Increased fat intake, impaired fat oxidation, and failure of fat cell proliferation result in ectopic fat storage, insulin resistance, and type 2 diabetes mellitus

Adipose tissue and skeletal muscle plasticity modulates metabolic health

Obesity, accumulation of adipose tissue, develops when energy intake exceeds energy expenditure. Adipose tissue is essential for buffering the differences between energy intake and expenditure by accumulating lipids while skeletal muscle is the energy burning machine. Here we adopted the concept that (i) adipose tissue ability to regulate the storage capacity for lipids as well as (ii) dynamic regulation of muscle and adipose tissue secretory and metabolic activity is important for maintaining the metabolic health. This might be at least in part related to tissue plasticity, a phenomenon enabling dynamic modulation of the tissue phenotype in different physiological and pathophysiological situations. Recent advances in our understanding of the complex endocrine function of adipose tissue in regulating lipid metabolism, adipogenesis, angiogenesis, extracellular matrix remodelling, inflammation and oxidative stress prompted us to review the role of tissue plasticity--dynamic changes in adipose tissue and skeletal muscle metabolic and endocrine phenotype--in determining the difference between metabolic health and disease.

Body composition, insulin sensitivity, and cardiovascular disease profile in healthy Europeans

OBJECTIVE

To assess whether insulin sensitivity can explain the associations of leg-fat mass (LFM) and trunk-fat mass (TFM) with the cardiovascular disease (CVD) risk profile in healthy European men and women.

METHODS AND PROCEDURES

We studied 142 healthy men and women of a multicenter European study on insulin sensitivity, aged 30-60 years, from the centres in Hoorn, the Netherlands and Rome, Italy. Whole-body dual-energy X-ray absorptiometry (DXA) was used to determine fat and lean soft tissue mass in the trunk and legs. Fasting glucose, insulin, and lipid levels were measured. Insulin sensitivity (M/I-ratio) was measured during a euglycemic-hyperinsulinemic clamp. Associations between fat distribution and CVD risk factors were studied with linear regression analyses with adjustment for other body compartments, and subsequent adjustment for insulin sensitivity.

RESULTS

In men, larger LFM was significantly and independently associated with lower triglyceride levels (TGs) and higher high-density lipoprotein (HDL) cholesterol (P < 0.10) and tended to be associated also with lower low-density lipoprotein (LDL) cholesterol, and lower fasting insulin levels. In women, larger LFM was associated with favorable values of all CVD risk factors, although the associations were not statistically significant. In both sexes, larger TFM was independently and significantly associated with unfavorable values of most CVD risk factors, and most associations did not markedly change after adjustment for insulin sensitivity.

DISCUSSION

In a relatively young and healthy European population, larger LFM is associated with a lower and TFM with a higher cardiovascular and metabolic risk, which can not be explained by insulin sensitivity.

The role of GM-CSF in adipose tissue inflammation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a proinflammatory cytokine that has a central action to reduce food intake and body weight. Consistent with this, GM-CSF knockout mice are more obese and hyperphagic than wild-type mice. However, in lung, GM-CSF is an important determinant of macrophage infiltration. Consequently, we sought to determine if GM-CSF might contribute to adipose tissue macrophage accumulation, insulin resistance, and low-grade inflammation that occurs when animals gain weight on a high-fat diet (HFD). We therefore determined how targeted genetic disruption of GM-CSF can affect adipose tissue macrophage and cytokine gene expression as well as glucose homeostasis by performing hyperinsulinemic-euglycemic clamps. The number of macrophages and CCR2 gene expression in adipose tissue of GM-CSF knockout mice was decreased relative to those in wild-type mice, and the adipocyte size of mesenteric fat was increased in GM-CSF knockout mice on a HFD compared with wild-type mice. The level of mRNA of the proinflammatory cytokines interleukin-1beta, tumor necrosis factor-alpha, and macrophage inflammatory protein-1alpha was significantly lower in mesenteric fat of GM-CSF knockout mice on the HFD than in wild-type mice. Using the hyperinsulinemic-euglycemic clamp technique, GM-CSF knockout mice had greater overall insulin sensitivity. This increase was due to enhanced peripheral uptake and utilization of glucose rather than to increased hepatic insulin sensitivity. Collectively, the data suggest that the GM-CSF knockout mutation ameliorates peripheral insulin resistance in spite of increased adiposity by reducing inflammation in adipose tissue in response to a HFD.

Independent and opposite associations of hip and waist circumference with metabolic syndrome components and with inflammatory and atherothrombotic risk factors in overweight and obese women

Recent studies have shown independent and opposite associations of hip circumference (HC) and waist circumference (WC) with glucose intolerance, insulin resistance, and type 2 diabetes mellitus. However, no studies have simultaneously considered the independent contributions of both markers to metabolic proinflammatory and atherosclerotic risk factors. In this study, we examine the independent associations of WC and HC with metabolic syndrome and with proinflammatory and atherothrombotic features. Independent associations of thigh muscle and adipose tissue (AT) compartments with metabolic features were also studied. Abdominal and thigh muscle and AT distributions were assessed by computed tomography in 140 overweight and obese women (mean +/- SD: age, 38.3 +/- 0.5 years; body mass index, 30.4 +/- 0.3 kg/m(2)). Blood lipids and inflammatory and atherothrombotic markers were measured. For a given WC, a larger HC was inversely associated with fasting insulin (beta = -0.288, P = .008), hemoglobin A(1c) (beta = -0.246, P = .041), and plasminogen activator inhibitor-1 concentrations (beta = -0.241, P = .023). Contrarily, WC was related with an unfavorable metabolic profile. For a given WC, higher total thigh AT and total thigh subcutaneous AT masses were associated with lower hemoglobin A(1c) (beta = -0.244, P = .049; beta = -0.233, P = .049) and low-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio (beta = -0.252, P = .040; beta = -0.245, P = .037). In addition, total thigh AT was related with leptin (beta = 0.310, P = .012), whereas total thigh subcutaneous AT revealed opposite associations with fasting insulin concentrations (beta = -0.239, P = .034). Total thigh muscular tissue mass was related with lower plasminogen activator inhibitor-1 (beta = -0.164, P = .049) and fibrinogen concentrations (beta = -0.222, P = .018). In conclusion, HC revealed independent and opposite associations with insulin resistance and atherothrombotic disturbances. Contrarily, a larger WC predicted an increased metabolic risk. These contrasting effects in diabetogenic and atherothrombotic disturbances were, respectively, mediated by gluteofemoral AT and thigh muscle tissue. Besides body mass index and WC screening relevance, HC can contribute to additionally predict health risk in overweight and obese women.

Is adiposopathy (sick fat) an endocrine disease?

OBJECTIVE

To review current consensus and controversy regarding whether obesity is a 'disease', examine the pathogenic potential of adipose tissue to promote metabolic disease and explore the merits of 'adiposopathy' and 'sick fat' as scientifically and clinically useful terms in defining when excessive body fat may represent a 'disease'.

METHODS

A group of clinicians and researchers, all with a background in endocrinology, assembled to evaluate the medical literature, as it pertains to the pathologic and pathogenic potential of adipose tissue, with an emphasis on metabolic diseases that are often promoted by excessive body weight.

RESULTS

The data support pathogenic adipose tissue as a disease. Challenges exist to convince many clinicians, patients, healthcare entities and the public that excessive body fat is often no less a 'disease' than the pathophysiological consequences related to anatomical abnormalities of other body tissues. 'Adiposopathy' has the potential to scientifically define adipose tissue anatomic and physiologic abnormalities, and their adverse consequences to patient health. Adiposopathy acknowledges that when positive caloric balance leads to adipocyte hypertrophy and visceral adiposity, then this may lead to pathogenic adipose tissue metabolic and immune responses that promote metabolic disease. From a patient perspective, explaining how excessive caloric intake might cause fat to become 'sick' also helps provide a rationale for patients to avoid weight gain. Adiposopathy also better justifies recommendations of weight loss as an effective therapeutic modality to improve metabolic disease in overweight and obese patients.

CONCLUSION

Adiposopathy (sick fat) is an endocrine disease.

