Estrogens influence many physiological processes in mammals, including but not limited to reproduction, cardiovascular health, bone integrity, cognition, and behavior. Given this widespread role for estrogen in human physiology, it is not surprising that estrogen is also implicated in the development or progression of numerous diseases, which include but are not limited to various types of cancer (breast, ovarian, colorectal, prostate, endometrial), osteoporosis, neurodegenerative diseases, cardiovascular disease, insulin resistance, lupus erythematosus, endometriosis, and obesity. In many of these diseases, estrogen mediates its effects through the estrogen receptor (ER), which serves as the basis for many therapeutic interventions. This Review will describe diseases in which estrogen, through the ER, plays a role in the development or severity of disease.

Tumor suppressor genes evolved as negative effectors of mitogen and nutrient signaling pathways, such that mutations in these genes can lead to pathological states of growth. Tuberous sclerosis (TSC) is a potentially devastating disease associated with mutations in two tumor suppressor genes, TSC1 and 2, that function as a complex to suppress signaling in the mTOR/S6K/4E-BP pathway. However, the inhibitory target of TSC1/2 and the mechanism by which it acts are unknown. Here we provide evidence that TSC1/2 is a GAP for the small GTPase Rheb and that insulin-mediated Rheb activation is PI3K dependent. Moreover, Rheb overexpression induces S6K1 phosphorylation and inhibits PKB phosphorylation, as do loss-of-function mutations in TSC1/2, but contrary to earlier reports Rheb has no effect on MAPK phosphorylation. Finally, coexpression of a human TSC2 cDNA harboring a disease-associated point mutation in the GAP domain, failed to stimulate Rheb GTPase activity or block Rheb activation of S6K1.

Syndrome X, typified by obesity, insulin resistance (IR), dyslipidemia, and other metabolic abnormalities, is responsive to antidiabetic thiazolidinediones (TZDs). Peroxisome proliferator-activated receptor (PPAR) gamma, a target of TZDs, is expressed abundantly in adipocytes, suggesting an important role for this tissue in the etiology and treatment of IR. Targeted deletion of PPARgamma in adipose tissue resulted in marked adipocyte hypocellularity and hypertrophy, elevated levels of plasma free fatty acids and triglyceride, and decreased levels of plasma leptin and ACRP30. In addition, increased hepatic glucogenesis and IR were observed. Despite these defects, blood glucose, glucose and insulin tolerance, and insulin-stimulated muscle glucose uptake were all comparable to those of control mice. However, targeted mice were significantly more susceptible to high-fat diet-induced steatosis, hyperinsulinemia, and IR. Surprisingly, TZD treatment effectively reversed liver IR, whereas it failed to lower plasma free fatty acids. These results suggest that syndrome X may be comprised of separable PPARgamma-dependent components whose origins and therapeutic sites may reside in distinct tissues.

Diabetes, a disease in which the body does not produce or use insulin properly, is a serious global health problem. Gut polypeptides secreted in response to food intake, such as glucagon-like peptide-1 (GLP-1), are potent incretin hormones that enhance the glucose-dependent secretion of insulin from pancreatic beta cells. Free fatty acids (FFAs) provide an important energy source and also act as signaling molecules in various cellular processes, including the secretion of gut incretin peptides. Here we show that a G-protein-coupled receptor, GPR120, which is abundantly expressed in intestine, functions as a receptor for unsaturated long-chain FFAs. Furthermore, we show that the stimulation of GPR120 by FFAs promotes the secretion of GLP-1 in vitro and in vivo, and increases circulating insulin. Because GLP-1 is the most potent insulinotropic incretin, our results indicate that GPR120-mediated GLP-1 secretion induced by dietary FFAs is important in the treatment of diabetes.

