Conflicting Actions of Inhalational Anesthetics, Neurotoxicity and Neuroprotection, Mediated by the Unfolded Protein Response

Effect of Propofol and Sevoflurane on Vanishing White Matter Models

BACKGROUND

The leukodystrophy vanishing white matter (VWM) most often has its onset in childhood and is characterized by chronic decline and additionally stress-provoked acute neurological deterioration. Anesthesia is a stressor that can trigger this acute decline. The commonly used inhalational anesthetic sevoflurane has been reported to activate the integrated stress response (ISR), whereas the intravenous anesthetic propofol has not. We aimed to assess the differential effects of these anesthetics in models of VWM.

METHODS

We investigated the molecular effects of sevoflurane and propofol on the ISR in a murine neural cell line and in cultured astrocytes from patients with VWM and control subjects with immunostainings for prototypic ISR marker activating transcription factor 4 (ATF4). We determined the effects of these anesthetics on clinical signs and expression of ISR mRNAs in VWM and wild-type mice.

RESULTS

In the murine cell line, sevoflurane increased ATF4 accumulation compared with its vehicle (+157%); in contrast, propofol's vehicle without (-22%) and with (-23%) propofol decreased tunicamycin-increased levels of ATF4 to similar degree. Sevoflurane activated the ISR in astrocytes from control subjects (+17-33%) but not from patients with VWM (+1-2%). Propofol and its vehicle did not impact the ISR in astrocytes. The anesthetics did not have prolonged effects on motor skills in VWM mice but had small differential effects on ISR mRNA levels, consistently higher with sevoflurane than with propofol.

CONCLUSIONS

We observed differential effects of the anesthetics in cultured neural cells and on expression levels of ISR markers in VWM mice, but not on clinical signs in VWM mice.

Egr2 contributes to age-dependent vulnerability to sevoflurane-induced cognitive deficits in mice

Sevoflurane inhalation is prone to initiate cognitive deficits in infants. The early growth response-2 (Egr-2) gene is DNA-binding transcription factor, involving in cognitive function. In this study we explored the molecular mechanisms underlying the vulnerability to cognitive deficits after sevoflurane administration. Six-day-old (young) and 6-week-old (early adult) mice received anesthesia with 3% sevoflurane for 2 h daily for 3 days. We showed that multiple exposures of sevoflurane induced significant learning ability impairment in young but not early adult mice, assessed in Morris water maze test on postnatal days 65. The integrated differential expression analysis revealed distinct transcription responses of Egr family members in the hippocampus of the young and early adult mice after sevoflurane administration. Particularly, Egr2 was significantly upregulated after sevoflurane exposure only in young mice. Microinjection of Egr2 shRNA recombinant adeno-associated virus into the dentate gyrus alleviated sevoflurane-induced cognitive deficits, and abolished sevoflurane-induced dendritic spins loss and BDNF downregulation in young mice. On the contrary, microinjection of the Egr2 overexpression virus in the dentate gyrus aggravated learning ability impairment induced by sevoflurane in young mice but not early adult mice. Furthermore, we revealed that sevoflurane markedly upregulated the nuclear factors of activated T-cells NFATC1 and NFATC2 in young mice, which were involved in Egr2 regulation. In conclusion, Egr2 serves as a critical factor for age-dependent vulnerability to sevoflurane-induced cognitive deficits.

Sevoflurane attenuates cognitive dysfunction and NLRP3-dependent caspase-1/11-GSDMD pathway-mediated pyroptosis in the hippocampus via upregulation of SIRT1 in a sepsis model

Septic encephalopathy (SE) is a devastating consequence of sepsis, a hyper-triggered host response against infectious challenge, which ultimately leads to brain damage. The present study examined whether sevoflurane (SVF), a volatile anaesthetic, can counteract the perturbation of homeostasis in a caecal ligation and puncture (CLP)-induced mouse model of SE. SVF enhances neurocognition in terms of spatial memory improvement via counter-regulation of activated oxidative-inflammatory stress and pyroptotic processes in SE. Further, the beneficial effects of SVF against SE are mediated by activation of silent information regulator 1 (SIRT1)-mediated reduction of reactive oxygen species (ROS) level, regulation of thioredoxin (TXN) and thioredoxin interacting protein (TIP) levels, reduction of inflammatory-pyroptotic signalling (NLRP3, caspase 1/11, GSDMD, TLR4 and TRIF) proteins, as well as a reduction of inflammatory cytokine (IL-1β and IL-18) levels. These findings suggest that SVF may have therapeutic potential for the treatment of SE and associated cognitive malfunction.

