Effect of high-fat diet on the gene expression of pancreatic GLUT2 and glucokinase in rats

The Role of Gut Microbiota in High-Fat-Diet-Induced Diabetes: Lessons from Animal Models and Humans

The number of diabetes mellitus patients is increasing rapidly worldwide. Diet and nutrition are strongly believed to play a significant role in the development of diabetes mellitus. However, the specific dietary factors and detailed mechanisms of its development have not been clearly elucidated. Increasing evidence indicates the intestinal microbiota is becoming abundantly apparent in the progression and prevention of insulin resistance in diabetes. Differences in gut microbiota composition, particularly butyrate-producing bacteria, have been observed in preclinical animal models as well as human patients compared to healthy controls. Gut microbiota dysbiosis may disrupt intestinal barrier functions and alter host metabolic pathways, directly or indirectly relating to insulin resistance. In this article, we focus on dietary fat, diabetes, and gut microbiome characterization. The promising probiotic and prebiotic approaches to diabetes, by favorably modifying the composition of the gut microbial community, warrant further investigation through well-designed human clinical studies.

The effect of high-fat diet and 13-cis retinoic acid application on lipid profile, glycemic response and oxidative stress in female Lewis rats

Vitamin A and its metabolites are key regulators of the development of adipose tissue and associated metabolic complications. The aim of this study was to determine the effect of high fat diet and 13-cis retinoic acid (13 cRA) application on metabolic parameters, adipogenic and inflammatory indicators in female Lewis rats. Female rats of Lewis strain were fed standard laboratory diet (STD) and high fat diet (HFD, 45% of saturated fatty acids) during 30 days. The groups were divided into additional 3 groups (6 rats each): two experimental groups that received 13 cRA orally on a daily basis during 30 days (7.5 mg/kg and 15 mg/kg, respectively) and the control group that was given sunflower oil. Animals were sacrificed after 60 days. Feeding of Lewis rats with chronic HFD diet with 13 cRA supplementation increased weight gain, adiposity index, dyslipidaemia, hyperleptinaemia, insulin resistance, VLDL concentrations, oxidative stress and atherogenic indices. Administration of 13 cRA in Lewis rats fed STD did not change the weight of the animals, but it slightly increased the atherogenic parameters. 13 cRA and HFD affect metabolic parameters, glucose and lipid metabolism in Lewis rats and its administration has a completely different effect on metabolism in rats fed STD, highlighting the complex role of vitamin A supplementation in obesity. Other factors, such as genetics, age, sex, adipose tissue distribution, also must be taken into consideration.

Glucose transporters in pancreatic islets

The fine-tuning of glucose uptake mechanisms is rendered by various glucose transporters with distinct transport characteristics. In the pancreatic islet, facilitative diffusion glucose transporters (GLUTs), and sodium-glucose cotransporters (SGLTs) contribute to glucose uptake and represent important components in the glucose-stimulated hormone release from endocrine cells, therefore playing a crucial role in blood glucose homeostasis. This review summarizes the current knowledge about cell type-specific expression profiles as well as proven and putative functions of distinct GLUT and SGLT family members in the human and rodent pancreatic islet and further discusses their possible involvement in onset and progression of diabetes mellitus. In context of GLUTs, we focus on GLUT2, characterizing the main glucose transporter in insulin-secreting β-cells in rodents. In addition, we discuss recent data proposing that other GLUT family members, namely GLUT1 and GLUT3, render this task in humans. Finally, we summarize latest information about SGLT1 and SGLT2 as representatives of the SGLT family that have been reported to be expressed predominantly in the α-cell population with a suggested functional role in the regulation of glucagon release.

Testosterone deficiency caused by castration increases adiposity in male rats in a tissue-specific and diet-dependent manner

Background

Testosterone deficiency in men is clinically associated with the development of metabolic syndrome, which manifests as obesity, hepatic steatosis, and type-2 diabetes. We investigated the effects of castration-induced testosterone deficiency on body adiposity and the expression of genes related to lipid metabolism and glucose uptake and androgen signaling in male rats fed a normal diet (ND) or a high-fat diet (HFD).

Methods

Changes in lipid and glucose metabolism and androgen signaling were investigated at physiological and molecular levels in the muscle, liver, and adipose tissues of non-castrated and castrated rats under ND or HFD feeding.

Results

Castration-induced testosterone deficiency predisposed animals on ND to early development of fatty liver by activating fatty acid (FA) synthesis, whereas HFD activated hepatic FA uptake CD36 expression, leading to the development of hepatic steatosis. In rats fed ND, castration induced muscle fat accumulation by activating CD36 expression. In the subcutaneous fat of ND-fed rats, castration increased adiposity and the expression of FA synthesis-related genes, but it decreased glucose transporter gene expression. In the abdominal fat of rats fed ND, castration increased adiposity by upregulating FA synthesis-related genes, and HFD promoted adiposity by inducing FA uptake, glucose transporter, and FA synthesis-related gene expression. In rats fed ND, castration decreased body growth and muscle weight and downregulated the expression of genes androgen signaling in the longissimus dorsi muscle.

Conclusions

Testosterone deficiency increases adiposity in a tissue-specific and diet-dependent manner. Testosterone deficiency decreases body and muscle weights and downregulates androgen signaling.

The genetic basis of high-carbohydrate and high-monosodium glutamate diet related to the increase of likelihood of type 2 diabetes mellitus: a review

Diabetes is one of the most common metabolic diseases. Aside from the genetic factor, previous studies stated that other factors such as environment, lifestyle, and paternal-maternal condition play critical roles in diabetes through DNA methylation in specific areas of the genome. One of diabetic cases is caused by insulin resistance and changing the homeostasis of blood glucose control so glucose concentration stood beyond normal rate (hyperglycemia). High fat diet has been frequently studied and linked to triggering diabetes. However, most Asians consume rice (or food with high carbohydrate) and food with monosodium glutamate (MSG). This habit could lead to pathophysiology of type 2 diabetes mellitus (T2D). Previous studies showed that high-carbohydrate or high-MSG diet could change gene expression or modify protein activity in body metabolism. This imbalanced metabolism can lead to pleiotropic effects of diabetes mellitus. In this study, the authors have attempted to relate various changes in genes expression or protein activity to the high-carbohydrate and high-MSG-induced diabetes. The authors have also tried to relate several genes that contribute to pathophysiology of T2D and proposed several ideas of genes as markers and target for curing people with T2D. These are done by investigating altered activities of various genes that cause or are caused by diabetes. These genes are selected based on their roles in pathophysiology of T2D.

Trans-fatty acids aggravate anabolic steroid-induced metabolic disturbances and differential gene expression in muscle, pancreas and adipose tissue

AIMS

Although anabolic steroids (AS) and trans-fatty acids overload exerts systemic toxicity and are independent risk factors for metabolic and cardiovascular disorders, their interaction remains poorly understood. Thus, we investigated the impact of a diet rich in trans-fatty acids (HFD) combined with AS on glycemic control, lipid profile, adipose tissue, skeletal muscle and pancreas microstructure and expression of genes involved in energy metabolism.

