Date of Award
3-3-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Bioinformatics
Abstract
Like many other vitamins, vitamin E does not refer to a single chemical compound but to a group of lipid-soluble antioxidants that effectively scavenge free radicals. Structurally, vitamin E molecules consist of an aromatic head, the chromanol ring, connected to a long aliphatic tail. Based on the methylation pattern of the chromanol head, they are divided into four classes: α, β, δ, and γ. Also, depending on whether the tail is phytyl or farnesyl, they are categorized as tocopherols or tocotrienols, respectively. Vitamin E tocotrienols are attracting more interest for their potential to treat and prevent various health conditions, including cardiovascular diseases, cancer, metabolic disorders, bone health problems, and neuroprotection. Recent research indicates that γ-tocotrienol (GT3) and δ-tocotrienol (DT3) effectively protect against ionizing radiation when administered before lethal doses in animal studies. Although tocotrienols exhibit greater biological activity, their therapeutic use is limited by a short plasma half-life, requiring higher and more frequent doses to reach and sustain therapeutic levels in the body. Tocotrienols are not effective as radiomitigators when administered after lethal radiation exposure, likely due to these pharmacokinetic limitations. Among all members of the vitamin E family, α-tocopherol (AT) has the longest half-life and is the only form suitable for once-a-day dosing. The reason for AT's extended presence in plasma is its preferential binding to α-tocopherol transfer protein (ATTP). ATTP is a liver protein that maintains AT levels in plasma by returning the molecule from the liver to systemic circulation, thereby reducing the rate of liver metabolism and excretion. In contrast, tocotrienols are poorly recycled into circulation after reaching the liver due to their low affinity for ATTP. This low affinity is due to their rotationally restricted tail structure, which prevents proper fitting into the protein's binding pocket. The novel vitamin E analog, δ-tocoflexol (DTF), was designed and synthesized in our laboratory as a molecule with improved binding to ATTP while maintaining the therapeutic properties of tocotrienols. DTF is developed to have enhanced therapeutic potential compared to tocopherols and tocotrienols. The hypothesis for this study is that the improved binding of DTF to ATTP will lead to a lower elimination rate and higher bioavailability. Increased bioavailability of DTF will enhance its effectiveness, giving DTF a better chance to demonstrate efficacy when administered after radiation exposure, a situation where time is of the essence for therapeutic intervention. To test our hypothesis, we examined the pharmacokinetics of DTF and DT3 after a single subcutaneous dose (200 mg/kg) in male C57BL/6J mice (n=6). The pharmacokinetic results showed that DTF reached therapeutic plasma levels (5 µM) much faster than DT3, and the AUC of tocoflexol over 192 hours was three times higher than that of DT3. We also demonstrated that DTF provides 70% survival in a 30-day radiomitigation study in mice (male C57BL/6J, n=10) when administered subcutaneously (200 mg/kg) 24 hours after lethal total body irradiation (8.5 Gy, LD80). To better understand DTF's mechanism of action and identify potential biomarkers of its therapeutic effect, we performed a 4-way proteomic analysis in mice subjected to the same radiomitigation model (n=10), with blood samples collected 10 days post-irradiation. The proteomic analysis identified several potential biomarkers indicating DTF activity and radiomitigation effectiveness. These markers are linked to antioxidant activation, DNA repair efficiency, immune regulation, and anti-inflammatory responses, collectively forming the molecular signature of radiomitigation efficacy. We also carried out molecular dynamics analyses that strongly support the idea that DTF’s increased conformational flexibility enhances its fit within the ATTP pocket, resulting in high-affinity binding and kinetic stability. The analyses showed that the DTF tail enables stable insertion into ATTP’s hydrophobic pocket, maintaining essential hydrogen bonds and hydrophobic contacts throughout the dynamic simulation. In conclusion, these studies demonstrate that DTF has a superior pharmacokinetic profile due to increased ATTP binding, making it the first tocol with radiomitigation effects against lethal radiation. Tocoflexol is a promising candidate for further preclinical development as a radiomitigator.
Recommended Citation
Abolade, Rachael Oluwakamiye, "Pharmacokinetics, Radiomitigation Eficacy, Proteomic Analyses, and Molecular Modeling Studies of the Vitamin E Analogue Tocoflexol" (2026). Theses and Dissertations. 1349.
https://research.ualr.edu/etd/1349
