Critical periods of increased fetal vulnerability to a maternal high fat diet

Molecular nutrition in life course perspective: Pinpointing metabolic pathways to target during periconception

Lifecourse nutrition encompasses nourishment from early development into parenthood. From preconception and pregnancy to childhood, late adolescence, and reproductive years, life course nutrition explores links between dietary exposures and health outcomes in current and future generations from a public health perspective, usually addressing lifestyle behaviours, reproductive well-being and maternal-child health strategies. However, nutritional factors that play a role in conceiving and sustaining new life might also require a molecular perspective and recognition of critical interactions between specific nutrients and relevant biochemical pathways. The present perspective summarises evidence about the links between diet during periconception and next-generation health and outlines the main metabolic networks involved in nutritional biology of this sensitive time frame.

Effects of maternal high-fat diet on fetal growth, placental nutrient transporters and circular RNA expression profiles

Epidemiological and experimental studies suggest that there is a strong correlation between maternal high-fat diet and fetal-placental development. The current study aims to investigate the effects of maternal high-fat diet on fetal growth, placental nutrient transporters and circular RNA expression profiles in a mouse model. Forty C57BL/6 female mice were randomly assigned to two groups, fed either a control (10% fat for energy) diet (CON) or a high-fat (60% fat for energy) diet (HFD) for 4 weeks before mating and throughout pregnancy, and were killed on day 19.5 of pregnancy. The serum glucose, total cholesterol and low-density lipoprotein, the glucolipid metabolism-related hormones, and the insulin resistance index were significantly increased. High-throughput sequencing showed that differentially expressed circRNAs (DE circRNAs) in the placenta can regulate various biological processes, cellular components, and molecular functions through various energy metabolism pathways, and mmu-let-7g-5p was found to target and bind to multiple DE circRNAs. In addition, this study also predicted that various circRNAs with protein coding functions can regulate maternal placental nutrient transport. In general, the ceRNA (circRNAs-miRNAs-mRNAs) regulatory network of maternal placental nutrient transport constructed in this study is of great significance for further understanding the effect of maternal nutrition on fetal growth in the future.

Preeclampsia-induced alterations in brain and liver gene expression and DNA methylation patterns in fetal mice

Exposure to pregnancy complications, including preeclampsia (PE), has lifelong influences on offspring's health. We have previously reported that experimental PE, induced in mice by administration of adenoviral sFlt1 at gestational day 8.5 combined with LPS at day 10.5, results in symmetrical growth restriction in female and asymmetrical growth restriction in male offspring. Here, we characterize the molecular phenotype of the fetal brain and liver with respect to gene transcription and DNA methylation at the end of gestation.In fetal brain and liver, expression and DNA methylation of several key regulatory genes is altered by PE exposure, mostly independent of fetal sex. These alterations point toward a decreased gluconeogenesis in the liver and stimulated neurogenesis in the brain, potentially affecting long-term brain and liver function. The observed sex-specific growth restriction pattern is not reflected in the molecular data, showing that PE, rather than tissue growth, drives the molecular phenotype of PE-exposed offspring.

Antioxidant Effects of N-Acetylcysteine Prevent Programmed Metabolic Disease in Mice

An adverse maternal in utero and lactation environment can program offspring for increased risk for metabolic disease. The aim of this study was to determine whether N-acetylcysteine (NAC), an anti-inflammatory antioxidant, attenuates programmed susceptibility to obesity and insulin resistance in offspring of mothers on a high-fat diet (HFD) during pregnancy. CD1 female mice were acutely fed a standard breeding chow or HFD. NAC was added to the drinking water (1 g/kg) of the treatment cohorts from embryonic day 0.5 until the end of lactation. NAC treatment normalized HFD-induced maternal weight gain and oxidative stress, improved the maternal lipidome, and prevented maternal leptin resistance. These favorable changes in the in utero environment normalized postnatal growth, decreased white adipose tissue (WAT) and hepatic fat, improved glucose and insulin tolerance and antioxidant capacity, reduced leptin and insulin, and increased adiponectin in HFD offspring. The lifelong metabolic improvements in the offspring were accompanied by reductions in proinflammatory gene expression in liver and WAT and increased thermogenic gene expression in brown adipose tissue. These results, for the first time, provide a mechanistic rationale for how NAC can prevent the onset of metabolic disease in the offspring of mothers who consume a typical Western HFD.

