Indoxyl sulfate enhances endothelin-1-induced contraction via impairment of NO/cGMP signaling in rat aorta

The microbiome-derived tryptophan metabolite, indoxyl sulfate, is considered a harmful vascular toxin. Here, we examined the effects of indoxyl sulfate on endothelin-1 (ET-1)-induced contraction in rat thoracic aortas. Indoxyl sulfate (10 −3 M, 60 min) increased ET-1-induced contraction but did not affect isotonic high-K + -induced contraction. The ET-1-induced contraction was enhanced by endothelial denudation in both control and indoxyl sulfate-treated groups. BQ123 (10 −6 M), an ET A receptor antagonist, reduced the ET-1-induced contraction in both control and indoxyl sulfate groups. BQ788 (10 −6 M), an ET B receptor antagonist, increased the contraction in the control group but had no effect on the indoxyl sulfate group. Conversely, indoxyl sulfate inhibited relaxation induced by IRL1620, an ET B receptor agonist. L-NNA, an NO synthase (NOS) inhibitor, increased the ET-1-induced contractions in both the control and indoxyl sulfate groups, whereas L-NPA (10 −6 M), a specific neuronal NOS inhibitor, did not affect the ET-1-induced contraction in both groups. However, ODQ, an inhibitor of soluble guanylyl cyclase, increased the ET-1-induced contraction in both groups. Organic anion transporter (OAT) inhibitor probenecid (10 −3 M) and antioxidant N-acetyl-L-cysteine (NAC; 5 × 10 −3 M) inhibited the effects of indoxyl sulfate. A cell-permeant superoxide scavenger reduced the ET-1-induced contraction in the indoxyl sulfate group. The aortic activity of SOD was reduced by indoxyl sulfate. The present study revealed that indoxyl sulfate augments ET-1-induced contraction in rat aortae. This enhancement may be due to the impairment of NO/cGMP signaling and may be attributed to impairment of the antioxidant systems via cellular uptake through OATs.