Propofol neurotoxicity is mediated by p75 neurotrophin receptor activation

Molecular Mechanisms of Anesthetic Neurotoxicity: A Review of the Current Literature

Data from epidemiologic studies and animal models have raised a concern that exposure to anesthetic agents during early postnatal life may cause lasting impairments in cognitive function. It is hypothesized that this is due to disruptions in brain development, but the mechanism underlying this toxic effect remains unknown. Ongoing research, particularly in rodents, has begun to address this question. In this review we examine currently postulated molecular mechanisms of anesthetic toxicity in the developing brain, including effects on cell death pathways, growth factor signaling systems, NMDA and GABA receptors, mitochondria, and epigenetic factors. The level of evidence for each putative mechanism is critically evaluated, and we attempt to draw connections between them where it is possible to do so. Although there are many promising avenues of research, at this time no consensus can be reached as to a definitive mechanism of injury.

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.

Inhibition of p75 neurotrophin receptor does not rescue cognitive impairment in adulthood after isoflurane exposure in neonatal mice

BACKGROUND

Isoflurane is widely used for anaesthesia in humans. Isoflurane exposure of rodents prior to post-natal day 7 (PND7) leads to widespread neurodegeneration in laboratory animals. Previous data from our laboratory suggest an attenuation of apoptosis with the p75 neurotrophin receptor (p75NTR) inhibitor TAT-Pep5. We hypothesized that isoflurane toxicity leads to behavioural and cognitive abnormalities and can be rescued with pre-anaesthesia administration of TAT-Pep5.

METHODS

Neonatal mouse pups were pretreated with either TAT-Pep5 (25 μl, 10 μM i.p.) or a scrambled control peptide (TAT-ctrl; 25 μl, 10 μM i.p.) prior to isoflurane exposure (1.4%; 4 h) or control ( n  = 15-26/group). Three to 5 months after exposure, behavioural testing and endpoint assays [brain volume (stereology) and immunoblotting] were performed.

RESULTS

No significant difference was observed in open field, T-maze, balance beam or wire-hanging testing. The Barnes maze revealed a significant effect of isoflurane ( P  = 0.019) in errors to find the escape tunnel during the day 5 probe trial, a finding indicative of impaired short-term spatial memory. No difference was found for brain volumes or protein expression. TAT-Pep5 treatment did not reverse the effects of isoflurane on neurocognitive behaviour.

CONCLUSION

A single isoflurane exposure to early post-natal mice caused a hippocampal-dependent memory deficit that was not prevented by pre-administration of TAT-Pep5, although TAT-Pep5, an inhibitor of p75NTR, has been shown to reduce isoflurane-induced apoptosis. These findings suggest that neuronal apoptosis is not requisite for the development of cognitive deficits in the adults attendant with neonatal anaesthetic exposure.

Sevoflurane exposure in postnatal rats induced long-term cognitive impairment through upregulating caspase-3/cleaved-poly (ADP-ribose) polymerase pathway

The association of anesthetic exposure in infants or young children with the long-term impairment of neurologic functions has been reported previously; however, the underlying mechanisms remain largely unknown. In order to identify dysregulated gene expression underlying long-term cognitive impairment caused by sevoflurane exposure at the postnatal stage, the present study initially performed behavioral tests on adult Wistar rats, which received 3% sevoflurane at postnatal day 7 (P7) for different time course. Subsequently, transcriptome profiling of hippocampal tissues from experimental and control rats was performed. Significant impairment of the working memory was observed in adult rats with sevoflurane exposure for 4-6 h, when compared with the control rats. The results indicated that a total of 264 genes were aberrantly expressed (51 downregulated and 213 upregulated; fold change >2.0; P<0.05; false discovery rate <0.05) in the hippocampus of experimental adult rats compared with those from control rats. Particularly, the expression of caspase-3 gene (CASP3), encoding caspase-3 protein, presented the most significant upregulation, which was further validated by quantitative polymerase chain reaction and immunohistochemical analysis. Further analysis revealed that CASP3 expression level was negatively correlated with the rats' spatial working memory performance, as indicated by the Y-maze test. The level of cleaved-poly (ADP-ribose) polymerase (PARP), a substrate of caspase-3, was also increased in the hippocampus of experimental adult rats. Thus, the present study revealed that upregulation of caspase-3/cleaved-PARP may be involved in long-term cognitive impairment caused by sevoflurane exposure in infants, which may be useful for the clinical prevention of cognitive impairment.

Insufficient Astrocyte-Derived Brain-Derived Neurotrophic Factor Contributes to Propofol-Induced Neuron Death Through Akt/Glycogen Synthase Kinase 3β/Mitochondrial Fission Pathway

BACKGROUND

Growing animal evidence demonstrates that prolonged exposure to propofol during brain development induces widespread neuronal cell death, but there is little information on the role of astrocytes. Astrocytes can release neurotrophic growth factors such as brain-derived neurotrophic factor (BDNF), which can exert the protective effect on neurons in paracrine fashion. We hypothesize that during propofol anesthesia, BDNF released from developing astrocytes may not be sufficient to prevent propofol-induced neurotoxicity.

