Lignin, an active component in the corn silk water extract, inhibits glycation

The formation of advanced glycation end products is associated with aging and diabetic complications such as neuropathy, retinopathy, and nephropathy. Thus, the suppression of AGEs formation could prevent and/or treat their related disorders. Corn silk is used as a traditional medicine for the prevention of diabetic complications and treatment of edema in Japan and China. Previous studies revealed the anti-glycation activity of flavonoids in the methanolic extract of corn silk. The anti-glycation activity of the corn silk water extract was higher than that of the methanolic extract; however, the active components of the water extract remained unidentified. The purpose of this study is to make clear the components showing anti-glycation activity in the corn silk water extract and elucidated their structural characteristics. The evaluation of anti-glycation activity was carried out by enzyme-linked immunosorbent assay to detect glycated bovine serum albumin. Remarkable anti-glycation activity was observed in the > 3 kDa fraction. Reversed-phase HPLC analysis of this fraction showed broad peaks characteristic of high-molecular-weight polyphenols. Decomposition reactions did not provide evidence of condensed or acid-hydrolyzable tannins. Therefore, polyphenols contained in the corn silk water extract were considered to be lignin-carbohydrate complex. The ¹H- and ¹³C-nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy spectra of the > 3 kDa fraction were in agreement with the values reported for lignin. Consequently, we concluded that lignin-carbohydrate complex is one of the active components against glycation in the corn silk water extract.