The effects of endocannabinoids on human, mouse and rabbit bone cells were investigated. At high concentrations anandamide and 2-arachidonyl glycerol (2-AG) inhibited human osteoclast formation with no effects at lower concentrations. The inhibition was not attenuated by antagonists for the CB<sub>1</sub>, CB<sub>2</sub> or TRPV1 receptors, indicating a non-receptor mediated effect. Conversely, anandamide and 2-AG increased mouse osteoclast formation. The effect of anandamide was enhanced in cells from fatty acid amide hydrolase (FAAH)-null mice and abolished in cells from CB<sub>1/2</sub> knockout mice. The effect of 2-AG was not eliminated in CB<sub>1/2</sub> knockout cells, indicating a non-CB<sub>1</sub>/CB<sub>2</sub> action. The CB<sub>1</sub> antagonist, AM251, and the CB<sub>2</sub> antagonist, AM630, both inhibited mouse osteoclast formation. These effects were not rescued in the CB<sub>1/2</sub>-knockout mouse cells. Both anandamide and 2-AG stimulated actin ring formation and osteoclast activity in human and rabbit osteoclast. This was prevented in the presence of AM630 but not AM251, indicating a CB<sub>2</sub>-mediated response. The endocannabinoids and the cannabinoid receptor antagonists do not have a regulatory action on osteoblast activity. The effects of the novel cyclooxygenase-2 (COX-2) metabolite of 2-AG, prostaglandin E<sub>2</sub>-glycerol ester (PGE<sub>2</sub>-G), on human osteoclasts were examined. Treatment with PGE<sub>2</sub>-G inhibited formation and ERK phosphorylation of human osteoclasts. These effects were attenuated by a selective EP<sub>4</sub> antagonist and mimicked by PGE<sub>2</sub> alone, indicating that PGF<sub>2</sub>-G is rapidly metabolised into PGE<sub>2</sub> in human osteoclast cultures. However, PGE<sub>2</sub>-G treatment elevated intracellular calcium levels in human osteoclasts, through a phospholipase C (PLC)- and IP<sub>3</sub>- dependent mechanism, indicative of a G-protein coupled receptor effect. This was not mimicked by PGE<sub>2</sub>, or prevented by the EP<sub>4</sub> antagonist, but blocked by a putative PGE<sub>2</sub>-G receptor antagonist, PDA-94 indicating that PDA-94 may be a PGE<sub>2</sub>-G receptor antagonist.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:510550 |
| Date | January 2009 |
| Creators | Ford, Lorna |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=33596 |
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