Antinociceptive effect of neo-clerodane diterpenes obtained from Baccharis flabellata

We report here for the first time antinociceptive effects of extracts from Baccharis flabellata. Two extracts in this analysis, one obtained in summer and the other during winter time. Our results indicate that both extract show strong antinociceptive effects, being the extracts obtained during the summer significantly more active. Our results suggest that this activity is mainly due to the presence of the diene-acid clerodane ent-15,16-epoxy-19-hydroxy-1,3,13(16),14-clerodatetraen-18-oic acid (DAC) and its dimer called DACD. Employing naloxone as an antagonist of opioid receptors, we demonstrated that both compounds act on opioid receptors, being the antinociceptive effect of DACD stronger than DAC. Thus, the antinociceptive activity of DACD was almost two times stronger than DAC (44.8 over 24.6 s in the hot-plate test) after one hour of treatments. In order to better understand the mechanism of action at molecular level of these compounds, we conducted a molecular modeling study analyzing the molecular interactions of DAC and DACD complexes with the κ-ORs. Our results suggest interactions for both DAC and DACD with Gln115, Val118, Tyr119, Asn122 and Tyr313 stabilizing their complexes; however, these interactions are significantly stronger for DACD with respect to DAC. This finding could explain why DACD have a higher affinity for the κ-ORs. These results are in agreement with the obtained antinociceptive effect. In addition, our results indicate that these neoclerodanes would have a mechanism of action similar to that of salvinorin A; such information can be very useful for the design of new inhibitors of κ-ORs.