Leptin down-regulates insulin action through phosphorylation of serine-318 in insulin receptor substrate 1

Molecular crosstalk between insulin-like growth factors and follicle-stimulating hormone in the regulation of granulosa cell function

Background

The last phase of folliculogenesis is driven by follicle-stimulating hormone (FSH) and locally produced insulin-like growth factors (IGFs), both essential for forming preovulatory follicles.

Methods

This review discusses the molecular crosstalk of the FSH and IGF signaling pathways in regulating follicular granulosa cells (GCs) during the antral-to-preovulatory phase.

Main findings

IGFs were considered co-gonadotropins since they amplify FSH actions in GCs. However, this view is not compatible with data showing that FSH requires IGFs to stimulate GCs, that FSH renders GCs sensitive to IGFs, and that FSH signaling interacts with factors downstream of AKT to stimulate GCs. New evidence suggests that FSH and IGF signaling pathways intersect at several levels to regulate gene expression and GC function.

Conclusion

FSH and locally produced IGFs form a positive feedback loop essential for preovulatory follicle formation in all species. Understanding the mechanisms by which FSH and IGFs interact to control GC function will help design new interventions to optimize follicle maturation, perfect treatment of ovulatory defects, improve in vitro fertilization, and develop new contraceptive approaches.

Excessive Pregestational Weight and Maternal Obstetric Complications: The Role of Adipokines

There is a high frequency of overweight and obesity in women of reproductive age. Women who start pregnancy with overweight or obesity have an increased risk of developing maternal obstetric complications such as gestational hypertension, pre-eclampsia, gestational diabetes mellitus, postpartum hemorrhage, and requiring C-section to resolve the pregnancy with a higher risk of C-section surgical site infection. Excessive weight in pregnancy is characterized by dysregulation of adipokines, the functions of which partly explain the predisposition of pregnant women with overweight or obesity to these maternal obstetric complications. This review compiles, organizes, and analyzes the most recent studies on adipokines in pregnant women with excess weight and the potential pathophysiological mechanisms favoring the development of maternal pregnancy complications.

Assessment of common risk factors of diabetes and chronic kidney disease: a Mendelian randomization study

Background

The increasing prevalence of diabetes and its significant impact on mortality and morbidity rates worldwide has led to a growing interest in understanding its common risk factors, particularly in relation to chronic kidney disease (CKD). This research article aims to investigate the shared risk factors between type 1 diabetes (T1D), type 2 diabetes (T2D), and CKD using a Mendelian randomization (MR) design.

Methods

The study utilized genome-wide association study (GWAS) datasets for T1D, T2D, and CKD from the FinnGen research project. GWAS summary statistics datasets for 118 exposure traits were obtained from the IEU OpenGWAS database. MR analyses were conducted to examine the causal relationships between exposure traits and each of the three outcomes. Multiple methods, including inverse-variance weighted, weighted median, and MR-Egger, were employed for the MR studies.

Results

Phenome-wide MR analyses revealed that eosinophil percentage exhibited a significant and suggestive causal association with T1D and CKD, respectively, suggesting its potential as a shared risk factor for T1D and CKD. For T2D, 34 traits demonstrated significant associations. Among these 34 traits, 14 were also significantly associated with CKD, indicating the presence of common risk factors between T2D and CKD, primarily related to obesity, height, blood lipids and sex hormone binding globulin, blood pressure, and walking pace.

Conclusion

This research has uncovered the eosinophil percentage as a potential common risk factor for both T1D and CKD, while also identifying several traits, such as obesity and blood lipids, as shared risk factors for T2D and CKD. This study contributes to the understanding of the common risk factors between diabetes and CKD, emphasizing the need for targeted interventions to reduce the risk of these diseases.

New Insights into Adipokines in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is the most common metabolic disorder of pregnancy and has considerable short- and long-term consequences for the health of both the mother and the newborn. Within its pathophysiology, genetic, nutritional, epigenetic, immunological, and hormonal components have been described. Within the last two items, it is known that different hormones and cytokines secreted by adipose tissue, known collectively as adipokines, are involved in the metabolic alterations underlying GDM. Although the maternal circulating profile of adipokines in GDM has been extensively studied, and there are excellent reviews on the subject, it is in recent years that more progress has been made in the study of their expression in visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), placenta, and their concentrations in the umbilical circulation. Thus, this review compiles and organizes the most recent findings on the maternal and umbilical circulating profile and the levels of expression of adipokines in VAT, SAT, and placenta in GDM.

Insulin's actions on vascular tissues: Physiological effects and pathophysiological contributions to vascular complications of diabetes

Background

Insulin has been demonstrated to exert direct and indirect effects on vascular tissues. Its actions in vascular cells are mediated by two major pathways: the insulin receptor substrate 1/2-phosphoinositide-3 kinase/Akt (IRS1/2/PI3K/Akt) pathway and the Src/mitogen-activated protein kinase (MAPK) pathway, both of which contribute to the expression and distribution of metabolites, hormones, and cytokines.

Scope of review

In this review, we summarize the current understanding of insulin's physiological and pathophysiological actions and associated signaling pathways in vascular cells, mainly in endothelial cells (EC) and vascular smooth muscle cells (VSMC), and how these processes lead to selective insulin resistance. We also describe insulin's potential new signaling and biological effects derived from animal studies and cultured capillary and arterial EC, VSMC, and pericytes. We will not provide a detailed discussion of insulin's effects on the myocardium, insulin's structure, or its signaling pathways' various steps, since other articles in this issue discuss these areas in depth.

Major conclusions

Insulin mediates many important functions on vascular cells via its receptors and signaling cascades. Its direct actions on EC and VSMC are important for transporting and communicating nutrients, cytokines, hormones, and other signaling molecules. These vascular actions are also important for regulating systemic fuel metabolism and energetics. Inhibiting or enhancing these pathways leads to selective insulin resistance, exacerbating the development of endothelial dysfunction, atherosclerosis, restenosis, poor wound healing, and even myocardial dysfunction. Targeted therapies to improve selective insulin resistance in EC and VSMC are thus needed to specifically mitigate these pathological processes.

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Insulin's actions in vascular cells have a significant influence on systemic metabolism.

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Insulin exerts its vascular effects through its receptors and signaling cascades.

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Inhibition or enhancement of different insulin signaling leads to selective insulin resistance.

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Loss of insulin's actions causes endothelial dysfunction and vascular complications in diabetes.

Pancreatic fat cells of humans with type 2 diabetes display reduced adipogenic and lipolytic activity

Obesity, especially visceral fat accumulation, increases the risk of type 2 diabetes (T2D). The purpose of this study was to investigate the impact of T2D on the pancreatic fat depot. Pancreatic fat pads from 17 partial pancreatectomized patients (PPP) were collected, pancreatic preadipocytes isolated, and in vitro differentiated. Patients were grouped using HbA1c into normal glucose tolerant (NGT), prediabetic (PD), and T2D. Transcriptome profiles of preadipocytes and adipocytes were assessed by RNAseq. Insulin sensitivity was estimated by quantifying AKT phosphorylation on Western blots. Lipogenic capacity was assessed with oil red O staining, lipolytic activity via fatty acid release. Secreted factors were measured using ELISA. Comparative transcriptome analysis of preadipocytes and adipocytes indicates defective upregulation of genes governing adipogenesis (NR1H3), lipogenesis (FASN, SCD, ELOVL6, and FADS1), and lipolysis (LIPE) during differentiation of cells from T2D-PPP. In addition, the ratio of leptin/adiponectin mRNA was higher in T2D than in NGT-PPP. Preadipocytes and adipocytes of NGT-PPP were more insulin sensitive than T2D-PPP cells in regard to AKT phosphorylation. Triglyceride accumulation was similar in NGT and T2D adipocytes. Despite a high expression of the receptors NPR1 and NPR2 in NGT and T2D adipocytes, lipolysis was stimulated by ANP 1.74-fold in NGT cells only. This stimulation was further increased by the PDE5 inhibitor dipyridamole (3.09-fold). Dipyridamole and forskolin increased lipolysis receptor independently 1.88-fold and 1.48-fold, respectively, solely in NGT cells. In conclusion, the metabolic status persistently affects differentiation and lipolysis of pancreatic adipocytes. These alterations could aggravate the development of T2D.

