Microplate methods for determination of serum cholesterol,high density lipoprotein cholesterol,triglyceride and apolipoproteins

Microtiter plate methods were developed for the enzymatic determination of serum total cholesterol (TC), high density lipoprotein cholesterol (HDL-C) and triglyceride (TG), and for the turbidometric determination of apolipoproteins. The micromethods resulted in accurate, precise values that were in good agreement with the conventional spectrophotometric assays. The coefficient of variation for TC determinations was 4.5% or less and bias was 5% or less. The lipid micromethod assays are sensitive to 10 mg/dL or less, and the apolipoprotein assay to 1 mg/dL. Less than 100 μL of serum suffices for TC, TG and apoprotein assays; HDL-C requires an additional 100 μL of serum. Advantages of the micromethods include reductions in assay time and in the amount of reagents required.     

Linear low-density polyethylene/high-density polyethylene blends: Effect of high-density polyethylene content on die swell and flow instability

This work aimed to evaluate the effect of high-density polyethylene (HDPE) content and of shear rate on the die swell and flow instability of linear low-density polyethylene (LLDPE)/HDPE blends. The results showed that the die swell of the LLDPE/HDPE blends increased with the increase in the shear rate. At high shear rates, the increase in the HDPE content led to an increase in the die swell of LLDPE/HDPE blends. The surface morphology analysis of the extrudates by optical and scanning electron microscopy revealed the presence of sharkskin and stick–slip flow instabilities in LLDPE and LLDPE/HDPE blends at the shear rates investigated. These instabilities were attenuated with the addition of HDPE and almost disappeared in the LLDPE/HDPE blend containing 50 wt% of HDPE.     

Effect of cocrystallization on kinetic parameters of high-density polyethylene/linear low-density polyethylene blend

The isothermal crystallization kinetics of a binary melt blend of high-density polyethylene (HDPE)/linear low-density polyethylene (LLDPE) is presented. An effort was made to understand the phenomenon of cocrystallization between these two constituting components of the blend with the help of kinetic parameters. The analysis based on the Avrami exponent entails that both HDPE and LLDPE undergo individual seeding of nuclei and they merge with each other in the growth process to form cocrystallites. The incorporation of the LLDPE segment in the HDPE crystallites progressively dilutes the properties of HDPE in the blend. The half-time of crystallization (t_1/2) shows variation in three distinct stages: The t_1/2 increases slowly in the region of 0–30% LLDPE content (HDPE-rich blend), remains constant in the 30–70% LLDPE-containing region (middle region of blend composition), and increases sharply thereafter. These variations of t_1/2 quite appreciably explain the change in % crystallinity, the Avrami exponent, and crystallite-size distribution. These observations were further supported by the small-angle light-scattering experiment. © 1996 John Wiley & Sons, Inc.     

A new relationship between total/high density lipoprotein cholesterol and polyunsaturated fatty acids

Dietary and plasma fatty acids have been linked to total cholesterol but not to the ratio of total/high-density lipoprotein cholesterol (TC/HDLC). To evaluate the relationship between dietary and plasma levels of polyunsaturated fatty acids (PUFA) and TC/HDLC, we analyzed cross-sectional and longitudinal data using 519 plasma samples (50% men, 50% women) from subjects participating in the Framingham Heart Study and results from a study feeding diets rich in either n-6 linoleic acid or n-3 α-linolenic acid with or without fish oil supplements (n-3 derivatives). Values of TC/HDLC are inversely related to the percent of plasma PUFA when both variables are measured at the same time in different subjects,R=0.82,P<0.000001. PUFA in phospholipids increase in response to increased dietary intake of different PUFA, either n-3 or n-6 or fish oils. There was a highly significant inverse relationship between TC/HDLC and the percent of PUFA in phospholipids,R=0.97,P<0.001. The relationship was similar regardless of the source and type of dietary fatty acids. A similar relationship existed when only the baseline points were considered. When plasma PUFA % increases, either in response to a diet high in PUFA or across different subjects, TC/HDLC ratios decline. Evaluation of plasma fatty acid profiles and increased balanced dietary intake of PUFA to bring fatty acid profiles of subjects with low PUFA plasma levels closer to the profile of a healthy reference group is an effective approach to reduce high TC/HDLC. Reductions of more than 50% in TC/HDLC appear feasible with dietary modification alone. Further research into fatty acid metabolic activity may determine the biochemical basis of common dysplipidemias.     

