Neonatal hyperglycemia alters the neurochemical profile, dendritic arborization and gene expression in the developing rat hippocampus

Neonatal dysglycemia: a review of dysglycemia in relation to brain health and neurodevelopmental outcomes

Neonatal dysglycemia has been a longstanding interest of research in neonatology. Adverse outcomes from hypoglycemia were recognized early but are still being characterized. Premature infants additionally introduced and led the reflection on the importance of neonatal hyperglycemia. Cohorts of infants following neonatal encephalopathy provided further information about the impacts of hypoglycemia and, more recently, highlighted hyperglycemia as a central concern for this population. Innovative studies exposed the challenges of management of neonatal glycemic levels with a "u-shape" relationship between dysglycemia and adverse neurological outcomes. Lately, glycemic lability has been recognized as a key factor in adverse neurodevelopmental outcomes. Research and new technologies, such as MRI and continuous glucose monitoring, offered novel insight into neonatal dysglycemia. Combining clinical, physiological, and epidemiological data allowed the foundation of safe operational definitions, including initiation of treatment, to delineate neonatal hypoglycemia as ≤47 mg/dL, and >150-180 mg/dL for neonatal hyperglycemia. However, questions remain about the appropriate management of neonatal dysglycemia to optimize neurodevelopmental outcomes. Research collaborations and clinical trials with long-term follow-up and advanced use of evolving technologies will be necessary to continue to progress the fascinating world of neonatal dysglycemia and neurodevelopment outcomes. IMPACT STATEMENT: Safe operational definitions guide the initiation of treatment of neonatal hypoglycemia and hyperglycemia. Innovative studies exposed the challenges of neonatal glycemia management with a "u-shaped" relationship between dysglycemia and adverse neurological outcomes. The importance of glycemic lability is also being recognized. However, questions remain about the optimal management of neonatal dysglycemia to optimize neurodevelopmental outcomes. Research collaborations and clinical trials with long-term follow-up and advanced use of evolving technologies will be necessary to progress the fascinating world of neonatal dysglycemia and neurodevelopment outcomes.

A Comprehensive Review of the Effects of Glycemic Carbohydrates on the Neurocognitive Functions Based on Gut Microenvironment Regulation and Glycemic Fluctuation Control

Improper glycemic carbohydrates (GCs) consumption can be a potential risk factor for metabolic diseases such as obesity and diabetes, which may lead to cognitive impairment. Although several potential mechanisms have been studied, the biological relationship between carbohydrate consumption and neurocognitive impairment is still uncertain. In this review, the main effects and mechanisms of GCs' digestive characteristics on cognitive functions are comprehensively elucidated. Additionally, healthier carbohydrate selection, a reliable research model, and future directions are discussed. Individuals in their early and late lives and patients with metabolic diseases are highly susceptible to dietary-induced cognitive impairment. It is well known that gut function is closely related to dietary patterns. Unhealthy carbohydrate diet-induced gut microenvironment disorders negatively impact cognitive functions through the gut-brain axis. Moreover, severe glycemic fluctuations, due to rapidly digestible carbohydrate consumption or metabolic diseases, can impair neurocognitive functions by disrupting glucose metabolism, dysregulating calcium homeostasis, oxidative stress, inflammatory responses, and accumulating advanced glycation end products. Unstable glycemic status can lead to more severe neurological impairment than persistent hyperglycemia. Slow-digested or resistant carbohydrates might contribute to better neurocognitive functions due to stable glycemic response and healthier gut functions than fully gelatinized starch and nutritive sugars.

