Dexmedetomidine ameliorates postoperative cognitive dysfunction by inhibiting Toll-like receptor 4 signaling in aged mice

PDTC improves cognitive impairment in LPS-induced ARDS by regulating miR-181c/NF-κB axis-mediated neuroinflammation

BACKGROUND

Cognitive impairment is a severe complication of acute respiratory distress syndrome (ARDS). Emerging studies have revealed the effects of pyrrolidine dithiocarbamate (PDTC) on improving surgery-induced cognitive impairment. The major aim of the study was to investigate whether PDTC protected against ARDS-induced cognitive dysfunction and to identify the underlying mechanisms involved.

METHODS

The rat model of ARDS was established by intratracheal instillation of lipopolysaccharide (LPS), followed by treatment with PDTC. The cognitive function of rats was analyzed by the Morris Water Maze, and pro-inflammatory cytokines were assessed by quantitative real-time PCR, enzyme-linked immunosorbent assay, and western blot assays. A dual-luciferase reporter gene assay was performed to identify the relationship between miR-181c and its target gene, TAK1 binding protein 2 (TAB2).

RESULTS

The results showed that PDTC improved cognitive impairment and alleviated neuroinflammation in the hippocampus in LPS-induced ARDS model. Furthermore, we demonstrated that miR-181c expression was downregulated in the hippocampus of the ARDS rats, which was restored by PDTC treatment. In vitro studies showed that miR-181c alleviated LPS-induced pro-inflammatory response by inhibiting TAB2, a critical molecule in the nuclear factor (NF)-κB signaling pathway.

CONCLUSION

PDTC improves cognitive impairment in LPS-induced ARDS by regulating miR-181c/NF-κB axis-mediated neuroinflammation, providing a potential opportunity for the treatment of this disease.

Study on the Mechanism of Eerdun Wurile's Effects on Post-operative Cognitive Dysfunction by the TLR4/NF-κB Pathway

The object of our work was to observe whether the Mongolian medicine Eerdun Wurile (EW) improve postoperative cognitive dysfunction (POCD) by affecting the TLR4/NF-κB. Mice (6-8-week-old male C57BL/6 J) were selected to establish an animal model of POCD by combining intracerebroventricular injection of lipopolysaccharide and nephrectomy; EW formulation and EW basic formulation were administered intra-gastrically for 7 consecutive days. The cognitive performance was assessed by Morris water maze test. H&E staining was examined to detect alterations in hippocampal tissue. Immunohistochemical staining was performed to evaluate MyD88, NF-κB, TLR4, iNOS, and IBA-1 expressions; Western blotting and RT-qPCR were performed to evaluate MyD88, NF-κB, and TLR4. The expressions of IL-6, IL-1β, and TNF-α were evaluated by ELISA. Intracerebroventricular injection of lipopolysaccharide combined with nephrectomy induced cognitive dysfunction in mice, stimulated TLR4/NF-κB and microglia, and promoted the secretion of murine TNF-α, IL-1β, and IL-6. EW formulation and EW basic formulation treatment are able to suppress the TLR4/NF-κB pathway activation and microglia, and the serum cytokine secretions related to proinflammation, and restore the cognitive performance. EW formulation and EW basic formulation can improve POCD in mice, and TLR4/NF-κB pathway seems to be one of the important mechanisms in EW's improvement of POCD.

Dexmedetomidine attenuates the neuroinflammation and cognitive dysfunction in aged mice by targeting the SNHG14/miR‑340/NF‑κB axis