Antioxidant activity of thiocholesterol on copper-induced oxidation of low-density lipoprotein

The effect of thiocholesterol (SH-Chol) on the copper-inducedin vitro oxidation of low-density lipoprotein (LDL; 1.019<d<1.063) was investigated. Among the antioxidants tested, including cysteine, glutathione, 2-mercaptoethanol, dithiothreitol, probucol, thiopalmitic acid,. and SH-Chol, SH-Chol was the most effective antioxidant in copper-induced LDL oxidation. Also, SH-Chol completely inhibited the formation oxysterols i.e., 7-hydroxycholesterol and 7-ketocholesterol, in LDL particles and reduced 1,1-diphenyl-2-picrylhydrazyl used as stable free-radical model. Moreover, SH-Chol suppressed the degradation of endogenous α-tocopherol in LDL particles. These findings indicate that SH-Chol acts as antioxidant in the oxidative damage of LDLin vitro and as a free-radical scavenger in lipid peroxidation.     

Mechanical and flow properties of high-density polyethylene/low-density polyethylene blends

The recycling of plastic waste is of particular interest in large urban areas where municipal waste represents a large ecological problem. To achieve their objective (consumer products from plastic waste), formulators of a recycling program have to understand the implications of working with mixtures of different resins. Furthermore, in a multiphase system, the thermomechanical history experienced by the resins during processing represents an important link between operating conditions, resin properties, and final product performance. High-density polyethylene/low-density polyethylene (HDPE/LDPE) blends (10, 20, 35, 50, 65, 80, and 90 percent by weight HDPE) were melt blended in an internal mixer. A complete rheological characterization was performed on each blend. The resulting blends were extruded under different processing conditions. The extruded sheets were further characterized to determine their mechanical properties, The experimental results show important differences in the mechanical properties (transverse and longitudinal) of the sheets obtained from the blends. These differences are explained on the basis of the processing conditions (thermomechanical history) and the rheological properties of the molten blends.     

Effects of additions of high-density polyethylene on the processability of linear low-density polyethylene

In considering the processing characteristics of typical linear low-density polyethylenes, it is very likely that the nature and amount of the “high-density” portion of the short chain branching distribution has a strong effect on rheological behavior. In this study, highdensity resins of varying molecular weight were blended into a linear low-density polyethylene base resin to determine the effect on viscosity, elasticity, and onset of haze. It was determined that it is not only the high-molecular-weight characteristics of the high-density portion but also the linear nature of the molecules that has a negative effect on processability. © 1993 John Wiley & Sons, Inc.     

The ratio of triglycerides to high-density lipoprotein cholesterol is associated with the risk of chronic kidney disease in Korean men

Dyslipidemia is nephrotoxic and can result in the development of chronic kidney disease (CKD). The ratio of triglycerides (TG) to high-density lipoprotein cholesterol (HDL-C) (TG/HDL-C ratio) is well-correlated with insulin resistance and cardiovascular events. The aim of this study is to examine the association between the TG/HDL-C ratio and CKD in Korean adults. This study was retrospectively designed based on the National Health Insurance Service-National Health Screening cohort. Seventy three thousand and fifty-two participants aged between 40 and 79 years old at baseline (2009–2010) were included in the final analyses. The study population was classified into three tertile groups (T₁, T₂, and T₃) according to the TG/HDL-C ratio by sex. Adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for CKD were calculated using Cox proportional hazard regression models. The median follow-up duration was 5.9 years. Higher tertile groups of the TG/HDL-C ratio had lower estimated glomerular filtration rates in both sexes. The cumulative incidence of CKD of T₁, T₂, and T₃ was 11.89%, 12.90%, and 12.91%, respectively, in men and 10.17%, 10.61%, and 14.87%, respectively, in women (all p values < 0.001). Compared with T₁ of the TG/HDL-C ratio, the HRs (95% CIs) of T₂ and T₃ for CKD were 1.212 (1.118–1.315) and 1.183 (1.087–1.287), respectively, in men and 0.895 (0.806–0.994) and 1.038 (0.937–1.150), respectively, in women after being fully adjusted. Higher TG/HDL-C ratios were positively associated with CKD development in men, while middle levels of TG/HDL ratios reduced the CKD incidence in women.     

