Pancreatic development and adult diabetes

Impact of prematurity for pancreatic islet and beta-cell development

As increasing numbers of babies born preterm survive into adulthood, it is becoming clear that, in addition to the well-described risks of neurodevelopmental sequelae, there also are increased risks for non-communicable diseases, including diabetes. Epidemiological studies indicate that risks are increased even for birth at late preterm and early term gestations and for both type 1 and type 2 diabetes. Thus, factors related to preterm birth likely affect development of the fetal and neonatal beta-cell in addition to effects on peripheral insulin sensitivity. These factors could operate prior to preterm birth and be related to the underlying cause of preterm birth, to the event of being born preterm itself, to the postnatal care of the preterm neonate or to a combination of these exposures. Experimental evidence indicates that factors may be operating during all these critical periods to contribute to altered development of beta-cell mass in those born preterm. Greater understanding of how these factors impact upon development of the pancreas may lead to interventions or management approaches that mitigate the increased risk of later diabetes.

Monitoring p53 by MDM2 and MDMX is required for endocrine pancreas development and function in a spatio-temporal manner

Although p53 is not essential for normal embryonic development, it plays a pivotal role in many biological and pathological processes, including cell fate determination-dependent and independent events and diseases. The expression and activity of p53 largely depend on its two biological inhibitors, MDM2 and MDMX, which have been shown to form a complex in order to tightly control p53 to an undetectable level during early stages of embryonic development. However, more delicate studies using conditional gene-modification mouse models show that MDM2 and MDMX may function separately or synergistically on p53 regulation during later stages of embryonic development and adulthood in a cell and tissue-specific manner. Here, we report the role of the MDM2/MDMX-p53 pathway in pancreatic islet morphogenesis and functional maintenance, using mouse lines with specific deletion of MDM2 or MDMX in pancreatic endocrine progenitor cells. Interestingly, deletion of MDM2 results in defects of embryonic endocrine pancreas development, followed by neonatal hyperglycemia and lethality, by inducing pancreatic progenitor cell apoptosis and inhibiting cell proliferation. However, unlike MDM2-knockout animals, mice lacking MDMX in endocrine progenitor cells develop normally. But, surprisingly, the survival rate of adult MDMX-knockout mice drastically declines compared to control mice, as blockage of neonatal development of endocrine pancreas by inhibition of cell proliferation and subsequent islet dysfunction and hyperglycemia eventually lead to type 1 diabetes-like disease with advanced diabetic nephropathy. As expected, both MDM2 and MDMX deletion-caused pancreatic defects are completely rescued by loss of p53, verifying the crucial role of the MDM2 and/or MDMX in regulating p53 in a spatio-temporal manner during the development, functional maintenance, and related disease progress of endocrine pancreas. Also, our study suggests a possible mouse model of advanced diabetic nephropathy, which is complementary to other established diabetic models and perhaps useful for the development of anti-diabetes therapies.

TSC1-mTOR signaling determines the differentiation of islet cells

Neurogenin3-driven deletion of tuberous sclerosis complex 1 (Tsc1) activated mechanistic target of rapamycin complex 1 (mTORC1) measured by the upregulation of mTOR and S6 phosphorylation in islet cells. Neurogenin3-Tsc1-/- mice demonstrated a significant increase in average islet size and mean area of individual islet cell. Insulin mRNA and plasma insulin levels increased significantly after weaning. Glucagon mRNA and plasma levels increased in neonate followed by modest reduction in adult. Somatostatin mRNA and plasma levels markedly increased. Neurogenin3-Tsc1-/- mice fed standard chow demonstrated a significant improvement in glucose tolerance and no alteration in insulin sensitivity. In Neurogenin3-Tsc1-/- mice fed 45% high-fat diets, both glucose tolerance and insulin sensitivity were significantly impaired. Rapamycin reversed the activation of mTORC1, attenuated β cells hypertrophy and abolished the improvement of glucose tolerance. TSC1-mTORC1 signaling plays an important role in the development of pancreatic endocrine cells and in the regulation of glucose metabolism.

Prenatal exposure to bisphenol A alters mouse fetal pancreatic morphology and islet composition

BACKGROUND

Exposure to bisphenol A (BPA), an endocrine disrupting chemical, during gestation is associated with a variety of metabolic dysfunctions in adulthood, including hyperinsulinemia, glucose intolerance and insulin resistance. These modifications in glucose homeostasis largely stem from alterations in pancreatic function. However, the effects of BPA on the fetal pancreas have never been explored. The present study addressed this important question by examining the effects of prenatal BPA exposure on the mouse fetal pancreatic development.

MATERIALS AND METHODS

Pregnant mice were fed a BPA diet (25 mg BPA/kg diet) from embryonic day 7.5 (E7.5) to E18.5. At E18.5, fetal pancreata were collected and analyzed for morphological changes in the endocrine pancreas such as islet size, number and β and α cell distribution.

RESULTS

We showed that BPA exposed fetal pancreata had a greater number of islet-cell clusters (ICCs; <300 μm(2); p<0.05) compared with controls. Furthermore, immunohistochemical analysis revealed that prenatal BPA exposure increased both glucagon expression in islets and the numbers of glucagon-expressing islet-cell clusters (p<0.05).

CONCLUSION

Considering that ICCs represent the initial stages of islet development in the fetal pancreas, our findings suggest that BPA promotes islet differentiation or delays the conversion of ICCs into mature islets. Moreover, the increase in glucagon expression suggests a potential alteration in the α:β-cell ratio in islets, which may have significant implications for the fetal pancreas both structurally and functionally. This study provides novel insight into the effects of BPA exposure on the fetal pancreata, indicating alterations in glucagon expression in islets and ICCs.

