The effects of bisphosphonate on pain-related behavior and immunohistochemical analyses in hindlimb-unloaded mice.

Objective: The aim of this study was to evaluate skeletal pain associated with immobility-induced osteoporosis and to examine the inhibitory effect of bisphosphonate (BP) administration on pain in hindlimb-unloaded (HU) mice.
Methods: The mechanism of osteoporotic pain in HU mice was evaluated through an examination of pain-related behavior, as well as immunohistochemical findings. In addition, the effects of alendronate (ALN), a potent osteoclast inhibitor, on these parameters were assessed.
Results: HU mice with tail suspension developed bone loss and mechanical hyperalgesia in the hindlimbs. The HU mice showed an increase in the number of calcitonin gene-related peptide (CGRP)-immunoreactive neurons and in transient receptor potential channel vanilloid subfamily member 1 (TRPV1)-immunoreactive neurons in the dorsal root ganglions (DRGs) innervating the hindlimbs. Furthermore, administration of ALN prevented HU-induced bone loss, mechanical hyperalgesia, and upregulation of CGRP and TRPV1 expressions in DRG neurons of immobility-induced osteoporotic animal models.
Conclusions: HU mice appear to be a useful model for immobility-induced osteoporotic pain and hindlimb-unloading-induced bone loss, as well as upregulation of CGRP and TRPV1 expressions in DRG neurons, and BP treatment prevented bone loss and mechanical hyperalgesia. The inhibitory effect of BP on osteoclast function might contribute to improving osteoporosis-related pain.
(Copyright © 2018 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)