Gerrina Ruiter

Dysregulated Renin–Angiotensin–Aldosterone System Contributes to Pulmonary Arterial Hypertension

RATIONALE Patients with idiopathic pulmonary arterial hypertension (iPAH) often have a low cardiac output. To compensate, neurohormonal systems such as the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system are up-regulated, but this may have long-term negative effects on the progression of iPAH. OBJECTIVES Assess systemic and pulmonary RAAS activity in patients with iPAH and determine the efficacy of chronic RAAS inhibition in experimental PAH. METHODS We collected 79 blood samples from 58 patients with iPAH in the VU University Medical Center Amsterdam (between 2004 and 2010) to determine systemic RAAS activity. MEASUREMENTS AND MAIN RESULTS We observed increased levels of renin, angiotensin (Ang)I, and AngII, which were associated with disease progression (P < 0.05) and mortality (P < 0.05). To determine pulmonary RAAS activity, lung specimens were obtained from patients with iPAH (during lung transplantation, n = 13) and control subjects (during lobectomy or pneumonectomy for cancer, n = 14). Local RAAS activity in pulmonary arteries of patients with iPAH was increased, demonstrated by elevated angiotensin-converting enzyme activity in pulmonary endothelial cells and increased AngII type 1 (AT(1)) receptor expression and signaling. In addition, local RAAS up-regulation was associated with increased pulmonary artery smooth muscle cell proliferation via enhanced AT(1) receptor signaling in patients with iPAH compared with control subjects. Finally, to determine the therapeutic potential of RAAS activity, we assessed the chronic effects of an AT(1) receptor antagonist (losartan) in the monocrotaline PAH rat model (60 mg/kg). Losartan delayed disease progression, decreased right ventricular afterload and pulmonary vascular remodeling, and restored right ventricular-arterial coupling in rats with PAH. CONCLUSIONS Systemic and pulmonary RAAS activities are increased in patients with iPAH and are associated with increased pulmonary vascular remodeling. Chronic inhibition of RAAS by losartan is beneficial in experimental PAH.

Iron deficiency is common in idiopathic pulmonary arterial hypertension

The aims of this study were to assess the prevalence of iron deficiency in idiopathic pulmonary arterial hypertension (IPAH) and investigate whether oral iron supplementation has effects in iron-deficient patients. Iron parameters were measure for all IPAH patients attending our centre (VU University Medical Center, Amsterdam, the Netherlands) between May 2009 and February 2010. Iron data were related to clinical parameters, including 6-min walking distance (6MWD), and haemodynamic parameters measured during right heart catheterisation. In a subset of iron-deficient patients, the uptake of iron from the bowel was studied after administering oral iron for 4 weeks. Iron deficiency was found in 30 (43%) out of 70 patients. 6MWD was reduced in iron-deficient patients compared with iron-sufficient patients (mean±sd 390±138 versus 460±143 m; p<0.05) irrespective of the existence of anaemia. In a subset of 18 patients that received oral iron, ferritin levels were significantly increased, although eight patients only slightly increased their iron storage. This study shows that iron deficiency is frequently present in IPAH and is associated with a lower exercise capacity. The small response to oral iron in 44% of the treated patients suggests impaired iron absorption in these patients.

Right Ventricular Failure in Idiopathic Pulmonary Arterial Hypertension Is Associated with Inefficient Myocardial Oxygen Utilization

