Abstract
Introduction
Cardiovascular disease (CVD) mortality is significantly higher in chronic kidney disease (CKD) patients, with vascular calcification and atherosclerosis proving to be major contributors. Endothelial dysfunction is an early marker of atherosclerosis, triggered by oxidative stress and reduced nitric oxide production. The uremic toxin indoxyl sulphate (IS), a protein-bound non-dialyzable molecule derived from dietary tryptophan that accumulates in the blood of CKD patients, activates the aryl hydrocarbon receptor (AhR) promoting downstream cytochrome P450 1A1 (CYP1A1) expression mediating oxidative stress and potentially endothelial dysfunction. Targeting IS-induced AhR activation in the endothelium has not previously been examined and may represent a novel approach in targeting endothelial dysfunction.
Purpose
To assess the ability of the AhR antagonist, CH223191, to inhibit IS-mediated impairment of endothelial function and disruption of redox balance.
Methods
To assess endothelium-dependent relaxation, the thoracic aorta from adult male Sprague Dawley rats (N=10) were used in ex vivo experiments. Rings (5mm) from the aorta were exposed to IS (300μM) in the presence and absence of the AhR antagonist CH223191 (1 and 10μM), prior to pre-constriction of the vessel with phenylephrine (30μM) followed by relaxation with acetylcholine (ACh; 1nM-30μM). Control rings were not exposed to IS or CH223191 to determine normal endothelial responses to ACh. Responses were recorded with isometric force transducers connected to a PowerLab using Chart Software. Tissue sections from these rings were stained for superoxide using dihydroethidium. To examine key AhR-mediated oxidative stress pathways, separate aortic rings were exposed to IS and CH223191, under the above conditions, for 4 hours prior to RNA extraction and real-time PCR analysis.
Results
IS reduced the maximum level of endothelium-dependent relaxation (Rmax) to 50.17±2.71% (P<0.001) compared to control (86.00±3.93%). In the presence of IS, CH223191 restored Rmax to 77.74±3.14% (1μM) and 81.63±3.27% (10μM) (Figure, P<0.001). The potency of ACh, known as the pEC50 (negative logarithm of the effective concentration of ACh to produce a relaxation response of 50%), in control tissues (−7.08±0.07) was increased 100-fold following exposure of IS (−5.10±0.13; P<0.001). CH223191 restored pEC50 back to control values (1μM, −6.62±0.09; 10μM, −6.83±0.08; P<0.05). IS-exposed rings increased superoxide expression (P<0.001) and CYP1A1 gene expression (P<0.001), CH223191 restored expression of both superoxide (P<0.001) and CYP1A1 (P<0.001) back to control levels.
CH223191 restores endothelial function
Conclusion
Our findings demonstrate the adverse impact of IS-mediated AhR activation on the vascular endothelium, where oxidative stress may play a critical role inducing endothelial dysfunction in the vasculature of the heart and kidneys. AhR inhibition may provide a novel therapy for CVD in the CKD setting.
Acknowledgement/Funding
National Health and Medical Research Council of Australia Program Grant
The Aryl Hydrocarbon Receptor-Activating Effect of Uremic Toxins from Tryptophan Metabolism: A New Concept to Understand Cardiovascular Complications of Chronic Kidney Disease
