In Vitro and in Vivo Anti-Hyperglycemic Activities of Taxifolin and Its Derivatives Isolated from Pigmented Rice (<i>Oryzae sativa</i> L. cv. Superhongmi)

Abstract

Superhongmi is a new rice variety, which was developed for the enrichment of bioactive compounds through cross-breeding three varieties of rice breeds in Korea. The high-performance liquid chromatography coupled with a photodiode array detector quadrupole and tandem time-of-flight mass spectrometry (HPLC/PDA/QTOF-MS) analysis has revealed that superhongmi bran extract contained four taxifolin derivatives as well as cyanidin 3-glucoside. The high-performance countercurrent chromatography (CCC) and reversed-phase HPLC led to the isolation of aforementioned five compounds, and spectroscopic analysis identified cyanidin 3-glucoside (<b>1</b>), along with (2<i>R</i>,3<i>R</i>)-taxifolin 3-<i>O</i>-β-d-glucopyranoside (<b>2</b>), (2<i>R</i>,3<i>R</i>)-4'-<i>O</i>-methyltaxifolin 3-<i>O</i>-β-d-glucopyranoside (a novel compound) (<b>3</b>), (2<i>R</i>,3<i>R</i>)-taxifolin (<b>4</b>), and (2<i>R</i>,3<i>R</i>)-4'-<i>O</i>-methyltaxifolin (<b>5</b>). Compound <b>2</b> had the highest rat small intestinal sucrase inhibitory activity (0.54 mM) relevant for potentially managing postprandial hyperglycemia, followed by compound <b>1</b> (0.97 mM) and compound <b>4</b> (1.74 mM, IC₅₀). The anti-hyperglycemic effect of compound <b>4</b> (taxifolin), a main peak in HPLC analysis was investigated using a Sprague-Dawley (SD) rat model. Compared to a control, taxifolin treatment (<i>p</i> < 0.001) reduced significantly after sucrose loading the observed postprandial blood glucose and the maximum blood glucose (<i>C</i>_max) by 15% (203.60 ± 15.86 to 172.30 ± 12.74). These results indicate that taxifolin derivatives that inhibit the activity of carbohydrate-hydrolyzing enzymes resulting in reduced dietary carbohydrate absorption can potentially be used as a strategy to manage diabetes.