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Quantification of low density lipoprotein binding and cholesterol accumulation by single human fibroblasts using fluorescence microscopy.

Using fluorescence microscopy, we have quantified low density lipoprotein (LDL) binding by indirect immunofluorescence and cellular cholesterol with the fluorescent sterol-binding polyene, filipin, in individual cultured human fibroblasts from normal subjects and from patients with heterozygous and homozygous familial hypercholesterolemia. LDL binding by fibroblasts from heterozygous patients was about 40% of that of the normal cells, and cholesterol accumulation upon incubation with LDL was decreased to a similar degree. Most fibroblasts from homozygous patients bound no detectable LDL and only rare cells demonstrated any accumulation of cholesterol after incubation with LDL.

Cells, Cultured↗

Differential effect of imidazole antibiotics on untransformed and virus-transformed rat cell lines.

The imidazole antimycotics clotrimazole and miconazole were tested on untransformed rat cell line 3Y1-B clone 1-6 (3Y1) and six transformed cell lines, which were independently isolated from 3Y1 or 3Y1-B clone 1 after infection with adenovirus 12 (AD-12) or with SV40, to determine their sensitivities to these drugs. The relative plating efficiency of three cell lines (T3, W4, and W5) transformed with AD-12 was reduced to 10(-1( of the initial value by clotrimazole (2 to 4 microgram/ml), whereas that of the parental cell line 3Y1 was reduced to 10(-1) of the initial value by clotrimazole (20 to 25 microgram/ml). By contrast, the differential effect of miconazole on 3Y1 and AD-12-transformed cell lines was found to be a factor of 2. The sensitivity of the SV40-transformed 3Y1 and the AD-12-transformed cell lines. The cellular sensitivity of untransformed 3Y1 cells to clotrimazole was significantly enhanced when exposed to various doses of the unsaturated fatty acid, linoleic acid. The untransformed and transformed cell lines showed sensitivities similar to the cytocidal activity of sterol-binding antimycotics, amphotericin B and filipin.

Amphotericin B↗

Differential effect of amphotericin B on the three evolutive stages of Trypanosoma cruzi and on the host cell-parasite interaction.

1. Amphotericin B (Am.B) was shown to have a direct effect on T. cruzi, with the three forms of the parasite presenting different susceptibilities to the drug in the following order: amastigotes > trypomastigotes > epimastigotes. These differences highlight the importance of using the vertebrate forms of the parasite in tests of new drugs. 2. The treated parasites showed alterations of the plasma membrane, suggesting that, as in fungi, the primary effect of Am.B was probably via formation of complexes with membrane components. 3. When exposed to filipin, another polyene antibiotic, the three parasite forms were observed to present a similar order of susceptibility, with comparable ultrastructural modifications. 4. Higher concentrations of Am.B were required to damage the intracellular parasites in vitro, 2.3 micrograms/ml for parasites inside peritoneal macrophages and 7 micrograms/ml for parasites inside heart muscle cells. 5. Am.B is effective against the parasite, but is also toxic to mammalian cells. Testing of Am.B for the control of Chagas' disease by blood transfusion may be useful, since bloodstream forms are lysed by lower concentrations of the drug than those required to affect intracellular parasites.

Amphotericin B↗

Genetic heterogeneity in Niemann-Pick C disease: a study using somatic cell hybridization and linkage analysis.

The primary molecular defect underlying Niemann-Pick C disease (NPC) is still unknown. A wide spectrum of clinical and biochemical phenotypes has previously been documented. Indication of genetic heterogeneity has recently been provided for one patient. In the present study, somatic cell hybridization experiments were carried out on skin fibroblast cultures from 32 unrelated NPC patients covering the range of known clinical and biochemical phenotypes. The criterion for complementation was the restoration of a normal intracellular fluorescent pattern in polykaryons stained with filipin to document cholesterol distribution. Crosses between the various cell lines revealed a major complementation group comprising 27 unrelated patients and a second minor group comprising 5 patients. Linkage analysis in one multiplex family belonging to the minor complementation group showed that the mutated gene does not map to the 18q11-12 region assigned to the major gene. Patients in the first group spanned the whole spectrum of clinical and cellular phenotypes. No consistent clinical or biochemical phenotypes was associated with the second complementation group. Three of the five group 2 patients, however, presented with a new rare phenotype associated with severe pulmonary involvement leading to death within the first year of life. No biochemical abnormality specific of either group could be demonstrated with regard to tissue lipid storage pattern, intralysosomal cholesterol storage, and regulation of cholesterol homeostasis. Mutations affecting at least two different genes have thus been shown to underlie NPC. The two gene products may function together or sequentially in a common metabolic pathway affecting intracellular cholesterol transport.