Differential Effects of Post-Weaning Diet and Maternal Obesity on Mouse Liver and Brain Metabolomes

Nutritional changes during developmental windows are of particular concern in offspring metabolic disease. Questions are emerging concerning the role of maternal weight changes before conception, particularly for weight loss, in the development of diet-related disorders. Understanding the physiological pathways affected by the maternal trajectories in the offspring is therefore essential, but a broad overview is still lacking. We recently reported both metabolic and behavioral negative outcomes in offspring born to obese or weight-loss mothers and fed a control of high-fat diet, suggesting long-term modeling of metabolic pathways needing to be further characterized. Using non-targeted LC–HRMS, we investigated the impact of maternal and post-weaning metabolic status on the adult male offspring’s metabolome in three tissues involved in energy homeostasis: liver, hypothalamus and olfactory bulb. We showed that post-weaning diet interfered with the abundance of several metabolites, including 1,5-anhydroglucitol, saccharopine and β-hydroxybutyrate, differential in the three tissues. Moreover, maternal diet had a unique impact on the abundance of two metabolites in the liver. Particularly, anserine abundance, lowered by maternal obesity, was normalized by a preconceptional weight loss, whatever the post-weaning diet. This study is the first to identify a programming long-term effect of maternal preconception obesity on the offspring metabolome.

Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period

Thirty years ago, there was an emerging appreciation for the significance of oxidative stress in newborn disease. This prompted a renewed interest in the impact of oxygen therapy for the newborn in the delivery room and beyond, especially in premature infants. Today, the complexity of oxidative stress both in normal regulation and pathology is better understood, especially as it relates to neonatal mitochondrial oxidative stress responses to hyperoxia. Mitochondria are recipients of oxidative damage and have a propensity for oxidative self-injury that has been implicated in the pathogenesis of neonatal lung diseases. Similarly, both intrauterine growth restriction (IUGR) and macrosomia are associated with mitochondrial dysfunction and oxidative stress. Additionally, reoxygenation with 100% O₂ in a hypoxic-ischemic newborn lamb model increased the production of pro-inflammatory cytokines in the brain. Moreover, the interplay between inflammation and oxidative stress in the newborn is better understood because of animal studies. Transcriptomic analyses have found a number of genes to be differentially expressed in murine models of bronchopulmonary dysplasia (BPD). Epigenetic changes have also been detected both in animal models of BPD and premature infants exposed to oxygen. Antioxidant therapy to prevent newborn disease has not been very successful; however, new therapeutic principles, like melatonin, are under investigation.

N-Acetylcysteine Resolves Placental Inflammatory-Vasculopathic Changes in Mice Consuming a High-Fat Diet

The mechanism by which poor maternal nutrition can affect the long-term health of offspring is poorly understood. In mice, we previously found that maternal high-fat diet (HFD) exposure results in reduced fetal growth regardless of maternal genotype. We tested our hypothesis that maternal HFD-induced inflammation contributes to metabolic disease susceptibility of the offspring via alterations in the placenta. The effect of maternal genotype, diet, and treatment with the anti-inflammatory compound N-acetylcysteine (NAC) on placental morphologic features was investigated. Placentas from wild-type dams maintained on a HFD but not those heterozygous (+/-) for Glut4 (Slc2a4) on the same diet had an increase in decidual inflammation and vasculopathy occurring together. NAC administration resulted in amelioration of HFD-induced decidual vasculopathy independent of offspring genotype and sex. Consistent with these morphologic improvements, placentas from HFD dams treated with NAC had decreased mRNA and immunostaining of IL-1β and monocyte chemoattractant protein-1, decreased mRNA of inflammatory genes, and increased mRNA of Vegfa. These results strongly suggest consumption of an HFD results in vascular changes in placenta reflected by alterations in expression of pivotal vascular developmental markers and inflammatory genes all of which are ameliorated by NAC. These placental changes play a key role in the increased programed metabolic disease of HFD-exposed offspring.

