Role of Damage Associated Molecular Pattern Molecules (DAMPs) in Aneurysmal Subarachnoid Hemorrhage (aSAH)

Damage-associated molecular patterns as a mechanism of sevoflurane-induced neuroinflammation in neonatal rodents

BACKGROUND

General anesthesia is inevitable for pediatric patients undergoing surgery, though volatile anesthetic agents may cause neuroinflammation and neurodevelopmental impairment; however, the underlying pathophysiology remains unclear. We aimed to investigate the neuroinflammation mechanism in developing rat brains associated with sevoflurane exposure time, by identifying the specific damage-associated molecular patterns (DAMPs) pathway and evaluating the effects of non-steroidal anti-inflammatory drugs (NSAIDs) in alleviating neuroinflammation.

METHODS

A three-step experiment was conducted to investigate neuroinflammation induced by sevoflurane. First, the exposure time required for sevoflurane to cause neuroinflammation was determined. Next, the specific pathways of DAMPs involved in neuroinflammation by sevoflurane were identified. Finally, the effects of NSAIDs on sevoflurane-induced neuroinflammation were investigated. The expression of various molecules in the rat brain were assessed using immunohistochemistry, immunofluorescence, quantitative real-time polymerase chain reaction, western blot analysis, and enzyme-linked immunosorbent assay.

RESULTS

In total, 112 rats (aged 7 days) were used, of which six rats expired during the experiment (mortality rate, 5.3%). Expression of CD68, HMGB-1, galectin-3, TLR4, TLR9, and phosphorylated NF-κB was significantly increased upon 6 h of sevoflurane exposure. Conversely, transcriptional levels of TNF-α and IL-6 significantly increased and IFN-γ significantly decreased after 6 h of sevoflurane exposure. Co-administration of NSAIDs with sevoflurane anesthesia significantly attenuated TNF-α and IL-6 levels and restored IFN-γ levels.

CONCLUSIONS

In conclusion, 6 h of sevoflurane exposure induces neuroinflammation through the DAMPs pathway, HMGB-1, and galectin-3. Co-administration of ibuprofen reduced sevoflurane-induced neuroinflammation.

Unveiling microglia heterogeneity in intracerebral hemorrhage

Microglia are important innate immune cells in the brain, and a rich diversity of subtypes has recently been discovered that expand beyond the traditional classification of traditional M1 (pro-inflammatory) and M2 (anti-inflammatory) classifications. Intracerebral hemorrhage (ICH) is a devastating form of stroke, and the understanding of its later-stage pathological mechanisms remains incomplete. In this study, through the analysis of single-cell transcripts from mice brains 14 days post-ICH, three disease-associated expression patterns of microglia were identified. These include a lipid metabolism and phagocytosis phenotype reminiscent of Disease-Associated Microglia (DAM) initially discovered in Alzheimer's disease models, a phenotype associated with angiogenesis, and a relatively independent phenotype similar to the pro-inflammatory M1 state. These findings were further validated through immunofluorescence in both mouse and human specimens. In addition, analysis of single-cell transcripts from mice brains 3 days post-ICH suggested that microglia involved in lipid metabolism and phagocytosis likely emerge from early proliferating populations. Given the distinct origins and phenotypic characteristics of pro-inflammatory and reparative microglia, interventions targeting these cells hold the potential to modulate the delicate balance between injury and repair during the pathophysiological process of ICH, highlighting a pivotal direction for future therapeutic strategies.

Proteomic profile and predictive markers of outcome in patients with subarachnoid hemorrhage

BACKGROUND

The molecular mechanisms underlying development of posthemorrhagic hydrocephalus (PHH) following subarachnoid hemorrhage (SAH) remain incompletely understood. Consequently, treatment strategies tailored towards the individual patient remain limited. This study aimed to identify proteomic cerebrospinal fluid (CSF) biomarkers capable of predicting shunt dependency and functional outcome in patients with SAH in order to improve informed clinical decision making.

METHODS

Ventricular CSF samples were collected twice from 23 patients with SAH who required external ventricular drain (EVD) insertion (12 patients with successful EVD weaning, 11 patients in need of permanent CSF shunting due to development of PHH). The paired CSF samples were collected acutely after ictus and later upon EVD removal. Cisternal CSF samples were collected from 10 healthy control subjects undergoing vascular clipping of an unruptured aneurysm. All CSF samples were subjected to mass spectrometry-based proteomics analysis. Proteomic biomarkers were quantified using area under the curve (AUC) estimates from a receiver operating curve (ROC).

RESULTS

CSF from patients with SAH displayed a distinct proteomic profile in comparison to that of healthy control subjects. The CSF collected acutely after ictus from patients with SAH was moreover distinct from that collected weeks later but appeared similar in the weaned and shunted patient groups. Sixteen unique proteins were identified as potential predictors of shunt dependency, while three proteins were identified as potential predictors of functional outcome assessed six months after ictus with the modified Rankin Scale.

CONCLUSIONS

We here identified several potential proteomic biomarkers in CSF from patients with SAH capable of predicting (i) shunt dependency and thus development of PHH and (ii) the functional outcome assessed six months after ictus. These proteomic biomarkers may have the potential to aid clinical decision making by predicting shunt dependency and functional outcome following SAH.

Causal relationship between mitochondrial-associated proteins and cerebral aneurysms: a Mendelian randomization study

Background

Cerebral aneurysm is a high-risk cerebrovascular disease with a poor prognosis, potentially linked to multiple factors. This study aims to explore the association between mitochondrial-associated proteins and the risk of cerebral aneurysms using Mendelian randomization (MR) methods.

Methods

We used GWAS summary statistics from the IEU Open GWAS project for mitochondrial-associated proteins and from the Finnish database for cerebral aneurysms (uIA, aSAH). The association between mitochondrial-associated exposures and cerebral aneurysms was evaluated using MR-Egger, weighted mode, IVW, simple mode and weighted median methods. Reverse MR assessed reverse causal relationship, while sensitivity analyses examined heterogeneity and pleiotropy in the instrumental variables. Significant causal relationship with cerebral aneurysms were confirmed using FDR correction.

Results

Through MR analysis, we identified six mitochondrial proteins associated with an increased risk of aSAH: AIF1 (OR: 1.394, 95% CI: 1.109-1.752, p = 0.0044), CCDC90B (OR: 1.318, 95% CI: 1.132-1.535, p = 0.0004), TIM14 (OR: 1.272, 95% CI: 1.041-1.553, p = 0.0186), NAGS (OR: 1.219, 95% CI: 1.008-1.475, p = 0.041), tRNA PusA (OR: 1.311, 95% CI: 1.096-1.569, p = 0.003), and MRM3 (OR: 1.097, 95% CI: 1.016-1.185, p = 0.0175). Among these, CCDC90B, tRNA PusA, and AIF1 demonstrated a significant causal relationship with an increased risk of aSAH (FDR q < 0.1). Three mitochondrial proteins were associated with an increased risk of uIA: CCDC90B (OR: 1.309, 95% CI: 1.05-1.632, p = 0.0165), tRNA PusA (OR: 1.306, 95% CI: 1.007-1.694, p = 0.0438), and MRM3 (OR: 1.13, 95% CI: 1.012-1.263, p = 0.0303). In the reverse MR study, only one mitochondrial protein, TIM14 (OR: 1.087, 95% CI: 1.004-1.177, p = 0.04), showed a causal relationship with aSAH. Sensitivity analysis did not reveal heterogeneity or pleiotropy. The results suggest that CCDC90B, tRNA PusA, and MRM3 may be common risk factors for cerebral aneurysms (ruptured and unruptured), while AIF1 and NAGS are specifically associated with an increased risk of aSAH, unrelated to uIA. TIM14 may interact with aSAH.

Conclusion

Our findings confirm a causal relationship between mitochondrial-associated proteins and cerebral aneurysms, offering new insights for future research into the pathogenesis and treatment of this condition.

T cell-mediated skin-brain axis: Bridging the gap between psoriasis and psychiatric comorbidities

Psoriasis, a chronic inflammatory skin condition, is often accompanied by psychiatric comorbidities such as anxiety, depression, suicidal ideation, and other mental disorders. Psychological disorders may also play a role in the development and progression of psoriasis. The intricate interplay between the skin diseases and the psychiatric comorbidities is mediated by the 'skin-brain axis'. Understanding the mechanisms underlying psoriasis and psychiatric comorbidities can help improve the efficacy of treatment by breaking the vicious cycle of diseases. T cells and related cytokines play a key role in the pathogenesis of psoriasis and psychiatric diseases, and are crucial components of the 'skin-brain axis'. Apart from damaging the blood-brain barrier (BBB) directly, T cells and secreted cytokines could interact with the hypothalamic-pituitary-adrenal axis (HPA axis) and the sympathetic nervous system (SNS) to exacerbate skin diseases or mental disorders. However, few reviews have systematically summarized the roles and mechanisms of T cells in the interaction between psoriasis and psychiatric comorbidities. In this review, we discussed several key T cells and their roles in the 'skin-brain axis', with a focus on the mechanisms underlying the interplay between psoriasis and mental commodities, to provide data that might help develop effective strategies for the treatment of both psoriasis and psychiatric comorbidities.

