Background: Isoflurane can significantly induce inflammation in children without surgical stress. The toll-like receptor 4 (TLR4) is closely related to noninfectious inflammation in the brain.

Objectives: To investigate the role of TLR4-small interfering RNA (siRNA) in learning and memory impairment in young mice induced by isoflurane.

Material and methods: The C57 newborn mice were randomly allocated into normal control (control), isoflurane anesthesia (isoflurane), TLR4 interference empty vector+isoflurane anesthesia (siRNA-NC), and TLR4 interference+isoflurane anesthesia (TLR-siRNA) groups. Their behavior and pathological condition were detected using Morris water maze and hematoxylin and eosin (H&E) staining, respectively. The TLR4, brain-derived neurotrophic factor (BDNF) and cyclic adenosine monophosphate response element-binding protein 1 (CREB1) mRNA expressions were detected using quantitative real-time polymerase chain reaction (qRT-PCR). Serum tumor necrosis factor alpha (TNF-α) and interleukin (IL)-6 were detected by means of the enzyme-linked immunosorbent assay (ELISA). Apoptosis rate was detected with terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). The TLR4, TNF-α, IL-6, BDNF, CREB1, extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun N-terminal kinase (JNK) protein expressions were detected using western blot (WB).

Results: Compared with the control group, the number of times the mice crossed the platform, and the time spent at the circumjacent area I and II of the platform were significantly decreased in the isoflurane group; the TLR4, TNF-α and IL-6 expressions were significantly increased in the isoflurane group, as compared to control; the results were reversed after the TLR4 interference. The hippocampal neurons in the isoflurane and siRNA-NC groups showed arrangement disorder and a high number of inflammatory infiltrates, while in the TLR-siRNA group they were closely and orderly arranged. Compared with the control group, the apoptosis rate and JNK protein expression in the isoflurane group were significantly increased, CREB1 protein expression was significantly decreased, and BDNF and ERK1/2 protein expressions showed no significant changes. Compared with the isoflurane group, the apoptosis rate of the TLR-siRNA group was significantly decreased, BDNF and CREB1 protein expressions were significantly increased, and ERK1/2 and JNK did not change significantly.

Conclusions: Isoflurane stimulates the overexpression of inflammatory response factors, playing an important role in the cognitive impairment process. As a mediator of the innate immune inflammatory response, TLR4 plays an important role in the process of cell injury, which may be delayed by blocking the TLR4 signal.

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Lin Lin et al.
Advances in Clinical and Experimental Medicine: Official Organ Wroclaw Medical University April 2022