Xenon is an inhibitor of tissue-plasminogen activator: adverse and beneficial effects in a rat model of thromboembolic stroke

Xenon gas as a potential treatment for opioid use disorder, alcohol use disorder, and related disorders

Xenon gas is considered to be a safe anesthetic and imaging agent. Research on its other potentially beneficial effects suggests that xenon may have broad efficacy for treating health disorders. A number of reviews on xenon applications have been published, but none have focused on substance use disorders. Accordingly, we review xenon effects and targets relevant to the treatment of substance use disorders, with a focus on opioid use disorder and alcohol use disorder. We report that xenon inhaled at subsedative concentrations inhibits conditioned memory reconsolidation and opioid withdrawal symptoms. We review work by others reporting on the antidepressant, anxiolytic, and analgesic properties of xenon, which could diminish negative affective states and pain. We discuss research supporting the possibility that xenon could prevent analgesic- or stress-induced opioid tolerance and, by so doing could reduce the risk of developing opioid use disorder. The rapid kinetics, favorable safety and side effect profiles, and multitargeting capability of xenon suggest that it could be used as an ambulatory on-demand treatment to rapidly attenuate maladaptive memory, physical and affective withdrawal symptoms, and pain drivers of substance use disorders when they occur. Xenon may also have human immunodeficiency virus and oncology applications because its effects relevant to substance use disorders could be exploited to target human immunodeficiency virus reservoirs, human immunodeficiency virus protein-induced abnormalities, and cancers. Although xenon is expensive, low concentrations exert beneficial effects, and gas separation, recovery, and recycling advancements will lower xenon costs, increasing the economic feasibility of its therapeutic use. More research is needed to better understand the remarkable repertoire of effects of xenon and its potential therapeutic applications.

Long lasting argon neuroprotection in a non-human primate model of transient endovascular ischemic stroke

In the past decade, noble gases have emerged as highly promising neuroprotective agents. Previous studies have demonstrated the efficacy of argon neuroprotection in rodent models of cerebral ischemia. The objective of the present pre-clinical study was to confirm the neuroprotective effect of argon in a non-human primate model of endovascular ischemic stroke. Thirteen adult Macaca mulatta were subjected to a focal cerebral ischemia induced by a transient (90 min) middle cerebral artery occlusion (tMCAO). The monkeys were randomly allocated to a control group (n = 8) and an argon group (n = 5). Pre-mixed gas (40-60 oxygen-argon) was applied 30 min after the onset of tMCAO to 30 min after reperfusion. Infarct volumes were measured from the MRI scans conducted 1 hour and 1 month after the reperfusion. A clinical neurological assessment was performed 24 hours and 1 month after tMCAO. Our results show that Argon dramatically reduced ischemic core volume after ischemia compared to the control group with a long-lasting improvement of post-stroke infarct volume at 1 month. In addition, the neurological scale suggests a better prognosis in argon-treated animals without reaching the significance threshold. These pre-clinical results in gyrencephalic non-human primates support the potential use of this therapeutic approach for future clinical studies.

Xenon Antiaggregant Effects

In in vitro model of short-term therapeutic inhalation of Xe/O2 mixture, xenon in millimolar concentrations led to a pronounced decrease in induced platelet aggregation in the platelet-enriched blood plasma. The maximum and statistically significant decrease occurred in response to induction by collagen (by ≈30%, p≤0.01) and ADP (by ≈25%, p≤0.01). A slightly weaker but statistically significant reduction in aggregation appeared in response to ristocetin (by ≈12%, p≤0.01) and epinephrine (by ≈9%, p≤0.01). It should be noted that the spontaneous aggregation exceeded the reference values in the control group. Nevertheless, even at minimal absolute values, spontaneous platelet aggregation decreased by 2 times in response to xenon (p≤0.01). The reasons for the decrease of spontaneous and induced aggregation are xenon accumulation in the lipid bilayer of the membrane with subsequent nonspecific (mechanical) disassociation of membrane platelet structures and specific block of its distinct from neuronal NMDA receptor.

Therapeutic management of severe spinal cord decompression sickness in a hyperbaric center

Introduction

Spinal cord decompression sickness (scDCS) unfortunately has a high rate of long-term sequelae. The purpose of this study was to determine the best therapeutic management in a hyperbaric center and, in particular, the influence of hyperbaric treatment performed according to tables at 4 atm (Comex 30) or 2.8 atm abs (USNT5 or T6 equivalent).

Methods

This was a retrospective study that included scDCS with objective sensory or motor deficit affecting the limbs and/or sphincter impairment seen at a single hyperbaric center from 2010 to 2020. Information on dive, time to recompression, and in-hospital management (hyperbaric and medical treatments such as lidocaine) were analyzed as predictor variables, as well as initial clinical severity and clinical deterioration in the first 24 h after initial recompression. The primary endpoint was the presence or absence of sequelae at discharge as assessed by the modified Japanese Orthopaedic Association score.

Results

102 divers (52 ± 16 years, 20 female) were included. In multivariate analysis, high initial clinical severity, deterioration in the first 24 h, and recompression tables at 4 atm versus 2.8 atm abs for both initial and additional recompression were associated with incomplete neurological recovery. Analysis of covariance comparing the effect of initial tables at 2.8 versus 4 atm abs as a function of initial clinical severity showed a significantly lower level of sequelae with tables at 2.8 atm. In studying correlations between exposure times to maximum or cumulative O2 dose and the degree of sequelae, the optimal initial treatment appears to be a balance between administration of a high partial pressure of O2 (2.8 atm) and a limited exposure duration that does not result in pulmonary oxygen toxicity. Further analysis suggests that additional tables in the first 24-48 h at 2.8 atm abs with a Heliox mixture may be beneficial, while the use of lidocaine does not appear to be relevant.

Conclusion

Our study shows that the risk of sequelae is related not only to initial severity but also to clinical deterioration in the first 24 h, suggesting the activation of biological cascades that can be mitigated by well-adapted initial and complementary hyperbaric treatment.

