N-acetylcysteine improves established monocrotaline-induced pulmonary hypertension in rats

Abstract

Background: The outcome of patients suffering from pulmonary arterial hypertension (PAH) are predominantly determined by the response of the right ventricle to the increase afterload secondary to high vascular pulmonary resistance. However, little is known about the effects of the current available or experimental PAH treatments on the heart. Recently, inflammation has been implicated in the pathophysiology of PAH. N-acetylcysteine (NAC), a well-known safe anti-oxidant drug, has immuno-modulatory and cardioprotective properties. We therefore hypothesized that NAC could reduce the severity of pulmonary hypertension (PH) in rats exposed to monocrotaline (MCT), lowering inflammation and preserving pulmonary vascular system and right heart function.

Methods: Saline-treated control, MCT-exposed, MCT-exposed and NAC treated rats (day 14-28) were evaluated at day 28 following MCT for hemodynamic parameters (right ventricular systolic pressure, mean pulmonary arterial pressure and cardiac output), right ventricular hypertrophy, pulmonary vascular morphometry, lung inflammatory cells immunohistochemistry (monocyte/macrophages and dendritic cells), IL-6 expression, cardiomyocyte hypertrophy and cardiac fibrosis.

Results: The treatment with NAC significantly decreased pulmonary vascular remodeling, lung inflammation, and improved total pulmonary resistance (from 0.71 ± 0.05 for MCT group to 0.50 ± 0.06 for MCT + NAC group, p < 0.05). Right ventricular function was also improved with NAC treatment associated with a significant decrease in cardiomyocyte hypertrophy (625 ± 69 vs. 439 ± 21 μm2 for MCT and MCT + NAC group respectively, p < 0.001) and heart fibrosis (14.1 ± 0.8 vs. 8.8 ± 0.1% for MCT and MCT + NAC group respectively, p < 0.001).

Conclusions: Through its immuno-modulatory and cardioprotective properties, NAC has beneficial effect on pulmonary vascular and right heart function in experimental PH.

Figure 1

NAC decreases MCT-induced pulmonary vascular remodeling. Percentage of not muscularized (A), partially muscularized (B), fully muscularized (C) and completely occluded (D) precapillary pulmonary arteries in control, MCT and MCT + NAC groups are represented in scatter dot plot. *P < 0.05 vs cont, ^#p < 0.05 vs MCT) (n = 7–14 per group).

Figure 2

NAC reduces monocrotaline-induced pulmonary accumulation of ED-1 and OX-62 positive cells. Representative fluorescent images compare the presence of (A) ED-1 positive monocytes/macrophages (red fluorescence arrows) in control rat (1) and lung of MCT-treated rats (2). NAC treatment substantially reduced the number of ED-1 positive cells in the lungs of MCT-treated rats (3). Immunofluorescent labelling for α-smooth muscle actin (green) was used to indentify vascular smooth muscle cells (blue fluorescence: nuclei). Presence of (B) dendritic cells OX62 positive leucocytes (red fluorescence arrows) in lung of control rat (1) and MCT-treated rats (2). NAC treatment substantially reduced the number of dendritic cells in the lungs of MCT-treated rats (3). 4: Bar graphs are summary data for mean number of ED-1+ cells/field and OX62+ cells/adventitia (mean ± SEM). *P < 0.05 vs cont, ^#p < 0.05 vs MCT) (n = 20–30 per group).

Figure 3

NAC decreases cardiomyocytes hypertrophy and fibrosis in RV rats with PH. In the first part (A), representative image of cardiomyocytes in RV of control rat (1) MCT rats (2) and MCT rats treated with NAC from days 14 to day 28 after MCT exposure (3). In the second part (B), representative image of collagen (red stained) content in RV of control rat (1) MCT rats (2) and MCT rats treated with NAC from days 14 to day 28 after MCT exposure (3). All photomicrographs were taken at G20 magnification. 4: Bar graphs are summary data for cardiomyocyte area (n = 180 per group) and collagen area fraction (n = 60 per group), as mean ± SEM and *P < 0.05 vs cont (n = 180 per group).