METHODS

Hippocampal astrocytes and neurons isolated from neonatal Sprague Dawley rats were exposed to propofol at a clinically relevant dose of 30 μM or dimethyl sulfoxide as control for 6 hours. Propofol-induced cell death was determined by propidium iodide (PI) staining in astrocyte-alone cultures, neuron-alone cultures, or cocultures containing either low or high density of astrocytes (1:9 or 1:1 ratio of astrocytes to neurons ratio [ANR], respectively). The astrocyte-conditioned medium was collected 12 hours after propofol exposure and measured by protein array assay. BDNF concentration in astrocyte-conditioned medium was quantified using enzyme-linked immunosorbent assay. Neuron-alone cultures were treated with BDNF, tyrosine receptor kinase B inhibitor cyclotraxin-B, glycogen synthase kinase 3β (GSK3β) inhibitor CHIR99021, or mitochondrial fission inhibitor Mdivi-1 before propofol exposure. Western blot was performed for quantification of the level of protein kinase B and GSK3β. Mitochondrial shape was visualized through translocase of the outer membrane 20 staining.

RESULTS

Propofol increased cell death in neurons by 1.8-fold (% of PI-positive cells [PI%] = 18.6; 95% confidence interval [CI], 15.2-21.9, P < .05) but did not influence astrocyte viability. The neuronal death was attenuated by a high ANR (1:1 cocultures; fold change [FC] = 1.17, 95% CI, 0.96-1.38, P < .05), but not with a low ANR [1:9 cocultures; FC = 1.87, 95% CI, 1.48-2.26, P > .05]). Astrocytes secreted BDNF in a cell density-dependent way and propofol decreased BDNF secretion from astrocytes. Administration of BDNF, CHIR99021, or Mdivi-1 significantly attenuated the propofol-induced neuronal death and aberrant mitochondria in neuron-alone cultures (FC = 0.8, 95% CI, 0.62-0.98; FC = 1.22, 95% CI, 1.11-1.32; FC = 1.35, 95% CI, 1.16-1.54, respectively, P < .05) and the cocultures with a low ANR (1:9; FC = 0.85, 95% CI, 0.74-0.97; FC = 1.08, 95% CI, 0.84-1.32; FC = 1.25, 95% CI, 1.1-1.39, respectively, P < .05). Blocking BDNF receptor or protein kinase B activity abolished astrocyte-induced neuroprotection in the cocultures with a high ANR (1:1).

CONCLUSIONS

Astrocytes attenuate propofol-induced neurotoxicity through BDNF-mediated cell survival pathway suggesting multiple neuroprotective strategies such as administration of BDNF, astrocyte-conditioned medium, decreasing mitochondrial fission, or inhibition of GSK3β.

Recent Insights Into Molecular Mechanisms of Propofol-Induced Developmental Neurotoxicity: Implications for the Protective Strategies

Mounting evidence has demonstrated that general anesthetics could induce developmental neurotoxicity, including acute widespread neuronal cell death, followed by long-term memory and learning abnormalities. Propofol is a commonly used intravenous anesthetic agent for the induction and maintenance of anesthesia and procedural and critical care sedation in children. Compared with other anesthetic drugs, little information is available on its potential contributions to neurotoxicity. Growing evidence from multiple experimental models showed a similar neurotoxic effect of propofol as observed in other anesthetic drugs, raising serious concerns regarding pediatric propofol anesthesia. The aim of this review is to summarize the current findings of propofol-induced developmental neurotoxicity. We first present the evidence of neurotoxicity from animal models, animal cell culture, and human stem cell-derived neuron culture studies. We then discuss the mechanism of propofol-induced developmental neurotoxicity, such as increased cell death in neurons and oligodendrocytes, dysregulation of neurogenesis, abnormal dendritic development, and decreases in neurotrophic factor expression. Recent findings of complex mechanisms of propofol action, including alterations in microRNAs and mitochondrial fission, are discussed as well. An understanding of the toxic effect of propofol and the underlying mechanisms may help to develop effective novel protective or therapeutic strategies for avoiding the neurotoxicity in the developing human brain.

Lasting impact of general anaesthesia on the brain: mechanisms and relevance

General anaesthesia is usually considered to safely induce a reversible brain state allowing the performance of surgery under optimal conditions. An increasing number of clinical and experimental observations, however, suggest that anaesthetic drugs, especially when they are administered at the extremes of age, can trigger long-term morphological and functional alterations in the brain. Here, we review available mechanistic data linking general-anaesthesia exposure to impaired cognitive performance in both young and mature nervous systems. We also provide a critical appraisal of the translational value of animal models and highlight the important challenges that need to be addressed to strengthen the link between laboratory work and clinical investigations in the field of anaesthesia-neurotoxicity research.

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.

Anesthetic neurotoxicity: Apoptosis and autophagic cell death mediated by calcium dysregulation

A number of findings suggested that general anesthetics induced neural cell death by apoptosis in various animal models. Although clinical evidence regarding the correlation between anesthetic exposures at young age and subsequent cognitive impairments remains unclear, repeated or consistent exposures to general anesthetics may be a potential harmful risk in developing human brains. The mechanisms underlying the anesthetic neurotoxicity have received extensive attention recently. We will attempt a brief review to summarize current understanding on the role of both apoptosis and autophagic cell death mediated by calcium dysregulation in anesthetic neurotoxicity.