Background— In idiopathic pulmonary arterial hypertension (IPAH), increased right ventricular (RV) power is required to maintain cardiac output. For this, RV O2 consumption (MVO2) must increase by augmentation of O2 supply and/or improvement of mechanical efficiency–ratio of power output to MVO2. In IPAH with overt RV failure, however, there is evidence that O2 supply (perfusion) reserve is reduced, leaving only increase in either O2 extraction or mechanical efficiency as compensatory mechanisms. We related RV mechanical efficiency to clinical and hemodynamic parameters of RV function in patients with IPAH and associated it with glucose metabolism. Methods and Results— The patients included were in New York Heart Association (NYHA) class II (n=8) and class III (n=8). They underwent right heart catheterization, MRI, and H2 15O-, 15O2-, C15O-, and 18FDG-PET. RV power and O2 supply were similar in both groups (NYHA class II versus class III: 0.54±0.14 versus 0.47±0.12 J/s and 0.109±0.022 versus 0.128±0.026 mL O2/min per gram, respectively). RV O2 extraction was near-significantly lower in NYHA class II compared with NYHA class III (63±17% versus 75±16%, respectively, P=0.10). As a result, MVO2 was significantly lower (0.066±0.012 versus 0.092±0.010 mL O2/min per gram, respectively, P=0.006). RV efficiency was reduced in NYHA class III (13.9±3.8%) compared with NYHA class II (27.8±7.6%, P=0.001). Septal bowing, measured by MRI, correlated with RV efficiency (r=−0.59, P=0.020). No relation was found between RV efficiency and glucose uptake rate. RV mechanical efficiency and ejection fraction were closely related (r=0.81, P<0.001). Conclusions— RV failure in IPAH was associated with reduced mechanical efficiency that was partially explained by RV mechanical dysfunction but not by a metabolic shift.

Right ventricular oxygen supply parameters are decreased in human and experimental pulmonary hypertension

BACKGROUND In pulmonary arterial hypertension (PAH), high right ventricular (RV) power output requires increased myocardial oxygen consumption. Oxygen supply, however, does not increase in proportion. It is unknown what cellular mechanisms underlie this lack of adaptation. We therefore determined oxygen supply parameters in RV tissue slices of deceased PAH patients and compared them with RV tissue of patients who died from left ventricular myocardial infarction (MI). Because autopsy tissue only reflects end-stage disease, rat models with stable and progressive pulmonary hypertension (PH) were studied as well. METHODS Myocardial tissue of 10 PAH and 10 MI patients was collected at autopsy. In rats, stable PH (n = 6) and progressive PH (n = 6) was induced by 40 or 60 mg/kg monocrotaline, respectively. Six rats were used as controls. RESULTS RV cardiomyocyte cross-sectional area was strongly increased in PAH compared with MI patients (p < 0.001), whereas capillary density decreased (p < 0.01). Rat data showed similar RV hypertrophy in stable and progressive PH, and RV capillary density was decreased in both (p < 0.01 and p < 0.0001 vs control rats, respectively). RV myoglobin protein content and functional concentration were reduced in both human and rat PH RVs. In rats, this results from a lack of increase in myoglobin mRNA transcription per cardiomyocyte nucleus. CONCLUSIONS All measured cellular oxygen supply parameters are decreased in the failing human and rat pulmonary hypertensive RV. In contrast to stable PH rats, compensatory adaptations do not occur in end-stage PAH, despite higher myocardial oxygen consumption.

Copper Dependence of Angioproliferation in Pulmonary Arterial Hypertension in Rats and Humans

Obliteration of the vascular lumen by endothelial cell growth is a hallmark of many forms of severe pulmonary arterial hypertension. Copper plays a significant role in the control of endothelial cell proliferation in cancer and wound-healing. We sought to determine whether angioproliferation in rats with experimental pulmonary arterial hypertension and pulmonary microvascular endothelial cell proliferation in humans depend on the proangiogenic action of copper. A copper-depleted diet prevented, and copper chelation with tetrathiomolybdate reversed, the development of severe experimental pulmonary arterial hypertension. The copper chelation-induced reopening of obliterated vessels was caused by caspase-independent apoptosis, reduced vessel wall cell proliferation, and a normalization of vessel wall structure. No evidence was found for a role of super oxide-1 inhibition or lysyl-oxidase-1 inhibition in the reversal of angioproliferation. Tetrathiomolybdate inhibited the proliferation of human pulmonary microvascular endothelial cells, isolated from explanted lungs from control subjects and patients with pulmonary arterial hypertension. These data suggest that the inhibition of endothelial cell proliferation by a copper-restricting strategy could be explored as a new therapeutic approach in pulmonary arterial hypertension. It remains to be determined, however, whether potential toxicity to the right ventricle is offset by the beneficial pulmonary vascular effects of antiangiogenic treatment in patients with pulmonary arterial hypertension.

