Zoledronic acid and bone cellular respiration

Abstract

Phosphorescence O2 analyzer was used to measure calvarial bone cellular respiration (cellular mitochondrial O2 consumption) in Taylor Outbred mice in the presence and absence of zoledronic acid. This potent bisphosphonate inhibits osteoclast-mediated calcium resorption, and its effects on bone respiration have not been previously investigated. The change of O2 concentration with time was measured in closed vials containing phosphate-buffered saline (PBS), 5mM glucose and 5-25mg calvarial bone fragments, and it was complex for t=0-30h. Cyanide (specific inhibitor of cytochrome oxidase) halted O2 consumption, confirming the oxidation occurred in the respiratory chain. Initial rate of respiration was estimated from the zero-order plots d[O2]/dt for t=0-4h. For untreated specimens, the rate (mean±SD) was 2.0±1.2µM O2h-1mg-1 (n=6). This value was 7-10 times lower than that of other murine organs, but similar to that reported for rat and Guinea pig calvaria (averaging, 2.7nmolO2h-1mg-1). The corresponding rate in the presence of 10-100µM zoledronic acid was 2.7±0.7µM O2h-1mg-1 (n=11), p=0.216. The first-order plots ln ([O2] t ÷[O2] t=0) versus time for t=0-30h were also used to compare treated and untreated specimens. The rate (h-1mg-1103) for specimens incubated in PBS without glucose was 1.3±0.6 (n=3, p=0.007), in PBS+glucose it was 10.7±6.9 (n=10), in PBS+glucose+10µM zoledronic acid it was 12.1±6.7 (n=10, p=0.579), in PBS+glucose+20µM zoledronic acid it was 12.9±3.3 (n=9, p=0.356), and in PBS+glucose+100µM zoledronic acid it was 13.7±7.7 (n=9, p=0.447). Thus, exposure to high-doses of zoledronic acid over several hours imposed a statistically insignificant increase in calvarial bone cellular respiration.