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PubMed1977

Influence of emulsion type and atmospheric oxygen on the fading of latent image in electron microscopic radioautography.

The intensity of radioautographic reactions in Ilford L4, Sakura NR-H2 and Kodak NTE emulsions was compared after exposure in either dry air or dry helium gas at 4 degrees C to test the stability of latent images in the presence or absence of oxygen. A light proof container is described in which slides bearing radioactive sections coated with the three emulsions were exposed in dry helium at a constant pressure of approximately 0.5 atm. The comparison of air and helium atmospheres during exposure of radioautographs was estimated qualitatively for 125I-labeled thyroid sections stored for several years and, in addition, quantitative data was derived from 3H-labeled methacrylate sections stored from 21 days to 1 year. With the three emulsions under study, the background fog remains low under both exposure conditions at 4 degrees C for as long as several years duration. Using L4 emulsion, similar high grain densities are obtained in air and helium, and therefore, the latent images in L4 emulsion remain stable in the presence of oxygen. In the case of NTE and NR-H2 emulsions, as the exposure time increases, substantially lower reaction intensities are observed in air than in helium. This difference in reaction intensity is evident by 3 weeks with NTE and after 4 weeks with NR-H2. Hence, there is fading of the latent images in the latter emulsions in the presence of oxygen. It is concluded that reliable results may be obtained with the L4 emulsion by exposure of radioautographs in dry air, whereas with the NR-H2 and NTE emulsions, exposure should be in an oxygen-free medium, such as is provided by a dry helium atmosphere.

Autoradiography↗
PubMed1995

Treatment of hepatic-metastatic colorectal cancer with a chemotherapeutic emulsion: interim results of a phase I trial.

BACKGROUND: Hepatic arterial infusion of 5-fluoro-2-deoxyuridine (FUdR) is associated with a 60% response rate among previously untreated patients who have hepatic-metastatic colorectal cancer. One obstacle to further dose escalation has been concomitant hepatic toxicity. We are evaluating a FUdR-containing chemotherapeutic emulsion to further dose intensify therapy without associated toxicity. METHODS: The in vitro pharmacokinetics of the emulsion were determined using high-pressure liquid chromatography (HPLC). The rate at which FUdR is released from emulsion into an overlying aqueous phase was determined in static and dynamic assays. Fifteen patients with hepatic-metastatic colorectal cancer were treated with intrahepatic arterial infusions of emulsion on a phase I dose-escalating clinical protocol. Serum collection determined systemic drug levels using HPLC. RESULTS: In vitro studies demonstrate that FUdR is slowly released from emulsion into overlying aqueous medium. The emulsion serves as a depot for FUdR. Therapy was well tolerated. Emulsion was sequestered in the liver after infusion in all treated patients. CONCLUSIONS: This Ethiodol-based, oil-in-water emulsion serves as a sustained-release preparation of FUdR. An Ethiodol-based oil-in-water emulsion is a clinically effective vehicle for delivering FUdR to hepatic-metastatic colorectal tumors.

Aged↗
PubMed2003

Cholesterol improves the utilization of parenteral lipid emulsions.

