In this study, procyanidins fractions of dimers and trimers (F1-F2) from the Leucosidea sericea total extract (LSTE) were investigated for their chemical constituents. The total extract and the procyanidins were employed in the synthesis of gold nanoparticles (Au NPs) and fully characterized. Au NPs of 6, 24 and 21 nm were obtained using LSTE, F1 and F2 respectively. Zeta potential and in vitro stability studies confirmed the stability of the particles. The enzymatic activity of LSTE, F1, F2 and their corresponding Au NPs showed strong inhibitory alpha-amylase activity where F1 Au NPs demonstrated the highest with IC 50 of 1.88 µg/mL. On the other hand, F2 Au NPs displayed the strongest alpha-glucosidase activity at 4.5 µg/mL. F2 and F2 Au NPs also demonstrated the highest antioxidant activity, 1834.0 ± 4.7 µM AAE/g and 1521.9 ± 3.0 µM TE/g respectively. The study revealed not only the ability of procyanidins dimers (F1 and F2) in forming biostable and bioactive Au NPs but also, a significant enhancement of the natural products activities, which could improve the smart delivery in future biomedical applications.Biomolecules 2020, 10, 452 2 of 24 applying nanoparticles through the green route is their biocompatibility [5]. Many green synthesized nanoparticles have demonstrated interesting biological activities [5,10] including antimicrobial and antidiabetic properties.Diabetes mellitus has undoubtedly become a serious health challenge. More worrisome is type II diabetes mellitus (T2DM), which accounts for 90% of diabetes mellitus. It occurs as a result of the inefficient processing of insulin [11]. As of 2017, the population of adults between the ages of 20 and 79 that suffered from diabetes was 425 million [12]. This is equivalent to 9.9% of the world's population [12]. By estimation, this disease would have drastically increased by 48% in 28 years if not properly managed [13]. Although drugs like miglitol, vigliobose as well as acarbose are available in the market, they are costly and their continuous use is associated with side effects like diarrhea, dropsy, heart failure, damage to the liver, weight gain, abdominal pain, hyperglycemia, and flatulence, necessitating the need for more potent and newer remedies [14][15][16].It is well established that bioactive compounds in various plants possess significant effects in delaying and management of T2DM [17]. Extracts from different plants have been reported as alpha-glucosidase and alpha-amylase inhibitors [18][19][20][21][22][23][24][25][26][27]. Additionally, biologically synthesized Au NPs using plant extracts showed interesting antidiabetic activity. The extracts of Chamalcostus cuspidatus [28], Gymnema sylvestre [29], Cassia fistula stem bark [30], Hericium erinaceus [31], Turbinaria conoides [32], Sambucus nigra [33] and Sargassum swartzi [34] displayed antidiabetic activities in various investigations. Silver/gold NPs of Ocimum basilicum [35] and cinnamon extract [36] also lowers glucose levels. The use of single molecules as reducing/stabilizing agents for ...
