Toxic and protective effects of inhaled anaesthetics on the developing animal brain: systematic review and update of recent experimental work

Exposure to halogenated ethers causes neurodegeneration and behavioural changes in young healthy experimental animals: a systematic review and meta analyses

The FDA issued a warning that repeated and prolonged use of inhalational anaesthetics in children younger than 3 years may increase the risk of neurological damage. Robust clinical evidence supporting this warning is however lacking. A systematic review of all preclinical evidence concerning isoflurane, sevoflurane, desflurane and enflurane exposure in young experimental animals on neurodegeneration and behaviour may elucidate how severe this risk actually is PubMed and Embase were comprehensively searched on November 23, 2022. Based on predefined selection criteria the obtained references were screened by two independent reviewers. Data regarding study design and outcome data (Caspase-3 and TUNEL for neurodegeneration, Morris water maze (MWM), Elevated plus maze (EPM), Open field (OF) and Fear conditioning (FC)) were extracted, and individual effect sizes were calculated and subsequently pooled using the random effects model. Subgroup analyses were predefined and conducted for species, sex, age at anesthesia, repeated or single exposure and on time of outcome measurement. Out of the 19.796 references screened 324 could be included in the review. For enflurane there were too few studies to conduct meta-analysis (n = 1). Exposure to sevoflurane, isoflurane and desflurane significantly increases Caspase-3 levels and TUNEL levels. Further, sevoflurane and isoflurane also cause learning and memory impairment, and increase anxiety. Desflurane showed little effect on learning and memory, and no effect on anxiety. Long term effects of sevoflurane and isoflurane on neurodegeneration could not be analysed due to too few studies. For behavioural outcomes, however, this was possible and revealed that sevoflurane caused impaired learning and memory in all three related outcomes and increased anxiety in the elevated plus maze. For isoflurane, impaired learning and memory was observed as well, but only sufficient data was available for two of the learning and memory related outcomes. Further, single exposure to either sevoflurane or isoflurane increased neurodegeneration and impaired learning and memory. In summary, we show evidence that exposure to halogenated ethers causes neurodegeneration and behavioural changes. These effects are most pronounced for sevoflurane and isoflurane and already present after single exposure. To date there are not sufficient studies to estimate the presence of long term neurodegenerative effects. Nevertheless, we provide evidence in this review of behavioral changes later in life, suggesting some permanent neurodegenerative changes. Altogether, In contrast to the warning issued by the FDA we show that already single exposure to isoflurane and sevoflurane negatively affects brain development. Based on the results of this review use of sevoflurane and isoflurane should be restrained as much as possible in this young vulnerable group, until more research on the long term permanent effects have been conducted.

Isoflurane-induced expression of miR-140-5p aggravates neurotoxicity in diabetic rats by targeting SNX12

MicroRNAs (miRNAs) are widely known as critical regulators in isoflurane-induced neurotoxicity during the development of brain. Moreover, isoflurane could aggravate cognitive impairment in diabetic rats. The present study was designed to investigate the role and mechanism of miR-140-5p on isoflurane-induced neurotoxicity in diabetic rats. Firstly, a diabetic rat model was established by injection of streptozotocin (STZ) and identified by Morris water maze test. The result indicated that isoflurane treatment exacerbated STZ-induced cognitive impairment, as demonstrated by increase of the latency to the platform and decrease of the proportion of time spent in the target quadrant. Secondly, miR-140-5p was up-regulated in diabetic rats treated with isoflurane. Functional assays revealed that knockdown of miR-140-5p attenuated neurotoxicity in diabetic rats, which was shown by a decrease of the latency to the platform and an increase of the proportion of time spent in the target quadrant. Mechanistically, we demonstrated that miR-140-5p directly bonded to SNX12 (sorting nexin 12). At last, the neuroprotective effect of miR-140-5p knockdown against isoflurane-aggravated neurotoxicity in diabetic rats was dependent on up-regulation of SNX12 and inhibition of cell apoptosis. In summary, these meaningful results demonstrated the mitigation of miR-140-5p knockdown against isoflurane-aggravated neurotoxicity in diabetic rats via SNX12, suggesting a novel target for neuroprotection in diabetes under isoflurane treatment.

