Sodium sulfide prevents water diffusion abnormality in the brain and improves long term outcome after cardiac arrest in mice

Therapeutic Hypothermia Combined with Hydrogen Sulfide Treatment Attenuated Early Blood-Brain Barrier Disruption and Brain Edema Induced by Cardiac Arrest and Resuscitation in Rat Model

Brain injury remains a major problem in patients suffering cardiac arrest (CA). Disruption of the blood-brain barrier (BBB) is an important factor leading to brain injury. Therapeutic hypothermia is widely accepted to limit neurological impairment. However, the efficacy is incomplete. Hydrogen sulfide (H2S), a signaling gas molecule, has protective effects after cerebral ischemia reperfusion injury. This study showed that combination of hypothermia and H2S after resuscitation was more beneficial for attenuated BBB disruption and brain edema than that of hypothermia or H2S treatment alone. CA was induced by ventricular fibrillation for 4 min. Hypothermia was performed by applying alcohol and ice bags to the body surface under anesthesia. We used sodium hydrosulphide (NaHS) as the H2S donor. We found that global brain ischemia induced by CA and cardiopulmonary resuscitation (CPR) resulted in brain edema and BBB disruption; Hypothermia or H2S treatment diminished brain edema, decreased the permeability and preserved the structure of BBB during the early period of CA and resuscitation, and more importantly, improved the neurologic function, increased the 7-day survival rate after resuscitation; the combination of hypothermia and H2S treatment was more beneficial than that of hypothermia or H2S treatment alone. The beneficial effects were associated with the inhibition of matrix metalloproteinase-9 expression, attenuated the degradation of the tight junction protein occludin, and subsequently protected the structure of BBB. These findings suggest that combined use of therapeutic hypothermia and hydrogen sulfide treatment during resuscitation of CA patients could be a potential strategy to improve clinical outcomes and survival rate.

Flufenamic acid improves survival and neurologic outcome after successful cardiopulmonary resuscitation in mice

Background

Brain injury is the main cause of high mortality and disability after successful cardiopulmonary resuscitation (CPR) from sudden cardiac arrest (CA). The transient receptor potential M4 (TRPM4) channel is a novel target for ameliorating blood–brain barrier (BBB) disruption and neuroinflammation. Herein, we tested whether flufenamic acid (FFA), which is reported to block TRPM4 with high potency, could confer neuroprotection against brain injury secondary to CA/CPR and whether its action was exerted by blocking the TRPM4 channel.

Methods

Wild-type (WT) and Trpm4 knockout (Trpm4^−/−) mice subjected to 10-min CA/CPR were randomized to receive FFA or vehicle once daily. Post-CA/CPR brain injuries including neurologic deficits, survival rate, histological damage, edema formation, BBB destabilization and neuroinflammation were assessed.

Results

In WT mice subjected to CA/CPR, FFA was effective in improving survival and neurologic outcome, reducing neuropathological injuries, attenuating brain edema, lessening the leakage of IgG and Evans blue dye, restoring tight junction protein expression and promoting microglia/macrophages from the pro-inflammatory subtype toward the anti-inflammatory subtype. In comparison to WT mice, Trpm4^−/− mice exhibited less neurologic deficiency, milder histological impairment, more BBB integrity and more anti-inflammatory microglia/macrophage polarization. As expected, FFA did not provide a benefit of superposition compared with vehicle in the Trpm4^−/− mice after CA/CPR.

Conclusions

FFA mitigates BBB breach and modifies the functional status of microglia/macrophages, thereby improving survival and neurologic deficits following CA/CPR. The neuroprotective effects occur at least partially by interfering with the TRPM4 channel in the neurovascular unit. These results indicate the significant clinical potential of FFA to improve the prognosis for CA victims who are successfully resuscitated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02571-2.

Inhaled nitric oxide improves post-cardiac arrest outcomes via guanylate cyclase-1 in bone marrow-derived cells

RATIONALE

Nitric oxide (NO) exerts its biological effects primarily via activation of guanylate cyclase (GC) and production of cyclic guanosine monophosphate. Inhaled NO improves outcomes after cardiac arrest and cardiopulmonary resuscitation (CPR). However, mechanisms of the protective effects of breathing NO after cardiac arrest are incompletely understood.