Paradoxical effect of mitochondrial respiratory chain impairment on insulin signaling and glucose transport in adipose cells

Adipocyte function is crucial for the control of whole body energy homeostasis. Pathway analysis of differentiating 3T3-L1 adipocytes reveals that major metabolic pathways induced during differentiation involve mitochondrial function. However, it is not clear why differentiated white adipocytes require enhanced respiratory chain activity relative to pre-adipocytes. To address this question, we used small interference RNA to interfere with the induction of the transcription factor Tfam, which is highly induced between days 2 and 4 of differentiation and is crucial for replication of mitochondrial DNA. Interference with Tfam resulted in cells with decreased respiratory chain capacity, reflected by decreased basal oxygen consumption, and decreased mitochondrial ATP synthesis, but no difference in many other adipocyte functions or expression levels of adipose-specific genes. However, insulin-stimulated GLUT4 translocation to the cell surface and subsequent glucose transport are impaired in Tfam knockdown cells. Paradoxically, insulin-stimulated Akt phosphorylation is significantly enhanced in these cells. These studies reveal independent links between mitochondrial function, insulin signaling, and glucose transport, in which impaired respiratory chain activity enhances insulin signaling to Akt phosphorylation, but impairs GLUT4 translocation. These results indicate that mitochondrial respiratory chain dysfunction in adipocytes can cause impaired insulin responsiveness of GLUT4 translocation by a mechanism downstream of the Akt protein kinase.

Fatty liver and chronic inflammation in Chinese adults

OBJECTIVE

To investigate the significance of fatty liver as predictor of insulin resistance (IR) and chronic inflammation.

RESEARCH DESIGN AND METHODS

This cross-sectional study included 450 adults of Han Chinese origin aged >or=35. Excluded were cases with hepatitis B or C, alcoholic liver disease, or currently using thiazolidinedione. The volunteers were screened for the presence of the components of metabolic syndrome (MtS). IR index was estimated by the homeostasis model assessment. The fatty liver index was evaluated by computed tomography, calculated as the liver/spleen (L/S) ratio arrived at by averaging Hounsfield values obtained for five 3-mm slices. Serum levels of adiponectin, C-reactive protein (CRP), leptin, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were checked in 100 subjects with low-L/S ratio and 100 age- and sex-matched controls.

RESULTS

Fatty liver index correlated with all MtS traits and IR index. The values of L/S ratios in subjects with 0, 1, 2, 3 and >or=4 traits of MtS were 1.25+/-0.13, 1.18+/-0.16, 1.12+/-0.21, 1.05+/-0.25 and 0.92+/-0.25, respectively (p<0.001). In our stepwise regression analysis to compare the L/S ratios to the conventional traits of MtS for association with adipokine dysregulation, we found L/S ratio to be independently associated with most of them: adiponectin (p<0.001), CRP (p<0.001), IL-6 (p=0.005) and TNF-alpha (p=0.014).

CONCLUSION

In Chinese, fatty liver index correlated well with IR index and can be a better marker of chronic inflammation than the conventional components of MtS.

Adipokine protein expression pattern in growth hormone deficiency predisposes to the increased fat cell size and the whole body metabolic derangements

CONTEXT

GH deficiency (GHD) in adults is associated with central adiposity, dyslipidemia, and insulin resistance.

OBJECTIVE

The objective of the study was to test the hypothesis that GHD might change the spectrum of adipokines and thus influence the adipose tissue and the whole-body metabolic and inflammatory status leading to development of insulin resistance.

DESIGN

This was a single-center observational study with a cross-sectional design.

PARTICIPANTS AND METHODS

Protein arrays were used to characterize adipokines expressed in the sc adipose tissue obtained from young GHD adults and compared with age-, gender-, and body mass index (BMI)-matched group of healthy individuals. All subjects underwent an oral glucose tolerance test, euglycemic hyperinsulinemic clamp, and magnetic resonance imaging examination.

RESULTS

Presence of abdominal obesity, enlarged adipocytes, increased circulating high-sensitivity C-reactive protein, impaired glucose tolerance, and decreased insulin action were found in GHD. Changes in adipokine protein expression due to GHD were highly dependent on the obesity phenotype. Lean GHD individuals (BMI approximately 23 kg/m(2)) had decreased protein levels for stem cell factor and epithelial growth factor, indicating a possible defect in adipocyte differentiation and proliferation. Decrease of vascular endothelial growth factor, stromal cell-derived factor, angiopoietin-2, and brain-derived neurotrophic factor advocated for attenuated angiogenesis and neurogenesis. Presence of obesity (BMI approximately 31 kg/m(2)) eliminated these inhibitory effects. However, adipose tissue expansion in GHD individuals was paralleled by an elevation of adipose tissue proinflammatory cytokines (IL-1beta, interferon-gamma) and chemoattractants (interferon-inducible T cell alpha-chemoattractant, monocyte chemotactic protein-2, monocyte chemotactic protein-3, eotaxin).

CONCLUSION

Our data demonstrate that GHD modulates adipokine and cytokine protein expression pattern, which might influence the adipose tissue growth and differentiation and predispose to tissue hypoxia, inflammation, and a defect in the whole-body insulin action.

Adiponectin and adiponectin receptor gene variants in relation to type 2 diabetes and insulin resistance-related phenotypes

BACKGROUND

Alterations in adiponectin-mediated pathways are known to be associated with glucose intolerance, insulin resistance (IR), obesity, and type 2 diabetes (T2D) mellitus. Genetic variations in adiponectin (ADIPOQ) and adiponectin 1 and 2 receptor (ADIPOR1 and ADIPOR2) could have effects on IR-related phenotypes and T2D. Here we examine whether the polymorphic markers rs2241766 (ADIPOQ), rs22753738 (ADIPOR1), rs11061971 and rs16928751 (both in ADIPOR2) are implicated in susceptibility to T2D in a Russian population.

METHODS

The polymorphic markers were genotyped in 129 T2D patients, and 117 non-diabetic controls, by polymerase chain reaction (PCR) restriction fragment length polymorphism approach. In the subjects, biochemical characteristics including serum insulin, plasma glucose and serum lipids/lipoproteins were measured and compared for correlation with the genetic variations studied.

RESULTS

Allele T of rs11061971 and allele A of rs16928751 showed association with higher risk of diabetes providing odds ratios (OR) of 2.05 (p = 0.0025) and 1.88 (p = 0.018), respectively. Haplotype A-G consisting of allele A of rs11061971 and allele G of rs16928751 was associated with reduced risk of T2D (OR = 0.59, pc = 0.0224). Compared to other variants, diabetic patients double homozygous for A/A of rs16928751 and G/G of rs16928751 had decreased homeostasis model assessment-insulin resistance (pc = 0.0375) and serum triglycerides (pc = 0.0285).

CONCLUSIONS

The variants of ADIPOR2 confer susceptibility to T2D and are associated with some IR-related phenotypes in the Russian study population.

Impaired skeletal muscle substrate oxidation in glucose-intolerant men improves after weight loss

OBJECTIVE

An impaired fatty acid handling in skeletal muscle may be involved in the development of insulin resistance and diabetes mellitus type 2 (DM2). We investigated muscle fatty acid metabolism in glucose-intolerant men (impaired glucose tolerance (IGT)), a prediabetic state, relative to BMI-matched control men (normal glucose tolerance (NGT)) during fasting and after a meal, because most people in the western society are in the fed state most of the day.

METHODS AND PROCEDURES

Skeletal muscle free fatty acid (FFA) uptake and oxidation were studied using the stable isotope tracer [2,2-(2)H]-palmitate and muscle indirect calorimetry in the forearm model during fasting and after a mixed meal (33 energy % (E%) carbohydrates, 61 E% fat). Intramyocellular triglycerides (IMTGs) were monitored with 1H-magnetic resonance spectroscopy. IGT men were re-examined after weight loss (-15% of body weight (BW)).

