The ET(A)-Receptor Antagonist LU 135252 Prevents the Progression of Established Pulmonary Hypertension Induced by Monocrotaline in Rats

Pathogenic Mechanisms of Pulmonary Arterial Hypertension: Homeostasis Imbalance of Endothelium-Derived Relaxing and Contracting Factors

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease. Sustained pulmonary vasoconstriction and concentric pulmonary vascular remodeling contribute to the elevated pulmonary vascular resistance and pulmonary artery pressure in PAH. Endothelial cells regulate vascular tension by producing endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs). Homeostasis of EDRF and EDCF production has been identified as a marker of the endothelium integrity. Impaired synthesis or release of EDRFs induces persistent vascular contraction and pulmonary artery remodeling, which subsequently leads to the development and progression of PAH. In this review, the authors summarize how EDRFs and EDCFs affect pulmonary vascular homeostasis, with special attention to the recently published novel mechanisms related to endothelial dysfunction in PAH and drugs associated with EDRFs and EDCFs.

Stable Gastric Pentadecapeptide BPC 157 Therapy for Monocrotaline-Induced Pulmonary Hypertension in Rats Leads to Prevention and Reversal

Background. Monocrotaline selectively injures the lung's vascular endothelium and induces pulmonary arterial hypertension. The stable gastric pentadecapeptide BPC 157 acts as a prototype cytoprotective agent that maintains endothelium, and its application may be a novel therapy. Besides, BPC 157 prevents and reverses thrombosis formation, maintains platelet function, alleviates peripheral vascular occlusion disturbances, and has anti-arrhythmic and anti-inflammatory effects. Monocrotaline-induced pulmonary arterial hypertension in rats (wall thickness, total vessel area, heart frequency, QRS axis deviation, QT interval prolongation, increase in right ventricle systolic pressure and bodyweight loss) can be counteracted with early or delayed BPC 157 therapy. Methods and Results. After monocrotaline (80 mg/kg subcutaneously), BPC 157 (10 μg/kg or 10 ng/kg, days 1-14 or days 1-30 (early regimens), or days 14-30 (delayed regimen)) was given once daily intraperitoneally (last application 24 h before sacrifice) or continuously in drinking water until sacrifice (day 14 or 30). Without therapy, the outcome was the full monocrotaline syndrome, marked by right-side heart hypertrophy and massive thickening of the precapillary artery's smooth muscle layer, clinical deterioration, and sometimes death due to pulmonary hypertension and right-heart failure during the 4th week after monocrotaline injection. With all BPC 157 regimens, monocrotaline-induced pulmonary arterial hypertension (including all disturbed parameters) was counteracted, and consistent beneficial effects were documented during the whole course of the disease. Pulmonary hypertension was not even developed (early regimens) as quickly as the advanced pulmonary hypertension was rapidly attenuated and then completely eliminated (delayed regimen). Conclusions. Thus, pentadecapeptide BPC 157 prevents and counteracts monocrotaline-induced pulmonary arterial hypertension and cor pulmonale in rats.

Macitentan treatment retards the progression of established pulmonary arterial hypertension in an animal model

BACKGROUND

Macitentan is a new endothelin receptor antagonist that is used to treat pulmonary arterial hypertension in humans. Treatment of established pulmonary hypertension with macitentan was studied using the monocrotaline model of pulmonary hypertension.

METHODS

Three groups of rats were created (n=12): control (CON: macitentan only), monocrotaline (MCT: monocrotaline only) and macitentan (MACI: macitentan and monocrotaline). Monocrotaline (60 mg/kg) was injected in the MCT and MACI groups on day 0; volume matched saline was injected in the CON groups. Macitentan therapy (30 mg/kg/day) was commenced on day 11 in the CON and MACI groups. Serial echocardiography and ECGs were performed. The rats were sacrificed if they showed clinical deterioration.

RESULTS

The MCT and MACI rats showed signs of pulmonary hypertension by day 7 (maximum pulmonary velocity, CON 1.15 ± 0.15m/s vs MCT 1.04 ± 0.10 m/s vs MACI 0.99 ± 0.18 m/s; p<0.05). Both the MCT and MACI groups developed pulmonary hypertension, but this was less severe in the MACI group (day 21 pulmonary artery acceleration time, MCT 17.55 ± 1.56 ms vs MACI 22.55 ± 1.00 ms; pulmonary artery deceleration, MCT 34.72 ± 3.72 m/s(2) vs MACI 17.30 ± 1.89 m/s(2); p<0.05). Right ventricular hypertrophy and QT interval increases were more pronounced in MCT than MACI (right ventricle wall thickness, MCT 0.13 ± 0.1cm vs MACI 0.10 ± 0.1cm; QT interval, MCT 85 ± 13 ms vs MACI 71 ± 14 ms; p<0.05). Survival benefit was not seen in the MACI group (p=0.50).

CONCLUSIONS

Macitentan treatment improves haemodynamic parameters in established pulmonary hypertension. Further research is required to see if earlier introduction of macitentan has greater effects.

