Approaches to Improve the Structure and Function of the Skeleton in Chronic Kidney Disease

Abstract

Chronic kidney disease (CKD) currently affects ~37 million Americans and causes substantially increased risk of skeletal fracture and fracture-related mortality. Current methods to treat CKD-related bone loss remain alarmingly ineffective. Skeletal fragility in CKD is predominately driven by deteriorations in cortical bone, highlighted by significant cortical porosity development. It is hypothesized that cortical porosity is largely driven by chronically high levels of parathyroid hormone (PTH), which alters the balance of bone remodeling in favor of rampant osteoclast activity and bone resorption. Restricting cortical bone deterioration and the development of cortical pores is likely essential to improve CKD patients’ bone health and reduce their fracture risk. The goal of this series of studies was to answer the following key questions: (1) to what degree do bisphosphonates, an approved pharmacological agent used in metabolic bone disease, accumulate in the skeleton of animals with CKD; (2) can smaller and more frequent doses of bisphosphonates alter skeletal accumulation and improve cortical architecture and the mechanical integrity of bone; (3) can non-bisphosphonate pharmacological interventions more specifically affect cortical bone deterioration. Utilizing epi-fluorescence and two-photon microscopy, our results show that bisphosphonates accumulate more in rats with renal impairment and fractionating bisphosphonates lowered skeletal accumulation irrespective of disease state. Further, studies in both rat and mouse models of CKD demonstrated different bisphosphonate treatments alone do not recover declines in cortical microarchitecture or mechanical properties in CKD. These findings demonstrate that a single intervention is not sufficient in managing CKD-induced bone alterations. Utilizing individual pore tracking analysis, we demonstrated cortical pores can be modulated with therapeutic interventions and can infill, despite the presence of CKD. Potent suppression of PTH led to significant pore infilling while more subtle reductions in PTH, via a calcimimetic, had less striking effects on bone. Calcimimetics mitigated cortical microarchitecture deterioration and reduced the rate of cortical pore expansion. Overall, these findings highlight the importance of PTH management for treating cortical deterioration in CKD. Although bisphosphonates can be utilized in ways that reduce skeletal accumulation, they appear to need co-therapies to reduce skeletal fragility associated with CKD.