Low Density Lipoprotein apoB Research Articles

Changes in Apolipoprotein B100-Containing Lipoprotein Metabolism Due to an Estrogen Plus Progestin Oral Contraceptive: A Stable Isotope Kinetic Study

Oral contraceptives with estrogen plus progestin are likely to influence apolipoprotein B (apoB)-containing lipoprotein metabolism by changing the expression of different enzymes or receptors that play a major role in this metabolism. However, the precise changes in apoB kinetic parameters induced by oral contraceptives that are now currently used are unknown. We studied the impact of Moneva, containing 30 microg ethinylestradiol and 75 microg gestodene, on the apoB production rate and fractional catabolic rate of very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL). Using a 16-h [(13)C]leucine infusion, we performed an apoB kinetic study in nine normolipidemic women before and 3 months after beginning Moneva. On Moneva, serum triglycerides increased moderately (+12%, P = 0.04) in the fed state, whereas serum LDL remained unchanged. LDL particles were richer in triglycerides in women on Moneva (7.5 +/- 1.5 vs. 4.3 +/- 1.0% of total LDL mass, P < 0.01). The apoB production rate of VLDL, IDL, and LDL increased by 49 (P = 0.04), 55 (P = 0.05), and 51% (P = 0.01), respectively. The fractional catabolic rate of apoB in LDL increased by 36% (P = 0.04). Consequently, the serum LDL apoB pool size remained unchanged (26.49 +/- 6.98 vs. 23.96 +/- 5.37 mg/kg). Oral contraception with ethinylestradiol plus gestodene induces an increase in the production rate of apoB-containing lipoproteins all along the VLDL-->IDL-->LDL cascade. The increased production rate of apoB in LDL is counterbalanced by a higher fractional catabolic rate of apoB in LDL, thus precluding an increase in the concentration of atherogenic LDL particles.

Mechanism of LDL binding and release probed by structure-based mutagenesis of the LDL receptor

The LDL receptor (LDL-R) mediates cholesterol metabolism in humans by binding and internalizing cholesterol transported by LDL. Several different molecular mechanisms have been proposed for the binding of LDL to LDL-R at neutral plasma pH and for its release at acidic endosomal pH. The crystal structure of LDL-R at acidic pH shows that the receptor folds back on itself in a closed form, obscuring parts of the ligand binding domain with the epidermal growth factor (EGF)-precursor homology domain. We have used a structure-based site-directed mutagenesis approach to examine 12 residues in the extracellular domain of LDL-R for their effect on LDL binding and release. Our studies show that the interface between the ligand binding domain and the EGF-precursor homology domain seen at acidic pH buries residues mediating both LDL binding and release. Our results are consistent with an alternative model of LDL-R whereby multiple modules of the extracellular domain interact with LDL at neutral pH, concurrently positioning key residues so that at acidic pH the LDL-R:LDL interactions become unfavorable, triggering release. After LDL release, the closed form of LDL-R may target its return to the cell surface.

PCSK9 Dominant Negative Mutant Results in Increased LDL Catabolic Rate and Familial Hypobetalipoproteinemia

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a central player in the regulation of cholesterol homeostasis, increasing the low-density lipoprotein (LDL) receptor degradation. Our study aimed at exploring the pathogenic consequences in vivo and in vitro of a PCSK9 prodomain mutation found in a family with hypobetalipoproteinemia (FHBL). A white 49-year-old diabetic man had profound FBHL (LDLC: 16 mg/dL) whereas his daughter and sister displayed a milder phenotype (LDLC 44 mg/dL and 57 mg/dL, respectively), all otherwise healthy with a normal liver function. A monoallelic PCSK9 double-mutant R104C/V114A cosegregated with FBHL, with no mutation found at other FHBL-causing loci. A dose-effect was also found in FBHL relatives for plasma APOB and PCSK9 (very-low to undetectable in proband, approximately 50% decreased in sister and daughter) and LDL catabolic rate (256% and 88% increased in proband and daughter). Transient transfection in hepatocytes showed severely impaired processing and secretion of the double mutant which acted as a dominant negative over secretion of wild-type PCSK9. These results show that heterozygous PCSK9 missense mutations may associate with profound hypobetalipoproteinemia and constitute the first direct evidence in human that decrease of plasma LDLC concentrations associated to PCSK9 LOF mutations are attributable to an increased clearance rate of LDL.

