Reduction of hypoxic-ischemic brain swelling in the neonatal rat with PAF antagonist WEB 2170: lack of long-term protection

Loss of PAFR prevents neuroinflammation and brain dysfunction after traumatic brain injury

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide, which is a major public health problem. Death caused by TBI accounts for a third of all damage related illnesses, which 75% TBI occurred in low and middle income countries. With the increasing use of motor vehicles, the incidence of TBI has been at a high level. The abnormal brain functions of TBI patients often show the acute and long-term neurological dysfunction, which mainly associated with the pathological process of malignant brain edema and neuroinflammation in the brain. Owing to the neuroinflammation lasts for months or even years after TBI, which is a pivotal causative factor that give rise to neurodegenerative disease at late stage of TBI. Studies have shown that platelet activating factor (PAF) inducing inflammatory reaction after TBI could not be ignored. The morphological and behavioral abnormalities after TBI in wild type mice are rescued by general knockout of PAFR gene that neuroinflammation responses and cognitive ability are improved. Our results thus define a key inflammatory molecule PAF that participates in the neuroinflammation and helps bring about cerebral dysfunction during the TBI acute phase.

Pathophysiology of an hypoxic–ischemic insult during the perinatal period

Hypoxia-ischemia is a leading cause of morbidity and mortality in the perinatal period with an incidence of 1/4000 live births. Biochemical events such as energy failure, membrane depolarization, brain edema, an increase of neurotransmitter release and inhibition of uptake, an increase of intracellular Ca(2+), production of oxygen-free radicals, lipid peroxidation, and a decrease of blood flow are triggered by hypoxia-ischemia and may lead to brain dysfunction and neuronal death. These abnormalities can result in mental impairments, seizures, and permanent motor deficits, such as cerebral palsy. The physical and emotional strain that is placed on the children affected and their families is enormous. The care that these individuals need is not only confined to childhood, but rather extends throughout their entire life span, so it is very important to understand the pathophysiology that follows a hypoxic-ischemic insult. This review will highlight many of the mechanisms that lead to neuronal death and include the emerging area of white matter injury as well as the role of inflammation and will provide a summary of therapeutic strategies. Hypothermia and oxygen will also be discussed as treatments that currently lack a specific target in the hypoxic/ischemic cascade.

Platelet-activating factor antagonist (ABT-491) decreases neuronal apoptosis in neonatal rat model of hypoxic ischemic brain injury

Hypoxic ischemic brain injury (HIBI) is a common cause of neonatal mortality and morbidity. To date, no study has investigated the role of platelet-activating factor (PAF) antagonists on neuronal apoptosis in neonatal rat model of HIBI. In the present study, we evaluated the effect of a highly potent and selective PAF antagonist (ABT-491) on neuronal apoptosis in neonatal rat model of HIBI. Seven-day-old Wistar rat pups were subjected to right common carotid artery ligation and hypoxia (92% nitrogen and 8% oxygen) for 2 h. They were treated with ABT-491 or saline either immediately before or after hypoxia. In sham group animals, neither ligation, nor hypoxia was performed. Neuronal apoptosis was evaluated by the terminal-transferase mediated dUTP biotin nick-end-labeling (TUNEL) and caspase-3 staining methods. Administration of ABT-491 either before or after hypoxia resulted in significant reduction of the numbers of apoptotic cells in both hemispheres, when compared to saline treatment group. The numbers of apoptotic cells in right hemispheres in all groups were significantly higher than that in the left hemispheres. These results suggested that ABT-491, a highly potent and selective PAF antagonist, administration either before or after hypoxia reduces apoptosis and we propose that ABT-491 may be a novel approach in the treatment of HIBI.

