The cardiovascular benefits of indiscriminate supplementation of omega-3 fatty acids; meta-analysis and decision-making approach

AIM

The meta-analysis was conducted to estimate of the cardiovascular benefits of indiscriminate supplementation of omega-3 capsules. The results, expressed in terms of quality adjusted life years (QALY) intuitively understood by the general public, can be the basis for the (personal) decision on whether to take omega-3 supplements.

METHODS

The results of meta-analysis of eight double-blind, placebo-controlled clinical trials are expressed in terms of QALY, using the Markov model and Monte Carlo simulations.

RESULTS

Omega-3 supplementation results in a 8% decrease of the risk of cardiac death, unless the patients are treated by statins. Results indicate that omega-3 supplementation may prolong QALY by about a month. Old people gain less, whereas DM-2 patients and people with history of CV events gain more.

DISCUSSION

Our analysis yielded an algorithm for estimating benefit from omega-3 supplementation, based on the age and the individual risk of CV events of the patient.

Evaluation of antioxidants: scope, limitations and relevance of assays

Peroxidation of lipids, particularly polyunsaturated fatty acid residues (PUFA) of phospholipids and cholesterol esters, is a process of marked implications: it shortens the shelf-life of food and drugs, it causes fragmentation of DNA, it damages cellular membranes and it promotes the genesis of many human diseases. Much effort is therefore devoted to a search for "potent antioxidants", both synthetic and from natural sources, mostly plants. This, in turn, requires a reliable, simple, preferably high throughput assay of the activity of alleged antioxidants. The most commonly used assays are based on measurements of the total antioxidant capacity (TAC) of a solution, as evaluated either by determining the rate of oxidation of the antioxidant or by measuring the protection of an easily determined indicator against oxidation by the antioxidants. The commonly used assays utilized for ranking antioxidants share three common problems: (i) They usually evaluate the effects of those antioxidants that quench free radicals, which constitute only a part of the body's antioxidative network, in which enzymes play the central role. (ii) Both the capacity and potency of antioxidants, as obtained by various methods, do not necessarily correlate with each other. (iii) Most estimates are based on methods conducted in solution and are therefore not necessarily relevant to processes that occur at the lipid-water interfaces in both membranes and micro emulsions (e.g. lipoproteins). Given this "state of art", many researchers, including us, try to develop a method based on the formation of hydroperoxides (LOOH) upon peroxidation of PUFA in lipoproteins or in model membranes, such as liposomes. In these systems, as well as in lipoproteins, the most apparent effect of antioxidants is prolongation of the lag time preceding the propagation of a free radical chain reaction. In fact, under certain conditions both water soluble antioxidants (e.g. vitamin C and urate) and the lipid soluble antioxidant tocopherol (vitamin E), promote or even induce peroxidation. Based on the published data, including our results, we conclude that terms such as 'antioxidative capacity' or 'antioxidative potency' are context-dependent. Furthermore, criteria of the efficacy of antioxidants based on oxidation in solution are not necessarily relevant to the effects of antioxidants on peroxidation in biological systems or model lipid assemblies, because the latter processes occur at water/lipid interfaces. We think that evaluation of antioxidants requires kinetic studies of the biomarker used and that the most relevant characteristic of 'oxidative stress' in the biological context is the kinetics of ex vivo peroxidation of lipids. We therefore propose studying the kinetics of lipid-peroxidation in the absence of the studied antioxidant and in its presence at different antioxidant concentrations. These protocols mean that antioxidants are assayed by methods commonly used to evaluate oxidative stress. The advantage of such evaluation is that it enables quantization of the antioxidants' efficacy in a model of relevance to biological systems. In view of the sensitivity of the lag time preceding peroxidation, we propose studying how much antioxidant is required to double the lag observed prior to rapid peroxidation. The latter quantity (C(2lag)) can be used to express the strength of antioxidants in the relevant system (e.g. LDL, serum or liposomes).

Copper-induced peroxidation of phosphatidylserine-containing liposomes is inhibited by nanomolar concentrations of specific antioxidants

