Inhibition of the RPS6KA1/FoxO1 signaling axis by hydroxycitric acid attenuates HFD-induced obesity through MCE suppression

BACKGROUND

Because obesity is associated with a hyperplasia-mediated increase in adipose tissue, inhibiting cell proliferation during mitotic clonal expansion (MCE) is a leading strategy for preventing obesity. Although (-)-hydroxycitric acid (HCA) is used to control obesity, the molecular mechanisms underlying its effects on MCE are poorly understood.

PURPOSE

This study aimed to investigate the potential effects of HCA on MCE and underlying molecular mechanisms affecting adipogenesis and obesity improvements.

METHODS

Preadipocyte cell line, 3T3-L1, were treated with HCA; oil red O, cell proliferation, cell cycle, and related alterations in signaling pathways were examined. High-fat diet (HFD)-fed mice were administered HCA for 12 weeks; body and adipose tissues weights were evaluated, and the regulation of signaling pathways in epidydimal white adipose tissue were examined in vivo.

RESULTS

Here, we report that during MCE, HCA attenuates the proliferation of the preadipocyte cell line, 3T3-L1, by arresting the cell cycle at the G0/G1 phase. In addition, HCA markedly inhibits Forkhead Box O1 (FoxO1) phosphorylation, thereby inducing the expression of cyclin-dependent kinase inhibitor 1B and suppressing the levels of cyclin-dependent kinase 2, cyclin E1, proliferating cell nuclear antigen, and phosphorylated retinoblastoma. Importantly, we found that ribosomal protein S6 kinase A1 (RPS6KA1) influences HCA-mediated inactivation of FoxO1 and its nuclear exclusion. An animal model of obesity revealed that HCA reduced high-fat diet-induced obesity by suppressing adipocyte numbers as well as epididymal and mesenteric white adipose tissue mass, which is attributed to the regulation of RPS6KA1, FoxO1, CDKN1B and PCNA that had been consistently identified in vitro.

CONCLUSIONS

These findings provide novel insights into the mechanism by which HCA regulates adipogenesis and highlight the RPS6KA1/FoxO1 signaling axis as a therapeutic target for obesity.

Dictyostelium Differentiation-Inducing Factor 1 Promotes Glucose Uptake via Direct Inhibition of Mitochondrial Malate Dehydrogenase in Mouse 3T3-L1 Cells

Differentiation-inducing factor 1 (DIF-1), found in Dictyostelium discoideum, has antiproliferative and glucose-uptake-promoting activities in mammalian cells. DIF-1 is a potential lead for the development of antitumor and/or antiobesity/antidiabetes drugs, but the mechanisms underlying its actions have not been fully elucidated. In this study, we searched for target molecules of DIF-1 that mediate the actions of DIF-1 in mammalian cells by identifying DIF-1-binding proteins in human cervical cancer HeLa cells and mouse 3T3-L1 fibroblast cells using affinity chromatography and liquid chromatography-tandem mass spectrometry and found mitochondrial malate dehydrogenase (MDH2) to be a DIF-1-binding protein in both cell lines. Since DIF-1 has been shown to directly inhibit MDH2 activity, we compared the effects of DIF-1 and the MDH2 inhibitor LW6 on the growth of HeLa and 3T3-L1 cells and on glucose uptake in confluent 3T3-L1 cells in vitro. In both HeLa and 3T3-L1 cells, DIF-1 at 10-40 μM dose-dependently suppressed growth, whereas LW6 at 20 μM, but not at 2-10 μM, significantly suppressed growth in these cells. In confluent 3T3-L1 cells, DIF-1 at 10-40 μM significantly promoted glucose uptake, with the strongest effect at 20 μM DIF-1, whereas LW6 at 2-20 μM significantly promoted glucose uptake, with the strongest effect at 10 μM LW6. Western blot analyses showed that LW6 (10 μM) and DIF-1 (20 μM) phosphorylated and, thus, activated AMP kinase in 3T3-L1 cells. Our results suggest that MDH2 inhibition can suppress cell growth and promote glucose uptake in the cells, but appears to promote glucose uptake more strongly than it suppresses cell growth. Thus, DIF-1 may promote glucose uptake, at least in part, via direct inhibition of MDH2 and a subsequent activation of AMP kinase in 3T3-L1 cells.

Elastin-derived peptide VGVAPG decreases differentiation of mouse embryo fibroblast (3T3-L1) cells into adipocytes

Elastin is a highly elastic protein present in connective tissue. As a result of protease activity, elastin hydrolysis occurs, and during this process, elastin-derived peptides (EDPs) are released. One of the constitutively repeating elastin and EDP building sequences is the hexapeptide VGVAPG. Therefore, the aim of our research was to define the effect of VGVAPG peptide on adipogenesis in a mouse 3T3-L1 cell line. 3T3-L1 cells were differentiated according to a previously described protocol and exposed to increasing concentrations of VGVAPG or VVGPGA peptide. The obtained results showed that VGVAPG peptide does not stimulate reactive oxygen species (ROS) production, caspase-1 activation, and 3T3-L1 cell proliferation. In the second part of the experiments, it was proved that VGVAPG peptide decreased lipid accumulation as measured by oil red O staining, which was confirmed by the profile of increased expression markers of undifferentiated preadipocytes. In our experiments, 10 nM VGVAPG added for differentiating to adipocytes increased the expression of Pref-1, serpin E1, and adiponectin as compared to rosiglitazone (PPARγ agonist)-treated group and simultaneously decreased the expression of VEGF and resistin as compared to the rosiglitazone-treated group. The obtained results show that VGVAPG peptide sustains 3T3 cells in undifferentiated state.

ABBREVIATIONS

DMSO: dimethyl sulphoxide; EBP: elastin-binding protein; EDPs: elastin-derived peptides; FBS: foetal bovine serum; Glb1: gene for beta-galactosidase; LDL: low-density-lipoprotein; PAI-1 (Serpin E1): plasminogen activator inhibitor-1; PBS: phosphate-buffered saline; PPARγ: peroxisome proliferator-activated receptor gamma; Pref-1: preadipocyte factor 1; ROS: reactive oxygen species; VEGF-A: vascular endothelial growth factor-A; VGVAPG: Val-Gly-Val-Ala-Pro-Gly; β-Gal: beta-galactosidase; ORO: oil red O; IBMX: 3-isobutyl-1-methylxanthine; H2DCFDA: 2',7'-dichlorodihydrofluorescein diacetate; DMEM: Dulbecco's Modified Eagle's Medium; VVGPGA: Val-Val-Gly-Pro-Gly-Ala.

Ergosterol Peroxide from the Medicinal Mushroom Ganoderma lucidum Inhibits Differentiation and Lipid Accumulation of 3T3-L1 Adipocytes

Ergosterol peroxide is a natural compound of the steroid family found in many fungi, and it possesses antioxidant, anti-inflammatory, anticancer and antiviral activities. The anti-obesity activity of several edible and medicinal mushrooms has been reported, but the effect of mushroom-derived ergosterol peroxide on obesity has not been studied. Therefore, we analyzed the effect of ergosterol peroxide on the inhibition of triglyceride synthesis at protein and mRNA levels and differentiation of 3T3-L1 adipocytes. Ergosterol peroxide inhibited lipid droplet synthesis of differentiated 3T3-L1 cells, expression of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAT/enhancer-binding protein alpha (C/EBPα), the major transcription factors of differentiation, and also the expression of sterol regulatory element-binding protein-1c (SREBP-1c), which promotes the activity of PPARγ, resulting in inhibition of differentiation. It further inhibited the expression of fatty acid synthase (FAS), fatty acid translocase (FAT), and acetyl-coenzyme A carboxylase (ACC), which are lipogenic factors. In addition, it inhibited the phosphorylation of mitogen-activated protein kinases (MAPKs) involved in cell proliferation and activation of early differentiation transcription factors in the mitotic clonal expansion (MCE) stage. As a result, ergosterol peroxide significantly inhibited the synthesis of triglycerides and differentiation of 3T3-L1 cells, and is, therefore, a possibile prophylactic and therapeutic agent for obesity and related metabolic diseases.

Exposure to bisphenol A: current levels from food intake are toxic to human cells

In the present work, cell lines of different origin were exposed to BPA levels from food intake reported elsewhere. Specifically, we used an in vitro assay to determine cytotoxicity of BPA in three cell lines: MCF7 (breast cancer), PC3 (prostate cancer) and 3T3-L1 (mouse fibroblast). Cytotoxic effects were observed at concentrations higher than 50 μg/mL which is above the involuntary exposure level of BPA described before in fresh, canned and frozen foods and beverages. Furthermore, medial inhibitory concentrations (IC50) of 85.17 μg/mL and 88.48 μg/mL were observed for PC3 and 3T3-L1, respectively, and a slightly lower IC50 of 64.67 μg/mL for MCF7. These results highlight BPA's toxicity potential at current levels from food intake. The cell line-dependent divergent response to BPA reported herein is discussed.

