Regional and temporal profiles of calpain and caspase-3 activities in postnatal rat brain following repeated propofol administration

Effect of sevoflurane anesthesia to neonatal rat hippocampus by RNA-seq

BACKGROUND

Sevoflurane is an inhalational anesthetic for the induction and maintenance of general anesthesia in pediatric surgery. However, few studies have paid attention to the multiple organ toxicity and the mechanism behind it.

METHODS

Inhalation anesthesia neonatal rat model were realized by exposing to 3.5% sevoflurane. RNA-seq was performed to find out how inhalation anesthesia affects the lung, cerebral cortex, hippocampus, and heart. Validation of RNA-seq results by QPCR after animal model establishment. Tunel assay detects cell apoptosis in each group. CCK-8, cell apoptosis assay and western blot assay validation of the role of siRNA-Bckdhb in the action of sevoflurane on rat hippocampal neuronal cells.

RESULTS

There are significant differences between different groups, especially the hippocampus and cerebral cortex. Bckdhb was significantly up-regulated in the hippocampus with sevoflurane-treated. Pathway analysis revealed several abundant pathways related to DEGs, e.g., protein digestion and absorption and PI3K-Akt signaling pathway. A series of cellular and animal experiments showed that siRNA-Bckdhb can inhibit the reduction of cellular activity caused by sevoflurane.

CONCLUSION

Bckdhb interference experiments indicated that sevoflurane induces hippocampal neuronal cells apoptosis by regulating Bckdhb expression. Our study provided new insights into the molecular mechanism of sevoflurane-induced brain damage in pediatrics.

Propofol-Induced Developmental Neurotoxicity: From Mechanisms to Therapeutic Strategies

Propofol is the most commonly used intravenous general anesthetic in clinical anesthesia, and it is also widely used in general anesthesia for pregnant women and infants. Some clinical and preclinical studies have found that propofol causes damage to the immature nervous system, which may lead to neurodevelopmental disorders and cognitive dysfunction in infants and children. However, its potential molecular mechanism has not been fully elucidated. Recent in vivo and in vitro studies have found that some exogenous drugs and interventions can effectively alleviate propofol-induced neurotoxicity. In this review, we focus on the relevant preclinical studies and summarize the latest findings on the potential mechanisms and therapeutic strategies of propofol-induced developmental neurotoxicity.

Calpain-TRPC6 signaling pathway contributes to propofol-induced developmental neurotoxicity in rats

Growing animal studies suggest a risk of neuronal damage following early childhood exposure to anesthesia and sedation drugs including propofol. Inhibition of transient receptor potential canonical 6 (TRPC6) degradation has been shown to protect neurons from neuronal damage induced by multiple brain injury models. Our aim was to investigate whether calpain-TRPC6 pathway is a target in propofol-induced neurotoxicity. Postnatal day (PND) 7 rats were exposed to five bolus injections of 25 mg/kg propofol or 10 % intralipid at hourly intervals. Neuronal injury was assessed by the expression pattern of TUNEL staining and cleaved-caspase-3. The Morris water maze test was used to evaluate learning and memory functions in later life. Pretreatments consisting of intracerebroventricular injections of a TRPC6 agonist, TRPC6 inhibitor, or calpain inhibitor were used to confirm the potential role of the calpain-TRPC6 pathway in propofol-induced neurotoxicity. Prolonged exposure to propofol induced neuronal injury, downregulation of TRPC6, and enhancement of calpain activity in the cerebral cortex up to 24 h after anesthesia. It also induced long-term behavioral disorders, manifesting as longer escape latency at PND40 and PND41 and as fewer platform-crossing times and less time spent in the target quadrant at PND42. These propofol-induced effects were attenuated by treatment with the TRPC6 agonist and exaggerated by the TRPC6 inhibitor. Pretreatment with the calpain inhibitor alleviated the propofol-induced TRPC6 downregulation and neuronal injury in the cerebral cortex. In conclusion, our data suggest that a calpain-TRPC6 signaling pathway contributes to propofol-induced acute cortical neuron injury and long-term behavioral disorders in rats.

Parvalbumin interneuron loss mediates repeated anesthesia-induced memory deficits in mice

Repeated or prolonged, but not short-term, general anesthesia during the early postnatal period causes long-lasting impairments in memory formation in various species. The mechanisms underlying long-lasting impairment in cognitive function are poorly understood. Here, we show that repeated general anesthesia in postnatal mice induces preferential apoptosis and subsequent loss of parvalbumin-positive inhibitory interneurons in the hippocampus. Each parvalbumin interneuron controls the activity of multiple pyramidal excitatory neurons, thereby regulating neuronal circuits and memory consolidation. Preventing the loss of parvalbumin neurons by deleting a proapoptotic protein, mitochondrial anchored protein ligase (MAPL), selectively in parvalbumin neurons rescued anesthesia-induced deficits in pyramidal cell inhibition and hippocampus-dependent long-term memory. Conversely, partial depletion of parvalbumin neurons in neonates was sufficient to engender long-lasting memory impairment. Thus, loss of parvalbumin interneurons in postnatal mice following repeated general anesthesia critically contributes to memory deficits in adulthood.