OBJECTIVE

To elucidate the mechanisms of beneficial effects of inhaled NO on outcomes after cardiac arrest.

METHODS

Adult male C57BL/6J wild-type (WT) mice, GC-1 knockout mice, and chimeric WT mice with WT or GC-1 knockout bone marrow were subjected to 8 min of potassium-induced cardiac arrest to determine the role of GC-1 in bone marrow-derived cells. Mice breathed air or 40 parts per million NO for 23 h starting at 1 h after CPR.

RESULTS

Breathing NO after CPR prevented hypercoagulability, cerebral microvascular occlusion, an increase in circulating polymorphonuclear neutrophils and neutrophil-to-lymphocyte ratio, and right ventricular dysfunction in WT mice, but not in GC-1 knockout mice, after cardiac arrest. The lack of GC-1 in bone marrow-derived cells diminished the beneficial effects of NO breathing after CPR.

CONCLUSIONS

GC-dependent signaling in bone marrow-derived cells is essential for the beneficial effects of inhaled NO after cardiac arrest and CPR.

Nitric Oxide in Post-cardiac Arrest Syndrome

Sudden cardiac arrest is a leading cause of death worldwide. Although the methods of cardiopulmonary resuscitation have been improved, mortality is still unacceptably high, and many survivors suffer from lasting neurological deficits due to the post-cardiac arrest syndrome (PCAS). Pathophysiologically, generalized vascular endothelial dysfunction accompanied by platelet activation and systemic inflammation has been implicated in the pathogenesis of PCAS. Because endothelial-derived nitric oxide (NO) plays a central role in maintaining vascular homeostasis, the role of NO-dependent signaling has been a focus of the intense investigation. Recent preclinical studies showed that therapeutic interventions that increase vascular NO bioavailability may improve outcomes after cardiac arrest complicated with PCAS. In particular, NO inhalation therapy has been shown to improve neurological outcomes and survival in multiple species. Clinical studies examining the safety and efficacy of inhaled NO in patients sustaining PCAS are warranted.

Cerebral Edema After Cardiopulmonary Resuscitation: A Therapeutic Target Following Cardiac Arrest?

We sought to review the role that cerebral edema plays in neurologic outcome following cardiac arrest, to understand whether cerebral edema might be an appropriate therapeutic target for neuroprotection in patients who survive cardiopulmonary resuscitation. Articles indexed in PubMed and written in English. Following cardiac arrest, cerebral edema is a cardinal feature of brain injury and is a powerful prognosticator of neurologic outcome. Like other conditions characterized by cerebral ischemia/reperfusion, neuroprotection after cardiac arrest has proven to be difficult to achieve. Neuroprotection after cardiac arrest generally has focused on protecting neurons, not the microvascular endothelium or blood-brain barrier. Limited preclinical data suggest that strategies to reduce cerebral edema may improve neurologic outcome. Ongoing research will be necessary to determine whether targeting cerebral edema will improve patient outcomes after cardiac arrest.

The Role of Inflammatory Cytokines in Cardiac Arrest

Introduction:

Post-cardiac arrest syndrome (PCAS) is characterized by systemic ischemia/reperfusion injury, anoxic brain injury, and post-arrest myocardial dysfunction superimposed on a precipitating pathology. The role of inflammatory cytokines in cardiac arrest remains unclear.

Aims:

We aimed to describe, with an emphasis on clinical applications, what is known about the role of inflammatory cytokines in cardiac arrest.

Data Sources:

A PubMed literature review was performed for relevant articles. Only articles in English that studied cytokines in patients with cardiac arrest were included.

Results:

Cytokines play a crucial role in the pathogenesis of PCAS. Following cardiac arrest, the large release of circulating cytokines mediates the ischemia/reperfusion injury, brain dysfunction, and myocardial dysfunction seen. Interleukins, tumor necrosis factor, and matrix metalloproteinases all play a unique prognostic role in PCAS. High levels of inflammatory cytokines have been associated with mortality and/or poor neurologic outcomes. Interventions to modify the systemic inflammation seen in PCAS continue to be heavily studied. Currently, the only approved medical intervention for comatose patients following cardiac arrest is targeted temperature management. Medical agents, including minocycline and sodium sulfide, have demonstrated promise in animal models.

