The post-cardiac arrest syndrome: A case for lung-brain coupling and opportunities for neuroprotection

Microbiological features of drowning-associated pneumonia: a systematic review and meta-analysis

BACKGROUND

Drowning-associated pneumonia (DAP) is frequent in drowned patients, and possibly increases mortality. A better understanding of the microorganisms causing DAP could improve the adequacy of empirical antimicrobial therapy. We aimed to describe the pooled prevalence of DAP, the microorganisms involved, and the impact of DAP on drowned patients.

METHODS

Systematic review and meta-analysis of studies published between 01/2000 and 07/2023 reporting on DAP occurrence and microorganisms involved.

RESULTS

Of 309 unique articles screened, 6 were included, involving 688 patients. All were retrospective cohort studies, with a number of patients ranging from 37 to 270. Studies were conducted in Europe (France N = 3 and Netherland N = 1), United States of America (N = 1) and French West Indies (N = 1). Mortality ranged between 18 to 81%. The pooled prevalence of DAP was 39% (95%CI 29-48), similarly following freshwater (pooled prevalence 44%, 95%CI 36-52) or seawater drowning (pooled prevalence 42%, 95%CI 32-53). DAP did not significantly impact mortality (pooled odds ratio 1.43, 95%CI 0.56-3.67) but this estimation was based on two studies only. Respiratory samplings isolated 171 microorganisms, mostly Gram negative (98/171, 57%) and mainly Aeromonas sp. (20/171, 12%). Gram positive microorganisms represented 38/171 (22%) isolates, mainly Staphylococcus aureus (21/171, 12%). Water salinity levels had a limited impact on the distribution of microorganisms, except for Aeromonas sp. who were exclusively found following freshwater drowning (19/106, 18%) and never following seawater drowning (0%) (p = 0.001). No studies reported multidrug-resistant organisms but nearly 30% of the isolated microorganisms were resistant to amoxicillin-clavulanate, the drug that was the most commonly prescribed empirically for DAP.

CONCLUSIONS

DAP are commonly caused by Gram-negative bacteria, especially Aeromonas sp. which is exclusively isolated following freshwater drowning. Empirical antimicrobial therapy should consider covering them, noting than amoxicillin-clavulanate may be inadequate in about one-third of the cases. The impact of DAP on patients' outcome is still unclear.

Inflammation, endothelial injury, and the acute respiratory distress syndrome after out-of-hospital cardiac arrest

Background

Acute respiratory distress syndrome (ARDS) is often seen in patients resuscitated from out-of-hospital cardiac arrest (OHCA). We aim to test whether inflammatory or endothelial injury markers are associated with the development of ARDS in patients hospitalized after OHCA.

Methods

We conducted a prospective, cohort, pilot study at an urban academic medical center in 2019 that included a convenience sample of adults with non-traumatic OHCA. Blood and pulmonary edema fluid (PEF) were collected within 12 hours of hospital arrival. Samples were assayed for cytokines (interleukin [IL]-1, tumor necrosis factor-α [TNF-α], tumor necrosis factor receptor1 [TNFR1], IL-6), epithelial injury markers (pulmonary surfactant-associated protein D), endothelial injury markers (Angiopoietin-2 [Ang-2] and glycocalyx degradation products), and other proteins (matrix metallopeptidase-9 and myeloperoxidase). Patients were followed for 7 days for development of ARDS, as adjudicated by 3 blinded reviewers, and through hospital discharge for mortality and neurological outcome. We examined associations between biomarker concentrations and ARDS, hospital mortality, and neurological outcome using multivariable logistic regression. Latent phase analysis was used to identify distinct biological classes associated with outcomes.

Results

41 patients were enrolled. Mean age was 58 years, 29% were female, and 22% had a respiratory etiology for cardiac arrest. Seven patients (17%) developed ARDS within 7 days. There were no significant associations between individual biomarkers and development of ARDS in adjusted analyses, nor survival or neurologic status after adjusting for use of targeted temperature management (TTM) and initial cardiac arrest rhythm. Elevated Ang-2 and TNFR-1 were associated with decreased survival (RR = 0.6, 95% CI = 0.3-1.0; RR = 0.5, 95% CI = 0.3-0.9; respectively), and poor neurologic status at discharge (RR = 0.4, 95% CI = 0.2-0.8; RR = 0.4, 95% CI = 0.2-0.9) in unadjusted associations.

Conclusion

OHCA patients have markedly elevated plasma and pulmonary edema fluid biomarker concentrations, indicating widespread inflammation, epithelial injury, and endothelial activation. Biomarker concentrations were not associated with ARDS development, though several distinct biological phenotypes warrant further exploration. Latent phase analysis demonstrated that patients with low biomarker levels aside from TNF-α and TNFR-1 (Class 2) fared worse than other patients. Future research may benefit from considering other tools to predict and prevent development of ARDS in this population.

Inflammatory response after out-of-hospital cardiac arrest-Impact on outcome and organ failure development

BACKGROUND

Post-cardiac arrest syndrome that occurs in out-of-hospital cardiac arrest (OHCA) patients is characterized by inflammatory response. We conducted a scoping review of current evidence regarding several inflammatory markers' usefulness for assessment of patient outcome and illness severity. We also discuss the proposed underlying mechanisms leading to inflammatory response after OHCA.

