Uptake of high-density lipoprotein by Y-organs of the crab,Cancer antennarius. I. characterization in vitro and effects of stimulators and inhibitors

Cholesterol is the obligate precursor for ecdysteroid hormone synthesis by the ecdysial glands (Y-organs) in crustaceans, and all cholesterol in the hemolymph is bound to high-density lipoprotein (HDL). The mechanism was studied of how Y-organ cells acquire cholesterol. Y-organ segments were incubated with HDL isolated from hemolymph and labeled with ¹²⁵I. After incubation, tissue was homogenized in acid to determine radioactivity in acid-precipitable (cell associated, intact) HDL and in acid-soluble (degraded) HDL. Both HDL uptake and degradation showed saturation kinetics. At saturation most of the total counts represented degraded HDL; by 3 h, degradation was 80%. Rates of HDL uptake and breakdown were higher in Y-organs from de-eyestalked crabs (deprived thereby of molt-inhibiting hormone, MIH) than in glands from intact crabs. Both parameters were depressed by inhibitors of glycolysis and oxidative phosphorylation dose dependently and by low temperature. HDL uptake also was depressed by cAMP added to the medium experimentally or through efflux from the tissue during incubation. These results indicate a mechanism for HDL uptake that entails receptor-mediated, energy-dependent endocytosis of the entire HDL-cholesterol complex. Also the results suggest that HDL uptake and degradation are mediated by cAMP and depressed by an eyestalk factor, presumably MIH. © 1995 Wiley-Liss, Inc.     

Mutations affecting the binding,internalization, and lysosomal hydrolysis of low density lipoprotein in cultured human fibroblasts,lymphocytes, and aortic smooth muscle cells

Studies comparing the metabolism of low density lipoprotein (LDL) in normal cells and in cells cultured from patients with homozygous familial hypercholesterolemia have disclosed the existence of a receptor for plasma LDL. This receptor has been identified on the surface of human fibroblasts, lymphocytes, and aortic smooth muscle cells. An extension of these studies to cell strains derived from patients with other single gene defects in cholesterol metabolism has provided additional insight into the normal mechanisms by which cells regulate their cholesterol content and how alterations in these genetic control mechanisms may predispose to atherosclerosis in man.     

Evaluation of serum lipids and high-density lipoprotein subfractions (HDL2, HDL3) in postmenopausal patients with breast cancer

Breast cancer patients are known to be at increased risk for developing other chronic diseases including cardiovascular disease. Studies by different investigators have shown a correlation between increased dietary fat or hypercholesterolemia and the occurrence of breast cancer. Since previous studies on lipoprotein subfractions in this type of cancer have been inconsistent, we evaluated the lipids and lipoprotein subfraction levels in postmenopausal patients with breast cancer in an attempt to identify the risk for the development of cardiovascular disease.The study included 132 patients, 56 of which were suffering from breast cancer, 32 from pancreatic and 44 age-matched controls. Total cholesterol (TC), triglycerides and lipoprotein fractions as well as TC/High density lipoprotein (HDL) and HDL2/HDL3 ratios were estimated by standard laboratory techniques.An increase in triglycerides and a decrease in HDL-cholesterol, especially in the HDL2 subfraction, were observed in patients with breast cancer as compared to the controls (P < 0.05). The maximum changes in TC, and HDL concentrations were observed in patients with advanced disease. Analysis of indexes of atherosclerosis (TC/HDL, and HDL2/HDL3 ratios) demonstrated that breast cancer patients had significantly higher TC/HDL ratio (6.44 ± 1.24) compared with controls (3.43 ± 0.57, p = 0.001), and patients with pancreatic cancer (3.79 ± 0.15, p = 0.027).The results have demonstrated an unfavourable lipid profile in untreated breast cancer patients with high atherosclerosis indexes. This observation is of great importance, considering the potential use of endocrine therapy that could result in further deterioration of lipid indexes. We propose the evaluation and monitoring of lipid profile prior and after the induction of hormonal therapy in breast cancer patients, as a routine in clinical setting. (Mol Cell Biochem 268: 19–24, 2005)     

Plasma levels of lecithin:cholesterol acyltransferase and risk of future coronary artery disease in apparently healthy men and women: a prospective case-control analysis nested in the EPIC-Norfolk population study

