Effects of rhBMP-2-loaded hydroxyapatite granules/beta-tricalcium phosphate hydrogel (HA/β-TCP/hydrogel) composite on a rat model of caudal intervertebral fusion

Targeting class A GPCRs for hard tissue regeneration

G protein-coupled receptors (GPCRs) play important roles in various pathogeneses and physiological regulations. Owing to their functional diversity, GPCRs are considered one of the primary pharmaceutical targets. However, drugs targeting GPCRs have not been developed yet to regenerate hard tissues such as teeth and bones. Mesenchymal stromal cells (MSCs) have high proliferation and multi-lineage differentiation potential, which are essential for hard tissue regeneration. Here, we present a strategy for targeting class A GPCRs for hard tissue regeneration by promoting the differentiation of endogenous MSCs into osteogenic and odontogenic progenitor cells. Through in vitro screening targeted at class A GPCRs, we identified six target receptors (LPAR1, F2R, F2RL1, F2RL2, S1PR1, and ADORA2A) and candidate drugs with potent biomineralization effects. Through a combination of profiling whole transcriptome and accessible chromatin regions, we identified that p53 acts as a key transcriptional activator of genes that modulate the biomineralization process. Moreover, the therapeutic potential of class A GPCR-targeting drugs was demonstrated in tooth pulpotomy and calvarial defect models. The selected drugs revealed potent regenerative effects in both tooth and bone defects, represented by newly formed highly mineralized regions. Consequently, this study provides translational evidence for a new regenerative strategy for damaged hard tissue.

Fusion rate of Escherichia coli-derived recombinant human bone morphogenetic protein-2 compared with local bone autograft in posterior lumbar interbody fusion for degenerative lumbar disorders

BACKGROUND CONTEXT

The use of recombinant human bone morphogenetic proteins-2 (rhBMP-2) for spinal fusion has been reported to be effective. However, most studies have focused on posterolateral and anterior lumbar interbody fusion, and few have investigated posterior lumbar interbody fusion (PLIF).

PURPOSE

This study aimed to determine the effectiveness and safety of the delivery of Escherichia coli-derived rhBMP-2 (E.BMP-2) with hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) poloxamer hydrogel composite carriers for PLIF.

STUDY DESIGN

A retrospective study.

PATIENT SAMPLE

Patients who underwent 1 to 3 levels of PLIF for lumbar degenerative disc disorders between 2015 and 2020 with a follow-up of ≥1 year were enrolled. In total, 254 patients (357 levels) were included in the analysis. The evaluation was performed at each segment level. In the E.BMP-2 group, 160 patients (221 levels) received autologous local bone with E.BMP-2 (maximum 0.5 mg/level), and in the control group, 94 patients (136 levels) received only local bone graft.

OUTCOME MEASURES

The primary outcome of this study was to compare the X-ray and CT fusion rates between the two groups. Secondary outcomes included analysis of the patients' clinical outcomes and postoperative complications on CT scans.

METHODS

Clinical evaluations were performed using a visual analog scale for back pain, the Oswestry Disability Index for disability, and physical and mental component summaries of the Short Form 36-Item Form Health Survey to assess functional effects and quality of life. The fusion was evaluated using radiography and CT. On radiography, solid fusion was defined when the difference between extension and flexion was less than 5°. On CT, solid fusion was defined when the upper and lower vertebral bodies were connected by the trabecular bone (bone bridge formation). In addition, complications such as osteolysis, cage subsidence, and screw loosening were investigated using CT.

RESULTS

All clinical results for low back pain, disability, and quality of life in both groups were excellent and showed statistically significant improvements compared with baseline (p<.0001). According to the X-ray evaluations, fusion was achieved in 92.31% (204/221) of the patients in the E.BMP-2 group and 82.35% (112/136) of the patients in the control group (p=.0041). According to the CT evaluations, the fusion rates were 93.21% (206/221) and 88.24% (120/136) in the E.BMP-2 and control groups (p=.1048), respectively. Except for screw loosening, which had a significantly higher incidence in the control group (p=.0014), the rates of most postoperative complications were not significantly different between the groups.

