Effect of valproic acid combined with therapeutic hypothermia on neurologic outcome in asphyxial cardiac arrest model of rats

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.

Dose optimization of early high-dose valproic acid for neuroprotection in a swine cardiac arrest model

Aim

High-dose valproic acid (VPA) improves the survival and neurologic outcomes after asphyxial cardiac arrest (CA) in rats. We characterized the pharmacokinetics, pharmacodynamics, and safety of high-dose VPA in a swine CA model to advance clinical translation.

Methods

After 8 ​min of untreated ventricular fibrillation CA, 20 male Yorkshire swine were resuscitated until return of spontaneous circulation (ROSC). They were block randomized to receive placebo, 75 ​mg/kg, 150 ​mg/kg, or 300 ​mg/kg VPA as 90-min intravenous infusion (n ​= ​5/group) beginning at ROSC. Animals were monitored for 2 additional hours then euthanized. Experimental operators were blinded to treatments.

Results

The mean(SD) total CA duration was 14.8(1.2) minutes. 300 ​mg/kg VPA animals required more adrenaline to maintain mean arterial pressure ≥80 ​mmHg and had worse lactic acidosis. There was a strong linear correlation between plasma free VPA C_max and brain total VPA (r² ​= ​0.9494; p ​< ​0.0001). VPA induced dose-dependent increases in pan- and site-specific histone H3 and H4 acetylation in the brain. Plasma free VPA C_max is a better predictor than peripheral blood mononuclear cell histone acetylation for brain H3 and H4 acetylation (r² ​= ​0.7189 for H3K27ac, r² ​= ​0.7189 for pan-H3ac, and r² ​= ​0.7554 for pan-H4ac; p ​< ​0.0001).

Conclusions

Up to 150 ​mg/kg VPA can be safely tolerated as 90-min intravenous infusion in a swine CA model. High-dose VPA induced dose-dependent increases in brain histone H3 and H4 acetylation, which can be predicted by plasma free VPA C_max as the pharmacodynamics biomarker for VPA target engagement after CA.

Histone Deacetylase Inhibitors: A Novel Strategy for Neuroprotection and Cardioprotection Following Ischemia/Reperfusion Injury

Ischemia/reperfusion injury is a complex molecular cascade that causes deleterious cellular damage and organ dysfunction. Stroke, sudden cardiac arrest, and acute myocardial infarction are the most common causes of ischemia/reperfusion injury without effective pharmacologic therapies. Existing preclinical evidence suggests that histone deacetylase inhibitors may be an efficacious, affordable, and clinically feasible therapy that can improve neurologic and cardiac outcomes following ischemia/reperfusion injury. In this review, we discuss the pathophysiology and epigenetic modulations of ischemia/reperfusion injury and focus on the neuroprotective and cardioprotective effects of histone deacetylase inhibitors. We also summarize the protective effects of histone deacetylase inhibitors for other vital organs and highlight the key research priorities for their successful translation to the bedside.

TBHQ improved neurological recovery after traumatic brain injury by inhibiting the overactivation of astrocytes

