High-throughput and virtual screening are widely used to discover novel leads for drug design. On examination, many screening hits appear non-drug-like: they act noncompetitively, show little relationship between structure and activity, and have poor selectivity. Attempts to develop these peculiar molecules into viable leads are often futile, and much time can be wasted on the characterization of these "phony" hits. Despite their common occurrence, the mechanism of action of these promiscuous molecules remains unknown. To investigate this problem, 45 diverse screening hits were studied. Fifteen of these were previously reported as inhibitors of various receptors, including beta-lactamase, malarial protease, dihydrofolate reductase, HIV Tar RNA, thymidylate synthase, kinesin, insulin receptor, tyrosine kinases, farnesyltransferase, gyrase, prions, triosephosphate isomerase, nitric oxide synthase, phosphoinositide 3-kinase, and integrase; 30 were from an in-house screening library of a major pharmaceutical company. In addition to their original targets, 35 of these 45 compounds were shown to inhibit several unrelated model enzymes. These 35 screening hits included compounds, such as fullerenes, dyes, and quercetin, that have repeatedly shown activity against diverse targets. When tested against the model enzymes, the compounds showed time-dependent but reversible inhibition that was dramatically attenuated by albumin, guanidinium, or urea. Surprisingly, increasing the concentration of the model enzymes 10-fold largely eliminated inhibition, despite a 1000-fold excess of inhibitor; a well-behaved competitive inhibitor did not show this behavior. One model to explain these observations was that the active form of the promiscuous inhibitors was an aggregate of many individual molecules. To test this hypothesis, light scattering and electron microscopy experiments were performed. The nonspecific inhibitors were observed to form particles of 30-400 nm diameter by both techniques. In control experiments, a well-behaved competitive inhibitor and an inactive dye-like molecule were not observed to form aggregates. Consistent with the hypothesis that the aggregates are the inhibitory species, the particle size and IC(50) values of the promiscuous inhibitors varied monotonically with ionic strength; a competitive inhibitor was unaffected by changes in ionic strength. Unexpectedly, aggregate formation appears to explain the activity of many nonspecific inhibitors and may account for the activity of many promiscuous screening hits. Molecules acting via this mechanism may be widespread in drug discovery screening databases. Recognition of these compounds may improve screening results in many areas of pharmaceutical interest.

OBJECTIVE

An optimal target for glucose control in ICU patients remains unclear. This prospective randomized controlled trial compared the effects on ICU mortality of intensive insulin therapy (IIT) with an intermediate glucose control.

METHODS

Adult patients admitted to the 21 participating medico-surgical ICUs were randomized to group 1 (target BG 7.8-10.0 mmol/L) or to group 2 (target BG 4.4-6.1 mmol/L).

RESULTS

While the required sample size was 1,750 per group, the trial was stopped early due to a high rate of unintended protocol violations. From 1,101 admissions, the outcomes of 542 patients assigned to group 1 and 536 of group 2 were analysed. The groups were well balanced. BG levels averaged in group 1 8.0 mmol/L (IQR 7.1-9.0) (median of all values) and 7.7 mmol/L (IQR 6.7-8.8) (median of morning BG) versus 6.5 mmol/L (IQR 6.0-7.2) and 6.1 mmol/L (IQR 5.5-6.8) for group 2 (p < 0.0001 for both comparisons). The percentage of patients treated with insulin averaged 66.2 and 96.3%, respectively. Proportion of time spent in target BG was similar, averaging 39.5% and 45.1% (median (IQR) 34.3 (18.5-50.0) and 39.3 (26.2-53.6)%) in the groups 1 and 2, respectively. The rate of hypoglycaemia was higher in the group 2 (8.7%) than in group 1 (2.7%, p < 0.0001). ICU mortality was similar in the two groups (15.3 vs. 17.2%).

CONCLUSIONS

In this prematurely stopped and therefore underpowered study, there was a lack of clinical benefit of intensive insulin therapy (target 4.4-6.1 mmol/L), associated with an increased incidence of hypoglycaemia, as compared to a 7.8-10.0 mmol/L target. (ClinicalTrials.gov # NCT00107601, EUDRA-CT Number: 200400391440).