Enhanced Cerebroprotection of Xenon-Loaded Liposomes in Combination with rtPA Thrombolysis for Embolic Ischemic Stroke

Xenon (Xe) has shown great potential as a stroke treatment due to its exceptional ability to protect brain tissue without inducing side effects. We have previously developed Xe-loaded liposomes for the ultrasound-activated delivery of Xe into the cerebral region and demonstrated their therapeutic efficacy. At present, the sole FDA-approved thrombolytic agent for stroke treatment is recombinant tissue plasminogen activator (rtPA). In this study, we aimed to investigate the potential of combining Xe-liposomes with an intravenous rtPA treatment in a clinically relevant embolic rat stroke model. We evaluated the combinational effect using an in vitro clot lysis model and an in vivo embolic middle cerebral artery occlusion (eMCAO) rat model. The treatment groups received intravenous administration of Xe-liposomes (20 mg/kg) at 2 h post-stroke onset, followed by the administration of rtPA (10 mg/kg) at either 2 or 4 h after the onset. Three days after the stroke, behavioral tests were conducted, and brain sections were collected for triphenyltetrazolium chloride (TTC) and TUNEL staining. Infarct size was determined as normalized infarct volume (%). Both in vitro and in vivo clot lysis experiments demonstrated that Xe-liposomes in combination with rtPA resulted in effective clot lysis comparable to the treatment with free rtPA alone. Animals treated with Xe-liposomes in combination with rtPA showed reduced TUNEL-positive cells and demonstrated improved neurological recovery. Importantly, Xe-liposomes in combination with late rtPA treatment reduced rtPA-induced hemorrhage, attributing to the reduction of MMP9 immunoreactivity. This study demonstrates that the combined therapy of Xe-liposomes and rtPA provides enhanced therapeutic efficacy, leading to decreased neuronal cell death and a potential to mitigate hemorrhagic side effects associated with late rtPA treatment.

Neuroprotection by the noble gases argon and xenon as treatments for acquired brain injury: a preclinical systematic review and meta-analysis

BACKGROUND

The noble gases argon and xenon are potential novel neuroprotective treatments for acquired brain injuries. Xenon has already undergone early-stage clinical trials in the treatment of ischaemic brain injuries, with mixed results. Argon has yet to progress to clinical trials as a treatment for brain injury. Here, we aim to synthesise the results of preclinical studies evaluating argon and xenon as neuroprotective therapies for brain injuries.

METHODS

After a systematic review of the MEDLINE and Embase databases, we carried out a pairwise and stratified meta-analysis. Heterogeneity was examined by subgroup analysis, funnel plot asymmetry, and Egger's regression.

RESULTS

A total of 32 studies were identified, 14 for argon and 18 for xenon, involving measurements from 1384 animals, including murine, rat, and porcine models. Brain injury models included ischaemic brain injury after cardiac arrest (CA), neurological injury after cardiopulmonary bypass (CPB), traumatic brain injury (TBI), and ischaemic stroke. Both argon and xenon had significant (P<0.001), positive neuroprotective effect sizes. The overall effect size for argon (CA, TBI, stroke) was 18.1% (95% confidence interval [CI], 8.1-28.1%), and for xenon (CA, TBI, stroke) was 34.1% (95% CI, 24.7-43.6%). Including the CPB model, only present for xenon, the xenon effect size (CPB, CA, TBI, stroke) was 27.4% (95% CI, 11.5-43.3%). Xenon, both with and without the CPB model, was significantly (P<0.001) more protective than argon.

CONCLUSIONS

These findings provide evidence to support the use of xenon and argon as neuroprotective treatments for acquired brain injuries. Current evidence suggests that xenon is more efficacious than argon overall.

Vascular Response to Spreading Depolarization Predicts Stroke Outcome

BACKGROUND

Cortical spreading depolarization (CSD) is a massive neuro-glial depolarization wave, which propagates across the cerebral cortex. In stroke, CSD is a necessary and ubiquitous mechanism for the development of neuronal lesions that initiates in the ischemic core and propagates through the penumbra extending the tissue injury. Although CSD propagation induces dramatic changes in cerebral blood flow, the vascular responses in different ischemic regions and their consequences on reperfusion and recovery remain to be defined.

METHODS

Ischemia was performed using the thrombin model of stroke and reperfusion was induced by r-tPA (recombinant tissue-type plasminogen activator) administration in mice. We used in vivo electrophysiology and laser speckle contrast imaging simultaneously to assess both electrophysiological and hemodynamic characteristics of CSD after ischemia onset. Neurological deficits were assessed on day 1, 3, and 7. Furthermore, infarct sizes were quantified using 2,3,5-triphenyltetrazolium chloride on day 7.

RESULTS

After ischemia, CSDs were evidenced by the characteristic propagating DC shift extending far beyond the ischemic area. On the vascular level, we observed 2 types of responses: some mice showed spreading hyperemia confined to the penumbra area (penumbral spreading hyperemia) while other showed spreading hyperemia propagating in the full hemisphere (full hemisphere spreading hyperemia). Penumbral spreading hyperemia was associated with severe stroke-induced damage, while full hemisphere spreading hyperemia indicated beneficial infarct outcome and potential viability of the infarct core. In all animals, thrombolysis with r-tPA modified the shape of the vascular response to CSD and reduced lesion volume.

CONCLUSIONS

Our results show that different types of spreading hyperemia occur spontaneously after the onset of ischemia. Depending on their shape and distribution, they predict severity of injury and outcome. Furthermore, our data show that modulating the hemodynamic response to CSD may be a promising therapeutic strategy to attenuate stroke outcome.

Neuroprotective Effects of the Inert Gas Argon on Experimental Traumatic Brain Injury In Vivo with the Controlled Cortical Impact Model in Mice

Simple Summary

Traumatic brain injuries remain one of the leading causes of death in the western world and developing countries. There is an urgent need for causal therapies for such injuries. The noble gas argon has already shown promising results in in-vitro models. The influence of argon on the extent of damage after a craniocerebral trauma will be investigated in this study, in vivo, in mice. After the trauma, the animals were examined for neurological impairments and their brains were removed to detect brain edema and microscopically detectable alterations.

Abstract

Argon has shown neuroprotective effects after traumatic brain injury (TBI) and cerebral ischemia in vitro and in focal cerebral ischemia in vivo. The purpose of this study is to show whether argon beneficially impacts brain contusion volume (BCV) as the primary outcome parameter, as well as secondary outcome parameters, such as brain edema, intracranial pressure (ICP), neurological outcome, and cerebral blood flow (CBF) in an in-vivo model. Subjects were randomly assigned to either argon treatment or room air. After applying controlled cortical impact (CCI) onto the dura with 8 m/s (displacement 1 mm, impact duration 150 ms), treatment was administered by a recovery chamber with 25%, 50%, or 75% argon and the rest being oxygen for 4 h after trauma. Two control groups received room air for 15 min and 24 h, respectively. Neurological testing and ICP measurements were performed 24 h after trauma, and brains were removed to measure secondary brain damage. The primary outcome parameter, BCV, and the secondary outcome parameter, brain edema, were not significantly reduced by argon treatment at any concentration. There was a highly significant decrease in ICP at 50% argon (p = 0.001), and significant neurological improvement (beamwalk missteps) at 25% and 50% argon (p = 0.01; p = 0.049 respectively) compared to control.