Inhibiting RIPK1-driven neuroinflammation and neuronal apoptosis mitigates brain injury following experimental subarachnoid hemorrhage

RIPK1, a receptor-interacting serine/threonine protein kinase, plays a crucial role in maintaining cellular and tissue homeostasis by integrating inflammatory responses and cell death signaling pathways including apoptosis and necroptosis, which have been implicated in diverse physiological and pathological processes. Suppression of RIPK1 activation is a promising strategy for restraining the pathological progression of many human diseases. Neuroinflammation and neuronal apoptosis are two pivotal factors in the pathogenesis of brain injury following subarachnoid hemorrhage (SAH). In this study, we established in vivo and in vitro models of SAH to investigate the activation of RIPK1 kinase in both microglia and neurons. We observed the correlation between RIPK1 kinase activity and microglia-mediated inflammation as well as neuronal apoptosis. We then investigated whether inhibition of RIPK1 could alleviate neuroinflammation and neuronal apoptosis following SAH, thereby reducing brain edema and ameliorating neurobehavioral deficits. Additionally, the underlying mechanisms were also explored. Our research findings revealed the activation of RIPK1 kinase in both microglia and neurons following SAH, as marked by the phosphorylation of RIPK1 at serine 166. The upregulation of p-RIPK1(S166) resulted in a significant augmentation of inflammatory cytokines and chemokines, including TNF-α, IL-6, IL-1α, CCL2, and CCL5, as well as neuronal apoptosis. The activation of RIPK1 in microglia and neurons following SAH could be effectively suppressed by administration of Nec-1 s, a specific inhibitor of RIPK1. Consequently, inhibition of RIPK1 resulted in a downregulation of inflammatory cytokines and chemokines and attenuation of neuronal apoptosis after SAH in vitro. Furthermore, the administration of Nec-1 s effectively mitigated neuroinflammation, neuronal apoptosis, brain edema, and neurobehavioral deficits in mice following SAH. Our findings suggest that inhibiting RIPK1 kinase represents a promising therapeutic strategy for mitigating brain injury after SAH by attenuating RIPK1-driven neuroinflammation and neuronal apoptosis.

Hydrogen exerts neuroprotective effects after subarachnoid hemorrhage by attenuating neuronal ferroptosis and inhibiting neuroinflammation

OBJECTIVE

Spontaneous subarachnoid hemorrhage (SAH), the third most common stroke subtype, is associated with high mortality and disability rates. Therefore, finding effective therapies to improve neurological function after SAH is critical. The objective of this study was to investigate the potential neuroprotective effects of hydrogen in the context of SAH, specifically, by examining its role in attenuating neuronal ferroptosis and inhibiting neuroinflammation, which are exacerbated by excess iron ions after SAH.

METHODS

Mice were exposed to chambers containing 3% hydrogen, and cells were cultured in incubators containing 60% hydrogen. Neurological function in mice was assessed using behavioral scores. Protein changes were detected using western blotting. Inflammatory factors were detected using enzyme linked immunosorbent assay. Probes, electron microscopy, and related kits were employed to detect oxidative stress and ferroptosis.

RESULTS

Hydrogen improved the motor function, sensory function, and cognitive ability of mice after SAH. Additionally, hydrogen facilitated Nuclear factor erythroid 2 -related factor 2 activation, upregulated Glutathione peroxidase 4, and inhibited Toll-like receptor 4, resulting in downregulation of inflammatory responses, attenuation of oxidative stress after SAH, and inhibition of neuronal ferroptosis.

CONCLUSION

Hydrogen exerts neuroprotective effects by inhibiting neuronal ferroptosis and attenuating neuroinflammation after SAH.

Cerebral Ischemic Reperfusion Injury: Preventative and Therapeutic Strategies

Acute ischemic stroke is a leading cause of morbidity and mortality in the United States. Treatment goals remain focused on restoring blood flow to compromised areas. However, a major concern arises after reperfusion occurs. Cerebral ischemic reperfusion injury is defined as damage to otherwise salvageable brain tissue occurring with the reestablishment of the vascular supply to that region. The pool of eligible patients for revascularization continues to grow, especially with the recently expanded endovascular therapeutic window. Neurointensivists should understand and manage complications of successful recanalization. In this review, we examine the pathophysiology, diagnosis, and potential management strategies in cerebral ischemic reperfusion injury.

Clinical Potential of Immunotherapies in Subarachnoid Hemorrhage Treatment: Mechanistic Dissection of Innate and Adaptive Immune Responses

Subarachnoid hemorrhage (SAH), classified as a medical emergency, is a devastating and severe subtype of stroke. SAH induces an immune response, which further triggers brain injury; however, the underlying mechanisms need to be further elucidated. The current research is predominantly focused on the production of specific subtypes of immune cells, especially innate immune cells, post-SAH onset. Increasing evidence suggests the critical role of immune responses in SAH pathophysiology; however, studies on the role and clinical significance of adaptive immunity post-SAH are limited. In this present study, we briefly review the mechanistic dissection of innate and adaptive immune responses post-SAH. Additionally, we summarized the experimental studies and clinical trials of immunotherapies for SAH treatment, which may form the basis for the development of improved therapeutic approaches for the clinical management of SAH in the future.

Modulation of Neuroinflammation: Advances in Roles and Mechanisms of the IL-33/ST2 Axis Involved in Ischemic Stroke

Interleukin (IL)-33 was initially recognized as a constituent of the IL-1 cytokine family in 2005. It exerts pleiotropic effects by regulating immune responses via its binding to the receptor ST2 (IL-33R). The IL-33/ST2 pathway has been linked to several inflammatory disorders. In human and rodents, the broad expression of IL-33 in spinal cord tissues and brain indicates its central nervous system-specific functions. Growing evidence supports the protective effects of the IL-33/ST2 pathway in ischemic stroke, along with a better understanding of the underlying mechanisms. IL-33 plays a crucial role in the regulation of the release of inflammatory molecules from glial cells in response to neuropathological lesions. Moreover, IL-33/ST2-mediated neuroprotection following cerebral ischemia may be linked to T-cell function, specifically regulatory T cells. Soluble ST2 (sST2) acts as a decoy receptor in the IL-33/ST2 axis, blocking IL-33 signaling through the membrane ST2 receptor. sST2 has also been identified as a potential inflammatory biomarker of ischemic stroke. Targeting sST2 specifically to eliminate its inhibition of the protective IL-33/ST2 pathway in ischemic brain tissues is a promising approach for the treatment of ischemic stroke.

Cortical Spreading Depolarization and Delayed Cerebral Ischemia; Rethinking Secondary Neurological Injury in Subarachnoid Hemorrhage

Poor outcomes in Subarachnoid Hemorrhage (SAH) are in part due to a unique form of secondary neurological injury known as Delayed Cerebral Ischemia (DCI). DCI is characterized by new neurological insults that continue to occur beyond 72 h after the onset of the hemorrhage. Historically, it was thought to be a consequence of hypoperfusion in the setting of vasospasm. However, DCI was found to occur even in the absence of radiographic evidence of vasospasm. More recent evidence indicates that catastrophic ionic disruptions known as Cortical Spreading Depolarizations (CSD) may be the culprits of DCI. CSDs occur in otherwise healthy brain tissue even without demonstrable vasospasm. Furthermore, CSDs often trigger a complex interplay of neuroinflammation, microthrombi formation, and vasoconstriction. CSDs may therefore represent measurable and modifiable prognostic factors in the prevention and treatment of DCI. Although Ketamine and Nimodipine have shown promise in the treatment and prevention of CSDs in SAH, further research is needed to determine the therapeutic potential of these as well as other agents.

Inflammatory Markers as Predictors of Shunt Dependency and Functional Outcome in Patients with Aneurysmal Subarachnoid Hemorrhage

The mechanisms underlying post-hemorrhagic hydrocephalus (PHH) development following subarachnoid hemorrhage (SAH) are not fully understood, which complicates informed clinical decisions regarding the duration of external ventricular drain (EVD) treatment and prevents the prediction of shunt-dependency in the individual patient. The aim of this study was to identify potential inflammatory cerebrospinal fluid (CSF) biomarkers of PHH and, thus, shunt-dependency and functional outcome in patients with SAH. This study was a prospective observational study designed to evaluate inflammatory markers in ventricular CSF. In total, 31 Patients with SAH who required an EVD between June 2019 and September 2021 at the Department of Neurosurgery, Rigshospitalet, Copenhagen, Denmark, were included. CSF samples were collected twice from each patient and analyzed for 92 inflammatory markers via proximity extension assay (PEA), and the prognostic ability of the markers was investigated. In total, 12 patients developed PHH, while 19 were weaned from their EVD. Their 6-month functional outcome was determined with the modified Rankin Scale. Of the 92 analyzed inflammatory biomarkers, 79 were identified in the samples. Seven markers (SCF, OPG, LAP TGFβ1, Flt3L, FGF19, CST5, and CSF1) were found to be predictors of shunt dependency, and four markers (TNFα, CXCL5, CCL20, and IL8) were found to be predictors of functional outcome. In this study, we identified promising inflammatory biomarkers that are able to predict (i) the functional outcome in patients with SAH and (ii) the development of PHH and, thus, the shunt dependency of the individual patients. These inflammatory markers may have the potential to be employed as predictive biomarkers of shunt dependency and functional outcome following SAH and could, as such, be applied in the clinic.

