XOR inhibition with febuxostat accelerates pulmonary endothelial barrier recovery and improves survival in lipopolysaccharide-induced murine sepsis

Sepsis is a leading cause of death among patients in the intensive care unit, resulting from multi-organ failure. Activity of xanthine oxidoreductase (XOR), a reactive oxygen species (ROS) producing enzyme, is known to be elevated in nonsurvivors of sepsis compared to survivors. We have previously demonstrated that XOR is critical for ventilator-induced lung injury. Using febuxostat, a novel nonpurine inhibitor of XOR, we sought to determine the role of XOR inhibition in a murine model of sepsis-induced lung injury and mortality. C57BL/6J mice were subjected to intravenous (IV) lipopolysaccharide (LPS) for various time points, and lungs were harvested for analyses. Subsets of mice were treated with febuxostat, pre or post LPS exposure, or vehicle. Separate groups of mice were followed up for mortality after LPS exposure. After 24 hr of IV LPS, mice exhibited an increase in XOR activity in lung tissue and a significant increase in pulmonary endothelial barrier disruption. Pretreatment of animals with febuxostat before exposure to LPS, or treatment 4 h after LPS, resulted in complete abrogation of XOR activity. Inhibition of XOR with febuxostat did not prevent LPS-induced pulmonary vascular permeability at 24 h, however, it accelerated recovery of the pulmonary endothelial barrier integrity in response to LPS exposure. Furthermore, treatment with febuxostat resulted in significant reduction in mortality. Inhibition of XOR with febuxostat accelerates recovery of the pulmonary endothelial barrier and prevents LPS-induced mortality, whether given before or after exposure to LPS.

Abstract 266: Phosphodiesterase 9A Deficiency Does Not Attenuate Chronic-hypoxic Pulmonary Hypertension

Background: Phosphodiesterase (PDE) inhibition is a cornerstone of therapy for pulmonary arterial hypertension. A novel role for PDE9A in natriuretic peptide-mediated left ventricular cyclic guanosine monophosphate (cGMP) signaling and remodeling has recently been described. Since cGMP-signaling can promote vaso-relaxation and prevent vascular smooth muscle cell proliferation and cardiac myocyte hypertrophy, we hypothesized that PDE9A deficiency would attenuate right ventricular (RV) and pulmonary vascular remodeling during chronic RV pressure overload.

Methods: Chronic-hypoxic pulmonary hypertension (CH-PH) was induced in mice lacking PDE9A expression ( Pde9a -/- ) and wild-type littermates ( Pde9a +/+ ) by exposure to normobaric hypoxia (FiO2 = 10%) for 3 weeks. RV systolic pressures were measured to quantify PH, and RV hypertrophy was quantified as the ratio of RV free wall mass to LV/septal mass (RV/LV+S). Heart, lung, and serum were flash frozen for biochemical analyses.

Results: In wild-type mice, exposure to chronic hypoxia resulted in significant increases in RV pressure (30 ± 2.4 vs. 20 ± 3.2 mm Hg; P = 0.0006) and RV hypertrophy (0.34 ± 0.04 vs. 0.25 ± 0.02; P < 0.0001). Serum ANP levels were increased 5-fold with CH-PH ( P = <0.0001), associated with a 72% reduction in lung Npr3 receptor expression (responsible for ANP clearance; P < 0.0001) but no increase in RV Nppa expression. After 3 weeks of CH-PH, tissue levels of cGMP were not increased in lung (993 ± 502 pg/mg vs. 667 ± 210 pg/mg; P = 0.27) or RV (47 ± 18 pg/mg vs. 49 ± 13 pg/mg; P = 0.88) homogenates. Accordingly, serine-239 phosphorylation of vasodilatory-stimulated phosphoprotein (VASP; a surrogate for protein kinase G activation) was not increased by CH-PH in lung or RV. Expression of Pde9a RNA was not increased by CH-PH in lung or RV. Pde9a -/- mice did not have attenuated CH-PH induced increases in RVH ( P = 0.27, 2-way ANOVA) or RVSP ( P = 0.23, 2-way ANOVA) when compared to Pde9a +/+ mice. In both Pde9a -/- and Pde9a +/+ mice, CH-PH was associated with significant increases in lung PDE5A expression.

