carbocyanines and Hypercholesterolemia

The autosomal recessive hypercholesterolemia (ARH) protein plays a critical role in regulating plasma low density lipoprotein (LDL) levels. Inherited defects in ARH lead to a hypercholesterolemia that closely phenocopies that caused by a defective LDL receptor. The elevated serum LDL-cholesterol levels typical of ARH patients and the pronounced accumulation of the LDL receptor at the cell surface of hepatocytes in ARH-null mice argue that ARH operates by promoting the internalization of the LDL receptor within clathrin-coated vesicles. ARH contains an amino-terminal phosphotyrosine-binding domain that associates physically with the LDL receptor internalization sequence and with phosphoinositides. The carboxyl-terminal half of ARH contains a clathrin-binding sequence and a separate AP-2 adaptor binding region providing a plausible mechanism for how ARH can act as an endocytic adaptor or CLASP (clathrin-associated sorting protein) to couple LDL receptors with the clathrin machinery. Because the interaction with AP-2 is highly selective for the independently folded appendage domain of the beta2 subunit, we have characterized the ARH beta2 appendage-binding sequence in detail. Unlike the known alpha appendage-binding motifs, ARH requires an extensive sequence tract to bind the beta appendage with comparably high affinity. A minimal 16-residue sequence functions autonomously and depends upon ARH residues Asp253, Phe259, Leu262, and Arg266. We suggested that biased beta subunit engagement by ARH and the only other beta2 appendage selective adaptor, beta-arrestin, promotes efficient incorporation of this mechanistically distinct subset of CLASPs into clathrin-coated buds.

Topics: Adaptor Proteins, Signal Transducing; Alanine; Amino Acid Motifs; Amino Acid Sequence; Animals; Arginine; Arrestins; beta-Arrestins; Calorimetry; Carbocyanines; Cholesterol, LDL; Clathrin; Cytosol; DNA; DNA-Binding Proteins; Endocytosis; Fluorescent Dyes; Genes, Recessive; Glutathione Transferase; Green Fluorescent Proteins; Humans; Hypercholesterolemia; Kinetics; Lipoproteins, LDL; Mice; Microtubule-Associated Proteins; Models, Molecular; Molecular Sequence Data; Mutagenesis; Peptides; Protein Binding; Protein Conformation; Protein Structure, Secondary; Protein Structure, Tertiary; Receptors, LDL; Sequence Homology, Amino Acid; Transcription Factor AP-2; Transcription Factors; Two-Hybrid System Techniques

Stimulatory effects of a novel isobenzofranone, MD-700, on low density lipoprotein (LDL) receptor activity were investigated in vitro and in vivo. MD-700 at 0.03 microg/ml elevated the expression of LDL receptor in HepG2 cells within 4 h. Corresponding to this, uptake of fluorescent labeled-LDL (3,3'-dioctadecylindocarbocyanine-LDL) by the cells increased linearly in time- and dose-dependent manner by MD-700 for up to 12 h. In the experiment using HepG2 cells transiently transfected with promoter-luciferase gene constructs, MD-700 increased luciferase activity in a dose-dependent manner from 0.03 to 0.1 microg/ml. In contrast, luciferase activity was not stimulated by MD-700 in construct with a deleted sterol regulatory element (SRE)-1, suggesting importance of SRE-1 in stimulation of the LDL receptor gene promoter by MD-700. Binding experiments on liver membranes from MD-700-treated hamsters showed about a 60% increase in 125I-labeled LDL binding. A Scatchard plot revealed that MD-700 increased the maximal binding without affecting binding affinity. In contrast to findings with an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, pravastatin, MD-700 had no effect on the sterol synthesis in hamster liver homogenates. These results suggest that MD-700 stimulates the expression of LDL receptor, presumably in a manner independent of change in sterol metabolism, and thereby promotes LDL clearance. Hypocholesterolemic actions of MD-700 in hamsters were then examined. MD-700 lowered serum cholesterol levels in hamsters fed normal chow or a high-fat diet. Fractionation of serum lipoproteins demonstrated that MD-700 selectively decreased LDL and very low density lipoprotein cholesterol. Dose-dependent decrease in serum cholesterol was also seen in hypercholesterolemic rats. Thus, the hypocholesterolemic action of MD-700 may be attributed to up-regulation of the LDL receptor, based on stimulation of the transcription of the LDL receptor gene. Although pravastatin stimulates LDL uptake and lowers serum cholesterol in a manner similar to that seen with MD-700, the mechanism responsible for hypocholesterolemic action appears to differ.