Neuroinflammation plays a key role in the pathogenesis of postoperative cognitive dysfunction (POCD). Results of our previous study demonstrated that dexmedetomidine (Dex) attenuates neuroinflammation in BV2 cells treated with lipopolysaccharide (LPS) by targeting the microRNA (miR)-340/NF-κB axis. However, the molecular mechanisms by which Dex improves POCD remain unclear. In the present study, the association between long non-coding (lnc)RNA small nucleolar RNA host gene 14 (SNHG14) and miR-340 in BV2 microglial cells was determined using a dual-luciferase reporter assay. In addition, SNHG14, miR-340 and NF-κB expression levels were measured in LPS-treated BV-2 cells and hippocampal tissues of mice with POCD, and an enzyme-linked immunosorbent assay was used to determine the levels of proinflammatory mediators. Results of the present study demonstrated that SNHG14 exhibited potential as a target of miR-340. In addition, SNHG14 knockdown increased the levels of miR-340 and reduced the levels of NF-κB in LPS-treated BV2 cells. In addition, Dex treatment significantly reduced the levels of SNHG14 and NF-κB, and elevated the levels of miR-340 in the hippocampus of aged mice with POCD. Moreover, Dex treatment notably decreased the expression levels of TNF-α, IL-1β, IL-2, IL-6, IL-8 and IL-12 in the hippocampus of aged mice with POCD by upregulating miR-340. The spatial memory impairments in aged mice with POCD were also notably increased following Dex treatment via upregulation of miR-340. Collectively, results of the present study demonstrated that Dex may protect microglia from LPS-induced neuroinflammation in vitro and attenuate hippocampal neuroinflammation in aged mice with POCD in vivo via the SNHG14/miR-340/NF-κB axis. The present study may provide further insights into the mechanisms underlying Dex in the treatment of POCD.

Counting the Toll of Inflammation on Schizophrenia-A Potential Role for Toll-like Receptors

Toll-like receptors (TLRs) are a family of pattern recognition receptors (PRRs) that are ubiquitously expressed in the human body. They protect the brain and central nervous system from self and foreign antigens/pathogens. The immune response elicited by these receptors culminates in the release of cytokines, chemokines, and interferons causing an inflammatory response, which can be both beneficial and harmful to neurodevelopment. In addition, the detrimental effects of TLR activation have been implicated in multiple neurodegenerative diseases such as Alzheimer's, multiple sclerosis, etc. Many studies also support the theory that cytokine imbalance may be involved in schizophrenia, and a vast amount of literature showcases the deleterious effects of this imbalance on cognitive performance in the human population. In this review, we examine the current literature on TLRs, their potential role in the pathogenesis of schizophrenia, factors affecting TLR activity that contribute towards the risk of schizophrenia, and lastly, the role of TLRs and their impact on cognitive performance in schizophrenia.

Dexmedetomidine attenuates neuroinflammation and microglia activation in LPS-stimulated BV2 microglia cells through targeting circ-Shank3/miR-140-3p/TLR4 axis

It has been shown that dexmedetomidine (Dex) could attenuate postoperative cognitive dysfunction (POCD) via targeting circular RNAs (circRNAs). Circ-Shank3 has been found to be involved in the neuroprotective effects of Dex against POCD. However, the role of circ-Shank3 in POCD remains largely unknown. Reverse transcription quantitative PCR (RT-qPCR) was performed to detect circ-Shank3 and miR-140-3p levels in lipopolysaccharide (LPS)-treated microglia BV-2 cells in the absence or presence of Dex. The relationship among circ-Shank3, miR-140-3p and TLR4 was confirmed by dual-luciferase reporter assay. Additionally, Western blot and immunofluorescence (IF) assays were conducted to evaluate TLR4, p65 and Iba-1 or CD11b levels in cells. In this study, we found that Dex notably decreased circ-Shank3 and TLR4 levels and elevated miR-140-3p level in LPS-treated BV2 cells. Mechanistically, circ-Shank3 harbor miR-140-3p, functioning as a miRNA sponge, and then miR-140-3p targeted the 3'-UTR of TLR4. Additionally, Dex treatment significantly reduced TLR4 level and phosphorylation of p65, and decreased the expressions of microglia markers Iba-1 and CD11b in LPS-treated BV2 cells. As expected, silenced circ-Shank3 further reduced TLR4, p65 and Iba-1 and CD11b levels in LPS-treated BV2 cells in the presence of Dex, whereas these phenomena were reversed by miR-140-3p inhibitor. Collectively, our results found that Dex could attenuate the neuroinflammation and microglia activation in BV2 cells exposed to LPS via targeting circ-Shank3/miR-140-3p/TLR4 axis. Our results might shed a new light on the mechanism of Dex for the treatment of POCD.