Neonatal administration of a subanaesthetic dose of JM-1232(-) in mice results in no behavioural deficits in adulthood

In animal models, neonatal exposure of general anaesthetics significantly increases apoptosis in the brain, resulting in persistent behavioural deficits later in adulthood. Consequently, there is growing concern about the use of general anaesthetics in obstetric and paediatric practice. JM-1232(−) has been developed as a novel intravenous anaesthetic, but the effects of JM-1232(−) on the developing brain are not understood. Here we show that neonatal administration of JM-1232(−) does not lead to detectable behavioural deficits in adulthood, contrarily to other widely-used intravenous anaesthetics. At postnatal day 6 (P6), mice were injected intraperitoneally with a sedative-equivalent dose of JM-1232(−), propofol, or midazolam. Western blot analysis of forebrain extracts using cleaved poly-(adenosine diphosphate-ribose) polymerase antibody showed that JM-1232(−) is accompanied by slight but measurable apoptosis 6 h after administration, but it was relatively small compared to those of propofol and midazolam. Behavioural studies were performed in adulthood, long after the neonatal anaesthesia, to evaluate the long-term effects on cognitive, social, and affective functions. P6 administration to JM-1232(−) was not accompanied by detectable long-term behavioural deficits in adulthood. However, animals receiving propofol or midazolam had impaired social and/or cognitive functions. These data suggest that JM-1232(−) has prospects for use in obstetric and paediatric practice.

New progress of isoflurane, sevoflurane and propofol in hypoxic-ischemic brain injury and related molecular mechanisms based on p75 neurotrophic factor receptor

Hypoxic ischemic brain injury (HIBI) is one of the most common clinical disorders, especially in neonates. The complex pathophysiology of HIBI is an important cause of disability and even death of patients, however, being without effective clinical treatments. Common anesthetics (such as isoflurane, propofol and sevoflurane) have an adverse impact on neuronal cells for HIBI via the regulation of p75 neurotrophic factor receptor (P75NTR). In order to protect the injured brains and study the effect of underlying treatments, it is particularly significant to understand and master the developmental mechanism of anesthetics for the occurrence of HIBI related molecular mechanisms. Therefore, this paper will mainly review the corresponding pathogenic and protective mechanisms about HIBI binding to the research progress of the role of P75NTR. In conclusion, the effects of neuroprotection and injured nerves are involved in the expression and activation of P75NTR, mainly increased P75NTR mRNA, protein levels and calpain-dependent for propofol, and inducing neuronal apoptosis for isoflurane and sevoflurane, and we look forward to that connection with P75NTR, common anaesthetic and HIBI may be a new direction of research and gain perfect outcomes in the future.

Neuroactive steroids alphaxalone and CDNC24 are effective hypnotics and potentiators of GABAA currents, but are not neurotoxic to the developing rat brain

BACKGROUND

The most currently used general anaesthetics are potent potentiators of γ-aminobutyric acid A (GABA_A) receptors and are invariably neurotoxic during the early stages of brain development in preclinical animal models. As causality between GABA_A potentiation and anaesthetic-induced developmental neurotoxicity has not been established, the question remains whether GABAergic activity is crucial for promoting/enhancing neurotoxicity. Using the neurosteroid analogue, (3α,5α)-3-hydroxy-13,24-cyclo-18,21-dinorchol-22-en-24-ol (CDNC24), which potentiates recombinant GABA_A receptors, we examined whether this potentiation is the driving force in inducing neurotoxicity during development.

METHODS

The neurotoxic potential of CDNC24 was examined vis-à-vis propofol (2,6-diisopropylphenol) and alphaxalone (5α-pregnan-3α-ol-11,20-dione) at the peak of rat synaptogenesis. In addition to the morphological neurotoxicity studies of the subiculum and medial prefrontal cortex (mPFC), we assessed the extra-, pre-, and postsynaptic effects of these agents on GABAergic neurotransmission in acute subicular slices from rat pups.

RESULTS

CDNC24, like alphaxalone and propofol, caused dose-dependent hypnosis in vivo, with a higher therapeutic index. CDNC24 and alphaxalone, unlike propofol, did not cause developmental neuroapoptosis in the subiculum and mPFC. Propofol potentiated post- and extrasynaptic GABA_A currents as evidenced by increased spontaneous inhibitory postsynaptic current (sIPSC) decay time and prominent tonic currents, respectively. CDNC24 and alphaxalone had a similar postsynaptic effect, but also displayed a strong presynaptic effect as evidenced by decreased frequency of sIPSCs and induced moderate tonic currents.

CONCLUSIONS

The lack of neurotoxicity of CDNC24 and alphaxalone may be at least partly related to suppression of presynaptic GABA release in the developing brain.

Inhibition of the electron transport chain in propofol induced neurotoxicity in zebrafish embryos

