Paul D. Taylor

Diet-Induced Obesity in Female Mice Leads to Offspring Hyperphagia, Adiposity, Hypertension, and Insulin Resistance A Novel Murine Model of Developmental Programming

Maternal obesity is increasingly prevalent and may affect the long-term health of the child. We investigated the effects of maternal diet-induced obesity in mice on offspring metabolic and cardiovascular function. Female C57BL/6J mice were fed either a standard chow (3% fat, 7% sugar) or a palatable obesogenic diet (16% fat, 33% sugar) for 6 weeks before mating and throughout pregnancy and lactation. Offspring of control (OC) and obese dams (OO) were weaned onto standard chow and studied at 3 and 6 months of age. OO were hyperphagic from 4 to 6 weeks of age compared with OC and at 3 months locomotor activity was reduced and adiposity increased (abdominal fat pad mass; P<0.01). OO were heavier than OC at 6 months (body weight, P<0.05). OO abdominal obesity was associated with adipocyte hypertrophy and altered mRNA expression of &bgr;-adrenoceptor 2 and 3, 11&bgr;HSD-1, and PPAR-&ggr; 2. OO showed resistance artery endothelial dysfunction at 3 months, and were hypertensive, as assessed by radiotelemetry (nighttime systolic blood pressure at 6 months [mm Hg] mean±SEM, male OO, 134±1 versus OC, 124±2, n=8, P<0.05; female OO, 137±2 versus OC, 122±4, n=8, P<0.01). OO skeletal muscle mass (tibialis anterior) was significantly reduced (P<0.01) OO fasting insulin was raised at 3 months and by 6 months fasting plasma glucose was elevated. Exposure to the influences of maternal obesity in the developing mouse led to adult offspring adiposity and cardiovascular and metabolic dysfunction. Developmentally programmed hyperphagia, physical inactivity, and altered adipocyte metabolism may play a mechanistic role.

Developmental programming of the metabolic syndrome by maternal nutritional imbalance: how strong is the evidence from experimental models in mammals?

The incidence of the metabolic syndrome, a cluster of abnormalities focusing on insulin resistance and associated with high risk for cardiovascular disease and diabetes, is reaching epidemic proportions. Prevalent in both developed and developing countries, the metabolic syndrome has largely been attributed to altered dietary and lifestyle factors that favour the development of central obesity. However, population‐based studies have suggested that predisposition to the metabolic syndrome may be acquired very early in development through inappropriate fetal or neonatal nutrition. Further evidence for developmental programming of the metabolic syndrome has now been suggested by animal studies in which the fetal environment has been manipulated through altered maternal dietary intake or modification of uterine artery blood flow. This review examines these studies and assesses whether the metabolic syndrome can be reliably induced by the interventions made. The validity of the different species, diets, feeding regimes and end‐point measures used is also discussed.

Developmental programming of obesity in mammals

Converging lines of evidence from epidemiological studies and animal models now indicate that the origins of obesity and related metabolic disorders lie not only in the interaction between genes and traditional adult risk factors, such as unbalanced diet and physical inactivity, but also in the interplay between genes and the embryonic, fetal and early postnatal environment. Whilst studies in man initially focused on the relationship between low birth weight and risk of adult obesity and metabolic syndrome, evidence is also growing to suggest that increased birth weight and/or adiposity at birth can also lead to increased risk for childhood and adult obesity. Hence, there appears to be increased risk of obesity at both ends of the birth weight spectrum. Animal models, including both under‐ and overnutrition in pregnancy and lactation lend increasing support to the developmental origins of obesity. This review focuses upon the influence of the maternal nutritional and hormonal environment in pregnancy in permanently programming appetite and energy expenditure and the hormonal, neuronal and autocrine mechanisms that contribute to the maintenance of energy balance in the offspring. We discuss the potential maternal programming ‘vectors’ and the molecular mechanisms that may lead to persistent pathophysiological changes resulting in subsequent disease. The perinatal environment, which appears to programme subsequent obesity, provides a potential therapeutic target, and work in this field will readily translate into improved interventional strategies to stem the growing epidemic of obesity, a disease which, once manifest, has proven particularly resistant to treatment.

Experimental models of developmental programming: consequences of exposure to an energy rich diet during development

