Inhibition of inflammatory actions of aminobisphosphonates by dichloromethylene bisphosphonate, a non-aminobisphosphonate

1 When injected intraperitoneally into mice in doses larger than those used clinically, all the amino derivatives of bisphosphonates (aminoBPs) tested induce a variety of inflammatory reactions such as induction of histidine decarboxylase (HDC, the histamine-forming enzyme), hypertrophy of the splee n, atrophy of the thymus, hypoglycaemia, ascites and accumulation of exudat e in the thorax, and an increase in the number of macrophages and/or granul ocytes in the peritoneal cavity of blood. On the other hand, dichloromethyl ene bisphosphonate (Cl2MBP) a typical non-aminoBP, has no such inflammatory actions. In the present study, we found that this agent can suppress the i nflammatory actions of aminoBPs. 2 Cl2MBP, when injected into mice before or after injection of 4-amino-1-hy droxybutylidene-1,1-bisphosphonic acid (AHBuBP; a typical aminoBP), inhibit ed the induction of HDC activity by AHBuBP in a dose- and time-dependent ma nner. The increase in HDC activity induced by AHBuBP was largely suppressed by the injection of an equimolar dose of Cl2MBP. Cl2MBP also inhibited oth er AHBuBP-induced inflammatory reactions, as well as the inflammatory actio ns of two other aminoBPs. However, Cl2MBP did not inhibit the increase in H DC activity induced by lipopolysaccharide (LPS). 3 We have previously reported that AHBuBP augments the elevation of HDC act ivity and the production of interleukin-1 beta (IL-1 beta) that are induced by LPS. These actions of AHBuBP were also inhibited by Cl2MBP. 4 Based on these results and reported actions of bisphosphonates, the mecha nisms underlying the contrasting effects of aminoBPs and Cl2MBP, a non-amin oBP are discussed. The results suggest that combined administration of Cl2M BP and an aminoBP in patients might be a useful way of suppressing the infl ammatory side effects of aminoBPs.