Protective effect of apolipoprotein E2 on coronary artery disease in African Americans is mediated through lipoprotein cholesterol

We studied the relationship of apolipoprotein E (apoE) isoforms and coronary artery disease (CAD) in 224 African Americans and 326 Caucasians undergoing diagnostic coronary angiography. The presence of CAD was defined as >50% stenosis in at least one artery. ApoE allele frequencies were 0.12, 0.62, and 0.26 for epsilon 2, epsilon 3, and epsilon 4, respectively, in African Americans and 0.08, 0.78, and 0.14 for epsilon 2, epsilon 3, and epsilon 4, respectively, in Caucasians. Among African Americans, CAD was present in 9 of 34 epsilon 2 carriers (26%), significantly smaller (P < 0.05) in proportion compared with 39 of 82 epsilon 3 carriers and 43 of 92 epsilon 4 carriers (48% and 47%, respectively), suggesting a protective effect of the epsilon 2 allele. No such difference was seen in Caucasians. In African Americans but not Caucasians, LDL cholesterol was lower in epsilon 2 carriers than in epsilon 3 and epsilon 4 carriers (106 vs. 127 and 134 mg/dl, respectively; P < 0.005). After adjusting for lipid levels, the association between apoE2 and CAD was no longer significant. Thus, the protective effect of apoE2 seen in African Americans could be explained by a favorable lipid profile in epsilon 2 carriers, whereas in Caucasians, the absence of such a protective effect could be attributable to the lack of effect of apoE2 on the lipid profile.     

Endogenous apoC-I increases hyperlipidemia in apoE-knockout mice by stimulating VLDL production and inhibiting LPL

Previous studies have shown that overexpression of human apolipoprotein C-I (apoC-I) results in moderate hypercholesterolemia and severe hypertriglyceridemia in mice in the presence and absence of apoE. We assessed whether physiological endogenous apoC-I levels are sufficient to modulate plasma lipid levels independently of effects of apoE on lipid metabolism by comparing apolipoprotein E gene-deficient/apolipoprotein C-I gene-deficient (apoe-/-apoc1-/-), apoe-/-apoc1+/-, and apoe-/-apoc1+/+ mice. The presence of the apoC-I gene-dose-dependently increased plasma cholesterol (+45%; P < 0.001) and triglycerides (TGs) (+137%; P < 0.001), both specific for VLDL. Whereas apoC-I did not affect intestinal [3H]TG absorption, it increased the production rate of hepatic VLDL-TG (+35%; P < 0.05) and VLDL-[35S]apoB (+39%; P < 0.01). In addition, apoC-I increased the postprandial TG response to an intragastric olive oil load (+120%; P < 0.05) and decreased the uptake of [3H]TG-derived FFAs from intravenously administered VLDL-like emulsion particles by gonadal and perirenal white adipose tissue (WAT) (-34% and -25%, respectively; P < 0.05). As LPL is the main enzyme involved in the clearance of TG-derived FFAs by WAT, and total postheparin plasma LPL levels were unaffected, these data demonstrate that endogenous apoC-I suffices to attenuate the lipolytic activity of LPL. Thus, we conclude that endogenous plasma apoC-I increases VLDL-total cholesterol and VLDL-TG dose-dependently in apoe-/- mice, resulting from increased VLDL particle production and LPL inhibition.     

ApoE genotype affects allele-specific apo[a] levels for large apo[a] sizes in African Americans: the Harlem-Basset Study