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.

Indices of Glucose Homeostasis in Cord Blood in Term and Preterm Newborns

OBJECTIVE

According to the thrifty phenotype hypothesis, intrauterine malnutrition has a role in the etiology of type 2 diabetes. This study was planned to determine the early alterations in indices of glucose homeostasis (glucose, insulin, and cortisol) in term and preterm newborns and the correlations of glucose, insulin, and cortisol levels with insulin resistance indices.

METHODS

A descriptive study comprising 35 term and 35 preterm newborns was carried out from December 2013 to June 2015. Venous cord blood was collected and plasma glucose was analyzed by the glucose oxidase-peroxidase method in an auto analyzer. Serum insulin and cortisol levels were assessed by the enzyme-linked immunosorbent assay. Homeostasis model assessment of insulin resistance (HOMA-IR), quantitative insulin sensitivity check index and glucose insulin ratio were calculated to assess insulin resistance. The data on physical and metabolic parameters were analyzed using standard tests for statistical significance.

RESULTS

In term newborns, mean glucose and cortisol levels (83.6±17.4 mg/dL and 11.88±5.78 µg/dL, respectively) were significantly higher than those in preterm infants (70.4±15.8 mg/dL and 8.9±4.6 µg/dL, respectively). Insulin and HOMA-IR levels were found higher in preterm newborns (10.8±4.8 µIU/mL and 1.52±0.66, respectively) than in term newborns (7.9±2.7 µIU/mL and 1.19±0.29, respectively). Insulin was found to positively correlate with HOMA-IR, whereas cortisol was negatively correlated with HOMA-IR in both term and preterm newborns.

CONCLUSION

Higher insulin levels and HOMA-IR values in the cord blood of preterm newborns support the theory of intrauterine origin of metabolic diseases.

Cord Blood Levels of Insulin, Cortisol and HOMA2-IR in Very Preterm, Late Preterm and Term Newborns

INTRODUCTION

Alteration in the glucose homeostasis is still the major cause of morbidity and mortality in the newborns. Intrauterine undernutrition plays an important role in causing adult insulin resistance and diabetes but the exact cause is still unknown.

AIM

To estimate the plasma glucose, serum insulin and cortisol levels at birth in newborns at different gestational age.

MATERIALS AND METHODS

The present cross-sectional study conducted from December 2014 to June 2015 included 58 newborns enrolled as per the inclusion criteria and further categorized into Group I (very preterm; n=19; gestational age < 32 weeks), Group II (late preterm; n=20; gestational age between 32-37 weeks) and Group III (full term; n=19; gestational age >37 weeks) newborns. Venous Cord Blood (VCB) was collected and plasma glucose was analysed by GOD-POD (Glucose Oxidase-Peroxidase) method in auto analyser whereas serum insulin and cortisol were analysed by ELISA (Enzyme Linked Immunosorbent Assay). HOMA2-IR (Homeostatic Model Assessment) calculator was used to assess insulin resistance. All parametric data was expressed as mean±SD and analysed using ANOVA with Tukey's as the Post-Hoc test. Correlation analysis was done using Pearson's correlation co-efficient with scatter plot as the graphical representation.

RESULTS

Significantly increased insulin and HOMA2-IR levels were found in group I (13.7±4.7μIU/mL and 1.6±0.58 respectively) when compared to group II (8.3±2.9μIU/mL and 0.93±0.2 respectively) and group III (8.3±2.1μIU/mL and 1.03±0.26 respectively). A positive correlation between cortisol levels and gestational age (r = 0.6, n = 58, p < 0.001) and a negative correlation between insulin and gestational age (r = -0.654, n = 58, p < 0.001) was observed in the study population.

CONCLUSION

Increased levels of insulin and HOMA2-IR as seen in the very preterm newborns signify the predisposition of these newborns to development of diabetes in later stages of life. The inverse association of cortisol and insulin with gestational age suggests that cortisol could also be responsible for impaired β cell function and insulin sensitivity.

The Role of Maternal Dietary Proteins in Development of Metabolic Syndrome in Offspring

The prevalence of metabolic syndrome and obesity has been increasing. Pre-natal environment has been suggested as a factor influencing the risk of metabolic syndrome in adulthood. Both observational and experimental studies showed that maternal diet is a major modifier of the development of regulatory systems in the offspring in utero and post-natally. Both protein content and source in maternal diet influence pre- and early post-natal development. High and low protein dams’ diets have detrimental effect on body weight, blood pressure191 and metabolic and intake regulatory systems in the offspring. Moreover, the role of the source of protein in a nutritionally adequate maternal diet in programming of food intake regulatory system, body weight, glucose metabolism and blood pressure in offspring is studied. However, underlying mechanisms are still elusive. The purpose of this review is to examine the current literature related to the role of proteins in maternal diets in development of characteristics of the metabolic syndrome in offspring.

Elevated glucocorticoids during ovine pregnancy increase appetite and produce glucose dysregulation and adiposity in their granddaughters in response to ad libitum feeding at 1 year of age

OBJECTIVE

Synthetic glucocorticoids (sGCs) are administered to women threatening preterm labor. We have shown multigenerational endocrine and metabolic effects of fetal sGC exposure. We hypothesized that sGC exposure would alter the second filial generation (F2) offspring neonatal leptin peak that controls development of appetitive behavior with metabolic consequences.

STUDY DESIGN

F0 nulliparous ewes were bred to a single ram. Beginning at day 103 of gestation (term 150 days), dexamethasone (DEX) ewes received 4 injections of 2 mg DEX intramuscularly, 12 hours apart. Control ewes received saline. Ewes lambed naturally. At 22 months of age, F1 offspring were mated to produce F2 offspring. At 10 months of age, F2 female offspring were placed on an ad libitum feeding challenge for 12 weeks.

