Cholesteryl Ether Research Articles

Optimization of transfection into cultured cells with siRNA lipoplexes prepared using a modified ethanol injection method

To simplify the preparation of cationic liposome/small interfering RNA (siRNA) complexes (siRNA lipoplexes), we previously developed a modified ethanol injection (MEI) method, in which siRNA-containing phosphate-buffered saline was rapidly poured into a small volume of a lipid-ethanol (EtOH) solution. In this study, to optimize the lipid composition and solvents for dissolving lipids and siRNA in the transfection of siRNA lipoplexes prepared using the MEI method, we selected five types of cationic lipids, three types of neutral lipids, and five types of polyethylene glycol (PEG)-lipids and prepared siRNA lipoplexes via the MEI method using a lipid-EtOH solution of cationic lipids, neutral lipids, and PEG-lipids. Regardless of the cationic lipid type, siRNA lipoplexes composed of cationic lipids, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, and poly(ethylene glycol) cholesteryl ether showed high gene knockdown efficiency in human breast tumor MCF-7 cells. Regardless of the PEG-lipid type, the size of the siRNA lipoplexes decreased with increasing amounts of PEG-lipid in the lipid-EtOH solution. However, the gene knockdown activity of the siRNA lipoplexes was not abolished via PEGylation when siRNA lipoplexes were PEGylated with PEG-lipids having short lipid anchors. Furthermore, the preparation of siRNA lipoplexes by mixing a lipid-dimethyl sulfoxide solution with a phosphate-buffered saline solution of siRNA increased the size of the siRNA lipoplexes compared with that using a lipid-EtOH solution. However, these lipoplexes showed high gene knockdown efficiency in cells. When prepared by mixing a lipid-EtOH solution with an isotonic glucose or sucrose solution of siRNA, the siRNA lipoplexes tended to reduce gene knockdown efficiency in the cells. These results indicate that the lipid composition and solvents used for dissolving the lipids and siRNA affect the transfection efficiency and size of the siRNA lipoplexes. This study provides information on the optimal preparation of siRNA lipoplexes using the MEI method.

Effect of vorinostat on protein expression in vitro and in vivo following mRNA lipoplex administration.

Previously, we demonstrated that cationic liposomes comprised of N-hexadecyl-N,N-dimethylhexadecan-1-aminium bromide, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine and poly(ethylene glycol) cholesteryl ether induced substantial protein expression both in vitro and in vivo following the administration of mRNA/cationic liposome complexes (mRNA lipoplexes). The present study evaluated the effect of vorinostat, a histone deacetylase inhibitor, on protein expression levels in vitro and in vivo following the administration of mRNA lipoplexes. The half-maximal inhibitory concentration (IC50) values of vorinostat for human cervical carcinoma HeLa and human liver cancer HepG2 cells were determined to be 7.8 and 2.6 µM, respectively, following a 24 h incubation period. Treatment with 1 µM vorinostat resulted in a 2.7-fold increase in luciferase (Luc) activity for HeLa cells and a 1.6-fold increase for HepG2 cells at 24 h post-transfection with firefly Luc (FLuc) mRNA lipoplexes compared with untreated cells. However, treatment with 10 µM vorinostat decreased Luc activity compared with treatment with 1 µM vorinostat. Intravenous injection of Cy5-labeled mRNA lipoplexes into mice resulted in mRNA accumulation primarily in the lungs; however, co-injection with vorinostat at doses of 5 or 25 mg/kg resulted in mRNA accumulation in both the lungs and liver. Furthermore, intravenous injection of FLuc mRNA lipoplexes resulted in high Luc activity in both the lungs and spleen. Nevertheless, co-injection with vorinostat slightly decreased Luc activity in the lungs but not in the spleen. These findings indicated that vorinostat enhances in vitro protein expression from transfected mRNA after treatment with a lower concentration of IC50; however, it does not largely affect in vivo protein expression from the transfected mRNA.

