What causes the insulin resistance underlying obesity?

Serum amyloid A impairs the antiinflammatory properties of HDL

HDL from healthy humans and lean mice inhibits palmitate-induced adipocyte inflammation; however, the effect of the inflammatory state on the functional properties of HDL on adipocytes is unknown. Here, we found that HDL from mice injected with AgNO3 fails to inhibit palmitate-induced inflammation and reduces cholesterol efflux from 3T3-L1 adipocytes. Moreover, HDL isolated from obese mice with moderate inflammation and humans with systemic lupus erythematosus had similar effects. Since serum amyloid A (SAA) concentrations in HDL increase with inflammation, we investigated whether elevated SAA is a causal factor in HDL dysfunction. HDL from AgNO3-injected mice lacking Saa1.1 and Saa2.1 exhibited a partial restoration of antiinflammatory and cholesterol efflux properties in adipocytes. Conversely, incorporation of SAA into HDL preparations reduced antiinflammatory properties but not to the same extent as HDL from AgNO3-injected mice. SAA-enriched HDL colocalized with cell surface-associated extracellular matrix (ECM) of adipocytes, suggesting impaired access to the plasma membrane. Enzymatic digestion of proteoglycans in the ECM restored the ability of SAA-containing HDL to inhibit palmitate-induced inflammation and cholesterol efflux. Collectively, these findings indicate that inflammation results in a loss of the antiinflammatory properties of HDL on adipocytes, which appears to partially result from the SAA component of HDL binding to cell-surface proteoglycans, thereby preventing access of HDL to the plasma membrane.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Visceral Adipose Tissue Mesothelial Cells: Living on the Edge or Just Taking Up Space?

Visceral adiposity and pathological adipose tissue remodeling, a result of overnutrition, are strong predictors of metabolic health in obesity. Factors intrinsic to visceral adipose depots are likely to play a causal role in eliciting the detrimental effects of this tissue on systemic nutrient homeostasis. The visceral adipose-associated mesothelium, a monolayer of epithelial cells of mesodermal origin that line the visceral serosa, has recently attracted attention for its role in metabolic dysfunction. Here we highlight and consolidate literature from various fields of study that points to the visceral adipose-associated mesothelium as a potential contributor to adipose development and remodeling. We propose a hypothesis in which adipose mesothelial cells represent a visceral depot-specific determinant of adipose tissue health in obesity.

Scientific Statement on the Diagnostic Criteria, Epidemiology, Pathophysiology, and Molecular Genetics of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous and complex disorder that has both adverse reproductive and metabolic implications for affected women. However, there is generally poor understanding of its etiology. Varying expert-based diagnostic criteria utilize some combination of oligo-ovulation, hyperandrogenism, and the presence of polycystic ovaries. Criteria that require hyperandrogenism tend to identify a more severe reproductive and metabolic phenotype. The phenotype can vary by race and ethnicity, is difficult to define in the perimenarchal and perimenopausal period, and is exacerbated by obesity. The pathophysiology involves abnormal gonadotropin secretion from a reduced hypothalamic feedback response to circulating sex steroids, altered ovarian morphology and functional changes, and disordered insulin action in a variety of target tissues. PCOS clusters in families and both female and male relatives can show stigmata of the syndrome, including metabolic abnormalities. Genome-wide association studies have identified a number of candidate regions, although their role in contributing to PCOS is still largely unknown.

Hepatic Insulin Resistance Following Chronic Activation of the CREB Coactivator CRTC2

Under fasting conditions, increases in circulating concentrations of glucagon maintain glucose homeostasis via the induction of hepatic gluconeogenesis. Triggering of the cAMP pathway in hepatocytes stimulates the gluconeogenic program via the PKA-mediated phosphorylation of CREB and dephosphorylation of the cAMP-regulated CREB coactivators CRTC2 and CRTC3. In parallel, decreases in circulating insulin also increase gluconeogenic gene expression via the de-phosphorylation and activation of the forkhead transcription factor FOXO1. Hepatic gluconeogenesis is increased in insulin resistance where it contributes to the attendant hyperglycemia. Whether selective activation of the hepatic CREB/CRTC pathway is sufficient to trigger metabolic changes in other tissues is unclear, however. Modest hepatic expression of a phosphorylation-defective and therefore constitutively active CRTC2S171,275A protein increased gluconeogenic gene expression under fasting as well as feeding conditions. Circulating glucose concentrations were constitutively elevated in CRTC2S171,275A-expressing mice, leading to compensatory increases in circulating insulin concentrations that enhance FOXO1 phosphorylation. Despite accompanying decreases in FOXO1 activity, hepatic gluconeogenic gene expression remained elevated in CRTC2S171,275A mice, demonstrating that chronic increases in CRTC2 activity in the liver are indeed sufficient to promote hepatic insulin resistance and to disrupt glucose homeostasis.

Effect of weight loss, with or without exercise, on body composition and sex hormones in postmenopausal women: the SHAPE-2 trial

Introduction

Physical inactivity and overweight are risk factors for postmenopausal breast cancer. The effect of physical activity may be partially mediated by concordant weight loss. We studied the effect on serum sex hormones, which are known to be associated with postmenopausal breast cancer risk, that is attributable to exercise by comparing randomly obtained equivalent weight loss by following a hypocaloric diet only or mainly by exercise.

Methods

Overweight, insufficiently active women were randomised to a diet (N = 97), mainly exercise (N = 98) or control group (N = 48). The goal of both interventions was to achieve 5–6 kg of weight loss by following a calorie-restricted diet or an intensive exercise programme combined with only a small caloric restriction. Primary outcomes after 16 weeks were serum sex hormones and sex hormone-binding globulin (SHBG). Body fat and lean mass were measured by dual-energy X-ray absorptiometry.

Results

Both the diet (−4.9 kg) and mainly exercise (−5.5 kg) groups achieved the target weight loss. Loss of body fat was significantly greater with exercise versus diet (difference −1.4 kg, P < 0.001). In the mainly exercise arm, the reduction in free testosterone was statistically significantly greater than that of the diet arm (treatment effect ratio [TER] 0.92, P = 0.043), and the results were suggestive of a difference for androstenedione (TER 0.90, P = 0.064) and SHBG (TER 1.05, P = 0.070). Compared with the control arm, beneficial effects were seen with both interventions, diet and mainly exercise, respectively, on oestradiol (TER 0.86, P = 0.025; TER 0.83, P = 0.007), free oestradiol (TER 0.80, P = 0.002; TER 0.77, P < 0.001), SHBG (TER 1.14; TER 1.21, both P < 0.001) and free testosterone (TER 0.91, P = 0.069; TER = 0.84, P = 0.001). After adjustment for changes in body fat, intervention effects attenuated or disappeared.

Conclusions

Weight loss with both interventions resulted in favourable effects on serum sex hormones, which have been shown to be associated with a decrease in postmenopausal breast cancer risk. Weight loss induced mainly by exercise additionally resulted in maintenance of lean mass, greater fitness, greater fat loss and a larger effect on (some) sex hormones. The greater fat loss likely explains the observed larger effects on sex hormones.

Trial registration

ClinicalTrials.gov identifier: NCT01511276. Registered on 12 January 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0633-9) contains supplementary material, which is available to authorized users.

