Zoledronic acid and bone cellular respiration

Phosphorescence O 2 analyzer was used to measure calvarial bone cellular respiration (cellular mitochondrial O 2 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 O 2 concentration with time was measured in closed vials containing phosphate-buffered saline (PBS), 5 mM glucose and 5–25 mg calvarial bone fragments, and it was complex for t = 0–30 h. Cyanide (specific inhibitor of cytochrome oxidase) halted O 2 consumption, confirming the oxidation occurred in the respiratory chain. Initial rate of respiration was estimated from the zero-order plots d[O 2 ]/d t for t = 0–4 h. For untreated specimens, the rate (mean ± SD) was 2.0 ± 1.2 µM O 2 h −1 mg −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, 2.7 nmol O 2 h −1 mg −1 ). The corresponding rate in the presence of 10–100 µM zoledronic acid was 2.7 ± 0.7 µM O 2 h −1 mg −1 ( n = 11), p = 0.216. The first-order plots ln ([O 2 ] t ÷ [O 2 ] t =0 ) versus time for t = 0–30 h were also used to compare treated and untreated specimens. The rate (h −1 mg −1 10 3 ) 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 + 10 µM zoledronic acid it was 12.1 ± 6.7 ( n = 10, p = 0.579), in PBS + glucose + 20 µM zoledronic acid it was 12.9 ± 3.3 ( n = 9, p = 0.356), and in PBS + glucose + 100 µM 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.