Thrombin preconditioning attenuates brain edema induced by erythrocytes and iron

Direct neuronal protection by the protease-activated receptor PAR4 antagonist ML354 after experimental stroke in mice

BACKGROUND AND PURPOSE

Thrombo-inflammation is a key feature of stroke pathophysiology and provides multiple candidate drug targets. Thrombin exerts coagulation-independent actions via protease-activated receptors (PAR), of which PAR1 has been implicated in stroke-associated neuroinflammation. The role of PAR4 in this context is less clear. This study examined if the selective PAR4 antagonist ML354 provides neuroprotection in experimental stroke and explored the underlying mechanisms.

EXPERIMENTAL APPROACH

Mouse primary cortical neurons were exposed to oxygen-glucose deprivation (OGD) and simulated reperfusion ± ML354. For comparison, functional Ca2+-imaging was performed upon acute stimulation with a PAR4 activating peptide or glutamate. Male mice underwent sham operation or transient middle cerebral artery occlusion (tMCAO), with ML354 or vehicle treatment beginning at recanalization. A subset of mice received a platelet-depleting antibody. Stroke size and functional outcomes were assessed. Abundance of target genes, proteins, and cell markers was determined in cultured cells and tissues by qPCR, immunoblotting, and immunofluorescence.

KEY RESULTS

Stroke up-regulated PAR4 expression in cortical neurons in vitro and in vivo. OGD augments spontaneous and PAR4-mediated neuronal activity; ML354 suppresses OGD-induced neuronal excitotoxicity and apoptosis. ML354 applied in vivo after tMCAO reduced infarct size, apoptotic markers, macrophage accumulation, and interleukin-1β expression. Platelet depletion did not affect infarct size in mice with tMCAO ± ML354.

CONCLUSIONS AND IMPLICATIONS

Selective PAR4 inhibition during reperfusion improves infarct size and neurological function after experimental stroke by blunting neuronal excitability, apoptosis, and local inflammation. PAR4 antagonists may provide additional neuroprotective benefits in patients with acute stroke beyond their canonical antiplatelet action.

Isoflurane preconditioning induced genomic changes in mouse cortex

Background

Altered patterns of genetic expression induced by isoflurane preconditioning in mouse brain have not yet been investigated. The aim of our pilot study is to examine the temporal sequence of changes in the transcriptome of mouse brain cortex produced by isoflurane preconditioning.

Methods

Twelve-wk-old wild-type (C57BL/6J) male mice were randomly assigned for the experiments. Mice were exposed to isoflurane 2% in air for 1 h and brains were harvested at the following time points-immediately (0 h), and at 6, 12, 24, 36, 48, and 72 h after isoflurane exposure. A separate cohort of mice were exposed to three doses of isoflurane on days 1, 2, and 3 and brains were harvested after the third exposure. The NanoString mouse neuropathology panel was used to analyse isoflurane-induced gene expression in the cortex. The neuropathology panel included 760 genes covering pathways involved in neurodegeneration and other nervous system diseases, and 10 internal reference genes for data normalisation.

Results

Genes involving several pathways were upregulated and downregulated by isoflurane preconditioning. Interestingly, a biphasic response was noted, meaning, an early expression of genes (until 6 h), followed by a transient pause (until 24 h), and a second wave of genomic response beginning at 36 h of isoflurane exposure was noted.

Conclusions

Isoflurane preconditioning induces significant alterations in the genes involved in neurodegeneration and other nervous system disorders in a temporal sequence. These data could aid in the identification of molecular mechanisms behind isoflurane preconditioning-induced neuroprotection in various central nervous system diseases.

Pathological mechanisms and future therapeutic directions of thrombin in intracerebral hemorrhage: a systematic review

Intracerebral hemorrhage (ICH), a common subtype of hemorrhagic stroke, often causes severe disability or death. ICH induces adverse events that might lead to secondary brain injury (SBI), and there is currently a lack of specific effective treatment strategies. To provide a new direction for SBI treatment post-ICH, the systematic review discussed how thrombin impacts secondary injury after ICH through several potentially deleterious or protective mechanisms. We included 39 studies and evaluated them using SYRCLE's ROB tool. Subsequently, we explored the potential molecular mechanisms of thrombin-mediated effects on SBI post-ICH in terms of inflammation, iron deposition, autophagy, and angiogenesis. Furthermore, we described the effects of thrombin in endothelial cells, astrocytes, pericytes, microglia, and neurons, as well as the harmful and beneficial effects of high and low thrombin concentrations on ICH. Finally, we concluded the current research status of thrombin therapy for ICH, which will provide a basis for the future clinical application of thrombin in the treatment of ICH.

Roots of Astragalus propinquus Schischkin Regulate Transmembrane Iron Transport and Ferroptosis to Improve Cerebral Ischemia-Reperfusion Injury

Background

The dried roots of the Astragalus propinquus Schischkin (RAP) plant, as a traditional Chinese medicine, has been widely used to treat stroke, cerebral ischemia, qi deficiency, and hypertension. Buyang Huanwu decoction is traditionally used to treat stroke in China for more than 200 years and has a significant effect on cerebral ischemia, and RAP is monarch medicine of Buyang Huanwu decoction. Therefore, this study was designed to observe the regulatory effect of RAP on transmembrane iron transporters and ferroptosis-related factors in cerebral ischemia-reperfusion injury (CIRI) in rats.

Methods

Middle cerebral artery occlusion (MCAO) was used to block blood flow in the blood supply area of the middle cerebral artery in seventy male SD rats to induce focal CIRI to establish a rat model of CIRI. RAP was administered to explore the regulatory effect of RAP on iron transmembrane transport under the condition of CIRI. The infarct size was measured using 2,3,5-triphenyl-tetrazolium chloride (TTC) staining, the pathological structure of brain tissue was observed by HE staining, and neuronal injury was evaluated by Nissl staining after treatment. Then, changes in the iron transporters ferritin (Fn), ferritin heavy chain (FHC), ferritin light chain (FLC), transferrin (Tf), transferrin receptor (TfR), divalent metal transporter 1 (DMT1), L-type calcium channel (LTCC), transient receptor potential canonical 6 (TRPC6), and ferroportin 1 (FPN1) were observed by immunohistochemistry staining (IHC) and Western blotting. The expression of key factors of ferroptosis, including the membrane sodium-dependent cystine/glutamate antiporter System Xc⁻ (System Xc⁻) light chain subunit (XCT) and heavy chain subunit (SLC3A2), glutathione peroxidase 4 (GPX4), nuclear factor erythroid 2-related factor (NRF2), heme oxygenase-1 (HO-1), and iron-responsive element-binding protein 2 (IREB2) in the brain tissues of rats was assessed by Western blotting. RAP decreased the infarct size and neuronal injury after CIRI in rats. Similarly, RAP treatment regulated the expression of iron transporters. As such, RAP was able to reduce the expression of Fn, FHC, FLC, Tf, TfR, DMT1, and TRPC6 and increase the expression of FPN1 through a Tf/TfR-independent pathway after CIRI in rats.

Conclusion

RAP stimulation inhibited ferroptosis by regulating the expression of the key ferroptosis factors XCT, SLC3A2, GPX4, NRF2, HO-1, and IREB2. In conclusion, RAP regulates transmembrane iron transport and ferroptosis to improve CIRI.

