Characterisation of cannabinoid receptors on immune cells and cell lines

Abstract

Cannabinoids may inhibit immune cell function by modulating cytokine/chemokine release but the receptors mediating these events are poorly characterised. The aim of this thesis is to characterise cannabinoid receptors mediating cytokine/chemokine release from immune and inflammatory cells by measuring the effects of cannabinoids on cytokine release using ELISA technique. Apoptosis of inflammatory cells was also assessed by visual evaluation of cells treated with cannabinoids using a nuclear fluorochrome 4'6-diamidino-2 phenyl indole dihydrochloride (DAPI). Non-selective cannabinoid receptor agonists CP55,940 (10-6 -10-4 M- 10 'S M), A? - THC (10 -10 M) and anandamide (10 M- 10-4 M) inhibited LPS-induced release of TNF-a from THP-1 cells, a monocytic cell line. The cannabinoid CB2 receptor antagonist SR144528 (10 -6 M) but not the cannabinoid CB1 receptor antagonist SR141716A (10 -6 M) antagonised the inhibitory effects of CP55,940 (pA2 = 6.1 t 0.1, n=6) on THP-1 cells. Similarly, CP55,940 (10-6-104 M -10 'S M), 09-THC (10 10 M -10 -S M) and anandamide (10 -6 M -10'4 M) inhibited PHA/PMA-induced IL-2 release from Jurkat cells, a lymphocytic cell line. However in contrast to THP-1 cells, neither SR141716A (10 -6 M) nor SR144528 (10 -6 M) antagonised the inhibitory effects of CP55,940 on this cell line. In peripheral blood mononuclear cells a nonselective cannabinoid receptor agonist WIN55212-2 (10'10 M-10'5 M) and a selective cannabinoid CB2 receptor agonist JWH 015 (10 -10 M- 10 -S M) inhibited PHAinduced release of IL-2. These effects were antagonised by SR144528 (10-6 M) (pA2 = 6.3 ± 0.1; 6.5 ± 0.1, n=5 respectively) but not by SR141716A (10 -6 M). CP55,940 (10 -10 M -10 -5 M) produced a small, non-significant (P> 0.05) inhibitory effect on IL-2 release. 09-THC (10 -10 M-10-6 M) and ACEA (10 -'0 M- 10 -6 M) had no significant inhibitory effect on the release of IL-2 from PBMC. CP55,940 (10 M) and A9- THC (10 M) antagonised the inhibitory effects of WIN55212-2 (pA2 = 6.1 ± 0.1; 6.96 ± 0.16, n=5 respectively). In HT-29 cells, CP55,940 (10"10 -10"5 M- 10 M), A9-THC (10 -10 M -10 -5 M), WIN55212-2 (10"10 M-10-5 M) and JWH 015 (10 -10 M- 10 -5 M) inhibited IL-8 release. SR141716A (10 -6 M) antagonised the inhibitory effects of CP55,940 (pA2 = 8.3 ± 0.2 n=6) but did not antagonise the effects of WIN55212-2 and JWH 015. SR144528 (10 -6 M) but not SR141716A (10 -6 M) antagonised the inhibitory effects of CP55,940 (pA2 = 8.2 ± 0.8, n=6), WIN55212-2 (pA2 = 7.1± 0.3, n=6), JWH 015 (pA2 = 7.6 ± 0.4, n=6) respectively. A protein the size of cannabinoid CB2 receptors was localised in this cell line by Western blotting. CP55,940 and WIN55212-2 inhibited basal and agonist-evoked increases in both intracellular cyclic AMP and intracellular calcium at the same concentration as that inhibiting TNF-a-induced release of IL-8. Furthermore anandamide (>1 μM) but not CP55,940 caused apoptosis in Jurkat and HT-29 cell. These data suggest that activation of cannabinoid CB2 receptors in THP-1 cells, PBMC and HT-29 cells could lead to inhibition of cytokine/chemokine release. Furthermore,c annabinoid-evokedin hibition of basal and agonist stimulated increases in HT-29 cells may be related to cannabinoid-evokedin hibition of IL-8 release.T hus data presented in this thesis suggest that cannabinoid CB2 receptor agonists with high efficacy may have potential clinical utility in the treatment of inflammatory conditions such as inflammatory bowel disease (IBD) or chronic obstructive pulmonary disease (COPD) and other inflammatory disorders where epithelial cells have a major role.