Prolonged drug-induced hypothermia in experimental stroke

N-acetyl aspartate levels early after ischemic stroke accurately reflect long-term brain damage

Background

Estimation of brain damage following an ischemic stroke is most often performed within the first few days after the insult, where large amounts of oedematous fluid have accumulated. This can potentially hamper correct measurement of infarcted area, since oedema formation poorly reflects infarct size. This study presents a non-invasive, easily applicable and reliable method to accurately predict long-term evolution and late-stage infarction.

Objective

We performed a longitudinal analysis of brain infarct evolution after MCAO in mice, in order to determine whether water-compensated N-Acetylaspartate (NAA) levels in the infarct area, measured 24 h after the insult, is a suitable marker for late-stage infarction and thereby prognosis.

Methods

Twenty mice were divided into 4 groups and scanned longitudinally at different time-points after MCAO, followed by euthanisation for histology: Group 1) MRI/MRS at day 1 after MCAO (n = 4), Group 2) MRI/MRS at days 1 and 7 after MCAO (n = 5), Group 3) MRI/MRS at days 1, 7, and 14 after MCAO (n = 3), and Group 4) MRI/MRS at days 1, 7, 14, and 28 after MCAO (n = 4). At days 1, 7, 14, and 28, NAA levels were correlated with histological determination of neuronal death based on Nissl and H&E stainings.

Results

Twenty-four hours after the insult, NAA levels in the infarcted area decreased by 35 %, but steadily returned to normal after 28 days. In the acute phases, NAA levels strongly correlated with loss of Nissl substance (r2 = -0.874, p = 0.002), whereas NAA levels in later stages reflect glial metabolism and tissue reorganisation. Most importantly, NAA levels 24 h after MCAO was highly correlated with late stage infarction at days 14 and 28 (r2 = 0.73, p = 0.01), in contrast to T2 (r2 = 0.06, p = 0.59).

Conclusions

By using a fixed voxel, which is easily positioned in the affected area, it is possible to obtain reliable measures of the extent of neuronal loss at early time points independent of oedema and brain deformation. Importantly, NAA levels 24 h after MCAO accurately reflects late-stage infarction, suggesting that NAA is a useful prognostic biomarker early after an ischemic stroke.

Non-Selective PDE4 Inhibition Induces a Rapid and Transient Decrease of Serum Potassium in Mice

Simple Summary

Inhibitors of phosphodiesterase 4 (PDE4), a group of isoenzymes that hydrolyze and inactivate the second messenger cAMP, produce promising therapeutic benefits, including anti-inflammatory and memory-enhancing effects. Here, we report that, unexpectedly, PDE4 inhibitors also reduce serum potassium levels in mice. As both the total potassium content of the body, as well as the distribution of potassium between intra- and extracellular compartments, are critical for normal cellular functions, we further explored this observation. Several structurally distinct PDE4 inhibitors reduce serum potassium levels in mice, suggesting it is a class effect of these drugs. Serum potassium levels decrease within 15 min of drug injection, suggesting that PDE4 inhibition lowers serum potassium levels by promoting a transcellular shift of potassium from the blood into cells. This shift is a characteristically fast process, compared to a loss of total-body potassium via the kidneys or digestive tract (e.g., diarrhea). Indeed, stimulating cAMP synthesis with β-adrenoceptor agonists is known to rapidly shift potassium into cells, and PDE4 inhibitors appear to mimic this process by preventing PDE4-mediated cAMP degradation. Our findings reveal that the various acute physiologic effects of PDE4 inhibitors are paralleled and/or may be affected by reduced serum potassium levels.