METHODS

We searched the MEDLINE, PubMed Central, Cochrane CENTRAL and Web of Science Core Collection databases with the following search terms: ("inflammation" OR "cytokines") AND "out-of-hospital cardiac arrest." Each inflammatory marker found was combined with "out-of-hospital cardiac arrest" using "AND" to find further relevant studies. We included original studies measuring inflammatory markers in adult OHCA patients that assessed their prognostic capabilities for mortality, neurological outcome, or organ failure severity.

RESULTS

Fifty-nine studies met the inclusion criteria, covering in total 65 different markers. Interleukin-6 (IL-6), procalcitonin (PCT) and C-reactive protein (CRP) were the most studied markers, and they were associated with poor outcomes in 13/15, 13/14 and 11/17 studies, respectively. Based on area under the receiver operating characteristic curve (AUC) value, the time point of best discriminatory capacity for poor outcome was ICU admission for IL-6 (median AUC 0.78, range 0.71-0.98) and day one after OHCA for PCT (median AUC 0.84, range 0.61-0.98). Seven studies reported AUCs for CRP (range 0.52-0.76) with no measurement time point being superior to others. The association of IL-6 and PCT with outcome appeared stronger in studies with more severely ill patients. Studies reported conflicting results regarding each marker's association with organ failure severity.

CONCLUSION

Inflammatory markers are potentially useful for early risk stratification after OHCA. PCT and IL-6 have moderate prognostic value during the first 24 h of the ICU stay. Predictive accuracy appears to be associated with the study overall event rate.

THE PROTECTIVE EFFECT OF C23 IN A RAT MODEL OF CARDIAC ARREST AND RESUSCITATION

ABSTRACT

Background : Systemic inflammation acts as a contributor to neurologic deficits after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). Extracellular cold-inducible RNA-binding, protein (CIRP) has been demonstrated to be responsible in part for the inflammation through binding to toll-like receptor 4 (TLR4) after cerebral ischemia. The short peptide C23 derived from CIRP has a high affinity for TLR4, we hypothesize that C23 reduces systemic inflammation after CA/CPR by blocking the binding of CIRP to TLR4. Methods : Adult male SD rats in experimental groups were subjected to 5 min of CA followed by resuscitation. C23 peptide (8 mg/kg) or normal saline was injected intraperitoneally at the beginning of the return of spontaneous circulation (ROSC). Results : The expressions of CIRP, TNF-α, IL-6, and IL-1β in serum and brain tissues were significantly increased at 24 h after ROSC ( P < 0.05). C23 treatment could markedly decrease the expressions of TNF-α, IL-6, and IL-1β in serum ( P < 0.05). Besides, it can decrease the expressions of TLR4, TNF-α, IL-6, and IL-1β in the cortex and hippocampus and inhibit the colocalization of CIRP and TLR4 ( P < 0.05). In addition, C23 treatment can reduce the apoptosis of hippocampus neurons ( P < 0.05). Finally, the rats in the C23 group have improved survival rate and neurological prognosis ( P < 0.05). Conclusions: These findings suggest that C23 can reduce systemic inflammation and it has the potential to be developed into a possible therapy for post-CA syndrome.

Bio-physiological susceptibility of the brain, heart, and lungs to systemic ischemia reperfusion and hyperoxia-induced injury in post-cardiac arrest rats

Cardiac arrest (CA) patients suffer from systemic ischemia-reperfusion (IR) injury leading to multiple organ failure; however, few studies have focused on tissue-specific pathophysiological responses to IR-induced oxidative stress. Herein, we investigated biological and physiological parameters of the brain and heart, and we particularly focused on the lung dysfunction that has not been well studied to date. We aimed to understand tissue-specific susceptibility to oxidative stress and tested how oxygen concentrations in the post-resuscitation setting would affect outcomes. Rats were resuscitated from 10 min of asphyxia CA. Mechanical ventilation was initiated at the beginning of cardiopulmonary resuscitation. We examined animals with or without CA, and those were further divided into the animals exposed to 100% oxygen (CA_Hypero) or those with 30% oxygen (CA_Normo) for 2 h after resuscitation. Biological and physiological parameters of the brain, heart, and lungs were assessed. The brain and lung functions were decreased after CA and resuscitation indicated by worse modified neurological score as compared to baseline (222 ± 33 vs. 500 ± 0, P < 0.05), and decreased PaO2 (20 min after resuscitation: 113 ± 9 vs. baseline: 128 ± 9 mmHg, P < 0.05) and increased airway pressure (2 h: 10.3 ± 0.3 vs. baseline: 8.1 ± 0.2 mmHg, P < 0.001), whereas the heart function measured by echocardiography did not show significant differences compared before and after CA (ejection fraction, 24 h: 77.9 ± 3.3% vs. baseline: 82.2 ± 1.9%, P = 0.2886; fractional shortening, 24 h: 42.9 ± 3.1% vs. baseline: 45.7 ± 1.9%, P = 0.4658). Likewise, increases of superoxide production in the brain and lungs were remarkable, while those in the heart were moderate. mRNA gene expression analysis revealed that CA_Hypero group had increases in Il1b as compared to CA_Normo group significantly in the brain (P < 0.01) and lungs (P < 0.001) but not the heart (P = 0.4848). Similarly, hyperoxia-induced increases in other inflammatory and apoptotic mRNA gene expression were observed in the brain, whereas no differences were found in the heart. Upon systemic IR injury initiated by asphyxia CA, hyperoxia-induced injury exacerbated inflammation/apoptosis signals in the brain and lungs but might not affect the heart. Hyperoxia following asphyxia CA is more damaging to the brain and lungs but not the heart.