Iron deficiency in systemic sclerosis patients with and without pulmonary hypertension

OBJECTIVES SSc-associated pulmonary hypertension (SSc-PH) has a worse prognosis compared with SSc without PH (SSc-nonPH). Iron deficiency (ID) was previously associated with worse clinical outcome and survival in other types of PH, but ID effects in SSc-PH are unknown. Therefore we investigated the prevalence and clinical significance of ID in systemic sclerosis patients with and without PH. METHODS Body iron status was determined in SSc-PH (n = 47) and SSc-nonPH patients (n = 122). ID was defined by circulating soluble transferrin receptor (sTfR) levels >28.1 nmol/l. Clinical and exercise parameters were compared between the groups. Four-year survival after iron measurements was determined. RESULTS ID prevalence was 46.1% in SSc-PH compared with 16.4% in SSc-nonPH patients (P < 0.001). Overall hepcidin levels were high compared with reference values and related to sTfR, but not with IL-6 (P = 0.82). Six-minute walking distance and maximal achieved work at ergometry was lower in SSc-PH compared with SSc-nonPH patients (P < 0.001 and P < 0.01, respectively) and was even further reduced in case of ID (P(interaction) < 0.05). In addition, ID SSc-PH patients had a poorer survival compared with non-ID patients [hazard ratio (HR) 0.34, 95% CI 0.14, 0.82, P < 0.05) and a similar trend was observed in SSc-nonPH patients (HR 0.16, 95% CI 0.02, 1.11, P = 0.06). CONCLUSION ID is more prevalent in SSc-PH than in SSc-nonPH patients and is associated with exercise impairment in both SSc-PH and SSc-nonPH. In addition, ID SSc-PH patients have a significantly worse survival compared with non-ID patients.

Systolic pulmonary artery pressure and heart rate are main determinants of oxygen consumption in the right ventricular myocardium of patients with idiopathic pulmonary arterial hypertension.

Increased afterload in idiopathic pulmonary arterial hypertension (IPAH) causes right ventricular (RV) hypertrophy and failure. Since RV remodelling occurs with alterations in RV oxygen metabolism, increasing our understanding in the factors determining RV O2 consumption in IPAH is necessary. In the left ventricle, it is known that heart rate and systolic blood pressure are the main determinants of myocardial O2 consumption (MVO2). However, the normal right heart has lower oxygen extraction and perfusion than the left myocardium, and RV energy metabolism is changed in hypertrophy. Therefore, it is not obvious that the relationsships of pressure and heart rate to MVO2 hold for the overloaded human right heart. We hypothesize that systolic pulmonary artery pressure (PAP) and heart rate (HR) are the major determinants of RV MVO2 in IPAH.

Intravenous iron therapy in patients with idiopathic pulmonary arterial hypertension and iron deficiency.

In patients with idiopathic pulmonary arterial hypertension (iPAH), iron deficiency is common and has been associated with reduced exercise capacity and worse survival. Previous studies have shown beneficial effects of intravenous iron administration. In this study, we investigated the use of intravenous iron therapy in iron-deficient iPAH patients in terms of safety and effects on exercise capacity, and we studied whether altered exercise capacity resulted from changes in right ventricular (RV) function and skeletal muscle oxygen handling. Fifteen patients with iPAH and iron deficiency were included. Patients underwent a 6-minute walk test, cardiopulmonary exercise tests, cardiac magnetic resonance imaging, and a quadriceps muscle biopsy and completed a quality-of-life questionnaire before and 12 weeks after receiving a high dose of intravenous iron. The primary end point, 6-minute walk distance, was not significantly changed after 12 weeks (409 ± 110 m before vs. 428 ± 94 m after; P = 0.07). Secondary end points showed that intravenous iron administration was well tolerated and increased body iron stores in all patients. In addition, exercise endurance time (P < 0.001) and aerobic capacity (P < 0.001) increased significantly after iron therapy. This coincided with improved oxygen handling in quadriceps muscle cells, although cardiac function at rest and maximal V ͘ o 2 were unchanged. Furthermore, iron treatment was associated with improved quality of life (P < 0.05). In conclusion, intravenous iron therapy in iron-deficient iPAH patients improves exercise endurance capacity. This could not be explained by improved RV function; however, increased quadriceps muscle oxygen handling may play a role. (Trial registration: ClinicalTrials.gov identifier NCT01288651)