Glucose homeostasis is regulated systemically by hormones such as insulin and glucagon, and at the cellular level by energy status. Glucagon enhances glucose output from the liver during fasting by stimulating the transcription of gluconeogenic genes via the cyclic AMP-inducible factor CREB (CRE binding protein). When cellular ATP levels are low, however, the energy-sensing kinase AMPK inhibits hepatic gluconeogenesis through an unknown mechanism. Here we show that hormonal and energy-sensing pathways converge on the coactivator TORC2 (transducer of regulated CREB activity 2) to modulate glucose output. Sequestered in the cytoplasm under feeding conditions, TORC2 is dephosphorylated and transported to the nucleus where it enhances CREB-dependent transcription in response to fasting stimuli. Conversely, signals that activate AMPK attenuate the gluconeogenic programme by promoting TORC2 phosphorylation and blocking its nuclear accumulation. Individuals with type 2 diabetes often exhibit fasting hyperglycaemia due to elevated gluconeogenesis; compounds that enhance TORC2 phosphorylation may offer therapeutic benefits in this setting.

Dysregulation of lipid metabolism in individual tissues leads to systemic disruption of insulin action and glucose metabolism. Utilizing quantitative lipidomic analyses and mice deficient in adipose tissue lipid chaperones aP2 and mal1, we explored how metabolic alterations in adipose tissue are linked to whole-body metabolism through lipid signals. A robust increase in de novo lipogenesis rendered the adipose tissue of these mice resistant to the deleterious effects of dietary lipid exposure. Systemic lipid profiling also led to identification of C16:1n7-palmitoleate as an adipose tissue-derived lipid hormone that strongly stimulates muscle insulin action and suppresses hepatosteatosis. Our data reveal a lipid-mediated endocrine network and demonstrate that adipose tissue uses lipokines such as C16:1n7-palmitoleate to communicate with distant organs and regulate systemic metabolic homeostasis.

OBJECTIVE

Androgen deprivation therapy with a gonadotropin-releasing hormone (GnRH) agonist is associated with increased fat mass and insulin resistance in men with prostate cancer, but the risk of obesity-related disease during treatment has not been well studied. We assessed whether androgen deprivation therapy is associated with an increased incidence of diabetes and cardiovascular disease.

METHODS

Observational study of a population-based cohort of 73,196 fee-for-service Medicare enrollees age 66 years or older who were diagnosed with locoregional prostate cancer during 1992 to 1999 and observed through 2001. We used Cox proportional hazards models to assess whether treatment with GnRH agonists or orchiectomy was associated with diabetes, coronary heart disease, myocardial infarction, and sudden cardiac death.

RESULTS

More than one third of men received a GnRH agonist during follow-up. GnRH agonist use was associated with increased risk of incident diabetes (adjusted hazard ratio [HR], 1.44; P < .001), coronary heart disease (adjusted HR, 1.16; P < .001), myocardial infarction (adjusted HR, 1.11; P = .03), and sudden cardiac death (adjusted HR, 1.16; P = .004). Men treated with orchiectomy were more likely to develop diabetes (adjusted HR, 1.34; P < .001) but not coronary heart disease, myocardial infarction, or sudden cardiac death (all P>> .20).

CONCLUSIONS

GnRH agonist treatment for men with locoregional prostate cancer may be associated with an increased risk of incident diabetes and cardiovascular disease. The benefits of GnRH agonist treatment should be weighed against these potential risks. Additional research is needed to identify populations of men at highest risk of treatment-related complications and to develop strategies to prevent treatment-related diabetes and cardiovascular disease.