In vitro and in vivo transfections using siRNA lipoplexes prepared by mixing siRNAs with a lipid-ethanol solution

Many methods, such as the dry thin film and ethanol injection methods, have been developed for the preparation of cationic liposomes for siRNA delivery; however, these methods often require special equipment. In this study, we evaluated a siRNA transfection method, in which siRNA/cationic liposome complexes (siRNA lipoplexes) can be prepared by simply mixing an siRNA solution with lipid-ethanol solution. We used dimethyldioctadecylammonium bromide, 1,2-dioleoyl-3-trimethylammonium-propane or 11-((1,3-bis(dodecanoyloxy)-2-((dodecanoyloxy)methyl)propan-2-yl)amino)-N,N,N-trimethyl-11-oxoundecan-1-aminium bromide as a cationic lipid, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine or cholesterol as a neutral helper lipid, and poly(ethylene glycol) cholesteryl ether as a dispersant to prepare the lipid-ethanol solution. A solution of phosphate-buffered saline containing siRNA was then quickly added to a small volume of the lipid-ethanol solution, and the mixture (siRNA lipoplexes) was directly transferred into the cells or injected into mice. siRNA lipoplexes showed high gene knockdown efficiency in MCF-7, Colon 26, and LLC cells regardless of the type of cationic lipids. Furthermore, these siRNA lipoplexes exhibited significant gene knockdown in the lungs of mice after systemic injection. These results suggest that our siRNA lipoplex preparation method has the potential to be widely applicable for in vitro and in vivo siRNA transfections.

Catalytic Degradation of Methylene Blue Using Gold Nanoparticles Capped by Polyoxyethylene Cholesteryl Ether

Simple spontaneous and eco-friendly green synthesis method for ultra-stable and catalytic gold nanoparticles (AuNPs) were synthesized through Polyoxyethylene cholesteryl ether (ChEO10) and sodium tetrachloroaurate (III) dihydrate (Na [AuCl4]-2H2O) were prepared at 27 °C (AuNPs were formed in < 2 h). Here the creation of distinct AuNPs is supported by reductive ChEO10 surfactant solution via complexation and in-situ reduction of AuCl4− ions in which ChEO10 acts as self-reducing and stabilising agent. This method is considered as simple and green. The positive development of colloidal AuNPs was monitored by simple UV-Vis spectroscopy. The complete characterization of synthesizing AuNPs was done in the previous part. The resulting AuNPs reveal outstanding catalytic properties for degradation of Methyl Blue (MB) to Leucomethylene blue (LMB) in the presence of NaBH4. We further comment on challenges and future direction of this exciting and rapidly expanding area of research.

Formulation of bicelles with cholesterol using a semi-spontaneous method

Stratum corneum intercellular lipids play an important role in skin barrier function and are therefore considered useful in pharmaceutical and cosmetics products. In this study, we formulated cholesterol (Cho), the main component of intercellular lipids, into bicelles using a semi-spontaneous method, with the ultimate aim of extending the utility of bicelles in cosmetics. Bicelles are disk-shaped structures in which the planar part comprises long-chain phospholipids and the rims comprise short-chain phospholipids. We used soybean lecithin (SL) and nonionic surfactants (NS) to formulate Cho into bicelles using a semi-spontaneous method. Cho was successfully formulated into bicelles using poly(oxyethylene) cholesteryl ether (with an average of 10 ethylene oxide units, ChEO10) as the NS. We identified the boundaries of the bicelle region in the SL-Cho-ChEO10 system by measuring particle sizes. A bicelle region was formed up to around a maximum mixing ratio of 10wt% Cho, representing a mole fraction (mol%) of approximately 33. Phase changes in the system were observed. Comparison of poly(oxyethylene) cholesteryl ethers containing an average of 10 or 20 (ChEO20) ethylene oxide units revealed that the size of the hydrophilic group affects both the bicelle formation region and the mixing ratio of Cho. We analyzed the state of the SL-Cho-ChEO10 bicelles by differential scanning calorimetry and found that samples containing only phospholipid (SL/Ch/ChEO10 = 1/0/0) provided an endothermic peak between 50 and 55 °C, corresponding to the gel-liquid crystal transition point of the phospholipid. In contrast, the bicelle regions (SL/Cho/ChEO10 = 0.4/0/0.6 and 0.37/0.05/0.58) lacked a gel liquid crystal transition point and a liquid-ordered state was induced by Cho or ChEO10. This indicates that these bicelles are highly stable towards thermal changes.

