Antinociceptive activity of Iranian Euphorbia species in mice: Preliminary phytochemical analysis of Euphorbia malleata

The exceedingly large genus Euphorbia is broadly distributed in all phytogeographical units and various habi-tats all over Iran. Iranian Traditional Medicine has referred to a variety of its biological properties, including pain alleviation. This study aimed to investigate the antinociceptive activity of four Iranian endemic Euphor-bia species (E. malleata, E. gypsicola, E. caspica, and E. sylvicola) for the first time. We used two pharmacologi-cal pain tests; tail-flick and writhing tests in mice. E. malleata showed the best effect among the species and was selected for further studies. The antinociceptive effects of different fractions of the methanolic extract of E. malleata were analyzed using the tail-flick test. The ethyl acetate fraction showed the highest antinocicep-tive activity and was selected for phytochemical analysis. This led to the isolation of six compounds, includ-ing oleanolic acid (1), methyl gallate (2), scopoletin (3), (2S)-5,7,3',5'-tetrahydroxyflavanone (4), (-)-catechin (5), and hyperoside (6). The structures of the compounds were identified by NMR and mass spectrometry. In addition, the antinociceptive activities of the compounds were assessed by the tail-flick test. Compounds 4 and 6, which have flavonoid structures, showed the best antinociceptive effects with ED50 values of 5.0 and 4.9 mg/kg, respectively. Pretreatment with naloxone (an opioid antagonist) attenuated the antinociceptive effects of each isolated compound in the tail-flick test. The molecular docking study showed that compound 6 had the best interaction with the active site of the mu-opioid receptor (5C1M). Based on findings, it can be concluded that E. malleata has antinociceptive effects. The reduction of the antinociceptive effect of the iso-lated compounds by naloxone, as well as the affinity for binding to the active site of mu receptor in docking study, suggest that opioid receptors may be involved in the antinociceptive effect.& COPY; 2023 SAAB. Published by Elsevier B.V. All rights reserved.