Standardized bending and breaking test for the normal and osteoporotic metaphyseal tibias of the rat: effect of estradiol, testosterone, and raloxifene

Effects of acute- and long-term aerobic exercises at different intensities on bone in mice

INTRODUCTION

Exercise intensity determines the benefits of aerobic exercise. Our objectives were, in aerobic exercise at different intensities, to determine (1) changes in bone metabolism-related genes after acute exercise and (2) changes in bone mass, strength, remodeling, and bone formation-related proteins after long-term exercise.

MATERIALS AND METHODS

Total 36 male C57BL/6J mice were divided into a control group and exercise groups at 3 different intensities: low, moderate, or high group. Each exercise group was assigned to acute- or long-term exercise groups. Tibias after acute exercise were evaluated by real-time PCR analysis. Furthermore, hindlimbs of long-term exercise were assessed by micro-CT, biomechanical, histological, and immunohistochemical analyses.

RESULTS

Acute moderate-intensity exercise decreased RANKL level as bone resorption marker, whereas low- and high-intensity exercise did not alter it. Additionally, only long-term exercise at moderate intensity increased bone mass and strength. Moderate-intensity exercise promoted osteoblast activity and suppressed osteoclast activity. After low- and high-intensity exercise, osteoblast and osteoclast activity were unchanged. An increase in the number of β-catenin-positive cells and a decrease in sclerostin-positive cells were observed in the only moderate group.

CONCLUSION

These results showed that moderate-intensity exercise can inhibit bone resorption earlier, and long-term exercise can increase bone mass and strength through promoted bone formation via the Wnt/β-catenin activation. High-intensity exercise, traditionally considered better for bone, may fail to stimulate bone remodeling, leading to no change in bone mass and strength. Our findings suggest that moderate-intensity exercise, neither too low nor high, can maintain bone health.

Treatment of osteoporosis using a selective androgen receptor modulator ostarine in an orchiectomized rat model

PURPOSE

The selective androgen receptor modulator ostarine has been shown to have advantageous effects on skeletal tissue properties, reducing muscle wasting and improving physical function in males. However, data on effects in male osteoporosis remain limited. In this study, the effects of ostarine on osteoporotic bone were evaluated in a rat model of male osteoporosis and compared with those of testosterone treatments.

METHODS

Eight-month-old male Sprague-Dawley rats were either non-orchiectomized to serve as a healthy control (Non-Orx, Group 1) or orchiectomized (Orx, Groups 2-6) and then grouped (n = 15/group): (1) Non-Orx, (2) Orx, (3) Ostarine Therapy, (4) Testosterone Therapy, (5) Ostarine Prophylaxis and (6) Testosterone Prophylaxis. Prophylaxis treatments started directly after orchiectomy and continued for 18 weeks, whereas Therapy treatments were initiated 12 weeks after Orx. Ostarine and Testosterone were applied orally at daily doses of 0.4 and 50 mg/kg body weight, respectively. The lumbar vertebral bodies and femora were analyzed using biomechanical, micro-CT, ashing, and gene expression analyses.

RESULTS

Ostarine Prophylaxis showed positive effects in preventing osteoporotic changes in cortical and trabecular bone (femoral trabecular density: 26.01 ± 9.1% vs. 20.75 ± 1.2% in Orx and in L4: 16.3 ± 7.3% vs 11.8 ± 2.9% in Orx); biomechanical parameters were not affected; prostate weight was increased (0.62 ± 0.13 g vs 0.18 ± 0.07 g in Orx). Ostarine Therapy increased solely the cortical density of the femur (1.25 ± 0.03 g/cm3 vs. 1.18 ± 0.04 g/cm3 in Orx); other bone parameters remained unaffected. Testosteron Prophylaxis positively influenced cortical density in femur (1.24 ± 0.05 g/cm3 vs. 1.18 ± 0.04 g/cm3 in Orx); Test. Therapy did not change any bony parameters.

CONCLUSION

Ostarine Prophylaxis could be further investigated as a preventative treatment for male osteoporosis, but an androgenic effect on the prostate should be taken into consideration, and combination therapies with other anti-osteoporosis agents could be considered.

Unfavorable effects of memantine on the skeletal system in female rats

Memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist used in the treatment of Alzheimer's disease (AD). NMDA receptors are expressed on bone cells. The aim of the present study was to investigate the effects of memantine on the rat musculoskeletal system. Taking into account that most of female AD patients are postmenopausal, the study was carried out on intact and ovariectomized (estrogen-deficient) rats. Mature Wistar rats were divided into following groups: non-ovariectomized (NOVX) control rats, NOVX rats treated with memantine, ovariectomized (OVX) control rats, and OVX rats treated with memantine. Memantine (2 mg/kg p.o.) was administered once daily for four weeks, starting one week after ovariectomy. The serum bone turnover marker and cytokine levels, bone density, mass, mineralization, mechanical properties, histomorphometric parameters of compact and cancellous bone, skeletal muscle mass and grip strength were determined. In NOVX rats, memantine slightly decreased the strength of compact bone of the femoral diaphysis (parameters in the yield point) and unfavorably affected histomorphometric parameters of cancellous bone (the femoral epiphysis and metaphysis). In OVX rats, in which estrogen deficiency induced osteoporotic changes, memantine increased the phosphorus content in the femoral bone mineral. No other effects on bone were observed in the memantine-treated OVX rats. In conclusion, the results of the present study indicated slight damaging skeletal effects of memantine in rats with normal estrogen levels.

Assessment and evaluation of Chitosan-Metamizole nanoparticles for the fracture healing and analgesic effect: Preclinical study in rat model

To assess and evaluate Chitosan-Metamizole nanoparticles for fracture healing and analgesic potential, nanoparticles were formulated using the ionotropic gelation method. The nanoparticles were evaluated for particle size, zeta potential, polydispersity index, loading efficiency, surface characteristics and drug release properties. The analgesic activity was determined in carrageenan-induced arthritic male Wister rats. Further fracture healing potency, mechanical testing, radiographic examination and bone histology of the femur were studied. The drug loading efficiency of 11.38%-17.45%, particle size of 140-220 nm, and zeta potential of 19.12-23.14 mV were observed with a spherical, smooth appearance. Nanoparticles showed sustained release behaviour over a longer period. Nearly 4-fold inhibition of oedema was observed in animals treated with nanoparticles with excellent fracture healing potential. The femurs treated with nanoparticles required greater force to fracture. Nanoparticles significantly improved the strength and healing process. Histopathological studies showed the potential of nanoparticles in the healing process. The study confirmed the potential of nanoparticles in fracture healing and enhancement of analgesic activity.

Validation of a novel testing machine for the investigation of the biomechanical properties of lumbar vertebrae in an osteoporotic rat model

BACKGROUND

For the investigation of the biomechanical properties of bone, various testing devices have been described. However, only a limited number have been developed to test the vertebral body of small animals. The aim of this study was to develop and validate a new bone testing device, which investigates the different biomechanical properties in small-animal vertebrae as a whole, three-dimensional unit, respecting its anatomical structure.

METHODS

Thirty-five twelve-week-old female Sprague Dawley rats were utilized. Group 1 was composed of 17 rats with a normal bone metabolism without osteoporosis, while Group 2 consisted of 18 rats with manifest osteoporosis, 8 weeks after ovariectomy. The 5th lumbar vertebra of each animal was tested using the new bone testing device. This device has the ability to be adjusted to the slanted nature of each individual vertebral body and fix the vertebra in a natural position to allow for a non-dislocating axial force application. The device is designed to respect the anatomical three-dimensional shape of the vertebral body, thus avoiding the application of non-anatomic, non-physiological forces and thus preventing a distortion of the biomechanical testing results. The parameters investigated were stiffness, yield load, maximum load and failure load, and the results were compared to current literature values.

RESULTS

The conduction of the biomechanical bone testing of the vertebral bodies with the new device was conductible without any instances of dislocation of the vertebrae or machine malfunctions. Significant differences were found for stiffness, maximum load and failure load between groups, with a lower value in the osteoporotic rats in each parameter tested. The yield load was also lower in the osteoporotic group, however not significantly. The values achieved correlate with those in current literature.

CONCLUSIONS

This study demonstrates that the newly developed testing machine is easy to handle and produces valid data sets for testing biomechanical bone parameters of whole vertebral bodies in an established small animal model. Therefore, it can be utilized, also as reference data, to test different structural properties and changes in vertebral bone, for example, in different metabolic settings or under the influence of different pharmaceutical entities in further studies.

Unfavorable effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors on the skeletal system of nondiabetic rats

Sodium-glucose cotransporter 2 (SGLT2) inhibitors are a new class of antidiabetic drugs, acting by inhibiting the reabsorption of glucose in the kidneys. They turned out to improve cardiovascular and renal outcomes not only in patients with type 2 diabetes but also in nondiabetic patients. At present, they are more and more widely used in patients without diabetes. Since there were concerns that SGLT2 inhibitors may increase fracture risk in diabetes, the aim of the study was to examine the effect of dapagliflozin and canagliflozin on the musculoskeletal system of nondiabetic, healthy rats. The experiments were carried out on mature female rats, divided into the control rats and rats treated with dapagliflozin (1.4 mg/kg p.o.) or canagliflozin (4.2 mg/kg p.o.) for 4 weeks. Serum bone turnover markers, skeletal muscle strength and mass, bone mass, density, histomorphometric parameters and mechanical properties were determined. Administration of the drugs did not affect the skeletal muscle mass and strength. There was no effect on serum bone turnover markers, and bone mass and composition. However, administration of both drugs resulted in disorders of cancellous bone microarchitecture and worsening of bone mechanical properties. In conclusion, both SGLT2 inhibitors unfavorably affected the skeletal system of healthy rats.