Effects of high-fat diets on fetal growth in rodents: a systematic review

BACKGROUND

Maternal nutrition during pregnancy has life-long consequences for offspring. However, the effects of maternal overnutrition and/ or obesity on fetal growth remain poorly understood, e.g., it is not clear why birthweight is increased in some obese pregnancies but not in others. Maternal obesity is frequently studied using rodents on high-fat diets, but effects on fetal growth are inconsistent. The purpose of this review is to identify factors that contribute to reduced or increased fetal growth in rodent models of maternal overnutrition.

METHODS

We searched Web of Science and screened 2173 abstracts and 328 full texts for studies that fed mice or rats diets providing ~ 45% or ~ 60% calories from fat for 3 weeks or more prior to pregnancy. We identified 36 papers matching the search criteria that reported birthweight or fetal weight.

RESULTS

Studies that fed 45% fat diets to mice or 60% fat diets to rats generally did not show effects on fetal growth. Feeding a 45% fat diet to rats generally reduced birth and fetal weight. Feeding mice a 60% fat diet for 4-9 weeks prior to pregnancy tended to increase in fetal growth, whereas feeding this diet for a longer period tended to reduce fetal growth.

CONCLUSIONS

The high-fat diets used most often with rodents do not closely match Western diets and frequently reduce fetal growth, which is not a typical feature of obese human pregnancies. Adoption of standard protocols that more accurately mimic effects on fetal growth observed in obese human pregnancies will improve translational impact in this field.

Maternal Stress Potentiates the Effect of an Inflammatory Diet in Pregnancy on Maternal Concentrations of Tumor Necrosis Factor Alpha

Maternal inflammation during pregnancy is known to adversely impact fetal development, birth outcomes, and offspring physical and mental health. Diet and stress have been identified as important determinants of inflammation, yet their combined effects have not been examined in the context of pregnancy. The aim of this study was to examine the relationship between maternal diet with inflammatory potential and psychological stress, and to determine their interaction effect on concentrations of tumor necrosis factor (TNF)-α across pregnancy. We conducted a prospective longitudinal study of n = 202 women with three assessments during pregnancy, which included: ecological momentary assessment (EMA) of maternal stress using the perceived stress scale (PSS) short version; 24-h dietary recalls from which the dietary inflammatory index (DII) was computed; and serum measurements of TNF-α. Across pregnancy, higher perceived stress was associated with consumption of a more pro-inflammatory diet (r = 0.137; p < 0.05). In a linear regression model adjusted for covariates, DII was positively associated with TNF-α (B = 0.093, p = 0.010). The effect of the pro-inflammatory diet on concentrations of TNF-α was more pronounced in women reporting higher levels of stress (B = 0.134, p = 0.018 for DII*PSS interaction). These results highlight the need to consider nutrition and stress concurrently in the context of inflammation during pregnancy.

Low-Dose Ionizing Radiation Exposure, Oxidative Stress and Epigenetic Programing of Health and Disease

Ionizing radiation exposure from medical diagnostic imaging has greatly increased over the last few decades. Approximately 80% of patients who undergo medical imaging are exposed to low-dose ionizing radiation (LDIR). Although there is widespread consensus regarding the harmful effects of high doses of radiation, the biological effects of low-linear energy transfer (LET) LDIR is not well understood. LDIR is known to promote oxidative stress, however, these levels may not be large enough to result in genomic mutations. There is emerging evidence that oxidative stress causes heritable modifications via epigenetic mechanisms (DNA methylation, histone modification, noncoding RNA regulation). These epigenetic modifications result in permanent cellular transformations without altering the underlying DNA nucleotide sequence. This review summarizes the major concepts in the field of epigenetics with a focus on the effects of low-LET LDIR (<100 mGy) and oxidative stress on epigenetic gene modification. In this review, we show evidence that suggests that LDIR-induced oxidative stress provides a mechanistic link between LDIR and epigenetic gene regulation. We also discuss the potential implication of LDIR exposure during pregnancy where intrauterine fetal development is highly susceptible to oxidative stress-induced epigenetic programing.

