Comparative effects of emu and olive oil on aortic early atherosclerosis and associated risk factors in hypercholesterolemic hamsters
Introduction
A recent review article summarizes several human studies showing that saturated fats (SFA) containing fatty acids of chain lengths 12:0–16:0 increase serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) and that monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) decrease LDL-C [1]. Although the elevations in plasma TC and LDL-C as a result of increased saturated fat and cholesterol consumption are important risk factors in the development of atherosclerosis, oxidative modification of LDL or increase lipid peroxidation may also play a key role [2], [3], [4], [5]. It has been hypothesized that atherosclerosis progresses when macrophages in the subendothelial space of an artery take up oxidized LDL through a nonregulated scavenger receptor and are converted to foam cells that contain excessive lipid, especially cholesterol ester. The continuing aggregation of foam cells and cholesterol esters in the subendothelial space leads to the formation of fatty streaks, which are the earliest identifiable lesions of atherosclerosis and can be referred to as early aortic atherosclerosis.
Non–human primate studies from our laboratory, as well as others, have shown that feeding a predominantly linoleic acid–containing fat such as corn oil or safflower oil can result in dramatic decreases in plasma levels of LDL-C that are associated with reductions in atherosclerosis [6], [7], [8], [9], [10]. However, in human studies, the magnitude of the plasma LDL-C reduction with linoleic acid-rich diets is approximately 20% and is often less. Thus, there is an enrichment of linoleic acid in the LDL molecule remaining in the plasma, which produces LDL particles that are more susceptible to oxidation [11], [12], [13] and are presumably more atherogenic [13]. Thus, a relative enrichment of MUFA in the diet, rather than PUFA, might confer additional protection by generating LDL particles relatively resistant to oxidative modification while optimizing both plasma LDL-C and HDL-C concentrations.
The principal aims of the present study were to 1) determine whether in hamsters fed emu oil, which is predominantly monounsaturated, although less so than olive oil, contains hypocholesterolemic, antioxidant and antiatherosclerotic properties relative to coconut oil; and 2) compare the efficacy of emu oil versus olive oil, relative to coconut oil in these parameters.
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Animals and experimental protocol
A total of 32 male, 8-week-old, F1B Golden Syrian hamsters (Mesocricetus auratus) (BioBreeders, Inc., Watertown, MA) were housed individually in suspended, stainless steel cages in a temperature controlled room (25°C) with a 12-h light:dark cycle. Hamsters were given food and water ad libitum. Animals were fed Purina chow 5001 (Ralston Purina, St. Louis, MO) for 1 week before the start of the study to get acclimated to the facility. Hamsters were then fed a chow-based nonpurified
Results
All hamsters in each group survived the entire length of the study. No significant differences were observed between dietary treatments for body weight before the treatment period or at the end of the study. Also, there were no significant differences for food consumption between the treatment diets (data not shown).
Plasma lipid and lipoprotein cholesterol concentrations between weeks 4 and 8 were not significantly different within dietary treatments and therefore the values were averaged (
Discussion
The aim of the present study was to determine whether emu oil, because of its moderate levels of oleate, is as hypocholesterolemic and antiatherogenic as olive oil, and whether these potential properties are associated with changes in plasma fatty acid composition, tocopherol concentrations, lipid hydroperoxidation, and/or hepatic cholesterol concentrations. Both of the emu oil diets and the olive oil diet significantly reduced plasma TC and LDL-C compared to the control diet. This is the first
Acknowledgments
Thomas A. Wilson, Subbiah Yoganathan, and Timothy Kotyla supervised the study protocol, performed work and analyses, and performed the major writing contributions for the manuscript. Robert J. Nicolosi supervised the entire project and helped with writing of the manuscript. Garry Handelman, Frank Orthoefer, and Paul Binford helped with the writing of the manuscript and additional information about emu oil and the processing of the emu oil. The authors also thank Benjamin Woolfrey, Catherine
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