Partial neuroprotective effect of pretreatment with tanshinone IIA on neonatal hypoxia-ischemia brain damage

Tanshinone IIA is a compound purified from the Chinese herb Danshen (Radix Salviae Miltiorrhiza Bge). The neuroprotective effect of tanshinone IIA was investigated in a neonatal rat model of hypoxia-ischemia brain damage. Hypoxia-ischemia encephalopathy was induced in rats at day 7 of postnatal age by ligation of the right common carotid artery, followed by 2 h of hypoxia. Tanshinone IIA (10 mg/kg, i.p.) was injected daily from day 2 before surgery for 9 or 16 d. Our results demonstrated significant and sustained brain damage in the hypoxia-ischemia- and vehicle-treated groups at 1 and 3 wk after surgery. Treatment with tanshinone IIA significantly reduced the severity of brain injury, as indicated by the increase in ipsilateral brain weight and neuron density, compared with those of sham-operated animals. The recovery of sensorimotor function and histology was observed in animals that received tanshinone IIA. The plasma of tanshinone IIA-treated rats exhibited higher antioxidant activities, as reflected by the oxygen radical absorbance capacity assay, compared with the vehicle-treated rats. In the neural progenitor cell line C17.2 that was subjected to 2,2'-azobis (2-amidino propane hydrochloride)-induced oxidative stress, tanshinone IIA increased cell viability and protected against mitochondrial damage (JC-1 assay). Our results suggest that tanshinone IIA has antioxidative activities and that treatment that is started before a hypoxic-ischemic insult is partially neuroprotective. Further studies are required to elucidate whether rescue treatment with tanshinone IIA is effective and to determine whether its protective effect is also associated with secondary cooling of the brain.

Neuroprotective effects of topiramate after hypoxia-ischemia in newborn piglets

BACKGROUND

Perinatal hypoxia-ischemia (HI) is associated with delayed cerebral damage, which involves receptor-mediated excitotoxicity. Until now, successful interventions to reduce excitotoxicity early after HI in experimental settings failed to transform into clinical applications owing to negative side effects. A promising new approach using the anticonvulsant Topiramate (TPM) has shown to be effective to reduce brain damage after early HI in a rodent model of combined TPM-hypothermia. Here, we used TPM solely administered 1 h after HI in a neonatal piglet model in order to verify possible neuroprotection.

METHODS

Newborn piglets were subjected to HI by transient occlusion of carotid arteries and hypotension (62-65% of baseline). Fifteen minutes later, an additional reduction of the inspired oxygen fraction to 0.06 was performed for 13 min. One cohort (VEHICLE, n = 8) received saline solution i.v. 1 h after HI and then twice a day. Two further cohorts were treated at same times with TPM (HI-TPM10, n = 8, loading dose 20 mg/kg; maintenance dose 10 mg/kg/day; HI-TPM20, n = 8, loading dose 50 mg/kg; maintenance dose 20 mg/kg/day). Untreated animals (CONTROL, n = 8) received all experimental procedures except HI. Animals were monitored 3 days after HI concerning occurrence of seizures as well as neurological and behavioral functions. After 72 h, the brains were perfused and processed to assess neuronal loss and DNA-fragments (TUNEL staining).

RESULTS

There was a significant reduction of neuronal cell loss in HI-TPM20 animals. However, apoptosis was increased in the frontal white matter of HI-TPM20 animals.

CONCLUSIONS

Exclusive TPM treatment shows neuroprotection in newborn piglets after HI.

Timing of neutrophil depletion influences long-term neuroprotection in neonatal rat hypoxic-ischemic brain injury

In neonatal rats, neutrophils do not accumulate in ischemic brain parenchyma to the extent that they do in adult rodents. They are also confined to the intravascular compartment during the first few hours of recovery. However, neonatal rats rendered neutropenic have less brain swelling after a hypoxic-ischemic (HI) insult. In this study, we used the Rice-Vannucci model of HI brain injury in 7-d-old rats, and we depleted neutrophils before injury in one group and 4-8 h after injury in another group to determine 1) whether neutrophils contribute to cerebral atrophy, 2) whether neutropenia induced within 8 h after recovery from HI is neuroprotective, and 3) whether neutropenia preserved energy metabolites during the HI insult. Brain energy metabolites were measured at 0 h and 6 h of recovery. Brain atrophy was measured morphometrically on brain slices at 2 wk of recovery. In 67 rats, we found that neutropenia induced before the HI insult, but not after HI, reduced brain swelling at 42 h of recovery by about 75% (p < 0.001). In another 60 rats, we found that cerebral atrophy was reduced by 61% provided that neutropenia was induced before HI (p < 0.05). Total adenine nucleotides were better preserved in the neutropenic rats at the end of the HI insult (0 h recovery); p < 0.05. We conclude that neutrophils do contribute to vascular dysfunction either during the HI insult or early hours (<4-8 h) of recovery. Antineutrophil strategies initiated after this time are unlikely to be protective in the neonatal rat.

