CHARACTERISTICS OF 10 CHARGE-DIFFERING SUBFRACTIONS ISOLATED FROM HUMAN NATIVE LOW-DENSITY LIPOPROTEINS (LDL) - NO EVIDENCE OF PEROXIDATIVEMODIFICATIONS

Native plasma low-density lipoproteins (LDL) were fractionated into te n subfractions with increasingly negative charges (LDL-1, the least el ectronegative, to LDL-10) using an anion-exchange column coupled to a fast protein-liquid chromatography system. Prior to fractionation, con taminating Lp(a) and apo A-I-containing lipoproteins were removed from LDL preparations by immunoaffinity chromatography. No significant dif ference in thiobarbituric acid-reactive substances, vitamin E or free aminogroup content was found among subfractions, and no peptide with a higher molecular weight than apo B was observed on SDS-PAGE. We obser ved a gradual increase in cholesterol esters and a concomitant decreas e in triglycerides from LDL-1 to LDL-7, and a reverse tendency from LD L-8 to LDL-10 (P < 0.01). Free cholesterol increased linearly from LDL -1 to LDL-10 (P < 0.01). LDL-1 to -3 had a homogeneous density profile , while other more electronegative subfractions showed a bimodal distr ibution with a second, minor peak of slightly higher density. A gradua l increase in apolipoprotein C-III content related to LDL electronegat ivity was observed (P < 0.001). Apolipoprotein E content was also incr eased in the last two subfractions (P < 0.01). LDL subfractions displa yed a similar binding fate on human fibroblasts, with the exception of the most electronegative subfractions [LDL-(9 + 10)], which bound mon actively to apo B/E receptors (P < 0.05). This study shows that charg e heterogeneity of native LDL is not related to lipid peroxidation or derivatization of free aminogroups of apolipoprotein B. In contrast, t he enrichment of LDL in apolipoproteins other than apo B may explain, in part, the difference in their particle charge.