Mechanical properties and morphology of high-density polyethylene/linear low-density polyethylene blend

The binary blend of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) in the range of composition from 100% HDPE to 100% LLDPE has been investigated for tensile and flexural properties and the morphology in the deformed state on tensile fracture. Tensile properties (initial modulus, yield stress, and elongation-at-yield, ultimate tensile strength and elongation-at-break, and work of yield and work of rupture) and flexural properties (flexural modulus and flexural yield stress) are studied as a function of blend composition. Behavior, in terms of these properties, is distinguishable in three zones of blend composition, viz. (i) HDPE-rich blend, (ii) LLDPE-rich blend, and (iii) the middle zone. In zones (i) and (ii), the variations of these properties are more or less linear, whereas in the middle region [i.e., zone (iii)], there is a reversal of trends in variation or sometimes a behavior opposite to the expected one. The results are explained on the basis of the effects of cocrystallization and the presence of octene-containing segments in the amorphous phase. Scanning electron micrographs of the tensile fracture surfaces are presented to illustrate the occurrence of transverse bands interconnecting the fibrils.     

Effect of mechanical recycling on crystallization,mechanical, and rheological properties of recycled high-density polyethylene and reinforcement based on virgin high-density polyethylene

This study investigated the effects of mechanical recycling on the crystallization, mechanical, thermal, and rheological properties of recycled high-density polyethylene (rHDPE), as well as vHDPE/rHDPE pellets and films made by different compositions. The results confirmed the presence of contaminants in rHDPEs, and the crystalline diameter of rHDPE is smaller than that of virgin high-density polyethylene (vHDPE), with diameters ranging from 0.60 to 0.72 μm. The content of 75 wt% vHDPE in rHDPE film could repair the defects of crystalline morphology to approximate that of vHDPE films and significantly improve the elongation at break. The temperature required for the transition from crystalline to amorphous state of rHDPE film was 2°C lower than that of vHDPE, and the crystallization time and crystallinity declined compared to that of vHDPE. For rheological performance, the apparent shear viscosity and melt fluidity of rHDPE were worse than those of vHDPE. The blending of low rHDPE with vHDPE is a feasible option not only to reduce plastic waste but also to maintain acceptable properties of the blend composition.     

Effect of garlic (Allium sativum linn) on serum lipoproteins and lipoprotein cholesterol levels in albino rats rendered hypercholesteremic by feeding cholesterol

The hypocholesteremic activity of garlic was tested by incorporating freeze-dried garlic powder at 0.5, 1.0, 2.0 and 3.0% levels in an atherogenic diet fed to rats. It was observed that 0.5 and 1.0% levels were not effective whereas the other 2 levels were. The group fed 2.0% garlic powder had much lower serum cholesterol level than the one fed 3%. The increased levels of low density lipoproteins (LDL) and LDL-cholesterol in rats fed the atherogenic diet were partly reversed in rats receiving a supplement of 2% garlic powder. On a cholesterol-containing diet, high density lipoproteins (HDL) and HDL-cholesterol levels were decreased. Inclusion of garlic powder in the atherogenic diet enhanced the percentage of HDL whereas no change was observed in HDL cholesterol levels. Commercial garlic pearls (equivalent to 0.15% garlic powder in the diet) produced a significant decrease in serum and liver cholesterol levels in rats fed the atherogenic diet. On the other hand, asafoetida at 1.5% level failed to reduce the serum cholesterol levels in the cholesterol-fed rats.     