Abstract

The analysis of blood samples from mice treated with the PDE4 inhibitor Roflumilast revealed an unexpected reduction in serum potassium levels, while sodium and chloride levels were unaffected. Treatment with several structurally distinct PAN-PDE4 inhibitors, including Roflumilast, Rolipram, RS25344, and YM976 dose-dependently reduced serum potassium levels, indicating the effect is a class-characteristic property. PDE4 inhibition also induces hypothermia and hypokinesia in mice. However, while general anesthesia abrogates these effects of PDE4 inhibitors, potassium levels decrease to similar extents in both awake as well as in fully anesthetized mice. This suggests that the hypokalemic effects of PDE4 inhibitors occur independently of hypothermia and hypokinesia. PDE4 inhibition reduces serum potassium within 15 min of treatment, consistent with a rapid transcellular shift of potassium. Catecholamines promote the uptake of potassium into the cell via increased cAMP signaling. PDE4 appears to modulate these adrenoceptor-mediated effects, as PDE4 inhibition has no additional effects on serum potassium in the presence of saturating doses of the β-adrenoceptor agonist Isoprenaline or the α₂-blocker Yohimbine, and is partially blocked by pre-treatment with the β-blocker Propranolol. Together, these data suggest that PDE4 inhibitors reduce serum potassium levels by modulating the adrenergic regulation of cellular potassium uptake.

Models and methods for conditioning the ischemic brain

BACKGROUND

In the last decades the need to find new neuroprotective targets has addressed the researchers to investigate the endogenous molecular mechanisms that brain activates when exposed to a conditioning stimulus. Indeed, conditioning is an adaptive biological process activated by those interventions able to confer resistance to a deleterious brain event through the exposure to a sub-threshold insult. Specifically, preconditioning and postconditioning are realized when the conditioning stimulus is applied before or after, respectively, the harmul ischemia.

AIMS AND RESULTS

The present review will describe the most common methods to induce brain conditioning, with particular regards to surgical, physical exercise, temperature-induced and pharmacological approaches. It has been well recognized that when the subliminal stimulus is delivered after the ischemic insult, the achieved neuroprotection is comparable to that observed in models of ischemic preconditioning. In addition, subjecting the brain to both preconditioning as well as postconditioning did not cause greater protection than each treatment alone.

CONCLUSIONS

The last decades have provided fascinating insights into the mechanisms and potential application of strategies to induce brain conditioning. Since the identification of intrinsic cell-survival pathways should provide more direct opportunities for translational neuroprotection trials, an accurate examination of the different models of preconditioning and postconditioning is mandatory before starting any new project.

Dihydrocapsaicin-induced hypothermia after asphyxiai cardiac arrest in rats

Cardiac arrest (CA) is one of the leading causes of mortality and morbidity in the world. Fast, reversible and controllable pharmaceutical-induced hypothermia (PIH) is strongly desired to treat ischemia-reperfusion brain injury. Dihydrocapsaicin (DHC), an agonist of transient receptor potential vanilloid type 1 cation channel (TRPV1), is an emerging candidate for PIH. Its capability to lower body temperature has been validated in both healthy and stroke animal models. However, DHC has shown cardiovascular effects and its safety and feasibility in a CA model has not been tested. Additionally, activated TRPV1 has multiple functions in addition to regulating body temperature and its effect on neurological recovery needs to be evaluated. In this study, we compared two methods of DHC administration, bolus injection and infusion via the femoral vein. We found that cardiovascular effects were only seen with a large dose DHC bolus injection. Then, we applied DHC-induced hypothermia in an asphyxial-CA rat model. We showed that DHC-treated rats were viable. Four-hour infusion of DHC at a rate of 0.75 mg/kg/h after CA maintained a body temperature of about 34 °C for at least 8 hours. DHC-treated rats had higher electrical activity during the first 4 hours after CA and had better neurological recovery during the 3 days after CA compared with normothermia rats. Additional pathway investigation of DHC administration following CA will further uncover the benefits of DHC-induced hypothermia.

Pharmacological hypothermia: a potential for future stroke therapy?

Mild physical hypothermia after stroke has been associated with positive outcomes. Despite the well-studied beneficial effects of hypothermia in the treatment of stroke, lack of precise temperature control, intolerance for the patient, and immunosuppression are some of the reasons which limit its clinical translation. Pharmacologically induced hypothermia has been explored as a possible treatment option following stroke in animal models. Currently, there are eight classes of pharmacological agents/agonists with hypothermic effects affecting a multitude of systems including cannabinoid, opioid, transient receptor potential vanilloid 1 (TRPV1), neurotensin, thyroxine derivatives, dopamine, gas, and adenosine derivatives. Interestingly, drugs in the TRPV1, neurotensin, and thyroxine families have been shown to have effects in thermoregulatory control in decreasing the compensatory hypothermic response during cooling. This review will briefly present drugs in the eight classes by summarizing their proposed mechanisms of action as well as side effects. Reported thermoregulatory effects of the drugs will also be presented. This review offers the opinion that these agents may be useful in combination therapies with physical hypothermia to achieve faster and more stable temperature control in hypothermia.

