Ischemic preconditioning in the brain

Preactivation of Notch1 in remote ischemic preconditioning reduces cerebral ischemia-reperfusion injury through crosstalk with the NF-κB pathway

Background

Remote ischemic preconditioning (RIPC) initiates endogenous protective pathways in the brain from a distance and represents a new, promising paradigm in neuroprotection against cerebral ischemia-reperfusion (I/R) injury. However, the underlying mechanism of RIPC-mediated cerebral ischemia tolerance is complicated and not well understood. We reported previously that preactivation of Notch1 mediated the neuroprotective effects of cerebral ischemic preconditioning in rats subjected to cerebral I/R injury. The present study seeks to further explore the role of crosstalk between the Notch1 and NF-κB signaling pathways in the process of RIPC-induced neuroprotection.

Methods

Middle cerebral artery occlusion and reperfusion (MCAO/R) in adult male rats and oxygen-glucose deprivation and reoxygenation (OGD/R) in primary hippocampal neurons were used as models of I/R injury in vivo and in vitro, respectively. RIPC was induced by a 3-day procedure with 4 cycles of 5 min of left hind limb ischemia followed by 5 min of reperfusion each day before MCAO/R. Intracerebroventricular DAPT injection and sh-Notch1 lentivirus interference were used to inhibit the Notch1 signaling pathway in vivo and in vitro, respectively. After 24 h of reperfusion, neurological deficit scores, infarct volume, neuronal apoptosis, and cell viability were assessed. The protein expression levels of NICD, Hes1, Phospho-IKKα/β (p-IKK α/β), Phospho-NF-κB p65 (p-NF-κB p65), Bcl-2, and Bax were assessed by Western blotting.

Results

RIPC significantly improved neurological scores and reduced infarct volume and neuronal apoptosis in rats subjected to I/R injury. OGD preconditioning significantly reduced neuronal apoptosis and improved cell viability after I/R injury on days 3 and 7 after OGD/R. However, the neuroprotective effect was reversed by DAPT in vivo and attenuated by Notch1-RNAi in vitro. RIPC significantly upregulated the expression of proteins related to the Notch1 and NF-κB pathways. NF-κB signaling pathway activity was suppressed by a Notch1 signaling pathway inhibitor and Notch1-RNAi.

Conclusions

The neuroprotective effect of RIPC against cerebral I/R injury was associated with preactivation of the Notch1 and NF-κB pathways in neurons. The NF-κB pathway is a downstream target of the Notch1 pathway in RIPC and helps protect focal cerebral I/R injury.

Post-ischemic administration of 5-methoxyindole-2-carboxylic acid at the onset of reperfusion affords neuroprotection against stroke injury by preserving mitochondrial function and attenuating oxidative stress

We previously reported that 5-methoxyindole-2-carboxylic acid (MICA) could induce preconditioning effect in the ischemic brain of rat. In the present study, we addressed the question of whether MICA could also trigger a postconditioning effect in ischemic stroke. To this end, MICA (100 mg/kg body weight) was injected intraperitoneally at the onset of 24 h reperfusion following 1 h ischemia in rat brain. Results indicate that stroked animals treated with MICA showed less brain infarction volume than that of vehicle-treated animals. Further experiments revealed that brain mitochondrial complexes I and IV showed elevated enzymatic activities in MICA treated group and the elevation in complex I activity was likely contributed by seemingly enhanced expression of many complex I subunits, which was determined by mass spectral peptide sequencing. When compared with vehicle-treated rats, the preservation of complexes I and IV activities was shown to be accompanied by enhanced mitochondrial membrane potential, increased ATP production, and decreased caspase-3 activity. Additional studies also indicate the involvement of NQO1 upregulation by the Nrf2 signaling pathway in this MICA postconditioning paradigm. Consequently, attenuated oxidative stress in the MICA treated group reflected by decrease in H2O2 production and protein carbonylation and lipid peroxidation was detected. Taken together, the present study demonstrates that MICA can also induce a postconditioning effect in the ischemic brain of rat and the underlying mechanism likely involves preservation of mitochondrial function, upregulation of cellular antioxidative capacity, and attenuation of oxidative stress.

