Apolipoprotein E and activity of cholesterol esters transport in type IIA and IIB hyperlipoproteinemia

The authors studied the activity of cholesterol esters transport (CET), concentrations of apolipoprotein E in the blood and high density lipoproteins (HDLP) in parallel with other parameters of lipoprotein metabolism in 79 males and 62 females. 122 of them had ischemic heart disease (IHD) and primary hyperlipoproteinemia (HLP). 19 healthy controls were normolipidemic. Activation of CET and relative lowering of apoE content in HDLP with relevant increase in lipoproteins containing apoB were seen only in type IIB HLP. CET activity in controls was related to a significant positive correlation with concentrations of both cholesterol (CS) and CS esters (CSE) in HDLP and HDLP3 and negative correlation with the proportion free CS/CSE in HDLP. Opposite to normolipidemic subjects, in type IIB HLP there was a negative relationship between CET activity and HDLP3 CS level and positive--between free CS/CSE in HDLP but not with concentration of CSE and total CS in HDLP. In type IIA HLP patients no relationships were registered between CET activity and HDLP content of total CS and CSE as well as with HDLP3 CS level. In type IIB HLP a significant correlation was found between level of HDLP CS and CET activity. Concentration of apoE in HDLP correlated with apoB level in the serum but not with quantity of HDLP CS. Patients with type IIA HLP exhibited a significant negative correlation between CET activity and HDLP apoE. These patients had no dependence of CET activity on HDLP CS but had positive correlation between HDLP apoE and HDLP CS in the serum. Thus, defects of reverse CS transport may be induced not only by changes in CET activity but also by apoE distribution among lipoproteins of different classes.     

The changes of lipids, lipoproteins and apolipoproteins in plasma in ischemic stroke

Contents of lipids (cholesterol CS, triglycerides) as well as levels of CS of lipoproteins of different density and of apolipoproteins A1 and B were measured in blood serum of 31 patients in different periods after of ischemic stroke. The majority of the indices studied were significantly decreased in men in acute periods of the stroke, especially in 8-21 days after the stroke development. Meanwhile, the levels of lipids, CS lipoproteins of both low and very low densities were increased later. Contents of CS of antiatherogenic lipoproteins of high density (HDLP) was low in different periods after the development of disorders of cerebral circulation. This confirms the concept that low level of HDLP is one of the risk factors of ischemic stroke. Decrease of the levels of both lipids and CS of lipoproteins of different density was more pronounced in patients with more severe atherosclerotic damages of the main cerebral arteries. Disorders of metabolism of lipoproteins in ischemic disorders of cerebral circulation are discussed with reference to literary data taking into consideration their heterogeneity. Genetically determined pathology of certain apolipoproteins plays a key role factor in the development of early atherosclerosis and in the elucidation of biochemical markers of the primary damages of cerebral vessels.     

Differences in lipoprotein lipid concentration and composition modify the plasma distribution of cyclosporine

PURPOSE: The purpose of this study was to define the relationship between lipoprotein (LP) lipid concentration and composition and the distribution of cyclosporine (CSA) in human plasma. METHODS: 3H-CSA LP distribution was determined in normolipidemic human plasma that had been separated into different LP and lipoprotein-deficient plasma (LPDP) fractions by either affinity chromatography coupled with ultracentrifugation, density gradient ultracentrifugation or fast protein liquid chromatography. 3H-CSA LP distribution (at a concentration of 1000 ng/ml) was also determined in patient plasma samples with defined dyslipidemias. Furthermore, 3H-CSA LP distribution was determined in patient plasma samples of varying LP lipid concentrations. Following incubation, the plasma samples were separated into their LP and LPDP fractions by sequential phosphotungistic acid precipitation in the dyslipidemia studies and by density gradient ultracentrifugation in the specific lipid profile studies and assayed for CSA by radioactivity. Total plasma and lipoprotein cholesterol (TC), triglyceride (TG) and protein (TP) concentrations in each sample were determined by enzymatic assays. RESULTS: When the LP distribution of CSA was determined using three different LP separation techniques, the percent of CSA recovered in the LP-rich fraction was greater than 90% and the LP binding profiles were similar with most of the drug bound to plasma high-density (HDL) and low-density (LDL) lipoproteins. When 3H-CSA was incubated in dyslipidemic human plasma or specific patient plasma of varying LP lipid concentrations the following relationships were observed. As the very low-density (VLDL) and LDL cholesterol and triglyceride concentrations increased, the percent of CSA recovered within the VLDL and LDL fractions increased. The percent of CSA recovered within the HDL fraction significantly decreased as HDL triglyceride concentrations increased. The percent of CSA recovered in the LPDP fraction remained constant except in hypercholesterolemic/hypertriglyceridemic plasma where the percent of CSA recovered decreased. Furthermore, increases in VLDL and HDL TG/TC ratio resulted in a greater percentage of CSA recovered in VLDL but less in HDL. CONCLUSIONS: These findings suggest that changes in the total and plasma LP lipid concentration and composition influence the LP binding of CSA and may explain differences in the pharmacological activity and toxicity of CSA when administered to patients with different lipid profiles.     

