| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Disruption of cholesterol homeostasis by plant sterols Yang, C., L. Yu, et al. (2004), J Clin Invest 114(6): 813-22. Abstract: The ABC transporters ABCG5 and ABCG8 limit absorption and promote excretion of dietary plant sterols. It is not known why plant sterols are so assiduously excluded from the body. Here we show that accumulation of plant sterols in mice lacking ABCG5 and ABCG8 (G5G8-/- mice) profoundly perturbs cholesterol homeostasis in the adrenal gland. The adrenal glands of the G5G8-/- mice were grossly abnormal in appearance (brown, not white) due to a 91% reduction in cholesterol content. Despite the very low cholesterol levels, there was no compensatory increase in cholesterol synthesis or in lipoprotein receptor expression. Moreover, levels of ABCA1, which mediates sterol efflux, were increased 10-fold in the G5G8-/- adrenals. Adrenal cholesterol levels returned to near-normal levels in mice treated with ezetimibe, which blocks phytosterol absorption. To determine which plant sterol(s) caused the metabolic changes, we examined the effects of individual plant sterols on cholesterol metabolism in cultured adrenal cells. Addition of stigmasterol, but not sitosterol, inhibited SREBP-2 processing and reduced cholesterol synthesis. Stigmasterol also activated the liver X receptor in a cell-based reporter assay. These data indicate that selected dietary plant sterols disrupt cholesterol homeostasis by affecting two critical regulatory pathways of lipid metabolism. |
| Disruption of cholesterol homeostasis in the developing brain as a potential mechanism contributing to the developmental neurotoxicity of ethanol: an hypothesis Guizzetti, M. and L. G. Costa (2005), Med Hypotheses 64(3): 563-7. Abstract: While excess cholesterol may have deleterious consequences, as in the case of atherosclerosis, too little cholesterol may endanger the development of the brain. Different degrees of mental retardation are often observed in inborn errors of cholesterol synthesis, such as the Smith-Lemli-Opitz syndrome or in maternal phenylketonuria, where the metabolite of accumulating phenylalanine, phenylacetate, is an inhibitor of cholesterol synthesis. Lack of cholesterol during brain development as a consequence of these genetic defects leads to severe brain damage, microencephaly and mental retardation, which are also hallmarks of the fetal alcohol syndrome (FAS). The brain relies on the in situ synthesis of cholesterol, which occurs mostly in astrocytes. Astrocyte-produced cholesterol is utilized for cell proliferation, or is released, via astrocyte-secreted high density lipoprotein-like particles containing apolipoprotein E, outside the cell, where it is taken up and utilized by neurons for dendrite outgrowth and to form synapses. We propose the hypothesis that ethanol may disrupt cholesterol homeostasis during brain development, and that this effect may be responsible, at least in part, for the central nervous system dysfunctions observed in the FAS, which include altered astrocyte proliferation, neuronal death and diminished synaptic contacts. |
| Disruption of membrane cholesterol stimulates MyD88-dependent NF-kappaB activation in immature B cells Flemming, J. A., K. H. Perkins, et al. (2004), Cell Immunol 229(1): 68-77. Abstract: Agents that extract or sequester membrane cholesterol stimulate IkappaB degradation and lead to NF-kappaB activation in a subset of B cells. Although the extraction of cholesterol by methyl-beta-cyclodextrin is the most potent stimulus of NF-kappaB, other agents that sequester cholesterol have similar effects. B cells and B cell lines with an immature phenotype are significantly more sensitive to the effects of cholesterol perturbation than their mature B cell counterparts. NF-kappaB activation does not involve signaling from the B cell receptor complex. Instead, the disruption of membrane cholesterol activates NF-kappaB through a MyD88-dependent pathway involving the pattern recognition receptor, Toll-like receptor 4. We suggest that lipid raft microdomains may serve not only to orchestrate receptor signaling, but to sequester signaling components one from one another, which serves to prevent receptor-mediated signaling from occurring. A role for this process during B cell development is suggested. |
