Thyroxine binding to the apolipoproteins of high density lipoproteins HDL2 and HDL3.

Four preparations of high density lipoprotein HDL2, five of HDL3, and purified apolipoproteins apoA-I, apoA-IV, and apoE were photoaffinity labeled with [125I]T4 and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gels were also immunoblotted with antiserum against apoA-I, apoA-II, apoA-IV, apoE, or apo(a), and the immunostained membrane was then autoradiographed. In HDL2, the two major radioactive bands migrated near the origin of the resolving gel and at 28-31 kilodaltons (kDa). The first band, stained by anti-apo(a) and anti-apoB-100, accounted for 40-96% of the total radioactivity and was attributed to lipoprotein(a), which is isolated in the same density range as HDL2. The second band, stained by anti-apoA-I, accounted for 1-57% [41-95% after correction for contaminating lipoprotein(a)] of the [125I]T4 in the resolving gel. In HDL3, the major radioactive band was identified as apoA-I and contained 93-94% of the [125I]T4 in the resolving gel. Minor radioactive bands in both HDL2 and HDL3 were identified as apoA-II (17-18 kDa), apoA-II monomer (7-10 kDa), apoE (36-38 kDa), and apoAII-apoE heterodimer (46 kDa). In addition, HDL3 contained apoA-IV (43 kDa). Photoaffinity labeling of isolated apoA-IV and apoE showed that each protein interacted with [125I]T4. In both HDL2 and HDL3, photoaffinity labeling in the presence of unlabeled L-T4 (1-10 microM) showed inhibition, suggesting a Kd in the micromolar range. This inhibition varied among different apo bands of the same HDL2 or HDL3 preparation and among the same bands of different preparations. Labeling in the presence of heparin or other inhibitors of T4 binding to plasma proteins (furosemide, diclofenac, and mefenamic acid) showed that HDL2-associated apoA-I was more sensitive to inhibition than HDL3-associated apoA-I. In conclusion, 1) HDL2 and HDL3 carry T4 mainly through apoA-I and secondarily through apoA-II and apoE. The inter- and intrasubclass variations in T4 binding and sensitivity to inhibitors can be explained by the known heterogeneity of HDL particles and possible differences in conformation of the apo. The findings reported here, that apo other than apoA-I and apoB exhibit saturable binding of T4, suggest that thyroid hormone-lipoprotein interactions may have even wider physiological implications than previously appreciated.     

丙型肝炎病毒蛋白与脂蛋白之间的相互作用

0引言肝脏是脂蛋白代谢的中枢,当嗜肝病毒引起肝细胞炎症和坏死,势必会引起肝内生化代谢紊乱,包括脂质代谢障碍和载脂蛋白合成异常.丙型肝炎病毒(HCV)与脂类代谢表现出更为密切的关系.与其他病毒性肝炎相比,HCV感染慢性化后,中重度肝细胞脂肪变性包括胞质内脂滴聚集是其典型组织病理学特征.在动物实验和动物模型中也可以观察到这一突出的病理改变.HCV与脂质的关系还有如下证据:HCV可与血清中不同的脂蛋白成分发生结合;低密度脂蛋白受体可作为HCV的一个候选受体;临床研究发现H.E.L.P-LDL血浆分离置换术可明显的降低HCVRNA的负载.…     

Metabolism of triglyceride-rich lipoproteins and transfer of lipids to high-density lipoproteins (HDL) in vegan and omnivore subjects