Effect of Administration of Azithromycin and/or Probiotic Bacteria on Bones of Estrogen-Deficient Rats

The gut microbiota plays an important role in maintaining homeostasis, including that of the skeletal system. Antibiotics may affect the skeletal system directly or indirectly by influencing the microbiota. Probiotic bacteria have been reported to favorably affect bones in conditions of estrogen deficiency. The aim of this study was to investigate the effects of azithromycin (AZM) administered alone or with probiotic bacteria (Lactobacillus rhamnosus; LR) on bones in estrogen-deficient rats. The experiments were carried out on mature rats divided into five groups: non-ovariectomized (NOVX) control rats, ovariectomized (OVX) control rats, and OVX rats treated with: LR, AZM, or AZM with LR. The drugs were administered for 4 weeks. Serum biochemical parameters, bone mineralization, histomorphometric parameters, and mechanical properties were examined. Estrogen deficiency increased bone turnover and worsened cancellous bone microarchitecture and mechanical properties. The administration of LR or AZM slightly favorably affected some skeletal parameters of estrogen-deficient rats. The administration of AZM with LR did not lead to the addition of the effects observed for the separate treatments, indicating that the effects could be microbiota-mediated.

Utilization of Mechanical Stress to Treat Osteoporosis: The Effects of Electrical Stimulation, Radial Extracorporeal Shock Wave, and Ultrasound on Experimental Osteoporosis in Ovariectomized Rats

Current treatment options for osteoporosis primarily involve pharmacotherapies, but they are often accompanied by undesirable side effects. Utilization of mechanical stress which can noninvasively induce bone formation has been suggested as an alternative to conventional treatments. Here, we examined the efficacy of mechanical stress induced by electrical stimulation, radial extracorporeal shock waves, and ultrasound for estrogen-deficient osteoporosis. Female Wistar rats were divided into following five groups: sham-operated group, untreated after ovariectomy, and treated with electrical stimulation, radial extracorporeal shock wave, or ultrasound starting at 8 weeks after ovariectomy for 4 weeks. Trabecular bone architecture of the femur was assessed by micro-CT and its biomechanical properties were obtained by mechanical testing. The femurs were further evaluated by histochemical, immunohistochemical, and real-time PCR analyses. Radial extracorporeal shock wave and ultrasound treatment improved trabecular bone microarchitecture and bone strength in osteoporotic rats, but not electrical stimulation. The shock wave decreased osteoclast activity and RANKL expression. The exposure of ultrasound increased osteoblast activity and β-catenin-positive cells, and they decreased sclerostin-positive osteocytes. These findings suggest that mechanical stress induced by radial extracorporeal shock wave and ultrasound can improve estrogen-deficient bone loss and bone fragility through promoted bone formation or attenuated bone resorption.

Multifunctional magnesium incorporated scaffolds by 3D-Printing for comprehensive postsurgical management of osteosarcoma

Clinical treatment of Osteosarcoma (OS) encounters great challenges of postsurgical tumor recurrence and extensive bone defect. To address these issues, innovative multifunctional PLGA/Mg porous scaffolds were designed for comprehensive postsurgical management of OS. The PLGA/Mg composite scaffolds exhibited several unique features: (1) The multiple functions of Mg particles were explored for the first time to fulfill the requirement for postsurgical management of OS. The intact Mg particles exhibits excellent photothermal effect for tumor eradication, and the released Mg ions could subsequently promote bone regeneration, thus endowing the PLGA/Mg scaffolds dual functions of suppressing OS recurrence and repairing bone defect in a sequential way; (2) A low temperature rapid prototyping (LT-RP) 3D-printing technology was used to fabricate the scaffolds with biomimetic hierarchical porous structures, which could structurally promote bone regeneration; (3) The PLGA/Mg scaffolds have excellent biodegradability and biocompatibility, exhibiting great promise for clinical translation. Finally, the PLGA/Mg scaffolds achieved complete suppression of tumor recurrence in the presence of near-infrared laser irradiation, as well as efficient bone defect repair in vivo. Activation of the AKT and β-catenin pathways of osteoblast cells by PLGA/Mg scaffolds was identified, which might be the modulators to accelerate the ossification. The innovative PLGA/Mg scaffolds demonstrated excellent capabilities in postsurgical OS recurrence suppression and bone regeneration, providing a promising clinical strategy for comprehensive postsurgical management of OS.

Nanoceria provides antioxidant and osteogenic properties to mesoporous silica nanoparticles for osteoporosis treatment

Osteoporosis, a chronic metabolic bone disease, is the most common cause of fractures. Drugs for treating osteoporosis generally inhibit osteoclast (OC) activity, but are rarely aimed at encouraging new bone growth and often cause severe systemic side effects. Reactive oxygen species (ROS) are one of the key triggers of osteoporosis, by inducing osteoblast (OB) and osteocyte apoptosis and promoting osteoclastogenesis. Here we tested the capability of the ROS-scavenger nanoceria encapsulated within mesoporous silica nanoparticles (Ce@MSNs) to treat osteoporosis using a pre-osteoblast MC3T3-E1 cell monoculture in stressed and normal conditions. Ce@MSNs (diameter of 80 ± 10 nm) were synthesised following a scalable two-step process involving sol-gel and wet impregnation methods. The Ce@MSNs at concentration of 100 μg mL^-1 induced a significant reduction in oxidative stress produced by t-butyl hydroperoxide and did not alter cell viability significantly. Confocal microscopy showed that MSNs and Ce@MsNs were internalised into the cytoplasm of the pre-osteoblasts after 24 h but were not in the nucleus, avoiding any DNA and RNA modifications. Ce@MSNs provoked mineralisation of the pre-osteoablasts without osteogenic supplements, which did not occur when the cells were exposed to MSN without nanoceria. In a co-culture system of MC3T3-E1 and RAW264.7 macrophages, the Ce@MSNs exhibited antioxidant capability and stimulated cell proliferation and osteogenic responses without adding osteogenic supplements to the culture. The work brings forward an effective platform based for facile synthesis of Ce@MSNs to interact with both OBs and OCs for treatment of osteoporosis.

Effect of Selective Androgen Receptor Modulator Enobosarm on Bone Healing in a Rat Model for Aged Male Osteoporosis

Enobosarm (ostarine, MK-2866, or GTx-024) is a non-steroidal selective androgen receptor modulator. This study evaluated the effect of various regimens of enobosarm (EN) on bone healing in an orchiectomized rat model for aged male osteoporosis and compared it to testosterone (T) treatment. Ninety eight-month-old male Sprague Dawley rats were either orchiectomized (Orx) or left intact (Non-Orx) and divided into groups (n = 15/group): (1) Non-Orx; (2) Orx; (3) Orx+T-th; (4) Orx+EN-th; (5) Orx+T-pr; and (6) Orx+EN-pr. Prophylaxis (Pr) treatments were applied immediately after Orx for up to 18 weeks. Therapy (Th) treatments were applied 12 weeks after Orx for up to 6 weeks. Bilateral tibia osteotomy with plate osteosynthesis was performed 12 weeks after Orx in all groups. EN and T were mixed with the diet; the daily dosage was 0.35 ± 0.06 and 41 ± 8 mg/kg BW, respectively. Both T treatments improved bone healing by increasing callus volume and area, bone volume and density, and cortical width; they had no effect on prostate or levator ani weight. EN-pr increased the callus area and callus density and decreased cortical density, but increased prostate weight. The effect of T-pr and T-th on bone was stronger than EN-pr. EN-th affected bone healing negatively by reducing callus density and area and delaying osteotomy bridging. Levator ani weight was increased in both EN groups. EN treatment after fracture is not advisable in aged males. EN-pr treatment as a therapy for bone healing in men could be further investigated; endocrinological side effects must be closely monitored.

Influence of bone defect position and span in 3-point bending tests: experimental and finite element analysis

Three-point bending test is the most common mechanical test used for quantifying the biomechanical quality of bone tissue and bone healing in small animals. However, there is a lack of standardization for evaluation of bone repair by cortical perforation. The aim of this study was to determine the influence of bone defect position in the proximal metaphysis of rat tibias during load application and different span configuration on the three-point bending test outcomes. Cortical defects with 1.6 mm diameter were created at a standardized location on the medial surface of 60 tibias of male Wistar rats. The animals were euthanized 7 days after surgery. Five specimens were used to create 3D models for finite element analysis using high-resolution micro-CT images. Two spans (6 and 10mm) and three positions of the bone defect in relation to the load application (upward, frontal and downward) were evaluated experimentally (n = 10) and in finite element analysis (n = 5). Maximum load (N) and stiffness (N/mm) were statistically analyzed with 2-way ANOVA and Tukey test (α = 0.05). The results demonstrated that span and orientation of the bone defect significantly influenced the fracture pattern, stress distribution and force versus displacement relation. Therefore, reliable outcome can be achieved creating the bone defect at 8 mm from the extremity of the proximal epiphysis; placing a 10 mm distance span and downward facing defect position to allow a better distribution of stress and more fracture patterns that reached the bone defect target area with less intra-group variability.

