Ouabain prevents pathological cardiac hypertrophy and heart failure through activation of phosphoinositide 3-kinase α in mouse.

Jian Wu,Lijun Liu,Mustafa Baldawi,Marjorie E Gable,Amir Askari,Daxiang Li,Lingling Du

doi:10.1186/s13578-015-0053-7

Abstract

Background Use of low doses of digitalis to prevent the development of heart failure was advocated decades ago, but conflicting results of early animal studies dissuaded further research on this issue. Recent discoveries of digitalis effects on cell signal pathways prompted us to reexamine the possibility of this prophylactic action of digitalis. The specific aim of the present study was to determine if subinotropic doses of ouabain would prevent pressure overload-induced cardiac remodeling in the mouse by activating phosphoinositide 3-kinase α (PI3Kα).ResultsStudies were done on an existing transgenic mouse deficient in cardiac PI3Kα (p85-KO) but with normal cardiac contractility, a control mouse (Con), and on cultured adult cardiomyocytes. In Con myocytes, but not in p85-KO myocytes, ouabain activated PI3Kα and Akt, and caused cell growth. This occurred at low ouabain concentrations that did not activate the EGFR-Src/Ras/Raf/ERK cascade. Con and p85-KO mice were subjected to transverse aortic constriction (TAC) for 8 weeks. A subinotropic dose of ouabain (50 µg/kg/day) was constantly administrated by osmotic mini-pumps for the first 4 weeks. All mice were monitored by echocardiography throughout. Ouabain early treatment attenuated TAC-induced cardiac hypertrophy and fibrosis, and improved cardiac function in TAC-operated Con mice but not in TAC-operated p85-KO mice. TAC downregulated α2-isoform of Na+/K+-ATPase but not its α1-isoform in Con hearts, and ouabain treatment prevented the downregulation of α2-isoform. TAC-induced reduction of α2-isoform did not occur in p85-KO hearts.ConclusionsOur results show that (a) safe doses of ouabain prevent or delay cardiac remodeling of pressure overloaded mouse heart; and (b) these prophylactic effects are due to ouabain binding to α2-isoform resulting in the selective activation of PI3Kα. Our findings also suggest that potential prophylactic use of digitalis for prevention of heart failure in man deserves serious consideration.Electronic supplementary materialThe online version of this article (doi:10.1186/s13578-015-0053-7) contains supplementary material, which is available to authorized users.

Highlights

Use of low doses of digitalis to prevent the development of heart failure was advocated decades ago, but conflicting results of early animal studies dissuaded further research on this issue
Our results summarized below are consistent with and reinforce those of Luo et al [16]: (1) In the p85-KO mouse, relative to Cre mice (Control mice), protein levels of p85α and p110α of phosphoinositide 3-kinase α (PI3Kα) were greatly reduced in the lysates of the whole heart or the isolated cardiomyocytes, whereas the levels of p110γ of PI3Kγ remained unchanged (Fig. 1a); (2) in cardiomyocyte lysates of the p85-KO mouse, relative to those of the control, the basal level of PI3Kα activity was greatly reduced, while the activity of PI3Kγ was unchanged (Fig. 1b)
The remaining 10 % of the PI3Kα activity in the lysate of the p85-KO myocytes is most likely due to myocytes that have escaped gene deletion as noted before [16], and as it has been established in cases of many other cardiac-specific deletions [14, 17]; (3) when intact cardiomyoyctes isolated from the p85-KO and the control mice were exposed to insulin, the expected activation of Akt was noted in the control myocytes, but greatly reduced in the p85-KO myocytes (Fig. 1c)

Summary

Introduction

Use of low doses of digitalis to prevent the development of heart failure was advocated decades ago, but conflicting results of early animal studies dissuaded further research on this issue. We present the results of initial studies using fresh experimental approaches to test for the possible prophylactic effect of digitalis on the heart that is subjected to pressure overload. Digitalis drugs (such as digoxin, digitoxin, and ouabain) are highly specific inhibitors of the Na+/K+-ATPase of the plasma membrane of most of higher eukaryotic cells [6, 7]. This enzyme (the sodium pump) catalyzes the coupled active transport of Na+ and K+, maintains resting membrane potential, regulates cell volume, and enables the Na+-coupled transports of a multitude of nutrients and other ions across the cell membrane. There are multiple isoforms of each subunit with tissue and species specificities, and variations among the digitalis sensitivities of the isoforms [6,7,8]

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