Christophe Guignabert

Pulmonary Arterial Hypertension in Patients Treated by Dasatinib

Background— The French pulmonary hypertension (PH) registry allows the survey of epidemiological trends. Isolated cases of precapillary PH have been reported in patients who have chronic myelogenous leukemia treated with the tyrosine kinase inhibitor dasatinib. Methods and Results— This study was designed to describe incident cases of dasatinib-associated PH reported in the French PH registry. From the approval of dasatinib (November 2006) to September 30, 2010, 9 incident cases treated by dasatinib at the time of PH diagnosis were identified. At diagnosis, patients had moderate to severe precapillary PH with functional and hemodynamic impairment. No other incident PH cases were exposed to other tyrosine kinase inhibitors at the time of PH diagnosis. Clinical, functional, or hemodynamic improvements were observed within 4 months of dasatinib discontinuation in all but 1 patient. Three patients required PH treatment with endothelin receptor antagonist (n=2) or calcium channel blocker (n=1). After a median follow-up of 9 months (min-max 3–36), the majority of patients did not demonstrate complete clinical and hemodynamic recovery, and no patients reached a normal value of mean pulmonary artery pressure (⩽20 mm Hg). Two patients (22%) died at follow-up (1 of unexplained sudden death and 1 of cardiac failure in the context of septicemia, respectively, 8 and 12 months after dasatinib withdrawal). The lowest estimate of incident PH occurring in patients exposed to dasatinib in France was 0.45%. Conclusions— Dasatinib may induce severe precapillary PH fulfilling the criteria of pulmonary arterial hypertension, thus suggesting a direct and specific effect of dasatinib on pulmonary vessels. Improvement is usually observed after withdrawal of dasatinib.

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.

An antiproliferative BMP-2/PPARγ/apoE axis in human and murine SMCs and its role in pulmonary hypertension

Loss-of-function mutations in bone morphogenetic protein receptor II (BMP-RII) are linked to pulmonary arterial hypertension (PAH); the ligand for BMP-RII, BMP-2, is a negative regulator of SMC growth. Here, we report an interplay between PPARgamma and its transcriptional target apoE downstream of BMP-2 signaling. BMP-2/BMP-RII signaling prevented PDGF-BB-induced proliferation of human and murine pulmonary artery SMCs (PASMCs) by decreasing nuclear phospho-ERK and inducing DNA binding of PPARgamma that is independent of Smad1/5/8 phosphorylation. Both BMP-2 and a PPARgamma agonist stimulated production and secretion of apoE by SMCs. Using a variety of methods, including short hairpin RNAi in human PASMCs, PAH patient-derived BMP-RII mutant PASMCs, a PPARgamma antagonist, and PASMCs isolated from PPARgamma- and apoE-deficient mice, we demonstrated that the antiproliferative effect of BMP-2 was BMP-RII, PPARgamma, and apoE dependent. Furthermore, we created mice with targeted deletion of PPARgamma in SMCs and showed that they spontaneously developed PAH, as indicated by elevated RV systolic pressure, RV hypertrophy, and increased muscularization of the distal pulmonary arteries. Thus, PPARgamma-mediated events could protect against PAH, and PPARgamma agonists may reverse PAH in patients with or without BMP-RII dysfunction.

Cross Talk Between Endothelial and Smooth Muscle Cells in Pulmonary Hypertension: Critical Role for Serotonin-Induced Smooth Muscle Hyperplasia

Background— The mechanism of pulmonary artery smooth muscle cell (PA-SMC) hyperplasia in idiopathic pulmonary artery hypertension (iPH) may involve both an inherent characteristic of PA-SMCs and abnormal control by external stimuli. We investigated the role of pulmonary microvascular endothelial cells (P-ECs) in controlling PA-SMC growth. Methods and Results— Serum-free medium of quiescent P-ECs elicited marked PA-SMC proliferation, and this effect was greater with P-ECs from patients with iPH than from control subjects and greater with PA-SMCs from these patients than from control subjects. Fluoxetine, which inhibits serotonin-induced mitogenesis by blocking the serotonin transporter, and p-chlorophenylalanine, which inhibits serotonin synthesis by blocking tryptophan hydroxylase (TPH), caused a similar 60% reduction in the growth-promoting effect of P-EC media, whereas endothelin receptor blockers had no effect. Assays of TPH activity in P-EC medium based on p-chlorophenylalanine–sensitive 5-hydroxytryptophan accumulation or serotonin determination indicated serotonin synthesis by P-ECs and an increase in this TPH-dependent process in iPH. Expression of the tph1 gene encoding the peripheral form of the TPH enzyme was increased in lungs and P-ECs from patients with iPH. Lung TPH1 immunostaining was confined to the pulmonary vessel intima. Conclusions— P-ECs produce paracrine factors governing PA-SMC growth. Serotonin, the main P-EC–derived growth factor, is overproduced in iPH and contributes to PA-SMC hyperplasia.

