Modification of type IIIVLDL, their remnants, and VLDL from ApoE-knockout mice by p-hydroxyphenylacetaldehyde, a product of myeloperoxidase activity,causes marked cholesteryl ester accumulation in macrophages

Very low density lipoproteins (VLDLs) from apolipoprotein (apo) E2/E2 subje cts with type III hyperlipoproteinemia, VLDL remnants, and VLDL from apoE-k nockout (EKO);mice are taken up poorly by macrophages. The present study ex amined whether VLDL modification by the reactive aldehyde p-hydroxyphenylac etaldehyde (pHA) enhances cholesteryl ester (CE) accumulation by J774A.1 ma crophages. pHA is the major product derived from the oxidation of L-tyrosin e by myeloperoxidase and is a component of human atherosclerotic lesions. I ncubation of 57744.1 cells with native type III VLDL, their remnants, and E KO-VLDL increased cellular CE by only 3-, 5-, and 5-fold, respectively, com pared with controls. In striking contrast, cells exposed to VLDL modified b y purified pHA (pHA-VLDL) exhibited marked increases in cellular CE of 38-, 47-, and 35-fold, respectively (P less than or equal to 0.0001). Addition of the lipoprotein lipase inhibitor tetrahydrolipstatin decreased cellular CE accumulation induced by the 3 pHA-modified VLDL preparations by 73%, 59% , and 73%, respectively. Addition of the acyl coenzyme A:cholesterol acyltr ansferase. inhibitor DuP 128 to cells incubated with the pHA-modified lipop roteins decreased cellular CE by 100%, 82%, and 95%, respectively, but had no effect on cellular triglycerides. To examine whether the type A scavenge r receptors (SR-As) mediated the uptake of pHA-VLDL, incubations were perfo rmed in the presence of polyinosine (poly I), a polynucleotide known to blo ck binding to SR-As (types I and II), or in cells preincubated with interfe ron-gamma (IFN-gamma), a cytokine known to decrease expression of SR-A type I. Coincubation of pHA-VLDL with poly I reduced cellular CE by only 38%; 4 4%, and 49%, respectively, whereas coincubation with IFN-gamma reduced CE b y only 18%, 27%, and 65%, respectively. In marked contrast to pHA-VLDL, bot h poly I and IFN-gamma inhibited, by >95%, CE accumulation induced by coppe r-oxidized VLDL. These results demonstrate a novel mechanism for the conver sion of type III VLDLs, their remnants, and EKO-VLDL into atherogenic parti cles and suggest that macrophage uptake of pHA-VLDL (1) requires catalytica lly active lipoprotein lipase, (2) involves acyl coenzyme A:cholesterol acy ltransferase-mediated cholesterol esterification, and (3) involves pathways distinct from the SR-A.