Adipocyte-specific Fatty Acid Binding Protein Research Articles

Adipocyte-Specific Fatty Acid-Binding Protein (AFABP) and Chemerin in Association with Gestational Diabetes: A Case-Control Study.

Background Adipocytokines participate in regulating the inflammatory response in glucose homeostasis and type 2 diabetes. However, among these peptides, the role of adipocyte-specific fatty-acid-binding protein (AFABP), chemerin, and secreted protein acidic and rich in cysteine (SPARC) in gestational diabetes (GDM) has not been fully investigated. Method The maternal fasting level of adipocytokines of 53 subjects with GDM and 43 normal pregnant (NGDM) was measured using multiplex immunoassay at 24–28 weeks, before delivery, immediate postpartum, and 2–6 months postpuerperium. Results Higher levels of AFABP were associated with a 3.7-fold higher risk of GDM. Low chemerin levels were associated with a 3.6-fold higher risk of GDM. Interleukin-10 (IL-10) was inversely associated with the risk of GDM. SPARC had no association with GDM. AFABP was directly correlated to interleukin-6 (r = 0.50), insulin resistance index (r = 0.26), and body mass index (r = 0.28) and inversely correlated to C-reactive protein (r = −0.27). Chemerin levels were directly and strongly correlated with IL-10 (r = 0.41) and interleukin-4 (r = 0.50) and inversely correlated to insulin resistance index (r = −0.23) in GDM but not NGDM. In the longitudinal assessment, there were no significant differences in AFABP and chemerin concentrations of both studied groups. Conclusion AFABP and chemerin were associated with a higher risk of GDM. These adipocytokines were related to insulin resistance, body mass index, and inflammation in pregnant women diagnosed with GDM.

3T3-L1 세포분화 중 지방축적 및 ROS 생성에 대한 연화 열수 및 에탄올 추출물의 효과

The present study was designed to investigate the effects of hot water and ethanol extracts of Nelumbo nucifera Gaertner flower on lipid accumulation and reactive oxygen species (ROS) production during adipogenesis in 3T3-L1 cells. 3T3-L1 preadipocytes were treated with both hot water and ethanol extracts for up to 8 days following standard induction of differentiation. Regarding anti-adipogenic activity, compared with the control, the hot water and ethanol extracts significantly inhibited lipid accumulation (37.4 and 66.6%, respectively) and ROS production (46.4 and 46.8%, respectively) during adipogenesis in 3T3-L1 cells. Treatment with hot water and ethanol extracts significantly inhibited mRNA expression of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/ enhancer-binding protein alpha (C/EBPα), thereby reducing the mRNA expression of adipocyte-specific fatty acid binding protein (aP2). Moreover, both the extracts significantly inhibited mRNA expression of NADPH oxidase (NOX4). Overall, our research suggests that N. nucifera Gaertner flower extracts might be a valuable source of bioactive compounds that exhibit anti-adipogenic activity and could have applications in the field of medicine and food industry.

Fabp4, a new player in the adipo-pancreatic axis.

Fabp4, a new player in the adipo-pancreatic axis.

PW174 Lipocalin-2, A-Fabp And Inflammatory Markers In Patients With Essential Hypertension

Adipocyte-specific fatty acid-binding protein (A-FABP) is a cytoplasmic protein that is expressed in adipocytes and is closely associated with insulin resistance, metabolic syndrome, and Type 2 diabetes. We investigated the relationship between A-FABP as a surrogate marker of metabolic syndrome and non-alcoholic fatty liver disease (NAFLD) in apparently healthy subjects. We assessed clinical and biochemical metabolic parameters and measured serum levels of A-FABP, high-sensitivity C-reactive protein and tumor necrosis factor-α (TNF-α) in 494 subjects who were divided into two groups according to the presence of NAFLD by abdominal ultrasonography. All parameters associated with metabolic syndrome were significantly higher in patients with NAFLD (P<.001). A-FABP showed positive correlation with TNF-α, homeostasis model assessment index of insulin resistance (HOMA-IR), and metabolic syndrome (P<.001) when adjusted for age and sex. The odds ratio for the risk of NAFLD in the highest tertile of A-FABP compared with the lowest tertile was 7.36 (CI 3.80–14.27, P<.001) after adjustment for age and sex; 4.52 (CI 2.22–9.20, P<.001) after adjustment for age, sex, HOMA-IR and metabolic syndrome and 2.86 (CI 1.11–7.35, P<.05) after further adjustment for all metabolic parameters including TNF-α. The serum level of A-FABP was independently associated with NAFLD and showed significant correlation with TNF-α, HOMA-IR, and metabolic syndrome.

