| Summary: | 博士 === 國立中興大學 === 生命科學系所 === 99 === Cerebral ischemia contributes significantly to death, disability, and healthcare costs. Inflammation plays an important role in the pathogenesis of ischemia, contributes to the late stages of ischemic injury and exacerbates of neurologic outcome. In this thesis, the release of several inflammatory mediators and growth factors, and their pathphysiological roles in cortical neurons facing glucose-oxygen-serum deprivation (GOSD) challenge were first investigated. Results showed that GOSD significantly damaged neurons in a time dependent manner. In response to GOSD, the amounts of cycloxygenase-2 (COX-2), leptin, transforming growth factor-β1 (TGF-β1), glial-cell-line-derived neurotrophic factor (GDNF) and neurotrophin-3 (NT-3) were increased significantly at early stage (6 h) of GOSD and proven to be neuroprotective. When these molecules and as well as peroxisome proliferators-activated receptor (PPAR) -γ and -α declined with time after GOSD, resulted in irreversible neuronal damage. Both nitric oxide (NO) and superoxide (O2-) showed a dual role in regulating the survival of GOSD neurons. At low concentrations (during the first 12 h of GOSD), NO and O2- appeared to protect neurons; a time-dependent culmination of these two factors however, exacerbated the death of GOSD neurons. The results suggest that early supplementation of COX-2, leptin, TGF-β1, GDNF, NT-3, and PPARs (-γ and -α) and late application of NO and O2- scavengers may benefit to neurons from ischemic insults.
To further understand the mechanisms involved in leptin-mediated neuroprotection against GOSD. Study continued to verify the interrelationships among leptin, IL-1β and glutamate in GOSD neurons and ischemic brain subjected to 90 min of cerebral ischemia. Results showed that GOSD triggered significant release of leptin and IL-1β from neurons at 6 h and both factors can protect neurons against GOSD-induced cell death. Leptin-mediated protection was in part IL-1β dependent and through IL-1β the glutamate release from GOSD neurons was inhibited. To further confirm the protective efficacy of leptin and IL-1β. In vivo, an ischemic animal model was developed by occluding right side of middle cerebral artery (MCAO) plus bilateral common carotid artery (CCAO) for 90 min followed by reperfusion for 24 h. Data showed that besides leptin, which has previously been investigated by one of my colleagues, IL-1β administration during the first 6 h of reperfusion period significantly reduced the ischemia/reperfusion-induced brain infarction. IL-1β-mediated brain protection was dose-dependent and 5 ng/rat provided the maximal protection. The protection was in part due to the inhibition of glutamate release within the ischemic brain. The results provided further support for the therapeutic value of IL-1β in cerebral ischemia.
In overall, results from the thesis further strengthen our knowledge about the kinetics versus the pathophysiological roles of several inflammatory mediators in GOSD neurons. Among them, leptin-mediated neuroprotection against ischemic insults was further investigated at mechanistic level and proven to rely on IL-1β-mediated inhibition of glutamate. Through the in vivo ischemic animal model, the therapeutic values of IL-1β and leptin in cerebral ischemia have all been demonstrated. The values of COX-2, TGF-β1, GDNF, NT-3, PPARs, NO and O2- scavengers will be further verified using the same experimental procedure applied in the study. In addition, GOSD and MCAO/CCAO experimental models can serve as reliable tools for future assessing and screening of therapeutic drugs of cerebral ischemia.
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