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Impact of tobacco-smoke on apolipoprotein exchangeability

Institution: Children's Hospital Oakland Research Institute
Investigator(s): Giorgio Cavigiolio, Ph.D.
Award Cycle: 2009 (Cycle 18) Grant #: 18KT-0021H Award: $324,000
Subject Area: Cardiovascular Disease
Award Type: New Investigator Awards
Abstracts

Initial Award Abstract
The overall aim of this research project is to understand at the molecular level how tobacco smoke leads to atherosclerosis. Cardiovascular disease is the leading cause of death in the United States and is primarily caused by the blocking of normal blood flow within an artery, either by direct deposition of cholesterol and lipids or indirectly as the result of a blood clot formed after the rupture of an atherosclerotic plaque within a blood vessel. Both events result from the slow accumulation of cholesterol and lipids in the arterial wall. A major risk factor for developing cardiovascular disease is tobacco smoking. Tobacco smoke directly impairs the normal function of lipoproteins, which are particles composed of lipids and proteins. Lipoproteins transport cholesterol in our blood and remove excess cholesterol from cells. Tobacco smoke reacts chemically with lipoproteins in a process called oxidation that increases the amount of cholesterol and lipids being deposited in the arteries and stimulates the formation of atherosclerotic plaques on the arterial walls. Tobacco smoke exposure also indirectly increases oxidative damage to lipoproteins by causing cells within atherosclerotic plaques to undergo an immune response that produces enzymes such as myeloperoxidase (MPO), which generate highly oxidative compounds. Together, direct and indirect oxidation damage the cholesterol transport system and increase the risk of a build up of the waxy plaque inside blood vessels, which is called atherosclerosis.

High density lipoproteins (HDL) - known as the ‘good’ cholesterol - are the major transporters that eliminate excess cholesterol and thereby reduce atherosclerosis. However, oxidation of HDL by tobacco smoke impairs their function and contributes to a buildup of cholesterol in blood vessels. HDL are primarily composed of a protein called apolipoprotein A-I (apoA-I), phospholipids, and cholesterol. ApoA-I in its ‘lipid-free’ state is the main recipient of the cholesterol that flows out or is ‘effluxed’ from cells. By acquiring cholesterol and lipids from cells, lipid-free apoA-I generates the HDL particle. The presence of lipid-free apoA-I is therefore necessary for the cholesterol efflux system to function efficiently.

Using a fluorescence-based assay that we developed, we recently showed that oxidation of apoA-I by enzymes such as MPO indeed reduces the ability of apoA-I to bind and release cholesterol and phospholipids, which is known as apoA-I exchangeability. Impairment of apoA-I exchangeability may therefore be a major cause of the reduced cholesterol efflux and atherosclerosis associated with such high oxidative conditions as tobacco smoking. We hypothesize that tobacco-induced oxidation of apoA-I will impair its exchangeability, thereby reducing the amount of lipid-free apoA-I available for cholesterol efflux. Measuring apoA-I exchangeability in blood samples may therefore provide a novel clinical indicator for physicians to determine a person’s risk of atherosclerosis.

The current assay to measure apoA-I exchangeability, however, is not suitable for analyzing clinical samples because other biomolecules present in blood interfere with the measurement and make the interpretation of the results very difficult. The studies proposed in our research plan will develop an enhanced assay that can measure apoA-I exchangeability of HDL in clinical plasma samples. This novel assay will then be used to determine if oxidation by tobacco smoke impairs apoA-I exchangeability and if this, in turn, reduces cholesterol efflux efficiency. It is anticipated that this research will significantly contribute to our understanding of the molecular mechanisms that link tobacco smoke-induced ‘oxidative stress’ to cardiovascular disease, as well as to our knowledge of the causes of atherosclerosis in other oxidative pathological states, such as obesity or diabetes. A new analytical test for assessing atherosclerosis risk in human patients will also be created as a result of the proposed research.
Publications

Folded functional lipid-poor apoliproprotein jA-I obtained by heating of high-density lipoproteins: relevance to HDL biogenesis
Periodical: Biochemical Journal Index Medicus:
Authors: Shobini Jayaraman, Giorigio Cavigiolio, Olga Gursky ART
Yr: 2012 Vol: 286 Nbr: 41 Abs: Pg: 35610-35623

Cholesteryl Ester Transfer Protein interactions with lipoproteins: insights into mechanisms by electron microscopy and molecular dynamics simulation
Periodical: Nature Chemical Biology Index Medicus:
Authors: Lei Zhang, Feng Yan, Shengli Zhang, Giorgio Cavigiolio, Dongsheng Lei, Ronald M. Krauss, M ART
Yr: 2012 Vol: 8 Nbr: 4 Abs: Pg: 342-349

Multiple-reaction monitoring-mass spectrometric assays can accurately measure the relative protein abundance in complex mixtures
Periodical: Clinical Chemistry Index Medicus:
Authors: Andrew N. Hoofnagle, Jessica O. Becker, Michael N. Oda, Giorgio Cavigiolio, Philip Mayer, ABS
Yr: 2012 Vol: 58 Nbr: 4 Abs: Pg: 777-781

High yield expression and purification of recombinant human apolipoprotein A-II in E. coli
Periodical: Journal of Lipid Research Index Medicus:
Authors: Loren E. Smith, Jun Yang, Leah Goodman, Xinqi Huang, Rong Huang, James Dressman, Jamie Mor ART
Yr: 2012 Vol: 53 Nbr: 8 Abs: Pg: 1708-1715