RESUMEN
Human LDL undergoes a reversible thermal order-disorder phase transition associated with the cholesterol ester packing in the lipid core. Structural changes associated with this phase transition have been shown to affect the resistance of LDL to oxidation in vitro studies. Previous electron cryo-microscopy studies have provided image evidence that the cholesterol ester is packed in three flat layers in the core at temperatures below the phase transition. To study changes in lipid packing, overall structure and particle morphology in three dimensions (3D) subsequent to the phase transition, we cryo-preserved human LDL at a temperature above phase transition (53°C) and examined the sample by electron microscopy and image reconstruction. The LDL frozen from 53°C adopted a different morphology. The central density layer was disrupted and the outer two layers formed a "disrupted shell"-shaped density, located concentrically underneath the surface density of the LDL particle. Simulation of the small angle X-ray scattering curves and comparison with published data suggested that this disrupted shell organization represents an intermediate state in the transition from isotropic to layered packing of the lipid. Thus, the results revealed, with 3D images, the lipid packing in the dynamic process of the LDL lipid-core phase transition.
Asunto(s)
Ésteres del Colesterol/química , LDL-Colesterol/química , Lipoproteínas LDL/química , LDL-Colesterol/ultraestructura , Microscopía por Crioelectrón , Humanos , Lipoproteínas LDL/ultraestructura , Transición de Fase , Dispersión del Ángulo Pequeño , Difracción de Rayos XRESUMEN
A female patient (64 years of age; body mass index, 26) had a markedly and relatively low low-density lipoprotein-cholesterol (LDL-C) level (97 mg/dl) despite high serum total cholesterol (TC) (331 mg/dl) and triacylglyceride levels (307 mg/dl). Since the expected LDL-C was 222 mg/dl, there was a significant difference between the calculation and measurement based on direct enzyme assay. Only 30% of serum cholesterol was associated with LDL-C in this patient. To determine the basis for the markedly low LDL-C/TC ratio, we isolated and analyzed lipoproteins from the patient as well as age- and gender-matched controls. The patient had lowered serum CETP activity and elevated paraoxonase activity with GOT and GPT values in the normal range. The very low-density lipoprotein particles from the patient were larger than those of the controls and enriched with lipid and protein, while the LDL from the patient (LDL-P) had a lower particle number and protein content than the controls. The LDL-P was more resistant to cupric ion-mediated oxidation. HDL2 from the patient (HDL2-P) had highly enhanced paraoxonase activity and antioxidant ability. The patient had a 1.5-fold higher level of apolipoprotein (apo) A-I expression in HDL2. ApoA-I in HDL2 and HDL3 from the patient showed no fragmentation, while the control had fragmented bands (17 and 21 kDa) in the HDL. The HDL2-P also had a larger particle size and greater protein content with less lipid content. HDL3-associated cholesteryl ester transfer protein was reduced in the patient, although the particle size was similar to the controls. In conclusion, a patient who had a markedly lower LDL-C/TC ratio despite hyperlipidemia associated with higher paraoxonase activity, higher apoA-I level and lower CETP activity without fragmentation of apoA-I in the HDL fraction is presented. The enhanced antioxidant and anti-inflammatory activity of HDL might contribute to the low LDL-C/TC ratio in this patient.
