The emerging role of neutrophils as modifiers of recovery after traumatic injury to the developing brain

Macrophages coordinate immune response to laser-induced injury via extracellular traps

BACKGROUND

Retinal degeneration results from disruptions in retinal homeostasis due to injury, disease, or aging and triggers peripheral leukocyte infiltration. Effective immune responses rely on coordinated actions of resident microglia and recruited macrophages, critical for tissue remodeling and repair. However, these phagocytes also contribute to chronic inflammation in degenerated retinas, yet the precise coordination of immune response to retinal damage remains elusive. Recent investigations have demonstrated that phagocytic cells can produce extracellular traps (ETs), which are a source of self-antigens that alter the immune response, which can potentially lead to tissue injury.

METHODS

Innovations in experimental systems facilitate real-time exploration of immune cell interactions and dynamic responses. We integrated in vivo imaging with ultrastructural analysis, transcriptomics, pharmacological treatments, and knockout mice to elucidate the role of phagocytes and their modulation of the local inflammatory response through extracellular traps (ETs). Deciphering these mechanisms is essential for developing novel and enhanced immunotherapeutic approaches that can redirect a specific maladaptive immune response towards favorable wound healing in the retina.

RESULTS

Our findings underscore the pivotal role of innate immune cells, especially macrophages/monocytes, in regulating retinal repair and inflammation. The absence of neutrophil and macrophage infiltration aids parenchymal integrity restoration, while their depletion, particularly macrophages/monocytes, impedes vascular recovery. We demonstrate that macrophages/monocytes, when recruited in the retina, release chromatin and granular proteins, forming ETs. Furthermore, the pharmacological inhibition of ETosis support retinal and vascular repair, surpassing the effects of blocking innate immune cell recruitment. Simultaneously, the absence of ETosis reshapes the inflammatory response, causing neutrophils, helper, and cytotoxic T-cells to be restricted primarily in the superficial capillary plexus instead of reaching the damaged photoreceptor layer.

CONCLUSIONS

Our data offer novel insights into innate immunity's role in responding to retinal damage and potentially help developing innovative immunotherapeutic approaches that can shift the immune response from maladaptive to beneficial for retinal regeneration.

Systemic Immune-Inflammation Index Predicts the Prognosis of Traumatic Brain Injury

OBJECTIVE

Systemic inflammation following traumatic brain injury (TBI) has been extensively studied over the past decades, as it contributes significantly to the pathophysiological injury mechanisms and subsequent poor outcomes. Systemic immune-inflammation (SII) index is a novel biomarker of systemic inflammatory response. However, its predictive value regarding TBI prognosis in clinical practice remains insufficiently investigated.

METHODS

A total of 102 TBI patients admitted to Nanjing Drum Tower Hospital from July 2019 to February 2022 were enrolled. We employed various statistical analyses to evaluate the correlation between inflammatory indicators upon admission and patient prognosis, compared the predictive accuracy of these indicators, and generated receiver operating curve analysis to test their prognostic performance.

RESULTS

The SII index, platelet count, absolute lymphocyte count, and neutrophil/lymphocyte ratio (NLR) were capable of distinguishing TBI prognosis according to univariate logistic regression models (P < 0.05). Multivariate logistic regression models revealed that increased SII index, platelet count, and NLR upon admission were independent predictors of poor TBI prognosis (P < 0.05). Receiver operating curve analysis further demonstrated that the SII index (area under the curve = 0.845, 95% confidence interval 0.769-0.921, P = 0.000) exhibited higher predictive ability than the NLR (area under the curve = 0.694, 95% confidence interval 0.591-0.796, P = 0.001).

CONCLUSIONS

Our findings suggested that increased SII index during the early stages of TBI was an independent risk factor for poor prognosis with satisfactory predictive value. The SII index provides a reliable, convenient, and cost-effective prognostic model to evaluate systemic inflammation after TBI and identify patients at risk of poor outcomes, thereby offering valuable guidance for clinical practice.

