Neutrophils and Neutrophil Extracellular Traps Cause Vascular Occlusion and Delayed Cerebral Ischemia After Subarachnoid Hemorrhage in Mice.

BACKGROUND: After subarachnoid hemorrhage (SAH), neutrophils are deleterious and contribute to poor outcomes. Neutrophils can produce neutrophil extracellular traps (NETs) after ischemic stroke. Our hypothesis was that, after SAH, neutrophils contribute to delayed cerebral ischemia (DCI) and worse outcomes via cerebrovascular occlusion by NETs. METHODS: SAH was induced via endovascular perforation, and SAH mice were given either a neutrophil-depleting antibody, a PAD4 (peptidylarginine deiminase 4) inhibitor (to prevent NETosis), DNAse-I (to degrade NETs), or a vehicle control. Mice underwent daily neurological assessment until day 7 and then euthanized for quantification of intravascular brain NETs (iNETs). Subsets of mice were used to quantify neutrophil infiltration, NETosis potential, iNETs, cerebral perfusion, and infarction. In addition, NET markers were assessed in the blood of aneurysmal SAH patients. RESULTS: In mice, SAH led to brain neutrophil infiltration within 24 hours, induced a pro-NETosis phenotype selectively in skull neutrophils, and caused a significant increase in iNETs by day 1, which persisted until at least day 7. Neutrophil depletion significantly reduced iNETs, improving cerebral perfusion, leading to less neurological deficits and less incidence of DCI (16% versus 51.9%). Similarly, PAD4 inhibition reduced iNETs, improved neurological outcome, and reduced incidence of DCI (5% versus 30%), whereas degrading NETs marginally improved outcomes. Patients with aneurysmal SAH who developed DCI had elevated markers of NETs compared with non-DCI patients. CONCLUSIONS: After SAH, skull-derived neutrophils are primed for NETosis, and there are persistent brain iNETs, which correlated with delayed deficits. The findings from this study suggest that, after SAH, neutrophils and NETosis are therapeutic targets, which can prevent vascular occlusion by NETs in the brain, thereby lessening the risk of DCI. Finally, NET markers may be biomarkers, which can predict which patients with aneurysmal SAH are at risk for developing DCI.

Subarachnoid Blood Clearance and Aneurysmal Subarachnoid Hemorrhage Outcomes: A Retrospective Review.

BACKGROUND: Delayed cerebral ischemia (DCI) continues to be a significant contributor to morbidity and mortality following aneurysmal subarachnoid hemorrhage (aSAH). Subarachnoid blood and its degradation products have been implicated in DCI, and faster blood clearance has been hypothesized to confer better outcomes. This study evaluates the relationship between blood volume and its clearance on DCI (primary outcome) and location at 30 days (secondary outcome) after aSAH. METHODS: This is a retrospective review of adult patients presenting with aSAH. Hijdra sum scores (HSS) were assessed independently for each computed tomography (CT) scan of patients with available scans on post-bleed days 0-1 and 2-10. This cohort was used to evaluate the course of subarachnoid blood clearance (group 1). A subset of patients in the first cohort with available CT scans on both post-bleed days 0-1 and post-bleed days 3-4 composed the second cohort (group 2). This group was used to evaluate the association between initial subarachnoid blood (measured via HSS post-bleed days 0-1) and its clearance (measured via percentage reduction [HSS %Reduction] and absolute reduction [HSS-Abs-Reduction] in HSS between days 0-1 and 3-4) on outcomes. Univariable and multivariable logistic regression models were used to identify outcome predictors. RESULTS: One hundred fifty-six patients were in group 1, and 72 patients were in group 2. In this cohort, HSS %Reduction was associated with decreased risk of DCI in univariate (odds ratio [OR] = 0.700 [0.527-0.923], p = 0.011) and multivariable (OR = 0.700 [0.527-0.923], p = 0.012) analyses. Higher HSS %Reduction was significantly more likely to have better outcomes at 30 days in the multivariable analysis (OR = 0.703 [0.507-0.980], p = 0.036). Initial subarachnoid blood volume was associated with outcome location at 30 days (OR = 1.331 [1.040-1.701], p = 0.023) but not DCI (OR = 0.945 [0.780-1.145], p = 0.567). CONCLUSIONS: Early blood clearance after aSAH was associated with DCI (univariable and multivariable analyses) and outcome location at 30 days (multivariable analysis). Methods facilitating subarachnoid blood clearance warrant further investigation.