Since the discovery of glucocorticoids in the 1940s and the recognition of their anti-inflammatory effects, they have been amongst the most widely used and effective treatments to control inflammatory and autoimmune diseases. However, their clinical efficacy is compromised by the metabolic effects of long-term treatment, which include osteoporosis, hypertension, dyslipidaemia and insulin resistance/type 2 diabetes mellitus. In recent years, a great deal of effort has been invested in identifying compounds that separate the beneficial anti-inflammatory effects from the adverse metabolic effects of glucocorticoids, with limited effect. It is clear that for these efforts to be effective, a greater understanding is required of the mechanisms by which glucocorticoids exert their anti-inflammatory and immunosuppressive actions. Recent research is shedding new light on some of these mechanisms and has produced some surprising new findings. Some of these recent developments are reviewed here.

The hallmark of type 2 diabetes is excessive hepatic glucose production. Several transcription factors and coactivators regulate this process in cultured cells. But gene ablation experiments have yielded few clues as to the physiologic mediators of this process in vivo. We show that inactivation of the gene encoding forkhead protein Foxo1 in mouse liver results in 40% reduction of glucose levels at birth and 30% reduction in adult mice after a 48 hr fast. Gene expression and glucose clamp studies demonstrate that Foxo1 ablation impairs fasting- and cAMP-induced glycogenolysis and gluconeogenesis. Pgc1alpha is unable to induce gluconeogenesis in Foxo1-deficient hepatocytes, while the cAMP response is significantly blunted. Conversely, Foxo1 deletion in liver curtails excessive glucose production caused by generalized ablation of insulin receptors and prevents neonatal diabetes and hepatosteatosis in insulin receptor knockout mice. The data provide a unifying mechanism for regulation of hepatic glucose production by cAMP and insulin.

Leptin, or OB protein, is produced by fat cells and may regulate body weight by acting on the brain. To reach the brain, circulating leptin must cross the blood-brain barrier (BBB). Intravenously injected radioiodinated leptin (125I-leptin) had an influx constant (Ki) into brain of (5.87)10(-4) ml/g-min, a rate 20 times greater than that of labeled albumin. Unlabeled leptin inhibited the influx of 125I-leptin in a dose-dependent manner whereas unlabeled tyrosine and insulin, which have saturable transport systems, were without effect. HPLC and acid precipitation showed that the radioactivity in brain and serum represented intact 125I-leptin. About 75% of the extravascular 125I-leptin in brain completely crossed the BBB to reach brain parenchyma. Autoradiography detected uptake at the choroid plexus, arcuate nuclei of the hypothalamus, and the median eminence. Saturable transport did not occur out of the brain. The results show that leptin is transported intact from blood to brain by a saturable system.

The serum- and glucocorticoid-inducible kinase-1 (SGK1) is ubiquitously expressed and under genomic control by cell stress (including cell shrinkage) and hormones (including gluco- and mineralocorticoids). Similar to its isoforms SGK2 and SGK3, SGK1 is activated by insulin and growth factors via phosphatidylinositol 3-kinase and the 3-phosphoinositide-dependent kinase PDK1. SGKs activate ion channels (e.g., ENaC, TRPV5, ROMK, Kv1.3, KCNE1/KCNQ1, GluR1, GluR6), carriers (e.g., NHE3, GLUT1, SGLT1, EAAT1-5), and the Na+-K+-ATPase. They regulate the activity of enzymes (e.g., glycogen synthase kinase-3, ubiquitin ligase Nedd4-2, phosphomannose mutase-2) and transcription factors (e.g., forkhead transcription factor FKHRL1, beta-catenin, nuclear factor kappaB). SGKs participate in the regulation of transport, hormone release, neuroexcitability, cell proliferation, and apoptosis. SGK1 contributes to Na+ retention and K+ elimination of the kidney, mineralocorticoid stimulation of salt appetite, glucocorticoid stimulation of intestinal Na+/H+ exchanger and nutrient transport, insulin-dependent salt sensitivity of blood pressure and salt sensitivity of peripheral glucose uptake, memory consolidation, and cardiac repolarization. A common ( approximately 5% prevalence) SGK1 gene variant is associated with increased blood pressure and body weight. SGK1 may thus contribute to metabolic syndrome. SGK1 may further participate in tumor growth, neurodegeneration, fibrosing disease, and the sequelae of ischemia. SGK3 is required for adequate hair growth and maintenance of intestinal nutrient transport and influences locomotive behavior. In conclusion, the SGKs cover a wide variety of physiological functions and may play an active role in a multitude of pathophysiological conditions. There is little doubt that further targets will be identified that are modulated by the SGK isoforms and that further SGK-dependent in vivo physiological functions and pathophysiological conditions will be defined.