Lipid emulsions have become an indispensable component of parenteral nutrition. Commercially available emulsions mostly have an identical composition of triglycerides (from plant oils) and egg-yolk phospholipids as emulsifier. Previous attempts to improve the composition of lipid emulsions have focused mainly on the triglyceride moiety. In the first fundamental modification of a lipid emulsion since their broader introduction into clinical medicine, we included free cholesterol in a lipid emulsion. We evaluated elimination and hydrolysis of triglycerides and lipid oxidation (by indirect calorimetry) in 10 healthy male normolipemic volunteers, comparing a conventional lipid emulsion (20% triglycerides) with an otherwise identical emulsion with the addition of 4 g/l free cholesterol. The rise in plasma triglycerides was mitigated during infusion of the cholesterol-enriched solution (323.8 +/- 27.5 vs. 202.0 +/- 18.9 mg.dL-1, p < 0.001), plasma half-life was reduced (41.6 +/- 5.4 vs. 29.3 +/- 5.1 min, p < 0.05), and total-body clearance was enhanced (0.96 +/- 0.1 vs. 1.52 +/- 0.2 ml.b.w.(.)min-1, p < 0.02). The rise in plasma free fatty acids (400.7 +/- 39.0 vs. 532.2 +/- 64.0 mumol.L-1; p < 0.02) and ketone bodies (beta-hydroxybutyrate) (151.6 +/- 37.0 vs. 226.3 +/- 33.01 mumol.L-1; p < 0.02) was augmented. Increases in plasma insulin and glucagon were less pronounced (p < 0.05). The fall in respiratory quotient was greater and the fraction of lipid oxidation as a percentage of total energy expenditure was increased (66.2% +/- 6.0 vs. 70.9% +/- 6.3, p < 0.05) during infusion of the modified solution. No impairment of gas exchange or other side effects were observed. Taken together these results indicate that the elimination of a cholesterol-supplemented lipid emulsion is accelerated, triglyceride hydrolysis is enhanced, and lipid oxidation is augmented. Thus, addition of cholesterol to a lipid emulsion might not only present a means of providing cholesterol in parenteral nutrition but also help to reshape artificial lipid particles to a more chylomicron-resembling composition and improve lipid utilization.

Adult↗
PubMed2001

Modulation of apolipoprotein E-mediated plasma clearance and cell uptake of emulsion particles by cholesteryl ester.

Cholesteryl ester, along with triglyceride (TG), is the major core component of plasma lipoproteins. We investigated the effect of core composition on the physical state and metabolic behavior of lipid emulsions, as model particles of lipoproteins. Fluorescence studies using 1,6-diphenylhexatriene analogs showed that although cholesteryl oleate (CO) significantly decreased core mobility, the surface rigidity of phosphatidylcholine (PC) monolayers was independent of core composition. When intravenously injected into rats, the increased amount of core CO tended to retard TG emulsion removal from plasma, and the initial clearance rate was correlated with the amount of apolipoprotein E (apoE) bound from plasma. In addition, PC liposomes with a similar emulsion particle size showed negligible binding of apoE and were cleared at a slower rate compared to all emulsions. Furthermore, the effect of CO on the binding behavior of apoE to the emulsion surface and the emulsion uptake by hepatocytes was assessed in vitro. Replacing core TG with CO was found to decrease the apoE binding capacity to emulsions markedly without changing the binding affinity and thereby to reduce the cell uptake of emulsion particles by HepG2 cells. These results indicate that the physical state of core lipids, which can be modulated by CO content, plays a role in emulsion metabolism through the alteration in apoE binding.

Apolipoproteins E↗
PubMed1988

Effects of phospholipid composition on the metabolism of triacylglycerol, cholesteryl ester and phosphatidylcholine from lipid emulsions injected intravenously in rats.

Lipid emulsions were prepared with a similar size and lipid composition to natural lymph chylomicrons, but in which the surface phospholipid was either egg phosphatidylcholine, dioleoyl-, dimyristoyl-, dipalmitoyl- or 1-palmitoyl-2-oleoylphosphatidylcholine (EYPC, DOPC, DMPC, DPPC or POPC). When injected into the bloodstream of conscious rats, the emulsions containing EYPC or POPC were metabolized similarly to natural chylomicrons, consistent with rapid lipoprotein lipase-mediated hydrolysis of triacylglycerols, followed by hepatic uptake of the remnants derived from the emulsions. Phospholipids from the injected emulsions were removed more slowly and became associated with the high-density lipoprotein fractions of the plasma. Emulsions containing DPPC were metabolized differently. Triacylglycerols disappeared very slowly from plasma, indicating lack of hydrolysis by lipoprotein lipase, and phospholipid radioactivity did not transfer to high-density lipoprotein. With emulsions containing DMPC, the plasma removal rates for emulsion triacylglycerols and cholesteryl esters were fast, but phospholipid radioactivity failed to transfer to the high-density lipoprotein fractions of plasma. With DOPC emulsions, clearances were slower than EYPC or POPC emulsions, but transfer to high-density lipoproteins was efficient. Therefore, an unsaturated chain at the glycerol 2-position was necessary for rapid hydrolysis by lipoprotein lipase and for efficient transfer of phospholipids to high-density lipoproteins. With an unsaturated chain at the glycerol 2-position, a saturated chain at the glycerol 1-position optimized the rate of remnant removal from the plasma.