The genetic variability of apolipoprotein E (apoE) influences plasma lipoprotein levels, and allele frequencies differ between African Americans and Caucasians. As African Americans have higher lipoprotein [a] (Lp[a]) levels than Caucasians, we investigated the effects of the apoE gene on allele-specific apolipoprotein [a] (apo[a]) levels across ethnicity. We determined apo[a] sizes, allele-specific apo[a] levels (i.e., levels associated with alleles defined by size), and the apoE gene polymorphism in 231 African Americans and 336 Caucasians. African Americans, but not Caucasians, with the apo E2 genotype had lower levels of Lp[a] compared with those with the apo E4 genotype (9.6 vs. 11.2 nmol/l; P = 0.034, expressed as square root levels). Distribution of apo[a] alleles across apoE genotypes were similar between African Americans and Caucasians. Among African Americans with large apo[a], the allele-specific apo[a] level was significantly lower among epsilon2 carriers compared with epsilon3 or epsilon4 carriers (5.4 vs. 6.6 and 7.4 nmol/l, respectively; P < 0.005, expressed as square root levels). In contrast, there was no significant difference in allele-specific apo[a] levels across apoE genotypes among Caucasians. For large apo[a] sizes, apoE genotype contributed to the observed African American-Caucasian differences in allele-specific apo[a] levels.     

Effect of apolipoprotein E genotype on apolipoprotein B-100 metabolism in normolipidemic and hyperlipidemic subjects

The effect of apolipoprotein (apo) E genotype on apoB-100 metabolism was examined in three normolipidemic apoE2/E2, five type III hyperlipidemic apoE2/E2, and five hyperlipidemic apoE3/E2 subjects using simultaneous administration of ¹³¹I-VLDL and ¹²⁵I-LDL, and multi-compartmental modeling. Compared with normolipidemic apoE2/E2 subjects, type III hyperlipidemic E2/E2 subjects had increased plasma and VLDL cholesterol, plasma and VLDL triglycerides, and VLDL and intermediate density lipoprotein (IDL) apoB concentrations (P < 0.05). These abnormalities were chiefly a consequence of decreased VLDL and IDL apoB fractional catabolic rate (FCR). Compared with hyperlipidemic E3/E2 subjects, type III hyperlipidemic E2/E2 subjects had increased IDL apoB concentration and decreased conversion of IDL to LDL particles (P < 0.05). In a pooled analysis, VLDL cholesterol was positively associated with VLDL and IDL apoB concentrations and the proportion of VLDL apoB in the slowly turning over VLDL pool, and was negatively associated with VLDL apoB FCR after adjusting for subject group. VLDL triglyceride was positively associated with VLDL apoB concentration and VLDL and IDL apoB production rates after adjusting for subject group. A defective apoE contributes to altered lipoprotein metabolism but is not sufficient to cause overt hyperlipidemia. Additional genetic mutations and environmental factors, including insulin resistance and obesity, may contribute to the development of type III hyperlipidemia.     

Antisense inhibition of apoB synthesis with mipomersen reduces plasma apoC-III and apoC-III-containing lipoproteins

Mipomersen, an antisense oligonucleotide that reduces hepatic production of apoB, has been shown in phase 2 studies to decrease plasma apoB, LDL cholesterol (LDL-C), and triglycerides. ApoC-III inhibits VLDL and LDL clearance, and it stimulates inflammatory responses in vascular cells. Concentrations of VLDL or LDL with apoC-III independently predict cardiovascular disease. We performed an exploratory posthoc analysis on a subset of hypercholesterolemic subjects obtained from a randomized controlled dose-ranging phase 2 study of mipomersen receiving 100, 200, or 300 mg/wk, or placebo for 13 wk (n = 8 each). ApoC-III-containing lipoproteins were isolated by immuno-affinity chromatography and ultracentrifugation. Mipomersen 200 and 300 mg/wk reduced total apoC-III from baseline by 6 mg/dl (38-42%) compared with placebo group (P < 0.01), and it reduced apoC-III in both apoB lipoproteins and HDL. Mipomersen 100, 200, and 300 mg doses reduced apoB concentration of LDL with apoC-III (27%, 38%, and 46%; P < 0.05). Mipomersen reduced apoC-III concentration in HDL. The drug had no effect on apoE concentration in total plasma and in apoB lipoproteins. In summary, antisense inhibition of apoB synthesis reduced plasma concentrations of apoC-III and apoC-III-containing lipoproteins. Lower concentrations of apoC-III and LDL with apoC-III are associated with reduced risk of coronary heart disease (CHD) in epidemiologic studies independent of traditional risk factors.     

