Increased mitochondrial arginine metabolism supports bioenergetics in asthma

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

Phosphorylation inactivation of endothelial nitric oxide synthesis in pulmonary arterial hypertension

The impairment of vasodilator nitric oxide (NO) production is well accepted as a typical marker of endothelial dysfunction in vascular diseases, including in the pathophysiology of pulmonary arterial hypertension (PAH), but the molecular mechanisms accounting for loss of NO production are unknown. We hypothesized that low NO production by pulmonary arterial endothelial cells in PAH is due to inactivation of NO synthase (eNOS) by aberrant phosphorylation of the protein. To test the hypothesis, we evaluated eNOS levels, dimerization, and phosphorylation in the vascular endothelial cells and lungs of patients with PAH compared with controls. In mechanistic studies, eNOS activity in endothelial cells in PAH lungs was found to be inhibited due to phosphorylation at T495. Evidence pointed to greater phosphorylation/activation of protein kinase C (PKC) α and its greater association with eNOS as the source of greater phosphorylation at T495. The presence of greater amounts of pT495-eNOS in plexiform lesions in lungs of patients with PAH confirmed the pathobiological mechanism in vivo. Transfection of the activating mutation of eNOS (T495A/S1177D) restored NO production in PAH cells. Pharmacological blockade of PKC activity by β-blocker also restored NO formation by PAH cells, identifying one mechanism by which β-blockers may benefit PAH and cardiovascular diseases through recovery of endothelial functions.

Future Research Directions in Asthma. An NHLBI Working Group Report

Asthma is a common chronic disease without cure. Our understanding of asthma onset, pathobiology, classification, and management has evolved substantially over the past decade; however, significant asthma-related morbidity and excess healthcare use and costs persist. To address this important clinical condition, the NHLBI convened a group of extramural investigators for an Asthma Research Strategic Planning workshop on September 18-19, 2014, to accelerate discoveries and their translation to patients. The workshop focused on (1) in utero and early-life origins of asthma, (2) the use of phenotypes and endotypes to classify disease, (3) defining disease modification, (4) disease management, and (5) implementation research. This report summarizes the workshop and produces recommendations to guide future research in asthma.

ID: 123: ROLE OF MICRORNA-1 IN REGULATING PULMONARY VASCULAR REMODELING IN PULMONARY ARTERIAL HYPERTENSION

Rationale

Pulmonary arterial hypertension (PAH) is a severe, progressive disease characterized by increased pulmonary arterial pressure and resistance due in part to uncontrolled vascular remodeling. The mechanisms contributing to vascular remodeling in PAH are poorly understood and involve rampant pulmonary artery smooth muscle cell (PASMC) proliferation. We recently demonstrated the important role of sphingosine kinase 1 (SphK1), a lipid kinase producing pro-proliferative sphingosine-1-phosphate (S1P), in the development of pulmonary vascular remodeling in PAH. However, the regulatory processes involved in upregulation of SphK1 in this disease are unknown.

Objective

In this study, we aimed to identify novel molecular mechanisms governing the regulation of SphK1 expression, with a focus on microRNA (miR). Using both in vitro studies in pulmonary artery smooth muscle cells (PASMCs) and an in vivo mouse model of experimental hypoxia-mediated pulmonary hypertension (HPH), we explored the role of miR in controlling SphK1 expression in the development of pulmonary vascular remodeling.

Methods and Results

In silico analysis identified hsa-miR-1-3p (miR-1) as a candidate targeting SphK1. We demonstrate miR-1 is down-regulated by hypoxia in human PASMCs and in lung tissues of mice with HPH, coinciding with upregulation of SphK1 expression. PASMCs isolated from patients with PAH had significantly reduced expression of miR-1. Transfection of human PASMCs with miR-1 mimics significantly attenuated activity of a SphK1-3'-UTR luciferase reporter construct and SphK1 protein expression. miR-1 overexpression in human PASMCs also inhibited proliferation and migration under normoxic and hypoxic conditions, both important in pathogenic vascular remodeling in PAH. Finally, we demonstrated that intravenous administration of miR-1 mimics prevents the development of experimental HPH in mice and attenuates induction of SphK1 in PASMCs.

Conclusion

These data demonstrate that miR-1 expression in reduced in PASMCs from PAH patients, is modulated by hypoxia, and regulates the expression of SphK1. Key phenotypic aspects of vascular remodeling are influenced by miR-1 and its overexpression can prevent the development of HPH in mice. These studies further our understanding of the mechanisms underlying pathogenic pulmonary vascular remodeling in PAH and could lead to novel therapeutic targets.

Supported by grants NIH/NHLBI R01 HL127342 and R01 HL111656 to RFM, NIH/NHLBI P01 HL98050 and R01 HL127342 to VN, American Heart Association Predoctoral Fellowship (15PRE2190004) to JRS, and NIH/NLHBI NRSA F30 Fellowship (FHL128034A) to JRS.

Eotaxin-Rich Proangiogenic Hematopoietic Progenitor Cells and CCR3+ Endothelium in the Atopic Asthmatic Response

Angiogenesis is closely linked to and precedes eosinophilic infiltration in asthma. Eosinophils are recruited into the airway by chemoattractant eotaxins, which are expressed by endothelial cells, smooth muscles cells, epithelial cells, and hematopoietic cells. We hypothesized that bone marrow-derived proangiogenic progenitor cells that contain eotaxins contribute to the initiation of angiogenesis and inflammation in asthma. Whole-lung allergen challenge of atopic asthma patients revealed vascular activation occurs within hours of challenge and before airway inflammation. The eotaxin receptor CCR3 was expressed at high levels on submucosal endothelial cells in patients and a murine model of asthma. Ex vivo exposure of murine endothelial cells to eotaxins induced migration and angiogenesis. In mechanistic studies, wild-type mice transplanted with eotaxin-1/2-deficient bone marrow had markedly less angiogenesis and inflammation in an atopic asthma model, whereas adoptive transfer of proangiogenic progenitor cells from wild-type mice in an atopic asthma model into the eotaxin-1/2-deficient mice led to angiogenesis and airway inflammation. The findings indicate that Th2-promoting hematopoietic progenitor cells are rapidly recruited to the lung upon allergen exposure and release eotaxins that coordinately activate endothelial cells, angiogenesis, and airway inflammation.

Reciprocal Changes in Phosphoenolpyruvate Carboxykinase and Pyruvate Kinase with Age Are a Determinant of Aging in Caenorhabditis elegans

Aging involves progressive loss of cellular function and integrity, presumably caused by accumulated stochastic damage to cells. Alterations in energy metabolism contribute to aging, but how energy metabolism changes with age, how these changes affect aging, and whether they can be modified to modulate aging remain unclear. In locomotory muscle of post-fertile Caenorhabditis elegans, we identified a progressive decrease in cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), a longevity-associated metabolic enzyme, and a reciprocal increase in glycolytic pyruvate kinase (PK) that were necessary and sufficient to limit lifespan. Decline in PEPCK-C with age also led to loss of cellular function and integrity including muscle activity, and cellular senescence. Genetic and pharmacologic interventions of PEPCK-C, muscle activity, and AMPK signaling demonstrate that declines in PEPCK-C and muscle function with age interacted to limit reproductive life and lifespan via disrupted energy homeostasis. Quantifications of metabolic flux show that reciprocal changes in PEPCK-C and PK with age shunted energy metabolism toward glycolysis, reducing mitochondrial bioenergetics. Last, calorie restriction countered changes in PEPCK-C and PK with age to elicit anti-aging effects via TOR inhibition. Thus, a programmed metabolic event involving PEPCK-C and PK is a determinant of aging that can be modified to modulate aging.

Clinical Implications of Having Reduced Mid Forced Expiratory Flow Rates (FEF25-75), Independently of FEV1, in Adult Patients with Asthma

INTRODUCTION

FEF25-75 is one of the standard results provided in spirometry reports; however, in adult asthmatics there is limited information on how this physiological measure relates to clinical or biological outcomes independently of the FEV1 or the FEV1/FVC ratio.

PURPOSE

To determine the association between Hankinson's percent-predicted FEF25-75 (FEF25-75%) levels with changes in healthcare utilization, respiratory symptom frequency, and biomarkers of distal airway inflammation.