Gelatin–thrombin Hemostatic Matrix-related Cyst Formation after Cerebral Hematoma Evacuation: A Report of Two Cases

The gelatin–thrombin matrix, Floseal, is an excellent novel hemostatic agent that is used in various surgical fields. Thrombin is a serine protease, and the conversion of prothrombin to thrombin is an essential step in the coagulation cascade. However, thrombin can induce blood–brain barrier (BBB) disruption and vasogenic brain edema. This report describes two cases of gelatin–thrombin matrix-related cyst formation after cerebral hematoma evacuation. An 82-year-old man with a gelatin–thrombin matrix-related cyst was treated by cyst drainage and fenestration to the lateral ventricle. Histological evaluation of the cyst wall showed a gelatin–thrombin matrix reserve, marked infiltration of inflammatory cells, and foam cell accumulation. In addition, an 85-year-old woman with a gelatin–thrombin matrix-related cyst was treated with steroids and responded well. In both cases, the post-treatment course was uneventful. Cyst shrinkage and no recurrence were observed. The gelatin–thrombin matrix can cause cyst formation with brain edema. This is the first report demonstrating the cyst wall pathology and the steroid responsivity on cyst shrinkage. The mechanism of cyst formation is thought to be thrombin-induced BBB disruption. Excess gelatin–thrombin matrix should be carefully removed from the surgical beds, particularly those having a blinded space from the neurosurgical microscope.

The Role of Thrombin in Brain Injury After Hemorrhagic and Ischemic Stroke

Thrombin is increased in the brain after hemorrhagic and ischemic stroke primarily due to the prothrombin entry from blood either with a hemorrhage or following blood-brain barrier disruption. Increasing evidence indicates that thrombin and its receptors (protease-activated receptors (PARs)) play a major role in brain pathology following ischemic and hemorrhagic stroke (including intracerebral, intraventricular, and subarachnoid hemorrhage). Thrombin and PARs affect brain injury via multiple mechanisms that can be detrimental or protective. The cleavage of prothrombin into thrombin is the key step of hemostasis and thrombosis which takes place in every stroke and subsequent brain injury. The extravascular effects and direct cellular interactions of thrombin are mediated by PARs (PAR-1, PAR-3, and PAR-4) and their downstream signaling in multiple brain cell types. Such effects include inducing blood-brain-barrier disruption, brain edema, neuroinflammation, and neuronal death, although low thrombin concentrations can promote cell survival. Also, thrombin directly links the coagulation system to the immune system by activating interleukin-1α. Such effects of thrombin can result in both short-term brain injury and long-term functional deficits, making extravascular thrombin an understudied therapeutic target for stroke. This review examines the role of thrombin and PARs in brain injury following hemorrhagic and ischemic stroke and the potential treatment strategies which are complicated by their role in both hemostasis and brain.

Cross Talk Between Ferroptosis and Cerebral Ischemia

Recently, ferroptosis has been revealed as a new form of regulated cell death. Distinct from apoptosis and necrosis, ferroptosis is evoked by iron-dependent lipid peroxidation. Furthermore, the metabolism of iron, lipids, and amino acids plays a significant regulatory role in ferroptosis, which can be reversed by glutathione peroxidase 4 and ferroptosis suppressor protein 1. Ferroptosis is implicated in the onset and development of numerous neurological diseases. Emerging studies have reported that ferroptosis induces and aggravates brain tissue damage following cerebral ischemia, whereas inhibition of ferroptosis dramatically attenuates induced damage. In this review, we have summarized the mechanistic relationship between ferroptosis and cerebral ischemia, including through iron overload, downregulation of glutathione peroxidase 4, and upregulation of lipid peroxidation. Although considerable attention has been paid to the effect of ferroptosis on cerebral ischemic injury, specific mechanisms need to be experimentally confirmed, including how cerebral ischemia induces ferroptosis and how ferroptosis deteriorates cerebral ischemia.

Effects of Hypoxic and Ischemic Clinical Conditions on the Outcomes of Acute Ischemic Stroke Patients

Background

Several studies have shown the neuroprotective role afforded by hypoxic and ischemic preconditioning in cerebrovascular disorders. There are several clinical conditions which simulate the hypoxic and ischemic conditioning in humans. The aim of this retrospective study is to identify whether the presence of any clinical scenarios mimicking the hypoxic and ischemic conditions prior to the current acute ischemic stroke (AIS) has a neuroprotective role in these patients.

Materials and methods

Data were collected for patients >18 years of age who underwent endovascular treatment for AIS from January 2009 to June 2015. A good outcome was defined as modified Rankin score (mRS) of 0 to 3 at discharge and a poor outcome as mRS of 4-6. A logistic regression analysis was performed to identify independent predictors of outcomes at discharge in both groups. A p value of <0.05 was considered statistically significant for all analyses.

Results

A total of 102 patients, aged 67 ± 16 years with median preprocedural National Institute of Health Stroke Scale (NIHSS) score 17.5 (1-36), were included. Twenty-one (21%) patients had a good outcome (mRS: 0-3) and 81 (79%) had a poor outcome (mRS: 4-6). A logistic regression analysis identified higher NIHSS score [odds ratio (OR): 1.251, confidence interval (CI): 1.11-1.40, p = 0.0002] and history of transient ischemic attack (TIA; OR: 7.881, CI: 1.05-21.01, p < 0.04) as predictors of a poor outcome at discharge.

Conclusion

Our data suggest that the occurrence of TIA preceding an AIS may be associated with the poor outcomes in patients with AIS, although this finding needs confirmation in larger studies.

How to cite this article

Athiraman U, Tempelhoff R, Karanikolas M. Effects of Hypoxic and Ischemic Clinical Conditions on the Outcomes of Acute Ischemic Stroke Patients. Indian J Crit Care Med 2020;24(2):104-108.

Regulation of AQP4 in the Central Nervous System

Aquaporin-4 (AQP4) is the main water channel protein expressed in the central nervous system (CNS). AQP4 is densely expressed in astrocyte end-feet, and is an important factor in CNS water and potassium homeostasis. Changes in AQP4 activity and expression have been implicated in several CNS disorders, including (but not limited to) epilepsy, edema, stroke, and glioblastoma. For this reason, many studies have been done to understand the various ways in which AQP4 is regulated endogenously, and could be regulated pharmaceutically. In particular, four regulatory methods have been thoroughly studied; regulation of gene expression via microRNAs, regulation of AQP4 channel gating/trafficking via phosphorylation, regulation of water permeability using heavy metal ions, and regulation of water permeability using small molecule inhibitors. A major challenge when studying AQP4 regulation is inter-method variability. A compound or phosphorylation which shows an inhibitory effect in vitro may show no effect in a different in vitro method, or even show an increase in AQP4 expression in vivo. Although a large amount of variability exists between in vitro methods, some microRNAs, heavy metal ions, and two small molecule inhibitors, acetazolamide and TGN-020, have shown promise in the field of AQP4 regulation.

The Potential Role of Ferroptosis in Neonatal Brain Injury

Ferroptosis is an iron-dependent form of cell death that is characterized by early lipid peroxidation and different from other forms of regulated cell death in terms of its genetic components, specific morphological features, and biochemical mechanisms. Different initiation pathways of ferroptosis have been reported, including inhibition of system X_c ^-, inactivation of glutathione-dependent peroxidase 4, and reduced glutathione levels, all of which ultimately promote the production of reactive oxygen species, particularly through enhanced lipid peroxidation. Although ferroptosis was first described in cancer cells, emerging evidence now links mechanisms of ferroptosis to many different diseases, including cerebral ischemia and brain hemorrhage. For example, neonatal brain injury is an important cause of developmental impairment and of permanent neurological deficits, and several types of cell death, including iron-dependent pathways, have been detected in the process of neonatal brain damage. Iron chelators and erythropoietin have both shown neuroprotective effects against neonatal brain injury. Here, we have summarized the potential relation between ferroptosis and neonatal brain injury, and according therapeutic intervention strategies.

