Eldecalcitol is less effective in suppressing parathyroid hormone compared to calcitriol in vivo

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.

Eldecalcitol Causes FGF23 Resistance for Pi Reabsorption and Improves Rachitic Bone Phenotypes in the Male Hyp Mouse

X-linked hypophosphatemia (XLH), the most common form of inheritable rickets, is caused by inactivation of phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) and leads to fibroblast growth factor (FGF) 23-dependent renal inorganic phosphate (Pi) wasting. In the present study, we investigated whether maintaining Pi homeostasis with a potent vitamin D3 analog, eldecalcitol [1α,25-dihydroxy-2β-(3-hydroxypropyloxy) vitamin D3; ED71], could improve hypophosphatemic rickets in a murine model of XLH, the Hyp mouse. Vehicle, ED71, or 1,25-dihydroxyvitamin D was subcutaneously injected five times weekly in wild-type (WT) and Hyp mice for 4 weeks, from 4 to 8 weeks of age. Injection of ED71 into WT mice suppressed the synthesis of renal 1,25-dihydroxyvitamin D and promoted phosphaturic activity. In contrast, administration of ED71 to Hyp mice completely restored renal Pi transport and NaPi-2a protein levels, although the plasma-intact FGF23 levels were further increased. In addition, ED71 markedly increased the levels of the scaffold proteins, renal sodium-hydrogen exchanger regulatory factor 1, and ezrin in the Hyp mouse kidney. Treatment with ED71 increased the body weight and improved hypophosphatemia, the bone volume/total volume, bone mineral content, and growth plate structure in Hyp mice. Thus, ED71 causes FGF23 resistance for phosphate reabsorption and improves rachitic bone phenotypes in Hyp mice. In conclusion, ED71 has opposite effects on phosphate homeostasis in WT and Hyp mice. Analysis of Hyp mice treated with ED71 could result in an additional model for elucidating PHEX abnormalities.

Effects of eldecalcitol on bone and skeletal muscles in glucocorticoid-treated rats

Glucocorticoids cause secondary osteoporosis and myopathy, characterized by type II muscle fiber atrophy. We examined whether a new vitamin D3 analogue, eldecalcitol, could inhibit glucocorticoid-induced osteopenia or myopathy in rats, and also determined the effects of prednisolone (PSL) and/or eldecalcitol on muscle-related gene expression. Six-month-old female Wistar rats were randomized into four groups: PSL group (10 mg/kg PSL); E group (0.05 µg/kg eldecalcitol); PSL + E group; and control group. PSL, eldecalcitol, and vehicles were administered daily for 2 or 4 weeks. Right calf muscle strength, muscle fatigue, cross-sectional areas (CSAs) of left tibialis anterior muscle fibers, and bone mineral density (BMD) were measured following administration. Pax7, MyoD, and myogenin mRNA levels in gastrocnemius muscles were also determined. Muscle strength was significantly higher in the PSL + E group than in the PSL group (p < 0.05) after 4 weeks, but not after 2 weeks. No significant difference in muscle fatigue was seen between groups at 2 or 4 weeks. CSAs of type II muscle fibers were significantly larger in the E group and the PSL + E group than in the PSL group at 4 weeks (p = 0.0093, p = 0.0443, respectively). Eldecalcitol treatment for 4 weeks maintained the same BMD as the PSL + E group. After 2 weeks, but not 4 weeks, eldecalcitol treatment significantly increased Pax7 and myogenin mRNA expression in gastrocnemius muscle, and PSL also stimulated myogenin expression. Eldecalcitol appears to increase muscle volume and to protect against femur BMD loss in PSL-administered rats, and it may also stimulate myoblast differentiation into early myotubes.

