Isoflurane-Induced Postoperative Neurovascular and Cognitive Dysfunction Is Associated with VEGF Overexpression in Aged Rats

Cellular Components of the Blood-Brain Barrier and Their Involvement in Aging-Associated Cognitive Impairment

Human life expectancy has been significantly extended, which poses major challenges to our healthcare and social systems. Aging-associated cognitive impairment is attributed to endothelial dysfunction in the cardiovascular system and neurological dysfunction in the central nervous system. The central nervous system is considered an immune-privileged tissue due to the exquisite protection provided by the blood-brain barrier. The present review provides an overview of the structure and function of blood-brain barrier, extending the cell components of blood-brain barrier from endothelial cells and pericytes to astrocytes, perivascular macrophages and oligodendrocyte progenitor cells. In particular, the pathological changes in the blood-brain barrier in aging, with special focus on the underlying mechanisms and molecular changes, are presented. Furthermore, the potential preventive/therapeutic strategies against aging-associated blood-brain barrier disruption are discussed.

Specific antagonist of receptor for advanced glycation end‑products attenuates delirium‑like behaviours induced by sevoflurane anaesthesia with surgery in aged mice partially by improving damage to the blood‑brain barrier

Postoperative delirium (POD), which occurs in hospital up to 1-week post-procedure or until discharge, is a common complication, especially in older adult patients. However, the pathogenesis of POD remains unclear. Although damage to blood-brain barrier (BBB) integrity is involved in the neuropathogenesis of POD, the specific role of the BBB in POD requires further elucidation. Anaesthesia using 2% isoflurane for 4 h results in the upregulation of hippocampal receptor for advanced glycation end-products (RAGE) expression and β-amyloid accumulation in aged rats. The present study investigated the role of RAGE in BBB integrity and its mechanisms in POD-like behaviours. The buried food, open field and Y maze tests were used to evaluate neurobehavioural changes in aged mice following 2.5% sevoflurane anaesthesia administration with exploratory laparotomy. Levels of tight junction proteins were assessed by western blotting. Multiphoton in vivo microscopy was used to observe the ultrastructural changes in the BBB in the hippocampal CA1 region. Anaesthesia with surgery decreased the levels of tight junction proteins occludin and claudin 5, increased matrix metalloproteinases (MMPs) 2 and 9, damaged the ultrastructure of the BBB and induced POD-like behaviour. FPS-ZM1, a specific RAGE antagonist, ameliorated POD-like behaviour induced by anaesthesia and surgery in aged mice. Furthermore, FPS-ZM1 also restored decreased levels of occludin and claudin 5 as well as increased levels of MMP2 and MMP9. The present findings suggested that RAGE signalling was involved in BBB damage following anaesthesia with surgery. Thus, RAGE has potential as a novel therapeutic intervention for the prevention of POD.

Neuroinflammation as the Underlying Mechanism of Postoperative Cognitive Dysfunction and Therapeutic Strategies

Postoperative cognitive dysfunction (POCD) is a common neurological complication following surgery and general anesthesia, especially in elderly patients. Severe cases delay patient discharge, affect the patient’s quality of life after surgery, and are heavy burdens to society. In addition, as the population ages, surgery is increasingly used for older patients and those with higher prevalences of complications. This trend presents a huge challenge to the current healthcare system. Although studies on POCD are ongoing, the underlying pathogenesis is still unclear due to conflicting results and lack of evidence. According to existing studies, the occurrence and development of POCD are related to multiple factors. Among them, the pathogenesis of neuroinflammation in POCD has become a focus of research in recent years, and many clinical and preclinical studies have confirmed the correlation between neuroinflammation and POCD. In this article, we reviewed how central nervous system inflammation occurred, and how it could lead to POCD with changes in peripheral circulation and the pathological pathways between peripheral circulation and the central nervous system (CNS). Furthermore, we proposed some potential therapeutic targets, diagnosis and treatment strategies at the cellular and molecular levels, and clinical applications. The goal of this article was to provide a better perspective for understanding the occurrence of POCD, its development, and preventive strategies to help manage these vulnerable geriatric patients.

