Quercus infectoria galls : bioactivities of the extracts and the isolated phytochemicals

Abstract

Quercus infectoria is widely used among society particularly in Malaysia as an alternative to improve various ailments and minimize progression of diseases. This plant was claimed to have antimicrobial, antioxidant and cytotoxic effects. Antibiotic resistant microorganism and antibiotics side effects are among the most worrisome issue for the treatment of microbial infections. The occurrence of cancer also has become a major cause of morbidity and mortality worldwide and the treatment remains challenging for medical practitioners. The aims of this study were to isolate secondary metabolites from Q. infectoria galls and to determine the antimicrobial, antioxidant and cytotoxicity of extracts and isolated compounds. The galls were extracted successively using Soxhlet apparatus with n-hexane (HEX), dichloromethane (DCM) and methanol (MeOH) and fractionated using chromatographic techniques. The isolated compounds were characterized using spectroscopic techniques. The antimicrobial activities were determined using disc diffusion method, MIC and MBC values, synergistic effect and effect on cell membrane. The antioxidant activities were determined by using total phenolic content, total flavonoid content, DPPH free radical scavenging, ?-carotene bleaching, superoxide anion scavenging and reducing power assays. The cytotoxicity of isolated compounds was tested on MCF-7 using MTT assay. Phytochemical screening of MeOH extract showed presence of phenol, phytosterols, flavonoid and protein. The HEX extract showed antimicrobial activity against Staphylococcus aureus ATCC 25923. The MeOH extract showed antimicrobial activity against S. aureus, Bacillus cereus ATCC 11778, Pseudomonas aeruginosa ATCC 11778 and Escherichia coli ATCC 25922. The HEX, DCM and MeOH extracts showed no antifungal activity against Candida albicans IMR C 523/11A, Candida krusei IMR C 434/07A and Aspergillus niger ATCC16404. The DCM extract showed no activity against all tested microorganism. Methyl gallate (16) and gallic acid (17) were isolated from MeOH extract. Compound 16 showed no antimicrobial activity against the tested microorganisms. Compound 17 showed inhibitory effect only on S. aureus with diameter of inhibition zone 11.33 mm ±0.58 and the MIC and MBC values were 125 µg/mL. The compound 17 caused microbial membrane leakage and showed synergistic effect in combination with chloramphenicol. DPPH scavenging activity of HEX, DCM and MeOH extracts were 11 %, 30 % and 96 %, respectively at 5 mg/mL and IC50 values of MeOH extract was 57.33 µg/mL. Both 16 and 17 showed 97 % and 95 % of inhibition with the IC50 values of 31.67 and 91.17 µg/mL, respectively. The ?-carotene bleaching activity of HEX, DCM, MeOH extracts, 16 and 17 were 58 %, 61 %, 72 %, 67 % and 66 %, respectively. Both 16 and 17 exhibited 59 % and 62 % superoxide anion scavenging activity with the IC50 values of 113.33 and 144.67 µg/mL, respectively. The IC50 values of 16 and 17 in reducing assay were 17.42 and 17.08 µg/mL, respectively and in MTT assay were 96.17 and 10.58 µg/mL, respectively. Present study was able to clarify the crucial role of 16 as a potent antimicrobial compound of the Q. infectoria galls and proved to act on the cell membrane of S. aureus. Combination of 16 and chloramphenicol enhanced the performance of antibiotic and reduced its dosage. Considering the antioxidants and cytotoxic activities, it can be concluded that these isolated compounds from Q. infectoria galls were promising candidates for cancer preventive approaches.