Mahmuda Hossain

Dexmedetomidine Attenuates Isoflurane-induced Neurocognitive Impairment in Neonatal Rats

Background:Neuroapoptosis is induced by the administration of anesthetic agents to the young. As α2 adrenoceptor signaling plays a trophic role during development and is neuroprotective in several settings of neuronal injury, the authors investigated whether dexmedetomidine could provide functional protection against isoflurane-induced injury. Methods:Isoflurane-induced injury was provoked in organotypic hippocampal slice cultures in vitro or in vivo in postnatal day 7 rats by a 6-h exposure to 0.75% isoflurane with or without dexmedetomidine. In vivo, the α2 adrenoceptor antagonist atipamezole was used to identify if dexmedetomidine neuroprotection involved α2 adrenoceptor activation. The γ-amino-butyric-acid type A antagonist, gabazine, was also added to the organotypic hippocampal slice cultures in the presence of isoflurane. Apoptosis was assessed using cleaved caspase-3 immunohistochemistry. Cognitive function was assessed in vivo on postnatal day 40 using fear conditioning. Results:In vivo dexmedetomidine dose-dependently prevented isoflurane-induced injury in the hippocampus, thalamus, and cortex; this neuroprotection was attenuated by treatment with atipamezole. Although anesthetic treatment did not affect the acquisition of short-term memory, isoflurane did induce long-term memory impairment. This neurocognitive deficit was prevented by administration of dexmedetomidine, which also inhibited isoflurane-induced caspase-3 expression in organotypic hippocampal slice cultures in vitro; however, gabazine did not modify this neuroapoptosis. Conclusion:Dexmedetomidine attenuates isoflurane-induced injury in the developing brain, providing neurocognitive protection. Isoflurane-induced injury in vitro appears to be independent of activation of the γ-amino-butyric-acid type A receptor. If isoflurane-induced neuroapoptosis proves to be a clinical problem, administration of dexmedetomidine may be an important adjunct to prevent isoflurane-induced neurotoxicity.

Xenon and Hypothermia Combine to Provide Neuroprotection from Neonatal Asphyxia

Perinatal asphyxia can result in neuronal injury with long‐term neurological and behavioral consequences. Although hypothermia may provide some modest benefit, the intervention itself can produce adverse consequences. We have investigated whether xenon, an antagonist of the N‐methyl‐D‐aspartate subtype of the glutamate receptor, can enhance the neuroprotection provided by mild hypothermia. Cultured neurons injured by oxygen‐glucose deprivation were protected by combinations of interventions of xenon and hypothermia that, when administered alone, were not efficacious. A combination of xenon and hypothermia administered 4 hours after hypoxic‐ischemic injury in neonatal rats provided synergistic neuroprotection assessed by morphological criteria, by hemispheric weight, and by functional neurological studies up to 30 days after the injury. The protective mechanism of the combination, in both in vitro and in vivo models, involved an antiapoptotic action. If applied to humans, these data suggest that low (subanesthetic) concentrations of xenon in combination with mild hypothermia may provide a safe and effective therapy for perinatal asphyxia. Ann Neurol 2005;58:182–193

Xenon mitigates isoflurane-induced neuronal apoptosis in the developing rodent brain.

Background:Anesthetics, including isoflurane and nitrous oxide, an antagonist of the N-methyl-d-aspartate subtype of the glutamate receptor, have been demonstrated to induce apoptotic neurodegeneration when administered during neurodevelopment. Xenon, also an N-methyl-d-aspartate antagonist, not only lacks the characteristic toxicity produced by other N-methyl-d-aspartate antagonists, but also attenuates the neurotoxicity produced by this class of agent. Therefore, the current study sought to investigate xenons putative protective properties against anesthetic-induced neuronal apoptosis. Method:Separate cohorts (n = 5 or 6 per group) of 7-day-old rats were randomly assigned and exposed to eight gas mixtures: air, 75% nitrous oxide, 75% xenon, 0.75% isoflurane, 0.75% isoflurane plus 35% or 75% nitrous oxide, 0.75% isoflurane plus 30% or 60% xenon for 6 h. Rats were killed, and cortical and hippocampal apoptosis was assessed using caspase-3 immunostaining. In separate cohorts, cortices were isolated for immunoblotting of caspase 3, caspase 8, caspase 9, and cytochrome c. Organotypic hippocampal slices of postnatal mice pups were derived and cultured for 24 h before similar gas exposures, as above, and subsequently processed for caspase-3 immunostaining. Results:In vivo administration of isoflurane enhances neuronal apoptosis. When combined with isoflurane, nitrous oxide significantly increases whereas xenon significantly reduces apoptosis to a value no different from that of controls. In vitro studies corroborate the ability of xenon to attenuate isoflurane-induced apoptosis. Isoflurane enhanced expression of indicators of the intrinsic and common apoptotic pathways; this enhancement was increased by nitrous oxide but attenuated by xenon. Conclusions:The current study demonstrates that xenon prevents isoflurane-induced neonatal neuronal apoptosis.

