Interaction between PGI2 and ET-1 pathways in vascular smooth muscle from Group-III pulmonary hypertension patients.

Pulmonary hypertension (PH) is characterized by an elevation of mean pulmonary artery pressure and it is classified into five groups. Among these groups, PH Group-III is defined as PH due to lung disease or hypoxia. Prostacyclin (PGI2) analogues (iloprost, treprostinil) and endothelin-1 (ET-1) receptor antagonists (ERA) (used alone or in combination) are therapies used for treating PH. The mechanisms underlying the positive/negative effects of combination treatment are not well documented, and in this study, we tested the hypothesis that the combination of a PGI2 analogue (iloprost, treprostinil) and an ERA may be more effective than either drug alone to treat vasculopathies observed in PH Group-III patients. Using Western blotting, ETA and ETB receptor expression were determined in human pulmonary artery (HPA) preparations derived from control and PH Group-III patients, and the physiologic impact of altered expression ratios was assessed by measuring ET-1 induced contraction of ex vivo HPA and human pulmonary veins (HPV) in an isolated organ bath system. In addition, the effects of single agent or combination treatments with a PGI2 analogue and an ERA on ET-1 release and HPA smooth muscle cells (hPASMCs) proliferation were determined by ELISA and MTT techniques, respectively. Our results indicate that the increased ETA/ETB receptor expression ratio in HPA derived from PH Group-III patients is primarily governed by a greatly depressed ETB receptor expression. However, contractions induced by ET-1 are not impacted in HPA and HPV derived from PH Group-III patients as compared to controls. Also, we found that the combination of an ETA receptor antagonist (BQ123) with iloprost provides greater inhibition of hPASMCs proliferation (-48±14% control; -32±06% PH) than either agent alone. Of note, while the ETB receptor antagonist (BQ788) increases ET-1 production from PH Group-III patients' preparations (HPA, parenchyma), even under these more proliferative conditions, iloprost and treprostinil are still effective to inhibit hPASMCs proliferation (-22/-24%). Our findings may provide new insights for the treatment of PH Group-III by combining a PGI2 analogue and a selective ETA receptor antagonist.

Prostanoid EP2 Receptors Are Up-Regulated in Human Pulmonary Arterial Hypertension: A Key Anti-Proliferative Target for Treprostinil in Smooth Muscle Cells.

Prostacyclins are extensively used to treat pulmonary arterial hypertension (PAH), a life-threatening disease involving the progressive thickening of small pulmonary arteries. Although these agents are considered to act therapeutically via the prostanoid IP receptor, treprostinil is the only prostacyclin mimetic that potently binds to the prostanoid EP2 receptor, the role of which is unknown in PAH. We hypothesised that EP2 receptors contribute to the anti-proliferative effects of treprostinil in human pulmonary arterial smooth muscle cells (PASMCs), contrasting with selexipag, a non-prostanoid selective IP agonist. Human PASMCs from PAH patients were used to assess prostanoid receptor expression, cell proliferation, and cyclic adenosine monophosphate (cAMP) levels following the addition of agonists, antagonists or EP2 receptor small interfering RNAs (siRNAs). Immunohistochemical staining was performed in lung sections from control and PAH patients. We demonstrate using selective IP (RO1138452) and EP2 (PF-04418948) antagonists that the anti-proliferative actions of treprostinil depend largely on EP2 receptors rather than IP receptors, unlike MRE-269 (selexipag-active metabolite). Likewise, EP2 receptor knockdown selectively reduced the functional responses to treprostinil but not MRE-269. Furthermore, EP2 receptor levels were enhanced in human PASMCs and in lung sections from PAH patients compared to controls. Thus, EP2 receptors represent a novel therapeutic target for treprostinil, highlighting key pharmacological differences between prostacyclin mimetics used in PAH.

Ex vivo relaxations of pulmonary arteries induced by prostacyclin mimetics are highly dependent of the precontractile agents.

