Comparison of Bone Regeneration in Different Forms of Bovine Bone Scaffolds with Recombinant Human Bone Morphogenetic Protein-2

Mitigation of BMP-induced inflammation in craniofacial bone regeneration and improvement of bone parameters by dietary hesperidin

Based on anti-inflammatory and osteogenic properties of hesperidin (HE), we hypothesized its systemic administration could be a cost-effective method of improving BMP-induced bone regeneration. Sprague-Dawley rats were allocated into 4 groups (n = 10/group): a 5-mm critical-sized mandible defect + collagen scaffold or, scaffold + 1 µg of BMP2 with and without dietary HE at 100 mg/kg. HE was administered by oral gavage 4 weeks prior to surgeries until euthanasia at day 7 or 14 post-surgery. The healing tissue within the defect collected at day 7 was subjected to gene expression analysis. Mandibles harvested at day 14 were subjected to microcomputed tomography and histology. HE + BMP2-treated rats had a statistically significant decrease in expression of inflammatory genes compared to BMP2 alone. The high-dose BMP2 alone caused cystic-like regeneration with incomplete defect closure. HE + BMP2 showed virtually complete bone fusion. Collagen fibril birefringence pattern (red color) under polarized light indicated high organization in BMP2-induced newly formed bone (NFB) in HE-supplemented group (p < 0.05). Clear changes in osteocyte lacunae as well as a statistically significant increase in osteoclasts were found around NFB in HE-treated rats. A significant increase in trabecular volume and thickness, and trabecular and cortical density was found in femurs of HE-supplemented rats (p < 0.05). Our findings show, for the first time, that dietary HE has a remarkable modulatory role in the function of locally delivered high-dose BMP2 in bone regeneration possibly via control of inflammation, osteogenesis, changes in osteocyte and osteoclast function and collagen maturation in regenerated and native bone. In conclusion, HE had a significant skeletal bone sparing effect and the ability to provide a more effective BMP-induced craniofacial regeneration.

Long-Term Changes in Adipose Tissue in the Newly Formed Bone Induced by Recombinant Human BMP-2 In Vivo

Recombinant human bone morphogenetic protein-2 (rhBMP-2) induces osteogenesis and adipogenesis in bone scaffolds. We evaluated rhBMP-2-induced long-term changes in adipose tissue in the newly formed bone in different scaffolds forms. Bovine bone particles and blocks were grafted along with rhBMP-2 in the subperiosteal space of a rat calvarial bone, and the formation of new bone and adipose tissue were evaluated at 6 and 16 weeks after the surgery. The bone mineral density (BMD) and trabecular thickness (TbTh) of the 16w particle group were significantly higher than those of the 6w particle group (p = 0.018 and 0.012, respectively). The BMD and TbTh gradually increased in the particle group from weeks 6 to 16. The average adipose tissue volume (ATV) of the 6w particle group was higher than that of the 16w particle group, although the difference was not significant (p > 0.05), and it decreased gradually. There were no significant changes in the bone volume (BV) and BMD between the 6w and 16w block groups. Histological analysis revealed favorable new bone regeneration in all groups. Adipose tissue was formed between the bone particles and at the center in the particle and block groups, respectively. The adipose tissue space decreased, and the proportion of new bone increased in the 16w particle group compared to that in the 6w group. To summarize, in the particle group, the adipose tissue decreased in a time-dependent manner, BMD and TbTh increased, and new bone formation increased from 6 to 16 weeks. These results suggest that rhBMP-2 effectively induces new bone formation in the long term in particle bone scaffolds.

BMP-2 Long-Term Stimulation of Human Pre-Osteoblasts Induces Osteogenic Differentiation and Promotes Transdifferentiation and Bone Remodeling Processes

Bone morphogenic protein (BMP-) 2 plays an important role in the regeneration of bone defects by promoting osteogenic differentiation. However, several animal studies have reported adverse side effects of BMP-2, including osteoclast activation, induction of peroxisome proliferator- activated receptor gamma (PPARG)expression, and inflammation. High BMP-2 concentrations are thought to be responsible for these side effects. For this reason, primary pre-osteoblasts were exposed to lower BMP-2 concentrations (1 and 2 µg/mL). Long-term exposure (up to 28 days) was performed to investigate whether this stimulation protocol may promote osteogenic differentiation without causing the side effects mentioned above. The results showed that BMP-2 treatment for 14 or 28 days resulted in increased osteogenesis, through an increase in runt-related transcription factor 2, osterix, alkaline phosphatase, and integrin-binding sialoprotein expression. However, an increase in tumor necrosis factor alpha and receptor activator of nuclear factor kappa-Β ligand protein levels was observed after BMP-2 exposure, indicating also an increased potential for osteoclast activation by osteoblasts. Additionally, morphological changes like intracellular, filled vacuoles could be detected. Enhanced PPARG and perilipin 1 mRNA transcripts and lipid droplets indicated an induced adipogenic differentiation. Overall, the data demonstrate that long-term BMP-2 exposure promotes not only osteogenic differentiation but also adipogenesis and regulates mediators involved in osteoclast activation in vitro.