Treatment of Pulmonary Hypertension With Angiotensin II Receptor Blocker and Neprilysin Inhibitor Sacubitril/Valsartan

Abstract

Background: Angiotensin II has been implicated in maladaptive right ventricular (RV) hypertrophy and fibrosis associated with pulmonary hypertension (PH). Natriuretic peptides decrease RV afterload by promoting pulmonary vasodilation and inhibiting vascular remodeling but are degraded by neprilysin. We hypothesized that angiotensin receptor blocker and neprilysin inhibitor, sacubitril/valsartan (Sac/Val, LCZ696), will attenuate PH and improve RV function by targeting both pulmonary vascular and RV remodeling.

Methods: PH was induced in rats using the SU5416/hypoxia model (Su/Hx), followed by 6-week treatment with placebo, Sac/Val, or Val alone. There were 4 groups: CON-normoxic animals with placebo (n=18); PH-Su/Hx rats+placebo (n=34); PH+Sac/Val (N=24); and PH+Val (n=16).

Results: In animals with PH, treatment with Sac/Val but not Val resulted in significant reduction in RV pressure (mm Hg: PH: 62±4, PH+Sac/Val: 46±5), hypertrophy (RV/LV+S: PH: 0.74±0.06, PH+Sac/Val: 0.46±0.06), collagen content (µg/50 µg protein: PH: 8.2±0.3, PH+Sac/Val: 6.4±0.4), pressures and improvement in RVs (mm/s: PH: 31.2±1.8, PH+Sac/Val: 43.1±3.6) compared with placebo. This was associated with reduced pulmonary vascular wall thickness, increased lung levels of ANP (atrial natriuretic peptide), BNP (brain-type natriuretic peptide), and cGMP, and decreased plasma endothelin-1 compared with PH alone. Also, PH+Sac/Val animals had altered expression of PKC isozymes in RV tissue compared with PH alone.

Conclusions: Sac/Val reduces pulmonary pressures, vascular remodeling, as well as RV hypertrophy in a rat model of PH and may be appropriate for treatment of pulmonary hypertension and RV dysfunction.

Keywords: angiotensin; fibrosis; hypertension, pulmonary; models, animal; natriuretic peptides; vasodilation.

Figure 1:. Sac/Val treatment improves pulmonary hemodynamics, RV function, and hypertrophy in PH.

Quantification of pulmonary acceleration time (A, PAT; n=11-28), RV s’ (B, n=9-25), and LV Ejection Fraction ( C, LVEF; n=11-26) at 3 weeks (pre) and 9 weeks (post) in normoxic (CON), pulmonary hypertension treated with placebo (PH), PH treated with Sac/Val (PH +SV) and PH treated with Val (PH + V) animals. PH animals were treated from week 3 to week 9. (For Panels A-C: *= p<0.05 paired t-test). Post treatment measurements from animals treated as in A of right ventricular systolic pressure (D, RVSP; n=11-29), right ventricular end-diastolic pressure (RVDP; E; n=11-24), VO₂max during exercise testing (F, n=11-15), and weight (Wt) ratio of RV to LV+S (G, n=10-20). Quantification of RV collagen content by Sircol assay (H, n=9-18) and RV hydroxyproline content (I, n=7-15) J. Quantification of LV collagen by Sircol assay (n=9-17). K-M Densitometry of relative PKCα, PKCßII, PKCδ expression normalized to Vinculin from RV lysates (n=8-17). N. Representative immunoblots for PKCα, PKCßII, PKCδ, and Vinculin from RV lysates. (For panel D-M: *= P<.05 vs CON, ψ P<.05 vs PH, #, P<0.05 vs PH +SV using One Way ANOVA SNK post-hoc test).

Figure 2:. Sac/Val treatment reduces PH-induced vascular remodeling, increases NP levels, and reduces vasoconstrictive peptide production.

A. Photomicrographs of lung tissue sections stained with hematoxylin and eosin from control (CON) rats at 9 weeks and rats with pulmonary hypertension treated for 6 weeks with placebo (PH), Sac/Val (PH +SV) or with Val alone (PH + V). B. Quantification of relative wall thickness from sections in A (n=8-21). Quantification of circulating (C), and lung (D) levels of ANP, BNP and cGMP as determined by ELISA (n=5-25). Quantification of plasma (E) and lung ET-1 (F) levels by ELISA (n=6-19). *= P<.05 vs CON, ψ P<.05 vs PH, #, P<0.05 vs PH +SV using One Way ANOVA SNK post-hoc test (B, D, E ) or Kruskal-Wallis One Way ANOVA on Ranks, Dunn’s test (C, F)