Conclusions: In a murine model of chronic RV pressure overload, PDE9A deficiency does not attenuate RV remodeling or PH, despite robust increases in circulating natriuretic peptide levels.

Hepatoma-derived Growth Factor Predicts Disease Severity and Survival in Pulmonary Arterial Hypertension

RATIONALE

Pulmonary arterial hypertension (PAH) is a fatal disease, and pulmonary microvascular remodeling is an important contributor to PAH development. Therefore, we hypothesized that a circulating angiogenic factor could predict disease severity and survival.

OBJECTIVES

We sought to assess the relationship of serum hepatoma-derived growth factor (HDGF) with PAH disease severity and survival.

METHODS

Using a newly developed enzyme-linked immunosorbent assay, we evaluated circulating HDGF levels in two independent PAH cohorts and two different characterized control cohorts. Clinical and laboratory data were also used to assess the value of HDGF as a PAH prognostic biomarker.

MEASUREMENTS AND MAIN RESULTS

Serum HDGF levels were significantly elevated in two independent PAH cohorts. Importantly, serum HDGF levels were not elevated in a noncardiac chronic disease cohort. Further, patients with elevated HDGF had significantly lower exercise tolerance, worse New York Heart Association functional class, and higher levels of N-terminal pro-brain natriuretic peptide. HDGF was a strong predictor of mortality, with an unadjusted hazard ratio of 4.5 (95% confidence interval, 1.9-10.3; P = 0.003 by log-rank test). In multivariable Cox proportional hazards models, elevated HDGF levels predicted decreased survival after being adjusted for age, PAH subtype, invasive hemodynamics, and N-terminal pro-brain natriuretic peptide.

CONCLUSIONS

Elevated HDGF was associated with worse functional class, exertional intolerance, and increased mortality in PAH, suggesting HDGF as a potential biomarker for predicting mortality and as having possible diagnostic value for distinguishing PAH from non-PAH. HDGF may add additional value in PAH risk stratification in clinical trials and may represent a potential target for future PAH drug development.

Poor survival in patients with scleroderma and pulmonary hypertension due to heart failure with preserved ejection fraction

Pulmonary hypertension due to heart failure with preserved ejection fraction (PH-HFpEF) has been poorly studied in patients with systemic sclerosis (SSc). We sought to compare clinical characteristics and survival of SSc patients with PH-HFpEF (SSc-PH-HFpEF) versus pulmonary arterial hypertension (SSc-PAH). We hypothesized that patients with SSc-PH-HFpEF have a similar poor overall prognosis compared with patients with SSc-PAH when matched for total right ventricular load. The analysis included 117 patients with SSc-PH (93 with SSc-PAH versus 24 with SSc-PH-HFpEF) enrolled prospectively in the Johns Hopkins PH Registry. We examined baseline demographics and hemodynamics at diagnostic right heart catheterization (RHC), two-dimensional echocardiographic characteristics, six-minute walking distance (6MWD), treatment modalities, and laboratory values (serum NT-proBNP, creatinine, uric acid, and sodium), and assessed survival. Demographics and clinical features were similar between the two groups. Baseline RHC showed significantly higher pulmonary and right heart pressures in the SSc-PH-HFpEF compared with the SSc-PAH group. Trans-pulmonary gradient (TPG), however, was equally elevated without significant difference between the groups. SSc-PH-HFpEF patients had left atrial enlargement on echocardiography compared with SSc-PAH patients. No significant differences were found between groups for 6MWD, NT-proBNP, and other laboratory values. Although overall median survival time was 4.6 years with no difference in mortality rate between the two groups (SSc-PH-HFpEF versus SSc-PAH: 75% versus 59%; P = 0.26), patients with SSc-PH-HFpEF had a twofold increased risk of death compared with SSc-PAH patients after adjusting for hemodynamics. Concomitant intrinsic pulmonary vascular disease and HFpEF likely contribute to very poor survival in patients with SSc-PH-HFpEF.

