Cytotoxic Effects ofCombretum platypetalumWelw. ex M.A. Lawson subsp. oatesii (Rolfe) Exell (Combretaceae) Leaf Extracts on Jurkat T-cells and Reversal of Effects by Reduced Glutathione

More than 60 % of anticancer drugs have been obtained from natural sources including plants, marine organisms and microorganisms. Leaves of Combretum platypetalum Welw. ex M.A. Lawson subsp. oatesii (Rolfe) Exell have been reported to be toxic to herbivores in Zimbabwe. The aim of this study was to determine if leaf extracts of C. platypetalum have cytotoxic effects on Jurkat-T leukemic cells and in the process determine possible link to toxicity. Leaf extracts of C. platypetalum were prepared and tested for their effects on Jurkat T cells. The effects of combining the plant extract 1,3-bis(2-chloroethyl)-1-nitrosourea (BiCNU) as well as the effects of the extract on the efflux of monochlorobimane conjugate from Jurkat cells were also determined. All extracts showed different cytotoxic effects, whereas the methanolic leaf extract exhibited the most cytotoxic effects at 125 μg/ml resulting in 1.5 % cell viability. There was decreased cell viability when the plant extract was combined with BiCNU. Incubation of the plant extract with reduced glutathione, showed that cell viability increased when the compound and the extract where combined. The efflux of the monochlorobimane GSH conjugate was inhibited when cells were incubated with the extract. The results showed that C. platypetalum extracts exhibited significant cytotoxic activities, and the extract may act by inducing oxidative stress in Jurkat T cells and inhibiting transport across the cell membranes.