Asunto(s)
Arildialquilfosfatasa/metabolismo , Proteínas de Transferencia de Ésteres de Colesterol/metabolismo , LDL-Colesterol/metabolismo , Hipercolesterolemia/complicaciones , Hipercolesterolemia/enzimología , Hipertrigliceridemia/complicaciones , Hipertrigliceridemia/enzimología , Antioxidantes/metabolismo , Apolipoproteína A-I/metabolismo , Western Blotting , HDL-Colesterol/sangre , HDL-Colesterol/metabolismo , HDL-Colesterol/ultraestructura , LDL-Colesterol/sangre , LDL-Colesterol/ultraestructura , Femenino , Humanos , Hipercolesterolemia/sangre , Hipertrigliceridemia/sangre , Hierro/metabolismo , Persona de Mediana Edad , Oxidación-ReducciónRESUMEN
The purpose of this investigation was to determine the independent and combined effects of aerobic exercise and omega-3 fatty acid (n-3fa) supplementation on lipid and lipoproteins. Sedentary, normoglycemic, nonsmoking men (n = 11) were assigned to perform rest and exercise before and during n-3fa supplementation. Exercise consisted of 3 consecutive days of treadmill walking at 65% maximum O(2) consumption for 60 min. Supplementation consisted of 42 days of 4.55 g/day of n-3fa. A two-way factorial ANOVA with repeated measures revealed significant reductions in total cholesterol (P = 0.001, -9.2%) and triglyceride (P = 0.007, -32.4%) concentrations postexercise. In addition, exercise increased LDL peak particle size (P = 0.001) from 26.2 to 26.4 nm, but not HDL size. The n-3fa supplementation resulted in a significant shift in the distribution of HDL-cholesterol (HDL-C) carried by HDL(2b+2a) (P = 0.001, 14.2%) and HDL(3a+3b) (P = 0.001, -22.8%), despite no significant changes in lipid and lipoprotein-cholesterol concentrations. The majority of the shift in HDL-C was noted in HDL(2b) (P = 0.001, 20.9%) and HDL(3a) (P < 0.001, -31.0%) particles. There were no combined effects of exercise and n-3fa supplementation on lipids and lipoproteins. Three consecutive days of aerobic exercise reduced triglyceride and total cholesterol concentrations with a concomitant increase in LDL peak particle size. In contrast, n-3fa supplementation shifted HDL-C from HDL(3) particles to HDL(2) particles, despite no significant changes in HDL(2)-C and HDL(3)-C concentrations. Exercise and n-3fa supplementation do not synergistically improve serum lipids and lipoproteins, but rather independently affect the metabolism of lipids and lipoproteins.
Asunto(s)
HDL-Colesterol/metabolismo , HDL-Colesterol/ultraestructura , LDL-Colesterol/metabolismo , LDL-Colesterol/ultraestructura , Ejercicio Físico/fisiología , Ácidos Grasos Omega-3/farmacología , Lipoproteínas HDL/metabolismo , Lipoproteínas HDL/ultraestructura , Lipoproteínas LDL/metabolismo , Lipoproteínas LDL/ultraestructura , Adulto , Umbral Anaerobio/fisiología , Dieta , Suplementos Dietéticos , Ingestión de Energía/fisiología , Hemoglobinas/metabolismo , Humanos , Lípidos/sangre , Masculino , Persona de Mediana Edad , Tamaño de la Partícula , Descanso/fisiología , Adulto JovenRESUMEN
One of the important risk factors for coronary heart disease is dyslipidemia. Several lipid abnormalities have been studied in patients with polycystic ovary syndrome (PCOS), but the relationship between PCOS and low-density lipoprotein (LDL) subclass pattern is not clear. A case-control study was designed to look into lipid differences, and LDL size was analyzed by a newly developed polyacrylamide tube gel electrophoresis method. Results indicated that only PCOS status and serum triglyceride levels were independently associated with LDL particle size. The apolipoprotein (Apo)A-I level was higher in PCOS patients with small dense LDL (sdLDL). PCOS seems to result in smaller LDL particle size and higher ApoA-I levels independent of triglyceride levels. After adjusting for triglyceride levels, other traits of insulin resistance syndrome (IRS) were not associated with LDL size phenotype, suggesting that the IRS-related sdLDL is linked most strongly to alterations in triglyceride levels.
