Antioxidant property of Eucalyptus globulus Labill. Extracts and inhibitory activities on carbohydrate metabolizing enzymes related to type-2 diabetes

This research evaluated the antioxidant property and carbohydrate metabolizing enzyme inhibitory activity of Eucalyptus globulus Labill leaf extracts. Ethanol extracts of the prior hexane-defatted (DEE) and the non-defatted (NEE) leaf samples of the plant were prepared and screened for constituent phytochemicals by HPLC-DAD. The extracts were tested for antioxidant activity, alpha-amylase and alpha-glucosidase inhibitory activities and molecular docking with selected protein targets were carried out. The two extracts showed notable antioxidant property. Lipid peroxidation inhibitory activities of DEE, NEE and ascorbic acid were 28.4 +/- 1.1 mu g/ml, 33.3 +/- 1.1 mu g/ml, and 34.5 +/- 1.2 mu g/ml, respectively, in terms of IC50. The extracts also demonstrated appreciable inhibition of the carbohydrate metabolizing enzymes when compared to acarbose. IC50 values for alpha-amylase inhibition were 23.6 +/- 1.2 mu g/ml, 14.8 +/- 1.2 mu g/ml and 5.2 +/- 1.3 mu g/ml for DEE, NEE and acarbose, respectively (p < 0.05), while IC50 values for alpha-glucosidase inhibition were 30.0 +/- 1.1 mu g/ml, 6.5 +/- 1.2 mu g/ml and 29.8 +/- 1.8 mu g/ml for DEE, NEE and acarbose, respectively (p < 0.05). HPLC analysis of the extracts indicated that the defatting process eliminated pinitol and robinetinidol, and reduced the concentration the remaining phytoconstituents in the defatted extract. Catechin, ergosterol, pinitol, quercetin and robinetinidol identified by HPLC from the defatted and non-defatted extract displayed good interaction with the carbohydrate metabolizing enzymes with ergosterol presenting the best interaction. These results show that both extracts could be explored in alternative therapeutic approaches for type-2 diabetes. The non-defatted extract appeared to demonstrate superior activities suggesting a positive contribution from the lipophilic constituents of the plant.