RESULTS

The postprandial increase in forearm muscle respiratory quotient (RQ) was blunted in IGT compared to NGT, but improved after weight loss. Weight loss also improved fasting-fat oxidation and tended to decrease IMTGs (P=0.08). No differences were found in fasting and postprandial forearm muscle fatty acid uptake between NGT and IGT, or in IGT before and after weight loss.

DISCUSSION

The ability to switch from fat oxidation to carbohydrate oxidation after a meal is already impaired in the prediabetic state, suggesting this may be an early factor in the development toward DM2. This impaired ability to regulate fat oxidation during fasting and after a meal (impaired metabolic flexibility) can be (partly) reversed by weight loss.

Pathogenic potential of adipose tissue and metabolic consequences of adipocyte hypertrophy and increased visceral adiposity

When caloric intake exceeds caloric expenditure, the positive caloric balance and storage of energy in adipose tissue often causes adipocyte hypertrophy and visceral adipose tissue accumulation. These pathogenic anatomic abnormalities may incite metabolic and immune responses that promote Type 2 diabetes mellitus, hypertension and dyslipidemia. These are the most common metabolic diseases managed by clinicians and are all major cardiovascular disease risk factors. 'Disease' is traditionally characterized as anatomic and physiologic abnormalities of an organ or organ system that contributes to adverse health consequences. Using this definition, pathogenic adipose tissue is no less a disease than diseases of other body organs. This review describes the consequences of pathogenic fat cell hypertrophy and visceral adiposity, emphasizing the mechanistic contributions of genetic and environmental predispositions, adipogenesis, fat storage, free fatty acid metabolism, adipocyte factors and inflammation. Appreciating the full pathogenic potential of adipose tissue requires an integrated perspective, recognizing the importance of 'cross-talk' and interactions between adipose tissue and other body systems. Thus, the adverse metabolic consequences that accompany fat cell hypertrophy and visceral adiposity are best viewed as a pathologic partnership between the pathogenic potential adipose tissue and the inherited or acquired limitations and/or impairments of other body organs. A better understanding of the physiological and pathological interplay of pathogenic adipose tissue with other organs and organ systems may assist in developing better strategies in treating metabolic disease and reducing cardiovascular disease risk.

Intramuscular lipid oxidation and obesity

There is an accumulating amount of evidence indicating that lipid oxidation is depressed in the skeletal muscle of obese individuals. Decrements in fatty acid oxidation (FAO) have been reported with obesity in models ranging from whole body measurements to isolated skeletal muscle preparations as well as in myotubes raised in culture. This reduction appears to be associated with a depression in the activities of enzymes involved in various steps of lipid oxidation, which subsequently partitions lipid entering the cell toward storage. The defect in FAO in skeletal muscle may be critical in relation to health, as a reduction in the capacity for lipid oxidation could directly or indirectly contribute to the insulin resistance commonly evident with obesity. Although less characterized, a decrement in FAO has also been linked with weight gain, which suggests that this characteristic may be an integral aspect leading to the obese state. In terms of intervention, weight loss does not seem to correct the defect in FAO with obesity. This review will provide evidence supporting a reduction in muscle FAO with obesity.

Abdominal obesity and the metabolic syndrome: contribution to global cardiometabolic risk

There is currently substantial confusion between the conceptual definition of the metabolic syndrome and the clinical screening parameters and cut-off values proposed by various organizations (NCEP-ATP III, IDF, WHO, etc) to identify individuals with the metabolic syndrome. Although it is clear that in vivo insulin resistance is a key abnormality associated with an atherogenic, prothrombotic, and inflammatory profile which has been named by some the "metabolic syndrome" or by others "syndrome X" or "insulin resistance syndrome", it is more and more recognized that the most prevalent form of this constellation of metabolic abnormalities linked to insulin resistance is found in patients with abdominal obesity, especially with an excess of intra-abdominal or visceral adipose tissue. We have previously proposed that visceral obesity may represent a clinical intermediate phenotype reflecting the relative inability of subcutaneous adipose tissue to act as a protective metabolic sink for the clearance and storage of the extra energy derived from dietary triglycerides, leading to ectopic fat deposition in visceral adipose depots, skeletal muscle, liver, heart, etc. Thus, visceral obesity may partly be a marker of a dysmetabolic state and partly a cause of the metabolic syndrome. Although waist circumference is a better marker of abdominal fat accumulation than the body mass index, an elevated waistline alone is not sufficient to diagnose visceral obesity and we have proposed that an elevated fasting triglyceride concentration could represent, when waist circumference is increased, a simple clinical marker of excess visceral/ectopic fat. Finally, a clinical diagnosis of visceral obesity, insulin resistance, or of the metabolic syndrome is not sufficient to assess global risk of cardiovascular disease. To achieve this goal, physicians should first pay attention to the classical risk factors while also considering the additional risk resulting from the presence of abdominal obesity and the metabolic syndrome, such global risk being defined as cardiometabolic risk.

Androgens and body fat distribution

An important sex difference in body fat distribution is generally observed. Men are usually characterized by the android type of obesity, with accumulation of fat in the abdominal region, whereas women often display the gynoid type of obesity, with a greater proportion of their body fat in the gluteal-femoral region. Accordingly, the amount of fat located inside the abdominal cavity (intra-abdominal or visceral adipose tissue) is twice as high in men compared to women. This sex difference has been shown to explain a major portion of the differing metabolic profiles and cardiovascular disease risk in men and women. Association studies have shown that circulating androgens are negatively associated with intra-abdominal fat accumulation in men, which explains an important portion of the link between low androgens and features of the metabolic syndrome. In women, the low circulating sex hormone-binding globulin (SHBG) levels found in abdominal obesity may indirectly indicate that elevated free androgens are related to increased visceral fat accumulation. However, data on non SHBG-bound and total androgens are not unanimous and difficult to interpret for total androgens. These studies focusing on plasma levels of sex hormones indirectly suggest that androgens may alter adipose tissue mass in a depot-specific manner. This could occur through site-specific modulation of preadipocyte proliferation and/or differentiation as well as lipid synthesis and/or lipolysis in mature adipocytes. Recent results on the effects of androgens in cultured adipocytes and adipose tissue have been inconsistent, but may indicate decreased adipogenesis and increased lipolysis upon androgen treatment. Finally, adipose tissue has been shown to express several steroidogenic and steroid-inactivating enzymes. Their mere presence in fat indirectly supports the notion of a highly complex enzymatic system modulating steroid action on a local basis. Recent data obtained in both men and women suggest that enzymes from the aldoketoreductase 1C family are very active and may be important modulators of androgen action in adipose tissue.

High visceral and low abdominal subcutaneous fat stores in the obese adolescent: a determinant of an adverse metabolic phenotype

OBJECTIVE

To explore whether an imbalance between the visceral and subcutaneous fat depots and a corresponding dysregulation of the adipokine milieu is associated with excessive accumulation of fat in the liver and muscle and ultimately with insulin resistance and the metabolic syndrome.

RESEARCH DESIGN AND METHODS

We stratified our multi-ethnic cohort of 118 obese adolescents into tertiles based on the proportion of abdominal fat in the visceral depot. Abdominal and liver fat were measured by magnetic resonance imaging and muscle lipid (intramyocellular lipid) by proton magnetic resonance spectroscopy.

RESULTS

There were no differences in age, BMI Z score, or fat-free mass across tertiles. However, as the proportion of visceral fat increased across tertiles, BMI and percentage of fat and subcutaneous fat decreased, while hepatic fat increased. In addition, there was an increase in 2-h glucose, insulin, c-peptide, triglyceride levels, and insulin resistance. Notably, both leptin and total adiponectin were significantly lower in tertile 3 than 1, while C-reactive protein and interleukin-6 were not different across tertiles. There was a significant increase in the odds ratio for the metabolic syndrome, with subjects in tertile 3 5.2 times more likely to have the metabolic syndrome than those in tertile 1.

CONCLUSIONS

Obese adolescents with a high proportion of visceral fat and relatively low abdominal subcutaneous fat have a phenotype reminiscent of partial lipodystrophy. These adolescents are not necessarily the most severely obese, yet they suffer from severe metabolic complications and are at a high risk of having the metabolic syndrome.

