Date of Award

11-26-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Bioinformatics

First Advisor

Cesar Compadre

Abstract

With the increased use of ionizing radiation for various purposes like radiotherapy, nuclear power generation, sterilization, the likelihood of intentional or unintentional radiation exposure is increasing and there is an unmet need for effective radiation countermeasures that are safe, efficient, easy to administer. Vitamin-E is a well-known antioxidant, consisting of eight different vitamers, including four tocopherols (α, β, γ and δ) and four tocotrienols (α, β, γ and δ), which are structurally very similar and collectively known as tocols. Though alpha-tocopherol has been considered the primary form of vitamin-E and extensively studied, tocotrienols have recently gained attention for their superior biological activity. Unfortunately, the poor pharmacokinetic profile of tocotrienols is limiting their applicability as radiation countermeasures. The reasons for tocotrienol’s superior biological activity despite their relatively minor structural differences with tocopherols, are not well understood. Based on available experimental and computational analyses, we hypothesized that the in vivo efficacy of tocols is controlled by a combination of their bioavailability, the rate and extent of their cell uptake, and their intrinsic activity. To test our hypothesis, we have determined cellular uptake levels of 6 vitamers, α, γ, δ tocopherols and α, γ, δ tocotrienols, in 3 different cellular systems including, endothelial (HUVEC) cells, motor-neuron like cells (NSC-34) and hepatocytes (HepG2) by incubating the cells with 5 µM tocols. To study their intrinsic activity, HUVEC cells were treated with tocol amounts that produced equimolar intracellular concentrations, irradiated with 2.5 Gy gamma-radiation, and the differences in gene expression between tocols was examined. None of the naturally occurring vitamin-E vitamer have the necessary pharmacokinetic profile to be an effective radiation countermeasure, namely rapid absorption and slow elimination. In order to develop effective tocol radiation countermeasures, a combination of tocols that produce a fast onset and prolonged duration of protection against radiation induced damage was optimized. The results of this project, imply a paradigm in which the observed differences in tocols biological activity can be explained by a multifactorial function: Tocol therapeutic efficacy = F (Intrinsic activity, Bioavailability, Cell-uptake) This paradigm can be used to identify or develop novel vitamin-E analogues as effective radiation countermeasures.

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