MAIN METHODS

Forty-eight C57BL/6 mice were randomized into 6 groups treated for 12 weeks with a standard diet (SD) or a diet rich in C18:1 trans-fatty isomers (HFD), alone or combined with 10 or 20 mg/kg testosterone cypionate (AS).

KEY FINDINGS

Our results indicated that AS improved glycemic control, upregulated gene expression of Glut-4 and CPT-1 in skeletal muscle, FAS, ACC and UCP-1 in adipose tissue. AS also reduced total and LDL cholesterol in mice fed a SD. When combined with the HFD, AS was unable to induce microstructural adaptations in adipose tissue, pancreatic islets and β-cells, but potentiated GCK and Glut-2 (pancreas) and Glut-4 and CPT-1 (skeletal muscle) upregulation. HFD plus AS also downregulated FAS and ACC gene expression in adipose tissue. Combined with HFD, AS increased triacylglycerol circulating levels, improved insulin sensitivity and glycemic control in mice.

SIGNIFICANCE

Our findings indicated that HFD and AS can interact to modulates glycemic control and lipid profile by a mechanism potentially related with a reprogramming of genes expression in organs such as the pancreas, adipose tissue and skeletal muscle.

WASH Regulates Glucose Homeostasis by Facilitating Glut2 Receptor Recycling in Pancreatic β-Cells

WASH is an endosomal protein belonging to the Wiskott-Aldrich syndrome protein superfamily that participates in endosomal receptor trafficking by facilitating tubule fission via activation of the ubiquitously expressed Arp2/3 complex. While several studies have begun to elucidate an understanding of the functions of WASH in cells lines, the in vivo function of WASH has not been fully elucidated, since total body deletion in mice leads to early embryonic lethality. To circumvent this problem, we have used a WASH conditional knockout mouse model to investigate the role of WASH in the pancreas. We find that pancreas-specific deletion of WASH leads to impaired blood glucose clearance and reduced insulin release upon glucose stimulation. Furthermore, WASH depletion results in impaired trafficking of Glut2 in pancreatic β-cells as a consequence of an intracellular accumulation of Glut2 and overall decreased levels of Glut2 protein. Taken together, these results indicate that WASH participates in pancreatic β-cell glucose sensing and whole-body glucose homeostasis. Thus, patients harboring mutations in components of the WASH complex could be at risk for developing type 2 diabetes.

Impaired β-cell glucokinase as an underlying mechanism in diet-induced diabetes

High-fat diet (HFD)-fed mouse models have been widely used to study early type 2 diabetes. Decreased β-cell glucokinase (GCK) expression has been observed in HFD-induced diabetes. However, owing to its crucial roles in glucose metabolism in the liver and in islet β-cells, the contribution of decreased GCK expression to the development of HFD-induced diabetes is unclear. Here, we employed a β-cell-targeted gene transfer vector and determined the impact of β-cell-specific increase in GCK expression on β-cell function and glucose handling in vitro and in vivo Overexpression of GCK enhanced glycolytic flux, ATP-sensitive potassium channel activation and membrane depolarization, and increased proliferation in Min6 cells. β-cell-targeted GCK transduction did not change glucose handling in chow-fed C57BL/6 mice. Although adult mice fed a HFD showed reduced islet GCK expression, impaired glucose tolerance and decreased glucose-stimulated insulin secretion (GSIS), β-cell-targeted GCK transduction improved glucose tolerance and restored GSIS. Islet perifusion experiments verified restored GSIS in isolated HFD islets by GCK transduction. Thus, our data identify impaired β-cell GCK expression as an underlying mechanism for dysregulated β-cell function and glycemic control in HFD-induced diabetes. Our data also imply an etiological role of GCK in diet-induced diabetes.This article has an associated First Person interview with the first author of the paper.

Compensatory hyperinsulinemia in high-fat diet-induced obese mice is associated with enhanced insulin translation in islets

A high-fat diet (HF) is associated with obesity, insulin resistance, and hyperglycemia. Animal studies have shown compensatory mechanisms in pancreatic β-cells after high fat load, such as increased pancreatic β-cell mass, enhanced insulin secretion, and exocytosis. However, the effects of high fat intake on insulin synthesis are obscure. Here, we investigated whether insulin synthesis was altered in correlation with an HF diet, for the purpose of obtaining further understanding of the compensatory mechanisms in pancreatic β-cells. Mice fed an HF diet are obese, insulin resistant, hyperinsulinemic, and glucose intolerant. In islets of mice fed an HF diet, more storage of insulin was identified. We analyzed insulin translation in mouse islets, as well as in INS-1 cells, using non-radioisotope chemicals. We found that insulin translational levels were significantly increased in islets of mice fed an HF diet to meet systemic demand, without altering its transcriptional levels. Our data showed that not only increased pancreatic β-cell mass and insulin secretion but also elevated insulin translation is the major compensatory mechanism of pancreatic β-cells.

Adverse association between obesity and menopause in mice treated with bezafibrate, a pan peroxisome proliferator-activated receptor agonist

OBJECTIVE

The goal of this study was to investigate the combined effects of ovariectomy (OVX) and high-fat diet (HF) on insulin sensitivity and pancreatic remodeling in C57BL/6 mice treated with bezafibrate.

METHODS

Female C57BL/6 mice were subjected to OVX or surgical procedure without removal of the ovary (SHAM). Animals received standard chow (SC; 10% lipids) or HF (60% lipids). After 13 weeks on the diets, the animals were subdivided into six groups based on diet, bezafibrate treatment, or both: SHAM-SC, SHAM-HF, SHAM-HFBz, OVX-SC, OVX-HF, and OVX-HFBz. After treatment for 5 weeks, the pancreas was removed and analyzed using morphometry, stereological tools, immunostaining, and multiplex assay kits.

RESULTS

SHAM-HF and OVX-HF mice showed increased fasting glucose levels, plasma insulin levels, homeostasis model of assessment for insulin resistance index, body mass, islet hypertrophy, β-cell mass, and insulin immunostaining, but decreased GLUT2 immunostaining. Bezafibrate treatment prevented islet hypertrophy and reduced body mass, plasma insulin levels, and homeostasis model of assessment for insulin resistance index.

CONCLUSIONS

OVX combined with HF accentuates the effects of menopause, leading to the development of insulin resistance. Bezafibrate treatment reduces body mass, plasma insulin levels, and pancreatic islet hypertrophy in mice fed HF.

