Effects of intracerebroventricular application of the delta opioid receptor agonist [D-Ala2, D-Leu5] enkephalin on neurological recovery following asphyxial cardiac arrest in rats

Inhibition of γδ T Cells Alleviates Blood-Brain Barrier in Cardiac Arrest and Cardiopulmonary Resuscitation in Mice

Ischemia/reperfusion (I/R) injury is the leading cause of death following cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). γδT cells are suggested to aggravate blood-brain barrier (BBB) injury in various pathological processes. We herein investigate the effects of γδT cells inhibitor (UC7-13D5) against I/R injury post-CA/CPR. C57BL/6 mice were subjected to CA through injection of KCL (70 μL of 0.5 mol/L) and cessation of mechanical ventilation followed by CPR. Flow cytometry was performed to measure the proportion of CD3-positive cells after intraperitoneal injection of 200 μg UC7-13D5 at 6 h, 24 h, and 48 h post-resuscitation into mice. Neurological scores and modified neurological severity scores were assessed to examine neurological functions. Brain edema was estimated via brain water content measurements. Immunohistochemistry of caspase-3 and immunofluorescence staining of claudin-1, ZO-1 and CD31 were performed to detect neuronal apoptosis, BBB integrity and angiogenesis. Microvascular morphology in the cortical area was assessed via H&E staining. Oxidative stress was determined by measuring malondialdehyde, myeloperoxidase, xanthine oxidase, superoxide dismutase, and glutathione peroxidase activities. Western blotting was performed to measure the protein levels of Nuclear factor-E2-related factor 2 (Nrf2) and Heme oxygenase-1 (HO-1). UC7-13D5 effectively depleted γδT cells. Inhibition of γδT cells improved neurological deficits and reduced brain edema post-CA/CPR. γδT cells depletion attenuated neuronal apoptosis, BBB disruption and oxidative stress and promoted angiogenesis following CA/CPR. Inhibition of γδT cells facilitated the activation of the Nrf2/HO-1 pathway in CA/CPR-induced mice. Inhibition of γδT cells alleviates neurological deficits and cerebral edema in mice with CA/CPR by inhibiting neuronal apoptosis, BBB disruption and oxidative stress, and promoting angiogenesis via activation of the Nrf2/HO-1 pathway.

Peptidomic Analysis Reveals Seasonal Neuropeptide and Peptide Hormone Changes in the Hypothalamus and Pituitary of a Hibernating Mammal

During the winter, hibernating mammals undergo extreme changes in physiology, which allow them to survive several months without access to food. These animals enter a state of torpor, which is characterized by decreased metabolism, near-freezing body temperatures, and a dramatically reduced heart rate. The neurochemical basis of this regulation is largely unknown. Based on prior evidence suggesting that the peptide-rich hypothalamus plays critical roles in hibernation, we hypothesized that changes in specific cell-cell signaling peptides (neuropeptides and peptide hormones) underlie physiological changes during torpor/arousal cycles. To test this hypothesis, we used a mass spectrometry-based peptidomics approach to examine seasonal changes of endogenous peptides that occur in the hypothalamus and pituitary of a model hibernating mammal, the thirteen-lined ground squirrel (Ictidomys tridecemlineatus). In the pituitary, we observed changes in several distinct peptide hormones as animals prepared for torpor in October, exited torpor in March, and progressed from spring (March) to fall (August). In the hypothalamus, we observed an overall increase in neuropeptides in October (pre-torpor), a decrease as the animal entered torpor, and an increase in a subset of neuropeptides during normothermic interbout arousals. Notable changes were observed for feeding regulatory peptides, opioid peptides, and several peptides without well-established functions. Overall, our study provides critical insight into changes in endogenous peptides in the hypothalamus and pituitary during mammalian hibernation that were not available from transcriptomic measurements. Understanding the molecular basis of the hibernation phenotype may pave the way for future efforts to employ hibernation-like strategies for organ preservation, combating obesity, and treatment of stroke.

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.

Activation of the δ opioid receptor relieves cerebral ischemic injury in rats via EGFR transactivation

Delta opioids are thought to relieve ischemic injury and have tissue-protective properties. However, the detailed mechanisms of delta opioids have not been well identified. Receptor tyrosine kinases (RTKs), such as epidermal growth factor receptor (EGFR), have been shown to mediate downstream signals of δ opioid receptor (δOR) activation through the metalloproteinase (MMP)-dependent EGF-like growth factor (HB-EGF) excretion pathway, which is called transactivation. In this study, to investigate the role of EGFR in δOR-induced anti-ischemic effects in the brain, we applied the middle cerebral artery occlusion (MCAO) model followed by reperfusion to mimic ischemic stroke injury in rats. Pre-treatment with the δOR agonist [D-ala², D-leu⁵] enkephalin (DADLE) improved the neurologic deficits and the decreased infarct volume caused by cerebral ischemia/reperfusion injury, which were blocked by the EGFR inhibitor AG1478 and the MMP inhibitor GM6001, respectively. Further results indicated that DADLE activated EGFR, Akt and ERK1/2 and upregulated EGFR expression in the hippocampus in a time-dependent manner, which were inhibited by AG1478 and GM6001. The enzyme-linked immunosorbent assay (ELISA) results showed that δOR activation led to an increase in HB-EGF release, but HB-EGF in tissue was downregulated at the mRNA and protein levels. Moreover, this protective action caused by δOR agonists may involve attenuated hippocampal cellular apoptosis. Overall, these results demonstrate that MMP-mediated transactivation of EGFR is essential for δOR agonist-induced MCAO/reperfusion injury relief. These findings provide a potential molecular mechanism for the neuroprotective property of δOR and may add new insight into mitigating or preventing injury.

