Cannabidiol Targets Mitochondria to Regulate Intracellular Ca2+ Levels
Journal of Neuroscience
Cannabinoids and the endocannabinoid system have attracted considerable interest for therapeutic applications. Nevertheless, the mechanism of action of one of the main nonpsychoactive phytocannabinoids, cannabidiol (CBD), remains elusive despite potentially beneficial properties as an anti-convulsant and neuroprotectant. Here, we characterize the mechanisms by which CBD regulates Ca 2ϩ homeostasis and mediates neuroprotection in neuronal preparations. Imaging studies in hippocampal cultures
... campal cultures using fura-2 AM suggested that CBD-mediated Ca 2ϩ regulation is bidirectional, depending on the excitability of cells. Under physiological K ϩ /Ca 2ϩ levels, CBD caused a subtle rise in [Ca 2ϩ ] i , whereas CBD reduced [Ca 2ϩ ] i and prevented Ca 2ϩ oscillations under high-excitability conditions (high K ϩ or exposure to the K ϩ channel antagonist 4AP). Regulation of [Ca 2ϩ ] i was not primarily mediated by interactions with ryanodine or IP 3 receptors of the endoplasmic reticulum. Instead, dual-calcium imaging experiments with a cytosolic (fura-2 AM) and a mitochondrial (Rhod-FF, AM) fluorophore implied that mitochondria act as sinks and sources for CBD's [Ca 2ϩ ] i regulation. Application of carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP) and the mitochondrial Na ϩ /Ca 2ϩ exchange inhibitor, CGP 37157, but not the mitochondrial permeability transition pore inhibitor cyclosporin A, prevented subsequent CBD-induced Ca 2ϩ responses. In established human neuroblastoma cell lines (SH-SY5Y) treated with mitochondrial toxins, CBD (0.1 and 1 M) was neuroprotective against the uncoupler FCCP (53% protection), and modestly protective against hydrogen peroxide-(16%) and oligomycin-(15%) mediated cell death, a pattern also confirmed in cultured hippocampal neurons. Thus, under pathological conditions involving mitochondrial dysfunction and Ca 2ϩ dysregulation, CBD may prove beneficial in preventing apoptotic signaling via a restoration of Ca 2ϩ homeostasis.