Animals↗
PubMed1991

Physico-chemical characterization of Intralipid emulsions.

Fat emulsions containing soy triacylglycerols (100-300 g/l) and egg-yolk phospholipids (12 g/l) are often used for intravenous feeding. Previous studies have shown that these emulsions contain chylomicron-like emulsion particles of diameters of 300-400 nm and excess phospholipids aggregated as vesicles (liposomes), which remain in the infranatant upon floatation of the emulsion particles by ultracentrifugation. This work is devoted to the characterization of the commercial lipid emulsions commonly denoted Intralipids, with special emphasis on the presently ill-defined liposomes. The lipid particles composing commercial lipid emulsions (10%, 20% and 30% Intralipids, Kabivitrum Nutrition) were characterized by the combined use of physical and chemical methods. Each of the emulsions was fractionated by ultracentrifugation in saline into a 'cream' layer which floats to the top of the dispersion upon ultracentrifugation and a relatively transparent infranatant. The cream layer contains large emulsion particles of diameters ranging from 300 to 400 nm, in agreement with theoretical considerations based on their chemical composition as determined by chemical analysis. The infranatants contain about 1 g/l triacylglycerols in addition to phospholipids (from 7.2 g/l in 10% Intralipid to 2.4 g/l in 30% Intralipid) in the form of smaller particles of 70-100 nm diameter. Cryo-transmission electron microscopy shows that the infranatants contain vesicles (mostly unilamellar) at the side of residual small emulsion particles. This conclusion is also consistent with the distribution of phospholipids between outer and inner lamellae, as determined by 31P-NMR.

Fat Emulsions, Intravenous↗
PubMed1987

Inhibition of vasoactive agents by perfluorochemical emulsion.

Perfluorochemicals are widely used in clinical and experimental studies as volume expanders with high oxygen carrying capacity. We noticed that contractions of rabbit aortic strips, induced by norepinephrine, were inhibited in FC-43 emulsion as compared to Krebs-Henseleit solution (KH). To study this inhibition, a comparative evaluation was made of the contractile responses of norepinephrine, serotonin and histamine in FC-43 emulsion and KH. The effect of these agents was significantly diminished in FC-43 emulsion; concentration-response curves were shifted to the right and the maximum response was diminished. A search was made for the individual constituents of FC-43 responsible for diminution of contraction of vascular smooth muscle. After centrifugation of FC-43 emulsion, the supernatant caused a reduction of contractility and reduced EC50-values of norepinephrine to the same degree as the fully constituted emulsion. This excluded perfluorotributylamine, the oxygen carrying particles, as being responsible for this inhibition. When the detergent Pluronic F-68 was added to KH in concentrations equal to that in FC-43 emulsion, inhibition of contraction occurred and EC50-values increased. Contractions induced by norepinephrine were equally inhibited by the addition to KH of a volume expander, hydroxyethylstarch, in a concentration equal to that in FC-43 emulsion. It is concluded that FC-43 emulsion inhibits vasoactive agents and attenuates its pharmacologic effects on vascular smooth muscle. The fractions of FC-43 emulsion responsible for inhibiting the effect of vasoactive agents are Pluronic F-68 and hydroxyethylstarch.

