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

为探讨吲哚硫酸盐在肾功能衰竭中的作用，观察了5/6肾切除后给予吲哚硫酸盐的尿毒症大鼠肾皮质中与肾小管间质纤维化相关的基因如转化生长因子-β1、组织抑制因子-1和I型胶原的表达。给药5周后，尿毒症大鼠肾组织中转化生长因子-β-1、金属蛋白酶组织抑制因子-1和I型胶原的表达水平较对照组显著升高，并伴有肾功能明显下降和肾小球硬化加重。因此，我们假设肾脏上蛋白质代谢产物如吲哚硫酸盐的超载促进了CRF的进展。此外，为了阐明吲哚硫酸盐对肾脏有机阴离子转运体(OAT)-1和OAT3表达的影响，我们对5/6肾切除的尿毒症大鼠给予吲哚硫酸盐16周。对照尿毒症大鼠肾脏近端肾小管上皮细胞，尤其是扩张的肾小管上皮细胞中可见吲哚硫酸盐的表达，给予吲哚硫酸盐后，肾小管上皮细胞的染色明显增强。硫代吲哚可进一步降低OAT1的表达，增加OAT3的表达。在OAT3阳性的近端小管中，吲哚硫酸盐的免疫染色比在OAT1阳性的近端小管中更强。总之，吲哚硫酸盐是通过肾近端小管基侧膜上的OAT1和OAT3主动摄取排泄到尿液中的。尿毒症大鼠，尤其是吲哚硫酸尿毒症大鼠，OAT1表达减少，OAT3表达增加。吲哚硫酸盐的肾毒性作用靶点似乎是近端小管上皮细胞表达的AT3。

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.