Background and aimsVegan diet excludes all foodstuffs of animal origin and leads to cholesterol lowering and possibly reduction of cardiovascular disease risk. The aim was to investigate whether vegan diet improves the metabolic pathway of triglyceride-rich lipoproteins, consisting in lipoprotein lipolysis and removal from circulation of the resulting remnants and to verify whether the diet alters HDL metabolism by changing lipid transfers to this lipoprotein.Methods and results21 vegan and 29 omnivores eutrophic and normolipidemic subjects were intravenously injected triglyceride-rich emulsions labeled with ¹⁴C-cholesterol oleate and ³H-triolein: fractional clearance rates (FCR, in min^?1) were calculated from samples collected during 60 min for radioactive counting. Lipid transfer to HDL was assayed by incubating plasma samples with a donor nanoemulsion labeled with radioactive lipids; % lipids transferred to HDL were quantified in supernatant after chemical precipitation of non-HDL fractions and nanoemulsion. Serum LDL cholesterol was lower in vegans than in omnivores (2.1 ± 0.8, 2.7 ± 0.7 mmol/L, respectively, p < 0,05), but HDL cholesterol and triglycerides were equal. Cholesteryl ester FCR was greater in vegans than in omnivores (0.016 ± 0.012, 0.003 ± 0.003, p < 0.01), whereas triglyceride FCR was equal (0.024 ± 0.014, 0.030 ± 0.016, N.S.). Cholesteryl ester transfer to HDL was lower in vegans than in omnivores (2.7 ± 0.6, 3.5 ± 1.5%, p < 0,05). Free-cholesterol, triglyceride and phospholipid transfer were equal, as well as HDL size.ConclusionRemnant removal from circulation, estimated by cholesteryl oleate FCR was faster in vegans, but the lipolysis process, estimated by triglyceride FCR was equal. Increased removal of atherogenic remnants and diminution of cholesteryl ester transfer may favor atherosclerosis prevention by vegan diet.     

Characterization of HDL and lipoproteins intermediate to LDL and HDL in the serum of pedigreed baboons fed an atherogenic diet

A lipoprotein species with ultracentrifugal flotation rates (F0(1.20) 9-28) intermediate to high density lipoproteins (HDL, F0(1.20) 0-9) and low density lipoproteins (LDL, F0(1.20) 28-56) found in the plasma of certain pedigreed baboons fed an atherogenic diet was studied by gradient gel electrophoresis (GGE) and ultracentrifugal techniques. These lipoproteins were found to be heterogeneous in size (125-220 A) and hydrated density (1.028-1.080 g/ml). The major apolipoprotein in all density subfractions of the F0(1.20) 9-28 lipoproteins exhibited the molecular weight (2.8 X 10(4) daltons) and immunochemical properties of apolipoprotein A-I (apoA-I). Protein corresponding to apolipoprotein E (apoE, 3.5 X 10(4) daltons) was observed primarily in the less dense subspecies of F0(1.20) 9-28 lipoproteins. Some low molecular weight (1.8 X 10(4), 1.3 X 10(4), and 1.1 X 10(4) daltons) apolipoproteins were also detected. At low serum F0(1.20) 9-28 lipoprotein concentrations, only the smaller, more dense, protein-rich species were present; at higher F0(1.20) 9-28 concentrations, the larger, less dense species were observed in addition to the small species. The HDL of pedigreed baboons in families with and without serum F0(1.20) 9-28 lipoproteins were also characterized. The HDL of both groups of progeny consisted of a similar set of 5 subpopulations designated HDL-I through HDL-V determined by GGE. HDL-I, consisting of material 100-125 A in size, was the major HDL subpopulation. ApoA-I was the major protein moiety in all HDL subpopulations; none contained apoE. Baboons in families with F0(1.20) 9-28 lipoproteins had more HLD-I (292 +/- 80 mg/dl vs. 235 +/- 55 mg/dl) and less HDL-II (86 +/- 22 mg/dl vs. 135 +/- 34 mg/dl) than baboons in families without F0(1.20) 9-28 lipoproteins; both groups showed identical total HDL concentrations (446 +/- 90 mg/dl and 444 +/- 49 mg/dl, respectively). Among those baboons in families with F0(1.20) 9-28 lipoproteins, there was an inverse correlation between F0(1.20) 9-28 concentration and total HDL, HDL-I and HDL-II concentrations, indicating a possible metabolic relationship between these HDL subpopulations and the F0(1.20) 9-28 species.     