LCAT plays a key role in the maturation of HDL, as evidenced by low HDL-cholesterol levels in carriers of deleterious mutations in LCAT. However, the role of LCAT in atherosclerosis is unclear. We set out to study this in a prospective study. Plasma LCAT levels, which strongly correlate with LCAT activity, were measured in baseline nonfasting samples of 933 apparently healthy men and women who developed coronary artery disease (CAD) and 1,852 matched controls who remained free of CAD during 6 year follow-up. LCAT levels did not differ between cases and controls but were higher in women than men. Stratification into LCAT quartiles revealed a positive association with plasma LDL-cholesterol and triglyceride levels in the unexpected absence of an association with HDL-cholesterol. In mixed-gender analyses, the odds ratio (OR) for future CAD in the highest LCAT quartile versus the lowest was 1.00 [confidence interval (CI): 0.76–1.29, P for linearity = 0.902], although opposite trends were observed in men and women. In fact, high LCAT levels were associated with an increased CAD risk in women (unadjusted OR 1.45, CI: 0.94–2.22, P for linearity = 0.036). In contrast to our studies in carriers of LCAT mutations, the current data show that low LCAT plasma levels are not associated with increased atherosclerosis in the general population.     

Biophysical characterization of the interaction of high-density lipoprotein (HDL) with endotoxins.

The interaction of bacterial endotoxins [lipopolysaccharide (LPS) and the 'endotoxic principle' lipid A], with high-density lipoprotein (HDL) from serum was investigated with a variety of physical techniques and biological assays. HDL exhibited an increase in the gel to liquid crystalline phase transition temperature Tc and a rigidification of the acyl chains of the endotoxins as measured by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The functional groups of the endotoxins interacting with HDL are the phosphates and the diglucosamine backbone. The finding of phosphates as target groups is in accordance to measurements of the electrophoretic mobility showing that the zeta potential decreases from -50 to -60 mV to -20 mV at binding saturation. The importance of the sugar backbone as further target structure is in accordance with the remaining negative potential and competition experiments with polymyxin B (PMB) and phase transition data of the system PMB/dephosphorylated LPS. Furthermore, endotoxin binding to HDL influences the secondary structure of the latter manifesting in a change from a mixed alpha-helical/beta-sheet structure to a predominantly alpha-helical structure. The aggregate structure of the lipid A moiety of the endotoxins as determined by small-angle X-ray scattering shows a change of a unilamellar/inverted cubic into a multilamellar structure in the presence of HDL. Fluorescence resonance energy transfer data indicate an intercalation of pure HDL, and of [LPS]-[HDL] complexes into phospholipid liposomes. Furthermore, HDL may enhance the lipopolysaccharide-binding protein-induced intercalation of LPS into phospholipid liposomes. Parallel to these observations, the LPS-induced cytokine production of human mononuclear cells and the reactivity in the Limulus test are strongly reduced by the addition of HDL. These data allow to develop a model of the [endotoxin]/[HDL] interaction.     

Regulation of the concentration of pre beta high-density lipoprotein in normal plasma by cell membranes and lecithin-cholesterol acyltransferase activity.

A minor fraction of plasma high-density lipoprotein (pre beta-1 HDL) has been shown to promote cholesterol efflux from peripheral cell membranes [Castro, G. R., & Fielding, C. J. (1988) Biochemistry 27, 25-29]. When isolated native plasma is incubated at 37 degrees C, this fraction is specifically decreased. On the other hand, the level of plasma pre beta-1 HDL is fully protected in the presence of even very low levels of fibroblasts, vascular smooth muscle cells, or macrophages. Blood cells were completely inactive in maintaining plasma pre beta-1 HDL levels in the absence of peripheral cells, even at the relatively high levels present in whole blood. The loss of pre beta-1 observed in isolated plasma was dependent upon lecithin-cholesterol acyltransferase (LCAT) activity. These data suggest that reverse cholesterol transport catalyzed by pre beta-1 HDL, and subsequent LCAT-mediated cholesterol esterification, is directly dependent upon the interaction between this HDL species and competent peripheral cells.     

Studies on the proteins involved in the interaction of high-density lipoprotein with isolated human small intestine epithelial cells.

