Antioxidant and antidiabetic activity of leaves of Ipomoea batatas grown in continental Croatia

Ipomoea batatas (L.) Lam. is a plant originating from subtropical and tropical areas of Americas. While its roots are widely used in human nutrition, the vines and leaves of Ipomoea batatas serve as a green feed for cattle. The purpose of this investigation was to determine antioxidant activity of ethanolic and aqueous extract of leaf of Ipomoea batatas grown in continental parts of Croatia. Furthermore, effect on the glutathione (GSH) level in glucose induced oxidative stress in cultured Hep G2 cells was established. Content of total phenols and flavonols were determined by using Folin Ciocalteu and aluminium chloride method, respectivelly. Antioxidant activities of the samples were determined by three different test systems, namely DPPH radical scavenging activity, β-carotene/linoleic acid and reducing power assay. Total glutathione levels were quantified using Cayman's GSH assay kit. Ethanolic extract was found to be rich in total phenolics (9.00±0.32%) and flavonols (4.31±0.26%), while the quantities of those compounds in aqueous extract were approximately ten and three times lower, respectively. The extracts were effective as antioxidants in model systems in concentration-dependent manner. Antioxidant activity of ethanolic extract was strongly pronounced and there were no statistically significant difference between activity of ethanolic extract and positive control butylated hydroxianisol in DPPH radical scavenging and β-carotene/linoleic acid assay (Student's t-test, P<0.05). Positive correlation was observed between DPPH radical scavenging activity potential (r ²>0.9) and total phenolic content of the extracts. In addition to that, aqueous and ethanolic extract significantly increased intracellular GSH levels at concentration of 50 and 10µg/mL, respectivelly. Our findings indicate that Ipomoea batatas leaf demonstrates a marked antioxidative potential that may be helpful in the prevention of diabetic complications associated with oxidative stress