The Evidence for Sparsentan-Mediated Inhibition of INa and IK(erg): Possibly Unlinked to Its Antagonism of Angiotensin II or Endothelin Type a Receptor.

Tzu-Hsien Chuang,Hsin-Yen Cho,Sheng-Nan Wu

doi:10.3390/biomedicines10010086

Abstract

Sparsentan is viewed as a dual antagonist of endothelin type A (ETA) receptor and angiotensin II (AngII) receptor and it could be beneficial in patients with focal segmental glomerulosclerosis. Moreover, it could improve glomerular filtration rate and augment protective tissue remodeling in mouse models of focal segmental glomerulosclerosis. The ionic mechanisms through which it interacts with the magnitude and/or gating kinetics of ionic currents in excitable cells were not thoroughly investigated. Herein, we aimed to examine the effects of varying sparsentan concentrations on ionic currents residing in pituitary GH3 somatolactotrophs. From whole-cell current recordings made in GH3 cells, sparsentan (0.3–100 μM) differentially inhibited the peak and late components of voltage-gated Na+ current (INa). The IC50 value of sparsentan required to exert a reduction in peak and late INa in GH3 cells was 15.04 and 1.21 μM, respectively; meanwhile, the KD value estimated from its shortening in the slow component of INa inactivation time constant was 2.09 μM. The sparsentan (10 μM) presence did not change the overall current–voltage relationship of INa; however, the steady-state inactivation curve of the current was shifted to more negative potential in its presence (10 μM), with no change in the gating charge of the curve. The window INa activated by a brief upsloping ramp was decreased during exposure to sparsentan (10 μM); moreover, recovery of peak INa became slowed in its presence. The Tefluthrin (Tef)-stimulated resurgent INa activated in response to abrupt depolarization followed by the descending ramp pulse was additionally attenuated by subsequent application of sparsentan. In continued presence of Tef (3 μM) or β-pompilidotoxin (3 μM), further application of sparsentan (3 μM) reversed their stimulation of INa. However, sparsentan-induced inhibition of INa failed to be overcome by subsequent application of either endothelin 1 (1 μM) or angiotensin II (1 μM); moreover, in continued presence of endothelin (1 μM) or angiotensin II (1 μM), further addition of sparsentan (3 μM) effectively decreased peak INa. Additionally, the application of sparsentan (3 μM) inhibited the peak and late components of erg-mediated K+ current in GH3 cells, although it mildly decreased the amplitude of delayed-rectifier K+ current. Altogether, this study provides a distinct yet unidentified finding that sparsentan may perturb the amplitude or gating of varying ionic currents in excitable cells.

Highlights

Sparsentan (40 -[(2-butyl-4-oxo-1,3-diazaspiro[4.4]non-1-en-3-yl)methyl]-N-(4,5-dimethyl3-isoxazolyl)-20 -(ethoxymethyl)[1,10 -biphenyl]-2-sulfonamide), known as RE-021, PS433540 and DARA-a, is a first-in-class, orally active, dual-acting, selective antagonist of the angiotensin II (AngII) type 1 receptor and the endothelin type A (ETA ) receptor [1]
We further studied the inhibitory effect of sparsentan on INa at different levels of membrane potentials, and an I-V relationship of peak INa without or with the sparsentan existence was established
Results in Figure showedfrom that, in th reflect that the presence of sparsentan causes significant prolongation in the3recovery trol, the peak amplitude of INa was almost comp inactivation of peak INawas in GH

Summary

Introduction

Sparsentan (40 -[(2-butyl-4-oxo-1,3-diazaspiro[4.4]non-1-en-3-yl)methyl]-N-(4,5-dimethyl3-isoxazolyl)-20 -(ethoxymethyl)[1,10 -biphenyl]-2-sulfonamide), known as RE-021, PS433540 and DARA-a, is a first-in-class, orally active, dual-acting, selective antagonist of the angiotensin II (AngII) type 1 receptor and the endothelin type A (ETA ) receptor [1]. It is expected to provide meaningful clinical benefits in mitigating proteinuria as well as in improving glomerular filtration rate, not related to a cardiovascular therapy [7,8,11,12] This compound could improve glomerular filtration rate and augment protective tissue remodeling in mouse models of focal segmental gloomerulosclerosis [14]. ETA receptor transcripts have been previously reported to be identified in rat anterior pituitary [15]. The binding of endothelin to ETA receptors in pituitary lactotrophs has been demonstrated to inhibit voltage-gated Ca2+ influx through Gi/o signaling pathway [16] and to decrease prolactin release [17]. Angiotensin II was previously reported to influence the growth and angiogenic activity in pituitary GH3 cells [18]. Endothelin was previously reported to induce degeneration of cultured motor neurons [19] or to exercise action on the vestibular nuclei and on the maintenance of equilibrium [20]

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