Formulation of Bicelles Based on Lecithin-Nonionic Surfactant Mixtures.

Bicelles have been intensively studied for use as drug delivery carriers and in biological studies, but their preparation with low-cost materials and via a simple process would allow their use for other purposes as well. Herein, bicelles were prepared through a semi-spontaneous method using a mixture of hydrogenated soybean lecithin (SL) and a nonionic surfactant, polyoxyethylene cholesteryl ether (ChEO10), and then we investigated the effect of composition and temperature on the structure of bicelles, which is important to design tailored systems. As the fraction of ChEO10 (XC) was increased, a bimodal particle size distribution with a small particle size of several tens of nanometers and a large particle size of several hundred nanometers was obtained, and only small particles were observed when XC ≥ 0.6, suggesting the formation of significant structure transition (liposomes to bicelles). The small-angle neutron scattering (SANS) spectrum for these particles fitted a core-shell bicelle model, providing further evidence of bicelle formation. A transition from a monomodal to a bimodal size distribution occurred as the temperature was increased, with this transition taking place at lower temperatures when higher SL-ChEO10 concentrations were used. SANS showed that this temperature-dependent size change was reversible, suggesting the SL-ChEO10 bicelles were stable against temperature, hence making them suitable for several applications.

Synthesis and Aggregation-Induced Emission Feature of Series of Polysiloxanes Containing Triphenylpyrrole Side-Chain

A series of aggregation-induced emission (AIE) active polysiloxanes (P7-1~P7-2, P29-1~P29-6) were prepared through hydrosilylation between polymethylhydrosiloxane (PMHS, DP=7 or 29) and AIE-active vinyl monomer 1-(4'-allyloxy-biphenyl)-2,5-diphenyl pyrrole (M-TPP), or with optical active monomer cholesteryl allyloxy ether (M-Chol*). Monomer M-TPP and all of the polymers exhibits aggeragation-induced emission enhancement properties. The fluorescence intensity of M-TPP in THF/H2O mixtures increases when the water fraction is higher than 60%, while is over 20% for polysiloxanes, which mainly because the entanglement of the flexible polysiloxane main-chain can restrict the molecular motion of triphenylpyrrole (TPP) derivates and induce the increasing of the fluorescence intensity. Moreover, the maximum relative fluorescence intensity (I/I0) is equal to 4 for M-TPP and 1.4~4.9 for polysiloxanes, and the grafted degree of the TPP derivative has effect on the AIE properties of polymers. The specific optical rotations of the chiral polymers increase with increasing the content of chiral cholesteryl ether moieties. All the target polymers possess good thermal stabilities and their decomposition points (Td) are greater than 320°C.

Unusual Stability and Catalytic Activity of Gold Nanoparticles in Polyoxyethylene Cholesteryl Ether.

We report a simple and spontaneous method for creation of extremely stable and catalytically active gold nanoparticles (AuNPs) from polyoxyethylene cholesteryl ether (ChEO15) and sodium tetrachloroaurate (III) dihydrate (Na[AuCl₄] · 2H₂O). AuNPs with uniform size and distribution were prepared at 27 °C (AuNPs were formed in <3 h) and at 50 °C (AuNPs were formed in <1 h). Our elucidations propose that creation of well-defined AuNPs is assisted by reductive ChEO15 surfactant solution via complexation and in-situ reduction of AuCl-₄ ions in which ChEO15 acts both as a reducing and consequently a stabilizing (capping) moiety. AuNPs size can be altered by suitably choosing the Au precursor concentration. The resulting AuNPs reveal outstanding catalytic activity for conversion of nitrophenols to aminophenol in the presence of NaBH₄ and also exhibit synthetic peroxidase-like activity. This simple yet effective synthesis technique opens prospect for creation of stable and active AuNPs.

