate the relationship between phthalate exposure and BP in pregnancy. A comprehensive literature search was carried out with PubMed, EMBASE, and Web of Science, and pertinent studies published up until 5 March 2023 were reviewed. Random-effects models were utilized to consolidate the findings of continuous outcomes, such as diastolic and systolic BP, as well as the binary outcomes of hypertensive disorders of pregnancy (HDP). The present study included a total of 10 studies. First-trimester MBP exposure exhibited a positive association with mean systolic and diastolic BP during both the second and third trimesters (β = 1.05, 95% CI: 0.27, 1.83, I² = 93%; β = 0.40, 95% CI: 0.05, 0.74, I² = 71%, respectively). Second-trimester monobenzyl phthalate (MBzP) exposure was positively associated with systolic and diastolic BP in the third trimester (β = 0.57, 95% CI: 0.01, 1.13, I² = 0; β = 0.70, 95% CI: 0.27, 1.13, I² = 0, respectively). Conversely, first-trimester mono-2-ethylhexyl phthalate (MEHP) exposure demonstrated a negative association with mean systolic and diastolic BP during the second and third trimesters (β = -0.32, 95% CI: -0.60, -0.05, I² = 0; β = -0.32, 95% CI: -0.60, -0.05, I² = 0, respectively). Additionally, monoethyl phthalate (MEP) exposure was found to be associated with an increased risk of HDP (OR = 1.12, 95% CI: 1.02, 1.23, I² = 26%). Our study found that several phthalate metabolites were associated with increased systolic and diastolic BP, as well as the risk of HDP across pregnancies. Nevertheless, given the limited number of studies analyzed, additional research is essential to corroborate these findings and elucidate the molecular mechanisms linking phthalates to BP changes during pregnancy.

LncRNA DANCR deficiency promotes high glucose-induced endothelial to mesenchymal transition in cardiac microvascular cells via the FoxO1/DDAH1/ADMA signaling pathway

Cardiac fibrosis is the main pathological basis of diabetic cardiomyopathy (DCM), and endothelial-to-meschenymal transition (EndMT) is a key driver to cardiac fibrosis and plays an important role in the pathogenesis of DCM. Asymmetric dimethylarginine (ADMA), a crucial pathologic factor in diabetes mellitus, is involved in organ fibrosis. This study aims to evaluate underlying mechanisms of ADMA in DCM especially for EndMT under diabetic conditions. A diabetic rat model was induced by streptozotocin (STZ) injection, and human cardiac microvascular endothelial cells (HCMECs) were stimulated with high glucose to induce EndMT. Subsequently, the role of ADMA in EndMT was detected either by exogenous ADMA or by over-expressing dimethylarginine dimethylaminohydrolase 1 (DDAH1, degradation enzyme for ADMA) before high glucose stimulation. Furthermore, the relationships among forkhead box protein O1 (FoxO1), DDAH1 and ADMA were evaluated by FoxO1 over-expression or FoxO1 siRNA. Finally, we examined the roles of LncRNA DANCR in FoxO1/DDAH1/ADMA pathway and EndMT of HCMECs. Here, we found that EndMT in HCMECs was induced by high glucose, as evidenced by down-regulated expression of CD31 and up-regulated expression of FSP-1 and collagen Ⅰ. Importantly, ADMA induced EndMT in HCMECs, and over-expressing DDAH1 protected from developing EndMT by high glucose. Furthermore, we demonstrated that over-expression of FoxO1-ADA with mutant phosphorylation sites of T24A, S256D, and S316A induced EndMT of HCMECs by down-regulating of DDAH1 and elevating ADMA, and that EndMT of HCMECs induced by high glucose was reversed by FoxO1 siRNA. We also found that LncRNA DANCR siRNA induced EndMT of HCMECs, activated FoxO1, and inhibited DDAH1 expression. Moreover, over-expression of LncRNA DANCR could markedly attenuated high glucose-mediated EndMT of HCMECs by inhibiting the activation of FoxO1 and increasing the expression of DDAH1. Collectively, our results indicate that LncRNA DANCR deficiency promotes high glucose-induced EndMT in HCMECs by regulating FoxO1/DDAH1/ADMA pathway.

Asymmetric Dimethylarginine in COPD Exacerbation

Objectives

Chronic obstructive pulmonary disease (COPD) is a disease with progressive airway limitation. The asymmetric dimethylarginine (ADMA) molecule is known to be effective in airway inflammation and remodeling. We investigated the relationship between ADMA and COPD, and its role in the course of the disease in cases with exacerbation.

Methods

This single-center study performed in our patient clinic included 56 patients (57.1% of males) with median age 67 (41-88) presented with COPD exacerbation and 26 sex-matched healthy controls. ADMA, white blood cell count, eosinophil, neutrophil, lymphocyte, C-reactive protein, fibrinogen, oxygen saturation%, and pulmonary function test values were compared.

Results

ADMA values were significantly higher (516.93 vs. 320.05 median, p<0.05) in the COPD group compared to the control group. No significant difference was demonstrated in ADMA concentrations according to Global Initiative for Chronic Obstructive Lung Disease Stages (p>0.05). In the receiver operating characteristic analysis to estimate the predictive power of COPD, the cutoff ADMA concentration >301 ng/ml was found to be able to distinguish COPD patients in all cases.

Conclusion

ADMA levels increase with complex mechanisms in COPD. It can be a significant indicator of the disease. However, more extensive research is needed for its use as a biomarker in severity and progression of COPD.

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.

