Mice deficient in interleukin-1 converting enzyme are resistant to neonatal hypoxic-ischemic brain damage

System x(c)- activity and astrocytes are necessary for interleukin-1 beta-mediated hypoxic neuronal injury

The purpose of this study was to elucidate the cellular/biochemical pathway(s) by which interleukin-1beta (IL-1beta) contributes to the pathogenesis of hypoxic-ischemic brain damage. In vivo, IL-1 receptor type I (IL-1RI)-deficient mice showed smaller infarcts and less neurological deficits than wild-type animals after a 90 min reversible middle cerebral artery occlusion. In vitro, IL-1beta mediated an enhancement of hypoxic neuronal injury in murine cortical cultures that was lacking in cultures derived from IL-1RI null mutant animals and was blocked by the IL-1 receptor antagonist or an IL-1RI blocking antibody. This IL-1beta-mediated potentiation of hypoxic neuronal injury was associated with an increase in both cellular cystine uptake ([cystine]i) and extracellular glutamate levels ([glutamate]e) and was prevented by either ionotropic glutamate receptor antagonism or removal of L-cystine, suggesting a role for the cystine/glutamate antiporter (System x(c)-). Indeed, dual System x(c)-/metabotropic glutamate receptor subunit 1 (mGluR1) antagonism but not selective mGluR1 antagonism prevented neuronal injury. Additionally, cultures derived from mGluR1-deficient mice exhibited the same potentiation in injury after treatment with IL-1beta as wild-type cultures, an effect prevented by System x(c)-/mGluR1 antagonism. Finally, assessment of System x(c)- function and kinetics in IL-1beta-treated cultures revealed an increase in velocity of cystine transport (Vmax), in the absence of a change in affinity (Km). Neither the enhancement in [cystine]i, [glutamate]e, or neuronal injury were observed in chimeric cultures consisting of IL-1RI(+/+) neurons plated on top of IL-1RI(-/-) astrocytes, highlighting the importance of astrocyte-mediated alterations in System x(c)- as a novel contributor to the development and progression of hypoxic neuronal injury.

Impact of indolent inflammation on neonatal hypoxic-ischemic brain injury in mice

This report describes a new experimental model to evaluate the effect of a recurrent systemic inflammatory challenge, after cerebral hypoxia-ischemia in immature mice, on the progression of brain injury. Treatment with a low dose of lipopolysaccharide (E. coli O55:B5, 0.2mg/kg for 3 days, then 0.1mg/kg for 2 days) daily for 5 days after unilateral cerebral hypoxia-ischemia (right carotid ligation followed by 35min in 10% O2) in 10-day-old mice resulted in increased right forebrain tissue damage (35.6% reduction in right hemisphere volume compared to 20.6% reduction in saline-injected controls), in bilateral reductions in corpus callosum area (by 12%) and myelin basic protein immunostaining (by 19%), and in suppression of injury-related right subventricular zone cellular proliferation. The post-hypoxic-ischemic lipopolysaccharide regimen that amplified brain injury was not associated with increased mortality, nor with changes in body temperature, weight gain or blood glucose concentrations. The results of the present study demonstrate that systemic inflammation influences the evolution of tissue injury after neonatal cerebral hypoxia-ischemia and may also impair potential recovery mechanisms.

Cisplatin-induced acute renal failure is associated with an increase in the cytokines interleukin (IL)-1beta, IL-18, IL-6, and neutrophil infiltration in the kidney

We have demonstrated that caspase-1-deficient (caspase-1(-/-)) mice are functionally and histologically protected against cisplatin-induced acute renal failure (ARF). Caspase-1 exerts proinflammatory effects via the cytokines interleukin (IL)-1beta, IL-18, IL-6, and neutrophil recruitment. We sought to determine the role of the cytokines IL-1beta, IL-18, and IL-6 and neutrophil recruitment in cisplatin-induced ARF. We first examined IL-1beta; renal IL-1beta increased nearly 2-fold in cisplatin-induced ARF and was reduced in the caspase-1(-/-) mice. However, inhibition with IL-1 receptor antagonist (IL-1Ra) did not attenuate cisplatin-induced ARF. Renal IL-18 increased 2.5-fold; however, methods to inhibit IL-18 using IL-18 antiserum and transgenic mice that overproduce IL-18-binding protein (a natural inhibitor of IL-18) did not protect. Renal IL-6 increased 3-fold; however, IL-6-deficient (IL-6(-/-)) mice still developed cisplatin-induced ARF. We next examined neutrophils; blood neutrophils increased dramatically after cisplatin injection; however, prevention of peripheral neutrophilia and renal neutrophil infiltration with the neutrophil-depleting antibody RB6-8C5 did not protect against cisplatin-induced ARF. In summary, our data demonstrated that cisplatin-induced ARF is associated with increases in the cytokines IL-1beta, IL-18, and IL-6 and neutrophil infiltration in the kidney. However, inhibition of IL-1beta, IL-18, and IL-6 or neutrophil infiltration in the kidney is not sufficient to prevent cisplatin-induced ARF.

Interleukin-1beta, interleukin-18, and interferon-gamma expression in the cerebrospinal fluid of premature infants with posthemorrhagic hydrocephalus--markers of white matter damage?

Posthemorrhagic hydrocephalus (PHHC) represents a major complication of preterm birth. The aim of this study was to determine whether cerebrospinal fluid (CSF) levels of the pro-inflammatory cytokines IL-1beta, IL-18, and interferon (IFN)-gamma are altered in the CSF of preterm infants with PHHC and may serve as a marker of white matter damage (WMD). Twenty-seven preterm infants with PHHC were included in the study; 13 of them had signs of cystic WMD (cWMD) on ultrasound examinations. CSF sample 1 was obtained at first ventriculostomy, sample 2 at shunt implantation. Results were compared with a control group of 20 age-matched patients without neurologic diseases. IL-1beta concentrations were elevated in CSF sample 1 of PHHC patients without WMD and in sample 1 of patients with cWMD. Concentrations of IL-18 were increased in both samples of patients without WMD and in sample 2 of patients with cWMD. CSF levels of IFN-gamma were elevated in sample 1 of PHHC patients with cWMD. The pro-inflammatory cytokine IL-1beta and IL-18 levels in the CSF are elevated in patients with PHHC. Higher IFN-gamma levels are detected in a subgroup of patients developing cWMD, indicating its involvement in the pathogenesis of cWMD in the context of PHHC.

N-acetylcysteine reduces lipopolysaccharide-sensitized hypoxic-ischemic brain injury

OBJECTIVE

Maternal inflammation/infection alone or in combination with birth asphyxia increases the risk for perinatal brain injury. Free radicals are implicated as major mediators of inflammation and hypoxia-ischemia (HI)-induced perinatal brain injury. This study evaluated the neuroprotective efficacy of a scavenging agent, N-acetylcysteine (NAC), in a clinically relevant model.

METHODS

Lipopolysaccharide (LPS)-sensitized HI brain injury was induced in 8-day-old neonatal rats. NAC was administered in multiple doses, and brain injury was evaluated at 7 days after HI.

RESULTS

NAC (200mg/kg) provided marked neuroprotection with up to 78% reduction of brain injury in the pre+post-HI treatment group and 41% in the early (0 hour) post-HI treatment group, which was much more pronounced protection than another free radical scavenger, melatonin. Protection by NAC was associated with the following factors: (1) reduced isoprostane activation and nitrotyrosine formation; (2) increased levels of the antioxidants glutathione, thioredoxin-2, and (3) inhibition of caspase-3, calpain, and caspase-1 activation.

INTERPRETATION

NAC provides substantial neuroprotection against brain injury in a model that combines infection/inflammation and HI. Protection by NAC was associated with improvement of the redox state and inhibition of apoptosis, suggesting that these events play critical roles in the development of lipopolysaccharide-sensitized HI brain injury.