Chemical Conditioning as an Approach to Ischemic Stroke Tolerance: Mitochondria as the Target

It is well established that the brain can be prepared to resist or tolerate ischemic stroke injury, and mitochondrion is a major target for this tolerance. The preparation of ischemic stroke tolerance can be achieved by three major approaches: ischemic conditioning, hypoxic conditioning and chemical conditioning. In each conditioning approach, there are often two strategies that can be used to achieve the conditioning effects, namely preconditioning (Pre-C) and postconditioning (Post-C). In this review, we focus on chemical conditioning of mitochondrial proteins as targets for neuroprotection against ischemic stroke injury. Mitochondrial targets covered include complexes I, II, IV, the ATP-sensitive potassium channel (mitoKATP), adenine dinucleotide translocase (ANT) and the mitochondrial permeability transition pore (mPTP). While numerous mitochondrial proteins have not been evaluated in the context of chemical conditioning and ischemic stroke tolerance, the paradigms and approaches reviewed in this article should provide general guidelines on testing those mitochondrial components that have not been investigated. A deep understanding of mitochondria as the target of chemical conditioning for ischemic stroke tolerance should provide valuable insights into strategies for fighting ischemic stroke, a leading cause of death in the world.

Neuroprotection by peripheral nerve electrical stimulation and remote postconditioning against acute experimental ischaemic stroke

OBJECTIVE

Local electrical stimulation (ES) was reported to protect the brain during ischaemic injury, while the protective effect of limb remote ischaemic postconditioning (RIPostC) was confirmed. The aim of this study was to explore whether remote peripheral nerve ES exerted neuroprotection and whether this procedure shared the same neuroprotective mechanism underlying RIPostC.

METHODS

Stroke in Sprague-Dawley rats was induced by distal middle cerebral artery occlusion (dMCAO). Rats were divided into five groups: dMCAO, RIPostC, ES, nerve resection (NR) + ES and RIPostC+ES. Twenty-four hours after reperfusion, rats were examined for neurobehavioural function, including forelimb fault placing test, Ludmila Belayev 12 score test, and infarct volume. The expression of Bcl-2 and cleaved-caspase-3 in ischaemic cortex was assessed by Western blot.

RESULTS

In forelimb fault placing test, as compared to the highest score in the stroke-only group, RIPostC, ES and RIPostC+ES groups showed a significantly (P < 0.01) lower score. The results were similar for the Ludmila Belayev 12 score test. The infarct volume of the treatment groups also exhibited significant (P < 0.01) reduction as compared to the stroke-only group. The volume of infarct tissue in the combination of RIPostC+ES was significantly less than RIPostC and ES alone (P < 0.05). Furthermore, NR blocked the ES's protection (P < 0.05) as compared to the ES group by using above-mentioned methods. Bcl-2 was upregulated, while cleaved-caspase-3 was downregulated in the experimental groups as compared to the control group. No difference was found among the experimental groups.

DISCUSSION

Peripheral nerve ES appears to have a neuroprotective effect in a rat dMCAO model. This effect may indicate a neural protective mechanism underlying beneficial effect of RIPostC.

Tumor necrosis factor-α promotes the expression of excitatory amino-acid transporter 2 in astrocytes: Optimal concentration and incubation time

The aim of the present study was to determine whether tumor necrosis factor (TNF)-α regulates the expression levels of excitatory amino-acid transporters (EAATs) in primary astrocytes and its roles in brain ischemia. Exogenous TNF-α was administered to pure cultured astrocytes and the expression levels of EAAT1, EAAT2 and glial fibrillary acidic protein (GFAP) were evaluated. The results showed that TNF-α at 10 ng/ml enhanced the expression of EAAT2 in a time-dependent manner, while the expression levels of EAAT1 and GFAP did not change. To determine whether the elevation in the levels of the EAAT2 protein induced by TNF-α had a beneficial effect on ischemic insult, TNF-α was applied to in vitro models of cerebral ischemia; the treatment was observed to increase neuronal viability. The present results suggest that a relatively short-term application of an optimal concentration of TNF-α may protect neurons against ischemic injury by elevating the expression of EAAT2 in astrocytes.

Protein redox modification as a cellular defense mechanism against tissue ischemic injury

Protein oxidative or redox modifications induced by reactive oxygen species (ROS) or reactive nitrogen species (RNS) not only can impair protein function, but also can regulate and expand protein function under a variety of stressful conditions. Protein oxidative modifications can generally be classified into two categories: irreversible oxidation and reversible oxidation. While irreversible oxidation usually leads to protein aggregation and degradation, reversible oxidation that usually occurs on protein cysteine residues can often serve as an “on and off” switch that regulates protein function and redox signaling pathways upon stress challenges. In the context of ischemic tolerance, including preconditioning and postconditioning, increasing evidence has indicated that reversible cysteine redox modifications such as S-sulfonation, S-nitrosylation, S-glutathionylation, and disulfide bond formation can serve as a cellular defense mechanism against tissue ischemic injury. In this review, I highlight evidence of cysteine redox modifications as protective measures in ischemic injury, demonstrating that protein redox modifications can serve as a therapeutic target for attenuating tissue ischemic injury. Prospectively, more oxidatively modified proteins will need to be identified that can play protective roles in tissue ischemic injury, in particular, when the oxidative modifications of such identified proteins can be enhanced by pharmacological agents or drugs that are available or to be developed.