Research progress in the application of proteomics technology in brain injury

The aim of this article is to review the application progress of proteomics technology in brain injury research in recent years, point out the current problems that need to be overcome, and explore the application prospects of proteomics analysis in brain injury. This study also aims to retrieve all literature on brain injury and proteomics and summarize it. Through searching and screening, the widespread application of proteomics technology in the treatment of traumatic brain injury (TBI) and the use of a large number of TBI biomarkers were discovered. The pathways mediated by some biomarkers and the physiological and pathological mechanisms of occurrence were elucidated. The current classification of brain injury is mainly based on subjective evaluation of clinical symptoms, combined with objective imaging. However, its practical value is often limited when applied to prognosis evaluation in brain injury. Proteomics technology can make up for this deficiency and provide a reference for the prevention and treatment of brain injury.

Can Neutrophil to Lymphocyte Ratio Predict Early Outcome in Patients with Spinal Cord Injury?

BACKGROUND

Spinal cord injury is a frequent debilitating neurologic condition with increasing prevalence and related morbidity over the last decades. The neutrophil-to-lymphocyte ratio is a promising biomarker for determining different medical conditions' disease course and outcome such as traumatic brain injury (TBI). This study aimed to investigate the predictive value of neutrophil to lymphocyte ratio (NLR) in the outcome of SCI.

METHOD

In a retrospective cross-sectional study from April 2019 to April 2022, all patients 18 to 65 years old, following spinal cord injury who were referred to Imam Khomeini Hospital and met inclusion and exclusion criteria enrolled in the study. A checklist including demographic data, lab, and clinical findings at admission, 24h, 48 h, and discharge were recorded. IBM SPSS Statistics software was used to analyze the data. A P-value of less than 0.05 was considered significant.

RESULTS

Six hundred patients met our inclusion criteria and enrolled in the study. The mean age of the patients was 40.93 ± 12.77, with 75% male and 25% female. There was a significant correlation between the N/L ratio at different time points (p.value=0.001), injury type, and ASIA score at admission and discharge (0.001). Furthermore, the NLR had approached significant value alone to predict outcomes in patients enrolled in the study (0.06).

CONCLUSIONS

A high NLR is unequivocally linked with poor outcomes in patients suffering from acute SCI and should be considered a negative prognostic factor; however, the NLR had approached significant predicting value in patients enrolled in the study.

Photopolymerizable Hydrogel for Enhanced Intramyocardial Vascular Progenitor Cell Delivery and Post-Myocardial Infarction Healing

Cell transplantation success for myocardial infarction (MI) treatment is often hindered by low engraftment due to washout effects during myocardial contraction. A clinically viable biomaterial that enhances cell retention can optimize intramyocardial cell delivery. In this study, a therapeutic cell delivery method is developed for MI treatment utilizing a photocrosslinkable gelatin methacryloyl (GelMA) hydrogel. Human vascular progenitor cells, capable of forming functional vasculatures upon transplantation, are combined with an in situ photopolymerization approach and injected into the infarcted zones of mouse hearts. This strategy substantially improves acute cell retention and promotes long-term post-MI cardiac healing, including stabilized cardiac functions, preserved viable myocardium, and reduced cardiac fibrosis. Additionally, engrafted vascular cells polarize recruited bone marrow-derived neutrophils toward a non-inflammatory phenotype via transforming growth factor beta (TGFβ) signaling, fostering a pro-regenerative microenvironment. Neutrophil depletion negates the therapeutic benefits generated by cell delivery in ischemic hearts, highlighting the essential role of non-inflammatory, pro-regenerative neutrophils in cardiac remodeling. In conclusion, this GelMA hydrogel-based intramyocardial vascular cell delivery approach holds promise for enhancing the treatment of acute myocardial infarction.