Revisiting the Effects of Xenon on Urate Oxidase and Tissue Plasminogen Activator: No Evidence for Inhibition by Noble Gases

Although chemically inert, Xe and other noble gases have been shown to have functional effects on biological systems. For example, Xe is a powerful anesthetic with neuroprotective properties. Recent reports have claimed that Xe inhibits the activity of tissue plasminogen activator (tPA) and urate oxidase (UOX), indicating that the use of Xe as an anesthetic may have undesirable side effects. Here, we revisited the methods used to demonstrate Xe inhibition of UOX and tPA, testing both indirect and direct gas delivery methods with variable bubble sizes and gas flowrates. Our results indicate that Xe or Kr do not affect the activity of UOX or tPA and that the previously reported inhibition is due to protein damage attendant to directly bubbling gases into protein solutions. The lack of evidence to support Xe inhibition of UOX or tPA alleviates concerns regarding possible side effects for the clinical application of Xe as an anesthetic. Furthermore, this study illustrates the importance of using indirect methods of gas dissolution for studying gas-protein interactions in aqueous solution.

Potential application value of xenon in stroke treatment

Stroke is an acute disease with extremely high mortality and disability, including ischemic stroke and hemorrhagic stroke. Currently only limited drugs and treatments have been shown to have neuroprotective effects in stroke. As a medical gas, xenon has been proven to have neuroprotective effect in considerable amount of previous study. Its unique properties are different from other neuroprotective agents, making it is promising to play a special therapeutic role in stroke, either alone or in combination with other treatments. In this article, we aim to review the role of xenon in the treatment of stroke, and summarize the mechanism of using xenon to produce therapeutic effects after stroke according to the existing research. Moreover, we intend to explore and demonstrate the feasibility and safety of xenon for clinical treatment of stroke. Despite the disadvantages of difficulty in obtaining and being expensive, as long as the use of reasonable methods, xenon can play an important role in the treatment of stroke.

Pulmonary static inflation with 50% xenon attenuates decline in tissue factor in patients undergoing Stanford type A acute aortic dissection repair

Background

The Stanford type A acute aortic dissection (AAD) carries a high risk of mortality and morbidity, and patients undergoing AAD surgery often bleed excessively and require blood products and transfusions. Thus, we studied how xenon alters coagulation using thromboelastography (TEG) and conventional hemostatic tests for patients with AAD undergoing aortic arch surgery involving cardiopulmonary bypass (CPB)/deep hypothermic circulatory arrest (DHCA).

Methods

This prospective single-center nonrandomized controlled clinical trial, registered in the Chinese Clinical Trial Registry (ChiCTR-ICR-15006435), assessed perioperative clinical variables and serological results from 50 subjects undergoing pulmonary static inflation with 50% nitrogen/50% oxygen from January 2013 to January 2014 and 50 subjects undergoing pulmonary static inflation with 50% xenon/50% oxygen from January 2014 to December 2014 during CPB for Stanford type A AAD. Repeated measures ANOVA were used to identify the effects of xenon on coagulation after surgery. The primary endpoint was perioperative changes in coagulation and fibrinolysis after intubation and 10 minutes, and 6 hours after the operation. The secondary endpoint was to assess the perioperative changes in serum level of tissue factor (TF), tissue factor pathway inhibitor (TFPI) and tissue plasminogen activator (tPA) after intubation and 10 minutes, and 6 hours after the operation.

Results

Mean prothrombin time (PT), activated partial thromboplastin time (APTT), international normalized ratio (INR), median fibrinogen degradation product (FDP), and D-dimer peaked and then decreased over 6 hours after surgery. TEG followed a similar trend. From the start to the end of surgery and until 6 h after surgery, mean TF decreased in controls (β -2.61, P<0.001 and β -2.83, P<0.001, respectively), but was maintained relatively stable in xenon group (β -0.5, P<0.001 and β -0.96, P<0.001, respectively).

Conclusions

Deterioration of coagulation function and activated fibrinolysis was confirmed by conventional tests and TEG analysis after Stanford type A AAD repair. Pulmonary static inflation with 50% xenon attenuates decline in TF in patients undergoing Stanford type A AAD repair.

Neurologic and cognitive outcomes associated with the clinical use of xenon: a systematic review and meta-analysis of randomized-controlled trials

BACKGROUND

Xenon has been shown to have positive neurologic effects in various pre-clinical models. This study systematically reviewed the randomized-controlled trials (RCTs) investigating neurologic and cognitive outcomes associated with the clinical use of xenon.

METHODS

We searched PubMed, CENTRAL, EMBASE, CINAHL, elibrary.ru (for Russian studies), Google Scholar (for Russian studies), and Wanfang (for Chinese studies) for appropriate RCTs comparing neurologic or cognitive outcomes after clinical use of xenon with control treatment or with other anesthetic agents.

RESULTS

Seventeen RCTs met the inclusion criteria. Two studies investigated the effects of xenon plus therapeutic hypothermia to treat neonatal asphyxia or out-of-hospital cardiac arrest. Compared with therapeutic hypothermia alone, xenon and therapeutic hypothermia reduced cerebral white matter abnormalities after cardiac arrest but had no effect on neurocognitive outcome and mortality. Xenon had no added value when used to treat neonatal asphyxia. Thirteen RCTs compared neurocognitive effects of xenon with other anesthetic agents in surgical patients. While xenon may be associated with improved short-term (< three hours) cognitive outcome, no medium-term (six hours to three months) advantage was observed, and longer-term data are lacking. No differences in biochemical (S-100β, neuron-specific enolase) and neuropsychologic (attentional performance) outcomes were found with xenon compared with other anesthetic drugs. Finally, two studies suggest that brief, intermittent administration of sub-anesthetic doses of xenon to patients during the acute phase of substance withdrawal may improve neurocognitive outcomes.