OBJECTIVE

Simple fasting methods to measure insulin resistance, such as the homeostasis model assessment (HOMA), fasting glucose/insulin ratio (FGIR), and quantitative insulin sensitivity check index (QUICKI) methods, have been widely promoted for adult studies but have not been evaluated formally among children and adolescents. The aim of this study was to compare the HOMA, FGIR, and QUICKI methods for measuring insulin resistance, expressed by oral glucose tolerance test (OGTT) results, among obese children and adolescents.

METHODS

Fifty-seven pubertal obese children and adolescents (30 girls and 27 boys; mean age, 12.04 +/- 2.90 years; mean BMI: 29.57 +/- 5.53) participated in the study. All participants underwent an OGTT. Blood samples were obtained 0, 30, 60, 90, and 120 minutes after oral glucose administration for glucose and insulin measurements, and 2 separate groups were studied, according to the presence or absence of insulin resistance. HOMA, FGIR, and QUICKI methods were studied for validation of insulin resistance determined with the OGTT for these groups.

RESULTS

The groups consisted of 25 obese children and adolescents with insulin resistance (14 girls and 11 boys; mean age: 12.88 +/- 2.88 years; mean BMI: 31.29 +/- 5.86) and 32 subjects without insulin resistance (16 girls and 16 boys; mean age: 11.38 +/- 2.79 years; mean BMI: 28.23 +/- 4.94). There were significant differences in the mean HOMA (6.06 +/- 4.98 and 3.42 +/- 3.14, respectively) and QUICKI (0.313 +/- 0.004 and 0.339 +/- 0.004, respectively) values between the 2 groups. Sensitivity and specificity calculations based on insulin resistance with receiver operating characteristic curve analysis indicated that HOMA had high sensitivity and specificity for measuring insulin resistance.

CONCLUSIONS

As a measure of insulin resistance among children and adolescents, HOMA is more reliable than FGIR and QUICKI. The present HOMA cutoff point for diagnosis of insulin resistance is 3.16. The HOMA cutoff point of >2.5 is valid for adults but not for adolescents.

Studies of Drosophila and mammals have revealed the importance of insulin signaling through phosphatidylinositol 3-kinase and the serine/threonine kinase Akt/protein kinase B for the regulation of cell, organ, and organismal growth. In mammals, three highly conserved proteins, Akt1, Akt2, and Akt3, comprise the Akt family, of which the first two are required for normal growth and metabolism, respectively. Here we address the function of Akt3. Like Akt1, Akt3 is not required for the maintenance of normal carbohydrate metabolism but is essential for the attainment of normal organ size. However, in contrast to Akt1-/- mice, which display a proportional decrease in the sizes of all organs, Akt3-/- mice present a selective 20% decrease in brain size. Moreover, although Akt1- and Akt3-deficient brains are reduced in size to approximately the same degree, the absence of Akt1 leads to a reduction in cell number, whereas the lack of Akt3 results in smaller and fewer cells. Finally, mammalian target of rapamycin signaling is attenuated in the brains of Akt3-/- but not Akt1-/- mice, suggesting that differential regulation of this pathway contributes to an isoform-specific regulation of cell growth.