Long Non-Coding RNA maternally expressed 3 (MEG3) regulates isoflurane-induced cognitive dysfunction by targeting miR-7-5p

This study aimed to investigate the role and mechanism of long non-coding RNA maternally expressed gene 3 (MEG3) in cognitive dysfunction induced by isoflurane (ISO). Morrier water maze analysis was performed to evaluate the cognitive function of rats. Modified modified neurological severity score (mNSS) scores were assessed for neurological damage. The levels of MEG3 in hippocampal tissues of rats and hippocampal neuron cell lines HT22 were examined by reverse transcription-quantitative polymerase chain reaction (qRT-PCR). Moreover, the cell viability and apoptosis were assessed by the Cell Counting Kit-8 (CCK-8) and flow cytometry assay. Indicators of inflammation and oxidative stress were determined using enzyme-linked immunosorbent assay (ELISA) and commercial assay kits. Relationship between MEG3 and microRNA (miR)-7-5p was verified by the dual-luciferase reporter gene assay. MEG3 was increased in hippocampal tissues and HT22 after ISO treatment (P < 0.05). MEG3 downregulation alleviated the increase in neurological severity score and cognitive dysfunction caused by ISO treatment (P < 0.05). In vitro, MEG3 downregulation alleviates the decrease in cell activity and increased apoptosis induced by ISO. What's more, MEG3 reduction eliminated activation of neuroinflammation and oxidative stress promoted by ISO treatment in rats and HT22 (P < 0.05). MEG3 was confirmed to specifically bind to miR-7-5p. Inhibition of miR-7-5p eliminated the alleviating effects of MEG3 downregulation on cognitive dysfunction caused by ISO treatment. Decreased MEG3 alleviates cognitive dysfunction caused by ISO by targeting miR-7-5p and play a neuroprotective effect. We present a strategy for MEG3 as a potential target for brain protection during anesthesia.

A multimodal sevoflurane-based sedation regimen in combination with targeted temperature management in post-cardiac arrest patients reduces the incidence of delirium: An observational propensity score-matched study

BACKGROUND

Recent studies suggest that volatile anaesthetics are safe, efficient, and reliable alternatives to the use of intravenous anaesthetics for out-of-hospital cardiac arrest (OHCA) patients admitted to the intensive care unit (ICU). We hypothesised that volatile anaesthetics may reduce the incidence of delirium rather than intravenous sedatives. This retrospective study aimed to investigate whether sevoflurane combined with higher targeted temperature management could decrease the incidence of delirium when compared with intravenous anaesthetics with lower targeted temperature management.

METHODS

Using a propensity score-matched analysis, we retrospectively compared a target temperature management (32-34 °C) method along with intravenous sedation (TTM-33/IV) and a modified target temperature management (34-36 °C) method along with sevoflurane sedation (mTTM-36/sevo). We used the confusion assessment method for the ICU to measure the incidence of delirium. We calculated the time-dependent risk on delirium using the multivariate Cox regression model.

RESULTS

The incidence of delirium was significantly lower (p = 0.001) in OHCA patients of the mTTM-36/sevo group (9/56, 16.1%) than in those of the TTM-33/IV group (25/67, 37.3%). Mechanical ventilation and lengths of stay in the ICU (p < 0.001) and hospital stay (p = 0.04) were shorter in the mTTM-36/sevo group. Patients in the TTM-33/IV group required more midazolam, propofol, and fentanyl. We observed no significant difference in mortality.

CONCLUSION

A multimodal sevoflurane-based sedation regimen together with targeted temperature management resulted in a lower incidence of delirium and a shorter duration for mechanical ventilation and ICU length of stay than did the treatment with intravenous sedation combined with the classical cooling protocol.

General anesthesia activates the mitochondrial unfolded protein response and induces age-dependent, long-lasting changes in mitochondrial function in the developing brain

General anesthesia induces changes in dendritic spine number and synaptic transmission in developing mice. These changes are rather disturbing, as similar changes are seen in animal models of neurodevelopmental disorders. We previously suggested that mTor-dependent upregulation of mitochondrial function may be involved in such changes. To further understand the significance of mitochondrial changes after general anesthesia during neurodevelopment, we exposed young mice to 2.5 % sevoflurane for 2 h followed by injection of rotenone, a mitochondrial complex I inhibitor. In postnatal day 17 (PND17) mice, intraperitoneal injection of rotenone not only blocked sevoflurane-induced increases in mitochondrial function, it also prevented sevoflurane-induced changes in excitatory synaptic transmission. Interestingly, similar changes were not observed in younger, neonatal mice (PND7). We next assessed whether the mitochondrial unfolded protein response (UPR^mt) acted as a link between anesthetic exposure and mitochondrial function. Expression of UPR^mt proteins, which help maintain protein-folding homeostasis and increase mitochondrial function, was increased 6 h after sevoflurane exposure. Our results show that a single, brief sevoflurane exposure induces age-dependent changes in mitochondrial function that constitute an important mechanism for the increase in excitatory synaptic transmission in late postnatal mice, and also suggest mitochondria and UPR^mt as potential targets for preventing anesthesia toxicity.