Conclusions:

The role of inflammatory cytokines for both short- and long-term outcomes is an important area for future investigation.

Glibenclamide Prevents Water Diffusion Abnormality in the Brain After Cardiac Arrest in Rats

BACKGROUND

Glibenclamide (GBC) improves neurological outcome after cardiac arrest (CA) in rats. In this study, we sought to elucidate the mechanism responsible for the neuroprotective effects of GBC by using a high-field MRI system.

METHODS

Male Sprague-Dawley rats were subjected to 10-min asphyxial CA followed by cardiopulmonary resuscitation (CPR). Diffusion-weighted imaging (DWI) as well as conventional T2-weighted imaging was conducted prior to CA and at 24, 48, and 72 h after resuscitation. Afterward, histological examination was performed.

RESULTS

Twelve rats were randomized to receive GBC (n = 6) or vehicle (n = 6) at 15 min after return of spontaneous circulation, while four rats were set as sham control. Rats that underwent CA/CPR and received vehicle exhibited distinct neurological deficit, which was alleviated by GBC treatment. Marked water diffusion abnormality as demonstrated by hyperintense DWI in vulnerable regions of the brain was detected after CA/CPR, with the most prominent hyperintense DWI observed in the hippocampal CA1 region at 72 h. Consistently, histological examination revealed neuronal swelling, dendritic injury, and activation of astrocytes and microglia in the hippocampal CA1 region in vehicle-treated rats. Correlation analysis revealed that the ADC values in the hippocampus were significantly correlated with the histological findings (all p < 0.05).

CONCLUSION

These results suggest that the neuroprotective effects of GBC after CA was exerted, as least in part, through prevention of water diffusion abnormality, namely brain edema.

H2S and polysulfide metabolism: Conventional and unconventional pathways

It is now well established that hydrogen sulfide (H₂S) is an effector of a wide variety of physiological processes. It is also clear that many of the effects of H₂S are mediated through reactions with cysteine sulfur on regulatory proteins and most of these are not mediated directly by H₂S but require prior oxidation of H₂S and the formation of per- and polysulfides (H₂S_n, n = 2-8). Attendant with understanding the regulatory functions of H₂S and H₂S_n is an appreciation of the mechanisms that control, i.e., both increase and decrease, their production and catabolism. Although a number of standard "conventional" pathways have been described and well characterized, novel "unconventional" pathways are continuously being identified. This review summarizes our current knowledge of both the conventional and unconventional.

Thiamine as a neuroprotective agent after cardiac arrest

AIMS

Reduction of pyruvate dehydrogenase (PDH) activity in the brain is associated with neurological deficits in animals resuscitated from cardiac arrest. Thiamine is an essential co-factor of PDH. The objective of this study was to examine whether administration of thiamine improves outcomes after cardiac arrest in mice. Secondarily, we aimed to characterize the impact of cardiac arrest on PDH activity in mice and humans.

METHODS

Animal study: Adult mice were subjected to cardiac arrest whereupon cardiopulmonary resuscitation was performed. Thiamine or vehicle was administered 2min before resuscitation and daily thereafter. Mortality, neurological outcome, and metabolic markers were evaluated. Human study: In a convenience sample of post-cardiac arrest patients, we measured serial PDH activity from peripheral blood mononuclear cells and compared them to healthy controls.

RESULTS

Animal study: Mice treated with thiamine had increased 10-day survival (48% versus 17%, P<0.01) and improved neurological function when compared to vehicle-treated mice. In addition, thiamine markedly improved histological brain injury compared to vehicle. The beneficial effects of thiamine were accompanied by improved oxygen consumption in mitochondria, restored thiamine pyrophosphate levels, and increased PDH activity in the brain at 10 days. Human study: Post-cardiac arrest patients had lower PDH activity in mononuclear cells than did healthy volunteers (estimated difference: -5.8O.D./min/mg protein, P<0.001).