Astragalus Polysaccharide Improves Insulin Sensitivity via AMPK Activation in 3T3-L1 Adipocytes

Astragalus polysaccharide (APS) is an important bioactive component of Astragalus membranaceus which is used as an anti-diabetes herb in traditional Chinese medicine. The objective of this study was to investigate the effects and mechanisms of APS on insulin-sensitizing of adipocytes. Mouse 3T3-L1 preadipocytes were used as a model. The results showed that APS increased preadipocytes proliferation in a dose dependent manner, and 0.1 μg/mL APS sufficiently increased Proliferating Cell Nuclear Antigen (PCNA) content (p < 0.01). Moreover, APS enhanced intracellular lipid accumulation and mRNA expression of proliferator-activated receptor γ (PPARγ, p < 0.01), CCAAT/enhancer binding protein α (C/EBPα, p < 0.01) and fatty acid binding protein (aP2, p < 0.01). As expected, corresponding protein contents were elevated. Importantly, APS increased 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)Amino)-2-Deoxyglucose (2-NBDG) uptake (p < 0.01). Meanwhile, both mRNA and protein content of glucose transporter 4 (Glut4) were elevated by APS (p < 0.01). The APS treatment enhanced tyrosine phosphorylation of insulin receptor substrate 1 (IRS1, p < 0.05) and phosphor-Akt content (p < 0.01). Besides, phosphorylated AMP-activated protein kinase (AMPK) content was increased in the APS treated cells (p < 0.01). Taken together, APS improved insulin sensitivity by enhancing glucose uptake, possibly through AMPK activation. These results suggested that APS might be a therapeutic candidate for insulin resistance.

Heme oxygenase-1 mediates anti-adipogenesis effect of raspberry ketone in 3T3-L1 cells

BACKGROUND

Obesity is caused by excessive accumulation of body fat and is closely related to complex metabolic diseases. Raspberry ketone (RK), a major aromatic compound in red raspberry, was recently reported to possess anti-obesity effects. However, its mechanisms are unclear.

AIM

Adipogenesis plays a critical role in obesity and, therefore, this study aimed to investigate the effect and mechanisms of action of RK on adipogenesis in 3T3-L1 preadipocytes.

MATERIALS AND METHODS

3T3-L1 preadipocytes were differentiated in medium containing insulin, dexamethasone, and 1-methyl-3-isobutylxanthine. Adipocyte lipid contents were determined using oil-red O staining while adipogenic transcription factor and lipogenic protein expressions were determined using western blotting.

RESULTS

RK (300-400µM) strongly inhibited lipid accumulation during 3T3-L1 preadipocyte differentiation into adipocytes. RK reduced the CCAAT/enhancer-binding protein-α (C/EBP-α), peroxisome proliferation-activated receptor-γ (PPAR-γ), fatty acid synthase (FAS), and fatty acid-binding protein 4 (FABP4) expressions and increased heme oxygenase-1 (HO-1), Wnt10b, and β-catenin expressions in 3T3-L1 adipocytes. Additionally, RK inhibited lipid accumulation, and adipogenic transcription factor and lipogenic protein expressions were all decreased by inhibiting HO-1 or β-catenin using tin protoporphyrin (SnPP) or β-catenin short-interfering RNA (siRNA), respectively. Furthermore, Wnt10b and β-catenin expressions were negatively regulation by SnPP.

CONCLUSION

RK may exert anti-adipogenic effects through modulation of the HO-1/Wnt/beta-catenin signaling pathway.

DNA Methylation Suppresses Leptin Gene in 3T3-L1 Adipocytes

Leptin is a key regulator of energy intake and expenditure. This peptide hormone is expressed in mouse white adipose tissue, but hardly expressed in 3T3-L1 adipocytes. Using bisulfite sequencing, we found that CpG islands in the leptin promoter are highly methylated in 3T3-L1cells. 5-azacytidine, an inhibitor of DNA methyltransferase, markedly increased leptin expression as pre-adipocytes matured into adipocytes. Remarkably, leptin expression was stimulated by insulin in adipocytes derived from precursor cells exposed to 5-azacytidine, but suppressed by thiazolidinedione and dexamethasone. In contrast, adipocytes derived from untreated precursor cells were unresponsive to both 5-azacytidine and hormonal stimuli, although lipid accumulation was sufficient to boost leptin expression in the absence of demethylation. Taken together, the results suggest that leptin expression in 3T3-L1 cells requires DNA demethylation prior to adipogenesis, transcriptional activation during adipogenesis, and lipid accumulation after adipogenesis.

Enzymatic Process for High-Yield Turanose Production and Its Potential Property as an Adipogenesis Regulator

Turanose is a sucrose isomer naturally existing in honey and a promising functional sweetener due to its low glycemic response. In this study, the extrinsic fructose effect on turanose productivity was examined in Neisseria amylosucrase reaction. Turanose was produced, by increasing the amount of extrinsic fructose as a reaction modulator, with high concentration of sucrose substrate, which resulted in 73.7% of production yield. In physiological functionality test, lipid accumulation in 3T3-L1 preadipocytes in the presence of high amounts of pure glucose was attenuated by turanose substitution in a dose-dependent manner. Turanose treatments at concentrations representing 50%, 75%, and 100% of total glucose concentration in cell media significantly reduced lipid accumulation by 18%, 35%, and 72%, respectively, as compared to controls. This result suggested that turanose had a positive role in controlling adipogenesis, and enzymatic process of turanose production has a potential to develop a functional food ingredient for controlling obesity and related chronic diseases.

Characterization of Secondary Metabolites from Purple Ipomoea batatas Leaves and Their Effects on Glucose Uptake

Ipomoea batatas has long been used in folk medicine for the treatment of hyperglycemia or as a food additive for the prevention of type 2 diabetes. However, neither the plant extract nor its active components have been evaluated systematically. In this work four crude extracts, including n-hexane- (IBH), 95% MeOH- (IBM), n-BuOH- (IBB), and H₂O-soluble (IBW) fractions, were prepared by fractionation of a methanolic extract of purple I. batatas leaves. Twenty-four pure compounds 1-24 were then isolated by various chromatographic techniques and their structures identified from NMR and MS data. Glucose uptake assays in differentiated 3T3-L1 adipocytes and rat primary hepatocytes, as well as western blot analysis, were carried out to evaluate the antidiabetic activity of this species. The IBH crude fraction, with methyl decanoate (22) as a major and active compound, showed the greatest effect on glucose uptake, most likely via activation of Glut4 and regulation of the PI3K/AKT pathway. Quercetin 3-O-β-d-sophoroside (1), quercetin (3), benzyl β-d-glucoside (10), 4-hydroxy-3-methoxybenzaldehyde (12), and methyl decanoate (22) could be important components contributing to the antidiabetic effects. We conclude that purple I. batatas leaves have potential as an antidiabetic plant source and the active constituents 1, 3, 10, 12, and 22 are promising lead candidates for future investigation.

Chronic endothelin-1 infusion causes adipocyte hyperplasia in rats

OBJECTIVE

The aim of this study was to investigate the regulatory mechanism of endothelin-1 (ET-1), an endothelium-derived vasoconstrictor, on adipogenesis in vitro and in vivo.

METHODS

3T3-L1 preadipocytes were used to explore the mechanisms mediating ET-1 actions on preadipocyte proliferation and adipocyte differentiation. To investigate the in vivo effect of ET-1, male Sprague-Dawley rats were infused with ET-1 or saline for 4 weeks via intraperitoneally implanted osmotic pumps, and the fat pad weight and adipocyte size of adipose tissues were measured.

RESULTS

ET-1 stimulated preadipocyte proliferation and increased the cell number at the mitotic clonal expansion stage of adipocyte differentiation via the endothelin A receptor (ETAR) and activation of the protein kinase C (PKC) pathway. ET-1, via ETAR, inhibited adipocyte differentiation partially through an ERK-dependent pathway. Furthermore, no significant difference in the body weight and fat pad weight was observed in either ET-1- or saline-infused rats. Compared with saline-infused rats, the adipocyte cell number was significantly increased but the adipocyte size was significantly decreased in ET-1-infused rats.

CONCLUSIONS

Chronic ET-1 infusion increased the number of small adipocytes without the change of white adipose tissue mass in rats, which were associated with ET-1-stimulated preadipocyte proliferation, but not ET-1-suppressed adipocyte differentiation.

Effects and Molecular Mechanism of GST-Irisin on Lipolysis and Autocrine Function in 3T3-L1 Adipocytes

Irisin, which was recently identified as a myokine and an adipokine, transforms white adipose tissue to brown adipose tissue and has increasingly caught the attention of the medical and scientific community. However, the signaling pathway of irisin and the molecular mechanisms responsible for the lipolysis effect remain unclear. In this study, we established an efficient system for the expression and purification of GST-irisin in Escherichia coli. The biological activity of GST-irisin was verified using the cell counting kit-8 assay and by detecting the mRNA expression of uncoupling protein 1. Our data showed that GST-irisin regulates mRNA levels of lipolysis-related genes such as adipose triglyceride lipase and hormone-sensitive lipase and proteins such as the fatty acid-binding protein 4, leading to increased secretion of glycerol and decreased lipid accumulation in 3T3-L1 adipocytes. In addition, exogenous GST-irisin can increase its autocrine function in vitro by regulating the expression of fibronectin type III domain-containing protein 5. GST-irisin could regulate glucose uptake in 3T3-L1 adipocytes. Hence, we believe that recombinant GST-irisin could promote lipolysis and its secretion in vitro and can potentially prevent obesity and related metabolic diseases.

