Subchronic Oral Cannabidiol (CBD) Attenuates Post-Injury Macrophage Density without Altering Olfactory Epithelial Regeneration

Bridger Menlove
Florida State University

Co-authors: Bridger Menlove¹, Olivia C. Turner¹, Zachary Arnold¹, Chloe Crespi¹, Madison Klick¹, Debra A. Fadool^1
1Florida State University

Background: Evidence supports that CBD may reverse neurogenic deficits in the central nervous system, as well as assist peripheral nerve repair. The olfactory epithelium maintains continuous, lifelong turnover of olfactory sensory neurons (OSNs). Albeit neurogenesis being well studied in this unique peripheral sensory organ, the ability for CBD to interact with the regenerative process of OSNs is completely unexplored.

Objective(s): This study examined whether subchronic, oral administration of CBD affects normal olfactory epithelial homeostasis or regenerative recovery in adult mice following acute chemical injury.

Methods: Adult male OMPtauEGFP reporter mice were administered vehicle control or 100 mg/kg CBD daily via voluntary oral consumption (strawberry jam) for two weeks prior to receiving either an intraperitoneal injection of saline (control) or 75 mg/kg methimazole (MeZ) to ablate mature OSNs. Mice were tested for anticipated anosmia using the buried cookie assay and then histologically evaluated across post-injury time points (3, 10, 15, and 30 days). OSN abundance, epithelial thickness, sustentacular cell integrity (CK18), cellular turnover (Ki67, Caspase-3), and macrophage density (Iba-1) were anatomically quantified using confocal microscopy facilitated by the GFP reporter expressed in mature olfactory neurons (Olfactory Marker Protein+).

Results: Subchronic CBD treatment significantly attenuated the acute macrophage accumulation three days post-ablation, marked by a reduction in olfactory mucosal macrophage density (1ba-1+ cells; p = 0.0262). Interestingly, the macrophage reduction was independent of epithelial regeneration. Following chemical injury, there was no main effect of CBD treatment on the recovery of olfactory ability across a 28-day window after the onset of produced anosmia . CBD did not significantly modulate OSN abundance (p = 0.6146) or epithelial thickness (p = 0.8969) in MeZ-treated mice during the recovery phase, and markers for cellular turnover similarly remained unchanged 30-days post-ablation (Ki67 p = 0.1599; Cas3 p = 0.5620). Finally, in uninjured control mice, subchronic CBD administration had no effect on gross olfactory behavior, baseline OSN abundance , epithelial thickness, macrophage density, or cellular turnover (all p > 0.05); demonstrating that CBD does not disrupt normal epithelial homeostasis.

Conclusions: We conclude that a subchronic, oral dose of CBD attenuates macrophage density in the olfactory system following chemical injury, while epithelial regeneration and homeostasis remain robustly independent  Our experiments suggest limited use of CBD as a peripheral neuro-regenerative agent and do not indicate off-target effects of oral CBD on olfactory function or homeostasis.