Fetal and neonatal exposure to propofol can lead to neuronal death and long-term neurobehavioral deficiencies in both rodents and nonhuman primates. Zebrafish embryo, which is fertilized ex-utero, has provided us a new model species to study the effects of general anesthetics on developing brain. Inhibited electron transport chain leads to mitochondrial dysfunction and insufficient energy production. The aim of this study was to dissect the role of electron transport chain in propofol-induced neurotoxicity. 6 h post fertilization (hpf) zebrafish embryos were exposed to control or 1, 2 or 4 μg/ml propofol until 48hpf. Acridine orange staining was used to assess cell apoptosis in the brain of zebrafish embryos. The activity of mitochondrial electron transport chain complex was assessed using colorimetric method. Expression of key subunit of cytochrome c oxidase was assessed by western blot and transcription level of cox4i1 was assessed by quantitative real time-PCR. The mitochondrial membrane potential and ATP content were assessed. Exposure to 1, 2 and 4 μg/ml propofol induced significant increases in cell apoptosis in the brain of zebrafish embryos in a dose-dependent manner and led to significant decreases in electron transport chain complex IV activity from (0.161 ± 0.023)μmol/mg/min in blank control-treated group to (0.096 ± 0.015)μmol/mg/min, (0.083 ± 0.013)μmol/mg/min and (0.045 ± 0.014)μmol/mg/min respectively, accompanied by decreased expression of key regulatory subunit of cytochrome c oxidase-subunit IV and decreased transcription level of cox4i1. Propofol exposure also decreased the mitochondrial membrane potential and ATP content. Our findings demonstrate that inhibition of the electron transport chain is involved in the mechanisms by which propofol induces neurotoxicity in the developing brain.

Propofol induces impairment of mitochondrial biogenesis through inhibiting the expression of peroxisome proliferator-activated receptor-γ coactivator-1α

Propofol is a commonly used general anesthetic in patient care. Recent studies have shown that propofol has neurological side effects especially in young children, which raises a concern regarding the safety of its use. We explored the effects of the molecular mechanism of propofol on neuronal mitochondrial function in SH-SY5Y cells. Our results demonstrate that clinically relevant doses of propofol reduce the expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) in a dose- and time-dependent manner. At a concentration of 2%, propofol suppresses the mitochondrial regulator nuclear respiratory factor 1 and mitochondrial transcription factor A and impairs neuronal mitochondrial biogenesis. These impairments involve reduction of mitochondrial mass and reduction of the ratio of mitochondrial to nuclear DNA as well as reduction of cytochrome C oxidase activity. Propofol treatment reduces intracellular adenosine triphosphate (ATP) production, the mitochondrial respiratory rate, and increases mitochondrial reactive oxygen species production, implying that it disturbs neuronal mitochondrial function. Overexpression of PGC-1α rescued propofol-induced reduced mitochondrial mass, ATP production, and respiratory rate, indicating that PGC-1α is the mediator of the effect of propofol on mitochondrial function. Finally, we demonstrate that propofol suppresses PGC-1α by inhibiting cAMP-response element binding protein (CREB) activation and promoting PKA RI expression, and the addition of cyclic adenosine monophosphate rescues propofol-mediated reduced PGC-1α. In conclusion, PGC-1α is the central mediator of propofol-induced impairment of mitochondrial biogenesis and neuronal mitochondrial dysfunction. Our study demonstrates the molecular mechanism behind propofol-induced neurotoxicity and provides valuable information regarding its side effects in clinical practice.

Both GSK-3β/CRMP2 and CDK5/CRMP2 pathways participate in the protection of dexmedetomidine against propofol-induced learning and memory impairment in neonatal rats

Dexmedetomidine has been reported to ameliorate propofol-induced neurotoxicity in neonatal animals. However, the underlying mechanism is still undetermined. Glycogen synthase kinase-3β (GSK-3β), cycline dependent kinase-5 (CDK5) and Rho-kinase (RhoA) pathways play critical roles in neuronal development. The present study is to investigate whether GSK-3β, CDK5 and RhoA pathways are involved in the neuroprotection of dexmedetomidine. Seven-day-old (P7) Sprague-Dawley rats were anesthetized with propofol for 6 h. Dexmedetomidine at various concentrations were administered before propofol exposure. Neuroapoptosis, the neuronal proliferation and the level of neurotransmitter in the hippocampus were evaluated. The effects of GSK-3β inhibitor SB415286, CDK5 inhibitor roscovitine or RhoA inhibitor Y276321 on propofol-induced neurotoxicity were assessed. Propofol induced apoptosis in the hippocampal neurons and astrocytes, inhibited neuronal proliferation in the DG region, down-regulated the level of γ-aminobutyric acid (GABA) and glutamate in the hippocampus, and impaired long-term cognitive function. These harmful effects were reduced by pretreatment with 50 μg·kg-1 dexmedetomidine. Moreover, propofol activated GSK-3β and CDK5 pathways, but not RhoA pathway, by reducing the phosphorylation of GSK-3β (ser 9), increasing the expression of CDK5 activator P25 and increasing the phosphorylation of their target sites on CRMP2 shortly after exposure. These effects were reversed by pretreatment with 50 μg·kg-1 dexmedetomidine. Furthermore, SB415286 and roscovitine, not Y276321, attenuated the propofol-induced neuroapoptosis, brain cell proliferation inhibition, GABA and glutamate downregulation, and learning and memory dysfunction. Our results indicate that dexmedetomidine reduces propofol-induced neurotoxicity and neurocognitive impairment via inhibiting activation of GSK-3β/CRMP2 and CDK5/CRMP2 pathways in the hippocampus of neonatal rats.

Ryanodine Receptors in Autophagy: Implications for Neurodegenerative Diseases?