[D-Ala2, D-Leu5] Enkephalin Inhibits TLR4/NF-κB Signaling Pathway and Protects Rat Brains against Focal Ischemia-Reperfusion Injury

Background

Cerebral ischemia-reperfusion (I/R) injury is the main cause of acute brain injury, which is a life-threatening disease due to the lack of effective treatments. [D-Ala², D-Leu⁵] enkephalin (DADLE) is a synthetic delta-opioid receptor agonist that is reported to confer neuroprotective effect; however, the underlying mechanism is still being explored. The purpose of the present study is to determine whether DADLE administrated intracerebroventricularly could attenuate the cerebral I/R injury, to determine if this is through inhibiting the toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) signaling pathway and therefore inhibiting neuroinflammation in an ischemic stroke model.

Methods

Rats were subjected to 120 minutes of ischemia by transient middle cerebral artery occlusion (MCAO). At 45 minutes after ischemia, DADLE or control vehicle (artificial cerebrospinal fluid, ACSF) was given to the rats intracerebroventricularly. Neurological deficit, cerebral infarct volume, and histopathological changes were assessed at 24 hours after reperfusion. Brain inflammation was assessed by measuring tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the ischemic penumbra by ELISA. The expression of TLR4 was determined by immunohistochemistry staining and western blotting. The expression of NF-κB was investigated by western blotting.

Results

Compared with the vehicle-treatment (ACSF), DADEL improved neurological deficit (9.6 ± 2.1 versus 13.8 ± 1.9), reduced cerebral infarct volume (18.74 ± 3.30% versus 10.57 ± 2.50%), and increased the number of normal neurons (29.72 ± 8.53% versus 51.37 ± 9.18%) after cerebral I/R injury in rats (all P < 0.05). Expressions of inflammatory molecules including TNF-α and IL-6 were highly expressed in the vehicle-treated rats, whereas treatment with DADLE downregulated these expressions (P < 0.05). Additionally, cerebral I/R injury significantly increased the TLR4 and NF-κB expression in vehicle-control group, which was markedly inhibited by DADLE (P < 0.05).

Conclusions

DADLE, administrated intracerebroventricularly at 45 minutes after cerebral ischemia, significantly ameliorated I/R-induced brain damage in rats. This kind of neuroprotective effect appears to be related to the downregulation of TLR4-mediated inflammatory responses.

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.

Delta opioid peptide [d-Ala2, d-Leu5] enkephalin confers neuroprotection by activating delta opioid receptor-AMPK-autophagy axis against global ischemia

Background

Ischemic stroke poses a severe risk to human health worldwide, and currently, clinical therapies for the disease are limited. Delta opioid receptor (DOR)-mediated neuroprotective effects against ischemia have attracted increasing attention in recent years. Our previous studies revealed that DOR activation by [d-Ala2, d-Leu5] enkephalin (DADLE), a selective DOR agonist, can promote hippocampal neuronal survival on day 3 after ischemia. However, the specific molecular and cellular mechanisms underlying the DOR-induced improvements in ischemic neuronal survival remain unclear.

Results

We first detected the cytoprotective effects of DADLE in an oxygen–glucose deprivation/reperfusion (OGD/R) model and observed increased viability of OGD/R SH-SY5Y neuronal cells. We also evaluated changes in the DOR level following ischemia/reperfusion (I/R) injury and DADLE treatment and found that DADLE increased DOR levels after ischemia in vivo and vitro. The effects of DOR activation on postischemic autophagy were then investigated, and the results of the animal experiment showed that DOR activation by DADLE enhanced autophagy after ischemia, as indicated by elevated LC3 II/I levels and reduced P62 levels. Furthermore, the DOR-mediated protective effects on ischemic CA1 neurons were abolished by the autophagy inhibitor 3-methyladenine (3-MA). Moreover, the results of the cell experiments revealed that DOR activation not only augmented autophagy after OGD/R injury but also alleviated autophagic flux dysfunction. The molecular pathway underlying DOR-mediated autophagy under ischemic conditions was subsequently studied, and the in vivo and vitro data showed that DOR activation elevated autophagy postischemia by triggering the AMPK/mTOR/ULK1 signaling pathway, while the addition of the AMPK inhibitor compound C eliminated the protective effects of DOR against I/R injury.

Conclusion

DADLE-evoked DOR activation enhanced neuronal autophagy through activating the AMPK/mTOR/ULK1 signaling pathway to improve neuronal survival and exert neuroprotective effects against ischemia.