Matrix metalloproteinase-9 gene knock-out protects the immature brain after cerebral hypoxia-ischemia

Inhibition of matrix metalloproteinase-9 (MMP-9) protects the adult brain after cerebral ischemia. However, the role of MMP-9 in the immature brain after hypoxia-ischemia (HI) is unknown. We exposed MMP-9(-/-) [MMP-9 knock-out (KO)] and wild-type (WT) mice to HI on postnatal day 9. HI was induced by unilateral ligation of the left carotid artery followed by hypoxia (10% O2; 36 degrees C). Gelatin zymography showed that MMP-9 activity was transiently increased at 24 h after HI in the ipsilateral hemisphere and MMP-9-positive cells were colocalized with activated microglia. Seven days after 50 min of HI, cerebral tissue volume loss was reduced in MMP-9 KO (21.8 +/- 1.7 mm3; n = 22) compared with WT (32.3 +/- 2.1 mm3; n = 22; p < 0.001) pups, and loss of white-matter components was reduced in MMP-9 KO compared with WT pups (neurofilament: WT, 50.9 +/- 5.4%; KO, 18.4 +/- 3.1%; p < 0.0001; myelin basic protein: WT, 57.5 +/- 5.8%; KO, 23.2 +/- 3.5%; p = 0.0001). The neuropathological changes were associated with a delayed and diminished leakage of the blood-brain barrier (BBB) and a decrease in inflammation in MMP-9-deficient animals. In contrast, the neuroprotective effects after HI in MMP-9-deficient animals were not linked to either caspase-dependent (caspase-3 and cytochrome c) or caspase-independent (apoptosis-inducing factor) processes. This study demonstrates that excessive activation of MMP-9 is deleterious to the immature brain, which is associated with the degree of BBB leakage and inflammation. In contrast, apoptosis does not appear to be a major contributing factor.

Activation of caspase-1 dependent interleukins in developmental brain trauma

Focal mechanical cortical trauma triggers diffuse apoptotic neurodegeneration in the developing rat brain which is associated with invasion of brain tissue with inflammatory mediators. We hypothesized that caspase-1 and the two caspase-1-processed cytokines, interleukin (IL)-1beta and IL-18, are involved in trauma-induced neuronal cell death in the developing brain. 7-day-old Wistar rats or C57/BL6 mice were subjected to head trauma using a weight drop device. Animals were sacrificed at defined time points following trauma and brains were processed for histology and molecular analyses. Neuronal cell death in the immature brain peaked at 12-24 h and was accompanied by a marked increase of mRNA and protein levels for caspase-1, IL-1beta and IL-18 within 2 to 12 h following the injury. Caspase-1 levels were elevated for 72 h, whereas IL-1beta decreased earlier at 48 h. IL-18 remained high over a period of 3 days and decreased to normal levels by day 7 after the injury. Intraperitoneal injection of recombinant human IL-18-binding protein (IL-18BP), a specific inhibitor of IL-18, attenuated traumatic brain injury. Mice deficient in IL-18 (IL-18-/-) were protected against trauma-induced brain damage. These findings indicate that IL-18 is involved in trauma-induced neuronal cell death in the immature rodent brain and might serve as a potential therapeutic target.

A nitric oxide donor reduces brain injury and enhances recovery of cerebral blood flow after hypoxia-ischemia in the newborn rat

Nitric oxide (NO) released in response to hypoxia-ischemia (HI) in the newborn brain may mediate both protective and pathologic responses. We sought to determine whether pharmacologic increase of NO using an NO donor would reduce neurologic injury resulting from HI in the postnatal day 7 rat. We measured NO levels and CBF in the presence of either a NOS inhibitor, N-nitro-l-arginine methyl ester (L-NAME) or an NO donor (Z)-1-[N-(2-amino-ethyl)-N-(2-ammonio-ethyl)amino]diazen-1-ium-1,2-diolate (DETANONOate). Both inhibition of NOS and administration of an NO donor reduced neuropathologic injury after 7-day recovery. NO levels decreased in both ischemic and contralateral hemispheres during HI. This response was prevented by treatment with DETANONOate. Despite the decrease in NO, CBF increased during ischemia in the contralateral hemisphere but decreased when combined with brief hypoxia. Treatment with L-NAME abolished these increases, which were not altered by DETANONOate. Reduction of cellular metabolism by mild hypothermia also reduced both NO and CBF. Following prolonged HI, CBF remained decreased in the ischemic hemisphere up to 24-h recovery. This decrease was prevented by treatment with DETANONOate. These data show that administration of an NO donor reduces neurologic injury following HI in the newborn rat. This mechanism of this protection, in part, is due to an increase in the rate of recovery of CBF compared to vehicle-treated animals. Augmentation of NO-dependent increases in CBF may serve to improve neurologic outcome after perinatal asphyxia.

Specific caspase inhibitor Q-VD-OPh prevents neonatal stroke in P7 rat: a role for gender

Hypoxia-ischaemia in the developing brain results in brain injury with prominent features of apoptosis. In the present study, a third generation dipeptidyl broad-spectrum caspase inhibitor, quinoline-Val-Asp(Ome)-CH2-O-phenoxy (Q-VD-OPh), was tested in a model of unilateral focal ischaemia with reperfusion in 7-day-old rats. Q-VD-OPh (1 mg/kg, i.p.) reduced cell death, resulting in significant neuroprotection at 48 h of recovery (infarct volume of 12.6 +/- 2.8 vs. 24.3 +/- 2.2%, p = 0.006). The neuroprotective effects observed at 48 h post-ischaemia hold up at 21 days of survival time and attenuate neurological dysfunction. Analysis by gender revealed that females were strongly protected (6.7 +/- 3.3%, p = 0.006), in contrast to males in which there was no significant effect, when Q-VD-OPh was given after clip removal on the left common carotid artery. Immunoblot analysis demonstrated that Q-VD-OPh inhibits caspase 3 cleavage into its p17 active form and caspase 1 up-regulation and cleavage in vivo. Following ischaemia in P7 rats, males and females displayed different time course and pattern of cytochrome c release and active p17 caspase 3 during the first 24 h of recovery. In contrast, no significant difference was observed for caspase 1 expression between genders. These results indicate that ischaemia activates caspases shortly after reperfusion and that the sex of the animal may strongly influences apoptotic pathways in the pathogenesis of neonatal brain injury. The specificity, effectiveness, and reduced toxicity of Q-VD-OPh may determine the potential use of peptide-derived irreversible caspase inhibitors as promising therapeutics.

Decreased retinal neuronal cell death in caspase-1 knockout mice

PURPOSE

To determine whether apoptosis of retinal neurons induced by excessive light exposure and ischemia-reperfusion injury is altered in caspase-1 knockout mice.

METHODS

Eight- to 10-week-old caspase-1 knockout mice (Casp1-/-) and wild-type (WT) mice (C57BL/6) were exposed to diffuse, cool, white fluorescent light of 25,000 lux for 2 h. Other mice were subjected to retinal ischemia by increasing the intraocular pressure to 110 mmHg for 45 min. Electroretinograms (ERGs) were recorded before and after the light exposure. TdT-dUTP terminal nick-end labeling (TUNEL) was performed to identify the apoptotic cells after the insults. The inner retinal thickness was measured to evaluate the retinal injury after the ischemia-reperfusion. Expression of caspase-1 protein was studied by immunohistochemical analysis and Western blotting. Caspase-1-like protease activity was determined by a colorimetric tetrapeptide substrate.

RESULTS

The morphology of the retina and the amplitudes of the a and b waves of the ERGs of Casp1-/- mice did not differ from those of WT mice. After the light exposure, TUNEL-positive cells were observed in the outer nuclear layer of the WT mice retina. The number of TUNEL-positive photoreceptor nuclei after the light exposure, and the number of nuclei in the inner nuclear layer after the ischemia-reperfusion injury, were significantly less in Casp1-/- mice than in WT mice. There were more caspase-1-positive photoreceptor cells in WT mice after the light injury. The inner retinal layer of Casp1-/- mice was significantly thicker in Casp1-/- mice than in WT mice 2 weeks after the ischemic insult.

