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

Serum homocysteine levels are affected by renal function during a 3-year period of minodronate therapy in female osteoporotic patients

Serum homocysteine is a possible marker to indicate bone quality. However, it is not clear whether changes are seen in serum homocysteine levels with long-term bisphosphonate therapy. We aimed to investigate the factors affecting serum homocysteine levels during a 3-year period of monthly minodronate therapy in osteoporotic women, and to examine if the serum homocysteine levels could reflect some aspects of bone metabolism. The study included 43 patients (age 72.3 ± 7.0 years) undergoing treatment for osteoporosis for the first time (New group) and 35 patients (age 74.4 ± 8.2 years) who switched from alendronate or risedronate to minodronate (Switch group). Minodronate (50 mg/every 4 weeks) was administered for 36 months. Lumbar, femoral neck, and total hip bone mineral densities (BMD), and serum homocysteine levels were monitored at baseline and after 9, 18, 27, and 36 months of treatment. Lumbar BMD increased significantly in both groups (New group 11.4%, Switch group 6.2%). However, femoral neck and total hip BMDs increased only in the New group (femoral neck 3.6%, total hip 4.1%). Serum homocysteine levels increased significantly at 18 and 27 months in all subjects. Multiple linear regression analysis revealed that changes in homocysteine levels during 18, 27, and 36 months significantly correlated with changes in creatinine clearance during the same corresponding periods (18 months: B = - 0.472, p = 0.003; 27 months: B = - 0.375, p = 0.021; 36 months: B = - 0.445, p = 0.012). Thus, serum homocysteine levels possibly reflect renal function instead of bone metabolism during minodronate therapy.

Minodronate for the treatment of osteoporosis

Minodronate is a third-generation bisphosphonate that was developed and approved for clinical use in osteoporosis therapy in Japan. The mechanism of action for suppressing bone resorption is the inhibition of farnesyl pyrophosphate synthase, a key enzyme in the mevalonic acid metabolic pathway of osteoclasts, to induce apoptosis of the cells. Minodronate is the strongest inhibitor of bone resorption among the currently available oral bisphosphonates. Large randomized, placebo-controlled, double-blind clinical trials have revealed an increase in bone mineral density of both the lumbar spine and femoral neck over 3 years of daily minodronate therapy and risk reduction in vertebral fractures over 2 years of therapy. The increase in bone mass and the prevention of vertebral fractures are similar to those with alendronate or risedronate. The incidence of adverse events, especially gastrointestinal disturbance, is the same as or less than that with weekly or daily alendronate or risedronate. The unique mechanism of action of minodronate via the inhibition of the P2X(2/3) receptor compared with other bisphosphonates may be an advantage in reducing low back pain in patients with osteoporosis. The monthly regimen of minodronate, introduced in 2011, is expected to have better patient adherence and longer persistence. In experimental animal models, minodronate preserved, or even ameliorated, bone microarchitectures, including microcracks and perforation of the trabeculae in the short term. The lowest incidence of bisphosphonate-related osteonecrosis of the jaw among all bisphosphonates and the lack of atypical femoral fractures attributed to its use to date, however, are partly because only a smaller population used minodronate than those using other bisphosphonates. To date, minodronate is available only in Japan. Hip fracture risk reduction has not been verified yet. More clinical studies on minodronate and its use in osteoporosis treatment, with a large number of subjects, should be conducted to verify hip fracture risk reduction and long-term results.

Changes of bone mineral density and serum pentosidine during a 27-month follow-up of monthly minodronate in osteoporotic patients

PURPOSE

Monthly regimen of minodronate for osteoporosis more than two years has not been reported yet. The aim of this study is to elucidate the effect of monthly minodronate (M-MIN) on bone mineral density (BMD) and serum pentosidine (Pen) during 27 months.

MATERIALS AND METHODS

The study consisted of 52 newly treated patients (73.3 ± 8.8 years) (new group) and 47 patients (75.9 ± 9.5 years) who were switched from either alendronate or risedronate (switch group). Monthly minodronate (50 mg/every 4 weeks) was administered for 27 months. Lumbar, femoral neck, and total hip BMDs and serum pentosidine were monitored at baseline and after 9, 18, and 27 months of treatment.