Exhaled nitric oxide in pulmonary arterial hypertension associated with systemic sclerosis

The fractional exhaled concentration of nitric oxide (FE_NO) has been shown to be reduced in idiopathic pulmonary arterial hypertension (PAH) but has not been adequately studied in PAH associated with systemic sclerosis (SSc). We measured FE_NO at an expiratory flow rate of 50 mL/s in 21 treatment-naive patients with SSc-associated PAH (SSc-PAH), 94 subjects with SSc without pulmonary involvement, and 84 healthy volunteers. Measurements of FE_NO at additional flow rates of 100, 150, and 250 mL/s were obtained to derive the flow-independent nitric oxide exchange parameters of maximal airway flux (J'aw_NO) and steady-state alveolar concentration (CA_NO). FE_NO at 50 mL/s was similar (P = 0.22) in the SSc-PAH group (19 ± 12 parts per billion [ppb]) compared with the SSc group (17 ± 12 ppb) and healthy control group (21 ± 11 ppb). No change was observed after 4 months of targeted PAH therapy in 14 SSc-PAH group patients (P = 0.9). J'aw_NO was modestly reduced in SSc group subjects without lung disease (1.2 ± 0.5 nl/s) compared with healthy controls (1.64 ± 0.9; P < 0.05) but was similar to that in the SSc-PAH group. CA_NO was elevated in individuals with SSc-PAH (4.8 ± 2.6 ppb) compared with controls with SSc (3.3 ± 1.4 ppb) and healthy subjects (2.6 ± 1.5 ppb; P < 0.001 for both). However, after adjustment for the diffusing capacity of CO, there was no significant difference in CA_NO between individuals with SSc-PAH and controls with SSc. We conclude that FE_NO is not useful for the diagnosis of PAH in SSc. Increased alveolar nitric oxide in SSc-PAH likely represents impaired diffusion into pulmonary capillary blood.

Heart Rate Dependence of the Pulmonary Resistance x Compliance (RC) Time and Impact on Right Ventricular Load

Background

The effect of heart rate (HR) and body surface area (BSA) on pulmonary RC time and right ventricular (RV) load is unknown.

Methods

To determine the association of HR and BSA with the pulmonary RC time and measures of RV load, we studied three large patient cohorts including subjects with 1) known or suspected pulmonary arterial hypertension (PAH) (n = 1008), 2) pulmonary hypertension due to left heart disease (n = 468), and 3) end-stage heart failure with reduced ejection fraction (n = 150). To corroborate these associations on an individual patient level, we performed an additional analysis using high-fidelity catheters in 22 patients with PAH undergoing right atrial pacing.

Results

A faster HR inversely correlated with RC time (p<0.01 for all), suggesting augmented RV pulsatile loading. Lower BSA directly correlated with RC time (p<0.05) although the magnitude of this effect was smaller than for HR. With incremental atrial pacing, cardiac output increased and total pulmonary resistance (TPR) fell. However, effective arterial elastance, its mean resistive component (TPR/heart period; 0.60±0.27 vs. 0.79±0.45;p = 0.048), and its pulsatile component (0.27±0.18 vs 0.39±0.28;p = 0.03) all increased at faster HR.

Conclusion

Heart rate and BSA are associated with pulmonary RC time. As heart rate increases, the pulsatile and total load on the RV also increase. This relationship supports a hemodynamic mechanism for adverse effects of tachycardia on the RV.

