An Amino Acids and Dipeptide Injection Inhibits the TNF-α/HMGB1 Inflammatory Signaling Pathway to Reduce Pyroptosis and M1 Microglial Polarization in POCD Mice: the Gut to the Brain

Vagus nerve stimulation (VNS) preventing postoperative cognitive dysfunction (POCD): two potential mechanisms in cognitive function

Postoperative cognitive dysfunction (POCD) impacts a significant number of patients annually, frequently impairing their cognitive abilities and resulting in unfavorable clinical outcomes. Aimed at addressing cognitive impairment, vagus nerve stimulation (VNS) is a therapeutic approach, which was used in many mental disordered diseases, through the modulation of vagus nerve activity. In POCD model, the enhancement of cognition function provided by VNS was shown, demonstrating VNS effect on cognition in POCD. In the present study, we primarily concentrates on elucidating the role of the VNS improving the cognitive function in POCD, via two potential mechanisms: the inflammatory microenvironment and epigenetics. This study provided a theoretical support for the feasibility that VNS can be a potential method to enhance cognition function in POCD.

D30 Alleviates β2-Microglobulin-Facilitated Neurotoxic Microglial Responses in Isoflurane/Surgery-Induced Cognitive Dysfunction in Aged Mice

Postoperative cognitive dysfunction (POCD) is a common complication with no effective treatment in elderly patients. POCD, Alzheimer disease (AD), and many other cognitive diseases mostly involve neurotoxic microglia response, and recently, β2-microglobulin (B2M) has been suggested to play a pivotal role. A novel pyromeconic acid-styrene hybrid compound D30 was synthesized by our team and shown to be safe and effective in some neurodegenerative mouse models. In this study, we evaluated D30 on POCD and its potential mechanism. Fourteen- to 18-month-old male C57BL/6 mice were used to establish POCD through isoflurane anesthesia and surgery. The plasma of elderly patients was collected pre- and postoperatively. Primary mouse microglia were subjected to various stimulations in multiple experimental designs to imitate in vivo POCD-like conditions. Morris water maze, fear conditioning, western blot, immunofluorescent staining, and blood-brain barrier (BBB) permeability tests were conducted in this study. D30 administration significantly improved learning and memory in aged mice following POCD. Neurotoxic M1 microglia cells were dramatically increased following POCD, manifested as morphologically changing into fewer and shorter branches, enlarged somatic areas, and upregulated expression of iNOS and C1q. Notably, following POCD, B2M was significantly upregulated in the plasma and the brain. D30 treatment significantly suppressed these pathologic changes, by inhibiting the POCD-induced BBB breakdown while suppressing the surge of plasma B2M levels. D30 treatment suppressed POCD-induced surge of B2M and Aβ plaques in the brain and preserved adult hippocampal neurogenesis vulnerable to POCD. Furthermore, postoperative levels of B2M were significantly elevated over the preoperative levels in patients aged 80 years and over. In parallel with mouse plasma after POCD, the postoperative patient plasma was also much more effective at activating M1 microglia. Of note, this POCD plasma-induced activation of M1 microglia was largely prevented by D30 treatment. Taken together, by inhibiting the surge of plasma B2M, protecting BBB integrity, and reducing inflammatory response, D30 protected aged mice from B2M-facilitated POCD.