Research progress of neuroinflammation-related cells in traumatic brain injury: A review

Neuroinflammation after traumatic brain injury (TBI) is related to chronic neurodegenerative diseases and is one of the causes of acute secondary injury after TBI. Therefore, it is particularly important to clarify the role of cellular mechanisms in the neuroinflammatory response after TBI. The objective of this article is to understand the involvement of cells during the TBI inflammatory response (for instance, astrocytes, microglia, and oligodendrocytes) and shed light on the recent progress in the stimulation and interaction of granulocytes and lymphocytes, to provide a novel approach for clinical research. We searched articles in PubMed published between 1950 and 2023, using the following keywords: TBI, neuroinflammation, inflammatory cells, neuroprotection, clinical. Articles for inclusion in this paper were finalized based on their novelty, representativeness, and relevance to the main arguments of this review. We found that the neuroinflammatory response after TBI includes the activation of glial cells, the release of inflammatory mediators in the brain, and the recruitment of peripheral immune cells. These inflammatory responses not only induce secondary brain damage, but also have a role in repairing the nervous system to some extent. However, not all of the mechanisms of cell-to-cell interactions have been well studied. After TBI, clinical treatment cannot simply suppress the inflammatory response, and the inflammatory phenotype of patients' needs to be defined according to their specific conditions after injury. Clinical trials of personalized inflammation regulation therapy for specific patients should be carried out in order to improve the prognosis of patients.

Neutrophil to Lymphocyte Ratio as a Predictor of Postoperative Outcomes in Traumatic Brain Injury: A Systematic Review and Meta-Analysis

(1) Introduction: Traumatic brain injury (TBI) is a leading cause of injury and mortality worldwide, carrying an estimated cost of $38 billion in the United States alone. Neutrophil to lymphocyte ratio (NLR) has been investigated as a standardized biomarker that can be used to predict outcomes of TBI. The aim of this review was to determine the prognostic utility of NLR among patients admitted for TBI. (2) Methods: A literature search was conducted in PubMed, Scopus, and Web of Science in November 2022 to retrieve articles regarding the use of neutrophil to lymphocyte ratio (NLR) as a prognostic measure in traumatic brain injury (TBI) patients. Inclusion criteria included studies reporting outcomes of TBI patients with associated NLR values. Exclusion criteria were studies reporting only non-primary data, those insufficiently disaggregated to extract NLR data, and non-English or cadaveric studies. The Newcastle-Ottawa Scale was utilized to assess for the presence of bias in included studies. (3) Results: Following the final study selection 19 articles were included for quantitative and qualitative analysis. The average age was 46.25 years. Of the 7750 patients, 73% were male. Average GCS at presentation was 10.51. There was no significant difference in the NLR between surgical vs. non-surgical cohorts (SMD 2.41 95% CI −1.82 to 6.63, p = 0.264). There was no significant difference in the NLR between bleeding vs. non-bleeding cohorts (SMD 4.84 95% CI −0.26 to 9.93, p = 0.0627). There was a significant increase in the NLR between favorable vs. non-favorable cohorts (SMD 1.31 95% CI 0.33 to 2.29, p = 0.0090). (4) Conclusions: Our study found that NLR was only significantly predictive for adverse outcomes in TBI patients and not surgical treatment or intracranial hemorrhage, making it nonetheless an affordable alternative for physicians to assess patient prognosis.

Temporal proteomics of human cerebrospinal fluid after severe traumatic brain injury