CONCLUSIONS

Retinal neuronal apoptosis was less prominent in Casp1-/- mice after excessive light exposure and ischemia-reperfusion injury. These data indicate that caspase-1 plays a role in retinal neuronal apoptosis.

Simvastatin reduces caspase-3 activation and inflammatory markers induced by hypoxia–ischemia in the newborn rat

The present study was undertaken to evaluate whether in a neonatal model of stroke a prophylactic neuroprotective treatment with simvastatin modulates hypoxia-ischemia-induced inflammatory and apoptotic signaling. Procaspase-3 and cleaved caspase-3 expression showed a peak at 24 h and returned to control values after 5 days. Caspase-3 activity followed the same pattern of caspase-3 proteolytic cleavage. In simvastatin-treated ischemic animals, the expression of these proteins and caspase-3 activity were significantly lower when compared to that of ischemic animals. alpha-Spectrin and protein kinase C-alpha (PKCalpha) cleavages were not affected by the treatment. Poly (ADP-ribose) polymerase fragmentation, caspase-1 activation, and IL-1beta and ICAM-1 mRNA expression were increased by hypoxia-ischemia and significantly reduced in simvastatin-treated animals. The results indicate that simvastatin-induced attenuation of hypoxia-ischemia brain injury in the newborn rat occurs through reduction of the inflammatory response, caspase-3 activation, and apoptotic cell death.

Strain variability, injury distribution, and seizure onset in a mouse model of stroke in the immature brain

Neonatal stroke is an important cause of neurologic morbidity and cerebral palsy. Recently, we have determined that in postnatal day 12 CD1 mice unilateral carotid ligation alone results in seizures and brain injury. We have shown that, in this model, seizure scores correlate with brain injury scores. We have applied this model to another strain of mice to assess strain-related differences in vulnerability to seizures and brain injury after unilateral carotid ligation. Under isoflurane anesthesia, unilateral right-sided carotid ligation was performed in postnatal day 12 C3HeB/FeJ mice followed by a 4-hour period of observation in a 35 degrees C incubator. Seizure scores and brain jury scores were assigned and compared to scores in mice receiving sham surgery. Timing of seizure onset and regional distribution of brain injury were compared in the CD1 and C3HeB/FeJ mice. Unilateral carotid ligation in postnatal day 12 C3HeB/FeJ mice resulted in seizure behavior and brain injury in some animals, with similar time to seizure onset and regional injury distribution, but affected a significantly smaller percentage of C3HeB/FeJ pups than that observed in postnatal day 12 CD1 mice, indicating strain-related vulnerability in this model.

Combined deficiency of IL-1beta18, but not IL-1alphabeta, reduces susceptibility to hypoxia-ischemia in the immature brain

Interleukin (IL)-1 and IL-18 belong to the IL-1 family. IL-18 deficiency has been shown to confer moderate protection after hypoxia-ischemia (HI) in the immature brain, while the contribution of the two isoforms of IL-1 (IL-1alpha and IL-1beta) in neonatal HI brain injury has not been investigated previously. The aim of this study was to examine the contribution of the different members of the IL-1 family to neonatal HI damage. Unilateral HI was induced at postnatal day 9 in IL-1beta, IL-1beta18, and IL-1alphabeta knockout and wild-type mice and brain injury was evaluated 1 week later. IL-1beta18-deficient mice showed 17% reduction in brain injury, while no significant reduction in injury was detected between any of the other groups. These results indicate that IL-18, but not IL-1beta, or the combination of IL-1alpha and IL-1beta, is a contributor to HI injury in the immature brain.

Hsp70 overexpression sequesters AIF and reduces neonatal hypoxic/ischemic brain injury

Apoptosis is implicated in neonatal hypoxic/ischemic (H/I) brain injury among various forms of cell death. Here we investigate whether overexpression of heat shock protein (Hsp) 70, an antiapoptotic protein, protects the neonatal brain from H/I injury and the pathways involved in the protection. Postnatal day 7 (P7) transgenic mice overexpressing rat Hsp70 (Tg) and their wild-type littermates (Wt) underwent unilateral common carotid artery ligation followed by 30 mins exposure to 8% O(2). Significant neuroprotection was observed in Tg versus Wt mice on both P12 and P21, correlating with a high level of constitutive but not inducible Hsp70 in the Tg. More prominent injury was observed in Wt and Tg mice on P21, suggesting its continuous evolution after P12. Western blot analysis showed that translocation of cytochrome c, but not the second mitochondria-derived activator of caspase (Smac)/DIABLO and apoptosis-inducing factor (AIF), from mitochondria into cytosol was significantly reduced in Tg 24 h after H/I compared with Wt mice. Coimmunoprecipitation detected more Hsp70 bound to AIF in Tg than Wt mice 24 h after H/I, inversely correlating with the amount of nuclear, but not cytosolic, AIF translocation. Our results suggest that interaction between Hsp70 and AIF might have reduced downstream events leading to cell death, including the reduction of nuclear AIF translocation in the neonatal brains of Hsp70 Tg mice after H/I.

Perinatal hypoxia/ischemia damages and depletes progenitors from the mouse subventricular zone

Hypoxia-ischemia (H/I) as a result of asphyxia at term remains a major cause of neurologic disability. Our previous studies in the P7 rat model of perinatal H/I have shown that progenitors within the subventricular zone (SVZ) are vulnerable to this insult. Since many investigators are using transgenic and knockout mice to determine the importance of specific molecules in the evolution of damage after a stroke, there is a need to perform comparative studies on the relative vulnerability of the mouse SVZ. Here we assess damage to the SVZ of 5-, 7- and 10-day-old C57BL/6 mice after unilateral common carotid artery cauterization followed by 70 min of H/I (10% O2). Whereas 5- and 7-day-old mice sustained little SVZ damage as assessed by hematoxylin and eosin staining, there was a 16% reduction of cellularity in 10-day-old animals by 18 h of recovery. Additionally, swollen cells were observed in the medial region of the SVZ of 10-day-old mice. However, few caspase-3+ and TUNEL+ cells were observed in this region, which contains the putative neural stem cells. Rather, the majority of the dying cells were situated in the mediolateral and lateral tail of the SVZ. At 18 h of recovery, there was a 2-fold increase in the frequency of TUNEL+ cells in the ipsilateral SVZ as well as a 3-fold increase in the frequency of active-caspase-3+ cells. We conclude that progenitors within the neonatal mouse SVZ are vulnerable to hypoxic/ischemic insult. The demise of these early progenitors likely leads to depletion of neuronal and late oligodendrocyte progenitors, contributing to cerebral dysgenesis.

Interleukin-1 and the interleukin-1 type 1 receptor are essential for the progressive neurodegeneration that ensues subsequent to a mild hypoxic/ischemic injury

Excessive inflammation has been implicated in the progressive neurodegeneration that occurs in multiple neurological diseases, including cerebral ischemia, and elevated levels of the proinflammatory cytokine interleukin-1 (IL-1) have been shown to exacerbate brain damage, whereas diminishing IL-1 levels limits the extent of injury. However, to date there is no consensus regarding which receptor(s) mediates the detrimental effects of IL-1. Because we have previously demonstrated that signaling through the IL-1 type 1 receptor (IL-1R1) is necessary for microglial activation and because results from other studies have implicated microglia as effectors of neurodegeneration, we hypothesized that inactivating the IL-1R1 would decrease the extent of damage caused by a hypoxic-ischemic (H/I) insult. It is shown that a mild insult initiates progressive neurodegeneration that leads to cystic infarcts, which can be prevented by inactivating the IL-1R1. The IL-1R1 null mice also show preserved sensorimotor function at 1 month's recovery. The mild insult induces multiple proinflammatory cytokines and activates microglia, and these responses are dramatically curtailed in mice lacking the IL-1R1. Importantly, the neuroinflammation precedes the progressive enlargement of the infarct, suggesting that the inflammation is causal rather than a consequence of the brain damage. These findings show that abrogating the inflammation consequent to a mild H/I insult will prevent brain damage and preserve neurological function. Additionally, these data incriminate the IL-1R1 as a master proinflammatory cytokine receptor.

