The Influence of Incorporated Cholesterol Auto-Oxides Upon The Permeability and Fluidity of Multilamellar Vesicles (Oxidized Sterols)
Mckeone, Barry Joseph
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https://hdl.handle.net/2142/70076
Description
Title
The Influence of Incorporated Cholesterol Auto-Oxides Upon The Permeability and Fluidity of Multilamellar Vesicles (Oxidized Sterols)
Author(s)
Mckeone, Barry Joseph
Issue Date
1984
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)
Agriculture, Food Science and Technology
Abstract
Autooxidation products of cholesterol were incorporated into multilamellar vesicles to determine if the addition of a polar substituent group to the sterol molecule had an effect on the permeability and fluidity of these model membrane systems. An additional goal was to determine whether or not the polar substituent groups altered the orientation of the sterol molecule within the membrane bilayer. Using cholesterol incorporation into multilamellar vesicles of egg yolk lecithin: dicetylphosphate as a basis for comparison, the glucose permeability of the following sterol oxides was measured; 7-ketocholesterol, cholestantriol, cholesterol-5(alpha),6(alpha)-epoxide, cholesterol-5(alpha)-hydroperoxide and 25-hydroxycholesterol. The cholesterol B ring substituted sterols (the triol, epoxide, hydroperoxide and 7-ketone) exhibited increases in glucose permeability over cholesterol multilamellar vesicles at 33 and 49 mol%, while the side chain sterol oxide, 25-hydroxycholesterol, exhibited a large increase in permeability over cholesterol vesicles from 5 to 49 mol%. Membrane fluidity was determined by differential scanning calorimetry and steady state fluorescence depolarization. Differential scanning calorimetry on dipalmitoyl lecithin:sterol dispersion of the B ring sterol oxides, 7-ketocholesterol and cholestan-triol, indicated that they were similar to cholesterol dispersions in their ability to reduce the enthalpy of the L(beta) to L(alpha) liquid crystal transition with an increase in the molar percentage of the sterol. 25-Hydroxycholesterol was incapable of reducing the enthalpy of the transition beyond 12 mol%. Fluorescence depolarization studies on dipalmitoyl lecithin:sterol dispersions of 7-ketocholesterol and cholestan-triol showed reduced microvisocisities at 33 and 50 mol% over cholesterol. The side chain sterol oxide, 25-hydroxycholesterol, exhibited a microviscosity similar to that of cholesterol at 50 mol% and a higher flow activation energy value than 33 mol% 25-hydroxycholesterol. This may be due to a limited solubility of the sterol in lecithin bilayers, which was determined experimentally. It was concluded that the polar substituents on the B ring sterol oxides were probably located at the aqueous interface of the membrane bilayer. It was not possible to conclude whether or not the side sterol oxide was oriented with both hydroxyl groups at the aqueous interface or if one of the hydroxyl groups was inserted into the hydrophobic portion of the membrane bilayer.
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