Brain iron overload following intracranial haemorrhage

Intracranial haemorrhages, including intracerebral haemorrhage (ICH), intraventricular haemorrhage (IVH) and subarachnoid haemorrhage (SAH), are leading causes of morbidity and mortality worldwide. In addition, haemorrhage contributes to tissue damage in traumatic brain injury (TBI). To date, efforts to treat the long-term consequences of cerebral haemorrhage have been unsatisfactory. Incident rates and mortality have not showed significant improvement in recent years. In terms of secondary damage following haemorrhage, it is becoming increasingly apparent that blood components are of integral importance, with haemoglobin-derived iron playing a major role. However, the damage caused by iron is complex and varied, and therefore, increased investigation into the mechanisms by which iron causes brain injury is required. As ICH, IVH, SAH and TBI are related, this review will discuss the role of iron in each, so that similarities in injury pathologies can be more easily identified. It summarises important components of normal brain iron homeostasis and analyses the existing evidence on iron-related brain injury mechanisms. It further discusses treatment options of particular promise.

Effect of thrombin preconditioning on migration of subventricular zone-derived cells after intracerebral hemorrhage in rats

OBJECTIVE

To investigate the effect of thrombin preconditioning (TPC) on the intracerebral hemorrhage (ICH)-induced proliferation, migration, and function of subventriclular zone (SVZ) cells and to find new strategies that enhance endogenous neurogenesis after ICH.

METHODS

Male Sprague-Dawley rats were randomly divided into 3 groups (ICH, TPC, and control group). Rats of each group were randomly divided into 5 subgroups (3-d, 7-d, 14-d, 21-d, and 28-d subgroup). ICH was caused by intrastrial stereotactic administration of collagenase type IV. Brdu was used to label newborn SVZ cells. Organotypic brain slices were cultured to dynamically observe the migration of SVZ cells at living brain tissue. Migration of Dil-labeled SVZ cells in living brain slices was traced by time-lapse microscopy. To assess whether SVZ cells migrating to injured striatum had the ability to form synapses with other cells, brain slices from each group were double immunolabeled with Brdu and synapsin I.

RESULTS

The number of Brdu-positive cells markedly increased in the ipsilateral SVZ and striatum 3 days after TPC, peaked at 14 days (P < 0.01), continued to 21 days, and then gradually decreased at 28 days with significant difference compared to the ICH group at each time point (P < 0.01). Migration of Dil-labeled SVZ cells in brain slices in each group was observed and imaged during a 12-h period. Dil-labeled SVZ cells in the TPC group were observed to migrate laterally toward striatum with time with a faster velocity compared to the ICH group (P < 0.01). Our study also demonstrated that TPC induced strong colocalization of Brdu and synapsin I in the ipsilateral striatum between 3 and 28 days after injury.TPC made colocalization of Brdu and synapsin I appear earlier and continue for a longer time compared to the ICH group.

CONCLUSIONS

Our results demonstrated that TPC could promote proliferation, migration, and function of SVZ cells after ICH, which may provide a new idea for enhancing endogenous neurogenesis and developing new therapeutic strategies against ICH-induced brain injury.

Deferoxamine inhibits microglial activation, attenuates blood-brain barrier disruption, rescues dendritic damage, and improves spatial memory in a mouse model of microhemorrhages

Cerebral microbleeds are strongly linked to cognitive dysfunction in the elderly. Iron accumulation plays an important role in the pathogenesis of intracranial hemorrhage. Deferoxamine (DFX), a metal chelator, removes iron overload and protects against brain damage in intracranial hemorrhage. In this study, the protective effects of DFX against microhemorrhage were examined in mice. C57BL6 and Thy-1 green fluorescent protein transgenic mice were subjected to perforating artery microhemorrhages on the right posterior parietal cortex using two-photon laser irradiation. DFX (100 mg/kg) was administered 6 h after microhemorrhage induction, followed by every 12 h for three consecutive days. The water maze task was conducted 7 days after induction of microhemorrhages, followed by measurement of blood-brain barrier permeability, iron deposition, microglial activation, and dendritic damage. Laser-induced multiple microbleeds in the right parietal cortex clearly led to spatial memory disruption, iron deposits, microglial activation, and dendritic damage, which were significantly attenuated by DFX, supporting the targeting of iron overload as a therapeutic option and the significant potential of DFX in microhemorrhage treatment. Irons accumulation after intracranial hemorrhage induced a serious secondary damage to the brain. We proposed that irons accumulation after parietal microhemorrhages impaired spatial cognition. After parietal multiple microhemorrhages, increased irons and ferritin contents induced blood-brain barrier disruption, microglial activation, and further induced dendrites loss, eventually impaired the water maze, deferoxamine treatment protected from these damages.

A Cannabinoid Receptor 2 Agonist Prevents Thrombin-Induced Blood-Brain Barrier Damage via the Inhibition of Microglial Activation and Matrix Metalloproteinase Expression in Rats

Thrombin mediates the life-threatening cerebral edema and blood-brain barrier (BBB) damage that occurs after intracerebral hemorrhage (ICH). We previously found that the selective cannabinoid receptor 2 (CB2R) agonist JWH-133 reduced brain edema and neurological deficits following germinal matrix hemorrhage (GMH). We explored whether CB2R stimulation ameliorated thrombin-induced brain edema and BBB permeability as well as the possible molecular mechanism involved. A total of 144 Sprague-Dawley (S-D) rats received a thrombin (20 U) injection in the right basal ganglia. JWH-133 (1.5 mg/kg) or SR-144528 (3.0 mg/kg) and vehicle were intraperitoneally (i.p.) injected 1 h after surgery. Brain water content measurement, Evans blue (EB) extravasation, Western blot, and immunofluorescence were used to study the effects of a CB2R agonist 24 h after surgery. The results demonstrated that JWH-133 administration significantly decreased thrombin-induced brain edema and reduced the number of Iba-1-positive microglia. JWH-133 also decreased the number of P44/P42(+)/Iba-1(+) microglia, lowered Evans blue extravasation, and inhibited the elevated matrix metallopeptidase (MMP)-9 and matrix metallopeptidase (MMP)-12 activities. However, a selective CB2R antagonist (SR-144528) reversed these effects. We demonstrated that CB2R stimulation reduced thrombin-induced brain edema and alleviated BBB damage. We also found that matrix metalloproteinase suppression may be partially involved in these processes.

Intercellular cross-talk in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating cerebrovascular disorder with high mortality and morbidity. Currently, there are few treatment strategies for ICH-induced brain injury. A recent increase in interest in the pathophysiology of ICH has led to elucidation of the pathways underlying ICH-induced brain injury, pathways where intercellular and hematoma to cell signaling play important roles. In this review, we summarize recent advances in ICH research focusing on intercellular and hematoma:cell cross-talk related to brain injury and recovery after ICH. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Effect of hirulog-like peptide on middle cerebral artery occlusion-induced brain injury in mice

Hirulog-like peptide (HLP) and low-molecular-weight heparin (LMWH) are thrombin inhibitor peptides. Our previous study demonstrated that HLP could reduce vascular neointimal formation or restenosis in animals undergoing balloon catheter injury in the carotid artery. However, the function of HLP during ischemic stroke is largely unknown. The present study investigated the effect of HLP on brain injury, which was induced by suture of middle cerebral artery occlusion in mice. Mice were divided into four groups, which included a sham group and three treatment groups. Ischemia was induced by transient suture insertion into the middle cerebral artery for 90 min, and mice were either treated with saline, HLP or LMWH. Infarct volume, neurologic deficits and apoptotic factors were measured following 1-14 days of ischemia. We demonstrated that HLP intravenous injection alleviated brain infarct volume and improved neurologic outcomes (p<0.05). HLP decreased levels of protease-activated receptor-1 (PAR-1), caspase-3, malondialdehyde (MDA) and Bcl-2-associated X protein (Bax), increased the activities of catalase and B cell lymphoma-2 (Bcl-2), and improved the ratio of Bcl-2/Bax compared with the control (p<0.05). This study indicates that HLP and LMWH reduced infarct volume and improved neurobehavioral outcomes induced by transient middle cerebral artery occlusion (tMCAO). In addition, HLP had a beneficial effect on the regulation of the thrombin receptor and key apoptosis regulators in the mouse brain. These results suggest that HLP may be a potential alternative therapy for arterial occlusion-induced cerebral ischemia.

