The effect of hypothermia on induction of heat shock protein (HSP)-72 in ischemic brain

Pharmacokinetics during therapeutic hypothermia in neonates: from pathophysiology to translational knowledge and physiologically-based pharmacokinetic (PBPK) modeling

INTRODUCTION

Perinatal asphyxia (PA) still causes significant morbidity and mortality. Therapeutic hypothermia (TH) is the only effective therapy for neonates with moderate to severe hypoxic-ischemic encephalopathy after PA. These neonates need additional pharmacotherapy, and both PA and TH may impact physiology and, consequently, pharmacokinetics (PK) and pharmacodynamics (PD).

AREAS COVERED

This review provides an overview of the available knowledge in PubMed (until November 2022) on the pathophysiology of neonates with PA/TH. In vivo pig models for this setting enable distinguishing the effect of PA versus TH on PK and translating this effect to human neonates. Available asphyxia pig models and methodological considerations are described. A summary of human neonatal PK of supportive pharmacotherapy to improve neurodevelopmental outcomes is provided.

EXPERT OPINION

To support drug development for this population, knowledge from clinical observations (PK data, real-world data on physiology), preclinical (in vitro and in vivo (minipig)) data, and molecular and cellular biology insights can be integrated into a predictive physiologically-based PK (PBPK) framework, as illustrated by the I-PREDICT project (Innovative physiology-based pharmacokinetic model to predict drug exposure in neonates undergoing cooling therapy). Current knowledge, challenges, and expert opinion on the future directions of this research topic are provided.

HSP70-mediated neuroprotection by combined treatment of valproic acid with hypothermia in a rat asphyxial cardiac arrest model

It has been reported that valproic acid (VPA) combined with therapeutic hypothermia can improve survival and neurologic outcomes in a rat asphyxial cardiac arrest model. However, neuroprotective mechanisms of such combined treatment of valproic acid with hypothermia remains unclear. We hypothesized that epigenetic regulation of HSP70 by histone acetylation could increase HSP70-mediated neuroprotection suppressed under hypothermia. Male Sprague-Dawley rats that achieved return of spontaneous circulation (ROSC) from asphyxial cardiac arrest were randomized to four groups: normothermia (37°C ± 1°C), hypothermia (33°C ± 1°C), normothermia + VPA (300 mg/kg IV initiated 5 minutes post-ROSC and infused over 20 min), and hypothermia + VPA. Three hours after ROSC, acetyl-histone H3 was highly expressed in VPA-administered groups (normothermia + VPA, hypothermia + VPA). Four hours after ROSC, HSP70 mRNA expression levels were significantly higher in normothermic groups (normothermia, normothermia + VPA) than in hypothermic groups (hypothermia, hypothermia + VPA). The hypothermia + VPA group showed significantly higher HSP70 mRNA expression than the hypothermia group. Similarly, at five hours after ROSC, HSP70 protein levels were significantly higher in normothermic groups than in hypothermic groups. HSP70 levels were significantly higher in the hypothermia + VPA group than in the hypothermia group. Only the hypothermia + VPA group showed significantly attenuated cleaved caspase-9 levels than the normothermia group. Hypothermia can attenuate the expression of HSP70 at transcriptional level. However, VPA administration can induce hyperacetylation of histone H3, leading to epigenetic transcriptional activation of HSP70 even in a hypothermic status. Combining VPA treatment with hypothermia may compensate for reduced activation of HSP70-mediated anti-apoptotic pathway.

Therapeutic Hypothermia and Neuroprotection in Acute Neurological Disease

Therapeutic hypothermia has consistently been shown to be a robust neuroprotectant in many labs studying different models of neurological disease. Although this therapy has shown great promise, there are still challenges at the clinical level that limit the ability to apply this routinely to each pathological condition. In order to overcome issues involved in hypothermia therapy, understanding of this attractive therapy is needed. We review methodological concerns surrounding therapeutic hypothermia, introduce the current status of therapeutic cooling in various acute brain insults, and review the literature surrounding the many underlying molecular mechanisms of hypothermic neuroprotection. Because recent work has shown that body temperature can be safely lowered using pharmacological approaches, this method may be an especially attractive option for many clinical applications. Since hypothermia can affect multiple aspects of brain pathophysiology, therapeutic hypothermia could also be considered a neuroprotection model in basic research, which would be used to identify potential therapeutic targets. We discuss how research in this area carries the potential to improve outcome from various acute neurological disorders.