CTL-Derived Granzyme B Participates in Hippocampal Neuronal Apoptosis Induced by Cardiac Arrest and Resuscitation in Rats

Hippocampal neuronal apoptosis is a devastating consequence of cardiac arrest (CA) and subsequent cardiopulmonary resuscitation (CPR). In this study, we assessed the contribution of cytotoxic T lymphocyte (CTL)-derived toxic mediator granzyme B (Gra-b) to the hippocampal neuronal apoptosis following CA/CPR in rats. Rats that experienced CA/CPA presented with cytosomal shrinkage, dense cytoplasm, and intensive eosinophilic staining in the CA1 region of dorsal hippocampus. CA/CPR rats also exhibited inability in spatial navigation and a local infiltration of peripheral CD8+ T cells into the hippocampus. The protein levels of Gra-b, cleaved Caspase-3, and cleaved PARP1 were significantly elevated in rats undergoing CA/CPR. Pretreatment with Gra-b inhibitor suppressed Gra-b release, attenuated hippocampal neuronal apoptosis, as well as improved cognitive impairment. Together, this study indicates that CTL-derived Gra-b is involved in the CA/CPR-induced neuronal apoptosis, and pharmacological manipulation of Gra-b may represent a novel avenue for the treatment of brain injury following CA/CPR.

Mitophagy in the Hippocampus Is Excessive Activated After Cardiac Arrest and Cardiopulmonary Resuscitation

This study examined the activation of mitophagy following cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) and the relationship between the change with time and apoptosis.

MAIN METHODS

The male Sprague-Dawley rats were randomized into four groups: Sham group, CPR24h group, CPR48h group, CPR72h group. The rat model of cardiac arrest was established by asphyxiation. We employed western blot to analyze the levels of mitophagy related proteins of hippocampus, JC-1 to detect mitochondrial membrane potential (MMP) and flow cytometry to measure the rate of apoptosis of hippocampal neurons. Moreover, we also intuitively observed the occurrence of mitophagy through electron microscopy.

KEY FINDINGS

The results showed that the levels of TOMM20 and Tim23 protein were significantly decreased after CPR, which were more remarkable following 72 h of CPR. However, the protein levels of dynamin related protein 1 (Drp1) and cytochrome C (Cyt-c) were strongly up-regulated after CPR. Meanwhile, the hippocampal MMP decreased gradually with time after CPR. Furthermore, we more intuitively verified the activation of mitophagy through electron microscopy. In addition, the rats of apoptosis rate of hippocampus after CPR were significantly increased, which were gradually enhanced over time from 24 h until at least 72 h following CPR.

SIGNIFICANCE

with the enhancement of mitophagy, the apoptosis of hippocampal neurons was gradually enhanced, which suggested mitophagy may be excessive activated and aggravating brain damage after CA and CPR.

Delta Opioids: Neuroprotective Roles in Preclinical Studies

Since ancient times, opioids have been used clinically and abused recreationally. In the early stages (about 1,000 AD) of opium history, an Arab physician, Avicenna, administered opioids to control diarrhea and eye diseases. ¹ Opioids have very strong pain relieving properties and they also regulate numerous cellular responses. Opioid receptors are expressed throughout the body, including the nervous system, heart, lungs, liver, gastrointestinal tract, and retina. ^2-6 Delta opioid receptors (DORs) are a very attractive target from the perspective of both receptor function and their therapeutic potential. Due to a rapid progress in mouse mutagenesis and development of small molecules as DOR agonist, novel functions and roles of DORs have emerged in recent years. This review article focuses on the recent advances in the neuroprotective roles of DOR agonists in general and retina neuroprotection in particular. Rather than being exhaustive, this review highlights the selected studies of DOR function in neuroprotection. We also highlight our preclinical studies using rodent models to demonstrate the potentials of DOR agonists for retinal neuroprotection. Based on existing literature and our recently published data on the eye, DOR agonists possess therapeutic abilities that protect the retina and optic nerve injury against glaucoma and perhaps other retinopathies as well. This review also highlights the signaling events associated with DOR for neuroprotection in the eye. There is a need for translational research on DORs to recognize their potential for clinical application such as in glaucoma.

α7 Nicotinic Acetylcholine Receptor Mediates the Neuroprotection of Remote Ischemic Postconditioning in a Rat Model of Asphyxial Cardiac Arrest

BACKGROUND

Remote ischemic postconditioning (RIPost) has been shown to reduce the ischemia-reperfusion injury of the heart and brain. However, the protection mechanisms have not yet been fully elucidated. We have observed that RIPost could alleviate the brain injury after cardiac arrest (CA). The aim of this study was to explore whether α7 nicotinic acetylcholine receptor (α7nAChR) mediates the neuroprotection of RIPost in a rat model of asphyxial CA.

MATERIALS AND METHODS

Asphyxial CA model was induced by occlusion of the tracheal tube for 8 min and resuscitated later. RIPost produced by three cycles of 15-min occlusion and 15-min release of the right hind limb by a tourniquet was performed respectively at the moment and the third hour after restoration of spontaneous circulation. The α7nAChR agonist PHA-543613 and the antagonist methyllycaconitine (MLA) were used to investigate the role of α7nAChR in mediating neuroprotective effects.