CONCLUSIONS

The provision of thiamine after cardiac arrest improved neurological outcome and 10-day survival in mice. PDH activity was markedly depressed in post-cardiac arrest patients suggesting that this pathway may represent a therapeutic target.

Hydrogen sulfide improves neural function in rats following cardiopulmonary resuscitation

The alleviation of brain injury is a key issue following cardiopulmonary resuscitation (CPR). Hydrogen sulfide (H₂S) is hypothesized to be involved in the pathophysiological process of ischemia-reperfusion injury, and exerts a protective effect on neurons. The aim of the present study was to investigate the effects of H₂S on neural functions following cardiac arrest (CA) in rats. A total of 60 rats were allocated at random into three groups. CA was induced to establish the model and CPR was performed after 6 min. Subsequently, sodium hydrosulfide (NaHS), hydroxylamine or saline was administered to the rats. Serum levels of H₂S, neuron-specific enolase (NSE) and S100β were determined following CPR. In addition, neurological deficit scoring (NDS), the beam walking test (BWT), prehensile traction test and Morris water maze experiment were conducted. Neuronal apoptosis rates were detected in the hippocampal region following sacrifice. After CPR, as the H₂S levels increased or decreased, the serum NSE and S100β concentrations decreased or increased, respectively (P<0.0w. The NDS results of the NaHS group were improved compared with those of the hydroxylamine group at 24 h after CPR (P<0.05). In the Morris water maze experiment, BWT and prehensile traction test the animals in the NaHS group performed best and rats in the hydroxylamine group performed worst. At day 7, the apoptotic index and the expression of caspase-3 were reduced in the hippocampal CA1 region, while the expression of Bcl-2 increased in the NaHS group; and results of the hydroxylamine group were in contrast. Therefore, the results of the present study indicate that H₂S is able to improve neural function in rats following CPR.

Thiosulfate Mediates Cytoprotective Effects of Hydrogen Sulfide Against Neuronal Ischemia

BACKGROUND

Hydrogen sulfide (H2S) exhibits protective effects in various disease models including cerebral ischemia-reperfusion (I/R) injury. Nonetheless, mechanisms and identity of molecules responsible for neuroprotective effects of H2S remain incompletely defined. In the current study, we observed that thiosulfate, an oxidation product of H2S, mediates protective effects of an H2S donor compound sodium sulfide (Na2S) against neuronal I/R injury.

METHODS AND RESULTS

We observed that thiosulfate in cell culture medium is not only required but also sufficient to mediate cytoprotective effects of Na2S against oxygen glucose deprivation and reoxygenation of human neuroblastoma cell line (SH-SY5Y) and murine primary cortical neurons. Systemic administration of sodium thiosulfate (STS) improved survival and neurological function of mice subjected to global cerebral I/R injury. Beneficial effects of STS, as well as Na2S, were associated with marked increase of thiosulfate, but not H2S, in plasma and brain tissues. These results suggest that thiosulfate is a circulating "carrier" molecule of beneficial effects of H2S. Protective effects of thiosulfate were associated with inhibition of caspase-3 activity by persulfidation at Cys163 in caspase-3. We discovered that an SLC13 family protein, sodium sulfate cotransporter 2 (SLC13A4, NaS-2), facilitates transport of thiosulfate, but not sulfide, across the cell membrane, regulating intracellular concentrations and thus mediating cytoprotective effects of Na2S and STS.

CONCLUSIONS

The protective effects of H2S are mediated by thiosulfate that is transported across cell membrane by NaS-2 and exerts antiapoptotic effects via persulfidation of caspase-3. Given the established safety track record, thiosulfate may be therapeutic against ischemic brain injury.

