Date of Award

January 2014

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Tanea T. Reed

Department Affiliation

Chemistry

Second Advisor

Darrin L. Smith

Department Affiliation

Chemistry

Third Advisor

Martin L. Brock

Department Affiliation

Chemistry

Abstract

Neurodegeneration is the loss of neuronal structures or functions, while neuroprotection is the delay or prevention of neurodegeneration. In traumatic brain injury (TBI), neurodegeneration can occur as the result of oxidative stress, the imbalance of oxidants and antioxidants levels; therefore, antioxidant approaches can be effective therapeutic methods for neuroprotection by attenuating oxidative stress. Glutathione (GSH), a naturally occurring antioxidant, plays an important role in the maintenance of intracellular redox homeostasis by scavenging reactive oxygen species (ROS) and reactive nitrogen species (RNS). In this thesis, we attempted to evaluate the abilities of a GSH precursor, gamma-glutamylcysteine ethyl ester (GCEE), to prevent neurodegeneration by combating intracellular oxidative stress in neurons and astrocytes. For in vivo experiments, controlled cortical impact (CCI) was performed on Wistar rats to simulate moderate TBI, and GCEE (150 mg/kg) or saline was administrated 30 min or 60 min after the brain injury. Fluoro Jade-B (FJB), an ionic fluorescein derivate, was adapted to selectively stain the degenerating neurons on the brain tissues, and FJB-positive neurons were quantified. Administration of GCEE (150 mg/kg) post- injury decreased the number of FJB positive neurons that were significantly increased in saline treated groups. Next, the protective roles of GCEE in vitro in rat primary cortical astrocytes were investigated using various concentrations of tert-butyl hydroperoxide (tBHP) in order to induce oxidative stress and further toxicity. Cell viability was measured by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. The status of oxidative stress was determined by measuring intracellular ROS levels through dichlorofluorescein (DCF) assay. GCEE restored cell viability that was significantly decreased in untreated cells by decreasing oxidative stress. Lastly, the antioxidant properties of GCEE in neurons and astrocytes were investigated in a time-dependent manner. GCEE was able to immediately attenuate intracellular oxidative stress both in neurons and astrocytes. Such decreased oxidative stress was progressively increased in neurons, whereas decreased oxidative stress remained in astrocytes. Overall, our current findings suggest the protective roles of GCEE in both neurons and astrocytes may contribute to the potential therapeutic effects on oxidative stress-associated neurodegeneration following traumatic brain injury.

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