Neuroinflammation and Brain Development: Possible Risk Factors in COVID-19-Infected Children.

COVID-19, a disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) betacoronavirus, affects children in a different way than it does in adults, with milder symptoms. However, several cases of neurological symptoms with neuroinflammatory syndromes, such as the multisystem inflammatory syndrome (MIS-C), following mild cases, have been reported. As with other viral infections, such as rubella, influenza, and cytomegalovirus, SARS-CoV-2 induces a surge of proinflammatory cytokines that affect microglial function, which can be harmful to brain development. Along with the viral induction of neuroinflammation, other noninfectious conditions may interact to produce additional inflammation, such as the nutritional imbalance of fatty acids and polyunsaturated fatty acids and alcohol consumption during pregnancy. Additionally, transient thyrotoxicosis induced by SARS-CoV-2 with secondary autoimmune hypothyroidism has been reported, which could go undetected during pregnancy. Together, those factors may pose additional risk factors for SARS-CoV-2 infection impacting mechanisms of neural development such as synaptic pruning and neural circuitry formation. The present review discusses those conditions in the perspective of the understanding of risk factors that should be considered and the possible emergence of neurodevelopmental disorders in COVID-19-infected children.

Neuroinflammatory contribution of microglia and astrocytes in fetal alcohol spectrum disorders.

Ethanol exposure to the fetus during pregnancy can result in fetal alcohol spectrum disorders (FASD). These disorders vary in severity, can affect multiple organ systems, and can lead to lifelong disabilities. Damage to the central nervous system (CNS) is common in FASD, and can result in altered behavior and cognition. The incidence of FASD is alarmingly high, resulting in significant personal and societal costs. There are no cures for FASD. Alcohol can directly alter the function of neurons in the developing CNS. In addition, ethanol can alter the function of CNS glial cells including microglia and astrocytes which normally maintain homeostasis in the CNS. These glial cells can function as resident immune cells in the CNS to protect against pathogens and other insults. However, activation of glia can also damage CNS cells and lead to aberrant CNS function. Ethanol exposure to the developing brain can result in the activation of glia and neuroinflammation, which may contribute to the pathology associated with FASD. This suggests that anti-inflammatory agents may be effective in the treatment of FASD.

Transgenerational inheritance of fetal alcohol exposure adverse effects on immune gene interferon-ϒ.

BACKGROUND: Alcohol exposures in utero have been shown to alter immune system functions in the offspring which persists into adulthood. However, it is not apparent why the in utero alcohol effect on the immune system persists into adulthood of fetal alcohol-exposed offspring. The objective of this study was to determine the long-term effects of fetal alcohol exposure on the production of interferon-ϒ (IFN-ϒ), a cytokine known to regulate both innate and adaptive immunity. METHODS: Isogenic Fisher 344 rats were bred to produce pregnant dams, which were fed with a liquid diet containing 6.7% alcohol between gestation days 7 and 21 and pair-fed with an isocaloric liquid diet or fed ad libitum with rat chow; their male and female offspring were used for the study. F1-F3 generation rats were used when they were 2 to 3 months old. Fetal alcohol exposure effects on the Ifn-ɣ gene was determined by measuring the gene promoter methylation and mRNA and protein expression in the spleen. Additionally, transgenerational studies were conducted to evaluate the germline-transmitted effects of fetal alcohol exposure on the Ifn-ɣ gene. RESULTS: Fetal alcohol exposure reduced the expression of Ifn-ɣ mRNA and IFN-ϒ protein while it increased the proximal promoter methylation of the Ifn-ɣ gene in both male and female offspring during the adult period. Transgenerational studies revealed that the reduced levels of Ifn-ɣ expression and increased levels of its promoter methylation persisted only in F2 and F3 generation males derived from the male germ line. CONCLUSION: Overall, these findings provide the evidence that fetal alcohol exposures produce an epigenetic mark on the Ifn-ɣ gene that passes through multiple generations via the male germ line. These data provide the first evidence that the male germ line transmits fetal alcohol exposure's adverse effects on the immune system.

Adverse health outcomes associated with fetal alcohol exposure: A systematic review focused on immune-related outcomes.