METHODS

In participants enrolled in the Severe Asthma Research Program 1-2, we compared outcomes across FEF25-75% quartiles. Multivariable analyses were done to avoid confounding by demographic characteristics, FEV1, and the FEV1/FVC ratio. In a sensitivity analysis, we also compared outcomes across participants with FEF25-75% below the lower limit of normal (LLN) and FEV1/FVC above LLN.

RESULTS

Subjects in the lowest FEF25-75% quartile had greater rates of healthcare utilization and higher exhaled nitric oxide and sputum eosinophils. In multivariable analysis, being in the lowest FEF25-75% quartile remained significantly associated with nocturnal symptoms (OR 3.0 [95%CI 1.3-6.9]), persistent symptoms (OR 3.3 [95%CI 1-11], ICU admission for asthma (3.7 [1.3-10.8]) and blood eosinophil % (0.18 [0.07, 0.29]). In the sensitivity analysis, those with FEF25-75%

CONCLUSIONS

After controlling for demographic variables, FEV1 and FEV1/FVC, a reduced FEF25-75% is independently associated with previous ICU admission, persistent symptoms, nocturnal symptoms, blood eosinophilia and bronchial hyperreactivity. This suggests that in some asthmatics, a reduced FEF25-75% is an independent biomarker for more severe asthma.

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Key Words Collapse

MESH Headings

• Adult
• Asthma/complications
• Asthma/physiopathology
• Biomarkers/metabolism
• Bronchial Hyperreactivity/complications
• Bronchial Hyperreactivity/physiopathology
• Female
• Forced Expiratory Flow Rates
• Forced Expiratory Volume
• Humans
• Male
• Middle Aged
• Multivariate Analysis
• Odds Ratio
• Young Adult

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Grants

• R01 HL069174 NHLBI NIH HHS
• U10 HL109164 NHLBI NIH HHS
• U10 HL109172 NHLBI NIH HHS
• HL069174-06 NHLBI NIH HHS

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Increased Mutagen Sensitivity and DNA Damage in Pulmonary Arterial Hypertension

RATIONALE

Pulmonary arterial hypertension (PAH) is a serious lung condition characterized by vascular remodeling in the precapillary pulmonary arterioles. We and others have demonstrated chromosomal abnormalities and increased DNA damage in PAH lung vascular cells, but their timing and role in disease pathogenesis is unknown.

OBJECTIVES

We hypothesized that if DNA damage predates PAH, it might be an intrinsic cell property that is present outside the diseased lung.

METHODS

We measured DNA damage, mutagen sensitivity, and reactive oxygen species (ROS) in lung and blood cells from patients with Group 1 PAH, their relatives, and unrelated control subjects.

MEASUREMENTS AND MAIN RESULTS

Baseline DNA damage was significantly elevated in PAH, both in pulmonary artery endothelial cells (P < 0.05) and peripheral blood mononuclear cells (PBMC) (P < 0.001). Remarkably, PBMC from unaffected relatives showed similar increases, indicating this is not related to PAH treatments. ROS levels were also higher (P < 0.01). DNA damage correlated with ROS production and was suppressed by antioxidants (P < 0.001). PBMC from patients and relatives also showed markedly increased sensitivity to two chemotherapeutic drugs, bleomycin and etoposide (P < 0.001). Results were consistent across idiopathic, heritable, and associated PAH groups.

CONCLUSIONS

Levels of baseline and mutagen-induced DNA damage are intrinsically higher in PAH cells. Similar results in PBMC from unaffected relatives suggest this may be a genetically determined trait that predates disease onset and may act as a risk factor contributing to lung vascular remodeling following endothelial cell injury. Further studies are required to fully characterize mutagen sensitivity, which could have important implications for clinical management.

Protein disulfide isomerase-endoplasmic reticulum resident protein 57 regulates allergen-induced airways inflammation, fibrosis, and hyperresponsiveness

BACKGROUND

Evidence for association between asthma and the unfolded protein response is emerging. Endoplasmic reticulum resident protein 57 (ERp57) is an endoplasmic reticulum-localized redox chaperone involved in folding and secretion of glycoproteins. We have previously demonstrated that ERp57 is upregulated in allergen-challenged human and murine lung epithelial cells. However, the role of ERp57 in asthma pathophysiology is unknown.

OBJECTIVES

Here we sought to examine the contribution of airway epithelium-specific ERp57 in the pathogenesis of allergic asthma.

METHODS

We examined the expression of ERp57 in human asthmatic airway epithelium and used murine models of allergic asthma to evaluate the relevance of epithelium-specific ERp57.

RESULTS

Lung biopsy specimens from asthmatic and nonasthmatic patients revealed a predominant increase in ERp57 levels in epithelium of asthmatic patients. Deletion of ERp57 resulted in a significant decrease in inflammatory cell counts and airways resistance in a murine model of allergic asthma. Furthermore, we observed that disulfide bridges in eotaxin, epidermal growth factor, and periostin were also decreased in the lungs of house dust mite-challenged ERp57-deleted mice. Fibrotic markers, such as collagen and α smooth muscle actin, were also significantly decreased in the lungs of ERp57-deleted mice. Furthermore, adaptive immune responses were dispensable for house dust mite-induced endoplasmic reticulum stress and airways fibrosis.

CONCLUSIONS

Here we show that ERp57 levels are increased in the airway epithelium of asthmatic patients and in mice with allergic airways disease. The ERp57 level increase is associated with redox modification of proinflammatory, apoptotic, and fibrotic mediators and contributes to airways hyperresponsiveness. The strategies to inhibit ERp57 specifically within the airways epithelium might provide an opportunity to alleviate the allergic asthma phenotype.

Cost effectiveness of bronchial thermoplasty in patients with severe uncontrolled asthma

RATIONALE

Based on its clinical effectiveness, bronchial thermoplasty (BT) was approved by the Food and Drug Administration in 2010 for the treatment of severe persistent asthma in patients 18 years and older whose asthma is not well-controlled with inhaled corticosteroids and long-acting beta-agonist medicines.

OBJECTIVE

Assess the 10 year cost-effectiveness of BT for individuals with severe uncontrolled asthma.

METHODS

Using a Markov decision analytic model, the cost-effectiveness of BT was estimated. The patient population involved a hypothetical cohort of 41-year-old patients comparing BT to usual care over a 10-year time frame. The main outcome measure was cost in 2013 dollars per additional quality adjusted life year (QALY).

RESULTS

Treatment with BT resulted in 6.40 QALYs and $7512 in cost compared to 6.21 QALYs and $2054 for usual care. The incremental cost-effectiveness ratio for BT at 10 years was $29,821/QALY. At a willingness to pay per QALY of $50,000, BT continues to be cost effective unless the probability of severe asthma exacerbation drops below 0.63 exacerbation per year or the cost of BT rises above $10,384 total for all three bronchoscopic procedures needed to perform thermoplasty and to cover the entire bronchial tree (baseline = $6690).

CONCLUSIONS

BT is a cost-effective treatment for asthmatics at high risk of exacerbations. Continuing to follow asthmatics treated with BT beyond 5 years will help inform longer efficacy and support its cost-effectiveness.

Hyaluronan and Its Heavy Chain Modification in Asthma Severity and Experimental Asthma Exacerbation

Hyaluronan (HA) is a large (>1500 kDa) polysaccharide of the extracellular matrix that has been linked to severity and inflammation in asthma. During inflammation, HA becomes covalently modified with heavy chains (HC-HA) from inter-α-inhibitor (IαI), which functions to increase its avidity for leukocytes. Our murine model of allergic pulmonary inflammation suggested that HC-HA may contribute to inflammation, adversely effecting lower airway remodeling and asthma severity. Our objective was to characterize the levels of HA and HC-HA in asthmatic subjects and to correlate these levels with asthma severity. We determined the levels and distribution of HA and HC-HA (i) from asthmatic and control lung tissue, (ii) in bronchoalveolar lavage fluid obtained from non-severe and severe asthmatics and controls, and (iii) in serum and urine from atopic asthmatics after an experimental asthma exacerbation. HC-HA distribution was observed (i) in the thickened basement membrane of asthmatic lower airways, (ii) around smooth muscle cells of the asthmatic submucosa, and (iii) around reserve cells of the asthmatic epithelium. Patients with severe asthma had increased HA levels in bronchoalveolar lavage fluid that correlated with pulmonary function and nitric oxide levels, whereas HC-HA was only observed in a patient with non-severe asthma. After an experimental asthma exacerbation, serum HA was increased within 4 h after challenge and remained elevated through 5 days after challenge. Urine HA and HC-HA were not significantly different. These data implicate HA and HC-HA in the pathogenesis of asthma severity that may occur in part due to repetitive asthma exacerbations over the course of the disease.

