Factors Influencing the Formation and Distribution of Cholesterol Esters in Human Plasma
Yen, Frances Theresa
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/77462
Description
Title
Factors Influencing the Formation and Distribution of Cholesterol Esters in Human Plasma
Author(s)
Yen, Frances Theresa
Issue Date
1987
Department of Study
Food Science
Discipline
Food Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Health Sciences, Nutrition
Language
eng
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.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