Effects of graded hypothermia on hypoxic-ischemic brain damage in the neonatal rat

OBJECTIVE

To investigate the effect of graded hypothermia on neuropathologic alterations of neonatal rat brain after exposed to hypoxic-ischemic insult at 37°C, 33°C, 31°C, and 28°C, respectively, and to observe the effect of hypothermia on 72-kDa heat shock protein (HSP72) expression after hypoxic-ischemic insult.

METHODS

Seven days old Wistar rats were subjected to unilateral common carotid artery ligation followed by exposure to hypoxia in 8% oxygen for 2 hours at 37°C, 33°C, 31°C, and 28°C, respectively. The brain temperature was monitored indirectly by inserting a mini-thermocouple probe into the temporal muscle during hypoxia. After hypoxia-ischemia their mortality was assessed. Neuronal damage was assessed with HE staining 72 hours after hypoxia. HSP72 expression at 0.5, 24, and 72 hours of recovery was immunohistochemically assessed using a monoclonal antibody to HSP72.

RESULTS

Hypoxia-ischemia caused 10.5% (2/19) of mortality in rat of 37°C group, but no death occurred in 33°C, 31°C or 28°C groups. HE staining showed neuropathologic damage was extensive in rats exposed to hypoxia-ischemia at 37°C (more than 80.0%). The incidence of severe brain damage was significantly decreased in 33°C (53.3%) and 31°C groups (44.4%), and no histologic injury was seen in the 28°C group of rats. Expression of HSP72 was manifest and persistent in the rat brain of 37°C group, but minimum in the rat brain of 28°C group.

CONCLUSION

Mild and moderate hypothermia might prevent cerebral visible neuropathologic damage associated with hypoxic-ischemic injury by decreasing stress response.

Critical care of traumatic spinal cord injury

Approximately 11 000 people suffer traumatic spinal cord injury (TSCI) in the United States, each year. TSCI incidences vary from 13.1 to 52.2 per million people and the mortality rates ranged from 3.1 to 17.5 per million people. This review examines the critical care of TSCI. The discussion will focus on primary and secondary mechanisms of injury, spine stabilization and immobilization, surgery, intensive care management, airway and respiratory management, cardiovascular complication management, venous thromboembolism, nutrition and glucose control, infection management, pressure ulcers and early rehabilitation, pharmacologic cord protection, and evolving treatment options including the use of pluripotent stem cells and hypothermia.

Management of brain injury after resuscitation from cardiac arrest

The devastating neurologic injury in survivors of cardiac arrest has been recognized since the development of modern resuscitation techniques. After numerous failed clinical trials, two trials showed that induced mild hypothermia can ameliorate brain injury and improve survival and functional neurologic outcome in comatose survivors of out-of-hospital cardiac arrest. This article provides a comprehensive review of the advances in the care of brain injury after cardiac arrest, with updates on the process of prognostication, the use of therapeutic hypothermia and adjunctive intensive care unit care for cardiac arrest survivors.

Intensive care for brain injury after cardiac arrest: therapeutic hypothermia and related neuroprotective strategies

Neurologic injury is the predominant cause of poor functional outcome in patients who are resuscitated from cardiac arrest. The management of these patients in the ICU can be challenging because of the paucity of effective therapies and lack of readily available diagnostic and prognostic tools. After several decades of failed pharmacologic neuroprotection trials, recent and well-designed randomized trials showed that therapeutic hypothermia is an effective neuroprotective measure in comatose survivors of cardiac arrest. Therapeutic hypothermia has been recommended by the International Liaison Committee on Resuscitation and has been incorporated in the American Heart Association CPR Guidelines. The American Academy of Neurology recently enhanced the delivery of care in survivors of cardiac arrest by providing evidence-based practice parameters on the prediction of poor outcome in comatose survivors of cardiac arrest, based on clinical evaluation and diagnostic tests. This article discusses these advances and their potential impact on the care provided in the ICU.