Asthma Is More Severe in Older Adults

Background

Severe asthma occurs more often in older adult patients. We hypothesized that the greater risk for severe asthma in older individuals is due to aging, and is independent of asthma duration.

Methods

This is a cross-sectional study of prospectively collected data from adult participants (N=1130; 454 with severe asthma) enrolled from 2002 – 2011 in the Severe Asthma Research Program.

Results

The association between age and the probability of severe asthma, which was performed by applying a Locally Weighted Scatterplot Smoother, revealed an inflection point at age 45 for risk of severe asthma. The probability of severe asthma increased with each year of life until 45 years and thereafter increased at a much slower rate. Asthma duration also increased the probability of severe asthma but had less effect than aging. After adjustment for most comorbidities of aging and for asthma duration using logistic regression, asthmatics older than 45 maintained the greater probability of severe asthma [OR: 2.73 (95 CI: 1.96; 3.81)]. After 45, the age-related risk of severe asthma continued to increase in men, but not in women.

Conclusions

Overall, the impact of age and asthma duration on risk for asthma severity in men and women is greatest over times of 18-45 years of age; age has a greater effect than asthma duration on risk of severe asthma.

Platelets from Asthmatic Individuals Show Less Reliance on Glycolysis

Asthma, a chronic inflammatory airway disease, is typified by high levels of T_H2-cytokines and excessive generation of reactive nitrogen and oxygen species, which contribute to bronchial epithelial injury and airway remodeling. While immune function plays a major role in the pathogenesis of the disease, accumulating evidence suggests that altered cellular metabolism is a key determinant in the predisposition and disease progression of asthma. Further, several studies demonstrate altered mitochondrial function in asthmatic airways and suggest that these changes may be systemic. However, it is unknown whether systemic metabolic changes can be detected in circulating cells in asthmatic patients. Platelets are easily accessible blood cells that are known to propagate airway inflammation in asthma. Here we perform a bioenergetic screen of platelets from asthmatic and healthy individuals and demonstrate that asthmatic platelets show a decreased reliance on glycolytic processes and have increased tricarboxylic acid cycle activity. These data demonstrate a systemic alteration in asthma and are consistent with prior reports suggesting that oxidative phosphorylation is more efficient asthmatic individuals. The implications for this potential metabolic shift will be discussed in the context of increased oxidative stress and hypoxic adaptation of asthmatic patients. Further, these data suggest that platelets are potentially a good model for the monitoring of bioenergetic changes in asthma.

Impaired Global Right Ventricular Longitudinal Strain Predicts Long-Term Adverse Outcomes in Patients with Pulmonary Arterial Hypertension

Background

New 2-dimensional strain echocardiography enables quantification of right ventricular (RV) mechanics by assessing global longitudinal strain of RV (GLSRV) in patients with pulmonary arterial hypertension (PAH). However, the prognostic significance of impaired GLSRV is unclear in these patients.

Methods

Comprehensive echocardiography was performed in 51 consecutive PAH patients without atrial fibrillation (40 females, 48 ± 14 years old) with long-term follow-up. GLSRV was measured with off-line with velocity vector imaging (VVI, Siemens Medical System, Mountain View, CA, USA).

Results

GLSRV showed significant correlation with RV fractional area change (r = -0.606, p < 0.001), tricuspid annular plane systolic excursion (r = -0.579, p < 0.001), and RV Tei index (r = 0.590, p < 0.001). It showed significant correlations with pulmonary vascular resistance (r = 0.469, p = 0.001) and B-natriuretic peptide concentration (r = 0.351, p = 0.012). During a clinical followup time (45 ± 15 months), 20 patients experienced one or more adverse events (12 death, 2 lung transplantation, and 15 heart failure hospitalization). After multivariate analysis, age [hazard ratio (HR) = 2.343, p = 0.040] and GLSRV (HR = 2.122, p = 0.040) were associated with adverse clinical events. Age (HR = 3.200, p = 0.016) and GLSRV (HR = 2.090, p = 0.042) were also significant predictors of death. Impaired GLSRV (≥ -15.5%) was associated with lower event-free survival (HR = 4.906, p = 0.001) and increased mortality (HR = 8.842, p = 0.005).

Conclusion

GLSRV by VVI showed significant correlations with conventional echocardiographic parameters indicating RV systolic function. Lower GLSRV (≥ -15.5%) was significantly associated with presence of adverse clinical events and deaths in PAH patients.

Metabolomic Endotype of Asthma

Metabolomics, the quantification of small biochemicals in plasma and tissues, can provide insight into complex biochemical processes and enable the identification of biomarkers that may serve as therapeutic targets. We hypothesized that the plasma metabolome of asthma would reveal metabolic consequences of the specific immune and inflammatory responses unique to endotypes of asthma. The plasma metabolomic profiles of 20 asthmatic subjects and 10 healthy controls were examined using an untargeted global and focused metabolomic analysis. Individuals were classified based on clinical definitions of asthma severity or by levels of fraction of exhaled NO (FENO), a biomarker of airway inflammation. Of the 293 biochemicals identified in the plasma, 25 were significantly different among asthma and healthy controls (p < 0.05). Plasma levels of taurine, lathosterol, bile acids (taurocholate and glycodeoxycholate), nicotinamide, and adenosine-5-phosphate were significantly higher in asthmatics compared with healthy controls. Severe asthmatics had biochemical changes related to steroid and amino acid/protein metabolism. Asthmatics with high FENO, compared with those with low FENO, had higher levels of plasma branched-chain amino acids and bile acids. Asthmatics have a unique plasma metabolome that distinguishes them from healthy controls and points to activation of inflammatory and immune pathways. The severe asthmatic and high FENO asthmatic have unique endotypes that suggest changes in NO-associated taurine transport and bile acid metabolism.

Arginine metabolic endotypes in pulmonary arterial hypertension

Decreased synthesis of nitric oxide (NO) by NO synthases (NOS) is believed to play an important role in the pathogenesis of pulmonary arterial hypertension (PAH). Multiple factors may contribute to decreased NO bioavailability, including increased activity of arginase, the enzyme that converts arginine to ornithine and urea, which may compete with NOS for arginine; inadequate de novo arginine production from citrulline; and increased concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NOS. We hypothesized that PAH patients with the lowest arginine availability secondary to increased arginase activity and/or inadequate de novo arginine synthesis might have a slower rate of NO synthesis and greater pulmonary vascular resistance. Nine patients with group 1 PAH and 10 healthy controls were given primed, constant intravenous infusions of (15)N2-arginine, (13)C,(2)H4-citrulline, (15)N2-ornithine, and (13)C-urea in the postabsorptive state. The results showed that, compared with healthy controls, PAH patients had a tendency toward increased arginine clearance and ornithine flux but no difference in arginine and citrulline flux, de novo arginine synthesis, or NO synthesis. Arginine-to-ADMA ratio was increased in PAH patients. Two endotypes of patients with low and high arginase activity were identified; compared with the low-arginase group, the patients with high arginase had increased arginine flux, slower NO synthesis, and lower plasma concentrations of ADMA. These results demonstrate that increased breakdown of arginine by arginase occurs in PAH and affects NO synthesis. Furthermore, there is no compensatory increase in de novo arginine synthesis to overcome this increased utilization of arginine by arginase.

Relationship between Right Ventricular Longitudinal Strain, Invasive Hemodynamics, and Functional Assessment in Pulmonary Arterial Hypertension

BACKGROUND AND OBJECTIVES

Right ventricular longitudinal strain (RVLS) is a new parameter of RV function. We evaluated the relationship of RVLS by speckle-tracking echocardiography with functional and invasive parameters in pulmonary arterial hypertension (PAH) patients.

SUBJECTS AND METHODS

Thirty four patients with World Health Organization group 1 PAH (29 females, mean age 45±13 years old). RVLS were analyzed with velocity vector imaging.

