Paul M. Hassoun

Endothelial Dysfunction in Pulmonary Hypertension

The pathogenesis of pulmonary hypertension (PH) involves a complex and multifactorial process. Endothelial dysfunction seems to play an integral role in mediating the structural changes in the pulmonary vasculature. Disordered endothelial cell proliferation along with concurrent neoangiogenesis, when exuberant, results in the formation of glomeruloid structures known as the plexiform lesions, which are common pathological features of the pulmonary vessels of patients with pulmonary arterial hypertension (PAH). In addition, an altered production of various endothelial vasoactive mediators, such as NO, prostacyclin, endothelin-1 (ET-1), serotonin, and thromboxane, has been increasingly recognized in patients with PH. Because most of these mediators affect the growth of the smooth muscle cells, an alteration in their production may facilitate the development of pulmonary vascular hypertrophy and structural remodeling characteristic of PH. It is conceivable that the beneficial effects of many of the treatments currently available for PAH, such as the use of prostacyclin, NO, and ET antagonists, result at least in part from restoring the balance between these mediators. However, the ultimate cellular and physiological targets of these treatments remain unknown.nnIn addition to the potential consequences of an imbalance in the endothelial production of various mediators, injury to the endothelium may expose the underlying vascular tissue to diverse blood-borne factors that may further promote pathological changes. Endothelial dysfunction may also have adverse consequences on pulmonary vascular hemostasis by altering the production of anticoagulant factors. Recent reports of genetic mutations in the endothelial cells of patients with PH further underscore the role of these cells in the disease pathogenesis.nnThe endothelium lining the normal lung is characterized by significant heterogeneity. Not only is it vastly different from systemic endothelium in ultrastructure and function, but it varies in various vessel types in the pulmonary vasculature itself.1 The main functions of the pulmonary endothelium include maintenance …

Diagnosis, Assessment, and Treatment of Non-Pulmonary Arterial Hypertension Pulmonary Hypertension

The 4th World Symposium on Pulmonary Hypertension was the first international meeting to focus not only on pulmonary arterial hypertension (PAH) but also on the so-called non-PAH forms of pulmonary hypertension (PH). The term non-PAH PH summarizes those forms of PH that are found in groups 2 to 5 of the current classification of PH, that is, those forms associated with left heart disease, chronic lung disease, recurrent venous thromboembolism, and other diseases. Many of these forms of PH are much more common than PAH, but all of them have been less well studied, especially in terms of medical therapy. The working group on non-PAH PH focused mainly on 4 conditions: chronic obstructive lung disease, interstitial lung disease, chronic thromboembolic PH, and left heart disease. The medical literature regarding the role of PH in these diseases was reviewed, and recommendations regarding diagnosis and treatment of PH in these conditions are provided. Given the lack of robust clinical trials addressing PH in any of these conditions, it is important to conduct further studies to establish the role of medical therapy in non-PAH PH.

Survival in pulmonary hypertension associated with the scleroderma spectrum of diseases: Impact of interstitial lung disease

OBJECTIVEnPulmonary hypertension (PH) is an important cause of mortality in systemic sclerosis (SSc), where it can be isolated (pulmonary arterial hypertension [PAH]) or associated with interstitial lung disease (ILD). This study was undertaken to characterize determinants of survival among SSc patients with either type of PH who received PAH-specific therapy.nnnMETHODSnConsecutive SSc patients with PAH or ILD-associated PH confirmed by right heart catheterization were included in the study. Kaplan-Meier and Cox proportional hazards models were used to compare survival between SSc patients with PAH and those with ILD-associated PH and to identify predictors of survival.nnnRESULTSnFifty-nine patients (39 with PAH and 20 with ILD-associated PH) were identified. The majority (15 of 20 with ILD-associated PH and 27 of 39 with PAH) received an endothelin receptor antagonist as initial therapy. Median followup time was 4.4 years (range 2.7-7.4 years). Survival was significantly worse in SSc patients with ILD-associated PH than in those with PAH (1-, 2-, and 3-year survival rates 82%, 46%, and 39% versus 87%, 79%, and 64%, respectively; P < 0.01 by log rank test). In a multivariable analysis, ILD-associated PH was associated with a 5-fold increase in risk of death compared with PAH. Pulmonary vascular resistance index was also an independent predictor of mortality in the overall cohort (hazard ratio 1.05, P < 0.01) and was a significant univariable risk factor in each group separately. Type of initial PAH therapy and the use of warfarin were not related to survival.nnnCONCLUSIONnSurvival in SSc complicated by PH remains poor despite currently available treatment options. While therapy may be associated with improved survival in PAH compared with historical controls, the prognosis for patients with ILD-associated PH is particularly grim. Early diagnosis and treatment may improve outcomes since worsening hemodynamic factors were associated with reduced survival.

