Gut alterations in a chronic kidney disease rat model with diet-induced vascular calcification.

Intestinal disorders and vascular calcification (VC) are often associated with chronic kidney disease (CKD). While gut barrier alterations have been reported in CKD (such as abnormal intestinal permeability, bacterial overgrowth, and inflammation), it is not clear if vascular calcification influences these alterations. To investigate whether the bidirectional relationships between VC and gut dysfunction could be mediated by increased inflammation and uremic toxin generation, we used the SNx-VC model of uremic vascular calcification (rats undergoing subtotal 5/6th nephrectomy and fed a procalcifying high-phosphate and vitamin D diet). We confirmed the presence of CKD and VC by von Kossa staining and observed increased gut-origin uremic toxin, indoxyl sulfate (IS), in SNx-VC animals compared to controls. In SNx-VC rats, we observed decreased mucus production (Alcian blue, Mucin 2 staining) in the colon and ileum which was correlated with the level of calcification. There was no change in inflammation markers or tight junction protein expression. We assessed intestinal levels in the NOD-like receptor family pyrin domain containing 6 (NLRP6) protein, known to regulate mucus secretion, and found no change in the colon or ileum. Nlrp6 mRNA was, however, decreased in the colon of SNx-VC rats, along with other mRNA (Ly96, Sod1), while Tlr2 was increased compared to controls. Our observations of low mucus, low Nlrp6 mRNA, and high IS in SNx-VC rats confirm a link between gut barrier alterations and uremic VC. This suggests that alterations in the mucus layer could favor the generation of gut-origin uremic toxins and promote VC in CKD. Thus, improving the gut mucus barrier function in the context of uremic VC could be considered as a possible therapeutic strategy in CKD patients.