Biomedical subjects

D Lichtenberg

Publications and source records attributed to D Lichtenberg.

At least 37 records · Page 2Linked to original sources

PubMed1998

LDL-associated phospholipase A does not protect LDL against lipid peroxidation in vitro.

The irreversible proteinase inhibitor Pefabloc (4-[2-aminoethyl] benzenesulfonyl fluoride) inactivates LDL-catalyzed hydrolysis of the short-chain fluorescent phospholipid C6-NBD-PC (1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)-aminocaproyl phosphatidylcholine). The dose-dependence of this inactivation is similar to that obtained previously for the inhibitory effect of Pefabloc on the hydrolysis of platelet activating factor (PAF) by the LDL-associated PAF acetylhydrolase (PAF-AH), in agreement with the notion that the hydrolysis of C6-NBD-PC and PAF is catalyzed by the same enzyme (LDL-associated phospholipase A; LDL-PLA). This conclusion is also supported by the finding that hydrolysis of C6-NBD-PC by LDL becomes inactivated by LDL oxidation only at late stages of the oxidation, similar to the effect of oxidation on the hydrolysis of PAF by the LDL-associated PAF-AH. Under conditions of complete inactivation of this enzyme towards C6-NBD-PC, the kinetics of lipid peroxidation, induced either by copper ions or by the free radical generator AAPH at varying doses of the prooxidant, was similar to that observed when the PLA was active (i.e., in the absence of Pefabloc). Hence, LDL-associated PLA (PAF-AH) does not protect LDL lipids from peroxidation. Similar results were obtained with fractionated LDL in albumin-containing buffer and for non-fractionated serum, in which copper-induced peroxidation was also not influenced by inactivation of the enzyme responsible for hydrolysis of C6-NBD-PC. Phospholipolysis of short chain phospholipids by LDL-PLA may still play a protective role against the toxic effects of oxidized phospholipids by reducing their internalization into cells (Schmitt et al. 1995).

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed1998

Simplified surveillance for nosocomial bloodstream infections.

OBJECTIVE: To compare a surveillance definition of noso comial bloodstream infections requiring only microbiology data to the Centers for Disease Control and Prevention's (CDC) current definition. SETTING: Six teaching hospitals. METHODS: We classified a representative sample of 73 positive blood cultures from six hospitals growing common skin contaminant isolates using a definition for bacteremia requiring only microbiology data and the CDC definition for primary bloodstream infection (National Nosocomial Infections Surveillance [NNIS] System review method). The classifications assigned during routine prospective surveillance also were noted, and the time required to classify isolates by the two methods was compared. RESULTS: Among 65 blood cultures growing common skin contaminant isolates obtained from adults, the agreement rate between the microbiology data method and the NNIS review method was 91%. Agreement was significantly poorer for the eight blood cultures growing common skin contaminant isolates obtained from pediatric patients. The microbiology data method requires approximately 20 minutes less time per isolate than does routine surveillance. CONCLUSIONS: A definition based on microbiology data alone yields the same result as the CDC's definition in the large majority of instances. It is more resource-efficient than the CDC's current definition.

Adult↗

PubMed1997

Imaging supramolecular aggregates in bile models and human bile.