Transient neonatal hyperglycemia induces metabolic shifts in the rat hippocampus: a 1H NMR-based metabolomics analysis

Diabetes has been reported to induce brain metabolic disturbance, but the effect of transient neonatal hyperglycemia (TNH) on brain metabolism remains unclear. Herein the rats were treated with a single intraperitoneal injection of 100 µg/g body weight of streptozotocin within 12 h after birth and displayed a typical clinical characteristic of TNH. Then we used NMR-based metabolomics to examine the metabolic changes in the hippocampus between TNH and normal control (Ctrl) rats at postnatal 7 days (P7) and 21 days (P21). The results show that TNH rats had significantly increased levels of N-acetyl aspartate, glutamine, aspartate and choline in the hippocampus relative to Ctrl rats at P7. Moreover, we found that the levels of alanine, myo-inositol and choline were significantly lower in TNH rats, although their blood glucose levels have been recovered to the normal level at P21. Therefore, our results suggest that TNH may have a long-term effect on hippocampal metabolic changes mainly involving neurotransmitter metabolism and choline metabolism.

Hyperglycemia and prematurity: a narrative review

Hyperglycemia is commonly encountered in extremely preterm newborns and physiologically can be attributed to immaturity in several biochemical pathways related to glucose metabolism. Although hyperglycemia is associated with a variety of adverse outcomes frequently described in this population, evidence for causality is lacking. Variations in definitions and treatment approaches have further complicated the understanding and implications of hyperglycemia on the immediate and long-term effects in preterm newborns. In this review, we describe the relationship between hyperglycemia and organ development, outcomes, treatment options, and potential gaps in knowledge that need further research. IMPACT: Hyperglycemia is common and less well described than hypoglycemia in extremely preterm newborns. Hyperglycemia can be attributed to immaturity in several cellular pathways involved in glucose metabolism in this age group. Hyperglycemia has been shown to be associated with a variety of adverse outcomes frequently described in this population; however, evidence for causality is lacking. Variations in definitions and treatment approaches have complicated the understanding and the implications of hyperglycemia on the immediate and long-term effects outcomes. This review describes the relationship between hyperglycemia and organ development, outcomes, treatment options, and potential gaps in knowledge that need further research.

Neonatal hyperbilirubinemia differentially alters the neurochemical profiles of the developing cerebellum and hippocampus in a preterm Gunn rat model

Neonatal hyperbilirubinemia (NHB) can lead to brain injury in newborn infants by affecting specific regions including the cerebellum and hippocampus. Extremely preterm infants are more vulnerable to bilirubin neurotoxicity, but the mechanism and extent of injury is not well understood. A preterm version of the Gunn rat model was utilized to investigate severe preterm NHB. Homozygous/jaundiced Gunn rat pups were injected (i.p.) on postnatal day (P) 5 with sulfadimethoxine, which increases serum free bilirubin capable of crossing the blood-brain barrier and causing brain injury. The neurochemical profiles of the cerebellum and hippocampus were determined using in vivo ¹ H MRS at 9.4 T on P30 and compared with those of heterozygous/non-jaundiced control rats. Transcript expression of related genes was determined by real-time quantitative PCR. MRI revealed significant morphological changes in the cerebellum of jaundiced rats. The concentrations of myo-inositol (+54%), glucose (+51%), N-acetylaspartylglutamate (+21%), and the sum of glycerophosphocholine and phosphocholine (+17%) were significantly higher in the cerebellum of the jaundiced group compared with the control group. Despite the lack of morphologic changes in the hippocampus, the concentration of myo-inositol (+9%) was higher and the concentrations of creatine (-8%) and of total creatine (-3%) were lower in the jaundiced group. In the hippocampus, expression of calcium/calmodulin dependent protein kinase II alpha (Camk2a), glucose transporter 1 (Glut1), and Glut3 transcripts were downregulated in the jaundiced group. In the cerebellum, glial fibrillary acidic protein (Gfap), myelin basic protein (Mbp), and Glut1 transcript expression was upregulated in the jaundiced group. These results indicate osmotic imbalance, gliosis, and changes in energy utilization and myelination, and demonstrate that preterm NHB critically affects brain development in a region-specific manner, with the cerebellum more severely impacted than the hippocampus.

