Effect of multiple neonatal sevoflurane exposures on hippocampal apolipoprotein E levels and learning and memory abilities

Complement C1q-mediated microglial synaptic elimination by enhancing desialylation underlies sevoflurane-induced developmental neurotoxicity

BACKGROUND

Repeated neonatal sevoflurane exposures led to neurocognitive disorders in young mice. We aimed to assess the role of microglia and complement C1q in sevoflurane-induced neurotoxicity and explore the underlying mechanisms.

METHODS

Neonatal mice were treated with sevoflurane on postnatal days 6, 8, and 10, and the Morris water maze was performed to assess cognitive functions. For mechanistic explorations, mice were treated with minocycline, C1q-antibody ANX005, and sialidase-inhibitor N-acetyl-2,3-dehydro-2-deoxyneuraminic acid (NADNA) before sevoflurane exposures. Western blotting, RT-qPCR, Golgi staining, 3D reconstruction and engulfment analysis, immunofluorescence, and microglial morphology analysis were performed. In vitro experiments were conducted in microglial cell line BV2 cells.

RESULTS

Repeated neonatal sevoflurane exposures resulted in deficiencies in learning and cognition of young mice, accompanied by microglial activation and synapse loss. Sevoflurane enhanced microglia-mediated synapse elimination through C1q binding to synapses. Inhibition of microglial activation and phagocytosis with minocycline significantly reduced the loss of synapses. We further revealed the involvement of neuronal sialic acids in this process. The enhanced activity of sialidase by sevoflurane led to the loss of sialic acids, which facilitated C1q binding to synapses. Inhibition of C1q with ANX005 or inhibition of sialidase with NADNA significantly rescued microglia-mediated synapse loss and improved neurocognitive function. Sevoflurane enhanced the engulfment of BV2 cells, which was reversed by ANX005.

CONCLUSIONS

Our findings demonstrated that C1q-mediated microglial synaptic elimination by enhancing desialylation contributed to sevoflurane-induced developmental neurotoxicity. Inhibition of C1q or sialidase may be a potential therapeutic strategy for this neurotoxicity.

The Effects of Propofol on a Human in vitro Blood-Brain Barrier Model

Background

Recently, the safety of repeated and lengthy anesthesia administration has been called into question, a subset of these animal studies demonstrated that anesthetics induced blood-brain barrier (BBB) dysfunction. The BBB is critical in protecting the brain parenchyma from the surrounding micro-vasculature. BBB breakdown and dysfunction has been observed in several neurodegenerative diseases and may contribute to both the initiation and the progression of the disease. In this study we utilize a human induced pluripotent stem cell (iPSC) derived-BBB model, exhibiting near in vivo properties, to evaluate the effects of anesthetics on critical barrier properties.

Methods

iPSC-derived brain microvascular endothelial cells (BMECs) expressed near in vivo barrier tightness assessed by trans-endothelial electrical resistance and para-cellular permeability. Efflux transporter activity was determined by substrate transport in the presence of specific inhibitors. Trans-cellular transport was measured utilizing large fluorescently tagged dextran. Tight junction localization in BMECs was evaluated with fluorescent microscopy. The anesthetic, propofol was exposed to BMECs at varying durations and concentrations and BBB properties were monitored post-exposure.

Results

Following propofol exposure, BMECs displayed reduced resistance and increased permeability indicative of a leaky barrier. Reduced barrier tightness and the dysregulation of occludin, a tight junction protein, were partly the result of an elevation in matrix metalloproteinase (MMP) levels. Efflux transporter activity and trans-cellular transport were unaffected by propofol exposure. Propofol induced barrier dysfunction was partially restored following matrix metalloproteinase inhibition.

Conclusion

For the first time, we have demonstrated that propofol alters BBB integrity utilizing a human in vitro BBB model that displays key in vivo characteristics. A leaky BBB enables otherwise impermeable molecules such as pathogens and toxins the ability to reach vulnerable cell types of the brain parenchyma. A robust human in vitro BBB model will allow for the evaluation of several anesthetics at fluctuating clinical scenarios and to elucidate mechanisms with the goal of ultimately improving anesthesia safety.

Neonatal Anesthesia and Oxidative Stress

Neonatal anesthesia, while often essential for surgeries or imaging procedures, is accompanied by significant risks to redox balance in the brain due to the relatively weak antioxidant system in children. Oxidative stress is characterized by concentrations of reactive oxygen species (ROS) that are elevated beyond what can be accommodated by the antioxidant defense system. In neonatal anesthesia, this has been proposed to be a contributing factor to some of the negative consequences (e.g., learning deficits and behavioral abnormalities) that are associated with early anesthetic exposure. In order to assess the relationship between neonatal anesthesia and oxidative stress, we first review the mechanisms of action of common anesthetic agents, the key pathways that produce the majority of ROS, and the main antioxidants. We then explore the possible immediate, short-term, and long-term pathways of neonatal-anesthesia-induced oxidative stress. We review a large body of literature describing oxidative stress to be evident during and immediately following neonatal anesthesia. Moreover, our review suggests that the short-term pathway has a temporally limited effect on oxidative stress, while the long-term pathway can manifest years later due to the altered development of neurons and neurovascular interactions.

