Contrasting effects of alendronate and clodronate on RAW 264 macrophages: the role of a bisphosphonate metabolite.

Clodronate (dichloromethylidene-bisphosphonate), a halogen-containing bisphosphonate, can inhibit the release of cytokines from RAW 264 macrophages and has anti-inflammatory properties in rheumatoid arthritis, whilst amino-containing bisphosphonates such as alendronate (4-amino-1-hydroxybutylidene-bisphosphonate), have pro-inflammatory properties and can cause an acute phase response. The basis for these pharmacological properties is unclear. Recently, it was demonstrated that clodronate is metabolised by certain cell lines in vitro to an analogue of ATP, whereas amino-bisphosphonates are not. We therefore investigated whether clodronate can also be metabolised by RAW 264 macrophages and whether intracellular accumulation of the metabolite (AppCCl2p) could account for the anti-inflammatory properties of clodronate. The effect of alendronate and AppCCl2p on the release of cytokines (IL-1beta, IL-6, and TNFalpha) from RAW 264 cells was compared, and the effect of the bisphosphonates and AppCCl2p on the DNA binding activities of transcription factors, NF-kappaB and AP-1, was investigated. Pretreatment of RAW 264 macrophages with alendronate augmented the LPS-stimulated release of IL-1beta and increased the binding of NF-kappaB to DNA in an electrophoretic mobility shift assay. Without LPS-induction, alendronate did not affect cytokine release or NF-kappaB binding. Clodronate was metabolised by RAW 264 cells to AppCCl2p. Like clodronate, AppCCl2p inhibited the LPS-induced release of cytokines and NO from RAW 264 macrophages. Both clodronate and its metabolite also inhibited the LPS-stimulated binding of NF-kappaB to DNA. In conclusion, these results suggest that the metabolite of clodronate may be responsible for the anti-inflammatory properties of clodronate, and that the contrasting effects of different bisphosphonates on the release of cytokines could be mediated partly through changes in the DNA binding activity of NF-kappaB.