Topically administered Risedronate shows powerful anti-osteoporosis effect in ovariectomized mouse model

Authors

So Hee Nam, Jae-Hwan Jeong, Xiangguo Che, Kyung-Eun Lim, Hyemi Nam, Jong-Sang Park, Je-Yong Choi

Abstract

We investigated the therapeutic effect of topical Risedronate (RIS) on a mouse model of estrogen-deficient osteoporosis. Fourteen-week-old female mice were ovariectomized and assigned to 4 groups: SHAM-operated (SHAM), OVX mice treated with vehicle (OVX-V), OVX mice treated with 0.2% RIS (OVX-0.2% RIS), and OVX-mice treated with 0.02% RIS (OVX-0.02% RIS). Topical samples containing RIS were prepared in 10% (w/w) polyethylene glycol (PEG, MW 400) and 80 μg of sample was spread on the mice's mid-backs every 3 days for 5 weeks. Micro-CT analysis of femora demonstrated that OVX-0.2% RIS exhibited a 29% greater bone mineral density and 24% greater bone volume fraction than that of OVX-V group. Investigation of the trabecular bone in OVX-0.2% RIS revealed a 24% higher bone volume (BV/TV), 51% higher trabecular number (Tb.N), and 40% lower trabecular separation (Tb.Sp) compared to OVX-V mice. Additionally, bone phenotypes of tibiae were further confirmed by histological analysis. OVX-0.2% RIS group exhibited a 494% greater BV/TV, 464% less Tb.Sp, 81% greater active osteoclast surface (Oc.S/BS) and 26% less osteoclast number (N.Oc/BS) than that of OVX-V group. Collectively, these results indicated that topical delivery of RIS has powerful pharmaceutical effects on the prevention of osteoporosis and bone turnover.

Link to Article

http://dx.doi.org/10.1016/j.bone.2011.10.017

Cell autonomous requirement of connexin 43 for osteocyte survival: consequences for endocortical resorption and periosteal bone formation

Authors

Nicoletta Bivi, Keith W. Condon, Matthew R. Allen, Nathan Farlow, Giovanni Passeri, Lucas R. Brun, Yumie Rhee, Teresita Bellido, Lilian I. Plotkin

Abstract

Connexin43 (Cx43) mediates osteocyte communication with other cells and with the extracellular milieu and regulates osteoblastic cell signaling and gene expression. We now report that mice lacking Cx43 in osteoblasts/osteocytes or only in osteocytes (Cx43ΔOt mice)exhibit increased osteocyte apoptosis, endocortical resorptionand periosteal bone formation, resulting in higher marrow cavityand total tissueareas measured at the femoral mid-diaphysis.Blockade of resorption reversed the increasedmarrow cavity but not total tissue area, demonstrating that endocortical resorption andperiosteal apposition are independently regulated.Anatomical mappingof apoptotic osteocytes,osteocytic protein expression, and resorption and formation,suggeststhat Cx43 controls osteoclast and osteoblast activity by regulating osteoprotegerin and sclerostinlevels, respectively, in osteocytes located in specific areas of the cortex.Whereas empty lacunae and living osteocytes lacking osteoprotegerinwere distributed throughout cortical bonein Cx43ΔOt mice, apoptotic osteocyteswere preferentially located in areas containing osteoclasts, suggesting that osteoclast recruitment requires active signaling from dying osteocytes.Furthermore, Cx43 deletion in cultured osteocytic cells resulted in increased apoptosis and decreased osteoprotegerin expression. Thus, Cx43 is essential in a cell-autonomous fashionin vivo and in vitrofor osteocyte survivaland for controlling the expression of osteocytic genesthat affectosteoclast and osteoblast function.

Link to Article

http://dx.doi.org/10.1002/jbmr.548

Yellow-bellied Marmots (Marmota flaviventris) preserve bone strength and microstructure during hibernation

Authors

Samantha J. Wojda, Meghan McGee-Lawrence, Richard A. Gridley, Janene Auger, Hal L. Black, Seth W. Donahue

Abstract

Reduced skeletal loading typically results in decreased bone strength and increased fracture risk for humans and many other animals. Previous studies have shown bears are able to prevent bone loss during the disuse that occurs during hibernation. Studies with smaller hibernators, which arouse intermittently during hibernation, show that they may lose bone at the microstructural level. These small hibernators, like bats and squirrels, do not utilize intracortical remodeling. However, slightly larger mammals like marmots do. In this study we examined the effects of hibernation on bone structural, mineral, and mechanical properties in yellow-bellied marmots (Marmota flaviventris). This was done by comparing cortical bone properties in femurs and trabecular bone properties in tibias from marmots killed before hibernation (fall) and after hibernation (spring). Age data were not available for this study; however, based on femur length the post-hibernation marmots were larger than the pre-hibernation marmots. Thus, cross-sectional properties were normalized by allometric functions of bone length for comparisons between pre- and post-hibernation. Cortical thickness and normalized cortical area were higher in post-hibernation samples; no other normalized cross-sectional properties were different. No cortical bone microstructural loss was evident in osteocyte lacunar measurements, intracortical porosity, or intracortical remodeling cavity density. Osteocyte lacunar area, porosity, and density were surprisingly lower in post-hibernation samples. Trabecular bone volume fraction was not different between pre- and post-hibernation. Measures of both trabecular and cortical bone mineral content were higher in post-hibernation samples. Three-point bending failure load, failure energy, elastic energy, ultimate stress, and yield stress were all higher in post-hibernation samples. These results support the idea that, like bears, marmots are able to prevent disuse osteoporosis during hibernation, thus preventing increased fracture risk and promoting survival of the extreme environmental conditions that occur in hibernation.