RESULTS

DEX F2 female offspring did not show a postnatal leptin peak and their plasma cortisol concentration was elevated in the first days of life. During the feeding challenge, DEX F2 offspring consumed 10% more feed and gained 20% more weight compared with control F2 offspring. At the end of the feeding challenge, DEX F2 offspring had greater adiposity compared with control F2 offspring. F2 sGC offspring showed impaired insulin secretion in response to an intravenous glucose tolerance test.

CONCLUSION

sGC administration to F0 mothers eliminates the neonatal leptin peak in F2 female offspring potentially by inhibition caused by elevated cortisol in the DEX F2 offspring. F2 offspring showed increased appetite, weight gain, and adiposity during an ad libitum feeding challenge accompanied by decreased insulin response to an intravenous glucose tolerance test.

Cord-blood lipoproteins, homocysteine, insulin sensitivity/resistance marker profile, and concurrence of dysglycaemia and dyslipaemia in full-term neonates of the Mérida Study

Early alterations in glucose homeostasis increase the risk of developing insulin resistance and obesity later in life. The concurrence of altered lipids and insulin sensitivity/resistance markers at birth has been scarcely investigated. The study aimed to ascertain level ranges of homocysteine (tHcyt), arylesterase (AE), lipids/lipoproteins, and insulin resistance/sensitivity markers in full-term neonates and to determine the concurrence effect of dyslipaemia and dysglycaemia on those parameters at birth. Participants were 197 full-term, 2.5 to <4.0 kg, without foetal distress Spanish newborns from the Mérida Study. Parameter percentiles for males and females were stated. The effect of the concurrence high glucose/high triglycerides (high glucose/high TG) or high glucose/low cholesterol transported by HDL (HDL-c) on tHcyt, LDL-c, HDL-c, lipoprotein (a) (Lp(a)), oxidised LDL (oxLDL), AE, glucose, insulin sensitivity (QUICKI) and insulin resistance index (HOMA-IR) was studied. Females had higher total cholesterol (TC), HDL-c, Apo A1, Lp(a) and HDL-c/Apo A1, but lower relative transport of TC (%TC) by the very low lipoprotein fraction than males. No gender differences were found for glucose, HOMA-IR and QUICKI. Neonates at the 2.5- to 2.999-kg range display more adequate HOMA-IR and QUICKI levels that their >3.0 kg counterparts. The concurrence of high glucose/high TG or high glucose/low HDL-c increased TC/HDL-c and HOMA-IR, but decreased, oxLDL, oxLDL/LDL-c and QUICKI with respect to that of low glucose/low TG or glucose/high HDL-c. The concurrence glucose/TG has predictive value for low QUICKI, whilst that of glucose/HDL-c for low QUICKI and high HOMA-IR, suggesting the importance of routine TG, HDL-c and glucose screening at birth as it would identify candidates for insulin resistance.

Perinatal bisphenol A exposure and adult glucose homeostasis: identifying critical windows of exposure

Bisphenol A (BPA) is a widespread endocrine-disrupting chemical used as the building block for polycarbonate plastics. Epidemiological evidence has correlated BPA exposure with higher risk of heart disease and type 2 diabetes. However, it remains unknown whether there are critical windows of susceptibility to BPA exposure on the development of dysglycemia. This study was an attempt to investigate the critical windows and the long-term consequences of perinatal exposure to BPA on glucose homeostasis. Pregnant mice were given either vehicle or BPA (100 µg/kg/day) at different time of perinatal stage: 1) on days 1–6 of pregnancy (P1–P6, preimplantation exposure); 2) from day 6 of pregnancy until postnatal day (PND) 0 (P6–PND0, fetal exposure); 3) from lactation until weaning (PND0–PND21, neonatal exposure); and 4) from day 6 of gestation until weaning (P6–PND21, fetal and neonatal exposure). At 3, 6 and 8 months of age, offspring in each group were challenged with glucose and insulin tolerance tests. Then islet morphometry and β-cell function were measured. The glucose homeostasis was impaired in P6-PND0 mice from 3 to 6 months of age, and this continued to 8 months in males, but not females. While in PND0-PND21 and P6-PND21 BPA-treated groups, only the 3-month-old male offspring developed glucose intolerance. Moreover, at the age of 3 months, perinatal exposure to BPA resulted in the increase of β-cell mass mainly due to the coordinate changes in cell replication, neogenesis, and apoptosis. The alterations of insulin secretion and insulin sensitivity, rather than β-cell mass, were consistent with the development of glucose intolerance. Our findings suggest that BPA may contribute to metabolic disorders relevant to glucose homeostasis and the effects of BPA were dose, sex, and time-dependent. Fetal development stage may be the critical window of susceptibility to BPA exposure.

Growth and insulin dynamics in two generations of female offspring of mothers receiving a single course of synthetic glucocorticoids

OBJECTIVE

Synthetic glucocorticoid administration to women threatening preterm delivery increases neonatal survival. However, mounting evidence shows that fetal exposure to glucocorticoid levels higher than appropriate for current maturation adversely programs offspring development. We examined fetal synthetic glucocorticoid multigenerational metabolic effects on F1 and F2 female offspring.

STUDY DESIGN

At 0.7 gestation, pregnant F0 ewes received 4 injections of dexamethasone (2 mg, approximately 60 ug.kg(-1) day(-1) 12 hours apart) or saline (control). F1 female offspring were bred to produce F2 female offspring. Postpubertal pancreatic β-cell function was tested in F1 and F2 by intravenous glucose tolerance test.