Relationship between lipoproteins including HDL subfractions and the intravenous fat tolerance test

There is a positive relationship between the HDL cholesterol concentration and the fractional removal rate k2 of intravenously administered Intralipid, the intravenous fat tolerance test (IVFTT). This relationship was analysed in 22 female and 20 male healthy normolipoproteinaemic volunteers with regard to HDL subfractions. A positive correlation between the IVFTT k2 value and HDL cholesterol (r = 0.40, P less than 0.05) was confirmed. The k2-HDL2 cholesterol relationship was strong and positive (r = 0.56, P less than 0.001), whereas the correlation between HDL3 cholesterol and k2 was negative (r = -0.37, P less than 0.05). These findings extend other observations indicating that HDL2 seems to be the HDL fraction, directly associated with removal of TG-rich particles from the circulation.     

Plasma lipoproteins from patients with poorly controlled diabetes mellitus and “in vitro” glycation of lipoproteins enhance the transfer rate of cholesteryl ester from HDL to apo-B-containing lipoproteins

Summary Alterations in the reverse cholesterol transport system have been described in diabetic mellitus patients in several but not all studies. Furthermore, recently published investigations suggest that a faster “in vitro” transfer rate of cholesteryl ester from high density lipoproteins to apoB-containing lipoproteins could be solely ascribed to variation of the plasma lipoprotein composition and concentration in the diabetic state. The present study analysed the influence of lipoprotein glycation on the cholesteryl ester transfer protein-mediated transfer of esterified cholesterol from high density lipoprotein and its subfractions to lighter density lipoproteins. For this purpose two sets of “in vitro” experiments were carried out utilizing:1) plasma lipoproteins drawn from diabetic and from normal subjects and; 2) normal lipoproteins or partially purified cholesteryl ester transfer protein submitted to “in vitro” glycation. The transfer rate of ¹⁴C-cholesteryl ester labelled HDL subfractions to low or very low density lipoproteins was measured in all experiments. After incubations with plasma d > 1.21 g/ml or with purified cholesteryl ester transfer protein, apoB-containing lipoproteins were precipitated with a dextran sulfate/MgCl₂ solution. The “in vitro” glycation of the partially purified cholesteryl ester transfer protein markedly impaired its activity. However, greater transfer rates were observed when lipoproteins from diabetic individuals or the “in vitro” glycated lipoproteins were utilized. This effect was attributed to glycation of the protein component of HDL. In conclusion, lipoprotein glycation elicits an enrichment of the apoB-containing lipoproteins with cholesteryl ester that is likely related to the premature atherosclerosis in patients with poorly controlled diabetes. [Diabetologia (1997) 40: 1085–1093] Received: 14 January 1997 and in revised form: 7 May 1997     

Role of high density lipoproteins (HDL) in reverse cholesterol transport

The atheromatous risk is negatively correlated with the plasma concentration of HDL cholesterol. This might be due to the role of HDL in the reverse cholesterol transport. In the first stage, free cholesterol molecules from peripheral cells are taken up by HDL through a receptor-dependent mechanism. In HDL, the esterification of cholesterol is catalysed by the lecithin: cholesterol acyl transferase. The progressive accumulation of cholesterol esters leads to the formation of HDL2. Through the action of cholesterol ester transfer protein, HDL2 become enriched in triglycerides and transfer cholesterol esters to LDL. Finally, cholesterol may be taken up by the liver through two routes which are: the receptor-mediated LDL endocytosis and the direct uptake of cholesterol esters which occurs during the degradation of HDL2 by hepatic lipase.     

