Jiyun Ahn

The anti-obesity effect of quercetin is mediated by the AMPK and MAPK signaling pathways

Quercetin is the most abundant flavonoid and is assumed to have protective roles against the pathogenesis of multiple diseases associated with oxidative stress. In the present study, we investigated the molecular mechanisms by which quercetin affects adipogenesis and apoptosis in 3T3-L1 cells. The exposure of 3T3-L1 preadipocytes to quercetin resulted in attenuated adipogenesis and decreased expression of adipogenesis-related factors and enzymes. Moreover, quercetin exposure up-regulated the levels of phosphorylated adenosine monophosphate-activated protein kinase (AMPK) and its substrate, acetyl-CoA carboxylase (ACC). Treatment of 3T3-L1 adipocytes with quercetin resulted in the induction of apoptosis and a concomitant decrease in ERK and JNK phosphorylation. Taken together, these data indicate that quercetin exerts anti-adipogenesis activity by activating the AMPK signal pathway in 3T3-L1 preadipocytes, while the quercetin-induced apoptosis of mature adipocytes was mediated by modulation of the ERK and JNK pathways, which play pivotal roles during apoptosis.

Curcumin-induced suppression of adipogenic differentiation is accompanied by activation of Wnt/β-catenin signaling

Curcumin, a polyphenol found in the rhizomes of Curcuma longa, improves obesity-associated inflammation and diabetes in obese mice. Curcumin also suppresses adipocyte differentiation, although the underlying mechanism remains unclear. Here, we used 3T3-L1 cells to investigate the details of the mechanism underlying the anti-adipogenic effects of curcumin. Curcumin inhibited mitogen-activated protein kinase (MAPK) (ERK, JNK, and p38) phosphorylation that was associated with differentiation of 3T3-L1 cells into adipocytes. During differentiation, curcumin also restored nuclear translocation of the integral Wnt signaling component beta-catenin in a dose-dependent manner. In parallel, curcumin reduced differentiation-stimulated expression of CK1alpha, GSK-3beta, and Axin, components of the destruction complex targeting beta-catenin. Accordingly, quantitative PCR analysis revealed that curcumin inhibited the mRNA expression of AP2 (mature adipocyte marker) and increased the mRNA expression of Wnt10b, Fz2 (Wnt direct receptor), and LRP5 (Wnt coreceptor). Curcumin also increased mRNA levels of c-Myc and cyclin D1, well-known Wnt targets. These results suggest that the Wnt signaling pathway participates in curcumin-induced suppression of adipogenesis in 3T3-L1 cells.

Dietary resveratrol alters lipid metabolism-related gene expression of mice on an atherogenic diet

BACKGROUND/AIMS Resveratrol, a polyphenolic activator of the silent information regulation 2 homolog 1 (SIRT1), is known to extend lifespan and improve metabolic disease. The aim of the present study is to test whether resveratrol protects against metabolic steatohepatitis through the modulation of lipid metabolism-related genes. METHODS We used a mouse model in which steatohepatitis can be induced by an atherogenic diet (Ath diet) to evaluate the effects of resveratrol on steatotic hepatitis and hepatic gene expression. RESULTS The Ath diet induced excessive weight gain, hepatomegaly, dyslipidemia, and steatohepatitis after 8 weeks. The addition of resveratrol protected against Ath diet-induced changes and also alleviated steatohepatitis. Whole-genome expression analysis revealed that an Ath diet altered the hepatic expression of genes involved in lipid metabolism, and the addition of resveratrol to the diet reversed that effect. Real-time PCR and Western blot analysis confirmed the Ath diet up-regulated the levels of genes related to lipogenesis and down-regulated genes involved in lipolysis. Resveratrol clearly suppressed the Ath diet-induced alterations of the expression of genes related to lipid metabolism. CONCLUSIONS Resveratrol ameliorated dyslipidemia and steatohepatitis induced by the Ath diet, and its beneficial effects were associated with the altered expression of hepatic genes involved in lipid metabolism.

