Eldecalcitol and calcitriol stimulates 'bone minimodeling,' focal bone formation without prior bone resorption, in rat trabecular bone

In vivo microCT-based time-lapse morphometry reveals anatomical site-specific differences in bone (re)modeling serving as baseline parameters to detect early pathological events

The bone structure is very dynamic and continuously adapts its geometry to external stimuli by modeling and remodeling the mineralized tissue. In vivo microCT-based time-lapse morphometry is a powerful tool to study the temporal and spatial dynamics of bone (re)modeling. Here an advancement in the methodology to detect and quantify site-specific differences in bone (re)modeling of 12-week-old BALB/c nude mice is presented. We describe our method of quantifying new bone surface interface readouts and how these are influenced by bone curvature. This method is then used to compare bone surface (re)modeling in mice across different anatomical regions to demonstrate variations in the rate of change and spatial gradients thereof. Significant differences in bone (re)modeling baseline parameters between the metaphyseal and epiphyseal, as well as cortical and trabecular bone of the distal femur and proximal tibia are shown. These results are validated using conventional static in vivo microCT analysis. Finally, the insights from these new baseline values of physiological bone (re)modeling were used to evaluate pathological bone (re)modeling in a pilot breast cancer bone metastasis model. The method shows the potential to be suitable to detect early pathological events and track their spatio-temporal development in both cortical and trabecular bone. This advancement in (re)modeling surface analysis and defined baseline parameters according to distinct anatomical regions will be valuable to others investigating various disease models with site-distinct local alterations in bone (re)modeling.

Histochemical characteristics on minimodeling-based bone formation induced by anabolic drugs for osteoporotic treatment

Modeling, the changes of bone size and shape, often takes place at the developmental stages, whereas bone remodeling-replacing old bone with new bone-predominantly occurs in adults. Unlike bone remodeling, bone formation induced by modeling i.e., minimodeling (microscopic modeling in cancellous bone) is independent of osteoclastic bone resorption. Although recently-developed drugs for osteoporotic treatment could induce minimodeling-based bone formation in addition to remodeling-based bone formation, few reports have demonstrated the histological aspects of minimodeling-based bone formation. After administration of eldecalcitol or romosozumab, unlike teriparatide treatment, mature osteoblasts formed new bone by minimodeling, without developing thick preosteoblastic layers. The histological characteristics of minimodeling-based bone formation is quite different from remodeling, as it is not related to osteoclastic bone resorption, resulting in convex-shaped new bone and smooth cement lines called arrest lines. In this review, we will show histological properties of minimodeling-based bone formation by osteoporotic drugs.

Effects of risedronate, alendronate, and minodronate alone or in combination with eldecalcitol on bone mineral density, quality, and strength in ovariectomized rats

Combination therapy of active vitamin D₃ with some bisphosphonates (BPs) has been reported to be clinically beneficial. However, combination therapy of eldecalcitol (ELD) with BP has to date not been validated as to whether it is beneficial in the clinical setting. Preclinical studies suggested that simultaneous treatment with ELD and some BPs is more effective than monotherapy. However, the relative potency of various BPs, when used in combination with ELD, is completely unknown. In this study, we examined and compared the effects of risedronate (RIS), alendronate (ALN), and minodronate (MIN) alone or in combination with ELD on bone mass, microarchitecture, strength, and material properties in ovariectomized Sprague-Dawley rats aged 13 weeks. RIS, ALN, MIN, and ELD were administered five times weekly for 16 weeks. Micro-computed tomography analysis, compression test, and Fourier transform infrared (FTIR) imaging analysis were performed 16 weeks after treatment initiation. Trabecular and cortical bone mineral density (BMD) in the fourth lumbar vertebra (L4) significantly increased in the RIS + ELD, ALN + ELD, and MIN + ELD groups compared with the vehicle group. Moreover, the bone microarchitecture of L4 in all the BP + ELD groups also significantly improved. On mechanical testing of L4, the maximum load was significantly increased in the RIS + ELD and ALN + ELD groups. FTIR analysis revealed that the mineral-to-collagen ratio of trabecular bone in L3 of all the BP + ELD groups was significantly increased compared with the vehicle group. By contrast, the carbonate-to-phosphate ratio, a parameter of mineral immaturity, was significantly decreased in the RIS + ELD and ALN + ELD groups. BP + ELD improved the BMD and structural properties of the bone to a similar extent. RIS + ELD and ALN + ELD also improved bone strength. Furthermore, treatment with BP + ELD improved the bone material. These results suggest that the combination therapy of BP and ELD is beneficial and warrants further clinical trials.

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Combination of bisphosphonates and eldecalcitol was superior to either monotherapy.

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Bone quality on FTIR imaging analysis correlated with bone strength.

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Combined bisphosphonate and eldecalcitol may be useful in the clinical setting.