Exercise has beneficial effects on human health, including protection against metabolic disorders such as diabetes. However, the cellular mechanisms underlying these effects are incompletely understood. The lysosomal degradation pathway, autophagy, is an intracellular recycling system that functions during basal conditions in organelle and protein quality control. During stress, increased levels of autophagy permit cells to adapt to changing nutritional and energy demands through protein catabolism. Moreover, in animal models, autophagy protects against diseases such as cancer, neurodegenerative disorders, infections, inflammatory diseases, ageing and insulin resistance. Here we show that acute exercise induces autophagy in skeletal and cardiac muscle of fed mice. To investigate the role of exercise-mediated autophagy in vivo, we generated mutant mice that show normal levels of basal autophagy but are deficient in stimulus (exercise- or starvation)-induced autophagy. These mice (termed BCL2 AAA mice) contain knock-in mutations in BCL2 phosphorylation sites (Thr69Ala, Ser70Ala and Ser84Ala) that prevent stimulus-induced disruption of the BCL2-beclin-1 complex and autophagy activation. BCL2 AAA mice show decreased endurance and altered glucose metabolism during acute exercise, as well as impaired chronic exercise-mediated protection against high-fat-diet-induced glucose intolerance. Thus, exercise induces autophagy, BCL2 is a crucial regulator of exercise- (and starvation)-induced autophagy in vivo, and autophagy induction may contribute to the beneficial metabolic effects of exercise.

OBJECTIVE

Fibroblast growth factor 21 (FGF21) has emerged as an important metabolic regulator of glucose and lipid metabolism. The aims of the current study are to evaluate the role of FGF21 in energy metabolism and to provide mechanistic insights into its glucose and lipid-lowering effects in a high-fat diet-induced obesity (DIO) model.

METHODS

DIO or normal lean mice were treated with vehicle or recombinant murine FGF21. Metabolic parameters including body weight, glucose, and lipid levels were monitored, and hepatic gene expression was analyzed. Energy metabolism and insulin sensitivity were assessed using indirect calorimetry and hyperinsulinemic-euglycemic clamp techniques.

RESULTS

FGF21 dose dependently reduced body weight and whole-body fat mass in DIO mice due to marked increases in total energy expenditure and physical activity levels. FGF21 also reduced blood glucose, insulin, and lipid levels and reversed hepatic steatosis. The profound reduction of hepatic triglyceride levels was associated with FGF21 inhibition of nuclear sterol regulatory element binding protein-1 and the expression of a wide array of genes involved in fatty acid and triglyceride synthesis. FGF21 also dramatically improved hepatic and peripheral insulin sensitivity in both lean and DIO mice independently of reduction in body weight and adiposity.

CONCLUSIONS

FGF21 corrects multiple metabolic disorders in DIO mice and has the potential to become a powerful therapeutic to treat hepatic steatosis, obesity, and type 2 diabetes.

Insulin resistance contributes to the pathophysiology of diabetes and is a hallmark of obesity, metabolic syndrome, and many cardiovascular diseases. Therefore, quantifying insulin sensitivity/resistance in humans and animal models is of great importance for epidemiological studies, clinical and basic science investigations, and eventual use in clinical practice. Direct and indirect methods of varying complexity are currently employed for these purposes. Some methods rely on steady-state analysis of glucose and insulin, whereas others rely on dynamic testing. Each of these methods has distinct advantages and limitations. Thus, optimal choice and employment of a specific method depends on the nature of the studies being performed. Established direct methods for measuring insulin sensitivity in vivo are relatively complex. The hyperinsulinemic euglycemic glucose clamp and the insulin suppression test directly assess insulin-mediated glucose utilization under steady-state conditions that are both labor and time intensive. A slightly less complex indirect method relies on minimal model analysis of a frequently sampled intravenous glucose tolerance test. Finally, simple surrogate indexes for insulin sensitivity/resistance are available (e.g., QUICKI, HOMA, 1/insulin, Matusda index) that are derived from blood insulin and glucose concentrations under fasting conditions (steady state) or after an oral glucose load (dynamic). In particular, the quantitative insulin sensitivity check index (QUICKI) has been validated extensively against the reference standard glucose clamp method. QUICKI is a simple, robust, accurate, reproducible method that appropriately predicts changes in insulin sensitivity after therapeutic interventions as well as the onset of diabetes. In this Frontiers article, we highlight merits, limitations, and appropriate use of current in vivo measures of insulin sensitivity/resistance.