Supramolecular gels of cholesterol-modified gellan gum with disc-like and worm-like micelles

The association between a hydrophobically modified polysaccharide, gellan gum, with micelles based on a surfactant bearing the same hydrophobic tail as pendant groups was investigated by rheology and small-angle neutron scattering (SANS). Gellan gum grafted with cholesterol groups (20% mol/mol tetrasaccharide unit), GeCh, was mixed with polyoxyethylene cholesteryl ether (ChEO10), which comprises a cholesterol group as the tail linked to a small polyoxyethylene headgroup, and self-assembles into micelles with an unusual disc-like morphology. The addition of 0.5% polymer to solutions of ChEO10 induced a remarkable transition from a Newtonian fluid to a predominantly solid-like viscoelastic behaviour, leading to a ×105 increase in zero-shear viscosity (with 5% ChEO10). Increasing surfactant concentration led to an enhancement of the viscoelasticity, but the elastic modulus G′ reached a plateau around 15% surfactant, attributed to a saturation of the sticker groups. The effect of micellar morphology on the network was studied by adding a small headgroup co-surfactant, triethylene glycol monododecyl ether, to ChEO10 micelles, which drives their elongation into wormlike micelles. Networks obtained with the long, flexible micelles displayed enhanced solid-like behaviour, with no cross-over between G′ and G″ over the measured range of frequencies, reflecting relaxation times of the order of minutes or hours. The morphology of the gels studied by SANS revealed a scattering dominated by strongly interacting micelles (described by discs of 140 Å diameter and a hydrated ∼38 Å PEO corona) and the presence of micellar clusters induced by the presence of the polymer. The scattering data therefore confirm that the onset of gelation is due to surfactant micelles acting as junction points for the network.

Biological Oxidase Enzyme Mimetic Cu‐Pt Nanoalloys: A Multifunctional Nanozyme for Colorimetric Detection of Ascorbic Acid and Identification of Mammalian Cells

AbstractNanomaterials serving as artificial enzymes of the new generation (nanozymes), exhibit enhanced catalytic performance, excellent stability, low cost of production, and other associated properties of nanoparticles. This emerging field of nanozymes has broad‐spectrum potential applications in the bridging area nanotechnology and biomedicine. Among metal‐based nanozymes, bimetallic nanoparticles have been found to show enhanced catalytic performance and display ability to catalyze multistep reactions typically not observed in their monometallic counterparts. Herein, we report the synthesis of Cu−Pt based bimetallic nanoalloys coated with a nonionic surfactant polyoxyethylene cholesteryl ether. The characterization data suggest that the developed nanoalloys have an almost uniform distribution of Cu and Pt (1:1) elements; therefore, this novel technique could be used for the large‐scale synthesis of Cu−Pt based nanozymes in a one‐step procedure. Further investigations showed that these bimetallic nanoalloys possess excellent biological oxidase enzyme‐like activity and the catalytic activity could be performed at harsh conditions of pH and temperature. Oxidase activity of Cu−Pt nanoalloys was utilized for the sensitive detection of ascorbic acid in the sub‐micromolar concentration range. Supplementing ATP in the oxidase reaction, the nanozyme showed enhanced catalytic activity, which was used for the detection of human liver cells.

