Greater oxidative susceptibility of the surface monolayer in small dense LDL may contribute to differences in copper-induced oxidation among LDL density subfractions

A Moderate-Fat Diet with One Avocado per Day Increases Plasma Antioxidants and Decreases the Oxidation of Small, Dense LDL in Adults with Overweight and Obesity: A Randomized Controlled Trial

BACKGROUND

Avocados are a nutrient-dense source of MUFAs and are rich in antioxidants. Avocados have an additional LDL cholesterol (LDL-C) lowering effect beyond that observed when their MUFAs are substituted for SFAs, especially on small, dense LDL (sdLDL) particles, which are susceptible to in vivo oxidation and associated with increased risk of cardiovascular disease (CVD).

OBJECTIVES

We investigated whether a healthy diet with 1 avocado daily decreased the following secondary outcomes: circulating oxidized LDL (oxLDL) and related oxidative stress markers.

METHODS

A randomized, crossover, controlled feeding trial was conducted with 45 men and women, aged 21-70 y, with overweight or obesity and elevated LDL-C (25th-90th percentile). Three cholesterol-lowering diets were provided (5 wk each) in random sequences: a lower-fat (LF) diet (24% calories from fat-7% SFAs, 11% MUFAs, 6% PUFAs) and 2 moderate-fat (MF) diets (34% calories from fat-6% SFAs, 17% MUFAs, 9% PUFAs): the avocado (AV) diet included 1 Hass avocado (∼136 g) per day, and the MF diet used high oleic acid oils to match the fatty acid profile of 1 avocado. A general linear mixed model was used to analyze the treatment effects.

RESULTS

Compared with baseline, the AV diet significantly decreased circulating oxLDL (-7.0 U/L, -8.8%, P = 0.0004) and increased plasma lutein concentration (19.6 nmol/L, 68.7%, P < 0.0001), and both changes differed significantly from that after the MF and LF diets (P ≤ 0.05). The change in oxLDL caused by the AV diet was significantly correlated with the changes in the number of sdLDL particles (r = 0.32, P = 0.0002) but not large, buoyant LDL particles.

CONCLUSIONS

One avocado a day in a heart-healthy diet decreased oxLDL in adults with overweight and obesity, and the effect was associated with the reduction in sdLDL. This trial was registered at http://www.clinicaltrials.gov as NCT01235832.

Endophilin-A2-mediated increase in scavenger receptor expression contributes to macrophage-derived foam cell formation

BACKGROUND AND AIMS

Macrophage-derived foam cell formation (MFCF) is a crucial step in the pathogenesis of atherosclerosis. Uptake of oxidized low-density lipoprotein (oxLDL) by scavenger receptors is indispensable for MFCF. Endophilin-A2 has been reported to regulate clathrin-mediated endocytosis (CME). In this study, we tested the hypothesis that endophilin-A2 regulates oxLDL uptake and MFCF by mediating CME of oxLDL-scavenger receptor complexes.

METHODS

In vitro MFCF was induced by oxLDL treatment. Involvement of endophilin-A2 in oxLDL cytomembrane binding, cellular uptake, and MFCF was evaluated by manipulation of endophilin-A2.

RESULTS

Endophilin-A2 was involved in MFCF via scavenger receptor CD36 and scavenger receptor-A (SR-A)-mediated positive feedback pathways. We observed that oxLDL triggered interaction of endophilin-A2 with CD36 or SR-A, and induced an endophilin-A2-dependent activation of the apoptosis signal-regulating kinase-1 (ASK1)/Jun N-terminal kinase (JNK)/p38 signaling pathway. The activation of ASK1-JNK/p38 signal increased expression of both CD36 and SR-A, which promoted oxLDL cytomembrane binding, cellular uptake, and MFCF. In the absence of oxLDL, endophilin-A2 up-regulated the expression of receptors and Dil-oxLDL binding and uptake, but not the intracellular accumulation of lipids. In the presence of oxLDL, the CME inhibitors pitstop2 and ikarugamycin mimicked the inhibiting effect of endophilin-A2 knockdown and eliminated the elevating effect of endophilin-A2 overexpression on oxLDL uptake and MFCF.

CONCLUSIONS

Endophilin-A2 was identified as a novel molecule regulating MFCF by mechanisms attributable to CME and beyond CME.

Simvastatin Efficiently Lowers Small LDL-IgG Immune Complex Levels: A Therapeutic Quality beyond the Lipid-Lowering Effect

We investigated a polyethylene glycol non-precipitable low-density lipoprotein (LDL) subfraction targeted by IgG and the influence of statin therapy on plasma levels of these small LDL-IgG-immune complexes (LDL-IgG-IC). LDL-subfractions were isolated from 6 atherosclerotic subjects and 3 healthy individuals utilizing iodixanol density gradient ultracentrifugation. Cholesterol, apoB and malondialdehyde (MDA) levels were determined in each fraction by enzymatic testing, dissociation-enhanced lanthanide fluorescence immunoassay and high-performance liquid chromatography, respectively. The levels of LDL-IgG-IC were quantified densitometrically following lipid electrophoresis, particle size distribution was assessed with dynamic light scattering and size exclusion chromatography. The influence of simvastatin (40 mg/day for three months) on small LDL-IgG-IC levels and their distribution among LDL-subfractions (salt gradient separation) were investigated in 11 patients with confirmed coronary artery disease (CAD). We demonstrate that the investigated LDL-IgG-IC are small particles present in atherosclerotic patients and healthy subjects. In vitro assembly of LDL-IgG-IC resulted in particle density shifts indicating a composition of one single molecule of IgG per LDL particle. Normalization on cholesterol levels revealed MDA values twice as high for LDL-subfractions rich in small LDL-IgG-IC if compared to dominant LDL-subfractions. Reactivity of affinity purified small LDL-IgG-IC to monoclonal antibody OB/04 indicates a high degree of modified apoB and oxidative modification. Simvastatin therapy studied in the CAD patients significantly lowered LDL levels and to an even higher extent, small LDL-IgG-IC levels without affecting their distribution. In conclusion simvastatin lowers levels of small LDL-IgG-IC more effectively than LDL-cholesterol and LDL-apoB levels in atherosclerotic patients. This antiatherogenic effect may additionally contribute to the known beneficial effects of this drug in the treatment of atherosclerosis.

Investigation of MDA-LDL (malondialdehyde-modified low-density lipoprotein) as a prognostic marker for coronary artery disease in patients with type 2 diabetes mellitus

BACKGROUND

Although increased circulating levels of malondialdehyde-modified low-density lipoprotein (MDA-LDL) are associated with coronary artery disease (CAD), there is no direct evidence that increased MDA-LDL is a prognostic factor for CAD.

METHODS

Forty-two patients (20 diabetic and 22 non-diabetic patients) who underwent percutaneous coronary intervention (PCI) were enrolled, and their baseline MDA-LDL levels were determined by immunoassay. Follow-up coronary angiography was performed at 2 to 7 months post-PCI. The patients were then divided into 2 groups, with in-stent restenosis (ISR) (n=13) and without ISR (n=29), and the baseline MDA-LDL levels were compared. We also studied 34 diabetics with CAD for up to 57 months until the onset of the next coronary event.

RESULTS

In the diabetic patients, the mean MDA-LDL level was significantly higher in those with ISR than in those without ISR (151+/-61 vs. 90+/-26 U/l, p=0.010). A baseline MDA-LDL value of 110 U/l for differentiating between diabetics with and without ISR was defined as the cut-off value. Kaplan-Meier analysis demonstrated that a circulating MDA-LDL of ≥ 110 U/l correlated significantly with a higher prevalence of cardiac events than MDA-LDL <110 U/l (p=0.032).

CONCLUSIONS

Circulating MDA-LDL is a useful prognostic marker for future cardiac event in diabetic patients with CAD.