Sialic acid content of low density lipoprotein and its relation to lipid concentrations and metabolism of low density lipoprotein and cholesterol

A low sialic acid content in low density lipoprotein (LDL) has been associated with atherogenicity and coronary artery disease (CAD) in many but not all studies. We investigated associations of the sialic acid-to-apolipoprotein B (apoB) ratio of LDL with lipoprotein lipid concentrations, kinetics of LDL, metabolism of cholesterol, and the presence of CAD in 98 subjects (CAD(+), n = 56; CAD(-), n = 42). The sialic acid ratios of total, dense, and very dense LDL were lower in the CAD(+) than CAD(-) subjects, especially at high sialic acid ratios. The LDL sialic acid ratio was inversely associated with respective lipid and apoB concentrations and positively with lipid-to-apoB ratios of LDL. The transport rates (TRs) for total and dense LDL apoB were negatively associated with their sialic acid ratios. The sialic acid ratio of dense LDL, but not that of total LDL, was inversely correlated with serum levels of cholesterol precursor sterols, indicators of cholesterol synthesis, and positively with serum levels of plant sterols, indicators of cholesterol absorption. In addition, the TR for dense LDL was positively correlated with cholesterol synthesis.In conclusion, a low LDL sialic acid ratio was associated with CAD, high numbers of small LDL particles, and a high TR for LDL apoB, and in dense LDL also with high synthesis and low absorption of cholesterol.     

Attenuated Age-Impact on Systemic Inflammatory Markers in the Presence of a Metabolic Burden

BackgroundThe overall burden of chronic disease, inflammation and cardiovascular risk increases with age. Whether the relationship between age and inflammation is impacted by presence of an adverse metabolic burden is not known.MethodsWe determined inflammatory markers in humans (336 Caucasians and 224 African Americans) and in mice, representing a spectrum of age, weight and metabolic burden.ResultsIn humans, levels of inflammatory markers increased significantly with age in subjects without the metabolic syndrome, (P=0.009 and P=0.037 for C-reactive protein, P<0.001 and P=0.001 for fibrinogen, P<0.001 and P=0.005 for serum amyloid-A, for Caucasians and African Americans, respectively). In contrast, trend patterns of inflammatory markers did not change significantly with age in subjects with metabolic syndrome in either ethnic group, except for fibrinogen in Caucasians. A composite z-score for systemic inflammation increased significantly with age in subjects without metabolic syndrome (P=0.004 and P<0.006 for Caucasians and African Americans, respectively) but not in subjects with metabolic syndrome (P=0.009 for difference in age trend between metabolic syndrome and non-metabolic syndrome). In contrast, no similar age trend was found in vascular inflammation. The findings in humans were paralleled by results in mice as serum amyloid-A levels increased across age (range 2-15 months, P<0.01) and were higher in ob/ob mice compared to control mice (P<0.001).ConclusionsPresence of a metabolic challenge in mice and humans influences levels of inflammatory markers over a wide age range. Our results underscore that already at a young age, presence of a metabolic burden enhances inflammation to a level that appears to be similar to that of decades older people without metabolic syndrome.     

Scavenger receptor BI facilitates hepatic very low density lipoprotein production in mice