Negligible Effect of Estrogen Deficiency on Development of Skeletal Changes Induced by Type 1 Diabetes in Experimental Rat Models

Although postmenopausal osteoporosis often occurs concurrently with diabetes, little is known about interactions between estrogen deficiency and hyperglycemia in the skeletal system. In the present study, the effects of estrogen deficiency on the development of biochemical, microstructural, and mechanical changes induced by streptozotocin-induced diabetes mellitus (DM) in the rat skeletal system were investigated. The experiments were carried out on nonovariectomized (NOVX) and ovariectomized (OVX) control and diabetic mature female Wistar rats. Serum levels of bone turnover markers (CTX-I and osteocalcin) and 23 cytokines, bone mass and mineralization, histomorphometric parameters, and mechanical properties of cancellous and compact bone were determined. The results were subjected to two-way ANOVA and principal component analysis (PCA). Estrogen deficiency induced osteoporotic changes, with increased bone resorption and formation, and worsening of microstructure (femoral metaphyseal BV/TV decreased by 13.0%) and mechanical properties of cancellous bone (the maximum load in the proximal tibial metaphysis decreased by 34.2%). DM in both the NOVX and OVX rats decreased bone mass, increased bone resorption and decreased bone formation, and worsened cancellous bone microarchitecture (for example, the femoral metaphyseal BV/TV decreased by 17.3% and 18.1%, respectively, in relation to the NOVX controls) and strength (the maximum load in the proximal tibial metaphysis decreased by 35.4% and 48.1%, respectively, in relation to the NOVX controls). Only in the diabetic rats, profound increases in some cytokine levels were noted. In conclusion, the changes induced by DM in female rats were only slightly intensified by estrogen deficiency. Despite similar effects on bone microstructure and strength, the influence of DM on the skeletal system was based on more profound systemic homeostasis changes than those induced by estrogen deficiency.

Gelatin-Modified Calcium/Strontium Hydrogen Phosphates Stimulate Bone Regeneration in Osteoblast/Osteoclast Co-Culture and in Osteoporotic Rat Femur Defects-In Vitro to In Vivo Translation

The development and characterization of biomaterials for bone replacement in case of large defects in preconditioned bone (e.g., osteoporosis) require close cooperation of various disciplines. Of particular interest are effects observed in vitro at the cellular level and their in vivo representation in animal experiments. In the present case, the material-based alteration of the ratio of osteoblasts to osteoclasts in vitro in the context of their co-cultivation was examined and showed equivalence to the material-based stimulation of bone regeneration in a bone defect of osteoporotic rats. Gelatin-modified calcium/strontium phosphates with a Ca:Sr ratio in their precipitation solutions of 5:5 and 3:7 caused a pro-osteogenic reaction on both levels in vitro and in vivo. Stimulation of osteoblasts and inhibition of osteoclast activity were proven during culture on materials with higher strontium content. The same material caused a decrease in osteoclast activity in vitro. In vivo, a positive effect of the material with increased strontium content was observed by immunohistochemistry, e.g., by significantly increased bone volume to tissue volume ratio, increased bone morphogenetic protein-2 (BMP2) expression, and significantly reduced receptor activator of nuclear factor kappa-B ligand (RANKL)/osteoprotegerin (OPG) ratio. In addition, material degradation and bone regeneration were examined after 6 weeks using stage scans with ToF-SIMS and µ-CT imaging. The remaining material in the defects and strontium signals, which originate from areas exceeding the defect area, indicate the incorporation of strontium ions into the surrounding mineralized tissue. Thus, the material inherent properties (release of biologically active ions, solubility and degradability, mechanical strength) directly influenced the cellular reaction in vitro and also bone regeneration in vivo. Based on this, in the future, materials might be synthesized and specifically adapted to patient-specific needs and their bone status.

Effects of diosgenin on the skeletal system in rats with experimental type 1 diabetes

There is a great interest in substances of plant origin, which may exert health-promoting activities in diabetes and its complications. Previous studies suggested that diosgenin may favorably affect both glucose metabolism and osteoporosis. The aim of the study was to investigate the effects of diosgenin on the skeletal disorders induced by experimental type 1 diabetes (T1D) in rats. The experiments were performed on 3-month-old female rats, divided into three groups: I - healthy control rats, II - streptozotocin-induced diabetic control rats, III - diabetic rats receiving diosgenin. T1D was induced by a single streptozotocin injection (60 mg/kg i.p.). Diosgenin administration (50 mg/kg/day p.o.) started two weeks later and lasted four weeks. Serum bone turnover markers and other biochemical parameters, bone mass and mineralization, mechanical properties and histomorphometric parameters were examined. Diabetes induced profound metabolic disturbances and disorders of cancellous bone microarchitecture and strength. Diosgenin did not favorably affect the serum bone turnover markers and other biochemical parameters, bone mass, mineralization and mechanical properties in the diabetic rats. However, it counteracted the effect of diabetes on the growth plate and cancellous bone microarchitecture in the distal femur, indicating some limited beneficial influence on the skeleton.

Bone-targeted lncRNA OGRU alleviates unloading-induced bone loss via miR-320-3p/Hoxa10 axis

Unloading-induced bone loss is a threat to human health and can eventually result in osteoporotic fractures. Although the underlying molecular mechanism of unloading-induced bone loss has been broadly elucidated, the pathophysiological role of long noncoding RNAs (lncRNAs) in this process is unknown. Here, we identified a novel lncRNA, OGRU, a 1816-nucleotide transcript with significantly decreased levels in bone specimens from hindlimb-unloaded mice and in MC3T3-E1 cells under clinorotation-unloading conditions. OGRU overexpression promoted osteoblast activity and matrix mineralization under normal loading conditions, and attenuated the suppression of MC3T3-E1 cell differentiation induced by clinorotation unloading. Furthermore, this study found that supplementation of pcDNA3.1(+)–OGRU via (DSS)₆–liposome delivery to the bone-formation surfaces of hindlimb-unloaded (HLU) mice partially alleviated unloading-induced bone loss. Mechanistic investigations demonstrated that OGRU functions as a competing endogenous RNA (ceRNA) to facilitate the protein expression of Hoxa10 by competitively binding miR-320-3p and subsequently promote osteoblast differentiation and bone formation. Taken together, the results of our study provide the first clarification of the role of lncRNA OGRU in unloading-induced bone loss through the miR-320-3p/Hoxa10 axis, suggesting an efficient anabolic strategy for osteoporosis treatment.

Isolated Cyclic Loading During Adolescence Improves Tibial Bone Microstructure and Strength at Adulthood

Bone is a unique living tissue, which responds to the mechanical stimuli regularly imposed on it. Adolescence facilitates a favorable condition for the skeleton that enables the exercise to positively influence bone architecture and overall strength. However, it is still dubious for how long the skeletal benefits gained in adolescence is preserved at adulthood. The current study aims to use a rat model to investigate the effects of in vivo low- (LI), medium- (MI), and high- (HI) intensity cyclic loadings applied during puberty on longitudinal bone development, morphometry, and biomechanics during adolescence as well as at adulthood. Forty-two young (4-week-old) male rats were randomized into control, sham, LI, MI, and HI groups. After a 5 day/week for 8 weeks cyclic loading regime applied on the right tibia, loaded rats underwent a subsequent 41-week, normal cage activity period. Right tibias were removed at 52 weeks of age, and a comprehensive assessment was performed using μCT, mechanical testing, and finite element analysis. HI and MI groups exhibited reduced body weight and food intake at the end of the loading period compared with shams, but these effects disappeared afterward. HI cyclic loading increased BMD, bone volume fraction, trabecular thickness, trabecular number, and decreased trabecular spacing after loading. All loading-induced benefits, except BMD, persisted until the end of the normal cage activity period. Moreover, HI loading induced enhanced bone area, periosteal perimeter, and moment of inertia, which remained up to the 52nd week. After the normal cage activity at adulthood, the HI group showed increased ultimate force and stress, stiffness, postyield displacement and energy, and toughness compared with the sham group. Overall, our findings suggest that even though both trabecular and cortical bone drifted through age-related changes during aging, HI cyclic loading performed during adolescence can render lifelong benefits in bone microstructure and biomechanics. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Can we enhance osteoporotic metaphyseal fracture healing through enhancing ultrastructural and functional changes of osteocytes in cortical bone with low-magnitude high-frequency vibration?