Identification of Ganglioside GM3 Molecular Species in Human Serum Associated with Risk Factors of Metabolic Syndrome

Serum GM3 molecular species were quantified in 125 Japanese residents using tandem mass spectrometry multiple reaction monitoring. Individuals were categorized by the presence or absence of metabolic disease risk factors including visceral fat accumulation, hyperglycemia and dyslipidemia. A total of 23 GM3 molecular species were measured, of these, eight were found to be significantly elevated in individuals with visceral fat accumulation and metabolic disease, defined as the presence of hyperglycemia and dyslipidemia. All of the GM3 molecular species were composed of the sphingoid base sphingosine (d18:1 (Δ4)) and, interestingly, six of the eight elevated GM3 molecular species contained a hydroxylated ceramide moiety. The hydroxylated GM3 species were, in order of decreasing abundance, d18:1-h24:0 ≈ d18:1-h24:1 > d18:1-h22:0 » d18:1-h20:0 > d18:1-h21:0 > d18:1-h18:1. Univariate and multiple linear regression analyses were conducted using a number of clinical health variables associated with obesity, type 2 diabetes, metabolic disease, atherosclerosis and hypertension. GM3(d18:1-h24:1) was identified as the best candidate for metabolic screening, proving to be significantly correlated with intima-media thickness, used for the detection of atherosclerotic disease in humans, and a number of metabolic disease risk factors including autotaxin, LDL-c and homeostatic model assessment insulin resistance (HOMA-IR).

GM3 and diabetes

We demonstrated the molecular pathogenesis of type 2 diabetes and insulin resistance focusing on the interaction between insulin receptor and GM3 ganglioside in adipocytes and propose a working hypothesis "metabolic disorders, such as type 2 diabetes, are membrane microdomain disorders caused by aberrant expression of gangliosides". It is expected that the development of novel diagnosis of metabolic syndrome by identifying the specific ganglioside species and a therapeutic strategy "membrane microdomain ortho-signaling therapy".

Circulating levels of ganglioside GM3 in metabolic syndrome: A pilot study

SUMMARY

BACKGROUND

Insulin resistance is a characteristic feature of metabolic syndrome. Ganglioside GM3 [α-Neu5Ac-(2-3)-β-Gal-(1-4)-β-Glc-(1-1)-ceramide] may impair insulin sensitivity in adipose tissue. We investigated the relationship between serum GM3 levels and adiposity indices, as well as between serum GM3 levels and metabolic risk variables.

METHODS

Study 1: we assessed serum GM3 levels in normal subjects and in patients with hyperglycemia and/or hyperlipidemia (HL). Study 2: we investigated the relationship between serum GM3 levels and metabolic risk variables in patients with type 2 diabetes.

RESULTS

Study 1: serum GM3 levels were higher in hyperglycemic patients (1.4-fold), hyperlipidemic patients (1.4-fold) and hyperglycemic patients with hyperlipidemia (1.6-fold), than in normal subjects. Study 2: serum GM3 levels were significantly increased in type 2 diabetic patients with severe obesity (visceral fat area (VFA) >200 cm(2), BMI > 30). The GM3 level was positively correlated with LDL-c (0.403, p = 0.012) in type 2 diabetes mellitus, but not affected by blood pressure. In addition, the high levels of small dense LDL (>10 mg/dL) were associated with the elevation of GM3.

CONCLUSIONS

Serum GM3 levels was affected by glucose and lipid metabolism abnormalities and by visceral obesity. GM3 may be a useful marker for severity of metabolic syndrome.

Immunological detection of large oxidized lipoproteins in hypertriglyceridemic serum

BACKGROUND

Triglyceride-rich, low-density lipoproteins (TG-rich LDL) have been reported as an oxidized lipoprotein species in patients with severe liver disease. Using TG-rich LDL as an immunogen, we obtained a monoclonal antibody (G11-6) that reacted with TG-rich LDL from patients with liver disease and with metal-oxidized LDL only in the early process of the oxidation reaction. This study determined the G11-6-reactive lipoproteins in hypertriglyceridemic serum.

METHODS

Serum samples from healthy volunteers (n = 12) and hypertriglyceridemic patients (n = 9) were fractionated by gel filtration and subjected to a sandwich enzyme-linked immunosorbent assay (ELISA) using G11-6 and polyclonal anti-apolipoprotein B antibodies.

RESULTS

Small LDL and larger lipoproteins reacted with G11-6. G11-6-reactive small LDL was identified in both the healthy subjects and hypertriglyceridemic patients, whereas G11-6-reactive larger lipoproteins were found only in the hypertriglyceridemic patients.

CONCLUSIONS

G11-6 is a useful tool for detecting increased large oxidized lipoproteins in hypertriglyceridemic patients.

Novel monoclonal antibody recognizing triglyceride-rich oxidized LDLs associated with severe liver disease and small oxidized LDLs in normal subjects

Background

Triglyceride-rich low-density lipoproteins (TG-rich LDLs) in the plasma of patients with severe liver disease are reported to change macrophages into foam cells in vitro.

Methods

Male BALB/c mice were immunized with TG-rich LDLs isolated from the plasma of a patient with severe liver disease. The resulting monoclonal antibody (G11-6) was used in a sandwich enzyme-linked immunosorbent assay (ELISA) in combination with polyclonal anti-apolipoprotein B antibodies. The time course of copper-mediated LDL oxidation was monitored using this ELISA. The results were compared with those of the two commercial ELISAs for oxidized LDLs using DLH or ML25, thiobarbituric acid reactive substances and the optical absorbance for the conjugated dienes generated in lipid peroxides. Furthermore, the lipoprotein fractions separated by gel filtration were tested with this ELISA in healthy volunteers ( n = 11) and patients ( n = 3) with liver disease.

Results

G11-6 reacted with oxidized LDLs during only the early phase of copper oxidation, being distinct from the other monoclonal antibodies and methods. G11-6 was confirmed to react with TG-rich LDLs in patients, while it reacted with small LDL particles in normal controls.

Conclusions

The monoclonal antibody G11-6 is useful for detecting oxidized small LDLs in normal controls and oxidized TG-rich LDLs in patients with severe liver disease.

Blood aging, safety, and transfusion: capturing the "radical" menace

Throughout their life span, circulating red blood cells (RBCs) transport oxygen (O(2)) primarily from the lungs to tissues and return with carbon dioxide (CO(2)) from respiring tissues for final elimination by lungs. This simplistic view of RBCs as O(2) transporter has changed in recent years as other gases, for example, nitric oxide (NO), and small molecules, such as adenosine triphosphate (ATP), have been shown to either be produced and/or carried by RBCs to perform other signaling and O(2) sensing functions. In spite of the numerous biochemical and metabolic changes occurring within RBCs during storage, prior to, and after transfusion, perturbations of RBC membrane are likely to affect blood flow in the microcirculation. Subsequent hemolysis due to storage conditions and/or hemolytic disorders may have some pathophysiological consequences as a result of the release of Hb. In this review, we show that evolution has provided a multitude of protection and intervention strategies against free Hb from "cradle" to "death"; from early biosynthesis to its final degradation and a lot more in between. Furthermore, some of the same naturally occurring protective mechanisms can potentially be employed to oxidatively inactivate this redox active protein and control its damaging side reactions when released outside of the RBC.

Physiopathological function of hematoside (GM3 ganglioside)

Since I was involved in the molecular cloning of GM3 synthase (SAT-I), which is the primary enzyme for the biosynthesis of gangliosides in 1998, my research group has been concentrating on our efforts to explore the physiological and pathological implications of gangliosides especially for GM3. During the course of study, we demonstrated the molecular pathogenesis of type 2 diabetes and insulin resistance focusing on the interaction between insulin receptor and gangliosides in membrane microdomains and propose a new concept: Life style-related diseases, such as type 2 diabetes, are a membrane microdomain disorder caused by aberrant expression of gangliosides. We also encountered an another interesting aspect indicating the indispensable role of gangliosides in auditory system. After careful behavioral examinations of SAT-I knockout mice, their hearing ability was seriously impaired with selective degeneration of the stereocilia of hair cells in the organ of Corti. This is the first observation demonstrating a direct link between gangliosides and hearing functions.

