Effect and mechanism of a subanesthetic dose of esketamine on postoperative neurocognitive disorders through the regulating of the TLR4/NF-κB pathway in microglia

Perioperative neurocognitive disorders (PND) are postoperative or anesthesia-related complications of the central nervous system, characterized by intelligence decline, memory loss, attention deficit, impaired decision-making skills, reduced language comprehension performance, and psychological disorders. This study aims to investigate the impact of a subanesthetic dose of esketamine on PND in aged mice by regulating the microglia toll-like receptor 4 (TLR4)/nuclear factor κB (NF-κB) pathway. An exploratory laparotomy model was established in 18-month-old C57BL/6 mice post-anesthesia. Behavioral evaluations such as open field tests and Morris water maze tests for autonomous activity and spatial learning and memory ability. Different esketamine doses were administered to aged mice, followed by behavioral assessment for autonomous activity and learning/memory abilities. Nucleic acid extraction employed magnetic nanoparticles, while qRT-PCR measured mRNA levels of tumor necrosis factor-α, interleukin-6, and interleukin-1β. Western Blot detected the Iba-1 and TLR4 protein expression and phosphorylation status of the P65 protein. Immunofluorescence determined the fluorescence intensity of Iba-1 and P-NF-κBp65. MTT assay evaluated cell viability. As a result, we demonstrated that a subanesthetic dose of esketamine effectively inhibited microglia activation and TLR4/NF-κB signaling pathway both in vivo and in vitro, resulting in decreased levels of inflammatory factors and improved neuroinflammatory responses, ultimately alleviating postoperative neurocognitive dysfunction. Notably, our findings revealed that laparotomy exploratory surgery-induced cognitive dysfunction, which can be improved by esketamine’s neuroprotective effects. Furthermore, our study also highlighted the protective effect of esketamine against lipopolysaccharide-induced inflammatory response in BV2 cells by inhibiting the TLR4/NF-κB signaling pathway.