Studies in both humans and experimental animals addressing the ‘Fetal Origins of Adult Disease’ hypothesis have established a relationship between an adverse intrauterine environment and offspring disease in adult life. This phenomenon, termed ‘fetal programming’ describes a process whereby a stimulus in utero establishes a permanent response in the fetus leading to enhanced susceptibility to later disease. However, the environment, during periods of developmental plasticity in postnatal life, can also ‘programme’ function. Thus, the terms ‘developmental programming’ and the ‘Developmental Origins of Adult Health and Disease’ are preferentially utilized. The ‘Thrifty Phenotype’ hypothesis explained the association between insufficient in utero nutrition and the later development of Type 2 diabetes. Most recently the ‘Predictive Adaptive Response’ hypothesis proposes that the degree of mismatch between the pre‐ and postnatal environments is an important determinant of subsequent disease. Epidemiological studies have indicated that fetal growth restriction correlates with later disease, implying that fetal nutritional deprivation is a strong programming stimulus. This prompted the development of experimental animal models using controlled maternal calorie, protein or macronutrient deficiency during key periods of gestation. However, in many societies, maternal and postnatal nutrition are either sufficient or excessive. Here, we examine findings from a range of nutritional studies examining maternal and/or postnatal nutritional excess. There is supportive evidence from a limited number of studies to test the ‘Predictive Adaptive Response’ hypothesis. These suggest that maternal over‐nutrition is deleterious to the health of offspring and can result in a phenotype of the offspring that is characteristic of metabolic syndrome.

Gender-Linked Hypertension in Offspring of Lard-Fed Pregnant Rats

Abstract—Epidemiological studies suggest an association between maternal nutrition and offspring cardiovascular disease. We previously demonstrated endothelial dysfunction and abnormal aortic fatty acid composition in adult female offspring of rats fed animal lard during pregnancy. We have now further investigated this model. Female Sprague-Dawley rats were fed a control breeding diet (5.3% fat) or a diet rich in lard (25.7% fat) 10 days before and throughout pregnancy and lactation. Male and female offspring were implanted with radiotelemeters for recording of blood pressure, heart rate, and activity at 80, 180, and 360 days of age. Reactivity to acetylcholine and to nitric oxide were assessed in isolated small mesenteric arteries from 80- and 180-day-old littermates. Systolic blood pressure (awake phase) was raised in female offspring (180 days: offspring of control, 130.7±1.6 mm Hg, n=5, versus offspring of lard-fed, 138.1±2.9, n=5, P =0.029; 360 days: offspring of control, 129.7±3.7 mm Hg, n=6, versus offspring of lard-fed, 142.1±3.2, n=6, P =0.005). Diastolic blood pressure was also raised at 180 days (offspring of control, 87.6±1.0 mm Hg, n=5, versus offspring of lard-fed, 94.7±2.6, n=5, P =0.011). Blood pressure was not raised in male offspring. Endothelium-dependent relaxation to acetylcholine was blunted in male and female offspring of lard-fed dams (80 and 180 days). Feeding a diet rich in lard to pregnant rats leads to gender-related cardiovascular dysfunction in normally fed offspring.

Maternal Obesity Induced by Diet in Rats Permanently Influences Central Processes Regulating Food Intake in Offspring

Hypothalamic systems which regulate appetite may be permanently modified during early development. We have previously reported hyperphagia and increased adiposity in the adult offspring of rodents fed an obesogenic diet prior to and throughout pregnancy and lactation. We now report that offspring of obese (OffOb) rats display an amplified and prolonged neonatal leptin surge, which is accompanied by elevated leptin mRNA expression in their abdominal white adipose tissue. At postnatal Day 30, before the onset of hyperphagia in these animals, serum leptin is normal, but leptin-induced appetite suppression and phosphorylation of STAT3 in the arcuate nucleus (ARC) are attenuated; the level of AgRP-immunoreactivity in the hypothalamic paraventricular nucleus (PVH), which derives from neurones in the ARC and is developmentally dependent on leptin, is also diminished. We hypothesise that prolonged release of abnormally high levels of leptin by neonatal OffOb rats leads to leptin resistance and permanently affects hypothalamic functions involving the ARC and PVH. Such effects may underlie the developmental programming of hyperphagia and obesity in these rats.

Predictive Adaptive Responses to Maternal High-Fat Diet Prevent Endothelial Dysfunction but Not Hypertension in Adult Rat Offspring

Background—Population-based studies suggest that fetal adaptive responses to maternal dietary imbalance confer survival benefit when the postnatal diet remains suboptimal but increase susceptibility to cardiovascular disease when postnatal nutrition is improved. We have investigated “predictive adaptive” responses in a rodent model in which adult offspring of fat-fed dams develop characteristics of the metabolic syndrome. Methods and Results—Sprague-Dawley rats were fed a fat-rich diet or normal chow throughout pregnancy and weaning. Vascular endothelial function and blood pressure were determined in 180-day-old offspring of fat-fed dams raised on standard chow (FC) or on the fat-rich diet (FF) and in offspring of chow-fed dams raised on chow (CON). Small mesenteric artery endothelium-dependent dilation to acetylcholine was impaired in male and female FC (by ANOVA, P<0.001 versus CON) but similar to CON in FF (P=NS). Blood glucose was lower in FF versus FC. Heart rate was reduced in male FC versus CON (P<0.05) but not in FF. Plasma triglyceride concentrations were reduced in male FF compared with CON (P<0.05). Blood pressure was raised in female FC (systolic, 132.5±3.0 mm Hg versus CON, 119.0±3.8 mm Hg, P<0.05; diastolic, 91.2±1.7 mm Hg versus CON, 81.1±1.4 mm Hg, P<0.05) and in female FF (systolic, 132.5±4.2 mm Hg versus CON, P<0.05; diastolic, 91.0±1.9 mm Hg versus CON, P<0.05). Blood pressure was similar to CON in male FC and FF. Conclusions—Predictive adaptive responses prevent endothelial dysfunction and reduced heart rate in offspring of fat-fed dams if offspring are raised on the same diet but do not prevent development of raised blood pressure.

