Partial characterization of lipoproteins containing apo[a] in human atherosclerotic lesions.
Previously we quantified the amounts of immunoreactive apo[a] found in human atherosclerotic lesions extracted sequentially with phosphate-buffered saline (PBS) and guanidine hydrochloride (GuHCl). In this study we have attempted to characterize lipoproteins containing apo[a] in such PBS and GuHCl fractions, obtained from autopsy samples, in order to eventually determine their structure-function relationships critical for evaluating the mechanisms that make them atherogenic. Apo[a] in the PBS extracts migrated slightly ahead of plasma Lp[a] on agarose electrophoresis. Although apo[a] in extracts showed the same isoforms as in plasma in SDS-PAGE, it was also highly fragmented. When a d < 1.10 g/ml ultracentrifugation fraction of the PBS extract was subjected to gel filtration, a major part of the immunoreactive apo[a] in this fraction co-isolated with plasma Lp[a]. When the Lp[a]-sized fraction was further separated by density gradient ultracentrifugation, a subpopulation was isolated containing apo[a] in the 1.06 < d < 1.08 g/ml density range that was free of lesion-derived low density lipoprotein (LDL) (A-LDL). This fraction contained immunoreactive apo[a] and apoB, had a total cholesterol to protein ratio of about 1, and demonstrated increases in fluorescence (360 ex/430 em) and conjugated dienes that were even greater than values obtained for the corresponding A-LDL sample. The void volume fraction following gel exclusion chromatography of the d < 1.10 g/ml fractions contained both apo[a] and apoB that comigrated on nondenaturing PAGE, suggesting that they were present on the same particle. Apo[a] in GuHCl extracts comigrated with plasma Lp[a] on agarose electrophoresis and contained apo[a] isoforms of similar molecular weights as those found in corresponding plasma samples. When the GuHCl extract was subjected directly to gel filtration in the presence of 6 M GuHCl, two included peaks of apo[a] immunoreactivity were present, one eluting slightly ahead of plasma Lp[a], the other slightly ahead of plasma LDL. Collectively, these data indicate that apo[a] is present in human atherosclerotic lesions in forms resembling intact but oxidized plasma Lp[a], as larger particles possibly representing Lp[a] complexed to itself or other plaque components, and as slightly smaller particles possibly representing degraded Lp[a].
Department of Cell Biology, Cleveland Clinic Foundation, OH 44195.
H F
HF
Hoff
J
J
O'Neil
A
A
Yashiro
D001011:Aorta / Q000737:chemistry*; D001054:Apolipoproteins A / Q000032:analysis* / Q000276:immunology; D001055:Apolipoproteins B / Q000032:analysis; D001161:Arteriosclerosis / Q000378:metabolism*; D001344:Autopsy; D019791:Guanidine; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D017270:Lipoprotein(a) / Q000032:analysis; D008074:Lipoproteins / Q000737:chemistry* / Q000187:drug effects; D010084:Oxidation-Reduction
D001054:Apolipoproteins A; D001055:Apolipoproteins B; D006146:Guanidines; D017270:Lipoprotein(a); D008074:Lipoproteins; D019791:Guanidine