Flavanones, a class of flavonoids, are abundant in fruits, vegetables, and herbs. They are known to have several biological activities, such as anti-inflammatory and anti-cancer activities, but their effects on obesity remain unclear. Obesity is closely associated with adipocyte differentiation and lipid accumulation in adipose tissue. Therefore, in this study, we examined the effects of flavanone derivatives on adipocyte differentiation and lipid accumulation by using 3T3-L1 cells. Among the 15 flavanone derivatives studied, 4′-phenylflavanone (4PF), with a biphenyl structure, significantly inhibited adipocyte differentiation-related lipid accumulation in 3T3-L1 cells; this inhibition of lipid accumulation was dose-dependent. Gene expression analysis showed that 4PF suppressed the expression of adipogenic marker genes. Although the induction of peroxisome proliferator activator γ2 (Pparγ2), a master regulator of adipocyte differentiation, and its target genes during adipocyte differentiation was attenuated in 4PF-treated cells, 4PF did not directly regulate Pparγ2 gene expression and its activation. In contrast, 4PF suppressed mitotic clonal expansion (MCE), which is associated with changes in the expression of proliferation-related genes at the early stages of adipocyte differentiation. Taken together, these results suggest that 4PF inhibits lipid accumulation because it suppresses MCE during adipocyte differentiation. Thus, our findings may help in the development of anti-obesity drugs.

Obesity is currently the most common cause of metabolic diseases including type 2 diabetes and hyperlipidemia. Obesity results from excess lipid accumulation in adipose tissue. Several studies have investigated the inhibitory effects of natural plant-derived products on adipocyte differentiation and lipid accumulation. In this study, we examined the effect of hydrolysable tannins composed of gallic acid and glucose on adipocyte differentiation in 3T3-L1 cells. 1,2,3,4,6-Penta-O-galloyl-β-D-glucose (PGG) (1), a representative gallotannin, inhibited lipid accumulation in 3T3-L1 cells, whereas ellagitannins (tellimagrandin I, eugeniin and casuarictin) did not. The expression of adipocyte differentiation-related genes, including peroxisome proliferator activator γ2 (Pparγ2), CCAAT/enhancer binding protein α (C/EBPα) and adipocyte fatty acid binding protein (aP2), was significantly suppressed in PGG (1)-treated 3T3-L1 cells beginning at day 2 after induction of differentiation. While PGG (1) did not directly reduce Pparγ2 expression, it reduced the expression of its target genes in mature adipocytes. In addition, PGG (1) treatment inhibited mitotic clonal expansion, one of earliest events of adipocyte differentiation. These findings indicate that PGG (1) has an inhibitory effect on adipocyte differentiation through the suppression of mitotic clonal expansion.

Obesity elevates the risk of cardiovascular disease and has been strongly associated with increases in the incidence of many metabolic diseases. Therefore, prevention of obesity leads to the prevention of metabolic diseases. In light of this, substances that exert anti-obesity effects are crucial for the prevention of obesity. Indirubin, a 3,2′ bisindole isomer of indigo, is the active component of the traditional Chinese medicine used for the treatment of chronic myelocytic leukemia. In particular, indirubin-3′-oxime (1) was shown to inhibit the differentiation of adipocytes. In this study, we investigated the inhibitory effects of nine indirubin-3′-oxime derivatives against lipid accumulation during differentiation in 3T3-L1 cells. Among the compounds tested, 5-methoxyindirubin-3′-oxime (2) and 6-bromoindirubin-3′-oxime (7) at 5 µM exhibited significantly stronger inhibitory activity than indirubin-3′-oxime (1). Furthermore, 5-methoxyindirubin-3′-oxime (2) and 6-bromoindirubin-3′-oxime (7) markedly suppressed the expression of CCAAT/enhancer-binding protein α, peroxisome proliferator activator γ2, and adipocyte protein 2, both of which are key adipogenic regulators at the intermediate stage of adipocyte differentiation. Our results demonstrate that 5-methoxyindirubin-3′-oxime (2) and 6-bromoindirubin-3′-oxime (7) significantly down-regulated lipid accumulation during differentiation of 3T3-L1 cells, suggesting their potential as novel therapeutic drugs against the development of obesity.