Simultaneous effects of the apolipoprotein E polymorphism on apolipoprotein E, apolipoprotein B, and cholesterol metabolism.

Human apolipoprotein (apo) E is polymorphic. We have investigated the effect of the apo-E polymorphism on quantitative plasma levels of apo E, apo B, and total cholesterol in a sample of 563 blood-bank donors from Marburg and Giessen, West Germany. The relative frequencies of the epsilon 2, epsilon 3, and epsilon 4 alleles are .063, .793, and .144, respectively. The average effects of the epsilon 2 allele are to raise apo-E levels by 0.95 mg/dl, lower apo B levels by 9.46 mg/dl, and lower total cholesterol levels by 14.2 mg/dl. The average effects of the epsilon 4 allele are to lower apo-E levels by 0.19 mg/dl, to raise apo-B levels by 4.92 mg/dl, and to raise total cholesterol levels by 7.09 mg/dl. The average effects of the epsilon 3 allele are near zero for all three phenotypes. The apo-E polymorphism accounts for 20% of the variability of plasma apo-E levels, 12% of the variability of plasma apo-B levels, and 4% of the variability of total plasma cholesterol levels. The inverse relationship between the genotype-specific average apo-E levels and both the genotype-specific average apo-B and cholesterol levels is offset by a positive relationship between apo-E levels and both apo-B and cholesterol levels within an apo-E genotype. The apo-E polymorphism also has a direct effect on the correlation between apo-E and total cholesterol levels. The implication of these results on multivariate genetic analyses of these phenotypes is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of different neutral phospholipids on apolipoprotein binding by artificial lipid particles in vivo

Soybean triacylglycerol particles, stabilized with egg yolk sphingomyelin (SPH), phosphatidylcholine (PC), phosphatidylethanolamine (PE), or PC-PE mixtures, with diameters ranging from 170 to 550 nm were prepared by sonication and isolated by ultracentrifugation. Binding of apoproteins to the lipid particles was studied in vivo using the strategy of Connelly and Kuksis. The recoveries of the injected particles, which had decreased in size and undergone minimal changes in lipid composition, ranged from 70% and 57% for SPH- and PC-stabilized particles to 14% for particles stabilized with egg yolk PC-PE mixtures. The apoprotein (apo) composition of the recovered particles showed qualitative and quantitative differences, which were affected by the number of washes during isolation. After four washes, the SPH and PC particles contained apoE, apoC-II, and apoC-III as major components and apoA-IV as minor components. In addition, all particles, except those stabilized with egg yolk PC, contained large amounts of albumin. In contrast to egg yolk PC, the dipalmitoyl PC particles bound albumin as a major component. The recovered PC-PE and PE particles were characterized by a relative decrease of apoC and greatly increased binding of albumin. The higher rate of clearance of the PE-containing particles was attributed to a relative absence of apoC-III, which is known to delay hepatic uptake of lipid particles containing it, and to a more rapid hydrolysis of PE by lipoprotein lipases. Since PE occurs as a minor and variable component of chylomicrons and plasma lipoproteins, the present observations are of physiological interest.     

Effects of sphingomyelin on apolipoprotein E- and lipoprotein lipase-mediated cell uptake of lipid particles

It has been reported that human plasma sphingomyelin (SM) levels are positively and independently related to coronary artery disease. The lipoprotein surface is mainly formed by phosphatidylcholine (PC) and SM together with cholesterol and apolipoproteins. However, the influence of SM on the cell uptake of triglyceride-rich lipoproteins and remnants is poorly understood. To clarify the role of SM in lipoprotein uptake, we prepared lipid emulsions containing triolein, PC and SM as model particles of lipoproteins. Apolipoprotein E (ApoE) binding studies revealed that incorporation of SM into the emulsion surface reduced the binding capacity of apoE without changing the affinity. Surface SM reduced apoE-mediated uptake of emulsions by HepG2 cells because of the decreased amount of binding apoE. Apolipoproteins C-II and C-III inhibited the apoE-mediated uptake of SM containing emulsions more effectively. The stimulatory effect of lipoprotein lipase (LPL) on emulsion uptake was decreased by replacing surface PC with SM. These results suggest that SM-induced changes in the binding properties of apolipoproteins and LPL correlate with decreased hepatic uptake of lipid particles.     

