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      Indoxyl Sulfate Induces IL-6 Expression in Vascular Endothelial and Smooth Muscle Cells through OAT3-Mediated Uptake and Activation of AhR/NF-κB Pathway

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          Background/Aims: Interleukin-6 (IL-6) is one of the inflammation biomarkers with highest predictive value for outcome in chronic kidney disease (CKD) patients. The present study aimed to determine the effects of indoxyl sulfate (IS) on IL-6 expression in vascular cells. Methods: IS was administered to normo- and hypertensive rats. Human umbilical vein endothelial cells (HUVECs) and human aortic smooth muscle cells (HASMCs) were incubated with or without IS. Results: Immunohistochemistry revealed that IS-administered rats showed increased expression of IL-6 in the aortic tissues. IS increased IL-6 expression in HUVECs and HASMCs in a time- and dose-dependent manner. Knockdown of organic anion transporter 3 (OAT3) using small interfering RNA (siRNA) inhibited IS-induced expression of IL-6 in HUVECs and HASMCs. IS induced activation of aryl hydrocarbon receptor (AhR) and nuclear factor-κB (NF-κB) subunit p65 in HUVECs and HASMCs. Both AhR siRNA and p65 siRNA inhibited IS-induced expression of IL-6. AhR siRNA inhibited IS-induced phosphorylation and nuclear translocation of p65 without change in total p65 level. However, p65 siRNA did not inhibit IS-induced nuclear translocation of AhR. Thus, AhR is responsible for IS-induced p65 signaling transduction. Conclusion: IS induces IL-6 expression in vascular endothelial and smooth muscle cells through OAT3/AhR/NF-κB pathway.

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          Most cited references 21

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          The uremic toxin 3-indoxyl sulfate is a potent endogenous agonist for the human aryl hydrocarbon receptor.

          The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor involved in the regulation of multiple cellular pathways, such as xenobiotic metabolism and Th17 cell differentiation. Identification of key physiologically relevant ligands that regulate AHR function remains to be accomplished. Screening of indole metabolites has identified indoxyl 3-sulfate (I3S) as a potent endogenous ligand that selectively activates the human AHR at nanomolar concentrations in primary human hepatocytes, regulating transcription of multiple genes, including CYP1A1, CYP1A2, CYP1B1, UGT1A1, UGT1A6, IL6, and SAA1. Furthermore, I3S exhibits an approximately 500-fold greater potency in terms of transcriptional activation of the human AHR relative to the mouse AHR in cell lines. Structure-function studies reveal that the sulfate group is an important determinant for efficient AHR activation. This is the first phase II enzymatic product identified that can significantly activate the AHR, and ligand competition binding assays indicate that I3S is a direct AHR ligand. I3S failed to activate either CAR or PXR. The physiological importance of I3S lies in the fact that it is a key uremic toxin that accumulates to high micromolar concentrations in kidney dialysis patients, but its mechanism of action is unknown. I3S represents the first identified relatively high potency endogenous AHR ligand that plays a key role in human disease progression. These studies provide evidence that the production of I3S can lead to AHR activation and altered drug metabolism. Our results also suggest that prolonged activation of the AHR by I3S may contribute to toxicity observed in kidney dialysis patients and thus represent a possible therapeutic target.
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            Indolic uremic solutes increase tissue factor production in endothelial cells by the aryl hydrocarbon receptor pathway.

            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.
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              Interleukin-6 predicts hypoalbuminemia, hypocholesterolemia, and mortality in hemodialysis patients.

              Low serum albumin and low serum cholesterol levels are among the most consistent predictors of mortality in patients with end-stage renal disease (ESRD) undergoing hemodialysis. Hypoalbuminemia is often interpreted as a marker of poor nutrition, but serum albumin and cholesterol levels can also be low as part of a cytokine-mediated acute-phase reaction to acute or chronic inflammation. Here we report the results from a 900-day prospective study designed to determine whether tumor necrosis factor-alfa (TNF-alpha) and interleukin-6 (IL-6) predict serum albumin and cholesterol levels and mortality in a group of 90 ambulatory, adult hemodialysis patients with no acute infection, hospitalization or surgery, and no known acquired immunodeficiency syndrome (AIDS), malignancy, or liver disease. Measurable levels of TNF-alpha and/or IL-6 were found in 89 of 90 patients. Significant relationships were found between TNF-alpha and IL-6 and the degree of hypoalbuminemia and dyslipoproteinemia. IL-6 was the strongest predictor of mortality in univariate and multivariate analysis, followed by age, albumin level, and body mass index (BMI). Although the cause of hypercytokinemia was not addressed in this study, the data support the view that hypoalbuminemia and hypocholesterolemia are negative acute-phase responses to inflammatory stimuli. These results suggest that efforts to identify the nature of the stimuli for cytokine production and to lower cytokine levels in hemodialysis patients might be effective in improving the survival of patients undergoing hemodialysis.

                Author and article information

                Nephron Exp Nephrol
                Cardiorenal Medicine
                S. Karger AG
                December 2014
                05 November 2014
                : 128
                : 1-2
                : 1-8
                aDepartment of Advanced Medicine for Uremia, Nagoya University Graduate School of Medicine, Nagoya, bBiomedical Research Laboratories, Kureha Co., Tokyo, and cFaculty of Health and Nutrition, Shubun University, Ichinomiya, Japan
                Author notes
                *Toshimitsu Niwa, MD, PhD, Faculty of Health and Nutrition, Shubun University, 6 Nikko-cho, Ichinomiya, Aichi 491-0938 (Japan), E-Mail tniwa@med.nagoya-u.ac.jp
                365217 Nephron Exp Nephrol 2014;128:1-8
                © 2014 S. Karger AG, Basel

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                Page count
                Figures: 6, Pages: 8
                Original Paper


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