Effects of isoflavones on breast tissue and the thyroid hormone system in humans: a comprehensive safety evaluation.

Isoflavones are secondary plant constituents of certain foods and feeds such as soy, linseeds, and red clover. Furthermore, isoflavone-containing preparations are marketed as food supplements and so-called dietary food for special medical purposes to alleviate health complaints of peri- and postmenopausal women. Based on the bioactivity of isoflavones, especially their hormonal properties, there is an ongoing discussion regarding their potential adverse effects on human health. This review evaluates and summarises the evidence from interventional and observational studies addressing potential unintended effects of isoflavones on the female breast in healthy women as well as in breast cancer patients and on the thyroid hormone system. In addition, evidence from animal and in vitro studies considered relevant in this context was taken into account along with their strengths and limitations. Key factors influencing the biological effects of isoflavones, e.g., bioavailability, plasma and tissue concentrations, metabolism, temporality (pre- vs. postmenopausal women), and duration of isoflavone exposure, were also addressed. Final conclusions on the safety of isoflavones are guided by the aim of precautionary consumer protection.

Tbc1d1 deletion suppresses obesity in leptin-deficient mice.

BACKGROUND: Variants in the gene TBC1D1 have been previously associated with obesity-related traits in several species, including humans, mice, rabbits and chicken. While in humans variants in TBC1D1 were linked to obesity, disruption of the Tbc1d1 gene reduced body weight in mice. TBC1D1 has been identified as a regulator of insulin-dependent glucose transport in skeletal muscle, however, its role in energy homeostasis in the obese state remains unclear. The impact of TBC1D1 deficiency on energy homeostasis, glucose and lipid metabolism in an established mouse model of obesity was examined. METHODS: Obese leptin (ob/ob)- and Tbc1d1-double-deficient mice (D1KO-ob/ob) were generated by crossing obese B6.V.Lep(ob/ob)-mice with lean Tbc1d1-deficient mice on a C57BL/6J background. Male mice on either standard (SD) or high-fat diet (HFD) were analyzed for body weight, body composition, food intake, voluntary physical activity and energy expenditure by indirect calorimetry. Glucose and insulin tolerance as well as glucose transport and fatty acid oxidation in skeletal muscle were analyzed. RESULTS: In obese mice, Tbc1d1 deficiency resulted in reduced body weight on both SD and HFD. However, food intake was unchanged on SD or even increased in HFD-fed Tbc1d1-deficient mice without alterations in voluntary physical activity. Despite substantially reduced insulin-stimulated glucose transport and increased fatty acid oxidation in intact isolated skeletal muscle, obese Tbc1d1-deficient mice showed no gross changes in glycemia and glucose tolerance compared with obese controls. Indirect calorimetry revealed that obese Tbc1d1-deficient mice had a decreased respiratory quotient together with increased daily energy expenditure. CONCLUSIONS: In obese leptin-deficient mice, lack of TBC1D1 has no impact on feeding behavior or energy intake but results in increased energy expenditure, altered energy substrate preference with increased fatty acid oxidation and suppression of obesity. TBC1D1 may have an evolutionary conserved role in regulating energy homeostasis in vertebrates.

Febrile temperatures unmask biophysical defects in Nav1.1 epilepsy mutations supportive of seizure initiation.

Generalized epilepsy with febrile seizures plus (GEFS+) is an early onset febrile epileptic syndrome with therapeutic responsive (a)febrile seizures continuing later in life. Dravet syndrome (DS) or severe myoclonic epilepsy of infancy has a complex phenotype including febrile generalized or hemiclonic convulsions before the age of 1, followed by intractable myoclonic, complex partial, or absence seizures. Both diseases can result from mutations in the Nav1.1 sodium channel, and initially, seizures are typically triggered by fever. We previously characterized two Nav1.1 mutants-R859H (GEFS+) and R865G (DS)-at room temperature and reported a mixture of biophysical gating defects that could not easily predict the phenotype presentation as either GEFS+ or DS. In this study, we extend the characterization of Nav1.1 wild-type, R859H, and R865G channels to physiological (37°C) and febrile (40°C) temperatures. At physiological temperature, a variety of biophysical defects were detected in both mutants, including a hyperpolarized shift in the voltage dependence of activation and a delayed recovery from fast and slow inactivation. Interestingly, at 40°C we also detected additional gating defects for both R859H and R865G mutants. The GEFS+ mutant R859H showed a loss of function in the voltage dependence of inactivation and an increased channel use-dependency at 40°C with no reduction in peak current density. The DS mutant R865G exhibited reduced peak sodium currents, enhanced entry into slow inactivation, and increased use-dependency at 40°C. Our results suggest that fever-induced temperatures exacerbate the gating defects of R859H or R865G mutants and may predispose mutation carriers to febrile seizures.