RESULTS

Patients with advanced symptoms {New York Heart Association (NYHA) functional class III/IV} had impaired RVLS in global RV (RVLSglobal, -17±5 vs. -12±3%, p<0.01) and RV free wall (RVLSFW, -19±5 vs. -14±4%, p<0.01 to NYHA class I/II). Baseline RVLSglobal and RVLSFW showed significant correlation with 6-minute walking distance (r=-0.54 and r=-0.57, p<0.01 respectively) and logarithmic transformation of brain natriuretic peptide concentration (r=0.65 and r=0.65, p<0.01, respectively). These revealed significant correlations with cardiac index (r=-0.50 and r=-0.47, p<0.01, respectively) and pulmonary vascular resistance (PVR, r=0.45 and r=0.45, p=0.01, respectively). During a median follow-up of 33 months, 25 patients (74%) had follow-up examinations. Mean pulmonary arterial pressure (mPAP, 54±13 to 46±16 mmHg, p=0.03) and PVR (11±5 to 6±2 wood units, p<0.01) were significantly decreased with pulmonary vasodilator treatment. RVLSglobal (-12±5 to -16±5%, p<0.01) and RVLSFW (-14±5 to -18±5%, p<0.01) were significantly improved. The decrease of mPAP was significantly correlated with improvement of RVLSglobal (r=0.45, p<0.01) and RVLSFW (r=0.43, p<0.01). The PVR change demonstrated significant correlation with improvement of RVLSglobal (r=0.40, p<0.01).

CONCLUSION

RVLS correlates with functional and invasive hemodynamic parameters in PAH patients. Decrease of mPAP and PVR as a result of treatment was associated with improvement of RVLS.

Endothelial uncoupling protein 2 regulates mitophagy and pulmonary hypertension during intermittent hypoxia

OBJECTIVES

Pulmonary hypertension (PH) is a process of lung vascular remodeling, which can lead to right heart dysfunction and significant morbidity. The underlying mechanisms leading to PH are not well understood, and therapies are limited. Using intermittent hypoxia (IH) as a model of oxidant-induced PH, we identified an important role for endothelial cell mitophagy via mitochondrial uncoupling protein 2 (Ucp2) in the development of IH-induced PH.

APPROACH AND RESULTS

Ucp2 endothelial knockout (VE-KO) and Ucp2 Flox (Flox) mice were subjected to 5 weeks of IH. Ucp2 VE-KO mice exhibited higher right ventricular systolic pressure and worse right heart hypertrophy, as measured by increased right ventricle weight/left ventricle plus septal weight (RV/LV+S) ratio, at baseline and after IH. These changes were accompanied by increased mitophagy. Primary mouse lung endothelial cells transfected with Ucp2 siRNA and subjected to cyclic exposures to CoCl2 (chemical hypoxia) showed increased mitophagy, as measured by PTEN-induced putative kinase 1 and LC3BII/I ratios, decreased mitochondrial biogenesis, and increased apoptosis. Similar results were obtained in primary lung endothelial cells isolated from VE-KO mice. Moreover, silencing PTEN-induced putative kinase 1 in the endothelium of Ucp2 knockout mice, using endothelial-targeted lentiviral silencing RNA in vivo, prevented IH-induced PH. Human pulmonary artery endothelial cells from people with PH demonstrated changes similar to Ucp2-silenced mouse lung endothelial cells.

CONCLUSIONS

The loss of endothelial Ucp2 leads to excessive PTEN-induced putative kinase 1-induced mitophagy, inadequate mitochondrial biosynthesis, and increased apoptosis in endothelium. An endothelial Ucp2-PTEN-induced putative kinase 1 axis may be effective therapeutic targets in PH.

Gene expression in relation to exhaled nitric oxide identifies novel asthma phenotypes with unique biomolecular pathways

RATIONALE

Although asthma is recognized as a heterogeneous disease associated with clinical phenotypes, the molecular basis of these phenotypes remains poorly understood. Although genomic studies have successfully broadened our understanding in diseases such as cancer, they have not been widely used in asthma studies.

OBJECTIVES

To link gene expression patterns to clinical asthma phenotypes.

METHODS

We used a microarray platform to analyze bronchial airway epithelial cell gene expression in relation to the asthma biomarker fractional exhaled nitric oxide (FeNO) in 155 subjects with asthma and healthy control subjects from the Severe Asthma Research Program (SARP).

MEASUREMENTS AND MAIN RESULTS

We first identified a diverse set of 549 genes whose expression correlated with FeNO. We used k-means to cluster the patient samples according to the expression of these genes, identifying five asthma clusters/phenotypes with distinct clinical, physiological, cellular, and gene transcription characteristics-termed "subject clusters" (SCs). To then investigate differences in gene expression between SCs, a total of 1,384 genes were identified that highly differentiated the SCs at an unadjusted P value < 10(-6). Hierarchical clustering of these 1,384 genes identified nine gene clusters or "biclusters," whose coexpression suggested biological characteristics unique to each SC. Although genes related to type 2 inflammation were present, novel pathways, including those related to neuronal function, WNT pathways, and actin cytoskeleton, were noted.

CONCLUSIONS

These findings show that bronchial epithelial cell gene expression, as related to the asthma biomarker FeNO, can identify distinct asthma phenotypes, while also suggesting the presence of underlying novel gene pathways relevant to these phenotypes.

Arginase 2 deficiency results in spontaneous steatohepatitis: a novel link between innate immune activation and hepatic de novo lipogenesis

BACKGROUND & AIMS

Innate immune activation has been postulated as a central mechanism for disease progression from hepatic steatosis to steatohepatitis in obesity-related fatty liver disease. Arginase 2 competes with inducible nitric oxide synthase (iNOS) for its substrate and the balance between these two enzymes plays a crucial role in regulating immune responses and macrophage activation. Our aim was to test the hypothesis that arginase 2 deficiency in mice favours progression from isolated hepatic steatosis, induced by high fat feeding, to steatohepatitis.

METHODS

Arginase 2-knockout (Arg2(-/-)) mice were studied for changes in liver histology and metabolic phenotype at baseline and after a short term course (7 week) feeding with a high fat (HFAT) diet. In additional experiments, Arg2(-/-) mice received tail vein injections of liposome-encapsulated clodronate (CLOD) over a three-week period to selectively deplete liver macrophages.

RESULTS

Unexpectedly, Arg2(-/-) mice showed profound changes in their livers at baseline, characterized by significant steatosis as demonstrated with histological and biochemical analysis. These changes were independent of systemic metabolic parameters and associated with marked mRNA level increases of genes involved in hepatic de novo lipogenesis. Liver injury and inflammation were present with elevated serum ALT, marked infiltration of F4/80 positive cells, and increased mRNA levels of inflammatory genes. HFAT feeding exacerbated these changes. Macrophage depletion after CLOD injection significantly attenuated lipid deposition and normalized lipogenic mRNA profile of livers from Arg2(-/-) mice.

CONCLUSIONS

This study identifies arginase 2 as a novel link between innate immune responses, hepatic lipid deposition, and liver injury.

Biomarker-based asthma phenotypes of corticosteroid response

BACKGROUND

Asthma is a heterogeneous disease with different phenotypes. Inhaled corticosteroid (ICS) therapy is a mainstay of treatment for asthma, but the clinical response to ICSs is variable.

OBJECTIVE

We hypothesized that a panel of inflammatory biomarkers (ie, fraction of exhaled nitric oxide [Feno], sputum eosinophil count, and urinary bromotyrosine [BrTyr] level) might predict steroid responsiveness.

METHODS

The original study from which this analysis originates comprised 2 phases: a steroid-naive phase 1 and a 28-day trial of ICSs (phase 2) during which Feno values, sputum eosinophil counts, and urinary BrTyr levels were measured. The response to ICSs was based on clinical improvements, including a 12% or greater increase in FEV1, a 0.5-point or greater decrease in Asthma Control Questionnaire score, and 2 doubling dose or greater increase in provocative concentration of adenosine 5'-monophosphate causing a 20% decrease in FEV1 (PC20AMP). Healthy control subjects were also evaluated in this study for comparison of biomarkers with those seen in asthmatic patients.

RESULTS

Asthmatic patients had higher than normal Feno values, sputum eosinophil counts, and urinary BrTyr levels during the steroid-naive phase and after ICS therapy. After 28-day trial of ICSs, Feno values decreased in 82% of asthmatic patients, sputum eosinophil counts decreased in 60%, and urinary BrTyr levels decreased in 58%. Each of the biomarkers at the steroid-naive phase had utility for predicting steroid responsiveness, but the combination of high Feno values and high urinary BrTyr levels had the best power (13.3-fold, P < .01) to predict a favorable response to ICS therapy. However, the magnitude of the decrease in biomarker levels was unrelated to the magnitude of clinical response to ICS therapy.