Asunto(s)
LDL-Colesterol/ultraestructura , Dislipidemias/etiología , Tamaño de la Partícula , Síndrome del Ovario Poliquístico/complicaciones , Síndrome del Ovario Poliquístico/fisiopatología , Adolescente , Adulto , Apolipoproteína A-I/sangre , Aterosclerosis/etiología , Estudios de Casos y Controles , LDL-Colesterol/sangre , Electroforesis en Gel de Poliacrilamida , Femenino , Humanos , Curva ROC , Triglicéridos/sangreRESUMEN
Lipoprotein(a) is composed of low-density lipoprotein linked both covalently and noncovalently to apolipoprotein(a). The structure of lipoprotein(a) and the interactions between low-density lipoprotein and apolipoprotein(a) were investigated by electron microscopy and correlated with analytical ultracentrifugation. Electron microscopy of rotary-shadowed and unidirectionally shadowed lipoprotein(a) prepared without glycerol revealed that it is a nearly spherical particle with no large projections. After extraction of both lipoprotein(a) and low-density lipoprotein with glycerol prior to rotary shadowing, the protein components were observed to consist of a ring of density made up of nodules of different sizes, with apolipoprotein(a) and apolipoprotein B-100 closely associated with each other. However, when lipoprotein(a) was treated with a lysine analogue, 6-aminohexanoic acid, much of the apolipoprotein(a) separated from the apolipoprotein B-100. In 6-aminohexanoic acid-treated preparations without glycerol extraction, lipoprotein(a) particles had an irregular mass of density around the core. In contrast, lipoprotein(a) particles treated with 6-aminohexanoic acid in the presence of glycerol had a long tail, in which individual kringles could be distinguished, extending from the ring of apolipoprotein B-100. The length of the tail was dependent on the particular isoform of apolipoprotein(a). Dissociation of the noncovalent interactions between apolipoprotein(a) and low-density lipoprotein as a result of shear forces or changes in the microenvironment may contribute to selective retention of lipoprotein(a) in the vasculature.
Asunto(s)
Lipoproteína(a)/química , LDL-Colesterol/química , LDL-Colesterol/ultraestructura , Ligandos , Lipoproteína(a)/ultraestructura , Lisina/química , Unión Proteica , Conformación Proteica , Isoformas de Proteínas/química , Isoformas de Proteínas/ultraestructura , UltracentrifugaciónRESUMEN
To compare the atherogenic potential of low density lipoprotein (LDL), intermediate density lipoprotein (IDL), and very low density lipoprotein (VLDL) under conditions where plasma levels of these lipoproteins are elevated, the influx of cholesterol in these lipoproteins into the aortic intima was measured in vivo in genetically hyperlipidemic rabbits from the St. Thomas's Hospital strain, an animal model that shares many of the features of the human disorder familial combined hyperlipidemia. Univariate linear regression showed that the arterial influx of LDL cholesterol (n = 25), IDL cholesterol (n = 14), and VLDL cholesterol (n = 10) was positively and linearly associated with plasma concentrations of LDL cholesterol in the range 0.2-6.4 mmol/l, of IDL cholesterol in the range 0.1-7.0 mmol/l, and of VLDL cholesterol in the range 0.7-8.5 mmol/l, respectively, and also with the extent of lesions in the arterial intima in the range 0-100% of the surface area. Multiple linear regression suggested that the arterial influx of LDL, IDL, and VLDL cholesterol was linearly dependent on plasma concentration, independent of lesion size. Furthermore, it appeared that the arterial influx of the three lipoproteins was linearly dependent on the extent of the lesions, independent of lipoprotein concentration. When influx was normalized for plasma concentration (intimal clearance) and for lesion size (compared within the same aorta), the intimal clearance of the larger IDL and VLDL particles was 15-35% less than that of the smaller LDL particles. These findings suggest that the quantitatively most important mechanism for transfer of plasma lipoproteins into the arterial intima involves nonspecific molecular sieving and that at elevated plasma levels, IDL and VLDL share with LDL the potential for causing atherosclerosis.
Asunto(s)
Aorta/metabolismo , LDL-Colesterol/metabolismo , VLDL-Colesterol/metabolismo , Colesterol/metabolismo , Hiperlipidemia Familiar Combinada/metabolismo , Lipoproteínas/metabolismo , Animales , Colesterol/sangre , LDL-Colesterol/sangre , LDL-Colesterol/ultraestructura , VLDL-Colesterol/sangre , VLDL-Colesterol/ultraestructura , Femenino , Lipoproteínas/sangre , Lipoproteínas/ultraestructura , Masculino , Microscopía Electrónica , Conejos , Análisis de RegresiónRESUMEN
Atherosclerotic lipid deposits found in the core region of fibrous plaques are almost entirely extracellular, but it is not known whether they are derived from necrosis of cells containing accumulated lipid or from direct extracellular lipid accumulation. New evidence pertaining to this question has been obtained through the use of recently developed techniques for preserving and staining lipids in electron microscopy, and through a detailed morphologic and chemical examination of human aortic fibrolipid lesions, which are progenitor lesions for fibrous plaques. The evidence favours a substantial role, perhaps a dominant role, for extracellular lipid accumulation in the formation of the fibrous plaque core region.