Eugenia brasiliensis leaves extract attenuates visceral and somatic inflammatory pain in mice

Eugenia brasiliensis Lam. (Myrtaceae) is a Brazilian tree distributed throughout Atlantic rain forest, since Bahia until Santa Catarina state, and is popularly known as "grumixaba, grumixameira, cumbixaba, ibaporoiti, and cereja-brasileira". The bark and leaves of Eugenia brasiliensis are used in folk medicine as adstringent, diuretic, energizing, anti-rheumatic and anti-inflammatory. This study aimed at investigating the chemical composition, antinociceptive and anti-inflammatory effect of the hydroalcoholic extract of Eugenia brasiliensis (HEEb).

Chemical composition of the HEEb was determined by High Performance Liquid Chromatography/ESI-Mass Spectrometry (HPLC-ESI-MS/MS). The antinociceptive and anti-inflammatory effects of HEEb (30-300 mg/kg) was verified in mice after oral administration by intra-gastric gavage (i.g.) 60 min prior to experimentation. It was investigated whether HEEb decreases visceral pain and leukocyte migration induced by an intraperitoneal (i.p.) injection of acetic acid (0.6%). We also evaluated whether HEEb decreases nociceptive behavior induced by formalin (including paw edema and temperature), prostaglandin E₂ (PGE₂), histamine, and compound 48/80. Finally, we evaluated the effect of HEEb in the chronic inflammatory (mechanical and thermal hypersensitivity) pain induced by complete Freund's adjuvant (CFA), as well as quantifying the concentration of the pro-inflammatory cytokines TNF-α and IL-6 in the paw by ELISA method.

Seven polyphenols were identified in HEEb by HPLC-ESI-MS/MS analysis. HEEb treatment alleviated nocifensive behavior and leukocyte migration caused by acetic acid. Moreover, HEEb also reduced the inflammatory pain and paw temperature induced by formalin, as well as it decreased nociceptive behavior induced by histamine and compound 48/80. Finally, acute and repeated treatment of animals with HEEb (100 mg/kg, i.g.) markedly reduced the mechanical and thermal (heat) hypersensitivity, besides decrease paw edema and temperature induced by CFA, and this effect was evident until the day 7. Moreover, repeated treatment with HEEb (100 mg/kg, i.g.) significantly reduced the levels of IL-6 and TNF-α in the paw when compared to the CFA group.

This is the first report showing that HEEb presents antinociceptive and anti-inflammatory effects in the visceral and somatic inflammatory pain in mice, possibly involving the inhibition of histamine receptors and pro-inflammatory cytokines activated pathways. Our results are of interest because they support the use of Eugenia brasiliensis as a potential source of phytomedicine for inflammatory diseases and pain.