A Scoping Review of the Mechanisms Underlying Developmental Anesthetic Neurotoxicity

Structural basis for the inhibition of cystathionine-β-synthase by isoflurane and its role in anaesthesia-induced social dysfunction in mice

BACKGROUND

Anaesthesia has been shown to impair social functioning, but the underlying mechanisms remain largely unknown. The volatile anaesthetic isoflurane potentially disrupts the methionine cycle and trans-sulphuration pathway, contributing to social deficits. Cystathionine-β-synthase (CBS), a key enzyme in this pathway, might be targeted by isoflurane. We investigated the CBS-isoflurane interaction and its role in neuronal function and social behaviour.

METHODS

Mice aged 3-15 months were anaesthetised with 2 vol% isoflurane for 2 h, and social behaviours were tested 24 h after exposure. Alterations in neuronal activity were assessed using electrophysiological analysis in vivo. Pharmacological activators (S-adenosylmethionine [SAM]) or inhibitors (amino-oxyacetic acid [AOAA]), and adeno-associated virus (AAV) were used to modulate CBS activity. The binding site of isoflurane on CBS was determined using X-ray crystallography. A novel transgenic model with a point mutation knock-in was constructed to eliminate the CBS-isoflurane interaction.

RESULTS

Isoflurane inhibited CBS activity (by 0.35-fold [0.07] vs 1.00-fold [0.05]; P<0.001), leading to neuronal hypoactivity in the anterior cingulate cortex (ACC) and social impairments in adult and elderly mice. SAM, AOAA, and AAV interventions demonstrated a causal link. Structural and functional analysis identified the lysine 273 (K273) in CBS to be involved in isoflurane inhibition. CBS K273A knock-in mice exhibited increased CBS activity compared with wild-type littermates after isoflurane exposure (2.2-fold [0.22] vs 1.0-fold [0.28]; P<0.001), with successful alleviation of ACC neuronal hypoactivity and social dysfunction.

CONCLUSIONS

These findings reveal a crucial role for CBS inhibition by isoflurane in anaesthesia-induced social impairment.

Comparing the Effects of Propofol and Thiopental on Human Renal HEK-293 Cells With a Focus on Reactive Oxygen Species (ROS) Production, Cytotoxicity, and Apoptosis: Insights Into Dose-Dependent Toxicity

OBJECTIVES

Propofol and thiopental are widely used as hypnotic, sedative, antiepileptic, and analgesic agents in general anesthesia and intensive care; however, their side effects remain unknown. They are used for long periods and at high doses for sedation in total intravenous anesthesia (TIVA) and intensive care units. Long-term and high-dose use of these drugs can lead to accumulation in plasma and tissues, resulting in high drug concentrations and increasing the risk of potential toxicity (e.g., nephrotoxicity). In our study, the cytotoxic and apoptotic effects of propofol and thiopental on kidney cells (HEK-293) and their effects on the formation of reactive oxygen species (ROS) when used in high doses were investigated and compared in vitro.

MATERIALS AND METHODS

The half-maximal inhibitory concentration (IC50) of each drug in HEK-293 cells was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. The apoptotic effects were assessed at two different doses of each drug using the annexin V method. Morphological examinations were conducted using the acridine orange/ethidium bromide method, and intracellular ROS levels were determined by flow cytometry.

RESULTS

The IC50 values of propofol and thiopental for HEK-293 cells were 206.59 μg/ml and 109.68 μg/ml, respectively. Compared to the control group, thiopental at ≥25 μg/ml and propofol at ≥50 μg/ml exhibited cytotoxicity. Additionally, propofol exhibited significantly lower cytotoxic effects than thiopental did.

CONCLUSION

Our study showed that both propofol and thiopental exerted significant cytotoxic effects on HEK-293 cells at concentrations exceeding clinical levels, primarily by increasing intracellular ROS levels and inducing apoptosis. Future research in this area will deepen our understanding of these mechanisms and improve patient safety in clinical anesthesia practice.

Early Postnatal Exposure to Midazolam Causes Lasting Histological and Neurobehavioral Deficits via Activation of the mTOR Pathway

Exposure to general anesthetics can adversely affect brain development, but there is little study of sedative agents used in intensive care that act via similar pharmacologic mechanisms. Using quantitative immunohistochemistry and neurobehavioral testing and an established protocol for murine sedation, we tested the hypothesis that lengthy, repetitive exposure to midazolam, a commonly used sedative in pediatric intensive care, interferes with neuronal development and subsequent cognitive function via actions on the mechanistic target of rapamycin (mTOR) pathway. We found that mice in the midazolam sedation group exhibited a chronic, significant increase in the expression of mTOR activity pathway markers in comparison to controls. Furthermore, both neurobehavioral outcomes, deficits in Y-maze and fear-conditioning performance, and neuropathologic effects of midazolam sedation exposure, including disrupted dendritic arborization and synaptogenesis, were ameliorated via treatment with rapamycin, a pharmacologic mTOR pathway inhibitor. We conclude that prolonged, repetitive exposure to midazolam sedation interferes with the development of neural circuitry via a pathologic increase in mTOR pathway signaling during brain development that has lasting consequences for both brain structure and function.