In chronic kidney disease (CKD), uremic solutes accumulate in blood and tissues. These compounds probably contribute to the marked increase in cardiovascular risk during the progression of CKD. The uremic solutes indoxyl sulfate and indole-3-acetic acid (IAA) are particularly deleterious for endothelial cells. Here we performed microarray and comparative PCR analyses to identify genes in endothelial cells targeted by these two uremic solutes. We found an increase in endothelial expression of tissue factor in response to indoxyl sulfate and IAA and upregulation of eight genes regulated by the transcription factor aryl hydrocarbon receptor (AHR). The suggestion by microarray analysis of an involvement of AHR in tissue factor production was confirmed by siRNA inhibition and the indirect AHR inhibitor geldanamycin. These observations were extended to peripheral blood mononuclear cells. Tissue factor expression and activity were also increased by AHR agonist dioxin. Finally, we measured circulating tissue factor concentration and activity in healthy control subjects and in patients with CKD (stages 3-5d), and found that each was elevated in patients with CKD. Circulating tissue factor levels were positively correlated with plasma indoxyl sulfate and IAA. Thus, indolic uremic solutes increase tissue factor production in endothelial and peripheral blood mononuclear cells by AHR activation, evoking a 'dioxin-like' effect. This newly described mechanism of uremic solute toxicity may help understand the high cardiovascular risk of CKD patients

In CKD, uremic solutes may induce endothelial dysfunction, inflammation, and oxidative stress, leading to increased cardiovascular risk. We investigated whether the uremic solute indole-3 acetic acid (IAA) predicts clinical outcomes in patients with CKD and has prooxidant and proinflammatory effects. We studied 120 patients with CKD. During the median study period of 966 days, 29 patients died and 35 experienced a major cardiovascular event. Kaplan-Meier analysis revealed that mortality and cardiovascular events were significantly higher in the higher IAA group (IAA.3.73 mM) than in the lower IAA group (IAA,3.73 mM). Multivariate Cox regression analysis demonstrated that serum IAA was a significant predictor of mortality and cardiovascular events after adjustments for age and sex; cholesterol, systolic BP, and smoking; C-reactive protein, phosphate, body mass index, and albumin; diastolic BP and history of cardiovascular disease; and uremic toxins p-cresyl sulfate and indoxyl sulfate. Notably, IAA level remained predictive of mortality when adjusted for CKD stage. IAA levels were positively correlated with markers of inflammation and oxidative stress: C-reactive protein and malondialdehyde, respectively. In cultured human endothelial cells, IAA activated an inflammatory nongenomic aryl hydrocarbon receptor (AhR)/p38MAPK/NF-kB pathway that induced the proinflammatory enzyme cyclooxygenase-2. Additionally, IAA increased production of endothelial reactive oxygen species. In conclusion, serum IAA may be an independent predictor of mortality and cardiovascular events in patients with CKD. In vitro, IAA induces endothelial inflammation and oxidative stress and activates an inflammatory AhR/p38MAPK/NF-kB pathway.

Patients with chronic kidney disease (CKD) have a higher risk of cardiovascular diseases and suffer from accelerated atherosclerosis. CKD patients are permanently exposed to uremic toxins, making them good candidates as pathogenic agents. We focus here on uremic toxins from tryptophan metabolism because of their potential involvement in cardiovascular toxicity: indolic uremic toxins (indoxyl sulfate, indole-3 acetic acid, and indoxyl-β-d-glucuronide) and uremic toxins from the kynurenine pathway (kynurenine, kynurenic acid, anthranilic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, and quinolinic acid). Uremic toxins derived from tryptophan are endogenous ligands of the transcription factor aryl hydrocarbon receptor (AhR). AhR, also known as the dioxin receptor, interacts with various regulatory and signaling proteins, including protein kinases and phosphatases, and Nuclear Factor-Kappa-B. AhR activation by 2,3,7,8-tetrachlorodibenzo-p-dioxin and some polychlorinated biphenyls is associated with an increase in cardiovascular disease in humans and in mice. In addition, this AhR activation mediates cardiotoxicity, vascular inflammation, and a procoagulant and prooxidant phenotype of vascular cells. Uremic toxins derived from tryptophan have prooxidant, proinflammatory, procoagulant, and pro-apoptotic effects on cells involved in the cardiovascular system, and some of them are related with cardiovascular complications in CKD. We discuss here how the cardiovascular effects of these uremic toxins could be mediated by AhR activation, in a “dioxin-like” effect.