Scavenger receptor BI (SR-BI) is a selective uptake receptor for HDL cholesterol but is also involved in the catabolism of apolipoprotein (apo)B-containing lipoproteins. However, plasma levels of apoB-containing lipoproteins increase following hepatic SR-BI overexpression, suggesting that SR-BI not solely mediates their catabolism. We therefore tested the hypothesis that hepatic SR-BI impacts on VLDL production. On day 7 following adenovirus (Ad)-mediated overexpression of SR-BI, VLDL-triglyceride and VLDL-apoB production rates were significantly increased (P < 0.001), whereas VLDL production was significantly lower in SR-BI knockout mice compared with controls (P < 0.05). In mice injected with AdSR-BI, hepatic cholesterol content increased (P < 0.001), microsomal triglyceride transfer protein activity was higher (P < 0.01) and expression of sterol-regulatory element binding protein (SREBP)2 and its target genes was decreased (P < 0.01). Conversely, in SR-BI knockout mice, microsomal triglyceride transfer protein activity was lower and expression of SREBP2 target genes was increased (P < 0.01). Finally, we demonstrate in vitro in isolated primary hepatocytes as well as in vivo that cholesterol derived from HDL and taken up via SR-BI into the liver can be resecreted within VLDL. These data indicate that hepatic SR-BI expression is linked to VLDL production, and within liver, a metabolic shunt might exist that delivers HDL cholesterol, at least in part, to a pool from which cholesterol is mobilized for VLDL production. These results might have implications for HDL-based therapies against atherosclerotic cardiovascular disease, especially with SR-BI as target.     

Apolipoprotein E polymorphism in Omani dyslipidemic patients with and without coronary artery disease

Apolipoprotein E (APOE) polymorphism is a predictor of interindividual variability in plasma levels of lipids and lipoproteins and a predictor of risk of coronary artery disease (CAD). We studied the relationship between APOE polymorphism and lipid profiles and risk of CAD in Omani dyslipidemic patients. This retrospective study included 244 dyslipidemic patients, of whom 67 had CAD. Fasting blood glucose, lipids, and plasma lipoprotein levels were measured using standard methods, and APOE genotypes were detected by PCR-RFLP. The dyslipidemic patients had the following APOE allele frequencies: APOE*2, 0.030; APOE*3, 0.894; and APOE*4, 0.076. APOE allele frequencies between patients with and without CAD showed no significant differences. Compared to APOE*3/*3 homozygotes, APOE*4 allele patients had higher mean levels of low-density lipoprotein (LDL) cholesterol (p = 0.014), apoB (p = 0.031), lower mean levels of apoA1 (p = 0.043), and a trend of higher mean level of total cholesterol (p = 0.084). Thirty-one percent of patients with CAD had the APOE*4 allele compared to 26% with the APOE*3 allele, but this difference was not significant. Compared with APOE*3/*3 homozygotes, patients with the APOE*4 allele had 1.3 times higher risk for CAD after ignoring dyslipidemia, but this risk was modified after adjusting for dyslipidemia. In conclusion, among dyslipidemic patients, carriers of APOE*4 compared to homozygous carriers of APOE*3 had significantly higher levels of LDL cholesterol and apoB, but no relationship with CAD was found.     

Rapid turnover of apolipoprotein C-III-containing triglyceride-rich lipoproteins contributing to the formation of LDL subfractions

The atherogenicity theory for triglyceride-rich lipoproteins (TRLs; VLDL + intermediate density lipoprotein) generally cites the action of apolipoprotein C-III (apoC-III), a component of some TRLs, to retard their metabolism in plasma. We studied the kinetics of multiple TRL and LDL subfractions according to the content of apoC-III and apoE in 11 hypertriglyceridemic and normolipidemic persons. The liver secretes mainly two types of apoB lipoproteins: TRL with apoC-III and LDL without apoC-III. Approximately 45% of TRLs with apoC-III are secreted together with apoE. Contrary to expectation, TRLs with apoC-III but not apoE have fast catabolism, losing some or all of their apoC-III and becoming LDL. In contrast, apoE directs TRL flux toward rapid clearance, limiting LDL formation. Direct clearance of TRL with apoC-III is suppressed among particles also containing apoE. TRLs without apoC-III or apoE are a minor, slow-metabolizing precursor of LDL with little direct removal. Increased VLDL apoC-III levels are correlated with increased VLDL production rather than with slow particle turnover. Finally, hypertriglyceridemic subjects have significantly greater production of apoC-III-containing VLDL and global prolongation in residence time of all particle types. ApoE may be the key determinant of the metabolic fate of atherogenic apoC-III-containing TRLs in plasma, channeling them toward removal from the circulation and reducing the formation of LDLs, both those with apoC-III and the main type without apoC-III.     

