CB1 and CB2 cannabinoid receptors differentially regulate the production of reactive oxygen species by macrophages.
Han, Ki Hoon 1,*,+; Lim, Sunny 1,+; Ryu, Jewon 1; Lee, Cheol-Whan 1; Kim, Yuna 1; Kang, Ju-Hee 1; Kang, Soon-Suk 2; Ahn, Yeong Ki 1; Park, Chan-Sik 2; Kim, Jae Joong 1
[Article] Cardiovascular Research. 84(3):378-386, December 1, 2009.

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Aims: We investigated the mechanism by which cannabinoid receptors-1 (CB1) and -2 (CB2) modulate inflammatory activities of macrophages.

Methods and results: Real-time polymerase chain reaction showed the predominant CB2 expression in freshly isolated human monocytes. PMA, a potent inducer of differentiation, upregulated CB1 and increased CB1:CB2 transcript ratio from 1:17.5 to 1:3 in 5 days of culture. Immunohistochemistry showed that CB1 protein was colocalized in CD68- and CD36-positive macrophages in human atheroma. Through selective expression of CB1 or CB2 to thioglycollate-elicited peritoneal macrophages, we proved that CB1 and CB2 mediate opposing influences on the production of reactive oxygen species (ROS). Flow cytometry showed that cannabinoid-induced ROS production by macrophages was CB1-dependent. Immunoblotting assays confirmed that macrophage CB1, not CB2, induced phosphorylation of p38-mitogen-activated protein kinase, which modulated ROS production and the subsequent synthesis of tumour necrosis factor-[alpha] and monocyte chemoattractant protein-1. Pull-down assays showed that the Ras family small G protein, Rap1 was activated by CB2. Dominant-negative Rap1 profoundly enhanced CB1-dependent ROS production by macrophages, suggesting CB2 Rap1-dependently inhibits CB1-stimulated ROS production.

Conclusion: CB1 promotes pro-inflammatory responses of macrophages through ROS production, which is negatively regulated by CB2 through Rap1 activation. Blocking CB1 together with selective activation of CB2 may suppress pro-inflammatory responses of macrophages.

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