CONCLUSION

A noninvasive panel of biomarkers in steroid-naive asthmatic patients predicts clinical responsiveness to ICS therapy.

Restoration of impaired endothelial myocyte enhancer factor 2 function rescues pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary arterioles, characterized by increased pulmonary arterial pressure and right ventricular failure. The cause of PAH is complex, but aberrant proliferation of the pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells is thought to play an important role in its pathogenesis. Understanding the mechanisms of transcriptional gene regulation involved in pulmonary vascular homeostasis can provide key insights into potential therapeutic strategies.

METHODS AND RESULTS

We demonstrate that the activity of the transcription factor myocyte enhancer factor 2 (MEF2) is significantly impaired in the PAECs derived from subjects with PAH. We identified MEF2 as the key cis-acting factor that regulates expression of a number of transcriptional targets involved in pulmonary vascular homeostasis, including microRNAs 424 and 503, connexins 37, and 40, and Krűppel Like Factors 2 and 4, which were found to be significantly decreased in PAH PAECs. The impaired MEF2 activity in PAH PAECs was mediated by excess nuclear accumulation of 2 class IIa histone deacetylases (HDACs) that inhibit its function, namely HDAC4 and HDAC5. Selective, pharmacological inhibition of class IIa HDACs led to restoration of MEF2 activity in PAECs, as demonstrated by increased expression of its transcriptional targets, decreased cell migration and proliferation, and rescue of experimental pulmonary hypertension models.

CONCLUSIONS

Our results demonstrate that strategies to augment MEF2 activity hold potential therapeutic value in PAH. Moreover, we identify selective HDAC IIa inhibition as a viable alternative approach to avoid the potential adverse effects of broad spectrum HDAC inhibition in PAH.

[Relevant issues in the pathology and pathobiology of pulmonary hypertension]

Knowledge of the pathobiology of pulmonary hypertension (PH) continues to accelerate. However, fundamental gaps remain in our understanding of the underlying pathological changes in pulmonary arteries and veins in the different forms of this syndrome. Although PH primarily affects the arteries, venous disease is increasingly recognized as an important entity. Moreover, prognosis in PH is determined largely by the status of the right ventricle, rather than the levels of pulmonary artery pressures. It is increasingly clear that although vasospasm plays a role, PH is an obstructive lung panvasculopathy. Disordered metabolism and mitochondrial structure, inflammation, and dysregulation of growth factors lead to a proliferative, apoptosis-resistant state. These abnormalities may be acquired, genetically mediated as a result of mutations in bone morphogenetic protein receptor-2 or activin-like kinase-1, or epigenetically inherited (as a result of epigenetic silencing of genes such as superoxide dismutase-2). There is a pressing need to better understand how the pathobiology leads to severe disease in some patients versus mild PH in others. Recent recognition of a potential role of acquired abnormalities of mitochondrial metabolism in the right ventricular myocytes and pulmonary vascular cells suggests new therapeutic approaches, diagnostic modalities, and biomarkers. Finally, dissection of the role of pulmonary inflammation in the initiation and promotion of PH has revealed a complex yet fascinating interplay with pulmonary vascular remodeling, promising to lead to novel therapeutics and diagnostics. Emerging concepts are also relevant to the pathobiology of PH, including a role for bone marrow and circulating progenitor cells and microribonucleic acids. Continued interest in the interface of the genetic basis of PH and cellular and molecular pathogenetic links should further expand our understanding of the disease. (J Am Coll Cardiol 2013;62:D4-12) a 2013 by the American College of Cardiology Foundation.

Impaired right ventricular-pulmonary vascular function in myeloproliferative neoplasms

BACKGROUND

Increased bone marrow hemangioblast numbers, alterations in erythroid/myeloid lineages, increased reticulin, and greater circulating bone marrow progenitor cells are present in patients with pulmonary arterial hypertension (PAH). The data suggest that myeloid progenitors contribute to the pathogenesis of PAH, but there are little data on the prevalence of pulmonary vascular disease among the different forms of myeloid diseases. We hypothesized that there would be a higher prevalence of pulmonary vascular disease in myeloproliferative neoplasms that have high circulating progenitor cells, such as myelofibrosis and chronic myelogenous leukemia (CML), compared with those with low circulating progenitors, such as in aplastic anemia.

METHODS

Patients with myelofibrosis, CML, and aplastic anemia who underwent echocardiographic evaluation of cardiac function in preparation for bone marrow transplantation at the Cleveland Clinic between 1997 and 2012 were identified and their electronic medical records were queried for demographic data, blood cell counts, and pulmonary function tests. All echocardiograms were uniformly analyzed in a blinded fashion by an advanced sonographer and cardiologist for measures of right and left ventricular function and estimation of pulmonary vascular disease.

RESULTS

Gender and race distribution among disease groups was similar. Patients with myelofibrosis (n = 19) and aplastic anemia (n = 30) had increased right ventricle (RV) wall thickness compared with CML (n = 82) patients (aplastic anemia, 0.7 ± 0.1; CML, 0.5 ± 0.1; and myelofibrosis, 0.7 ± 0.1; p = 0.02). Patients with myelofibrosis had higher levels of estimated RV systolic pressure compared with the other groups (aplastic anemia, 29.9 ± 1.5; CML, 26.2 ± 1.1; and myelofibrosis, 36.7 ± 3.7 mm Hg; p < 0.01).

CONCLUSIONS

The findings suggest an important role for myeloid progenitors in the maintenance of pulmonary-vascular health, in which abnormal myeloproliferative progenitors are associated with RV pathology.

An airway epithelial iNOS-DUOX2-thyroid peroxidase metabolome drives Th1/Th2 nitrative stress in human severe asthma

Severe refractory asthma is associated with enhanced nitrative stress. To determine the mechanisms for high nitrative stress in human severe asthma (SA), 3-nitrotyrosine (3NT) was compared with Th1 and Th2 cytokine expression. In SA, high 3NT levels were associated with high interferon (IFN)-γ and low interleukin (IL)-13 expression, both of which have been reported to increase inducible nitric oxide synthase (iNOS) in human airway epithelial cells (HAECs). We found that IL-13 and IFN-γ synergistically enhanced iNOS, nitrite, and 3NT, corresponding with increased H(2)O(2). Catalase inhibited whereas superoxide dismutase enhanced 3NT formation, supporting a critical role for H(2)O(2), but not peroxynitrite, in 3NT generation. Dual oxidase-2 (DUOX2), central to H(2)O(2) formation, was also synergistically induced by IL-13 and IFN-γ. The catalysis of nitrite and H(2)O(2) to nitrogen dioxide radical (NO(2)(•)) requires an endogenous peroxidase in this epithelial cell system. Thyroid peroxidase (TPO) was identified by microarray analysis ex vivo as a gene distinguishing HAEC of SA from controls. IFN-γ induced TPO in HAEC and small interfering RNA knockdown decreased nitrated tyrosine residues. Ex vivo, DUOX2, TPO, and iNOS were higher in SA and correlated with 3NT. Thus, a novel iNOS-DUOX2-TPO-NO(2)(•) metabolome drives nitrative stress in HAEC and likely in SA.

Coenzyme Q supplementation in pulmonary arterial hypertension

Mitochondrial dysfunction is a fundamental abnormality in the vascular endothelium and smooth muscle of patients with pulmonary arterial hypertension (PAH). Because coenzyme Q (CoQ) is essential for mitochondrial function and efficient oxygen utilization as the electron carrier in the inner mitochondrial membrane, we hypothesized that CoQ would improve mitochondrial function and benefit PAH patients. To test this, oxidized and reduced levels of CoQ, cardiac function by echocardiogram, mitochondrial functions of heme synthesis and cellular metabolism were evaluated in PAH patients (N=8) in comparison to healthy controls (N=7), at baseline and after 12 weeks oral CoQ supplementation. CoQ levels were similar among PAH and control individuals, and increased in all subjects with CoQ supplementation. PAH patients had higher CoQ levels than controls with supplementation, and a tendency to a higher reduced-to-oxidized CoQ ratio. Cardiac parameters improved with CoQ supplementation, although 6-minute walk distances and BNP levels did not significantly change. Consistent with improved mitochondrial synthetic function, hemoglobin increased and red cell distribution width (RDW) decreased in PAH patients with CoQ, while hemoglobin declined slightly and RDW did not change in healthy controls. In contrast, metabolic and redox parameters, including lactate, pyruvate and reduced or oxidized gluthathione, did not change in PAH patients with CoQ. In summary, CoQ improved hemoglobin and red cell maturation in PAH, but longer studies and/or higher doses with a randomized placebo-controlled controlled design are necessary to evaluate the clinical benefit of this simple nutritional supplement.