Diosgenin regulates adipokine expression in perivascular adipose tissue and ameliorates endothelial dysfunction via regulation of AMPK

Perivascular adipose tissue (PVAT) has been recognized as an active contributor to vascular function due to its paracrine effects on cells contained within vascular wall. The present study was designed to investigate the effect of diosgenin on adipokine expression in PVAT with emphasis on the regulation of endothelial function. Palmitic acid (PA) stimulation induced inflammation and dysregulation of adipokine expression in PVAT. Diosgenin treatment inhibited IKKβ phosphorylation and downregulated mRNA expressions of proinflammatory cytokines/proteins including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), monocyte chemoattractant protein (MCP-1), and inducible nitric oxide synthase (iNOS), while reduced gene expressions for adiponectin, PPARγ, and arginase 1 (Arg-1) were reversed by diosgenin treatment. Diosgenin enhanced AMPK phosphorylation under basal and inflammatory conditions in PVAT, whereas knockdown of AMPK by SiRNA diminished its modulatory effect, indicating that diosgenin inhibited inflammation in an AMPK-dependent manner. We prepared conditioned medium from PA-stimulated PVAT to induce endothelial dysfunction and found that pre-treatment of PVAT with diosgenin effectively restored the loss of ACh-induced vasodilation and increased eNOS phosphorylation in rat aorta. High-fat diet feeding in rats induced inflammation in PVAT and the impairment of endothelium-dependent vasodilation, whereas these alterations were prevented by oral administration of diosgenin at doses of 20 and 40 mg/kg. In conclusion, the obtained data showed that diosgenin ameliorated inflammation-associated adipokine dysregulation, and thereby prevented endothelial dysfunction. Our findings would shed a novel insight into the potential mechanism by which diosgenin protected endothelial function against inflammatory insult.

Vitamin D decreases adipocyte lipid storage and increases NAD-SIRT1 pathway in 3T3-L1 adipocytes

OBJECTIVE

Previous studies suggest that low vitamin D status is associated with obesity characterized by excess lipid storage in adipocytes. The aim of the present study was to determine the effects of the most hormonally active form of vitamin D 1,25-dihydroxyvitamin D [1,25(OH)2D] on adipocyte fat storage and lipid metabolism in mature 3T3-L1 cells.

METHODS

Differentiated 3T3-L1 cells were treated with various concentrations of 1,25(OH)2D. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell proliferation, intracellular lipid content, and basal and isoproterenol-stimulated lipolysis were measured to investigate the regulatory role of 1,25(OH)2D in adipocyte lipid metabolism. Reverse transcription polymerase chain reaction was performed to determine the effects of 1,25(OH)2D on adipogenesis-related markers, fatty acid oxidation-associated genes, and lipolytic enzymes. Sirtulin 1 (SIRT1) activity, nicotinamide adenine dinucleotide (NAD) and NADH were measured.

RESULTS

1,25(OH)2D treatment (24 h, 100 nmol/L) induced a decrease in intracellular fat accumulation and an increase of basal and isoproterenol-stimulated lipolysis without cell toxicity in adipocytes. Adipogenic gene levels were decreased. In contrast, mRNA levels of β-oxidation-related genes, lipolytic enzymes, and vitamin D responsive gene were elevated by 1,25(OH)2D. Additionally, significant incremental changes in NAD levels, the ratio of NAD to NADH, and SIRT1 expression and activity were noted in 1,25(OH)2D-treated 3T3-L1 adipocytes.

CONCLUSIONS

The observed potent inhibitory effect of 1,25(OH)2D on adipocyte fat storage in mature 3T3-L1 cells suggests that vitamin D might improve adipocyte metabolic function and protect against obesity. Increased NAD concentrations and SIRT1 ​activity may play a role in the mechanism of 1,25(OH)2D action.

Effect of high hydrostatic pressure extract of fresh ginseng on adipogenesis in 3T3-L1 adipocytes

BACKGROUND

Red ginseng is produced by steaming and drying fresh ginseng. Through this processing, chemical compounds are modified, and then biological activities are changed. In the food-processing industry, high hydrostatic pressure (HHP) has become an alternative to heat processing to make maximum use of bioactive compounds in food materials. This study comparatively investigated the anti-adipogenic effects of water extract of red ginseng (WRG) and high hydrostatic pressure extract of fresh ginseng (HPG) in 3T3-L1 adipocytes.

RESULTS

Both WRG and HPG inhibited the accumulation of intracellular lipids and triglycerides, and the activity of glycerol-3-phosphate dehydrogenase (GPDH), a key enzyme in triglyceride biosynthesis. Intracellular lipid content and GPDH activity were significantly lower in the HPG group compared to the WRG group. In addition, mRNA expression of adipogenic genes, including CEBP-α, SREBP-1c and aP2, were lower in HPG-treated cells compared to WRG-treated cells. HPG significantly increased the activity of AMPK, and WRG did not.

CONCLUSION

Results suggested that HPG may have superior beneficial effects on the inhibition of adipogenesis compared with WRG. The anti-adipogenic effects of HPG were partially associated with the inhibition of GPDH activity, suppression of adipogenic gene expression and activation of AMPK in 3T3-L1 adipocytes.

A-type ECG and EGCG dimers disturb the structure of 3T3-L1 cell membrane and strongly inhibit its differentiation by targeting peroxisome proliferator-activated receptor γ with miR-27 involved mechanism

The effects of four proanthocyanidin dimers including epicatechin-(4β→8, 2β→O→7)-epicatechin (A-type EC dimer), epicatechin-(4β→8)-epicatechin (B-type EC dimer), epicatechin-3-gallate-(4β→8, 2β→O→7)-epicatechin-3-gallate (A-type ECG dimer) and epigallocatechin-3-gallate-(4β→8, 2β→O→7)-epigallocatechin-3-gallate (A-type EGCG dimer) on 3T3-L1 preadipocyte cell differentiation and the underlying mechanisms were explored and compared. The results showed that A-type ECG dimer and A-type EGCG dimer significantly reduced the intracellular lipid accumulation in 3T3-L1 preadipocyte cells by targeting miR-27a and miR-27b as well as peroxisome proliferator-activated receptor γ (PPARγ) in the early stage of differentiation, while A-type EC dimer and B-type EC dimer showed little effect. In addition, our results revealed that the inhibitory effects of proanthocyanidin dimers on 3T3-L1 preadipocyte differentiation were highly structure-dependent and the effects were associated with the dimer-membrane interactions. The presence of galloyl moieties and A-type linkage within the structure of proanthocyanidins might be crucial for their inhibitory effect on adipogenesis. The strong disturbing effects of A-type ECG and A type EGCG dimers on the fluidity, hydrophobicity and permeability of membrane of 3T3-L1 preadipocyte cell were at least, in part, responsible for their distinct inhibitory effects on adipocyte hyperplasia.

Rutin Stimulates Adipocyte Differentiation and Adiponectin Secretion in 3T3-L1 Adipocytes

Rutin is aflavonoid, which is found in many plants. It has been shown to reduce blood glucose and increase insulin levels in diabetic rats. In the present study, the authors aimed to elucidate the molecular basis for the observed antidiabetic activity using murine 3T3-L1 preadipocyte cultures. The treatment of differentiating 3T3-L1 cells with rutin at concentrations of 3, 10, 30 and 100 µM significantly increased lipid accumulation and mRNA expression of transcription factors, such as peroxisome proliferator-activated receptor gamma, CCAAT/enhancer-binding protein alpha, and adipocyte fatty acid-binding protein. Furthermore, rutin at concentrations of 10, 30 and 100 µM increased adiponectin mRNA expression together with stimulating the secretion of adiponectin in differentiating 3T3-L1 cells. These results indicate that the stimulatory effect of rutin on adipocyte differentiation likely occurs through up-regulation of adipogenic transcription factors and downstream adipocyte-specific gene expression. Such effects of rutin on adiponectin secretion and adipocyte activity may account for, at least in part, the antidiabetic effects of consumption of food containing rutin.

