Whole-Body and Hepatic Insulin Resistance in Obese Children

Background

Insulin resistance may be assessed as whole body or hepatic.

Objective

To study factors associated with both types of insulin resistance.

Methods

Cross-sectional study of 182 obese children. Somatometric measurements were registered, and the following three adiposity indexes were compared: BMI, waist-to-height ratio and visceral adiposity. Whole-body insulin resistance was evaluated using HOMA-IR, with 2.5 as the cut-off point. Hepatic insulin resistance was considered for IGFBP-1 level quartiles 1 to 3 (<6.67 ng/ml). We determined metabolite and hormone levels and performed a liver ultrasound.

Results

The majority, 73.1%, of obese children had whole-body insulin resistance and hepatic insulin resistance, while 7% did not have either type. HOMA-IR was negatively associated with IGFBP-1 and positively associated with BMI, triglycerides, leptin and mother''s BMI. Girls had increased HOMA-IR. IGFBP-1 was negatively associated with waist-to-height ratio, age, leptin, HOMA-IR and IGF-I. We did not find HOMA-IR or IGFBP-1 associated with fatty liver.

Conclusion

In school-aged children, BMI is the best metric to predict whole-body insulin resistance, and waist-to-height ratio is the best predictor of hepatic insulin resistance, indicating that central obesity is important for hepatic insulin resistance. The reciprocal negative association of IGFBP-1 and HOMA-IR may represent a strong interaction of the physiological processes of both whole-body and hepatic insulin resistance.     

Hepatic Circadian-Clock System Altered by Insulin Resistance,Diabetes and Insulin Sensitizer in Mice

Circadian rhythms are intrinsic rhythms that are coordinated with the rotation of the Earth and are also generated by a set of circadian-clock genes at the intracellular level. Growing evidence suggests a strong link between circadian rhythms and energy metabolism; however, the fundamental mechanisms remain unclear. In the present study, neonatal streptozotocin (STZ)-treated mice were used to model the molecular and physiological progress from insulin resistance to diabetes. Two-day-old male C57BL/6 mice received a single injection of STZ and were tested for non-obese, hyperglycemic and hyperinsulinemic conditions in the early stage, insulin resistance in the middle stage, and diabetes in the late stage. Gene expression levels of the hepatic circadian-clock system were examined by real-time quantitative PCR. Most of the components of the hepatic circadian-clock gene expression system, such as the mRNAs of Bmal1 (brain and muscle Arnt-like protein-1), Per2 (period 2) and Cry1 (cryptochrome 1), were elevated, and circadian patterns were retained in the early and middle stages of insulin-resistant conditions. The insulin sensitizer, rosiglitazone, returns the physiological and molecular changes associated with the diabetic phenotype to normal levels through peroxisome proliferator-activated receptor γ (PPARγ) rather than PPARα. Early and chronic treatment with rosiglitazone has been shown to be effective to counter the diabetic condition. Over time, this effect acts to attenuate the increased gene expression levels of the hepatic circadian-clock system and delay the severity of diabetic conditions. Together, these results support an essential role for the hepatic circadian-clock system in the coordinated regulation and/or response of metabolic pathways.     

Insulin Resistance Induces Posttranslational Hepatic Sortilin 1 Degradation in Mice

Insulin promotes hepatic apolipoprotein B100 (apoB100) degradation, whereas insulin resistance is a major cause of hepatic apoB100/triglyceride overproduction in type 2 diabetes. The cellular trafficking receptor sortilin 1 (Sort1) was recently identified to transport apoB100 to the lysosome for degradation in the liver and thus regulate plasma cholesterol and triglyceride levels. Genetic variation of SORT1 was strongly associated with cardiovascular disease risk in humans. The major goal of this study is to investigate the effect and molecular mechanism of insulin regulation of Sort1. Results showed that insulin induced Sort1 protein, but not mRNA, in AML12 cells. Treatment of PI3K or AKT inhibitors decreased Sort1 protein, whereas expression of constitutively active AKT induced Sort1 protein in AML12 cells. Consistently, hepatic Sort1 was down-regulated in diabetic mice, which was partially restored after the administration of the insulin sensitizer metformin. LC-MS/MS analysis further revealed that serine phosphorylation of Sort1 protein was required for insulin induction of Sort1 in a casein kinase 2-dependent manner and that inhibition of PI3K signaling or prevention of Sort1 phosphorylation accelerated proteasome-dependent Sort1 degradation. Administration of a PI3K inhibitor to mice decreased hepatic Sort1 protein and increased plasma cholesterol and triglyceride levels. Adenovirus-mediated overexpression of Sort1 in the liver prevented PI3K inhibitor-induced Sort1 down-regulation and decreased plasma triglyceride but had no effect on plasma cholesterol in mice. This study identified Sort1 as a novel target of insulin signaling and suggests that Sort1 may play a role in altered hepatic apoB100 metabolism in insulin-resistant conditions.     