Targeting mTORC1-mediated metabolic addiction overcomes fludarabine resistance in malignant B cells

MTOR complex-1(mTORC1) activation occurs frequently in cancers, yet clinical efficacy of rapalogs is limited because of the associated activation of upstream survival pathways. An alternative approach is to inhibit downstream of mTORC1; therefore, acquired resistance to fludarabine (Flu), a purine analogue and antimetabolite chemotherapy, active agent for chronic lymphocytic leukemia (CLL) was investigated. Elevated phospho-p70S6K, also known as RPS6KB1 (ribosomal protein S6 kinase, 70kDa, polypeptide 1) (T389), an mTORC1 activation marker, predicted Flu resistance in a panel of B-cell lines, isogenic Flu-resistant (FluR) derivatives, and primary human CLL cells. Consistent with the anabolic role of mTORC1, FluR cells had higher rates of glycolysis and oxidative phosphorylation than Flu-sensitive (FluS) cells. Rapalogs (everolimus and rapamycin) induced moderate cell death in FluR and primary CLL cells, and everolimus significantly inhibited glycolysis and oxidative phosphorylation in FluR cells. Strikingly, the higher oxidative phosphorylation in FluR cells was not coupled to higher ATP synthesis. Instead, it contributed primarily to an essential, dihydroorotate dehydrogenase catalyzed, step in de novo pyrimidine biosynthesis. mTORC1 promotes pyrimidine biosynthesis by p70S6 kinase-mediated phosphorylation of CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase; Ser1859) and favors S-phase cell-cycle progression. We found increased phospho-CAD (S1859) and higher S-phase population in FluR cells. Pharmacological inhibition of de novo pyrimidine biosynthesis using N-phosphonacetyl-l-aspartate and leflunomide, RNAi-mediated knockdown of p70S6K, and inhibition of mitochondrial respiration were selectively cytotoxic to FluR, but not FluS, cells. These results reveal a novel link between mTORC1-mediated metabolic reprogramming and Flu resistance identifying mitochondrial respiration and de novo pyrimidine biosynthesis as potential therapeutic targets.

IMPLICATIONS

This study provides the first evidence for mTORC1/p70S6K-dependent regulation of pyrimidine biosynthesis in a relevant disease setting.

Bone marrow-derived vascular modulatory cells in pulmonary arterial hypertension

Hematopoiesis and vascular homeostasis are closely linked to each other via subsets of circulating bone marrow-derived cells with potent activity to repair endothelial injury and promote angiogenesis. As a consequence, abnormalities in hematopoiesis will eventually affect vascular health. Pulmonary arterial hypertension (PAH) is a vascular disease characterized by severe remodeling of the pulmonary artery wall. Over the past decade, circulating hematopoietic cells have been assigned an increasing role in the remodeling, such that these cells have been used in new therapeutic strategies. More recently, research has been extended to the bone marrow where these cells originate to identify abnormalities in hematopoiesis that may underlie PAH. Here, we review the current literature and identify gaps in knowledge of the myeloid effects on PAH.

An official American Thoracic Society Statement: pulmonary hypertension phenotypes

BACKGROUND

Current classification of pulmonary hypertension (PH) is based on a relatively simple combination of patient characteristics and hemodynamics. This limits customization of treatment, and lacks the clarity of a more granular identification based on individual patient phenotypes. Rapid advances in mechanistic understanding of the disease, improved imaging methods, and innovative biomarkers now provide an opportunity to define PH phenotypes on the basis of biomarkers, advanced imaging, and pathobiology. This document organizes our current understanding of PH phenotypes and identifies gaps in our knowledge.

METHODS

A multidisciplinary committee with expertise in clinical care (pulmonary, cardiology, pediatrics, and pathology), clinical research, and/or basic science in the areas of PH identified important questions and reviewed and synthesized the literature.

RESULTS

This document describes selected PH phenotypes and serves as an initial platform to define additional relevant phenotypes as new knowledge is generated. The biggest gaps in our knowledge stem from the fact that our present understanding of PH phenotypes has not come from any particularly organized effort to identify such phenotypes, but rather from reinterpreting studies and reports that were designed and performed for other purposes.

CONCLUSIONS

Accurate phenotyping of PH can be used in research studies to increase the homogeneity of study cohorts. Once the ability of the phenotypes to predict outcomes has been validated, phenotyping may also be useful for determining prognosis and guiding treatment. This important next step in PH patient care can optimally be addressed through a consortium of study sites with well-defined goals, tasks, and structure. Planning and support for this could include the National Institutes of Health and the U.S. Food and Drug Administration, with industry and foundation partnerships.

Relevant issues in the pathology and pathobiology of pulmonary hypertension

Knowledge of the pathobiology of pulmonary hypertension (PH) continues to accelerate. However, fundamental gaps remain in our understanding of the underlying pathological changes in pulmonary arteries and veins in the different forms of this syndrome. Although PH primarily affects the arteries, venous disease is increasingly recognized as an important entity. Moreover, prognosis in PH is determined largely by the status of the right ventricle, rather than the levels of pulmonary artery pressures. It is increasingly clear that although vasospasm plays a role, PH is an obstructive lung panvasculopathy. Disordered metabolism and mitochondrial structure, inflammation, and dysregulation of growth factors lead to a proliferative, apoptosis-resistant state. These abnormalities may be acquired, genetically mediated as a result of mutations in bone morphogenetic protein receptor-2 or activin-like kinase-1, or epigenetically inherited (as a result of epigenetic silencing of genes such as superoxide dismutase-2). There is a pressing need to better understand how the pathobiology leads to severe disease in some patients versus mild PH in others. Recent recognition of a potential role of acquired abnormalities of mitochondrial metabolism in the right ventricular myocytes and pulmonary vascular cells suggests new therapeutic approaches, diagnostic modalities, and biomarkers. Finally, dissection of the role of pulmonary inflammation in the initiation and promotion of PH has revealed a complex yet fascinating interplay with pulmonary vascular remodeling, promising to lead to novel therapeutics and diagnostics. Emerging concepts are also relevant to the pathobiology of PH, including a role for bone marrow and circulating progenitor cells and microribonucleic acids. Continued interest in the interface of the genetic basis of PH and cellular and molecular pathogenetic links should further expand our understanding of the disease.

Effect of rare variants in ADRB2 on risk of severe exacerbations and symptom control during longacting β agonist treatment in a multiethnic asthma population: a genetic study

BACKGROUND

Severe adverse life-threatening events associated with longacting β agonist (LABA) use have caused the US Food and Drug Administration (FDA) to review the safety of these drugs, resulting in a boxed warning and a mandatory safety study in 46 800 patients with asthma. Identification of an at-risk, susceptible subpopulation on the basis of predictive biomarkers is crucial for understanding LABA safety. The β2-adrenergic receptor gene (ADRB2) contains a common, non-synonymous single nucleotide polymorphism, Gly16Arg, that is unlikely to account for the rare, life-threatening events seen with LABA use. We hypothesise that rare ADRB2 variants modulate therapeutic responses to LABA therapy and contribute to rare, severe adverse events.

METHODS

In this genetic study, ADRB2 was sequenced in 197 African American, 191 non-Hispanic white, and 73 Puerto Rican patients. Sequencing identified six rare variants, which were genotyped in 1165 patients with asthma. The primary hypothesis was that severe asthma exacerbations requiring hospital admission were associated with rare ADRB2 variants in patients receiving LABA therapy. This outcome was assessed overall and by ethnic group. Replication was done in 659 non-Hispanic white patients with asthma.

