Development of nanoparticles for delivering recombinant human secretory leukocyte protease inhibitor (rhSLPI) for enhancing human osteoblast differentiation

The global number of elderly people has been increasing and the world can now be considered as an aging society. One of the most concerning health problems in the elderly is a musculoskeletal disease, in which fractures and osteoporosis are the most common problems. The deteriorating bone quality in the elderly is a limitation for treatment and for patient recovery. Several drugs and biomolecules have been studied for enhancing osteoblast properties and differentiation. The secretory leukocyte protease inhibitor (SLPI), which is a serine protease inhibitory protein, has been reported to enhance osteoblast cell adhesion, proliferation, and differentiation. However, the application of SLPI in real clinical settings is limited due to its short half-life in circulation and the fact that it can be destroyed by circulating protease enzymes. Therefore, the application of nanoparticle encapsulation might be of benefit for SLPI delivery. This study aims to fabricate the liposome nanoparticles encapsulating recombinant human SLPI or rhSLPI (rhSLPI-LNPs) for augmenting the half-life and enhancing human osteoblast differentiation. The liposome nanoparticles (LNPs) were fabricated by the thin film hydration method. Encapsulation of rhSLPI was performed by adding 0.33 µg/mL rhSLPI in ultrapure water to the thin film lipid and then rhSLPI-LNPs formed into vesicles. The size and zeta potential of blank-LNPs or rhSLPI-LNPs were measured by scanning electron microscopy (SEM) and dynamic light scattering (DLS). The results showed that the size of both blank-LNPs and rhSLPI-LNPs was approximately 200 nm, and the zeta potentials were −55.6 ± 16.90 mV and −64 ± 7.86 mV, respectively. The rhSLPI encapsulation was confirmed by ELISA. The results showed that liposome nanoparticles could encapsulate rhSLPI. For cytotoxicity, rhSLPI-LNPs treatment did not cause any toxicity to the human osteoblast cell line (hFOB 1.19). In addition, pre-incubation of hFOB 1.19 with rhSLPI-LNPs could significantly enhance osteoblast adhesion when compared with the untreated group.