Mulberry Anthocyanins Inhibit Oleic Acid Induced Lipid Accumulation by Reduction of Lipogenesis and Promotion of Hepatic Lipid Clearance

Mulberry (Morus alba L.) has been considered to possess different benefits such as protecting liver; improving fever, urine excretion disorder, hypertension, and diabetic syndrome; and preventing cardiovascular diseases. Recently, mounting evidence has shown that mulberry anthocyanin extract (MAE) is beneficial to hyperlipidemia; however, the mechanisms remain unclear. The present study was aimed to investigate the protective effects of MAE on hepatocyte cultured with high fatty acid and the underlying mechanisms. By using human hepatoma cell HepG2 as cell model, the results showed that MAE suppressed fatty acid synthesis and enhanced fatty acid oxidation, contributing to amelioration of lipid accumulation induced by oleic acid (OA). Moreover, MAE also inhibited acetyl coenzyme A carboxylase (ACC) activities by stimulating adenosine monophosphate-activated protein kinase (AMPK). MAE attenuated the expression of sterol regulatory element-binding protein-1 (SREBP-1) and its target molecules, such as fatty acid synthase (FAS). Similar results were also found in the expressions of enzymes involved in triglyceride and cholesterol biosyntheses including glycerol-3-phosphate acyltransferase (GPAT), 3-hydroxy-3-methyl-glutaryl CoA reductase (HMGCoR), adipocyte-specific fatty acid binding protein (A-FABP), and SREBP-2. In contrast, the lipolytic enzyme expressions of peroxisome proliferator activated receptor α (PPARα) and carnitinepalmitol- transferase-1 (CPT1) were increased. This study suggests the hypolipidemic effects of MAE occur via phosphorylation of AMPK and inhibition of lipid biosynthesis and stimulation of lipolysis. Therefore, the mulberry anthocyanins may actively prevent nonalcoholic fatty liver disease.

6‐Gingerol Inhibits Rosiglitazone‐Induced Adipogenesis in 3T3‐L1 Adipocytes

We investigated the effects of 6-gingerol ((S)-5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-3-decanone) on the inhibition of rosiglitazone (RGZ)-induced adipogenesis in 3T3-L1 cells. The morphological changes were photographed based on staining lipid accumulation by Oil-Red O in RGZ (1 µmol/l)-treated 3T3-L1 cells without or with various concentrations of 6-gingerol on differentiation day 8. Quantitation of triglycerides content was performed in cells on day 8 after differentiation induction. Differentiated cells were lysed to detect mRNA and protein levels of adipocyte-specific transcription factors by real-time reverse transcription-polymerase chain reaction and Western blot analysis, respectively. 6-gingerol (50 µmol/l) effectively suppressed oil droplet accumulation and reduced the sizes of the droplets in RGZ-induced adipocyte differentiation in 3T3-L1 cells. The triglyceride accumulation induced by RGZ in differentiated 3T3-L1 cells was also reduced by 6-gingerol (50 µmol/l). Treatment of differentiated 3T3-L1 cells with 6-gingerol (50 µmol/l) antagonized RGZ-induced gene expression of peroxisome proliferator-activated receptor (PPAR)γ and CCAAT/enhancer-binding protein α. Additionally, the increased levels of mRNA and protein in adipocyte-specific fatty acid binding protein 4 and fatty acid synthase induced by RGZ in 3T3-L1 cells were decreased upon treatment with 6-gingerol. Our data suggests that 6-gingerol may be beneficial in obesity, by reducing adipogenesis partly through the down-regulating PPARγ activity.