Animals↗
PubMed2006

Influence of oil droplet surface charge on the performance of antibody--emulsion conjugates.

Targeted drug delivery requires binding of (and subsequent uptake by) the carrier to target cells. The purpose of our present study is to compare the binding and uptake of emulsions with different electric surface properties to SK-BR3 cell line, which over-expresses the HER2 receptor. Cationic emulsion was prepared by incorporating 0.25% w/w of the cationic lipid, stearylamine in the formulation while the anionic emulsion formulation was identical but lacking stearylamine. Immunoemulsions were prepared by conjugating the 2-iminothiolane derivative of the monoclonal antibody trastuzumab (Herceptin) through the reactive maleimide group of the octadecyl-4-(maleimidomethyl)cyclohexane-carboxylic amide linker which was incorporated in the oil phase of the anionic and cationic emulsions. Cationic emulsion exhibited a droplet size of approximately 130 nm and a zeta potential of +50 mV compared to anionic emulsion with a droplet size of approximately 140 nm and a zeta potential of -30 mV which decreased to -5 mV following antibody coupling. There was no significant difference in the coupling efficiency of trastuzumab to anionic and cationic emulsions which was in the range of 60-70%. The cationic emulsion and immunoemulsion appeared to be physically stable over a long period of time, as indicated by particle-size measurements while the droplets of the anionic immunoemulsion coalesced with time resulting in phase separation within 20 days storage at 4 degrees C. The results of binding and uptake to cells showed that both cationic and anionic immunoemulsions bind and internalized to cells much more than the respective blank emulsions. The enhanced penetration of the probe coumarin-6 with both immunoemulsions clearly indicated that the internalization process was mainly controlled by a cell-receptor endocytosis mechanism mediated by the binding affinity of trastuzumab to the cell surface receptor since the uptake of the cationic immunoemulsion was not significantly different from the uptake of the anionic immunoemulsion. However, only the cationic immunoemulsion might be considered for further investigation in view of its long standing physical stability.

Anions↗
PubMed2006

Improvement of graft function and animal survival by fat emulsion in liver transplant rats.

Nutritional supports are required for liver transplant patients. However, no systematical assessment has been made of the optimal composition of energy yielding substrates in these patients. This study is to evaluate whether mixed energy system consisting of carbohydrate and lipid emulsions is more advantageous over single energy source of glucose for nutritional support in liver transplant recipients and whether structured lipid emulsion (STG) is superior to medium-chain triglyceride/long-chain triglycerides (MCT/LCT) and long-chain triglycerides (LCT) using a total parenteral nutrition model. Liver transplant rats were randomly divided to four groups according to the energy source, i.e. glucose (GLU), MCT/LCT, STG and LCT groups. Sham operated rats served as control. Hepatic function and lipid profile were determined to investigate the roles of lipid emulsion in hepatic function and lipid metabolism. Morphological changes of liver were observed, and nitrogen balance was determined. The results showed that infusion of lipid emulsion was well tolerated. The 1-week survival rate in the lipid emulsion groups was significantly higher than in the GLU group (100% versus 50%, P<0.05); compared with the GLU group, hepatic function recovered quickly and returned to normal level, and morphological alterations were less severer in the lipid emulsion groups, especially in the STG group; the lipid emulsions groups had normal serum TG and TC levels, especially STG and MCT/LCT groups; the lipid emulsions groups achieved a positive nitrogen balance on day 7 compared with the GLU group, and the STG group had the highest nitrogen balance. In conclusion, lipid emulsion is beneficial in improving hepatic function and the recipients' survival and does not influence the lipid metabolism. Mixed energy system consisting of carbohydrate and lipid is more advantageous over single energy source of glucose after liver transplantation, and STG is superior to MCT/LCT and LCT.

Animals↗
PubMed2006

Importance of bacterial surface properties to control the stability of emulsions.