| Disruption of nerve tissue cholesterol metabolism in the case of an excess of vitamin A in the growing body Oparina, T. I., A. Bliudzin Iu, et al. (1995), Vopr Med Khim 41(3): 20-3. Abstract: Subcellular distribution and the rate of labelled precursors incorporation into fractions of cholesterol esters were studied in brain and spinal cord of growing rats consuming overdoses of vitamin A. Per os administration of retinyl acetate during 10-16 days of postnatal period at a dose of 1,000 IU resulted in intracellular imbalance of cholesterol content and in distinct increase of cholesterol esters in all the subcellular fractions studied. A decrease of 2-(14)C- acetate incorporation into cholesterol esters of nervous tissue caused by vitamin A overloading was also detected. Analysis of gas chromatograms showed an increase in content of palmitic acid as well as a decrease of unsaturated acids in fractions of cholesterol esters of these animals brain tissues. The impairments of cholesterol metabolism found in nervous tissue of growing body under conditions of retinol overloading may be responsible for deterioration of myelinization. |
| Disruption of the acyl-CoA:cholesterol acyltransferase gene in mice: evidence suggesting multiple cholesterol esterification enzymes in mammals Meiner, V. L., S. Cases, et al. (1996), Proc Natl Acad Sci U S A 93(24): 14041-6. Abstract: The microsomal enzyme acyl-CoA:cholesterol acyltransferase (ACAT; EC 2.3.1.26) catalyzes the esterification of cellular cholesterol with fatty acids to form cholesterol esters. ACAT activity is found in many tissues, including macrophages, the adrenal glands, and the liver. In macrophages, ACAT is thought to participate in foam cell formation and thereby to contribute to atherosclerotic lesion development. Disruption of the gene for ACAT (Acact) in mice resulted in decreased cholesterol esterification in ACAT-deficient fibroblasts and adrenal membranes, and markedly reduced cholesterol ester levels in adrenal glands and peritoneal macrophages; the latter finding will be useful in testing the role of ACAT and macrophage foam cell formation in atherosclerosis. In contrast, the livers of ACAT-deficient mice contained substantial amounts of cholesterol esters and exhibited no reduction in cholesterol esterification activity. These tissue-specific reductions in cholesterol esterification provide evidence that in mammals this process involves more than one form of esterification enzyme. |
| Disruption of the murine lecithin:cholesterol acyltransferase gene causes impairment of adrenal lipid delivery and up-regulation of scavenger receptor class B type I Ng, D. S., O. L. Francone, et al. (1997), J Biol Chem 272(25): 15777-81. Abstract: Lecithin:cholesterol acyltransferase (LCAT) is the major determinant of the cholesteryl ester (CE) content of high density lipoprotein (HDL) in plasma. The selective uptake of HDL-CE is postulated to participate in delivery of tissue-derived cholesterol both to the liver and steroidogenic tissues. Recent studies comparing mice with similarly low levels of HDL, due to the absence of either of the two major HDL-associated apolipoproteins apoA-I and apoA-II, suggest that apoA-I is crucial in modulating this process, possibly through interaction with scavenger receptor class B type I (SR-BI). Because of the central role of LCAT in determining the size, lipid composition, and plasma concentration of HDL, we have created LCAT-deficient mice by gene targeting to examine the effect of LCAT deficiency on HDL structure and composition and adrenal cholesterol delivery. The HDL in the LCAT-deficient mice was reduced in its plasma concentration (92%) and CE content (96%). The HDL particles were heterogeneous in size and morphology and included numerous discoidal particles, mimicking those observed in LCAT-deficient humans. The adrenals of the male Lcat (-/-) mice were severely depleted of lipid stores, which was associated with a 2-fold up-regulation of the adrenal SR-BI mRNA. These studies demonstrate that LCAT deficiency, similar to apoA-I deficiency, is associated with a marked decrease in adrenal cholesterol delivery and supports the hypothesis that adrenal SR-BI expression is regulated by the adrenal cholesterol. |