Fragility fractures are related to the loss of bone integrity and deteriorated morphology of osteocytes. Our previous studies have reported that low-magnitude high-frequency vibration (LMHFV) promoted osteoporotic fracture healing. As osteocytes are known for mechanosensing and initiating bone repair, we hypothesized that LMHFV could enhance osteoporotic fracture healing through enhancing morphological changes in the osteocyte lacuna-canalicular network (LCN) and mineralization. A metaphyseal fracture model was established in female Sprague-Dawley rats to investigate changes in osteocytes and healing outcomes from early to late phase post-fracture. Our results showed that the LCN exhibited an exuberant outgrowth of canaliculi in the osteoporotic fractured bone at day 14 after LMHFV. LMHFV upregulated the E11, dentin matrix protein 1 (DMP1), and fibroblast growth factor 23 (FGF23), but downregulated sclerostin (Sost) in osteocytes. Moreover, LMHFV promoted mineralization with significant enhancements of Ca/P ratio, mineral apposition rate (MAR), mineralizing surface (MS/BS), and bone mineral density (BMD) in the osteoporotic group. Consistently, better healing was confirmed by microarchitecture and mechanical properties, whereas the enhancement in osteoporotic group was comparable or even greater than the normal group. This is the first report to reveal the enhancement effect of LMHFV on the osteocytes' morphology and functions in osteoporotic fracture healing.

Osteogenesis enhancement of silk fibroin/ α-TCP cement by N-acetyl cysteine through Wnt/β-catenin signaling pathway in vivo and vitro

High brittleness and lack osteogenesis are two major limitations of calcium phosphate cement (CPC) in application in bone defect reconstruction. Here we prepared a composite calcium phosphate cement by mixing N-acetyl cysteine loaded silk fibroin solution with α-tricalcium phosphate. In vitro cytology experiment revealed that SF-NAC/α-TCP could significantly increase the activity of exocrine ALP and up-regulated expression of bone-related genes. However, NAC up-regulated gene expression could be significantly suppressed by DKK1. We propose that NAC functioning as osteogenic factor by activating the Wnt/β-catenin signaling pathway may be the possible mechanism of up-regulation of osteogenic genes. Bone regeneration in vivo shown in a rat femur defect was enhanced by the addition of NAC in SF/α-TCP. In addition, the combination intensity of cement-bone interface was improved. The combination SF-NAC/α-TCP might be developed into a promising tool for bone tissue repair in the clinic.

Effects of loratadine, a histamine H1 receptor antagonist, on the skeletal system of young male rats

Background

Histamine H₁ receptor antagonists are widely used in the treatment of allergic diseases. H₁ receptors are expressed on bone cells and histamine takes part in regulation of bone metabolism. Loratadine is often prescribed to children.

Purpose

The aim of the present study was to investigate the effects of loratadine on the skeletal system of young rats.

Material and methods

Loratadine (0.5, 5, and 50 mg/kg p.o. daily) was administered for 4 weeks to male Wistar rats, 6-week-old at the start of the experiment. Bone mass, mass of bone mineral, calcium, and phosphorus content in the bone mineral of the tibia, femur, and L-4 vertebra, histomorphometric parameters of the femur, mechanical properties of the proximal tibial metaphysis, femoral diaphysis and femoral neck, and serum levels of bone turnover markers were examined.

Results

Loratadine at 0.5 and 5 mg/kg did not significantly affect the skeletal system of young rats. At 50 mg/kg, loratadine decreased the femoral length, increased content of calcium and phosphorus in the bone mineral of the vertebra, and tended to improve mechanical properties of the tibial metaphysis.

Conclusion

High-dose loratadine slightly but significantly affected development of the skeletal system in rapidly growing rats.

High Impact Exercise Improves Bone Microstructure and Strength in Growing Rats

Physical activity is beneficial for skeletal development. However, impact sports during adolescence, leading to bone growth retardation and/or bone quality improvement, remains unexplained. This study investigated the effects of in vivo low (LI), medium (MI), and high (HI) impact loadings applied during puberty on bone growth, morphometry and biomechanics using a rat model. 4-week old rats (n = 30) were divided into control, sham, LI, MI, and HI groups. The impact was applied on the right tibiae, 5 days/week for 8 weeks mimicking walking (450 µε), uphill running (850 µε) and jumping (1250 µε) conditions. Trabecular and cortical parameters were determined by micro-CT, bone growth rate by calcein labeling and toluidine blue staining followed by histomorphometry. Bio-mechanical properties were evaluated from bending tests. HI group reduced rat body weight and food consumption compared to shams. Bone growth rate also decreased in MI and HI groups despite developing thicker hypertrophic and proliferative zone heights. HI group showed significant increment in bone mineral density, trabecular thickness, cortical and total surface area. Ultimate load and stiffness were also increased in MI and HI groups. We conclude that impact loading during adolescence reduces bone growth moderately but improves bone quality and biomechanics at the end of the growing period.

The use of selective estrogen receptor modulators on bone health in men

Selective estrogen receptor modulators (SERMs) represent a class of drugs that act as agonist or antagonist for estrogen receptor in a tissue-specific manner. The SERMs drugs are initially used for the prevention and treatment of osteoporosis in postmenopausal women. Bone health in prostate cancer patients has become a significant concern, whereby patients undergo androgen deprivation therapy is often associated with deleterious effects on bone. Previous preclinical and epidemiological findings showed that estrogens play a dominant role in improving bone health as compared to testosterone in men. Therefore, this evidence-based review aims to assess the available evidence derived from animal and human studies on the effects of SERMs on the male skeletal system. The effects of SERMs on bone mineral density (BMD)/content (BMC), bone histomorphometry, bone turnover, bone strength and fracture risk have been summarized in this review.

Effect of the lipoxygenase inhibitor baicalein on bone tissue and bone healing in ovariectomized rats

BACKGROUND

Osteoporosis is one of the world's major medical burdens in the twenty-first century. Pharmaceutical intervention currently focusses on decelerating bone loss, but phytochemicals such as baicalein, which is a lipoxygenase inhibitor, may rescue bone loss. Studies evaluating the effect of baicalein in vivo are rare.

METHODS

We administered baicalein to sixty-one three-month-old female Sprague-Dawley rats. They were divided into five groups, four of which were ovariectomized (OVX) and one non-ovariectomized (NON-OVX). Eight weeks after ovariectomy, bilateral tibial osteotomy with plate osteosynthesis was performed and bone formation quantified. Baicalein was administered subcutaneously using three doses (C1: 1 mg/kg BW; C2: 10 mg/kg BW; and C3: 100 mg/kg BW) eight weeks after ovariectomy for four weeks. Finally, femora and tibiae were collected. Biomechanical tests, micro-CT, ashing, histological and gene expression analyses were performed.

RESULTS

Biomechanical properties were unchanged in tibiae and reduced in femora. In tibiae, C1 treatment enhanced callus density and cortical width and decreased callus area. In the C3 group, callus formation was reduced during the first 3 weeks after osteotomy, correlating to a higher mRNA expression of Osteocalcin, Tartrate-resistant acid phosphatase and Rankl. In femora, baicalein treatments did not alter bone parameters.

CONCLUSIONS

Baicalein enhanced callus density and cortical width but impaired early callus formation in tibiae. In femora, it diminished the biomechanical properties and calcium-to-phosphate ratio. Thus, it is not advisable to apply baicalein to treat early bone fractures. To determine the exact effects on bone healing, further studies in which baicalein treatments are started at different stages of healing are needed.

Changes in Musculoskeletal System and Metabolism in Osteoporotic Rats Treated With Urocortin

Objective: In aging population, postmenopausal osteoporosis and decline of musculoskeletal function, referred to as "frailty syndrome" lead to loss of bone and muscle, causing falls, and fall-related injuries. To limit the impact of this portentous duo, simultaneous treatment of both is needed. Urocortin (UCN) has been reported to improve osteoporotic bone properties while its effect on muscle has not been addressed yet. Design and Methods: We aimed to investigate the effect of urocortin in vivo on skeletal muscle structure in osteopenic rats. Sixty Sprague-Dawley rats were divided into five groups: four were ovariectomized (OVX) and one underwent sham operation (SHAM). One ovariectomized group was left untreated (OVX), while one was treated with urocortin s.c. in 3 μg/kg body weight (bw) (OVX+UCN low), one with 30 μg/kg (OVX+UCN high), while one group was treated with estradiol orally (OVX+E: 0.2 mg/kg bw), each for 35 days. Mm. gastrocnemius, longissimus, and soleus were isolated and capillary density as well as diameters of type I and II fibers were measured. In addition, we examined the effect of UCN on tibia using biomechanical, micro-CT and ashing analysis and investigated the blood serum. Results: We demonstrated a positive effect of UCN on M. soleus, in which fiber diameter was positively influenced. The biomechanical and structural parameters of bone were not changed in UCN treated rats. The higher cholesterol, glucose and triglyceride levels in the "UCN high" group raise concern about this treatment. Conclusions: Our results portray urocortin as a substance that can be assessed for future therapeutic treatments of estrogen deficiency. New and Noteworthy: Urocortin has a positive effect on M. soleus (diameter). Urocortin raises serum cholesterol and triglyceride levels. Bone tissue was not affected by UCN.

