Abstract

The methanol extract of stem bark of Senna siamea (Fabaceae) was found to contain compounds with anti-poliovirus activity. Bioassay-guided fractionation of the extract resulted in the isolation and identification of six compounds; three triterpenoids- lupenone (1) lupeol (4) and betulinic acid (5); two antraquinones- chrysophanol (2) and physcion (3); and β- sitosterol glucoside (6). To evaluate the capacity of the compounds to inhibit the cytophatic effect of poliovirus in tissue culture, the reduction of viability of infected or uninfected cell cultures was measured using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] colorimetric assay. The selective indices of compounds with antiviral activity were determined by comparing the ratio of cytotoxic concentration at 50% to inhibitory concentration at 50% (CC₅₀/IC₅₀). Lupeol was the most active compound with IC₅₀ value of 0.014 µg/mL but chrysophanol with IC₅₀ 0.46 µg/mL was more selective with selective index (SI) of 32.1. The detection of pharmacologically active compounds in S. siamea extracts provides evidence that Nigerian ethno-medicines may be an important source of anti-poliovirus compounds. This study justifies ethnomedicinal uses of Senna as an anti-viral agent and also provides chemical entities that could lead to discovery and development of antiviral agents.

Key words: Antraquinones, triterpenoids, Senna siamea, MTT colorimetric assay, anti-poliovirus.