A long-term high-carbohydrate diet causes an altered ontogeny of pancreatic islets of Langerhans in the neonatal rat

Maternal diet during pregnancy and adaptive changes in the maternal and fetal pancreas have implications for future metabolic health

Fetal and neonatal development is a critical period for the establishment of the future metabolic health and disease risk of an individual. Both maternal undernutrition and overnutrition can result in abnormal fetal organ development resulting in inappropriate birth size, child and adult obesity, and increased risk of Type 2 diabetes and cardiovascular diseases. Inappropriate adaptive changes to the maternal pancreas, placental function, and the development of the fetal pancreas in response to nutritional stress during pregnancy are major contributors to a risk trajectory in the offspring. This interconnected maternal-placental-fetal metabolic axis is driven by endocrine signals in response to the availability of nutritional metabolites and can result in cellular stress and premature aging in fetal tissues and the inappropriate expression of key genes involved in metabolic control as a result of long-lasting epigenetic changes. Such changes result is insufficient pancreatic beta-cell mass and function, reduced insulin sensitivity in target tissues such as liver and white adipose and altered development of hypothalamic satiety centres and in basal glucocorticoid levels. Whilst interventions in the obese mother such as dieting and increased exercise, or treatment with insulin or metformin in mothers who develop gestational diabetes, can improve metabolic control and reduce the risk of a large-for-gestational age infant, their effectiveness in changing the adverse metabolic trajectory in the child is as yet unclear.

Rodent models of metabolic disorders: considerations for use in studies of neonatal programming

Epidemiologically, metabolic disorders have garnered much attention, perhaps due to the predominance of obesity. The early postnatal life represents a critical period for programming multifactorial metabolic disorders of adult life. Though altricial rodents are prime subjects for investigating neonatal programming, there is still no sufficiently generalised literature on their usage and methodology. This review focuses on establishing five approach-based models of neonatal rodents adopted for studying metabolic phenotypes. Here, some modelled interventions that currently exist to avoid or prevent metabolic disorders are also highlighted. We also bring forth recommendations, guidelines and considerations to aid research on neonatal programming. It is hoped that this provides a background to researchers focused on the aetiology, mechanisms, prevention and treatment of metabolic disorders.

Impact of the exposome on the development and function of pancreatic β-cells

The development and plasticity of the endocrine pancreas responds to both the intrauterine and postnatal exposome in a constant attempt to predict and respond to alterations in nutritional availability and metabolic requirements. Both under- and over-nutrition in utero, or exposure to adverse environmental pollutants or maternal behaviors, can each lead to altered β-cell or function at birth, and a subsequent mismatch in pancreatic hormonal demands and secretory capacity postnatally. This can be further exacerbated by metabolic stress postnatally such as from obesity or pregnancy, resulting in an increased risk of gestational diabetes, type 2 diabetes, and even type 1 diabetes. This review will discuss evidence identifying the cellular pathways in early life whereby the plasticity of the endocrine pancreatic can become pathologically limited. By necessity, much of this evidence has been gained from animal models, although extrapolation to human fetal development is possible from the fetal growth trajectory and study of the newborn. Cellular limitations to plasticity include the balance between β-cell proliferation and apoptosis, the appearance of β-cell oxidative stress, impaired glucose-stimulated insulin secretion, and sensitivity to circulating cytokines and responsiveness to programmed death receptor-1. Evidence suggests that many of the cellular pathways responsible for limiting β-cell plasticity are related to paracrine interactions within the islets of Langerhans.

Brief neonatal nutritional supplementation has sex-specific effects on glucose tolerance and insulin regulating genes in juvenile lambs

BACKGROUND

The nutritional plane and composition during fetal life can impact upon growth and epigenetic regulation of genes affecting pancreatic β-cell development and function. However, it is not clear whether β-cell development can be altered by nutritional factors or growth rate after birth. We therefore investigated the effect of neonatal nutritional supplements on growth, glucose tolerance, and pancreatic development in lambs.

