Abstract. In uremic patients, various uremic toxins are accumulated and exert various biologic effects on uremia. Indoxyl sulfate (IS) is one of uremic toxins that is derived from dietary protein, and serum levels of IS are markedly increased in both uremic rats and patients. It has been previously reported that the accumulation of IS promotes the progression of chronic renal failure (CRF). This study demonstrates the role of rat organic anion transporters (rOATs) in the transport of IS and the induction of its nephrotoxicity. The administration of IS to 5/6-nephrectomized rats caused a faster progression of CRF, and immunohistochemistry revealed that IS was detected in the proximal and distal tubules where rOAT1 (proximal tubules) and/or rOAT3 (proximal and distal tubules) were also shown to be localized. In in vitro study, the proximal tubular cells derived from mouse that stably express rOAT1 (S2 rOAT1) and rOAT3 (S2 rOAT3) were established. IS inhibited organic anion uptake by S2 rOAT1 and S2 rOAT3, and the Ki values were 34.2 and 74.4 M, respectively. Compared with mock, S2 rOAT1 and S2 rOAT3 exhibited higher levels of IS uptake, which was inhibited by probenecid and cilastatin, organic anion transport inhibitors. The addition of IS induced a decrease in the viability of S2 rOAT1 and S2 rOAT3 as compared with the mock, which was rescued by probenecid. These results suggest that rOAT1 and rOAT3 play an important role in the transcellular transport of IS and the induction of its nephrotoxicity.

AST-120 reduces the gene expression of TGF-beta1, TIMP-1 and pro-alpha1(I)collagen in the kidneys, and delays the progression of CRF, at least in part, by alleviating the overload of indoxyl sulphate on remnant proximal tubular epithelial cells.

Background/Aims: An oral adsorbent, AST-120, removes uremic toxins such as indoxyl sulfate, and delays the progression of renal failure. This study was designed to investigate the effects of AST-120 on the molecular basis of interstitial inflammation and fibrosis, using Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus. Methods: Four weeks after unilateral nephrectomy, the uninephrectomized OLETF (1/2NxOLETF) rats were divided into two groups: AST-120-administered and control 1/2NxOLETF rats. After the administration of AST-120 for 48 weeks, we examined the effects of AST-120 on renal functional, pathological, and gene expressional changes. Results: The administration of AST-120 to the 1/2NxOLETF rats attenuated the progression of renal dysfunction, proteinuria, glomerular sclerosis, tubular injury, and interstitial inflammation and fibrosis. AST-120 significantly reduced renal expression of intercellular adhesion molecule (ICAM)-1, osteopontin, monocyte chemotactic protein (MCP)-1, and transforming growth factor (TGF)-β1, as well as clusterin. All the five molecules were expressed mainly in tubular cells. AST-120 also decreased serum and urinary levels of indoxyl sulfate and the overload of indoxyl sulfate in tubular cells. Conclusion: AST-120 ameliorates tubulointerstitial injury by reducing renal expression of ICAM-1, osteopontin, MCP-1, TGF-β1 and clusterin in 1/2NxOLETF rats.

Diabetic nephropathy is a common cause of end-stage renal disease. The administration of an oral adsorbent, AST-120, prevents the progression of chronic renal failure in uremic rats and undialyzed uremic patients. This study was designed to determine if AST-120 slows the progression of diabetic nephropathy using Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetic mellitus. At 21 weeks of age the OLETF rats were divided into 2 groups: AST-120-administered OLETF rats (n = 7), and control OLETF rats (n = 7). LETO rats, which are genetically similar to the OLETF rats but not diabetic, were also included. After the oral administration of AST-120 for 65 weeks, renal function and pathological changes were investigated in the 3 groups. The administration of AST-120 to the OLETF rats attenuated the progression of glomerular sclerosis, interstitial fibrosis, tubular injury as well as renal dysfunction, and reduced the serum and urinary levels of indoxyl sulfate. Furthermore, AST-120 administration reduced the interstitial expression of transforming growth factor (TGF)-β₁ and tissue inhibitor of metalloproteinase (TIMP)-1, as well as interstitial infiltration of macrophages. The TGF-β₁-stained interstitial area showed positive correlations with the interstitial fibrosis area, the number of TIMP-1-positive cells, and the number of macrophages, and showed a negative correlation with creatinine clearance. In conclusion, AST-120 reduced the interstitial expression of TGF-β₁ and TIMP-1, and the interstitial infiltration of macrophages, and ameliorates the progression of diabetic nephropathy in OLETF rats.