title: Thermal stability of human plasma electronegative low-density lipoprotein: A paradoxical behavior of low-density lipoprotein aggregation.
abstract: Low-density lipoprotein (LDL) aggregation is central in triggering atherogenesis. A minor fraction of electronegative plasma LDL, termed LDL(-), plays a special role in atherogenesis. To better understand this role, we analyzed the kinetics of aggregation, fusion and disintegration of human LDL and its fractions, LDL(+) and LDL(-). Thermal denaturation of LDL was monitored by spectroscopy and electron microscopy. Initially, LDL(-) aggregated and fused faster than LDL(+), but later the order reversed. Most LDL(+) disintegrated and precipitated upon prolonged heating. In contrast, LDL(-) partially retained lipoprotein morphology and formed soluble aggregates. Biochemical analysis of all fractions showed no significant degradation of major lipids, mild phospholipid oxidation, and an increase in non-esterified fatty acid (NEFA) upon thermal denaturation. The main baseline difference between LDL subfractions was higher content of NEFA in LDL(-). Since NEFA promote lipoprotein fusion, increased NEFA content can explain rapid initial aggregation and fusion of LDL(-) but not its resistance to extensive disintegration. Partial hydrolysis of apoB upon heating was similar in LDL subfractions, suggesting that minor proteins importantly modulate LDL disintegration. Unlike LDL(+), LDL(-) contains small amounts of apoA-I and apoJ. Addition of exogenous apoA-I to LDL(+) hampered lipoprotein aggregation, fusion and precipitation, while depletion of endogenous apoJ had an opposite effect. Therefore, the initial rapid aggregation of LDL(-) is apparently counterbalanced by the stabilizing effects of minor proteins such as apoA-I and apoJ. These results help identify key determinants for LDL aggregation, fusion and coalescence into lipid droplets in vivo.
authors.affiliation: Cardiovascular Biochemistry Group, Research Institute of the Hospital de Sant Pau (IIB Sant Pau), Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Rull
authors.affiliation: Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
authors.forename: Shobini
authors.initials: S
authors.lastname: Jayaraman
authors.affiliation: Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Gantz
authors.affiliation: Cardiovascular Biochemistry Group, Research Institute of the Hospital de Sant Pau (IIB Sant Pau), Barcelona, Spain; Biochemistry and Molecular Biology Department, Universitat Autònoma de Barcelona, Cerdanyola, Spain.
authors.forename: Andrea
authors.initials: A
authors.lastname: Rivas-Urbina
authors.affiliation: Cardiovascular Biochemistry Group, Research Institute of the Hospital de Sant Pau (IIB Sant Pau), Barcelona, Spain.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Pérez-Cuellar
authors.affiliation: Cardiovascular Biochemistry Group, Research Institute of the Hospital de Sant Pau (IIB Sant Pau), Barcelona, Spain; Biochemistry and Molecular Biology Department, Universitat Autònoma de Barcelona, Cerdanyola, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Ordóñez-Llanos
authors.affiliation: Cardiovascular Biochemistry Group, Research Institute of the Hospital de Sant Pau (IIB Sant Pau), Barcelona, Spain. Electronic address: jsanchezq@santpau.cat.
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Sánchez-Quesada
authors.affiliation: Department of Physiology & Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA. Electronic address: gursky@bu.edu.
authors.forename: Olga
authors.initials: O
authors.lastname: Gursky
mesh_terms: D016632:Apolipoprotein A-I / Q000378:metabolism*; D050197:Atherosclerosis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051152:Clusterin / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D066292:Lipid Droplets / Q000378:metabolism / Q000473:pathology; D008077:Lipoproteins, LDL / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D066263:Protein Aggregation, Pathological / Q000235:genetics; D055550:Protein Stability; D013696:Temperature
chemical_list: D016632:Apolipoprotein A-I; C495242:CLU protein, human; D051152:Clusterin; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein
keywords: Apolipoprotein A-I; Apolipoprotein J; Atherogenesis; Electronegative LDL; Lipoprotein aggregation, fusion and droplet formation; Thermal denaturation