RESULTS

Results showed that α7nAChR was decreased in hippocampus and cortex after resuscitation, whereas RIPost could attenuate the reduction. The use of PHA-543613 provided neuroprotective effects against cerebral injury after CA. Furthermore, RIPost decreased the levels of neuron-specific enolase, inflammatory mediators, the number of apoptotic cells, and phosphorylation of nuclear factor-κB while increased the phosphorylation of signal transducer and activator of transcription-3. However, the above effects of RIPost were attenuated by α7nAChR antagonist methyllycaconitine.

CONCLUSIONS

Neuroprotection of RIPost was related with the activation of α7nAChR, which could suppress nuclear factor-κB and activate signal transducer and activator of transcription-3 in a rat asphyxial CA model.

Delta Opioid Peptide [d-Ala2, d-Leu5] Enkephalin (DADLE) Exerts a Cytoprotective Effect in Astrocytes Exposed to Oxygen-Glucose Deprivation by Inducing Autophagy

Astrocytes protection and functional regulation are important strategies to protect against neuronal damage caused by ischemia. Activation of the delta opioid receptor (DOR) could reduce astrocytes damage, although the mechanism remains unclear. The present study aimed to test the effect of DOR activation on autophagy in astrocytes exposed to oxygen-glucose deprivation (OGD), and to further investigate whether this effect has a protective effect on astrocytes. Primary cultured rat cortical astrocytes were treated with various doses of [d-Ala2, d-Leu5]-Enkephalin (DADLE, a selective DOR agonist) followed by 6 h OGD. Cell viability was evaluated by CCK-8 assay and lactate dehydrogenase release. Autophagic vacuole was analyzed with LC3 immunofluorescent staining. The levels of autophagy and apoptosis-related proteins were analyzed by western blot. Results demonstrated that treatment with 10 nM DADLE was sufficient to increase cell viability and induced autophagy in astrocytes. The DADLE-induced autophagy displayed a cytoprotective effect on astrocytes. Inhibition of autophagy by 3-methyladenine (3-MA, an autophagy inhibitor) reversed the protective effect of DADLE. Naltrindole (a DOR antagonist) only partially antagonized the role of DADLE, which indicated that DADLE might have a cytoprotective mechanism independent of DOR. Further results showed that DADLE significantly enhanced the level of Bcl-2 protein and reduced the level of Bax protein in astrocytes exposed to OGD. Our results suggest a novel mechanism in which DADLE induces autophagy in astrocytes and exerts cytoprotective effects by inhibiting apoptosis.

The protective effects of distal ischemic treatment on apoptosis and mitochondrial permeability in the hippocampus after cardiopulmonary resuscitation

Apoptosis and mitochondrial dysfunction are the main cause of neurological injury after cardiopulmonary resuscitation (CPR). However, the effects of distal ischemic treatments on ischemia induced apoptosis are rarely studied, and the mechanism by which mitochondrial dysfunction contributes to CPR still unclear. A rat model of distal ischemia was established by clipping the right femoral artery. Rats were divided into blank, model, pre distal ischemic treatment, per-treatment, and post-treatment groups. Neurological deficit score was scored to evaluate neurologic function after cardiopulmonary resuscitation for 72 hr. We employed TUNEL and flow cytometry to measure the rate of apoptosis of hippocampal neurons, the integrity of mitochondrial membrane and the degree of mitochondrial permeability transition pore (mPTP) opening. The rate of apoptosis rate of hippocampal CA1 neurons in the pre-treatment and post-treatment groups were significantly lower than that of the model group. Moreover, the integrity of the mitochondrial membrane in the pre-treatment and post-treatment groups was higher than that in the model and per- treatment groups. Furthermore, the degree of mPTP opening was lower in the pre-treatment and post-treatment groups than the untreated and per-treatment groups. Taken together, our results show that ischemic preconditioning and post processing can maintain the integrity of mitochondria, perhaps by inhibiting the opening of mPTP, and reducing apoptosis of hippocampal neurons by regulating expression of apoptosis related proteins after CPR, to improve neurological function. This study highlights a novel target pathway for treatment of CPR.

RETRACTED: Activation of the PI3K-Akt pathway promotes neuroprotection of the δ-opioid receptor agonist against cerebral ischemia-reperfusion injury in rat models

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. The authors contacted the journal to request a retraction: "Recently, we found that some experimental animal samples from another research were mistakenly used in this paper, resulting in the results and conclusions unreliable". Concern was also raised about the reliability of the brain section images in Figure 1, which seem to appear in other publications, as detailed here: https://pubpeer.com/publications/8AF402957928F3F27A1F46B6D556AD; and here: https://docs.google.com/spreadsheets/d/1r0MyIYpagBc58BRF9c3luWNlCX8VUvUuPyYYXzxWvgY/edit#gid=262337249. In addition, suspected image duplications were detected in Figures 2A, 3B and 4B. The journal requested the corresponding author comment on these concerns and provide the raw data. The author did not fulfil this request and the Editor-in-Chief decided to retract the article.

