LDL OXIDATION BY ACTIVATED MONOCYTES - CHARACTERIZATION OF THE OXIDIZED LDL AND REQUIREMENT FOR TRANSITION-METAL IONS

Monocytes can be activated by incubation with opsonized zymosan (Zop), and under these conditions can oxidize low density lipoprotein (LDL), We have characterized the biochemical changes in the lipoprotein afte r this oxidation, We found that monocyte-oxidized LDL has increased mo bility on agarose gels, increased absorbance at 234 mm, increased cont ent of lysophosphatidylcholine, and fluorescence at 430 nm when excite d at 350 mm, All these features were somewhat less pronounced in monoc yte-oxidized LDL than in LDL oxidized by 5 mu M CuSO4. Under appropria te conditions, Zop-stimulated monocytes oxidized LDL to a form recogni zed by macrophage scavenger receptors, Monocytes stimulated by Zop pro duced superoxide and also oxidized LDL, whereas monocytes stimulated b y phorbol ester produced slightly more superoxide but did not oxidize LDL, We found that the chelators EDTA and diethylenetriaminepentaaceti c acid inhibited LDL oxidation by Zop-stimulated monocytes, implying a requirement for transition metal ions, We found that Zop contained ap proximately 5 mmol iron per mg, probably as Fe3+, Zop stripped of its iron supported superoxide production by monocytes, but did not support LDL oxidation, Furthermore, Fe2+ appeared in the medium when monocyte s were incubated with Zop, but not with iron-stripped Zop.jlr Taken to gether, these results imply that monocytes stimulated by Zop are able to oxidize LDL only because of contaminating iron in the commercial zy mosan preparations.