Effects of intravenous infusions of commercial fat emulsions (Intralipid 10 or 20%) on rat plasma lipoproteins: phospholipids in excess are the main precursors of lipoprotein-X-like particles

New Parenteral Lipid Emulsions for Clinical Use

Routine use of parenteral lipid emulsions (LE) in clinical practice began in 1961, with the development of soybean oil (SO) - based LE. Although clinically safe, experimental reports indicated that SO-based LE could exert a negative influence on immunological functions. Those findings were related to its absolute and relative excess of omega-6 polyunsaturated fatty acids (PUFA) and the low amount of omega-3 PUFA and also to its high PUFA content with an increased peroxidation risk. This motivated the development of new LE basically designed along the reduction of omega-6 PUFA and the omega-3 PUFA addition in order to obtain balanced levels of the omega-6/omega-3 ratio. The new LE for clinical use (available in Europe and South America) are differentiated by their content in polyunsaturated (omega-6 and omega-3), monounsaturated, and saturated fatty acids (FA), as well as FA source of their origin, including soy, coconut, olive, and fish oil. This article presents the new LE nutrition and energy functions but also its biochemical, metabolic, and immunomodulating aspects, according to their FA content. LE at 20% when infused from 1.0 to 2.0 g/kg body weight/day rates, either alone or in association with amino acids and glucose, are safe and well tolerated in routine clinical practice. LE combining SO with medium-chain triglycerides and/or olive oil have less omega-6 PUFA and are better metabolized, with less inflammatory and immunosuppressive effects than in relation to pure SO-based LE. The omega-3 PUFA used alone or as component of a new and complex LE (soy, MCT, olive and fish oil) has demonstrated anti-inflammatory and immunomodulatory effects.

Review: The lipemia of sepsis: triglyceride-rich lipoproteins as agents of innate immunity

Bacterial endotoxin (LPS) elicits dramatic responses in the host including elevated plasma lipid levels due to the increased synthesis and secretion of triglyceride (TG)-rich lipoproteins by the liver, and the inhibition of lipoprotein lipase. This cytokine-induced hyperlipoproteinemia, clinically termed the `lipemia of sepsis', was customarily thought to represent the mobilization of lipid stores to fuel the host response to infection. However, since lipoproteins can also bind and neutralize LPS, we hypothesize that TG-rich lipoproteins (VLDL and chylomicrons) are also components of an innate, non-adaptive host immune response to infection. Herein we review data demonstrating the capacity of lipoproteins to bind LPS, protect against LPS-induced toxicity, and modulate the overall host response to this bacterial toxin. Lastly, we propose a pathway whereby lipoprotein-bound LPS may represent a novel, endogenous mechanism for regulating the hepatic acute phase response.

Effect of lipid viscosity and high-pressure homogenization on the physical stability of "Vitamin E" enriched emulsion

Recently there has been a growing interest in vitamin E for its potential use in cancer therapy. The objective of this work was therefore to formulate a physically stable parenteral lipid emulsion to deliver higher doses of vitamin E than commonly used in commercial products. Specifically, the objectives were to study the effects of homogenization pressure, number of homogenizing cycles, viscosity of the oil phase, and oil content on the physical stability of emulsions fortified with high doses of vitamin E (up to 20% by weight). This was done by the use of a 27-run, 4-factor, 3-level Box-Behnken statistical design. Viscosity, homogenization pressure, and number of cycles were found to have a significant effect on particle size, which ranged from 213 to 633 nm, and on the percentage of vitamin E remaining emulsified after storage, which ranged from 17 to 100%. Increasing oil content from 10 to 20% had insignificant effect on the responses. Based on the results it was concluded that stable vitamin E rich emulsions could be prepared by repeated homogenization at higher pressures and by lowering the viscosity of the oil phase, which could be adjusted by blending the viscous vitamin E with medium-chain triglycerides (MCT).

Triglyceride-rich lipoproteins as agents of innate immunity

Bacterial endotoxin (i.e., lipopolysaccharide [LPS]) elicits dramatic responses in the host, including elevated plasma lipid levels due to increased synthesis and secretion of triglyceride-rich lipoproteins by the liver and inhibition of lipoprotein lipase. This cytokine-induced hyperlipoproteinemia, clinically termed the "lipemia of sepsis," was customarily thought to involve the mobilization of lipid stores to fuel the host response to infection. However, because lipoproteins can also bind and neutralize LPS, we have long postulated that triglyceride-rich lipoproteins (very-low-density lipoproteins and chylomicrons) are also components of an innate, nonadaptive host immune response to infection. Recent research demonstrates the capacity of lipoproteins to bind LPS, protect against LPS-induced toxicity, and modulate the overall host response to this bacterial toxin.

Effects of a medium-chain triacylglycerol/long-chain triacylglycerol fat emulsion containing a reduced ratio of phospholipid to triacylglycerol in pediatric surgical patients

OBJECTIVE

Medium-chain triacylglycerol (MCT) has been shown to provide better nutritional support than long-chain triacylglycerol (LCT). We compared the efficacy of MCT/LCT fat emulsions containing a usual (0.12) or a decreased (0.06) ratio of phospholipid to triacylglycerol (PL:TG) in pediatric patients under surgical stress.

