Objective. Adenosine, acting at the A2A receptor,
mediates the antiinflammatory effects of methotrexate
(MTX) in models of inflammation. We previously reported
that A2A receptor ligation diminishes wear
particle–driven osteolysis. The aim of this study was to
investigate whether MTX treatment could prevent bone
resorption caused by inflammatory osteolysis.
Methods. C57BL/6 mice (6–8 weeks old) received
intraperitoneal injections of 1 mg/kg MTX (n 10) or
0.9% saline (n 5), starting 2 weeks prior to surgical
implantation of 3 mg of wear particles (ultrahigh molecular
weight polyethylene [UHMWPE] particles). The
MTX-treated mice received daily injections of vehicle or
ZM241385 at the surgical site until they were killed, 14
days later. XenoLight RediJect Bone Probe was injected
intravenously, and fluorescence analysis of the calvaria
using an IVIS imaging system was performed to assess
bone formation. Micro–computed tomography (micro-
CT) and immunostaining for osteoclast and osteoblast
markers were performed.
Results. Implantation of wear particles induced
bone pitting and thinning, as shown by micro-CT. MTX
treatment markedly reduced osteolysis, and this effect
was abrogated by treatment with the A2A receptor
antagonist ZM241385. Implantation of UHMWPE reduced
new bone formation, and MTX treatment restored
new bone formation, an effect that was completely
reversed by treatment with ZM241385.
Histologic examination of particle-exposed calvarias
demonstrated that MTX prevented accumulation of an
inflammatory infiltrate at the site of particle implantation,
increased the number of osteoblasts, and reduced
the number of osteoclasts at the site of inflammation, an
effect that was reversed by treatment with ZM241385.
Conclusion. MTX reduces inflammatory osteolysis
indirectly via stimulation of A2A receptor and may
represent a novel approach to enhance orthopedic implant
survival, delaying or eliminating the need for
revision arthroplasty surgery.NI
