Idiopathic Pulmonary Arterial Hypertension Clinical Trial
Official title:
Physiopathology of Pulmonary Arterial Hypertension: Mechanistic Studies
The current aims to combine analysis of different inflammatory biomarkers and BMPR2 mutations, which are currently analyzed in each patient diagnosed with idiopathic or familial PAH, to establish an earlier diagnosis and consequently better orientate the therapeutic strategy in PAH.
BACKGROUND
Pulmonary hypertension is a severe disorder defined by an elevated mean pulmonary arterial
pressure (mPAP) as >25 mmHg at rest. A classification of the different types of pulmonary
hypertension has been established according to shared pathologic and clinical features as
well as similar therapeutic options and recently updated. Five major categories have been
defined including 1) pulmonary arterial hypertension (PAH), 2) PH owing to left heart
diseases, 3) PH owing to lung diseases and/or hypoxia, 4) chronic thromboembolic PH (CTEPH)
and 5) PH with unclear multifactorial mechanisms.
PAH commonly defined by an elevated PAP (>25 mmHg at rest) and a normal pulmonary arterial
wedge pressure (<15 mmHg), is characterized by a pre-capillary arteriopathy with the
presence of vascular remodeling and formation of plexiform lesions, an increased pulmonary
vascular resistance (PVR), which may result in right heart failure. PAH may be idiopathic
(IPAH), heritable (HPAH) or associated with drug/toxin exposure or other medical conditions
including connective tissue diseases, congenital heart diseases, human immunodeficiency
virus or portal hypertension. Familial cases were already reported in the early fifties and,
in 2000, bone morphogenic protein receptor type 2 gene (BMPR2) was identified as the gene
responsible for more than 70% of HPAH and about 20% of IPAH. BMPR2 belongs to a superfamily
of growth factor receptors, including bone morphogenic protein (BMPs) and transforming
growth factor beta (TGF-β) and consequently controls cellular functions such as
proliferation, migration, differentiation or apoptosis. BMPR2 mutations may favor activation
of p38MAPK-dependent pro-proliferative pathways, which is also ; a key player in
cytokine-induced inflammatory signaling pathways. Although BMPR2 mutation carriers develop
PAH 10 years earlier than non-carriers and display more severe hemodynamic changes, only 20%
of BMPR2 mutation carriers will further develop PAH. A role of inflammation in the
pathogenesis of PAH has been suggested. A predictive role of various cytokines has been
recently evidenced in PAH. The investigators have observed elevated C-reactive protein (CRP)
circulating levels in PAH and evidenced a predictive role of CRP in PAH. Interestingly,
heterozygous null BMPR2 mice failed to develop PAH unless an additional inflammatory insult
was applied. More recently, inhibition of leukocyte recruitment has been shown to impair PAH
progression in mice with genetic ablation of endothelial BMPR-II. This consequently suggests
that inflammation could play the role of a second hit in BMPR2 mutation carriers to further
develop PAH.
Besides, lipoprotein-associated phospholipase A2 (Lp-PLA2) also named plasma
platelet-activating factor-acetylhydrolase (PAF-AH), is the product of PLA2G7 gene and is an
enzyme capable of inactivating platelet-activating factor (PAF), a potent lipid mediator of
inflammation and a potent vasoconstrictor, and its analogs. Several studies have evidenced
an increase in PAF-AH mass and activity in hypercholesterolemia and coronary heart disease.
In a recent meta-analysis including more than 70,000 patients from 32 epidemiologic studies,
high circulating PAF-AH levels have been identified as an independent predictive risk factor
for cardiovascular events. When over-expressed in rodents, Lp-PLA2 displayed
anti-inflammatory properties and reduced atherogenesis, suggesting a potential
anti-inflammatory role of Lp-PLA2. Lp-PLA2 polymorphisms have been identified and Lp-PLA2
activity has been strongly associated with genetic variants related to LDL- cholesterol
levels. In a preliminary study, the investigators have observed a diminished Lp-PLA2
activity in the plasma of PAH patients, together with low total and LDL-cholesterol levels.
HYPOTHESIS & OBJECTIVES
Regarding previous and current results by the investigators, they hypothesized that
combining analysis of different inflammatory biomarkers and BMPR2 mutations, which are
currently analyzed in each patient diagnosed with idiopathic or familial PAH, could
contribute to establish an earlier diagnosis and consequently better orientate the
therapeutic strategy. Moreover, BMPR2 gene mutations are responsible for more than 70% of
HPAH and about 20% of IPAH; among human BMPR2 mutation carriers, only 20% will further
develop PAH, suggesting that BMPR2 mutation itself is not the unique cause for developing
PAH and that a second hit, such as inflammation, would be required and play a triggering
role in the development of PAH.
METHODOLOGY
1. Identification of biomarkers
For the current study, one aim is to identify one or several biomarkers which could
predict adverse outcome in PAH. To address this aim, the investigators would like to
evaluate the levels of CRP, total cholesterol, HDL-cholesterol, triglycerides, albumin,
Lp-PLA2 activity, Thrombin Activatable Fibrinolysis Inhibitor (TAFI) and vitamin D in
blood plasma from all patients diagnosed with PAH at the UZ Leuven (Campus
Gasthuisberg).
To perform these analyses, the investigators would need 5 tubes of blood:
- one on EDTA to be sent to the Hospital Laboratory (CRP, lipid profile and
albumin);
- one on citrate to further measure TAFI (Laboratory of Pharmaceutical Biology, KU
Leuven);
- one on EDTA to prepare plasma to be further stored in the laboratory of Pneumology
(KU Leuven), from which an aliquot will be sent to INSERM UMRS937 (Paris, France),
to measure Lp-PLA2 activity;
- one on EDTA is sent to the CME genomic DNA isolation to study BMPR2, ALK-1 and ENG
mutations; genomic DNA will be stored for potential future genetic;
- one with Silica Clot Activator to be sent to the Hospital Laboratory (vitamin D).
2. Human pulmonary arterial cell isolation
Another aim is to investigate whether a relationship between impaired BMPR2 signaling
and inflammation could result in dysfunction of pulmonary arterial cells in PAH. To
achieve our objective, the investigators propose to investigate:
i. the in vitro effects of inflammatory mediators and macrophages on the activation of
human pre-capillary pulmonary arterial endothelial cell (PAEC) and on the proliferating
and migrating properties of PASMC from BMPR2 carriers and non-carriers PAH patients;
ii. expression and distribution of inflammatory mediators, their receptors and BMPR2 in
human lung parenchyma and distal pulmonary arteries;
iii. the ex-vivo vasoreactive effects of inflammatory mediators mentioned above on
isolated human pre-capillary pulmonary arteries.
iv. Moreover, pulmonary arterial endothelial cells will be harvested from patients
undergoing right heart catheterization using a recently described technique, consisting
in isolating endothelial cells from the balloon of a Swan-Ganz catheter commonly used
to performed right heart catheterization in patients.
3. Pulmonary tissue collection
Lung parenchyma will be collected from i) PAH patients at the time of lung transplantation,
ii) eventually unused donor lungs and iii) tissue surrounding lung tumour resection from
patients without COPD. Pulmonary pre-capillary endothelial and smooth muscle cells will be
isolated, maintained in culture and further stored at low passage number in liquid nitrogen.
Two pieces of lung parenchyma will be snap frozen for further RNA isolation and protein
extraction; one piece will be fixed in paraformaldehyde and further processed for
immunohistochemistry analyses.
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