Salidroside postconditioning attenuates ferroptosis-mediated lung ischemia-reperfusion injury by activating the Nrf2/SLC7A11 signaling axis

BACKGROUND

Ferroptosis, an iron-dependent programmed necrosis, is linked to lung ischemia-reperfusion injury. Salidroside is a glycoside derived from the Rhodiola rosea plant that exhibits anti-inflammatory and antioxidant properties. However, it is uncertain whether salidroside alleviates lung ischemia-reperfusion injury. This investigation explored the function of salidroside in ferroptosis in lung ischemia-reperfusion injury.

METHODS

A lung ischemia-reperfusion model was established in wild-type and Nrf2^-/- mice, and pulmonary epithelial cells were exposed to hypoxia/regeneration in vitro. We evaluated ferroptosis-related factors by western blotting, transmission electron microscopy, and fluorescence microscopy. To investigate the regulation of Nrf2 by salidroside, coimmunoprecipitation and luciferase reporter assays were used. Transwell assays were used to detect macrophage migration.

RESULTS

The data indicated that salidroside postconditioning significantly reduced ferroptosis and alleviated lung ischemia-reperfusion injury in wild-type mice, as evidenced by improved histology and inflammation, reduced lipid peroxides and iron overload, and the induction of Nrf2, SLC7A11, and GPX4 expression. Salidroside activated Nrf2 signaling, resulting in Keap1-Nrf2 dissociation, nuclear translocation, and increased antioxidant-response element reporter activity. Sal consistently inhibited hypoxia/regeneration-induced pulmonary epithelial cell ferroptosis by activating the Nrf2 signaling pathway. Furthermore, ferroptotic cells recruited macrophages via CCL2, whereas salidroside lowered CCL2 expression and inhibited ferroptosis-induced macrophage chemotaxis in lung ischemia-reperfusion injury. Additionally, the antiferroptotic effects of salidroside against lung ischemia-reperfusion injury were eliminated in Nrf2^-/- mice.

CONCLUSIONS

This study clearly shows that salidroside postconditioning attenuates ferroptosis-mediated lung ischemia-reperfusion injury by activating the Nrf2/SLC7A11 signaling axis.

Markers of neutrophil mediated inflammation associate with disturbed continuous electroencephalogram after out of hospital cardiac arrest

BACKGROUND

Achieving an acceptable neurological outcome in cardiac arrest survivors remains challenging. Ischemia-reperfusion injury induces inflammation, which may cause secondary neurological damage. We studied the association of ICU admission levels of inflammatory biomarkers with disturbed 48-hour continuous electroencephalogram (cEEG), and the association of the daily levels of these markers up to 72 h with poor 6-month neurological outcome.

METHODS

This is an observational, post hoc sub-study of the COMACARE trial. We measured serum concentrations of procalcitonin (PCT), high-sensitivity C-reactive protein (hsCRP), osteopontin (OPN), myeloperoxidase (MPO), resistin, and proprotein convertase subtilisin/kexin type 9 (PCSK9) in 112 unconscious, mechanically ventilated ICU-treated adult OHCA survivors with initial shockable rhythm. We used grading of 48-hour cEEG monitoring as a measure for the severity of the early neurological disturbance. We defined 6-month cerebral performance category (CPC) 1-2 as good and CPC 3-5 as poor long-term neurological outcome. We compared the prognostic value of biomarkers for 6-month neurological outcome to neurofilament light (NFL) measured at 48 h.

RESULTS

Higher OPN (p = .03), MPO (p < .01), and resistin (p = .01) concentrations at ICU admission were associated with poor grade 48-hour cEEG. Higher levels of ICU admission OPN (OR 3.18; 95% CI 1.25-8.11 per ln[ng/ml]) and MPO (OR 2.34; 95% CI 1.30-4.21) were independently associated with poor 48-hour cEEG in a multivariable logistic regression model. Poor 6-month neurological outcome was more common in the poor cEEG group (63% vs. 19% p < .001, respectively). We found a significant fixed effect of poor 6-month neurological outcome on concentrations of PCT (F = 7.7, p < .01), hsCRP (F = 4.0, p < .05), and OPN (F = 5.6, p < .05) measured daily from ICU admission to 72 h. However, the biomarkers did not have independent predictive value for poor 6-month outcome in a multivariable logistic regression model with 48-hour NFL.

CONCLUSION

Elevated ICU admission levels of OPN and MPO predicted disturbances in cEEG during the subsequent 48 h after cardiac arrest. Thus, they may provide early information about the risk of secondary neurological damage. However, the studied inflammatory markers had little value for long-term prognostication compared to 48-hour NFL.

Conservative oxygen therapy in critically ill and perioperative period of patients with sepsis-associated encephalopathy

OBJECTIVES

Sepsis-associated encephalopathy (SAE) patients in the intensive care unit (ICU) and perioperative period are administrated supplemental oxygen. However, the correlation between oxygenation status with SAE and the target for oxygen therapy remains unclear. This study aimed to examine the relationship between oxygen therapy and SAE patients.

METHODS

Patients diagnosed with sepsis 3.0 in the intensive care unit (ICU) were enrolled. The data were collected from the Medical Information Mart for Intensive Care IV (MIMIC IV) database and the eICU Collaborative Research Database (eICU-CRD) database. The generalized additive models were adopted to estimate the oxygen therapy targets in SAE patients. The results were confirmed by multivariate Logistic, propensity score analysis, inversion probability-weighting, doubly robust model, and multivariate COX analyses. Survival was analyzed by the Kaplan-Meier method.

