Maternal fructose consumption alters messenger RNA expression of hippocampal StAR, PBR, P450(11β), 11β-HSD, and 17β-HSD in rat offspring

Can early-life high fructose exposure induce long-term depression and anxiety-like behaviours? - A preclinical systematic review

Early-life environmental factors, such as maternal diet or early-life nutrition, have been described as significant risk factors for anxiety and depression later in life. With the rising intake of fructose since the 1960 s, several adverse effects have been described, but little is known about the impact of early-life high fructose exposure on the risk of developing depression and anxiety later in life. Since animal models provide ways to test this hypothesis longitudinally in an experimental and controlled environment, we performed a systematic review to investigate whether high fructose exposure during early life influences the risk of developing depression or anxiety-like behaviours in animals. We adopted a high-sensitivity strategy to find potential studies. We included 1805 papers for screening, but only found nine eligible studies that tested only high fructose exposure during development, all conducted in rats. Data extraction and analysis revealed that 6 studies found evidence indicating that fructose exposure in early life increases the risk of anxiety or depression. The remaining 3 studies found no altered behavior after fructose exposure. The discrepancies may be caused by multiple factors, such as time of diet exposure, animal strain, behavioural testing differences, and fructose's metabolic influence. Due to weak and contradictory evidence, we could not conclude if early-life fructose exposure influences the risk of anxiety or depression-like behaviors. We propose future directions and suggestions for future studies to strengthen their findings.

Maternal fructose intake predisposes rat offspring to metabolic disorders via abnormal hepatic programming

Given that fructose consumption has increased by more than 10-fold in recent decades, it is possible that excess maternal fructose consumption causes harmful effects in the next generation. This study attempted to elucidate the mechanism of the harmful effects of excessive maternal fructose intake from the perspective of offspring liver function. Female rats during gestation and lactation were fed water containing fructose, and their offspring were fed normal water. We attempted to elucidate the mechanism of fructose-induced transgenerational toxicity by conducting a longitudinal study focusing on hepatic programming prior to disease onset. Impaired Insulin resistance and decreased high-density lipoprotein-cholesterol levels were observed at 160 days of age. However, metabolic disorders were not observed in 60-day-old offspring. Microarray analysis of 60-day-old offspring livers showed the reduction of hepatic insulin-like growth factor-1 (Igf1) mRNA expression. This reduction continued until the rats were aged 160 days and attenuated Igf1 signaling. Hepatic microRNA-29 (miR-29a) and miR-130a, which target Igf1 mRNA, were also found to be upregulated. Interestingly, these miRNAs were upregulated in the absence of metabolic disorder. In this study, we found that maternal fructose intake resulted in dysregulated expression of Igf1 and its target miRNAs in the offspring liver, and that these offspring were more likely to develop metabolic disorders. Abnormal hepatic programming induced by an imbalanced maternal nutritional environment is maintained throughout life, implying that it may contribute to metabolic disorders.

Maternal fructose consumption downregulates hippocampal catalase expression via DNA methylation in rat offspring

Some studies have demonstrated that excessive fructose consumption negatively impact brain function. Recently, the Developmental Origins of Health and Disease hypothesis - which suggests that maternal nutritional status during gestation and lactation can alter offspring phenotype - has received much attention. In a previous study, we demonstrated that maternal fructose consumption increases levels of lipid peroxides in hippocampi of offspring. The hypothesis in the present study was that maternal fructose intake would affect hippocampal antioxidant enzyme via epigenetic regulation. Upon confirmation of gestation, female rats were assigned to receive either water (control group) or a 20% fructose solution (fructose-fed group). Water or fructose solution were administered to dams from day 1 of gestation to postnatal day 21. Immediately after weaning, hippocampi of offspring were removed for analysis of antioxidant enzyme (Sod1, Sod2, Gpx1, Gpx4, and Cat) messenger RNA transcript levels. Levels of the Cat transcript were significantly lower in the fructose-fed relative to the control group. The Cat protein level was also significantly lower in the fructose-fed relative to the control group as with the messenger RNA transcript levels. Moreover, Cat promoter DNA methylation levels were higher in the fructose-fed group. The present study indicates that maternal fructose consumption may decrease offspring hippocampal Cat transcript levels via altered DNA methylation, which may result in higher levels of oxidative stress due to a decreased ability to neutralize lipid peroxides.

Testosterone and Adult Neurogenesis

It is now well established that neurogenesis occurs throughout adulthood in select brain regions, but the functional significance of adult neurogenesis remains unclear. There is considerable evidence that steroid hormones modulate various stages of adult neurogenesis, and this review provides a focused summary of the effects of testosterone on adult neurogenesis. Initial evidence came from field studies with birds and wild rodent populations. Subsequent experiments with laboratory rodents have tested the effects of testosterone and its steroid metabolites upon adult neurogenesis, as well as the functional consequences of induced changes in neurogenesis. These experiments have provided clear evidence that testosterone increases adult neurogenesis within the dentate gyrus region of the hippocampus through an androgen-dependent pathway. Most evidence indicates that androgens selectively enhance the survival of newly generated neurons, while having little effect on cell proliferation. Whether this is a result of androgens acting directly on receptors of new neurons remains unclear, and indirect routes involving brain-derived neurotrophic factor (BDNF) and glucocorticoids may be involved. In vitro experiments suggest that testosterone has broad-ranging neuroprotective effects, which will be briefly reviewed. A better understanding of the effects of testosterone upon adult neurogenesis could shed light on neurological diseases that show sex differences.