Effect of n−3 fatty acids on the key enzymes involved in cholesterol and triglyceride turnover in rat liver

The effect of long-chain n−3 fatty acids on hepatic key enzymes of cholesterol metabolism and triglyceride biosynthesis was investigated in two rat models. In the first model, rats were intravenously infused for two weeks with a fat emulsion containing 20% of triglycerides in which either n−6 or n−3 fatty acids predominated. The treatment with n−3 fatty acids led to a reduction primarily of serum cholesterol (45%), but also of serum triglycerides (18%). HMG-CoA reductase activity and cholesterol 7α-hydroxylase activity were reduced by 45% and 36%, respectively. There were no significant effects on diacylglycerol acyltransferase (DGAT) or phosphatidate phosphohydrolase (PAP) activities. In the second model, rats were fed a diet enriched with sucrose, coconut oil and either sunflower oil (n−6 fatty acids) or fish oil (long-chain n−3 fatty acid ethyl esters). The treatment with n−3 fatty acids decreased serum triglycerides (41%) and, to a lesser extent, serum cholesterol (17%). Neither glycerol 3-phosphate acyltransferase (GPAT) or DGAT were affected by n−3 fatty acids. In contrast, PAP activity was reduced by 26%. HMG-CoA reductase was not significantly affected, whereas cholesterol 7α-hydroxylase activity was reduced by 36%. The results indicate that part of the TG-lowering effect of long-chain n−3 fatty acids may be mediated by inhibition of the soluble phosphatidate phosphohydrolase. The effect on serum cholesterol may be partly due to inhibition of HMG-CoA reductase.     

Linalyl acetate and methyl silicone effects on cholesterol and triglyceride oxidation in heated lard

The effectiveness of linalyl acetate (LA) at 0.02 and 0.04% as a high-temperature antioxidant was tested in lard with two levels (2 times and 10 times) of added cholesterol. Lard samples with and without added LA or methyl silicone (MS, 0.2 and 1.0 ppm) and a control with no additives were heated at 180°C for 10 hr/day for up to 240 hr. The loss of cholesterol, the formation of cholesterol oxidation products (COP) and the percentage fatty acid retention were measured during the heating periods. Addition of 1.0 ppm MS was significantly effective in reducing the loss of fatty acids (p<0.0005) in lard with 2 times the added cholesterol, but MS at 0.2 ppm was not effective in lard with 10 times the added cholesterol. Addition of LA at 0.02 and 0.04% had little effect at reducing changes in cholesterol loss, COP formation and fatty acid loss in lard samples with both cholesterol levels. But there was a tendency for MS and 0.04% LA to reduce formation of some COP in lard containing 2 times the added cholesterol and to reduce the loss of cholesterol. Presented in part at the 80th AOCS Annual Meeting, Cincinnati, OH, in May, 1989.     

Effect of dietary cholesterol on low density lipoprotein-receptor, 3-hydroxy-3-methylglutaryl-CoA reductase, and low density lipoprotein receptor-related protein mRNA expression in healthy humans

We investigated the possibility that dietary cholesterol downregulates the expression of low density lipoprotein (LDL) receptor and 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase genes of circulating mononuclear cells in vivo in healthy humans. We also studied the variations of the LDL receptor-related protein (LRP) gene in the same conditions. Dieters (n=5) were submitted to a 4-d fat restriction (mean cholesterol intake: 6±4 mg/d), followed by a 7-d cholesterol (a mean of 791±150 mg/d) supplementation. Controls (n=3) did not change their diet. During fat restriction, serum total and LDL cholesterol decreased significantly (P<0.05), and LDL receptor and HMG-CoA reductase mRNA copy numbers in mononuclear cells increased by 57 and 147%, respectively (P<0.05). After reintroducing cholesterol, serum cholesterol was stable whereas LDL receptor and HMG-CoA reductase mRNA decreased by 46 and 72% (P<0.05) and LRP mRNA increased by 59% (P<0.005). The changes in LDL receptor and HMG-CoA reductase mRNA abundance were correlated (r=+0.79, P=0.02) during cholesterol reintroduction as were LDL receptor and LRP mRNA levels, but negatively (r=−0.70, P=0.05). Also, 70% of the variability in LRP mRNA (P<0.005) was explained by dietary cholesterol. Thus, the basic mechanisms regulating cellular cholesterol content, the coordinate feedback repression of genes governing the synthesis and uptake of cholesterol, are operating in vivo in humans. However, serum cholesterol did not increase in response to dietary cholesterol, suggesting that these mechanisms may not play as predominant a role as previously believed in the short-term control of serum cholesterol in vivo in humans. A new finding is that LRP gene is also sensitive to dietary cholesterol, suggesting that it may participate in the control of serum cholesterol. Further in vivo studies in humans are warranted to explore the molecular mechanisms of the physiological response to dietary cholesterol in humans.     