Phloridzin, an Apple Polyphenol, Exerted Unfavorable Effects on Bone and Muscle in an Experimental Model of Type 2 Diabetes in Rats

It is believed that apple fruits contain components with health-promoting effects, including some antidiabetic activity. One of the most known apple compounds is phloridzin, a glucoside of phloretin. Phloridzin and phloretin were reported to exert some favorable skeletal effects in estrogen-deficient rats and mice. The aim of the study was to investigate the effects of phloridzin on musculoskeletal system in rats with type 2 diabetes induced by a high-fat diet (HFD) and streptozotocin (STZ). The experiments were performed on mature female Wistar rats, divided into control rats (fed a standard laboratory diet), HFD/STZ control rats, and HFD/STZ rats receiving phloridzin (20 or 50 mg/kg/day per os) for four weeks. Serum biochemical parameters, muscle mass and strength, bone mass, density, histomorphometric parameters and mechanical properties were determined. The HFD/STZ rats developed hyperglycemia, with decreases in the muscle mass and strength and profound osteoporotic changes. Phloridzin at 20 mg/kg markedly augmented the unfavorable effects of diabetes on the muscle mass and strength and decreased growth of bones, whereas, at 50 mg/kg, it did not affect most of the investigated musculoskeletal parameters. Results of the study indicate the possibility of unfavorable effects of phloridzin on the musculoskeletal system in conditions of hyperglycemia.

Increased calcium uptake and improved trabecular bone properties in intestinal alkaline phosphatase knockout mice

Previous studies have demonstrated a negative correlation between intestinal alkaline phosphatase (IAP) activity and calcium (Ca) absorption in the gut, as IAP acts as a protective mechanism inhibiting high Ca entry into enterocytes, preventing Ca overload. Here we evaluated Ca absorption and bone properties in knockout mice (KO) completely devoid of duodenal IAP (Akp3 ^-/- mice). Female C57BL/6 control mice (WT, n = 7) and KO mice (n = 10) were used to determine Ca absorption in vivo and by in situ isolated duodenal loops followed by histomorphometric analysis of duodenal villi and crypts. Bone mineral density, morphometry, histomorphometry and trabecular connectivity and biomechanical properties were measured on bones. We observed mild atrophy of the villi with lower absorption surface and a significantly higher Ca uptake in KO mice. While no changes were seen in cortical bone, we found better trabecular connectivity and biomechanical properties in the femurs of KO mice compared to WT mice. Our data indicate that IAP KO mice display higher intestinal Ca uptake, which over time appears to correlate with a positive effect on the biomechanical properties of trabecular bone.

Porcine-induced pluripotent stem cell-derived osteoblast-like cells ameliorate trabecular bone mass of osteoporotic rats

AIM

We created rat models of osteoporosis and verified a novel idea to recover bone mass via local cell transplantation.

MATERIALS & METHODS

The rats were treated with ovariectomy, 0.1% calcium diet or 3 mg/kg body weight/day of prednisolone and porcine-induced pluripotent stem cell (piPSC)-derived osteoblast-like cells were transplanted into the medullary cavity of the left femurs.

RESULTS

The piPSC-derived osteoblast-like cells exerted therapeutic potential on prednisolone treatment group, which confirmed by improvements in trabecular bone volume (15.93 ± 2.20%), bone surface/volume ratio (27.82 ± 1.40 1/mm), thickness (1.40 ± 0.01 mm), separation (0.99 ± 0.10 mm), number (1.13 ± 0.13 1/mm) and total porosity (84.06 ± 2.20%).

CONCLUSION

These results first uncovered therapeutic potential of xenotransplantation with piPSCs for glucocorticoid-induced osteoporosis treatment in the rat models.

Effects of RANKL Knockdown by Virus-like Particle-Mediated RNAi in a Rat Model of Osteoporosis

Rebalancing of the RANKL/OPG system seems to be an effective treatment strategy in postmenopausal osteoporosis. Here, we evaluate the knockdown of RANKL by in-vivo-delivered siRNA in a rat model of osteoporosis. Virus-like-particles (VLPs) derived from polyoma JC virus were used for delivering RANKL siRNA in ovariectomized (OVX) rats. 48 rats were ovariectomized and treated with either 17β-estradiol (E2), VLPs containing RANKL siRNA (siRANKL), or VLPs containing non-cognate siRNA (siCtrl). All OVX groups were subdivided into the prophylaxis group (PG) and the therapy group (TG). The PG received treatment directly after being OVX for 10 weeks. The TG received treatment 5 weeks after being OVX for 5 weeks. Rats were sacrificed 10 weeks after being OVX. Bone and blood samples were analyzed. E2 and siRANKL showed a significant knockdown of RANKL mRNA. A protein knockdown was observed with E2 and siRANKL in the TG but not in the PG. No distinct improvements in biomechanical and morphological properties of the bones were observed after siRANKL treatment. In the PG, E2 protected the bone structure. We demonstrated successful mRNA and protein knockdown by VLP-mediated RNAi in vivo. Knockdown of membranous RANKL did not result in significant improvements of bone properties in this model of early-stage postmenopausal osteoporosis.

Effects of constrained dynamic loading, CKIP‑1 gene knockout and combination stimulations on bone loss caused by mechanical unloading

Mechanical stimulation plays an important role in maintaining the growth and normal function of the skeletal system. Mechanical unloading occurs, for example, in astronauts spending long periods of time in space or in patients on prolonged bed rest, and causes a rapid loss of bone mass. Casein kinase 2‑interacting protein‑1 (CKIP‑1) is a novel negative bone regulation factor that has been demonstrated to reduce bone loss and enhance bone formation. The aim of this study was to investigate the effect of constrained dynamic loading (Loading) in combination with CKIP‑1 gene knockout (KO) on unloading‑induced bone loss in tail‑suspension mice. The blood serum metabolism index [alkaline phosphatase (ALP) activity and osteocalcin (OCN) levels], tibia mechanical behavior (including bone trabecular microstructure parameters and tibia biomechanical properties), osteoblast‑related gene expression [ALP, OCN, collagen I and bone morphogenetic protein‑2 and osteoprotegerin (OPG)] and osteoclast‑related gene expression [receptor activators of NF‑kB ligand (RANKL)] were measured. The results demonstrated that mice experienced a loss of bone mass after four weeks of tail suspension compared with a wild type group. The mechanical properties, microarchitecture and mRNA expression were significantly increased in mice after Loading + KO treatment (P<0.05). Furthermore, compared with loading or KO alone, the ratio of OPG/RANKL was increased in the combined treatment group. The combined effect of Loading + KO was greater than that observed with loading or KO alone (P<0.05). The present study demonstrates that Loading + KO can counter unloading‑induced bone loss, and combining the two treatments has an additive effect. These results indicate that combined therapy could be a novel strategy for the clinical treatment of disuse osteoporosis associated with space travel or bed rest.

Can the contralateral limb be used as a control during the growing period in a rodent model?

The contralateral limb is often used as a control in various clinical, forensic and anthropological studies. However, no studies have been performed to determine if the contra-lateral limb is a suitable control during the bone development period. The aim of this study was to determine the bilateral symmetry of growing rat tibiae in terms of geometric shape, mechanical strength and bone morphological parameters with developmental stages. Left and right tibias of 18 male Sprague-Dawley rats at 4, 8 and 12 weeks of age were scanned with micro-CT for bone-morphometric evaluation and for 3D deviation analysis to quantify the geometric shape variations between left and right tibiae. Overall tibial lengths and curvatures were also measured, and bone mechanical strength was investigated using three-point bending tests. Deviation distributions between bilateral tibiae remained below 0.5 mm for more than 80% of the geometry for all groups. Tibial lengths, longitudinal tibial curvatures, bone-morphometric parameters and mechanical strengths changed significantly during the growing period but kept a strong degree of symmetry between bilateral tibiae. These results suggest that bilateral tibiae can be considered symmetrical in nature and that contralateral limb can be used as a control during the growing period in different experimental scenarios.

Low-energy extracorporeal shockwave therapy (ESWT) improves metaphyseal fracture healing in an osteoporotic rat model

Purpose

As result of the current demographic changes, osteoporosis and osteoporotic fractures are becoming an increasing social and economic burden. In this experimental study, extracorporeal shock wave therapy (ESWT), was evaluated as a treatment option for the improvement of osteoporotic fracture healing.

Methods

A well-established fracture model in the metaphyseal tibia in the osteoporotic rat was used. 132 animals were divided into 11 groups, with 12 animals each, consisting of one sham-operated group and 10 ovariectomized (osteoporotic) groups, of which 9 received ESWT treatment. Different energy flux intensities (0.15 mJ/mm², 0.35 mJ/mm², or 0.55 mJ/mm²) as well as different numbers of ESWT applications (once, three times, or five times throughout the 35-day healing period) were applied to the osteoporotic fractures. Fracture healing was investigated quantitatively and qualitatively using micro-CT imaging, quantitative real-time polymerase chain reaction (qRT-PCR) analysis, histomorphometric analysis and biomechanical analysis.

Results

The results of this study show a qualitative and quantitative improvement in the osteoporotic fracture healing under low-energy (energy flux intensity: 0,15 mJ/mm²) ESWT and with fewer treatment applications per healing period.