Endothelial Dysfunction in Diabetes

Diabetes is a worldwide health issue closely associated with cardiovascular events. Given the pandemic of obesity, the identification of the basic underpinnings of vascular disease is strongly needed. Emerging evidence has suggested that endothelial dysfunction is a critical step in the progression of atherosclerosis. However, how diabetes affects the endothelium is poorly understood. Experimental and clinical studies have illuminated the tight link between insulin resistance and endothelial dysfunction. In addition, macrophage polarization from M2 towards M1 contributes to the process of endothelial damage. The possibility that novel classes of anti-hyperglycemic agents exert beneficial effects on the endothelial function and macrophage polarization has been raised. In this review, we discuss the current status of knowledge regarding the pathological significance of insulin signaling in endothelium. Finally, we summarize recent therapeutic strategies against endothelial dysfunction with an emphasis on macrophage polarity.

Helicobacter pylori and non-alcoholic fatty liver disease: A new enigma?

BACKGROUND AND AIM

The relationship between Helicobacter pylori (H. pylori) and nonalcoholic fatty liver disease (NAFLD) is a matter of debate. We achieved this prospective work to study whether H. pylori infection is a risk factor for NAFLD.

METHODS

A cohort multicenter pilot study of 369 adults without NAFLD at baseline was followed up for 2 years. Serum leptin, insulin, tumor necrosis factor-α, adiponectin, and interleukin-6 were measured using an enzyme-linked immunosorbent assay (ELISA). Homeostasis model assessment of insulin resistance (HOMA-IR) and leptin/adiponectin ratio (LAR) were calculated. Fecal H. pylori antigen was measured by ELISA. A total of 127 participants with H. pylori positive were treated and then followed up for 3 months.

RESULTS

Helicobacter pylori-positive patients (46.3%) were associated with an increase in IR, proinflammatory cytokines, C-reactive protein (CRP), LAR, NAFLD-liver fat score (NAFLD-LFS), and hepatic steatosis index (HSI) (all P < 0.01). Multivariate analysis of NAFLD according to HSI and NAFLD-LFS reported that presence of H. pylori, LAR, CRP, IL-6, smoking, and age (all P < 0.01) were independent risk factors for the presence of NAFLD. Multiple models adjusted for potential mediators or confounders such as metabolic, inflammatory, and biochemical factors were constructed. After therapy of H. pylori infection, there was a significant reduction in lipogenic profile, IR, leptin, LAR, CRP, proinflammatory cytokines, HSI, and NAFLD-LFS, as well as, increasing HDL.

CONCLUSION

Helicobacter pylori infection was related to an increased risk of NAFLD development, through increased markers of IR, inflammatory mediators, and lipid metabolism. Moreover, its eradication can recover these NAFLD risk factors.

Metabolic Syndrome in Long-Term Survivors of Hematopoietic Stem-Cell Transplantation

Since its introduction more than 50 years ago, hematopoietic stem-cell transplantation (HSCT) has transformed from an inescapably fatal procedure to one where cure from malignant and other nonmalignant hematologic diseases is becoming increasingly common. Nevertheless, longevity is not entirely restored. New causes of mortality have emerged; of particular importance is that of increased cardiovascular disease (CVD), related to metabolic syndrome and its components. Controversy exists over whether the metabolic abnormalities induced are a direct effect of HSCT itself or a consequence of other therapies involved. Analysis of the mechanisms that promote the changes in metabolic components will give insight into future HSCT therapy as well as CVD pathogenesis and prevention.

The Possible Role of Helicobacter pylori Infection in Non-alcoholic Fatty Liver Disease

Helicobacter pylori (H. pylori) which colonizes the stomach can cause a wide array of gastric disorders, including chronic gastritis, peptic ulcer, and gastric cancer. Recently, accumulating evidence has implicated H. pylori infection in extragastrointestinal diseases such as cardiovascular diseases, neurological disorders, and metabolic diseases. At the same time, many scholars have noted the relationship between H. pylori infection and non-alcoholic fatty liver disease (NAFLD). Despite the positive association between H. pylori and NAFLD reported in some researches, there are opposite perspectives denying their relationship. Due to high prevalence, unclear etiology and difficult treatment of NAFLD, confirming the pathogenicity of H. pylori infection in NAFLD will undoubtedly provide insights for novel treatment strategies for NAFLD. This paper will review the relationship between H. pylori infection and NAFLD and the possible pathogenic mechanisms.

Endoplasmic reticulum stress mediates JNK-dependent IRS-1 serine phosphorylation and results in Tau hyperphosphorylation in amyloid β oligomer-treated PC12 cells and primary neurons

AIMS

Endoplasmic reticulum stress (ERS) and insulin signaling impairment are commonly observed in Alzheimer's disease (AD), but the association between these two factors in AD has not been carefully studied. In peripheral insulin signaling impairment, ERS interferes with insulin signaling through c-Jun. N-terminal kinase (JNK)-dependent insulin receptor substance-1 (IRS-1) serine phosphorylation. We conducted this study to determine whether a similar mechanism contributes to insulin signaling impairment in AD pathogenesis.

METHODS

Changes in the levels of ERS markers, JNK activation, the insulin signaling status and Tau hyperphosphorylation were examined in amyloid β1-42 (Aβ1-42) oligomer-treated PC12 cells and primary neurons by western blotting and real-time fluorescence quantitative PCR. Inhibitors of ERS and JNK were utilized to confirm their association.

RESULTS

Our results demonstrated that Aβ1-42 oligomers significantly induced ERS and JNK activation. In addition, in response to Aβ1-42 oligomers, IRS-1 phosphorylation at serines 307, 318 and 612 was increased. Further, an increase in Tau hyperphosphorylation at threonine 181 was observed following Aβ1-42 oligomer treatment. Moreover, inhibition of ERS or JNK could partially reverse the changes induced by the Aβ1-42 oligomers.

CONCLUSIONS

These findings suggest that ERS may contribute to insulin signaling impairment in AD through JNK-dependent IRS-1 serine phosphorylation. The ERS/JNK/IRS-1 pathway may be involved in Aβ1-42 oligomer-induced Tau hyperphosphorylation in AD.

Central obesity, type 2 diabetes and insulin: exploring a pathway full of thorns

The prevalence of type 2 diabetes (T2D) is rapidly increasing. This is strongly related to the contemporary lifestyle changes that have resulted in increased rates of overweight individuals and obesity. Central (intra-abdominal) obesity is observed in the majority of patients with T2D. It is associated with insulin resistance, mainly at the level of skeletal muscle, adipose tissue and liver. The discovery of macrophage infiltration in the abdominal adipose tissue and the unbalanced production of adipocyte cytokines (adipokines) was an essential step towards novel research perspectives for a better understanding of the molecular mechanisms governing the development of insulin resistance. Furthermore, in an obese state, the increased cellular uptake of non-esterified fatty acids is exacerbated without any subsequent β-oxidation. This in turn contributes to the accumulation of intermediate lipid metabolites that cause defects in the insulin signaling pathway. This paper examines the possible cellular mechanisms that connect central obesity with defects in the insulin pathway. It discusses the discrepancies observed from studies organized in cell cultures, animal models and humans. Finally, it emphasizes the need for therapeutic strategies in order to achieve weight reduction in overweight and obese patients with T2D.