Neuroprotective mechanisms and translational potential of therapeutic hypothermia in the treatment of ischemic stroke

Stroke is a leading cause of disability and death, yet effective treatments for acute stroke has been very limited. Thus far, tissue plasminogen activator has been the only FDA-approved drug for thrombolytic treatment of ischemic stroke patients, yet its application is only applicable to less than 4–5% of stroke patients due to the narrow therapeutic window (< 4.5 hours after the onset of stroke) and the high risk of hemorrhagic transformation. Emerging evidence from basic and clinical studies has shown that therapeutic hypothermia, also known as targeted temperature management, can be a promising therapy for patients with different types of stroke. Moreover, the success in animal models using pharmacologically induced hypothermia (PIH) has gained increasing momentum for clinical translation of hypothermic therapy. This review provides an updated overview of the mechanisms and protective effects of therapeutic hypothermia, as well as the recent development and findings behind PIH treatment. It is expected that a safe and effective hypothermic therapy has a high translational potential for clinical treatment of patients with stroke and other CNS injuries.

Pramipexole-Induced Hypothermia Reduces Early Brain Injury via PI3K/AKT/GSK3β pathway in Subarachnoid Hemorrhage rats

Previous studies have shown neuroprotective effects of hypothermia. However, its effects on subarachnoid hemorrhage (SAH)-induced early brain injury (EBI) remain unclear. In this study, a SAH rat model was employed to study the effects and mechanisms of pramipexole-induced hypothermia on EBI after SAH. Dose-response experiments were performed to select the appropriate pramipexole concentration and frequency of administration for induction of mild hypothermia (33–36 °C). Western blot, neurobehavioral evaluation, Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and Fluoro-Jade B (FJB) staining were used to detect the effects of pramipexole-induced hypothermia on SAH-induced EBI, as well as to study whether controlled rewarming could attenuate these effects. Inhibitors targeting the PI3K/AKT/GSK3β pathway were administered to determine whether the neuroprotective effect of pramipexole-induced hypothermia was mediated by PI3K/AKT/GSK3β signaling pathway. The results showed that intraperitoneal injection of pramipexole at 0.25 mg/kg body weight once per 8 hours was found to successfully and safely maintain rats at mild hypothermia. Pramipexole-induced hypothermia ameliorated SAH-induced brain cell death, blood-brain barrier damage and neurobehavioral deficits in a PI3K/AKT/GSK3β signaling-dependent manner. Therefore, we may conclude that pramipexole-induced hypothermia could effectively inhibit EBI after SAH in rats via PI3K/AKT/GSK3β signaling pathway.

Systemically administered anti-TNF therapy ameliorates functional outcomes after focal cerebral ischemia

Background

The innate immune system contributes to the outcome after stroke, where neuroinflammation and post-stroke systemic immune depression are central features. Tumor necrosis factor (TNF), which exists in both a transmembrane (tm) and soluble (sol) form, is known to sustain complex inflammatory responses associated with stroke. We tested the effect of systemically blocking only solTNF versus blocking both tmTNF and solTNF on infarct volume, functional outcome and inflammation in focal cerebral ischemia.

Methods

We used XPro1595 (a dominant-negative inhibitor of solTNF) and etanercept (which blocks both solTNF and tmTNF) to test the effect of systemic administration on infarct volume, functional recovery and inflammation after focal cerebral ischemia in mice. Functional recovery was evaluated after one, three and five days, and infarct volumes at six hours, 24 hours and five days after ischemia. Brain inflammation, liver acute phase response (APR), spleen and blood leukocyte profiles, along with plasma microvesicle analysis, were evaluated.

Results

We found that both XPro1595 and etanercept significantly improved functional outcomes, altered microglial responses, and modified APR, spleen T cell and microvesicle numbers, but without affecting infarct volumes.