Efficacy and safety of eldecalcitol, a new active vitamin D3 analog, in the bone metabolism of postmenopausal women receiving maintenance hemodialysis

Eldecalcitol (ELD), a new active vitamin D3 analog developed in Japan, has attracted attention as an effective osteoporotic therapeutic drug. However, because ELD leads to greater calcium absorption than does conventional active vitamin D3, it has yet to be used in patients with renal insufficiency. Therefore, we evaluated the efficacy and safety of ELD treatment in 27 postmenopausal women receiving maintenance dialysis in our institution and underwent ELD treatment (starting at 0.5 μg/day) for 6 months. The mean serum albumin-corrected calcium (Caalb) level was significantly increased following treatment (9.01 ± 0.60 before versus 9.56 ± 0.55 after treatment, mean ± SD). Severe hypercalcemia was prevented through cessation or adjustment of the dosage of calcium-containing phosphate binders or existing active vitamin D. The mean serum phosphorus and intact parathyroid hormone levels were well-controlled throughout. The median levels of bone turnover markers, bone-specific alkaline phosphatase and tartrate-resistant acid phosphatase-5b were significantly decreased. The mean lumbar spine bone mineral density (BMD) was increased, a significant difference being observed in age-matched Z-scores (-0.60 ± 1.6 versus -0.36 ± 1.5, p = 0.018). The average change in lumbar spine BMD after ELD treatment was 3.10%, and in patients with a T-score of <-4.0, it was 5.63%. There was no effect on forearm BMD. Although this study is based on short-term observation in a single institution, our results suggest that ELD could be used to increase bone density in dialysis patients.

Vitamin D3 analogs for the treatment of osteoporosis

Vitamin D supplementation is recommended whenever patients are given therapeutic drugs for osteoporosis, to make their calcium (Ca) balance positive. Vitamin D is converted to 25-hydroxyvitamin D in the liver, and then activated to become 1α,25-dihydroxyvitamin D in the kidneys. The active vitamin D acts in the intestine to stimulate Ca absorption and maintain the Ca balance. 2β-(3-Hydroxypropyloxy)-1α,25-dihydroxyvitamin D3 (eldecalcitol) and 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D3 (2MD) are newly developed vitamin D analogs, with a substitution at the 2 position of 1α,25-dihydroxyvitamin D3 (calcitriol). Eldecalcitol and 2MD share common structural and biological characteristics. Both compounds increase serum Ca levels more markedly than calcitriol, increase bone mineral density (BMD), and improve bone strength in ovariectomized (OVX) rats. In a randomized, placebo-controlled, double-blind, 1 year clinical trial, eldecalcitol dose-dependently increased lumbar and hip BMD and suppressed bone turnover markers in patients with osteoporosis. Whereas, 2MD markedly increased the bone turnover markers, but it did not change the BMD of postmenopausal women with osteopenia in a 1 year clinical trial. After a randomized, double-blind, 3 year fracture-prevention trial comparing it with alfacalcidol, eldecalcitol was approved for the treatment of osteoporosis in Japan. On the other hand, the manufacturer discontinued the clinical development of 2MD. In this review, we discuss the similarities and differences between these 2 compounds, and the reasons why different outcomes resulted from their clinical trials.

Relationship between the effect of eldecalcitol and serum 25(OH)D level

In previous studies, we demonstrated that 12-month treatment with 0.75μg/day eldecalcitol increased bone mineral density in osteoporotic patients regardless of serum 25-hydroxyvitamin D (25(OH)D) level, and in a 3-year randomized double-blind clinical trial, eldecalcitol significantly reduced the incidences of vertebral and wrist fractures compared to alfacalcidol. However, it remains unclear whether the fracture risk reduction by eldecalcitol is affected by serum 25(OH)D. In the fracture prevention trial, patients with low 25(OH)D level at baseline were supplemented with 400IU/day native vitamin D3. In the current study, patients from that trial were divided according to the tertiles of serum 25(OH)D level at 6 months after treatment initiation. The increases in lumbar and hip BMD by eldecalcitol were significantly higher in all tertiles than those by alfacalcidol. The incidences of vertebral and osteoporotic fractures tended to be lower in each tertile of the eldecalcitol-treated group than in the corresponding tertile of the alfacalcidol-treated group, with the exception of vertebral fractures in the low tertile. We also investigated whether eldecalcitol treatment affected levels of serum 25(OH)D, serum 1,25(OH)2D, and parathyroid hormone in patients without vitamin D supplementation. With eldecalcitol treatment, serum 1,25(OH)2D concentration was reduced by approximately 50%, whereas serum levels of parathyroid hormone and 25(OH)D were not affected. The major findings of the present study were that eldecalcitol did not affect serum 25(OH)D levels, and that it reduced the incidence of osteoporotic fractures and increased BMD in comparison with alfacalcidol regardless of serum 25(OH)D level within the range of serum 25(OH)D concentrations at or higher than 20ng/mL. Whether eldecalcitol is similarly effective at vitamin D deficient serum 25(OH)D levels remains to be clarified. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Vitamin D analogs and bone: preclinical and clinical studies with eldecalcitol