Etanercept, an inhibitor of TNF-a, prevents propofol-induced neurotoxicity in the developing brain

Propofol can induce acute neuronal apoptosis, neuronal loss or long-term cognitive impairment when exposed in neonatal rodents, but the mechanisms by which propofol induces developmental neurotoxicity are unclear. Recent studies have demonstrated that propofol can increase the TNF-α level in the developing brain, but there is a lack of direct evidence to show whether TNF-α is partially or fully involved in propofol-induced neurotoxicity. The present study shows that propofol exposure in neonatal rats induces an increase of TNF-α in the cerebral spinal fluid, hippocampus and prefrontal cortex (PFC). Etanercept, a TNF-α inhibitor, prevents propofol-induced short- or long-term neuronal apoptosis, neuronal loss, synaptic loss and long-term cognitive impairment. Furthermore, mTNF-α (precursor of TNF-α) expression in microglia cells is increased after propofol anaesthesia in either the hippocampus or PFC, but mTNF-α expression in neurons is only increased in the PFC. These findings suggest that TNF-α may mediate propofol-induced developmental neurotoxicity, and etanercept can provide neural protection. Microglia are the main cellular source of TNF-α after propofol exposure, while the synthesis of TNF-α in neurons is brain-region selective.

Neuroprotective effects of caffeic acid phenethyl ester against sevoflurane‑induced neuronal degeneration in the hippocampus of neonatal rats involve MAPK and PI3K/Akt signaling pathways

Millions of infants and children are exposed to anesthesia every year during medical care. Sevoflurane is a volatile anesthetic that is frequently used for pediatric anesthesia. However, previous reports have suggested that the administration of sevoflurane promotes neurodegeneration, raising concerns regarding the safety of its usage. The present study aimed to investigate caffeic acid phenethyl ester (CAPE) and its protective effect against sevoflurane‑induced neurotoxicity in neonatal rats. Rat pups were administered with CAPE at 10, 20 or 40 mg/kg body weight from postnatal day 1 (P1) to P15. The P7 rats were exposed to sevoflurane (2.9%) for 6 h. Control group rats received no sevoflurane or CAPE. Neuronal apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick‑end labeling assay. The expression levels of caspases (caspase‑3, ‑8 and ‑9), apoptotic pathway proteins [Bcl‑2‑associated X protein (Bax), B cell CCL/lymphoma 2 (Bcl‑2), Bcl‑2‑like 1 (Bcl‑xL), Bcl‑2‑associated agonist of cell death (Bad) and phosphorylated (p)‑Bad], mitogen‑activated protein kinases (MAPK) signaling pathway proteins [c‑Jun N‑terminal kinase (JNK), p‑JNK, extracellular signal‑regulated kinase (ERK)1/2, p‑ERK1/2, p38, p‑p38 and p‑c‑Jun] and the phosphoinositide 3‑kinase (PI3K)/Akt cascade were evaluated by western blotting following sevoflurane and CAPE treatment. In addition, the expression of cleaved caspase‑3 was analyzed by immunohistochemistry. CAPE significantly reduced sevoflurane‑induced apoptosis, downregulated the expression levels of caspases and pro‑apoptotic proteins (Bax and Bad) and elevated the expression levels of Bcl‑2 and Bcl‑xL when compared with sevoflurane treatment. Furthermore, CAPE appeared to modify the expression levels of MAPKs and activate the PI3K/Akt signaling pathway. Thus, the present study demonstrated that CAPE effectively inhibited sevoflurane‑induced neuroapoptosis by modulating the expression and phosphorylation of apoptotic pathway proteins and MAPKs, and by regulating the PI3K/Akt pathway.

Prolonged Treatment with Propofol Transiently Impairs Proliferation but Not Survival of Rat Neural Progenitor Cells In Vitro

Neurocognitive dysfunction is common in survivors of intensive care. Prolonged sedation has been implicated but the mechanisms are unclear. Neurogenesis continues into adulthood and is implicated in learning. The neural progenitor cells (NPC) that drive neurogenesis have receptors for the major classes of sedatives used clinically, suggesting that interruption of neurogenesis may partly contribute to cognitive decline in ICU survivors. Using an in vitro system, we tested the hypothesis that prolonged exposure to propofol concentration- and duration-dependently kills or markedly decreases the proliferation of NPCs. NPCs isolated from embryonic day 14 Sprague-Dawley rat pups were exposed to 0, 2.5, or 5.0 μg/mL of propofol, concentrations consistent with deep clinical anesthesia, for either 4 or 24 hours. Cells were assayed for cell death and proliferation either immediately following propofol exposure or 24 hours later. NPC death and apoptosis were measured by propidium iodine staining and cleaved caspase-3 immunocytochemistry, respectively, while proliferation was measured by EdU incorporation. Staurosporine (1μM for 6h) was used as a positive control for cell death. Cells were analyzed with unbiased high-throughput immunocytochemistry. There was no cell death at either concentration of propofol or duration of exposure. Neither concentration of propofol impaired NPC proliferation when exposure lasted 4 h, but when exposure lasted 24 h, propofol had an anti-proliferative effect at both concentrations (P < 0.0001, propofol vs. control). However, this effect was transient; proliferation returned to baseline 24 h after discontinuation of propofol (P = 0.37, propofol vs. control). The transient but reversible suppression of NPC proliferation, absence of cytotoxicity, and negligible effect on the neural stem cell pool pool suggest that propofol, even in concentrations used for clinical anesthesia, has limited impact on neural progenitor cell biology.

