Distribution of apolipoprotein E between apo B- and non apo B-containing lipoproteins according to apo E phenotype

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 levels and apolipoprotein E genotypes in incident cardiovascular disease risk in subjects of the Prevention of Renal and Vascular End-stage disease study

BACKGROUND

Apolipoprotein E (apoE) is a component of all major lipoprotein classes with multiple functions including clearance of circulating triglyceride-rich lipoprotein particles and hepatic production of triglyceride-rich lipoprotein, thus affording several avenues for apoE involvement in atherosclerosis development. ApoE has 3 isoforms (E2, E3, and E4) based on a common genetic polymorphism. Numerous studies have been performed assessing cardiovascular disease (CVD) risk relative to the 6 resulting genotypes; however, surprisingly, few studies have been performed assessing risk attributable to apoE plasma levels either alone or in addition also taking into account apoE genotypes.

OBJECTIVE

To examine the role of apoE levels together with apoE genotypes on incident CVD risk in a large population-based cohort and also to afford preliminary characterization of atherogenic apoE-containing lipoprotein particles.

METHODS

Cox multivariable proportional hazards modeling was performed on a cohort of the Prevention of Renal and Vascular End-Stage Disease (PREVEND) study as a function of apoE levels and apoE genotypes adjusted for age, gender, and past history of CVD. Further modeling was performed with single addition of clinical and biomarker parameters to elucidate the nature of apoE-associated risk.

RESULTS

High apoE levels were demonstrated to be associated with CVD risk (hazard ratio per apoE standard deviation, 1.20; 95% confidence interval, 1.11-1.31; P < .0001) both overall and within the high-frequency apoE genotype groups (ε2ε3, ε3ε3, and ε3ε4). Only on addition of apoB-containing lipoprotein parameters to models, did apoE levels lose association with risk.

CONCLUSIONS

ApoE levels positively associate with incident CVD risk with apoE-associated risk likely residing in apoB-containing lipoproteins.

Apolipoprotein E genotype and plasma lipid levels in Caucasian diabetic patients

OBJECTIVE

Apo E polymorphism has been shown to affect lipid profiles in non-diabetic and diabetic populations. We evaluated the relationship between Apo E phenotype and fasting lipid plasma levels in type 2 diabetes patients.

METHODS

Two hundred and ten French type 2 diabetic patients (115 men and 95 women) without any lipid lowering drugs were studied. Fasting lipids were measured by usual methods and Apo E genotype was established for each patient: PCR was followed by digestion of the amplification product with restriction enzymes and separation of the fragments by polyacrylamide gel.

RESULTS

Genotypes epsilon3/epsilon3, epsilon2/epsilon3 and epsilon3/epsilon4, epsilon2/epsilon2 and epsilon2/epsilon4 were found in 68.1%, 14.8%, 15.7%, 1.0% and 0.5%, respectively. No patient had the epsilon4/epsilon4 genotype. Lipid plasma levels were compared between E3 group (epsilon3/epsilon3) as a reference and E2 (epsilon2/epsilon2 or epsilon2/epsilon3) or E4 (epsilon3/epsilon4 or epsilon2/epsilon4). Total cholesterol, LDL cholesterol and Apo B levels were lower in the E2 group. Total cholesterol, LDL cholesterol and Apo B levels were higher in the E4 group. HDL cholesterol levels were increased in the E4 group, as only previously observed in Japanese populations.

CONCLUSION

These results agree with those already reported in diabetic patients of several western European countries. E4 allele carriers have a greater cardio-vascular risk and this could be partially explained by the metabolic variation in lipid metabolism induced by E4 with higher LDL cholesterol and Apo B levels. These results observed in French diabetic subjects without any lipid-lowering drugs may be used as a reference for other studies performed in France.

