Beta Blockade Prevents Cardiac Morphological and Molecular Remodelling in Experimental Uremia

Abstract

Heart failure and chronic kidney disease (CKD) share several mediators of cardiac pathological remodelling. Akin to heart failure, this remodelling sets in motion a vicious cycle of progressive pathological hypertrophy and myocardial dysfunction in CKD. Several decades of heart failure research have shown that beta blockade is a powerful tool in preventing cardiac remodelling and breaking this vicious cycle. This phenomenon remains hitherto untested in CKD. Therefore, we set out to test the hypothesis that beta blockade prevents cardiac pathological remodelling in experimental uremia. Wistar rats had subtotal nephrectomy or sham surgery and were followed up for 10 weeks. The animals were randomly allocated to the beta blocker metoprolol (10 mg/kg/day) or vehicle. In vivo and in vitro cardiac assessments were performed. Cardiac tissue was extracted, and protein expression was quantified using immunoblotting. Histological analyses were performed to quantify myocardial fibrosis. Beta blockade attenuated cardiac pathological remodelling in nephrectomised animals. The echocardiographic left ventricular mass and the heart weight to tibial length ratio were significantly lower in nephrectomised animals treated with metoprolol. Furthermore, beta blockade attenuated myocardial fibrosis associated with subtotal nephrectomy. In addition, the Ca⁺⁺- calmodulin-dependent kinase II (CAMKII) pathway was shown to be activated in uremia and attenuated by beta blockade, offering a potential mechanism of action. In conclusion, beta blockade attenuated hypertrophic signalling pathways and ameliorated cardiac pathological remodelling in experimental uremia. The study provides a strong scientific rationale for repurposing beta blockers, a tried and tested treatment in heart failure, for the benefit of patients with CKD.

Keywords: CKD; beta blocker; cardiac remodelling; uremia.

Figure 1

The central theme of several decades of heart failure research demonstrating a vicious cycle set in motion between pathological cardiac remodelling and myocardial dysfunction and the mechanisms and mediators of such pathology. The figure also shows the common mediators of pathological hypertrophy shared between heart failure and CKD. CKD: chronic kidney disease, SNS: sympathetic nervous system, RAAS: renin angiotensin aldosterone system, FGF23: fibroblast growth factor 23.

Figure 2

Subtotal nephrectomy increases serum creatinine and urea levels. Serum creatinine (µmol/L) (A) and urea (mmol/L) (B) at 10 weeks post-sham or -STNx ± metoprolol. (*** p < 0.001, **** p < 0.0001) (n = 7–12).

Figure 3

Metoprolol attenuates subtotal nephrectomy induced indices of cardiac mass. Echocardiographic assessment of left ventricular mass (A) and interventricular septal thickness in diastole (B) and systole (C), 8 weeks post-sham or -STNx ± metoprolol. (* p < 0.05, ** p < 0.01, *** p < 0.001) (n = 8–12).

Figure 4

Effect of metoprolol on cardiac hemodynamics. Cardiac parameters as assessed by Millar pressure-volume conductance catheters. Heart rate (A), blood pressure (B), left ventricular ejection fraction (C) and end diastolic pressure (D) measured 10 weeks post-sham or -STNx ± metoprolol. (* p < 0.05, ** p < 0.01, *** p < 0.001) (n = 8–11).

Figure 5

Metoprolol attenuates subtotal nephrectomy-induced left ventricular hypertrophy. Ventricular weight/tibia length ratio (cardiac weight index) from animals 10 weeks post-sham or -STNx ± metoprolol (A). Histological assessment of left ventricular mass 10 weeks post-sham or -STNx ± metoprolol (B). Hearts stained with H&E. (* p < 0.05, ** p < 0.01) (n = 4–12). Scale bars 200 µm.

Figure 6

Metoprolol attenuates subtotal nephrectomy-induced cardiac fibrosis. Fibrosis is increased in ventricles of the heart 10 weeks post-nephrectomy, an effect attenuated with metoprolol. Representative histological images of 5µm sections of ventricle stained for collagen with picrosirius red in sham hearts (A) following STNx alone (B) and co-treatment with metoprolol (C). Summary of quantification of collagen staining in ventricles of rats 10 weeks post-sham or -STNx ± metoprolol (D). (* p < 0.05, ** p < 0.01) (n = 7–8). Scale bar 200 µm.

Figure 7

Metoprolol attenuates subtotal nephrectomy-induced CaMKII activation. Representative western blots of phosphorylated CaMKII (CaMKII-p) and beta-actin along with summary of CaMKII-p quantification (A) and representative western blot of total CAMKII and the corresponding summary of total CAMII quantification (B) in ventricles of rats 10 weeks post-sham or -STNx ± metoprolol. (* p < 0.05, ** p < 0.01) (n = 6–7).

Figure 8

Metoprolol attenuates subtotal nephrectomy-induced PKA activation. Representative western blots of phosphorylated phosphorylate PKA (PKA-p) and beta-actin along with summary of PKA-p quantification (A) and representative western blot of total PKA and the corresponding summary of total PKA quantification (B) in ventricles of rats 10 weeks post-sham or -STNx ± metoprolol. (* p < 0.05, ** p < 0.01,*** p < 0.001) (n = 8–13).