Estrogen deficiency aggravates insulin resistance and induces ß-cell loss and diabetes in female New Zealand obese mice.

In several rodent strains such as the New Zealand Obese (NZO) mouse, the incidence of obesity-associated diabetes mellitus is much higher in males than in females. In the present study, we investigated the effects of ovariectomy on glucose homeostasis in female NZO mice in order to elucidate the mechanism of their diabetes resistance. NZO females were ovariectomized at the age of 4 weeks, received a high-fat diet and body weight, body fat, glucose and insulin tolerance were investigated in comparison to sham-operated mice. In a second experiment, operated mice were fed a carbohydrate-free diet up to the age of 19 weeks before they received the high-fat diet. In comparison with a sham-operated control group, ovariectomized female NZO mice exhibited similar body weights, a reduced glucose tolerance, developed significantly higher blood glucose levels, lost insulin producing ß-cells, which finally resulted in a diabetes prevalence of 73% at the age of 16 weeks vs. 25% in controls. Similar to male NZO mice, ovariectomized females presented a more severe insulin resistance in the insulin tolerance test than sham-operated controls. Furthermore, the more severe insulin resistance in ovariectomized mice preceded the development of diabetes and pancreatic insulin depletion that was caused by a dietary regimen of carbohydrate restriction and subsequent re-exposure. In summary our data demonstrate that estrogen protects NZO females from ß-cell loss and obesity-associated diabetes mellitus. This effect is due to a reduced insulin resistance and possibly also to a reduced sensitivity of ß-cells to glucolipotoxic conditions.

Body iron stores and risk of type 2 diabetes: results from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam study.

AIMS/HYPOTHESIS: The aim of this study was to prospectively examine the association between body iron stores and risk of type 2 diabetes. METHODS: We designed a case-cohort study among 27,548 individuals within the population-based European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam study. During 7 years of follow-up, 849 incident cases of type 2 diabetes were identified. Of these, 607 remained for analyses after exclusion of participants with missing data or abnormal glucose levels at baseline. A sub-cohort of 2,500 individuals was randomly selected from the full cohort, comprising 1,969 individuals after applying the same exclusion criteria. RESULTS: After adjustment for age, sex, BMI, waist circumference, sports activity, bicycling, education, occupational activity, smoking habit, alcohol consumption and circulating levels of γ-glutamyltransferase, alanine aminotransferase, fetuin-A, high-sensitivity C-reactive protein, adiponectin, HDL-cholesterol and triacylglycerol, higher serum ferritin concentrations were associated with a higher risk of type 2 diabetes (RR in the highest vs lowest quintile, 1.73; 95% CI 1.15, 2.61; p(trend) = 0.002). No significant association was observed for soluble transferrin receptor (RR 1.33; 95% CI 0.85, 2.09; p(trend) = 0.50). The soluble transferrin receptor-to-ferritin ratio was significantly inversely related to risk (RR 0.61; 95% CI 0.41, 0.91; p(trend) = 0.02). CONCLUSIONS/INTERPRETATION: High ferritin levels are associated with higher risk of type 2 diabetes independently of established diabetes risk factors and a range of diabetes biomarkers whereas soluble transferrin receptor concentrations are not related to risk. These results support the hypothesis that higher iron stores below the level of haemochromatosis are associated with risk of type 2 diabetes.

