Cannabinoid 2 receptor signalling in endotoxin-induced uveitis

Abstract

Activation of the cannabinoid 2 receptor (CB2R) is anti-inflammatory in models of ocular inflammation. The objective of this study was to examine the anti-inflammatory actions of the novel highly potent and selective CB2R agonists, RO6871304 and RO6871085, that originate from two chemically diverse series, as well as a novel structurally related CB2R inverse agonist, RO6851228, in a model of experimental endotoxin-induced uveitis (EIU). We used the CB2R agonists, HU308 and HU910, for comparison. Both of these cannabinoids are based on the structure of the classical cannabinoid, 9-tetrahydrocannabinol (THC). EIU was induced by intravitreal injection of lipopolysaccharide (LPS) into wild-type (WT) and CB2R genetic knockout mice. Leukocyte-endothelial adhesion in the iris microvasculature was studied 6 h after LPS injection using intravital microscopy. Topical treatment with the CB2R agonists, RO6871304, RO6871085, and HU910, significantly decreased LPS-induced leukocyte-endothelial adhesion compared to vehicle. Conversely, treatment with the CB2R inverse agonist, RO6851228, increased LPS-induced leukocyte-endothelial adhesion. Consistent with in vivo inhibition of leukocyte adhesion, the CB2R agonist, RO6871304, significantly decreased neutrophil migration in vitro compared to vehicle. Topical treatment with RO6871304 in neutrophil-depleted mice 5 h prior to leukocyte adoptive transfer, significantly decreased LPS-induced adhesion of adoptively-transferred leukocytes compared to vehicle; this suggests that the effect of CB2R agonists on leukocyte adhesion is likely meditated by a reduction in activation of resident ocular immune cells. Taken together, these data demonstrate an anti-inflammatory role for CB2R in the eye and suggest that drugs targeting the endocannabinoid system may be useful therapeutics for ocular inflammatory disease.