CBD: a molecular lever addressing the challenges of bone regeneration

In oral and maxillofacial surgery, the management of critical-size bone defects remains a major challenge. When inflammation progresses beyond the physiological phase to become chronic, it stimulates osteoclastogenesis and compromises tissue stability, making spontaneous healing impossible. Faced with the limitations of conventional grafts — donor site morbidity and infection risks — research is turning to the immunomodulatory properties of Cannabis sativa L. This plant possesses a remarkable biochemical complexity with over 450 bioactive constituents, including approximately 70 phytocannabinoids.

This analysis aims specifically to decipher the chemical and biological mechanisms underlying the effects of cannabidiol (CBD) on wound healing and bone regeneration. The study tests the hypothesis of a multimodal action of CBD capable of restoring homeostasis. Unlike conventional approaches centred on CB1 and CB2 receptors, the authors herein explore an extended endocannabinoid network. The central hypothesis relies on the interaction of CBD with non-canonical receptors, such as GPR18 and GPR55, to modulate the immune response and stimulate reparative processes without the psychotropic effects associated with THC.

Methodology of the analysis

This study adopts a systemic analysis approach aimed at characterising the molecular mechanisms of cannabidiol (CBD) in tissue repair processes. The objective is to evaluate how this bioactive compound can direct the immune response towards a pro-regenerative resolution.

• Study design: Comprehensive synthesis and critical evaluation of the biological and chemical properties of phytocannabinoids, focusing on immunomodulation and osteogenesis.
• Sampling and scope: The analysis encompasses data relating to the 450 constituents of Cannabis sativa L., with particular attention to the 70 identified phytocannabinoids and their interactions with the endocannabinoid system.
• Evaluation protocol: The examination is structured around the analysis of molecular structures (dibenzopyran nucleus) and the activation of cellular receptors. It specifically explores the signalling pathways of the CB1, CB2 receptors and the orphan receptors GPR18 (sensitive to NAGly) and GPR55 (involving Gq proteins, RhoA and calcium mobilisation).
• Comparison models: The study analyses the four phases of healing — haemostasis, inflammation, proliferation and remodelling — by comparing normal physiological trajectories to critical-size bone defects resulting from dysregulated processes.
• Clinical variables examined: The analysis includes the evaluation of dosing strategies, various routes of administration, galenic formulations and the regulatory frameworks governing therapeutic use.

Modulation of receptors and signalling pathways

The analysis of biological mechanisms reveals that cannabidiol (CBD) interacts with an extensive network of receptors beyond the classical endocannabinoid system (CB1/CB2). The data highlight a specific interaction with the orphan receptors GPR18 and GPR55, identified in immune cells and the bone microenvironment.

• GPR18: CBD acts as an antagonist or an inverse agonist. This receptor is involved in neutrophil migration and macrophage phenotype modulation.
• GPR55: Unlike classical CB receptors, it signals via G_12/13 and G_q proteins, activating RhoA pathways and intracellular calcium mobilisation, essential for angiogenesis and cell proliferation.

Impact on osteogenesis and inflammation (Li et al. study)

The results reported on bone marrow mesenchymal stem cells (BMSCs) stimulated by lipopolysaccharides (LPS) demonstrate a dual action of CBD: a reduction in the inflammatory response and a stimulation of bone formation markers.

Biological Target	Effect of CBD (Observation)	Specific Markers
Pro-inflammatory cytokines	Reduction of mRNA expression	TNF-α, IL-6
Osteogenic markers	Increased expression	Runx2, ALP, OCN

Healing and vascularisation (Yan et al. study)

Topical administration of CBD has been evaluated for its cutaneous regenerative potential. Qualitative and molecular observations indicate a significant improvement in the repair processes:

• Wound closure: Acceleration of the closure process compared to control groups.
• Vascularisation: Increased formation of new vessels in the granulation tissue.
• Key mediator: These effects are correlated with an upregulation of vascular endothelial growth factor (VEGF).

Although the trends are statistically significant according to the cited authors, the precise numerical values (p-values, exact percentages) are not detailed in this summary report, which focuses on the validation of the molecular pathways involved.

Bone under endocannabinoid control: a complex network

The study highlights that the endocannabinoid system (ECS) is not limited to the central nervous system. CB1 and CB2 receptors are expressed directly within bone marrow stromal cells and the bone immune microenvironment. This presence suggests a direct role for the ECS in regulating osteoblast and osteoclast activity. Unlike Δ9-THC, CBD acts indirectly on these classical receptors, thereby avoiding any psychotropic effect, which facilitates its clinical acceptance.

Beyond classical receptors: GPR18 and GPR55

One of the key strengths of this analysis lies in the exploration of the "extended endocannabinoid system". CBD modulates so-called orphan receptors such as GPR18 and GPR55. GPR18, expressed by immune cells, influences neutrophil migration and macrophage modulation, while GPR55 participates in calcium mobilisation and angiogenesis via the RhoA pathway. In clinical practice, this molecular versatility translates into a dual action: the attenuation of excessive inflammation and the potential support of vascularisation, two essential pillars for the survival of a bone substitute.

The transition between inflammation and regeneration

The success of a graft or implant placement relies on the smooth transition between the inflammatory phase and the proliferative phase. The study shows that a dysregulated immune response stimulates osteoclastogenesis, compromising tissue stability. By modulating the cytokine response and oxidative stress, CBD could act as a biological stabiliser, preventing the defect from progressing to chronic inflammation detrimental to the forming bone matrix.

Synthesis of biological mechanisms

This analysis highlights the role of cannabidiol (CBD) in bone regeneration via the modulation of the extended endocannabinoid system. Unlike THC, CBD interacts with non-canonical receptors such as GPR18 and GPR55, present in immune cells and the bone microenvironment. This action regulates the activity of osteoblasts and osteoclasts while avoiding psychotropic effects, offering a promising pathway to stabilise remodelling processes disrupted by chronic inflammation.

In practical terms, for the practitioner:

• Management of complex defects: Consider CBD as a future therapeutic approach for treating critical-size bone defects, where persistent inflammation normally prevents spontaneous healing.
• Biological understanding: Note that the effect of CBD extends beyond the classic CB1/CB2 receptors; it specifically targets neutrophil migration and lymphocyte maturation via the GPR18 receptor to promote tissue homeostasis.
• Clinical perspective: Although the data are still primarily preclinical, CBD is emerging as a potential adjunct to biomaterials to improve osseointegration without the risks of immune incompatibility associated with allogeneic grafts.

The management of critical-sized bone defects — those unable to heal spontaneously — remains a major challenge in oral surgery. While autologous grafts and biomaterials constitute the standard, the limitations related to donor site morbidity and immune integration are driving research towards natural bioactive compounds. Among them, Cannabidiol (CBD) stands out for its ability to modulate the inflammatory response without the psychotropic effects of Δ9-THC.