A low temperature flotation method to rapidly isolate lipoproteins from plasma

To minimize oxidative modification, a low temperature, sequential flotation method was developed to isolate plasma lipoproteins in 18 h using a benchtop ultracentrifuge. The protein distributions were characterized using agarose and SDS-polyacrylamide gel electrophoresis, and an SDS-Lowry protein assay. The lipid distributions were assessed using a gas chromatography-mass spectrometric assay for cholesterol and an enzymatic assay for triglycerides. To validate the rapid flotation method, lipoproteins were also isolated from the same plasma samples using a modified Havel et al. flotation method (J. Clin. Invest. 34: 1345-1353, 1955). The same lipoproteins and apolipoproteins were present in fractions of comparable density, and the summed recoveries of protein, cholesterol, and triglyceride were also identical for the Havel et al. and rapid flotation procedures. Likewise, the amount of cholesterol and triglyceride in corresponding very low, intermediate, and low density lipoprotein (VLDL/IDL and LDL) fractions was the same for the two flotation procedures. The triglyceride and cholesterol levels in high density lipoprotein (HDL) isolated by rapid flotations, however, were 9-12% higher than in the HDL as isolated by Havel et al. Because a 9-12% increase in the HDL fraction reflects only 1-4% of the total triglyceride and cholesterol in plasma, we conclude that, while maintained at 4 degrees C, lipoproteins were quantitatively isolated from human plasma in 1 day.     

Plasma apolipoprotein profiles of male and female rats

To determine if sex differences exist in the apolipoprotein profile of the rat, the concentrations of the major apolipoproteins and lipids of 12-week-old male and female rats were measured in the plasma as well as in the individual lipoprotein fractions. Plasma apo B, triglyceride, and cholesterol concentrations were significantly higher in male rats than in female rats. Plasma concentrations of apo A-I, apo E, apo A-IV, and apo C-III did not differ between the sexes. Male rats had higher concentrations of apo B in the very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), and the low density lipoproteins (LDL). These results further support the evidence that sex hormones influence lipoprotein metabolism in the rat.     

Efflux of intracellular versus plasma membrane cholesterol in HepG2 cells: different availability and regulation by apolipoprotein A-I

We have compared the efflux of cholesterol from different cellular pools of human hepatoma cells HepG2 using intact cells or isolated membrane fractions. To label different pools, cells were incubated with either unesterified [14C]cholesterol that had been incorporated into high density lipoproteins ([14C]FC-HDL), low density lipoproteins ([14C]FC-LDL), or phosphatidylcholine liposomes ([14C]FC-PC), or with [14C]acetate. Cell fractionation revealed that labeling of cells with [14C]FC-PC resulted in the incorporation of [14C]cholesterol almost exclusively into the plasma membrane (PM), while incubation with [14C]FC-HDL resulted in the majority of [14C]cholesterol incorporation into the PM, but with a smaller component associated with lysosomes. Labeling with [14C]FC-LDL or [14C]acetate led to an accumulation of [14C]cholesterol predominantly in lysosomes or the endoplasmic reticulum (ER), respectively. When the kinetics of [14C]cholesterol efflux was analyzed after pulse-labeling of different cellular pools, half-times of cholesterol efflux from lysosomes and ER were significantly longer than that from PM. In another set of experiments, when both labeling and efflux times varied, efflux of [14C]cholesterol from the PM to human serum after 1.5 h pulse and chase incubations was double that from lysosomes and 8-fold that from ER. Extension of the incubation times from 1.5 to 3 h diminished the difference in cholesterol efflux from different membranes. Further incubation to 6 h almost abolished the different responses. Cell-free preparations of membranes, obtained from cells labeled with [14C]cholesterol, showed no differences in cholesterol efflux. No differences in the distribution of [14C]cholesterol released into serum among lipoprotein subfractions was observed. Pretreatment of the serum with Fab fragments of polyclonal rabbit anti-human apolipoprotein A-I antibodies reduced its ability to promote efflux of cholesterol from the ER by 77%, but had no effect on cholesterol efflux from the PM. Fab fragments of non-immune IgG had no effect on the efflux of both ER and PM cholesterol. We conclude that the availability of cellular cholesterol for efflux from HepG2 cells is strongly influenced by its subcellular location, and is regulated by apolipoprotein A-I.     

