Background and purpose: We investigated expression of cannabinoid receptors and the effects of the endogenous cannabinoid virodhamine and the synthetic agonist CP55,940 on cAMP accumulation and interleukin-8 (IL-8) release in human bronchial epithelial cells.
Experimental approach: Human bronchial epithelial (16HBE14o(-)) cells were used. Total mRNA was isolated and cannabinoid receptor mRNAs were detected by RT-PCR. Expression of CB(1) and CB(2) receptor proteins was detected with Western blotting using receptor-specific antibodies. cAMP accumulation was measured by competitive radioligand binding assay. IL-8 release was measured by ELISA.
Key results: CB(1) and CB(2) receptor mRNAs and proteins were found. Both agonists concentration-dependently decreased forskolin-induced cAMP accumulation. This effect was inhibited by the CB(2) receptor antagonist SR144528, and was sensitive to Pertussis toxin (PTX), suggesting the involvement of CB(2) receptors and G(i/o)-proteins. Cell pretreatment with PTX unmasked a stimulatory component, which was blocked by the CB(1) receptor antagonist SR141716A. CB(2) receptor-mediated inhibition of cAMP production by virodhamine and CP55,940 was paralleled by inhibition of tumor necrosis factor-alpha (TNF-alpha) induced IL-8 release. This inhibition was insensitive to SR141716A. In the absence of agonist, SR144528 by itself reduced TNF-alpha induced IL-8 release.
Conclusions and implications: Our results show for the first time that 16HBE14o(-) cells respond to virodhamine and CP55,940. CB(1) and CB(2) receptor subtypes mediated activation and inhibition of adenylyl cyclase, respectively. Stimulation of the dominant CB(2) receptor signalling pathway diminished cAMP accumulation and TNF-alpha-induced IL-8 release. These observations may imply that cannabinoids exert anti-inflammatory properties in airways by modulating cytokine release.