The potential for macitentan, a new dual endothelin receptor antagonist, in the treatment of pulmonary arterial hypertension

In recent years in the management of pulmonary arterial hypertension (PAH), endothelin receptor antagonists (ERAs) represent a well-established class of therapeutic agents with clear beneficial effects. Macitentan (Opsumit®), a dual ERA optimized for efficacy and safety, is the newest drug in the class. Macitentan presents a number of key beneficial characteristics, including increased in vivo preclinical efficacy versus existing ERAs, resulting from sustained receptor binding and physicochemical properties that allow enhanced tissue penetration. The clinical pharmacokinetics studies also indicated a low predilection of macitentan for drug–drug interactions. In the SERAPHIN trial, a phase III long-term study of PAH, macitentan significantly reduced morbidity and mortality by 45% versus placebo, providing sustained long-term improvements in exercise capacity. No association was found between changes in exercise capacity and long-term clinical outcomes, but improved cardiopulmonary hemodynamics were recorded in macitentan-treated patients irrespective of baseline background PAH therapy or World Health Organization functional class. Based on these favorable data, the US Food and Drug Administration approved the 10 mg/day dose in late 2013 and the same process has recently been concluded by the European Medicines Agency.

The endothelin system in pulmonary hypertension

Pulmonary hypertension (PH) may result from numerous clinical entities affecting the pulmonary circulation primarily or secondarily. It is recognized that vascular endothelial dysfunction contributes to the development and perpetuation of PH by creating an imbalance between vasodilating and antiproliferative forces and between vasoconstrictive and proliferative forces. In that context, endothelin-1 (ET-1) overproduction was rapidly targeted as a plausible contributor to the pathogenesis of PH. The lung is recognized as the major site for ET production and clearance. In all animal models of PH studied, circulating plasma ET-1 levels are elevated, accompanied by an increase in lung tissue expression of the peptide. The use of selective ETA and dual ETA-ETB receptor antagonists in these models both in prevention and in therapeutic studies have confirmed the contribution of ET-1 to the rise in pulmonary vascular tone, pulmonary medial hypertrophy, and right ventricular hypertrophy. This is found consistently in models affecting the pulmonary circulation primarily or producing PH secondarily. Recent clinical trials in patients with pulmonary arterial hypertension have confirmed the therapeutic effectiveness of ET-receptor antagonists in humans. We offer a systematic review of the pathogenic role of the ET system in the development of PH as well as the rationale behind the preclinical and ongoing clinical trials with this new class of agents.

New therapeutics that antagonize endothelin: promises and frustrations

The discovery of endothelin--a highly potent endogenous vasoconstrictor - in 1988 has led to considerable efforts to develop antagonists of endothelin receptors that could have therapeutic potential in disorders including hypertension, heart failure and renal diseases. However, in general, the results of trials in humans have not mirrored the highly promising effects in animal disease models. Here, we discuss preclinical and clinical results with endothelin antagonists, and consider possible approaches to fully realizing the potential of endothelin antagonism.

Effect of ABT-627 (A-147627), a potent selective ET(A) receptor antagonist, on the cardiopulmonary profile of newborn lambs with surgically-induced diaphragmatic hernia

1. Postnatal mortality in isolated congenital diaphragmatic hernia (CDH) is mainly related to the associated pulmonary hypertension (PH) and to right-to-left shunting. 2. Endothelins (ETs) are potent vasoconstrictors and pro-mitogenic peptides. Strong evidences support their participation in CDH and in the etiology of PH via the activation of ET(A) receptors (ET(A)-Rs). 3. Evaluation of the effect of ABT-627, a selective non-peptidic ET(A)-R antagonist, given from -15 to 210 min post-delivery (1 mg kg(-1) bolus +0.01 mg kg(-1) h(-1) infusion, i.v.), was conducted in the lamb model of CDH. 4. Severity of CDH was assessed in comparison to untreated controls (n=5). Untreated CDH lambs (n=7) had a higher mean pulmonary arterial pressure (MPAP; P<0.0001), lower mean blood pressure (MBP; P=0.0004), higher MPAP / MBP ratio (P<0.0001), lower arterial pH (P<0.0001), higher paCO(2) (P<0.0001), lower paO(2) (P<0.0001) and lower post-ductal pulsatile SaO(2) (P<0.0001) than untreated controls. 5. Treated controls (n=7) showed a higher MPAP, lower MBP, higher MPAP/MBP ratio, lower arterial pH, higher paCO(2), lower paO(2), lower post-ductal pulsatile SaO(2) and lower plasmatic ir-ET ratios compared to untreated controls (P<0.0001). 6. Treated CDH lambs (n=8) showed a higher MBP (P<0.0001), lower MPAP / MBP ratio (P<0.0001), higher arterial pH (P<0.0001), lower paCO(2) (P<0.0001), higher paO(2) (P=0.0228), higher post-ductal pulsatile SaO(2) (P=0.0016) and lower plasmatic ir-ET ratios (P=0.0247) when compared to untreated CDH lambs. 7. These observations revealed that, although acute perinatal treatment with a selective non-peptidic ET(A)-R antagonist had some adverse effects in controls, it attenuated the progressive cardiopulmonary deterioration that occurred after birth in CDH lambs.

New and experimental therapies for pulmonary hypertension

Advances in the understanding of the molecular and cellular pathogeneses of PPH have led clinicians beyond simple pulmonary vasodilation as the only treatment for PPH and to a realization that what were previously believed to be irreversible vascular lesions may, in fact, be reversible. The development of agents that target the known endothelial and nonendothelial defects in patients with PPH is well underway. Clinicians are witnessing an exciting new era for physicians and patients dealing with this disease.