High post-natal mortality associated with defects in lung maturation and reduced adiposity in mice with gestational exposure to high fat and N-acetylcysteine

Studies have demonstrated that maternal consumption of a high fat diet (HFD) increases offspring susceptibility to metabolic disease. This study was initiated to identify the mechanistic contribution of oxidative stress on this phenomenon. Two weeks prior to mating, dams were fed either HFD or Control diet with or without supplementation with the anti-oxidant N-acetylcysteine (NAC). Pups born to HFD dams had reduced crown rump length (CRL) at birth and higher neonatal mortality compared to pups from Control dams. Supplementation with NAC normalized CRL in pups from HFD dams, but notably increased mortality. Histological examination of the lungs postnatally and prenatally, revealed normal branching morphogenesis but delayed alveolarization in pups from dams fed HFD+NAC. Discontinuation of NAC at ED17.5 with re-introduction at PD3 improved offspring survival and lung maturation. Additionally, interscapular brown adipose tissue (BAT) was reduced in ED18.5 embryos from HFD dams. These findings suggest that increased mortality in offspring from dams fed HFD+NAC during pregnancy may in part be the result of delayed pulmonary alveolarization and decreased BAT.

Role of placental insufficiency and intrauterine growth restriction on the activation of fetal hepatic glucose production

Glucose is the major fuel for fetal oxidative metabolism. A positive maternal-fetal glucose gradient drives glucose across the placenta and is sufficient to meet the demands of the fetus, eliminating the need for endogenous hepatic glucose production (HGP). However, fetuses with intrauterine growth restriction (IUGR) from pregnancies complicated by placental insufficiency have an early activation of HGP. Furthermore, this activated HGP is resistant to suppression by insulin. Here, we present the data demonstrating the activation of HGP in animal models, mostly fetal sheep, and human pregnancies with IUGR. We also discuss potential mechanisms and pathways that may produce and support HGP and hepatic insulin resistance in IUGR fetuses.

Decreased basal insulin secretion from pancreatic islets of pups in a rat model of maternal obesity

Maternal obesity (MO) is a deleterious condition that enhances susceptibility of adult offspring to metabolic diseases such as type 2 diabetes. The objective is to study the effect of MO on in vitro insulin secretion and pancreatic cellular population in offspring. We hypothesize that a harmful antenatal metabolic environment due to MO diminishes the basal glucose-responsive secretory function of pancreatic beta cells in offspring. Mothers were fed a control (C) or high-fat diet from weaning through pregnancy (120 days) and lactation. At postnatal days (PNDs) 36 and 110, pups were killed, peripheral blood was collected and pancreatic islets were isolated. Basal insulin secretion was measured in vitro in islets for 60 min. It was found that blood insulin, glucose and homeostasis model assessment (HOMA) index were unaffected by maternal diet and age in females. However, male MO offspring at PND 110 showed hyperinsulinemia and insulin resistance compared with C. Body weight was not modified by MO, but fat content was higher in MO pups compared with C pups. Triglycerides and leptin concentrations were higher in MO than in C offspring in all groups except in females at PND 36. Pancreatic islet cytoarchitecture was unaffected by MO. At PND 36, islets of male and female C and MO offspring responded similarly to glucose, but at PND 110, male and female MO offspring islets showed a 50% decrease in insulin secretion. It was concluded that MO impairs basal insulin secretion of offspring with a greater impact on males than females, and this effect mainly manifests in adulthood.

Maternal fructose drives placental uric acid production leading to adverse fetal outcomes

Maternal metabolic diseases increase offspring risk for low birth weight and cardiometabolic diseases in adulthood. Excess fructose consumption may confer metabolic risks for both women and their offspring. However, the direct consequences of fructose intake per se are unknown. We assessed the impact of a maternal high-fructose diet on the fetal-placental unit in mice in the absence of metabolic syndrome and determined the association between maternal serum fructose and placental uric acid levels in humans. In mice, maternal fructose consumption led to placental inefficiency, fetal growth restriction, elevated fetal serum glucose and triglyceride levels. In the placenta, fructose induced de novo uric acid synthesis by activating the activities of the enzymes AMP deaminase and xanthine oxidase. Moreover, the placentas had increased lipids and altered expression of genes that control oxidative stress. Treatment of mothers with the xanthine oxidase inhibitor allopurinol reduced placental uric acid levels, prevented placental inefficiency, and improved fetal weights and serum triglycerides. Finally, in 18 women delivering at term, maternal serum fructose levels significantly correlated with placental uric acid levels. These findings suggest that in mice, excess maternal fructose consumption impairs placental function via a xanthine oxidase/uric acid-dependent mechanism, and similar effects may occur in humans.