Degradable Poly(amino acid) Vesicles Modulate DNA-Induced Inflammation after Traumatic Brain Injury

Following brain trauma, secondary injury from molecular and cellular changes causes progressive cerebral tissue damage. Acute/chronic neuroinflammation following traumatic brain injury (TBI) is a key player in the development of secondary injury. Rapidly elevated cell-free DNAs (cfDNAs) due to cell death could lead to production of inflammatory cytokines that aggravate TBI. Herein, we designed poly(amino acid)-based cationic nanoparticles (cNPs) and applied them intravenously in a TBI mice model with the purpose of scavenging cfDNA in the brain and suppressing the acute inflammation. In turn, these cNPs could effectively eliminate endogenous cfDNA, inhibit excessive activation of inflammation, and promote neural functional recovery.

Differential proteomic profile of lumbar and ventricular cerebrospinal fluid

BACKGROUND

Pathological cerebral conditions may manifest in altered composition of the cerebrospinal fluid (CSF). Although diagnostic CSF analysis seeks to establish pathological disturbances in the brain proper, CSF is generally sampled from the lumbar compartment for reasons of technical ease and ethical considerations. We here aimed to compare the molecular composition of CSF obtained from the ventricular versus the lumbar CSF compartments to establish a relevance for employing lumbar CSF as a proxy for the CSF bathing the brain tissue.

METHODS

CSF was collected from 46 patients with idiopathic normal pressure hydrocephalus (iNPH) patients during their diagnostic workup (lumbar samples) and in connection with their subsequent CSF diversion shunt surgery (ventricular samples). The mass-spectrometry-based proteomic profile was determined in these samples and in addition, selected biomarkers were quantified with ELISA (S100B, neurofilament light (NfL), amyloid-β (Aβ₄₀, Aβ₄₂), and total tau (T-tau) and phosphorylated tau (P-tau) forms). The latter analysis was extended to include paired porcine samples obtained from the lumbar compartment and the cerebromedullary cistern closely related to the ventricles.

RESULTS

In total 1231 proteins were detected in the human CSF. Of these, 216 distributed equally in the two CSF compartments, whereas 22 were preferentially (or solely) present in the ventricular CSF and four in the lumbar CSF. The selected biomarkers of neurodegeneration and Alzheimer's disease displayed differential distribution, some with higher (S100B, T-tau, and P-tau) and some with lower (NfL, Aβ₄₀, Aβ₄₂) levels in the ventricular compartment. In the porcine samples, all biomarkers were most abundant in the lumbar CSF.

CONCLUSIONS

The overall proteomic profile differs between the ventricular and the lumbar CSF compartments, and so does the distribution of clinically employed biomarkers. However, for a range of CSF proteins and biomarkers, one can reliably employ lumbar CSF as a proxy for ventricular CSF if or a lumbar/cranial index for the particular molecule has been established. It is therefore important to verify the compartmental preference of the proteins or biomarkers of interest prior to extrapolating from lumbar CSF to that of the ventricular fluid bordering the brain.

Melatonin as an Antioxidant Agent in Stroke: An Updated Review

Stroke is a devastating disease associated with high mortality and disability worldwide, and is generally classified as ischemic or hemorrhagic, which share certain similar pathophysiological processes. Oxidative stress is a critical factor involved in stroke-induced injury, which not only directly damages brain tissue, but also enhances a series of pathological signaling cascades, contributing to inflammation, brain edema, and neuronal death. To alleviate these serious secondary brain injuries, neuroprotective agents targeting oxidative stress inhibition may serve as a promising treatment strategy. Melatonin is a hormone secreted by the pineal gland, and has various properties, such as antioxidation, anti-inflammation, circadian rhythm modulation, and promotion of tissue regeneration. Numerous animal experiments studying stroke have confirmed that melatonin exerts considerable neuroprotective effects, partially via anti-oxidative stress. In this review, we introduce the possible role of melatonin as an antioxidant in the treatment of stroke based on the latest published studies of animal experiments and clinical research.

Progress in Research on TLR4-Mediated Inflammatory Response Mechanisms in Brain Injury after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is one of the common clinical neurological emergencies. Its incidence accounts for about 5-9% of cerebral stroke patients. Even surviving patients often suffer from severe adverse prognoses such as hemiplegia, aphasia, cognitive dysfunction and even death. Inflammatory response plays an important role during early nerve injury in SAH. Toll-like receptors (TLRs), pattern recognition receptors, are important components of the body's innate immune system, and they are usually activated by damage-associated molecular pattern molecules. Studies have shown that with TLR 4 as an essential member of the TLRs family, the inflammatory transduction pathway mediated by it plays a vital role in brain injury after SAH. After SAH occurrence, large amounts of blood enter the subarachnoid space. This can produce massive damage-associated molecular pattern molecules that bind to TLR4, which activates inflammatory response and causes early brain injury, thus resulting in serious adverse prognoses. In this paper, the process in research on TLR4-mediated inflammatory response mechanism in brain injury after SAH was reviewed to provide a new thought for clinical treatment.

Specific signature biomarkers highlight the potential mechanisms of circulating neutrophils in aneurysmal subarachnoid hemorrhage

Background: Aneurysmal subarachnoid hemorrhage (aSAH) is a devastating hemorrhagic stroke with high disability and mortality. Neuroinflammation and the immunological response after aSAH are complex pathophysiological processes that have not yet been fully elucidated. Therefore, attention should be paid to exploring the inflammation-related genes involved in the systemic response to the rupture of intracranial aneurysms.

Methods: The datasets of gene transcriptomes were downloaded from the Gene Expression Omnibus database. We constructed a gene co-expression network to identify cluster genes associated with aSAH and screened out differentially expressed genes (DEGs). The common gene was subsequently applied to identify hub genes by protein-protein interaction analysis and screen signature genes by machine learning algorithms. CMap analysis was implemented to identify potential small-molecule compounds. Meanwhile, Cibersort and ssGSEA were used to evaluate the immune cell composition, and GSEA reveals signal biological pathways.

Results: We identified 602 DEGs from the GSE36791. The neutrophil-related module associated with aSAH was screened by weighted gene co-expression network analysis (WGCNA) and functional enrichment analysis. Several small molecular compounds were predicted based on neutrophil-related genes. MAPK14, ITGAM, TLR4, and FCGR1A have been identified as crucial genes involved in the peripheral immune activation related to neutrophils. Six significant genes (CST7, HSP90AB1, PADI4, PLBD1, RAB32, and SLAMF6) were identified as signature biomarkers by performing the LASSO analysis and SVM algorithms. The constructed machine learning model appears to be robust by receiver-operating characteristic curve analysis. The immune feature analysis demonstrated that neutrophils were upregulated post-aSAH and PADI4 was positively correlated with neutrophils. The NETs pathway was significantly upregulated in aSAH.

Conclusion: We identified core regulatory genes influencing the transcription profiles of circulating neutrophils after the rupture of intracranial aneurysms using bioinformatics analysis and machine learning algorithms. This study provides new insight into the mechanism of peripheral immune response and inflammation after aSAH.

New insight into neurological degeneration: Inflammatory cytokines and blood–brain barrier

Neurological degeneration after neuroinflammation, such as that resulting from Alzheimer’s disease (AD), stroke, multiple sclerosis (MS), and post-traumatic brain injury (TBI), is typically associated with high mortality and morbidity and with permanent cognitive dysfunction, which places a heavy economic burden on families and society. Diagnosing and curing these diseases in their early stages remains a challenge for clinical investigation and treatment. Recent insight into the onset and progression of these diseases highlights the permeability of the blood–brain barrier (BBB). The primary factor that influences BBB structure and function is inflammation, especially the main cytokines including IL-1β, TNFα, and IL-6, the mechanism on the disruption of which are critical component of the aforementioned diseases. Surprisingly, the main cytokines from systematic inflammation can also induce as much worse as from neurological diseases or injuries do. In this review, we will therefore discuss the physiological structure of BBB, the main cytokines including IL-1β, TNFα, IL-6, and their mechanism on the disruption of BBB and recent research about the main cytokines from systematic inflammation inducing the disruption of BBB and cognitive impairment, and we will eventually discuss the need to prevent the disruption of BBB.