Xenon Preconditioning Protects against Renal Ischemic-Reperfusion Injury via HIF-1 alpha Activation

The mortality rate from acute kidney injury after major cardiovascular operations can be as high as 60%, and no therapies have been proved to prevent acute kidney injury in this setting. Here, we show that preconditioning with the anesthetic gas xenon activates hypoxia-inducible factor 1alpha (HIF-1alpha) and its downstream effectors erythropoietin and vascular endothelial growth factor in a time-dependent manner in the kidneys of adult mice. Xenon increased the efficiency of HIF-1alpha translation via modulation of the mammalian target of rapamycin pathway. In a model of renal ischemia-reperfusion injury, xenon provided morphologic and functional renoprotection; hydrodynamic injection of HIF-1alpha small interfering RNA demonstrated that this protection is HIF-1alpha dependent. These results suggest that xenon preconditioning is a natural inducer of HIF-1alpha and that administration of xenon before renal ischemia can prevent acute renal failure. If these data are confirmed in the clinical setting, then preconditioning with xenon may be beneficial before procedures that temporarily interrupt renal perfusion.

Xenon Preconditioning Reduces Brain Damage from Neonatal Asphyxia in Rats

Xenon attenuates on-going neuronal injury in both in vitro and in vivo models of hypoxic-ischaemic injury when administered during and after the insult. In the present study, we sought to investigate whether the neuroprotective efficacy of xenon can be observed when administered before an insult, referred to as ‘preconditioning’. In a neuronal–glial cell coculture, preexposure to xenon for 2 h caused a concentration-dependent reduction of lactate dehydrogenase release from cells deprived of oxygen and glucose 24 h later; xenons preconditioning effect was abolished by cycloheximide, a protein synthesis inhibitor. Preconditioning with xenon decreased propidium iodide staining in a hippocampal slice culture model subjected to oxygen and glucose deprivation. In an in vivo model of neonatal asphyxia involving hypoxic–ischaemic injury to 7-day-old rats, preconditioning with xenon reduced infarction size when assessed 7 days after injury. Furthermore, a sustained improvement in neurologic function was also evident 30 days after injury. Phosphorylated cAMP (cyclic adenosine 3′,5′-monophosphate)-response element binding protein (pCREB) was increased by xenon exposure. Also, the prosurvival proteins Bcl-2 and brain-derived neurotrophic factor were upregulated by xenon treatment. These studies provide evidence for xenons preconditioning effect, which might be caused by a pCREB-regulated synthesis of proteins that promote survival against neuronal injury.

Xenon and Sevoflurane Protect against Brain Injury in a Neonatal Asphyxia Model

Background: Perinatal hypoxia–ischemia causes significant morbidity and mortality. Xenon and sevoflurane may be used as inhalational analgesics for labor. Therefore, the authors investigated the potential application of these agents independently and in combination to attenuate perinatal injury. Methods: Oxygen–glucose deprivation injury was induced in pure neuronal or neuronal–glial cocultures 24 h after preconditioning with xenon and/or sevoflurane. Cell death was assessed by lactate dehydrogenase release or staining with annexin V–propidium iodide. The mediating role of phosphoinositide-3-kinase signaling in putative protection was assessed using wortmannin, its cognate antagonist. In separate in vivo experiments, perinatal asphyxia was induced 4 hours after preconditioning with analgesic doses alone and in combination; infarct size was assessed 7 days later, and neuromotor function was evaluated at 30 days in separate cohorts. The role of phosphorylated cyclic adenosine monophosphate response element binding protein in the preconditioning was assessed by immunoblotting. Results: Both anesthetics preconditioned against oxygen–glucose deprivation in vitro alone and in combination. The combination increased cellular viability via phosphoinositide-3- kinase signaling. In in vivo studies, xenon (75%) and sevoflurane (1.5%) alone as well as in combination (20% xenon and 0.75% sevoflurane) reduced infarct size in a model of neonatal asphyxia. Preconditioning with xenon and the combination of xenon and sevoflurane resulted in long-term functional neuroprotection associated with enhanced phosphorylated cyclic adenosine monophosphate response element binding protein signaling. Conclusions: Preconditioning with xenon and sevoflurane provided long-lasting neuroprotection in a perinatal hypoxic–ischemic model and may represent a viable method to preempt neuronal injury after an unpredictable asphyxial event in the perinatal period.