Electroacupuncture Ameliorates Propofol-Induced Cognitive Impairment via an Opioid Receptor-Independent Mechanism

While general anesthesia is known to induce cognitive deficits in elderly and pediatric patients, its influence on adults is less well-characterized. The present study was designed to evaluate the influence of propofol on the learning and memory of young adult rats, as well as the potential neuroprotective role of electroacupuncture (EA) in propofol-induced cognitive impairment. Intravenous anesthesia with propofol was administered to young adult male Sprague–Dawley (SD) rats for 6 h, and EA was administered three times before and after anesthesia. The Morris Water Maze (MWM) test was conducted to determine the rat’s cognitive performance following the anesthesia treatment. Our results showed that propofol induced obvious cognitive impairment in young adult rats, which could be ameliorated by multiple EA treatments. Moreover, the decreased level of phosphorylated glycogen synthase kinase 3 β (pGSK-3β) in the CA1 region of the hippocampus accompanying the cognitive impairment was also reversed by EA treatment. Further experiments demonstrated that neither 2 nor 10 mg/kg (I.P.) naloxone blocked the effect of EA, indicating that the neuroprotective effect of EA on propofol-induced cognitive impairment was not mediated via the opioid receptors. The present study suggests that EA could ameliorate the cognitive impairment induced by prolonged anesthesia with propofol in young adult rats, which is likely associated with pGSK-3β levels in the CA1 independently of opioid receptors. These findings imply that EA may be used as a potential neuroprotective therapy for post-operative cognitive dysfunction (POCD).

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.

Continuous monitoring of caspase-3 activation induced by propofol in developing mouse brain

The neurotoxicity of anesthetics on the developing brain has drawn the attention of anesthesiologists. Several studies have shown that apoptosis is enhanced by exposure to anesthesia during brain development. Although apoptosis is a physiological developmental step occurring before the maturation of neural networks and the integration of brain function, pathological damage also involves apoptosis. Previous studies have shown that prolonged exposure to anesthetics causes apoptosis. Exactly when the apoptotic cascade starts in the brain remains uncertain. If it starts during the early stage of anesthesia, even short-term anesthesia could harm the brain. Therefore, apoptogenesis should be continuously monitored to elucidate when the apoptotic cascade is triggered by anesthesia. Here, we describe the development of a continuous monitoring system to detect caspase-3 activation using an in vivo model. Brain slices from postnatal days 0-4 SCAT3 transgenic mice with a heterozygous genotype (n=20) were used for the monitoring of caspase-3 cleavage. SCAT3 is a fusion protein of ECFP and Venus connected by a caspase-3 cleavable peptide, DEVD. A specimen from the hippocampal CA1 sector was mounted on a confocal laser microscope and was continuously superfused with artificial cerebrospinal fluid, propofol (2,6-diisopropylphenol, 1μM or 10μM), and dimethyl sulfoxide. Images were obtained every hour for five hours. A pixel analysis of the ECFP/Venus ratio images was performed using a histogram showing the number of pixels with each ratio. In the histogram of the ECFP/Venus ratio, an area with a ratio>1 indicated the number of pixels from caspase-3-activated CA1 neurons. We observed a shift in the histogram toward the right over time, indicating caspase-3 activation. This right-ward shift dramatically changed at five hours in the propofol 1μM and 10μM groups and was obviously different from that in the control group. Thus, real-time fluorescence energy transfer (FRET) imaging was capable of identifying the onset of apoptosis triggered by propofol in neonatal brain slices. This model may be a useful tool for monitoring apoptogenesis in the developing brain.

Tissue plasminogen activator (tPA) attenuates propofol-induced apoptosis in developing hippocampal neurons

Background

We investigated the effect of propofol on the tissue plasminogen activator (tPA) release in developing hippocampal neurons, and explored the effects of exogenous tPA on the propofol-induced neuron apoptosis.

Methods

Primary hippocampal neurons isolated from neonatal Sprague-Dawley rats were exposed to propofol (20, 50, and 100 μM) for 6 h either one time or three times. Finally, neurons were pretreated with exogenous tPA (5 µg/ml), followed by propofol exposure (100 μM, 6 h). The neuron apoptosis was detected by terminal transferase deoxyuridine triphosphate-biotin nick-end labeling (TUNEL) and the protein expression of cleaved caspase-3 (Cl-Csp3) was analyzed by western blot, the tPA in media was tested by enzyme-linked immunosorbent assay.

Results

Propofol exposure significantly increased the number of TUNEL-positive neurons and Cl-Csp3 expression in developing hippocampal neurons. Propofol decreased tPA level in the media of developing hippocampal neurons. The neuron appotosis induced by propofol was attenuated by pretreatment of tPA.

Conclusion

Propofol exposure decreased tPA release in developing hippocampal neurons. The addition of tPA could partially reverse the apoptotic effect of propofol.

Anaesthesia in early childhood - is the development of the immature brain in danger?

Experimental studies performed on immature animal brains had demonstrated a neurotoxic effect following sedation and general anaesthetics administration. The same magnitude of neurotoxicity has been suggested but not been proven to neonates, infants and small children who have undergone anaesthesia. There is a justified and increasing inquiry regarding the administration of general anaesthesia to paediatric patients.

Propofol-Induced Neurotoxicity in the Fetal Animal Brain and Developments in Modifying These Effects-An Updated Review of Propofol Fetal Exposure in Laboratory Animal Studies

In the past twenty years, evidence of neurotoxicity in the developing brain in animal studies from exposure to several general anesthetics has been accumulating. Propofol, a commonly used general anesthetic medication, administered during synaptogenesis, may trigger widespread apoptotic neurodegeneration in the developing brain and long-term neurobehavioral disturbances in both rodents and non-human primates. Despite the growing evidence of the potential neurotoxicity of different anesthetic agents in animal studies, there is no concrete evidence that humans may be similarly affected. However, given the growing evidence of the neurotoxic effects of anesthetics in laboratory studies, it is prudent to further investigate the mechanisms causing these effects and potential ways to mitigate them. Here, we review multiple studies that investigate the effects of in utero propofol exposure and the developmental agents that may modify these deleterious effects.