TLR4-Pathway-Associated Biomarkers in Subarachnoid Hemorrhage (SAH): Potential Targets for Future Anti-Inflammatory Therapies

Subarachnoid hemorrhage is associated with severe neurological deficits for survivors. Among survivors of the initial bleeding, secondary brain injury leads to additional brain damage. Apart from cerebral vasospasm, secondary brain injury mainly results from cerebral inflammation taking place in the brain parenchyma after bleeding. The brain’s innate immune system is activated, which leads to disturbances in brain homeostasis, cleavage of inflammatory cytokines and, subsequently, neuronal cell death. The toll-like receptor (TLR)4 signaling pathway has been found to play an essential role in the pathophysiology of acute brain injuries such as subarachnoid hemorrhage (SAH). TLR4 is expressed on the cell surface of microglia, which are key players in the cellular immune responses of the brain. The participants in the signaling pathway, such as TLR4-pathway-like ligands, the receptor itself, and inflammatory cytokines, can act as biomarkers, serving as clues regarding the inflammatory status after SAH. Moreover, protein complexes such as the NLRP3 inflammasome or receptors such as TREM1 frame the TLR4 pathway and are indicative of inflammation. In this review, we focus on the activity of the TLR4 pathway and its contributors, which can act as biomarkers of neuroinflammation or even offer potential new treatment targets for secondary neuronal cell death after SAH.

Janus Faced HMGB1 and Post-Aneurysmal Subarachnoid Hemorrhage (aSAH) Inflammation

Aneurysmal subarachnoid hemorrhage (aSAH), resulting majorly from the rupture of intracranial aneurysms, is a potentially devastating disease with high morbidity and mortality. The bleeding aneurysms can be successfully secured; however, the toxic and mechanical impact of the blood extravasation into the subarachnoid space damages the brain cells leading to the release of different damage-associated molecular pattern molecules (DAMPs). DAMPs upregulate the inflammation after binding their cognate receptors on the immune cells and underlies the early and delayed brain injury after aSAH. Moreover, these molecules are also associated with different post-aSAH complications, which lead to poor clinical outcomes. Among these DAMPs, HMGB1 represents a prototypical protein DAMP that has been well characterized for its proinflammatory role after aSAH and during different post-aSAH complications. However, recent investigations have uncovered yet another face of HMGB1, which is involved in the promotion of brain tissue remodeling, neurovascular repair, and anti-inflammatory effects after SAH. These different faces rely on different redox states of HMGB1 over the course of time after SAH. Elucidation of the dynamics of these redox states of HMGB1 has high biomarker as well as therapeutic potential. This review mainly highlights these recent findings along with the conventionally described normal role of HMGB1 as a nuclear protein and as a proinflammatory molecule during disease (aSAH).

Long-Term Elevated Siglec-10 in Cerebral Spinal Fluid Heralds Better Prognosis for Patients with Aneurysmal Subarachnoid Hemorrhage

The presence of aneurysmal subarachnoid hemorrhage (aSAH) is usually accompanied by excessive inflammatory response leading to damage of the central nervous system, and the sialic acid-binding Ig-like lectin 10 (Siglec-10) is a recognized factor being able to modify the inflammatory reaction. To investigate the potential role of Siglec-10 in aSAH, we collected the cerebrospinal fluid (CSF) of control (n = 11) and aSAH (n = 14) patients at separate times and measured the Siglec-10 concentration utilizing the enzyme-linked immunosorbent assay (ELISA) and evaluated the alterations of GOS and GCS during the disease process. In accordance with the STROBE statement, results showed that Siglec-10 in CSF rose quickly in response aSAH attack and then fell back to a slightly higher range above baseline, while it remained at relative high concentration and last longer in several severely injured patients. In general, higher Siglec-10 expression over a longer period usually indicated a better clinical prognosis. This prospective cohort study suggested that Siglec-10 could possibly be used as a biomarker for predicting prognosis of aSAH due to its ability to balance aSAH-induced nonsterile inflammation. Additionally, these findings might provide novel therapeutic perspectives for aSAH and other inflammation-related diseases.

Immune response treated with bone marrow mesenchymal stromal cells after stroke

Stroke is a leading cause of death and long-term disability worldwide. Tissue plasminogen activator (tPA) is an effective treatment for ischemic stroke. However, only a small part of patients could benefit from it. Therefore, finding a new treatment is necessary. Bone marrow mesenchymal stromal cells (BMSCs) provide a novel strategy for stroke patients. Now, many patients take stem cells to treat stroke. However, the researches of the precise inflammatory mechanism of cell replacement treatment are still rare. In this review, we summarize the immune response of BMSCs treated to stroke and may provide a new perspective for stem cell therapy.

New Mechanisms and Targets of Subarachnoid Hemorrhage: A Focus on Mitochondria

Spontaneous subarachnoid hemorrhage (SAH) accounts for 5-10% of all strokes and is a subtype of hemorrhagic stroke that places a heavy burden on health care. Despite great progress in surgical clipping and endovascular treatment for ruptured aneurysms, cerebral vasospasm (CVS) and delayed cerebral ischemia (DCI) threaten the long-term outcomes of patients with SAH. Moreover, there are limited drugs available to reduce the risk of DCI and adverse outcomes in SAH patients. New insight suggests that early brain injury (EBI), which occurs within 72 h after the onset of SAH, may lay the foundation for further DCI development and poor outcomes. The mechanisms of EBI mainly include excitotoxicity, oxidative stress, neuroinflammation, blood-brain barrier (BBB) destruction, and cellular death. Mitochondria are a double-membrane organelle, and they play an important role in energy production, cell growth, differentiation, apoptosis, and survival. Mitochondrial dysfunction, which can lead to mitochondrial membrane potential (Δψm) collapse, overproduction of reactive oxygen species (ROS), release of apoptogenic proteins, disorders of mitochondrial dynamics, and activation of mitochondria-related inflammation, is considered a novel mechanism of EBI related to DCI as well as post-SAH outcomes. In addition, mitophagy is activated after SAH. In this review, we discuss the latest perspectives on the role of mitochondria in EBI and DCI after SAH. We emphasize the potential of mitochondria as therapeutic targets and summarize the promising therapeutic strategies targeting mitochondria for SAH.

Association of cerebrospinal fluid advanced oxidation protein products levels with early brain injury and prognosis of aneurysmal subarachnoid hemorrhage: A preliminary prospective study

OBJECTIVES

In this study, we investigated the time course in the cerebrospinal fluid (CSF) advanced oxidation protein products (AOPPs) levels in patients with aneurysmal subarachnoid hemorrhage (aSAH), and ascertained the relationship between the levels of AOPPs and early brain injury (EBI), hydrocephalus and prognosis of patients with aSAH.

METHODS

We measured the CSF AOPPs levels in 50 patients with aSAH at 1-3 d, 4-6 d, 7-9 d, and 10-12 d after hemorrhage. The modified Fisher grades, Hunt-Hess grades, CSF IL-6 levels, peripheral blood count of white blood cells, cerebral edema scores and hydrocephalus were used to assess the severity of brain injury. Modified Rankin Scale (mRS) scores were used to assess the prognosis. Patients with mRS scores greater than 2 were considered to have a poor outcome.

RESULTS

CSF AOPPs levels were significantly higher in patients with aSAH with poor prognosis, compared to patients with good prognosis and peaked in the early stage. Among patients with aSAH, the levels of CSF AOPPs on days 1-3 were significantly correlated with modified Fisher grades, Hunt-Hess grades, CSF IL-6 levels, peripheral blood count of white blood cells, and cerebral edema scores. Also, in patients with hydrocephalus, early CSF AOPPs levels were significantly elevated. Levels of CSF AOPPs in aSAH patients on days 1-3, 4-6, and 7-9 were independently associated with poor prognosis at the 90-day follow-up, and the optimal area under the curve (AUC) values for CSF AOPPs levels were found on days 1-3.

CONCLUSIONS

AOPPs may serve as the potential biomarker to assess the severity of EBI and prognosis in patients with aSAH.

Melatonin as a Potential Neuroprotectant: Mechanisms in Subarachnoid Hemorrhage-Induced Early Brain Injury

Subarachnoid hemorrhage (SAH) is a common cerebrovascular disease with high mortality and disability rates. Despite progressive advances in drugs and surgical techniques, neurological dysfunction in surviving SAH patients have not improved significantly. Traditionally, vasospasm has been considered the main cause of death and disability following SAH, but anti-vasospasm therapy has not benefited clinical prognosis. Many studies have proposed that early brain injury (EBI) may be the primary factor influencing the prognosis of SAH. Melatonin is an indole hormone and is the main hormone secreted by the pineal gland, with low daytime secretion levels and high nighttime secretion levels. Melatonin produces a wide range of biological effects through the neuroimmune endocrine network, and participates in various physiological activities in the central nervous system, reproductive system, immune system, and digestive system. Numerous studies have reported that melatonin has extensive physiological and pharmacological effects such as anti-oxidative stress, anti-inflammation, maintaining circadian rhythm, and regulating cellular and humoral immunity. In recent years, more and more studies have been conducted to explore the molecular mechanism underlying melatonin-induced neuroprotection. The studies suggest beneficial effects in the recovery of intracerebral hemorrhage, cerebral ischemia-reperfusion injury, spinal cord injury, Alzheimer’s disease, Parkinson’s disease and meningitis through anti-inflammatory, antioxidant and anti-apoptotic mechanisms. This review summarizes the recent studies on the application and mechanism of melatonin in SAH.