Nav 1.1 dysfunction in genetic epilepsy with febrile seizures-plus or Dravet syndrome.

Relatively few SCN1A mutations associated with genetic epilepsy with febrile seizures-plus (GEFS+) and Dravet syndrome (DS) have been functionally characterized. In contrast to GEFS+, many mutations detected in DS patients are predicted to have complete loss of function. However, functional consequences are not immediately apparent for DS missense mutations. Therefore, we performed a biophysical analysis of three SCN1A missense mutations (R865G, R946C and R946H) we detected in six patients with DS. Furthermore, we compared the functionality of the R865G DS mutation with that of a R859H mutation detected in a GEFS+ patient; the two mutations reside in the same voltage sensor domain of Na(v) 1.1. The four mutations were co-expressed with ß1 and ß2 subunits in tsA201 cells, and characterized using the whole-cell patch clamp technique. The two DS mutations, R946C and R946H, were nonfunctional. However, the novel voltage sensor mutants R859H (GEFS+) and R865G (DS) produced sodium current densities similar to those in wild-type channels. Both mutants had negative shifts in the voltage dependence of activation, slower recovery from inactivation, and increased persistent current. Only the GEFS+ mutant exhibited a loss of function in voltage-dependent channel availability. Our results suggest that the R859H mutation causes GEFS+ by a mixture of biophysical defects in Na(v) 1.1 gating. Interestingly, while loss of Na(v) 1.1 function is common in DS, the R865G mutation may cause DS by overall gain-of-function defects.

Diet dependence of diabetes in the New Zealand Obese (NZO) mouse: total fat, but not fat quality or sucrose accelerates and aggravates diabetes.

BACKGROUND: Obesity and diabetes in mice can be modified by dietary variables. Here we systematically analysed the effect of the sucrose and fat content and of the fat quality in New Zealand Obese mice, a mouse model of the metabolic syndrome. RESULTS: Male NZO mice fed a semi-purified diet with sucrose exhibited an identical weight gain and diabetes incidence as controls without sucrose. In contrast, mice on a chow diet gained weight more slowly and developed diabetes approximately 10 weeks later than those on the semi-purified diet (energy density 3.05 vs. 3.85 kcal/g; fibre content 12.9 vs. 4.7%). In a second experimental series, neither the fat content (10 vs. 40% of the total energy) nor the quality of the fat (lard, safflower oil, or fish oil) of semi-purified diets modified weight gain. However, diabetes started approximately 2 weeks earlier and appeared more severe (blood glucose 30 vs. 20 mmol/l at week 13) in the high-fat diet group (energy density 4.58 kcal/g; fibre content 5.7%). CONCLUSIONS: Obesity in NZO mice develops independent of the dietary sucrose or fat content, and of the fat quality. However, the dietary fat content accelerates the onset of diabetes without enhancing adiposity. In contrast, chow diet exerts an anti-adipogenic/anti-diabetogenic effect that appears to be due to its lower caloric density and/or its higher fibre content.

Non-fasting lipids and risk of cardiovascular disease in patients with diabetes mellitus.

AIMS/HYPOTHESIS: The aim of this study was to examine the effect of postprandial time on the associations and predictive value of non-fasting lipid levels and cardiovascular disease risk in participants with diabetes. METHODS: This study was conducted among 1,337 participants with diabetes from the Dutch and German (Potsdam) contributions to the European Prospective Investigation into Cancer and Nutrition. At baseline, total cholesterol, LDL- and HDL-cholesterol and triacylglycerol concentrations were measured and the ratio of total cholesterol/HDL-cholesterol was calculated. Participants were followed for incidence of cardiovascular disease. RESULTS: Lipid concentrations changed minimally with increasing postprandial time, except for triacylglycerol which was elevated just after a meal and declined over time (1.86 at 0.1 h to 1.33 at >6 h, p for trend <0.001). During a mean follow-up of 8 years, 116 cardiovascular events were documented. After adjustment for potential confounders, triacylglycerol (HR for third tertile compared with first tertile (HR(t)3(to)1), 1.73 [95% CI 1.04, 2.87]), HDL-cholesterol (HR(t)3(to)1, 0.41 [95% CI 0.23, 0.72]) and total cholesterol/HDL-cholesterol ratio (HR(t)3(to)1, 1.65 [95% CI 0.95, 2.85]) were associated with cardiovascular disease, independent of postprandial time. Cardiovascular disease risk prediction using the UK Prospective Diabetes Study risk engine was not affected by postprandial time. CONCLUSIONS/INTERPRETATION: Postprandial time did not affect associations between lipid concentrations and cardiovascular disease risk in patients with diabetes, nor did it influence prediction of cardiovascular disease. Therefore, it may not be necessary to use fasting blood samples to determine lipid concentrations for cardiovascular disease risk prediction in patients with diabetes.