Gestational protein restriction impairs insulin-regulated glucose transport mechanisms in gastrocnemius muscles of adult male offspring

Type II diabetes originates from various genetic and environmental factors. Recent studies showed that an adverse uterine environment such as that caused by a gestational low-protein (LP) diet can cause insulin resistance in adult offspring. The mechanism of insulin resistance induced by gestational protein restriction is not clearly understood. Our aim was to investigate the role of insulin signaling molecules in gastrocnemius muscles of gestational LP diet-exposed male offspring to understand their role in LP-induced insulin resistance. Pregnant Wistar rats were fed a control (20% protein) or isocaloric LP (6%) diet from gestational day 4 until delivery and a normal diet after weaning. Only male offspring were used in this study. Glucose and insulin responses were assessed after a glucose tolerance test. mRNA and protein levels of molecules involved in insulin signaling were assessed at 4 months in gastrocnemius muscles. Muscles were incubated ex vivo with insulin to evaluate insulin-induced phosphorylation of insulin receptor (IR), Insulin receptor substrate-1, Akt, and AS160. LP diet-fed rats gained less weight than controls during pregnancy. Male pups from LP diet-fed mothers were smaller but exhibited catch-up growth. Plasma glucose and insulin levels were elevated in LP offspring when subjected to a glucose tolerance test; however, fasting levels were comparable. LP offspring showed increased expression of IR and AS160 in gastrocnemius muscles. Ex vivo treatment of muscles with insulin showed increased phosphorylation of IR (Tyr972) in controls, but LP rats showed higher basal phosphorylation. Phosphorylation of Insulin receptor substrate-1 (Tyr608, Tyr895, Ser307, and Ser318) and AS160 (Thr642) were defective in LP offspring. Further, glucose transporter type 4 translocation in LP offspring was also impaired. A gestational LP diet leads to insulin resistance in adult offspring by a mechanism involving inefficient insulin-induced IR, Insulin receptor substrate-1, and AS160 phosphorylation and impaired glucose transporter type 4 translocation.

The effect of Helicobacter pylori eradication on insulin resistance and HbA1c level in people with normal glucose levels: a prospective study

BACKGROUND AND AIM

Helicobacter pylori (H. pylori) infection is reported to be associated with various extragastrointestinal conditions such as insulin resistance, diabetes mellitus and metabolic syndrome. These conditions are attributed to systemic inflammation, leptin or ghrelin changes due to H. pylori infection. Therefore, increasing trends in the management of H. pylori infection are ordered to maintain glycemic control. In this study, we evaluated the effect of H. pylori eradication on insulin resistance in patients with normal blood glucose concentrations.

METHOD

A total of 370 patients with successful eradication were included in the study. Patients with H. pylori were given triple eradication treatment. All patients with H. pylori infection were tested for fasting glucose, fasting insulin, glicated hemoglobin (HbA1c) at baseline and 6 months after eradication treatment. Also, insulin resistance was calculated using the homeostatic model assessment of insulin resistance (HOMA-IR). Body mass index was also determined as a metabolic syndrome criteria effecting insulin resistance.

RESULTS

There were significant differences in fasting glucose, fasting insulin, HbA1c, and HOMA-IR values between before treatment and after treatment(P <0.04, <0.01, <0.01, <0.01). The favorable effect of eradication was more significant in patients with BMI≥25 mg/m(2)(P<0.05).

CONCLUSION

Eradication treatment has beneficial effects on insulin resistance in patients with normal glucose concentrations.

Insulin and metabolic stress stimulate multisite serine/threonine phosphorylation of insulin receptor substrate 1 and inhibit tyrosine phosphorylation

IRS1 and IRS2 are key substrates of the insulin receptor tyrosine kinase. Mass spectrometry reveals more than 50 phosphorylated IRS1 serine and threonine residues (Ser(P)/Thr(P) residues) in IRS1 from insulin-stimulated cells or human tissues. We investigated a subset of IRS1 Ser(P)/Thr(P) residues using a newly developed panel of 25 phospho-specific monoclonal antibodies (αpS/TmAb(Irs1)). CHO cells overexpressing the human insulin receptor and rat IRS1 were stimulated with insulin in the absence or presence of inhibitors of the PI3K → Akt → mechanistic target of rapamycin (mTOR) → S6 kinase or MEK pathways. Nearly all IRS1 Ser(P)/Thr(P) residues were stimulated by insulin and significantly suppressed by PI3K inhibition; fewer were suppressed by Akt or mTOR inhibition, and none were suppressed by MEK inhibition. Insulin-stimulated Irs1 tyrosine phosphorylation (Tyr(P)(Irs1)) was enhanced by inhibition of the PI3K → Akt → mTOR pathway and correlated with decreased Ser(P)-302(Irs1), Ser(P)-307(Irs1), Ser(P)-318(Irs1), Ser(P)-325(Irs1), and Ser(P)-346(Irs1). Metabolic stress modeled by anisomycin, thapsigargin, or tunicamycin increased many of the same Ser(P)/Thr(P) residues as insulin, some of which (Ser(P)-302(Irs1), Ser(P)-307(Irs1), and four others) correlated significantly with impaired insulin-stimulated Tyr(P)(Irs1). Thus, IRS1 Ser(P)/Thr(P) is an integrated response to insulin stimulation and metabolic stress, which associates with reduced Tyr(P)(Irs1) in CHO(IR)/IRS1 cells.

Helicobacter pylori infection and diabetes: Is it a myth or fact?

Helicobacter pylori (H. pylori) is one of the most common human bacterial pathogens, and infection causes a wide array of gastric disorders, including simple gastritis, peptic ulcers and gastric malignancies. Gastrointestinal inflammation caused by H. pylori can influence the absorption of glucose and lipids, which are also abnormal in diabetes mellitus. Type 2 diabetes mellitus (T2DM), formerly known as non-insulin-dependent diabetes mellitus or adult-onset diabetes, is a metabolic disorder that is characterized by high levels of blood glucose resulting from insulin resistance and relative insulin deficiency. It is an emerging pandemic and is rapidly becoming a serious threat to public health. Emerging data now indicate a strong relationship between H. pylori infection and the incidence of T2DM. The mechanisms underlying the pathogenesis of diabetes are complex, involving insulin resistance, chronic inflammation, insulin secretion deficiency as a result of pancreas β-cell dysfunction, glucotoxicity, and lipotoxicity. H. pylori infection is known to be involved in the pathogenesis of insulin resistance, and the growing awareness of its role in diabetes is important for the early detection of glucose dysregulation and prevention of T2DM in high-risk communities. This review probes the possible relationship between H. pylori and diabetes according to epidemiological surveys and discusses putative mechanisms underlying this correlation.

The mechanisms linking adiposopathy to type 2 diabetes

Obesity is defined as excessive accumulation of body fat in proportion to body size. When obesity occurs, the functions of adipose tissue may be deregulated, which is termed as adiposopathy. Adiposopathy is an independent risk factor for many diseases, including diabetes and cardiovascular diseases. In overweight or obese subjects with adiposopathy, hyperlipidemia exerts lipotoxicity in pancreatic islet and liver and induces pancreatic β cell dysfunction and liver insulin resistance, which are the decisive factors causing type 2 diabetes. Moreover, adipokines have been shown to play important roles in the regulation of glucose homeostasis. When adiposopathy occurs, abnormal changes in the serum adipokine profile correlate with the development and progression of pancreatic β cell dysfunction and insulin resistance in peripheral tissue. The current paper briefly discusses the latest findings regarding the effects of adiposopathy-related lipotoxicity and cytokine toxicity on the development of type 2 diabetes.

Pegylated Fgf21 rapidly normalizes insulin-stimulated glucose utilization in diet-induced insulin resistant mice

Fibroblast growth factor 21 (FGF21) is a novel hormone-like polypeptide that when administered exogenously, has been shown to have beneficial effects on food intake, body weight, and metabolism. The in vivo mechanisms of action for its positive metabolic effects remain to be fully elucidated. It has been shown that PEGylation of human FGF21 at specific and preferred sites confer superior metabolic pharmacology. We therefore hypothesized that low doses of PEGylated (30K PEG on position Q108) FGF21 (PEG30-Q108) would improve insulin action, independent of any effect on food intake or body weight. We identified a dose (0.25mg/kg) that had no effect on food intake or body weight, yet did show beneficial metabolic effects. Four groups of 12 weeks, high-fat fed, insulin resistant mice were studied: mice dosed subcutaneously once with vehicle or 0.25mg/kg of PEG30-Q108 24h before the experiment, or mice dosed 4 times over 2 weeks with vehicle or PEG30-Q108. Conscious, unrestrained mice were fasted for 5h and underwent a hyperinsulinemic-euglycemic clamp. Both PEG30-Q108 treatments significantly lowered fasting insulin compared to vehicle, with no difference in food intake or body weight. Insulin-stimulated whole body glucose utilization was normalized to that of lean mice with both PEG30-Q108 treatments compared to vehicle. This accounted for all of the enhanced insulin action, as there was no improvement in insulin's ability to suppress endogenous glucose production. In line with these findings, neither PEG30-Q108 treatment lowered hepatic triglycerides. These results demonstrate the profound ability of PEG30-Q108 to increase whole body insulin sensitivity.

