C. Rössle

Effects of essential fatty acid contents of lipid emulsions on erythrocyte polyunsaturated fatty acid composition in patients on long-term parenteral nutrition.

The effect of the long-term intravenous infusion of 2 lipid emulsions, differing in essential fatty acid (EFA) content, on fatty acid pattern of red blood cell (RBC) was investigated in 5 patients with inflammatory bowel disease. They were randomly assigned to receive daily intravenous infusion of either a soybean emulsion or a mixed medium-chain triacyl-glycerols (MCT): soybean emulsion, followed by the other, each for a period of 3 months. The soybean emulsion contained exclusively long-chain triacylglycerols (LCT) with 54% of C18:2n-6 and 6% of C18:3n-3. The mixed emulsion consisted of a 50:50 (w:w) mixture of soybean LCT and MCT, providing half the amount of the same EFA compared to LCT emulsion. The same phospholipid emulsifier was used in both preparations. Infusion of LCT for a 3 month period modified RBC fatty acid pattern as follows: 18:2n-6 increased, 20:4n-6 decreased as well as n-6:n-3 ratio. By contrast, infusion of MCT/LCT did not alter RBC fatty acids, and even tended to correct a pattern altered by the previous LCT infusion. The study demonstrates that soybean LCT provides an excess of C18: 2n-6 which affects the balance between RBC fatty acids in adult patients. Decreasing the intake of C18:2n-6 and C18: 3n-3, by using a mixed MCT/LCT emulsion, appears more appropriate for keeping a balanced pattern.

Manipulation of tissue fatty acid profile by intravenous lipids in dogs.

This study was undertaken to determine the effects on the fatty acid (FA) composition of various dog tissues of 4 different lipid emulsions (a 100% long-chain triacylglycerol (LCT) derived from soya bean oil emulsion, a mixed 50% medium-chain triacylglycerol (MCT)/50% LCT emulsion as well as both these emulsions supplemented with 10% fish oil (FO) triacylglycerols), when daily infused over 15 days as a substantial component of total parenteral nutrition. Lipids represented 55% of the non-protein energy. Blood samples as well as biopsies from liver, muscle and adipose tissue were taken 15 days before, and again immediately after TPN. In addition, the spleen was also removed immediately after TPN. Tissue FA composition was analysed by gas liquid chromatography of each lipid component after separation by thin layer chromatography. No differences in either safety or tolerance were detected between the different TPN preparations. In particular, infusion over 2 weeks of fat emulsions containing 10% fish oil was tolerated as well as conventional LCT and MCT/LCT emulsions. Relative linoleate content of tissue triacylglycerol (TG) was markedly increased in animals that received the LCT emulsions (e.g. from 22.6 +/- 2.5% to 32.2 +/- 0.6% in the liver), this effect being markedly reduced with MCT/LCT preparations. n-3FA were slightly incorporated into liver TG (from 0.0 +/- 0.0% to 2.3 +/- 0.7% and 1.2 +/- 0.4% for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) respectively, with LCT + FO), but remained undetectable in extrahepatic tissue TG. Of interest, medium chain FA were found in tissue TG after infusion of the mixed MCT/LCT emulsions. As expected, changes of tissue phospholipid (PL) composition involved only long-chain FA. Infusion of soya bean oil emulsion was associated with an increased content of linoleate in liver PL (from 13.6 +/- 0.4% to 17.7 +/- 0.4%), but not in other tissues. MCT/LCT did not markedly affect PL/FA pattern in any tissue. Supplementation with fish oil was associated with an efficient incorporation of n-3FA into tissue PL, particularly in the liver (from 0.4 +/- 0.1% to 2.5 +/- 0.3% for EPA and from 3.9 +/- 0.8% to 9.1 +/- 0.4% for DHA, with the LCT + FO emulsion).

Modification of erythrocyte membrane lipid composition induced by a single intravenous infusion of phospholipid-triacylglycerol emulsions in man

The study aimed to investigate whether, during short term infusion of lipid emulsions in man, red blood cell (RBC) membrane lipid composition was altered and RBC-free cholesterol (FC) could serve as a source of FC accumulated in the plasma. 3 normal subjects were infused intravenously with either 10% Intralipid [10% IL; PL:triglyceride (TG) weight ratio of 0.12] at the rates of 0.1, 0.2 and 0.3 g TG.kg(-1).h(-1) (providing PL intakes of 12, 24, 36 mg.kg(-1).h(-1), respectively) or with 30% Intralipid (30% IL; PL:TG ratio of 0.04) at the rate of 0.3 g TG.kg(-1).h(-1) (providing 12 mg PL.kg(-1).h(-1)). Infusion of 10% IL at a slow rate and 30% IL at a high rate caused no change in RBC and plasma FC content. However, 10% IL infusion at intermediate and high rates induced a significant decrease in RBC-FC: PL ratio. This change was still present at 18 h after the cessation of high rate infusion. RBC-FC: PL ratio and plasma PL measured during infusion were significantly correlated (r = -0.87, p < 0.001). FC efflux from RBC appears to contribute to the rise in plasma FC. This study indicates that the excessive amount of PL present as liposomes in some intravenous lipid emulsions can alter erythrocyte membrane lipid composition.

Stabilisation of plasma substrate concentrations: A model for conducting metabolic studies

Metabolic studies involving changes in plasma substrate concentrations are frequently carried out after an overnight fast. This condition, however, is a transition between the post-prandial period and the beginning of starvation, and thus is associated with rapid changes in the plasma concentration of many substrates. Such alterations might interfere with the interpretation of modifications in plasma concentrations resulting from experimental manipulations. Infusion of glucose at a rate of 250 mg kg(-1) h(-1) for 1h and subsequently at 162 mg kg(-1) h(-1) together with amino-acids at 50 mg kg(-1) h(-1) is used to stabilise the plasma concentration of most substrates within 3 h, a condition which is maintained for the subsequent 5 h or more. This study offers a model which is more suitable for many metabolic investigations than overnight fasting and which takes little time or expense to prepare.

Parenteral verabreichte mittelkettige triglyzeride induzieren veränderungen im carnitin-stoffwechsel

Es wird generell behauptet, daβ mittelkettige Triglyzeride unabhangig von Carnitin verstoffwechselt werden. In der vorliegenden Studie wurde der Einfluβ einer Infusion von mittelkettigen Triglyzeriden auf die Plasmakonzentrationen von freiem und acyliertem Carnitin sowie von β-Hydroxybutyrat bei vier gesunden mannlichen Probanden untersucht. Zunachst erhielten die Versuchspersonen eine dreistundige Infusion von Glukose und Aminosauren. Anschlieβend wurde wahrend 5½ Stunden zusatzlich eine Fettemulsion infundiert, die entweder nur langkettige Triglyzeride oder eine Mischung aus lang- und mittelkettigen Triglyzeriden (50:50; w/w) enthielt. Wahrend der fett-freien Infusionsperiode stieg die Plasmakonzentration von freiem Carnitin, wahrend diejenigen der Acylcarnitine abnahmen. Die Infusion der kombinierten Emulsion erniedrigte die Konzentration des freien Carnitins starker (32,4 ± 4,7 μmol/L) als die reinen langkettigen Triglyzeride (44,4 ± 2,7 μmol/L). Im Gegensatz dazu erhohten sich die Plasma-Konzentrationen von kurzkettigem Acylcarnitin (12,1 ± 3,3 vs. 5,4 ± 1,9 μmol/L; p