Adolescent↗

Transport of cholesterol from the endoplasmic reticulum to the plasma membrane is constitutive in CaCo-2 cells and differs from the transport of plasma membrane cholesterol to the endoplasmic reticulum.

The transport of newly synthesized cholesterol from its site of synthesis, the endoplasmic reticulum, to the plasma membrane was studied in CaCo-2 cells. The appearance of newly synthesized cholesterol on the cell surface was rapid. By 30 min, 50% of the total labeled cholesterol was observed in the plasma membrane. The arrival of cholesterol at the plasma membrane was independent of new protein synthesis, a functional Golgi apparatus, or microtubular function. Progesterone, verapamil, and trifluoperazine, inhibitors of p-glycoprotein which are known to inhibit cholesterol transport from the plasma membrane to the endoplasmic reticulum, reduced the amount of newly synthesized cholesterol reaching the plasma membrane. The p-glycoprotein inhibitors, however, caused the accumulation of sterol intermediates in the plasma membrane, suggesting that sterol trafficking to the plasma membrane remained intact, but that trafficking from the plasma membrane to the endoplasmic reticulum was disrupted. In contrast, nigericin, another potent inhibitor of cholesterol movement from the plasma membrane to the endoplasmic reticulum, did not alter the transport of newly synthesized cholesterol to the plasma membrane. Moreover, promoting cholesterol transport from the plasma membrane to the endoplasmic reticulum by sphingomyelin hydrolysis or by micellar cholesterol influx did not alter the percent of newly synthesized cholesterol transported to the plasma membrane. Likewise, preventing plasma membrane cholesterol from reaching the endoplasmic reticulum by incubating cells with lysophosphatidylcholine, filipin, or digitonin did not alter the arrival of newly synthesized cholesterol to the plasma membrane. The results suggest that the amount of cholesterol moving to the plasma membrane from the endoplasmic reticulum is constitutive and regulated at the level of cholesterol synthesis and not at the level of the transport process. The pathways of cholesterol transport to and from the plasma membrane are distinct.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Adult-onset Niemann-Pick type C disease. Clinical, biochemical, and genetic study.

BACKGROUND: Niemann-Pick type C disease is an autosomal recessive neurometabolic disorder of unknown origin mapped to chromosome 18q11-12 in most of the studied families. In contrast to the sphingomyelin lipidoses, in Niemann-Pick type C disease, fibroblasts are impaired in intracellular homeostatic responses to exogenous low-density lipoprotein (LDL) cholesterol. Biochemical heterogeneity of the disorder in relation to abnormal LDL processing is associated with various clinical presentations, but adult-onset Niemann-Pick type C disease is rare and has not been comprehensively characterized. OBJECTIVE: To describe clinical, biochemical, and genetic features of adult-onset Niemann-Pick type C disease in 3 siblings. DESIGN AND SETTING: Case series in a tertiary care center. PATIENTS: The 3 siblings manifested a variable combination of vertical supranuclear ophthalmoplegia, ataxia, and splenomegaly. Brain magnetic resonance imaging showed cerebellar atrophy; brainstem auditory evoked responses were unobtainable, and bone marrow examination disclosed typical foam cells. The patients were 20, 26, and 28 years old and belonged to a sibship of 13 born of consanguineous healthy parents. METHODS: Esterification of exogenous LDL cholesterol in cultured skin fibroblasts and filipin staining for free intracellular cholesterol. Polymerase chain reaction-based DNA linkage study using AC microsatellite markers D18S40, D18S44, D18S480, and D18S66. RESULTS: Fibroblasts of the 3 patients showed a 23% to 58% block in the induced cholesterol esterification after 4 1/2 hours and a mild to moderate accumulation of free cholesterol. DNA study demonstrated linkage to the major 18q11-12 Niemann-Pick type C locus and identified unaffected carriers. CONCLUSIONS: These results confirm the diagnosis of the least biochemically affected Niemann-Pick type C phenotype in this family with adult-onset disease and support a correlation between the mild laboratory and clinical findings in this age group.