Hyperbaric oxygenation prevented brain injury induced by hypoxia-ischemia in a neonatal rat model

The occurrence of hypoxia-ischemia (HI) during early fetal or neonatal stages of an individual leads to the damaging of immature neurons resulting in behavioral and psychological dysfunctions, such as motor or learning disabilities, cerebral palsy, epilepsy or even death. No effective treatment is currently available and this study is the first to use hyperbaric oxygen (HBO) as a treatment for neonatal HI. Herein, we sought out to determine if HBO is able to offer neuroprotectivity against an HI insult. Seven-day-old rat pups were subjected to unilateral carotid artery ligation followed by 2.5 h of hypoxia (8% O(2) at 37 degrees C). HBO treatment was administered by placing pups in a chamber (3 ATA for 1 h) 1 h after hypoxia exposure. Brain injury was assessed based on ipsilateral hemispheric weight divided by contralateral hemispheric weight, light microscopy, and EM. Sensorimotor functional tests were administered at 5 weeks after hypoxia exposure. After HI, the ipsilateral hemisphere was 52.65 and 57.64% (P<0.001) of the contralateral hemisphere at 2 and 6 weeks, respectively. In HBO treated groups, the ipsilateral hemisphere was 77.77 and 84.19% (P<0.001) at 2 and 6 weeks. There was much less atrophy and apoptosis in HBO treated animals under light or electron microscopy. Sensorimotor function was also improved by HBO at 5 weeks after hypoxia exposure (Chi-square, P<0.050). The results suggest that HBO is able to attenuate the effects of HI on the neonatal brain by reducing the progression of neuronal injury and increasing sensorimotor function.

Animal models of neonatal stroke

Neonatal stroke occurs in approximately 1 in 4,000 to 1 in 10,000 newborns, and more than 80% involve the vascular territory supplied by the middle cerebral artery. Neonatal stroke is associated with many acquired and genetic prothrombotic factors, and follow-up studies indicate that as many as two thirds of neonates develop neurologic deficits. In the past two decades unilateral carotid occlusion with 8% hypoxia has been used to study focal and global ischemia in the newborn, and recently a filament model of middle cerebral artery occlusion has been developed. This review describes the results of studies in these two newborn models covering aspects of the injury cascade that occurs after focal ischemia. A likely requirement is that therapeutic efforts be directed less at using thrombolytic therapy and more toward treatment of events associated with reperfusion injury, the inflammatory cascade, and apoptosis. Additional areas of research that have received attention in the past year include inhibition of nitric oxide and free-radical formation, use of iron chelating agents, the potential role of hypoxia-inducible factors and mediators of caspase activity, use of growth factors, hypothermia, and administration of magnesium sulfate.

Platelet-activating factor antagonist BN 50730 attenuates hypoxic-ischemic brain injury in neonatal rats

Platelet-activating factor (PAF) is a lipid derived from breakdown of cell membranes that is postulated to be a mediator of cerebral ischemic injury. PAF regulates CNS gene transcription via intracellular binding sites. To test the hypothesis that PAF mediates CNS injury in part by modulating gene transcription, we evaluated the neuroprotective efficacy of the drug BN 50730, an antagonist of the intracellular (microsomal) CNS PAF binding site, in the neonatal rat model of unilateral cerebral hypoxia-ischemia. Seven-day-old rats underwent right carotid ligation followed by a 2.5-h exposure to 8% O(2), and were then treated with BN 50730 (2.5 or 25 mg/kg per dose) or vehicle, at 0 and 2 h after the end of hypoxia. Ipsilateral cortical, striatal, and hippocampal damage was quantitated either 5 d later, or at 5 wk after the insult. Treatment with BN 50730 resulted in approximately 60- 80% reduction in ipsilateral tissue loss at both times. Learning and memory were evaluated 5 wk after insult using the Morris Watermaze place navigation task. Severity of cortical and striatal damage correlated significantly with learning and memory deficits. These results support the hypothesis that PAF is a pathogenetic mediator of hypoxic-ischemic damage in the immature brain. Accumulating evidence suggests that PAF mediates its deleterious effects in the immature CNS via multiple mechanisms.