Induction of creatine kinase release from cultured osteoclasts via the pharmacological action of aminobisphosphonates

Brain-Type Creatine Kinase Release from Cultured Osteoclasts Exposed to Neridronate in Children Affected by Osteogenesis Imperfecta Type 1

Brain-type creatine kinase (CK-BB) increases during osteoclastogenesis, with high circulating amounts in type I osteogenesis imperfecta (OI) following treatment with neridronate, a bisphosphonate able to inhibit osteoclast activity and survival. The aim of this study was to demonstrate the correlation between osteoclastogenesis and CK-BB release from OI patients' osteoclasts treated with different concentrations of neridronate. Our patients showed reduced bone quality, increased levels of CTX I, a marker of bone resorption, and decreased levels of OPG, an inhibitor of osteoclastogenesis. In OI patients, the presence of MCSF and RANKL determined an increased secretion of CK-BB from osteoclasts (p = 0.04) compared with control conditions without these cytokines; interestingly, in the absence of these factors, the secretion of CK-BB is significantly elevated at 3 µmol/L compared with 0.03 and 1 µmol/L (p = 0.007). In healthy donors' cultures, the higher concentration of CK-BB can be detected following stimulation with 3 µmol/L neridronate compared with the untreated condition both with and without MCSF and RANKL (p = 0.03 and p = 0.006, respectively). Consistently, in osteoclast cultures, neridronate treatment is associated with a decrease in multinucleated TRAP+ cells, together with morphology changes typical of apoptosis. Consistently, in the media of the same osteoclast cultures, we demonstrated a significant increase in caspase-3 levels. In conclusion, our findings support the idea that CK-BB levels increase in the serum of OI-treated patients.

Minodronic acid induces morphological changes in osteoclasts at bone resorption sites and reaches a level required for antagonism of purinergic P2X2/3 receptors

Minodronic acid is an aminobisphosphonate that is an antagonist of purinergic P2X2/3 receptors involved in pain. The aim of this study was to investigate the action and distribution of minodronic acid and the potential for P2X2/3 receptor antagonism based on the estimated concentration of minodronic acid. Microlocalization of radiolabeled minodronic acid was examined in the femur of neonatal rats. The bone-binding characteristics of minodronic acid and morphological changes in osteoclasts were analyzed in vitro. The minodronic acid concentration around bone resorption lacunae was predicted based on bone binding and the shape of lacunae. In microautoradiography, radioactive silver grains were abundant in bone-attached osteoclasts and were detected in calcified and ossification zones and in the cytoplasm of osteoclasts but not in the hypertrophic cartilage zone. In an osteoclast culture with 1 µM minodronic acid, 65% of minodronic acid was bound to bone, and C-terminal cross-linking telopeptide release was inhibited by 96%. Cultured osteoclasts without minodronic acid treatment formed ruffled borders and bone resorption lacunae and had rich cytoplasm, whereas those treated with 1 µM minodronic acid were not multinucleated, stained densely with toluidine blue, and were detached from the bone surface. In the 1 µM culture, the estimated minodronic acid concentration in resorption lacunae was 880 µM, which is higher than the IC₅₀ for minodronic acid antagonism of P2X2/3 receptors. Thus, inhibition of P2X2/3 receptors around osteoclasts may contribute to the analgesic effect of minodronic acid.

Serum creatine kinase isoenzymes in children with osteogenesis imperfecta

This study evaluates serum creatine kinase isoenzyme activity in children with osteogenesis imperfecta to determine its usefulness as a biochemical marker during treatment with bisphosphonate. The changes of creatine kinase (CK) isoenzyme activity during and after discontinuation therapy were observed. These results could be useful in addressing over-treatment risk prevention.

INTRODUCTION

The brain isoenzyme of creatine kinase (CKbb) is highly expressed in mature osteoclasts during osteoclastogenesis, thus plays an important role in bone resorption. We previously identified high serum CKbb levels in 18 children with osteogenesis imperfect (OI) type 1 treated for 1 year with bisphosphonate (neridronate). In the present study, serum CK isoenzymes were evaluated in the same children with continuous versus discontinued neridronate treatment over a further 2-year follow-up period.

METHODS

This study included 18 children with OI type 1, 12 with continued (group A) and 6 with ceased (group B) neridronate treatment. Auxological data, serum biochemical markers of bone metabolism, bone mineral density z-score, and serum total CK and isoenzyme activities were determined in both groups.

RESULTS

Serum CKbb was progressively and significantly increased in group A (p < 0.004) but rapidly decreased to undetectable levels in group B. In both groups, the cardiac muscle creatine kinase isoenzyme (CKmb) showed a marked decrease, while serum C-terminal telopeptide (CTx) levels were almost unchanged.

CONCLUSIONS

This study provides evidence of the cumulative effect of neridronate administration in increasing serum CKbb levels and the reversible effect after its discontinuation. This approach could be employed for verifying the usefulness of serum CKbb as a biochemical marker in patients receiving prolonged bisphosphonate treatment. Moreover, the decreased serum CKmb levels suggest a systemic effect of these drugs.