Dysbiosis of the gut microbiome and related metabolites in chronic kidney disease (CKD) have been intimately associated with the prevalence of cardiovascular diseases. Unfortunately, thus far, there is a paucity of sufficient knowledge of gut microbiome and related metabolites on CKD progression partly due to the severely limited investigations. Using a 5/6 nephrectomized (NX) rat model, we carried out 16S rRNA sequence and untargeted metabolomic analyses to explore the relationship between colon's microbiota and serum metabolites. Marked decline in microbial diversity and richness was accompanied by significant changes in 291 serum metabolites, which were mediated by altered enzymatic activities and dysregulations of lipids, amino acids, bile acids and polyamines metabolisms. Interestingly, CCr was directly associated with some microbial genera and polyamine metabolism. However, SBP was directly related to certain microbial genera and glycine-conjugated metabolites in CKD rats. Administration of poricoic acid A (PAA) and Poria cocos (PC) ameliorated microbial dysbiosis as well as attenuated hypertension and renal fibrosis. In addition, treatments with PAA and PC lowered serum levels of microbial-derived products including glycine-conjugated compounds and polyamine metabolites. Collectively, the present study confirmed the CKD-associated gut microbial dysbiosis and identified a novel dietary and therapeutic strategy to improve the gut microbial dysbiosis and the associated metabolomic disorders and retarded the progression of kidney disease in the rat model of CKD.

Early detection is critical in prevention and treatment of kidney disease. However currently clinical laboratory and histopathological tests do not provide region-specific and accurate biomarkers for early detection of kidney disease. The present study was conducted to identify sensitive biomarkers for early detection and progression of tubulo-interstitial nephropathy in aristolochic acid I-induced rats at weeks 4, 8 and 12. Biomarkers were validated using aristolochic acid nephropathy (AAN) rats at week 24, adenine-induced chronic kidney disease (CKD) rats and CKD patients. Compared with control rats, AAN rats showed anemia, increased serum urea and creatinine, progressive renal interstitial fibrosis, activation of nuclear factor-kappa B, and up-regulation of pro-inflammatory, pro-oxidant, and pro-fibrotic proteins at weeks 8 and 12. However, no significant difference was found at week 4. Metabolomics identified 12-ketodeoxycholic acid, taurochenodesoxycholic acid, LPC(15:0) and docosahexaenoic acid as biomarkers for early detection of tubulo-interstitial nephropathy. With prolonging aristolochic acid I exposure, LPE(20:2), cholic acid, chenodeoxycholic acid and LPC(17:0) were identified as biomarkers for progression from early to advanced AAN and lysoPE(22:5), indoxyl sulfate, uric acid and creatinine as biomarkers of advanced AAN. These biomarkers were reversed by treatment of irbesartan and ergone in AAN rats at week 24 and adenine-induced CKD rats. In addition, these biomarkers were also reversed by irbesartan treatment in CKD patients.

Renal fibrosis is a common end point of the progression of chronic kidney disease (CKD). Suppressing the development and progression of renal fibrosis is essential in the treatment of kidney disease. Our previous study demonstrated that the ethyl acetate extract of the surface layer of Poria cocos exhibited beneficial antitubulointerstitial fibrosis. In this study, we isolated new diterpene (PZF) and triterpenes (PZG and PZH) and examined their antifibrotic effect. TGF-β1 upregulated the collagen I protein expression in HK-2 cells, and PZG and PZH treatment significantly inhibited the upregulated collagen I expression (TGF group 0.59 ± 0.08 vs TGF+PZG group 0.36 ± 0.08, P < 0.01; TGF+PZH group 0.39 ± 0.12, P < 0.01). Triterpenes, PZG and PZH, exhibited a stronger inhibitory effect on renal fibrosis and podocyte injury than PZF. PZG and PZH further showed a stronger inhibitory effect on the activation of the renin-angiotensin system (RAS) than PZF. Additionally, PZG and PZH markedly inhibited the activation of Wnt/β-catenin signaling, which played an important role in fibrogenesis. Interestingly, PZG and PZH suppressed the TGF-β/Smad pathway by selectively inhibiting the phosphorylation of Smad3 through blocking the interactions of SARA with TGFβI and Smad3. The analysis of the structure-activity relationship demonstrated that their antifibrotic effects were closely associated with the first six-membered ring structure and the number of carboxyl groups in this type of compounds. Additionally, fifteen known triterpenes were identified. These novel tetracyclic triterpenoid compounds provided the potential lead compounds for the research and development of antifibrosis drug, and they possessed the potential to be utilized as RAS inhibitors.