Correlation of Non–High-Density Lipoprotein Cholesterol and Low-Density Lipoprotein Cholesterol With Apolipoprotein B During Simvastatin + Fenofibrate Therapy in Patients With Combined Hyperlipidemia (A Subanalysis of the SAFARI Trial)

Guidelines have recommended non-high-density lipoprotein (non-HDL) cholesterol as a secondary target for therapy after the low-density lipoprotein (LDL) cholesterol goals have been met in patients with hypertriglyceridemia; non-HDL cholesterol is viewed as a surrogate for apolipoprotein (Apo)B, an alternate end point of treatment. The present analysis of the previously reported Simvastatin plus Fenofibrate for Combined Hyperlipidemia (SAFARI) trial assessed the associations of non-HDL cholesterol and LDL cholesterol with ApoB levels in patients with combined hyperlipidemia treated with combination simvastatin (20 mg) and fenofibrate (160 mg) or simvastatin monotherapy (20 mg). The correlations of these factors were analyzed in the overall modified intent-to-treat population (n = 594) and in patient subgroups stratified by triglyceride (TG) tertiles. Simvastatin plus fenofibrate and simvastatin alone significantly reduced LDL cholesterol, TG, non-HDL cholesterol and ApoB levels and non-HDL cholesterol/ApoB ratio (p < or =0.0004), regardless of the TG level. The greatest reductions occurred with combination treatment. The baseline levels of non-HDL cholesterol and LDL cholesterol correlated highly with ApoB and were stronger in the lower TG tertiles than in the higher TG tertiles. After 12 weeks, the correlations had changed little with simvastatin monotherapy but had increased substantially with combination therapy and were most improved at high TG levels. In conclusion, these results suggest that both non-HDL cholesterol and ApoB provide similar information in relation to treatment response in patients with combined hyperlipidemia and hypertriglyceridemia, and that non-HDL cholesterol is a good indicator of ApoB-containing lipoproteins, supporting its recommended use as a secondary therapeutic target in these patients.

Advanced Lipoprotein Testing and Subfractionation Are Not (Yet) Ready for Routine Clinical Use

Standard lipid tests measure the cholesterol or triglyceride content of lipoproteins, expressed as mg/dL (or mmol/L) of cholesterol or triglyceride. A standard lipid panel includes total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides. These lipids are carried within lipoprotein particles that are heterogeneous in size, density, charge, core lipid composition, specific apolipoproteins, and function.1 A variety of lipoprotein assays have been developed that subfractionate lipoprotein particles according to some of these properties such as size, density, or charge.2 These lipoprotein assays have been proposed for improving assessment of risk of cardiovascular disease (CVD) and for guiding lipid-lowering therapies. They are mostly used today in specialized lipid clinics or research studies, and their general utility for clinical practice is not well delineated.3 In this review, I first provide a summary of current guideline statements that address this topic. Then I give a brief overview of the different laboratory methods available for clinical use and discuss the literature evaluating these methods. Finally, I discuss current limitations to the widespread clinical application of these methods. Response by Superko on p 2404 The Third Adult Treatment Panel of the National Cholesterol Education Program4 and the American Heart Association5 recommend measuring a standard lipid panel in adults and targeting lipid-lowering therapy on the basis of levels of LDL cholesterol, and non-HDL cholesterol in subjects with hypertriglyceridemia. European and Canadian guidelines recommend measuring standard lipids while also emphasizing the total/HDL cholesterol ratio in risk assessment.6,7 Current guidelines do not recommend routine use of advanced lipoprotein tests, mainly because it is unclear how much incremental prognostic information is provided by these tests beyond that available from a standard lipid panel.4,6,7 Recently, an international panel proposed that cardiovascular risk may be more closely related to atherogenic lipoprotein …

