摘要:

Metabolic heterogeneity in low density lipoprotein (LDL) may be detected by examination of the daily urinary excretion rate of radioactivity after injection of trace-labeled lipoprotein. Two distinct pools are observed within LDL. The first (pool A) is cleared rapidly from the plasma, whereas the second (pool B) is catabolized more slowly. In the present study we examined LDL metabolism in seven hypercholesterolemic subjects (six women and one man) before and during fenofibrate therapy. Comparison with normocholesterolemic individuals showed that the pretreatment high LDL levels in the hypercholesterolemic subjects resulted from an accumulation of apoprotein-LDL (apo-LDL) mass in pool B (2,077 ±174 mg versus 787 ±70 mg in normal subjects,p< 0.002). Pool A apo-LDL was present at normal levels (-1,000 mg), although its fractional catabolic rate was reduced (0.39±0.06 versus 0.61 ±0.03 pool/day in normal subjects,p<0.01). Fenofibrate therapy (100 mg t.i.d. for 8 weeks) produced substantial reductions in plasma cholesterol (29%;p<0.001), triglycerides (36%;p<0.001), and LDL cholesterol (30%;p<0.001). The latter was associated with a 30% decrease in circulating apo-LDL mass (2,312 ±200 mg versus 3,279 ±264 mg before treatment,p< 0.005). This resulted from a combination of two effects. First, although overall LDL apoprotein B production did not change, there was a shift from pool B to pool A. Pool A input was 400±74 mg/day pretreatment versus 706±62 mg/day on fenofibrate; pool B input was 422 ±35 mg/day pretreatment versus 258±41 mg/day on the drug. At the same time, catabolism of pool A rose from 0.39±0.06 to 0.66±0.08 pool/day (p<0.05). We hypothesize that the shift from pool B to pool A resulted from a drug-induced decrease in the particle size of very low density lipoprotein made by the liver, which in turn favored the formation of more rapidly catabolized LDL. Overall, the rate of apo-LDL degradation by the receptor route (as detected using a combination of native and 1,2-cyclohexanedione-modified LDL tracers) rose 43% on the drug, whereas the amount cleared by the receptor-independent pathway did not change. Fenofibrate, therefore, appears not only to promote LDL catabolism via the receptor-mediated pathway but also, by lowering plasma triglyceride levels, inhibits the formation of slowly metabolized, potentially atherogenic LDL particles.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The influence of different plasma triglyceride concentrations on the heterogeneity of low density lipoprotein (LDL) and on the susceptibility of LDL to copper oxidation was investigated. By density gradient ultracentrifugation, LDL subfractions were isolated from the plasma of 10 normolipidemic control subjects and 12 hypertriglyceridemic patients both before and after clofibrate treatment. In the plasma of control subjects three LDL subfractions were present: LDL1 (d= 1.030-1.033 g/mL), LDL2 (d=1.033-1.040 g/mL), and LDL3 (d= 1.040-1.045 g/mL). In the plasma of nine moderately hypertriglyceridemic subjects up to five LDL subfractions could be detected: LDL1-LDL3, LDL4 (d= 1.045-1.049 g/mL), and LDL5 (4= 1.049-1.054 g/mL). This polydispersity of LDL was replaced by monodispersity with increasing plasma triglyceride concentrations in three subjects with chylomicronemia, in whom LDL was concentrated in the narrow LDL5 density range. Clofibrate treatment resulted in a lighter LDL subfraction pattern (LDL1-LDL4). In both the control and the moderately hypertriglyceridemic subjects, the small dense LDL subfractions appeared more prone to oxidative modification in vitro than the light LDL subfractions, as measured by the decreased lag time preceding the onset of lipid peroxidation. Furthermore, the dense LDL subfractions were more extensively modified over time, as