Nanoparticle-Induced Airway Eosinophilia Is Independent of ILC2 Signaling but Associated With Sex Differences in Macrophage Phenotype Development

The majority of lung diseases occur with a sex bias in terms of prevalence and/or severity. Previous studies demonstrated that, compared with males, female mice develop greater eosinophilic inflammation in the airways after multiwalled carbon nanotube (MWCNT) exposure. However, the mechanism by which this sex bias occurs is unknown. Two immune cells that could account for the sex bias are type II innate lymphoid cells (ILC2s) and alveolar macrophages (AMs). In order to determine which immune cell type was responsible for MWCNT-induced airway eosinophil recruitment and subsequent sex differences in inflammation and disease, male and female C57BL/6 mice were exposed to MWCNTs (2 mg/kg) via oropharyngeal aspiration, and the respiratory immune response was assessed 7 d later. Greater eosinophilia and eotaxin 2 levels were observed in MWCNT-treated females and corresponded with greater changes in airway hyperresponsiveness than those in MWCNT-treated males. In MWCNT-treated females, there was a significant increase in the frequency of ILC2s within the lungs compared with control animals. However, depletion of ILC2s via α-CD90.2 administration did not decrease eosinophil recruitment 24 h and 7 d after MWCNT exposure. AMs isolated from control and MWCNT-treated animals demonstrated that M2a macrophage phenotype gene expression, ex vivo cytokine production, and activation of (p)STAT6 were upregulated to a significantly greater degree in MWCNT-treated females than in males. Our findings suggest that sex differences in AM phenotype development, not ILC2 signaling, are responsible for the observed female bias in eosinophilic inflammation after MWCNT inhalation.

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.

New views on endothelial dysfunction in gestational hypertension and potential therapy targets

The placenta has vital roles in metabolite exchange, fetal growth, and pre-eclampsia (PE). In this review, we discuss the pathogenesis of hypertension in pregnancy, focusing on four major theories to explain PE, discussing endothelial roles in those theories. We focus in particular on the roles of nitric oxide (NO) and prostacyclin (PGI₂) in placental endothelium, and propose new hypotheses for the influence and mechanisms of endothelial NO and PGI₂ signaling pathways in PE.

Scarred Lung. An Update on Radiation-Induced Pulmonary Fibrosis

Radiation-induced pulmonary fibrosis is a common severe long-time complication of radiation therapy for tumors of the thorax. Current therapeutic options used in the clinic include only supportive managements strategies, such as anti-inflammatory treatment using steroids, their efficacy, however, is far from being satisfactory. Recent studies have demonstrated that the development of lung fibrosis is a dynamic and complex process, involving the release of reactive oxygen species, activation of Toll-like receptors, recruitment of inflammatory cells, excessive production of nitric oxide and production of collagen by activated myofibroblasts. In this review we summarized the current state of knowledge on the pathophysiological processes leading to the development of lung fibrosis and we also discussed the possible treatment options.

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.

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.

Asymmetric dimethylarginine: An crucial regulator in tissue fibrosis

Fibrosis is a reparative process with very few therapeutic options to prevent its progression to organ dysfunction. Chronic fibrotic diseases contribute to an estimated 45% of all death in the industrialized world. Asymmetric dimethylarginine (ADMA), an endothelial nitric oxide synthase inhibitor, plays a crucial role in the pathogenesis of various cardiovascular diseases associated with endothelial dysfunction. Recent reports have focused on ADMA in the pathogenesis of tissue fibrosis. This review discusses the current knowledge about ADMA biology, its association with risk factors of established fibrotic diseases and the potential pathophysiological mechanisms implicating ADMA in the process of tissue fibrosis.

Effect of N-(2-aminoethyl) ethanolamine on hypertrophic scarring changes in vitro: Finding novel anti-fibrotic therapies

Hypertrophic scars (HS) limit movement, decrease quality of life, and remain a major impediment to rehabilitation from burns. However, no effective pharmacologic therapies for HS exist. Here we tested the in vitro anti-fibrotic effects of the novel chemical N-(2-aminoethyl) ethanolamine (AEEA) at non-toxic concentrations. Scanning electron microscopy showed that AEEA markedly altered the structure of the extracellular matrix (ECM) produced by primary dermal fibroblasts isolated from a HS of a burn patient (HTS). Compression atomic force microscopy revealed that AEEA stiffened the 3D nanostructure of ECM formed by HTS fibroblasts. Western blot analysis in three separate types of primary human dermal fibroblasts (including HTS) showed that AEEA exposure increased the extractability of type I collagen in a dose- and time-dependent fashion, while not increasing collagen synthesis. A comparison of the electrophoretic behavior of the same set of samples under native and denaturing conditions suggested that AEEA alters the 3D structure of type I collagen. The antagonization effect of AEEA to TGF-β1 on ECM formation was also observed. Furthermore, analyses of the anti-fibrotic effects of analogs of AEEA (with modified pharmacophores) suggest the existence of a chemical structure-activity relationship. Thus, AEEA and its analogs may inhibit HS development; further study and optimization of analogs may be a promising strategy for the discovery for effective HS therapies.

