Changes of HDL subfraction concentration and particle size by intralipid in vivo.

The effects of the artificial triglyceride-phospholipid emulsion (10% intralipid) on HDL subfraction were studied in vivo. After a 14-h fast, subjects received intralipid via a 4-h infusion. Serum lipoproteins were analyzed before and at 4 and 6 h after the start of the infusion. At 4-h the following acute changes by infusion were observed. Triglyceride, phospholipid, free cholesterol, and esterified cholesterol in chylomicrons and VLDL increased. HDL2 as well as triglyceride, phospholipid, free cholesterol and protein within the HDL2 increased, while HDL3 decreased. An increase in HDL3 triglyceride was observed. The masses of apo A-I and A-II in the HDL2 density interval rose while these parameters fell in HDL3. There were decreases of apo C-II and C-III in the HDL subfractions and elevations in chylomicrons and VLDL. The particle size of the HDL subfractions increased. However, most of these acute changes at 4 h tended to disappear by 6 h. These results suggest that there is exchange of lipids and reversible transfer of apo C-II and C-III between HDL subfractions and intralipid, and conversion of HDL3 to HDL2 followed by the reverse conversion of HDL2 to HDL3 as the synthetic emulsion is cleared from the plasma.

Artificial induction of intravascular lipolysis by lipid-heparin infusion leads to insulin resistance in man.

Although extensive evidence indicates that free fatty acids can decrease glucose utilization in vitro, it is still controversial how an increase in lipolysis affects glucose metabolism in man. To test the hypothesis that an increase in lipolysis is related to insulin resistance, we examined the effect of lipid-heparin infusion on glucose metabolism in ten normal subjects by the euglycaemic glucose clamp technique and isotopic determination of glucose turnover. In the control euglycaemic clamp studies with insulin infusion at 0.2 and 1.0 mU.kg-1.min-1, endogenous glucose production was suppressed from the basal rate of 2.0 +/- 0.3 mg.kg-1min-1 to 1.1 +/- 0.7 mg.kg-1.min-1 and -0.4 +/- 0.7 mg.kg-1min-1 respectively. Glucose utilization increased from the basal rate of 2.0 +/- 0.3 mg.kg-1min-1 to 2.3 +/- 0.5 mg.kg-1min-1 and 5.9 +/- 1.8 mg.kg-1min-1 respectively. When the euglycaemic clamp studies were coupled with lipid-heparin infusion at comparable low and high rates of insulin infusion, endogenous glucose production increased (1.8 +/- 0.7 mg.kg-1.min-1, p less than 0.001, and 0.3 +/- 0.6 mg.kg-1.min-1, p less than 0.05, respectively), and glucose utilization decreased (2.1 +/- 0.3 mg.kg-1.min-1, not significant, and 3.2 +/- 0.7 mg.kg-1.min-1, p less than 0.001 respectively). These data suggest that the artificial induction of intravascular lipolysis by lipid-heparin infusion leads to a state of insulin resistance in man.

Immediate intralipid clearance from plasma in critically ill patients after a single-dose injection.

Plasma fractional removal rates (k2) of Intralipid injected in parallel with 125I albumin were analyzed in five healthy males and nine critically ill patients. The k2 values of critically ill patients were similar to those of healthy subjects. However, the initial plasma concentrations of Intralipid calculated by extrapolation to zero-time (y0) were markedly different. The mean y0 value in the critically ill patients was 43% that of healthy subjects. No plasma loss of 125I albumin occurred throughout the test. Intralipid to 125I albumin plasma concentration ratios during the removal phase paralleled the curves obtained from the iv fat tolerance test. This suggests that these ratios depend on Intralipid clearance rather than leakage from the circulation. The immediate loss of Intralipid suggests that the pulmonary vasculature, the first capillary bed through which the emulsion passes, could be the site where a substantial uptake of the emulsion occurs in critically ill patients.

Plasma clearance of fat emulsion during continuous heparin infusion.

Intravenous fat tolerance was tested in two groups of patients given a continuous i.v. infusion of heparin for several days. One group of 11 patients with deep vein thrombosis (DVT) of the leg was given 25,000-35,000 IU heparin daily for 4-5 days. The other group comprised 10 patients who had central venous catheters (CVC) for total parenteral nutrition. These patients were given 20,000 IU heparin daily for 6 days as prophylaxis against CVC-related thrombosis. In the DVT group heparinization was associated with a 44% decrease in plasma fat removal capacity (P less than 0.05). This reduction persisted for 2 days after the discontinuation of heparin therapy. In the CVC group the plasma fat removal capacity decreased by 29% during heparinization (P greater than 0.05, NS). During heparinization activated partial thromboplastin time was more than three times the basal value in the DVT group but less than twice those in the CVC group. One week after the heparin therapy the serum triglyceride levels were higher in both groups compared with initial values (DVT group: 1.2 +/- 0.2 s.e. mean vs. 1.7 +/- 0.3 mmol/l; P less than 0.05. CVC group: 1.0 +/- 0.1 vs. 1.4 +/- 0.2 mmol/l; NS). The possibility that full-dose heparinization reduces plasma fat removal capacity and that this may be due to a partial depletion of lipoprotein lipase stores is discussed.