Noninvasive tracking of gene transcript and neuroprotection after gene therapy

Gene therapy holds exceptional potential for translational medicine by improving the products of defective genes in diseases and/or providing necessary biologics from endogenous sources during recovery processes. However, validating methods for the delivery, distribution and expression of the exogenous genes from such therapy can generally not be applicable to monitor effects over the long term because they are invasive. We report here that human granulocyte colony-stimulating factor (hG-CSF) cDNA encoded in scAAV-type 2 adeno-associated virus, as delivered through eye drops at multiple time points after cerebral ischemia using bilateral carotid occlusion for 60 min (BCAO-60) led to significant reduction in mortality rates, cerebral atrophy, and neurological deficits in C57black6 mice. Most importantly, we validated hG-CSF cDNA expression using translatable magnetic resonance imaging (MRI) in living brains. This noninvasive approach for monitoring exogenous gene expression in the brains has potential for great impact in the area of experimental gene therapy in animal models of heart attack, stroke, Alzheimer’s dementia, Parkinson’s disorder and amyotrophic lateral sclerosis, and the translation of such techniques to emergency medicine.

Mitochondria-targeted hydrogen sulfide donor AP39 improves neurological outcomes after cardiac arrest in mice

AIMS

Mitochondria-targeted hydrogen sulfide donor AP39, [(10-oxo-10-(4-(3-thioxo-3H-1,2-dithiol-5yl)phenoxy)decyl) triphenylphosphonium bromide], exhibits cytoprotective effects against oxidative stress in vitro. We examined whether or not AP39 improves the neurological function and long term survival in mice subjected to cardiac arrest (CA) and cardiopulmonary resuscitation (CPR).

METHODS

Adult C57BL/6 male mice were subjected to 8 min of CA and subsequent CPR. We examined the effects of AP39 (10, 100, 1000 nmol kg(-1)) or vehicle administered intravenously at 2 min before CPR (Experiment 1). Systemic oxidative stress levels, mitochondrial permeability transition, and histological brain injury were assessed. We also examined the effects of AP39 (10, 1000 nmol kg(-1)) or vehicle administered intravenously at 1 min after return of spontaneous circulation (ROSC) (Experiment 2). ROSC was defined as the return of sinus rhythm with a mean arterial pressure >40 mm Hg lasting at least 10 seconds.

RESULTS

Vehicle treated mice subjected to CA/CPR had poor neurological function and 10-day survival rate (Experiment 1; 15%, Experiment 2; 23%). Administration of AP39 (100 and 1000 nmol kg(-1)) 2 min before CPR significantly improved the neurological function and 10-day survival rate (54% and 62%, respectively) after CA/CPR. Administration of AP39 before CPR attenuated mitochondrial permeability transition pore opening, reactive oxygen species generation, and neuronal degeneration after CA/CPR. Administration of AP39 1 min after ROSC at 10 nmol kg(-1), but not at 1000 nmol kg(-1), significantly improved the neurological function and 10-day survival rate (69%) after CA/CPR.

CONCLUSION

The current results suggest that administration of mitochondria-targeted sulfide donor AP39 at the time of CPR or after ROSC improves the neurological function and long term survival rates after CA/CPR by maintaining mitochondrial integrity and reducing oxidative stress.

Comparison of Shenfu Injection () and epinephrine on catecholamine levels in a porcine model of prolonged cardiac arrest

OBJECTIVE

To compare the effects of Shenfu Injection (SFI) and epinephrine (EPI) on catecholamine levels in a porcine model of prolonged cardiac arrest (CA).

METHODS

After 8 min of untreated ventricular fibrillation, 24 Wuzhishan miniature pigs were randomly assigned to one of the three groups (n=8 per group) and received central venous injection, respectively: SFI group (1 mL/kg), EPI group (20 μg/kg EPI), and normal saline (NS) group. Cardiac output (CO), maximum rate of increase/decrease in left ventricular pressure (±dp/dt), serum levels of EPI, norepinephrine (NE), and dopamine (DA) were determined at baseline and at 0.5, 1, 2, and 4 h after restoration of spontaneous circulation.

RESULTS

The duration of cardiopulmonary resuscitation was shorter in the EPI and SFI groups than in the NS group (P<0.05). The EPI level increased significantly after restoration of spontaneous circulation (ROSC) in all three groups, and was significantly different between the EPI group and the other two groups immediately after ROSC (both P<0.01), but these differences gradually disappeared over time. There were no significant differences in NE or DA levels among the three groups, and there were no correlations between catecholamine levels and CO or dp/dt (P>0.05).