Copper-induced peroxidation of liposomal palmitoyllinoleoyl-phosphatidylcholine (PLPC) is inhibited by alpha-tocopherol at micromolar concentrations. In our previous study we found that when the liposomes contain phosphatidylserine (PS), nanomolar concentrations of Toc were sufficient to inhibit peroxidation. In an attempt to gain understanding of the origin of this extreme antioxidative potency, we tested the antioxidative potency of 36 additional antioxidants and the dependence of their potency on the presence of PS in the liposomes. The results of these studies reveal that only 11 of the tested antioxidants possess similar antioxidative potency to that of Toc. These include trolox, butylated hydroxytoluene (BHT), curcumin, nordihydroguaiaretic acid (NDGA), diethylstilbestrol (DES), 2 of the 13 tested flavonoids (luteolin and 7,3',4'-trihydroxyflavone; T-414), alpha-naphthol, 1,5-, 1,6- and 1,7-dihydroxynaphthalenes (DHNs). Propyl gallate (PG), methyl syringate, rosmarinic acid, resveratrol, other flavonoids, as well as beta-naphthol, 1,2-, 1,3-, 1,4-, 2,3-, 2,6-, and 2,7-DHNs were either moderately antioxidative or pro-oxidative. For liposomes made of PLPC (250 microM) and PS (25 microM) the "lag" preceding copper-induced peroxidation (5 microM copper) was doubled upon addition of 30-130nM of the "super-active" antioxidants. We propose that the mechanism responsible for the extreme antioxidative potency against copper-induced peroxidation in PS-containing liposomes involves replenishment of the antioxidant in a ternary PS-copper-antioxidant complex. Based on structure-activity relationship of the 37 tested antioxidants, the "super-antioxidative potency" is attributed to the recycling of relatively stable semiquinone or semiquinone-like radicals.

Oxidation of liposomal cholesterol and its effect on phospholipid peroxidation

Lipid peroxidation is believed to play an important role in the pathogenesis of many diseases. Much research has therefore been devoted to peroxidation of different lipids in biomembranes and in model systems (liposomes) of different compositions. Yet, in spite of the relative simplicity of the liposomes, the existing literature is insufficient to reach definite conclusions regarding basic questions including the susceptibility of cholesterol to oxidation, its effect on the peroxidation of polyunsaturated phospholipids such as palmitoyllinoleoylphosphatidylcholine (PLPC) and how cholesterol influences the effect of water-soluble antioxidants such as urate on the peroxidation. The aim of the present study was to clarify these issues. Its major findings are that: (i) AAPH-induced peroxidation of cholesterol is slow and independent of the peroxidation of PLPC. In turn, AAPH-induced peroxidation of PLPC is not affected by cholesterol, independent of the presence of urate in the system. (ii) Cholesterol is not susceptible to copper-induced oxidation, but its inclusion in PLPC liposomes affects the peroxidation of PLPC, slowing down the initial stage of oxidation but promoting later stages. (iii) Addition of urate accelerates copper-induced peroxidation of PLPC in the absence of cholesterol, whereas in cholesterol-containing liposomes it inhibits PLPC oxidation. We attribute the complexity of the observed kinetics to the known cholesterol-induced rigidization of liquid crystalline bilayers.

Acute myocardial infarction is associated with increased susceptibility of serum lipids to copper-induced peroxidation in vitro

BACKGROUND

Low-density lipoprotein (LDL) oxidation in the arterial intima plays a pivotal role in atherogenesis. Under physiologic conditions, several mechanisms protect LDL against oxidation, including hydrolysis of oxidation products by high-density lipoprotein (HDL)-associated enzymes. Some of these protective mechanisms are less effective under acute phase conditions.

HYPOTHESIS

Conditions of acute phase response, including acute myocardial infarction (MI), may be expected to result in increased susceptibility of serum lipids to oxidation. The present study was undertaken to test this possibility.

METHODS

Using our previously developed spectroscopic method, we have monitored prospectively the kinetics of copper-induced oxidation of serum lipids obtained from 15 men during and after acute MI. This was tested within 6 h from the onset of chest pain, on Days 1, 3, and 7 of infarction and 1 year after recovery.

RESULTS

The lag phase preceding oxidation of serum lipids was much shorter during the first week after MI when compared with values obtained after recovery (52-59 vs. 107 min, respectively, p <0.001). During the first week after MI, we observed no significant correlations between kinetic parameters and serum lipid composition, in contrast both to the correlations previously reported for hyperlipidemic patients and to the similar correlations observed in the present study after recovery.

CONCLUSIONS

Acute MI is associated with an increased susceptibility of serum lipids to oxidation in vitro. This propensity for oxidation may reflect enhanced in vivo formation of free radicals and/or reduced efficiency of defense mechanisms. Both these possibilities may carry detrimental effects on the course, complications, and prognosis of the patients after acute MI.