shown by an increased oxidation rate and a greater number of dienes formed after 6 hours of oxidation. These results suggest an enhanced atherogenic potential of the small, dense LDL subfractions within each LDL subfraction profile. The hypertriglyceridemic LDL subfractions before therapy (LDL3- LDL5) were less resistant to in vitro oxidation than the light, control LDL subfractions (LDL1-LDL3). This lower resistance was probably related to the decrease in the vitamin E content from LDL1 to LDL5. After clofibrate treatment both the vitamin E content of the LDL subfractions and the lag time increased, indicating an enhanced resistance against oxidation.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Hepatic lipase (HL) is an important enzyme in the metabolism of triglyceride-rich lipoproteins and high density lipoproteins. The clinical syndrome of HL deficiency is rare and difficult to identify. We studied carriers of mutant HL to ascertain whether there are distinctive clinical and/or biochemical characteristics of the heterozygous state. In an Ontario kindred, compound heterozygosity for two HL mutations, S267F and T383M, underlies the clinical syndrome of complete HL deficiency. We report that simple heterozygotes for either HL mutant do not have a discrete lipoprotein abnormality, except for relative triglyceride enrichment of lipoprotein fractions withd> 1.006 g/mL. Postheparin HL activity is depressed to a greater degree in carriers of S267F compared with carriers of T383M. Retinyl palmitate loading studies in a compound heterozygote revealed impaired clearance of chylomicron remnants. The dyslipoproteinemia in a compound heterozygote was ameliorated by lovastatin. There was no difference in the quantity and distribution of HL mRNA in the liver of a compound heterozygote when compared with that of a normal subject. Thus, HL deficiency associated with structural variation of the HL gene is characterized by premature atherosclerosis, triglyceride enrichment of lipoprotein fractions withd> 1.006 g/mL, the presence of circulating β-very low density lipoproteins, and abnormal catabolism of postprandial triglyceride-rich lipoproteins.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The regulation of expression of the intestinal low density lipoprotein (LDL) receptor by luminal (apical) sterol flux was investigated in the human intestinal cell line CaCo-2. Cells were cultured on semipermeable micropore filters, which separated an upper and lower well. To the apical media were added solutions containing either taurocholate micelles alone or micelles containing sterols. Because of an efflux of cholesterol, which occurred from cells incubated with micelles alone, LDL receptor mRNA levels increased threefold. With an influx of micellar sterols, receptor mRNA levels decreased in a dose-dependent manner. Synthesis and degradation of the LDL receptor were addressed by pulse-chase experiments. In cells incubated with micelles containing 25-hydroxycholesterol, the rate of receptor synthesis was significantly decreased, whereas the rate of receptor turnover remained unchanged. As assessed by immunoblots and steady-state labeling of proteins followed by immunoprecipitation of the LDL receptor, cells incubated with micellar 25-hydroxycholesterol contained substantially less receptor protein. These cells also bound and degraded less LDL. In contrast, in cells incubated with micelles alone, the rate of receptor synthesis was increased and cells contained more LDL receptor protein, although this was not reflected in an increase in LDL binding. The results suggest that LDL receptor expression in CaCo-2 cells is regulated by luminal sterol flux and that this regulation occurs at the level of transcription.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

