α1A-Subtype adrenergic agonist therapy for the failing right ventricle

Abstract

Failure of the right ventricle (RV) is a serious disease with a poor prognosis and limited treatment options. Signaling by α₁-adrenergic receptors (α₁-ARs), in particular the α_1A-subtype, mediate cardioprotective effects in multiple heart failure models. Recent studies have shown that chronic treatment with the α_1A-subtype agonist A61603 improves function and survival in a model of left ventricular failure. The goal of the present study was to determine if chronic A61603 treatment is beneficial in a RV failure model. We used tracheal instillation of the fibrogenic antibiotic bleomycin in mice to induce pulmonary fibrosis, pulmonary hypertension, and RV failure within 2 wk. Some mice were chronically treated with a low dose of A61603 (10 ng·kg^-1·day^-1). In the bleomycin model of RV failure, chronic A61603 treatment was associated with improved RV fractional shortening and greater in vitro force development by RV muscle preparations. Cell injury markers were reduced with A61603 treatment (serum cardiac troponin I, RV fibrosis, and expression of matrix metalloproteinase-2). RV oxidative stress was reduced (using the probes dihydroethidium and 4-hydroxynonenal). Consistent with lowered RV oxidative stress, A61603 was associated with an increased level of the cellular antioxidant superoxide dismutase 1 and a lower level of the prooxidant NAD(P)H oxidase isoform NOX4. In summary, in the bleomycin model of RV failure, chronic A61603 treatment reduced RV oxidative stress, RV myocyte necrosis, and RV fibrosis and increased both RV function and in vitro force development. These findings suggest that in the context of pulmonary fibrosis, the α_1A-subtype is a potential therapeutic target to treat the failing RV.NEW & NOTEWORTHY Right ventricular (RV) failure is a serious disease with a poor prognosis and no effective treatments. In the mouse bleomycin model of RV failure, we tested the efficacy of a treatment using the α_1A-adrenergic receptor subtype agonist A61603. Chronic A61603 treatment improved RV contraction and reduced multiple indexes of RV injury, suggesting that the α_1A-subtype is a therapeutic target to treat RV failure.

Keywords: oxidative stress; reactive oxygen species; right ventricle; α1-adrenergic therapy.

Fig. 1.

Chronic A61603 treatment improved failing right ventricular (RV) function without affecting lung injury. Values from individual animals are shown with group means ± SE superimposed. A: echocardiographic assessment of RV fractional shortening (FS) 2 wk after tracheal instillation of bleomycin (Bleo) or saline (nonfailing) both with or without treatment with A61603. After bleomycin instillation, RV fractional shortening was reduced versus the nonfailing RV (***P < 0.001). After bleomycin instillation, RV fractional shortening was higher with A61603 treatment (**P < 0.01). B: lung weight (relative to body weight) was increased by bleomycin instillation (****P < 0.0001) but was not affected by A61603 treatment (ns, not significant; P > 0.999), suggesting lung injury was not reduced by A61603 treatment. C: lung histology showed that relative to saline instillation, bleomycin instillation resulted in severe lung fibrosis that was not affected by A61603 treatment (magnification ×40).

Fig. 2.

Chronic A61603 treatment reduced right ventricular (RV) injury due to bleomycin (Bleo). A: serum levels of cardiac troponin I (cTnI) 2 wk after tracheal instillation of bleomycin or saline (nonfailing) both with or without treatment with A61603. Compared with the nonfailing RV, after bleomycin instillation cTnI was increased (****P < 0.0001) but was appreciably lower with concurrent A61603 treatment (****P < 0.0001). B: compared with the nonfailing RV, after bleomycin instillation RV fibrosis was increased versus the nonfailing RV (***P < 0.001) but was lower with concurrent A61603 treatment (*P < 0.05).

Fig. 3.

Chronic A61603 treatment improved myofilament force development. A: myofilament force development in demembranated right ventricular (RV) muscle samples at various levels of activator Ca²⁺ concentration ([Ca²⁺]), expressed as pCa (−log [Ca²⁺]). Compared with the nonfailing RV, force development was impaired in the bleomycin (Bleo) model. Force development was higher with concurrent A61603 treatment. B: maximum Ca²⁺-activated force (F_max) determined by fitting data to the Hill equation (35). The reduction of F_max in the bleomycin model (****P < 0.0001) was attenuated by A61603 (***P < 0.001).

Fig. 4.

Chronic A61603 treatment improved contraction and reduced cardiomyocyte necrosis. Shown is a summary of averaged data for right ventricular (RV) fractional shortening (FS; black circles) and maximum myofilament force (F_max; gray triangles) relative to the serum level of cardiac troponin I (cTnI; from data shown in Figs. 1–3). Bleomycin (Bleo) increased cTnI and caused proportional reductions in both RV FS and F_max. These changes were attenuated by concurrent treatment with A61603.

Fig. 5.

Chronic A61603 treatment reduced expression of two isoforms of matrix metalloproteinase-2 (MMP-2). A and B: summary of quantitative RT-PCR measurements of the expression of two MMP-2 isoforms: the canonical full-length isoform (FL-MMP-2; A) and the NH₂-terminal truncated isoform (NTT-MMP-2; B). *P < 0.05. Bleo, bleomycin.

Fig. 6.

Chronic A61603 treatment reduced reactive oxygen species (ROS)-dependent dihydroethidium (DHE) fluorescence. A: representative images of DHE fluorescence from frozen sections of right ventricular myocardium. DHE fluorescence was low in nonfailing hearts and markedly increased in the bleomycin (Bleo) model. This increase was prevented with concurrent treatment with A61603. B: pooled data. *P < 0.05; **P < 0.01.

Fig. 7.

Chronic A61603 treatment reduced reactive oxygen species-dependent 4-hydroxynonenal (4-HNE). A: Western blot for detection of 4-HNE in right ventricular homogenates. B: pooled data showing that 4-HNE was increased in the bleomycin (Bleo) model and that this increase was prevented with chronic A61603 treatment. **P < 0.01.

Fig. 8.

Chronic A61603 treatment increased superoxide dismutase 1 (SOD1). A: Western blot for detection of SOD1 in right ventricular homogenates. B: pooled data showing that SOD1 was increased in the bleomycin (Bleo) model with chronic A61603 treatment. *P < 0.05.

Fig. 9.

Chronic A61603 treatment reduced NAD(P)H oxidase 4 (NOX4). A: Western blot for detection of NOX4 in right ventricular homogenates. B: pooled data showing that NOX4 was lower in the bleomycin (Bleo) model with chronic A61603 treatment. *P < 0.05.

Fig. 10.

Hypothetical scheme linking chronic A61603 treatment to a beneficial effect on the failing right ventricle (RV) via lowering of oxidative stress. NOX4, NAD(P)H oxidase 4; ROS, reactive oxygen species; SOD1, superoxide dismutase 1; MMP-2, matrix metalloproteinase-2.