Brain-Oriented Strategies for Neuroprotection of Asphyxiated Newborns in the First Hours of Life

Perinatal asphyxia represents the first cause of severe neurological disabilities and the second cause of neonatal death in term-born babies. Currently, no treatment can prevent immediate cell death from necrosis, but some therapeutic interventions, such as therapeutic hypothermia (TH), can reduce delayed cell death from apoptosis. TH significantly improves the combined outcome of mortality or major neurodevelopmental disability, but the number of patients to be treated is 7 to get 1 child with no adverse neurological outcome. The aim of this educational review is to analyze the other care strategies to be implemented to improve the neurological outcome of children with hypoxic ischemic encephalopathy (HIE). Hypocapnia, hypoglycemia, pain control, and functional brain monitoring are recognized as appropriate approaches to improve outcome in critically ill infants with HIE. Pharmacologic neuroprotective adjuncts are currently under investigation. New drugs such as allopurinol and melatonin seem to provide positive effects although more randomized controlled trials are required to establish the effective therapeutic scheme. In the meantime, sustaining the respiratory, metabolic, and cardiovascular system during TH can be a valuable aid in managing and treating the patient with HIE in an optimal way.

Female and male C57BL/6J offspring exposed to maternal obesogenic diet develop altered hypothalamic energy metabolism in adulthood

Maternal obesity is exceedingly common and strongly linked to offspring obesity and metabolic disease. Hypothalamic function is critical to obesity development. Hypothalamic mechanisms causing obesity following exposure to maternal obesity have not been elucidated. Therefore, we studied a cohort of C57BL/6J dams, treated with a control or high-fat-high-sugar diet, and their adult offspring to explore potential hypothalamic mechanisms to explain the link between maternal and offspring obesity. Dams treated with obesogenic diet were heavier with mild insulin resistance, which is reflective of the most common metabolic disease in pregnancy. Adult offspring exposed to maternal obesogenic diet had no change in body weight but significant increase in fat mass, decreased glucose tolerance, decreased insulin sensitivity, elevated plasma leptin, and elevated plasma thyroid-stimulating hormone. In addition, offspring exposed to maternal obesity had decreased energy intake and activity without change in basal metabolic rate. Hypothalamic neurochemical profile and transcriptome demonstrated decreased neuronal activity and inhibition of oxidative phosphorylation. Collectively, these results indicate that maternal obesity without diabetes is associated with adiposity and decreased hypothalamic energy production in offspring. We hypothesize that altered hypothalamic function significantly contributes to obesity development. Future studies focused on neuroprotective strategies aimed to improve hypothalamic function may decrease obesity development.NEW & NOTEWORTHY Offspring exposed to maternal diet-induced obesity demonstrate a phenotype consistent with energy excess. Contrary to previous studies, the observed energy phenotype was not associated with hyperphagia or decreased basal metabolic rate but rather decreased hypothalamic neuronal activity and energy production. This was supported by neurochemical changes in the hypothalamus as well as inhibition of hypothalamic oxidative phosphorylation pathway. These results highlight the potential for neuroprotective interventions in the prevention of obesity with fetal origins.

Intranasal Insulin Attenuates the Long-Term Adverse Effects of Neonatal Hyperglycemia on the Hippocampus in Rats