Reduced Apolipoprotein Glycosylation in Patients with the Metabolic Syndrome

Objective

The purpose of this study was to compare the apolipoprotein composition of the three major lipoprotein classes in patients with metabolic syndrome to healthy controls.

Methods

Very low density (VLDL), intermediate/low density (IDL/LDL, hereafter LDL), and high density lipoproteins (HDL) fractions were isolated from plasma of 56 metabolic syndrome subjects and from 14 age-sex matched healthy volunteers. The apolipoprotein content of fractions was analyzed by one-dimensional (1D) gel electrophoresis with confirmation by a combination of mass spectrometry and biochemical assays.

Results

Metabolic syndrome patients differed from healthy controls in the following ways: (1) total plasma - apoA1 was lower, whereas apoB, apoC2, apoC3, and apoE were higher; (2) VLDL - apoB, apoC3, and apoE were increased; (3) LDL - apoC3 was increased, (4) HDL -associated constitutive serum amyloid A protein (SAA4) was reduced (p<0.05 vs. controls for all). In patients with metabolic syndrome, the most extensively glycosylated (di-sialylated) isoform of apoC3 was reduced in VLDL, LDL, and HDL fractions by 17%, 30%, and 25%, respectively (p<0.01 vs. controls for all). Similarly, the glycosylated isoform of apoE was reduced in VLDL, LDL, and HDL fractions by 15%, 26%, and 37% (p<0.01 vs. controls for all). Finally, glycosylated isoform of SAA4 in HDL fraction was 42% lower in patients with metabolic syndrome compared with controls (p<0.001).

Conclusions

Patients with metabolic syndrome displayed several changes in plasma apolipoprotein composition consistent with hypertriglyceridemia and low HDL cholesterol levels. Reduced glycosylation of apoC3, apoE and SAA4 are novel findings, the pathophysiological consequences of which remain to be determined.     

LDL-apheresis depletes apoE-HDL and pre-β1-HDL in familial hypercholesterolemia: relevance to atheroprotection

Subnormal HDL-cholesterol (HDL-C) and apolipoprotein (apo)AI levels are characteristic of familial hypercholesterolemia (FH), reflecting perturbed intravascular metabolism with compositional anomalies in HDL particles, including apoE enrichment. Does LDL-apheresis, which reduces HDL-cholesterol, apoAI, and apoE by adsorption, induce selective changes in HDL subpopulations, with relevance to atheroprotection? Five HDL subpopulations were fractionated from pre- and post-LDL-apheresis plasmas of normotriglyceridemic FH subjects (n = 11) on regular LDL-apheresis (>2 years). Apheresis lowered both plasma apoE (−62%) and apoAI (−16%) levels, with preferential, genotype-independent reduction in apoE. The mass ratio of HDL2:HDL3 was lowered from ∼1:1 to 0.72:1 by apheresis, reflecting selective removal of HDL2 mass (80% of total HDL adsorbed). Pre-LDL-apheresis, HDL2 subpopulations were markedly enriched in apoE, consistent with ∼1 copy of apoE per 4 HDL particles. Large amounts (50-66%) of apoE-HDL were removed by apheresis, preferentially in the HDL2b subfraction (−50%); minor absolute amounts of apoE-HDL were removed from HDL3 subfractions. Furthermore, pre-β1-HDL particle levels were subnormal following removal (−53%) upon apheresis, suggesting that cellular cholesterol efflux may be defective in the immediate postapheresis period. In LDL-receptor (LDL-R) deficiency, LDL-apheresis may enhance flux through the reverse cholesterol transport pathway and equally attenuate potential biglycan-mediated deposition of apoE-HDL in the arterial matrix.     

The ethnicity-specific association of biomarkers with the angiographic severity of coronary artery disease

Background

Risk factor burden and clinical characteristics of patients with coronary artery disease (CAD) differ among ethnic groups. We related biomarkers to CAD severity in Caucasians, Chinese, Indians and Malays.