Adult↗

Schnyder corneal crystalline dystrophy: description of a new family with evidence of abnormal lipid storage in skin fibroblasts.

Schnyder corneal crystalline dystrophy (SCCD) comprises corneal opacities often associated with precocious arcus senilis and genua valga. The metabolic defect seems to be related to abnormal lipid storage in the central part of the cornea, especially the anterior stroma, consisting mainly of nonesterified cholesterol. Plasma lipid levels are not always increased suggesting that the disease may be due to abnormal lipid metabolism limited to the cornea. We observed a family with typical SCCD, in 1 case associated with mental retardation and mild cerebellar hypoplasia. Results of serum lipid analysis of all patients were normal. Ultrastructural study of a skin biopsy specimen and fibroblast pellet showed membrane-bound spherical vacuoles containing lipid material. Cultured fibroblasts stained by filipin, a fluorescent probe that specifically binds unesterified cholesterol, showed abnormal cytoplasmic fluorescent material, suggesting abnormal cholesterol metabolism. The presence of neurological impairment, associated with SCCD in 1 of our cases, may be regarded as coincidental. Evidence of storage lipids in skin and cultured fibroblasts suggests that the disorder of intracellular cholesterol metabolism is not limited to the cornea and that skin biopsy may be a useful method to confirm the diagnosis.

Adult↗

Niemann-Pick disease type C: two cases and an update.

We describe two patients with juvenile-onset Niemann-Pick disease type C (NPC) to illustrate the variable neurologic features of this condition. One presented with hypersplenism at age 10 and was misdiagnosed with Gaucher disease. He developed complex partial seizures in his teens but remained otherwise neurologically asymptomatic until his mid 30s. At age 45, he had mild dementia and dysarthria, vertical supranuclear ophthalmoplegia, axonal sensorimotor polyneuropathy, and cerebellar ataxia. The second patient presented with rapidly progressive dystonia at age 8, and mild hepatosplenomegaly, vertical supranuclear ophthalmoplegia, severe behavioral disorder, and dementia by age 14. The diagnosis of NPC was based on deficient cholesterol esterification and excessive lysosomal filipin staining in cultured skin fibroblasts. Current notions about diagnosis and pathogenesis of NPC are reviewed.

Adolescent↗

Frontal lobe atrophy due to a mutation in the cholesterol binding protein HE1/NPC2.

This is the first description of slowly progressive Niemann-Pick disease type C (NPC) without the typical lysosomal storage in bone marrow and viscera in two descendants of a group of 17th century French-Canadians. The index patient was a married 43-year-old woman with onset of dementia in her thirties, later followed by the development of ataxia and athetoid movements. Her autopsy disclosed frontal lobe atrophy, neurolysosomal storage with oligolamellar inclusion and tau-positive neurofibrillary tangles. Of the 119 family members screened, only a married 42-year-old sister displayed symptoms of a dementia. Both women displayed vertical supranuclear ophthalmoplegia; expressive aphasia; concrete, stimulus-bound, perseverative behavior; and impaired conceptualization and planning. Cultured fibroblasts showed decreased cholesterol esterification and positive filipin staining, but no mutation was detected in coding or promoter regions of the NPC1 gene using conformation sensitive gel electrophoresis and sequencing. Sequencing showed a homozygous gene mutation that is predicted to result in an amino acid substitution, V39M, in the cholesterol binding protein HE1 (NPC2). Adult-onset NPC2 with lysosomal storage virtually restricted to neurons represents a novel phenotypic and genotypic variant with diffuse cognitive impairment and focal frontal involvement described for the first time.

Adult↗

Antifibroblast antibodies from systemic sclerosis patients are internalized by fibroblasts via a caveolin-linked pathway.