Severe Insulin Resistance and Hypertriglyceridemia After Childhood Total Body Irradiation

ObjectiveTo characterize the metabolic phenotype of 2 cases of normal weight young women who developed type 2 diabetes (T2D), severe insulin resistance (insulin requirement >200 units/day), marked hypertriglyceridemia (>2000 mg/dL), and hepatic steatosis beginning 9 years after undergoing total body irradiation (TBI) and bone marrow transplantation for childhood cancer.MethodsFasting plasma glucose, insulin, free fatty acids (FFAs), leptin, adiponectin, resistin, TNFα, and IL-6 were measured in each case and in 8 healthy women; Case 1 was also assessed after initiating pioglitazone. Coding regions and splice junctions of PPARG, LMNA, and AKT2 were sequenced in Case 1 and of PPARG in Case 2 to evaluate for familial partial lipodystrophies. Genotyping of APOE was performed in Case 1 to rule out type III hyperlipoproteinemia.ResultsBoth cases had elevated plasma levels of insulin, leptin, resistin, and IL-6, high-normal to elevated TNFα, and low to low-normal adiponectin in keeping with post-receptor insulin resistance and adipose tissue inflammation. Case 1 experienced a biochemical response to pioglitazone. No causative mutations for partial lipodystrophies or type III hyperlipoproteinemia were identified.ConclusionThough metabolic derangements have previously been reported in association with TBI, few cases have described insulin resistance and hypertriglyceridemia as severe as that seen in our patients. We speculate that early childhood TBI may impede adipose tissue development leading to metabolic complications from an attenuated ability of adipose tissue to accommodate caloric excess, and propose that this extreme metabolic syndrome be evaluated for as a late complication of TBI. (Endocr Pract. 2013;19:51-58)     

异氟醚与七氟醚复合麻醉在小儿全身麻醉中的应用

目的:探讨异氟醚及七氟醚复合麻醉在患儿全身麻醉中的应用。方法:选取陕西省榆林市第一医院儿科收治的需行ASAⅠ或Ⅱ级行外科手术患儿86例,随机分为两组,其中对照组43例给予异氟醚全身麻醉诱导;实验组43例予以异氟醚及七氟醚复合全身麻醉诱导。观察比较两组麻醉诱导时间(T1)、苏醒时间(T2)、aldrete评分达9分或9分以上时间(T3)以及不良反应发生率。结果:实验组患儿麻醉诱导时间、苏醒时间、aldrete评分为9分或9分以上时间均明显少于对照组,差异具有统计学意义(P0.05);实验组患儿不良反应发生率明显低于对照组,差异具有统计学意义(P0.05)。结论:异氟醚及七氟醚复合麻醉能够缩短麻醉诱导时间、苏醒时间及术后恢复时间,具有较高的安全性,值得临床推广应用。     

High-Fat Diet Induces Hepatic Insulin Resistance and Impairment of Synaptic Plasticity

