Inhibition of rat C6 glioma cell proliferation by endogenous and syntheticcannabinoids. Relative involvement of cannabinoid and vanilloid receptors

The effects of the endocannabinoids anandamide (AEA) and 2-arachidonoylglyc erol (2-AG) upon rat C6 glioma cell proliferation were examined and compare d with a series of synthetic cannabinoids and related compounds. Cells were treated with the compounds each day and cell proliferation was monitored f or up to 5 days of exposure. AEA time- and concentration-dependently inhibi ted C6 cell proliferation, After 4 days of treatment, AEA and 2-AG inhibite d C6 cell proliferation with similar potencies (IC50 values of 1.6 and 1.8 muM, respectively), whereas palmitoylethanolamide showed no significant ant iproliferative effects at concentrations up to 10 muM. The antiproliferativ e effects of both AEA and 2-AG were blocked completely by a combination of antagonists at cannabinoid receptors (SR141716A and SR144528 or AM251 and A M630) and vanilloid receptors (capsazepine) as well as by alpha -tocopherol (0.1 and 10 muM), and reduced by calpeptin (10 muM) and fumonisin B-1 (10 muM), but not by L-cycloserine (1 and 100 muM). CP 55,940, JW015, olvanil, and arachidonoyl-serotonin were all found to affect C6 glioma cell prolifer ation (IC50 values of 5.6, 3.2, 5.5, and 1.6 muM, respectively), but the in hibition could not be blocked by cannabinoid + vanilloid receptor antagonis ts. It is concluded that the antiproliferative effects of the endocannabino ids upon C6 cells are brought about by a mechanism involving combined activ ation of both vanilloid receptors and to a lesser extent cannabinoid recept ors, and leading to oxidative stress and calpain activation. However, there is at present no obvious universal mechanism whereby plant-derived, synthe tic, and endogenous cannabinoids affect cell viability and proliferation.