Advances in the Science, Treatment, and Prevention of the Disease of Obesity: Reflections From a Diabetes Care Editors' Expert Forum

As obesity rates increase, so too do the risks of type 2 diabetes, cardiovascular disease, and numerous other detrimental conditions. The prevalence of obesity in U.S. adults more than doubled between 1980 and 2010, from 15.0 to 36.1%. Although this trend may be leveling off, obesity and its individual, societal, and economic costs remain of grave concern. In June 2014, a Diabetes Care Editors' Expert Forum convened to review the state of obesity research and discuss the latest prevention initiatives and behavioral, medical, and surgical therapies. This article, an outgrowth of the forum, offers an expansive view of the obesity epidemic, beginning with a discussion of its root causes. Recent insights into the genetic and physiological factors that influence body weight are reviewed, as are the pathophysiology of obesity-related metabolic dysfunction and the concept of metabolically healthy obesity. The authors address the crucial question of how much weight loss is necessary to yield meaningful benefits. They describe the challenges of behavioral modification and predictors of its success. The effects of diabetes pharmacotherapies on body weight are reviewed, including potential weight-neutral combination therapies. The authors also summarize the evidence for safety and efficacy of pharmacotherapeutic and surgical obesity treatments. The article concludes with an impassioned call for researchers, clinicians, governmental agencies, health policymakers, and health-related industries to collectively embrace the urgent mandate to improve prevention and treatment and for society at large to acknowledge and manage obesity as a serious disease.

Pioglitazone is an effective treatment for patients with post-stroke depression combined with type 2 diabetes mellitus

The antidepressive effects of the antidiabetic medicine, pioglitazone, were recently reported in several studies. These effects may ameliorate the depressive symptoms of patients with post-stroke depression (PSD). The present study aimed to evaluate the antidepressive effect of pioglitazone in patients with PSD combined with type 2 diabetes. A total of 118 consecutive patients with stroke who had depression were studied for an average of 3 months. The Diagnostic and Statistical Manual of Mental Disorders (fourth edition) was used to assess whether a patient was depressed or not. The severity of depression was evaluated by the Hamilton depression rating scale (HAMD). In accordance with their HAMD scores, the 118 patients were divided into a severe depression group (n=40) and a mild and moderate (MM) depression group (n=78). These subjects were then divided into pioglitazone [30 mg once daily (qd)] and metformin (0.5 g twice daily) subgroups. All patients were given fluoxetine (20 mg qd). Follow-up evaluations, which included HAMD scores, activities of daily living (ADL) scores, fasting blood glucose (FBG) levels and fasting insulin (FINS) levels, were conducted on the first and third month following the beginning of the treatment. In the MM depression group, the HAMD score in the pioglitazone subgroup was lower than that in the metformin subgroup following treatment for 1 or 3 months. In the severe depression group, the HAMD score in the pioglitazone subgroup was lower than that in the metformin subgroup following 3 months of treatment. The FINS levels of the pioglitazone subgroup gradually decreased in the 3 months of treatment. No noticeable improvement was observed in the ADL scores and FBG values. In conclusion, the results of the current study demonstrate that pioglitazone effectively decreased HAMD scores and FINS values in patients with PSD, suggesting that pioglitazone may be useful for the treatment of patients with PSD combined with type 2 diabetes.

Obesity, fat distribution, and risk of frailty in two population-based cohorts of older adults in Spain

OBJECTIVE

To evaluate for the first time the longitudinal relationship between abdominal obesity and the onset of frailty.

METHODS

Study based on results from two population-based cohorts, the Seniors-ENRICA, with 1801 individuals aged ≥60, and the Toledo Study for Healthy Ageing (TSHA), with 1289 participants ≥65 years. Incident frailty was assessed with the Fried criteria.

RESULTS

During 3.5 years of follow-up, 125 individuals with incident frailty in Seniors-ENRICA and 162 in TSHA were identified. After adjustment for the main confounders, the pooled odds ratio (pooled OR) for general obesity and risk of frailty was 1.73 (95% confidence interval [CI]: 1.18-2.28). Abdominal obesity was also associated with frailty (pooled OR: 1.67; 95% CI: 1.09-2.25). Compared with individuals with BMI <25 kg/m(2) and no abdominal obesity, the risk of frailty was highest among individuals with concurrent general and abdominal obesity (pooled OR: 2.55; 95% CI: 1.23-3.86). General obesity was associated with increased risk of exhaustion (pooled OR: 1.66; 95% CI: 1.11-2.21), low physical activity (pooled OR: 1.57; 95% CI: 1.08-2.05), and weakness (pooled OR: 1.63; 95% CI: 1.12-2.05). For abdominal obesity, results were in the same direction, although they showed statistical significance only for weakness (OR: 1.46; 95% CI: 1.11-1.80).

CONCLUSIONS

General and abdominal obesity are associated with incident frailty in the elderly.

Visceral obesity is associated with increased soluble CD163 concentration in men with type 2 diabetes mellitus

Monocyte/macrophage-specific soluble CD163 (sCD163) concentration is associated with insulin resistance and increases with deteriorating glycemic control independently of BMI. This led to the proposal of the hypothesis that obesity-associated white adipose tissue inflammation varies between individuals. The objective was to examine the effect of male overweight/obesity and type 2 diabetes mellitus (T2DM) on associations between adiposity parameters and sCD163. A total of 23 overweight/obese non-diabetic men, 16 overweight/obese men with T2DM, and a control group of 20 normal-weight healthy men were included. Body composition and regional body fat distribution were determined by whole-body dual X-ray absorptiometry scan and abdominal computed tomography (CT) scan. Serum sCD163 concentrations were determined by ELISA. Associations between adiposity parameters and sCD163 were investigated using multiple linear regression analysis. In the normal-weight healthy men, there was no significant association between adiposity parameters and sCD163, whereas in the overweight/obese non-diabetic men, measures of general and regional adiposity were positively associated with sCD163. In the overweight/obese men with T2DM, only visceral adipose tissue (VAT) and the ratio of VAT to abdominal subcutaneous adipose tissue (SAT), a measure of relative body fat distribution between VAT and SAT depots, were positively associated with sCD163. In a multivariate analysis, including VAT, upper-body SAT, and lower-body fat, adjusted for BMI and age, VAT remained a significant predictor of sCD163 in the overweight/obese T2DM men, but not in the overweight/obese non-diabetic men. Our results indicate that VAT inflammation is exaggerated in men with T2DM, and that propensity to store excess body fat viscerally is particularly detrimental in men with T2DM.

Low Visceral Fat Content is Associated with Poor Prognosis in a Database of 507 Upper Gastrointestinal Cancers

BACKGROUND

Excess visceral adipose tissue may promote cancer development and progression via an obesity-related metabolic derangements, including adipocytokine-related inflammation, insulin resistance, and hypoxia. The relationship between visceral fat content and patient prognosis has been reported in some types of cancers, but not in the upper gastrointestinal cancer. The purpose of this retrospective study was to investigate the relationship between visceral fat status and clinical outcome in patients with upper gastrointestinal cancers (esophageal cancer and gastric cancer) treated by surgical resection.

METHODS

This retrospective study was conducted in a single, academic hospital in Kumamoto, Japan, and involved 507 patients with upper gastrointestinal cancers between April 2005 and December 2010. Preoperative visceral fat content was quantified by radiologic measures using standard computed tomography scans.

RESULTS

Higher visceral fat mount was correlated with male sex, presence of preoperative comorbidity, absence of preoperative therapy, low tumor depth, low tumor stage, and gastric cancer. Compared to high visceral fat cases, low visceral fat cases experienced a higher overall mortality rate [log-rank p = 0.0050; univariate hazard ratio (HR) = 1.73, 95 % confidence interval (CI) 1.16-2.54; p = 0.0075; multivariate HR 1.57; 95 % CI 1.02-2.37; p = 0.031]. Interestingly, the influence of low visceral fat on patient outcome was modified by age at surgery (p for interaction = 0.036); low visceral fat was associated with a poor prognosis, especially in elderly patients (log-rank p < 0.0001).

CONCLUSION

Visceral fat content in the upper gastrointestinal cancers was associated with a poor prognosis, thus suggesting that it has potential for use as a prognostic biomarker.