Quercetin Reduces High‐Fat Diet‐Induced Fat Accumulation in the Liver by Regulating Lipid Metabolism Genes

To understand the molecular mechanisms underlying the influence of quercetin on the physiological effects of hyperlipidemia, we investigated its role in the prevention of high‐fat diet (HFD)‐induced obesity and found that it regulated hepatic gene expression related to lipid metabolism. Quercetin supplementation in mice significantly reduced the HFD‐induced gains in body weight, liver weight, and white adipose tissue weight compared with the mice fed only with HFD. It also significantly reduced HFD‐induced increases in serum lipids, including cholesterol, triglyceride, and thiobarbituric acid‐reactive substance (TBARS). Consistent with the reduced liver weight and white adipose tissue weight, hepatic lipid accumulation and the size of lipid droplets in the epididymal fat pads were also reduced by quercetin supplementation. To further investigate how quercetin may reduce obesity, we analyzed lipid metabolism‐related genes in the liver. Quercetin supplementation altered expression profiles of several lipid metabolism‐related genes, including Fnta, Pon1, Pparg, Aldh1b1, Apoa4, Abcg5, Gpam, Acaca, Cd36, Fdft1, and Fasn, relative to those in HFD control mice. The expression patterns of these genes observed by quantitative reverse transcriptase‐polymerase chain reaction were confirmed by immunoblot assays. Collectively, our results indicate that quercetin prevents HFD‐induced obesity in C57B1/6 mice, and its anti‐obesity effects may be related to the regulation of lipogenesis at the level of transcription. Copyright

MicroRNA-146b promotes adipogenesis by suppressing the SIRT1-FOXO1 cascade

Sirtuin 1 (SIRT1) plays a critical role in the maintenance of metabolic homeostasis and promotes fat mobilization in white adipose tissue. However, regulation of SIRT1 during adipogenesis, particularly through microRNAs, remains unclear. We observed that miR‐146b expression was markedly increased during adipogenesis in 3T3‐L1 cells. Differentiation of 3T3‐L1 was induced by overexpression of miR‐146b. Conversely, inhibition of miR‐146b decreased adipocyte differentiation. Bioinformatics‐based studies suggested that SIRT1 is a target of miR‐146b. Further analysis confirmed that SIRT1 was negatively regulated by miR‐146b. We also observed that miR‐146b bound directly to the 3′‐untranslated region of SIRT1 and inhibited adipogenesis through SIRT1 downregulation. The miR‐146b/SIRT1 axis mediates adipogenesis through increased acetylation of forkhead box O1 (FOXO1). Expression of miR‐146b was increased and SIRT1 mRNA subsequently decreased in the adipose tissues of diet‐induced and genetically obese mice. Furthermore, in vivo knockdown of miR‐146b by a locked nucleic acid miR‐146b antagomir significantly reduced body weight and fat volume in accordance with upregulation of SIRT1 and subsequent acetylation of FOXO1. Therefore, the miR‐146b/SIRT1 pathway could be a potential target for obesity prevention and treatment.

High fat diet induced downregulation of microRNA-467b increased lipoprotein lipase in hepatic steatosis

Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatic fat accumulation and is presently the most common chronic liver disease. However, the mechanisms underlying the development of steatosis remain unclear. MicroRNAs (miRNAs) are small non-coding RNAs that modulate a variety of biological functions. We have investigated the role of miRNA in the development of steatosis. We found that miR-467b expression is significantly downregulated in liver tissues of high-fat diet fed mice and in steatosis-induced hepatocytes. The downregulation of miR-467b resulted in the upregulation of hepatic lipoprotein lipase (LPL), the direct target of miR-467b. Moreover, the interaction between miR-467b and LPL was associated with insulin resistance, a major cause of NAFLD. These results suggest that downregulation of miR-467b is involved in the development of hepatic steatosis by modulating the expression of its target, LPL.

Curcumin attenuates diet-induced hepatic steatosis by activating AMP-activated protein kinase.

Curcumin is a well‐known component of traditional turmeric (Curcuma longa), which has been reported to prevent obesity and diabetes. However, the effect of curcumin on hepatic lipid metabolism remains unclear. The aim of this study was to examine the effects of curcumin on hepatic steatosis in high‐fat/cholesterol diet (HFD)‐induced obese mice. Male C57BL/6J mice were fed a normal diet (ND), HFD or HFD with 0.15% curcumin (HFD+C) for 11 weeks. We found that curcumin significantly lowered the body‐weight and adipose tissue weight of mice in the HFD+C group compared with the findings for the HFD group (p < 0.05). The levels of total cholesterol, fasting glucose and insulin in serum were decreased, and HFD‐induced impairment of insulin sensitivity was improved by curcumin supplementation (p < 0.05). Curcumin protected against the development of hepatic steatosis by reducing hepatic fat accumulation. Moreover, curcumin activated AMP‐activated protein kinase (AMPK) and elevated the gene expression of peroxisome proliferator‐activated receptor alpha. By contrast, curcumin suppressed the HFD‐mediated increases in sterol regulatory element‐binding protein‐1, acetyl‐CoA carboxylase 1, fatty acid synthase and cluster of differentiation 36 expression. Taken together, these findings indicate that curcumin attenuates HFD‐induced hepatic steatosis by regulating hepatic lipid metabolism via AMPK activation, suggesting its use as a therapeutic for hepatic steatosis.