Hypertonic saline infusion suppresses apoptosis of hippocampal cells in a rat model of cardiopulmonary resuscitation

Hypertonic saline (HS) attenuates cerebral edema, improves microcirculation perfusion and alleviates inflammation. However, whether the beneficial effect of HS on neurological function after cardiopulmonary resuscitation (CPR) in rat model of asphyxial cardiac arrest (CA) is mediated via attenuating apoptosis of neurons is not known. We studied the neuroprotective effect of HS in rats after CA and CPR, and explored the likely underlying mechanisms. Animals were randomly assigned to 4 equal groups (n = 15 each) according to the different infusions administered during resuscitation: control (C), normal saline (NS), hypertonic saline (HS), and hydroxyethyl starch (HES) groups. NDS at 12, 24, 48 and 72 h post-ROSC in the HS group were significantly higher than those in the NS and HES groups. Western blot analysis demonstrated a significant increase in Bcl-2 expression in HS, as compared to that in the NS and HES groups. However, Bax and Caspase-3 expressions in HS were significantly lower than that in the NS and HES groups. The apoptosis rate in HS was significantly lower than that in the NS and HES groups, suggesting HS treatment during resuscitation could effectively suppress neuronal cell apoptosis in hippocampal CA1 post-ROSC and improve neuronal function.

Therapeutic Hypothermia Enhances Cold-Inducible RNA-Binding Protein Expression and Inhibits Mitochondrial Apoptosis in a Rat Model of Cardiac Arrest

Therapeutic hypothermia is well known for its protective effect against brain injury after cardiac arrest, but the exact mechanism remains unclear. Cold-inducible RNA-binding protein (CIRP), a member of cold shock protein, enables mammalian cells to withstand decreased temperature by regulating gene translation. However, the role of CIRP in global cerebral ischemia after therapeutic hypothermia has not been clearly elucidated. In the present study, rats resuscitated from 4 min of cardiac arrest were separately treated with therapeutic hypothermia (immediately after return of spontaneous circulation (ROSC); targeted temperature at 33 °C) and therapeutic normothermia (targeted temperature at 36.8 °C) for 6 h. The hippocampus was harvested at 0 h (baseline), 6 h, 12 h, 1 day, 3 days, and 7 days after ROSC. The expression of CIRP messenger RNA (mRNA) was assessed by real-time PCR. CIRP and mitochondrial apoptosis-associated proteins were tested by Western blot. The histological changes and neurological function were respectively evaluated by hematoxylin-eosin staining and neurological deficit score (NDS). Compared with baseline, rats resuscitated from cardiac arrest showed increased expression of CIRP, Bax, Caspase 9, and Caspase 3 and decreased expression of Bcl-2 in hippocampus (P < 0.05). However, therapeutic hypothermia after ROSC alleviated the alterations of Bax, Caspase 9, Caspase 3, and Bcl-2, while further increased the hippocampal expression of CIRP mRNA and protein, when compared with the normothermia rats (P < 0.05). In addition, compared with the therapeutic normothermia rats, histopathological damage in CA1 zone and NDS were respectively decreased and increased in the hypothermia rats (P < 0.05). Our findings suggest that 32 °C therapeutic hypothermia exerts an important neuroprotective effects by up-regulating CIRP expression and inhibiting mitochondrial apoptosis factor production in the cardiac arrest rat model.

Glibenclamide Improves Survival and Neurologic Outcome After Cardiac Arrest in Rats

OBJECTIVES

Glibenclamide confers neuroprotection in animal models as well as in retrospective clinical studies. This study determines whether glibenclamide improves outcome after cardiac arrest in rats.

DESIGN

Prospective randomized laboratory study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats (n = 126).

INTERVENTIONS

Rats successfully resuscitated from 8-minute asphyxial cardiac arrest were randomized to glibenclamide or vehicle group. Rats in the glibenclamide group were intraperitoneally administered glibenclamide with a loading dose of 10 μg/kg at 10 minutes and a maintenance dose of 1.2 μg at 6, 12, 18, and 24 hours after return of spontaneous circulation, whereas rats in the vehicle group received equivalent volume of vehicle solution.

MEASUREMENTS AND MAIN RESULTS

Survival was recorded every day, and neurologic deficit scores were assessed at 24, 48, and 72 hours and 7 days after return of spontaneous circulation (n = 22 in each group). Results showed that glibenclamide treatment increased 7-day survival rate, reduced neurologic deficit scores, and prevented neuronal loss in the hippocampal cornu ammonis 1 region. To investigate the neuroprotective effects of glibenclamide in acute phase, we observed neuronal injury at 24 hours after return of spontaneous circulation and found that glibenclamide significantly decreased the rate of neuronal necrosis and apoptosis. In addition, glibenclamide reduced the messenger RNA expression of tumor necrosis factor-α and monocyte chemoattractant protein-1 in the cortex after return of spontaneous circulation. Furthermore, the sulfonylurea receptor 1 and transient receptor potential M4 heteromers, the putative therapeutic targets of glibenclamide, were up-regulated after cardiac arrest and cardiopulmonary resuscitation, indicating that they might be involved in neuroprotective effect of glibenclamide.

CONCLUSIONS

Glibenclamide treatment substantially improved survival and neurologic outcome throughout a 7-day period after return of spontaneous circulation. The salutary effects of glibenclamide were associated with suppression of neuronal necrosis and apoptosis, as well as inflammation in the brain.