Prostacyclin (PGI2) mimetics (iloprost, treprostinil) are potent vasodilators (primarily via IP-receptor activation) and major therapeutic interventions for pulmonary hypertension (PH). Increased plasma levels of endothelin (ET-1), thromboxane (TxA2) and catecholamines have been demonstrated from patients with PH. In this study, we aimed to compare relaxant effects of iloprost and treprostinil on human (HPA) and rat pulmonary arteries precontracted with either ET-1, thromboxane (U46619) or an α-adrenergic receptor agonist (Norepinephrine, NE or phenylephrine, PE). Treprostinil and iloprost induced vasorelaxation of HPA precontracted with NE, ET-1 or U46619. We obtained greater relaxation response and sensitivity to treprostinil when ET-1 or U46619 were used to induce the precontraction in comparison to NE. In contrast, iloprost showed less relaxation response and sensitivity in HPA precontracted with U46619 versus NE. In the rat, treprostinil and iloprost induced vasorelaxation of pulmonary arteries precontracted with PE and U46619 but minimally with ET-1. However, in rat pulmonary arteries, PE-induced precontractions were comparatively low amplitude. Our study showed that the ex vivo relaxation or sensitivity of pulmonary arteries induced by PGI2 mimetics is highly dependent on both the pre-contraction agent and the species. To best extrapolate to effects on human tissue, our results suggest that U46619 is the appropriate contractile agent for assessing the relaxant effect of PGI2 mimetics in rat pulmonary arteries. Finally we suggest that in PH patients with high plasma concentration of TxA2, treprostinil (not iloprost) would be a preferential treatment. On the other hand, if the ET-1 plasmatic level is high, either treprostinil or iloprost will be effective.

Absence of inflammatory conditions in human varicose saphenous veins.

INTRODUCTION: Varicose veins affect one-third of the adult population in western countries, but their pathogenesis is incompletely characterized. One of the most controversial issues is the role of inflammation. It is well known that inflammation involves an increased expression/activity of inflammatory mediators. OBJECTIVE: The aim of this study was to investigate the presence or absence of mediators of inflammation in varicose as compared to healthy veins. METHODS AND RESULTS: Using immunohistofluorescence on varicose and healthy veins, we investigated the presence of inflammatory cells. They were not detectable. Venous wall C-reactive protein (CRP), fibrinogen (EIA) and pentraxin-3 (Western blot) content were measured. CRP was significantly lower in varicose veins, but no difference was found for fibrinogen or pentraxin-3 between varicose and healthy veins. No difference was observed for enzymes involved in inflammation and responsible for arachidonic acid metabolism such as the acute phase reactant secreted phospholipase A2-IIA and cyclooxygenase-2, as determined in varicose and healthy veins by Western blot and real-time qRT-PCR. CONCLUSIONS: Our experiments demonstrate no increase in the presence of mediators of inflammation in varicose as compared to healthy veins, suggesting that inflammation may not be an important contributor to the pathogenesis of varicose veins.

Control of human vascular tone by prostanoids derived from perivascular adipose tissue.

Perivascular adipose tissue (PVAT) surrounds most vessels and has now been recognized as a regulator of vascular functions. This effect of PVAT has been mostly demonstrated in vessels obtained from rats and mice. Thus, the aim of this study was to investigate anti-contractile effect of PVAT surrounding human coronary bypass grafts such as saphenous vein (SV) and internal mammary artery (IMA). Moreover, we aimed to determine the involvement of prostanoids in the anticontractile effect of PVAT. Human SV and IMA preparations were set up in an organ bath. The presence of PVAT in SV and IMA preparations significantly attenuated the contractile response to noradrenaline (NA). Preincubation with indomethacin, a cyclooxygenase inhibitor, increased NA contraction in SV preparations with PVAT. This effect was not observed in IMA preparation with PVAT incubated with indomethacin. The lower measurements of prostaglandin E2 (PGE2) released from PVAT surrounding IMA versus SV supported these effects. In conclusion, our results show that PVAT of SV could attenuate NA-induced contraction by releasing both PGE2 and prostacyclin (PGI2). In contrast to SV, PVAT of IMA exerts its anti-contractile effect independently from prostanoids. These observations suggest that retaining PVAT in human SV and IMA preparations may have potential clinical implications to improve coronary bypass graft patency.

A comparative study of PGI2 mimetics used clinically on the vasorelaxation of human pulmonary arteries and veins, role of the DP-receptor.