METHODS

Three patient groups (n=10 in each) received equivalent amounts of glucose (12 g.kg(-1).d(-1)) and amino acids (2 g.kg(-1).d(-1)), but group A received a 10% MCT fat emulsion (PL:TG 0.06), group B received a 20% MCT fat emulsion (PL:TG 0.06), and group C received a 10% MCT/LCT fat emulsion (PL:TG 0.12) in amounts of 1.5 g.kg(-1).d(-1) in a randomized study. Total parenteral nutrition was given for 7 d. Blood samples were collected before total parenteral nutrition administration and on days 4 and 7 for determination of various biochemical indexes.

RESULTS

Serum phospholipid concentrations were significantly higher in group C than in group A or B on days 4 and 7 (P<0.05). Serum triacylglycerol and cholesterol concentrations and the very-low-density lipoprotein percentage were also significantly higher in group C than in group A or B on days 4 and 7 (P<0.05). The high-density lipoprotein percentage was significantly higher in group B on days 4 and 7 (P<0.05).

CONCLUSIONS

In pediatric patients under surgical stress, a total parenteral nutrition regimen containing an MCT/LCT fat emulsion with a decreased PL:TG ratio (0.06) is likely to result in partly better lipid and lipoprotein metabolism than an emulsion containing the usual ratio (0.12).

Evaluation of the carrier potential for the lipid dispersion system with lipophilic compound

KW-3902 (a newly synthesized adenosine A(1)-receptor antagonist) has potent diuretic and renal protective activities and was formulated in lipid dispersion systems, i.e., lipid emulsions and liposomes. The objective of the present study was to evaluate the carrier potential of these lipid dispersion systems, which is explained here as the ability of the formulation to retain the drug in its dispersed phase. The relative affinity of the drug to the formulation, K(f/b), was defined as a parameter in order to assess the performance of the formulations and was obtained from the in vitro blood component binding study. The results indicated that KW-3902 showed higher relative affinity to the liposome formulation than to the lipid emulsion. Moreover, the total amount of drug retained in the dispersion system depended on both K(f/b) and the dosing volume. The usefulness of the parameter, K(f/b), was discussed as an indicator for a carrier potential to understand the properties of the formulations.

Role of the lipid emulsion on an injectable formulation of lipophilic KW-3902, a newly synthesized adenosine A1-receptor antagonist

KW-3902 (a newly synthesized adenosine A1-receptor antagonist) has potent diuretic and renal protective activities. We investigated the influence of the emulsion formulation on the pharmacokinetics of KW-3902 and its metabolite (M1) in rats using three different formulations, i.e., a lipid emulsion about 130 nm in diameter composed of egg yolk lecithin: soybean oil: oleic acid=1:1:0.048, a liposome about 100 nm in diameter composed of egg yolk lecithin, and a saline solution containing 1% (v/v) each of dimethyl sulfoxide and 1 N NaOH. There was no significant difference in the pharmacokinetic parameters of KW-3902 (elimination half-life (T1/2), area under the plasma concentration-time curves (AUC0-infinity), total body clearance (CL), mean residence time (MRT) and volume of distribution at steady-state (Vdss) and M1 (Cmax, T1/2, AUC0-infinity and MRT) after injection of these three dosage forms. Moreover, we investigated in vitro the binding of KW-3902 to blood components using these three formulations. KW-3902 was completely partitioned into the blood components regardless of its dosage form. These findings suggested that KW-3902 dissociated rapidly from the lipid emulsion or liposome in blood after injection and showed intrinsic pharmacokinetics of KW-3902 at doses of 0.1 and 1 mg/kg. Thus, the lipid emulsion formulation of KW-3902 was defined as a solvent, which was a vehicle for dissolving the drugs to prepare the injection, at its expected effective doses.

Effects of intravenous supplementation with alpha-tocopherol in patients receiving total parenteral nutrition containing medium- and long-chain triglycerides

OBJECTIVE

To compare the effects of a lipid emulsion containing medium-chain triglycerides (MCT) and supplemented with alpha-tocopherol to a conventional long-chain triglyceride (LCT) emulsion.

DESIGN

Randomised double blind study.

SETTING

Department of Internal Medicine, Antwerp University Hospital.

SUBJECTS AND INTERVENTIONS

Twenty-four patients with an indication for total parenteral nutrition for a minimum of 10 days were randomly assigned to two groups: group E received as lipid source MCT/LCT (50/50) suplemented with 100 mg DL-alpha-tocopherol/day and group C received LCT. Blood samples were analysed at inclusion, after 4-6 and after 9-11 days.

RESULTS

In group E, serum alpha-tocopherol doubled from 11.4+/-6.9 at inclusion to 20.9+/-7.9 and to 23.8+/-8.8 microg/ml after 4 and 9 days, respectively, but did not change in group C (P=0.008). Production of thiobarbituric acid-reacting substances (TBARS) after 120 min incubation with copper decreased from 66+/-34 at inclusion to 29+/-25 nmol MDA/mg LDL and VLDL-cholesterol after 4 and to 42+/-17 after 9 days (P=0.022 when compared to group C, which underwent no significant changes). Velocity of production of fluorescent products decreased in group E but not in group C (P=0.026).

CONCLUSIONS

Supplementation of TPN containing MCT/LCT with 100 mg DL-alpha-tocopherol/day leads to a doubling in serum alpha-tocopherol and to a decrease in the susceptibility of LDL and VLDL to peroxidation in vitro.

