A fraction of unripe kiwi fruit extract regulates adipocyte differentiation and function in 3T3-L1 cells.

Adipocyte dysfunction is strongly associated with the development of insulin resistance and diabetes, and regulation of adipogenesis is important in prevention of diabetes. We prepared a 100% methanol fraction of methanolic extract from unripe kiwi fruit (Actinidia deliciosa), designated KMF (kiwi fruit methanol fraction). When applied to 3T3-L1 preadipocyte cells, KMF promoted adipocyte differentiation, increased glycerol-3-phosphate dehydrogenase (GPDH) activity, and increased triglyceride (TG) content. KMF markedly increased mRNA expression of peroxisome proliferator-activated receptor gamma (PPARgamma)-the master adipogenic transcription factor-and its target genes. Moreover, KMF increased mRNA expression and protein secretion of adiponectin, whereas mRNA expression and secretion of monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6) were decreased. Compared with troglitazone, KMF decreased the production of reactive oxygen species (ROS) and nuclear factor-kappaB (NFkappaB) activation. Glucose uptake was stimulated by KMF in differentiated 3T3-L1 adipocytes. Taken together, these results indicate that KMF may exert beneficial effects against diabetes via its ability to regulate adipocyte differentiation and function.

Flavanone exhibits PPARgamma ligand activity and enhances differentiation of 3T3-L1 adipocytes.

Flavanones are class of polyphenolic compounds, some of which are found in foods and provide health benefits. In this study, we show that flavanone significantly enhances differentiation of 3T3-L1 preadipocytes. During adipogenesis, flavanone enhanced expression of genes and accumulation of proteins that are involved in adipocyte function. Some reports have indicated that flavanone inhibits proliferation of mammalian cells, and down-regulates expression of growth-related proteins. Such proteins include phosphorylated ERK1/2, cyclins, and Cdks that are important for an early event in adipogenesis, mitotic clonal expansion (MCE). We demonstrated that flavanone did not inhibit MCE or expression of MCE-related proteins, except for a modest inhibition of cyclin D1 expression. Using luciferase reporter assays, we found that flavanone acted as a peroxisome proliferator-activated receptor gamma (PPARgamma) ligand in a dose-dependent manner. Together, our results suggest that flavanone enhances adipogenesis, at least in part, through its PPARgamma ligand activity.

Sakuranetin induces adipogenesis of 3T3-L1 cells through enhanced expression of PPARgamma2.

Sakuranetin (5,4'-dihydroxy-7-methoxyflavone) belongs to the flavanone class of polyphenols predominantly known as phytoalexin in rice plant. In this study, we demonstrate that sakuranetin strongly induces differentiation of 3T3-L1 preadipocytes, as evidenced by increased triglyceride accumulation and glycerol-3-phosphate dehydrogenase (GPDH) activity. In addition, even in the absence of adipogenic hormonal stimuli, sakuranetin strongly induced adipogenesis and expression of genes that are critical for the adipocytes phenotype. Time-course analyses indicated that sakuranetin induces PPARgamma2 expression without prior induction of C/EBPbeta, a transcriptional regulator of PPARgamma2 in adipogenesis. In 3T3-L1 preadipocytes, the transcriptional factors GATA-2 and GATA-3 are known to down-regulate adipogenesis by direct binding to the C/EBPbeta protein and to the GATA-binding site on the PPARgamma2 promoter. We found that sakuranetin significantly reduced the expression of GATA-2. Moreover, we observed that sakuranetin stimulated glucose uptake in differentiated 3T3-L1 adipocytes. These results suggest that sakuranetin may contribute to maintain glucose homeostasis in animals.

Nobiletin enhances differentiation and lipolysis of 3T3-L1 adipocytes.

Nobiletin is a polymethoxylated flavone found in certain citrus fruits. Here we demonstrate that nobiletin enhance differentiation of 3T3-L1 preadipocytes. Nobiletin dose-dependently increased accumulation of lipid droplets in adipocytes. Quantitative RT-PCR analyses indicated that nobiletin increased the expression of genes critical for acquisition of the adipocyte phenotype. Some of them were known peroxisome proliferator activated receptor gamma (PPARgamma) targets and PPARgamma itself, however, nobiletin did not exhibit PPARgamma ligand activity. We observed the expression of CCAAT/enhancer binding protein beta (C/EBPbeta), a transcription factor for PPARgamma, was increased by nobiletin. The activation of cAMP-responsive element binding protein (CREB) and extracellular signal-regulated kinase (ERK), which play important roles in C/EBPbeta expression were also potentiated by nobiletin. Furthermore, nobiletin stimulated lipolysis in differentiated adipocytes, which is known to be stimulated by cAMP pathway. These results suggested that nobiletin enhanced both differentiation and lipolysis of adipocyte through activation of signaling cascades mediated by cAMP/CREB.

Sennidin stimulates glucose incorporation in rat adipocytes.