Prostacyclin (PGI2) and its mimetics (iloprost, treprostinil, beraprost and MRE-269) are potent vasodilators (via IP-receptor activation) and a major therapeutic intervention for pulmonary hypertension (PH). These PGI2 mimetics have anti-proliferative and potent vasodilator effects on pulmonary vessels. We compared the relaxant effects induced by these recognized IP-agonists in isolated human pulmonary arteries (HPA) and veins (HPV). In addition, using selective antagonists, the possible activation of other prostanoid relaxant receptors (DP, EP4) was investigated. Iloprost and treprostinil were the more potent relaxant agonists when both vessels were analyzed. HPA were significantly more sensitive to iloprost than to treprostinil, pEC50 values: 7.94±0.06 (n=23) and 6.73±0.08 (n=33), respectively. In contrast, in HPV these agonists were equipotent. The relaxations induced by treprostinil were completely or partially inhibited by IP-antagonists in HPA or HPV, respectively. The effects of the IP-agonists were not significantly modified by the EP4 antagonist. Finally, DP-antagonists inhibited the relaxations induced by treprostinil in HPV, suggesting that the DP-receptor plays a role in treprostinil-induced relaxation in the HPV. These data suggest that iloprost and treprostinil should be the most effective clinically available agonists to decrease pulmonary vascular resistance and to prevent oedema formation (by similar decrease in HPA and HPV resistance) in PH patients.

Downregulation of PGI2 pathway in Pulmonary Hypertension Group-III patients.

Pulmonary hypertension (PH) is a progressive and life-threating lung disorder characterized by elevated pulmonary artery pressure and vascular remodeling. PH is classified into five groups, and one of the most common and lethal forms, PH Group-III is defined as PH due to lung diseases and/or hypoxia. Due to the lack of studies in this group, PH-specific drug therapies including prostacyclin (PGI2) analogues have not been approved or recommended for use in these patients. PGI2 is synthesized by the PGI2 synthase (PGIS) enzyme, and its production is determined by measuring its stable metabolite, 6-keto-PGF1α. An impaired PGI2 pathway has been observed in PH animal models and in PH Group-I patients; however, there are contradictory results. The aim of this study is to determine whether PH Group-III is associated with altered expression of PGIS and production of PGI2 in humans. To explore this hypothesis, we measured PGIS expression (by western blot) and PGI2 production (by ELISA) in a large variety of preparations from the pulmonary circulation including human pulmonary artery, pulmonary vein, distal lung tissue, pulmonary artery smooth muscle cells (hPASMC), and bronchi in PH Group-III (n = 35) and control patients (n = 32). Our results showed decreased PGIS expression and/or 6-keto-PGF1α levels in human pulmonary artery, hPASMC, and distal lung tissue derived from PH Group-III patients. Moreover, the production of 6-keto-PGF1α from hPASMC positively correlated with PGIS expression and was inversely correlated with mean pulmonary artery pressure. On the other hand, PH Group-III pulmonary veins and bronchi did not show altered PGI2 production compared to controls. The deficit in PGIS expression and/or PGI2 production observed in pulmonary artery and distal lung tissue in PH Group-III patients may have important implications in the pathogenesis and treatment of PH Group-III.

Bronchodilation induced by PGE2 is impaired in Group III pulmonary hypertension.

BACKGROUND AND PURPOSE: In patients with pulmonary hypertension (PH) associated with lung disease and/or hypoxia (Group III), decreased pulmonary vascular tone and tissue hypoxia is therapeutically beneficial. PGE2 and PGI2 induce potent relaxation of human bronchi from non-PH (control) patients via EP4 and IP receptors, respectively. However, the effects of PGE2 /PGI2 and their mimetics on human bronchi from PH patients are unknown. Here, we have compared relaxant effects of several PGI2 -mimetics approved for treating PH Group I with several PGE2 -mimetics, in bronchial preparations derived from PH Group III and control patients. EXPERIMENTAL APPROACH: Relaxation of bronchial muscle was assessed in samples isolated from control and PH Group III patients. Expression of prostanoid receptors was analysed by western blot and real-time PCR, and endogenous PGE2 , PGI2 , and cAMP levels were determined by ELISA. KEY RESULTS: Maximal relaxations induced by different EP4 receptor agonists (PGE2 , L-902688, and ONO-AE1-329) were decreased in human bronchi from PH patients, compared with controls. However, maximal relaxations produced by PGI2 -mimetics (iloprost, treprostinil, and beraprost) were similar for both groups of patients. Both EP4 and IP receptor protein and mRNA expressions were significantly lower in human bronchi from PH patients. cAMP levels significantly correlated with PGI2 but not with PGE2 levels. CONCLUSION AND IMPLICATIONS: The PGI2 -mimetics retained maximal bronchodilation in PH Group III patients, whereas bronchodilation induced by EP4 receptor agonists was decreased. Restoration of EP4 receptor expression in airways of PH Group III patients with respiratory diseases could bring additional therapeutic benefit.