SPONSORSHIP

This study was partly financed by B Braun Medical NVSA, Diegem, Belgium.

Endogenous lipoproteins impact the response to endotoxin in humans

OBJECTIVE

To determine whether endogenous lipoproteins can abrogate the host response to lipopolysaccharide (LPS) in vivo.

DESIGN

Randomized, placebo-controlled study.

SETTING

Urban public hospital with academic affiliation.

SUBJECTS

Eighteen healthy, normolipidemic, normal weight volunteers, 21-35 yrs of age.

INTERVENTIONS

Fasting and postprandial (hypertriglyceridemic) subjects were injected with endotoxin (LPS, Lot EC-5, 4 ng/kg = 20 endotoxin units/kg) as either a bolus or following preincubation of the LPS with autologous whole blood vs. saline. In addition, LPS-induced cytokine production was determined ex vivo to examine the capacity of fasting vs. hypertriglyceridemic whole blood to attenuate the effect of large, potentially lethal concentrations of LPS in humans.

MEASUREMENTS

Vital signs were recorded and serial blood samples analyzed for changes in white blood cell count, cytokine, and stress hormone levels over 24 hrs. The distribution of lipoproteins in fasting and postprandial blood after preincubation was determined using 125I-LPS.

MAIN RESULTS

Endogenous lipoproteins abrogated the host response to LPS in vivo, but only after preincubation with the LPS. Peak oral temperature (p < .05) and white blood cell count (p < .05), and plasma tumor necrosis factor (TNF)-alpha (p < .01) and adrenocorticotropic hormone levels (p < .03) were significantly reduced in volunteers injected with LPS preincubated with whole blood vs. LPS preincubated with saline. Approximately 80% of the LPS was bound to lipoproteins after preincubation with either fasting or hypertriglyceridemic blood. Thus, protection was associated with lipoprotein binding. In addition, hypertriglyceridemic but not fasting blood inhibited the ex vivo TNF-alpha response to large, highly toxic doses of LPS (p < .05). Without the preincubation of lipoproteins with LPS, there was a trend for an exaggerated clinical and TNF-alpha response in the hypertriglyceridemic subjects.

CONCLUSION

Preincubation of LPS with whole blood promotes lipoprotein-LPS binding and is associated with an attenuated response to this toxic macromolecule. Although the clinical relevance of these data requires further elucidation, our results continue to support a lipid-based therapeutic strategy to combat gram-negative sepsis.

Measurement of human chylomicron triglyceride clearance with a labeled commercial lipid emulsion

Human chylomicron triglyceride (TG) kinetics has been difficult to determine directly owing to technical limitations. This report describes a new method for studying chylomicron metabolism. Healthy volunteers (n = 10) sipped a drink providing 175 mg fat x kg(-1) h(-1) for 7.5 h to produce a steady-state chylomicronemia. A commercial 10% intravenous lipid emulsion was labeled with [3H]triolein, purified by high-performance liquid chromatography, and sterilized. A trace amount of labeled emulsion was injected intravenously 30 min before (i.e., in the fasting state) and 5, 6, and 7 h after sipping began (i.e., triplicate determinations in the fed state). Chylomicron half-lives were calculated from the monoexponential decay curves, and apparent distribution volumes were estimated by back-extrapolation to time zero. Plasma and estimated chylomicron TG concentrations increased from 89+/-13 and 0.8+/-0.3 to 263+/-43 and 91+/-39 mg/dL (mean +/- SEM), respectively, with feeding. Tracer-determined chylomicron TG half-lives were 5.34+/-0.58 and 6.51+/-0.58 min during the fasting and fed states, respectively (P < 0.01). The apparent distribution volume during the fasting state was 24% greater than plasma volume (4515+/-308 vs. 3630+/-78 mL, P < 0.02), consistent with significant margination of lipid emulsion particles to endothelial binding sites. Margination was reduced during the fed state, suggesting that native chylomicrons competed with lipid emulsion particles for endothelial lipoprotein lipase. The results indicate that a radiolabeled commercial lipid emulsion is metabolized in a fashion similar to native chylomicron TG, and thus can be used to study chylomicron TG kinetics.

A new method for the study of chylomicron kinetics in vivo

Our understanding of the metabolism of chylomicrons, the lipoprotein that transports dietary fat from the intestine to peripheral tissues, is incomplete. The present studies were conducted to determine whether a labeled intravenous lipid emulsion could be used to estimate chylomicron triglyceride (TG) rate of appearance (R(a)) and thereby quantify the rate of intestinal fat absorption. After an overnight fast, healthy volunteers (n = 6) sipped a (3)H-labeled drink over 6.5 h at a rate of 175 mg fat. kg(-1). h(-1). Beginning at hour 5, an HPLC-purified, (14)C-labeled lipid emulsion was infused intravenously for 90 min. During the study, plasma total and chylomicron TG concentrations increased from 100 +/- 21 to 237 +/- 40 mg/dl and from undetectable to steady-state levels of 35 +/- 13 mg/dl, respectively. After a minor correction for VLDL contamination, tracer-determined chylomicron TG R(a) was 175 +/- 30 mg. kg(-1). h(-1), equal to the presumed ingestion rate. In summary, a radiolabeled intravenous lipid emulsion is able to accurately estimate chylomicron TG R(a) and therefore can be used to measure in vivo fat absorption rates.

