Extracranial hypothermia during cardiac arrest and cardiopulmonary resuscitation is neuroprotective in vivo

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.

Reproducibility of whole-brain temperature mapping and metabolite quantification using proton magnetic resonance spectroscopy

Assessing brain temperature can provide important information about disease processes (e.g., stroke, trauma) and therapeutic effects (e.g., cerebral hypothermia treatment). Whole-brain magnetic resonance spectroscopic imaging (WB-MRSI) is increasingly used to quantify brain metabolites across the entire brain. However, its feasibility and reliability for estimating brain temperature needs further validation. Therefore, the present study evaluates the reproducibility of WB-MRSI for temperature mapping as well as metabolite quantification across the whole brain in healthy volunteers. Ten healthy adults were scanned on three occasions 1 week apart. Brain temperature, along with four commonly assessed brain metabolites-total N-acetyl-aspartate (tNAA), total creatine (tCr), total choline (tCho) and myo-inositol (mI)-were measured from WB-MRSI data. Reproducibility was evaluated using the coefficient of variation (CV). The measured mean (range) of the intra-subject CVs was 0.9% (0.6%-1.6%) for brain temperature mapping, and 4.7% (2.5%-15.7%), 6.4% (2.4%-18.9%) and 14.2% (4.4%-52.6%) for tNAA, tCho and mI, respectively, with reference to tCr. Consistently larger variability was found when using H₂ O as the reference for metabolite quantifications: 7.8% (3.3%-17.8%), 7.8% (3.1%-18.0%), 9.8% (3.7%-31.0%) and 17.0% (5.9%-54.0%) for tNAA, tCr, tCho and mI, respectively. Further, the larger the brain region (indicated by a greater number of voxels within that region), the better the reproducibility for both temperature and metabolite estimates. Our results demonstrate good reproducibility of whole-brain temperature and metabolite measurements using the WB-MRSI technique.

Effects of regional body temperature variation during asphyxial cardiac arrest on mortality and brain damage in a rat model

To date, hypothermia has focused on improving rates of resuscitation to increase survival in patients sustaining cardiac arrest (CA). Towards this end, the role of body temperature in neuronal damage or death during CA needs to be determined. However, few studies have investigated the effect of regional temperature variation on survival rate and neurological outcomes. In this study, adult male rats (12 week-old) were used under the following four conditions: (i) whole-body normothermia (37 ± 0.5 °C) plus (+) no asphyxial CA, (ii) whole-body normothermia + CA, (iii) whole-body hypothermia (33 ± 0.5 °C)+CA, (iv) body hypothermia/brain normothermia + CA, and (v) brain hypothermia/body normothermia + CA. The survival rate after resuscitation was significantly elevated in groups exposed to whole-body hypothermia plus CA and body hypothermia/brain normothermia plus CA, but not in groups exposed to whole-body normothermia combined with CA and brain hypothermia/body normothermia plus CA. However, the group exposed to hypothermia/brain normothermia combined with CA exhibited higher neuroprotective effects against asphyxial CA injury, i.e. improved neurological deficit and neuronal death in the hippocampus compared with those involving whole-body normothermia combined with CA. In addition, neurological deficit and neuronal death in the group of rat exposed to brain hypothermia/body normothermia and CA were similar to those in the rats subjected to whole-body normothermia and CA. In brief, only brain hypothermia during CA was not associated with effective survival rate, neurological function or neuronal protection compared with those under body (but not brain) hypothermia during CA. Our present study suggests that regional temperature in patients during CA significantly affects the outcomes associated with survival rate and neurological recovery.

Glomerular filtrate proteins in acute cardiorenal syndrome

Acute cardiorenal syndrome (CRS-1) is a morbid complication of acute cardiovascular disease. Heart-to-kidney signals transmitted by "cardiorenal connectors" have been postulated, but investigation into CRS-1 has been limited by technical limitations and a paucity of models. To address these limitations, we developed a translational model of CRS-1, cardiac arrest and cardiopulmonary resuscitation (CA/CPR), and now report findings from nanoscale mass spectrometry proteomic exploration of glomerular filtrate 2 hours after CA/CPR or sham procedure. Filtrate acquisition was confirmed by imaging, molecular weight and charge distribution, and exclusion of protein specific to surrounding cells. Filtration of proteins specific to the heart was detected following CA/CPR and confirmed with mass spectrometry performed using urine collections from mice with deficient tubular endocytosis. Cardiac LIM protein was a CA/CPR-specific filtrate component. Cardiac arrest induced plasma release of cardiac LIM protein in mice and critically ill human cardiac arrest survivors, and administration of recombinant cardiac LIM protein to mice altered renal function. These findings demonstrate that glomerular filtrate is accessible to nanoscale proteomics and elucidate the population of proteins filtered 2 hours after CA/CPR. The identification of cardiac-specific proteins in renal filtrate suggests a novel signaling mechanism in CRS-1. We expect these findings to advance understanding of CRS-1.