Right Ventricular Angiogenesis is an Early Adaptive Response to Chronic Hypoxia-Induced Pulmonary Hypertension

OBJECTIVE

Myocardial angiogenesis is presumed to play a role in RV adaptation to PH, though definitive evidence and functional correlations are lacking. We aimed to use definitive methods to correlate RV angiogenesis, hypertrophy, and function in a murine PH model.

METHODS

Mice were exposed to CH for 21 days to induce PH and RV remodeling. We used unbiased stereology and flow cytometry to quantify angiogenesis and myocyte hypertrophy, and pressure-volume loops to measure RV function.

RESULTS

Within seven days, RV-specific increases in total capillary length (10,576 ± 2574 cm vs. 6822 ± 1379 cm; p = 0.02), surface area (10 ± 3.3 cm(2) vs. 4.9 ± 1.5 cm(2) ; p = 0.01), and volume (0.0013 ± 0.0005 cm(3) vs. 0.0006 ± 0.0001 cm(3) ; p = 0.02) were observed, and RV EC proliferation increased nearly 10-fold. Continued exposure led to progressive RVH without additional angiogenesis. RV function was preserved, but activation of hypoxia-dependent gene expression was observed in both ventricles after 21 days.

CONCLUSIONS

Early RV remodeling in CH-PH is associated with RV angiogenesis and preserved RV function. Continued CH-PH is associated with RVH but not angiogenesis, leading to biventricular activation of hypoxia-dependent gene expression.

Right Ventricular Functional Reserve in Pulmonary Arterial Hypertension

BACKGROUND

Right ventricular (RV) functional reserve affects functional capacity and prognosis in patients with pulmonary arterial hypertension (PAH). PAH associated with systemic sclerosis (SSc-PAH) has a substantially worse prognosis than idiopathic PAH (IPAH), even though many measures of resting RV function and pulmonary vascular load are similar. We therefore tested the hypothesis that RV functional reserve is depressed in SSc-PAH patients.

METHODS AND RESULTS

RV pressure-volume relations were prospectively measured in IPAH (n=9) and SSc-PAH (n=15) patients at rest and during incremental atrial pacing or supine bicycle ergometry. Systolic and lusitropic function increased at faster heart rates in IPAH patients, but were markedly blunted in SSc-PAH. The recirculation fraction, which indexes intracellular calcium recycling, was also depressed in SSc-PAH (0.32±0.05 versus 0.50±0.05; P=0.039). At matched exercise (25 W), SSc-PAH patients did not augment contractility (end-systolic elastance) whereas IPAH did (P<0.001). RV afterload assessed by effective arterial elastance rose similarly in both groups; thus, ventricular-vascular coupling declined in SSc-PAH. Both end-systolic and end-diastolic RV volumes increased in SSc-PAH patients to offset contractile deficits, whereas chamber dilation was absent in IPAH (+37±10% versus +1±8%, P=0.004, and +19±4% versus -1±6%, P<0.001, respectively). Exercise-associated RV dilation also strongly correlated with resting ventricular-vascular coupling in a larger cohort.

CONCLUSIONS

RV contractile reserve is depressed in SSc-PAH versus IPAH subjects, associated with reduced calcium recycling. During exercise, this results in ventricular-pulmonary vascular uncoupling and acute RV dilation. RV dilation during exercise can predict adverse ventricular-vascular coupling in PAH patients.

Identification of Rare Variants in ATP8B4 as a Risk Factor for Systemic Sclerosis by Whole-Exome Sequencing

OBJECTIVE

To determine the contribution of rare variants as genetic modifiers of the expressivity, penetrance, and severity of systemic sclerosis (SSc).

METHODS

We performed whole-exome sequencing of 78 European American patients with SSc, including 35 patients without pulmonary arterial hypertension (PAH) and 43 patients with PAH. Association testing of case-control probability for rare variants was performed using the unified sequence kernel association test with optimal kernel weighting and small sample adjustment by comparing all SSc patients with a reference population of 3,179 controls from the Exome Sequencing Project 5,500 exome data set. Replication genotyping was performed in an independent sample of 3,263 patients (415 patients with SSc and 2,848 controls). We conducted expression profiling of messenger RNA from 61 SSc patients (19 without PAH and 42 with PAH) and 41 corresponding controls.