Treatment of 125I-labelled high-density lipoprotein ([125I]HDL3) with monospecific polyclonal antibodies against apolipoproteins A-I and A-II resulted in a dose-dependent inhibition of the [125I]HDL3 binding to isolated human small intestine epithelial cells by 25% and 50%, respectively. Both antibodies also inhibited intracellular degradation of [125I]HDL3 by 80%. Treatment of enterocytes with polyclonal antibody against apolipoprotein A-I binding protein, a putative HDL receptor, inhibited both binding and degradation of [125I]HDL3 by these cells by 50%. Antibodies to apolipoprotein A-I, A-II and apo A-I-binding protein also inhibited [125I]HDL3 binding to cholesterol-loaded cells.     

Expression and functional analyses of novel mutations of ATP-binding cassette transporter-1 in Japanese patients with high-density lipoprotein deficiency.

ATP-binding cassette transporter-1 (ABCA1) gene is mutated in patients with familial high-density lipoprotein deficiency (FHD). In order to know the molecular basis for FHD, we characterized three different ABCA1 mutations associated with FHD (G1158A/A255T, C5946T/R1851X, and A5226G/N1611D) with respect to their expression in the passaged fibroblasts from the patients and in the cells transfected with the mutated cDNAs. Fibroblasts from the all patients showed markedly decreased cholesterol efflux to apolipoprotein (apo)-Al. In the fibroblasts homozygous for G1158A/A255T, the immunoreactive mass of ABCA1 could not be detected, even when stimulated by 9-cis-retinoic acid and 22-R-hydroxycholesterol. In the fibroblasts homozygous for C5946T/R1851X, ABCA1 mRNA was comparable. Because the mutant ABCA1 protein (R1851X) was predicted to lack the epitope for the antibody used, we transfected FLAG-tagged truncated mutant (R1851X/ABCA1-FLAG) cDNA into Cos-7 cells, showing that the mutant protein expression was markedly reduced. The expression of N1611D ABCA1 protein was comparable in both fibroblasts and overexpressing cells, although cholesterol efflux from the cells was markedly reduced. These data indicated that, in the three patients investigated, the abnormalities and dysfunction of ABCA1 occurred at the different levels, providing important information about the expression, regulation, and function of ABCA1.     

Thermodynamic and structural destabilization of apoE3 by hereditary mutations associated with the development of lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a dominant inherited kidney disorder characterized by lipoprotein thrombi in glomerular capillaries. Single-amino-acid mutations in apoE have been associated with the development of the disease, although the mechanism is unknown. In an effort to gain mechanistic insight linking the presence of such mutations and the development of LPG, we evaluated the effects of three of the most common apoE3 variants associated with this disease, namely R145P(Sendai), R147P(Chicago), and R158P(Osaka or Kurashiki), on the structural and conformational integrity of the protein. All three variants were found to have significantly reduced helical content, to expose a larger portion of hydrophobic surface to the solvent, and to be significantly thermodynamically destabilized, often lacking functionally relevant unfolding intermediates. Furthermore, all variants were aggregation prone and had enhanced sensitivity to protease digestion. Finally, although the variants were able to form discoidal lipoprotein particles, discrete subpopulations of poorly formed or aberrant particles were evident. Furthermore, these lipoprotein particles were thermodynamically destabilized and aggregation prone. Overall, our data suggest that these mutations induce a generalized unfolding of the N-terminal domain of apoE3 toward a molten-globule-like structure. ApoE3 N-terminal domain unfolding due to mutation may constitute a common mechanism underlying the protein''s association with the pathogenesis of LPG.     

A simplified and efficient procedure for the purification of apolipoprotein AI from human serum high-density lipoprotein-3 by preparative isoelectric focussing on polyacrylamide gel beads

An improved method is described for the purification of milligram amounts of apolipoprotein AI from serum apo-HDL₃ by isoelectric focussing on polyacrylamide gel beads. The procedure involves a single focussing over a narrow (1.3 unit) pH gradient, and permits isolation of apo-AI of exceptional purity and in high yield (75% recovery of HDL₃ protein, ca. 50% corresponding to pure apo-AI). The electrophoretic mobility, pI values, molecular weight, antigenicity and amino acid composition of such apo-AI were indistinguishable from those reported in the literature. A rabbit antiserum to apo-AI isolated by focusing exhibited similar immunological reactivity to one prepared from an antigen isolated by gel filtration chromatography; moreover, apo-AI purified by the respective procedures reacted identically with both antisera. We conclude that isoelectric focussing on a support of polyacrylamide gel beads (as Bio-Gel P60) presents certain advantages for the isolation of highly purified apo-AI over both conventional chromatographic procedures and isoelectric focussing on a Sephadex support.     