RESULTS

A total of 10055 patients from eICU-CRD and 1685 from MIMIC IV were included. The incidence of SAE patients was 58.43%. The range of PaO2 (97-339) mmHg, PaO2/FiO2 (189-619), and SPO2≥93% may reduce the incidence of SAE, which were verified by multivariable Logistic regression, propensity score analysis, inversion probability-weighting, and doubly robust model estimation in MIMIC IV database and eICU database. The range of PaO2/FiO2 (189-619) and SPO2≥93% may reduce the hospital mortality of SAE were verified by multivariable COX regression.

CONCLUSIONS

SAE patients in ICU, including perioperative period, require conservative oxygen therapy. We should maintain SPO2≥93%, PaO2 (97-339) mmHg and PaO2/FiO2 (189-619) in SAE patients.

The difference between arterial pCO2 and etCO2 after cardiac arrest - Outcome predictor or marker of unfavorable resuscitation circumstances?

INTRODUCTION

In former studies, the arterio-alveolar carbon dioxide gradient (ΔCO₂) predicted in-hospital mortality after initially survived cardiac arrest. As early outcome predictors are urgently needed, we evaluated ΔCO₂ as predictor for good neurological outcome in our cohort.

METHODS

We retrospectively analyzed all patients ≥18 years of age after non-traumatic in- and out of hospital cardiac arrest in the year 2018 from our resuscitation database. Patients without advanced airway management, incomplete datasets or without return of spontaneous circulation were excluded. The first arterial pCO₂ after admission and the etCO₂ in mmHg at the time of blood sampling were recorded from patient's charts. We then calculated ΔCO₂ (pCO₂ - etCO₂). For baseline analyses, ΔCO₂ was dichotomized into a low and high group with separation at the median. Good neurological outcome on day 30, expressed as Cerebral Performance Category 1-2, defined our primary endpoint. Survival to 30 days was used as secondary endpoint.

RESULTS

Out of 302 screened patients, 128 remained eligible for analyses. ΔCO₂ was lower in 30-day survivors with good neurological outcome (12.2 mmHg vs. 18.8 mmHg, p = 0.009) and in 30-day survivors (12.5 mmHg vs. 20.0 mmHg, p = 0.001). In patients with high ΔCO₂, a cardiac etiology of arrest was found less often. They had a higher body mass index, longer duration of resuscitation, higher amounts of epinephrine, lower pO₂ levels but both higher pCO2 and blood lactate levels, resulting in lower blood pH and HCO₃^- levels at admission. In a crude binary logistic regression analysis, ΔCO₂ was associated with 30-day neurological outcome (OR = 1.041 per mmHg of ΔCO₂, 95% CI 1.008-1.074, p = 0.014). This association persisted after the adjustment for age, sex, witnessed arrest and shockable first rhythm. However, after addition of the duration of resuscitation or the cumulative epinephrine dosage to the model, ΔCO₂ lost its association.

CONCLUSION

ΔCO₂ at admission after a successfully resuscitated cardiac arrest is associated with 30 days survival with good neurological outcome. However, a higher ΔCO₂ may rather be a surrogate for unfavorable resuscitation circumstances than an independent outcome predictor.

Inhibition of Γδ T Cells Alleviates Brain Ischemic Injury in Cardiopulmonary-Cerebral Resuscitation Mice

BACKGROUND

A half-million people in the United States suffer from cardiac arrest (CA) requiring cardiopulmonary resuscitation (CPR). An inflammatory mechanism is associated with neuronal injury in the presence of cerebral ischemia. T lymphocytes are identified as crucial regulators of inflammation. Therefore, we investigated the relationship between CA/CPR-induced ischemia injury and T lymphocytes.

METHODS

C57BL/6 mice were subjected to CA through injection of KCl (30 μL of 0.5 mol/L) and cessation of mechanical ventilation followed by CPR. The survival rate and neurologic deficit scores were assessed. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining was carried out to detect neuronal death. Histologic changes were observed by hematoxylin-eosin staining. The levels of Trgv4, Trgv5 and Trgv7 were quantified by RT-qPCR. Inflammatory responses were identified by measurement of IL-1β, IL-6 and IL-17.

RESULTS

Downregulated γδ T cells improved survival and neurologic outcomes and inhibits neuronal apoptosis. γδ T inhibition protected brains from CA/CPR-mediated tissue damage. UC7-13D5 treatment inhibited the levels of γδ T markers. Knockdown of γδ T cells ameliorated neuroinflammation.

CONCLUSIONS

Inhibition of γδ T cells ameliorates ischemic injury in mice with CA/CPR by attenuating inflammation and neuronal apoptosis.

LncRNA GAS5/miR-137 Is a Hypoxia-Responsive Axis Involved in Cardiac Arrest and Cardiopulmonary Cerebral Resuscitation

Background

Cardiac arrest/cardiopulmonary resuscitation (CA/CPR) represents one of the devastating medical emergencies and is associated with high mortality and neuro-disability. Post-cardiac arrest syndrome (PCAS) is mechanistically ascribed to acute systemic ischemia/reperfusion(I/R) injury. The lncRNA/microRNA/mRNA networks have been found to play crucial roles in the pathogenesis of the hypoxia-responsive diseases. Nonetheless, the precise molecular mechanisms by which lncRNA/miRNA/mRNA axes are involved in the astrocyte-microglia crosstalk in CA/CPR have not been fully elucidated.