Moderate brain hypothermia started before resuscitation improves survival and neurobehavioral outcomes after CA/CPR in mice

AIM OF THE STUDY

No definitive experimental or clinical evidence exists whether brain hypothermia before, rather than during or after, resuscitation can reduce hypoxic-ischemic brain injury following cardiac arrest/cardiopulmonary resuscitation (CA/CPR) and improve outcomes. We examined the effects of moderate brain hypothermia before resuscitation on survival and histopathological and neurobehavioral outcomes in a mouse model.

METHODS

Adult C57BL/6 male mice (age: 8-12 weeks) were subjected to 8-min CA followed by CPR. The animals were randomly divided into sham, normothermia (NT; brain temperature 37.5 °C), and extracranial hypothermia (HT; brain temperature 28-32 °C) groups. The hippocampal CA1 was assessed 7 day after resuscitation by histochemical staining. Neurobehavioral outcomes were evaluated by the Barnes maze (BMT), openfield (OFT), rotarod, and light/dark (LDT) tests. Cleaved caspase-3 and heat shock protein 60 (HSP70) levels were investigated by western blotting.

RESULTS

The HT group exhibited higher survival and lower CA1 neuronal injury than did the NT group. HT mice showed improved spatial memory in the BMT compared with NT mice. NT mice travelled a shorter distance in the OFT and tended to spend more time in the light compartment in the LDT than did sham and HT mice. The levels of cleaved caspase-3 and HSP70 were non-significantly higher in the NT than in the sham and HT groups.

CONCLUSIONS

Moderate brain hypothermia before resuscitation improved survival and reduced histological neuronal injury, spatial memory impairment, and anxiety-like behaviours after CA/CPR in mice.

Social interaction modulates the neuroinflammatory response to global cerebral ischemia in male mice

Social isolation is a risk factor for cardiovascular and cerebrovascular diseases, although the underlying mechanisms remain underspecified. Considering the potential of microglia to become sensitized by stressors and their role in neuroinflammation, we hypothesized that social isolation primes microglia, resulting in an exaggerated neuroimmune response to experimental cerebral ischemia. First, major histocompatibility complex II (MHC II) gene expression, an indicator of microglial priming, was compared between mice that were socially isolated or pair-housed. MHC II increased in the hippocampus and cortex of socially isolated mice, which is suggestive of isolation-induced microglial priming. In experiment 2, isolated and pair-housed mice underwent ∼8min of global cerebral ischemia. Hippocampal mRNA expression of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) was significantly increased among both isolated and pair-housed ischemia groups relative to sham controls. Hippocampal expression of interleukin 1 beta (IL-1β) and cortical TNF-α, IL-1β and IL-6, were significantly increased 24-h post ischemia in isolated mice, but not pair-housed mice, relative to controls. Ischemia-induced increases in microglial cell body area and percent area fraction of ionized calcium binding adaptor molecule 1 (Iba-1) positive staining were also observed in isolated, but not pair-housed mice, relative to controls. For experiment 3, brain sections from socially isolated and pair-housed mice underwent 15min of oxygen glucose deprivation (OGD), an ex vivo model of cerebral ischemia. IL-6 gene expression was significantly elevated following OGD only in hippocampi from mice that had been socially isolated, indicating that isolation prior to ischemia is sufficient to modulate the neuroinflammatory response. Together, these data suggest microglial priming as a possible mechanism underlying the detrimental effects of social isolation on cerebral ischemia outcome.

Determination of renal function and injury using near-infrared fluorimetry in experimental cardiorenal syndrome