CONCLUSIONS

This study demonstrated that the adjunctive use of a low dose of E.BMP-2 with HA and β-TCP hydrogel can effectively promote bone fusion, making it a promising option for patients with limited autograft availability or compromised bone quality in PLIF.

Concentration-Dependent Efficacy of Recombinant Human Bone Morphogenetic Protein-2 Using a HA/β-TCP Hydrogel Carrier in a Mini-Pig Vertebral Oblique Lateral Interbody Fusion Model

Bone morphogenetic protein-2 (BMP-2) is used in the treatment of degenerative spinal disease and vertebral fractures, spine fusion, dental surgery, and facial surgery. However, high doses are associated with side effects such as inflammation and osteophytes. In this study, we performed spinal fusion surgery on mini-pigs using BMP-2 and a HA/β-TCP hydrogel carrier, and evaluated the degree of fusion and osteophyte growth according to time and dosage. Increasing the dose of BMP-2 led to a significantly higher fusion rate than was observed in the control group, and there was no significant difference between the 8-week and 16-week samples. We also found that the HA + β-TCP hydrogel combination helped maintain the rate of BMP-2 release. In conclusion, the BMP-2-loaded HA/β-TCP hydrogel carrier used in this study overcame the drawback of potentially causing side effects when used at high concentrations by enabling the sustained release of BMP-2. This method is also highly efficient, since it provides mineral matter to accelerate the fusion rate of the spine and improve bone quality.

Advances in bone regeneration with growth factors for spinal fusion: A literature review

Bone tissue is regenerated via the spatiotemporal involvement of various cytokines. Among them, the bone morphogenetic protein (BMP), which plays a vital role in the bone regeneration process, has been applied clinically for the treatment of refractory orthopedic conditions. Although BMP therapy using a collagen carrier has shown efficiency in bone regeneration over the last two decades, a major challenge-considerable side effects associated with the acute release of high doses of BMPs-has also been revealed. To improve BMP efficiency, the development of new carriers and biologics that can be used in conjunction with BMPs is currently underway. In this review, we describe the current status and future prospects of bone regeneration therapy, with a focus on BMPs. Furthermore, we outline the characteristics and molecular signaling pathways involving BMPs, clinical applications of BMPs in orthopedics, clinical results of BMP use in human spinal surgeries, drugs combined with BMPs to provide synergistic effects, and novel BMP carriers.

A Pre-clinical Standard Operating Procedure for Evaluating Orthobiologics in an In Vivo Rat Spinal Fusion Model

The rat animal model is a cost effective and reliable model used in spinal pre-clinical research. Complications from various surgical procedures in humans often arise that were based on these pre-clinical animal models. Therefore safe and efficacious pre-clinical animal models are needed to establish continuity into clinical trials. A Standard Operating Procedure (SOP) is a validated method that allows researchers to safely and carefully replicate previously successful surgical techniques. Thus, the aim of this study is to describe in detail the procedures involved in a common rat bilateral posterolateral intertransverse spinal fusion SOP used to test the efficacy and safety different orthobiologics using a collagen-soaked sponge as an orthobiologic carrier. Only two orthobiologics are currently FDA approved for spinal fusion surgery which include recombinant bone morphogenetic protein 2 (rhBMP-2), and I-FACTOR. While there are many additional orthobiologics currently being tested, one way to show their safety profile and gain FDA approval, is to use well established pre-clinical animal models. A preoperative, intraoperative, and postoperative surgical setup including specific anesthesia and euthanasia protocols are outlined. Furthermore, we describe different postoperative methods used to validate the spinal fusion SOP, which include μCT analysis, histopathology, biomechanical testing, and blood analysis. This SOP can help increase validity, transparency, efficacy, and reproducibly in future rat spinal fusion surgery procedures.