Estimation of the uptake rate constants for polycyclic aromatic hydrocarbons accumulated by semipermeable membrane devices and triolein-embedded cellulose acetate membranes

In this paper we report an extension of our previous work on the triolein-embedded cellulose acetate membrane (TECAM) as a passive sampling device (PSD) and describe the results from simultaneous exposure of TECAMs and triolein-containing semipermeable membrane devices (SPMDs) to PAHs in lake water for 16 days. The data obtained provided a comparison of the uptake rates of specific PAHs by the two PSDs. Using 16-day accumulation tests, similar PAH distribution patterns in TECAMs and in SPMDs (R2 = 0.89, p < 0.0001) were observed. However, it was noted that TECAMs could take up greater amounts of PAHs than SPMDs (735 ng/g of TECAM vs 630 ng/g of SPMD). Uptake rate constants of TECAMs and SPMDs for 16 priority pollutant (PP) PAHs, corrected for dissolved organic carbon, ranged from 0.28 to 2.94 L d(-1) and from 0.16 to 0.91 L d(-1), respectively. The elimination rate constants of TECAMs were 1.4-6.7 times greater than those observed for SPMDs, thereby indicating that PAHs required shorter times to achieve equilibrium in TECAMs than in SPMDs. Thus, the results of the present study suggest that TECAMs have significant potential as a good monitor to assess the pollution of hydrophobic pollutants in aquatic environments.

Apolipoprotein B is conformationally flexible but anchored at a triolein/water interface: a possible model for lipoprotein surfaces

Apolipoprotein B (apoB) is one of a unique group of proteins that form and bind to fat droplets, stabilize the emulsified fat, and direct their metabolism. ApoB, secreted on lipoproteins (emulsions), remains bound during lipid metabolism yet exhibits conformational flexibility. It has amphipathic beta-strand (AbetaS)-rich domains and amphipathic alpha-helix (AalphaH)-rich domains. We showed that two consensus AbetaS peptides of apoB bound strongly to hydrophobic interfaces [triolein/water (TO/W) and dodecane/water], were elastic, and were not pushed off the interface when the surface was compressed. In contrast, an AalphaH peptide modeling helical parts of apoB was forced off the TO/W interface by compression and readsorbed when the interface was expanded. In this report, the surface behavior of apoB-100 was studied at the TO/W interface. Solubilized apoB lowered the interfacial tension of TO/W in a concentration-dependent fashion. At equilibrium tension, if the surface was compressed, part of apoB was pushed off but quickly readsorbed when the surface was expanded. Even when the surface area was compressed by approximately 55%, part of the apoB molecule remained bound. The maximum surface pressure that apoB could withstand without being partially ejected was 13 mN/m. ApoB showed high elasticity at the TO/W interface. Based on studies of the consensus AbetaS and AalphaH peptides, we suggest that AbetaSs anchor apoB and are its nonexchangeable motif, whereas its conformational flexibility arises from both the elastic nature of the AbetaS and the ability of AalphaH domains of the molecule to desorb and readsorb rapidly in response to surface pressure changes.

Accelerated lipid absorption in mice overexpressing intestinal SR-BI

Dietary cholesterol absorption contributes to a large part of the circulating cholesterol. However, the mechanism of sterol intestinal uptake is not clearly elucidated. Scavenger receptor class B type I (SR-BI), major component in the control of cholesterol homeostasis, is expressed in the intestine, but its role in this organ remains unclear. We have generated transgenic mice overexpressing SR-BI primarily in the intestine by using the mouse SR-BI gene under the control of intestinal specific "apoC-III enhancer coupled with apoA-IV promoter." We found SR-BI overexpression with respect to the natural protein along the intestine and at the top of the villosities. After a meal containing [(14)C]cholesterol and [(3)H]triolein, SR-BI transgenic mice presented a rise in intestinal absorption of both lipids that was not due to a defect in chylomicron clearance nor to a change in the bile flow or the bile acid content. Nevertheless, SR-BI transgenic mice showed a decrease of total cholesterol but an increase of triglyceride content in plasma without any change in the high density lipoprotein apoA-I level. Thus, we described for the first time a functional role in vivo for SR-BI in cholesterol but also in triglyceride intestinal absorption.

Structural Study on Polymorphism of Cis-Unsaturated Triacylglycerol: Triolein

To clarify the influence of cis-unsaturation on solid-state structures of triacylglycerols (TAGs), the crystal structures of three crystalline phases (alpha, beta' and beta) of triolein [C3H5(OCOC17H33)3] were investigated by powder X-ray diffractometry and IR and Raman spectroscopy. The influence on the structural change of the alpha phase in the course of cooling was also studied. With respect to the subcell structure and conformational order of hydrocarbon chains in the beta and beta' phases, triolein resembles saturated TAGs; trans-zigzag hydrocarbon chains are adopted in the T(parallel) subcell for the beta phase and in the O(perpendicular) subcell for the beta' phase. The influence of cis-unsaturation was most obvious in the structure of the alpha phase and its temperature dependence. The alpha phase of triolein does not form the ordinary hexagonal subcell but a rather loose distorted subcell, which hardly changes in cooling, forming a striking contrast to the hexagonal-->pseudohexagonal subcell transformation found in the alpha phase of saturated TAGs.

Val-407 and Ile-408 in the beta5'-loop of pancreatic lipase mediate lipase-colipase interactions in the presence of bile salt micelles

In a previous study, we demonstrated that the beta5'-loop in the C-terminal domain of human pancreatic triglyceride lipase (hPTL) makes a major contribution in the function of hPTL (Chahinian et al. (2002) Biochemistry 41, 13725-13735). In the present study, we characterized the contribution of three residues in the beta5'-loop, Val-407, Ile-408, and Leu-412, to the function of hPTL. By substituting charged residues, aspartate or lysine, in these positions, we altered the hydrophilic to lipophilic ratio of the beta5'-loop. Each of the mutants was expressed, purified, and characterized for activity and binding with both monolayers and emulsions and for binding to colipase. Experiments with monolayers and with emulsions suggested that the interaction of hPTL with a phospholipid monolayer differs from the interaction of the hPTL-colipase complex with a dicaprin monolayer or a triglyceride emulsion (i.e. neutral lipids). Val-407, Ile-408, and Leu-412 make major contributions to interactions with monolayers, whereas only Val-407 and Ile-408 appear essential for activity on triglyceride emulsions in the presence of bile salt micelles. In solutions of taurodeoxycholate at micellar concentrations, a major effect of the beta5'-loop mutations is to change the interaction between hPTL and colipase. These observations support a major contribution of residues in the beta5'-loop in the function of hPTL and suggest that a third partner, bile salt micelles or the lipid interface or both, influence the binding of colipase and hPTL through interactions with the beta5'-loop.

Enzyme Catalyzed Production of Biodiesel From Olive Oil

Biodiesel (fatty acid methyl esters) was produced by transesterification of triglycerides (triolein) present in olive oil with methanol and Novozym435. The effect of the molar ratio of methanol to triolein, semibatch (stepwise addition of methanol) vs batch operation, enzyme activity, and reaction temperature on overall conversion was determined. Stepwise methanolysis with a 3:1 methanol to triolein molar ratio and an overall ratio of 8:1 gave the best results. The final conversion and yield of biodiesel were unaffected by initial enzyme concentrations greater than 500 U/mL olive oil. The optimum reaction temperature was 60 degrees C. Comparison of conversion data between a test-tube scale reactor and a 2-L batch reactor revealed that the difference in conversion was within 10%. Experiments were also carried out with used cooking oil; the conversion with used cooking oil was slightly lower but no major differences were observed. The efficacy of Novozym435 was determined by reusing the enzyme; although the enzyme's relative activity decreased with reuse, it still retained 95% of its activity after five batches and more than 70% after as many as eight batches.

