Relaxation Of Pulmonary Arteries Research Articles

Differential expression of the enzymes regulating myosin light chain phosphorylation are responsible for the slower relaxation of pulmonary artery than mesenteric artery in rats.

While arterial tone is generally determined by the phosphorylation of Ser19 in myosin light chain (p-MLC2), Thr18/Ser19 diphosphorylation of MLC2 (pp-MLC2) has been suggested to hinder the relaxation of smooth muscle. In a dual-wire myography of rodent pulmonary artery (PA) and mesenteric artery (MA), we noticed significantly slower relaxation in PA than in MA after 80 mM KCl-induced condition (80K-contraction). Thus, we investigated the MLC2 phosphorylation and the expression levels of its regulatory enzymes; soluble guanylate cyclase (sGC), Rho-A dependent kinase (ROCK) and myosin light chain phosphatase target regulatory subunit (MYPT1). Immunoblotting showed higher sGC-α and ROCK2 in PA than MA, while sGC-β and MYPT1 levels were higher in MA than in PA. Interestingly, the level of pp-MLC2 was higher in PA than in MA without stimulation. In the 80K-contraction state, the levels of p-MLC2 and pp-MLC2 were commonly increased. Treatment with the ROCK inhibitor (Y27632, 10 μM) reversed the higher pp-MLC2 in PA. In the myography study, pharmacological inhibition of sGC (ODQ, 10 μM) slowed relaxation during washout, which was more pronounced in PA than in MA. The simultaneous treatment of Y27632 and ODQ reversed the impaired relaxation in PA and MA. Although treatment of PA with Y27632 alone could increase the rate of relaxation, it was still slower than that of MA without Y27632 treatment. Taken together, we suggest that the higher ROCK and lower MYPT in PA would have induced the higher level of MLC2 phosphorylation, which is responsible for the characteristic slow relaxation in PA.

Pulmonary hypertension associated with diazoxide: the SUR1 paradox.

The ATP-sensitive potassium channels and their regulatory subunits, sulfonylurea receptor 1 (SUR1/Kir6.2) and SUR2/Kir6.1, contribute to the pathophysiology of pulmonary hypertension (PH). Loss-of-function pathogenic variants in the ABCC8 gene, which encodes for SUR1, have been associated with heritable pulmonary arterial hypertension. Conversely, activation of SUR1 and SUR2 leads to the relaxation of pulmonary arteries and reduces cell proliferation and migration. Diazoxide, a SUR1 activator, has been shown to alleviate experimental PH, suggesting its potential as a therapeutic option. However, there are paradoxical reports of diazoxide-induced PH in infants. This review explores the role of SUR1/2 in the pathophysiology of PH and the contradictory effects of diazoxide on the pulmonary vascular bed. Additionally, we conducted a comprehensive literature review of cases of diazoxide-associated PH and analysed data from the World Health Organization pharmacovigilance database (VigiBase). Significant disproportionality signals link diazoxide to PH, while no other SUR activators have been connected with pulmonary vascular disease. Diazoxide-associated PH seems to be dose-dependent and potentially related to acute effects on the pulmonary vascular bed. Further research is required to decipher the differing pulmonary vascular consequences of diazoxide in different age populations and experimental models.

T18/S19 diphosphorylation of myosin regulatory light chain impairs pulmonary artery relaxation in monocrotaline-induced pulmonary hypertensive rats.

Phosphorylation of Ser19 (S19-p) on the myosin regulatory light chain (MLC2) is critical for arterial contraction. It has been shown that elevated RhoA-dependent kinase (ROCK) activity or decreased MLC phosphatase (MLCP) activity leads to further phosphorylation of Thr18 (T18/S19-pp), which has been linked to vasospastic diseases. However, this phenomenon has not yet been studied in the context of pulmonary arterial hypertension (PAH). In the monocrotaline-induced PAH (PAH-MCT) rat model, we observed a significant delay in pulmonary artery (PA) relaxation following high potassium-induced contraction, which persisted even with the use of an L-type calcium channel blocker or in a calcium-free solution. Immunoblot analysis showed increased levels of both S19-p and T18/S19-pp in unstimulated PAs from PAH-MCT rats. Proteomics analysis revealed a reduction in soluble guanylate cyclase (sGC) and protein kinase G (PKG) levels, and immunoblotting confirmed decreased levels of MYPT1 (a component of MLCP) and increased ROCK in PAH-MCT. In the control PAs, the pharmacological inhibition of sGC with ODQ resulted in a prominent delay of relaxation and increased T18/S19-pp as in PAH-MCT. The delayed relaxation and the T18/S19-pp in PAH-MCT were reversed by ROCK inhibitor, Y27632, while not by membrane permeable 8-Br-cGMP. The delayed relaxation and T18/S19-diP in the ODQ-treated control PA were also reversed by Y27632. Taken together, the decreased sGC and MLCP, and increased ROCK increased T18/S19-pp, which leads to the decreased ability of PA to relax in PAH-MCT rats. PA specific inhibition of ROCK or activation of MLCP are expected to serve as potential drugs in the treatment of PAH.