Methods

In the Dutch-Singaporean UNICORN coronary angiography cohort (n = 2033) we compared levels of five cardiovascular biomarkers: N-terminal pro-brain natriuretic peptide (NTproBNP), high-sensitivity C-reactive protein (hsCRP), cystatin C (CysC), myeloperoxidase (MPO) and high-sensitivity troponin I (hsTnI). We assessed ethnicity-specific associations of biomarkers with CAD severity, quantified by the SYNTAX score.

Results

Adjusted for baseline differences, NTproBNP levels were significantly higher in Malays than in Chinese and Caucasians (72.1 vs. 34.4 and 41.1 pmol/l, p < 0.001 and p = 0.005, respectively). MPO levels were higher in Caucasians than in Indians (32.8 vs. 27.2 ng/ml, p = 0.026), hsTnI levels were higher in Malays than in Caucasians and Indians (33.3 vs. 16.4 and 17.8 ng/l, p < 0.001 and p = 0.029) and hsTnI levels were higher in Chinese than in Caucasians (23.3 vs. 16.4, p = 0.031). We found modifying effects of ethnicity on the association of biomarkers with SYNTAX score. NTproBNP associated more strongly with the SYNTAX score in Malays than Caucasians (β 0.132 vs. β 0.020 per 100 pmol/l increase in NTproBNP, p = 0.032). For MPO levels the association was stronger in Malays than Caucasians (β 1.146 vs. β 0.016 per 10 ng/ml increase, p = 0.017). Differing biomarker cut-off levels were found for the ethnic groups.

Conclusion

When corrected for possible confounders we observe ethnicity-specific differences in biomarker levels. Moreover, biomarkers associated differently with CAD severity, suggesting that ethnicity-specific cut-off values should be considered.     

A novel method for oral delivery of apolipoprotein mimetic peptides synthesized from all L-amino acids

Administered subcutaneously, D-4F or L-4F are equally efficacious, but only D-4F is orally efficacious because of digestion of L-4F by gut proteases. Orally administering niclosamide (a chlorinated salicylanilide used as a molluscicide, antihelminthic, and lampricide) in temporal proximity to oral L-4F (but not niclosamide alone) in apoE null mice resulted in significant improvement (P < 0.001) in the HDL-inflammatory index (HII), which measures the ability of HDL to inhibit LDL-induced monocyte chemotactic activity in endothelial cell cultures. Oral administration of L-[113-122]apoJ with niclosamide also resulted in significant improvement (P < 0.001) in HII. Oral administration of niclosamide and L-4F together with pravastatin to female apoE null mice at 9.5 months of age for six months significantly reduced aortic sinus lesion area (P = 0.02), en face lesion area (P = 0.033), and macrophage lesion area (P = 0.02) compared with pretreatment, indicating lesion regression. In contrast, lesions were significantly larger in mice receiving only niclosamide and pravastatin or L-4F and pravastatin (P < 0.001). In vitro niclosamide and L-4F tightly associated rendering the peptide resistant to trypsin digestion. Niclosamide itself did not inhibit trypsin activity. The combination of niclosamide with apolipoprotein mimetic peptides appears to be a promising method for oral delivery of these peptides.     

Augmented atherogenesis in LDL receptor deficient mice lacking both macrophage ABCA1 and ApoE

Aim

ABCA1 protects against atherosclerosis by facilitating cholesterol efflux from macrophage foam cells in the arterial wall to extracellular apolipoprotein (apo) A-I. In contrast to apoA-I, apoE is secreted by macrophages and can, like apoA-I, induce ABCA1-mediated cholesterol efflux. Yet, the combined effect of macrophage ABCA1 and apoE on lesion development is unexplored.