[Anabolic action of teriparatide to osteoporotic patients]

Intermittent administration of human parathyroid hormone (PTH) [1-34], or teriparatide, has been used for osteoporotic treatment, which is available for daily and weekly administration for the osteoporotic patients in Japan, increasing bone mass and reduce bone fracture risk. In general, continuous PTH infusion shows catabolic effects in bone, while the intermittent administration of PTH results in anabolic action in osteoporotic patients. Intermittent PTH administration promotes preosteoblastic proliferation, as well as stimulates osteoblastic bone formation dependent on cell coupling with osteoclasts. Dosing frequency of PTH administration may affect resultant bone mass, and therefore, we have examined the anabolic effects of the high and low frequency of PTH administration using a mouse model. As a consequence, the high frequency of PTH administration accelerated the preosteoblastic proliferation with forming thick preosteoblastic network, osteoclastogenesis inside the preosteoblastic network, as well as osteoblastic bone formation. In contrast, the low frequency of PTH administration promoted osteoblastic bone formation, but, did not stimulate preosteoblastic proliferation and osteoclastogenesis. In addition, the high or low frequency of PTH administration demonstrated bone formation by manners of accelerated bone remodeling or bone remodeling/mini-modeling, respectively. Thus, the different dosing frequency of PTH administration may induce the different cellular mechanism of anabolic effects in bone.

Eldecalcitol, an active vitamin D analog, effectively prevents cyclophosphamide-induced osteoporosis in rats

Cyclophosphamide (CTX) as an alkylating agent is used for treating a range of tumor types and allergic diseases. However, high-dose application may induce rapid bone loss and increase the risk of osteoporotic fractures. Eldecalcitol (ED-71), a clinically approved active vitamin D analog, has been approved for osteoporosis treatment. It potently inhibited bone resorption while maintaining osteoblastic function in estrogen-deficient and high-turnover osteoporosis in model rats. The aim of the present study was to clarify the treatment effect of ED-71 on bone loss in a well-established rat model of osteoporosis with CTX administration. After 15 days of CTX treatment, ED-71 was administered, while estradiol valerate (E2V) was used as a positive control. At 2 and 4 weeks after ED-71 or E2V administration, rats were sacrificed and fixed. The tibiae were extracted for histochemical analysis using hematoxylin and eosin staining and immunohistochemistry. When compared with the untreated control group, the CTX group displayed clear osteoporotic features, including a decreased number of bone trabeculae and increased trabecular separation. ED-71 and E2V successfully rescued CTX-induced bone loss. The ED-71 group displayed denser and increasingly mature trabecular bone than the E2V group. Furthermore, ED-71 administration led to significant suppression of tartrate-resistant acid phosphatase (TRAP), cathepsin K (CK), matrix metalloproteinase 9 (MMP9), alkaline phosphatase (ALP) and Osteopontin (OPN), which was less pronounced than in E2V administration but was similar to the values exhibited in the normal control group. These results indicated that ED-71 had a moderate and increased effect on bone turnover compared with E2V. Therefore, the present study suggests that ED-71 is a potential inhibitor of CTX-induced osteoporosis, successfully rescuing bone loss without excessively suppressing bone turnover, and may be a suitable treatment for preventing bone loss in patients receiving CTX.

Sequential Treatment with Eldecalcitol After PTH Improves Bone Mechanical Properties of Lumbar Spine and Femur in Aged Ovariectomized Rats

Parathyroid hormone (PTH) analogs have a powerful anabolic effect on bone and are used in the treatment of patients with severe osteoporosis. However, there are limitations to how long they can be safely administered. Withdrawal of PTH results in the cancelation of its effects, necessitating subsequent treatment to maintain the bone quantity and quality. This study assessed the effects of Eldecalcitol (ELD), an active vitamin D3 derivative, after PTH in estrogen-deficient osteoporotic rats. Six-month-old female rats were ovariectomized, and PTH administration was started 7 weeks later. After 4 weeks of PTH treatment, the animals were divided into three groups and either continued to receive PTH (PTH-PTH), or were switched to ELD (PTH-ELD) or vehicle (PTH-Veh) for an additional 4 weeks. In the femur, increased BMD by 4 weeks treatment of PTH was significantly reduced in PTH-Veh but not in PTH-PTH and PTH-ELD. The same tendency was observed in the lumbar vertebrae. MicroCT imaging and histomorphometry analysis revealed that the favorable bone structure changes by PTH administration were also maintained in the femurs and tibias of the PTH-PTH and PTH-ELD groups. Increased bone strength by 4-week treatment of PTH in lumber also maintained in PTH-ELD. Furthermore, minimodeling was observed in the PTH-ELD group. These results demonstrate that treatment with ELD sequentially following PTH prevented the bone quantity and strength reduction that accompanies PTH withdrawal in estrogen-deficient rats.

