Abstract

Background: This study evaluated the antioxidant activities and alleviation of insulin resistance of three Sweet Potato Leaf Extracts (SPLE) with 70% ethanol prepared by lyophilization and oven-drying 40 °C.

Methods: Content of total phenols, flavonoids, total anthocyanins, and anthocyanidin composition was analyzed. Moreover, DPPH radicals, Trolox equivalent antioxidant capacity, and ferrous ironchelating activity were determined. Cell culture and viability test and effect of plant extracts on glucose uptake were also studied.

Results: For total phenol, flavonoid, and anthocyanin contents, both CYY98 and TN64 showed better antioxidant contents than did CN1927. Anthocyanidin compositions of cyanidin and malvidin were both rich in lyophilized CYY98. The 40 °C-dried CN1927 had significantly lower DPPH radical-scavenging activity than the other tested samples. Red leaves showed a higher ABTS-scavenging efficacy than CN1927 and CYY98 for each processing method. The 40 °C dried CYY98 had the highest iron-chelating capacity. EC50 values of the iron-chelating activity of all lyophilized leaves of each variety were higher than those 40 °C dried leaves. The highest improvement in insulin-resistant FL83B cells was achieved by 40 °C drying of TN64. Relative expression levels of the insulin receptor and IR substrate-1 in hepatocyte cells significantly increased by lyophilization of CN1927, 40 °C drying of TN64, and lyophilization of CYY98. All SPLEs treatments significantly increased expressions of glucose transporter-2 relative to that of a tumor necrosis factor-α -treated group.

Conclusion: The lyophilized CN1927 and CYY98 SPLEs, and 40 °C-dried TN64 can improve TNF-α -induced insulin resistance by activating insulin signaling, thus resulting in increased glucose uptake.

Keywords: Glucose uptake, sweet potato leaf extracts, antioxidant activity, total phenols, flavonoids, sweet potato leaf extracts (SPLE).

Graphical Abstract