Methods

We collected and purified the exosomes from the blood of CA/CPR patients and supernatant of OGD/R-stimulated astrocytes. On the basis of microarray analysis, bioinformatic study, and luciferase activity determination, we speculated that lncRNA GAS5/miR-137 is implicated in the astrocyte-microglia crosstalk under the insult of systemic I/R injury. The regulation of lncRNA GAS5/miR-137 on INPP4B was examined by cellular transfection in OGD/R cell culture and by lateral ventricle injection with miR-137 agomir in CA/CPR mice model. Flow cytometry and immunofluorescence staining were performed to detect the microglial apoptosis, M1/M2 phenotype transformation, and neuroinflammation. Neurological scoring and behavior tests were conducted in CA/CPR group, with miR-137 agomir lateral-ventricle infusion and in their controls.

Results

In all the micRNAs, miR-137 was among the top 10 micRNAs that experienced greatest changes, in both the blood of CA/CPR patients and supernatant of OGD/R-stimulated astrocytes. Bioinformatic analysis revealed that miR-137 was sponged by lncRNA GAS5, targeting INPP4B, and the result was confirmed by Luciferase activity assay. qRT-PCR and Western blotting showed that lncRNA GAS5 and INPP4B were over-expressed whereas miR-137 was downregulated in the blood of CA/CPR patients, OGD/R-stimulated astrocytes, and brain tissue of CA/CPR mice. Silencing lncRNA GAS5 suppressed INPP4B expression, but over-expression of miR-137 negatively modulated its expression. Western blotting exhibited that PI3K and Akt phosphorylation was increased when lncRNA GAS5 was silenced or miR-137 was over-expressed. However, PI3K and Akt phosphorylation was notably suppressed in the absence of miR-137, almost reversing their phosphorylation in the silencing lncRNA GAS5 group. Then we found that GAS5 siRNA or miR-137 mimic significantly increased cell viability and alleviated apoptosis after OGD/R injury. Furthermore, over-expression of miR-137 attenuated microglial apoptosis and neuroinflammation in CA/CPR mice model, exhibiting significantly better behavioral tests after CA/CPR.

Conclusion

LncRNA GAS5/miR-137 may be involved in the astrocyte-microglia communication that inhibits PI3K/Akt signaling activation via regulation of INPP4B during CA/CPR.

Dexmedetomidine post-conditioning attenuates cerebral ischemia following asphyxia cardiac arrest through down-regulation of apoptosis and neuroinflammation in rats

Background

Neuroprotection strategies after cardiac arrest (CA)/cardiopulmonary resuscitation (CPR) remain key areas of basic and clinical research. This study was designed to investigate the neuroprotective effects of dexmedetomidine following resuscitation and potential mechanisms.

Methods

Anesthetized rats underwent 6-min asphyxia-based cardiac arrest and resuscitation, after which the experimental group received a single intravenous dose of dexmedetomidine (25 μg/kg). Neurological outcomes and ataxia were assessed after the return of spontaneous circulation. The serum levels and brain expression of inflammation markers was examined, and apoptotic cells were quantified by TUNEL staining.

Results

Neuroprotection was enhanced by dexmedetomidine post-conditioning after the return of spontaneous circulation. This enhancement was characterized by the promotion of neurological function scores and coordination. In addition, dexmedetomidine post-conditioning attenuated the serum levels of the pro-inflammatory cytokine tumor necrosis factor (TNF)-α at 2 h, as well as interleukin IL-1β at 2, 24, and 48 h. TUNEL staining showed that the number of apoptotic cells in the dexmedetomidine post-conditioning group was significantly reduced compared with the control group. Further western blot analysis indicated that dexmedetomidine markedly reduced the levels of caspase-3 and nuclear factor-kappa B (NF-κB) in the brain.

Conclusions

Dexmedetomidine post-conditioning had a neuroprotective effect against cerebral injury following asphyxia-induced cardiac arrest. The mechanism was associated with the downregulation of apoptosis and neuroinflammation.

Development and Evaluation of a Novel Mouse Model of Asphyxial Cardiac Arrest Revealed Severely Impaired Lymphopoiesis After Resuscitation

Background Animal disease models represent the cornerstone in basic cardiac arrest (CA) research. However, current experimental models of CA and resuscitation in mice are limited. In this study, we aimed to develop a mouse model of asphyxial CA followed by cardiopulmonary resuscitation (CPR), and to characterize the immune response after asphyxial CA/CPR. Methods and Results CA was induced in mice by switching from an O2/N2 mixture to 100% N2 gas for mechanical ventilation under anesthesia. Real-time measurements of blood pressure, brain tissue oxygen, cerebral blood flow, and ECG confirmed asphyxia and ensuing CA. After a defined CA period, mice were resuscitated with intravenous epinephrine administration and chest compression. We subjected young adult and aged mice to this model, and found that after CA/CPR, mice from both groups exhibited significant neurologic deficits compared with sham mice. Analysis of post-CA brain confirmed neuroinflammation. Detailed characterization of the post-CA immune response in the peripheral organs of both young adult and aged mice revealed that at the subacute phase following asphyxial CA/CPR, the immune system was markedly suppressed as manifested by drastic atrophy of the spleen and thymus, and profound lymphopenia. Finally, our data showed that post-CA systemic lymphopenia was accompanied with impaired T and B lymphopoiesis in the thymus and bone marrow, respectively. Conclusions In this study, we established a novel validated asphyxial CA model in mice. Using this new model, we further demonstrated that asphyxial CA/CPR markedly affects both the nervous and immune systems, and notably impairs lymphopoiesis of T and B cells.

