Bisphosphonates (BPs) containing nitrogen (N-BPs) exhibit far stronger anti-bone-resorptive effects than non-N-BPs. However, repeated administration of N-BPs causes osteonecrosis selectively in jawbones. As BPs accumulate in large amounts within inflamed bones, any N-BP released from the pool accumulated within jawbones might directly act on cells in the surrounding soft-tissues and induce inflammation or necrosis. Here, we examined the local and systemic effects of zoledronate (the most potent N-BP with the highest incidence of jawbone-necrosis) on inflammatory cytokines in mice. Locally within ear-pinnas: (i) zoledronate induced long-lasting accumulation of interleuikin-1β (IL-1β) and IL-18, but not tumor necrosis factor-α (TNF-α), (ii) zoledronate and lipopolysaccharide (LPS, a cell-wall component of Gram-negative bacteria) mutually augmented the productions of IL-1β, IL-18, and TNF-α, and (iii) oxidronate (a toxic non-N-BP) by itself produced not only IL-1β and IL-18, but also TNF-α. In systemic experiments using intraperitoneal injection of zoledronate and/or LPS, (i) zoledronate by itself increased none of the above cytokines in serum, and (ii) in mice pretreated (3 d before) with zoledronate, the LPS-induced increases in serum IL-1β and IL-18 were greatly augmented with a delayed slight TNF-α augmentation. These results, together with previous ones, suggest that (a) pro-IL-1β and pro-IL-18 accumulate within cells in soft-tissues exposed to N-BPs, and infection may augment not only their production, but also the release of their mature forms, (b) IL-1β and IL-18 (possibly together with TNF-α) may play important roles in N-BP-induced inflammation and/or necrosis, and (c) mechanisms underlying the cytotoxic effects of BPs may differ between N-BPs and non-N-BPs.
Keywords: bisphosphonate; interleuikin-1 (IL-1); interleukin-18 (IL-18); lipopolysaccharide; tumor necrosis factor-α (TNF-α); zoledronate.