CONCLUSIONS

SFI did not significantly affect endogenous catecholamine levels during cardiopulmonary resuscitation after prolonged ventricular fibrillation. However, SFI improved oxygen metabolism, and produced a better hemodynamic status compared with EPI. SFI might be a potentially vasopressor drug for the treatment of CA.

Hydrogen sulfide inhalation decreases early blood-brain barrier permeability and brain edema induced by cardiac arrest and resuscitation

The effects of hydrogen sulfide (H2S) on blood-brain barrier (BBB) and brain edema after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) remain poorly understood. We investigated the effects of exogenous 80-p.p.m. H2S gas on BBB, brain water content, neurologic outcome, and survival rate after CA and CPR. Cardiopulmonary resuscitation followed CA induced in rats by ventricular fibrillation for 6 minutes. Results show that inhalation of 80-p.p.m. H2S significantly reduced the permeability of the BBB in both in the cortex and hippocampus at 24 hours after resuscitation. Hydrogen sulfide also lessened brain edema in the cortex and hippocampus, ameliorated neurologic outcome as evaluated by neurologic deficit score and tape removal test, and improved the 14-day survival rate. Hydrogen sulfide also attenuated CA and CPR-induced increases of matrix metalloproteinase-9 (MMP-9) activity and vascular endothelial growth factor (VEGF) expression, and increased the expression of angiogenin-1 (Ang-1). These results indicate that inhalation of 80-p.p.m. H2S immediately after CPR attenuated BBB permeability and brain edema, and improved neurologic outcome and 14-day survival of rats after CA. The therapeutic benefits of H2S could be associated with suppression of MMP-9 and VEGF expression and increased expression of Ang-1.

Protective effects of the melanocortin analog NDP-α-MSH in rats undergoing cardiac arrest

We previously reported that melanocortins afford cardioprotection in conditions of experimental myocardial ischemia/reperfusion, with involvement of the janus kinases (JAK), extracellular signal-regulated kinases (ERK) and signal transducers and activators of transcription (STAT) signalings. We investigated the influence of the melanocortin analog [Nle(4), D-Phe(7)]α-melanocyte-stimulating hormone (NDP-α-MSH) on short-term detrimental responses to cardiac arrest (CA) induced in rats by intravenous (i.v.) administration of potassium chloride, followed by cardiopulmonary resuscitation (CPR) plus epinephrine treatment. In CA/CPR rats i.v. treated with epinephrine (0.1 mg/kg) and returned to spontaneous circulation (48%) we recorded low values of mean arterial pressure (MAP) and heart rate (HR), alteration of hemogasanalysis parameters, left ventricle low expression of the cardioprotective transcription factors pJAK2 and pTyr-STAT3 (JAK-dependent), increased oxidative stress, up-regulation of the inflammatory mediators tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and down-regulation of the anti-inflammatory cytokine IL-10, as assessed at 1h and 3h after CPR. On the other hand, i.v. treatment during CPR with epinephrine plus NDP-α-MSH (340 μg/kg) almost completely restored the basal conditions of MAP and HR, reversed metabolic acidosis, induced left ventricle up-regulation of pJAK2, pTyr-STAT3 and IL-10, attenuated oxidative stress, down-regulated TNF-α and IL-6 levels, and improved survival rate by 81%. CA/CPR plus epinephrine alone or in combination with NDP-α-MSH did not affect left ventricle pSer-STAT3 (ERK1/2-dependent) and pERK1/2 levels. These results indicate that melanocortins improve return to spontaneous circulation, reverse metabolic acidosis, and inhibit heart oxidative stress and inflammatory cascade triggered by CA/CPR, likely via activation of the JAK/STAT signaling pathway.

