Hypothalamic Suppression during Adolescence Varies By Bone Envelope

Authors

Saine, M.E.; Barbe, M.F.; Agah, M.R.; Yingling, V.R.

Abstract

The purpose of this study was to suppress estradiol levels in adolescent (post pubertal rats) using gonadotropin releasing hormone antagonist (GnRH-a) injections and determine the changes in bone structure and mechanical strength. In an IACUC approved study, female rats at 23 days of age were assigned to a baseline group (BL65) (n=10) sacrificed on day 65, a control group (C) (n=15) sacrificed on day 90, or an experimental group (AMEN) (n=9) sacrificed on day 90 that received daily injections of GnRH-a for a 25 day period from 65 to 90 days of age (2.5 mg/kg/dose). Body weights were similar on day 65 however, the AMEN group was significantly heavier than C (17%, p=.001) on day 90. In the AMEN rats relative to C, plasma estradiol levels were reduced by 36% (p=.0001), and plasma IGF-1 levels were 24 % higher (p=.003). In the femur, there was no change in periosteal bone apposition or total cross-sectional area. The marrow area increased by 13.7% (p=.05) resulting in a 7.8% decrease in relative cortical area (p=.012), and endocortical bone formation rate increased by 39.4% (p=.04). trabecular volume and number decreased by 51.5% (p=.0003) and 49.5% (p=.0003), respectively. The absolute peak moment of the tibiae and femurs were unchanged in the AMEN group relative to C, but were reduced by 8.8% (p=.03) and 7.5% (p=.09) respectively when normalized by body weight. Suppression of estradiol by 25 days of GnRH antagonist administration to 65-day old (post pubertal) rats, reduced trabecular volume and number by about 50%, increased endocortical bone turnover, and reduced relative cortical thickness without changing tibial and femoral total area. These changes in bone structure were associated with no change in absolute mechanical strength possibly due to increases in body weight or in IGF-1 concentrations.

Link to Article

http://dx.doi.org/10.1249/MSS.0b013e3181f56a2c

Contribution of Mineral to Bone Structural Behavior and Tissue Mechanical Properties

Authors

Eve Donnelly, Dan X. Chen, Adele L. Boskey, Shefford P. Baker and Marjolein C. H. van der Meulen

Abstract

Bone geometry and tissue material properties jointly govern whole-bone structural behavior. While the role of geometry in structural behavior is well characterized, the contribution of the tissue material properties is less clear, partially due to the multiple tissue constituents and hierarchical levels at which these properties can be characterized. Our objective was to elucidate the contribution of the mineral phase to bone mechanical properties across multiple length scales, from the tissue material level to the structural level. Vitamin D and calcium deficiency in 6-week-old male rats was employed as a model of reduced mineral content with minimal collagen changes. The structural properties of the humeri were measured in three-point bending and related to the mineral content and geometry from microcomputed tomography. Whole-cortex and local bone tissue properties were examined with infrared (IR) spectroscopy, Raman spectroscopy, and nanoindentation to understand the role of altered mineral content on the constituent material behavior. Structural stiffness (−47%) and strength (−50%) were reduced in vitamin D-deficient (−D) humeri relative to controls. Moment of inertia (−38%), tissue mineral density (TMD, −9%), periosteal mineralization (−28%), and IR mineral:matrix ratio (−19%) were reduced in −D cortices. Thus, both decreased tissue mineral content and changes in cortical geometry contributed to impaired skeletal load-bearing function. In fact, 97% of the variability in humeral strength was explained by moment of inertia, TMD, and IR mineral:matrix ratio. The strong relationships between structural properties and cortical material composition demonstrate a critical role of the microscale material behavior in skeletal load-bearing performance.