Icariin reduces cognitive dysfunction induced by surgical trauma in aged rats by inhibiting hippocampal neuroinflammation

Postoperative cognitive dysfunction (POCD) is a common postsurgical complication in elderly individuals, significantly impacting the quality of life of patients; however, there is currently no effective clinical treatment for POCD. Recent studies have shown that Icariin (ICA) has antiaging effects and improves cognitive function, but its effect in POCD has not been studied. In this study, we investigated the influence of ICA on cognitive function and the TLR4/NF-κB signaling pathway in a POCD rat model. We found that ICA reduced surgery-induced memory impairment, decreased hippocampal inflammatory responses, ameliorated neuronal injury in the hippocampus and inhibited microglial activation. In addition, we also observed that ICA inhibited activation of the TLR4/NF-κB signaling pathway. In summary, our research suggest that ICA can ameliorate surgery-induced memory impairment and that the improvements resulting from administration of ICA may be associated with inhibition of hippocampal neuroinflammation. Our research findings also provide insight into potential therapeutic targets and methods for POCD.

Selective TLR4 Antagonism Prevents and Reverses Morphine-Induced Persistent Postoperative Cognitive Dysfunction, Dysregulation of Synaptic Elements, and Impaired BDNF Signaling in Aged Male Rats

Perioperative neurocognitive disorders (PNDs) are characterized by confusion, difficulty with executive function, and episodic memory impairment in the hours to months following a surgical procedure. Postoperative cognitive dysfunction (POCD) represents such impairments that last beyond 30 d postsurgery and is associated with increased risk of comorbidities, progression to dementia, and higher mortality. While it is clear that neuroinflammation plays a key role in PND development, what factors underlie shorter self-resolving versus persistent PNDs remains unclear. We have previously shown that postoperative morphine treatment extends POCD from 4 d (without morphine) to at least 8 weeks (with morphine) in aged male rats, and that this effect is likely dependent on the proinflammatory capabilities of morphine via activation of toll-like receptor 4 (TLR4). Here, we extend these findings to show that TLR4 blockade, using the selective TLR4 antagonist lipopolysaccharide from the bacterium Rhodobacter sphaeroides (LPS-RS Ultrapure), ameliorates morphine-induced POCD in aged male rats. Using either a single central preoperative treatment or a 1 week postoperative central treatment regimen, we demonstrate that TLR4 antagonism (1) prevents and reverses the long-term memory impairment associated with surgery and morphine treatment, (2) ameliorates morphine-induced dysregulation of the postsynaptic proteins postsynaptic density 95 and synaptopodin, (3) mitigates reductions in mature BDNF, and (4) prevents decreased activation of the BDNF receptor TrkB (tropomyosin-related kinase B), all at 4 weeks postsurgery. We also reveal that LPS-RS Ultrapure likely exerts its beneficial effects by preventing endogenous danger signal HMGB1 (high-mobility group box 1) from activating TLR4, rather than by blocking continuous activation by morphine or its metabolites. These findings suggest TLR4 as a promising therapeutic target to prevent or treat PNDs.SIGNIFICANCE STATEMENT With humans living longer than ever, it is crucial that we identify mechanisms that contribute to aging-related vulnerability to cognitive impairment. Here, we show that the innate immune receptor toll-like receptor 4 (TLR4) is a key mediator of cognitive dysfunction in aged rodents following surgery and postoperative morphine treatment. Inhibition of TLR4 both prevented and reversed surgery plus morphine-associated memory impairment, dysregulation of synaptic elements, and reduced BDNF signaling. Together, these findings implicate TLR4 in the development of postoperative cognitive dysfunction, providing mechanistic insight and novel therapeutic targets for the treatment of cognitive impairments following immune challenges such as surgery in older individuals.

