Plasma concentration of apolipoprotein E in intermediate-sized remnant-like lipoproteins in normolipidemic and hyperlipidemic subjects

Oxylipin transport by lipoprotein particles and its functional implications for cardiometabolic and neurological disorders

Lipoprotein metabolism is critical to inflammation. While the periphery and central nervous system (CNS) have separate yet connected lipoprotein systems, impaired lipoprotein metabolism is implicated in both cardiometabolic and neurological disorders. Despite the substantial investigation into the composition, structure and function of lipoproteins, the lipoprotein oxylipin profiles, their influence on lipoprotein functions, and their potential biological implications are unclear. Lipoproteins carry most of the circulating oxylipins. Importantly, lipoprotein-mediated oxylipin transport allows for endocrine signaling by these lipid mediators, long considered to have only autocrine and paracrine functions. Alterations in plasma lipoprotein oxylipin composition can directly impact inflammatory responses of lipoprotein metabolizing cells. Similar investigations of CNS lipoprotein oxylipins are non-existent to date. However, as APOE4 is associated with Alzheimer's disease-related microglia dysfunction and oxylipin dysregulation, ApoE4-dependent lipoprotein oxylipin modulation in neurological pathologies is suggested. Such investigations are crucial to bridge knowledge gaps linking oxylipin- and lipoprotein-related disorders in both periphery and CNS. Here, after providing a summary of existent literatures on lipoprotein oxylipin analysis methods, we emphasize the importance of lipoproteins in oxylipin transport and argue that understanding the compartmentalization and distribution of lipoprotein oxylipins may fundamentally alter our consideration of the roles of lipoprotein in cardiometabolic and neurological disorders.

Plasma ApoE elevations are associated with NAFLD: The PREVEND Study

Non-alcoholic fatty liver disease (NAFLD) is featured by increased plasma very low density lipoproteins (VLDL). The extent to which plasma apolipoprotein E (ApoE) levels are elevated in NAFLD is unclear. We determined whether plasma ApoE is elevated in subjects with suspected NAFLD. Plasma ApoE and genotypes were determined in 6,762 participants of the Prevention of Renal and Vascular End-Stage Disease (PREVEND) cohort. A Fatty Liver Index (FLI) ≥ 60 was used as a proxy of NAFLD. A total of 1,834 participants had a FLI ≥ 60, which coincided with increased triglycerides, non-HDL cholesterol, ApoB and ApoE (all P<0.001). In multivariable linear regression analysis, plasma ApoE levels were positively associated with an elevated FLI when taking account of ApoE genotypes and other clinical and laboratory covariates (fully adjusted model: β = 0.201, P<0.001). Stratified analysis for ApoE genotypes (ApoE ε3ε3 homozygotes, ApoE ε2 carriers, and ApoE ε3ε4 and ε4ε4 carriers combined), also showed positive associations of plasma ApoE levels with an elevated FLI in each group (all P<0.001). In conclusion, it is suggested that NAFLD is characterized by increased plasma ApoE levels, even when taking account of the various ApoE genotypes. Increased plasma ApoE may contribute to altered VLDL metabolism and to increased atherosclerosis susceptibility in NAFLD.

Apolipoprotein E binds to and reduces serum levels of DNA-mimicking, pyrrolated proteins

Lysine N-pyrrolation, converting lysine residues to N ^ϵ-pyrrole-l-lysine, is a recently discovered post-translational modification. This naturally occurring reaction confers electrochemical properties onto proteins that potentially produce an electrical mimic to DNA and result in specificity toward DNA-binding molecules such as anti-DNA autoantibodies. The discovery of this unique covalent protein modification provides a rationale for establishing the molecular mechanism and broad functional significance of the formation and regulation of N ^ϵ-pyrrole-l-lysine-containing proteins. In this study, we used microbeads coupled to pyrrolated or nonpyrrolated protein to screen for binding activities of human serum-resident nonimmunoglobin proteins to the pyrrolated proteins. This screen identified apolipoprotein E (apoE) as a protein that innately binds the DNA-mimicking proteins in serum. Using an array of biochemical assays, we observed that the pyrrolated proteins bind to the N-terminal domain of apoE and that oligomeric apoE binds these proteins better than does monomeric apoE. Employing surface plasmon resonance and confocal microscopy, we further observed that apoE deficiency leads to significant accumulation of pyrrolated serum albumin and is associated with an enhanced immune response. These results, along with the observation that apoE facilitates the binding of pyrrolated proteins to cells, suggest that apoE may contribute to the clearance of pyrrolated serum proteins. Our findings uncover apoE as a binding target of pyrrolated proteins, providing a key link connecting covalent protein modification, lipoprotein metabolism, and innate immunity.

Apolipoprotein E-mediated cell cycle arrest linked to p27 and the Cox2-dependent repression of miR221/222

OBJECTIVE

In addition to its effects on cholesterol levels, apoE3 has lipid-independent effects that contribute to cardiovascular protection; one of these effects is the ability to inhibit cell cycling in VSMCs. The goal of this study was to identify and characterize cell cycle-regulatory mechanisms responsible for the anti-mitogenic effect of apoE.

METHODS AND RESULTS

Primary VSMCs were stimulated with serum in the absence or presence of apoE3. apoE3 upregulated expression of the cdk inhibitor, p27(kip1), in primary VSMCs, and this effect required Cox2 and activation of PGI(2)-IP signaling. The microRNA family, miR221/222 has recently been identified as a post-translational regulator of p27, and apoE3 inhibited miR221/222 expression in a Cox2- and PGI(2)/IP-dependent manner. Moreover, reconstituted miR222 expression was sufficient to override the effects of apoE on p27 expression and S phase entry. The ability to repress expression of miR221/222 is shared by apoE3-containing HDL but is absent from apoA-1, LDL and apoE-depleted HDL. All three apoE isoforms regulate miR221/222, and the effect is independent of the C-terminal lipid-binding domain. miR221/222 levels are increased in the aortae of apoE3-null mice and reduced when apoE3 expression is reconstituted by adeno-associated virus infection. Thus, regulation of miR221/222 by apoE3 occurs in vivo as well as in vitro.

CONCLUSIONS

ApoE inhibits VSMC proliferation by regulating p27 through miR221/222. Control of cell cycle-regulatory microRNAs adds a new dimension to the spectrum of cardiovascular protective effects afforded by apoE and apoE-HDL.

Multidimensional profiling of plasma lipoproteins by size exclusion chromatography followed by reverse-phase protein arrays

The composition of lipoproteins and the association of proteins with various particles are of much interest in the context of cardiovascular disease. Here, we describe a technique for the multidimensional analysis of lipoproteins and their associated apolipoproteins. Plasma is separated by size exclusion chromatography (SEC), and fractions are analyzed by reverse-phase arrays. SEC fractions are spotted on nitrocellulose slides and incubated with different antibodies against individual apolipoproteins or antibodies against various apolipoproteins. In this way, tens of analytes can be measured simultaneously in 100 μl of plasma from a single SEC separation. This methodology is particularly suited to simultaneous analysis of multiple proteins that may change their distribution to lipoproteins or alter their conformation, depending on factors that influence circulating lipoprotein size or composition. We observed changes in the distribution of exchangeable apolipoproteins following addition of recombinant apolipoproteins or interaction with exogenous compounds. While the cholesteryl ester transfer protein (CETP)-dependent formation of pre-β-HDL was inhibited by the CETP inhibitors torcetrapib and anacetrapib, it was not reduced by the CETP modulator dalcetrapib. This finding was elucidated using this technique.

The aminoterminal 1-185 domain of human apolipoprotein E suffices for the de novo biogenesis of apoE-containing HDL-like particles in apoA-I deficient mice

AIMS

Recently we showed that apolipoprotein E promotes the de novo biogenesis of apoE-containing HDL particles in a process that requires the function of the lipid transporter ABCA1. Here, we sought to identify the domain of apoE that is responsible for its functional interactions with ABCA1 and the formation of apoE-rich HDL-like particles.

