Antioxidant activities and phytochemical constituents of Antidesma thwaitesianum Müll. Arg. leaf extracts.

OBJECTIVE To investigate the antioxidant activities as well as phytochemical constituents of Antidesma thwaitesianum Müll. Arg. leaf extracts. METHODS The leaves of A. thwaitesianum were extracted using three different methods: blending with distilled water, maceration with ethanol and decoction. The chemical antioxidant activity of the plant leaf extracts was evaluated using 2,2-diphenyl-1-picryhydrazyl (DPPH) radical and 2,2'-azinobis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS⁺) radical scavenging assays, as well as the ferric reducing antioxidant power assay. Cellular antioxidant activity was determined by superoxide and nitric oxide scavenging assays. The cytotoxicity of the leaf extracts in RAW 264.7 and differentiated HL-60 cells was tested in parallel using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assays, respectively. The total phenolic and flavonoid contents were also assessed by spectrophotometric analysis. Phytochemical constituents of the most potent extract were investigated by liquid chromatography with an electrospray ionization quadrupole time-of-flight mass spectrometer (LC-ESI-QTOF-MS/MS). RESULTS The ethanolic (ME) and decoction (LW) extracts of dried leaves had the highest chemical scavenging activity against DPPH and ABTS⁺ free radicals with half maximal effective concentration (EC50) values ranging from 3.54 to 6.44 μg/mL. ME and LW exerted moderate ferric reducing activity, with ferric reducing antioxidant power values of 847.41 and 941.26 mg Fe2+/g extract, respectively. Similarly, ME showed potent cellular scavenging activity against superoxide and nitric oxide radicals with EC50 values of 58.12 and 71.90 μg/mL, respectively. However, LW exhibited only strong nitric oxide scavenging activity with an EC50 value of 91.20 μg/mL. The cell viability of RAW 264.7 and HL-60 cells was greater than 70% in all tested concentrations of both extracts, thus confirming the absence of their cytotoxicity. ME and LW contained high total phenolic contents of 231.14 and 274.42 mg gallic acid equivalents per gram, respectively, as well as high total flavonoid contents of 18.82 and 22.17 mg quercetin equivalents per gram, respectively. LC-ESI-QTOF-MS/MS analysis revealed the presence of 52 structurally characterized compounds in ME, 43 of which were tentatively identified. Hydroxycinnamic acids such as caffeic acid and its derivatives were the predominant phenolic compounds. CONCLUSION This is the first report describing potent chemical and cellular antioxidant effects of the ethanolic leaf extract of A. thwaitesianum. The extract contained high total phenolic and flavonoid contents. LC-ESI-QTOF-MS/MS analysis further revealed an abundance of caffeic acid derivatives and flavonoids. These data support its potential use as dietary supplements in oxidative stress prevention.