Effect of iron chelators on methemoglobin and thrombin preconditioning

Cell loss immediately adjacent to an intracerebral hemorrhage may be mediated in part by the toxicities of extracellular hemoglobin (Hb) and thrombin. However, at low concentrations, these proteins induce tolerance to hemin and iron that may limit further peri-hematomal injury as erythrocyte lysis progresses. The mechanisms mediating these preconditioning effects have not been completely defined, but increased expression of both heme oxygenase (HO)-1 and iron binding proteins likely contributes. In the present study, we hypothesized that iron chelator therapy would attenuate this protective response. Pretreatment of cortical glial cultures (> 90 % GFAP+) with 3 μM methemoglobin (metHb) or 5 units/ml thrombin for 24 h was nontoxic per se, and increased HO-1 and ferritin expression. When challenged with a toxic concentration of hemin, the increase in cellular redox-active iron was attenuated in preconditioned cultures and cell survival was increased. However, if cultures were pretreated with metHb or thrombin plus deferoxamine or 2,2'-bipyridyl, ferritin induction was prevented and cellular redox-active iron increased with hemin treatment. Preconditioning-mediated cytoprotection was consistently reduced by deferoxamine, while 2,2'-bipyridyl had a variable effect. Neither chelator altered HO-1 expression. A cytoprotective response was preserved when chelator therapy was limited to 11 hours of the 24 h preconditioning interval. These results suggest a potentially deleterious effect of continuous iron chelator therapy after ICH. Intermittent therapy may remove peri-hematomal iron without negating the benefits of exposure to low concentrations of Hb or thrombin.

Is there a place for cerebral preconditioning in the clinic?

Preconditioning (PC) describes a phenomenon whereby a sub-injury inducing stress can protect against a later injurious stress. Great strides have been made in identifying the mechanisms of PC-induced protection in animal models of brain injury. While these may help elucidate potential therapeutic targets, there are questions over the clinical utility of cerebral PC, primarily because of questions over the need to give the PC stimulus prior to the injury, narrow therapeutic windows and safety. The object of this review is to address the question of whether there may indeed be a clinical use for cerebral PC and to discuss the deficiencies in our knowledge of PC that may hamper such clinical translation.

Endogenous protease nexin-1 protects against cerebral ischemia

The serine protease thrombin plays a role in signalling ischemic neuronal death in the brain. Paradoxically, endogenous neuroprotective mechanisms can be triggered by preconditioning with thrombin (thrombin preconditioning, TPC), leading to tolerance to cerebral ischemia. Here we studied the role of thrombin’s endogenous potent inhibitor, protease nexin-1 (PN-1), in ischemia and in tolerance to cerebral ischemia induced by TPC. Cerebral ischemia was modelled in vitro in organotypic hippocampal slice cultures from rats or genetically engineered mice lacking PN-1 or with the reporter gene lacZ knocked into the PN-1 locus PN-1HAPN-1-lacZ/HAPN-1-lacZ (PN-1 KI) exposed to oxygen and glucose deprivation (OGD). We observed increased thrombin enzyme activity in culture homogenates 24 h after OGD. Lack of PN-1 increased neuronal death in the CA1, suggesting that endogenous PN-1 inhibits thrombin-induced neuronal damage after ischemia. OGD enhanced β-galactosidase activity, reflecting PN-1 expression, at one and 24 h, most strikingly in the stratum radiatum, a glial cell layer adjacent to the CA1 layer of ischemia sensitive neurons. TPC, 24 h before OGD, additionally increased PN-1 expression 1 h after OGD, compared to OGD alone. TPC failed to induce tolerance in cultures from PN-1^−/− mice confirming PN-1 as an important TPC target. PN-1 upregulation after TPC was blocked by the c-Jun N-terminal kinase (JNK) inhibitor, L-JNKI1, known to block TPC. This work suggests that PN-1 is an endogenous neuroprotectant in cerebral ischemia and a potential target for neuroprotection.

Thrombin and hemin as central factors in the mechanisms of intracerebral hemorrhage-induced secondary brain injury and as potential targets for intervention

Intracerebral hemorrhage (ICH) is a subtype of stoke that may cause significant morbidity and mortality. Brain injury due to ICH initially occurs within the first few hours as a result of mass effect due to hematoma formation. However, there is increasing interest in the mechanisms of secondary brain injury as many patients continue to deteriorate clinically despite no signs of rehemorrhage or hematoma expansion. This continued insult after primary hemorrhage is believed to be mediated by the cytotoxic, excitotoxic, oxidative, and inflammatory effects of intraparenchymal blood. The main factors responsible for this injury are thrombin and erythrocyte contents such as hemoglobin. Therapies including thrombin inhibitors, N-methyl-D-aspartate antagonists, chelators to bind free iron, and antiinflammatory drugs are currently under investigation for reducing this secondary brain injury. This review will discuss the molecular mechanisms of brain injury as a result of intraparenchymal blood, potential targets for therapeutic intervention, and treatment strategies currently in development.

Serum biomarkers of spontaneous intracerebral hemorrhage induced secondary brain injury

Intracerebral hemorrhage (ICH) is a devastating form of stroke associated with a high rate of morbidity and mortality. It is now believed that much of this damage occurs in the subacute period following the initial insult via a cascade of complex pathophysiologic pathways that continues to be investigated. Increased levels of certain serum proteins have been identified as biomarkers that may reflect or directly participate in the inflammation, blood brain barrier disruption, endothelial dysfunction, and neuronal and glial toxicity that occur during this secondary period of cerebral injury. Some of these biomarkers have the potential to serve as therapeutic targets or surrogate endpoints for future research or clinical trials. Others may someday augment current clinical techniques in diagnosis, risk-stratification, prognostication, treatment decision and measurement of therapeutic efficacy. While much work remains to be done, biomarkers show significant potential to expand clinical options and improve clinical management, thereby reducing mortality and improving functional outcomes in ICH patients.

Role of protease-activated receptor-1 in brain injury after experimental global cerebral ischemia

BACKGROUND AND PURPOSE

Evidence suggests that the protease-activated receptor-1 (PAR-1), a thrombin receptor, mediates neuronal injury in experimental cerebral ischemia. The present study investigated whether PAR-1 plays a role in brain injury after global cerebral ischemia.

METHODS

Adult male wild-type or PAR-1 knockout mice underwent a 20-minute bilateral common carotid artery occlusion or a sham operation. Behavior tests were performed before ischemia and 1, 2, and 3 days after bilateral common carotid artery occlusion. Mice were euthanized at different time points for thrombin activity, brain edema, Western blot analysis, and brain histology.

RESULTS

Thrombin activity and PAR-1 expression were increased in the brain after bilateral common carotid artery occlusion. Compared with wild-type mice, PAR-1 knockout mice had less brain edema formation, neuronal death, and behavior impairment after bilateral common carotid artery occlusion. In addition, bilateral common carotid artery occlusion-induced activation of mitogen-activated protein kinases was absent in PAR-1 knockout mice.

CONCLUSIONS

PAR-1 contributes to the brain injury induced by global cerebral ischemia, which may be related to activation of mitogen-activated protein kinases.