Use of plant cell cultures to study graminicide effects on lipid metabolism

Graminicides belonging to the cyclohexanedione and aryloxyphenoxypropionate classes are well established to act by disrupting acyl lipid biosynthesis via specific inhibition of acetyl-CoA carboxylase. Species of grass inherently resistant to such herbicides, or biotypes of grassy weed species which display acquired resistance to recommended rates of graminicide application, are known to possess an altered plastidic multifunctional acetyl-CoA carboxylase showing reduced sensitivity to these herbicides in vitro. Studies reported here demonstrate that cell suspension cultures of maize, a graminicide-sensitive species and Poa annua, a graminicide-insensitive species, display a similar differential sensitivity of acyl lipid biosynthesis as tissue from corresponding intact plants. Acyl lipid biosynthesis in P. annua can be inhibited if sufficiently high concentrations of graminicide are used. The major plastidic form and the minor cytosolic forms of acetyl-CoA carboxylase were successfully purified from maize cell suspensions, were compared to those from leaf tissue and were shown to be differentially inhibited by graminicides in a similar manner to their counterparts from leaf tissue. These studies demonstrate that cell suspensions are useful for studying the mode of action of graminicides, especially in view of the limited amount of material obtainable from many grassy species which are very fine-growing.     

Association of apolipoprotein E with the low density lipoprotein receptor: demonstration of its co-operativity on lipid microemulsion particles

When human apolipoprotein E (apoE), which forms a self-associated tetramer in an aqueous solution, bound to the surface of triolein/phosphatidylcholine microemulsion with a particle diameter of 26 nm, it became monomeric on the lipid particle surface without strong evidence for its accumulation on a particular particle that might be expected from its tetramer formation in the aqueous phase. ApoE in the form of the self-associated tetramer did not inhibit binding of human low density lipoprotein (LDL) to its receptor on cultured human skin fibroblast. LDL binding was inhibited only when apoE was bound to the lipid particle surface. The affinity of the apoE-containing lipid particle to the LDL receptor was of the same order as that of LDL on the basis of particle molarity when the surface of the particle was covered with apoE up to 40 to 50% of the saturation level. When the particle was covered more with apoE, the affinity increased by some 20 times. Since the surface of the lipid particle was saturated with 7 apoE molecules, the particle seemed to require to have at least 4 apoE molecules on its surface in order to obtain high binding affinity to LDL receptor.     

Self-associated tetramer of human apolipoprotein E does not lead to its accumulation on a lipid particle

The data of differential measurements of apo E-containing and -free lipid particles in equilibrium binding (J. Biochem. (1989) 105, 582-587) showed complete fit to the calculated curve showing that distribution of apo E among the lipid particles is purely statistical among lipid particles. It was also demonstrated that 5 apo E molecules are required for the saturation of the surface of LDL-size lipid particle in good agreement with 7 +/- 1 given by the binding isotherm. Thus, it is concluded that tetramer formation of apo E in an aqueous phase (J. Biol. Chem. (1985) 260, 16375-16382) does not result in its accumulation on particular lipid particles.     

Contributions of 18 additional DNA sequence variations in the gene encoding apolipoprotein E to explaining variation in quantitative measures of lipid metabolism

Apolipoprotein E (ApoE) is a major constituent of many lipoprotein particles. Previous genetic studies have focused on six genotypes defined by three alleles, denoted epsilon2, epsilon3, and epsilon4, encoded by two variable exonic sites that segregate in most populations. We have reported studies of the distribution of alleles of 20 biallelic variable sites in the gene encoding the ApoE molecule within and among samples, ascertained without regard to health, from each of three populations: African Americans from Jackson, Miss.; Europeans from North Karelia, Finland; and non-Hispanic European Americans from Rochester, Minn. Here we ask (1) how much variation in blood levels of ApoE (lnApoE), of total cholesterol (TC), of high-density lipoprotein cholesterol (HDL-C), and of triglyceride (lnTG) is statistically explained by variation among APOE genotypes defined by the epsilon2, epsilon3, and epsilon4 alleles; (2) how much additional variation in these traits is explained by genotypes defined by combining the two variable sites that define these three alleles with one or more additional variable sites; and (3) what are the locations and relative allele frequencies of the sites that define multisite genotypes that significantly improve the statistical explanation of variation beyond that provided by the genotypes defined by the epsilon2, epsilon3, and epsilon4 alleles, separately for each of the six gender-population strata. This study establishes that the use of only genotypes defined by the epsilon2, epsilon3, and epsilon4 alleles gives an incomplete picture of the contribution that the variation in the APOE gene makes to the statistical explanation of interindividual variation in blood measurements of lipid metabolism. The addition of variable sites to the genotype definition significantly improved the ability to explain variation in lnApoE and in TC and resulted in the explanation of variation in HDL-C and in lnTG. The combination of additional sites that explained the greatest amount of trait variation was different for different traits and varied among the six gender-population strata. The role that noncoding variable sites play in the explanation of pleiotropic effects on different measures of lipid metabolism reveals that both regulatory and structural functional variation in the APOE gene influences measures of lipid metabolism. This study demonstrates that resequencing of the complete gene in a sample of >/=20 individuals and an evaluation of all combinations of the identified variable sites, separately for each population and interacting environmental context, may be necessary to fully characterize the impact that a gene has on variation in related traits of a metabolic system.     