Alterations in plasma and tissue lipids associated with obesity and metabolic syndrome

The MS (metabolic syndrome) is a cluster of clinical and biochemical abnormalities characterized by central obesity, dyslipidaemia [hypertriglyceridaemia and decreased HDL-C (high-density lipoprotein cholesterol)], glucose intolerance and hypertension. Insulin resistance, hyperleptinaemia and low plasma levels of adiponectin are also widely related to features of the MS. This review focuses on lipid metabolism alterations associated with the MS, paying special attention to changes in plasma lipids and cellular fatty acid oxidation. Lipid metabolism alterations in liver and peripheral tissues are addressed, with particular reference to adipose and muscle tissues, and the mechanisms by which some adipokines, namely leptin and adiponectin, mediate the regulation of fatty acid oxidation in those tissues. Activation of the AMPK (AMP-dependent kinase) pathway, together with a subsequent increase in fatty acid oxidation, appear to constitute the main mechanism of action of these hormones in the regulation of lipid metabolism. Decreased activation of AMPK appears to have a role in the development of features of the MS. In addition, alteration of AMPK signalling in the hypothalamus, which may function as a sensor of nutrient availability, integrating multiple nutritional and hormonal signals, may have a key role in the appearance of the MS.

Adipokines: linking obesity and cardiovascular disease

Obesity is fast becoming one of the most important contributors to cardiovascular disease. Adipose tissue is gaining recognition as a key endocrine organ that secretes a growing number of adipokines, linking adiposity with inflammation, endothelial dysfunction and the initiation of atherosclerosis. In particular, accumulation of visceral adipose tissue is implicated in the development of cardiovascular disease as it is associated with increased macrophage infiltration and oversecretion of proinflammatory and prothrombotic factors, such as TNF-α, IL-6, plasminogen activator inhibitor-1, leptin, resistin and angiotensinogen, and reduced secretion of the antiatherogenic factor adiponectin. As adipokines represent a key molecular link between obesity and the atherogenic state, research directed at understanding the physiology and biochemistry of these factors should open the door for discovery of novel therapeutics.

Increased hepatic CD36 expression contributes to dyslipidemia associated with diet-induced obesity

OBJECTIVE

The etiology of type 2 diabetes often involves diet-induced obesity (DIO), which is associated with elevated plasma fatty acids and lipoprotein associated triglycerides. Since aberrant hepatic fatty acid uptake may contribute to this, we investigated whether increased expression of a fatty acid transport protein (CD36) in the liver during DIO contributes to the dyslipidemia that precedes development of type 2 diabetes.

RESEARCH DESIGN AND METHODS

We determined the effect DIO has on hepatic CD36 protein expression and the functional consequence of this in terms of hepatic triglyceride storage and secretion. In addition, in vivo adenoviral gene delivery of CD36 to the livers of lean mice was performed to determine if increased hepatic CD36 protein was sufficient to alter hepatic fatty acid uptake and triglyceride storage and secretion.

RESULTS

During DIO, CD36 protein levels in the liver are significantly elevated, and these elevated levels correlate with increased hepatic triglyceride storage and secretion. These alterations in liver lipid storage and secretion were also observed upon forced expression of hepatic CD36 in the absence of DIO and were accompanied with a marked rise in hepatic fatty acid uptake in vivo, demonstrating that increased CD36 expression is sufficient to recapitulate the aberrant liver lipid handling observed in DIO.

CONCLUSIONS

Increased expression of hepatic CD36 protein in response to DIO is sufficient to exacerbate hepatic triglyceride storage and secretion. As these CD36-mediated effects contribute to the dyslipidemia that often precedes the development of type 2 diabetes, increased hepatic CD36 expression likely plays a causative role in the pathogenesis of type 2 diabetes.

Deterioration of insulin sensitivity and beta-cell function in overweight Hispanic children during pubertal transition: a longitudinal assessment

PURPOSE

To examine 1-year changes in insulin dynamics in overweight Hispanic children at high-risk of type 2 diabetes as a function of body composition and pubertal transition.

EXPERIMENTAL DESIGN

Longitudinal changes in insulin dynamics, body composition and maturation were determined in 132 Hispanic children (70 boys/62 girls; aged 10.9 +/- 1.8 years).

METHODS

Body composition was determined by dual energy x-ray absorptiometry and Tanner stage by physical examination. Insulin sensitivity (SI), the acute insulin response to glucose (AIR) and the disposition index (DI; an index of beta-cell function) were determined using an insulin modified intravenous glucose tolerance test. These measures were conducted at baseline and 1-year later.

RESULTS

Fat mass increased by 13% (3.0 kg) and SI declined by 24%. In repeated measures analysis of variance, the fall in insulin sensitivity over 1 year remained highly significant even after adjusting for baseline fat mass, age, gender and change in fat mass. The fall in SI was not significantly influenced by Tanner stage. However, subjects in earlier maturation showed a compensatory increase in AIR (i.e. appropriate beta-cell compensation), whereas subjects in the latter stages of maturation did not (i.e. poor compensation).

CONCLUSIONS

These results indicate that failure to increase AIR in response to the fall in SI may be one factor in the pathogenesis of the progression of pediatric type 2 diabetes in this at risk population.

Diet, energy metabolism and mitochondrial biogenesis

PURPOSE OF REVIEW

This review highlights some recent findings regarding nutritional and endocrine regulators of mitochondrial mass and function and their association with insulin resistance.

RECENT FINDINGS

Insulin resistance is central to many chronic metabolic diseases, including obesity, type 2 diabetes, dyslipidemia, and hypertension. Insulin resistance in skeletal muscle is associated with lower mitochondrial mass and reduced oxidative phosphorylation. Part of the mitochondrial dysfunction can be triggered by adverse nutrition. Increased fatty acid exposure, resulting from high fats diets or overfeeding, is linked to both decreased mitochondrial number and markers of oxidative phosphorylation. Caloric restriction and the adiponectin signaling pathway, however, can stimulate mitochondrial biogenesis by elevating the transcriptional machinery that regulates mitochondrial mass, improving mitochondrial efficiency, activating the peroxisome proliferator-activated receptor coactivator 1alpha mediated reactive oxygen species scavenging mechanism, and lowering reactive oxygen species production.

SUMMARY

States of insulin resistance are characterized by defects in lipid and carbohydrate metabolism. Abnormalities in oxidative capacity, however, can be partially normalized by caloric restriction by modulating mitochondrial mass in an insulin sensitizing manner.

Serum retinol-binding protein is more highly expressed in visceral than in subcutaneous adipose tissue and is a marker of intra-abdominal fat mass

Intra-abdominal fat is associated with insulin resistance and cardiovascular risk. Levels of serum retinol-binding protein (RBP4), secreted by fat and liver cells, are increased in obesity and type 2 diabetes (T2D). Here we report that, in 196 subjects, RBP4 is preferentially expressed in visceral (Vis) versus subcutaneous (SC) fat. Vis fat RBP4 mRNA was increased approximately 60-fold and 12-fold in Vis and SC obese subjects respectively versus lean subjects, and approximately 2-fold with impaired glucose tolerance/T2D subjects versus normoglycemic subjects. In obese subjects, serum RBP4 was increased 2- to 3-fold, and serum transthyretin, which stabilizes RBP4 in the circulation, was increased 35%. Serum RBP4 correlated positively with adipose RBP4 mRNA and intra-abdominal fat mass and inversely with insulin sensitivity, independently of age, gender, and body mass index. RBP4 mRNA correlated inversely with GLUT4 mRNA in Vis fat and positively with adipocyte size in both depots. RBP4 levels are therefore linked to Vis adiposity, and Vis fat may be a major source of RBP4 in insulin-resistant states.

