Depth of the Steroid Core Location Determines the Mode of Na,K-ATPase Inhibition by Cardiotonic Steroids.

Artem M Tverskoi,Olga D Lopina,Yuri M Poluektov,Sergei N Orlov,Vladimir A Mitkevich,Elizaveta A Klimanova,Irina Yu Petrushanko,Alexander A Makarov

doi:10.3390/ijms222413268

Abstract

Cardiotonic steroids (CTSs) are specific inhibitors of Na,K-ATPase (NKA). They induce diverse physiological effects and were investigated as potential drugs in heart diseases, hypertension, neuroinflammation, antiviral and cancer therapy. Here, we compared the inhibition mode and binding of CTSs, such as ouabain, digoxin and marinobufagenin to NKA from pig and rat kidneys, containing CTSs-sensitive (α1S) and -resistant (α1R) α1-subunit, respectively. Marinobufagenin in contrast to ouabain and digoxin interacted with α1S-NKA reversibly, and its binding constant was reduced due to the decrease in the deepening in the CTSs-binding site and a lower number of contacts between the site and the inhibitor. The formation of a hydrogen bond between Arg111 and Asp122 in α1R-NKA induced the reduction in CTSs’ steroid core deepening that led to the reversible inhibition of α1R-NKA by ouabain and digoxin and the absence of marinobufagenin’s effect on α1R-NKA activity. Our results elucidate that the difference in signaling, and cytotoxic effects of CTSs may be due to the distinction in the deepening of CTSs into the binding side that, in turn, is a result of a bent-in inhibitor steroid core (marinobufagenin in α1S-NKA) or the change of the width of CTSs-binding cavity (all CTSs in α1R-NKA).

Highlights

Cardiotonic steroids (CTSs) or cardiac glycosides are a group of steroid compounds originally found in plants that were used for the treatment of heart failure
That ouabain and digoxin are pseudo-irreversible inhibitors due to the slow dissociation of the CTS–NKA complex [70,71]. We confirmed this in our experiment, where inhibitory effects of ouabain and digoxin, which were preincubated with α1S-NKA in E2P-conformation, were preserved after the dilution of complex CTS–NKA (Figure 2C,D)
We demonstrated differences between the interaction of ouabain, digoxin and marinobufagenin with α1S- and α1R-NKA

Summary

Introduction

Cardiotonic steroids (CTSs) or cardiac glycosides are a group of steroid compounds originally found in plants that were used for the treatment of heart failure. Later, they were found in the skin of toads, and some CTSs were isolated from human and animal biological liquids (endogenous CTSs). It was demonstrated that the increase in the endogenous CTSs concentration in human and animal blood may be involved in the development of preeclampsia, chronic kidney disease, hypertension and other cardiovascular diseases [7–12]. Interest in different CTSs is induced by their application in the treatment of cardiac diseases and potential use as agents with recently discovered anticancer [14] and antiviral activity [15–22]. All CTSs share a common structure: they have a steroid core with four cis-trans-cis-fused rings, a lactone ring at the 17-th position and a hydroxyl

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Discussion

Conclusion