The pathophysiology of traumatic brain injury (TBI) requires further characterization to fully elucidate changes in molecular pathways. Cerebrospinal fluid (CSF) provides a rich repository of brain-associated proteins. In this retrospective observational study, we implemented high-resolution mass spectrometry to evaluate changes to the CSF proteome after severe TBI. 91 CSF samples were analyzed with mass spectrometry, collected from 16 patients with severe TBI (mean 32 yrs; 81% male) on day 0, 1, 2, 4, 7 and/or 10 post-injury (8-16 samples/timepoint) and compared to CSF obtained from 11 non-injured controls. We quantified 1152 proteins with mass spectrometry, of which approximately 80% were associated with CSF. 1083 proteins were differentially regulated after TBI compared to control samples. The most highly-upregulated proteins at each timepoint included neutrophil elastase, myeloperoxidase, cathepsin G, matrix metalloproteinase-8, and S100 calcium-binding proteins A8, A9 and A12-all proteins involved in neutrophil activation, recruitment, and degranulation. Pathway enrichment analysis confirmed the robust upregulation of proteins associated with innate immune responses. Conversely, downregulated pathways included those involved in nervous system development, and several proteins not previously identified after TBI such as testican-1 and latrophilin-1. We also identified 7 proteins (GM2A, Calsyntenin 1, FAT2, GANAB, Lumican, NPTX1, SFRP2) positively associated with an unfavorable outcome at 6 months post-injury. Together, these findings highlight the robust innate immune response that occurs after severe TBI, supporting future studies to target neutrophil-related processes. In addition, the novel proteins we identified to be differentially regulated by severe TBI warrant further investigation as potential biomarkers of brain damage or therapeutic targets.

Neutrophil-lymphocyte ratio as a predictor of outcome following traumatic brain injury: Systematic review and meta-analysis

Objectives

The neutrophil-to-lymphocyte ratio (NLR) is a simple and routinely performed hematological parameter; however, studies on NLR as a prognostic tool in traumatic brain injury (TBI) have yielded contradictory results.

Materials and Methods

This systematic review and meta-analysis was conducted according to the Preferred Reporting Items in the Systematic Review and Meta-Analysis guidelines 2020. Electronic databases of PubMed, Cochrane Library, Web of Science, and Scopus were searched. The population consisted of TBI patients in the absence of moderate and severe extracranial injury. Day 1 NLR was taken for the analysis. The outcomes evaluated were mortality and the Glasgow Outcome Scale (GOS). No restrictions were placed on the language, year and country of publication, and duration of follow-up. Animal studies were excluded from the study. Studies, where inadequate data were reported for the outcomes, were included in the qualitative synthesis but excluded from the quantitative synthesis. Study quality was evaluated using the Newcastle-Ottawa scale (NOS). The risk of bias was estimated using the Cochrane RoBANS risk of bias tool.

Results

We retrieved 7213 citations using the search strategy and 2097 citations were excluded based on the screening of the title and abstract. Full text was retrieved for 40 articles and subjected to the eligibility criteria, of which 28 were excluded from the study. Twelve studies were eligible for the synthesis of the systematic review while seven studies qualified for the meta-analysis. The median score of the articles was 8/9 as per NOS. The risk of selection bias was low in all the studies while the risk of detection bias was high in all except one study. Ten studies were conducted on adult patients, while two studies reported pediatric TBI. A meta-analysis for GOS showed that high NLR predicted unfavorable outcomes at ≥6 months with a mean difference of -5.18 (95% confidence interval: -10.04, -0.32); P = 0.04; heterogeneity (I2), being 98%. The effect estimates for NLR and mortality were a mean difference of -3.22 (95% confidence interval: -7.12, 0.68), P = 0.11, and an I2 of 85%. Meta-analysis for Area under the curve (AUC) receiver operating characteristic of the included studies showed good predictive power of NLR in predicting outcomes following TBI with AUC 0.706 (95% CI: 0.582-0.829).

Conclusion

A higher admission NLR predicts an increased mortality risk and unfavorable outcomes following TBI. However, future research will likely address the existing gaps.

Traumatic Injury to the Developing Brain: Emerging Relationship to Early Life Stress

Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.