RESULTS

The ATP8B4 gene was associated with a significant increase in the risk of SSc (P = 2.77 × 10(-7)). Among the 64 ATP8B4 variants tested, a single missense variant, c.1308C>G (F436L, rs55687265), provided the most compelling evidence of association (P = 9.35 × 10(-10), odds ratio [OR] 6.11), which was confirmed in the replication cohort (P = 0.012, OR 1.86) and meta-analysis (P = 1.92 × 10(-7), OR 2.5). Genes involved in E3 ubiquitin-protein ligase complex (ASB10) and cyclic nucleotide gated channelopathies (CNGB3) as well as HLA-DRB5 and HSPB2 (heat-shock protein 27) provided additional evidence of association (P < 10(-5)). Differential ATP8B4 expression was observed among the SSc patients compared to the controls (P = 0.0005).

CONCLUSION

ATP8B4 may represent a putative genetic risk factor for SSc and pulmonary vascular complications.

Ambrisentan and Tadalafil Up-front Combination Therapy in Scleroderma-associated Pulmonary Arterial Hypertension

BACKGROUND

Scleroderma-associated pulmonary arterial hypertension (SSc-PAH) is a rare disease characterized by a very dismal response to therapy and poor survival. We assessed the effects of up-front combination PAH therapy in patients with SSc-PAH.

METHODS

In this prospective, multicenter, open-label trial, 24 treatment-naive patients with SSc-PAH received ambrisentan 10 mg and tadalafil 40 mg daily for 36 weeks. Functional, hemodynamic, and imaging (cardiac magnetic resonance imaging and echocardiography) assessments at baseline and 36 weeks included changes in right ventricular (RV) mass and pulmonary vascular resistance as co-primary endpoints and stroke volume/pulmonary pulse pressure ratio, tricuspid annular plane systolic excursion, 6-minute walk distance, and N-terminal pro-brain natriuretic peptide as secondary endpoints.

RESULTS

At 36 weeks, we found that treatment had resulted in significant reductions in median (interquartile range [IQR]) RV mass (28.0 g [IQR, 20.6-32.9] vs. 32.5 g [IQR, 23.2-41.4]; P < 0.05) and median pulmonary vascular resistance (3.1 Wood units [IQR, 2.0-5.7] vs. 6.9 Wood units [IQR, 4.0-12.9]; P < 0.0001) and in improvements in median stroke volume/pulmonary pulse pressure ratio (2.6 ml/mm Hg [IQR, 1.8-3.5] vs. 1.4 ml/mm Hg [IQR 8.9-2.4]; P < 0.0001) and mean ( ± SD) tricuspid annular plane systolic excursion (2.2 ± 0.12 cm vs. 1.65 ± 0.11 cm; P < 0.0001), 6-minute walk distance (395 ± 99 m vs. 343 ± 131 m; P = 0.001), and serum N-terminal pro-brain natriuretic peptide (647 ± 1,127 pg/ml vs. 1,578 ± 2,647 pg/ml; P < 0.05).

CONCLUSIONS

Up-front combination therapy with ambrisentan and tadalafil significantly improved hemodynamics, RV structure and function, and functional status in treatment-naive patients with SSc-PAH and may represent a very effective therapy for this patient population. In addition, we identified novel hemodynamic and imaging biomarkers that could have potential value in future clinical trials. Clinical trial registered with www.clinicaltrials.gov (NCT01042158).