Metabolomic profiling of human lung tumor tissues - nucleotide metabolism as a candidate for therapeutic interventions and biomarkers

Although metabolomics has attracted considerable attention in the field of lung cancer (LC) detection and management, only a very limited number of works have applied it to tissues. As such, the aim of this study was the thorough analysis of metabolic profiles of relevant LC tissues, including the most important histological subtypes (adenocarcinoma and squamous cell lung carcinoma). Mass spectrometry‐based metabolomics, along with genetic expression and histological analyses, were performed as part of this study, the widest to date, to identify metabolic alterations in tumors of the most relevant histological subtypes in lung. A total of 136 lung tissue samples were analyzed and 851 metabolites were identified through metabolomic analysis. Our data show the existence of a clear metabolic alteration not only between tumor vs. nonmalignant tissue in each patient, but also inherently intrinsic changes in both AC and SCC. Significant changes were observed in the most relevant biochemical pathways, and nucleotide metabolism showed an important number of metabolites with high predictive capability values. The present study provides a detailed analysis of the metabolomic changes taking place in relevant biochemical pathways of the most important histological subtypes of LC, which can be used as biomarkers and also to identify novel targets.

Systemic concentrations of asymmetric dimethylarginine (ADMA) in chronic obstructive pulmonary disease (COPD): state of the art

Experimental evidence suggests that oxidative stress (OS) may increase the activity of arginine methylating enzymes that produce the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA). In addition, it is well documented that OS can significantly decrease the synthesis and/or activity of ADMA degrading enzymes, thus causing ADMA accumulation in biological fluids. Recent reports have focused on circulating methylated arginine concentrations in chronic obstructive pulmonary disease, a disease characterized by a significant increase in OS. This review discusses the results of these studies and the opportunities for further research in this area.

Phe71 in Type III Trypanosomal Protein Arginine Methyltransferase 7 (TbPRMT7) Restricts the Enzyme to Monomethylation

Protein arginine methyltransferase 7 (PRMT7) is unique within the PRMT family as it is the only isoform known to exclusively make monomethylarginine (MMA). Given its role in epigenetics, the mechanistic basis for the strict monomethylation activity is under investigation. It is thought that PRMT7 enzymes are unable to add a second methyl group because of steric hindrance in the active site that restricts them to monomethylation. To test this, we probed the active site of trypanosomal PRMT7 (TbPRMT7) using accelerated molecular dynamics, site-directed mutagenesis, kinetic, binding, and product analyses. Both the dynamics simulations and experimental results show that the mutation of Phe71 to Ile converts the enzyme from a type III methyltransferase into a mixed type I/II, that is, an enzyme that can now perform dimethylation. In contrast, the serine and alanine mutants of Phe71 preserve the type III behavior of the native enzyme. These results are inconsistent with a sterics-only model to explain product specificity. Instead, molecular dynamics simulations of these variants bound to peptides show hydrogen bonding between would-be substrates and Glu172 of TbPRMT7. Only in the case of the Phe71 to Ile mutation is this interaction between MMA and the enzyme maintained, and the geometry for optimal S_N2 methyl transfer is obtained. The results of these studies highlight the benefit of combined computational and experimental methods in providing a better understanding for how product specificity is dictated by PRMTs.

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.

Positive correlation of airway resistance and serum asymmetric dimethylarginine level in COPD patients with systemic markers of low-grade inflammation

The major feature of COPD is a progressive airflow limitation caused by chronic airway inflammation and consequent airway remodeling. Modified arginase and nitric oxide synthase (NOS) pathways are presumed to contribute to the inflammation and fibrosis. Asymmetric dimethylarginine (ADMA) may shunt L-arginine from the NOS pathway to the arginase one by uncoupling and competitive inhibition of NOS and by enhancing arginase activity. To attest the interplay of these pathways, the relationship between ADMA and airflow limitation, described by airway resistance (R_aw), was investigated in a cohort of COPD patients. Every COPD patient willing to give consent to participate (n=74) was included. Case history, laboratory parameters, serum arginine and ADMA, pulmonary function (whole-body plethysmography), and disease-specific quality of life (St George’s Respiratory Questionnaire) were determined. Multiple linear regression was used to identify independent determinants of R_aw. The final multiple model was stratified based on symptom control. The log R_aw showed significant positive correlation with log ADMA in the whole sample (Pearson’s correlation coefficient: 0.25, P=0.03). This association remained significant after adjusting for confounders in the whole data set (β: 0.42; confidence interval [CI]: 0.06, 0.77; P=0.022) and in the worse-controlled stratum (β: 0.84; CI: 0.25, 1.43; P=0.007). Percent predicted value of forced expiratory flow between 25% and 75% of forced vital capacity showed that significant negative, elevated C-reactive protein exhibited significant positive relationship with R_aw in the final model. Positive correlation of R_aw with ADMA in COPD patients showing evidence of a systemic low-grade inflammation implies that ADMA contributes to the progression of COPD, probably by shunting L-arginine from the NOS pathway to the arginase one.

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.

IL-4 promotes asymmetric dimethylarginine accumulation, oxo-nitrative stress, and hypoxic response-induced mitochondrial loss in airway epithelial cells

BACKGROUND

Obesity is known to increase asthma risk and severity. Increased levels of asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, are associated with mitochondrial toxicity, asthma, and metabolic syndrome. IL-4 upregulates the expression of protein arginine methyltransferases, which are essential for ADMA formation. Importantly, cross-talk between IL-4, ADMA, and mitochondrial dysfunction could explain how obesity and IL-4 can synergize to exacerbate allergic inflammation.

OBJECTIVE

We sought to investigate how IL-4, a key asthma-associated cytokine, can influence ADMA-related effects on lungs.

METHODS

BEAS2B (bronchial epithelial) cells were treated with IL-4 followed by ADMA and investigated for oxo-nitrative stress and resultant mitochondrial toxicity after 48 hours by using flow cytometry, confocal imaging, immunoblotting, and fluorimetric assays.

