Characterization of endocannabinoids and related acylethanolamides in the synovial fluid of dogs with osteoarthritis: a pilot study

Background: Cannabis-based drugs have been shown to be effective in inflammatory diseases. A number of endocannabinoids including N-arachidonoylethanolamide (anandamide, AEA) and 2-arachidonyl glycerol (2-AG) with activity at the cannabinoid receptors (CBR) CBR1 and CBR2, have been identified. Other structurally related endogenous fatty acid compounds such as oleoylethanolamide (OEA) and palmitoyl ethanolamide (PEA) have been identified in biological tissues. These compounds do not bind to CBR but might be involved in facilitating the actions of directly acting endocannabinoids and thus are commonly termed " entourage" compounds due to their ability to modulate the endocannabinoid system. The aim of this study was to evaluate the presence of endocannabinoids and entourage compounds in the synovial fluid of dogs with osteoarthritis subjected to arthrotomy of the knee joint. Cytokines and cytology were studied as well. Results: AEA, 2-AG, OEA and PEA were all present in the synovial fluid of arthritic knees and in the contralateral joints; in addition, a significant increase of OEA and 2AG levels were noted in SF from OA knees when compared to the contralateral joints. Conclusion: The identification and quantification of endocannabinoids and entourage compounds levels in synovial fluids from dogs with OA of the knee is reported for the first time. Our data are instrumental for future studies involving a greater number of dogs. Cannabinoids represent an emerging and innovative pharmacological tool for the treatment of OA and further studies are warranted to evaluate the effectiveness of cannabinoids in veterinary medicine.