Traumatic brain injury (TBI) is a major leading cause of death and long-term disability. Although astrocytes play a key role in neuroprotection after TBI in the early stage, the overactivation of astrocytes can lead to long-term functional deficits, and the underlying pathophysiological mechanisms remain unclear. In addition, it is unknown whether the nuclear factor erythroid 2-related factor2/haem oxygenase-1 (Nrf-2/HO-1) pathway could elicit a neuroprotective effect by decreasing astrocyte overactivation after TBI. We aimed to study the effects of tert-butylhydroquinone (TBHQ) in reducing astrocyte overactivation after TBI and explored the underlying mechanisms. We first established a controlled cortical impact (CCI) model in rats and performed Haematoxylin and eosin (H&E) staining to observe brain tissue damage. The cognitive function of rats was assessed by modified neurological severity scoring (mNSS) and Morris water maze (MWM) test. Astrocyte and microglia activation was detected by immunofluorescence staining. Oxidative stress conditions were investigated using Western blotting. An enzyme-linked immunosorbent assay (ELISA) was designed to assess the level of the proinflammatory factor tumour necrosis factor-alpha (TNF-α). Dihydroethidium (DHE) staining was used to detect reactive oxygen species (ROS). Apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The results showed that the administration of TBHQ ameliorated motor function and cognitive deficits and decreased the lesion volume. In addition, TBHQ significantly decreased astrocyte overactivation, diminished the pro-inflammatory phenotype M1 and inflammatory cytokines production after TBI, increased Nrf-2 nuclear accumulation, and enhanced the levels of the Nrf-2 downstream antioxidative genes HO-1 and NADPH-quinone oxidoreductase-1 (NQO-1). Furthermore, TBHQ treatment alleviated apoptosis and neuronal death in the cerebral cortex. Overall, our data indicated that the upregulation of Nrf-2 expression could enhance neuroprotection and decrease astrocyte overactivation and might represent a new theoretical basis for treating TBI.

Systematic review and meta-analysis of experimental studies evaluating the organ protective effects of histone deacetylase inhibitors

The clinical efficacy of organ protection interventions are limited by the redundancy of cellular activation mechanisms. Interventions that target epigenetic mechanisms overcome this by eliciting genome wide changes in transcription and signaling. We aimed to review preclinical studies evaluating the organ protection effects of histone deacetylase inhibitors (HDACi) with a view to informing the design of early phase clinical trials. A systematic literature search was performed. Methodological quality was assessed against prespecified criteria. The primary outcome was mortality, with secondary outcomes assessing mechanisms. Prespecified analyses evaluated the effects of likely moderators on heterogeneity. The analysis included 101 experimental studies in rodents (n = 92) and swine (n = 9), exposed to diverse injuries, including: ischemia (n = 72), infection (n = 7), and trauma (n = 22). There were a total of 448 comparisons due to the evaluation of multiple independent interventions within single studies. Sodium valproate (VPA) was the most commonly evaluated HDACi (50 studies, 203 comparisons). All of the studies were judged to have significant methodological limitations. HDACi reduced mortality in experimental models of organ injury (risk ratio = 0.52, 95% confidence interval 0.40-0.68, p < 0.001) without heterogeneity. HDACi administration resulted in myocardial, brain and kidney protection across diverse species and injuries that was attributable to increases in prosurvival cell signaling, and reductions in inflammation and programmed cell death. Heterogeneity in the analyses of secondary outcomes was explained by differences in species, type of injury, HDACi class (Class I better), drug (trichostatin better), and time of administration (at least 6 hours prior to injury better). These findings highlight a potential novel application for HDACi in clinical settings characterized by acute organ injury.

Targeted Temperature Management in Brain Injured Patients

Evidence from animal models indicates that lowering temperature by a few degrees can produce substantial neuroprotection. In humans, hypothermia has been found to be neuroprotective with a significant impact on mortality and long-term functional outcome only in cardiac arrest and neonatal hypoxic-ischemic encephalopathy. Clinical trials have explored the potential role of maintaining normothermia and treating fever in critically ill brain injured patients. This review concentrates on basic concepts to understand the physiologic interactions of thermoregulation, effects of thermal modulation in critically ill patients, proposed mechanisms of action of temperature modulation, and practical aspects of targeted temperature management.

Targeted Temperature Management in Brain Injured Patients

Evidence from animal models indicates that lowering temperature by a few degrees can produce substantial neuroprotection. In humans, hypothermia has been found to be neuroprotective with a significant impact on mortality and long-term functional outcome only in cardiac arrest and neonatal hypoxic-ischemic encephalopathy. Clinical trials have explored the potential role of maintaining normothermia and treating fever in critically ill brain injured patients. This review concentrates on basic concepts to understand the physiologic interactions of thermoregulation, effects of thermal modulation in critically ill patients, proposed mechanisms of action of temperature modulation, and practical aspects of targeted temperature management.