OBJECTIVE

Nonalcoholic steatohepatitis (NASH) may progress to cirrhosis; whether NASH plays also a role in the development of hepatocellular carcinoma (HCC) is unknown.

METHODS

Among 641 cirrhosis-associated HCCs, we retrospectively identified 44 patients with cryptogenic cirrhosis (CC). Of these, 23 were actively followed up and were compared in a case-control study with viral- and alcohol-associated HCC. Family and personal history of diabetes, hypertension, coronary heart disease, dyslipidemia, obesity, and biochemical data were compared between groups. Iron status and presence of mutations in the HFE gene of familiar hemochromatosis were also determined.

RESULTS

Family history was not different in relation to etiology. The prevalence of obesity and diabetes was significantly higher in patients with CC. Although liver function was similar, CC patients had higher glucose, cholesterol, and triglyceride plasma levels, increased parameters of insulin resistance, and lower aminotransferase levels. Iron status and prevalence of mutations in the HFE gene did not differ. Logistic regression analysis identified in sequence hypertriglyceridemia, diabetes, and normal aminotransferases as independent factors associated with HCC arising in CC.

CONCLUSIONS

Features suggestive of NASH are more frequently observed in HCC arising in patients with CC than in age- and sex-matched HCC patients of well-defined viral or alcoholic etiology. HCC may represent a late complication of NASH-related cirrhosis.

Although several early phase clinical trials raised enthusiasm for the use of insulin-like growth factor I receptor (IGF1R)-specific antibodies for cancer treatment, initial Phase III results in unselected patients have been disappointing. Further clinical studies may benefit from the use of predictive biomarkers to identify probable responders, the use of rational combination therapies and the consideration of alternative targeting strategies, such as ligand-specific antibodies and receptor-specific tyrosine kinase inhibitors. Targeting insulin and IGF signalling also needs to be considered in the broader context of the pathophysiology that relates obesity and diabetes to neoplasia, and the effects of anti-diabetic drugs, including metformin, on cancer risk and prognosis. The insulin and IGFI receptor family is also relevant to the development of PI3K-AKT pathway inhibitors.

The physiological role of glucagon-like peptide-1 7-36 amide (GLP-1 7-36) in man was investigated. GLP-1 7-36-like immunoreactivity was found in the human bowel; its circulating level rose after oral glucose and after a test breakfast. When it was infused into seven volunteers at a rate to mimic its postprandial plasma concentration in the fasting state, plasma insulin levels rose significantly and glucose and glucagon concentrations fell. During an intravenous glucose load, it greatly enhanced insulin release and significantly reduced peak plasma glucose concentrations, compared with a control saline infusion, even inducing postinfusion reactive hypoglycaemia. By comparison, infusion of glucose-dependent insulinotropic peptide (GIP) to physiological levels was less effective in stimulating insulin release. These observations suggest that GLP-1 7-36 is a physiological incretin and that it is more powerful than GIP. The observation of greatly increased postprandial plasma GLP-1 7-36 levels in patients with postgastrectomy dumping syndrome suggests that it may mediate the hyperinsulinaemia and reactive hypoglycaemia of this disorder.

Aberrant protein aggregation is a common feature of late-onset neurodegenerative diseases, including Alzheimer's disease, which is associated with the misassembly of the Abeta(1-42) peptide. Aggregation-mediated Abeta(1-42) toxicity was reduced in Caenorhabditis elegans when aging was slowed by decreased insulin/insulin growth factor-1-like signaling (IIS). The downstream transcription factors, heat shock factor 1, and DAF-16 regulate opposing disaggregation and aggregation activities to promote cellular survival in response to constitutive toxic protein aggregation. Because the IIS pathway is central to the regulation of longevity and youthfulness in worms, flies, and mammals, these results suggest a mechanistic link between the aging process and aggregation-mediated proteotoxicity.

