Fatty Acid-Binding Protein 4 in Patients with and without Diabetic Retinopathy.

BACKGROUND: Fatty acid-binding protein 4 (FABP4) has been demonstrated to be a predictor of early diabetic nephropathy. However, little is known about the relationship between FABP4 and diabetic retinopathy (DR). This study explored the value of FABP4 as a biomarker of DR in patients with type 2 diabetes mellitus (T2DM). METHODS: A total of 238 subjects were enrolled, including 20 healthy controls and 218 T2DM patients. Serum FABP4 levels were measured using a sandwich enzyme-linked immunosorbent assay. The grade of DR was determined using fundus fluorescence angiography. Based on the international classification of DR, all T2DM patients were classified into the following three subgroups: non-DR group, non-proliferative diabetic retinopathy (NPDR) group, and proliferative diabetic retinopathy (PDR) group. Multivariate logistic regression analyses were employed to assess the correlation between FABP4 levels and DR severity. RESULTS: FABP4 correlated positively with DR severity (r=0.225, P=0.001). Receiver operating characteristic curve analysis was used to assess the diagnostic potential of FABP4 in identifying DR, with an area under the curve of 0.624 (37% sensitivity, 83.6% specificity) and an optimum cut-off value of 76.4 µg/L. Multivariate logistic regression model including FABP4 as a categorized binary variable using the cut-off value of 76.4 µg/L showed that the concentration of FABP4 above the cut-off value increased the risk of NPDR (odds ratio [OR], 3.231; 95% confidence interval [CI], 1.574 to 6.632; P=0.001) and PDR (OR, 3.689; 95% CI, 1.306 to 10.424; P=0.014). CONCLUSION: FABP4 may be used as a serum biomarker for the diagnosis of DR.

MiR-195 promotes pancreatic ß-cell dedifferentiation by targeting Mfn2 and impairing Pi3k/Akt signaling in type 2 diabetes.

OBJECTIVE: The aim of this study was to research the role and underlying mechanism of miR-195 involved in pancreatic ß-cell dedifferentiation induced by hyperlipemia in type 2 diabetes mellitus. METHODS: High-fat-diet-induced obese C57BL/6J mice and palmitate-stimulated Min6 cells were used as the models of ß-cell dedifferentiation in vivo and in vitro, respectively. The expression of miR-195 and insulin secretion during ß-cell dedifferentiation were measured. Also, the influence of regulated miR-195 expression on ß-cell dedifferentiation was examined. Meanwhile, the IRS-1/2/Pi3k/Akt pathway and mitofusin-2 (Mfn2) expression were investigated during ß-cell dedifferentiation. RESULTS: MiR-195 was upregulated during lipotoxicity-induced ß-cell dedifferentiation in both in vivo and in vitro experiments, and miR-195 functionally contributed to lipotoxicity-induced ß-cell dedifferentiation. Furthermore, miR-195 inhibited IRS-1/2/Pi3k/Akt pathway activation, which accompanied ß-cell dedifferentiation. Mfn2, a target of miR-195, was found to be downregulated and was associated with increased mitochondrial production of reactive oxygen species during ß-cell dedifferentiation. Instructively, inhibition of miR-195, at least partially, reversed the downregulation of Mfn2, restored IRS-1/2/Pi3k/Akt pathway activation, and prevented ß-cell dedifferentiation. CONCLUSIONS: MiR-195 promoted ß-cell dedifferentiation through negatively regulating Mfn2 expression and inhibiting the IRS-1/2/Pi3k/Akt pathway, providing a promising treatment for type 2 diabetes mellitus.

Shift of Glucose Peak Time During Oral Glucose Tolerance Test is Associated with Changes in Insulin Secretion and Insulin Sensitivity After Therapy with Antidiabetic Drugs in Patients with Type 2 Diabetes.