6-Gingerol prevents adipogenesis and the accumulation of cytoplasmic lipid droplets in 3T3-L1 cells

6-Gingerol ((S)-5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-3-decanone) is one of the pungent constituents of Zingiber zerumbet (L) Smith (Zingiberaceae family). In this study, we investigated the effects of 6-gingerol on the inhibition of adipogenesis in 3T3-L1 cells. After treatment with 6-gingerol in differentiation medium for 4 or 8 days, the 3T3-L1 cells were lysed for experimental analysis. Cells were stained with Oil-Red-O to detect oil droplets in adipocytes. The 3T3-L1 cells were lysed and measured for triglyceride contents. The protein expression of adipogenesis-related transcription factor was evaluated by Western blot analysis. 6-Gingerol suppressed oil droplet accumulation and reduced the droplet size in a concentration (5–15μg/ml)- and time-dependent manner. Treatment of 3T3-L1 cells with 6-gingerol reduced the protein levels of peroxisome proliferator-activated receptor (PPAR)γ and CCAAT/enhancer-binding protein (C/EBP)α. Additionally, the protein levels of fatty acid synthase (FAS) and adipocyte-specific fatty acid binding protein (aP2) decreased upon treatment with 6-gingerol. Meanwhile, 6-gingerol diminished the insulin-stimulated serine phosphorylation of Akt (Ser473) and GSK3β (Ser9). These results suggest that 6-gingerol effectively suppresses adipogenesis and that it exerts its role mainly through the significant down-regulation of PPARγ and C/EBPα and subsequently inhibits FAS and aP2 expression. 6-Gingerol also inhibited differentiation in 3T3-L1 cells by attenuating the Akt/GSK3β pathway. Our findings provide important insights into the mechanisms underlying the anti-adipogenic activity of 6-gingerol.

Association of Serum Adipocyte-Specific Fatty Acid Binding Protein with Fatty Liver Index as a Predictive Indicator of Nonalcoholic Fatty Liver Disease

BackgroundAdipocyte-specific fatty acid-binding protein (A-FABP) is a cytoplasmic protein expressed in macrophages and adipocytes and it plays a role in insulin resistance and metabolic syndrome. Recently, the fatty liver index (FLI) was introduced as an indicator of nonalcoholic fatty liver disease (NAFLD). In this study, we aimed to investigate the relationship between baseline serum A-FABP levels and FLI after 4 years in apparently healthy subjects.MethodsA total of 238 subjects without a past history of alcoholism or hepatitis were recruited from a medical check-up program. The NAFLD state was evaluated 4 years later in the same subjects using FLI. Fatty liver disease was diagnosed as diffusely increased echogenicity of the hepatic parenchyma compared to the kidneys, vascular blurring, and deep-echo attenuation. NAFLD was defined as subjects with fatty liver and no history of alcohol consumption (>20 g/day).ResultsBaseline serum A-FABP levels were significantly associated with FLI after adjustment for age and sex (P<0.001). The subjects with higher A-FABP levels had a higher mean FLI (P for trend=0.006). After adjusting for age and sex, serum A-FABP levels at baseline were shown to be significantly associated with FLI as a marker of development of NAFLD after 4 years (odds ratio, 2.68; 95% confidence interval, 1.24 to 5.80 for highest tertile vs. lowest tertile; P=0.012).ConclusionThis study demonstrated that higher baseline serum A-FABP levels were associated with FLI as a predictive indicator of NAFLD after 4 years of follow-up in healthy Korean adults.

