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