Inhibition of ganglioside biosynthesis as a novel therapeutic approach in insulin resistance

A new concept "Life style-related diseases, such as type 2 diabetes, are a membrane microdomain disorder caused by aberrant expression of gangliosides" has arisen. By examining this working hypothesis, we demonstrate the molecular pathogenesis of type 2 diabetes and insulin resistance focusing on the interaction between insulin receptor and gangliosides in microdomains microdomains and propose the new therapeutic strategy "membrane microdomain ortho-signaling therapy".

Nuclear Magnetic Resonance Lipoprotein Subclasses and the APOE Genotype Influence Carotid Atherosclerosis in Patients with Systemic Lupus Erythematosus

Objective.

Patients with systemic lupus erythematosus (SLE) have accelerated atherosclerosis. Since the conventional lipid profile (total plasma cholesterol, triglycerides, low and high density lipoprotein cholesterol) is not consistently altered in SLE, we hypothesized that investigation of lipoprotein subclasses would improve prediction of risk of atherosclerosis in these patients.

Methods.

As a quantitative index of atherosclerosis, we measured the carotid intima-media thickness (IMT) in 68 patients with SLE and related the atherosclerosis to a detailed lipoprotein profile generated using nuclear magnetic resonance (NMR). We measured the cholesterol transported by the pool of remnant lipoproteins (RLPc) and evaluated the modulatory effect of the APOE genotype on the lipoprotein subclass profile and atherosclerosis associated with SLE.

Results.

Circulating lipoprotein remnant particles [RLPc and intermediate density lipoprotein (IDL)] were positively correlated with IMT, and among them, the indicator that explained 20.2% of the variability in carotid atherosclerosis measured in these patients was IDL, as assessed by NMR. Carriers of the APOE2 allele were at increased risk due to a significant accumulation of IDL particles.

Conclusion.

Lipoprotein subclasses are more associated with subclinical atherosclerosis in patients with SLE than the lipid variables that are routinely measured. The IDL fraction, which is significantly modulated by the APOE genotype, is the most strongly, significantly, and positively correlated with IMT.

Membrane microdomains and insulin resistance

A new concept, that "metabolic disorders, such as type 2 diabetes, are membrane microdomain disorders caused by aberrant expression of gangliosides", has arisen. By examining this working hypothesis, we demonstrate the molecular pathogenesis of type 2 diabetes and insulin resistance focusing on the interaction between insulin receptor and gangliosides in microdomains and propose the new therapeutic strategy "membrane microdomain ortho-signaling therapy".

Atherogenic dyslipidemia and oxidative stress: a new look

Although results from in vitro studies and clinical trials demonstrate strong associations between oxidative stress and cardiovascular risk, to date still no convincing data are available to suggest that treatment with antioxidants might reduce vascular events. Oxidative modifications of low-density lipoproteins (LDL) represent an early stage of atherosclerosis, and small, dense LDL are more susceptible to oxidation than larger, more buoyant particles. Oxidized LDL are independent predictors of subclinical and clinical atherosclerosis. Recent studies suggested that novel therapeutic strategies may take into account the removal of such particles from circulation. Future research is required to explore the potential synergistic impact of markers of oxidative stress and atherogenic dyslipidemia, particularly small dense LDL, on cardiovascular risk.

Gender differences in the lipid profile of dyslipidemic subjects

OBJECTIVE

We evaluated the gender-associated differences in lipid profile of subjects intended to receive lipid-lowering therapy with emphasis on the associations between triglycerides (TG) and other plasma lipid variables.

DESIGN

Lipid profiles of 1385 patients [aged 55+/-11 years, 549 women (40%)] were evaluated. Eligible subjects fulfilled one or more of the following criteria: total cholesterol (TC)>or=6.2 mmol/l, TG>or=1.7 mmol/l, and high-density lipoprotein cholesterol (HDL-C)<1.0 mmol/l. Patients were divided into subgroups according to TG and HDL-C levels.

RESULTS

Women aged on average 3.5 years older, had higher TC and HDL-C, lower TG and a correspondingly lower TC/HDL-C ratio than men. High TG and low HDL-C in tandem appeared twice more frequently in men. Inverse correlations between HDL-C and TG levels were found to exist in the entire cohort (r=-0.354, p<0.001) and in all various subgroups. In the subgroup with TG<1.7 mmol/l, women had higher TC and HDL-C, lower TG levels and lower TC/HDL-C ratio compared with men. In the subgroup with TG>or=1.7 mmol/l, women had higher TC and HDL-C levels and lower TC/HDL ratio compared with men. In the subgroup with HDL-C>or=1.0 mmol/l women had higher HDL-C, lower TG levels and lower TC/HDL-C ratio compared with men.

CONCLUSIONS

Elevated TG levels and low HDL-C in tandem are common lipid abnormalities in the clinical setting of primary and secondary preventions. Gender-associated differences in the lipid profile are evident in subjects presenting with dyslipidemia and might be of potential relevance for diagnostics and therapy for the prevention of atherosclerosis.

Association of oxidative stress and PON1 with LDL and HDL particle size in middle-aged subjects

BACKGROUND

Alterations in plasma lipoprotein subclass distributions affect atherosclerosis risk. Smaller, denser low-density lipoprotein (LDL) particles (sdLDL) are more susceptible to oxidation. In contrast, most of the protective effects of high-density lipoproteins (HDL) are attributable to larger particles. This study investigates the connection between LDL and HDL particle heterogeneity and oxidative stress, antioxidative defence (AOD) and paraoxonase (PON1) status in a healthy middle-aged Serbian population.

MATERIALS AND METHODS

LDL and HDL particle sizes and subclass distributions were measured by gradient gel electrophoresis in 104 men and 103 women, aged 53 +/- 9.4 years. PON1 activities and PON1(Q192R) phenotypes were determined with paraoxon and diazoxon as substrates. The oxidative stress/AOD status was estimated by measuring malondialdehyde (MDA) and superoxide-anion (O2*(-)) levels and superoxide-dismutase (SOD) activity.

RESULTS

Subjects with sdLDL had significantly higher MDA (P < 0.001) and O2*(-)(P < 0.05) levels and greater diazoxonase (DZOase) activity (P < 0.05) compared to subjects with larger LDL particles. A high MDA concentration was a significant predictor of the sdLDL phenotype (P < 0.005). Increased levels of and MDA were associated with smaller HDL(3) subclass abundance. Reduced HDL particle size was associated with lower DZOase activity (P < 0.01).

CONCLUSIONS

Even in the absence of symptoms of atherosclerosis, sdLDL particles are associated with increased oxidative stress, which may stimulate a compensatory rise in PON1 DZOase activity. Elevated oxidative stress may significantly affect HDL subclass distribution, resulting in the accumulation of smaller, denser HDL particles with diminished antioxidative capacity.

Statins in atherosclerosis: lipid-lowering agents with antioxidant capabilities

Low-density lipoprotein (LDL) cholesterol is an established risk factor for coronary heart disease (CHD). In the presence of oxidative stress LDL particles can become oxidized to form a lipoprotein species that is particularly atherogenic. Indeed, oxidized LDL (oxLDL) is pro-inflammatory, it can cause endothelial dysfunction and it readily accumulates within the arterial wall. Several factors may influence the susceptibility of LDL to oxidation, including its size and composition, and the presence of endogenous antioxidant compounds, such as alpha-tocopherol. Individuals with type 2 diabetes or the metabolic syndrome have high levels of oxidative stress and consequently are at an increased risk for cardiovascular events. Reducing oxidative stress has been proposed as a potential approach to prevent CHD and antioxidant vitamins have been employed with encouraging results in experimental models of atherosclerosis. However, clinical trials have not demonstrated consistent beneficial effects of antioxidants on cardiovascular outcomes. Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are the first-line choice for lowering total and LDL cholesterol levels and they have been proven to reduce the risk of CHD. Recent data suggest that these compounds, in addition to their lipid-lowering ability, can also reduce the production of reactive oxygen species and increase the resistance of LDL to oxidation. It may be that the ability of statins to limit the oxidation of LDL contributes to their effectiveness at preventing atherosclerotic disease.