Effect of Eriodictyol on Glucose Uptake and Insulin Resistance in Vitro

Eriodictyol [2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-2,3-dihydrochromen-4-one] is a flavonoid with anti-inflammatory and antioxidant activities. Because inflammation and oxidative stress play critical roles in the pathogenesis of diabetes mellitus, the present study was designed to explore whether eriodictyol has therapeutic potential for the treatment of type 2 diabetes. The results show that eriodictyol increased insulin-stimulated glucose uptake in both human hepatocellular liver carcinoma cells (HepG2) and differentiated 3T3-L1 adipocytes under high-glucose conditions. Eriodictyol also up-regulated the mRNA expression of peroxisome proliferator-activated receptor γ2 (PPARγ2) and adipocyte-specific fatty acid-binding protein (aP2) as well as the protein levels of PPARγ2 in differentiated 3T3-L1 adipocytes. Furthermore, it reactivated Akt in HepG2 cells with high-glucose-induced insulin resistance. This response was strongly inhibited by pretreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, indicating that eriodictyol increased Akt phosphorylation by activating the PI3K/Akt pathway. These results imply that eriodictyol can increase glucose uptake and improve insulin resistance, suggesting that it may possess antidiabetic properties.

AS-263: Serum Adipocyte-Specific Fatty Acid-Binding Protein is a Predictable Marker of Coronary Artery Disease and Diabetes Mellitus

AS-263: Serum Adipocyte-Specific Fatty Acid-Binding Protein is a Predictable Marker of Coronary Artery Disease and Diabetes Mellitus

Different regulation role of myostatin in differentiating pig ADSCs and MSCs into adipocytes

Myostation (MSTN), which is primarily expressed in muscle, plays an important role in myogenic and adipogenic cells. However, there is little information about whether MSTN displays different roles between adipose-derived stem cells (ADSCs) and muscle satellite cells (MSCs). The two kinds of cells can both exist in the muscle and differentiate into adiposities. In this research, we isolated ADSCs and MSCs from porcine fat tissues and semitendinosus muscle, respectively, to investigate the effect of MSTN on the adipogenesis of those cells. ADSCs and MSCs were treated with recombinant human MSTN during the induction of adipogenesis or before the induction of differentiation. Then, we evaluated adipogenesis by Oil Red O staining and assessed the expression patterns of adipocyte-specific fatty acid binding protein (aP2) and peroxisome proliferator-activated receptor (PPAR) γ using real-time polymerase chain reaction methods. Our results indicated that the treatment with MSTN before or during the induction of differentiation in MSCs could both inhibit the adipogenesis. However, the treatment with MSTN only during the induction of differentiation in ADSCs could suppress the adipogenesis. Those results showed that MSTN had different roles in the adipogenesis of ADSCs and MSCs. It can shed new light on the origin of adipocyte located in muscle.

Morus alba L. root bark stimulates adipocyte differentiation in 3T3-L1 cells

Mori Cortex (MC), the root bark of the mulberry tree (Morus alba L.), has been used traditionally in several Asian countries for medicinal purposes due to its anti-inflammatory, hypoglycemic, and antibacterial activities, as well as its antiviral effects. In the present study, we found that ethanolic extract of Morus alba L. root bark (MC) accelerated differentiation of 3T3-L1 preadipocyte cells. Treatment with MC resulted in enhanced triglyceride (TG) accumulation and increased mRNA levels of C/EBPα (CCAAT/enhancer-binding protein α) and PPARγ (peroxisome proliferator-activated receptors γ); however, their upstream regulator, C/EBPδ, showed a dose-dependent decrease during adipocyte differentiation. Immunoblot analysis indicated that MC induced an increase in expression of adipogenic maker proteins, such as PPARγ, adipocyte-specific fatty acid binding protein 4 (aP2), and GLUT4 (glucose transporter 4). Results of the reporter gene assay revealed that MC did not show PPARγ ligand activity even at a high dose (50 μg/mL), suggesting that enhanced expression of PPARγ resulted not from PPARγ ligand activity but by other mechanisms that might be related to the PPARγ signal pathway. In conclusion, our findings suggest the potential for use of MC as a possible therapeutic material for treatment of dyslipidemia and type 2 diabetes by increasing PPARγ transcriptional activities.