Quantitative EEG and neurological recovery with therapeutic hypothermia after asphyxial cardiac arrest in rats

We test the hypothesis that quantitative electroencephalogram (qEEG) can be used to objectively assess functional electrophysiological recovery of brain after hypothermia in an asphyxial cardiac arrest rodent model. Twenty-eight rats were randomly subjected to 7-min (n = 14) and 9-min (n = 14) asphyxia times. One half of each group (n = 7) was randomly subjected to hypothermia (T = 33 degrees C for 12 h) and the other half (n = 7) to normothermia (T = 37 degrees C). Continuous physiologic monitoring of blood pressure, EEG, and core body temperature monitoring and intermittent arterial blood gas (ABG) analysis was undertaken. Neurological recovery after resuscitation was monitored using serial Neurological Deficit Score (NDS) calculation and qEEG analysis. Information Quantity (IQ), a previously validated measure of relative EEG entropy, was employed to monitor electrical recovery. The experiment demonstrated greater recovery of IQ in rats treated with hypothermia compared to normothermic controls in both injury groups (P < 0.05). The 72-h NDS of the hypothermia group was also significantly improved compared to the normothermia group (P < 0.05). IQ values measured at 4 h had a strong correlation with the primary neurological outcome measure, 72-h NDS score (Pearson correlation 0.746, 2-tailed significance <0.001). IQ is sensitive to the acceleration of neurological recovery as measured NDS after asphyxial cardiac arrest known to occur with induced hypothermia. These results demonstrate the potential utility of qEEG-IQ to track the response to neuroprotective hypothermia during the early phase of recovery from cardiac arrest.

Cold as a therapeutic agent

The use of cold as a therapeutic agent has a long and colorful history. The Edwin Smith Papyrus, the most ancient medical text known, dated 3500 B.C., made numerous references to the use of cold as therapy. Baron de Larrey, a French army surgeon during Napoleon's Russian campaign, packed the limbs in ice prior to amputations to render the procedures painless. In the early twentieth century, a neurosurgeon, Temple Fay, pioneered "human refrigeration" as a treatment for malignancies and head injuries. In 1961, Irving Cooper developed the first closed cryoprobe system and ushered in the modern era of cryogenic surgery with his imperturbable convictions. Fay's early work fell victim to the disruptive sequel of the World War II. The Nazis confiscated his data (presented before the Third International Cancer Congress in 1939) forwarded to Belgium for publication and brutally applied his refrigeration techniques experimentally without any benefit of anesthesia in the concentration camps, especially Dachau. Hypothermia became associated in the public mind with the atrocities exposed at the war trials in Nürnberg. After lying dormant for decades, the interest was rekindled in the late 80s when mild hypothermia was shown to confer dramatic neuroprotection in a number of experimental models of brain injury. With several large multi-center clinical studies currently under way, hypothermia is receiving unprecedented attention from the medical and scientific communities.

Effect of intra-ischemic hypothermia on the expression of c-Fos and c-Jun, and DNA binding activity of AP-1 after focal cerebral ischemia in rat brain

It is unknown whether immediate early gene (IEG) induction and subsequent late gene regulation after ischemia is beneficial or deleterious. The aim of this study was to examine the effect of hypothermia on expression of c-Fos and c-Jun, and AP-1 DNA binding activity, after transient focal cerebral ischemia in rat brain, and clarify the role of IEGs and AP-1 after insults. Male Wistar rats underwent right middle cerebral artery occlusion for 1 h with the intraluminal suture method. During ischemia, animals were assigned to either normothermic (NT) or hypothermic (HT) groups. In the NT group, brain temperature was observed to spontaneously increase to 40 degrees C during ischemia. In the HT group, brain temperature decreased to 30 degrees C. Infarct volume in cortex was decreased in the HT group, compared with that in the NT group (P<0.001). Increased c-Fos immunoreactivity in the cortex was observed at 3 h after reperfusion in the HT, but not the NT group, while c-Jun expression was not affected by HT treatment. There was also a significant increase in AP-1 DNA binding activity at 3 h in the HT group when compared to the NT group (P<0.01). In conclusion, hypothermia decreased cerebral infarction in association with early increases in c-Fos expression and AP-1 DNA binding activity in peri-infarct cortex. It remains to be established whether such responses are a cause or consequence of cell survival, but these results clearly establish that altered transcription is a key feature of tissue spared following hypothermic focal ischemia.

