Raloxifene Prevents Skeletal Fragility in Adult Female Zucker Diabetic Sprague-Dawley Rats

Authors

Kathleen M. Hill Gallant, Maxime A. Gallant, Drew M. Brown, Amy Y. Sato, Justin N. Williams, David B. Burr

Abstract

Fracture risk in type 2 diabetes is increased despite normal or high bone mineral density, implicating poor bone quality as a risk factor. Raloxifene improves bone material and mechanical properties independent of bone mineral density. This study aimed to determine if raloxifene prevents the negative effects of diabetes on skeletal fragility in diabetes-prone rats. Adult Zucker Diabetic Sprague-Dawley (ZDSD) female rats (20-week-old, n = 24) were fed a diabetogenic high-fat diet and were randomized to receive daily subcutaneous injections of raloxifene or vehicle for 12 weeks. Blood glucose was measured weekly and glycated hemoglobin was measured at baseline and 12 weeks. At sacrifice, femora and lumbar vertebrae were harvested for imaging and mechanical testing. Raloxifene-treated rats had a lower incidence of type 2 diabetes compared with vehicle-treated rats. In addition, raloxifene-treated rats had blood glucose levels significantly lower than both diabetic vehicle-treated rats as well as vehicle-treated rats that did not become diabetic. Femoral toughness was greater in raloxifene-treated rats compared with both diabetic and non-diabetic vehicle-treated ZDSD rats, due to greater energy absorption in the post-yield region of the stress-strain curve. Similar differences between groups were observed for the structural (extrinsic) mechanical properties of energy-to-failure, post-yield energy-to-failure, and post-yield displacement. These results show that raloxifene is beneficial in preventing the onset of diabetes and improving bone material properties in the diabetes-prone ZDSD rat. This presents unique therapeutic potential for raloxifene in preserving bone quality in diabetes as well as in diabetes prevention, if these results can be supported by future experimental and clinical studies.

Link To Article

http://dx.doi.org/10.1371/journal.pone.0108262

Effect of isolated hyperglycemia on native mechanical and biologic shoulder joint properties in a rat model

Authors

Stephen J. Thomas, Joseph J. Sarver, Sarah M. Yannascoli, Jennica J. Tucker, John D. Kelly IV, Rexford S. Ahima, Mary F. Barbe and Louis J. Soslowsky

Abstract

Recently, diabetes has been linked to rotator cuff disease and adhesive capsulitis, conditions with increased stiffness and inflammation. Unfortunately, limited research exists examining how hyperglycemia affects the native shoulder (tendon and capsule) properties. Therefore, the objectives of this study were to compare shoulder joint mechanics, tendon properties (mechanics and immunohistochemistry), and capsule of healthy control and hyperglycemic rats 8 weeks following induction of hyperglycemia with a submaximal dose of streptozotocin (STZ). Eighteen rats were injected with STZ to induce hyperglycemia or citrate buffer (control) and underwent normal cage activity for 8 weeks. Passive joint mechanics demonstrated significantly less external rotation in the hyperglycemic group compared to controls, with no other group differences. Tendon mechanical properties (stiffness and modulus) were not significantly different between groups at both the insertion site and mid-substance. Immunohistochemistry staining of the tendon and capsule demonstrated significantly increased interleukin 1-beta (IL1-β) and advanced glycated end-products (AGE) staining localized to the insertion and mid-substance of the tendon but not the capsule. In addition, tumor necrosis factor alpha (TNF-α) staining was significantly increased in the superior capsule but not the supraspinatus tendon. This study demonstrates that isolated hypergylcemia does not diminish shoulder mechanical properties but does induce a chronic inflammatory response.

Link To Article

http://dx.doi.org/10.1002/jor.22695

Palmitic Acid and DGAT1 Deficiency Enhance Osteoclastogenesis while Oleic Acid-Induced Triglyceride Formation Prevents it

Authors

Zoi Drosatos-Tampakaki, Konstantinos Drosatos, Yasemin Siegelin, Shan Gong, Salmiyeh Khan, Thomas Van Dyke, Ira J. Goldberg, P. Christian Schulze, Ulrike Schulze-Späte

Abstract

Both obesity and diabetes mellitus are associated with alterations in lipid metabolism as well as a change in bone homeostasis and osteoclastogenesis. We hypothesized that increased fatty acid levels affect bone health by altering precursor cell differentiation and osteoclast activation. Here we show that palmitic acid (PA, 16:0) enhances RANKL-stimulated osteoclastogenesis and is sufficient to induce osteoclast differentiation even in the absence of RANKL. TNFα expression is crucial for PA-induced osteoclastogenesis as shown by increased TNFα mRNA levels in PA-treated cells and abrogation of PA-stimulated osteoclastogenesis by TNFα neutralizing antibodies. In contrast, oleic acid (OA, 18:1) does not enhance osteoclast differentiation, leads to increased intracellular triglyceride accumulation and inhibits PA-induced osteoclastogenesis. Adenovirus-mediated expression of diacylglycerol acyl transferase (DGAT) 1, a gene involved in triglyceride synthesis, also inhibits PA-induced osteoclastogenesis, suggesting a protective role of DGAT1 for bone health. Accordingly, Dgat1 knockout mice have larger bone marrow-derived osteoclasts and decreased bone mass indices. In line with these findings, mice on a high fat PA-enriched diet have a greater reduction in bone mass and structure than mice on a high fat OA-enriched diet. Thus, we propose that TNFα mediates saturated fatty acid-induced osteoclastogenesis that can be prevented by DGAT activation or supplementation with OA.

