Characterisation and effectiveness of bioactive compounds from selected medicinal plants used in the treatment of malaria in Zimbabwe

Abstract

Background: Significant investments and efforts in the fight against malaria have resulted in a notable reduction in new cases and deaths globally. An important challenge is the emergence of Plasmodium falciparum strains resistant to antimalarial drugs, affecting prophylaxis. Limited published information exists on the use of herbal medicine against malaria. This study aims to identify and scientifically evaluate medicinal plants used in malaria treatment in Zimbabwe. Methodology: A comprehensive literature analysis and database mining were conducted to identify plants used in malaria treatment in Zimbabwe. Plant samples were air dried and exposed to ethanol, water, and ethyl acetate. The activities of plant extracts against Plasmodium falciparum and their toxicities against healthy erythrocytes were determined using modified Trager and Jensen (1976) method and MTT-based colorimetric assay. Crude extracts with selectivity index (SI) >7 were selected for phytochemical screening using qualitative and FTIR profiling. Plant extracts with SI >10 underwent further examination based on GC-MS analysis. Results: A total of 61 plant species belonging to 30 families were identified, with Fabaceae being the most represented family, accounting for 17% of the species recorded. Five categories of indigenous practices used in malaria treatment, including herbal medicines, were identified. Twenty-seven plant extracts assessed were active against Plasmodium falciparum, with IC50 below 100μg/ml. The most active extracts were from Tabernaemontana. elegans (IC50 below 5 μg/ml). Most crude extracts (24/27) exhibited good selectivity (SI > 2). Bioactive compounds like terpenoids, cardiac glycosides, alkaloids, and tannins were present in all screened plant extracts. Nineteen phytochemicals were identified, including 9-Octadecenamide, cis-Vaccenic acid, 9, 12-Octadecadienoic acid (Z, Z) - and n-Hexadecanoic acid. Conclusion: This study provides scientific evaluation of selected medicinal plants used against malaria treatment in Zimbabwe and identifies T. elegans as a promising source of antiplasmodial compounds. The strong antiplasmodial activity, selectivity, and diverse phytochemical composition of its stem bark extract highlight its potential as a source of lead compounds for antimalarial drug discovery. These findings contribute to the growing search for plant-derived antimalarial agents and provide a foundation for future isolation and characterisation of bioactive molecules.