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Inflammation and Oxidative Stress: Potential Targets for Improving Prognosis After Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) has a high mortality rate and causes long-term disability in many patients, often associated with cognitive impairment. However, the pathogenesis of delayed brain dysfunction after SAH is not fully understood. A growing body of evidence suggests that neuroinflammation and oxidative stress play a negative role in neurofunctional deficits. Red blood cells and hemoglobin, immune cells, proinflammatory cytokines, and peroxidases are directly or indirectly involved in the regulation of neuroinflammation and oxidative stress in the central nervous system after SAH. This review explores the role of various cellular and acellular components in secondary inflammation and oxidative stress after SAH, and aims to provide new ideas for clinical treatment to improve the prognosis of SAH.

The Role of the Glycocalyx in the Pathophysiology of Subarachnoid Hemorrhage-Induced Delayed Cerebral Ischemia

The glycocalyx is an important constituent of blood vessels located between the bloodstream and the endothelium. It plays a pivotal role in intercellular interactions in neuroinflammation, reduction of vascular oxidative stress, and provides a barrier regulating vascular permeability. In the brain, the glycocalyx is closely related to functions of the blood-brain barrier and neurovascular unit, both responsible for adequate neurovascular responses to potential threats to cerebral homeostasis. An aneurysmal subarachnoid hemorrhage (aSAH) occurs following rupture of an intracranial aneurysm and leads to immediate brain damage (early brain injury). In some cases, this can result in secondary brain damage, also known as delayed cerebral ischemia (DCI). DCI is a life-threatening condition that affects up to 30% of all aSAH patients. As such, it is associated with substantial societal and healthcare-related costs. Causes of DCI are multifactorial and thought to involve neuroinflammation, oxidative stress, neuroinflammation, thrombosis, and neurovascular uncoupling. To date, prediction of DCI is limited, and preventive and effective treatment strategies of DCI are scarce. There is increasing evidence that the glycocalyx is disrupted following an aSAH, and that glycocalyx disruption could precipitate or aggravate DCI. This review explores the potential role of the glycocalyx in the pathophysiological mechanisms contributing to DCI following aSAH. Understanding the role of the glycocalyx in DCI could advance the development of improved methods to predict DCI or identify patients at risk for DCI. This knowledge may also alter the methods and timing of preventive and treatment strategies of DCI. To this end, we review the potential and limitations of methods currently used to evaluate the glycocalyx, and strategies to restore or prevent glycocalyx shedding.

Brain Immune Interactions-Novel Emerging Options to Treat Acute Ischemic Brain Injury

Ischemic stroke is still among the leading causes of mortality and morbidity worldwide. Despite intensive advancements in medical sciences, the clinical options to treat ischemic stroke are limited to thrombectomy and thrombolysis using tissue plasminogen activator within a narrow time window after stroke. Current state of the art knowledge reveals the critical role of local and systemic inflammation after stroke that can be triggered by interactions taking place at the brain and immune system interface. Here, we discuss different cellular and molecular mechanisms through which brain–immune interactions can take place. Moreover, we discuss the evidence how the brain influence immune system through the release of brain derived antigens, damage-associated molecular patterns (DAMPs), cytokines, chemokines, upregulated adhesion molecules, through infiltration, activation and polarization of immune cells in the CNS. Furthermore, the emerging concept of stemness-induced cellular immunity in the context of neurodevelopment and brain disease, focusing on ischemic implications, is discussed. Finally, we discuss current evidence on brain–immune system interaction through the autonomic nervous system after ischemic stroke. All of these mechanisms represent potential pharmacological targets and promising future research directions for clinically relevant discoveries.

Differential polarization and activation dynamics of systemic T helper cell subsets after aneurysmal subarachnoid hemorrhage (SAH) and during post-SAH complications

Aneurysmal subarachnoid hemorrhage (SAH) is associated with high morbidity and mortality. Devastating post-SAH complications, such as cerebral vasospasm (CVS), delayed cerebral ischemia or seizures to mention a few, are mainly responsible for the poor clinical outcome. Inflammation plays an indispensable role during early brain injury (EBI) and delayed brain injury (DBI) phases over which these complications arise. T helper cells are the major cytokine secreting cells of adaptive immunity that can polarize to multiple functionally unique sub-populations. Here, we investigate different CD4+ T cell subsets during EBI and DBI phases after SAH, and their dynamics during post-SAH complications. Peripheral venous blood from 15 SAH patients during EBI and DBI phases, was analyzed by multicolour flowcytometry. Different subsets of CD3+ CD4+ T cells were characterized by differential cell surface expression of CXCR3 and CCR6 into Th1, Th2, Th17, whereas Tregs were defined by CD25^hiCD127^lo. The analysis of activation states was done by the expression of stable activation markers CD38 and HLA-DR. Interestingly, compared to healthy controls, Tregs were significantly increased during both EBI and DBI phases. Different activation states of Tregs showed differential significant increase during EBI and DBI phases compared to controls. HLA-DR− CD38+ Tregs were significantly increased during DBI phase compared to EBI phase in SAH patients developing CVS, seizures and infections. However, HLA-DR− CD38− Tregs were significantly reduced during EBI phase in patients with cerebral ischemia (CI) compared to those without CI. HLA-DR− CD38− Th2 cells were significantly increased during EBI phase compared to controls. A significant reduction in Th17/Tregs and HLA-DR− CD38+ Th17/Tregs ratios was observed during both EBI and DBI phases compared to controls. While HLA-DR− CD38− Th17/Tregs and HLA-DR− CD38− Th1/Th2 ratios were impaired only during EBI phase compared to controls. In conclusion, CD4+ T cell subsets display dynamic and unique activation patterns after SAH and during the course of the manifestation of post-SAH complications, which may be helpful for the development of precision neurovascular care. However, to claim this, confirmatory studies with larger patient cohorts, ideally from different ethnic backgrounds, are required. Moreover, our descriptive study may be the grounds for subsequent lab endeavors to explore the underlying mechanisms of our observations.

Phthalide derivative CD21 attenuates tissue plasminogen activator-induced hemorrhagic transformation in ischemic stroke by enhancing macrophage scavenger receptor 1-mediated DAMP (peroxiredoxin 1) clearance

BACKGROUND

Hemorrhagic transformation (HT) is a critical issue in thrombolytic therapy in acute ischemic stroke. Damage-associated molecular pattern (DAMP)-stimulated sterile neuroinflammation plays a crucial role in the development of thrombolysis-associated HT. Our previous study showed that the phthalide derivative CD21 attenuated neuroinflammation and brain injury in rodent models of ischemic stroke. The present study explored the effects and underlying mechanism of action of CD21 on tissue plasminogen activator (tPA)-induced HT in a mouse model of transient middle cerebral artery occlusion (tMCAO) and cultured primary microglial cells.

METHODS

The tMCAO model was induced by 2 h occlusion of the left middle cerebral artery with polylysine-coated sutures in wildtype (WT) mice and macrophage scavenger receptor 1 knockout (MSR1^-/-) mice. At the onset of reperfusion, tPA (10 mg/kg) was intravenously administered within 30 min, followed by an intravenous injection of CD21 (13.79 mg/kg/day). Neuropathological changes were detected in mice 3 days after surgery. The effect of CD21 on phagocytosis of the DAMP peroxiredoxin 1 (Prx1) in lysosomes was observed in cultured primary microglial cells from brain tissues of WT and MSR1^-/- mice.

RESULTS

Seventy-two hours after brain ischemia, CD21 significantly attenuated neurobehavioral dysfunction and infarct volume. The tPA-infused group exhibited more severe brain dysfunction and hemorrhage. Compared with tPA alone, combined treatment with tPA and CD21 significantly attenuated ischemic brain injury and hemorrhage. Combined treatment significantly decreased Evans blue extravasation, matrix metalloproteinase 9 expression and activity, extracellular Prx1 content, proinflammatory cytokine mRNA levels, glial cells, and Toll-like receptor 4 (TLR4)/nuclear factor κB (NF-κB) pathway activation and increased the expression of tight junction proteins (zonula occludens-1 and claudin-5), V-maf musculoaponeurotic fibrosarcoma oncogene homolog B, and MSR1. MSR1 knockout significantly abolished the protective effect of CD21 against tPA-induced HT in tMCAO mice. Moreover, the CD21-induced phagocytosis of Prx1 was MSR1-dependent in cultured primary microglial cells from WT and MSR1^-/- mice, respectively.

CONCLUSION

The phthalide derivative CD21 attenuated tPA-induced HT in acute ischemic stroke by promoting MSR1-induced DAMP (Prx1) clearance and inhibition of the TLR4/NF-κB pathway and neuroinflammation.