Reverse Regulatory Pathway (H2S / PGE2 / MMP) in Human Aortic Aneurysm and Saphenous Vein Varicosity.

Hydrogen sulfide (H2S) is a mediator with demonstrated protective effects for the cardiovascular system. On the other hand, prostaglandin (PG)E2 is involved in vascular wall remodeling by regulating matrix metalloproteinase (MMP) activities. We tested the hypothesis that endogenous H2S may modulate PGE2, MMP-1 activity and endogenous tissue inhibitors of MMPs (TIMP-1/-2). This regulatory pathway could be involved in thinning of abdominal aortic aneurysm (AAA) and thickening of saphenous vein (SV) varicosities. The expression of the enzyme responsible for H2S synthesis, cystathionine-γ-lyase (CSE) and its activity, were significantly higher in varicose vein as compared to SV. On the contrary, the endogenous H2S level and CSE expression were lower in AAA as compared to healthy aorta (HA). Endogenous H2S was responsible for inhibition of PGE2 synthesis mostly in varicose veins and HA. A similar effect was observed with exogenous H2S and consequently decreasing active MMP-1/TIMP ratios in SV and varicose veins. In contrast, in AAA, higher levels of PGE2 and active MMP-1/TIMP ratios were found versus HA. These findings suggest that differences in H2S content in AAA and varicose veins modulate endogenous PGE2 production and consequently the MMP/TIMP ratio. This mechanism may be crucial in vascular wall remodeling observed in different vascular pathologies (aneurysm, varicosities, atherosclerosis and pulmonary hypertension).

Decreased PGE2 content reduces MMP-1 activity and consequently increases collagen density in human varicose vein.

UNLABELLED: Varicose veins are elongated and dilated saphenous veins. Despite the high prevalence of this disease, its pathogenesis remains unclear. AIMS: In this study, we investigated the control of matrix metalloproteinases (MMPs) expression by prostaglandin (PG)E2 during the vascular wall remodeling of human varicose veins. METHODS AND RESULTS: Varicose (small (SDv) and large diameter (LDv)) and healthy saphenous veins (SV) were obtained after surgery. Microsomal and cytosolic PGE-synthases (mPGES and cPGES) protein and mRNA responsible for PGE2 metabolism were analyzed in all veins. cPGES protein was absent while its mRNA was weakly expressed. mPGES-2 expression was similar in the different saphenous veins. mPGES-1 mRNA and protein were detected in healthy veins and a significant decrease was found in LDv. Additionally, 15-hydroxyprostaglandin dehydrogenase (15-PGDH), responsible for PGE2 degradation, was over-expressed in varicose veins. These variations in mPGES-1 and 15-PGDH density account for the decreased PGE2 level observed in varicose veins. Furthermore, a significant decrease in PGE2 receptor (EP4) levels was also found in SDv and LDv. Active MMP-1 and total MMP-2 concentrations were significantly decreased in varicose veins while the tissue inhibitors of metalloproteinases (TIMP -1 and -2), were significantly increased, probably explaining the increased collagen content found in LDv. Finally, the MMP/TIMP ratio is restored by exogenous PGE2 in varicose veins and reduced in presence of an EP4 receptor antagonist in healthy veins. CONCLUSIONS: In conclusion, PGE2 could be responsible for the vascular wall thickening in human varicose veins. This mechanism could be protective, strengthening the vascular wall in order to counteract venous stasis.

Prostaglandin E2 receptor subtypes in human blood and vascular cells.

Prostaglandin E(2) is produced in inflammatory responses via the cyclooxygenase pathway and regulates a variety of physiological and pathological reactions through four different receptor subtypes; EP(1), EP(2), EP(3) and EP(4). The role of the classical prostanoid receptors stimulated by prostaglandin I(2) and thromboxane A(2) in the blood circulation has been largely studied, whereas the other receptors such as EP activated by prostaglandin E(2), have been recently shown to be also implicated. There is now increasing evidence suggesting an important role of EP(3) and EP(4) receptor subtypes in the control of the human vascular tone and remodeling of the vascular wall as well in platelet aggregation and thrombosis. These receptors are implicated in vascular homeostasis and in the development of some pathological situations, such as atherosclerosis, aneurysms and hypertension. The use of specific EP agonists/antagonists would provide a novel cardiovascular therapeutic approach. In this review, we discuss the role of prostaglandin E(2) receptors in the control of human blood and vascular cells.