Regulation of endothelial barrier function by reactive oxygen and nitrogen species

Excessive generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), by activated neutrophils and endothelial cells, has been implicated in the pathophysiology of endothelial barrier dysfunction. Disruption of the integrity of this barrier markedly increases permeability to fluids, solutes and inflammatory cells and is the hallmark of many disorders such as acute lung injury (ALI) and sepsis. There has been considerable progress in our understanding of the sequence of molecular and structural events that mediate the response of endothelial cells to oxidants and nitrosants. In addition, substantial experimental evidence demonstrates improvement of endothelial barrier dysfunction with antioxidant strategies. However, no significant benefits have been observed, so far, in clinical trials of antioxidants for the treatment of endothelial barrier dysfunction. This article will review the available evidence implicating ROS and RNS in endothelial barrier dysfunction, explore potential underlying mechanisms, and identify areas of further research.

Right Ventricular Dysfunction in Systemic Sclerosis–Associated Pulmonary Arterial Hypertension

Background—Systemic sclerosis–associated pulmonary artery hypertension (SScPAH) has a worse prognosis compared with idiopathic pulmonary arterial hypertension (IPAH), with a median survival of 3 years after diagnosis often caused by right ventricular (RV) failure. We tested whether SScPAH or systemic sclerosis–related pulmonary hypertension with interstitial lung disease imposes a greater pulmonary vascular load than IPAH and leads to worse RV contractile function. Methods and Results—We analyzed pulmonary artery pressures and mean flow in 282 patients with pulmonary hypertension (166 SScPAH, 49 systemic sclerosis–related pulmonary hypertension with interstitial lung disease, and 67 IPAH). An inverse relation between pulmonary resistance and compliance was similar for all 3 groups, with a near constant resistance×compliance product. RV pressure–volume loops were measured in a subset, IPAH (n=5) and SScPAH (n=7), as well as SSc without PH (n=7) to derive contractile indexes (end-systolic elastance [Ees] and preload recruitable stroke work [Msw]), measures of RV load (arterial elastance [Ea]), and RV pulmonary artery coupling (Ees/Ea). RV afterload was similar in SScPAH and IPAH (pulmonary vascular resistance=7.0±4.5 versus 7.9±4.3 Wood units; Ea=0.9±0.4 versus 1.2±0.5 mm Hg/mL; pulmonary arterial compliance=2.4±1.5 versus 1.7±1.1 mL/mm Hg; P>0.3 for each). Although SScPAH did not have greater vascular stiffening compared with IPAH, RV contractility was more depressed (Ees=0.8±0.3 versus 2.3±1.1, P<0.01; Msw=21±11 versus 45±16, P=0.01), with differential RV-PA uncoupling (Ees/Ea=1.0±0.5 versus 2.1±1.0; P=0.03). This ratio was higher in SSc without PH (Ees/Ea=2.3±1.2; P=0.02 versus SScPAH). Conclusions—RV dysfunction is worse in SScPAH compared with IPAH at similar afterload, and may be because of intrinsic systolic function rather than enhanced pulmonary vascular resistive and pulsatile loading.

Systemic Sclerosis-associated Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a devastating vascular complication of a number of connective tissue diseases, including systemic sclerosis (SSc), where it has a dramatic impact on the clinical course and overall survival and is the single most common cause of death in patients afflicted with this syndrome. Although remarkable advances have been achieved in elucidating the pathogenesis of PAH over the past 2 decades, leading to the development of disease-targeted therapies for the idiopathic form of this condition (IPAH), the response to therapy is suboptimal in SSc-related PAH (SSc-PAH), and survival remains very poor. Factors accounting for striking clinical and prognostic differences between these two syndromes are unclear but may include a more pronounced autoimmune, cellular, and inflammatory response, and a higher prevalence of comorbidities in SSc-PAH, including cardiac and pulmonary venous and parenchymal involvement. Furthermore, currently available markers of disease severity and clinical tools to assess response to therapy, which may be reliable in IPAH, are either limited or lacking in SSc-PAH. Thus, a more focused approach, including a better understanding of the pathogenesis and genetic factors underlying the development of SSc-PAH, a search for more specific and reliable tools to adequately assess functional impairment and monitor therapy, as well as the design of novel targeted therapies, are all urgently required to alter the dismal course of this syndrome.

Systemic sclerosis–related pulmonary hypertension associated with interstitial lung disease: Impact of pulmonary arterial hypertension therapies