The Effects of General Anesthetics on Synaptic Transmission

General anesthetics are a class of drugs that target the central nervous system and are widely used for various medical procedures. General anesthetics produce many behavioral changes required for clinical intervention, including amnesia, hypnosis, analgesia, and immobility; while they may also induce side effects like respiration and cardiovascular depressions. Understanding the mechanism of general anesthesia is essential for the development of selective general anesthetics which can preserve wanted pharmacological actions and exclude the side effects and underlying neural toxicities. However, the exact mechanism of how general anesthetics work is still elusive. Various molecular targets have been identified as specific targets for general anesthetics. Among these molecular targets, ion channels are the most principal category, including ligand-gated ionotropic receptors like γ-aminobutyric acid, glutamate and acetylcholine receptors, voltage-gated ion channels like voltage-gated sodium channel, calcium channel and potassium channels, and some second massager coupled channels. For neural functions of the central nervous system, synaptic transmission is the main procedure for which information is transmitted between neurons through brain regions, and intact synaptic function is fundamentally important for almost all the nervous functions, including consciousness, memory, and cognition. Therefore, it is important to understand the effects of general anesthetics on synaptic transmission via modulations of specific ion channels and relevant molecular targets, which can lead to the development of safer general anesthetics with selective actions. The present review will summarize the effects of various general anesthetics on synaptic transmissions and plasticity.

Post-stroke treatment with argon attenuated brain injury, reduced brain inflammation and enhanced M2 microglia/macrophage polarization: a randomized controlled animal study

BACKGROUND

In recent years, argon has been shown to exert neuroprotective effects in an array of models. However, the mechanisms by which argon exerts its neuroprotective characteristics remain unclear. Accumulating evidence imply that argon may exert neuroprotective effects via modulating the activation and polarization of microglia/macrophages after ischemic stroke. In the present study, we analyzed the underlying neuroprotective effects of delayed argon application until 7 days after reperfusion and explored the potential mechanisms.

METHODS

Twenty-one male Wistar rats underwent transient middle cerebral artery occlusion or sham surgery randomly for 2 h using the endoluminal thread model. Three hours after transient middle cerebral artery occlusion induction and 1 h after reperfusion, animals received either 50% vol Argon/50% vol O2 or 50% vol N2/50% vol O2 for 1 h. The primary outcome was the 6-point neuroscore from 24 h to d7 after reperfusion. Histological analyses including infarct volume, survival of neurons (NeuN) at the ischemic boundary zone, white matter integrity (Luxol Fast Blue), microglia/macrophage activation (Iba1), and polarization (Iba1/Arginase1 double staining) on d7 were conducted as well. Sample size calculation was performed using nQuery Advisor + nTerim 4.0. Independent t test, one-way ANOVA and repeated measures ANOVA were performed, respectively, for statistical analysis (SPSS 23.0).

RESULTS

The 6-point neuroscore from 24 h to d7 after reperfusion showed that tMCAO Ar group displayed significantly improved neurological performance compared to tMCAO N2 group (p = 0.026). The relative numbers of NeuN-positive cells in the ROIs of tMCAO Ar group significantly increased compared to tMCAO N2 group (p = 0.010 for cortex and p = 0.011 for subcortex). Argon significantly suppressed the microglia/macrophage activation as revealed by Iba1 staining (p = 0.0076) and promoted the M2 microglia/macrophage polarization as revealed by Iba1/Arginase 1 double staining (p = 0.000095).

CONCLUSIONS

Argon administration with a 3 h delay after stroke onset and 1 h after reperfusion significantly alleviated neurological deficit within the first week and preserved the neurons at the ischemic boundary zone 7 days after stroke. Moreover, argon reduced the excessive microglia/macrophage activation and promoted the switch of microglia/macrophage polarization towards the anti-inflammatory M2 phenotype. Studies making efforts to further elucidate the protective mechanisms and to benefit the translational application are of great value.

