Although bone morphogenetic protein-2 (BMP-2) has received considerable attention because of its strong osteoinductivity, the clinical application of BMP-2 is limited due to its degradation and deactivation under physiological conditions. Negatively charged heparin is known to form polyelectrolyte complexes with BMP-2 to prevent deactivation and enhance the osteoinduction capability of BMP-2. Herein, we report the sulfonated polyrotaxanes (S-PRX) composed of α-cyclodextrin threaded onto a linear polymer for the protection of BMP-2 through the polyelectrolyte complex formation. When MC3T3-E1 osteoprogenitor cells were treated with the S-PRX/BMP-2 complexes, significantly high alkaline phosphatase production and mineralized matrix deposition were observed compared with that of free BMP-2 and heparin/BMP-2 complexes. Note that the S-PRXs showed negligible anticoagulant activity and cytotoxicity, whereas heparin showed strong anticoagulant activity. Accordingly, the S-PRXs are promising candidates for enhanced osteoinduction ability of BMP-2 without toxicity and anticoagulant activity and could contribute to clinical bone regeneration.
Macrophages play an important role in the regulation of inflammation and immune response as well as the pathogenesis of chronic inflammatory diseases and cancer. Therefore, targeted delivery of therapeutic reagents to macrophages is an effective method for treatment and diagnosis. We previously examined the therapeutic applications of polyrotaxanes (PRXs) comprised of multiple cyclodextrins (CDs) threaded on a polymer chain and capped with bulky stopper molecules. In the present study, we designed an α-d-mannose-modified α-CD/poly(ethylene glycol)-based PRX (Man-PRX). The intracellular uptake of Man-PRX through the interaction with macrophage mannose receptor (MMR) in macrophage-like RAW264.7 cells was examined. Intracellular Man-PRX uptake was observed in MMR-positive RAW264.7 cells but was negligible in MMR-negative NIH/3T3 cells. In addition, the intracellular Man-PRX uptake in RAW264.7 cells was significantly inhibited in the presence of free α-d-mannose and an anti-MMR antibody, which suggests that MMR is involved in the intracellular uptake of Man-PRX. Moreover, the polarization of RAW264.7 cells affected the Man-PRX internalization efficiency. These results indicate that Man-PRX is an effective candidate for selective targeting of macrophages through a specific interaction with the MMR.
Bone morphogenetic protein 2 (BMP-2) has received considerable attention because of its osteoinductivity, but its use is limited owing to its instability and adverse effects. To reduce the dose of BMP-2, complexation with heparin is a promising approach, because heparin enhances the osteoinductivity of BMP-2. However, the clinical use of heparin is restricted because of its anticoagulant activity. Herein, to explore alternative polymers that show heparin-like activity, four polycarboxylates, poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), poly(aspartic acid) (PAsp), and poly(glutamic acid) (PGlu), were selected and their capability to modulate the osteoinductivity of BMP-2 was evaluated. Dynamic light scattering indicated that these polycarboxylates formed polyelectrolyte complexes with BMP-2. The osteogenic differentiation efficiency of MC3T3-E1 cells treated with the polycarboxylate/BMP-2 complexes was investigated in comparison to that of the heparin/BMP-2 complex. As a result, PGlu/BMP-2 complex showed the highest activity of alkaline phosphatase, which is an early-stage marker of osteogenic differentiation, and rapid mineralization. Based on these observations, PGlu could serve as an alternative to heparin in the regenerative therapy of bone using BMP-2.
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