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Cannabinoid receptor activity of polyacetylenes and polyenes from Echinacea pallida
Echinacea products are among the best-selling herbal preparations in the western world, mainly used for the treatment of upper respiratory tract infections and the common cold. The fractionation of a supercritical CO2-extract of Echinacea pallida (Nutt.) Nutt. roots led to the isolation of seven polyacetylenes and polyenes. The structures were determined by UV, NMR and MS in comparison with data from literature , . The aim of our recent study was to investigate the potential cannabinoid receptor activity of the isolated compounds on human CB1R and CB2R and compare those results with prior studies . So far only alkamides have been shown to bind to the human CB2R with high affinity , . As cannabinoid receptors couple to Gi/G0 proteins, the activity of the intrinsic GTPase can be measured using the radioactively labelled GTP derivative [γ-32P]GTP. The amount of 32Pi release allows a conclusion to be drawn about the pharmacological behaviour of the tested compound . Dose-response curves focusing on CB2R activity were drawn for (8Z)-pentadeca-8,11-diene-2-one and (8Z)-pentadeca-8-ene-2-one, resulting in logEC50 values in the micromolar range (–5.66±0.27 and –5.02±0.26, respectively) and a stimulation of GTPase activity of 10%±6 and 14%±2, respectively as compared to basal GTPase activation. This is in contrast to some Echinacea alkamides that stimulated GTPase activity up to 136±14%. Observing no significant activity at either receptor, these findings support the hypothesis that polyacetylenes and polyenes do not affect the immune system via the cannabinergic system .
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