BISPHOSPHONATES INDUCE APOPTOSIS IN MOUSE MACROPHAGE-LIKE CELLS IN-VITRO BY A NITRIC OXIDE-INDEPENDENT MECHANISM

Bisphosphonates (BPs) are an important class of antiresorptive drugs u sed in the treatment of bone diseases, including osteoporosis, Althoug h their mechanism of action has not been identified at the molecular l evel, there is substantial evidence that BPs can have a direct effect on osteoclasts by mechanisms that may lead to osteoclast cell death by apoptosis, BPs call also inhibit proliferation and cause cell death i n macrophages in vitro, We have now shown that the toxic effect of BPs on macrophages is also due to the induction of apoptotic, rather than necrotic, cell death, Morphological and biochemical features that are definitive of apoptosis (chromatin condensation, nuclear fragmentatio n, and endonuclease-mediated internucleosomal cleavage of DNA) could b e identified in mouse macrophage-like J774 and RAW264 cells, following treatment with 100 mu M pamidronate, alendronate, and ibandronate for 24 h or more, Clodronate was much less potent, even at 2000 mu M, whi le 2000 mu M etidronate did not cause apoptosis, Apoptosis was not due to increased synthesis of nitric oxide and could not be prevented by inhibitors of nitric oxide synthases. Since macrophages, like osteocla sts, are particularly susceptible to BPs, these observations support t he recent suggestion that the mechanism by which BPs inhibit bone reso rption may involve osteoclast apoptosis, Furthermore, the macrophage-l ike cell lines used in this study may be a convenient model with which to identify the molecular mechanisms by which BPs promote apoptosis i n osteoclasts, Induction of macrophage apoptosis by BPs in vivo may al so account, at least in part, for the anti-inflammatory properties of BPs as well as the ability of BPs to cause an acute phase response.