INTRODUCTION: Delay in peak blood glucose during an oral glucose tolerance test (OGTT) predicts declining ß-cell function and poor ability to regulate glucose metabolism. Glucose peak time has not been used as a comparative indicator of the improvement in islet function after treatment with exenatide, insulin, or oral antidiabetic drugs (OADs). We evaluated the efficacy of three types of antidiabetic drugs on the basis of blood glucose peak time in patients with non-newly diagnosed type 2 diabetes. METHODS: The data from 100 patients with diabetes who completed two OGTTs within 6 months were collected. Thirty-seven of them with type 2 diabetes were treated with Humalog Mix25, 28 patients with OADs (metformin, acarbose, and gliclazide), and 35 patients with exenatide. RESULTS: Glycated hemoglobin improved in all three groups after treatment (P < 0.05). Subcutaneous adipose tissue (P < 0.01) and visceral adipose tissue (P < 0.0001) significantly decreased in the exenatide group. The insulinogenic index (IGI) (P = 0.01) and IGI × oral glucose insulin sensitivity (OGIS) (P = 0.01) improved in the exenatide group only. Homeostatic assessment of ß-cell function (HOMA-ß) and OGIS were greater in the exenatide and OAD groups than in the Humalog Mix25 group (all P < 0.05). A shift to an earlier peak was observed in 57.1%, 35.7%, and 27.0% of patients in the exenatide, OAD, and Humalog Mix25 groups, respectively (P = 0.029). OGIS (odds ratio [OR] 0.54, 95% confidence interval [CI] 0.33-0.89, P = 0.026) and IGI × OGIS (OR 1.72, 95% CI 0.44-6.68, P = 0.012) were independently related to shifts in glucose peak time. CONCLUSION: Exenatide, Humalog Mix25, and OADs improved glycemic metabolism. However, exenatide exhibited superior efficacy in shifting blood glucose peak time to an earlier point, while it improved insulin secretion and insulin sensitivity. Hence, the shift of glucose peak time may be considered an indicator for the evaluation of the effect of hypoglycemic drugs.

Effects of Exenatide and Humalog Mix25 on Fat Distribution, Insulin Sensitivity, and ß-Cell Function in Normal BMI Patients with Type 2 Diabetes and Visceral Adiposity.

In China, most normal BMI (body mass index of ≥18.5 to <25 kg/m2) adults with type 2 diabetes (T2DM) exhibit visceral adiposity. This study compared the effects of exenatide and humalog Mix25 on normal BMI patients with T2DM and visceral adiposity. A total of 95 patients were randomized to receive either exenatide or humalog Mix25 treatment for 24 weeks. Subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) were quantified by magnetic resonance imaging (MRI) and liver fat content (LFC) by liver proton magnetic resonance spectroscopy (1H MRS). Each patient's weight, waist circumference, BMI, blood glucose, insulin sensitivity, pancreatic ß-cell function, and fibroblast growth factor 21 (FGF-21) levels were measured. Data from 81 patients who completed the study (40 and 41 in the exenatide and humalog Mix25 groups, respectively) were analysed. The change in 2 h plasma blood glucose was greater in the exenatide group (P = 0.039). HOMA-IR and MBCI improved significantly after exenatide therapy (P < 0.01, P = 0.045). VAT and LFC decreased in both groups (P < 0.01 for all) but to a greater extent in the exenatide group, while SAT only decreased with exenatide therapy (P < 0.01). FGF-21 levels declined more in the exenatide group (P < 0.01), but were positively correlated with VAT in the entire cohort before (r = 0.244, P = 0.043) and after (r = 0.290, P = 0.016) the intervention. The effects of exenatide on glycaemic metabolism, insulin resistance, pancreatic ß-cell function, and fat deposition support its administration to normal BMI patients with T2DM and visceral adiposity.

Delay in glucose peak time during the oral glucose tolerance test as an indicator of insulin resistance and insulin secretion in type 2 diabetes patients.