RESULTS

F1 and F2 ewe lambs showed reduced birthweight and morphometrics, and similar increased fasting glucose and decreased intravenous glucose tolerance test β-cell response.

CONCLUSION

This is the first demonstration of multigenerational programming of later life β-cell response by clinically relevant doses of synthetic glucocorticoid indicating the need for study of long-term effects of fetal exposure to synthetic glucocorticoid.

Nutrition, epigenetics, and metabolic syndrome

SIGNIFICANCE

Epidemiological and animal studies have demonstrated a close link between maternal nutrition and chronic metabolic disease in children and adults. Compelling experimental results also indicate that adverse effects of intrauterine growth restriction on offspring can be carried forward to subsequent generations through covalent modifications of DNA and core histones.

RECENT ADVANCES

DNA methylation is catalyzed by S-adenosylmethionine-dependent DNA methyltransferases. Methylation, demethylation, acetylation, and deacetylation of histone proteins are performed by histone methyltransferase, histone demethylase, histone acetyltransferase, and histone deacetyltransferase, respectively. Histone activities are also influenced by phosphorylation, ubiquitination, ADP-ribosylation, sumoylation, and glycosylation. Metabolism of amino acids (glycine, histidine, methionine, and serine) and vitamins (B6, B12, and folate) plays a key role in provision of methyl donors for DNA and protein methylation.

CRITICAL ISSUES

Disruption of epigenetic mechanisms can result in oxidative stress, obesity, insulin resistance, diabetes, and vascular dysfunction in animals and humans. Despite a recognized role for epigenetics in fetal programming of metabolic syndrome, research on therapies is still in its infancy. Possible interventions include: 1) inhibition of DNA methylation, histone deacetylation, and microRNA expression; 2) targeting epigenetically disturbed metabolic pathways; and 3) dietary supplementation with functional amino acids, vitamins, and phytochemicals.

FUTURE DIRECTIONS

Much work is needed with animal models to understand the basic mechanisms responsible for the roles of specific nutrients in fetal and neonatal programming. Such new knowledge is crucial to design effective therapeutic strategies for preventing and treating metabolic abnormalities in offspring born to mothers with a previous experience of malnutrition.

Maternal adaptations and inheritance in the transgenerational programming of adult disease

Adverse exposures in utero have long been linked with an increased susceptibility to adult cardio-renal and metabolic diseases. Clear gender differences exist, whereby growth-restricted females, although exhibiting some phenotypic modifications, are often protected from overt disease outcomes. One of the greatest physiological challenges facing the female gender, however, is that of pregnancy; yet little research has focused on the outcomes associated with this, as a potential 'second-hit' for those who were small at birth. We review the limited evidence suggesting that pregnancy may unmask cardio-renal and metabolic disease states and the consequences for long-term maternal health in females who were born small. Additionally, a growing area of research in this programming field is in the transgenerational transmission of low birth weight and disease susceptibility. Pathways for transmission might include an abnormal adaptation to pregnancy by the growth-restricted mother and/or inheritance via the parental germline. Strategies to optimise the pregnancy environment and/or prevent the consequences of inheritance of programmed deficits and dysfunction are of critical importance for future generations.

Fetal programming and metabolic syndrome

Metabolic syndrome is reaching epidemic proportions, particularly in developing countries. In this review, we explore the concept-based on the developmental-origin-of-health-and-disease hypothesis-that reprogramming during critical times of fetal life can lead to metabolic syndrome in adulthood. Specifically, we summarize the epidemiological evidence linking prenatal stress, manifested by low birth weight, to metabolic syndrome and its individual components. We also review animal studies that suggest potential mechanisms for the long-term effects of fetal reprogramming, including the cellular response to stress and both organ- and hormone-specific alterations induced by stress. Although metabolic syndrome in adulthood is undoubtedly caused by multiple factors, including modifiable behavior, fetal life may provide a critical window in which individuals are predisposed to metabolic syndrome later in life.

Corticosteroid-mediated programming and the pathogenesis of obesity and diabetes

Epidemiological studies have shown that low birthweight is associated with increased risk of development of diabetes and obesity in later life. Over-exposure of the developing fetus to glucocorticoids is one of the major hypotheses that has been proposed to explain this association. In animal models, a range of manipulations that increase fetal glucocorticoid load, 'programme' permanent changes in glucose and insulin metabolism and adiposity. This may be mediated by alterations in regulation of the hypothalamic-pituitary-adrenal (HPA) axis. In humans, low birthweight is associated with increased circulating glucocorticoid levels, and an increased cortisol response to physiological and psychosocial stressors, in child- and adulthood. This activation of the HPA axis is also associated with increased risk of development of diabetes and obesity in later life.

Fetal origins of adult diabetes

According to the fetal origin of adult diseases hypothesis, the intrauterine environment through developmental plasticity may permanently influence long-term health and disease. Therefore, intrauterine growth restriction (IUGR), due either to maternal, placental, or genetic factors, may permanently alter the endocrine-metabolic status of the fetus, driving an insulin resistance state that can promote survival at the short term but that facilitates the development of type 2 diabetes mellitus and metabolic syndrome in adult life, especially when the intrauterine nutrient restriction is followed by a postnatal obesogenic environment. Furthermore, an energy-rich environment during fetal programming may also drive the development of excess abdominal fat and type 2 diabetes in later life, demonstrating that both intrauterine nutrient restriction as well as intrauterine nutrient excessive supply may predispose for the development of adult diabetes.

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.