Caspase-1-processed interleukins in hyperoxia-induced cell death in the developing brain

Infants born prematurely may develop neurocognitive deficits without an obvious cause. Oxygen, which is widely used in neonatal medicine, constitutes one possible contributing neurotoxic factor, because it can trigger neuronal apoptosis in the developing brain of rodents. We hypothesized that two caspase-1-processed cytokines, interleukin (IL)-1beta and IL-18, are involved in oxygen-induced neuronal cell death. Six-day-old Wistar rats or C57/BL6 mice were exposed to 80% oxygen for various time periods (2, 6, 12, 24, and 48 hours). Neuronal cell death in the brain, as assessed by Fluoro-Jade B and silver staining, peaked at 12 to 24 hours and was preceded by a marked increase in mRNA and protein levels of caspase 1, IL-1beta, IL-18, and IL-18 receptor alpha (IL-18Ralpha). Intraperitoneal injection of recombinant human IL-18-binding protein, a specific inhibitor of IL-18, attenuated hyperoxic brain injury. Mice deficient in IL-1 receptor-associated kinase 4 (IRAK-4), which is pivotal for both IL-1beta and IL-18 signal transduction, were protected against oxygen-mediated neurotoxicity. These findings causally link IL-1beta and IL-18 to hyperoxia-induced cell death in the immature brain. These cytokines might serve as useful targets for therapeutic approaches aimed at preserving neuronal function in the immature brain, which is exquisitely sensitive to a variety of iatrogenic measures including oxygen.

White matter injury in the immature brain: role of interleukin-18

Inflammation is likely to be important in the pathophysiology of white matter damage in the immature brain. In order to investigate the involvement of interleukin (IL)-18, we subjected 9-day-old IL-18-deficient and wild-type (WT) mice to hypoxia-ischemia (HI) (unilateral carotid ligation and exposure to 10% oxygen) and white matter injury was evaluated after 3 days by immunostaining for myelin basic protein (MBP) and neurofilament (NF). The immunoreactivity of MBP was significantly higher by 92, 49 and 21%, respectively, in subcortical white matter, striatum and thalamus in IL-18-deficient mice versus WT mice following HI. Similarly, there was a more pronounced immunoreactivity of NF by 78% in the subcortical white matter in IL-18 KO versus WT mice. IL-18 was expressed by astrocytes and microglia, whereas the IL-18 receptor was mainly found in astrocytes localized in and around the subventricular white matter. Taken together, these results indicate that release of IL-18 may play an important role in the development of white matter injury in the neonatal brain.

Inflammatory gene profiling in the developing mouse brain after hypoxia-ischemia

Brain ischemia triggers an inflammatory reaction that progresses for days to weeks and seems to have a role in secondary progression of injury. Inflammation induces a complex pattern of signaling molecules with partly contradictory actions, and the responses may be different in the immature and adult brain. The authors characterized the global inflammatory gene expression in the developing brain as a first step toward understanding the protective and deleterious effects of inflammation after hypoxia-ischemia. Oligonucleotide arrays were used to investigate inflammatory genes in cortex, hippocampus, thalamus, and striatum at 2, 8, 24, and 72 hours after hypoxia-ischemia, which was induced in 9-day-old mice by left carotid artery ligation followed by hypoxia. After hypoxia-ischemia, 148 inflammatory genes were differentially expressed. More than 97% of the genes were upregulated and 93% had not previously been reported after hypoxia-ischemia in the immature brain. The results indicate that microglia/macrophages, T- and B-cells, NK-cells, mast cells, dendritic cells, and polymorphonuclear leukocytes may participate in the response to hypoxia-ischemia. In addition, novel cytokines/chemokines, complement-related, interferon-regulated, components of the TIR/nuclear factor-kappaB pathway, and a number of immunomodulatory genes were induced. Several of these genes may of pathophysiologic significance after neonatal hypoxia-ischemia.

Interleukin-1: a master regulator of neuroinflammation

Interleukins 1alpha and 1beta (IL-1) are very potent signaling molecules that are expressed normally at low levels, but are induced rapidly in response to local or peripheral insults. IL-1 coordinates systemic host defense responses to pathogens and to injury and not surprisingly it has similar effects within the central nervous system (CNS). Numerous reports have correlated the presence of IL-1 in the injured or diseased brain, and its effects on neurons and nonneuronal cells in the CNS, but it is only recently that the importance of IL-1 signaling has been recognized. This article reviews studies that demonstrate that IL-1 is at or near the top of the hierarchical cytokine signaling cascade in the CNS that results in the activation of endogenous microglia and vascular endothelial cells to recruit peripheral leukocytes (i.e., neuroinflammation). The IL-1 system thus provides an attractive target for therapeutic intervention to ameliorate the destructive consequences of neuroinflammation.

A new model of stroke and ischemic seizures in the immature mouse

Ischemic brain injury from stroke is an important cause of disability in infants and children, but current experimental models for the disorder are complex. These preparations require occlusion of small intracerebral vessels or common carotid artery ligation combined with exposure to reduced levels of oxygen. Unilateral carotid artery ligation alone was sufficient to cause brain injury in more than 70% of 12-day-old CD1 mice. Using a blinded behavioral rating scale of seizure activity in mice, a direct, highly significant correlation between the severity of seizures over the 4-hour period after ligation and the severity of histologic brain injury 7 days later (Spearman's rho = 0.835, P < 0.001) was documented. This study presents the first model of stroke in immature mice produced by unilateral carotid artery ligation alone, and the first to demonstrate a clear correlation between acute ischemia-induced seizures and brain injury. This new model should be useful for examining the pathogenesis of stroke in the immature brain and the potential contribution of seizures to final outcome.

Neonatal hypoxic-ischemic injury increases forebrain subventricular zone neurogenesis in the mouse

Neurogenesis persists throughout life in the rodent subventricular zone (SVZ)-olfactory bulb pathway and increases in the adult after brain insults. The influence of neonatal injury on SVZ neural precursors is unknown. We examined the effects of hypoxia-ischemia (HI) on neonatal mouse SVZ cell proliferation and neurogenesis. Postnatal day 10 (P10) mice underwent right carotid artery ligation followed by 10% O2 exposure for 45 min. The SVZ area and hemispheric injury were quantified morphometrically 1-3 weeks later. Bromodeoxyuridine (BrdU) was used to label proliferating cells, and cell phenotypes of the progeny were identified by immunohistochemistry. HI significantly enlarged the ipsilateral SVZ at P18, P24, and P31, and increases in the SVZ area correlated directly with the degree of hemispheric damage. HI also stimulated cell proliferation and neurogenesis in the SVZ and peri-infarct striatum. Some newborn cells expressed a neuronal phenotype at P24, but not at P31, indicating that neurogenesis was short-lived. These results suggest that augmenting SVZ neuroblast recruitment and survival may improve neural repair after neonatal brain injury.