| Disruption of the sterol carrier protein 2 gene in mice impairs biliary lipid and hepatic cholesterol metabolism Fuchs, M., A. Hafer, et al. (2001), J Biol Chem 276(51): 48058-65. Abstract: Hepatic up-regulation of sterol carrier protein 2 (Scp2) in mice promotes hypersecretion of cholesterol into bile and gallstone formation in response to a lithogenic diet. We hypothesized that Scp2 deficiency may alter biliary lipid secretion and hepatic cholesterol metabolism. Male gallstone-susceptible C57BL/6 and C57BL/6(Scp2(-/-)) knockout mice were fed a standard chow or lithogenic diet. Hepatic biles were collected to determine biliary lipid secretion rates, bile flow, and bile salt pool size. Plasma lipoprotein distribution was investigated, and gene expression of cytosolic lipid-binding proteins, lipoprotein receptors, hepatic regulatory enzymes, and intestinal cholesterol absorption was measured. Compared with chow-fed wild-type animals, C57BL/6(Scp2(-/-)) mice had higher bile flow and lower bile salt secretion rates, decreased hepatic apolipoprotein expression, increased hepatic cholesterol synthesis, and up-regulation of liver fatty acid-binding protein. In addition, the bile salt pool size was reduced and intestinal cholesterol absorption was unaltered in C57BL/6(Scp2(-/-)) mice. When C57BL/6(Scp2(-/-)) mice were challenged with a lithogenic diet, a smaller increase of hepatic free cholesterol failed to suppress cholesterol synthesis and biliary cholesterol secretion increased to a much smaller extent than phospholipid and bile salt secretion. Scp2 deficiency did not prevent gallstone formation and may be compensated in part by hepatic up-regulation of liver fatty acid-binding protein. These results support a role of Scp2 in hepatic cholesterol metabolism, biliary lipid secretion, and intracellular cholesterol distribution. |
| Dissecting the role of the golgi complex and lipid rafts in biosynthetic transport of cholesterol to the cell surface Heino, S., S. Lusa, et al. (2000), Proc Natl Acad Sci U S A 97(15): 8375-80. Abstract: In this study, we compared the transport of newly synthesized cholesterol with that of influenza virus hemagglutinin (HA) from the endoplasmic reticulum to the plasma membrane. The arrival of cholesterol on the cell surface was monitored by cyclodextrin removal, and HA transport was monitored by surface trypsinization and endoglycosidase H digestion. We found that disassembly of the Golgi complex by brefeldin A treatment resulted in partial inhibition of cholesterol transport while completely blocking HA transport. Further, microtubule depolymerization by nocodazole inhibited cholesterol and HA transport to a similar extent. When the partitioning of cholesterol into lipid rafts was analyzed, we found that newly synthesized cholesterol began to associate with low-density detergent-resistant membranes rapidly after synthesis, before it was detectable on the cell surface, and its raft association increased further upon chasing. When cholesterol transport was blocked by using 15 degrees C incubation, the association of newly synthesized cholesterol with low-density detergent-insoluble membranes was decreased and cholesterol accumulated in a fraction with intermediate density. Our results provide evidence for the partial contribution of the Golgi complex to the transport of newly synthesized cholesterol to the cell surface and suggest that detergent-resistant membranes are involved in the process. |
| Dissemination of guidelines on cholesterol. Effect on patterns of practice of general practitioners and family physicians in Ontario. Ontario Task Force on the Use and Provision of Medical Services Rosser, W. W. and W. H. Palmer (1993), Can Fam Physician 39: 280-4. Abstract: A telephone survey of a random sample of Ontario family physicians was conducted 6 to 8 months after disseminating evidence-based guidelines for screening and managing asymptomatic hypercholesterolemia. Seventy-eight percent of respondents stated they followed these guidelines. However, specific questions revealed as few as 5% of respondents actually followed the guidelines. |