CONCLUSIONS

Despite promising pre-clinical results, the evidence for positive clinical neurologic and cognitive outcomes associated with xenon administration is modest. Nevertheless, there is some evidence to suggest that xenon may be associated with better neurologic outcomes compared with the standard of care therapy in certain specific clinical situations. More clinical trials are needed to determine any potential benefit linked to xenon administration.

Xenon-Protein Interactions: Characterization by X-Ray Crystallography and Hyper-CEST NMR

The physiological activity of xenon has long been recognized, though the exact nature of its interactions with biomolecules remains poorly understood. Xe is an inert noble gas, but can act as a general anesthetic, most likely by binding internal hydrophobic cavities within proteins. Understanding Xe-protein interactions, therefore, can provide crucial insight regarding the mechanism of Xe anesthesia and potentially other general anesthetic agents. Historically, Xe-protein interactions have been studied primarily through X-ray crystallography and nuclear magnetic resonance (NMR). In this chapter, we first describe our methods for preparing Xe derivatives of protein crystals and identifying Xe-binding sites. Second, we detail our procedure for ¹²⁹Xe hyper-CEST NMR spectroscopy, a versatile NMR technique well suited for characterizing the weak, transient nature of Xe-protein interactions.

Delivery of xenon-containing echogenic liposomes inhibits early brain injury following subarachnoid hemorrhage

Xenon (Xe), a noble gas, has promising neuroprotective properties with no proven adverse side-effects. We evaluated neuroprotective effects of Xe delivered by Xe-containing echogenic liposomes (Xe-ELIP) via ultrasound-controlled cerebral drug release on early brain injury following subarachnoid hemorrhage (SAH). The Xe-ELIP structure was evaluated by ultrasound imaging, electron microscopy and gas chromatography-mass spectroscopy. Animals were randomly divided into five groups: Sham, SAH, SAH treated with Xe-ELIP, empty ELIP, or Xe-saturated saline. Treatments were administrated intravenously in combination with ultrasound application over the common carotid artery to trigger Xe release from circulating Xe-ELIP. Hematoma development was graded by SAH scaling and quantitated by a colorimetric method. Neurological evaluation and motor behavioral tests were conducted for three days following SAH injury. Ultrasound imaging and electron microscopy demonstrated that Xe-ELIP have a unique two-compartment structure, which allows a two-stage Xe release profile. Xe-ELIP treatment effectively reduced bleeding, improved general neurological function, and alleviated motor function damage in association with reduced apoptotic neuronal death and decreased mortality. Xe-ELIP alleviated early SAH brain injury by inhibiting neuronal death and bleeding. This novel approach provides a noninvasive strategy of therapeutic gas delivery for SAH treatment.

Delayed xenon post-conditioning mitigates spinal cord ischemia/reperfusion injury in rabbits by regulating microglial activation and inflammatory factors

The neuroprotective effect against spinal cord ischemia/reperfusion injury in rats exerted by delayed xenon post-conditioning is stronger than that produced by immediate xenon post-conditioning. However, the mechanisms underlying this process remain unclear. Activated microglia are the main inflammatory cell type in the nervous system. The release of pro-inflammatory factors following microglial activation can lead to spinal cord damage, and inhibition of microglial activation can relieve spinal cord ischemia/reperfusion injury. To investigate how xenon regulates microglial activation and the release of inflammatory factors, a rabbit model of spinal cord ischemia/reperfusion injury was induced by balloon occlusion of the infrarenal aorta. After establishment of the model, two interventions were given: (1) immediate xenon post-conditioning—after reperfusion, inhalation of 50% xenon for 1 hour, 50% N₂/50%O₂ for 2 hours; (2) delayed xenon post-conditioning—after reperfusion, inhalation of 50% N₂/50%O₂ for 2 hours, 50% xenon for 1 hour. At 4, 8, 24, 48 and 72 hours after reperfusion, hindlimb locomotor function was scored using the Jacobs locomotor scale. At 72 hours after reperfusion, interleukin 6 and interleukin 10 levels in the spinal cord of each group were measured using western blot assays. Iba1 levels were determined using immunohistochemistry and a western blot assay. The number of normal neurons at the injury site was quantified using hematoxylin-eosin staining. At 72 hours after reperfusion, delayed xenon post-conditioning remarkably enhanced hindlimb motor function, increased the number of normal neurons at the injury site, decreased Iba1 levels, and inhibited interleukin-6 and interleukin-10 levels in the spinal cord. Immediate xenon post-conditioning did not noticeably affect the above-mentioned indexes. These findings indicate that delayed xenon post-conditioning after spinal cord injury improves the recovery of neurological function by reducing microglial activation and the release of interleukin-6 and interleukin-10.

Xenon-helium gas mixture at equimolar concentration of 37.5% protects against oxygen and glucose deprivation-induced injury and inhibits tissue plasminogen activator

Xenon (Xe) is considered to be the golden standard neuroprotective gas. However, Xe has a higher molecular weight and lower thermal conductivity and specific heat than those of nitrogen, the main diluent of oxygen in air. These physical characteristics could impair or at least reduce the intrinsic neuroprotective action of Xe by increasing the patient's respiratory workload and body temperature. In contrast, helium (He) is a cost-efficient gas with a lower molecular weight and higher thermal conductivity and specific heat than those of nitrogen, but is far less potent than Xe. In this study, we hypothesized that mixing Xe and He could allow obtaining a neuroprotective gas mixture with advantageously reduced molecular weight and increased thermal conductivity. We found that Xe and He at the equimolar concentration of 37.5% reduced oxygen-glucose deprivation-induced increase in lactate dehydrogenase in brain slices, an ex vivo model of acute ischemic stroke. These results together with the effects of Xe-He on the thrombolytic efficiency of tissue plasminogen activator are discussed.

Modulation by the Noble Gas Helium of Tissue Plasminogen Activator: Effects in a Rat Model of Thromboembolic Stroke

INTERVENTIONS

Helium has been shown to provide neuroprotection in mechanical model of acute ischemic stroke by inducing hypothermia, a condition shown by itself to reduce the thrombolytic and proteolytic properties of tissue plasminogen activator. However, whether or not helium interacts with the thrombolytic drug tissue plasminogen activator, the only approved therapy of acute ischemic stroke still remains unknown. This point is not trivial since previous data have shown the critical importance of the time at which the neuroprotective noble gases xenon and argon should be administered, during or after ischemia, in order not to block tissue plasminogen activator-induced thrombolysis and to obtain neuroprotection and inhibition of tissue plasminogen activator-induced brain hemorrhages.