Ethanol extract of Psoralea corylifolia L. and its main constituent, bakuchiol, reduce bone loss in ovariectomised Sprague-Dawley rats

The aim of the present study was to investigate whether ethanol extracts of Psoralea corylifolia L. (PCE) and its active component protect against bone loss in ovariectomised rats. We screened oestrogenic activities of the main extract fractions using in vitro assays and identified bakuchiol as the most active oestrogenic component by HPLC and LC/MS, and then demonstrated that bakuchiol had strong binding affinity for oestrogen receptor (ER) alpha. Seventy female Sprague-Dawley rats were assigned to either a sham-operated group (n 10) or an ovariectomised group (n 60). The ovariectomised group was subdivided into six groups, each containing ten rats: vehicle group, two bakuchiol-treated groups (dose of 15 mg/kg per d or 30 mg/kg per d; ten rats for each group), two PCE-supplemented groups (0.25 % or 0.5 % extracts of diets; ten rats for each group) and a 17beta-oestradiol (E2)-treated group (20 microg/kg per d). We recorded weight and feed intake every week, and killed all animals after 6 weeks. Blood was collected, and the uterus, kidneys and livers were removed. Bakuchiol has a three-fold higher binding affinity for ERalpha than for ERbeta. Bakuchiol and PCE treatments had no uterotrophic activity even though they demonstrated oestrogenic activity in the in vitro assays. Bakuchiol and PCE treatments reduced postmenopausal bone loss by increasing alkaline phosphatase, Ca concentrations, serum E2 concentration and bone mineral density, and by decreasing the inorganic P level. The present study indicated that bakuchiol and PCE treatments could protect against bone loss.

Estrogenic activities of Psoralea corylifolia L. seed extracts and main constituents

Estrogenic activities of ethanol extract and its active components from Psoralea corylifolia L. were studied using various in vitro assays. The main components from ethanol extract were analyzed to be bakuchiol, psoralen, isobavachalcone, isobavachromene, and bavachinin. In a fractionation procedure, hexane and chloroform fractions showed estrogenic activity in yeast transactivation assay and E-screen assay. In yeast transactivation assay, ethanol extract, hexane, and chloroform fractions showed significantly higher activities at a concentration of 1.0 ng/ml, and bakuchiol at the concentration of 10(-6) M was showed the highest activity, especially, which was higher than genistein at the same concentration. In E-screen assay, cell proliferation of bakuchiol (10(-6) M) showed similar estrogenic activity with genistein (10(-6) M). In ER binding assay, bakuchiol displayed the strongest ER-binding affinity (IC(50) for ERα=1.01×10(-6) M, IC(50) for ERβ=1.20×10(-6) M) and bakuchiol showed five times higher affinity for ERα than for ERβ.

Anti-obesity effects of glabridin-rich supercritical carbon dioxide extract of licorice in high-fat-fed obese mice

Licorice (Glycyrrhiza glabra Linne) is a well-known medicinal plant and glabridin is an isoflavan isolated from licorice. In this study, we investigated the anti-obesity effect of glabridin and glabridin-rich supercritical fluid extract of licorice (LSC). Glabridin effectively inhibited adipogenesis in 3T3-L1 cells. Moreover, LSC showed inhibitory effect on adipogenesis in a dose-dependent manner. The inhibitory effect of LSC resulted from inhibiting the induction of the transcriptional factors CCAAT enhancer binding protein alpha and peroxisome proliferator-activated receptor gamma. Then we fed mice with high-fat diet containing none, 0.1% and 0.25% LSC for 8weeks to explore the anti-obesity effect of LSC in vivo. LSC significantly reduced weight gain by high-fat diet in a dose-dependent manner. The reductions of the hypertrophy of white adipose tissue and of fat cell size were also observed. In the liver, LSC supplementation effectively inhibited high-fat diet-induced hepatic steatosis through downregulation of gluconeogenesis related phosphoenolpyruvate carboxykinase and glucose 6-phosphatase and upregulation of the β-oxidation related carnitine palmitoyltransferase 1. Taken together, our results suggest that glabridin and glabridin-rich licorice extract would be effective anti-obesity agents.