Feasibility study of use of desflurane combined with dexmedetomidine in inhibiting postoperative neurocognitive disorders in elderly patients under general anesthesia: A perspective study

This study aimed to explore whether the combined application of desflurane and dexmedetomidine (Dex) reduces the occurrence of postoperative neurocognitive disorders (PND) in patients. We selected patients in our hospital who underwent surgery under general anesthesia, and divided them into two groups: Dex and desflurane (Dex + Des) and desflurane (Des) groups. The data of patients were collected and the Mini-Mental State Examination (MMSE) score was used to assess cognitive status. The blood cell counts were determined preoperatively and on postoperative days 1, 3, and 6, and the percentage of neutrophils and lymphocytes were also recorded. The statistical methods used were the independent-samples t-test and the χ 2 test. Pearson's correlation was used to analyze the correlation between PND and inflammation. The incidence of PND in the Dex + Des group was lower than that in the Des group. The postoperative MMSE scores in the Dex + Des group were higher than those in the Des group (p = 0.032). The percentage of neutrophils in the Dex + Des group was significantly lower than that in the Des group on the first and third days after surgery (p = 0.007; p = 0.028). The MMSE scores on the first day after surgery were negatively correlated with the multiple changes in white blood counts and the percentage of neutrophils (r = -0.3038 and -0.3330). Dex combined with Des reduced the incidence of PND and reduced the postoperative inflammatory cell counts.

Anti-Inflammatory Action of Dexmedetomidine on Human Microglial Cells

Neuroinflammation, where inflammatory cytokines are produced in excess, contributes to the pathogenesis of delirium. Microglial cells play a central role in neuroinflammation by producing and releasing inflammatory cytokines in response to infection, tissue damage and neurodegeneration. Dexmedetomidine (DEX) is a sedative, which reduces the incidence of delirium. Thus, we hypothesized that DEX may alleviate delirium by exhibiting anti-inflammatory action on microglia. In the present study, we investigated the anti-inflammatory action of DEX on human microglial HMC3 cells. The results indicated that DEX partially suppressed the IL-6 and IL-8 production by lipopolysaccharide (LPS)-stimulated HMC3 cells as well as the phosphorylation of p38 MAPK and IκB and the translocation of NF-κB. Furthermore, DEX substantially suppressed IL-6 and IL-8 production by unstimulated HMC3 cells as wells as the phosphorylation of p38 MAPK and IκB and the translocation of NF-κB. These observations suggest that DEX exhibits anti-inflammatory action on not only LPS-stimulated but also unstimulated microglial cells via the suppression of inflammatory signaling and cytokine production.

Influence of dexmedetomidine on postoperative cognitive dysfunction in the elderly: A meta-analysis of randomized controlled trials

INTRODUCTION

Dexmedetomidine (Dex) is suggested to be neuroprotective. However, influence of Dex on postoperative cognitive dysfunction (POCD) in the elderly remains unknown.

METHODS

We performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the effect of Dex on POCD. Relevant studies were obtained by search of PubMed, Embase, and Cochrane's Library databases. A random-effect model was used to pool the results.

RESULTS

Fourteen RCTs including 1626 adults of 60 years or older who received surgery with general anesthesia were included. Because methodologically diverse scales were used for POCD, eight RCTs with POCD diagnosed with Mini-Mental State Examination (MMSE) were included in the meta-analysis, while the remaining six RCTs with POCD diagnosed with other scales were qualitative synthesized. Pooled results of RCTs with MMSE showed that Dex significantly reduced the incidence of POCD (risk ratio: 0.47, 95% confidence interval: 0.37-0.60, p < 0.001) with no significant heterogeneity (I²  = 0%) or publication bias (p for Egger's regression test = 0.579). For the remaining six RCTs with POCD diagnosed with other scales, three of them showed that Dex was associated with a significantly lower incidence of POCD, while the other three RCTs did not show a significant difference.

