MO058INHIBITION OF OSTEOCLAST DIFFERENTIATION BY 1.25-D AND THE CALCIMIMETIC KP2326 REVEALS 1.25-D RESISTANCE IN ADVANCED CKD

Abstract

Abstract Background and Aims Active vitamin D analogs and calcimimetics are cornerstones for managing secondary hyperparathyroidism (SHPT) in chronic kidney disease (CKD). Their direct effects on bone cells remain to be determined. Method Peripheral blood mononuclear cells (PBMCs) of 19 pediatric CKD patients and 6 healthy donors (HD) were differentiated into osteoclasts in presence of M-CSF and RANKL. Effect of combined or single treatment with active vitamin D (1.25-D) and/or the calcimimetic KP2326 were evaluated onto osteoclast differentiation and osteoclast mediated bone resorption. Results 1.25-D inhibited osteoclastic differentiation, a significant resistance to 1.25-D was observed when CKD worsens. A significant albeit less important inhibitory effect of KP2326 on osteoclastic differentiation was also found both in cells derived from HD and CKD patients, through an activation of the Erk pathway. This inhibitory effect was not modified by CKD stage. Combinatorial treatment with 1.25-D and KP2326 did not result in synergistic effects. Last, KP2326 significantly inhibited human osteoclast-mediated bone resorption. Conclusion Both 1.25-D and KP2326 inhibit osteoclastic differentiation, however to a different extent. Whilst 1.25-D has no significant effect on bone resorption, KP2326 inhibits bone resorption. Recent data showed that calcimimetics also have a direct anabolic effect on bone, through the stimulation of osteoblastic differentiation and mineralization in human mesenchymal stem cells in vitro. All these results provide a strong rationale for a global positive effect of calcimimetics on bone remodeling. Calcimimetics also significantly decrease FGF23 levels. In the setting of global systematic deleterious effects of high FGF23 levels in CKD, and keeping in mind that active vitamin D analogs stimulate FGF 23 production, all these data could favor the use of decreased doses of 1.25-D with low-doses of calcimimetics in SHPT in dialysis, the combination of these two therapies already being proposed in the 2017 K-DIGO guidelines.