In vitro antihyperlipidemic potential of triterpenes from stem bark of Protorhus longifolia

Two lanostane triterpenes, 3β-hydroxylanosta-9,24-dien-21-oic acid (1) and methyl-3β-hydroxylanosta-9,24-dien-21-oate (2), were isolated from the stem bark of Protorhus longifolia. Their structures were deduced on the basis of spectroscopic analysis (NMR, HRMS, IR). This study investigated the in vitro anti-adipogenic activity of the two triterpenes. Their inhibitory activity was evaluated on selected lipid digestive enzymes (pancreatic lipase and cholesterol esterase). The inhibitory activity of the compounds on hormone-sensitive lipase and their ability to bind bile acids were also evaluated. The effect of the compounds on glucose uptake in C2C12 muscle cells and 3T3-L1 adipocytes, and on triglyceride accumulation in 3T3-L1 adipocytes was investigated. The triterpenes effectively inhibited the activities of the enzymes with IC50 values ranging from 0.04 to 0.31 mg/mL. The compounds showed a high affinity for secondary bile acids. Both compounds stimulated glucose uptake in C2C12 muscle cells and 3T3-L1 adipocytes. Compound 1 significantly reduced triglyceride accumulation in mature differentiated 3T3-L1 adipocytes. It is apparent that these lanostane triterpenes enhance glucose uptake and suppress adipogenesis, which together with their inhibitory effects on lipid digestive enzymes suggests that they have antihyperlipidemic potential.

Isomeric C12-alkamides from the roots of Echinacea purpurea improve basal and insulin-dependent glucose uptake in 3T3-L1 adipocytes

Echinacea purpurea has been used in traditional medicine as a remedy for the treatment and prevention of upper respiratory tract infections and the common cold. Recent investigations have indicated that E. purpurea also has an effect on insulin resistance. A dichloromethane extract of E. purpurea roots was found to enhance glucose uptake in adipocytes and to activate peroxisome proliferator-activated receptor γ. The purpose of the present study was to identify the bioactive compounds responsible for the potential antidiabetic effect of the dichloromethane extract using a bioassay-guided fractionation approach. Basal and insulin-dependent glucose uptake in 3T3-L1 adipocytes were used to assess the bioactivity of extract, fractions and isolated metabolites. A peroxisome proliferator-activated receptor γ transactivation assay was used to determine the peroxisome proliferator-activated receptor γ activating properties of the extract, active fractions and isolated metabolites. Two novel isomeric dodeca-2E,4E,8Z,10E/Z-tetraenoic acid 2-methylbutylamides together with two known C12-alkamides and α-linolenic acid were isolated from the active fractions. The isomeric C12-alkamides were found to activate peroxisome proliferator-activated receptor γ, to increase basal and insulin-dependent glucose uptake in adipocytes in a dose-dependent manner, and to exhibit characteristics of a peroxisome proliferator-activated receptor γ partial agonist.

2,4,5-trimethoxybenzaldehyde, a bitter principle in plants, suppresses adipogenesis through the regulation of ERK1

Because of the prevalence of obesity, there is particular interest in finding potential therapeutic targets. In a previous study, we demonstrated that 2,4,5-trimethoxybenzaldehyde (2,4,5-TMBA), a bitter principle in plants and a natural cyclooxygenase II (COX-2) inhibitor, suppressed the differentiation of preadipocyts into adipocytes at the concentration of 0.5 mM. In this current study, we aimed to investigate the stage during adipogenesis that is critically affected by 2,4,5-TMBA and the effects of 2,4,5-TMBA on the time-course expression of signaling molecules MAP kinase kinase (MAPKK, represented by MEK) and extracellular signal-regulated kinase (ERK), transcription factors CCAAT/enhancer binding protein (C/EBP)α, β, and δ and peroxisome proliferator-activated receptor (PPAR)γ, lipogenic enzymes acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), and lipid droplet-coating protein perilipin A. When preadipocytes were co-cultured with 2,4,5-TMBA (0.5 mM) specifically at post-induction days 0-2, 2-4, 4-6, or 6-8 only, relative lipid accumulation was decreased by 67.93, 34.65, 49.56, and 34.32%, respectively. A time-course study showed that treatment of 2,4,5-TMBA suppressed the phosphorylation of ERK1 at the initial stage of adipogenesis but upregulated the phosphorylation at the late stage, which is opposite to the conditions required for the differentiation process. The overall expression of C/EBPα, β, and δ, PPARγ2, ACC, FAS, and perilipin A in preadipocytes was downregulated by the treatment of 2,4,5-TMBA. Taken together, our findings suggest that 2,4,5-TMBA suppresses adipogenesis through the regulation of ERK1 phosphorylation. Although results from in vitro studies cannot be directly extrapolated into clinical effects, our study will help to elucidate the anti-adipogenic potential of 2,4,5-TMBA.

Stearic acid serves as a potent inhibitor of protein tyrosine phosphatase 1B

BACKGROUND/AIMS

Free fatty acids (FFAs) are implicated in diverse signal transduction pathways. The present study investigated the effects of the saturated FFA stearic acid on protein tyrosine phosphatase 1B (PTP1B) activity, Akt activity, and glucose uptake into cells relevant to insulin signal.

METHODS

PTP1B activity was assayed under the cell-free conditions. Phosphorylation of insulin receptor and Akt and glucose uptake into cells were monitored in differentiated 3T3-L1-GLUT4myc adipocytes.

RESULTS

In the cell-free PTP1B assay, stearic acid suppressed PTP1B activity in a concentration (1-30 μM)-dependent manner. For 3T3-L1- GLUT4myc adipocytes insulin phosphorylated insulin receptor at Tyr1185 and Akt at Thr308 and Ser473 in a concentration (100 fM-100 nM)-dependent manner and stimulated glucose uptake into cells in a concentration (0.1-100 nM)-dependent manner. Stearic acid (30 μM) significantly increased insulin-induced phosphorylation of insulin receptor at Tyr1185, but insulin-induced phosphorylation of Akt was not significantly enhanced. Stearic acid (30 μM) by itself promoted glucose uptake into adipocytes.

CONCLUSION

The results of the present study indicate that stearic acid serves as a potent PTP1B inhibitor, possibly causing an enhancement in the insulin receptor signaling to stimulate glucose uptake into adipocytes.

Anti-adipogenic activity of the edible brown alga Ecklonia stolonifera and its constituent fucosterol in 3T3-L1 adipocytes

Fucosterol is a sterol metabolite of brown algae and regulates genes involved with cholesterol homeostasis. As a part of our continuous search for anti-obesity agents from natural marine sources, the anti-adipogenic activities of Ecklonia stolonifera and its sterol, fucosterol, were evaluated for the inhibition of adipocyte differentiation and lipid formation. Oil Red O staining was used to evaluate triglyceride contents in 3T3-L1 pre-adipocytes primed by differentiation medium (DM) I and DM II. The methanolic extract of E. stolonifera showed strong anti-adipogenic activity, and was thus fractionated with several solvents. Among the tested fractions, the dichloromethane (CH2Cl2) fraction was found to be the most active fraction, with significant inhibition (40.5 %) of intracellular lipid accumulation at a non-toxic concentration, followed by the ethyl acetate fraction (30.2 %) at the same concentration, while the n-butanol and water fractions did not show inhibitory activity within the tested concentrations. The strong anti-adipogenic CH2Cl2-soluble fraction was further purified by a repeated chromatography to yield fucosterol. Fucosterol reduced lipid contents in a concentration-dependent manner without showing any cytotoxicity. Fucosterol treatment also yielded a decrease in the expression of the adipocyte marker proteins peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα) in a concentration-dependent manner. Taken together, these results suggest that fucosterol inhibits expression of PPARγ and C/EBPα, resulting in a decrease of lipid accumulation in 3T3-L1 pre-adipocytes, indicating that the potential use of E. stolonifera and its bioactive fucosterol as an anti-obesity agent.

Anthocyanins inhibit lipogenesis during adipocyte differentiation of 3T3-L1 preadipocytes

Anthocyanins have been shown to suppress body weight and fat mass in animal studies. However, the effect of anthocyanins on the process of lipid accumulation during adipocyte differentiation is not fully understood and the lipogenic transcription factors regulated by anthocyanins have not been identified. We investigated the effects of anthocyanins on lipogenesis pathways during adipocyte differentiation in 3T3-L1 cells. Anthocyanins reduced triglyceride (TG) accumulation in a dose-dependent manner during adipocyte differentiation. Accumulation of TG was rapidly reversed by anthocyanin withdrawal. Anthocyanins markedly reduced gene and protein expression levels of lipogenic transcription factors such as liver X receptor α, sterol regulatory element-binding protein-1c, peroxisome proliferators-activated receptor-γ, and CCAAT enhancer-binding protein-α. In addition, the target gene and protein expression of these lipogenic transcription factors such as fatty acid synthase, stearoyl-CoA desaturase-1, and acetyl-CoA carboxylase α were markedly suppressed by anthocyanins. Thus, anthocyanins suppress lipid accumulation in adipocytes due to broad inhibition of the transcription factors regulating lipogenesis. This may partially explain the mechanism by which anthocyanins exert their anti-obesity effect.

Apigenin isolated from Daphne genkwa Siebold et Zucc. inhibits 3T3-L1 preadipocyte differentiation through a modulation of mitotic clonal expansion

AIMS

Obesity develops when energy intake chronically exceeds total energy expenditure. We sought to assess whether the flavonoid-rich fraction of crude extracts from Daphne genkwa Siebold et Zuccarini (GFF) might inhibit adipogenesis of 3T3-L1 cells.

