Methanol extract of Napoleona vogelii demonstrates anti-nociceptive and anti-inflammatory activities through dopaminergic mechanism and inhibition of inflammatory mediators in rodents

Napoleona vogelii (Lecythidaceae) is used in traditional medicine for the management of pain and inflammatory disorders. This study was conducted to investigate the anti-nociceptive and anti-inflammatory activity of the methanol stem bark extract of N. vogelii in rodents. The extract (100–400 mg/kg) was administered 1 h before intraperitoneal and intraplantar injection of 0.2 mL of 0.6% v/v acetic acid and 0.05 mL of 2% v/v formalin, respectively. Anti-inflammatory activity was investigated using the carrageenan-induced paw edema and formalin-induced arthritis models. Mechanistic studies were conducted by exploring opioidergic, dopaminergic pathways, and inflammatory mediators. There was 62.26% inhibition of inflammatory pain at 400 mg/kg in the formalin-induced paw licking test. In the acetic acid-induced mouse writhing assay, the extract produced a dose-dependent inhibition of writhes with peak effect at 400 mg/kg producing 54.87% inhibition compared with diclofenac at 71.09%. The extract produced 90.98% inhibition of the late phase of carrageenan-induced paw edema and 82.81% inhibition in the formalin-induced arthritis test. The anti-nociceptive activity of the extract was blocked by sulpiride (D₂ receptor antagonist; 1 mg/kg) but not by naloxone (opioid receptor antagonist; 5 mg/kg). In addition, pre-treatment of mice with the extract produced 95.08% inhibition of histamine-induced inflammation similar to that of indomethacin at 97.54% and inhibition of serotonin-induced inflammation at 46.79% compared with indomethacin which produced 94.26%. This study demonstrates that the extract possesses anti-nociceptive and anti-inflammatory activity mediated through inhibition of dopaminergic pathways and inflammatory mediators.