Effects of NF-kappaB oligonucleotide "decoys" on gene expression in P7 rat hippocampus after hypoxia/ischemia

"Decoy" oligonucleotides can be used as gene-specific nuclear factor (NF-kappaB) inhibitors to regulate gene expression. We applied two different decoy oligonucleotides that contained the NF-kappaB binding consensus sequences present in the immunoglobulin G (IgG)-kappaB and Bcl-x promoter into 7-day-old (P7) rat lateral ventricles before hypoxia/ischemia (HI) and compared their effects on gene expression in hippocampi to saline-treated, scrambled decoy-treated, or untreated hippocampi exposed to HI. Left hippocampi were collected at 12 hr after HI. Electrophoretic mobility shift assays (EMSAs) showed that the two decoy treatments had different effects on NF-kappaB binding to the IgG-kappaB and Bcl-x promoter-specific consensus sequences, respectively. We assessed the decoys' effects on gene expression 12 hr after HI using ribonuclease protection assays (RPAs) and Affymetrix DNA microarrays. RPAs showed that both decoys significantly decreased interleukin (IL)-1alpha mRNA levels but had no impact on IL-1beta, IL-6, and IL-10 mRNA levels. IgG-kappaB decoys significantly decreased tumor necrosis factor (TNF)-alpha and TNF-beta mRNA levels compared to minimal changes after treatment with Bcl-x decoys. DNA microarray analyses showed that Bcl-x decoy treatment significantly decreased Bcl-x(L) mRNA levels. The decreased Bcl-x(L) mRNA levels after Bcl-x decoy treatment was confirmed by RPA analysis. DNA microarray data also indicated that several other genes were affected by both decoys. Our results suggest that different NF-kappaB decoy treatments could differentially regulate transcriptional responses to central nervous system trauma. Careful design of decoy sequences, however, is essential to acquire selective effects on cell death outcome.

The powerful neuroprotective action of C1-inhibitor on brain ischemia-reperfusion injury does not require C1q

C1-inhibitor (C1-INH) is a major regulator of the complement classical pathway. Besides this action, it may also inhibit other related inflammatory systems. We have studied the effect of C1-INH in C57BL/6 mice with focal transient brain ischemia induced by 30 minutes of occlusion of the middle cerebral artery. C1-INH induced a dose-dependent reduction of ischemic volume that, with the dose of 15 U/mouse, reached 10.8% of the volume of saline-treated mice. Four days after ischemia the treated mice had significantly lower general and focal neurological deficit scores. Fluoro-Jade staining, a marker for neuronal degeneration, showed that C1-INH-treated mice had a lower number of degenerating cells. Leukocyte infiltration, as assessed by CD45 immunostaining, was also markedly decreased. We then investigated the response to ischemia in C1q(-/-) mice. There was a slight, nonsignificant decrease in infarct volume in C1q(-/-) mice (reduction to 72.3%) compared to wild types. Administration of C1-INH to these mice was still able to reduce the ischemic volume to 31.4%. The study shows that C1-INH has a strong neuroprotective effect on brain ischemia/reperfusion injury and that its action is independent from C1q-mediated activation of classical pathway.

Inflammation in central nervous system injury

Inflammation is a key component of host defence responses to peripheral inflammation and injury, but it is now also recognized as a major contributor to diverse, acute and chronic central nervous system (CNS) disorders. Expression of inflammatory mediators including complement, adhesion molecules, cyclooxygenase enzymes and their products and cytokines is increased in experimental and clinical neurodegenerative disease, and intervention studies in experimental animals suggest that several of these factors contribute directly to neuronal injury. Most notably, specific cytokines, such as interleukin-1 (IL-1), have been implicated heavily in acute neurodegeneration, such as stroke and head injury. In spite of their diverse presentation, common inflammatory mechanisms may contribute to many neurodegenerative disorders and in some (e.g. multiple sclerosis) inflammatory modulators are in clinical use. Inflammation may have beneficial as well as detrimental actions in the CNS, particularly in repair and recovery. Nevertheless, several anti-inflammatory targets have been identified as putative treatments for CNS disorders, initially in acute conditions, but which may also be appropriate to chronic neurodegenerative conditions.

Neuronal death/survival signaling pathways in cerebral ischemia

Cumulative evidence suggests that apoptosis plays a pivotal role in cell death in vitro after hypoxia. Apoptotic cell death pathways have also been implicated in ischemic cerebral injury in in vivo ischemia models. Experimental ischemia and reperfusion models, such as transient focal/global ischemia in rodents, have been thoroughly studied and the numerous reports suggest the involvement of cell survival/death signaling pathways in the pathogenesis of apoptotic cell death in ischemic lesions. In these models, reoxygenation during reperfusion provides a substrate for numerous enzymatic oxidation reactions. Oxygen radicals damage cellular lipids, proteins and nucleic acids, and initiate cell signaling pathways after cerebral ischemia. Genetic manipulation of intrinsic antioxidants and factors in the signaling pathways has provided substantial understanding of the mechanisms involved in cell death/survival signaling pathways and the role of oxygen radicals in ischemic cerebral injury. Future studies of these pathways may provide novel therapeutic strategies in clinical stroke.

Caspase inhibition after neonatal ischemia in the rat brain

Caspase-3 has been identified as a key protease in the execution of apoptosis and appears to be an important downstream event after hypoxia-ischemia in the immature brain. The efficacy of a pan-caspase inhibitor, boc-aspartyl-(Ome)-fluoromethyl-ketone (BAF), was tested in a model of unilateral focal ischemia with reperfusion in 7-day-old rats. The BAF inhibitor was given intraperitoneally 5 minutes before reperfusion via the carotid artery. This procedure reduced the activity of caspase-3 by 79% but did not induce a significant reduction in infarct volume (23.8 +/- 7.5% versus 30.1 +/- 6.4%). Animals were distributed in two populations. One population exhibited an infarct, whereas the other appeared to be fully protected. BAF-treated animals exhibiting an infarct mostly displayed necrotic cell death, whereas apoptotic nuclei were observed in untreated or vehicle-treated animals. Repeated dose of BAF (5 minutes before and 9 hours after reperfusion) did not also provide benefit after neonatal ischemia, although a general trend to reduce lesion was observed (20.5 +/- 3.7% versus 34.4 +/- 5.9%). These findings raise critical questions about the use of peptide ketone apoptotic inhibitors in improving histopathologic outcomes after neonatal stroke.

Brain injury and neurofunctional deficit in neonatal mice with hypoxic-ischemic encephalopathy

Birth asphyxia accounts for the majority of developmental motor and cognitive deficits. Studies were undertaken to develop a reproducible murine model of perinatal hypoxic-ischemic encephalopathy (HIE) which would permit both anatomic and neurofunctional quantification of injury. Short-term neurofunctional outcomes consisted of three developmental reflexes (righting, cliff aversion and geotaxis) assessed in 7-day-old mouse pups 24 h after unilateral carotid artery ligation followed by inhalation of 8% oxygen. Cerebral infarct volume was dependent on duration of hypoxia, being approximately 2.5-fold greater with longer (60 min) versus shorter (30 min) hypoxia exposure (P=0.001). All three sensorimotor neonatal reflexes assessed at 24 h after HIE injury correlated significantly with long-term neurofunction evaluated using a water-maze test of navigational learning and memory assessed 8 weeks later in the same animals. Cerebral atrophy, a delayed consequence of HIE in this model, also correlated strongly with water-maze performance (r=0.86, P=0.002). These data demonstrate for the first time that murine neonatal sensorimotor reflex performance can be rigorously quantified in the acute phase of perinatal HIE and has strong predictive value not only for anatomic extent of cerebral injury, but also for long-term neurofunctional outcome.

Protection against murine leukemia virus-induced spongiform myeloencephalopathy in mice overexpressing Bcl-2 but not in mice deficient for interleukin-6, inducible nitric oxide synthetase, ICE, Fas, Fas ligand, or TNF-R1 genes

Some murine leukemia viruses (MuLVs), among them Cas-Br-E and ts-1 MuLVs, are neurovirulent, inducing spongiform myeloencephalopathy and hind limb paralysis in susceptible mice. It has been shown that the env gene of these viruses harbors the determinant of neurovirulence. It appears that neuronal loss occurs by an indirect mechanism, since the target motor neurons have not been found to be infected. However, the pathogenesis of the disease remains unclear. Several lymphokines, cytokines, and other cellular effectors have been found to be aberrantly expressed in the brains of infected mice, but whether these are required for the development of the neurodegenerative lesions is not known. In an effort to identify the specific effectors which are indeed required for the initiation and/or development of spongiform myeloencephalopathy, we inoculated gene-deficient (knockout [KO]) mice with ts-1 MuLV. We show here that interleukin-6 (IL-6), inducible nitric oxide synthetase (iNOS), ICE, Fas, Fas ligand (FasL), and TNF-R1 KO mice still develop signs of disease. However, transgenic mice overexpressing Bcl-2 in neurons (NSE/Bcl-2) were largely protected from hind limb paralysis and had less-severe spongiform lesions. These results indicate that motor neuron death occurs in this disease at least in part by a Bcl-2-inhibitable pathway not requiring the ICE, iNOS, Fas/FasL, TNF-R1, and IL-6 gene products.