Studies on the mechanism of the ursodeoxycholic acid-induced increase in hepatic low-density lipoprotein binding

Previously, we have shown, in golden Syrian hamsters, that chronic feeding of ursodeoxycholic acid (UDCA), in contrast to that of its 7α-epimer, chenodeoxycholic acid (CDCA), produced a significant increment in hepatic low-density lipoprotein (LDL) uptake, despite similar suppression of bile acid synthesis by both bile acids. Evidence for a direct effect of this bile acid on hepatic LDL metabolism was shownin vitro, with isolated hamster hepatocytes, suggesting that this effect was unique to UDCA and specific for receptor-mediated LDL catabolism. The aim of the present study was to define the cellular mechanism(s) associated with this phenomenon, using male golden Syrian hamsters. Regardless of chronic exposure of the liver to either UDCA or CDCA, acute incubation with UDCA consistently resulted in an increase of LDL binding to isolated hepatocytes by 15 to 40%. Furthermore, chronic treatment with either UDCA or CDCA did not result in alterations in lipoprotein particle composition. Likewise, incubation of hepatocytes with UDCA was not associated with a change of the membrane lipid composition. In isolated liver membrane fractions, UDCA increased both the maximum number of LDL binding sites and the affinity constant for LDL by around 35% suggesting an interaction of UDCA with the LDL receptor, at the plasma membrane level, independent of an effect on receptor cycling. The results of the studies support a role for UDCA in the recruitment of cryptic LDL receptors from a cellular membrane pool, possibly due to the unique localization of UDCA in the plasma membrane lipid bilayer.     

Effect of chylomicron remnants on cholesterol metabolism in cultured rabbit hepatocytes: Very low density lipoprotein and bile acid production

The interrelationship between very low density lipoprotein (VLDL) secretion and bile acid production was studied in primary culture of rabbit hepatocytes. Chylomicron remnants (CR) were added to the cultures to study their effect on VLDL secretion and bile acid production. After 24 hr preincubation of cells with CR (10–50 μg protein/mL), intercellular neutral lipid content was increased 1.5–4-fold in a dose-dependent manner. Neutral lipid accumulation was accompanied by a 70–90% reduction of [¹⁴C]acetate incorporation into cholesterol, while no stimulation of [¹⁴C]oleate incorporation into cholesteryl esters was observed. Incubation of cells with CR increased secretion of free cholesterol, triacylglycerol and apoproteins B and E in VLDL. Stimulation of VLDL cholesterol secretion was accompanied by a reduction of taurocholic acid synthesis. These data demonstrate the existence of an inverse relationship between secretion of VLDL cholesterol and bile acid production under conditions of effective uptake of triacylglycerol-rich CR by hepatocytes.     