Prenatal alcohol exposure (PAE) has well-known teratogenic effects on the developing fetus, potentially resulting in neurologic impairments. However, there is increasing interest regarding other potential adverse health outcomes related to prenatal alcohol exposure. The objective of this study was to undertake a systematic review to identify all the available clinical and preclinical literature investigating immune-related outcomes in offspring with PAE. A systematic review searching four electronic databases (PubMed, CINAHL, Web of Science, and Embase) was conducted. Potential articles were screened against strict inclusion/exclusion criteria. This review specifically focused on evaluating studies related to immune-related outcomes following PAE. Twelve clinical studies were included in the current review. Six included allergy outcomes, four included infection outcomes, and two studies included both. Thirty-nine preclinical studies were identified examining a wide range of immune outcomes. The current review provides some preliminary clinical evidence that PAE can influence immune function, including atopic allergy and infection outcomes. However, there was variability in results across studies, particularly in the atopy area. Preclinical studies demonstrated some changes in lymphocytes and cytokines in offspring following PAE. More research investigating the effects of PAE on immune responses is warranted.

Role of zinc insufficiency in fetal alveolar macrophage dysfunction and RSV exacerbation associated with fetal ethanol exposure.

BACKGROUND: We previously reported that maternal alcohol use significantly increases the risk of sepsis in premature and term newborns. In the mouse, fetal ethanol exposure results in an immunosuppressed phenotype for the alveolar macrophage (AM) and decreases bacterial phagocytosis. In pregnant mice, ethanol decreased AM zinc homeostasis, which contributed to immunosuppression and impaired AM phagocytosis. In this study, we explored whether ethanol-induced zinc insufficiency extended to the pup AMs and contributed to immunosuppression and exacerbated viral lung infections. METHODS: C57BL/6 female mice were fed a liquid diet with 25% ethanol-derived calories or pair-fed a control diet with 25% of calories as maltose-dextrin. Some pup AMs were treated in vitro with zinc acetate before measuring zinc pools or transporter expression and bacteria phagocytosis. Some dams were fed additional zinc supplements in the ethanol or control diets, and then we assessed pup AM zinc pools, zinc transporters, and the immunosuppressant TGFß1. On postnatal day 10, some pups were given intranasal saline or respiratory syncytial virus (RSV), and then AM RSV phagocytosis and the RSV burden in the airway lining fluid were assessed. RESULTS: Fetal ethanol exposure decreased pup AM zinc pools, zinc transporter expression, and bacterial clearance, but in vitro zinc treatments reversed these alterations. In addition, the expected ethanol-induced increase in TGFß1 and immunosuppression were associated with decreased RSV phagocytosis and exacerbated RSV infections. However, additional maternal zinc supplements blocked the ethanol-induced perturbations in the pup AM zinc homeostasis and TGFß1 immunosuppression, thereby improving RSV phagocytosis and attenuating the RSV burden in the lung. CONCLUSION: These studies suggest that, despite normal maternal dietary zinc intake, in utero alcohol exposure results in zinc insufficiency, which contributes to compromised neonatal AM immune functions, thereby increasing the risk of bacterial and viral infections.

Maternal alcohol binge drinking induces persistent neuroinflammation associated with myelin damage and behavioural dysfunctions in offspring mice.

Alcohol binge drinking is on the increase in the young adult population, and consumption during pregnancy can be deleterious for foetal development. Maternal alcohol consumption leads to a wide range of long-lasting morphological and behavioural deficiencies known as foetal alcohol spectrum disorders (FASD), associated with neurodevelopmental disabilities. We sought to test the effects of alcohol on neuroimmune system activation and its potential relation to alcohol-induced neurodevelopmental and persistent neurobehavioural effects in offspring after maternal alcohol binge drinking during the prenatal period or in combination with lactation. Pregnant C57BL/6 female mice underwent a procedure for alcohol binge drinking either during gestation or both the gestation and lactation periods. Adult male offspring were assessed for cognitive functions and motor coordination. Early alcohol exposure induced motor coordination impairments in the rotarod test. Object recognition memory was not affected by maternal alcohol binge drinking, but Y-maze performance was impaired in pre- and early postnatal alcohol-exposed mice. Behavioural effects were associated with an upregulation of pro-inflammatory signalling (Toll-like receptor 4, nuclear factor-kappa B p65, NOD-like receptor protein 3, caspase-1, and interleukin-1ß), gliosis, neuronal cell death and a reduction in several structural myelin proteins (myelin-associated glycoprotein, myelin basic protein, myelin proteolipid protein and myelin regulatory factor) in both the prefrontal cortex and hippocampus of adult mice exposed to alcohol. Altogether, our results reveal that maternal binge-like alcohol consumption induces neuroinflammation and myelin damage in the brains of offspring and that such effects may underlie the persistent cognitive and behavioural impairments observed in FASD.

Neurotrophins in the Brain: Interaction With Alcohol Exposure During Development.