Neuroprotective interaction produced by xenon and dexmedetomidine on in vitro and in vivo neuronal injury models.

Xenon, an NMDA receptor antagonist and dexmedetomidine (Dex), an alpha(2)-adrenoceptor agonist, both exhibit neuroprotective effects. We investigated the nature of their interaction. In vitro: a primary co-culture of neuronal and glial cells derived from neonatal mice was exposed to oxygen and glucose deprivation (OGD) and the resulting neuronal injury was assessed by the release of lactate dehydrogenase (LDH). In vivo: Postnatal rats aged 7 days underwent right common carotid artery ligation followed by 90 min of hypoxia. The area of infarction was assessed at four days post-injury by morphological criteria. Long-term neurological function was evaluated at 30 days post-injury by testing co-ordination on rotarod. Both xenon and Dex concentration-dependently reduced LDH release with IC50 values of 42% atm (95% CI: 35-52) and 0.10 microM (95% CI: 0.08-0.16), respectively. Isobolographic analysis showed that combined effect of xenon and Dex in vitro was additive. In vivo, a combination of xenon and Dex, at doses that are individually not neuroprotective, produced significant neuroprotective effect as measured by reduction in area of infarction. The long-term neurological function data corroborated these morphological data. Our study demonstrates that the combination of xenon and Dex offers neuroprotection additively in vitro and synergistically in vivo.

Combination of Xenon and Isoflurane Produces a Synergistic Protective Effect against Oxygen–Glucose Deprivation Injury in a Neuronal–Glial Co-culture Model

SUSTAINED exposure to glutamate causes neuronal death by overactivation of its receptors, particularly those of the N-methyl-D-aspartate (NMDA) subtype. This process, denoted by the term excitotoxicity, is believed to play an important role in ongoing neuronal injury and death in acute insults, such as ischemic stroke and head trauma. Consequently, the neuroprotective effects of NMDA receptor antagonists, including xenon, have been investigated in a variety of both in vitro and in vivo models of neuronal injury of the type that may occur perioperatively. Notwithstanding their putative beneficial effects, the clinical use of NMDA antagonists has been hindered by the observation that several drugs of this class of compound produce neurotoxicity, characterized by distinctive behavioral and morphologic effects. Although xenon does not seem to have this side effect, it may be desirable to use lower concentrations because of the prohibitive cost of this gas and to permit adequate oxygenation. Therefore, we sought to investigate whether neuroprotective efficacy can be observed when this NMDA receptor antagonist is combined with another putative neuroprotective agent that acts by modulating the -aminobutyric acid (GABA) receptor. The neuronal damage from ischemia may also be a result of loss of inhibitory influences. In the brain, GABA acts as the major inhibitory neurotransmitter; an agonist of the A subtype of the GABA receptor (GABAA) has been shown to be neuroprotective in a transient forebrain ischemia model. Isoflurane potentiates activation of the GABAA receptors, 13 and its neuroprotective effect has been demonstrated previously. Because these anesthetics exert their neuroprotectant properties through different mechanisms, we hypothesized that in combination, their efficacy would be enhanced. To test our hypothesis, we studied the neuroprotective effect of the combination of xenon and isoflurane versus oxygen– glucose deprivation (OGD) injury in a neuronal–glial co-culture model.

Dexmedetomidine exerts dose-dependent age-independent antinociception but age-dependent hypnosis in Fischer rats.

Dexmedetomidine (Dex), an &agr;2-adrenoceptor agonist, is an effective analgesic and sedative drug in adults; however, little information is available about its efficacy in pediatric populations. Some anesthetics exhibit an age-dependent analgesic effect, e.g., nitrous oxide, being relatively ineffective in newborn rats. We investigated the analgesic and hypnotic efficacy of Dex using 6 cohorts of Fischer rats aged 7, 15, 19, 23, and 29 days and adults exposed to either Dex (10 or 50 &mgr;g/kg) or saline subcutaneously. Formalin plantar testing was used to mimic inflammatory pain, and its effect was assessed using immunohistochemical (c-Fos staining) and behavioral methods. The hypnotic action of Dex was assessed by loss of righting reflex. Formalin administration produced a typical nociceptive response in each age group; these nociceptive responses were significantly attenuated by Dex 50 &mgr;g/kg at all ages (P < 0.05), whereas Dex 10 &mgr;g/kg had little effect. Neonatal rats showed the greatest hypnotic sensitivity to Dex (P < 0.05).