OBJECTIVE: Fibroblast activation is a crucial event in the development of systemic sclerosis (SSc). Antifibroblast autoantibodies (AFAs), detectable in the sera of SSc patients, are able to induce a proinflammatory phenotype on cultured fibroblasts. This study was undertaken to investigate the mechanisms of the interaction between AFAs and living fibroblasts. METHODS: We coupled to fluorescein 1) IgG purified from AFA-positive and AFA-negative SSc sera (as assessed by cellular enzyme-linked immunosorbent assay) and 2) single healthy donor and pooled normal IgG. The interaction of IgG with living cultured fibroblasts from healthy individuals and from a patient with SSc was visualized by real-time confocal microscopy. Intracellular colocalization of caveolin and internalized AFA-positive IgG was assessed by immunofluorescence. RESULTS: AFA-positive IgG bound to living fibroblasts and was internalized with a cytoplasmic fibrillar pattern, in contrast to AFA-negative IgG. In the IgG tested, no correlation with antinuclear antibody activity was found. Preincubation of fibroblasts with normal IgG did not affect internalization. Internalized AFA-positive IgG colocalized with caveolin, and internalization was entirely inhibited by disassembling fibroblast caveolae with filipin. CONCLUSION: The finding that both normal and pathologic fibroblasts specifically internalized AFA-positive, but not AFA-negative, IgG demonstrates that AFAs in SSc patient sera interact with constitutively expressed membrane molecules on fibroblasts, via an Fc-independent mechanism. The results of colocalization and inhibition experiments suggest that microdomains containing caveolin are involved in the interaction between AFAs and fibroblasts. These data, together with the reported ability of AFAs to activate fibroblasts, provide evidence for a role of AFAs in the pathogenesis of SSc.

Adult↗

Chlordecone is a potent in vitro inhibitor of oligomycin-insensitive Mg2+ -ATPase of rat bile canaliculi-enriched fraction.

The oligomycin-insensitive Mg2+ -ATPase (OIMATPase) of rat bile canaliculi-enriched fraction (BCEF) was inhibited by chlordecone (CD) in vitro (IC-50 = 25 microM). Kinetic analysis indicated noncompetitive inhibition. Inhibition of OIMATPase by filipin but not by atractyloside verified plasma membrane origin of activity. The cholestatic agents alpha-naphthyl isothiocyanate (ANIT) and taurolithocholate (TLC) decreased OIMATPase activity at in vitro concentrations of 33 and 162 microM, while taurocholate (a choleretic bile salt), ethynylestradiol, and manganese did not. Cholestatic drugs with primary intracellular sites of action (colchicine and phalloidin) were ineffective OIMATPase inhibitors in this concentration range. Inhibition of OIMATPase by N-ethylmaleimide (NEM) and dicyclohexylcarbodiimide (DCCD) indicated some H+ -ATPase activity in BCEF. In vitro sensitivity of OIMATPase of BCEF to CD, ANIT, and TLC suggested the bile canaliculus as a subcellular-level target for their cholestatic actions.

Animals↗

Amphotericin B resistance is recessive in Chinese hamster hybrid cells.

Previous studies from our laboratory have shown that Chinese hamster V79 cells mutated to high level resistance to amphotericin B have a lower cellular level of cholesterol, the target molecule for the polyene antibiotic. Two amphotericin B-resistant (AMBR) mutants were each hybridized to their parental amphotericin B-sensitive (AMBS) V79 cells. All the hybrids derived from AMBR/AMBS fusions were as sensitive to polyene antibiotics (amphotericin B, filipin, and pimaricin) as AMBS cells or AMBS/AMBS hybrids. The AMBR/AMBS hybrids were found to contain cholesterol per phospholipids that is comparable to those in AMBS or AMBS/AMBS. The analysis of hybrids formed between mutant and wild-type cells thus indicated that resistance to amphotericin B is a recessive marker, and that the cellular level of cholesterol is compensated in the AMBS/AMBR hybrids. Hybrids of AMBR and AMBR cells were all resistant, so that the three AMBR mutants all fell into a single complementation group.

Amphotericin B↗

Internalization and trafficking of the human and rat growth hormone-releasing hormone receptor.