[Effect of propofol on apoptosis of PC12 cells under hypoxic condition and the mechanism]

OBJECTIVE

To investigate the mechanism by which propofol exposure causes PC12 cell apoptosis under hypoxic conditions.

METHODS

PC12 cells were exposed to room air, 35% oxygen, or 5% oxygen (hypoxia) for 24 h in the presence of either 10 µmol/L lipid emulsion or 10 µmol/L propofol. After the treatments, the cell apoptosis was measured by flow ceytometry, and the level of reactive oxygen species (ROS) and the activity of superoxide dismutase (SOD) were evaluated.

RESULTS

In room air, PC12 cells treated with propofol showed increased apoptosis rate and ROS production as compared with the cells treated with the lipid emulsion; propofol treatment of the cells exposed to 35% oxygen showed obvious enhancement of the apoptosis rate, ROS production and SOD activity. Under the hypoxic condition, propofol treatment even further increased the apoptosis rate, ROS production and SOD activity. Lipid emulsion caused no such changes in cells exposed to room air, 35% oxygen or 5% oxygen.

CONCLUSION

Under hypoxic conditions, propofol can cause apoptosis in PC12 cells by inducing oxidative stress injury.

Proneurotrophin Binding to P75 Neurotrophin Receptor (P75ntr) Is Essential for Brain Lesion Formation and Functional Impairment after Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) initiates an excessive mediator release of e.g. neurotrophins, which promote neuronal survival, differentiation, and modulate synaptic plasticity. Paradoxically, mature forms of neurotrophins promote neuronal survival, whereas unprocessed forms of neurotrophins induce cell death through p75 neurotrophin receptor (p75NTR) signaling. p75NTR is widely expressed during synaptogenesis and is subsequently downregulated in adulthood. Repair mechanisms after acute cerebral insults can reactivate its expression. Therefore, the influence of p75NTR on secondary brain damage was addressed. mRNA levels of p75NTR and its ligands were quantified in brain tissue up to 7 days after experimental TBI (controlled cortical impact; CCI). Brain damage, motor function and inflammatory marker gene expression were determined in mice lacking the proneurotrophin-binding site of the p75NTR protein (NGFR(-/-)) and wild type littermates (NGFR(+/+)) 24 h and 5 days after CCI. In addition, the effect of TAT-Pep5 (pharmacological inhibitor of the intracellular p75NTR death domain) on lesion volume was evaluated 24 h after insult. p75NTR mRNA levels were induced nine-fold by TBI. In NGFR(-/-) mice, lesion volume was reduced by 29% at 24 h and by 21% 5 days after CCI. Motor coordination was significantly improved 24 h after trauma compared with the wild type. Pharmacological inhibition of the p75NTR signaling reduced lesion volume by 18%. The present study presents first time evidence that genetic mutation of the neurotrophin interaction site of p75NTR strongly limits post-traumatic cell death. In addition, we revealed pharmacological targeting of the intracellular p75NTR cell death domain as a promising approach to limit acute brain damage.

Efficacy of rutin in inhibiting neuronal apoptosis and cognitive disturbances in sevoflurane or propofol exposed neonatal mice

Sevoflurane and propofol are widely used in pediatric anesthesia. Neurotoxicity of sevoflurane and propofol in developing brain has been reported and these effects raise concerns on the usage of the drugs. We investigated the influence of rutin, a flavonoid on the neurodegenerative effects of sevoflurane and propofol and on memory and cognition in neonatal rodent model. Separate groups of neonatal mice (C57BL/6) were administered with rutin at 25 or 50 mg/kg body weight (b.wt) from post natal day 2 (P1) to P21. P7 mice were exposed to 2.9% sevoflurane and/or propofol (150 mg/kg b.wt). Neuroapoptosis was assessed by measuring activated caspase-3 and by Fluoro-Jade C staining. Plasma S100β levels were detected by ELISA. Morris water maze test was performed to test learning and memory impairments in the animals. General behaviour of the mice was also assessed. Anesthesia exposure caused severe neuroapoptosis and also raised the levels of plasma S100β. Neuroapoptosis, memory and cognitive deficits observed following anesthetics were comparatively more profound in mice on exposure to combined drug (sevoflurane and propofol) than in those exposed to either of the anesthetics. Rutin at both the doses was effective in reducing the apoptotic cell counts and enhanced the memory and cognitive abilities. Rutin supplementation offered significant protection against anesthetic induced neurodegeneration and learning and memory disturbances.

Anesthetic Propofol Attenuates Apoptosis, Aβ Accumulation, and Inflammation Induced by Sevoflurane Through NF-κB Pathway in Human Neuroglioma Cells

Anesthetics have been reported to promote Alzheimer's disease neuropathogenesis by inducing amyloid beta (Aβ) protein accumulation and apoptosis. The aim of this study was to evaluate the effect of propofol on the apoptosis, Aβ accumulation, and inflammation induced by sevoflurane in human neuroglioma cells. Human neuroglioma cells were treated with or without sevoflurane and then co-incubated with or without propofol. Cell apoptosis was evaluated by fluorescence-activated cell sorting analysis (FACS) using AV-PI kits, and data showed that apoptosis induced by sevoflurane was significantly attenuated by propofol treatment. In addition, with the reactive oxygen species (ROS) production measured by FACS after staining with dichloro-dihydrofluorescein diacetate, propofol could significantly reduce the production of ROS as well as the accumulation of Aβ induced by sevoflurane assessed by enzyme-linked immuno sorbent assay (ELISA) analysis. On the other hand, the same treatment decreased the inflammation factor production of interleukin-6. Moreover, the level of nuclear factor-kappa B (NF-κB) was tested by Western blot and immunofluorescence assay. We found that the activation of NF-κB pathway was suppressed by propofol. The results suggest that propofol can effectively attenuate the apoptosis, Aβ accumulation, and inflammation induced by sevoflurane in human neuroglioma cells through NF-κB signal pathway.

