Patrick O. Mitchell

Rosiglitazone Attenuates Chronic Hypoxia–Induced Pulmonary Hypertension in a Mouse Model

Chronic hypoxia contributes to pulmonary hypertension through complex mechanisms that include enhanced NADPH oxidase expression and reactive oxygen species (ROS) generation in the lung. Stimulation of peroxisome proliferator-activated receptor gamma (PPARgamma) reduces the expression and activity of NADPH oxidase. Therefore, we hypothesized that activating PPARgamma with rosiglitazone would attenuate chronic hypoxia-induced pulmonary hypertension, in part, through suppressing NADPH oxidase-derived ROS that stimulate proliferative signaling pathways. Male C57Bl/6 mice were exposed to chronic hypoxia (CH, Fi(O2) 10%) or room air for 3 or 5 weeks. During the last 10 days of exposure, each animal was treated daily by gavage with either the PPARgamma ligand, rosiglitazone (10 mg/kg/d) or with an equal volume of vehicle. CH increased: (1) right ventricular systolic pressure (RVSP), (2) right ventricle weight, (3) thickness of the walls of small pulmonary vessels, (4) superoxide production and Nox4 expression in the lung, and (5) platelet-derived growth factor receptor beta (PDGFRbeta) expression and activity and reduced phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression. Treatment with rosiglitazone prevented the development of pulmonary hypertension at 3 weeks; reversed established pulmonary hypertension at 5 weeks; and attenuated CH-stimulated Nox4 expression and superoxide production, PDGFRbeta activation, and reductions in PTEN expression. Rosiglitazone also attenuated hypoxia-induced increases in Nox4 expression in pulmonary endothelial cells in vitro despite hypoxia-induced reductions in PPARgamma expression. Collectively, these findings indicate that PPARgamma ligands attenuated hypoxia-induced pulmonary vascular remodeling and hypertension by suppressing oxidative and proliferative signals providing novel insights for mechanisms underlying therapeutic effects of PPARgamma activation in pulmonary hypertension.

The Role of NADPH Oxidase in Chronic Intermittent Hypoxia-Induced Pulmonary Hypertension in Mice

Obstructive sleep apnea, characterized by intermittent periods of hypoxemia, is an independent risk factor for the development of pulmonary hypertension. However, the exact mechanisms of this disorder remain to be defined. Enhanced NADPH oxidase expression and superoxide (O2(-).) generation in the pulmonary vasculature play a critical role in hypoxia-induced pulmonary hypertension. Therefore, the current study explores the hypothesis that chronic intermittent hypoxia (CIH) causes pulmonary hypertension, in part, by increasing NADPH oxidase-derived reactive oxygen species (ROS) that contribute to pulmonary vascular remodeling and hypertension. To test this hypothesis, male C57Bl/6 mice and gp91phox knockout mice were exposed to CIH for 8 hours per day, 5 days per week for 8 weeks. CIH mice were placed in a chamber where the oxygen concentration was cycled between 21% and 10% O2 45 times per hour. Exposure to CIH for 8 weeks increased right ventricular systolic pressure (RVSP), right ventricle (RV):left ventricle (LV) + septum (S) weight ratio, an index of RV hypertrophy, and thickness of the right ventricular anterior wall as measured by echocardiography. CIH exposure also caused pulmonary vascular remodeling as demonstrated by increased muscularization of the distal pulmonary vasculature. CIH-induced pulmonary hypertension was associated with increased lung levels of the NADPH oxidase subunits, Nox4 and p22phox, as well as increased activity of platelet-derived growth factor receptor beta and its associated downstream effector, Akt kinase. These CIH-induced derangements were attenuated in similarly treated gp91phox knockout mice. These findings demonstrate that NADPH oxidase-derived ROS contribute to the development of pulmonary vascular remodeling and hypertension caused by CIH.