METHODS AND RESULTS

Recombinant attenuated adenoviruses expressing carboxy-terminal truncated forms of apoE4 (apoE4[1-259], apoE4[1-229], apoE4[1-202], and apoE4[1-185]) were administered to apoA-I-deficient mice at a low dose of 8×10(8) pfu and five days post-infection plasma samples were isolated and analyzed for HDL formation. Fractionation of plasma lipoproteins of the infected mice by density gradient ultracentrifugation and FPLC revealed that all forms were capable of promoting HDL formation. Negative staining electron microscopy analysis of the HDL density fractions confirmed that all C-terminal truncated forms of apoE4 promoted the formation of particles with diameters in the HDL region. Interestingly, apoE4[1-259], apoE4[1-229], and apoE4[1-202] led to the formation of spherical particles while plasma from apoE4[1-185] expressing mice contained a mixture of spherical and discoidal particles.

CONCLUSIONS

Taken together, our data establish that the aminoterminal 1-185 region of apoE suffices for the formation of HDL particles in vivo. Our findings may have important ramifications in the design of new biological drugs for the treatment of dyslipidemia, atherosclerosis and coronary heart disease.

A novel function of apolipoprotein E: upregulation of ATP-binding cassette transporter A1 expression

Despite the well known importance of apolipoprotein (Apo) E in cholesterol efflux, the effect of ApoE on the expression of ATP-binding cassette transporter A1 (ABCA1) has never been investigated. The objective of this study was to determine the effect of ApoE on ApoB-carrying lipoprotein-induced expression of ABCA1, a protein that mediates cholesterol efflux. Our data demonstrate that ApoB-carrying lipoproteins obtained from both wild-type and ApoE knockout mice induced ApoAI-mediated cholesterol efflux in mouse macrophages, which was associated with an enhanced ABCA1 promoter activity, and an increased ABCA1 mRNA and protein expression. In addition, these lipoproteins increased the level of phosphorylated specificity protein 1 (Sp1) and the amount of Sp1 bound to the ABCA1 promoter. However, all these inductions were significantly diminished in cells treated with ApoE-free lipoproteins, when compared to those treated with wild-type lipoproteins. Enrichment with human ApoE3 reversed the reduced inducibility of ApoE-free lipoproteins. Moreover, we observed that inhibition of Sp1 DNA-binding by mithramycin A diminished ABCA1 expression and ApoAI-mediated cholesterol efflux induced by ApoB-carrying lipoproteins, and that mutation of the Sp1-binding motif in the ABCA1 promoter region diminished ApoB-carrying lipoprotein-induced ABCA1 promoter activity. Collectively, these data suggest that ApoE associated with ApoB-carrying lipoproteins has an upregulatory role on ABCA1 expression, and that induction of Sp1 phosphorylation is a mechanism by which ApoE upregulates ABCA1 expression.

Increased apolipoprotein E level and reduced high-density lipoprotein mean particle size associate with low high-density lipoprotein cholesterol and features of metabolic syndrome

The metabolic syndrome (MetS) pandemic predisposes patients to low high-density lipoprotein cholesterol (HDL-C). To successfully treat low HDL-C, there is an urgent need for a better understanding of the changes in HDL particles in the low-HDL-C state. Especially, apolipoprotein (apo) E metabolism in HDL particles is an emerging and important issue. Therefore, we determined HDL subspecies, apo E distribution, and the impact of the MetS in subjects with low and high HDL-C. We studied 246 subjects derived from the Finnish Health 2000 Health Examination Survey. The 2 groups included 113 low-HDL-C (≤10th percentile) and 133 high-HDL-C (≥90th percentile) subjects. The low-HDL-C subjects had higher apo E concentration (39.4 ± 19.4 vs 25.6 ± 8.0 μg/mL, P < .001) and smaller HDL mean particle size (9.0 ± 0.2 vs 9.8 ± 0.3 nm, P < .001). The distribution of apo E genetic isoforms could not explain the difference. Apolipoprotein E content of very low-density lipoprotein particles was comparable between the study groups. In the low-HDL-C subjects, apo E level in large HDL particles was lower (P < .001) compared with that in the high-HDL-C subjects. The subjects with MetS had smaller HDL mean particle size and higher serum apo E concentration. Serum apo E concentration associated positively with different MetS markers (waist circumference, triglycerides, and glucose), whereas HDL mean particle size associated with those negatively. Our results highlight that, in the low-HDL-C state, there are changes in the size and composition of HDL particles associating with MetS. Apolipoprotein E, although generally considered antiatherogenic, associates with MetS and low HDL-C. Our results emphasize the need for a better understanding of apo E metabolism in HDL particles.

High expression of apolipoprotein E impairs lipid storage and promotes cell proliferation in human adipocytes

Apolipoprotein E (apoE), a key regulator of lipid metabolism, is highly produced by adipose tissue and adipocytes. However, there is little information about its role on adipocyte functions. Because apoE-deficiency in adipocytes was shown to impair adipocyte differentiation, we investigated the consequences of apoE high expression on differentiation and proliferation of a human adipocytic cell line (SW872). SW872 cells were transfected with human apoE to induce a fivefold increase in apoE production and secretion. Adipocyte differentiation and proliferation were assayed by measuring lipid content, adipogenic gene expression, cell number, cell resistance to serum deprivation, and cell division kinetics. Cultured apoE-transfected cells accumulated less triglycerides and less cholesterol than control cells. This decrease in lipid accumulation was associated with a strong downregulation of peroxisome proliferator-activated receptors gamma1 and gamma2 and stearoyl-CoA desaturase 1. The decrease in lipid accumulation was not dependent on the presence of lipids, lipoproteins, or PPAR-gamma agonists in the culture medium, nor was it observed with exogenously added apoE. Moreover, we observed that apoE-transfected cells were more resistant to death induced by serum deprivation, and that these cells underwent more cell divisions than control cells. These results bring new evidence of apoE-involvement in metabolic disorders at the adipocyte level.

Habitual consumption of eggs does not alter the beneficial effects of endurance training on plasma lipids and lipoprotein metabolism in untrained men and women

Changes in plasma lipid and apolipoprotein profiles were evaluated in 12 healthy, unfit subjects (VO(2peak) 39.1+/-2.8 ml.kg(-1).min(-1); 5 women, 7 men) at baseline and following endurance exercise training. The exercise protocol consisted of a 6-week endurance exercise training program (4-5 days week(-1); 60 min.session(-1); > or =65% HR(max)). Subjects were randomly assigned to consume an egg- (n=6; 12 eggs.week(-1)) or no-egg (n=6; 0 eggs.week(-1))-based, eucaloric, standardized diet for 8 weeks. Both diets were macronutrient balanced [60% carbohydrate, 30% fat, 10% protein (0.8 g.kg(-1).day(-1))] and individually designed for weight maintenance. Plasma lipids were measured twice within the same week at baseline and following exercise training. At baseline, subjects were normolipidemic with values of 163.9+/-41.8, 84.8+/-36.7, 60.6+/-15.4 and 93.1+/-52 mg dl(-1) for total cholesterol, LDL cholesterol and HDL cholesterol and triglyceride concentrations, respectively. A two-way ANOVA was used to analyze diet and exercise effects and interactions. In both groups, endurance exercise training resulted in a significant 10% increase in HDL-C (P<.05), a 19% decrease in Apo B concentrations (P<.05) and reductions in plasma CETP activity (P<.05). Plasma LDL-C decreased by 21% (P=.06). No main effects of diet or interactions with plasma lipids or Apo B concentrations were observed. These data demonstrate that endurance training improved the plasma lipid profiles of previously unfit, normolipidemic subjects independent of dietary cholesterol intake from eggs.

