Combination of Isoflurane and Propofol as General Anesthesia During Orthopedic Surgery of Perioperative Cerebral Hypoperfusion Rats to Avoid Cognitive Impairment

Sub-dose anesthetics combined with chloride regulators protect the brain against chronic ischemia-hypoxia injury

BACKGROUND

Cerebral ischemia-hypoxia leads to excitotoxicity-mediated neuronal damage and cognitive dysfunction, especially in the elderly. Excessive intracellular [Cl- ]i accumulation weakens γ-aminobutyric acid (GABA) compensatory effects. Sub-anesthetic dose of propofol protected the brain against ischemia-hypoxia, which was abolished by blocking Cl- efflux transporter K+ /Cl- cotransporter 2 (KCC2). We aimed to determine whether low-dose anesthetic combined with [Cl- ]i regulators could restore the compensatory GABAergic system and improve cognitive function.

METHODS

Chronic cerebral hypoxia (CCH) model was established by bilateral carotid artery ligation in aged rats. Sub-dose of anesthetics (propofol and sevoflurane) with or without KCC2 agonist N-ethylmaleimide (NEM) or Na+ /K+ /Cl- cotransporter 1 (NKCC1) antagonist bumetanide (BTN) was administered systemically 30 days post-surgery. Primary rat hippocampal neuronal cultures were subjected to hypoxic injury with or without drug treatment. Memory function, hippocampal neuronal survival, GABAergic system functioning, and brain-derived neurotrophic factor (BDNF) expressions were evaluated.

RESULTS

Sub-anesthetic dose of combined propofol (1.2 μg mL-1 ) and sevoflurane [0.7 MAC (minimum alveolar concentration)] did not aggravate the hypoxic brain injury in rats or cell damage in neuronal cultures. Adding either BTN or NEM protected against hypoxic injury, associated with improved cognitive function in vivo, less intracellular accumulation of [Cl- ]i , reduced cell death, restored GABAergic compensation, and increased BDNF expression both in vivo and in vitro.

CONCLUSION

Sub-anesthetic dose of propofol and sevoflurane is a recommended anesthesia regimen in at-risk patients. Restoration of [Cl- ]i homeostasis and GABAergic could further reduce the brain damage caused by ischemia-hypoxia.

1% Isoflurane and 1.2 μg/ml of Propofol: A Combination of Anesthetics That Causes the Least Damage to Hypoxic Neurons

Backgrounds: Aging-related impairment of cerebral blood flow regulation leads to the disruption of neuronal micro-environmental homeostasis. Anesthetics should be carefully selected for aging patients since they have less cognition capacity. Effects and mechanisms of propofol or isoflurane have been widely investigated. However, how different combinations of propofol and isoflurane affect neurons and the mechanism still needs to be demonstrated.

Methods: We cultured rat hippocampal neurons and established a hypoxic injury model to imitate the micro-environment of aging brains. Three different combinations of propofol and isoflurane were applied to find out an optimum group via Cell Counting Kit-8 (CCK8) assay, lactic acid dehydrogenase (LDH) assay, real-time qPCR, and immunofluorescence of key proteins. Then BiP was silenced by small interfering RNA (siRNA) to explore the mechanism of how isoflurane and propofol affect neurons. Endoplasmic reticulum (ER) stress was measured by Western blot and immunofluorescence. To detect GABA_AR α1 subunit proteostasis and its function, real-time qPCR, immunoprecipitation, and Western blot were carried out.

Results: Hypoxic neurons showed no different changes on cell viability, LDH leakage, and ER stress after treatment with 1% isoflurane and 1.2 μg/ml of propofol. Hypoxic neurons showed a sharp increase of LDH leakage and ER stress and a decrease of cell viability after treatment with 1.4% isoflurane and 0.6 μg/ml of propofol or 0.5% isoflurane and 1.8 μg/ml of propofol. After knockdown of BiP, the application of 1% isoflurane and 1.2 μg/ml of propofol led to the decrease of GABA_AR α1 subunit protein content and viability of cell, as well as aggravation of ER stress.

Conclusion: A combination of 1% isoflurane and 1.2 μg/ml of propofol causes the least damage than do other dosages of both two drugs, and endogenous BiP plays an important role in this process.