Medicinal cannabis extracts are neuroprotective against Aβ_1-42-mediated toxicity in vitro

Phytocannabinoids inhibit the aggregation and neurotoxicity of the neurotoxic Alzheimer's disease protein β amyloid (Aβ). We characterised the capacity of five proprietary medical cannabis extracts, heated and non-heated, with varying ratios of cannabidiol and Δ⁹-tetrahydrocannabinol and their parent carboxylated compounds to protect against lipid peroxidation and Aβ-evoked neurotoxicity in PC12 cells.

Neuroprotection against lipid peroxidation and Aβ_1-42-induced cytotoxicity was assessed using the thiazolyl blue tetrazolium bromide (MTT) assay. Transmission electron microscopy was used to visualise phytocannabinoid effects on Aβ_1-42 aggregation and fluorescence microscopy.

Tetrahydrocannabinol (THC)/tetrahydrocannabinolic acid (THCA)-predominant cannabis extracts demonstrated the most significant overall neuroprotection against Aβ_1-42-induced loss of PC12 cell viability. These protective effects were still significant after heating of extracts, while none of the extracts provided significant neuroprotection to lipid peroxidation via tbhp exposure. Modest inhibition of Aβ_1-42 aggregation was demonstrated only with the non-heated BC-401 cannabis extract, but overall, there was no clear correlation between effects on fibrils and conferral of neuroprotection.

These findings highlight the variable neuroprotective activity of cannabis extracts containing major phytocannabinoids THC/THCA and cannabidiol (CBD)/cannabidiolic acid (CBDA) on Aβ-evoked neurotoxicity and inhibition of amyloid β aggregation. This may inform the future use of medicinal cannabis formulations in the treatment of Alzheimer's disease and dementia.