High-fat diet (HFD)-induced obesity is associated with insulin resistance, which may affect brain synaptic plasticity through impairment of insulin-sensitive processes underlying neuronal survival, learning, and memory. The experimental model consisted of 3 month-old C57BL/6J mice fed either a normal chow diet (control group) or a HFD (60% of calorie from fat; HFD group) for 12 weeks. This model was characterized as a function of time in terms of body weight, fasting blood glucose and insulin levels, HOMA-IR values, and plasma triglycerides. IRS-1/Akt pathway was assessed in primary hepatocytes and brain homogenates. The effect of HFD in brain was assessed by electrophysiology, input/output responses and long-term potentiation. HFD-fed mice exhibited a significant increase in body weight, higher fasting glucose- and insulin levels in plasma, lower glucose tolerance, and higher HOMA-IR values. In liver, HFD elicited (a) a significant decrease of insulin receptor substrate (IRS-1) phosphorylation on Tyr608 and increase of Ser307 phosphorylation, indicative of IRS-1 inactivation; (b) these changes were accompanied by inflammatory responses in terms of increases in the expression of NFκB and iNOS and activation of the MAP kinases p38 and JNK; (c) primary hepatocytes from mice fed a HFD showed decreased cellular oxygen consumption rates (indicative of mitochondrial functional impairment); this can be ascribed partly to a decreased expression of PGC1α and mitochondrial biogenesis. In brain, HFD feeding elicited (a) an inactivation of the IRS-1 and, consequentially, (b) a decreased expression and plasma membrane localization of the insulin-sensitive neuronal glucose transporters GLUT3/GLUT4; (c) a suppression of the ERK/CREB pathway, and (d) a substantial decrease in long-term potentiation in the CA1 region of hippocampus (indicative of impaired synaptic plasticity). It may be surmised that 12 weeks fed with HFD induce a systemic insulin resistance that impacts profoundly on brain activity, i.e., synaptic plasticity.     

The Role of PTEN in Chronic Growth Hormone-Induced Hepatic Insulin Resistance

Chronic growth hormone (GH) therapy has been shown to cause insulin resistance, but the mechanism remains unknown. PTEN, a tumor suppressor gene, is a major negative regulator of insulin signaling. In this study, we explored the effect of chronic GH on insulin signaling in the context of PTEN function. Balb/c healthy mice were given recombinant human or bovine GH intraperitoneally for 3 weeks. We found that phosphorylation of Akt was significantly decreased in chronic GH group and the expression of PTEN was significantly increased. We further examined this effect in the streptozotocin-induced Type I diabetic mouse model, in which endogenous insulin secretion was disrupted. Insulin/PI3K/Akt signaling was impaired. However, different from the observation in healthy mice, the expression of PTEN did not increase. Similarly, PTEN expression did not significantly increase in chronic GH-treated mice with hypoinsulinemia induced by prolonged fasting. We conducted in-vitro experiments in HepG2 cells to validate our in-vivo findings. Long-term exposure to GH caused similar resistance of insulin/PI3K/Akt signaling in HepG2 cells; and over-expression of PTEN enhanced the impairment of insulin signaling. On the other hand, disabling the PTEN gene by transfecting the mutant PTEN construct C124S or siPTEN, disrupted the chronic GH induced insulin resistance. Our data demonstrate that PTEN plays an important role in chronic-GH-induced insulin resistance. These findings may have implication in other pathological insulin resistance.     

Hepatic Insulin Resistance in Obese Non-Diabetic Subjects and in Type 2 Diabetic Patients

Objective: Obese non-diabetic patients are characterized by an extra-hepatic insulin resistance. Whether obese patients also have decreased hepatic insulin sensitivity remains controversial. Research Methods and Procedures: To estimate their hepatic insulin sensitivity, we measured the rate of exogenous insulin infusion required to maintain mildly elevated glycemia in obese patients with type 2 diabetes, obese non-diabetic patients, and lean control subjects during constant infusions of somatostatin and physiological low-glucagon replacement infusions. To account for differences in insulin concentrations among the three groups of subjects, an additional protocol was also performed in healthy lean subjects with higher insulin infusion rates and exogenous dextrose infusion. Results: The insulin infusion rate required to maintain glycemia at 8.5 mM was increased 4-fold in obese patients with type 2 diabetes and 1.5-fold in obese non-diabetic patients. The net endogenous glucose production (measured with 6,6-²H₂-glucose) and total glucose output (measured with 2-²H₁-glucose) were ∼30% lower in the patients than in the lean subjects. Net endogenous glucose production and total glucose output were both markedly increased in both groups of obese patients compared with lean control subjects during hyperinsulinemia. Discussion: Our data indicate that both obese non-diabetic and obese type 2 diabetic patients have a blunted suppressive action of insulin on glucose production, indicating hepatic and renal insulin resistance.     