H2S during circulatory shock: some unresolved questions

Numerous papers have been published on the role of H2S during circulatory shock. Consequently, knowledge about vascular sulfide concentrations may assume major importance, in particular in the context of "acute on chronic disease", i.e., during circulatory shock in animals with pre-existing chronic disease. This review addresses the questions (i) of the "real" sulfide levels during circulatory shock, and (ii) to which extent injury and pre-existing co-morbidity may affect the expression of H2S producing enzymes under these conditions. In the literature there is a huge range on sulfide blood levels during circulatory shock, in part as a result of the different analytical methods used, but also due to the variable of the models and species studied. Clearly, some of the very high levels reported should be questioned in the context of the well-known H2S toxicity. As long as "real" sulfide levels during circulatory shock are unknown and/or undetectable "on line" due to the lack of appropriate techniques, it appears to be premature to correlate the measured blood levels of hydrogen sulfide with the severity of shock or the H2S therapy-related biological outcomes. The available data on the tissue expression of the H2S-releasing enzymes during circulatory shock suggest that a "constitutive" CSE expression may play a crucial role of for the maintenance of organ function, at least in the kidney. The data also indicate that increased CBS and CSE expression, in particular in the lung and the liver, represents an adaptive response to stress states.

Beneficial effects of nitric oxide on outcomes after cardiac arrest and cardiopulmonary resuscitation in hypothermia-treated mice

BACKGROUND

Therapeutic hypothermia (TH) improves neurological outcomes after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). Although nitric oxide prevents organ injury induced by ischemia and reperfusion, role of nitric oxide during TH after CPR remains unclear. In this article, the authors examined the impact of endogenous nitric oxide synthesis on the beneficial effects of hypothermia after CA/CPR. The authors also examined whether or not inhaled nitric oxide during hypothermia further improves outcomes after CA/CPR in mice treated with TH.

METHODS

Wild-type mice and mice deficient for nitric oxide synthase 3 (NOS3(−/−)) were subjected to CA at 37 °C and then resuscitated with chest compression. Body temperature was maintained at 37 °C (normothermia) or reduced to 33 °C (TH) for 24 h after resuscitation. Mice breathed air or air mixed with nitric oxide at 10, 20, 40, 60, or 80 ppm during hypothermia. To evaluate brain injury and cerebral blood flow, magnetic resonance imaging was performed in wild-type mice after CA/CPR.

RESULTS

Hypothermia up-regulated the NOS3-dependent signaling in the brain (n = 6 to 7). Deficiency of NOS3 abolished the beneficial effects of hypothermia after CA/CPR (n = 5 to 6). Breathing nitric oxide at 40 ppm improved survival rate in hypothermia-treated NOS3(−/−) mice (n = 6) after CA/CPR compared with NOS3(−/−) mice that were treated with hypothermia alone (n = 6; P < 0.05). Breathing nitric oxide at 40 (n = 9) or 60 (n = 9) ppm markedly improved survival rates in TH-treated wild-type mice (n = 51) (both P < 0.05 vs. TH-treated wild-type mice). Inhaled nitric oxide during TH (n = 7) prevented brain injury compared with TH alone (n = 7) without affecting cerebral blood flow after CA/CPR (n = 6).

CONCLUSIONS

NOS3 is required for the beneficial effects of TH. Inhaled nitric oxide during TH remains beneficial and further improves outcomes after CA/CPR. Nitric oxide breathing exerts protective effects after CA/CPR even when TH is ineffective due to impaired endogenous nitric oxide production.

A systematic review of neuroprotective strategies after cardiac arrest: from bench to bedside (part II-comprehensive protection)

Neurocognitive deficits remain a significant source of morbidity in survivors of cardiac arrest. We conducted a literature review of treatment protocols designed to evaluate neurologic outcome and survival following global cerebral ischemia associated with cardiac arrest. The search was limited to investigational therapies that were implemented either during cardiopulmonary resuscitation or after return of spontaneous circulation in studies that included assessment of impact on neurologic outcome. Given that complex pathophysiology underlies global brain hypoxic ischemia following cardiac arrest, neuroprotective strategies targeting multiple stages of neuropathologic cascades should promise to improve survival and neurologic outcomes in cardiac arrest victims. In Part II of this review, we discuss several approaches that can provide comprehensive protection against global brain injury associated with cardiac arrest, by modulating multiple targets of neuropathologic cascades. Pharmaceutical approaches include adenosine and growth factors/hormones including brain-derived neurotrophic factor, insulin-like growth factor-1 and glycine-proline-glutamate, granulocyte colony stimulating factor and estrogen. Preclinical studies of these showed some benefit but were inconclusive in models of global brain injury involving systemic ischemia. Several medical gases that can mediate neuroprotection have been evaluated in experimental settings. These include hydrogen sulfide, hyperbaric oxygen and molecular hydrogen. Hyperbaric oxygen and molecular hydrogen showed promising results; however, further investigation is required prior to clinical application of these agents in cardiac arrest patients.