METHODS

Newborn lambs were randomized to daily nutritional supplements, calculated to increase macronutrient intake to a similar degree as human breast milk fortifier, or an equivalent volume of water, for 2 wk while continuing to suckle ewe milk. Intravenous glucose tolerance test (IVGTT) was performed at 4 mo of age, and pancreata collected for molecular analysis.

RESULTS

Supplemented lambs had slower weight gain than controls. In supplemented lambs, insulin response to IVGTT was increased in males but decreased in females, compared to same sex controls, and was unrelated to growth rate. mRNA expression of key genes in β-cell development showed sexually dimorphic effects. Epigenetic change occurred in the promotor region of PDX1 gene with decreased suppression and increased activation marks in supplemented lambs of both sexes.

CONCLUSION

Nutritional interventions in early life have long-term, sex-specific effects on pancreatic function.

Epigenetic modulation of DNA methylation by nutrition and its mechanisms in animals

It is well known that phenotype of animals may be modified by the nutritional modulations through epigenetic mechanisms. As a key and central component of epigenetic network, DNA methylation is labile in response to nutritional influences. Alterations in DNA methylation profiles can lead to changes in gene expression, resulting in diverse phenotypes with the potential for decreased growth and health. Here, I reviewed the biological process of DNA methylation that results in the addition of methyl groups to DNA; the possible ways including methyl donors, DNA methyltransferase (DNMT) activity and other cofactors, the critical periods including prenatal, postnatal and dietary transition periods, and tissue specific of epigenetic modulation of DNA methylation by nutrition and its mechanisms in animals.

Effects of genetics and in utero diet on murine pancreatic development

Intrauterine (IU) malnutrition could alter pancreatic development. In this study, we describe the effects of high-fat diet (HFD) during pregnancy on fetal growth and pancreatic morphology in an 'at risk' animal model of metabolic disease, the glucose transporter 4 (GLUT4) heterozygous mouse (G4+/-). WT female mice mated with G4+/- males were fed HFD or control diet (CD) for 2 weeks before mating and throughout pregnancy. At embryonic day 18.5, fetuses were killed and pancreata isolated for analysis of morphology and expression of genes involved in insulin (INS) cell development, proliferation, apoptosis, glucose transport and function. Compared with WT CD, WT HFD fetal pancreata had a 2.4-fold increase in the number of glucagon (GLU) cells (P=0.023). HFD also increased GLU cell size by 18% in WT pancreata compared with WT CD. Compared with WT CD, G4+/- CD had an increased number of INS cells and decreased INS and GLU cell size. Compared with G4+/- CD, G4+/- HFD fetuses had increased pancreatic gene expression of Igf2, a mitogen and inhibitor of apoptosis. The expression of genes involved in proliferation, apoptosis, glucose transport, and INS secretion was not altered in WT HFD compared with G4+/- HFD pancreata. In contrast to WT HFD pancreata, HFD exposure did not alter pancreatic islet morphology in fetuses with GLUT4 haploinsufficiency; this may be mediated in part by increased Igf2 expression. Thus, interactions between IU diet and fetal genetics may play a critical role in the developmental origins of health and disease.

Islet organogenesis, angiogenesis and innervation

The pancreas is characterized by a major component, an exocrine and ductal system involved in digestion, and a minor component, the endocrine islets represented by islet micro-organs that tightly regulate glucose homoeostasis. Pancreatic organogenesis is strictly co-ordinated by transcription factors that are expressed sequentially to yield functional islets capable of maintaining glucose homoeostasis. Angiogenesis and innervation complete islet development, equipping islets to respond to metabolic demands. Proper regulation of this triad of processes during development is critical for establishing functional islets.

Early postnatal nutrition and programming of the preterm neonate

Early postnatal nutrition is a vital determinant of adult health; this is particularly true for the infant born prematurely and cared for in a hospital setting such as the neonatal intensive care unit. Human and animal studies support the contribution of postnatal dietary composition and the rate of extrauterine growth to long-term metabolic outcomes. One mechanism by which postnatal nutrition affects long-term outcome is via developmental programming. Programming, or the modulation of gene expression to impart a short-term advantage accompanied by a long-term cost, may be achieved by epigenetic modifications to chromatin. This review summarizes the details of postnatal nutritional content and rate of growth on the development of metabolic disease. The role of epigenetics in developmental programming of the preterm infant is also discussed, with an emphasis on animal models of dietary manipulation and directions in which the field must move in order to formulate effective feeding strategies for the preterm infant.