Lipid clearance and total parenteral nutrition: the importance of monitoring plasma lipids

Lipid provides two major advantages for total parenteral nutrition (TPN). First, it provides essential fatty acids, thus avoiding essential fatty acid deficiency, and secondly, it is a useful energy source, providing 9 kcal/g. However, we describe a patient who had TPN containing Intralipid, where problems of lipid clearance developed. We also review the literature of lipid clearance problems in TPN patients and suggest ways by which such problems can be managed. We suggest that patients taking TPN should have their plasma lipids (triacylglycerols) measured before and during TPN initiation. This is particularly important in patients who are at high risk of impaired fat clearance, such as those who are hyperlipidemic, diabetic, septic, or with impaired renal or hepatic function, or those who are critically ill.

Utilization of docosahexaenoic acid from intravenous egg yolk phospholipid

Docosahexaenoic acid (DHA, 22:6n-3) is provided directly to human premature infants during parenteral nutrition from the egg yolk fraction of an intravenous fat emulsion. This study aimed to determine whether the high egg yolk phospholipid content of Intralipid 10% (IL 10%, Pharmacia, Uppsala, Sweden) relative to the standard emulsion Intralipid 20% (IL 20%, Pharmacia) could be a strategy to increase the delivery of DHA to the developing brain. Male, Large White piglets were randomly selected from sows 3 d after birth. Piglets were assigned to receive a 9-d continuous intravenous infusion commencing 5 d after birth of either Intralipid (IL) 10%, IL 20%, or Lipofundin S 20% (LFS; B. Braun, Melsungen, Germany). There were four piglets in each treatment group. IL 10% provides twice as much DHA as IL 20%, while LFS provides no DHA. Protein and other nutrients were provided enterally using a low-fat milk formula. After 9 d, animals were killed, and the fatty acid compositions of blood, liver, and cerebral cortex were analyzed. IL 10% infusion approximately doubled the amount of plasma phospholipid DHA (microg/mL of plasma) in comparison to IL 20%. However, red blood cells, liver, and cerebral cortex phospholipid DHA levels were indistinguishable between these two groups. LFS was associated with reduced levels of DHA in plasma, red blood cell and liver phospholipids in comparison to IL 20%. We conclude that infusion of additional phospholipid is an ineffective strategy for increasing DHA delivery to piglet tissues. This may be due to the formation of inert phospholipid particles in plasma. The data do not support the concept of using IL 10% as a means of providing additional DHA to premature human infants.

Structure and metabolic fate of triacylglycerol- and phospholipid-rich particles of commercial parenteral fat emulsions

The lipid emulsions used in parenteral nutrition are constituted of particles rich in triacylglycerols (TAG) called artificial chylomicrons (200-500 nm in diameter; monolayer of phospholipids [PL] enveloping a TAG core) and PL-rich particles called liposomes (diameter inferior to 80 nm; bilayer of PL around an aqueous phase), which represent the excess emulsifier. Introduced into the circulation, the two populations of particles come into contact with circulating lipoproteins and cell membranes and experience the same overall fate: exchanges and transfers of lipids and apolipoproteins, enzymatic hydrolysis of TAG and PL, and internalization by different tissues. The relative importance of these different metabolic processes varies depending on the type of particle. The artificial chylomicrons undergo a hydrolysis of their TAG by lipoprotein lipase, with a release of fatty acids and formation of smaller particles of remnants, which are rapidly removed by the liver. In delivering fatty acids to the tissue, artificial chylomicrons fulfill an energy transport function similar to the natural chylomicrons. The liposomes hold little energy interest, and they also have deleterious effects when infused in excess. They inhibit the lipolysis of artificial chylomicrons and, by actively capturing endogenous cholesterol, they stimulate tissue cholesterogenesis and accumulate in the blood as lipoprotein-X, a long-lived abnormal lipoprotein. To limit as much as possible the metabolic perturbations due to the intravenous administration of exogenous PL, the emulsion has to be infused at a low rate, and should contain the minimal amount of excess PL.

Surface composition regulates clearance from plasma and triolein lipolysis of lipid emulsions

Sphingomyelin (SM) and cholesterol (Chol) are major surface lipid constituents of plasma lipoproteins. We investigated the effects of SM and Chol on the plasma clearance of lipid emulsions as a model for lipoprotein particles in rats. The presence of Chol facilitated the removal of emulsion particles from plasma, whereas SM delayed particle removal. Preinjection of lactoferrin, an inhibitor of the apolipoprotein E (apoE) receptor, revealed that the differences in clearance of emulsions were due to the differences in affinity for the apoE receptor. Measurement of apolipoprotein binding suggested that the balance of apoE and apoC (apoC-II and apoC-III) bound to emulsions caused the difference in plasma clearance of emulsion particles. That is to say, SM in the emulsion surface decreased binding of apoE, which led to a longer circulation of emulsion particles in plasma. Chol, on the other hand, decreased the ratio of apoC to apoE, which may have promoted emulsion uptake through the apoE receptor. We also examined in vitro lipolysis using immobilized lipoprotein lipase (LPL) in a heparin affinity column. Lipolysis rates were significantly reduced by the incorporation of SM into the emulsion surface, but not by the incorporation of Chol, indicating that SM in the lipoprotein surface is an important lipid component regulating LPL-mediated lipolysis. Our results suggest that the presence of SM and Chol in the lipoprotein surface plays an important role in the circulation behavior and LPL-mediated lipolysis of lipid emulsions through their effect on the selectivity of plasma protein binding.