Phosphodiesterase type 9 opposes relaxation of mouse pulmonary artery but does not influence chronic hypoxia-induced pulmonary hypertension in mouse

PDE9 is a phosphodiesterase which has recently emerged as a regulator of cGMP in cardiac and vascular myocytes. Its contribution in vasculature is, however, unclear. We sought to investigate PDE9 expression and function in mouse pulmonary artery by comparing wild type (WT) and PDE9-deficient, Pde9a(-/-), mice. We also addressed the hypothesis that PDE9 could represent a new therapeutic target to treat pulmonary arterial hypertension, a severe, deadly disease. PDE9 expression was examined in mouse tissues and human pulmonary artery from subjects with or without pulmonary arterial hypertension using RT-PCR and immunoblots. Relaxant responses were studied in mouse pulmonary arteries mounted on a myograph and contracted with phenylephrine. A challenge with 21-day, 10% O2-hypoxia was used as a model of pulmonary hypertension in mice and was compared to normoxia. Right ventricle and pulmonary artery morphology and function were determined by echocardiography, right ventricle catheterization and gravimetric analysis. PDE9 protein and Pde9a transcript were detected in human and mouse pulmonary arteries, respectively. Pulmonary arteries from Pde9a(-/-) mice displayed more potent relaxant responses to acetylcholine, to the NO donor diethylamine NONOate and to atrial natriuretic peptide than vessels from WT animals. Following hypoxia, Pde9a expression was increased in lung and right ventricle from WT mice. PDE9 deficiency failed to ameliorate pulmonary hypertension hemodynamic criteria, namely higher right ventricular systolic pressure and lower echocardiographic pulmonary arterial acceleration time. Right ventricle hypertrophy, reflected by increased Fulton index, right ventricle thickness and fetal genes expression, were also similar in Pde9a(-/-) and WT groups. PDE9 is expressed in pulmonary artery and takes part in the relaxant responses mediated by the cGMP pathway. The ablation of Pde9a in mouse, however, does not prevent the development of pulmonary hypertension in a 21-day hypoxia model, nor does it attenuate right ventricle deleterious remodeling.

Effects of a Soluble Guanylate Cyclase Stimulator Riociguat on Contractility of Isolated Pulmonary Artery and Hemodynamics of U46619-Induced Pulmonary Hypertension in Dogs

Soluble guanylate cyclase (sGC) stimulator riociguat is a relatively novel therapeutic agent for pulmonary hypertension (PH) in human medicine. Riociguat induces endothelium-independent pulmonary artery (PA) relaxation by directly activating the sGC-cyclic guanosine-3',5'-monophosphate (cGMP) pathway in muscle cells. Although riociguat may be effective in the treatment of dogs with refractory PH, basic studies on its clinical application in veterinary medicine are lacking. The present study aimed to explore the effects of riociguat on the contractility of an isolated canine PA and the hemodynamics of dogs with acute PH. In an isolated endothelium-denuded canine PA, the effects of riociguat on endothelin (ET)-1-induced contraction and cGMP levels were investigated using the Magnus method and ELISA, respectively. The effect of riociguat on the hemodynamics of the thromboxane A2 analog U46619-induced PH model dog was examined by invasive catheterization. Riociguat increased cGMP levels and reduced ET-1-induced contraction of the isolated PA. Riociguat inhibited the U46619-induced elevation of PA pressure and pulmonary vascular resistance and increased cardiac output, but it had no effect on basal systemic blood pressure. These results demonstrate for the first time that riociguat can inhibit the elevation of PA pressure through PA relaxation via an endothelium-independent increase in cGMP in dogs with PH.

Abstract 10523: Involvement of Sur2/Kir6.1 In the Physiopathology of Pulmonary Arterial Hypertension