Early Development of the GABAergic System and the Associated Risks of Neonatal Anesthesia

Human and animal studies have elucidated the apparent neurodevelopmental effects resulting from neonatal anesthesia. Observations of learning and behavioral deficits in children, who were exposed to anesthesia early in development, have instigated a flurry of studies that have predominantly utilized animal models to further interrogate the mechanisms of neonatal anesthesia-induced neurotoxicity. Specifically, while neonatal anesthesia has demonstrated its propensity to affect multiple cell types in the brain, it has shown to have a particularly detrimental effect on the gamma aminobutyric acid (GABA)ergic system, which contributes to the observed learning and behavioral deficits. The damage to GABAergic neurons, resulting from neonatal anesthesia, seems to involve structure-specific changes in excitatory-inhibitory balance and neurovascular coupling, which manifest following a significant interval after neonatal anesthesia exposure. Thus, to better understand how neonatal anesthesia affects the GABAergic system, we first review the early development of the GABAergic system in various structures that have been the focus of neonatal anesthesia research. This is followed by an explanation that, due to the prolonged developmental curve of the GABAergic system, the entirety of the negative effects of neonatal anesthesia on learning and behavior in children are not immediately evident, but instead take a substantial amount of time (years) to fully develop. In order to address these concerns going forward, we subsequently offer a variety of in vivo methods which can be used to record these delayed effects.

Sevoflurane Sedation with AnaConDa-S Device for a Child Undergoing Extracorporeal Membrane Oxygenation

Background

Deep sedation in critically ill children undergoing extracorporeal membrane oxygenation (ECMO) can be challenging. Volatile anesthetics like sevoflurane can be a good alternative for patients hospitalized in pediatric intensive care units, in whom adequate sedation is difficult to obtain.

Case Description

We report here the first pediatric case of a patient under extracorporeal membrane oxygenation receiving sedation by sevoflurane using the AnaConDa-S device. This 2-year-old girl, suffering from congenital diaphragmatic hernia, was put on extracorporeal membrane oxygenation due to a persistent pulmonary hypertension following metapneumovirus infection. Despite high doses of drugs, neither satisfactory sedation nor analgesia could be reached. Sevoflurane allowed her to be released and we were able to wean her from certain drugs. Her physiological parameters and the indicators of pain and sedation improved.

Conclusion

Anesthesia using sevoflurane with the AnaConDa-S device is efficient for children under ECMO.

Clinical significance

This is the first pediatric report on anesthesia with sevoflurane under ECMO.

How to cite this article

Soreze Y, Piloquet J-E, Amblard A, Constan I, Rambaud J, Leger P-L. Sevoflurane Sedation with AnaConDa-S Device for a Child Undergoing Extracorporeal Membrane Oxygenation. Indian J Crit Care Med 2020;24(7):596–598.

Effects of neonatal isoflurane anesthesia exposure on learning-specific and sensory systems in adults

Millions of children undergo general anesthesia each year, and animal and human studies have indicated that exposure to anesthesia at an early age can impact neuronal development, leading to behavioral and learning impairments that manifest later in childhood and adolescence. Here, we examined the effects of isoflurane, a commonly-used general anesthetic, which was delivered to newborn rabbits. Trace eyeblink classical conditioning was used to assess the impact of neonatal anesthesia exposure on behavioral learning in adolescent subjects, and a variety of MRI techniques including fMRI, MR volumetry, spectroscopy and DTI captured functional, metabolic, and structural changes in key regions of the learning and sensory systems associated with anesthesia-induced learning impairment. Our results demonstrated a wide array of changes that were specific to anesthesia-exposed subjects, which supports previous studies that have pointed to a link between early anesthesia exposure and the development of learning and behavioral deficiencies. These findings point to the need for caution in avoiding excessive use of general anesthesia in young children and neonates.

Protective effects of Coenzyme Q10 against sevoflurane-induced cognitive impairment through regulating apolipoprotein E and phosphorylated Tau expression in young mice

