Differential effects of CB1 and CB2 agonists on cAMP levels and MAP kinase activation in human peripheral blood mononuclear cells.

In addition to their well known psychotrophic effects, the cannabinoids also display immunosuppressive and anti inflammatory properties including inhibition of T and B lymphocyte proliferation and inhibition of macrophage microbiocidal acitivity. Two subtypes of cannabinoid receptors, CB1 and CB2 have been described [1,2]. While CB1, the central cannabinoid receptor, is predominantly found in the central nervous system, CB1 mRNA is also found in resting B and T lymphocytes, monocytes and neutrophils [3]. The CB2 receptor has only been detected in the periphery. Both receptors are G protein linked. The principal psychoactive cannabinoid, A’tetrahydrocannabinol (THC) has been shown to act as an agonist at the CB1 receptor and as an antagonist at the CB2 receptor [4]. In contrast palmitoyl ethanolamine (PEA), the putative endogenous ligand for CB2, has been shown to act as an agonist for CB2 receptors and as an antagonist for CB1 [5]. We have investigated the effects of these CB ligands on CAMP levels and MAP kinase activation in human peripheral blood mononuclear cells (PBMC’s). Blood from healthy volunteers was obtained by venepuncture and collected into heparin (10 Ulml blood), the red cells were dextran sedimented and the PBMC’s separated over a Ficoll -Paque gradient. The cells were then incubated with either A’THC or PEA at 37°C for 3 hours and then isoproternol at 10dM for 10 minutes at 37%. Cyclic AMP was measured using the Biotrak CAMP kit from Amersham. The results in Figure 1 show that neither A’ THC nor PEA on their own stimulate CAMP production. However while A’ THC inhibits isoprotemol induced stimulation, PEA increases the levels of CAMP produced following isoproternol treatment.