Winai Dahlan

Plasma lipid and plasma lipoprotein concentrations in low birth weight infants given parenteral nutrition with twenty or ten percent lipid emulsion.

Because 10% and 20% intravenously administered lipid emulsions (intralipid preparations) differ in their phospholipid/triglyceride ratio (0.12 and 0.06, respectively), 28 low birth weight infants requiring parenteral nutrition for at least 1 week were selected at random to receive either emulsion to determine the effects on plasma lipids and lipoproteins. Triglyceride intake was progressively increased to reach 2 gm/kg per day between days 4 and 7. During that period, all plasma lipids in samples taken 6 hours after infusion were higher in the 10% intralipid group. In comparison with day 0 values, triglyceride concentrations decreased (63 +/- 7 to 45 +/- 4 mg/dl; p less than 0.05) in the 20% group. Cholesterol levels increased in both groups, but the rise was more than twofold higher in the 10% group. Phospholipid increase was approximately 25% in the 20% group but more than 125% in patients receiving the 10% emulsion (p less than 0.005). The changes in plasma cholesterol and phospholipid levels were almost entirely in low-density lipoproteins. After 7 days, eight infants from each group were given the alternate emulsion, which resulted in a reversal of lipid patterns in each patient. We conclude that the higher phospholipid intake in 10% than in 20% intralipid is associated with higher plasma triglyceride concentrations and leads to accumulation of cholesterol and phospholipids in low-density lipoproteins. Emulsions with lower phospholipid content may be preferable for low birth weight infants and perhaps other patient populations with impaired removal of parenteral fat emulsions.

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.

Intravascular metabolism of different fatty acids during lipid infusion in man

The differential intravascular metabolism of individual fatty acids contained in triacylglycerol-rich particles was studied by infusing 6 normal subjects for 5h with a conventional soy-based emulsion and an experimental olive oil-based emulsion. Both emulsions contained similar amounts of palmitate (11%) and stearate (3-4%) but the former was quite rich in linoleate (54%) and alpha-linolenate (7%), while the latter was rich in oleate (69%). During hydrolysis of circulating triacylglycerols by endothelial lipases, the associated rise of non-esterified fatty acids (FFA) in plasma represents the balance between fatty acid release and tissue uptake. Plasma levels of triacylglycerols and FFA increased about 3 fold and total body fat oxidation was raised to similar values with both emulsions. Fatty acid pattern quickly changed in plasma triacylglycerols to resemble the composition of emulsion particles, with an exception for palmitate which increased markedly more, suggesting a high level of hepatic re-esterification and re-appearance in nascent very low density lipoprotein triglycerides (VLDL-TG) secreted into the circulation. In plasma FFA, stearate and palmitate increased more and alpha-linolenate much less than expected from their content in the emulsion, indicating probably low tissue uptake for the former ones but avid removal for the latter.

Interactions between exogenous fat and plasma/lipoproteins

Fat emulsions are essentially composed of triglycerides and phospholipids. Their elimination from the plasma--which is generally rapid--is influenced by the amount and the composition of both these components. During their short stay in the vascular compartment, exogenous particles undergo major compositional changes. They acquire various apolipoproteins--namely C-II, C-III, E and A-IV--by transfer from HDL. They also acquire esterified cholesterol from HDL and LDL and transfer exogenous triglycerides and phospholipids to these endogenous lipoproteins. These exchanges are affected by the type of triglyceride fatty acids and the amount of phospholipids present in fat emulsions, as well as by the infusion rate. Some 10% of emulsions--with a high phospholipid: triglyceride ratio--contain a huge phospholipid excess which can be isolated as a separate fraction from the triglyceride-rich particles. These phospholipids markedly interfere with the metabolism of cholesterol and the plasma lipoprotein profile.

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