Recombinant human erythropoietin improves gut barrier function in a hemorrhagic shock and resuscitation rat model

BACKGROUND

Gut injury and bacterial translocation develop and persist after limited periods of hemorrhagic shock. Erythropoietin (EPO) can exert hemodynamic, anti-inflammatory, and tissue protective effects. We tested the hypothesis that EPO given at the time of resuscitation with saline will reduce functional ileal injury 24 hours after shock.

METHODS

Sprague-Dawley rats (n = 6 per group) were randomized to sham surgery or hemorrhagic shock maintained at mean arterial pressure 40 mm Hg for 60 minutes and then treated with either saline resuscitation (three times the volume of shed blood) or saline + recombinant human EPO (rHuEPO) resuscitation. Intravenous rHuEPO (1,000 U/kg) was given at the start of saline resuscitation, and at 24 hours ileal function was evaluated using quantitative cultures of mesenteric lymph nodes to assess for bacterial translocation (colony-forming units per gram of tissue [CFU/g]), determination of portal vein plasma endotoxin levels and histopathological evaluation using semi-thin plastic sections of the distal ileum. In a second series of animals, fluorescein isothiocyanate-dextran 4000 (FD-4) was used to assess mucosal permeability of the distal ileum to macromolecules.

RESULTS

At 24 hours, the saline group had morphologic evidence of intestinal injury when compared with the sham group, and the degree of mucosal injury was less in the saline + rHuEPO when compared with the saline group, which demonstrated significantly reduced bacterial translocation to the mesenteric lymph nodes (383 CFU/g ± 111 CFU/g vs. 1130 CFU/g ± 297 CFU/g; p < 0.05) and decreased terminal ileum permeability to FD-4 (3.08 μg/mL ± 0.31 μg/mL vs. 5.14 μg/mL ± 0.88 μg/mL; p < 0.05). No significant difference was found in the portal vein endotoxin levels between the two groups. Histopathological evaluation demonstrated a trend for decreased enterocyte disarray or disruption and vacuolization in the saline + rHuEPO versus saline group.

CONCLUSION

Using rHuEPO at time of saline resuscitation resulted in decreased bacterial translocation and permeability to macromolecules 24 hours after shock. These observations suggest that rHuEPO can mediate a protective effect on intestinal mucosal barrier function during ischemic injury.

Protecting motor networks during perinatal ischemia: the case for delta-opioid receptors

Perinatal ischemia is a common clinical problem with few successful therapies to prevent neuronal damage. Delta opioid receptor (DOR) activation is a versatile, evolutionarily conserved, endogenous neuroprotective mechanism that blocks several steps in the deleterious cascade of neurological events during ischemia. DOR activation prior to ischemia or severe hypoxia is neuroprotective in spinal motor networks, as well as cortical, cerebellar, and hippocampal neural networks. In addition to providing acute and long-lasting neuroprotection against ischemia, DOR activation appears to provide neuroprotection when given before, during, or following the onset of ischemia. Finally, DORs can be upregulated by several physiological and experimental perturbations. Potential adverse side effects affecting motor control, such as respiratory depression and seizures, are not well established in young mammals and may be mitigated by altering drug choice and method of drug administration. The unique features of DOR-dependent neuroprotection make it an attractive potential therapy that may be given to at-risk pregnant mothers shortly before delivery to provide long-lasting neuroprotection against unpredictable perinatal ischemic events.

Is There a Future for Neuroprotective Agents in Cardiac Surgery?

This article gives an overview of neuroprotective drugs that were recently tested in clinical trials in cardiac surgery. Also, recommendations are given for successful translational research and considerations for management during cardiac surgery.

Neuroprotective effect of combined hypoxia-induced VEGF and bone marrow-derived mesenchymal stem cell treatment

PURPOSES

To avoid unwanted adverse effects of higher doses of single treatment of stem cells and gene therapy and increase the therapeutic efficacies, we hypothesized the combined therapy with stem cells and gene therapy. This study assessed the neuroprotective effects of combined gene therapy and stem cell treatment under ischemic hypoxia conditions using hypoxia-inducible vascular endothelial growth factor (VEGF) and bone marrow-derived mesenchymal stem cells (BMSC).

