## 4 Discussion  
The biological activities of ginseng have been largely attributed to ginseng produced by different processing methods and/or biotransformation by human intestinal bacteria [16; 17; 24]. Although Rb1 is the most abundant ginseng in ginseng root and white ginseng, red ginseng produced by a steaming process substantially increases the concentration of Rg3, which is also known to be produced by human intestinal bacteria from Rb1 [22; 23; 24]. Several studies have therefore been aimed at converting ginseng Rb1 to Rg3 by various methods, including steaming, fermentation, or acidic and enzymatic treatments [15; 46]. However, few studies have investigated the anti-diabetic potential of Rb1 in combination with Rg3, which may better reflect actual human consumption and thus biological activities. Intervention studies in humans and animals have demonstrated that ginseng extracts and ginseng improve insulin sensitivity [47; 48]. In vitro studies have also shown their modulatory effects on PPARy, a nuclear receptor for anti-diabetic drugs, and the expression of its downstream target genes [36; 38]. However, literature on the effect of specific ginsenosides Rb1 or Rg3 on adipocyte differentiation and function is currently inconsistent and unclear. Some studies have reported inhibitory effects of ginseng on PPARy expression and adipocyte differentiation [30; 34; 35], while other studies have shown stimulatory effects [36; 37; 38]. These contradictory results from different studies might be attributable to differences in the concentrations of ginsenosides used (i.e., inhibitory with high and stimulatory with low concentrations), cell culture models (i.e., differentiating vs. mature adipocytes), and/or experimental conditions. In the present study, we found that ginseng Rb1 significantly increased PPARy expression and enhanced the differentiation of 3T3-L1 preadipocytes at concentrations between 1 and 50 \(\upmu\)M, whereas Rg3 showed a maximal stimulatory effect at 1 \(\upmu\)M with a dose-dependent decrease at 10 and 50 \(\upmu\)M concentrations (Figures 1 and 2). The ability of Rb1 and Rg3 to increase PPARy mRNA suggests that these ginsenosides may have potential as a natural bioactive component for increasing insulin sensitivity. Our data also indicate that Rb1 and Rg3 may confer insulin-sensitizing effects through the upregulation of adiponectin and GLUT4 gene expression, leading to subsequent glucose uptake and utilization in adipocytes. Interestingly, we also observed similar and comparable effects of Rb1 and Rg3 co-treatment (in a ratio of 9:1) on GLUT4 and adiponectin gene expression (Figure 5). It is worth noting that the ratio of Rb1 and Rg3 (9:1) that has a maximal stimulatory effect on GLUT4 and adiponectin was similar to the profile we typically observed in steamed or fermented ginseng (in a ratio of \(\sim\)8:1). One line of research suggests that adiponectin is an insulin-sensitizing hormone that is expressed exclusively in adipocytes [49]. The mRNA expression of adiponectin and its plasma levels in adipose tissue were highly correlated with obesity-induced insulin resistance, which was reversed by the administration of adiponectin [50; 51]. Further, the insulin-sensitizing actions of TZDs are also known to be mediated by targeting PPARy and adiponectin in adipocytes [52; 53]. A clear association between impaired adipocyte differentiation and insulin resistance has been explained by the observation that TZDs promote adipocyte differentiation, generating small adipocytes that are more insulin sensitive than enlarged adipocytes [54]. It cannot be determined from the present study whether ginseng Rb1, Rg3, or both increases the number of small adipocytes. However, the ability of Rb1 and Rg3 to upregulate the expression of PPARy, GLUT4, and adiponectin mRNAs (Figures 2 and 3) may account for their anti-hyperglycemic effects observed in vivo [55].