MAIN METHODS

Cell viability of 3T3-L1 preadipocytes was assessed by MTT assays, and lipid accumulation was measured by Oil Red O. Adipogenesis related factors were checked by Western blot analysis. Flow cytometry was used to analyze the mitotic cell cycle during the mitotic clonal expansion phase.

KEY FINDINGS

Among five flavonoids isolated from GFF, only apigenin potently inhibited the differentiation of 3T3-L1 cells. Apigenin reduced CCAAT/enhancer binding protein (C/EBP) α and peroxisome proliferator-activated receptor γ levels. Apigenin-treated 3T3-L1 cells failed to undergo clonal expansion during the early phase of adipocyte differentiation. Apigenin arrested cell cycle progression at the G0/G1 phase. This effect was associated with a marked decrease in cyclin D1 and cyclin-dependent kinase 4 expression, with the concomitant and sustained expression of p27(Kip1). In addition, apigenin inhibited the DNA-binding activity of C/EBPβ in differentiating 3T3-L1 cells by down-regulating the 35kDa isoform of C/EBPβ (liver-enriched activating protein) and up-regulating the expression of two different sets of C/EBP inhibitors: C/EBP homologous protein and the phospho-liver-enriched inhibitory protein isoform of C/EBPβ.

SIGNIFICANCE

These findings suggest that apigenin can prevent 3T3-L1 preadipocyte differentiation by the inhibition of the mitotic clonal expansion and the adipogenesis related factors and upregulation of the expression of multiple C/EBPβ inhibitors.

Nicotinamide, a glucose-6-phosphate dehydrogenase non-competitive mixed inhibitor, modifies redox balance and lipid accumulation in 3T3-L1 cells

AIMS

Excessive energy uptake of dietary carbohydrates results in their storage as fat and requires glucose-6-phosphate dehydrogenase (G6PD)-mediated NADPH production. We sought to assess whether the nicotinamide-induced reduction of G6PD activity might modulate redox balance and lipid accumulation in 3T3-L1 cells.

MAIN METHODS

3T3-L1 preadipocytes (days 4 and 6 of differentiation) and adipocytes were cultured in the presence of 5 or 25 mM glucose. The cells cultured in 25 mM glucose were supplemented with nicotinamide (5-15 mM). Next, we evaluated the following parameters: cell viability, apoptosis, lipid accumulation, lipolysis, reducing power, reactive oxygen species (ROS), NAD(P)H and NAD(P)(+), isocitrate dehydrogenase (IDP), malic enzyme and G6PD, as well as the protein and mRNA levels of G6PD. We also analysed the kinetics of the nicotinamide-induced inhibition of G6PD.

KEY FINDINGS

G6PD mRNA levels increased at day 4 of adipocyte differentiation, whereas G6PD activity progressively increased at days 4 and 6 of differentiation and was reduced in adipocytes. Concomitantly, ROS, reducing power and lipid accumulation increased gradually as the preadipocytes matured into adipocytes. High glucose increased the activity of G6PD, which coincided with an increase in ROS, reducing power and lipid accumulation. All of these changes are prevented by nicotinamide, with the exception of lipid accumulation in adipocytes. Nicotinamide increased IDP activity without affecting NADPH levels. Lastly, nicotinamide inhibited G6PD in a non-competitive mixed way.

SIGNIFICANCE

Nicotinamide modulates G6PD via a non-competitive mixed inhibition and decreases high glucose-dependent oxidative stress and lipid accumulation. Nicotinamide maintains NADPH levels by increasing the activity of IDP.

Cyclic restricted feeding enhances lipid storage in 3 T3-L1 adipocytes

BACKGROUND

People who skip breakfast have more visceral fat than those who eat breakfast; however, the mechanism underlying this difference is unclear. In this study, we examined 3 T3-L1 adipocytes and assessed 1) whether restricted feeding (i.e., "breakfast skipping") alters the cyclic expression of brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like protein 1 (BMAL1) and lipogenic proteins and 2) whether repeated exposure to growth media at the time-points with enhanced lipogenic regulatory signals increases de novo lipogenesis and lipid storage.

METHODS

Differentiated adipocytes were divided into two groups: a control group and a restricted feeding group, for which incubation with growth medium from ZT 9 to ZT 12 was withheld.

RESULTS

A bout of restricted feeding disrupted the cyclic expression of BMAL1 protein and increased the expression of lipogenic proteins, such as fatty acid synthase and peroxisome proliferator-activated receptor gamma in adipocytes. Furthermore, the repeated exposure to growth media at the time-points with enhanced lipogenic regulatory signals increased de novo lipogenesis and lipid storage.

CONCLUSION

These findings suggest that direct disruption of intracellular molecular clock systems by breakfast skipping and the concurrent changes in the daily cycle of lipogenic proteins in adipocytes, as a consequence of repeated nutrition at the time-points with enhanced lipogenic regulatory signals, would result in increased lipogenesis and lipid storage. These alterations are important molecular mechanisms underlying augmented adiposity induced by breakfast skipping.

Role of sulfur containing amino acids as an adjuvant therapy in the prevention of diabetes and its associated complications

Amino acid supplementation is gaining acceptance as an important adjuvant therapy in the treatment of diabetes and its associated complications. Numerous studies in the literature report the impaired amino acid metabolism in diabetes and the beneficial effects of amino acids are positively correlated with the increase in plasma levels of those amino acids. Oxidative stress is known to play a major role in diabetic pathophysiology. Sulfur containing compounds are well known in the treatment of oxidative stress induced pathological disorders. Methionine, cysteine, and homocysteine are the three common sulfur containing amino acids. In addition, taurine, a sulfonic acid containing an amino group (amino sulfonic acid), is found in substantial amounts in mammalian tissues. Both experimental and clinical studies reported the modulatory effects of cysteine, N-acetyl cysteine, or compounds having cysteine moiety in the regulation of insulin secretion and plasma glucose levels. Taurine supplementation has been found to prevent the onset of diabetes mellitus in experimental models of both insulin dependent and insulin independent pathways. Recent reports suggest that the beneficial role of cysteine or taurine is mediated via their ability in reducing glycooxidation and preventing the generation of intracellular reactive intermediates. Studies with methionine or S-adinosyl methionine has been shown to increase mitochondrial DNA density in skeletal muscle, improve insulin sensitivity and prevent body weight gain. Homocysteine, on the other hand, is an emerging risk factor for cardiovascular disease and diabetic patients have higher levels of this sulfur containing amino acid. Supplementation with cysteine or taurine, however, was found to be effective in reducing plasma homocysteine levels. This review will discuss the role of sulfur containing amino acids in the regulation of hyperglycemia and in the development of its associated pathological dysfunctions.

[Effects of ursolic acid on c-Cbl-associated protein expression in 3T3-L1 adipocytes with insulin resistance]

OBJECTIVE

To observe the effects of ursolic acid (UA) on insulin resistance and cell differentiation in 3T3-L1 adipocytes and to explore the mechanisms.

METHODS

3T3-L1 adipocytes were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with glucose (25 mmol/L) and insulin (10(-6) mol/L) to induce insulin resistance. After culture, glucose consumption of the adipocytes was detected by glucose oxidase method and glucose uptake was detected by using tritium-marked glucose. Drug concentration for following test was determined through detecting the effects of different concentrations of UA on the activity of 3T3-L1 adipocytes with insulin resistance by methyl thiazolyl tetrazolium (MTT) staining. 3T3-L1 adipocytes with insulin resistance were cultured with DMEM, rosiglitazone, and low- and high-dose UA, and then, glucose uptake and differentiation of 3T3-L1 adipocytes were detected. Finally, real-time fluorescence quantitative polymerase chain reaction and Western blot methods were used to detect the effects of UA on expressions of adipocyte lipid binding protein (aP2), c-Cbl-associated protein (CAP) and matrix metalloproteinase-1 (MMP-1) in 3T3-L1 cells with insulin resistance.

RESULTS

After dealing with high glucose/hyperinsulin for 24 h, insulin resistance was induced successfully in the 3T3-L1 adipocytes. The concentrations of UA were defined to be 4 to 20 μmol/L. Compared with the model group, the glucose uptake was significantly increased in the rosiglitazone group and groups treated with low- and high-dose UA (P<0.01). The differentiation levels of 3T3-L1 adipocytes in the UA groups were lower than those in the control group and the rosiglitazone group. Effects of UA on the expressions of aP2 and MMP-1 were not obvious, but UA could up-regulate expression of CAP both in mRNA and protein levels (P<0.01).

CONCLUSION

Low- and high-dose UA can improve the glycometabolism and differentiation of 3T3-L1 adipocytes with insulin resistance by up-regulating the expression of CAP.

