Phytochemical Screening, Antiplasmodial and Antioxidant Activities of Combretum rhodanthum Extracts

Abstract

Background: Plasmodium falciparum is responsible for over 90% of malaria cases and the vast majority of malaria-related deaths globally. Oxidative stress, an imbalance between free radicals and antioxidants, plays a key role in the malaria pathogenesis, potentially leading to increased severity of the disease. Growing evidence has shown that Plasmodium species have become resistant to currently available drugs. Thus, there is a pressing need to search for effective treatments against malaria. Because of drug resistance to antimalarial agents, the World Health Organization recommends the use of medicinal plant extracts as alternative therapy for malaria. Combretum rhodanthum is such a plant, which is traditionally used to treat malaria symptoms. Objective: This study sought to investigate the antiplasmodial and antioxidant activities of Combretum rhodanthum extracts. Methods: To this end, the ethanol extraction of Combretum rhodanthum was carried out by maceration. The as-prepared extract was partitioned with hexane, ethyl acetate and n-butanol. The n-butanol fraction, which was found to be the most potent antiplasmodial fraction was chromatographed to yield eight sub-fractions. Antiplasmodial activity was performed in vitro on chloroquino-sensitive (Plasmodium falciparum 3D7; Pf3D7) and multi-resistant (Plasmodium falciparum Dd2; PfDd2) strains of P. falciparum using the SYBR Green-I assay. Antioxidant activity and phytochemical analysis of the most active extracts were performed using standard methods. The acute toxicity of the active extract was studied according to the OECD (Organisation for Economic Co-operation and Development) protocol, guideline number 423. Results: Upon incubation of C. rhodanthum extracts with PfDd2 and Pf3D7, mean inhibitory concentrations ranged from 10.21 to 24.73 μg/mL and from 18.48 to 39.56 μg/mL, respectively. The n-butanol extract, which was chromatographed yielded eight antiplasmodial sub-extracts, the most potent being subfraction [D] (90% ethyl acetate/10% methanol) with IC50 values of 5.30 and 11.21 μg/mL on PfDd2 and Pf3D7, respectively and selectivity for the multidrug-resistant strain (Resistance index<1). Phytochemical analysis of the ethanol extract showed the presence of tannins, terpenoids, phenolic compounds, and glycosides. Upon DPPH and ABTS assays, extracts and fractions scavenged free radicals with mean radical scavenging concentrations (SC50) lower than 39 μg/mL. Moreover, C. rhodanthum extracts reduced Fe3+ into Fe2+ with mean reduction concentration (RS50) less than 26.1 μg/mL. Acute toxicity study revealed no signs of toxicity in Wistar rats at 2000 mg/kg. Conclusion: This novel contribution demonstrates the antiplasmodial and antioxidant activities of Combretum rhodanthum extracts, thus substantiating the ethnomedicinal use of this plant in treating malaria-like symptoms.