The fat:carbohydrate energy ratio of the weaning diet programs later susceptibility to obesity in male sprague dawley rats

Dietary fat intake, which is high during suckling, is markedly reduced when food and drinks are introduced into the diet. We investigated whether alterations in the fat:carbohydrate (CHO) content of the weaning diet influenced the later development of adiposity and insulin sensitivity. Three groups of male rats (24/group) were fed from age 16-37 d (phase I) with weaning diets varying in their fat:CHO energy (E) ratios, 10:70 low-fat, high-CHO (LFHC); 30:50 medium-fat, medium-CHO (MFMC), and 60:30 high-fat, high-CHO (HFLC), on an isocaloric basis. Then, all groups consumed ad libitum first a low-fat diet (13% fat E) for 30 wk (phase II) and subsequently a high-fat diet (45% fat E) for another 18 wk (phase III). At the end of phase I, the group fed the HFLC diet demonstrated higher plasma glucose and insulin responses to an oral glucose tolerance test (P < 0.05), but this effect was transient and did not persist into adulthood (phases II and III). By contrast, when challenged with a high-fat diet later in life (age 35.3-53.3 wk), the LFHC group had greater gains in weight (as percent initial weight) and body fat (as absolute and percent body weight) than the other 2 groups that had been weaned with diets higher in fat (P < 0.04 for all). These results provide evidence that metabolic programming by altering the dietary fat:CHO ratio can occur during the weaning period and emphasizes the importance of the fat:CHO ratio of the complementary diet and its relation to the susceptibility to develop adiposity later in life.

New insights into endocrine pancreatic development: the role of environmental factors

The pancreas is a mixed gland that contains endocrine and exocrine components. Within the pancreatic islets, beta cells produce insulin and control the glycemia. Their deficiency leads to diabetes and several potential complications. In the last decade, numerous studies have focused on pancreas development. The objective was to characterize the cellular and molecular factors that control the differentiation of endocrine and exocrine cell types. Investigation of the role of transcription factors by using genetic approaches led to the discovery of key molecules that are expressed both in rodents and humans. Some of them are ubiquitous, and some others are specifically involved in endocrine or exocrine specification. In addition to these intrinsic factors, recent studies have focused on the role of environmental factors. In the present review, we describe the roles of nutrients and oxygen in the embryonic pancreas. Interestingly, these extrinsic parameters can interfere with beta-cell differentiation and function. Altogether, these data should help to generate beta cells in vitro and define strategies for a cell-based therapy of type 1 diabetes.

Aortic vasoreactivity during a postnatal critical window of the pancreas in rats

Changes in aortic vasoreactivity during the postnatal pancreatic critical window, where insulin and glucose, which modify vasoreactivity, are elevated, were studied and compared to those in control and metabolic syndrome (MS) rats. Twelve 21- and 28-day-old rats were used. To develop MS rats, male Wistar animals were given 30% sucrose in drinking water since weaning and used when 6 months old. Glucose and insulin levels were higher during suckling and decreased after weaning, and insulin and triglycerides levels increased in MS rats. Contraction elicited by norepinephrine (NE) was stronger than KCl contraction at all ages. KCl-induced contraction increased with, age being stronger in control rats; it further increased in MS rats. Norepinephrine-induced contraction increased from day 12 to day 28 but stabilized from day 21 to day 28; it was stronger in controls and increased in MS rats. Vasorelaxation to acetylcholine in NE precontracted rings did not change during the neonatal period, being similar to MS rats and lower than in controls. Insulin-induced increase in contraction elicited by KCl increased from day 12 to day 28 and increased from control to MS rats. There is a postnatal critical window in vasoreactivity that might predispose to cardiovascular diseases in adults.

