Submitted on July 12, 2004
Revised on December 20, 2004
Accepted on January 10, 2005
Cholesterol esterase action on human high density lipoproteins and inhibition studies detected by MALDI-TOF MS
Olaf Zschörnig, Markus Pietsch, Rosemarie Süß, Jürgen Schiller, and Michael Gütschow
Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig 04107
Corresponding Author: zsco{at}medizin.uni-leipzig.de
The modification of human lipoproteins by lipolytic enzymes like cholesterol esterase (CEase) is nowadays assumed to play an important role in the pathogenesis of atherosclerosis. However, details of activation and inhibition of this enzyme remained to be explained. In this study matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) is used in order to investigate the organic extracts of human lipoproteins after treatment with CEase and to monitor the effects of the recently introduced inhibitor DOT-3. This approach has the advantage that all lipid classes can be independently detected, and, therefore, conclusions on the substrate spectrum of the applied enzyme are possible. Besides the expected decrease of cholesteryl esters in high-density lipoproteins (HDL) under the influence of the enzyme, a significantly enhanced content of lysophosphatidylcholine (LPC) was also detected indicating a broad substrate specificity of CEase. It was also demonstrated by MALDI-TOF MS that DOT-3 significantly inhibited the CEase-catalyzed cleavage of cholesteryl esters in HDL. Phospholipid vesicles prepared from phosphatidylcholine or phosphatidylcholine and cholesteryl linoleate, respectively, were treated with CEase, and the changes in lipid composition were investigated. From the analysis of the generated LPC species in HDL and the isolated lipid mixtures, it is evident that CEase affects the fatty acid residues in both, the sn-1 and sn-2 position of the phospholipids.
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