When cells of the established preadipose line 3T3-L1 enter a resting state, they accumulate triglyceride and convert to adipose cells. The adipose conversion is brought about by a large increase in the rate of triglyceride synthesis, as measured by the incorporation rate of labeled palmitate, acetate, and glucose. In a resting 3T3 subline which dose not undergo the adipose conversion, the rate of triglyceride synthesis from these precursors is very low, and similar to that of growing 3T3-L1 cells, before their adipose conversion begins. If 3T3-L1 cells incorporate bromodeoxyuridine during growth, triglyceride synthesis does not increase when the cells reach a stationary state, and triglycerides do not accumulate. As would be expected from their known actions on tissue adipose cells, lipogenic and lipolytic hormones and drugs affect the rate of synthesis and accumulation of triglyceride by 3T3-L1 cells, but in contrast to bromodeoxyuridine, these modulating agents do not seem to affect the proportion of cells which undergoes the adipose conversion. Insulin markedly increases the rate of synthesis and accumulation of triglyceride by fatty 3T3-L1 cells, and produces a related increase in cell protein content. Of 20 randomly selected clones isolated from the original 3T3 stock, 19 are able to convert to adipose cells. The probability of such a conversion varies greatly among the different clones, in most cases being much lower than for 3T3-L1; but once the conversion takes place, the adipose cells produced from all of the 19 clones appear similar. The adipose conversion would seem to depend on an on-off switch, which is on with a different probability in different clones. This probability is quasistably inherited by the clonal progeny.

OBJECTIVE

Increased intra-abdominal fat is associated with insulin resistance and an atherogenic lipoprotein profile. Circulating concentrations of adiponectin, an adipocyte-derived protein, are decreased with insulin resistance. We investigated the relationships between adiponectin and leptin, body fat distribution, insulin sensitivity and lipoproteins.

METHODS

We measured plasma adiponectin, leptin and lipid concentrations, intra-abdominal and subcutaneous fat areas by CT scan, and insulin sensitivity index (S(I)) in 182 subjects (76 M/106F).

RESULTS

Adiponectin concentrations were higher in women than in men (7.4+/-2.9 vs 5.4+/-2.3 micro g/ml, p<0.0001) as were leptin concentrations (19.1+/-13.7 vs 6.9+/-5.1 ng/ml, p<0.0001). Women were more insulin sensitive (S(I): 6.8+/-3.9 vs 5.9+/-4.4 x 10(-5) min(-1)/(pmol/l), p<0.01) and had more subcutaneous (240+/-133 vs 187+/-90 cm(2), p<0.01), but less intra-abdominal fat (82+/-57 vs 124+/-68 cm(2), p<0.0001). By simple regression, adiponectin was positively correlated with age ( r=0.227, p<0.01) and S(I) ( r=0.375, p<0.0001), and negatively correlated with BMI ( r=-0.333, p<0.0001), subcutaneous ( r=-0.168, p<0.05) and intra-abdominal fat ( r=-0.35, p<0.0001). Adiponectin was negatively correlated with triglycerides ( r=-0.281, p<0.001) and positively correlated with HDL cholesterol ( r=0.605, p<0.0001) and Rf, a measure of LDL particle buoyancy ( r=0.474, p<0.0001). By multiple regression analysis, adiponectin was related to age ( p<0.0001), sex ( p<0.005) and intra-abdominal fat ( p<0.01). S(I) was related to intra-abdominal fat ( p<0.0001) and adiponectin ( p<0.0005). Both intra-abdominal fat and adiponectin contributed independently to triglycerides, HDL cholesterol and Rf.

CONCLUSIONS

These data suggest that adiponectin concentrations are determined by intra-abdominal fat mass, with additional independent effects of age and sex. Adiponectin could link intra-abdominal fat with insulin resistance and an atherogenic lipoprotein profile.