Effect of infusion of a triacylglycerol emulsion on low-density lipoprotein composition and oxidizability

Six, healthy, male volunteers aged 19-48 years received a 4-h infusion of a triacylgycerol emulsion (Intralipid 10%) after an overnight fast. Plasma triacylglycerol (TAG) and low-density lipoprotein (LDL) -TAG, -protein and -phospholipid concentrations all rose significantly during the course of the infusion and remained elevated 90 min after its end. The weight/weight ratio of LDL-TAG to -protein also increased significantly (from 0.43+/-0.14 to 0.79+/-0.30 at 4 h and 0.63+/-0.31 90 min later), indicating TAG-enrichment of LDL particles. There were no significant changes in LDL particle density. Susceptibility of LDL to copper-induced oxidation, as measured by the lag time for conjugated diene formation, was less at the end of and 90 min after the end of the infusion than in the fasting state (59.3+/-16.5, 47.4+/-17.4 and 34.8+/-19.6 min, respectively). Lag time was positively correlated with LDL TAG in the fasting state (rS=0.900, P < 0.0001) and the correlation continued with the post-infusion TAG-enriched LDL (rs=0.886, P < 0.05). Acute hypertriglyceridaemia induced by infusion of Intralipid therefore causes TAG-enrichment and a decrease in the susceptibility to oxidation of LDL. TAG-enrichment of LDL may lead to subsequent potentially atherogenic changes in LDL following TAG hydrolysis.

Comparison between two fat emulsions: Intralipid 30 cent vs intralipid 10 cent in critically ill patients

Fat emulsions, Intralipid 30% and Intralipid 10% were compared in terms of the resulting plasma levels of different lipid components and clinical tolerance in critically-ill patients with multi-injuries. Sixteen critically-ill patients with severe systemic inflammatory response were randomly assigned to two groups, each one comprised of eight patients. Each group was administered the same quantity of fat/Kg/day either Intralipid 30% or Intralipid 10%. The infusion lasted 12|h daily for 6 days. During the infusion of the fat emulsion, a lower median plasma concentration of triglycerides, phospolipids and free cholesterol was observed in patients who received Intralipid 30% compared with those who received Intralipid 10%. The above observations were sustained 4 h after the termination of the infusion. Free fatty acids had a higher mean plasma concentration in the group of patients who received Intralipid 30%. There were no differences between the two groups as far as the median plasma concentration of cholesterol and lipoproteins (LDL, HDL, VLDL) are concerned. On the contrary, there was an increase in LpX in the Intralipid 10% group. From the above findings, we draw the conclusion that Intralipid 30% revealed better profiles of different lipid components than Intralipid 10% in critically-ill patients. The new emulsion of higher concentration in triglyceride was proved clinically safe and its use is suggested for critically-ill patients who require total parenteral nutrition.

Reverse cholesterol transport in the rat following a short-term intravenous infusion of fat emulsion

The effect on cholesterol transport of an intravenous infusion of a fat emulsion (10%) Intralipid or 10% Lipovenös) in vivo was investigated in the rat. Intralipid (1.85 ml/hr/kg body weight in rts for 3 hr) caused a reduction (P < 0.05) in free cholesterol in the aorta (by 25%), in plasma high-density lipoproteins (64%) and in erythrocytes (11%) with a concomitant enrichment of liver free cholesterol (16%), suggesting an enhanced reverse cholesterol transport in this species. Lipovenös under the same conditions gave similar results. Our data support our previous in vivo study in man indicating that infusion of a fat emulsion is able even to remove cholesterol from the arterial wall and thereby possibly be considered as an antiatherosclerotic agent.

Phospholipid-rich particles in commercial parenteral fat emulsions. An overview

In parenteral nutrition, the infusion of a fat EMU supplies both concentrated energy and covers the essential fatty acid requirements, the basic objective being to mimic as well as possible the input of chylomicrons into the blood. This objective is well met by the TAGRP of the EMU, which behave as true chylomicrons. However, commercial EMU also contain an excess of emulsifier in the form of PLRP. The number of these PLRP depends directly on the PL/TAG ratio of the EMU. They differ from the TAGRP by their composition (PL vs TAG and PL), their structure (PL in bilayer versus monolayer), and their granulometry (mean diameter 70-100 nm for PL vs 200-500 nm). The metabolic fate of the PLRP is similar in several ways to that of the TAGRP: exchanges of PL with the PL of the different cellular membranes and of the lipoproteins; captation of free CH from these same structures; and enrichment in apolipoproteins. However, because the TAGRP are the preferred substrates of the lipolytic enzymes, their clearance is much more rapid (half-life < 1 h) than that of the PLRP. As the infusion is continued, the PLRP end up accumulating and being transformed into LP-X (free CH/PL = 1; half-life of several days). As soon as the EMU is infused, the PLRP enter into competition with the TAGRP, in the lipolysis process as well as for sites of binding and for catabolism. The sites for catabolism of the two types of PAR are not the same: adipose tissues and muscles utilize the fatty acids and monoacylglycerols released by the lipolysis of the TAGRP; hepatocytes take up their remnants; the RES and the hepatocytes participate in the catabolism of the PLRP and the LP-X. Thus, prolonged infusion of EMU rich in PLRP leads to a hypercholesterolemia, or at least a dyslipoproteinemia, due to elevated LP-X, associated with a depletion of cells in CH, stimulating thus tissue cholesterogenesis. However, parenteral nutrition has evolved towards the utilization of EMU with a low PL/TAG ratio (availability of 30% formula) and less rapid delivery. For these reasons, the hypercholesterolemias that used to be observed with the 10% EMU have become much less spectacular or have even disappeared. It is interesting to note that patients on prolonged TPN, in particular those with a short small intestine, have weak cholesterolemia, reflecting a lowering of HDL and LDL not masked by elevated LP-X. At present, it seems difficult to produce sufficiently stable parenteral EMU devoid of PLRP. Notwithstanding, all the observations made since the introduction of the EMU in TPN are in favour of the use of PLRP-poor EMU. It is clear that the 10% formulas, and generally those with a PL/TAG ratio of 12/100, are ill-advised, especially in patients with a retarded clearance of circulating lipids.