Mild hypothermia increases Bcl-2 protein expression following global cerebral ischemia

Mild hypothermia protects the brain against experimental ischemia, but the reasons are not well known. We examined whether the protective effects of mild hypothermia could be correlated with alterations in expression of Bcl-2, an anti-apoptotic protein in a rat model of transient global ischemia. Following 10 min of forebrain ischemia, hippocampal neurons were examined 72 h later for survival, expression of Bcl-2 family proteins and apoptosis. Intraischemic mild hypothermia was applied for 3 h (33 degrees C, isch-33) or normal body temperature was maintained (37 degrees C, isch-37). Survival of CA1 neurons was significantly improved in the isch-33 group compared to the isch-37 group (90 vs. 53% survival; P<0.01). The proportion of Bcl-2-positive cells among surviving CA1 neurons in the isch-33 group was increased compared to that of sham and isch-37 groups (P<0.01). Bax expression in CA1 was no different between sham and isch-33 groups, but was significantly decreased in isch-37 (P<0.05). TUNEL staining was positive in many isch-37 CA1 neurons, but absent in isch-33. Utilizing electron microscopy, more cells meeting criteria for apoptosis were observed in the isch-37 than isch-33. These data suggest that mild hypothermia attenuates apoptotic death, and that this protection may be related to increases in Bcl-2.

Establishment of a local cooling model against spinal cord ischemia representing prolonged induction of heat shock protein

OBJECTIVES

Paraplegia is one of the serious complications of thoracoabdominal aortic operations. Regional hypothermia protects against spinal cord ischemia although the protective mechanism remains unknown. We attempted to create a simple model of local cooling under transient spinal cord ischemia and evaluated the effect using functional and histologic findings.

METHODS

Male domesticated rabbits were divided into 3 groups: control, normothermic group (group N), and local hypothermic group (group H). A balloon catheter was used for spinal cord ischemia by abdominal aortic clamping. A cold pack attached to the lumbar region could lower the regional cord temperature initially. Neurologic function was evaluated by the Johnson score. Cell damage was analyzed by observing motor neurons with the use of hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated deoxy-uracil triphosphate biotin in situ nick end labeling (TUNEL), and immunoreactivity of heat shock protein.

RESULTS

Physiologic estimation showed that local hypothermia improved the functional deficits (group N, 1.3 +/- 0.9; group H, 4.9 +/- 0.3; P =.0020). Seven days after reperfusion, there was a significant difference in the motor neuron numbers between groups N and H (group N, 7.2 +/- 1.9; group H, 20.4 +/- 3.2; P =.0090). The number of TUNEL-positive motor neurons was reduced significantly (group N, 7.2 +/- 2.4; group H, 1.0 +/- 0.7; P =.0082). Heat shock protein immunoreactivity was prolonged up to 2 days after reperfusion in the hypothermic group.

CONCLUSIONS

These results suggest that local hypothermia extended the production of heat shock protein in spinal cord motor neurons after reperfusion and inhibited their apoptotic change.

Mild hypothermia decreases the incidence of transient ADC reduction detected with diffusion MRI and expression of c-fos and hsp70 mRNA during acute focal ischemia in rats

The effects of mild hypothermia on the apparent diffusion coefficient of water (ADC) and expression of c-fos and hsp70 mRNA were examined during acute focal cerebral ischemia. Young adult rats were subjected to 60-min middle cerebral artery occlusion under either normothermia (37.5 degrees C) or hypothermia (33 degrees C). Diffusion-weighted echo-planar magnetic resonance imaging was used to monitor changes in ADC throughout the ischemic period. Perfusion MRI with dysprosium contrast was used at the end of the ischemic period to verify that the occlusion was successful. C-fos and hsp70 mRNA expression were examined with in situ hybridization at the end of the ischemic period. The results indicate that the size of the region that exhibited reduced ADC was smaller during hypothermia than during normothermia. Hypothermia also decreased the frequency of occurrence of transient ADC reductions, especially in dorsal aspects of cortex. Expression of both c-fos and hsp70 mRNA were markedly reduced by hypothermia. Transient ADC reduction and c-fos expression are associated with spreading depression, which is believed to contribute to lesion expansion during acute focal ischemia. The results suggest that part of the neuroprotective effect of hypothermia may be due to a reduced incidence of spreading depression.