The relationship between metabolic status and levels of adiponectin and ghrelin in lean women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is commonly associated with insulin resistance, obesity, dyslipidemia and hypertension. Adiponectin, an adipocyte-specific protein with important roles in glucose and lipid homeostasis, possesses antidiabetic and insulin-sensitizing properties. Ghrelin, a protein ligand for the growth hormone secretagog receptor, has been shown to stimulate food intake and to influence energy balance, insulin signaling and glucose metabolism. We aimed to evaluate the relationships between metabolic alterations and adiponectin and ghrelin levels in lean PCOS women, compared with lean and obese women. The study was carried out on 20 non-obese PCOS women aged 20 - 48 years and age-matched groups of 45 healthy lean and 37 obese women. Hormonal and biochemical parameters, adiponectin and ghrelin concentrations and anthropometric data were determined. In PCOS subjects, we found increased homeostasis model assessment - insulin resistance index (HOMA-IR) with non-significant differences in adiponectin and ghrelin concentrations compared with healthy women, although the PCOS group showed a tendency to lower adiponectin levels. However, ghrelin levels in PCOS women were significantly higher than in obese women. Moreover, we observed a negative correlation between adiponectin and testosterone, cholesterol, triglycerides, glucose and diastolic blood pressure in PCOS. In conclusion, it can be suggested that higher values of HOMA-IR with lower adiponectin levels may indicate future development of metabolic syndrome or other metabolic disturbances in lean PCOS women.

Adipose tissue distribution and risk of metabolic disease: does thiazolidinedione-induced adipose tissue redistribution provide a clue to the answer?

The relative effect of visceral and subcutaneous obesity on the risk of chronic metabolic disease has been a matter of long-term dispute. While ample data support either of the fat depots being causative or associative, valid argument for one depot often automatically belittles the other. Paradigms such as the visceral/portal hypothesis and the acquired lipodystrophy/ectopic fat storage and endocrine hypothesis have been proposed. Nevertheless, neither hypothesis alone explains the entire pathophysiological setting. Treatment of diabetes with thiazolidinediones selectively increases fat partitioning to the subcutaneous adipose depot but does not change visceral fat accumulation. This is in contrast to the preferential visceral fat mobilisation by diet and exercise. Surgical removal of visceral or subcutaneous adipose tissue yields relatively long-lasting metabolic improvement only when combined with procedures that ameliorate adipose tissue cell composition. These studies illustrate that human adipose tissue in different anatomic locations does not work in isolation, and that there is a best-fit relationship in terms of volume and function among different fat depots that needs to be met to maintain the systemic energy balance and to prevent the complications related to obesity.

Development of insulin resistance and its relation to diet in the obese child

The incidence rate of obesity in youth has continued to increase worldwide and about 30% of obese children display insulin resistance (IR) and other metabolic abnormalities. The present study reviews the mechanisms for development of IR in the obese child and possible links between IR and dietary factors in childhood and adolescence. Although increased concentrations of plasma free fatty acids (FFA) and their counter part at intracellular level, long-chain acyl-coenzyme A (LC acyl-CoA), have been related to the early onset of IR in childhood obesity, a new endocrine paradigm states that adipose tissue secretes a wide variety of hormones and cytokines that regulate lipid energy metabolism. These hormonal changes precede any changes in metabolites such as FFA and glucose and appear to be associated with early IR in childhood. Excessive caloric intake increases IR in children; opposite, substantial reduction of overweight achieved by a hypocaloric diet decreases it. Elevated consumption of animal protein, particularly in early life, as well as diets rich in saturated, trans, and n-6 polyunsaturated fatty acids, and diets with a high carbohydrate to fat ratio, besides a high glycaemic and low-fiber diet also appear to exacerbate adiposity and IR.

Central administration of melanocortin agonist increased insulin sensitivity in diet-induced obese rats

In this study, we examined the effects of intracerebroventricular administration of melanotan II (MTII), a melanocortin agonist, on insulin sensitivity in diet-induced obese (DIO) rats. Although MTII treatment significantly decreased food intake and body weight for 10 days, there was no significant difference in body weight between MTII and pair-fed groups. The insulin tolerance test showed that insulin sensitivity was significantly improved in the MTII group compared to the pair-fed group. Furthermore, MTII treatment increased the number of small-sized adipocytes in epididymal white adipose tissues, suggesting that MTII increased insulin sensitivity through action on the white adipose tissues in DIO rats.

Unsupervised clustering of gene expression data points at hypoxia as possible trigger for metabolic syndrome

Background

Classification of large volumes of data produced in a microarray experiment allows for the extraction of important clues as to the nature of a disease.

Results

Using multi-dimensional unsupervised FOREL (FORmal ELement) algorithm we have re-analyzed three public datasets of skeletal muscle gene expression in connection with insulin resistance and type 2 diabetes (DM2). Our analysis revealed the major line of variation between expression profiles of normal, insulin resistant, and diabetic skeletal muscle. A cluster of most "metabolically sound" samples occupied one end of this line. The distance along this line coincided with the classic markers of diabetes risk, namely obesity and insulin resistance, but did not follow the accepted clinical diagnosis of DM2 as defined by the presence or absence of hyperglycemia. Genes implicated in this expression pattern are those controlling skeletal muscle fiber type and glycolytic metabolism. Additionally myoglobin and hemoglobin were upregulated and ribosomal genes deregulated in insulin resistant patients.

Conclusion

Our findings are concordant with the changes seen in skeletal muscle with altitude hypoxia. This suggests that hypoxia and shift to glycolytic metabolism may also drive insulin resistance.

Increased subcutaneous and epicardial adipose tissue production of proinflammatory cytokines in cardiac surgery patients: possible role in postoperative insulin resistance

CONTEXT

Hyperglycemia and insulin resistance frequently occur in critically ill patients even without a history of diabetes.

OBJECTIVE

Our objective was to study the role of adipose tissue hormonal production in the development of insulin resistance in cardiac surgery patients. PARTICIPANTS, INTERVENTIONS, AND SETTINGS: Fifteen patients with elective cardiac surgery underwent blood sampling before, at the end, and 6, 12, 24, 48, and 120 h after the end of their operation. Epicardial and sc adipose tissue sampling was done at the beginning and at the end of surgery in the Department of Cardiac Surgery.

MAIN OUTCOME MEASURES

We measured serum concentrations and sc and epicardial adipose tissue mRNA expression of IL-6, monocyte chemoattractant protein-1 (MCP-1), TNF-alpha, leptin, resistin, and adiponectin and sc and epicardial adipose tissue mRNA expression of CD14, CD45, and CD68.

RESULTS

The rate of insulin infusion required to maintain euglycemia increased up to 7-fold 12 h after the operation, suggesting the development of insulin resistance. Serum IL-6 levels increased 43-fold 12 h after surgery. MCP-1 peaked 6-fold at the end of surgery. Smaller peaks of TNF-alpha and leptin appeared 6 and 12 h after surgery, respectively. Resistin levels peaked 4-fold 24 h after surgery, but adiponectin levels were not significantly affected. TNF-alpha and CD45 mRNA expression increased markedly during the operation in sc adipose tissue. IL-6, resistin, and MCP-1 mRNA expression increased in both sc and epicardial adipose tissue. Leptin, adiponectin, CD14, and CD68 mRNA expression did not change significantly.

CONCLUSIONS

Both sc and epicardial adipose tissue is a source of proinflammatory cytokines in cardiac surgery patients and may contribute to the development of postoperative insulin resistance.

Alanine aminotransferase levels and fatty liver in childhood obesity: associations with insulin resistance, adiponectin, and visceral fat

BACKGROUND

Concurrent with the rise in obesity, nonalcoholic fatty liver disease is recognized as the leading cause of serum aminotransferase elevations in obese youth. Nevertheless, the complete metabolic phenotype associated with abnormalities in biomarkers of liver injury and intrahepatic fat accumulation remains to be established.

METHODS

In a multiethnic cohort of 392 obese adolescents, alanine aminotransferase (ALT) levels were related with parameters of insulin sensitivity, glucose, and lipid metabolism as well as adipocytokines and biomarkers of inflammation. A subset of 72 adolescents had determination of abdominal fat partitioning and intrahepatic fat accumulation using magnetic resonance imaging.

