Phytochemical Composition, Antioxidant, Anti-Helicobacter pylori, and Enzyme Inhibitory Evaluations of Cleistocalyx operculatus Flower Bud and Leaf Fractions

Six solvent fractions isolated from flower bud and leaf ethanolic extracts of Cleistocalyx operculatus were analyzed for their phytochemical contents including phenolics, flavonoids, saponins, tannins, and alkaloids. Antioxidant activities were measured using the ABTS, DPPH, and FRAP assays. The results showed that flower bud aqueous fraction (BAF) and leaf aqueous fraction (LAF) rich in phenolic content (768.18 and 490.74 mg GAE/g dry extract, respectively) exhibited significantly higher antioxidant activities than other fractions. Flower bud hexane fraction (BHF) had remarkably high flavonoid and saponin contents (134.77 mg QE/g and 153.33 mg OA/g dry extract, respectively), followed by that of leaf hexane fraction (LHF) (76.54 mg QE/g and 88.25 mg OA/g dry extract, respectively). BHF and LHF were found to have extremely high antibacterial activity against two H. pylori strains ATCC 51932 and 43504 (MICs of 125 µg/ml). Interestingly, DMC (2’,4’-Dihydroxy-6’-methoxy-3’,5’-dimethylchalcone) isolated from BHF displayed greater antibacterial activity against the bacterial strains (MICs of 25–50 µg/ml) than those of the fractions. In addition, DMC presented potent inhibitory effects on H. pylori-urease (IC50 of 3.2 µg/ml) and α-amylase (IC50 of 83.80 µg/ml), but no inhibition against α-glucosidase. It was also demonstrated that DMC showed its pronounced inhibitory effects on urease activity and biofilm formation of H. pylori, and could increase the membrane permeability of the bacterial cells. Scanning electron micrographs depict that BHF and DMC had strong effects on the cell shape and significantly induced distortion and damage of the cell membrane. The fractions and DMC showed no significant toxicity to four tested human cell lines. Efforts to reduce antibiotic use indicate the need for further researches of the flower buds and DMC as potential products to prevent or treat gastric H. pylori infections.