Uveitis is
inflammation of the uvea which consists of the iris, ciliary body and the choroid of the eye.
Uveitis can lead to impaired vision and is responsible for 10% of all cases of
blindness globally. Using an
endotoxin-induced
uveitis (EIU) rodent model, our previous data implicated the endogenous
cannabinoid system (ECS) in the amelioration of many of the components of the inflammatory response. Here, we test the hypothesis that the reduction in inflammatory mediators in the EIU model by the CB2 agonist,
HU308, is associated with changes in ECS endogenous
ligands as well as related
lipids,
prostaglandins (PGs), 2-acyl glycerols, and lipoamines. Analysis of leukocytes and neutrophils, CB2
mRNA, and 26
lipids in the eye of WT mice after EIU induction and
HU308 treatment were compared to the same analyses in the CB2 knock-out (CB2 KO) mouse. Endothelial leukocyte adhesion and neutrophil migration were significantly increased in both WT and CB2 KO after EIU.
HU308 significantly reduced the leukocyte adhesion and neutrophil recruitment in the WT animals.
HU308 also significantly reduced leukocyte adhesion in the CB2 KO mouse, yet, had no effect on neutrophil infiltration suggesting an important off-target effect of
HU308. Lipidomics profiles revealed significant increases in 6 non-ECS
lipids after EIU in the WT and that
HU308 effectively reduced these back to control levels; in addition,
HU308 increased levels of 2-acyl glycerols and decreased all N-acyl glycines. CB2 KOs with saline-injection compared to WT had significantly elevated levels of 2-acyl glycerols, whereas levels of
N-oleoyl ethanolamine (OEA), N-stearoyl
ethanolamine (SEA), and
PGE2 were reduced. CB2 KOs with EIU had 13
lipids that were significantly lower than WT with EIU including 4 N-acyl glycines.
HU308 had no effect on
lipid concentrations in the CB2 KOs with EIU, however, it did cause further reductions on 3 additional
lipids compared to saline controls.
HU308 appears to be acting at a non-CB2 target for the reduction of leukocyte infiltration in the EIU model; however, our data suggest that
HU308 is working through CB2 to reduce neutrophil migration and for the regulation of multiple
lipid signaling pathways including PGs, lipoamines, and 2-acyl glycerols. These data implicate ocular CB2 as a key component of
lipid signaling in the eye and part of the regulatory processes of
inflammation.