Treatment with enalapril and not diltiazem ameliorated progression of chronic kidney disease in rats, and normalized renal AT1 receptor expression as measured with PET imaging

Abstract

ACE inhibitors are considered first line of treatment in patients with many forms of chronic kidney disease (CKD). Other antihypertensives such as calcium channel blockers achieve similar therapeutic effectiveness in attenuating hypertension-related renal damage progression. Our objective was to explore the value of positron emission tomography (PET) imaging of renal AT1 receptor (AT1R) to guide therapy in the 5/6 subtotal-nephrectomy (Nx) rat model of CKD. Ten weeks after Nx, Sprague-Dawley rats were administered 10mg/kg/d enalapril (NxE), 30mg/kg/d diltiazem (NxD) or left untreated (Nx) for an additional 8-10 weeks. Kidney AT1R expression was assessed using in vivo [18F]fluoropyridine-losartan PET and in vitro autoradiography. Compared to shams, Nx rats exhibited higher systolic blood pressure that was reduced by both enalapril and diltiazem. At 18-20 weeks, plasma creatinine and albuminuria were significantly increased in Nx, reduced to sham levels in NxE, but enhanced in NxD rats. Enalapril treatment decreased kidney angiotensin II whereas diltiazem induced significant elevations in plasma and kidney levels. Reduced PET renal AT1R levels in Nx were normalized by enalapril but not diltiazem, and results were supported by autoradiography. Reduction of renal blood flow in Nx was restored by enalapril, while no difference was observed in myocardial blood flow amongst groups. Enhanced left ventricle mass in Nx was not reversed by enalapril but was augmented with diltiazem. Stroke volume was diminished in untreated Nx compared to shams and restored with both therapies. [18F]Fluoropyridine-Losartan PET allowed in vivo quantification of kidney AT1R changes associated with progression of CKD and with various pharmacotherapies.

Fig 1. Study timeline of the 5/6 nephrectomy animal model of chronic kidney disease.

Treatment (Rx): ACEI (Enalapril 10mg/kg) or CCB (Diltiazem 30mg/kg) started at 10 weeks post-surgery and all parameters assessed at 18–20 weeks post-surgery. SBP: systolic blood pressure; RBF: renal blood flow; MBF: myocardial blood flow; RIA: radioimmunoassay.

Fig 2

Body weight data obtained weekly over 10 weeks (A), terminal left kidney weight for sham (N = 8), Nx (N = 8), NxE (N = 6) and NxD (N = 8) (B) and heart weight for sham (N = 8), Nx (N = 9), NxE (N = 9) and NxD (N = 8) (C) normalized to body weight at 18–20 weeks post-surgery. Data are presented as mean±SD. * p<0.05 vs sham, ^$ p<0.05 vs Nx, ^# p<0.05 vs NxE (p<0.05).

Fig 3

Ang II levels in plasma samples of sham (N = 4), Nx (N = 5), NxE (N = 5) and NxD (N = 6) (A), left kidney samples of sham (N = 5), Nx (N = 6), NxE (N = 5) and NxD (N = 5) (B) and left ventricle samples of sham (N = 6), Nx (N = 7), NxE (N = 5) and NxD (N = 6) (C) samples of Sham, Nx, NxE and NxD groups at 18–20 weeks post-surgery. In boxplots, horizontal lines represent median and whiskers represent minimum and maximum values. Data are presented as mean±SD. * p<0.05 vs sham, ^$ p<0.05 vs Nx, ^# p<0.05 vs NxE (p<0.05).

Fig 4

Representative coronal view microPET scans showing liver and kidney uptake obtained at 5–10 min post-injection of [¹⁸F]FPyr-losartan in all groups at 18–20 weeks post-surgery; Sham (A), Nx (B), NxE (C) and NxD (D). Images are displayed using same SUV scale. Kidney distribution volume (DV, ml/cm³) of [¹⁸F]FPyr-losartan obtained with PET in vivo in sham (N = 6), Nx (N = 7), NxE (N = 7) and NxD (N = 6) (E); and ¹²⁵I-[Sar¹, Ile⁸]Ang II binding density (counts/mm²) obtained with in vitro autoradiography in sham (N = 4), Nx (N = 4), NxE (N = 6) and NxD (N = 4) (F) at 18–20 weeks post-surgery. In boxplots, horizontal lines represent median and whiskers represent minimum and maximum values. Data are presented as mean±SD. * p<0.05 vs sham, ^$ p<0.05 vs Nx, ^# p<0.05 vs NxE (p<0.05).

Fig 5

Renal blood flow in sham (N = 7), Nx (N = 7), NxE (N = 5) and NxD (N = 7) groups (A); and myocardial blood flow values in sham (N = 6), Nx (N = 5), NxE (N = 6) and NxD (N = 5) (B) at 18–20 weeks post-surgery. Blood flow was assessed by [¹³N]ammonia PET imaging. In boxplots, horizontal lines represent median and whiskers represent minimum and maximum values. Data are presented as mean±SD. * p<0.05 vs sham, ^$ p<0.05 vs Nx, ^# p<0.05 vs NxE (p<0.05).