Identification of some bioactive metabolites and inhibitory receptors in the antinociceptive activity of Tagetes lucida Cav.

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Tagetes lucida Cav. is an ancient medicinal plant used to treat different ailments involving neurological diseases and pain. However, scientific studies to validate their medicinal properties as analgesic have not been described. The aim of this study was to evaluate the T. lucida antinociceptive response using pain models. Bioactive compounds and a possible mechanism of action were also explored. Dose-response effects of an ethanol crude extract were investigated in the writhing and formalin tests in mice and rats, respectively. The extract was fractionated to isolate active fractions and bioactive compounds (quercetagetin 7‑O‑β‑d‑glucoside and 6,7‑dimethoxycoumarin) using the formalin test. The antinociceptive effects were compared to the reference drugs (tramadol 10 mg/kg, diclofenac 50 mg/kg, and/or ketorolac 1 mg/kg, i.p.). The ethanol extract was explored in the presence of naloxone (3 mg/kg, i.p. a non-selective opioid receptor antagonist) and WAY100635 (0.5 mg/kg, s.c., a selective 5-HT1A receptor antagonist) to screen their participation as possible inhibitory mechanisms involved in the antinociceptive response of T. lucida. The ethanol crude extract, fractions, and pure compounds caused a significant antinociceptive response resembling the effect of the reference drugs. Both opioid and 5-HT1A receptors participated in the analgesic –like activity of the extract, which did not produce gastric damage. On the contrary, the gastric damage produced as an adverse effect of the analgesic ketorolac was prevented when combined with the extract. In conclusion, these preliminary data provide evidence and give support to the properties attributed to T. lucida in the traditional medicine to alleviate pain.