Gluten-free diet reduces adiposity, inflammation and insulin resistance associated with the induction of PPAR-alpha and PPAR-gamma expression

Gluten exclusion (protein complex present in many cereals) has been proposed as an option for the prevention of diseases other than coeliac disease. However, the effects of gluten-free diets on obesity and its mechanisms of action have not been studied. Thus, our objective was to assess whether gluten exclusion can prevent adipose tissue expansion and its consequences. C57BL/6 mice were fed a high-fat diet containing 4.5% gluten (Control) or no gluten (GF). Body weight and adiposity gains, leukocyte rolling and adhesion, macrophage infiltration and cytokine production in adipose tissue were assessed. Blood lipid profiles, glycaemia, insulin resistance and adipokines were measured. Expression of the PPAR-α and γ, lipoprotein lipase (LPL), hormone sensitive lipase (HSL), carnitine palmitoyl acyltransferase-1 (CPT-1), insulin receptor, GLUT-4 and adipokines were assessed in epidydimal fat. Gluten-free animals showed a reduction in body weight gain and adiposity, without changes in food intake or lipid excretion. These results were associated with up-regulation of PPAR-α, LPL, HSL and CPT-1, which are related to lipolysis and fatty acid oxidation. There was an improvement in glucose homeostasis and pro-inflammatory profile-related overexpression of PPAR-γ. Moreover, intravital microscopy showed a lower number of adhered cells in the adipose tissue microvasculature. The overexpression of PPAR-γ is related to the increase of adiponectin and GLUT-4. Our data support the beneficial effects of gluten-free diets in reducing adiposity gain, inflammation and insulin resistance. The data suggests that diet gluten exclusion should be tested as a new dietary approach to prevent the development of obesity and metabolic disorders.

Regulation of insulin sensitivity by serine/threonine phosphorylation of insulin receptor substrate proteins IRS1 and IRS2

The insulin receptor substrate proteins IRS1 and IRS2 are key targets of the insulin receptor tyrosine kinase and are required for hormonal control of metabolism. Tissues from insulin-resistant and diabetic humans exhibit defects in IRS-dependent signalling, implicating their dysregulation in the initiation and progression of metabolic disease. However, IRS1 and IRS2 are regulated through a complex mechanism involving phosphorylation of >50 serine/threonine residues (S/T) within their long, unstructured tail regions. In cultured cells, insulin-stimulated kinases (including atypical PKC, AKT, SIK2, mTOR, S6K1, ERK1/2 and ROCK1) mediate feedback (autologous) S/T phosphorylation of IRS, with both positive and negative effects on insulin sensitivity. Additionally, insulin-independent (heterologous) kinases can phosphorylate IRS1/2 under basal conditions (AMPK, GSK3) or in response to sympathetic activation and lipid/inflammatory mediators, which are present at elevated levels in metabolic disease (GRK2, novel and conventional PKCs, JNK, IKKβ, mPLK). An emerging view is that the positive/negative regulation of IRS by autologous pathways is subverted/co-opted in disease by increased basal and other temporally inappropriate S/T phosphorylation. Compensatory hyperinsulinaemia may contribute strongly to this dysregulation. Here, we examine the links between altered patterns of IRS S/T phosphorylation and the emergence of insulin resistance and diabetes.

Anti-tumor necrosis factor therapy improves insulin resistance, beta cell function and insulin signaling in active rheumatoid arthritis patients with high insulin resistance

INTRODUCTION

Prevalence of insulin resistance and the metabolic syndrome has been reported to be high in rheumatoid arthritis (RA) patients. Tumor necrosis factor (TNF), a pro-inflammatory cytokine with a major pathogenetic role in RA, may promote insulin resistance by inducing Ser312 phosphorylation (p-Ser312) of insulin receptor substrate (IRS)-1 and downregulating phosphorylated (p-)AKT. We examined whether anti-TNF therapy improves insulin resistance in RA patients and assessed changes in the insulin signaling cascade.

METHODS

Prospective study of RA patients receiving anti-TNF agents (infliximab, n = 49, adalimumab, n = 11, or etanercept, n = 1) due to high disease activity score in 28 joints (DAS28 > 5.1). A complete biochemical profile was obtained at weeks 0 and 12 of treatment. Insulin resistance, insulin sensitivity and pancreatic beta cell function were measured by the Homeostasis Model Assessment (HOMA-IR), the Quantitative Insulin Sensitivity Check Index (QUICKI) and the HOMA-B respectively. Protein extracts from peripheral blood mononuclear cells were assayed by western blot for p-Ser312 IRS-1 and p-AKT. RA patients treated with abatacept (CTLA4.Ig) were used as a control group for insulin signaling studies.

RESULTS

At study entry, RA patients with high insulin resistance (HOMA-IR above median) had significantly higher mean DAS28 (P = 0.011), serum triglycerides (P = 0.015), and systolic blood pressure levels (P = 0.024) than patients with low insulin resistance. After 12 weeks of anti-TNF therapy, patients with high insulin resistance demonstrated significant reduction in HOMA-IR (P < 0.001), HOMA-B (P = 0.001), serum triglycerides (P = 0.039), and increase in QUICKI (P < 0.001) and serum HDL-C (P = 0.022). Western blot analysis in seven active RA patients with high insulin resistance showed reduction in p-Ser312 IRS-1 (P = 0.043) and increase in p-AKT (P = 0.001) over the study period. In contrast, the effect of CTLA4.Ig on p-Ser312 IRS-1 and p-AKT levels was variable.

CONCLUSIONS

Anti-TNF therapy improved insulin sensitivity and reversed defects in the insulin signaling cascade in RA patients with active disease and high insulin resistance. The impact of these biochemical changes in modifying cardiovascular disease burden in active RA patients remains to be seen.

Aromatase up-regulation, insulin and raised intracellular oestrogens in men, induce adiposity, metabolic syndrome and prostate disease, via aberrant ER-α and GPER signalling

For some years now, reduced testosterone levels have been related to obesity, insulin resistance, type 2 diabetes, heart disease, benign prostatic hypertrophy and even prostate cancer--often considered guilty more by association, than actual cause--with little attention paid to the important role of increased intracellular oestrogen, in the pathogenesis of these chronic diseases. In the final stage of the steroidogenic cascade, testosterone is metabolised to oestradiol by P450 aromatase, in the cytoplasm of adipocytes, breast cells, endothelial cells and prostate cells, to increase intracellular oestradiol concentration at the expense of testosterone. It follows therefore, that any compound that up-regulates aromatase, or any molecule that mimics oestrogen, will not only increase the activation of the mainly proliferative, classic ER-α, oestrogen receptors to induce adipogenesis and growth disorders in oestrogen-sensitive tissues, but also activate the recently identified transmembrane G protein-coupled oestrogen receptors (GPER), and deleteriously alter important intracellular signalling sequences, that promote mitogenic growth and endothelial damage. This paper simplifies how stress, xeno-oestrogens, poor dietary choices and reactive toxins up-regulate aromatase to increase intracellular oestradiol production; how oestradiol in combination with leptin and insulin cause insulin resistance and leptin resistance through aberrant serine phosphorylation; how the increased oestradiol, insulin and leptin stimulate rapid, non-genomic G protein-coupled phosphorylation cascades, to increase fat deposition and create the vasoconstrictive, dyslipidemic features of metabolic syndrome; how aberrant GPER signalling induces benign prostatic hypertrophy; and how increased intracellular oestradiol stimulates mitogenic change and tumour-cell activators, to cause prostate cancer. In essence, the up-regulation of aromatase produces increased intracellular oestradiol, increases ER-α activation and increases GPER activation, in combination with insulin, to cause aberrant downstream transduction signaling, and thus induce metabolic syndrome and mitogenic prostate growth. To understand this fact, that raised intracellular oestradiol levels in men, induce and promote obesity, gynecomastia, metabolic syndrome, type two diabetes, benign prostatic hypertrophy and prostate cancer, rather than low testosterone, represents a shift in medical thinking, a new awareness, that will reduce the rising incidence of obesity, metabolic syndrome and prostate disease, and significantly improve the health of men worldwide.