Investigation of cholesterol crystallization is essential for the understanding of gallstone formation. Previous work has revealed a variety of aggregates of different sizes and shapes prior to the appearance of "classical" plate-like cholesterol monohydrate crystals both in native biles and model systems. In this article, we review existing data based on various microscopic techniques and present data on microstructural pathways leading to cholesterol crystal formation in two different bile models and in native bile. In continuation of our recent investigation of microstructures in nucleating human bile, we now present data suggesting that polymorphism is not limited to complex native bile, but also appears in two, simplified model systems. These studies employed cryo-transmission electron microscopy (cryo-TEM) and video-enhanced light microscopy, using Nomarski optics (VELM). Only the combined use of these two complementary, non-perturbing direct methods can cover the whole range of microstructures ranging from a few nanometers to several microns. Concentrated isotropic solutions of bile models, composed of cholesterol, lecithin and taurocholate, were diluted to induce cholesterol supersaturation and start an evolution of microstructures, leading to cholesterol crystallization. Initially, small spheroidal micelles were observed by cryo-TEM. Subsequently, uni-, oligo- and multilamellar vesicles, compatible with structures seen at the same time by VELM, appeared in coexistence with micelles. Thereafter, during a dynamic phase of cholesterol crystallization, filaments, tubular and helical microstructures, as well as classical plate-like cholesterol monohydrate crystals were noted by light microscopy. Eventually, large plate-like crystals were observed by VELM, while cryo-TEM revealed only small spheroidal micelles. The crystallization process in native human bile during ex vivo incubation was found to bear close resemblance to the findings in the model systems, further supporting the applicability of these systems to the exploration of microstructural aspects of nucleating human bile.

Bile↗

PubMed1997

The effect of albumin on copper-induced LDL oxidation.

In an attempt to gain deeper understanding of the mechanism or mechanisms responsible for the protective effect of serum albumin against Cu(2+)-induced peroxidation of low density lipoprotein (LDL), we have examined the influence of the concentrations of bovine serum albumin (BSA), Cu2+ and LDL on the kinetics of peroxidation. Since the common method of monitoring the oxidation by continuous recording of the absorbance of conjugated dienes at 234 nm cannot be used at high BSA-concentrations because of the intensive absorption of BSA, we have monitored the time-dependent increase of absorbance at 245 nm. At this wavelength, conjugated dienes absorb intensely, whereas the background absorbance of BSA is low. Using this method, as well as the TBARS assay for determination of malondialdehyde, over a large range of BSA concentrations, we show that in many cases the influence of BSA on the kinetics of oxidation can be compensated for by increasing the concentration of copper. This reconciles the apparent contradiction between previously published data. Detailed studies of the kinetic profiles obtained under different conditions indicate that binding of Cu2+ to albumin plays the major role in its protective effect while other mechanisms contribute much less than copper binding. This conclusion is consistent with the less pronounced effect of BSA on the oxidation induced by the free radical generator AAPH. It is also shown that the copper-albumin complex is capable of inducing LDL oxidation, although the kinetics of the latter process is very different from that of copper-induced oxidation. Nevertheless, when compared to copper induced oxidation at similar concentration of the oxidation-promotor, the kinetics of oxidation induced by copper-albumin complex is very different and is consistent with a tocopherol mediated peroxidation, characteristic under low radical flux. Similar kinetics was observed for copper-induced oxidation only at much lower copper concentrations.

Amidines↗

PubMed1997

Biosynthesis of medium-chain triacylglycerols and phospholipids by HepG-2 cells.

In an attempt to understand the metabolism by the liver of fatty acids (FA) of different chain length, we have studied the incorporation of [1(-14)C]-labeled C2, C8, C10, C12, and C16 into cellular lipids by HepG-2 cells. Over 90% of the radiolabeled FA were detected in phospholipids (PL) and triacylglycerols (TAG). The incorporation of C12 and C16 was three to four times higher than that of C8 and C10 (and reached 35 nmoles per mg protein after 1.5 h). The radioactivity of C2, C8, and C10 was recovered mainly in PL. C12 and C16 were incorporated at approximately equal amounts into PL and TAG. The radioactivity of both C2 and C8 was recovered exclusively in long-chain FA, suggesting oxidation of C8 into C2 units prior to FA synthesis. C10 likewise yielded mainly long-chain FA. However 10% of unchanged C10 was found in PL and up to 30% in TAG. 14C-C12 was largely incorporated unchanged. Under these conditions, the presence of C10 and C12 in PL and TAG was shown also by gas-liquid chromatography. In the presence of either C2, C8, or C10, up to 30% of 14C-monounsaturated FA were detected in PL and TAG. With C12 and C16, the fraction of 14C-monounsaturated FA was much smaller suggesting that extensive desaturation occurred during de novo synthesis.