Reproducibility and validity of ultrasound for the measurement of visceral and subcutaneous adipose tissues

BACKGROUND

Ultrasound represents a low-cost and widely available field method for assessing visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) but its measurement properties are uncertain. The aim of the current study was to examine the reproducibility and validity of ultrasound to quantify abdominal fat compartments.

METHODS

In two study centers, VAT and SAT thicknesses were quantified by ultrasound two times by two observers each among 127 adults aged 20-70 years. In a separate sample of 30 adults, the ultrasound method was validated by comparing VAT and SAT thicknesses with VAT and SAT areas at vertebrae L2/L3 as obtained by a single magnetic resonance imaging (MRI) slice.

RESULTS

For VAT, the intra-rater reproducibility values for observers 1 and 2 were r=0.996 (95% CI=0.994-0.997) and r=0.999 (95% CI=0.999-0.999), respectively. For SAT, the intra-rater reproducibility values were r=0.992 (95% CI=0.989-0.994) and r=0.993 (95% CI=0.990-0.995), respectively. The inter-rater reproducibility values for VAT and SAT were r=0.998 (95% CI=0.997-0.999) and r=0.990 (95% CI=0.986-0.993), respectively. For VAT and SAT, the correlation coefficients between ultrasound and MRI measurements were r=0.898 (P<0.001) and r=0.705 (P<0.001), respectively.

CONCLUSION

Ultrasound provides reproducible and valid estimates of VAT and SAT and represents a useful method to assess abdominal fat in large scale epidemiologic studies.

Visceral fat accumulation is associated with colorectal cancer in postmenopausal women

Background

Obesity is a known risk factor for colorectal cancer (CRC), and emerging data suggest that this association is mediated by visceral fat rather than total body fat. However, there is a lack of studies evaluating the association between visceral fat area and the prevalence of CRC.

Methods

To investigate the relationship between visceral adiposity and prevalence of CRC, data of 497 women diagnosed with CRC and 318 apparently healthy women were analysed and data of well-balanced 191 pairs of women with CRC and healthy women matched based on propensity scores were additionally analysed. Diagnosis of CRC was confirmed by colonoscopy and histology. Metabolic parameters were assessed, along with body composition, using computed tomography.

Results

The median visceral fat area was significantly higher in the CRC group compared with the control group before and after matching. The prevalence of CRC increased significantly with increasing visceral fat tertiles after matching (p for trend <0.01). A multivariate analysis showed that mean visceral fat area of individuals in the 67^th percentile or greater group was associated with an increased prevalence of CRC (adjusted odds ratio: 1.80; 95% confidence interval: 1.12–2.91 before matching and adjusted odds ratio: 2.96; 95% confidence interval: 1.38–6.33) compared with that of individuals in the 33^th percentile or lower group.

Conclusion

Thus, we conclude that visceral fat area is positively associated with the prevalence of CRC. Although we could not determine the causality, visceral adiposity may be associated with the risk of CRC. Further prospective studies are required to determine the benefits of controlling visceral obesity for reducing CRC risk.

Thin-fat insulin-resistant phenotype also present in South Asian neonates born in the Netherlands

Several studies have shown that South Asian neonates have a characteristic thin-fat insulin-resistant phenotype. The aim of our study was to determine whether this phenotype is also present in South Asians who have migrated to a Western country (the Netherlands). South Asian and white Dutch pregnant women were included in our study. After delivery, cord blood was collected and neonatal anthropometry was measured within 72 h. Compared with white Dutch mothers, South Asian mothers were younger (28.5 v. 32.2 years, P<0.001) and had a higher prepregnancy body mass index (25.1 v. 23.0, P=0.001). Gestational age at delivery was on average 4 days shorter in South Asians (274.9 v. 278.8, P=0.001). To compare the two groups of neonates, we calculated sex- and gestation-specific s.d. scores using the values for mean and s.d. obtained from the white Dutch subjects as a reference. All measurements were smaller in South Asian neonates, except for those of the skinfolds. The largest difference was found in abdominal circumference (s.d. score 1.39, 95% CI -1.76 to -1.01). Triceps and subscapular skinfolds were similar in both groups (triceps s.d. score -0.34, 95% CI -0.88 to +0.20 and subscapular s.d. score -0.03, 95% CI -0.31 to +0.25). South Asian neonates had higher cord plasma levels of triglycerides (0.40 v. 0.36, P=0.614), glucose (5.4 v. 4.8, P=0.079) and insulin (6.3 v. 4.0, P=0.051). However, these differences were not statistically significant. After adjustment for birth weight, the difference in insulin became statistically significant (P=0.001). We therefore conclude that the thin-fat insulin-resistant phenotype is also present in South Asian neonates in the Netherlands.

Effect of exercise on insulin sensitivity in healthy postmenopausal women: the SHAPE study

BACKGROUND

An inactive lifestyle is a risk factor for several types of cancer. A proposed pathway through which exercise influences cancer risk is via insulin. We aim to investigate the effect of a one-year exercise intervention on insulin sensitivity, and the role of body fat in this association, in healthy, normal to overweight/obese, postmenopausal women.

METHODS

In the Sex Hormones And Physical Exercise (SHAPE) study, 189 healthy, inactive and postmenopausal women [ages, 50-69 years; body mass index (BMI), 22-40 kg/m(2)] were randomly assigned to a one-year aerobic and strength exercise intervention (150 min/wk), or a control group. Between-group differences in fasting insulin, glucose, and homeostatic model assessment of insulin resistance (HOMA2) over time were estimated using linear mixed models.

RESULTS

Follow-up measurements of insulin sensitivity were available for 181 (95.8%) and 182 (96.3%) women at 4 and 12 months, respectively. The intention-to-treat analysis showed no significant differences between the two study groups [treatment effect ratio of the exercise group vs. control (β; 95% confidence interval): insulin, β, 1.07 (0.96-1.19); glucose, β, 1.01 (0.99-1.02); and HOMA2, β, 1.07 (0.96-1.20)]. Similar results were found in a per protocol analysis in compliant women, and in a subgroup of women who lost >2% body fat [measured by dual-energy X-ray absorptiometry (DEXA)].

CONCLUSIONS

Participation in a one-year aerobic and strength exercise intervention program did not result in changes in insulin sensitivity in healthy postmenopausal and inactive women.

IMPACT

Our findings suggest that 150 min/wk of exercise, as recommended by current guidelines, is not enough to achieve improvements in insulin sensitivity and subsequent cancer risk, in healthy postmenopausal women.

Autophagy and non-alcoholic fatty liver disease

Autophagy, or cellular self-digestion, is a catabolic process that targets cell constituents including damaged organelles, unfolded proteins, and intracellular pathogens to lysosomes for degradation. Autophagy is crucial for development, differentiation, survival, and homeostasis. Important links between the regulation of autophagy and liver complications associated with obesity, non-alcoholic fatty liver disease (NAFLD), have been reported. The spectrum of these hepatic abnormalities extends from isolated steatosis to non-alcoholic steatohepatitis (NASH), steatofibrosis, which sometimes leads to cirrhosis, and hepatocellular carcinoma. NAFLD is one of the three main causes of cirrhosis and increases the risk of liver-related death and hepatocellular carcinoma. The pathophysiological mechanisms of the progression of a normal liver to steatosis and then more severe disease are complex and still unclear. The regulation of the autophagic flux, a dynamic response, and the knowledge of the role of autophagy in specific cells including hepatocytes, hepatic stellate cells, immune cells, and hepatic cancer cells have been extensively studied these last years. This review will provide insight into the current understanding of autophagy and its role in the evolution of the hepatic complications associated with obesity, from steatosis to hepatocellular carcinoma.

