Regulation of osteoclast function by poly(ethylene sodium phosphate)

Abstract

Event Abstract Back to Event Regulation of osteoclast function by poly(ethylene sodium phosphate) Yasuhiko Iwasaki1*, Sujit Kootala2* and Jöns Hilborn2* 1 Kansai University, Department of Chemistry and Materials Engineering, Japan 2 Uppsala University, Department of Chemistry, Sweden Introduction: An imbalance in bone resorption relative to bone formation is the origin of many metabolic bone diseases, including osteoporosis [1]. In the current field of clinical osteology, bisphosphonates (BPs), which reduce bone resorption, comprise a major class of drugs used in the treatment of osteoporosis. Although BPs are reliable molecules for bone treatment, medication-related osteonecrosis of the jaw has emerged as a serious complication in patients treated with high BP doses. Therefore, new therapeutic agents showing BP-like activity could be beneficial. Recently, we have clarified that polyphosphoester ionomers exhibited clearly superior physicochemical properties for mineralization and biocompatibility when compared with pamidronate [2]. Our hypothesis is that polyphosphoesters, in similarity to bisphosphonates, inhibit osteoclast growth without affecting osteoblasts. Therefore, we studied the effects of poly(ethylene sodium phosphate) (PEP·Na) treatment on bone slice-cultured osteoclasts. Materials and Method: Poly(ethylene sodium phosphate) (PEP·Na) was synthesized as previously reported [3]. Peripheral blood mononuclear cells (PBMCs) were seeded on one side of each bovine cortical bone slice placed in a 24-well cell culture insert; each culture contained a poly(ethylene terephthalate) (PET) trans well membrane and was maintained for 3 weeks with a change of medium every 3 days to induce monocyte differentiation into mature osteoclasts. Cultures of mature human osteoclasts on bone slices were exposed for 24 h to six different concentrations of PEP·Na to assess the toxicity. As a measure of cell viability the numbers of adherent cells were determined from microscopic images using Image J software. TRAcP activity was assessed with a leukocyte acid phosphatase kit. TRAcP-positive multinucleated cells were defined as cells with 3 or more nuclei. Results and Discussion: Optical microscopic data of osteoclasts incubated with different concentrations of PEP·Na are shown in Figure 1. The cells were stained for TRAcP and included giant cells. In the control, which was not treated with PEP·Na, many cells adhered to the bone slice and large, well-spread cells were observed. When a low concentration of PEP·Na was added to the cultivation medium, the number of mature osteoclasts that remained adhered increased, although many smaller adherent cells were also observed. By increasing the concentration of PEP·Na, the number of adherent cells decreased significantly, and their sizes were also reduced. Kanatani and colleagues reported that inorganic phosphate inhibited osteoclast differentiation both by upregulating osteoprotegrin (OPG) expression and through direct action on osteoclast precursor cells [4]. Polyphosphoester degradation is likely to increase the concentration of inorganic phosphate in the cultivation medium and upregulate both the intracellular osteoclast and extracellular inorganic phosphate concentrations. Conclusion: In the present study, the possibility of using polyphosphoesters for selective inhibition of human osteoclast functions was validated. Polyphosphoesters then have a potential to be used as a prodrug for treatment of osteoporosis. JSPS KAKENHI Grant Number 26107719