12周高强度间歇训练对不同基因型载脂蛋白E血脂异常人群的调脂作用

目的:观察12周高强度间歇训练(HIIT)对不同载脂蛋白E(ApoE)基因型血脂异常人群的血脂调节作用。方法:通过测试空腹血脂指标,筛选出88例血脂异常患者作为受试对象,采集受试对象口腔粘膜进行载脂蛋白E基因型检测,测定12周高强度间歇训练干预前后的血脂水平。结果:88例血脂异常者中共检测出5种基因型,其分布为ApoE3/3＞ApoE3/4 ＞ApoE2/3＞ApoE2/2＞ApoE2/4,等位基因ε3＞ε2=ε4。运动干预前,血脂异常人群中ε4等位基因组的总胆固醇水平显著高于ε2和ε3基因组(P＜0.01),低密度脂蛋白胆固醇水平显著高于ε2基因组(P＜0.05),其余指标在各组间无显著性差异(P＞0.05)。12周的高强度间歇训练显著降低ε3基因组血清总胆固醇、甘油三酯和低密度脂蛋白胆固醇水平,升高高密度脂蛋白胆固醇水平。ε4基因组在运动干预后血清总胆固醇和低密度脂蛋白胆固醇降低,甘油三酯和高密度脂蛋白胆固醇无显著性改变。ε2基因组在运动干预后血清脂质无明显改善。结论:血脂异常人群载脂蛋白E基因多态性影响运动的调脂效果,12周高强度间歇训练可以作为ε3和ε4等位基因携带者调节血脂的运动干预方式。     

Lead and copper effects on lipid metabolism in cultured lichen photobionts with different phosphorus status

We evaluated the ability of heavy metals (copper, lead) to alter lipid metabolism in four algal lichen photobionts following short term exposure. Metal concentrations (10 microM) were equivalent to environmentally relevant levels that have been reported to have effects on intact algae. The algae were grown under normal or deficient phosphate conditions to assess any interactions with the heavy metal stress. Given the frequent sensitivity of lichens to copper and lead, there were surprisingly small changes on lipid metabolism, as assessed by radiolabelling from [1-14C]acetate. The main effects, which were seen in a number of cases, were an overall inhibition of total lipid labelling and a relative increase in the labelling of triacylglycerols in the non-polar fraction. Both of these changes can be viewed as reflecting general toxicity of heavy metals. The Coccomyxa photobiont species were more sensitive than Trebouxia species, which fits with the general distribution of the latter in lichens inhabiting harsh environments.     

Site-specific glycations of apolipoprotein A-I lead to differentiated functional effects on lipid-binding and on glucose metabolism

Prolonged hyperglycemia in poorly controlled diabetes leads to an increase in reactive glucose metabolites that covalently modify proteins by non-enzymatic glycation reactions. Apolipoprotein A-I (apoA-I) of high-density lipoprotein (HDL) is one of the proteins that becomes glycated in hyperglycemia. The impact of glycation on apoA-I protein structure and function in lipid and glucose metabolism were investigated.ApoA-I was chemically glycated by two different glucose metabolites (methylglyoxal and glycolaldehyde). Synchrotron radiation and conventional circular dichroism spectroscopy were used to study apoA-I structure and stability. The ability to bind lipids was measured by lipid-clearance assay and native gel analysis, and cholesterol efflux was measured by using lipid-laden J774 macrophages. Diet induced obese mice with established insulin resistance, L6 rat and C2C12 mouse myocytes, as well as INS-1E rat insulinoma cells, were used to determine in vivo and in vitro glucose uptake and insulin secretion.Site-specific, covalent modifications of apoA-I (lysines or arginines) led to altered protein structure, reduced lipid binding capability and a reduced ability to catalyze cholesterol efflux from macrophages, partly in a modification-specific manner. The stimulatory effects of apoA-I on the in vivo glucose clearance were negatively affected when apoA-I was modified with methylglyoxal, but not with glycolaldehyde. The in vitro data showed that both glucose uptake in muscle cells and insulin secretion from beta cells were affected. Taken together, glycation modifications impair the apoA-I protein functionality in lipid and glucose metabolism, which is expected to have implications for diabetes patients with poorly controlled blood glucose.     