Hyperglycemia due to relative hypoinsulinism is common in extremely preterm infants and is associated with hippocampus-mediated long-term cognitive impairment. In neonatal rats, hypoinsulinemic hyperglycemia leads to oxidative stress, altered neurochemistry, microgliosis, and abnormal synaptogenesis in the hippocampus. Intranasal insulin (INS) bypasses the blood-brain barrier, targets the brain, and improves synaptogenesis in rodent models, and memory in adult humans with Alzheimer's disease or type 2 diabetes, without altering the blood levels of insulin or glucose. To test whether INS improves hippocampal development in neonatal hyperglycemia, rat pups were subjected to hypoinsulinemic hyperglycemia by injecting streptozotocin (STZ) at a dose of 80 mg/kg i.p. on postnatal day (P) 2 and randomized to INS, 0.3U twice daily from P3-P6 (STZ + INS group), or no treatment (STZ group). The acute effects on hippocampal neurochemical profile and transcript mRNA expression of insulin receptor (Insr), glucose transporters (Glut1, Glut4, and Glut8), and poly(ADP-ribose) polymerase-1 (Parp1, a marker of oxidative stress) were determined on P7 using in vivo 1H MR spectroscopy (MRS) and qPCR. The long-term effects on the neurochemical profile, microgliosis, and synaptogenesis were determined at adulthood using 1H MRS and histochemical analysis. Relative to the control (CONT) group, mean blood glucose concentration was higher from P3 to P6 in the STZ and STZ + INS groups. On P7, MRS showed 10% higher taurine concentration in both STZ groups. qPCR showed 3-folds higher Insr and 5-folds higher Glut8 expression in the two STZ groups. Parp1 expression was 18% higher in the STZ group and normal in the STZ + INS group. At adulthood, blood glucose concentration in the fed state was higher in the STZ and STZ + INS groups. MRS showed 59% higher brain glucose concentration and histochemistry showed microgliosis in the hippocampal subareas in the STZ group. Brain glucose was normal in the STZ + INS group. Compared with the STZ group, phosphocreatine and phosphocreatine/creatine ratio were higher, and microglia in the hippocampal subareas fewer in the STZ + INS group (p < 0.05 for all). Neonatal hyperglycemia was associated with abnormal glucose metabolism and microgliosis in the adult hippocampus. INS administration during hyperglycemia attenuated these adverse effects and improved energy metabolism in the hippocampus.

Cerebral Effects of Neonatal Dysglycemia

This article summarizes the available evidence reporting the relationship between perinatal dysglycemia and long-term neurodevelopment. We review the physiology of perinatal glucose metabolism and discuss the controversies surrounding definitions of perinatal dysglycemia. We briefly review the epidemiology of hypoglycemia and hyperglycemia in fetal, preterm, and term infants. We discuss potential pathophysiologic mechanisms contributing to dysglycemia and its effect on neurodevelopment. We highlight current strategies to prevent and treat dysglycemia in the context of neurodevelopmental outcomes. Finally, we discuss areas of future research and the potential role of continuous glucose monitoring.

Early Hyperglycemia in Very Preterm Infants Is Associated with Reduced White Matter Volume and Worse Cognitive and Motor Outcomes at 2.5 Years

INTRODUCTION

Hyperglycemia in very preterm infants is associated with increased morbidity and mortality. We aimed to investigate potential associations between early hyperglycemia, neonatal cerebral magnetic resonance imaging (MRI), and neurodevelopment at 2.5 years.

METHODS

The study population included 69 infants with gestational age (GA) 22.3-31.9 weeks (n = 29 with GA <28 weeks), born 2011-2014. Plasma glucose concentrations during the first week were checked according to clinical routines. Hyperglycemia was defined as glucose concentrations above 8.3 mmol/L (150 mg/dL) and above 10 mmol/L (180 mg/dL), respectively, categorized as the highest glucose days 0-2, number of days above 8.3 and 10 mmol/L, and prolonged (yes/no) 2 days or more above 8.3 and 10 mmol/L. The MRI analysis included morphological assessment, regional brain volumes, and assessment of apparent diffusion coefficient (ADC). Neurodevelopmental impairment (NDI) developed in 13 of 67 infants with available outcomes, of which 57 were assessed with the Bayley-III. Univariate and multiple linear and logistic regressions were performed with adjustments for GA, birth weight z-scores, and illness severity expressed as days on mechanical ventilation.

RESULTS

Hyperglycemia above 8.3 mmol/L and 10 mmol/L was present in 47.8% and 31.9% of the infants. Hyperglycemia correlated independently with lower white matter volume, but not with other regional brain volumes, and was also associated with lower ADC values in white matter. Hyperglycemia also correlated with lower Bayley-III cognitive and motor scores in infants with GA <28 weeks, but there was no significant effect on NDI.

CONCLUSION

Early hyperglycemia is associated with white matter injury and poorer neurodevelopment in very preterm infants.