AIMS/INTRODUCTION: Previous studies have shown that glucose peak time during the oral glucose tolerance test varies in type 2 diabetes patients; however, characteristics of this heterogeneity remain unclear. This research aimed to investigate the characteristics of delayed glucose peak time in type 2 diabetes. MATERIALS AND METHODS: A total of 178 participants who underwent the oral glucose tolerance test were divided into five groups according to glucose peak time. RESULTS: A total of 25 participants with normal glucose tolerance had a glucose peak at 30 min. Among participants with type 2 diabetes, 28 had a glucose peak at 60 min, 48 at 90 min, 45 at 120 min and 32 at 150 min. With the glucose peak time delayed, glycated hemoglobin, area under the glucose curve and homeostatic model assessment of insulin resistance increased gradually (P = 0.038, P < 0.0001, P < 0.0001, respectively), and oral glucose insulin sensitivity, homeostatic model assessment of ß-cell function, insulinogenic index, modified ß-cell function index and disposition indices decreased (P < 0.0001 for all). On multinominal logistic regression, insulinogenic index (odds ratio 0.73, 95% confidence interval 0.57-0.93, P = 0.01), modified ß-cell function index (odds ratio 0.67, 95% confidence interval 0.47-0.94, P = 0.023) and oral glucose insulin sensitivity (odds ratio 0.91, 95% confidence interval 0.87-0.96, P < 0.0001) were independently correlated with delayed glucose peak time. CONCLUSIONS: Delay in glucose peak time indicated an increase in blood glucose and a decrease in insulin sensitivity and secretion. Furthermore, insulinogenic index, modified ß-cell function index and oral glucose insulin sensitivity contributed to delayed glucose peak time.

PKM2 aggravates palmitate-induced insulin resistance in HepG2 cells via STAT3 pathway.

Studies have identified that PKM2 is related to the development of glucose intolerance and insulin resistance in rodents and humans. However, the underlying mechanism remains largely unknown. In the present study, we found that PKM2 expression was significantly elevated in insulin-resistant hepatic tissues and hepatocytes, implicating an association between PKM2 expression and hepatic insulin resistance (IR). In vitro study revealed that overexpression of PKM2 impaired the insulin signaling pathway by decreasing the phosphorylation of protein kinase B (Akt) and glycogen synthase kinase-3ß (GSK3ß). Furthermore, PKM2 overexpression enhanced the effects of PA on the lipid accumulation, the expression of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) and hepatic glucose uptake. Intriguingly, PA-induced insulin resistance was suppressed following by the ablation of PKM2 in HepG2 cells. We also found that STAT3 was significantly activated by PKM2 overexpression. Moreover, we identified that PKM2 could interact directly with STAT3. Taken together, these studies demonstrate that PKM2 may promote hepatic IR via STAT3 pathway and would provide a new insight into dissecting the molecular pathogenesis of hepatic insulin resistance.

KPNBeta1 promotes palmitate-induced insulin resistance via NF-kappaB signaling in hepatocytes

It has been intensively studied that inflammation contributes to the insulin resistance development in obesity-induced type 2 diabetes mellitus (T2DM). In this study, we assessed the effect of karyopherin Beta1 (KPNBeta1) in hepatic insulin resistance and the underlying mechanisms using high-fat diet (HFD) fed mice and palmitate (PA)-stimulated hepatocytes (HepG2). KPNBeta1 expression is increased in the HFD fed mice liver. PA upregulated KPNBeta1 expression in HepG2 cells in a time-dependent manner. PA also increased pro-inflammatory cytokines expression, including tumor necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), and interleukin 1Beta (IL-1Beta). KPNBeta1 knockdown reversed PA-induced pro-inflammatory cytokines expression and insulin-stimulated glucose uptake in HepG2 cells. In addition, KPNBeta1 knockdown reduced intracellular lipid accumulation. Mechanistically, KPNBeta1 transports nuclear factor kB (NF-kappaB) p65 from the cytoplasm to the nucleus to increase pro-inflammatory genes expression. In summary, KPNBeta1 acts as a positive regulator in the NF-kappaB pathway to enhance palmitate-induced inflammation response and insulin resistance in HepG2 cells

TRAF1 knockdown alleviates palmitate-induced insulin resistance in HepG2 cells through NF-κB pathway.