Sulforaphane inhibits mitotic clonal expansion during adipogenesis through cell cycle arrest

Obesity is a risk factor for numerous metabolic disorders such as type 2 diabetes, hypertension, and coronary heart disease. Adipocyte differentiation is triggered by adipocyte hyperplasia, which leads to obesity. In this study, the inhibitory effect of sulforaphane, an isothiocyanate, on adipogenesis in 3T3-L1 cells was investigated. Sulforaphane decreased the accumulation of lipid droplets stained with Oil Red O and inhibited the elevation of triglycerides in the adipocytes (half-maximal inhibitory concentration = 7.3 µmol/l). The expression of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), major transcription factors for adipocyte differentiation, was significantly reduced by sulforaphane. The major effects of sulforaphane on the inhibition of adipocyte differentiation occurred during the early stage of adipogenesis. Thus, the expression of C/EBPβ, an early-stage biomarker of adipogenesis, decreased in a concentration-dependent manner when the adipocytes were exposed to sulforaphane (0, 5, 10, and 20 µmol/l). The proliferation of adipocytes treated with 20 µmol/l sulforaphane for 24 and 48 h was also suppressed. These results indicate that sulforaphane may specifically affect mitotic clonal expansion to inhibit adipocyte differentiation. Sulforaphane arrested the cell cycle at the G(0)/G(1) phase, increased p27 expression, and decreased retinoblastoma (Rb) phosphorylation. Additionally, sulforaphane modestly decreased the phosphorylation of ERK1/2 and Akt. Our results indicate that the inhibition of early-stage adipocyte differentiation by sulforaphane may be associated with cell cycle arrest at the G(0)/G(1) phase through upregulation of p27 expression.

Effects of a leucine and pyridoxine-containing nutraceutical on fat oxidation, and oxidative and inflammatory stress in overweight and obese subjects

Leucine stimulates tissue protein synthesis and may also attenuate adiposity by increasing fatty acid oxidation and mitochondrial biogenesis in muscle and adipocytes. Accordingly, the effects of a nutraceutical containing 2.25 g leucine and 30 mg pyridoxine (Vitamin B6) (NuFit active blend) were tested in cell culture and in a clinical trial. 3T3L1 adipocytes were treated with leucine (0.25 mM or 0.5 mM) and/or Pyridoxal Phosphate (PLP) (50 nM or 100 nM) for 48 h. For the clinical trial, twenty overweight or obese subjects received the NuFit active blend or placebo three times/day for 4 weeks without energy restriction. Leucine decreased fatty acid synthase (FAS) expression and triglyceride content in adipocytes, and PLP addition significantly augmented this effect. Administration of NuFit active blend in the clinical trial increased fat oxidation by 33.6 g/day (p < 0.04), decreased respiratory quotient, improved HOMA_IR, reduced oxidative and inflammatory biomarkers (plasma MDA, 8-isoprostane-F_2α, TNF-α, C-reactive protein), and increased the anti-inflammatory marker adiponectin. These data indicate that the NuFit active blend significantly increased fat oxidation and insulin sensitivity, and reduced oxidative and inflammatory stress. Therefore, the NuFit active blend appears to be a useful nutraceutical in the management of obesity and associated co-morbidities.

An in vitro assessment of the effect of Athrixia phylicoides DC. aqueous extract on glucose metabolism

Athrixia phylicoides DC. is an aromatic shrub indigenous to the eastern parts of Southern Africa. Indigenous communities brew "bush tea" from dried twigs and leaves of A. phylicoides, which is consumed as a beverage and used for its medicinal properties. Plant polyphenols have been shown to be beneficial to Type 2 diabetes mellitus (T2D) and obesity. Aqueous extracts of the plant have been shown to be rich in polyphenols, in particular phenolic acids, which may enhance glucose uptake and metabolism. The aim of this study was to determine the phenolic composition of a hot water A. phylicoides extract and assess its in vitro effect on cellular glucose utilisation. The most abundant phenolic compounds in the extract were 6-hydroxyluteolin-7-O-glucoside, chlorogenic acid, protocatechuic acid, a di-caffeoylquinic acid and a methoxy-flavonol derivative. The extract increased glucose uptake in C2C12, Chang and 3T3-L1 cells, respectively. Intracellular glucose was utilised by both oxidation (C2C12 myocytes and Chang cells; p < 0.01 and p < 0.05, respectively) and by increased glycogen storage (Chang cells; p < 0.05). No cytotoxicity was observed in Chang cells at the concentrations tested. The effects of the extract were not dose-dependent. A. phylicoides aqueous extract stimulated in vitro glucose uptake and metabolism, suggesting that consumption of this phenolic-rich extract could potentially ameliorate metabolic disorders related to obesity and T2D.

Suppression of pre adipocyte differentiation and promotion of adipocyte death by anti-HIV drugs

In the present study, we investigated the ability of anti-HIV drugs to interfere with normal cell cycle progression and to induce oxidative stress by perturbing the redox environment. Our results provide evidence that anti-HIV drugs have a differential effect on adipocyte cell cycle and differentiation, being able to modify the response to oxidative stress through an increase of reactive oxygen species (ROS) that compromises the induction of phase-2 and antioxidant enzymes. In detail, saquinavir, efavirenz, and stavudine exert antiadipogenic influences on the model 3T3-L1 cell line, perturbing the oxidative response and inducing of apoptosis. When considered together, the effects of anti-HIV drugs on 3T3-L1 pre adipocytes are distinct but commonly antiadipogenic, thus suggesting another additional possible mechanism by which antiretroviral therapies could contribute to lipoatrophy.

Isoprenylated flavonoids and adipogenesis-promoting constituents from Morus nigra

Ten new isoprenylated flavonoids, nigrasins A-J (1-10), and three known compounds were isolated from the twigs of Morus nigra. Compounds 8 and 9 promoted adipogenesis, characterized by increased lipid droplet and triglyceride content in 3T3L1 cells, and induced up-regulation of the expression of adipocyte-specific genes, aP2 and GLUT4.

Andrographolide attenuates tumor necrosis factor-alpha-induced insulin resistance in 3T3-L1 adipocytes

Andrographolide (AG), the primary bioactive component of Andrographils paniculate Nees, has showed an anti-diabetic effect. However, the molecular mechanism has not been clarified. In this study, we demonstrated that AG increased glucose uptake in 3T3-L1 cells in a time- and dosedependent manner. The activation of insulin signaling by AG was initiated from phosphotyrosine of IRS-1 and further passed on through phosphatidylinositol 3-kinase (PI3K) and the downstream signaling cascades. Moreover importantly, pretreatment cells with AG suppressed the TNF-α induced activation of NF-κB signaling pathway and its downstream inflammatory factors expression, therefore ameliorating insulin resistance. In conclusion, AG can improve insulin sensitivity through inhibition of NF-κB pathway. These findings are helpful in understanding the anti-diabetic properties of AG and can be of interest for the therapeutic application of AG in glucose controlling.

CNP/GC-B system: a new regulator of adipogenesis

Adipogenesis is regulated by a wide variety of compounds. An adipogenic cocktail containing insulin (INS), dexamethasone (DEX) and 3-isobutyl-1-methyl xanthine (IBMX) is routinely used to induce adipogenesis in 3T3-L1 preadipocytes, but the biochemical actions in adipogenesis of IBMX, a non-specific phosphodiesterase inhibitor, are not completely understood. In this study we show that C-type natriuretic peptide (CNP) is an endogenous adipogenesis regulator which can largely replace the function of IBMX. In 3T3-L1 preadipocytes, CNP potently elevated cGMP production through guanylyl cyclase-B (GC-B). Lipid droplets were evident in these cells upon stimulation with CNP for 12 days in the presence of INS and DEX, and their adiposity, evaluated by Oil Red O, was significantly higher than in cells stimulated with INS and DEX only. Membrane-permeable cGMP analogue also enhanced adiposity when cells were cultured together with INS and DEX, and KT5823, a non-specific cGMP-dependent kinase (cGK) inhibitor, suppressed the stimulatory effect of IBMX on adipogenesis, revealing that IBMX-stimulated adipogenesis is mediated through cGK. The enhancement of adiposity elicited by CNP was accompanied by increased mRNA levels of adipocyte-specific genes including those encoding peroxisome proliferator-activated receptor gamma and glucose transporter 4. Interestingly, the mRNA level of CNP itself was markedly enhanced in 3T3-L1 cells upon stimulation with INS, DEX and IBMX, reaching a maximum at 8h incubation with the cocktail. These observations suggest that the CNP/GC-B system participates in regulation of adipogenesis, particularly at an early stage in the process.

Naringenin chalcone improves adipocyte functions by enhancing adiponectin production

Naringenin chalcone is a flavonoid contained in tomato peel. In this study, we investigated its effects on adipocyte functions related to metabolic processes, including adipocytokine production. Naringenin chalcone promoted the gene expression (8.0-fold, p<0.001) and protein secretion (2.2-fold, p<0.001) of adiponectin from 3T3-L1 adipocytes. Reporter gene assays revealed that naringenin enhanced the activity of peroxisome proliferator-activated receptor gamma. DNA microarray experiments and Gene Ontology analysis revealed that naringenin chalcone also up-regulated the genes associated with mitochondrial energy metabolism, reflecting its insulin-sensitizing effects. Conversely, genes in categories such as those for cell adhesion were down-regulated. The expression of one adiponectin receptor, AdipoR2, was also increased (1.8-fold, p<0.01), suggesting that naringenin chalcone could activate the adiponectin pathway through the elevation of both the ligand and its receptor. These results indicate that naringenin chalcone is a potent tomato flavonoid that improves adipocyte metabolic functions and exerts insulin-sensitizing effects by activating an adiponectin-related pathway.