Effect of a Short-Term Graded Exhaustive Exercise on the Susceptibility of Serum Lipids to Oxidation

The objective of our study was to evaluate the effect of short-term intensive exercise on the susceptibility of serum lipids to ex-vivo peroxidation. We assessed the association between aerobic capacity, serum composition, and serum lipid oxidizability as well as the association between aerobic capacity and the effect of short-term maximal exercise on the kinetics of ex-vivo copper-induced peroxidation of serum lipids. The study involved 30 healthy male volunteers (age 22-39 years, BMI 19.4-29.8). Following 12-hr fasting, blood was withdrawn for determination of blood lipids, LDL, HDL, and TG, and Vitamin E, and for oxidizability assay of the serum lipids. Subsequently, each volunteer underwent an incremental all-out cardiopulmonary exercise stress test (CPET), performed on a motor-driven treadmill (Quinton Q65, USA). The test protocol was a modified Balke protocol. The results of this test were expressed in terms of mass-dependent maximal oxygen uptake (VO2max, ml.kg(-1).min (-1)) and of ventilatory anaerobic threshold (VAT, ml.kg(-1).min(-1)). Immediately after exercise, blood was re-drawn for the determination of serum Vitamin E and for ex-vivo oxidizibility assay, expressed in terms of maximal absorption of oxidation products (OD(max), absorbance units), maximal rate of their production (V(max), OD min(-1)) and the time at which the rate was maximal (t(max), min). Maximal graded exercise had no significant effect on the susceptibility of serum lipids to peroxidation as measured by OD(max) (p = 0.38 at 245 nm, and 0.27 at 268 nm),V(max) (p = 0.34 at 245 nm, and 0.49 at 268 nm) and t(max) (p = 0.17 at 245 nm, and 0.07 at 268 nm). Also no effect was found on the concentration of serum Vitamin E (p = 0.39). Aerobic capacity was not associated either with the susceptibility of serum lipids to ex-vivo peroxidation or with serum Vitamin E concentration. The present findings indicate that a short graded maximal exercise, lasting 8-12 min, is not sufficient to increase the susceptibility of the serum lipids to peroxidation. Thus it may be assumed that the antioxidant capacity of most healthy subjects provides proper protection from a short exhaustive exercise challenge. Also, aerobic capacity in the range represented by our subjects does not seem to influence the susceptibility of serum lipids to peroxidation.

Curcumin synergistically potentiates the growth-inhibitory and pro-apoptotic effects of celecoxib in osteoarthritis synovial adherent cells

OBJECTIVES

Osteoarthritis (OA) is the Western world's leading cause of disability. Cyclo-oxygenase-2 (COX-2) inhibitors are efficient anti-inflammatory agents commonly used in the treatment of osteoarthritis. However, recent studies have shown that their long-term use may be limited due to cardiovascular toxicity. The anti-inflammatory efficacy of the phytochemical curcumin has been demonstrated in several in vitro and animal models. This study was undertaken to investigate whether curcumin augments the growth-inhibitory and pro-apoptotic effects of celecoxib in OA synovial adherent cells.

METHODS

OA synovial adherent cells were prepared from human synovial tissue collected during total knee replacement surgery. The cells were exposed to different concentrations of celecoxib (0-40 mum), curcumin (0-20 mum) and their combination. Flow cytometric analysis was used to measure the percentage of cells with a subdiploid DNA content, the hallmark of apoptosis. COX-2 activity was assessed by measuring production of prostaglandin E(2) by enzyme-linked immunoassay.

RESULTS

A synergistic effect was observed in inhibition of cell growth when the cells were exposed to various concentrations of celecoxib combined with curcumin. The inhibitory effect of the combination on cell growth was associated with an increased induction of apoptosis. The synergistic effect was mediated through a mechanism that involves inhibition of COX-2 activity.

CONCLUSIONS

This effect may enable the use of celecoxib at lower and safer concentrations, and may pave the way for a novel combination treatment in osteoarthritis and other rheumatological disorders.

The effect of cholesterol on the solubilization of phosphatidylcholine bilayers by the non-ionic surfactant Triton X-100

Most of the studies on the solubilization of model membranes by Triton X-100 (TR) involve one lipid. The aim of the present study was to evaluate the effect of the addition of cholesterol on the solubilization of bilayers made of palmitoyloleoylphosphatidylcholine (POPC) or dipalmitoylphosphatidylcholine (DPPC). Detailed investigation of the kinetics of solubilization of the cholesterol-containing bilayers by TR at different temperatures reveals that: (i) At 4 degrees C, solubilization of both systems is relatively slow. Hence, in order to prevent misleading conclusions from turbidity measurements it is important to monitor the solubilization after steady-state values of optical density (OD) are reached. (ii) Studies of the temperature-induced changes of the aggregates present in mixtures of TR, POPC and cholesterol indicate that the state of aggregation at all temperatures (including 4 degrees C) represents equilibrium. By contrast, for DPPC/cholesterol/TR mixtures "kinetic traps" may occur not only at 4 degrees C but at higher temperatures as well (e.g. 37 degrees C). (iii) The presence of cholesterol in POPC bilayers makes the bilayers more resistant to solubilization at low temperatures, especially at 4 degrees C. As a consequence, the temperature dependence of the TR concentration required for complete solubilization (Dt(sol)) is no longer a monotonically increasing function (as for POPC bilayers) but a bell-shaped function, with a minimum at about 25 degrees C. Inclusion of cholesterol in DPPC bilayers makes the bilayers more resistant to solubilization at all temperatures except 4 degrees C. In this system, we observe a bell-shaped dependence of Dt(sol) on temperature, with a minimum at 37 degrees C. (iv) Both the rate of vesicle size growth and the rate of the solubilization of POPC vesicles are not affected by the inclusion of cholesterol in the bilayers. Similarly, cholesterol did not affect significantly the rate of size growth of DPPC bilayers at all temperatures, but reduced the rate of solubilization at 4 degrees C.

