Phenolic composition, antioxidant potential and in vitro inhibitory activity of leaves and acorns of Quercus suber on key enzymes relevant for hyperglycemia and Alzheimer's disease

Abstract

This work reports the in vitro antioxidant and inhibitory activities of hexane, methanol and water extracts of cork oak (Quercus suber) against acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), α-amylase and α-glucosidase. The total content of phenolics (TPC), tannins (TTC) and flavonoids (TFC), and the HPLC profile of the main phenolic compounds present in the extracts, were also determined. In the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay the best results were obtained with the methanol and water extracts from both leaves and acorns (41–49%). In the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) method the highest activity was observed with the methanol and leaf water extracts (63–71%). The most significant effects on cholinesterase activity were obtained with the methanol leaf extract at the concentration of 1mg/mL, yielding inhibition values of 79 and 80% on AChE and BuChE, respectively. No relevant activity was detected against α-amylase, but samples significantly inhibited α-glucosidase from baker's yeast, and the best results were obtained with the water and methanol leaf extracts with values of 97 and 89%, respectively, higher than the positive controls used (acarbose and glucobay). The methanol leaf extract had the highest TPC (211mg GAE/g, DW) and TFC (8.2mg RE/g, DW), whereas the water extracts had the highest tannin levels (87CE/g, DW). The main compound in the methanol leaf extract was gentisic acid (24.3mg/g, DW). Our results suggest that leaves and acorns from cork oak contain compounds useful for alleviating symptoms associated with Alzheimer disease and other neurodegenerative ailments as well as diabetes.