High-fat diet (HFD) and inflammation are key contributors to insulin resistance (IR) and Type 2 diabetes mellitus (T2DM). With HFD, plasma free fatty acids (FFAs) can activate the nuclear factor-κB (NF-κB) in target tissues, then initiate negative crosstalk between FFAs and insulin signaling. However, the molecular link between IR and inflammation remains to be identified. We here reported that tumor necrosis factor receptor-associated factor 1 (TRAF1), an adapter in signal transduction, was involved in the onset of IR in hepatocytes. TRAF1 was significantly up-regulated in insulin-resistant liver tissues and palmitate (PA)-treated HepG2 cells. In addition, we showed that depletion of TRAF1 led to inhibition of the activity of NF-κB. Given the fact that the activation of NF-κB played a facilitating role in IR, the phosphorylation of Akt and GSK3ß was also analyzed. We found that depletion of TRAF1 markedly reversed PA-induced attenuation of the phosphorylation of Akt and GSK3ß in the cells. The accumulation of lipid droplets in hepatocyte and expression of two key gluconeogenic enzymes, PEPCK and G6Pase, were also determined and found to display a similar tendency with the phosphorylation of Akt and GSK3ß. Glucose uptake assay indicated that knocking down TRAF1 blocked the effect of PA on the suppression of glucose uptake. These data implicated that TRAF1 knockdown might alleviate PA-induced IR in HepG2 cells through NF-κB pathway.

KPNß1 promotes palmitate-induced insulin resistance via NF-κB signaling in hepatocytes.

It has been intensively studied that inflammation contributes to the insulin resistance development in obesity-induced type 2 diabetes mellitus (T2DM). In this study, we assessed the effect of karyopherin ß1 (KPNß1) in hepatic insulin resistance and the underlying mechanisms using high-fat diet (HFD) fed mice and palmitate (PA)-stimulated hepatocytes (HepG2). KPNß1 expression is increased in the HFD fed mice liver. PA upregulated KPNß1 expression in HepG2 cells in a time-dependent manner. PA also increased pro-inflammatory cytokines expression, including tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), and interleukin 1ß (IL-1ß). KPNß1 knockdown reversed PA-induced pro-inflammatory cytokines expression and insulin-stimulated glucose uptake in HepG2 cells. In addition, KPNß1 knockdown reduced intracellular lipid accumulation. Mechanistically, KPNß1 transports nuclear factor kB (NF-κB) p65 from the cytoplasm to the nucleus to increase pro-inflammatory genes expression. In summary, KPNß1 acts as a positive regulator in the NF-κB pathway to enhance palmitate-induced inflammation response and insulin resistance in HepG2 cells.

The Role of PTP1B O-GlcNAcylation in Hepatic Insulin Resistance.

Protein tyrosine phosphatase 1B (PTP1B), which can directly dephosphorylate both the insulin receptor and insulin receptor substrate 1 (IRS-1), thereby terminating insulin signaling, reportedly plays an important role in insulin resistance. Accumulating evidence has demonstrated that O-GlcNAc modification regulates functions of several important components of insulin signal pathway. In this study, we identified that PTP1B is modified by O-GlcNAcylation at three O-GlcNAc sites (Ser104, Ser201, and Ser386). Palmitate acid (PA) impaired the insulin signaling, indicated by decreased phosphorylation of both serine/threonine-protein kinase B (Akt) and glycogen synthase kinase 3 beta (GSK3ß) following insulin administration, and upregulated PTP1B O-GlcNAcylation in HepG2 cells. Compared with the wild-type, intervention PTP1B O-GlcNAcylation by site-directed gene mutation inhibited PTP1B phosphatase activity, resulted in a higher level of phosphorylated Akt and GSK3ß, recovered insulin sensitivity, and improved lipid deposition in HepG2 cells. Taken together, our research showed that O-GlcNAcylation of PTP1B can influence insulin signal transduction by modulating its own phosphatase activity, which participates in the process of hepatic insulin resistance.

TAB3 involves in hepatic insulin resistance through activation of MAPK pathway.