The lipoprotein lipase S447X polymorphism and plasma lipids

We studied 4,058 subjects from a representative sample of the Singapore population 1) to determine the association between the S447X polymorphism at the LPL locus and serum lipid concentration in Chinese, Malays, and Asian Indians living in Singapore and 2) to explore any interactions with apolipoprotein E (APOE) genotype, exercise, obesity, cigarette smoking, and alcohol intake. Information on obesity, lifestyle factors (including smoking, alcohol consumption, and exercise frequency), glucose tolerance, and fasting lipids was obtained. Male and female carriers of the X447 allele had lower serum triglyceride concentrations and higher HDL cholesterol (HDL-C) concentrations. The association between the X447 allele and serum HDL-C concentration was modulated by APOE genotype in males and cigarette smoking and alcohol intake in females. The effect of the X447 allele was greatest in men who carried the E4 allele and women who smoked or consumed alcohol. The X447 allele at the LPL locus is common and associated with a less atherogenic lipid profile in Asian populations. Interactions with APOE genotype, cigarette smoking, and alcohol intake reinforce the importance of examining genetic associations, such as this one, in the context of the population of interest.

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.

Is age-related macular degeneration associated with serum lipoprotein and lipoparticle levels?

OBJECTIVE

The etiology of age-related macular degeneration (ARMD) is poorly understood. Risk factors for cardiovascular disease have been thought to be associated with ARMD. Our purpose was to measure the concentration of atherogenic apolipoproteins (apo) and lipoparticles in serum from ARMD patients.

METHODS

We analyzed lipids, lipoparticles and apolipoproteins concentrations in 84 unrelated patients with ARMD and compared the results with those of age- and sex-matched control subjects (n=62). Serum lipid concentrations were determined enzymatically; apolipoproteins levels by kinetic nephelometry and lipoparticles by electroimmunodiffusion.

RESULTS

No difference in total cholesterol, triglycerides, phospholipids, high- and low-density lipoprotein-cholesterol (lHDL-C and LDL-C) concentrations were observed between ARMD patients and controls. Apo E and LpE non-B concentrations were found to be higher in serum from patients than in serum from controls. In contrast, Apo C-III and LpC-III non-B concentrations were lower in serum from patients than in serum from controls.

CONCLUSIONS

The main differences observed between ARMD patients and controls are in Apo E, Apo C-III, LpC-III non-B and LpE non-B concentrations. These lipoparticles belong to the HDL family, which is considered to consist of anti-atherogenic lipoproteins. These results raise the possibility that cardiovascular risk factors are not associated with ARMD. Furthermore, we can hypothesize that ARMD development is linked to perturbations of HDL metabolism.

Apolipoprotein E in Apolipoprotein B (apo B)- and Non-apo B-containing Lipoproteins in 3523 Participants in the Stanislas Cohort: Biological Variation and Genotype-specific Reference Limits

Background: Apolipoprotein (apo) E is a component of two major classes of plasma lipoproteins, apo B- (apo E-LpB) and non-apo B-containing (apo E-Lp-non-B) lipoproteins. The factors that affect total apo E in particles [lipoprotein E (LpE), apo E-Lp-non-B, and apo E-LpB], are incompletely characterized.

Methods: We studied the determinants of these lipoparticles in a sample population of presumably healthy individuals: 1784 children (age range, 8–18 years) and 1739 adults (age range, 19–50 years). Serum concentrations of LpE and apo E-Lp-non-B were measured by electroimmunoassays, and the concentration of apo E-LpB was calculated by a difference method.

Results: Serum LpE and apo E-Lp-non-B were higher in females than in males. Their concentrations decreased with age until 20–25 years and then increased in men but not in women. apo E-LpB concentrations increased up to 20–25 years and were similar in both sexes. Thereafter, adult men had higher values than women. Individuals carrying the ε2 allele had higher mean apo E-Lp-non-B concentrations and lower apo E-LpB concentrations than did individuals carrying the ε3 allele. Individuals with the ε4 allele showed an inverse profile compared with those with the ε2 allele. Age, gender, the common apo E polymorphism, puberty, serum lipid concentrations, and alcohol consumption were significantly associated with total LpE, apo E-Lp-non-B, and apo E-LpB concentrations. Reference limits were established according to age, gender, and the common apo E polymorphism.

