Je-Hyuk Lee

Vitamin C as an Antioxidant: Evaluation of Its Role in Disease Prevention

Vitamin C in humans must be ingested for survival. Vitamin C is an electron donor, and this property accounts for all its known functions. As an electron donor, vitamin C is a potent water-soluble antioxidant in humans. Antioxidant effects of vitamin C have been demonstrated in many experiments in vitro. Human diseases such as atherosclerosis and cancer might occur in part from oxidant damage to tissues. Oxidation of lipids, proteins and DNA results in specific oxidation products that can be measured in the laboratory. While these biomarkers of oxidation have been measured in humans, such assays have not yet been validated or standardized, and the relationship of oxidant markers to human disease conditions is not clear. Epidemiological studies show that diets high in fruits and vegetables are associated with lower risk of cardiovascular disease, stroke and cancer, and with increased longevity. Whether these protective effects are directly attributable to vitamin C is not known. Intervention studies with vitamin C have shown no change in markers of oxidation or clinical benefit. Dose concentration studies of vitamin C in healthy people showed a sigmoidal relationship between oral dose and plasma and tissue vitamin C concentrations. Hence, optimal dosing is critical to intervention studies using vitamin C. Ideally, future studies of antioxidant actions of vitamin C should target selected patient groups. These groups should be known to have increased oxidative damage as assessed by a reliable biomarker or should have high morbidity and mortality due to diseases thought to be caused or exacerbated by oxidant damage.

Inhibition of the intestinal glucose transporter GLUT2 by flavonoids

We tested whether the dominant intestinal sugar transporter GLUT2 was inhibited by intestinal luminal compounds that are inefficiently absorbed and naturally present in foods. Because of their abundance in fruits and vegetables, flavonoids were selected as model compounds. Robust inhibition of glucose and fructose transport by GLUT2 expressed in Xenopus laevis oocytes was produced by the flavonols myricetin, fisetin, the widely consumed flavonoid quercetin, and its glucoside precursor isoquercitrin. IC50s for quercetin, myricetin, and isoquercitrin were ∼200‐ to 1000‐fold less than glucose or fructose concentrations, and noncompetitive inhibition was observed. The two other major intestinal sugar transporters, GLUT5 and SGLT1, were unaffected by flavonoids. Sugar transport by GLUT2 overexpressed in pituitary cells and naturally present in Caco‐2E intestinal cells was similarly inhibited by quercetin. GLUT2 was detected on the apical side of Caco‐2E cells, indicating that GLUT2 was in the correct orientation to be inhibited by luminal compounds. Quercetin itself was not transported by the three major intestinal glucose transporters. Because the flavonoid quercetin, a food component with an excellent pharmacology safety profile, might act as a potent luminal inhibitor of sugar absorption independent of its own transport, flavonols show promise as new pharmacologic agents in the obesity epidemic.—Kwon, O., Eck, P., Chen, S., Corpe, C. P., Lee, J‐H., Kruhlak, M., Levine, M. Inhibition of the intestinal glucose transporter GLUT2 by flavonoids. FASEB J. 21, 366–377 (2007)

Antiadipogenic Effects of Salvia plebeia R. Br. Extracts by Extraction Conditions in 3T3-L1 Preadipocytes

*YD Life Science Research Institutes, YD Life Science Co. Ltd., Seongnam 462-807, Korea.**Department of Food and Nutrition, Kongju National University, Yesan 340-802, Korea.ABSTRACT : This study was carried out to investigate the effects of Salvia plebeia R. Br. ethanolic extract with differentaspects (stem/leaf and whole plant) on differentiation and lipid accumulation in 3T3-L1 preadipocytes. The morphologicalchanges and the degrees of lipid accumulation in 3T3-L1 cells were measured by Oil Red O staining and intra-cellular trig-lyceride (TG) assay. The mRNA expressions of special peroxisome proliferation activated receptor- genes (PPAR), CCAAT/enhancer-binding protein (C/EBPα), fatty acid synthase (FAS) and lipoprotein lipase (LPL) were detected by reverse tran-scriptase polymerase chain reaction (RT-PCR). The 50% ethanolic extracts (100μg/mL) of stem and leaf (SALE) and 30%ethanolic extracts (100 g/mL) of whole plant (SAE) from Salvia plebeia R. Br. were significantly attenuated lipid accumula-tion during adipogenesis in 3T3-L1 cells. Ethyl acetate-soluble fractions (50μg/mL) significantly inhibited lipid dropletaccumulation in 3T3-L1 cells. In addition, SALE induced down-regulation of specific adipogenic transcriptional factors (C/EBPα and PPARγ) and target genes (FAS and LPL) during adipogenesis. Salvia plebeia R. Br. may be used as a safe and effi-cient natural substance to manage obesity.Key Words : Salvia plebeia, 3T3-L1, Adipogenesis, C/EBP α, PPARγ, FAS, LPL