Lipid peroxidation cannot be used as a universal criterion of oxidative stress

Oxidative stress is a term used to denote the imbalance between the concentrations of reactive oxygen and nitrogen species and the defense mechanisms of the body. Although it is generally accepted that such an imbalance plays a pivotal role in many pathologies, the term "oxidative stress" remains ill defined. In an attempt to evaluate the relationship between various assays of oxidative stress, we have analyzed the correlations between the results reported in those publications in which "oxidative stress" has been assayed by at least two methods. We found good correlations between the concentrations of several peroxidation products, including malondialdehyde, F2-Isoprostanes, lipid hydroperoxides, conjugated dienes, glutathione and protein carbonyls, but not with other criteria of "individual oxidative status" such as the concentration of antioxidants and products of DNA fragmentation (the "comet" assay). In light of these findings, we divide the assays used for evaluation of "oxidative stress" into the following three categories: (i) assays based on measuring the concentrations of oxidation products of lipids, proteins and DNA, as well as the concentrations of antioxidants, (ii) assays used to evaluate the oxidative and reductive capacity of biological fluids and (iii) assays used to evaluate the ex vivo susceptibility of lipids to oxidation upon their exposure to a source of free radicals. Our analyses demonstrate that oxidative stress cannot be defined in universal terms. Two results are of special interest:1.the commonly used criteria based on lipid peroxidation can not be regarded as a general estimate of the individual "oxidative status".2.the levels of antioxidants exhibit a non-monotonic relation with other criteria for oxidative stress. Further research is required to evaluate the significance of the latter finding.

Temperature-dependence of the solubilization of dipalmitoylphosphatidylcholine (DPPC) by the non-ionic surfactant Triton X-100, kinetic and structural aspects

Most of the studies on the solubilization of model membranes conducted thus far involved model membranes made of liquid-crystalline phospholipids. Relatively little is known on the influence of temperature and of the phase of the lipid bilayers on their solubilization by detergents. The aim of the present study was to gain knowledge about the temperature and phase dependence of the solubilization of phospholipid bilayers by the non-ionic detergent Triton X-100 (TR). Detailed investigation of the kinetics of the solubilization of dipalmitoylphosphatidylcholine (DPPC), as well as of palmitoyloleoylphosphatidylcholine (POPC) by TR at different temperatures reveals that: (i) solubilization of DPPC is a relatively slow process, especially below Tm. This means that in order to prevent misleading conclusions it is important to monitor the solubilization after a steady state is established. (ii) Both the steady state structure and size of DPPC/TR aggregates and the kinetics of solubilization depend on temperature. (iii) The TR concentration required for solubilization of POPC bilayers is an increasing function of temperature, although no phase change of bilayers occurs in the studied temperature range. (iv) Detailed studies of the temperature-induced changes of the aggregates present in DPPC/TR or POPC/TR mixtures suggest that the state of aggregation at any temperature above 23 degrees C represents equilibrium. By contrast, for DPPC/TR mixtures at 4 degrees C all the processes are very slow, which complicates the interpretation of results obtained through the common practice of studying "rafts" by investigating detergent-resistant membranes.