RESULTS

IL-4-induced mitotoxicity in BEAS2B cells was significantly higher in the presence of exogenous ADMA. IL-4 treatment led to proteolytic degradation of dimethylarginine dimethylaminohydrolase 2, which catabolizes ADMA. IL-4 pretreatment was associated with increased intracellular ADMA accumulation and increased ADMA-induced mitotoxicity. Airway epithelial cells treated with IL-4 followed by ADMA showed exaggerated oxo-nitrative stress and potent induction of the cellular hypoxic response, despite normoxic conditions. The hypoxic response was associated with reduced mitochondrial function but was reversible by overexpression of the mitochondrial biogenesis factor, mitochondrial transcription factor A.

CONCLUSION

We conclude that IL-4 promotes intracellular ADMA accumulation, leading to mitochondrial loss through oxo-nitrative stress and hypoxic response. This provides a novel understanding of how obesity, with high ADMA levels, and asthma, with high IL-4 levels, might potentiate each other and highlights the potential of mitochondrial-targeted therapeutics in obese subjects with asthma.

Biochemistry and regulation of the protein arginine methyltransferases (PRMTs)

Many key cellular processes can be regulated by the seemingly simple addition of one, or two, methyl groups to arginine residues by the nine known mammalian protein arginine methyltransferases (PRMTs). The impact that arginine methylation has on cellular well-being is highlighted by the ever growing evidence linking PRMT dysregulation to disease states, which has marked the PRMTs as prominent pharmacological targets. This review is meant to orient the reader with respect to the structural features of the PRMTs that account for catalytic activity, as well as provide a framework for understanding how these enzymes are regulated. An overview of what we understand about substrate recognition and binding is provided. Control of product specificity and enzyme processivity are introduced as necessary but flexible features of the PRMTs. Precise control of PRMT activity is a critical component to eukaryotic cell health, especially given that an arginine demethylase has not been identified. We therefore conclude the review with a comprehensive discussion of how protein arginine methylation is regulated.

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

INTRODUCTION

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Metabolic Syndrome Is Associated with Increased Oxo-Nitrative Stress and Asthma-Like Changes in Lungs

Epidemiological studies have shown an increased obesity-related risk of asthma. In support, obese mice develop airway hyperresponsiveness (AHR). However, it remains unclear whether the increased risk is a consequence of obesity, adipogenic diet, or the metabolic syndrome (MetS). Altered L-arginine and nitric oxide (NO) metabolism is a common feature between asthma and metabolic syndrome that appears independent of body mass. Increased asthma risk resulting from such metabolic changes would have important consequences in global health. Since high-sugar diets can induce MetS, without necessarily causing obesity, studies of their effect on arginine/NO metabolism and airway function could clarify this aspect. We investigated whether normal-weight mice with MetS, due to high-fructose diet, had dysfunctional arginine/NO metabolism and features of asthma. Mice were fed chow-diet, high-fat-diet, or high-fructose-diet for 18 weeks. Only the high-fat-diet group developed obesity or adiposity. Hyperinsulinemia, hyperglycaemia, and hyperlipidaemia were common to both high-fat-diet and high-fructose-diet groups and the high-fructose-diet group additionally developed hypertension. At 18 weeks, airway hyperresponsiveness (AHR) could be seen in obese high-fat-diet mice as well as non-obese high-fructose-diet mice, when compared to standard chow-diet mice. No inflammatory cell infiltrate or goblet cell metaplasia was seen in either high-fat-diet or high-fructose-diet mice. Exhaled NO was reduced in both these groups. This reduction in exhaled NO correlated with reduced arginine bioavailability in lungs. In summary, mice with normal weight but metabolic obesity show reduced arginine bioavailability, reduced NO production, and asthma-like features. Reduced NO related bronchodilation and increased oxo-nitrosative stress may contribute to the pathogenesis.

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.

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.

The many faces of asthma in obesity

Obesity is a major risk factor for the development of asthma, and causes severe, uncontrolled disease that responds poorly to therapy. The obese state alters early onset allergic asthma, and leads to the development of a novel form of late onset asthma secondary to obesity. The presentation of early onset allergic asthma is altered through effects on immune function. Factors such as mechanical loading, effects of adipokines on airways, altered diet, insulin resistance and altered metabolism of nitric oxide likely all contribute to increased airway reactivity in obesity, causing late onset asthma in obesity. Obesity also alters responses to environmental factors such as ozone and particulate matter. Focused studies to understand the importance of these factors in the pathogenesis of airway disease in obesity will be essential to develop therapies to intervene in this new epidemic of airway disease.

Adiposity, fractional exhaled nitric oxide, and asthma in U.S. children

RATIONALE

Whether allergic airway inflammation mediates the association between overweight or obesity and childhood asthma is unknown.

OBJECTIVES

To examine adiposity, asthma, and fractional exhaled nitric oxide (FeNO) in U.S. children.

METHODS

Cross-sectional study of indicators of adiposity or obesity, FeNO (a biomarker of eosinophilic airway inflammation), and asthma in 2,681 children aged 6-17 years in the 2007-2010 National Health and Nutrition Examination Survey. Adiposity measures included body mass index (BMI), percent body fat (PBF), and waist circumference (WC).

