Binding kinetics of a fluorescently labeled bisphosphonate as a tool for dynamic monitoring of bone mineral deposition in vivo

Systemically administered zoledronic acid activates locally implanted synthetic hydroxyapatite particles enhancing peri-implant bone formation: A regenerative medicine approach to improve fracture fixation

Fracture fixation in an ageing population is challenging and fixation failure increases mortality and societal costs. We report a novel fracture fixation treatment by applying a hydroxyapatite (HA) based biomaterial at the bone-implant interface and biologically activating the biomaterial by systemic administration of a bisphosphonate (zoledronic acid, ZA). We first used an animal model of implant integration and applied a calcium sulphate (CaS)/HA biomaterial around a metallic screw in the tibia of osteoporotic rats. Using systemic ZA administration at 2-weeks post-surgery, we demonstrated that the implant surrounded by HA particles showed significantly higher peri‑implant bone formation compared to the unaugmented implants at 6-weeks. We then evaluated the optimal timing (day 1, 3, 7 and 14) of ZA administration to achieve a robust effect on peri‑implant bone formation. Using fluorescent ZA, we demonstrated that the uptake of ZA in the CaS/HA material was the highest at 3- and 7-days post-implantation and the uptake kinetics had a profound effect on the eventual peri‑implant bone formation. We furthered our concept in a feasibility study on trochanteric fracture patients randomized to either CaS/HA augmentation or no augmentation followed by systemic ZA treatment. Radiographically, the CaS/HA group showed signs of increased peri‑implant bone formation compared with the controls. Finally, apart from HA, we demonstrated that the concept of biologically activating a ceramic material by ZA could also be applied to β-tricalcium phosphate. This novel approach for fracture treatment that enhances immediate and long-term fracture fixation in osteoporotic bone could potentially reduce reoperations, morbidity and mortality. STATEMENT OF SIGNIFICANCE: • Fracture fixation in an ageing population is challenging. Biomaterial-based augmentation of fracture fixation devices has been attempted but lack of satisfactory biological response limits their widespread use. • We report the biological activation of locally implanted microparticulate hydroxyapatite (HA) particles placed around an implant by systemic administration of the bisphosphonate zoledronic acid (ZA). The biological activation of HA by ZA enhances peri‑implant bone formation. •Timing of ZA administration after HA implantation is critical for optimal ZA uptake and consequently determines the extent of peri‑implant bone formation. • We translate the developed concept from small animal models of implant integration to a proof-of-concept clinical study on osteoporotic trochanteric fracture patients. • ZA based biological activation can also be applied to other calcium phosphate biomaterials.

Effect of adjuvant bisphosphonates on treatment of periodontitis: Systematic review with meta-analyses

Background

Previous systematic reviews showed additional benefit of adjuvant bisphosphonates (BP) in the treatment of periodontitis. In contrast, it is unclear the effect of BP in patients with diabetes and smokers, its pooled effect when administered locally or systemically is also unknown.

Objectives

This study aimed to systematically review the literature about the use of BP as adjuvant to nonsurgical scaling and root planning (SRP).

Methodology

This study followed the PRISMA guideline. This study included randomized clinical trials that administered locally or systemically BPs as adjuvant for periodontal treatment. Five databases were used. Meta-analyses were performed, using the pooled mean differences (MD) for clinical attachment level (CAL) and probing pocket depth (PPD). Standard mean difference (SMD) was used for radiographic assessment (RADIO). Subgroup analyses were performed for locally delivered meta-analyses, considering diabetes and smoking exposure.

Results

Thirteen studies were included. It was showed MD of 1.52 ​mm (95%CI: 0.97-2.07) and 1.44 ​mm (95%CI: 1.08-1.79) for PPD reduction and CAL gain, respectively, for locally delivered BP. BP was not able to provide significant improvements in smokers (subgroup analysis) when considering CAL (MD: 1.37; 95%CI: -0.17-2.91) and PPD (MD: 1.35; 95%CI: -0.13-2.83). Locally delivered BP also improved significantly the RADIO assessments (SMD: 4.34; 95%CI: 2.94-5.74). MD for systemically administered BP was 0.40 ​mm (95%CI: 0.21-0.60), 0.51 ​mm (95%CI: 0.19-0.83) and 1.05 (95%CI: 0.80-1.31) for PPD, CAL and RADIO, respectively.

Conclusion

The administration of BP in adjunct to SRP may result in additional clinical effects.