Nutritional regulation of glucokinase: a cross-species story

The glucokinase (GK) enzyme (EC 2.7.1.1.) is essential for the use of dietary glucose because it is the first enzyme to phosphorylate glucose in excess in different key tissues such as the pancreas and liver. The objective of the present review is not to fully describe the biochemical characteristics and the genetics of this enzyme but to detail its nutritional regulation in different vertebrates from fish to human. Indeed, the present review will describe the existence of the GK enzyme in different animal species that have naturally different levels of carbohydrate in their diets. Thus, some studies have been performed to analyse the nutritional regulation of the GK enzyme in humans and rodents (having high levels of dietary carbohydrates in their diets), in the chicken (moderate level of carbohydrates in its diet) and rainbow trout (no carbohydrate intake in its diet). All these data illustrate the nutritional importance of the GK enzyme irrespective of feeding habits, even in animals known to poorly use dietary carbohydrates (carnivorous species).

A maternal diet rich in fish oil may improve cardiac Akt-related signaling in the offspring of diabetic mother rats

OBJECTIVE

Newborns of diabetic mothers have abnormal circulatory organs, so in this study, we explore insulin signaling in the newborn rat heart.

METHODS

Pregnant rats were divided into streptozotocin-induced diabetic groups (DM) and control groups (CM). Rats were fed lard (21% fat), fish oil (21% fat), or a control diet (7% fat). To examine changes in insulin signaling in the hearts of infants of diabetic mothers (IDM) in relation to diet, we isolated the hearts from the IDM and control infants and determined the phosphorylation levels of Akt308, Akt473, p38, c-jun-NH2-terminal protein kinase (JNK), and extracellular signal-regulated protein kinase (ERK), and the expression levels of phosphoinositide-dependent protein kainase1 (PDK1) and mammalian target of rapamycin (mTOR).

RESULTS

The mean blood glucose levels in the DM group and their infants were significantly higher than those in the CM group (P < 0.05) and their infants (P < 0.05), but the mean blood glucose levels of all infants was normal on postnatal d 4. Phosphorylation levels of Akt (Thr 308) (P < 0.05) and Akt (Ser 473) and the expression levels of PDK1 and mTOR were lower in infants of diabetic mothers (IDM) than in control infants. The phosphorylation level of Akt (Ser 473) and the expression level of mTOR increased in IDM fed the fish oil diet compared with those fed the lard diet (P < 0.05).

CONCLUSION

A maternal diet rich in fish oil improves cardiac Akt-related signaling in the offspring of diabetic rats.

Endocrine pancreatic development: impact of obesity and diet

During embryonic development, multipotent endodermal cells differentiate to form the pancreas. Islet cell clusters arising from the pancreatic bud form the acini tissue and exocrine ducts whilst pancreatic islets form around the edges of the clusters. The successive steps of islet differentiation are controlled by a complex network of transcription factors and signals that influence cell differentiation, growth and lineage. A Westernized lifestyle has led to an increased consumption of a high saturated fat diet, and an increase in maternal obesity. The developing fetus is highly sensitive to the intrauterine environment, therefore any alteration in maternal nutrition during gestation and lactation which affects the in-utero environment during the key developmental phases of the pancreas may change the factors controlling β-cell development and β-cell mass. Whilst the molecular mechanisms behind the adaptive programming of β-cells are still poorly understood it is established that changes arising from maternal obesity and/or over-nutrition may affect the ability to maintain fetal β-cell mass resulting in an increased risk of type 2 diabetes in adulthood.

Nutrition-/diet-induced changes in gene expression in pancreatic β-cells

β-Cell dysfunction is a critical component in the development of type 2 diabetes. Whilst both genetic and environmental factors contribute to the development of the disease, relatively little is known about the molecular network that is responsible for diet-induced functional changes in pancreatic β-cells. Recent genome-wide association studies for diabetes-related traits have generated a large number of candidate genes that constitute possible links between dietary factors and the genetic susceptibility for β-cell failure. Here, we summarize recent approaches for identifying nutritionally regulated transcripts in islets on a genome-wide scale. Polygenic mouse models for type 2 diabetes have been instrumental for investigating the mechanism of diet-induced β-cell dysfunction. Enhanced oxidative metabolism, triggered by a combination of dietary carbohydrates and fat, appears to play a critical role in the pathophysiology of diet-induced impairment of islets. More systematic studies of gene-diet interactions in β-cells of rodent models in combination with genetic profiling might reveal the regulatory circuits fundamental for the understanding of diet-induced impairments of β-cell function in humans.

Alterations of NADPH oxidase activity in rat pancreatic islets induced by a high-fat diet

OBJECTIVE

The aim of this study was to evaluate the effect of a high-fat diet (HFD) on nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in rat pancreatic islets. We investigated if changes in NADPH oxidase are connected to beta cell dysfunction reported in obese animals.

METHODS

Male Wistar rats were fed a HFD or control diet for 3 months. DNA fragmentation, insulin secretion, and [U-C]glucose oxidation were examined in isolated pancreatic islets. The oxidative stress markers nitrotyrosine and 4-hydroxy-2-nonenal were assessed by immunohistochemistry. The protein content of gp91 and p47 was evaluated by Western blotting. Production of reactive oxygen species (ROS) was determined by a fluorescence assay using hydroethidine.

RESULTS

Occurrence of DNA fragmentation was reduced in pancreatic islets from HFD rats. There were no differences in oxidative stress markers between the groups. Glucose oxidation and insulin secretion were elevated due to high glucose in pancreatic islets from HFD rats. Protein concentrations of p47 and gp91 subunits were reduced and ROS production was diminished in pancreatic islets from HFD rats.

CONCLUSIONS

The diminished content of NADPH oxidase subunits and ROS concentrations may be associated with increased glucose oxidation and insulin secretion in an attempt to compensate for the peripheral insulin resistance elicited by the HFD.

High fat programming of beta-cell failure

High saturated fat intake contributes to insulin resistance, beta-cell failure, and type 2 diabetes. Developmental programming refers to a stimulus or insult during critical periods of life which includes fetal and subsequent early neonatal life. Programming alters offspring physiology and metabolism with both immediate and lasting consequences. Maternal nutrition in gestation and lactation shapes offspring development and health. A high saturated fat diet ingested by mothers during gestation and/or lactation is a form of nutritional insult that induces diabetogenic changes in offspring physiology and metabolism. High fat programming is induced by maternal high saturated fat intake during defined periods of gestation and/or lactation and programs the physiology and metabolism of the offspring in early life. This more recently adopted form of developmental programming reflects society in both affluent and developing countries. High fat programming induces adverse changes in beta-cell development and function in neonatal and weanling offspring. These changes are characterized by compromised beta-cell development and function, evident by altered expression of key factors that maintain the beta-cell phenotype. High fat programming is likely to result in beta-cell failure and eventual type 2 diabetes.