Lipoproteins, vascular-related genetic factors, and human longevity

The relationships among lipoprotein metabolism, genetic vascular factors, vascular disease, and Alzheimer's disease suggest that the examination of centenarian populations in relation to certain genes or lipoprotein metabolism provide insights into human longevity. The findings on the higher frequency of the apolipoprotein E epsilon4 allele in middle-aged subjects than in centenarians were substantially confirmed. On the contrary, recent findings did not confirm previous data on increased prevalence of the high-risk angiotensin I converting enzyme D allele in French centenarians. The variability in the strength of association between angiotensin I converting enzyme polymorphism and longevity could be related to regional differences in angiotensin I converting enzyme D allele frequency in Europe recently showed, as also recently reported for apolipoprotein Eepsilon2 and epsilon4 allele in centenarians. Indeed some studies of lipoprotein profiles in centenarians have also had contradictory outcomes, with evidence of lower serum levels of high-density lipoprotein cholesterol, with higher high-density lipoprotein 2 cholesterol subfraction, larger high-density lipoprotein and low-density lipoprotein particle sizes, and higher lipoprotein(a) concentration in centenarians, which is apparently disadvantageous for human longevity. Elevated lipoprotein(a) serum levels, increasing the risk for cerebrovascular disease, may play a role in determining clinical Alzheimer's disease, but lipoprotein(a) elevation in centenarians, in the absence of other coronary artery disease risk factors, appears as a positive survival factor. In different populations, there are significant trends in the reduction of serum apolipoprotein E levels from apolipoprotein E epsilon2- to epsilon4-carriers and significant differences in serum apolipoprotein E levels with respect to age in epsilon4-carriers but only after adjustment for high-density lipoprotein cholesterol. While further studies are needed to confirm the possible role of apolipoprotein E concentration as putative longevity factor this paper provides an overview of many of the investigated vascular factors with respect to longevity.

Evaluation of new apolipoprotein C-II and apolipoprotein C-III automatized immunoturbidimetric kits

BACKGROUND

Apolipoprotein C-II and apolipoprotein C-III play an important and complex role in plasma triglycerides metabolism, respectively, as inhibitor and activator of lipoprotein lipase. Thus, they appear to be suitable markers for clinical studies of triglyceride-rich lipoproteins and related cardiovascular risk. Our aim was to evaluate, for routine analysis, the accuracy to quantify these apolipoprotein in human sera.

METHODS

Precision (intra- and inter-run), limit of detection and quantification, linearity, common interferents (lipids, haemoglobin, bilirubin) and reference intervals were determined according to guidelines of the French Society of Clinical Biology and ISO Norm 5725 specifications.

RESULTS

Intra- and inter-run CVs were respectively less than 5.0% and 7.5%. Linearities extended from 10.8 mg/L to 112.9 mg/L for apolipoprotein C-II and from 31.8 mg/L to 375.5 mg/L for apolipoprotein C-III. Haemolysis (up to 227.6 micromol/L haemoglobin) and lipemia (up to 19.3 mmol/L triglycerides) do not interfere, contrary to bilirubin, which has a positive effect above 350 micromol/L. Comparison of methods shows good agreement between immunoturbidimetric and electro-immunodiffusion methods for measuring apolipoprotein C-III in 62 samples within a wide range (n = 62, r = 0.954, y = 3.81 x -14.4).

CONCLUSION

This study shows the reliability of these kits for measuring apolipoprotein C-II and apolipoprotein C-III in human sera, and their suitability for routine analysis.

Accumulation of apoE-enriched triglyceride-rich lipoproteins in patients with coronary artery disease

Triglycerides (TGs) are vehicled by multiple particles with different abilities to promote atherosclerosis. Among plasma TG-rich lipoproteins (TRLs), subspecies may or may not contain apolipoprotein E (apoE) molecules: in this study, we evaluated the relative contribution of apoE-rich and apoE-poor TRLs to coronary atherosclerosis. We selected a group of males with premature coronary artery disease (CAD) without any of the classical nonlipid risk factors and/or high plasma lipid levels and evaluated the plasma concentration of TRL subspecies in comparison with healthy controls. Patients with CAD and controls had total cholesterol and TG levels within the normal range (despite slightly, even if significantly, higher TG levels in patients with CAD) and low-density lipoprotein cholesterol levels near optimal values. Nevertheless, patients with CAD had significantly lower high-density lipoprotein cholesterol, smaller low-density lipoprotein peak particle size, and a reduced HDL2b subfraction than controls. In addition, we observed higher concentrations of total TRL in patients with CAD together with a selective increase in apoE-rich particles. All these data were confirmed after correction for TG levels. We also investigated which parameters were associated with the spread of coronary atherosclerosis. Subjects with a single-vessel disease had selectively lower levels of apoE-rich fractions than patients with a multivessel disease. This was confirmed by multivariate analysis. Patients with a premature CAD free of nonlipid conventional risk factors, despite not having elevated lipid levels, show several lipoprotein abnormalities. Besides known atherogenic alterations, the accumulation of apoE-rich TRL subfractions may represent an additive factor that can potentially promote and initiate the atherosclerotic process.

Carbohydrate restriction alters lipoprotein metabolism by modifying VLDL, LDL, and HDL subfraction distribution and size in overweight men

To determine the effects of carbohydrate restriction (CR) with and without soluble fiber on lipoprotein metabolism, 29 men participated in a 12-wk weight loss intervention. Subjects were matched by age and BMI and randomly assigned to consume 3 g/d of either a soluble fiber supplement (n=14) or placebo (n=15) with a macronutrient energy distribution of approximately 10% carbohydrate, approximately 65% fat, and approximately 25% protein. Because the groups did not differ in any of the variables measured, all data were pooled and comparisons were made between baseline and 12 wk. After 12 wk, subjects had a mean weight loss of 7.5 kg (P<0.001), and abdominal fat was reduced by 20% (P<0.001). Plasma LDL cholesterol and triglycerides (TG) were significantly reduced by 8.9 and 38.6%, respectively. Similarly, apolipoproteins C-I (-13.8%), C-III (-21.2%) and E (-12.5%) were significantly lower after the intervention. In contrast plasma HDL-cholesterol concentrations were increased by 12% (P<0.05). Changes in plasma TG were positively correlated with reductions in large (r=0.615, P<0.01) and medium VLDL particles (r=0.432, P<0.05) and negatively correlated with LDL diameter (r=-0.489, P<0.01). Changes in trunk fat were positively correlated with medium VLDL (r=0.474, P<0.0) and small LDL (r=0.405, P<0.05) and negatively correlated with large HDL (r=-0.556, P<0.01). We conclude that weight loss induced by CR favorably alters the secretion and processing of plasma lipoproteins, rendering VLDL, LDL, and HDL particles associated with decreased risk for atherosclerosis and coronary heart disease.

Weight loss associated with reduced intake of carbohydrate reduces the atherogenicity of LDL in premenopausal women

The effect of a 3-tier intervention including dietary modifications (ie, moderate energy restriction, decreased carbohydrate, increased protein), increased physical activity, and the use of carnitine as a dietary supplement was evaluated on plasma lipids and the atherogenicity of low-density lipoprotein (LDL) particles in a population of overweight and obese premenopausal (aged 20-45 years) women. Carnitine or a placebo (cellulose) was randomly assigned to the participants using a double-blind design. Carnitine supplementation was postulated to enhance fat oxidation resulting in lower concentrations of plasma triglycerides. Seventy women completed the 10-week protocol, which followed a reduction in their energy intake by 15% and a macronutrient energy distribution of 30% protein, 30% fat, and 40% carbohydrate. In addition, subjects increased the number of steps taken per day by 4500. As no differences were observed between the carnitine and placebo groups in all the measured parameters, all subjects were pooled together for statistical analysis. Participants decreased (P<.01) their caloric intake (between 4132.8 and 7770 kJ) and followed prescribed dietary modifications as assessed by dietary records. The average number of steps increased from 8950+/-3432 to 12764+/-4642 (P<.001). Body weight, plasma total cholesterol, LDL cholesterol, and triglyceride were decreased by 4.5%, 8.0%, 12.3%, and 19.2% (P<.0001), respectively, after the intervention. Likewise, apolipoproteins B and E decreased by 4.5% and 15% (P<.05) after 10 weeks. The LDL mean particle size was increased from 26.74 to 26.86 nm (P<.01), and the percent of the smaller LDL subfraction (P<.05) was decreased by 26.5% (P<.05) after 10 weeks. In addition, LDL lag time increased by 9.3% (P<.01), and LDL conjugated diene formation decreased by 23% (P<.01), indicating that the susceptibility of LDL to oxidation was decreased after the intervention. This study suggests that moderate weight loss (<5% of body weight) associated with reduced caloric intake, lower dietary carbohydrate, and increased physical activity impacts the atherogenicity of LDL.