N-terminal domain of apolipoprotein B has structural homology to lipovitellin and microsomal triglyceride transfer protein: a "lipid pocket" model for self-assembly of apob-containing lipoprotein particles.

The process of assembly of apolipoprotein (apo) B-containing lipoprotein particles occurs co-translationally after disulfide-dependent folding of the N-terminal domain of apoB but the mechanism is not understood. During a recent database search for protein sequences that contained similar amphipathic beta strands to apoB-100, four vitellogenins, the precursor form of lipovitellin, an egg yolk lipoprotein, from chicken, frog, lamprey, and C. elegans appeared on the list of candidate proteins. The X-ray crystal structure of lamprey lipovitellin is known to contain a "lipid pocket" lined by antiparallel amphipathic beta sheets. Here we report that the first 1000 residues of human apoB-100 (the alpha(1) domain plus the first 200 residues of the beta(1) domain) have sequence and amphipathic motif homologies to the lipid-binding pocket of lamprey lipovitellin. We also show that most of the alpha(1) domain of human apoB-100 has sequence and amphipathic motif homologies to human microsomal triglyceride transfer protein (MTP), a protein required for assembly of apoB-containing lipoproteins. Based upon these results, we suggest that an LV-like "proteolipid" intermediate containing a "lipid pocket" is formed by the N-terminal portion of apoB alone or, more likely, as a complex with MTP. This intermediate produces a lipid nidus required for assembly of apoB-containing lipoprotein particles; pocket expansion through the addition of amphipathic beta strands from the beta(1) domain of apoB results in the formation of a progressively larger high density lipoprotein (HDL)-like, then very low density lipoprotein (VLDL)-like, spheroidal lipoprotein particle.     

Early exposure to a high-fat diet has more drastic consequences on metabolism compared with exposure during adulthood in rats

The aim of this study was determine whether the introduction of a high-fat diet during the peripubertal phase induces significant changes in body weight control, glucose homeostasis and the parasympathetic tonus compared with the administration of this diet to adult rats. High-fat diet was offered to male Wistar rats at weaning or during adulthood. A group of rats received high-fat diet for 60 days, from weaning to 81-day-old (HF81) or from 60 to 120-day-old (HF120), whereas 2 other groups received a normal-fat diet (i. e., NF81 and NF120). We analyzed adiposity, glucose homeostasis, insulin sensitivity, and vagal nerve activity. High-fat diet increased the accumulation of adipose tissue in all of the rats, but the difference was greater in the rats that were fed the high-fat diet since weaning (p<0.001). The HF rats showed glucose intolerance with high levels of insulin secretion during the glucose tolerance test (p<0.01). Rats that were fed the high-fat diet presented severe insulin resistance, indicated by a low K itt (p<0.01). Interestingly, the HF81 rats exhibited greater insulin resistance compared with the HF120 rats (p<0.05). The recordings of vagus nerve activity showed that the HF rats had higher parasympathetic activity than the NF rats irrespective of age (p<0.01). Our results show that a high-fat diet offered to rats just after weaning or in adulthood both cause impairment of glycemic homeostasis and imbalance in parasympathetic activity. Importantly, the consumption of high-fat diet immediately after weaning has more drastic consequences compared with the consumption of the same diet during adulthood.     

Beyond lipids, pharmacological PPARalpha activation has important effects on amino acid metabolism as studied in the rat