FINDINGS

Elevated ALT (> 35 U/liter) was found in 14% of adolescents, with a predominance of male gender and white/Hispanic race/ethnicity. After adjusting for potential confounders, rising ALT was associated with reduced insulin sensitivity and glucose tolerance as well as rising free fatty acids and triglycerides. Worsening of glucose and lipid metabolism was already evident as ALT levels rose into the upper half of the normal range (18-35 U/liter). When hepatic fat fraction was assessed using fast magnetic resonance imaging, 32% of subjects had an increased hepatic fat fraction, which was associated with decreased insulin sensitivity and adiponectin, and increased triglycerides, visceral fat, and deep to superficial sc fat ratio. The prevalence of the metabolic syndrome was significantly greater in those with fatty liver.

INTERPRETATION

Deterioration in glucose and lipid metabolism is associated even with modest ALT elevations. Hepatic fat accumulation in childhood obesity is strongly associated with the triad of insulin resistance, increased visceral fat, and hypoadiponectinemia. Hence, hepatic steatosis may be a core feature of the metabolic syndrome.

PAI-1 and the Metabolic Syndrome

The link between plasminogen activator inhibitor (PAI)-1 and the metabolic syndrome with obesity was established many years ago. Increased PAI-1 level can be now considered a true component of the syndrome. The metabolic syndrome is associated with an increased risk of developing cardiovascular disease, and PAI-1 overexpression may participate in this process. The mechanisms of PAI-1 overexpression during obesity are complex, and it is conceivable that several inducers are involved at the same time at several sites of synthesis. Interestingly, recent in vitro and in vivo studies showed that besides its role in atherothrombosis, PAI-1 is also implicated in adipose tissue development and in the control of insulin signaling in adipocytes. These findings suggest PAI-1 inhibitors serve in the control of atherothrombosis and insulin resistance.

Signaling specificity of interleukin-6 action on glucose and lipid metabolism in skeletal muscle

We identified signaling pathways by which IL-6 regulates skeletal muscle differentiation and metabolism. Primary human skeletal muscle cells were exposed to IL-6 (25 ng/ml either acutely or for several days), and small interfering RNA gene silencing was applied to measure glucose and fat metabolism. Chronic IL-6 exposure increased myotube fusion and formation and the mRNA expression of glucose transporter 4, peroxisome proliferator activated receptor (PPAR)alpha, PPARdelta, PPARgamma, PPARgamma coactivator 1, glycogen synthase, myocyte enhancer factor 2D, uncoupling protein 2, fatty acid transporter 4, and IL-6 (P < 0.05), whereas glucose transporter 1, CCAAT/enhancer-binding protein-alpha, and uncoupling protein 3 were decreased. IL-6 increased glucose incorporation into glycogen, glucose uptake, lactate production, and fatty acid uptake and oxidation, concomitant with increased phosphorylation of AMP-activated protein kinase (AMPK), signal transducer and activator of transcription 3, and ERK1/2. IL-6 also increased phosphatidylinositol (PI) 3-kinase activity (450%; P < 0.05), which was blunted by subsequent insulin-stimulation (P < 0.05). IL-6-mediated glucose metabolism was suppressed, but lipid metabolism was unaltered, by inhibition of PI3-kinase with LY294002. The small interfering RNA-directed depletion of AMPK reduced IL-6-mediated fatty acid oxidation and palmitate uptake but did not reduce glycogen synthesis. In summary, IL-6 increases glycogen synthesis via a PI3-kinase-dependent mechanism and enhances lipid oxidation via an AMPK-dependent mechanism in skeletal muscle. Thus, IL-6 directly promotes skeletal muscle differentiation and regulates muscle substrate utilization, promoting glycogen storage and lipid oxidation.

Increased subcutaneous and epicardial adipose tissue production of proinflammatory cytokines in cardiac surgery patients: possible role in postoperative insulin resistance

CONTEXT

Hyperglycemia and insulin resistance frequently occur in critically ill patients even without a history of diabetes.

OBJECTIVE

Our objective was to study the role of adipose tissue hormonal production in the development of insulin resistance in cardiac surgery patients. PARTICIPANTS, INTERVENTIONS, AND SETTINGS: Fifteen patients with elective cardiac surgery underwent blood sampling before, at the end, and 6, 12, 24, 48, and 120 h after the end of their operation. Epicardial and sc adipose tissue sampling was done at the beginning and at the end of surgery in the Department of Cardiac Surgery.

MAIN OUTCOME MEASURES

We measured serum concentrations and sc and epicardial adipose tissue mRNA expression of IL-6, monocyte chemoattractant protein-1 (MCP-1), TNF-alpha, leptin, resistin, and adiponectin and sc and epicardial adipose tissue mRNA expression of CD14, CD45, and CD68.

RESULTS

The rate of insulin infusion required to maintain euglycemia increased up to 7-fold 12 h after the operation, suggesting the development of insulin resistance. Serum IL-6 levels increased 43-fold 12 h after surgery. MCP-1 peaked 6-fold at the end of surgery. Smaller peaks of TNF-alpha and leptin appeared 6 and 12 h after surgery, respectively. Resistin levels peaked 4-fold 24 h after surgery, but adiponectin levels were not significantly affected. TNF-alpha and CD45 mRNA expression increased markedly during the operation in sc adipose tissue. IL-6, resistin, and MCP-1 mRNA expression increased in both sc and epicardial adipose tissue. Leptin, adiponectin, CD14, and CD68 mRNA expression did not change significantly.

CONCLUSIONS

Both sc and epicardial adipose tissue is a source of proinflammatory cytokines in cardiac surgery patients and may contribute to the development of postoperative insulin resistance.

Serum adiponectin and leptin concentrations in HIV-infected children with fat redistribution syndrome

Human immunodeficiency virus (HIV)-related lipodystrophy is characterized by adipose tissue redistribution, dyslipidemia, and insulin resistance. We hypothesized that fat redistribution and metabolic abnormalities in HIV-infected children are related to alterations in endocrine function of adipose tissue. A multicenter study was conducted in 130 HIV-infected children. Lipodystrophy definition was based on the central to peripheral skinfold ratio. Fasting adiponectin, leptin, insulin concentrations, glycemia, and lipid profile were measured in all children. Fat redistribution syndrome was apparent in 32 children: 14 with atrophic (LPDA) and 18 with hypertrophic lipodystrophy (LPDH). Mean serum adiponectin levels were significantly decreased in LPDA and LPDH groups compared with the group with no lipodystrophy (LPD-). Fasting insulin concentration was significantly higher in LPDA and LPDH groups versus LPD-. Mean serum leptin concentration was significantly increased only in LPDH compared with LPDA and LPD- groups. Triglyceride levels were significantly increased and high-density lipoprotein (HDL)-cholesterol concentration decreased in the LPDA versus LPD- group. Controlling for puberty stage, gender, percentage of total fat mass, serum lipids, HIV treatment, and disease severity, adiponectin was significantly and inversely associated with central obesity and insulin/glucose ratio. Fat redistribution had no significant effect on leptin concentration, which was directly related to the percentage of body fat, female gender, and insulin/glucose ratio. In conclusion, HIV-infected children with symptoms of fat redistribution have decreased levels of adiponectin, associated with insulin resistance and dyslipidemia.

Molecular cloning of Chinese hamster 1q31 chromosomal fragile site DNA that is important to mdr1 gene amplification reveals a novel gene whose expression is associated with spermatocyte and adipocyte differentiation

DNA amplification plays important roles in the development of drug resistance and tumor progression. One mechanism of DNA amplification involves the breakage-fusion-bridge (BFB) cycle. We previously reported that in Chinese hamster ovary (CHO) cell line, breakage at fragile site 1q31 was associated with mdr1 gene amplification through the BFB mechanism. To elucidate the molecular basis of BFB-mediated DNA amplification, we cloned 1q31 fragile site DNA from a Chinese hamster cell line containing an integrated neomycin-resistance marker. Sequence analyses revealed many characteristics similar to those in other common fragile sites. Moreover, this fragile site contains an evolutionarily conserved novel gene, designated fragile site-associated (FSA) gene. FSA encodes a approximately 16-kb mRNA, from which an unusually large open reading frame (orf) of 5005 amino acids can be deduced. The C-terminal portion of FSA shares a striking sequence similarity to that of Caenorhabditi elegans lipid depleted-3 (lpd-3) gene whose function has been demonstrated to involve in lipid storage. We also demonstrated that expression of FSA is associated with the developmental programs of spermatogenesis and adipogenesis. Our results suggest that the Chinese hamster 1q31 fragile site has many important functions including regulation of mdr1 amplification and differentiation of adipocytes and spermatocytes.