Studies on preparation of surfactant-assisted elliptical hydroxyapatite nanoparticles and their protein-interactive ability

Addition of poly (oxyethylene)cholesteryl ether in the synthesis promoted the formation of the hydroxyapatite nanoparticles (HAp NPs) with the elliptical morphologies. The adsorption mechanism, interfacial interactions and conformation of the adsorbed fibrinogen (Fgn) on the HAp NP films were investigated. The Fgn adsorption behavior demonstrated the higher affinity of Fgn with the HAp NP films. At the lower temperature at 22 °C, Fgn was preferentially adsorbed on the gold though hydrophobic interactions with the larger Fgn adsorption amount. At the higher temperature at 37 °C or at the higher phosphate ion concentrations caused the structural changes of the adsorbed Fgn. Moreover, the temperature increment in PBS increased the Fgn adsorption amount with the rearrangement into the end-on orientation of the Fgn. Accordingly, HAp induced the electrostatic force and hydrogen bonding to be the stable Fgn-HAp NP film, minimizing the interactions among the water molecules. The HAp NP films with the preferentially elliptical crystalline shapes induced the Fgn steric conformation structures, and the secondary structural changes of the adsorbed Fgn by the increment of temperature were also supported by the Fourier transform infrared spectroscopy (FTIR) deconvolution results.

Novel synthesis of polyoxyethylene cholesteryl ether coated Fe-Pt nanoalloys: A multifunctional and cytocompatible bimetallic alloy exhibiting intrinsic chemical catalysis and biological enzyme-like activities

Fe−Pt alloy nanoparticles (NPs) with dendritic shells are efficaciously created by the chemical reduction of K2PtCl4 and FeCl3 species in a low-concentration of nonionic surfactant polyoxyethylene cholesteryl ether (ChEO15) solution. The dissimilarity in reduction potentials of the two soluble metal salts (Fe(III) and Pt(IV) species) plays a crucial role in the one-step synthesis of the bimetallic nanostructure, which is confirmed by TEM and XRD. Interestingly, Fe−Pt alloy NPs exhibit oxidase enzyme-like activity as well as a chemical catalyst. The kinetic parameters calculations revealed that this catalyst enhances the velocity of reaction 10 folds when compared with the reported oxidase-like activity exhibiting nanomaterials. The Fe-Pt alloy NPs also displayed high catalytic activity in the hydrogenation reaction of nitrophenol to aminophenol. The safety assessment of Fe-Pt alloy NPs revealed that these NPs are highly biocompatible to human normal liver cells up to 150 μM concentration. Therefore, the synthesized Fe-Pt alloy NPs showing excellent oxidase enzyme-like activity hold the promise to be used for multiple biomedical applications.

Enhanced foamability and foam stability of polyoxyethylene cholesteryl ether in occurrence of ionic surfactants

The micellization and foam studies of binary surfactant mixtures assembled of nonionic polyoxyethylene cholesteryl ether (ChEOn; where n = 30), cationic hexadecyltrimethylammonium bromide (CTAB) and anionic sodium dodecylbenzenesulfonate (SDBS) was investigated by surface tension, foaming behavior and viscosity measurements. As an exceptional outcome it was observed that foam stability and foamability of nonionic surfactant ChEO30 in mixtures with ionic surfactants is much superior to the individual ChEO30, CTAB or SDBS components. Moreover, the mixed surfactant systems (ChEO30+CTAB) and (ChEO30+SDBS) have much lower critical micellar concentrations (CMCs) than corresponding sole surfactants. The negative values of interaction parameter (β) estimated from Rubingh’s theory specify synergism amongst mixed ChEO30+CTAB and ChEO30+SDBS surfactants systems.

Radiolabeled cholesteryl ethers: A need to analyze for biological stability before use

Radiolabeled cholesteryl ethers are widely used as non-metabolizable tracers for lipoproteins and lipid emulsions in a variety of in vitro and in vivo experiments. Since cholesteryl ethers do not leave cells after uptake and are not hydrolyzed by mammalian cellular enzymes, these compounds can act as markers for cumulative cell uptakes of labeled particles. We have employed [3H]cholesteryl oleoyl ether to study the uptake and distribution of triglyceride-rich emulsion particles on animal models. However, questionable unexpected results compelled us to analyze the stability of these ethers. We tested the stability of two commercially available radiolabeled cholesteryl ethers - [3H]cholesteryl oleoyl ether and [3H]cholesteryl hexadecyl ether from different suppliers, employing in vitro, in vivo and chemical model systems. Our results show that, among the two cholesteryl ethers tested, one ether was hydrolyzed to free cholesterol in vitro, in vivo and chemically under alkaline hydrolyzing agent. Free cholesterol, unlike cholesteryl ether, can then re-enter the circulation leading to confounding results. The other ether was not hydrolyzed to free cholesterol and remained as a stable ether. Hence, radiolabeled cholesteryl ethers should be analyzed for biological stability before utilizing them for in vitro or in vivo experiments.