Conclusion

In conclusion, low-energy ESWT seems to exhibit a beneficial effect on the healing of osteoporotic fractures, leading to improved biomechanical properties, enhanced callus-quantity and -quality, and an increase in the expression of bone specific transcription factors. The results suggest that low-energy ESWT, as main treatment or as adjunctive treatment in addition to a surgical intervention, may prove to be an effective, simple to use, and cost-efficient option for the qualitative and quantitative improvement of osteoporotic fracture healing.

Elastic Modulus of Osteoporotic Mouse Femur Based on Femoral Head Compression Test

A biomechanical test is a good evaluation method that describes the structural, functional, and pathological differences in the bones, such as osteoporosis and fracture. The tensile test, compression test, and bending test are generally performed to evaluate the elastic modulus of the bone using mice. In particular, the femoral head compression test is mainly used for verifying the osteoporosis change of the femoral neck. This study conducted bone mineral density analysis using in vivo microcomputed tomography (micro-CT) to observe changes in osteoporosis over time. It proposed a method of identifying the elastic modulus of the femur in the normal group (CON group) and the osteoporotic group (OVX group) through finite element analysis based on the femoral head compression test and also conducted a comparative analysis of the results. Through the femoral head compression test, it was verified that the CON group's ultimate and yield loads were significantly higher than those of the OVX group. It was considered that this result was caused by the fact that the bone mineral density change by osteoporosis occurred in the proximal end more often than in the femur diaphysis. However, the elastic modulus derived from the finite element analysis showed no significant difference between the two groups.

Caffeine at a Moderate Dose Did Not Affect the Skeletal System of Rats with Streptozotocin-Induced Diabetes

Diabetes may lead to the development of osteoporosis. Coffee drinking, apart from its health benefits, is taken into consideration as an osteoporosis risk factor. Data from human and animal studies on coffee and caffeine bone effects are inconsistent. The aim of the study was to investigate effects of caffeine at a moderate dose on the skeletal system of rats in two models of experimental diabetes induced by streptozotocin. Effects of caffeine administered orally (20 mg/kg aily for four weeks) were investigated in three-month-old female Wistar rats, which, two weeks before the start of caffeine administration, received streptozotocin (60 mg/kg, intraperitoneally) alone or streptozotocin after nicotinamide (230 mg/kg, intraperitoneally). Bone turnover markers, mass, mineral density, histomorphometric parameters, and mechanical properties were examined. Streptozotocin induced diabetes, with profound changes in the skeletal system due to increased bone resorption and decreased bone formation. Although streptozotocin administered after nicotinamide induced slight increases in glucose levels at the beginning of the experiment only, slight, but significant unfavorable changes in the skeletal system were demonstrated. Administration of caffeine did not affect the investigated skeletal parameters of rats with streptozotocin-induced disorders. In conclusion, caffeine at a moderate dose did not exert a damaging effect on the skeletal system of diabetic rats.

Effect of the lipoxygenase-inhibitors baicalein and zileuton on the vertebra in ovariectomized rats

Osteoporosis is one of the most common diseases worldwide. In osteoporosis, vertebral fractures represent a major burden. Lipoxygenase (LOX) inhibitors such as baicalein and zileuton may represent a promising therapeutic option owing to their antioxidative effects and suppression of various inflammatory processes in muscle and bone. The effect of these LOX inhibitors on the spine was studied in osteopenic rats. Female Sprague-Dawley rats were divided two times into five groups: four groups each were ovariectomized (OVX) and one control group was non-ovariectomized (NON-OVX). Eight weeks after ovariectomy, three concentrations of baicalein (1mg/kg body weight [BW], 10mg/kgBW, and 100mg/kgBW) were administered subcutaneously daily in three OVX groups for 4weeks. Similarly, zileuton was administered in three concentrations via food for 5weeks. In vivo computed tomography (pQCT) of the spine was performed before the treatments and at the end of the experiment. Lumbar vertebrae were subjected to a compression test, micro-CT, and ashing analyses. After baicalein treatment, cortical bone mineral density (BMD) was improved; trabecular connectivity and trabecular BMD were diminished at high dose. After zileuton treatment, the total BMD, anorganic weight, trabecular nodes, and trabecular area were improved. The in vivo stress-strain index was increased and alkaline phosphatase activity in serum was enhanced after both treatments. A dose-dependent effect was not clearly observed after both treatments. The treatments using baicalein for 4 and zileuton for 5weeks were not sufficient to change the biomechanical properties and bone volume fraction (BV/TV). Overall, baicalein improved the cortical bone parameters whereas zileuton had a favorable effect on the trabecular structure. Moreover, both treatments increased the bone formation rate. Longer trials, a combination of both LOX inhibitors, and their effect at the cellular and molecular levels should be investigated in further studies.

Opioid receptor agonists may favorably affect bone mechanical properties in rats with estrogen deficiency-induced osteoporosis

The results of epidemiological, clinical, and in vivo and in vitro experimental studies on the effect of opioid analgesics on bone are inconsistent. The aim of the present study was to investigate the effect of morphine (an agonist of opioid receptors), buprenorphine (a partial μ opioid receptor agonist and κ opioid receptor antagonist), and naloxone (an antagonist of opioid receptors) on the skeletal system of female rats in vivo. The experiments were carried out on 3-month-old Wistar rats, divided into two groups: nonovariectomized (intact; NOVX) rats and ovariectomized (OVX) rats. The bilateral ovariectomy was performed 7 days before the start of drug administration. Morphine hydrochloride (20 mg/kg/day s.c.), buprenorphine (0.05 mg/kg/day s.c.), or naloxone hydrochloride dihydrate (2 mg/kg/day s.c.) were administered for 4 weeks to NOVX and OVX rats. In OVX rats, the use of morphine and buprenorphine counteracted the development of osteoporotic changes in the skeletal system induced by estrogen deficiency. Morphine and buprenorphine beneficially affected also the skeletal system of NOVX rats, but the effects were much weaker than those in OVX rats. Naloxone generally did not affect the rat skeletal system. The results confirmed the role of opioid receptors in the regulation of bone remodeling processes and demonstrated, in experimental conditions, that the use of opioid analgesics at moderate doses may exert beneficial effects on the skeletal system, especially in estrogen deficiency.

Implant-derived magnesium induces local neuronal production of CGRP to improve bone-fracture healing in rats

Orthopedic implants containing biodegradable magnesium have been used for fracture repair with considerable efficacy; however, the underlying mechanisms by which these implants improve fracture healing remain elusive. Here we show the formation of abundant new bone at peripheral cortical sites after intramedullary implantation of a pin containing ultrapure magnesium into the intact distal femur in rats. This response was accompanied by substantial increases of neuronal calcitonin gene-related polypeptide-α (CGRP) in both the peripheral cortex of the femur and the ipsilateral dorsal root ganglia (DRG). Surgical removal of the periosteum, capsaicin denervation of sensory nerves or knockdown in vivo of the CGRP-receptor-encoding genes Calcrl or Ramp1 substantially reversed the magnesium-induced osteogenesis that we observed in this model. Overexpression of these genes, however, enhanced magnesium-induced osteogenesis. We further found that an elevation of extracellular magnesium induces magnesium transporter 1 (MAGT1)-dependent and transient receptor potential cation channel, subfamily M, member 7 (TRPM7)-dependent magnesium entry, as well as an increase in intracellular adenosine triphosphate (ATP) and the accumulation of terminal synaptic vesicles in isolated rat DRG neurons. In isolated rat periosteum-derived stem cells, CGRP induces CALCRL- and RAMP1-dependent activation of cAMP-responsive element binding protein 1 (CREB1) and SP7 (also known as osterix), and thus enhances osteogenic differentiation of these stem cells. Furthermore, we have developed an innovative, magnesium-containing intramedullary nail that facilitates femur fracture repair in rats with ovariectomy-induced osteoporosis. Taken together, these findings reveal a previously undefined role of magnesium in promoting CGRP-mediated osteogenic differentiation, which suggests the therapeutic potential of this ion in orthopedics.

Effects of fenoterol on the skeletal system depend on the androgen level

BACKGROUND

The role of sympathetic nervous system in the osseous tissue remodeling is not clear enough.

METHODS

The effects of fenoterol, a selective β₂-adrenomimetic drug, on the skeletal system of normal and androgen deficient (orchidectomized) rats were studied in vivo. Osteoclastogenesis and mRNA expression in osteoblasts were investigated in vitro in mouse cell cultures.

RESULTS

Fenoterol administered to animals with physiological androgen level unfavorably affected the skeletal system, damaging the bone microarchitecture. Androgen deficiency induced osteoporotic changes, and fenoterol protected the osseous tissue from consequences of androgen deficiency. The results of in vitro studies correlated with the in vivo observations. A significantly increased number of osteoclasts in bone marrow cell cultures to which testosterone and fenoterol were added simultaneously was demonstrated. In cultures without the addition of testosterone, fenoterol significantly inhibited osteoclastogenesis in comparison with control cultures.

CONCLUSIONS

The results indicate the favorable action of fenoterol in conditions of testosterone deficiency, and its destructive influence upon the skeleton in the presence of androgens. The results confirm the key role of sympathetic nervous system in the regulation of bone remodeling.

