Treprostinil treatment decreases circulating platelet microvesicles and their procoagulant activity in pediatric pulmonary hypertension

Platelet extracellular vesicles: Darkness and light of autoimmune diseases

Autoimmune diseases are characterized by a breakdown of immune tolerance, leading to inflammation and irreversible end-organ tissue damage. Platelet extracellular vesicles are cellular elements that are important in blood circulation and actively participate in inflammatory and immune responses through intercellular communication and interactions between inflammatory cells, immune cells, and their secreted factors. Therefore, platelet extracellular vesicles are the "accelerator" in the pathological process of autoimmune diseases; however, this robust set of functions of platelet extracellular vesicles has also prompted new advances in therapeutic strategies for autoimmune diseases. In this review, we update fundamental mechanisms based on platelet extracellular vesicles communication function in autoimmune diseases. We also focus on the potential role of platelet extracellular vesicles for the treatment of autoimmune diseases. Some recent studies have found that antiplatelet aggregation drugs, specific biological agents can reduce the release of platelet extracellular vesicles. Platelet extracellular vesicles can also serve as vehicles to deliver drugs to targeted cells. It seems that we can try to silence or inhibit microRNA carried by platelet extracellular vesicles transcription and regulate the target cells to treat autoimmune diseases as platelet extracellular vesicles can transfer microRNA to other cells to regulate immune-inflammatory responses. Hopefully, the information presented here will provide hope for patients with autoimmune diseases.

Abnormal Platelet Aggregation in Pediatric Pulmonary Hypertension

Endogenous prostacyclin stimulates pulmonary vasodilation and inhibits platelet aggregation. For the synthetic analog treprostinil, used in the treatment of pulmonary hypertension (PH), conflicting, anecdotal evidence exists regarding its effects on clinically relevant platelet function. This study investigated whether treprostinil therapy results in inhibition of platelet aggregation in pediatric PH patients. This is a single institution, prospective, cohort study. Pediatric patients ≤18 years of age on medical therapy for PH underwent platelet function testing by light transmission aggregometry with U‐46619—a stable analog of endoperoxide prostaglandin H₂, exhibiting properties similar to thromboxane A2 (TXA2). Results were compared for those on continuous treprostinil therapy (TRE) versus those on other, non‐prostacyclin therapies (non‐TRE). Thirty‐five patients were enrolled: 18 in the TRE group and 17 in the non‐TRE group. There was no difference in platelet aggregation abnormalities between the two groups: 44% (n = 8) in the TRE group and 41% (n = 7) in the non‐TRE group were abnormal. Furthermore, subgroup analysis showed no difference based on treprostinil dosing. This study demonstrated similar, moderately high rates of abnormal platelet aggregation in pediatric PH patients on continuous treprostinil therapy compared to those on other, non‐prostacyclin therapies. The high rate of abnormal platelet aggregation in the entire cohort, however, warrants follow‐up study to identify a potential inherent risk in this population.

Treprostinil palmitil inhibits the hemodynamic and histopathological changes in the pulmonary vasculature and heart in an animal model of pulmonary arterial hypertension

Treprostinil palmitil (TP) is a long-acting inhaled pulmonary vasodilator prodrug of treprostinil (TRE). In this study, TP was delivered by inhalation (treprostinil palmitil inhalation suspension, TPIS) in a rat Sugen 5416 (Su)/hypoxia (Hx) model of pulmonary arterial hypertension (PAH) to evaluate its effects on hemodynamics, pulmonary vascular remodeling, and cardiac performance and histopathology. Male Sprague-Dawley rats received Su (20 mg/kg, s.c), three weeks of Hx (10% O2) and 5 or 10 weeks of normoxia (Nx). TPIS was given during the 5-10 week Nx period after the Su/Hx challenge. Su/Hx increased the mean pulmonary arterial blood pressure (mPAP) and right heart size (Fulton index), reduced cardiac output (CO), stroke volume (SV) and heart rate (HR), and increased the thickness and muscularization of the pulmonary arteries along with obliteration of small pulmonary vessels. In both the 8- and 13-week experiments, TPIS at inhaled doses ranging from 39.6 to 134.1 μg/kg, QD, dose-dependently improved pulmonary vascular hemodynamics, reduced the increase in right heart size, enhanced cardiac performance, and attenuated most of the histological changes induced by the Su/Hx challenge. The PDE5 inhibitor sildenafil, administered at an oral dose of 50 mg/kg, BID for 10 weeks, was not as effective as TPIS. These results in Su/Hx challenged rats demonstrate that inhaled TPIS may have superior effects to oral sildenafil. We speculate that the improvement of the pathobiology in this PAH model induced by TPIS involves effects on pulmonary vascular remodeling due to the local effects of TRE in the lungs.