Neuroprotective Strategies in Aneurysmal Subarachnoid Hemorrhage (aSAH)

Aneurysmal subarachnoid hemorrhage (aSAH) remains a disease with high mortality and morbidity. Since treating vasospasm has not inevitably led to an improvement in outcome, the actual emphasis is on finding neuroprotective therapies in the early phase following aSAH to prevent secondary brain injury in the later phase of disease. Within the early phase, neuroinflammation, thromboinflammation, disturbances in brain metabolism and early neuroprotective therapies directed against delayed cerebral ischemia (DCI) came into focus. Herein, the role of neuroinflammation, thromboinflammation and metabolism in aSAH is depicted. Potential neuroprotective strategies regarding neuroinflammation target microglia activation, metalloproteases, autophagy and the pathway via Toll-like receptor 4 (TLR4), high mobility group box 1 (HMGB1), NF-κB and finally the release of cytokines like TNFα or IL-1. Following the link to thromboinflammation, potential neuroprotective therapies try to target microthrombus formation, platelets and platelet receptors as well as clot clearance and immune cell infiltration. Potential neuroprotective strategies regarding metabolism try to re-balance the mismatch of energy need and supply following aSAH, for example, in restoring fuel to the TCA cycle or bypassing distinct energy pathways. Overall, this review addresses current neuroprotective strategies in aSAH, hopefully leading to future translational therapy options to prevent secondary brain injury.

Prognostic value of albumin-fibrinogen ratio in subarachnoid hemorrhage patients

ABSTRACT

Inflammation plays an important role in the pathophysiology of subarachnoid hemorrhage (SAH). Recent studies have indicated that the albumin to fibrinogen ratio (AFR) is a useful biomarker of inflammation.This research aimed to determine the ability of AFR to predict the prognosis of patients with SAH.A total of 440 patients with SAH who had been diagnosed within 72 hours of symptom onset were retrospectively reviewed. Clinical findings and laboratory data were retrieved from the hospital database. Functional outcome was measured according to the modified Rankin scale at 30 days. Logistic regression analysis was used to evaluate the correlation between AFR and the prognosis of patients with SAH. Receiver operating characteristic (ROC) analysis was performed to determine the prognostic ability of AFR at admission to predict the 30-day outcomes.The average age of all 440 patients with SAH was 56.75 ± 11.19 years and 31.4% (138) were male. Of these patients, 161 exhibited unfavorable outcomes at 30 days. According to the multivariate logistic regression analysis, the AFR was positively correlated with the outcome of patients with SAH (odds ratio 0.939, 95% confidence interval 0.885-0.996, P = .038). The ROC analysis revealed an area under the curve of 0.713 for AFR's ability to predict the 30-day outcomes.AFR is independently associated with the outcome of SAH patients. As a parameter that can be easily assessed at admission, AFR could be used to help the decision-making of clinical treatment.

Role of Adaptor Protein Myeloid Differentiation 88 (MyD88) in Post-Subarachnoid Hemorrhage Inflammation: A Systematic Review

Myeloid differentiation 88 (MyD88) is a well-established inflammatory adaptor protein. It is one of the essential downstream proteins of the toll-like receptor 4 (TLR4) signaling pathway. TLRs are pattern recognition receptors that are usually activated by the damage-associated molecular pattern molecules (DAMPs). Sterile inflammation is triggered by the endogenous DAMPs released in response to global cerebral ischemia and from extravasated blood after subarachnoid hemorrhage (SAH). In this review, we highlight the importance of the neuroinflammatory role of the MyD88 in the SAH. We also explore a few possible pharmacological agents that can be used to decrease SAH-associated neuroinflammation by modulating the MyD88 dependent functions. Pharmacological agents such as flavonoids, melatonin, fluoxetine, pentoxifylline and progesterone have been investigated experimentally to reduce the SAH-associated inflammation. Inhibition of the MyD88 not only reduces the expression of pro-inflammatory cytokines, but also potentially inhibits other processes that can augment the SAH associated inflammation. Further investigations are required to translate these findings in the clinical setting.

DAMPs and RAGE Pathophysiology at the Acute Phase of Brain Injury: An Overview

Early or primary injury due to brain aggression, such as mechanical trauma, hemorrhage or is-chemia, triggers the release of damage-associated molecular patterns (DAMPs) in the extracellular space. Some DAMPs, such as S100B, participate in the regulation of cell growth and survival but may also trigger cellular damage as their concentration increases in the extracellular space. When DAMPs bind to pattern-recognition receptors, such as the receptor of advanced glycation end-products (RAGE), they lead to non-infectious inflammation that will contribute to necrotic cell clearance but may also worsen brain injury. In this narrative review, we describe the role and ki-netics of DAMPs and RAGE at the acute phase of brain injury. We searched the MEDLINE database for “DAMPs” or “RAGE” or “S100B” and “traumatic brain injury” or “subarachnoid hemorrhage” or “stroke”. We selected original articles reporting data on acute brain injury pathophysiology, from which we describe DAMPs release and clearance upon acute brain injury, and the implication of RAGE in the development of brain injury. We will also discuss the clinical strategies that emerge from this overview in terms of biomarkers and therapeutic perspectives

Oleanolic acid exerts neuroprotective effects in subarachnoid hemorrhage rats through SIRT1-mediated HMGB1 deacetylation

Anti-inflammatory therapy for early brain injury after subarachnoid hemorrhage is a promising treatment for improving the prognosis. HMGB1 is the initiator of early inflammation after subarachnoid hemorrhage. Oleanolic acid is a natural pentacyclic triterpenoid compound with strong anti-inflammatory activity. It can relieve early brain injury in subarachnoid hemorrhage rats, but its mechanism is not very clear. Here, we study the potential mechanism of Oleanolic acid in the treatment of subarachnoid hemorrhage. First, we demonstrated that oleanolic acid alleviated early brain injury after subarachnoid hemorrhage, including improvement of grading score, neurological score, brain edema and permeability of brain blood barrier. Then we found that oleanolic acid could inhibit the transfer of HMGB1 from nucleus to cytoplasm and reduce the level of serum HMGB1. Furthermore, we found that oleanolic acid decreased the acetylation level of HMGB1 by increasing SIRT1 expression rather than by inhibiting JAK/STAT3 pathway. SIRT1 inhibitor sirtinol eliminated all beneficial effects of oleanolic acid on subarachnoid hemorrhage, which indicated that oleanolic acid inhibited the acetylation of HMGB1 by up regulating SIRT1. In addition, oleanolic acid treatment also reduced the levels of TLR4 and apoptosis related factors and reduced neuronal apoptosis after subarachnoid hemorrhage. In summary, our findings suggest that oleanolic acid may activate SIRT1 by acting as an activator of SIRT1, thereby reducing the acetylation of HMGB1, thus playing an anti-inflammatory role to alleviate early brain injury after subarachnoid hemorrhage.

The Role of Tenascin-C in Tissue Injury and Repair After Stroke

Stroke is still one of the most common causes for mortality and morbidity worldwide. Following acute stroke onset, biochemical and cellular changes induce further brain injury such as neuroinflammation, cell death, and blood-brain barrier disruption. Matricellular proteins are non-structural proteins induced by many stimuli and tissue damage including stroke induction, while its levels are generally low in a normal physiological condition in adult tissues. Currently, a matricellular protein tenascin-C (TNC) is considered to be an important inducer to promote neuroinflammatory cascades and the resultant pathology in stroke. TNC is upregulated in cerebral arteries and brain tissues including astrocytes, neurons, and brain capillary endothelial cells following subarachnoid hemorrhage (SAH). TNC may be involved in blood-brain barrier disruption, neuronal apoptosis, and cerebral vasospasm via the activation of mitogen-activated protein kinases and nuclear factor-kappa B following SAH. In addition, post-SAH TNC levels in cerebrospinal fluid predicted the development of delayed cerebral ischemia and angiographic vasospasm in clinical settings. On the other hand, TNC is reported to promote fibrosis and exert repair effects for an experimental aneurysm via macrophages-induced migration and proliferation of smooth muscle cells. The authors review TNC-induced inflammatory signal cascades and the relationships with other matricellular proteins in stroke-related pathology.

The potential for immune checkpoint modulators in cerebrovascular injury and inflammation

Introduction: Neuroinflammation has been linked to poor neurologic and functional outcomes in many cerebrovascular disorders. Immune checkpoints are upregulated in the setting of traumatic brain injury, intracerebral hemorrhage, ischemic stroke, central nervous systems vasculitis, and post-hemorrhagic vasospasm, and are potential mediators of pathologic inflammation. Burgeoning evidence suggests that immune checkpoint modulation is a promising treatment strategy to decrease immune cell recruitment, cytokine secretion, brain edema, and neurodegeneration.Areas covered: This review discusses the role of immune checkpoints in neuroinflammation, and the potential for therapeutic immune checkpoint modulation in inflammatory cerebrovascular disorders. A search of Pubmed and clinicaltrials.gov was performed to find relevant literature published within the last 50 years.Expert opinion: The clinical success of immune-activating checkpoint modulators in human cancers has shown the immense clinical potential of checkpoint-based immunotherapy. Given that checkpoint blockade can also precipitate a pathologic pro-inflammatory or autoimmune response, it is plausible that these pathways may also be targeted to quell aberrant inflammation. A limited but growing number of studies suggest that immune checkpoints play a critical role in regulating the immune response in the central nervous system in a variety of contexts, and that immune-deactivating checkpoint modulators may be a promising treatment strategy for acute and chronic neuroinflammation in cerebrovascular disorders.