Endothelial dysfunction is characterized by a shift of the actions of the endothelium toward reduced vasodilation, a proinflammatory state, and prothrombic properties. It is associated with most forms of cardiovascular disease, such as hypertension, coronary artery disease, chronic heart failure, peripheral artery disease, diabetes, and chronic renal failure. Mechanisms that participate in the reduced vasodilatory responses in endothelial dysfunction include reduced nitric oxide generation, oxidative excess, and reduced production of hyperpolarizing factor. Upregulation of adhesion molecules, generation of chemokines such as macrophage chemoattractant peptide-1, and production of plasminogen activator inhibitor-1 participate in the inflammatory response and contribute to a prothrombic state. Vasoactive peptides such as angiotensin II and endothelin-1; the accumulation of asymmetric dimethylarginine, an endogenous nitric oxide inhibitor; hypercholesterolemia; hyperhomocysteinemia; altered insulin signaling; and hyperglycemia can contribute to these different mechanisms. Detachment and apoptosis of endothelial cells (anoikis) are associated phenomena. Endothelial dysfunction is an important early event in the pathogenesis of atherosclerosis, contributing to plaque initiation and progression. Reductions in circulating endothelial progenitor cells that participate in regeneration of the endothelium participate in endothelial pathophysiology. The severity of endothelial dysfunction has been shown to have prognostic value for cardiovascular events. Correction of endothelial dysfunction may be associated with reduced cardiovascular risk. Circulating endothelial progenitor cells may represent a potential therapeutic approach for endothelial dysfunction.

Insulin resistance is often characterized as the most critical factor contributing to the development of type 2 diabetes. SIRT1 has been reported to be involved in the processes of glucose metabolism and insulin secretion. However, whether SIRT1 is directly involved in insulin sensitivity is still largely unknown. Here we show that SIRT1 is downregulated in insulin-resistant cells and tissues and that knockdown or inhibition of SIRT1 induces insulin resistance. Furthermore, increased expression of SIRT1 improved insulin sensitivity, especially under insulin-resistant conditions. Similarly, resveratrol, a SIRT1 activator, enhanced insulin sensitivity in vitro in a SIRT1-dependent manner and attenuated high-fat-diet-induced insulin resistance in vivo at a dose of 2.5 mg/kg/day. Further studies demonstrated that the effect of SIRT1 on insulin resistance is mediated by repressing PTP1B transcription at the chromatin level. Taken together, the finding that SIRT1 improves insulin sensitivity has implications toward resolving insulin resistance and type 2 diabetes.

The nuclear receptor family of PPARs was named for the ability of the original member to induce hepatic peroxisome proliferation in mice in response to xenobiotic stimuli. However, studies on the action and structure of the 3 human PPAR isotypes (PPARalpha, PPARdelta, and PPARgamma) suggest that these moieties are intimately involved in nutrient sensing and the regulation of carbohydrate and lipid metabolism. PPARalpha and PPARdelta appear primarily to stimulate oxidative lipid metabolism, while PPARgamma is principally involved in the cellular assimilation of lipids via anabolic pathways. Our understanding of the functions of PPARgamma in humans has been increased by the clinical use of potent agonists and by the discovery of both rare and severely deleterious dominant-negative mutations leading to a stereotyped syndrome of partial lipodystrophy and severe insulin resistance, as well as more common sequence variants with a much smaller impact on receptor function. These may nevertheless have much greater significance for the public health burden of metabolic disease. This Review will focus on the role of PPARgamma in human physiology, with specific reference to clinical pharmacological studies, and analysis of PPARG gene variants in the abnormal lipid and carbohydrate metabolism of the metabolic syndrome.

OBJECTIVE

To assess pairwise differences between placebo, unopposed estrogen, and each of three estrogen/progestin regimens on selected heart disease risk factors in healthy postmenopausal women.

METHODS

A 3-year, multicenter, randomized, double-blind, placebo-controlled trial.