Topics: Animals; Benzofurans; Blotting, Northern; Carbocyanines; Carcinoma, Hepatocellular; Cell Membrane; Cholesterol; Cricetinae; Disease Models, Animal; DNA Primers; Fluorescent Dyes; Humans; Hypercholesterolemia; Lipoproteins, LDL; Lipoproteins, VLDL; Liver Neoplasms; Male; Promoter Regions, Genetic; Rats; Rats, Wistar; Receptors, LDL; RNA, Messenger; RNA, Neoplasm; Sterols; Transcription, Genetic; Tumor Cells, Cultured; Up-Regulation

We have recently characterized a strain of rabbits that shows a low atherosclerotic response (LAR) to dietary hypercholesterolemia in contrast to the usual high atherosclerotic response (HAR) of rabbits [1]. Presently, we have focused on three well established and important stages of atherogenesis, i.e., monocyte adhesion to endothelium, cell mediated peroxidative modification of lipoproteins and induction of a receptor that recognizes modified low density lipoprotein (LDL). The results obtained show that (1) beta-very low density lipoprotein (beta-VLDL) from LAR and HAR rabbits enhanced monocyte adhesion to endothelial cells to the same extent; (2) Cell mediated peroxidation of LDL and beta-VLDL, tested by loss of alpha-tocopherol and formation of thiobarbituric acid reacting substances (TBARS), was compared using macrophages, fibroblasts and smooth muscle cells (SMC) of LAR and HAR rabbits and no significant differences were found; (3) Induction of scavenger receptor by phorbol ester (phorbol 12-myristate 13-acetate (PMA)) and platelet-derived growth factor-BB (PDGF-BB) was determined in SMC or fibroblasts from LAR and HAR rabbits using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate-acetylated LDL (DiL-acLDL). We found a significantly higher uptake of DiI-acLDL in SMC and fibroblasts derived from HAR rabbits as compared with cells from LAR rabbits. Similar results were also obtained with [125I]-acLDL in fibroblasts from LAR and HAR rabbits with respect to cellular lipoprotein degradation after PMA pretreatment. Even though the attenuated atherosclerotic response to hypercholesterolemia of LAR rabbits may have multiple underlying causes, the most prominent so far is an apparent difference in inducibility of scavenger receptor in SMC and fibroblasts.

Topics: Animals; Arteriosclerosis; Carbocyanines; Cell Adhesion; Cells, Cultured; Diet, Atherogenic; Endothelium, Vascular; Fibroblasts; Gene Expression Regulation; Humans; Hypercholesterolemia; Lipid Peroxidation; Lipoproteins; Lymphoma, Large B-Cell, Diffuse; Macrophages; Membrane Proteins; Monocytes; Muscle, Smooth, Vascular; Platelet-Derived Growth Factor; Rabbits; Receptors, Immunologic; Receptors, LDL; Receptors, Lipoprotein; Receptors, Scavenger; Scavenger Receptors, Class B; Tetradecanoylphorbol Acetate; Thiobarbituric Acid Reactive Substances; Tumor Cells, Cultured; Vitamin E

Numerous studies have reported successful allotransplantation of hepatocytes. However, none have shown long-term correction of a liver-related metabolic defect. In this study, we used a method of regional hepatocyte transplantation and subsequent induction of transplanted cell proliferation by regeneration response in the transplant-bearing liver lobes. New Zealand White rabbits were used as cell donors and Watanabe heritable hyperlipidemic (WHHL) rabbits were used as cell recipients (2 x 10(8) cells/rabbit). All recipient rabbits were maintained on daily cyclosporine. Two weeks after baseline serum cholesterol determination, group I WHHL rabbits (n = 7) received an infusion of cells into the right lateral liver lobe, and a loose ligature was placed around the portal venous branch supplying the anterior lobe. After 1 week, to allow engraftment, the portal venous branch was ligated, which resulted in the atrophy of the affected liver parenchyma and induction of hyperplasia in the transplant-bearing liver tissue. Group II rabbits (n = 6) were transplanted with New Zealand White hepatocytes without portal branch ligation (PBL) and group III rabbits (n = 4) were subjected to sham transplantation (saline) and PBL. The experimental period extended to 150 days after transplantation. All WHHL rabbits transplanted with normal hepatocytes showed reduction in serum cholesterol and low-density lipoprotein (LDL) levels. Group I (PBL-stimulated) recipients demonstrated a more pronounced and sustained effect than group II animals (P < 0.05). Group III controls showed only a slight, typical for aging decrease in serum cholesterol. Group I recipient livers perfused with LDL labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI) showed much higher numbers of DiI-LDL-positive hepatocytes than those of group II recipients. In conclusion, a liver regeneration stimulus enhanced the population of transplanted hepatocytes and their functional effect in a large animal model of inborn error of liver metabolism.