In colloidal media such as emulsions or food matrixes, the stability results from physicochemical interactions. The same type of interaction is involved in the attachment processes of microorganisms, through their surface properties, to interfaces. When bacteria are present in a food matrix, it is probable that their surface interacts with the other constituents. In this paper, the involvement of bacterial surface properties of Lactococcus lactis subsp lactis biovar diacetylactis (LLD) on the stability of model emulsions has been studied. The hydrophobic and electrostatic cell-surface properties were characterized by the MATH method and by microelectrophoresis, respectively. The oil-in-water emulsions were stabilized by various surface-active compounds, CTAB, SDS or Tween 20, giving differently charged droplets. Two strains with different surface characteristics were added to the emulsion. Contrasting with emulsions made with the non-ionic surfactant, for which the stability was not modified by the addition of bacteria, the emulsions made with ionic surface-active compounds were unstable in the presence of bacteria when the bacterial surface charge was opposite to the one of the emulsion droplets. Moreover, aggregation and flocculation phenomena were observed for emulsions stabilized with the cationic surfactant, particularly for more negatively charged bacteria. The effect of bacteria on the emulsion stability depended on the strain which shows the importance of the choice of the microorganism according to of the characteristics of the colloidal media to obtain a stable system. In addition, these results suggest that the interactions between bacteria and other food components can influence the position of bacteria in food matrixes.

Bacterial Adhesion↗
PubMed2006

Inhibition of liver metastasis by all-trans retinoic acid incorporated into O/W emulsions in mice.

All-trans retinoic acid (ATRA) was incorporated into lipid emulsions in an attempt to alter its distribution characteristics and improve its inhibition of liver cancer metastasis. Lipid emulsions composed of egg phosphatidylcholine, cholesterol, and soybean oil were the optimized carriers for ATRA delivery, as shown by the submicron particle size and high incorporation efficiency. The particle size and zeta potential of ATRA incorporated into emulsions were about 133 nm and -11 mV, respectively. In vitro drug release study demonstrated that the release of ATRA from emulsions was sustained in the absence and present of bovine serum albumin, suggesting that ATRA was stable when incorporated in emulsions. After intravenous administration in mice, [3H]cholesteryl hexadecyl ether incorporated into emulsion, which is the inherent distribution of emulsions, accumulated gradually mainly in the liver. The blood concentration and hepatic accumulation of [3H]ATRA incorporated into emulsion was significantly higher than that of serum dissolving [3H]ATRA, which represent the original distribution characteristic of free ATRA. In a murine liver metastasis model by colon adenocarcinoma, the liver metastasis number and liver weight were significantly reduced and the survival time of mice was prolonged following intravenous injection of ATRA incorporated into emulsions.

Animals↗
PubMed2005

Changes in two-phase emulsion morphology in temperature-amphiphile concentration or fish diagram for ternary amphiphile/oil/water systems.

We examined the morphologies of two-phase emulsions in the ternary 2-butoxyethanol/n-decane/water system at various temperatures and water-to-oil ratios (WORs). The two-phase emulsion morphologies depended on temperature, WOR, and amphiphile concentration, and the results are presented in a temperature-amphiphile concentration coordinate system or a "fish" diagram. The observations made in this work contradict the predictions by the phase-inversion-temperature (PIT) concept. At WOR<1, a vertical inversion line was observed at T T(uc) (upper critical endpoint temperature) and at low amphiphile concentrations, only B/T emulsions appeared, irrespective of temperature. At WOR>1, the situation was reversed; T/B emulsions at T T(uc), and T/B emulsions at low amphiphile concentrations, irrespective of temperature. At WOR=1, two horizontal inversion lines, one each at T T(uc), were observed. The morphologies of the two-phase emulsions were B/T or T/B emulsions at low amphiphile concentrations, and at higher amphiphile concentrations T/B at T T(uc). All these findings along with three-phase emulsion data result in complete emulsion morphology diagrams in the temperature-amphiphile concentration space or fish diagram.