Macrophage Migration Inhibitory Factor: A Novel Inhibitor of Apoptosis Signal-Regulating Kinase 1-p38-Xanthine Oxidoreductase-Dependent Cigarette Smoke-Induced Apoptosis

Cigarette smoke (CS) exposure is the leading cause of emphysema. CS mediates pathologic emphysematous remodeling of the lung via apoptosis of lung parenchymal cells resulting in enlargement of the airspaces, loss of the capillary bed, and diminished surface area for gas exchange. Macrophage migration inhibitory factor (MIF), a pleiotropic cytokine, is reduced both in a preclinical model of CS-induced emphysema and in patients with chronic obstructive pulmonary disease, particularly those with the most severe disease and emphysematous phenotype. MIF functions to antagonize CS-induced DNA damage, p53-dependent apoptosis of pulmonary endothelial cells (EndoCs) and resultant emphysematous tissue remodeling. Using primary alveolar EndoCs and a mouse model of CS-induced lung damage, we investigated the capacity and molecular mechanism(s) by which MIF modifies oxidant injury. Here, we demonstrate that both the activity of xanthine oxidoreductase (XOR), a superoxide-generating enzyme obligatory for CS-induced DNA damage and EndoC apoptosis, and superoxide concentrations are increased after CS exposure in the absence of MIF. Both XOR hyperactivation and apoptosis in the absence of MIF occurred via a p38 mitogen-activated protein kinase-dependent mechanism. Furthermore, a mitogen-activated protein kinase kinase kinase family member, apoptosis signal-regulating kinase 1 (ASK1), was necessary for CS-induced p38 activation and EndoC apoptosis. MIF was sufficient to directly suppress ASK1 enzymatic activity. Taken together, MIF suppresses CS-mediated cytotoxicity in the lung, in part by antagonizing ASK1-p38-XOR-dependent apoptosis.

Right atrial pressure/pulmonary artery wedge pressure ratio: A more specific predictor of survival in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a progressive, fatal disease. Current prognostic models are not ideal, and identifying more accurate prognostic variables is needed. The objective of this study was to evaluate the relative prognostic value of the right atrial pressure/pulmonary artery wedge pressure (RAP/PAWP) ratio in PAH patients. We hypothesized that the RAP/PAWP ratio is more predictive of survival than any of the other measured or calculated hemodynamic variables.

METHODS

We performed a secondary analysis of a PAH cohort (Cohort 1) and validated our results in a separate cohort (Cohort 2). Cohort 1 included primarily patients enrolled in prospective, short-term, randomized clinical trials and subsequently followed long term. Cohort 2 included patients prospectively enrolled in a PAH registry at a tertiary PAH referral center.

RESULTS

Cohort 1 (n = 847) and Cohort 2 (n = 697) had a mean age of 47 and 54 years, respectively. Most were female (78% and 73%, respectively), Caucasian (83% and 82%), with advanced functional class disease status (New York Heart Association Functional Class III/IV 85% and 68%) and with significantly elevated hemodynamics (mean RAP/PAWP ratio: 1.2 and 1.0; pulmonary vascular resistance: 13.5 and 9.4 Wood units). RAP/PAWP ratio indicated a 1-year hazard ratio of 1.44 (p = 0.0001) and 1.35, respectively (p < 0.0001), and was the most consistently predictive hemodynamic variable across the 2 cohorts. These results remain valid even when adjusted for other covariables in multivariable regression models.

CONCLUSIONS

The RAP/PAWP ratio is a more specific predictor of survival than any other hemodynamic variable, and we recommend that it be used in clinical prognostication and PAH predictive models.

