Differential maintenance of cortical and cancellous bone strength following discontinuation of bone-active agents

Repurpose dasatinib and quercetin: Targeting senescent cells ameliorates postmenopausal osteoporosis and rejuvenates bone regeneration

Clinical therapies developed for estrogen-deficiency-driven postmenopausal osteoporosis (PMO) and related diseases, such as bone degeneration, show multiple adverse effects nowadays. Targeting senescent cells (SnCs) and the consequent senescence-associated secretory phenotype (SASP) with a combination of dasatinib and quercetin (DQ) is a recently developed novel therapy for multiple age-related diseases. Herein, we found that estrogen deficiency induced-bone loss was attributed to a pro-inflammatory microenvironment with SASP secretions and accelerated SnC accumulation, especially senescent mesenchymal stem cells (MSCs) characterized by exhaustion and dysfunction in middle aged rats. Systematically targeting SnCs with DQ strikingly ameliorated PMO and restored MSC function. Local administration of DQ and bone morphogenetic protein 2 (BMP2) in combination promoted osteogenic differentiation of MSCs and rejuvenated osteoporotic bone regeneration. Our results repurposed DQ as an attractive therapy for treating PMO and related diseases.

Short Cyclic Regimen With Parathyroid Hormone (PTH) Results in Prolonged Anabolic Effect Relative to Continuous Treatment Followed by Discontinuation in Ovariectomized Rats

Despite the potent effect of intermittent parathyroid hormone (PTH) treatment on promoting new bone formation, bone mineral density (BMD) rapidly decreases upon discontinuation of PTH administration. To uncover the mechanisms behind this adverse phenomenon, we investigated the immediate responses in bone microstructure and bone cell activities to PTH treatment withdrawal and the associated long-term consequences. Unexpectedly, intact female and estrogen-deficient female rats had distinct responses to the discontinuation of PTH treatment. Significant tibial bone loss and bone microarchitecture deterioration occurred in estrogen-deficient rats, with the treatment benefits of PTH completely lost 9 weeks after discontinuation. In contrast, no adverse effect was observed in intact rats, with sustained treatment benefit 9 weeks after discontinuation. Intriguingly, there is an extended anabolic period during the first week of treatment withdrawal in estrogen-deficient rats, during which no significant change occurred in the number of osteoclasts, whereas the number of osteoblasts remained elevated compared with vehicle-treated rats. However, increases in number of osteoclasts and decreases in number of osteoblasts occurred 2 weeks after discontinuation of PTH treatment, leading to significant reduction in bone mass and bone microarchitecture. To leverage the extended anabolic period upon early withdrawal from PTH, a cyclic administration regimen with repeated cycles of on and off PTH treatment was explored. We demonstrated that the cyclic treatment regimen efficiently alleviated the PTH withdrawal-induced bone loss, improved bone mass, bone microarchitecture, and whole-bone mechanical properties, and extended the treatment duration. © 2021 American Society for Bone and Mineral Research (ASBMR).

Anomalous bone changes in ovariectomized type 2 diabetic rats: inappropriately low bone turnover with bone loss in an estrogen-deficient condition

Estrogen deprivation accelerates bone resorption, leading to imbalance of bone remodeling and osteoporosis in postmenopausal women. In the elderly, type 2 diabetes mellitus (T2DM) frequently coexists as an independent factor of bone loss. However, little is known about the skeletal changes in a combined condition of estrogen deficiency and T2DM. Herein, we performed ovariectomy (OVX) in nonobese Goto-Kakizaki (GK) T2DM rats to examine changes associated with calcium and phosphate metabolism and bone microstructures and strength. As expected, wild-type (WT) rats subjected to ovariectomy (OVX-WT) had low trabecular bone volume and serum calcium with increased dynamic histomorphometric and serum bone markers, consistent with the high turnover state. T2DM in GK rats also led to low trabecular volume and serum calcium. However, the dynamic histomorphometric markers of bone remodeling were unaffected in these GK rats, indicating the distinct mechanism of T2DM-induced bone loss. Interestingly, OVX-GK rats were found to have anomalous and unique changes in bone turnover-related parameters, i.e., decreased osteoblast and osteoclast surfaces with lower COOH-terminal telopeptide of type I collagen levels compared with OVX-WT rats. Furthermore, the levels of calciotropic hormones, i.e., parathyroid hormone and 1,25(OH)₂D₃, were significantly decreased in OVX-GK rats. Although the OVX-induced bone loss did not further worsen in GK rats, a three-point bending test indicated that OVX-GK bones exhibited a decrease in bone elasticity. In conclusion, T2DM and estrogen deficiency both led to microstructural bone loss, the appearance of which did not differ from each factor alone. Nevertheless, the combination worsened the integrity and suppressed the turnover, which might eventually result in adynamic bone disease.

