Equilibrium-dependent bisphosphonate interaction with crystalline bone mineral explains anti-resorptive pharmacokinetics and prevalence of osteonecrosis of the jaw in rats

Abstract

Bisphosphonates (BPs) are chemically stable analogs of pyrophosphate exhibiting strong affinity to bone and have been used for the treatment of diseases characterized by excessive bone resorption. Contrary to the widely accepted BP accumulation model in bone after repeated applications, we report here that an equilibrium-dependent BP-crystalline bone mineral interaction may better explain BP bio-distribution and anti-catabolic bone remodeling and may be relevant to the appearance of osteonecrosis of the jaw (ONJ) in rats. Fluorescent-labeled BP analogs were synthesized and used to evaluate the mode of bone adsorption. After fluorescent-labeled BP adsorbed on crystalline calcium phosphates in vitro, subsequent BP application replaced the previously absorbed BP depending on the dose and the relative binding affinity to hydroxyapatite. The in vivo intravenous zoledronate (ZOL) injection of repeated fractional doses resulted in lower serum CTX and TRAP5b measurements than a single bolus injection in spite of the equivalent cumulative dose. Repeated injections resulted in the distribution of fluorescent-labeled BP on the large area of bone surfaces; whereas the single bolus injection gave rise to the intense BP bio-distribution at selected bone sites such as the alveolar process of jawbones. Necrotic maxillary alveolar bone was predominantly observed in vitamin D deficiency rats treated with bolus ZOL injection. The palatal necrotic bone was characteristically sequestrated by the fistulation of hyperplastic oral epithelium, suggesting the initial development of ONJ-like lesions in rats. Our results suggest that equilibrium-dependent BP-bone interaction may, in part, determine the effectiveness and influence side effects of long-term and repeated applications of BPs.

Fluorescent Bisphosphonate and Carboxyphosphonate Probes: A Versatile Imaging Toolkit for Applications in Bone Biology and Biomedicine

“…Antiresorptive activity was recently confirmed for 5-FAM-ZOL in a rat model in vivo. 19 5(6)-ROX-RIS was also active in inhibiting prenylation (Figure 3A). By contrast, cells treated with two near-infrared dye BP conjugates, AF647-RIS and 800CW-ZOL up to 100 µM did not show accumulation of unprenylated Rap1A.…”

Bisphosphonate Uptake in Areas of Tooth Extraction or Periapical Disease

“…5-FAM-ZOL binds with high affinity to synthetic calcium phosphate–coated discs, with binding characteristics that follow the classic Langmuir adsorption isotherm. 29 Importantly, 5-FAM-ZOL retains approximately 50% of the parent drug's anti-resorptive activity in vivo and appreciably increases trabecular bone volume and structural parameters in the long bones of rats deficient in vitamin D. 29 …”

“…34 Moreover, 5-FAM-ZOL has been used to evaluate long bone and mandible adsorption of zoledronic acid administered as a single injection versus repeated injections. 29 …”

Skeletal accumulation of fluorescently tagged zoledronate is higher in animals with early stage chronic kidney disease

“…At 25-weeks of age, normal animals (NL, n=6) and the one half of CKD animals (n=6) were administered a single subcutaneous injection of zoledronic acid conjugated with 5-carboxyfluorescein (FAM-ZOL; 180 μg/kg). This FAM-ZOL compound has previously been administered to rats and shown to allow assessment of bone surface-binding [26]. Unlike other fluorescent bisphosphonates [27], FAM-ZOL at this dose has also been shown to have in vivo biological efficacy as determined by measures of BV/TV in an ovariectomy model [26].…”