Prolonged exercise augments plasma triglyceride clearance.

We studied ten male distance runners before and after a marathon to determine the effects of prolonged exercise on serum lipoprotein values and the capacity to clear plasma triglycerides. Serum lipid and lipoprotein concentrations, intravenous fat clearance, and postheparin plasma lipolytic activities were measured 24 hours before and 18 hours after the race. The clearance rate of exogenous fat increased 76% +/- 64%, postheparin lipoprotein lipase activity increased 46% +/- 35%, and fasting triglyceride levels decreased 26% +/- 13% after the race. High-density lipoprotein (HDL) cholesterol level increased 10% +/- 8%, primarily due to a 19% +/- 17% increase in the HDL2 subfraction. Changes in the clearance rate of exogenous fat were directly related to changes in HDL cholesterol level and the HDL2 subfraction. Thus, the rise in HDL cholesterol concentrations after prolonged exercise may be a consequence of enhanced fat clearance.

Utilization of Intralipid in septic rats: effects of sepsis on the clearance of exogenous fat emulsion from various organs.

The rats were used for the study of the effects of sepsis on the utilization of exogenous fat emulsion. The studies were carried out by measuring the rate and the pattern of clearance of intravenously-administered 14C-Intralipid from the plasma, liver, spleen, kidney, and muscle of control and septic rats. Plasma clearance of the exogenous fat measured for 14C at 30, 60, 90, 120, 360 min (n = 5) after intravenous injection revealed that the clearance was retarded by sepsis. In the liver, the initial 14C uptake was much greater in the septic rats than those in the control group (34.8 +/- 3.6% vs 14.4 +/- 1.6%, p less than 0.01). Six hr after injection, as high as 19.6 +/- 2.4% of the injected dose was detected in the liver of the septic rats, but the control rats had only 4.4 +/- 0.8%. In spleen, kidney, and muscle, however, both the 14C uptake and the rate of its clearance were greater for the control rats than those of the septic group. The increase in the amount of liver uptake of the exogenous fat by the septic rat and the retained large amount of the fat may account for the decreased plasma clearance and the decrease in its subsequent utilization by other organs and tissues. Significant increase in liver contents of total lipid and triglyceride with a decrease in nonesterified fatty acid (NEFA) at the end of a 6-hr period in septic rats suggest that accumulation of fat in the liver may be a result of impaired triglyceride hydrolysis, possibly due to suppressed lipoprotein lipase activity.

Intralipid disappearance in critically ill patients.

Intralipid elimination patterns were compared in 25 healthy controls, 12 patients recovering from uncomplicated cholecystectomy, and 25 critically ill patients. The intravenous fat tolerance test revealed a similar fractional removal rate (k2) in healthy controls and critically ill patients, but k2 was increased in cholecystectomy patients. The concentration of cross-reactive protein (CRP) correlated positively to the concentration of total triglyceride and low-density lipoprotein-triglyceride, and negatively to low-density lipoprotein-cholesterol and high-density lipoprotein-cholesterol. The extrapolated zero-time concentration of Intralipid in the critically ill patients was only one-third of the value in healthy controls. After this initial loss, however, Intralipid was removed from the circulation after first-order kinetics. These low concentrations of Intralipid were not correlated with concentrations of CRP. Possible explanations for this phenomenon include a change in the configuration of the lipid particles, the so-called creaming phenomenon, and/or immediate and substantial uptake of the emulsion by certain organs.

Comparison of the elimination of 10 and 20% TRAVAMULSION lipid emulsion from the blood of beagle dogs.

Metabolic utilization of fat emulsions containing 20% lipid and 10% lipid were compared using beagles. The key parameter measured was elimination of the lipid from the bloodstream, which serves as an indication of the emulsion's availability for metabolism. Nonlinear kinetic analysis was used in this determination. Blood concentrations of free fatty acids, phospholipid, and cholesterol were also measured as additional ways of determining emulsion metabolism. The 10 and 20% emulsions appeared to be equivalent in elimination of the caloric substrate triglyceride from the blood stream. Results also showed an adaptation to emulsion infusion over time at both dosages administered (3 and 6 g/kg of body weight). This was indicated by increased elimination capacity and stabilization of each lipid class measured. However, blood concentrations of phospholipid and cholesterol indicate that the 20% emulsion provides a lesser lipid load for the amount of calories administered when compared to an emulsion containing 10% lipid.