PPARalpha agonists have been characterized largely in terms of their effects on lipids and glucose metabolism, whereas little has been reported about effects on amino acid metabolism. We studied responses to the PPARalpha agonist WY 14,643 (30 micromol x kg(-1) x day(-1) for 4 wk) in rats fed a saturated fat diet. Plasma and urine were analyzed with proton NMR. Plasma amino acids were measured using HPLC, and hepatic gene expression was assessed with DNA arrays. The high-fat diet elevated plasma levels of insulin and triglycerides (TG), and WY 14,643 treatment ameliorated this insulin resistance and dyslipidemia, lowering plasma insulin and TG levels. In addition, treatment decreased body weight gain, without altering cumulative food intake, and increased liver mass. WY 14,643 increased plasma levels of 12 of 22 amino acids, including glucogenic and some ketogenic amino acids, whereas arginine was significantly decreased. There was no alteration in branched-chain amino acid levels. Compared with the fat-fed control animals, WY 14,643-treated animals had raised plasma urea and ammonia levels as well as raised urine levels of N-methylnicotinamide and dimethylglycine. WY 14,643 induced changes in a number of key genes involved in amino acid metabolism in addition to expected effects on hepatic genes involved in lipid catabolism and ketone body formation. In conclusion, the present results suggest that, in rodents, effects of pharmacological PPARalpha activation extend beyond control of lipid metabolism to include important effects on whole body amino acid mobilization and hepatic amino acid metabolism.     

Effect of particle size and temperature on the conformation and physiological behavior of apolipoprotein E bound to model lipoprotein particles

The effect of particle size and structural order/disorder of the lipid domain on the conformation and physiological behavior of lipid-associated apolipoprotein E (apoE) was evaluated. Circular dichroic (CD) spectra of apoE bound to large (LME) and small (SME) microemulsion particles, composed of dimyristoylphosphatidylcholine (DMPC) and cholesteryl oleate (CO), and to DMPC disks revealed that at 4 degrees C, where all of the lipid constituents were in an ordered state, apoE bound to LME displayed approximately 60% alpha-helicity, while apoE bound to SME and DMPC disks displayed 73% and 95% helicity, respectively. Over the temperature range 4-50 degrees C, encompassing the lipid thermal transitions, only apoE bound to LME demonstrated an abrupt change in its CD spectrum (decrease in alpha-helicity) in response to temperature. To determine the source of the abrupt CD change, the constants for dissociation (Kd) of apoE from the surface of the large and small microemulsion particles were determined at 4, 25, and 37 degrees C. These results demonstrated that at 4 degrees C, the KdS for binding of apoE to the LME and SME were approximately equal; however, between 4 and 25 degrees C, there was a 5-fold increase in the Kd for binding of apoE to the LME, whereas the Kd for binding to the SME remained constant. The physiological effects of these differences in apoE secondary structure and equilibrium binding were examined by measuring the capacity of each apoE-containing particle to complete with LDL for binding to human fibroblasts, and by measuring the capacity of the apoE-microemulsion particles to suppress HMG-CoA reductase activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Early effects of chemical carcinogens as compared to induced cell proliferation. II. Automated image analysis

Static automated image analysis was applied to study early variations of chromatin structure in Feulgen-stained liver nuclei from rats injected i.p. with a single dose of dimethylnitrosamine (DMNA), a well known hepatocarcinogen. An increase of nuclear area and a correspondent decrease of average optical density (integrated optical density/area) was observed, as compared with controls, in nuclei from rats treated with 5.4 mg/kg of DMNA. These findings, which were comparable with those induced by partial hepatectomy, indicate the existence in DMNA-treated cells of a chromatin DNA relaxation similar to the G0-G1 transition previously described for human diploid fibroblasts stimulated to proliferate. Because similar results were independently obtained by flow microfluorimetry, it seems reasonable to hypothesize that chromatin decondensation could be a prerequisite for cancer induction.     

Time-dependent effects of exposure to static magnetic field on glucose and lipid metabolism in rat

In the following study, we investigate the effects of static magnetic field (SMF) (128 mT, 1 h/day during 5 or 15 consecutive days) on anthropometric parameters, glucose and lipid metabolism in rats. Exposure to SMF during 5 days induced a decrease (-8%, p < 0.05) in relative liver weight and serum insulin concentration (-56%, p < 0.001), while blood glucose level was increased (+10%, p < 0.001). By contrast, the same treatment failed to alter body weight, relative kidney weight and levels of lactate, cholesterol, triglycerides and phospholipids. Exposure to SMF during 15 days induced a decrease (-15 %, p < 0.001) in body weight, liver weight (-15 %, p < 0.05), insulin concentration (-63%, p < 0.001), plasmatic lactate level (-55%, p < 0.05) and increased glucose (+24%, p < 0.001), cholesterol (+30%, p < 0.01,) and phospholipids levels (+58%, p < 0.001), whereas, triglycerides decreased (-28%, p < 0.001). These results showed that SMF effects on glucose and lipid metabolism are time-dependent.