Effects of Trigonelline, an Alkaloid Present in Coffee, on Diabetes-Induced Disorders in the Rat Skeletal System

Diabetes increases bone fracture risk. Trigonelline, an alkaloid with potential antidiabetic activity, is present in considerable amounts in coffee. The aim of the study was to investigate the effects of trigonelline on experimental diabetes-induced disorders in the rat skeletal system. Effects of trigonelline (50 mg/kg p.o. daily for four weeks) were investigated in three-month-old female Wistar rats, which, two weeks before the start of trigonelline administration, received streptozotocin (60 mg/kg i.p.) or streptozotocin after nicotinamide (230 mg/kg i.p.). Serum bone turnover markers, bone mineralization, and mechanical properties were studied. Streptozotocin induced diabetes, with significant worsening of bone mineralization and bone mechanical properties. Streptozotocin after nicotinamide induced slight glycemia increases in first days of experiment only, however worsening of cancellous bone mechanical properties and decreased vertebral bone mineral density (BMD) were demonstrated. Trigonelline decreased bone mineralization and tended to worsen bone mechanical properties in streptozotocin-induced diabetic rats. In nicotinamide/streptozotocin-treated rats, trigonelline significantly increased BMD and tended to improve cancellous bone strength. Trigonelline differentially affected the skeletal system of rats with streptozotocin-induced metabolic disorders, intensifying the osteoporotic changes in streptozotocin-treated rats and favorably affecting bones in the non-hyperglycemic (nicotinamide/streptozotocin-treated) rats. The results indicate that, in certain conditions, trigonelline may damage bone.

Effects of 8-Prenylnaringenin and Whole-Body Vibration Therapy on a Rat Model of Osteopenia

Background. 8-Prenylnaringenin (8-PN) is the phytoestrogen with the highest affinity for estrogen receptor-α (ER-α), which is required to maintain BMD. The osteoprotective properties of 8-PN have been demonstrated previously in tibiae. We used a rat osteopenia model to perform the first investigation of 8-PN with whole-body vertical vibration (WBVV). Study Design. Ovariectomy was performed on 52 of 64 Sprague-Dawley rats. Five weeks after ovariectomy, one group received daily injections (sc) of 8-PN (1.77 mg/kg) for 10 weeks; a second group was treated with both 8-PN and WBVV (twice a day, 15 min, 35 Hz, amplitude 0.47 mm). Other groups received either only WBVV or no treatment. Methods. The rats were sacrificed 15 weeks after ovariectomy. Lumbar vertebrae and femora were removed for biomechanical and morphological assessment. Results. 8-PN at a cancer-safe dose did not cause fundamental improvements in osteoporotic bones. Treatment with 8-PN caused a slight increase in uterine wet weight. Combined therapy using WBVV and 8-PN showed no significant improvements in bone structure and biomechanical properties. Conclusion. We cannot confirm the osteoprotective effects of 8-PN at a cancer-safe dose in primary affected osteoporotic bones. Higher concentrations of 8-PN are not advisable for safety reasons. Adjunctive therapy with WBVV demonstrates no convincing effects on bones.

The Impact of Strontium Ranelate on Metaphyseal Bone Healing in Ovariectomized Rats

The following questions were addressed: whether therapy with strontium ranelate (SR) should be continued or interrupted if the fractures occur during SR treatment and whether SR could be applied directly after fracture to improve bone healing. Sprague-Dawley rats (3 month old) were ovariectomized (Ovx, n = 48) or left intact (n = 12). After 8 weeks, a bilateral transverse osteotomy of the tibia metaphysis was created in all rats. Ovx rats were divided into four groups: Ovx; SR applied directly after Ovx until osteotomy (prophylaxis, SR pr, 8 weeks); SR applied after osteotomy (therapy, SR th, 5 weeks); SR applied during the whole experiment (pr + th, 13 weeks). SR dosage was 625 mg/kg body weight/day, administered in the feed. Five weeks later, tibiae were analyzed by biomechanical, histological, micro-CT, and gene expression analyses. The SR pr + th treatment increased total bone mineral density (BMD), bone volume fraction, cortical BMD and volume, callus area and density, serum alkaline phosphatase, tartrate-resistant acid phosphatase mRNA, accelerated osteotomy bridging, and callus formation at weeks 2 and 3 of healing and decreased the osteoprotegerin/receptor activator of nuclear factor kB ligand mRNA ratio. SR th enlarged callus area and improved callus formation during the 5th week of healing. SR pr improved cortical BMD preserving bone after SR discontinuation (5-week rest); the bone healing was not affected. SR content in the tibia metaphysis was the highest in SR pr + th group and was not different between SR pr and SR th. SR has a positive effect on osteoporotic bone healing in rat and SR treatment can be continued after the fracture occurs or applied directly after the fracture.

A new, low cost, locking plate for the long-term fixation of a critical size bone defect in the ratfemur: in vivo performance, biomechanical and finite element analysis

BACKGROUND

The optimum fixation device for the critical size bone defect is not established yet.

OBJECTIVE

A reliable, feasible and low-cost fixation device for the long-term maintenance of a critical bone defect.

METHODS

A custom-made plate made of poly-methyl-methacrylate was used for the fixation of a critical defect of rats' femurs. The screws were securely fixing both on the plate and the bone. A three point bending test, aimed to resemble the in vivo loading pattern, a Finite Element Analysis and a 24-week in vivo monitoring of the integrity of the plate fixation were utilized.

RESULTS

The plate has linear and reproducible behavior. It presents no discontinuities in the stress field of the fixation. Its properties are attributed to the material and the locking principle. It fails beyond the level of magnitude of the normal ambulatory loads. In vivo, 100% of the plates maintained the bone defect intact up to 12 weeks and 85% of them at 24 weeks.

CONCLUSION

This novel locking plate shows optimal biomechanical performance and reliability with high long-term in vivo survival rate. It is fully implantable, inexpensive and easily manufactured. It can be qualified for long term critical defect fixation in bone regeneration studies.

Targeted delivery of lovastatin and tocotrienol to fracture site promotes fracture healing in osteoporosis model: micro-computed tomography and biomechanical evaluation

Osteoporosis is becoming a major health problem that is associated with increased fracture risk. Previous studies have shown that osteoporosis could delay fracture healing. Although there are potential agents available to promote fracture healing of osteoporotic bone such as statins and tocotrienol, studies on direct delivery of these agents to the fracture site are limited. This study was designed to investigate the effects of two potential agents, lovastatin and tocotrienol using targeted drug delivery system on fracture healing of postmenopausal osteoporosis rats. The fracture healing was evaluated using micro CT and biomechanical parameters. Forty-eight Sprague-Dawley female rats were divided into 6 groups. The first group was sham-operated (SO), while the others were ovariectomized (OVx). After two months, the right tibiae of all rats were fractured at metaphysis region using pulsed ultrasound and were fixed with plates and screws. The SO and OVxC groups were given two single injections of lovastatin and tocotrienol carriers. The estrogen group (OVx+EST) was given daily oral gavages of Premarin (64.5 µg/kg). The Lovastatin treatment group (OVx+Lov) was given a single injection of 750 µg/kg lovastatin particles. The tocotrienol group (OVx+TT) was given a single injection of 60 mg/kg tocotrienol particles. The combination treatment group (OVx+Lov+TT) was given two single injections of 750 µg/kg lovastatin particles and 60 mg/kg tocotrienol particles. After 4 weeks of treatment, the fractured tibiae were dissected out for micro-CT and biomechanical assessments. The combined treatment group (OVx+Lov+TT) showed significantly higher callus volume and callus strength than the OVxC group (p<0.05). Both the OVx+Lov and OVx+TT groups showed significantly higher callus strength than the OVxC group (p<0.05), but not for callus volume. In conclusion, combined lovastatin and tocotrienol may promote better fracture healing of osteoporotic bone.

A novel device for resistance-free biomechanical testing of the metaphysis of long bones

BACKGROUND

Biomechanical testing is an essential component of bone research. In order to test the metaphyseal region of long bones, a typical location for the nowadays increasing field of osteoporotic bone changes, three-point bending and breaking test devices are suitable and widely used. The aim of our study was to increase the effectiveness of this method by using a newly developed ball-mounted platform design. This new design eliminates the negative effects of friction, present in previous studies, caused by the lengthening of the distal tibia along its diaphyseal axis while sliding over the surface of a fixed aluminum block.

METHODS

70 tibiae of 35 twelve week old, female Sprague Dawley rats were separated into two groups for a metaphyseal bending/breaking test. Group 1 was made up of the rat's right tibiae, Group 2 of the left tibiae. Group 1 was tested on a solid metal block according to previously established testing devices whereas Group 2 was tested on the newly designed device: the resistance-free gliding, ball-mounted platform. Stiffness (N/mm), yield Load (N), and failure Load (N) were registered. In the evaluation of both testing procedures, the results of the right and left tibiae were compared according to the rat they originated from.

