Abstract
Background: Microglial cells can be regarded as the macrophages of the central nervous system. Their activation has protective functions in the destruction of pathogens, removal of debris and release of neurotrophic factors, but excessive activation can exacerbate the effects of inflammation contributing to neurodegenerative conditions, e.g. Alzheimers disease. The phytocannabinoid cannabidiol (CBD) has a variety of anti-inflammatory properties and the aim of this study was to examine the potential effects and mechanisms of action of cannabidiol and related phytocannabinoids on the function of microglial cells in vitro. Methods: BV-2 murine microglial cells were activated using bacterial lipopolysaccharide (LPS). Expression of cannabinoid CB1 and CB2 receptor mRNA was determined by qPCR. Nitric oxide (NO) was determined with a Griess assay. Western immunoblotting was used to measure the expression of NFκB P65, IKB α, inducible nitric oxide synthase (iNOS), COX-2, and total and phosphorylated forms of the MAP kinases, P38, JNK1/2 and ERK1/2; blots were analysed with an Odyssey imaging system (Li- Cor Bioscience). The effect of CBD on LPS-stimulated phagocytosis was investigated by measuring ingestion of to latex beads. Result: BV-2 cells did not express CB1 or CB2 receptor mRNA. CBD (10μM) decreased NO release from LPS (100ng/ml)-activated cells (65±0.03%). Phagocytosis was similarly reduced by CBD (43%control). CBD inhibited LPS-enhancement of both iNOS (1.5±0.9) and COX-2 expression. LPS significantly induced phosphorylation of ERK 1/2, P38 and JNK and CBD (10μM) inhibited LPS-induced P38 phosphorylation but was without effect on phosphorylation of ERK1/2 and JNK. The P38 inhibiter SB203580 (10 μM) also significantly reduced iNOS expression after 24 hours of LPS stimulation. LPS significantly increased NF-ҚB P65 expression and this was significantly attenuated by CBD (10μM). LPS also stimulated NF-ҚB P65 translocation to the nucleus whereas CBD (10μM) inhibited the effect. Other phytocannabinoids (CBG, CBDV, THCV, CBDA and CBGA (Pertwee, 2008) (all 10 μM) were without effect. Conclusion: The results are compatible with the proposal that CBD inhibits the function of microglial cells, as demonstrated by reductions in both phagocytosis and production of pro-inflammatory mediators. The mechanism of action appears to involve reduced P38 activation leading to attenuation of the action of the pro-inflammatory transcription factor NF-ҚB. The putative receptor(s) mediating the effect of CBD are unknown, but the absence of CB1/2 expression in this BV-2 cell line rules out the involvement of these cannabinoid receptors.