METHODS

A total of 875 healthy postmenopausal women aged 45 to 64 years who had no known contraindication to hormone therapy.

METHODS

Participants were randomly assigned in equal numbers to the following groups: (1) placebo; (2) conjugated equine estrogen (CEE), 0.625 mg/d; (3) CEE, 0.625 mg/d plus cyclic medroxyprogesterone acetate (MPA), 10 mg/d for 12 d/mo; (4) CEE, 0.625 mg/d plus consecutive MPA, 2.5 mg/d; or (5) CEE, 0.625 mg/d plus cyclic micronized progesterone (MP), 200 mg/d for 12 d/mo. PRIMARY ENDPOINTS: Four endpoints were chosen to represent four biological systems related to the risk of cardiovascular disease: (1) high-density lipoprotein cholesterol (HDL-C), (2) systolic blood pressure, (3) serum insulin, and (4) fibrinogen.

METHODS

Analyses presented are by intention to treat. P values for primary endpoints are adjusted for multiple comparisons; 95% confidence intervals around estimated effects were calculated without this adjustment.

RESULTS

Mean changes in HDL-C segregated treatment regimens into three statistically distinct groups: (1) placebo (decrease of 0.03 mmol/L [1.2 mg/dL]); (2) MPA regimens (increases of 0.03 to 0.04 mmol/L [1.2 to 1.6 mg/dL]); and (3) CEE with cyclic MP (increase of 0.11 mmol/L [4.1 mg/dL]) and CEE alone (increase of 0.14 mmol/L [5.6 mg/dL]). Active treatments decreased mean low-density lipoprotein cholesterol (0.37 to 0.46 mmol/L [14.5 to 17.7 mg/dL]) and increased mean triglyceride (0.13 to 0.15 mmol/L [11.4 to 13.7 mg/dL]) compared with placebo. Placebo was associated with a significantly greater increase in mean fibrinogen than any active treatment (0.10 g/L compared with -0.02 to 0.06 g/L); differences among active treatments were not significant. Systolic blood pressure increased and postchallenge insulin levels decreased during the trial, but neither varied significantly by treatment assignment. Compared with other active treatments, unopposed estrogen was associated with a significantly increased risk of adenomatous or atypical hyperplasia (34% vs 1%) and of hysterectomy (6% vs 1%). No other adverse effect differed by treatment assignment or hysterectomy status.

CONCLUSIONS

Estrogen alone or in combination with a progestin improves lipoproteins and lowers fibrinogen levels without detectable effects on postchallenge insulin or blood pressure. Unopposed estrogen is the optimal regimen for elevation of HDL-C, but the high rate of endometrial hyperplasia restricts use to women without a uterus. In women with a uterus, CEE with cyclic MP has the most favorable effect on HDL-C and no excess risk of endometrial hyperplasia.

The signal transducer and activator of transcription, STAT5b, has been implicated in signal transduction pathways for a number of cytokines and growth factors, including growth hormone (GH). Pulsatile but not continuous GH exposure activates liver STAT5b by tyrosine phosphorylation, leading to dimerization, nuclear translocation, and transcriptional activation of the STAT, which is proposed to play a key role in regulating the sexual dimorphism of liver gene expression induced by pulsatile plasma GH. We have evaluated the importance of STAT5b for the physiological effects of GH pulses using a mouse gene knockout model. STAT5b gene disruption led to a major loss of multiple, sexually differentiated responses associated with the sexually dimorphic pattern of pituitary GH secretion. Male-characteristic body growth rates and male-specific liver gene expression were decreased to wild-type female levels in STAT5b-/- males, while female-predominant liver gene products were increased to a level intermediate between wild-type male and female levels. Although these responses are similar to those observed in GH-deficient Little mice, STAT5b-/- mice are not GH-deficient, suggesting that they may be GH pulse-resistant. Indeed, the dwarfism, elevated plasma GH, low plasma insulin-like growth factor I, and development of obesity seen in STAT5b-/- mice are all characteristics of Laron-type dwarfism, a human GH-resistance disease generally associated with a defective GH receptor. The requirement of STAT5b to maintain sexual dimorphism of body growth rates and liver gene expression suggests that STAT5b may be the major, if not the sole, STAT protein that mediates the sexually dimorphic effects of GH pulses in liver and perhaps other target tissues. STAT5b thus has unique physiological functions for which, surprisingly, the highly homologous STAT5a is unable to substitute.

