Direct non-genomic effect of steroid hormones on superoxide anion generation in the bone resorbing osteoclasts

We have investigated the possible acute effect of steroid hormones, includi ng lcr,25 dihydroxycholecalciferol (l alpha,25(OH)(2)D-3) and estradiol, on the generation of superoxide anion (O-2(.-)) in bone resorbing osteoclasts . Evidence is presented demonstrating acute non-genomic stimulatory action of 1 alpha,25(OH)(2)D-3 on the production of free radicals by rat osteoclas ts cultured on calcified matrix. The increase in O-2(.-) production was obs erved in the range of 6-10 s (n = 5) following exposure of enriched osteocl asts to 1 alpha,25(OH)(2)D-3 and was found to be transient with the peak re sponse being in the range of 5-45 s (n = 5). The decline in the transient w as much slower than the elevation, time for the decay being in the range 1- 5 min (n = 5) and remained above the levels present prior to the addition. The exposure of the osteoclast to dexamethasone was found to have no effect on O-2(.-) generation, whilst estradiol was found to be inhibitory. The mo de of stimulation and the kinetics of the transients of O-2(.-) in the bone resorbing osteoclasts produced by 1 alpha,25(OH)(2)D-3 were similar to tha t of parathyroid hormone (PTH) and pertussis. The exposure of the bone reso rbing osteoclasts to cholera toxin was found to have no effect, suggesting that the stimulatory action is unlikely to be mediated via cAMP elevation. The importance of these observations is discussed in the context of calcium homeostasis and bone physiology. (C) 1999 Elsevier Science Ireland Ltd. Al l rights reserved.