Insulin resistance is often accompanied by chronic inflammatory responses. The mitogen-activated protein kinase (MAPK) pathway is rapidly activated in response to many inflammatory cytokines. But the functional role of MAPKs in palmitate-induced insulin resistance has yet to be clarified. In this study, we found that transforming growth factor ß-activated kinase binding protein-3 (TAB3) was up-regulated in insulin resistance. Considering the relationship between transforming growth factor ß-activated kinase (TAK1) and MAPK pathway, we assumed TAB3 involved in insulin resistance through activation of MAPK pathway. To certify this hypothesis, we knocked down TAB3 in palmitate treated HepG2 cells and detected subsequent biological responses. Importantly, TAB3 siRNA directly reversed insulin sensitivity by improving insulin signal transduction. Moreover, silencing of TAB3 could facilitate hepatic glucose uptake, reverse gluconeogenesis and improve ectopic fat accumulation. Meanwhile, we found that the positive effect of knocking down TAB3 was more significant when insulin resistance occurred. All these results indicate that TAB3 acts as a negative regulator in insulin resistance through activation of MAPK pathway.

PRDX1 is involved in palmitate induced insulin resistance via regulating the activity of p38MAPK in HepG2 cells.

Studies have identified that type 2 diabetes mellitus (T2DM) patients displayed higher levels of plasma peroxiredoxin1(PRDX1) than non-diabetics. However, the impact of PRDX1 on insulin resistance and the underlying mechanism remains totally unknown. Here, we investigated the influence of PRDX1 on hepatic insulin resistance. We showed that the protein and mRNA levels of PRDX1 were significantly elevated under insulin-resistant conditions. In addition, we showed that interference of PRDX1 ameliorated palmitate-induced insulin resistance in HepG2 cells, which was indicated by elevated phosphorylation of protein kinase B (AKT) and of glycogen synthase kinase-3 (GSK3ß). Furthermore, the expression of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), two key gluconeogenic enzymes, were down-regulated following PRDX1 depletion. Accordingly, glucose uptake was suppressed in PRDX1-interferred HepG2 cells. In addition, Over-expression of PRDX1 enhanced PA-induced insulin resistance in HepG2 cells. Moreover, we found that knocking down PRDX1 improves insulin sensitivity and decreased the activation of p38 mitogen-activated protein kinase (p38MAPK). Our results demonstrate that PRDX1 can induce hepatic insulin resistance by activating p38MAPK signaling and identifies potential targets for new treatments.

PCBP2 regulates hepatic insulin sensitivity via HIF-1α and STAT3 pathway in HepG2 cells.

Elevated free fatty acids (FFAs) are fundamental to the pathogenesis of hepatic insulin resistance. However, the molecular mechanisms of insulin resistance remain not completely understood. Transcriptional dysregulation, post-transcriptional modifications and protein degradation contribute to the pathogenesis of insulin resistance. Poly(C) binding proteins (PCBPs) are RNA-binding proteins that are involved in post-transcriptional control pathways. However, there are little studies about the roles of PCBPs in insulin resistance. PCBP2 is the member of the RNA-binding proteins and is thought to participate in regulating hypoxia inducible factor-1 (HIF-1α) and signal transducers and activators of transcription (STAT) pathway which are involved in regulating insulin signaling pathway. Here, we investigated the influence of PCBP2 on hepatic insulin resistance. We showed that the protein and mRNA levels of PCBP2 were down-regulated under insulin-resistant conditions. In addition, we showed that over-expression of PCBP2 ameliorates palmitate (PA)-induced insulin resistance, which was indicated by elevated phosphorylation of protein kinase B (AKT) and glycogen synthase kinase 3ß (GSK3ß). We also found that over-expression of PCBP2 inhibits HIF1α and STAT3 pathway. Furthermore, glucose uptake was found to display a similar tendency with the phosphorylation of Akt. The expressions of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), two key gluconeogenic enzymes, were down-regulated following Over-expression of PCBP2. Accordingly, PA-induced intracellular lipid accumulation was suppressed in over-expression of PCBP2 HepG2 cells. In addition, we found that over-expression of PCBP2 inhibits HIF1α and STAT3 pathway. Our results demonstrate that PCBP2 was involved in hepatic insulin sensitivity might via HIF-1α and STAT3 pathway in HepG2 cells.

TRAM1 protect HepG2 cells from palmitate induced insulin resistance through ER stress-JNK pathway.