Introduction: The ATP-sensitive K+ channels (KATP) regulatory subunit ABCC8 may be considered a new therapeutic target for pulmonary arterial hypertension (PAH). Hypothesis: We hypothesised that the second KATP regulatory subunit (ABCC9) contributes to PAH pathogenesis. ABCC9 gene encodes for two regulatory subunits of KATP channels: the SUR2A and SURB proteins. In the KATP channel, the SUR2 subunits are associated with the K+ channel Kir6.1. We investigated how the SUR2/Kir6.1 channel contributes to PAH pathogenesis and its potential as a therapeutic target against PAH. Methods: Using in vitro, ex vivo, and in vivo approaches, we analysed the localisation and expression of SUR2A, SUR2B, and Kir6.1 in pulmonary vasculature of controls and patients with PAH as in experimental PH rat models and its contribution to PAH physiopathology. Finally, we deciphered the consequences of in vivo activation of SUR2/Kir6.1 in the monocrotaline (MCT)-induced PH model. Results: We demonstrated that SUR2A, SUR2B, and Kir6.1 were expressed in the lungs of controls and patients with PAH and MCT-induced PH rat model. Myograph experiments showed that activation of SUR2 by pinacidil induced pulmonary arterial relaxation. In vitro experiments on human pulmonary arterial smooth muscle cells and endothelial cells (hPASMCs and hPAECs) in controls and PAH patients showed decreased cell proliferation and migration after SUR2 activation. Using patch-clamp, we demonstrated that SUR2 activation in rat right ventricular (RV) cardiomyocytes reduced RV action potential duration. Chronic pinacidil administration in control rats increased heart rate without changes in hemodynamic parameters. Finally, in vivo pharmacological activation of SUR2 on MCT-induced-PH rats showed an improvement of PH during the preventive and curative protocol. Conclusions: We demonstrated that SUR2A, SUR2B, and Kir6.1 were expressed in hPASMCs and hPAECs of controls and PAH patients. In vivo SUR2 activation reduced MCT-induced PH phenotype, suggesting that SUR2 activation should be considered for treatment of PAH.

Salusin-β, a TOR2A gene product, promotes proliferation, migration, fibrosis, and calcification of smooth muscle cells and accelerates the imbalance of vasomotor function and vascular remodeling in monocrotaline-induced pulmonary hypertensive rats.

Purpose: The hyper-proliferation, promoted migration, fibrosis, and calcification of pulmonary arterial smooth muscle cells (PASMCs) play critical roles in pulmonary artery (PA) continuous contraction and vascular remodeling, leading to elevated pulmonary arterial resistance and pulmonary hypertension (PH). In this study, we sought to ascertain the effects of a TOR2A gene product, salusin-β, on PASMCs’ proliferation, migration, fibrosis, calcification, and the imbalance of vasomotor function as well as pulmonary vascular remodeling in monocrotaline (MCT)-induced PH rats and their underlying mechanisms. Methods: Knockdown or overexpression of salusin-β in rats or PASMCs was performed through tail vein injection or cell transfection of virus. The right ventricular systolic pressure (RVSP) of the rat was measured by right ventricle catheterization. Sodium nitroprusside (SNP) or acetylcholine (ACh)-induced dose-dependent relaxation was used to evaluate the vasodilatation function. Primary PASMCs were isolated from the PAs of control and PH rats. Results: The salusin-β protein expressions were significantly increased in PAs and PASMCs isolated from PH rats compared with control rats. Knockdown of salusin-β in rats decreased high K+ solution-induced contraction, RVSP and RV hypertrophy index, improved SNP or ACh-induced vascular relaxation of PAs, and relieved vascular remodeling and calcification of PAs from PH rats. Silencing salusin-β in PASMCs isolated from PH rats alleviated the proliferation, migration, fibrosis, and calcification, as well as the NAD(P)H oxidase activity and reactive oxygen species (ROS) level. Overexpression of salusin-β exerted the opposite effects on vasomotor function and vascular remodeling, and PASMCs proliferation, migration, fibrosis and calcification. Conclusion: Increased salusin-β activity in PAs from PH rats contributes to PASMCs proliferation, migration, fibrosis, and calcification, leading to the imbalance of vascular contraction and relaxation and vascular remodeling through stimulating the production of NAD(P)H oxidase derived ROS.

Abstract P2024: Novel Inhibitor Of P38 Mitogen-activated Protein Kinase Reverses Hypoxia-induced Pulmonary Hypertension In Rats