Activation of peroxisome proliferator-activated receptor-α enhances fatty acid oxidation in human adipocytes

Peroxisome proliferator-activated receptor-α (PPARα) is a key regulator for maintaining whole-body energy balance. However, the physiological functions of PPARα in adipocytes have been unclarified. We examined the functions of PPARα using human multipotent adipose tissue-derived stem cells as a human adipocyte model. Activation of PPARα by GW7647, a potent PPARα agonist, increased the mRNA expression levels of adipocyte differentiation marker genes such as PPARγ, adipocyte-specific fatty acid-binding protein, and lipoprotein lipase and increased both GPDH activity and insulin-dependent glucose uptake level. The findings indicate that PPARα activation stimulates adipocyte differentiation. However, lipid accumulation was not changed, which is usually observed when PPARγ is activated. On the other hand, PPARα activation by GW7647 treatment induced the mRNA expression of fatty acid oxidation-related genes such as CPT-1B and AOX in a PPARα-dependent manner. Moreover, PPARα activation increased the production of CO2 and acid soluble metabolites, which are products of fatty acid oxidation, and increased oxygen consumption rate in human adipocytes. The data indicate that activation of PPARα stimulates both adipocyte differentiation and fatty acid oxidation in human adipocytes, suggesting that PPARα agonists could improve insulin resistance without lipid accumulation in adipocytes. The expected effects of PPARα activation are very valuable for managing diabetic conditions accompanied by obesity, because PPARγ agonists, usually used as antidiabetic drugs, induce excessive lipid accumulation in adipocytes in addition to improvement of insulin resistance.

Amelioration of Insulin Resistance by Scopoletin in High-Glucose-Induced, Insulin-Resistant HepG2 Cells

Insulin resistance plays an important role in the development of type 2 diabetes mellitus. Scopoletin, a phenolic coumarin, is reported to regulate hyperglycemia and diabetes. To examine its effect on insulin resistance, we treated high-glucose-induced, insulin-resistant HepG2 cells with scopoletin and measured phosphatidylinositol 3-kinase (PI3 K)-linked protein kinase B (Akt/PKB) phosphorylation. Scopoletin significantly stimulated the reactivation of insulin-mediated Akt/PKB phosphorylation. This effect was blocked by LY294002, a specific PI3 K inhibitor. The ability of scopoletin to activate insulin-mediated Akt/PKB was greater than that of rosiglitazone, a thiazolidinedione, and scopoletin was less adipogenic than rosiglitazone, as shown by the extent of lipid accumulation in differentiated adipocytes. Scopoletin increased the gene expression of both peroxisome proliferator-activated receptor γ2 (PPARγ2), a target receptor for rosiglitazone, and adipocyte-specific fatty acid binding protein, but not to the level induced by rosiglitazone. However, the PPARγ2 protein level was increased equally by rosiglitazone and scopoletin in differentiated adipocytes. Our results suggest that scopoletin can ameliorate insulin resistance in part by upregulating PPARγ2 expression. With its lower adipogenic property, scopoletin may be a useful candidate for managing metabolic disorders, including type 2 diabetes mellitus.

Puerarin enhances adipocyte differentiation, adiponectin expression, and antioxidant response in 3T3‐L1 cells