Developmental origins of obesity and the metabolic syndrome: the role of maternal obesity.

Obesity and its sequelae may prove to be the greatest threat to human lifestyle and health in the developed world this century. The so called obesity epidemic has seen the incidence of obesity and overweight almost double in Western societies and the trend is mirrored in nations that are transitioning to first world economies. There is no doubt that much of the rise in obesity can be attributed to lifestyle factors such as the excess consumption of energy-dense foods and the decline in physical activity. However, the ‘fetal origins’hypothesis, first proposed by Barker and colleagues and elaborated by several groups over the past 15 years to be termed the ‘Developmental Origins of Adult Health and Disease’ (DOHaD), provides an alternative explanation for the rising rates of obesity. The DOHaD hypothesis states that exposure to an unfavourable environment during development (either in utero or in the early postnatal period) programmes changes in fetal or neonatal development such that the individual is then at greater risk of developing adulthood disease. This chapter discusses the effects of maternal obesity on fetal development and birth outcomes as well as the manner in which DOHaD may contribute to the obesity epidemic.

Maternal obesity during pregnancy and lactation programs the development of offspring non-alcoholic fatty liver disease in mice.

BACKGROUND & AIMS Obesity induced, non-alcoholic fatty liver disease (NAFLD), is now the major cause in affluent countries, of the spectrum of steatosis-to-cirrhosis. Obesity and NAFLD rates in reproductive age women, and adolescents, are rising worldwide. Our hypothesis was that maternal obesity and lactation transmit to the offspring a pre-disposition to dysmetabolism, obesity and NAFLD. METHODS Female mice were fed standard or obesogenic chow, before, throughout pregnancy, and during lactation. The critical developmental period was studied by cross-fostering offspring of lean and obese dams. Offspring were then weaned onto standard chow and studied at 3months. Read-outs included markers of metabolic dysfunction, biochemical and histological indicators of NAFLD, induction of liver fibrogenesis, and activation of pro-fibrotic pathways. Mechanisms involved in programming a dysmetabolic and NAFLD phenotype were investigated by assaying breast milk components. RESULTS Offspring of obese dams had a dysmetabolic, insulin resistant and NAFLD phenotype compared to offspring of lean dams. Offspring of lean dams that were suckled by obese dams showed an exaggerated dysmetabolic and NAFLD phenotype, with increased body weight, as well as increased levels of insulin, leptin, aspartate transaminase, interleukin-6, tumour necrosis factor-alpha, liver triglycerides, steatosis, hepatic fibrogenesis, renal norepinephrine, and liver alpha1-D plus beta1-adrenoceptors, indicative of sympathetic nervous system activation. Obese dams also had raised breast milk leptin levels compared to lean dams. CONCLUSIONS Maternal obesity programs development of a dysmetabolic and NAFLD phenotype, which is critically dependent on the early postnatal period and possibly involving alteration of hypothalamic appetite nuclei signalling by maternal breast milk and neonatal adipose tissue derived, leptin.

Developmental programming of aortic and renal structure in offspring of rats fed fat-rich diets in pregnancy

Evidence from human and animal studies suggests that maternal nutrition can induce developmental programming of adult hypertension in offspring. We have previously described a model of maternal dietary imbalance in Sprague‐Dawley rats whereby administration of a maternal diet rich in animal lard programmes the development of increased blood pressure, insulin resistance, dyslipidaemia, obesity and mesenteric artery endothelial dysfunction in adult offspring. To further characterize the mechanism of hypertension in this model we have examined vascular and renal structure in adult offspring of Sprague‐Dawley rats fed a control diet (OC) or lard‐rich diet (OHF) during pregnancy and suckling followed by a control diet post‐weaning. To gain further insight, we assessed aortic reactivity and elasticity in an organ bath preparation and renal renin and Na+,K+‐ATPase activity. Plasma aldosterone concentration was also measured. Stereological examination of the aorta in OHF demonstrated reduced endothelial cell volume and smooth muscle cell number compared with OC. Adult OHF animals showed increased aortic stiffness and reduced endothelium‐dependent relaxation. Renal stereology showed no differences in kidney weight, glomerular number or volume in OHF compared with OC, but renin and Na+,K+‐ATPase activity were significantly reduced in OHF compared with controls. Programmed alterations to aortic structure and function are consistent with previous observations that exposure to maternal high fat diets produces systemic vascular changes in the offspring. Despite normal renal stereology, altered renal Na+,K+‐ATPase and renin activity offers further insight into the mechanism underlying the increased blood pressure characteristic of this model.