G4120, L-cysteine, A$mercaptoacetyl)-D-tyrosyl-L-arginylglycyl-L-tt-aspartyl-cyclic(l-»5)-sulfide, 5-oxide, a synthetic cyclic Arg-Gly-Asp-containing pentapeptide, has a high affinity (dissociation constant of 4 nM) for the platelet glycoprotein (GP) Ilb/IIIa receptor. The effects of its intravenous or endobronchial administration on thrombolysis, reocclusion, and bleeding time prolongation induced with 0.45 mg/kg bolus injections of recombinant tissue-type plasminogen activator in combination with intravenous heparin (4,000-unit bolus and 1,000 units each hour) were studied in a canine model consisting of an erythrocyte-rich blood clot in the left anterior descending coronary artery. Coronary patency was monitored for 3 hours both by ultrasonic flow probe and by repeat coronary angiography. Four groups of six to 10 dogs were studied with intravenous infusions of 0, 0.1, 0.2, or 0.3 mg/kg G4120 over 60 minutes. G4120 at a dose of 0.3 mg/kg reduced the time to reflow from a mean control value of 45 to 8 minutes (p=0.036) and delayed reocclusion (p=0.001). Four groups of five or six dogs were studied with endobronchial instillation of G4120 in a randomized, blinded study design using 0,0.13,0.25, or 0.5 mg/kg G4120. Endobronchial G4120 at a dose of 0.5 mg/kg reduced the time to reflow from a mean control value of 52 to 7 minutes (p=0.039) and abolished cyclic reocclusion and reflow (p=0.008). G4120 induced a dose-related transient prolongation of the template bleeding time and inhibition of ADP-induced platelet aggregation. G4120, a synthetic low-molecular-weight GPIIb/IIIa inhibitor that may be produced by chemical synthesis, may be of clinical value as a conjunctive agent for thrombolysis in patients with ischemic coronary syndromes.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Previous work has shown heparin and heparan sulfates to be potent inhibitors of vascular smooth muscle cell (VSMC) growth. This laboratory has previously isolated a VSMC line insensitive to the antiproliferative action of heparin by subjecting VSMCs that grew out from rat aortic medial explants to continuous passage in media containing heparin at 200 μg/ml. In the present study, we have isolated two additional heparin-resistant (HR) cell lines and have used the HR cells to investigate cellular mechanisms responsible for the potent antiproliferative activity of heparin. In contrast to normal heparin-sensitive VSMCs, the HR cells were smaller, displayed elongated processes, and possessed altered growth characteristics; however, both HR and normal cells bound and internalized comparable amounts of heparin. Immunohistochemical detection of smooth muscle cell-specific actin in growth-arrested cells showed staining of nearly all normal VSMCs and of a much smaller percentage of HR cells; heparin treatment caused a marked increase in the percentage of HR cells expressing smooth muscle cell a-actin, indicating that the antiproliferative and differentiation-promoting actions of heparin are independent. Proteins from control VSMCs and HR cells were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and heparin affinity chromatography. Several proteins were expressed preferentially by either HR cells or normal VSMCs, with the most significant difference being the secretion of a high-affinity, heparin-binding protein (M, 38,000) by control VSMCs but not by HR cells. We conclude that the aortic VSMC population may give rise to HR cells under selective conditions and that their unique characteristics, such as alterations in their ability to produce heparin-binding proteins, will prove useful in deciphering the cellular mechanisms involved in heparin's regulation of VSMC growth and differentiation.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Human lipoprotein [a] contains at least two high-molecular-weight, disulfide-linked apolipoproteins, apo[a] and apo B-100. Apo[a] is a highly glycosylated, hydrophilic apoprotein that somewhat resembles plasminogen by containing an extended kringle domain and a carboxyl-terminal serine protease domain. The apo [a] kringle domain is composed of 11 distinct kringle types. Ten of these display high sequence homology to plasminogen kringle 4 (PGK4). The crystallographic coordinates for PGK4 were used to generate three-dimensional molecular models of the apo[a] kringle types, and the lysine-binding region of PGK4 was used to compare the different potential receptor-ligand and ligand-binding sites contained in each different PGK4-like kringle of apo [a]. A receptor-ligand site can be proposed for each kringle type. Potential serine protease cleavage sites, containing arginine-threonine and threonine-arginine, are located on the surface of the kringles. The ligand-binding site of one apo [a] kringle model is almost identical to that of PGK4 and may be a lysine-binding site of apo [a]. Four other apo [a] kringle models appear to have structurally similar lysine-binding sites, but with differences that may influence ligand-polypeptide specificity. Five apofa] kringle models have ligand-binding sites that probably do not bind lysine; one of these is the highly repeated kringle in the known apo [a] polymorph.

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:1049-8834    

出版商:OVID    

年代:1993

数据来源: OVID