Kinetics of lipid peroxidation in mixtures of HDL and LDL, mutual effects

In view of the proposed central role of LDL oxidation in atherogenesis and the established role of HDL in reducing the risk of atherosclerosis, several studies were undertaken to investigate the possible effect of HDL on LDL peroxidation. Since these investigations yielded contradictory results, we have conducted systematic kinetic studies on the oxidation in mixtures of HDL and LDL induced by different concentrations of copper, 2, 2'-azo bis (2-amidinopropane) hydrochloride (AAPH) and myeloperoxidase (MPO). These studies revealed that oxidation of LDL induced either by AAPH or MPO is inhibited by HDL under all the studied conditions, whereas copper-induced oxidation of LDL is inhibited by HDL at low copper/lipoprotein ratio but accelerated by HDL at high copper/lipoprotein ratio. The antioxidative effects of HDL are only partially due to HDL-associated enzymes, as indicated by the finding that reconstituted HDL, containing no such enzymes, inhibits peroxidation induced by low copper concentration. Reduction of the binding of copper to LDL by competitive binding to the HDL also contributes to the antioxidative effect of HDL. The acceleration of copper-induced oxidation of LDL by HDL may be attributed to the hydroperoxides formed in the "more oxidizable" HDL, which migrate to the "less oxidizable" LDL and enhance the oxidation of the LDL lipids induced by bound copper. This hypothesis is supported by the results of experiments in which native LDL was added to oxidizing lipoprotein at different time points. When the native LDL was added prior to decomposition of the hydroperoxides in the oxidizing lipoprotein, the lag preceding oxidation of the LDL was much shorter than the lag observed when the native LDL was added at latter stages, after the level of hydroperoxides became reduced due to their copper-catalyzed decomposition. The observed dependence of the interrelationship between the oxidation of HDL and LDL on the oxidative stress should be considered in future investigations regarding the oxidation of lipoprotein mixtures.

The dose-dependent effect of copper-chelating agents on the kinetics of peroxidation of low-density lipoprotein (LDL)

Copper-induced peroxidation of lipoproteins involves continuous production of free radicals via a redox cycle of copper. Formation of Cu(I) during Cu(II)-induced peroxidation of LDL was previously demonstrated by accumulation of the colored complexes of Cu(I) in the presence of one of the Cu(I)-specific chelators bathocuproine (BC) or neocuproine (NC). All the studies conducted thus far employed high concentrations of these chelators (chelator/Cu(II) > 10). Under these conditions, at low copper concentrations the chelators prolonged the lag preceding oxidation, whereas at high copper concentrations the chelators shortened the lag. In an attempt to gain understanding of these non-monotonic effects, we have studied systematically the peroxidation of LDL (0.1 microM, 50 microg protein/mL) at varying concentrations of NC or BC over a wide range of concentrations of the chelators and copper. These studies revealed that: (i) At copper concentrations of 5 microM and below, NC prolonged the lag in a monotonic, dose-dependent fashion typical for other complexing agents. However, unlike with other chelators, the maximal rate of oxidation was only slightly reduced (if at all). (ii) At copper concentrations of 15 microM and above, the addition of about 20 microM NC or BC resulted in prolongation of the lag, but this effect became smaller at higher concentrations of the chelators, and at yet higher concentrations the lag became much shorter than that observed in the absence of chelators. Throughout the whole range of NC concentrations, the maximal rate of peroxidation increased monotonically upon increasing the NC concentration. (iii) Unlike in the absence of chelators, the prooxidative effect of copper did not exhibit saturation with respect to copper, up to copper concentrations of 30 microM. Based on these results we conclude that the copper-chelates can partition into the hydrophobic core of LDL particles and induce peroxidation by forming free radicals within the core. This may be significant with respect to the understanding of the possible mechanisms of peroxidation by chelated transition metals in vivo.

Phase boundaries in mixtures of membrane-forming amphiphiles and micelle-forming amphiphiles

The phase behavior of mixtures of phospholipids and detergents in aqueous solutions is an issue of basic importance for understanding the solubilization and reconstitution of biological membranes. We review the existing knowledge on the compositionally induced reversible transformation of phospholipid bilayers into lipid-detergent mixed micelles. First, we describe the experimental protocols used for preparation of such mixtures and emphasize the scope and limitations of the various techniques used for evaluation of the microstructures of the self-assembled amphiphiles in the mixture. Subsequently, we interpret the existing data in terms of the spontaneous curvature of the amphiphiles and the finite size of the mixed micelles. These considerations lead to a general description of the phase behavior, which forms the basis for a rational approach to solubilization and reconstitution experiments.

Inhibition of phospholipase A(2) as a therapeutic target

The hydrolysis of cell membrane phospholipids by phospholipase A(2) (PLA(2)) leads to the production of numerous lipid mediators of diverse pathological conditions, mainly inflammatory diseases. These include lysophospholipids and their derivatives, and arachidonic acid and its derivatives (the eicosanoids). Both these groups of mediators are produced predominantly by the secretory PLA(2)s (sPLA(2)s) which hydrolyze the phospholipids of the cell surface membrane. Protection of cell membrane from these 'inflammatory enzymes' can therefore be used for the treatment of inflammatory processes. A prototype of cell-impermeable PLA(2) inhibitors, which protect the cell membrane from different sPLA(2)s without affecting vital phospholipid metabolism, is presented and discussed in the present review.