Interaction of melt spinning and drawing variables on the crystalline morphology and mechanical properties of high-density and low-density polyethylene fiber

An experimental study of the spinnability and the variation in crystallinity and orientation in high-density and low-density polyethylene fibers with melt spinning and drawing conditions has been carried out. Three polymers (two high-density and one low-density) and eicosane (C₂₀H₄₂) were studied. The maximum spinnability was in the lower molecular weight high-density polyethylene. Hermans-Stein a, b, and c crystallographic axis orientation factors were computed from wide-angle x-ray scattering patterns. In the spun fiber, small take-up velocities cause the b axis to become perpendicular to the fiber axis in each fiber. The c axis increasingly orients itself parallel to the fiber axis as take-up velocity increases. The a axis orientation is different for each polymer. The results are interpreted in terms of modern theories of crystalline morphology, specifically the development of row structures. In the drawing experiments, the two high-density polyethylenes necked. A phenomenological theory of necking is discussed. The a, b, and c axis orientation factors were determined for different stages of drawing. In the necked regions and in completely drawn fibers, the c axis was parallel to the fiber axis and the a and b axes are perpendicular to the fiber axis. The tangent Young's modulus and tensile strength of the spun fibers increased with take-up velocity and in the drawn fibers were an order of magnitude higher than in the spun fiber. The mechanical properties of spun fiber may be correlated with the c axis (Hermans) orientation factor. The drawn fiber shows significant variations in Young's modulus and tensile strength at constant unit cell orientation.     

Effects of diet and high density lipoprotein subfractions on the removal of cellular cholesterol

The effects of isocaloric substitutions of dietary polyunsaturated and saturated fat on the composition and function of plasma high density lipoproteins (HDLs) were studied in 3 normal subjects who were fed saturate-rich and polyunsaturate-rich diet programs. Compared to the saturated diets (P/S=0.4), polyunsaturated fat diets (P/S=4 or 2) reduced both plasma cholesterol and triglyceride levels. In 2 of the subjects, HDL cholesterol concentrations increased with polyunsaturated fat caused a reduction in HDL fatty acyl content of oleate and an increase in linoleate. To determine whether the altered composition affected the removal of cell membrane cholesterol, HDL and their subfractions, HDL₂ and HDL₃, which were isolated from each of the diets, were incubated with Ehrlich ascites cells in vitro. The cells were prelabeled with [³H] cholesterol, and the release of labeled cholesterol from the cells into the medium containing the various HDL fractions was determined. HDL, irrespective of the type of dietary fat, caused a release of [³H] cholesterol from the cells into the medium. The amount of [³H] cholesterol recovered in the medium was dependent on the absolute concentration of HDL cholesterol added to the cells and was independent of the type of diet. These results indicate that HDL facilitates the removal of cholesterol from cells, but that the amount and rate of removal are independent of the changes in HDL composition that can be obtained by dietary perturbations.     

Human milk: Quantitative gas-liquid chromatographic analysis of triglyceride and cholesterol content during lactation

Gas-liquid chromatography has been used to follow changes in the triglyceride composition of human colostrum and milk from one donor during the first 10 days postpartum and to compare the compositions obtained with those at later stages of lactation. New triglycerides of low molecular weight appeared during the first 5 days postpartum. Lower molecular weight triglycerides (<C₄₈) continued to increase until the eighth day. Triglyceride C₄₈ and total cholesterol content remained almost constant during the period of the study. Comparison of triglyceride fatty acid composition on the third, sixth, and ninth days postpartum showed considerable specificity in all cases, but a tendency for randomization to occur as lactation proceeded. The advantage of triglyceride over fatty acid analysis for this type of investigation is that in the former, new molecules appear. In the latter, only changes in the proportions of fatty acids occur.     

二乙烯基苯对低密度聚苯乙烯密度及尺寸的影响

研究了悬浮聚合法合成氏密度聚苯乙烯（LDPS）微粒子过程中，二乙烯基苯（DVB）的加入对树脂粒径及密度的影响。结果表明，二乙烯基苯从单体分散阶段开始影响单体液滴的分散尺寸，加入DVB后，单体液滴尺寸变小，最终产物粒径变小。且在实验条件下，随DVB量增加，最终LDPS粒径减小，当用明胶做分散剂，二乙烯基苯与苯乙烯之比（DVB／St）大于1时，粒径减小变化趋于平缓；当有致孔剂存在时，LDPS的密度随DVB量增加而减小。