Antioxidant and antiplasmodial activities of Razafimandimbisonia minor (Baill.) Kainul. & B. Bremer leaves (Rubiaceae)

Background Razafimandimbisonia minor (Baill.) Kainul. & B. Bremer (Rubiaceae), a specie endemic to Madagascar, is traditionally used in Malagasy medicine. A decoction of the leaves is employed to treat liver disorders, fatigue and fever. The aim of this study was to assess the plant's antioxidant activity, determine the content of total phenolic compounds and flavonoids, and analyze the antiplasmodial potential. Methods The leaves were collected, shade dried and ground. The methanol extract obtained by maceration was partitioned by liquid-liquid to produce hexane, ethyl acetate and aqueous fractions. Phytochemical screening was carried out using standard methods, followed by analysis of phenol and flavonoid contents, as well as antioxidant and antiplasmodial activity tests. Quantification of total polyphenols and flavonoids was carried out by UV spectrophotometry, using colorimetry with 10% Folin-Ciocalteu reagent and 2% aluminum chloride respectively. Antioxidant activity was measured by the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging assay. Antimalaria activity was assessed by measuring fluorescence with the SYBR Green dye on the chloroquine-resistant Plasmodium falciparum strain FCM29. Results were analyzed by ANOVA with Tukey's test. Results The methanol extract had a high polyphenol and flavonoid content, with concentrations of 280.8 ± 4.6 mg EGA/g and 50.4 ± 2.3 mg ER/g respectively. Biological tests revealed a better antioxidant activity of this extract, with a 50% inhibitory concentration of free radicals measured at 21.58 ± 0.05 µg/mL. But, the hexane and ethyl acetate extracts showed moderate antiplasmodial activity with concentrations of 21.32 and 24.42 µg/mL respectively, while the aqueous and methanol extracts showed weaker activity with concentrations of 41.5 µg/mL and 50.71 µg/mL, respectively. Conclusion These results display the phenolic and flavonoid content of the methanol extract of Razafimandimbisonia minor leaves, which corroborates with antioxidant activity, but the antimalarial activity is rather weak. They underline the value of using this plant for phytomedicinal properties, confirming the important role in malagasy traditional medicine.