Kinetic analysis of copper-induced peroxidation of HDL, autoaccelerated and tocopherol-mediated peroxidation

Comparison of the kinetic profiles of copper-induced peroxidation of HDL and LDL at different copper concentrations reveals that under all the studied experimental conditions HDL is more susceptible to oxidation than LDL. The mechanism responsible for HDL oxidation is a complex function of the copper/HDL ratio and of the tocopherol content of the HDL. At high copper concentrations, the kinetic profiles were similar to those observed for LDL oxidation, namely, relatively rapid accumulation of oxidation products, via an autoaccelerated, noninhibited mechanism, was preceded by an initial "lag phase." Under these conditions, the maximal peroxidation rate (V(max)) of HDL and LDL depended similarly on the molar ratio of bound copper/lipoprotein. Analysis of this dependency in terms of the binding characteristics of copper to lipoprotein, yielded similar dissociation constant (K = 10(-6) M) but different maximal binding capacities for the two lipoproteins (8 Cu(+2)/HDL as compared to 17 Cu(+2)/LDL). Given the size difference between HDL and LDL, these results imply that the maximal surface density of bound copper is at least 2-fold higher for HDL than for LDL. This difference may be responsible for the higher susceptibility of HDL to copper-induced oxidation in the presence of high copper concentrations. At relatively low copper concentrations, the kinetic profile of HDL oxidation was biphasic, similar to but more pronounced than the biphasic kinetics observed for the oxidation of LDL lipids at the same concentration of copper. Our results are consistent with the hypothesis that the first phase of rapid oxidation occurs via a tocopherol-mediated-peroxidation (TMP) mechanism. Accordingly, enrichment of HDL with tocopherol resulted in enhanced accumulation of hydroperoxides during the first phase of copper-induced oxidation. Notably, the maximal accumulation during the first phase decreased upon increasing the ratio of bound copper/HDL. This behavior can be predicted theoretically for peroxidation via a TMP mechanism, in opposition to autoaccelerated peroxidation. The possible pathophysiological significance of these findings is discussed.

Prolonged antibiotic prophylaxis after cardiovascular surgery and its effect on surgical site infections and antimicrobial resistance

BACKGROUND

Despite evidence supporting short antibiotic prophylaxis (ABP), it is still common practice to continue ABP for more than 48 hours after coronary artery bypass graft (CABG) surgery.

METHODS AND RESULTS

To compare the effect of short (<48 hours) versus prolonged (>48 hours) ABP on surgical site infections (SSIs) and acquired antimicrobial resistance, we conducted an observational 4-year cohort study at a tertiary-care center. An experienced infection control nurse performed prospective surveillance of 2641 patients undergoing CABG surgery. The main exposure was the duration of ABP, and main outcomes were the adjusted rate of SSI and the isolation of cephalosporin-resistant enterobacteriaceae and vancomycin-resistant enterococci (acquired antibiotic resistance). Adjustment for confounding was performed by multivariable modeling. A total of 231 SSIs (8.7%) occurred after a median of 16 days, including 93 chest-wound infections (3.5%) and 13 deep-organ-space infections (0. 5%). After 1502 procedures using short ABP, 131 SSIs were recorded, compared with 100 SSIs after 1139 operations with prolonged ABP (crude OR, 1.0; CI, 0.8 to 1.3). After adjustment for possible confounding, prolonged ABP was not associated with a decreased risk of SSI (adjusted OR, 1.2; CI, 0.8 to 1.6) and was correlated with an increased risk of acquired antibiotic resistance (adjusted OR, 1.6; CI, 1.1 to 2.6).

CONCLUSIONS

Our findings confirm that continuing ABP beyond 48 hours after CABG surgery is still widespread; however, this practice is ineffective in reducing SSI, increases antimicrobial resistance, and should therefore be avoided.

Interaction of hyaluronic acid-linked phosphatidylethanolamine (HyPE) with LDL and its effect on the susceptibility of LDL lipids to oxidation

The amphiphilic polysaccharide hyaluronic acid-linked phosphatidylethanolamine (HyPE), synthesized by covalently binding dipalmitoyl-phosphatidylethanolamine (DPPE) to short chain hyaluronic acid (mol. wt. approximately = 30 000), interacts with low-density lipoproteins (LDL), to form a 'sugar-decoration' of the LDL surface. This results in an increase in the apparent size of the LDL particles, as studied by photon correlation spectroscopy, and in broadening of the 1H NMR signals of the LDL's phospholipids. Experiments conducted with fluorescently-labeled HyPE indicate that the interaction of HyPE with LDL involves incorporation of the hydrocarbon chains of this amphiphilic polysaccharide into the outer monolayer of the LDL. This interaction also inhibits the copper-induced oxidation of the LDL polyunsaturated fatty acids, avoiding oxidation altogether when the concentration of HyPE is higher than a tenth of the concentration of the LDL's phospholipids. This can not be attributed to competitive binding of copper by HyPE. We propose that the protection of LDL lipids against copper-induced oxidation is due to formation of a sugar network around the LDL.

