DEVELOPMENT OF ROBUST ANIMAL MODELS FOR VITAMIN C FUNCTION

Abstract

<p>Vitamin C inhibits the oxidation of biologically important molecules and may have a potential protective role against cancer, cardiovascular diseases, and aging. Clinically relevant models of vitamin C function are essential for understanding the role of the antioxidant in the pathogenesis of these complex diseases, and its therapeutic potential. In this thesis, we examine ascorbic acid synthesis and deficiency in animal models, and develop these animal models into powerful tools to examine specific questions of vitamin C function. This thesis first presents a review on the existing animal models for antioxidant function in human nutrition, focusing on their clinical relevance in chronic diseases. We concluded that equivocal proof of beneficial effects of high dose antioxidant supplementation has not been established, and further investigations of animal models of antioxidant function are needed to resolve outstanding questions.</p> <p>We then examined the feasibility and efficacy of an alternative vitamin C delivery method using gene therapeutic lentivirus vectors in a guinea pig model of vitamin C function. The guinea pig exhibits an inactivated gulonolactone oxidase gene (<em>Gulo</em>), which is required for endogenous ascorbic acid synthesis, and as such must acquire vitamin C from the diet. Using a lentivirus vector carrying the mouse <em>Gulo</em> under the murine cytomegalovirus (mCMV) promoter, which was previously developed as a part of my undergraduate thesis, we examined the ability of this gene therapeutic vector to mediate the expression of GULO and the production of ascorbic acid in guinea pigs. At a titre of 10¹⁰ viral particles per animal, the life of lentivirus-treated guinea pigs were prolonged by 35 days compared to the scorbutic control, which was given an ascorbic acid-free diet. Ascorbic acid was produced in the liver of the treated guinea pigs, but the amount produced was not sufficient to elevate plasma concentrations or fully correct the metabolic deficiency. We conclude that lenti-mCMV-<em>Gulo</em> is able to mediate the expression of GULO and endogenous production of vitamin C in guinea pigs.</p> <p>To test the role of vitamin C in cancer etiology and outcome, we are currently in the process of introgressing the <em>Gulo</em>^-/- inactivation mutation, developed by Maeda <em>et al.</em> in 2000, from the C57BL/6 strain background into the FVB/N strain background. The FVB/N strain is also the background for several models of <em>erbB2/neu</em> overexpression in human breast cancer, associated with increased metastasis and low patient survival rates. Taken together, this thesis develops two animal models of vitamin C function, which can be employed in future applications.</p>