In STRATEGY-CKD, we worked towards the identification of novel targets related to the gut-kidney axis to improve outcome of patients with CKD. For this aim patient sample collections were used, and cell culture set-ups and animal models were established. State-of-the-art -omic approaches, bioinformatics and systems biology were trained and applied. ESRs collaborated intensively and shared their expertise. Intestinal bacterial metagenome data of CKD patients in different stages of the disease pointed out changes in composition and function in different patients cohorts. The results support further research into preserving or restoring the balance between saccharolytic and proteolytic fermentation. On parallel samples, plasma metabolomic, urinary proteome and fecal proteome analyses was performed Applied systems biology approaches to study cell-cell and host-microbiome interactions from omics technologies and multi-omics were developed. In a mouse model and in kidney-on-a-chip bioengineered human tubular cells, short-chain fatty acid (SCFA), an important product of saccharolytic fermentation, was found to promote kidney resilience to acute kidney injury (AKI), decreasing inflammation and preserving the downregulation of kidney protective genes such as klotho, respectively. Also in a CKD rodent model, gut microbiome proteolytic fermentation was also found to be enhanced. Moreover, the absorption of UT precursors increased in CKD rats. Lastly, SCFAs were identified as a potential therapeutic agent able to boost the activity of the organic anion transporter-1 in proximal tubule cells. A novel in vitro model in both 2D and 3D systems, stimulating caco2 cells to secrete an apical homogeneous mucus layer, was developed. These systems allowed confirmation of a role mediated by the mucus as a protective barrier against biological fluids as well as its role as a modulator of cell metabolism, enhancing detoxification processes from intestinally UT precursors. A rodent model of subtotal 5/6th nephrectomy fed with a high phosphate and vitamin D diet (SNx-vascular calcification (VC) model) was characterized by a decrease in mucus production in colon and ileum that correlated with calcification severity. Studies also focused on gender differences in pharmacokinetics and haemostatic dysfunction in CKD patients with a UT of intestinal origin exerting both pro-inflammatory and pro-coagulant effects. Finally, the effects of an orally administered human milk oligosaccharide, in a 5/6th nephrectomy CKD rat model revealed significant changes in various inflammatory parameters. Also in an AhR-KO Caco-2 cell line, the oligosaccharide was shown to have potential beneficial effects on the intestinal barrier. All combined, the ESRs have joined efforts to set-up the technical methods and to establish the experimental models to explore the gut-kidney axis in CKD, indicating new mechanisms, which can be targeted by future therapies to further improve cardiovascular outcome of CKD patients.