Gestational high-fat programming impairs insulin release and reduces Pdx-1 and glucokinase immunoreactivity in neonatal Wistar rats

Hyperglycemia and compromised beta-cell development were demonstrated in neonatal rats programmed with a gestational high-fat diet. The aim of this study was to determine whether these changes were attributed to impaired insulin release and altered immunoreactivity of Pdx-1, glucokinase (GK), and glucose transporter (GLUT)-2 in high-fat-programmed neonates. Fetuses were maintained, via maternal nutrition, on either a standard laboratory diet (control) or a high-fat diet throughout gestation (HFG). Pancreata from 1-day-old neonates were excised for islet isolation and the subsequent measurement of insulin release at 2.8, 6.5, 13, and 22 mmol/L glucose. Other pancreata were either snap frozen for quantitative polymerase chain reaction or formalin fixed for immunohistochemistry followed by image analysis. The HFG neonates had reduced insulin release at 13- and 22-mmol/L glucose concentrations. No significant differences were found in Pdx-1, GK, or GLUT-2 messenger RNA expression. In HFG neonates, immunoreactivity of both Pdx-1 and GK was significantly reduced, with a nonsignificant reduction in GLUT-2. Gestational high-fat programming impairs insulin release and reduces Pdx-1 and GK immunoreactivity.

The glucose transporter 2 undergoes plasma membrane endocytosis and lysosomal degradation in a secretagogue-dependent manner

In beta-cells of the pancreas, the glucose transporter (GLUT)-2 facilitative glucose transporter protein is localized to the plasma membrane and functions as part of the glucose sensing mechanism for the stimulation of insulin secretion. We observed that expressed GLUT2 protein in the cultured Min6B1 cell line undergoes enhanced endocytosis at high extracellular glucose concentrations that stimulate insulin secretion. Moreover, the internalized GLUT2 protein undergoes rapid degradation induced by chronic high-glucose or arginine stimulation but does not undergo plasma membrane recycling or accumulation in any microscopically apparent intracellular membrane compartment. The rapid degradation of GLUT2 was prevented by lysosomal inhibition (chloroquine) concomitant with the accumulation of GLUT2 in endomembrane structures. In contrast, neither endocytosis nor the lack of internal membrane localized GLUT2 remained completely unaffected by proteosomal inhibition (lactacystin) or an heat shock protein-90 inhibitor (geldanamycin). Moreover, the endocytosis and degradation of GLUT2 was specific for beta-cells because expression of GLUT2 in 3T3L1 adipocytes remained cell surface localized and did not display a rapid rate of degradation. Together, these data demonstrate that hyperglycemia directly affects beta-cell function and activates a trafficking pathway that results in the rapid endocytosis and degradation of the cell surface GLUT2 glucose transporter.

Impact of short-term high-fat feeding on glucose and insulin metabolism in young healthy men

A high-fat, high-calorie diet is associated with obesity and type 2 diabetes. However, the relative contribution of metabolic defects to the development of hyperglycaemia and type 2 diabetes is controversial. Accumulation of excess fat in muscle and adipose tissue in insulin resistance and type 2 diabetes may be linked with defective mitochondrial oxidative phosphorylation. The aim of the current study was to investigate acute effects of short-term fat overfeeding on glucose and insulin metabolism in young men. We studied the effects of 5 days' high-fat (60% energy) overfeeding (+50%) versus a control diet on hepatic and peripheral insulin action by a hyperinsulinaemic euglycaemic clamp, muscle mitochondrial function by (31)P magnetic resonance spectroscopy, and gene expression by qrt-PCR and microarray in 26 young men. Hepatic glucose production and fasting glucose levels increased significantly in response to overfeeding. However, peripheral insulin action, muscle mitochondrial function, and general and specific oxidative phosphorylation gene expression were unaffected by high-fat feeding. Insulin secretion increased appropriately to compensate for hepatic, and not for peripheral, insulin resistance. High-fat feeding increased fasting levels of plasma adiponectin, leptin and gastric inhibitory peptide (GIP). High-fat overfeeding increases fasting glucose levels due to increased hepatic glucose production. The increased insulin secretion may compensate for hepatic insulin resistance possibly mediated by elevated GIP secretion. Increased insulin secretion precedes the development of peripheral insulin resistance, mitochondrial dysfunction and obesity in response to overfeeding, suggesting a role for insulin per se as well GIP, in the development of peripheral insulin resistance and obesity.

Nutrigenomics, beta-cell function and type 2 diabetes

INTRODUCTION

The present investigation was designed to investigate the accuracy and precision of lactate measurement obtained with contemporary biosensors (Chiron Diagnostics, Nova Biomedical) and standard enzymatic photometric procedures (Sigma Diagnostics, Abbott Laboratories, Analyticon).

MATERIALS AND METHODS

Measurements were performed in vitro before and after the stepwise addition of 1 molar sodium lactate solution to samples of fresh frozen plasma to systematically achieve lactate concentrations of up to 20 mmol/l.

RESULTS

Precision of the methods investigated varied between 1% and 7%, accuracy ranged between 2% and -33% with the variability being lowest in the Sigma photometric procedure (6%) and more than 13% in both biosensor methods.

CONCLUSION

Biosensors for lactate measurement provide adequate accuracy in mean with the limitation of highly variable results. A true lactate value of 6 mmol/l was found to be presented between 4.4 and 7.6 mmol/l or even with higher difference. Biosensors and standard enzymatic photometric procedures are only limited comparable because the differences between paired determinations presented to be several mmol. The advantage of biosensors is the complete lack of preanalytical sample preparation which appeared to be the major limitation of standard photometry methods.

Compromised beta-cell development and beta-cell dysfunction in weanling offspring from dams maintained on a high-fat diet during gestation

OBJECTIVES

Reported here are the effects of a high-fat diet (HFD) fed to dams during pregnancy on the weight, beta- and alpha-cell development, and beta-cell function of their weanling offspring.

METHODS

Offspring were obtained from dams maintained on an HFD for the first, second, or third week of gestation or throughout gestation and then on a standard laboratory diet for the duration of lactation. Weanling weights and circulating glucose and insulin concentrations were measured on postnatal day 21, after which pancreata were excised and snap-frozen for quantitative polymerase chain reaction of glucokinase (GK) or processed for immunohistochemical examination and image analysis (beta- and alpha-cell volume, number, and size, and GK immunoreactivity).

RESULTS

All of the weanlings had low body weights and were hypoinsulinemic. In weanlings maintained on an HFD for either the first, second, or third week of gestation, hyperglycemia and a reduction in beta-cell volume and number, in beta- and alpha-cell size, and in both GK messenger RNA expression and immunoreactivity were observed. The development of beta and alpha cells was normal in weanlings maintained on an HFD throughout gestation.

CONCLUSIONS

Maintenance of dams on an HFD for any single week of gestation results in weanling offspring with an impairment in beta-cell development and function.

