Indoxyl Sulfate and Its Potential Role in Mineralocorticoid Receptor Transactivation in Chronic Kidney Disease

Figure 1. Clinical parameters and immunohistological findings in the sham and 5/6 nephrectomy rat models. A–C: serum levels of creatinine, indoxyl sulfate (IS), and urinary proteins were significantly increased in the 5/6 nephrectomy (5/6 Nx) group compared with the sham group, n=6 each group, *p<0.01; D: plasma levels of aldosterone decreased in the 5/6 Nx group, *p<0.05 vs. sham group; E: Immunohistochemical findings with anti-mineralocorticoid receptor (MR) antibody or anti-IS antibody. MR proteins were expressed in the distal/collecting ducts in both sham and 5/6 Nx groups. IS accumulation was observed in the damaged tubules in the 5/6 Nx rat model. IS expression (red arrow) was colocalized in the distal/collecting ducts where MR proteins were expressed (black arrow) by serial section evaluation; Scale bar: 100 μm.

Figure 2. Aldosterone and indoxyl sulfate enhanced the mineralocorticoid receptor transcriptional activity in COS-7 cells. A: concentration-response curve to aldosterone. COS-7 cells were transfected with MR reporter, incubated with or without aldosterone (10−12 to 10−6 mol/L) for 24 hours, and luciferase reporter assay was performed. n=4 for each group. *p<0.01 vs. aldosterone 0. B: effects of IS (10-500 μmol/L) on luciferase activity without aldosterone. n=4 for each group. *p<0.01 vs. IS 0. C: effects of IS (250–500 μmol/L) on luciferase activity with aldosterone 10−10 mol/L, n=5 each group. *p<0.01 vs. IS 0.

Figure 3. Antioxidants inhibited mineralocorticoid receptor activation by indoxyl sulfate in COS-7 cells. A, B : luciferase reporter assay. Mineralocorticoid receptor (MR) transcriptional activity by indoxyl sulfate (IS) was significantly suppressed by α-lipoic acid (10−3 mol/L) without (A) and with (B) aldosterone, n=5 each group, *p<0.05, **p<0.01; C: the increase in MR protein levels by IS was significantly suppressed by α-lipoic acid without aldosterone, n=6 each group, *p<0.05, **p< 0.01; D: with aldosterone, IS significantly increased MR protein expression; however, the suppression of MR protein levels by α-lipoic acid was not significant, n=5 each group, *p<0.05, DMSO: dimethyl sulfoxide.