Nx rats feces collected in nd week

5/6Nx rats’ feces collected in 2 nd week, 4 th week, 6 th week, 8 th week and 10 th week were tested by 16S rDNA sequencing. The 16S rDNA sequencing data was analyzed in the level of PHYLUM, CLASS, ORDER, FAMILY and GENUS. There are more than 1000 types of gut microbiota in the level of Genus [50], so, in order to study the dynamic changes of gut microbiota on the whole and to show the change of the gut microbiota intuitively, the ORDER level of gut microbiota were chosen and analyzed. Fig. 7 shows that there was a gradual change after modeling, the abundance of gut microbiota in 2 nd and 10 th week had the most obvious change, such as Chlamydiales, Rhodospirillales, Rhodobacterales, Rhizobiales, Xanthomonadales, Lactobacillales, Legionellales, Rhodocyclales, etc. Most changed gut microbiota mentioned above belong to these changed microbial community, such as Lactobacillus belongs to Lactobacillales. It suggests that gut microbiota appeared to be disordered along with the progression of CKD. As shown in Fig. 4, the concentration of some amino acids in 5/6Nx rats feces increased significantly compared with sham, but some amino acids in 5/6Nx rats’ feces decreased. Although experimental evidences suggest that the intestinal microbiota is able to incorporate and degrade some of the available amino acids, it appears that the microbiota is also able to synthesize amino acids raising the view that amino N6-Methyl-dATP exchange between the microbiota and host can proceed in both directions [46], [47]. Whether the amino acid concentration increases or decreases, all of these changes may be related to the progression of CKD, besides tryptophan and tyrosine, phenylalanine is also an amino acid which can be used to produced IS [48], and the concentration of phenylalanine was increased in the gut of 5/6 Nx rats. Low urinary glycine and histidine are associated with incident CKD [49] and etc. More work is needed to clarify the overall effects of the intestinal microbiota on nitrogenous compound metabolism and consequences on gut in 5/6Nx rats and more generally host health.
Conclusion In this paper, we analyzed and compared uremic toxin (IS, PCS), uremic toxin precursor (indole, p-cresol), amino acids, gut microbiota and metagenome in 5/6Nx rats and sham operation rats. 5/6 Nx rats showed increased plasma IS, PCS concentration and increased fecal indole, p-cresol concentration. 5/6 Nx rats also showed disordered gut amino acids metabolism profile which became more significant along with the progression of CKD. The abundance of some specific gut bacteria and their metagenome also changed significantly in 5/6 Nx rats along with CKD progression. Our study showed that gut amino acids metabolism profile was disordered with CKD progression, which was highly related to the gut microbiota dysbiosis and metagenome change. Those significantly elevated genes may be responsible for the amino acid related indole/p-cresol formation and accumulation. And that regulation of gut amino acids metabolism pathway may be a possible way to intervene the progression of CKD.
Acknowledgements This work was supported by National Natural Science Foundation of China (No. 81473408, 81773983), Open Project Program of Jiangsu Key Laboratory for High Technology Research of TCM Formulae and Jiangsu Collaborative Innovation Center of Chinese Medicinal Resources Industrialization (No. FJGJS-2015-03), “Six Talent Peaks Program” of Jiangsu Province of China (2013 YY–009), Jiangsu 333 Project for the Cultivation of High-level Innovative Talents, Key Research Project in Basic Science of Jiangsu College and University (No. 13KJA360002).
Introduction Branched-chain amino acids (BCAAs: leucine, isoleucine, and valine) are essential amino acids for protein synthesis in humans. The content of amino acids in animal proteins is as high as ∼20%, and the BCAA composition (Leu:Ile:Val) in the proteins is found at an approximate ratio of 2:1:1. The high ratio of leucine might reflect its function as the most physiologically potent amino acid among the three BCAAs. In contrast to the high BCAAs content in proteins, the concentrations of free BCAAs in the amino acid pool of human skeletal muscle are as low as ∼0.65 mM, and have an approximate ratio of 2:1:3 [1]. The levels of BCAAs in the amino acid pool under post-absorptive conditions are relatively stable [2]. Ingestion of proteins and BCAA supplements rapidly increases the concentrations of free BCAAs in the amino acid pool, with plasma BCAA concentrations reportedly peaking ∼30 min after BCAA supplement intake [2]. This rapid rise of BCAA concentrations in the amino acid pool exerts the physiological effects of amino acids on protein and glucose metabolism. In this review, we summarize characteristics of the regulation of BCAA catabolism and the recent findings regarding the physiological functions of free BCAAs.