Propofol: a review of its role in pediatric anesthesia and sedation

Propofol is an intravenous agent used commonly for the induction and maintenance of anesthesia, procedural, and critical care sedation in children. The mechanisms of action on the central nervous system involve interactions at various neurotransmitter receptors, especially the gamma-aminobutyric acid A receptor. Approved for use in the USA by the Food and Drug Administration in 1989, its use for induction of anesthesia in children less than 3 years of age still remains off-label. Despite its wide use in pediatric anesthesia, there is conflicting literature about its safety and serious adverse effects in particular subsets of children. Particularly as children are not "little adults", in this review, we emphasize the maturational aspects of propofol pharmacokinetics. Despite the myriad of propofol pharmacokinetic-pharmacodynamic studies and the ability to use allometrical scaling to smooth out differences due to size and age, there is no optimal model that can be used in target controlled infusion pumps for providing closed loop total intravenous anesthesia in children. As the commercial formulation of propofol is a nutrient-rich emulsion, the risk for bacterial contamination exists despite the Food and Drug Administration mandating addition of antimicrobial preservative, calling for manufacturers' directions to discard open vials after 6 h. While propofol has advantages over inhalation anesthesia such as less postoperative nausea and emergence delirium in children, pain on injection remains a problem even with newer formulations. Propofol is known to depress mitochondrial function by its action as an uncoupling agent in oxidative phosphorylation. This has implications for children with mitochondrial diseases and the occurrence of propofol-related infusion syndrome, a rare but seriously life-threatening complication of propofol. At the time of this review, there is no direct evidence in humans for propofol-induced neurotoxicity to the infant brain; however, current concerns of neuroapoptosis in developing brains induced by propofol persist and continue to be a focus of research.

Early Exposure to General Anesthesia Disrupts Spatial Organization of Presynaptic Vesicles in Nerve Terminals of the Developing Rat Subiculum

Exposure to general anesthesia (GA) during critical stages of brain development induces widespread neuronal apoptosis and causes long-lasting behavioral deficits in numerous animal species. Although several studies have focused on the morphological fate of neurons dying acutely by GA-induced developmental neuroapoptosis, the effects of an early exposure to GA on the surviving synapses remain unclear. The aim of this study is to study whether exposure to GA disrupts the fine regulation of the dynamic spatial organization and trafficking of synaptic vesicles in presynaptic terminals. We exposed postnatal day 7 (PND7) rat pups to a clinically relevant anesthetic combination of midazolam, nitrous oxide, and isoflurane and performed a detailed ultrastructural analysis of the synaptic vesicle architecture at presynaptic terminals in the subiculum of rats at PND 12. In addition to a significant decrease in the density of presynaptic vesicles, we observed a reduction of docked vesicles, as well as a reduction of vesicles located within 100 nm from the active zone, in animals 5 days after an initial exposure to GA. We also found that the synaptic vesicles of animals exposed to GA are located more distally with respect to the plasma membrane than those of sham control animals and that the distance between presynaptic vesicles is increased in GA-exposed animals compared to sham controls. We report that exposure of immature rats to GA during critical stages of brain development causes significant disruption of the strategic topography of presynaptic vesicles within the nerve terminals of the subiculum.

Report of the fourth PANDA Symposium on "Anesthesia and Neurodevelopment in Children"

On April 12, 2014, the Pediatric Anesthesia and NeuroDevelopment Assessment (PANDA) study team held its fourth biennial scientific symposium at Morgan Stanley Children's Hospital of New York (MS-CHONY). The symposium was organized by the PANDA study team and co-sponsored by the Morgan Stanley Children's Hospital of New York-Presbyterian and the Department of Anesthesiology of Columbia University. The PANDA symposium has become a platform to review current preclinical and clinical data related to anesthetic neurotoxicity, to discuss relevant considerations in study design and approaches to future research among clinicians and researchers, and finally to engage key stakeholders in this controversial public health topic. Program attendants and speakers represented many of the most active investigators in the area of pediatric anesthetic neurotoxicity as well as stakeholders from many different backgrounds outside of anesthesia that provided their own unique perspectives, concerns, and input regarding anesthetic-related neurotoxicity in children.

