Detailed characterization of the endocannabinoid system in human macrophages and foam cells, and anti-inflammatory role of type-2 cannabinoid receptor

Activation of GPR55 Receptors Exacerbates oxLDL-Induced Lipid Accumulation and Inflammatory Responses, while Reducing Cholesterol Efflux from Human Macrophages

The G protein-coupled receptor GPR55 has been proposed as a new cannabinoid receptor associated with bone remodelling, nervous system excitability, vascular homeostasis as well as in several pathophysiological conditions including obesity and cancer. However, its physiological role and underlying mechanism remain unclear. In the present work, we demonstrate for the first time its presence in human macrophages and its increased expression in ox-LDL-induced foam cells. In addition, pharmacological activation of GPR55 by its selective agonist O-1602 increased CD36- and SRB-I-mediated lipid accumulation and blocked cholesterol efflux by downregulating ATP-binding cassette (ABC) transporters ABCA1 and ABCG1, as well as enhanced cytokine- and pro-metalloprotease-9 (pro-MMP-9)-induced proinflammatory responses in foam cells. Treatment with cannabidiol, a selective antagonist of GPR55, counteracted these pro-atherogenic and proinflammatory O-1602-mediated effects. Our data suggest that GPR55 could play deleterious role in ox-LDL-induced foam cells and could be a novel pharmacological target to manage atherosclerosis and other related cardiovascular diseases.

The endocannabinoid system and its therapeutic implications in rheumatoid arthritis

Since the discovery of the endogenous receptor for Δ(9)-tetrahydrocannabinol, a main constituent of marijuana, the endocannabinoid system (comprising cannabinoid receptors and their endogenous ligands, as well as the enzymes involved in their metabolic processes) has been implicated as having multiple regulatory functions in many central and peripheral conditions, including rheumatoid arthritis (RA). RA is an immune-mediated inflammatory disease that is associated with the involvement of many kinds of cells (such as fibroblastlike synoviocytes [FLSs], osteoclasts, T cells, B cells, and macrophages) and molecules (such as interleukin-1β, tumor necrosis factor-α, interleukin-6, matrix metalloproteinases [MMPs], and chemokines). Increasing evidence suggests that the endocannabinoid system, especially cannabinoid receptor 2 (CB2), has an important role in the pathophysiology of RA. Many members of the endocannabinoid system are reported to inhibit synovial inflammation, hyperplasia, and cartilage destruction in RA. In particular, specific activation of CB2 may relieve RA by inhibiting not only the production of autoantibodies, proinflammatory cytokines, and MMPs, but also bone erosion, immune response mediated by T cells, and the proliferation of FLSs. In this review, we will discuss the possible functions of the endocannabinoid system in the modulation of RA, which may be a potential target for treatment.

Endocannabinoid signalling in innate and adaptive immunity

The immune system can be modulated and regulated not only by foreign antigens but also by other humoral factors and metabolic products, which are able to affect several quantitative and qualitative aspects of immunity. Among these, endocannabinoids are a group of bioactive lipids that might serve as secondary modulators, which when mobilized coincident with or shortly after first-line immune modulators, increase or decrease many immune functions. Most immune cells express these bioactive lipids, together with their set of receptors and of enzymes regulating their synthesis and degradation. In this review, a synopsis of the manifold immunomodulatory effects of endocannabinoids and their signalling in the different cell populations of innate and adaptive immunity is appointed, with a particular distinction between mice and human immune system compartments.

Activation of cannabinoid receptor 2 attenuates synovitis and joint distruction in collagen-induced arthritis

OBJECTIVES

Recent studies have suggested immunomodulatory and anti-inflammatory effects of cannabinoid receptor 2 (CB2R) activation, which is devoid of psychoactivity. We have demonstrated the expression of CB2R in synovial tissue from patients with rheumatoid arthritis (RA), and its specific activation shows inhibitory effects on fibroblast-like synoviocytes. However, it is still unclear whether selective activation of CB2R inhibits joint inflammation or protects joint damage in RA.

METHODS

A murine model of collagen-induced arthritis (CIA) was used to evaluate the therapeutic efficacy of HU-308, a selective CB2R agonist. The disease severity was evaluated by semi-quantitative scoring of joint swelling, histological assessment of joint inflammation and structure, and radiographic assessment of joint destruction by using digital plain radiographs and micro-CT scans. The concentrations of various isotypes of anti-collagen II antibodies in sera and the levels of cytokines in culture supernatants were determined by ELISA.

RESULTS

Compared with vehicle treatment, protective treatment with intraperitoneal injection of HU-308 (0.3-1.0 mg/kg) failed to decrease the incidence of the development of CIA, but it effectively suppressed the severity of the disease. In CIA mice, treatment with HU-308 significantly decreased joint swelling, synovial inflammation, and joint destruction, as well as serum levels of anti-collagen II antibodies. In vitro, HU-308 (1-10 μM) significantly suppressed the production of proinflammatory cytokines IL-6 and TNF-α from lipopolysaccharide-stimulated murine peritoneal macrophages with intact CB2R in dose-dependent manners. HU-308 failed to elicit any inhibitory effect of on lipopolysaccharide-stimulated macrophages from CB2R-knockout mice.

CONCLUSIONS

Activation of CB2R by HU-308 has therapeutic potential for RA to suppress synovitis and alleviate joint destruction by inhibiting the production of autoantibodies and proinflammatory cytokines.