Targeting Hemoglobin to Reduce Delayed Cerebral Ischemia After Subarachnoid Hemorrhage.

Delayed cerebral ischemia (DCI) continues to be a sequela of aneurysmal subarachnoid hemorrhage (aSAH) that carries significant morbidity and mortality. Aside from nimodipine, no therapeutic agents are available to reduce the incidence of DCI. Pathophysiologic mechanisms contributing to DCI are poorly understood, but accumulating evidence over the years implicates several factors. Those have included microvessel vasoconstriction, microthrombosis, oxidative tissue damage, and cortical spreading depolarization as well as large vessel vasospasm. Common to these processes is red blood cell leakage into the cerebrospinal fluids (CSF) and subsequent lysis which releases hemoglobin, a central instigator in these events. This has led to the hypothesis that early blood removal may improve clinical outcome and reduce DCI. This paper will provide a narrative review of the evidence of hemoglobin as an instigator of DCI. It will also elaborate on available human data that discuss blood clearance and CSF drainage as a treatment of DCI. Finally, we will address a recent novel device that is currently being tested, the Neurapheresis CSF Management System™. This is an automated dual-lumen lumbar drainage system that has an option to filter CSF and return it to the patient.

Epigenetics in blood-brain barrier disruption.

The vessels of the central nervous system (CNS) have unique barrier properties. The endothelial cells (ECs) which comprise the CNS vessels contribute to the barrier via strong tight junctions, specific transporters, and limited endocytosis which combine to protect the brain from toxins and maintains brain homeostasis. Blood-brain barrier (BBB) leakage is a serious secondary injury in various CNS disorders like stroke, brain tumors, and neurodegenerative disorders. Currently, there are no drugs or therapeutics available to treat specifically BBB damage after a brain injury. Growing knowledge in the field of epigenetics can enhance the understanding of gene level of the BBB and has great potential for the development of novel therapeutic strategies or targets to repair a disrupted BBB. In this brief review, we summarize the epigenetic mechanisms or regulators that have a protective or disruptive role for components of BBB, along with the promising approaches to regain the integrity of BBB.

Haptoglobin Genotype Affects Inflammation after Aneurysmal Subarachnoid Hemorrhage.

BACKGROUND: Haptoglobin (Hp) binds to and facilitates clearance of heme. Compared with HP 1-1 and 1-2 genotypes, HP 2-2 has a weaker binding affinity and has been linked with increased inflammation and vasospasm after aneurysmal subarachnoid hemorrhage (SAH). OBJECTIVE: This study aims to assess levels of inflammatory cytokines in the context of different HP genotypes. METHODS: Patients were enrolled among those presenting with spontaneous aneurysmal SAH. Blood was drawn at four time points; <24 hours (T1), 24-48 hours (T2), 3-5 days (T3), and 6-8 days (T4). Blood was analyzed for levels of 41 cytokines at each time point, as well as for HP genotypes. These data were analyzed using mixed-effect models to assess the association between HP genotypes and cytokine levels. The modified Rankin Scale (mRS) score was obtained at discharge, 3 months, and 6 months. RESULTS: Fifty-seven patients were enrolled. Compared with HP 1-1 and 1-2, subjects encoding HP 2-2 had elevated levels of the following cytokines at all time points: FLT3L, IFNγ, IL-17A, TGFα, and VEGF-A. Elevations were also seen at some time points for IL-8, CSF2, FGF2, IL-7, IL-12p70, and TNFα. This study was not powered to detect differences in the functional outcome; however, there were no significant differences in dichotomized mRS scores between patients with HP 1-1/1-2 or HP 2-2. CONCLUSION: Our findings indicate that HP 2-2 genotype leads to increased proinflammatory cytokine levels compared with HP 1-1/1-2 genotypes. These data may provide guidance for further studies seeking to identify testable markers for functional prognosis or targets for treatment.