Localization of Minodronate in Mouse Femora Through Isotope Microscopy

Abstract

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.

Osteocytic Osteolysis in PTH-treated Wild-type and Rankl−/− Mice Examined by Transmission Electron Microscopy, Atomic Force Microscopy, and Isotope Microscopy

“…Serial semi-thin sections of epoxy resin-embedded, undecalcified specimens of the middle region of tibial cortical bones were alternately mounted on silicon wafers and glass slides. Semi-thin sections mounted on silicon wafers were subjected to sputter coating with Au before observation under an isotope microscope 51–54 at Isotope Imaging Laboratory, Creative Research Institute, Hokkaido University, Sapporo, Japan.…”

Dynamic Analyses of the Short‐Term Effects of Different Bisphosphonates Using Intravital Two‐Photon Microscopy

“…Recent studies have reported that radiolabeled BPs, including risedronate, alendronate, and minodronate, attach to the bone surface within 24 hours after i.v. injection . Osteoclasts secrete protons on the mineral surface to resorb bone tissues, resulting in the dissociation of BPs from the bone surface.…”

“…The exact localization of BPs within bones, as well as the ability of osteoclasts to take up BPs, has been well‐studied. Previous studies using radioactive isotopes reported that radiolabeled BPs localized to bone tissues and were taken up by osteoclasts within 24 hours after treatment in animal models . Another study using a fluorescent BP analogue also reported the localization of BPs on the bone surface and its cellular uptake by osteoclasts .…”

Bone Formation Parameters of the Biopsied Ilium Differ between Subtrochanteric and Diaphyseal Atypical Femoral Fractures in Bisphosphonate-Treated Patients

“…In mouse femora, minodronate accumulates in bone underneath osteoblasts rather than under osteoclasts and minodronate-coated bone matrix is resistant to osteoclastic resorption, suggesting bone-preserving effect by examining through isotope microscopy (Hongo et al 2016). In our study, case 8 was treated with minodronate for 4.1 years following with alendronate for 1.3 years and ES/BS in case 8 (3.19%) was not suppressed.…”