Fetal alcohol spectrum disorders (FASDs) are a result of the teratogenic effects of alcohol on the developing fetus. Decades of research examining both individuals with FASDs and animal models of developmental alcohol exposure have revealed the devastating effects of alcohol on brain structure, function, behavior, and cognition. Neurotrophic factors have an important role in guiding normal brain development and cellular plasticity in the adult brain. This chapter reviews the current literature showing that alcohol exposure during the developmental period impacts neurotrophin production and proposes avenues through which alcohol exposure and neurotrophin action might interact. These areas of overlap include formation of long-term potentiation, oxidative stress processes, neuroinflammation, apoptosis and cell loss, hippocampal adult neurogenesis, dendritic morphology and spine density, vasculogenesis and angiogenesis, and behaviors related to spatial memory, anxiety, and depression. Finally, we discuss how neurotrophins have the potential to act in a compensatory manner as neuroprotective molecules that can combat the deleterious effects of in utero alcohol exposure.

Inflammatory responses to alcohol in the CNS: nuclear receptors as potential therapeutics for alcohol-induced neuropathologies.

Fetal alcohol spectrum disorder (FASD), which results from ethanol exposure during pregnancy, and alcohol use disorder (AUD), which includes both binge and chronic alcohol abuse, are strikingly common and costly at personal and societal levels. These disorders are associated with significant pathology, including that observed in the CNS. It is now appreciated in both humans and animal models that ethanol can induce inflammation in the CNS. Neuroinflammation is hypothesized to contribute to the neuropathologic and behavioral consequences in FASD and AUD. In this review, we: 1) summarize the evidence of alcohol-induced CNS inflammation, 2) outline cellular and molecular mechanisms that may underlie alcohol induction of CNS inflammation, and 3) discuss the potential of nuclear receptor agonists for prevention or treatment of neuropathologies associated with FASD and AUD.

Neonatal binge alcohol exposure increases microglial activation in the developing rat hippocampus.

Aberrant activation of the developing immune system can have long-term negative consequences on cognition and behavior. Teratogens, such as alcohol, activate microglia, the brain's resident immune cells, which could contribute to the lifelong deficits in learning and memory observed in humans with Fetal Alcohol Spectrum Disorders (FASD) and in rodent models of FASD. The current study investigates the microglial response of the brain 24 h following neonatal alcohol exposure (postnatal days (PDs) 4-9, 5.25 g/kg/day). On PD10, microglial cell counts and area of cell territory were assessed using unbiased stereology in the hippocampal subfields CA1, CA3 and dentate gyrus (DG), and hippocampal expression of pro- and anti-inflammatory genes was analyzed. A significant decrease in microglial cell counts in CA1 and DG was found in alcohol-exposed and sham-intubated (SI) animals compared to undisturbed suckle controls (SCs), suggesting overlapping effects of alcohol exposure and intubation alone on the neuroimmune response. Cell territory was decreased in alcohol-exposed animals in CA1, CA3, and DG compared to controls, suggesting the microglia have shifted to a more activated state following alcohol treatment. Furthermore, both alcohol-exposed and SI animals had increased levels of pro-inflammatory cytokines IL-1ß, TNF-α, CD11b, and CCL4; in addition, CCL4 was significantly increased in alcohol-exposed animals compared to SI as well. Alcohol-exposed animals also showed increased levels of anti-inflammatory cytokine TGF-ß compared to both SI and SCs. In summary, the number and activation of microglia in the neonatal hippocampus are both affected in a rat model of FASD, along with increased gene expression of pro- and anti-inflammatory cytokines. This study shows that alcohol exposure during development induces a neuroimmune response, potentially contributing to long-term alcohol-related changes to cognition, behavior and immune function.

Prenatal Alcohol Exposure and the Developing Immune System.

Evidence from research in humans and animals suggest that ingesting alcohol during pregnancy can disrupt the fetal immune system and result in an increased risk of infections and disease in newborns that may persist throughout life. Alcohol may have indirect effects on the immune system by increasing the risk of premature birth, which itself is a risk factor for immune-related problems. Animal studies suggest that alcohol exposure directly disrupts the developing immune system. A comprehensive knowledge of the mechanisms underlying alcohol's effects on the developing immune system only will become clear once researchers establish improved methods for identifying newborns exposed to alcohol in utero.

Fetal alcohol spectrum disorders and neuroimmune changes.

