Postconditioning with isoflurane reduced ischemia-induced brain injury in rats

Volatile anesthetics attenuate oxidative stress-reduced activity of glutamate transporter type 3

BACKGROUND

Volatile anesthetics enhance the activity of glutamate transporter Type 3 (also called excitatory amino acid transporter Type 3, EAAT3), the major neuronal EAAT. In addition to glutamate, EAAT3 can also uptake L-cysteine, the rate-limiting substrate for the synthesis of glutathione. Our previous study showed that oxidative stress inhibited glutamate-induced EAAT3 activity. We determined whether oxidative stress would reduce L-cysteine-induced EAAT3 activity and whether this reduction would be attenuated by volatile anesthetics.

METHODS

Rat EAAT3 was expressed in Xenopus oocytes. L-glutamate- and L-cysteine-induced membrane currents were recorded using the 2-electrode voltage clamp technique. The peak current was quantified to reflect the amount of transported substrates because transport of substrates via EAATs is electrogenic.

RESULTS

Exposure of oocytes to 5 mM tert-butyl hydroperoxide, an organic oxidant, for 10 min reduced the V(max), but did not affect the K(m), of EAAT3 for L-cysteine. The volatile anesthetics isoflurane, sevoflurane, and desflurane at concentrations from 1% to 3% attenuated the tert-butyl hydroperoxide-reduced EAAT3 activity for L-glutamate and L-cysteine.

CONCLUSIONS

Our results suggest that volatile anesthetics preserve EAAT3 function to transport L-glutamate and L-cysteine under oxidative stress, which may be a mechanism for the neuroprotective effects of volatile anesthetics.

Delayed treatment with isoflurane attenuates lipopolysaccharide and interferon gamma-induced activation and injury of mouse microglial cells

BACKGROUND

Isoflurane pretreatment can induce protection against lipopolysaccharide and interferon gamma (IFNgamma)-induced injury and activation of mouse microglial cells. This study's goal was to determine whether delayed isoflurane treatment is protective.

METHODS

Mouse microglial cells were exposed to various concentrations of isoflurane for 1 h immediately after the initiation of lipopolysaccharide (10 or 1000 ng/ml) and IFNgamma (10 U/ml) stimulation or to 2% isoflurane for 1 h at various times after initiation of the stimulation. Nitrite production, lactate dehydrogenase release, and cell viability measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay were assessed after stimulation with lipopolysaccharide and IFNgamma for 24 h. Inducible nitric oxide synthase (iNOS) protein expression was quantified by Western blotting. The iNOS expression in mouse brain was also studied.

RESULTS

Isoflurane applied 0 and 2 h after the initiation of lipopolysaccharide and IFNgamma stimulation improved cell viability. Isoflurane at 2%, but not at 1 or 3%, reduced the lipopolysaccharide and IFNgamma-induced nitrite production and decreased cell viability. Aminoguanidine, an iNOS inhibitor, also attenuated this decreased cell viability. Chelerythrine and bisindolylmalemide IX, protein kinase C inhibitors, abolished isoflurane effects on cell viability and iNOS expression after lipopolysaccharide and IFNgamma application. Isoflurane also decreased lipopolysaccharide-induced iNOS expression in mouse brain. Late isoflurane application to microglial cells reduced lipopolysaccharide and IFNgamma-induced lactate dehydrogenase release that was not inhibited by aminoguanidine.

CONCLUSIONS

These results suggest that delayed isoflurane treatment can reduce lipopolysaccharide and IFNgamma-induced activation and injury of microglial cells. These effects may be mediated by protein kinase C.

Effects of sevoflurane on primary neuronal cultures of embryonic rats

BACKGROUND AND OBJECTIVE

Commonly used anaesthetics can cause neurodegeneration in the developing brain. Sevoflurane, a widely used substance in paediatric anaesthesia, has not been analysed thus far. This study was carried out to investigate the effects of sevoflurane on neuronal cell viability.

METHODS

Primary cortical neuronal cultures were prepared from Wistar rat embryos (E18), kept in 100 microl Gibco-Neurobasal-A medium and exposed to 4 and 8 Vol.% sevoflurane for up to 48 h. Cell viability was assessed using the methyltetrazolium assay and was related to untreated controls. To evaluate the role of gamma-aminobutyric acid type A receptors, untreated cells were preincubated with the receptor antagonists gabazine or picrotoxin and were subsequently exposed to 8 Vol.% sevoflurane and the receptor antagonist. Cell viability was assessed and compared with that of sevoflurane-treated controls.