| Dissemination of peroxidative stress via intermembrane transfer of lipid hydroperoxides: model studies with cholesterol hydroperoxides Vila, A., W. Korytowski, et al. (2000), Arch Biochem Biophys 380(1): 208-18. Abstract: Lipid hydroperoxides (LOOHs) can be generated in cells when cholesterol (Ch) and other unsaturated lipids in cell membranes are degraded under conditions of oxidative stress. If LOOHs escape reductive detoxification by glutathione-dependent selenoperoxidases, they may undergo iron-catalyzed one-electron reduction to free radical species, thus triggering peroxidative chain reactions which exacerbate oxidative membrane damage. LOOHs are more polar than parent lipids and much longer-lived than free radical precursors or products. Accordingly, intermembrane transfer of LOOHs (analogous to that of unoxidized precursors) might be possible, and this could jeopardize acceptor membranes. We have investigated this possibility, using photoperoxidized (14)CCh-labeled erythrocyte ghosts as cholesterol hydroperoxide (ChOOH) donors and unilamellar liposomes e.g., dimyristoyl-phosphatidylcholine/Ch, 9:1 mol/mol as acceptors. ChOOH material consisted mainly of 5alpha-hydroperoxide, a singlet oxygen adduct. Time-dependent transfer of ChOOH versus Ch at 37 degrees C was determined, using high-performance liquid and thin-layer chromatographic methods to analyze liposomal extracts for these species. A typical experiment in which the starting ChOOH/Ch mol ratio in ghosts was approximately 0.05 showed that the initial transfer rate of ChOOH was approximately 16 times greater than that of parent Ch. Using (14)CCh as a reporter in liposome acceptors, we found that transfer-acquired ChOOHs, when exposed to a lipophilic iron chelate and ascorbate, could trigger strong peroxidative chain reactions, as detected by accumulation of (14)CCh oxidation products. These findings support the hypothesis that intermembrane transfer of ChOOHs can contribute to their prooxidant membrane damaging and cytotoxic potential. |
| Dissociation between postprandial lipemia and high density lipoprotein cholesterol concentrations in endurance-trained men Cohen, J. C., J. Stray-Gundersen, et al. (1991), Arterioscler Thromb 11(4): 838-43. Abstract: Previous studies have indicated an inverse relation between circulating high density lipoprotein (HDL) concentrations and the rate of chylomicron clearance. Because chronic exercise has been shown to augment chylomicron clearance, we measured HDL cholesterol concentrations and plasma triglyceride and retinyl palmitate responses to high- (140 g) and low- (50 g) fat meals in endurance-trained men. Plasma HDL cholesterol concentrations in these men ranged from 36 to 105 mg/dl. Intraindividual variation in the cholesterol concentration of the HDLs occurred primarily in HDL2. The magnitude of postprandial lipemia induced by both the high- and the low-fat meals was uniformly low compared with values reported previously for sedentary men and was not correlated with HDL cholesterol concentrations. Postprandial retinyl palmitate concentrations, which reflect chylomicron remnant metabolism, also showed no correlation with HDL cholesterol concentrations. These data indicate that the degree of postprandial lipemia is not the primary determinant of HDL cholesterol concentrations in endurance-trained men. Accordingly, the wide range of HDL cholesterol concentrations measured in these men must be attributable to other factors. |
| Dissolution of calcium bilirubinate and calcium carbonate debris remaining after methyl tert-butyl ether dissolution of cholesterol gallstones Nelson, P. E., T. P. Moyer, et al. (1990), Gastroenterology 98(5 Pt 1): 1345-50. Abstract: Methyl tert-butyl ether rapidly dissolves cholesterol gallstones, although insoluble debris may remain. Total gallstone dissolution could be achieved if safe solvents for these noncholesterol components can be developed. We evaluated the in vitro ability of ethylenediaminetetraacetic acid, citrate, dimethyl sulfoxide, and ionic or nonionic detergents to dissolve the predominantly calcium bilirubinate and calcium carbonate debris remaining after methyl tert-butyl ether