A recent study conducted by researchers at the University of Edinburgh is suggesting a strong link between osteoarthritis, which causes pain and stiffness in the joints and is the most common form of arthritis, and the endocannabioid system, which is found in the synovial tissue and fluid that surround joints. The endocannabinoid system is composed of cannabinoid receptors (which are more popularly known for managing the body’s response to the psychoactive effects of cannabis) and endocannabinoid ligands*. The type 2 cannabinoid receptor (CB2), is proving to be a significant source of defence against this potentially debilitating disease, which can affect all ages and is particularly common among the elderly.
The findings, which offer the eventual promise of new forms of protection, were presented at the 41st European Calcified Tissue Society Congress, held in Prague on May 17 – 20, 2014, by Professor Stuart Ralston, Arthritis Research UK Professor of Rheumatology at the University of Edinburgh. Prof Ralston described how a study of mice with destabilised knee joints showed that cartilage degeneration, which lies at the heart of osteoarthritis, was up to 40% more severe in mice who were deficient in CB2 receptors, when compared to ‘normal’ mice, with the figure reaching up to 60% more severe among aged mice that developed spontaneous osteoarthritis and were deficient in CB2 receptors, when compared to their aged ‘normal’ counterparts.
The study also showed that a synthesised cannabinoid ligand, HU308, significantly inhibited the progression of arthritis in younger mice with normal levels of CB2 and had no effect on those with CB2 receptor deficiency.
Professor Ralston said: “Learning what provides natural protection against osteoarthritis can potentially give us a much greater insight into how we can develop treatments. We know from this study that, in mice, a CB2 receptor deficiency means a much higher likelihood of developing osteoarthritis and that the use of the synthesised cannabinoid, HU308, in normal mice offers additional protection against the disease.
“Our next step, we hope, is to investigate the role of the CB2 pathway in humans with osteoarthritis.”
* About receptors and ligands
Receptors and ligands carry out a great deal of physiology on the subcellular level. Receptors are sites on the surface of cells that allow specific molecules to bind to them. Ligands are these specific molecules. An agonist is a ligand that binds to the active site of a receptor and initiates some change in body function. An antagonist is a ligand that does not bring about a functional change when it binds to receptors. (Campbell, 1996).
European Calcified Tissue Society