Acidolysis between triolein and short-chain fatty acid by lipase in organic solvents

Ten kinds of lipases were examined as biocatalysts for the incorporation of short-chain fatty acids (acetic, propionic, and butyric acids) into triolein in order to produce one kind of reduced-calorie structured lipids. Trans-esterification (acidolysis) was successfully done in n-hexane by several microbial lipases. Among them, lipase from Aspergillus oryzae was used to investigate the effects of incubation time, substrate molar ratio, and water content on acidolysis. Finally, more than 80% of triolein was incorporated by butyric acid (molar ratio of triolein to butyric acid, 1:10) in the dried n-hexane at 52 degrees C for 72 h. More than 90% of the products was monosubstituent, which was esterified with this short chain fatty acid at the 1-position of the glycerol moiety of triolein. These results suggest that A. oryzae lipase would be a powerful biocatalyst for the synthesis of low caloric oil, such as triacylglycerol containing a mixture of long- and short-chain aliphatic acids.

Lipase-catalyzed biosynthesis of cinnamoylated lipids in a selected organic solvent medium

Biosynthesis of cinnamoylated lipids through the lipase-catalyzed transesterification reaction of cinnamic acid with triolein was investigated in organic solvent media. Electrospray ionization-mass spectroscopy (ESI-MS) structural analysis of the reaction mixture revealed the formation of two major end products, monoleyl-1(3)-cinnamate and dioleyl-2-cinnamate. Decreasing the molar ratio of cinnamic acid to triolein from 1:1 to 1:4.5 resulted in an increase in the maximum bioconversion yield of cinnamoylated lipids from 19 to 42%, which remained constant at a lower ratio of 1:6. However, an excess of triolein appeared to have a more beneficial effect on the formation of dioleyl-2-cinnamate than monoleyl-1(3)-cinnamate, leading to different end product compositions at ratios of substrates. With cinnamic acid to triolein ratios of 1:4.5 and 1:6.0, an increase in the bioconversion yield of cinnamoylated lipids to 55% was achieved by adding 2.2 mgmL(-1) silica gel to the reaction mixture. Radical scavenging activity of cinnamoylated lipids, with 50% of radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging, was found to be higher than that of its corresponding phenolic acid.

Biodiesel production from triolein and short chain alcohols through biocatalysis

Oleic acid alkyl esters (biodiesel) were synthesised by biocatalysis in solvent-free conditions. Different commercial immobilised lipases, namely Candida antarctica B, Rizhomucor miehei, and Pseudomonas cepacia, were tested towards the reaction between triolein and butanol to produce butyl oleate. Pseudomonas cepacia lipase resulted to be the most active enzyme reaching 100% of conversion after 6h. Different operative conditions such as reaction temperature, water activity, and reagent stoichiometric ratio were investigated and optimised. These conditions were then used to investigate the effect of linear and branched short chain alcohols. Methanol and 2-butanol were the worst alcohols: the former, probably, due to its low miscibility with the oil and the latter because secondary alcohols usually are less reactive than primary alcohols. Conversely, linear and branched primary alcohols with short alkyl chains (C(2)--C(4)) showed high reaction rate and conversion. A mixture of linear and branched short chain alcohols that mimics the residual of ethanol distillation (fusel oil) was successfully used for oleic acid ester synthesis. These compounds are important in biodiesel mixtures since they improve low temperature properties.

Partitioning of polychlorinated biphenyls in octanol/water, triolein/water, and membrane/water systems

The use of the octanol/water partition constant (Kow) as a surrogate parameter for lipid/water partitioning of persistent organic pollutants (POPs) was reassessed by comparing the measured Kow of 12 selected polychlorinated biphenyl congeners (PCBs) with partition constants in triolein/water (Ktw) and membrane/water (Kmw) systems. Kow and Ktw were measured by the slow-stirring method. Kmw was measured by an adaptation of the slow-stirring method using suspensions of phosphatidylcholine and phosphatidylserine liposomes. Partitioning of POPs to octanol, triolein, and liposomes is similar but not equal. The log-log correlation for Kow and Ktw is excellent (r2 = 0.982) and that for Kow and Kmw is somewhat weaker (r2 = 0.856). Ktw values are greater than Kow by a factor of 1.6. Kmw of some PCB congeners exceed both Kow and Ktw by an order of magnitude. The differences are attributed to different PCB activity coefficients in the different lipid phases. The results imply that Kow can be used as a reasonable conservative estimate of lipid/water partitioning. But the observed differences between Kow and Kmw also indicate that using Kow to predict accumulation of POPs, particularly highly hydrophobic ones, in the polar lipids of organisms will underestimate their concentrations at equilibrium.

[Preparation of triolein-embedded CA membrane and its characteristics]

Triolein is successfully embedded into cellulose acetate (CA) by phase inversion. This prepared flat membrane can effectively remove trace lipophilic organic pollutants from water. Structure of hybrid membrane is mainly observed by scanning electron microscope (SEM). Triolein dispersion by mechanical rabbling and ultrasound are investigated. Ultrasound can more effectively strengthen triolein dispersion than mechanical rabbling. Effect of casting membrane temperature (room temperature, 0 degrees C) shows low temperature can help to forming smaller triolein droplets. In addition, interaction between triolein and CA belongs to physical mixing by the observation of FT-IR, accordingly triolein structure is not changed and adsorptive capacity for persistent organic pollutants is not affected. Triolein in hexane is analyzed by fluorometric measure. The results show that triolein is completely embedded into membrane, so it is impossible that triolein leaks into water in the process of the adsorption.

The interfacial properties of ApoA-I and an amphipathic alpha-helix consensus peptide of exchangeable apolipoproteins at the triolein/water interface

Apolipoprotein A-I (apoA-I) is the major protein in high density lipoprotein (HDL). During lipid metabolism, apoA-I moves among HDL and triacylglycerol-rich lipoproteins. The main structure and the major lipid binding motif of apoA-I is the amphipathic alpha-helix. To understand how apoA-I behaves at hydrophobic lipoprotein interfaces, the interfacial properties of apoA-I and an amphipathic alpha-helical consensus sequence peptide (CSP) were studied at the triolein/water (TO/W) interface. CSP ((PLAEELRARLRAQLEELRERLG)2-NH2) contains two 22-residue tandem repeat sequences that form amphipathic alpha-helices modeling the central part of apoA-I. ApoA-I or CSP added into the aqueous phase surrounding a triolein drop lowered the interfacial tension (gamma) of TO/W in a concentration- and time-dependent fashion. The gamma(TO/W) was lowered approximately 16 millinewtons (mN)/m by apoA-I at 1.4 x 10(-6) m and approximately 15 mN/m by CSP at 2.6 x 10(-6) m. At equilibrium gamma, both apoA-I and CSP desorbed from the interface when compressed and readsorbed when expanded. The maximum surface pressure CSP could withstand without being ejected (PiMAX) was 16 mN/m. The PiMAX) of apoA-I was only 14.8 mN/m, but re-adsorption kinetics suggested that only part of the apoA-I desorbed at Pi between 14.8 and 19 mN/m. However, above approximately 19 mN/m (PiOFF) the entire apoA-I molecule desorbed into the water. ApoA-I was more flexible at the TO/W interface than CSP and showed more elasticity at oscillation periods 4-128 s even at high compression, whereas CSP was elastic only at faster periods (4 and 8 s) and moderate compression. Flexibility and surface pressure-mediated desorption and re-adsorption of apoA-I probably provides lipoprotein stability during metabolic-remodeling reactions in plasma.

Purification and characterization of an extracellular lipase from Geotrichum marinum

An extracellular lipase (EC 3.1.1.3) from Geotrichum marinum was purified 76-fold with 46% recovery using Octyl Sepharose 4 Fast Flow and Bio-Gel A 1.5 m chromatography. The purified enzyme showed a prominent band on SDS-PAGE and a single band on native PAGE based on the activity staining. The molecular mass of the lipase was estimated to be 62 kDa using SDS-PAGE and Bio-Gel A chromatography, indicating that the lipase likely functions as a monomer. The pl of the lipase was determined to be 4.54. The apparent V(max) and Km were 1000 micromol/min/mg protein and 11.5 mM, respectively, using olive oil emulsified with taurocholic acid as substrate. The lipase demonstrated a pH optimum at pH 8.0 and a temperature optimum at 40 degrees C. At 6 mM, Na+, K+, Ca2+, and Mg2+ stimulated activity, but Na+ and K+ at 500 mM and Fe2+ and Mn2+ at 6 mM reduced lipase activity. The anionic surfactant, taurocholic acid, and the zwitterionic surfactant, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, enhanced the activity at 0.1 mM. Other anionic surfactants such as SDS and sodium dioctyl sulfosuccinate, the cationic surfactants methylbenzethonium bromide and cetyltriethylammonium bromide, and the nonionic surfactants Tween-20 and Triton X-100 inhibited the lipase activity to different extents. The lipase was found to have a preference for TG containing cis double bonds in their FA side chains, and the reaction rate increased with an increasing number of double bonds in the side chain. The lipase had a preference for ester bonds at the sn-1 and sn-3 positions over the ester bond at the sn-2 position.

