Nutritional intervention and modeling of acute ischemic stroke .

摘要

The documented origins of functional-foods and disease intervention date back thousands of years to ancient Egyptian culture where honey was used as a wound dressing. Recent scientific review has explored and affirmed the therapeutic benefits of this olden remedy. While septic wounds were a leading cause of death then, modern man faces very different causes and contributors of morbidity today. Stroke is currently the third leading cause of death in the United States. The purpose of this work was to study potential nutritional interventions for risk factors and outcomes affecting acute ischemic stroke and to develop a robust pre-clinical stroke model to improve the translation of potential therapeutics to the clinic.;Objective. The objectives of this dissertation were three-fold: (i) To characterize a basis for nutritional intervention of acute ischemic stroke risk factors by using niacin-bound chromium in the prevention of metabolic syndrome; (ii) to determine the in vivo relevance of the natural vitamin E, alpha-tocotrienol, in neuroprotection following acute ischemic stroke; and (iii) to develop a pre-clinical model of acute ischemic stroke in canines to bridge the translational gap that exists between laboratory and clinical stroke research; and to improve upon existing stroke models for testing alpha-tocotrienol efficacy prior to clinical study.;Experimental approach and results. As part of this dissertation, we first described a nutritional intervention for metabolic syndrome, a constellation of risk factors that are known to contribute to incidence and severity of outcomes in stroke. To model metabolic syndrome, we employed mice with a spontaneous mutation that induced obesity, glucose intolerance, and dyslipidemia. Prophylactic supplementation of these mice with a chromium complex significantly improved their lipid profile and modestly improved glucose clearance. Examination of the adipose tissue transcriptome using genome-wide microarray analysis revealed a myogenic response to chromium supplementation.;Next, we assessed the in vivo potential for a direct nutritional intervention of stroke-induced pathology with a natural vitamin E isoform, alpha-tocotrienol (alphaT3). A multi-generational supplementation study was conducted to determine alphaT3 tissue concentration for biological relevance. High pressure liquid chromatography analysis of alphaT3 concentration in brain tissue was found to be within the nanomolar range relevant to in vitro study neuroprotection results. We followed up these findings by testing the neuroprotective potential of alphaT3 in a rodent model of stroke. Spontaneously hypertensive rats, prone to stroke, had significantly reduced infarct volume when supplemented with alphaT3 as compared to placebo controls. The mechanism of neuroprotection by alphaT3 in cell culture study was reportedly by two cytosolic targets, c-Src and 12-lipoxygenase (12-Lox). The active form of phosphorylated 12-Lox was reduced in stroke affected tissue of orally administered alphaT3 rats as compared to placebo controls. Supporting the role of 12-Lox as a key mediator of stroke-induced cell death, 12-Lox deficient mice had significantly smaller infarct volume as compared to wild-type matched controls. 12-Lox metabolizes arachidonic acid from the lipid bilayer into the eicosanoid 12-S-hydroperoxyeicosatetraenoic acid (12-S-HPETE). The rate of respiration in isolated brain mitochondria was inhibited by incubation with 12-S-HPETE. Furthermore,12-S-HPETE promoted mitochondrial dysfunction by reducing inner membrane potential, and exacerbating permeability transition pore opening (PTP). 12-S-HPETE induction of PTP was inhibited in isolated brain mitochondria by co-treating them with alphaT3.;The final objective of this thesis was to develop a pre-clinical model of stroke in which potential neuroprotective agents, such as alphaT3, could be tested prior to clinical trial. We developed a minimally invasive method of transient middle cerebral artery (MCA) occlusion in canines which benefits from a neuroradiological approach to visualize the stroke event. Using 3T magnetic resonance imaging (MRI), we quantified the infarct volume in canines (n=4) and reported very tight reproducibility. Histological analysis of stroke and contralateral cortex confirmed stroke-induced neurodegeneration in the MCA territory.;Conclusions. This dissertation describes prospective nutritional interventions for stroke-related risk factors and stroke-induced infarction. These natural dietary factors hold great promise in reducing the incidence and severity of stroke. Development of a minimally invasive pre-clinical model of stroke will further help to bridge the gap between laboratory benchwork and clinical study so that potential therapeutics, such as these, can be identified and translated to the clinical setting.