Pulmonary arterial hypertension (PAH) is a disease characterized by pulmonary vascular changes with subsequent right ventricular (RV) failure. This work investigated the hypothesis that a new p38-alpha mitogen-activated protein kinase (p38-alpha MAPK) inhibitor, named LASSBio-1824, could interfere on PH model in rats. Methods: HP was induced in male Wistar rats through the exposure to hypoxia (10% O2) during 3 weeks, in combination to i.p. injection of an antagonist of vascular endothelial growth factor receptor (SU5416; 20 mg/kg/weekly). Control rats were kept in normoxia. After 3 weeks, echocardiography images confirmed PH using the pulmonary artery (PA) outflow waveform. After disease onset, animals were randomly divided into three groups: control + vehicle (DMSO), PH + vehicle and PH + LASSBio-1824 (50 mg/kg/day), in which vehicle and LASSBio-1824 were orally administered (gavage) during two weeks. All experiments were in accordance with the Animal Care and Use Committee at Federal University of Rio de Janeiro (039/19). Results: Pulmonary acceleration time (PAT; ms) was reduced from 40.0 ± 2.1 (control) to 24.2 ± 1.8 in PH + vehicle group (p < 0.05) and restored to 36.8 ± 2.9 after treatment with LASSBio-1824 (p < 0.05). RV afterload was detected in PH group because of the increase of systolic pressure (mmHg) from 23.2 ± 1.5 (control) to 46.7 ± 2.8 (p < 0.05) which was reduced to 19.4 ± 2.7 with LASSBio1824 treatment. Medial wall thickness (%) of distal pulmonary arteries (PA, < 50 μm) was evaluated by using immunohistochemistry for alpha smooth muscle actin (alpha-SMA) which was increased from 64.0 ± 4.9 (control) to 80.8 ± 2.7 in PH group (p < 0.05), but it was significantly reduced to 55.0 ± 1.3 after treatment with the inhibitor (p < 0.05). Acetylcholine (ACh)-induced maximal relaxation (%) of PA from normal and PH rats, was reduced from 67.5 ± 1.6 to 51.9 ± 4.9 (p < 0.05). Therefore, the treatment with the p38 inhibitor normalized vascular reactivity to 73.0 ± 3.3 %. The immunohistochemistry for c-fos protein, a product of the p38 pathway related to cell proliferation, showed an increase of stained myocyte nuclei (%) in PH animals of 36.5 ± 1.5 when compared to normal group of 20.2 ± 4.2. The inhibitor significantly reduced ratio to 24.0 ± 2.3% (p < 0.05). PH increased the inflammatory condition because the expression of inducible nitric oxide synthase altered from 10.4 ± 1.9% (control) to 31.9 ± 2.2% and it was recovered by the inhibitor to 15.5 ± 2.2% (p < 0.05). In conclusion, the new p38-alpha MAPK inhibitor represents an important approach for the future treatment of PH, since it improves the underlying remodeling and inflammation processes.

Artemisinin and Its Derivate Alleviate Pulmonary Hypertension and Vasoconstriction in Rodent Models.

Background Pulmonary arterial hypertension (PAH) is a complex pulmonary vasculature disease characterized by progressive obliteration of small pulmonary arteries and persistent increase in pulmonary vascular resistance, resulting in right heart failure and death if left untreated. Artemisinin (ARS) and its derivatives, which are common antimalarial drugs, have been found to possess a broad range of biological effects. Here, we sought to determine the therapeutic benefit and mechanism of ARS and its derivatives treatment in experimental pulmonary hypertension (PH) models. Methods Isolated perfused/ventilated lung and isometric tension measurements in arteries were performed to test pulmonary vasoconstriction and relaxation. Monocrotaline (MCT) and hypoxia+Su5416 (SuHx) were administered to rats to induce severe PH. Evaluation methods of ARS treatment and its derivatives in animal models include echocardiography, hemodynamics measurement, and histological staining. In vitro, the effect of these drugs on proliferation, viability, and hypoxia-inducible factor 1α (HIF1α) was examined in human pulmonary arterial smooth muscle cells (hPASMCs). Results ARS treatment attenuated pulmonary vasoconstriction induced by high K+ solution or alveolar hypoxia, decreased pulmonary artery (PA) basal vascular tension, improved acetylcholine- (ACh-) induced endothelial-dependent relaxation, increased endothelial nitric oxide (NO) synthase (eNOS) activity and NO levels, and decreased levels of NAD(P)H oxidase subunits (NOX2 and NOX4) expression, NAD(P)H oxidase activity, and reactive oxygen species (ROS) levels of pulmonary arteries (PAs) in MCT-PH rats. NOS inhibitor, L-NAME, abrogated the effects of ARS on PA constriction and relaxation. Furthermore, chronic application of both ARS and its derivative dihydroartemisinin (DHA) attenuated right ventricular systolic pressure (RVSP), Fulton index (right ventricular hypertrophy), and vascular remodeling of PAs in the two rat PH models. In addition, DHA inhibited proliferation and migration of hypoxia-induced PASMCs. Conclusions In conclusion, these results indicate that treatment with ARS or DHA can inhibit PA vasoconstriction, PASMC proliferation and migration, and vascular remodeling, as well as improve PA endothelium-dependent relaxation, and eventually attenuate the development and progression of PH. These effects might be achieved by decreasing NAD(P)H oxidase generated ROS production and increasing eNOS activation to release NO in PAs. ARS and its derivatives might have the potential to be novel drugs for the treatment of PH.