Inhibiting Rho kinase 2 reduces memory dysfunction in adult rats exposed to sevoflurane at postnatal days 7-9

The aim of the present study was to investigate the roles of Rho protein A (RhoA) and Rho kinases 2 (ROCK2) in the memory dysfunction of adult rats exposed to sevoflurane at postnatal days 7-9 (P7-9). One-week-old Sprague-Dawley rats were divided into four groups known as C, S1, S3 and F. Rats in the S1 (2 h at P7) and S3 groups (2 h/day at P7-9) were exposed to sevoflurane. The rats in the F group were treated with the ROCK2 inhibitor and subsequent sevoflurane exposure (2 h/day at P7-9). The rats in the C group received no sevoflurane. The protein levels of RhoA, ROCK2 and cleaved caspase-3 (Cl-Csp3) in the adult hippocampus were assessed by western blot analysis. Learning and memory of rats at postnatal 45-50 days (P45-50) were detected by the Morris water maze (MWM) test. During the training of MWM, the latency and distance of rats in the S3 group were significantly longer than that of the C group (P<0.05, respectively). In the probe test, the percentages of time and distance in the target quadrant for the S3 group were evidently less than that of the C group (P<0.05). There was no significant difference in the behaviors between the C and S1 groups (P>0.05, respectively). Corresponding to the behavioral changes, the levels of RhoA, ROCK2 and Cl-Csp3 in the hippocampus of the S3 group significantly increased, compared to that of the C and S1 groups (P<0.05). Additionally, the ROCK2 inhibitor clearly decreased ROCK2 and Cl-Csp3 expression and shortened the latency during the training (P<0.05, P46-49 respectively) and probe test (P<0.05) in the F group, compared to that of the S3 group. Compared to the C group, the expression of RhoA, ROCK2 and Cl-Csp3 in the hippocampus of the S1 group had no significant difference (P>0.05). Multiple inhalation of sevoflurane can induce neurotoxicity and memory dysfunction. RhoA and ROCK2 played important roles in the impairment of learning and memory of adults rats exposed to sevoflurane at the postnatal early stage.

Chronic treatment with anesthetic propofol improves cognitive function and attenuates caspase activation in both aged and Alzheimer's disease transgenic mice

There is a need to seek new treatment(s) for Alzheimer's disease (AD). A recent study showed that AD patients may have decreased levels of functional GABA receptors. Propofol, a commonly used anesthetic, is a GABA receptor agonist. We therefore set out to perform a proof of concept study to determine whether chronic treatment with propofol (50 mg/kg/week) can improve cognitive function in both aged wild-type (WT) and AD transgenic (Tg) mice. Propofol was administrated to the WT and AD Tg mice once a week for 8 or 12 weeks, respectively. Morris water maze was used to assess the cognitive function of the mice following the propofol treatment. Activation of caspase-3, caspase-9, and caspase-8 was investigated using western blot analysis at the end of the propofol treatment. In the mechanistic studies, effects of propofol, amyloid-β protein (Aβ), and GABA receptor antagonist flumazenil on caspase-3 activation and opening of the mitochondrial permeability transition pore were assessed in H4 human neuroglioma and mouse neuroblastoma cells by western blot analysis and flow cytometry. Here we showed that the propofol treatment improved cognitive function and attenuated brain caspase-3 and caspase-9 activation in both aged WT and AD Tg mice. Propofol attenuated Aβ-induced caspase-3 activation and opening of the mitochondrial permeability transition pore in the cells, and flumazenil inhibited the propofol's effects. These results suggested that propofol might improve cognitive function via attenuating the Aβ-induced mitochondria dysfunction and caspase activation, which explored the potential that anesthetic propofol could improve cognitive function in elderly and AD patients.

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.

Positron Emission Tomography with [(18)F]FLT Revealed Sevoflurane-Induced Inhibition of Neural Progenitor Cell Expansion in vivo

Neural progenitor cell expansion is critical for normal brain development and an appropriate response to injury. During the brain growth spurt, exposures to general anesthetics, which either block the N-methyl-d-aspartate receptor or enhance the γ-aminobutyric acid receptor type A can disturb neuronal transduction. This effect can be detrimental to brain development. Until now, the effects of anesthetic exposure on neural progenitor cell expansion in vivo had seldom been reported. Here, minimally invasive micro positron emission tomography (microPET) coupled with 3'-deoxy-3' [(18)F] fluoro-l-thymidine ([(18)F]FLT) was utilized to assess the effects of sevoflurane exposure on neural progenitor cell proliferation. FLT, a thymidine analog, is taken up by proliferating cells and phosphorylated in the cytoplasm, leading to its intracellular trapping. Intracellular retention of [(18)F]FLT, thus, represents an observable in vivo marker of cell proliferation. Here, postnatal day 7 rats (n = 11/group) were exposed to 2.5% sevoflurane or room air for 9 h. For up to 2 weeks following the exposure, standard uptake values (SUVs) for [(18)F]-FLT in the hippocampal formation were significantly attenuated in the sevoflurane-exposed rats (p < 0.0001), suggesting decreased uptake and retention of [(18)F]FLT (decreased proliferation) in these regions. Four weeks following exposure, SUVs for [(18)F]FLT were comparable in the sevoflurane-exposed rats and in controls. Co-administration of 7-nitroindazole (30 mg/kg, n = 5), a selective inhibitor of neuronal nitric oxide synthase, significantly attenuated the SUVs for [(18)F]FLT in both the air-exposed (p = 0.00006) and sevoflurane-exposed rats (p = 0.0427) in the first week following the exposure. These findings suggested that microPET in couple with [(18)F]FLT as cell proliferation marker could be used as a non-invasive modality to monitor the sevoflurane-induced inhibition of neural progenitor cell proliferation in vivo.

Comparison of neurodegeneration and cognitive impairment in neonatal mice exposed to propofol or isoflurane

Background

While previous studies have demonstrated neuronal apoptosis and associated cognitive impairment after isoflurane or propofol exposure in neonatal rodents, the effects of these two anesthetics have not been directly compared. Here, we compare and contrast the effectiveness of isoflurane and propofol to cause neurodegeneration in the developing brain and associated cognitive dysfunction.