FT-IR spectroscopy of lipoproteins—A comparative study

FT-IR spectra, in the frequency region 4000–600 cm −1, of four major lipoprotein classes: very low density lipoprotein (VLDL), low density lipoprotein (LDL) and two subclasses of high density lipoproteins (HDL 2 and HDL 3) were analyzed to obtain their detailed spectral characterization. Information about the protein domain of particle was obtained from the analysis of amide I band. The procedure of decomposition and curve fitting of this band confirms the data already known about the secondary structure of two different apolipoproteins: apo A-I in HDL 2 and HDL 3 and apo B-100 in LDL and VLDL. For information about the lipid composition and packing of the particular lipoprotein the well expressed lipid bands in the spectra were analyzed. Characterization of spectral details in the FT-IR spectrum of natural lipoprotein is necessary to study the influence of external compounds on its structure.

ABCB1 and ABCC1 expression in peripheral mononuclear cells is influenced by gene polymorphisms and atorvastatin treatment

This study investigated the effects of atorvastatin on ABCB1 and ABCC1 mRNA expression on peripheral blood mononuclear cells (PBMC) and their relationship with gene polymorphisms and lowering-cholesterol response. One hundred and thirty-six individuals with hypercholesterolemia were selected and treated with atorvastatin (10 mg/day/4 weeks). Blood samples were collected for serum lipids and apolipoproteins measurements and DNA and RNA extraction. ABCB1 (C3435T and G2677T/A) and ABCC1 (G2012T) gene polymorphisms were identified by polymerase chain reaction-restriction (PCR)-RFLP and mRNA expression was measured in peripheral blood mononuclear cells by singleplex real-time PCR. ABCB1 polymorphisms were associated with risk for coronary artery disease (CAD) ( p < 0.05). After atorvastatin treatment, both ABCB1 and ABCC1 genes showed 50% reduction of the mRNA expression ( p < 0.05). Reduction of ABCB1 expression was associated with ABCB1 G2677T/A polymorphism ( p = 0.039). Basal ABCB1 mRNA in the lower quartile (<0.024) was associated with lower reduction rate of serum low-density lipoprotein (LDL) cholesterol (33.4 ± 12.4%) and apolipoprotein B (apoB) (17.0 ± 31.3%) when compared with the higher quartile (>0.085: LDL-c = 40.3 ± 14.3%; apoB = 32.5 ± 10.7%; p < 0.05). ABCB1 substrates or inhibitors did not affect the baseline expression, while ABCB1 inhibitors reversed the effects of atorvastatin on both ABCB1 and ABCC1 transporters. In conclusion, ABCB1 and ABCC1 mRNA levels in PBMC are modulated by atorvastatin and ABCB1 G2677T/A polymorphism and ABCB1 baseline expression is related to differences in serum LDL cholesterol and apoB in response to atorvastatin.

Extended-Release Niacin Alters the Metabolism of Plasma Apolipoprotein (Apo) A-I and ApoB-Containing Lipoproteins

Extended-release niacin effectively lowers plasma TG levels and raises plasma high-density lipoprotein (HDL) cholesterol levels, but the mechanisms responsible for these effects are unclear. We examined the effects of extended-release niacin (2 g/d) and extended-release niacin (2 g/d) plus lovastatin (40 mg/d), relative to placebo, on the kinetics of apolipoprotein (apo) A-I and apoA-II in HDL, apoB-100 in TG-rich lipoproteins (TRL), intermediate-density lipoproteins (IDL) and low-density lipoproteins (LDL), and apoB-48 in TRL in 5 men with combined hyperlipidemia. Niacin significantly increased HDL cholesterol and apoA-I concentrations, associated with a significant increase in apoA-I production rate (PR) and no change in fractional catabolic rate (FCR). Plasma TRL apoB-100 levels were significantly lowered by niacin, accompanied by a trend toward an increase in FCR and no change in PR. Niacin treatment significantly increased TRL apoB-48 FCR but had no effect on apoB-48 PR. No effects of niacin on concentrations or kinetic parameters of IDL and LDL apoB-100 and HDL apoA-II were noted. The addition of lovastatin to niacin promoted a lowering in LDL apoB-100 attributable to increased LDL apoB-100 FCR. Niacin treatment was associated with significant increases in HDL apoA-I concentrations and production, as well as enhanced clearance of TRL apoB-100 and apoB-48.