Changes of skeletal muscle adiponectin content in diet-induced insulin resistant rats

The current study examined the relationship between skeletal muscle levels of adiponectin and parameters of insulin sensitivity. A high fat/sucrose diet (HFD) for 20 weeks resulted in significant increases in body weight, serum insulin, triglycerides (TG), and free fatty acids (FFA) (all p < 0.01). Interestingly, this diet leads to a slight increase in serum adiponectin, but significant decreases in gastrocnemius muscle and white adipose adiponectin (all p < 0.05). HFD for 4 weeks also resulted in a significant decrease in muscle adiponectin, which correlated with serum insulin, TG, and FFA (all p < 0.05). Treatment of the 4-week HFD rats with a PPARgamma agonist GI262570 ameliorated the diet-induced hyperinsulinemia and dyslipidemia, and effectively restored muscle adiponectin (all p < 0.05). This study demonstrated that HFD-induced hyperinsulinemia and dyslipidemia appeared without changes in serum adiponectin, but were associated with decreased tissue adiponectin. This provides the first evidence for a connection between tissue adiponectin and diet-induced hyperinsulinemia and dyslipidemia.

Associations of anthropometric characteristics with blood cholesterol fractions among adults. The Greek EPIC study

OBJECTIVE

To explore the independent associations of body height, body mass index (BMI), waist circumference and hip circumference with high-density lipoprotein-cholesterol (HDL-cholesterol) and non-high-density lipoprotein-cholesterol (non-HDL-cholesterol), in a large general population sample.

DESIGN

Cross sectional.

SETTING

Urban and rural areas throughout Greece.

SUBJECTS

In total,10 837 volunteers, 2034 men and 8803 women, aged 25-82 years, participants in the European Prospective Investigation into Cancer and Nutrition study (EPIC), who have never smoked and never been treated for dyslipidemia.

INTERVENTIONS

None.

RESULTS

The effect of height on non-HDL-cholesterol was opposite but in absolute terms almost as important as that of BMI with no gender interaction. Among women, hip circumference was inversely associated with non-HDL-cholesterol (standardized coefficient bst = -1.11, with standard error (s.e.)=0.42) and positively with HDL-cholesterol (bst = 0.85, s.e.= 0.12) whereas, waist circumference was inversely associated with HDL-cholesterol (bst = -1.16, s.e.=0.13) and strongly positively with non-HDL-cholesterol (bst = 8.83, s.e.= 0.45). Among men, associations were generally weaker (in absolute terms by about 50%) and for hip circumference the association with non-HDL-cholesterol was actually non significantly positive.

CONCLUSIONS

Height was inversely associated with HDL and non-HDL-cholesterol implicating early life phenomena in the regulation of these variables. Larger hip circumference among women had beneficial effects on blood cholesterol fractions by increasing HDL-cholesterol and reducing non-HDL-cholesterol, whereas among men the relevant effects were less clear cut. The detrimental consequences of large waist circumference on both HDL (reduction) and non-HDL-cholesterol (increase) were also particularly marked among women.

SPONSORSHIP

The European Prospective Investigation into Cancer and Nutrition (EPIC) is coordinated by the International Agency for Research on Cancer (World Health Organization) and supported by the Europe Against Cancer Program of the European Commission. The Greek segment of the EPIC study is also supported by the Greek Ministry of Health and the Greek Ministry of Education. This study was additionally supported by the fellowship 'Vassilios and Nafsika Tricha'.

The melanocortin system and energy balance

The melanocortins, a family of peptides produced from the post-translational processing of pro-opiomelanocortin (POMC), regulate ingestive behavior and energy expenditure. Loss of function mutations of genes encoding POMC, or of either of two melanocortin receptors expressed in the central nervous system (MC3R, MC4R), are associated with obesity. The analyses of MC4R knockout mice indicate that activation of this receptor is involved in the regulation of appetite, the adaptive metabolic response to excess caloric consumption, and negative energy balance associated with cachexia induced by cytokines. In contrast, MC3R knockout mice exhibit a normal, or even exaggerated, response to signals that induce a state of negative energy balance. However, loss of the MC3R also results in an increase in adiposity. This article discusses the regulation of energy balance by the melanocortins. Published and newly presented data from studies analyzing of energy balance of MC3R and MC4R knockout mice indicate that increased adiposity observed in both models involves an imbalance in fat intake and oxidation.

Globular adiponectin decreases leptin-induced tumor necrosis factor-alpha expression by murine macrophages: involvement of cAMP-PKA and MAPK pathways

Several lines of evidence have supported a link between obesity and inflammation. The present study investigated the capacity of leptin and globular adiponectin to affect tumor necrosis factor alpha (TNF-alpha) production in murine peritoneal macrophages. Leptin stimulated TNF-alpha production at mRNA as well as protein levels in a dose- and time-dependent manner. Intracellular cAMP concentration was increased and protein kinase A (PKA) was activated with the treatment of leptin, subsequently downstream MAPK signal proteins, ERK1/2 and p38, were phosphorylated. Specific inhibitors for the signal proteins, Rp cAMPS, H89, PD98059, and U0126, or SB203580, suppressed the signaling pathway and TNF-alpha expression. Although gAd partially increased cAMP concentration and PKA activity, it directly reduced leptin-induced ERK1/2 and p38 MAPK phosphorylation thus inhibiting TNF-alpha production. In conclusion, leptin promotes inflammation by stimulating TNF-alpha production, which is mediated by cAMP-PKA-ERK1/2 and p38 MAPK pathways. gAd inhibited leptin-induced TNF-alpha production through suppressing phosphorylation of ERK1/2 and p38 pathways.

Dietary fat intake and insulin resistance in black and white children

OBJECTIVE

The purpose of this study was to determine whether dietary fat intake above current Acceptable Macronutrient Distribution Range (AMDR) guidelines was associated with greater insulin resistance in black and white children.

RESEARCH METHODS AND PROCEDURES

We studied 142 healthy children (n = 81 whites, n = 61 blacks), 6.5 to 14 years old. Dietary composition was determined by repeated 24-hour dietary recall, body composition by DXA, visceral fat by computed tomography, and insulin sensitivity (SI) and acute insulin response to glucose (AIRg) by frequently sampled intravenous glucose tolerance test. Subjects were categorized by ethnicity (white/black) and dietary fat intake (above-AMDR/within-AMDR guidelines), and differences were analyzed by 2 x 2 analysis of covariance, adjusting for covariates.

RESULTS

After adjusting for total body fat, gender, and Tanner stage, subjects consuming dietary fat above AMDR intake guidelines had lower SI and higher AIRg. This effect was specific to black children (32% lower SI and 62% higher AIRg in above-AMDR compared with within-AMDR blacks) and was not seen in whites.

DISCUSSION

In black, but not white, children, those with dietary fat intake above current AMDR guidelines had lower SI and higher AIRg than those who met AMDR guidelines. These findings support current AMDR guidelines for dietary fat in black children and adolescents. The mechanism(s) underlying the ethnic differences in the relationship between dietary fat intake and SI in children require further investigation.