Methods

Seven-day-old mice were used. Mice in the isoflurane treatment group received 6 h of 1.5% isoflurane, while mice in propofol treatment group received one peritoneal injection (150 mg/kg), which produced persistent anesthesia with loss of righting for at least 6 h. Mice in control groups received carrying gas or a peritoneal injection of vehicle (intralipid). At 6 h after anesthetic treatment, a subset of each group was sacrificed and examined for evidence of neurodegeneration, using plasma levels of S100β, and apoptosis using caspase-3 immunohistochemistry in the cerebral cortex and hippocampus and Western blot assays of the cortex. In addition, biomarkers for inflammation (interleukin-1, interleukin-6, and tumor necrosis factor alpha) were examined with Western blot analyses of the cortex. In another subset of mice, learning and memory were assessed 32 days after the anesthetic exposures using the Morris water maze.

Results

Isoflurane significantly increased plasma S100β levels compared to controls and propofol. Both isoflurane and propofol significantly increased caspase-3 levels in the cortex and hippocampus, though isoflurane was significantly more potent than propofol. However, there were no significant differences in the inflammatory biomarkers in the cortex or in subsequent learning and memory between the experimental groups.

Conclusion

Both isoflurane and propofol caused significant apoptosis in the mouse developing brain, with isoflurane being more potent. Isoflurane significantly increased levels of the plasma neurodegenerative biomarker, S100β. However, these neurodegenerative effects of isoflurane and propofol in the developing brain were not associated with effects on inflammation or with cognitive dysfunction in later life.

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.

Propofol exposure in pregnant rats induces neurotoxicity and persistent learning deficit in the offspring

Propofol is a general anesthetic widely used in surgical procedures, including those in pregnant women. Preclinical studies suggest that propofol may cause neuronal injury to the offspring of primates if it is administered during pregnancy. However, it is unknown whether those neuronal changes would lead to long-term behavioral deficits in the offspring. In this study, propofol (0.4 mg/kg/min, IV, 2 h), saline, or intralipid solution was administered to pregnant rats on gestational day 18. We detected increased levels of cleaved caspase-3 in fetal brain at 6 h after propofol exposure. The neuronal density of the hippocampus of offspring was reduced significantly on postnatal day 10 (P10) and P28. Synaptophysin levels were also significantly reduced on P28. Furthermore, exploratory and learning behaviors of offspring rats (started at P28) were assessed in open-field trial and eight-arm radial maze. The offspring from propofol-treated dams showed significantly less exploratory activity in the open-field test and less spatial learning in the eight-arm radial maze. Thus, this study suggested that propofol exposure during pregnancy in rat increased cleaved caspsase-3 levels in fetal brain, deletion of neurons, reduced synaptophysin levels in the hippocampal region, and persistent learning deficits in the offspring.

Anesthesia and the developing brain: relevance to the pediatric cardiac surgery

Anesthetic neurotoxicity has been a hot topic in anesthesia for the past decade. It is of special interest to pediatric anesthesiologists. A subgroup of children potentially at greater risk for anesthetic neurotoxicity, based on a prolonged anesthetic exposure early in development, are those children receiving anesthesia for surgical repair of congenital heart disease. These children have a known risk of neurologic deficit after cardiopulmonary bypass for surgical repair of congenital heart disease. Yet, the type of anesthesia used has not been considered as a potential etiology for their neurologic deficits. These children not only receive prolonged anesthetic exposure during surgical repair, but also receive repeated anesthetic exposures during a critical period of brain development. Their propensity to abnormal brain development, as a result of congenital heart disease, may modify their risk of anesthetic neurotoxicity. This review article provides an overview of anesthetic neurotoxicity from the perspective of a pediatric cardiac anesthesiologist and provides insight into basic science and clinical investigations as it relates to this unique group of children who have been studied over several decades for their risk of neurologic injury.

Chronic treatment with anesthetic propofol attenuates β-amyloid protein levels in brain tissues of aged mice

Alzheimer's disease (AD) is the most common form of dementia. At the present time, however, AD still lacks effective treatments. Our recent studies showed that chronic treatment with anesthetic propofol attenuated brain caspase-3 activation and improved cognitive function in aged mice. Accumulation of β-amyloid protein (Aβ) is a major component of the neuropathogenesis of AD dementia and cognitive impairment. We therefore set out to determine the effects of chronic treatment with propofol on Aβ levels in brain tissues of aged mice. Propofol (50 mg/kg) was administrated to aged (18 month-old) wild-type mice once a week for 8 weeks. The brain tissues of mice were harvested one day after the final propofol treatment. The harvested brain tissues were then subjected to enzyme-linked immunosorbent assay (ELISA) and Western blot analysis. Here we report that the propofol treatment reduced Aβ (Aβ40 and Aβ42) levels in the brain tissues of the aged mice. Moreover, the propofol treatment decreased the levels of β-site amyloid precursor protein cleaving enzyme (the enzyme for Aβ generation), and increased the levels of neprilysin (the enzyme for Aβ degradation) in the brain tissues of the aged mice. These results suggested that the chronic treatment with propofol might reduce brain Aβ levels potentially via decreasing brain levels of β-site amyloid precursor protein cleaving enzyme, thus decreasing Aβ generation; and via increasing brain neprilysin levels, thus increasing Aβ degradation. These preliminary findings from our pilot studies have established a system and postulated a new hypothesis for future research.