A New PCSK9 Gene Promoter Variant Affects Gene Expression and Causes Autosomal Dominant Hypercholesterolemia

Autosomal dominant hypercholesterolemia (ADH) is a genetic disorder characterized by increased low-density lipoprotein (LDL)-cholesterol levels, leading to high risk of premature cardiovascular disease. More than 900 mutations in LDL receptor, six in APOB and 10 in PCSK9 have been identified as a cause of the disease in different populations. All known mutations in PCSK9 causing hypercholesterolemia produce an increase in the enzymatic activity of this protease. Up to now, there are data about the implication of PCSK9 in ADH in a low number of populations, not including a Spanish population. The objective of the study was to study the prevalence of PCSK9 mutations in ADH Spanish population. We screened PCSK9 gene in 42 independent ADH patients in whom mutations in LDL receptor and APOB genes had been excluded. None of the known mutations causing ADH was detected in our sample, but we found two variations in the promoter region that could cause ADH, c.-288G>A and c.-332C>A (each in one proband). The analysis of the effect of these two variations on the transcription activity of the PCSK9 promoter showed that c.-288G>A did not modify the transcription, whereas c.-332C>A variant caused a 2.5-fold increase when compared with the wild-type sequence, either with or without lovastatin. PCSK9 is a rare cause of ADH in Spanish population and, up to what we know, none of the previously described mutations has been detected. We have identified a new mutation that could cause ADH by increasing the transcription of PCSK9.

The hyperenergetic-fed obese dog, a model of disturbance of apolipoprotein B-100 metabolism associated with insulin resistance: kinetic study using stable isotopes

The hyperenergetic-fed beagle dog model of obesity-associated insulin resistance has previously demonstrated lipoprotein abnormalities similar to those of obese insulin-resistant humans. The aim of this study was to check, in the insulin-resistant dog, the mechanism leading to abnormalities in the mass of apolipoprotein B-100 (apo B-100) containing lipoproteins. Six healthy male beagle dogs were overfed with a high-fat diet for 28 ± 2.5 weeks. Obesity was associated with insulin resistance as assessed by the euglycemic hyperinsulinemic clamp technique. The kinetics of very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) apo B-100 were recorded in dogs, at healthy and insulin-resistant states, using a primed constant infusion of [5,5,5-D 3]leucine. Isotopic enrichment was measured by gas chromatography–mass spectrometry (GC-MS). A multicompartmental model was used for the analysis of tracer kinetics data. Apolipoprotein B-100 concentration was higher in VLDL (2.8-fold, P < .05) but lower in LDL (2-fold, P < .05) in the insulin-resistant compared to the healthy state. Kinetic analysis showed a higher VLDL apo B-100 production (1.7-fold, P < .05). The fractional catabolic rate of VLDL did not change significantly, but the lipolysis was decreased significantly (3-fold, P < .05). The lower LDL apo B-100 level in insulin-resistant dogs was explained by a higher LDL fractional catabolic rate (2.5-fold, P < .05). The mechanisms leading to hypertriglyceridemia (higher production rate and lower lipolysis of VLDL) in insulin-resistant dogs were similar to those described in the insulin-resistant humans.