A novel small molecule compound which exerts insulin mimetic is desirable. Dozens of natural products that have quinone, naphthoquinone, or anthraquinone structure, were tested by a glucose incorporation assay. We found that sennidin A, anthraquinone derivative, stimulated glucose incorporation to near level of maximal insulin-stimulated and sennidin B, a stereoisomer of sennidin A, also stimulated, but the activity of sennidin B was lower than sennidin A. Sennidin A-stimulated glucose incorporation was completely inhibited by wortmannin. Sennidin A did not induce tyrosine phosphorylation of insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), but induced phosphorylation of Akt and glucose transporter 4 (GLUT4) translocation. Our results suggest that in rat adipocytes, sennidin A stimulates glucose incorporation in the phosphatidylinositol 3-kinase (PI3K)- and Akt-dependent, but in the IR/IRS1-independent manner.

Effects of compounds in leaves of Salix matsudana on arachidonic acid metabolism.

Apigenin 7-O-beta-D-glucopyranuronide (1), luteolin 7-O-beta-D-glucopyranuronide (2), m-hydroxybenzyl beta-D-glucoside (3), and chrysoeriol 7-O-beta-D-glucopyranuronide (4) were isolated for the first time from the leaves of Salix matsudana. Furthermore, the effects of compounds 1, 2 and 3 on arachidonic acid metabolism were studied. These compounds inhibited significantly the production of 12-hydroxy-5, 8, 10, 14-eicosatetraenoic acid (12-HETE). In addition, the aglycon apigenin inhibited not only 12-HETE but also thromboxane B(2) (TXB(2)). The effect of compound (4) on arachidonic acid metabolism is now under investigation.

Enhancement of insulin sensitivity in adipocytes by ginger.

Antidiabetic and hypoglycemic drugs have been reported to enhance adipocyte differentiation of 3T3-L1 preadipocytes. We previously reported that ginseng (active constituents: ginsenosides) enhanced the differentiation [1]. In this experiment, effect of some ginger group food extracts on the adipocyte differentiation was investigated using cultured mouse 3T3-L1 preadipocytes. 3T3-L1 cells were grown as monolayer cultures at 37 degrees C in DMEM supplemented by 10% FBS under the atmosphere of 5% CO(2)-95% air. Ginger extracts were found to enhance the adipocyte differentiation. Active constituent was purified and identified as gingerol. In the gingerol-treated cells, insulin-sensitive glucose uptake was increased. It is expected that ginger enhance the insulin-sensitivity, and improve chronic disease, such as diabetes.

Effect of extraction method on the concentrations of selected bioactive compounds in mandarin juice.

A mandarin-type citrus fruit, ponkan (Citrus reticulata), was processed by in-line, chopper pulper, and hand-press extractions to investigate the effect of extraction method on the concentrations of bioactive compounds in processed juice. Concentrations of polymethoxylated flavones (tangeretin, nobiletin, and sinensetin) and beta-cryptoxanthin in juice, and inhibitory activities against arachidonate cyclooxygenase and lipoxygenases of the juice extract were analyzed. The juice processed by hand-press extraction contained the largest amounts of nobiletin (3.56 mg/100 mL), tangeretin (4.10 mg/100 mL), and sinensetin (0.13 mg/100 mL). Concentrations of beta-cryptoxanthin were 0.66, 0.59, 0.55, and 0.50 mg/100 mL in chopper pulper, in-line (5/64 in.), in-line (8/64 in.) and hand-press juices, respectively. Both extracts of in-line juices showed greater inhibitory activity toward platelet 12-lipoxygenase than the others. The inhibitory effect of hand-press juice extract on platelet cyclooxygenase activity was remarkable among juice extracts. All juice extracts effectively inhibited polymorphonuclear 5-lipoxygenase activity at nearly the same rate.

A novel inhibitory effect of D-allose on production of reactive oxygen species from neutrophils.

The rare sugar D-allose produced from D-psicose using an immobilized L-rhamnose isomerase bioreactor was shown to have weak scavenging activity toward reactive oxygen species (ROS) and potent inhibitory effect on production of ROS from stimulated neutrophils. These findings may have important implications in understanding the ameliorative effect of D-allose in transplantation and ischemia/reperfusion injury.

Bisphenol A in combination with insulin can accelerate the conversion of 3T3-L1 fibroblasts to adipocytes.

The confluent cultures of 3T3-L1 fibroblasts were treated with or without bisphenol A (BPA) for 2 days and subsequently treated with insulin (INS) alone for 9 days. When BPA was absent during the first 2-day treatment period, the cultures contained 1.6 microg/microg DNA of triacylglycerol (TG), 202 mU/mg DNA of lipoprotein lipase (LPL) activity, and 462 nmol/min/mg DNA of glycerol-3-phosphate dehydrogenase (GPDH) activity. The presence of BPA during the same period caused a 150% increase in the TG content, a 60% increase in the LPL activity, and a 500% increase in the GPDH activity. Thus, BPA by itself can trigger 3T3-L1 fibroblasts to differentiate into adipocytes. Next, the confluent cultures were treated with BPA for 2 days and subsequently treated with a combination of INS and BPA for 9 days. The simultaneous presence of BPA with INS caused a 370% increase in the TG content, a 200% increase in the LPL activity, and a 225% increase in the GPDH activity compared with the cultures treated with INS alone. The amount of [(3)H]thymidine incorporated into DNA was lower in the cultures treated with INS in the presence of BPA than in those treated with INS alone, indicating that BPA has an anti-proliferative activity on 3T3-L1 cells. Taken together, our results indicate that BPA in combination with INS can accelerate the adipocyte conversion.