Sarcopoterium spinosum extract as an antidiabetic agent: in vitro and in vivo study

ETHNOPHARMACOLOGICAL RELEVANCE

Sarcopoterium spinosum (L.) sp., a common plant in the Mediterranean region, is widely used as an antidiabetic drug by Bedouin healers. However, the antidiabetic properties of Sarcopoterium spinosum had not been fully validated using scientific tools.

AIM OF THE STUDY

To determine the effectiveness of Sarcopoterium spinosum extract as an antidiabetic agent in vitro and in vivo.

MATERIALS AND METHODS

RINm pancreatic beta-cells, L6 myotubes, 3T3-L1 adipocytes and AML-12 hepatocytes were treated with an aqueous Sarcopoterium spinosum extract (0.001-10mg/ml). The effect of the extract on specific physiological functions, including insulin secretion, pancreatic beta-cell viability, GSK3 beta phosphorylation, lipolysis and glucose uptake was measured. In vivo studies were performed using KK-A(y) mice, given the extract for several weeks. IPGTT was performed, and plasma insulin, FFA, food consumption and body weight were measured. In addition, diabetic KK-A(y) mice were given a single dose of the extract, and IPGTT was performed.

RESULTS

Sarcopoterium spinosum extract increased basal and glucose/forskolin-induced insulin secretion in RINm cells, and increased cell viability. The extract inhibited lipolysis in 3T3-L1 adipocytes, and induced glucose uptake in these cells as well as in AML-12 hepatocytes and L6 myotubes. GSK3 beta phosphorylation was also induced in L6 myotubes, suggesting increased glycogen synthesis. Sarcopoterium spinosum extract had a preventive effect on the progression of diabetes in KK-A(y) mice. Catechin and epicatechin were detected in Sarcopoterium spinosum extract using hyphenated LC-MS/MS.

CONCLUSIONS

Sarcopoterium spinosum extract has effects that mimic those of insulin and provide the basis for antidiabetic activity of the extract.

Homoisoflavonoids from the fibrous roots of Polygonatum odoratum with glucose uptake-stimulatory activity in 3T3-L1 adipocytes

The EtOAc-soluble fraction of a 90% MeOH extract of the fibrous roots of Polygonatum odoratum was found to potentiate insulin-stimulated glucose uptake in differentiated 3T3-L1 adipocytes. Bioassay-guided fractionation yielded nine homoisoflavonoids (1-9), four of which were new (1-4), together with an isoflavone glycoside (10) and a flavanone glycoside (11). The structures of new compounds were elucidated on the basis of extensive 1D and 2D NMR spectroscopy, and the absolute configurations were deduced by CD spectra. All 11 compounds showed effects of sensitizing adipocytes for insulin in a cell-based glucose uptake assay using 3T3-L1 adipocytes. The results indicate that homoisoflavonoids may be potential insulin sensitizers.

Inhibition of thrombin action ameliorates insulin resistance in type 2 diabetic db/db mice

The binding of thrombin to its receptor stimulates inflammatory cytokines including IL-6 and monocyte chemoattractant protein-1 (MCP-1); both are associated with the development of insulin resistance. Because increased adiposity enhanced the expression of coagulation factor VII that stimulates the coagulation pathway in adipose tissue, we tested whether the inhibition of thrombin action ameliorates insulin resistance in obese diabetic (Lpr(-/-):db/db) mice. The 4-wk administration of argatroban, a selective thrombin inhibitor, reduced fasting plasma glucose and ameliorated insulin resistance in these mice. It also reduced adipocyte size and macrophage infiltration into adipose tissue. The aberrant gene expression of MCP-1, IL-6, adiponectin, and factor VII and suppressed insulin receptor substrate-1-Akt signaling in adipose tissue of db/db mice were reversed by argatroban treatment. These results demonstrate that increased adiposity enhances the production of thrombin in adipose tissue by stimulating factor VII expression and suggest that increased thrombin activity in adipose tissue plays an important role in the development of insulin resistance via enhancing MCP-1 production, leading to macrophage infiltration and insulin receptor substrate-1-Akt pathway inactivation.

Mechanisms regulating repression of haptoglobin production by peroxisome proliferator-activated receptor-gamma ligands in adipocytes

Obesity leads to inflammation of white adipose tissue involving enhanced secretion of cytokines and acute-phase proteins in response in part to the accumulation of excess lipids in adipocytes. Haptoglobin is an acute-phase reactant secreted by white adipose tissue and induced by inflammatory cytokines such as TNFalpha. In this study, we investigated the mechanisms regulating haptoglobin expression in adipocytes. Peroxisome proliferator-activated receptor (PPAR)-gamma agonists such as thiazolidinediones (TZDs) as well as non-TZD ligands can repress in vitro and in vivo haptoglobin expression in adipocytes and also prevent its induction by TNFalpha. This action requires direct involvement of PPAR gamma in regulating haptoglobin gene transcription because mutation of critical amino acids within helix 7 of the ligand-binding domain of PPAR gamma prevents repression of the haptoglobin gene by the synthetic ligands. Chromatin immunoprecipitation analysis shows active binding of PPAR gamma to a distal region of the haptoglobin promoter, which contains putative PPAR gamma binding sites. Additionally, PPAR gamma induces transcription of a luciferase reporter gene when driven by the distal promoter region of the haptoglobin gene, and TZD treatment significantly reduces the extent of this induction. Furthermore, the mutated PPAR gamma is incapable of enhancing luciferase activity in these in vitro reporter gene assays. In contrast to other adipokines repressed by TZDs such as resistin and chemerin, repression of haptoglobin does not require either CCAAT/enhancer-binding protein C/EBP alpha or the corepressors C-terminal binding protein 1 or 2. These data are consistent with a model in which synthetic PPAR gamma ligands selectively activate PPAR gamma bound to the haptoglobin gene promoter to arrest haptoglobin gene transcription.

Identification of antiadipogenic constituents of the rhizomes of Anemarrhena asphodeloides

Three new phenolic compounds, (E)-4'-demethyl-6-methyleucomin (1), anemarcoumarin A (2), and anemarchalconyn (3), were isolated from an ethyl acetate extract of the rhizomes of Anemarrhena asphodeloides, together with seven known compounds (4-10). The structures of the new compounds (1-3) were determined on the basis of spectroscopic data interpretation. Compound 3 exhibited a potent inhibitory effect against the differentiation of preadipocyte 3T3-L1 cells with an IC50 value of 5.3 microM.

Administration of myostatin does not alter fat mass in adult mice

AIM

Myostatin, a member of the TGF-beta superfamily, is produced by skeletal muscle and acts as a negative regulator of muscle mass. It has also been suggested that low-dose administration of myostatin (2 mug/day) in rodents can reduce fat mass without altering muscle mass. In the current study, we attempted to further explore the effects of myostatin on adipocytes and its potential to reduce fat mass, since myostatin administration could potentially be a useful strategy to treat obesity and its complications in humans.

METHODS

Purified myostatin protein was examined for its effects on adipogenesis and lipolysis in differentiated 3T3-L1 adipocytes as well as for effects on fat mass in wild-type, myostatin null and obese mice.

RESULTS

While myostatin was capable of inhibiting adipogenesis in 3T3-L1 cells, it did not alter lipolysis in fully differentiated adipocytes. Importantly, pharmacological administration of myostatin over a range of doses (2-120 mug/day) did not affect fat mass in wild-type or genetically obese (ob/ob, db/db) mice, although muscle mass was significantly reduced at the highest myostatin dose.

CONCLUSIONS

Our results suggest that myostatin does not reduce adipose stores in adult animals. Contrary to prior indications, pharmacological administration of myostatin does not appear to be an effective strategy to treat obesity in vivo.

The role of Akt on arsenic trioxide suppression of 3T3-L1 preadipocyte differentiation

The present study investigates the molecular details of how arsenic trioxide inhibits preadipocyte differentiation and examines the role of Akt/PKB in regulation of differentiation and apoptosis. Continual exposure of arsenic trioxide, at the clinic achievable dosage that does not induce apoptosis, suppressed 3T3-L1 cell differentiation into fat cells by inhibiting the expression of PPARgamma and C/EBPalpha and disrupting the interaction between PPARgamma and RXRalpha, which determines the programming of the adipogenic genes. Interestingly, if we treated the cells for 12 or 24 h and then withdrew arsenic trioxide, the cells were able to differentiate to the comparable levels of untreated cells as assayed by the activity of GAPDH, the biochemical marker of preadipocyte differentiation. Long term treatment blocked the differentiation and the activity of GAPDH could not recover to the comparable levels of untreated cells. Continual exposure of arsenic trioxide caused accumulation in G2/M phase and the accumulation of p21. We found that arsenic trioxide induced the expression and the phosphorylation of Akt/PKB and it inhibited the interaction between Akt/PKB and PPARgamma . Akt/PKB inhibitor appears to block the arsenic trioxide suppression of differentiation. Our results suggested that Akt/PKB may play a role in suppression of apoptosis and negatively regulate preadipocyte differentiation.