Altered DNA methylation and differential expression of genes influencing metabolism and inflammation in adipose tissue from subjects with type 2 diabetes

Genetics, epigenetics, and environment may together affect the susceptibility for type 2 diabetes (T2D). Our aim was to dissect molecular mechanisms underlying T2D using genome-wide expression and DNA methylation data in adipose tissue from monozygotic twin pairs discordant for T2D and independent case-control cohorts. In adipose tissue from diabetic twins, we found decreased expression of genes involved in oxidative phosphorylation; carbohydrate, amino acid, and lipid metabolism; and increased expression of genes involved in inflammation and glycan degradation. The most differentially expressed genes included ELOVL6, GYS2, FADS1, SPP1 (OPN), CCL18, and IL1RN. We replicated these results in adipose tissue from an independent case-control cohort. Several candidate genes for obesity and T2D (e.g., IRS1 and VEGFA) were differentially expressed in discordant twins. We found a heritable contribution to the genome-wide DNA methylation variability in twins. Differences in methylation between monozygotic twin pairs discordant for T2D were subsequently modest. However, 15,627 sites, representing 7,046 genes including PPARG, KCNQ1, TCF7L2, and IRS1, showed differential DNA methylation in adipose tissue from unrelated subjects with T2D compared with control subjects. A total of 1,410 of these sites also showed differential DNA methylation in the twins discordant for T2D. For the differentially methylated sites, the heritability estimate was 0.28. We also identified copy number variants (CNVs) in monozygotic twin pairs discordant for T2D. Taken together, subjects with T2D exhibit multiple transcriptional and epigenetic changes in adipose tissue relevant to the development of the disease.

Differential association of insulin resistance with cognitive and somatic symptoms of depression

AIM

To examine the associations of depressive symptoms with insulin resistance, evaluating somatic and cognitive depressive symptoms separately.

METHODS

A total of 328 individuals (mean age 60 years) referred for exercise stress testing, taking part in the Mechanisms and Outcomes of Silent Myocardial Ischemia study, completed the Beck Depression Inventory II. A fasting venous blood sample was collected for assessments of insulin and glucose level; the HOMA-IR (homeostatic model assessment of insulin resistance) was calculated. In principal component analysis, Beck Depression Inventory II items were forced to load onto two components (somatic and cognitive depressive symptoms). Adjusting for age, sex, BMI, medication use, smoking, physical activity, diabetes and cardiovascular disease, general linear model analyses were conducted to examine the associations between the components and log HOMA-IR .

RESULTS

Principal component analysis showed that nine items loaded onto a cognitive depressive symptoms component and 10 items loaded onto a somatic depressive symptoms component. When examined separately, both components were significantly associated with log HOMA-IR however, when including both components simultaneously in the model, only somatic depressive symptoms remained significantly associated with log HOMA-IR. Back-transformed, a one-unit change in somatic depressive symptoms was associated with a 1.07 (95% CI 1.002, 1.14) change in HOMA-IR and a one-unit change in cognitive depressive symptoms was associated with a 1.03 (95% CI 0.97, 1.14) change in HOMA-IR.

CONCLUSION

Somatic depressive symptoms seem to be more strongly associated with insulin resistance than do cognitive depressive symptoms. Monitoring somatic depressive symptoms may be more appropriate than monitoring cognitive depressive symptoms among depressed individuals with high insulin resistance.

The association between hematological parameters and insulin resistance is modified by body mass index - results from the North-East Italy MoMa population study

Objective

Increments in red blood cell count (RBC), hemoglobin (Hb) and hematocrit (Ht) levels are reportedly associated with higher insulin resistance (IR). Obesity may cause IR, but underlying factors remain incompletely defined, and interactions between obesity, hematological parameters and IR are incompletely understood. We therefore determined whether: 1) BMI and obesity per se are independently associated with higher RBC, hemoglobin and hematocrit; 2) hematological parameters independently predict insulin resistance in obese individuals.

Design and Methods

We investigated the associations between BMI, hematological parameters and insulin resistance as reflected by homeostasis model assessment (HOMA) in a general population cohort from the North-East Italy MoMa epidemiological study (M/F = 865/971, age = 49±1).

Results

In all subjects, age-, sex- and smoking-adjusted hematological parameters were positively associated with BMI in linear regression (P<0.05), but not after adjustment for HOMA or waist circumference (WC) and potential metabolic confounders. No associations were found between hematological parameters and BMI in lean, overweight or obese subgroups. Associations between hematological parameters and HOMA were conversely independent of BMI in all subjects and in lean and overweight subgroups (P<0.01), but not in obese subjects alone.

Conclusions

In a North-East Italy general population cohort, obesity per se is not independently associated with altered RBC, Hb and Ht, and the association between BMI and hematological parameters is mediated by their associations with abdominal fat and insulin resistance markers. High hematological parameters could contribute to identify insulin resistance in non-obese individual, but they do not appear to be reliable insulin resistance biomarkers in obese subjects.

Dissecting adipose tissue lipolysis: molecular regulation and implications for metabolic disease

Lipolysis is the process by which triglycerides (TGs) are hydrolyzed to free fatty acids (FFAs) and glycerol. In adipocytes, this is achieved by sequential action of adipose TG lipase (ATGL), hormone-sensitive lipase (HSL), and monoglyceride lipase. The activity in the lipolytic pathway is tightly regulated by hormonal and nutritional factors. Under conditions of negative energy balance such as fasting and exercise, stimulation of lipolysis results in a profound increase in FFA release from adipose tissue (AT). This response is crucial in order to provide the organism with a sufficient supply of substrate for oxidative metabolism. However, failure to efficiently suppress lipolysis when FFA demands are low can have serious metabolic consequences and is believed to be a key mechanism in the development of type 2 diabetes in obesity. As the discovery of ATGL in 2004, substantial progress has been made in the delineation of the remarkable complexity of the regulatory network controlling adipocyte lipolysis. Notably, regulatory mechanisms have been identified on multiple levels of the lipolytic pathway, including gene transcription and translation, post-translational modifications, intracellular localization, protein-protein interactions, and protein stability/degradation. Here, we provide an overview of the recent advances in the field of AT lipolysis with particular focus on the molecular regulation of the two main lipases, ATGL and HSL, and the intracellular and extracellular signals affecting their activity.

MitoNEET-mediated effects on browning of white adipose tissue

MitoNEET is an outer mitochondrial membrane protein that, upon overexpression in white adipose tissue (WAT), exerts a positive impact on tissue expansion and whole-body lipid and carbohydrate homeostasis by altering mitochondrial matrix iron metabolism. Here we determine the key transcriptional events in subcutaneous WAT of mice in response to mitoNEET overexpression and a high-fat diet (HFD). Microarray analyses at key points during weight gain upon body-weight divergence with wild-type mice demonstrate that mitoNEET-enriched sWAT early on upregulates a browning signature program that limits WAT expansion in transgenic mice for a period of up to 12-weeks of HFD. This compensatory browning phenotype is subsequently lost, resulting in rapid WAT expansion and body-weight gain. Exposure to thermoneutral temperatures during HFD prompts weight gain significantly earlier. Similar WAT expansion is achieved upon infection with an adeno-associated virus expressing mitoNEET. Collectively, the mitoNEET enriched fat-pads feature a more vascularized, anti-inflammatory and less fibrotic environment.

Prevalence, trends and risk factors for the diabetes epidemic in China: a systematic review and meta-analysis

AIMS

To describe the prevalence and trends of diabetes and to quantitatively assess its risk factors in mainland China.

METHODS

Thirty-one epidemiological studies were identified by a systematic search of four databases. Prevalence estimates were mapped and summarized by meta-analysis in each region of China. The pooled ORs and 95% CIs of risk factors for diabetes were also calculated.