Eldecalcitol [1α,25-dihydroxy-2β-(3-hydroxypropyloxy)vitamin D3] is an analog of 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], bearing a hydroxypropyloxy residue at the 2β position. In preclinical studies, eldecalcitol suppressed bone resorption to a greater extent than alfacalcidol but had a similar effect on bone formation and Ca metabolism, resulting in a greater increase in bone mineral density (BMD) in ovariectomized (OVX) rats. Histological analysis in OVX rats immediately after ovariectomy revealed that eldecalcitol reduced osteoclast number and bone resorption parameters with a decrease in bone formation parameters. Eldecalcitol also promoted focal bone formation independent of bone resorption, a process known as bone minimodeling. In clinical studies, eldecalcitol showed stronger effects than alfacalcidol in increasing BMD and reducing bone resorption markers in osteoporotic patients under vitamin D supplementation. A 3-year randomized, double-blind, active-comparator clinical trial demonstrated that once-daily 0.75 μg eldecalcitol reduced vertebral fracture incidence by 26% compared with 1.0 μg alfacalcidol. Eldecalcitol also reduced the incidence of wrist fractures by 71% compared with alfacalcidol. Although this may be due to the previously reported effect of vitamin D in reducing the incidence of falls, it is not known whether eldecalcitol has a stronger effect in preventing falls than alfacalcidol. Because eldecalcitol stimulates intestinal Ca absorption and improves Ca balance in addition to its skeletal effects, combination treatment with antiresorptive agents may be able to show better effects than native vitamin D and Ca supplementation in preventing fractures in osteoporotic patients. Further studies are warranted to clarify these issues.

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.

Mechanism of inhibitory action of eldecalcitol, an active vitamin D analog, on bone resorption in vivo

Bone-resorbing osteoclasts differentiate from hematopoietic precursors under the strict regulation of bone-forming osteoblasts. Osteoblasts express two cytokines essentially required for osteoclastogenesis; macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor κB ligand (RANKL). Osteoblasts express constitutively M-CSF, and inducibly RANKL in response to bone resorption-stimulating factors. The active form of vitamin D3, 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], is known to be a hormone which enhances RANKL expression in vitro. Nevertheless, Calcitoriol [1α,25(OH)2D3] and its prodrug, Alfacalcidol (1α-hydroxyvitamin D3) have been taken as therapeutic drugs in osteoporotic patients in Japan. In addition, Eldecalcitol [2β-(3-hydroxypropoxy)-1α,25(OH)2D3], a new analog of 1α,25(OH)2D3, was approved as a therapeutic agent for osteoporosis in Japan in 2011. Interestingly, those vitamin D compounds increased bone mineral density due to the suppression of bone resorption in vivo. We previously showed that cycle-arrested quiescent osteoclast precursors (QOPs) were the direct osteoclasts precursors in vivo. We then investigated effects of daily administration of Eldecalcitol on bone resorption in mice. Bone mineral density was increased through the suppression of RANKL expression in osteoblasts in mice treated with Eldecalcito. The number of QOPs remained unchanged in bone. These results suggest that a long-term exposure of osteoblasts to vitamin D compounds down-regulate RANKL expression. This article is part of a Special Issue entitled '15th Vitamin D Workshop'.

Eldecalcitol: newly developed active vitamin D(3) analog for the treatment of osteoporosis

INTRODUCTION

Eldecalcitol is an active vitamin D(3) analog, characterized by high stability in the circulation and also in the peripheral tissues, and by strong activity in increasing bone mass in osteoporotic patients. The objective of the present review was to evaluate the effect of eldecalcitol on bone compared with active vitamin D or placebo in preclinical and clinical studies.

