Dose-dependent, therapeutic potential of angiotensin-(1-7) for the treatment of pulmonary arterial hypertension

Abstract

The effects of the heptapeptide angiotensin-(1-7) (Ang-(1-7)), via its receptor Mas, oppose many of the effects of the classic angiotensin II signaling pathway, and pharmacological exploitation of this effect is currently actively pursued for a wide range of cardiovascular, neoplastic, or immunological disorders. On the basis of its vasodilatory and antiproliferative properties, Ang-(1-7) has consequentially also been proposed as a novel therapeutic strategy for the treatment of pulmonary arterial hypertension (PAH). In this study, we tested the effectiveness of Ang-(1-7) and its stable, cyclic analog cAng-(1-7) over a range of doses for their therapeutic potential in experimental PAH. In the monocrotaline (MCT) rat model of PAH, Ang-(1-7) or cAng-(1-7) were injected in doses of 30, 100, 300, or 900 μg kg(-1) day(-1), and effects on pulmonary hemodynamics and vascular remodeling were assessed. Five weeks after MCT injection, right ventricular systolic pressure (RVSP) was significantly reduced for 3 dose groups treated with Ang-(1-7) (100, 300, and 900 μg kg(-1) day(-1)) and for all dose groups treated with cAng-(1-7), as compared to untreated controls, yet the total reduction of RVSP was <50% at best and thus markedly lower than that with a positive treatment control with ambrisentan. Medial-wall thickness in pulmonary arterioles was only slightly reduced, without reaching significance, for any of the tested Ang-(1-7) compounds and doses. The reported moderate attenuation of PAH does not confirm the previously postulated high promise of this strategy, and the therapeutic usefulness of Ang-(1-7) may be limited in PAH relative to that in other cardiovascular diseases.

Keywords: pulmonary hypertension; renin-angiotensin system; vascular remodeling.

Figure 1

Dose-dependent effects of angiotensin-(1–7) (Ang-(1–7)) on pulmonary arterial hypertension, lung vascular remodeling, and right ventricular hypertrophy in the monocrotaline (MCT) model. Rats were injected with either vehicle (Contr), MCT only (MCT 0), or MCT plus Ang-(1–7) in doses of 30, 100, 300, or 900 μg kg⁻¹ day⁻¹. Group data show right ventricular systolic pressure (RVSP; A), the ratio of right ventricular to left-ventricular-plus-septal weight (RV/(LV + S); B), and medial-wall thickness for pulmonary arterioles 20–50 μm (C) or 50–100 μm (D) in diameter. Each bar represents mean ± SEM of 4–9 experiments; *P < 0.05 versus MCT-only treatment.

Figure 2

Dose-dependent effects of cyclic angiotensin-(1–7) (cAng-(1–7)) on pulmonary arterial hypertension, lung vascular remodeling, and right ventricular hypertrophy in the monocrotaline (MCT) model. Rats were injected with either vehicle (Contr), MCT only (MCT 0), or MCT plus cAng-(1–7) in doses of 30, 100, 300, or 900 μg kg⁻¹ day⁻¹. Group data show right ventricular systolic pressure (RVSP; A), the ratio of right ventricular to left-ventricular-plus-septal weight (RV/(LV + S); B), and medial-wall thickness for pulmonary arterioles 20–50 μm (C) or 50–100 μm (D) in diameter. Each bar represents mean ± SEM of 4–9 experiments; *P < 0.05 versus MCT-only treatment.

Figure 3

Effects of ambrisentan (AMB) on pulmonary arterial hypertension, lung vascular remodeling, and right ventricular hypertrophy in the monocrotaline (MCT) model. Rats were injected with either vehicle (Contr), MCT only (MCT 0), or MCT with subsequent administration of 90 μg kg⁻¹ day⁻¹ AMB with the drinking water. Group data show right ventricular systolic pressure (RVSP; A), the ratio of right ventricular to left-ventricular-plus-septal weight (RV/(LV + S); B), and medial-wall thickness for pulmonary arterioles 20–50 μm (C) or 50–100 μm (D) in diameter. Each bar represents mean ± SEM of 4–9 experiments; *P < 0.05 versus MCT-only treatment.

Figure 4

Dose-dependent effect of angiotensin-(1–7) (Ang-(1–7); A) or cyclic Ang-(1–7) (cAng-(1–7); B) on relative Mas receptor expression in the monocrotaline (MCT) pulmonary arterial hypertension model. Representative immunoblots are shown, and quantitative densitometric data were normalized to GAPDH and expressed as percentage of control (Contr); each bar represents mean ± SEM of 3–6 experiments.

Figure 5

Dose-dependent effect of angiotensin-(1–7) (Ang-(1–7); A–C) or cyclic Ang-(1–7) (cAng-(1–7); D–F) on endothelial NO synthase (eNOS) expression and phosphorylation in the monocrotaline (MCT) pulmonary arterial hypertension model: A, D, Relative eNOS expression; B, E, relative phospho-eNOS (p-eNOS) expression; C, F, ratio of p-eNOS to eNOS expression. Representative immunoblots are shown, and quantitative densitometric data were normalized to GAPDH and expressed as percentage of control (Contr). Each bar represents mean ± SEM of 3–6 experiments.

Figure S1

Angiotensin-(1–7) (Ang-(1–7)) levels in lung homogenate. Ang-(1–7) concentration was determined by enzyme-linked immunosorbent assay in lung homogenates of rats who had been injected with either vehicle (Contr), monocrotaline (MCT) only (MCT 0), or MCT plus Ang-(1–7) in doses of 30, 100, 300, or 900 μg kg⁻¹ day⁻¹. Each bar represents mean ± SEM of 6 experiments.