Argon attenuates the emergence of secondary injury after traumatic brain injury within a 2-hour incubation period compared to desflurane: an in vitro study

Despite years of research, treatment of traumatic brain injury (TBI) remains challenging. Considerable data exists that some volatile anesthetics might be neuroprotective. However, several studies have also revealed a rather neurotoxic profile of anesthetics. In this study, we investigated the effects of argon 50%, desflurane 6% and their combination in an in vitro TBI model with incubation times similar to narcotic time slots in a daily clinical routine. Organotypic hippocampal brain slices of 5- to 7-day-old mice were cultivated for 14 days before TBI was performed. Slices were eventually incubated for 2 hours in an atmosphere containing no anesthetic gas, argon 50% or desflurane 6% or both. Trauma intensity was evaluated via fluorescent imagery. Our results show that neither argon 50% nor desflurane 6% nor their combination could significantly reduce the trauma intensity in comparison to the standard atmosphere. However, in comparison to desflurane 6%, argon 50% displayed a rather neuroprotective profile within the first 2 hours after a focal mechanical trauma (P = 0.015). A 2-hour incubation in an atmosphere containing both gases, argon 50% and desflurane 6%, did not result in significant effects in comparison to the argon 50% group or the desflurane 6% group. Our findings demonstrate that within a 2-hour incubation time neither argon nor desflurane could affect propidium iodide-detectable cell death in an in vitro TBI model in comparison to the standard atmosphere, although cell death was less with argon 50% than with desflurane 6%. The results show that within this short time period processes concerning the development of secondary injury are already taking place and may be manipulated by argon.

Effect of propofol, sevoflurane, and isoflurane on postoperative cognitive dysfunction following laparoscopic cholecystectomy in elderly patients: A randomized controlled trial

STUDY OBJECTIVE

To compare the incidence of postoperative cognitive dysfunction (POCD) in elderly surgical patients (>60years) receiving different anesthetics (propofol, sevoflurane, or isoflurane) and to identify potential biomarkers of POCD in this patient population.

DESIGN

Prospective, randomized, double-blind clinical trial.

SETTING

University-affiliated teaching hospital.

PATIENTS

One hundred and fifty elderly patients scheduled for laparoscopic cholecystectomy.

INTERVENTIONS

Elderly patients undergoing laparoscopic cholecystectomy were randomly assigned to receive propofol, sevoflurane, or isoflurane anesthesia.

MEASUREMENTS

Cognitive function was assessed using neuropsychological tests at baseline (1day before surgery [D0]), and on postoperative day 1 (D1) and day 3 (D3). Plasma S-100β and Aβ_1-40 protein, IL-1β, IL-6 and TNF-α concentrations were assessed before induction of anesthesia (T0), after extubation (T1), and 1h (T2) and 24h (T3) postoperatively.

MAIN RESULTS

The incidence of POCD was significantly lower in the propofol group compared to the isoflurane group and the sevoflurane group at D1 and D3 (propofol vs. isoflurane: D1 and D3, P<0.001; propofol vs. sevoflurane: D1, P=0.012; D3, P=0.013). The incidence of POCD was significantly lower in the sevoflurane group compared to the isoflurane group at D1 (P=0.041), but not at D3. Postoperatively, plasma S-100β and Aβ_1-40 protein, IL-1β, IL-6, and TNF-α concentrations were significantly decreased in the propofol group compared to the isoflurane group.

CONCLUSIONS

Propofol anesthesia may be an option for elderly surgical patients.

Differential Suppression of Spontaneous and Noxious-evoked Somatosensory Cortical Activity by Isoflurane in the Neonatal Rat

BACKGROUND

The effect of neonatal anesthesia and pain on the developing brain is of considerable clinical importance, but few studies have evaluated noxious surgical input to the infant brain under anesthesia. Herein, the authors tested the effect of increasing isoflurane concentration on spontaneous and evoked nociceptive activity in the somatosensory cortex of rats at different postnatal ages.