Hyperglycaemia and reduced glucokinase expression in weanling offspring from dams maintained on a high-fat diet

High-fat feeding reduces the expression of GLUT-2 and the glycolytic enzyme glucokinase (GK). The transcription factor, pancreatic duodenal homeobox-1 (Pdx-1), is important for β-cell maintenance. The aim of the present study was to determine, in weanling Wistar rats, the effect of a maternal high-fat diet (HFD) during defined periods of gestation and lactation, on body weight, circulating glucose and insulin concentrations, and the expression of GLUT-2, GK and Pdx-1. At postnatal day 21, weights were recorded and glucose and insulin concentrations were measured. The expression levels for mRNA were quantified by LightCycler PCR. Pancreatic sections, immunostained for GLUT-2, GK or Pdx-1, were assessed by image analysis. Weanlings from dams fed an HFD throughout gestation were lighter, with heavier weanlings produced from dams fed an HFD throughout gestation and lactation. Both these groups of weanlings were normoglycaemic, all the others being hyperglycaemic. Hypoinsulinaemia was evident in weanlings from dams fed an HFD throughout gestation only and also for either the first week of lactation or throughout lactation. GLUT-2 mRNA expression was reduced and GLUT-2 immunoreactivity was increased in most of the weanlings. GK mRNA expression and immunoreactivity was reduced in most of the offspring. Pdx-1 mRNA expression was increased in weanlings from dams fed an HFD throughout both gestation and lactation and reduced in those from dams only fed a lactational HFD. Normal Pdx-1 immunoreactivity was found in all of the weanlings. A maternal HFD induces hyperglycaemia in weanlings concomitant with reduced GK expression which may compromise β-cell function.

Islet cell response in the neonatal rat after exposure to a high-fat diet during pregnancy

Although pancreatic beta-cells are capable of adapting their mass in response to insulin requirements, evidence has shown that a dietary insult could compromise this ability. Fetal malnutrition has been linked to low birth weight and the development of type 2 diabetes later in life, while reduced beta-cell mass has been reported in adult rats fed a high-fat diet (HFD). Reported here are the effects of exposure to a HFD, during different periods of gestation, on neonatal rat weight and beta- and alpha-cell development. The experimental groups were composed of neonatal offspring obtained from Wistar rats fed a high-fat (40% as energy) diet for either the first (HF1), second (HF2), or third (HF3) week, or all three (HF1-3) weeks of gestation. Neonatal weights and circulating glucose and insulin concentrations were measured on postnatal day 1, after which the pancreata were excised and processed for histological immunocytochemical examination and image analysis. HF1 and HF2 neonates were hypoglycemic, whereas HF1-3 neonates were hyperglycemic. Low birth weights were observed only in HF1 neonates. No significant differences were detected in the circulating insulin concentrations in the neonates, although beta-cell volume and numbers were reduced in HF1-3 neonates. beta-cell numbers also declined in HF1 and HF3 neonates. alpha-cell volume, number and size were, however, increased in HF1-3 neonates. alpha-cell size was also increased in HF1 and HF3 neonates. In neonates, exposure to a maternal HFD throughout gestation was found to have the most adverse effect on beta-cell development and resulted in hyperglycemia.

Acute high-fat diet paradigms link galanin to triglycerides and their transport and metabolism in muscle

To compare the effects of acute exposure to dietary fat to those of chronic exposure, Sprague-Dawley rats were given a high-fat diet (50% fat) or moderate-fat diet (25% fat) for 1 day, 2 h or 3 weeks. With measurements of various parameters, the high-fat diet for 21 days produced the expected changes of: (1) a significant increase in total caloric intake and dissected fat pad weights; (2) a rise in leptin and the metabolites, triglycerides (TG), non-esterified fatty acids and glucose; (3) an increase in muscle beta-hydroxyacyl-CoA dehydrogenase (HADH) and adipose lipoprotein lipase (aLPL) activity, along with a decrease in LPL activity in muscle (mLPL); and (4) elevated galanin (GAL) expression and peptide levels in the anterior region of the paraventricular nucleus (PVN), with no change in the arcuate nucleus. The acute 1-day or 2-h high-fat diet similarly increased circulating lipids, HADH activity and PVN GAL mRNA but stimulated rather than suppressed mLPL activity. These effects occurred in the absence of a change in total caloric intake, fat pad weights, and adipose-related measures, suggesting that they resulted more from the rise in dietary fat from 25% to 50% than from increased adiposity or hyperphagia. Moreover, PVN GAL mRNA in the different groups was consistently and positively correlated with the specific measures of TG levels and both HADH and mLPL activity, linking it to metabolic processes related to the transport and capacity for oxidation of TG in muscle, rather than adipose tissue.

The effect of high-fat and high-fructose diets on glucose tolerance and plasma lipid and leptin levels in rats

AIM

High-fat and high-fructose diets are usually used to induce animal model diabetes mellitus. The purposes of this research were to compare the abnormalities of glucose metabolism caused by high-fructose diet and a high-fat diet and the effects of the high-fructose diet and high-fat diet on plasma leptin.

METHODS

In this research, 24 Sprague-Dawley rats were used as the experimental animals, which were divided into three groups: chow diet (control group), high-fructose diet (60% fructose w/w) and high-fat diet (20% lard w/w). They were fed for a period of 8 weeks, during which an oral glucose tolerance test was conducted in the seventh week, and after completion of the eighth week, the abdominal adipose tissue and liver of the rats were excised and weighed, and the plasma cholesterol, triglyceride, insulin and leptin concentrations were assayed.

RESULTS

The high-fat diet group presented a fasting blood glucose concentration that was higher than that of the control group. Furthermore, after 2 h of glucose challenge, the rats in the high-fat and high-fructose diet groups all presented higher plasma glucose concentrations than did the control group. The high-fat diet group showed higher body weight, higher relative liver weight, a higher plasma cholesterol concentration and higher amylase activity than did the other groups, whereas the high-fructose diet group showed higher fasting insulin and triglyceride concentrations. As for adipose tissue, the high-fat diet group presented an amount that was higher than that of the high-fructose and control groups, but the plasma leptin concentration of the high-fructose group was higher than that of the control group.

CONCLUSIONS

It can be concluded from the above-mentioned experimental results that a high-fructose diet can cause hyperinsulinaemia, while a high-fat diet can result in impaired pancreatic function of insulin secretion and glucose intolerance, indicating that high-fructose diet and a high-fat diet may exert divergent effects on glucose metabolism in rats.

Long-term high-fat feeding leads to severe insulin resistance but not diabetes in Wistar rats

Although lipid excess can impair beta-cell function in vitro, short-term high-fat feeding in normal rats produces insulin resistance but not hyperglycemia. This study examines the effect of long-term (10-mo) high polyunsaturated fat feeding on glucose tolerance in Wistar rats. The high fat-fed compared with the chow-fed group was 30% heavier and 60% fatter, with approximately doubled fasting hyperinsulinemia (P < 0.001) but only marginal fasting hyperglycemia (7.5 +/- 0.1 vs. 7.2 +/- 0.1 mmol/l, P < 0.01). Insulin sensitivity was approximately 67% lower in the high-fat group (P < 0.01). The acute insulin response to intravenous arginine was approximately double in the insulin-resistant high-fat group (P < 0.001), but that to intravenous glucose was similar in the two groups. After the intravenous glucose bolus, plasma glucose decline was slower in the high fat-fed group, confirming mild glucose intolerance. Therefore, despite severe insulin resistance, there was only a mildly elevated fasting glucose level and a relative deficiency in glucose-stimulated insulin secretion; this suggests that a genetic or congenital susceptibility to beta-cell impairment is required for overt hyperglycemia to develop in the presence of severe insulin resistance.

