Cannabinoids as novel anti-inflammatory drugs

 

Cannabinoids are a group of compounds that mediate their effects through cannabinoid receptors. The discovery of Δ9-tetrahydrocannabinol (THC) as the major psychoactive principle in marijuana, as well as the identification of cannabinoid receptors and their endogenous ligands, has led to a significant growth in research aimed at understanding the physiological functions of cannabinoids. Cannabinoid receptors include CB1, which is predominantly expressed in the brain, and CB2, which is primarily found on the cells of the immune system. The fact that both CB1 and CB2 receptors have been found on immune cells suggests that cannabinoids play an important role in the regulation of the immune system. Recent studies demonstrated that administration of THC into mice triggered marked apoptosis in T cells and dendritic cells, resulting in immunosuppression. In addition, several studies showed that cannabinoids downregulate cytokine and chemokine production and, in some models, upregulate T-regulatory cells (Tregs) as a mechanism to suppress inflammatory responses. The endocannabinoid system is also involved in immunoregulation. For example, administration of endocannabinoids or use of inhibitors of enzymes that break down the endocannabinoids, led to immunosuppression and recovery from immune-mediated injury to organs such as the liver. Manipulation of endocannabinoids and/or use of exogenous cannabinoids in vivocan constitute a potent treatment modality against inflammatory disorders. This review will focus on the potential use of cannabinoids as a new class of anti-inflammatory agents against a number of inflammatory and autoimmune diseases that are primarily triggered by activated T cells or other cellular immune components.

Cannabis, commonly known as marijuana, is a product of the Cannabis sativaplant and the active compounds from this plant are collectively referred to as cannabinoids. For several centuries, marijuana has been used as an alternative medicine in many cultures and, recently, its beneficial effects have been shown in: the treatment of nausea and vomiting associated with cancer chemotherapy; anorexia and cachexia seen in HIV/AIDS patients; and in neuropathic pain and spasticity in multiple sclerosis. Cannabinoid pharmacology has made important advances in recent years after the discovery of the cannabinoid receptors(CB1 and CB2). Cannabinoid receptors and their endogenous ligands have provided an excellent platform for the investigation of the therapeutic effects of cannabinoids. It is well known that CB1 and CB2 are heterotrimeric Gi/o-protein-coupled receptors and that they are both expressed in the periphery and the CNS. However, CB1 expression is predominant in the CNS, especially on presynaptic nerves, and CB2 is primarily expressed on immune cells.

Arachidonic acid metabolites have been shown to exhibit properties similar to compounds found in Cannabis sativa. These metabolites are hence referred to as endocannabinoids. These ubiquitous endogenous cannabinoids act as natural ligands for the cannabinoid receptors expressed in mammalian tissue, thus constituting an important lipid-signaling system termed the endocannabinoid system. The endocannabinoid system is an important biological regulatory system that has been shown to be highly conserved from lower invertebrates to higher mammals [7]. Other than the lipid transmitters that serve as ligands for the cannabinoid receptors, the endocannabinoid family also comprises the enzymes for biosynthesis and degradation of the ligands. The endocannabinoids include N-arachidonoylethanolamine, anandamide (AEA), 2-