Lipid changes in plasma and blood cells following intravenous 10% fat infusion in man

The effects of a 500 ml 4 hr infusion of 10% fat emulsion (Lipovenös) on the lipid content of plasma lipoproteins and blood cells, and on the platelet aggregation rate, were studied in ten volunteers. The infusion resulted in a significant (P < 0.05) initial increase in plasma total triglycerides (more than 5 times), phospholipids (28.7%) and free cholesterol (43.3%), but a decrease in the free cholesterol content of erythrocytes and mononuclear cells (by 4.4% and by 22.7%, respectively). Plasma cholesteryl ester was reduced by 18.2% after the infusion, most of the reduction being accounted for by the 16.5% reduction in high-density lipoproteins. Our findings suggest more than 35% of the free cholesterol accumulated in plasma to derive from peripheral tissues, in turn suggesting overall reverse cholesterol transport from peripheral tissues to plasma to be enhanced. Post-infusion platelet aggregation in response to adenosine disphophate was significantly reduced, the peak rate by 31% and 1 min. rate by 20.6% (P < 0.05 in both cases). These changes in plasma lipids found in normal volunteers suggest that a short-term intravenous infusion of 10% Lipovenös might also be beneficial in preventing atherosclerosis.

Total parenteral nutrition stimulates hepatic cholesterol synthesis in the rat

Cholesterol synthesis was studied in parenterally fed rats, as compared to orally fed rats with or without saline infusion. Conditions of total parenteral nutrition (TPN) involved the intravenous infusion of a nutritive mixture containing 20% Intralipid as the lipid source (50% of non-protein energy) at the continuous rate of 2 ml per h, for five days. In rats maintained in isotopic steady state by daily injections of [3H]cholesterol, isotope dilution indicated that the endogenous plasma cholesterol input was significantly higher (+15%, P < 0.05) in TPN than in orally fed rats, which suggested a slight stimulation of whole body cholesterogenesis. Cholesterol synthesis was assessed in TPN and orally fed rats by the in vivo incorporation of [1,2-13C]- and [1-14C]acetate into hepatic and intestinal sterols, and by the activity of HMG-CoA reductase in microsomes isolated from liver and small intestine. Both methods demonstrated that TPN markedly stimulated the hepatic cholesterol synthesis, since the radioactivity of liver sterols was 6- to 10-fold higher, and the activity of HMG-CoA reductase 5-fold higher, in TPN than in orally fed rats. Despite the weight reduction of the small intestine, by about 20% after TPN, the incorporation of exogenous [14C]acetate into intestinal sterols was similar in TPN and orally fed rats. As the liver and intestine are the main organs responsible for the appearance of endogenous cholesterol in plasma, it may be concluded that the increased endogenous plasma cholesterol input was mainly due to a strong stimulation of hepatic cholesterol synthesis in TPN rats.

Effects of administration of different intravenous lipid emulsions on plasma LP-X concentrations in the rat

BACKGROUND

Prolonged parenteral nutrition with lipid emulsions is essential to provide sufficient energy supply and to avoid essential fatty acid deficiency in preterm infants. However, chronic administration of lipid emulsions may lead to the development of pathological plasma lipid and LP-X concentrations. The aim of this study was to evaluate the relative importance of the phospholipid-triglyceride (PL-TG) ratio and the source of phospholipid in lipid emulsions, with respect to plasma lipid and LP-X levels.

METHODS

Rats were infused for 9 days with IV lipid emulsion containing 10% (IL-10) or 20% (IL-20) egg lecithin or Lipofundin containing 20% soya lecithin (LF), with PL-TG ratios of .12, .06, and 0.75, respectively.

RESULTS

LF significantly increased plasma triglyceride concentration (p < .01), whereas the rise in cholesterol levels observed with all emulsions was primarily caused by the increase in low-density lipoprotein cholesterol concentrations. The plasma phospholipid concentration was increased most by IL-10 (p < .005). There was a strong correlation between the PL-TG ratio of emulsions and the developing plasma phospholipid and LP-X concentrations (r2 = .91 and .96, respectively), despite the different origin of phospholipids in the emulsions, suggesting that it is the PL-TG ratio, rather than the source of phospholipids in lipid emulsions that primarily influences developing plasma lipid and LP-X concentrations.