Copper-induced LDL peroxidation: interrelated dependencies of the kinetics on the concentrations of copper, hydroperoxides and tocopherol

Excessive uptake of oxidized low density lipoprotein plays a role in the onset of atherosclerosis. Lipid-associated antioxidants, the most abundant of which is tocopherol (vitamin E), are therefore believed to have anti-atherogenic properties. By contrast, hydroperoxides enhance the peroxidation of low density lipoprotein. We demonstrate that none of these compounds markedly affect the maximal rate of oxidation of low density lipoprotein, whereas the lag preceding rapid oxidation is prolonged by tocopherol but shortened by hydroperoxides. The corresponding 'prolongation' and 'shortening' can be compensated by each other in low density lipoprotein preparations enriched with both these compounds. The dependence of the balance between the effects of tocopherol and hydroperoxides on the copper concentration indicates that the antioxidative effect of vitamin E increases with the oxidative stress.

Susceptibility of serum lipids to copper-induced peroxidation correlates with the level of high density lipoprotein cholesterol

As a first step in evaluating the significance of our recently developed method of monitoring the kinetics of copper-induced oxidation in unfractionated serum, we recorded the kinetics of lipid oxidation in the sera of 62 hyperlipidemic patients and analyzed the correlation between oxidation and lipid composition of the sera [high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, and triglycerides]. We used six factors to characterize the kinetics of oxidation, namely, the maximal absorbance of oxidation products (ODmax), the maximal rate of their production (Vmax), and the time at which the rate was maximal (t(max)) at two wavelengths (245 nm, where 7-ketocholesterol and conjugated dienic hydroperoxides absorb intensely, and 268 nm, where the absorbance is mostly due to dienals). The major conclusions of our analyses are that: (i) Both ODmax and Vmax correlate positively with the sum of concentrations of the major oxidizable lipids, cholesterol, and cholesteryl esters. (ii). The value of t(max), which is a measure of the lag preceding oxidation and therefore reflects the resistance of the serum lipids to copper-induced oxidation, exhibits a negative correlation with HDL cholesterol. Although this finding accords with the observation of shorter lags for HDL than for LDL, it is apparently inconsistent with the role of HDL as an antirisk factor in coronary heart diseases.

Simplified surveillance for nosocomial bloodstream infections

OBJECTIVE

To compare a surveillance definition of noso comial bloodstream infections requiring only microbiology data to the Centers for Disease Control and Prevention's (CDC) current definition.

SETTING

Six teaching hospitals.

METHODS

We classified a representative sample of 73 positive blood cultures from six hospitals growing common skin contaminant isolates using a definition for bacteremia requiring only microbiology data and the CDC definition for primary bloodstream infection (National Nosocomial Infections Surveillance [NNIS] System review method). The classifications assigned during routine prospective surveillance also were noted, and the time required to classify isolates by the two methods was compared.

RESULTS

Among 65 blood cultures growing common skin contaminant isolates obtained from adults, the agreement rate between the microbiology data method and the NNIS review method was 91%. Agreement was significantly poorer for the eight blood cultures growing common skin contaminant isolates obtained from pediatric patients. The microbiology data method requires approximately 20 minutes less time per isolate than does routine surveillance.

CONCLUSIONS

A definition based on microbiology data alone yields the same result as the CDC's definition in the large majority of instances. It is more resource-efficient than the CDC's current definition.

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

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

Lipid oxidation in unfractionated serum and plasma

In an attempt to develop an assay for the susceptibility of plasma lipids to oxidation, we have studied the kinetics of copper-induced oxidation in diluted serum and plasma prepared with different anticoagulants (heparin, citrate and EDTA) by monitoring the absorbance of oxidation-products at several wavelengths. These studies revealed the complex and interrelated effects of the water-soluble antioxidant ascorbic acid, citrate and chloride ions on the kinetics of copper-induced oxidation of plasma lipids. Specifically, the onset of oxidation induced by copper-citrate chelates is only slightly affected by chloride ions and is accelerated upon increasing the copper concentration. By contrast, in the absence of citrate, the lag preceding oxidation in diluted serum or plasma (but not the maximal rate of oxidation) depends markedly on the chloride concentration in the diluting medium. In the absence of Cl-, the lag preceding oxidation is a decreasing saturable function of copper concentration, whereas in a normal phosphate-buffered saline solution (PBS), the lag shows a biphasic dependence on copper concentration such that at copper concentrations above 10-30 microM (depending on the extent of plasma dilution), increasing the concentration of copper results in prolongation of the lag. This dependence of copper-induced oxidation on the concentration of copper is not observed for dialyzed serum unless ascorbic acid is added. Our interpretation of these results is that water-soluble reductants and chloride ions act synergistically to stabilize Cu+, on the expense of Cu2+. Quenching of free radicals by Cu+ may be responsible for the prolongation of the lag at high copper concentrations, with no reduction of the maximal rate of oxidation. In spite of the complex dependencies described above, spectrophotometric monitoring of the kinetics of oxidation of plasma lipids, under 'optimized conditions' (50-fold diluted serum, in PBS containing 720 microM sodium citrate and 100 microM copper), agrees with independent measurements of the consumption of polyunsaturated fatty acids. Hence, the spectroscopic method may become useful for evaluation of the susceptibility of plasma lipids to oxidation. This possibility, however, has yet to be elucidated through investigations of the correlation between the susceptibility of serum lipids to copper-induced oxidation in vitro and clinical factors of significance.