Astrocytic ceruloplasmin expression, which is induced by IL-1beta and by traumatic brain injury, increases in the absence of the IL-1 type 1 receptor

IL-1alpha and IL-1beta are induced immediately after insults to the brain, and signaling through the type 1 IL-1 receptor is essential for a normal microglial and astroglial response to injury. To better understand which genes are induced in astrocytes by IL-1beta, we used the unbiased technique of differential display to analyze mouse astroglial gene expression after IL-1beta treatment. Two novel genes were induced, as well as the gene for ceruloplasmin, a ferroxidase with antioxidant properties. Ceruloplasmin was analyzed further by Northern and Western blot. RNA and protein levels of ceruloplasmin were increased when astrocytes were treated with IL-1beta. To determine whether the IL-1 type 1 receptor (IL-1R1) is essential for the injury-induced expression of ceruloplasmin, a Western blot analysis was performed after a traumatic brain injury on mice that were IL-1R1-deficient. Ceruloplasmin increased significantly above controls after injury; however, injury-induced levels of ceruloplasmin were lower in IL-1R1-deficient (2.7-fold increase) than in the wild-type animals (3.5-fold increase). These data indicate that while IL-1R1 deletion has a slight effect on ceruloplasmin expression, it is not essential for either the basal or the induced expression of ceruloplasmin in vivo. Since ceruloplasmin buffers free copper, oxidizes ferrous iron, and catalyzes the dismutation of free radicals, increased levels of ceruloplasmin likely protect neurons and glia from sustaining damage after injury. Furthermore, as the IL-1R1 has been proposed to be a target for achieving neuroprotection after injury, these data suggest that the protection afforded by ceruloplasmin will be retained even when the IL-1R1 is antagonized.

Reactive oxygen radicals and pathogenesis of neuronal death after cerebral ischemia

Reactive oxygen species have been implicated in brain injury after cerebral ischemia. These oxidants can damage proteins, lipids, and DNA, and lead to cell injury and necrosis. Oxidants are also initiators in intracellular cell death signaling pathways that may lead to apoptosis. The possible targets of this redox signaling include mitochondria, death membrane receptors, and DNA repair enzymes. Genetic manipulation of intrinsic antioxidants and the factors in the signaling pathways has provided substantial progress in understanding the mechanisms in cell death signaling pathways and involvement of oxygen radicals in ischemic brain injury. Future studies of these pathways may provide novel therapeutic strategies in clinical stroke.

Challenge of conducting trials of neuroprotection in the asphyxiated term infant

There has been much progress in understanding the pathogenesis of hypoxic-ischemic brain injury in the near-term and term infant. Although gaps in our knowledge base persist, advances over the past two decades have led to the development of specific brain oriented therapies directed at critical events contributing to tissue damage. The primary goal of these interventions is to prevent or attenuate neurologic and developmental sequelae of brain injury. Examples of current potential treatments include modest reductions in brain temperature, receptor antagonists of excitatory neurotransmitters, reductions in O2 free radicals, blockade of inflammatory mediators, and inhibition of apoptotic pathways. At present, some of these treatments have sufficient animal data that demonstrate benefit, to justify moving experiments from the laboratory to the clinical arena. Modest hypothermia represents the neuroprotective intervention that has been investigated in the most complete fashion for the newborn, and there are multiple ongoing clinical trials testing its efficacy. This review will address specific challenges that are pertinent to the evaluation of any neuroprotective therapy implemented shortly after birth. Specific issues to be covered include the therapeutic window, establishing a diagnosis of hypoxic-ischemic encephalopathy, patient selection, characteristics of an effective therapy, safety considerations, appropriate outcome variables, and sample size considerations. Since clinical trials of brain hypothermia are in progress, many of these issues will be addressed from the perspective of this specific intervention.

Traumatic brain injury in infants and children: mechanisms of secondary damage and treatment in the intensive care unit

Unfortunately no specific pharmacologic therapies are available for the treatment of TBI in patients. Current investigation of contemporary therapies for the treatment of TBI consists of recycling of previously tested therapies in the era of contemporary neurointensive care. These therapies include hypothermia, decompressive craniectomy, osmotherapy, and controlled hyperventilation. It is hoped that more detailed knowledge regarding the dominant pathophysiologic mechanisms associated with TBI-excitotoxicity, CBF dysregulation, oxidative stress, and programmed cell death-will catapult an efficacious intervention from the laboratory bench to the bedside. This intervention may be a potent agent targeting a single dominant pathway, a broad-spectrum intervention such as hypothermia, or, more likely, a combination of therapies. Meanwhile, practitioners must offer meticulous supportive neurointensive care using clinically proven therapies aimed at minimizing cerebral swelling for the management of pediatric patients who are victims of TBI.

Differential roles of tumor necrosis factor-alpha and interleukin-1 beta in lipopolysaccharide-induced brain injury in the neonatal rat

Increasing data provide support for the hypothesis that inflammatory cytokines mediate inflammation-induced injury to developing white matter. In the present study, roles of tumor necrosis factor-alpha (TNFalpha) and interleukin-1 beta (IL-1beta) in mediating lipopolysaccharide (LPS)-induced brain injury were investigated by co-administration of LPS with IL-1 receptor antagonist (IL-1ra) or TNFalpha antibody in the 5-day-old rat brain. Intracerebral injection of LPS and other agents was performed in a stereotaxic apparatus at the location of 1.0 mm posterior and 1.0 mm lateral to the bregma, and 2.0 mm deep to the skull surface at the left hemisphere. Brain injury was examined in brain sections 3 and 11 days after LPS injection. LPS-induced inflammatory responses were evidenced by great increases in TNFalpha and IL-1beta concentrations in the neonatal rat brain 6 h after LPS injection. White matter rarefaction was observed in 71% (five out of seven) of the rat brains 3 days after LPS injection and bilateral ventricle dilation was found in 71% (five out of seven) of the P8 rat brains and in 100% of the P16 rat brains (four out of four). These alterations were not found in the control rat brains. No apparent histological changes in gray matter were observed in the LPS-injected rat brains. LPS injection also resulted in injuries to oligodendrocytes (OLs) and hypomyelination, as indicated by reduced immunostaining for O4 and myelin basic protein (MBP). Increased astrogliosis, as indicated by increased glial fibrillary acidic protein (GFAP) immunostaining, was also observed in the LPS-injected, but not the control rat brain. Co-administration of LPS with IL-1ra, but not with TNFalpha antibody, significantly attenuated LPS-induced white matter injury, as indicated by decreases in ventricle dilation, white matter rarefaction, GFAP positive staining and by improved O4 and MBP immunostaining. Co-administration of LPS with IL-1ra significantly reduced LPS-induced elevation of caspase-3 activity in the rat brain. While TNFalpha antibody had no effect on LPS-induced elevation of caspase-3 activity, co-administration of LPS with TNFalpha antibody partially, but significantly, decreased LPS-stimulated increase in IL-1beta in the neonatal rat brain. These data suggest that IL-1beta may play an important role in mediating LPS-induced brain injury and TNFalpha may have complicated, probably dual, effects in LPS-induced brain injury.

