Cannabinoid-based therapy as a future for joint degeneration. Focus on the role of CB2 receptor in the arthritis progression and pain: an updated review

Abstract
Over the last several decades, the percentage of patients suffering from different forms of arthritis has increased due to the ageing population and the increasing risk of civilization diseases, e.g. obesity, which contributes to arthritis development. Osteoarthritis and rheumatoid arthritis are estimated to affect 50–60% of people over 65 years old and cause serious health and economic problems. Currently, therapeutic strategies are limited and focus mainly on pain attenuation and maintaining joint functionality. First-line therapies are nonsteroidal anti-inflammatory drugs; in more advanced stages, stronger analgesics, such as opioids, are required, and in the most severe cases, joint arthroplasty is the only option to ensure joint mobility. Cannabinoids, both endocannabinoids and synthetic cannabinoid receptor (CB) agonists, are novel therapeutic options for the treatment of arthritis-associated pain. CB1 receptors are mainly located in the nervous system; thus, CB1 agonists induce many side effects, which limit their therapeutic efficacy. On the other hand, CB2 receptors are mainly located in the periphery on immune cells, and CB2 modulators exert analgesic and anti-inflammatory effects in vitro and in vivo. In the current review, novel research on the cannabinoid-mediated analgesic effect on arthritis is presented, with particular emphasis on the role of the CB2 receptor in arthritis-related pain and the suppression of inflammation.