Rhabdomyolysis has been reported in patients who abuse synthetic cannabinoids. However, no studies have yet assessed whether these cases reflect the direct cytotoxicity of synthetic cannabinoids on skeletal muscle, a possibility that the present study sought to address. Specifically, this study investigated the cytotoxicity of the synthetic cannabinoid CP-55,940, a compound that acts equally on both types of cannabinoid receptors (CB1 and CB2), in a human embryonic rhabdomyosarcoma (RD) cell line. Exposure of these cells to CP-55,940 resulted in concentration-dependent decreases in cell viability. These effects were attenuated by pre-incubation with AM251 (30 µM), a selective CB1 receptor antagonist, but not by pre-incubation with AM630 (30 µM), a selective CB2 receptor antagonist. Following treatment with CP-55,940, RD cells exhibited apoptosis, as indicated by the accumulation of annexin-V, activation of caspase-3, and a loss of the mitochondrial membrane potential. Additionally, CP-55,940 treatment of RD cells led to increases in intracellular Ca2+ levels. CP-55,940-induced cell death was significantly attenuated in the absence of extracellular Ca2+, and was partially decreased by pre-incubation with verapamil (5 µM) or diltiazem (5 µM), compounds that block the L-type Ca2+ channel. Our results indicate that the cytotoxicity of CP-55,940 towards RD cells (skeletal muscle cells) is mediated by the CB1 receptor, but not by the CB2 receptor. Our results further suggest that calcium influx through the L-type channel may play an important role in the apoptosis induced by these compounds.
Keywords: Apoptosis; Cannabinoid (CB1) receptor; Caspase-3; L-type calcium channel; Mitochondrial membrane potential; Rhabdomyosarcoma (RD) cell line; Synthetic cannabinoid CP-55,940.