Effects of Post-Resuscitation Normoxic Therapy on Oxygen-Sensitive Oxidative Stress in a Rat Model of Cardiac Arrest

Background

Cardiac arrest (CA) can induce oxidative stress after resuscitation, which causes cellular and organ damage. We hypothesized that post‐resuscitation normoxic therapy would protect organs against oxidative stress and improve oxygen metabolism and survival. We tested the oxygen‐sensitive reactive oxygen species from mitochondria to determine the association with hyperoxia‐induced oxidative stress.

Methods and Results

Sprague–Dawley rats were subjected to 10‐minute asphyxia‐induced CA with a fraction of inspired O₂ of 0.3 or 1.0 (normoxia versus hyperoxia, respectively) after resuscitation. The survival rate at 48 hours was higher in the normoxia group than in the hyperoxia group (77% versus 28%, P<0.01), and normoxia gave a lower neurological deficit score (359±140 versus 452±85, P<0.05) and wet to dry weight ratio (4.6±0.4 versus 5.6±0.5, P<0.01). Oxidative stress was correlated with increased oxygen levels: normoxia resulted in a significant decrease in oxidative stress across multiple organs and lower oxygen consumption resulting in normalized respiratory quotient (0.81±0.05 versus 0.58±0.03, P<0.01). After CA, mitochondrial reactive oxygen species increased by ≈2‐fold under hyperoxia. Heme oxygenase expression was also oxygen‐sensitive, but it was paradoxically low in the lung after CA. In contrast, the HMGB‐1 (high mobility group box‐1) protein was not oxygen‐sensitive and was induced by CA.

Conclusions

Post‐resuscitation normoxic therapy attenuated the oxidative stress in multiple organs and improved post‐CA organ injury, oxygen metabolism, and survival. Additionally, post‐CA hyperoxia increased the mitochondrial reactive oxygen species and activated the antioxidation system.

Hypoxia-induced inflammation: Profiling the first 24-hour posthypoxic plasma and central nervous system changes

Central nervous system and visual dysfunction is an unfortunate consequence of systemic hypoxia in the setting of cardiopulmonary disease, including infection with SARS-CoV-2, high-altitude cerebral edema and retinopathy and other conditions. Hypoxia-induced inflammatory signaling may lead to retinal inflammation, gliosis and visual disturbances. We investigated the consequences of systemic hypoxia using serial retinal optical coherence tomography and by assessing the earliest changes within 24h after hypoxia by measuring a proteomics panel of 39 cytokines, chemokines and growth factors in the plasma and retina, as well as using retinal histology. We induced severe systemic hypoxia in adult C57BL/6 mice using a hypoxia chamber (10% O2) for 1 week and rapidly assessed measurements within 1h compared with 18h after hypoxia. Optical coherence tomography revealed retinal tissue edema at 18h after hypoxia. Hierarchical clustering of plasma and retinal immune molecules revealed obvious segregation of the 1h posthypoxia group away from that of controls. One hour after hypoxia, there were 10 significantly increased molecules in plasma and 4 in retina. Interleukin-1β and vascular endothelial growth factor were increased in both tissues. Concomitantly, there was significantly increased aquaporin-4, decreased Kir4.1, and increased gliosis in retinal histology. In summary, the immediate posthypoxic period is characterized by molecular changes consistent with systemic and retinal inflammation and retinal glial changes important in water transport, leading to tissue edema. This posthypoxic inflammation rapidly improves within 24h, consistent with the typically mild and transient visual disturbance in hypoxia, such as in high-altitude retinopathy. Given hypoxia increases risk of vision loss, more studies in at-risk patients, such as plasma immune profiling and in vivo retinal imaging, are needed in order to identify novel diagnostic or prognostic biomarkers of visual impairment in systemic hypoxia.

What is 'Alzheimer's disease'? The neuropathological heterogeneity of clinically defined Alzheimer's dementia

PURPOSE OF REVIEW

Beta-amyloid with paired helical filaments (PHF)-tau neurofibrillary tangles define hallmark Alzheimer's disease neuropathologic changes (AD-NC). Yet persons with Alzheimer's dementia, defined broadly as an amnestic multidomain progressive dementia, often exhibit postmortem evidence of other neuropathologies including other neurodegenerative (Lewy body disease and transactive response DNA-binding protein disease) and vascular-related brain lesions. Clinicopathologic and epidemiologic analyses demonstrate the significance of these substrates, as coinciding neuropathologies mitigate the threshold for diagnosis of Alzheimer's dementia. In addition, other biologic processes may also independently underlie a progressive amnestic dementia. Advances in research on the relationship between age-related cognitive decline and the underlying neuropathologic substrates indicate that consensus neuropathologic criteria or disease nomenclature may need new considerations or refinement. This review appraises seminal literature as well as mixed pathologies and biological factors that may be determinants of clinical and pathologic disease.