Accumulation of organochlorine pesticides from water using triolein embedded cellulose acetate membranes

A new type of composite membrane, triolein embedded cellulose acetate membrane (TECAM), was produced by embedding triolein drops in the matrix of cellulose acetate polymers. The distribution of six organochlorine pesticides (OCPs) between water and TECAM was investigated in a static water system. Its field application was tested in Taihu Lake (China). Results from both laboratory and field experiments indicate that TECAM quickly and efficiently accumulated hydrophobic OCPs from water. Under laboratory conditions, uptake equilibrium was achieved within 24 h for all of the six OCPs. Significant correlations were obtained between log Kp TECAM (TECAM-water partition coefficient) and log Kow (octanol-water partition coefficient); between log Ktw (triolein-water partition coefficient, triolein in TECAM) and log Kow; and between log Ktw and log BCF (bioconcentration factor in rainbow trout calculated from literatures). Triolein in TECAM significantly increased the accumulation of strongly hydrophobic OCPs when compared to the use of cellulose acetate polymers alone. Temperature had only slight effects on the Kp TECAM values of the strongly hydrophobic OCPs. The partition coefficient obtained by measuring OCP concentrations in TECAM under field conditions could be successfully applied to estimate OCPs concentrations in surface water.

Determination of serum triglycerides using lipase, glycerol kinase, glycerol-3-phosphate oxidase and peroxidase co-immobilized onto alkylamine glass beads

A method for determination of serum triglycerides (Tgs) using lipase, glycerol kinase, glycerol-3-phosphate oxidase and peroxidase co-immobilized onto alkylamine glass beads (pore diameter 55 nm) through glutaraldehyde coupling was developed and evaluated. The minimum detection limit of the method was 0.54 mM. The analytical recovery of added triolein in the serum was 97.55 +/- 1.5% (mean +/- S.D.). The mean value of serum Tgs, determined by the present method showed a good correlation (r = 0.984) with the Bayer's kit method, employing free enzymes. The within and between batch coefficients of variation (CV) were < 2.25% and < 1.35% respectively. No significant loss of activity was observed, when co-immobilized enzymes were reused for about 200 times and stored at 4 degrees C in distilled water. The cost of Tg determination for 200 serum samples was less, as compared with Bayer's kit method.

Method for testing the aquatic toxicity of sediment extracts for use in identifying organic toxicants in sediments

Biologically directed fractionation techniques are a fundamental tool for identifying the cause of toxicity in environmental samples, but few are available for studying mixtures of organic chemicals in aquatic sediments. This paper describes a method for extracting organic chemicals from sediments and then re-introducing them into water column toxicity tests in a way that mimics, at least in part, the partitioning processes that govern bioavailability in sediment. This involves transferring solvent extracts of sediment into triolein and then placing the mixture inside low-density polyethylene dialysis tubing in a configuration similar to semipermeable membrane devices (SPMDs) used for environmental monitoring. For four model compounds, SPMDs were shown to effectively maintain water column exposure in static systems for 10-14 d, with partition coefficients similar to K(OW). Toxicity tests indicated that the SPMDs were compatible with four of five freshwater organisms tested and could be used to measure both lethal and sublethal end points. An example application showed good correspondence between organism responses in intactsediment and extracts in SPMDsfor both field-collected and spiked sediments. The SPMD-based method offers a simple, flexible test design, amenable to several different test organisms, and the ability to work with complex mixtures of contaminants while maintaining partitioning behavior similar to that within intact sediments.

Interfacial properties of amphipathic β strand consensus peptides of apolipoprotein B at oil/water interfaces

The region between residues 968 and 1882 of apolipoprotein B (apoB-21 to apoB-41) is rich in amphipathic beta strands (AbetaSs) and promotes the assembly of primordial triacylglyceride (TAG)-rich lipoproteins. To understand the importance of AbetaS in recruiting TAG, the interfacial properties of two AbetaS consensus peptides, P12 and P27, were studied at dodecane/water (DD/W) and triolein/water (TO/W) interfaces. P12 (acetyl-LSLSLNADLRLK-amide) and P27 (acetyl-LSLSLNADLRLKNGNLSLSLNADLRLK-amide), when added into the aqueous phase surrounding a suspended oil drop (dodecane or triolein), decreased the interfacial tension (gamma) in a concentration-dependent manner. At the DD/W interface, 1 x 10(-5) M P12 decreased gamma to approximately 20 mN/m and 6.6 x 10(-6) M P27 decreased gamma to approximately 13 mN/m. At the TO/W interface, 1.5 x 10(-5) M P12 decreased gamma to approximately 14 mN/m and 9.0 x 10(-6) M P27 decreased gamma to approximately 12 mN/m. The surface area of both peptides was between 11.2 and 15.1 angstroms2 per residue, consistent with beta sheets lying flat on DD/W and TO/W interfaces. P12 and P27 are almost purely elastic on DD/W, TO/W, and air/water interfaces. When P12 and P27 were compressed beyond the equilibrium gamma to as low as 4 mN/m, they could not be readily desorbed from either interface. These properties probably help in assembling nascent TAG-rich lipoproteins, and AbetaS may anchor apoB to beta lipoproteins.

Application of solvent engineering to optimize lipase-catalyzed 1,3-diglyacylcerols by mixture response surface methodology

1,3-Diacylglycerol (DAG) has been introduced in Japan as a cooking oil under the trade name of Econa to reduce body fat accumulation. Solvent engineering was applied to determine the optimum solvent mixtures for the lipase-catalyzed synthesis of 1,3-DAG by mixture response surface methodology. n-Hexane was required to maintain the lipase activity and the product selectivity could be adjusted by changing the hydrophobicity of reaction medium. The optimum yield (approximately 40%) of 1,3-DAG synthesis was obtained with n-hexane/octane (1:1, v/v).

Lag phase and hydrolysis mechanisms of triacylglycerol film lipolysis

We here present novel insights into the dynamic changes of a nanosized lipid film during enzymatic degradation. When adding an aqueous solution containing a triacylglycerol lipase to an approximately 100nm thin triolein film, which is supported on a hard surface, the film thickness, elasticity, viscosity, and chemical composition were obtained continuously. Both a mechanical technique (quartz crystal microbalance with dissipation monitoring) and a spectroscopic technique (attenuated total reflection Fourier transform infrared spectroscopy) were utilised for this study. Detailed data revealed the effects of pH, Ca(2+), and catalytic rate on lipolysis, including product release from the film. It was found that under basic conditions and without Ca(2+), the lipolytic activity commence instantaneously upon addition of enzyme, whereas product release from the substrate film awaits conditions that favours release. A model for removal of degradation products from the film is introduced, including a novel interpretation of the lag phase phenomenon.

Differential lipid affinity of xenobiotics and natural compounds

Octanol-1/water partitioning currently provides the most widely used model system to simulate both phospholipid target lipids and triglyceride storage lipids. A differentiation between the two lipid classes is now achieved by making use of a water-induced lipid phase separation. Coefficients (K(TG/PC)) for partitioning between trioleoylglycerol (TG) and phosphatidylcholine (PC) were determined for 20 xenobiotics and two biological lipids. K(TG/PC) values are related to KOW through the relationship, log K(TG/PC)=0.33 log KOW-1.078. The present results will allow better predictions on whether drugs and xenobiotics are bioaccumulated, degraded or reach toxicity-related sites. In addition, applications to natural lipophilic compounds and disease-related proteins are discussed.

