So-Youn Mok

Identification of flavonoids and flavonoid rhamnosides from Rhododendron mucronulatum for. albiflorum and their inhibitory activities against aldose reductase

To investigate the therapeutic potential of compounds from natural sources, Rhododendron mucronulatum for. albiflorum flowers (RMAF) and R. mucronulatum flowers (RMF) were tested for inhibition of aldose reductase (AR). The methanol extracts of RMAF and RMF exhibited AR inhibitory activities (IC(50) values 1.07 and 1.29 μg/mL, respectively). The stepwise polarity fractions of RMAF were tested for in vitro inhibition of AR from rat lenses. Of these, the ethyl acetate (EtOAc) fraction exhibited AR inhibitory activity (IC(50) 0.15 μg/mL). A chromatography of the active EtOAc fraction of RMAF led to the isolation of six flavonoids, which were identified by spectroscopic analysis as kaempferol (1), afzelin (2), quercetin (3), quercitrin (4), myricetin (5) and myricitrin (6). Compounds 1-6 exhibited high AR inhibitory activity, with IC(50) values of 0.79, 0.31, 0.48, 0.13, 11.92 and 2.67 μg/mL, respectively. HPLC/UV analysis revealed that the major flavonoids of RMAF and RMF are quercitrin (4) and myricitrin (6). Our results suggest that RMAF containing these six flavonoids could be a useful natural source in the development of a novel AR inhibitory agent against diabetic complications.

Isolation of astragalin from flowers of Rhododendron mucronulatum for. albiflorum

A flavonoid was isolated from the flowers of Rhododendron mucronulatum Turcz. for. albiflorum T. Lee by column chromatography. Interpretation of the spectroscopic analysis revealed the structure of the flavonoid to be astragalin. A reverse phase column was used, and a gradient solvent system of water and acetonitrile was employed as the mobile phase. The flow rate was kept constant at 1.0 mL per minute, and the peaks were identified using UV absorbance at 330 nm. The content of astragalin was measured in the flowers of R. mucronulatum (2.67 mg·g−1) and R. mucronulatum Turcz. for. albiflorum T. Lee (2.96 mg·g−1) by HPLC/UV analysis. In addition, astragalin from R. mucronulatum Turcz. for. albiflorum T. Lee flowers showed aldose reductase inhibitory activity (IC50 value of 3.88 M) that was comparable to that of the positive control, quercetin (IC50 value of 2.52 M). This is first report regarding the isolation of astragalin from R. mucronulatum Turcz. for. albiflorum T. Lee. R. mucronulatum Turcz. for. albiflorum T. Lee may be used as a possible source material for natural health supplements in the future.

Antioxidant activity of the methanolic extract of the newly generated vegetable, baemuchae (xBrassicoraphanus).

We investigated the radical scavenging activity and protective effects of the methanol extract (ME) and ferulic acid (FA) from baemuchae (xBrassicoraphanus) against oxidative stress in vitro and on a cellular system using LLC-PK1 renal epithelial cells. In vitro, ME and FA showed dose-dependent radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radicals. LLC-PK1 cells displayed decreased viability in response to nitric oxide-induced oxidative stress. However, ME and FA significantly increased LLC-PK1 cell viability in a dose-dependent manner. Based on HPLC/UV analysis, the FA content was higher in the shoot of baemuchae than in the root. The results of the present study suggest that baemuchae may be a promising source of antioxidants against oxidative stress induced by free radicals.