Gene Polymorphisms Increasing the Risk of Intracranial Aneurysms: Interleukin-6 -174G>C and -572G>C (Part II)

Introduction The interleukin-6 (IL-6), a proinflammatory cytokine, supports the adaptive immune response and regulates inflammatory processes. The -174 G>C and -572 G>C promoter polymorphisms of the IL-6 gene take part in the pathogenesis of intracranial aneurysms (IAs) and influence the clinical presentation of subarachnoid hemorrhage. This meta-analysis purposes to evaluate whether and which IL-6 allelic variations are related to a risk of IAs formation. Methods A PRISMA-based literature search was performed on the PubMed/Medline and Web of Science databases. The keywords used were "interleukin-6," "IL-6," "polymorphism," "interleukin-6 genotype," combined with "intracranial aneurysms" and "subarachnoid hemorrhage." Only human case-control studies, with a study (IAs) and a control group, written in English, and published in the last 15 years were selected. A meta-analysis was performed, estimating odds ratios and 95% confidence intervals in fixed- or random-effects models, as applicable. Statistical analysis was conducted with RevMan 5.0 software. Results 9 studies were eligible. No associations were found between -174 G>C polymorphisms and IAs susceptibility. Notable results were reported by the analysis of -572G>C polymorphisms. -572GG/GC/CC genotypes were strongly related to IAs occurrence with a statistical significance of p=0.03, p=0.0009, and p=0.00001, respectively. Conclusion A higher incidence of -572G>C promoter polymorphisms were demonstrated in the IAs group, highlighting the pivotal role of inflammatory genes in the natural history of brain aneurysms. Additional studies are required considering the racial heterogenicity and the need to widen the population sample.

Cerebral nitric oxide and mitochondrial function in patients suffering aneurysmal subarachnoid hemorrhage-a translational approach

Background

Cerebral ischemia and neuroinflammation following aneurysmal subarachnoid hemorrhage (SAH) are major contributors to poor neurological outcome. Our study set out to investigate in an exploratory approach the interaction between NO and energy metabolism following SAH as both hypoxia and inflammation are known to affect nitric oxide (NO) metabolism and NO in turn affects mitochondria.

Methods

In seven patients under continuous multimodality neuromonitoring suffering poor-grade aneurysmal SAH, cerebral metabolism and NO levels (determined as a sum of nitrite plus nitrate) were determined in cerebral microdialysate for 14 days following SAH. In additional ex vivo experiments, rat cortex homogenate was subjected to the NO concentrations determined in SAH patients to test whether these NO concentrations impair mitochondrial function (determined by means of high-resolution respirometry).

Results

NO levels showed biphasic kinetics with drastically increased levels during the first 7 days (74.5 ± 29.9 μM) and significantly lower levels thereafter (47.5 ± 18.7 μM; p = 0.02). Only during the first 7 days, NO levels showed a strong negative correlation with brain tissue oxygen tension (r = − 0.78; p < 0.001) and a positive correlation with cerebral lactate (r = 0.79; p < 0.001), pyruvate (r = 0.68; p < 0.001), glutamate (r = 0.65; p < 0.001), as well as the lactate-pyruvate ratio (r = 0.48; p = 0.01), suggesting mitochondrial dysfunction. Ex vivo experiments confirmed that the increase in NO levels determined in patients during the acute phase is sufficient to impair mitochondrial function (p < 0.001). Mitochondrial respiration was inhibited irrespectively of whether glutamate (substrate of complex I) or succinate (substrate of complex II) was used as mitochondrial substrate suggesting the inhibition of mitochondrial complex IV. The latter was confirmed by direct determination of complex IV activity.

Conclusions

Exploratory analysis of our data suggests that during the acute phase of SAH, NO plays a key role in the neuronal damage impairing mitochondrial function and facilitating accumulation of mitochondrial substrate; further studies are required to understand mechanisms underlying this observation.

Gene Polymorphisms Increasing the Risk of Intracranial Aneurysms: Interleukin-1β -511C>T (Part I)

Introduction Intracranial aneurysms (IAs) are devastating cerebrovascular diseases with multifactorial etiology. The role of inflammation is indisputable, and interleukins are pivotal in supporting local inflammatory pathways and endothelial dysfunction at the aneurysm wall. In the light of insufficient evidence reported in the literature, this meta-analysis was aimed to investigate the genetic linkage between IL-1β (rs16944) -511C>T polymorphisms and IAs susceptibility. Methods A comprehensive online literature review was completed using the PubMed/Medline and Web of Science databases in accordance with the PRISMA guidelines. "Interleukin-1β," "IL-1β," "polymorphism," "intracranial aneurysm," and "subarachnoid hemorrhage" were the main keywords. Only human case-control studies, published from 2005 to 2021, written in English or translated, were screened. In the statistical analysis, we applied the fixed- and random-effect models, according to the level of heterogeneity, to assess the odds ratios (ORs) and 95% confidence intervals (CIs). RevMan 5.0 software was used for the statistics. Results Only 4 studies were eligible, with a total of 2070 patients, 1050 of which were assigned to the study group. Combined results showed a statistically significant association between the risk of IAs and -511CC (OR=0.79, 95% CI [0.65-0.95], p=0.01), and CT (OR=0.69, 95% CI [0.58-0.82], p<0.0001; OR=0.71, 95% CI [0.55-0.93], p=0.01) allele variations, both in the fixed- and random- models. No correlation was identified for the -511TT genotype (p=0.42; p=0.78). All the texts showed a low level of publication bias. Conclusion The present meta-analysis proved a potential role of IL-1β -511CC/CT genotypes in the pathogenesis of IAs. Additional studies are imperative to explain the underlying neuroimmune mechanisms, also allowing tailoring the potential inflammatory-target therapies for IAs.

The Stroke-Induced Blood-Brain Barrier Disruption: Current Progress of Inspection Technique, Mechanism, and Therapeutic Target

Stroke is one of the leading causes of mortality and morbidity worldwide. The blood-brain barrier (BBB) is a characteristic structure of microvessel within the brain. Under normal physiological conditions, the BBB plays a role in the prevention of harmful substances entering into the brain parenchyma within the central nervous system. However, stroke stimuli induce the breakdown of BBB leading to the influx of cytotoxic substances, vasogenic brain edema, and hemorrhagic transformation. Therefore, BBB disruption is a major complication, which needs to be addressed in order to improve clinical outcomes in stroke. In this review, we first discuss the structure and function of the BBB. Next, we discuss the progress of the techniques utilized to study BBB breakdown in in-vitro and in-vivo studies, along with biomarkers and imaging techniques in clinical settings. Lastly, we highlight the mechanisms of stroke-induced neuroinflammation and apoptotic process of endothelial cells causing BBB breakdown, and the potential therapeutic targets to protect BBB integrity after stroke. Secondary products arising from stroke-induced tissue damage provide transformation of myeloid cells such as microglia and macrophages to pro-inflammatory phenotype followed by further BBB disruption via neuroinflammation and apoptosis of endothelial cells. In contrast, these myeloid cells are also polarized to anti-inflammatory phenotype, repairing compromised BBB. Therefore, therapeutic strategies to induce anti-inflammatory phenotypes of the myeloid cells may protect BBB in order to improve clinical outcomes of stroke patients.

Inflammasome Caspase-1 Activity is Elevated in Cerebrospinal Fluid After Aneurysmal Subarachnoid Hemorrhage and Predicts Functional Outcome

BACKGROUND/OBJECTIVE

Subarachnoid hemorrhage (SAH) is a devastating neurological injury, further complicated by few available methods to objectively predict outcomes. With the recent shift in focus to neuroinflammation as a potential cause of adverse outcomes following SAH, we investigated the inflammasome-derived enzyme, caspase-1, as a potential biomarker for poor functional outcome.

METHODS

SAH patients were recruited from a regional stroke referral center. Cerebrospinal fluid (CSF) samples from 18 SAH subjects were collected via an external ventricular drain and obtained as close as possible to admission (within 72 h). For control subjects, we collected CSF from 9 patients undergoing lumbar puncture with normal CSF. Caspase-1 activity was measured using commercially available luminescence assays. SAH subjects were categorized at hospital discharge into those with good outcomes (Glasgow Outcome Scale, GOS, of 4-5) and poor outcomes (GOS of 1-3).

