Analgesic and anti-inflammatory activity and pharmacokinetics of alkaloids from seeds of Strychnos nux-vomica after transdermal administration: effect of changes in alkaloid composition

Abstract

Ethnopharmacological relevance: Strychnos nux-vomica L. (Loganiaceae) is grown extensively in southern Asian countries. The dried seed of this plant, nux vomica, has been clinically used in Chinese folk medicine for improving blood circulation, relieving rheumatic pain, reducing swelling and treating cancer.

Aim of the study: This study was carried out to investigate the effect of removing most strychnine from the total alkaloid fraction (TAF) extracted from nux vomica on analgesic and anti-inflammatory activity and pharmacokinetics after transdermal administration.

Materials and methods: Most strychnine was removed from TAF and the resulted modified total alkaloid fraction (MTAF) was obtained. The contents of strychnine and brucine in TAF and MTAF were determined. Then the analgesic and anti-inflammatory activity of TAF, MTAF, brucine and strychnine dissolved in hydrogel was compared after transdermal administration. Furthermore, in vitro and in vivo transdermal absorption profiles of brucine after administration of TAF, MTAF and brucine dissolved in hydrogel were also compared.

Results: In contrast to TAF, most strychnine was removed from MTAF and the ratio of brucine to strychnine was adjusted from 1:1.8 to 2.7:1. MTAF showed significant analgesic activity in all the chemical-, thermal- and physical- induced nociception models, which indicated the presence of both centrally and peripherally mediated activities. MTAF also showed significant anti-inflammatory activity against xylene-induced ear edema. But TAF and strychnine demonstrated little activity in all those pharmacological tests. Brucine showed to be effective in acetic acid-induced writhing and xylene-induced ear edema test. Brucine in MTAF was absorbed more completely than it alone at the same dosage of brucine after transdermal administration.

Conclusions: The results from the present study appeared to support the viewpoint that most strychnine should be removed from TAF to improve analgesic and anti-inflammatory activity. The relatively higher pharmacological activity of MTAF compared to brucine alone is partly due to the enhanced transdermal absorption of brucine.