The aim of this study was to evaluate skeletal pain associated with osteoporosis and to examine the inhibitory effect of bisphosphonate (BP) on pain in an ovariectomized (OVX) mouse model. We evaluated skeletal pain in OVX mice through an examination of pain-like behavior as well as immunohistochemical findings. In addition, we assessed the effects of alendronate (ALN), a potent osteoclast inhibitor, on those parameters. The OVX mice showed a decrease in the pain threshold value, and an increase in the number of c-Fos immunoreactive neurons in laminae I-II of the dorsal horn of the spinal cord. Alendronate caused an increase in the pain threshold value and inhibited c-Fos expression. The serum level of tartrate-resistant acid phosphatase 5b, a marker of osteoclast activity, was significantly negatively correlated with the pain threshold value. Furthermore, we found that an antagonist of the transient receptor potential channel vanilloid subfamily member 1, which is an acid-sensing nociceptor, improved pain-like behavior in OVX mice. These results indicated that the inhibitory effect of BP on osteoclast function might contribute to an improvement in skeletal pain in osteoporosis patients.

ABSTRACT:We have recently demonstrated that pathological changes leading to increased bone resorption by osteoclast activation are related to the induction of pain-like behavior in ovariectomized (OVX) mice. In addition, bisphosphonate and the antagonist of transient receptor potential vanilloid type 1 (TRPV1), an acid-sensing nociceptor, improved the threshold value of pain-like behaviors accompanying an improvement in the acidic environment in the bone tissue based on osteoclast inactivation. The aim of this study was to evaluate the effect of (i) an inhibitor of vacuolar H þ -ATPase, known as an proton pump, (ii) an antagonist of acid-sensing ion channel (ASIC) 3, as another acid-sensing nociceptor, and (iii) the P2X2/3 receptor, as an ATP-ligand nociceptor, on pain-like behavior in OVX mice. This inhibitor and antagonists were found to improve the threshold value of pain-like behavior in OVX mice. These results indicated that the skeletal pain accompanying osteoporosis is possibly associated with the acidic microenvironment and increased ATP level caused by osteoclast activation under a high bone turnover state. Skeletal pain resulting from fragility fractures and skeletal deformity is the most common problem observed in osteoporosis patients. 1 On the other hand, several studies have indicated that osteoporosis patients also experience idiopathic skeletal pain independent of those fractures or deformity. [2][3][4] One factor underlying the induction of idiopathic skeletal pain is the acidic microenvironment created by activated osteoclasts, which results in pain through the same mechanism as that observed for cancer-induced bone pain. 5,6 Moreover, recent studies have demonstrated that bisphosphonate (BP), an anti-bone resorption drug which works via the inhibition of osteoclast activity, improves skeletal pain in osteoporosis patients. 2,3,7 We have also demonstrated that the pathological changes leading to increased bone resorption by osteoclast activation are related to the induction of painlike behavior in an ovariectomized (OVX) mouse model. In addition, BP treatment improved the threshold value of the pain-like behavior accompanied by an improvement in the acidic environment in the bone tissue through osteoclast inactivation. 8 Furthermore, the antagonist to transient receptor potential vanilloid type 1 (TRPV1), a member of a family of polymodal and nonselective cation channels that are predominantly expressed by sensory nerve fibers and sensitized by protons, 9 was also found to improve the threshold value. 8 Therefore, we speculate that the skeletal pain accompanying osteoporosis is associated with the acidic microenvironment resulting from osteoclast activation.On the other hand, with regard to the improvement in the pain threshold, the effect of TRPV1 was likely to be limited in comparison with that of BP. These results encouraged us to clarify the other mechanisms by which pathological changes under a high bone turnover state resulting from osteoclast activation might induce skeletal pain in oste...

Tetranectin is a plasminogen-binding protein that enhances plasminogen activation, which has been suggested to play a role in tissue remodeling. Recently, we showed that tetranectin has a role in the wound-healing process. In this study, we investigated whether tetranectin plays a role in fracture healing. The fracture-healing process was studied using a femoral osteotomy model in tetranectin-null mice, previously generated by the authors. Radiographic imaging, micro-computed tomography (μCT), and histological analysis were used to evaluate osteotomy healing. In wild-type mice, a callus was apparent from 7 days, and most samples showed marked callus formation and rebridging of the cortices at the osteotomy site at 21 days. In contrast, in the tetranectin-null mice there was no callus formation at 7 days and much less callus formation and no bridging of cortices were observed at 21 days. At 35 days, all osteotomy sites showed clear rebridging, and secondary bone formation was achieved in wild-type mice by 42 days. In contrast, no clear rebridging or secondary bone formation was observed at 42 days in the tetranectin-null mice. Analysis using μCT at 21 days after osteotomy revealed that the callus area in tetranectin-null mice was smaller than that in wild-type mice. Histological analysis also showed that soft tissue and callus formation were smaller in the tetranectin-null mice at the early stage of the healing process after drill-hole injury. These results suggested that tetranectin could have a role in the positive regulation at the early stage of the fracture-healing process, which was reflected in the delayed fracture healing in tetranectin-deficient mice.

We carried out arthrography in 19 thumbs of 18 patients in whom duplication was observed at the interphalangeal (Wassel type II) or metacarpophalangeal (Wassel type IV) joints on radiographs. The average age at surgery was 12.3 months and average duration of post-surgical follow-up was 21.3 months. Based on the arthrographic findings, the types of cartilaginous connections were subdivided into five groups. In group 1, there was a cartilaginous connection at the base of duplicated phalanges. In group 2, there was a cartilaginous connection of the radial digit between the distal and proximal phalanges, or between the proximal phalanx and metacarpal. In group 3, the phalanges separated at a common joint without any cartilaginous connection. In group 4, the radial digit demonstrated fibrous attachment to the capsule without any joint formation. In group 5, each joint was completely separated without any cartilaginous connection. These arthrographic findings could not be detected on radiographs. Different surgical procedures were carried out according to the form of cartilaginous connection.

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