MEASUREMENTS AND MAIN RESULTS

We show that helium of 25-75 vol% inhibits in a concentration-dependent fashion the catalytic and thrombolytic activity of tissue plasminogen activator in vitro and ex vivo. In vivo, in rats subjected to thromboembolic brain ischemia, we found that intraischemic helium at 75 vol% inhibits tissue plasminogen activator-induced thrombolysis and subsequent reduction of ischemic brain damage and that postischemic helium at 75 vol% reduces ischemic brain damage and brain hemorrhages.

CONCLUSIONS

In a clinical perspective for the treatment of acute ischemic stroke, these data suggest that helium 1) should not be administered before or together with tissue plasminogen activator therapy due to the risk of inhibiting the benefit of tissue plasminogen activator-induced thrombolysis; and 2) could be an efficient neuroprotective agent if given after tissue plasminogen activator-induced reperfusion.

Argon Exposure Induces Postconditioning in Myocardial Ischemia-Reperfusion

BACKGROUND AND PURPOSE

Cardioprotection against ischemia-reperfusion (I/R) damages remains a major concern during prehospital management of acute myocardial infarction. Noble gases have shown beneficial effects in preconditioning studies. Because emergency proceedings in the context of myocardial infarction require postconditioning strategies, we evaluated the effects of argon in such protocols on mammalian cardiac tissue.

EXPERIMENTAL APPROACHES

In rat, cardiac I/R was induced in vivo by transient coronary artery ligature and cardiac functions were evaluated by magnetic resonance imaging. Hypoxia-reoxygenation (H/R)-induced arrhythmias were evaluated in vitro using intracellular microelectrodes on both rat-isolated ventricle and a model of border zone in guinea pig ventricle. Hypoxia-reoxygenation loss of contractile force was assessed in human atrial appendages. In those models, postconditioning was induced by 5 minutes application of argon at the time of reperfusion.

KEY RESULTS

In the in vivo model, I/R produced left ventricular ejection fraction decrease (24%) and wall motion score increase (36%) which was prevented when argon was applied in postconditioning. In vitro, argon postconditioning abolished H/R-induced arrhythmias such as early after depolarizations, conduction blocks, and reentries. Recovery of contractile force in human atrial appendages after H/R was enhanced in the argon group, increasing from 51% ± 2% in the nonconditioned group to 83% ± 7% in the argon-treated group ( P < .001). This effect of argon was abolished in the presence of wortmannin and PD98059 which inhibit prosurvival phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) and MEK/extracellular receptor kinase 1/2 (ERK 1/2), respectively, or in the presence of the mitochondrial permeability transition pore opener atractyloside, suggesting the involvement of the reperfusion injury salvage kinase pathway.

CONCLUSION AND IMPLICATIONS

Argon has strong cardioprotective properties when applied in conditions of postconditioning and thus appears as a potential therapeutic tool in I/R situations.

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.

Anti-inflammatory signaling: the point of convergence for medical gases in neuroprotection against ischemic stroke

Recent studies suggest that a variety of medical gases confer neuroprotective effects against cerebral ischemia, extending function beyond their regular clinical applications. The mechanisms underlying ischemic neuroprotection afforded by medical gases have been intensively studied over the past two decades. A number of signaling pathways have been proposed, among which anti-inflammatory signaling has been proven to be critical. Pursuit of the role for anti-inflammatory signaling may shed new light on the translational application of medical gas-afforded neuroprotection.

Structural Basis for Xenon Inhibition in a Cationic Pentameric Ligand-Gated Ion Channel

GLIC receptor is a bacterial pentameric ligand-gated ion channel whose action is inhibited by xenon. Xenon has been used in clinical practice as a potent gaseous anaesthetic for decades, but the molecular mechanism of interactions with its integral membrane receptor targets remains poorly understood. Here we characterize by X-ray crystallography the xenon-binding sites within both the open and "locally-closed" (inactive) conformations of GLIC. Major binding sites of xenon, which differ between the two conformations, were identified in three distinct regions that all belong to the trans-membrane domain of GLIC: 1) in an intra-subunit cavity, 2) at the interface between adjacent subunits, and 3) in the pore. The pore site is unique to the locally-closed form where the binding of xenon effectively seals the channel. A putative mechanism of the inhibition of GLIC by xenon is proposed, which might be extended to other pentameric cationic ligand-gated ion channels.

Preclinical neuroprotective actions of xenon and possible implications for human therapeutics: a narrative review

PURPOSE

The purpose of this report is to facilitate an understanding of the possible application of xenon for neuroprotection in critical care settings. This narrative review appraises the literature assessing the efficacy and safety of xenon in preclinical models of acute ongoing neurologic injury.

SOURCE

Databases of the published literature (MEDLINE® and EMBASE™) were appraised for peer-reviewed manuscripts addressing the use of xenon in both preclinical models and disease states of acute ongoing neurologic injury. For randomized clinical trials not yet reported, the investigators' declarations in the National Institutes of Health clinical trials website were considered.

PRINCIPAL FINDINGS

While not a primary focus of this review, to date, xenon cannot be distinguished as superior for surgical anesthesia over existing alternatives in adults. Nevertheless, studies in a variety of preclinical disease models from multiple laboratories have consistently shown xenon's neuroprotective properties. These properties are enhanced in settings where xenon is combined with hypothermia. Small randomized clinical trials are underway to explore xenon's efficacy and safety in clinical settings of acute neurologic injury where hypothermia is the current standard of care.

CONCLUSION

According to the evidence to date, the neuroprotective efficacy of xenon in preclinical models and its safety in clinical anesthesia set the stage for the launch of randomized clinical trials to determine whether these encouraging neuroprotective findings can be translated into clinical utility.

Xenon Blocks Neuronal Injury Associated with Decompression

Despite state-of-the-art hyperbaric oxygen (HBO) treatment, about 30% of patients suffering neurologic decompression sickness (DCS) exhibit incomplete recovery. Since the mechanisms of neurologic DCS involve ischemic processes which result in excitotoxicity, it is likely that HBO in combination with an anti-excitotoxic treatment would improve the outcome in patients being treated for DCS. Therefore, in the present study, we investigated the effect of the noble gas xenon in an ex vivo model of neurologic DCS. Xenon has been shown to provide neuroprotection in multiple models of acute ischemic insults. Fast decompression compared to slow decompression induced an increase in lactate dehydrogenase (LDH), a well-known marker of sub-lethal cell injury. Post-decompression administration of xenon blocked the increase in LDH release induced by fast decompression. These data suggest that xenon could be an efficient additional treatment to HBO for the treatment of neurologic DCS.