Drug-induced hypothermia in stroke models: does it always protect?

Ischemic stroke is a common neurological disorder lacking a cure. Recent studies show that therapeutic hypothermia is a promising neuroprotective strategy against ischemic brain injury. Several methods to induce therapeutic hypothermia have been established; however, most of them are not clinically feasible for stroke patients. Therefore, pharmacological cooling is drawing increasing attention as a neuroprotective alternative worthy of further clinical development. We begin this review with a brief introduction to the commonly used methods for inducing hypothermia; we then focus on the hypothermic effects of eight classes of hypothermia-inducing drugs: the cannabinoids, opioid receptor activators, transient receptor potential vanilloid, neurotensins, thyroxine derivatives, dopamine receptor activators, hypothermia-inducing gases, adenosine, and adenine nucleotides. Their neuroprotective effects as well as the complications associated with their use are both considered. This article provides guidance for future clinical trials and animal studies on pharmacological cooling in the setting of acute stroke.

Delta opioid receptor agonist BW373U86 attenuates post-resuscitation brain injury in a rat model of asphyxial cardiac arrest

OBJECTIVE

The aim of this study was to investigate whether the DOR agonist BW373U86 conferred neuroprotection following ACA when given after resuscitation and to determine the long-term effects of chronic BW373U86 treatment on ACA-elicited brain injury.

METHODS

Animals were divided into acute and chronic treatment groups. Each group consisted of four sub-groups, including Sham, ACA, BW373U86 (BW373U86+ACA), and Naltrindole groups (Naltrindole and BW373U86+ACA). The DOR antagonist Naltrindole was used to confirm the possible receptor-dependent effects of BW373U86. ACA was induced by 8min of asphyxiation followed by resuscitation. All drugs were administered either immediately after the restoration of spontaneous circulation (ROSC) in acute-treatment groups or over 6 consecutive days in chronic-treatment groups. Alterations of cAMP response element-binding protein (CREB) and phosphorylated CREB (pCREB) were analyzed by western blot and immunohistochemistry. Neurological functions were assessed by neurological deficit score (NDS) and Morris Water Maze performance. Neurodegeneration was monitored by immunofluorescence and Nissl staining.

RESULTS

ACA induced massive neuron loss and serious neurological function deficits. BW373U86 significantly reduced both of these negative effects and increased CREB and pCREB expression in the hippocampus; these effects were reversed with acute Naltrindole treatment. The protective effects of BW373U86 persisted until 28d post-ROSC with chronic treatment, but these effects were not reversed by Naltrindole.

CONCLUSIONS

BW373U86 attenuates global cerebral ischemic injury induced by ACA through both DOR-dependent and DOR-independent mechanisms. CREB might be an important molecule in mediating these neuroprotective effects.

[D-Ala2,D-Leu5]-enkephalin (DADLE) and morphine-induced postconditioning by inhibition of mitochondrial permeability transition pore, in human myocardium

The aim of the study was to examine the cardioprotective effect of morphine and Delta 2 opioid D-Ala2-Leu5 enkephalin(DADLE) administered, at early reoxygenation, in isolated human myocardium exposed to hypoxia–reoxygenation. Then,we tested the involvement of mitochondrial permeability transition pore in morphine and DADLE-induced postconditioning.Human right atrial trabeculae were obtained during cardiac surgery (coronary artery bypass and aortic valve replacement).Isometrically contracting isolated human right atrial trabeculae were exposed to 30-min hypoxia and 60-min reoxygenation(control group). In treatment groups, morphine 0.5 mmol, DADLE 10 nmol, DADLE 50 nmol and DADLE 100 nmol were administered during the first 15 min of reoxygenation. In two additional groups, morphine and DADLE 100 nmol were administered in the presence of atractyloside 50 mmol, the mitochondrial permeability transition pore opener. The force of contraction at the end of 60-min reoxygenation period (FoC60 expressed as % of baseline) was compared (mean+standard deviation) between the groups by an analysis of variance. Morphine (FoC60: 81+9% of baseline), DADLE50 nmol (FoC60: 76+11% of baseline) and DADLE 100 nmol (FoC60: 81+4% of baseline) increased significantly (P,0.001) the FoC60 as compared with the control group (FoC60: 53+3% of baseline). DADLE 10 nmol did not modify the FoC60 (50+9% of baseline; P ¼ 0.60 versus control group). The enhanced recovery of FoC60 induced by morphine and DADLE 100 nmol were abolished in the presence of atractyloside (FoC60: respectively 57+6% and 44+7% of baseline;P, 0.001). In conclusion, the administration of morphine and DADLE, in early reoxygenation period, protected human myocardium, in vitro, against hypoxia–reoxygenation injury, at least in part, by the inhibition of mitochondrial permeability transition pore opening.

