R(+)-methanandamide induces cyclooxygenase-2 expression in human neuroglioma cells via a non-cannabinoid receptor-mediated mechanism

Cannabinoids affect prostaglandin (PG) formation in the central nervous sys tem through as yet unidentified mechanisms. Using H4 human neuroglioma cell s, the present study investigates the effect of R(+)-methanandamide (metabo lically stable analogue of the endocannabinoid anandamide) on the expressio n of the cyclooxygenase-2 (COX-2) enzyme. Incubation of cells with R(+)-met hanandamide was accompanied by concentration-dependent increases in COX-2 m RNA, COX-2 protein, and COX-2-dependent PGE(2) synthesis. Moreover, treatme nt of cells with R(+)-methanandamide in the presence of interleukin-1 beta led to an overadditive induction of COX-2 expression. The stimulatory effec t of R(+)-methanandamide on COX-2 expression was mimicked by the structural ly unrelated cannabinoid Delta (9)-tetrahydrocannabinol. Stimulation of bot h COX-2 mRNA expression and subsequent PGE(2) synthesis by R(+)-methanandam ide was not affected by the selective CB1 receptor antagonist AM-251 or the G(i/o) protein inactivator pertussis toxin. Enhancement of COX-2 expressio n by R(+)-methanandamide was paralleled by time-dependent phosphorylations of p38 mitogen-activated protein kinase (MAPK) and p42/44 MAPK. Consistent with the activation of both kinases, R(+)-methanandamide-induced COX-2 mRNA expression and PGE(2) formation were abrogated in the presence of specific inhibitors of p38 MAPK (SB203580) and p42/44 MAPK activation (PD98059). To gether, our results demonstrate that R(+)-methanandamide induces COX-2 expr ession in human neuroglioma cells via a cannabinoid receptor-independent me chanism involving activation of the MAPK pathway. In conclusion, induction of COX-2 expression may represent a novel mechanism by which cannabinoids m ediate PG-dependent effects within the central nervous system. (C) 2001 Aca demic Press.