CYTOTOXIC ELECTRONEGATIVE LDL SUBFRACTION IS PRESENT IN HUMAN PLASMA

By using fast protein liquid chromatography, we isolated from human pl asma a minor electronegative LDL subfraction designated LDL(-). After immunoaffinity chromatography against apolipoprotein (apo)(a) and apo A-I, LDL(-) represented 6.7+/-0.9% (mean+/-SD; n=18) of to al LDL. Com pared with the major LDL subfraction, designated LDL(+), LDL(-) contai ned similar amounts of thiobarbituric acid-reactive substances, conjug ated dienes, and vitamin E and had a similar lipid/protein ratio and m ean density. Moreover, the apo B of LDL(-) was not aggregated and its LDL receptor-binding activity was slightly increased. These results we re consistent with the nonoxidized nature of LDL(-). LDL(-) showed inc reased contents of sialic acid (38.1+/-5.2 versus 28.9+/-3.3 nmol/mg p rotein; n=7; P<.01), apo C-III (1.43+/-0.21% versus 0.14+/-0.04%; n=7; P<.01), and apo E (1.64+/-0.26% versus 0.10+/-0.05%; n=7; P<.0005). Co mpared with LDL(+), LDL(-) displayed enhanced cytotoxic effects on cul tured human umbilical vein endothelial cells, as shown by lactate dehy drogenase assay (P<.003; n=6), neutral red uptake (P<.02; n=6), and mo rphological studies. We also studied the relationship of LDL(-) to age and plasma lipid levels in 133 subjects. The percentage of contributi on of LDL(-) to total plasma LDL correlated with age (P<.05), total ch olesterol (P<.05), and LDL cholesterol (P<.003). In conclusion, this s tudy shows that LDL(-), a circulating human plasma LDL, is an electron egative native LDL subfraction with cytotoxic effects on endothelial c ells. This subfraction, which correlates positively with common athero sclerotic risk factors, might induce atherogenesis by actively contrib uting to alteration of the vascular endothelium.