The effect of leptin on maturing porcine oocytes is dependent on glucose concentration

Increased body weight is often accompanied by increased circulating levels of leptin and glucose, which alters glucose metabolism in various tissues, including perhaps the oocyte. Alteration of glucose metabolism impacts oocyte function and may contribute to the subfertility often associated with obese individuals. The objective of this study was to determine the effect of leptin (0, 10, and 100 ng/ml) on the oocyte and cumulus cells during in vitro maturation under differing glucose concentrations. We examined the effects of leptin on oocyte maturation, blastocyst development, and/or gene expression in oocytes and cumulus cells (IRS1, IGF1, PPARγ, IL6, GLUT1) in a physiological glucose (2 mM) and high glucose (50 mM) environment. We also evaluated the effect of leptin on glucose metabolism via glycolysis and the pentose phosphate pathway. In a physiological glucose environment, leptin did not have an influence on oocyte maturation, blastocyst development, or oocyte gene expression. Expression of GLUT1 in cumulus cells was downregulated with 100 ng/ml leptin treatment, but did not affect oocyte glucose metabolism. In a high glucose environment, oocyte maturation and glycolysis were decreased, but in the presence of 100 ng/ml leptin, these parameters were improved to levels similar to control. This effect is potentially mediated by an upregulation of oocyte IRS1 and a correction of cumulus cell IGF1 expression. The present study demonstrates that in a physiological glucose concentration, leptin plays a negligible role in oocyte function. However, leptin appears to modulate the deleterious impact of a high glucose environment on oocyte function.

Insulin immuno-neutralization in fed chickens: effects on liver and muscle transcriptome

Chickens mimic an insulin-resistance state by exhibiting several peculiarities with regard to plasma glucose level and its control by insulin. To gain insight into the role of insulin in the control of chicken transcriptome, liver and leg muscle transcriptomes were compared in fed controls and "diabetic" chickens, at 5 h after insulin immuno-neutralization, using 20.7K-chicken oligo-microarrays. At a level of false discovery rate <0.01, 1,573 and 1,225 signals were significantly modified by insulin privation in liver and muscle, respectively. Microarray data agreed reasonably well with qRT-PCR and some protein level measurements. Differentially expressed mRNAs with human ID were classified using Biorag analysis and Ingenuity Pathway Analysis. Multiple metabolic pathways, structural proteins, transporters and proteins of intracellular trafficking, major signaling pathways, and elements of the transcriptional control machinery were largely represented in both tissues. At least 42 mRNAs have already been associated with diabetes, insulin resistance, obesity, energy expenditure, or identified as sensors of metabolism in mice or humans. The contribution of the pathways presently identified to chicken physiology (particularly those not yet related to insulin) needs to be evaluated in future studies. Other challenges include the characterization of "unknown" mRNAs and the identification of the steps or networks, which disturbed tissue transcriptome so extensively, quickly after the turning off of the insulin signal. In conclusion, pleiotropic effects of insulin in chickens are further evidenced; major pathways controlled by insulin in mammals have been conserved despite the presence of unique features of insulin signaling in chicken muscle.

Protein kinase Cβ deficiency attenuates obesity syndrome of ob/ob mice by promoting white adipose tissue remodeling

To explore the role of leptin in PKCβ action and to determine the protective potential of PKCβ deficiency on profound obesity, double knockout (DBKO) mice lacking PKCβ and ob genes were created, and key parameters of metabolism and body composition were studied. DBKO mice had similar caloric intake as ob/ob mice but showed significantly reduced body fat content, improved glucose metabolism, and elevated body temperature. DBKO mice were resistant to high-fat diet-induced obesity. Moreover, PKCβ deficiency increased β-adrenergic signaling by inducing expression of β1- and β3-adrenergic receptors (β-ARs) in white adipose tissue (WAT) of ob/ob mice. Accordingly, p38(MAPK) activation and expression of PGC-1α and UCP-1 were increased in WAT of DBKO mice. Consistent with results of in vivo studies, inhibition of PKCβ in WAT explants from ob/ob mice also increased expression of above β-ARs. In contrast, induction of PGC-1α and UCP-1 expression in brown adipose tissue of DBKO mice was not accompanied by changes in the expression of these β-ARs. Collectively, these findings suggest that PKCβ deficiency may prevent genetic obesity, in part, by remodeling the catabolic function of adipose tissues through β-ARs dependent and independent mechanisms.

The role of diet in the prevention of type 2 diabetes

Type 2 diabetes mellitus is an important preventable disease and a growing public health problem. Epidemiologic and interventional studies suggest that weight loss is the main driving force to reduce diabetes risk. Landmark clinical trials of lifestyle changes in subjects with prediabetes have shown that diet and exercise leading to weight loss consistently reduce the incidence of diabetes. However, from these studies it cannot be established whether dietary changes alone play a significant role in preventing diabetes. Here we review epidemiologic and clinical trial evidence relating nutrients, foods and dietary patterns to diabetes risk and the possible mechanisms involved. The differential effects of carbohydrate and fat quantity and quality, and those of specific foods and whole diets are discussed. Importantly, most dietary components influencing diabetes risk have similar effects on biomarkers of cardiovascular risk and inflammation. The conclusion is that there is no universal dietary strategy to prevent diabetes or delay its onset. Together with the maintenance of ideal body weight, the promotion of the so-called prudent diet (characterized by a higher intake of food groups that are generally recommended for health promotion, particularly plant-based foods, and a lower intake of red meat, meat products, sweets, high-fat dairy and refined grains) or a Mediterranean dietary pattern rich in olive oil, fruits and vegetables, including whole grains, pulses and nuts, low-fat dairy, and moderate alcohol consumption (mainly red wine) appears as the best strategy to decrease diabetes risk, especially if dietary recommendations take into account individual preferences, thus enabling long-time adherence.

Paraoxonase-1 activity, malondialdehyde and glutathione peroxidase in non-alcoholic fatty liver disease and the effect of atorvastatin

BACKGROUND AND STUDY AIMS

The prevalence of non-alcoholic fatty liver disease (NAFLD) appears to be increasing. The aim of the present study was to investigate the relationship between hepatic antioxidant paraoxonase 1 (PON1) activity, lipid peroxidation and antioxidant enzymes in patients with NAFLD and the effect of atorvastatin.

PATIENTS AND METHODS

This study was conducted on 50 patients with NAFLD and 20 normal subjects matched for age and sex. All of them were subjected to the following investigations: abdominal ultrasonography, serum PON1 activity level, liver function tests, serum lipid profile, fasting and postprandial blood glucose and serum levels of malondialdehyde (MDA) and glutathione peroxidase (GP). NAFLD patients were further randomly classified into two groups (25 patients each), groups Ia and Ib. Only group Ia received atorvastatin 40mg tablet for 8months.

RESULTS

Obesity, dyslipidaemia and impaired glucose tolerance were prevalent in group I. There was a significant decrease in serum PON1 activity with a significant increase in MDA and GP activity (i.e., there is a significant increase in lipid peroxidation rate) in group I compared with group II. After atorvastatin therapy, there was a significant increase in serum PNO1 activity and significant decrease in serum MDA levels.

CONCLUSION

Patients with NAFLD show enhanced oxidative stress which may lead to non-alcoholic steatohepatitis (NASH). Reduced PON1 activity and increased MDA could be considered a biochemical marker for lipid peroxidation, which require follow-up in patients with NAFLD. Atorvastatin may have a role in prevention of, or delay, the transformation of liver steatosis into NASH.