Argon blocks the expression of locomotor sensitization to amphetamine through antagonism at the vesicular monoamine transporter-2 and mu-opioid receptor in the nucleus accumbens

We investigated the effects of the noble gas argon on the expression of locomotor sensitization to amphetamine and amphetamine-induced changes in dopamine release and mu-opioid neurotransmission in the nucleus accumbens. We found (1) argon blocked the increase in carrier-mediated dopamine release induced by amphetamine in brain slices, but, in contrast, potentiated the decrease in KCl-evoked dopamine release induced by amphetamine, thereby suggesting that argon inhibited the vesicular monoamine transporter-2; (2) argon blocked the expression of locomotor and mu-opioid neurotransmission sensitization induced by repeated amphetamine administration in a short-term model of sensitization in rats; (3) argon decreased the maximal number of binding sites and increased the dissociation constant of mu-receptors in membrane preparations, thereby indicating that argon is a mu-receptor antagonist; (4) argon blocked the expression of locomotor sensitization and context-dependent locomotor activity induced by repeated administration of amphetamine in a long-term model of sensitization. Taken together, these data indicate that argon could be of potential interest for treating drug addiction and dependence.

Combination of therapeutic hypothermia and other neuroprotective strategies after an ischemic cerebral insult

Abrupt deprivation of substrates to neuronal tissue triggers a number of pathological events (the “ischemic cascade”) that lead to cell death. As this is a process of delayed neuronal cell death and not an instantaneous event, several pharmacological and non-pharmacological strategies have been developed to attenuate or block this cascade. The most promising neuroprotectant so far is therapeutic hypothermia and its beneficial effects have inspired researchers to further improve its protective benefit by combining it with other neuroprotective agents. This review provides an overview of all neuroprotective strategies that have been combined with therapeutic hypothermia in rodent models of focal cerebral ischemia. A distinction is made between drugs interrupting only one event of the ischemic cascade from those mitigating different pathways and having multimodal effects. Also the combination of therapeutic hypothermia with hemicraniectomy, gene therapy and protein therapy is briefly discussed. Furthermore, those combinations that have been studied in a clinical setting are also reviewed.

Crystallographic Studies with Xenon and Nitrous Oxide Provide Evidence for Protein-dependent Processes in the Mechanisms of General Anesthesia

Background:

The mechanisms by which general anesthetics, including xenon and nitrous oxide, act are only beginning to be discovered. However, structural approaches revealed weak but specific protein–gas interactions.

Methods:

To improve knowledge, we performed x-ray crystallography studies under xenon and nitrous oxide pressure in a series of 10 binding sites within four proteins.

Results:

Whatever the pressure, we show (1) hydrophobicity of the gas binding sites has a screening effect on xenon and nitrous oxide binding, with a threshold value of 83% beyond which and below which xenon and nitrous oxide, respectively, binds to their sites preferentially compared to each other; (2) xenon and nitrous oxide occupancies are significantly correlated respectively to the product and the ratio of hydrophobicity by volume, indicating that hydrophobicity and volume are binding parameters that complement and oppose each other’s effects; and (3) the ratio of occupancy of xenon to nitrous oxide is significantly correlated to hydrophobicity of their binding sites.

Conclusions:

These data demonstrate that xenon and nitrous oxide obey different binding mechanisms, a finding that argues against all unitary hypotheses of narcosis and anesthesia, and indicate that the Meyer–Overton rule of a high correlation between anesthetic potency and solubility in lipids of general anesthetics is often overinterpreted. This study provides evidence that the mechanisms of gas binding to proteins and therefore of general anesthesia should be considered as the result of a fully reversible interaction between a drug ligand and a receptor as this occurs in classical pharmacology.

Xenon impairs reconsolidation of fear memories in a rat model of post-traumatic stress disorder (PTSD)

Xenon (Xe) is a noble gas that has been developed for use in people as an inhalational anesthestic and a diagnostic imaging agent. Xe inhibits glutamatergic N-methyl-D-aspartate (NMDA) receptors involved in learning and memory and can affect synaptic plasticity in the amygdala and hippocampus, two brain areas known to play a role in fear conditioning models of post-traumatic stress disorder (PTSD). Because glutamate receptors also have been shown to play a role in fear memory reconsolidation--a state in which recalled memories become susceptible to modification--we examined whether Xe administered after fear memory reactivation could affect subsequent expression of fear-like behavior (freezing) in rats. Male Sprague-Dawley rats were trained for contextual and cued fear conditioning and the effects of inhaled Xe (25%, 1 hr) on fear memory reconsolidation were tested using conditioned freezing measured days or weeks after reactivation/Xe administration. Xe administration immediately after fear memory reactivation significantly reduced conditioned freezing when tested 48 h, 96 h or 18 d after reactivation/Xe administration. Xe did not affect freezing when treatment was delayed until 2 h after reactivation or when administered in the absence of fear memory reactivation. These data suggest that Xe substantially and persistently inhibits memory reconsolidation in a reactivation and time-dependent manner, that it could be used as a new research tool to characterize reconsolidation and other memory processes, and that it could be developed to treat people with PTSD and other disorders related to emotional memory.

Non-pharmaceutical therapies for stroke: mechanisms and clinical implications

Stroke is deemed a worldwide leading cause of neurological disability and death, however, there is currently no promising pharmacotherapy for acute ischemic stroke aside from intravenous or intra-arterial thrombolysis. Yet because of the narrow therapeutic time window involved, thrombolytic application is very restricted in clinical settings. Accumulating data suggest that non-pharmaceutical therapies for stroke might provide new opportunities for stroke treatment. Here we review recent research progress in the mechanisms and clinical implications of non-pharmaceutical therapies, mainly including neuroprotective approaches such as hypothermia, ischemic/hypoxic conditioning, acupuncture, medical gases and transcranial laser therapy. In addition, we briefly summarize mechanical endovascular recanalization devices and recovery devices for the treatment of the chronic phase of stroke and discuss the relative merits of these devices.