Eldecalcitol is more effective in promoting osteogenesis than alfacalcidol in Cyp27b1-knockout mice

Calcium (Ca) absorption from the intestinal tract is promoted by active vitamin D (1α,25D3). Vitamin D not only promotes Ca homeostasis, but it also inhibits bone resorption and promotes osteogenesis, thus playing a role in the maintenance of normal bone metabolism. Because 1α,25D3 plays an important role in osteogenesis, vitamin D formulations, such as alfacalcidol (ALF) and eldecalcitol (ELD), are used for treating osteoporosis. While it is known that, in contrast to ALF, ELD is an active ligand that directly acts on bone, the reason for its superior osteogenesis effects is unknown. Cyp27b1-knockout mice (Cyp27b1-/-mice) are congenitally deficient in 1α,25D3 and exhibit marked hypocalcemia and high parathyroid hormone levels, resulting in osteodystrophy involving bone hypocalcification and growth plate cartilage hypertrophy. However, because the vitamin D receptor is expressed normally in Cyp27b1-/-mice, they respond normally to 1α,25D3. Accordingly, in Cyp27b1-/-mice, the pharmacological effects of exogenously administered active vitamin D derivatives can be analyzed without being affected by 1α,25D3. We used Cyp27b1-/-mice to characterize and clarify the superior osteogenic effects of ELD on the bone in comparison with ALF. The results indicated that compared to ALF, ELD strongly induces ECaC2, calbindin-D9k, and CYP24A1 in the duodenum, promoting Ca absorption and decreasing the plasma concentration of 1α,25D3, resulting in improved osteogenesis. Because bone morphological measurements demonstrated that ELD has stronger effects on bone calcification, trabecular formation, and cancellous bone density than ALF, ELD appears to be a more effective therapeutic agent for treating postmenopausal osteoporosis, in which cancellous bone density decreases markedly. By using Cyp27b1-/-mice, this study was the first to succeed in clarifying the osteogenic effect of ELD without any influence of endogenous 1α,25D3. Furthermore, ELD more strongly enhanced bone mineralization, trabecular proliferation, and cancellous bone density than did ALF. Thus, ELD is expected to show an effect on postmenopausal osteoporosis, in which cancellous bone mineral density decreases markedly. In the future, this study may enable the development of next-generation active vitamin D derivatives with higher affinity for bone than ELD.

Evidence for Ongoing Modeling-Based Bone Formation in Human Femoral Head Trabeculae via Forming Minimodeling Structures: A Study in Patients with Fractures and Arthritis

Bone modeling is a biological process of bone formation that adapts bone size and shape to mechanical loads, especially during childhood and adolescence. Bone modeling in cortical bone can be easily detected using sequential radiographic images, while its assessment in trabecular bone is challenging. Here, we performed histomorphometric analysis in 21 bone specimens from biopsies collected during hip arthroplasty, and we proposed the criteria for histologically identifying an active modeling-based bone formation, which we call a "forming minimodeling structure" (FMiS). Evidence of FMiSs was found in 9 of 20 specimens (45%). In histomorphometric analysis, bone volume was significant higher in specimens displaying FMiSs compared with the specimens without these structures (BV/TV, 31.7 ± 10.2 vs. 23.1 ± 3.9%; p < 0.05). Osteoid parameters were raised in FMiS-containing bone specimens (OV/BV, 2.1 ± 1.6 vs. 0.6 ± 0.3%; p < 0.001, OS/BS, 23.6 ± 15.5 vs. 7.6 ± 4.2%; p < 0.001, and O.Th, 7.4 µm ± 2.0 vs. 5.2 ± 1.0; p < 0.05). Our results showed that the modeling-based bone formation on trabecular bone surfaces occurs even during adulthood. As FMiSs can represent histological evidence of modeling-based bone formation, understanding of this physiology in relation to bone homeostasis is crucial.

Eldecalcitol, an Active Vitamin D3 Derivative, Prevents Trabecular Bone Loss and Bone Fragility in Type I Diabetic Model Rats

Diabetes mellitus is known to adversely affect the bones and be associated with increased fracture risk. We examined whether eldecalcitol (ELD), an active vitamin D₃ derivative, could inhibit the diabetic bone loss in streptozotocin-induced type I diabetic rats. ELD (10, 20, or 40 ng/kg), alfacalcidol (ALF; 25, 50, or 100 ng/kg), or vehicle was administered 5 times per week for 12 weeks from 1 week after diabetes induction. Normal control rats received the vehicle. Bone turnover markers, bone mineral density (BMD), and biomechanical strength of the lumbar spine and femur were measured, and bone histomorphometry was performed. Content of advanced glycation end products (AGEs) in the femoral shaft was also determined. In diabetic rats, serum osteocalcin (OC) concentration was lower and urinary excretion of deoxypyridinoline (DPD) tended to be higher than in normal rats. Areal BMD and maximum load of the lumbar vertebrae and femoral shaft were lower in diabetic rats than in normal rats. All doses of ELD and the highest dose of ALF reduced urinary DPD excretion, but had no effect on serum OC. The 20 and 40 ng/kg doses of ELD prevented decreases in BMD and the highest dose of ELD prevented the reduction in maximum load of the lumbar vertebrae, while ALF did not change these parameters. ELD and ALF did not affect areal BMD or biomechanical strength of the femoral shaft. In diabetic rats, bone volume and trabecular thickness in the trabecular bone of the lumbar vertebrae decreased and trabecular separation increased compared to normal rats. ELD and ALF prevented diabetes-induced deterioration of trabecular microstructure. AGE content in the femoral cortical bone increased in the diabetic rats, and ELD and ALF did not change AGE content compared to the diabetic rats. These results indicated that ELD suppressed bone resorption and prevented trabecular bone loss and deterioration of trabecular microstructure, resulting in prevention of reduction in biomechanical strength in type I diabetic rats.