Alkanes↗
PubMed1998

Stable lipiodolized emulsions for hepatoma targeting and treatment by transcatheter arterial chemoembolization.

We attempted to develop lipiodolized emulsions that remain in the tumour for a long period, release drug in a sustained release pattern, and thus improve the conventional treatment of hepatocellular carcinoma (HCC) [1]. Polyoxyethylene derivatives of hydrogenated castor oil (HCO) were the most suitable emulsifiers in stabilizing emulsions containing Lipiodol as an oil phase. The length of ethylene oxide coupled to HCO rather than the hydrophilic-lipophilic balance (HLB) values was an important factor in preparing stable emulsions and in achieving sustained-release characteristics. When distilled water was replaced with Iopamiro, a heavy water soluble contrast medium with a specific gravity of 1.335, more stable lipiodolized emulsions with longer sustained release behaviour could be prepared with smaller amount of HCO. To study the in vivo stability of the w/o Lipiodol emulsion and the sustained-release characteristics of doxorubicin from the emulsion, the pharmacokinetic study was performed with normal dogs using transcatheter arterial chemoembolization technique. The area under the plasma concentration-time curve for the first eight hours (AUC0-8) and AUCtotal values of the stabilized emulsion were three to four times higher than those of the coarse emulsion prepared lacking HCO 60. From the in vitro and in vivo studies, Lipiodol based water in oil emulsion with HCO 60 containing doxorubicin showed higher stability and released doxorubicin in a sustained fashion.

Animals↗
PubMed1997

CTL induction using synthetic peptides delivered in emulsions--critical role of the formulation procedure.

Emulsions have been used with variable degrees of success to deliver antigen to stimulate immune responses. We have investigated three different ways of incorporating peptide antigen into soybean emulsions to induce CTL responses in mice. Two of these emulsions (oil-in-water, o/w, and water-in-oil-in-water, w/o/w) had peptide incorporated at the formulation stage, while the third had peptide added to a pre-formed o/w emulsion. High levels of CTL activity were induced when peptide was dispersed into the o/w or w/o/w emulsions, in contrast to addition of peptide to the pre-formed o/w emulsion, which did not stimulate a CTL response. Induction of CTL activity was independent of emulsion globule size but was correlated with a negative zeta potential and dispersion of peptide in the oil phase. The ability of peptide in soybean oil emulsion to induce CTL is critically dependent on dispersion of peptide at the time of emulsion formation.

Adjuvants, Immunologic↗
PubMed2001

Physical properties and stability of two emulsion formulations of propofol.

We have compared the physical properties of two commercial emulsion formulations of the intravenous anaesthetic propofol, (Diprivan, AstraZeneca, and Propofol Intravenous Emulsion, Gensia Sicor Pharmaceuticals) which appear to differ primarily in the additive content and formulation pH. Diprivan contains disodium edetate and has a pH of 7-8.5, while the Gensia product contains sodium metabisulphite and is formulated to a pH of 4.5-6.4. The average zeta potential of Diprivan at pH 8 was -50 mV while that of the Gensia product at pH 4-5 was -40 mV. This information suggests that the physical stability of Propofol Intravenous Emulsion should be lower than that of Diprivan. Three random batches of both products were subjected to a range of stability tests, including shaking, thermal cycling, and freeze-thaw cycling, and the emulsion droplet size distribution was then assessed by dynamic light scattering, light diffraction, and electrical and optical zone sensing. Both emulsions initially showed narrow submicrometre particle size distributions. An increased level of droplets larger than 5 microm could be detected in Propofol Intravenous Emulsion after as little as 4 h shaking (300 strokes/min at room temperature) and visible free oil could be detected after 8-12 h shaking. In contrast, Diprivan showed no increase in the large droplet count after shaking for times up to 16 h. A similar difference in the emulsions was found after one freeze-thaw cycle, with Propofol Intravenous Emulsion exhibiting extensive coalescence, while that of Diprivan was at the limits of detection. We conclude that these two products have different physical stability characteristics, and that this may in part be due to the reduced zeta potential in Propofol Intravenous Emulsion compared to that of Diprivan.