Differential and targeted vesiculation: pathologic cellular responses to elevated arterial pressure

Extracellular vesicles are small membrane-enclosed particles released during cell activation or injury. They have been investigated for several decades and found to be secreted in various diseases. Their pathogenic role is further supported by the presence of several important molecules among their cargo, including proteins, lipids, and nucleic acids. Many studies have reported enhanced and targeted extracellular vesicle biogenesis in diseases that involve chronic or transient elevation of arterial pressure resulting in endothelial dysfunction, within either the general circulatory system or specific local vascular beds. In addition, several associated pathologic processes have been studied and reported. However, the role of elevated pressure as a common pathogenic trigger across vascular domains and disease chronicity has not been previously described. This review will therefore summarize our current knowledge of the differential and targeted biogenesis of extracellular vesicles in major diseases that are characterized by elevated arterial pressure leading to endothelial dysfunction and propose a unified theory of pressure-induced extracellular vesicle-mediated pathogenesis.

Hypoxia-activated platelets stimulate proliferation and migration of pulmonary arterial smooth muscle cells by phosphatidylserine/LOX-1 signaling-impelled intercellular communication

Continuous recruitment and inappropriate activation of platelets in pulmonary arteries contribute to pulmonary vascular remodeling in pulmonary hypertension (PH). Our previous study has demonstrated that lectin like oxidized low-density lipoprotein receptor-1 (LOX-1) regulates the proliferation of pulmonary arterial smooth muscle cells (PASMCs). Phosphatidylserine exposed on the surface of activated platelets is a ligand for LOX-1. However, whether hypoxia-activated platelets stimulate the proliferation and migration of PASMCs by phosphatidylserine/LOX-1 signaling-impelled intercellular communication remains unclear. The present study found that rats treated with hypoxia (10% O₂) for 21 days revealed PH with the activation of platelets and the recruitment of platelets in pulmonary arteries, and LOX-1 knockout inhibited hypoxia-induced PH and platelets activation. Notably, co-incubation of PASMCs with hypoxic PH rats-derived platelets up-regulated LOX-1 expression in PASMCs leading to the proliferation and migration of PASMCs, which was inhibited by the phosphatidylserine inhibitor annexin V or the LOX-1 neutralizing antibody. LOX-1 knockout led to decreased proliferation and migration of PASMCs stimulated by hypoxia-activated platelets. In rats, hypoxia up-regulated the phosphorylation of signal transducer and activator of transcription 3 (Stat3) and the expression of Pim-1 in pulmonary arteries. Hypoxia-activated platelets also up-regulated the phosphorylation of Stat3 and the expression of Pim-1 in PASMCs, which was inhibited by annexin V, the LOX-1 neutralizing antibody, the protein kinase C inhibitor and LOX-1 knockout. In conclusion, we for the first time demonstrated that hypoxia-activated platelets stimulated the proliferation and migration of PASMCs by phosphatidylserine/LOX-1/PKC/Stat3/Pim-1 signaling-impelled intercellular communication, thereby potentially contributing to hypoxic pulmonary vascular remodeling.

Pharmacokinetics of treprostinil in children with functional single-ventricle pulmonary arterial hypertension: a randomized controlled trial

Background

Application of Treprostinil (TRE) in the patients with single ventricle (SV) physiology is very limited, and the optimal dose for children has not been determined. In this study, we aimed to analyze plasma samples to assess the attainment of clinically therapeutic concentrations of TRE and its efficacy and safety in the treatment of pediatric functional SV pulmonary arterial hypertension (FSV-PAH)..

Methods

Pediatric patients with FSV-PAH were recruited in this study. IV TRE at an initial rate of 5 ng/kg/min was administered through the femoral vein with an increase in rate to 10 ng/kg/min every 30 minuntil the aiming dose of 80 ng/kg/min had been reached. The drug was gradually discontinued after 12 h of treatment at a stable dose. The mean postoperative pulmonary artery pressure (mPAP), pulmonary-to-systemic arterial pressure ratio (Pp/Ps), and the ratio between arterial oxygen partial pressure and inhaled oxygen concentration (PaO₂/FiO₂) were used to evaluate the efficacy of TRE treatment. A multiple linear regression model was used to explore the relevant factors associated with TRE blood concentration.

