Alterations in osteoclast function and phenotype induced by different inhibitors of bone resorption--implications for osteoclast quality.
BACKGROUND
Normal osteoclasts resorb bone by secretion of acid and proteases. Recent studies of patients with loss of function mutations affecting either of these processes have indicated a divergence in osteoclastic phenotypes. These difference in osteoclast phenotypes may directly or indirectly have secondary effects on bone remodeling, a process which is of importance for the pathogenesis of both osteoporosis and osteoarthritis. We treated human osteoclasts with different inhibitors and characterized their resulting function.


METHODS
Human CD14 + monocytes were differentiated into mature osteoclasts using RANKL and M-CSF. The osteoclasts were cultured on bone in the presence or absence of various inhibitors: Inhibitors of acidification (bafilomycin A1, diphyllin, ethoxyzolamide), inhibitors of proteolysis (E64, GM6001), or a bisphosphonate (ibandronate). Osteoclast numbers and bone resorption were monitored by measurements of TRACP activity, the release of calcium, CTX-I and ICTP, as well as by counting resorption pits.


RESULTS
All inhibitors of acidification were equally potent with respect to inhibition of both organic and inorganic resorption. In contrast, inhibition of proteolysis by E64 potently reduced organic resorption, but only modestly suppressed inorganic resorption. GM6001 alone did not greatly affect bone resorption. However, when GM6001 and E64 were combined, a complete abrogation of organic bone resorption was observed, without a great effect on inorganic resorption. Ibandronate abrogated both organic and inorganic resorption at all concentrations tested [0.3-100 microM], however, this treatment dramatically reduced TRACP activity.


CONCLUSIONS
We present evidence highlighting important differences with respect to osteoclast function, when comparing the different types of osteoclast inhibitors. Each class of osteoclast inhibitors will lead to different alterations in osteoclast quality, which secondarily may lead to different bone qualities.
Neutzsky-Wulff
Anita V
AV
Nordic Bioscience A/S, Herlev DK 2730, Denmark.
Sørensen
Mette G
MG
Kocijancic
Dino
D
Leeming
Diana J
DJ
Dziegiel
Morten H
MH
Karsdal
Morten A
MA
Henriksen
Kim
K
D000818:Animals; D050071:Bone Density Conservation Agents / Q000494:pharmacology*; D001862:Bone Resorption / Q000188:drug therapy* / Q000473:pathology*; D002417:Cattle; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D004164:Diphosphonates / Q000494:pharmacology / Q000627:therapeutic use; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D000077557:Ibandronic Acid; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use; D018942:Macrolides / Q000494:pharmacology / Q000627:therapeutic use; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D009000:Monocytes / Q000187:drug effects / Q000473:pathology; D010010:Osteoclasts / Q000187:drug effects* / Q000473:pathology; D010641:Phenotype; D011480:Protease Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D053245:RANK Ligand / Q000494:pharmacology
D050071:Bone Density Conservation Agents; D004164:Diphosphonates; D004791:Enzyme Inhibitors; D018942:Macrolides; D011480:Protease Inhibitors; D053245:RANK Ligand; C505688:TNFSF11 protein, human; D016173:Macrophage Colony-Stimulating Factor; C040929:bafilomycin A1; D007930:Leucine; C024974:E 64; D000077557:Ibandronic Acid