Agglutinate formation in serum samples mixed with intravenous fat emulsions.

The degree of fat agglutination (the so-called "creaming phenomenon") was measured in sera from 51 critically ill patients, 200 ambulatory patients and 24 healthy volunteers. A 400-microliter serum sample was mixed with 10 microliter of a fat emulsion (Intralipid), incubated at 37 degrees C, and examined after 2, 6, and 24 h. Almost all samples from critically ill patients exhibited creaming, as did 31% of the samples from ambulatory patients. Serum samples from healthy volunteers were incubated with purified C-reactive protein (CRP). At a CRP concentration of 40 mg/L, creaming was always observed. Creaming also occurred at normal serum levels of CRP, but at increased concentrations of other serum proteins. Finally, the creaming test was performed with 12 different fat emulsions, mixed with sera from critically ill and healthy subjects. Healthy sera produced no creaming and sera from critically ill patients invariably showed creaming with every emulsion.

The turbid specimen as an analytical medium: hemoglobin determination as a model.

The quantitation of chemical constituents in lipemic samples is a major problem confronting the clinical laboratory. Currently, a number of cumbersome and time-consuming methods are used to clarify samples before analysis. However, the use of enzymic hydrolysis of triglycerides along with efficient chemical removal of the formed non-esterified fatty acids is exemplified here as an excellent alternative to the current methods of clarification such as ultracentrifugation, extraction or chemical precipitation of low density and very low density lipoproteins. This method of clarifying milky serum has been used by us to assay hemoglobin in severely lipemic blood samples as an analytical model.

[Analytical interference of lipid parenteral feeding with the determination of methemoglobin levels by an autoanalyzer]. / Interférence analytique de l'alimentation parentérale lipidique avec la détermination du taux de méthémoglobine par autoanalyseur.

We report here an unusual cause of analytical interference observed in methemoglobin values of patients parenterally given nutritive lipid emulsions. In these patients, harboured in intensive care department, T Hb, % O2 Hb, % COHb, Met Hb values are systematically measured using IL 282 CO-Oximeter autoanalyser in addition to daily blood gas determination (pH, PaCO2, PaO2). An increase in % Met Hb rate up to 10-20% was observed in lipid emulsions receiving patients. We first verified that washing red blood cells with saline instantaneously lowers Met Hb values to less than 1%. The mechanism of this interference was addressed by performing three Met Hb determination methods in normal blood in vitro added with variable amounts of lipid emulsions: CO-Oximeter determination, classical Evelyn Malloy method, analysis of continuous absorption spectra between 480 and 640 nm. Results corroborate the spectral origin of the analytical interference observed with CO-Oximeter and leading to false positive values. Blood lipids increase unspecifically the wave length proportional absorption between 480 and 640 nm. Evelyn Malloy's technique suppresses this interference since it uses the ratio of differences in optical densities. Our results emphasize the necessity of knowing patients therapeutics when performing laboratory investigations.

Lack of effect of exogenous or endogenous gastric inhibitory polypeptide on the elimination rate of Intralipid in man.

Six healthy subjects were studied by means of an intravenous fat tolerance test on three occasions, in the fasting state, in the postprandial state, and during an intravenous infusion of gastric inhibitory polypeptide (GIP). No effects on the elimination rate of Intralipid were seen either by endogenous or exogenous GIP.

[Clearance and utilization of infused fat emulsions]. / Clearance und Verwertung infundierter Fettemulsionen.

Fat emulsions are an important source of energy for parenteral nutrition. The utilization of fat emulsions can be differentiated in elimination and oxidation. Biphasic elimination curves are observed, indicating zero order kinetics for removal at high substrate concentrations and first order kinetics at low substrate concentrations. During elimination from plasma apolipoproteins are transferred to the artificial fat particles. The elimination rate is determined by the composition of the fat particles, the nutritional status and the illness of the patient. The oxidation of the infused fatty acids is not strongly correlated with elimination. For clinical purposes the elimination is a suitable parameter for utilization.

Isolation and characterization of human apolipoprotein A-IV from lipoprotein-depleted serum.