Comparison of the effects of denosumab between a native vitamin D combination and an active vitamin D combination in patients with postmenopausal osteoporosis

The aim of this 12-month, retrospective study was to compare the effects of denosumab (DMAb; 60 mg subcutaneously every 6 months) plus native vitamin D (VD) (cholecalciferol) combination therapy with DMAb plus active VD analog (alfacalcidol) combination therapy in patients with postmenopausal osteoporosis. Patients [N = 127; mean age 75.6 years (range 58-93 years); 28 treatment-naïve patients, 59 patients treated with oral bisphosphonate therapy, 40 patients treated with teriparatide daily] were allocated to either (1) the DMAb plus native VD group (n = 60; cholecalciferol, 10 μg, plus calcium, 610 mg/day; 13 treatment-naïve patients, 28 patients treated with oral bisphosphonate therapy, and 19 patients treated with teriparatide daily) or (2) the DMAb plus active VD group [n = 67; alfacalcidol, 0.8 ± 0.0 μg, plus calcium, 99.2 ± 8.5 mg/day; 15 treatment-naïve patients, 31 patients treated with oral bisphosphonate therapy, and 21 patients treated with teriparatide daily) on the basis of each physician's decision. Changes in bone mineral density (BMD), serum bone turnover marker levels, and fracture incidence were monitored every 6 months. There were no significant differences in baseline age, BMD, bone turnover marker levels, and prior treatments between the two groups. After 12 months, compared with the DMAb plus native VD group, the DMAb plus active VD group showed similar increases in the BMD of the lumbar spine (6.4% vs 6.5%) and total hip (3.3% vs 3.4%), but significantly greater increases in the BMD of the femoral neck (1.0% vs 4.9%, P < 0.001) and the distal part of the forearm (third of radius) (-0.8% vs 3.9%, P < 0.01). These tendencies were similar regardless of the differences in the prior treatments. The rates of decrease of bone turnover marker levels were similar for tartrate-resistant acid phosphatase isoform 5b (-49.0% vs -49.0%), procollagen type I N-terminal propeptide (-45.9% vs -49.3%), and undercarboxylated osteocalcin (-56.0  vs -66.5%), whereas serum intact parathyroid hormone levels were significantly lower in the DMAb plus active VD group (47.6 pg/mL vs 30.4 pg/mL, P < 0.001). The rate of hypocalcemia was 1.7% in the DMAb plus native VD group and 1.5% in the DMAb plus active VD group, and the rate of clinical fracture incidence was 8.3% in the DMAb plus native VD group and 4.5% in the DMAb plus active VD group, with no significant difference between the groups. DMAb with active VD combination therapy may be a more effective treatment option than DMAb with native VD combination therapy in terms of increasing BMD of the femoral neck and distal part of the forearm and also maintaining serum intact parathyroid hormone at lower levels.

Histomorphometric analysis of minimodeling in the vertebrae in postmenopausal patients treated with anti-osteoporotic agents

Minimodeling is a type of focal bone formation that is characterized by the lack of precedent bone erosion by osteoclasts. Although this form of bone formation has been described for more than a decade, how anti-osteoporotic agents that are currently used in clinical practice affect the kinetics of minimodeling is not fully understood. We performed a bone morphometric analysis using human vertebral specimens collected from postmenopausal patients who underwent spinal surgery. Patients were divided into three groups according to osteoporosis medication; non-treated, Eldecalcitol (ELD, a vitamin D derivative that has recently been approved to treat patients with osteoporosis in Japan)-treated, and bisphosphonate-treated groups. Five to six patients were enrolled in each group. There was a trend toward enhanced minimodeling in ELD-treated patients and suppressed of it in bisphosphonate-treated patients compared with untreated patients. The differences of minimodeling activity between ELD-treated and bisphosphonate-treated patients were statistically significant. The present study suggests that ELD and bisphosphonates have opposite effects on minimodeling from one another, and show that minimodeling also takes place in vertebrae as has been described for the ilium and femoral head in humans.

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We aimed to evaluate the potential effects of a new vitamin D3 analog, Eldecalcitol and BPs on minimodeling in humans using surgical specimens.

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We found that minimodeling is readily observed in the humans.

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We found that patients who had been treated with Eldecalcitol prior to surgery tend to have increased minimodeling activity.

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Our data indicate that Eldecalcitol can activate minimodeling in patients with post-menopausal osteoporosis while bisphosphonates have negative or little impact on this form of bone formation.

