Indoxyl Sulfate Activates NLRP3 Inflammasome to Induce Cardiac Contractile Dysfunction Accompanied by Myocardial Fibrosis and Hypertrophy

In patients with chronic kidney diseases (CKD), high serum indoxyl sulfate (IS) levels correlate with cardiac fibrosis and hypertrophy and thus a critical risk factor for heart failure. The aim of this study was to determine the effects of IS on cardiac function and inflammasome pathway in a rat model of CKD. We assessed the physiological and pathological changes and measured biomarkers of fibrosis and hypertrophy in the hearts of Dahl salt-sensitive (DS), DS hypertensive (DH), and DH IS-treated rats (DH + IS). Low left ventricular (LV) ejection fraction, LV dilatation, and advanced myocardial fibrosis and hypertrophy were observed in DH + IS, which resemble changes found in uremic cardiomyopathy. These changes were independent of renal function and blood pressure. RT-PCR and western blotting analysis showed upregulation of fibrosis and hypertrophy-related biomarkers and adhesion molecules in the hearts of DH + IS rats. IS activated aryl hydrocarbon receptor (AHR) pathway, nuclear factor kappa B p65 (NF-κB p65), and inflammasome in the myocardium of DH + IS rat. Moreover, IS upregulated the expression of critical NLRP3 inflammasome components (NLRP3, ASC, and procaspase-1) and increased production of IL-1β and IL-18. Finally, IS upregulated various inflammatory cytokines, such as MCP-1, TNF-α, IL-6, and TGFβ1, in the myocardium. Our results suggested that IS induced cardiac fibrosis and hypertrophy and impaired LV function through activation of cardiac NLRP3 inflammasome via the AHR/NF-κB pathway.