Cardiorenal syndrome type 1 causes acute kidney injury but is poorly understood; animal models and diagnostic aids are lacking. Robust noninvasive measurements of glomerular filtration rate are required for injury models and clinical use. Several have been described but are untested in translational models and suffer from biologic interference. We developed a mouse model of cardiorenal syndrome and tested the novel near-infrared fluorophore ZW800-1 to assess renal and cardiac function. We performed murine cardiac arrest and cardiopulmonary resuscitation followed by transthoracic echocardiography, 2 and 24 h later. Transcutaneous fluorescence of ZW800-1 bolus dispersion and clearance was assessed with whole animal imaging and compared with glomerular filtration rate (GFR; inulin clearance), tubular cell death (using unbiased stereology), and serum creatinine. Correlation, Bland-Altman, and polar analyses were used to compare GFR with ZW800-1 clearance. Cardiac arrest and cardiopulmonary resuscitation caused reversible cardiac failure, halving fractional shortening of the left ventricle (n = 12, P = 0.03). Acute kidney injury resulted with near-zero GFR and sixfold increase in serum creatinine 24 h later (n = 16, P < 0.01). ZW800-1 biodistribution and clearance were exclusively renal. ZW800-1 t_1/2 and clearance correlated with GFR (r = 0.92, n = 31, P < 0.0001). ZW800-1 fluorescence was reduced in cardiac arrest, and cardiopulmonary resuscitation-treated mice compared with sham animals 810 s after injection (P < 0.01) and bolus time-dispersion curves demonstrated that ZW800-1 fluorescence dispersion correlated with left ventricular function (r = 0.74, P < 0.01). Cardiac arrest and cardiopulmonary resuscitation lead to experimental cardiorenal syndrome type 1. ZW800-1, a small near-infrared fluorophore being developed for clinical intraoperative imaging, is favorable for evaluating cardiac and renal function noninvasively.

Efficacy of mild hypothermia for the treatment of patients with cardiac arrest

BACKGROUND

Therapeutic hypothermia has been recommended for the treatment of cardiac arrest patients who remain comatose after the return of spontaneous circulation. The aim of this study was to evaluate the effectiveness and safety of mild hypothermia on patients with cardiac arrest by conducting a meta-analysis.

METHODS

The relevant trials were searched in Cochrane Library, PubMed, Web of Science, Embase, CNKI and Wan Fang Data from the date of their establishment to October 2014. Thereafter, the studies retrieved were screened based on predefined inclusion and exclusion criteria. Data were extracted, and the quality of the included studies was evaluated. A meta-analysis was conducted using the Cochrane Collaboration Review Manager 5.2 software.

RESULTS

Six randomized controlled trials involving 531 cases were included, among which 273 cases were assigned to the treatment group and the other 258 cases to the control group. The meta-analysis indicated that mild hypothermia therapy after cardiac arrest produced significant differences in survival rate (relative risk [RR] =1.23, 95% confidence interval [CI]: 1.02-1.48, P = 0.03) and neurological function (RR = 1.33, 95% CI: 1.08-1.65, P = 0.007) after 6 months compared with normothermia therapy. However, no significant differences were observed in the survival to the hospital discharge (RR = 1.35, 95% CI: 0.87-2.10, P = 0.18), favorable neurological outcome at hospital discharge (RR = 1.53, 95% CI: 0.95-2.45, P = 0.08) and adverse events.

CONCLUSIONS

The meta-analysis demonstrated that mild hypothermia can improve the survival rate and neurological function of patients with cardiac arrest after 6 months. On the other hand, regarding the survival to hospital discharge, favorable neurological outcome at hospital discharge, and adverse events, our meta-analysis produced nonsignificant results.

Pulse Oximetry: A Non-Invasive, Novel Marker for the Quality of Chest Compressions in Porcine Models of Cardiac Arrest

Objective

Pulse oximetry, which noninvasively detects the blood flow of peripheral tissue, has achieved widespread clinical use. We have noticed that the better the quality of cardiopulmonary resuscitation (CPR), the better the appearance of pulse oximetry plethysmographic waveform (POP). We investigated whether the area under the curve (AUC) and/or the amplitude (Amp) of POP could be used to monitor the quality of CPR.

Design

Prospective, randomized controlled study.

Setting

Animal experimental center in Peking Union Medical Collage Hospital, Beijing, China.

Subjects

Healthy 3-month-old male domestic swine.

Interventions

34 local pigs were enrolled in this study. After 4 minutes of untreated ventricular fibrillation, animals were randomly assigned into two resuscitation groups: a “low quality” group (with a compression depth of 3cm) and a “high quality” group (with a depth of 5cm). All treatments between the two groups were identical except for the depth of chest compressions. Hemodynamic parameters [coronary perfusion pressure (CPP), partial pressure of end-tidal carbon dioxide (P_ETCO₂)] as well as AUC and Amp of POP were all collected and analyzed.

Measurements and Findings

There were statistical differences between the “high quality” group and the “low quality” group in AUC, Amp, CPP and P_ETCO₂ during CPR (P<0.05). AUC, Amp and CPP were positively correlated with P_ETCO₂, respectively (P<0.01). There was no statistical difference between the heart rate calculated according to the POP (F_CPR) and the frequency of mechanical CPR at the 3^rd minute of CPR. The F_CPR was lower than the frequency of mechanical CPR at the 6^th and the 9^th minute of CPR.

Conclusions

Both the AUC and Amp of POP correlated well with CPP and P_ETCO₂ in animal models. The frequency of POP closely matched the CPR heart rate. AUC and Amp of POP might be potential noninvasive quality monitoring markers for CPR.