Semicarbazide-sensitive amine oxidase catalyzes endothelial cell-mediated low density lipoprotein oxidation

doi:10.1016/S0008-6363(01)00208-5

Cardiovascular Research 2001 50(3):583-588; doi:10.1016/S0008-6363(01)00208-5
© 2001 by European Society of Cardiology

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Semicarbazide-sensitive amine oxidase catalyzes endothelial cell-mediated low density lipoprotein oxidation

Markus Exner^a, Marcela Hermann^b, Roland Hofbauer^a, Stylianos Kapiotis^a^,c, Peter Quehenberger^a, Wolfgang Speiser^a, Irmtraud Held^d and Bernhard M.K Gmeiner^d^,*

^aClinical Institute of Medical and Chemical Laboratory Diagnostics, University of Vienna, Vienna, Austria
^bInstitute of Molecular Genetics, University of Vienna, Vienna, Austria
^cDepartment of Laboratory Medicine, Hospital Neunkirchen, University of Vienna, Vienna, Austria
^dInstitute of Medical Chemistry, University of Vienna, Vienna, Austria

^* Corresponding author. Fax: +43-1-4277-60881 bernhard.gmeiner{at}univie.ac.at

Objective: Deamination products of semicarbazide-sensitive amineoxidases (SSAO), i.e. aldehydes, superoxide and ammonia havebeen shown to initiate vascular damage. SSAOs are copper-enzymes,present in endothelial (EC), smooth muscle cells (SMC) and inblood. Transition metals ions (Cu, Fe) mediate the oxidative(atherogenic) modification of LDL by SMC and EC. The physiologicalsource of the active metal ions is still under debate. We hypothesizethat SSAOs may catalyze LDL oxidation by endothelial cells viaenzyme-complexed Cu⁺⁺. Methods: EC isolated from human umbilicalveins and cultured in 35 mm wells in RPMI-1640 medium were usedas LDL oxidation system. Results: Diamine oxidase (DAO), a SSAOwhich activity is elevated in tissues and sera of diabetic patients,catalyzes the oxidation of LDL by EC. In the presence of purifiedDAO (0.07 to 70 U/l) LDL oxidation was increased up to 10-foldas measured by thiobarbituric acid reactive substance (TBARS)formation as well as apoprotein modification of LDL. Chemicalblockage of the SSAO substrate binding site did not inhibitthe catalytic effect of DAO on LDL oxidation. Denaturation ofthe enzyme did not destroy the ability of the preparation tofacilitate LDL oxidation by EC. The potential of the enzymeto catalyze LDL oxidation was not suppressed in the presenceof serum. However, selective removing of enzyme–coppercompletely abolished the ability of the enzyme to trigger cell-mediatedLDL oxidation. Conclusion: DAO, beside generating angiopathicdeamination products, has the potential to act as a pathophysiologicalcatalyst of LDL atherogenic modification by vascular cells.

KEYWORDS Atherosclerosis; Lipoproteins; Endothelial function

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