Creation of Gold Nanoparticles by UV Photoactivation of Polyoxyethylene Cholesteryl Ether

Creation of Gold Nanoparticles by UV Photoactivation of Polyoxyethylene Cholesteryl Ether

Optimised conditions for the synthesis of 17O and 18O labelled cholesterol

Conditions are described for the preparation of cholesterol with 17O and 18O labels from i-cholesteryl methyl ether using minimal amounts of isotopically enriched water. Optimum yields employed trifluoromethanesulfonic acid as catalyst in 1,4-dioxane at room temperature with 5 equivalents of water. An isotopic enrichment >90% of that of the water used for the reaction could be attained. Tetrafluoroboric acid could also be used as catalyst, at the expense of a lower overall reaction yield. Byproducts from the reaction included dicholesteryl ether, methyl cholesteryl ether, compounds formed by ether hydrolysis, and olefins arising from elimination reactions. Reactions in tetrahydrofuran yielded significant amounts of cholesteryl ethers formed by reaction with alcohols arising from hydrolysis of the solvent.

Polymersomes from Amphiphilic Glycopolymers Containing Polymeric Liquid Crystal Grafts.

For the first time, polymersomes were obtained by self-assembly in water of amphiphilic grafted glycopolymers based on dextran polysaccharidic backbone and polymeric liquid crystal grafts (poly(diethylene glycol cholesteryl ether acrylate), PDEGCholA). After measuring the properties of these glycopolymers in term of surfactancy, the influence of their structural parameters on their self-assemblies once dispersed in water was investigated by static and dynamic light scattering and by cryogenic transmission electron microscopy (cryo-TEM). Based on the results, a proper design of Dex-gN-PDEGCholAF leads to hollow vesicular structure formulation known as polymersome.

Remarkable viscoelasticity in mixtures of cyclodextrins and nonionic surfactants.

We report the effect of native cyclodextrins (α, β, and γ) and selected derivatives in modulating the self-assembly of the nonionic surfactant polyoxyethylene cholesteryl ether (ChEO10) and its mixtures with triethylene glycol monododecyl ether (C12EO3), which form wormlike micelles. Cyclodextrins (CDs) generally induce micellar breakup through a host-guest interaction with surfactants; instead, we show that a constructive effect, leading to gel formation, is obtained with specific CDs and that the widely invoked host-guest interaction may not be the only key to the association. When added to wormlike micelles of ChEO10 and C12EO3, native β-CD, 2-hydroxyethyl-β-CD (HEBCD), and a sulfated sodium salt of β-CD (SULFBCD) induce a substantial increase of the viscoelasticity, while methylated CDs rupture the micelles, leading to a loss of the viscosity, and the other CDs studied (native α- and γ- and hydroxypropylated CDs) show a weak interaction. Most remarkably, the addition of HEBCD or SULFBCD to pure ChEO10 solutions (which are low-viscosity, Newtonian fluids of small, ellipsoidal micelles) induces the formation of transparent gels. The combination of small-angle neutron scattering, dynamic light scattering, and cryo-TEM reveals that both CDs drive the elongation of ChEO10 aggregates into an entangled network of wormlike micelles. (1)H NMR and fluorescence spectroscopy demonstrate the formation of inclusion complexes between ChEO10 and methylated CDs, consistent with the demicellization observed. Instead, HEBCD forms a weak complex with ChEO10, while no complex is detected with SULFBCD. This shows that inclusion complex formation is not the determinant event leading to micellar growth. HEBCD:ChEO10 complex, which coexists with the aggregated surfactant, could act as a cosurfactant with a different headgroup area. For SULFBCD, intermolecular interactions via the external surface of the CD may be more relevant.