Lipoprotein separation in a novel iodixanol density gradient, for composition, density, and phenotype analysis

Separation of lipoproteins by traditional sequential salt density floatation is a prolonged process ( approximately 72 h) with variable recovery, whereas iodixanol-based, self-generating density gradients provide a rapid ( approximately 4 h) alternative. A novel, three-layered iodixanol gradient was evaluated for its ability to separate lipoprotein fractions in 63 subjects with varying degrees of dyslipidemia. Lipoprotein cholesterol, triglycerides, and apolipoproteins were measured in 21 successive iodixanol density fractions. Iodixanol fractionation was compared with sequential floatation ultracentrifugation. Iodixanol gradient formation showed a coefficient of variation of 0.29% and total lipid recovery from the gradient of 95.4% for cholesterol and 84.7% for triglyceride. Recoveries for VLDL-, LDL-, and HDL-cholesterol, triglycerides, and apolipoproteins were approximately 10% higher with iodixanol compared with sequential floatation. The iodixanol gradient effectively discriminated classic lipoproteins and their subfractions, and there was evidence for improved resolution of lipoproteins with the iodixanol gradient. LDL particles subfractionated by the gradient showed good correlation between density and particle size with small, dense LDL (<25.5 nm) separated in fractions with density >1.028 g/dl. The new iodixanol density gradient enabled rapid separation with improved resolution and recovery of all lipoproteins and their subfractions, providing important information with regard to LDL phenotype from a single centrifugation step with minimal in-vitro modification of lipoproteins.

Prevalence and Determinants of Elevated Apolipoprotein B and Dense Low-Density Lipoprotein in Youths with Type 1 and Type 2 Diabetes

The objective of the study was to assess the prevalence and determinants of elevated apolipoprotein B (apoB) and dense low-density lipoprotein (LDL) in United States youth with type 1 or type 2 diabetes. We conducted cross-sectional analyses of apoB concentrations, LDL density, and prevalence of elevated apoB levels and dense LDL from the SEARCH for Diabetes in Youth study, a six-center U.S.-based study of youth with diabetes onset younger than 20 years of age (2657 with type 1 and 345 with type 2). Among youth with type 1 diabetes, 11% had elevated apoB (>or=100 mg/dl, 1.95 mm/liter), 8% had dense LDL (relative flotation rate<or=0.237), and 12% had elevated LDL-cholesterol (>or=130 mg/dl, 3.36 mm/liter). In contrast, among youth with type 2 diabetes, 36% had elevated apoB, 36% had dense LDL, but only 23% had elevated LDL-cholesterol. Dense LDL and apoB each increased with hemoglobin A1c in both types. Among type 1 diabetics in poor glycemic control (hemoglobin A1c>or=9.5%), 28% had elevated apoB, and 18% had dense LDL, whereas 72% of poorly controlled type 2 diabetics had elevated apoB and 62% had dense LDL. In youth with type 1 diabetes, elevated apoB and dense LDL were not highly prevalent, whereas elevated apoB and dense LDL were common lipoprotein abnormalities in youth with type 2 diabetes. The prevalence of these risk factors substantially increased with poor glycemic control in both groups, stressing the importance of achieving and maintaining an optimal glucose control.

The paraoxonase gene polymorphism in stroke patients and lipid profile

The paraoxonase (PON) gene can reduce the risk of developing atherosclerosis. We investigated the associations between PON polymorphisms and ischemic stroke. We also investigated the associations between PON polymorphisms and lipid profile in stroke patients. A total of 350 patients with ischemic stroke and 242 control subjects in Korean population were genotyped for the PON1M55 L, PON1Q192R, PON2A148 G and PON2S311C polymorphisms using melting point analysis with LightCycler real-time polymerase chain reaction (PCR) technology. There were no significant differences in genotype and allele distribution of the PON polymorphisms between the ischemic stroke patients and control subjects. The concentration of total homocysteine was significantly different in the PON1M55 L polymorphism (P = 0.047), and the apolipoprotein (Apo)B concentration was significantly different in the PON1Q192R polymorphism (P = 0.02) in stroke patients. The concentrations of low-density lipoprotein (LDL) cholesterol and ApoB were significantly different between the PON2A148 G (P = 0.011, P = 0.000, respectively) and PON2S311C polymorphisms (P = 0.046, P = 0.003, respectively) in stroke patients. This study did not provide association between PON gene polymorphisms and ischemic stroke. However, it confirmed that the PON1L55 L allele is associated with plasma concentration of total homocysteine and that the PON2G148 G and PON2S311S allele is associated with plasma concentrations of LDL cholesterol and ApoB.