Treatment with the combination of ibandronate plus eldecalcitol has a synergistic effect on inhibition of bone resorption without suppressing bone formation in ovariectomized rats

Bisphosphonates are widely used in the treatment of osteoporosis and contribute to the reduction of bone fractures. Ibandronate (IBN) is a highly potent, nitrogen-containing bisphosphonate, which is administered orally or intravenously at extended dosing intervals. Vitamin D or active vitamin D3 derivatives are also used in the treatment of osteoporosis, and are often used in combination with other drugs. In this study, we investigated the effect of treatment with the combination of once-monthly s.c. dosing of IBN plus once-daily oral eldecalcitol (ELD), an active vitamin D3 derivative, using aged ovariectomized (OVX) rats. Treatment was started the day after OVX, and analyses were performed 4, 8, and 12 weeks thereafter by determination of bone markers, bone mineral density, biomechanical properties, and histomorphometry. The combination treatment showed a synergistic effect in increasing both lumbar and femoral BMD, and resulted in a significant increase in bone ultimate load. The combination of IBN plus ELD acted synergistically to reduce bone resorption, whereas bone formation did not decrease any more than with monotherapy with either IBN or ELD. Bone formation independent of bone resorption (a process known as 'minimodeling') was not changed in vehicle treated OVX rats despite the increase in bone turnover. ELD upregulated minimodeling, which was however not diminished in the combination treatment. In conclusion, treatment with the combination of IBN plus ELD was beneficial in the treatment of osteoporosis in aged OVX rats. It exhibited a synergistic inhibitory effect on bone resorption and keeps bone formation at the level of sham controls. This uncoupling of bone resorption/bone formation was affected, to some extent, by minimodeling-based bone formation which is independent of bone resorption. This combination regimen which showed synergistic effect on BMD and bone ultimate load without inhibition of bone formation may be beneficial in long-term osteoporosis treatment to prevent bone fractures.

Effects of eldecalcitol on cortical bone response to mechanical loading in rats

Background

Mechanical loading of bones activates modeling and suppresses remodeling by promoting bone formation. Eldecalcitol is approved for the treatment of osteoporosis in Japan and is often used in patients undergoing exercise therapy. However, the effects of eldecalcitol on bone formation during mechanical loading are unknown. The aim of this study was to clarify the influence of eldecalcitol administration on bone response to mechanical loading using a four-point bending device.

Methods

Forty six-month-old female Wistar rats were randomized into four groups based on eldecalcitol dose (vehicle administration (VEH), low dose (ED-L), medium dose (ED-M), and high dose (ED-H)). Loads of 38 N were applied in vivo to the right tibia for 36 cycles at 2 Hz, by four-point bending, 3 days per week for 3 weeks. After calcein double-labeling, rats were sacrificed and tibial cross sections were prepared from the region with maximal bending at the central diaphysis. Histomorphometry was performed on the entire periosteal and endocortical surface of the tibiae, dividing the periosteum into lateral and medial surfaces.

Results

The effects of external loading on bone formation parameters were significant at all three surfaces. Bone formation parameters were highest in the ED-H group, and the effects of eldecalcitol on bone formation rate were significant at the endocortical surface. In addition, the interaction between loading and eldecalcitol dose significantly affected bone formation rate at the endocortical surface.

Conclusions

Eldecalcitol enhanced the cortical bone response to mechanical loading and a synergistic effect was observed in a rat model.

Monitoring in vivo (re)modeling: a computational approach using 4D microCT data to quantify bone surface movements

Bone undergoes continual damage repair and structural adaptation to changing external loads with the aim of maintaining skeletal integrity throughout life. The ability to monitor bone (re)modeling would allow for a better understanding in how various pathologies and interventions affect bone turnover and subsequent bone strength. To date, however, current methods to monitor bone (re)modeling over time and in space are limited. We propose a novel method to visualize and quantify bone turnover, based on in vivo microCT imaging and a 4D computational approach. By in vivo tracking of spatially correlated formation and resorption sites over time it classifies bone restructuring into (re)modeling sequences, the spatially and temporally linked sequences of formation, resorption and quiescent periods on the bone surface. The microCT based method was validated using experimental data from an in vivo mouse tibial loading model and ex vivo data of the mouse tibia. In this application, the method allows the visualization of time-resolved cortical (re)modeling and the quantification of short-term and long-term modeling on the endocortical and periosteal surface at the mid-diaphysis of loaded and control mice tibiae. Both short-term and long-term modeling processes, independent formation and resorption events, could be monitored and modeling (spatially not correlated formation and resorption) and remodeling (resorption followed by new formation at the same site) could be distinguished on the bone surface. This novel method that combines in vivo microCT with a computational approach is a powerful tool to monitor bone turnover in animal models now and is waiting to be applied to human patients in the near future.