Internalization and intracellular trafficking of the growth hormone-releasing hormone receptor (GHRH-R) were studied in rat anterior pituitary and human (h) and rat (r) GHRH-R-transfected BHK cells, with the GHRH agonist, [N(alpha)-5-carboxyfluoresceinyl-D-Ala(2), Ala(8), Ala(15), Lys(22)]hGHRH(1-29)NH(2) (Fluo-GHRH). Time- and temperature-dependent internalization of stimulated GHRH-R was blocked by phenyl arsine oxide (PAO) in both cell types. In anterior pituitary and rGHRH-R-transfected BHK cells, only filipin III and cerulenin blocked receptor-mediated internalization of Fluo-GHRH while in hGHRH-R-transfected BHK cells, only hyperosmolar sucrose inhibited this process. These results suggest that hGHRH-R internalization is clathrin-dependent, while fatty acid acylation of rGHRH-R appears to be a prerequisite to caveolin-dependent internalization. Experiments in anterior pituitary using Bodipy-FL-C(5) ganglioside GM1, a specific marker of lipid rafts such as caveolae, confirmed this latter pathway. Co-localization of Fluo-GHRH with LysoTracker indicated that Fluo-GHRH was directed to acidic organelles in both cell types. Finally, studies using cycloheximide and monensin showed that upon stimulation with GHRH, an optimal concentration of functional GHRH-R was maintained at the plasma membrane due to de novo synthesis and recycling in pituitary cells and to de novo synthesis solely in hGHRH-R-transfected BHK cells. This first study on the dynamics of the GHRH/GHRH-R complexes using fluorescence imaging in a native environment compared to cell system models, revealed that both receptor primary structure and concentration at the plasma membrane play important roles in internalization and trafficking of specific G-protein-coupled receptors (GPCR).

Animals↗

Lipopolysaccharide accelerates caspase-independent but cathepsin B-dependent death of human lung epithelial cells.

Caspase-independent cell death has drawn increasing attention. In the present study, we found that lipopolysaccharide (LPS) accelerated spontaneous death of human lung epithelial A549 cells in a serum- and cell density-dependent manner: while serum starvation has been demonstrated to induce apoptosis in the same cell line, LPS-induced cell death was only observed in the presence of serum; in addition, the cell death was not observed when the cells were seeded at 10- or 100-fold lower density. The apoptotic features were demonstrated by TUNEL assay, DNA laddering and Annexin V staining. However, treatment of cells with two commonly used pan-caspase inhibitors, zVAD.fmk or BOC-D.fmk, failed to block cell death. In contrast, two cathepsin B inhibitors, Ca074-Me or N-1845, reduced cell death significantly. A time-dependent activation of cathepsin B, but not caspase 3, was observed in both control and LPS-treated cells. Although LPS did not further activate cathepsin B or its release, it increased expression and translocation of apoptosis inducing factor from mitochondria to the nucleus, and increased release of cytochrome c from mitochondria. LPS-induced cell death was significantly attenuated by either N-acetyl-L-cysteine or pyrrolidine-dithiocarbamate, both free radical scavengers. Disruption of lipid raft formation with filipin or methyl-beta-cyclodextrin also reduced apoptosis significantly, suggesting that lipid raft-dependent signaling is essential. These data imply that confluent cells undergo spontaneous cell death mediated by cathepsin B; LPS may accelerate this caspase-independent cell death through release of mitochondrial contents and reactive oxygen species.

Caspase 3↗

Freeze-fracture of lipids and model membrane systems.

Model membrane systems are used extensively in all aspects of membrane research, and freeze-fracture is the preeminent procedure for directly visualizing local structure in these lipid dispersions. Here we describe in detail the formation of liposomes and how freeze-fracture is routinely employed as a complementary technique to biophysical and biochemical procedures in the characterization of multilamellar vesicles (most commonly known as liposomes) and unilamellar vesicles. Many preparative procedures exist for the formation of multi- and unilamellar vesicles. Examples of each system are given and their properties as well as freeze-fracture morphology are discussed. The detection of lipid-phase transitions is considered, in particular, with emphasis on the application of freeze-fracture to the study of lipid polymorphism. We briefly discuss the fracturing of apolar lipids which do not adopt bilayer structures but which can be stabilized into microemulsions by a phospholipid monolayer. Finally, a critical assessment is made of filipin as a morphological marker for cholesterol domains in the plane of the bilayer.

