Hemodynamic and Histopathologic Benefits of Early Treatment with Macitentan in a Rat Model of Pulmonary Arterial Hypertension.

Abstract

Background and ObjectivesMacitentan (MAC) reduces morbidity and mortality among advanced-stage pulmonary arterial hypertension (PAH) patients. However, data regarding the histopathologic and hemodynamic benefits of MAC treatment at an early stage of PAH is lacking.MethodsOne week after monocrotaline (MCT) injection, rats were randomly assigned to MAC (n=16), MAC combined with sildenafil (SIL) (MAC+SIL, n=16), or normal saline (MCT, n=16). Twelve sham rats (Sham) were included for comparison. Right ventricular (RV) systolic function was assessed via echocardiography as the RV fractional area change (RV-FAC). An invasive pressure-volume analysis using a Millar conductance catheter was performed 7 weeks after MCT injection. Rats were subsequently euthanized for histopathologic analysis.ResultsRV-right atrial pressure gradient on echocardiography was significantly increased 3 weeks after MCT injection, but was maintained in the Sham. RV-FAC was less deteriorated in the MAC, compared to that in the MCT (44±3% vs. 25±7%, p<0.05), and the co-administration of SIL showed no additional benefit (45±8%, p>0.05 vs. the MAC). On invasive hemodynamic analyses, RV end-systolic (196±78 µL) and end-diastolic volumes (310±86 µL), pulmonary artery systolic pressure (89±7.2 mmHg), and end-systolic pressure-volume relationship (−254±25.1) were significantly worse in the MCT vs. in the MAC (101±45 µL, 235±55 µL, 40±10.5 mmHg, and −145±42.1, respectively) and MAC+SIL (109±47 µL, 242±46 µL, 38±9.2 mmHg, and −151±39.2, respectively) (all p<0.05). However, the MAC and MAC+SIL did not differ (all p>0.05). On histopathology, both RV and lung fibrosis were significantly reduced in the MAC and MAC+SIL vs. in the MCT (all p<0.05); the 2 treatment groups did not differ.ConclusionsMAC treatment at an earlier stage significantly attenuated experimental PAH progression hemodynamically and histopathologically.