Stimulating effect of indoxyl sulfate on progression of renal failure and development of an inhibitor of its production

为了阐明硫酸吲哚酚在肾衰竭进展中的作用，我们在给予硫酸吲哚酚的5/6肾切除的尿毒症大鼠肾皮质中检测了与肾小管间质纤维化相关的基因TGF-b1、TIMP-1和proal (I)胶原的表达。硫酸吲哚酚给药5周后，与对照组相比，尿毒症大鼠体内转化生长因子(TGF)-β1、金属蛋白酶组织抑制剂(TIMP)-1和前al(I)胶原mRNA水平显著升高，肾功能明显下降，肾小球硬化加重。因此，我们假设肾单位上的蛋白质代谢物（如硫酸吲哚酚）过载促进了CRF的进展。此外，为了阐明硫酸吲哚酚是否会影响肾脏中有机阴离子转运蛋白(OAT)-1和OAT3的表达，对5/6肾切除的尿毒症大鼠给予硫酸吲哚酚16周。硫酸吲哚酚定位于尿毒症大鼠肾脏近端小管上皮细胞，尤其是扩张小管，硫酸吲哚酚给药显著增加硫酸吲哚酚的小管染色。硫酸吲哚酚进一步降低了OAT1的表达，增加了OAT3的表达。硫酸吲哚酚的免疫染色在oat3阳性的近端小管中比在oat1阳性的近端小管中更强烈。综上所述，硫酸吲哚酚通过肾近端小管基底外膜上的OAT1和OAT3的主动摄取排泄到尿液中。尿毒症大鼠，尤其是硫酸吲哚酚给药的尿毒症大鼠，OAT1表达降低，OAT3表达升高。硫酸吲哚酚的肾毒性靶点似乎是表达oat3的近端小管。

To clarify the role of indoxyl sulfate in the progression of renal failure, the expressions of genes related to tubulointerstitial fibrosis such as TGF-b1, TIMP-1 and pro al(I) collagen were examined in the renal cortex of 5/6-nephrectomized uremic rats given indoxyl sulfate. The administration of indoxyl sulfate for 5 weeks significantly increased the mRNA levels of transforming growth factor (TGF)-β1, tissue inhibitor of metalloproteinases (TIMP)-1 and pro al(I) collagen in the uremic rats given indoxyl sulfate compared with the control uremic rats, accompanied by a significant decline in renal function and worsening of glomerular sclerosis. Thus, we hypothesized that the overload of protein metabolites such as indoxyl sulfate on nephrons promotes the progression of CRF.Further, to clarify if indoxyl sulfate administration affects the expression of organic anion transporter (OAT)-1 and OAT3 in the kidneys, indoxyl sulfate was administered to 5/6-nephrectomized uremic rats for 16 weeks. Indoxyl sulfate was localized in the proximal tubular epithelial cells, especially of dilated tubules, of the control uremic rat kidneys, and that indoxyl sulfate administration markedly increased the tubular staining of indoxyl sulfate. The administration of indoxyl sulfate further dccreased the expression of OAT1 and increased the expression of OAT3. The immunostaining of indoxyl sulfate was more intense in the OAT3-positive proximal tubules rather than in the OAT1-positive proximal tubules. In conclusion, indoxyl sulfate is excreted to urine through active uptake by OAT1 and OAT3 in the basolateral membranes of renal proximal tubules. Uremic rats, especially indoxyl sulfate-administered uremic rats, showed decreased expression of OAT1 and increased expression of OAT3. The target of nephrotoxicity of indoxyl sulfate seems to te OAT3-expressed proximal tubules.