T18/S19 diphosphorylation of myosin regulatory Light Chain is Responsible for the impaired relaxation of pulmonary arteries in pulmonary hypertensive rats

Pulmonary arteries (PA) are exposed to hemodynamic environment and contractile stimuli different from those of systemic arteries. Previous studies reported that in situapplication of sodium nitroprusside (SNP, NO donor) lowered the PA pressure, which was less prominent than the response of systemic arteries. Here, we investigated the relaxation speed and the in vitro effects of NO‐dependent signaling modulators to compare between isolated PA and mesenteric arteries (MA) of rats. In the dual‐wire myography study, PA showed significantly slower relaxation after the response to 80 mM KCl (80K) or to pharmacological agonists (U46619 and PGF2a). Surprisingly, addition of 30 mM SNP could not prevent the 80K contraction in PA while significantly attenuated the contraction of MA. The pretreatment with soluble guanylate cyclase (sGC) inhibitor (ODQ, 10 mM) markedly further slowed the relaxation of PA after 80K or agonist‐induced contraction. Perplexingly, immunoblot assay revealed higher expression of sGC‐a with similar level of sGC‐b1 in PA than MA. The expression of RhoA‐kinase (ROCK) was higher while myosin light chain phosphatase (MYPT) appeared lower in PA than MA. The treatment with ROCK inhibitor (Y27632, 10 mM) could abolish the different of relaxation response between PA and MA. Taken together, we speculate that despite the higher expression and the functional importance of NO/sGC pathway in PA, the higher level of ROCK and relatively low MYPT in PA are responsible for the characteristic slow relaxation after removal of stimuli.

Role of Rho‐associated kinase (ROCK) in the different speed of relaxation between pulmonary arteries and mesentery arteries of rats

Pulmonary arteries (PA) are exposed to hemodynamic environment and contractile stimuli different from those of systemic arteries. Previous studies reported that in situapplication of sodium nitroprusside (SNP, NO donor) lowered the PA pressure, which was less prominent than the response of systemic arteries. Here, we investigated the relaxation speed and the in vitro effects of NO‐dependent signaling modulators to compare between isolated PA and mesenteric arteries (MA) of rats. In the dual‐wire myography study, PA showed significantly slower relaxation after the response to 80 mM KCl (80K) or to pharmacological agonists (U46619 and PGF2a). Surprisingly, addition of 30 μM SNP could not prevent the 80K contraction in PA while significantly attenuated the contraction of MA. The pretreatment with soluble guanylate cyclase (sGC) inhibitor (ODQ, 10 μM) markedly further slowed the relaxation of PA after 80K or agonist‐induced contraction. Perplexingly, immunoblot assay revealed higher expression of sGC‐a with similar level of sGC‐b1 in PA than MA. The expression of RhoA‐kinase (ROCK) was higher while myosin light chain phosphatase (MYPT) appeared lower in PA than MA. The treatment with ROCK inhibitor (Y27632, 10 μM) could abolish the different of relaxation response between PA and MA. Taken together, we speculate that despite the higher expression and the functional importance of NO/sGC pathway in PA, the higher level of ROCK and relatively low MYPT in PA are responsible for the characteristic slow relaxation after removal of stimuli.

Kv7 Channels in Cyclic-Nucleotide Dependent Relaxation of Rat Intra-Pulmonary Artery.

Pulmonary hypertension is treated with drugs that stimulate cGMP or cAMP signalling. Both nucleotides can activate Kv7 channels, leading to smooth muscle hyperpolarisation, reduced Ca2+ influx and relaxation. Kv7 activation by cGMP contributes to the pulmonary vasodilator action of nitric oxide, but its contribution when dilation is evoked by the atrial natriuretic peptide (ANP) sensitive guanylate cyclase, or cAMP, is unknown. Small vessel myography was used to investigate the ability of Kv7 channel blockers to interfere with pulmonary artery relaxation when cyclic nucleotide pathways were stimulated in different ways. The pan-Kv7 blockers, linopirdine and XE991, caused substantial inhibition of relaxation evoked by NO donors and ANP, as well as endothelium-dependent dilators, the guanylate cyclase stimulator, riociguat, and the phosphodiesterase-5 inhibitor, sildenafil. Maximum relaxation was reduced without a change in sensitivity. The blockers had relatively little effect on cAMP-mediated relaxation evoked by forskolin, isoprenaline or treprostinil. The Kv7.1-selective blocker, HMR1556, had no effect on cGMP or cAMP-dependent relaxation. Western blot analysis demonstrated the presence of Kv7.1 and Kv7.4 proteins, while selective activators of Kv7.1 and Kv7.4 homomeric channels, but not Kv7.5, caused pulmonary artery relaxation. It is concluded that Kv7.4 channels contribute to endothelium-dependent dilation and the effects of drugs that act by stimulating cGMP, but not cAMP, signalling.

SUR1 As a New Therapeutic Target for Pulmonary Arterial Hypertension.

