MO255: Sparsentan Protects the Glomerular Basement Membrane and Glycocalyx, and Attenuates Proteinuria in a Rat Model of Focal Segmental Glomerulosclerosis (FSGS)
Authors: Bedard Patricia , Jenkinson Celia , Komers Radko 
Published: May 2022

Abstract

BACKGROUND AND AIMS
Sparsentan is a novel, dual acting, highly selective antagonist of the endothelin (ET-1) type A receptor (ETAR) and the angiotensin II (Ang II) subtype 1 receptor (AT1R). This first in class dual endothelin angiotensin receptor antagonist (DEARA) is being investigated in phase 3 clinical trials for focal segmental glomerulosclerosis (FSGS) and IgA nephropathy. Considering the broad spectrum of renal actions of ET-1 and Ang II, inhibition of both pathways using sparsentan is postulated to target multiple renal cell types and thereby ameliorate multiple pathophysiologic aspects of glomerular disease. The Adriamycin-induced nephropathy (ADR) rat model is a well-established model characterized by rapid podocyte injury and proteinuria followed by glomerulosclerosis (GS), with lesions reflective of those in human FSGS. The ADR rat model was used to assess the ability of sparsentan to attenuate kidney injury in an experimental FSGS setting.

METHOD
ADR was induced by a single IV dose of Adriamycin to male Sprague Dawley rats. Sham control animals (n = 10) received the Adriamycin vehicle only. Following disease induction, rats (10/group) were administered 0.5% MC/0.25% Tween 80 vehicle (VEH) or sparsentan at 20 (Spar20), 60 (Spar60), or 180 mg/kg (Spar180) by oral gavage once daily for 35 days and underwent periodic measurements of proteinuria (urine protein: creatinine ratio; UPCR). At the end of the treatment period, histological evaluations of the kidney were made by light and electron microscopy, and by immunohistochemistry to determine GS score (GSS, glomerular staining as %field area), podocyte number (p57 positive nuclei, count per glomerular area), glomerular basement membrane (GBM) morphology, glomerular glycocalyx (GLX) integrity (colloidal iron), and inflammatory cell infiltration (ED1 positivity, area of glomerular staining as %field area).

RESULTS
Numeric data are presented as mean ± SD. In groups dosed with Spar60 or Spar180 compared with VEH: the development of GSS was significantly reduced (P &lt; .0001; Spar60, 1.14 ± 0.21 or Spar180, 1.23 ± 0.21 versus VEH, 2.70 ± 0.14), increase in GBM width was significantly attenuated (Fig. 1), GLX staining was significantly greater (P = .0079, Spar60, 18.6 ± 1.86 or P = 0.0112, Spar180, 17.6 ± 2.40 versus VEH, 10 ± 1.18), and inflammatory cell infiltrate was significantly reduced (P = .0058, Spar60, 1.5 ± 0.43 or P = .0004, Spar180, 1.1 ± 0.16 versus VEH, 4.1 ± 0.66) in sparsentan-treated rats as compared with VEH. Additionally, podocyte number was significantly higher in the Spar180 group compared with VEH (P = .004, Spar180, 6.9 ± 0.91 versus VEH, 4.1 ± 0.31). Sparsentan-treated groups showed a consistent trend toward preservation of podocyte foot process width and number compared with VEH (Fig. 1). Further, Spar180 significantly attenuated development of UPCR at Day 14 compared with VEH (P = .0033) and there was a trend toward dose-dependent attenuation on both Day 14 and Day 33.

CONCLUSION
Dual antagonism of ETAR and AT1R by sparsentan protected rat kidneys in the ADR model of FSGS, as measured by its impact on multiple pathological disease features of the model, including attenuation of UPCR and podocyte loss, maintenance of GBM width, protection of GLX and reduction in glomerular macrophage infiltration.