HYPOGLYCEMIC EFFECTS, ANTIOXIDANT, ANTIGLYCATION AND DIGESTIVE ENZYME INHIBITION BY THE MAIN BIOACTIVE COMPOUNDS IN COFFEE LEAF EXTRACTS

Coffee leaves of the species Coffea arabica are a significant source of polyphenolic compounds that display many positive biologic effects, including high antioxidant capacity. The current study focused on investigating antioxidant capacity, antiglycation activity and the inhibitory effects on the digestive enzymes, α-glucosidase and pancreatic lipase, of extracts from C. arabica leaves using in vitro models. The leaves of coffee trees (Coffea arabica) were collected in the plantations located at the Experimental Farm of the Agricultural Research Company of Minas Gerais (EPAMIG). The extraction procedure was conducted in a domestic microwave oven at maximum power (1000 W) for four minutes, to simulate a tea infusion. Exhaustive extraction by a Soxhlet apparatus. Initially, the extraction was performed with 250 mL of hexane (3x - 3 hours) to promote the removal of the lipid phase from the plant material. Subsequently, the same procedure was repeated using methanol. HPLC-DAD analysis of the aqueous extracts elucidated a chemical profile qualitatively characterized by three classes of polyphenols (xanthone, chlorogenic acid and rutin) along with the alkaloid caffeine. The α-glucosidase inhibitory activity of the extracts was evaluated according to the chromogenic method reported by Shinde et al. (2008) with slight modification. Anti-lipase activity was performed according to the methodology of Jaradat et al. (2017) with some modifications. Assays to determine the deactivation activity of the 2-20-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) radical (ABTS), the peroxyl radical (ROO) (measured by the oxygen radical absorbance capacity (ORAC) assay), the superoxide radical generated by the NADH/PMS system, and the hypochlorous acid (HOCl) were conducted according to Melo et al. (2015). The hydrogen peroxide (H2O2) scavenging activity was determined according to Chisté et al. (2011). Preliminary cytotoxicity tests were performed showing non-toxic concentration at 250 g/mL for both extractions. Analysis showed higher antioxidant capacity for microwave oven technique extraction compared to Soxhlet extraction in all scavenging activity in vitro models, with higher amount of total polyphenolic compounds in the microwave oven technique extraction, with the extracts containing, on average, 60.87 ± 0.02 mg of GAE/g of total polyphenolic compounds. Mangiferin, one of the main bioactive compounds from coffee leaves, could be responsible for the scavenging activity. The aqueous extracts also demonstrated strong inhibition of α-glucosidase (IC50 = 85.50 ± 0.08 μg/mL) and pancreatic lipase (IC50 = 109.5 ± 0.04 μg/mL) with higher potency than the positive controls acarbose and orlistat, respectively. In addition, methanol extracts from coffee leaves (EL1 and EL2), showed a reduction in fluorescence indicating potential anti-glycation activity.