AMPK has emerged as a critical mechanism for salutary effects of polyphenols on lipid metabolic disorders in type 1 and type 2 diabetes. Here we demonstrate that AMPK interacts with and directly phosphorylates sterol regulatory element binding proteins (SREBP-1c and -2). Ser372 phosphorylation of SREBP-1c by AMPK is necessary for inhibition of proteolytic processing and transcriptional activity of SREBP-1c in response to polyphenols and metformin. AMPK stimulates Ser372 phosphorylation, suppresses SREBP-1c cleavage and nuclear translocation, and represses SREBP-1c target gene expression in hepatocytes exposed to high glucose, leading to reduced lipogenesis and lipid accumulation. Hepatic activation of AMPK by the synthetic polyphenol S17834 protects against hepatic steatosis, hyperlipidemia, and accelerated atherosclerosis in diet-induced insulin-resistant LDL receptor-deficient mice in part through phosphorylation of SREBP-1c Ser372 and suppression of SREBP-1c- and -2-dependent lipogenesis. AMPK-dependent phosphorylation of SREBP may offer therapeutic strategies to combat insulin resistance, dyslipidemia, and atherosclerosis.

BACKGROUND

Size regulation is fundamental in developing multicellular organisms and occurs through the control of cell number and cell size. Studies in Drosophila have identified an evolutionarily conserved signaling pathway that regulates organismal size and that includes the Drosophila insulin receptor substrate homolog Chico, the lipid kinase PI(3)K (Dp110), DAkt1/dPKB, and dS6K.

RESULTS

We demonstrate that varying the activity of the Drosophila insulin receptor homolog (DInr) during development regulates organ size by changing cell size and cell number in a cell-autonomous manner. An amino acid substitution at the corresponding position in the kinase domain of the human and Drosophila insulin receptors causes severe growth retardation. Furthermore, we show that the Drosophila genome contains seven insulin-like genes that are expressed in a highly tissue- and stage-specific pattern. Overexpression of one of these insulin-like genes alters growth control in a DInr-dependent manner.

CONCLUSIONS

This study shows that the Drosophila insulin receptor autonomously controls cell and organ size, and that overexpression of a gene encoding an insulin-like peptide is sufficient to increase body size.

Interest in how the gut microbiome can influence the metabolic state of the host has recently heightened. One postulated link is bacterial fermentation of "indigestible" prebiotics to short-chain fatty acids (SCFAs), which in turn modulate the release of gut hormones controlling insulin release and appetite. We show here that SCFAs trigger secretion of the incretin hormone glucagon-like peptide (GLP)-1 from mixed colonic cultures in vitro. Quantitative PCR revealed enriched expression of the SCFA receptors ffar2 (grp43) and ffar3 (gpr41) in GLP-1-secreting L cells, and consistent with the reported coupling of GPR43 to Gq signaling pathways, SCFAs raised cytosolic Ca2+ in L cells in primary culture. Mice lacking ffar2 or ffar3 exhibited reduced SCFA-triggered GLP-1 secretion in vitro and in vivo and a parallel impairment of glucose tolerance. These results highlight SCFAs and their receptors as potential targets for the treatment of diabetes.

OBJECTIVE

To evaluate baseline risk factors for coronary artery disease in patients with type 2 diabetes mellitus.

METHODS

A stepwise selection procedure, adjusting for age and sex, was used in 2693 subjects with complete data to determine which risk factors for coronary artery disease should be included in a Cox proportional hazards model.

METHODS

3055 white patients (mean age 52) with recently diagnosed type 2 diabetes mellitus and without evidence of disease related to atheroma. Median duration of follow up was 7.9 years. 335 patients developed coronary artery disease within 10 years.

METHODS

Angina with confirmatory abnormal electrocardiogram; non-fatal and fatal myocardial infarction.

