The effect of cannabinoids on single-level lumbar arthrodesis outcomes in a rat model

BACKGROUND CONTEXT

The opioid epidemic is a public health crisis affecting spine care and pain management. Medical marijuana is a potential nonopioid analgesic yet to be studied in the surgical setting since its effects on bone healing are not fully understood. Studies have demonstrated analgesic and potentially osteoinductive properties of cannabinoids with endocannabinoid receptor expression in bone tissue.

PURPOSE

We hypothesize that tetrahydrocannabinol (THC) and cannabidiol (CBD) will not decrease bone healing in spinal fusion.

STUDY DESIGN

Seventy-eight adult Sprague-Dawley rats were used for this study. Utilizing allogenic bone grafts (6 donor rats), posterolateral inter-transverse lumbar fusion at the L4-L5 level was performed. The animals were equally divided into four treatment groups, each receiving 0.1 ml intraperitoneal injections weekly as follows: placebo (saline), 5 mg/kg THC, 5 mg/kg CBD, and a combination of 5 mg/kg THC and 5mg/kg CBD (Combo).

METHODS

Callus tissue was harvested 2- and 8-weeks postsurgery for qPCR assessment to quantify changes in the expression of osteogenic genes. Manual palpation was done to assess the strength of the L4-L5 arthrodesis on all rats. μCT image-based callus analysis and histology were performed. One-way ANOVA followed by post hoc comparisons was performed.

RESULTS

μCT demonstrated no significant differences. Treatment groups had slightly increased bone volume and density compared to control. qPCR at 2 weeks indicated downregulated RANKL/OPG ratios skewing towards osteogenesis in the CBD group, with the THC and CBD+THC groups demonstrating a downward trend (p>.05). ALPL, BMP4, and SOST were significantly higher in the CBD group, with CTNNB1 and RUNX2 also showing an upregulating trend. The CBD group showed elevation in Col1A1 and MMP13. Data at eight weeks showed ALPL, RUNX2, BMP4, and SOST were downregulated for all treatment groups. In the CBD+THC group, RANK, RANKL, and OPG were downregulated. OPG downregulation reached significance for the THC and CBD+THC group compared to saline. Interestingly, the RANKL/OPG ratio showed upregulation in the CBD and CBD+THC groups. RANKL showed upregulation in the CBD group. At 2 and 8 weeks, the CBD treatment group showed superior histological progression, increasing between time points.

CONCLUSION

This study demonstrates that CBD and THC have no adverse effect on bone healing and the rate of spinal fusion in rats. Osteogenic factors were upregulated in the CBD-treated groups at 2 weeks, which indicates a potential for bone regeneration. In this group, compared to control, the RANKL/OPG ratio at the early healing phase demonstrates the inhibition of osteoclast differentiation, enhancing bone formation. Interestingly, it shows promoted osteoclast differentiation at the later healing phase, enhancing bone remodeling. This aligns with the physiological expectation of a lower ratio in the early phases and a higher ratio in the later remodeling phases.

CLINICAL SIGNIFICANCE

CBD and THC showed no inhibitory effects on bone healing in a spinal fusion model. Moreover, histologic and gene expression analysis demonstrated that CBD may, in fact, enhance bone healing. Further research is needed to confirm the safe usage of THC and CBD in the postoperative setting following spinal fusions.

Stimulation of fracture mineralization by salt-inducible kinase inhibitors

Introduction

Over 6.8 million fractures occur annually in the US, with 10% experiencing delayed- or non-union. Anabolic therapeutics like PTH analogs stimulate fracture repair, and small molecule salt inducible kinase (SIK) inhibitors mimic PTH action. This study tests whether the SIK inhibitor YKL-05-099 accelerates fracture callus osteogenesis.

Methods

126 female mice underwent femoral shaft pinning and midshaft fracture, receiving daily injections of PBS, YKL-05-099, or PTH. Callus tissues were analyzed via RT-qPCR, histology, single-cell RNA-seq, and μCT imaging. Biomechanical testing evaluated tissue rigidity. A hydrogel-based delivery system for PTH and siRNAs targeting SIK2/SIK3 was developed and tested.

Results

YKL-05-099 and PTH-treated mice showed higher mineralized callus volume fraction and improved structural rigidity. RNA-seq indicated YKL-05-099 increased osteoblast subsets and reduced chondrocyte precursors. Hydrogel-released siRNAs maintained target knockdown, accelerating callus mineralization.

Discussion

YKL-05-099 enhances fracture repair, supporting selective SIK inhibitors' development for clinical use. Hydrogel-based siRNA delivery offers targeted localized treatment at fracture sites.