Plasma metabolism of apoB-containing lipoproteins in patients with hepatic lipase deficiency

The metabolism of apoB-containing lipoproteins was investigated in the fasted state in three complete and three partial hepatic lipase (HL)-deficient subjects as well as in seven normotriglyceridemic (NTG) and two hypertriglyceridemic (HTG) controls using a 12 h primed-constant infusion of L-[5,5,5-D(3)]-leucine. Two males with complete HL deficiency had increased plasma pool sizes of VLDL and IDL apoB-100 due to substantial reductions in fractional catabolic rate (FCR) of VLDL and IDL apoB-100 compared with both NTG and HTG controls. Reductions in LDL apoB-100 production rate (PR) were also observed in these two patients compared with NTG and HTG controls. Complete HL deficiency in the female proband was associated with normal VLDL apoB-100 kinetics, while plasma IDL apoB-100 pool size was increased by 124% due to an 82% decrease in the FCR of IDL apoB-100. The FCR and PR of LDL apoB-100 were reduced by 64 and 51%, respectively, in the proband compared with sex-matched controls. Partial HL-deficient patients were characterized by apoB-containing lipoprotein metabolism similar to that of controls. These results indicate that complete HL deficiency is associated with a potentially atherogenic apoB-containing lipoprotein metabolism that can be modulated considerably by secondary factors such as gender and abdominal obesity.

The lowering of plasma lipids following a weight reduction program is related to increased expression of the LDL receptor and lipoprotein lipase

To determine whether changes in plasma lipids following a weight loss program were related to modifications in gene expression of the LDL receptor (LDL-R), lipoprotein lipase (LPL), and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, overweight/obese premenopausal women were recruited. The 10-wk, randomized, double-blind intervention consisted of a hypoenergetic diet, high in protein (30% energy) and low in carbohydrate (40% energy), increased physical activity (number of steps taken per day), and intake of a supplement (carnitine or placebo). Our initial hypothesis was that carnitine would enhance the beneficial effects of weight loss on plasma lipids and anthropometrics. Because the carnitine and placebo groups did not differ in any of the measured variables, data for all subjects were pooled and comparisons were made between baseline and postintervention. Mean weight loss was 4.4 kg (P < 0.001), and plasma triglycerides (TG), total, and LDL cholesterol (LDL-C) were reduced by 31.8, 9.9, and 11.9%, respectively (P < 0.001). The expression of the genes of interest was measured in RNA extracted from mononuclear cells at baseline and postintervention using a semiquantitative RT-PCR method. Glyceraldehyde-3-phosphate dehydrogenase was used as an internal control. After 10 wk, there was a 25.7% increase in the abundance of LPL mRNA (P < 0.01) and a 27.7% increase in that of LDL-R mRNA (P < 0.01). The expression of HMG-CoA reductase was not altered by weight loss. The results suggest that the increased expression of the LDL-R and LPL after the intervention might have contributed to the lower plasma LDL-C and TG observed in these women.

Carbohydrate intake is correlated with biomarkers for coronary heart disease in a population of overweight premenopausal women

The associations between macronutrient intake and plasma parameters associated with increased risk for coronary heart disease (CHD) were evaluated in 80 overweight premenopausal women. We hypothesized that higher carbohydrate intake would be associated with a more detrimental plasma lipid profile. Dietary data were collected using a validated food frequency questionnaire (FFQ). Plasma total cholesterol (TC), triglycerides (TGs), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) were determined from two fasting blood samples. In addition, selected apolipoproteins (apo) and LDL peak size were measured. Values for TC, TG and HDL were not in the range of risk classification; however, the mean values of LDL-C, 2.7 +/- 0.7 mmol/L, were higher than the current recommendations. Carbohydrate intake was positively associated with TG and apo C-III (P < .01) concentrations, and negatively associated with LDL diameter (P < .01). Participants were divided into low (<53% of energy) or high (> or = 53% energy) carbohydrate intake groups. Individuals in the <53% carbohydrate group consumed more cholesterol and total fat, but also had higher intake of polyunsaturated and monounsaturated fatty acids (SFAs). In contrast, subjects in the > or =53% group consumed higher concentrations of glucose and fructose than those in the low-carbohydrate (LC) group. In addition, subjects consuming <53% carbohydrate had lower concentrations of LDL-C and apo B (P < .01) and a larger LDL diameter (P < .05) than the > or =53% group. These results suggest that the lower LDL-C in the LC group may be related to both the amount of carbohydrate and the type of fatty acids consumed by these subjects.

Increased apoC-III production is a characteristic feature of patients with hypertriglyceridemia

Apolipoprotein (apo) C-III plays an important role in regulating plasma triglyceride (TG) metabolism. In order to further investigate the plasma metabolism of apoC-III in hypertriglyceridemic subjects, we have studied the plasma kinetics of VLDL apoC-III, HDL apoC-III and total plasma apoC-III with a primed constant intravenous infusion of deuterated leucine in a group of male patients with mixed hyperlipidemia (type IIb hyperlipoproteinemia, HLP, n=6) and in a group with type III HLP (n=6). Compared to normolipidemic control subjects (n=5), patients with type IIb and type III HLP had significantly higher levels of plasma TG (0.89 +/- 0.15 mmol/l vs 2.56 +/- 0.40 mmol/l vs 8.76 +/- 1.39 mmol/l, respectively, P <0.01), plasma apoC-III (9.5 +/- 0.8 mg/dl vs 20.8 +/- 2.5 mg/dl vs 41.7 +/- 5.6 mg/dl, P <0.01) and VLDL apoC-III (3.6 +/- 0.8 mg/dl vs 14.6 +/- 2.2 mg/dl vs 35.4 +/- 5.1 mg/dl, P <0.01). VLDL apoC-III production rates were significantly elevated in type IIb and type III patients (1.35 +/- 0.23 mg kg(-1) day(-1) vs 3.53 +/- 0.43 mg kg(-1) day(-1) vs 5.60 +/- 0.78 mg kg(-1) day(-1), P <0.01), as were total plasma apoC-III production rates (1.80 +/- 0.22 mg kg(-1) day(-1) vs 4.16 +/- 0.44 mg kg(-1) day(-1) vs 7.26 +/- 0.74 mg kg(-1) day(-1), P <0.01). VLDL apoC-III but not total plasma apoC-III fractional catabolic rates were reduced in type IIb and type III patients. Together with our previous results showing an increase of apoC-III production in patients with type IV HLP, and in overweight subjects with reduced insulin sensitivity, our data suggest that increased apoC-III production is a characteristic feature of patients with hypertriglyceridemia.

Post-transcriptional regulation of apoC-I synthesis and secretion in human HepG2 cells

ApoC-I plays an important role in controlling plasma lipid metabolism, however little is known about factors regulating the hepatic synthesis and secretion of this apolipoprotein. In the present study, we have carried out experiments with human hepatoma (HepG2) cells, in order to determine the effect of different tissue culture conditions on cellular lipid levels and on the production of apoC-I (and apoE) at the protein and mRNA level. Cells incubated for 48 h with 10% human serum had significantly higher cellular triglyceride (22%, P<0.05) and cholesterol levels (19%, P<0.01), higher medium apoC-I and apoE levels (2.6- and 2.9-fold, respectively), but similar levels of apoC-I and apoE mRNA, compared to cells incubated with 10% human lipoprotein-deficient serum (LPDS). Serum containing only HDL, or containing HDL with LDL, also increased cellular lipids and increased secreted apoC-I and apoE levels without altering apoC-I and apoE mRNA levels. Incubation of cells with Intralipid triglyceride (625 microM), increased cellular triglyceride (2.8-fold, P<0.001), decreased cellular cholesterol (32%, P<0.01), decreased cellular and medium apoC-I (24 and 26%, P<0.01) and had no effect on apoC-I mRNA levels. Additional experiments in which cells were loaded with cholesterol (incubation with 10 microg/ml cholesterol plus 1 microg/ml 25-hydroxycholesterol) or depleted of cholesterol (statin treatment) confirmed that secretion of apoC-I by HepG2 cells was dependent on cellular cholesterol levels and independent of changes in apoC-I mRNA levels. These results demonstrate that cellular cholesterol rather than triglyceride levels play a role in controlling apoC-I production by HepG2 cells and that this regulation occurs at a post-transcriptional level.