RESULTS

There was a large geographical imbalance with regard to the prevalence of diabetes. Region-pooled prevalence was highest in the eastern region (8.0%, 95% CI: 6.1-10.0%) and lowest in the western region (4.6%, 95% CI: 3.3-6.0%), which was consistent with regional levels of economic development. The overall prevalence of diabetes has been increasing since 1980. Traditional risk factors such as age, family history of diabetes, obesity, hypertension and elevated triglycerides were found to be associated with diabetes. In addition, urban residence and being from ethnic minorities were also significantly associated.

CONCLUSION

Based on the meta-analyses, we found that the prevalence of diabetes is different in different parts of China but it has been increasing sharply during the last three decades. Some risk factors were quantitatively derived in the study, which are free from the diversity of a single sample.

Relationship of thyroid hormone levels and cardiovascular events in patients with type 2 diabetes

Alterations in thyroid hormone levels are found associated with inflammation in patients with non-thyroidal illness (NTIS) and are common in patients with type 2 diabetes mellitus (T2DM). Inflammation has also been linked with development of cardiovascular events (CVE) in T2DM. Our objective was to assess whether thyroid hormone abnormalities typical of NTIS in patients with T2DM are related to inflammation and CVE. This was a cross-sectional study of 140 subjects; 70 with T2DM and 70 as a control group paired by age, sex and body mass index (BMI). We recorded age, sex, BMI, waist/hip ratio, diabetes duration, HbA1c, CVE history, serum amyloid A (SAA), TSH, total (T) and free (F) T4 and T3, reverse T3 (rT3) and TT3/rT3 ratio. Patients with T2DM had lower levels of TT4 (p = 0.012), TT3 (p < 0.001), FT3 (p < 0.001) and TT3/rT3 (p = 0.002). They also showed higher FT4 (p < 0.001) and similar TSH levels (p = 0.627) compared to the control group. SAA levels correlated positively with rT3 (r = 0.45; p < 0.001) and inversely with TT3/rT3 (r = -0.38; p = 0.001). Patients with T2DM and history of CVE had higher rT3 (p = 0.006) and lower TT3/rT3 (p = 0.002), along with higher SAA levels (p = 0.002) than patients without this characteristic. Multiple logistic regression showed that factors independently associated with CVE were older age (OR = 1.159, 95 % CI 1.011-1.329), male sex (OR = 4.391, 95 % CI 1.081-17.829) and higher TT3/rT3 (OR = 0.993, 95 % CI 0.987-0.999). We have confirmed the presence of NTIS in T2DM. We also showed that thyroid hormone abnormalities are associated to inflammatory activity and to CVE in these patients.

Leucine supplementation protects from insulin resistance by regulating adiposity levels

Background

Leucine supplementation might have therapeutic potential in preventing diet-induced obesity and improving insulin sensitivity. However, the underlying mechanisms are at present unclear. Additionally, it is unclear whether leucine supplementation might be equally efficacious once obesity has developed.

Methodology/Principal Findings

Male C57BL/6J mice were fed chow or a high-fat diet (HFD), supplemented or not with leucine for 17 weeks. Another group of HFD-fed mice (HFD-pairfat group) was food restricted in order to reach an adiposity level comparable to that of HFD-Leu mice. Finally, a third group of mice was exposed to HFD for 12 weeks before being chronically supplemented with leucine. Leucine supplementation in HFD-fed mice decreased body weight and fat mass by increasing energy expenditure, fatty acid oxidation and locomotor activity in vivo. The decreased adiposity in HFD-Leu mice was associated with increased expression of uncoupling protein 3 (UCP-3) in the brown adipose tissue, better insulin sensitivity, increased intestinal gluconeogenesis and preservation of islets of Langerhans histomorphology and function. HFD-pairfat mice had a comparable improvement in insulin sensitivity, without changes in islets physiology or intestinal gluconeogenesis. Remarkably, both HFD-Leu and HFD-pairfat mice had decreased hepatic lipid content, which likely helped improve insulin sensitivity. In contrast, when leucine was supplemented to already obese animals, no changes in body weight, body composition or glucose metabolism were observed.

Conclusions/Significance

These findings suggest that leucine improves insulin sensitivity in HFD-fed mice by primarily decreasing adiposity, rather than directly acting on peripheral target organs. However, beneficial effects of leucine on intestinal gluconeogenesis and islets of Langerhans's physiology might help prevent type 2 diabetes development. Differently, metabolic benefit of leucine supplementation is lacking in already obese animals, a phenomenon possibly related to the extent of the obesity before starting the supplementation.

Adipose tissue dysfunction and the pathogenesis of metabolic syndrome

Metabolic syndrome is a growing research area. The underlying mechanisms of metabolic syndrome are still not very clear. Insulin resistance, obesity, inflammation and oxidative stress may play an important role in the pathogenesis of metabolic syndrome. The role of adipose tissue dysfunction is emphasized during the development of obesity. Adipose tissue is identified as a complex endocrine organ and its metabolic functions extend well beyond the classical actions of thermoregulation and of storage and release of fatty acids. Chronic low-grade inflammation activated by the immune system in adipose tissue is a key contributing factor to type 2 diabetes mellitus and cardiovascular diseases. Visceral obesity results in cell autonomous impairment in insulin signaling that leads to insulin resistance. Chronic inflammation in adipose tissue has gained acceptance as a lead promoter of insulin resistance in obesity. Furthermore, obesity creates oxidative stress conditions in adipose tissue that not only correlates with insulin resistance but is also causative in its development. Oxidative stress may be a mechanistic link between several components of metabolic syndrome and cardiovascular diseases, through its role in inflammation and its ability to disrupt insulin-signaling. The study around adipose tissue dysfunction will help to understand the pathogenesis of metabolic syndrome and may bring effective therapy in treatment of metabolic syndrome related diseases. Therefore, this review mainly focuses on the roles of adipose tissue dysfunction in inflammation, insulin resistance, and oxidative stress in the pathogenesis of metabolic syndrome.

Loss of Krüppel-like factor 3 (KLF3/BKLF) leads to upregulation of the insulin-sensitizing factor adipolin (FAM132A/CTRP12/C1qdc2)

Krüppel-like factor 3 (KLF3) is a transcriptional regulator that we have shown to be involved in the regulation of adipogenesis in vitro. Here, we report that KLF3-null mice are lean and protected from diet-induced obesity and glucose intolerance. On a chow diet, plasma levels of leptin are decreased, and adiponectin is increased. Despite significant reductions in body weight and adiposity, wild-type and knockout animals show equivalent energy intake, expenditure, and excretion. To investigate the molecular events underlying these observations, we used microarray analysis to compare gene expression in Klf3(+/+) and Klf3(-/-) tissues. We found that mRNA expression of Fam132a, which encodes a newly identified insulin-sensitizing adipokine, adipolin, is significantly upregulated in the absence of KLF3. We confirmed that KLF3 binds the Fam132a promoter in vitro and in vivo and that this leads to repression of promoter activity. Further, plasma adipolin levels were significantly increased in Klf3(-/-) mice compared with wild-type littermates. Boosting levels of adipolin via targeting of KLF3 offers a novel potential therapeutic strategy for the treatment of insulin resistance.

The presentation of metabolic dysfunction and the relationship with energy output in breast cancer survivors: a cross-sectional study

Background

Breast cancer prognosis can be adversely influenced by obesity, physical inactivity and metabolic dysfunction. Interventions aimed at improving surrogate markers of breast cancer risk such as insulin resistance may result in improved breast cancer outcomes. The design of such interventions may be improved through increased understanding of metabolic presentation in this cohort. This cross-sectional study aimed to characterise the metabolic profile of breast cancer survivors relative to abdominal obesity and insulin resistance. A secondary aim was to compare measures of energy output across these groups.

