Acute Cardiopulmonary Hemodynamic Effects of Brain Natriuretic Peptide in Patients With Pulmonary Arterial Hypertension

Novel Experimental Therapies for Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive and devastating disease characterized by pulmonary artery vasoconstriction and vascular remodeling leading to vascular rarefaction with elevation of pulmonary arterial pressures and pulmonary vascular resistance. Often PAH will cause death from right heart failure. Current PAH-targeted therapies improve functional capacity, pulmonary hemodynamics and reduce hospitalization. Nevertheless, today PAH still remains incurable and is often refractory to medical therapy, underscoring the need for further research. Over the last three decades, PAH has evolved from a disease of unknown pathogenesis devoid of effective therapy to a condition whose cellular, genetic and molecular underpinnings are unfolding. This article provides an update on current knowledge and summarizes the progression in recent advances in pharmacological therapy in PAH.

Pulmonary arterial hypertension specific therapy: The old and the new

Pulmonary arterial hypertension (PAH) is a vascular disorder associated with high morbidity and mortality rate and is characterized by pulmonary vascular remodeling and increased pulmonary vascular resistance, ultimately resulting in right ventricular failure and death. Over the past few decades, significant advances in the understanding of the epidemiology, pathogenesis, and pathophysiology of pulmonary arterial hypertension have occured. This has led to the development of disease specific treatment including prostanoids, endothelin receptor antagonists, phosphodiesterase inhibitors, and soluble guanylate cyclase stimulators. These therapies significantly improve exercise capacity, quality of life, pulmonary hemodynamics, but none of the current treatments are actually curative and long-term prognosis remains poor. Thus, there is a clear need to develop new therapies. Several potential pharmacologic agents for the treatment of pulmonary arterial hypertension are under clinical development and some promising results with these treatments have been reported. These agents include tyrosine protein kinase inhibitors, rho-kinase inhibitors, synthetically produced vasoactive intestinal peptide, antagonists of the 5-HT2 receptors, and others. This article will review several of these promising new therapies and will discuss the current evidence regarding their potential benefit in pulmonary arterial hypertension.

WHO Group 1 pulmonary arterial hypertension: current and investigative therapies

Major advances have been made in the treatment of World Health Organization Group 1 pulmonary arterial hypertension (PAH). Since the mid-1990s, nine medications have become available in the United States to target three key pathophysiologic derangements in PAH - the prostacyclin, endothelin, and nitric oxide pathways. As a group, these agents have led to improvements in functional capacity, symptoms, hemodynamics, and survival. Most patients with mild to moderate PAH are started on orally active agents such as endothelin receptor antagonists or phosphodiesterase inhibitors. Patients with more severe disease, particularly those with evidence of right heart failure, should be treated with continuous prostacyclin infusion or a combination of a prostacyclin and oral therapy. Each medication has unique properties and clinical considerations, and the selection of an appropriate therapy must be tailored to the individual patient. None of the currently available WHO Group 1 PAH therapies are curative, however, and it is the hope that new therapies in development may halt or reverse disease progression. This review will discuss the major therapeutic classes of presently available medications and their role in managing the patient with PAH. We will also review data supporting the use of combination therapy, adjuvant background therapy, and new agents currently under investigation.

Pulmonary hemodynamic response to acute combination and monotherapy with sildenafil and brain natriuretic peptide in rats with monocrotaline-induced pulmonary hypertension

BACKGROUND

The lungs of patients with pulmonary arterial hypertension (PAH) exhibit decreased bioavailability of nitric oxide and downstream signaling through cyclic guanosine monophosphate (cGMP). Therapies that enhance cGMP-mediated vasodilation have shown efficacy in treating PAH. We tested the hypothesis that combination therapy with sildenafil, a cGMP phosphodiesterase type 5 inhibitor, and brain natriuretic peptide (BNP), a receptor-mediated guanosine cyclase stimulator, synergistically attenuates monocrotaline-induced PAH in rats compared with either monotherapy.

METHODS

Adult male Sprague-Dawley rats were subcutaneously injected with monocrotaline (n = 41, 50 mg/kg). After approximately 4 weeks, the rats were infused intravenously with vehicle solution, sildenafil (42 and 85 microg/kg/min), or BNP (50 and 100 ng/kg/min), alone and in varied combination. The primary endpoint was the relative change in right ventricular systolic pressure (RVSP) and mean arterial systemic pressure (MAP). Secondary endpoints included heart rate and dP/dt.

RESULTS

Vehicle infusions did not alter hemodynamic variables. Sildenafil85 (85 microg/kg/min) alone decreased RVSP (-16.6 +/- 5.6%) and decreased MAP (-4.0 +/- 4.7%). BNP50 (50 ng/kg/min) and BNP100 (100 ng/kg/min) decreased RVSP (-23.3 +/- 5.7% and -27.1 +/- 2.9%, respectively) and MAP (-6.4 +/- 5.8% and -14.3 +/- 4.1%, respectively). Combination therapy with sildenafil42 and BNP50 decreased RVSP (-20.7 +/- 5.6%) and showed a lessened systemic effect (MAP = -11.6 +/- 5.9%). Combination therapy with sildenafil85 and BNP100 decreased RVSP (-27.6 +/- 3.2%, P = NS) and showed increased systemic effect (MAP = -20.7 +/- 3.1%, P < 0.05) in comparison with sildenafil85.

CONCLUSIONS

This study suggests that intravenous administration of both sildenafil and BNP monotherapy produces significant improvement in RVSP, making them potentially viable options for the treatment of PAH, whereas combination therapy produces no additional improvement in pulmonary hemodynamics.