Association of apolipoprotein A5 variants with LDL particle size and triglyceride in Japanese Americans

A new apolipoprotein (apo) gene, APOA5, was recently identified on chromosome 11q23, and common variants in the gene have been associated with plasma triglyceride (TG) levels in several studies. The purpose of the present study was to examine the association of five single nucleotide polymorphisms (SNPs) and haplotypes in the APOA5 gene with low-density lipoprotein (LDL) particle size using a community-based sample of Japanese American families, including examining whether the associations with LDL size are independent of, or primarily reflecting, TG levels. Genetic association analyses were performed using 154 unrelated individuals, quantitative transmission disequilibrium tests (TDT) in 238 nuclear families, a sample of 24 hypertriglyceridemic subjects with matched, normotriglyceridemic controls, and using haplotype analyses. There was a high degree of allelic association between several of the SNPs, with complete linkage disequilibrium (LD) between -1131C>T and the -3A>G SNP which alters a potential Kozak sequence. All approaches demonstrated associations between the -3A>G APOA5 variant and both decreased LDL size and increased TG levels. The frequency of the rare allele was higher than reported for Caucasian, Hispanic, and African Americans, but similar to that in Japan and China. Therefore, the haplotype containing the -1131C and -3G variants, and possibly specifically the -3A>G SNP in APOA5, may be a major genetic determinant of LDL particle size and TG levels among ethnic Asians.

Treatment of small dense LDL

The increased frequency of small, dense LDL is associated with the risk of coronary heart disease (CHD). Possible mechanisms include the increased susceptibility of small, dense LDL to oxidation and its high affinity for LDL-receptor-independent cell surface binding sites. Although more than 30% of adult men in the USA have been reported to have small,dense LDL, only 5.4% of young Japanese men are affected. However, more than 76% of Japanese diabetics with coronary heart disease have small, dense LDL. Furthermore, almost half of all obese women (BMI > 35 kg/m(2)) have small, dense LDL. Our previous observation revealed that type 2 diabetics had smaller LDL even if they were apparently normolipidemic. In the normotriglycelidemic group there was also a close relationship between LDL size and plasma triglyceride. Diabetics with microalbuminuria had smaller LDL than those with normoalbuminuria, indicating the early nephrotoxicity of small, dense LDL. We also found that young men with high-normal blood pressure have smaller LDL than those with optimal blood pressure. Furthermore, LDL size was decreased not only in preeclamptic women but also in normal pregnant women. Finally, weight reduction by obese women through strict diet control, the treatment of diabetics by acarbose or troglitazone, and the treatment of hyperlipidemia by new statins as well as fibrates were all successful in increasing LDL size associated with decreased plasma triglyceride.

In vitro and in vivo lipolysis of plasma triglycerides increases the resistance to oxidative modification of low-density lipoproteins

BACKGROUND

The majority of studies on low-density lipoprotein (LDL) particle size and susceptibility to oxidative modification have been either descriptive or interventional, but there are few mechanistic studies.

MATERIALS AND METHODS

Effects of exhaustive in vitro and in vivo lipolysis of serum and plasma triglycerides, respectively, by lipoprotein lipase (LPL) were investigated in healthy normotriglyceridemic men. The LDL end-product of lipolysis of very low-density lipoprotein (VLDL) underwent compositional analysis, gradient gel electrophoresis and an assessment of resistance to copper-induced oxidative modification.

RESULTS

The LDL particle contents of free fatty acid and alpha-tocopherol increased, whereas the contents of free and esterified cholesterol, alpha-carotene and coenzyme Q10 decreased upon incubation of serum with LPL in vitro. The LDL particle size decreased and the resistance to the oxidative modification of LDL increased. Lipolysis of plasma triglycerides in vivo, achieved by intravenous injection of heparin, did not alter the LDL particle size but increased the resistance to the oxidative modification of LDL. This change was accompanied by an increase in the LDL particle content of alpha-tocopherol, whereas the free fatty acid content was unaltered.

CONCLUSIONS

The results show that the increased resistance to oxidative modification of LDL after lipolysis of plasma triglycerides was concomitant with an increased LDL particle content of alpha-tocopherol, and that free fatty acids did not seem to contribute to the increased resistance to oxidative modification of LDL in vivo. Furthermore, our data indicate that the resistance of LDL to oxidative modification is not dependent on particle size.

Assay methods of modified lipoproteins in plasma

Modified lipoproteins, especially oxidatively modified low-density lipoprotein (Ox-LDL), are present in the plasma of patients with atherosclerosis and related diseases. The modification of LDL is believed to play an important role in the development of atherosclerosis. Thus, measurement of plasma Ox-LDL is essential not only for investigating its relevance to atherosclerotic diseases, but also for diagnosis. Chromatographic methods are effective for indirectly measuring the oxidatively modified state of LDL or directly measuring the modified LDL. Indirect determination can be done by estimating the LDL subfraction, LDL particle size, oxidized amino acids in apolipoprotein B, lipid hydroperoxide or F(2)-isoprostane in LDL. Direct determination of the modified LDL in plasma can be done with chromatographic methods such as anion-exchange chromatography and size-exclusion chromatography. Other methods for estimating the modified state of LDL include electromigration methods such as agarose gel, polyacrylamide gradient gel and capillary electrophoresis. Recently, enzyme-linked immunosorbent assay methods of malondialdehyde (MDA)-LDL and autoantibodies against Ox-LDL have been developed to assess Ox-LDL in plasma. This review article summarizes the detection and assay methods of modified lipoproteins in plasma.

HMG-CoA reductase inhibitor decreases small dense low-density lipoprotein and remnant-like particle cholesterol in patients with type-2 diabetes

Patients with type 2 diabetes are known to have abnormalities in their remnant metabolism and low density lipoprotein (LDL) subfraction pattern, with a preponderance of small dense LDL. The effects of pitavastatin, a newly synthesized 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, on lipoprotein profiles in patients with type 2 diabetes were determined. Thirty-three patients were treated with pitavastatin with a daily dose of 2 mg for 8 weeks. After treatment, triglyceride, total and LDL cholesterol were significantly reduced by 28.7 +/- 36.7%, 25.2 +/- 14.3% and 36.1 +/- 14.3%, respectively. Remnant-like particle cholesterol (RLP-C), an independent risk factor for CAD which is known to be elevated in diabetic patients, was also significantly reduced (-30.9 +/- 30.5%) by the treatment and this decrease correlated well with the decrease in triglyceride level. The proportion of small dense LDL, which is known for its atherogenisity, decreased from 29.9 +/- 26.2% to 19.7 +/- 22.7% and the mean LDL particle size significantly increased from 26.36 +/- 1.13 nm to 27.10 +/- 1.36 nm. Pitavastatin, which is known to improve triglyceride levels and cholesterol levels, also improves RLP-C level and LDL subfraction profiles, and this in turn may reduce the cardiovascular risk in patients with type 2 diabetes and dyslipidemia.

