Decreased renal AT1 receptor binding in rats after subtotal nephrectomy: PET study with [18F]FPyKYNE-losartan

Abstract

BackgroundSignificant renal mass reduction induced by 5/6 subtotal nephrectomy (Nx) is associated with a chain of events that culminates in hypertension and chronic kidney disease (CKD). Numerous studies have provided evidence for the role of angiotensin (Ang) II type 1 receptor (AT1R) in the promotion and progression of the disease; however, conflicting results were reported on intrarenal AT1R levels in CKD models.MethodsMale Sprague-Dawley rats (n = 26) underwent Nx or sham operations. Animals were scanned at 8–10 weeks post-surgery with PET using the novel AT1R radioligand [18F]FPyKYNE-losartan. Radioligand binding was quantified by kidney-to-blood ratio (KBR), standard uptake value (SUV), and distribution volume (DV). After sacrifice, plasma and kidney Ang II levels were measured. Western blot and 125I-[Sar1, Ile8]Ang II autoradiography were performed to assess AT1R expression.ResultsAt 8–10 weeks post-surgery, Nx rats developed hypertension, elevated plasma creatinine levels, left ventricle hypertrophy, increased myocardial blood flow (MBF), and reduced Ang II levels compared to shams. PET measurements displayed significant decrease in KBR (29 %), SUV (24 %), and DV (22 %) induced by Nx (p < 0.05), and these findings were confirmed by in vitro assays.ConclusionsReduced renal AT1Rs in hypertensive rats measured with [18F]FPyKYNE-losartan PET at 8–10 weeks following Nx support further use of this non-invasive approach in longitudinal studies to better understand the AT1R role in CKD progression.

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

“…Nx rats were hypertensive and had significantly higher plasma Cr levels compared to sham rat group before the start of therapy at 8–10 weeks post-surgery as we previously reported [31]. Nx rats had significantly higher SBP at 18–20 weeks post-surgery compared to shams (1.5-fold; p <0.001).…”

“…In prior work, we have shown reduced [ 18 F]FPyr-losartan retention (-23%) in the hypertrophied remnant kidney of Nx rats at 8–10 weeks compared to shams [31]. In this study, the -28% reduction obtained at 18–20 weeks with the same tracer was comparable to the early timepoint, indicating sustained reduced expression of renal AT 1 Rs in the untreated Nx rat.…”

“…In addition to being an important prognostic factor in progressive CKD, albuminuria is considered as an independent predictor of cardiovascular morbidity and mortality [ 44 , 45 ]. We have recently reported that induction of Nx in rats caused elevations in SBP and plasma Cr without evidence of albuminuria at 8–10 weeks post-surgery indicating intact glomerular barrier at that stage [ 31 ]. In the current work, development of significant albuminuria was observed with sustained hypertension and renal impairment at 18–20 weeks post-surgery.…”

“…However, this reduction in blood flow is not assumed to be the cause for diminished [ 18 F]FPyr-losartan uptake, since the AT 1 R reduction with PET was confirmed by [ 125 I]-[Sar 1 , Ile 8 ]Ang II autoradiography. This assumption is further validated by the fact that using the same model of CKD, Nx rats exhibited no change in the renal blood flow associated with the PET AT 1 R reduction at 8–10 weeks post-surgery [ 31 ]. Indeed, local factors as Ang II, tumor growth factor-beta (TGF-βa) [ 24 ] and endothelin-1 [ 54 ], or reduction of nitric oxide production [ 55 ] among others, can be implicated in the changes in the renal hemodynamics.…”

“…Preliminary PET studies with [ 18 F]fluoropyridine (FPyr)-losartan radioligand exhibited high binding selectivity for kidney AT1R over AT2R and rapid metabolism in rats, which supported the potential of this tracer for further renal AT1R evaluation. We have successfully demonstrated an in vivo reduction of renal AT 1 R cortical expression in rats with CKD at 8–10 weeks post 5/6 nephrectomy (Nx) using [ 18 F]FPyr-losartan with PET imaging [ 31 ]. The hypothesis of the present work was that PET imaging of AT 1 Rs would aid in identification of the kidney AT 1 R alterations in association with different actions of the drug treatments used in management of CKD.…”