Cannabinoids as novel anti-inflammatory drugs

Abstract

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 vivo can 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.

Figure 1. Cannabinoids and multiple sclerosis

The three main cell types that are involved in demyelination of the nerve fibers and axons in the CNS include activated T-cells, microglia and astrocytes. In activated T-cells, treatment with WIN 55,212-12, AEA and JWH-015 has been shown to inhibit cytokine production, infiltration of cells into the spinal cord and in vitro recall response to myelin oligodendrocyte glycoprotein by T-cells. Cannabinoids also inhibit the antigen presenting abilities of microglia by downregulating MHCII expression, costimulatory molecule CD40 expression, as well as cytokine secretion. Astrocytes, the major cell population in the brain, are also affected, as cannabinoid binding to the receptors leads to inhibition of inflammatory molecules, such as nitric oxide, cytokines and chemokines. In addition, anandamide binding leads to secretion of neural growth factor secretion and protection of the neurons in the CNS. ACEA: Arachidonyl-2-ethylamide; NGF: Neuronal growth factor.

Figure 2

Endocannabinoids, CB1 antagonists and CB2 agonists as potential drugs for the treatment of liver injury.