Connexin 43 gap junction-mediated astrocytic network reconstruction attenuates isoflurane-induced cognitive dysfunction in mice

Background

Postoperative cognitive dysfunction (POCD) is a common complication following anesthesia and surgery. General anesthetic isoflurane has potential neurotoxicity and induces cognitive impairments, but the exact mechanism remains unclear. Astrocytes form interconnected networks in the adult brain through gap junctions (GJs), which primarily comprise connexin 43 (Cx43), and play important roles in brain homeostasis and functions such as memory. However, the role of the GJ-Cx43-mediated astrocytic network in isoflurane-induced cognitive dysfunction has not been defined.

Methods

4-month-old male C57BL/6 mice were exposure to long-term isoflurane to induce cognitive impairment. To simulate an in vitro isoflurane-induced cognitive dysfunction‐like condition, primary mouse astrocytes were subjected to long-term isoflurane exposure. Cognitive function was assessed by Y-maze and fear conditioning tests. Western blot was used to determine the expression levels of different functional configurations of Cx43. The morphology of the GJs-Cx43 was evaluated by immunofluorescence staining. Levels of IL-1β and IL-6 were examined by ELISA. The ability of GJs-Cx43-mediated intercellular communication was examined by lucifer yellow dye transfer assay. Ethidium bromide uptake assays were used to measure the activity of Cx43 hemichannels. The ultrastructural morphology of astrocyte gap junctions and tripartite synapse were observed by transmission electron microscopy.

Results

After long-term isoflurane anesthesia, the GJs formed by Cx43 in the mouse hippocampus and primary mouse astrocytes were significantly reduced, GJs function was impaired, hemichannel activity was enhanced, the levels of IL-1β and IL-6 were increased, and mice showed significant cognitive impairment. After treatment with the novel GJ-Cx43 enhancer ZP1609, GJ-Cx43-mediated astrocytic network function was enhanced, neuroinflammation was alleviated, and ameliorated cognition dysfunction induced by long-term isoflurane exposure. However, ZP1609 enhances the astrocytic network by promoting Cx43 to form GJs without affecting hemichannel activity. Additionally, our data showed that long-term isoflurane exposure does not alter the structure of tripartite synapse.

Conclusion

Our results reveal a novel mechanism of the GJ-Cx43-mediated astrocytic network involved in isoflurane-induced neuroinflammation and cognitive impairments, which provides new mechanistic insight into the pathogenesis of POCD and identifies potential targets for its treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02424-y.

Cefazolin Improves Anesthesia and Surgery-Induced Cognitive Impairments by Modulating Blood-Brain Barrier Function, Gut Bacteria and Short Chain Fatty Acids

Emerging evidence suggests that anesthesia and surgery may induce gut dysbiosis. Gut dysbiosis leads to imbalance in circulating contents of microbiota-derived metabolites and disrupts the integrity of the blood-brain barrier (BBB), contributing to postoperative cognitive dysfunction (POCD). The composition of gut microbiota may be influenced by various antibiotics. However, how perioperative use of antibiotics affects POCD needs more explorations. In the present study, we explored the effect of cefazolin, a common antibiotic used in perioperative period, on cognitive function, BBB integrity, gut bacteria and short chain fatty acids (SCFAs), a group of widely studied metabolites in aged mice, using 18-month-old male mice. Significant BBB disruptions and decreased levels of tight junction proteins, zonula occludens-1 (ZO-1) and Occludin (OCLN) were seen in the mice of POCD model. Cefazolin treatment attenuated these changes induced by anesthesia and surgery. Furthermore, cefazolin reversed the changes in several fecal bacteria (β-, γ/δ-, ε-Proteobacteria, and Bacteroidetes) as determined by qPCR tests. Analysis of plasma SCFAs showed that almost all types of SCFAs were reduced in POCD and cefazolin administration reversed the changes in expression of the two most abundant SCFAs (acetic and propionic acids). In conclusion, this study demonstrated that cefazolin improved POCD. Mechanistically, cefazolin suppressed the disruption of BBB, gut microbiota or SCFAs, thereby ameliorating POCD.

Sevoflurane inhalation has a cognitive impairing effect of aging rats involving the regulation of AChE and ChAT

Background

Acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) are closely related to the regulation of learning and memory. Nevertheless, whether sevoflurane has influence on cognition through regulating the expression of AChE and ChAT remains unclear.