Kinetic analysis of copper-induced peroxidation of LDL

We have employed our recently developed spectroscopic method of continuous monitoring of lipid oxidation to study the formation and decomposition of hydroperoxides in the time course of LDL oxidation. The results show satisfactory agreement with simulated time courses based on the following assumptions: (a) Both the rates of formation and decomposition of hydroperoxides depend on the ratio of bound copper to LDL as computed under the assumption that each LDL particle has 17 equivalent copper binding sites characterized by a dissociation constant K = 1 microM. (b) Peroxidation is initiated by copper-catalyzed decomposition of hydroperoxides (LOOH) into peroxy radicals (LOO.) and other products, including dienals. Under these assumptions, the rate of accumulation of LOOH can be computed from the equation (equation in text). The agreement between the simulated and experimentally-observed kinetics supports the assumptions used for simulations. The close agreement between the values of lipid oxidizability (kp/square root 2kt) obtained for LDL (0.035 (Ms)[-1/2]) and previously published data on the oxidizability of linoleates (0.02-0.11 (Ms)[-1/2]) lends further support for these assumptions.

Imaging supramolecular aggregates in bile models and human bile

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

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

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

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

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

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

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

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

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

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

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

The effect of albumin on copper-induced LDL oxidation

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

A clinical data repository enhances hospital infection control

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

Effect of sperm preparation with TEST yolk buffer on sperm-binding capacity under hemizona assay conditions

The study was conducted to evaluate the diverse effect and clinical significance of TEST yolk buffer treatment on sperm samples of 128 infertile men. Sperm samples were incubated with TEST yolk buffer and control medium (Ham's F-10) at room temperature for 2 h. The hemizona indices (mean +/- SE) of the TEST yolk buffer and medium-treated sperm samples were 29 +/- 2.3% and 22 +/- 1.6%, respectively. Inspection of the individual response of each sperm sample to TEST yolk buffer revealed that 63 samples (49%) improved (double the interassay variation = 28%) their binding to zona pellucida, 36 (28%) remained unchanged, whereas the binding capacity of 29 samples (23%) decreased. Furthermore, TEST yolk buffer treatment of 24 samples (19%) resulted in an increased binding beyond the hemizona index threshold set up at 23%. This level was previously shown to be the cut-off point between fertile and infertile sperm samples. It was concluded that when applied to an unselected group of infertile men, TEST yolk buffer significantly increased sperm binding capacity to the zona pellucida. However, only 19% of the sperm samples showed improvement with clinical significance. The other sperm samples may have improved, remained unchanged or even deteriorated independently on basic sperm variables. Thus, the effect of TEST yolk buffer treatment on sperm binding should be tested prior to its clinical use to avoid possible damage to certain sperm samples.

Does lipid infusion affect bile composition in humans?

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

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

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

Aggregation of phospholipid vesicles by water-soluble polymers

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

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

OBJECTIVES

Oxidation of polyunsaturated fatty acids in lipoproteins is supposed to play a crucial role at the early stages of atherogenesis. The polyunsaturated lipids (PUFAs) become oxidized and, thus, the degree and rate of lipid oxidation depend on their concentration and, probably, on the lipid moiety to which they are attached.

DESIGN AND METHODS

To determine the relative oxidation susceptibilities of sphingo- and glycerolipid-bound fatty acyl chains, we used fluorescent analogs of the respective compounds, in which one natural fatty acyl chain was replaced by fluorescent diphenylhexatriene propionic acid.

RESULTS

Oxidation susceptibilities of the fluorescent acyl chains in the presence of Cu2+ or AAPH depended, in general, on the phospholipid to which they were bound and the lipoprotein. Phospholipids were oxidized faster in HDL than in LDL or Lp(a). Plasmalogens were more susceptible to oxidation than phosphatidylcholine and sphingomyelin.

CONCLUSION

Thus, HDL and plasmalogens may be considered as preferred targets of lipid oxidation before the bulk of polyunsaturated phospholipids (mainly phosphatidylcholine) in LDL is subject to free radical attack.