CLDN1 and chronic kidney disease: In all CKD patients (CKD stage I–IV and ESKD), the expression of occludin and claudin-1 in the intestinal mucosa (immunohistochemical semi-quantification) was significantly inversely correlated with endotoxin concentration (r = −0.616, p < 0.001 for occludin and r = −0.417, p < 0.01 for claudin-1).