Tau hyperphosphorylation: a downstream effector of isoflurane-induced neuroinflammation in aged rodents

Propofol ameliorates cognitive deficits following splenectomy in aged rats by inhibiting ferroptosis via the SIRT1/Nrf2/GPX4 pathway

The aim of this study was to investigate the mechanism by which propofol reduces postoperative cognitive dysfunction after splenectomy in aged rats. The rats in the model group and propofol group were subjected to splenectomy, and anesthetized with isoflurane and propofol, respectively. Utilizing the western blotting to assess the expression of sirtuin-1 (SIRT1) in the hippocampus. Molecular docking technology was used to predict the binding ability of propofol and SIRT1. Behavioral tests were performed using the Morris water maze, and the hippocampus was isolated for mechanistic investigations. Molecular docking showed that propofol and SIRT1 had a strong binding affinity. The expression of SIRT1 and its related proteins Nrf2, HO-1, NQO1, and GPX4 in the model rats was decreased compared with the sham group. Moreover, the model group exhibited cognitive decline, such as extended escape latency and decreased number of platform crossings. Pathological analysis showed that the number of apoptotic neurons, the levels of oxidative stress and neuroinflammation, the iron deposition, and the expressions of ACSL4 and TFR1 were increased, while the expressions of SLC7A11 and FTH1 were decreased in the hippocampal CA1 region within the model group. These pathological changes in the propofol group were, however, less than those in the model group. Nevertheless, the SIRT1 inhibitor increased these pathological changes compared with the propofol group. Compared with isoflurane, propofol inhibits ferroptosis in the hippocampus of splenectomized rats by causing less downregulation of the SIRT1/Nrf2/GPX4 pathway, thereby reducing the negative impact on cognitive function.

Persistent Depletion of Neuroprotective Factors Accompanies Neuroinflammatory, Neurodegenerative, and Vascular Remodeling Spectra in Serum Three Months after Non-Emergent Cardiac Surgery

We hypothesized that the persistent depletion of neuroprotective markers accompanies neuroinflammation and neurodegeneration in patients after cardiac surgery. A total of 158 patients underwent elective heart surgery with their blood collected before surgery (tbaseline) and 24 h (t24hr), seven days (t7d), and three months (t3m) post-surgery. The patients' serum was measured for markers of neurodegeneration (τau, τaup181-183, amyloid β1-40/β2-42, and S100), atypical neurodegeneration (KLK6 and NRGN), neuro-injury (neurofilament light/heavy, UC-HL, and GFAP), neuroinflammation (YKL-40 and TDP-43), peripheral nerve damage (NCAM-1), neuroprotection (apoE4, BDNF, fetuin, and clusterin), and vascular smoldering inflammation (C-reactive protein, CCL-28 IL-6, and IL-8). The mortality at 28 days, incidence of cerebrovascular accidents (CVA), and functional status were followed for three months. The levels of amyloid β1-40/β1-42 and NF-L were significantly elevated at all time points. The levels of τau, S100, KLK6, NRGN, and NCAM-1 were significantly elevated at 24 h. A cluster analysis demonstrated groupings around amyloids, KLK6, and NCAM-1. YKL-40, but not TDP-43, was significantly elevated across all time points. BDNF, apoE4, fetuin, and clusterin levels were significantly diminished long-term. IL-6 and IL-8 levles returned to baseline at t3m. The levels of CRP, CCL-28, and Hsp-70 remained elevated. At 3 months, 8.2% of the patients experienced a stroke, with transfusion volume being a significant variable. Cardiac-surgery patients exhibited persistent peripheral and neuronal inflammation, blood vessel remodeling, and the depletion of neuroprotective factors 3 months post-procedure.

Dexmedetomidine suppresses the isoflurane-induced neurological damage by upregulating Heme Oxygenase-1 via activation of the mitogen-activated protein kinase kinase 1/extracellular regulated protein kinases 1/nuclear factor erythroid 2-related factor 2 axis in aged rats