Beneficial effects of weight loss on plasma apolipoproteins in postmenopausal women

A total of 39 postmenopausal women 40-70 years of age and undergoing hormone replacement therapy participated in a 6-month weight reduction program, which consisted of a low calorie diet (5040 KJ/day) and phentermine hydrochloride therapy. Subjects had an average body mass index of 35.95+/-5.32 kg/m(2) and 42.20+/-11.0 kg of total fat. Body mass index, plasma lipids, total and trunk fat, and plasma apoproteins were measured at baseline and after 3 and 6 months of the weight reduction program. Subjects experienced an overall 10% weight loss during the treatment period (P<0.001). Plasma LDL cholesterol and triglycerides were reduced by 18% and 15% (P<0.01) respectively, whereas HDL cholesterol was increased by 9% (P<0.01) over the 6-month period. Plasma apoproteins were significantly affected by weight loss. Plasma apolipoprotein (apo) B concentrations were reduced 6.5% (P<0.01), and apo C-III and apo E were reduced by 9% over 6 months (P<0.01). The observed decreases in plasma apo B were significantly correlated with the observed changes in plasma cholesterol (r=0.356, P<0.01) over 3 months. In addition, changes in plasma triglycerides were correlated with changes in both apo C-III (r=0.436) and apo E (r=0.354) over 6 months. These results suggest that weight loss may have multifactorial effects on lipoprotein metabolism, resulting in better plasma lipid and apoprotein profiles.

Synthesis and secretion of apoC-I and apoE during maturation of human SW872 liposarcoma cells

Little is known about the regulation of apolipoprotein (apo) C-I production by human adipocytes. The aim of the present study, therefore, was to investigate the effect of different tissue culture conditions on the synthesis and secretion of apoC-I and apoE in human SW872 liposarcoma cells. After 3-4 d in culture (0.5 x 10(6) cells/well, DMEM/F-12 medium with 10% fetal calf serum), cells reached confluence and became growth arrested. The molar ratio of apoE:apoC-I in the cell was 8.9 +/- 0.6 and in the medium was 6.6 +/- 0.5. After 17 d in culture, SW872 cells contained significantly more cholesterol (100%) and triglyceride (3-fold) and secreted more apoC-I [4 vs. 17 d: 0.11 +/- 0.01 vs. 0.23 +/- 0.01 pmol/(10(6) cells . 24 h), P < 0.001] and apoE [0.7 +/- 0.1 vs. 3.1 +/- 0.3 pmol/(10(6) cells . 24 h), P < 0.001]. Cellular apoC-I increased 7-fold and apoE increased 16-fold. Cell maturation was associated with significantly higher levels of apoE mRNA but not apoC-I mRNA. Increases in cell lipids, apoC-I, and apoE were not dependent on the presence of extracellular lipids because similar changes occurred in cells incubated with lipoprotein-deficient serum or in cells incubated without serum. Treatment (7 d) of cells during maturation with insulin (10 or 1000 nmol/L) significantly reduced the secretion of apoC-I and apoE. These results demonstrate that in maturing SW872 cells, cholesterol and triglyceride accumulation in the presence or absence of extracellular lipids, is associated with increased apoC-I and apoE production. Furthermore, apoC-I and apoE production are differentially regulated at the transcriptional level, and long-term treatment with insulin has an inhibitory rather than stimulatory effect on apoC-I and apoE production.

Dietary cholesterol does not increase biomarkers for chronic disease in a pediatric population from northern Mexico

BACKGROUND

An increased incidence of coronary artery disease (CAD) is prevalent in northern Mexico. Effects of specific dietary components on risk factors for CAD have not been evaluated in children.

OBJECTIVE

The purpose was to evaluate the effects of dietary cholesterol provided by whole eggs on the lipoprotein profile, LDL size, and phenotype in children from this region.

DESIGN

Children (29 girls and 25 boys aged 8-12 y) were randomly assigned to either 2 eggs/d (EGG period; 518 additional mg cholesterol) or the equivalent amount of egg whites (SUB period; 0 additional mg cholesterol) for 30 d. After a 3-wk washout period, the children were assigned to the alternate treatment.

RESULTS

Subjects were classified as hyporesponders (no increase or </=0.05 mmol/L increase in plasma cholesterol for 100 mg additional cholesterol) or hyperresponders (>/=0.06 mmol/L increase). During the EGG period, the hyperresponders (n = 18) had an elevation in both LDL cholesterol (from 1.54 +/- 0.38 to 1.93 +/- 0.36 mmol/L) and HDL cholesterol (from 1.23 +/- 0.26 to 1.35 +/- 0.29 mmol/L) with no changes in LDL:HDL. In contrast, hyporesponders (n = 36) had no significant alterations in plasma LDL or HDL cholesterol. All subjects had an increase in LDL peak diameter during the EGG period (P < 0.01) and a decrease (P < 0.01) in the smaller LDL subfractions. In addition, 5 of the children having LDL phenotype B (15%) shifted from this high-risk pattern to pattern A after the EGG treatment.

CONCLUSIONS

Intake of 2 eggs/d results in the maintenance of LDL:HDL and in the generation of a less atherogenic LDL in this population of Mexican children.

Storage of human plasma samples leads to alterations in the lipoprotein distribution of apoC-III and apoE

The effect of frozen storage on lipoprotein distribution of apolipoprotein C-III (apoC-III) and apoE was investigated by measuring apoC-III and apoE by ELISA in HDL and apoB-containing lipoproteins of human plasma samples (n = 16) before and after 2 weeks of frozen storage (-20 degrees C). HDLs were separated by heparin-manganese precipitation (HMP) or by fast-protein liquid chromatography (FPLC). Total plasma apoC-III and apoE levels were not affected by frozen storage. HDL-HMP apoC-III and apoE levels were significantly higher in frozen versus fresh samples: 7.7 +/- 0.7 versus 6.7 +/- 0.7 mg/dl (P < 0.05) and 2.0 +/- 0.1 versus 1.2 +/- 0.1 mg/dl (P < 0.001), respectively. HDL-FPLC apoC-III and apoE, but not triglyceride (TG) or cholesterol, levels were also higher in frozen samples: 12.0 +/- 1.2 versus 7.5 +/- 0.6 mg/dl (P < 0.001) and 2.7 +/- 0.2 versus 1.6 +/- 0.2 mg/dl (P < 0.001), respectively. Frozen storage led to a decrease in apoC-III (-17 +/- 9%) and apoE (-19 +/- 9%) in triglyceride-rich lipoprotein. Redistribution of apoC-III and apoE was most evident in samples with high TG levels. HDL apoC-III and apoE levels were also significantly higher when measured in plasma stored at -80 degrees C. Our results demonstrate that lipoprotein distribution of apoC-III and apoE is affected by storage of human plasma, suggesting that analysis of frozen plasma should be avoided in studies relating lipoprotein levels of apoC-III and/or apoE to the incidence of coronary artery disease.

Secreted apolipoprotein E reduces macrophage-mediated LDL oxidation in an isoform-dependent way

As an inflammatory cell, the macrophage produces various oxidizing agents, such as free radical species. These can modify LDL as a secondary effect and doing so may favor atherogenic processes. Any molecule able to counteract these reactions would be of much benefit, especially if secreted by the macrophage itself at the lesion site. Such is the case for apolipoprotein E (apoE), which has been shown to exert antioxidant properties in some studies, mostly in relation to Alzheimer's disease. In this study, we assessed the antioxidant potential of the various isoforms of apoE (E2, E3, and E4) using a metal-induced LDL oxidation system with exogenous recombinant apoE and an in vitro model of macrophage-mediated LDL oxidation. We found that all three isoforms had an antioxidant capacity. However, whereas apoE2 was the most protective isoform in the cell-free system, the opposite was observed in apoE-transfected J774 macrophages. In the latter model, cellular cholesterol efflux was found to be more important with apoE2, possibly explaining the larger quantity of oxidative indices observed in the medium. It is proposed that the antioxidant property of apoE results from a balance between direct apoE antioxidant capacities, such as the ability to trap free radicals, and potentially pro-oxidative indirect events associated with cholesterol efflux from cells. Our observations add to the therapeutic potential of apoE. However, they also suggest the need for more experiments in order to achieve careful selection of the apoE isoform to be targeted, especially in the perspective of apoE transgene use.