Sequential treatment with zoledronic acid followed by teriparatide or vice versa increases bone mineral density and bone strength in ovariectomized rats

Bisphosphonates (BPs) and teriparatide (TPTD) are both effective treatments for osteoporosis, but BP treatment prior to daily TPTD treatment has been shown to impair the effect of TPTD in some clinical studies. In contrast, the loss of bone mineral density (BMD) that occurs after withdrawal of TPTD can be prevented by BP treatment. Although various studies have investigated the combination and/or sequential use of BP and TPTD, there have been no clinical studies investigating sequential treatment with zoledronic acid (ZOL) and TPTD (or vice versa). In this study, we evaluated the effects of sequential treatment with TPTD followed by ZOL, and ZOL followed by TPTD, using ovariectomized (OVX) rats. Two months after OVX, osteopenic rats were treated with ZOL, TPTD, or vehicle for a period of 4 months (first treatment period), and then the treatments were switched and administered for another 4 months (second treatment period). The group treated with ZOL followed by TPTD showed an immediate increase in BMD of the proximal tibia and greater BMD and bone strength of the lumbar vertebral body, femoral diaphysis, and proximal femur than the group treated with ZOL followed by vehicle. Serum osteocalcin, a marker of bone formation, increased rapidly after switching to TPTD from ZOL. The group treated with TPTD followed by ZOL did not lose BMD in the proximal tibia after TPTD was stopped, while the group treated with TPTD followed by vehicle did lose BMD. The BMD and bone strength of the lumbar vertebral body, femoral diaphysis, and proximal femur were greater in the group treated with TPTD followed by ZOL than in the group treated with TPTD followed by vehicle. The increase in serum osteocalcin and urinary CTX after withdrawal of TPTD was prevented by the switch from TPTD to ZOL. In conclusion, our results demonstrate that switching from ZOL to TPTD resulted in a non-attenuated anabolic response in the lumbar spine and femur of OVX rats. In addition, switching from TPTD to ZOL caused BMD to be maintained or further increased. If these results can be reproduced in a clinical setting, the sequential use of ZOL followed by TPTD or vice versa in the treatment of osteoporosis patients would contribute to increases in BMD that, hopefully, would translate into a corresponding decrease in the incidence of vertebral and non-vertebral fractures.

Intermittent Ibandronate Maintains Bone Mass, Bone Structure, and Biomechanical Strength of Trabecular and Cortical Bone After Discontinuation of Parathyroid Hormone Treatment in Ovariectomized Rats

Although parathyroid hormone (PTH) expresses an anabolic effect on bone mass, the increased bone mass disappears once PTH treatment is withdrawn. Therefore, sequential treatment with anti-bone-resorptive agents is required to maintain bone mass after PTH treatment. We examined the effect of sequential treatment with ibandronate (IBN), a nitrogen-containing bisphosphonate, following PTH in ovariectomized (OVX) rats. Wistar-Imamichi rats (27 weeks old) were ovariectomized and treated with PTH (10 µg/kg, s.c.; 5 times/week; PTH group) for 8 weeks from 8 weeks after OVX. Thereafter, PTH was withdrawn and rats were administered IBN (10 µg/kg, s.c.; every 4 weeks; PTH-IBN group) or vehicle (PTH-Veh group) for another 8 weeks. PTH increased bone mineral density (BMD) measured by dual-energy X-ray absorptiometry and biomechanical strength in the lumbar spine and femur as compared to the disease control rats. BMD and biomechanical strength in the PTH-Veh group were lower than in the PTH group, whereas in the PTH-IBN group they were maintained at the level of the PTH group. Microstructure of the trabecular and cortical bone in the PTH-IBN group was not significantly different from that in the PTH group. In histomorphometric analysis of the lumbar vertebra, eroded surface and osteoclast surface in the PTH-Veh group were no different from those in the PTH group, whereas they were lower in the PTH-IBN group. Osteoid surface, osteoblast surface, and mineralize surface decreased in both PTH-IBN and PTH-Veh groups compared to the PTH group, and these parameters in the PTH-IBN group were lower than in the PTH-Veh group. These results indicated that intermittent IBN after PTH treatment suppressed bone turnover and maintained BMD, biomechanical strength, and microstructure in the lumbar spine and femur of OVX rats.