gallstone dissolution. Ethylenediaminetetraacetic acid 1% or 2% at pH 9.5 was the most effective of the solvents studied for dissolving calcium and bile pigment. The addition of cholate (25-200 mM) or polysorbate (1%-10%) to ethylenediaminetetraacetic acid 1% at pH 9.5 enhanced pigment dissolution compared to ethylenediaminetetraacetic acid alone. Dissolution of pellets prepared from human gallstones and composed predominantly of either calcium bilirubinate or calcium carbonate was 80% and 85% at 4 h using ethylenediaminetetraacetic acid 1% plus polysorbate-20 1% at pH 9.5. We conclude that ethylenediaminetetraacetic acid, either alone or with a detergent, is an effective solvent for methyl tert-butyl ether-insoluble gallstone debris and deserves assessment in vivo. |
| Dissolution of cholesterol gall stones using methyltertbutyl ether: a safe effective treatment McNulty, J., A. Chua, et al. (1991), Gut 32(12): 1550-3. Abstract: Methyltertbutyl ether (MTBE) administered by percutaneous transhepatic catheter rapidly dissolves radiolucent cholesterol gall bladder stones. However, complete dissolution and clearance of non-cholesterol debris is essential to prevent recurrence. In this study we analysed 25 consecutive patients with reference to efficacy and recurrence based on the presence or absence of non-cholesterol stone fragments after dissolution. Placement of the catheter was successful in 24 patients, one patient requiring cholecystectomy for bile peritonitis. MTBE was infused and aspirated continuously, four to six cycles per minute, resulting in rapid stone dissolution (median six hours; range 4-23 hours for solitary stones and median seven hours, range 4-30 hours for multiple stones). In 18 patients who had complete dissolution, four (22%) had recurrent stones within six to 18 months. Five patients had residual debris which failed to clear completely despite bile acid treatment. One patient with an incomplete rim of calcium in a large stone did not respond to MTBE treatment. A further patient required cholecystectomy for symptomatic recurrence. There were no serious side effects observed. MTBE treatment is a rapid, safe, and effective treatment for patients who refuse surgery or who for medical reasons cannot undergo cholecystectomy. The results of this study confirm that complete dissolution of all fragments is essential and may prevent recurrence. |
| Dissolution of cholesterol gallbladder stones with methyl tert-butyl ether in patients with increased surgical risk Eidsvoll, B. E., E. Aadland, et al. (1993), Scand J Gastroenterol 28(8): 744-8. Abstract: The safety and efficacy of methyl tert-butyl ether (MTBE) dissolution of cholesterol gallbladder stones were evaluated in 25 patients with increased risk for surgery. Two patients were treated twice. The MTBE was infused and aspirated manually through a percutaneous transhepatic catheter to the gallbladder. The placement of the catheter failed in three patients (11%). In 19 of 24 patients (79%) there was complete dissolution of stones after a mean treatment time of 12.2 h (range, 4.3-19.5 h). In five patients treatment was discontinued before complete dissolution owing to technical problems or side effects. Side effects were nausea, pain, vasovagal reaction, and fever. Fifteen patients were followed up for a mean of 15.7 months after dissolution. Stone recurrence was found in eight patients, five of whom suffered symptomatic relapse. We conclude that dissolution therapy with MTBE is a safe and adequate alternative to surgery in selected high-risk patients. |
| Dissolution of cholesterol gallstones in mice by the oral administration of a fatty acid bile acid conjugate Gilat, T., A. Leikin-Frenkel, et al. (2002), Hepatology 35(3): 597-600. Abstract: Gallstones, mostly cholesterol stones, affect some 15% of the population. Oral bile salts dissolve human cholesterol gallstones, but with low efficacy, and surgery remains the main therapeutic option. Fatty acid bile acid conjugates (FABACs) were shown to prevent formation of cholesterol gallstones in experimental animals. The aim of this study was to test whether these compounds could dissolve preexisting cholesterol gallstones via oral administration. Inbred, gallstone-susceptible