Exploring drug delivery systems for treating osteoporosis

Development of PEI-RANK siRNA Complex Loaded PLGA Nanocapsules for the Treatment of Osteoporosis

Osteoporosis, which is characterized by low bone mineral density and susceptibility to fracture, is caused by increased osteoclastic activity. Receptor activator of nuclear factor kappa B ligand (RANKL)/RANK signaling plays an important role in osteoclast differentiation and activation. The current treatment strategies for osteoporosis do not directly address this underlying cause and generates undesired side effects. This led to emergence of controlled delivery systems to increase drug bioavailability and efficacy specifically at the bone tissue. With better understanding of molecular pathology of bone, the use of small interfering RNA (siRNA) to inhibit translation of abnormal gene expression in cells is becoming a promising approach. In this study, we report a siRNA delivery system consisting of PEI:RANK siRNA complex entrapped in nanosized poly(lactic acid-co-glycolic acid) (PLGA) capsules intended to be used in the treatment of osteoporosis. The nanosize will enable the nanoparticles to be administered by intravenous injection. The RANK siRNA was complexed with polyethylenimine (PEI) and loaded into biodegradable PLGA nanocapsules (NCs). The PEI:RANK siRNA loaded nanocapsules significantly reduced (47%) RANK mRNA levels. The differentiation of osteoclast precursors to mature osteoclasts was significantly suppressed (∼54%). The reduction in the osteoclastic activity of the differentiated osteoclasts (55%) was found to be statistically significant. The siRNA delivery system developed in the study is planned to be tested i.v. in mouse and has the potential to be used as a novel alternative approach for the systemic treatment of osteoporosis.

Degradation, intra-articular retention and biocompatibility of monospheres composed of [PDLLA-PEG-PDLLA]-b-PLLA multi-block copolymers

In this study, we investigated the use of microspheres with a narrow particle size distribution ('monospheres') composed of biodegradable poly(DL-lactide)-PEG-poly(DL-lactide)-b-poly(L-lactide) multiblock copolymers that are potentially suitable for local sustained drug release in articular joints. Monospheres with sizes of 5, 15 and 30μm and a narrow particle size distribution were prepared by a micro-sieve membrane emulsification process. During in vitro degradation, less crystallinity, higher swelling and accelerated mass loss during was observed with increasing the PEG content of the polymer. The monospheres were tested in both a small (mice/rat) and large animal model (horse). In vivo imaging after injection with fluorescent dye loaded microspheres in mice knees showed that monospheres of all sizes retained within the joint for at least 90days, while the same dose of free dye redistributed to the whole body within the first day after intra-articular injection. Administration of monospheres in equine carpal joints caused a mild transient inflammatory response without any clinical signs and without degradation of the cartilage, as evidenced by the absence of degradation products of sulfated glycosaminoglycans or collagen type 2 in the synovial fluid. The excellent intra-articular biocompatibility was confirmed in rat knees, where μCT-imaging and histology showed neither changes in cartilage quality nor quantity. Given the good intra-articular retention and the excellent biocompatibility, these novel poly(DL-lactide)-PEG-poly(DL-lactide)-b-poly(L-lactide)-based monospheres can be considered a suitable platform for intra-articular drug delivery.

STATEMENT OF SIGNIFICANCE

This paper demonstrates the great potential in intra-articular drug delivery of monodisperse biodegradable microspheres which were prepared using a new class of biodegradable multi-block copolymers and a unique membrane emulsification process allowing the preparation of microspheres with a narrow particle size distribution (monospheres) leading to multiple advantages like better injectability, enhanced reproducibility and predictability of the in vivo release kinetics. We report not only on the synthesis and preparation, but also in vitro characterization, followed by in vivo testing of intra-articular biocompatibility of the monospheres in both a small and a large animal model. The favourable intra-articular biocompatibility combined with the prolonged intra-articular retention (>90days) makes these monospheres an interesting drug delivery platform. What should also be highlighted is the use of horses; a very accurate translational model for the human situation, making the results not only relevant for equine healthcare, but also for the development of novel human OA therapies.

Biomechanical properties: effects of low-level laser therapy and Biosilicate® on tibial bone defects in osteopenic rats

PURPOSE

The aim of this study was to investigate the effects of laser therapy and Biosilicate® on the biomechanical properties of bone callus in osteopenic rats.

METHODS

Fifty female Wistar rats were equally divided into 5 groups (n=10/group): osteopenic rats with intact tibiae (SC); osteopenic rats with unfilled and untreated tibial bone defects (OC); osteopenic rats whose bone defects were treated with Biosilicate® (B); osteopenic rats whose bone defects were treated with 830-nm laser, at 120 J/cm2 (L120) and osteopenic rats whose bone defects were treated with Biosilicate® and 830-nm laser, at 120 J/cm2 (BL120). Ovariectomy (OVX) was used to induce osteopenia. A non-critical bone defect was created on the tibia of the osteopenic animals 8 weeks after OVX. In Biosilicate® groups, bone defects were completely filled with the biomaterial. For the laser therapy, an 830-nm laser, 120 J/cm2 was used. On day 14 postsurgery, rats were euthanized, and tibiae were removed for biomechanical analysis.

RESULTS

Maximal load and energy absorption were higher in groups B and BL120, according to the indentation test. Animals submitted to low-level laser therapy (LLLT) did not show any significant biomechanical improvement, but the association between Biosilicate® and LLLT was shown to be efficient to enhance callus biomechanical properties. Conversely, no differences were found between study groups in the bending test.

CONCLUSIONS

Biosilicate® alone or in association with low level laser therapy improves biomechanical properties of tibial bone callus in osteopenic rats.

Bi-directionally selective bone targeting delivery for anabolic and antiresorptive drugs: a novel combined therapy for osteoporosis?

Osteoporosis is a progressive systemic skeletal disease, in which the equilibrium of bone resorption and bone formation is disturbed. The drugs for osteoporosis can be divided into two categories according to their predominant effects: antiresorptive drugs and anabolic drugs. Antiresorptive drugs are designed to inhibit bone resorption and anabolic drugs are aiming to stimulate bone formation. On the other hand, most antiresorptive drugs usually decrease anabolic activities and reduce bone formation, while anabolic drugs can unintendedly increase bone resorption. Furthermore, both types of drugs show no preferential distribution in bone and can locate generally in the areas of both bone formation and bone resorption. Consequently, the non-specific interaction of these drugs with non-targeting area and cells can lead to a compromised efficacy. Combined therapies of antiresorptive and anabolic drugs do not necessarily yield superiority when compared to monotherapy. Here, basing on the targeting cells of these two kinds of drugs and the spatial distribution of osteoblasts and osteoclasts, we propose a novel drug delivery system of bi-directionally selective targeting in order to facilitate the efficacy of antiresorptive and anabolic drugs in combined therapy. In the system, an antiresorptive drug will be linked with a peptide of the eight repeating sequences of aspartate--(Asp)8 that can preferentially guide the drugs to bone resorption zone; while an anabolic drug linked with a peptide of six repeats of the sequence aspartate, serine, serine--(Asp-Ser-Ser)6 that can favorably guide the drugs to bone formation zone. The novel delivery system will improve the specific interaction between the drugs and their targeting cells. Furthermore, the system will reduce the non-specific interaction of the anabolic and antiresorptive drugs with their respective non-targeting cells, which will maximally reduce their side-effects. Therefore, we postulate that the new bone targeting drug delivery system will be a blessing for osteoporotic patients.