Bidimensional measurements of right ventricular function for prediction of survival in patients with pulmonary hypertension: comparison of reproducibility and time of analysis with volumetric cardiac magnetic resonance imaging analysis

We tested the hypothesis that bidimensional measurements of right ventricular (RV) function obtained by cardiac magnetic resonance imaging (CMR) in patients with pulmonary arterial hypertension (PAH) are faster than volumetric measures and highly reproducible, with comparable ability to predict patient survival. CMR-derived tricuspid annular plane systolic excursion (TAPSE), RV fractional shortening (RVFS), RV fractional area change (RVFAC), standard functional and volumetric measures, and ventricular mass index (VMI) were compared with right heart catheterization data. CMR analysis time was recorded. Receiver operating characteristic curves, Kaplan-Meier, Cox proportional hazard (CPH), and Bland-Altman test were used for analysis. Forty-nine subjects with PAH and 18 control subjects were included. TAPSE, RVFS, RVFAC, RV ejection fraction, and VMI correlated significantly with pulmonary vascular resistance and mean pulmonary artery pressure (all P < 0.05). Patients were followed up for a mean (± standard deviation) of 2.5 ± 1.6 years. Kaplan-Meier curves showed that death was strongly associated with TAPSE <18 mm, RVFS <16.7%, and RVFAC <18.8%. In CPH models with TAPSE as dichotomized at 18 mm, TAPSE was significantly associated with risk of death in both unadjusted and adjusted models (hazard ratio, 4.8; 95% confidence interval, 2.0-11.3; P = 0.005 for TAPSE <18 mm). There was high intra- and interobserver agreement. Bidimensional measurements were faster (1.5 ± 0.3 min) than volumetric measures (25 ± 6 min). In conclusion, TAPSE, RVFS, and RVFAC measures are efficient measures of RV function by CMR that demonstrate significant correlation with invasive measures of PAH severity. In patients with PAH, TAPSE, RVFS, and RVFAC have high intra- and interobserver reproducibility and are more rapidly obtained than volumetric measures. TAPSE <18 mm by CMR was strongly and independently associated with survival in PAH.

Abstract 378: Endothelial Cell Hypoxia-inducible Factor (HIF) Activity is Necessary for Right Ventricular Remodeling in a Murine Model of Chronic-hypoxic Pulmonary Hypertension

Introduction: Pulmonary hypertension induced myocardial remodeling is required to minimize RV wall stress as pulmonary arterial pressures increase. Myocardial angiogenesis is presumed to play an integral role in early RV remodeling, though molecular regulators remain undefined. Endothelial cell (EC) expression of HIF-1 is necessary for adaptive LV remodeling during chronic pressure overload, with loss of EC-specific HIF-1 activity associated with reduced LV capillary density. We hypothesized that EC HIF activity may also be necessary for adaptive RV remodeling and angiogenesis in a model of chronic RV pressure overload.

Methods: We used a murine model of chronic hypoxic pulmonary hypertension (CH-PH) to induce RV remodeling. Conditional transgenic mice lacking expression of the obligate HIF-1α/HIF-2α co-factor ARNT (aryl hydrocarbon receptor nuclear translocator) in Tie2+ lineage cells ( ARNT fl/fl ; Tie2-Cre +/- ) and ARNT fl/fl ;Tie2-Cre -/- controls were exposed to normobaric hypoxia (10% FiO 2 ) for 1-5 weeks. We measured RV hypertrophy (RVH), RV systolic pressure (RVSP), and myocardial EC proliferation (flow cytometry) as a marker for sprouting angiogenesis.

Results: After three weeks of CH-PH, RVH was observed in ARNT fl/fl ;Tie2-Cre -/- control mice, as anticipated (0.332±0.02 vs. 0.231±0.02; P < 0.05). CH-PH induced RVH in ARNT fl/fl ;Tie2-Cre -/- mice was associated with an early (1 week) increase in RV EC proliferation (vs. LV, 4.5±1.3% vs.1.8±0.5%; P < 0.05). Conversely, ARNT fl/fl ; Tie2 - Cre +/- mice did not develop RVH after 3 weeks of CH ( 0.222±0.01 vs. 0.241±0.02; P = NS), and early RV EC proliferation was attenuated (vs. LV, 2.9±1.2% vs. 1.5±0.3%; P = NS). Despite similar increases in CH-PH induced RVSP after 3 weeks, after 5 weeks RVSP normalized in ARNT fl/fl ; Tie2 - Cre +/- mice, but remained elevated in ARNT fl/fl ;Tie2-Cre -/- controls.