Metabolic programming: Role of nutrition in the immediate postnatal life

Although genes and dietary habits are generally implicated in the aetiology of the prevailing obesity epidemic, the steep increase in the incidence of obesity within a relatively short span of time suggests that other contributing factors may be at play. The role of nutritional experience during the very early periods of life is increasingly being recognized as contributing to growth and metabolic changes in later life. Epidemiological data and studies from animal models have established a strong correlation between an aberrant intrauterine environment and adult-onset disorders in offspring. The nutritional experience in the immediate postnatal life is another independent factor contributing to the development of metabolic diseases in adulthood. Although studies on the small-litter rat model have shown that overnourishment during the suckling period results in adult-onset metabolic disorders, our studies have shown that a change in the quality of calories-specifically, increased carbohydrate intake by newborn rat pups in the immediate postnatal period-results in chronic hyperinsulinaemia and adult-onset obesity. Several functional alterations in islets and in the hypothalamic energy homeostatic mechanism appear to support this phenotype. Remarkably, female rats that underwent the high-carbohydrate dietary modification as neonates spontaneously transmitted the obesity phenotype to their offspring, thus establishing a vicious generational effect. The high-carbohydrate diet-fed rat model has particular relevance in the context of the current human infant feeding practices: reduction in breast feeding and increase in formula feeding for infants, accompanied by early introduction of carbohydrate-enriched baby foods.

Increased islet neogenesis without increased islet mass precedes autoimmune attack in diabetes-prone rats

We reported previously that young BioBreeding diabetes-prone (BBdp) rats display increased neogenic extra-islet insulin+ clusters (EICs, <4 insulin+ cells) without an increase in beta-cell mass. Therefore, we investigated the possibility that abnormal islet expansion occurs in BBdp rats before the appearance of islet inflammation. Islet expansion was analyzed in pancreata from 14 to 45 day BBdp and control (BioBreeding control, BBc) rats using immunohistochemistry, morphometry, laser capture microdissection and reverse transcriptase-PCR. mRNA expression for Neurogenin-3, a developmental marker of endocrine progenitors, was three-fold greater in EIC of weanling BBdp and BBc rats compared with islet cells. With increasing age (14-30 days), Neurogenin-3 expression decreased in EIC and increased in islets. In BBdp rats, EIC number and beta-cell proliferation within EIC was greater compared with BBc animals; apoptosis did not differ. The area of small and medium islets in BBdp rats was greater than BBc rats between 14 and 30 days, but this did not result in increased total islet area or beta-cell mass. In addition, the number and area of very large islets was low at 45 days. The frequency of proliferating beta-cells decreased with increasing islet size in BBdp but was constant in BBc rats. Cell cycle analysis of islets revealed more G1 cells and fewer G2 cells in BBdp rats. The ratio of cyclinD2/Cdkn1a, genes that respectively promote or inhibit cell cycle progression, was decreased in BBdp islets. These results suggest that despite increased islet neogenesis, the capacity for islet expansion in diabetes-prone rats is compromised possibly due to decreased proliferative capacity with increasing islet size associated with a partial block at the G1/S cell cycle boundary in islet cells.

Metabolic programming in the pathogenesis of insulin resistance

This review focuses on different animal models of nutrient perturbations, inclusive of restrictive and excessive states mimicking human situations during pregnancy and lactation that cause aberrations in the offspring. These aberrations consist of diminished insulin sensitivity in the presence of defective insulin production. These phenotypic changes are due to altered peripheral tissue post-insulin receptor signaling mechanisms and pancreatic beta-islet insulin synthesis and secretion defects. While these changes during in utero or postnatal life serve as essential adaptations to overcome adverse conditions, they become maladaptive subsequently and set the stage for type 2 diabetes mellitus. Pregnancy leads to gestational diabetes with trans-generational propagation of the insulin resistant phenotype. This is in response to the metabolically aberrant maternal in utero environment, and tissue specific epigenetic perturbations that permanently alter expression of critical genes transmitted to future generations. These heritable aberrations consisting of altered DNA methylation and histone modifications remodel chromatin and affect transcription of key genes. Along with an altered in utero environment, these chromatin modifications contribute to the world-wide epidemic of type 2 diabetes mellitus, with nutrient excess dominating in developed and nutrient restriction in developing countries.