Potent modification of low density lipoprotein by group X secretory phospholipase A2 is linked to macrophage foam cell formation

The deposition of cholesterol ester within foam cells of the artery wall is fundamental to the pathogenesis of atherosclerosis. Modifications of low density lipoprotein (LDL), such as oxidation, are prerequisite events for the formation of foam cells. We demonstrate here that group X secretory phospholipase A2 (sPLA2-X) may be involved in this process. sPLA2-X was found to induce potent hydrolysis of phosphatidylcholine in LDL leading to the production of large amounts of unsaturated fatty acids and lysophosphatidylcholine (lyso-PC), which contrasted with little, if any, lipolytic modification of LDL by the classic types of group IB and IIA secretory PLA2s. Treatment with sPLA2-X caused an increase in the negative charge of LDL with little modification of apolipoprotein B (apoB) in contrast to the excessive aggregation and fragmentation of apoB in oxidized LDL. The sPLA2-X-modified LDL was efficiently incorporated into macrophages to induce the accumulation of cellular cholesterol ester and the formation of non-membrane-bound lipid droplets in the cytoplasm, whereas the extensive accumulation of multilayered structures was found in the cytoplasm in oxidized LDL-treated macrophages. Immunohistochemical analysis revealed marked expression of sPLA2-X in foam cell lesions in the arterial intima of high fat-fed apolipoprotein E-deficient mice. These findings suggest that modification of LDL by sPLA2-X in the arterial vessels is one of the mechanisms responsible for the generation of atherogenic lipoprotein particles as well as the production of various lipid mediators, including unsaturated fatty acids and lyso-PC.

Lipid risk factor correlates of ischemic heart disease as diagnosed by myocardial perfusion scintigraphy

Patients with known coronary artery disease frequently change their lifestyles (e.g., diet, exercise, and smoking habit) after the diagnosis is made. Such changes can alter lipid risk factor levels and obscure etiologic risk factor associations with the presence of coronary artery disease. It is therefore preferable to determine the contribution of potential risk factors before the diagnosis of coronary artery disease has been established. In this trial, we used stress nuclear myocardial perfusion imaging to diagnose coronary artery disease in patients presenting for evaluation of chest pain. Two groups of age- and sex-matched patients were identified: a normal group (patients with no evidence of coronary artery disease), and an abnormal group (patients whose scans indicated the presence of significant coronary artery disease due to either fixed or reversible perfusion defects). Blood samples were drawn before scanning and analyzed for lipid risk factors. Compared to the normal group, the abnormal group had higher levels of triglycerides (189±91 vs. 135±51 mg/dL, p=0.003), lower levels of high-density lipoprotein cholesterol (39±9 vs. 45±14 mg/dL, p=0.037), and higher levels of small, dense low-density lipoprotein (LDL(3)) (42±18 vs. 32±13 mg/dL, p=0.007). Total cholesterol, low-density lipoprotein, and lipoprotein(a) levels were similar between groups. These findings suggest that ischemic heart disease, as assessed by myocardial perfusion scintigraphy, is more closely associated with the low high-density lipoprotein/high triglyceride syndrome than with increased low-density lipoprotein or total cholesterol levels. (c) 2000 by CHF, Inc.

Comparison of LDL fatty acid and carotenoid concentrations and oxidative resistance of LDL in volunteers from countries with different rates of cardiovascular disease

Within Europe there are differences in cardiovascular disease (CVD) risk between countries and this might be related to dietary habits. Oxidative modification of LDL is suggested to increase the risk of CVD and both the fatty acid and antioxidant content of LDL can affect its oxidation. In the present study, concentration of LDL fatty acid and antioxidant micronutrients (tocopherols and carotenoids) and ex vivo oxidative resistance of LDL (lag phase) was compared in volunteers from five countries with different fruit and vegetable intakes and reported rates of CVD. Eighty volunteers (forty males, forty females per centre), age range 25-45 years, were recruited from France, Northern Ireland, UK, Republic of Ireland, The Netherlands, and Spain, and their LDL composition and lag phase were measured. There were some differences in LDL carotenoid and alpha-tocopherol concentrations between countries. alpha-Tocopherol was low and beta- + gamma-tocopherol were high (P<0.001) in the Dutch subjects. Beta-Carotene concentrations were significantly different between the French and Spanish volunteers, with French showing the highest and Spanish the lowest concentration. LDL lycopene was not different between centres in contrast to lutein, which was highest in French (twofold that in the Dutch and Spanish and threefold that in Northern Ireland and the Republic of Ireland, P<0.001). However absolute LDL saturated, monounsaturated, polyunsaturated and total unsaturated fatty acid concentrations were different between countries (P<0.001, total unsaturated highest in Northern Ireland) there was little difference in unsaturated:saturated fatty acid concentration ratios and no difference in polyunsaturated:saturated fatty acid concentration ratios. LDL from the Republic of Ireland (a region with a high rate of CVD) had greater resistance to Cu-stimulated oxidation than samples obtained from volunteers in other countries. In conclusion, LDL composition did not predict resistance to Cu-stimulated oxidation, nor is there evidence that LDL from volunteers in countries with lower rates of CVD have greater resistance to oxidation.

Intravascular hemolysis increases atherogenicity of diet-induced hypercholesterolemia in rabbits in spite of heme oxygenase-1 gene and protein induction

Free radical mediated oxidation of apoB lipoproteins in the arterial intima appears to contribute to atherogenicity of the entrapped particles. A plausible pathogenic mechanism for oxidation is the one induced by heme leaking from erythrocytes that is then carried into the arterial wall by its high affinity for lipoproteins. In the intima, in the presence of H(2)O(2) secreted by macrophages, heme can be a potent oxidant. To study the role of heme as a promoter of oxidative stress damage in vivo we used a model of intravascular hemolysis (IVH) caused by phenylhydrazine in rabbits with and without diet-induced moderate hypercholesterolemia (MHC). Evaluation of the antioxidant status of plasma indicated that at the end of the treatment period this was compromised by the MHC-IVH. After 10 weeks the animals with combined MHC-IVH showed more of the aorta surface covered by lesions (27%+/-8, mean (SD) than the animals with only MHC (11%+/-7), in spite of having similar plasma levels of VLDL+LDL lipoproteins. The animals with only IVH, as well as the controls, showed minimal lesions (<1%). Heme oxygenase (HO-1) expression in aorta and other tissues was markedly increased in the group with MHC-IVH and it was correlated with the extent of IVH. The data suggest that the oxidative stress associated with IVH potentiates the atherogenicity of moderate hypercholesterolemia and that in spite of a strong induction of HO-1 this is not sufficient to counteract the atherogenicity of the combined condition.

Age-related effects of genetic variation on lipid levels: The Columbia University BioMarkers Study

OBJECTIVES

To examine the genotype:phenotype association in children compared with their parents.

METHODS

Variations at 4 key gene loci, namely lipoprotein lipase (LPL S447X), hepatic lipase (HL -480C>T), cholesteryl ester transfer protein (CETP TaqIB), and apolipoprotein CIII (APOC3 -455T>C and -482C>T), were examined in children (n = 495) and their parents (n = 353) in the Columbia University BioMarkers Study, 1994 to 1998.

RESULTS

The frequencies of the rare alleles of the HL -480C>T and APOC3 -455T>C and -482C>T (but not LPL S447X or CETP TaqIB) were significantly lower in non-Hispanic white participants compared with Hispanics. Overall, genotype effects seen in the adults were weaker in the children, although similar trends were seen. In an examination of the effect of body fat on the genotypic effects in the children, there was significant HL -480C>T:sum of skinfold interaction.

CONCLUSIONS

All genotypes were associated with clear relationships to plasma lipid levels in adults, but the effects were weaker in their children, unless stressed by body fat. atherosclerosis, cardiovascular disease, child, lipids, genetics.

Cardiovascular risk factors and LDL subfraction profile in Type 2 diabetes mellitus subjects with good glycaemic control

OBJECTIVES

To compare cardiovascular risk factors and LDL particle size in well-controlled Type 2 diabetes mellitus and normal subjects.

METHODS

Ninety-three Type 2 diabetic males and 186 age-matched, male controls were studied. Glycaemic control was stable for at least 3 months prior to recruitment. None were on insulin or lipid lowering therapy. Anthropometric indices, blood pressure, lipids, glucose, insulin, apolipoprotein A1 and B, LDL subfraction by density ultracentrifugation were obtained after an overnight fast of 10 h.