METHODS

Experimental groups included the control which was N2A cells transfected with empty vectors, the transfection only group which was N2A cells treated with pEpo-SV-VEGF alone, the BMSC only group which was N2A cells transfected with empty vectors and cocultured with BMSCs, and the combined treatment group which was N2A cells treated with pEpo-SV-VEGF and cocultured with BMSCs. Each group was transfected for 4 h and cultured at 37 degrees C and 5% CO2 for 24 h. Each group was then cultivated under hypoxic conditions (1% O2) for 12 h. Neuroprotective effects were assessed by reverse transcription polymerase chain reaction, annexin V, and cytotoxicity assay.

RESULTS

Neurons exposed to hypoxic conditions exhibited neuronal apoptosis. Compared to single treatments, the combined hypoxia-inducible VEGF and BMSC treatment demonstrated a significant increase in VEGF expression and decreased neuronal apoptosis.

CONCLUSIONS

These results suggest that combined pEpo-SV-VEGF and BMSC treatment is effective in protecting neurons against hypoxic ischemic injury.

Cerebrospinal fluid following cerebral ischemia accelerates the proliferation of bone marrow stromal cells in vitro

The central nervous system in the embryo develops around the cerebrospinal fluid (CSF), which regulates cell proliferation and differentiation. Neurogenesis has been also reported in the subventricular zone (SVZ), which is close to CSF, after stroke in rats. In this study, CSF extracted following stroke in rats was added to bone marrow stromal cell (MSC) culture in vitro, and the proliferation and differentiation of MSCs were studied. Primary cultures of MSCs were obtained from 7-week-old Lewis rats and incubated in a plastic tissue culture flask. CSF was retrieved from other rats 48 hrs after 0, 15 and 75 min after middle cerebral artery occlusion (MCAO). CSF from these three groups were added to respective MSC culture solutions, and the cells were then incubated for 72 hrs. Western blots of the extracellular signal-regulated kinase-1 and -2 (Erk1/2) were obtained just after the CSF induction. The expressions of CD34, CD45, CD90 and CD108 were assessed by flow cytometric analysis. The proliferation of MSCs was accelerated by the addition of post-stroke CSF, especially in the 15-min MCAO, in a dose-dependent manner. The morphology and surface antigens of the cells were maintained in all groups. Phosphorylated-Erk1/2 was elevated in all the CSF-treated groups, although this effect was more enhanced in the 15-min MCAO group. Our data indicate that the addition of post-stroke CSF to the primary medium stimulated the proliferation of MSCs, and that these MSCs maintained their characteristics through the p-Erk1/2 pathway. These results suggest that use of post-stroke CSF as a component of culture media could facilitate the autologous transplantation of MSCs.

Mild hypobaric hypoxia preconditioning up-regulates expression of transcription factors c-Fos and NGFI-A in rat neocortex and hippocampus

Transcription factors c-Fos and NGFI-A encoded by immediate early genes largely participate in the biochemical cascade leading to genomically driven lasting adaptation by neurons to injurious exposures including hypoxia/ischemia. Present study was designed to examine the involvement of c-Fos and NGFI-A in the development of brain hypoxic tolerance induced by mild hypoxic preconditioning. Earlier we have reported that preconditioning by repetitive mild hypobaric hypoxia (MHH) considerably increases neuronal resistance to subsequent severe injurious exposures. Herein, changes of c-Fos and NGFI-A expression in vulnerable rat brain areas (hippocampus, neocortex) in response to preconditioning MHH itself were studied using quantitative immunocytochemistry. Exposure to MHH differentially enhanced c-Fos and NGFI-A expression in neocortex and hippocampal fields 3-24h following the last MHH trial. The c-Fos up-regulation was the most pronounced in neocortex, CA1, and dentate gyrus, but it was twice lower in CA3/CA4. The up-regulation of NGFI-A in CA1, dentate gyrus and neocortex was 1.5-2-fold lower than that of c-Fos; but in CA3 and CA4 the rates of the c-Fos and NGFI-A induction were comparable. The present findings indicate that cooperative but differential activation of c-Fos and NGFI-A expression in vulnerable brain areas contribute to the development of tolerance achieved by MHH preconditioning.

