Bioactivity and chemical constituents of selected medicinal plants from leguminosae family in Malaysia

Flowers and leaves of three plants from Leguminosae family (Caesalpiniodeae subfamily), namely Bauhinia kockiana, Caesalpinia pulcherrima and Cassia surattensis were screened for their bioactivities such as antibacterial, cytotoxicity and antioxidant activities. Antibacterial activity was determined using disc diffusion (Kirby-Bauer) and macrobroth dilution methods, while the cytotoxicity was assessed using MTT cell viability assay. Antioxidant properties were evaluated by determining the total phenolic (TPC), total flavonoid (TFC), total anthocyanin (TAC) contents and various antioxidant activity assays (2,2-diphenyl-1-picrylhydrazyl radical scavenging, ferric reducing power, ferrous ion chelating and lipid peroxidation inhibition). It was found that the plant extracts exhibited moderate antibacterial activity, with MIC values in the range 100 - 230 µg/mL. All extracts exhibited moderate cytotoxicity towards MCF-7 breast cancer cells, and the GI50 values ranged from 25 - 49 µg/mL. It was found that C. pulcherrima displayed the strongest cytotoxicity (26 - 32 µg/mL), followed by B. kockiana (32 - 45 µg/mL) and C. surattensis (43 - 49 µg/mL). B. kockiana flower was found to possess the highest TPC (8280 ± 498 mg GAE/100g), free radical scavenging activity (AEAC 14600 ± 2360 mg AA/100 g) and reducing ability (72.4 ± 8.7 mg GAE/g). C. pulcherrima leaf displayed the highest ferrous ion chelating and lipid peroxidation inhibition activities. Bioassay-guided (based on anti-MRSA and cytotoxicity) fractionation and isolation of bioactive phytochemicals from ethyl acetate and methanol extracts of B. kockiana flower afforded two phenolic compounds, namely gallic acid and methyl gallate. This is the first report on the presence of these two phenol constituents from B. kockiana. Antibacterial activity against MRSA by gallic acid and methyl gallate was examined and it was found that methyl gallate exhibited stronger antibacterial activity (MIC values 237 - 373 µg/mL) than gallic acid (MIC values 363 - 560 µg/mL). The cytotoxicity of gallic acid and methyl gallate was evaluated in five cancer cell lines : breast (MCF-7), prostate (PC-3, LNCaP and DU145) and colon (HCT-116). It was found that gallic acid is more cytotoxic than methyl gallate, whereby it displayed moderate cytotoxicity towards MCF-7 and PC-3 cell lines. Weak cytotoxicity towards LNCaP and HCT-116 cell lines was observed but it was not active against DU145 cell line. Observation under fluorescence microscopy of gallic acid treated PC-3 cells stained with acridine orange (AO) and propidium iodide (PI) showed that gallic acid induces apoptosis in PC-3 cells in dose-dependent manner.