RESULTS

Diabetic subjects (mean HbA(1c) 6.6%+/-0.10) did not differ from controls in total cholesterol levels (5.04+/-0.08 vs. 5.16+/-0.05 mmol/l, respectively) but had lower serum HDL cholesterol (0.98+/-0.03 vs. 1.12+/-0.02 mmol/l, P<0.001), higher serum triglyceride (2.38+/-0.16 vs. 1.80+/-0.08 mmol/l, P<0.001), lower LDL(1) and LDL(2) and higher LDL(3) concentration. An LDL(3) concentration exceeding 100 mg/dl was found in 59.1% of diabetics and 39.1% of non-diabetics (P<0.001). Diabetic subjects also had higher body mass index, waist to hip ratio and insulin resistance (HOMA). Difference in LDL subfraction between groups disappeared after adjustments were made for either triglyceride or HDL cholesterol.

CONCLUSION

Well controlled Type 2 diabetes mellitus subjects exhibit an increased cardiovascular burden through low HDL cholesterol and predominance of small, dense LDL particles.

Enhanced oxidative susceptibility and reduced antioxidant content of metabolic precursors of small, dense low-density lipoproteins

PURPOSE

Elevated plasma concentrations of low-density lipoproteins (LDL) increase risk for coronary heart disease. However, lipoprotein profiles rich in small, dense LDL particles confer greater risk than those that mainly consist of large, buoyant LDL. This may be due, in part, to the greater oxidative susceptibility of small, dense LDL. In the current studies, we tested whether differences in the oxidative behavior of buoyant and dense LDL arise from differences in their immediate metabolic precursors, intermediate-density lipoproteins.

SUBJECTS AND METHODS

We compared the properties of intermediate-density lipoproteins and buoyant and dense LDL subfractions in 9 subjects with the large, buoyant LDL phenotype versus 6 with the small, dense LDL phenotype. Oxidative susceptibility was evaluated based on conjugated diene formation and parinaric acid oxidation induced by copper. Antioxidants (ubiquinol-10 and alpha-tocopherol) were measured by high-performance liquid chromatography.

RESULTS

Oxidative susceptibility was increased and antioxidant concentrations were decreased with increasing lipoprotein density (intermediate intermediate-density lipoproteins to buoyant LDL to dense LDL). Intermediate-density lipoproteins from subjects with the small, dense LDL phenotype had a greater oxidative susceptibility (by the parinaric acid test) and lower antioxidant concentrations than corresponding particles from subjects with the large, buoyant LDL phenotype.

CONCLUSIONS

Differences in oxidative susceptibility between large, buoyant and small, dense LDL particles are apparent in their lipoprotein precursors. These results suggest that lipoprotein oxidative susceptibility may be metabolically programmed and that intermediate-density lipoproteins may contribute to the increased risk associated with the small, dense LDL phenotype.

Activated platelets in patients with severe hypertriglyceridemia: effects of triglyceride-lowering therapy

Hypertriglyceridemia, a risk factor for cardiovascular disease, has been associated with hypercoagulability, but whether platelet activation is implicated is unknown. This study was designed to compare the in vivo platelet activation status between patients with severe hypertriglyceridemia and age- and sex-matched control subjects, and to evaluate the effects of triglyceride-lowering therapy. Sixteen patients with primary hypertriglyceridemia were included in a double-blind, placebo-controlled cross-over trial with 400 mg bezafibrate once daily. Platelet activation was analysed by double label flow cytometry, using monoclonal antibodies against GP53, P-selectin, and platelet-bound fibrinogen. Surface expression of the lysosomal membrane protein GP53 was significantly higher in the hypertriglyceridemic patients at baseline as compared to the group of age- and sex-matched controls (16.3+/-4.8% vs. 8.9+/-3.4%, respectively, P<0.001). No differences in the expression of P-selectin and fibrinogen binding were observed. In response to bezafibrate therapy, the expression of GP53 in the patient group decreased from 16.3+/-4.8% to 13.1+/-4.1% (P=0.018). The expression of P-selectin and fibrinogen binding was not affected by bezafibrate therapy. In conclusion, patients with hypertriglyceridemia have an increased in vivo platelet activation status, which can be improved by bezafibrate therapy.

Phospholipase A2 and small, dense low-density lipoprotein

High levels of small, dense LDL in plasma are associated with increased risk for cardiovascular disease. There are some biochemical characteristics that may render small, dense LDL particles more atherogenic than larger, buoyant LDL particles. First, small, dense LDL particles contain less phospholipids and unesterified cholesterol in their surface monolayer than do large, buoyant LDL particles. This difference in lipid content appears to induce changes in the conformation of apolipoprotein B-100, leading to more exposure of proteoglycan-binding regions. This may be one reason for the high-affinity binding of small, dense LDL to arterial proteoglycans. Reduction of the phospholipid content in the surface monolayer LDL by treatment with secretory phospholipase A2 (sPLA2) forms small, dense LDL with an enhanced tendency to interact with proteoglycans. Circulating levels of sPLA2-IIA appears to be an independent risk factor for coronary artery disease and a predictor of cardiovascular events. In addition, in-vivo studies support the hypothesis that sPLA2 proteins contribute to atherogenesis and its clinical consequences. These data suggest that modification of LDL by sPLA2 in the arterial tissue or in plasma may be a mechanism for the generation of atherogenic lipoprotein particles in vivo, with a high tendency to be entrapped in the arterial extracellular matrix.

The capacity of various non-esterified fatty acids to suppress lipid transfer inhibitor protein activity is related to their perturbation of the lipoprotein surface

Lipid transfer inhibitor protein (LTIP) regulates cholesteryl ester transfer protein (CETP) activity by selectively impeding lipid transfer events involving low density lipoproteins (LDLs). We previously demonstrated that LTIP activity is suppressed in a dose-dependent manner by sodium oleate and that its activity can be blocked by physiological levels of free fatty acids [R.E. Morton, D. J. Greene, Arterioscler. Thromb. Vasc. Biol. 17 (1997)]. These data further suggested that palmitate has greater LTIP suppressive activity than oleate. In this report we define the ability of the major non-esterified fatty acids (NEFAs) in plasma to modulate LTIP activity. The greater suppression of LTIP activity by palmitate compared to oleate noted above was also seen in lipid transfer assays with various lipoprotein substrates and in the presence of albumin, showing that the relative effects of these two NEFAs are independent of assay conditions. To assess the effect of other NEFAs on LTIP activity, pure NEFAs were added to assays containing (3)H-cholesteryl ester labeled LDLs, unlabeled high density lipoproteins (HDLs) and CETP+/-LTIP. Whereas myristate, palmitate, stearate, oleate and linoleate stimulated CETP activity to varying extents, all NEFAs suppressed LTIP activity. Among these NEFAs, LTIP suppressive activity was greatest for the long-chain saturated and monounsaturated NEFAs. In contrast, linoleate and myristate were poor inhibitors of LTIP activity. The effects of increasing amounts of a given NEFA on LTIP activity correlated well with the increase in LDL negative charge induced by that NEFA, yet this relationship was unique for each NEFA, especially stearate. Notably, as measured by fluorescence anisotropy, the suppression of LTIP was highly and negatively correlated with the decreased order in the molecular packing of lipoprotein surface phospholipids caused by all NEFAs. Long-chain, saturated and monounsaturated NEFAs appear to be most effective in this regard partly because of their preferential association with LDLs where LTIP inhibition likely takes place. We hypothesize that NEFAs suppress LTIP activity by perturbing the surface properties of LDLs and counteracting the heightened molecular packing normally caused by LTIP. Diets rich in long-chain saturated and monounsaturated fatty acids may lead to a greater suppression of LTIP activity in vivo, which would allow LDLs to participate more actively in CETP-mediated lipid transfer reactions.