Diagnosis of type III hyperlipoproteinemia from plasma total cholesterol, triglyceride, and apolipoprotein B

Our objective was to develop a simple algorithm that could be applied in routine clinical practice to diagnose type III hyperlipoproteinemia based on plasma total cholesterol, triglyceride and apolipoprotein (Apo) B. Analysis of plasma lipid, lipoprotein lipid, and apolipoprotein data from 1771 patients in a tertiary care lipid clinic, from whom all data had been collected prospectively by standardized methods. Of the 1771, based on the Fredrickson classification, 16 had type I hyperlipoproteinemia, 736 type IIa hyperlipoproteinemia, 371 type IIb hyperlipoproteinemia, 38 type III hyperlipoproteinemia, 509 type IV hyperlipoproteinemia, and 101 type V hyperlipoproteinemia. Mean plasma ApoB was highest in type IIb (1.53 ± 0.36 g/L), borderline high (1.1 ± 0.23 g/L) in type IV, normal in type III and type V (1.04 ± 0.21 g/L and 0.96 ± 0.40 g/L, respectively) and low in type I (0.48 ± 0.16 g/L). In type III hyperlipoproteinemia, very low-density lipoprotein ApoB (ie, d<1.006 g/mL) accounted for 42.3% of total ApoB, a value that was substantially higher than in any of the other dyslipoproteinemias. The total cholesterol (TC)/ApoB ratio was similar in the uncommon dyslipoproteinemias-type I, III, and V hyperlipoproteinemia (10.5 ± 4.8, 8.7 ± 1.8, 10.3 ± 7.7, respectively)-and much higher than in the common dyslipoproteinemias-type IIa, IIb, and type IV hyperlipoproteinemia (5.0 ± 0.4, 4.6 ± 0.4, 4.9 ± 1.1, respectively). Notwithstanding that the TC/ApoB area under the curve-receiver operating characteristic (AUC-ROC) was very high (0.93), it did not discriminate among the uncommon dyslipoproteinemias. However, the triglyceride (TG)/ApoB ratio was much higher in type I (42.4 ± 28.8) and type V (25.6 ± 30.2) than in type III (5.8 ± 3.2). All cases of type III had a TC/ApoB ratio >6.2 and a TG/ApoB ratio of <10.0. Using these cutpoints, there were also no false positives. Based on the TC/ApoB ratio and the TG/ApoB ratio, the AUC-ROC was 0.99. These data indicate that type III hyperlipoproteinemia can be reliably diagnosed based on plasma cholesterol, TG, and ApoB.

Functional LCAT deficiency in human apolipoprotein A-I transgenic, SR-BI knockout mice

Reduction of plasma LCAT activity has been observed in several conditions in which the size of HDL particles is increased; however, the mechanism of this reduction remains elusive. We investigated the plasma activity, mass, and in vivo catabolism of LCAT and its association with HDL particles in human apolipoprotein A-I transgenic, scavenger receptor class B type I knockout (hA-ITg SR-BI-/-) mice. Compared with hA-ITg mice, hA-ITg SR-BI-/- mice had a 4-fold higher total plasma cholesterol concentration, which occurred predominantly in 13-18 nm diameter HDL particles, a significant reduction in plasma esterified cholesterol-total cholesterol (EC/TC) ratio, and significantly lower plasma LCAT activity, suggesting a decrease in LCAT protein. However, LCAT protein in plasma, hepatic mRNA for LCAT, and in vivo turnover of 35S-radiolabeled LCAT were similar in both genotypes of mice. HDL from hA-ITg SR-BI-/- mice was enriched in sphingomyelin (SM), relative to phosphatidylcholine, and had less associated [35S]LCAT radiolabel and endogenous LCAT activity compared with HDL from hA-ITg mice. We conclude that the decreased EC/TC ratio in the plasma of hA-ITg SR-BI-/- mice is attributed to a reduction in LCAT reactivity with SM-enriched HDL particles.

