Cardiac glycosides cause cytotoxicity in human macrophages and ameliorate white adipose tissue homeostasis.

BACKGROUND AND PURPOSE Cardiac glycosides (CGs) inhibit the Na+ ,K+ -ATPase and are widely prescribed medicines for chronic heart failure and cardiac arrhythmias. Recently, CGs have been described to induce inflammasome activation and pyroptosis in human macrophages, suggesting a cytotoxicity that remains to be elucidated in tissues. EXPERIMENTAL APPROACH To determine the cell type specificity of CG-mediated cytotoxicity, we used human primary monocyte-derived macrophages (hMDMs) and non-adherent peripheral blood cells isolated from healthy donors. Omental white adipose tissue (WAT) and stromal vascular fraction (SVF)-derived pre-adipocytes and adipocytes were isolated from obese patients undergoing bariatric surgery. All these primary cells/tissues were treated with nanomolar concentrations of ouabain (50nM, 100nM and 500nM) to investigate its degree of cytotoxicity and mechanisms leading to cell death. In WAT, we further explored the consequences of ouabain-mediated cytotoxicity by measuring insulin sensitivity, adipose tissue function and extracellular matrix (ECM) deposition ex vivo. KEY RESULTS The ouabain-induced cell death is through pyroptosis and apoptosis, and more efficient in hMDMs compared to non-adherent PBMC populations. This selective cytotoxicity is dependent on K+ flux, as ouabain causes an intracellular depletion of K+ , while inducing accumulation of Na+ and Ca2+ levels. Consistently, the cell-death caused by these ion imbalances can be rescued by addition of potassium chloride in hMDMs. Remarkably, when WAT explants from obese patients are cultured with nanomolar concentrations of ouabain, this causes depletion of macrophages, down-regulation of type VI collagen levels, and amelioration of insulin sensitivity ex vivo. CONCLUSIONS AND IMPLICATIONS These results suggest that the usage of nanomolar concentration of CGs can be an attractive therapeutic avenue in metabolic syndrome characterised by pathogenic infiltration and activation of macrophages.