Poly(ethylene glycol)-cholesterol inhibits L-type Ca2+ channel currents and augments voltage-dependent inactivation in A7r5 cells.

Cholesterol distributes at a high density in the membrane lipid raft and modulates ion channel currents. Poly(ethylene glycol) cholesteryl ether (PEG-cholesterol) is a nonionic amphipathic lipid consisting of lipophilic cholesterol and covalently bound hydrophilic PEG. PEG-cholesterol is used to formulate lipoplexes to transfect cultured cells, and liposomes for encapsulated drug delivery. PEG-cholesterol is dissolved in the external leaflet of the lipid bilayer, and expands it to flatten the caveolae and widen the gap between the two leaflets. We studied the effect of PEG-cholesterol on whole cell L-type Ca2+ channel currents (I Ca,L) recorded from cultured A7r5 arterial smooth muscle cells. The pretreatment of cells with PEG-cholesterol decreased the density of I Ca,L and augmented the voltage-dependent inactivation with acceleration of time course of inactivation and negative shift of steady-state inactivation curve. Methyl-β-cyclodextrin (MβCD) is a cholesterol-binding oligosaccharide. The enrichment of cholesterol by the MβCD:cholesterol complex (cholesterol (MβCD)) caused inhibition of I Ca,L but did not augment voltage-dependent inactivation. Incubation with MβCD increased I Ca,L, slowed the time course of inactivation and shifted the inactivation curve to a positive direction. Additional pretreatment by a high concentration of MβCD of the cells initially pretreated with PEG-cholesterol, increased I Ca,L to a greater level than the control, and removed the augmented voltage-dependent inactivation. Due to the enhancement of the voltage-dependent inactivation, PEG-cholesterol inhibited window I Ca,L more strongly as compared with cholesterol (MβCD). Poly(ethylene glycol) conferred to cholesterol the efficacy to induce sustained augmentation of voltage-dependent inactivation of I Ca,L.

Scavenger receptor-BI is a receptor for lipoprotein(a)

Scavenger receptor class B type I (SR-BI) is a multi-ligand receptor that binds a variety of lipoproteins, including high density lipoprotein (HDL) and low density lipoprotein (LDL), but lipoprotein(a) [Lp(a)] has not been investigated as a possible ligand. Stable cell lines (HEK293 and HeLa) expressing human SR-BI were incubated with protein- or lipid-labeled Lp(a) to investigate SR-BI-dependent Lp(a) cell association. SR-BI expression enhanced the association of both (125)I- and Alexa Fluor-labeled protein from Lp(a). By confocal microscopy, SR-BI was also found to promote the internalization of fluorescent lipids (BODIPY-cholesteryl ester (CE)- and DiI-labeled) from Lp(a), and by immunocytochemistry the cellular internalization of apolipoprotein(a) and apolipoprotein B. When dual-labeled ((3)H-cholesteryl ether,(125)I-protein) Lp(a) was added to cells expressing SR-BI, there was a greater relative increase in lipid uptake over protein, indicating that SR-BI mediates selective lipid uptake from Lp(a). Compared with C57BL/6 control mice, transgenic mice overexpressing human SR-BI in liver were found to have increased plasma clearance of (3)H-CE-Lp(a), whereas mouse scavenger receptor class B type I knockout (Sr-b1-KO) mice had decreased plasma clearance (fractional catabolic rate: 0.63 ± 0.08/day, 1.64 ± 0.62/day, and 4.64 ± 0.40/day for Sr-b1-KO, C57BL/6, and human scavenger receptor class B type I transgenic mice, respectively). We conclude that Lp(a) is a novel ligand for SR-BI and that SR-BI mediates selective uptake of Lp(a)-associated lipids.