Inhibitory effect of (-)-epigallocatechin-3-gallate on lipid accumulation of 3T3-L1 cells

OBJECTIVE

The objective of this study was to investigate the molecular mechanisms underlying the attenuating effect of (-)-epigallocatechin-3-gallate (EGCG) on proliferation and lipid accumulation of 3T3-L1 cells, with a focus on the duration of EGCG treatment.

RESEARCH METHODS AND PROCEDURES

Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assay and diamidino-2-phenylindole staining. The anti-adipogenic effect of EGCG on 3T3-L1 cells was analyzed by glycerol-3-phosphate dehydrogenase activity and Oil red O staining. Western blot analysis was used to detect adenosine monophosphate-activated protein kinase (AMPK) activation and phosphorylation of its substrate, acetyl-CoA carboxylase (ACC), and expression of insulin (INS) receptor, INS receptor substrate-1 (IRS-1), and adipocyte marker proteins.

RESULTS

Exposure to EGCG during the early period of adipogenesis (7 days) was sufficient to prevent lipid accumulation. During this period, EGCG greatly decreased expression of the adipocyte marker proteins peroxisome proliferator-activated receptor gamma2 (PPARgamma2) and liver X receptor (LXR)-alpha. Furthermore, EGCG significantly induced generation of reactive oxygen species (ROS), which led to AMPK activation, and these effects were eliminated by N-acetylcysteine (NAC) treatment. Also, EGCG increased the tyrosine phosphorylation of INS receptor and INS-1 with increasing incubation time. In contrast, EGCG treatment did not alter glycerol release in the presence or absence of 2',5'-dideoxyadenosine (DDA), indicating that EGCG had no effect on lipolysis.

DISCUSSION

Our data demonstrate that EGCG decreased cell viability and inhibited differentiation of 3T3-L1 cells in a manner dependent on the duration of treatment. Also, we showed that inhibition of adipocyte differentiation by EGCG was associated with decreased glycerol-3-phosphate dehydrogenase (GPDH) activity accompanied by a strong inhibition of PPARgamma2-induced transcriptional activity. Furthermore, the inhibition of adipocyte differentiation by EGCG involved generation of ROS and activation of AMPK.

Gallic acid induces apoptosis in 3T3-L1 pre-adipocytes via a Fas- and mitochondrial-mediated pathway

Gallic acid (3,4,5-trihydroxybenzoic acid) is a naturally abundant plant phenolic compound. Our previous studies have shown that some phenolic acids such as gallic acid inhibit cell growth and induce apoptosis in 3T3-L1 pre-adipocytes. However, the molecular mechanism of gallic acid in the induction of cell apoptosis is still unclear. In this study, we investigated the effect of gallic acid on the apoptotic pathway in 3T3-L1 pre-adipocytes. Western blot data revealed that gallic acid stimulated an increase in the protein expression of Fas, FasL, and p53. The ratio of expression levels of pro- and anti-apoptotic Bcl-2 family members was changed by gallic acid treatment. Gallic acid released mitochondrial cytochrome c into the cytosol and subsequently induced the activation of caspase-9 and caspase-3, which were followed by the cleavage of poly(ADP-ribose) polymerase. Pretreatment with a general caspase-9 inhibitor (Z-LEHD-FMK) and caspase-3 inhibitor (Z-DEVD-FMK) prevented gallic acid from inhibiting cell viability in 3T3-L1 pre-adipocytes. The data also indicated that treatment with gallic acid inhibited histone deacetylase activity in 3T3-L1 pre-adipocytes. These results demonstrate that gallic acid induces apoptosis in 3T3-L1 pre-adipocytes through the Fas and mitochondrial pathway. The induction of cell apoptosis by gallic acid may prove to be a pivotal mechanism for decreased pre-adipocyte proliferation.

Adipogenic action of vanadium: a new dimension in treating diabetes

Vanadium is a well known anti-diabetic agent which mimics most of the actions of insulin on mature adipocytes. We report here the effect of vanadium on proliferation and differentiation of 3T3-L1 preadipocytes. Like insulin, vanadium treatment leads to increased proliferation as evidenced by H(3)thymidine uptake studies and differentiation of 3T3-L1 cells into adipocytes as evidenced by oil-red-O staining. Adipogenic potential of vanadium can be attributed to CREB activation, as documented by phospho-CREB antibody staining. This adipogenic potential is of significance in an in vivo scenario as the new adipocytes are likely to be insulin sensitive as against resistant existing mature adipocytes and thus indirectly may help in reduction of insulin resistance. Till today decrease in insulin resistance by vanadium treatment has been mainly attributed to its potential to inhibit PTP-1B, however the present study opens a new dimension in vanadium treatment for diabetes due to its novel role in adipogenesis.

Accumulation of endogenous methylglyoxal impaired insulin signaling in adipose tissue of fructose-fed rats

Increased accumulation of methylglyoxal (MG) has been linked to different insulin resistance states including diabetes and hypertension. In this study, the effects of MG on insulin signaling pathway were investigated. Following 9 weeks of fructose treatment, an insulin resistance state was developed in Sprague-Dawley (SD) rats, demonstrated as increased triglyceride and insulin levels, high blood pressure, and decreased insulin-stimulated glucose uptake by adipose tissue. More importantly, we observed a close correlation between the development of insulin resistance and elevated MG level in serum and adipose tissue. Both insulin resistance state and the elevated MG level were reversed by the MG scavenger, N-acetyl cysteine (NAC). When 3T3-L1 adipocytes were treated directly with MG, the impaired insulin signaling was also observed, indicated by decreased insulin-induced insulin-receptor substrate-1 (IRS-1) tyrosine phosphorylation and the decreased kinase activity of phosphatidylinositol (PI) 3-kinase (PI3K). The ability of NAC to block MG-impairment of PI3K activity and IRS-1 phosphorylation further confirmed the role of MG in the development of insulin resistance. In conclusion, the increase in endogenous MG accumulation impairs insulin-signaling pathway and decreases insulin-stimulated glucose uptake in adipose tissue, which may contribute to the development of insulin resistance.

SHP-2 positively regulates adipogenic differentiation in 3T3-L1 cells

The Src homology domain 2 (SH2)-containing tyrosine phosphatase SHP-2 has been implicated in the regulation of proliferation and differentiation in various cell types. Here, we investigated the ability of SHP-2 to mediate insulin-induced adipogenic differentiation of mouse 3T3-L1 cells. We found that the expression of SHP-2 was increased along with adipogenic differentiation. Overexpression of wild-type SHP-2 in 3T3-L1 cells resulted in enhanced adipocyte differentiation. Furthermore, insulin-stimulated adipogenic differentiation of 3T3-L1 cells was abolished by down-regulating SHP-2 expression using short interfering RNA. These results suggest that SHP-2 is a positive effector in signal transduction pathways necessary for adipocyte differentiation. In SHP-2 knockdown cells, the expression of peroxisome proliferator-activated receptor gamma, a master regulator of adipogenesis, was entirely suppressed even in the late phase of differentiation, whereas the expression level of C/EBPdelta was unchanged. These results highlight a novel role of SHP-2 in the signal transduction pathways regulating adipocyte differentiation.

IGF-binding protein-2 protects against the development of obesity and insulin resistance

Proliferation of adipocyte precursors and their differentiation into mature adipocytes contributes to the development of obesity in mammals. IGF-I is a potent mitogen and important stimulus for adipocyte differentiation. The biological actions of IGFs are closely regulated by a family of IGF-binding proteins (IGFBPs), which exert predominantly inhibitory effects. IGFBP-2 is the principal binding protein secreted by differentiating white preadipocytes, suggesting a potential role in the development of obesity. We have generated transgenic mice overexpressing human IGFBP-2 under the control of its native promoter, and we show that overexpression of IGFBP-2 is associated with reduced susceptibility to obesity and improved insulin sensitivity. Whereas wild-type littermates developed glucose intolerance and increased blood pressure with aging, mice overexpressing IGFBP-2 were protected. Furthermore, when fed a high-fat/high-energy diet, IGFBP-2-overexpressing mice were resistant to the development of obesity and insulin resistance. This lean phenotype was associated with decreased leptin levels, increased glucose sensitivity, and lower blood pressure compared with wild-type animals consuming similar amounts of high-fat diet. Our in vitro data suggest a direct effect of IGFBP-2 preventing adipogenesis as indicated by the ability of recombinant IGFBP-2 to impair 3T3-L1 differentiation. These findings suggest an important, novel role for IGFBP-2 in obesity prevention.