Sex differences in steroid levels and steroidogenesis in the nervous system: Physiopathological role

The nervous system, in addition to be a target for steroid hormones, is the source of a variety of neuroactive steroids, which are synthesized and metabolized by neurons and glial cells. Recent evidence indicates that the expression of neurosteroidogenic proteins and enzymes and the levels of neuroactive steroids are different in the nervous system of males and females. We here summarized the state of the art of neuroactive steroids, particularly taking in consideration sex differences occurring in the synthesis and levels of these molecules. In addition, we discuss the consequences of sex differences in neurosteroidogenesis for the function of the nervous system under healthy and pathological conditions and the implications of neuroactive steroids and neurosteroidogenesis for the development of sex-specific therapeutic interventions.

Silencing of GPR82 with Interference RNA Improved Metabolic Profiles in Rats with High Fructose Intake

Metabolic syndrome (MS) is a clinical condition, constituted by alterations that lead to the onset of type II diabetes and cardiovascular disease. It has been reported that orphan G-protein-coupled receptor 82 (GPR82) participates in metabolic processes. The aim of this study was to evaluate the function of GPR82 in MS using a small interfering RNA (siRNA) against this receptor. We used Wistar rats of 10-12 weeks of age fed with a high-fructose solution (70%) for 9 weeks to induce MS. Subsequently, the rats were treated with an intrajugular dose of an siRNA against GPR82 and the effects were evaluated on day 3 and 7 after administration. On day 3 the siRNA had a transient effect on decreasing blood pressure and triglycerides and increasing high-density lipoprotein cholesterol, which recovered to the MS control on day 7. Decreased gene expressions of GPR82 mRNA in the aorta and heart were observed on day 3; moreover, decreased gene expression was maintained in the aorta on day 7. Therefore, we conclude that the orphan receptor GPR82 participates in the development of MS induced by fructose and the silencing of this receptor could ameliorate metabolic components.

Perinatal Nutrition and Programmed Risk for Neuropsychiatric Disorders: A Focus on Animal Models

Maternal nutrition is critically important for fetal development. Recent human studies demonstrate a strong connection between diet during pregnancy and offspring risk for neuropsychiatric disorders including depression, anxiety, and attention-deficit/hyperactivity disorder. Animal models have emerged as a crucial tool for understanding maternal nutrition's contribution to prenatal programming and the later development of neuropsychiatric disorders. This review highlights preclinical studies examining how maternal consumption of the three macronutrients (protein, fats, and carbohydrates) influence offspring negative-valence behaviors relevant to neuropsychiatric disorders. We highlight the translational aspects of animal models and so examine exposure periods that mirror the neurodevelopmental stages of human gestation. Because of our emphasis on programmed changes in neurobehavioral development, studies that continue diet exposure until assessment in adulthood are not discussed. The presented research provides a strong foundation of preclinical evidence of nutritional programming of neurobehavioral impairments. Alterations in risk assessment and response were observed alongside neurodevelopmental impairments related to neurogenesis, synaptogenesis, and synaptic plasticity. To date, the large majority of studies utilized rodent models, and the field could benefit from additional study of large-animal models. Additional future directions are discussed, including the need for further studies examining how sex as a biological variable affects the contribution of maternal nutrition to prenatal programming.

Maternal fructose intake disturbs ovarian estradiol synthesis in rats

AIMS

Recent increases in fructose consumption have raised concerns regarding the potential adverse intergenerational effects, as maternal fructose intake may induce physiological dysfunction in offspring. However, no reports are available regarding the effect of excess maternal fructose on reproductive tissues such as the ovary. Notably, the maternal intrauterine environment has been demonstrated to affect ovarian development in the subsequent generation. Given the fructose is transferred to the fetus, excess fructose consumption may affect offspring ovarian development. As ovarian development and its function is maintained by 17β-estradiol, we therefore investigated whether excess maternal fructose intake influences offspring ovarian estradiol synthesis. Rats received a 20% fructose solution during gestation and lactation. After weaning, offspring ovaries were isolated.

KEY FINDINGS

Offspring from fructose-fed dams showed reduced StAR and P450(17α) mRNA levels, along with decreased protein expression levels. Conversely, attenuated P450arom protein level was found in the absence of mRNA expression alteration. Consistent with these phenomena, decreased circulating levels of estradiol were observed. Furthermore, estrogen receptor α (ERα) protein levels were also down-regulated. In accordance, the mRNA for progesterone receptor, a transcriptional target of ERα, was decreased. These results suggest that maternal fructose might alter ovarian physiology in the subsequent generation.