Expression of epigenetic machinery genes is sensitive to maternal obesity and weight loss in relation to fetal growth in mice

BACKGROUND

Maternal obesity impacts fetal growth and pregnancy outcomes. To counteract the deleterious effects of obesity on fertility and pregnancy issue, preconceptional weight loss is recommended to obese women. Whether this weight loss is beneficial/detrimental for offspring remains poorly explored. Epigenetic mechanisms could be affected by maternal weight changes, perturbing expression of key developmental genes in the placenta or fetus. Our aim was to investigate the effects of chronic maternal obesity on feto-placental growth along with the underlying epigenetic mechanisms. We also tested whether preconceptional weight loss could alleviate these effects.

RESULTS

Female mice were fed either a control diet (CTRL group), a high-fat diet (obese (OB) group), or a high-fat diet switched to a control diet 2 months before conception (weight loss (WL) group). At mating, OB females presented an obese phenotype while WL females normalized metabolic parameters. At embryonic day 18.5 (E18.5), fetuses from OB females presented fetal growth restriction (FGR; -13 %) and 28 % of the fetuses were small for gestational age (SGA). Fetuses from WL females normalized this phenotype. The expression of 60 epigenetic machinery genes and 32 metabolic genes was measured in the fetal liver, placental labyrinth, and junctional zone. We revealed 23 genes altered by maternal weight trajectories in at least one of three tissues. The fetal liver and placental labyrinth were more responsive to maternal obesity than junctional zone. One third (18/60) of the epigenetic machinery genes were differentially expressed between at least two maternal groups. Interestingly, genes involved in the histone acetylation pathway were particularly altered (13/18). In OB group, lysine acetyltransferases and Bromodomain-containing protein 2 were upregulated, while most histone deacetylases were downregulated. In WL group, the expression of only a subset of these genes was normalized.

CONCLUSIONS

This study highlights the high sensitivity of the epigenetic machinery gene expression, and particularly the histone acetylation pathway, to maternal obesity. These obesity-induced transcriptional changes could alter the placental and the hepatic epigenome, leading to FGR. Preconceptional weight loss appears beneficial to fetal growth, but some effects of previous obesity were retained in offspring phenotype.

The effect of maternal Inflammation on foetal programming of metabolic disease

Maternal obesity during pregnancy increases the child's risk of developing obesity and obesity-related diseases later in life. Key components in foetal programming of metabolic risk remain to be identified; however, chronic low-grade inflammation associated with obesity might be responsible for metabolic imprinting in the offspring. We have therefore surveyed the literature to evaluate the role of maternal obesity-induced inflammation in foetal programming of obesity and related diseases. The literature on this topic is limited, so this review also includes animal models where maternal inflammation is mimicked by single injections with lipopolysaccharide (LPS). An LPS challenge results in an immunological response that resembles the obesity-induced immune profile, although LPS injections provoke a stronger response than the subclinical obesity-associated response. Maternal LPS or cytokine exposures result in increased adiposity and impaired metabolic homeostasis in the offspring, similar to the phenotype observed after exposure to maternal obesity. The cytokine levels might be specifically important for the metabolic imprinting, as cytokines are both transferable from maternal to foetal circulation and have the capability to modulate placental nutrient transfer. However, the immune response associated with obesity is moderate and therefore potentially weakened by the pregnancy-driven immune modulation, dominated by anti-inflammatory Treg and Th2 cells. We know from other low-grade inflammatory diseases, such as rheumatoid arthritis, that pregnancy can improve disease state. If pregnancy is also capable of suppressing the obesity-associated inflammation, the immunological markers might be less likely to affect metabolic programming in the developing foetus than otherwise implied.