Ischemic preconditioning attenuates brain edema after experimental intracerebral hemorrhage

Ischemic preconditioning (IPC) provides protection against subsequent severe ischemic injury. A recent study found that cerebral IPC prolongs bleeding time. In this study, we examined whether IPC protects against intra-cerebral hemorrhage (ICH)-induced brain edema formation and whether IPC affects blood coagulation. There were three sets of experiments in this study. In the first set, male Sprague-Dawley rats were preconditioned with either 15 min of left middle cerebral artery occlusion, an IPC stimulus, or a sham operation. Three days later, rats received an infusion of autologous whole blood in the ipsilateral or contralateral caudate. Rats were killed 24 h later for brain water content measurement. In the second set, rats underwent 15 min of IPC or a sham operation. Three days later, rats were used for bleeding and thrombin clotting time tests. In the third set, the levels of p44/42 mitogen-activated protein kinases (MAPKs), heme oxygenase-1 (HO-1), transferrin (Tf), and transferrin receptor (TfR) in the brain 24 or 72 h after IPC were examined. We found that IPC reduced ICH-induced brain edema when blood was injected into the ipsilateral caudate but it did not when blood was injected into the contralateral caudate. IPC resulted in prolongation of bleeding time and thrombin clotting time. IPC also induced the activation of p44/42 MAPKs and upregulation of HO-1, Tf, and TfR levels in the ipsilateral caudate. These results suggest that IPC protects against ICH-induced brain edema formation and decreases blood coagulation. The protection of IPC against ICH is mainly due to local factors in the brain and may be related to activation of p44/42 MAPKs and upregulation of HO-1, Tf, and TfR.

Iron accumulation and neurotoxicity in cortical cultures treated with holotransferrin

Nonheme iron accumulates in CNS tissue after ischemic and hemorrhagic insults and may contribute to cell loss. The source of this iron has not been precisely defined. After blood-brain barrier disruption, CNS cells may be exposed to plasma concentrations of transferrin-bound iron (TBI), which exceed that in the CSF by over 50-fold. In this study, the hypothesis that these concentrations of TBI produce cell iron accumulation and neurotoxicity was tested in primary cortical cultures. Treatment with 0.5-3mg/ml holotransferrin for 24h resulted in the loss of 20-40% of neurons, associated with increases in malondialdehyde, ferritin, heme oxygenase-1, and iron; transferrin receptor-1 expression was reduced by about 50%. Deferoxamine, 2,2'-bipyridyl, Trolox, and ascorbate prevented all injury, but apotransferrin was ineffective. Cell TBI accumulation was significantly reduced by deferoxamine, 2,2'-bipyridyl, and apotransferrin, but not by ascorbate or Trolox. After treatment with (55)Fe-transferrin, approximately 40% of cell iron was exported within 16h. Net export was increased by deferoxamine and 2,2'-bipyridyl, but not by apotransferrin. These results suggest that downregulation of transferrin receptor-1 expression is insufficient to prevent iron-mediated death when neurons are exposed to plasma concentrations of TBI. Chelator therapy may be beneficial for acute CNS injuries associated with loss of blood-brain barrier integrity.

Functional roles of transferrin in the brain

BACKGROUND

Transferrin is synthesized in the brain by choroid plexus and oligodendrocytes, but only that in the choroid plexus is secreted. Transferrin is a major iron delivery protein to the brain, but the amount transcytosed across the brain microvasculature is minimal. Transferrin is the major source of iron delivery to neurons. It may deliver iron to immature oligodendrocytes but this trophic effect declines over time while iron requirements for maintaining myelination continue. Finally, transferrin may play an important role in neurodegenerative diseases through its ability to mobilize iron.

SCOPE OF REVIEW

The role of transferrin in maintaining brain iron homeostasis and the mechanism by which it enters the brain and delivers iron will be discussed. Its relevance to neurological disorders will also be addressed.

MAJOR CONCLUSIONS

Transferrin is the major iron delivery protein for neurons and the microvasculature, but has a limited role for glial cells. The main source of transferrin in the brain is likely from the choroid plexus although the concentration of transferrin at any given time in the brain includes that synthesized in oligodendrocytes. Little is known about brain iron egress or the role of transferrin in this process.

GENERAL SIGNIFICANCE

Neuron survival requires iron, which is predominantly delivered by transferrin. The concentration of transferrin in the cerebrospinal fluid is reflective of brain iron availability and can function as a biomarker in disease. Accumulation of iron in the brain contributes to neurodegenerative processes, thus an understanding of the role that transferrin plays in regulating brain iron homeostasis is essential. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Clot formation, vascular repair and hematoma resolution after ICH, a coordinating role for thrombin?

Following intracerebral hemorrhage (ICH) there is a sequential response involving activation of the coagulation cascade/platelet plug formation, vascular repair, upregulation of endogenous defense mechanisms and clot resolution. How these responses are coordinated and modified by different hematoma sizes has received little attention. This paper reviews evidence that thrombin can modulate and may coordinate the components of the endogenous response. This has potential consequences for treatment of ICH with a number of modalities.

Time course of heme oxygenase-1 and oxidative stress after experimental intracerebral hemorrhage

BACKGROUND

Heme oxygenase-1 (HO-1), the rate-limiting enzyme for heme catabolism and iron production, its role in intracerebral hemorrhage (ICH) is controversial. The study was to investigate correlations between brain oxidative injury and HO-1 after experimental ICH.

METHOD

Sprague-Dawley rats received intra-striatal infusions of 100 μl autologous whole blood as ICH models. HO-1 were examined by immunohistochemical and reverse transcription polymerase chain reaction (RT-PCR) analysis. Brain oxidative stress was quantitated by malondialdehyde (MDA); antioxidation were measured by copper-zinc superoxide dismutase (Cu/Zn-SOD) activity using RT-PCR assay.

RESULTS

The expression of the HO-1 upregulated and reached its peak at days 3 and 7 after ICH (P < 0.01). There was a significant increase of MDA and a top at 3-day post-ICH (P < 0.01); Cu/Zn-SOD was upregulated post-ICH and reached the top at day 7 (P < 0.001); HO-1 was correlated significantly with brain MDA content at days 7 and 14 following ICH (r = 0.435-0.501, P < 0.001) but there is no definite correlation between them on 1 to 3 days (P > 0.05); conversely, HO-1 was correlated significantly with Cu/Zn-SOD on 1 to 3 days after ICH (r = 0.433-0.621, P < 0.001) but there is no definite correlation between them at days 7 and 14 (P > 0.05).

CONCLUSIONS

HO-1 has both antioxidant and prooxidant properties in ICH. The early upregulation of HO-1 possibly fit with the events and be protective against oxidative stress, whereas its overexpression in the late stages may result in its dysfunction and be toxic. So it should be prudent to intervene ICH with the inhibitor/activator of HO-1.

Thrombin preconditioning reduces iron-induced brain swelling and brain atrophy

Cerebral preconditioning with a low dose of thrombin attenuates brain edema induced by intracerebral hemorrhage (ICH), a large dose of thrombin or iron. This study examined whether or not thrombin preconditioning (TPC) reduces neuronal death and brain atrophy caused by iron. The right hippocampus of rats was pretreated with or without thrombin, and iron was then injected into the same location 3 days later. Rats were killed at 1 day or 7 days after iron injection, and the brains were used for histology. We found that TPC reduced neuronal death and brain swelling in the hippocampus 1 day after iron injection, and hippocampal atrophy 7 days later. Western blots showed that thrombin activates p44/42 mitogen-activated protein kinase (p44/42 MAPK) and 70-kDa ribosomal protein S6 kinase (p70 S6K). Our results indicate that TPC reduction of iron-induced neuronal death may be through the p44/42 MAPK /p70 S6K signal transduction pathway.