RECENT FINDINGS

Cognition in aging (spanning from normal cognition to dementia) represents a clinical continuum. Traditional neuropathologic substrates of dementia however do not explain the variability of cognitive decline. Conversely, not all patients with AD-NC exhibit symptomatology of Alzheimer's dementia. In addition to diagnostic plaques and tangles, other neurodegenerative, cerebrovascular, and perivascular substrates manifest through discrete tissue lesions. Factors related to energetics, neurogenetics, neuroimmunology, resilience, proteinopathies, and waste clearance are increasingly suggested to be general drivers of disease. Recognition of novel neuroimmune pathways and brain-body connections further suggest there may be broader extracranial determinants of person-specific disease.

SUMMARY

Alzheimer's dementia is a pathologically heterogeneous and biologically multilayered disease. Recent studies and exercises in nomenclature reveal shortcomings in existing terminologies. Recognizing and overcoming these limitations is required for experts to effectively communicate about and ultimately prevent and treat Alzheimer's dementia.

Post-Cardiac Arrest Syndrome

More than 356 000 out-of-hospital cardiac arrests occur in the United States annually. Complications involving post-cardiac arrest syndrome occur because of ischemic-reperfusion injury to the brain, lungs, heart, and kidneys. Post-cardiac arrest syndrome is a clinical state that involves global brain injury, myocardial dysfunction, macrocirculatory dysfunction, increased vulnerability to infection, and persistent precipitating pathology (ie, the cause of the arrest). The severity of outcomes varies and depends on precipitating factors, patient health before cardiac arrest, duration of time to return of spontaneous circulation, and underlying comorbidities. In this article, the pathophysiology and treatment of post-cardiac arrest syndrome are reviewed and potential novel therapies are described.

MCC950, a selective NLPR3 inflammasome inhibitor, improves neurologic function and survival after cardiac arrest and resuscitation

Background

Cardiac arrest (CA) is associated with high morbidity and mortality, even after spontaneous circulation is re-established. This dire situation is partly due to post-CA syndrome for which no specific and effective intervention is available. One key component of post-CA syndrome is sterile inflammation, which affects various organs including the brain. A major effector of sterile inflammation is activated NLRP3 inflammasome, which leads to increased release of interleukin (IL)-1β. However, how NLRP3 inflammasome impacts neuroinflammation and neurologic outcome after CA is largely undefined.

Methods

Mice were subjected to a potassium-based murine CA and cardiopulmonary resuscitation (CPR) model. MCC950 was used to suppress activation of NLRP3 inflammasome after CA/CPR. Levels of protein and mRNA were examined by Western blotting and quantitative PCR, respectively. Immunologic changes were assessed by measuring cytokine expression and immune cell compositions. CA outcomes, including neurologic deficits, bacterial load in the lung, and survival rate, were evaluated.

Results

Using our CA/CPR model, we found that NLRP3 inflammasome was activated in the post-CA brain, and that pro-inflammatory cytokine levels, including IL-1β, were increased. After treatment with MCC950, a potent and selective NLRP3 inflammasome inhibitor, mice exhibited improved functional recovery and survival rate during the 14-day observational period after CA/CPR. In line with these findings, IL-1β mRNA levels in the post-CA brain were significantly suppressed after MCC950 treatment. Interestingly, we also found that in MCC950- vs. vehicle-treated CA mice, immune homeostasis in the spleen was better preserved and bacterial load in the lung was significantly reduced.

Conclusions

Our data demonstrate that activation of NLRP3 inflammasome could be a key event shaping the post-CA immuno- and neuro-pathology, and identify this pathway as a unique and promising therapeutic target to improve outcomes after CA/CPR.

Ac2-26 Alleviates Brain Injury after Cardiac Arrest and Cardiopulmonary Resuscitation in Rats via the eNOS Pathway

Background

Brain injury is the leading cause of death following cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). Ac2-26 and endothelial nitric oxide synthase (eNOS) have been shown to reduce neuroinflammation. This study is aimed at determining the mechanism by which Ac2-26 protects against inflammation during brain injury following CA and CPR.

Methods

Sixty-four rats were randomized into sham, saline, Ac2-26, and Ac2-26+L-NIO (endothelial nitric oxide synthase (eNOS) inhibitor) groups. Rats received Ac2-26, Ac2-26+L-NIO, or saline after CPR. Neurologic function was assessed at baseline, 24, and 72 hours after CPR. At 72 hours after resuscitation, serum and brain tissues were collected.

Results

Blood-brain barrier (BBB) permeability increased, and the number of surviving neurons and neurological function decreased in the saline group compared to the sham group. Anti-inflammatory and proinflammatory factors, neuron-specific enolase (NSE) levels, and the expression of eNOS, phosphorylated (p)-eNOS, inducible nitric oxide synthase (iNOS), and oxidative stress-related factors in the three CA groups significantly increased (P < 0.05). BBB permeability decreased, and the number of surviving neurons and neurological function increased in the Ac2-26 group compared to the saline group (P < 0.05). Ac2-26 increased anti-inflammatory and reduced proinflammatory markers, raised NSE levels, increased the expression of eNOS and p-eNOS, and reduced the expression of iNOS and oxidative stress-related factors compared to the saline group (P < 0.05). The effect of Ac2-26 on brain injury was reversed by L-NIO (P < 0.05).

Conclusions

Ac2-26 reduced brain injury after CPR by inhibiting oxidative stress and neuroinflammation and protecting the BBB. The therapeutic effect of Ac2-26 on brain injury was largely dependent on the eNOS pathway.

