Blood tau-PT217 contributes to the anesthesia/surgery-induced delirium-like behavior in aged mice

Anesthesia/surgery activate MMP9 leading to blood-brain barrier disruption, triggering neuroinflammation and POD-like behavior in aged mice

Anesthesia and surgery activate matrix metalloproteinase 9 (MMP9), leading to blood-brain barrier (BBB) disruption and postoperative delirium (POD)-like behavior, especially in the elderly. Aged mice received intraperitoneal injections of either the MMP9 inhibitor SB-3CT, melatonin, or solvent, and underwent laparotomy under 3 % sevoflurane anesthesia(anesthesia/surgery). Behavioral tests were performed 24 h pre- and post-operatively. Serum and cortical tissue levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) were measured using ELISA. Levels of PDGFRβ, MMP9, tight junction, Mfsd2a, caveolin-1, synaptophysin, and postsynaptic densin (PSD)-95 proteins in the prefrontal cortex were assayed using Western blotting. BBB permeability was assessed by detecting IgG in the prefrontal cortex and serum S100β levels. Anesthesia/surgery-induced peripheral inflammation activated MMP9, which in turn injured pericytes and tight junctions and increased transcytosis, thereby disrupting the BBB. Impaired BBB allowed the migration of peripheral inflammation into the central nervous system (CNS), thereby inducing neuroinflammation, synaptic dysfunction, and POD-like behaviors. However, MMP9 inhibition reduced pericyte and tight junction injury and transcytosis, thereby preserving BBB function and preventing the migration of peripheral inflammation into the CNS, thus attenuating synaptic dysfunction and POD-like behavior. In addition, to further validate the above findings, we showed that melatonin exerted similar effects through inhibition of MMP9. The present study shows that after anesthesia/surgery, inflammatory cytokines upregulation is involved in regulating BBB permeability in aged mice through activation of MMP9, suggesting that MMP9 may be a potential target for the prevention of POD.

Nanotherapeutics for Alleviating Anesthesia-Associated Complications

Current management of anesthesia-associated complications falls short in terms of both efficacy and safety. Nanomaterials with versatile properties and unique nano-bio interactions hold substantial promise as therapeutics for addressing these complications. This review conducts a thorough examination of the existing nanotherapeutics and highlights the strategies for developing prospective nanomedicines to mitigate anesthetics-related toxicity. Initially, general, regional, and local anesthesia along with the commonly used anesthetics and related prevalent side effects are introduced. Furthermore, employing nanotechnology to prevent and alleviate the complications of anesthetics is systematically demonstrated from three aspects, that is, developing 1) safe nano-formulization for anesthetics; 2) nano-antidotes to sequester overdosed anesthetics and alter their pharmacokinetics; 3) nanomedicines with pharmacodynamic activities to treat anesthetics toxicity. Finally, the prospects and challenges facing the clinical translation of nanotherapeutics for anesthesia-related complications are discussed. This work provides a comprehensive roadmap for developing effective nanotherapeutics to prevent and mitigate anesthesia-associated toxicity, which can potentially revolutionize the management of anesthesia complications.

Nanoscale imaging of pT217-tau in aged rhesus macaque entorhinal and dorsolateral prefrontal cortex: Evidence of interneuronal trafficking and early-stage neurodegeneration

INTRODUCTION

Tau phosphorylated at threonine-217 (pT217-tau) is a novel fluid-based biomarker that predicts onset of Alzheimer's disease (AD) symptoms, but little is known about how pT217-tau arises in the brain, as soluble pT217-tau is dephosphorylated post mortem in humans.

METHODS

We used multilabel immunofluorescence and immunoelectron microscopy to examine the subcellular localization of early-stage pT217-tau in entorhinal and prefrontal cortices of aged macaques with naturally occurring tau pathology and assayed pT217-tau levels in plasma.

RESULTS

pT217-tau was aggregated on microtubules within dendrites exhibiting early signs of degeneration, including autophagic vacuoles. It was also seen trafficking between excitatory neurons within synapses on spines, where it was exposed to the extracellular space, and thus accessible to cerebrospinal fluid (CSF)/blood. Plasma pT217-tau levels increased across the age span and thus can serve as a biomarker in macaques.

DISCUSSION

These data help to explain why pT217-tau predicts degeneration in AD and how it gains access to CSF and plasma to serve as a fluid biomarker.