Results

A total of eight patients were enrolled in the investigation, with an age range of 2.5-9.9 years. The median stable dose of TRE was 70 ng/kg/min with a range of 55-75 ng/kg/min. The median subliminal dose was 55 ng/kg/min with a range of 25-75 ng/kg/min. A linear relationship was established between the TRE dose and the plasma concentration. TRE blood concentrations were associated with dose and patient height. After TRE treatment, mPAP, Pp/Ps, and PaO₂/FiO₂ were significantly improved (P<0.05).

Conclusions

A linear relationship was found between the blood concentration of TRE and its dose. IV TRE was an effective therapy without serious side effects in pediatric patients with FSV-PAH.

Trial Registration

ClinicalTrials.gov Identifier: NCT02865733.

Prostacyclin Analogues Inhibit Platelet Reactivity, Extracellular Vesicle Release and Thrombus Formation in Patients with Pulmonary Arterial Hypertension

(1) Background: Prostacyclin analogues (epoprostenol, treprostinil, and iloprost) induce vasodilation in pulmonary arterial hypertension (PAH) but also inhibit platelet function. (2) Objectives: We assessed platelet function in PAH patients treated with prostacyclin analogues and not receiving prostacyclin analogues. (3) Methods: Venous blood was collected from 42 patients treated with prostacyclin analogues (49.5 ± 15.9 years, 81% female) and 38 patients not receiving prostacyclin analogues (55.5 ± 15.6 years, 74% female). Platelet reactivity was analyzed by impedance aggregometry using arachidonic acid (AA; 0.5 mM), adenosine diphosphate (ADP; 6.5 µM), and thrombin receptor-activating peptide (TRAP; 32 µM) as agonists. In a subset of patients, concentrations of extracellular vesicles (EVs) from all platelets (CD61⁺), activated platelets (CD61⁺/CD62P⁺), leukocytes (CD45⁺), and endothelial cells (CD146⁺) were analyzed by flow cytometry. Platelet-rich thrombus formation was measured using a whole blood perfusion system. (4) Results: Compared to controls, PAH patients treated with prostacyclin analogues had lower platelet reactivity in response to AA and ADP (p = 0.01 for both), lower concentrations of platelet and leukocyte EVs (p ≤ 0.04), delayed thrombus formation (p ≤ 0.003), and decreased thrombus size (p = 0.008). Epoprostenol did not affect platelet reactivity but decreased the concentrations of platelet and leukocyte EVs (p ≤ 0.04). Treprostinil decreased platelet reactivity in response to AA and ADP (p ≤ 0.02) but had no effect on the concentrations of EVs. All prostacyclin analogues delayed thrombus formation and decreased thrombus size (p ≤ 0.04). (5) Conclusions: PAH patients treated with prostacyclin analogues had impaired platelet reactivity, EV release, and thrombus formation, compared to patients not receiving prostacyclin analogues.

An overview of the biology of a long-acting inhaled treprostinil prodrug

Treprostinil (TRE) is a prostanoid analog pulmonary vasodilator drug marketed with subcutaneous, intravenous (i.v.), oral, and inhaled routes of administration for the treatment of pulmonary arterial hypertension (PAH). Due to its short half-life, TRE requires either continuous infusion or multiple dosing, which exacerbates its side effects. Therefore, a long-acting prostanoid analog that maintains the positive attributes of TRE but has fewer TRE-related side effects could be of clinical benefit. In this report, we describe the discovery, preclinical development, and biology of the TRE ester prodrug, treprostinil palmitil (TP), which is formulated in a lipid nanoparticle (LNP) for administration as a nebulized inhaled suspension (TPIS). In screening assays focused on the conversion of prodrug to TRE, TP (16 carbon alkyl chain) had the slowest rate of conversion compared with short-alkyl chain TRE prodrugs (i.e., 2-8 carbon alkyl chain). Furthermore, TP is a pure prodrug and possesses no inherent binding to G-protein coupled receptors including prostanoid receptors. Pharmacokinetic studies in rats and dogs demonstrated that TPIS maintained relatively high concentrations of TP in the lungs yet had a low maximum plasma concentrations (C_max) of both TP and, more importantly, the active product, TRE. Efficacy studies in rats and dogs demonstrated inhibition of pulmonary vasoconstriction induced by exposure to hypoxic air or i.v.-infused U46619 (thromboxane mimetic) over 24 h with TPIS. Cough was not observed with TPIS at an equivalent dose at which TRE caused cough in guinea pigs and dogs, and there was no evidence of desensitization to the inhibition of pulmonary vasoconstriction in rats with repeat inhaled dosing. TPIS was also more efficacious than i.v.-infused TRE in a sugen/hypoxia rat model of PAH to inhibit pulmonary vascular remodeling, an effect likely driven by local activities of TRE within the lungs. TPIS also demonstrated antifibrotic and anti-inflammatory activity in the lungs in rodent models of pulmonary fibrosis and asthma. In a phase 1 study in healthy human participants, TPIS (referred to as INS1009) had a lower plasma TRE C_max and fewer respiratory-related side effects at equimolar doses compared with inhaled TRE. We have now formulated TP as an aerosol powder for delivery by a dry powder inhaler (referred to as treprostinil palmitil inhalation powder-TPIP), and as an aerosol solution in a fluorohydrocarbon solvent for delivery by a metered dose inhaler. These options may reduce drug administration time and involve less device maintenance compared with delivery by nebulization.