Effects of diets containing tallow and soybean oil with and without cholesterol on hepatic metabolism of lipids and lipoproteins in the preruminant calf

The effects of long-chain fatty acids (230 g/kg of dietary DM) from tallow and from soybean oil, with or without cholesterol (10 g/kg of dietary DM), on hepatic lipid contents and on in vivo hepatic production rates of lipids and lipoproteins were investigated in 22 preruminant male calves fitted with chronic catheters and with electromagnetic blood flow probes implanted in the hepatic vessels. Diets containing soybean oil and soybean oil with cholesterol led to the development of triglyceride infiltration in the liver and to higher apparent hepatic secretion of very low density lipoproteins than did diets containing tallow or tallow with cholesterol. Addition of cholesterol to diets favored accumulation of low density lipoproteins in plasma and the net apparent secretion of these particles by the liver, especially for the diet containing soybean oil with cholesterol. Regardless of the diet, calf liver clearly removed large high density lipoproteins of type 1 that were rich in cholesteryl esters but secreted heavy high density lipoproteins that were rich in proteins. The intensity of removal of high density lipoproteins of type 1 by the liver depended on the plasma concentration of these particles, probably by mass action. This removal did not prevent the accumulation of high density lipoproteins of type 1 in plasma, such as it did in calves fed soybean oil.     

Gas gangrene due to Clostridium septicum in a patient with an occult colonic neoplasm. A case report and review of the literature

The study included 30 IHD patients with primary hypercholesterolemia (22 males and 8 females). 18 and 12 patients have received a single daily dose of fluvastatin 20 and 40 mg, respectively, in the evening for 12 weeks. The drug effect was assessed by changes in the clinical status, lipid spectrum, transport-metabolic and absorption-secretory functions of the liver. IHD patients with hypercholesterolemia were found to have dysfunction of the hepatobiliary system. Fluvastatin treatment reduced the level of total cholesterol (Ch), LDLP Ch, triglycerides. HDLP Ch levels remained unchanged. Atherogenic lipoproteins aggregation diminished. Positive changes occurred in hepatic metabolism: bilirubin concentrations lowered, serum albumin went up, absorption-secretory function of hepatocytes normalized, hepatic mono-oxidase system activated. Fluvastatin-related hepatic damage was not reported in the course of 12-month follow-up.     

Management of facial fractures

A new analytical procedure for determining the fraction composition (FC) of lipoproteins (LP) is developed on the basis of the physical method small-angle X-ray scattering (SAXS). This method quantitatively determines the levels of the basic fractions of LP and their subfractions in plasma or serum to analyze LP FC and to diagnose lipid metabolic disturbances. The results obtained by this procedure were compared with those of gel-electrophoresis, biochemistry, and medical diagnosis. There was a good agreement of SAXS and routine methods. The new procedure shows extremely rapid (1.0-1.5 hr) analysis, uses a single reagent (such as the saccharose type), has a high accuracy, and resolution. The analysis requires as high as 0.05 ml of plasma or serum. LP FC may be analyzed both in protein-free and whole native plasma and sera. The findings may be used in clinical care for diagnosis of dyslipidemias and for researches.     