The sustained granulopoietic effect of progenipoietin encapsulated in multivesicular liposomes

Progenipoietin (ProGP), a dual receptor agonist of fetal liver tyrosine kinase-3 (flt3) and granulocyte colony-stimulating factor (G-CSF) receptors, has been shown to significantly enhance production of both polymorphonuclear leukocytes and dendritic cells (DCs) in the peripheral blood and spleen of mice, when administered as daily s.c. injections for about 10 days. Here, we have successfully designed a sustained-delivery formulation for this novel chimeric protein using multivesicular liposomes (DepoFoam), and studied the effects of changing both the triglyceride and phospholipid composition of the lipid matrix to modulate its delivery profile. Encapsulation of ProGP in these particles led to retention of its structural integrity, and maintenance of its biological activity in vivo. Administration of a single s.c. dose of 1mg/kg of an optimized DepoProGP formulation in rats, led to significant elevation of absolute neutrophil counts (ANC) that were maintained at levels >10,000 microliter(-1) for 9-11 days, in a reproducible manner. In contrast, administration of the unencapsulated ProGP at the same dose, resulted in elevation of neutrophils by day 1, followed by a quick decline to base line levels by day 3. These data suggest the possibility of administering a single dose of DepoFoam-encapsulated ProGP to improve hematopoietic recovery time after chemotherapy, and for other indications that require multiple daily doses of ProGP.

Gas chromatographic investigation of acrylamide formation in browning model systems

Acrylamide formed in browning model systems was analyzed using a gas chromatograph with a nitrogen-phosphorus detector. Asparagine alone produced acrylamide via thermal degradation at the level of 0.99 microgram/g of asparagine. When asparagine was heated with triolein-which produced acrolein at the level of 1.82 +/- 0.31 (n = 5) mg/L of headspace by heat treatment-acrylamide was formed at the level of 88.6 microgram/g of asparagine. When acrolein gas was sprayed onto asparagine heated at 180 degrees C, a significant amount of acrylamide was formed (114 microgram/g of asparagine). On the other hand, when acrolein gas was sprayed onto glutamine under the same conditions, only a trace amount of acrylamide was formed (0.18 microgram/g of glutamine). Relatively high levels of acrylamide (753 microgram/g of ammonia) were formed from ammonia and acrolein heated at 180 degrees C in the vapor phase. The reaction of acrylic acid, which is an oxidation product of acrolein and ammonia, produced a high level of acrylamide (190 000 microgram/g of ammonia), suggesting that ammonia and acrolein play an important role in acrylamide formation in lipid-rich foods. Acrylamide can be formed from asparagine alone via thermal degradation, but carbonyl compounds, such as acrolein, promote its formation via a browning reaction.

The amino acid sequences of the carboxyl termini of human and mouse hepatic lipase influence cell surface association

Human hepatic lipase (hHL) mainly exists cell surface bound, whereas mouse HL (mHL) circulates in the blood stream. Studies have suggested that the carboxyl terminus of HL mediates cell surface binding. We prepared recombinant hHL, mHL, and chimeric proteins (hHLmt and mHLht) in which the carboxyl terminal 70 amino acids of hHL were exchanged with the corresponding sequence from mHL. The hHL, mHL, and hHLmt proteins were catalytically active using triolein and tributyrin as substrates. In transfected cells, the majority of hHLs bound to the cell surface, with only 4% of total extracellular hHL released into heparin-free media, whereas under the same conditions, 61% of total extracellular mHLs were released. Like mHL, hHLmt showed decreased cell surface binding, with 68% of total extracellular hHLmt released. To determine the precise amino acid residues involved in cell surface binding, we prepared a truncated hHL mutant (hHL471) by deleting the carboxyl terminal five residues (KRKIR). The hHL471 also retained hydrolytic activity with triolein and tributyrin, and showed decreased cell surface binding, with 40% of total extracellular protein released into the heparin-free media. These data suggest that the determinants of cell surface binding exist within the carboxyl terminal 70 amino acids of hHL, of which the last five residues play an important role.

Accumulation of organochlorinated pesticides by triolein-containing semipermeable membrane device (triolein-SPMD) and rainbow trout

An important advance in aquatic ecotoxicology is the development and application of biomimetic sampling technology for hydrophobic contaminants. In this paper, accumulation kinetics of five organochlorinated pesticides, i.e. hexachlorobenzene, lindan, aldrin, heptachlor epoxide and 4,4'-DDT, by triolein-containing semipermeable membrane device (triolein-SPMD) and by fish (rainbow trout) were compared in a laboratory continuous flow system. Accumulation kinetics of organochlorinated pesticides by the triolein-SPMD and by rainbow trout were linear during the exposure period of 20 d, except for lindan. Approach of an asymptote could be observed for lindan at the end of the exposure for rainbow trout. When the kinetic data were used to calculate the first-order uptake rate constants, it was found that the uptake rates of the chemicals in triolein-SPMD were 1-2.5 times higher than those in the fish. The estimated bioconcentration factors of the five pesticides in rainbow trout were in the range of 1000-7000 and the device concentration factor in the range of 1500-18000. Although equilibrium was not reached for most pesticides under 21-d exposure period, correlations between C(L)/C(w) and K(ow) (R(2)=0.887) and C(f)/C(w) and K(ow) (R(2)=0.931) could be observed which was a clear indication that triolein-SPMD accumulates chlorinated pesticides in a quite similar way as fish do. Our results show that triolein-SPMD could serve as a good surrogate for rainbow trout for simulating accumulations of chlorinated pesticides and may be used as a universal surrogate for fish in natural waters.

Biokinetics and radiation dosimetry for patients undergoing a glycerol tri[1-14C]oleate fat malabsorption breath test

The glycerol tri[1-14C]olein test for fat malabsorption was carried out in two male volunteers and measurements of the loss of 14C in expired air, urine and faeces and the retention of 14C in biopsy samples of abdominal fat were made using accelerator mass spectrometry. Exhalation accounted for 73% and 55% of the administered activity and could be described by three-component exponential functions with halftimes of about 1h, 2 days and 150 days, respectively. Urinary excretion accounted for 24% of the administered activity, almost all during the first 24h after administration; about 2% was excreted in the faeces in 48h. The halftime of retention of 14C in fat ranged from 137 to 620 days. Absorbed dose calculations indicate that for a normal adult the largest dose, 1.5-7.0mGy/MBq is received by the adipose tissue, and that the effective dose is 0.3-0.5mSv/MBq. It is concluded that no restrictions need to be placed on radiation safety grounds on the administration of 0.05-0.1MBq 14C-triolein for the triolein breath test.

Dynamics of competitive adsorption of alphas-casein and beta-casein at planar triolein-water interface: evidence for incompatibility of mixing in the interfacial film

Competitive adsorption of alpha(s)-casein and beta-casein from a bulk solution mixture to the triolein-water interface has been studied. Although the binding affinity of alpha(s)-casein to the triolein-water interface was lower than that of beta-casein in single-component systems, in a 1:1 mixture of alpha(s)-casein and beta-casein in the bulk solution the ratio of interfacial concentrations of alpha(s)-casein to beta-casein at equilibrium was about 2:1, indicating that alpha(s)-casein was preferentially adsorbed to the triolein-water interface. Furthermore, the equilibrium composition of alpha(s)-casein and beta-casein in the interfacial film at various bulk concentration ratios did not follow a simple Langmuir adsorption model. This deviation from ideal behavior was mainly due to thermodynamic incompatibility of mixing of these caseins in the interfacial region. The value of the incompatibility parameter, X(12), for these caseins at the triolein-water interface was much greater than that at the air-water interface. Displacement experiments showed that while alpha(s)-casein could dynamically displace beta-casein when the latter was in an unsaturated monolayer state at the interface, it could not do so when beta-casein was in a saturated monolayer film state. It is hypothesized that, because of thermodynamic incompatibility of mixing, the alpha(s)-casein and beta-casein mixed film at the oil-water interface may undergo two-dimensional phase separation.

