Δ8-Tetrahydrocannabinol induces cytotoxicity in macrophage J774-1 cells: Involvement of cannabinoid receptor 2 and p38 MAPK

Tetrahydrocannabinol (THC), a psychoactive component of marijuana, is known to exert cytotoxicity in immune cells. In the present study, we examined the cytotoxicity of Δ8-THC in mouse macrophage J774-1 cells and a possible involvement of cannabinoid receptors and stress-responsive mitogen-activated protein kinases (MAPKs) in the cytotoxic process. J774-1 cells were treated with Δ8-THC (0–20 μM) for up to 6 h. As measured by the MTT and LDH assays, Δ8-THC induced cell death of J774-1 cells in a concentration- and/or exposure time-dependent manner. Δ8-THC-induced cell damage was associated with vacuole formation, cell swelling, chromatin condensation, and nuclear fragmentation. The cytotoxic effect of Δ8-THC was significantly prevented by a caspase-1 inhibitor Ac-YVAD-cmk but not a caspase-3 inhibitor z-DEVD-fmk. The pretreatment with SR144528, a CB2 receptor-selective antagonist, effectively suppressed Δ8-THC-induced cytotoxicity in J774-1 cells, which exclusively expressed CB2 receptors as indicated by real-time polymerase chain reaction analysis. In contrast, AM251, a CB1 receptor-selective antagonist, did not affect the cytotoxicity. Pertussis toxin and α-tocopherol significantly attenuated Δ8-THC-induced cytotoxicity suggesting that Gi/o protein coupling signal transduction and oxidative stress are responsible for the cytotoxicity. Δ8-THC stimulated the phosphorylation of p38 MAPK and c-Jun N-terminal kinase (JNK) in J774-1 cells, which were effectively antagonized by the pretreatment with SR144528. In addition, SB203580, a p38 MARK inhibitor, significantly attenuated the cytotoxic effect of Δ8-THC, whereas SP600125, a JNK inhibitor, significantly enhanced the cytotoxicity. These results suggest that the cytotoxicity of Δ8-THC to J774-1 cells is exerted mediated through the CB2 receptor followed by the activation of p38 MAPK.