METHODS

Intracortical extracellular field potentials evoked by hind paw C-fiber electrical stimulation were recorded in the rat somatosensory cortex at postnatal day (P) 7, P14, P21, and P30 during isoflurane anesthesia (n = 7 per group). The amplitudes of evoked potentials and the energies of evoked oscillations (1 to 100 Hz over 3 s) were measured after equilibration at 1.5% isoflurane and during step increases in inspired isoflurane. Responses during and after plantar hind paw incision were compared at P7 and P30 (n = 6 per group).

RESULTS

At P7, cortical activity was silent at 1.5% isoflurane but noxious-evoked potentials decreased only gradually in amplitude and energy with step increases in isoflurane. The resistance of noxious-evoked potentials to isoflurane at P7 was significantly enhanced after surgical hind paw incision (69 ± 16% vs. 6 ± 1% in nonincised animals at maximum inspired isoflurane). This resistance was age dependent; at P14 to P30, noxious-evoked responses decreased sharply with increasing isoflurane (step 3 [4%] P7: 50 ± 9%, P30: 4 ± 1% of baseline). Hind paw incision at P30 sensitized noxious-evoked potentials, but this was suppressed by higher isoflurane concentrations.

CONCLUSIONS

Despite suppression of spontaneous activity, cortical-evoked potentials are more resistant to isoflurane in young rats and are further sensitized by surgical injury.

Desflurane impairs outcome of organotypic hippocampal slices in an in vitro model of traumatic brain injury

Decreased mortality and disability after traumatic brain injury is a significant medical challenge. Desflurane, a widely used volatile anesthetic has proven to be neuroprotective in a variety of in vitro and in vivo models of ischemic brain injury. The aim of this study was to investigate whether desflurane exhibits neuroprotective properties in an in vitro model of traumatic brain injury. Organotypic hippocampal slice cultures were prepared from brains of 5–7-day-old C57/BL6 mouse pups. After 14 days of culture, the slices were subjected to a focal mechanical trauma and thereafter incubated with three different concentrations of desflurane (2, 4 and 6%) for 2, 24 and 72 hours. Cell injury was assessed with propodium iodide uptake. Our results showed that after 2 hours of desflurane exposure, no significant change in trauma intensity was observed. However, 2% and 4% desflurane could reduce the trauma intensity significantly in the no trauma group than in the no desflurane and trauma group. Incubation with 4% desflurane for 24 hours doubled the trauma intensity in comparison to the trauma control group and the trauma intensity further increased after 72 hours of incubation. Furthermore, a dose-dependent increase of trauma intensity after 24 hours exposure was observed. Our results suggest that a general neuroprotective attribute of desflurane in an in vitro model of traumatic brain injury was not observed.

Post-Exposure Exercise Fails to Ameliorate Memory Impairment Induced by Propofol and Ketamine in Developing Rats

Background

This aim of this study was to determine the effects of ketamine-propofol combination on learning and memory, as well as exercise, on anesthetic neurotoxicity.

Material/Methods

A ketamine-propofol combination was administered once (group SKP, Single Ketamine Propofol) on P7 (postnatal day 7) or in 3 treatments on P6, P8, and P10 (group MKP, Multiple Ketamine Propofol). Rat pups in group C (Control) received equivalent volumes of normal saline in 3 injections on P6, P8, and P10. Rats designated MKPR (Multiple Ketamine Propofol and running) and CR (Control and running) began running exercise on P21 on wheels. Learning and memory was assessed by Morris water maze and fear conditioning tests. Hippocampal neurogenesis of rats was detected by BrdU immunofluorescence.

Results

MKP rats had longer latency to platform than group C during training in the Morris water maze; SKP rats stayed in the target quadrant longer than MKP rats during testing (P<0.05). Rats in running groups had shorter latency than non-running rats, but running had no interaction with anesthesia exposure.

Conclusions

Repeat ketamine-propofol combination doses increase risk of memory impairment in developing rats. Running has no impact on anesthetic neurotoxicity.