Inflammation and Immunity in the Pathogenesis of Pulmonary Arterial Hypertension

This review summarizes an expanding body of knowledge indicating that failure to resolve inflammation and altered immune processes underlie the development of pulmonary arterial hypertension. The chemokines and cytokines implicated in pulmonary arterial hypertension that could form a biomarker platform are discussed. Pre-clinical studies that provide the basis for dysregulated immunity in animal models of the disease are reviewed. In addition, we present therapies that target inflammatory/immune mechanisms that are currently enrolling patients, and discuss others in development. We show how genetic and metabolic abnormalities are inextricably linked to dysregulated immunity and adverse remodeling in the pulmonary arteries.

Serotonin Transporter Inhibition Prevents and Reverses Monocrotaline-Induced Pulmonary Hypertension in Rats

Background—Progression of pulmonary hypertension (PH) is associated with increased lung expression of the serotonin transporter (5-HTT), which leads to hyperplasia of the pulmonary artery smooth muscle cells (PA-SMCs). Given the postulated causal relation between 5-HTT overexpression and PH, we herein investigated whether the highly selective 5-HTT inhibitor fluoxetine prevented and/or reversed PH induced by monocrotaline (MCT) in rats. Selective 5-HT1B/1D, 5-HT2A, and 5-HT2B receptor antagonists were used for comparative testing. Methods and Results—MCT injection (60 mg/kg SC) was followed by an early peak in lung 5-HTT expression on day 1, which preceded the onset of PH. Established PH on day 15 was associated with a sustained 5-HTT increase. Continued fluoxetine treatment completely prevented PA-SMC proliferation and PH development and also suppressed the late 5-HTT increase, without affecting the early peak. The 5-HT receptor antagonists did not affect PH. Fluoxetine (10 mg · kg−1 · d−1 PO) started 3 weeks after MCT injection completely reversed established PH, normalizing PA pressure and structure. MCT-induced PH was also associated with increased expression of various cytokines, but only interleukin-1&bgr; and monocyte chemotactic protein-1 increased at the early phase and stimulated 5-HTT expression by cultured PA-SMCs. Conclusion—Upregulation of lung 5-HTT induced by MCT appears necessary to initiate the development of pulmonary vascular remodeling, whereas a sustained increase in 5-HTT expression may underlie both the progression and the maintenance of MCT-induced PH. Complete reversal of established PH by fluoxetine provides a rationale for new therapeutic strategies in human PH.

Transgenic Mice Overexpressing the 5-Hydroxytryptamine Transporter Gene in Smooth Muscle Develop Pulmonary Hypertension

One intrinsic abnormality of pulmonary artery smooth muscle cells (PA-SMCs) in human idiopathic pulmonary hypertension (iPH) is an exaggerated proliferative response to internalized serotonin (5-HT) caused by increased expression of the 5-HT transporter (5-HTT). To investigate whether 5-HTT overexpression in PA-SMCs is sufficient to produce PH, we generated transgenic mice overexpressing 5-HTT under the control of the SM22 promoter. Studies in SM22-LacZ+ mice showed that the transgene was expressed predominantly in SMCs of pulmonary and systemic vessels. Compared with wild-type mice, SM22–5-HTT+ mice exhibited a 3- to 4-fold increase in lung 5-HTT mRNA and protein, together with increased lung 5-HT uptake activity, but no changes in platelet 5-HTT activity or blood 5-HT levels. At 8 weeks of age, SM22–5-HTT+ mice exhibited PH, with marked increases in right ventricular systolic pressure (RVSP), right ventricle/left ventricle+septum ratio, and muscularization of distal pulmonary vessels, but no changes in systemic arterial pressure. PH worsened with age. Except a marked decrease in Kv channels, no changes in the lung expression of mediators of pulmonary vascular remodeling were observed in SM22–5-HTT+ mice. Compared with wild-type mice, SM22–5-HTT+ mice showed depressed hypoxic pulmonary vasoconstriction contrasting with greater severity of hypoxia- or monocrotaline-induced PH. These results show that increased 5-HTT expression in PA-SMCs, to a level close to that found in human iPH, lead to PH in mice. They further support a central role for 5-HTT in the pathogenesis of PH, making 5-HTT a potential therapeutic target.