Potencies of lipoproteins in fasting and postprandial plasma to accept additional cholesterol molecules released from cell membranes

To investigate the role of various lipoproteins in plasma to promote cholesterol efflux from cell membranes, potencies of lipoproteins in normolipidemic fasting and postprandial (PP) plasmas to accept additional cholesterol molecules from cell membranes were determined. We used red blood cells (RBCs) and lipoproteins in fresh blood as donors and acceptors of cell membrane cholesterol, respectively. When fresh fasting plasma (n=24) containing active lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer proteins (CETP) was incubated with a 3-fold excess of autologous RBCs at 37 degrees C for 18 hours, plasma cholesterol levels increased by 19.6% (38.5+/-14.2 mg/dL) owing to an exclusive increase in the CE level. Very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL) fractions retained 48.1%, 26.3%, and 25.6% of the net cholesterol mass increase in fasting plasma, resulting in 91%, 8%, and 21% increases in their cholesterol contents, respectively. The PP plasma was 1.3-fold more potent than fasting plasma in promoting cholesterol efflux from RBCs by associating excess cholesterol with chylomicrons, resulting in a 356% increase in the cholesterol content of chylomicrons. These increases in lipoprotein cholesterol content indicate that chylomicrons were about 3.9x, 44x, and 17x more potent than fasting VLDL, LDL, and HDL, respectively, in accepting additional cholesterol molecules released from RBCs. The capacity of PP plasma to promote cholesterol efflux from RBCs was significantly correlated with plasma cholesterol levels (r=0.60, P<0.005), triglycerides (r=0.68, P<0.001), chylomicrons (r=0.90, P<0.001), VLDL (r=0.65, P<0.001), and LDL (r=0.47, P<0.025) but not with the levels of HDL (r= -0.34, P<0.20). In fasting plasma containing a low level of VLDL and HDL, isolated chylomicrons supplemented to the plasma were approximately 9x more potent than HDL in boosting the capacity of plasma to promote cholesterol efflux from RBCs. This study indicates that chylomicrons in PP plasma are the most potent ultimate acceptors of cholesterol released from cell membranes and that a low HDL level is not a factor that limits the ability of PP plasma to promote cholesterol efflux from cell membranes. Our data obtained from an in-vitro system suggest that PP chylomicrons may play a major role in promoting reverse cholesterol transport in vivo, since the transfer of cholesterol from cell membranes to chylomicrons will lead to the rapid removal of this cholesterol by the liver. HDL in vivo may promote reverse cholesterol transport by enhancing the rapid removal of chylomicrons from the circulation, since the rate of clearance of chylomicrons is positively correlated with the HDL level in plasma.     

Lipoprotein composition in the insulin-deficient non-acidotic phase of type I diabetic patients and early evolution after the start of insulin therapy

Lipoproteins, including intermediate density lipoproteins and lipoprotein(a), and apolipoproteins A-I, B, C-II, C-III and E, were studied in 13 newly-diagnosed type I diabetic patients with severe insulinopenia without dehydration or acidosis. At baseline, the main finding was a significant increase in serum triglycerides due to raised triglyceride concentrations in all lipoproteins, particularly triglyceride-rich lipoproteins. Cholesterol concentrations were slightly increased in lipoproteins and led to a significant increase in serum cholesterol. Two days after the start of insulin therapy, lipoprotein profiles had normalized except for the LDL triglyceride contents, which remained significantly increased on the fifth day of treatment. No significant modifications were observed in lipoprotein(a), apolipoproteins A-I and E concentrations throughout the study. However, serum apolipoproteins B, C-II and C-III were increased at baseline and fell to normal levels 2 days after the start of insulin therapy. On the other hand, apolipoprotein C-II/C-III ratios in high and very low density lipoprotein, showed no significant differences at baseline compared with controls, suggesting that an apolipoprotein C-II deficiency or apolipoproteins Cs imbalance can be ruled out. In conclusion, significant lipoprotein abnormalities were observed in the insulin-deficient state of type I diabetes mellitus; insulin therapy normalizes the lipoprotein profile in two days, except for low density lipoprotein triglyceride contents which remain increased at the fifth day.     

The influence of dietary protein intake on milk production and blood composition of high-yielding dairy cows