CONCLUSION

These results indicate that the administration of lipid emulsions with lower PL-TG ratios should be considered, to avoid the development of pathological plasma lipoprotein concentrations.

Effect of intralipid infusion on serum high- and low-density lipoprotein cholesterol, lecithin:cholesterol acyltransferase, and lipoprotein lipase in tumor-bearing rats

We compared the effects of 0.45% normal saline (NS), 5% Intralipid (IL), and 16.7% glucose (Glu) infusions on total serum triglycerides and cholesterol, serum high-(HDL-c) and low-density lipoprotein cholesterol (LDL-c), and activity of serum lecithin:cholesterol acyltransferase (LCAT), and serum lipoprotein lipase (LPL) in rats implanted with a fibrosarcoma. In tumor-bearing rats given NS, a two-fold increase in total serum cholesterol, a four-fold increase in LDL-c, and a five-fold decrease in the HDL-c/LDL-c ratio were observed compared to tumor-free rats. In tumor-bearing rats administered IL, a two-fold increase in total serum triglyceride and cholesterol, a three-fold increase in HDL-c and HDL-c/LDL-c ratio, and a two-fold increase in LPL activity were observed compared to tumor-bearing rats administered NS. In tumor-bearing rats administered Glu, a two-fold decrease in total serum cholesterol, a two-fold decrease in HDL-c, and a three-fold decrease in LDL-c were observed compared to tumor-bearing rats administered NS. Tumor weights and LCAT activity did not differ significantly between treatment groups. Previous results have demonstrated that lipophilic compounds that interact with plasma lipoproteins have altered pharmacological effects when administered with IL. Therefore, this study suggests that IL infusions alter the HDL-c/LDL-c ratio and could affect the pharmacological behavior of anticancer compounds that predominantly distribute into the LDL fraction upon entrance into the bloodstream.

Lipid composition and structure of commercial parenteral emulsions

In order to study the influence of the phospholipid/triacylglycerol (PL/TG) ratio of parenteral emulsions on the distribution and the physico-chemical properties of their fat particles, commercial 10, 20 or 30% fat formulas were fractionated by centrifugation into an upper lipid cake (resuspended in aqueous glycerol) and a subnatant or mesophase, from which a PL-rich subfraction (d = 1.010-1.030 g/l) was purified by density gradient ultracentrifugation. Chemical and 31P-NMR analyses of these fractions indicated that at least two types of fat particles coexist in parenteral emulsions: (i) TG-rich particles (mean diameter: 330, 400, 470 nm in the 10, 20, 30% emulsion) which contain practically all the TG and esterified phytosterols of native emulsions, but only a fraction of their PL, unesterified cholesterol and phytosterols, and other minor lipids; (ii) PL-bilayer particles or liposomes (mean diameter: 80-100 nm) which are constituted with the remaining PL and relatively very small amounts of TG and other lipids. The higher the oil content of the emulsion, the lower the amount of these PL-rich particles, which represent the major particle population of the mesophase. Indeed, minute amounts of TG-rich particles (probably the smallest ones) are also present in the mesophase, even in the PL-rich subfraction which contains the bulk of liposomal PL. Since the PL-rich particles of the infused emulsion generate lipoprotein X-like particles, only the large TG-rich particles can be considered as true chylomicron counterparts.

Entrapping efficiency and drug release profile of an oil-in-water (o/w) emulsion formulation using a polydimethylsiloxane-coated glass bead assay

Evaluation of entrapping efficiency is difficult for an o/w emulsion formulation containing a lipophilic oily drug, isocarbacyclin methyl ester (TEI-9090), by commonly employed techniques (dialysis, ultrafiltration, or gel filtration), because of its adsorption to the system materials. Employing this characteristic of TEI-9090, we developed an adsorption technique with polydimethylsiloxane-coated glass beads (PDMS-GB). The assay is based on the quantitative adsorption of unentrapped TEI-9090 to the PDMS-GB. The entrapping efficiency of a 10% soybean oil emulsion containing [3H]TEI-9090 (1 microgram/mL) assayed by this method approached 100%. The PDMS-GB assay was performed for the emulsion diluted 100 times with physiological saline at different time intervals after dilution over a period of 24 hr. A plot of [3H]TEI-9090 in the emulsion particles versus time showed rapid release within 1 hr, followed by very slow release, reaching equilibrium. Applying first-order kinetics, the data were found to fit to a biexponential equation over the first hour of release. The terminal release resembled the first-order release of the drug from the phospholipid-rich infranatant, which was separated from the creamy layer by ultracentrifugation of the emulsion and contained 35% [3H]TEI-9090. These results suggest that the drug is released from two components in the emulsion.