Link To Article

http://dx.doi.org/10.1002/jbmr.2150

Streptozotocin-induced diabetes in rats diminishes the size of the osteoprogenitor pool in bone marrow

Authors

E. Weinberg, T. Maymon, O. Moses, M. Weinre

Abstract

Aims

Bone formation is reduced in animals and humans with type 1 diabetes, leading to lower bone mass and inferior osseous healing. Since bone formation greatly depends on the recruitment of osteoblasts from their bone marrow precursors, we tested whether experimental type 1 diabetes in rats diminishes the number of bone marrow osteoprogenitors.

Methods

Diabetes was induced by 65 mg/kg streptozotocin and after 4 weeks, femoral bone marrow cells were extracted and cultured. Tibia and femur were frozen for further analysis.

Results

The size of the osteoprogenitor pool in bone marrow of diabetic rats was significantly reduced, as evidenced by 1) lower (∼35%) fraction of adherent stromal cells (at 24 h of culture); 2) lower (20-25%) alkaline phosphatase activity at 10 days of culture; and 3) lower (∼40%) mineralized nodule formation at 21 days of culture. Administration of insulin to hyperglycemic rats normalized glycemia and abrogated most of the decline in ex-vivo mineralized nodule formation. Apoptotic cells in tibial bone marrow were more numerous in hyperglycemic rats. Also, the levels of malondialdehyde (indicator of oxidative stress) were significantly elevated in bone marrow of diabetic animals.

Conclusions

Experimental type 1 diabetes diminishes the osteoprogenitor population in bone marrow, possibly due to increased apoptosis via Oxidative Stress. Reduced number of osteoprogenitors is likely to impair osteoblastogenesis, bone formation, and bone healing in diabetic animals.

Link to Article

http://dx.doi.org/10.1016/j.diabres.2013.11.015

Gαo represses insulin secretion by reducing vesicular docking in pancreatic beta-cells

Authors

Aizhen Zhao, Mica Ohara-Imaizumi, Marcella Brissova, Richard K P Benninger, Yanwen Xu, Yuhan Hao, Joel Abramowitz, Guylain Boulay, Alvin C Powers, David Piston, Meisheng Jiang, Shinya Nagamatsu, Lutz Birnbaumer, Guoqiang Gu

Abstract

OBJECTIVE: Pertussis toxin uncoupling-based studies have shown that Gαi and Gαo can inhibit insulin secretion in pancreatic β-cells. Yet it is unclear whether Gαi and Gαo operate through identical mechanisms and how these G-protein-mediated signals inhibit insulin secretion in vivo. Our objective is to examine whether/how Gαo regulates islet development and insulin secretion in β-cells. RESEARCH DESIGN AND METHODS: Immunoassays were used to analyze the Gαo expression in mouse pancreatic cells. Gαo was specifically inactivated in pancreatic progenitor cells by pancreatic cell-specific gene deletion. Hormone expression and insulin secretion in response to different stimuli were assayed in vivo and in vitro. Electron microscope and total internal reflection fluorescence-based assays were used to evaluate how Gαo regulates insulin vesicle docking and secretion in response to glucose stimulation. RESULTS: Islet cells differentiate properly in Gαo(-/-) mutant mice. Gαo inactivation significantly enhances insulin secretion both in vivo and in isolation. Gαo nullizygous β-cells contain an increased number of insulin granules docked on the cell plasma membrane, although the total number of vesicles per β-cell remains unchanged. CONCLUSIONS: Gαo is not required for endocrine islet cell differentiation, but it regulates the number of insulin vesicles docked on the β-cell membrane.

Link to Article

http://dx.doi.org/10.2337/db09-1719

The Effect of Rosiglitazone on Bone Mass and Fragility Is Reversible and Can Be Attenuated With Alendronate

Authors

Sanjay Kumar, Sandra J Hoffman, Rana Samadfam, Peter Mansell, Jacquelin Jolette, Susan Y Smith, Robert E Guldberg, Lorraine A Fitzpatrick

Abstract

Rosiglitazone (RSG) is an antidiabetic drug that has been associated with increased peripheral fractures, primarily in postmenopausal women. In this report, we investigated the underlying mechanisms of RSG-associated bone loss in ovariectomized (OVX) rats and determined whether changes in bone parameters associated with RSG administration are reversible on treatment cessation or preventable by coadministration with an antiresorptive agent. Nine-month-old Sprague-Dawley rats underwent OVX or sham operation. Sham-operated rats received oral vehicle only; OVX animals were randomized to receive vehicle, RSG, alendronate (ALN), or RSG plus ALN for 12 weeks. All treatment started the day after ovariectomy. After the 12-week treatment period, the OVX and RSG groups also underwent an 8-week treatment-free recovery period. Bone densitometry measurements, bone turnover markers, biomechanical testing, and histomorphometric analysis were conducted. Microcomputed tomography was also used to investigate changes in microarchitecture. RSG significantly increased deoxypyridinoline levels compared with OVX. Significant exacerbation of OVX-induced loss of bone mass, strength, and microarchitectural deterioration was observed in RSG-treated OVX animals compared with OVX controls. These effects were observed predominantly at sites rich in trabecular bone, with less pronounced effects in cortical bone. Coadministration of RSG and ALN prevented the bone loss associated with RSG treatment. Following cessation of RSG treatment, effects on bone mass and strength showed evidence of reversal. Thus, treatment of OVX rats with RSG results in loss of bone mass and strength, primarily at sites rich in trabecular bone, mainly due to increased bone resorption. These effects can be prevented by concomitant treatment with ALN and may be reversed following discontinuation of RSG.

Link to Article

http://dx.doi.org/10.1002/jbmr.1918