Puerarin, a major isoflavone glycoside from Kudzu root (Pueraria lobata), has been reported to exert antihyperglycemic and antioxidant effects and thus have pharmacological actions in the treatment of diabetes and cardiovascular diseases. We investigated the effects of puerarin on the changes of key gene expression associated with adipocyte differentiation and insulin sensitivity and link to cellular antioxidant response pathways. Puerarin treatment significantly enhanced differentiation of 3T3-L1 preadipocytes accompanying increased lipid accumulation and glucose-6-phosphate dehydrogenase (G6PDH) activity. At a molecular level, puerarin upregulated mRNA expression of peroxisome proliferator-activated receptor γ (PPARγ) and its target genes, an adipocyte-specific fatty acid binding protein (aP2) and GLUT4. Puerarin also caused a significant increase in mRNA level of adiponectin, an important insulin-sensitizing adipocytokine that is downregulated in insulin-resistant and diabetic states. In addition, treatment with puerarin was found to upregulate mRNA levels of G6PDH, glutathione reductase, and catalase, all of which are important for endogenous antioxidant responses. These data suggest that the hypoglycemic effects of puerarin can be attributed to the upregulation of PPARγ and its downstream target genes, GLUT4 and adiponectin expression, leading to increased glucose utilization. Puerarin may also be effective in preventing the rise of oxidative stress during adipocyte differentiation by increasing endogenous antioxidant responses.

Serum Osteocalcin Is Inversely Associated With Adipocyte-Specific Fatty Acid–Binding Protein in the Korean Metabolic Syndrome Research Initiatives

Recent studies (1) have reported that adipokines might act in a paracrine manner on osteoblasts and suppress osteoblast activity or differentiation—or both—in pathological conditions. Adipocyte-specific fatty acid–binding protein (A-FABP) is highly expressed in adipose tissue and may act systemically to regulate lipid and glucose metabolism (2). However, the association between serum osteocalcin with adipokines and A-FABP remains unclear in humans. Therefore, the aim of this study was to clarify the relationship between serum osteocalcin and the parameters of the metabolic syndrome and the association of serum osteocalcin with adipokines and A-FABP. This was a cross-sectional study carried out by the Korean Metabolic Syndrome Research Initiative. The 124 obese subjects underwent a standardized examination at four university hospitals in Korea. The control …

Serum adipocyte-specific fatty acid-binding protein is associated with nonalcoholic fatty liver disease in apparently healthy subjects

Adipocyte-specific fatty acid-binding protein (A-FABP) is a cytoplasmic protein that is expressed in adipocytes and is closely associated with insulin resistance, metabolic syndrome, and Type 2 diabetes. We investigated the relationship between A-FABP as a surrogate marker of metabolic syndrome and non-alcoholic fatty liver disease (NAFLD) in apparently healthy subjects. We assessed clinical and biochemical metabolic parameters and measured serum levels of A-FABP, high-sensitivity C-reactive protein and tumor necrosis factor-α (TNF-α) in 494 subjects who were divided into two groups according to the presence of NAFLD by abdominal ultrasonography. All parameters associated with metabolic syndrome were significantly higher in patients with NAFLD ( P<.001). A-FABP showed positive correlation with TNF-α, homeostasis model assessment index of insulin resistance (HOMA-IR), and metabolic syndrome ( P<.001) when adjusted for age and sex. The odds ratio for the risk of NAFLD in the highest tertile of A-FABP compared with the lowest tertile was 7.36 (CI 3.80–14.27, P<.001) after adjustment for age and sex; 4.52 (CI 2.22–9.20, P<.001) after adjustment for age, sex, HOMA-IR and metabolic syndrome and 2.86 (CI 1.11–7.35, P<.05) after further adjustment for all metabolic parameters including TNF-α. The serum level of A-FABP was independently associated with NAFLD and showed significant correlation with TNF-α, HOMA-IR, and metabolic syndrome.

