Avaliação da susceptibilidade in vitro de isolados de campo de Plasmodium falciparum e Plasmodium vivax a substâncias e extratos de plantas amazônicas

Abstract

The species Plasmodium falciparum and P. vivax are important etiological agents that cause human malaria and represent one of the greatest challenges for public health in the world. These parasites present resistance to the antimalarials presently available for treatment. The main classes of antimalarials used in the world, namely the quinolone alkaloids and derivatives of artemisinin, owe their origins to the natural products quinine and artemisinin, isolated from antimalarial plants. Natural products isolated from antimalarial plants from the Amazon are promising sources of antimalarial substances. This work aimed to evaluate the in vitro susceptibility of field isolates of P. falciparum and P. vivax to extracts and substances isolated from antimalarial plants from the Brazilian Amazon. These Plasmodium field isolates represent the genotypes and phenotypes of the parasites that presently circulate in this region. The isolated compounds ellipticine (1, alkaloid indólico), O,O-diacetyl-4-nerolidylcatechol (2, terpene-phenylpropanoid), neosergeolide (3, quassinoid), 6α-acetoxygedunina (4) e 6α- hidroxydeacetilgedunina (5, limonoids) and the crude extracts of the aerial parts of Andropogon leucostachyus (methanol) and the branch ethanol and leaf chloroform extracts of Xylopia amazônica. These samples had previously been characterized in vitro against standardized strains of P. falciparum and were re-evaluated in the present study against the standardized K1 and 3D7 strains for comparative purposes. Thirty-two P. vivax field isolates and 2 previously stabilized P. falciparum field isolates (MRV and AL) were used. The effects of the isolated substances, extracts and commercial antimalarial standards were determined by applying the microtest and the DELI (Double-site enzyme-linked immunodetection) test. The median inhibitory concentration (IC50) was determined against P. falciparum strains MRV and AL for 1, 2, 3, 4 and 5 (IC50 0.48-0.77; 4.2-4.6; 0.004-0.01; 7.0-6.2 and 6.1-5.7 μM, respectively) and A. leucostachyus and X. amazônica ethanol and chloroform extracts IC50 7.0-7.2, 9.8-9.5 and 7.8-7.4 μg/mL, respectively). Of 32 P. vivax field isolates, 24 exhibited curves from which IC50 were interpretable. Twelve of these P. vivax isolates were evaluated using the microtest and exhibited sensitivity to 1, 2, 3, 4 and 5 (IC50 2.19; 4.01; 0.13; 5.32 and 5.76 μM, respectively) and A. leucostachyus and X. amazônica ethanol and chloroform extracts (IC50 14.0, 15.7 and 13.6 μg/mL, respectively). The 12 P. vivax field isolates evaluated using the DELI-test also exhibited sensitivity to 1, 2 and 3 (IC50 4.7; 9.0; and 0.01 μM, respectively). The field isolates exhibited good susceptibility to the natural products tested in some cases. Substance 3 was the most active against P. falciparum (IC50 0,004-0,01 μM) and P. vivax (IC50 0,01-0,13 μM). The P. vivax field isolates were only a little less sensitive than the standardized strains of P. falciparum used in previous studies of these same substances and extracts. These results show that P. vivax and P. falciparum field isolates exhibit different sensitivity profiles with respect to the natural products evaluated as well as to commerciallyavailable antimalarials. Despite the larger IC50 values exhibited against P. vivax versus P. falciparum field isolates, the natural products investigated exhibited good antiplasmodial activity against P. vivax.