Flurbiprofen axetil attenuates cerebral ischemia/reperfusion injury by reducing inflammation in a rat model of transient global cerebral ischemia/reperfusion

Ischemic stroke has been ranked as the second cause of death in patients worldwide. Inflammation which is activated during cerebral ischemia/reperfusion (I/R) is an important mechanism leading to brain injury. The present study aimed to investigate the effect of flurbiprofen axetil on cerebral I/R injury and the role of inflammation in this process. Rats were subjected to sham operation or global cerebral I/R with or without flurbiprofen axetil (5 or 10 mg/kg). Global cerebral ischemia was achieved by occlusion of bilateral common carotid arteries combined with hypotension for 20 min followed by reperfusion for 72 h. Then the neurological deficit score, hippocampal cell apoptosis, levels of aquaporin (AQP) 4, AQP9, intercellular cell adhesion molecule-1 (ICAM-1), nuclear factor-κB (NF-κB), tumor necrosis factor (TNF-α), interleukin-1 β (IL-1β), thromboxane B2 (TXB2), and 6-keto-PGI1α were assessed. After reperfusion, neurological deficit score was significantly increased accompanied by severe neuronal damage (exacerbated morphological deficit, increased terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay (TUNEL)-positive cells and cleaved caspase-3 protein expression in hippocampal CA1 region). Cerebral I/R injury also enhanced expressions of TNF-α, IL-1β, NF-κB, AQP4 and AQP9 as well as TXB2 and TXB2/6-keto-PGI1α. All these changes were reversed by pretreatment with flurbiprofen axetil. Flurbiprofen axetil protects the brain from cerebral I/R injury through reducing inflammation and brain edema.

Valproic Acid Combined With Postcardiac Arrest Hypothermic-Targeted Temperature Management Prevents Delayed Seizures and Improves Survival in a Rat Cardiac Arrest Model

OBJECTIVES

High-dose valproic acid in combination with hypothermic-targeted temperature management has been reported to synergistically improve neurologic outcomes after cardiac arrest. This study investigated the potential synergistic mechanisms.

DESIGN

Prospective, randomized, experimental study.

SETTING

University research institution.

SUBJECTS

Male Long Evans rats.

INTERVENTION

Rats resuscitated from asphyxial cardiac arrest were randomized to one of the three groups: normothermic-targeted temperature management (37°C ± 1°C), hypothermic-targeted temperature management (33° ± 1° × 24 hr + placebo infusion), hypothermic-targeted temperature management plus high-dose valproic acid (300 mg/kg IV × 1 initiated 5 min post return of spontaneous circulation and infused over 20 min) (hypothermic-targeted temperature management + valproic acid).

MEASUREMENTS AND MAIN RESULTS

Seventy-two-hour survival was significantly greater with hypothermic-targeted temperature management + valproic acid, compared to hypothermic-targeted temperature management and normothermic-targeted temperature management (p < 0.05). Survival with good neurologic function, neurodegeneration, expression of HSP70, phosphorylation of Akt and Erk1/2 were not significantly different between hypothermic-targeted temperature management and hypothermic-targeted temperature management + valproic acid. The prevalence of seizures during the first 72-hour postcardiac arrest was significantly lower with hypothermic-targeted temperature management + valproic acid compared to hypothermic-targeted temperature management and normothermic-targeted temperature management (p = 0.01).

CONCLUSIONS

High-dose valproic acid combined with hypothermic-targeted temperature management prevents postcardiac arrest seizures and improves survival. It remains to be determined if the mechanism of seizure prevention is through the antiepileptic effect of valproic acid or direct neuroprotection. Overall, the combination of high-dose valproic acid and hypothermic-targeted temperature management remains a promising strategy to improve cardiac arrest outcomes.