Biomedical Sciences ETDs

Publication Date

Winter 12-14-2017

Abstract

Cardiovascular disease (CVD) is the leading global cause of death, and cigarette smoking (CS) is a major risk factor for CVD. Although there are smoking cessation programs that include a combination of pharmacological and behavior treatments, failure to curb behavioral habits and pharmacological addiction leads to low cessation success rates. Thus, developing a treatment to decrease CVD risk is critical. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) decrease oxidative stress and have been shown to restore endothelial function, an indicator of CV health, in cigarette smokers. Metabolites of n-3 PUFAs have been shown to have CV-protective effects, but the mechanism by which n-3 PUFAs or their metabolites restore endothelial function and increase antioxidant capacity has not been fully elucidated.

The goal of this project is to determine the antioxidant mechanism by which n-3 PUFAs or their metabolites increase antioxidant responses. The long term goals of this project are to investigate the relationships between n-3 PUFAs, their metabolites and antioxidant markers, oxidative stress and vascular function.

Previous studies have shown increases in Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) expression with n-3 PUFA eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). In order to investigate the specific mechanism through which n-3 PUFAs activate Nrf2, we treated an antioxidant response element (ARE) luciferase plasmid stably-transfected hepatocyte cell line with EPA and DHA, their epoxide metabolites, and cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 metabolism inhibitors. We made the observations that only DHA activated Nrf2, and that inhibiting COX, LOX or P450 pathways further increased Nrf2 activation. Upon further investigation, we discovered oxidation products in our DHA stock that were not present in newer stocks of DHA, and when assessed, these oxidation products included ketones. Only one ketone, 17-oxo-4(Z),7(Z),10(Z),13(Z),15(E),19(Z)-DHA (17-oxo-DHA), is commercially available; we found that 17-oxo-DHA activates Nrf2, increases Nrf2 localization to the nucleus in human umbilical vein endothelial cells (HUVECs), and increased downstream antioxidant genes including heme-oxegenase-1 (Hmox1), glutamate cysteine ligase catalytic subunit (Gclc), and NADPH dehydrogenase quinone 1 (Nqo1). These results suggest that DHA oxidation increases antioxidant responses.

In order to investigate the relationship between vascular function, n-3 PUFAs and their metabolites and antioxidant markers, we conducted flow-mediated dilation in subjects between 19 and 50 yrs old. We found that an omega-3 index (RBC% eicosapentaenoic plus docosahexaenoic acids [EPA+DHA]) ≥ 4.5% was associated with higher FMD, but not lower oxidative stress. Conjugated linoleic acid (CA), palmitic acid (PA), and the ratio of linoleic acid diol-to-epoxide metabolites were predictive of MDA; 14,15-epoxyeicosatetraenoic acid (EET) and 10,17-dihydroxydocosahexaenoic acid (DiHDHA) were predictive of 8-epi-PGF2α; and oleic acid (OA), 16,17-dihydroxydocosapentaenoic acid (DiHDPA), and eicosenoic acid (EA) were predictive of FMD. These results suggest that n-3 PUFAs may be vasoprotective in young healthy smokers, but other dietary fatty acids may also be beneficial.

These studies contribute to the understanding of antioxidant mechanisms of n-3 PUFAs, in particular DHA, and how DHA may protect against oxidative stress present in CS-induced CVD. Furthermore, these findings contribute to the development of therapeutic treatment to decrease CVD risk in smokers.

Keywords

Omega-3 Polyunsaturated Fatty Acids, Lipid Metabolism, Endothelial Function, Flow-Mediated Dilation, Oxidative Stress, Cigarette Smoke

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Committee Member (Chair)

Mary K. Walker

Second Committee Member

Matthew J. Campen, PhD

Third Committee Member

Nancy L. Kanagy, PhD

Fourth Committee Member

Laurie G. Hudson, PhD

Fifth Committee Member

Mary Vilay, PharmD

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