Systemic but no local effects of combined zoledronate and parathyroid hormone treatment in experimental autoimmune arthritis

Zoledronic acid prevents disuse osteopenia and augments gene expression of osteoclastic differentiation markers in mice

OBJECTIVES

Disuse is characterized by a rapid and profound bone resorption. Zoledronic acid (Zol) inhibits osteoclastic bone resorption. The aim of the study was to prevent disuse osteopenia with Zol and investigate gene expression markers of osteoclastic differentiation.

METHODS

Disuse osteopenia was induced by injecting botulinum toxin (BTX) into the right hind limb of 16-week-old C57BL/6J female mice. Zol (100 µg/kg) was injected s.c. once at study start. The immobilized bones were investigated with DEXA, microCT, mechanical testing, dynamic bone histomorphometry, and RT-qPCR.

RESULTS

The BTX-injections resulted in a loss of cortical and trabecular bone as well as mechanical strength compared to intact baseline and control mice. Treatment with Zol prevented the loss of bone and mechanical strength. Interestingly, treatment with Zol resulted in a higher expression of Nfatc1 and Dcstamp, which are markers osteoclastic differentiation.

CONCLUSIONS

Zol effectively prevented BTX-induced disuse osteopenia. Furthermore, gene expression markers of osteoclastic differentiation were increased in Zol treated immobilized mice, indicating that Zol only affect mature bone resorbing osteoclasts in vivo. However, the current findings are preliminary and calls for further studies.

A Combinatorial effect of carboxymethyl cellulose based scaffold and microRNA-15b on osteoblast differentiation

The present study was aimed to synthesize and characterize a bio-composite scaffold containing carboxymethyl cellulose (CMC), zinc doped nano-hydroxyapatite (Zn-nHAp) and ascorbic acid (AC) for bone tissue engineering applications. The fabricated bio-composite scaffold was characterized by SEM, FT-IR and XRD analyses. The ability of scaffold along with a bioactive molecule, microRNA-15b (miR-15b) for osteo-differentiation at cellular and molecular levels was determined using mouse mesenchymal stem cells (mMSCs). miR-15b acts as posttranscriptional gene regulator and regulates osteoblast differentiation. The scaffold and miR-15b were able to promote osteoblast differentiation; when these treatments were combined together on mMSCs, there was an additive effect on promotion of osteoblast differentiation. Thus, it appears that the combination of CMC/Zn-nHAp/AC scaffold with miR-15b would provide more efficient strategy for treating bone related defects and bone regeneration.

High-dose therapy improves the bone remodelling compartment canopy coverage and bone formation in multiple myeloma

Bone loss in multiple myeloma (MM) is caused by an uncoupling of bone formation to resorption trigged by malignant plasma cells. Increasing evidence indicates that the bone remodelling compartment (BRC) canopy, which normally covers the remodelling sites, is important for coupled bone remodelling. Loss of this canopy has been associated with bone loss. This study addresses whether the bone remodelling in MM is improved by high-dose therapy. Bone marrow biopsies obtained from 20 MM patients, before and after first-line treatment with high-dose melphalan followed by autologous stem cell transplantation, and from 20 control patients with monoclonal gammopathy of undetermined significance were histomorphometrically investigated. This investigation confirmed that MM patients exhibited uncoupled bone formation to resorption and reduced canopy coverage. More importantly, this study revealed that a good response to anti-myeloma treatment increased the extent of formative bone surfaces with canopy, and reduced the extent of eroded surfaces without canopy, reverting the uncoupled bone remodelling, while improving canopy coverage. The association between improved coupling and the canopy coverage supports the notion that canopies are critical for the coupling of bone formation to resorption. Furthermore, this study supports the observation that systemic bone disease in MM can be reversed in MM patients responding to anti-myeloma treatment.

The reversal phase of the bone-remodeling cycle: cellular prerequisites for coupling resorption and formation

The reversal phase couples bone resorption to bone formation by generating an osteogenic environment at remodeling sites. The coupling mechanism remains poorly understood, despite the identification of a number of ‘coupling' osteogenic molecules. A possible reason is the poor attention for the cells leading to osteogenesis during the reversal phase. This review aims at creating awareness of these cells and their activities in adult cancellous bone. It relates cell events (i) on the bone surface, (ii) in the mesenchymal envelope surrounding the bone marrow and appearing as a canopy above remodeling surfaces and (iii) in the bone marrow itself within a 50-μm distance of this canopy. When bone remodeling is initiated, osteoprogenitors at these three different levels are activated, likely as a result of a rearrangement of cell–cell and cell–matrix interactions. Notably, canopies are brought under the osteogenic influence of capillaries and osteoclasts, whereas bone surface cells become exposed to the eroded matrix and other osteoclast products. In several diverse pathophysiological situations, including osteoporosis, a decreased availability of osteoprogenitors from these local reservoirs coincides with decreased osteoblast recruitment and impaired initiation of bone formation, that is, uncoupling. Overall, this review stresses that coupling does not only depend on molecules able to activate osteogenesis, but that it also demands the presence of osteoprogenitors and ordered cell rearrangements at the remodeling site. It points to protection of local osteoprogenitors as a critical strategy to prevent bone loss.