Effect of berberine on hepatic glucokinase and its regulatory protein in insulin-resistant rats

AIM: To investigate the effects of berberine on hepatic glucokinase (GK) activity, protein expression and GK's regulatory protein (GKRP) in insulin-resistant rats.

METHODS: Male Wistar rats were fed with high-fat diet for 8 wk to induce the model of insulin resistance. Then the insulin-resistant rats were randomly divided into 3 groups: model, berberine, and metformin groups which were treated with the corresponding preparations. Meanwhile, a normal control group was designed. The differences in insulin sensitivity, hepatic glycogen, hepatic GK activity, and protein expression (using Western blot) of hepatic GK and GKRP were compared among the groups.

RESULTS: As compared with those in model group, the insulin sensitivity (-4.93 ± 0.30 vs -5.35 ± 0.40, P < 0.05), hepatic glycogen level (136.58 ± 52.57 µg/g vs 65.88 ± 27.80 µg/g, P < 0.05), GK activity (226.55 ± 10.62 µkat/g vs 92.69 ± 6.43 µkat/g, P < 0.05), and hepatic GK protein expression (1.71±0.49 vs 1.24±0.22, P < 0.05) were significantly elevated in berberine group, while the expression of GKRP protein weaker (1.19 ± 0.20 vs 1.94 ± 0.56, P < 0.01). Meanwhile, the hepatic glycogen level in berberine group was markedly higher than that in metformin group (136.584 ± 52.574 µg/g vs 89.427 ± 31.971 µg/g, P < 0.05), but the other indexes were not significantly different between them (all P > 0.05).

CONCLUSION: Berberine may decrease insulin resistance by increasing of the hepatic GK activity.

Restructuring of pancreatic islets and insulin secretion in a postnatal critical window

Function and structure of adult pancreatic islets are determined by early postnatal development, which in rats corresponds to the first month of life. We analyzed changes in blood glucose and hormones during this stage and their association with morphological and functional changes of alpha and beta cell populations during this period. At day 20 (d20), insulin and glucose plasma levels were two- and six-fold higher, respectively, as compared to d6. Interestingly, this period is characterized by physiological hyperglycemia and hyperinsulinemia, where peripheral insulin resistance and a high plasmatic concentration of glucagon are also observed. These functional changes were paralleled by reorganization of islet structure, cell mass and aggregate size of alpha and beta cells. Cultured beta cells from d20 secreted the same amount of insulin in 15.6 mM than in 5.6 mM glucose (basal conditions), and were characterized by a high basal insulin secretion. However, beta cells from d28 were already glucose sensitive. Understanding and establishing morphophysiological relationships in the developing endocrine pancreas may explain how events in early life are important in determining adult islet physiology and metabolism.

Metabolic programming: fetal origins of obesity and metabolic syndrome in the adult

Exposure of the fetus to the intrauterine milieu can have profound effects on the health of the offspring in adulthood. Results of a series of studies demonstrate the powerful influence of the mother's metabolic state on whether the emerging adult develops obesity and hyperinsulinemia. Importantly, these attributes can be passed on to the next generation nongenetically and can be reversed and prevented.

Maternal hyperinsulinemia predisposes rat fetuses for hyperinsulinemia, and adult-onset obesity and maternal mild food restriction reverses this phenotype

We have previously shown that artificial rearing of newborn female rat pups on a high-carbohydrate (HC) milk formula resulted in chronic hyperinsulinemia and adult-onset obesity (HC phenotype) and that the maternal HC phenotype was transmitted to their progeny (2-HC rats) because of fetal development in the HC female rat. The aims of this study were to investigate 1) the fetal adaptations that predisposed the progeny for the expression of the HC phenotype in adulthood and 2) whether the transfer of the HC phenotype to the progeny could be reversed by maternal food restriction. Fetal parameters such as plasma insulin and glucose levels, mRNA level of preproinsulin gene, pancreatic insulin content, and islet insulin secretory response in vitro were determined. On gestational day 21, 2-HC fetuses were hyperinsulinemic, had increased insulin content and mRNA level of the preproinsulin gene in their pancreata and demonstrated an altered glucose-stimulated insulin secretory response by isolated islets. Modification of the intrauterine environment in HC female rats was achieved by pair feeding them to the amount of diet consumed by age-matched control rats from the time of their weaning. This mild dietary restriction reversed their HC phenotype and also prevented the development of the HC phenotype in their progeny. These findings show that mal-programming of the progeny of the hyperinsulinemic-obese HC female for the expression of the HC phenotype is initiated in utero and that normalization of the maternal environment in HC female rats by mild food restriction resulted in the normal phenotype in their progeny.