Plasma thiols inhibit hemin-dependent oxidation of human low-density lipoprotein

Oxidative modification of human low-density lipoprotein (LDL) renders it atherogenic. Previous studies demonstrated that plasma thiols promote oxidation of LDL by free ferric iron (Fe3+). The current study investigated effects of plasma thiols on oxidation of LDL by hemin, a physiological Fe3+-protoporphyrin IX complex thought to be capable of initiating LDL oxidation in vivo. In contrast to free Fe3+ which is incapable of oxidizing LDL in the absence of an exogenous reductant, hemin readily promoted LDL oxidation. During incubation of LDL (0.2 mg of protein/ml) with hemin (10 microM) at 37 degrees C for 6 h, thiobarbituric acid-reactive substances (TBARS), a marker of lipid oxidation, increased from 0.3 (+/-0.1) nmol/mg of LDL protein to a maximal concentration of 45.8 (+/-5.2) nmol/mg of LDL protein. Under the same experimental conditions, lipid-conjugated dienes, another marker of lipid oxidation, increased from non-detectable to near-maximal levels of 78-187 nmol/mg of LDL protein, and lipoprotein polyunsaturated fatty acyl-containing cholesteryl ester content decreased to 15-36% of that present in native (i.e. unoxidized) LDL. Continued incubation of LDL with hemin for up to 24 h resulted in no further significant alterations in lipoprotein levels of TBARS, lipid-conjugated dienes, and cholesteryl esters. In addition to these chemical modifications indicative of lipoprotein oxidation, agarose gel electrophoretic analysis indicated that exposure of LDL to hemin resulted in conversion of the lipoprotein to an atherogenic form as evidenced by its increased anodic electrophoretic mobility. Addition of physiological concentrations of plasma thiols (either cysteine, homocysteine or reduced glutathione; 1-100 microM, each) inhibited hemin-mediated oxidation of LDL. Thus, whereas the maximal TBARS concentration was achieved following 6 h of incubation of LDL with hemin alone, addition of thiol extended the time required to attain maximal TBARS concentration to > or = 12 h. Similar antioxidant effects of thiols on formation of lipid-conjugated dienes, loss of cholesteryl esters, and lipoprotein anodic electrophoretic mobility were also observed. However, all thiols were not equally effective at inhibiting hemin-dependent LDL oxidation. Thus, whereas reduced glutathione was most effective at inhibiting hemin-dependent LDL oxidation, an intermediate effect was observed for homocysteine, and cysteine was least effective. The inhibition of hemin-mediated LDL oxidation by plasma thiols reported here confirms a previous observation that, under certain conditions, thiols can function as antioxidants, but contrasts with the previously documented pro-oxidant effect of the same thiols on oxidation of LDL by free Fe3+. These contrasting effects of plasma thiols on hemin- and free Fe3+-mediated LDL oxidation indicate that, in vivo, the ability of thiols to function as either anti- or pro-oxidants during LDL oxidation may, at least in part, be determined by the type of oxidant stress to which the lipoprotein is exposed.

Alpha-tocopherol supplementation decreases the oxidative susceptibility of LDL in renal failure patients on dialysis therapy

Atherosclerotic cardiovascular disease is the leading cause of death in patients with end stage renal disease (ESRD) who have undergone dialysis treatment. The oxidation of low density lipoprotein (LDL) appears to be a crucial step in the pathogenesis of atherosclerosis. The increased oxidative stress and attendant increased oxidizability of lipoproteins, such as LDL could contribute to the accelerated atherosclerosis in dialysis patients. Since alpha-tocopherol (AT) is the major antioxidant in LDL, the aim of the present study was to test the effectiveness of RRR-AT supplementation (800 I.U. per day) for 12 weeks on the susceptibility of LDL to oxidation. The study subjects comprised patients with chronic renal failure on hemodialysis (HD), peritoneal dialysis (PD), and age and sex matched controls (C). Plasma fatty acids, lipoproteins and AT levels were measured in these subjects before and after supplementation. Also, LDL AT and oxidizability was studied. LDL was isolated by ultracentrifugation at baseline and after 12 weeks of supplementation, and subjected to a 5-h time course of copper catalyzed oxidation. Oxidation was measured by the formation of conjugated dienes (CD) and lipid peroxides (LP). Supplementation with AT did not alter the plasma lipid or lipoprotein profile of these subjects. Plasma lipid-standardized AT and LDL AT concentrations were not different among the groups at baseline. AT supplementation significantly increased plasma lipid-standardized AT (C=150%, HD=149%, PD=217%, P<0.001) and LDL AT concentrations (C=94%, HD=94%, PD=135%, P<0.003). AT enrichment of LDL resulted in a significant prolongation in conjugated diene lag phase in all groups (C=34%, HD=21%, PD=54%, P<0.02). Lipid peroxide lag phase was also increased significantly in C (27%,) and PD (40%) groups after AT supplementation (P<0.01). There was a significant positive correlation between plasma lipid standardized AT and lag phase (r=0. 54, P=0.0003). Overall, AT decreased the susceptibility of LDL to oxidation in patients with chronic renal failure but the benefit appears to be greater in patients on PD. Therefore, AT supplementation may also provide a measure of protection against CAD in patients with chronic renal failure on dialysis therapy.

Dietary cholesterol increases the susceptibility of low density lipoprotein to oxidative modification

Evidence suggests that oxidative modification of low density lipoprotein (LDL) occurs in vivo, increasing the atherogenecity of the particle. A total of 13 subjects (age range 46-78 years) with an LDL cholesterol concentration >3.36 mmol/l consumed each of four diets for 32-day periods. The diets contained 30% energy as fat of which 2/3 was either corn oil or beef tallow with and without 115 mg/4.2 MJ of supplemental cholesterol in the form of cooked egg yolk. The susceptibility of LDL to oxidation was assessed during a challenge with hemin and hydrogen peroxide, and results are expressed as lag time to oxidation in minutes. Addition of moderate amounts of cholesterol to either the corn oil or beef tallow enriched diet resulted in increased susceptibility of LDL to oxidation (decreased lag time): 69+/-22 min versus 96+/-24 min in the corn oil diet with versus without supplemental cholesterol, respectively, P = 0.006; 82+/-20 min versus 96+/-26 min in the beef tallow diet with versus without supplemental cholesterol, respectively, P = 0.025. A stepwise equation indicated that as plasma oleic acid concentrations increased and/or linoleic acid concentrations decreased, lag time increased (decreased susceptibility to oxidation), whereas as dietary cholesterol concentrations increased, lag time decreased (increased susceptibility to oxidation). In conclusion, these data suggest that addition of a moderate amount of dietary cholesterol to a reduced fat diet rich in polyunsaturated or saturated fatty acids increased the in vitro susceptibility of LDL to oxidation.

Novel physiological function of sphingomyelin in plasma. Inhibition of lipid peroxidation in low density lipoproteins

Although sphingomyelin (SPH) is a major constituent of all lipoproteins, its physiological function in plasma is not known. In this study, we tested the hypothesis that SPH inhibits lipid peroxidation in low density lipoproteins (LDL) because of its effects on surface fluidity and packing density and that the relative resistance of the buoyant LDL to oxidation, compared with the dense LDL, is partly due to their higher SPH content. Depletion of SPH by treatment with SPHase resulted in shortened lag times and increased rates of oxidation in both LDL subfractions, as measured by the conjugated diene formation in the presence of Cu(2+). Oxidation of LDL by soybean lipoxygenase was similarly stimulated by the degradation of SPH. Oxidation-induced fluorescence decay of diphenylhexatriene-labeled phosphatidylcholine (PC), equilibrated with LDL-PC, was accelerated significantly by the enzymatic depletion of SPH from the lipoprotein. Oxidation of 16:0-18:2 PC in the proteoliposomes was inhibited progressively by the incorporation of increasing amounts of egg SPH into the liposomes. Treatment of SPH-containing proteoliposomes with SPHase reversed the effect of SPH, showing that the presence of intact SPH is necessary for the inhibition of oxidation. Although the incorporation of SPH into the same liposome as the PC (intrinsic SPH) protected the PC against oxidation, the addition of SPH liposomes to PC liposomes (extrinsic SPH) was not effective. Oxidation of 16:0-18:2 PC in liposomes was also inhibited by the incorporation of dipalmitoyl-PC, but not by free cholesterol. These results suggest that SPH acts as a physiological inhibitor of lipoprotein oxidation, possibly by modifying the fluidity of the phospholipid monolayer and thereby inhibiting the lateral propagation of the lipid peroxy radicals.