Intracellular Ca²⁺ signaling is important in the regulation of several cellular processes including autophagy. The endoplasmic reticulum (ER) is the main and largest intracellular Ca²⁺ store. At the ER two protein families of Ca²⁺ release channels, inositol 1,4,5-trisphosphate receptors (IP₃Rs) and ryanodine receptors (RyRs), are expressed. Several studies have reported roles in the regulation of autophagy for the ubiquitously expressed IP₃R. For instance, IP₃R-mediated Ca²⁺ release supresses basal autophagic flux by promoting mitochondrial metabolism, while also promoting the rapid initial increase in autophagic flux in response to nutrient starvation. Insights into the contribution of RyRs in autophagy have been lagging significantly compared to the advances made for IP₃Rs. This is rather surprising considering that RyRs are predominantly expressed in long-lived cells with specialized metabolic needs, such as neurons and muscle cells, in which autophagy plays important roles. In this review article, recent studies revealing roles for RyRs in the regulation of autophagy will be discussed. Several RyR-interacting proteins that have been established to modulate both RyR function and autophagy will also be highlighted. Finally, the involvement of RyRs in neurodegenerative diseases will be addressed. Inhibition of RyR channels has not only been shown to be beneficial for treating several of these diseases but also regulates autophagy.

Propofol Affects Neurodegeneration and Neurogenesis by Regulation of Autophagy via Effects on Intracellular Calcium Homeostasis

BACKGROUND

In human cortical neural progenitor cells, we investigated the effects of propofol on calcium homeostasis in both the ryanodine and inositol 1,4,5-trisphosphate calcium release channels. We also studied propofol-mediated effects on autophagy, cell survival, and neuro- and gliogenesis.

METHODS

The dose-response relationship between propofol concentration and duration was studied in neural progenitor cells. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase release assays. The effects of propofol on cytosolic calcium concentration were evaluated using Fura-2, and autophagy activity was determined by LC3II expression levels with Western blot. Proliferation and differentiation were evaluated by bromodeoxyuridine incorporation and immunostaining with neuronal and glial markers.

RESULTS

Propofol dose- and time-dependently induced cell damage and elevated LC3II expression, most robustly at 200 µM for 24 h (67 ± 11% of control, n = 12 to 19) and 6 h (2.4 ± 0.5 compared with 0.6 ± 0.1 of control, n = 7), respectively. Treatment with 200 μM propofol also increased cytosolic calcium concentration (346 ± 71% of control, n = 22 to 34). Propofol at 10 µM stimulated neural progenitor cell proliferation and promoted neuronal cell fate, whereas propofol at 200 µM impaired neuronal proliferation and promoted glial cell fate (n = 12 to 20). Cotreatment with ryanodine and inositol 1,4,5-trisphosphate receptor antagonists and inhibitors, cytosolic Ca chelators, or autophagy inhibitors mostly mitigated the propofol-mediated effects on survival, proliferation, and differentiation.

CONCLUSIONS

These results suggest that propofol-mediated cell survival or neurogenesis is closely associated with propofol's effects on autophagy by activation of ryanodine and inositol 1,4,5-trisphosphate receptors.

Neuroprotection and neurotoxicity in the developing brain: an update on the effects of dexmedetomidine and xenon

Growing and consistent preclinical evidence, combined with early clinical epidemiological observations, suggest potentially neurotoxic effects of commonly used anesthetic agents in the developing brain. This has prompted the FDA to issue a safety warning for all sedatives and anesthetics approved for use in children under three years of age. Recent studies have identified dexmedetomidine, the potent α2-adrenoceptor agonist, and xenon, the noble gas, as effective anesthetic adjuvants that are both less neurotoxic to the developing brain, and also possess neuroprotective properties in neonatal and other settings of acute ongoing neurologic injury. Dexmedetomidine and xenon are effective anesthetic adjuvants that appear to be less neurotoxic than other existing agents and have the potential to be neuroprotective in the neonatal and pediatric settings. Although results from recent clinical trials and case reports have indicated the neuroprotective potential of xenon and dexmedetomidine, additional randomized clinical trials corroborating these studies are necessary. By reviewing both the existing preclinical and clinical evidence on the neuroprotective effects of dexmedetomidine and xenon, we hope to provide insight into the potential clinical efficacy of these agents in the management of pediatric surgical patients.

Propofol Inhibits Neurogenesis of Rat Neural Stem Cells by Upregulating MicroRNA-141-3p

Prolonged or high-dose exposure to anesthetics, such as propofol, can cause brain cell degeneration and subsequent long-term learning or memory deficits, particularly in the developing brain. However, the cellular and molecular mechanisms underlying the deleterious effects of propofol at certain stages of development remain unclear. In this study we found that propofol inhibited the proliferation, neuronal differentiation, and migration of neural stem cells (NSCs) while upregulating miR-141-3p. Silencing of miR-141-3p abrogated the effects of propofol on NSC neurogenesis. Propofol treatment downregulated IGF2BP2, a direct target of miR-141-3p, whereas overexpression of IGF2BP2 attenuated the effects of propofol and miR-141-3p on NSC neurogenesis. In short, propofol inhibits NSC neurogenesis through a mechanism involving the miR-141-3p/IGF2BP2 axis. Our results may provide a potential approach for preventing the neurodegenerative effects of propofol in the developing brain.