Methods

Aging rat model was established by subcutaneously injection of D-galactose for 6 consecutive weeks. To determine the role of AChE and ChAT in sevoflurane-induced cognitive impairment, the Morris water maze (MWM) was used to assess the cognitive and memory function after sevoflurane exposure. Then, the variations of AChE and ChAT was detected by western blotting analysis and quantitative real-time polymerase chain reaction (qRT-PCR) respectively.

Results

Our result indicated that aging model rats had showed cognition decline at 2 hours and 1week after exposure to sevoflurane. Moreover, the expression of AChE and ChAT enhanced in rats that had inhaled sevoflurane. Interestingly, our study also found that the increase of oxygen concentration had a positive impact on the gene expression of ChAT.

Conclusion

We have identified that the overexpression of AChE and ChAT improved significantly cognitive function after sevoflurane exposure.

The Non-peptide Angiotensin-(1-7) Mimic AVE 0991 Attenuates Delayed Neurocognitive Recovery After Laparotomy by Reducing Neuroinflammation and Restoring Blood-Brain Barrier Integrity in Aged Rats

Delayed neurocognitive recovery (dNCR) after surgery is a common postoperative complication in older adult patients. Our previous studies have demonstrated that cognitive impairment after surgery involves an increase in the brain renin-angiotensin system (RAS) activity, including overactivation of the angiotensin 2/angiotensin receptor-1 (Ang II/AT1) axis, which provokes the disruption of the hippocampal blood-brain barrier (BBB). Nevertheless, the potential role of the counter-regulatory RAS axis, the Ang-(1–7)/Mas pathway, in dNCR remains unknown. Using an aged rat model of dNCR, we dynamically investigated the activity of both axes of the RAS following laparotomy. AVE 0991, a nonpeptide analog of Ang-(1–7), was administered intranasally immediately after laparotomy. We found that the elevation of Ang II, induced by surgery was accompanied by a decrease of Ang-(1–7) in the hippocampus, but not in the circulation. Surgery also significantly downregulated hippocampal Mas receptor expression at 24 h postsurgery. Mas activation with intranasal AVE 0991 treatment significantly improved hippocampus-dependent learning and memory deficits induced by surgery. Furthermore, it attenuated hippocampal neuroinflammation, as shown by the decreased level of the microglial activation marker cluster of differentiation 11b (CD11b) and the decreased production of several inflammatory molecules. Along with these beneficial effects, the AVE 0991 treatment also alleviated the imbalance between matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of matrix metalloproteinase-3 (TIMP-3), modulated the expression of occludin, and alleviated the IgG extravasation, thereby restoring the integrity of the BBB. In conclusion, these data indicate that activation of Mas by AVE 0991 attenuates dNCR after surgery by reducing neuroinflammation and restoring BBB integrity. Our findings suggest that the Ang-(1–7)/Mas pathway may be a novel therapeutic target for treating dNCR after surgery in older adult patients.

Apoptosis inhibition is involved in improvement of sevoflurane-induced cognitive impairment following normobaric hyperoxia preconditioning in aged rats

Sevoflurane, a commonly used anesthetic agent has been confirmed to induce cognitive impairment in aged rats. Normobaric hyperoxia preconditioning has been demonstrated to induce neuroprotection in rats. The present study aimed to determine whether normobaric hyperoxia preconditioning could ameliorate cognitive deficit induced by sevoflurane and the possible mechanism by which it may exert its effect. A total of 66, 20-month-old male Sprague-Dawley rats were randomly divided into 3 groups (n=22 each): Rats in the control (C) and sevoflurane anesthesia (S) groups received no normobaric hyperoxia preconditioning before sevoflurane exposure, rats in the normobaric hyperoxia pretreatment (HO) group received normobaric hyperoxia preconditioning before sevoflurane exposure (95% oxygen for 4 continuous h daily for 6 consecutive days). The anesthesia rats (S and HO groups), were exposed to 2.5% sevoflurane for 5 h, while the sham anesthesia rats (C group) were exposed to no sevoflurane. The neurobehavioral assessment was performed using a Morris water maze test, the expressions of the apoptosis proteins were determined using western blot analysis, and the apoptosis rate and cytosolic calcium concentration were measured by flow cytometry. Normobaric hyperoxia preconditioning improved prolonged escape latency and raised the number of platform crossings induced by sevoflurane in the Morris water maze test, increased the level of bcl-2 protein, and decreased the level of bax and active caspase-3 protein, the apoptosis rate and cytosolic calcium concentration in the hippocampus 24 h after sevoflurane exposure. The findings of the present study may imply that normobaric hyperoxia preconditioning attenuates sevoflurane-induced spatial learning and memory impairment, and this effect may be partly related to apoptosis inhibition in the hippocampus. In conclusion, normobaric hyperoxia preconditioning may be a promising strategy against sevoflurane-induced cognitive impairment by inhibiting the hippocampal neuron apoptosis.

