Decoding the extracts of Lippia alnifolia Schauer (Verbenaceae): Chemical composition and its impacts on nociception...

Lippia alnifolia Schauer (Verbenaceae) is an aromatic medicinal plant known as "alecrim-de-vaqueiro" and endemic to the Brazilian Caatinga. Its leaves are traditionally used by local populations for the treatment of infections and as a natural antiseptic.

This study aimed to perform the first chemical characterization of extracts obtained from the leaves and inflorescences of L. alnifolia, to evaluate their antinociceptive and anti-inflammatory activities, and to investigate the mechanisms underlying these effects.

The chemical composition of extracts and isolated compounds was determined by chromatographic and spectrometric procedures. Experimental animal models were used to evaluate the antinociceptive and anti-inflammatory effects in male mice. Toxicological evaluation was conducted separately in female mice. The extracts were administered orally at doses of 75, 150 and 300 mg/kg, and their effects were compared to both positive and negative controls across all protocols. In selected assays, animals were pre-treated with pharmacological antagonists (naloxone, glutamate and cinnamaldehyde) to explore potential mechanisms.

LC-MS/MS analysis revealed the presence of phenolic compounds, iridoids, and phenylpropanoids, and the bioactive compounds jaceosidin and verbascoside were isolated. The extracts showed no signs of acute toxicity and did not impair motor coordination, indicating the absence of central nervous system depression. In the acetic acid-induced writhing test, the leaf and inflorescence extracts reduced the number of writhings by 49.39 ± 7.9 % and 58.24 ± 8.8 %, respectively, compared with the control group. In the formalin test, the leaf extract reduced paw licking time by 55.76 ± 2,8 % (phase I) and 67.52 ± 4,5 % (phase II), while the inflorescence extract produced inhibitions of 54.39 ± 1,9 % (phase I) and 72.56 ± 3,1 % (phase II). In the hot plate test, the leaves and inflorescences extracts produced a significant response in the first 30 min with the highest dose 300 mg/kg (27,3 ± 4,1 s and 25,5 ± 5,7 s, respectively). In the Randall-Selitto test, both extracts increased the mechanical hyperalgesia threshold at all tested doses. In the formalin-induced paw edema model, the highest dose (300 mg/kg) produced significant inhibition of edema at 60, 120, and 180 min. Mechanistic assays indicated that the antinociceptive effects are not mediated by opioid receptors.

These findings provide experimental support for the ethnopharmacological use of L. alnifolia in conditions associated with inflammation and pain. Although antimicrobial activity was not evaluated, the observed peripheral anti-inflammatory and antinociceptive effects may contribute to symptom relief in infection-related conditions. The differences observed between leaf and inflorescence extracts indicate that plant part selection is a relevant factor in future pharmacological, phytochemical, and standardization studies.