Method parameters' impact on mortality and variability in rat stroke experiments: a meta-analysis

Background

Even though more than 600 stroke treatments have been shown effective in preclinical studies, clinically proven treatment alternatives for cerebral infarction remain scarce. Amongst the reasons for the discrepancy may be methodological shortcomings, such as high mortality and outcome variability, in the preclinical studies. A common approach in animal stroke experiments is that A) focal cerebral ischemia is inflicted, B) some type of treatment is administered and C) the infarct sizes are assessed. However, within this paradigm, the researcher has to make numerous methodological decisions, including choosing rat strain and type of surgical procedure. Even though a few studies have attempted to address the questions experimentally, a lack of consensus regarding the optimal methodology remains.

Methods

We therefore meta-analyzed data from 502 control groups described in 346 articles to find out how rat strain, procedure for causing focal cerebral ischemia and the type of filament coating affected mortality and infarct size variability.

Results

The Wistar strain and intraluminal filament procedure using a silicone coated filament was found optimal in lowering infarct size variability. The direct and endothelin methods rendered lower mortality rate, whereas the embolus method increased it compared to the filament method.

Conclusions

The current article provides means for researchers to adjust their middle cerebral artery occlusion (MCAo) protocols to minimize infarct size variability and mortality.

Modulation by the noble gas argon of the catalytic and thrombolytic efficiency of tissue plasminogen activator

Argon has been shown to provide cortical as well as, under certain conditions, subcortical neuroprotection in all models so far (middle cerebral artery occlusion, trauma, neonatal asphyxia, etc.). This has led to the suggestion that argon could be a cost-efficient alternative to xenon, a metabolically inert gas thought to be gold standard in gas pharmacology but whose clinical development suffers its little availability and excessive cost of production. However, whether argon interacts with the thrombolytic agent tissue plasminogen activator, which is the only approved therapy of acute ischemic stroke to date, still remains unknown. This latter point is not trivial since previous data have clearly demonstrated the inhibiting effect of xenon on tPA enzymatic and thrombolytic efficiency and the critical importance of the time at which xenon is administered, during or after ischemia, in order not to block thrombolysis and to obtain neuroprotection. Here, we investigated the effect of argon on tPA enzymatic and thrombolytic efficiency using in vitro methods shown to provide reliable prediction of the in vivo effects of both oxygen and the noble inert gases on tPA-induced thrombolysis. We found that argon has a concentration-dependent dual effect on tPA enzymatic and thrombolytic efficiency. Low and high concentrations of argon of 25 and 75 vol% respectively block and increase tPA enzymatic and thrombolytic efficiency. The possible use of argon at low and high concentrations in the treatment of acute ischemic stroke if given during ischemia or after tPA-induced reperfusion is discussed as regards to its neuroprotectant action and its inhibiting and facilitating effects on tPA-induced thrombolysis. The mechanisms of argon-tPA interactions are also discussed.

Prothrombolytic action of normobaric oxygen given alone or in combination with recombinant tissue-plasminogen activator in a rat model of thromboembolic stroke

The potential benefit of 100 vol% normobaric oxygen (NBO) for the treatment of acute ischemic stroke patients is still a matter of debate. To advance this critical question, we studied the effects of intraischemic normobaric oxygen alone or in combination with recombinant tissue-plasminogen activator (rtPA) on cerebral blood flow and ischemic brain damage and swelling in a clinically relevant rat model of thromboembolic stroke. We show that NBO provides neuroprotection by achieving cerebral blood flow restoration equivalent to 0.9 mg/kg rtPA through probable direct interaction and facilitation of the fibrinolytic properties of endogenous tPA. In contrast, combined NBO and rtPA has no neuroprotective effect on ischemic brain damage despite producing cerebral blood flow restoration. These results 1) by providing a new mechanism of action of NBO highlight together with previous findings the way by which intraischemic NBO shows beneficial action; 2) suggest that NBO could be an efficient primary care therapeutic intervention for patients eligible for rtPA therapy; 3) indicate that NBO could be an interesting alternative for patients not eligible for rtPA therapy; and 4) caution the use of NBO in combination with rtPA in acute stroke patients.

Ex vivo and in vivo neuroprotection induced by argon when given after an excitotoxic or ischemic insult

In vitro studies have well established the neuroprotective action of the noble gas argon. However, only limited data from in vivo models are available, and particularly whether postexcitotoxic or postischemic argon can provide neuroprotection in vivo still remains to be demonstrated. Here, we investigated the possible neuroprotective effect of postexcitotoxic-postischemic argon both ex vivo in acute brain slices subjected to ischemia in the form of oxygen and glucose deprivation (OGD), and in vivo in rats subjected to an intrastriatal injection of N-methyl-D-aspartate (NMDA) or to the occlusion of middle-cerebral artery (MCAO). We show that postexcitotoxic-postischemic argon reduces OGD-induced cell injury in brain slices, and further reduces NMDA-induced brain damage and MCAO-induced cortical brain damage in rats. Contrasting with its beneficial effect at the cortical level, we show that postischemic argon increases MCAO-induced subcortical brain damage and provides no improvement of neurologic outcome as compared to control animals. These results extend previous data on the neuroprotective action of argon. Particularly, taken together with previous in vivo data that have shown that intraischemic argon has neuroprotective action at both the cortical and subcortical level, our findings on postischemic argon suggest that this noble gas could be administered during but not after ischemia, i.e. before but not after reperfusion has occurred, in order to provide cortical neuroprotection and to avoid increasing subcortical brain damage. Also, the effects of argon are discussed as regards to the oxygen-like chemical, pharmacological, and physical properties of argon.

Moderately delayed post-insult treatment with normobaric hyperoxia reduces excitotoxin-induced neuronal degeneration but increases ischemia-induced brain damage

Background

The use and benefits of normobaric oxygen (NBO) in patients suffering acute ischemic stroke is still controversial.

Results

Here we show for the first time to the best of our knowledge that NBO reduces both NMDA-induced calcium influxes in vitro and NMDA-induced neuronal degeneration in vivo, but increases oxygen and glucose deprivation-induced cell injury in vitro and ischemia-induced brain damage produced by middle cerebral artery occlusion in vivo.

Conclusions

Taken together, these results indicate that NBO reduces excitotoxin-induced calcium influx and subsequent neuronal degeneration but favors ischemia-induced brain damage and neuronal death. These findings highlight the complexity of the mechanisms involved by the use of NBO in patients suffering acute ischemic stroke.