Treatment with eldecalcitol positively affects mineralization, microdamage, and collagen crosslinks in primate bone

Eldecalcitol (ELD), an active form of vitamin D analog approved for the treatment of osteoporosis in Japan, increases lumbar spine bone mineral density (BMD), suppresses bone turnover markers, and reduces fracture risk in patients with osteoporosis. We have previously reported that treatment with ELD for 6 months improved the mechanical properties of the lumbar spine in ovariectomized (OVX) cynomolgus monkeys. ELD treatment increased lumbar BMD, suppressed bone turnover markers, and reduced histomorphometric parameters of both bone formation and resorption in vertebral trabecular bone. In this study, we elucidated the effects of ELD on bone quality (namely, mineralization, microarchitecture, microdamage, and bone collagen crosslinks) in OVX cynomolgus monkeys in comparison with OVX-vehicle control monkeys. Density fractionation of bone powder prepared from lumbar vertebrae revealed that ELD treatment shifted the distribution profile of bone mineralization to a higher density, and backscattered electron microscopic imaging showed improved trabecular bone connectivity in the ELD-treated groups. Higher doses of ELD more significantly reduced the amount of microdamage compared to OVX-vehicle controls. The fractionated bone powder samples were divided according to their density, and analyzed for collagen crosslinks. Enzymatic crosslinks were higher in both the high-density (≥2.0 mg/mL) and low-density (<2.0 mg/mL) fractions from the ELD-treated groups than in the corresponding fractions in the OVX-vehicle control groups. On the other hand, non-enzymatic crosslinks were lower in both the high- and low-density fractions. These observations indicated that ELD treatment stimulated the enzymatic reaction of collagen crosslinks and bone mineralization, but prevented non-enzymatic reaction of collagen crosslinks and accumulation of bone microdamage. Bone anti-resorptive agents such as bisphosphonates slow down bone remodeling so that bone mineralization, bone microdamage, and non-enzymatic collagen crosslinks all increase. Bone anabolic agents such as parathyroid hormone decrease bone mineralization and bone microdamage by stimulating bone remodeling. ELD did not fit into either category. Histological analysis indicated that the ELD treatment strongly suppressed bone resorption by reducing the number of osteoclasts, while also stimulating focal bone formation without prior bone resorption (bone minimodeling). These bidirectional activities of ELD may account for its unique effects on bone quality.

Beneficial effects of calcitriol on hypertension, glucose intolerance, impairment of endothelium-dependent vascular relaxation, and visceral adiposity in fructose-fed hypertensive rats

Besides regulating calcium homeostasis, the effects of vitamin D on vascular tone and metabolic disturbances remain scarce in the literature despite an increase intake with high-fructose corn syrup worldwide. We investigated the effects of calcitriol, an active form of vitamin D, on vascular relaxation, glucose tolerance, and visceral fat pads in fructose-fed rats. Male Wistar-Kyoto rats were divided into 4 groups (n = 6 per group). Group Con: standard chow diet for 8 weeks; Group Fru: high-fructose diet (60% fructose) for 8 weeks; Group Fru-HVD: high-fructose diet as Group Fru, high-dose calcitriol treatment (20 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding; and Group Fru-LVD: high-fructose diet as Group Fru, low-dose calcitriol treatment (10 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding. Systolic blood pressure was measured twice a week by the tail-cuff method. Blood was examined for serum ionized calcium, phosphate, creatinine, glucose, triglycerides, and total cholesterol. Intra-peritoneal glucose intolerance test, aortic vascular reactivity, the weight of visceral fat pads, adipose size, and adipose angiotensin II levels were analyzed at the end of the study. The results showed that the fructose-fed rats significantly developed hypertension, impaired glucose tolerance, heavier weight and larger adipose size of visceral fat pads, and raised adipose angiotensin II expressions compared with the control rats. High- and low-dose calcitriol reduced modestly systolic blood pressure, increased endothelium-dependent aortic relaxation, ameliorated glucose intolerance, reduced the weight and adipose size of visceral fat pads, and lowered adipose angiotensin II expressions in the fructose-fed rats. However, high-dose calcitriol treatment mildly increased serum ionized calcium levels (1.44 ± 0.05 mmol/L). These results suggest a protective role of calcitriol treatment on endothelial function, glucose tolerance, and visceral adiposity in fructose-fed rats.

Long-term treatment with eldecalcitol (1α, 25-dihydroxy-2β- (3-hydroxypropyloxy) vitamin D3) suppresses bone turnover and leads to prevention of bone loss and bone fragility in ovariectomized rats

The purpose of this study is to estimate the efficacy of eldecalcitol (1α, 25-Dihydroxy-2β- (3-hydroxypropyloxy) vitamin D3; ELD) on bone metabolism after long-term administration. Six-month-old Wistar-Imamichi rats were ovariectomized (OVX) and administered ELD orally at doses of 7.5, 15, or 30 ng/kg daily. Bone mineral density (BMD), urinary excretion of deoxypyridinoline (DPD), a bone resorption marker, and serum total alkaline phosphatase (ALP), a surrogate marker of bone formation, were assessed after 3, 6, and 12 months of treatment. After 12 months of treatment, the biomechanical strength of the L4 lumbar vertebra and femoral shaft was measured, and bone histomorphometry was performed on the L3 lumbar vertebra and the tibia diaphysis. ELD prevented OVX-induced decreases in BMD of the lumbar vertebrae and femur throughout the treatment period. ELD significantly suppressed OVX-induced increases in urinary DPD excretion throughout the treatment period with minimal effects on ALP. OVX resulted in significant decreases in ultimate load and stiffness of the L4 lumbar vertebra and femoral shaft, and ELD significantly prevented the reduction in these biomechanical parameters. Bone histomorphometry at the L3 lumbar vertebra revealed that OVX induced increases in bone resorption parameters (osteoclast surface and osteoclast number) and bone formation parameters (osteoblast surface, osteoid surface, and bone formation rate), and ELD suppressed these parameters after 12 months treatment. Activation frequency, which was elevated in the OVX/vehicle group, was significantly suppressed to baseline levels in ELD-treated groups, indicating that ELD maintained bone turnover at a normal level. ELD also prevented OVX-induced deterioration of microstructure in trabecular and cortical bone. These results indicated that long-term treatment of OVX rats with ELD suppressed bone turnover, and prevented OVX-induced bone loss, deterioration of bone microstructure, and reduction in bone biomechanical strength.

