Treatment with a botanical mixture of cannabidiol:Δ9-tetrahydrocannabinol enhances microglial phagocytosis and shapes amyloid plaques in a mouse model of Alzheimer’s disease

The potential use of phytocannabinoids in neurodegenerative disorders is currently under intense investigation based on their potential anti-inflammatory, antioxidant, and neuroprotective effects. Here, we tested the effects of chronic (28 days) treatment with a complex botanical mixture of purified cannabidiol:Δ⁹-tetrahydrocannabinol (CBD:THC, 99:1) in male 5xFAD mice, a murine model of Alzheimer's disease that recapitulates amyloid pathology. Effects of exposure to this cannabinoid mixture were evaluated using behavioral tests (elevated plus maze for anxiety, tail suspension for depression-like behavior, rotarod for motor coordination, open field for locomotor activity, and novel object recognition for memory), quantification of protein expression (IL-1β, CD40, TREM2, COX2), assessment of functional parameters (microglial phagocytic activity by flow cytometry), and in vivo multiphoton microscopy (time-course of changes of neuritic plaque structural features). Twice daily dosing with 50 mg/kg subcutaneously (s.c.) significantly reduced locomotion, increased anxiety- and depression-like behaviors and had no effect on memory and motor coordination. In vivo imaging experiments suggest that the CBD:THC treatment enhanced microglial phagocytic activity on amyloid plaques; this effect was observed both in plaque features (multiphoton microscopy measurements) as well as in microglia (flow cytometry data). Exposure to CBD:THC induced significant changes in in vivo microglia-amyloid interactions, increasing phagocytic activity and reducing the amyloid peptide accumulation in the neuritic plaques. Thus, CBD:THC (99:1) may be a promising treatment to reduce amyloid pathology, though caution should be noted due to the behavioral alterations observed, i.e., increased anxiety- and depression-like behaviors as well as decreased locomotion.