RESULTS

Up to 6 (8 Vol.%) and 12 h (4 Vol.%) of exposure to sevoflurane, cell viability was equal when compared with untreated controls. Only longer exposure times led to significantly lowered cell viability. After 12 h of exposure, no significant differences in cell viability were found between these two series. Cell viability of cultures treated with sevoflurane and the receptor antagonists showed no significant differences when compared with sevoflurane-exposed controls.

CONCLUSION

These results suggest that sevoflurane does not cause neurodegeneration in primary cortical neurons of the rat following clinically relevant exposure times and concentrations.

Limb remote ischemic postconditioning protects against focal ischemia in rats

Remote ischemic postconditioning (RIP) refers to an ischemia conducted in a distant organ that protects against a prior ischemia in another organ. We tested whether RIP protects against focal ischemia in the rat brain. Stroke was generated by a permanent occlusion of the left distal middle cerebral artery combined with a 30-min occlusion of the bilateral common carotid arteries (CCA) in male rats. After CCA release, RIP was generated by three cycles of 15-min occlusion/15-min release of the left-hind femoral artery. The results showed that rapid RIP performed immediately after CCA release reduced infarction by 67% measured at 2 days after stroke. In addition, delayed RIP initiated as late as 3 h, but not 6 h, still robustly reduced infarction by 43% 2 days after stroke. RIP's protective effect was abolished by injecting the protein synthesis inhibitor, cycloheximide, and the afferent nerve blocker, capsaicin, suggesting that RIP blocks ischemic injury by modulating protein synthesis and nerve activity. Nevertheless, rapid RIP did not reduce infarction size 2 months after stroke while it ameliorated the outcome of the behavioral test. In conclusion, RIP attenuates brain injury after focal ischemia.

Isoflurane induces a postconditioning effect on bovine pulmonary arterial endothelial cells exposed to oxygen-glucose deprivation

Application of volatile anesthetics during the onset of reperfusion reduced ischemia-induced cardiac and brain injury (anesthetic postconditioning). This study was designed to evaluate whether volatile anesthetics induced a postconditioning effect in endothelial cells. Bovine pulmonary arterial endothelial cell (BPAEC) cultures were exposed to oxygen-glucose deprivation, a condition to simulate ischemia in vitro, for 3 h. The volatile anesthetics isoflurane and desflurane were applied during the early phase of simulated reperfusion. Cell injury was quantified by lactate dehydrogenase (LDH) release and flow cytometrical measurement after annexin V and propidium iodide staining. Oxygen-glucose deprivation and the subsequent simulated reperfusion increased LDH release and annexin V-positive staining cells, a characteristic of cell apoptosis. Posttreatment with isoflurane, but not desflurane, reduced this cell injury. This protection was apparent even when 2% isoflurane was applied at 60 min after the onset of reperfusion. The isoflurane postconditioning effect was abolished by glybenclamide, a general ATP sensitive K(+) (K(ATP)) channel blocker, 5-hydroxydecanoate, a mitochondrial K(ATP) channel blocker, and chelerythrine, a protein kinase C inhibitor. Diazoxide, a mitochondrial K(ATP) channel activator, applied at the onset of reperfusion also decreased oxygen-glucose deprivation-induced endothelial cell injury. This diazoxide-induced protection was abolished by chelerythrine and 5-hydroxydecanoate. We conclude that isoflurane induced a postconditioning effect in BPAEC. The effective time window of isoflurane postconditioning was from 0 to 60 min after the onset of reperfusion. This isoflurane postconditioning effect may be mediated by mitochondrial K(ATP) channels and PKC. PKC may be downstream of mitochondrial K(ATP) channels for this isoflurane effect.

Ischemic postconditioning as a novel avenue to protect against brain injury after stroke

Ischemic postconditioning initially referred to a stuttering reperfusion performed immediately after reperfusion, for preventing ischemia/reperfusion injury in both myocardial and cerebral infarction. It has evolved into a concept that can be induced by a broad range of stimuli or triggers, and may even be performed as late as 6 h after focal ischemia and 2 days after transient global ischemia. The concept is thought to be derived from ischemic preconditioning or partial/gradual reperfusion, but in fact the first experiment for postconditioning was carried out much earlier than that of preconditioning or partial/gradual reperfusion, in the research on myocardial ischemia. This review first examines the protective effects and parameters of postconditioning in various cerebral ischemic models. Thereafter, it provides insights into the protective mechanisms of postconditioning associated with reperfusion injury and the Akt, mitogen-activated protein kinase (MAPK), protein kinase C (PKC), and ATP-sensitive K+ (K(ATP)) channel cell signaling pathways. Finally, some open issues and future challenges regarding clinical translation of postconditioning are discussed.

