Validation of an HPLC-method for an antiplasmodially active stem bark extract of Nauclea pobeguinii

Stem bark extracts of Nauclea pobeguinii (Rubiaceae) are widely used in African traditional medicine against malaria. Alkaloids, such as the major compound strictosamide, may be responsible for this activity [1,2]. An HPLC-method for the quantification of strictosamide in the stem bark extract of N. pobeguinii was developed. The method was validated according to the ICH guidelines. The response function of ajmalicine HCl, used as a secondary standard, was linear in a range from 4.2 to 21.2µg/mL. The method was shown to be precise in respect to the time (RSD of 2.2%, 3 days, n=6) and with respect to the concentration (RSD of 2.6%, 3 levels, n=6). The accuracy of the method was investigated by means of a recovery experiment (mean recovery of 92.2% and RSD of 9.4%).

A crude ethanolic extract of the bark, containing 5.6% (w/w) strictosamide, was evaluated in vivo in the Plasmodium berghei mouse model (PO at 300mg/kg for two times 5 daily doses). Chloroquine was used as positive control at 10mg/kg. Treatment with the crude extract resulted in moderate depression of parasitaemia during dosing, however quickly followed by a full relapse (mean survival time=about 13 days). One group received the treatment by intraperitoneal (IP) route at the same dosing regimen and showed the same results. At termination of the experiment at day 21, a single survivor in the PO group, was apparently cured (no parasitaemia). The single survivor in the IP group showed high parasitaemia and was in a moribund state. It can be concluded that the crude extract of N. pobeguinii has slight antimalarial potential when administered orally in a suppressive dosing regimen of two times 5 days at 300mg/kg. Its action is likely to be static since full relapse occurs quickly after ending the daily dosing.

References: [1] Zeches, M. et al. (1985)J. Nat. Prod. 48:42–46.

[2] Abreu, P. et al. (2001) Nat. Prod. Lett. 15:43–48.