Genetic variant in the IGF2BP2 gene may interact with fetal malnutrition to affect glucose metabolism

OBJECTIVE

Fetal malnutrition may predispose to type 2 diabetes through gene programming and developmental changes. Previous studies showed that these effects may be modulated by genetic variation. Genome-wide association studies discovered and replicated a number of type 2 diabetes-associated genes. We investigated the effects of such well-studied polymorphisms and their interactions with fetal malnutrition on type 2 diabetes risk and related phenotypes in the Dutch Famine Birth Cohort.

RESEARCH DESIGN AND METHODS

The rs7754840 (CDKAL1), rs10811661 (CDKN2AB), rs1111875 (HHEX), rs4402960 (IGF2BP2), rs5219 (KCNJ11), rs13266634 (SLC30A8), and rs7903146 (TCF7L2) polymorphisms were genotyped in 772 participants of the Dutch Famine Birth Cohort Study (n = 328 exposed, n = 444 unexposed). Logistic and linear regression models served to analyze their interactions with prenatal exposure to famine on type 2 diabetes, impaired glucose tolerance (IGT), and area under the curves (AUCs) for glucose and insulin during oral glucose tolerance testing (OGTT).

RESULTS

In the total population, the TCF7L2 and IGF2BP2 variants most strongly associated with increased risk for type 2 diabetes/IGT and increased AUC for glucose, while the CDKAL1 polymorphism associated with decreased AUC for insulin. The IGF2BP2 polymorphism showed an interaction with prenatal exposure to famine on AUC for glucose (beta = -9.2 [95% CI -16.2 to -2.1], P = 0.009).

CONCLUSIONS

The IGF2BP2 variant showed a nominal interaction with exposure to famine in utero, decreasing OGTT AUCs for glucose. This may provide a clue that modulation of the consequences of fetal environment depends on an individual's genetic background.

Maternal nutrition, intrauterine programming and consequential risks in the offspring

It is traditionally believed that genetic susceptibility and adult faulty lifestyle lead to type 2 diabetes, a chronic non-communicable disease. The "Developmental Origins of Health and Disease" (DOHaD) model proposes that the susceptibility to type 2 diabetes originates in the intrauterine life by environmental fetal programming, further exaggerated by rapid childhood growth, i.e. a biphasic nutritional insult. Both fetal under nutrition (sometimes manifested as low birth weight) and over nutrition (the baby of a diabetic mother) increase the risk of future diabetes. The common characteristic of these two types of babies is their high adiposity. An imbalance in nutrition seems to play an important role, and micronutrients seem particularly important. Normal to high maternal folate status coupled with low vitamin B(12) status predicted higher adiposity and insulin resistance in Indian babies. Thus, 1-C (methyl) metabolism seems to play a key role in fetal programming. DOHaD represents a paradigm shift in the model for prevention of the chronic non-communicable diseases.

Characterization of Munc13-1 and insulin secretion during pancreatic development in rats

Munc13-1 may be a key factor in regulating insulin exocytosis, but its exact expression and role have not been clarified yet, especially during pancreatic development. We attempted to investigate the expression and function of Munc13-1 during embryonic pancreatic development in rats and determine the effects on insulin secretion. In the present study, pancreata of rats at embryonic day 12.5 (E12.5), E15.5, E18.5, new-born, 21 after birth (P21), and adult stage were dissected under microscope. The rat model of intrauterine growth retardation (IUGR) was made by 50% calorie restriction in pregnant rats from gestational day 15 until term. The expression of Munc13-1 and insulin secretion was studied by the techniques of RTPCR, real-time PCR, Western blot, and enzyme-linked immunosorbent assay. Immunohistochemistry and immunofluorescence were used to define the location of Munc13- 1. We found that Munc13-1 was located at islet along with insulin. Insulin- and Munc13-1-specific mRNA were not detected until E12.5 and E15.5, respectively, and increased with the development of the fetus. Western blot showed that Munc13-1 was low at E15.5 and E18.5 and increased later. The blood insulin level and Munc13-1 were reduced simultaneously in IUGR newborn rats compared with normal ones. These results suggest that Munc13-1 exists in pancreas islets during fetus development and its deficiency in the pancreas, as occurs in IUGR, was in accordance with decreased blood insulin level. Munc13-1 may play an essential role in insulin exocytosis.

Prenatal origins of adult disease

PURPOSE OF REVIEW

Human epidemiological and animal studies show that many chronic adult conditions have their antecedents in compromised fetal and early postnatal development. Developmental programming is defined as the response by the developing mammalian organism to a specific challenge during a critical time window that alters the trajectory of development with resulting persistent effects on phenotype. Mammals pass more biological milestones before birth than any other time in their lives. Each individual's phenotype is influenced by the developmental environment as much as their genes. A better understanding is required of gene-environment interactions leading to adult disease.

RECENT FINDINGS

During development, there are critical periods of vulnerability to suboptimal conditions when programming may permanently modify disease susceptibility. Programming involves structural changes in important organs; altered cell number, imbalance in distribution of different cell types within the organ, and altered blood supply or receptor numbers. Compensatory efforts by the fetus may carry a price. Effects of programming may pass across generations by mechanisms that do not necessarily involve structural gene changes. Programming often has different effects in males and females.

SUMMARY

Developmental programming shows that epigenetic factors play major roles in development of phenotype and predisposition to disease in later life.

