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), 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 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 = 0-4 h. For untreated specimens, the rate (mean ± SD) was 2.0 ± 1.2 µM O2 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 O2 h-1 mg-1). The corresponding rate in the presence of 10-100 µM zoledronic acid was 2.7 ± 0.7 µM O2 h-1 mg-1 (n = 11), p = 0.216. The first-order plots ln ([O2] t ÷ [O2] t=0) versus time for t = 0-30 h were also used to compare treated and untreated specimens. The rate (h-1 mg-1 103) 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.
Keywords: Bisphosphonates; Cellular bioenergetics; Mitochondria; Oxygen consumption; Respiratory chain.