Dissociation of lipotoxicity and glucotoxicity in a mouse model of obesity associated diabetes: role of forkhead box O1 (FOXO1) in glucose-induced beta cell failure.

AIMS/HYPOTHESIS: Carbohydrate-free diet prevents hyperglycaemia and beta cell destruction in the New Zealand Obese (NZO) mouse model. Here we have used a sequential dietary regimen to dissociate the effects of obesity and hyperglycaemia on beta cell function and integrity, and to study glucose-induced alterations of key transcription factors over 16 days. METHODS: Mice were rendered obese by feeding a carbohydrate-free diet for 18 weeks. Thereafter, a carbohydrate-containing diet was given. Plasma glucose, plasma insulin and total pancreatic insulin were determined, and forkhead box O1 protein (FOXO1) phosphorylation and the transcription factors pancreatic and duodenal homeobox 1 (PDX1), NK6 homeobox 1 protein (NKX6.1) and v-maf musculoaponeurotic fibrosarcoma oncogene family, protein A (avian) (MAFA) were monitored by immunohistochemistry for 16 days. RESULTS: Dietary carbohydrates produced a rapid and continuous increase in plasma glucose in NZO mice between day 2 and 16 after the dietary challenge. Hyperglycaemia caused a dramatic dephosphorylation of FOXO1 at day 2, followed by a progressive depletion of insulin stores. The loss of beta cells was triggered by apoptosis (detectable at day 8), associated with reduction of crucial transcription factors (PDX1, NKX6.1 and MAFA). Incubation of isolated islets from carbohydrate-restricted NZO mice or MIN6 cells with palmitate and glucose for 48 h resulted in a dephosphorylation of FOXO1 and thymoma viral proto-oncogene 1 (AKT) without changing the protein levels of both proteins. CONCLUSIONS/INTERPRETATION: The dietary regimen dissociates the effects of obesity (lipotoxicity) from those of hyperglycaemia (glucotoxicity) in NZO mice. Obese NZO mice are unable to compensate for the carbohydrate challenge by increasing insulin secretion or synthesising adequate amounts of insulin. In response to the hyperglycaemia, FOXO1 is dephosphorylated, leading to reduced levels of beta cell-specific transcription factors and to apoptosis of the cells.

Fasting plasma glucose and Type 2 diabetes risk: a non-linear relationship.

AIMS: The current definition of impaired fasting glucose (IFG, >or=100 mg/dl) has been criticized as being too low for selective identification of individuals at risk for Type 2 diabetes. Furthermore, it is unclear whether any cut-off is justifiable from the shape of association between fasting plasma glucose (FPG) and diabetes. We therefore evaluated the association between FPG and incidence of Type 2 diabetes in a prospective, population-based study. METHODS: A case-cohort study within the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam cohort study involved 589 fasted participants in a randomly selected subcohort and 153 incident cases. Restricted cubic spline regression was used to examine non-linearity of associations and we calculated pairs of sensitivities and specificities for different cut-offs of FPG. RESULTS: Spline regression with adjustment for age, sex, body mass index, waist circumference, education, physical activity, alcohol consumption, and plasma levels of triglycerides, high-density lipoprotein cholesterol and gamma-glutamyltransferase indicated that FPG was associated with risk in a non-linear fashion. Risk with higher FPG increased only above approximately 84 mg/dl. FPG>or=84 mg/dl yielded a sensitivity of 95.4% at a false-positive rate of 86.8%. In comparison, FPG>or=100 and>or=110 mg/dl yielded sensitivities of 78.4 and 42.5% and false-positive rates of 27.8 and 6.8%, respectively. The optimal cut-off of FPG was at approximately 102 mg/dl (sensitivity: 75.8%, false-positive rate: 20.7%). CONCLUSIONS: Although our study suggests a threshold for increasing diabetes risk at 84 mg/dl, this cut-off would classify the vast majority of the population as at risk. The statistically optimal cut-off supports the current definition of IFG (>or=100 mg/dl).

