Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
Cholesterol oxidation in the milk fat globule membrane
Abstract
Cholesterol is a major component of plasma membranes, a precursor for bile acids and steroid hormones, and a structural component of serum lipoproteins. Although cholesterol is essential for normal cell function, it oxidizes under a variety of conditions. The resulting oxides are known to produce varying degrees of toxicity. The oxidation of cholesterol in foods or cell membranes is influenced significantly by the interactions among cholesterol, its neighboring molecules and other environmental factors. The purpose of this study was to examine the role of such interactions in cholesterol oxidation. Such examinations were carried out by monitoring the destruction of cholesterol and the formation and destruction of cholesterol oxides in dry and aqueous model systems as well as in the milk fat globule membrane. In cell membranes, a delicate balance exists between the various antioxidative and oxidative factors present. Numerous factors can influence such balance. In dry model systems, the amino acids and sugars tested inhibited, and triacylglycerols and free fatty acids accelerated, cholesterol oxidation. The added phospholipids were protective and/or destructive depending on their head groups, fatty acyl chains and temperature. In aqueous systems, amino acids were protective but added sugars accelerated cholesterol oxidation in the early stages of incubation. The effects of phospholipids were significantly influenced by their head groups, acyl chains, concentration, sonication and pH. In dry model systems, added lipid components significantly changed not only the oxidation rate, but also the oxidation pathway. However, in the aqueous model systems, cholesterol oxidation patterns and the resulting oxide profiles were common in most of the conditions tested. Cholesterol in turn, also influenced the oxidation of mixed lipid. The milk fat globule membrane exhibited high protective effect on cholesterol oxidation in aqueous environment. It contains a non-lipid fraction that protects, and a lipid fraction that accelerates cholesterol oxidation. In the absence of water, the net balance between these two opposing factors is destructive. The presence of water tips this balance in favor of protection. The results in this study indicate that certain physicochemical factors exist in biological membranes so as to protect the membrane against destruction.
Subject Area
Organic chemistry
Recommended Citation
Kim, Sunki, "Cholesterol oxidation in the milk fat globule membrane" (1990). Doctoral Dissertations Available from Proquest. AAI9035400.
https://scholarworks.umass.edu/dissertations/AAI9035400