Topics: Alanine Transaminase; Animals; Carbocyanines; Cell Transplantation; Cholesterol; Fluorescent Dyes; Hypercholesterolemia; Lipoproteins, LDL; Liver; Liver Regeneration; Organ Size; Rabbits

The transport pathways of low density lipoproteins (LDL) across the endothelium at the branched and unbranched regions of the artery were studied in high cholesterol diet-fed rats. Rat tissues were analyzed by perfusing in situ human or rat LDL labeled with colloidal gold or fluorescein 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). Results indicated that more LDL-DiI accumulated in the branched regions than in the unbranched regions of the artery. LDL-gold conjugates were observed in the plasmalemmal vesicles, multivesicular bodies and in the subendothelial space in both the branched and the unbranched regions of the arteries. Quantitative study revealed that the volume densities of plasmalemmal vesicles which contained the LDL-gold particles in the branched regions of the aortic arch were significantly (P < 0.05) higher than the density value in the unbranched regions of the thoracic aorta, whereas there was no marked difference in the density value of multivesicular bodies between these two regions. The open junctions with gap widths of 30-450 nm between adjacent endothelial cells were only observed in the branched regions of the aortic arch, whereas no open junctions were present in the unbranched regions of the thoracic aorta. Moreover, the LDL-gold conjugates were present within most of these open junctions. In all specimens examined, no gold particles were found in the normal intercellular channels (i.e., 25 nm and less) of both regions. These results indicated that the major visible routes for transport of LDL across the endothelium in the branched regions of the arteries are open junctions as well as plasmalemmal vesicles. The region-associated permeability changes of LDL might account for the incidence of atherosclerosis in the branched areas of arteries.

Topics: Animals; Aorta, Thoracic; Biological Transport; Body Weight; Carbocyanines; Cholesterol, Dietary; Diet, Atherogenic; Endothelium, Vascular; Fluorescent Dyes; Humans; Hypercholesterolemia; Immunohistochemistry; Intercellular Junctions; Lipoproteins, LDL; Male; Microscopy, Fluorescence; Rats; Rats, Sprague-Dawley

A flow-cytometric method with fluorescence-labeled monoclonal antibodies (MABs) against the low density lipoprotein (LDL) receptor (C7A MAB) or 3,3'-dioctadecylindocarbocyanin-iodide (DiI) LDL has been developed that allows the quantification of LDL receptors on leukocytes and the identification of patients with familial hypercholesterolemia (FH) within 48 hours. Leukocytes were isolated from 10 mL anticoagulated blood by density gradient centrifugation. To induce maximal expression of LDL receptors, mononuclear cells were preincubated with either phytohemagglutinine (PHA) or lipoprotein-deficient serum (LPDS). LPDS-treated monocytes provided a more homogeneous cell population with regard to LDL receptor activity than did the PHA-treated lymphocytes; they also provided a greater discrimination between the fluorescence of the receptor probes and cellular autofluorescence. The C7A MAB was able to compete for DiI LDL binding by about 40%. In competition with unlabeled LDL, DiI LDL revealed linear binding, indicating an affinity similar to native LDL. The binding characteristics of DiI LDL were also similar to 125I-LDL binding. LDL isolated from familial defective apolipoprotein B-100 was not able to compete for DiI LDL binding on monocytes, whereas native LDL reduced it by about 80%. In monocytes from FH heterozygous patients, the cellular mean fluorescence using either C7A MAB or DiI LDL at 4 degrees C was 30% to 70%; in FH homozygotes, cellular mean fluorescence was less than 20% of that in monocytes from normal individuals. In patients with familial defective apolipoprotein B-100 antibody binding was normal, but one patient's own LDL failed to compete with normal DiI LDL for 4 degrees C binding on U937 test monocytes. Patient monocytes having internalization defects showed normal 4 degrees C DiI LDL binding, but at 20 degrees C cell-associated fluorescence was reduced by about 40%. In our study 384 hypercholesterolemic patients (preselected according to serum cholesterol levels, clinical symptoms, and family history) were analyzed for LDL receptor expression using the C7A MAB-based assay. In 71.8% of the patients with cholesterol levels higher than 300 mg/dL, an LDL receptor deficiency was observed. Apolipoprotein E isoforms and lipoprotein[a] were found to be independent from the LDL receptor status. In some patients with high cholesterol levels but normal LDL receptor expression with the C7A MAB assay, LDL receptor defects could be diagnosed when either

Topics: Adult; Antibodies, Monoclonal; Binding Sites, Antibody; Carbocyanines; Cell Separation; Diagnosis, Differential; Female; Flow Cytometry; Humans; Hypercholesterolemia; Leukocytes, Mononuclear; Male; Monocytes; Receptors, LDL