Use of triolein-semipermeable membrane devices to assess the bioconcentration and sediment sorption of hydrophobic organic contaminants in the Huaihe River, China

Triolein-containing semipermeable membrane devices (triolein-SPMD) were deployed I m above the sediments at two sampling sites in the Huaihe River, China, for a period of 28 d. Sediment and fish samples were simultaneously collected from the same sampling sites. Concentrations of substituted benzenes, selected pesticides, polycyclic aromatic hydrocarbon (PAH), and polychlorinated biphenyls (PCBs) were measured in triolein-SPMDs, sediments, and fishes. The concentrations of these hydrophobic organic contaminants (HOCs) in fish and in sediment organic carbon were correlated with HOCs accumulation in triolein-SPMDs. Our results showed reasonably good correlations between the log concentrations of contaminants in fish lipid and in triolein-SPMDs. Good correlations were also found between the log concentrations of contaminants in sediment organic carbon and in triolein-SPMDs (except for PAHs). The results were discussed in terms of the partitioning of hydrophobic organic contaminants among different compartments in the aquatic environment and the suitability of using triolein-SPMDs to predict bioconcentration factor (BCF) and sediment-water partitioning coefficient (K(oc)).

Review of the background and application of triolein-containing semipermeable membrane devices in aquatic environmental study

This paper briefly reviews research on passive in situ samplers for aquatic environments but focuses on the development and application of the triolein-containing semipermeable membrane device in aquatic environmental monitoring. Special attention is paid to the calibration of the devices, quality control issues, and its potential uses in environmental assessments of aquatic contaminants. Also, the suitability of the technique for incorporation with selected bioassays is examined.

Structure and properties of triolein-based polyurethane networks

Polyurethane networks based on vegetable oils have very heterogeneous composition, and it is difficult to find a close correlation between their structure and properties. To establish benchmark structure-properties relationships, we have prepared model polyurethane networks based on triolein and 4,4'-diphenylmethane diisocyanate (MDI). Cross-linking in the middle of fatty acid chains leaves significant parts of the triglyceride as dangling chains. To examine their effect on properties, we have synthesized another polyurethane network using triolein without dangling chains (removed by metathesis). The structure of polyols was studied in detail since it affects the structure of polyurethane networks. The network structure was analyzed from swelling and mechanical measurements and by applying network and rubber elasticity theories. The cross-linking density in both networks was found to be close to theoretical. The triolein-based model network displayed modulus (around 6 MPa), tensile strength (8.7 MPa), and elongation at break (136%), characteristic of hard rubbers. Glass transition temperatures of the networks from triolein and its metathesis analogue were 25 and 31.5 degrees C, respectively.

Edible arabinoxylan-based films. 1. Effects of lipid type on water vapor permeability, film structure, and other physical characteristics

Arabinoxylans (AX) are natural fibers extracted from maize bran, an industrial byproduct. To promote this polymer as a food ingredient, development of edible coatings and films had been proposed. Indeed, composite arabinoxylan-based films were prepared by emulsifying a fat: palmitic acid, oleic acid, triolein, or a hydrogenated palm oil (OK35). Lipid effects on water vapor permeability (WVP), surface hydrophobicity (contact angles), lipid particle size, and mechanical properties were investigated. Results showed that OK35-AX emulsion films had the lowest WVP. Emulsified films presented a bimodal particle size distribution; however, the smallest particle mean diameter (0.54 microm) was observed in OK35-AX emulsion films. Contact angles of water comparable to those observed for LDPE films (>90 degrees ) are measured on the OK35-AX film surface. Finally, only triolein-AX emulsion films had elongation higher than films without lipid. These results suggest that OK35 enhances functional properties of AX-based films and should be retained for further research.

Uptake of a cholesterol-rich emulsion by breast cancer

OBJECTIVE

Overexpression of low-density lipoprotein (LDL) receptors occurs in several cancer cell lines and offers a unique strategy for drug targeting by using LDL as vehicle. However, the native lipoprotein is difficult to obtain and handle. Previously, we showed that a lipidic emulsion (LDE) similar to the lipid structure of native LDL may bind to LDL receptors and be taken up by acute myelocytic leukemia cells. We also showed that LDE can also concentrate in ovarian cancer tissue. In this study, we tested whether LDE is taken up by breast carcinoma.

METHODS

LDE labeled with (99m)Tc was injected into 18 breast cancer patients, and nuclear medicine images of the tumor and metastatic sites were acquired. Subsequently, LDE labeled with [3H]cholesteryl oleate was intravenously injected into 14 breast cancer patients 24-30 h before total mastectomy procedure. Fragments of normal and of breast cancer tissue excised during surgery were lipid extracted with chloroform/methanol and their radioactivity was measured in a scintillation solution.

RESULTS

(99m)Tc-LDE images of the primary tumor and of metastasis sites were obtained in all 18 breast cancer patients. As directly measured in the tumor and in the normal mammary tissue, the amount of the emulsion radioactive label in the tumor was 4.5 times greater than in the normal tissue (range 1.2- to 8.8-fold).

CONCLUSION

LDE concentrates much more in malignant breast tumor tissue than in the normal tissue. Thus it has potential to carry drugs or radionuclides directed against mammary carcinoma cells for diagnostic or therapeutic purposes.

Dual parallel electrospray ionization and atmospheric pressure chemical ionization mass spectrometry (MS), MS/MS and MS/MS/MS for the analysis of triacylglycerols and triacylglycerol oxidation products

Two mass spectrometers, in parallel, were employed simultaneously for analysis of triacylglycerols in canola oil, for analysis of triolein oxidation products, and for analysis of triacylglycerol positional isomers separated using reversed-phase high-performance liquid chromatography. A triple quadrupole mass spectrometer was interfaced via an atmospheric pressure chemical ionization (APCI) interface to two reversed-phase liquid chromatographic columns in series. An ion trap mass spectrometer was coupled to the same two columns using an electrospray ionization (ESI) interface, with ammonium formate added as electrolyte. Electrospray ionization mass spectrometry (ESI-MS) under these conditions produced abundant ammonium adduct ions from triacylglycerols, which were then fragmented to produce MS/MS spectra and then fragmented further to produce MS/MS/MS spectra. ESI-MS/MS of the ammoniated adduct ions gave product ion mass spectra which were similar to mass spectra obtained by APCI-MS. ESI-MS/MS produced diacylglycerol fragment ions, and additional fragmentation (MS/MS/MS) produced [RCO](+) (acylium) ions, [RCOO+58](+) ions, and other related ions which allowed assignment of individual acyl chain identities. APCI-MS of triacylglycerol oxidation products produced spectra like those reported previously using APCI-MS. APCI-MS/MS produced ions related to individual fatty acid chains. ESI-MS of triacylglycerol oxidation products produced abundant ammonium adduct ions, even for those molecules which previously produced little or no intact molecular ions under APCI-MS conditions. Fragmentation (MS/MS) of the [M+NH(4)](+) ions produced results similar to those obtained by APCI-MS. Further fragmentation (MS/MS/MS) of the diacylglycerol fragments of oxidation products provided information on the oxidized individual fatty acyl chains. ESI-MS and APCI-MS were found to be complementary techniques, which together contributed to a better understanding of the identities of the products formed by oxidation of triacylglycerols.

Modeling of alpha-tocopherol loss and oxidation products formed during thermoxidation in triolein and tripalmitin mixtures

The degradation of alpha-tocopherol and the formation of alpha-tocopherol and triacylglycerol oxidation products at high temperatures (150-250 degrees C) over a heating period (0-4 h) for a model system ranging between triolein and tripalmitin were modeled by use of an experimental design. The oxidation products of alpha-tocopherol formed under these conditions were alpha-tocopherolquinone (1 .4-7.7%) and epoxy-alpha-tocopherolquinones (4.3-34.8%). The results indicate a very high susceptibility of alpha-tocopherol to capture peroxyl radicals upon oxidation, leading to the formation of polar tocopherol oxidation products. Both alpha-tocopherolquinone and epoxy-alpha-tocopherolquinones were not stable upon prolonged heating and were further degraded to other unknown oxidation products. The kinetics of alpha-tocopherol oxidation were significantly influenced by the triolein/tripalmitin ratio. By increasing the level of triacylglycerol unsaturation the rate of alpha-tocopherol recovery after heating increased significantly from 2.2 to 44.2% whereas in the meantime triacylglycerol polymerization increased from 0 to 3.7%.