Microglial exosome miR-124-3p in hippocampus alleviates cognitive impairment induced by postoperative pain in elderly mice

Cognitive impairment induced by postoperative pain severely deteriorates the rehabilitation outcomes in elderly patients. The present study focused on the relationship between microglial exosome miR-124-3p in hippocampus and cognitive impairment induced by postoperative pain. Cognitive impairment model induced by postoperative pain was constructed by intramedullary nail fixation after tibial fracture. Morphine intraperitoneally was carried out for postoperative analgesia. Morris water maze tests were carried out to evaluate the cognitive impairment, while mRNA levels of neurotrophic factors (BDNF, NG) and neurodegenerative biomarker (VILIP-1) in hippocampus were tested by q-PCR. Transmission electron microscope was used to observe the axon degeneration in hippocampus. The levels of pro-inflammatory factors (TNF-α, IL-1β, IL-6), the levels of anti-inflammatory factors (Ym, Arg-1, IL-10) and microglia proliferation marker cyclin D1 in hippocampus were measured to evaluate microglia polarization. Bioinformatics analysis was conducted to identify key exosomes while BV-2 microglia overexpressing exosome miR-124-3p was constructed to observe microglia polarization in vitro experiments. Exogenous miR-124-3p-loaded exosomes were injected into hippocampus in vivo. Postoperative pain induced by intramedullary fixation after tibial fracture was confirmed by decreased mechanical and thermal pain thresholds. Postoperative pain induced cognitive impairment, promoted axon demyelination, decreased BDNF, NG and increased VILIP-1 expressions in hippocampus. Postoperative pain also increased pro-inflammatory factors, cyclin D1 and decreased anti-inflammatory factors in hippocampus. However, these changes were all reversed by morphine analgesia. Bioinformatics analysis identified the critical role of exosome miR-124-3p in cognitive impairment, which was confirmed to be down-regulated in hippocampus of postoperative pain mice. BV-2 microglia overexpressing exosome miR-124-3p showed decreased pro-inflammatory factors, cyclin D1 and increased anti-inflammatory factors. In vivo, stereotactic injection of exogenous miR-124-3p into hippocampus decreased pro-inflammatory factors, cyclin D1 and increased anti-inflammatory factors. The cognitive impairment, axon demyelination, decreased BDNF, NG and increased VILIP-1 expressions in hippocampus were all alleviated by exogenous exosome miR-124-3p. Microglial exosome miR-124-3p in hippocampus alleviates cognitive impairment induced by postoperative pain through microglia polarization in elderly mice.

The Association Between Surgery and Mild Cognitive Impairment: Insight from a Case-Control Study

Background

Surgery may be associated with postoperative cognitive impairment in elder participants, yet the extent of its association with mild cognitive impairment (MCI) remains undetermined.

Objective

To determine the relationship between surgery and MCI.

Methods

The data of participants from the Alzheimer's Disease Neuroimaging Initiative were analyzed, including individuals with MCI or normal cognition. We focused on surgeries conducted after the age of 45, categorized by the number of surgeries, surgical risk, and the age at which surgeries occurred. Multivariable logistic regression was employed to determine the association between surgery and the development of MCI.

Results

The study is comprised of 387 individuals with MCI and 578 cognitively normal individuals. The overall surgery exposure (adjusted OR = 1.14, [95% CI 0.83, 1.56], p = 0.43) and the number of surgeries (adjusted OR = 0.92  [0.62, 1.36], p = 0.67 for single exposure, adjusted OR = 1.12 [0.71, 1.78], p = 0.63 for two exposures, adjusted OR = 1.38 [0.95, 2.01], p = 0.09 for three or more exposures compared to no exposure as the reference) were not associated with the development of MCI. However, high-risk surgeries (adjusted OR = 1.79 [1.00, 3.21], p = 0.049) or surgeries occurring after the age of 75 (adjusted OR = 2.01 [1.03, 3.90], p = 0.041) were associated with a greater risk of developing MCI.

Conclusions

High risk surgeries occurring at an older age contribute to the development of MCI, indicating a complex of mechanistic insights for the development of postoperative cognitive impairment.

Nanoscale imaging of pT217-tau in aged rhesus macaque entorhinal and dorsolateral prefrontal cortex: Evidence of interneuronal trafficking and early-stage neurodegeneration

INTRODUCTION

pT217-tau is a novel fluid-based biomarker that predicts onset of Alzheimer's disease (AD) symptoms, but little is known about how pT217-tau arises in brain, as soluble pT217-tau is dephosphorylated postmortem in humans.

METHODS

We utilized multi-label immunofluorescence and immunoelectron-microscopy to examine the subcellular localization of early-stage pT217-tau in entorhinal and prefrontal cortices of aged macaques with naturally-occurring tau pathology and assayed pT217-tau levels in plasma.

RESULTS

pT217-tau was aggregated on microtubules within dendrites exhibiting early signs of degeneration, including autophagic vacuoles. It was also seen trafficking between excitatory neurons within synapses on spines, where it was exposed to the extracellular space, and thus accessible to CSF/blood. Plasma pT217-tau levels increased across the age-span and thus can serve as a biomarker in macaques.

DISCUSSION

These data help to explain why pT217-tau predicts degeneration in AD and how it gains access to CSF and plasma to serve as a fluid biomarker.