OBJECTIVEnPrecapillary pulmonary hypertension (PH) is an important cause of death in patients with systemic sclerosis (SSc). It can occur in isolation (pulmonary arterial hypertension [PAH]) or in association with interstitial lung disease (ILD). Importantly, the outcomes and efficacy of PAH therapies in patients with SSc-related PH complicating ILD (PH-ILD) remain unknown. This study was undertaken to evaluate our experience with PH-ILD with regard to the efficacy and safety of PAH therapies in this patient cohort.nnnMETHODSnWe conducted a retrospective analysis of consecutive SSc patients from 2 large referral centers who had PH-ILD confirmed by right-sided heart catheterization and who received targeted PAH therapies. World Health Organization (WHO) functional class, 6-minute walk distance, and hemodynamic parameters were assessed at baseline and after a mean ± SD of 7.7 ± 6.2 months of treatment for PAH. Kaplan-Meier and Cox proportional hazards models were used to analyze survival and to identify prognostic factors.nnnRESULTSnSeventy patients were included in the study. No significant changes were observed in WHO functional class, 6-minute walk distance, or hemodynamic parameters after therapy. The 1-, 2-, and 3-year survival estimates were 71%, 39%, and 21%, respectively. In the multivariate model, worsening oxygenation during followup and reduced renal function were the only significant risk factors for death.nnnCONCLUSIONnThis study represents the largest series to date in which the impact of PAH therapies in SSc-related PH-ILD was examined. In this cohort, PAH therapies were associated with no clear benefits. Deterioration in oxygenation was an important determinant of long-term survival. Prospective clinical trials focusing on this group of patients are warranted.

Science review: Searching for gene candidates in acute lung injury

Acute lung injury (ALI) is a complex and devastating illness, often occurring within the setting of sepsis, and carries an annual mortality rate of 30–50%. Although the genetic basis of ALI has not been fully established, an increasing body of evidence suggests that genetic predisposition contributes to disease susceptibility and severity. Significant difficulty exists, however, in defining the exact nature of these genetic factors, including large phenotypic variance, incomplete penetrance, complex gene–environment interactions, and strong potential for locus heterogeneity. We utilized the candidate gene approach and an ortholog gene database to provide relevant gene ontologies and insights into the genetic basis of ALI. We employed a Medline search of selected basic and clinical studies in the English literature and studies sponsored by the HopGene National Institutes of Health sponsored Program in Genomic Applications. Extensive gene expression profiling studies in animal models of ALI (rat, murine, canine), as well as in humans, were performed to identify potential candidate genes http://www.hopkins-genomics.org/. We identified a number of candidate genes for ALI, with blood coagulation and inflammation gene ontologies being the most highly represented. The candidate gene approach coupled with extensive gene profiling and novel bioinformatics approaches is a valuable way to identify genes that are involved in ALI.

Mitogen Activated Protein Kinase Activated Protein Kinase 2 Regulates Actin Polymerization and Vascular Leak in Ventilator Associated Lung Injury

Mechanical ventilation, a fundamental therapy for acute lung injury, worsens pulmonary vascular permeability by exacting mechanical stress on various components of the respiratory system causing ventilator associated lung injury. We postulated that MK2 activation via p38 MAP kinase induced HSP25 phosphorylation, in response to mechanical stress, leading to actin stress fiber formation and endothelial barrier dysfunction. We sought to determine the role of p38 MAP kinase and its downstream effector MK2 on HSP25 phosphorylation and actin stress fiber formation in ventilator associated lung injury. Wild type and MK2−/− mice received mechanical ventilation with high (20 ml/kg) or low (7 ml/kg) tidal volumes up to 4 hrs, after which lungs were harvested for immunohistochemistry, immunoblotting and lung permeability assays. High tidal volume mechanical ventilation resulted in significant phosphorylation of p38 MAP kinase, MK2, HSP25, actin polymerization, and an increase in pulmonary vascular permeability in wild type mice as compared to spontaneous breathing or low tidal volume mechanical ventilation. However, pretreatment of wild type mice with specific p38 MAP kinase or MK2 inhibitors abrogated HSP25 phosphorylation and actin polymerization, and protected against increased lung permeability. Finally, MK2−/− mice were unable to phosphorylate HSP25 or increase actin polymerization from baseline, and were resistant to increases in lung permeability in response to HVT MV. Our results suggest that p38 MAP kinase and its downstream effector MK2 mediate lung permeability in ventilator associated lung injury by regulating HSP25 phosphorylation and actin cytoskeletal remodeling.

Systemic Sclerosis-Associated Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is the leading cause of death in systemic sclerosis (SSc) and affects up to 12% of all patients with SSc, with a 50% mortality rate within 3 years of PAH diagnosis. Compared with the idiopathic form of PAH (IPAH), patients with SSc-associated PAH (SSc-PAH) have a threefold increased risk of death and may receive a diagnosis late in the course of disease because of insidious onset and the high prevalence of cardiac, musculoskeletal, and pulmonary parenchymal comorbidities. Treatment with conventional forms of PAH therapy often yield poor results compared with IPAH cohorts; unfortunately, the exact reasons behind this remain poorly understood but likely include variations in the pathologic mechanisms, differences in cardiovascular response to increasing afterload, and inadequate strategies to detect and treat SSc-PAH early in its course. Current methods for screening and longitudinal evaluation of SSc-PAH, such as the 6-min walk test, transthoracic echocardiography, and MRI, each have notable advantages and disadvantages. We provide an up-to-date, focused review of SSc-PAH and how it differs from IPAH, including pathogenesis, appropriate screening for disease onset, and new approaches to treatment and longitudinal assessment of this disease.