Caprylates↗

PubMed1997

Partitioning of octyl glucoside between octyl glucoside/phosphatidylcholine mixed aggregates and aqueous media as studied by isothermal titration calorimetry.

Stepwise dilution of lipid-surfactant mixed micelles first results in extraction of surfactant from the mixed micelles into the aqueous medium. Subsequently mixed micelles transform into vesicles, within a range of compositions that corresponds to equilibrium coexistence between these two types of aggregates. Further dilution results in extraction of surfactant from the resultant mixed vesicles. In the present study, we have investigated the heat evolution of these processes, as they occur in mixed systems composed of egg phosphatidylcholine (PC) and the nonionic surfactant octylglucoside (OG). A combined use of isothermal titration calorimetry (ITC) and photon correlation spectroscopy (PCS), capable of monitoring phase transformations, revealed that 1) The sum of all of the studied processes (i.e., extraction of OG from mixed micelles and vesicles and the phase transformation) is isocaloric at approximately 40 degrees C throughout the whole dilution. At lower temperatures, all of the dilution steps are exothermic, whereas at higher temperatures all of them are endothermic. 2) At all temperatures, the absolute value of the heat associated with each dilution step within the range of coexistence of micelles and vesicles is almost constant and larger than in either the micellar or the vesicular range. We give an interpretation of these calorimetric data in terms of the relationship between the composition of the mixed aggregates Re and the aqueous concentration of surfactant monomers Dw. Assuming that the main contribution to the heat evolution is due to extraction of surfactant from mixed aggregates to the aqueous solution, we deduce the relationship Dw(Re) characterizing the system over the whole range of compositions. We find that, in accord with thermodynamic expectations, Dw is almost constant throughout the range of coexistence of mixed micelles and vesicles.

Absorptiometry, Photon↗

PubMed1997

The heat of transfer of lipid and surfactant from vesicles into micelles in mixtures of phospholipid and surfactant.

We study the heat associated with the transformation of vesicles into micelles in mixtures of bilayer-forming phospholipids and micelle-forming surfactants. We subdivide the total heat evolution deltaQ(coex) within the range of coexistence of vesicles and micelles into three contributions related to the transition of dN(D)m-b molecules of surfactant and dN(L)m-b molecules of lipid from micelles to vesicles and to the extraction of dN(D)m-w molecules of surfactant from micelles to the aqueous solution, so that deltaQ(coex) = deltaH(D)m-w x dN(D)m-w + deltaH(D)m-b x dN(D)m-b + deltaH(L)m-b x dN(L)m-b where deltaH(D)m-w, deltaH(L)m-b, and deltaH(D)m-b are the respective molar "transfer" enthalpies. We design a method for the evaluation of all three molar enthalpies, from isothermal calorimetric titrations conducted according to two different protocols of titration of lipid-surfactant mixtures. In the first protocol the mixture is titrated with an aqueous solution of pure lipid vesicles, and in the second the mixture is titrated with an aqueous solution of pure surfactant. Titration of the mixed systems by a buffer solution serves to verify the results obtained under these protocols. In addition to the values of molar enthalpies, our method yields the cmc value of the pure surfactant. We apply our method to investigating the heat evolution in mixtures of egg yolk phosphatidylcholine and the nonionic surfactant octylglucoside in a phosphate-buffered saline solution at 28 degrees C. These studies gave the following values: deltaH(D)m-w = -1732 cal/mol, deltaH(L)m-b = -592 cal/mol, deltaH(D)m-b = 645 cal/mol, and cmc = 23.5 mM. We discuss the possible physical insight of these values and the perspectives of applications of the proposed method.

Calorimetry↗

PubMed1997

The use of commercially available lipid emulsions for the preparation of amphotericin B-lipid admixtures.