Methods and Results

LDL receptor knockout (KO) mice were transplanted with bone marrow from ABCA1/apoE double KO (dKO) mice, their respective single KO''s, and wild-type (WT) controls and were challenged with a high-fat/high-cholesterol diet for 9 weeks. In vitro cholesterol efflux experiments showed no differences between ABCA1 KO and dKO macrophages. The serum non-HDL/HDL ratio in dKO transplanted mice was 1.7-fold and 2.4-fold (p<0.01) increased compared to WT and ABCA1 KO transplanted mice, respectively. The atherosclerotic lesion area in dKO transplanted animals (650±94×10³ µm²), however, was 1.9-fold (p<0.01) and 1.6-fold (p<0.01) increased compared to single knockouts (ABCA1 KO: 341±20×10³ µm²; apoE KO: 402±78×10³ µm², respectively) and 3.1-fold increased (p<0.001) compared to WT (211±20×10³ µm²). When normalized for serum cholesterol exposure, macrophage ABCA1 and apoE independently protected against atherosclerotic lesion development (p<0.001). Moreover, hepatic expression levels of TNFα and IL-6 were highly induced in dKO transplanted animals (3.0-fold; p<0.05, and 4.3-fold; p<0.001, respectively). In agreement, serum IL-6 levels were also enhanced in ABCA1 KO transplanted mice (p<0.05) and even further enhanced in dKO transplanted animals (3.1-fold as compared to ABCA1 KO transplanted animals; p<0.05).

Conclusions

Combined deletion of macrophage ABCA1 and apoE results in a defect in cholesterol efflux and, compared to ABCA1 KO transplanted mice, elevated serum total cholesterol levels. Importantly, these mice also suffer from enhanced systemic and hepatic inflammation, together resulting in the observed augmented atherosclerotic lesion development.     

Changes in lipoprotein(a), oxidized phospholipids, and LDL subclasses with a low-fat high-carbohydrate diet

Low-fat diets have been shown to increase plasma concentrations of lipoprotein(a) [Lp(a)], a preferential lipoprotein carrier of oxidized phospholipids (OxPLs) in plasma, as well as small dense LDL particles. We sought to determine whether increases in plasma Lp(a) induced by a low-fat high-carbohydrate (LFHC) diet are related to changes in OxPL and LDL subclasses. We studied 63 healthy subjects after 4 weeks of consuming, in random order, a high-fat low-carbohydrate (HFLC) diet and a LFHC diet. Plasma concentrations of Lp(a) (P < 0.01), OxPL/apolipoprotein (apo)B (P < 0.005), and OxPL-apo(a) (P < 0.05) were significantly higher on the LFHC diet compared with the HFLC diet whereas LDL peak particle size was significantly smaller (P < 0.0001). Diet-induced changes in Lp(a) were strongly correlated with changes in OxPL/apoB (P < 0.0001). The increases in plasma Lp(a) levels after the LFHC diet were also correlated with decreases in medium LDL particles (P < 0.01) and increases in very small LDL particles (P < 0.05). These results demonstrate that induction of increased levels of Lp(a) by an LFHC diet is associated with increases in OxPLs and with changes in LDL subclass distribution that may reflect altered metabolism of Lp(a) particles.     

Immuno-electron cryo-microscopy imaging reveals a looped topology of apoB at the surface of human LDL

A single copy of apoB is the sole protein component of human LDL. ApoB is crucial for LDL particle stabilization and is the ligand for LDL receptor, through which cholesterol is delivered to cells. Dysregulation of the pathways of LDL metabolism is well documented in the pathophysiology of atherosclerosis. However, an understanding of the structure of LDL and apoB underlying these biological processes remains limited. In this study, we derived a 22 Å-resolution three-dimensional (3D) density map of LDL using cryo-electron microscopy and image reconstruction, which showed a backbone of high-density regions that encircle the LDL particle. Additional high-density belts complemented this backbone high density to enclose the edge of the LDL particle. Image reconstructions of monoclonal antibody-labeled LDL located six epitopes in five putative domains of apoB in 3D. Epitopes in the LDL receptor binding domain were located on one side of the LDL particle, and epitopes in the N-terminal and C-terminal domains of apoB were in close proximity at the front side of the particle. Such image information revealed a looped topology of apoB on the LDL surface and demonstrated the active role of apoB in maintaining the shape of the LDL particle.