Monitoring priority pollutants in a sewage treatment process by dichloromethane extraction and triolein-semipermeable membrane device (SPMD)

Semipermeable membrane devices containing a neutral lipid triolein (triolein-SPMD) and conventional dichloromethane extraction were used to monitor the presence and concentrations of priority organic pollutants in a sewage treatment process in Beijing, China. Both samples gave similar information on the presence of target PCB congeners, PAHs, Organochlorine pesticides and substituted benzenes in sewage at all sites. After 20 days' sampling, the concentrations of contaminants in triolein of SPMD were much higher than those in dichloromethane extracts, which resulted in easier analysis, improved the detection limits, and increased the accuracy. Previous field mean sampling rates for SPMD were used to estimate concentrations of PCB congeners in sewage, which compared to their determined concentrations by dichloromethane extraction. The consistency and superiority of SPMD technology were proved for the detection of priority organic contaminants from sewage. Lower removal rates for PCB congeners and PAHs coincided with the persistence of them in environment. More attention should be paid to urban sewage treatment process adopting activated-sludge method, where priority organic pollutants might not be removed, even present higher concentrations after treatment.

Identification of alpha-tocopherol oxidation products in triolein at elevated temperatures

The effect of high-temperature treatment on the stability of alpha-tocopherol (1) in triolein was assessed under a reduced-pressure atmosphere (4-40 mbar) simulating the deodorization step of the refining of vegetable oils. A marked degradation of 1 was observed, which increased with increasing temperature (180-260 degrees C) and heating time (20-80 min). The degradation of 1 in triolein at 240 degrees C was inhibited by the addition of the synthetic antioxidant TBHQ or when heating was performed under nitrogen atmosphere, indicating oxidative degradation. The oxidation products were isolated and identified as alpha-tocopherolquinone (2), 4a,5-epoxy-alpha-tocopherolquinone (3), and 7,8-epoxy-alpha-tocopherolquinone (4).

Effect of oleic and linoleic acids on the production of deep-fried odor in heated triolein and trilinolein

To determine sources of desirable deep-fried flavor in frying oils, degradation products from heated triolein and trilinolein with 5-31% polar compounds representing low to high deterioration were evaluated by purge-trap gas chromatography-mass spectrometry-olfactometry. (E,E)-2,4-Decadienal, 2-heptenal, 2-octenal, 2,4-nonadienal, and 2,4-octadienal produced deep-fried odor at moderate-strong intensities in heated trilinolein. However, unexpected aldehydes-2,4-decadienal, 2,4-undecadienal, 2,4-nonadienal, and 2-octenal (all <15 ppm)-were produced in triolein heated for 6 h. These dienals possibly were produced by hydroperoxidation and/or hydroxylation followed by dehydration of 2-alkenals. The 2-alkenals were produced from thermal decomposition of hydroperoxides, epoxides, and keto and dimeric compounds produced during the heating of triolein. These aldehydes produced low intensities of deep-fried odor in triolein. This information helps to explain sources of the deep-fried flavor that is characteristic of high linoleic frying oils but which is only at low intensity levels in high oleic frying oils.

Meal fatty acid uptake in human adipose tissue: technical and experimental design issues

The adipose tissue uptake of dietary fat has been studied using fatty acid radiotracers incorporated into a meal, followed by adipose tissue biopsies. A number of experimental design issues, including the use of isotopic tracers to measure meal fatty acid oxidation and plasma appearance of tracer, as well as the heterogeneity of adipose tissue fatty acid uptake, have been addressed. We examined these questions in a study of 24 volunteers (12 men and 12 women) who consumed a meal containing [(3)H]triolein and [(14)C]triolein. Slight differences in the purity of [(3)H]triolein vs. [(14)C]triolein were found, which could affect the apparent adipose tissue uptake of meal fatty acids. The adipose tissue triglyceride specific activity from bilateral biopsy sites agreed well, implying that a unilateral biopsy is satisfactory for measuring tracer uptake. Meal fatty acid oxidation measured using [(3)H]triolein and [(14)C]triolein was well correlated (r = 0.79, P < 0.0001). The peak tracer appearance in plasma chylomicrons occurred 1 h after the ingestion of a second, unlabeled meal. Our findings have implications for the experimental design of future meal fatty acid tracer/adipose tissue biopsy studies.

Determination of the conjugated linoleic acid-containing triacylglycerols in New Zealand bovine milk fat

Reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection at 233 nm was used to separate, quantify, and identify the triacylglycerols (TAG) of milk fat that contain conjugated linoleic acid (CLA). The absorbance at 233 nm was substantially due to CLA-TAG (chromatography of some representative TAG devoid of CLA, such as tripalmitin and triolein, showed poor responses at 233 nm, 1/800th that of CLA-TAG). A CLA molar extinction coefficient at 233 nm of 23,360 L mol(-1) cm(-1) and an HPLC UV response factor were obtained from a commercially available cis-9,trans-11-CLA standard. This molar extinction coefficient was only 86% of reported literature values. Summation of all chromatographic peaks absorbing at 233 nm using the corrected response factor gave good agreement with independent determinations of total CLA by gas chromatography and UV spectrophotometry. This agreement allowed quantification of individual CLA-TAG peaks in the HPLC separation of a typical New Zealand bovine milk fat. Three CLA-containing TAG, CLA-dipalmitin, CLA-oleoyl-palmitin and CLA-diolein, were prepared by interesterification of tripalmitin with the respective fatty acid methyl esters and used to assign individual peaks in the reversed-phase chromatography of total milk fat, of which CLA-oleoyl-palmitin was coincident with the largest UV peak. Band fractions from argentation thin-layer chromatography of total milk fat were similarly employed to identify five predominant CLA-TAG groups in total milk fat: CLA-disaturates, CLA-oleoyl-saturates, CLA-vaccenyl-saturates, CLA-vaccenyl-olein, and CLA-diolein.

Non-volatile products of triolein produced at frying temperatures characterized using liquid chromatography with online mass spectrometric detection

Oxidation products from triolein under model heated frying conditions have been analyzed using liquid chromatography with an evaporative light scattering detector and atmospheric pressure chemical ionization (APCI) mass spectrometric detection. Triolein was heated at 190 degrees C with 2% water added each hour, to simulate the moisture of a frozen product, until polar components reached approximately 30%. The samples were separated using reversed-phase high-performance liquid chromatography with APCI-MS detection. Triolein oxidation products included hydroperoxides, epoxides and a ketone. Other products were formed by shortening of an acyl chain on the intact triolein. Normal and oxygen-containing products formed by the dimerization of triolein were also observed. Other products included chain addition products formed by addition of acyl chain subunits to intact triolein to form higher molecular weight products.

Modification of lipoprotein lipase catalytic activity by sialic acids

The role of sialic acid linked with lipoprotein lipase (LPL) in its catalytic activity was studied. When LPL was treated with sialidase, the molecular weight decreased by 2000. The sialidase-treated LPL showed unchanged hydrolyzing activity for tributyrin, a water-soluble substrate of esterase, compared with the untreated LPL. The sialidase-treated LPL also showed similar hydrolyzing activity for triolein emulsified with Triton X-100, phosphatidylcholine and phosphatidylethanolamine, whereas it showed significantly increased hydrolyzing activity for triolein emulsified with phosphatidylserine and cardiolipin (152% and 183%, compared with untreated LPL, respectively). In addition, the sialidase-treated LPL showed significantly increased hydrolyzing activity against triolein incorporated into very low-density lipoproteins and chylomicrons (151% and 186%, compared with the untreated LPL, respectively). These results suggest that the loss of sialic acids does not modify the function of the catalytic site of LPL, but facilitates the interaction of the enzyme with the interface of the surface of substrate lipoproteins.

A thermodynamic analysis of the partitioning of cholesterol and related compounds between trioleoylglycerol and egg phosphatidylcholine bilayers

The free energy of transfer of a number of alcohols, including cholesterol, from a bulk isotropic lipid phase, trioleoylglycerol (TG), to an anisotropic lipid phase, egg phosphatidylcholine (PC), was determined. n-Alkane-1-ols partitioned preferentially into the bilayer phase; for example, the free energy of transfer of octanol-1 from TG to PC was about -1.0 kcal/mol. This preference declined with increasing number of carbons at a rate of 40 cal/mol of CH2. Cholesterol had a much stronger preference for the bilayer with a free energy of -1.3 kcal/mol, compared to an extrapolated value of -0.2 kcal/mol for a normal alkane-1-ol with the same number of carbon atoms. Thus, the excess free energy of -1.1 kcal/mol represents the favourable interaction of the cholesterol skeleton with the bilayer phase. This conclusion was confirmed by comparing cholesterol 3-hemisuccinate to oleic acid. Substituting TG for water as the standard state has eliminated the large hydrophobic effect and has permitted us to identify for the first time the subtle binding increment of the steroid ring system.