Waist circumference is a better predictor than body mass index of coronary heart disease risk in overweight premenopausal women

Waist circumference (WC) has been postulated to have stronger associations with biomarkers of coronary heart disease (CHD) than BMI. In this study, we measured the level of activity by determining steps walked per day and select biomarkers for CHD risk in 80 overweight or obese (BMI = 25-37 kg/m(2)) premenopausal women to evaluate whether these biomarkers are associated with WC or BMI. The plasma biomarkers measured, using samples from women who had fasted for 12 h, were lipids, apolipoproteins (apo), LDL peak diameter, LDL susceptibility to oxidation, glucose, leptin, and insulin. We identified subjects with the metabolic syndrome (11%) and insulin resistance (30%) to further distinguish subjects at increased risk for CHD. Both BMI and WC were positively correlated with insulin (r = 0.376 and 0.384, respectively, P < 0.05) and leptin (r = 0.614 and 0.512, respectively, P < 0.01) and negatively correlated with the number of steps taken per day (r = -0.245 and -0.354, respectively, P < 0.05). In addition, WC had positive correlations with diastolic blood pressure (r = 0.250, P < 0.05), plasma triglycerides (TG) (r = 0.270, P < 0.05), and apo C-III (r = 0.240, P < 0.05). Women with BMI > or = 30 kg/m(2) or WC > 88 cm had significantly higher leptin concentrations than women having a BMI < 30 kg/m(2) or a WC < or = 88 cm; women with WC > 88 cm also had higher diastolic pressure (P < 0.05), and higher plasma TG (P < 0.05) and apo C-III (P < 0.05) concentrations than those with WC < or = 88. In addition, subjects with the higher WC walked an average of 1000 fewer steps per day (P < 0.01). These results suggest that WC is a stronger predictor of CHD risk than BMI and is more closely associated with the level of exercise in premenopausal women.

Vascular genetic factors and human longevity

Complex inter-relationships between age-associated illnesses, such as vascular disease and Alzheimer's disease (AD), suggest that biological and genetic pathways may be worthy of examination in centenarian populations to provide insights into human longevity. This is also borne out by the involvement of lipoprotein metabolism and a number of vascular genetic risk factors. Repeated findings of a higher frequency of the apolipoprotein E (APOE) epsilon4 allele in middle-aged subjects compared with centenarians were reported. Furthermore, we have also shown how in different populations there is a significant trend in reduction of serum APOE levels from APOE epsilon2- to epsilon4-carrier as well as significant differences in serum APOE levels respect to age in epsilon4-carriers but only after adjustment for HDL cholesterol. In contrast, findings of increased prevalence of the angiotensin I converting enzyme 1 (ACE1) D allele in French centenarians have not been replicated, suggesting the possibility that regional differences may occur in ACE1(*)D frequency within Europe in centenarians, as has been recently reported for APOE epsilon2 and epsilon4 alleles. A number of studies have examined the potential role in longevity of other genes involved in vascular risk, haemostasis, and blood pressure regulation [methyltetrahydrofolatereductase (MTHFR), apolipoprotein A1 (APOA-I), apolipoprotein C3 (APOC-III), apolipoprotein A4 (APOA-IV), paraoxonase 1 (PON1), plasminogen activator inhibitor type I (PAI-1)], with contrasting results. While further studies are needed to confirm the possible role of APOE concentration as putative longevity factor, this paper provides an overview of genetic vascular factors potentially involved in human longevity.

Plasma turnover of HDL apoC-I, apoC-III, and apoE in humans: in vivo evidence for a link between HDL apoC-III and apoA-I metabolism

Numerous factors are known to affect the plasma metabolism of HDL, including lipoprotein receptors, lipid transfer protein, lipolytic enzymes and HDL apolipoproteins. In order to better define the role of HDL apolipoproteins in determining plasma HDL concentrations, the aims of the present study were: a) to compare the in vivo rate of plasma turnover of HDL apolipoproteins [i.e., apolipoprotein A-I (apoA-I), apoC-I, apoC-III, and apoE], and b) to investigate to what extent these metabolic parameters are related to plasma HDL levels. We thus studied 16 individuals with HDL cholesterol levels ranging from 0.56-1.66 mmol/l and HDL apoA-I levels ranging from 89-149 mg/dl. Plasma kinetics of HDL apolipoproteins were investigated using a primed constant (12 h) infusion of deuterated leucine. Plasma HDL apolipoprotein levels were 41.8 +/- 1.5, 9.7 +/- 0.5, 4.9 +/- 0.5, and 0.7 +/- 0.1 micromol/l for apoA-I, apoC-I, apoC-III and apoE. Plasma transport rates (TRs) were 388.6 +/- 24.7, 131.5 +/- 12.5, 66.5 +/- 9.1, and 31.4 +/- 3.3 nmol.kg-1.day-1; and residence times (RTs) were 5.1 +/- 0.4, 3.7 +/- 0.3, 3.6 +/- 0.3, and 1.1 +/- 0.1 days, respectively. HDL cholesterol and apoA-I levels were significantly correlated with HDL apoA-I RT (r = 0.69 and r = 0.56), and were not significantly correlated with HDL apoA-I TR. In contrast, HDL apoC-I, apoC-III, and apoB levels were all positively related to their TRs and not their RTs. HDL apoC-III TR was positively correlated with levels of HDL apoC-III (r = 0.73, P < 0.01), and with those of HDL cholesterol and apoA-I (r = 0.54 and r = 0.53, P < 0.05, respectively). HDL apoC-III TR was in turn related to HDL apoA-I RT (r = 0.51, P < 0.05). Together, these results provide in vivo evidence for a link between the metabolism of HDL apoC-III and apoA-I, and suggest a role for apoC-III in the regulation of plasma HDL levels.

Effect of atorvastatin on ApoE and ApoC-I synthesis and secretion by THP-1 macrophages

Apolipoprotein (apo) E and C-I are plasma apolipoproteins that have been implicated in the etiology of atherosclerosis and obesity, respectively. Both proteins are synthesized and secreted by macrophages, though pharmacological regulation of their production is poorly understood. The authors compared the effect of 2 HMG-CoA reductase inhibitors, atorvastatin and cerivastatin, on the synthesis and secretion of apoE and apoC-I by THP-1 macrophages. Atorvastatin reduced medium apoE and cellular apoE mRNA of PMA-activated THP-1 cells in a dose-dependent manner (-24% and -22%, respectively, at 1-micromol/L, P < 0.01). ApoC-I in the medium was also reduced by atorvastatin in a dose-dependent manner, though to a lesser extent (-15% at 1-micromol/L, P < 0.05). Cerivastatin similarly reduced medium apoE (-20% at 1-micromol/L, P < 0.05) and cellular apoE mRNA (-31% at 1-micromol/L, P < 0.05), and significantly lowered cellular apoC-I mRNA (-15%, P < 0.05), but not apoC-I in the medium. In experiments with THP-1 macrophages loaded with cholesterol (ie, 24-hour incubation with acetyl-LDL), atorvastatin and cerivastatin (1-micromol/L) significantly (P < 0.05) reduced both medium apoE (-30% and -25%, respectively) and cellular apoE mRNA (-25% and -17%, respectively). A lower and less consistent effect was observed on medium apoC-I (-6% and -18%, respectively) and cellular apoC-I mRNA (-13% and -19%, respectively). These data demonstrate that statins have the capacity to reduce the synthesis and secretion of both apoE and apoC-I in THP-1 macrophages loaded or unloaded with cholesterol.