C57J/L mice were given a lithogenic diet for 2 months, and the presence of gallstones was ascertained. The mice were then switched to a regular diet while part of them were given in addition C20-FABAC, by gavage, at a dose of 0.5 or 3 mg per animal per day. All mice tested had cholesterol gallstones after 2 months on the lithogenic diet. In study I, after 2 months on the regular diet, 3 of 4 (75%) of the controls had gallstones, whereas none of the 6 FABAC-fed animals (3 mg/d) had stones (P =.033). In study II, evaluating 2 FABAC doses, after 2 months on the regular diet, 8 of 8 (100%) of the controls had gallstones, which were found in 2 of 7 (28%) and 1 of 8 (12%) of the mice supplemented with 0.5 mg/d (P =.007) or 3 mg/d (P =.001) FABAC, respectively. On a molar basis, the dose of 0.5 mg FABAC is equivalent to 14 mg/kg/d of a bile acid. In conclusion, FABACs given orally can dissolve preexisting cholesterol gallstones in mice. This was accomplished with a dose of FABAC equivalent to the dose of bile acids used in human gallstone dissolution. |
| Dissolution of cholesterol gallstones using methyl tert-butyl ether Williams, H. J., Jr., C. E. Bender, et al. (1990), Cardiovasc Intervent Radiol 13(4): 272-7. Abstract: Symptomatic cholelithiasis affects a large segment of the population. Several nonoperative therapeutic alternatives for treatment of these gallstones have recently been developed. We present here the technical aspects and results of gallstone dissolution in 75 patients with the use of methyl tert-butyl ether (MTBE) administered via a small percutaneously placed cholecystostomy catheter. Successful stone dissolution was achieved in 69 patients. The average time required for stone dissolution was 12.4 h over an average of 2.4 days, with the success and rate of dissolution being very dependent on technique. Six patients have developed recurrent gallstones. Future efforts will focus on decreasing the labor intensity of the procedure, dealing with the noncholesterol components of gallstones, and preventing gallstone recurrence. |
| Dissolution of human cholesterol gallstones in bile salt/lecithin mixtures: effect of bile salt hydrophobicity and various pHs Angelico, M., L. Mogavero, et al. (1995), Scand J Gastroenterol 30(12): 1178-85. Abstract: BACKGROUND: Unconjugated bile salts currently available for gallstone dissolution are poorly effective. We evaluated in vitro the litholytic potency of taurine-amidated bile salts against human cholesterol gallstones. METHODS: Seventy radiolucent gallstones with similar size and composition (cholesterol content, 70.1 +/- 0.9%) from a single patient were incubated in model biles composed of 100 mM of either taurochenodeoxycholate (TCDC), taurocholate (TC), taurohyodeoxycholate (THDC) or tauroursodeoxycholate (TUDC) and of 45 mM egg yolk lecithin in saline buffered with tris/HCl (at pHs 7 and 8) or phosphate (at pHs 4 and 6). Biles (total lipids, 10 g/dl; cholesterol saturation, 99%) were incubated at 37 degrees C for 40 days. Gallstones were periodically weighed and returned to the dissolution vials, and the biliary cholesterol concentration was monitored. RESULTS: Model biles remained optically clear during the initial 48 h of incubation. Then, biles containing THDC and TUDC, but not those with TC and TCDC, became progressively turbid until, after several days, a white precipitate surrounded the residual stone. Abundant liquid crytalline droplets were observed at polarizing microscopy in biles containing TUDC and THDC. Gallstone dissolution was closely related to cholesterol solubilization and decreased in the order TCDC > THDC > or = TC > TUDC, being highest at pH 8. At the physiologic pH of 7 THDC was more litholythic than TC. CONCLUSIONS: In vitro, the litholytic potency of bile salts on cholesterol gallstones primarily depends on their hydrophobicity. THDC is a new potential gallstone-dissolving agent, deserving in vivo studies. |