FINDINGS

Patients receiving LABA with a rare ADRB2 variant had increased asthma-related hospital admissions (15 [44%] of 34 patients with rare variant vs 121 [22%] of 553 patients with common ADRB2 alleles admitted to hospital in past 12 months; meta-analysis for all ethnic groups, p=0·0003). Specifically, increases in hospital admission rates were recorded in LABA-treated non-Hispanic white patients with the rare Ile 164 allele compared with non-Hispanic white patients with the common allele (odds ratio [OR] 4·48, 95% CI 1·40-13·96, p=0·01) and African American patients with a 25 bp promoter polynucleotide insertion, -376ins, compared with African American patients with the common allele (OR 13·43, 95% CI 2·02-265·42, p=0·006). The subset of non-Hispanic white and African American patients receiving LABAs with these rare variants had increased exacerbations requiring urgent outpatient health-care visits (non-Hispanic white patients with or without the rare Ile 164 allele, 2·6 [SD 3·5] vs 1·1 [2·1] visits, p<0·0001; and African American patients with or without the rare insertion, 3·7 [4·6] vs 2·4 [3·4] visits, p=0·01), and more frequently were treated with chronic systemic corticosteroids (OR 4·25, 95% CI 1·38-14·41, p=0·01, and 12·83, 1·96-251·93, p=0·006). Non-Hispanic white patients from the primary and replication cohorts with the rare Ile 164 allele were more than twice as likely as Thr 164 homozygotes to have uncontrolled, persistent symptoms during LABA treatment (p=0·008-0·04).

INTERPRETATION

The rare ADRB2 variants Ile164 and -376ins are associated with adverse events during LABA therapy and should be evaluated in large clinical trials including the current FDA-mandated safety study.

FUNDING

US National Institutes of Health.

A novel method for pulmonary research: assessment of bioenergetic function at the air-liquid interface

Air–liquid interface cell culture is an organotypic model for study of differentiated functional airway epithelium in vitro. Dysregulation of cellular energy metabolism and mitochondrial function have been suggested to contribute to airway diseases. However, there is currently no established method to determine oxygen consumption and glycolysis in airway epithelium in air–liquid interface. In order to study metabolism in differentiated airway epithelial cells, we engineered an insert for the Seahorse XF24 Analyzer that enabled the measure of respiration by oxygen consumption rate (OCR) and glycolysis by extracellular acidification rate (ECAR). Oxidative metabolism and glycolysis in airway epithelial cells cultured on the inserts were successfully measured. The inserts did not affect the measures of OCR or ECAR. Cells under media with apical and basolateral feeding had less oxidative metabolism as compared to cells on the inserts at air-interface with basolateral feeding. The design of inserts that can be used in the measure of bioenergetics in small numbers of cells in an organotypic state may be useful for evaluation of new drugs and metabolic mechanisms that underlie airway diseases.

•

Endothelial cells generate hydrogen peroxide through several enzymatic systems and the mitochondrial electron transport chain

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Redox-sensitive thiols within specific families of proteins such as kinases are key targets for hydrogen peroxide in endothelial cells

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Hydrogen peroxide regulates fundamental processes in endothelial cells including cell growth, proliferation, angiogenesis and vascular tone

Endothelial cell energy metabolism, proliferation, and apoptosis in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by impaired regulation of pulmonary hemodynamics and excessive growth and dysfunction of the endothelial cells that line the arteries in PAH lungs. Establishment of methods for culture of pulmonary artery endothelial cells from PAH lungs has provided the groundwork for mechanistic translational studies that confirm and extend findings from model systems and spontaneous pulmonary hypertension in animals. Endothelial cell hyperproliferation, survival, and alterations of biochemical-metabolic pathways are the unifying endothelial pathobiology of the disease. The hyperproliferative and apoptosis-resistant phenotype of PAH endothelial cells is dependent upon the activation of signal transducer and activator of transcription (STAT) 3, a fundamental regulator of cell survival and angiogenesis. Animal models of PAH, patients with PAH, and human PAH endothelial cells produce low nitric oxide (NO). In association with the low level of NO, endothelial cells have reduced mitochondrial numbers and cellular respiration, which is associated with more than a threefold increase in glycolysis for energy production. The shift to glycolysis is related to low levels of NO and likely to the pathologic expression of the prosurvival and proangiogenic signal transducer, hypoxia-inducible factor (HIF)-1, and the reduced mitochondrial antioxidant manganese superoxide dismutase (MnSOD). In this article, we review the phenotypic changes of the endothelium in PAH and the biochemical mechanisms accounting for the proliferative, glycolytic, and strongly proangiogenic phenotype of these dysfunctional cells, which consequently foster the panvascular progressive pulmonary remodeling in PAH.

Bronchial thermoplasty: Long-term safety and effectiveness in patients with severe persistent asthma

BACKGROUND

Bronchial thermoplasty (BT) has previously been shown to improve asthma control out to 2 years in patients with severe persistent asthma.

OBJECTIVE

We sought to assess the effectiveness and safety of BT in asthmatic patients 5 years after therapy.

METHODS

BT-treated subjects from the Asthma Intervention Research 2 trial (ClinicalTrials.govNCT01350414) were evaluated annually for 5 years to assess the long-term safety of BT and the durability of its treatment effect. Outcomes assessed after BT included severe exacerbations, adverse events, health care use, spirometric data, and high-resolution computed tomographic scans.

RESULTS

One hundred sixty-two (85.3%) of 190 BT-treated subjects from the Asthma Intervention Research 2 trial completed 5 years of follow-up. The proportion of subjects experiencing severe exacerbations and emergency department (ED) visits and the rates of events in each of years 1 to 5 remained low and were less than those observed in the 12 months before BT treatment (average 5-year reduction in proportions: 44% for exacerbations and 78% for ED visits). Respiratory adverse events and respiratory-related hospitalizations remained unchanged in years 2 through 5 compared with the first year after BT. Prebronchodilator FEV₁ values remained stable between years 1 and 5 after BT, despite a 18% reduction in average daily inhaled corticosteroid dose. High-resolution computed tomographic scans from baseline to 5 years after BT showed no structural abnormalities that could be attributed to BT.

CONCLUSIONS

These data demonstrate the 5-year durability of the benefits of BT with regard to both asthma control (based on maintained reduction in severe exacerbations and ED visits for respiratory symptoms) and safety. BT has become an important addition to our treatment armamentarium and should be considered for patients with severe persistent asthma who remain symptomatic despite taking inhaled corticosteroids and long-acting β₂-agonists.

Novel therapeutic approaches to preserve the right ventricle

The right ventricle (RV) is increasingly recognized for its role in heart disease. In fact, RV function is a strong predictor of outcome in patients with cardiovascular disease. Although the focus in heart failure has been on the left ventricle (LV), recently the spotlight has been shifting to include the RV. The RV and LV have different embryological origins and respond differently to stressors and to therapies. Newer therapies targeting the RV have been investigated in an attempt to improve right-ventricular adaptation to cardiovascular diseases. In this review, we summarize the differences between the RV and LV and focus on novel therapies that target the RV.

Characteristics of perimenstrual asthma and its relation to asthma severity and control: data from the Severe Asthma Research Program

BACKGROUND

Although perimenstrual asthma (PMA) has been associated with severe and difficult-to-control asthma, it remains poorly characterized and understood. The objectives of this study were to identify clinical, demographic, and inflammatory factors associated with PMA and to assess the association of PMA with asthma severity and control.

METHODS

Women with asthma recruited to the National Heart, Lung, and Blood Institute Severe Asthma Research Program who reported PMA symptoms on a screening questionnaire were analyzed in relation to basic demographics, clinical questionnaire data, immunoinflammatory markers, and physiologic parameters. Univariate comparisons between PMA and non-PMA groups were performed. A severity-adjusted model predicting PMA was created. Additional models addressed the role of PMA in asthma control.

RESULTS

Self-identified PMA was reported in 17% of the subjects (n = 92) and associated with higher BMI, lower FVC % predicted, and higher gastroesophageal reflux disease rates. Fifty-two percent of the PMA group met criteria for severe asthma compared with 30% of the non-PMA group. In multivariable analyses controlling for severity, aspirin sensitivity and lower FVC % predicted were associated with the presence of PMA. Furthermore, after controlling for severity and confounders, PMA remained associated with more asthma symptoms and urgent health-care utilization.

CONCLUSIONS

PMA is common in women with severe asthma and associated with poorly controlled disease. Aspirin sensitivity and lower FVC % predicted are associated with PMA after adjusting for multiple factors, suggesting that alterations in prostaglandins may contribute to this phenotype.