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.

Programming of islet functions in the progeny of hyperinsulinemic/obese rats

Neonatal female rat pups that were raised artificially on a high-carbohydrate (HC) milk formula during their suckling period developed hyperinsulinemia immediately, maintained chronic hyperinsulinemia in the postweaning period on laboratory diet, and developed obesity in adulthood. Pups (second-generation HC [2-HC]) born to such female rats (first-generation HC [1-HC]) spontaneously developed chronic hyperinsulinemia and adult-onset obesity (HC phenotype) without the requirement for any dietary intervention in their suckling period. Leftward shift in the insulin secretory response to a glucose stimulus, increase in hexokinase activity, and increased preproinsulin gene transcription were observed in islets from 28-day-old 2-HC rats, and these adaptations are similar to those reported for islets from 12-day-old and 100-day-old 1-HC rats. Unlike 1-HC islets, the ability to secrete moderate amounts of insulin in the absence of glucose and calcium and the incretin input for augmentation of insulin secretion were not observed in 2-HC islets. These results show that a dietary modification in the early postnatal life of the 1-HC female rat sets up a vicious cycle of spontaneous transfer of the HC phenotype to its progeny, implicating a new component to the growing list of factors that contribute to the fetal origins of adult-onset diseases.

Neonatal nutrition: metabolic programming of pancreatic islets and obesity

Obese individuals are more likely to suffer from diseases termed the "metabolic syndrome," which includes type 2 diabetes. It is now recognized that early life dietary experiences play an important role in the etiology of such diseases. In this context, the consequences of a high carbohydrate (HC) dietary intervention in neonatal rats is being studied in our laboratory. Artificial rearing of 4-day-old rat pups on a HC milk formula up to Day 24 results in the immediate onset of hyperinsulinemia, which persists throughout the period of dietary intervention. Several adaptations at the biochemical, cellular, and molecular levels in the islets of these HC rats support the onset and persistence of the hyperinsulinemic condition during this period. Some of these adaptations include a distinct leftward shift in the insulin secretory capacity, increased hexokinase activity, increased gene expression of preproinsulin and related transcription factors and specific kinases in 12-day-old HC islets, and alterations in the number and size of islets. These adaptations are programmed and expressed in adulthood thereby sustain the hyperinsulinemic condition in the postweaning period and form the basis for adult-onset obesity. HC females spontaneously transmit the HC phenotype (chronic hyperinsulinemia and adult-onset obesity) to their progeny. Collectively, our results indicate that even a mere switch in the nature of the source of calories (from fat rich in rat milk to carbohydrate rich in the HC milk formula) during critical phases of early development in the rat results in metabolic programming of islet functions leading to chronic hyperinsulinemia (throughout life) and adult-onset obesity. This metabolic programming, once established, forms a vicious cycle because HC female rats spontaneously transmit the HC phenotype to their progeny. The results from our laboratory in the context of metabolic programming due to neonatal nutritional experiences are discussed in this review.

