The atypical cannabinoid O-1602 protects against experimental colitis and inhibits neutrophil recruitment

Background: Cannabinoids are known to reduce intestinal inflammation. Atypical cannabinoids produce pharmacological effects via unidentified targets. We were interested in whether the atypical cannabinoid O-1602, reportedly an agonist of the putative cannabinoid receptor GPR55, reduces disease severity of dextran sulfate sodium (DSS) and trinitrobenzene sulfonic acid (TNBS)-induced colitis in C57BL/6N and CD1 mice. Methods: DSS (2.5% and 4%) was supplied in drinking water for 1 week while TNBS (4 mg) was applied as a single intrarectal bolus. Results: Both treatments caused severe colitis. Injection of O-1602 (5 mg/kg intraperitoneally) significantly reduced macroscopic and histological colitis scores, and myeloperoxidase activity. The protective effect was still present in cannabinoid receptor 1 (CB ₁) and 2 (CB ₂) double knockout mice and mice lacking the GPR55 gene. To investigate a potential mechanism underlying the protection by O-1602 we performed neutrophil chemotactic assays. O-1602 concentration-dependently inhibited migration of murine neutrophils to keratinocyte-derived chemokine (KC), N-formyl-methionyl- leucyl-phenylalanine (fMLP), and the N-formyl-peptide receptor ligand WKYMVm. The inhibitory effect of O-1602 was preserved in neutrophils from CB ₁/CB ₂ double knockout and GPR55 knockout mice. No differences were seen in locomotor activity between O-1602-treated and control mice, indicating lack of central sedation by this compound. Conclusions: Our data demonstrate that O-1602 is protective against experimentally induced colitis and inhibits neutrophil recruitment independently of CB ₁, CB ₂, and GPR55 receptors. Thus, atypical cannabinoids represent a novel class of therapeutics that may be useful for the treatment of inflammatory bowel diseases.