Six-Transmembrane Epithelial Antigen of Prostate 3 Promotes Hepatic Insulin Resistance and Steatosis

Nonalcoholic fatty liver disease (NAFLD) is a clinicopathological syndrome characterized by excessive deposition of fatty acids in the liver. Further deterioration leads to nonalcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma, creating a heavy burden on human health and the social economy. Currently, there are no effective and specific drugs for the treatment of NAFLD. Therefore, it is important to further investigate the pathogenesis of NAFLD and explore effective therapeutic targets for the prevention and treatment of the disease. Six-transmembrane epithelial antigen of prostate 3 (STEAP3), a STEAP family protein, is a metalloreductase. Studies have shown that it can participate in the regulation of liver ischemia-reperfusion injury, hepatocellular carcinoma, myocardial hypertrophy, and other diseases. In this study, we found that the expression of STEAP3 is upregulated in NAFLD. Deletion of STEAP3 inhibits the development of NAFLD in vivo and in vitro, whereas its overexpression promotes palmitic acid/oleic acid stimulation-induced lipid deposition in hepatocytes. Mechanistically, it interacts with transforming growth factor beta-activated kinase 1 (TAK1) to regulate the progression of NAFLD by promoting TAK1 phosphorylation and activating the TAK1-c-Jun N-terminal kinase/p38 signaling pathway. Taken together, our results provide further insight into the involvement of STEAP3 in liver pathology.     

Acute Hepatic Insulin Resistance Contributes to Hyperglycemia in Rats Following Myocardial Infarction

Although hyperglycemia is common in patients with acute myocardial infarction (MI), the underlying mechanisms are largely unknown. Insulin signaling plays a key role in the regulation of glucose homeostasis. In this study, we test the hypothesis that rapid alteration of insulin signaling pathways could be a potential contributor to acute hyperglycemia after MI. Male rats were used to produce MI by ligation of the left anterior descending coronary artery. Plasma glucose and insulin levels were significantly higher in MI rats than those in controls. Insulin-stimulated tyrosine phosphorylation of insulin receptor substrate 1 (IRS1) was reduced significantly in the liver tissue of MI rats compared with controls, followed by decreased attachment of phosphatidylinositol 3-kinase (PI3K) p85 subunit with IRS1 and Akt phosphorylation. However, insulin-stimulated signaling was not altered significantly in skeletal muscle after MI. The relative mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) and G6Pase were slightly higher in the liver tissue of MI rats than those in controls. Rosiglitazone (ROSI) markedly restored hepatic insulin signaling, inhibited gluconeogenesis and reduced plasma glucose levels in MI rats. Insulin resistance develops rapidly in liver but not skeletal muscle after MI, which contributes to acute hyperglycemia. Therapy aimed at potentiating hepatic insulin signaling may be beneficial for MI-induced hyperglycemia.     

Unaltered Prion Pathogenesis in a Mouse Model of High-Fat Diet-Induced Insulin Resistance

Epidemiological, clinical, and experimental animal studies suggest a strong correlation between insulin resistance and Alzheimer’s disease. In fact, type-2 diabetes is considered an important risk factor of developing Alzheimer’s disease. In addition, impaired insulin signaling in the Alzheimer’s disease brain may promote Aβ production, impair Aβ clearance and induce tau hyperphosphorylation, thereby leading to deterioration of the disease. The pathological prion protein, PrP^Sc, deposits in the form of extracellular aggregates and leads to dementia, raising the question as to whether prion pathogenesis may also be affected by insulin resistance. We therefore established high-fat diet-induced insulin resistance in tga20 mice, which overexpress the prion protein. We then inoculated the insulin-resistant mice with prions. We found that insulin resistance in tga20 mice did not affect prion disease progression, PrP^Sc deposition, astrogliosis or microglial activation, and had no effect on survival. Our study demonstrates that in a mouse model, insulin resistance does not significantly contribute to prion pathogenesis.     