Secreção da insulina: efeito autócrino da insulina e modulação por ácidos graxos

A insulina exerce um papel central na regulação da homeostase da glicose e atua de maneira coordenada em eventos celulares que regulam os efeitos metabólicos e de crescimento. A sub-unidade beta do receptor de insulina possui atividade tirosina quinase intrínseca. A autofosforilação do receptor, induzida pela insulina, resulta na fosforilação de substratos protéicos intracelulares, como o substrato-1 do receptor de insulina (IRS-1). O IRS-1 fosforilado associa-se a domínios SH2 e SH3 da enzima PI 3-quinase, transmitindo, desta maneira, o sinal insulínico. A insulina parece exercer feedback positivo na sua secreção, pela interação com seu receptor em células B pancreáticas. Alterações nos mecanismos moleculares da via de sinalização insulínica sugerem uma associação entre resistência à insulina e diminuição da secreção deste hormônio, semelhante ao observado em diabetes mellitus tipo 2. Uma das anormalidades associadas à resistência à insulina é a hiperlipidemia. O aumento do pool de ácidos graxos livres circulantes pode modular a atividade de enzimas e de proteínas que participam na exocitose da insulina. Essa revisão descreve também os possíveis mecanismos de modulação da secreção de insulina pelos ácidos graxos em ilhotas pancreáticas.

The brain response to 2-deoxy glucose is blocked by a glial drug

Two brain regions - the basomedial hypothalamus and area postrema (AP) - react to changes in circulating glucose levels by altering feeding behavior and the secretion of pituitary and non-pituitary hormones. The precise identity of cells responding to glucose in these regions is uncertain. The recent detection of high-capacity glucose transporter proteins in astrocytes in these areas has suggested that astrocytes may play a role in glucose sensing by the brain. To test this hypothesis, rats were injected with either saline or methionine sulfoximine (MS), a compound that produces alterations in carbohydrate and glutamate metabolism in astrocytes. Eighteen hours later, rats were injected with either saline or 2-deoxy glucose (2-DG) and brain sections were stained to demonstrate 2-DG-activated neurons immunoreactive for Fos protein. MS-treated rats showed a 70% reduction in numbers of Fos+ neurons in the AP region (p<0.05). Also, specialized, Gomori+ astrocytes were particularly abundant in both glucose sensitive regions and showed a distribution identical to that reported for high-capacity glucose transporter proteins. These data suggest that specialized astrocytes influence the glucose-sensing function of the brain.

Toward a wholly nutritional therapy for type 2 diabetes

It may now be feasible to target specific supplemental nutrients to each of the key dysfunctions which conspire to maintain hyperglycemia in type 2 diabetes: bioactive chromium for skeletal muscle insulin resistance, conjugated linoleic acid for adipocyte insulin resistance, high-dose biotin for excessive hepatic glucose output, and coenzyme Q(10) for beta cell failure. Nutritional strategies which disinhibit hepatic fatty acid oxidation (involving hydroxycitrate, carnitine, pyruvate, and other adjuvants) may likewise prove beneficial - in the short term, by decreasing serum free fatty acids and, in the longer term, by promoting regression of visceral obesity. The nutrients and food factors recommended here appear to be safe and well tolerated, and thus may have particular utility for diabetes prevention.

High-dose biotin, an inducer of glucokinase expression, may synergize with chromium picolinate to enable a definitive nutritional therapy for type II diabetes

Glucokinase (GK), expressed in hepatocyte and pancreatic beta cells, has a central regulatory role in glucose metabolism. Efficient GK activity is required for normal glucose-stimulated insulin secretion, postprandial hepatic glucose uptake, and the appropriate suppression of hepatic glucose output and gluconeogenesis by elevated plasma glucose. Hepatic GK activity is subnormal in diabetes, and GK may also be decreased in the beta cells of type II diabetics. In supraphysiological concentrations, biotin promotes the transcription and translation of the GK gene in hepatocytes; this effect appears to be mediated by activation of soluble guanylate cyclase. More recent evidence indicates that biotin likewise increases GK activity in islet cells. On the other hand, high-dose biotin suppresses hepatocyte transcription of phosphoenolpyruvate carboxykinase, the rate-limiting enzyme for gluconeogenesis. Administration of high-dose biotin has improved glycemic control in several diabetic animals models, and a recent Japanese clinical study concludes that biotin (3 mg t.i.d. orally) can substantially lower fasting glucose in type II diabetics, without side-effects. The recently demonstrated utility of chromium picolinate in type II diabetes appears to reflect improved peripheral insulin sensitivity--a parameter which is unlikely to be directly influenced by biotin. Thus, the joint administration of supranutritional doses of biotin and chromium picolinate is likely to combat insulin resistance, improve beta-cell function, enhance postprandial glucose uptake by both liver and skeletal muscle, and inhibit excessive hepatic glucose production. Conceivably, this safe, convenient, nutritional regimen will constitute a definitive therapy for many type II diabetics, and may likewise be useful in the prevention and management of gestational diabetes. Biotin should also aid glycemic control in type I patients.

Can correction of sub-optimal coenzyme Q status improve beta-cell function in type II diabetics?

A stimulus to mitochondrial respiratory activity is a crucial component of the signal transduction mechanism whereby increased plasma glucose evokes insulin secretion by beta-cells. Efficient function of the glycerol-3-phosphate shuttle is important in this regard, and the rate-limiting enzyme in this shuttle--the mitochondrial glycerol-3-phosphate dehydrogenase (G3PD)--is underexpressed in the beta cells of human type II diabetics as well of rodents that are models for this disorder. Suboptimal tissue levels of coenzyme Q10 (CoQ) could be expected to further impair G3PD activity. Clinical reports from Japan suggest that supplemental CoQ may often improve beta-cell function and glycemic control in type II diabetics. Thus, it is proposed that correction of suboptimal CoQ status, by aiding the efficiency of G3PD and of respiratory chain function, will improve the glucose-stimulated insulin secretion of diabetic beta-cells.

Whole body glucose metabolism

This review describes major factors that, singly or together, influence the concentration and distribution of D-glucose in mammals, particularly in humans, with emphasis on rest, physical activity, and alimentation. It identifies areas of uncertainty: distribution and concentrations of glucose in interstitial fluid, kinetics and mechanism of transcapillary glucose transport, kinetics and mechanism of glucose transport via its transporters into cells, detailed mechanisms by which hormones, exercise, and hypoxia affect glucose movement across cell membranes, whether translocation of glucose transporters to the cell membrane accounts completely, or even mainly, for insulin-stimulated glucose uptake, whether exercise stimulates release of a circulating insulinomimetic factor, and the relation between muscle glucose uptake and muscle blood flow. The review points out that there is no compartment of glucose in the body at which all glucose is at the same concentration, and that models of glucose metabolism, including effects of insulin on glucose metabolism based on assumptions of concentration homogeneity, cannot be entirely correct. A fresh approach to modeling is needed.