Improved lactational nutrition and postnatal growth ameliorates impairment of glucose tolerance by uteroplacental insufficiency in male rat offspring

Intrauterine growth restriction and accelerated postnatal growth predict increased risk of diabetes. Uteroplacental insufficiency in the rat restricts fetal growth but also impairs mammary development and postnatal growth. We used cross fostering to compare the influence of prenatal and postnatal nutritional restraint on adult glucose tolerance, insulin secretion, insulin sensitivity, and hypothalamic neuropeptide Y content in Wistar Kyoto rats at 6 months of age. Bilateral uterine vessel ligation (restricted) to induce uteroplacental insufficiency or sham surgery (control) was performed on d-18 gestation. Control, restricted, and reduced (reducing litter size of controls to match restricted) pups were cross fostered onto a control or restricted mother 1 d after birth. Restricted pups were born small compared with controls. Restricted males, but not females, remained lighter up to 6 months, regardless of postnatal environment. By 10 wk, restricted-on-restricted males ate more than controls. At 6 months restricted-on-restricted males had increased hypothalamic neuropeptide Y content compared with other groups, and together with reduced-on-restricted males had increased retroperitoneal fat weight (percent body weight) compared with control-on-controls. Restricted-on-restricted males had impaired glucose tolerance, reduced first-phase insulin secretion, but unaltered insulin sensitivity, compared with control-on-controls. In males, being born small and exposed to an impaired lactational environment adversely affects adult glucose tolerance and first-phase insulin secretion, but improving lactation partially ameliorates this condition. This study identifies early life as a target for intervention to prevent later diabetes after prenatal restraint.

Insulin and carbohydrate metabolism

Fetal glucose exposure and consequent fetal insulin secretion is normally tightly regulated by glucose delivery from the mother during pregnancy. Maternal hyperglycaemia and gestational diabetes (GDM) are known to be detrimental to offspring, although defining the criteria for diagnosis of GDM is controversial. Recent data suggest that the risk of poor fetal outcome appears to be a continuous variable across the range of glucose control, and that the level of maternal blood glucose for a diagnosis of gestational diabetes needs to be reviewed. After birth, rapid adaptation is necessary for infants to be able to maintain independent glucose homeostasis. This adaptation is compromised in infants who are small for gestational age (SGA), premature, or large for gestational age (LGA). Interestingly, the infants who are born at the extremes of birth weight are also at increased risk of impaired glucose tolerance and diabetes in later life.

Mechanisms underlying the role of glucocorticoids in the early life programming of adult disease

Compelling epidemiological evidence suggests that exposure to an adverse intrauterine environment, manifested by low-birth weight, is associated with cardiometabolic and behavioural disorders in adulthood. These observations have led to the concept of ‘fetal programming’. The molecular mechanisms that underlie this relationship remain unclear, but are being extensively investigated using a number of experimental models. One major hypothesis for early life physiological programming implicates fetal overexposure to stress (glucocorticoid) hormones. Several animal studies have shown that prenatal glucocorticoid excess, either from endogenous overproduction with maternal stress or through exogenous administration to the mother or fetus, reduces birth weight and causes lifelong hypertension, hyperglycaemia and behavioural abnormality in the offspring. Intriguingly, these effects are transmitted across generations without further exposure to glucocorticoids, which suggests an epigenetic mechanism. These animal observations could have huge implications if extrapolated to humans, where glucocorticoids have extensive therapeutic use in obstetric and neonatal practice.

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.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Transcription factors, pancreatic development, and β-cell maintenance

Transcription factors play an important role during pancreatic development ensuring normal differentiation of the islet endocrine cells. In mature beta-cells, expression of specific transcription factors is essential in maintaining normal beta-cell function.

Life-long echoes--a critical analysis of the developmental origins of adult disease model

The hypothesis that there is a developmental component to subsequent adult disease initially arose from epidemiological findings relating birth size to either indices of disease risk or actual disease prevalence in later life. While components of the epidemiological analyses have been challenged, there is strong evidence that developmental factors contribute to the later risk of metabolic disease--including insulin resistance, obesity, and heart disease--as well as have a broader impact on osteoporosis, depression and schizophrenia. We suggest that disease risk is greater when there is a mismatch between the early developmental environment (i.e., the phase of developmental plasticity) versus that experienced in mature life (i.e., adulthood), and that nutritional influences are particularly important. It is also critical to distinguish between those factors acting during the developmental phase that disrupt development from those influences that are less extreme and act through regulated processes of epigenetic change. A model of the relationship between the developmental and mature environment is proposed and suggests interventional strategies that will vary in different population settings.

The developmental origins of the metabolic syndrome

Both epidemiological and clinical evidence suggest relationships between the antenatal environment and the risk of developing insulin resistance and associated cardiovascular disease (part of the metabolic syndrome) in middle age. However, interpretation of these findings has been controversial. Recent experimental observations provide considerable evidence for a causal model linking adaptive responses to early environmental cues and the later risk of disease. Evolutionary and life history theory provide possible explanations of why these phenomena have persisted and how they might cause disease. In this article, we review the clinical and experimental perspectives on the "developmental origins of disease" model in the context of these new concepts.

Expression in murine teratocarcinoma f9 cells of transcription factors involved in pancreas development

BACKGROUND

Although it has been established that formation and functional differentiation of the pancreas from embryonic endoderm is associated with activation/inactivation of many genes controlled by specific sets of transcription factors, the role and activation sequence of individual transcription factors has not yet been fully elucidated. This study sought to differentiate a murine teratocarcinoma cell line, F9, to endodermal-like cells and, subsequently; to investigate the effects of regulated expression of transcription factors in pancreas development.

METHODS

Following differentiation using retinoic acid and db cAMP (RAC), resulting F9 cells (F9-RAC) were transfected with cDNAs for PDX-1, ngn3, beta 2/NeuroD (beta 2), and Nkx2.2, singly or in combination. Expression of these transcription factors was investigated using RT-PCR and immunofluorescence techniques. RT-PCR analysis was used to assess the subsequent effects of expression of these factors on endogenous genes related to pancreas development.