Human apolipoprotein A-IV is an acidic polypeptide of molecular weight 46,000 that is secreted into lymph on the surface of nascent chylomicrons, but which exists in circulation unassociated with lipoproteins. Previous studies of this protein have utilized material isolated from a d < 1.006 g/ml fraction of human serum and from human lymph. Although it has been suggested that apoA-IV circulating in plasma is the product of dissociation from the surface of nascent chylomicrons, it has been characterized by immunological techniques only. We have isolated human apoA-IV on a preparative scale from lipoprotein-depleted serum using a technique of adsorption to a phospholipid-triglyceride emulsion, followed by delipidation and preparative gel electrophoresis. The molecular weight, pI, and amino acid composition of material thus prepared agree with literature values for apoA-IV derived from chylomicrons. We have determined that apoA-IV is a glycoprotein containing 6% carbohydrate by weight (mannose 1.8%, galactose 1.55%, N-acetyl glucosamine 1.55%, sialic acid 1.1%). Electroimmunoassay of human serum using a monospecific rabbit antibody to serum-derived apoA-IV found 13.1 +/- 1.8 mg/dl, a value in agreement with determinations using antibodies to chylomicron-derived apoA-IV. We conclude that apoA-IV may be easily purified from normal human serum, and that the material thus isolated has identical chemical, physical, and immunological properties to apoA-IV obtained from human lymph. It is therefore likely that the dissociation of apoA-IV from the surface of nascent chylomicrons following their entry into circulation is not attended by changes in the structure or composition of this apoprotein.-Weinberg, R. B., and A. M. Scanu. Isolation and characterization of human apolipoprotein A-IV from lipoprotein-depleted serum.

Metabolic utilization of intravenous fat emulsion during total parenteral nutrition.

The effect of nutritional therapy on the utilization of an intravenous fat emulsion was studied in patients with injury, infection, and nutritional depletion using I-14C-trioleate labeled Intralipid. The plasma fractional removal rate and 14C-Intralipid oxidation rate was 55% ad 25% higher, respectively, in patients following trauma and during periods of infection receiving 5% dextrose than in healthy control subjects. Total parenteral nutrition (TPN) was administered as either 1) nonprotein calories given as glucose (Glucose System) or 2) equal proportions of glucose and intravenous fat emulsion (Lipid System). In comparison to TPN with the Lipid System, administration using the Glucose System resulted in higher plasma clearance rates and lower oxidation rates in both acutely ill and depleted patients. There was no correlation between the rates of plasma removal and oxidation of the intravenous fat emulsion (r = -0.04; NS) indicating that the removal of exogenous fat from plasma cannot be used as an indicator of oxidation. A negative linear relationship was seen between the oxidation rate of intravenous fat and carbohydrate intake (r = -0.92; p less than 0.001). Glucose intakes exceeding energy expenditure did not totally inhibit oxidation of the fat emulsion. The oxidation rate of 14C-Intralipid was linearly related to net whole body fat oxidation calculated using indirect calorimetry (r = -0.90; p less than 0.001) suggesting that the fat emulsion was oxidized in a similar manner to endogenous lipids. This study suggests that intravenous fat emulsions are utilized as an energy substrate in patients with major injury, infection or nutritional depletion. This observation, along with a relative unresponsiveness to glucose in surgical patients suggests that fat emulsions may be useful as a calorie source in patients receiving parenteral nutrition.

Intravenous fat tolerance test with Intralipid in chronic renal failure.

The intravenous fat tolerance test with Intralipid has been used to evaluate the triglyceride (TG) removal capacity in 34 male patients with varying degree of chronic renal failure (CRF). The investigations were repeated in 10 patients after 2-3 years when the renal function had deteriorated further. The fractional removal rate of Intralipid (k2) was low compared to controls, regardless of degree of renal function, etiology of renal disease or treatment with antihypertensive drugs. The k2 value did not change in patients investigated twice, although there was a considerable decrease in renal function. Both in patients and controls there was a strong negative correlation between k2 and the very low density lipoprotein (VLDL) TG concentration. However, at the same k2 value, the VLDL TG concentration was higher in patients than in controls. These data suggest that the hypertriglyceridemia commonly seen in patients with CRF is caused both by an increased VLDL production and a decreased VLDL removal from the circulation. Furthermore, these changes in TG metabolism are induced early in the course of renal insufficiency.

Protein binding of valproic acid in the presence of elevated free fatty acids in patient and normal human serum.

Two recent reports indicate that free fatty acids (FFA) can decrease the binding of valproic acid (VPA) to plasma proteins. Since FFA can increase in several physiological and clinical situations, it becomes necessary to define the relationship between elevated FFA and VPA free fraction. This study was conducted in two phases. In the first phase, serum was obtained from nine patients who were receiving Intralipid. A base-line sample was taken when therapy was absent. A second sample was taken during or immediately after Intralipid therapy. Protein binding VPA (equilibrium dialysis) and FFA levels were determined on each sample. FFA increased in eight patients; the median increase was 80.1%. VPA free fractions increased in six of the eight patients showing an increase in FFA; the median increase in free fraction was 18.7%. Rank correlation between FFA differences and free fraction differences indicated a significant positive linear correlation (r = 0.800). In the second phase, oleic acid was added to normal serum in five different concentrations (500-5,000 microEq/liter) with VPA at 100 microgram/ml. Free fraction of VPA increased continuously from a blank value of 9.6% (+/- 1.4) to 44.1% (+/- 2.5) with increasing concentrations of oleic acid.