Evolution of the neurochemical profile after transient focal cerebral ischemia in the mouse brain

Evolution of the neurochemical profile consisting of 19 metabolites after 30 mins of middle cerebral artery occlusion was longitudinally assessed at 3, 8 and 24 h in 6 to 8 microL volumes in the striatum using localized 1H-magnetic resonance spectroscopy at 14.1 T. Profound changes were detected as early as 3 h after ischemia, which include elevated lactate levels in the presence of significant glucose concentrations, decreases in glutamate and a transient twofold glutamine increase, likely to be linked to the excitotoxic release of glutamate and conversion into glial glutamine. Interestingly, decreases in N-acetyl-aspartate (NAA), as well as in taurine, exceeded those in neuronal glutamate, suggesting that the putative neuronal marker NAA is rather a sensitive marker of neuronal viability. With further ischemia evolution, additional, more profound concentration decreases were detected, reflecting a disruption of cellular functions. We conclude that early changes in markers of energy metabolism, glutamate excitotoxicity and neuronal viability can be detected with high precision non-invasively in mice after stroke. Such investigations should lead to a better understanding and insight into the sequential early changes in the brain parenchyma after ischemia, which could be used for identifying new targets for neuroprotection.

Reduced acute brain injury in PGE2 EP3 receptor-deficient mice after cerebral ischemia

Ischemic stroke is one of the leading causes of mortality and morbidity in humans. During brain ischemia and the subsequent reperfusion that occurs with stroke, the generation of the so-called "proinflammatory" prostaglandin E(2) (PGE(2)) increases significantly. Therefore, interest is growing regarding the differential functions of the individual PGE(2) receptors (EP1-4) and their relative contribution to brain damage following ischemic and inflammatory stimuli. Here, we address the contribution of the EP3 receptor in dictating early outcomes after transient cerebral ischemia. An oxygen-glucose deprivation (OGD)-induced in vitro model of brain ischemia was used in mouse hippocampal slice cultures. For transient ischemia, the right middle cerebral artery (MCA) of wildtype (WT) and EP3 knockout (EP3(-/-)) C57BL/6 male mice was occluded for 90 min and reperfused for 48 or 96 h, after which neurobehavioral scores and infarct volumes were determined. Mean arterial blood pressure, pH, blood gases (PaO(2) and PaCO(2)), cerebral blood flow, and body temperature were also determined before and during ischemia and reperfusion. OGD-induced cell death was significantly lower in brain slice cultures of EP3(-/-) mice than in those of WT mice. EP3(-/-) mice that underwent transient ischemia had significantly smaller infarct volumes than did WT mice at 48 h, but this difference was not sustained at 96 h. Neurological score deficits correlated with infarct volume, but no significant differences in the physiological parameters monitored were detected between the two genotypes. The results further support a role for EP3 receptors in contributing to acute ischemic stroke, but EP3 is not likely the sole contributor to the long-term detrimental consequences of PGE(2).

Delayed postconditioning protects against focal ischemic brain injury in rats

Background

We and others have reported that rapid ischemic postconditioning, interrupting early reperfusion after stroke, reduces infarction in rats. However, its extremely short therapeutic time windows, from a few seconds to minutes after reperfusion, may hinder its clinical translation. Thus, in this study we explored if delayed postconditioning, which is conducted a few hours after reperfusion, offers protection against stroke.

Methods and Results

Focal ischemia was generated by 30 min occlusion of bilateral common carotid artery (CCA) combined with permanent occlusion of middle cerebral artery (MCA); delayed postconditioning was performed by repetitive, brief occlusion and release of the bilateral CCAs, or of the ipsilateral CCA alone. As a result, delayed postconditioning performed at 3h and 6h after stroke robustly reduced infarct size, with the strongest protection achieved by delayed postconditioning with 6 cycles of 15 min occlusion/15 min release of the ipsilateral CCA executed from 6h. We found that this delayed postconditioning provided long-term protection for up to two months by reducing infarction and improving outcomes of the behavioral tests; it also attenuated reduction in 2-[¹⁸F]-fluoro-2-deoxy-D-glucose (FDG)-uptake therefore improving metabolism, and reduced edema and blood brain barrier leakage. Reperfusion in ischemic stroke patients is usually achieved by tissue plasminogen activator (tPA) application, however, t-PA's side effect may worsen ischemic injury. Thus, we tested whether delayed postconditioning counteracts the exacerbating effect of t-PA. The results showed that delayed postconditioning mitigated the worsening effect of t-PA on infarction.

Conclusion

Delayed postconditioning reduced ischemic injury after focal ischemia, which opens a new research avenue for stroke therapy and its underlying protective mechanisms.