RESULTS

Coronary artery disease was significantly associated with increased concentrations of low density lipoprotein cholesterol, decreased concentrations of high density lipoprotein cholesterol, and increased triglyceride concentration, haemoglobin A1c, systolic blood pressure, fasting plasma glucose concentration, and a history of smoking. The estimated hazard ratios for the upper third relative to the lower third were 2.26 (95% confidence interval 1.70 to 3.00) for low density lipoprotein cholesterol, 0.55 (0.41 to 0.73) for high density lipoprotein cholesterol, 1.52 (1.15 to 2.01) for haemoglobin A1c, and 1.82 (1.34 to 2.47) for systolic blood pressure. The estimated hazard ratio for smokers was 1.41 (1.06 to 1.88).

CONCLUSIONS

A quintet of potentially modifiable risk factors for coronary artery disease exists in patients with type 2 diabetes mellitus. These risk factors are increased concentrations of low density lipoprotein cholesterol, decreased concentrations of high density lipoprotein cholesterol, raised blood pressure, hyperglycaemia, and smoking.

OBJECTIVE

To examine the relation between adult weight change and the risk for clinical diabetes mellitus among middle-aged women.

METHODS

Prospective cohort study with follow-up from 1976 to 1990.

METHODS

11 U.S. states.

METHODS

114,281 female registered nurses aged 30 to 55 years who did not have diagnosed diabetes mellitus, coronary heart disease, stroke, or cancer in 1976.

METHODS

Non-insulin-dependent diabetes mellitus.

RESULTS

2204 cases of diabetes were diagnosed during 1.49 million person-years of follow-up. After adjustment for age, body mass index was the dominant predictor of risk for diabetes mellitus. Risk increased with greater body mass index, and even women with average weight (body mass index, 24.0 kg/m2) had an elevated risk. Compared with women with stable weight (those who gained or lost less than 5 kg between age 18 years and 1976) and after adjustment for age and body mass index at age 18 years, the relative risk for diabetes mellitus among women who had a weight gain of 5.0 to 7.9 kg was 1.9 (95% CI, 1.5 to 2.3). The corresponding relative risk for women who gained 8.0 to 10.9 kg was 2.7 (CI, 2.1 to 3.3). In contrast, women who lost more than 5.0 kg reduced their risk for diabetes mellitus by 50% or more. These results were independent of family history of diabetes.

CONCLUSIONS

The excess risk for diabetes with even modest and typical adult weight gain is substantial. These findings support the importance of maintaining a constant body weight throughout adult life and suggest that the 1990 U.S. Department of Agriculture guidelines that allow a substantial weight gain after 35 years of age are misleading.

BACKGROUND

Insulin-like growth factor (IGF)-I, a mitogenic and antiapoptotic peptide, can affect the proliferation of breast epithelial cells, and is thought to have a role in breast cancer. We hypothesised that high circulating IGF-I concentrations would be associated with an increased risk of breast cancer.

METHODS

We carried out a nested case-control study within the prospective Nurses' Health Study cohort. Plasma concentrations of IGF-I and IGF binding protein 3 (IGFBP-3) were measured in blood samples collected in 1989-90. We identified 397 women who had a diagnosis of breast cancer after this date and 620 age-matched controls. IGF-I concentrations were compared by logistic regression with adjustment for other breast-cancer risk factors.

RESULTS

There was no association between IGF-I concentrations and breast-cancer risk among the whole study group. In postmenopausal women there was no association between IGF-I concentrations and breast-cancer risk (top vs bottom quintile of IGF-I, relative risk 0.85 [95% CI 0.53-1.39]). The relative risk of breast cancer among premenopausal women by IGF-I concentration (top vs bottom tertile) was 2.33 (1.06-5.16; p for trend 0.08). Among premenopausal women less than 50 years old at the time of blood collection, the relative risk was 4.58 (1.75-12.0; p for trend 0.02). After further adjustment for plasma IGFBP-3 concentrations these relative risks were 2.88 and 7.28, respectively.

