Previous studies have suggested that aortic plaques contain a substantial quantity of LDL-protein or apoB not removed by conventional buffer extraction. We have examined the extraction of this remaining apoB from pellets of aortic intimal homogenates under a variety of conditions. Triton X-100 was the most effective of five detergents listed for their ability to extract residual apoB. This fraction was quantified by an electroimmunoassay (EIA) relative to an LDL standard treated with Triton. Standard slopes of peak height versus concentration were flatter for Triton-treated LDL than native LDL. On Ouchterlony plates lines of complete identity were obtained between native LDL, Triton-treated LDL, and buffer-extracted apoB, but only partial identity between Triton-extracted residual apoB and the above. However, when whole minces of aortic plaques were homogenized and extracted with Triton, the amount of apoB obtained was comparable to the sum of buffer-extractable and detergent-extractable apoB. When exogenous Triton-treated LDL was added to aortic pellets or to supernatant fractions of Triton-extracted pellets, recovery appeared to be complete within the error of the system. Extraction of residual apoB from plaque pellets with Triton appeared complete since no apoB could be detected by immunofluorescence techniques in the pellets remaining after three extractions with Triton or by EIA in the third extract. In twelve cases studied normal intima contained predominantly buffer-extracted apoB, while plaques contained nearly equal amounts of buffer- and Triton-extracted apoB. These results suggest that the plaques contain a tightly bound fraction of apoB in contrast to the normal intima.
ASJC Scopus subject areas
- Pathology and Forensic Medicine
- Molecular Biology
- Clinical Biochemistry