Local administration of calcitriol positively influences bone remodeling and maturation during restoration of mandibular bone defects in rats

The aim of this study was to investigate the influence of calcitriol on osteoinduction following local administration into mandibular bone defects. Calcitriol-loaded absorbable collagen membrane scaffolds were prepared using the polydopamine coating method and characterized by scanning electron microscopy. Composite scaffolds were implanted into rat mandibular bone defects in the following groups: no graft material (control), bare collagen membrane (CM group), collagen membrane bearing polydopamine coating (DOP/CM group), and collagen membrane bearing polydopamine coating absorbed with calcitriol (CAL/DOP/CM group). At 1, 2, 4 and 8weeks post-surgery, the osteogenic potential of calcitriol was examined by histological and immunohistochemical methods. Following in vivo implantation, calcitriol-loaded composite scaffolds underwent rapid degradation with pronounced replacement by new bone and induced reunion of the bone marrow cavity. Calcitriol showed strong potential in inhibiting osteoclastogenesis and promotion of osteogenic differentiation at weeks 1, and 2. Furthermore, statistical analysis revealed that the newly formed bone volume in the CAL/DOP/CM group was significantly higher than other groups at weeks 1, and 2. At weeks 4, and 8, the CAL/DOP/CM group showed more mineralized bone and uniform collagen structure. These data suggest that local administration of calcitriol is promising in promoting osteogenesis and mineralization for restoration of mandibular bone defects.

Nanoparticulate drug delivery platforms for advancing bone infection therapies

INTRODUCTION

The ongoing surge of resistance of bacterial pathogens to antibiotic therapies and the consistently aging median member of the human race signal an impending increase in the incidence of chronic bone infection. Nanotechnological platforms for local and sustained delivery of therapeutics hold the greatest potential for providing minimally invasive and maximally regenerative therapies for this rare but persistent condition.

AREAS COVERED

Shortcomings of the clinically available treatment options, including poly(methyl methacrylate) beads and calcium sulfate cements, are discussed and their transcending using calcium-phosphate/polymeric nanoparticulate composites is foreseen. Bone is a composite wherein the weakness of each component alone is compensated for by the strength of its complement and an ideal bone substitute should be fundamentally the same.

EXPERT OPINION

Discrepancy between in vitro and in vivo bioactivity assessments is highlighted, alongside the inherent imperfectness of the former. Challenges entailing the cross-disciplinary nature of engineering a new generation of drug delivery vehicles are delineated and it is concluded that the future for the nanoparticulate therapeutic carriers belongs to multifunctional, synergistic and theranostic composites capable of simultaneously targeting, monitoring and treating internal organismic disturbances in a smart, feedback fashion and in direct response to the demands of the local environment.

Eldecalcitol improves mechanical strength of cortical bones by stimulating the periosteal bone formation in the senescence-accelerated SAM/P6 mice - a comparison with alfacalcidol

Eldecalcitol (ELD), a 2β-hydroxypropyloxy derivative of 1α,25(OH)2D3, is a potent inhibitor of bone resorption that has demonstrated a greater effect at reducing the risk of fracture in osteoporotic patients than alfacalcidol (ALF). In the present study, we used the senescence-accelerated mouse strain P6 (SAM/P6), which has low bone mass caused by osteoblast dysfunction, to evaluate the effect of ELD on cortical bone in comparison with ALF. Four-month-old SAM/P6 mice were given either ELD (0.025 or 0.05μg/kg) or ALF (0.2 or 0.4μg/kg) by oral gavage 5 times/week for 6 weeks. Both ELD and ALF increased serum calcium (Ca) in a dose-dependent manner. Serum Ca levels in the ELD 0.05μg/kg group were comparable to those of the ALF 0.2μg/kg group. ELD 0.05μg/kg significantly improved the bone biomechanical properties of the femur compared with the vehicle control group (p<0.001) and the ALF 0.2μg/kg group (p<0.05) evaluated by 3-point bending test. The cortical area of the mid-femur in the ELD 0.05μg/kg group but not the ALF 0.2μg/kg group was significantly higher than those of the vehicle control group (p<0.001). Bone histomorphometry revealed that in the femoral endocortical surface, the suppression of bone resorption parameters (N.Oc/BS) and bone formation parameters (MS/BS) by ELD (0.05μg/kg) was greater than that by ALF (0.2μg/kg). In contrast, in the femoral periosteal surface, ELD 0.05μg/kg significantly increased bone formation parameters (BFR/BS, MS/BS) compared with the vehicle control group (p<0.05, p<0.01, respectively), whereas ALF 0.2μg/kg did not alter these parameters. These results indicate that ELD improved the biomechanical properties of femoral cortical bone not only by inhibiting endocortical bone resorption but also by stimulating the periosteal bone formation in SAM/P6 mice. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Multifunctional and potent roles of the 3-hydroxypropoxy group provide eldecalcitol's benefit in osteoporosis treatment