Children with multiple exposures to anesthesia and surgery may be more likely to develop the learning disability. Coenzyme Q10 (CoQ10) was reported to reduce the multiple sevoflurane treatment-induced cognitive deficiency in 6-day-old young mice. However, its specific mechanisms have not yet been found. This research aimed to reveal the role of ApoE in the pathogenesis of cognitive deficiency caused by sevoflurane anesthesia and the protective mechanism of CoQ10 in a multiple sevoflurane treatment model of young mice. The mice were randomly divided into four groups: Control + corn oil, Sevoflurane + corn oil, Control + CoQ10, and Sevoflurane + CoQ10. Sevoflurane group mice were anesthetized with 3% sevoflurane and 60% oxygen 2 hr a day for 3 days, while control group mice received only 60% oxygen. Mice received an intraperitoneal injection of 50 mg/kg CoQ10 or the same volume of corn oil 30 min before the inhalation of oxygen or sevoflurane for 3 days. Mice received sevoflurane anesthesia or control treatment from the 6th to 8th day after birth. The cortex and hippocampus were harvested on the 8th day. The ATP, MMP, ApoE mRNA, total ApoE, ApoE fragments, Aβ1-40, Aβ1-42, Tau5, AT8, and PHF levels were detected. The Morris water maze (MWM) tests were performed from P30 to p36 after anesthesia or control treatment. The results indicated that the injection of CoQ10 ahead of sevoflurane treatment could reverse the anesthesia-induced energy deficiency, mitochondrial dysfunction, ApoE, and its fragments expression, Aβ1-42 generation, Tau phosphorylation, and cognitive impairment in young mice. These data reveal that the ApoE and its fragments enhancement may play an important role in the pathogenesis of cognitive deficiency caused by sevoflurane anesthesia. CoQ10 could reduce ApoE expression by improving energy replenishment and mitochondrial functions, thereby alleviating sevoflurane-induced brain damage and cognitive impairment.

Coenzyme Q10 alleviates sevoflurane‑induced neuroinflammation by regulating the levels of apolipoprotein E and phosphorylated tau protein in mouse hippocampal neurons

Sevoflurane may exert neurotoxic effects on the developing brain. Coenzyme Q10 (CoQ10) has been reported to reduce sevoflurane anesthesia-induced cognitive deficiency in 6-day-old mice. However, its specific mechanisms remain unknown. Apolipoprotein E (ApoE) has been reported to lead to the initiation of neurodegeneration in patients with Alzheimer's disease (AD) and may serve an important role in anesthesia-induced neurotoxicity. The present study aimed to reveal the role of ApoE in the pathogenesis of tau protein hyperphosphorylation and neuroinflammation enhancement caused by sevoflurane anesthesia, as well as the protective mechanism of CoQ10 in an anesthetic sevoflurane treatment model of primary mouse hippocampal neurons. For that purpose, the neurons were randomly assigned to the following groups: i) Control; ii) sevoflurane; iii) control+corn oil; iv) sevoflurane+corn oil; v) control+CoQ10; and vi) control+CoQ10. CoQ10 or corn oil alone was added to the medium on day 4 of neuron culture. The neurons in the sevoflurane group were treated with 21% O₂, 5% CO₂ and 4.1% sevoflurane for 4 h, whereas the control group only with 21% O₂ and 5% CO₂ on day 5. Samples were collected immediately after anesthesia or control treatment. ATP, superoxidase dismutase (SOD)1, ApoE mRNA, total ApoE, full-length ApoE, ApoE fragments, Tau5, Tau-PS202/PT205 (AT8), Tau-PSer396/404 (PHF1), tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β levels were measured with ELISA, quantitative PCR, western blotting and immunocytochemistry. The results of the present study indicated that sevoflurane anesthesia significantly decreased the ATP and SOD levels, but increased ApoE mRNA, total ApoE protein, full-length ApoE, ApoE fragments, phosphorylated tau (AT8 and PHF1) and neuroinflammatory factor (TNF-α, IL-6 and IL-1β) expression levels compared with those in the control group. The use of CoQ10 reversed the expression of these factors. These results suggested that sevoflurane treatment damaged mouse hippocampal neurons, which may be associated with the expression of ApoE and its toxic fragments. CoQ10 improved energy replenishment and inhibited oxidative stress, which may lead to a decrease in ApoE and phosphorylated tau protein expression, thus mitigating the sevoflurane-induced neuroinflammation in mouse hippocampal neurons.

Impact of anesthesia exposure in early development on learning and sensory functions

Each year, millions of children undergo anesthesia, and both human and animal studies have indicated that exposure to anesthesia at an early age can lead to neuronal damage and learning deficiency. However, disorders of sensory functions were not reported in children or animals exposed to anesthesia during infancy, which is surprising, given the significant amount of damage to brain tissue reported in many animal studies. In this review, we discuss the relationship between the systems in the brain that mediate sensory input, spatial learning, and classical conditioning, and how these systems could be affected during anesthesia exposure. Based on previous reports, we conclude that anesthesia can induce structural, functional, and compensatory changes in both sensory and learning systems. Changes in myelination following anesthesia exposure were observed as well as the neurodegeneration in the gray matter across variety of brain regions. Disproportionate cell death between excitatory and inhibitory cells induced by anesthesia exposure can lead to a long-term shift in the excitatory/inhibitory balance, which affects both learning-specific networks and sensory systems. Anesthesia may directly affect synaptic plasticity which is especially critical to learning acquisition. However, sensory systems appear to have better ability to compensate for damage than learning-specific networks.