Mouse models to study the effect of cardiovascular risk factors on brain structure and cognition

Recent clinical data indicates that hemodynamic changes caused by cardiovascular diseases such as atherosclerosis, heart failure, and hypertension affect cognition. Yet, the underlying mechanisms of the resulting vascular cognitive impairment (VCI) are poorly understood. One reason for the lack of mechanistic insights in VCI is that research in dementia primarily focused on Alzheimer's disease models. To fill in this gap, we critically reviewed the published data and various models of VCI. Typical findings in VCI include reduced cerebral perfusion, blood-brain barrier alterations, white matter lesions, and cognitive deficits, which have also been reported in different cardiovascular mouse models. However, the tests performed are incomplete and differ between models, hampering a direct comparison between models and studies. Nevertheless, from the currently available data we conclude that a few existing surgical animal models show the key features of vascular cognitive decline, with the bilateral common carotid artery stenosis hypoperfusion mouse model as the most promising model. The transverse aortic constriction and myocardial infarction models may be good alternatives, but these models are as yet less characterized regarding the possible cerebral changes. Mixed models could be used to study the combined effects of different cardiovascular diseases on the deterioration of cognition during aging.

Clinical correlates in an experimental model of repetitive mild brain injury

OBJECTIVE

Although there is growing awareness of the long-term cognitive effects of repetitive mild traumatic brain injury (rmTBI; eg, sports concussions), whether repeated concussions cause long-term cognitive deficits remains controversial. Moreover, whether cognitive deficits depend on increased amyloid β deposition and tau phosphorylation or are worsened by the apolipoprotein E4 allele remains unknown. Here, we use an experimental model of rmTBI to address these clinical controversies.

METHODS

A weight drop rmTBI model was used that results in cognitive deficits without loss of consciousness, seizures, or gross or microscopic evidence of brain damage. Cognitive function was assessed using a Morris water maze (MWM) paradigm. Immunostaining and enzyme-linked immunosorbent assay (ELISA) were used to assess amyloid β deposition and tau hyperphosphorylation. Brain volume and white matter integrity were assessed by magnetic resonance imaging (MRI).

RESULTS

Mice subjected to rmTBI daily or weekly but not biweekly or monthly had persistent cognitive deficits as long as 1 year after injuries. Long-term cognitive deficits were associated with increased astrocytosis but not tau phosphorylation or amyloid β (by ELISA); plaques or tangles (by immunohistochemistry); or brain volume loss or changes in white matter integrity (by MRI). APOE4 was not associated with worse MWM performance after rmTBI.

INTERPRETATION

Within the vulnerable time period between injuries, rmTBI produces long-term cognitive deficits independent of increased amyloid β or tau phosphorylation. In this model, cognitive outcome is not influenced by APOE4 status. The data have implications for the long-term mental health of athletes who suffer multiple concussions.

Improving outcomes after cardiac arrest using NO inhalation

Despite advances in cardiopulmonary resuscitation (CPR) methods including therapeutic hypothermia (TH), long-term neurological outcomes and survival after sudden cardiac arrest (CA) remains to be dismal. While nitric oxide (NO) prevents organ injury induced by ischemia and reperfusion (I/R), systemic vasodilation induced by intravenous NO-donor compounds typically precludes its use in post-CA patients in whom blood pressure is often low and unstable. Although developed as a selective pulmonary vasodilator, inhaled NO has systemic benefits in a variety of pre-clinical and clinical studies without causing potentially harmful systemic vasodilation. Breathing NO after CPR may prevent post-CA brain injury and improve long-term outcomes after CA and CPR.