Caffeic Acid Phenethyl Ester Inhibits Differentiation to Adipocytes in 3T3-L1 Mouse Fibroblasts

We investigated the inhibitory effect of caffeic acid phenethyl ester (CAPE) on the differentiation of 3T3-L1 mouse fibroblasts to adipocytes. 3T3-L1 cells were differentiated for adipocytes given high glucose Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 1 microM dexamethasone (DEX), 500 microM isobutylmethylxanthine (IBMX), and 5 microg/ml insulin for 7 days. After differentiation, cells were stained with Oil-Red-O to detect oil droplets in adipocytes. Additionally, the cells were lysed and measured for triglyceride contents. Total RNA was isolated from differentiated cells on day 0, 4 and 7. Then, RNA was analyzed using reverse transcription (RT)-polymerase chain reaction (PCR). CAPE dose-dependently suppressed oil droplet accumulation and reduced the droplet size. These findings showed that CAPE at concentrations of 25 to 50 microM could significantly inhibit triglyceride deposition (p<0.05). Treatment of 3T3-L1 with CAPE reduced the mRNA levels of peroxisome proliferator-activated receptor (PPAR) gamma and CCAAT/enhancer-binding protein (C/EBPalpha). Fatty acid synthase (Fas) and adipocyte-specific fatty acid binding protein (aP2) are known to be associated with lipid metabolism in adipocytes, and both Fas mRNA and aP2 mRNA were significantly suppressed by CAPE treatment. These findings suggested that CAPE suppresses 3T3-L1 differentiation to adipocytes through inhibition of PPARgamma, C/EBPalpha, Fas and aP2 expression.

7-O-Methylaromadendrin Stimulates Glucose Uptake and Improves Insulin Resistance in Vitro

The stimulation of glucose uptake into peripheral tissues is an important mechanism for the removal of glucose in blood and for the management of diabetes mellitus (DM). Since recent results have demonstrated the beneficial effects of flavonoids in relation to DM, this study was designed to examine the effects of 7-O-methylaromadendrin (7-O-MA), a flavonoid isolated from Inula viscosa, on glucose uptake into liver and fat tissue, and investigate the molecular mechanisms involved. 7-O-MA at 10 microM significantly stimulated insulin-induced glucose uptake measured by 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG) in both human hepatocellular liver carcinoma (HepG2) cells and differentiated 3T3-L1 adipocytes. Adipocyte-specific fatty acid binding protein (aP2) gene expression was increased by 7-O-MA in adipocytes, and both gene and protein level of peroxisome proliferator-activated receptor gamma2 (PPARgamma2) was also increased. Moreover, 7-O-MA stimulated the reactivation of insulin-mediated phosphorylation of phosphatidylinositol 3-kinase (PI3K)-linked protein kinase B (Akt/PKB) and adenosine 5'-monophosphate-activated protein kinase (AMPK) in high glucose-induced, insulin-resistant HepG2 cells, and this effect was blocked by either LY294002, a PI3K inhibitor, or compound C, an AMPK inhibitor. Therefore, these results suggest that 7-O-MA might stimulate glucose uptake via PPARgamma2 activation and improve insulin resistance via PI3K and AMPK-dependent pathways, and be a potential candidate for the management of type 2 DM.

Bixin regulates mRNA expression involved in adipogenesis and enhances insulin sensitivity in 3T3-L1 adipocytes through PPARγ activation

Insulin resistance is partly due to suppression of insulin-induced glucose uptake into adipocytes. The uptake is dependent on adipocyte differentiation, which is controlled at mRNA transcription level. The peroxisome proliferator-activated receptor (PPAR), a ligand-regulated nuclear receptor, is involved in the differentiation. Many food-derived compounds serve as ligands to activate or inactivate PPAR. In this study, we demonstrated that bixin and norbixin (annatto extracts) activate PPARγ by luciferase reporter assay using GAL4–PPAR chimera proteins. To examine the effects of bixin on adipocytes, 3T3-L1 adipocytes were treated with bixin or norbixin. The treatment induced mRNA expression of PPARγ target genes such as adipocyte-specific fatty acid-binding protein (aP2), lipoprotein lipase (LPL), and adiponectin in differentiated 3T3-L1 adipocytes and enhanced insulin-dependent glucose uptake. The observations indicate that bixin acts as an agonist of PPARγ and enhances insulin sensitivity in 3T3-L1 adipocytes, suggesting that bixin is a valuable food-derived compound as a PPAR ligand to regulate lipid metabolism and to ameliorate metabolic syndrome.