Delta opioid receptors in brain function and diseases

Evidence that the delta opioid receptor (DOR) is an attractive target for the treatment of brain disorders has strengthened in recent years. This receptor is broadly expressed in the brain, binds endogenous opioid peptides, and shows as functional profile highly distinct from those of mu and kappa opioid receptors. Our knowledge of DOR function has enormously progressed from in vivo studies using pharmacological tools and genetic approaches. The important role of this receptor in reducing chronic pain has been extensively overviewed; therefore this review focuses on facets of delta receptor activity relevant to psychiatric and other neurological disorders. Beneficial effects of DOR agonists are now well established in the context of emotional responses and mood disorders. DOR activation also regulates drug reward, inhibitory controls and learning processes, but whether delta compounds may represent useful drugs in the treatment of drug abuse remains open. Epileptogenic and locomotor-stimulating effects of delta agonists appear drug-dependent, and the possibility of biased agonism at DOR for these effects is worthwhile further investigations to increase benefit/risk ratio of delta therapies. Neuroprotective effects of DOR activity represent a forthcoming research area. Future developments in DOR research will benefit from in-depth investigations of DOR function at cellular and circuit levels.

DOR activation inhibits anoxic/ischemic Na+ influx through Na+ channels via PKC mechanisms in the cortex

Activation of delta-opioid receptors (DOR) is neuroprotective against hypoxic/ischemic injury in the cortex, which is at least partially related to its action against hypoxic/ischemic disruption of ionic homeostasis that triggers neuronal injury. Na(+) influx through TTX-sensitive voltage-gated Na(+) channels may be a main mechanism for hypoxia-induced disruption of K(+) homeostasis, with DOR activation attenuating the disruption of ionic homeostasis by targeting voltage-gated Na(+) channels. In the present study we examined the role of DOR in the regulation of Na(+) influx in anoxia and simulated ischemia (oxygen-glucose deprivation) as well as the effect of DOR activation on the Na(+) influx induced by a Na(+) channel opener without anoxic/ischemic stress and explored a potential PKC mechanism underlying the DOR action. We directly measured extracellular Na(+) activity in mouse cortical slices with Na(+) selective electrodes and found that (1) anoxia-induced Na(+) influx occurred mainly through TTX-sensitive Na(+) channels; (2) DOR activation inhibited the anoxia/ischemia-induced Na(+) influx; (3) veratridine, a Na(+) channel opener, enhanced the anoxia-induced Na(+) influx; this could be attenuated by DOR activation; (4) DOR activation did not reduce the anoxia-induced Na(+) influx in the presence of chelerythrine, a broad-spectrum PKC blocker; and (5) DOR effects were blocked by PKCβII peptide inhibitor, and PKCθ pseudosubstrate inhibitor, respectively. We conclude that DOR activation inhibits anoxia-induced Na(+) influx through Na(+) channels via PKC (especially PKCβII and PKCθ isoforms) dependent mechanisms in the cortex.

Hypoxic preconditioning attenuates global cerebral ischemic injury following asphyxial cardiac arrest through regulation of delta opioid receptor system

This study was designed to investigate whether delta opioid receptor (DOR) is involved in the neuroprotective effect induced by hypoxic preconditioning (HPC) in the asphyxial cardiac arrest (CA) rat model. Twenty-four hours after the end of 7-day HPC, the rats were subjected to 8-min asphyxiation and resuscitated with a standardized method. In the asphyxial CA rat model, HPC improved the neurological deficit score (NDS), inhibited neuronal apoptosis, and increased the number of viable hippocampal CA1 neurons at 24 h, 72 h, or 7 days after restoration of spontaneous circulation (ROSC); however, the above-mentioned neuroprotection of HPC was attenuated by naltrindole (a selective DOR antagonist). The expression of hypoxia-inducible factor-1α (HIF-1α) and DOR, and the content of leucine enkephalin (L-ENK) in the brain were also investigated after the end of 7-day HPC. HPC upregulated the neuronal expression of HIF-1α and DOR, and synchronously elevated the content of L-ENK in the rat brain. HIF-1α siRNA was used to further elucidate the relationship between HIF-1α and DOR in the HPC-treated brain. Knockdown of HIF-1α by siRNA markedly abrogated the HPC induced upregulation of HIF-1α and DOR. The present study demonstrates that the expression of DOR in the rat brain is upregulated by HIF-1α following exposure to 7-day HPC, at the same time, HPC also increases the production of endogenous DOR ligand L-ENK in the brain. DOR activation after HPC results in prolonged neuroprotection against subsequent global cerebral ischemic injury, suggesting a new mechanism of HPC-induced neuroprotection on global cerebral ischemia following CA and resuscitation.

Endogenous opiates and behavior: 2010

This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

RU486 (mifepristone) ameliorates cognitive dysfunction and reverses the down-regulation of astrocytic N-myc downstream-regulated gene 2 in streptozotocin-induced type-1 diabetic rats

Diabetic cognitive dysfunction (DCD), usually accompanied with chronically elevated glucocorticoids and hippocampal astrocytic alterations, is one of the most serious complications in patients with type-1 diabetes. However, the role for chronically elevated glucocorticoids and hippocampal astrocytic activations in DCD remains to be elucidated, and it is not clear whether astrocytic N-myc downstream-regulated gene 2 (NDRG2, involved in cell differentiation and development) participated in DCD. In the present study, three months after streptozotocin (STZ)-induced type-1 diabetes onset, rats showed cognitive impairments in Morris water maze test as well as elevated corticosterone level. Diabetic rats also presented down-regulation of glial fibrillary acidic protein (GFAP, a key indicator of astrocytic reactivity) and NDRG2 in hippocampus revealed by immunohistochemistry staining, real-time PCR and Western blot. Moreover, the diabetic cognitive impairments were ameliorated by 9-day glucocorticoids receptor (GR) blockade with RU486, and the down-regulation of hippocampal NDRG2 and GFAP in diabetic animals was also attenuated by 9-day GR blockade. These results suggest that glucocorticoids-GR system is crucial for DCD, and that astrocytic reactivity and NDRG2 are involved in these processes. Thus, inhibiting GR activation in the hippocampus may be a novel therapeutic strategy for treating DCD.

