Aryl Hydrocarbon Receptor and Uremic Toxins from the Gut Microbiota in Chronic Kidney Disease Patients: Is There a Relationship between Them?

Recent studies have suggested that uremic toxins such as indoxyl sulfate (IS) and indole-3-acetic acid (IAA) from the metabolism of the gut microbiota may be involved in the inflammatory signaling pathway in chronic kidney disease (CKD) patients through the activation of the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor. The objective of this study was to investigate the possible relationship between uremic toxins (IS and IAA) and AhR protein expression in CKD patients. A cross-sectional observational study involving 17 hemodialysis (HD) [11 men, 55.5 ± 11.7 years of age, 54.0 (25.5-136.0) months of HD, body mass index (BMI) of 25.8 ± 3.8 kg/m] and 15 non-dialysis-dependent (NDD) CKD (8 men, 54.1 ± 18.2 years of age, glomerular filtration rate of 34.8 ± 21.0 mL/min/1.73 m, BMI of 27.4 ± 5.0 kg/m) patients was conducted. IS and IAA levels were measured by reversed-phase high-performance liquid chromatography, and the protein expression levels of AhR and nuclear factor κ B (NF-κB) were evaluated by a Western blot assay. There was no difference in the expression of either AhR or NF-κB in the patients, and as expected, uremic toxin levels were higher in HD patients than in NDD patients. In the overall analysis, AhR protein expression was positively associated with IAA plasma levels ( r = 0.4; p = 0.03) and NF-κB protein expression ( r = 0.62; p = 0.001). Although the role of AhR in inflammation and CVD in CKD patients is far from being completely understood, the association between IAA and AhR observed in this study suggests a possible role for uremic toxins in the cell signaling pathway involved in inflammation in CKD patients.