Aspidosperma (Apocynaceae) plant cytotoxicity and activity towards malaria parasites. Part II: experimental studies withAspidosperma ramiflorum in vivo and in vitro

Abstract

Several species of Aspidosperma plants are used to treat diseases in the tropics, including Aspidosperma ramiflorum, which acts against leishmaniasis, an activity that is experimentally confirmed. The species, known as guatambu-yellow, yellow peroba, coffee-peroba and matiambu, grows in the Atlantic Forest of Brazil in the South to the Southeast regions. Through a guided biofractionation of A. ramiflorum extracts, the plant activity against Plasmodium falciparum was evaluated in vitro for toxicity towards human hepatoma G2 cells, normal monkey kidney cells and nonimmortalised human monocytes isolated from peripheral blood. Six of the seven extracts tested were active at low doses (half-maximal drug inhibitory concentration < 3.8 µg/mL); the aqueous extract was inactive. Overall, the plant extracts and the purified compounds displayed low toxicity in vitro. A nonsoluble extract fraction and one purified alkaloid isositsirikine (compound 5) displayed high selectivity indexes (SI) (= 56 and 113, respectively), whereas compounds 2 and 3 were toxic (SI < 10). The structure, activity and low toxicity of isositsirikine in vitro are described here for the first time in A. ramiflorum, but only the neutral and precipitate plant fractions were tested for activity, which caused up to 53% parasitaemia inhibition of Plasmodium berghei in mice with blood-induced malaria. This plant species is likely to be useful in the further development of an antimalarial drug, but its pharmacological evaluation is still required.

Fig. 1:. major monoterpenoid indole alkaloids from Aspidosperma ramiflorum. Drawing, displaying and characterising the chemical structures, substructures and reactions were performed using Marvin 5.4.1.1, 2011 (ChemAxon) (chemaxon.com).

Fig. 2:. flowchart fractionation of Aspidosperma ramiflorumusing acid base crude extract from stem bark of the plant. IC50: half-maximal drug inhibitory concentration.

Fig. 3:. off-line ESI-MS of crude extract from stem bark ofAspidosperma ramiflorum. Ion at m/z467 corresponding to ramiflorine A (1) and ramiflorine B (2), ion at m/z 327 corresponding to 10-methoxy-geissoschizol (3) and ion at m/z 355 corresponding to β-yohimbine (4) and isositsikine (5).