Advances in neuroprotective strategies: potential therapies for intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is associated with higher mortality and morbidity than any other form of stroke. However, there currently are no treatments proven to improve outcomes after ICH, and therefore, new effective therapies are urgently needed. Growing insight into ICH pathophysiology has led to the development of neuroprotective strategies that aim to improve the outcome through reduction of secondary pathologic processes. Many neuroprotectants target molecules or pathways involved in hematoma degradation, inflammation or apoptosis, and have demonstrated potential clinical benefits in experimental settings. We extensively reviewed the current understanding of ICH pathophysiology as well as promising experimental neuroprotective agents with particular focus on their mechanisms of action. Continued advances in ICH knowledge, increased understanding of neuroprotective mechanisms, and improvement in the ability to modulate molecular and pathologic events with multitargeting agents will lead to successful clinical trials and bench-to-bedside translation of neuroprotective strategies.

Thrombin-induced neuronal protection: role of the mitogen activated protein kinase/ribosomal protein S6 kinase pathway

Our previous studies have found that intracerebral pretreatment with a low dose of thrombin (thrombin preconditioning, TPC) reduces infarct volume and attenuates brain edema after focal cerebral ischemia. In this study, we examined whether TPC protects against the neuronal death induced by oxygen glucose deprivation (OGD), and whether the protection is through thrombin receptors and the p44/42 mitogen activated protein kinases (MAPK)/ribosomal protein S6 kinases (p70 S6K) pathway. Expression of protease-activated receptors (PARs) mRNA was detected in cultured primary rat neurons and thrombin upregulated PAR-1 and PAR-4 mRNA expression. TPC reduced OGD-induced neuronal death (e.g. dead cells: 52.5 ± 5.4% vs. 72.3 ± 7.2% in the control group, n=6, p<0.01). Agonists of PAR-1 and PAR-4 mimicked the effects of thrombin and reduced OGD-induced neuronal death. Pretreatment with thrombin or PAR agonists induced the upregulation of activated p44/42 MAPK and p70S6K (Thr 421/Ser 424). PD98059, an inhibitor of p44/42 MAPK kinase, blocked thrombin-induced upregulation of activated p44/42 MAPK and p70S6K. It also reduced TPC-induced neuronal protection (e.g. dead cells: 68.2 ± 5.2% vs. 56.9 ± 4.6% in vehicle+TPC group, n=6, p<0.05). These results suggest that TPC-induced ischemic tolerance is through activation of thrombin receptors and the p44/42 MAPK/p70S6K pathway.

Activation of c-Jun in the nuclei of neurons of the CA-1 in thrombin preconditioning occurs via PAR-1

Recently it has been shown that the c-Jun N-terminal kinase (JNK) plays a role in thrombin preconditioning (TPC) in vivo and in vitro. To investigate further the pathways involved in TPC, we performed an immunohistochemical study in hippocampal slice cultures. Here we show that the major target of JNK, the AP-1 transcription factor c-Jun, is activated by phosphorylation in the nuclei of neurons of the CA1 region by using phospho-specific antibodies against the two JNK phosphorylation sites. The activation is early and transient, peaking at 90 min and not present by 3 hr after low-dose thrombin administration. Treatment of cultures with a synthetic thrombin receptor agonist results in the same c-Jun activation profile and protection against subsequent OGD, both of which are prevented by specific JNK inhibitors, showing that thrombin signals through PAR-1 to JNK. By using an antibody against the Ser 73 phosphorylation site of c-Jun, we identify possible additional TPC substrates.

Genomic analysis of ischemic preconditioning in adult rat hippocampal slice cultures

Understanding endogenous mechanisms of neuroprotection may have important clinical applications. It is well established that brain tissue becomes more resistant to ischemic injury following a sublethal ischemic insult. This process, called ischemic preconditioning (IPC), can be induced in adult rat hippocampal slice cultures by a brief oxygen-glucose deprivation (OGD) [Hassen, G.W., Tian, D., Ding, D., Bergold, P.J., 2004. A new model of ischemic preconditioning using young adult hippocampal slice cultures. Brain Res. Brain Res. Protoc. 13, 135-143]. We have analyzed the changes in gene expression brought about by IPC in this model in order to understand the mechanisms involved. Total RNA was isolated at different time points following a brief OGD (3, 6 and 12 h) and used to probe genome-wide expression microarrays. Genes were identified that were significantly up- or down-regulated relative to controls. We placed genes that were differentially expressed into statistically significant groups based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and gene ontology (GO) terms. Genes involved in signal transduction, transcription, and oxidative phosphorylation are differentially expressed at each time point. The analysis demonstrates that alterations in signaling pathways (TGF-beta, Wnt, MAPK, ErbB, Toll-like receptor, JAK-STAT, VEGF) consistently accompany IPC. RT-PCR was used to confirm that members of these signaling pathways are regulated as predicted by the microarray analysis. We verified that protein translation following OGD is necessary for IPC. We also found that blocking the NMDA receptor during OGD does not significantly inhibit IPC in this model or produce large changes in gene expression. Our data thus suggests that changes in signaling pathways and their down-stream targets play an important role in triggering endogenous neuroprotection.

Brain edema after intracerebral hemorrhage in rats: the role of iron overload and aquaporin 4

OBJECT

Brain edema formation following intracerebral hemorrhage (ICH) appears to be partly related to erythrocyte lysis and hemoglobin release. An increase of brain water content was associated with an increase of brain iron, which is an erythrocyte degradation product. Expression of AQP4 is highly modified in several brain disorders, and it can play a key role in cerebral edema formation. However, the question whether AQP4 is regulated by drugs lacks reliable evidence, and the interacting roles of iron overload and AQP4 in brain edema after ICH are unknown. The goal of this study was to clarify the relationship between iron overload and AQP4 expression and to characterize the effects of the iron chelator deferoxamine (DFO) on delayed brain edema after experimental ICH.

METHODS

A total of 144 Sprague-Dawley rats weighing between 250 and 300 g were used in this work. The animals were randomly divided into 4 groups. The ICH models (Group C) were generated by injecting 100 microl autologous blood stereotactically into the right caudate nucleus; surgical control rats (Group B) were generated in a similar fashion, by injecting 100 microl saline into the right caudate nucleus. Intervention models (Group D) were established by intraperitoneal injection of DFO into rats in the ICH group. Healthy rats (Group A) were used for normal control models. Brain water content, iron deposition, and AQP4 in perihematomal brain tissue were evaluated over the time course of the study (1, 3, 7, and 14 days) in each group.

RESULTS

Iron deposition was found in the perihematomal zone as early as the 1st day after ICH, reaching a peak after 7 days and remaining at a high level thereafter for at least 14 days following ICH. Rat brain water content around the hematoma increased progressively over the time course, reached its peak at Day 3, and still was evident at Day 7 post-ICH. Immunohistochemical analysis showed that AQP4 was richly expressed over glial cell processes surrounding microvessels in the rat brain; there was upregulation of the AQP4 expression in perihematomal brain during the observation period, and it reached maximum at 3 to 7 days after ICH. The changes of brain water content were accompanied by an alteration of AQP4. The application of the iron chelator DFO significantly reduced iron overload, brain water content, and AQP4 level in the perihematomal area compared with the control group.

CONCLUSIONS

Iron overload and AQP4 may play a critical role in the formation of brain edema after ICH. In addition, AQP4 expression was affected by iron concentration. Importantly, treatment with DFO significantly reduced brain edema in rats and inhibited the AQP4 upregulation after ICH. Deferoxamine may be a potential therapeutic agent for treating ICH.