Neurogenesis and developmental anesthetic neurotoxicity

The mechanism by which anesthetics might act on the developing brain in order to cause long term deficits remains incompletely understood. The hippocampus has been identified as a structure that is likely to be involved, as rodent models show numerous deficits in behavioral tasks of learning that are hippocampal-dependent. The hippocampus is an unusual structure in that it is the site of large amounts of neurogenesis postnatally, particularly in the first year of life in humans, and these newly generated neurons are critical to the function of this structure. Intriguingly, neurogenesis is a major developmental event that occurs during postulated windows of vulnerability to developmental anesthetic neurotoxicity across the different species in which it has been studied. In this review, we examine the evidence for anesthetic effects on neurogenesis in the early postnatal period and ask whether neurogenesis should be studied further as a putative mechanism of injury. Multiple anesthetics are considered, and both in vivo and in vitro work is presented. While there is abundant evidence that anesthetics act to suppress neurogenesis at several different phases, evidence of a causal link between these effects and any change in learning behavior remains elusive.

Cognitive Dysfunction in Children with Heart Disease: The Role of Anesthesia and Sedation

As physicians and caregivers of children with congenital heart disease, we are aware of the increasing need for procedures requiring anesthesia. While these procedures may be ideal for medical and cardiac surgical management, the risks and benefits must be assessed carefully. There are well known risks of cardiovascular and respiratory complications from anesthesia and sedation and a potentially under-appreciated risk of neurocognitive dysfunction. Both animal and human studies support the detrimental effects of repeated anesthetic exposure on the developing brain. Although the studies in humans are less convincing of this risk, the Society of Pediatric Anesthesia jointly with SmartTots provided a consensus statement on the use of anesthetic and sedative drugs in infants and toddlers when speaking to families. (www.pedsanesthesia.org; http://smarttots.org/wp-content/uploads/2015/10/ConsensusStatementV910.5.2015.pdf). An excerpt of the statement is "Concerns regarding the unknown risk of anesthetic exposure to your child's brain development must be weighed against the potential harm associated with cancelling or delaying a needed procedure. Each child's care must be evaluated individually based on age, type, and urgency of the procedure and other health factors. This review provides a summary of the current evidence regarding anesthesia-induced neurotoxicity and the developing brain and its implications for children with congenital heart disease.

Posttraumatic Propofol Neurotoxicity Is Mediated via the Pro-Brain-Derived Neurotrophic Factor-p75 Neurotrophin Receptor Pathway in Adult Mice

OBJECTIVES

The gamma-aminobutyric acid modulator propofol induces neuronal cell death in healthy immature brains by unbalancing neurotrophin homeostasis via p75 neurotrophin receptor signaling. In adulthood, p75 neurotrophin receptor becomes down-regulated and propofol loses its neurotoxic effect. However, acute brain lesions, such as traumatic brain injury, reactivate developmental-like programs and increase p75 neurotrophin receptor expression, probably to foster reparative processes, which in turn could render the brain sensitive to propofol-mediated neurotoxicity. This study investigates the influence of delayed single-bolus propofol applications at the peak of p75 neurotrophin receptor expression after experimental traumatic brain injury in adult mice.

DESIGN

Randomized laboratory animal study.

SETTING

University research laboratory.

SUBJECTS

Adult C57BL/6N and nerve growth factor receptor-deficient mice.

INTERVENTIONS

Sedation by IV propofol bolus application delayed after controlled cortical impact injury.

MEASUREMENTS AND MAIN RESULTS

Propofol sedation at 24 hours after traumatic brain injury increased lesion volume, enhanced calpain-induced αII-spectrin cleavage, and increased cell death in perilesional tissue. Thirty-day postinjury motor function determined by CatWalk (Noldus Information Technology, Wageningen, The Netherlands) gait analysis was significantly impaired in propofol-sedated animals. Propofol enhanced pro-brain-derived neurotrophic factor/brain-derived neurotrophic factor ratio, which aggravates p75 neurotrophin receptor-mediated cell death. Propofol toxicity was abolished both by pharmacologic inhibition of the cell death domain of the p75 neurotrophin receptor (TAT-Pep5) and in mice lacking the extracellular neurotrophin binding site of p75 neurotrophin receptor.

CONCLUSIONS

This study provides first evidence that propofol sedation after acute brain lesions can have a deleterious impact and implicates a role for the pro-brain-derived neurotrophic factor-p75 neurotrophin receptor pathway. This observation is important as sedation with propofol and other compounds with GABA receptor activity are frequently used in patients with acute brain pathologies to facilitate sedation or surgical and interventional procedures.

The Fas Ligand/Fas Death Receptor Pathways Contribute to Propofol-Induced Apoptosis and Neuroinflammation in the Brain of Neonatal Rats

A number of experimental studies have reported that exposure to common, clinically used anesthetics induce extensive neuroapoptosis and cognitive impairment when applied to young rodents, up to 2 weeks old, in phase of rapid synaptogenesis. Propofol is the most used general anesthetic in clinical practice whose mechanisms of neurotoxicity on the developing brain remains to be examined in depth. This study investigated effects of different exposures to propofol anesthesia on Fas receptor and Fas ligand expressions, which mediate proapoptotic and proinflammation signaling in the brain. Propofol (20 mg/kg) was administered to 7-day-old rats in multiple doses sufficient to maintain 2-, 4- and 6-h duration of anesthesia. Animals were sacrificed at 0, 4, 16 and 24 h after termination of anesthesia. It was found that propofol anesthesia induced Fas/FasL and downstream caspase-8 expression more prominently in the thalamus than in the cortex. Opposite, Bcl-2 and caspase-9, markers of intrinsic pathway activation, were shown to be more influenced by propofol treatment in the cortex. Further, we have established upregulation of caspase-1 and IL-1β cytokine transcription as well as subsequent activation of microglia that is potentially associated with brain inflammation. Behavioral analyses revealed that P35 and P60 animals, neonatally exposed to propofol, had significantly higher motor activity during three consecutive days of testing in the open field, though formation of the intersession habituation was not prevented. This data, together with our previous results, contributes to elucidation of complex mechanisms of propofol toxicity in developing brain.