Pressure-response analysis of anesthetic gases xenon and nitrous oxide on urate oxidase: a crystallographic study

The remarkably safe anesthetics xenon (Xe) and, to lesser extent, nitrous oxide (N(2)O) possess neuroprotective properties in preclinical studies. To investigate the mechanisms of pharmacological action of these gases, which are still poorly known, we performed both crystallography under a large range of gas pressure and biochemical studies on urate oxidase, a prototype of globular gas-binding proteins whose activity is modulated by inert gases. We show that Xe and N(2)O bind to, compete for, and expand the volume of a hydrophobic cavity located just behind the active site of urate oxidase and further inhibit urate oxidase enzymatic activity. By demonstrating a significant relationship between the binding and biochemical effects of Xe and N(2)O, given alone or in combination, these data from structure to function highlight the mechanisms by which chemically and metabolically inert gases can alter protein function and produce their pharmacological effects. Interestingly, the effects of a Xe:N(2)O equimolar mixture were found to be equivalent to those of Xe alone, thereby suggesting that gas mixtures containing Xe and N(2)O could be an alternative and efficient neuroprotective strategy to Xe alone, whose widespread clinical use is limited due to the cost of production and availability of this gas.

Xenon reduces activation of transient receptor potential vanilloid type 1 (TRPV1) in rat dorsal root ganglion cells and in human TRPV1-expressing HEK293 cells

AIMS

Xenon provides effective analgesia in several pain states at sub-anaesthetic doses. Our aim was to examine whether xenon may mediate its analgesic effect, in part, through reducing the activity of transient receptor potential vanilloid type 1 (TRPV1), a receptor known to be involved in certain inflammatory pain conditions.

MAIN METHODS

We studied the effect of xenon on capsaicin-evoked cobalt uptake in rat cultured primary sensory neurons and in human TRPV1 (hTRPV1)-expressing human embryonic kidney 293 (HEK293) cells. We also examined xenon's effect on the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in the rat spinal dorsal horn evoked by hind-paw injection of capsaicin.

KEY FINDINGS

Xenon (75%) reduced the number of primary sensory neurons responding to the TRPV1 agonist, capsaicin (100 nM-1 μM) by ~25% to ~50%. Xenon reduced the number of heterologously-expressed hTRPV1 activated by 300 nM capsaicin by ~50%. Xenon (80%) reduced by ~40% the number of phosphorylated ERK1/2-expressing neurons in rat spinal dorsal horn resulting from hind-paw capsaicin injection.

SIGNIFICANCE

Xenon substantially reduces the activity of TRPV1 in response to noxious stimulation by the specific TRPV1 agonist, capsaicin, suggesting a possible role for xenon as an adjunct analgesic where hTRPV1 is an active contributor to the excitation of primary afferents which initiates the pain sensation.

Anaesthetic-related neuroprotection: intravenous or inhalational agents?

In designing the anaesthetic plan for patients undergoing surgery, the choice of anaesthetic agent may often appear irrelevant and the best results obtained by the use of a technique or a drug with which the anaesthesia care provider is familiar. Nevertheless, in those surgical procedures (cardiopulmonary bypass, carotid surgery and cerebral aneurysm surgery) and clinical situations (subarachnoid haemorrhage, stroke, brain trauma and post-cardiac arrest resuscitation) where protecting the CNS is a priority, the choice of anaesthetic drug assumes a fundamental role. Treating patients with a neuroprotective agent may be a consideration in improving overall neurological outcome. Therefore, a clear understanding of the relative degree of protection provided by various agents becomes essential in deciding on the most appropriate anaesthetic treatment geared to these objectives. This article surveys the current literature on the effects of the most commonly used anaesthetic drugs (volatile and gaseous inhalation, and intravenous agents) with regard to their role in neuroprotection. A systematic search was performed in the MEDLINE, Cumulative Index to Nursing and Allied Health Literature (CINHAL®) and Cochrane Library databases using the following keywords: 'brain' (with the limits 'newborn' or 'infant' or 'child' or 'neonate' or 'neonatal' or 'animals') AND 'neurodegeneration' or 'apoptosis' or 'toxicity' or 'neuroprotection' in combination with individual drug names ('halothane', 'isoflurane', 'desflurane', 'sevoflurane', 'nitrous oxide', 'xenon', 'barbiturates', 'thiopental', 'propofol', 'ketamine'). Over 600 abstracts for articles published from January 1980 to April 2010, including studies in animals, humans and in vitro, were examined, but just over 100 of them were considered and reviewed for quality. Taken as a whole, the available data appear to indicate that anaesthetic drugs such as barbiturates, propofol, xenon and most volatile anaesthetics (halothane, isoflurane, desflurane, sevoflurane) show neuroprotective effects that protect cerebral tissue from adverse events--such as apoptosis, degeneration, inflammation and energy failure--caused by chronic neurodegenerative diseases, ischaemia, stroke or nervous system trauma. Nevertheless, in several studies, the administration of gaseous, volatile and intravenous anaesthetics (especially isoflurane and ketamine) was also associated with dose-dependent and exposure time-dependent neurodegenerative effects in the developing animal brain. At present, available experimental data do not support the selection of any one anaesthetic agent over the others. Furthermore, the relative benefit of one anaesthetic versus another, with regard to neuroprotective potential, is unlikely to form a rational basis for choice. Each drug has some undesirable adverse effects that, together with the patient's medical and surgical history, appear to be decisive in choosing the most suitable anaesthetic agent for a specific situation. Moreover, it is important to highlight that many of the studies in the literature have been conducted in animals or in vitro; hence, results and conclusions of most of them may not be directly applied to the clinical setting. For these reasons, and given the serious implications for public health, we believe that further investigation--geared mainly to clarifying the complex interactions between anaesthetic drug actions and specific mechanisms involved in brain injury, within a setting as close as possible to the clinical situation--is imperative.

Human recombinant tissue-plasminogen activator (alteplase): why not use the 'human' dose for stroke studies in rats?

Since a pioneer work that has shown in vitro that the rat's fibrinolytic system is 10-fold less sensitive to recombinant tissue-plasminogen activator (rtPA) than the human system, most preclinical studies are performed with 10 instead of 0.9 mg/kg rtPA (the clinical dose in stroke patients). In this study, we compared the effects of these doses on mean time to reperfusion, reperfusion slope, brain infarct volume and edema in a rat model of thrombo-embolic stroke. Our data provide evidence that the dose of 0.9 mg/kg rtPA is as appropriate as that of 10 mg/kg for preclinical stroke studies in rodents.