Synthesis, characterization and biological activity of trans-platinum(II) complexes with chloroquine

Three platinum-chloroquine complexes, trans-Pt(CQDP)₂(I)₂ [1], trans-Pt(CQDP)₂(Cl)₂ [2] and trans-Pt(CQ)₂(Cl)₂ [3], were prepared and their most probable structure was established through a combination of spectroscopic analysis and density functional theory (DFT) calculations. Their interaction with DNA was studied and their activity against 6 tumor cell lines was evaluated. Compounds 1 and 2 interact with DNA primarily through electrostatic contacts and hydrogen bonding, with a minor contribution of a covalent interaction, while compound 3 binds to DNA predominantly in a covalent fashion, with weaker secondary electrostatic interactions and possibly hydrogen bonding, this complex also exerted greater cytotoxic activity against the tumor cell lines.     

The characterization of lipoprotein lipase isolated from the post-heparin plasma of the rainbow trout, Salmo gairdneri Richardson.

1. Intravenous injection of heparin into the trout resulted in the appearance in the plasma of a lipase with the properties of lipoprotein lipase. 2. The enzyme was purified to apparent electrophoretic homogeneity by means of heparin-Sepharose affinity chromatography. The enzyme was eluted with 1.5 M-NaCl and had a specific activity approx. 450-fold that of the post-heparin plasma. 3. The activity of the purified enzyme was inhibited by 1.0 M-NaCl and protamine sulphate and was stimulated between 3- and 8.8-fold by the addition of trout plasma. 4. The activity was strongly stimulated by trout very low density lipoproteins and to a lesser extent by high density lipoproteins. 5. The isolated enzyme fraction gave a single band on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and had an apparent subunit M4 of 63 000. 6. These results suggest that the uptake of lipid by the tissues in the trout can occur by a process similar to that in mammals.     

肌动蛋白结合脂筏促进巨噬细胞摄入土拉弗朗西斯菌

观察土拉弗朗西斯菌LVS借助脂筏以肌动蛋白为动力被鼠巨噬细胞摄入的过程。细胞胆固醇用菲律平Ⅲ染色,结合神经节苷酯GM1的霍乱毒素B亚基用键合了Alexa 594的兔抗霍乱毒素B亚基二抗显色;肌动蛋白用键合了Alexa 594的鬼笔环肽显色。免疫荧光显微镜观察到脂筏成分中的胆固醇、神经节苷酯GM1均可与细菌共定位;胆固醇可与肌动蛋白共定位。随着感染时间的延长,细菌可离开脂筏。离开脂筏的细菌囊泡可与肌动蛋白共定位。这些发现提示肌动蛋白与脂筏结合,在弗朗西斯菌早期进入巨噬细胞期间发挥重要作用。     

Ultrastructural characterization of the delimiting membranes of isolated autophagosomes and amphisomes by freeze-fracture electron microscopy

The delimiting membranes of isolated autophagosomes from rat liver had extremely few transmembrane proteins, as indicated by the paucity of intramembrane particles in freeze-fracture images (about 20 particles/microm2, whereas isolated lysosomes had about 2000 particles/microm2). The autophagosomes also appeared to lack peripheral surface membrane proteins, since attempts to surface-biotinylate intact autophagosomes only yielded biotinylation of proteins from contaminating damaged mitochondria. All the membrane layers of multilamellar autophagosomes were equally particle-poor; the same was true of the autophagosome-forming, sequestering membrane complexes (phagophores). Isolated amphisomes (vacuoles formed by fusion between autophagosomes and endosomes) had more intramembrane particles than the autophagosomes (about 90 particles/microm2), and freeze-fracture images of these organelles frequently showed particle-rich endosomes fusing with particle-poor or particle-free autophagosomes. The appearence of multiple particle clusters suggested that a single autophagic vacuole could undergo multiple fusions with endosomes. Only the outermost membrane of bi- or multilamellar autophagic vacuoles appeared to engage in such fusions.     