Intra-nasal administration of sperm head turns neutrophil into reparative mode after PGE1- and/or Ang II receptor-mediated phagocytosis followed by expression of sperm head's coding RNA

Having played homeostatic role, the immune system maintains the integrity of the body. Such a characteristic makes immune system as an attractive candidate for resolution of inflammatory disease followed by tissue repair. As first responder cells, neutrophils direct immune response playing key role in tissue remodeling. Previous studies revealed that sperm attracts neutrophils and promotes uterine remodeling suitable for fetus growth. Accordingly, sperm and more efficiently sperm head had remodeling effects on damaged brain in Alzheimer's disease (AD) model. To further reveal the mechanism, two kinds of in vivo study, including kinetic study and inhibition of neutrophil phagocytosis on AD model, as well as in vitro study using co-culture of neutrophil and sperm head were performed. Kinetic study revealed that sperm head recruited neutrophil to nasal mucosa similar to that of uterus and sperm head-phagocytizing neutrophils acquired new activation status comparing to control. In vitro study also demonstrated that sperm head-phagocytizing neutrophils acquire new activation status and express coding RNAs of sperm head. Accordingly, inhibition of neutrophil phagocytic activity abrogated therapeutic effects of sperm head. Neutrophils activation status is important in the fate of inflammatory process. Modulation but not suppression of neutrophils helps remodeling and repair of damaged tissue. Sperm head is an intelligent cell and not just a simple particle to remove by phagocytosis but instead can program neutrophils and consequently immune response into reparative mode after phagocytosis.

Antithrombin III ameliorates post-traumatic brain injury cerebral leukocyte mobilization enhancing recovery of blood brain barrier integrity

BACKGROUND

Acute traumatic coagulopathy often accompanies traumatic brain injury (TBI) and may impair cognitive recovery. Antithrombin III (AT-III) reduces the hypercoagulability of TBI. Antithrombin III and heparinoids such as enoxaparin (ENX) demonstrate potent anti-inflammatory activity, reducing organ injury and modulating leukocyte (LEU) activation, independent of their anticoagulant effect. It is unknown what impact AT-III exerts on cerebral LEU activation and blood-brain barrier (BBB) permeability after TBI. We hypothesized that AT-III reduces live microcirculatory LEU-endothelial cell (EC) interactions and leakage at the BBB following TBI.

METHODS

CD1 mice (n = 71) underwent either severe TBI (controlled cortical impact (CCI), 6-m/s velocity, 1-mm depth, and 4-mm diameter) or sham craniotomy and then received either AT-III (250 IU/kg), ENX (1.5 mg/kg), or vehicle (saline) every 24 hours. Forty-eight hours post-TBI, cerebral intravital microscopy visualized in vivo penumbral microvascular LEU-EC interactions and microvascular leakage to assess BBB inflammation/permeability. Body weight loss and the Garcia neurological test (motor, sensory, reflex, balance) served as surrogates of clinical recovery.

RESULTS

Both AT-III and ENX similarly reduced in vivo penumbral LEU rolling and adhesion (p < 0.05). Antithrombin III also reduced live BBB leakage (p < 0.05). Antithrombin III animals demonstrated the least 48-hour body weight loss (8.4 ± 1%) versus controlled cortical impact and vehicle (11.4 ± 0.5%, p < 0.01). Garcia neurological test scores were similar among groups.

CONCLUSION

Antithrombin III reduces post-TBI penumbral LEU-EC interactions in the BBB leading to reduced neuromicrovascular permeability. Antithrombin III further reduced body weight loss compared with no therapy. Further study is needed to determine if these AT-III effects on neuroinflammation affect longer-term neurocognitive recovery after TBI.

Clinical predictors of prognosis in patients with traumatic brain injury combined with extracranial trauma