MEASUREMENTS AND MAIN RESULTS

BMI, PBF, and WC were associated with asthma among children with low FeNO (odds ratio, 1.54-1.68; P < 0.01), but not among children with increased FeNO. Among children without asthma, BMI, PBF, and WC were associated with higher FEV1 and FVC, and lower FEV1/FVC. Among children with asthma and a high FeNO, all adiposity indicators were associated with decreased FEV1/FVC (β = -1.5% to -1.7% per z score) but not with FEV1 or FVC. Higher BMI or PBF was associated with worse asthma severity or control in children with asthma and increased FeNO, but not in children with asthma and low FeNO. Similar results were obtained in a secondary multivariate analysis of overweight or obesity (defined as BMI ≥85th percentile) and asthma or indicators of asthma severity or control, stratified by FeNO level.

CONCLUSIONS

Adiposity indicators are associated with asthma in children with low FeNO. Among children with asthma, adiposity indicators are associated with worse asthma severity or control in those with high FeNO.

Arginine metabolism in asthma

Nitric oxide (NO) is important in the regulation of airway tone and airway responsiveness. Alterations in the L-arginine metabolism resulting in reduced availability of the substrate L-arginine for NO synthases, as well as the presence of NO synthase inhibitors such as asymmetric dimethylarginine, contribute to the reduced NO formation and airway dysfunction in asthma. Therapeutic interventions aiming to modulate the impaired L-arginine metabolism may help correct the enhanced airway tone and responsiveness in asthma.

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

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

Asymmetric dimethylarginine in exhaled breath condensate and serum of children with asthma

BACKGROUND

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor and uncoupler of nitric oxide synthase. By promoting the formation of peroxynitrite, ADMA is believed to contribute to several aspects of asthma pathogenesis (ie, airway inflammation, oxidative stress, bronchial hyperresponsiveness, and collagen deposition). The aim of the present study was to compare this mediator in healthy children and children with asthma using the completely noninvasive exhaled breath condensate (EBC) technique.

METHODS

We recruited 77 children with asthma (5-16 years of age) and 65 healthy children (5-15 years of age) who underwent EBC collection and spirometry. Serum ADMA levels and fractional exhaled nitric oxide levels were measured on the same day in a subgroup of children with asthma. EBC was collected using the Turbo-Deccs (Medivac). ADMA levels were measured using the ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) technique.

RESULTS

ADMA could be detected in the EBC of 71 subjects with asthma and 64 healthy subjects. ADMA levels in the EBC of children with asthma were significantly higher than in the healthy control subjects (median, 0.12 [interquartile range, 0.05-0.3] vs 0.07 [0.05-0.12]; P = .017), whereas no difference emerged between the children with asthma who were or were not receiving inhaled steroid treatment. No correlation was found between serum and EBC ADMA levels (P &gt; .5).

CONCLUSIONS

We measured ADMA in EBC by UPLC-MS/MS, a reference analytical technique. Higher ADMA levels were found in children with asthma, supporting a role for this mediator in asthma pathogenesis. This oxidative stress-related mediator also seems to be scarcely affected by steroid therapy. We speculate that ADMA might be a target for new therapeutic strategies designed to control oxidative stress in asthma.

Asymmetric dimethylarginine blocks nitric oxide-mediated alcohol-stimulated cilia beating

The airway epithelium is exposed to alcohol during drinking through direct exhalation of volatized ethanol from the bronchial circulation. Alcohol exposure leads to a rapid increase in the cilia beat frequency (CBF) of bronchial epithelial cells followed by a chronic desensitization of cilia stimulatory responses. This effect is governed in part by the nitric oxide regulation of cyclic guanosine and adenosine monophosphate-dependent protein kinases (PKG and PKA) and is not fully understood. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is implicated in the pathogenesis of several pulmonary disorders. We hypothesized that the inhibition of nitric oxide synthase by ADMA blocks alcohol-stimulated increases in CBF. To test this hypothesis, ciliated primary bovine bronchial epithelial cells (BBEC) were preincubated with ADMA (100 µM) and stimulated with 100 mM ethanol. CBF was measured and PKA assayed. By 1 hr, ethanol activated PKA, resulting in elevated CBF. Both alcohol-induced PKA activation and CBF were inhibited in the presence of ADMA. ADMA alone had no effect on PKA activity or CBF. Using a mouse model overexpressing the ADMA-degrading enzyme, dimethylarginine dimethylaminohydrolase (DDAH), we examined PKA and CBF in precision-cut mouse lung slices. Alcohol-stimulated increases in lung slice PKA and CBF were temporally enhanced in the DDAH mice versus control mice.

Serum methylarginines and spirometry-measured lung function in older adults

Rationale

Methylarginines are endogenous nitric oxide synthase inhibitors that have been implicated in animal models of lung disease but have not previously been examined for their association with spirometric measures of lung function in humans.

Objectives

This study measured serum concentrations of asymmetric and symmetric dimethylarginine in a representative sample of older community-dwelling adults and determined their association with spirometric lung function measures.

Methods

Data on clinical, lifestyle, and demographic characteristics, methylated arginines, and L-arginine (measured using LC-MS/MS) were collected from a population-based sample of older Australian adults from the Hunter Community Study. The five key lung function measures included as outcomes were Forced Expiratory Volume in 1 second, Forced Vital Capacity, Forced Expiratory Volume in 1 second to Forced Vital Capacity ratio, Percent Predicted Forced Expiratory Volume in 1 second, and Percent Predicted Forced Vital Capacity.

Measurements and Main Results

In adjusted analyses there were statistically significant independent associations between a) higher asymmetric dimethylarginine, lower Forced Expiratory Volume in 1 second and lower Forced Vital Capacity; and b) lower L-arginine/asymmetric dimethylarginine ratio, lower Forced Expiratory Volume in 1 second, lower Percent Predicted Forced Expiratory Volume in 1 second and lower Percent Predicted Forced Vital Capacity. By contrast, no significant associations were observed between symmetric dimethylarginine and lung function.