Methods

Sixty-nine women (mean (SD) age 53.43 (9.39) years) who had completed adjuvant chemotherapy and radiotherapy for breast cancer were recruited. All measures were completed during one assessment conducted 3.1 (1.0) years post diagnosis. Body composition was measured by bioimpedance analysis and waist circumference (WC). Fasting (12 hour) blood samples were drawn to measure lipid profile, glucose, insulin, glycosylated haemoglobin A1c (HBA1c) and C-reactive protein (CRP). Insulin resistance was estimated by the homeostatic model assessment index (HOMA-IR)). Energy output was evaluated by resting metabolic rate (RMR) measured by indirect calorimetry and physical activity measured by accelerometry. Characteristics were compared across four groups (1. WC <80 cm, not insulin resistant; 2. WC 80–87.9 cm, not insulin resistant; 3. WC >88 cm, not insulin resistant; 4. WC >80 cm, insulin resistant) using ANOVA (p < 0.05).

Results

Group 4 was characterised by significant disturbances in measures of glucose metabolism (glucose, insulin, HOMA-IR and HBA1c) and raised CRP compared to other groups. Group 4 also displayed evidence of dyslipidemia and higher body composition values compared to Groups 1 and 2. Both absolute and adjusted RMR were significantly higher in the Group 4 versus all other groups. Physical activity levels were similar for all groups.

Conclusions

The results from this study suggest that participants who were both centrally obese and insulin resistant showed evidence of dyslipidemia, low-grade inflammation and glucose dysregulation. Metabolic profiles of participants who were centrally obese only were not significantly different from lean participants. Consideration of baseline metabolic presentation may be useful when considering the therapeutic targets for future interventions in this cohort.

Obese adipocytes show ultrastructural features of stressed cells and die of pyroptosis

We previously suggested that, in obese animals and humans, white adipose tissue inflammation results from the death of hypertrophic adipocytes; these are then cleared by macrophages, giving rise to distinctive structures we denominated crown-like structures. Here we present evidence that subcutaneous and visceral hypertrophic adipocytes of leptin-deficient (ob/ob and db/db) obese mice exhibit ultrastructural abnormalities (including calcium accumulation and cholesterol crystals), many of which are more common in hyperglycemic db/db versus normoglycemic ob/ob mice and in visceral versus subcutaneous depots. Degenerating adipocytes whose intracellular content disperses in the extracellular space were also noted in obese mice; in addition, increased anti-reactive oxygen species enzyme expression in obese fat pads, documented by RT-PCR and immunohistochemistry, suggests that ultrastructural changes are accompanied by oxidative stress. RT-PCR showed NLRP3 inflammasome activation in the fat pads of both leptin-deficient and high-fat diet obese mice, in which formation of active caspase-1 was documented by immunohistochemistry in the cytoplasm of several hypertrophic adipocytes. Notably, caspase-1 was not detected in FAT-ATTAC transgenic mice, where adipocytes die of apoptosis. Thus, white adipocyte overexpansion induces a stress state that ultimately leads to death. NLRP3-dependent caspase-1 activation in hypertrophic adipocytes likely induces obese adipocyte death by pyroptosis, a proinflammatory programmed cell death.

New insights into pancreatic cancer-induced paraneoplastic diabetes

Up to 85% of patients with pancreatic cancer have diabetes or hyperglycaemia, which frequently manifests as early as 2-3 years before a diagnosis of pancreatic cancer. Conversely, patients with new-onset diabetes have a 5-8-fold increased risk of being diagnosed with pancreatic cancer within 1-3 years of developing diabetes. Emerging evidence now indicates that pancreatic cancer causes diabetes. As in type 2 diabetes, β-cell dysfunction and peripheral insulin resistance are seen in pancreatic cancer-induced diabetes. However, unlike in patients with type 2 diabetes, glucose control worsens in patients with pancreatic cancer in the face of ongoing, often profound, weight loss. Diabetes and weight loss, which precede cachexia onset by several months, are paraneoplastic phenomena induced by pancreatic cancer. Although the pathogenesis of these pancreatic cancer-induced metabolic alterations is only beginning to be understood, these are likely mechanisms to promote the survival and growth of pancreatic cancer in a hostile and highly desmoplastic microenvironment. Interestingly, these metabolic changes could enable early diagnosis of pancreatic cancer, if they can be distinguished from the ones that occur in patients with type 2 diabetes. One such possible biomarker is adrenomedullin, which is a potential mediator of β-cell dysfunction in pancreatic cancer-induced diabetes.

Adipose tissue angiogenesis: impact on obesity and type-2 diabetes

The growth and function of tissues are critically dependent on their vascularization. Adipose tissue is capable of expanding many-fold during adulthood, therefore requiring the formation of new vasculature to supply growing and proliferating adipocytes. The expansion of the vasculature in adipose tissue occurs through angiogenesis, where new blood vessels develop from those pre-existing within the tissue. Inappropriate angiogenesis may underlie adipose tissue dysfunction in obesity, which in turn increases type-2 diabetes risk. In addition, genetic and developmental factors involved in vascular patterning may define the size and expandability of diverse adipose tissue depots, which are also associated with type-2 diabetes risk. Moreover, the adipose tissue vasculature appears to be the niche for pre-adipocyte precursors, and factors that affect angiogenesis may directly impact the generation of new adipocytes. Here we review recent advances on the basic mechanisms of angiogenesis, and on the role of angiogenesis in adipose tissue development and obesity. A substantial amount of data points to a deficit in adipose tissue angiogenesis as a contributing factor to insulin resistance and metabolic disease in obesity. These emerging findings support the concept of the adipose tissue vasculature as a source of new targets for metabolic disease therapies. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Adipose tissue remodeling in rats exhibiting fructose-induced obesity

PURPOSE

To explore the effect of a fructose-rich diet on morphological and functional changes in white adipose tissue (WAT) that could contribute to the development of insulin resistance.

METHODS

Adult sedentary rats were fed a fructose-rich diet for 8 weeks. Glucose tolerance test was carried out together with measurement of plasma triglycerides, non-esterified fatty acids and lipid peroxidation. In subcutaneous abdominal and intra-abdominal WAT, number and size of adipocytes together with cellular insulin sensitivity and lipolytic activity were assessed.

RESULTS

Rats fed a fructose-rich diet exhibited a significant increase in plasma insulin, triglycerides, non-esterified fatty acids and lipid peroxidation, together with significantly increased body lipids and epididymal and mesenteric WAT, compared to controls. Mean adipocyte volume in subcutaneous abdominal WAT was significantly lower, while mean adipocyte volume in intra-abdominal WAT was significantly higher, in rats fed a fructose-rich diet compared to controls. A significant increase in larger adipocytes and a significant decrease in smaller adipocytes were found in intra-abdominal WAT in rats fed a fructose-rich diet compared to controls. Insulin's ability to inhibit lipolysis was blunted in subcutaneous abdominal and intra-abdominal adipocytes from fructose-fed rats. Accordingly, lower p-Akt/Akt ratio was found in WAT in rats fed a fructose-rich diet compared to controls.

CONCLUSIONS

Long-term consumption of high levels of fructose elicits remarkable morphological and functional modifications, particularly in intra-abdominal WAT, that are highly predictive of obesity and insulin resistance and that contribute to the worsening of metabolic alterations peculiar in a fructose-rich, hypolipidic diet.

