Uremic Toxicity and Bone in CKD

Patients with chronic kidney disease (CKD), especially those on dialysis treatment, are at high risk of bone fracture. In CKD-mineral and bone disorder (CKD-MBD), secondary hyperparathyroidism in patients with advanced CKD induces bone abnormalities, and skeletal resistance to parathyroid hormone (PTH) starts in the early stages of kidney disease. Uremic toxins such as indoxyl sulfate and p-cresyl sulfate reduce the expression of PTH receptor as well as PTH-induced cyclic adenosine 3',5' monophosphate production in osteoblasts. CKD also impairs bone strength, especially quality. In a rat model, kidney damage reduces the bone-storage modulus and changes the cortical bone chemical composition with or without hyperparathyroidism. The oral charcoal adsorbent AST-120 improves CKD-induced bone abnormalities as blood levels of indoxyl sulfate decrease. Uremic osteoporosis, a new concept of CKD-related bone fragility, is a main cause of CKD-induced bone abnormalities, particularly impaired bone quality. There is limited information about the effect and safety of anti-osteoporotic drugs for patients with CKD, especially those on dialysis, but the use of AST-120 and renin-angiotensin system inhibitors may modulate bone quality and decrease the incidence of fracture. Thus, the management of CKD-MBD plus use of other therapeutic interventions for uremic osteoporosis is necessary to prevent bone fragility in patients with CKD.