title: Cytotoxicity of myeloperoxidase/nitrite-oxidized low-density lipoprotein toward endothelial cells is due to a high 7beta-hydroxycholesterol to 7-ketocholesterol ratio.
abstract: Oxygenated cholesterols (oxysterols) formed during oxidation of low-density lipoprotein (LDL) are associated with endothelial dysfunction and atherogenesis. We compared the profile of oxysterols in modified human LDL obtained on reaction with myeloperoxidase/H2O2 plus nitrite (MPO/H2O2/nitrite-oxLDL) with that on Cu2+ -catalyzed oxidation. The 7beta-hydroxycholesterol/7-ketocholesterol ratio was markedly higher in MPO/H2O2/nitrite-oxLDL than in Cu2+ -oxidized LDL (7.9 +/- 3.0 versus 0.94 +/- 0.10). Like MPO/H2O2/nitrite-oxLDL, 7beta-hydroxycholesterol was cytotoxic toward endothelial cells through eliciting oxidative stress. Cytotoxicity was accompanied by DNA fragmentation and was prevented by the NADPH oxidase inhibitor apocynin, suggesting stimulation of NADPH oxidase-mediated O2-* formation. 7-Ketocholesterol was only cytotoxic when added alone, whereas a 1:1-mixture with 7beta-hydroxycholesterol surprisingly was noncytotoxic. We conclude from our data that (i) 7beta-hydroxycholesterol is a pivotal cytotoxic component of oxidized LDL, (ii) 7-ketocholesterol protects against 7beta-hydroxycholesterol in oxysterol mixtures or oxLDL, (iii) the 7beta-hydroxycholesterol/7-ketocholesterol ratio is a crucial determinant for cytotoxicity of oxidized LDL species and oxysterol mixtures, and (iv) the low share of 7-ketocholesterol explains the higher cytotoxicity of MPO/H2O2/nitrite-oxLDL than other forms of oxidized LDL. The dietary polyphenol (-)-epicatechin inhibited not only formation but also cytotoxic actions of both oxLDL and oxysterols.
authors.affiliation: Institut für Biochemie und Molekularbiologie I, Heinrich-Heine-Universität, Postfach 101007, D-40001 Düsseldorf, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Steffen
authors.forename: Ingrid
authors.initials: I
authors.lastname: Wiswedel
authors.forename: Daniela
authors.initials: D
authors.lastname: Peter
authors.forename: Tankred
authors.initials: T
authors.lastname: Schewe
authors.forename: Helmut
authors.initials: H
authors.lastname: Sies
mesh_terms: D002392:Catechin / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects*; D004730:Endothelium, Vascular / Q000166:cytology; D006801:Humans; D006888:Hydroxycholesterols / Q000378:metabolism*; D007653:Ketocholesterols / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity*; D009573:Nitrites / Q000737:chemistry*; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism*; D014471:Umbilical Veins / Q000166:cytology
chemical_list: D006888:Hydroxycholesterols; D007653:Ketocholesterols; D008077:Lipoproteins, LDL; D009573:Nitrites; C011724:cholest-5-en-3 beta,7 alpha-diol; D002392:Catechin; D009195:Peroxidase; C003001:7-ketocholesterol