Cyclic parenteral nutrition in hospitalized adult patients: a 9-year experience

We are reporting our 9-year experience of cyclic parenteral nutrition with 200 in-patients (mean age 52 years) treated 64 +/- (SEM)3 days (range: 15-230) for Gl diseases. During the first period (A, n = 38), all-in-one nutritive bags with intralipid 10% were used; in a second period (B, n = 135), intralipid 10% was infused separately over the first 6 h of nutrition; in the final period (C, n = 27), Intralipid 20% was used in all-in-one nutritive bags. Indications for parenteral nutrition were non-malignant digestive diseases in 89.5% of the cases. The frequency of complications appearing during cyclic parenteral nutrition was the following: catheter-related sepsis 8%, catheter obstruction 8%, hypertriglyceridemia 33%, hypercholesterolemia 14.7%, liver function test abnormalities 28% and biliary sludge and/or lithiasis 31.6%. 5 patients, with chronic obstructive small bowel disease, developed jaundice with no identifiable cause other than parenteral nutrition. The prevalence of catheter obstruction significantly decreased (P < 0.01) during period B, as compared with periods A and C. The prevalence of liver function test abnormalities decreased significantly (P < 0.01) during periods B and C, as compared with period A. Mortality rate related to cyclic parenteral nutrition was 3%. These results suggest that a) the separate infusion of lipid emulsion reduces the prevalence of catheter obstruction; b) as compared with 10% intralipid in all-in-one nutritive bags, the separate infusion of 10% Intralipid or the 20% Intralipid given in all-in-one nutritive bags is associated with a decreased prevalence of liver function test abnormalities; c) chronic small intestine obstruction seems to play a key role in parenteral-associated jaundice.

Investigation of the particle size distribution of a model intravenous emulsion

The size distribution of a model intravenous (iv) emulsion was investigated with special regard to the lower size classes. The special interest in the lower size classes is related to their possible responsibility for a number of side effects as well as their possible influence on pharmacokinetics of incorporated drugs. The particle size distribution of the unfractionated emulsion observed by photon correlation spectroscopy (PCS) showed no particles with diameters < 140 nm. In contrast, a three-dimensional analysis of transmission electron micrographs (TEM) resulted in a mean particle diameter of approximately 68 nm. 31P NMR experiments revealed that approximately 48 mol% of the emulsifier forms particles smaller than approximately 100 nm in diameter. The results from TEM observations and NMR spectroscopy suggest that the majority of particles by number have diameters < 100 nm. PCS measurements of fractionated samples of the emulsion, in combination with their chemical analysis, confirmed the predominance of particles with diameters < 100 nm. The relevance of PCS data analysis for the characterization of unfractionated iv emulsions, consisting of particles differing in structure and showing a broad size distribution by number, seems limited.

Cholesterol and bile acid biodynamics after total small bowel resection and bile diversion in humans

BACKGROUND

In humans, the patterns of cholesterol and bile acid biodynamics in the absence of the small intestine are not yet known. They are described in two parenterally fed patients several months after total enterectomy and bile diversion.

METHODS

After an intravenous pulse of [3H]cholesterol, a long-term study involved the analysis of both the decay in the specific activity of plasma cholesterol and the biliary outputs of sterols and bile acids.

RESULTS

Plasma cholesterol input reached 2-3 g/day (vs. 1 g/day in healthy patients), mostly from synthesis. As assessed by sterol balance, whole body cholesterol synthesis approximated 6 g/day (vs. 0.6-0.8 g/day). Unusually, about 60% of the newly synthesized cholesterol was eliminated, without prior transit into the bloodstream, from the liver into the bile. Bile acid conversion concerned over 90% (vs. 40%-50%) of the cholesterol meant to be excreted, issued from plasma or hepatic synthesis. In addition to cholic and chenodeoxycholic acids, one patient secreted up to 1 g/day of 7-epicholic acid.

CONCLUSIONS

The stimulation (up to 10-fold) of the cholesterol and bile acid synthesis, stronger than that observed following ileal bypass or resection or complete bile diversion, could well be partially linked to the absence of small bowel tissue per se.

Total parenteral nutrition and plasma lipoproteins in the rat: evidence for accelerated clearance of apo-A-I-rich HDL

The effect of total parenteral nutrition (TPN) containing fat on plasma lipoproteins and apo-A-I-rich HDL catabolism was studied in the rat. TPN rats were intravenously infused for 5 days with a nutritive mixture containing amino acids, lipids (Intralipid 20%) and glucose. In spite of similar plasma levels of total cholesterol in TPN and control orally fed rats, density gradient ultracentrifugation of plasma samples gave evidence of marked differences in the lipoprotein profiles. In the density range 1.010-1.040, were found elevated amounts of apo-B-100 and apo-B-48 containing lipoproteins, as well as an increase in free cholesterol and phospholipids, the latter indicating that the plasma of TPN rats contained abnormal lipoprotein-X-like particles. The level of apo-E-rich HDL (density: 1.040-1.063) was not markedly changed, whereas that of typical HDL (d > 1.063) was lowered, with less apo-A-I and apo-A-IV, and low amounts of cholesterol and phospholipids were found in the most dense HDL3 fractions (d > 1.090) containing the bulk of apo-A-I-rich particles. After intravenous infusion of homologous [14C]sucrose-labelled HDL3, the clearance of these particles was 2-fold faster in TPN than in control rats, with a tissue uptake increased in the liver (+40%) and decreased in the small and large intestines (-60%). Because the pool of apo-A-I-rich HDL was dramatically reduced after 5 days of artificial feeding, the absolute catabolic rate of these lipoproteins was similar in the two groups. These data suggest that, in TPN rats lacking of chylomicron coat components as a source for HDL material, the fall in plasma levels of apo-A-I-rich HDL resulted mainly from accelerated turnover of these particles, mediated by increased uptake by the liver. Conversely, mucosa atrophy was probably involved in the reduced uptake of apo-A-I-rich HDL by the gastrointestinal tract.

Physico-chemical characterization of Intralipid emulsions

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