Phytochemicals Analysis, In vitro Anti-plasmodium Activity of Delonix regia Bark and Carica papaya Leaf Extracts in Combination with Chloroquine

Background: The effectiveness of treating malaria may be jeopardized by artemisinin-resistant parasites. Pharmaceutical companies have been using plants for a very long time to generate the prototype molecules needed to treat Plasmodium infections. Objective: To evaluate anti-plasmodial potency of extracts of Delonix regia and Carica papaya when used in combinations with chloroquine. Methods: The plants were collected from Homa-Bay County in Kenya, dried under shade to a consistent weight, and then milled into a fine powder. Organic solvents were then used for extraction. After phytochemical screening of the extracts was conducted, In vitro tests were done on the extracts against Plasmodium falciparum, with a starting concentration of 100µg/mL. To prepare the test concentration ranges, the extracts were serially diluted 2-fold in growth medium. In a sealed gas chamber, the assay plates were incubated at 370C for 72 hours with 3% O2 and 4% CO2 with N2 as the balance. By comparing each well's absorbance to that of a well that contained the drug-free control, the number of parasites still present at each concentration of the test substance were ascertained. Plotting survival against concentration enabled the determination of the IC50 values by a non-linear dose response curve fitting. Results: In this investigation, the extracts from Delonix regia showed significant synergism (based on IC50 shifts) with CQ for both the ethyl acetate and methanol extracts with the exception of the highest combination dosage. Carica papaya extracts were much improved by the presence of CQ; however, this was not consistently reflected in the corresponding CQ IC50. Conclusion: The results of this study which revealed synergism between the study plants extracts and chloroquine, support the reasons why some traditional healers have started combining medicinal herbs with chloroquine to boost its potency.