CONCLUSIONS

A positive relation between circulating IGF-I concentration and risk of breast cancer was found among premenopausal but not postmenopausal women. Plasma IGF-I concentrations may be useful in the identification of women at high risk of breast cancer and in the development of risk reduction strategies. Additional larger studies of this association among premenopausal women are needed to provide more precise estimates of effect.

Metabolic syndrome is defined by a constellation of interconnected physiological, biochemical, clinical, and metabolic factors that directly increases the risk of cardiovascular disease, type 2 diabetes mellitus, and all cause mortality. Insulin resistance, visceral adiposity, atherogenic dyslipidemia, endothelial dysfunction, genetic susceptibility, elevated blood pressure, hypercoagulable state, and chronic stress are the several factors which constitute the syndrome. Chronic inflammation is known to be associated with visceral obesity and insulin resistance which is characterized by production of abnormal adipocytokines such as tumor necrosis factor α , interleukin-1 (IL-1), IL-6, leptin, and adiponectin. The interaction between components of the clinical phenotype of the syndrome with its biological phenotype (insulin resistance, dyslipidemia, etc.) contributes to the development of a proinflammatory state and further a chronic, subclinical vascular inflammation which modulates and results in atherosclerotic processes. Lifestyle modification remains the initial intervention of choice for such population. Modern lifestyle modification therapy combines specific recommendations on diet and exercise with behavioural strategies. Pharmacological treatment should be considered for those whose risk factors are not adequately reduced with lifestyle changes. This review provides summary of literature related to the syndrome's definition, epidemiology, underlying pathogenesis, and treatment approaches of each of the risk factors comprising metabolic syndrome.

The biochemical mechanisms involved in regulation of insulin secretion are not completely understood. The rat INS-1 cell line has been used to gain insight in this area because it secretes insulin in response to glucose concentrations in the physiological range. However, the magnitude of the response is far less than that seen in freshly isolated rat islets. In the current study, we have stably transfected INS-1 cells with a plasmid containing the human proinsulin gene. After antibiotic selection and clonal expansion, 67% of the resultant clones were found to be poorly responsive to glucose in terms of insulin secretion (< or =2-fold stimulation by 15 mmol/l compared with 3 mmol/l glucose), 17% of the clones were moderately responsive (2- to 5-fold stimulation), and 16% were strongly responsive (5- to 13-fold stimulation). The differences in responsiveness could not be ascribed to differences in insulin content. Detailed analysis of one of the strongly responsive lines (832/13) revealed that its potent response to glucose (average of 10-fold) was stable over 66 population doublings (approximately 7.5 months of tissue culture) with half-maximal stimulation at 6 mmol/l glucose. Furthermore, in the presence of 15 mmol/l glucose, insulin secretion was potentiated significantly by 100 pmol/l isobutylmethylxanthine (320%), 1 mmol/l oleate/palmitate (77%), and 50 nmol/l glucagon-like peptide 1 (60%), whereas carbachol had no effect. Glucose-stimulated insulin secretion was also potentiated by the sulfonylurea tolbutamide (threefold at 3 mmol/l glucose and 50% at 15 mmol/l glucose) and was abolished by diazoxide, which demonstrates the operation of the ATP-sensitive K+ channel (K(ATP)) in 832/13 cells. Moreover, when the K(ATP) channel was bypassed by incubation of cells in depolarizing K+ (35 mmol/l), insulin secretion was more effectively stimulated by glucose in 832/13 cells than in parental INS-1 cells, which demonstrates the presence of a K(ATP) channel-independent pathway of glucose sensing. We conclude that clonal selection of INS-1 cells allows isolation of cell lines that exhibit markedly enhanced and stable responsiveness to glucose and several of its known potentiators. These lines may be attractive new vehicles for studies of beta-cell function.