Efficacy of Oral Ribavirin in Lung Transplant Patients With Respiratory Syncytial Virus Lower Respiratory Tract Infection

BACKGROUND Respiratory syncytial virus (RSV) can cause severe lower respiratory tract infection (LRI) and is a risk factor for the development of bronchiolitis obliterans syndrome (BOS) after lung transplantation (LTx). Currently, the most widely used therapy for RSV is inhaled ribavirin. However, this therapy is costly and cumbersome. We investigated the utility of using oral ribavirin for the treatment of RSV infection after LTx. METHODS RSV was identified in nasopharyngeal swabs (NPS) or bronchoalveolar lavage (BAL) using direct fluorescent antibody (DFA) in 5 symptomatic LTx patients diagnosed with LRI. Data were collected from December 2005 and August 2007 and included: age; gender; type of LTx; underlying disease; date of RSV; pulmonary function prior to, during and up to 565 days post-RSV infection; need for mechanical ventilation; concurrent infections; and radiographic features. Patients received oral ribavirin for 10 days with solumedrol (10 to 15 mg/kg/day intravenously) for 3 days, until repeat NPS were negative. RESULTS Five patients had their RSV-LRI diagnosis made at a median of 300 days post-LTx. Mean forced expiratory volume in 1 second (FEV(1)) fell 21% (p < 0.012) during infection. After treatment, FEV(1) returned to baseline and was maintained at follow-up of 565 days. There were no complications and no deaths with oral therapy. A 10-day course of oral ribavirin cost

Receptor for Advanced Glycation End Products in Donor Lungs Is Associated with Primary Graft Dysfunction After Lung Transplantation

700 compared with

Gastroesophageal Reflux Disease Is Associated With an Increased Rate of Acute Rejection in Lung Transplant Allografts

14,000 for nebulized ribavirin at 6 g/day. CONCLUSIONS Treatment of RSV after LTx with oral ribavirin and corticosteroids is well tolerated, effective and less costly than inhaled ribavirin. Further studies are needed to directly compare the long-term efficacy of oral vs nebulized therapy for RSV.

Multiple roles of calcineurin in skeletal muscle growth.

Development of primary graft dysfunction (PGD) is associated with poor outcomes after transplantation. We hypothesized that Receptor for Advanced Glycation End‐products (RAGE) levels in donor lungs is associated with the development of PGD. Furthermore, we hypothesized that RAGE levels would be increased with PGD in recipients after transplantation. We measured RAGE in bronchoalveolar lavage fluid (BALf) from 25 donors and 34 recipients. RAGE was also detected in biopsies (transbronchial biopsy) from recipients with and without PGD. RAGE levels were significantly higher in donor lungs that subsequently developed sustained PGD versus transplanted lungs that did not display PGD. Donor RAGE level was a predictor of recipient PGD (odds ratio = 1.768 per 0.25 ng/mL increase in donor RAGE level). In addition, RAGE levels remained high for 14 days in those recipients that developed severe graft dysfunction. Recipients may be at higher risk for developing PGD if they receive transplanted organs that have higher levels of soluble RAGE prior to explantation. Moreover, the clinical and pathologic abnormalities associated with PGD posttransplantation are associated with increased RAGE expression. These findings also raise the possibility that targeting the RAGE signaling pathway could be a novel strategy for treatment and/or prevention of PGD.

Human immunodeficiency virus-1 transgene expression increases pulmonary vascular resistance and exacerbates hypoxia-induced pulmonary hypertension development

PURPOSE Gastric fundoplication (GF) for gastroesophageal reflux disease (GERD) may protect against the progression of chronic rejection in lung transplant (LT) recipients. However, the association of GERD with acute rejection episodes (ARE) is uncertain. This study sought to identify if ARE were linked to GERD in LT patients. METHODS This single-center retrospective observational study, of patients transplanted from January 1, 2000, to January 31, 2009, correlated results of pH probe testing for GERD with ARE (≥International Society for Heart and Lung Transplantation A1 or B1). We compared the rates of ARE among patients with GERD (DeMeester Score > 14.7) versus without GERD as number of ARE per 1,000 patient-days after LT. Patients undergoing GF prior to LT were excluded. RESULTS The analysis included 60 LT subjects and 9,249 patient-days: 33 with GERD versus 27 without GERD. We observed 51 ARE among 60 LT recipients. The rate of ARE was highest among patients with GERD: 8.49 versus 2.58, an incidence density ratio (IDR) of 3.29 (P = .00016). Upon multivariate negative binomial regression modeling, only GERD was associated with ARE (IDR 2.15; P = .009). Furthermore, GERD was associated with multiple ARE (36.4% vs 0%; P < .0001) and earlier onset compared with patients without GERD: ARE proportion at 2 months was 0.55 versus 0.26 P = .004). CONCLUSION In LT recipients, GERD was associated with a higher rate, multiple events, and earlier onset of ARE. The efficacy of GF to reduce ARE among patients with GERD needs further evaluation.

Alcohol primes the airway for increased interleukin-13 signaling.