The use of Intralipid as a dilution medium for Fungizone, previously proposed by several groups to reduce the toxicity of amphotericin B, is limited by the instability of amphotericin B-lipid admixtures. We have shown that Fungizone-lipid admixtures with three different lipid emulsions can be stabilized by vigorous agitation. Unlike in preparations made by gentle shaking, in stable emulsions made by agitation for 18 h, most of the amphotericin B remains associated with the lipid phase for at least 1 month at 4 degrees C. The MICs of all the admixtures against various Candida spp. were similar to that of Fungizone and did not change following storage for at least 2 weeks at 4 degrees C. Furthermore, the toxicity of the admixtures, as evaluated by their haemolytic activity and amphotericin B-induced K+-leakage from human red blood cells, was much lower than that of Fungizone. Hence, amphotericin B-containing lipid emulsions made by extended agitation may be advantageous in clinical practice as they are efficient, stable, non-toxic and can be easily produced at low cost from commercially available ingredients approved for clinical use.

Amphotericin B↗

PubMed1997

Reduction of sperm cholesterol:phospholipid ratio is a possible mechanism for enhancement of human sperm binding to the zona pellucida following incubation with phosphatidylcholine liposomes.

TEST (TES (N-tris[hydroxymethyl]methyl-2-aminoethanesulfonic acid) and Tris) yolk buffer (TYB) has recently been shown to improve the binding capacity of spermatozoa to zona pellucidae. The present study had two objectives: 1) to elucidate which component(s) of TYB dominates this effect and 2) to define the responsible mechanism. Sperm samples obtained from subfertile men were incubated for 2 h in either TYB or media containing egg yolk lipoproteins or phospholipids. After incubation, sperm binding was tested by the hemizona assay. Yolk lipoprotein-treated spermatozoa bound hemizonae with efficiency equal to that of the spermatozoa incubated in control medium. Conversely, incubation of spermatozoa in media containing either TYB, yolk-phospholipids, or pure phosphatidylcholine (PC) resulted in a 2- to 3-fold increased binding capacity (p < 0.01). A close correlation was found between the effect of yolk-phospholipids and TYB on the binding capacity of the same sperm samples, compared to spermatozoa incubated in control medium. Incubation of spermatozoa in yolk phospholipid medium caused a dose-dependent increase of sperm binding capacity (p < 0.05). Treatment of sperm samples with 1 mg/ml or more of purified PC preparation also resulted in a reduction of the sperm cholesterol:phospholipid molar ratio. Significant correlations between the effects of the treatments on sperm cholesterol: phospholipid molar ratio and sperm binding were obtained with yolk-phospholipids (r = -0.55) or 1 mg/ml purified PC (r = -0.61). We conclude that 1) the enhanced binding capacity of human spermatozoa following TYB treatment is probably due to yolk-phospholipids, mainly egg yolk PC; and 2) it appears that the enhanced binding capacity of human spermatozoa following treatment with egg yolk-containing media may be a result of the reduction of the cholesterol:phospholipid molar ratio in the sperm cells.

Acrosome↗

PubMed1997

A clinical data repository enhances hospital infection control.

We describe the benefits of a relational database of hospital clinical data (Clinical Data Repository; CDR) for an infection control program. The CDR consists of > 40 Sybase tables, and is directly accessible for ad hoc queries by members of the infection control unit who have been granted privileges for access by the Information Systems Department. The data elements and functional requirements most useful for surveillance of nosocomial infections, antibiotic use, and resistant organisms are characterized. Specific applications of the CDR are presented, including the use of automated definitions of nosocomial infection, graphical monitoring of resistant organisms with quality control limits, and prospective detection of inappropriate antibiotic use. Hospital surveillance and quality improvement activities are significantly benefited by the availability of a querable set of tables containing diverse clinical data.

Bacteremia↗

PubMed1996

Oxidation of fluorescent glycero- and sphingophospholipids in human plasma lipoproteins: alkenylacyl subclasses are preferred targets.