The Impact of Severity of Acute Respiratory Distress Syndrome Following Cardiac Arrest on Neurologic Outcomes

The aim of this study was to evaluate the incidence and determinants of acute respiratory distress syndrome (ARDS) after cardiac arrest (CA). We conducted an observational, retrospective cohort study with consecutive adult out-of-hospital and in-hospital (occurred only in the emergency department, ED) CA survivors from our ED. Development of ARDS was identified by results of arterial blood gases, chest images, and transthoracic echocardiography according to the Berlin definition. The primary outcome was the poor neurologic outcome, defined as cerebral performance category ≥3 at 28 days, and secondary outcomes were 28-day mortality, recovery rate from ARDS, duration of mechanical ventilator use, and length of stay. Among 295 enrolled patients, 30 patients who received extracorporeal membrane oxygenation and 19 patents who had cardiogenic pulmonary edema were excluded. ARDS had developed in 119 (48.4%) patients on admission (mild 20 [16.8%], moderate 48 [40.3%], and severe 51 [42.9%]) and 54 (45.4%) patients recovered before hospital discharge. Development of ARDS was associated with poor neurologic outcomes at 28 days (adjusted hazard ratio (HR) 1.44 [95% confidence interval (CI): 1.05-1.98]). Moreover, more severe ARDS was associated with a higher risk of poor neurological outcomes (mild: reference; moderate: adjusted HR 1.66 [95% CI: 1.10-2.49]; and severe: adjusted HR 1.76 [95% CI: 1.16-2.65]). Therefore, development of ARDS after CA was associated with unfavorable neurologic outcomes and had a linear association with ARDS severity. Early recognition and proper management of ARDS may be useful during post-CA care.

Characterization of neutrophil-neuronal co-cultures to investigate mechanisms of post-ischemic immune-mediated neurotoxicity

BACKGROUND

Immune-mediated reperfusion injury is a critical component of post-ischemic central nervous system (CNS) damage. In this context, the activation and recruitment of polymorphonuclear neutrophils (PMNs) to the CNS induces neurotoxicity in part through the release of degradative enzymes, cytokines, and reactive oxygen species. However, the extent to which close-range interactions between PMNs and neurons contribute to injury in this context has not been directly investigated.

NEW METHOD

We devised a co-culture model to investigate mechanisms of PMN-dependent neurotoxicity. Specifically, we established the effect of PMN dose, co-incident neuronal ischemia, lipopolysaccharide (LPS)-induced PMN priming, and the requirement for cell-cell contact on cumulative neuron damage.

RESULTS AND COMPARISON TO EXISTING METHOD(S)

Pre-exposure of day in vitro 10 primary cortical neurons to oxygen-glucose deprivation (OGD) enhanced PMN-dependent neuronal death. Likewise, LPS-induced priming of the PMN donor further increased PMN-induced toxicity in vitro compared to saline-injected controls. Compartmentalization of LPS-primed PMNs using net wells confirmed the requirement for close-range cell-cell interactions in the process of PMN-induced neuronal injury. Moreover, time-lapse imaging and quantitative neurite analyses implicate PMN-neurite interactions in this pathological response. These experiments establish a platform to investigate immune and neural factors that contribute to post-ischemic neurodegeneration.

CONCLUSIONS

Ischemic and immune priming enhance neurotoxicity in PMN-neuronal co-cultures. Moreover, cell-cell contact and neurite destruction are prominent features in the observed mechanism of post-ischemic neuronal death.

Impact of Lung Compliance on Neurological Outcome in Patients with Acute Respiratory Distress Syndrome Following Out-of-Hospital Cardiac Arrest

(1) Background: Acute respiratory distress syndrome (ARDS) following cardiac arrest is common and associated with in-hospital mortality. We aim to investigate whether lung compliance during targeted temperature management is associated with neurological outcome in patients with ARDS after out-of-hospital cardiac arrest (OHCA). (2) Methods: This observational study is conducted in the emergency intensive care unit from January 2011 to April 2019 using data from a prospective patient registry. Adult patients (age ≥18 years) who survived non-traumatic OHCA and subsequently developed ARDS based on the Berlin definition are included. Mechanical ventilator parameters such as plateau pressure, tidal volume, minute ventilation, positive end expiratory pressure, and compliance are recorded for 7 days or until death, and categorized as maximum, median, and minimum. The primary outcome is a favorable neurological outcome defined as a Cerebral Performance Category score of 1 or 2 at hospital discharge. (3) Results: Regarding 246 OHCA survivors, 119 (48.4%) patients developed ARDS. A favorable neurologic outcome was observed in 23 (19.3%). Patients with a favorable outcome have a significantly higher lung compliance (38.6 mL/cm H₂O versus 27.5 mL/cm H₂O), lower inspiratory pressure (12.0 cm H₂O versus 16.0 cm H₂O), and lower plateau pressure (17.0 cm H₂O versus 21.0 cm H₂O) than those with a poor neurologic outcome (all p < 0.01). Concerning time-dependent cox regression models, all maximum (adjusted hazard ratio [HR] 1.05, 95% confidence interval [CI] 1.02–1.09), minimum (HR 1.08, 95% CI 1.03–1.13), and median (HR 1.06, 95% CI 1.02–1.09) compliances are independently associated with a good neurologic outcome. Maximum compliance, >32.5 mL/cm H₂O at day 1, has the highest area under the receiver operating characteristic curve (0.745) with a positive predictive value of 90.4%. (4) Conclusions: Lung compliance may be an early predictor of intact neurologic survival in patients with ARDS following cardiac arrest.