Anesthetics, Intravenous↗
PubMed2003

The effects of serum on the stability and the transfection activity of the cationic lipid emulsion with various oils.

The emulsions with various oils such as linseed oil, soybean oil and squalene were prepared to obtain the relationship between the stability and the transfection activity of the emulsions. 1,2-Dioleoyl-sn-glycero-3-trimethylammonium-propane (DOTAP) was used as a single cationic lipid emulsifier. The droplet sizes and size distributions of DOTAP emulsions were dependent on oils which had different interfacial tensions. The droplet sizes followed the order of squalene emulsion soybean oil emulsion>linseed oil emulsion>DOTAP liposome. The squalene emulsion showed the least cytotoxicity with or without serum. For in vivo gene transfer, the squalene emulsion also had the most potent transfection activity in the mouse after intravenous administration. Squalene as the oil component can enhance the stability of cationic emulsion more effectively that could be useful for the transfer of genes in vitro and in vivo.

Animals↗
PubMed2003

Formulation of intravenous carbamazepine emulsions by SolEmuls technology.

Oil in water (O/W) emulsions for parenteral nutrition can be employed as intravenous (i.v.) carriers for drugs that are poorly soluble in water and in oil by localising the drug in the interfacial lecithin layer, e.g. Amphotericin B emulsions. By now, the emulsion production required organic solvents. SolEmuls technology localises the drug in the interfacial layer by a solvent-free high-pressure homogenisation process. SolEmuls was applied to produce Carbamazepine emulsions at increasing drug concentrations from 0.5 to 10mg/ml. Drug powder and Lipofundin emulsion were mixed and homogenised at 1500bar. Characterisation of emulsions and short-term stability were performed by photon correlation spectroscopy (PCS) and laser diffractometry. Drug incorporation (absence of non-dissolved drug crystals) was investigated by light microscopy and a centrifugation test. The emulsions were physically stable and complete drug dissolution is possible up to 3mg/ml. Up to 10mg/ml drug hybrid dispersions of emulsion droplets and ultrafine nanocrystals were obtained. Both, emulsions and hybrid dispersions are suitable as i.v. injectables regarding size and stability.

Carbamazepine↗
PubMed1983

Triolein-cholesteryl oleate-cholesterol-lecithin emulsions: structural models of triglyceride-rich lipoproteins.

The organization of lipids within emulsions composed of triolein (TO), cholesteryl oleate (CO), cholesterol (C), and egg yolk phosphatidylcholine (L) was examined. CO was substituted for TO in a series of emulsions to obtain TO:CO ratios comparable to the triglyceride:cholesterol ester ratios observed in subfractions of triglyceride-rich lipoproteins. The weight fraction of TO in the surface phase (0.02-0.05) was independent of the TO content of the emulsions. However, the weight fraction of CO in the surface phase depended upon the percentage of CO in the emulsions and was less than 0.004 even when 13.7% CO was present in the emulsion. When CO was substituted for TO, the percent of the total particle C which was carried in the droplet oil phase was increased. The interparticle equilibration of lipids was studied in subfractions of sonicated emulsions with particle sizes comparable to triglyceride-rich lipoproteins. The TO:CO ratios of the subfractions of a given emulsion were constant and independent of size, but the C:L ratio decreased in particles of smaller diameter. However, the surface C:L ratio was the same in all particles from a given emulsion. The size dependence of the C:L ratios was attributed to the partitioning of C into the oil cores of the emulsions. Because large droplets have the greatest core:surface mass ratios, more of their total particle C is carried in the core.

Chemical Phenomena↗