Trabecular bone histomorphometry in humans with type 1 diabetes Mellitus

Authors

Laura A.G. Armas, Mohammed P. Akhter, Andjela Drincic, Robert R. Recker

Abstract

Patients with Type 1 Diabetes Mellitus (DM) have markedly increased risk of fracture, but little is known about abnormalities in bone micro-architecture or remodeling properties that might give insight into the pathogenesis of skeletal fragility in these patients. We report here a case–control study comparing bone histomorphometric and micro-CT results from iliac biopsies in 18 otherwise healthy subjects with Type 1 Diabetes Mellitus with those from healthy age- and sex- matched non-diabetic control subjects. Five of the diabetics had histories of low-trauma fracture. Transilial bone biopsies were obtained after tetracycline labeling. The biopsy specimens were fixed, embedded, and scanned using a desktop μCT at 16 micron resolution. They were then sectioned and quantitative histomorphometry was performed as previously described by Recker et al. 1988.[1] Two sections, > 250 μm apart, were read from the central part of each biopsy. Overall there were no significant differences between diabetics and controls in histomorphometric or micro-CT measurements. However, fracturing diabetics had structural and dynamic trends different from nonfracturing diabetics by both methods of analysis. In conclusion, Type 1 Diabetes Mellitus does not result in abnormalities in bone histomorphometric or micro-CT variables in the absence of manifest complications from the diabetes. However, diabetics suffering fractures may have defects in their skeletal microarchitecture that may underlie the presence of excess skeletal fragility.

Link to Article

http://dx.doi.org/10.1016/j.bone.2011.09.055

Lamin A/C deficiency is associated with fat infiltration of muscle and bone

Authors

Jessica Tong, Wei Li, Christopher Vidal, Li Sze Yeo, Diane Fatkin, Gustavo Duque

Abstract

Sarcopenia and osteopenia are two common components of the frailty syndrome that may share a common underlying mechanism. Since frailty has been associated with increased fat infiltration in muscle and bone, we hypothesized that lamin A/C, a protein of the nuclear envelope that regulates adipose differentiation, could be associated with the pathophysiology of both osteo and sarcopenia in the frailty syndrome. Four-week-old lamin A/C null (Lmna−/−), heterozygous (Lmna+/−) and wild type (WT) mice were sacrificed and their mid-thigh analyzed for fat infiltration using invasive (histology) and non-invasive (μCT) methods. Lmna−/− mice showed a significant increase in inter- (∼4-fold) and intra-myofiber (∼2.5-fold) fat and marrow fat infiltration (∼40-fold), with a significant decrease in muscle volume (−42.8%) and bone volume (−21.8%), as compared with WT controls. Furthermore, fat infiltration happened concomitantly with a significant decline in muscle and bone strength in Lmna−/− mice. From a mechanistic approach, high levels of pro-adipogenic factors PPARγ and C/EBPα were associated with a reduction in myogenic and osteogenic factors from the Wnt-10b/β-catenin signalling pathway in Lmna−/− mice. In conclusion, lamin A/C could constitute the determinant factor in the pathogenesis and potential treatment of both sarcopenia and osteopenia, which are commonly observed in the frailty syndrome.

Link to Article

http://dx.doi.org/10.1016/j.mad.2011.09.004

Nanostructured implant surface effect on osteoblast gene expression and bone-to-implant contact in vivo

Authors

Gustavo Mendonça, Daniela Baccelli Silveira Mendonça, Luis Gustavo Pagotto Simões, André Luis Araújo, Edson Roberto Leite, Alexsander Luiz Golin, Francisco J.L. Aragão, Lyndon F. Cooper

Abstract

The aim of this study was to investigate the response of nanostructured implant surfaces at the level of osteoblast differentiation and its effects in bone-to-implant contact (BIC) and removal-torque values (RTV). CpTi grade IV implants (1.6 × 4.0 mm) were machined or machined and subsequently coated with an oxide solution. The surfaces were divided into: machined (M), titania-anatase (An), titania-rutile (Ru), and zirconia (Zr). Surfaces were examined by scanning electron microscopy, atomic force microscopy, and by X-ray microanalysis. Implants were inserted in rat tibia and harvested from 0 to 21 days for measurement of Alkaline Phosphatase, Bone Sialoprotein, Osteocalcin, Osteopontin, and RUNX-2 mRNA levels by real time PCR; from 0 to 56 days for RTV; and from 0 to 56 days for BIC. The roughness parameter (Sa) was compared by one-way ANOVA followed by Tukey Test. Comparison of Torque removal values and histomorphometric measurements on implants in vivo was performed by Kruskal–Wallis test and the significance level for all statistical analyses was set at p ≤ 0.05. mRNA levels on all nanostructured surfaces were increased compared to M. At 56 days, the mean RTV in Ncm was 11.6 ± 2.5, 11.3 ± 2.4, 11.1 ± 3.5, 9.7 ± 1.4 for An, Ru, Zr, and M, respectively. Higher BIC (%) was measured for all the nanostructured surfaces versus M at 21 and 56 days (p < 0.05). Nanostructured topographic features composed of TiO2 or ZrO2 applied to machined cpTi implant promoted greater mesenchymal stem cell commitment to the osteoblast phenotype and associated increased BIC and physical association with bone.

Link to Article

http://dx.doi.org/10.1016/j.msec.2011.08.021

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