Studies on the inhibition of pancreatic and carboxylester lipases by protamine

The basic protein protamine strongly inhibited hydrolysis of triolein emulsified with soybean phosphatidylcholine (PC) by pancreatic and carboxylester lipases; 10 micrograms/ml protamine, about 1000 times lower than the concentration of bovine serum albumin for the same effect, inhibited triolein hydrolysis completely. This inhibition was not affected by the incubation pH or bile salt concentration. Two other basic proteins, histone and purothionin, also inhibited hydrolysis of triolein emulsified with soybean PC, but they did not inhibit triolein hydrolysis by gastric lipase. When gum arabic was used as an emulsifier instead of soybean PC, these basic proteins did not affect triolein hydrolysis by pancreatic or carboxylester lipases. The effects of protamine on triolein hydrolysis by pancreatic and carboxylester lipases was studied using various phospholipids as emulsifiers. Protamine (10 micrograms/ml) did not inhibit hydrolysis of triolein emulsified with dicaproyl PC (DCPC), phosphatidic acid (PA), or phosphatidylserine (PS) by pancreatic and carboxylester lipases. Conversely, protamine at high concentrations slightly stimulated hydrolysis of triolein emulsified with DCPC or PA. Hydrolysis of triolein-phosphatidylethanolamine (PE) emulsion was inhibited slightly by protamine. The profiles of protamine inhibition of triolein-phosphatidyl-N,N-dimethyl ethanolamine (PDME) and triolein-phosphatidyl-N-monomethyl ethanolamine (PMME) emulsions were intermediate between those of PC and PE emulsions. These results suggest that the phospholipid species, especially choline moieties and fatty acid chain length, affect the lipase inhibitory activity of protamine profoundly. In vivo, oral administration of protamine to rats reduced and delayed the peak plasma triacylglycerol concentration, but neither bovine serum albumin nor an amino acid mixture with an amino acid composition identical to protamine affected plasma triacylglycerol levels.

Monoacylglycerols alter the lipid composition and molecular mobility of phosphatidylcholine bilayers: 13C NMR evidence of dynamic lipid remodeling

The physical effects of monoacylglycerols (MAG) in small unilamellar vesicles composed of phosphatidyl-choline (PC), triolein, cholesterol, and varying amounts of monopalmitin and monoolein were studied by 13C-NMR. The signal to noise ratio of the carbonyls of PC and triolein were enhanced by the addition of 1,2-di-[1-13C]palmitoylphosphatidylcholine and tri-[1-13C]oleoylglycerol. The linewidths of the carbonyl-13C, choline methyl, olefinic carbon, and terminal methyl resonances were measured digitally from vesicles with 0 to 42 mol % of MAG. Significant increases in the linewidth of carbonyl (P < 0.05), olefinic and terminal methyl carbons (P < 0.01) of vesicles containing 42 mol % monopalmitin indicated that these groups experienced restricted molecular mobility at high monopalmitin concentrations. However, more striking was the apparent displacement of triolein from the surface environment of PC bilayers to an oil-like environment in systems containing only 8 mol % monopalmitin. Displacement of triolein from the surface by monoolein occurred only above 15 mol %. Thus, saturated and monounsaturated monoacylglycerols, natural products of lipoprotein metabolism, dynamically alter both the lipid composition and molecular mobility of lipoprotein surfaces in distinct ways.

Incorporation of medium chain triacylglycerols into phospholipid bilayers: effect of long chain triacylglycerols, cholesterol, and cholesteryl esters

The ability of water-insoluble molecules such as triacylglycerols to partition from oil phases into phospholipid interfaces may be crucial to their hydrolysis by lipases in the aqueous environment of plasma and cells. This study uses high resolution and magic angle spinning 13C NMR spectros-copy to measure the solubility of the 8-carbon medium chain triacylglycerol, trioctanoin, in the lamellar structure of phospholipids (vesicles and multilayers) in the presence of other neutral lipids that may compete for an interfacial location (long chain triacylglycerol, cholesteryl ester, and cholesterol). In the presence of a saturating concentration of triolein (approximately 3 mole%), the solubility of trioctanoin in egg phosphatidylcholine vesicles decreased from 10 mole% to 7 mole%. The presence of a saturating concentration of trioctanoin (approximately 10 mole%) decreased the interfacial solubility of long chain triolein to approximately 1 mole%. Cholesteryl oleate in phospholipid vesicles slightly diminished the incorporation of trioctanoin into the surface. The presence of cholesterol reduced the interfacial solubility of trioctanoin, but at a high level of cholesterol (30 mole%), trioctanoin had a solubility of 3 mole%. Thus, even in the presence of other competing neutral lipids, medium chain triacylglycerol retains a favorable location and surface concentration for efficient hydrolysis. 13C NMR analysis thus provides an explanation for preferential hydrolysis of medium, compared to long chain triacylglycerol, in a physical blend of medium and long chain triacylglycerol in a single emulsion particle, and in general, a valuable approach to determine substrate availability at phospholipid surfaces.

Stereoselectivity of lipases in supercritical carbon dioxide. I. Dependence of the regio- and enantioselectivity of porcine pancreas lipase on the water content during the hydrolysis of triolein and its partial glycerides

The stereoselectivity of porcine pancreas lipase (PPL) was investigated during the enzymatic hydrolysis of triolein and its partial glycerides in the presence of supercritical carbon dioxide (SCCO2) as reaction medium. The water content of the immobilized lipases was varied. The partial glycerides were separated into mono- and diglycerides by TLC, converted to their 3,5-dinitrophenylurethane derivatives and subsequently resolved into sn-1,2 and sn-2,3 enantiomers (estimation of dioleins) or into sn-1 and sn-3 enantiomers (estimation of monooleins) by HPLC on a chiral stationary phase (Sumichiral OA-4100). In all reactions under the conditions employed, PPL revealed a distinct preference for the sn-3 position of the glycerol. However, the stereoselectivity depends on the reaction time, the substances initially used and the enzyme water content. It seems that the effect of the enzyme water content on the activity and selectivity of porcine pancreas lipase in SCCO2 is based on a modification of the "micro-environment' of the enzyme by the solution of CO2 in water, causing a decrease of the pH value.

Characteristics of current induced potential oscillations of a triolein impregnated membrane placed between identical salt solutions

Periodic oscillations of electric potential were induced by DC electric current between identical salt solutions separated by a membrane filter impregnated with triolein. The oscillation period was controlled by the base electric potential, and temperature dependence of base conductance and conductance amplitude were both close to that of the electric conductivity of the aqueous salt solution. Effects of salt concentration on membrane conductance and on oscillation characteristics were experimentally investigated, and the lifetime of the membrane and of each oscillation were much improved by regulating the concentration of the salt solution. Moreover, characteristics of oscillation curves could be controlled. All the experimental results could be explained by a model where the oscillation was generated by a periodic change of the diameter of a hole through the membrane, which opened in one of the pores filled with triolein.