The role of oestrogen in the pathogenesis of obesity, type 2 diabetes, breast cancer and prostate disease

A detailed review of the literature was performed in a bid to identify the presence of a common link between specific hormone interactions and the increasing prevalence of global disease. The synergistic action of unopposed oestrogen and leptin, compounded by increasing insulin, cortisol and xeno-oestrogen exposure directly initiate, promote and exacerbate obesity, type 2 diabetes, uterine overgrowth, prostatic enlargement, prostate cancer and breast cancer. Furthermore these hormones significantly contribute to the incidence and intensity of anxiety and depression, Alzheimer's disease, heart disease and stroke. This review, in collaboration with hundreds of evidence-based clinical researchers, correlates the significant interactions these hormones exert upon the upregulation of p450 aromatase, oestrogen, leptin and insulin receptor function; the normal status quo of their binding globulins; and how adduct formation alters DNA sequencing to ultimately produce an array of metabolic conditions ranging from menopausal symptoms and obesity to Alzheimer's disease and breast and prostate cancer. It reveals the way that poor diet, increased stress, unopposed endogenous oestrogens, exogenous oestrogens, pesticides, xeno-oestrogens and leptin are associated with increased aromatase activity, and how its products, increased endogenous oestrogen and lowered testosterone, are associated with obesity, type 2 diabetes, Alzheimer's disease and oestrogenic disease. This controversial break-through represents a paradigm shift in medical thinking, which can prevent the raging pandemic of diabetes, obesity and cancer currently sweeping the world, and as such, it will reshape health initiatives, reduce suffering, prevent waste of government expenditure and effectively transform preventative medicine and global health care for decades.

Leptin promotes fibroproliferative acute respiratory distress syndrome by inhibiting peroxisome proliferator-activated receptor-γ

RATIONALE

Diabetic patients have a lower incidence of acute respiratory distress syndrome (ARDS), and those who develop ARDS are less likely to die. The mechanisms that underlie this protection are unknown.

OBJECTIVES

To determine whether leptin resistance, a feature of diabetes, prevents fibroproliferation after lung injury.

METHODS

We examined lung injury and fibroproliferation after the intratracheal instillation of bleomycin in wild-type and leptin-resistant (db/db) diabetic mice. We examined the effect of leptin on transforming growth factor (TGF)-β(1)-mediated transcription in primary normal human lung fibroblasts. Bronchoalveolar lavage fluid (BAL) samples from patients with ARDS and ventilated control subjects were obtained for measurement of leptin and active TGF-β(1) levels.

MEASUREMENTS AND MAIN RESULTS

Diabetic mice (db/db) were resistant to lung fibrosis. The db/db mice had higher levels of peroxisome proliferator-activated receptor-γ (PPARγ), an inhibitor of the transcriptional response to TGF-β(1), a cytokine critical in the pathogenesis of fibroproliferative ARDS. In normal human lung fibroblasts, leptin augmented the transcription of profibrotic genes in response to TGF-β(1) through a mechanism that required PPARγ. In patients with ARDS, BAL leptin levels were elevated and correlated with TGF-β(1) levels. Overall, there was no significant relationship between BAL leptin levels and clinical outcomes; however, in nonobese patients, higher BAL leptin levels were associated with fewer intensive care unit- and ventilator-free days and higher mortality.

CONCLUSIONS

Leptin signaling is required for bleomycin-induced lung fibrosis. Leptin augments TGF-β(1) signaling in lung fibroblasts by inhibiting PPARγ. These findings provide a mechanism for the observed protection against ARDS observed in diabetic patients.

Peripheral blood leukocyte gene expression patterns and metabolic parameters in habitually snoring and non-snoring children with normal polysomnographic findings

BACKGROUND

Children who snore but do not have gas exchange abnormalities or alterations of sleep architecture have primary snoring (PS). Since increasing evidence suggest that PS may be associated with morbidity, we hypothesized that assessing genome-wide gene expression in peripheral blood leukocytes (PBL) will identify a distinct signature in PS children.

METHODS

Children (aged 4-9 years) with and without habitual snoring and a normal PSG were designated as either PS or controls. Whole genome expression profiles of PBL and metabolic parameters in 30 children with PS and 30 age-, gender-, ethnicity-, and BMI-matched controls were compared. Pathway-focused gene network analysis of the PBL transcriptome was performed. Metabolic parameters were measured in an independent follow-up cohort of 98 children (64 PS and 34 controls) to evaluate the computationally derived findings.

RESULTS

PS was not associated with a distinct transcriptional signature in PBL. Exploratory functional network analysis of enriched gene sets identified a number of putative pathways-including those mapping to insulin signaling, adipocyte differentiation, and obesity-with significant alterations in glucose metabolism and insulin sensitivity emerging in the follow-up cohort of children with PS, but no differences in lipid profiles.

CONCLUSIONS

PS children do not exhibit global perturbations in their PBL transcriptional response, suggesting that current normative PSG criteria are overall valid. However, subtle differences in functionally coherent pathways involved in glycemic homeostasis were detected and confirmed in a larger independent pediatric cohort indicating that PS may carry increased risk for end-organ morbidity in susceptible children.

A comparison between metabolic syndrome post-hematopoietic stem cell transplantation and spontaneously occurring metabolic syndrome

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is used in the treatment of several hematological and non-hematological disorders. An increasing number of long-term survivors recover from their primary disease, but they are at risk of adverse late effects, including metabolic syndrome (MS), which seems to be common in long-term survivors of HSCT.

AIM

To compare common metabolic parameters and adipohormone profiles in post-transplant and spontaneously occurring or "classic" MS patients.

SUBJECTS AND METHODS

Post-transplant MS patients (15 women and 14 men; 49.8±9.3 yr) were compared to "classic" MS patients (15 women and 14 men; 52.9±8.0 yr). For each subject a record of conventional clinical parameters was made; moreover, serum leptin, insulin, quantitative C-reactive protein (CRP), tumor necrosis factor-α [TNF-α], and adiponectin concentrations were measured.

RESULTS

The patients with post-HSCT MS had significantly higher levels of leptin, CRP, and TNF-α than the patients with "classic" MS. A generalized linear model comprising serum insulin (p=0.022), body mass index (p<0.001), gender (p<0.001), and group (i.e. healthy, post-HSCT with MS, or suffering from "classic" MS; p<0.001) explained serum leptin variability (adjusted R(2)=0.741). Serum leptin concentrations and BMI were related in the patients with "classic" MS but not in those with post-HSCT MS.

CONCLUSIONS

A possible pathogenetic mechanism in the development of MS after HSCT could be hyperleptinemia. A potential interaction among circulating leptin, components of MS, and immune function might explain the role of this adipokine in mediating cardiovascular risk after HSCT.

Osteopontin is required for the early onset of high fat diet-induced insulin resistance in mice

BACKGROUND

Insulin resistance is manifested in muscle, adipose tissue, and liver and is associated with adipose tissue inflammation. The cellular components and mechanisms that regulate the onset of diet-induced insulin resistance are not clearly defined.

METHODOLOGY AND PRINCIPAL FINDINGS

We initially observed osteopontin (OPN) mRNA over-expression in adipose tissue of obese, insulin resistant humans and rats which was normalized by thiazolidinedione (TZD) treatment in both species. OPN regulates inflammation and is implicated in pathogenic maladies resulting from chronic obesity. Thus, we tested the hypothesis that OPN is involved in the early development of insulin resistance using a 2-4 week high fat diet (HFD) model. OPN KO mice fed HFD for 2 weeks were completely protected from the severe skeletal muscle, liver and adipose tissue insulin resistance that developed in wild type (WT) controls, as determined by hyperinsulinemic euglycemic clamp and acute insulin-stimulation studies. Although two-week HFD did not alter body weight or plasma free fatty acids and cytokines in either strain, HFD-induced hyperleptinemia, increased adipose tissue inflammation (macrophages and cytokines), and adipocyte hypertrophy were significant in WT mice and blunted or absent in OPN KO mice. Adipose tissue OPN protein isoform expression was significantly altered in 2- and 4-week HFD-fed WT mice but total OPN protein was unchanged. OPN KO bone marrow stromal cells were more osteogenic and less adipogenic than WT cells in vitro. Interestingly, the two differentiation pathways were inversely affected by HFD in WT cells in vitro.

CONCLUSIONS

The OPN KO phenotypes we report reflect protection from insulin resistance that is associated with changes in adipocyte biology and adipose tissue inflammatory status. OPN is a key component in the development of HFD-induced insulin resistance.