Reverse cholesterol transport,high density lipoproteins and HDL cholesterol: recent data

Unlike LDL cholesterol, which is a major cardiovascular risk factor, HDL cholesterol plays an important anti-atherogenic role through reverse cholesterol transport from peripheral cells to the liver. Some recent biochemical and epidemiological data shed light on this key function. In the hereditary Tangier disease with disseminated lipid storage, the main biochemical feature is a dramatically low level of HDL cholesterol. Different mutations in the ATP-binding cassette transporter A1 (ABCA1) gene have been recently described, which interfere with cellular cholesterol efflux. This results in low HDL plasma level, and defective reverse cholesterol transport to the liver. Moreover, selective hepatic uptake of HDL cholesteryl esters by SR-B1, a class B scavenger receptor, also plays a key role. In the follow-up of the PROCAM Study, the relative risk of coronary events is high in a cluster of patients with increased total cholesterol/HDL-cholesterol ratio. In the prospective secondary prevention VA-HIT study, the relative risk of coronary events in patients with low HDL cholesterol levels is decreased of 22% with a treatment by gemfibrozil. If the present available range of drugs targeted at increasing HDL cholesterol levels is rather narrow, future therapies will be encouraging, especially with agonists of PPARs.     

High-density lipoproteins (HDL) inhibit endotoxin-induced leukocyte adhesion on endothelial cells in rats: effect of the acute-phase HDL

High-density lipoprotein (HDL) plays an important role not only in protecting against atherosclerosis but also in innate immunity. Several lines of evidence showed that HDL could ameliorate the toxic effects of endotoxin or lipopolysaccharide (LPS). In this study, we examined whether HDL could inhibit LPS-induced leukocyte adhesion on endothelial cells in rats. Normal HDL and acute-phase HDL (AP-HDL) were purified from plasma of hamsters that received normal saline and LPS injection, respectively. Wistar rats were given LPS injection and the number of leukocytes adhering to endothelial cells of the mesenteric venules was determined using intravital fluorescence videomicroscopy. Intravenous injection of LPS enhanced leukocyte adhesion to the mesenteric venules. However, when LPS was preincubated with normal HDL, leukocyte adhesion on endothelial cells in response to LPS was significantly attenuated in a dose-dependent manner. AP-HDL was also able to significantly decrease LPS-induced leukocyte adhesion on endothelial cells. It appeared to be more effective than normal HDL since lower concentrations were required. This inhibitory effect of HDL was not due to HDL itself but it requires preincubation of HDL with LPS. When HDL was separated into protein and lipid fractions, it was found that lipid-free apoHDL was able to significantly inhibit LPS-induced leukocyte adhesion, whereas lipid component of HDL had no effect. In conclusion, HDL, both normal and acute-phase, could inhibit an inflammatory effect of LPS on endothelial cells in vivo. AP-HDL was more potent than normal HDL in inhibiting LPS-induced leukocyte adhesion, and this effect was attributed to the protein component of HDL.     

Interaction of Schistosoma japonicum with Salmonellae and other gram-negative bacteria

The in vitro and in vivo interaction of Schistosoma japonicum with salmonellae and other gram-negative bacteria was studied. In vitro, S. japonicum associated with salmonellae and other gram-negative bacteria, and more male than female schistosomes associated with the bacteria. By using the various strains and mutants of salmonellae, we showed that Salmonella typhimurium had a higher degree of association than did Salmonella enteritidis and that the piliated strains of S. typhimurium associated much more frequently than did the nonpiliated strains. However, in vivo studies demonstrated more frequent association of salmonellae with female than with male schistosomes and that the piliated and nonpiliated strains of salmonella did not differ in their association with the worms.     