Conclusions: These preliminary findings confirm that EC-specific HIF activity is necessary for CH-PH induced RVH, and suggest that reduced EC proliferation (and potentially angiogenesis) may contribute to abrogated RV remodeling in ARNT fl/fl ; Tie2 - Cre +/- mice. We hypothesize that late normalization of RVSP in these mice may be indicative of premature RV failure.

Right ventricular remodeling in idiopathic and scleroderma-associated pulmonary arterial hypertension: two distinct phenotypes

Patients with scleroderma (SSc)-associated pulmonary arterial hypertension (PAH) have worse survival than patients with idiopathic PAH (IPAH). We hypothesized that the right ventricle (RV) adapts differently in SSc-PAH versus IPAH. We used cardiac magnetic resonance imaging (cMRI) and hemodynamic characteristics to assess the relationship between RV morphology and RV load in patients with SSc-PAH and IPAH. In 53 patients with PAH (35 with SSc-PAH and 18 with IPAH) diagnosed by right heart catheterization (RHC), we examined cMRIs obtained within 48 hours of RHC and compared RV morphology between groups. Regression analysis was used to assess the association between diagnosis (IPAH vs. SSc-PAH) and RV measurements after adjusting for age, sex, race, body mass index (BMI), left ventricular (LV) mass, and RV load. There were no significant differences in unadjusted comparisons of cMRI measurements between the two groups. Univariable regression showed RV mass index (RVMI) was linearly associated with measures of RV load in both the overall cohort and within each group. Multivariable linear regression models revealed a significant interaction between disease type and RVMI adjusting for pulmonary vascular resistance (PVR), age, sex, race, BMI, and LV mass. This model showed a decreased slope in the relationship between RVMI and PVR in the SSc-PAH group compared with the IPAH group. RVMI varies linearly with measures of RV load. After adjusting for multiple potential confounders, patients with SSc-PAH demonstrated significantly less RV hypertrophy with increasing PVR than patients with IPAH. This difference in adaptive hypertrophy may in part explain previously observed decreased contractility and poorer survival in SSc-PAH.

The right ventricle in scleroderma (2013 Grover Conference Series)

Pulmonary arterial hypertension (PAH) results from severe remodeling of the distal lung vessels leading irremediably to death through right ventricular (RV) failure. PAH (Group 1 of the World Health Organization classification of pulmonary hypertension) can be idiopathic (IPAH) or associated with other disorders, such as connective tissue diseases. Prominent among the latter is systemic sclerosis (SSc), a heterogeneous disorder characterized by endothelium dysfunction, dysregulation of fibroblasts resulting in excessive collagen production, and immune abnormalities. For as-yet-unknown reasons, SSc-associated PAH (SSc-PAH) carries a significantly worse prognosis compared with any other form of PAH in Group 1, including IPAH. We have previously shown that patients with SSc-PAH have a median survival of only 3 years, compared with 8 years for IPAH, despite modern PAH therapy. Because death is principally due to RV failure, we speculated that RV adaptation to PAH differed between the two entities due to disparate pulmonary artery loading, perhaps from vessel stiffening, or intrinsic RV myocardial disease that might limit function and adaptation to high afterload. In SSc, RV function may also be impaired by inflammatory processes, excess fibrosis of the myocardium, or altered angiogenesis, which may all contribute to impaired contractile reserve exacerbating cardiopulmonary impedance mismatch. This is now suggested by recent findings from our group that demonstrate that, although pulmonary vascular load may be similar between patients with IPAH and those with SSc-PAH, the latter display reduced myocardial contractility as assessed by pressure-volume loop measurements. This review focuses on fundamental hemodynamic, structural, and functional differences in RV from patients with SSc-PAH compared with IPAH, which may account for survival discrepancies between the two populations. Possible underlying basic mechanisms are discussed.