Comparison of photoacoustic and fluorescence tomography for the in vivo imaging of ICG-labelled liposomes in the medullary cavity in mice

Few reports quantitatively compare the performance of photoacoustic tomography (PAT) versus fluorescence molecular tomography (FMT) in vivo. We compared both modalities for the detection of signals from injected ICG liposomes in the tibial medullary space of 10 BALB/c mice in vivo and ex vivo. Signals significantly correlated between modalities (R² = 0.69) and within each modality in vivo versus ex vivo (PAT: R² = 0.70, FMT: R² = 0.76). Phantom studies showed that signals at 4 mm depth are detected down to 3.3 ng ICG by PAT and 33 ng by FMT, with a nominal spatial resolution below 0.5 mm in PAT and limited to 1 mm in FMT. Our study demonstrates comparable in vivo sensitivity, but superior ex vivo sensitivity and in vivo resolution for our ICG liposomes of the VevoLAZR versus the FMT2500. PAT provides a useful new tool for the high-resolution imaging of bone marrow signals, for example for monitoring drug delivery.

Comparison of the Efficacy and Renal Safety of Bisphosphonate Between Low-Dose/High-Frequency and High-Dose/Low-Frequency Regimens in a Late-Stage Chronic Kidney Disease Rat Model

The efficacy and renal safety of low-dose/high-frequency (LDHF) dosing and high-dose/low-frequency (HDLF) dosing of bisphosphonates (BPs) are comparable in patients with normal kidney function but might be different in patients with late-stage chronic kidney disease (CKD). This study aimed to compare the efficacy and renal safety of two different dosage regimens of a BP, alendronate (ALN), in stage 4 CKD using a rat model. Male, 10-week-old Sprague-Dawley rats were subjected to either 5/6 nephrectomy or sham surgery. The animals received subcutaneous administration of vehicle (daily) or ALN in LDHF dosage regimen (LDHF-ALN: 0.05 mg/kg/day) or HDLF dosage regimen (HDLF-ALN: 0.70 mg/kg/2 weeks). Medications commenced at 20 weeks of age and continued for 10 weeks. Micro-computed tomography, histological analysis, infrared spectroscopic imaging, and serum and urine assays were performed to examine the efficacy and renal safety of the ALN regimens. Both LDHF-ALN and HDLF-ALN increased bone mass, improved micro-structure, and enhanced mechanical properties, without causing further renal impairment in CKD rats. Histologically, however, HDLF-ALN more efficiently suppressed bone turnover, leading to more mineralized trabecular bone, than LDHF-ALN in CKD rats, whereas such differences between LDHF-ALN and HDLF-ALN were not observed in sham rats. Both LDHF-ALN and HDLF-ALN showed therapeutic effects on high bone turnover osteoporosis in CKD stage 4 rats without causing further renal impairment. However, as HDLF-ALN more efficiently suppressed bone turnover than LDHF-ALN in late-stage CKD, HDLF-ALN might be more appropriate than LDHF-ALN for fracture prevention in high bone turnover osteoporosis patients with late-stage CKD.

Fluorescence Detection of Bone Microcracks Using Monophosphonated Carbon Dots

Phosphonated compounds, in particular, bisanalogs are widely applied in clinical settings for the treatment of severe bone turnovers and recently as imaging probes when conjugated with organic fluorophores. Herein, we introduce a bone seeking luminescent probe that shows a high binding affinity toward bone minerals based on monophosphonated carbon dots (CDs). Spheroidal CDs tethered with PEG monophosphates are synthesized in a one-pot hydrothermal method and are physicochemically characterized, where the retention of phosphonates is confirmed by ¹³P NMR and X-ray photoelectron spectroscopy. Interestingly, the high abundance of multiple monodentate phosphonates exhibited strong binding to hydroxyapatite, the main bone mineral constituent. The remarkable optophysical properties of monophosphonated CDs were confirmed in an ex vivo model of the bovine cortical bone where the imaging feasibility of microcracks, which are calcium-rich regions, was demonstrated. The in vivo studies specified the potential application of monophosphonated CDs for imaging when injected intramuscularly. The biodigestible nature and cytocompatibility of the probe presented here obviate the demand for a secondary fluorophore, while offering a nanoscale strategy for bone targeting and can eventually be employed for potential bone therapy in the future.

A new multiple trauma model of the mouse

Background

Blunt trauma is the most frequent mechanism of injury in multiple trauma, commonly resulting from road traffic collisions or falls. Two of the most frequent injuries in patients with multiple trauma are chest trauma and extremity fracture. Several trauma mouse models combine chest trauma and head injury, but no trauma mouse model to date includes the combination of long bone fractures and chest trauma. Outcome is essentially determined by the combination of these injuries. In this study, we attempted to establish a reproducible novel multiple trauma model in mice that combines blunt trauma, major injuries and simple practicability.

