Correlation of apolipoprotein B retention with the structure of atherosclerotic plaques from human aortas

The amounts of loosely and tightly bound apolipoprotein B (apoB) were documented in 35 raised aortic plaques from six subjects by first quantitating the buffer-extracted fraction of apoB in homogenates and then a remaining fraction of apoB extractable with Triton X-100. A number of statistically significant correlations were found when these apoB values were compared to the size of the lesion obtained by morphometric analyses of cross-sections of plaques. The percentage of total apoB extracted by buffer or by Triton correlated positively with the percentage of the total cross-sectional area that was fibrotic or necrotic, respectively. These findings were substantiated by a subsequent study in which the fibrotic and necrotic regions of 21 plaques from 10 cases were separated by microdissection and the apoB content of the buffer- and Triton-extracted fractions measured separately. Fibrotic regions contained predominantly loosely bound or buffer-extracted apoB whereas necrotic regions contained mainly tightly bound or Triton-extracted apoB. These results suggest that within the atherosclerotic lesion morphologically different regions have different affinities for apoB. Fibrotic regions contain apoB in a form presumed to represent low density lipoproteins and very low density lipoproteins loosely trapped in a matrix of glycosaminoglycans. Necrotic regions contain apoB either in a delipidated form, or as low density lipoproteins or very low density lipoproteins tightly adhered to plaque components.