Ethanol and Water Extract of Purple Sweet Potato Exhibits Anti-Atherosclerotic Activity and Inhibits Protein Glycation

Abstract

It is well known that extracts of purple sweet potato (PSP) have potent antioxidant activity. However, it has not been established whether extracts of PSP inhibit oxidation of low-density lipoprotein (LDL) or protein glycation. LDL oxidation and protein glycation are well-known risk factors for chronic metabolic diseases, such as atherosclerosis and diabetes mellitus. Chopped and sliced PSP and yellow sweet potato (YSP) were extracted individually at a concentration of 1 g of PSP tuber/mL using either ethanol or water for 6 hours. The PSP ethanol extract (100-fold diluted) showed stronger radical (2,2-diphenyl-1-picrylhydrazyl radical) scavenging activity than the water extract of PSP and the ethanol extract of YSP (up to a sixfold higher activity). The ethanol extract of PSP also exhibited the highest increase in ferric reducing ability among all extracts. Cupric ion-mediated LDL oxidation was strongly inhibited by the ethanol extract of PSP, with similar potency to vitamin C treatment (final concentration, 10 mM). The PSP extract strongly inhibited fructose-mediated protein glycation as determined by fluorescence spectroscopy. The PSP extract-treated apolipoprotein (apo) A-I showed a decreased multimerization pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, whereas glycated apoA-I showed the strongest multimeric band. PSP extract treatment also inhibited the uptake of oxidized LDL into human macrophage cells with suppression of malondialdehyde production in the cell culture medium. In conclusion, these results suggest that the extract of PSP can be used as a putative anti-atherosclerotic and antidiabetic agent with strong antioxidant functions. This is the first report to show the biological functions of PSP extract to treat hyperlipidemic and hyperglycemic disorders.