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.

Endothelial-derived FGF2 contributes to the progression of pulmonary hypertension in humans and rodents.

Pulmonary hypertension (PH) is a progressive, lethal lung disease characterized by pulmonary artery SMC (PA-SMC) hyperplasia leading to right-sided heart failure. Molecular events originating in pulmonary ECs (P-ECs) may contribute to the PA-SMC hyperplasia in PH. Thus, we exposed cultured human PA-SMC to medium conditioned by P-EC from patients with idiopathic PH (IPH) or controls and found that IPH P-EC-conditioned medium increased PA-SMC proliferation more than control P-EC medium. Levels of FGF2 were increased in the medium of IPH P-ECs over controls, while there was no detectable difference in TGF-beta1, PDGF-BB, or EGF levels. No difference in FGF2-induced proliferation or FGF receptor type 1 (FGFR1) mRNA levels was detected between IPH and control PA-SMCs. Knockdown of FGF2 in P-EC using siRNA reduced the PA-SMC growth-stimulating effects of IPH P-EC medium by 60% and control P-EC medium by 10%. In situ hybridization showed FGF2 overproduction predominantly in the remodeled vascular endothelium of lungs from patients with IPH. Repeated intravenous FGF2-siRNA administration abolished lung FGF2 production, both preventing and nearly reversing a rat model of PH. Similarly, pharmacological FGFR1 inhibition with SU5402 reversed established PH in the same model. Thus, endothelial FGF2 is overproduced in IPH and contributes to SMC hyperplasia in IPH, identifying FGF2 as a promising target for new treatments against PH.

Right Ventricular Diastolic Impairment in Patients With Pulmonary Arterial Hypertension

Background— The role of right ventricular (RV) diastolic stiffness in pulmonary arterial hypertension (PAH) is not well established. Therefore, we investigated the presence and possible underlying mechanisms of RV diastolic stiffness in PAH patients. Methods and Results— Single-beat RV pressure-volume analyses were performed in 21 PAH patients and 7 control subjects to study RV diastolic stiffness. Data are presented as mean±SEM. RV diastolic stiffness (&bgr;) was significantly increased in PAH patients (PAH, 0.050±0.005 versus control, 0.029±0.003; P<0.05) and was closely associated with disease severity. Subsequently, we searched for possible underlying mechanisms using RV tissue of PAH patients undergoing heart/lung transplantation and nonfailing donors. Histological analyses revealed increased cardiomyocyte cross-sectional areas (PAH, 453±31 &mgr;m2 versus control, 218±21 &mgr;m2; P<0.001), indicating RV hypertrophy. In addition, the amount of RV fibrosis was enhanced in PAH tissue (PAH, 9.6±0.7% versus control, 7.2±0.6%; P<0.01). To investigate the contribution of stiffening of the sarcomere (the contractile apparatus of RV cardiomyocytes) to RV diastolic stiffness, we isolated and membrane-permeabilized single RV cardiomyocytes. Passive tension at different sarcomere lengths was significantly higher in PAH patients compared with control subjects (>200%; Pinteraction<0.001), indicating stiffening of RV sarcomeres. An important regulator of sarcomeric stiffening is the sarcomeric protein titin. Therefore, we investigated titin isoform composition and phosphorylation. No alterations were observed in titin isoform composition (N2BA/N2B ratio: PAH, 0.78±0.07 versus control, 0.91±0.08), but titin phosphorylation in RV tissue of PAH patients was significantly reduced (PAH, 0.16±0.01 arbitrary units versus control, 0.20±0.01 arbitrary units; P<0.05). Conclusions— RV diastolic stiffness is significantly increased in PAH patients, with important contributions from increased collagen and intrinsic stiffening of the RV cardiomyocyte sarcomeres.