Objective: The purpose of this study was to investigate whether routine blood tests on admission and clinical characteristics can predict prognosis in patients with traumatic brain injury (TBI) combined with extracranial trauma. Methods: Clinical data of 182 patients with TBI combined with extracranial trauma from April 2018 to December 2019 were retrospectively collected and analyzed. Based on GOSE score one month after discharge, the patients were divided into a favorable group (GOSE 1-4) and unfavorable group (GOSE 5-8). Routine blood tests on admission and clinical characteristics were recorded. Results: Overall, there were 48 (26.4%) patients with unfavorable outcome and 134 (73.6%) patients with favorable outcome. Based on multivariate analysis, independent risk factors associated with unfavorable outcome were age (odds ratio [OR], 1.070; 95% confidence interval [CI], 1.018-1.124; p<0.01), admission Glasgow Coma Scale (GCS) score (OR, 0.807; 95% CI, 0.675-0.965; p<0.05), heart rate (OR, 1.035; 95% CI, 1.004-1.067; p<0.05), platelets count (OR, 0.982; 95% CI, 0.967-0.997; p<0.05), and tracheotomy (OR, 15.201; 95% CI, 4.121-56.078; p<0.001). Areas under the curve (AUC) of age, admission GCS, heart rate, tracheotomy, and platelets count were 0.678 (95% CI, 0.584-0.771), 0.799 (95% CI, 0.723-0.875), 0.652 (95% CI, 0.553-0.751), 0.776 (95% CI, 0.692-0.859), and 0.688 (95% CI, 0.606-0.770), respectively. Conclusions: Age, admission GCS score, heart rate, tracheotomy, and platelets count can be recognized as independent predictors of clinical prognosis in patients with severe TBI combined with extracranial trauma.

Sensorimotor dysfunction in a mild mouse model of cortical contusion injury without significant neuronal loss is associated with increases in inflammatory proteins with innate but not adaptive immune functions

Traumatic brain injury is a leading cause of mortality and morbidity in the United States. Acute trauma to the brain triggers chronic secondary injury mechanisms that contribute to long-term neurological impairment. We have developed a single, unilateral contusion injury model of sensorimotor dysfunction in adult mice. By targeting a topographically defined neurological circuit with a mild impact, we are able to track sustained behavioral deficits in sensorimotor function in the absence of tissue cavitation or neuronal loss in the contused cortex of these mice. Stereological histopathology and multiplex enzyme-linked immunosorbent assay proteomic screening confirm contusion resulted in chronic gliosis and the robust expression of innate immune cytokines and monocyte attractant chemokines IL-1β, IL-5, IL-6, TNFα, CXCL1, CXCL2, CXCL10, CCL2, and CCL3 in the contused cortex. In contrast, the expression of neuroinflammatory proteins with adaptive immune functions was not significantly modulated by injury. Our data support widespread activation of innate but not adaptive immune responses, confirming an association between sensorimotor dysfunction with innate immune activation in the absence of tissue or neuronal loss in our mice.

A new neutrophil subset promotes CNS neuron survival and axon regeneration

Transected axons typically fail to regenerate in the central nervous system (CNS), resulting in chronic neurological disability in individuals with traumatic brain or spinal cord injury, glaucoma and ischemic reperfusion injury of the eye. Although neuroinflammation is often depicted as detrimental, there is growing evidence that alternatively activated, reparative leukocyte subsets and their products can be deployed to improve neurological outcomes. In the current study we identify a unique granulocyte subset, with characteristics of an immature neutrophil, that had neuroprotective properties and drove CNS axon regeneration in vivo, in part via secretion of a cocktail of growth factors. This pro-regenerative neutrophil promoted repair in the optic nerve and spinal cord, demonstrating its relevance across CNS compartments and neuronal populations. Our findings could ultimately lead to the development of novel immunotherapies that reverse CNS damage and restore lost neurological function across a spectrum of diseases.

The role of astrocytes in oxidative stress of central nervous system: A mixed blessing

Central nervous system (CNS) maintains a high level of metabolism, which leads to the generation of large amounts of free radicals, and it is also one of the most vulnerable organs to oxidative stress. Emerging evidences have shown that, as the key homeostatic cells in CNS, astrocytes are deeply involved in multiple aspects of CNS function including oxidative stress regulation. Besides, the redox level in CNS can in turn affect astrocytes in morphology and function. The complex and multiple roles of astrocytes indicate that their correct performance is crucial for the normal functioning of the CNS, and its dysfunction may result in the occurrence and progression of various neurological disorders. To date, the influence of astrocytes in CNS oxidative stress is rarely reviewed. Therefore, in this review we sum up the roles of astrocytes in redox regulation and the corresponding mechanisms under both normal and different pathological conditions.