Bisphosphonate Withdrawal: Effects on Bone Formation and Bone Resorption in Maturing Male Mice

Bisphosphonates are being increasingly used to treat pediatric patients with skeletal disorders. However, the effects of long-term bisphosphonate therapy and cessation of therapy during growth are unclear. Thus, studies were undertaken to determine the effects of alendronate discontinuation after treatment of C57Bl/6 mice during the period of rapid skeletal growth. Compared with vehicle-treated mice, 16 weeks of alendronate treatment starting at age 18 days resulted in a 3.7-fold increase in trabecular bone in the setting of suppressed bone formation. Alendronate therapy for 8 weeks followed by 8 weeks of vehicle treatment resulted in a more pronounced increase in trabecular bone compared with mice treated with alendronate for 16 weeks (1.7-fold) and to vehicle-treated controls (6.5-fold). Mice that received alendronate for 8 weeks followed by 8 weeks of vehicle exhibited increased osteoblast surface (2.5-fold), mineralizing surface (5.7-fold), and bone formation rate (5.1-fold) compared with mice treated continuously with alendronate. However, these parameters were not restored to the levels observed in the vehicle-treated mice. Thus, partial resumption of bone formation upon cessation of bisphosphonate therapy leads to a greater increase in trabecular bone than that found when bisphosphonates are administered continuously to growing mice. These data suggest that intermittent administration of bisphosphonates may optimize their beneficial effects on the growing skeleton. © 2017 American Society for Bone and Mineral Research.

Fibroblast Growth Factor Receptor 3 Deficiency Does Not Impair the Osteoanabolic Action of Parathyroid Hormone on Mice

Summary: PTH stimulates bone formation in Fgfr3 knockout mice through promotion of proliferation and differentiation in osteoblasts.

Introduction: Previous studies showed that endogenous fibroblast growth factor 2 (FGF-2) is required for parathyroid hormone (PTH)-stimulated bone anabolic effects, however, the exact mechanisms by which PTH stimulate bone formation and the function of FGF receptors in mediating these actions are not fully defined. FGF receptor 3 (FGFR3) has been characterized as an important regulator of bone metabolism and is confirmed to cross-talk with PTH/PTHrP signal in cartilage and bone development.

Methods: Fgfr3 knockout and wild-type mice at 2-month-old and 4-month-old were intraperitoneally injected with PTH intermittently for 4 weeks and then the skeletal responses to PTH were assessed by dual energy X-ray absorptiometry (DEXA), micro-computed tomography (μCT) and bone histomorphometry.

Results: Intermittent PTH treatment improved bone mineral density (BMD) and femoral mechanical properties in both Fgfr3^-/- and wild-type mice. Histomorphometric analysis showed that bone formation and bone resorption were increased in both genotypes following PTH treatment. PTH treatment increased trabecular bone volume (BV/TV) in WT and Fgfr3-deficient mice. The anabolic response in Fgfr3-deficient and wild-type bone is characterized by an increase of both bone formation and resorption-related genes following PTH treatment. In addition, we found that Fgfr3 null osteoblasts (compared to wild-type controls) maintained normal abilities to response to PTH-stimulated increase of proliferation, differentiation, expression of osteoblastic marker genes (Cbfa1, Osteopontin and Osteocalcin), and phosphorylation of Erk1/2.

Conclusions: Bone anabolic effects of PTH were not impaired by the absence of FGFR3, suggesting that the FGFR3 signaling may not be required for osteoanabolic effects of PTH activities.