AREAS COVERED

Eldecalcitol increased bone mineral density and reduced bone turnover markers greater than alfacalcidol and placebo. Interestingly, in a 3-year clinical trial, bone resorption marker remained suppressed during the eldecalcitol treatment, whereas bone formation markers gradually recovered after initial suppression. The incidences of vertebral fractures and wrist fractures in eldecalcitol-treated group were significantly lower than those in alfacalcidol-treated group by 26 and 71%, respectively. In the patients whose baseline bone turnover was low, eldecalcitol treatment did not further suppress bone turnover markers during the 3-year treatment period.

EXPERT OPINION

Eldecalcitol reduced wrist fractures much greater than alfacalcidol and one of the reasons may be a stronger effect of eldecalcitol on preventing falls. Although the effect of eldecalcitol on bone turnover markers was stronger than that of alfacalcidol or placebo, eldecalcitol is not a mere antibone resorptive agent, rather act as a bone turnover modulator.

Daily administration of eldecalcitol (ED-71), an active vitamin D analog, increases bone mineral density by suppressing RANKL expression in mouse trabecular bone

Eldecalcitol (ED-71) is a new vitamin D₃ derivative recently approved for the treatment of osteoporosis in Japan. Previous studies have shown that the daily administration of ED-71 increases bone mineral density (BMD) by suppressing bone resorption in various animal models. In this study, we examined how ED-71 suppresses bone resorption in vivo, by analyzing bone histomorphometry and ex vivo osteoclastogenesis assays. Daily administration of ED-71 (50 ng/kg body weight) to 8-week-old male mice for 2 and 4 weeks increased BMD in the femoral metaphysis without causing hypercalcemia. Bone and serum analyses revealed that ED-71 inhibited bone resorption and formation, indicating that the increase in BMD is the result of the suppression of bone resorption. This suppression was associated with a decrease in the number of osteoclasts in trabecular bone. We previously identified cell cycle-arrested receptor activator of NF-κB (RANK)-positive bone marrow cells as quiescent osteoclast precursors (QOPs) in vivo. Daily administration of ED-71 affected neither the number of RANK-positive cells in vivo nor the number of osteoclasts formed from QOPs in ex vivo cultures. In contrast, ED-71 suppressed the expression of RANK ligand (RANKL) mRNA in femurs. Immunohistochemical experiments also showed that the perimeter of the RANKL-positive cell surface around the trabecular bone was significantly reduced in ED-71-treated mice than in the control mice. ED-71 administration also increased BMD in 12-week-old ovariectomized mice, through the suppression of RANKL expression in the trabecular bone. These results suggest that the daily administration of ED-71 increases BMD by suppressing RANKL expression in trabecular bone in vivo.

The vitamin D analog 1α,25-Dihydroxy-2β-(3-Hydroxypropyloxy) vitamin D(3) (Eldecalcitol) is a potent regulator of calcium and phosphate metabolism

The vitamin D analog 1α,25-dihydroxy-2β-(3-hydroxypropyloxy)vitamin D(3) (ED-71 or eldecalcitol) has been developed for treatment of osteoporosis, but its effects on mineral metabolism have not been investigated in detail. In the present study, we compared the effects of eldecalcitol and calcitriol on calcium (Ca) and phosphate (Pi) handling in rats. Oral administration of eldecalcitol (0, 7.5, 20, or 50 pmol) q.o.d. for 2 weeks dose-dependently increased ionized Ca, intestinal Ca absorption, and urinary Ca excretion, while these doses of calcitriol had no significant effects. The highest dose of eldecalcitol did not alter serum Pi but stimulated both intestinal Pi absorption and urinary Pi excretion; the latter was attributable, in part, to increased serum FGF-23. The effects of high-dose eldecalcitol on Ca and Pi absorption and urinary excretion and FGF-23 persisted for several days following cessation of treatment. The higher potency of eldecalcitol on Ca and Pi handling was also observed in parathyroidectomized rats infused with PTH, excluding a role for differential regulation of PTH. Direct measurement of duodenal Ca absorption by the in situ loop method confirmed the higher potency of eldecalcitol in this segment via induction of TRPV6. These studies indicated that with chronic administration eldecalcitol is more potent than calcitriol at stimulating intestinal absorption of Ca and Pi, as well as FGF-23. The mechanisms responsible for the higher potency of eldecalcitol are speculated to be its higher vitamin D-binding protein (DBP) affinity and resistance to metabolism.