Conclusions

Our data suggest that XPro1595 and etanercept improve functional outcome after focal cerebral ischemia by altering the peripheral immune response, changing blood and spleen cell populations and decreasing granulocyte infiltration into the brain. Blocking solTNF, using XPro1595, was just as efficient as blocking both solTNF and tmTNF using etanercept. Our findings may have implications for future treatments with anti-TNF drugs in TNF-dependent diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0203-6) contains supplementary material, which is available to authorized users.

Drug-induced hypothermia by 5HT1A agonists provide neuroprotection in experimental stroke: new perspectives for acute patient treatment

BACKGROUND

Drug-induced hypothermia reduces brain damage in animal stroke models and is an undiscovered potential in human stroke treatment. We studied hypothermia induced by the serotonergic agonists S14671 (1-[2-(2-thenoylamino)ethyl]-4[1-(7- methoxynaphtyl)]piperazine) and ipsapirone in a rat stroke model and in man by literature meta-analysis.

METHODS

Rats had 60 minutes of middle cerebral artery occlusion (MCAO) and then 7 days of survival. Body temperatures were monitored for 22 hours. Thirty minutes after MCAO, 1 group (n = 9) received bolus of S14671 (.75 mg/kg) and continuous infusion of .06 mg/kg hour(-1) S14671 for 20 hours. Other MCAO rats (n = 7) had bolus of ipsapirone (.75 mg/kg) and continuous infusion of .25 mg/kg hour(-1) ipsapirone for 3 hours. Controls (n = 9; n = 5) received similar amounts of vehicle as bolus and continuous infusion for 20 hours/3 hours. Additional controls of the S14761 effect in MCAO were performed as previously mentioned (n = 10) but with rats kept normothermic by a heating lamp for 22 hours. Finally, a meta-analysis of ipsapirone-induced hypothermia in man was included.

RESULTS

Infarct volumes were reduced by 50% in hypothermic rats versus controls (P < .05). S14671 rats kept normothermic did not show infarct reduction (P > .05). The body temperature after stroke was reduced 1.0-3.0°C compared with controls for 20 hours with S14671 treatment and for 6 hours with ipsapirone treatment. In humans, ipsapirone reduced temperature in average with .55 °C ranging between .1-1.4 °C.

CONCLUSIONS

5-hydroxytryptamine receptor 1A (5HT(1A)) agonists significantly reduce infarct volumes in MCAO rats primarily because of the hypothermic drug effect. 5HT(1A) agonists may be introduced to reduce body temperatures rapidly and prepare patients for further therapeutic hypothermia.

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.

Estimation of the hypothermic component in neuroprotection provided by cannabinoids following cerebral ischemia

Cannabinoids have neuroprotective potentials, and the expression of endocannabinoids as well as cannabinoid receptors is induced after cerebral ischemia. They also induce hypothermia by lowering the hypothalamic set point. We have estimated the significance of such hypothermia in ischemic neuroprotection following systemic administration of WIN 55,212-2, a synthetic cannabinoid receptor agonist. Results showed that WIN 55,212-2 significantly reduced infarct volumes of rats subjected to focal cerebral ischemia (middle cerebral artery occlusion) and significantly decreased ischemic CA1 damage in rats subjected to global cerebral ischemia (two-vessel occlusion). A significant (approximately 50%) part of this neuroprotection was provided by WIN 55,212-2 induced hypothermia (33.7+/-1.1 degrees C/34.9+/-1.6 degrees C), because prevention of hypothermia by maintaining body core temperatures between 37.0 and 38.0 degrees C dissolved the neuroprotective effect into a hypothermic component and an unidentified component. Finally, the ability of WIN 55,212-2 to reduce levels of the proinflammatory cytokine IFNgamma in the infarcted hemisphere of rats subjected to focal cerebral ischemia required hypothermia. For the cannabinoid WIN 55,212-2, we have isolated and directly demonstrated that hypothermia is only part of, although significant, cannabinoid mediated neuroprotection in both global and focal cerebral ischemia. We conclude that cannabinoids are reliable candidates for drug-induced hypothermia and neuroprotection. These neuroprotective effects of cannabinoids could provide the basis for potential therapeutic uses of cannabinoids and/or endocannabinoids in stroke.