Isolated rat adipocytes were incubated with serum lipoproteins or lymphchylomicrons which contained 14c-labeled cholesterol. The specific activity of lipoprotein free cholesterol decreased and that of cellular free cholesterol increased linearly up to 7 h. At this time the cell cholesterol specific activity was only 11% of that of medium cholesterol indicating that the rate of exchange was slow. The specific activity of lipoprotein esterified cholesterol remained unchanged while that of cells showed a slight increase suggesting esterification of incorporated free cholesterol. No detectable change of the lipoprotein or cellular cholesterol concentration occurred indicating that the uptake of radioactive free cholesterol was due to exchange without net movement of sterol. The radioactive cholesterol was incorporated into both membrane fraction and the fat droplet of the adipocytes. The rate of cholesterol exchange was temperature-dependent but it was not influenced by the metabolic state of the cells and not by addition of metabolic inhibitors. Trypsin or pronase treatment of the cells were without influence on the rate of the exchange and denaturation of the plasma lipoproteins with formalin increased the rate of exchange. These results indicate that the exchange of cholesterol is a physical chemical process, which is not linked to energy metabolism of the cells, and which is not mediated by either specific lipoprotein receptors on fat cell membranes or pinocytic uptake of lipoproteins. The rate of free cholesterol exchange showed a linear correlation with the concentration of lipoprotein particles in the medium. The relative transfer rate was highest for chylomicrons and decreased in order chylomicron remnants greater than very low density lipoprotein greater than low density lipoprotein greater than high density lipoprotein. A saturation of the system could be obtained only with high density lipoprotein.     

Overexpression of hepatic lipase in transgenic mice decreases apolipoprotein B-containing and high density lipoproteins. Evidence that hepatic lipase acts as a ligand for lipoprotein uptake

To determine the mechanisms by which human hepatic lipase (HL) contributes to the metabolism of apolipoprotein (apo) B-containing lipoproteins and high density lipoproteins (HDL) in vivo, we developed and characterized HL transgenic mice. HL was localized by immunohistochemistry to the liver and to the adrenal cortex. In hemizygous (hHLTg+/0) and homozygous (hHLTg+/+) mice, postheparin plasma HL activity increased by 25- and 50-fold and plasma cholesterol levels decreased by 80% and 85%, respectively. In mice fed a high fat, high cholesterol diet to increase endogenous apoB-containing lipoproteins, plasma cholesterol decreased 33% (hHLTg+/0) and 75% (hHLTg+/+). Both apoB-containing remnant lipoproteins and HDL were reduced. To extend this observation, the HL transgene was expressed in human apoB transgenic (huBTg) and apoE-deficient (apoE-/-) mice, both of which have high plasma levels of apoB-containing lipoproteins. (Note that the huBTg mice that were used in these studies were all hemizygous for the human apoB gene.) In both the huBTg,hHLTg+/0 mice and the apoE-/-,hHLTg+/0 mice, plasma cholesterol decreased by 50%. This decrease was reflected in both the apoB-containing and the HDL fractions. To determine if HL catalytic activity is required for these decreases, we expressed catalytically inactive HL (HL-CAT) in apoE-/- mice. The postheparin plasma HL activities were similar in the apoE-/- and the apoE-/-,HL-CAT+/0 mice, reflecting the activity of the endogenous mouse HL and confirming that the HL-CAT was catalytically inactive. However, the postheparin plasma HL activity was 20-fold higher in the apoE-/-,hHLTg+/0 mice, indicating expression of the active human HL. Immunoblotting demonstrated high levels of human HL in postheparin plasma of both apoE-/-,hHLTg+/0 and apoE-/-,HL-CAT+/0 mice. Plasma cholesterol and apoB-containing lipoprotein levels were approximately 60% lower in apoE-/-,HL-CAT+/0 mice than in apoE-/- mice. However, the HDL were only minimally reduced. Thus, the catalytic activity of HL is critical for its effects on HDL but not for its effects on apoB-containing lipoproteins. These results provide evidence that HL can act as a ligand to remove apoB-containing lipoproteins from plasma.     

Diurnal heterogeneity in structure and function of low density lipoproteins of normolipidemic males

Structural changes in low density lipoproteins (LDL) have been shown to alter their metabolism and atherogenic potential. We investigated the diurnal changes in size and composition of LDL in seven healthy, non-obese, normolipidemic male volunteers consuming a standard diet (14.5% protein, 31.9% fat, 53.6% carbohydrate and 383 mg cholesterol/day) and continuing their daily routine. The food was divided into three meals and three snacks, and blood samples were obtained at 7 AM (after 12 h fasting), noon, 8 PM, midnight and 3 AM. LDL were isolated by both sequential and density gradient ultracentrifugation (d = 1.019 - 1.050 g/ml), and analyzed for lipids, apolipoproteins, size, and affinity to LDL receptors. Diurnal LDL preparations differ from fasting LDL in both chemical and physical parameters. The former get richer in triglyceride (TG/cholesterol weight ratio 0.23 vs. 0.16), larger in diameter (21.2 +/- 0.2 vs. 22.4 +/- 0.1 nm), and enriched in a more buoyant fraction (74.0 +/- 4.6 vs. 41.9 +/- 3.8% of LDL cholesterol in d = 1.019 - 1.035 g/ml). These structural changes in LDL were associated with enhanced affinity to LDL receptors in both human skin fibroblasts and HepG2 cells, as demonstrated by competition experiments with fasting human 125I-LDL. The observed diurnal heterogeneity in both the structure and the function of LDL may be attributed to the absorptive state as it did not occur during prolonged fasting. These diurnal changes may be important for better understanding LDL metabolism in vivo and for the elucidation of the atherogenic process.     