Dexmedetomidine (DEX) displays a neuroprotective role in aged rats with isoflurane (ISO)-induced cognitive impairment through antioxidant, and anti-inflammatory, and anti-apoptotic effects. Therefore, the present study was performed to define the molecular mechanism of DEX on ISO-induced neurological impairment in aged rats in relation to the MEK1/ERK1/Nrf2/HO-1 axis. The study enrolled elderly patients undergoing ISO anesthesia. Patient cognitive function following treatment with DEX was evaluated using mini-mental state examination (MMSE). The results revealed that DEX supplementation of anesthesia contributed to higher MMSE scores in patients one week post treatment. Rat model of neurological impairment was also induced in 18-month-age Wistar rats by ISO, followed by DEX treatment. Based on the results of Morris water maze experiment, ELISA, and TUNEL and hematoxylin-eosin staining, in vivo experiments confirmed that DEX could reduce the oxidative stress and neurological damage induced by ISO in rats. DEX activated the nuclear factor erythroid 2-related factor (Nrf2)/Heme Oxygenase 1 (HO-1) pathway. DEX upregulated the expression of Nrf2 and HO-1 by activating the MEK1/ERK1 pathway, whereby attenuating the ISO-caused oxidative stress and neurological damage in rats. Collectively, DEX suppresses the ISO-induced neurological impairment in the aged rats by promoting HO-1 through activation of the MEK1/ERK1/Nrf2 axis.

A cellular approach to understanding and treating Gulf War Illness

Gulf War Illness (GWI), a disorder suffered by approximately 200,000 veterans of the first Gulf War, was caused by exposure to low-level organophosphate pesticides and nerve agents in combination with battlefield stress. To elucidate the mechanistic basis of the brain-related symptoms of GWI, human-induced pluripotent stem cells (hiPSCs) derived from veterans with or without GWI were differentiated into forebrain glutamatergic neurons and then exposed to a Gulf War (GW) relevant toxicant regimen consisting of a sarin analog and cortisol, a human stress hormone. Elevated levels of total and phosphorylated tau, reduced microtubule acetylation, altered mitochondrial dynamics/transport, and decreased neuronal activity were observed in neurons exposed to the toxicant regimen. Some of the data are consistent with the possibility that some veterans may have been predisposed to acquire GWI. Wistar rats exposed to a similar toxicant regimen showed a mild learning and memory deficit, as well as cell loss and tau pathology selectively in the CA3 region of the hippocampus. These cellular responses offer a mechanistic explanation for the memory loss suffered by veterans with GWI and provide a cell-based model for screening drugs and developing personalized therapies for these veterans.

Gut microbiota: a new player in the pathogenesis of perioperative neurocognitive disorder?

Perioperative neurocognitive disorder (PND), including postoperative delirium and postoperative cognitive dysfunction (POCD), is a common postoperative complication in elderly patients, who represent an expanding segment of our population. PND is a multifactorial disease resulting in higher morbidity and mortality. The precise mechanism of PND is yet to be fully delineated. Identifying the modifiable risk factors and mechanisms for PND would be an important step forward in preventing such adverse events and thus improving patients' outcomes. It is increasingly recognized that gut microbiota also manifest effects in the central nervous system via the microbiota-gut-brain axis, which has emerged as an important player in shaping aspects of behavior and cognitive function. Recent studies have found that patients with cognitive dysfunction after surgery and anesthesia have obvious gut microbiome disorders. These findings are paralleled by a growing body of preclinical investigations aimed at better understanding how surgery and anesthesia affect the central nervous system and possibly contribute to cognitive decline. Here, we present a broad topical review of the literature supporting the role of gut microbiota in PND. We provide an overview of the mechanisms underlying the pathogenesis of PND from pre-clinical and human studies. Therefore, gut microbiota could be a putative therapeutic target for PND in the future.

Resveratrol Mitigates Hippocampal Tau Acetylation and Cognitive Deficit by Activation SIRT1 in Aged Rats following Anesthesia and Surgery

Postoperative cognitive dysfunction (POCD) is a sever postsurgical neurological complication in the elderly population. As the global acceleration of population ageing, POCD is proved to be a great challenge to the present labor market and healthcare system. In the present study, our findings showed that tau acetylation mediated by SIRT1 deficiency resulted in tau hyperphosphorylation in the hippocampus of the aged POCD model and consequently contributed to cognitive impairment. Interestingly, pretreatment with resveratrol almost restored the expression of SIRT1, reduced the levels of acetylated tau and hyperphosphorylated tau in the hippocampus, and improved the cognitive performance in the behavioral tests. What is more, we observed that microglia-derived neuroinflammation resulting from SIRT1 inhibition in microglia probably aggravated the tau acetylation in cultured neurons in vitro. Our findings supported the notion that activation SIRT1 provided dually beneficial effect in the aged POCD model. Taken together, our findings provided the initial evidence that tau acetylation was associated with cognitive impairment in the aged POCD model and paved a promising avenue to prevent POCD by inhibiting tau acetylation in a SIRT1-dependent manner.