Propofol, but not etomidate, increases corticosterone levels and induces long-term alteration in hippocampal synaptic activity in neonatal rats

Animal studies provide strong evidence that general anesthetics (GAs), administered during the early postnatal period, induce long-term cognitive and neurological abnormalities. Because the brain growth spurt in rodents is delayed compared to that in humans, a fundamental question is whether the postnatal human brain is similarly vulnerable. Sevoflurane and propofol, GAs that share positive modulation of the gamma-aminobutyric acid type A receptor (GABAAR) function cause marked increase in corticosterone levels and induce long-term developmental alterations in synaptic activity in rodents. If synaptogenesis is affected, investigation of mechanisms of the synaptic effects of GAs is of high interest because synaptogenesis in humans continues for several years after birth. Here, we compared long-term synaptic effects of etomidate with those of propofol. Etomidate and propofol both positively modulate GABAAR activity, but in contrast to propofol, etomidate inhibits the adrenal synthesis of corticosterone. Postnatal day (P) 4, 5, or 6 rats received five injections of etomidate, propofol, or vehicle control during 5h of maternal separation. Endocrine effects of the anesthetics were evaluated by measuring serum levels of corticosterone immediately after anesthesia or maternal separation. The frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs) in hippocampal CA1 pyramidal neurons were measured at P24-40 and P≥80. Only propofol caused a significant increase in serum corticosterone levels (F(4.26)=17.739, P<0.001). In contrast to increased frequency of mIPSCs in the propofol group (F(4.23)=8.731, p<0.001), mIPSC activity in the etomidate group was not different from that in the vehicle groups. The results of this study together with previously published data suggest that anesthetic-caused increase in corticosterone levels is required for GABAergic GAs to induce synaptic effects in the form of a long-term increase in the frequency of hippocampal mIPSCs.

Xenon depresses aEEG background voltage activity whilst maintaining cardiovascular stability in sedated healthy newborn pigs

BACKGROUND

Changes in electroencephalography (EEG) voltage range are used to monitor the depth of anaesthesia, as well as predict outcome after hypoxia-ischaemia in neonates. Xenon is being investigated as a potential neuroprotectant after hypoxic-ischaemic brain injury, but the effect of Xenon on EEG parameters in children or neonates is not known. This study aimed to examine the effect of 50% inhaled Xenon on background amplitude-integrated EEG (aEEG) activity in sedated healthy newborn pigs.

METHODS

Five healthy newborn pigs, receiving intravenous fentanyl sedation, were ventilated for 24 h with 50%Xenon, 30%O2 and 20%N2 at normothermia. The upper and lower voltage-range of the aEEG was continuously monitored together with cardiovascular parameters throughout a 1 h baseline period with fentanyl sedation only, followed by 24 h of Xenon administration.

RESULTS

The median (IQR) upper and lower aEEG voltage during 1 h baseline was 48.0 μV (46.0-50.0) and 25.0 μV (23.0-26.0), respectively. The median (IQR) aEEG upper and lower voltage ranges were significantly depressed to 21.5 μV (20.0-26.5) and 12.0 μV (12.0-16.5) from 10 min after the onset of 50% Xenon administration (p=0.002). After the initial Xenon induced depression in background aEEG voltage, no further aEEG changes were seen over the following 24h of ventilation with 50% xenon under fentanyl sedation. Mean arterial blood pressure and heart rate remained stable.

CONCLUSION

Mean arterial blood pressure and heart rate were not significantly influenced by 24h Xenon ventilation. 50% Xenon rapidly depresses background aEEG voltage to a steady ~50% lower level in sedated healthy newborn pigs. Therefore, care must be taken when interpreting the background voltage in neonates also receiving Xenon.

Total intravenous anesthesia will supercede inhalational anesthesia in pediatric anesthetic practice

Inhalational anesthesia has dominated the practice of pediatric anesthesia. However, as the introduction of agents such as propofol, short-acting opioids, midazolam, and dexmedetomidine a monumental change has occurred. With increasing use, the overwhelming advantages of total intravenous anesthesia (TIVA) have emerged and driven change in practice. These advantages, outlined in this review, will justify why TIVA will supercede inhalational anesthesia in future pediatric anesthetic practice.