Early cytotoxic lymphocyte localization to the brain following resuscitation in a porcine model of asphyxial cardiac arrest: A pilot study

Blood-brain barrier disruption and neuroinflammation in the hippocampus of a cardiac arrest porcine model: Single-cell RNA sequencing analysis

JOURNAL/nrgr/04.03/01300535-202602000-00043/figure1/v/2025-05-05T160104Z/r/image-tiff Global brain ischemia and neurological deficit are consequences of cardiac arrest that lead to high mortality. Despite advancements in resuscitation science, our limited understanding of the cellular and molecular mechanisms underlying post-cardiac arrest brain injury have hindered the development of effective neuroprotective strategies. Previous studies primarily focused on neuronal death, potentially overlooking the contributions of non-neuronal cells and intercellular communication to the pathophysiology of cardiac arrest-induced brain injury. To address these gaps, we hypothesized that single-cell transcriptomic analysis could uncover previously unidentified cellular subpopulations, altered cell communication networks, and novel molecular mechanisms involved in post-cardiac arrest brain injury. In this study, we performed a single-cell transcriptomic analysis of the hippocampus from pigs with ventricular fibrillation-induced cardiac arrest at 6 and 24 hours following the return of spontaneous circulation, and from sham control pigs. Sequencing results revealed changes in the proportions of different cell types, suggesting post-arrest disruption in the blood-brain barrier and infiltration of neutrophils. These results were validated through western blotting, quantitative reverse transcription-polymerase chain reaction, and immunofluorescence staining. We also identified and validated a unique subcluster of activated microglia with high expression of S100A8, which increased over time following cardiac arrest. This subcluster simultaneously exhibited significant M1/M2 polarization and expressed key functional genes related to chemokines and interleukins. Additionally, we revealed the post-cardiac arrest dysfunction of oligodendrocytes and the differentiation of oligodendrocyte precursor cells into oligodendrocytes. Cell communication analysis identified enhanced post-cardiac arrest communication between neutrophils and microglia that was mediated by neutrophil-derived resistin, driving pro-inflammatory microglial polarization. Our findings provide a comprehensive single-cell map of the post-cardiac arrest hippocampus, offering potential novel targets for neuroprotection and repair following cardiac arrest.

Investigation of fingolimod-induced lymphocyte sequestration on inflammatory response and neurological damages after cardiac arrest

BACKGROUND

A sepsis-like syndrome is known to occur after cardiac arrest, leading to cerebral infiltration by white blood cells (WBC). We hypothesized that pharmacological sequestration of WBC, and more specifically lymphocytes within lymphoid tissues, could reduce the cerebral infiltration by these inflammatory cells and subsequent acute brain injury in a porcine model of cardiac arrest. Lymphocyte sequestration was induced by the sphingosine-1 phosphate receptors agonist fingolimod.

METHODS

In a first set of experiments, anesthetized pigs underwent a sham instrumentation with no cardiac arrest (n = 4). They received an administration of fingolimod (1 mg/kg, i.v.) in order to confirm its effect on WBC. In a second set of experiments, animals randomly received fingolimod or saline two hours prior to an episode of ventricular fibrillation (14 min) with subsequent resuscitation (n = 6 in each group). Neurological injury was assessed 24 h after resuscitation.