Plasma concentration and lipoprotein distribution of ApoC-I is dependent on ApoE genotype rather than the Hpa I ApoC-I promoter polymorphism

An Hpa I restriction site located 317 bp upstream of the transcription initiation site of the apoC-I gene has been shown to increase apoC-I gene transcription in vitro. The aim of the present study was to determine whether this genetic polymorphism was associated in vivo with increased plasma levels of apoC-I. In a cohort of French-Canadians (n=391) recruited for a family study, we found strong linkage disequilibrium between the genes for apoC-I and apoE (as reported before for European-Americans), such that the apoC-I Hpa I-negative (H1) allele was strongly associated with apoE epsilon 3, whereas the apoC-I Hpa I-positive (H2) allele was strongly associated with apoE epsilon 2 and epsilon 4. ApoC-I and apoE were measured by ELISA in total plasma and in very low-density lipoproteins (VLDL) separated by ultracentrifugation (d<1.006 g/ml), and then by difference for the non-VLDL fraction (d>1.006 g/ml), in a subset of families selected for their diverse apoE genotypes. Subjects were divided into normolipidemic (NL, n=89, TG<2.3 mmol/l, LDL-C<3.8 mmol/l) and hyperlipidemic groups (HL, n=88, TG>2.3 mmol/l and/or LDL-C>3.8 mmol/l). In NL subjects, apoC-I levels were not significantly associated with apoC-I genotype (H1/H1, H1/H2 or H2/H2). They were, however, related to apoE genotype, such that apoE3/2 subjects tended to have higher and apoE4/3 subjects tended to have lower concentrations of total plasma and non-VLDL apoC-I and apoE. Total plasma, VLDL and non-VLDL apoC-I and E levels were also higher in HL subjects with an apoE2/2 or apoE3/2 genotype. These results suggest that plasma levels of apoC-I are more strongly influenced by apoE genotype than by the Hpa I apoC-I promoter polymorphism, which probably reflects an effect of different apoE isoforms on plasma lipoprotein and plasma apoC-I metabolism, rather than a direct effect of apoE alleles on apoC-I transcription.

Men classified as hypo- or hyperresponders to dietary cholesterol feeding exhibit differences in lipoprotein metabolism

The purpose of this study was to evaluate the differences that occur within the plasma compartment of normolipidemic men, classified on the basis of their response to prolonged consumption of additional dietary cholesterol. Using a crossover design, 40 men aged 18-57 y were randomly allocated to an egg (640 mg/d additional dietary cholesterol) or placebo group (0 mg/d additional dietary cholesterol), for two 30-d periods, which were separated by a 3-wk washout period. Subjects were classified as hypo- [increase in plasma total cholesterol (TC) of <0.05 mmol/L for each additional 100 mg of dietary cholesterol consumed] or hyperresponders (increase in TC of > or =0.06 mmol/L for each additional 100 mg of dietary cholesterol consumed) on the basis of their plasma reaction to the additional dietary cholesterol provided. Male hyporesponders did not experience an increase in LDL cholesterol (LDL-C) or HDL cholesterol (HDL-C) during the egg period, whereas both lipoproteins were significantly (P < 0.0001 and P < 0.05, respectively) elevated in hyperresponders. Although the LDL/HDL ratio was increased in male hyperresponders after the high cholesterol period, the mean increase experienced by this population was still within National Cholesterol Education Program guidelines. Furthermore, male hyperresponders had higher lecithin cholesterol acyltransferase (P < 0.05) and cholesteryl ester transfer protein (P < 0.05) activities during the egg period, which suggests an increase in reverse cholesterol transport. These data suggest that additional dietary cholesterol does not increase the risk of developing an atherogenic lipoprotein profile in healthy men, regardless of their response classification.

Apolipoprotein E (APOE) polymorphism influences serum APOE levels in Alzheimer's disease patients and centenarians

Vascular factors may play a role in the etiology of Alzheimer's disease (AD) and increased serum apolipoprotein E (APOE) levels in AD could be of interest, as APOE concentration is associated with vascular disease. Aims of this study were to evaluate the influence of APOE genotype on serum APOE levels, and, secondly, to study serum APOE concentrations in relation to age and AD. APOE genotypes, serum total cholesterol, LDL cholesterol, HDL cholesterol, total cholesterol/HDL cholesterol ratio, triglycerides, and serum APOE were performed on 52 healthy centenarians, 49 AD patients, 45 age-matched controls, and 72 young healthy adults. In all study population a significant trend in reduction of serum APOE levels from APOE epsilon2- to epsilon4 carriers was observed. The difference in serum APOE levels among age groups significantly decreased in epsilon4 carriers only, including HDL cholesterol; no significant differences between AD patients and age-matched controls were found. In these highly selected populations, APOE genotype distribution strongly influences serum APOE concentration, not suggesting, at present, a possible role as a biochemical marker for AD, but only as a putative longevity factor.

Bovine apolipoprotein E in plasma: increase of ApoE concentration induced by fasting and distribution in lipoprotein fractions

Apolipoprotein E (apoE) is a protein constituent of lipoproteins, and acts as a receptor-binding ligand. Although the existence of bovine apoE in lipoprotein fractions has already been reported, quantitative studies on the changes of apoE in plasma and lipoprotein fractions are lacking. In the present study, an increase of a 38 kDa protein in the very low-density lipoprotein (VLDL) fraction obtained from fasted calves was detected. This 38 kDa protein was identified as bovine apoE by determination of the N-terminal amino acid sequence. Bovine apoE was purified and an enzyme-linked immunosorbent assay (ELISA) was developed. Using this system, the effect of fasting on the concentration of apoE in plasma and the distribution of apoE in lipoprotein fractions were investigated. After 3 days of fasting, the concentration of plasma apoE increased significantly (p<0.05) by 280 %, and was returned to the basal level by 3 days of refeeding. The lipoprotein fractions obtained from before and after fasting was separated by ultracentrifugation. ApoE was significantly increased in VLDL, low-density lipoprotein (LDL) and non-lipoprotein fractions by fasting (p<0.05). On the other hand, in high-density lipoprotein (HDL) fractions obtained from both before and after fasting, the level of apoE was very low compared to the other fractions. These results suggested that bovine apoE contents in triglyceride-rich lipoproteins are modulated by nutritional treatment and closely associated with triglyceride-rich lipoprotein metabolism.

Overexpression of apoC-I in apoE-null mice: severe hypertriglyceridemia due to inhibition of hepatic lipase

Apolipoprotein C-I (apoC-I) has been proposed to act primarily via interference with apoE-mediated lipoprotein uptake. To define actions of apoC-I that are independent of apoE, we crossed a moderately overexpressing human apoC-I transgenic, which possesses a minimal phenotype in the WT background, with the apoE-null mouse. Surprisingly, apoE-null/C-I mice showed much more severe hyperlipidemia than apoE-null littermates in both the fasting and non-fasting states, with an almost doubling of cholesterol, primarily in IDL+LDL, and a marked increase in triglycerides; 3-fold in females to 260 +/- 80 mg/dl and 14-fold in males to 1409 +/- 594 mg/dl. HDL lipids were not significantly altered but HDL were apoC-I-enriched and apoA-II-depleted. Production rates of VLDL triglyceride were unchanged as was the clearance of post-lipolysis remnant particles. Plasma post-heparin hepatic lipase and lipoprotein lipase levels were undiminished as was the in vitro hydrolysis of apoC-I transgenic VLDL. However, HDL from apoC-I transgenic mice had a marked inhibitory effect on hepatic lipase activity, as did purified apoC-I. LPL activity was minimally affected. Atherosclerosis assay revealed significantly increased atherosclerosis in apoE-null/C-I mice assessed via the en face assay. Inhibition of hepatic lipase may be an important mechanism of the decrease in lipoprotein clearance mediated by apoC-I.

Effect of atorvastatin on plasma apoE metabolism in patients with combined hyperlipidemia

Atorvastatin, a synthetic HMG-CoA reductase inhibitor used for the treatment of hyperlipidemia and the prevention of coronary artery disease, significantly lowers plasma cholesterol and low-density lipoprotein cholesterol (LDL-C) levels. It also reduces total plasma triglyceride and apoE concentrations. In view of the direct involvement of apoE in the pathogenesis of atherosclerosis, we have investigated the effect of atorvastatin treatment (40 mg/day) on in vivo rates of plasma apoE production and catabolism in six patients with combined hyperlipidemia using a primed constant infusion of deuterated leucine. Atorvastatin treatment resulted in a significant decrease (i.e., 30-37%) in levels of total triglyceride, cholesterol, LDL-C, and apoB in all six patients. Total plasma apoE concentration was reduced from 7.4 +/- 0.9 to 4.3 +/- 0.2 mg/dl (-38 +/- 8%, P < 0.05), predominantly due to a decrease in VLDL apoE (3.4 +/- 0.8 vs. 1.7 +/- 0.2 mg/dl; -42 +/- 11%) and IDL/LDL apoE (1.9 +/- 0.3 vs. 0.8 +/- 0.1 mg/dl; -57 +/- 6%). Total plasma lipoprotein apoE transport (i.e., production) was significantly reduced from 4.67 +/- 0.39 to 3.04 +/- 0.51 mg/kg/day (-34 +/- 10%, P < 0.05) and VLDL apoE transport was reduced from 3.82 +/- 0.67 to 2.26 +/- 0.42 mg/kg/day (-36 +/- 10%, P = 0.057). Plasma and VLDL apoE residence times and HDL apoE kinetic parameters were not significantly affected by drug treatment. Percentage decreases in VLDL apoE concentration and VLDL apoE production were significantly correlated with drug-induced reductions in VLDL triglyceride concentration (r = 0.99, P < 0.001; r = 0.88, P < 0.05, respectively, n = 6). Our results demonstrate that atorvastatin causes a pronounced decrease in total plasma and VLDL apoE concentrations and a significant decrease in plasma and VLDL apoE rates of production in patients with combined hyperlipidemia.