Conclusions

After adjusting for clinical, demographic, biochemical, and pharmacological confounders, higher serum asymmetric dimethylarginine was independently associated with a reduction in key measures of lung function. Further research is needed to determine if methylarginines predict the decline in lung function.

γ-tocopherol nebulization decreases oxidative stress, arginase activity, and collagen deposition after burn and smoke inhalation in the ovine model

More than 20,000 burn injury victims suffer from smoke inhalation injury in the United States annually. In an ovine model of acute lung injury, γ-tocopherol had a beneficial effect when nebulized into the airway. We hypothesize that γ-tocopherol scavenges reactive oxygen species (ROS) and reactive nitrogen species resulting from burn and smoke inhalation injury and that these ROS/reactive nitrogen species activate the arginase pathway, leading to increased collagen deposition and decreased pulmonary function. To test this hypothesis, ewes were operatively prepared for chronic study, then they were randomly divided into groups (n = 8): uninjured, injured, or injured with nebulization (γ-tocopherol [950 mg/g] and α-tocopherol [40 mg/g] from hours 3 to 48 after the injury). The injury, under deep anesthesia, consisted of a 20% total body surface burn and 36 breaths of cotton smoke; all animals were killed after 3 weeks. Treatment increased lung γ-tocopherol at 3 weeks after γ-tocopherol nebulization compared with injured sheep (1.75 ± 0.62 nmol/g vs. 0.45 ± 0.06, P < 0.05). The expression of dimethylarginine dimethylaminohydrolase-2, which degrades asymmetrical dimethylarginine, a nitric oxide synthase inhibitor, significantly increases with γ-tocopherol treatment compared with injured sheep (P < 0.05). Arginase activity (0.15 ± 0.02 μM urea/μg protein vs. 0.24 ± 0.009, P < 0.05), ornithine aminotransferase (11,720 ± 888 vs. 13,170 ± 1,775), and collagen deposition (0.62 ± 0.12 μM hydroxyproline/μg protein vs. 1.02 ± 0.13, P < 0.05) significantly decrease with γ-tocopherol compared with injured animals without γ-tocopherol. The decreases in arginase and collagen with γ-tocopherol are associated with significantly increased diffusion capacity (P < 0.05) and decreased lung wet-to-dry ratio (P < 0.05). Smoke-induced chronic pulmonary dysfunction is mediated through the ROS/asymmetrical dimethylarginine/arginase pathway, and ROS scavengers such as γ-tocopherol may be a potential therapeutic management of burn patients with inhalation injury.

Arginine and nitric oxide pathways in obesity-associated asthma

Obesity is a comorbidity that adversely affects asthma severity and control by mechanisms that are not fully understood. This review will discuss evidence supporting a role for nitric oxide (NO) as a potential mechanistic link between obesity and late-onset asthma (>12 years). Several studies have shown that there is an inverse association between increasing body mass index (BMI) and reduced exhaled NO. Newer evidence suggests that a potential explanation for this paradoxical relationship is related to nitric oxide synthase (NOS) uncoupling, which occurs due to an imbalance between L-arginine (NOS substrate) and its endogenous inhibitor, asymmetric di-methyl arginine (ADMA). The review will propose a theoretical framework to understand the relevance of this pathway and how it may differ between early and late-onset obese asthmatics. Finally, the paper will discuss potential new therapeutic approaches, based on these paradigms, for improving the respiratory health of obese subjects with asthma.

Method development and validation for rat serum fingerprinting with CE-MS: application to ventilator-induced-lung-injury study

In the search for a noninvasive and reliable rapid screening method to detect biomarkers, a metabolomics fingerprinting approach was developed and applied to rat serum samples using capillary electrophoresis coupled to an electrospray ionization-time of flight-mass spectrometer (CE-TOF-MS). An ultrafiltration method was used for sample pretreatment. To evaluate performance the method was validated with carnitine, choline, ornithine, alanine, acetylcarnitine, betaine, and citrulline, covering the entire electropherogram of pool of rat serum. The linearity for all metabolites was >0.99, with good recovery and precision. Approximately 34 compounds were also confirmed in the pool of rat serum. The method was successfully applied to real serum samples from rats with ventilator-induced lung injury, an experimental rat model for acute lung injury (ALI), giving a total of 1163 molecular features. By use of univariate and multivariate statistics 18 significant compounds were found, of which five were confirmed. The involvement of arginase and nitric oxide synthase has been proved for other lung diseases, meaning the increase of asymmetric dimethyl arginine (ADMA) and ornithine and the decrease of arginine found were in accordance with published literature. Ultimately this fingerprinting approach offers the possibility of identifying biomarkers that could be regularly screened for as part of routine disease control. In this way it might be possible to prevent the development of ALI in patients in critical care units.