Effects of selective nitric oxide synthase inhibition on IGF-1, caspases and cytokines in a newborn piglet model of perinatal hypoxia-ischaemia

Selective inhibition of neuronal and inducible nitric oxide synthase (NOS) with 2-iminobiotin previously showed a reduction in brain cell injury. In the present study, we investigated the effects of 2-iminobiotin treatment on insulin-like growth factor-1 (IGF-1) expression, caspase activity and cytokine expression in a newborn piglet model of perinatal hypoxia-ischaemia. Newborn piglets were subjected to 1 h of hypoxia-ischaemia and were treated intravenously with vehicle or 2-iminobiotin. Vehicle-treated piglets showed reduced IGF-1 mRNA expression and increased caspase-3 activity and DNA fragmentation. 2-Iminobiotin treatment, administered immediately upon reperfusion, prevented these observations. No differences in caspase-8 and -9 activity and cytokine [interleukin (IL)-1alpha/beta, IL-6, tumour necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta] mRNA expression were demonstrated between vehicle- and 2-iminobiotin-treated piglets at 24 h following hypoxia-ischaemia. IGF-1 mRNA correlated inversely with caspase-3 and transferase-mediated dUTP-biotin in situ nick end labelling score in the cortex, but positively with caspase-8. Cytokine mRNA did not correlate with IGF-1 mRNA, caspase-3 activity or DNA fragmentation. The present results indicate that the previously demonstrated neuroprotective effect of 2-iminobiotin treatment after perinatal hypoxia-ischaemia coincided with a preservation of the endogenous IGF-1 production and reduced caspase-3 activity, but not with a significant decrease in cytokine production.

[Blood-brain barrier pathophysiology and ischaemic brain oedema]

Cerebral oedema is a potentially lethal complication of brain infarction. Ischemia, by altering membrane ionic pump function, induces cell swelling and cytotoxic oedema. It also initiates early oxidative and inflammatory cascades leading to blood-brain barrier disruption, vasogenic oedema and haemorrhagic transformation. The mechanisms of blood-brain barrier disruption involve endothelial cell activation and endothelial basal membrane degradation by matrix metalloproteinases. Reperfusion by tissue plasminogen activators is the only treatment improving stroke prognosis. This treatment also increases vasogenic oedema and the risk of symptomatic haemorrhagic transformation, reducing the benefit of reperfusion. Experimental studies suggest that the inhibition of blood-brain barrier proteolysis reduces vasogenic oedema and the risk of haemorrhage. This recent progress in the understanding of blood-brain barrier disruption during ischaemia brings forward new therapeutic strategies using agents capable of interfering with the ischaemic cascade in order to increase the therapeutic window between the onset of ischaemia and thrombolytic reperfusion.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.

Aggravated brain damage after hypoxic ischemia in immature adenosine A2A knockout mice

BACKGROUND AND PURPOSE

Cerebral hypoxic ischemia (HI) is an important cause of brain injury in the newborn infant. Adenosine is believed to protect against HI brain damage. However, the roles of the different adenosine receptors are unclear, particularly in young animals. We examined the role of adenosine A2A receptors (A2AR) using 7-day-old A2A knockout (A2AR(-/-)) mice in a model of HI.

METHODS

HI was induced in 7-day-old CD1 mice by exposure to 8% oxygen for 30 minutes after occlusion of the left common carotid artery. The resulting unilateral focal lesion was evaluated with the use of histopathological scoring and measurements of residual brain areas at 5 days, 3 weeks, and 3 months after HI. Behavioral evaluation of brain injury by locomotor activity, rotarod, and beam-walking test was made 3 weeks and 3 months after HI. Cortical cerebral blood flow, assessed by laser-Doppler flowmetry, and rectal temperature were measured during HI.

RESULTS

Reduction in cortical cerebral blood flow during HI and rectal temperature did not differ between wild-type (A2AR(+/+)) and knockout mice. In the A2AR(-/-) animals, brain injury was aggravated compared with wild-type mice. The A2AR(-/-) mice subjected to HI displayed increased forward locomotion and impaired rotarod performance in adulthood compared with A2AR(+/+) mice subjected to HI, whereas beam-walking performance was similarly defective in both groups.

CONCLUSIONS

These results suggest that, in contrast to the situation in adult animals, A2AR play an important protective role in neonatal HI brain injury.

Immunohistochemical and biochemical assessment of caspase-3 activation and DNA fragmentation following transient focal ischemia in the rat

In the present study, we evaluated the time-course of caspase-3 activation, and the evolution of cell death following focal cerebral ischemia produced by transient middle cerebral artery occlusion in rats. Ischemia-induced active caspase-3 immunoreactivity in the striatum but not the cortex at 3 and 6 h time points post-reperfusion. Furthermore, using a novel approach to visualize enzymatic activity, deltaC-APP, a C-terminal cleavage product of APP generated by caspase-3, was found to immunolocalize to the same areas as active caspase-3. Double-labeling studies demonstrated co-localization of these two proteins at the cellular level. Further double-labeling experiments revealed that active caspase-3 was confined to neuronal cells which were still viable and thus immunoreactive for NeuN. DNA fragmentation, assessed histologically by terminal dUTP nick-end labeling (TUNEL), was observed in a small number of cells in the striatum as early as 3 h, but only began to appear in the cortex by 6 h. DNA fragmentation was progressive, and by 24 h post-reperfusion, large portions of both the striatum and cortex showed TUNEL positive cells. However, double-labeling of active caspase-3 with TUNEL showed only minimal co-localization at all time-points. Thus, caspase-3 activation is an event that appears to occur prior to DNA fragmentation. As a confirmation of the histological TUNEL data, 24 h ischemia also induced the generation of nucleosome fragments, evidenced by cell death enzyme-linked immunosorbent assay. Using a novel ischemia-induced substrate cleavage biochemical approach, spectrin P120 fragment, a caspase-specific cleavage product of alpha II spectrin, a cytoskeletal protein, was shown to be elevated by western blotting. Brain concentrations of both nucleosomes and spectrin P120 correlate with the degree of injury previously assessed by triphenyltetrazolium chloride staining and infarct volume calculation. Together, our findings suggest a possible association between caspase-3 activation and ischemic cell death following middle cerebral artery occlusion brain injury.

Neuroprotection by complement (C1) inhibitor in mouse transient brain ischemia

The authors investigated the effect of the C1 inhibitor (C1-INH), the only known inhibitor of complement C1, in a murine model of transient focal ischemia. Ischemia was induced by intraluminal occlusion of the middle cerebral artery. After 2 hours, reperfusion was produced by removing the nylon monofilament occluding the artery. The effect of 15 U C1-INH (intravenously) was evaluated in terms of general and focal neurologic deficits, ischemic volume, neutral red staining (to identify the brain areas subject to ischemic damage), and glial fibrillary acidic protein immunoreactivity (to show astrocytic response). Forty-eight hours after ischemia, C1-INH significantly improved general and focal deficits by 36% and 54%, respectively, and significantly reduced infarct volume (CI-INH, 6.69% +/- 2.93%; saline, 24.24% +/- 8.24%) of total brain. Neutral red staining further showed the strong protective effect of C1-INH in cortex, hippocampus, and striatum. Astrocyte activation induced by ischemia was not affected by C1-INH. These findings show that C1-INH displayed a potent neuroprotective action by effectively reducing ischemia-reperfusion injury.

Pathogenesis of hypoxic-ischemic cerebral injury in the term infant: current concepts

Multiple, biochemical cascades contribute to the pathogenesis of neonatal hypoxic-ischemic brain injury. This article summarizes experimental evidence that supports the role of excitatory amino acids, calcium, free radicals, nitric oxide, proinflammatory cytokines, and bioactive lipids. Specific vulnerabilities that distinguish the response of the immature brain from that of the mature brain are highlighted. These include increased susceptibility to excitotoxicity and free radical injury, greater tendency to apoptotic death, and heightened vulnerability of developing oligodendrocytes. Available supportive evidence from human studies is also included. Implications for clinical neuroprotective strategies are discussed.

