THE ROLE OF REACTIVE OXYGEN INTERMEDIATES IN OSTEOCLASTIC BONE-RESORPTION

Osteoclasts have been shown to produce reactive oxygen intermediates ( ROI) and it has been suggested that ROI are involved in the process of bone resorption. ROI have also been shown to play a central role in t he activation of the multisubunit transcription factor NF-kappa B that enhances the transcription of genes encoding defence and signaling pr oteins. Therefore, we have assessed the effect of pyrrolidine dithioca rbamate (PDTC), an oxygen-radical scavenger and metal chelator that is a selective and potent inhibitor of NF-kappa B activation, on osteocl astic bone resorption in the bone slice assay. PDTC (0.001 - 0.1 mM) d ose-dependently and non-cytotoxically inhibited osteoclast activity wi th an IC50 of 0.01 mM. PDTC (0.01 mM) caused no change in the ratio of resorption pit area to resorption pit depth as measured by Lasertec c onfocal microscopy, indicating that ROI are not involved in the resorp tive process per se. This view is supported by time-course studies sho wing that addition of PDTC or N-acetyl cysteine (NAG; an ROI scavenger , but not metal chelator), 6 hr after the start of the assay had no si gnificant effect on subsequent bone resorption. Desferal (100 mu M), a chelator of iron and other metal ions, had no significant effect on b one resorption, indicating (along with the results with NAG) that ROI- scavenging rather than metal chelation is responsible for inhibition o f osteoclastic bone resorption by PDTC. Taken together these results i ndicate that ROI produced by osteoclasts in the bone slice assay are n ot involved in the process of bone resorption, but are important durin g osteoclast activation for bone resorption, possibly being involved i n activation of the transcription factor NF-kappa B. (C) 1995 Academic Press, Inc.