Ovarian hormones influence corticotropin releasing factor receptor colocalization with delta opioid receptors in CA1 pyramidal cell dendrites

Stress interacts with addictive processes to increase drug use, drug seeking, and relapse. The hippocampal formation (HF) is an important site at which stress circuits and endogenous opioid systems intersect and likely plays a critical role in the interaction between stress and drug addiction. Our prior studies demonstrate that the stress-related neuropeptide corticotropin-releasing factor (CRF) and the delta-opioid receptor (DOR) colocalize in interneuron populations in the hilus of the dentate gyrus and stratum oriens of CA1 and CA3. While independent ultrastructural studies of DORs and CRF receptors suggest that each receptor is found in CA1 pyramidal cell dendrites and dendritic spines, whether DORs and CRF receptors colocalize in CA1 neuronal profiles has not been investigated. Here, hippocampal sections of adult male and proestrus female Sprague-Dawley rats were processed for dual label pre-embedding immunoelectron microscopy using well-characterized antisera directed against the DOR for immunoperoxidase and against the CRF receptor for immunogold. DOR-immunoreactivity (-ir) was found presynaptically in axons and axon terminals as well as postsynaptically in somata, dendrites and dendritic spines in stratum radiatum of CA1. In contrast, CRF receptor-ir was predominantly found postsynaptically in CA1 somata, dendrites, and dendritic spines. CRF receptor-ir frequently was observed in DOR-labeled dendritic profiles and primarily was found in the cytoplasm rather than at or near the plasma membrane. Quantitative analysis of CRF receptor-ir colocalization with DOR-ir in pyramidal cell dendrites revealed that proestrus females and males show comparable levels of CRF receptor-ir per dendrite and similar cytoplasmic density of CRF receptor-ir. In contrast, proestrus females display an increased number of dual-labeled dendritic profiles and an increased membrane density of CRF receptor-ir in comparison to males. We further examined the functional consequences of CRF receptor-ir colocalization with DOR-ir in the same neuron using the hormone responsive neuronal cell line NG108-15, which endogenously expresses DORs, and assayed intracellular cAMP production in response to CRF receptor and DOR agonists. Results demonstrated that short-term application of DOR agonist SNC80 inhibited CRF-induced cAMP accumulation in NG108-15 cells transfected with the CRF receptor. These studies provide new insights on opioid-stress system interaction in the hippocampus of both males and females and establish potential mechanisms through which DOR activation may influence CRF receptor activity.

Effect of therapeutic hypothermia vs δ-opioid receptor agonist on post resuscitation myocardial function in a rat model of CPR

AIM

This study is to compare the effect of the δ-opioid receptor agonist, D-Ala(2)-D-Leu(5) enkephalin (DADLE) with normothermic control and therapeutic hypothermia on post resuscitation myocardial function and 72-h survival in a rat model of cardiac arrest and resuscitation.

METHODS

Ventricular fibrillation (VF) was induced in 15 male Sprague-Dawley rats. After 8 min of untreated VF, cardiopulmonary resuscitation was performed for 8 min before defibrillation. Animals were randomized to three groups of five: (a) normothermia; (b) hypothermia (32 °C); and (c) normothermia with DADLE intravenous infusion (1 mg/kg h(-1)). Hypothermia and drug infusion were started after successful defibrillation. Myocardial functions, including cardiac output (CO), left ventricular ejection fraction (LVEF), and myocardial performance index (MPI) were measured echocardiographically together with duration of survival.

RESULTS

The 72-h survival was significantly greater in the hypothermic group than in both DADLE and normothermic group (p = 0.02). However, the survival time of the DADLE treated animals was significantly longer than that of the normothermia group (51.8 ± 18.9 vs 18.8 ± 10.1h, p < 0.01). DADLE group showed significantly better CO (PR 60 min, p = 0.049), better LVEF (PR 60 min, p = 0.044; PR 240 min, p < 0.001) and lower MPI (PR 60 min, p = 0.043; PR 240 min, p = 0.045) than normothermic group. Hypothermia group also showed significantly better CO (PR 60m in, p = 0.044; PR 240 min, p = 0.007), better LVEF (PR 60 min, p = 0.001; PR 240 min, p < 0.001) and lower MPI (PR 60 min, p = 0.003; PR 240 min, p = 0.012) than the normothermic group.

CONCLUSIONS

DADLE attenuated post resuscitation myocardial dysfunction and increased short term survival time. However, the 72-h survival in the DADLE group was less than that in the hypothermia group.