Diet-induced gene expression of isolated pancreatic islets from a polygenic mouse model of the metabolic syndrome.

AIMS/HYPOTHESIS: Numerous new genes have recently been identified in genome-wide association studies for type 2 diabetes. Most are highly expressed in beta cells and presumably play important roles in their function. However, these genes account for only a small proportion of total risk and there are likely to be additional candidate genes not detected by current methodology. We therefore investigated islets from the polygenic New Zealand mouse (NZL) model of diet-induced beta cell dysfunction to identify novel genes and pathways that may play a role in the pathogenesis of diabetes. METHODS: NZL mice were fed a diabetogenic high-fat diet (HF) or a diabetes-protective carbohydrate-free HF diet (CHF). Pancreatic islets were isolated by laser capture microdissection (LCM) and subjected to genome-wide transcriptome analyses. RESULTS: In the prediabetic state, 2,109 islet transcripts were differentially regulated (>1.5-fold) between HF and CHF diets. Of the genes identified, 39 (e.g. Cacna1d, Chd2, Clip2, Igf2bp2, Dach1, Tspan8) correlated with data from the Diabetes Genetics Initiative and Wellcome Trust Case Control Consortium genome-wide scans for type 2 diabetes, thus validating our approach. HF diet induced early changes in gene expression associated with increased cell-cycle progression, proliferation and differentiation of islet cells, and oxidative stress (e.g. Cdkn1b, Tmem27, Pax6, Cat, Prdx4 and Txnip). In addition, pathway analysis identified oxidative phosphorylation as the predominant gene-set that was significantly upregulated in response to the diabetogenic HF diet. CONCLUSIONS/INTERPRETATION: We demonstrated that LCM of pancreatic islet cells in combination with transcriptional profiling can be successfully used to identify novel candidate genes for diabetes. Our data strongly implicate glucose-induced oxidative stress in disease progression.

Functional analysis of novel KCNQ2 mutations found in patients with Benign Familial Neonatal Convulsions.

Benign Familial Neonatal Convulsions (BFNC) are a rare epilepsy disorder with an autosomal-dominant inheritance. It is linked to mutations in the potassium channel genes KCNQ2 and KCNQ3. These encode for Kv7.2 and Kv7.3 potassium ion channels, which produce an M-current that regulates the potential firing action in neurons through modulation of the membrane potential. We report on the biophysical and biochemical properties of V589X, T359K and P410fs12X mutant-KCNQ2 ion channels that were detected in three BFNC families. Mutant KCNQ2 cDNAs were co-expressed with WT-KCNQ2 and KCNQ3 cDNAs in HEK293 cells to mimic heterozygous expression of the KCNQ2 mutations in BFNC patients. The resulting potassium currents were measured using patch-clamp techniques and showed an approximately 75% reduction in current and a depolarized shift in the voltage dependence of activation. Furthermore, the time-constant of activation of M-currents in cells expressing T359K and P410fs12X was slower compared to cells expressing only wild-type proteins. Immunofluorescent labeling of HEK293 cells stably expressing GFP-tagged KCNQ2-WT or mutant alpha-subunits indicated cell surface expression of WT, V589X and T359K mutants, suggesting a loss-of-function, while P410fs12X was predominantly retained in the ER and sub-cellular compartments outside the ER suggesting an effectively haplo-insufficient effect.