OBJECTIVES: Oxidation of polyunsaturated fatty acids in lipoproteins is supposed to play a crucial role at the early stages of atherogenesis. The polyunsaturated lipids (PUFAs) become oxidized and, thus, the degree and rate of lipid oxidation depend on their concentration and, probably, on the lipid moiety to which they are attached. DESIGN AND METHODS: To determine the relative oxidation susceptibilities of sphingo- and glycerolipid-bound fatty acyl chains, we used fluorescent analogs of the respective compounds, in which one natural fatty acyl chain was replaced by fluorescent diphenylhexatriene propionic acid. RESULTS: Oxidation susceptibilities of the fluorescent acyl chains in the presence of Cu2+ or AAPH depended, in general, on the phospholipid to which they were bound and the lipoprotein. Phospholipids were oxidized faster in HDL than in LDL or Lp(a). Plasmalogens were more susceptible to oxidation than phosphatidylcholine and sphingomyelin. CONCLUSION: Thus, HDL and plasmalogens may be considered as preferred targets of lipid oxidation before the bulk of polyunsaturated phospholipids (mainly phosphatidylcholine) in LDL is subject to free radical attack.

Amidines↗

PubMed1996

Aggregation of phospholipid vesicles by water-soluble polymers.

Water-soluble polymers such as dextran and polyethylene glycol are known to induce aggregation and size growth of phospholipid vesicles. The present study addresses the dependence of these processes on vesicle size and concentration, polymer molecular weight, temperature, and compartmentalization of the vesicles and polymers, using static and dynamic light scattering. Increasing the molecular weight of the polymers resulted in a reduction of the concentration of polymer needed for induction of aggregation of small unilamellar vesicles. The aggregation was fully reversible (by dilution), within a few seconds, up to a polymer concentration of at least 20 wt %. At relatively low phosphatidylcholine (PC) concentrations (up to approximately 1 mM), increasing the PC concentration resulted in faster kinetics of aggregation and reduced the threshold concentration of polymer required for rapid aggregation (CA). At higher PC concentrations, CA was only slightly dependent on the concentration of PC and was approximately equal to the overlapping concentration of the polymer (C*). The extent of aggregation was similar at 37 and 4 degrees C. Aggregation of large unilamellar vesicles required a lower polymer concentration, probably because aggregation occurs in a secondary minimum (without surface contact). In contrast to experiments in which the polymers were added directly to the vesicles, dialysis of the vesicles against polymer-containing solutions did not induce aggregation. Based on this result, it appears that exclusion of polymer from the hydration sphere of vesicles and the consequent depletion of polymer molecules from clusters of aggregated vesicles play the central role in the induction of reversible vesicle aggregation. The results of all the other experiments are consistent with this conclusion.

Dextrans↗

PubMed1996

Effect of water-soluble polymers on the state of aggregation, vesicle size, and phase transformations in mixtures of phosphatidylcholine and sodium cholate.

The state of aggregation and the steady-state size of mixed aggregates made of phospholipids and surfactants are both determined by the surfactant/lipid ratio in the mixed aggregates (Re). Water-soluble polymers, such as dextrans and polyethylene glycols (PEGs) of different molecular weights, induce reversible aggregation of phospholipid vesicles, mostly due to dehydration of the vesicle surface and depletion forces, and only at much higher concentrations, PEGs (but not dextran) also induce irreversible size growth of the vesicles. Here we show that the water-soluble polymers dextrans and PEGs do not affect the vesicle-micelle phase boundaries in mixtures of phosphatidylcholine and the anionic surfactant sodium cholate. By contrast, these polymers affect markedly the steady-state size of cholate-containing vesicles. As compared with pure phosphatidylcholine vesicles, the cholate-containing vesicles have a lower tendency to undergo polymer-induced aggregation, probably due to the electrostatic repulsion between the negatively charged vesicles, but a higher tendency to undergo irreversible size growth at relatively low polymer concentrations. Such irreversible size growth was observed not only for PEG but also for dextran, which in the absence of cholate is incapable of inducing vesicle size growth. These findings are consistent with the prevailing concept that the polymer-induced size growth is due to the effect of large structural fluctuations in the bilayers of deformed aggregated vesicles, the surface of which is dehydrated by the polymer. The presence of cholate in the bilayers at sufficiently high concentrations induces such fluctuations, yielding irreversible size growth within the clusters of dehydrated vesicles formed upon mixing with polymers.