Effects of cerebral ischemia on neuronal hemoglobin

This study examined whether neuronal hemoglobin (Hb) is present in rats. It then examined whether cerebral ischemia or ischemic preconditioning (IPC) affects neuronal Hb levels in vivo and in vitro. In vivo, male Sprague-Dawley rats were subjected to either 15 mins of transient middle cerebral artery occlusion (MCAO) with 24 h of reperfusion, an IPC stimulus, or 24 h of permanent MCAO (pMCAO), or IPC followed 3 days later by 24 h of pMCAO. In vitro, primary cultured neurons were exposed to 2 h of oxygen-glucose deprivation (OGD) with 22 h of reoxygenation. Results showed that Hb is widely expressed in rat cerebral neurons but not astrocytes. Hemoglobin expression was significantly upregulated in the ipsilateral caudate and the cortical core of the middle cerebral artery territory after IPC. Hemoglobin levels also increased more in the penumbral cortex and the contralateral hemisphere 24 h after pMCAO, but expressions in the ipsilateral caudate and the cortical core area were decreased. Ischemic preconditioning modified pMCAO-induced brain Hb changes. Neuronal Hb levels in vitro were increased by 2 h of OGD and 22 h of reoxygenation. These results indicate that Hb is synthesized in neurons and can be upregulated by ischemia.

Thrombin and brain recovery after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a common and often fatal subtype of stroke and produces severe neurological deficits in survivors. At present, there is lack of effective treatments that improve outcome in ICH. A neglected aspect of ICH research is the development of approaches that can be effectively used to improve recovery. Although previous studies have showed that thrombin induces blood-brain barrier leakage, brain edema, and neuronal death after ICH, our recent studies have shown that thrombin may have a role in brain recovery after ICH. An understanding of the mechanisms by which thrombin affects neurogenesis, angiogenesis, and plasticity may facilitate brain recovery after ICH.

Prodeath or prosurvival: two facets of hypoxia inducible factor-1 in perinatal brain injury

Hypoxia, which occurs in the brain when oxygen availability drops below the normal level, is a major cause of perinatal hypoxic-ischemic injury (HII). The transcriptional factor hypoxia inducible factor-1 (HIF-1) is a key regulator in the pathophysiological response to the stress of hypoxia. Genes regulated by HIF-1 are involved in energy metabolism, erythropoiesis, angiogenesis, vasodilatation, cell survival and apoptosis. Compared with the adult brain, the neonatal brain is different in physiological structure, function, cellular composition and signaling pathway related gene activation and response after hypoxia. The purpose of this review is to determine if developmental susceptibility of the brain after hypoxic/ischemic injury is related to HIF-1alpha, which also plays a pivotal role in the normal brain development. HIF-1alpha regulates both prosurvival and prodeath responses in the neonatal brain and various mechanisms underlie the apparent contradictory effects, including duration of ischemic injury and severity, cell-types, and/or dependent on the nature of the stimulus after HII. Studies report an excessive induction of HIF-1 in the immature brain, which suggests that a cell death promoting role of HIF may prevail. Inhibition of HIF-1alpha and targeted activation of its prosurvival genes appear as a favorable therapeutic strategy. However, a better understanding of multifaceted HIF-1 function during brain development is required to explore potential targets for further therapeutic interventions in the neonate.

Autophagy after experimental intracerebral hemorrhage

Autophagy contributes to ischemic brain injury, but it is not clear if autophagy occurs after intracerebral hemorrhage (ICH). This study examined whether ICH-induced cell death is partly autophagic. It then examined the role of iron in inducing this form of cell death after ICH. Male, adult Sprague-Dawley rats received an infusion of autologous whole blood or ferrous iron into the right basal ganglia. Control rats (sham) had a needle insertion. The rats were killed at 1, 3, 7, or 28 days later. Some rats were treated with either deferoxamine or vehicle after ICH. Microtubule-associated protein light chain-3 (LC3), a biomarker of autophagosome, and cathepsin D, a lysosomal biomarker, were measured by Western blot analysis and immunohistochemistry. Immunofluorescent double-labeling was used to identify the cell types expressing cathepsin D. Electron microscopy was performed to examine the cellular ultrastructure changes after ICH. We found that conversion of LC3-I to LC3-II, cathepsin D expression, and vacuole formation are increased in the ipsilateral basal ganglia after ICH. Intracerebral infusion of iron also resulted in enhanced conversion of LC3-I to LC3-II and increased cathepsin D levels. Deferoxamine (an iron chelator) treatment significantly reduced the conversion of LC3-I to LC3-II and cathepsin D levels after ICH. Our results demonstrated that autophagy occurs after ICH, and iron has a key role in ICH-induced autophagy. This also suggests that iron-induced autophagy may play a role in brain injury in other diseases associated with iron overload.

Effects of deferoxamine-activated hypoxia-inducible factor-1 on the brainstem after subarachnoid hemorrhage in rats

OBJECTIVE

Hypoxia-inducible factor (HIF)-1 is a transcription factor that regulates the expression of various neuroprotective genes. The goal of this study was to clarify the relationship between HIF-1 expression and subarachnoid hemorrhage (SAH) and to characterize the effects of deferoxamine (DFO)-induced increases in HIF-1 protein levels on the brainstem and the basilar artery (BA) after experimental SAH.

METHODS

Rat single- and double-hemorrhage models (injected on Days 0 and 2) of SAH were used. We assessed the time courses for HIF-1 protein levels in the brainstems and the BA diameters within 10 minutes and 6 hours on Days 1 and 2 in the single-SAH model, and also on Day 7 in the double-SAH model. After induction of double hemorrhage in rats, DFO was injected intraperitoneally. We then evaluated HIF-1 protein expression and brainstem activity, BA diameter, and brainstem blood flow.

RESULTS

After the rats experienced SAH, HIF-1 protein expression was significantly greater at 10 minutes in the single-injection model and at 7 days in the double-injection model than at similar time points in the control group, and these increases correlated with degrees of cerebral vasospasm. DFO injection resulted in significant increases in HIF-1 protein expression and activity in the brainstems of rats with SAH, compared with the rats with SAH that were given placebos, and the rats without SAH in the double-hemorrhage model. Cerebral vasospasm and reduction of brainstem blood flow were significantly attenuated in the rats that were administered DFO.

CONCLUSION

These results show that a DFO-induced increase in HIF-1 protein level and activity exerts significant attenuation of BA vasospasm and reduction of brainstem blood flow in the rat model of SAH. DFO may be a promising agent for treating clinical SAH.

Preconditioning with hyperbaric oxygen attenuates brain edema after experimental intracerebral hemorrhage

OBJECT

Preconditioning with hyperbaric oxygen (HBO2) reduces ischemic brain damage. Activation of p44/42 mitogen-activated protein kinases (p44/42 MAPK) has been associated with preconditioning-induced brain ischemic tolerance. This study investigated if preconditioning with HBO2 protects against intracerebral hemorrhage (ICH)-induced brain edema formation and examined the role of p44/42 MAPK in such protection.

METHODS

The study had three experimental groups. In Group 1, Sprague-Dawley rats received two, three, or five consecutive sessions of preconditioning with HBO2 (3 ata, 100% oxygen, 1 hour daily). Twenty-four hours after preconditioning with HBO2, rats received an infusion of autologous blood into the caudate. They were killed 1 or 3 days later for brain edema measurement. Rats in Group 2 received either five sessions of preconditioning with HBO2 or control pretreatment and were killed 24 hours later for Western blot and immunohistochemical analyses. In Group 3, rats received an intracaudate injection of PD098059 (an inhibitor of p44/42 MAPK activation) before the first of five sessions of preconditioning with HBO2. Twenty-four hours after the final preconditioning with HBO2, rats received an intracaudate blood infusion. Brain water content was measured 24 hours after ICH.