Essential role of glucose transporter GLUT3 for post-implantation embryonic development.

Deletion of glucose transporter gene Slc2a3 (GLUT3) has previously been reported to result in embryonic lethality. Here, we define the exact time point of growth arrest and subsequent death of the embryo. Slc2a3(-/-) morulae and blastocysts developed normally, implanted in vivo, and formed egg-cylinder-stage embryos that appeared normal until day 6.0. At day 6.5, apoptosis was detected in the ectodermal cells of Slc2a3(-/-) embryos resulting in severe disorganization and growth retardation at day 7.5 and complete loss of embryos at day 12.5. GLUT3 was detected in placental cone, in the visceral ectoderm and in the mesoderm of 7.5-day-old wild-type embryos. Our data indicate that GLUT3 is essential for the development of early post-implanted embryos.

Deletion of glucose transporter GLUT8 in mice increases locomotor activity.

Transport of glucose into neuronal cells is predominantly mediated by the glucose transporters GLUT1 and GLUT3. In addition, GLUT8 is expressed in some regions of the brain. By in situ hybridization we detected GLUT8-mRNA in hippocampus, thalamus, and cortex. However, its cellular and physiological function is still unknown. Thus, GLUT8 knockout (Slc2a8 -/-) mice were used for a screening approach in the modified hole board (mHB) behavioral test to analyze the role of GLUT8 in the central nervous system. Slc2a8 -/- mice showed increased mean velocity, total distance traveled and performed more turns in the mHB test. This hyperactivity of Slc2a8 -/- mice was confirmed by monitoring locomotor activity in the home cage and voluntary activity in a running wheel. In addition, Slc2a8 -/- mice showed increased arousal as indicated by elevated defecation, reduced latency to the first defecation and a tendency to altered grooming. Furthermore, the mHB test gave evidence that Slc2a8 -/- mice exhibit a reduced risk assessment because they performed less rearings in an unprotected area and showed significantly reduced latency to stretched body posture. Our data suggest that behavioral alterations of Slc2a8 -/- mice are due to dysfunctions in neuronal processes presumably as a consequence of defects in the glucose metabolism.

[Validation of the German Diabetes Risk Score with metabolic risk factors for type 2 diabetes]. / Validierung des Deutschen Diabetes-Risiko-Scores mit metabolischen Risikofaktoren für Typ-2-Diabetes.

BACKGROUND AND AIMS: The German Diabetes Risk Score (DRS) was developed at the German Institute of Human Nutrition from data of the European Prospective Investigation into Cancer and Nutrition (EPIC-Potsdam) in order to estimate the 5-year probability of developing type 2 diabetes, based on anthropometric measures and lifestyle as well as diet information. This study evaluated associations between the DRS and metabolic risk factors of type 2 diabetes for the purpose of further validating the risk score. METHODS: 2500 participants of the EPIC-Potsdam study were randomly selected, and glucose, HbA1c, triglycerides, HDL cholesterol, hs-C-reactive protein, and gamma-glutamyltransferase were determined. After exclusion of participants with known diabetes (n = 120), those for whom not all biomarkers could be determined (n = 92) and those with elevated plasma glucose concentrations (random glucose >or= 200 mg/dl or fasting glucose >or= 126 mg/dl, n = 9) or with low plasma glucose concentrations (< 50 mg/dl, n = 38), the data on 2223 participants (839 men and 1384 women) remained for analysis of which 640 (252 men and 388 women) were fasting at the time blood samples had been obtained. RESULTS: The DRS significantly correlated with all biomarkers (p < 0.001). Pearson correlation coefficients ranged from 0.25 for glucose and 0.45 for triglycerides. While glucose, HbA (1c), triglycerides, hs-CRP and gamma-glutamyltransferase increased with increasing DRS points, HDL cholesterol was inversely associated. The mean concentrations of glucose, HbA (1c) and triglycerides for persons with < 300 DRS points were 83 mg/dl, 6.2 % und 62 mg/dl. In contrast, mean concentrations were 100 mg/dl for glucose, 6,9 % HbA (1c) und 171 mg/dl triglycerides among participants with >or= 700 DRS points. HDL cholesterol was considerably lower (37.6 mg/dl) among participants with >or= 700 DRS points than those with < 300 DRS points (55 mg/dl). There were also considerable differences in biomarker concentrations for hs-CRP and gamma-glutamyltransferase in relation to the DRS. Associations were generally similar for men and women. CONCLUSIONS: Our data suggest that the DRS allows to detect persons with prediabetes with high sensitivity and specificity. Thus the DRS could be used as a routine medical checkup in programs for the prevention of type 2 diabetes.