HuR is required for IL-17-induced Act1-mediated CXCL1 and CXCL5 mRNA stabilization

IL-17, a major inflammatory cytokine plays a critical role in the pathogenesis of many autoimmune inflammatory diseases. In this study, we report a new function of RNA-binding protein HuR in IL-17-induced Act1-mediated chemokine mRNA stabilization. HuR deficiency markedly reduced IL-17-induced chemokine expression due to increased mRNA decay. Act1-mediated HuR polyubiquitination was required for the binding of HuR to CXCL1 mRNA, leading to mRNA stabilization. Although IL-17 induced the coshift of Act1 and HuR to the polysomal fractions in a sucrose gradient, HuR deficiency reduced the ratio of translation-active/translation-inactive IL-17-induced chemokine mRNAs. Furthermore, HuR deletion in distal lung epithelium attenuated IL-17-induced neutrophilia. In summary, HuR functions to couple receptor-proximal signaling to posttranscriptional machinery, contributing to IL-17-induced inflammation.

Genome-wide association study identifies TH1 pathway genes associated with lung function in asthmatic patients

BACKGROUND

Recent meta-analyses of genome-wide association studies in general populations of European descent have identified 28 loci for lung function.

OBJECTIVE

We sought to identify novel lung function loci specifically for asthma and to confirm lung function loci identified in general populations.

METHODS

Genome-wide association studies of lung function (percent predicted FEV1 [ppFEV1], percent predicted forced vital capacity, and FEV1/forced vital capacity ratio) were performed in 4 white populations of European descent (n = 1544), followed by meta-analyses.

RESULTS

Seven of 28 previously identified lung function loci (HHIP, FAM13A, THSD4, GSTCD, NOTCH4-AGER, RARB, and ZNF323) identified in general populations were confirmed at single nucleotide polymorphism (SNP) levels (P < .05). Four of 32 loci (IL12A, IL12RB1, STAT4, and IRF2) associated with ppFEV1 (P < 10(-4)) belong to the TH1 or IL-12 cytokine family pathway. By using a linear additive model, these 4 TH1 pathway SNPs cumulatively explained 2.9% to 7.8% of the variance in ppFEV1 values in 4 populations (P = 3 × 10(-11)). Genetic scores of these 4 SNPs were associated with ppFEV1 values (P = 2 × 10(-7)) and the American Thoracic Society severe asthma classification (P = .005) in the Severe Asthma Research Program population. TH2 pathway genes (IL13, TSLP, IL33, and IL1RL1) conferring asthma susceptibility were not associated with lung function.

CONCLUSION

Genes involved in airway structure/remodeling are associated with lung function in both general populations and asthmatic subjects. TH1 pathway genes involved in anti-virus/bacterial infection and inflammation modify lung function in asthmatic subjects. Genes associated with lung function that might affect asthma severity are distinct from those genes associated with asthma susceptibility.

Nascent endothelium initiates Th2 polarization of asthma

Asthma airway remodeling is linked to Th2 inflammation. Angiogenesis is a consistent feature of airway remodeling, but its contribution to pathophysiology remains unclear. We hypothesized that nascent endothelial cells in newly forming vessels are sufficient to initiate Th2-inflammation. Vascular endothelial (VE)-cadherin is a constitutively expressed endothelial cell adhesion molecule that is exposed in its monomer form on endothelial tip cells prior to adherens junction formation. Abs targeted to VE-cadherin monomers inhibit angiogenesis by blocking this adherens junction formation. In this study, VE-cadherin monomer Ab reduced angiogenesis in the lungs of the allergen-induced murine asthma model. Strikingly, Th2 responses including, IgE production, eosinophil infiltration of the airway, subepithelial fibrosis, mucus metaplasia, and airway-hyperreactivity were also attenuated by VE-cadherin blockade, via mechanisms that blunted endothelial IL-25 and proangiogenic progenitor cell thymic stromal lymphopoietin production. The results identify angiogenic responses in the origins of atopic inflammation.

High mobility group box 1 contributes to the pathogenesis of experimental pulmonary hypertension via activation of Toll-like receptor 4

Survival rates for patients with pulmonary hypertension (PH) remain low, and our understanding of the mechanisms involved are incomplete. Here we show in a mouse model of chronic hypoxia (CH)-induced PH that the nuclear protein and damage-associate molecular pattern molecule (DAMP) high mobility group box 1 (HMGB1) contributes to PH via a Toll-like receptor 4 (TLR4)-dependent mechanism. We demonstrate extranuclear HMGB1 in pulmonary vascular lesions and increased serum HMGB1 in patients with idiopathic pulmonary arterial hypertension. The increase in circulating HMGB1 correlated with mean pulmonary artery pressure. In mice, we similarly detected the translocation and release of HMGB1 after exposure to CH. HMGB1-neutralizing antibody attenuated the development of CH-induced PH, as assessed by measurement of right ventricular systolic pressure, right ventricular hypertrophy, pulmonary vascular remodeling and endothelial activation and inflammation. Genetic deletion of the pattern recognition receptor TLR4, but not the receptor for advanced glycation end products, likewise attenuated CH-induced PH. Finally, daily treatment of mice with recombinant human HMGB1 exacerbated CH-induced PH in wild-type (WT) but not Tlr4(-/-) mice. These data demonstrate that HMGB1-mediated activation of TLR4 promotes experimental PH and identify HMGB1 and/or TLR4 as potential therapeutic targets for the treatment of PH.

Fatty acid binding protein 4 regulates VEGF-induced airway angiogenesis and inflammation in a transgenic mouse model: implications for asthma

Neovascularization of the airways occurs in several inflammatory lung diseases, including asthma. Vascular endothelial growth factor (VEGF) plays an important role in vascular remodeling in the asthmatic airways. Fatty acid binding protein 4 (FABP4 or aP2) is an intracellular lipid chaperone that is induced by VEGF in endothelial cells. FABP4 exhibits a proangiogenic function in vitro, but whether it plays a role in modulation of angiogenesis in vivo is not known. We hypothesized that FABP4 promotes VEGF-induced airway angiogenesis and investigated this hypothesis with the use of a transgenic mouse model with inducible overexpression of VEGF165 under a CC10 promoter [VEGF-TG (transgenic) mice]. We found a significant increase in FABP4 mRNA levels and density of FABP4-expressing vascular endothelial cells in mouse airways with VEGF overexpression. FABP4(-/-) mouse airways showed a significant decrease in neovessel formation and endothelial cell proliferation in response to VEGF overexpression. These alterations in airway vasculature were accompanied by attenuated expression of proinflammatory mediators. Furthermore, VEGF-TG/FABP4(-/-) mice showed markedly decreased expression of endothelial nitric oxide synthase, a well-known mediator of VEGF-induced responses, compared with VEGF-TG mice. Finally, the density of FABP4-immunoreactive vessels in endobronchial biopsy specimens was significantly higher in patients with asthma than in control subjects. Taken together, these data unravel FABP4 as a potential target of pathologic airway remodeling in asthma.

Disulfide bond as a switch for copper-zinc superoxide dismutase activity in asthma

AIM

Loss of superoxide dismutase (SOD) activity is a defining biochemical feature of asthma. However, mechanisms for the reduced activity are unknown. We hypothesized that loss of asthmatic SOD activity is due to greater susceptibility to oxidative inactivation.

RESULT

Activity assays of blood samples from asthmatics and healthy controls revealed impaired dismutase activity of copper-zinc SOD (CuZnSOD) in asthma. CuZnSOD purified from erythrocytes or airway epithelial cells from asthmatic was highly susceptible to oxidative inactivation. Proteomic analyses identified that inactivation was related to oxidation of cysteine 146 (C146), which is usually disulfide bonded to C57. The susceptibility of cysteines pointed to an alteration in protein structure, which is likely related to the loss of disulfide bond. We speculated that a shift to greater intracellular reducing potential might account for the change. Strikingly, measures of reduced and oxidized glutathione confirmed greater reducing intracellular state in asthma, compared with controls. Similarly, greater free thiol in CuZnSOD was confirmed by ~2-fold greater N-ethylmaleimide binding to C146 in asthma as compared with controls.

INNOVATION

Greater reducing potential under a chronic inflammatory state of asthma, thus, leads to susceptibility of CuZnSOD to oxidative inactivation due to cleavage of C57-C146 disulfide bond and exposure of usually unavailable cysteines.

CONCLUSION

Vulnerability of CuZnSOD influenced by redox likely amplifies injury and inflammation during acute asthma attacks when reactive oxygen species are explosively generated. Overall, this study identifies a new paradigm for understanding the chemical basis of inflammation, in which redox regulation of thiol availability dictates protein susceptibility to environmental and endogenously generated reactive species.