The behavioral consequences of fetal alcohol spectrum disorders (FASD) are serious and persist throughout life. The causative mechanisms underlying FASD are poorly understood. However, much has been learned about FASD from human structural and functional studies as well as from animal models, which have provided a greater understanding of the mechanisms underlying FASD. Using animal models of FASD, it has been recently discovered that ethanol induces neuroimmune activation in the developing brain. The resulting microglial activation, production of proinflammatory molecules, and alteration in expression of developmental genes are postulated to alter neuron survival and function and lead to long-term neuropathological and cognitive defects. It has also been discovered that microglial loss occurs, reducing microglia's ability to protect neurons and contribute to neuronal development. This is important, because emerging evidence demonstrates that microglial depletion during brain development leads to long-term neuropathological and cognitive defects. Interestingly, the behavioral consequences of microglial depletion and neuroimmune activation in the fetal brain are particularly relevant to FASD. This chapter reviews the neuropathological and behavioral abnormalities of FASD and delineates correlates in animal models. This serves as a foundation to discuss the role of the neuroimmune system in normal brain development, the consequences of microglial depletion and neuroinflammation, the evidence of ethanol induction of neuroinflammatory processes in animal models of FASD, and the development of anti-inflammatory therapies as a new strategy for prevention or treatment of FASD. Together, this knowledge provides a framework for discussion and further investigation of the role of neuroimmune processes in FASD.

Neuroimmune mechanisms in fetal alcohol spectrum disorder.

Fetal alcohol spectrum disorder (FASD) is a major health concern worldwide and results from maternal consumption of alcohol during pregnancy. It produces tremendous individual, social, and economic losses. This review will first summarize the structural, functional, and behavior changes seen in FASD. The development of the neuroimmune system will be then be described with particular emphasis on the role of microglial cells in the normal regulation of homeostatic function in the central nervous system (CNS) including synaptic transmission. The impact of alcohol on the neuroimmune system in the developing CNS will be discussed in the context of several key immune molecules and signaling pathways involved in neuroimmune mechanisms that contribute to FASD. This review concludes with a summary of the development of early therapeutic approaches utilizing immunosuppressive drugs to target alcohol-induced pathologies. The significant role played by neuroimmune mechanisms in alcohol addiction and pathology provides a focus for future research aimed at understanding and treating the consequences of FASD.

Fetal exposure to ethanol has long-term effects on the severity of influenza virus infections.

Alcohol use by pregnant women is a significant public health issue despite well-described risks to the fetus including physical and intellectual growth retardation and malformations. Although clinical studies are limited, they suggest that in utero alcohol exposure also results in significant immune deficiencies in naive neonates. However, little is known about fetal alcohol exposure (FAE) effects on adult infections. Therefore, to determine the long-term effects of FAE on disease susceptibility and the adult immune system, we infected FAE adult mice with influenza virus. In this study, we demonstrate that mice exposed to ethanol during gestation and nursing exhibit enhanced disease severity as well as increased and sustained pulmonary viral titers following influenza virus infection. Secondary exposure to alcohol as an adult further exacerbates these effects. Moreover, we demonstrate that FAE mice have impaired adaptive immune responses, including decreased numbers of virus-specific pulmonary CD8 T cells, a decreased size and frequency of pulmonary B cell foci, and reduced production of influenza-specific Ab following influenza infection. Together, our results suggest that FAE induces significant and long-term defects in immunity and susceptibility to influenza virus infection and that FAE individuals could be at increased risk for severe and fatal respiratory infections.

Prenatal alcohol exposure and fetal programming: effects on neuroendocrine and immune function.

Alcohol abuse is known to result in clinical abnormalities of endocrine function and neuroendocrine regulation. However, most studies have been conducted on males. Only recently have studies begun to investigate the influence of alcohol on endocrine function in females and, more specifically, endocrine function during pregnancy. Alcohol-induced endocrine imbalances may contribute to the etiology of fetal alcohol syndrome. Alcohol crosses the placenta and can directly affect developing fetal cells and tissues. Alcohol-induced changes in maternal endocrine function can disrupt maternal-fetal hormonal interactions and affect the female's ability to maintain a successful pregnancy, thus indirectly affecting the fetus. In this review, we focus on the adverse effects of prenatal alcohol exposure on neuroendocrine and immune function, with particular emphasis on the hypothalamic-pituitary-adrenal (HPA) axis and the concept of fetal programming. The HPA axis is highly susceptible to programming during fetal development. Early environmental experiences, including exposure to alcohol, can reprogram the HPA axis such that HPA tone is increased throughout life. We present data that demonstrate that maternal alcohol consumption increases HPA activity in both the maternal female and the offspring. Increased exposure to endogenous glucocorticoids throughout the lifespan can alter behavioral and physiologic responsiveness and increase vulnerability to illnesses or disorders later in life. Alterations in immune function may be one of the long-term consequences of fetal HPA programming. We discuss studies that demonstrate the adverse effects of alcohol on immune competence and the increased vulnerability of ethanol-exposed offspring to the immunosuppressive effects of stress. Fetal programming of HPA activity may underlie some of the long-term behavioral, cognitive, and immune deficits that are observed following prenatal alcohol exposure.