Development of diabetes in obese, insulin-resistant mice: essential role of dietary carbohydrate in beta cell destruction.

AIMS/HYPOTHESIS: The role of dietary carbohydrate in the pathogenesis of type 2 diabetes is still a subject of controversial debate. Here we analysed the effects of diets with and without carbohydrate on obesity, insulin resistance and development of beta cell failure in the obese, diabetes-prone New Zealand Obese (NZO) mouse. MATERIALS AND METHODS: NZO mice were kept on a standard diet (4% [w/w] fat, 51% carbohydrate, 19% protein), a high-fat diet (15, 47 and 17%, respectively) and a carbohydrate-free diet in which carbohydrate was exchanged for fat (68 and 20%, respectively). Body composition and blood glucose were measured over a period of 22 weeks. Glucose tolerance tests and euglycaemic-hyperinsulinaemic clamps were performed to analyse insulin sensitivity. Islet morphology was assessed by immunohistochemistry. RESULTS: Mice on carbohydrate-containing standard or high-fat diets developed severe diabetes (blood glucose >16.6 mmol/l, glucosuria) due to selective destruction of pancreatic beta cells associated with severe loss of immunoreactivity of insulin, glucose transporter 2 (GLUT2) and musculoaponeurotic fibrosarcoma oncogene homologue A (MafA). In contrast, mice on the carbohydrate-free diet remained normoglycaemic and exhibited hyperplastic islets in spite of a morbid obesity associated with severe insulin resistance and a massive accumulation of macrophages in adipose tissue. CONCLUSIONS/INTERPRETATION: These data indicate that the combination of obesity, insulin resistance and the inflammatory response of adipose tissue are insufficient to cause beta cell destruction in the absence of dietary carbohydrate.

A meta-analysis of quantitative trait loci associated with body weight and adiposity in mice.

OBJECTIVE: Cross-breeding experiments with different mouse strains have successfully been used by many groups to identify genetic loci that predispose for obesity. In order to provide a statistical assessment of these quantitative trait loci (QTL) as a basis for a systematic investigation of candidate genes, we have performed a meta-analysis of genome-wide linkage scans for body weight and body fat. DATA: From a total of 34 published mouse cross-breeding experiments, we compiled a list of 162 non-redundant QTL for body weight and 117 QTL for fat weight and body fat percentage. Collectively, these studies include data from 42 different parental mouse strains and >14,500 individual mice. METHODS: The results of the studies were analyzed using the truncated product method (TPM). RESULTS: The analysis revealed significant evidence (logarithm of odds (LOD) score >4.3) for linkage of body weight and adiposity to 49 different segments of the mouse genome. The most prominent regions with linkage for body weight and body fat (LOD scores 14.8-21.8) on chromosomes 1, 2, 7, 11, 15, and 17 contain a total of 58 QTL for body weight and body fat. At least 34 candidate genes and genetic loci, which have been implicated in regulation of body weight and body composition in rodents and/or humans, are found in these regions, including CCAAT/enhancer-binding protein alpha (C/EBPA), sterol regulatory element-binding transcription factor 1 (SREBP-1), peroxisome proliferator activator receptor delta (PPARD), and hydroxysteroid 11-beta dehydrogenase 1 (HSD11B1). Our results demonstrate the presence of numerous distinct consensus QTL regions with highly significant LOD scores that control body weight and body composition. An interactive physical map of the QTL is available online at (http://www.obesitygenes.org).