Similar time-course of interleukin-1 beta production and extracellular-signal-regulated kinase (ERK) activation in permanent focal brain ischemic injury

The present study investigated the activation of extracellular-signal-regulated kinase (ERK) and the potential role of interleukin-1 beta (IL-1beta) in the brain's response to focal brain ischemia in the permanent middle cerebral artery occlusion (pMCAO) model. Phosphorylated ERK p44 and p42 were increased time-dependently and significantly 18- and 28-fold, respectively, at 24-h post-pMCAO. Similarly, IL-1beta protein levels were significantly increased with the peak at 24 h in the lesioned core of the ischemic hemisphere compared to the contralateral side. Previous studies using various stimuli have shown ERK-dependent IL-1 induction. The results from our study suggest that this relation may also exist in vivo in ischemic brain tissue. Based on the progressive nature of IL-1 induction, we hypothetized that inhibition of interleukin-converting enzyme (ICE) could provide an extended time-window for neuroprotection. Therefore, we applied N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD x fmk), an ICE blocker 3 or 6 h after pMCAO. Reductions of infarct volume, however, were not observed. Taken together with previous results, where we showed protective activity of zVAD x fmk when given immediately after pMCAO, we conclude that the time window for zVAD x fmk is less than 3 h.

Seizure-induced neuronal death in the immature brain

The response of the developing brain to epileptic seizures and to status epilepticus is highly age-specific. Neonates with their low cerebral metabolic rate and fragmentary neuronal networks can tolerate relatively prolonged seizures without suffering massive cell death, but severe seizures in experimental animals inhibit brain growth, modify neuronal circuits, and can lead to behavioral deficits and to increases in neuronal excitability. Past infancy, the developing brain is characterized by high metabolic rate, exuberant neuronal and synaptic networks and overexpression of receptors and enzymes involved in excitotxic mechanisms. The outcome of seizures is highly model-dependent. Status epilepticus may produce massive neuronal death, behavioral deficits, synaptic reorganization and chronic epilepsy in some models, little damage in others. Long-term consequences are also highly age- and model-dependent. However, we now have some models which reliably lead to spontaneous seizures and chronic epilepsy in the vast majority of animals, demonstrating that seizure-induced epileptogenesis can occur in the developing brain. The mode cell death from status epilepticus is largely (but not exclusively) necrotic in adults, while the incidence of apoptosis increases at younger ages. Seizure-induced necrosis has many of the biochemical features of apoptosis, with early cytochrome release from mitochondria and capase activation. We speculate that this form of necrosis is associated with seizure-induced energy failure.

Interleukin-18 involvement in hypoxic-ischemic brain injury

Inflammation is a critical factor for development of hypoxic-ischemic (HI) brain injury. Interleukin-18 (IL-18) is a proinflammatory cytokine expressed in microglia and processed by caspase-1. Our aim was to characterize the expression of IL-18 and its receptor in relation to caspase-1 and IL-1beta after HI and to evaluate to what extent IL-18 contributes to HI brain injury. Seven-day-old rats were subjected to HI, and brain tissue was sampled at different time points (3 hr to 14 d) after insult. The mRNA for IL-18 and caspase-1 were analyzed with reverse transcriptase PCR, protein was analyzed by Western blot (IL-18, caspase-1) or ELISA (IL-1beta), and the regional distribution was assessed by immunohistochemistry. HI was also induced in C57BL/6 mice, and brain injury in IL-18-deficient animals was compared with that in wild-type animals. The expression of mRNA/protein for caspase-1 and IL-18 in brain homogenates increased progressively at 12 hr to 14 d after HI, whereas IL-1beta peaked at 8 hr. A widespread expression of caspase-1 and IL-18 protein in microglia was found in the HI hemisphere. The IL-18 receptor was expressed on neurons of the cerebral cortex and thalamus. IL-1beta was primarily found in microglia in the habenular nucleus of the thalamus. The infarct volume was reduced by 21% (p = 0.01), and the neuropathology score was significantly decreased in the cerebral cortex (-35%), hippocampus (-22%), striatum (-18%), and thalamus (-17%) in mice with IL-18 deficiency compared with wild-type mice. In conclusion, we found that IL-18 expression in microglia was markedly increased after HI and that IL-18 appears to be important for the development of HI brain injury.

Association between cerebrospinal fluid interleukin-6 concentrations and outcome after severe human traumatic brain injury

Acute inflammation plays a significant role in the pathophysiology of traumatic brain injury (TBI). However, the specific relationships between inflammatory mediators and patient outcome following TBI have not been fully established. In this study, we measured plasma and cerebrospinal fluid interleukin-1 (IL-1) and interleukin-6 (IL-6) concentrations in 36 patients, following severe TBI. Patients were monitored with continuous measurements of somatosensory-evoked potentials (SSEP) to derive an established surrogate outcome measurement, the 96-h evoked potential (SSEP96). Clinical outcomes were assessed at 3 months using the Glasgow Outcome Scale (GOS). Peak cerebrospinal fluid (CSF) IL-1 and IL-6 concentrations were significantly higher than those observed in the plasma [median 6.5 pg/mL (range 1.4-25.0) vs. 3.0 (0.8-7.6) for IL-1, and 650 (130-7,214) vs. 253 (52-1,506) for IL-6, p < 0.001 for both]. Peak CSF IL-6 levels correlated with SSEP96 (r = 0.42; p = 0.0133), and peak CSF IL-6 levels were higher with improved GOS (p = 0.024). Multiple regression analysis identified that age (p = 0.0072), pupillary abnormality (p = 0.021), the presence of mass lesion (p = 0.023), and peak CSF IL-6 concentrations (p = 0.026) were all statistically significant predictors of clinical outcome following TBI. These results suggest that peak CSF IL-6 concentrations correlate with improved outcome following TBI. This finding helps to characterize the inflammatory reaction associated with TBI and may help to develop improved treatment strategies for patients with TBI.

Extracellular ATP and P2X7 receptors in neurodegeneration

Neuronal injury and cell death in the central nervous system (CNS) are underlying features of neurodegenerative disorders. However, our understanding of the fundamental mechanisms involved is still limited. Inflammatory processes mediated by cytokines, and interleukin-1 (IL-1) in particular, play a significant role in neuronal death following pathological insults. Despite this growing area of research, very little is known about the factors regulating the expression, cleavage and release of interleukin-1 in the brain. Recent studies on immune cells demonstrate that extracellular ATP can act as a potent stimulus for the maturation and release of interleukin-1beta, via activation of P2X7 receptors. Stimulation of P2X7 receptors with ATP has dramatic cytotoxic properties and a wider role in neurodegenerative processes is possible. This review discusses the potential involvement of extracellular ATP and P2X7 receptors as regulators of interleukin-1-mediated neuropathologies and thus as a mediator of cell death following pathological insults.

Minocycline markedly protects the neonatal brain against hypoxic-ischemic injury

Hypoxic-ischemic brain injury in the perinatal period is a major cause of morbidity and mortality. Presently, there are no proven effective therapies with which to safeguard the human neonatal brain against this type of injury. Minocycline, a semisynthetic tetracycline, has been shown to be neuroprotective in certain adult ischemic injury/stroke and neurodegenerative disease models. However, minocycline's neuroprotective effects have not been assessed after insults to the neonatal brain. We now report that minocycline administered either immediately before or immediately after a hypoxic-ischemic insult substantially blocks tissue damage in a rodent model of neonatal hypoxic-ischemic brain injury. Minocycline treatment prevents the formation of activated caspase-3, a known effector of apoptosis, as well as the appearance of a calpain cleaved substrate, a marker of excitotoxic/necrotic cell death. To our knowledge, this is the first report of a systemic treatment that can be administered after a hypoxic-ischemic insult, which provides robust, nearly complete neuroprotection to the developing brain. Our data suggest that minocycline or a related neuroprotective tetracycline may be a candidate to consider in human clinical trials to protect the developing brain against hypoxic-ischemic-induced damage.