RESULTS

Regulated differentiation of F9 cells generated endodermal-like cell types. Following transfection, PDX-1, ngn3, beta 2, and Nkx2.2 were expressed in F9-RAC cells, with their proteins localized mainly in cellular nuclei. Expression of these factors apparently did not affect the endogenous expression of preproinsulin, PDX-1, beta 2, Isl1, Pax4, Pax6, Sonic hedgehog, and Indian hedgehog.

CONCLUSION

This study describes the successful transient expression of transcription factors related to pancreas development, following directed differentiation of F9 cells to endoderm-like cells, and shows that treatment of F9 cells with a combination of RAC causes up-regulation of genes relevant to pancreatic development. The lack of further effect of regulated transcription factor expression on these genes may suggest that parietal endoderm- like cells derived from F9 cells is not the optimal lineage from which to develop beta cells. It may be useful to include F9-derived visceral endoderm in future studies.

Independent and opposite associations of waist and hip circumferences with diabetes, hypertension and dyslipidemia: the AusDiab Study

OBJECTIVE

Fat distribution as measured by waist-to-hip ratio has been shown to be an important independent predictor of glucose intolerance. Few studies, however, have considered the contributions of the waist and hip circumferences independently. The aim of this study was to investigate the independent associations of waist and hip circumference with diabetes in a large population-based study, and to investigate whether they also apply to other major components of the metabolic syndrome (hypertension and dyslipidemia). In addition, as previous studies were performed in older persons, we investigated whether these associations were present across adult age groups.

METHODS

Weight, height, waist and hip circumferences were measured in 11 247 participants of the nationally representative Australian Diabetes, Obesity and Lifestyle (AusDiab) Study. HDL-cholesterol, triglycerides, fasting and 2-h postload glucose were determined, and diastolic and systolic blood pressure was measured. After exclusion of persons already known to have diabetes, hypertension or dyslipidemia, logistic and linear regression were used to study cross-sectional associations of anthropometric variables with newly diagnosed diabetes, hypertension and dyslipidemia, and with continuous metabolic measures, all separately for men (n=3818) and women (n=4582). Analyses were repeated in the same population stratified for age.

RESULTS

After adjustment for age, body mass index and waist, a larger hip circumference was associated with a lower prevalence of undiagnosed diabetes (odds ratio (OR) per one s.d. increase in hip circumference 0.55 (95% CI 0.41-0.73) in men and 0.42 (0.27-0.65) in women) and undiagnosed dyslipidemia (OR 0.58 (0.50-0.67) in men and 0.37 (0.30-0.45) in women). Associations with undiagnosed hypertension were weaker (OR 0.80 (0.69-0.93) in men and 0.88 (0.70-1.11) in women). As expected, larger waist circumference was associated with higher prevalence of these conditions. Similar associations were found using continuous metabolic variables as outcomes in linear regression analyses. Height partly explained the negative associations with hip circumference. When these analyses were performed stratified for age, associations became weaker or disappeared in the oldest age groups (age > or =75 y in particular), except for HDL-cholesterol.

CONCLUSION

We found independent and opposite associations of waist and hip circumference with diabetes, dyslipidemia and less strongly with hypertension in a large population-based survey. These results emphasize that waist and hip circumference are important predictors for the metabolic syndrome and should both be considered in epidemiological studies. The associations were consistent in all age groups, except in age > or =75 y. Further research should be aimed at verifying hypotheses explaining the 'protective' effect of larger hips.

Insulin secretion and GLUT-2 expression in undernourished neonate rats

In previous studies, we verified increased insulin sensitivity in adult male offspring of lactating rats readjusting to lack of insulin secretion reduction brought about by protein restriction during lactation. The present study aims to evaluate the effects of maternal protein undernutrition during lactation on glucose-induced insulin secretion and GLUT-2 expression in beta-cells of neonate male and female rats. Lactating Wistar rats were given a protein-free diet during the first 10 days and a normal diet (22% of protein) until weaning. The neonates were separated at birth by sex and diet and studied at 4, 8 and 21 days of lactation. Glucose-induced insulin secretion by pancreatic islets was analyzed by radioimmunoassay and GLUT-2 expression in beta-cells by Western blot. Glucose-induced insulin secretion of the undernourished groups was higher than in the control groups except among females. When comparing the male and female groups and the control and undernourished groups, female neonates showed significantly greater insulin secretion than the male group. Also it was noted that undernutrition induced greater GLUT-2 expression. For instance, comparing the undernourished male and female neonates there was an increase in female GLUT-2 expression on day 4. On the other hand, in undernourished male neonates a GLUT-2 expression increased later in lactation. In conclusion, during a short term, maternal undernutrition induces an increase of the glucose-induced insulin secretion only in male neonates and is associated with an increase in GLUT-2 expression in the beta-cell.

Pathways of infant and childhood growth that lead to type 2 diabetes

OBJECTIVE

Although a link between small body size at birth and later type 2 diabetes has been repeatedly documented, less is known about the associations between the disease and growth during infancy. The aim of this study was to explore the pathways of infant and early growth that lead to type 2 diabetes in adult life.

RESEARCH DESIGN AND METHODS

We carried out a longitudinal study of 8760 subjects born in Helsinki from 1934 to 1944. On average, they had 8 measurements of height and weight between birth and 1 year of age and another 10 measurements between 1 and 12 years of age. We identified people with type 2 diabetes using a national register.