Cholic Acid↗

PubMed1996

Continuous monitoring of intermediates and final products of oxidation of low density lipoprotein by means of UV-spectroscopy.

The most widely used routine technique for determination of LDL 'oxidizability' is the continuous monitoring of the absorption at 234 nm in the UV spectrum of LDL, following the addition of an oxidation promotor such as copper ions. This absorption is commonly attributed to the conjugated dienes formed upon oxidation as the major intermediate, namely the hydroperoxides of polyunsaturated fatty acids, mostly linoleate hydroperoxides. These, however, are not the only products of oxidation that absorb light at 234 nm. Other products, particularly 7-ketocholesterol, also absorb light at the same wavelength. Furthermore, enals and dienals also absorb in the wavelength range of 210-300 nm. The aim of the present work was to develop a simple spectroscopic method for more detailed investigation of the kinetics of lipoprotein oxidation. The method is based on continuous measurement of the UV spectrum in the wavelength range of 210-300 nm and subsequent decomposition of the spectra into four absorption bands due to hydroperoxides, 7-ketocholesterol, dienals and enals. The sixth derivatives of the spectra, recorded during the first seven hours of copper-induced oxidation of LDL were used to monitor the growth and subsequent decay of the hydroperoxides. The resultant time course, in conjunction with difference spectra obtained after the concentration of these intermediates decay to zero, enabled us to determine the spectra of the other oxidation products and, by that, to evaluate their time dependencies. Based on these results, we present a series of four simple equations that can be used to evaluate the concentrations of the individual products of LDL oxidation from UV absorption measurements of the mixtures ar merely four different wavelengths. The resultant time dependencies of the accumulation of four major products of lipid oxidation are consistent with published data obtained through separation and chemical analysis. This simple method can be used for more meaningful routine kinetic measurements of lipids oxidation.

Copper↗

PubMed1996

Does lipid infusion affect bile composition in humans?

A prospective study was performed to investigate the effect of short-term lipid infusion on bile composition and its lithogenicity in humans. The study group comprised 44 patients scheduled for laparotomy. The patients were hospitalized 48 h prior to elective surgery and randomized to be infused with a lipid emulsion of either long chain triglycerides (LCT) or a mixture of medium and long chain triglycerides (MCT/LCT) for 6 h of each 24 h, or with glucose-saline. Bile samples were obtained by puncture of the gallbladder during operation. In non-gallstone patients, both lipids caused an elevation of biliary cholesterol and phospholipids, but this effect was more pronounced and significant (P <0.001) only with the mixture of MCT/LCT emulsion. The fatty acid composition of biliary phospholipids was not affected by either lipid infusion. The Cholesterol Saturation Index increased significantly (P <0.005) with the MCT/LCT emulsion and there was insignificant shortening in the nucleation time. In contrast to patients with cholelithiasis, no effects could be demonstrated on gallbladder bile composition, cholesterol saturation index, nucleation time, or fatty acid composition of phospholipids. The effects of both lipid emulsions on plasma lipids and lipoproteins were similar in all groups. Our results indicate that lipid emulsions containing MCT/LCT induce lithogenic changes in the composition of human bile. We propose that the lack of effect of lipid infusion on bile composition in patients with cholelithiasis may be due to precipitation of excess cholesterol in the gallbladder of cholesterol gallstone patients whose bile is already saturated. These findings imply that patients with cholesterol gallstones cannot be grouped with non-gallstone patients in studies of alterations of bile composition.

Bile↗

PubMed1995

Copper-induced lipid oxidation in unfractionated plasma: the lag preceding oxidation as a measure of oxidation-resistance.