11C-Acetate Clearance as an Index of Oxygen Consumption of the Right Myocardium in Idiopathic Pulmonary Arterial Hypertension: A Validation Study Using 15O-Labeled Tracers and PET

Idiopathic pulmonary arterial hypertension (IPAH) results in increased right ventricular (RV) workload and oxygen demand. It has been shown that myocardial oxygen consumption (MVO2) of the hypertrophied right ventricle of IPAH patients can be measured using PET and 15O-labeled tracers. This method is, however, not very suitable for routine clinical practice. The purpose of the present study was to assess whether MVO2 can also be determined in the right ventricle of IPAH patients from the clearance of 11C-acetate, a simple method that is in use for MVO2 measurements of the left myocardium. Methods: Seventeen of 26 IPAH patients performed the total PET study. Nine other patients were scanned only for 11C-acetate. 15O-H2O, 15O-O2, and 15O-CO scans were used to derive RV flow, oxygen extraction fraction, and blood volume, respectively, from which RV MVO2 was calculated. The rate of clearance determined by monoexponential curve fitting (Kmono) and the efflux rate constant k2 were derived from the 11C-acetate scan. The RV rate–pressure product was also determined by means of right heart catheterization, as an index of the RV MVO2, and was calculated as the product of systolic pulmonary artery pressure and heart rate. Results: Both 11C-acetate clearance rates, Kmono (R2 = 0.41, P = 0.006) and k2 (R2 = 0.45, P = 0.003), correlated with RV MVO2. They also correlated with RV rate–pressure product (Kmono, R2 = 0.41, P = 0.0005; k2, R2 = 0.48, P < 0.0001). Conclusion: 11C-acetate clearance rates correlated moderately with quantitative RV MVO2 measurements in IPAH. Therefore, 11C-acetate PET can be used only as an index of RV oxidative metabolism in IPAH patients.

Reversibility of the monocrotaline pulmonary hypertension rat model

To the Editor : Pulmonary hypertension (PH) is a disease characterised by progressive remodelling of the pulmonary vasculature eventually leading to right heart failure. Various animal models have been used to mimic the disease, involving pigs, dogs, rats and mice [1]. The most commonly used model is the monocrotaline (MCT) rat model. In this model MCT is injected subcutaneously and becomes metabolically activated, as a pyrrolizidine alkaloid, by hepatic cytochrome P450 3A [2, 3]. The active MCT pyrrole is pneumotoxic and damages the pulmonary artery endothelial cells (PAECs), which leads to a disturbed barrier function [4]. Other features of MCT-induced pulmonary vascular remodelling are arterial medial hyperplasia of axial arteries, interstitial oedema, adventitial inflammation, haemorrhage and, eventually, fibrosis [1, 2, 5, 6]. As a result, pulmonary vascular resistance (PVR) increases and the right ventricle compensates by hypertrophy and eventually fails [7, 8]. Besides the MCT PH rat model, chronic hypoxia with or without Sugen 5416 and pulmonary artery banding are used to study experimental PH [1]. The PH animal model of choice is mostly dependent on the research question that needs to be answered. Ideally, an animal model would recapitulate the progressive and irreversible pulmonary vascular remodelling, which is the hallmark of human PH [1, 4, 9]. However, none of the animal models fulfil this criterion. Concerns have been raised about the MCT rat model since many therapies were successful in MCT rats but not in humans with PH [4]. We, therefore, investigated the long-term progression and reversibility of MCT-induced PH in rats over 12 weeks, using a dose of 40 mg·kg−1 in a randomised placebo-controlled study design. Since it is known that a high dose …