Fatty acid binding proteins (FABPs) are small cytoplasmic proteins that are expressed in a highly tissue-specific manner and bind to fatty acids such as oleic and retinoic acid. Mice with a null mutation in aP2, the gene encoding the adipocyte FABP, were developmentally and metabolically normal. The aP2-deficient mice developed dietary obesity but, unlike control mice, they did not develop insulin resistance or diabetes. Also unlike their obese wild-type counterparts, obese aP2-/- animals failed to express in adipose tissue tumor necrosis factor-alpha (TNF-alpha), a molecule implicated in obesity-related insulin resistance. These results indicate that aP2 is central to the pathway that links obesity to insulin resistance, possibly by linking fatty acid metabolism to expression of TNF-alpha.

The bile acid receptor farnesoid X receptor (FXR; NR1H4) is a central regulator of bile acid and lipid metabolism. We show here that FXR plays a key regulatory role in glucose homeostasis. FXR-null mice developed severe fatty liver and elevated circulating FFAs, which was associated with elevated serum glucose and impaired glucose and insulin tolerance. Their insulin resistance was confirmed by the hyperinsulinemic euglycemic clamp, which showed attenuated inhibition of hepatic glucose production by insulin and reduced peripheral glucose disposal. In FXR-/- skeletal muscle and liver, multiple steps in the insulin signaling pathway were markedly blunted. In skeletal muscle, which does not express FXR, triglyceride and FFA levels were increased, and we propose that their inhibitory effects account for insulin resistance in that tissue. In contrast to the results in FXR-/- mice, bile acid activation of FXR in WT mice repressed expression of gluconeogenic genes and decreased serum glucose. The absence of this repression in both FXR-/- and small heterodimer partner-null (SHP-/-) mice demonstrated that the previously described FXR-SHP nuclear receptor cascade also targets glucose metabolism. Taken together, our results identify a link between lipid and glucose metabolism mediated by the FXR-SHP cascade.

Diabetic retinopathy remains a frightening prospect to patients and frustrates physicians. Destruction of damaged retina by photocoagulation remains the primary treatment nearly 50 years after its introduction. The diabetes pandemic requires new approaches to understand the pathophysiology and improve the detection, prevention, and treatment of retinopathy. This perspective considers how the unique anatomy and physiology of the retina may predispose it to the metabolic stresses of diabetes. The roles of neural retinal alterations and impaired retinal insulin action in the pathogenesis of early retinopathy and the mechanisms of vision loss are emphasized. Potential means to overcome limitations of current animal models and diagnostic testing are also presented with the goal of accelerating therapies to manage retinopathy in the face of ongoing diabetes.

Glucagon-like peptide-1 (GLP-1) is an enteric hormone that stimulates insulin secretion and improves glycaemia in type 2 diabetes. Although GLP-1-based treatments are clinically available, alternative strategies to increase endogenous GLP-1 release from L cells are hampered by our limited physiological understanding of this cell type. By generating transgenic mice with L cell-specific expression of a fluorescent protein, we studied the characteristics of primary L cells by electrophysiology, fluorescence calcium imaging, and expression analysis and show that single L cells are electrically excitable and glucose responsive. Sensitivity to tolbutamide and low-millimolar concentrations of glucose and alpha-methylglucopyranoside, assessed in single L cells and by hormone secretion from primary cultures, suggested that GLP-1 release is regulated by the activity of sodium glucose cotransporter 1 and ATP-sensitive K(+) channels, consistent with their high expression levels in purified L cells by quantitative RT-PCR. These and other pathways identified using this approach will provide exciting opportunities for future physiological and therapeutic exploration.