Link to Article

http://dx.doi.org/10.1016/j.bone.2011.10.013

Differential Effects of Oral Doxercalciferol (Hectorol®) or Paricalcitol (Zemplar®) in the Cyp27b1-Null Mouse Model of Uremia

Authors

René St-Arnaud, Alice Arabian, Omar Akhouayri, Joyce C. Knutson, Stephen A. Strugnell

Abstract

Kidney disease patients experience declining calcitriol levels and develop secondary hyperparathyroidism (SHPT). Animal models of uremia based on 5/6 nephrectomy (NTX) do not consistently reproduce this calcitriol deficiency. We developed an animal model, the NTX Cyp27b1-null mouse, which completely lacks endogenous calcitriol, and examined the suitability of this model for evaluation of treatment with vitamin D analogs in uremia. Methods: NTX was performed at 2 months of age. One week post-NTX, animals were treated for 4 weeks with vehicle; doxercalciferol at 30, 100 or 300 pg/g body weight (b.w.); or paricalcitol at 100, 300 or 1,000 pg/g b.w. by gavage 3 times per week. Serum blood urea nitrogen and creatinine were elevated. Vehicle-treated NTX null mice had hypocalcemia and SHPT. Doxercalciferol at 100 or 300 pg/g b.w. normalized serum calcium and parathyroid hormone (PTH) levels. Paricalcitol at 300 or 1,000 pg/g normalized serum calcium, but PTH levels remained elevated. Osteomalacia was corrected by 100 pg/g b.w. of doxercalciferol or 1,000 pg/g b.w. of paricalcitol. The highest dose of doxercalciferol, but not of paricalcitol, significantly reduced osteitis fibrosa. Our results reveal the differential efficacy of doxercalciferol and paricalcitol in this novel animal model incorporating both calcitriol deficiency and renal insufficiency.

Link to Article

http://dx.doi.org/10.1159/000329663

Inhibition of β-catenin signaling in chondrocytes induces delayed fracture healing in mice

Authors

Yang Huang, Xiaoling Zhang, Kewei Du, Fei Yang, Yu Shi, Jingang Huang, Tingting Tang, Di Chen, Kerong Dai

Abstract

Appropriate and controlled chondrogenesis and endochondral ossification play fundamental roles in the fracture healing cascade, a regenerative process involved in highly coordinated biological events, including the Wnt/β-catenin signaling pathway. To examine the role and importance of this pathway in chondrocytes, we studied bone repair of closed tibias fractures in Col2a1-ICAT transgenic mice, in which the Wnt/β-catenin signaling pathway is specially inhibited in chondrocytes. Radiological, histological, and histomorphometric analyses at 7, 9, 12, 14, 21, and 28 days after fracture demonstrated the bone repairs were retarded in Col2a1-ICAT transgenic mice, due to reduced and delayed cartilage formation, chondrocyte hypertrophy, and bone generation. In addition, at 5 weeks, Col2a1-ICAT transgenic mice exhibited a weak mechanical tolerance to four-point bending. Furthermore, quantitative-PCR analysis revealed that the expression of genes associated specifically with cartilage extracellular matrix formation (collagen II, collagen X, and mmp13), bone remodeling (alp, collagen I, and osteocalcin), and vascular extravagation (vegf), and transcriptional activators involved in cartilage generation and ossification (sox9 and runx2) was decreased and delayed in the fracture sites of Col2a1-ICAT transgenic mice during healing. Collectively, these results suggest that Wnt/β-catenin signaling is critical for fracture healing, especially with respect to chondrogenesis and endochondral ossification. Thus, our study provides insight into the possible mechanisms of and therapeutic targets for improving normal facture repair and the healing of non-union fractures.

Link to Article

http://dx.doi.org/10.1002/jor.21505

Bone fragility and decline in stem cells in prematurely aging DNA repair deficient trichothiodystrophy mice

Authors

Karin E. M. Diderich, Claudia Nicolaije, Matthias Priemel, Jan H. Waarsing, Judd S. Day, Renata M. C. Brandt, Arndt F. Schilling, Sander M. Botter, Harrie Weinans and Gijsbertus T. J. van der Horst, et al.

Abstract

Trichothiodystrophy (TTD) is a rare, autosomal recessive nucleotide excision repair (NER) disorder caused by mutations in components of the dual functional NER/basal transcription factor TFIIH. TTD mice, carrying a patient-based point mutation in the Xpd gene, strikingly resemble many features of the human syndrome and exhibit signs of premature aging. To examine to which extent TTD mice resemble the normal process of aging, we thoroughly investigated the bone phenotype. Here, we show that female TTD mice exhibit accelerated bone aging from 39 weeks onwards as well as lack of periosteal apposition leading to reduced bone strength. Before 39 weeks have passed, bones of wild-type and TTD mice are identical excluding a developmental defect. Albeit that bone formation is decreased, osteoblasts in TTD mice retain bone-forming capacity as in vivo PTH treatment leads to increased cortical thickness. In vitro bone marrow cell cultures showed that TTD osteoprogenitors retain the capacity to differentiate into osteoblasts. However, after 13 weeks of age TTD females show decreased bone nodule formation. No increase in bone resorption or the number of osteoclasts was detected. In conclusion, TTD mice show premature bone aging, which is preceded by a decrease in mesenchymal stem cells/osteoprogenitors and a change in systemic factors, identifying DNA damage and repair as key determinants for bone fragility by influencing osteogenesis and bone metabolism.

Link to Article

http://dx.doi.org/10.1007/s11357-011-9291-8