Temperature threshold and preservation of signaling for mitochondrial membrane proteins during ischemia in rabbit heart

Temperature modulates both myocardial energy requirements and production. We have previously demonstrated that myocardial protection induced by hypothermic adaptation preserves expression of genes regulating heat shock protein and the nuclear-encoded mitochondrial proteins, the adenine nucleotide translocator isoform 1 (ANT1), and the beta subunit of F1-ATPase (beta F1-ATPase). This preservation is associated with a reduction in ATP depletion similar to that noted in cardioplegic arrested hearts preserved at a critical temperature (30 degrees C) or below. We tested the hypothesis that expression of these genes may also be subject to this temperature threshold phenomenon. Isolated perfused rabbit hearts were subjected to ischemic cardioplegic arrest at 4, 30, or 34 degrees C for 120 min. Cardiac function indices and steady-state mRNA levels for ANT1, beta F1-ATPase, and HSP70-1 were measured prior to ischemia (B) and after 45 min of reperfusion. Cardiac function was significantly depressed in the 34 degrees C group. Ischemia at 34 degrees C reduced steady-state mRNA levels for ANT1 and beta F1-ATPase from B, but these levels were similarly preserved at 4 and 30 degrees C. HSP70-1 levels were mildly elevated (fourfold) above B to similar levels at all three temperatures. These results indicate that mRNA expression for ANT1 and beta F1-ATPase is specifically preserved in a pattern consistent with the temperature threshold phenomenon. HSP70-1 expression is not influenced by ischemic temperature. Preservation of gene expression for these mitochondrial proteins implies that signaling for mitochondrial biogenesis or resynthesis is maintained after ischemic insult.

Hypothermia preserves function and signaling for mitochondrial biogenesis during subsequent ischemia

Hypothermia is known to protect myocardium during ischemia, but its role in induction of a protective stress response before ischemia has not been evaluated. As cold incites stress responses in other tissues, including heat shock protein induction and signaling mitochondrial biogenesis, we postulated that hypothermia in perfused hearts would produce similar phenomena while reducing injury during subsequent ischemia. Studies were performed in isolated perfused rabbit hearts (n = 77): a control group (C) and a hypothermic group (H) subjected to decreasing infusate temperature from 37 to 31 degrees C over 20 min. Subsequent ischemia during cardioplegic arrest at 34 degrees C for 120 min was followed by reperfusion. At 15 min of reperfusion, recovery of left ventricular developed pressure (LVDP), maximum first derivative of left ventricular pressure (LV dP/dtmax), LV -dP/dtmax, and the product of heart rate and LVDP was significantly increased in H (P < 0.01) compared with C hearts. Ischemic contracture started later in H (97.5 +/- 3.6 min) than in C (67.3 +/- 3.3 min) hearts. Myocardial ATP preservation and repletion during ischemia and reperfusion were higher in H than in C hearts. mRNA levels of the nuclear-encoded mitochondrial proteins adenine nucleotide translocase isoform 1 (ANT1) and beta-F1-adenosine-triphosphatase (beta-F1-ATPase) normalized to 28S RNA decreased in C hearts but were preserved in H hearts after reperfusion. Inducible heat shock protein (HSP70-1) mRNA was elevated nearly 4-fold after ischemia in C hearts and 12-fold in H hearts. These data indicate that hypothermia preserves myocardial function and ATP stores during subsequent ischemia and reperfusion. Signaling for mitochondrial biogenesis indexed by ANT1 and beta-F1-ATPase mRNA levels is also preserved during a marked increase in HSP70-1 mRNA.

Noninvasive cerebral cooling in a swine model of cardiac arrest

OBJECTIVE

Mild cerebral hypothermia improves neurologic outcome in animals resuscitated from cardiac arrest. This study examined whether one practical external cooling method, i.e., local application of ice to the heads and necks of swine, during resuscitation induces cerebral cooling.