PON1 Activity is Inversely Related to LDL ApoB Carbonyl Content in Patients with Coronary Artery Disease

The objective of this study was to investigate apolipoprotein B (apoB) carbonyl content as a parameter for studying low-density lipoprotein (LDL) oxidation in coronary artery disease (CAD) risk assessment and to explore the relationship between apoB carbonyl content (an index of protein oxidation) and paraoxonase 1 (PON1) activity in CAD patients and controls. A total of 200 patients suffering from CAD and 150 normal individuals were included in the present study. CAD patients were classified into two groups on the basis of associated risk factors (diabetes mellitus, hypertension): group 1 (n = 120; CAD patients with associated risk factors) and group 2 (n = 80; CAD patients with no associated risk factors). All subjects were assayed for apoB carbonyl content, LDL-malondialdehyde (LDL-MDA), PON1 activity, and lipid and apolipoprotein levels. ApoB carbonyl content was significantly (p < 0.01) raised in CAD patients (with or without associated risk factors) as compared to controls. Patients also had relatively raised LDL-MDA levels. Serum PON1 activity was significantly low (p < 0.01) in CAD patients. A significantly (p < 0.01) negative coefficient of correlation was observed between apoB carbonyl content and PON1 activity in both patients and controls. CAD patients with associated risk factors had highly raised (p < 0.01) apoB carbonyl content and considerably depressed PON1 activity compared to those with no associated risk factors. LDL-MDA levels did not differ significantly (p > 0.05) between the two groups. CAD patients in group 1 also had significantly raised apoB levels and low HDL-cholesterol and apoA1 levels as compared to patients in group 2, while the other lipid variables did not show any significant difference. A significantly negative coefficient of correlation was observed between apoB carbonyl content and PON1 activity in both patients and controls. This is a new piece of information that needs to be further explored. Quantification of apoB carbonyl content may act as a suitable parameter for studying LDL oxidation in the evaluation of CAD risk, especially when confounding risk factors are present.

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.

Relationships between changes in plasma lipid transfer proteins and apolipoprotein B-100 kinetics during fenofibrate treatment in the metabolic syndrome

The aim of the present study was to investigate the association between changes in apoB (apolipoprotein B-100) kinetics and plasma PLTP (phospholipid transfer protein) and CETP (cholesteryl ester transfer protein) activities in men with MetS (the metabolic syndrome) treated with fenofibrate. Eleven men with MetS underwent a double-blind cross-over treatment with fenofibrate (200 mg/day) or placebo for 5 weeks. Compared with placebo, fenofibrate significantly increased the FCRs (fractional catabolic rates) of apoB in VLDL (very-low-density lipoprotein), IDL (intermediate-density lipoprotein) and LDL (low-density lipoprotein) (all P<0.01), with no significant reduction (-8%; P=0.131) in VLDL-apoB PR (production rate), but an almost significant increase (+15%, P=0.061) in LDL-apoB PR. Fenofibrate significantly lowered plasma TG [triacylglycerol (triglyceride); P<0.001], the VLDL-TG/apoB ratio (P=0.003) and CETP activity (P=0.004), but increased plasma HDL (high-density lipoprotein)-cholesterol concentration (P<0.001) and PLTP activity (P=0.03). The increase in PLTP activity was positively associated with the increase in both LDL-apoB FCR (r=0.641, P=0.034) and PR (r=0.625, P=0.040), and this was independent of the fall in plasma CETP activity and lathosterol level. The decrease in CETP activity was positively associated with the decrease in VLDL-apoB PR (r=0.615, P=0.044), but this association was not robust and not independent of changes in PLTP activity and lathosterol levels. Hence, in MetS, the effects of fenofibrate on plasma lipid transfer protein activities, especially PLTP activity, may partially explain the associated changes in apoB kinetics.