Effect of sequential treatments with alendronate, parathyroid hormone (1-34) and raloxifene on cortical bone mass and strength in ovariectomized rats

Anti-resorptive and anabolic agents are often prescribed for the treatment of osteoporosis continuously or sequentially for many years. However their impact on cortical bone quality and bone strength is not clear.

METHODS

Six-month old female rats were either sham operated or ovariectomized (OVX). OVX rats were left untreated for two months and then were treated with vehicle (Veh), hPTH (1-34) (PTH), alendronate (Aln), or raloxifene (Ral) sequentially for three month intervals, for a total of three periods. Mid-tibial cortical bone architecture, mass, mineralization, and strength were measured on necropsy samples obtained after each period. Bone indentation properties were measured on proximal femur necropsy samples.

RESULTS

Eight or more months of estrogen deficiency in rats resulted in decreased cortical bone area and thickness. Treatment with PTH for 3months caused the deposition of endocortical lamellar bone that increased cortical bone area, thickness, and strength. These improvements were lost when PTH was withdrawn without followup treatment, but were maintained for the maximum times tested, six months with Ral and three months with Aln. Pre-treatment with anti-resorptives was also somewhat successful in ultimately preserving the additional endocortical lamellar bone formed under PTH treatment. These treatments did not affect bone indentation properties.

SUMMARY

Sequential therapy that involved both PTH and anti-resorptive agents was required to achieve lasting improvements in cortical area, thickness, and strength in OVX rats. Anti-resorptive therapy, either prior to or following PTH, was required to preserve gains attributable to an anabolic agent.

Treatment with Rhizoma Dioscoreae extract has protective effect on osteopenia in ovariectomized rats

The aims of this study were to evaluate the osteoprotective effect of aqueous extract from Rhizoma Dioscoreae (RDE) on rats with ovariectomy- (OVX-) induced osteopenia. Our results show that RDE could inhibit bone loss of OVX rats after a 12-week treatment. The microarray analysis showed that 68 genes were upregulated and that 100 genes were downregulated in femurs of the RDE group rats compared to those in the OVX group. The Ingenuity Pathway Analysis (IPA) showed that several downregulated genes had the potential to code for proteins that were involved in the Wnt/ β -catenin signaling pathway (Sost, Lrp6, Tcf7l2, and Alpl) and the RANKL/RANK signaling pathway (Map2k6 and Nfatc4). These results revealed that the mechanism for an antiosteopenic effect of RDE might lie in the synchronous inhibitory effects on both the bone formation and the bone resorption, which is associated with modulating the Wnt/ β -catenin signaling and the RANKL/RANK signaling.

Combined treatment with a traditional Chinese medicine, Hachimi-jio-gan (Ba-Wei-Di-Huang-Wan) and alendronate improves bone microstructure in ovariectomized rats

ETHNOPHARMACOLOGICAL RELEVANCE

Hachimi-jio-gan is one of the most common recipes in traditional Chinese, Japanese and Korean medicines and has been used for preventing and treating various diseases associated with aging, including osteoporosis.

AIM OF THE STUDY

The present study was performed to examine the combined effects of a traditional Chinese medicine, Hachimi-jio-gan (HJG) and antiresorptive agent, alendronate (ALN) on ovariectomy-induced bone loss in rats.

MATERIALS AND METHODS

Six-month-old female Sprague-Dawley rats were underwent ovariectomy (OVX) or sham operation. Eight weeks later, the OVX rats were treated either with HJG or ALN alone or in combination of both. The skeletal response was evaluated using micro-computed tomography (micro-CT), image analysis software, and biochemical markers.

RESULTS

This study demonstrated that treatment with HJG or ALN alone increased trabecular bone volume and bone mineral density (BMD), and partially improved bone microstructure of the proximal tibia and vertebra in OVX rats. Treatment with ALN to OVX rats resulted in significant reduction in both bone resorption and bone formation. Treatment with HJG to OVX rats inhibited bone resorption, with no marked effects on bone formation. Combined treatment of HJG and ALN significantly improved trabecular bone mass and bone microstructure, compared with either agent alone.

CONCLUSIONS

We conclude that the combined treatment with HJG and ALN has beneficial effects on trabecular bone mass, improving the structural properties of both tibia and vertebra in OVX rats.