Sleep Deprivation Aggravates Cognitive Impairment by the Alteration of Hippocampal Neuronal Activity and the Density of Dendritic Spine in Isoflurane-Exposed Mice

Isoflurane contributes to cognitive deficits when used as a general anesthetic, and so does sleep deprivation (SD). Patients usually suffer from insomnia before an operation due to anxiety, fear, and other factors. It remains unclear whether preoperative SD exacerbates cognitive impairment induced by isoflurane. In this study, we observed the effects of pretreated 24-h SD in adult isoflurane-exposed mice on the cognitive behaviors, the Ca²⁺ signals of dorsal hippocampal CA1 (dCA1) neurons in vivo with fiber photometry, and the density of dendritic spines in hippocampal neurons. Our results showed that in cognitive behavior tasks, short-term memory damages were more severe with SD followed by isoflurane exposure than that with SD or isoflurane exposure separately, and interestingly, severe long-term memory deficits were induced only by SD followed by isoflurane exposure. Only the treatment of SD followed by isoflurane exposure could reversibly decrease the amplitude of Ca²⁺ signals when mice were freely moving and increase the duration of Ca²⁺ signals during the long-term memory behavior test. The density of dendritic spines with both SD and isoflurane exposure was lower than that with SD alone. This study suggests that SD should be avoided preoperatively in patients undergoing elective surgery under isoflurane anesthesia.

Chikusetsu saponin IVa alleviated sevoflurane-induced neuroinflammation and cognitive impairment by blocking NLRP3/caspase-1 pathway

BACKGROUND

Neuroinflammation plays a dominant role in the progression of postoperative cognitive dysfunction (POCD). This study was carried out to explore the neuroprotective effect of Chikusetsu saponin IVa (ChIV) against sevoflurane-induced neuroinflammation and cognitive impairment.

METHODS

The neuroprotective activity of ChIV against sevoflurane-induced cognitive dysfunction in aged rats was evaluated by Morris water maze, NOR test and Y-maze test, respectively. The expression of NLRP3, ASC and caspase-1, pro-inflammatory cytokines and apoptotic-related protein were detected in the hippocampus and primary neurons using western blot. TUNEL assay and immunohistochemistry staining were applied to assess the apoptotic cell and number of NLRP3-positive cells in the hippocampus. The oxiSelectIn Vitro ROS/RNS assay kit was used to detect the ROS level. The CCK-8 assay was applied to measure the viability of primary neurons. Flow cytometry was carried out to determine cell apoptosis.

RESULTS

Pretreatment with ChIV significantly alleviated neurological dysfunction in aged rat exposure to sevoflurane. Mechanistically, ChIV treatment significantly alleviated sevoflurane-induced apoptotic cell and neuroinflammation. Of note, the neuroprotective effect of ChIV against sevoflurane-induced neurotoxicity through blocking NLRP3/caspase-1 pathway. In consistent with in vivo studies, ChIV was also able to repress sevoflurane-induced apoptosis and neuroinflammation in primary neurons. Furthermore, pretreatment with NLRP3/caspase-1 pathway inhibitor (MCC950) significantly augmented the neuroprotective effect of ChIV.

CONCLUSION

Our finding confirmed that ChIV provides a neuroprotective effect against sevoflurane-induced neuroinflammation and cognitive impairment by blocking the NLRP3/caspase-1 pathway, which may be an effective strategy for the clinical treatment of elderly patients with POCD induced by anesthesia.