RESULTS

CSF analysis demonstrated a nearly seven-fold increase in caspase-1 activity in SAH patients compared to controls (p < 0.0001). Within the SAH group, 10 patients (55.6%) had good outcomes and 8 patients (44.4%) had poor outcomes. Mean caspase-1 activity in the poor outcome group was approximately three-times higher than the good outcome group (p = 0.001). Caspase-1 activity was significantly correlated with GOS score (r = - 0.705, p = 0.001). Receiver operating characteristic curve analysis showed that caspase-1 activity can accurately differentiate between patients with good versus poor functional outcome (area under the curve 0.944, p = 0.002).

CONCLUSIONS

Inflammasome-derived caspase-1 activity is elevated in the CSF of SAH patients compared to controls and higher levels correlate with worse functional outcome.

Berberine Ameliorates Subarachnoid Hemorrhage Injury via Induction of Sirtuin 1 and Inhibiting HMGB1/Nf-κB Pathway

Excessive cerebral inflammation plays a key role in early brain injury (EBI) after subarachnoid hemorrhage (SAH). Berberine, an isoquinoline alkaloid isolated from Chinese herb Coptis chinensis, possesses anti-inflammatory, and neuroprotective effects. Here we evaluated the beneficial effects of berberine against SAH-induced inflammatory response and the subsequent brain injury. Our data showed that berberine treatment significantly inhibited microglia activation and proinflammatory cytokines release. Concomitant with suppressed cerebral inflammation, berberine mitigated the subsequent brain injury as demonstrated by improved neurological behavior, reduced brain edema, and decreased neural apoptosis. Moreover, berberine significantly inhibited high mobile group box 1 (HMGB1)/nuclear factor-κB (Nf-κB)-dependent pathway and enhanced sirtuin 1 (SIRT1) expression after SAH. Treatment with ex527, a selective SIRT1 inhibitor, reversed berberine-induced SIRT1 activation and inhibitory effects on HMGB1/Nf-κB activation. In addition, ex527 pretreatment abated the anti-inflammatory and neuroprotective effects of berberine on SAH. Taken together, these findings suggest that berberine provides beneficial effects against SAH-triggered cerebral inflammation by inhibiting HMGB1/Nf-κB pathway, which may be modulated by SIRT1 activation.

Intraoperative Peritoneal Interleukin-6 Concentration Changes in Relation to the High-Mobility Group Protein B1 and Heat Shock Protein 70 Levels in Children Undergoing Cholecystectomy

The aim was the evaluation of IL-6 concentration in peritoneal lavage fluid of children which underwent cholecystectomy to ascertain if there is a difference in early inflammatory response depending on the type of surgical approach (open vs. laparoscopy). The analysis of high-mobility group protein B1 (HMGB1) and heat shock protein 70 (HSP70) was performed to find out if the source of IL-6 was related to tissue damage. IL-6 concentration in peritoneal lavage fluid samples, obtained at the beginning and at the end of the laparoscopic (N = 23) and open cholecystectomy (N = 14), was tested with a routinely used electrochemiluminescence assay. The concentrations of HMGB1 and HSP70 were analyzed with the use of an ELISA method. Statistical analysis was performed using the STATISTICA PL release 12.5 Program. The differences were assessed using the Mann-Whitney U test and Wilcoxon matched pairs test. Correlations were studied by using the Spearman correlation test. Our results demonstrated significant peritoneal lavage fluid IL-6 concentration growth measured at the end of the cholecystectomy as compared to the beginning, regardless of the type of the procedure. IL-6 growth during open cholecystectomy was greater compared to laparoscopic cholecystectomy (62.51-fold vs. 3.19-fold). IL-6 concentration did not correlate with HMGB1 and HSP70, which indicate that the significant growth of this cytokine was not related to mechanical tissue damage due to surgical procedure. A clinical significance of the study could be related to the fact that the evaluation of IL-6 concentration in peritoneal lavage fluid may be useful to assess an early local inflammatory response.

Significance and Diagnostic Accuracy of Early S100B Serum Concentration after Aneurysmal Subarachnoid Hemorrhage

Background: Early brain injuries (EBI) are one of the most important causes of morbidity and mortality after subarachnoid hemorrhage. At admission, a third of patients are unconscious (spontaneously or sedated) and EBI consequences are not evaluable. To date, it is unclear who will still be comatose (with severe EBI) and who will recover (with less severe EBI) once the aneurysm is treated and sedation withdrawn. The objective of the present study was to determine the diagnostic accuracy of S100B levels at hospital admission to identify patients with severe neurological consequences of EBI. Methods: Patients were consecutively included in this prospective blinded observational study. A motor component of the Glasgow coma score under 6 on day 3 was used to define patients with severe neurological consequences of EBI. Results: A total of 81 patients were included: 25 patients were unconscious at admission, 68 were treated by coiling. On day 3, 12 patients had severe consequences of EBI. A maximal S100B value between admission and day 1 had an area under the receiver operating characteristic curve (AUC) of 86.7% to predict severe EBI consequences. In patients with impaired consciousness at admission, the AUC was 88.2%. Conclusion: Early S100B seems to have a good diagnostic value to predict severe EBI. Before claiming the usefulness of S100B as a surrogate marker of EBI severity to start earlier multimodal monitoring, these results must be confirmed in an independent validation cohort.

Elevated level of cerebrospinal fluid and systemic chemokine CCL5 is a predictive biomarker of clinical outcome after aneurysmal subarachnoid hemorrhage (aSAH)

BACKGROUND

Pathophysiology of aneurysmal subarachnoid hemorrhage (aSAH) is highly complex. Bleeding from ruptured aneurysm causes increase in intracranial pressure that disrupts blood-brain barrier leading to infiltration of peripheral immune cells. Interactions between the infiltrated leukocytes and the resident brain cells in the injured tissue mainly determine the delayed tissue damage. Recruitment of leukocytes in the injured brain is mainly mediated by the chemokines. Chemokine C-C motif ligand 5 (CCL5) is a potent pro-inflammatory chemokine shown to be upregulated in preclinical SAH studies. However, detailed clinical investigations exploring the association of cerebrospinal fluid (CSF) and systemic CCL5 and post-aSAH complications and clinical outcome are still lacking. This study investigated CSF and systemic CCL5 after aSAH and its association with clinical outcome and post-aSAH complications.

METHODS

CSF and serum from control and aSAH patients were obtained after centrifugation of the CSF and peripheral blood, and were preserved at -80 °C until quantification by an enzyme-linked immunoassay. Patient pertinent data, post-aSAH complications and clinical outcome (modified Rankin scale [mRS] and Glasgow outcome scale [GOS]) were retrieved from patient records.

RESULTS

A significant increase in CSF and serum CCL5 levels was observed on post-aSAH day 1 and day 7 compared to control patients. Dichotomization of patients to poor (mRS 3-6 or GOS 1-3) and good (mRS 0-2 or GOS 4-5) clinical outcomes showed significantly higher serum CCL5 levels in patients with good clinical outcome at discharge, but lower CSF CCL5 levels. Interestingly, significantly lower serum CCL5 levels were observed on post-aSAH day 7 in patients who have additional intracerebral bleeding or the patients who developed chronic hydrocephalus or pneumonia. Whereas, CSF CCL5 levels significantly increased on post-aSAH day 1 in patients developing chronic hydrocephalus, delayed ischemic neurological deficits and intraventricular hemorrhage. CSF CCL5 levels on post-aSAH day 1 were correlated with poor clinical outcome, however, serum CCL5 levels on post-aSAH day 7 were correlated with good clinical outcome.

CONCLUSION

Systemic and CSF CCL5 levels were elevated after aSAH and levels of serum CCL5 on day 7 were associated independently with clinical outcome (GOS and mRS) at discharge. Therapeutic approaches targeting CCL5 might be beneficial in aSAH.

Choroid plexus and the blood-cerebrospinal fluid barrier in disease

The choroid plexus (CP) forming the blood-cerebrospinal fluid (B-CSF) barrier is among the least studied structures of the central nervous system (CNS) despite its clinical importance. The CP is an epithelio-endothelial convolute comprising a highly vascularized stroma with fenestrated capillaries and a continuous lining of epithelial cells joined by apical tight junctions (TJs) that are crucial in forming the B-CSF barrier. Integrity of the CP is critical for maintaining brain homeostasis and B-CSF barrier permeability. Recent experimental and clinical research has uncovered the significance of the CP in the pathophysiology of various diseases affecting the CNS. The CP is involved in penetration of various pathogens into the CNS, as well as the development of neurodegenerative (e.g., Alzheimer´s disease) and autoimmune diseases (e.g., multiple sclerosis). Moreover, the CP was shown to be important for restoring brain homeostasis following stroke and trauma. In addition, new diagnostic methods and treatment of CP papilloma and carcinoma have recently been developed. This review describes and summarizes the current state of knowledge with regard to the roles of the CP and B-CSF barrier in the pathophysiology of various types of CNS diseases and sets up the foundation for further avenues of research.