METHODS

Local external cerebral cooling was examined in a prospective laboratory investigation using 24 female swine in a model of cardiac arrest. The swine were randomized into hypothermia and normothermia groups. Intracerebral temperature was measured in the parietal cortex. Eight minutes after induction of ventricular fibrillation, chest compressions and mechanical ventilation were initiated. The hypothermia group was treated with 1,500 mL of ice in plastic bags applied to the head and neck, while the normothermia group received no extra interventions. Data were analyzed using repeated-measures ANOVA.

RESULTS

In the normothermia group, there was no significant change in nasopharyngeal (-0.8 +/- 0.6 degree C), intracerebral (-0.6 +/- 0.8 degree C), or esophageal (-0.2 +/- 0.6 degree C) temperatures during 20 minutes of resuscitation. However, in the hypothermia group, application of ice during resuscitation significantly reduced nasopharyngeal (-2.9 +/- 1.4 degrees C), intracerebral (-2.1 +/- 0.6 degrees C), and esophageal (-1.4 +/- 0.8 degrees C) temperatures.

CONCLUSIONS

External application of ice packs during resuscitation effectively reduced intracerebral temperatures in swine by an amount that improved neurologic outcomes in previous large animal studies. These data suggest that clinically significant cerebral cooling could be accomplished with a noninvasive, inexpensive, and universally available intervention. Further studies are required to assess the clinical feasibility and therapeutic efficacy of this intervention.

GFAP-immunoreactivity following hypothermic forebrain ischemia

This study investigated the effect of intra-ischemic hypothermia on astroglial reactions in the hippocampus following cerebral ischemia. Mongolian gerbils were subjected to forebrain ischemia by bilateral carotid occlusion of 10 min at a) 30 degrees C and b) 37 degrees C followed by normothermic reperfusion ranging from 1 to 3 days (d). The astrocytes were visualized by immunostaining against glial fibrillary acidic protein (GFAP), and neuronal injury was evaluated by using hematoxylin-eosin staining. In normothermic brains, reactive astrocytosis was noted in 1 and 2 d postischemic animals, becoming prominent in the 3 d postischemic group. Intense GFAP-positive cells with thickened processes were noted in all regions of the hippocampus, especially the CA1 region. These cells were seen to have migrated toward the stratum pyramidale which was normally devoid of such staining. Hypothermia significantly inhibited the GFAP-upregulation seen 3 d after normothermic ischemia. There was no significant neuronal damage in the 3 d hypothermic ischemic group. Since glial cell activation, as evidenced by GFAP-upregulation, precedes as well as accompanies neuronal damage, and since hypothermia, known to be neuroprotective, inhibits glial cell activation in the 3 d postischemic brain, it appears that glial cells play critical roles in neuronal survival or death following ischemia.

Expression of c-fos and fos-B proteins following transient forebrain ischemia: effect of hypothermia

Immediate early genes are induced by transient global ischemia. Using immunohistochemistry we studied the effect of intraischemic hypothermia (30 degrees C) on the expression of c-fos and fos-B proteins following 10 min forebrain ischemia in the gerbil. Postischemia (PI) periods of 1 hour (h), 6 h, 1 day (d) and 2 d and nonischemic controls were examined in normothermic and hypothermic brains. In normothermic ischemic brains, marked expression of c-fos occurred in the dentate gyrus after 1 h PI which extended to CA2-4 regions by 6 h. Hypothermia hastened the time course of c-fos expression as it was expressed simultaneously in the dentate gyrus as well as CA2-4 regions after only 1 h, and by 6 h the expression remained only in the CA2-4 regions and not the dentate gyrus in hypothermic ischemic brains. There was no difference in its expression between normothermic and hypothermic brains in the 1 d and 2 d PI animals. Somewhat similar changes were noted in fos-B expression. In normothermic ischemic brains fos-B was induced in the dentate gyrus by 1 h PI, and by 6 h it extended to involve CA1-4 cells. The hypothermic ischemic brains showed faster induction of fos-B so that the dentate gyrus as well as CA1-4 regions were immunopositive at 1 h PI. There was no difference in its expression between normothermic and hypothermic brains in the subsequent PI periods of 6 h, 1 d and 2 d. The shift towards faster sequential induction of these genes by hypothermia in ischemic brains may be indicative of preservation of or faster recovery of mechanisms involved in intracellular signalling.