Blocking Nuclear Factor-Kappa B Protects against Diet-Induced Hepatic Steatosis and Insulin Resistance in Mice

Inflammation critically contributes to the development of various metabolic diseases. However, the effects of inhibiting inflammatory signaling on hepatic steatosis and insulin resistance, as well as the underlying mechanisms remain obscure. In the current study, male C57BL/6J mice were fed a chow diet or high-fat diet (HFD) for 8 weeks. HFD-fed mice were respectively treated with p65 siRNA, non-silence control siRNA or vehicle every 4^th day for the last 4 weeks. Vehicle-treated (HF) and non-silence siRNA-treated (HFNS) mice displayed overt inflammation, hepatic steatosis and insulin resistance compared with chow-diet-fed (NC) mice. Upon treatment with NF-κB p65 siRNA, HFD-fed (HFPS) mice were protected from hepatic steatosis and insulin resistance. Furthermore, Atg7 and Beclin1 expressions and p-AMPK were increased while p-mTOR was decreased in livers of HFPS mice in relative to HF and HFNS mice. These results suggest a crosslink between NF-κB signaling pathway and liver AMPK/mTOR/autophagy axis in the context of hepatic steatosis and insulin resistance.     

A Proteomic Investigation of Hepatic Resistance to Ascaris in a Murine Model

The helminth Ascaris causes ascariasis in both humans and pigs. Humans, especially children, experience significant morbidity including respiratory complications, growth deficits and intestinal obstruction. Given that 800 million people worldwide are infected by Ascaris, this represents a significant global public health concern. The severity of the symptoms and associated morbidity are related to the parasite burden and not all hosts are infected equally. While the pathology of the disease has been extensively examined, our understanding of the molecular mechanisms underlying resistance and susceptibility to this nematode infection is poor. In order to investigate host differences associated with heavy and light parasite burden, an experimental murine model was developed utilising Ascaris-susceptible and -resistant mice strains, C57BL/6J and CBA/Ca, respectively, which experience differential burdens of migratory Ascaris larvae in the host lungs. Previous studies identified the liver as the site where this difference in susceptibility occurs. Using a label free quantitative proteomic approach, we analysed the hepatic proteomes of day four post infection C57BL/6J and CBA/Ca mice with and without Ascaris infection to identify proteins changes potentially linked to both resistance and susceptibility amongst the two strains, respectively. Over 3000 proteins were identified in total and clear intrinsic differences were elucidated between the two strains. These included a higher abundance of mitochondrial proteins, particularly those associated with the oxidative phosphorylation pathway and reactive oxygen species (ROS) production in the relatively resistant CBA/Ca mice. We hypothesise that the increased ROS levels associated with higher levels of mitochondrial activity results in a highly oxidative cellular environment that has a dramatic effect on the nematode’s ability to successfully sustain a parasitic association with its resistant host. Under infection, both strains had increased abundances in proteins associated with the oxidative phosphorylation pathway, as well as the tricarboxylic acid cycle, with respect to their controls, indicating a general stress response to Ascaris infection. Despite the early stage of infection, some immune-associated proteins were identified to be differentially abundant, providing a novel insight into the host response to Ascaris. In general, the susceptible C57BL/6J mice displayed higher abundances in immune-associated proteins, most likely signifying a more active nematode cohort with respect to their CBA/Ca counterparts. The complement component C8a and S100 proteins, S100a8 and S100a9, were highly differentially abundant in both infected strains, signifying a potential innate immune response and the importance of the complement pathway in defence against macroparasite infection. In addition, the signatures of an early adaptive immune response were observed through the presence of proteins, such as plastin-2 and dipeptidyl peptidase 1. A marked decrease in proteins associated with translation was also observed in both C57BL/6J and CBA/Ca mice under infection, indicative of either a general response to Ascaris or a modulatory effect by the nematode itself. Our research provides novel insights into the in vivo host-Ascaris relationship on the molecular level and provides new research perspectives in the development of Ascaris control and treatment strategies.     