The role of dimethylarginine dimethylaminohydrolase (DDAH) in pulmonary fibrosis

Pulmonary fibrosis is a devastating and progressive parenchymal lung disease with an extremely poor prognosis. Patients suffering from idiopathic pulmonary fibrosis (IPF) display a compromised lung function alongside pathophysiological features such as highly increased production of extracellular matrix, alveolar epithelial cell dysfunction, and disordered fibroproliferation - features that are due to a dysregulated response to alveolar injury. Under pathophysiological conditions of IPF, abnormally high concentrations of nitric oxide (NO) are found, likely a result of increased activity of the inducible nitric oxide synthase (NOS2), giving rise to products that contribute to fibrosis development. It is known that pharmacological inhibition or knockdown of NOS2 reduces pulmonary fibrosis, suggesting a role for NOS inhibitors in the treatment of fibrosis. Recent reports identified a critical enzyme, dimethylarginine dimethylaminohydrolase (DDAH), which is exceedingly active in patients suffering from IPF and in mice treated with bleomycin. An up-regulation of DDAH was observed in primary alveolar epithelial type II (ATII) cells from mice and patients with pulmonary fibrosis, where it co-localizes with NOS2. DDAH is a key enzyme that breaks down an endogenous inhibitor of NOS, asymmetric dimethylarginine (ADMA), by metabolizing it to l-citrulline and dimethylamine. DDAH was shown to modulate key fibrotic signalling cascades, and inhibition of this enzyme attenuated many features of the disease in in vivo experiments, suggesting a possible new therapeutic strategy for the treatment of patients suffering from IPF.

An association between L-arginine/asymmetric dimethyl arginine balance, obesity, and the age of asthma onset phenotype

RATIONALE

Increasing body mass index (BMI) has been associated with less fractional exhaled nitric oxide (Fe(NO)). This may be explained by an increase in the concentration of asymmetric dimethyl arginine (ADMA) relative to L-arginine, which can lead to greater nitric oxide synthase uncoupling.

OBJECTIVES

To compare this mechanism across age of asthma onset groups and determine its association with asthma morbidity and lung function.

METHODS

Cross-sectional study of participants from the Severe Asthma Research Program, across early- (<12 yr) and late- (>12 yr) onset asthma phenotypes.

MEASUREMENTS AND MAIN RESULTS

Subjects with late-onset asthma had a higher median plasma ADMA level (0.48 μM, [interquartile range (IQR), 0.35-0.7] compared with early onset, 0.37 μM [IQR, 0.29-0.59], P = 0.01) and lower median plasma l-arginine (late onset, 52.3 [IQR, 43-61] compared with early onset, 51 μM [IQR 39-66]; P = 0.02). The log of plasma L-arginine/ADMA was inversely correlated with BMI in the late- (r = -0.4, P = 0.0006) in contrast to the early-onset phenotype (r = -0.2, P = 0.07). Although Fe(NO) was inversely associated with BMI in the late-onset phenotype (P = 0.02), the relationship was lost after adjusting for L-arginine/ADMA. Also in this phenotype, a reduced L-arginine/ADMA was associated with less IgE, increased respiratory symptoms, lower lung volumes, and worse asthma quality of life.

CONCLUSIONS

In late-onset asthma phenotype, plasma ratios of L-arginine to ADMA may explain the inverse relationship of BMI to Fe(NO). In addition, these lower L-arginine/ADMA ratios are associated with reduced lung function and increased respiratory symptom frequency, suggesting a role in the pathobiology of the late-onset phenotype.

Impact of ADMA (asymmetric dimethylarginine) on physiology with respect to diabetes mellitus and respiratory system BEAS-2B cells (human bronchial epithelial cells)

OBJECTIVES

Asymmetric dimethylarginine (ADMA) is a non-selective nitric oxide (NO) synthase inhibitor associated with cardiovascular and metabolic disorders. This study aimed to investigate ADMA with respect to both diabetes and respiratory disease.

METHODS

Glucose was determined by hexokinase method, insulin by a radioimmunoassay. Griess test was used for NO assay and cytokinines were assayed by ELISA. Ciliary beat frequency was determined by high speed video using a microscope.

KEY FINDINGS

ADMA induced an increase in blood glucose and plasma insulin levels in rats; the ratio of these effects indicates the induction of a diabetic situation (insulin resistance). L-arginine increased blood glucose and initially slightly decreased plasma insulin. A pretreatment with ADMA abolished these effects. ADMA shows similar effects in vitro (insulin-secreting cell line, INS-1 cells). L-arginine increased production of NO, which was reversed by ADMA (INS-1 cells). ADMA also reduced NO production positively modulated by various substances, namely metformin, ciglitazone, losartan and nateglinide, but nevertheless inhibited insulin release induced by these compounds. ADMA stimulated the production of cytokines such as interleukin (IL-6) and macrophage inflammatory protein-2 (MIP-2) (rat IL-8 analogue) from INS-1 cells. 5-Aminoimidazole-4-carboxamide-1-β-4-ribofuranoside (AICAR), a direct adenosine monophosphate protein kinase (AMPK) activator and anti-inflammatory agent, induced NO production and reduced cytokine release. In contrast to diabetes parameters, ADMA had no effect of on the respiratory system (cytokine secretion from BEAS-2B cells (IL-8, regulated on activation, normal T cell expressed and secreted, and tumour necrosis factor-α), ciliary beat frequency and smooth muscle contraction of rat trachea).

CONCLUSIONS

ADMA has a pathophysiological impact leading to a diabetic situation but has no impact on the respiratory system.