Nutrition and management of glycemia in neonates with neonatal encephalopathy treated with hypothermia

Adequate nutrition and glycemic homeostasis are increasingly recognized as potentially neuroprotective for the developing brain. In the context of hypoxia-ischemia, evidence is scarce regarding optimal nutritional support and administration route, as well as the short- and long-term consequences of such interventions. In this review, we summarize current knowledge on disturbances of brain metabolism of glucose and substrates by hypoxia-ischemia, and compound effects of these mechanisms on brain injury characterized by specific patterns on EEG and MRI. Risks and benefits of nutrition delivery via parenteral or enteral routes are examined. Nutrition could mitigate adverse neurodevelopmental outcomes, and the impact of nutritional strategies and specific nutritional interventions are reviewed. Limited literature highlights the need for further studies to understand the changes in energy metabolism during and after hypoxic-ischemic injury, to optimize nutritional regimens and glucose management, and to inform the neuroprotective role of nutrition.

Long-term behavioral effects observed in mice chronically exposed to static ultra-high magnetic fields

PURPOSE

The primary goal of this study was to investigate whether chronic exposures to ultra-high B₀ fields can induce long-term cognitive, behavioral, or biological changes in C57BL/6 mice.

METHODS

C57BL/6 mice were chronically exposed to 10.5-T or 16.4-T magnetic fields (3-h exposures, two exposure sessions per week, 4 or 8 weeks of exposure). In vivo single-voxel ¹ H magnetic resonance spectroscopy was used to investigate possible neurochemical changes in the hippocampus. In addition, a battery of behavioral tests, including the Morris water-maze, balance-beam, rotarod, and fear-conditioning tests, were used to examine long-term changes induced by B₀ exposures.

RESULTS

Hippocampal neurochemical profile, cognitive, and basic motor functions were not impaired by chronic magnetic field exposures. However, the balance-beam-walking test and the Morris water-maze testing revealed B₀ -induced changes in motor coordination and balance. The tight-circling locomotor behavior during Morris water-maze tests was found as the most sensitive factor indexing B₀ -induced changes. Long-term behavioral changes were observed days or even weeks subsequent to the last B₀ exposure at 16.4 T but not at 10.5 T. Fast motion of mice in and out of the 16.4-T magnet was not sufficient to induce such changes.

CONCLUSION

Observed results suggest that the chronic exposure to a magnetic field as high as 16.4 T may result in long-term impairment of the vestibular system in mice. Although observation of mice may not directly translate to humans, nevertheless, they indicate that studies focused on human safety at very high magnetic fields are necessary.

The Effects of Early-Life Iron Deficiency on Brain Energy Metabolism

Iron deficiency (ID) is one of the most prevalent nutritional deficiencies in the world. Iron deficiency in the late fetal and newborn period causes abnormal cognitive performance and emotional regulation, which can persist into adulthood despite iron repletion. Potential mechanisms contributing to these impairments include deficits in brain energy metabolism, neurotransmission, and myelination. Here, we comprehensively review the existing data that demonstrate diminished brain energetic capacity as a mechanistic driver of impaired neurobehavioral development due to early-life (fetal-neonatal) ID. We further discuss a novel hypothesis that permanent metabolic reprogramming, which occurs during the period of ID, leads to chronically impaired neuronal energetics and mitochondrial capacity in adulthood, thus limiting adult neuroplasticity and neurobehavioral function. We conclude that early-life ID impairs energy metabolism in a brain region- and age-dependent manner, with particularly strong evidence for hippocampal neurons. Additional studies, focusing on other brain regions and cell types, are needed.

The neuroprotective effect and action mechanism of polyphenols in diabetes mellitus-related cognitive dysfunction

BACKGROUND

Diabetes mellitus (DM) is a complex and prevalent metabolic disorder worldwide. Strong evidence has emerged that DM is a risk factor for the accelerated rate of cognitive decline and the development of dementia. Though traditional pharmaceutical agents are efficient for the management of DM and DM-related cognitive decrement, long-term use of these drugs are along with undesired side effects. Therefore, tremendous studies have focused on the therapeutic benefits of natural compounds at present. Ample evidence exists to prove that polyphenols are capable to modulate diabetic neuropathy with minimal toxicity and adverse effects.