RESULTS

In the first set of experiments, WBC and blood lymphocyte counts were significantly reduced by - 61 ± 10% and - 75 ± 6% two hours after fingolimod administration. In the second set of experiments, blood lymphocyte counts, but not WBC, were also significantly reduced after cardiac arrest in Fingolimod vs Control group. However, most cytokine blood levels were not different among groups, including Interleukin (IL)-1ra, IL-8 or IL-18 blood levels. A difference was only observed for IL-6, which decreased in Fingolimod vs Control (e.g., 5.6 ± 4.8 vs 59.4 ± 20.6 pg/ml at 2 h after cardiac arrest, respectively; p = 0.126). Neurofilament light chain (NFL) blood levels were not different among groups (57 ± 25 vs 84 ± 41 pg/ml in Fingolimod vs Control at 6 h after resuscitation, respectively). After awakening, 3 and 2 animals were prematurely euthanized for ethical reasons due to recurrent seizures in Fingolimod and Control groups, respectively. At Day 1, neurological dysfunction score was not different between groups (87 ± 7 vs 87 ± 5% in Fingolimod vs Control, respectively). Conversely, a decrease in the number of CD3 + cells was observed in the brain of surviving animals in Fingolimod vs Control group (3.10 ± 0.50 vs 7.53 ± 0.57 CD3 + cells/field, respectively; p = 0.0286).

CONCLUSION

Fingolimod-induced WBC sequestration, and more specifically lymphocytes sequestration, did not improve clinical neurological dysfunction following cardiac arrest although it reduced cerebral infiltration by lymphocytes.

Fingerprint of Circulating Immunocytes as Biomarkers for the Prognosis of Brain Inflammation and Neuronal Injury after Cardiac Arrest

Cardiac arrest is one of the most dangerous health problems in the world. Outcome prognosis is largely based on cerebral performance categories determined by neurological evaluations. Few systemic tests are currently available to predict survival to hospital discharge. Here, we present the results from the preclinical studies of cardiac arrest and resuscitation (CAR) in mice to identify signatures of circulating immune cells as blood-derived biomarkers to predict outcomes after CAR. Two flow cytometry panels for circulating blood lymphocytes and myeloid-derived cells, respectively, were designed to correlate with neuroinflammation and neuronal and dendritic losses in the selectively vulnerable regions of bilateral hippocampi. We found that CD4+CD25+ regulatory T cells, CD11b+CD11c- and CD11b+Ly6C+Ly6G+ myeloid-derived cells, and cells positive for the costimulatory molecules CD80 and CD86 in the blood were correlated with activation of microglia and astrocytosis, and CD4+CD25+ T cells are additionally correlated with neuronal and dendritic losses. A fingerprint pattern of blood T cells and monocytes is devised as a diagnostic tool to predict CAR outcomes. Blood tests aimed at identifying these immunocyte patterns in cardiac arrest patients will guide future clinical trials to establish better prognostication tools to avoid unnecessary early withdrawal from life-sustaining treatment.

Effect of Clemastine on Neurophysiological Outcomes in an Ovine Model of Neonatal Hypoxic-Ischemic Encephalopathy

Originally approved by the U.S. Food and Drug Administration (FDA) for its antihistamine properties, clemastine can also promote white matter integrity and has shown promise in the treatment of demyelinating diseases such as multiple sclerosis. Here, we conducted an in-depth analysis of the feasibility, safety, and neuroprotective efficacy of clemastine administration in near-term lambs (n = 25, 141-143 days) following a global ischemic insult induced via an umbilical cord occlusion (UCO) model. Lambs were randomly assigned to receive clemastine or placebo postnatally, and outcomes were assessed over a six-day period. Clemastine administration was well tolerated. While treated lambs demonstrated improvements in inflammatory scores, their neurodevelopmental outcomes were unchanged.

The immunology of the post-cardiac arrest syndrome

Patients successfully resuscitated from cardiac arrest often have brain injury, myocardial dysfunction, and systemic ischemia-reperfusion injury, collectively termed the post-cardiac arrest syndrome (PCAS). To improve outcomes, potential therapies must be able to be administered early in the post-arrest course and provide broad cytoprotection, as ischemia-reperfusion injury affects all organ systems. Our understanding of the immune system contributions to the PCAS has expanded, with animal models detailing biologically plausible mechanisms of secondary injury, the protective effects of available immunomodulatory drugs, and how immune dysregulation underlies infection susceptibility after arrest. In this narrative review, we discuss the dysregulated immune response in PCAS, human trials of targeted immunomodulation therapies, and future directions for immunomodulation following cardiac arrest.