Conclusions: Because measurements of LpE, apo E-Lp-non-B, and apo E-LpB concentrations may improve cardiovascular risk assessment, the proposed reference limits will aid interpretation of the results in clinical or therapeutic trials.

Apolipoproteins E and C-III in apo B- and non-apo B-containing lipoproteins in middle-aged women from the Stanislas cohort: effect of oral contraceptive use and common apolipoprotein E polymorphism

Oral contraceptive (OC) use and common apo E polymorphism are well known to modify serum lipid and lipoprotein concentrations. The combined effect of OC use and apo E genotype on the concentration of apo E or apo C-III in apo B- (apo E-LpB or apo C-III-LpB) or in non-apo B-containing lipoparticles (apo E-Lp-non-B or apo C-III-Lp-non-B) are unknown. Our study comprised 613 women, aged 30-45 years, genotyped for common apo E polymorphism and who differed in their combined low-dose OC consumption. The concentrations of apo C-III, apo C-III-LpB and apo C-III-Lp-non-B were significantly higher in OC users than in non-users by 13, 23 and 8% respectively, without significant interaction with the apo E genotype. The concentrations of apo E and apo E-Lp-non-B were significantly lower (differences being -14% and -31% respectively) in OC users than in controls whereas the apo E-LpB concentration was significantly higher (+19%), resulting in a redistribution of apo E from Lp-non-B towards LpB. Total apo E and apo E-Lp-non-B concentrations were higher in subjects carrying the epsilon2 allele and lower in those with the epsilon4 allele when compared to epsilon3/epsilon3 subjects (P < 0.001). The opposite held for the apo E- LpB concentration (P < 0.05). The main finding is the significant interaction between apo E genotype and OC use (P < 0.01) on apo E-Lp-non-B concentration, the epsilon4 carriers showing the smallest differences between OC users and non-users in comparison with the epsilon2 or epsilon3/epsilon3 carriers. These results suggest that the common apo E polymorphism can modulate the OC use effect.

Apolipoprotein E and apolipoprotein D expression in a murine model of singlet oxygen-induced cerebral stroke

Apolipoprotein E (apoE)-deficient mice exhibit neuronal abnormalities similar to those in Alzheimer's disease and enhanced sensitivity to stroke-associated injuries. Here, we show that apoE deficiency results in impaired microglia/macrophage recruitment and accumulation after cerebral infarct. Astrogliosis and apolipoprotein D (apoD) expression are unaffected, suggesting that the neurological abnormalities of apoE-deficient mice could be due to impaired microglia/macrophage recruitment/accumulation, which is important for the clearance of neurodegenerative products via reverse cholesterol transport. To our knowledge, the results presented herein provide the first experimental evidence that brain microglia/macrophage recruitment/accumulation is affected by apoE deficiency. The insights gained from this study should facilitate the elucidation of the role of apoE in neurological disorders such as dementia with stroke and Alzheimer's disease.

Independent effects of Apo E phenotype and plasma triglyceride on lipoprotein particle sizes in the fasting and postprandial states