Dietary fructose in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in adults and children. A number of genetic and environmental factors are known to predispose individuals to NAFLD. Certain dietary sugars, particularly fructose, are suspected to contribute to the development of NAFLD and its progression. The increasing quantity of fructose in the diet comes from sugar additives (most commonly sucrose and high fructose corn syrup) in beverages and processed foods. Substantial links have been demonstrated between increased fructose consumption and obesity, dyslipidemia, and insulin resistance. Growing evidence suggests that fructose contributes to the development and severity of NAFLD. In human studies, fructose is associated with increasing hepatic fat, inflammation, and possibly fibrosis. Whether fructose alone can cause NAFLD or if it serves only as a contributor when consumed excessively in the setting of insulin resistance, positive energy balance, and sedentary lifestyle is unknown. Sufficient evidence exists to support clinical recommendations that fructose intake be limited through decreasing foods and drinks high in added (fructose-containing) sugars.

Changes in mineral status are associated with improvements in insulin sensitivity in obese patients following L-arginine supplementation

PURPOSE

The aim of this study is to evaluate the long-term influence of L-arginine intake on mineral concentration in patients with obesity and to assess the changes in lipid serum levels, fat content, and insulin resistance that result.

METHODS

A randomized double-blind placebo-controlled study was conducted. 88 obese patients were randomly assigned to receive either 9 g of L-arginine or placebo daily, for 6 months. At baseline and after 6 months, selected anthropometrical measurements and blood biochemical analyses were performed and mineral levels were assessed. To assess insulin sensitivity, the gold-standard euglycemic clamp methodology was used.

RESULTS

We found that 6 months of L-arginine supplementation resulted in significant increases in insulin sensitivity (Δ1.1 mg/kg/min, P < 0.01) and zinc levels (Δ1.5 μmol/L, P < 0.001). Moreover, a positive correlation between the change in zinc concentration in serum and the change in insulin sensitivity was observed (R = 0.80, P < 0.01). In the group of patients treated with L-arginine, a negative correlation between the change in zinc concentration in serum and the change in body fat content was noted (R = -0.38, P < 0.05).

CONCLUSIONS

L-Arginine supplementation affects zinc status in obese patients. One beneficial influence is related to the improvements in insulin sensitivity.

Opioid μ-receptors as new target for insulin resistance

Type-2 diabetes is one of the fastest growing public health problems worldwide resulting from both environmental and genetic factors. Activation of μ-opioid receptor (MOR) could result in reversal of the impairment of insulin-stimulated glucose disposal in genetically obese Zucker rats via exercise training. This improvement of insulin resistance was associated with an elevation of circulating β-endorphin to ameliorate the post-receptor insulin signaling cascade, including downstream effectors of the phosphatidylinositol 3-kinase (PI3-kinase) signaling pathway. In insulin resistant rats, Loperamide treatment effected on the insulin receptor substrate (IRS)-1/PI3-kinase/Akt signaling cascade and subsequent insulin-stimulated glucose transport trafficking on skeletal muscle, which were all suppressed by MOR antagonism. In addition, induction of insulin resistance by the intake of high fructose is more rapid in MOR knockout mice than in wild-type mice. Improvements in insulin sensitivity through the peripheral MOR activation overcoming defects related to the post-receptor in IRS-1-associated PI3-kinase step have been defined. Opioid receptor activation, especially of the μ-subtype, may provide merits in the amelioration of defective insulin action. Atypical zeta (ζ) isoform of protein kinase C serves as a factor that integrates with peripheral MOR pathway and insulin signals for glucose utilization. The developments call new insights into the chemical compounds and/or herbal products that might enhance opioid peptide secretion and/or stimulate MOR in peripheral insulin-sensitive tissues to serve as potential agents or adjuvants for helping the glucose metabolism. In the present review, we update these topics and discuss the concept of targeting peripheral MOR pathway for the treatment of insulin resistance.

Adipose tissue plasticity from WAT to BAT and in between

Adipose tissue plays an essential role in regulating energy balance through its metabolic, cellular and endocrine functions. Adipose tissue has been historically classified into anabolic white adipose tissue and catabolic brown adipose tissue. An explosion of new data, however, points to the remarkable heterogeneity among the cells types that can become adipocytes, as well as the inherent metabolic plasticity of mature cells. These data indicate that targeting cellular and metabolic plasticity of adipose tissue might provide new avenues for treatment of obesity-related diseases. This review will discuss the developmental origins of adipose tissue, the cellular complexity of adipose tissues, and the identification of progenitors that contribute to adipogenesis throughout development. We will touch upon the pathological remodeling of adipose tissue and discuss how our understanding of adipose tissue remodeling can uncover new therapeutic targets. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Insulin resistance: a risk marker for disease and disability in the older person

Clinical metabolic studies have demonstrated that insulin action declines progressively with age in humans. In addition to its close association with Type 2 diabetes, which reduces life expectancy in older people, age-related insulin resistance is implicated in pathogenesis of several highly prevalent disorders for which ageing is a major risk factor. These include atherosclerotic cardiovascular disease, dementia, frailty and cancer. Accordingly, insulin resistance may be viewed as biomarker of age-related ill health and reduced lifespan. The rapidly rising number of older people, coupled with a high prevalence of insulin resistance resulting from obesity and sedentary lifestyles, presents unprecedented public health and societal challenges. Studies of centenarians have shown that preserved whole-body sensitivity to insulin is associated with longevity. The mechanisms through which insulin action is associated with age-related diseases remain unclear. Changes in body composition, i.e. sarcopenia and excess adiposity, may be more potent than age per se. Moreover, the impact of insulin resistance has been difficult to disentangle from the clustering of vascular risk factors that co-segregate with the insulin resistance-hyperinsulinaemia complex. Potentially modifiable mediators of age-related changes in insulin sensitivity include alterations in adipocytokines, impaired skeletal myocyte mitochondrial function and brown fat activity. The hypothesis that improving or maintaining insulin sensitivity preserves health and extends lifespan merits further evaluation. Practical non-pharmacological interventions directed against age-related insulin resistance remain underdeveloped. Novel metabolically active pharmacological agents with theoretical implications for some age-related disorders are entering clinical trials. However, recent adverse experiences with the thiazolidinediones suggest the need for a cautious approach to the use of insulin sensitizing drugs in older people. This could be particularly important in the absence of diabetes where the risk to benefit analysis may be less favourable.

Protein carbonylation, mitochondrial dysfunction, and insulin resistance

Oxidative stress has been identified as a common mechanism for cellular damage and dysfunction in a wide variety of disease states. Current understanding of the metabolic changes associated with obesity and the development of insulin resistance has focused on the role of oxidative stress and its interaction with inflammatory processes at both the tissue and organismal level. Obesity-related oxidative stress is an important contributing factor in the development of insulin resistance in the adipocyte as well as the myocyte. Moreover, oxidative stress has been linked to mitochondrial dysfunction, and this is thought to play a role in the metabolic defects associated with oxidative stress. Of the various effects of oxidative stress, protein carbonylation has been identified as a potential mechanism underlying mitochondrial dysfunction. As such, this review focuses on the relationship between protein carbonylation and mitochondrial biology and addresses those features that point to either the causal or casual relationship of lipid peroxidation-induced protein carbonylation as a determining factor in mitochondrial dysfunction.

Glargine safety, diabetes and cancer

INTRODUCTION

In 2009, several epidemiological studies suggested a higher frequency of malignancy in insulin glargine -treated patients. A number of follow-up epidemiological population studies as well as two randomized, controlled clinical studies, one a 5000-patient retinopathy study and the other a 12,000-patient cardiovascular outcomes trial (ORIGIN), found no higher frequency of malignancy in glargine-treated patients.

AREAS COVERED

We reviewed the existing literature as well as U.S. FDA records to investigate the association of cancer, diabetes, and insulin. There is a 20 - 40% higher incidence of malignancy in type 2 diabetes patients. Certain cancers are more common, including hepatocellular and pancreatic carcinoma, colorectal cancer, renal cancer, and breast and endometrial cancer, and non-Hodgkin's lymphoma. There are numerous inter-related factors which may promote both diabetes and malignancy, including dietary patterns, obesity, insulin resistance, and alcoholism. Patients who receive insulin treatment are typically older and "sicker" than those who receive oral agents.