BACE1 gene silencing alleviates isoflurane anesthesia‑induced postoperative cognitive dysfunction in immature rats by activating the PI3K/Akt signaling pathway

Postoperative cognitive dysfunction (POCD) is a severe complication characterized by cognitive dysfunction following anesthesia and surgery. The aim of the present study was to investigate the effects of β-site amyloid precursor protein cleavage enzyme 1 (BACE1) gene silencing on isoflurane anesthesia-induced POCD in immature rats via the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway. Rat models were established and then transfected with BACE1 small interfering RNA and wortmannin (an inhibitor of PI3K). Blood gas analysis was performed, and a series of behavioral experiments were conducted to evaluate the cognitive function, learning ability and locomotor activity of rats. Reverse transcription quantitative polymerase chain reaction and western blot analysis were employed to determine the mRNA and protein expression of the associated genes. An ELISA was used to detect the inflammatory indicators and the content of amyloid precursor protein (APP) and amyloid-β (Aβ). Apoptosis of the hippocampal CA1 region was observed by terminal deoxynucleotidyl transferase dUTP nick-end labeling staining. Initially, it was revealed that the percentage of stagnation time in rats was increased by BACE1 gene silencing; the escape latency and swimming distance were markedly reduced from the 4th to the 6th day, the time the rats spent in first passing the target area was shortened, and the times of passing the target area were increased by BACE1 gene silencing, demonstrating that BACE1 gene silencing enhanced the spatial memory ability of rats. Additionally, it was determined that silencing BACE1 improved the pathological state induced by isoflurane anesthesia in immature rats, and attenuated the inflammatory response and the levels of APP and Aβ in hippocampal tissues. Furthermore, it was suggested that silencing BACE1 may have promoted the activation of the PI3K/Akt signaling pathway, thereby inhibiting the apoptosis of the hippocampal CA1 region. Taken together, these results indicated that BACE1 gene silencing may improve isoflurane anesthesia-induced POCD in immature rats by activating the PI3K/Akt signaling pathway and inhibiting the Aβ generated by APP.

Neuroprotective effects of vitexin against isoflurane-induced neurotoxicity by targeting the TRPV1 and NR2B signaling pathways

Vitexin is a bioactive compound extracted from hawthorn leaves, which reduces blood pressure and has anti‑inflammatory and potential anticancer effects. However, the mechanisms underlying the protective effects of vitexin against isoflurane‑induced neurotoxicity remain elusive. Therefore, the aim of the present study was to investigate these mechanisms further. Sprague Dawley rats received 1.4% isoflurane in a 100% oxygen environment for 2 h. Human PC12 pheochromocytoma neurosecretory cells were exposed to 2% isoflurane for 12 h before they were treated with 1, 10 or 100 µM vitexin for a further 24 h. Vitexin inhibited the isoflurane-induced cell cytotoxicity and weakened isoflurane-induced neuroinflammation and oxidative stress pathways in PC12 cells. In addition, treatment with vitexin suppressed isoflurane‑induced caspase‑3 activation and increased β-secretase 1 levels in PC12 cells. Furthermore, vitexin treatment decreased the levels of isoflurane‑induced cytosolic calcium and reactive oxygen species, and downregulated the expression of transient receptor potential cation channel subfamily V member 1 (TRPV1) and glutamate ionotropic receptor NMDA type subunit 2B (NR2B) protein expression in isoflurane-treated PC12 cells. These results suggest that vitexin mediates its protective effects against isoflurane-induced neurotoxicity by targeting the TRPV1 and NR2B signaling pathways.

Sugammadex-Enhanced Neuronal Apoptosis following Neonatal Sevoflurane Exposure in Mice

In rodents, neonatal sevoflurane exposure induces neonatal apoptosis in the brain and results in learning deficits. Sugammadex is a new selective neuromuscular blockade (NMB) binding agent that anesthesiologists can use to achieve immediate reversal of an NMB with few side effects. Given its molecular weight of 2178, sugammadex is thought to be unable to pass through the blood brain barrier (BBB). Volatile anesthetics can influence BBB opening and integrity. Therefore, we investigated whether the intraperitoneal administration of sugammadex could exacerbate neuronal damage following neonatal 2% sevoflurane exposure via changes in BBB integrity. Cleaved caspase-3 immunoblotting was used to detect apoptosis, and the ultrastructure of the BBB was examined by transmission electron microscopy. Exposure to 2% sevoflurane for 6 h resulted in BBB ultrastructural abnormalities in the hippocampus of neonatal mice. Sugammadex alone without sevoflurane did not induce apoptosis. The coadministration of sugammadex with sevoflurane to neonatal mice caused a significant increase (150%) in neuroapoptosis in the brain compared with 2% sevoflurane. In neonatal anesthesia, sugammadex could influence neurotoxicity together with sevoflurane. Exposure to 2% sevoflurane for 6 h resulted in BBB ultrastructural abnormalities in the hippocampus of neonatal mice.

