Effect of Dietary Aryl Hydrocarbon Receptor Ligands on Indoxyl Sulfate-Induced Endothelial Activation

Patients with chronic kidney disease (CKD) are exposed to high levels of uremic toxins and have an increased risk of cardiovascular disease. Among these toxins, indolic compounds such as indoxyl sulfate (IS) are predictors of cardiovascular events and mortality in CKD patients and induce a procoagulant and proinflammatory vascular phenotype through activation of the aryl hydrocarbon receptor (AhR). Targeting AhR activation by indolic toxins may therefore help prevent cardiovascular complications in CKD. To this end, we investigated in vitro whether natural dietary AhR ligands (galangin, quercetin, curcumin and indole-3-carbinol) could antagonize IS-induced AhR activation and the associated inflammatory response in endothelial cells. The activation of the AhR genomic pathway was assessed by measuring the expression of AhR target genes (CYP1A1, CYP1B1, and AHRR) in endothelial cells and by evaluating AhR-dependent transcriptional activity using a CALUX-AHRE luciferase reporter assay in HG40/6 cells. In parallel, endothelial inflammation was evaluated by analyzing the expression of AhR-related inflammatory genes: F3/tissue factor, PTGS2/COX-2, CCL2/MCP-1, and CXCL8/IL-8. Quercetin was the only ligand capable of antagonizing IS-induced AhR transcriptional activity, as well as the upregulation of the endothelial AhR target genes CYP1A1 and CYP1B1. In contrast, galangin, curcumin, and I3C exhibited no inhibitory effects. Moreover, none of the tested dietary AhR ligands suppressed the IS-induced upregulation of endothelial inflammatory genes; instead, they tended to potentiate IS-induced inflammatory responses at high concentrations. In conclusion, among the AhR ligands tested, quercetin was the only one that attenuated IS-induced activation of the AhR genomic pathway in endothelial cells. However, it may also enhance IS-mediated endothelial inflammation, an effect also observed at specific concentrations of galangin, curcumin, and I3C. These findings suggest that the potential beneficial effects of natural dietary AhR ligands should be carefully considered in the context of CKD patients exhibiting high levels of indolic uremic toxins.