Lipid circulation in spiders. Transport of phospholipids,free acids and triacylglycerols as the major lipid classes by a high-density lipoprotein fraction isolated from plasma of Polybetes pythagoricus

A high-density lipoprotein (HDL) fraction was isolated from the hemolymphatic plasma of the spider Polybetes pythagoricus by density-gradient ultracentrifugation. Hydrated density (1.13 g/ml), electrophoretic mobility (SDS—PAGE) of apoproteins and lipid classes composition were determined. Lipids were identified by HP-TLC and auxiliary techniques; they were quantified by TLC-FID. The protein moiety is composed of two main apoproteins (250 and 76 kDa, respectively) and several polypeptides of low molecular weight. It resembles the apoliphorins of insects and some other arachnids. The lipid composition differs from most lipophorins. Phospholipids amount to more than 60% of total lipids, while diacylglycerols (2.4%) are supplanted by triacylglycerols (16.5%) as the main circulating energetic lipids.     

Circadian Rhythm of the Liver of Male Rats Pre-Treated with Phenobarbital—ii. Hexobarbital Sleeping Time and Lipids Content in Liver and Serum

The circadian rhythm of hexobarbital sleeping time and lipids content in liver and serum were studied in 226 male Sprague-Dawley rats pretreated daily at 0800-0900 with 70 mg/kg (study 1 or 3) or 50 mg/kg (study 2) phenobarbital (PB) orally for 7 days. Thereafter, eight (study 1) or five (study 2 and 3) rats each were studied at 4-hr intervals at 1000, 1400, 1800, 2200, 0200, 0600 and 1000 through the following day. The lighting schedule in the colony was 12:12 ± light:dark (light from 0600 to 1800). The hexobarbital sleeping times of PB-pretreated rats were generally shortened compared to the controls and no circadian rhythm was observed. PB-treatment increased slightly the liver content of cholesterol, and significantly that of triglycerides and phospholipids. Liver cholesterol and phospholipids showed circadian rhythms with peaks during the dark phase. No circadian rhythm of liver triglycerides existed. In serum, levels of triglycerides and phospholipids were slightly lowered by PB-treatment, while levels of cholesterol and beta-lipoprotein were not influenced. Serum values did not exhibit circadian rhythms.     

LDL oxidation by arterial wall macrophages depends on the oxidative status in the lipoprotein and in the cells: Role of prooxidants vs. antioxidants

Oxidized LDL is highly atherogenic as it stimulates macrophage cholesterol accumulation and foam cell formation, it is cytotoxic to cells of the arterial wall and it stimulates inflammatory and thrombotic processes. LDL oxidation can lead to its subsequent aggregation, which further increases cellular cholesterol accumulation.All major cells in the arterial wall including endothelial cells, smooth muscle cells and monocyte derived macrophages can oxidize LDL. Macrophage-mediated oxidation of LDL is probably a hallmark in early atherosclerosis, and it depends on the oxidative state of the LDL and that of the macrophages. The LDL oxidative state is elevated by increased ratio of poly/mono unsaturated fatty acids, and it is reduced by elevation of LDL-associated antioxidants such as vitamin E, -carotene, lycopene, and polyphenolic flavonoids.The macrophage oxidative state depends on the balance between cellular NADPH -oxidase and the glutathione system. LDL-associated polyphenolic flavonoids which inhibit its oxidation, can also reduce macrophage oxidative state, and subsequently the cell-mediated oxidation of LDL. Oxidation of the macrophage lipids, which occurs under oxidative stress, can lead to cell-mediated oxidation of LDL even in the absence of transition metal ions ,and may be operable in vivo.Finally, elimination of Ox-LDL from extracellular spaces, after it was formed under excessive oxidative stress, can possibly be achieved by the hydrolytic action of HDL-associated paraoxonase on lipoprotein's lipid peroxides. The present review article summarizes the above issues with an emphasis on our own data.