Alterations in carbohydrate and lipid metabolism induced by a diet rich in coconut oil and cholesterol in a rat model

OBJECTIVE

The type of dietary fat as well as the amount of cholesterol occurring in the diet have been associated with several metabolic disorders. Thus, the aim of the present study was to investigate the influence of a hypercholesterolemic diet enriched with coconut oil and cholesterol on carbohydrate and lipid metabolism in a rat model.

METHODS

Twenty male Wistar rats weighing about 190 g were assigned to two dietary groups. One group received a semipurified control diet and the other was given a diet enriched in coconut oil (25% by weight) and cholesterol (1% by weight) for 26 days.

RESULTS

Our results indicated a significant increase in serum total cholesterol (+285%; p<0.001), low-density lipoproteins (+154%; p<0.01), liver cholesterol (+1509%; p<0.001), as well as a significant increase in liver weight (+46%; p<0.001) in those rats fed the hypercholesterolemia-inducing diet as compared to controls. Moreover, a significant decrease in serum high-density lipoproteins (-67%; p<0.001), triacylglycerols levels (-33%; p<0.05), and abdominal fat weight (-39%; p<0.01) were found. The observed alterations in serum lipid and lipoprotein profile resembled a situation of type IIa hyperlipidemia in humans. Measurement of several enzymes concerned with lipid utilization revealed a significant increase in 3-hydroxy-3-methylglutaryl-CoA reductase activity (+68%; p<0.01) in the liver of animals fed the hypercholesterolemic diet, while a significant reduction in plasma lecithin-cholesterol acyltransferase activity (-66%; p<0.001) was found. The situation of hypoglycemia (-18%; p<0.05) was accompanied by lower levels of serum insulin (-45%; p<0.01) and liver glycogen (-30%; p<0.05) in the hypercholesterolemic rats. Furthermore, glucose utilization was altered since lower glucose-6-Pase (-33%; p<0.05) and increased glucokinase (+212%; p<0.001) activities in the liver were found in the rat model of hypercholesterolemia.

CONCLUSION

These results provide new evidence that a diet-induced hypercholesterolemia in rats is associated with several adaptative changes in carbohydrate metabolism. These findings may be of importance not only considering the role of western diets on cholesterogenesis, but also in other metabolic disturbances involving lipid and carbohydrate metabolism.

Differential functions of hypothalamic galanin cell grows in the regulation of eating and body weight

Evidence suggests that hypothalamic galanin (GAL) has a variety of functions related to energy and nutrient balance, reproduction, water balance, and neuroendocrine regulation. The focus of this chapter is the role of GAL in eating and body weight regulation. Findings described herein demonstrate that GAL, in a cell group of the anterior region of the paraventricular nucleus (aPVN) that projects to the median eminence, has a role in the control of fat intake, fat metabolism, and body fat. This function of aPVN GAL neurons is carried out in close relation to circulating insulin and glucose. Galanin-expressing perikarya in the medial preoptic area (MPOA) have a similar function, although GAL here operates in association with the female steroids estrogen and progesterone. These GAL cell groups of the aPVN and MPOA contrast with those in the arcuate nucleus as well as the magnocellular vasopressin-containing neurons of the PVN and supraoptic nucleus, which show no relation to fat balance. This evidence reveals differential functions for the distinct GAL neuronal cell groups of the hypothalamus.

Behavioral and endocrine traits of obesity-prone and obesity-resistant rats on macronutrient diets

Patterns of eating behavior, body weight gain, and hormone changes were examined in normal-weight albino Sprague-Dawley rats on macronutrient diets. These diets consisted of either three separate jars with pure macronutrients, fat, carbohydrate and protein, from which to choose, or a single diet with different concentrations of fat and carbohydrate. Similar patterns on the choice-diet and single-diet paradigms were observed. During the first 7-10 days on these diets but not subsequently, the rats consuming a fat-rich diet exhibit significant hyperphagia, an increase in both total and fat intake that produces higher body weight gain. Compared with a 10% fat diet, a 30% fat diet is associated with a decline in insulin and corticosterone (CORT) levels, whereas a 60% fat diet produces an increase in circulating glucose. Levels of glucose are positively correlated with fat intake, and together these measures are consistently related to body fat. These relationships are most strongly expressed in rats that consume a fat-rich diet with >30% fat. Whereas insulin levels are also positively related to body fat, CORT is inversely related in these normal-weight subjects. In animals consuming a high-fat diet, a clear separation can be seen between "obesity-prone" (OP) rats with 100% greater body fat than "obesity-resistant" (OR) rats. The OP rats, which consume 15% more total calories, have significantly higher insulin and glucose levels. In animals that consume a diet with >30% fat, it is the OP but not the OR rats that exhibit a positive relation between fat intake, glucose levels, and body fat and reveal an additional association between carbohydrate intake, insulin, and body fat. Thus these rats on macronutrient diets exhibit distinct traits that relate behavior to hormone disturbances and adiposity and distinguish subjects that are prone vs. resistant to obesity.

A distinct difference in the metabolic stimulus-response coupling pathways for regulating proinsulin biosynthesis and insulin secretion that lies at the level of a requirement for fatty acyl moieties

The regulation of proinsulin biosynthesis in pancreatic beta-cells is vital for maintaining optimal insulin stores for glucose-induced insulin release. The majority of nutrient fuels that induce insulin release also stimulate proinsulin biosynthesis, but since insulin exocytosis and proinsulin synthesis involve different cellular mechanisms, a point of divergence in the respective metabolic stimulus-response coupling pathways must exist. A parallel examination of the metabolic regulation of proinsulin biosynthesis and insulin secretion was undertaken in the same beta-cells. In MIN6 cells, glucose-induced proinsulin biosynthesis and insulin release shared a requirement for glycolysis to generate stimulus-coupling signals. Pyruvate stimulated both proinsulin synthesis (threshold 0.13-0.2 mM) and insulin release (threshold 0.2-0.3 mM) in MIN6 cells, which was eliminated by an inhibitor of pyruvate transport (1 mM alpha-cyano-4-hydroxycinnamate). A combination of alpha-oxoisohexanoate and glutamine also stimulated proinsulin biosynthesis and insulin release in MIN6 cells, which, together with the effect of pyruvate, indicated that anaplerosis was necessary for instigating secondary metabolic stimulus-coupling signals in the beta-cell. A consequence of increased anaplerosis in beta-cells is a marked increase in malonyl-CoA, which in turn inhibits beta-oxidation and elevates cytosolic fatty acyl-CoA levels. In the beta-cell, long-chain fatty acyl moieties have been strongly implicated as metabolic stimulus-coupling signals for regulating insulin exocytosis. Indeed, it was found in MIN6 cells and isolated rat pancreatic islets that exogenous oleate, palmitate and 2-bromopalmitate all markedly potentiated glucose-induced insulin release. However, in the very same beta-cells, these fatty acids in contrast inhibited glucose-induced proinsulin biosynthesis. This implies that neither fatty acyl moieties nor beta-oxidation are required for the metabolic stimulus-response coupling pathway specific for proinsulin biosynthesis, and represent an early point of divergence of the two signalling pathways for metabolic regulation of proinsulin biosynthesis and insulin release. Therefore alternative metabolic stimulus-coupling factors for the specific control of proinsulin biosynthesis at the translational level were considered. One possibility examined was an increase in glycerophosphate shuttle activity and change in cytosolic redox state of the beta-cell, as reflected by changes in the ratio of alpha-glycerophosphate to dihydroxyacetone phosphate. Although 16.7 mM glucose produced a significant rise in the alpha-glycerophosphate/dihydroxyacetone phosphate ratio, 1 mM pyruvate did not. It follows that the cytosolic redox state and fatty acyl moieties are not necessarily involved as secondary metabolic stimulus-coupling factors for regulation of proinsulin biosynthesis. However, the results indicate that glycolysis and the subsequent increase in anaplerosis are indeed necessary for this signalling pathway, and therefore an extramitochondrial product of beta-cell pyruvate metabolism (that is upstream of the increased cytosolic fatty acyl-CoA) acts as a key intracellular secondary signal for specific control of proinsulin biosynthesis by glucose at the level of translation.