Freeze Fracturing↗

Morphology of mammalian sperm membranes during differentiation, maturation, and capacitation.

The mammalian spermatozoon is a highly polarized cell whose surface membrane can be divided into five functionally, structurally, and biochemically distinct domains. These domains are formed during spermatogenesis, continue to be modified during passage through the epididymis, and are further refined in the female reproductive tract. The integrity of these domains appears to be necessary for the sperm to perform its function--fusion with the egg and subsequent fertilization. The domains can be identified morphologically by their surface contours and texture, the content, distribution, and organization of intramembranous particles after freeze-fracture, and by the density of surface and cytoplasmic electron-dense coatings in thin sections. By using a variety of labels that stain carbohydrates (lectins), lipids (filipin and polymyxin B), and monoclonal antibodies to specific membrane constituents, the biochemical composition of these contiguous membrane regions has also been partly elucidated. We review here what is known about the structure, composition, and behavior of each membrane domain in the mature sperm and include some information regarding domain formation during spermatogenesis. The sperm is an excellent model system to study the creation and maintenance of cell polarity, granule exocytosis, and fertilization. Hopefully this review will provide impetus for future studies aimed more directly at addressing the relationship of its morphology to its functions.

Acrosome↗

[Effect of polyene macrolide antibiotics on normal and cell wall deficient Escherichia coli W1655F+ cells].

The polyene macrolide antibiotics are active against yeast, fungi, and other eukaryotic cells, but are with a few exceptions inactive against bacteria. The resistance of bacteria against these compounds is usually explained by the absence of sterols in their cells, the target sites of polyene antibiotics. However, in our experiments with mycotrienin, nystatin, tetramycin, lucenosmycin, rimocidin, filipin, lagosin, flavofungin, flavomycoin, antibiotic 2814P, antibiotic 5001P, and candicidin it was demonstrated that bacteria may be susceptible to polyene antibiotics, too, if the wall-less stable protoplast type L-form of E. coli W1655F+ is used. The measured growth inhibition concentrations were comparable with those of typical antibacterial antibiotics. Our experiments have shown that the normal rod form and the wall-less L-form of E. coli W1655F+ contain traces of sterols in nearly the same concentration range. This means that the selective sensitivity of the L-form cannot be explained by higher sterol content of these cells in comparison to the resistant normal rod form cells. We assume that the bacterial cell wall is responsible for the resistance of the normal rod form by masking internal target sites.

Anti-Bacterial Agents↗

Mechanistic study of the uptake of wheat germ agglutinin-conjugated PLGA nanoparticles by A549 cells.

The purpose of this study was to evaluate the extent and mechanism of uptake of wheat germ agglutinin-conjugated PLGA nanoparticles by A549 cells. PLGA nanoparticles of 150 nm were prepared by a solvent diffusion method and covalently conjugated to FITC-WGA (fWGA) or FITC-bovine serum albumin (fBSA) by a two-step carbodiimide method. Uptake of fWGA-PLGA and fBSA-PLGA nanoparticles by confluent A549 cells was quantified by fluorometry. A549 cellular uptake of fWGA-PLGA nanoparticles at 2 h, 37 degrees C was 5.02-fold that of fBSA-PLGA nanoparticles at a loading concentration of 2.65 mg/mL. The difference in uptake between the two types of nanoparticles was increased to 7.84-fold at a higher loading concentration of 5.3 mg/mL, but was reduced to 2.07-fold by lowering the uptake temperature to 4 degrees C. Coincubation with 5 mg/mL of unlabeled WGA negated the differential uptake of fWGA-PLGA nanoparticles at 4 degrees C, suggesting that the nanoparticles interacted with a specific WGA-binding receptor on the cell membrane. Internalization of the fWGA-PLGA nanoparticles by the A549 cells was confirmed by confocal microscopy. Filipin (1 microg/mL), a known inhibitor of caveolae, reduced the 1-h uptake of the nanoparticles by 75%. Surface modification of PLGA nanoparticles with WGA significantly enhanced its endocytosis by A549 cells by a receptor-mediated, caveola-dependent pathway.

Biomechanical Phenomena↗