Pre-menopausal women, classified as hypo- or hyperresponders, do not alter their LDL/HDL ratio following a high dietary cholesterol challenge

BACKGROUND

Cholesterol is the dietary component that has elicited the most public interest in conjunction with coronary heart disease. However, the impact of excess dietary cholesterol intake on plasma cholesterol levels cannot be accurately predicted; therefore, its role in disease progression is not straightforward. Individual response variation can be due to factors such as ethnicity, hormonal status, obesity and genetic predisposition.

OBJECTIVE

The purpose of this study was to evaluate the differences that occur within the plasma compartment of normolipidemic pre-menopausal women, classified based on their response to a high dietary cholesterol challenge.

DESIGN

We recruited 51 pre-menopausal women (29 Caucasian and 22 of Hispanic origin) aged 18 to 49 years with initial plasma cholesterol concentrations ranging from 3.62 to 5.17 mmol/L. Using a cross-over research design, women were randomly allocated to an egg (640 mg additional dietary cholesterol per day) or placebo group (0 mg additional dietary cholesterol per day) initially, and the two 30 day periods were separated by a three-week washout.

RESULTS

An initial evaluation of the ethnicity effects revealed elevations in both plasma LDL-C (p < 0.0001) and HDL-C (p < 0.001) concentrations in both Hispanics and Caucasians during the high dietary cholesterol period. However, these increases were not accompanied by a change in the LDL/HDL ratio. Subjects were then classified as hypo- (< 0.05 mmol/L increase in total plasma cholesterol per each additional 100 mg of dietary cholesterol consumed per day) or hyper-responders (> or =0.06 mmol/L increase in total blood cholesterol per each additional 100 mg of dietary cholesterol consumed per day), based on their reaction to the additional dietary cholesterol provided. Hypo-responders did not experience an increase in LDL-C or HDL-C during the egg period, while both lipoproteins were elevated in hyper-responders. However, the LDL/HDL ratio, an important parameter of coronary heart disease risk, was maintained for all subjects during the egg period independent of response. Furthermore, hyper-responders had higher concentrations of apo C-III (p < 0.001), apo B (p < 0.001) and cholesterol ester transfer protein (CETP) (p < 0.05) during this period.

CONCLUSION

These data revealed that excess dietary cholesterol does not increase the risk of developing an atherogenic lipoprotein profile in pre-menopausal women, regardless of their response classification. Although the addition of 640 mg of cholesterol to the diet did result in an increase in plasma cholesterol in hyperresponders, the LDL/HDL ratio was maintained. This result, accompanied by increases in CETP activity, leads to the speculation that hyper-responders may process the excess cholesterol in the plasma compartment through an enhancement of the reverse cholesterol transport pathway. With this mechanism identified, further measurement of additional parameters is needed to verify this conclusion.

Apolipoprotein C-I expression in the brain in Alzheimer's disease

The H2 allele of apolipoprotein (apo) C-I is associated with Alzheimer's disease (AD). However, this association is potentially confounded by the linkage disequilibrium of H2 with the epsilon2 and epsilon4 alleles of apoE and of H1 with the epsilon3 allele. To establish plausibility for a direct role for apoC-I in AD, we compared apoC-I and apoE protein and mRNA levels in postmortem specimens of frontal cortex and hippocampus from AD patients with levels in nondemented controls. In H2-allelic individuals (usually also epsilon4 carriers), apoC-I mRNA levels were strikingly lower with AD (by 65%, P < 0.05), but apoC-I protein levels in AD were significantly higher (by 34%, P < 0.05). The opposite direction of the apoC-I mRNA and apoC-I protein level changes in AD in the epsilon4/H2 genotype may reflect decreased clearance of CNS lipoproteins associated with apoE4. In H1/H1 (usually epsilon3/epsilon3) individuals, both apoC-I protein and mRNA were lower in AD. ApoC-I protein levels in hippocampus were nearly twice those in frontal cortex. Immunohistochemistry of hippocampus revealed colocalization of apoC-I protein with the astrocytic marker GFAP. In addition, cultured human astrocytes expressed the mRNA for apoC-I. This study confirms apoC-I expression in the CNS and identifies astrocytes as the source of apoC-I. In addition, it has revealed differences in apoC-I expression based on site, genotype, and disease status that may reflect a role for apoC-I in the pathogenesis of AD.

Domains of apolipoprotein E contributing to triglyceride and cholesterol homeostasis in vivo. Carboxyl-terminal region 203-299 promotes hepatic very low density lipoprotein-triglyceride secretion

Apolipoprotein (apo) E has been implicated in cholesterol and triglyceride homeostasis in humans. At physiological concentration apoE promotes efficient clearance of apoE-containing lipoprotein remnants. However, high apoE plasma levels correlate with high plasma triglyceride levels. We have used adenovirus-mediated gene transfer in apoE-deficient mice (E(-)/-) to define the domains of apoE required for cholesterol and triglyceride homeostasis in vivo. A dose of 2 x 10(9) plaque-forming units of apoE4-expressing adenovirus reduced slightly the cholesterol levels of E(-)/- mice and resulted in severe hypertriglyceridemia, due to accumulation of cholesterol and triglyceride-rich very low density lipoprotein particles in plasma. In contrast, the truncated form apoE4-202 resulted in a 90% reduction in the plasma cholesterol levels but did not alter plasma triglyceride levels in the E(-)/- mice. ApoE secretion by cell cultures, as well as the steady-state hepatic mRNA levels in individual mice expressing apoE4 or apoE4-202, were similar. In contrast, very low density lipoprotein-triglyceride secretion in mice expressing apoE4, but not apoE4-202, was increased 10-fold, as compared with mice infected with a control adenovirus. The findings suggest that the amino-terminal 1-202 region of apoE4 contains the domains required for the in vivo clearance of lipoprotein remnants. Furthermore, the carboxyl-terminal 203-299 residues of apoE promote hepatic very low density lipoprotein-triglyceride secretion and contribute to apoE-induced hypertriglyceridemia.

Relation between RLP-triglyceride to RLP-cholesterol ratio and particle size distribution in RLP-cholesterol profiles by HPLC

Remnant-Like Particles (RLP) isolated by an immunoseparation method are heterogeneous in their physical and biochemical properties. The objective of this study was to examine the relation between RLP-triglyceride (RLP-TG) to RLP-cholesterol (RLP-C) ratio and particle size distribution in RLP-C profiles from patients with hyperlipoproteinemia by HPLC. RLP were isolated from serum samples from 147 subjects. RLP-C and RLP-TG were quantified by respective enzymatic methods. Particle sizes of the RLP were measured using HPLC with 4 connected TSKgel LipopropakXL columns. Based on HPLC profiles of RLP-C from individual subjects, three different types were classified: predominantly LDL, predominantly VLDL, and mostly VLDL types. All patients with type III hyperlipidemia were mostly VLDL type but with smaller particle size of VLDL (32 nm) than other subjects. Severe hypertriglyceridemic (TG>4.52 mmoll(-1)) subjects were mostly VLDL type with large particle size (41 nm). As for all subjects (n=105) without predominantly LDL type, a significant correlation between RLP particle size and RLP-TG to RLP-C ratio (r=0. 432, P<0.001) was obtained, but not in case of serum TG to RLP-C ratio (r=0.062). It suggests that RLP-TG to RLP-C ratio might be used for discrimination of atherogenic smaller-sized lipoprotein from larger-sized TG-rich lipoprotein remnants.