Enforced expression of protein kinase C in skeletal muscle causes physical inactivity, fatty liver and insulin resistance in the brain

Among the multitude of dysregulated signalling mechanisms that comprise insulin resistance in divergent organs, the primary events in the development of type 2 diabetes are not well established. As protein kinase C (PKC) activation is consistently present in skeletal muscle of obese and insulin resistant subjects, we generated a transgenic mouse model that overexpresses constitutively active PKC-β₂ in skeletal muscle to test whether activation of PKC is sufficient to cause an aversive whole-body phenotype. Upon this genetic modification, increased serine phosphorylation in Irs1 was observed and followed by impaired ³H-deoxy-glucose uptake and muscle glycogen content, and transgenic mice exhibited insulin and glucose intolerance as they age. Muscle histochemistry revealed an increase in lipid deposition (intramyocellular lipids), and transgenic mice displayed impaired expression of transcriptional regulators of genes involved in fatty acid oxidation (peroxisome proliferator-activated receptor-γ, PGC-1β, acyl-CoA oxidase) and lipolysis (hormone-sensitive lipase). In this regard, muscle of transgenic mice exhibited a reduced capacity to oxidize palmitate and contained less mitochondria as determined by citrate synthase activity. Moreover, the phenotype included a profound decrease in the daily running distance, intra-abdominal and hepatic fat accumulation and impaired insulin action in the brain. Together, our data suggest that activation of a classical PKC in skeletal muscle as present in the pre-diabetic state is sufficient to cause disturbances in whole-body glucose and lipid metabolism followed by profound alterations in oxidative capacity, ectopic fat deposition and physical activity.

Intracellular molecular effects of insulin resistance in patients with metabolic syndrome

Aim of the study

Patients with metabolic syndrome (MetS) have an increased risk of cardiovascular disease. Data obtained from muscle biopsies have demonstrated altered insulin signaling (IS) in patients with MetS. The IS regulates critical cell functions including molecular-regulated cellular metabolite fluxes, protein and energetic metabolism, cell proliferation and apoptosis with consequent regulation of cell life including endothelial homeostasis and blood coagulation. However, little is known about blood cell IS in MetS patients. The aim of this study was to develop a method to evaluate IS in peripheral lymphocytes to identify altered intracellular molecules in patients with MetS to use as risk biomarkers of vascular thrombosis.

Patients and Methods

We investigated 40 patients with MetS and 20 controls. MetS was defined according to guidelines from the US National Cholesterol Education Program Adult Treatment Panel III. Blood samples were taken from all participants. Total mononuclear cells were isolated from peripheral blood using density gradient centrifugation. IS molecules were evaluated using Western blot analysis followed by computer-assisted densitometer evaluation.

Results

Lymphocytes of MetS patients showed a reduced mTOR expression (the mammalian target of rapamycin) which is a fundamental molecule of IS. Major impairment of IS was confirmed by reduced upstream and downstream mTOR molecules which regulate fundamental cells metabolic functions.

Conclusions

In patients with MetS, we found a reduction of mTOR and other mTOR-related molecules involved in insulin resistance, cell repair, coagulation and vasculogenesis. A reduced expression of mTOR may reflect an increased risk of vascular thrombosis.

Protein kinase C-delta is involved in the inflammatory effect of IL-6 in mouse adipose cells

AIMS/HYPOTHESIS

The aim of the study was to address the role of protein kinase C-delta (PKCdelta) on phosphorylation of signal transducer and activator of transcription 3 (STAT3) and activation of inflammatory genes in response to IL-6 in adipose cells.

METHODS

Differentiated mouse 3T3-L1 adipocytes preincubated with the PKCdelta inhibitor rottlerin and mouse embryonic fibroblasts (MEFs) lacking PKCdelta were incubated with IL-6 and/or insulin. RNA was extracted and the gene expression was analysed by real-time PCR, while the proteins from total, nuclear and cytoplasmic lysates were analysed by immunoblotting.

RESULTS

Inhibition of PKCdelta by rottlerin significantly reduced both Ser-727 and Tyr-705 phosphorylation of STAT3. Consequently, nuclear translocation of STAT3 and the IL-6-induced gene transcription and protein release of the inflammatory molecule serum amyloid A 3 (SAA3) were reduced. Similarly, the IL-6-regulated gene transcription of Il-6 (also known as Il6) to Hp and the feedback inhibitor of IL-6, Socs3, were also attenuated by rottlerin. Furthermore, PKCdelta was found to translocate to the nucleus following IL-6 treatment and this was also reduced by rottlerin. In agreement with the effect of rottlerin, Pkcdelta (also known as Prkcd) ( -/- ) MEFs also displayed a markedly reduced ability of IL-6 to activate the transcription of Saa3, Hp, Socs3 and Il6 genes compared with wild-type MEFs. These results correlated with a reduced nuclear translocation and phosphorylation of STAT3.

CONCLUSIONS/INTERPRETATION

These results show that PKCdelta plays a key role in the inflammatory effect of IL-6 in adipose cells and may be a suitable target for novel anti-inflammatory agents.

Effect of Helicobacter pylori eradication on insulin resistance, serum lipids and low-grade inflammation

BACKGROUND/AIM

Many studies have revealed a close relationship between Helicobacter pylori (HP) infection and insulin resistance. The aim of this study was to investigate the effects of HP eradication on insulin resistance, serum lipids and low-grade inflammation.

MATERIALS AND METHODS

This was a prospective, open-label, single-center study which consisted of 159 patients. The patients with HP infection received a 14-day sequential regimen. A HOMA-IR (homeostasis model assessment of insulin resistance) level was used to assess insulin resistance.

RESULTS

Eighty-eight patients with HP infection and seventy-one patients without HP infection were studied. HOMA-IR, total cholesterol (TC), triglyceride (TG), LDL cholesterol (LDL-C) and C reactive protein (CRP) levels were significantly higher and HDL-cholesterol (HDL-C) levels were significantly lower in patients with HP infection compared to the patients without HP infection (P<0.05). The HP eradication rates with a sequential regimen in dyspeptic patients were 53.4%. Six weeks after the end of eradication therapy, the mean fasting insulin, HOMA-IR, TC, TG, LDL-C, and CRP levels in patients with successful eradication were significantly decreased from the pretreatment levels (P<0.05) and HDL-C level was significantly increased from the pretreatment levels (P<0.05). The mean fasting insulin, HOMA-IR, TC, TG, LDL-C, CRP levels and HDL-C levels in patients with unsuccessful eradication were not significantly changed from pretreatment levels (P<0.05).

CONCLUSION

This study showed beneficial effects of HP eradication on insulin resistance, atherogenic lipid abnormalities and low-grade inflammation. The results suggest that HP eradication may prevent coronary artery disease and metabolic syndrome.

Insulin-mediated cortical activity in the slow frequency range is diminished in obese mice and promotes physical inactivity

AIMS/HYPOTHESIS

There is evidence from mouse models and humans that alterations in insulin action in the brain are accompanied by an obese phenotype; however, the impact of insulin with regard to behavioural aspects such as locomotion is unknown.

METHODS

To address insulin action in the brain with regard to cortical activity in distinct frequency bands and the behavioural consequences, the insulin signalling pathway was followed from the receptor to electrical activity and locomotion. Western blot analysis, electrocorticograms with intracerebroventricular (i.c.v.) application of insulin, and measurements of locomotor activity were performed in lean and obese, as well as Toll-like receptor (TLR) 2/4-deficient, mice.

RESULTS

We show that insulin application i.c.v. into lean mice was accompanied by a profound increase in cortical activity in the slow frequency range, while diet-induced obese mice displayed insulin resistance. In parallel, insulin administered i.c.v. increased locomotor activity in lean mice, whereas a phosphatidylinositol-3 (PI3) kinase inhibitor or obesity abolished insulin-mediated locomotion. A potential candidate that links insulin signalling to locomotion is the Kv1.3 channel that is activated by PI3-kinase. Pharmacological inhibition of Kv1.3 channels that bypassed insulin receptor activation promoted activity. Moreover, mice deficient in TLR2/4-dependent signalling displayed an increase in cortical activity in the slow frequency range that was correlated with improved spontaneous and insulin-mediated locomotor activity.

CONCLUSIONS/INTERPRETATION

Our data provide functional evidence for a direct effect of insulin on brain activation patterns in the slow frequency bands and locomotor activity in lean mice, while in obese mice, insulin-mediated locomotion is blunted and further aggravates physical inactivity.

The insulin effect on cerebrocortical theta activity is associated with serum concentrations of saturated nonesterified Fatty acids

CONTEXT

Insulin action in the brain contributes to adequate regulation of body weight, neuronal survival, and suppression of endogenous glucose production. We previously demonstrated by magnetoencephalography in lean humans that insulin stimulates activity in beta and theta frequency bands, whereas this effect was abolished in obese individuals.