Carotenoids in biological emulsions: solubility, surface-to-core distribution, and release from lipid droplets

Data on the physico-chemical properties of carotenoids in biological emulsions are essential to our knowledge of carotenoid metabolism. Therefore, we determined the behavior of carotenoids in phospholipid-stabilized triglyceride emulsions, a model for biological emulsions such as dietary emulsions, triglyceride-rich lipoproteins, and intracellular storage droplets. The solubility of beta-carotene (a model for apolar carotenoids, carotenes) in pure bulk triglycerides (0.112 to 0.141 wt % according to triglycerides) was significantly higher than zeaxanthin (a model for polar carotenoids, xanthophylls) (0.022 to 0.088 wt %). The solubility of both carotenoids increased when the chain-length of the triglycerides' fatty acids decreased. The amount of zeaxanthin associated with lipid droplet dramatically increased in phospholipid-triglyceride droplets as compared to the pure corresponding triglyceride droplets, whereas the amount of beta-carotene associated with lipid droplets increased only slightly beta-Carotene distributed almost exclusively in the core of triolein-lecithin-carotenoid droplets, while zeaxanthin distributed preferentially at the droplet's surface. A significant percentage (8.3%) of zeaxanthin was spontaneously transferred from lipid droplets to aqueous phase and the remaining part was transferred during triglyceride hydrolysis catalysed by pancreatic lipase, while beta-carotene absolutely required triglyceride lipolysis to be transferred to the aqueous phase. Our results show that polar and apolar carotenoids behave differently in biological emulsions. They further our understanding of the bioavailability of polar and apolar carotenoids and of their distribution between lipoprotein particles.

Calorimetry of apolipoprotein-A1 binding to phosphatidylcholine-triolein-cholesterol emulsions

The thermotropic properties of triolein-rich, low-cholesterol dipalmitoyl phosphatidylcholine (DPPC) emulsion particles with well-defined chemical compositions (approximately 88% triolein, 1% cholesterol, 11% diacyl phosphatidylcholine) and particle size distributions (mean diameter, approximately 1000-1100 A) were studied in the absence and presence of apolipoprotein-A1 by a combination of differential scanning and titration calorimetry. The results are compared to egg yolk PC emulsions of similar composition and size. Isothermal titration calorimetry at 30 degrees C was used to saturate the emulsion surface with apo-A1 and rapidly quantitate the binding constants (affinity Ka = 11.1 +/- 3.5 x 10(6) M-1 and capacity N = 1.0 +/- 0.09 apo-A1 per 1000 DPPC) and heats of binding (enthalpy H = -940 +/- 35 kcal mol-1 apo-A1 or -0.92 +/- 0.12 kcal mol-1 DPPC). The entropy of association is -3070 cal deg-1 mol-1 protein or -3 cal deg-1 mol-1 DPPC. Without protein on the surface, the differential scanning calorimetry heating curve of the emulsion showed three endothermic transitions at 24.3 degrees C, 33.0 degrees C, and 40.0 degrees C with a combined enthalpy of 1.53 +/- 0.2 kcal mol-1 DPPC. With apo-A1 on the surface, the heating curve showed the three transitions more clearly, in particular, the second transition became more prominent by significant increases in both the calorimetric and Van't Hoff enthalpies. The combined enthalpy was 2.70 +/- 0.12 kcal mol-1 DPPC and remained constant upon repeated heating and cooling. Indicating that the newly formed DPPC emulsion-Apo-A1 complex is thermally reversible during calorimetry. Thus there is an increase in delta H of 1.17 kcal mol-1 DPPC after apo-A1 is bound, which is roughly balanced by the heat released during binding (-0.92 kcal) of apo-A1. The melting entropy increase, +3.8 cal deg-1 mol-1 DPPC of the three transitions after apo-A1 binds, also roughly balances the entropy (-3 cal deg-1 mol-1 DPPC) of association of apo-A1. These changes indicate that apo-A1 increases the amount of ordered gel-like phase on the surface of DPPC emulsions when added at 30 degrees C. From the stoichiometry of the emulsions we calculate that the mean area of DPPC at the triolein/DPPC interface is 54.5 A2 at 41 degrees C and 54.2 A2 at 30 degrees C. The binding of apo-A1 at 30 degrees C to the emulsion reduces the surface area per DPPC molecule from 54.2 A2 to 50.8 A2. At 30 degrees apo-A1 binds with high affinity and low capacity to the surface of DPPC emulsions and increases the packing density of the lipid domain to which it binds. Apo-A1 was also titrated onto DPPC emulsions at 45 degrees C. This temperature is above the gel liquid crystal transition. No heat was released or adsorbed. Furthermore, egg yolk phosphatidylcholine emulsions of nearly identical composition were also titrated at 30 degrees C with apo-A1 and were euthermic. Association constants were previously measured using a classical centrifugation assay and were used to calculate the entropy of apo-A1 binding (+28 cal deg-1 mol-1 apo-A1). This value indicates that apo-A1 binding to a fluid surface like egg yolk phosphatidylcholine or probably DPPC at 45 degrees C is hydrophobic and is consistent with hydrocarbon lipid or protein moities coming together and excluding water. Thus the binding of apo-A1 to partly crystalline surfaces is entropically negative and increases the order of the already partly ordered phases, whereas binding to liquid surfaces is mainly an entropically driven hydrophobic process.

Effects of the neutral lipid content of high density lipoprotein on apolipoprotein A-I structure and particle stability

Alterations in high density lipoprotein (HDL) composition that occur in dyslipidemic states may modulate a number of events involved in cholesterol homeostasis. To elucidate the details of how HDL-core composition can affect the molecular structure of different kinds of HDL particles, the conformation and stability of apoA-I have been investigated in homogeneous recombinant HDL particles (LpA-I) containing palmitoyloleoyl phosphatidylcholine (POPC), triolein (TG), and/or cholesteryl linoleate (CE). In a discoidal particle containing two molecules of apoA-I and 85 molecules of POPC, apoA-I exhibits an alpha-helix content of 70% and a free energy of stability of its alpha-helical segments (delta G0D) of 2.2 kcal/mol. Inclusion of eight molecules of TG into the complex significantly reduces the alpha-helix content and stability of apoA-I, whereas inclusion of four molecules of CE into the complex has an opposite effect in that the alpha-helix content is significantly reduced and the stability of the remaining alpha-helical structure of apoA-I is increased. Neutral lipids have a different effect on apoA-I conformation in spherical LpA-I particles. In a sonicated-spherical LpA-I particle containing two molecules of apoA-I and 70 molecules of POPC, apoA-I exhibits an alpha-helix content of about 60% and a delta G0D of 1.2 kcal/mol apoA-I. Inclusion of either 10 molecules of TG or six molecules of CE into such a particle increases both the alpha-helix content and stability of apoA-I. Increasing the CE/TG ratio in LpA-I particles that contain both neutral lipids enhances the stability of the alpha-helical segments. ApoA-I molecules tend to dissociate and cause particle instability when delta G0D for the lipid-bound alpha-helices is less than that for helices in the lipid-free state. The stabilities of both discoidal and spherical LpA-I particles are relatively low when the only neutral lipid present is TG but the particle stability is enhanced by the presence of CE molecules. Such dissociation of apoA-I molecules from LpA-I particles that have a low CE/TG ratio would be promoted in the hypertriglyceridemic state in vivo.

Fluorescence study of the motional states of core and surface lipids in native and reconstituted low density lipoproteins

Low density lipoproteins (LDL) consist of an apolar core of cholesterol esters and triglycerides surrounded by a monolayer of phospholipid, cholesterol, and a single molecule of apolipoprotein B (apoB-100). To determine the influence of core and surface constituents on the surface of LDL, we have measured core and surface order parameters for native LDL, and reconstituted LDLs (rLDL) whose apolar core lipids were extracted and replaced with either cholesterol oleate (CO) or triolein (TO). Order parameters were measured by fluorescence depolarization of diphenylhexatriene (DPH), which is located primarily in the core, and of trimethylammoniumdiphenylhexatriene (TMA-DPH), which is anchored at the water-phospholipid interface. DPH order parameters for LDL reconstituted with TO (r-[TO]LDL) were much lower than those for LDL reconstituted with CO (r-[CO]LDL), consistent with the physical properties of TO, a nonviscous liquid at all temperatures studied, and CO, which exists in a liquid crystalline or viscous liquid state at the temperatures studied. Although core cholesterol esters in r[CO]LDL and native LDL undergo distinct order-disorder transitions, these transitions were not detected by DPH. This is most likely due to the difference between the time scale for end-over-end tumbling of cholesterol esters and the fluorescence lifetime of DPH. Despite the fact that the core lipids of r-[CO]LDL were much more ordered than those of r-[TO]LDL, surface order parameters for both lipoproteins were similar. We conclude that the motional states of the core and surface lipids are relatively independent. Surface order parameters for native LDL were higher than those for reconstituted LDLs.(ABSTRACT TRUNCATED AT 250 WORDS)