RESULTS

Stiffness (S) showed highly significant differences (p = 0.002) with 202.25 ± 27.010 N/mm SD (Group 1) and 184.66 ± 35.875 N/mm SD (Group 2). Yield Load (yL) showed highly significant differences (p < 0.001) with 55.31 ± 13.074 N SD (Group1) and 37.17 ± 12.464 N SD (Group2). The mean failure Load (fL) did not differ significantly (p < 0.231) between Group 1: 81.34 ± 11.972 N SD and Group 2: 79.63 ± 10.345 N SD.

CONCLUSIONS

We therefore conclude that, used in the three-point bending/breaking test, the mobile, ball-mounted platform device is able to efficiently eliminate the influence of friction in terms of stiffness and yield load. Failure Load was not affected. We suggest that the new ball-mounted platform device, when compared to other existing techniques, generates more accurate test results when used in the three-point bending/breaking test of the metaphysis of long bones.

Whole body vibration during fracture healing intensifies the effects of estradiol and raloxifene in estrogen-deficient rats

Current osteoporosis therapies aim to delay bone destruction and have additional anabolic effects. While they have demonstrated some positive effects on bone healing, more progress is needed in this area. This study used the well-known osteoporotic agents estrogen (E) and raloxifene (R) in conjunction with biomechanical whole body vibration (WBV) at a frequency of 70 Hz twice daily for six weeks to stimulate bone healing. Eighty-four 3-month old female Sprague-Dawley rats (12 per group) were bilaterally ovariectomized to develop osteopenia within eight weeks. Osteotomy of the metaphyseal tibiae was performed and fracture healing was then studied using mechanical tests, histomorphometry, computed tomography (μCT), and gene analysis. We found that E and R improved the structure of osteopenic bones as did WBV alone, although significant levels for WBV were seldom reached. Combination treatments significantly enhanced stiffness (R+WBV; p<0.05), endosteal bone (R+WBV; p<0.01), and trabecular density (E+WBV; p<0.05, R+WBV; p<0.05). In addition, the expression of osteoclast-specific Trap was significantly reduced after treatment with E, R, or their combination with WBV (p<0.01). The effects were additive and not inhibitory, leading us to conclude that the combined applications of WBV with E or R may improve the healing of osteopenic bones. The therapies studied are all currently approved for human use, suggesting ready applicability to clinical practice. To better understand the effects of WBV on osteopenic bones, the ideal vibration regime will require further study.

Effect of low-magnitude whole-body vibration combined with alendronate in ovariectomized rats: a random controlled osteoporosis prevention study

BACKGROUND

Alendronate (ALE) is a conventional drug used to treat osteoporosis. Low-magnitude whole-body vibration (WBV) exercise has been developed as a potential treatment for osteoporosis. The aim of this study was to investigate whether low-magnitude WBV could enhance the protective effect of ALE on bone properties in ovariectomized rats.

METHODS

A total of 128 Sprague-Dawley rats were randomly divided into five groups (SHAM, OVX+VEH, OVX+WBV, OVX + ALE, OVX+WBV+ALE). The level of WBV applied was 0.3 g at 45-55 Hz for 20 min/day, 5 day/week and for 3 months. ALE was administered in dose of 1 mg/Kg once a week. Every four weeks eight rats from each group were sacrificed and their blood and both tibiae were harvested. The expression of osteocalcin and CTX in serum was measured by enzyme-linked immunosorbent assay (ELISA) and the tibiae were subjected to metaphyseal three-point bending and μCT analysis.

RESULTS

Osteocalcin rose after ovariectomy and was not appreciably changed by either alendronate or WBV alone or in combination. Alendronate treatment significantly prevented an increase in CTX. WBV alone treatment did not alter this effect. Compared with the OVX+WBV group, nearly all tested indices such as the BV/TV, TV apparent, Tb.N, Tb.Th, and Conn.D were higher in the OVX+ALE group at week 12.Compared with the OVX+WBV group, certain tested indices such as BV/TV, TV apparent, Tb.N, and Con.D, were higher in the OVX+WBV+ALE group at week 12. At week 12, tibiae treated with WBV+ALE exhibited a significantly higher Fmax compared to the OVX+VEH group, and a significant difference was also found in energy absorption between the OVX+WBV+ALE and OVX+VEH groups.

CONCLUSIONS

Compared with the WBV, ALE was more effective at preventing bone loss and improved the trabecular architecture. However, WBV enhanced the effect of alendronate in ovariectomized rats by inducing further improvements in trabecular architecture.

Local injection of a single dose of simvastatin augments osteoporotic bone mass in ovariectomized rats

The aim of this study was to evaluate the effects and explore the mechanism of a local injection of a single dose of simvastatin as a strategy to strengthen target bone. Simvastatin was injected into the femurs (5 or 10 mg) or caudal vertebrae (1 or 2 mg) of ovariectomized rats, with an equal volume of vehicle injected as a control. Bone mineral density (BMD), bone microstructure and strength were evaluated at 1 and 5 months post-injection for the femurs and at 12 days post-injection for the vertebrae. Bone mass, adipocyte numbers and Runx2 expression were also examined using histology and immunohistochemistry. Compared with controls, simvastatin significantly increased BMD, bone volume fraction (BV/TV), improved bone microstructural parameters and bone strength in the femurs at both time points (all P < 0.01). Simvastatin-treated femurs contained fewer adipocytes and a higher Runx2 expression. For the caudal vertebrae, simvastatin significantly improved BV/TV, bone microstructures, and bone strength (all P < 0.01) as compared with controls. In conclusion, local injection of a single dose of simvastatin induces early onset and long-lasting bone augmentation in osteoporotic bone, significantly improving BMD, and bone microstructure and biomechanical strength. Simvastatin induces Runx2 expression, which may function to induce osteogenesis and inhibit adipogenesis as an underlying mechanism to augment bone mass.

Effect of glimepiride on the skeletal system of ovariectomized and non-ovariectomized rats

BACKGROUND

Diabetes mellitus type 2 and osteoporosis are major health problem, especially in postmenopausal women. Glimepiride is a third-generation sulfonylurea derivative and is used as a first-line drug in the treatment of type 2 diabetes mellitus. The effect of this drug on bone tissue is unknown. The aim of the present study was to investigate the influence of glimepiride on the skeletal system in ovariectomized and non-ovariectomized rats.

METHODS

The experiment was conducted on 3-month-old female Wistar rats, divided into 4 groups (n=10 per group): I (NOVX)-non-ovariectomized control rats, II (NOVX+G)-non-ovariectomized rats receiving glimepiride (0.8 mg/kg po), III (OVX)-ovariectomized control rats, IV (OVX+G)-ovariectomized rats receiving glimepiride (0.8 mg/kg po). Bilateral ovariectomy was performed 7 days before the start of the experiment, under ketamine-xylazine anesthesia. Glimepiride was administered once daily for 28 days. The effect of glimepiride on the skeletal system was assessed based on macrometric parameters, histomorphometric parameters and mechanical properties of the tibial metaphysis, femoral diaphysis and femoral neck. Bone mass, mineral mass, calcium and phosphorus content, as well as serum estrogen, osteocalcin and RatLaps levels were also studied.

RESULTS

Estrogen deficiency in ovariectomized rats caused increased bone remodeling, with an intensification of bone resorption and formation, and mineralization impairment. Glimepiride in ovariectomized rats inhibited the development of changes in the skeletal system caused by estrogen deficiency, intensifying bone formation. In the presence of estrogens (in non-ovariectomized rats), glimepiride also intensified bone formation, but to a lesser extent.

CONCLUSIONS

Glimepiride, in the therapy of type 2 diabetes mellitus in postmenopausal women, may have a beneficial effect on bone remodeling and may reduce the risk of development of osteoporosis.

Differences of bone healing in metaphyseal defect fractures between osteoporotic and physiological bone in rats

Discrepancies in bone healing between osteoporotic and non-osteoporotic bone remain uncertain. The focus of the current work is to evaluate potential healing discrepancies in a metaphyseal defect model in rat femora. Female Sprague-Dawley rats were either ovariectomized (OVX, n=14) and combined with a calcium-, phosphorus- and vitamin D3-, soy- and phytoestrogen-free diet or received SHAM operation with standard diet rat (SHAM, n=14). Three months post-ovariectomy, DEXA measurement showed a reduction of bone mineral density reflecting an osteoporotic bone status in OVX rats. Rats then underwent a 3 mm wedge-shaped osteotomy at the distal metaphyseal area of the left femur stabilized with a T-shaped mini-plate and allowed to heal for 6 weeks. Biomechanical competence by means of a non-destructive three-point bending test showed significant lower flexural rigidity in the OVX rats at 3 mm lever span compared to SHAM animals (p=0.048) but no differences at 10 mm lever span. Microcomputer tomography (μCT) showed bridging cortices and consolidation of the defect in both groups, however, no measurable differences were found in either total ossified tissue or vascular volume fraction. Furthermore, histology showed healing discrepancies that were characterized by cartilaginous remnant and more unmineralized tissue presence in the OVX rats compared to more mature consolidation appearance in the SHAM group. In summary, bone defect healing in metaphyseal bone slightly differs between osteoporotic and non-osteoporotic bone in the current 3 mm defect model in both 3mm lever span biomechanical testing and histology.