In spite of the pathological significance of oxidation of plasma lipids, no method is currently available for the evaluation of the susceptibility of these lipids to oxidation in unfractionated plasma. Here we demonstrate that copper-induced oxidation of diluted plasma, in the presence of citrate can be monitored continuously by recording the absorbance at 245 nm. The kinetics of accumulation of oxidation products in unfractionated plasma is a sum of lipid oxidation products obtained in low and high density lipoproteins isolated from the same plasma. The kinetic profiles are reproducible and can be performed with plasma samples even after prolonged storage at 4 degrees C (up to two months) or after freezing and thawing of the plasma. Being simple and reproducible, yet correlating with the oxidizability of low and high density lipoproteins, this method can be used to evaluate the "oxidation resistance" of plasma lipids and thus serve as a standard index of the susceptibility of the plasma lipids of patients to oxidation-inflicted pathologies, including atherosclerosis.

Anticoagulants↗

PubMed1995

Cholesterol precipitation from cholesterol-supersaturated bile models.

Bile-model systems containing cholesterol (CH), phosphatidylcholine (PC) and sodium cholate (NaC) at concentrations similar to those found in supersaturated human gall bladder bile ([CH]/[PC] = 0.60 +/- 0.01; CH saturation index, CSI = 1.58 +/- 0.03) were prepared by mixing PC-CH vesicles with NaC micellar solutions. Following mixing, the dispersion became transparent and gave rise to high resolution 1H-NMR spectra typical of mixed micellar systems. Cryo-transmission electron micrographs of specimens vitrified at that stage support the conclusion that the vesicles had become completely micellized. Following micellization, the metastable (cholesterol-supersaturated) bile-models spontaneously underwent a series of reorganizational steps: first, cholesterol-rich vesicles with a [CH]/[PC] ratio of 1.57 +/- 0.69 were formed, in co-existence with a mixed micellar system with [CH]/[PC] = 0.43 +/- 0.01 and CSI = 1.12 +/- 0.03. The resultant cholesterol-rich vesicles subsequently aggregated and cholesterol crystals of varying sizes and shapes appeared within the aggregates: needle-like structures were first observed, followed by clusters of those crystals and of helical crystals. Eventually, typical plate-like cholesterol crystals appeared, at which time some of the PC returned to the non-particulate (isotropic) phase. Consequently, the system contained cholesterol crystals coexisting with mixed micelles, whose composition was close to the limit of saturation (CSI = 1.08). These findings confirm the sequence of events preceding the appearance of cholesterol crystals, as previously proposed in our less detailed studies ((1990) Hepatology 12, 149S) and support the relevance of the morphologically similar results of Konikoff et al. ((1992) J. Clin. Invest. 90, 1155) obtained in a very dilute supersaturated bile-model.

Bile↗

PubMed1995

The effect of albumin on the state of aggregation and phase transformations in phosphatidylcholine-sodium cholate mixtures.

Dilution of phospholipid-detergent mixed micellar systems results in an increase of the fraction of monomeric detergent and, consequently, in a decrease of the effective ratio Re between non-monomeric detergent and phospholipid. The value of Re has been previously shown to be the main determinant of the state of aggregation in such mixtures: at Re values below a critical value ReSAT, the mixture is vesicular; at Re values higher than ReSOL, the mixture is micellar, whereas within the range of ReSAT-ReSOL, vesicles and micelles co-exist. Albumin binds bile salts. Therefore, in PC-cholate mixtures, Re is reduced by the presence of albumin in the system. Within the range of PC concentrations of 2-23 mM, cholate concentrations of 2-15 mM and BSA concentrations of 0-100 mg/ml, binding of cholate to BSA results in reduction of the effective cholate concentration to the extent of 0.11 mM cholate per 1 mg/ml BSA, namely up to 7 cholate molecules bind to each BSA molecule. Yet, the values of ReSAT and ReSOL are essentially independent of BSA. In addition, at any given Re value, the size of vesicles made by dilution of mixed micelles is a complex function of albumin and PC concentrations. Possible mechanistic details which may cause this effect are discussed. These effects of albumin on the state of aggregation of PC-cholate mixtures must be taken into account in studies of such mixtures in the presence of albumin when other effects of albumin (e.g., on phospholipolysis) are investigated. Practical conclusions are reached with respect to the procedures that can be used to prepare vesicles of identical composition and size in the presence of different concentrations of albumin.

Cholic Acid↗