Link to Article

http://dx.doi.org/10.1007/s00223-010-9404-x

Effects of the Combination Treatment of Raloxifene and Alendronate on the Biomechanical Properties of Vertebral Bone

Authors

Tamim Diab, Jason Wang, Susan Reinwald, Robert E. Guldberg, David B. Burr

Abstract

Raloxifene (RAL) and alendronate (ALN) improve the biomechanical properties of bone by different mechanisms. The goal here was to investigate the effects of combination treatment of RAL and ALN on the biomechanical properties of vertebral bone. Six-month-old Sprague-Dawley rats (n=80) were randomized into 5 experimental groups (Sham, OVX, OVX+RAL, OVX+ALN, OVX+RAL+ALN; n=16/group). Following sacrifice, structural and derived material biomechanical properties of vertebral bodies were assessed. Density and dynamic histomorphometric measurements were made on cancellous bone. The results demonstrate that the structural biomechanical properties of vertebral bone are improved with the combination treatment. Stiffness and ultimate load of the OVX+RAL and OVX+ALN groups were significantly lower than sham, but the combination treatment with RAL+ALN was not significantly different than sham. Furthermore, the OVX+RAL+ALN group was the only agent-treated group in which the ultimate load was significantly higher than OVX (p<0.05). Cancellous bone fractional volume (BV/TVcanc) and mineral density (aBMD) were also improved with the combination treatment. BV/TVcanc of the OVX+RAL+ALN group was 6.7% and 8.7% greater than the OVX+RAL (p<0.05) and OVX+ALN (p<0.05) groups, respectively. aBMD of the OVX+RAL or OVX+ALN groups were not significantly different than OVX, but the combination treatment was significantly higher than OVX or OVX+RAL alone, and not significantly different from sham. Turnover rates of both the RAL+ALN and ALN alone groups were lower than the RAL alone group (p<0.05). We conclude that the combination treatment of raloxifene and alendronate has beneficial effects on bone volume, resulting in an improvement of the structural properties of vertebral bone.

Link to Article

http://dx.doi.org/10.1002/jbmr.197

The Ewing's Sarcoma Fusion Protein, EWS-FLI, Binds Runx2 and Blocks Osteoblast Differentiation

Authors

Xiaodong Li,Meghan E. McGee-Lawrence, Matthew Decker, Jennifer J. Westendorf

Abstract

Ewing's sarcomas are highly aggressive round cell tumors of bone and soft tissues that afflict children and young adults. The majority of these tumors harbor the t(11;22) translocation and express the fusion protein EWS-FLI. Modern molecular profiling experiments indicate that Ewing's tumors originate from mesenchymal precursors in young individuals. EWS-FLI alters the morphology of mesenchymal cells and prevents lineage specification; however, the molecular mechanisms for differentiation arrest are unclear. We recently showed that EWS-FLI binds Runx2, a master regulator of osteoblast differentiation. In this report, we demonstrate that FLI sequences within EWS-FLI are responsible for interactions with Runx2. EWS-FLI blocks the expression of osteoblastic genes in a multipotent progenitor cell line that requires Runx2 to integrate bone morphogenic protein (Bmp)2 signaling while increasing proliferation and altering cell morphology. These results demonstrate that EWS-FLI blocks the ability of Runx2 to induce osteoblast specification of a mesenchymal progenitor cell. Disrupting interactions between Runx2 and EWS-FLI1 may promote differentiation of the tumor cell

Link to Article

http://dx.doi.org/10.1002/jcb.22782

Vitamin D Deficiency Promotes Growth of MCF-7 Human Breast Cancer in a Rodent Model of Osteosclerotic Bone Metastasis

Authors

Li Laine Ooia, Yu Zhenga, Hong Zhoua, Trupti Trivedia, Arthur D. Conigraveb, Markus J. Seibela, and Colin R. Dunstan

Abstract

Breast cancer metastases to bone are common in advanced stage disease. We have recently demonstrated that vitamin D deficiency enhances breast cancer growth in an osteolytic mouse model of breast cancer metastasis. In this study, we examined the effects of vitamin D deficiency on tumor growth in an osteosclerotic model of intra-skeletal breast cancer in mice.
Methods

The effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on proliferation and apoptosis of MCF-7 breast cancer cells, and changes in the expression of genes within the vitamin D metabolic pathway (VDR, 1α- and 24-hydroxylase) were examined in vitro. MCF-7 breast cancer cells were injected intra-tibially into vitamin D deficient and vitamin D sufficient mice co-treated with and without osteoprotegerin (OPG). The development of tumor-related lesions was monitored via serial X-ray analysis. Tumor burden and indices of proliferation and apoptosis were determined by histology along with markers of bone turnover and serum intact PTH levels.
Results

In vitro, MCF-7 cells expressed critical genes for vitamin D signalling and metabolism. Treatment with 1,25(OH)2D3 inhibited cell growth and proliferation, and increased apoptosis. In vivo, osteosclerotic lesions developed faster and were larger at endpoint in the tibiae of vitamin D deficient mice compared to vitamin D sufficient mice (1.49 ± 0.08 mm2 versus 1.68 ± 0.15 mm2, p < 0.05). Tumor area was increased by 55.8% in vitamin D deficient mice (0.81 ± 0.13 mm2 versus 0.52 ± 0.11 mm2 in vitamin D sufficient mice). OPG treatment inhibited bone turnover and caused an increase in PTH levels, while tumor burden was reduced by 90.4% in vitamin D sufficient mice and by 92.6% in vitamin D deficient mice. Tumor mitotic activity was increased in the tibiae of vitamin D deficient mice and apoptosis was decreased, consistent with faster growth.
Conclusion

Vitamin D deficiency enhances both the growth of tumors and the tumor-induced osteosclerotic changes in the tibiae of mice following intratibial implantation of MCF-7 cells. Enhancement of tumor growth appears dependent on increased bone resorption rather than increased bone formation induced by these tumors.

Link to Article

http://dx.doi.org/10.1016/j.bone.2010.07.012

Modification of Osteoarthritis in the Guinea Pig with Pulsed Low-Intensity Ultrasound Treatment

Authors

Gurkan, I. and Ranganathan, A. and Yang, X. and Horton Jr, W.E. and Todman, M. and Huckle, J. and Pleshko, N. and Spencer, R.G.

Abstract

Objective: The Hartley guinea pig develops articular cartilage degeneration similar to that seen in idiopathic human osteoarthritis (OA). We investigated whether the application of pulsed low-intensity ultrasound (PLIUS) to the Hartley guinea pig joint would prevent or attenuate the progression of this degenerative process.

Methods: Treatment of male Hartley guinea pigs was initiated at the onset of degeneration (8 weeks of age) to assess the ability of PLIUS to prevent OA, or at a later age (12 months) to assess the degree to which PLIUS acted to attenuate the progression of established disease. PLIUS (30mW/cm2) was applied to stifle joints for 20min/day over periods ranging from 3 to 10 months, with contralateral limbs serving as controls. Joint cartilage histology was graded according to a modified Mankin scale to evaluate treatment effect. Immunohistochemical staining for interleukin-1 receptor antagonist (IL-1ra), matrix metalloproteinase (MMP)-3, MMP-13, and transforming growth factor (TGF)-β1 was performed on the cartilage to evaluate patterns of expression of these proteins.

Results: PLIUS did not fully prevent cartilage degeneration in the prevention groups, but diminished the severity of the disease, with the treated joints showing markedly decreased surface irregularities and a much smaller degree of loss of matrix staining as compared to controls. PLIUS also attenuated disease progression in the groups with established disease, although to a somewhat lesser extent as compared to the prevention groups. Immunohistochemical staining demonstrated a markedly decreased degree of TGF-β1 production in the PLIUS-treated joints. This indicates less active endogenous repair, consistent with the marked reduction in cartilage degradation.

Conclusions: PLIUS exhibits the ability to attenuate the progression of cartilage degeneration in an animal model of idiopathic human OA. The effect was greater in the treatment of early, rather than established, degeneration.

Link to Article

http://linkinghub.elsevier.com/retrieve/pii/S1063458410000336