PURPOSE

To describe the benefits and mechanisms of polyphenols on DM-induced cognitive dysfunction. In this review, we introduce an updated overview of associations between DM and cognitive dysfunction. The risk factors as well as pathological and molecular mechanisms of DM-induced cognitive dysfunction are summarized. More importantly, many active polyphenols that possess preventive and therapeutic effects on DM-induced cognitive dysfunction and the potential signaling pathways involved in the action are highlighted.

CONCLUSIONS

The therapeutic effects of polyphenols on DM-related cognitive dysfunction pave a novel way for the management of diabetic encephalopathy.

Childhood Metabolic Biomarkers Are Associated with Performance on Cognitive Tasks in Young Children

OBJECTIVE

To evaluate the hypothesis that metabolic measures (fasting glucose, insulin, and Homeostatic Model of Assessment for Insulin Resistance [HOMA-IR] levels) are inversely associated with performance on cognitive tasks using data from young (4- to 6-year-old), typically developing, healthy children.

STUDY DESIGN

Data were obtained from children participating in the Healthy Start study, a pre-birth cohort in Colorado. HOMA-IR, glucose, and insulin values were centered and scaled using the study sample means and SD. Thus, they are reported in number of SD units from the mean. Fully corrected T scores for inhibitory control (Flanker task), cognitive flexibility (Dimensional Change Card Sort test), and receptive language (Picture Vocabulary test) were obtained via the National Institutes of Health Toolbox cognition battery.

RESULTS

Children included in this analysis (n = 137) were 4.6 years old, on average. Per 1-SD unit, fasting glucose (B = -2.0, 95% CI -3.5, -0.5), insulin (B = -1.7, 95% CI -3.0, -0.4), and HOMA-IR values (B = -1.8, 95% CI -3.1, -0.5) were each significantly and inversely associated with inhibitory control (P < .05 for all, respectively). Fasting glucose levels were also inversely associated with cognitive flexibility (B = -2.0, 95% CI -3.7, -0.2, P = .03).

CONCLUSIONS

Our data suggest that metabolic health may impact fluid cognitive function in healthy, young children.

Neonatal hyperglycemia induces CXCL10/CXCR3 signaling and microglial activation and impairs long-term synaptogenesis in the hippocampus and alters behavior in rats

BACKGROUND

Hyperglycemia is common in extremely low gestational age newborns (ELGAN) and is associated with increased mortality and morbidity, including abnormal neurodevelopment. Hippocampus-mediated cognitive deficits are common in this population, but the specific effects of hyperglycemia on the developing hippocampus are not known.

METHODS

The objective of this study was to determine the acute and long-term effects of hyperglycemia on the developing hippocampus in neonatal rats using a streptozotocin (STZ)-induced model of hyperglycemia. STZ was injected on postnatal day (P) 2, and littermates in the control group were injected with an equivalent volume of citrate buffer. The acute effects of hyperglycemia on markers of oxidative stress, inflammatory cytokines, microglial activation, and reactive astrocytosis in the hippocampus were determined in the brain tissue collected on P6. The long-term effects on hippocampus-mediated behavior and hippocampal dendrite structure were determined on P90.

RESULTS

On P6, the transcript and protein expression of markers of oxidative stress and inflammatory cytokines, including the CXCL10/CXCR3 pathway, were upregulated in the hyperglycemia group. Histological evaluation revealed microglial activation and astrocytosis. The long-term assessment on P90 demonstrated abnormal performance in Barnes maze neurobehavioral testing and altered dendrite structure in the hippocampus of formerly hyperglycemic rats.

CONCLUSIONS

Neonatal hyperglycemia induces CXCL10/CXCR3 signaling, microglial activation, and astrocytosis in the rat hippocampus and alters long-term synaptogenesis and behavior. These results may explain the hippocampus-specific cognitive deficits common in ELGAN who experience neonatal hyperglycemia.