RESULTS

In the new condition, lumbar, neck, and total hip BMDs increased significantly by 9.07%, 3.15%, and 3.06%, respectively. Only the lumbar BMD significantly increased in the switch condition. Serum Pen increased in both groups in a time-dependent manner. In the group switch, multivariate logistic regression analysis revealed that the initial change in serum intact procollagen type I N-terminal propeptide (P1NP) at 9 months was an independent predictor of changes in neck and total hip BMDs at 27 months (OR = 1.039, 95% CI 1.003-1.077, p = 0.032 for neck and OR = 1.055, 95% CI 1.009-1.104, p = 0.020 for total hip).

CONCLUSIONS

Monthly minodronate treatment increased BMDs in newly treated patients over 27 months. Serum Pen increased with M-MIN therapy, possibly indicating prolonged bone turnover. The initial 9-month changes in serum P1NP predicted the 27-month changes in hip BMDs when M-MIN replaced alendronate or risedronate.

Localization of Minodronate in Mouse Femora Through Isotope Microscopy

Minodronate is highlighted for its marked and sustained effects on osteoporotic bones. To determine the duration of minodronate's effects, we have assessed the localization of the drug in mouse bones through isotope microscopy, after labeling it with a stable nitrogen isotope ([(15)N]-minodronate). In addition, minodronate-treated bones were assessed by histochemistry and transmission electron microscopy (TEM). Eight-week-old male ICR mice received [(15)N]-minodronate (1 mg/kg) intravenously and were sacrificed after 3 hr, 24 hr, 1 week, and 1 month. Isotope microscopy showed that [(15)N]-minodronate was present mainly beneath osteoblasts rather than nearby osteoclasts. At 3 hr after minodronate administration, histochemistry and TEM showed osteoclasts with well-developed ruffled borders. However, osteoclasts were roughly attached to the bone surfaces and did not feature ruffled borders at 24 hr after minodronate administration. The numbers of tartrate-resistant acid phosphatase-positive osteoclasts and alkaline phosphatase-reactive osteoblastic area were not reduced suddenly, and apoptotic osteoclasts appeared in 1 week and 1 month after the injections. Von Kossa staining demonstrated that osteoclasts treated with minodronate did not incorporate mineralized bone matrix. Taken together, minodronate accumulates in bone underneath osteoblasts rather than under bone-resorbing osteoclasts; therefore, it is likely that the minodronate-coated bone matrix is resistant to osteoclastic resorption, which results in a long-lasting and bone-preserving effect.

Attenuation of Antiresorptive Action in Withdrawal of Minodronic Acid for Three Months After Treatment for Twelve Months in Ovariectomized Rats

The purpose of this study was to evaluate the effects of withdrawal of minodronic acid (MIN) for 3 months after 12 months of treatment in ovariectomized (OVX) rat. OVX rats were orally treated with MIN (6, 30, and 150 µg/kg/day) for 12 months and necropsied on the day after the last dosing or following 3 months of withdrawal. Lumbar and femoral BMD were decreased in OVX controls. MIN dose-dependently increased BMD. Withdrawal eliminated the effect of MIN on BMD loss after treatment at 6 µg/kg, but not after treatment at 30 and 150 µg/kg. In MIN-treated rats, trabecular thinning occurred during withdrawal after treatment at 6 µg/kg, but the trabecular microstructure was maintained at 30 and 150 µg/kg. In a mechanical test of the femoral diaphysis, stiffness of in OVX controls was decreased but ultimate load was similar to that in sham after withdrawal. MIN increased ultimate load and stiffness, but endosteal length decreased after withdrawal. Suppression of bone turnover by MIN based on bone turnover markers and histomorphometric indices was attenuated by withdrawal after treatment at 6 and 30 µg/kg and partially at 150 µg/kg. The MIN concentration in the humerus decreased during withdrawal, and half-life at 30 µg/kg was shorter than that at 150 µg/kg. These results show that the antiresorptive action of MIN was dose-dependently attenuated by 3-month withdrawal in a rat OVX model. An absence of BMD increase was only observed at a low dose but decreases in antiresorptive activity occurred over a wide dose range.

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.