RESULTS

Among babies whose birth weights were <or=3.5 kg, the rate of infant growth was unrelated to later type 2 diabetes. Among babies with birth weights >3.5 kg, slow growth in length between birth and 3 months of age predicted later disease. Rapid gain in BMI after age 2 years increased the risk of later disease in both groups of babies, but this effect was greatest among children who had slow growth in length between birth and 3 months of age. In children whose Z-scores for length decreased, an SD increase in BMI at age 12 years was associated with an odds ratio (OR) for type 2 diabetes of 1.77 (95% CI 1.50-2.09). The corresponding OR in subjects whose Z-scores for length increased was 1.42 (95% CI 1.20-1.69). Rapid gain in childhood BMI was associated with high maternal BMI and socioeconomic factors (fewer people in the home and lower social class).

CONCLUSIONS

Babies with above-average birth weights may develop type 2 diabetes later in life if poor living conditions lead to faltering growth in length in the first few months after birth. We speculate that growth faltering at this time is associated with lifelong impairment of insulin metabolism and inability to meet the challenge of rapid childhood increase in BMI.

Endocrine-Related Causes and Consequences of Intrauterine Growth Retardation

The term intrauterine growth retardation (IUGR) is assigned to newborns born with a birth weight and/or birth length below the tenth percentile for their gestational age. Intrauterine growth retardation is usually due to maternal, fetal factors, or placental insufficiency, while endocrine factors represent just a small minority in its etiology. Main endocrine-related causes of IUGR are disorders in insulin or insulin-like growth factor-I (IGF-I) secretion or action. Newborns with IUGR are at increased risk to develop a metabolic syndrome later in life, namely obesity, arterial hypertension, hypercholesterolemia, cardiovascular disease, impaired glucose tolerance, or diabetes mellitus type 2. This association is the result of the adaptational changes of the fetal endocrine-metabolic mechanisms to the impaired intrauterine milieu to assure survival in the short term. The persistence of these changes after birth can be detrimental in adult life. Furthermore, premature adrenarche, as well as ovarian hyperandrogenism, seem to be associated with IUGR in girls, demonstrating that IUGR may have long-lasting effects on both somatic health and reproductive function. Finally, the intrauterine exposure of the fetus to stressors may affect the individual's ability to face stress in postnatal life. Therefore, if optimization of somatic and psychosocial well-being of the individual is the golden goal of medicine, special attention should be paid to maintain an optimal intrauterine milieu devoid of any stressors with adequate nutrient supply and to reserve ideal psychosocial support to the pregnant woman.

Genes expressed in the developing endocrine pancreas and their importance for stem cell and diabetes research

The genes that regulate endocrine pancreas development, maintain adult endocrine cells, and stimulate progenitor/stem cells during regeneration remain largely unstudied. There is ample evidence that many of the genes involved in endocrine pancreas development also function in the homeostasis of the adult islet. In light of the potential benefits to diabetic research, it is surprising that there is little information about the genes expressed throughout the ontogeny of the endocrine pancreas. In the past few years, efforts have been made to establish the Endocrine Pancreas Consortium database (EPConDB), in which many of the genes expressed in the developing endocrine pancreas are in a database with a corresponding publicly available clone bank. In addition, advances in microarray technology now allow for a quantitative expression analysis of thousands of genes simultaneously, which makes it possible to generate a quantitative catalog of the genes expressed at each step of endocrine differentiation, from embryonic endoderm to mature beta cells. In this review, I will discuss how genes discovered by virtue of their role in endocrine pancreas development may function in the maintenance of pancreatic stem cells and the regeneration of islets. I will further summarize the recent advances in genomics-based studies of the developing endocrine pancreas and will discuss how they might impact on the discovery of diagnostics and research into stem cell-based approaches for the treatment of diabetes.

Lessons for human diabetes from experimental mouse models

A precise knowledge of the defects underlying type 1 and type 2 diabetes is essential for designing appropriate therapeutic strategies. Because experiments in humans are limited, naturally occurring, and especially genetically engineered rodent models, have revolutionized research in diabetes. We review some of the models created recently and discuss their impact on human diabetes.

Larger thigh and hip circumferences are associated with better glucose tolerance: the Hoorn study

OBJECTIVE

A higher waist-to-hip ratio, which can be due to a higher waist circumference, a lower hip circumference, or both, is associated with higher glucose levels and incident diabetes. A lower hip circumference could reflect either lower fat mass or lower muscle mass. Muscle mass might be better reflected by thigh circumference. The aim of this study was to investigate the contributions of thigh and hip circumferences, independent of waist circumference, to measures of glucose metabolism.

RESEARCH METHODS AND PROCEDURES

For this cross-sectional study we used baseline data from the Hoorn Study, a population-based cohort study of glucose tolerance among 2484 men and women aged 50 to 75. Glucose tolerance was assessed by a 75-g oral glucose tolerance test; hemoglobin A(1c) and fasting insulin were also measured. Anthropometric measurements included body mass index (BMI) and waist, hip, and thigh circumferences.

RESULTS

Stratified analyses and multiple linear regression showed that after adjustment for age, BMI, and waist circumference, thigh circumference was negatively associated with markers of glucose metabolism in women, but not in men. Standardized beta values in women were -0.164 for fasting, -0.206 for post-load glucose, -0.190 for hemoglobin A(1c) (all p < 0.001), and -0.065 for natural log insulin levels (p = 0.061). Hip circumference was negatively associated with markers of glucose metabolism in both sexes (standardized betas ranging from -0.093 to -0.296, p < 0.05) except for insulin in men. Waist circumference was positively associated with glucose metabolism.

DISCUSSION

Thigh circumference in women and hip circumference in both sexes are negatively associated with markers of glucose metabolism independently of the waist circumference, BMI, and age. Both fat and muscle tissues may contribute to these associations.