LDL particle sizes and Apo E phenotypes were determined in 212 subjects of whom 51 had angina. LDL diameter was significantly less in subjects with an epsilon2 allele (24.76+/-0.08 vs 24.94+/-0.02 nm, P=0.02), and this was evident for both E2/E3 (24.77+/-0.09 nm) and E2/E4 (24.69+/-0.08 nm) phenotypes. Although there was a negative relation between LDL diameter and plasma triglyceride, the effect of apo E2 was still evident with adjustment for triglyceride. In multiple regression analysis, the significant determinants of LDL diameter were gender (with females having larger particles than males), body mass index, and the presence (or absence) of E2. HDL particle sizes and compositions were determined on fasting samples and, additionally, 5 and 8 hours after a fat-rich meal for 48 coronary heart disease cases and 49 control subjects. Fasting HDL particle sizes were not related to the presence of E2 but were significantly smaller for subjects possessing an epsilon4 allele (8. 09+/-0.08 vs 8.39+/-0.05 nm, P=0.003) and were negatively related to plasma triglyceride. However, the effect of E4 persisted after adjustment for triglyceride. In a multiple regression analysis, the only significant determinant of fasting HDL diameter was the presence (or absence) of E4 with fasting plasma triglyceride just failing to reach significance (P=0.06). There was a postprandial increase in HDL diameter that was less marked in subjects with coronary heart disease. The postprandial increase in HDL diameter was of sufficient magnitude to result in size reclassification of HDL particles. The influence of E4 was also evident at both postprandial time points. Compositional analysis demonstrated that the increase in HDL diameters postprandially could be attributed to triglyceride enrichment, with an accompanying fall in cholesterol ester content. Phospholipid changes postprandially were biphasic with an initial fall followed by a rise in concentration. The increase in triglyceride content was significantly less in those subjects with angina despite an equivalent rise in plasma triglyceride. The present study demonstrates significant, but different, effects of variation in apo E phenotype on the particle sizes of both HDL and LDL. Such effects were still evident with adjustment for differences in plasma triglyceride and suggests that variation in apo E phenotype exerts effects on lipoprotein particle sizes by mechanisms additional to those dependent on change in plasma triglyceride.

Apolipoprotein E polymorphism and the distribution profile of very low density lipoproteins; an influence of the E4 allele on large (Sf > 60) particles

Very low density lipoprotein (VLDL) distribution and composition have been examined as a function of apo E genotype (E2/2 + E2/3 vs. E3/3 vs. E3/4 + E4/4) in healthy, normolipaemic subjects. Apo E genotype had a marked impact on plasma concentrations of apo E rich VLDL, but no influence on concentrations of apo E free particles. Thus, there was a trend to lower concentrations of apo E rich total VLDL in apo E4 carriers (mg/dl; E2, 49.1 +/- 35.2; E3, 52.5 +/- 30.9; E4 35.2 +/- 22.3; ANOVA P = 0.16; when comparing E4 with E2 + E3, P = 0.06). Consequently, there were highly significant differences between apo E-defined subgroups in terms of the percentage distribution of bound and non-bound fractions (% total VLDL non-bound to apo E: E2, 44.0 +/- 12.7%; E3, 39.7 +/- 8.7%; E4 51.0 +/- 12.2%; ANOVA P = 0.007). Subfractionation of VLDL into density subclasses revealed that genotype differences were restricted to large VLDL (Sf > 60). Significantly lower concentrations of apo E-rich particles were observed in E4 carriers for VLDL-1 Sf 400-100 (ANOVA P = 0.004) and VLDL-2 (P = 0.009) but not for small VLDL-3 Sf 60-20 (P = 0.34). No differences in plasma concentrations of apo E free VLDL were observed between genotype subclasses across the density spectrum. Compositional differences between the apo E defined VLDL were also evident for the core lipids. Apo E containing VLDL was enriched in esterified cholesterol and depleted in triglycerides compared to apo E poor VLDL: the difference became more marked with increasing density of the particles. Lipoprotein composition was not modulated to any great extent by apo E genotype. In patients with familial hypercholesterolaemia, relative concentrations of apo E rich, large VLDL were significantly higher than in controls. Treatment lowered concentrations of both apo E rich and apo E free VLDL but led to a greater relative enrichment of large VLDL in apo E containing particles. Apo E polymorphism appears to influence plasma concentrations of VLDL particles. The data are consistent with more pronounced receptor-mediated elimination of apo E4 containing VLDL. This may be a contributory factor to the down regulation of receptor activity which is suggested to be of major importance in provoking higher cholesterol levels associated with the apo E4 isoform.