Prostanoids in pediatric pulmonary hypertension: clinical response, time-to-effect, and dose-response

For pediatric pulmonary arterial hypertension (PAH) patients treated with parenteral prostanoids, response predictors, and the dose-effect relationship are ill defined. We determined the following: (1) which pulmonary vascular hemodynamic variable, after initiating prostanoids, best correlates with a significant clinical response; (2) the time interval after treatment when if no pulmonary hemodynamic improvement has occurred, none is ever likely to; and (3) the relationship between the prostanoid dose and its hemodynamic effects. This is a retrospective cohort study of 31 pediatric patients with Group 1 PAH treated with parenteral prostanoids. We found the following: (1) A fall in mean pulmonary arterial pressure (mPAP) of ≥25% predicted freedom from adverse clinical events with 80.7% accuracy and was also associated with improved functional class. (2) Thirty-three percent of patients who avoided an adverse clinical event demonstrated a ≥25% reduction in mPAP after 1 year of treatment, and 65% by 2 years. (3) Lower mPAP was seldom seen with doses of epoprostenol >60 ng/kg/min (100 ng/kg/min for treprostinil). Cardiac index was positively correlated with the dose of epoprostenol but not treprostinil; cardiac index >4 l/min/m² was seen at modest as well as high doses. We conclude that a ≥25% fall in mPAP on prostanoids indicates a positive clinical response which, if validated in other studies, may be useful for patient management or clinical trials. Some patients take more than 2 years for this change. Exceptionally high doses were generally not more effective than lower, although we could not determine whether lower doses would have been as effective.

Stox1 induced the proliferation and cell cycle arrest in pulmonary artery smooth muscle cells via AKT signaling pathway

BACKGROUND

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by the vascular remodeling that also involves proliferation and migration of pulmonary artery smooth muscle cells (PASMCs). Overexpression of Storkhead box (STOX1) regulates genes involved hypoxia, redox balance, nitric oxide, and energy metabolism. In this study, we supposed Stox1 adjusted cells proliferation and migration in PASMCs development and played an important role in the pulmonary arterial vascular remodeling.

METHODS

Hemodynamic assay and Right ventricular morphometric assay were used to check the rat model of PAH. HE staining was used to examine the arterial wall thickness. Masson staining showed that the deposition of collagen was significantly increased in PAH. In addition, Stox1 were assessed by immunofluorescence and immunohistochemistry staining. The effect of Stox1 on PASMCs was assessed by cell counting Kit-8 assay (CCK-8 assay), Scratch-Wound assay, EdU staining assay, Cell cycle analysis and Western blot.

RESULTS

Right ventricular systolic pressure (RVSP) and right ventricular were significantly increased in hypoxia group and monocrotaline group compared to control group. The expression of Stox1 was increased in lung tissues in PAH rats. In vitro, the expression of Stox1 was up-regulated with time-dependent manner in hypoxia condition. Meanwhile, Stxo1 promoted the proliferation and migration in hypoxia-treated PASMCs. Moreover, we found that hypoxia promoted the expression of PCNA, Cyclin E and Cyclin A, increased more cells from G₀/G₁ phase to S phase and induced the activation of AKT proteins, which was significantly attenuated by inhibition of Stox1 expression in PASMCs.

CONCLUSION

These findings indicated that Stox1 induced proliferation of PASMCs and the effect is, at least in part, mediated through AKT signaling pathway.