In this review article, the crucial roles of adipocytes in the development of so-called metabolic syndrome and vascular disease are reviewed, focusing on adipocyte-derived bioactive substances, adipocytokines. Recent progress in adipocyte biology shows that adipocytes are not merely energy-storing cells but that they secrete a variety of hormones cytokines, growth factors, and other bioactive substances. To search for novel adipocytokines by the large-scale random sequence analysis of expressed genes in adipocytes, we identified an adipose-specific collagen-like molecule, adiponectin. This novel adipocytokine has plural biofunctions, such as antidiabetic, antiatherosclerotic, and antiinflammatory functions. Adiponectin plasma levels decrease with the accumulation of visceral adipose tissue. In this review, we discuss the link of adiponectin to visceral adiposity, insulin resistance, and vascular diseases.

Acetylation is increasingly recognized as an important metabolic regulatory posttranslational protein modification, yet the metabolic consequence of mitochondrial protein hyperacetylation is unknown. We find that high-fat diet (HFD) feeding induces hepatic mitochondrial protein hyperacetylation in mice and downregulation of the major mitochondrial protein deacetylase SIRT3. Mice lacking SIRT3 (SIRT3KO) placed on a HFD show accelerated obesity, insulin resistance, hyperlipidemia, and steatohepatitis compared to wild-type (WT) mice. The lipogenic enzyme stearoyl-CoA desaturase 1 is highly induced in SIRT3KO mice, and its deletion rescues both WT and SIRT3KO mice from HFD-induced hepatic steatosis and insulin resistance. We further identify a single nucleotide polymorphism in the human SIRT3 gene that is suggestive of a genetic association with the metabolic syndrome. This polymorphism encodes a point mutation in the SIRT3 protein, which reduces its overall enzymatic efficiency. Our findings show that loss of SIRT3 and dysregulation of mitochondrial protein acetylation contribute to the metabolic syndrome.

This review will provide insight on the current understanding of the regulation of insulin signaling in both physiological and pathological conditions through modulations that occur with regards to the functions of the insulin receptor substrate 1 (IRS1). While the phosphorylation of IRS1 on tyrosine residue is required for insulin-stimulated responses, the phosphorylation of IRS1 on serine residues has a dual role, either to enhance or to terminate the insulin effects. The activation of PKB in response to insulin propagates insulin signaling and promotes the phosphorylation of IRS1 on serine residue in turn generating a positive-feedback loop for insulin action. Insulin also activates several kinases and these kinases act to induce the phosphorylation of IRS1 on specific sites and inhibit its functions. This is part of the negative-feedback control mechanism induced by insulin that leads to termination of its action. Agents such as free fatty acids, cytokines, angiotensin II, endothelin-1, amino acids, cellular stress and hyperinsulinemia, which induce insulin resistance, lead to both activation of several serine/threonine kinases and phosphorylation of IRS1. These agents negatively regulate the IRS1 functions by phosphorylation but also via others molecular mechanisms (SOCS expression, IRS degradation, O-linked glycosylation) as summarized in this review. Understanding how these agents inhibit IRS1 functions as well as identification of kinases involved in these inhibitory effects may provide novel targets for development of strategies to prevent insulin resistance.

Type 1 diabetes (T1D) in children results from autoimmune destruction of pancreatic beta cells, leading to insufficient production of insulin. A number of genetic determinants of T1D have already been established through candidate gene studies, primarily within the major histocompatibility complex but also within other loci. To identify new genetic factors that increase the risk of T1D, we performed a genome-wide association study in a large paediatric cohort of European descent. In addition to confirming previously identified loci, we found that T1D was significantly associated with variation within a 233-kb linkage disequilibrium block on chromosome 16p13. This region contains KIAA0350, the gene product of which is predicted to be a sugar-binding, C-type lectin. Three common non-coding variants of the gene (rs2903692, rs725613 and rs17673553) in strong linkage disequilibrium reached genome-wide significance for association with T1D. A subsequent transmission disequilibrium test replication study in an independent cohort confirmed the association. These results indicate that KIAA0350 might be involved in the pathogenesis of T1D and demonstrate the utility of the genome-wide association approach in the identification of previously unsuspected genetic determinants of complex traits.