Isoflurane anesthesia exacerbates learning and memory impairment in zinc-deficient APP/PS1 transgenic mice

Zinc (Zn) is known to play crucial roles in numerous brain functions including learning and memory. Zn deficiency is believed to be widespread throughout the world, particularly in patients with Alzheimer's disease (AD). A number of studies have shown that volatile anesthetics, such as isoflurane, might be potential risk factors for the development of AD. However, whether isoflurane exposure accelerates the process of AD and cognitive impairment in AD patients with Zn deficiency is yet to be documented. The aim of the present study was to explore the effects of 1.4% isoflurane exposure for 2 h on learning and memory function, and neuropathogenesis in 10-month-old Zn-adequate, Zn-deficient, and Zn-treated APP/PS1 mice with the following parameters: behavioral tests, neuronal apoptosis, Aβ, and tau pathology. The results demonstrated that isoflurane exposure showed no impact on learning and memory function, but induced transient elevation of neuroapoptosis in Zn-adequate APP/PS1 mice. Exposure of isoflurane exhibited significant neuroapoptosis, Aβ generation, tau phosphorylation, and learning and memory impairment in APP/PS1 mice in the presence of Zn deficiency. Appropriate Zn treatment improved learning and memory function, and prevented isoflurane-induced neuroapoptosis in APP/PS1 mice. Isoflurane exposure may cause potential neurotoxicity, which is tolerated to some extent in Zn-adequate APP/PS1 mice. When this tolerance is limited, like in AD with Zn deficiency, isoflurane exposure markedly exacerbated learning and memory impairment, and neuropathology, indicating that AD patients with certain conditions such as Zn deficiency may be vulnerable to volatile anesthetic isoflurane.

Exposure to general anesthesia and the risk of dementia

Exposure to anesthesia and surgery has been hypothesized to increase the risk of developing Alzheimer's disease (AD). While the exact pathogenesis of AD remains unknown, it potentially involves specific proteins (eg, amyloid beta and tau) and neuroinflammation. A growing body of preclinical evidence also suggests that anesthetic agents interact with the components that mediate AD neuropathology at multiple levels. However, it remains unclear whether anesthesia and surgery are associated with an increased risk of AD in humans. To date, there have not been randomized controlled trials to provide evidence for such a causal relationship. Besides, observational studies showed inconsistent results. A meta-analysis of 15 case-control studies revealed no statistically significant association between general anesthesia and the development of AD (pooled odds ratio [OR] =1.05; P=0.43). However, a few retrospective cohort studies have demonstrated that exposure to anesthesia and surgery is associated with an increased risk of AD. Thus, well-designed studies with longer follow-up periods are still needed to define the role of anesthesia in relation to the development of AD.

Suberoylanilide hydroxamic acid, a histone deacetylase inhibitor, attenuates postoperative cognitive dysfunction in aging mice

Postoperative cognitive dysfunction (POCD) is a recognized clinical entity characterized with cognitive deficits after anesthesia and surgery, especially in aged patients. Previous studies have shown that histone acetylation plays a key role in hippocampal synaptic plasticity and memory formation. However, its role in POCD remains to be determined. Here, we show that suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, attenuates POCD in aging Mice. After exposed to the laparotomy, a surgical procedure involving an incision into abdominal walls to examine the abdominal organs, 16- but not 3-month old male C57BL/6 mice developed obvious cognitive impairments in the test of long-term contextual fear conditioning. Intracerebroventricular (i.c.v.) injection of SAHA at the dose of (20 μg/2 μl) 3 h before and daily after the laparotomy restored the laparotomy-induced reduction of hippocampal acetyl-H3 and acetyl-H4 levels and significantly attenuated the hippocampus-dependent long-term memory (LTM) impairments in 16-month old mice. SAHA also reduced the expression of cleaved caspase-3, inducible nitric oxide synthase (iNOS) and N-methyl-D-aspartate (NMDA) receptor-calcium/calmodulin dependent kinase II (CaMKII) pathway, and increased the expression of brain-derived neurotrophic factor (BDNF), synapsin 1, and postsynaptic density 95 (PSD95). Taken together, our data suggest that the decrease of histone acetylation contributes to POCD and may serve as a target to improve the neurological outcome of POCD.