A systematic review of methodology applied during preclinical anesthetic neurotoxicity studies: important issues and lessons relevant to the design of future clinical research

Preclinical evidence suggests that anesthetic agents harm the developing brain thereby causing long-term neurocognitive impairments. It is not clear if these findings apply to humans, and retrospective epidemiological studies thus far have failed to show definitive evidence that anesthetic agents are harmful to the developing human brain.

AIM

The aim of this systematic review was to summarize the preclinical studies published over the past decade, with a focus on methodological issues, to facilitate the comparison between different preclinical studies and inform better design of future trials.

METHOD

The literature search identified 941 articles related to the topic of neurotoxicity. As the primary aim of this systematic review was to compare methodologies applied in animal studies to inform future trials, we excluded a priori all articles focused on putative mechanism of neurotoxicity and the neuroprotective agents. Forty-seven preclinical studies were finally included in this review.

RESULTS

Methods used in these studies were highly heterogeneous-animals were exposed to anesthetic agents at different developmental stages, in various doses and in various combinations with other drugs, and overall showed diverse toxicity profiles. Physiological monitoring and maintenance of physiological homeostasis was variable and the use of cognitive tests was generally limited to assessment of specific brain areas, with restricted translational relevance to humans.

CONCLUSION

Comparison between studies is thus complicated by this heterogeneous methodology and the relevance of the combined body of literature to humans remains uncertain. Future preclinical studies should use better standardized methodologies to facilitate transferability of findings from preclinical into clinical science.

Induction of TNF-α signaling cascade in neonatal rat brain during propofol anesthesia

Propofol anesthesia can trigger pro- and anti-apoptotic signaling pathways in the rat brain. In our previous work, we demonstrated that propofol causes widespread apoptotic neurodegeneration in 7-postnatal-day-old (PND7) but not in PND14 rat neurons. The mechanism responsible for these opposing outcomes is unknown, apparently linked to the specific stage of brain development. The present study aims to elucidate the anti-apoptotic process that is activated in the cortex and thalamus of PND14 Wistar rats during the first 48 h after the onset of propofol anesthesia. We showed that the expression of tumor necrosis factor-α (TNF-α) and several components of its pathway, TNFR1 and caspase-8, was significantly increased in the cortex and thalamus. Nuclear factor kappa B (NF-κB) p65 was downregulated in the cortex and upregulated in the thalamus. The expression of c-Fos was upregulated only in the cortex, showing opposed profile compared to NF-κB p65. Double immunofluorescence staining revealed the colocalization of NF-κB p65 with neuronal marker (NeuN), but with predominantly cytoplasmic localization. Finally, X-linked inhibitor of apoptosis protein (XIAP) was upregulated in both examined structures. Immunohistochemical staining with Iba-1 revealed that the treatment did not induce changes in microglial morphology. Our results (i) reveal that the simultaneous activation of pro- and anti-apoptotic signaling occurs after propofol anesthesia, and (ii) pinpoint the potential neuroprotective role of XIAP in anesthesia-induced neurotoxicity.

Repeated neonatal propofol administration induces sex-dependent long-term impairments on spatial and recognition memory in rats

Propofol is an anesthetic agent that gained wide use because of its fast induction of anesthesia and rapid recovery post-anesthesia. However, previous studies have reported immediate neurodegeneration and long-term impairment in spatial learning and memory from repeated neonatal propofol administration in animals. Yet, none of those studies has explored the sex-specific long-term physical changes and behavioral alterations such as social (sociability and social preference), emotional (anxiety), and other cognitive functions (spatial working, recognition, and avoidance memory) after neonatal propofol treatment. Seven-day-old Wistar-Kyoto (WKY) rats underwent repeated daily intraperitoneal injections of propofol or normal saline for 7 days. Starting fourth week of age and onwards, rats were subjected to behavior tests including open-field, elevated-plus-maze, Y-maze, 3-chamber social interaction, novel-object-recognition, passive-avoidance, and rotarod. Rats were sacrificed at 9 weeks and hippocampal protein expressions were analyzed by Western blot. Results revealed long-term body weight gain alterations in the growing rats and sex-specific impairments in spatial (female) and recognition (male) learning and memory paradigms. A markedly decreased expression of hippocampal NMDA receptor GluN1 subunit in female- and increased expression of AMPA GluR1 subunit protein expression in male rats were also found. Other aspects of behaviors such as locomotor activity and coordination, anxiety, sociability, social preference and avoidance learning and memory were not generally affected. These results suggest that neonatal repeated propofol administration disrupts normal growth and some aspects of neurodevelopment in rats in a sex-specific manner.