Signaling from the DAF-2/insulin receptor to the DAF-16/FOXO transcription factor controls longevity, metabolism, and development in disparate phyla. To identify genes that mediate the conserved biological outputs of daf-2/insulin-like signaling, we used comparative genomics to identify 17 orthologous genes from Caenorhabditis and Drosophila, each of which bears a DAF-16 binding site in the promoter region. One-third of these DAF-16 downstream candidate genes were regulated by daf-2/insulin-like signaling in C. elegans, and RNA interference inactivation of the candidates showed that many of these genes mediate distinct aspects of daf-16 function, including longevity, metabolism, and development.

Non-alcoholic fatty liver disease (NAFLD) is rapidly becoming the most common liver disease worldwide. The prevalence of NAFLD in the general population of Western countries is 20-30%. About 2-3% of the general population is estimated to have non-alcoholic steatohepatitis (NASH), which may progress to liver cirrhosis and hepatocarcinoma. As a rule, the prevalence of NAFLD is higher in males and increases with increasing age, and it is influenced by the diagnostic method and the characteristics of the population, especially lifestyle habits. Population-based studies provide better estimates of the prevalence of NAFLD as compared to autoptic and clinical studies, but few such studies have been performed to date. The diagnosis of NAFLD in population studies is usually obtained by ultrasonography, which is known to underestimate the prevalence of fatty liver. The Dallas Heart Study and the Dionysos Study reported that 30% of the adults in the USA and 25% in Italy have NAFLD. In these studies, 79% and 55% of patients with NAFLD had normal aminotransferase levels, showing that liver enzymes are not surrogate markers of NAFLD in the general population. Noninvasive markers such as the fatty liver index obtained from the Dionysos Study may be useful to screen for NAFLD in the general population. The most important risk factors for NAFLD are male gender, age, obesity, insulin resistance and the cardiometabolic alterations that define the metabolic syndrome. The prevalence of NAFLD is 80-90% in obese adults, 30-50% in patients with diabetes and up to 90% in patients with hyperlipidemia. The prevalence of NAFLD among children is 3-10%, rising up to 40-70% among obese children. Moreover, pediatric NAFLD increased from about 3% a decade ago to 5% today, with a male-to-female ratio of 2:1. The incidence and natural history of NAFLD are still not well defined, but it is recognized that the majority of individuals with NAFLD do not develop NASH. The incidence of NAFLD is probably increasing in Western countries, strictly linked to lifestyle habits.

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy in women of reproductive age, with a prevalence of up to 10%. Various diagnostic criteria have been proposed, generally centered around the features of hyperandrogenism and/or hyperandrogenemia, oligo-ovulation and polycystic ovarian morphology. Insulin resistance is present in a majority of cases, with compensatory hyperinsulinemia contributing to hyperandrogenism via stimulation of ovarian androgen secretion and inhibition of hepatic sex hormone-binding globulin production. Adipose tissue dysfunction has been implicated as a contributor to the insulin resistance observed in PCOS. Environmental and genetic factors also have a role in the development of PCOS. The syndrome is associated with numerous morbidities, including infertility, obstetrical complications, type 2 diabetes mellitus, cardiovascular disease, and mood and eating disorders. Despite these morbidities, PCOS may be common in our society owing to evolutionary advantages of the syndrome in ancient times, including smaller family sizes, reduced exposure to childbirth-related mortality, increased muscle mass and greater capacity to store energy. The diagnosis of PCOS hinges on establishing key features while ruling out other hyperandrogenic or oligo-ovulatory disorders. Treatment is focused on the goals of ameliorating hyperandrogenic symptoms, inducing ovulation and preventing cardiometabolic complications.