Cannabinoid CB2 Receptor Potentiates Obesity-Associated Inflammation,Insulin Resistance and Hepatic Steatosis

Background

Obesity-associated inflammation is of critical importance in the development of insulin resistance and non-alcoholic fatty liver disease. Since the cannabinoid receptor CB2 regulates innate immunity, the aim of the present study was to investigate its role in obesity-induced inflammation, insulin resistance and fatty liver.

Methodology

Murine obesity models included genetically leptin-deficient ob/ob mice and wild type (WT) mice fed a high fat diet (HFD), that were compared to their lean counterparts. Animals were treated with pharmacological modulators of CB2 receptors. Experiments were also performed in mice knock-out for CB2 receptors (Cnr2 −/−).

Principal Findings

In both HFD-fed WT mice and ob/ob mice, Cnr2 expression underwent a marked induction in the stromal vascular fraction of epididymal adipose tissue that correlated with increased fat inflammation. Treatment with the CB2 agonist JWH-133 potentiated adipose tissue inflammation in HFD-fed WT mice. Moreover, cultured fat pads isolated from ob/ob mice displayed increased Tnf and Ccl2 expression upon exposure to JWH-133. In keeping, genetic or pharmacological inactivation of CB2 receptors decreased adipose tissue macrophage infiltration associated with obesity, and reduced inductions of Tnf and Ccl2 expressions. In the liver of obese mice, Cnr2 mRNA was only weakly induced, and CB2 receptors moderately contributed to liver inflammation. HFD-induced insulin resistance increased in response to JWH-133 and reduced in Cnr2 −/− mice. Finally, HFD-induced hepatic steatosis was enhanced in WT mice treated with JWH-133 and blunted in Cnr2 −/− mice.

Conclusion/Significance

These data unravel a previously unrecognized contribution of CB2 receptors to obesity-associated inflammation, insulin resistance and non-alcoholic fatty liver disease, and suggest that CB2 receptor antagonists may open a new therapeutic approach for the management of obesity-associated metabolic disorders.     

Metformin and Improvement of the Hepatic Insulin Resistance Index Independent of Anthropometric Changes

ObjectiveTo determine the change in the hepatic insulin resistance index (HIRI) after metformin treatment.MethodsIn this retrospective cohort study, Mexican mestizo patients with a body mass index (BMI) of 25 kg/m² or greater were evaluated. Participants were classified into 2 groups: patients who received metformin and patients who did not. Both groups were followed up for a median of 6 months (range. 4-10 months). The HIRI was calculated at baseline and at follow-up in both groups. We evaluated the independent effect of metformin on HIRI after adjustment for the difference in basal and final values (DELTA) of BMI, waist circumference, glucose, and insulin.ResultsA total of 71 patients were enrolled (51 [72%] female). Forty-one patients received metformin and 30 patients did not. Mean age was 36.3 ± 12.2 years and mean BMI was 42.2 ± 10.7 kg/m². After metformin treatment. HIRI significantly decreased from 38 ± 10.7 to 34.7 ± 9.5 (P = .03). In contrast. the control group had a nonsignificant increase in HIRI (37.6 ± 11.7 to 40.0 ± 14.0, P = .22). Weight significantly decreased in both groups (group 1: 114.6 ± 33.8 kg to 107.6 ± 28.9 kg, P < .01; group 2: 104.8 ± 28.5 kg to 98.9 ± 26.0 kg, P < .01). After BMI adjustment, the total metformin dosage correlated negatively with HIRI (r = –0.36, P = .03). Using a linear regression model (F = 6.0, r² = 0.37, P = .002) adjusted for DELTA BMI and DELTA waist circumference. the administration of metformin resulted in independent improvement in the HIRI level (standardized β = –0.29, t = –2.0, P = .04).ConclusionsMetformin improves HIRI independently of anthropometric changes. In persons with elevated HIRI levels, metformin may be considered among the treatment options. (Endocr Pract. 2012;18:8-16)