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Dissertation
Effects of dietary fatty acids on the production and properties of apoprotein B-containing lipoproteins of rat hepatoma MCA-RH7777 cells
Doctor of Philosophy (Ph.D.), Allegheny University of the Health Sciences
Oct 1996
DOI:
https://doi.org/10.17918/00009996
Abstract
Atherosclerosis is the major cause of death in Western societies. Positive correlations have been established between plasma levels of apoprotein B (apoB) and the development of atherosclerosis. Also, correlations between amount and types of fat in the diet and plasma cholesterol levels have been demonstrated. In this study, we have sought to use an in vitro system to conveniently test effects of individual dietary fatty acids on hepatic apoB production. We have chosen the rat hepatoma cell system, McA-RH7777 for this purpose due to its ability to both vigorously secrete lipoproteins in all density classes and, in limited previous studies, to respond to fatty acids in ways similar to more intact systems, such as animals and human subjects. Experiments were conducted in which McA-RH7777 cells were incubated for 6 hours with 0.8 mM dietary fatty acids complexed to BSA in a 5:1 molar ratio, or an equimolar amount of BSA alone. Of the fatty acids tested in this manner, lauric acid (12:0), stearic acid (18:0), oleic acid (OA, 18:1) and linoleic acid (18:2) did not affect secretion of newly-synthesized apoB, compared to incubation with BSA alone. Myristic acid (MA, 14:0) and palmitic acid (16:0) increased total newly-synthesized apoB secretion by 54% and 35%, respectively, compared to BSA alone. Docosahexaenoic acid (DHA, 22:6) decreased total newly-synthesized apoB secretion by 68%. Fatty acid effects on apoB secretion were not due to effects on triglyceride or protein synthesis. Pulse-chase analysis showed the promotion of apoB100 secretion by MA to be due to decreased intracellular degradation of apoB100, compared to the results for OA. With the use of protein trafficking inhibitors we found multiple sites of intracellular degradation of apoB100 which were utilized differentially after incubation with various fatty acids. That is, after incubation with MA, apoB100 was degraded in the endoplasmic reticulum when blocked in that compartment while incubation with OA led to apoB100 degradation in a post-ER compartment. Further experimentation showed that incubation with MA, while increasing apoB100 secretion and not affecting triglyceride synthesis, decreased secretion of newly- synthesized triglycerides. After incubation with MA, conditioned media were subjected to density gradient ultracentrifugation, and the majority of the apoB-containing lipoproteins were recovered at densities from 1.063 to 1.117 g/ml. Thus, incubation of McA-RH7777 cells with MA led to the secretion of a dense, triglyceride-poor apoB-containing lipoprotein. We conclude that fatty acids can regulate both the amounts and physical characteristics of apoB-lipoproteins produced by liver cells by affecting apoB degradation and its association with lipids.
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Details
- Title
- Effects of dietary fatty acids on the production and properties of apoprotein B-containing lipoproteins of rat hepatoma MCA-RH7777 cells
- Creators
- Emma Kummrow
- Contributors
- Edward A. Fisher (Advisor) - Drexel University, Allegheny University of the Health Sciences (1996-1998)
- Awarding Institution
- Allegheny University of the Health Sciences
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Allegheny University of the Health Sciences; Philadelphia, Pennsylvania
- Number of pages
- xv, 153 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Biochemistry [Historical]; Allegheny University of the Health Sciences (1996-1998); School of Medicine (1996-1998)
- Other Identifier
- 991021889011704721