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Title:Factors Influencing the Formation and Distribution of Cholesterol Esters in Human Plasma
Author(s):Yen, Frances Theresa
Department / Program:Food Science
Discipline:Food Science
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Health Sciences, Nutrition
Abstract:Experiments were conducted to determine the relative importance of factors influencing the lecithin-cholesterol acyltransferase (LCAT) and lipid transfer protein (LTP) reactions in plasma. These two plasma proteins play important roles in determining the formation and distribution of cholesterol esters in plasma.
The LCAT activity was analyzed using plasma substrates, since it reflects not only enzyme levels, but also substrate availability. To measure this, a rapid and simple method for radioactively labelling free cholesterol in plasma using ($\sp3$H) cholesterol-lysophosphatidylcholine micelles was developed. After equilibration, the relative distribution of the ($\sp3$H) cholesterol among plasma lipoproteins was found to reflect that of unlabelled free cholesterol. To use this method for measurement of LCAT activity, the equilibration step is necessary to avoid erroneous values of the enzyme activity.
To determine the factors that influence the plasma LCAT reaction, plasma substrate activity was modified by the addition of purified LCAT, LTP, and native or synthetic lipid particles. The addition of purified LTP, even in the presence of excess LCAT, did not alter the initial rate of cholesterol esterification. In contrast, the supplementation of plasma with purified LCAT resulted in a linear increase of the initial rate of cholesterol esterification up to a concentration of LCAT 3 times that in plasma. This linear response to exogenous LCAT was further extended in plasma obtained during the absorptive state. Purified human plasma lipoproteins and egg phosphatidylcholine vesicles were equilibrated with labelled plasma before measurement of the enzyme activity. The addition of egg phosphatidylcholine vesicles gave the most pronounced effect in enhancing the initial rate of LCAT reaction in both the presence and absence of exogenous LCAT. The supplementation of low density lipoprotein (LDL) to d $>$ 1.063 g/ml fraction substantially increased the initial rate of cholesterol esterification, as compared to very low density lipoprotein (VLDL), which had no appreciable effect.
The newly formed ($\sp3$H) cholesterol esters by the LCAT reaction was observed to be transferred into the lower density lipoprotein fractions at a slower rate than ($\sp3$H) cholesterol oleate, which served as a marker for preexisting cholesterol esters in HDL.
Issue Date:1987
Description:169 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.
Other Identifier(s):(UMI)AAI8803243
Date Available in IDEALS:2015-05-13
Date Deposited:1987

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