Propofol inhibits proliferation and induces neuroapoptosis of hippocampal neurons in vitro via downregulation of NF-κB p65 and Bcl-2 and upregulation of caspase-3

Propofol is widely used in paediatric anaesthesia and intensive care unit because of its essentially short-acting anaesthetic effect. Recent data have shown that propofol induced neurotoxicity in developing brain. However, the mechanisms are not extremely clear. To gain a better insight into the toxic effects of propofol on hippocampal neurons, we treated cells at the days in vitro 7 (DIV 7), which were prepared from Sprague-Dawley embryos at the 18th day of gestation, with propofol (0.1-1000 μM) for 3 h. A significant decrease in neuronal proliferation and a remarkable increase in neuroapoptosis were observed in DIV 7 hippocampal neurons as measured by 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide assay and apoptosis assay respectively. Moreover, propofol treatment decreased the nuclear factor kappaB (NF-κB) p65 expression, which was accompanied by a reduction in B-cell lymphoma 2 (Bcl-2) mRNA and protein levels, increased caspase-3 mRNA and activation of caspase-3 protein. These results indicated that downregulation of NF-κB p65 and Bcl-2 were involved in the potential mechanisms of propofol-induced neurotoxicity. This likely led to the caspase-3 activation, triggered apoptosis and inhibited the neuronal growth and proliferation that we have observed in our in vitro systems.

Down-regulation of microRNA-21 is involved in the propofol-induced neurotoxicity observed in human stem cell-derived neurons

BACKGROUND

Recent studies in various animal models have suggested that anesthetics such as propofol, when administered early in life, can lead to neurotoxicity. These studies have raised significant safety concerns regarding the use of anesthetics in the pediatric population and highlight the need for a better model to study anesthetic-induced neurotoxicity in humans. Human embryonic stem cells are capable of differentiating into any cell type and represent a promising model to study mechanisms governing anesthetic-induced neurotoxicity.

METHODS

Cell death in human embryonic stem cell-derived neurons was assessed using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick end labeling staining, and microRNA expression was assessed using quantitative reverse transcription polymerase chain reaction. miR-21 was overexpressed and knocked down using an miR-21 mimic and antagomir, respectively. Sprouty 2 was knocked down using a small interfering RNA, and the expression of the miR-21 targets of interest was assessed by Western blot.

RESULTS

Propofol dose and exposure time dependently induced significant cell death (n = 3) in the neurons and down-regulated several microRNAs, including miR-21. Overexpression of miR-21 and knockdown of Sprouty 2 attenuated the increase in terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick end labeling-positive cells following propofol exposure. In addition, miR-21 knockdown increased the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick end labeling-positive cells by 30% (n = 5). Finally, activated signal transducer and activator of transcription 3 and protein kinase B (Akt) were down-regulated, and Sprouty 2 was up-regulated following propofol exposure (n = 3).

CONCLUSIONS

These data suggest that (1) human embryonic stem cell-derived neurons represent a promising in vitro human model for studying anesthetic-induced neurotoxicity, (2) propofol induces cell death in human embryonic stem cell-derived neurons, and (3) the propofol-induced cell death may occur via a signal transducer and activator of transcription 3/miR-21/Sprouty 2-dependent mechanism.

Propofol anesthesia induces proapoptotic tumor necrosis factor-α and pro-nerve growth factor signaling and prosurvival Akt and XIAP expression in neonatal rat brain

Previously we observed that prolonged exposure to propofol anesthesia causes caspase-3- and calpain-mediated neuronal death in the developing brain. The present study examines the effects of propofol anesthesia on the expression of tumor necrosis factor-α (TNFα), pro-nerve growth factor (NGF), and their receptors in the cortex and the thalamus. We also investigated how propofol influences the expression of Akt and X-linked inhibitor of apoptosis (XIAP) expression, proteins that promote prosurvival pathways. Seven-day-old rats (P7) were exposed to propofol anesthesia lasting 2, 4, or 6 hr and killed 0, 4, 16, or 24 hr after anesthesia termination. The relative levels of mRNA and protein expression were estimated by RT-PCR and Western blot analysis, respectively. The treatments caused marked activation of TNFα and its receptor TNFR-1 and pro-NGF and p75(NTR) receptor expression. In parallel with the induction of these prodeath signals, we established that propofol anesthesia promotes increased expression of the prosurvival molecules pAkt and XIAP during the 24-hr postanesthesia period. These results show that different brain structures respond to propofol anesthesia with a time- and duration of exposure-dependent increase in proapoptotic signaling and with concomitant increases in activities of prosurvival proteins. We hypothesized that the fine balance between these opposing processes sustains homeostasis in the immature rat brain and prevents unnecessary damage after exposure to an injurious stimulus. The existence of this highly regulated process provides a time frame for potential therapeutic intervention directed toward suppressing the deleterious component of propofol anesthesia.

Anaesthetics-induced neurotoxicity in developing brain: an update on preclinical evidence

Every year millions of young people are treated with anaesthetic agents for surgery and sedation in a seemingly safe manner. However, growing and convincing preclinical evidence in rodents and nonhuman primates, together with recent epidemiological observations, suggest that exposure to anaesthetics in common clinical use can be neurotoxic to the developing brain and lead to long-term neurological sequelae. These findings have seriously questioned the safe use of general anaesthetics in obstetric and paediatric patients. The mechanisms and human applicability of anaesthetic neurotoxicity and neuroprotection have remained under intense investigation over the past decade. Ongoing pre-clinical investigation may have significant impact on clinical practice in the near future. This review represents recent developments in this rapidly emerging field. The aim is to summarise recently available laboratory data, especially those being published after 2010, in the field of anaesthetics-induced neurotoxicity and its impact on cognitive function. In addition, we will discuss recent findings in mechanisms of early-life anaesthetics-induced neurotoxicity, the role of human stem cell-derived models in detecting such toxicity, and new potential alleviating strategies.