Reduced early hypoxic/ischemic brain damage is associated with increased GLT-1 levels in mice expressing mutant (P301L) human tau

Mutations in tau proteins are associated with a group of neurodegenerative diseases, termed tauopathies. To investigate whether over-expressing human tau with P301L mutation also affects stroke-induced brain damage, we performed hypoxia/ischemia (H/I) in young adult P301L tau transgenic mice. Surprisingly, brain infarct volume was significantly smaller in transgenic mice compared to wild-type mice 24 h after H/I induction. TUNEL staining also revealed less brain apoptosis in transgenic mice following H/I. H/I resulted in a significant increase in tau fragments generated by caspase activation and a marked decrease in tau phosphorylation at residue T231 in cortex of wild-type but not transgenic mice. Activation of calpain and caspase-3 following H/I was also reduced in transgenic compared to wild-type mice, as reflected by lower levels of the specific spectrin breakdown products generated by calpain or caspase-3. Finally, basal levels of the glial glutamate transporter, GLT-1, were higher in brains of transgenic as compared to wild-type mice. These results support the idea that enhanced levels of GLT-1 in transgenic mice are responsible for reducing H/I-induced brain damage by decreasing extracellular glutamate accumulation and subsequent calpain and caspase activation.

Hippocampal transcriptome after status epilepticus in mice rendered seizure damage-tolerant by epileptic preconditioning features suppressed calcium and neuronal excitability pathways

Preconditioning brain with a sub-lethal stressor can temporarily generate a damage-refractory state. Microarray analyses have defined the changes in hippocampal gene expression that follow brief preconditioning seizures, but not the transcriptome after a prolonged and otherwise injurious seizure in previously preconditioned brain. Presently, microarray analysis was performed 24 h after status epilepticus in mice that had received previously either seizure preconditioning (tolerance) or sham-preconditioning (injury). Transcriptional changes in the hippocampal CA3 subfield of >or=2 fold were detected for 1357 genes in the tolerance group compared to a non-seizure control group, with 54% up-regulated. Of these regulated genes, 792 were also regulated in the injury group. Among the remaining 565 genes regulated only in tolerance, 73% were down-regulated. Analysis of the genes differentially suppressed in tolerance identified calcium signaling, ion channels and excitatory neurotransmitter receptors, and the synapse as over-represented among pathways, functions and compartments. Finally, 12 days continuous EEG recordings determined mice with induced tolerance had fewer spontaneous electrographic seizures compared to the injury group. Our data suggest the transcriptional phenotype of neuroprotection in tolerance may be dictated by the biology of the preconditioning stressor, functions by transcriptional reduction of vulnerability to excitotoxicity, and has anti-epileptogenic effects.

Preconditioning induces prolonged expression of transcription factors pCREB and NF-kappa B in the neocortex of rats before and following severe hypobaric hypoxia

Preconditioning using mild repetitive hypobaric hypoxia is known to increase a tolerance of brain neurons to severe hypoxia and other injurious exposures. In the present study, the effects of mild hypoxic preconditioning on the expression of transcription factors NF-kappaB and phosphorylated CREB (pCREB) has been studied in the neocortex of rats exposed to severe hypobaric hypoxia. As revealed by quantitative immunocytochemistry, the injurious severe hypobaric hypoxia (180 Torr, 3 h) remarkably reduced the neocortical levels of pCREB and NF-kappaB. The three-trial hypoxic preconditioning (360 Torr, 2 h, 3 days) induced persistent up-regulation of pCREB and NF-kappaB expression in the neocortex of rats 3-24 h following the severe hypoxia. In addition, the preconditioning alone which was not followed by the severe hypoxia, considerably increased neocortical pCREB and NF-kappaB levels. The findings suggest a role for transcription factors cAMP response element-binding protein and NF-kappaB in the neuroprotective mechanisms activated by the hypoxic preconditioning.

Leukaemia inhibitory factor is over-expressed by ischaemic brain tissue concomitant with reduced plasma expression following acute stroke