高密度脂蛋白抑制L-选择素对心血管的保护作用

目的　从炎症反应的角度探讨 HDL 保护冠心病的机制。方法　冠心病患者 30例 ,健康对照组 19例 ,分别测定两组血清中可溶性 L-选择素 (L- selectin)和 HDL。结果　 1冠心病组 HDL 水平 [(0 .74± 0 .33) mm ol/ L]较对照组 [(1.4 5± 0 .37) mm ol/ L]明显降低 (P<0 .0 5 ) ,而可溶性 L- selectin冠心病组 [(1.34± 0 .36 ) μg/ ml]较对照组 [(1.0 5± 0 .39)μg/ ml]明显升高 (P<0 .0 5 )。 2 4 9例受试者的可溶性 L - selectin和 HDL两者间呈明显负相关 (r=- 0 .88,P<0 .0 0 1)。结论　 1冠心病组 HDL较对照组低 ,符合 HDL有心血管保护作用的理论。可溶性 L - selectin在冠心病组较对照组高表明 L - selectin参与冠心病的发作。 2 HDL与可溶性 L - selectin间有明显负相关性 ,表明HDL 有可能通过抑制 L- selectin激活而起心血管保护作用的     

High-density lipoproteins (HDL) are present in stenotic aortic valves and may interfere with the mechanisms of valvular calcification

ObjectiveTo determine whether differences exist in valvular high density lipoprotein (HDL) content between non-stenotic and stenotic aortic valves, and whether HDL could retard valvular calcification locally.MethodsStenotic aortic valves were obtained from valve replacement surgery and non-stenotic control valves from cardiac transplantations or at autopsy. The valvular localization and concentration of apolipoproteinA-I (apoA-I) were analyzed by immunohistochemistry and ELISA. The effects of HDL on the secretion of calcifying mediators and proinflammatory cytokines by cultured aortic valve myofibroblasts were assessed by ELISA and real-time PCR.ResultsThe concentration of apoA-I was higher in control than in stenotic valves (p < 0.05). ApoA-I surrounded the calcific deposits in stenotic valves, co-localizing with apoB, apoE, and osteoprotegerin (OPG). Incubation of cultured valve myofibroblasts with HDL increased their secretion of OPG (p < 0.001). Furthermore, incubation of myofibroblasts with HDL led to decreased mRNA expression of tumor necrosis factor alpha (TNF-α) (p < 0.05).ConclusionsThe amount of valvular HDL is reduced in aortic valve stenosis. HDL both induces the secretion of OPG and reduces the expression of TNF-α in vitro. Since OPG is known to inhibit and TNF-α to promote aortic valve calcification, HDL may have an anti-calcifying effect in human aortic valves.     

Interrelationship of triglycerides with lipoproteins and high-density lipoproteins

Triglycerides are transported by the largest and most lipid-rich of the lipoprotein particles, namely, chylomicrons and very low density lipoproteins (VLDL). These particles are buoyant because of the high triglyceride content, which makes up approximately 90% by weight of the chylomicron and 70% by weight of the VLDL. The chylomicron transports exogenous or dietary fat and cholesterol, whereas VLDL transports endogenous triglyceride and cholesterol in lipoproteins synthesized and secreted by the liver. Both chylomicrons and VLDL are hydrolyzed at the capillary surface by the enzyme lipoprotein lipase. Lipoprotein lipase catalyzes the hydrolysis of triglyceride in the lipid core of these particles, producing smaller particles known as remnants. We currently believe the remnants are atherogenic and that this is one reason why hypertriglyceridemia may predispose to coronary artery disease. Chylomicron remnants are recognized and removed by hepatic receptors that contain apolipoprotein (apo) E. The rate of clearance of remnant particles depends on which subfraction of apo E is present. Particles containing apo EII are removed more slowly than those with apo EIII and EIV. The dietary cholesterol from the chylomicron remnant particles is thought to down-regulate the hepatic low-density lipoprotein (LDL) receptors. VLDL remnants, also called intermediate-density lipoprotein (IDL), contain apo E and may be removed by the liver through the LDL or B/E receptor. The decrease in activity of these receptors results in apparent oversynthesis of LDL, the end-product of VLDL and IDL metabolism. LDL is the major cholesterol carrier, followed by high-density lipoprotein (HDL).(ABSTRACT TRUNCATED AT 250 WORDS)