Eldecalcitol (1α,25-dihydroxy-2β-(3-hydroxypropoxy)vitamin D3, [developing code: ED-71]), a new osteoporosis treatment drug that was recently approved in Japan, is a best-in-class drug in the class of calcitriol (1α,25-dihydroxyvitamin D3) and its prodrug alfacalcidol (1α-hydroxyvitamin D3), which have been used to treat osteoporosis for 30 years. In a comparative Phase III clinical study with alfacalcidol in osteoporosis patients, eldecalcitol demonstrated superior efficacy in the endpoints of increment of bone mineral density and reduction of bone fracture with equivalent safety to alfacalcidol. Eldecalcitol was discovered by searching synthetic analogs of calcitriol and alfacalcidol, and its main structural characteristic is having the 3-hydroxypropoxy group at the 2β-position. This review discusses why introducing the group leads to excellent efficacy and safety in osteoporosis treatment and elucidates the functional roles of the 3-hydroxypropoxy group. Briefly, the functional roles of the group are, first, realizing the metabolism switching in which eldecalcitol shows resistance to CYP24A1 and is metabolized in the liver; second, increasing the affinity to the serum carrier protein and prolonging the half-life to 53h; and third, stabilizing the eldecalcitol-receptor complex. Taken together, these functional roles of the 3-hydroxypropoxy group are beneficial in osteoporosis treatment. This review attempts to give a detailed account of the mode of action of eldecalcitol by clarifying these multifunctional roles of the 3-hydroxypropoxy group from the medicinal chemist's perspective.

Eldecalcitol for the treatment of osteoporosis

Eldecalcitol (1α, 25-dihydroxy-2β-[3-hydroxypropyloxy] vitamin D₃; ED-71) is a new analog of the active form of vitamin D. Eldecalcitol has recently been approved for the treatment of osteoporosis in Japan. In addition to regulation of calcium metabolism carried out by conventional vitamin D analogs, eldecalcitol possesses a strong inhibitory effect on bone resorption and causes a significant increase in bone mineral density. A Phase III clinical trial on osteoporosis showed that eldecalcitol reduced the incidence of new vertebral fractures over 3 years by 26% compared with alfacalcidol. Although the overall risk of nonvertebral fractures was not reduced by eldecalcitol, the risk of wrist fracture was decreased significantly in the eldecalcitol group (71%) compared with the alfacalcidol group. The serum level of 25-hydroxyvitamin D (25[OH]D) was normalized by supplementation of native vitamin D in this trial, so the desirable effects on bone by eldecalcitol were considered to be derived from its distinctive pharmacological action. Increased blood calcium was observed in 21% of patients treated with eldecalcitol, and hypercalcemia (>11.5 mg/dL) occurred in 0.4% of eldecalcitol recipients, so serum calcium concentration should be monitored after starting eldecalcitol treatment. Eldecalcitol has dual effects on the metabolism of bone and calcium and is useful for the treatment of osteoporosis, especially for elderly patients (who frequently suffer from vitamin D deficiency). This article reviews the clinical efficacy and safety of eldecalcitol in the treatment of osteoporosis.

The role of the serum vitamin D binding protein in the actions of the vitamin D analog eldecalcitol (ED-71) on bone and mineral metabolism

The vitamin D analog ED-71 (eldecalcitol) has been shown to be superior to calcitriol and its precursor alfacalcidol in maintaining or increasing bone mass in women and animal models with osteoporosis. The mechanism for the greater effectiveness of ED-71 is unknown. In the present study, we tested the hypothesis that the higher activity of ED-71 is due to its higher affinity for the serum vitamin D binding protein (DBP) by comparing the activities of orally administered ED-71, calcitriol and 22-oxacalcitriol (OCT) in wild type (WT) and DBP-ablated (DBPko) mice. In 8-week-old male WT mice, the effects of the analogs on serum and urinary calcium and phosphate were ED-71 > calcitriol > OCT. The results in DBPko mice were identical to those of the WT mice for all parameters tested. In ovariectomized mice, ED-71 was more effective than calcitriol in increasing bone mineral density, but again, there were no differences in the responses of the WT versus DBPko OVX mice. This lack of an effect of DBP ablation on the activities of oral ED-71 occurred despite the finding that peak circulating levels of ED-71 were 100 times lower and disappeared quickly in the DBPko mice while the peak levels at 1 h in WT mice were maintained for at least 24 h. These findings indicate that although DBP has a major influence on circulating levels of vitamin D compounds, it is not responsible for the greater efficacy of ED-71 on bone and mineral metabolism.