Leukaemia inhibitory factor (LIF) is a glycoprotein of the interleukin-6 family, which has potent pro-inflammatory properties and is involved in regulation of neuronal differentiation. We have previously identified its upregulation in gene microarrays following acute ischaemic stroke in man. LIF expression and localization was measured in human ischaemic stroke autopsy specimens, in a rat model of middle cerebral artery occlusion (MCAO) and in human foetal neural cell cultures following oxygen-glucose deprivation (OGD) by Western blotting and immunohistochemistry. Circulating LIF was determined in the plasma of patients in the hyper-acute stroke phase using a multiplex enzyme-linked-immunosorbent serologic assay system. Patients demonstrated an increase in LIF expression in peri-infarcted regions with localization in neurons and endothelial cells of microvessels surrounding the infarcted core. The rat MCAO model showed similar upregulation in neurons with a peak increase at 90 min. Circulating serum LIF expression was significantly decreased in the hyper-acute phase of stroke. Brain-derived neurons and glia cultured in vitro demonstrated an increase in gene/protein and protein expression respectively following exposure to OGD. Increased LIF expression in peri-infarcted regions and sequestration from the peripheral circulation in acute stroke patients are characteristic of the pathobiological response to ischaemia and tissue damage.

The role of glutamate transporters in neurodegenerative diseases and potential opportunities for intervention

Extracellular concentrations of the predominant excitatory neurotransmitter, glutamate, and related excitatory amino acids are maintained at relatively low levels to ensure an appropriate signal-to-noise ratio and to prevent excessive activation of glutamate receptors that can result in cell death. The latter phenomenon is known as 'excitotoxicity' and has been associated with a wide range of acute and chronic neurodegenerative disorders, as well as disorders that result in the loss of non-neural cells such as oligodendroglia in multiple sclerosis. Unfortunately clinical trials with glutamate receptor antagonists that would logically seem to prevent the effects of excessive receptor activation have been associated with untoward side effects or little clinical benefit. In the mammalian CNS, the extracellular concentrations of glutamate are controlled by two types of transporters; these include a family of Na(+)-dependent transporters and a cystine-glutamate exchange process, referred to as system X(c)(-). In this review, we will focus primarily on the Na(+)-dependent transporters. A brief introduction to glutamate as a neurotransmitter will be followed by an overview of the properties of these transporters, including a summary of the presumed physiologic mechanisms that regulate these transporters. Many studies have provided compelling evidence that impairing the function of these transporters can increase the sensitivity of tissue to deleterious effects of aberrant activation of glutamate receptors. Over the last decade, it has become clear that many neurodegenerative disorders are associated with a change in localization and/or expression of some of the subtypes of these transporters. This would suggest that therapies directed toward enhancing transporter expression might be beneficial. However, there is also evidence that glutamate transporters might increase the susceptibility of tissue to the consequences of insults that result in a collapse of the electrochemical gradients required for normal function such as stroke. In spite of the potential adverse effects of upregulation of glutamate transporters, there is recent evidence that upregulation of one of the glutamate transporters, GLT-1 (also called EAAT2), with beta-lactam antibiotics attenuates the damage observed in models of both acute and chronic neurodegenerative disorders. While it seems somewhat unlikely that antibiotics specifically target GLT-1 expression, these studies identify a potential strategy to limit excitotoxicity. If successful, this type of approach could have widespread utility given the large number of neurodegenerative diseases associated with decreases in transporter expression and excitotoxicity. However, given the massive effort directed at developing glutamate receptor agents during the 1990s and the relatively modest advances to date, one wonders if we will maintain the patience needed to carefully understand the glutamatergic system so that it will be successfully targeted in the future.

Effect of ischemic preconditioning on brain tissue gases and pH during temporary cerebral artery occlusion

Previous studies have demonstrated that a brief period of ischemia protect against subsequent severe ischemic insults to the brain, i.e. preconditioning. We evaluated the effects of ischemic preconditioning, produced by 2 min proximal temporary artery occlusion, on brain tissue gases and acidity during clipping of cerebral aneurysm. Twelve patients with aneurysmal subarachnoid hemorrhage were recruited. All patients received standard anesthetics. After craniotomy, a calibrated multiparameter catheter was inserted to measure oxygen (PtO2) tension, carbon dioxide (PtCO2) tension and pH (pHt) in tissue at risk of ischemia during temporary artery occlusion. In patients assigned to the preconditioning group, proximal artery was occluded initially for 2 min and was allowed to reperfuse for 30 min. All patients underwent cerebral artery occlusion for clipping of aneurysm. The rate of change in PtO2, PtCO2 and pHt after artery occlusion were compared between groups using unpaired t test. Baseline brain tissue gases and pHt were similar between groups. Following artery occlusion, the decline in PtO2 and pHt were significantly slower in the preconditioning group compared with the routine care group. These results suggested that ischemic preconditioning attenuates tissue hypoxia during subsequent artery occlusion. Brief occlusion of the proximal artery may be a simple maneuver for brain protection during complex cerebrovascular surgery.