Whole-body insulin resistance in the absence of obesity in FVB mice with overexpression of Dgat1 in adipose tissue

Insulin resistance is often associated with obesity. We tested whether augmentation of triglyceride synthesis in adipose tissue by transgenic overexpression of the diacylglycerol aclytransferase-1 (Dgat1) gene causes obesity and/or alters insulin sensitivity. Male FVB mice expressing the aP2-Dgat1 had threefold more Dgat1 mRNA and twofold greater DGAT activity levels in adipose tissue. After 30 weeks of age, these mice had hyperglycemia, hyperinsulinemia, and glucose intolerance on a high-fat diet but were not more obese than wild-type littermates. Compared with control littermates, Dgat1 transgenic mice were both insulin and leptin resistant and had markedly elevated plasma free fatty acid levels. Adipocytes from Dgat1 transgenic mice displayed increased basal and isoproterenol-stimulated lipolysis rates and decreased gene expression for fatty acid uptake. Muscle triglyceride content was unaffected, but liver mass and triglyceride content were increased by 20 and 300%, respectively. Hepatic insulin signaling was suppressed, as evidenced by decreased phosphorylation of insulin receptor-beta (Tyr(1,131)/Tyr(1,146)) and protein kinase B (Ser473). Gene expression data suggest that the gluconeogenic enzymes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, were upregulated. Thus, adipose overexpression of Dgat1 gene in FVB mice leads to diet-inducible insulin resistance, which is secondary to redistribution of fat from adipose tissue to the liver in the absence of obesity.

Fetal and neonatal exposure to nicotine in Wistar rats results in increased beta cell apoptosis at birth and postnatal endocrine and metabolic changes associated with type 2 diabetes

AIMS/HYPOTHESIS

Epidemiological studies report an increased risk of obesity and type 2 diabetes in children born to women who smoked during pregnancy. This study examines the effect of fetal and neonatal exposure to nicotine, the major addictive component of cigarettes, on postnatal growth, adiposity and glucose homeostasis.

METHODS

Female Wistar rats were given either saline (vehicle) or nicotine (1 mg kg(-1) day(-1)) during pregnancy and lactation. Serum and pancreas tissue were collected from the infant rats at birth. Postnatal growth was assessed weekly until the rats reached 26 weeks of age and glucose homeostasis was examined by OGTTs performed at 7 and 26 weeks of age.

RESULTS

Exposure to nicotine resulted in increased postnatal growth and adiposity. Nicotine exposure also resulted in dysglycaemia at 7 and 26 weeks of age. Serum insulin concentrations were decreased in the pups exposed to nicotine at birth. This was associated with increased beta cell apoptosis (pups of saline-treated mothers 8.8+/-1.21% apoptotic beta cells; pups of nicotine-treated mothers 27.8+/-3.1% apoptotic beta cells).

CONCLUSIONS/INTERPRETATION

Fetal and neonatal exposure to nicotine results in metabolic changes in the offspring that are consistent with obesity and type 2 diabetes. We propose that these metabolic changes may be a consequence of the initial insult to the beta cell during fetal life and that this animal model has many characteristics of diabetes in humans.

Pediatric obesity and insulin resistance: chronic disease risk and implications for treatment and prevention beyond body weight modification

The study of childhood obesity has continued to grow exponentially in the past decade. This has been driven in part by the increasing prevalence of this problem and the widespread potential effects of increased obesity in childhood on lifelong chronic disease risk. The focus of this review is on recent findings regarding the link between obesity and disease risk during childhood and adolescence. We describe recent reports relating to type 2 diabetes in youth (2), prediabetes (69, 166), metabolic syndrome (33, 35), polycystic ovarian syndrome (77), and nonalcoholic fatty liver disease (58, 146), and the mediating role of insulin resistance in these conditions. In addition, we review the implications of this research for the design of more effective treatment and prevention strategies that focus more on the improvement of obesity-related metabolic abnormalities and chronic disease risk reduction than on the conventional energy balance approach that focuses on weight management.

Inactivity, exercise, and visceral fat. STRRIDE: a randomized, controlled study of exercise intensity and amount

Despite the importance of randomized, dose-response studies for proper evaluation of effective clinical interventions, there have been no dose-response studies on the effects of exercise amount on abdominal obesity, a major risk factor for metabolic syndrome, diabetes, and cardiovascular disease. One hundred seventy-five sedentary, overweight men and women with mild to moderate dyslipidemia were randomly assigned to participate for 6 mo in a control group or for approximately 8 mo in one of three exercise groups: 1) low amount, moderate intensity, equivalent to walking 12 miles/wk (19.2 km) at 40-55% of peak oxygen consumption; 2) low amount, vigorous intensity, equivalent to jogging 12 miles/wk at 65-80% of peak oxygen consumption; or 3) high amount, vigorous intensity, equivalent to jogging 20 miles/wk (32.0 km). Computed tomography scans were analyzed for abdominal fat. Controls gained visceral fat (8.6 +/- 17.2%; P = 0.001). The equivalent of 11 miles of exercise per week, at either intensity, prevented significant accumulation of visceral fat. The highest amount of exercise resulted in decreased visceral (-6.9 +/- 20.8%; P = 0.038) and subcutaneous (-7.0 +/- 10.8%; P < 0.001) abdominal fat. Significant gains in visceral fat over only 6 mo emphasize the high cost of continued inactivity. A modest exercise program, consistent with recommendations from the Centers for Disease Control/American College of Sports Medicine (CDC/ACSM), prevented significant increases in visceral fat. Importantly, a modest increase over the CDC/ACSM exercise recommendations resulted in significant decreases in visceral, subcutaneous, and total abdominal fat without changes in caloric intake.

Substrate cycling between de novo lipogenesis and lipid oxidation: a thermogenic mechanism against skeletal muscle lipotoxicity and glucolipotoxicity

Life is a combustion, but how the major fuel substrates that sustain human life compete and interact with each other for combustion has been at the epicenter of research into the pathogenesis of insulin resistance ever since Randle proposed a 'glucose-fatty acid cycle' in 1963. Since then, several features of a mutual interaction that is characterized by both reciprocality and dependency between glucose and lipid metabolism have been unravelled, namely: the inhibitory effects of elevated concentrations of fatty acids on glucose oxidation (via inactivation of mitochondrial pyruvate dehydrogenase or via desensitization of insulin-mediated glucose transport),the inhibitory effects of elevated concentrations of glucose on fatty acid oxidation (via malonyl-CoA regulation of fatty acid entry into the mitochondria), and more recentlythe stimulatory effects of elevated concentrations of glucose on de novo lipogenesis, that is, synthesis of lipids from glucose (via SREBP1c regulation of glycolytic and lipogenic enzymes). This paper first revisits the physiological significance of these mutual interactions between glucose and lipids in skeletal muscle pertaining to both blood glucose and intramyocellular lipid homeostasis. It then concentrates upon emerging evidence, from calorimetric studies investigating the direct effect of leptin on thermogenesis in intact skeletal muscle, of yet another feature of the mutual interaction between glucose and lipid oxidation: that of substrate cycling between de novo lipogenesis and lipid oxidation. It is proposed that this energy-dissipating substrate cycling that links glucose and lipid metabolism to thermogenesis could function as a 'fine-tuning' mechanism that regulates intramyocellular lipid homeostasis, and hence contributes to the protection of skeletal muscle against lipotoxicity.

Adenovirus-mediated adiponectin expression augments skeletal muscle insulin sensitivity in male Wistar rats

In this study, we investigated the chronic in vivo effect of adiponectin on insulin sensitivity and glucose metabolism by overexpressing the adiponectin protein in male Wistar rats using intravenous administration of an adenovirus (Adv-Adipo). Virally infected liver secreted adiponectin as high and low molecular weight complexes. After 7 days of physiological or supraphysiological hyperadiponectinemia, the animals displayed enhanced insulin sensitivity during the glucose tolerance and insulin tolerance tests. Glucose clamp studies performed at submaximal and maximal insulin infusion rates (4 and 25 mU x kg(-1) x min(-1), respectively) also demonstrated increased insulin sensitivity in Adv-Adipo animals, with the insulin-stimulated glucose disposal rate being increased by 20-67%. In contrast, insulin's effect on the suppression of hepatic glucose output and plasma free fatty acid levels was not enhanced in Adv-Adipo rats compared with controls, suggesting that high levels of adiponectin expression in the liver may lead to a local desensitization. Consistent with the clamp data, the activation of AMP-activated protein kinase was significantly enhanced in skeletal muscle (by 50%) but not in liver. One interesting finding was that in male Wistar rats, both AdipoR1 and AdipoR2 expression levels were higher in skeletal muscle than in liver, as it is the case in humans. These results indicate that chronic adiponectin treatment enhances insulin sensitivity and could serve as a therapy for human insulin resistance.