Mutations in ABCC8 have been identified in pulmonary arterial hypertension (PAH). ABCC8 encodes SUR1, a regulatory subunit of the ATP-sensitive potassium channel Kir6.2. However, the pathophysiological role of the SUR1/Kir6.2 channel in PAH is unknown. We hypothesized that activation of SUR1 could be a novel potential target for PAH. We analyzed the expression of SUR1/Kir6.2 in the lungs and pulmonary artery (PA) in human PAH or experimental pulmonary hypertension (PH). The contribution of SUR1 in human or rat PA tone was evaluated, and we measured the consequences of invivo activation of SUR1 in control and PH rats. SUR1 and Kir6.2 protein expression was not reduced in the lungs or human pulmonary arterial endothelial cells and smooth muscle cells from PAH or experimentally induced PH. We showed that pharmacological activation of SUR1 by three different SUR1 activators (diazoxide, VU0071063, and NN414) leads to PA relaxation. Conversely, the inhibition of SUR1/Kir6.2 channels causes PA constriction. In vivo, long- and short-term activation of SUR1 with diazoxide reversed monocrotaline-induced PH in rats. In addition, invivo diazoxide application (short protocol) reduced the severity of PH in chronic-hypoxia rats. Moreover, 3 weeks of diazoxide exposure in control rats had no cardiovascular effects. Finally, invivo, activation of SUR1 with NN414 reduced monocrotaline-induced PH in rats. In PAH and experimental PH, the expression of SUR1/Kir6.2 was still present. In vivo pharmacological SUR1 activation by two different molecules alleviated experimental PH, providing proof of concept that SUR1 activation should be considered for PAH and evaluated more thoroughly.

Beneficial effects of a preventive treatment with anethole trithione on pulmonary hypertension

Pulmonary hypertension (PH) is a multifactorial disease characterized by pulmonary arteries (PA) and right ventricular (RV) alterations. Mitochondria dysfunction and associated reactive oxygen species production were shown to contribute to these phenomena. OP2 Drugs start-up demonstrated that anethole trithione (ATT), the active ingredient of its principal lead OP2113, specifically inhibits mitochondrial ROS production from complex I. In this context, this study aims to assess the effects of ATT on PH set-up. By using osmotic mini-pump, influence of a preventive treatment with ATT or its vehicle was tested on PH development in male rats exposed to three weeks of chronic hypoxia (CH - 10 % O2). PA and cardiac PH hallmarks (remodelling, fibrosis and hemodynamic parameters) were assessed. Contraction and intracellular calcium signal of isolated cardiomyocytes from RV were simultaneously measured by IonOptix system. We quantified cardiac mitochondrial mass by measuring VDAC1 expression by western blotting. The effect of preventive or acute treatment with ATT on PA reactivity was measured by isometric tension. In rats with PH, preventive treatment with ATT reduced PA remodelling and RV systolic pressure, whereas RV hypertrophy and fibrosis seemed not to be affected. However, this preventive treatment abolished the decrease of both speed of cardiomyocytes contraction and VDAC1 expression induced by CH. Preventive and acute treatment with ATT reversed PA hyperreactivity to 5-HT in rats with PH. Acute ATT treatment triggered a sustained relaxation of preconstricted PA in both control and PH conditions. L-NAME (eNOS inhibitor) and CHAPS (non-denaturing detergent used to remove endothelium) did not affect the acute effect of ATT on PA contraction and relaxation whereas glibenclamide (KATP channel inhibitor) attenuated ATT induced relaxation. Y27632 (a ROCK inhibitor) and ATT induced additive reduction of 5-HT contraction. Altogether, these results highlighted the benefit of an ATT preventive treatment on PA reactivity and remodelling as well as RV cardiac function suggesting a potential therapeutic interest of ATT in PH set-up. Whereas ATT effect on reactivity seemed to be endothelium and ROCK-independent, KATP channel was partly involved in ATT-induced relaxation.

Vasorelaxant and anti-proliferative effects of lefluomide

Leflunomide (LEF) is a immunomodulator indicated in various diseases including rheumatoid arthritis. Recently, a link between this drug and pulmonary arterial hypertension (PAH) has been suggested (Lacoste Palasset et al., 2021, Ann Am Thorac Soc). Our aim was to examine the effect of LEF on pulmonary artery (PA) tone, whose abnormality is associated with PAH. Distal intralobar PAs and mesenteric arteries (MA) were isolated from male Wistar rats. PA were also collected from subjects with lung cancer, distal from tumor areas. PAs segments were mounted on a myograph for measurement of isometric tension and stimulated with various contractile agents and inhibitors. Experiments were conducted in the presence of LEF, its metabolite teriflunomide (TER) or vehicle (DMSO) (<0.7%). LEF (100 μM) dramatically inhibited the contractile response to high K + , phenylephrine (PE) and U46619 in rat PAs. LEF decreased E max of PE by 77% and induced a 3-fold increase in EC 50 compared to vehicle. Similar effects were observed in MA. Effect of LEF was unaffected by endothelium removal and was relieved after LEF wash out. Concentrations >10 μM of LEF produced a dose-dependent relaxation of PAs precontracted with U46619. TER had intermediary effect on K + response in PA and MA. TER exerted similar inhibition as LEF on PE-evoked contraction in MA, but had a milder effect in PA. In the latter, TER decreased E max by 42% and did not change EC 50 of PE. With calcium-free solution or nifedipine LEF still inhibited response to PE, suggesting the effect is not caused by Ca 2+ influx inhibition. Preliminary data showed that LEF inhibited contractile responses to K + and PE in human PAs, but surprisingly had no effect on U46619 response. Concentrations ≥100 μM inhibit proliferation of human pulmonary arterial smooth muscle cells(hPASMCs) LEF evoked a robust inhibitory effect of rat and human vascular tone at high, yet clinically relevant concentrations. Experiments are currently ongoing in order to clarify the actual mechanism.