Nuclear magnetic resonance‐determined lipoprotein subclass profile in the DCCT/EDIC cohort: associations with carotid intima‐media thickness

To relate nuclear magnetic resonance lipoprotein subclass profiles (NMR-LSP) and other lipoprotein-related factors with carotid intima-media thickness (IMT) in Type 1 diabetes. Lipoprotein-related factors were determined in sera (obtained in 1997-1999) from 428 female [age 39 +/- 7 years (mean +/- SD)] and 540 male (age 40 +/- 7 years) Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) participants. NMR quantifies chylomicrons, three very low-density lipoprotein (VLDL) subclasses, intermediate density lipoprotein (IDL), three low-density lipoprotein (LDL) subclasses, two high-density lipoprotein (HDL) subclasses, mean VLDL, LDL and HDL size, and LDL particle concentration. Conventional lipids, ApoA1, ApoB and Lp(a) and in vitro LDL oxidizibility were also measured. IMT was determined (in 1994-1995) using high-resolution B-mode ultrasound. Relationships between IMT and lipoproteins were analysed by multiple linear regression, controlling for age, diabetes-related factors, and cardiovascular disease (CVD) risk factors. IMT associations with lipoproteins were stronger for the internal than the common carotid artery, predominantly involving LDL. Internal carotid IMT was positively (P < 0.05) associated with NMR-based LDL subclasses and particle concentration, and with conventional LDL-cholesterol and ApoB in both genders. Common carotid IMT was associated, in men only, with large VLDL, IDL, conventional LDL cholesterol and ApoB. NMR-LSP reveals significant associations with carotid IMT in Type 1 diabetic patients, even 4 years after IMT measurement. NMR-LSP may aid early identification of high-risk diabetic patients and facilitate monitoring of interventions. Longer DCCT/EDIC cohort follow-up will yield CVD events and IMT progression, permitting more accurate assessment of pre-morbid lipoprotein profiles as determinants of cardiovascular risk in Type 1 diabetes.

Quantitative analysis of SR-BI-dependent HDL retroendocytosis in hepatocytes and fibroblasts

Previous studies have suggested that HDL retroendocytosis may play a role in scavenger receptor class B type I (SR-BI)-dependent selective lipid uptake in a cell-specific manner. To investigate this possibility, we developed methods to quantitatively measure HDL uptake and resecretion in fibroblast (COS-7) and hepatocyte (HepG2) cells expressing exogenous SR-BI. Approximately 17% and 24% of HDL associated in an SR-BI-dependent manner with COS-7 and HepG2 cells, respectively, accumulates intracellularly after a 10 min incubation. To determine whether this intracellular HDL undergoes retroendocytosis, we developed a pulse-chase assay whereby internalized biotinylated (125)I-HDL(3) secreted from cells is quantitatively precipitated from cell supernatants using immobilized streptavidin. Our results show a rapid secretion of a portion of intracellular HDL from both cell types (representing 4-7% of the total cell-associated HDL) that is almost complete within 30 min (half-life approximately 10 min). In COS-7 cells, the calculated rate of HDL secretion ( approximately 0.5 ng HDL/mg/min) was >30-fold slower than the rate of SR-BI-dependent selective cholesteryl ester (CE) uptake ( approximately 17 ng HDL/mg/min), whereas the rate of release of HDL from the cell surface ( approximately 19 ng HDL/mg/min) was similar to the rate of selective CE uptake. Notably, the rate of SR-BI-dependent HDL resecretion in COS-7 and HepG2 cells was similar. BLT1, a compound that inhibits selective CE uptake, does not alter the amount of SR-BI-mediated HDL retroendocytosis in COS-7 cells. From these data, we conclude that HDL retroendocytosis in COS-7 and HepG2 cells is similar and that the vast majority of SR-BI-dependent selective uptake occurs at the cell surface in both cell types.