Novel large apolipoprotein E-containing lipoproteins of density 1.006-1.060 g/ml in human cerebrospinal fluid

Although the critical role of apolipoprotein E (apoE) allelic variation in Alzheimer's disease and in the outcome of CNS injury is now recognized, the functions of apoE in the CNS remain obscure, particularly with regard to lipid metabolism. We used density gradient ultracentrifugation to identify apoE-containing lipoproteins in human CSF. CSF apoE lipoproteins, previously identified only in the 1.063-1.21 g/ml density range, were also demonstrated in the 1.006-1.060 g/ml density range. Plasma lipoproteins in this density range include low-density lipoprotein and high-density lipoprotein (HDL) subfraction 1 (HDL1). The novel CSF apoE lipoproteins are designated HDL1. No immunoreactive apolipoprotein A-I (apo A-I) or B could be identified in the CSF HDL1 fractions. Large lipoproteins 18.3 +/- 6.6 nm in diameter (mean +/- SD) in the HDL1 density range were demonstrated by electron microscopy. Following fast protein liquid chromatography of CSF at physiologic ionic strength, apoE was demonstrated in particles of average size greater than particles containing apoA-I. The largest lipoproteins separated by this technique contained apoE without apoA-I. Thus, the presence of large apoE-containing lipoproteins was confirmed without ultracentrifugation. Interconversion between the more abundant smaller apoE-HDL subfractions 2 and 3 and the novel larger apoE-HDL1 is postulated to mediate a role in cholesterol redistribution in brain.     

Association of risk factor variables and coronary artery disease documented with angiography

Stepwise linear discrimination was used to analyze risk factors in 431 consecutive patients who underwent coronary angiography to determine which variables were most closely associated with coronary artery disease. Twenty-one risk factors were considered: total plasma cholesterol and triglycerides; the cholesterol and triglyceride content of high-density lipoproteins (HDL), low-density lipoproteins (LDL) and very low density lipoproteins (VLDL); and the percentage of total cholesterol and triglycerides in each fraction. Age, smoking history, family history, hypertension, diabetes mellitus and relative weight were also considered. Coronary artery disease was assessed using three standard grading scores. There were significant differences in risk factors between males and females. In males, LDL cholesterol and age were selected by multivariate analysis. In females, the ratio of HDL cholesterol to total cholesterol, as well as relative weight, family history, age and smoking were selected. The discriminating value of HDL cholesterol as the percentage of total cholesterol was significantly greater than that of HDL cholesterol itself. Despite highly significant associations between risk factors and the presence of coronary artery disease, the discrimination did not provide sufficient separation of the groups to give results that are useful diagnostically in individual patients.     

The distribution of fatty acid ethyl esters among lipoproteins and albumin in human serum

Fatty acid ethyl esters (FAEEs) are nonoxidative products of ethanol metabolism and have been implicated as mediators of ethanol-induced organ damage. Previous studies have demonstrated that FAEEs bind to lipoproteins and albumin in human plasma after ethanol ingestion. Analysis of human serum with varying blood ethanol levels and endogenously formed FAEEs revealed a positive correlation between serum FAEE concentration and the percentage of FAEEs associated with lipoproteins, predominantly very low density and low density lipoprotein. Similar results were obtained when increasing amounts of FAEEs were added to serum with zero blood ethanol. Additional studies indicated that free fatty acids and FAEEs do not compete for binding to albumin or lipoproteins. Data support the conclusion that the distribution of FAEEs among their carriers in the serum is dependent on serum FAEE concentration.     

