The chloride channel inhibitor NS3736 [corrected] prevents bone resorption in ovariectomized rats without changing bone formation.
Chloride channel activity is essential for osteoclast function. Consequently, inhibition of the osteoclastic chloride channel should prevent bone resorption. Accordingly, we tested a chloride channel inhibitor on bone turnover and found that it inhibits bone resorption without affecting bone formation. This study indicates that chloride channel inhibitors are highly promising for treatment of osteoporosis.


BACKGROUND
The chloride channel inhibitor, NS3736, blocked osteoclastic acidification and resorption in vitro with an IC50 value of 30 microM. When tested in the rat ovariectomy model for osteoporosis, daily treatment with 30 mg/kg orally protected bone strength and BMD by approximately 50% 6 weeks after surgery. Most interestingly, bone formation assessed by osteocalcin, mineral apposition rate, and mineralized surface index was not inhibited.


METHODS
Analysis of chloride channels in human osteoclasts revealed that ClC-7 and CLIC1 were highly expressed. Furthermore, by electrophysiology, we detected a volume-activated anion channel on human osteoclasts. Screening 50 different human tissues showed a broad expression for CLIC1 and a restricted immunoreactivity for ClC-7, appearing mainly in osteoclasts, ovaries, appendix, and Purkinje cells. This highly selective distribution predicts that inhibition of ClC-7 should specifically target osteoclasts in vivo. We suggest that NS3736 is inhibiting ClC-7, leading to a bone-specific effect in vivo.


CONCLUSIONS
In conclusion, we show for the first time that chloride channel inhibitors can be used for prevention of ovariectomy-induced bone loss without impeding bone formation. We speculate that the coupling of bone resorption to bone formation is linked to the acidification of the resorption lacunae, thereby enabling compounds that directly interfere with this process to be able to positive uncouple this process resulting in a net bone gain.
Schaller
Sophie
S
Nordic Bioscience A/S, Herlev, Denmark.
Henriksen
Kim
K
Sveigaard
Christina
C
Heegaard
Anne-Marie
AM
Hélix
Nathalie
N
Stahlhut
Martin
M
Ovejero
Maria C
MC
Johansen
Jens V
JV
Solberg
Helene
H
Andersen
Thomas L
TL
Hougaard
Dorit
D
Berryman
Mark
M
Shiødt
Christine B
CB
Sørensen
Bjørn H
BH
Lichtenberg
Jens
J
Christophersen
Palle
P
Foged
Niels T
NT
Delaissé
Jean-Marie
JM
Engsig
Michael T
MT
Karsdal
Morten A
MA
D000818:Animals; D001862:Bone Resorption / Q000517:prevention & control*; D002478:Cells, Cultured; D018118:Chloride Channels / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000235:genetics; D003034:Coated Pits, Cell-Membrane / Q000187:drug effects; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D013777:Tetrazoles / Q000008:administration & dosage / Q000494:pharmacology*; D014018:Tissue Distribution
C086321:CLC-1 channel; C097540:CLCN7 protein, human; D018118:Chloride Channels; C494393:N53736; D013777:Tetrazoles