Excess serum free fatty acids (FFAs) are fundamental to the pathogenesis of insulin resistance. Chronic endoplasmic reticulum (ER) stress is a major contributor to obesity-induced insulin resistance in the liver. With high-fat feeding (HFD), FFAs can activate chronic endoplasmic reticulum (ER) stress in target tissues, initiating negative crosstalk between FFAs and insulin signaling. However, the molecular link between insulin resistance and ER stress remains to be identified. We here reported that translocating chain-associated membrane protein 1 (TRAM1), an ER-resident membrane protein, was involved in the onset of insulin resistance in hepatocytes. TRAM1 was significantly up-regulated in insulin-resistant liver tissues and palmitate (PA)-treated HepG2 cells. In addition, we showed that depletion of TRAM1 led to hyperactivation of CHOP and GRP78, and the activation of downstream JNK pathway. Given the fact that the activation of ER stress played a facilitating role in insulin resistance, the phosphorylation of Akt and GSK-3ß was also analyzed. We found that depletion of TRAM1 markedly attenuated the phosphorylation of Akt and GSK-3ß in the cells. Moreover, application with JNK inhibitor SP600125 reversed the effect of TRAM1 interference on Akt phosphorylation. The accumulation of lipid droplets and expression of two key gluconeogenic enzymes, PEPCK and G6Pase, were also determined and found to display a similar tendency with the phosphorylation of Akt. Glucose uptake assay indicated that knocking down TRAM1 augmented PA-induced down-regulation of glucose uptake, and inhibition of JNK using SP600125 could block the effect of TRAM1 on glucose uptake. These data implicated that TRAM1 might protect HepG2 cells against PA-induced insulin resistance through alleviating ER stress.

Gender differences of lower extremity amputation risk in patients with diabetic foot: a meta-analysis.

In this meta-analysis, we aim to evaluate gender differences of lower extremity amputation risk in patients with diabetic foot. Systematic computerized searches of PubMed and Web of Knowledge were performed. The pooled odds ratio (OR) and 95% confidence interval (CI) for amputation risk were calculated. Twenty studies with 15 385 case (present amputation) and 438 760 control (absent amputation) patients were included in the meta-analysis. The pooled crude OR was 1.676 (95% CI 1.307-2.149; Z = 4.07, P = .000). In the retrospective study subgroup, the pooled OR was 1.708 (95% CI = 1.235-2.363; Z = 3.24, P = .001); in the prospective study subgroup, the pooled OR was 1.478 (95% CI = 1.189-1.838; Z = 3.51, P = .000). The pooled adjusted OR was 1.439 (95% CI = 1.238-1.671; Z = 4.76, P = .000). In retrospective study subgroup, the pooled OR was 1.440 (95% CI = 1.208-1.717; Z = 4.07, P = .000); in prospective study subgroup, the pooled OR was 1.478 (95% CI = 1.080-2.024; Z = 2.44, P = .015). No significant publication bias was found. Sensitivity analyses by omitting a heterogeneity study showed the results were robust. In conclusion, our meta-analysis indicates that men with diabetic foot have about one half increased amputation risk than women with diabetic foot. Men with diabetes should receive more complete follow-up and more adequate health education.

Stimulation of insulin secretion by large-dose oral arginine administration in healthy adults.

The effects of large-dose oral arginine administration on the secretion of insulin by islet ß-cells in healthy adults were determined. Eight non-obese healthy volunteers with normal glucose tolerance participated randomly in tests with four stages (with an interval of at least 3 days): the 300 ml purified water stage (PWS), the 75 g glucose stage (GSS), the 30 g arginine stage (ARS) and the 75 g glucose with 30 g arginine stage (GAS). Venous blood samples were collected to detect the concentrations of glucose and insulin at baseline (0) and at 15, 30, 45, 60 and 120 min after drug administration. The glucose and insulin levels were steady in the PWS. The remaining three stages had similarly shaped insulin concentration-time curves, which differed from that of the PWS. The peak concentration of blood insulin and the net incremental area under the curve of blood insulin in the GSS, ARS and GAS were significantly higher compared with those in the PWS (P<0.05). In the ARS, the glucose levels remained stable; however, the net incremental area under the curve for blood insulin in the ARS was much lower compared with that in the GSS or GAS (P<0.05). Large-dose oral arginine administration may slightly stimulate insulin secretion by islet ß-cells in healthy adults with normal glucose tolerance in a manner that is independent of glucose concentration.