Antimalarial activity of the aqueous extract and anthraquinones from the root of Senna siamea (LAM) H.S. Irwin & Barneby (Fabaceae).

This study evaluated the antimalarial properties of the aqueous extract of the root of S. siamea in mice and identified two bioactive phytoconstituents from the antimalarial ethyl acetate fraction. The extract demonstrated interesting antimalarial activity with significant ( P < 0.5) percentage parasitaemia suppression of 88.02±1.46 % and clearance of 80.96±3.25 % in Plasmodium beighei -infected mice. The ED 50 values were 194.98 for the suppressive assay and 100 mg/kg for the curative assay. LD 50 was above 2000 mg/kg. Two anthraquinones, Chrysophanol and Cassiamin A, with remarkable antimalarial activity were isolated. These compounds at 10 mg/kg body weight produced % parasitaemia clearance of 68.90 % by Chrysophanol and 70.25 % by Cassiamin A in Rane's curative assay. Mice treated with both compounds recorded a higher haem concentration relative to the untreated group, suggesting haem polymerization as a possible mechanism of antiplasmodial action. The aqueous root extract of S. siamea possesses antimalarial properties. Chrysophanol and Cassiamin A from the ethyl acetate fraction showed antimalarial activity. The compounds act by preventing the conversion of parasite-toxic haem into inactive haemozoin within parasitized erythrocytes. The antimalarial activity of the aqueous extract of S. siamea and Cassiamin A are reported for the first time. Our findings provide a rationale for the continued use of S. siamea root decoction in the traditional treatment of malaria in Ghana.