Implication of the KATP Sur2b/Kir6.1 in the physiopathology of pulmonary arterial hypertension

PAH is a severe cardiopulmonary disease which is defined by an elevation of the mPAP >25 mmHg. ABCC9 mutations are responsible of Cantu syndrome, a disease characterised by several cardiac disorders and for some case pulmonary hypertension. ABCC9 gene encodes for SUR2 protein, a regulatory subunit of KATP channels. We hypothesized that SUR2/Kir6.1 channel contributes to PAH pathogenesis and could be a therapeutic target in PAH. We used a combination of in vitro, ex-vivo and in vitro approaches to analyse localisation, expression and function (proliferation, migration and contraction) of SUR2/Kir6.1 in PAH physiopathology. Finally, we performed in vivo pharmacological activation of SUR2/Kir6.1 with pinacidil on MCT induced-PH rats. We demonstrated that SUR2A, SUR2B and Kir6.1 are expressed in lungs from control and PAH patients and in experimental-PH models. Myograph experiments demonstrated that pharmacological activation of SUR2 induced pulmonary arterial relaxation in human and rat isolated pulmonary arteries. PA relaxation was still present in PA from MCT-rats but reduced compared to control rats. In vitro experiments on human PASMCs from control and PAH patients show a decrease of the cell proliferation and migration after SUR2 activation. Finally, pharmacological activation in vivo of SUR2 on MCT induced-PH rats show an improvement of the hemodynamic parameters in preventive and curative protocol. This study demonstrates the role of SUR2B/Kir6.1on pulmonary vasculature and provides the proof of concept that it's pharmacological activation could be a therapeutic option for PAH.

GPR18-Mediated Relaxation of Human Isolated Pulmonary Arteries.

GPR18 receptor protein was detected in the heart and vasculature and appears to play a functional role in the cardiovascular system. We investigated the effects of the new GPR18 agonists PSB-MZ-1415 and PSB-MZ-1440 and the new GPR18 antagonist PSB-CB-27 on isolated human pulmonary arteries (hPAs) and compared their effects with the previously proposed, but unconfirmed, GPR18 ligands NAGly, Abn-CBD (agonists) and O-1918 (antagonist). GPR18 expression in hPAs was shown at the mRNA level. PSB-MZ-1415, PSB-MZ-1440, NAGly and Abn-CBD fully relaxed endothelium-intact hPAs precontracted with the thromboxane A2 analog U46619. PSB-CB-27 shifted the concentration-response curves (CRCs) of PSB-MZ-1415, PSB-MZ-1440, NAGly and Abn-CBD to the right; O-1918 caused rightward shifts of the CRCs of PSB-MZ-1415 and NAGly. Endothelium removal diminished the potency and the maximum effect of PSB-MZ-1415. The potency of PSB-MZ-1415 or NAGly was reduced in male patients, smokers and patients with hypercholesterolemia. In conclusion, the novel GPR18 agonists, PSB-MZ-1415 and PSB-MZ-1440, relax hPAs and the effect is inhibited by the new GPR18 antagonist PSB-CB-27. GPR18, which appears to exhibit lower activity in hPAs from male, smoking or hypercholesterolemic patients, may become a new target for the treatment of pulmonary arterial hypertension.

Abstract 9511: Implication of the KATP SUR2B/kir6.1 in the Physiopathology of Pulmonary Arterial Hypertension