CONCLUSIONS

Dex is associated with a reduced risk of POCD in elderly patients receiving surgeries with general anesthesia, and the results were mainly obtained in studies with POCD diagnosed with MMSE. Based on these findings, Dex may be considered as a preventative measure for POCD in elderly patients.

Progress in the correlation of postoperative cognitive dysfunction and Alzheimer's disease and the potential therapeutic drug exploration

Postoperative cognitive dysfunction (POCD) is a decrease in mental capacity that can occur days to weeks after a medical procedure and may become permanent and rarely lasts for a longer period of time. With the continuous development of research, various viewpoints in academic circles have undergone subtle changes, and the role of anesthesia depth and anesthesia type seems to be gradually weakened; Alzheimer's disease (AD) is a latent and progressive neurodegenerative disease in the elderly. The protein hypothesis and the synaptic hypothesis are well-known reasons. These changes will also lead to the occurrence of an inflammatory cascade. The exact etiology and pathogenesis need to be studied. The reasonable biological mechanism affecting brain protein deposition, neuroinflammation, and acetylcholine-like effect has a certain relationship between AD and POCD. Whereas there is still further uncertainty about the mechanism and treatment, and it is elusive whether POCD is a link in the continuous progress of AD or a separate entity, which has doubts about the diagnosis and treatment of the disease. Therefore, this review is based on the current common clinical characteristics of AD and POCD, and pathophysiological research, to search for their common points and explore the direction and new strategies for future treatment.

An Update on Postoperative Cognitive Dysfunction Following Cardiac Surgery

Postoperative cognitive dysfunction is extremely prevalent following cardiac surgery. The increasing patient age and comorbidity profile increases their susceptibility to cognitive impairment. The underlying pathophysiological mechanisms leading to cognitive impairment are not clearly elucidated. Using the contemporary literature (2015-present), this narrative review has three aims. Firstly, to provide an overview of postoperative cognitive impairment. Secondly, to analyse the predominant pathophysiological mechanisms leading to cognitive dysfunction following cardiac surgery such as inflammation, cerebral hypoperfusion, cerebral microemboli, glycaemic control and anaesthesia induced neurotoxicity. Lastly, to assess the current therapeutic strategies of interest to address these pathophysiological mechanisms, including the administration of dexamethasone, the prevention of prolonged cerebral desaturations and the monitoring of cerebral perfusion using near-infrared spectroscopy, surgical management strategies to reduce the neurological effects of microemboli, intraoperative glycaemic control strategies, the effect of volatile vs. intravenous anaesthesia, and the efficacy of dexmedetomidine.

Protective role of dexmedetomidine against sevoflurane-induced postoperative cognitive dysfunction via the microRNA-129/TLR4 axis

The involvement of Dexmedetomidine (Dex) has been indicated in postoperative cognitive dysfunction (POCD), while the mechanism is not well characterized. This study estimated the mechanism of Dex in POCD. Rats were anesthetized with sevoflurane (SEV) to evoke POCD and then subjected to Morris water maze test to detect the cognitive and behavioral function. Then, the damage of hippocampus and cortex, and apoptosis and activity of neurons were examined. Microarray analysis was performed to screen out the differentially expressed microRNAs (miRs) in rats after Dex treatment. The cognitive and behavioral functions and neuronal activity of rats were detected after miR-129 antagomir injection. The target of miR-129 was predicted. The levels of TLR4 and NF-κB p65 in hippocampus and cortex were measured. Dex treatment alleviated SEV-induced behavior and cognitive impairments in rats, promoted neuronal activity and hindered neuronal apoptosis. After treatment with Dex, miR-129 expression was elevated in brain tissues, and the neuroprotection of Dex on POCD rats was partially annulled after injection of miR-129 antagomir. Furthermore, miR-129 targeted TLR4 and prevented the phosphorylation of NF-κB p65. In summary, Dex ameliorated SEV-induced POCD by elevating miR-129 and inhibiting TLR4 and NF-κB p65 phosphorylation. This study may shed new lights on POCD treatment.