Hepatic lipase affects both HDL and ApoB-containing lipoprotein levels in the mouse

Transgenic mice were created overproducing a range of human HL (hHL) activities (4-23-fold increase) to further examine the role of hepatic lipase (HL) in lipoprotein metabolism. A 5-fold increase in heparin releasable HL activity was accompanied by moderate (approx. 20%) decreases in plasma total and high density lipoprotein (HDL) cholesterol and phospholipid (PL) but no significant change in triglyceride (TG). A 23-fold increase in HL activity caused a more significant decrease in plasma total and HDL cholesterol, PL and TG (77%, 64%, 60%, and 24% respectively), and a substantial decrease in lipoprotein lipids amongst IDL, LDL and HDL fractions. High levels of HL activity diminished the plasma concentration of apoA-I, A-II and apoE (76%, 48% and 75%, respectively). In contrast, the levels of apoA-IV-containing lipoproteins appear relatively resistant to increased titers of hHL activity. Increased hHL activity was associated with a progressive decrease in the levels and an increase in the density of LpAI and LpB48 particles. The increased rate of disappearance of 125I-labeled human HDL from the plasma of hHL transgenic mice suggests increased clearance of HDL apoproteins in the transgenic mice. The effect of increased HL activity on apoB100-containing lipoproteins was more complex. HL-deficient mice have substantially decreased apoB100-containing low density lipoproteins (LDL) compared to controls. Increased HL activity is associated with a transformation of the lipoprotein density profile from predominantly buoyant (VLDL/IDL) lipoproteins to more dense (LDL) fractions. Increased HL activity from moderate (4-fold) to higher (5-fold) levels decreased the levels of apoB100-containing particles. Thus, at normal to moderately high levels in the mouse, HL promotes the metabolism of both HDL and apoB-containing lipoproteins and thereby acts as a key determinant of plasma levels of both HDL and LDL.     

Platelet production time in surgery

A protein factor from the d greater than 1.25 g/ml plasma fraction controls the transfer of cholesterol esters between high density lipoproteins and very low density lipoproteins. This transfer is time-dependent, and follows saturation kinetics relative to the concentration ratio of acceptor to donor lipoproteins. Although the process is reversible, the transfer rates are faster from high density to very low density lipoproteins and result in a net increase of cholesterol esters in the very low density lipoproteins. Under the same conditions, there is also a net mass transfer of cholesterol esters from high density lipoproteins to chylomicrons. This constitutes the first demonstration of cholesterol ester mass transfer between isolated lipoproteins and contrasts with the equilibrium of cholesterol esters between HDL and LDL which we previously demonstrated [4]. The apparent maximum transfer rate of cholesterol esters from high density to very low density lipoproteins was calculated to be about 80 nmoles cholesterol esters/h/ml plasma, which is very similar to the initial rate of reaction of lecithin:cholesterol acyltransferase in plasma. It is concluded that cholesterol ester formation in high density lipoproteins and their transfer to triglyceride-rich lipoproteins may be closely coupled.     

An efficient chromatographic system for lipoprotein fractionation using whole plasma

We have validated a semi-automatic procedure for the efficient isolation of plasma lipoproteins from 300 microl of whole plasma (actual injection volume 200 microl) by Fast Phase Liquid Chromatography (FPLC). Modified enzymatic assays were established to allow the determination of low concentrations (1-20 mg/dl) of triglycerides and cholesterol using the Beckman CX-5 Autoanalyzer. The sum of the cholesterol contents in the fractions corresponding to low density (LDL) and high density lipoprotein (HDL) can be demonstrated to be highly correlated to values obtained with dextran sulfate/MgCl2 precipitation for HDLc (slope = 0.98, r2 = 0.997) and ultracentrifugation (beta-quant) for LDLc (slope = 1.03, r2 = 0.988). Using pure lipoprotein fractions isolated by ultracentrifugation, linear ranges of detection for HDLc and HDL apoA-I were performed at 18-95 mg/dl and 59-262 mg/dl, respectively. The ranges for LDLc were 41-435 mg/dl and 21-280 mg/dl for LDL apoB. The mean (range) fractional standard deviations for quadruplicate runs for 15 individual plasma samples ranging widely in lipoprotein concentrations were 0.97 (0.29-2.86%) for LDLc (range: 101.5-258.5 mg/dl), 3.67 (0.62-14.11%) for HDLc (range: 27.1-85.1 mg/dl) and 2.19 (0.16-6.56%) for VLDL-TG (range: 6.1-515.0 mg/dl).