Introduction: PAH is a severe and rare cardiopulmonary disease which is defined by an elevation of the mean pulmonary artery pressure &gt;25mmHg. ABCC9 mutations are responsible of Cantu syndrome, a disease characterised by several cardiac disorders and for some case pulmonary hypertension (PH). ABCC9 gene encodes for SUR2 protein, a regulatory subunit of KATP channels. KATP are composed of SUR1 or SUR2 and Kir6.1 or Kir6.2 subunits. We hypothesized that SUR2 / Kir6.1 channel contributes to PAH pathogenesis and could be a therapeutic target against PAH. Methods: Using a combination of in vitro , ex vivo and in vivo approaches, we analysed the localisation and expression of SUR2A, SUR2B and Kir6.1 in pulmonary vasculature from control and PAH patients as well as in experimental PH rat-models. We also analysed the role of SUR2/Kir6.1 in PAH physiopathology (PASMCs proliferation, migration and contraction). Finally, we deciphered the consequences of in vivo pharmacological activation of SUR2/Kir6.1 in experimental model of PH. Results: We demonstrated that SUR2A, SUR2B and Kir6.1 are expressed (mRNA and protein) in lungs from control and PAH patients and in MCT induced-PH model.Myograph experiments demonstrated that pharmacological activation of SUR2 by pinacidil induced pulmonary arterial relaxation in human and rat isolated pulmonary arteries. PA relaxation was still present in PA from MCT-rats but reduced compared to control rats. In vitro experiments on human PASMCs (hPASMCs) from control and PAH patients show a decrease of the cell proliferation and migration after SUR2 activation (pinacidil). Using Patch-clamp technique, we demonstrated that SUR2 activator (pinacidil) in adult rat RV cardiomyocytes reduces RV action potential. Finally, pharmacological activation in vivo of SUR2 by pinacidil (1mg/kg/day) on MCT induced-PH rats show an improvement of the hemodynamic parameters as the mean right ventricular systolic pressure during preventive and curative protocol. Conclusions: We demonstrated that SUR2A, SUR2B and Kir6.1 are expressed in hPASMCs and hPECs from control and iPAH patients. The in vivo SUR2 activation by pinacidil treatment reduced MCT induced-PH phenotype suggesting that SUR2 pharmacological activation should be considered for PAH.

Hydrogen Sulfide Metabolism and Pulmonary Hypertension.

Pulmonary hypertension (PH) is a severe and multifactorial disease characterized by a progressive elevation of pulmonary arterial resistance and pressure due to remodeling, inflammation, oxidative stress, and vasoreactive alterations of pulmonary arteries (PAs). Currently, the etiology of these pathological features is not clearly understood and, therefore, no curative treatment is available. Since the 1990s, hydrogen sulfide (H2S) has been described as the third gasotransmitter with plethoric regulatory functions in cardiovascular tissues, especially in pulmonary circulation. Alteration in H2S biogenesis has been associated with the hallmarks of PH. H2S is also involved in pulmonary vascular cell homeostasis via the regulation of hypoxia response and mitochondrial bioenergetics, which are critical phenomena affected during the development of PH. In addition, H2S modulates ATP-sensitive K+ channel (KATP) activity, and is associated with PA relaxation. In vitro or in vivo H2S supplementation exerts antioxidative and anti-inflammatory properties, and reduces PA remodeling. Altogether, current findings suggest that H2S promotes protective effects against PH, and could be a relevant target for a new therapeutic strategy, using attractive H2S-releasing molecules. Thus, the present review discusses the involvement and dysregulation of H2S metabolism in pulmonary circulation pathophysiology.

Leflunomide, an immunomodulator, inhibits vascular tone ex vivo

Leflunomide (LEF) is an immunomodulator indicated in various diseases including rheumatoid arthritis. Recently, a link between this drug and pulmonary arterial hypertension (PAH) has been suggested (Lacoste-Palasset et al., 2021, Ann Am Thorac Soc ). Our aim was to document the effect of LEF on distal pulmonary arteries (PAs) reactivity, whose abnormality is associated with PAH. Distal intralobar PAs and mesenteric arteries (MAs) were isolated from male Wistar rats. PA were also collected from subjects with lung cancer, distal from tumor areas. PA segments were mounted on a myograph for measurement of isometric tension and stimulated with various contractile agents and inhibitors. Experiments were conducted in the presence of LEF, its metabolite teriflunomide (TER) or vehicle (DMSO) (< 0.7%). LEF (100 μM) dramatically inhibited the contractile response to high K + , phenylephrine (PE) and U46619 in rat PAs. LEF decreased E max of PE by 77% and induced a 3-fold increase in EC 50 compared to vehicle. Similar effects were observed in MA. Effect of LEF was unaffected by endothelium removal and was relieved after LEF wash out. Concentrations > 10 μM of LEF produced a dose-dependent relaxation of PAs precontracted with U46619. TER had intermediary effect on K + response in PA and MA. TER exerted similar inhibition as LEF on PE-evoked contraction in MA, but had a milder effect in PA. In the latter, TER decreased E max by 42% and did not change EC 50 of PE. With calcium-free solution or nifedipine LEF still inhibited response to PE, suggesting the effect is not caused by Ca 2+ influx inhibition. Preliminary data showed that LEF inhibited contractile responses to K + and PE in human PAs, but surprisingly had no effect on U46619 response. LEF evoked a robust inhibitory effect of rat and human vascular tone at high, yet clinically relevant concentrations. Experiments are currently ongoing in order to clarify the actual mechanism.