Cafeteria diet differentially alters the expression of feeding-related genes through DNA methylation mechanisms in individual hypothalamic nuclei

We evaluated the effect of cafeteria diet (CAF) on the mRNA levels and DNA methylation state of feeding-related neuropeptides, and neurosteroidogenic enzymes in discrete hypothalamic nuclei. Besides, the expression of steroid hormone receptors was analyzed. Female rats fed with CAF from weaning increased their energy intake, body weight, and fat depots, but did not develop metabolic syndrome. The increase in energy intake was related to an orexigenic signal of paraventricular (PVN) and ventromedial (VMN) nuclei, given principally by upregulation of AgRP and NPY. This was mildly counteracted by the arcuate nucleus, with decreased AgRP expression and increased POMC and kisspeptin expression. CAF altered the transcription of neurosteroidogenic enzymes in PVN and VMN, and epigenetic mechanisms associated with differential promoter methylation were involved. The changes observed in the hypothalamic nuclei studied could add information about their differential role in food intake control and how their action is disrupted in obesity.

Fructose intake during gestation and lactation differentially affects the expression of hippocampal neurosteroidogenic enzymes in rat offspring

Neurosteroids, steroidal hormones synthesized de novo from cholesterol within the brain, stimulate hippocampal functions such as neuron protection and synapse formation. Previously, we examined the effect of maternal fructose on the transcriptional regulation of neurosteroidogenic enzymes. We found that the mRNA expression level of the steroidogenic acute regulatory protein (StAR), peripheral benzodiazepine receptor (PBR), cytochrome P450(11β), 11β-hydroxysteroid dehydrogenase (HSD), and 17β-HSD was altered. However, we could not determine whether maternal fructose intake played a role in the gestation or lactation period because the dam rats were fed fructose solution during both periods. Thus, in this study, we analyzed the hippocampi of the offspring of dams fed fructose during the gestation or lactation period. Maternal fructose consumption during either the gestation or lactation period did not affect the mRNA levels of StAR, P450(17α), 11β-HSD-2, and 17β-HSD-1. PBR expression was down-regulated, even when rats consumed fructose during the lactation period only, while fructose consumption during gestation tended to activate the expression of P450(11β)-2. We found that maternal fructose intake during gestation and lactation differentially affected the expression of hippocampal neurosteroidogenic enzymes in the offspring.

Fructose consumption induces hypomethylation of hepatic mitochondrial DNA in rats

AIMS

Fructose may play a crucial role in the pathogenesis of metabolic syndrome (MetS). However, the pathogenic mechanism of the fructose-induced MetS has not yet been investigated fully. Recently, several reports have investigated the association between mitochondrial DNA (mtDNA) and MetS. We examined the effect of fructose-rich diets on mtDNA content, transcription, and epigenetic changes.

MAIN METHODS

Four-week-old male Sprague-Dawley rats were offered a 20% fructose solution for 14weeks. We quantified mRNAs for hepatic mitochondrial genes and analyzed the mtDNA methylation (5-mC and 5-hmC) levels using ELISA kits.

KEY FINDINGS

Histological analysis revealed non-alcoholic fatty liver disease (NAFLD) in fructose-fed rats. Hepatic mtDNA content and transcription were higher in fructose-fed rats than in the control group. Global hypomethylation of mtDNA was also observed in fructose-fed rats.

SIGNIFICANCE

We showed that fructose consumption stimulates hepatic mtDNA-encoded gene expression. This phenomenon might be due to epigenetic changes in mtDNA. Fructose-induced mitochondrial epigenetic changes appear to be a novel mechanism underlying the pathology of MetS and NAFLD.

High fructose consumption induces DNA methylation at PPARα and CPT1A promoter regions in the rat liver

DNA methylation status is affected by environmental factors, including nutrition. Fructose consumption is considered a risk factor for the conditions that make up metabolic syndrome such as dyslipidemia. However, the pathogenetic mechanism by which fructose consumption leads to metabolic syndrome is unclear. Based on observations that epigenetic modifications are closely related to induction of metabolic syndrome, we hypothesized that fructose-induced metabolic syndrome is caused by epigenetic alterations. Male SD rats were designated to receive water or 20% fructose solution for 14 weeks. mRNA levels for peroxisome proliferator-activated receptor alpha (PPARα) and carnitine palmitoyltransferase 1A (CPT1A) was analyzed using Real-time PCR. Restriction digestion and real-time PCR (qAMP) was used for the analysis of DNA methylation status. Hepatic lipid accumulation was also observed by fructose intake. Fructose feeding also significantly decreased mRNA levels for PPARα and CPT1A. qAMP analysis demonstrated the hypermethylation of promoter regions of PPARα and CTP1A genes. Fructose-mediated attenuated gene expression may be mediated by alterations of DNA methylation status, and pathogenesis of metabolic syndrome induced by fructose relates to DNA methylation status.