IL-33 mediates multi-walled carbon nanotube (MWCNT)-induced airway hyper-reactivity via the mobilization of innate helper cells in the lung

Allergic asthma is a chronic inflammatory disorder of the airway associated with bronchial obstruction, airway hyper-reactivity (AHR), and mucus production. The epithelium may direct and propagate asthmatic-like responses. Central to this theory is the observation that viruses, air pollution, and allergens promote epithelial damage and trigger the generation of IL-25, IL-33, and TSLP via innate pathways such as TLRs and purinergic receptors. Similarly, engineered nanomaterials promote a Th2-associated pathophysiology. In this study, we tested the hypothesis that instillation of multi-walled carbon nanotubes (MWCNT) impair pulmonary function in C57Bl/6 mice due to the development of IL-33-dependent Th2-associated inflammation. MWCNT exposure resulted in elevated levels of IL-33 in the lavage fluid (likely originating from airway epithelial cells), enhanced AHR, eosinophil recruitment, and production of Th2-associated cytokines and chemokines. Moreover, these events were dependent on IL-13 signaling and the IL-33/ST2 axis, but independent of T and B cells. Finally, MWCNT exposure resulted in the recruitment of innate lymphoid cells. Collectively, our data suggest that MWCNT induce epithelial damage that results in release of IL-33, which in turn promotes innate lymphoid cell recruitment and the development of IL-13-dependent inflammatory response.

Pseudomonas aeruginosa is associated with increased lung cytokines and asymmetric dimethylarginine compared with methicillin-resistant Staphylococcus aureus

The objective of the study was to investigate pulmonary responses to Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) using ovine and mice models of sepsis with emphasis on lung cytokine expression, asymmetric dimethylarginine (ADMA) concentration, and the arginase pathway. Sheep were instilled with either MRSA, P. aeruginosa, or saline under deep anesthesia; mechanically ventilated; resuscitated with fluid; and killed after 24 h. Mice were instilled with either MRSA, P. aeruginosa, or saline under deep anesthesia and killed after 8 h. Lungs were assessed for ADMA concentration, arginase activity, oxidative stress, and cytokine expression, and plasma was assessed for nitrate/nitrite concentrations. The severity of lung injury was more pronounced in P. aeruginosa sepsis compared with MRSA. The significant changes in sheep lung function after P. aeruginosa sepsis were associated with significantly increased ADMA concentrations and arginase activity compared with MRSA. However, the plasma concentration of nitrites and nitrates were significantly increased in MRSA sepsis compared with P. aeruginosa sepsis. In the mice model, P. aeruginosa significantly increased lung cytokine expression (IL-1 and IL-13), protein oxidation, and arginase activity compared with MRSA. Our data suggest that the greater expression of cytokines and ADMA concentrations may be responsible for severity of acute lung injury in P. aeruginosa sepsis. The lack of arginase activity may explain the greater nitric oxide production in MRSA sepsis.

Hypoxia response in asthma: differential modulation on inflammation and epithelial injury

Oxygen-sensing prolyl-hydroxylase (PHD)-2 negatively regulates hypoxia-inducible factor (HIF)1-α and suppresses the hypoxic response. Hypoxia signaling is thought to be proinflammatory but also attenuates cellular injury and apoptosis. Although increased hypoxic response has been noted in asthma, its functional relevance is unknown. The objectives of this study were to dissect the mechanisms and role of the hypoxic response in asthma pathophysiology. Experimental studies were conducted in mice using acute and chronic allergic models of asthma. The hypoxic response in allergically inflamed lungs was modulated by using pharmacologic PHD inhibitors (ethyl-3-4-dihydroxybenzoic acid [DHB], 1-10 mg/kg) or siRNA-mediated genetic knockdowns. Increased hypoxia response led to exacerbation of the asthma phenotype, with HIF-1α knockdown being beneficial. Chronically inflamed lungs from mice treated with 10 mg/kg DHB showed diffuse up-regulation of the hypoxia response, severe airway remodeling, and inflammation. Fatal asphyxiation during methacholine challenge was noted. However, bronchial epithelium restricted up-regulation of the hypoxia response seen with low-dose DHB (1 mg/kg) reduced epithelial injury and attenuated the asthmatic phenotype. Up-regulation of the hypoxia response was associated with increased expression of CX3CR1, a lymphocyte survival factor, and increased inflammatory cell infiltrate. This study shows that an exaggerated hypoxia response may contribute to airway inflammation, remodeling, and the development of asthma. However, the hypoxia response may also be protective of epithelial apoptosis at lower levels, and the net effects of modulating the hypoxia response may vary based on the context.

Aryl hydrocarbon receptor (AhR) regulates silica-induced inflammation but not fibrosis

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is responsible for mediating a variety of pharmacological and toxicological effects caused by halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent evidence has revealed that the AhR also has numerous physiological roles aside from xenobiotic metabolism, including regulation of immune and inflammatory signaling as well as normal development and homeostasis of several organs. To investigate the role of the AhR in crystalline silica (SiO(2))-induced inflammation and fibrosis, C57Bl/6 and AhR(-/)(-) mice were exposed to SiO(2) or vehicle. Similarly, C57Bl/6 mice were exposed to SiO(2) and TCDD either simultaneously or sequentially to assess whether AhR activation alters inflammation and fibrosis. SiO(2)-induced acute lung inflammation was more severe in AhR(-)(/-) mice; however, the fibrotic response of AhR(-)(/-) mice was attenuated compared with C57Bl/6 mice. In a model of chronic SiO(2) exposure, AhR activation by TCDD in C57Bl/6 mice resulted in reduced inflammation; however, the fibrotic response was not affected. Bone marrow-derived macrophages (BMM) from AhR(-)(/-) mice also produced higher levels of cytokines and chemokines in response to SiO(2). Analysis of gene expression revealed that BMM derived from AhR(-)(/-) mice exhibit increased levels of pro-interleukin (IL)-1β, IL-6, and Bcl-2, yet decreased levels of signal transducers and activators of transcription (STAT)2, STAT5a, and serpin B2 (Pai-2) in response to SiO(2).