Fetal alcohol exposure attenuates interleukin-1beta-induced fever: neuroimmune mechanisms.

Central mechanisms for the attenuating effects of fetal alcohol exposure (FAE) on interleukin-1beta (IL-1beta)-induced fever were studied in adult male offspring of dams fed a liquid diet supplemented with ethanol (E), in pair-fed (P) control and in normal (N) offspring. Hypothalamic levels of IL-1 were significantly lower in E than in N rats at 2 h, but not at 4 and 6 h, after intraperitoneal administration of lipopolysaccharide. Fever induced by intracerebroventricular (i.c.v.) IL-1 was significantly lower in E than in N and P rats. In contrast, E rats showed a normal febrile response to i.c.v. prostaglandin-E2. Thus, whereas FAE does not affect central thermoregulatory mechanisms, per se, FAE alters the kinetics of hypothalamic IL-1 production/appearance and decreases the responsiveness of central mechanisms which mediate the febrile response to IL-1.

Effects of in utero alcohol exposure on B cell development in neonatal spleen and bone marrow.

The effects of in utero alcohol exposure on neonatal lymphopoiesis were examined in a murine model of fetal alcohol syndrome. At birth, both immature and mature B cells were decreased in the spleens of neonatal animals and these subpopulations of B cells did not recover to normal levels until 3-4 weeks of life. Pre-B cells and total B cells were decreased as well in the bone marrow of ethanol-exposed animals. By 3-4 weeks of life, the number of B cells in the bone marrow recovered to normal levels, but the pre-B cells remained below normal levels through 5 weeks of age. Furthermore, a recently described early B cell progenitor was reduced in frequency in ethanol-exposed neonates. Together, these data suggest that in utero exposure to ethanol can result in abnormalities in B cell development that may initiate at an early stage of B cell development.

Effects of in utero alcohol exposure on B-cell development in the murine fetal liver.

Fetal alcohol syndrome is one of the leading causes of birth defects in this country. Children exposed to alcohol in utero suffer from growth and mental retardation, physical abnormalities, and immune dysfunction. Previous work from this laboratory demonstrated that B lymphopoiesis is delayed in mice exposed to alcohol in utero. The deficit in B-cell development was apparent shortly after birth and extended to well after weaning. Because lymphopoiesis begins in the fetal liver, the current study was done to determine if fetal B-cell development was affected as well by in utero exposure to alcohol. We now show that the effects of in utero alcohol exposure on B lymphopoiesis do not become apparent until late in gestation. Flow cytometry was used to enumerate several intermediates in the B-cell developmental pathway. These phenotypic analyses showed that before day 17 of gestation, B-lineage intermediates developed normally when compared with control animals. However, between days 17 and 18 of gestation, an abnormality in the population dynamics of B-lineage intermediates became apparent in the fetal liver of alcohol-exposed mice. Early intermediates in the B-cell developmental pathway were present in normal numbers; however, the more mature progenitors as well as B cells were decreased in number by gestational day 18. These data suggest that in utero alcohol exposure disrupts the ability of B-lineage intermediates to progress along the developmental pathway to maturity, thereby leaving the animal immunocompromised at birth.

Chronic and acute prenatal and postnatal ethanol exposure on lymphocyte subsets from offspring thymic, splenic, and intestinal intraepithelial sources.

The overall objective of this study was to analyze the effects of a combined prenatal and postnatal (entire gestational human chronic drinking model) ethanol exposure on T-cell development in mice. Specifically, this study evaluated the effects of chronic exposure to prenatal ethanol on lymphocyte makeup and proliferative capabilities of postnatal offspring's (4 and 12 weeks) peripheral lymphoid tissues. Chronic exposure regimens were conducted over the entire gestational period and through postnatal day 14 or 21. Thymus, spleen, and intestinal intraepithelial lymphocytes were harvested and analyzed by flow cytometry for percentages of T-cell subsets. Splenic lymphocytes were also analyzed for their ability to proliferate in response to a T-cell mitogen. Limited effects of chronic ethanol exposure were seen.