Fetal insulin-like growth factor-2 production is impaired in the GK rat model of type 2 diabetes

At late fetal age (21.5 days postcoitum [dpc]), GK rats present a severely reduced beta-cell mass compared with Wistar rats. This anomaly largely antedates the onset of hyperglycemia in GK rats. Thus, the beta-cell mass deficit could represent the primary defect leading to type 2 diabetes in the adult. The aim of this work was to investigate, in GK fetuses at the end of fetal age (21.5 dpc), whether impaired availability of growth factors such as insulin, growth hormone, and IGFs and their IGF binding proteins (IGFBPs) could be instrumental in this anomaly. Although it confirms that GK fetuses are hypoinsulinemic despite enhanced plasma glucose level due to maternal hyperglycemia, the present study shows for the first time that IGF-2 expression in the liver and pancreas and IGF-2 serum levels are decreased in GK fetuses. Serum level as well as liver and pancreatic mRNA expression of IGFBP-2 were found to be normal in GK fetuses, whereas serum level and liver mRNA expression of IGFBP-1 were increased. Finally, we found that the maximal beta-cell mitogenic response to IGFs in vitro is kept intact, therefore suggesting that the direct biological action of IGFs on fetal GK beta-cells is not grossly impaired. In conclusion, in GK fetuses at 21.5 dpc, the defective IGF-2 production appears to be an early landmark in the pathological sequence leading to retardation of beta-cell growth in the fetal GK rat.

Molecular adaptations in islets from neonatal rats reared artificially on a high carbohydrate milk formula

Four day-old rat pups artificially raised on a high carbohydrate (HC) milk formula during their suckling period immediately develop hyperinsulinemia which persists into adulthood despite weaning onto lab chow on day 24. The present study investigates the molecular adaptations in islets isolated from neonatal rats in response to this dietary treatment during their suckling period. There is a significant increase in the level of preproinsulin mRNA and insulin biosynthesis in 12 day-old HC islets compared to islets from age-matched mother-fed (MF) control rats. Pancreatic duodenal homeobox factor-1 (PDX-1) modulates pancreatic ontogeny as well as preproinsulin gene expression in islets from neonatal rats. The mRNA level, DNA binding activity and protein content of PDX-1 are significantly increased in HC islets. The stress-activated protein kinase-2 and phosphatidylinositol 3-kinase have been reported to modulate PDX-1 activity in islets. The mRNA levels of these kinases are increased in HC islets. The mRNA level of upstream stimulatory factor (a modulator of PDX-1 gene expression) is also significantly increased in HC islets. These results indicate that the upregulation of several molecular events, including increases in the gene expression of preproinsulin, transcription factors and kinases may contribute to the chronic hyperinsulinemic state in the HC rats.

Use of a cDNA array for the identification of genes induced in islets of suckling rats by a high-carbohydrate nutritional intervention

Four-day-old rat pups that are raised artificially on a high-carbohydrate (HC) milk formula immediately develop hyperinsulinemia, which persists into adulthood without any further nutritional stimulus. cDNA array analysis was used to identify large-scale changes in gene expression patterns in islets from 12- and 100-day-old HC rats in response to the HC dietary modification during the suckling period. It was observed that the expression of several genes that belong to clusters involved in beta-cell development and/or beta-cell function was significantly upregulated in islets from 12- and 100-day-old HC rats. It is inferred that in addition to predicted changes in gene expression, for example preproinsulin gene, global changes in gene expression contribute to the hyperinsulinemic state in the HC rat.

Programming into adulthood of islet adaptations induced by early nutritional intervention in the rat

To investigate the influence of a high carbohydrate (HC) intake during the suckling period on pancreatic function in adult life, neonatal rats were artificially reared on a HC milk formula during the preweaning period and then weaned onto lab chow. In the adult HC rat, hyperinsulinemia is sustained by a variety of biochemical and molecular adaptations induced in the HC islets during the suckling period. The adult HC islets showed a distinct left shift in the glucose-stimulated insulin-secretory pattern. HC islets were also able to secrete moderate levels of insulin in the absence of glucose and in the presence of Ca(2+) channel inhibitors. In addition, the mRNA levels of preproinsulin, somatostatin transcription factor-1, upstream stimulatory factor-1, stress-activated protein kinase-2, phosphatidylinositol kinase, and GLUT-2 genes were significantly increased in HC islets. These results show that consumption of a HC formula during the suckling period programs pancreatic islet function in adult rats, resulting in the maintenance of hyperinsulinemia in the postweaning period and eventually leading to the development of obesity in adult life.