Methods

Ninety-six male C57BL/6 N mice (n = 8/group) were subjected to trauma for isolated femur fracture and a combination of femur fracture and chest injury. Serum samples of mice were obtained by heart puncture at defined time points of 0 h (hour), 6 h, 12 h, 24 h, 3 d (days), and 7 d.

Results

A tendency toward reduced weight and temperature was observed at 24 h after chest trauma and femur fracture. Blood analyses revealed a decrease in hemoglobin during the first 24 h after trauma. Some animals were killed by heart puncture immediately after chest contusion; these animals showed the most severe lung contusion and hemorrhage. The extent of structural lung injury varied in different mice but was evident in all animals. Representative H&E-stained (Haematoxylin and Eosin-stained) paraffin lung sections of mice with multiple trauma revealed hemorrhage and an inflammatory immune response. Plasma samples of mice with chest trauma and femur fracture showed an up-regulation of IL-1β (Interleukin-1β), IL-6, IL-10, IL-12p70 and TNF-α (Tumor necrosis factor- α) compared with the control group. Mice with femur fracture and chest trauma showed a significant up-regulation of IL-6 compared to group with isolated femur fracture.

Conclusions

The multiple trauma mouse model comprising chest trauma and femur fracture enables many analogies to clinical cases of multiple trauma in humans and demonstrates associated characteristic clinical and pathophysiological changes. This model is easy to perform, is economical and can be used for further research examining specific immunological questions.

Osthole Promotes Endochondral Ossification and Accelerates Fracture Healing in Mice

Osthole has been found to restore bone mass in preclinical osteoporotic models. In the present study, we investigated the effects of osthole on bone fracture repair in mice. Adult C57BL/6 mice were subjected to transverse femoral fractures and administrated orally with 20 mg/kg osthole and vehicle solvent daily from week 1 post-operation. Fracture callus were analyzed by plain radiography, micro-computed tomography, histology, molecular imaging and immunohistochemistry and tartrate-resistant acid phosphatase staining. Results demonstrated that osthole treatment enhanced removal of cartilage and bony union during reparative stage without significant interfering on remodeling process. In vivo molecular imaging showed bone formation rate of the treatment group was almost twofold of control group at week 2 post-operation. Osthole augmented the expression of alkaline phosphatase and collagen type X in hypertrophic chondrocytes as well as expression of bone morphogenetic protein-2, osteocalcin and alkaline phosphatase in osteoblastic cells, indicating it promoted mineralization of hypertrophic cartilage and woven bone growth simultaneously during endochondral healing. In summary, osthole promotes endochondral ossification via upregulation of maturation osteogenic marker genes in chondrocytes and subsequently accelerates fracture repair and bony fusion.

Osteotropic nanoscale drug delivery systems based on small molecule bone-targeting moieties

Bone-targeted drug delivery is an active research area because successful clinical applications of this technology can significantly advance the treatment of bone injuries and disorders. Molecules with bone-targeting potential have been actively investigated as promising moieties in targeted drug delivery systems. In general, bone-targeting molecules are characterized by their high affinity for bone and their predisposition to persist in bone tissue for prolonged periods, while maintaining low systemic concentrations. Proteins, such as monoclonal antibodies, have shown promise as bone-targeting molecules; however, they suffer from several limitations including large molecular size, high production cost, and undesirable immune responses. A viable alternative associated with significantly less side effects is the use of small molecule-based targeting moieties. This review provides a summary of recent findings regarding small molecule compounds with bone-targeting capacity, as well as nanoscale targeted drug delivery approaches employing these molecules.

Minodronic acid ameliorates vertebral bone strength by increasing bone mineral density in 9-month treatment of ovariectomized cynomolgus monkeys