RESULTS

Fewer than five sessions of preconditioning with HBO2 did not significantly attenuate brain edema after ICH. Five sessions of preconditioning with HBO2 reduced perihematomal edema 24 and 72 hours after ICH (p < 0.05). Strong p44/42 MAPK immunoreactivity was detected in the basal ganglia 24 hours after preconditioning with HBO2. Intracaudate infusion of PD098059 abolished HBO2 preconditioning-induced protection against ICH-induced brain edema formation.

CONCLUSIONS

Preconditioning with HBO2 protects against brain edema formation following ICH. Activation of the p44/42 MAPK pathway contributes to that protection. Preconditioning with HBO2 may be a way of limiting brain injury during invasive neurosurgical procedures that cause bleeding.

Thrombin-induced ischemic tolerance is prevented by inhibiting c-jun N-terminal kinase

We have studied ischemic tolerance induced by the serine protease thrombin in two different models of experimental ischemia. In organotypic hippocampal slice cultures, we demonstrate that incubation with low doses of thrombin protects neurons against a subsequent severe oxygen and glucose deprivation. L-JNKI1, a highly specific c-jun N-terminal kinase (JNK) inhibitor, and a second specific JNK inhibitor, SP600125, prevented thrombin preconditioning (TPC). We also show that the exposure to thrombin increases the level of phosphorylated c-jun, the major substrate of JNK. TPC, in vivo, leads to significantly smaller lesion sizes after a 30-min middle cerebral artery occlusion (MCAo), and the preconditioned mice were better off in the three tests used to evaluate functional recovery. In accordance with in vitro results, TPC in vivo was prevented by administration of L-JNKI1, supporting a role for JNK in TPC. These results, from two different TPC models and with two distinct JNK inhibitors, show that JNK is likely to be involved in TPC.

Brain Injury After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke with high morbidity and mortality. The mechanisms underlying ICH-induced brain injury have become better understood during the past decade. Experimental investigations have indicated that thrombin formation, red blood cell lysis, and iron toxicity play a major role in ICH-induced injury and that these mechanisms may provide new therapeutic targets. This article reviews the role of thrombin and iron in ICH-induced injury.

Heat acclimation: a unique model of physiologically mediated global preconditioning against traumatic brain injury

Sub-lethal exposure to practically any harmful stimulus has been shown to induce consequent protection against more severe stress. This preconditioning (PC) effect may be achieved by exposure to different stressors, indicating that the induction of tolerance involves activation of common protective pathways. Chronic exposure to moderate heat (heat acclimation, HA) is a unique PC model, since this global physiological adaptation, as opposed to discrete organ PC, has been shown to induce cross-tolerance against other stressors, including closed head injury (CHI). HA animals show accelerated functional recovery after injury which is accompanied by reduced secondary brain damage. However, the precise mechanisms underlying this phenomenon have not been thoroughly studied until recently. Here we will address the concept of PC, highlighting the unique properties of HA as a model which can be used for the study of endogenous protective pathways triggered by PC procedures. Several molecular mechanisms which are suggested to mediate HA-induced neuroprotection will also be discussed, bringing to light their potential contribution to the development of traumatic brain injury treatment strategies utilizing therapeutic augmentation of endogenous defense mechanisms.

Protease-activated receptor-1 mediates protection elicited by thrombin preconditioning in a rat 6-hydroxydopamine model of Parkinson's disease

The etiology of Parkinson's disease remains poorly understood, and current treatment options do not slow disease progression. Recently, chemical (thrombin) preconditioning (TPC) was found to be protective in a 6-hydroxydopamine (6-OHDA) model of the disease. It is important to understand the mechanisms behind these thrombin-induced protective effects. The current study was conducted in the rat to determine whether the protective effects of TPC are mediated via activation of protease-activated receptors (PARs). Preconditioning with specific local infusion of agonist peptides for PAR-1 and PAR-4 3 days before unilateral 6-OHDA administration (10 microg into the medial forebrain bundle) was tested. In addition, co-administration of a PAR-1 antagonist with TPC was examined. In a neurobehavioral assessment battery, PAR-1 agonist preconditioning provided protection in a vibrissae-elicited forelimb placing test, a forelimb-use asymmetry test, and a corner turn test. In addition, inclusion of a PAR-1 antagonist prevented the protective effects elicited by TPC. In contrast to the effects of the PAR-1 agonist, PAR-4 agonist preconditioning afforded no such protection. Indeed, in a lower-dose model of 6-OHDA (5 microg), PAR-4 preconditioning significantly increased behavioral deficits. These results indicate that the protective effects of TPC in this model are mediated through PAR-1 activation. Neither the effects of PAR-1 nor TPC on later 6-OHDA-induced behavioral deficits appeared to be mediated through (DA) content sparing. Further mechanistic studies on the actions of PAR-1 and PAR-4 as detrimental in experimental models of Parkinson's disease are warranted.

Brain capillary endothelial cells mediate iron transport into the brain by segregating iron from transferrin without the involvement of divalent metal transporter 1

Rats were studied for [(59)Fe-(125)I]transferrin uptake in total brain, and fractions containing brain capillary endothelial cells (BCECs) or neurons and glia. (59)Fe was transported through BCECs, whereas evidence of similar transport of transferrin was questionable. Intravenously injected transferrin localized to BCECs and failed to accumulate within neurons, except near the ventricles. No significant difference in [(125)I]transferrin distribution was observed between Belgrade b/b rats with a mutation in divalent metal transporter I (DMT1), and Belgrade +/b rats with regard to accumulation in vascular and postvascular compartments. (59)Fe occurred in significantly lower amounts in the postvascular compartment in Belgrade b/b rats, indicating impaired iron uptake by transferrin receptor and DMT1-expressing neurons. Immunoprecipitation with transferrin antibodies on brains from Belgrade rats revealed lower uptake of transferrin-bound (59)Fe. In postnatal (P)0 rats, less (59)Fe was transported into the postvascular compartment than at later ages, suggesting that BCECs accumulate iron at P0. Supporting this notion, an in situ perfusion technique revealed that BCECs accumulated ferrous and ferric iron only at P0. However, BCECs at P0 together with those of older age lacked DMT1. In conclusion, BCECs probably mediate iron transport into the brain by segregating iron from transferrin without involvement of DMT1.

Deferoxamine reduces CSF free iron levels following intracerebral hemorrhage

Iron overload occurs in brain after intracerebral hemorrhage (ICH). Deferoxamine, an iron chelator, attenuates perihematomal edema and oxidative stress in brain after ICH. We investigated the effects of deferoxamine on cerebrospinal fluid (CSF) free iron and brain total iron following ICH. Rats received an infusion of 100-microL autologous whole blood into the right basal ganglia, then were treated with either deferoxamine (100 mg/kg, i.p., administered 2 hours after ICH and then at 12-hour intervals for up to 7 days) or vehicle. The rats were killed at different time points from 1 to 28 days for measurement of free and total iron. Behavioral tests were also performed. Free iron levels in normal rat CSF were very low (1.1 +/- 0.4 micromol). After ICH, CSF free iron levels were increased at all time points. Levels of brain total iron were also increased after ICH (p < 0.05). Deferoxamine given 2 hours after ICH reduced free iron in CSF at all time points. Deferoxamine also reduced ICH-induced neurological deficits (p < 0.05), but did not reduce total brain iron. In conclusion, CSF free iron levels increase after ICH and do not clear for at least 28 days. Deferoxamine reduces free iron levels and improves functional outcome in the rat, indicating that it may be a potential therapeutic agent for ICH patients.