EXPERT OPINION

It is very difficult to prove causal associations between diabetes and cancer due to the host of confounding factors. The hypothesis that hyperinsulinemia and IGF-1 receptor activation promote cancer is strong, but confounded by the association of hyperinsulinemia with obesity, which separately promotes malignancy. Although statistical techniques to adjust for confounding variables can improve epidemiological comparisons, the lesson of the glargine cancer controversy is that controlled clinical trials are the only means to definitely prove hypotheses.

Altered gene expression involved in insulin signaling pathway in type II diabetic osteoporosis rats model

It is well established that both estrogen loss and type II diabetes mellitus (DMII) can impair bone metabolism, but whether estrogen loss exacerbates the effects of DMII is unclear. Therefore, we determined if ovariectomy (OVX) of rats on a long-term high-fat/sugar diet and injection of a low dose of streptozotocin (DMII) decreased bone mineral density (BMD) more than OVX or DMII alone. Bone insulin signaling is known to support bone metabolism; therefore, we also tested the hypothesis that OVX DMII rats (DOVX) would exhibit greater reductions in the expression of proteins important in insulin signaling, including IRS-1, IRS-2, and IGF-1. As hypothesized, BMD and plasma estrogen levels were decreased more in DOVX rats than in rats following OVX (NOVX) or DMII (DS) alone. IGF-1 expression was decreased in the liver, kidney, skeletal muscle, and bone of DOVX, DS, and NOVX rats; however, the decrease was larger and occurred sooner in DOVX rats. While IRS-1 and IRS-2 decreased in most groups in all tissues examined, the expression patterns differed in both a group- and tissue-dependent fashion. In conclusion, these data demonstrate that estrogen loss and DMII induced by a high-fat/sugar diet interact to produce osteoporosis and support the hypothesis that the bone loss may be mediated at least in part by concurrent decreases in the insulin signaling proteins in bone.

Adipokines mediate inflammation and insulin resistance

For many years, adipose tissue was considered as an inert energy storage organ that accumulates and stores triacylglycerols during energy excess and releases fatty acids in times of systemic energy need. However, over the last two decades adipose tissue depots have been established as highly active endocrine and metabolically important organs that modulate energy expenditure and glucose homeostasis. In rodents, brown adipose tissue plays an essential role in non-shivering thermogenesis and in energy dissipation that can serve to protect against diet-induced obesity. White adipose tissue collectively referred too as either subcutaneous or visceral adipose tissue is responsible for the secretion of an array of signaling molecules, termed adipokines. These adipokines function as classic circulating hormones to communicate with other organs including brain, liver, muscle, the immune system, and adipose tissue itself. The dysregulation of adipokines has been implicated in obesity, type 2 diabetes, and cardiovascular disease. Recently, inflammatory responses in adipose tissue have been shown as a major mechanism to induce peripheral tissue insulin resistance. Although leptin and adiponectin regulate feeding behavior and energy expenditure, these adipokines are also involved in the regulation of inflammatory responses. Adipose tissue secretes various pro- and anti-inflammatory adipokines to modulate inflammation and insulin resistance. In obese humans and rodent models, the expression of pro-inflammatory adipokines is enhanced to induce insulin resistance. Collectively, these findings have suggested that obesity-induced insulin resistance may result, at least in part, from an imbalance in the expression of pro- and anti-inflammatory adipokines. Thus we will review the recent progress regarding the physiological and molecular functions of adipokines in the obesity-induced inflammation and insulin resistance with perspectives on future directions.

Visceral adiposity in gastrointestinal and hepatic carcinogenesis

There is emerging evidence that the association between obesity and cancer is mediated by visceral rather than generalised body fat. Visceral fat has been directly implicated in the risk and progression of several gastrointestinal cancers including colorectal, oesophageal, pancreatic and hepatocellular carcinomas. Excess visceral adipose tissue induces a state of chronic systemic inflammation and altered metabolic activity that promotes a pro-oncogenic environment. This review examines the evidence linking visceral fat in gastrointestinal and hepatic carcinogenesis and explores our current understanding of the mechanisms underlying this relationship.

Insulin resistance: metabolic mechanisms and consequences in the heart

Insulin resistance is a characteristic feature of obesity and type 2 diabetes mellitus and impacts the heart in various ways. Impaired insulin-mediated glucose uptake is a uniformly observed characteristic of the heart in these states, although changes in upstream kinase signaling are variable and dependent on the severity and duration of the associated obesity or diabetes mellitus. The understanding of the physiological and pathophysiological role of insulin resistance in the heart is evolving. To maintain its high energy demands, the heart is capable of using many metabolic substrates. Although insulin signaling may directly regulate cardiac metabolism, its main role is likely the regulation of substrate delivery from the periphery to the heart. In addition to promoting glucose uptake, insulin regulates long-chain fatty acid uptake, protein synthesis, and vascular function in the normal cardiovascular system. Recent advances in understanding the role of metabolic, signaling, and inflammatory pathways in obesity have provided opportunities to better understand the pathophysiology of insulin resistance in the heart. This review will summarize our current understanding of metabolic mechanisms for and consequences of insulin resistance in the heart and will discuss potential new areas for investigating novel mechanisms that contribute to insulin resistance in the heart.

Chemerin: a potential endocrine link between obesity and type 2 diabetes

Obesity and type 2 diabetes have reached epidemic levels and account for a substantial portion of the annual health expenditures of developed nations. While there is an abundance of epidemiological evidence demonstrating that obesity is a primary risk factor for developing type 2 diabetes, the mechanism(s) underlying this linkage are not completely understood. Given the enormous impact of these disorders on global health, considerable research effort has been devoted to elucidate the pathophysiological relationship between these two disorders. Two factors believed to contribute to the causal link between obesity and type 2 diabetes are chronic inflammation and altered secretion of adipose-derived signaling molecules (adipokines). Independent lines of investigation have implicated the novel adipokine chemerin as a regulator of adipogenesis, inflammation, and glucose metabolism through interactions with the cognate cell surface receptor chemokine-like receptor 1. Increased levels of chemerin that occur with obesity are hypothesized to be a causal factor in the development of type 2 diabetes as a consequence of dysregulation of the key physiological processes regulated by this adipokine. This review summarizes current research on the biological roles of chemerin and chemokine-like receptor 1, and highlights key questions to guide future research on the role of this adipokine in mediating obesity and the development of type 2 diabetes.

The long and winding TRAIL to weight loss

TRAIL [TNF (tumour necrosis factor)-related apoptosis-inducing ligand] is in clinical trials for the treatment of cancer. In the present issue of Clinical Science, Bernardi and co-workers report that the administration of TRAIL in mice fed on a high-fat diet resulted in reduced adiposity and improved metabolic responses to a glucose and insulin tolerance test compared with mice without TRAIL. The metabolic improvements were associated with a higher rate of apoptotic fat cells and with a reduction in the levels of pro-inflammatory cytokines. These results suggest that TRAIL could be an exciting new therapeutic for treating obesity, but further studies are required to determine its major mechanisms of action.

Autophagy, signaling and obesity

Autophagy is a cellular pathway crucial for development, differentiation, survival and homeostasis. Autophagy can provide protection against aging and a number of pathologies such as cancer, neurodegeneration, cardiac disease and infection. Recent studies have reported new functions of autophagy in the regulation of cellular processes such as lipid metabolism and insulin sensitivity. Important links between the regulation of autophagy and obesity including food intake, adipose tissue development, β cell function, insulin sensitivity and hepatic steatosis exist. This review will provide insight into the current understanding of autophagy, its regulation, and its role in the complications associated with obesity.