Adequate muscle mass and function are critical for human health. Several types of skeletal muscle growth, including regeneration and growth after atrophy, can occur in the rehabilitative period after orthopaedic surgery. The molecular pathways regulating growth of skeletal muscle in adults are understood poorly. The role of calcineurin in regulating regeneration and growth of atrophied skeletal muscle is discussed. Understanding the molecular and cellular pathways that regulate such muscle growth may lead to the development of strategies to enhance muscle growth, thereby facilitating rehabilitation after orthopaedic surgery.

Junctional Adhesion Molecule A Promotes Epithelial Tight Junction Assembly to Augment Lung Barrier Function

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by increased pulmonary arterial resistance and vessel remodeling. Patients living with human immunodeficiency virus-1 (HIV-1) have an increased susceptibility to develop severe pulmonary hypertension (PH) irrespective of their CD4+ lymphocyte counts. While the underlying cause of HIV-PAH remains unknown, the interaction of HIV-1 proteins with the vascular endothelium may play a critical role in HIV-PAH development. Hypoxia promotes PH in experimental models and in humans, but the impact of HIV-1 proteins on hypoxia-induced pulmonary vascular dysfunction and PAH has not been examined. Therefore, we hypothesize that the presence of HIV-1 proteins and hypoxia synergistically augment the development of pulmonary vascular dysfunction and PH. We examined the effect of HIV-1 proteins on pulmonary vascular resistance by measuring pressure-volume relationships in isolated lungs from wild-type (WT) and HIV-1 Transgenic (Tg) rats. WT and HIV-1 Tg rats were exposed to 10% O2 for four weeks to induce experimental pulmonary hypertension to assess whether HIV-1 protein expression would impact the development of hypoxia-induced PH. Our results demonstrate that HIV-1 protein expression significantly increased pulmonary vascular resistance (PVR). HIV-1 Tg mice demonstrated exaggerated pulmonary vascular responses to hypoxia as evidenced by greater increases in right ventricular systolic pressures, right ventricular hypertrophy and vessel muscularization when compared to wild-type controls. This enhanced PH was associated with enhanced expression of HIF-1α and PCNA. In addition, in vitro studies reveal that medium from HIV-infected monocyte derived macrophages (MDM) potentiates hypoxia-induced pulmonary artery endothelial proliferation. These results indicate that the presence of HIV-1 proteins likely impact pulmonary vascular resistance and exacerbate hypoxia-induced PH.

Na,K-ATPase Expression Is Increased in the Lungs of Alcohol-Fed Rats

BACKGROUND Using an experimental model of airway fibrosis following lung transplantation, we recently showed that chronic alcohol ingestion by donor rats amplifies airway fibrosis in the recipient. Associated with alcohol-mediated amplification of airway fibrosis is increased transforming growth factor beta-1(TGFbeta(1)) and alpha-smooth muscle actin expression. Other studies have shown that interleukin-13 (IL-13) modulates TGFbeta(1) signaling during experimentally-induced airway fibrosis. Therefore, we hypothesized that IL-13 is a component of alcohol-mediated amplification of pro-fibrotic mediators in the alcoholic lung. METHODS To test this hypothesis, we analyzed tracheal epithelial cells and type II alveolar cells from control- or alcohol-fed rats, alcohol-treated mouse lung fibroblasts, and human bronchial epithelial cells in vitro for expression of various components of the IL-13 signaling pathway. Signaling via the IL-13 pathway was assessed by measuring levels of phosphorylated signal transducers and activators of transcription-6 (STAT6). In addition, we performed heterotopic tracheal transplantation using control-fed and alcohol-fed donor rats and analyzed tracheal allografts for expression of components of the IL-13 signaling pathway by RT-PCR and immunocytochemical analyses. RESULTS Interleukin-13 expression was detected in type II alveolar epithelial cells and human bronchial epithelial cells, but not in lung fibroblasts. IL-13 expression was decreased in whole lung and type II cells in response to alcohol exposure. In all cell types analyzed, expression of IL-13 signaling receptor (IL-13R alpha(1)) mRNA was markedly increased. In contrast, mRNA and protein expression of the IL-13 decoy receptor (IL-13R alpha(2)) were decreased in all cells analyzed. Exposure to alcohol also increased STAT6 phosphorylation in response to IL-13 and lipopolysaccharide. CONCLUSIONS Data from multiple cell types in the pulmonary system suggest that IL-13 and its receptors play a role in alcohol-mediated activation of pro-fibrotic pathways. Taken together, these data suggest that alcohol primes the airway for increased IL-13 signaling and subsequent tissue remodeling upon injury such as transplantation.