Thesis Abstract and Dissertation Abstracts
The Physical Properties of Lipoproteins
Abstract Category: Science
Course / Degree: Engineering and Physical Sciences in Medicine
Institution / University: Imperial College, London, United Kingdom
Published in: 1994
In recent years, much of the impetus for research into Lipoproteins has come from their likely association with Atherosclerotic Vascular Disease. Cholesterol is associated with Lipoprotein complexes and it is well known that a high Serum Cholesterol level is a major risk factor for Coronary Heart Disease, the prevailing cause of death in North America and Europe. The major cholesterol-carrying Lipoprotein in the Human serum is Low Density Lipoprotein and has been recognised as the major atherogenic lipoprotein. LDL cholesterol has been targeted for cholesterol intervention in North America. Before the way in which lipoproteins interact with blood vessel components such as Elastin, Collagen and Proteoglycans, their Physical Properties must be more widely investigated. In particular, the way in which particle size, electrophoretic mobility and surface charge change with pH and ionic strength of the supporting medium require further study.
It was the aim of this thesis to use standard techniques to investigate particle size and electrophoretic mobility under varying pH and ionic strength. The range of pH covered was from 2.70 to 10.15. Freshly prepared samples of HDL and LDL were dialysed both at ‘low’ (0.015M NaCl) and ‘high’ (0.15M NaCl) ionic strengths. These were then analysed using a Malvern 11c Zetasizer TM that was software controlled. A second batch of LPs were extracted and again dialysed at low and high ionic strengths of NaCl. This time, aliquots of gradually increasing concentrations of calcium chloride were added and the effect of this species of polycation was documented in detail. The Malvern Zetasizer combines the advantages of a cross beam Laser anemometer, for optimum electrophoresis, and a parallel beam along the axis of the measurement cell for optimum sizing, particularly of larger particles. This study represents one of the few occasions in which this sensitive instrument was used exclusively for the study of LP behaviour under variable conditions of pH and ionic strength.
The phenomenon of Oxidative Modification of LPs is well documented in this study. Modification of LP molecules apparently occurred after only three days of extraction, despite storage under nitrogen gas at 40 C and the addition of EDTA and sodium azide. This alone makes the study of LPs problematic and measurements less reliable. It is not yet clear whether the storage of isolated LPs brings about changes in composition like those to which they are subject during the storage of plasma. But the ultimate degradation product is almost certainly a similar aggregate. The loss of integrity of the LPs also leads to changes in their electrical properties, of which the increase in EM is the most easily observed. There is also an increase in the conductivity of the solution, the cause of which is beyond the scope of this study.
Among the findings of this study, were that increasing the concentration of CaCl2 reduced the mobility of HDL dialysed in 0.015M NaCl to almost zero. A similar phenomenon was observed with LDL at the same ionic strength. Also, adding small amounts (mM) of CaCl2 caused a reversal in the surface charge of HDL at 0.15M NaCl, but not in LDL at the same ionic strength. The Isoelectric Point of HDL dialysed at 0.015M NaCl was found to be at approximately pH 6.4 with a 10 mM aliquot of CaCl2 present in the solution. For LDL under the same conditions, the IP was at 6.5.
Thesis Keywords/Search Tags:
Lipoproteins, Atherosclerotic Disease, Low Density Lipoproteins, High Density Lipoproteins
This Thesis Abstract may be cited as follows:
Armoogum, K. A. "The Physical Properties of Lipoproteins". MSc Thesis (1994). Imperial College, London
Submission Details: Thesis Abstract submitted by Kris Armoogum from United Kingdom on 09-Sep-2004 19:34.
Abstract has been viewed 3344 times (since 7 Mar 2010).
Kris Armoogum Contact Details: Email: KArmoogum@netscape.net
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