Mouse macrophages primed with al“endronate down-regulate monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1α (MIP-1α) production in response to Toll-like receptor (TLR) 2 and TLR4 agonist via Smad3 activation

Alendronate is one of the nitrogen-containing bisphosphonates (NBPs) used as anti-bone resorptive drugs. However, NBPs have inflammatory side effects including osteomyelitis and osteonecrosis of the jaw. In the present study, we examined the effects of alendronate on chemokine production by the macrophage-like cell line, J774.1, when incubated with Pam3CSK4 (a Toll-like receptor (TLR) 2 agonist) and Lipid A (a TLR4 agonist). Pretreatment of J774.1 cells with alendronate decreased the production of TLR ligand-induced monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1α (MIP-1α) but did not influence nuclear factor-κB (NF-κB) activation. While this agent induced caspase-8 activation, a caspase-8 inhibitor did not affect the decrease in MCP-1 production by alendronate and TLR ligands. Thus, the alendronate-mediated decrease in chemokine production was independent of NF-κB and caspase-8 activation. Although transforming growth factor-β1 (TGF-β1) is known to inhibit chemokine production by various cell types via Smad3 activation, pretreatment with alendronate did not increase TGF-β1 production by J774.1 cells incubated in the presence or absence of TLR ligands. However, alendronate directly activated Smad3.These results suggest that by down-regulating MCP-1 and MIP-1α production via Smad3, long-term use of alendronate might inhibit normal activation and migration of osteoclasts and cause osteonecrosis.