The effect of treatment for 9months with minodronic acid, a nitrogen-containing bisphosphonate, on vertebral mechanical strength was examined in ovariectomized (OVX) cynomolgus monkeys. Forty skeletally mature female monkeys were randomized into four OVX groups and one sham group (n=8) based on lumbar bone mineral density (BMD). OVX animals were treated orally with 15 and 150μg/kg QD of minodronic acid or 500μg/kg QD alendronate as a reference drug. Measurements of bone turnover markers and lumbar BMD were conducted at 0, 4 and 8months. Measurements of bone mechanical strength and minodronic acid concentration in vertebral bodies were also performed. OVX resulted in a decrease in lumbar BMD and an increase in bone turnover markers at 4 and 8months, compared to the sham group, and the ultimate load on the lumbar vertebra was decreased in OVX animals. Minodronic acid and alendronate prevented the OVX-induced increase in bone turnover markers and decrease in lumbar BMD. Minodronic acid at 150μg/kg increased the ultimate load on lumbar vertebra compared to untreated OVX animals. Regression analysis revealed that the ultimate load was correlated with lumbar BMD and bone mineral content (BMC), and most strongly with the increase in lumbar BMD and BMC over 8months. In a separate analysis within the sham-OVX controls and minodronic acid and alendronate treatment groups, the ultimate loads were also correlated with BMD and BMC. The load-BMD (BMC) correlation in the minodronic acid group showed a trend for a shift to a higher load from the basal relationship in the sham-OVX controls. These results indicate that treatment with minodronic acid for 9months increases vertebral mechanical strength in OVX monkeys, mainly by increasing BMD and BMC.

Targeted delivery to bone and mineral deposits using bisphosphonate ligands

The high concentration of mineral present in bone and pathological calcifications is unique compared with all other tissues and thus provides opportunity for targeted delivery of pharmaceutical drugs, including radiosensitizers and imaging probes. Targeted delivery enables accumulation of a high local dose of a therapeutic or imaging contrast agent to diseased bone or pathological calcifications. Bisphosphonates (BPs) are the most widely utilized bone-targeting ligand due to exhibiting high binding affinity to hydroxyapatite mineral. BPs can be conjugated to an agent that would otherwise have little or no affinity for the sites of interest. This article summarizes the current state of knowledge and practice for the use of BPs as ligands for targeted delivery to bone and mineral deposits. The clinical history of BPs is briefly summarized to emphasize the success of these molecules as therapeutics for metabolic bone diseases. Mechanisms of binding and the relative binding affinity of various BPs to bone mineral are introduced, including common methods for measuring binding affinity in vitro and in vivo. Current research is highlighted for the use of BP ligands for targeted delivery of BP conjugates in various applications, including (1) therapeutic drug delivery for metabolic bone diseases, bone cancer, other bone diseases, and engineered drug delivery platforms; (2) imaging probes for scintigraphy, fluorescence, positron emission tomography, magnetic resonance imaging, and computed tomography; and (3) radiotherapy. Last, and perhaps most importantly, key structure-function relationships are considered for the design of drugs with BP ligands, including the tether length between the BP and drug, the size of the drug, the number of BP ligands per drug, cleavable tethers between the BP and drug, and conjugation schemes.

Utilizing time-lapse micro-CT-correlated bisphosphonate binding kinetics and soft tissue-derived input functions to differentiate site-specific changes in bone metabolism in vivo

The turnover of bone is a tightly regulated process between bone formation and resorption to ensure skeletal homeostasis. This process differs between bone types, with trabecular bone often associated with higher turnover than cortical bone. Analyses of bone by micro-computed tomography (micro-CT) reveal changes in structure and mineral content, but are limited in the study of metabolic activity at a single time point, while analyses of serum markers can reveal changes in bone metabolism, but cannot delineate the origin of any aberrant findings. To obtain a site-specific assessment of bone metabolic status, bisphosphonate binding kinetics were utilized. Using a fluorescently-labeled bisphosphonate, we show that early binding kinetics monitored in vivo using fluorescent molecular tomography (FMT) can monitor changes in bone metabolism in response to bone loss, stimulated by ovariectomy (OVX), or bone gain, resulting from treatment with the anabolic bone agent parathyroid hormone (PTH), and is capable of distinguishing different, metabolically distinct skeletal sites. Using time-lapse micro-CT, longitudinal bone turnover was quantified. The spine showed a significantly greater percent resorbing volume and surface in response to OVX, while mice treated with PTH showed significantly greater resorbing volume per bone surface in the spine and significantly greater forming surfaces in the knee. Correlation studies between binding kinetics and micro-CT suggest that forming surfaces, as assessed by time-lapse micro-CT, are preferentially reflected in the rate constant values while forming and resorbing bone volumes primarily affect plateau values. Additionally, we developed a blood pool correction method which now allows for quantitative multi-compartment analyses to be conducted using FMT. These results further expand our understanding of bisphosphonate binding and the use of bisphosphonate binding kinetics as a tool to monitor site-specific changes in bone metabolism in vivo.