Phospholipase A(2) modification of low density lipoproteins forms small high density particles with increased affinity for proteoglycans and glycosaminoglycans

The presence of a lipoprotein profile with abundance of small, dense low density lipoproteins (LDL), low levels of high density lipoproteins (HDL), and elevated levels of triglyceride-rich very low density lipoproteins is associated with an increased risk for coronary heart disease. The atherogenicity of small, dense LDL is believed to be one of the main reasons for this association. This particle contains less phospholipids (PL) and unesterified cholesterol than large LDL, and the apoB-100 appears to occupy a more extensive area at its surface. Although there are experiments that suggest a metabolic pathway leading to the overproduction of small, dense LDL, no clear molecular model exists to explain its association with atherogenesis. A current hypothesis is that small, dense LDL, because of its higher affinity for proteoglycans, is entrapped in the intima extracellular matrix and is more susceptible to oxidative modifications than large LDL. Here we describe how a specific reduction of approximately 50% of the PL of a normal buoyant LDL by immobilized phospholipase A(2) (PLA(2)) (EC 3.1.1.4) produces smaller and denser particles without inducing significant lipoprotein aggregation (<5%). These smaller LDL particles display a higher tendency to form nonsoluble complexes with proteoglycans and glycosaminoglycans than the parent LDL. Binding parameters of LDL and glycosaminoglycans and proteoglycans produced by human arterial smooth muscle cells were measured at near to physiological conditions. The PLA(2)-modified LDL has about 2 times higher affinity for the sulfated polysaccharides than control LDL. In addition, incubation of human plasma in the presence of PLA(2) generated smaller LDL and HDL particles compared with the control plasma incubated without PLA(2). These in vitro results indicate that the reduction of surface PL characteristic of small, dense LDL subfractions, besides contributing to its small size and density, may enhance its tendency to be retained by proteoglycans.

Lipoprotein atherogenicity: an overview of current mechanisms

Raised serum cholesterol does not adequately explain the increased risk of CHD within populations or the relationship between diet and CHD. Nevertheless, the principal transport vehicle of cholesterol in the circulation, LDL, must still be regarded as the most atherogenic lipoprotein species, but not because of its contribution to serum cholesterol. The atherogenic potential of LDL in the majority of individuals arises from an increase in the number of small dense LDL particles and not from its cholesterol content per se. There is now a wealth of evidence from cross-sectional and prospective studies to show that LDL particle size is significantly associated with CHD and predictive of increased coronary risk. Moreover, there are a number of credible mechanisms to link small dense LDL with the atherogenic process. The rate of influx of serum lipoproteins into the arterial wall is a function of particle size, and will thus be more rapid for small dense LDL. Components of the extracellular tissue matrix in the intima, most notably proteoglycans, selectively bind small dense LDL with high affinity, sequestering this lipoprotein in a pro-oxidative environment. The oxidation of LDL promotes the final deposition of cholesterol in the arterial wall, and numerous studies have shown small dense LDL to be more susceptible to oxidative modification than its larger and lighter counterparts. An increase in the number of small dense LDL particles may originate from a defect in the metabolism of triacylglycerol-rich lipoproteins. One mechanism may involve the overproduction and increased residence time of large triacylglycerol-rich VLDL in the postprandial phase, a situation thought to arise through pathways of insulin resistance.

Varying dietary fat type of reduced-fat diets has little effect on the susceptibility of LDL to oxidative modification in moderately hypercholesterolemic subjects

The effect of the fatty acid composition of reduced-fat diets on the in vitro oxidation of LDL was examined in 14 moderately hypercholesterolemic [low density lipoprotein (LDL) > 3.36 mmol/L] postmenopausal female and male subjects (age 44-78 y). Each subject consumed each of five reduced-fat diets [30 energy percent (E%) fat, 17 E% protein and 53 E% carbohydrate] enriched in beef tallow, canola oil, corn oil, olive oil or rice bran oil (20 E%) for 32-d periods. In vitro oxidation of LDL was assessed by incubating LDL with hemin and hydrogen peroxide, and measuring the time required for the reaction to reach maximum velocity (lag time). LDL lag times were 93.2 +/- 25.8, 95.9 +/- 26.4, 104.2 +/- 32.7, 108.0 +/- 26.6 and 113.1 +/- 24.0 min for corn oil, beef tallow, rice bran oil, canola oil and olive oil periods, respectively. When the data from all dietary phases were pooled, LDL alpha-tocopherol level (r = 0.30, P = 0.01) and plasma 18:1/18:2 ratio (r = 0.22, P = 0.08) were positively related to resistance of LDL to oxidation. Differences induced by the dietary perturbations in LDL content of beta-cryptoxanthin, lutein/zeaxanthin, lycopene, alpha-carotene or beta-carotene, and LDL particle size were not related to resistance of LDL to oxidation. In conclusion, in middle-aged and elderly moderately hypercholesterolemic subjects, the consumption of reduced-fat diets enriched in animal fat or vegetable oils with a relatively wide range of fatty acid profiles did not alter the in vitro susceptibility of LDL to oxidation. The advantages of reducing the saturated fat content of the diet were reflected in lower total and LDL cholesterol levels.

Measurement of LDL particle size in whole plasma and serum by high performance gel-filtration chromatography using a fluorescent lipid probe

We have recently described a technique for measuring LDL size by high performance gel-filtration chromatography (HPGC) with UV detection (Scheffer et al., Clin Chem 1997;43:1904–12). A drawback of this method is the necessity of LDL isolation before chromatography. We now describe a modification of this method based on selective detection of lipoproteins by postcolumn labeling with parinaric acid, a fluorescent lipid probe. Measuring the size of isolated LDL by HPGC in 56 subjects, we obtained diameters of 25.72 ± 0.60 nm with UV detection and of 25.74 ± 0.58 nm with fluorescence detection. The modified method is suitable for LDL size measurement in whole plasma or serum. LDL sizes measured in whole plasma correlated strongly with the respective values in isolated LDL (r = 0.976) but were on average 0.18 nm larger (P &lt; 0.001). CVs for within- and between-series imprecision were &lt;0.25%. The present method requires only 5 μL plasma or serum without sample preparation and is suitable for the unattended analysis of large series of samples.

ACP Broad Sheet no 151: September 1997. Investigation of dyslipidaemias

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Cellular consequences of the association of apoB lipoproteins with proteoglycans. Potential contribution to atherogenesis

Many of the discussed results come from empirical experiments performed with in vitro models whose relevance to the complex environment of the intima is limited. However, they are consistent with the line of reasoning that intima PGs interact specifically with apoB lipoproteins and contribute to their retention. This could provide the residence time and the initial alterations of the lipoproteins that favor their further modifications by oxidative processes and hydrolytic enzymes. Products of such modifications, and the modified particles, may be stimuli for changes in the functionality of endothelium, smooth muscle cells, and macrophages. The focal synthesis of PGs with high affinity for apoB lipoproteins could make the phenomena chronic. Clinical and laboratory studies indicate that dense LDL, poor in surface polar lipids, is associated with an atherogenic phenotype. Particles with these properties may contribute to the disease via its high affinity for arterial PGs. This affinity can be modulated by diet, lifestyle, and lipid-lowering drugs.