OBJECTIVE

The present study aims to define metabolic signals associated with the suppression of the cerebrocortical response in obese humans.

DESIGN AND SETTING

We determined insulin-mediated modulation of spontaneous cerebrocortical activity by magnetoencephalography during a hyperinsulinemic euglycemic clamp and related it to measures of ectopic fat deposition and mediators of peripheral insulin resistance. Visceral fat mass and intrahepatic lipid content were quantified by magnetic resonance imaging and spectroscopy. Multiple regression analysis was used to analyze associations of cerebrocortical insulin sensitivity and metabolic markers related to obesity.

PARTICIPANTS

Forty-nine healthy, nondiabetic humans participated in the study.

RESULTS

In a multiple regression, insulin-mediated stimulation of theta activity was negatively correlated to body mass index, visceral fat mass, and intrahepatic lipid content. Although fasting saturated nonesterified fatty acids mediated the correlations of theta activity with abdominal and intrahepatic lipid stores, adipocytokines displayed no independent correlation with insulin-mediated cortical activity in the theta frequency band.

CONCLUSIONS

Thus, insulin action at the level of cerebrocortical activity in the brain is diminished in the presence of elevated levels of saturated nonesterified fatty acids.

Dietary sucrose intake is related to serum leptin concentration in overweight pregnant women

BACKGROUND

Overweight, characterized by low-degree systemic inflammation, predisposes women to impaired glucose metabolism during pregnancy. Adipokine leptin participates in the regulation of energy balance and immune action.

AIMS OF THE STUDY

Objective of the study was to evaluate if aberrations in glucose metabolism during pregnancy are related to leptin concentration and whether serum leptin concentration is affected by diet composition.

SUBJECTS AND METHODS

Normal-weight (n = 61) and overweight or obese (BMI > 25, n = 42) pregnant women visited study clinic at third trimester of pregnancy and one month postpartum. Serum fasting leptin and insulin as well as plasma glucose concentrations were measured, insulin resistance (HOMA) and sensitivity (QUICKI) calculated, and dietary intake from food records determined.

RESULTS

In overweight women leptin concentration was significantly higher both in pregnancy, 45.27 (95% CI 39.40-51.14) ng/ml, and postpartum, 31.84 (27.38-36.30) ng/ml, than in normal-weight women, 31.09 (95% CI 27.80-34.37) ng/ml and 16.23 (13.93-18.53) ng/ml, respectively. Equally, blood glucose concentration during pregnancy was higher, 4.82 (4.67-4.97)mmol/l, and insulin concentration, 15.34 (12.00-18.68) mU/l, more pronounced in overweight compared to normal-weight women, 4.51 (4.42-4.61) mmol/l and 8.28 (7.21-9.36) mU/l, respectively. Significantly higher HOMA and lower QUICKI were also detected in overweight compared to normal-weight women. At third trimester of pregnancy, leptin concentration correlated positively with insulin concentration in normal-weight (r = 0.561, P = 0.002) and overweight women (r = 0.736, P < 0.001), as well as with HOMA (r = 0.568, P = 0.002 and r = 0.731, P < 0.001, respectively) whereas negative association was found with QUICKI in normal-weight (r = -0.484, P = 0.011) and overweight women (r = -0.711, P < 0.001). Importantly, serum leptin concentration was affected by dietary sucrose intake both as quantitatively (r = 0.424, P = 0.009) and relative to energy intake (r = 0.408, P = 0.012) in overweight but not in normal-weight pregnant women.

CONCLUSIONS

Overweight-related elevation in serum leptin is associated with impaired regulation of glucose metabolism during pregnancy. The novel finding that dietary sucrose intake is related to serum leptin concentration is in line with the current dietary recommendations to overweight pregnant women with impaired glucose metabolism advising the lower intake of sucrose during pregnancy.

Investigation of the acute effect of leptin on the inhibition of glycogen catabolism by insulin in rat liver perfused in situ

Leptin, a cytokine secreted by adipose tissue, has been implicated in the insulin resistance associated with obesity. Here we examined the acute influence of leptin at physiological (10 ng/ml) and supraphysiological (50 ng/ml and 100 ng/ml) concentrations on the inhibition of glycogen catabolism promoted by insulin in rat liver perfusion experiments. Perfusion of the liver with insulin (20 microU/ml) decreased the activation of glucose production (p < 0.05) and glycogenolysis by cAMP (3 microM). However, the infusion of leptin, at concentrations similar to those found in non-obese (10 ng/ml), obese (50 ng/ml), and morbidly obese (100 ng/ml) individuals did not influence the acute inhibitory effect of insulin (20 microU/ml) on glucose production and glycogenolysis stimulated by cAMP (p > 0.05).We conclude that neither physiological nor supraphysiological concentrations of leptin directly influence the inhibition of glycogen catabolism promoted by insulin in rat liver perfused in situ.

Differential metabolic effects of pravastatin and simvastatin in hypercholesterolemic patients

BACKGROUND

Lipophilic and hydrophilic statins have different effects on adiponectin and insulin resistance in experimental studies and different effects on the rate of onset of new diabetes in large scale clinical studies. Therefore, we hypothesized that simvastatin and pravastatin may have differential metabolic effects in hypercholesterolemic patients.

METHODS

This was a randomized, single-blind, placebo-controlled, parallel study. Age, gender, and body mass index were matched. Forty-three patients were given placebo, simvastatin 20mg, or pravastatin 40 mg, respectively once daily for 2 months.

RESULTS

Simvastatin and pravastatin therapy significantly changed lipoprotein levels and improved flow-mediated dilation after 2 months when compared with baseline (P<0.001) or placebo treatment (P<0.001 by ANOVA). Simvastatin therapy significantly increased insulin levels (mean % changes; 127%, P=0.014) and decreased plasma adiponectin levels (10%, P=0.012) and insulin sensitivity as assessed by QUICKI (6%, P=0.007) when compared with baseline. By contrast, pravastatin therapy did not significantly change insulin levels (-3%, P=0.437) but significantly increased plasma adiponectin levels (9%, P=0.011) and insulin sensitivity (6%, P=0.008) when compared with baseline. In addition, these effects of simvastatin were significant when compared with pravastatin (P<0.001 for insulin levels by ANOVA on Ranks, P<0.001 for adiponectin and P=0.001 for QUICKI by ANOVA). When compared with baseline, simvastatin significantly increased plasma leptin levels (35%, P=0.028), but pravastatin did not (1%, P=0.822).

CONCLUSIONS

Despite causing comparable changes in lipoprotein and endothelium-dependent dilation, simvastatin and pravastatin therapy had differential metabolic effects in hypercholesterolemic patients that may be clinically relevant.

Leptin resistance and insulin resistance

Leptin resistance and insulin resistance are the common pathology of various metabolic diseases, and make great contribution to the metabolic syndrome. Many researches have proved that the two processes affected each other, whereas the exploration of the resistance mechanism was often independently carried out. Here, we'd like to make a review focusing on the relationship between leptin resistance and insulin resistance, and their interactions at multiple levels.

Phosphorylation of IRS proteins, insulin action, and insulin resistance

Insulin signaling at target tissues is essential for growth and development and for normal homeostasis of glucose, fat, and protein metabolism. Control over this process is therefore tightly regulated. It can be achieved by a negative feedback control mechanism whereby downstream components inhibit upstream elements along the insulin-signaling pathway (autoregulation) or by signals from apparently unrelated pathways that inhibit insulin signaling thus leading to insulin resistance. Phosphorylation of insulin receptor substrate (IRS) proteins on serine residues has emerged as a key step in these control processes under both physiological and pathological conditions. The list of IRS kinases implicated in the development of insulin resistance is growing rapidly, concomitant with the list of potential Ser/Thr phosphorylation sites in IRS proteins. Here, we review a range of conditions that activate IRS kinases to phosphorylate IRS proteins on "hot spot" domains. The flexibility vs. specificity features of this reaction is discussed and its characteristic as an "array" phosphorylation is suggested. Finally, its implications on insulin signaling, insulin resistance and type 2 diabetes, an emerging epidemic of the 21st century are outlined.