| Dissolution rate of cholesterol and palmitic acid mixtures in cholelitholytic cosolvent systems O'Reilly, E. B. and O. I. Corrigan (1995), J Pharm Sci 84(2): 203-7. Abstract: The dissolution rates and solubilities of cholesterol monohydrate, palmitic acid, and their mixtures in the cholelitholytic solvents monooctanoin (MO) and methyl tert-butyl ether (MTBE) and mixtures of these two solvents were determined. The dissolution rates obtained were consistent with the diffusion-controlled two-component noninteracting model. The addition of MTBE as cosolvent to MO resulted in an increase in the solubility of both cholesterol monohydrate and palmitic acid; in the case of the former, the solubility peaked at 80% MTBE. Neither solute exhibited a log-linear solubility relationship on addition of MTBE as cosolvent. Furthermore the increases in the dissolution rates of both components were much larger than could be explained by the solubility increases alone. Mass transfer coefficients increased dramatically with increasing MTBE content of the solvent, were consistently higher for palmitic acid, and reflected the decline in solvent viscosity. Incorporation of relationships among solubility, viscosity, and cosolvent composition into the two-component noninteracting model gave good correlation between predicted and observed rates over nearly 3 orders of magnitude. |
| Distinct endosomal compartments in early trafficking of low density lipoprotein-derived cholesterol Sugii, S., P. C. Reid, et al. (2003), J Biol Chem 278(29): 27180-9. Abstract: We previously studied the early trafficking of low density lipoprotein (LDL)-derived cholesterol in mutant Chinese hamster ovary cells defective in Niemann-Pick type C1 (NPC1) using cyclodextrin (CD) to monitor the arrival of cholesterol from the cell interior to the plasma membrane (PM) (Cruz, J. C., Sugii, S., Yu, C., and Chang, T.-Y. (2000) J. Biol. Chem. 275, 4013-4021). We found that newly hydrolyzed cholesterol derived from LDL first appears in certain CD-accessible pool(s), which we assumed to be the PM, before accumulating in the late endosome/lysosome, where NPC1 resides. To determine the identity of the early CD-accessible pool(s), in this study, we performed additional experiments, including the use of revised CD incubation protocols. We found that prolonged incubation with CD (>30 min) caused cholesterol in internal membrane compartment(s) to redistribute to the PM, where it became accessible to CD. In contrast, a short incubation with CD (5-10 min) did not cause such an effect. We also show that one of the early compartments contains acid lipase (AL), the enzyme required for liberating cholesterol from cholesteryl ester in LDL. Biochemical and microscopic evidence indicates that most of the AL is present in endocytic compartment(s) distinct from the late endosome/lysosome. Our results suggest that cholesterol is liberated from LDL cholesteryl ester in the hydrolytic compartment containing AL and then moves to the NPC1-containing late endosome/lysosome before reaching the PM or the endoplasmic reticulum. |
| Distinct immuno-localization of mucin and other biliary proteins in human cholesterol gallstones de la Porte, P. L., N. Domingo, et al. (1996), J Hepatol 25(3): 339-48. Abstract: BACKGROUND/AIMS: Cholesterol gallstones consist of cholesterol crystals and smaller amounts of pigments and calcium salts, arrayed on a mucin plus protein matrix. The localization of the various biliary proteins in the stones has not been characterized. We aimed to localize several biliary proteins in gallstones in order to determine their possible role in stone formation and growth. METHODS: The distribution of several matrix proteins and their relationships to the minerals were determined using immunostaining and EDAX microanalysis on hemisected cholesterol gallstones. RESULTS: Pigment areas were rich in calcium and contained Cu, P and S. These elements were absent in cholesterol regions. Mucin was identified in a three-dimensional network intercalated between cholesterol crystals and as septa between deposits of pigments and cholesterol; APF/CBP and ApN coated only the pigment deposits. No specific topographical localization was found for albumin or IgA. CONCLUSIONS: This suggests a role for mucin, APF/ CBP and ApN in the formation of cholesterol gallstones. We propose that cholesterol crystals bind directly to mucin, whereas calcium salts and pigments deposit on APF/CBP and ApN bind to the mucin. |