Propofol at clinically relevant concentrations increases neuronal differentiation but is not toxic to hippocampal neural precursor cells in vitro

BACKGROUND

Propofol in the early postnatal period has been shown to cause brain cell death. One proposed mechanism for cognitive dysfunction after anesthesia is alteration of neural stem cell function and neurogenesis. We examined the effect of propofol on neural precursor or stem cells (NPCs) grown in vitro.

METHODS

Hippocampal-derived NPCs from postnatal day 2 rats were exposed to propofol or Diprivan. NPCs were then analyzed for bromodeoxyuridine incorporation to measure proliferation. Cell death was measured by lactate dehydrogenase release. Immunocytochemistry was used to evaluate the expression of neuronal and glial markers in differentiating NPCs exposed to propofol.

RESULTS

Propofol dose dependently increases the release of lactate dehydrogenase from NPCs under both proliferating and differentiating conditions at supraclinical concentrations (more than 7.1 µM). Both Diprivan and propofol had the same effect on NPCs. Propofol-mediated release of lactate dehydrogenase is not inhibited by blocking the γ-aminobutyric acid type A receptor or extracellular calcium influx and is not mediated by caspase-3/7. Direct γ-aminobutyric acid type A receptor activation did not have the same effect. In differentiating NPCs, 6 h of propofol at 2.1 µM increased the number neurons but not glial cells 4 days later. Increased neuronal differentiation was not blocked by bicuculline.

CONCLUSIONS

Only supraclinical concentrations of propofol or Diprivan kill NPCs in culture by a non-γ-aminobutyric acid type A, noncaspase-3 mechanism. Clinically relevant doses of propofol increase neuronal fate choice by a non-γ-aminobutyric acid type A mechanism.

Low-dose dexamethasone treatment promotes the pro-survival signalling pathway in the adult rat prefrontal cortex

Synthetic glucocorticoid dexamethasone (DEX), a highly potent anti-inflammatory and immunosuppressive agent, is widely used in the treatment of brain cancer, as well as for inflammatory and autoimmune diseases. The present study aimed to determine whether low-dose subchronic DEX treatment (100 μg/kg for eight consecutive days) exerts long-term effects on apoptosis in the adult rat prefrontal cortex (PFC) by examining the expression of cell death-promoting molecules [poly(ADP-ribose) polymerase (PARP), p53, procaspase 3, cleaved caspase 3, Bax] and cell-survival molecules (AKT, Bcl-2). The results obtained revealed that body, thymus and adrenal gland weights, as well corticosterone levels, in the serum and PFC were reduced 1 day after the last DEX injection. In the PFC, DEX caused activation of AKT, augmentation of pro-survival Bcl-2 protein and an enhanced Bcl-2/Bax protein ratio, as well Bcl-2 translocation to the mitochondria. An unaltered profile with respect to the protein expression of apoptotic molecules PARP, procaspase 3 and Bax was detected, whereas p53 protein was decreased. Reverse transcriptase -polymerase chain reaction analysis showed a decrease of p53 mRNA levels and no significant difference in Bcl-2 and Bax mRNA expression in DEX-treated rats. Finally, a DNA fragmentation assay and Fluoro-Jade staining demonstrated no considerable changes in apoptosis in the rat PFC. Our findings support the concept that low-dose DEX creates a hypocorticoid state in the brain and also indicate that subchronic DEX treatment activates the pro-survival signalling pathway but does not change apoptotic markers in the rat PFC. This mechanism might be relevant for the DEX-induced apoptosis resistance observed during and after chemotherapy of patients with brain tumours.

Effect of propofol in the immature rat brain on short- and long-term neurodevelopmental outcome

Background

Propofol is commonly used as sedative in newborns and children. Recent experimental studies led to contradictory results, revealing neurodegenerative or neuroprotective properties of propofol on the developing brain. We investigated neurodevelopmental short- and long-term effects of neonatal propofol treatment.

Methods

6-day-old Wistar rats (P6), randomised in two groups, received repeated intraperitoneal injections (0, 90, 180 min) of 30 mg/kg propofol or normal saline and sacrificed 6, 12 and 24 hrs following the first injection. Cortical and thalamic areas were analysed by Western blot and quantitative real-time PCR (qRT-PCR) for expression of apoptotic and neurotrophin-dependent signalling pathways. Long-term effects were assessed by Open-field and Novel-Object-Recognition at P30 and P120.

Results

Western blot analyses revealed a transient increase of activated caspase-3 in cortical, and a reduction of active mitogen-activated protein kinases (ERK1/2, AKT) in cortical and thalamic areas. qRT-PCR analyses showed a down-regulation of neurotrophic factors (BDNF, NGF, NT-3) in cortical and thalamic regions. Minor impairment in locomotive activity was observed in propofol treated adolescent animals at P30. Memory or anxiety were not impaired at any time point.

Conclusion

Exposing the neonatal rat brain to propofol induces acute neurotrophic imbalance and neuroapoptosis in a region- and time-specific manner and minor behavioural changes in adolescent animals.