Obesity on a high-fat diet: role of hypothalamic galanin in neurons of the anterior paraventricular nucleus projecting to the median eminence

Previous studies have suggested that the peptide galanin (GAL) in the hypothalamus is related to the preference of an animal for dietary fat. The present report investigates this relationship further to identify the specific GAL-synthesizing cell groups involved and to characterize their association to circulating glucose or hormones and their possible contribution to body fat deposition. Male albino Sprague Dawley rats were tested in different feeding paradigms with diets containing the macronutrients, fat, carbohydrate, or protein. These studies, using multiple techniques, identify a cell group in the hypothalamus that expresses GAL and that shows a shift in peptide activity in close relation to dietary fat, circulating glucose, and body fat. In all paradigms, a rise in fat intake, from 10 to 30%, is associated with reduced levels of insulin and corticosterone and normal glucose levels, whereas a further increase in fat ingestion (>30%) leads to hyperglycemia along with greater adiposity. In the hypothalamus, GAL gene expression, peptide production, and peptide release rise significantly (by 40%) in association with fat ingestion, showing no relation to either carbohydrate or protein ingestion. This change is highly site specific, evident predominantly in GAL-synthesizing neurons in the anterior parvocellular region of the paraventricular nucleus (aPVN) and in GAL-containing terminals in the external zone of the median eminence (ME). Positive correlations detected between mRNA abundance in the aPVN and GAL peptide in the ME support the existence of an aPVN-ME projection system related to fat intake and fat deposition. When activated by dietary fat, the contribution of this projection to body fat is suggested by consistent positive correlations between aPVN-ME GAL and either dietary fat, circulating glucose, or body fat and by significantly higher GAL levels (+30%) in obesity-prone compared with obesity-resistant rats. This evidence supports a role for this hypothalamic GAL projection system in the development of obesity produced by the overconsumption of fat.

Pancreatic cancer in rats and hamsters does not induce IAPP-related hyperglycaemia

Many patients with exocrine pancreatic cancer develop diabetes mellitus due to insulin resistance. This may relate to concurrent over-production of islet amyloid polypeptide (IAPP) by the pancreatic beta cells. We investigated the effects of pancreatic cancer on circulating IAPP and glucose homeostasis in azaserine-treated rats (developing acinar pancreatic tumours) and BOP-treated hamsters (developing ductular pancreatic tumours). Glucose, insulin and IAPP levels in plasma were neither affected in azaserine-only treated rats nor in animals with enhanced carcinogenesis after chronic caerulein treatment. Azaserine-treated rats on a high-fat diet had decreased insulin levels and enhanced IAPP/insulin ratios in plasma, without hyperglycaemia. All BOP-treated hamsters showed pancreatic carcinogenesis at 6 months post-treatment. Supranormal plasma glucose levels in animals on a low-fat diet were the only change observed. After a second 6-month period, subnormal plasma glucose levels, at least 4-fold decreased plasma insulin and up to 2-fold decreased plasma IAPP levels were present in all hamsters. Remarkably, both in azaserine-treated rats on high-fat and in BOP-treated hamsters, decreased insulin levels and elevated IAPP/insulin ratios are not associated with hyperglycaemia. In contrast to humans with pancreatic cancer, IAPP over-production and hyperglycaemia do not develop in rats and hamsters with (pre-)neoplastic pancreatic lesions.

High-fat diet-induced hyperglycemia and obesity in mice: differential effects of dietary oils

Mice fed a high-fat diet develop hyperglycemia and obesity. Using non-insulin-dependent diabetes mellitus (NIDDM) model mice, we investigated the effects of seven different dietary oils on glucose metabolism: palm oil, which contains mainly 45% palmitic acid (16:0) and 40% oleic acid (18:1); lard oil, 24% palmitic and 44% oleic acid; rapeseed oil, 59% oleic and 20% linoleic acid (18:2); soybean oil, 24% oleic and 54% linoleic acid; safflower oil, 76% linoleic acid; perilla oil, 58% alpha-linolenic acid; and tuna fish oil, 7% eicosapentaenoic acid and 23% docosahexaenoic acid. C57BL/6J mice received each as a high-fat diet (60% of total calories) for 19 weeks (n = 6 to 11 per group). After 19 weeks of feeding, body weight induced by the diets was in the following order: soybean > palm > or = lard > or = rapeseed > or = safflower > or = perilla > fish oil. Glucose levels 30 minutes after a glucose load were highest for safflower oil (approximately 21.5 mmol/L), modest for rapeseed oil, soybean oil, and lard (approximately 17.6 mmol/L), mild for perilla, fish, and palm oil (approximately 13.8 mmol/L), and minimal for high-carbohydrate meals (approximately 10.4 mmol/L). Only palm oil-fed mice showed fasting hyperinsulinemia (P < .001). By stepwise multiple regression analysis, body weight (or white adipose tissue [WAT] weight) and intake of linoleic acid (or n-3/n-6 ratio) were chosen as independent variables to affect glucose tolerance. By univariate analysis, the linoleic acid intake had a positive correlation with blood glucose level (r = .83, P = .02) but not with obesity (r = .46, P = .30). These data indicate that (1) fasting blood insulin levels vary among fat subtypes, and a higher fasting blood insulin level in palm oil-fed mice may explain their better glycemic control irrespective of their marked obesity; (2) a favorable glucose response induced by fish oil feeding may be mediated by a decrease of body weight; and (3) obesity and a higher intake of linoleic acid are independent risk factors for dysregulation of glucose tolerance.