Low-density Lipoprotein Subclasses Research Articles

Differential effect of two nicotinic acid preparations on low-density lipoprotein subclass distribution in patients classified as low-density lipoprotein pattern A, B, or I

We tested the hypothesis that treatment with nicotinic acid results in a differential blood lipid response in subjects classified as having a low-density lipoprotein (LDL) pattern A or B. One hundred eighty hypercholesterolemic subjects were randomized to placebo (n = 61), immediate-release niacin (3,000 mg/day, n = 59), or extended-release niacin (1,500 mg/day, n = 60) for 14 weeks. Lipids and lipoprotein cholesterol were determined with enzymatic methods. LDL subclass distribution was determined with 2% to 16% polyacrylamide gradient gel electrophoresis. Extended- and immediate-release niacin had significant effects on the decrease of triglycerides, total cholesterol, LDL cholesterol, apoprotein B, lipoprotein(a), and apoprotein A-I and significantly increased high-density lipoprotein cholesterol. The 2 nicotinic acid compounds and doses significantly increased mean LDL peak particle diameter and percent distribution in large LDL I and IIa, with a significant decrease in small LDL IIIa, IIIb, and IVb. In patients with LDL pattern B compared with those with pattern A, extended-release niacin (1,500 mg/day) increased LDL peak particle diameter significantly more and decreased the percent distributions of small LDL IIIa, LDL IIIb, and LDL IVa significantly more. With 3,000 mg/day, immediate-release nicotinic acid in patients with LDL pattern B exhibited a significantly greater increase in LDL peak particle diameter and large LDL IIa and IIb and significantly greater decreases in small LDL IIIa, IIIb, and IVa compared with patients with pattern A. These differences in response between patients with LDL pattern A and those with pattern B were not reflected by changes in the standard lipid profile, including apoproteins A-I and B. Nicotinic acid has a significantly different effect on lipids and lipoprotein subclass distribution in subjects classified as having LDL subclass pattern A or B. Nicotinic acid has a significantly greater effect on the decrease of small LDL subclass distribution and increase in LDL peak particle diameter in pattern B versus pattern A.

Effects of atorvastatin on triglyceride-rich lipoproteins, low-density lipoprotein subclass, and C-reactive protein in hemodialysis patients

Dyslipidemia is an important risk factor for cardiovascular disease in patients with chronic renal failure (CRF). We evaluated the safety and efficacy of atorvastatin in patients with dyslipidemia associated with CRF who were undergoing hemodialysis (HD). Thirty-five patients who were receiving HD were given atorvastatin (10 mg/d) for 3 months. Chylomicron (CM), light and dense very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and light and dense low-density lipoprotein (LDL) were separated by ultracentrifugation. Apolipoprotein (apo) B was measured by electroimmunoassay. Mean LDL particle diameter was measured by gradient gel electrophoresis. Atorvastatin therapy reduced LDL-cholesterol (C) by 36% and remnant-like particle (RLP)-C by 58%. Atorvastatin significantly reduced apo B, apo CIII, and apo E in VLDL by 40% to 46% and IDL-apo B by 66%. Atorvastatin also significantly reduced cholesterol in CM, light VLDL, and dense VLDL without consistently affecting triglyceride (TG) in these lipoproteins. Atorvastatin similarly reduced both light and dense LDL-apo B by 38%. LDL particle size in the HD patients significantly increased during atorvastatin treatment from 25.7 ± 0.4 to 26.2 ± 0.6 nm. High sensitive C-reactive protein (HS-CRP) was halved by atorvastatin decreasing from 0.08 ± 0.05 to 0.04 ± 0.03 mg/dL. Atorvastatin treatment did not affect the creatinine kinase level, and no classical adverse effects were observed during the study. These results suggest that atorvastatin is safe and effective for the management of dyslipidemia in patients with CFR who are receiving HD, which may help to suppress the development of atherosclerosis.

High intake of cholesterol results in less atherogenic low-density lipoprotein particles in men and women independent of response classification*1

<h2>Abstract</h2> The influence of a high-cholesterol diet on the atherogenicity of the low-density lipoprotein (LDL) particle was examined by measuring LDL peak diameter and composition, LDL susceptibility to oxidation, and the distribution of cholesterol between LDL subclasses. The crossover intervention randomly assigned 27 premenopausal women and 25 men (18 to 50 years) to an egg (640 mg/d additional dietary cholesterol) or placebo (0 mg/d additional dietary cholesterol) diet for 30 days, followed by a 3-week washout period. Subjects were classified as either hyperresponders (>2.5 mg/dL increase in plasma cholesterol for each 100 mg additional dietary cholesterol consumed) or hyporesponders to dietary cholesterol. Sex was found to have a significant effect on 3 of the parameters examined. LDL peak diameter was significantly larger (<i>P</i> < .005) in females (26.78 ± 0.59 nm, n=27) as compared with males (26.52 ± 0.49 nm, n=25), regardless of response to dietary cholesterol. The LDL particles of the male participants also had a higher number of triglyceride (TG) and cholesteryl ester (CE) molecules (<i>P</i> < .01); however, cholesterol ester transfer protein (CETP) activity was higher in females (<i>P</i> < .05). Response classification also revealed significant differences in the determination of LDL subclasses. Independent of sex, the LDL-1 particle (<i>P</i> < .05), which is considered to be less atherogenic, was predominant in hyperresponders and this finding was associated with increased cholesterol intake (interactive effect, <i>P</i> < .001). In addition, CETP and lecithin: cholesterol acyltransferase (LCAT) activities were higher in hyperresponders during the egg period (interactive effect, <i>P</i> < .05). Sex, response to cholesterol intake, and diet were not found to affect the susceptibility of LDL to oxidation (<i>P</i> > 0.5). Because LDL peak diameter was not decreased and the larger LDL-1 subclass was greater in hyperresponders following egg intake, these data indicate that the consumption of a high-cholesterol diet does not negatively influence the atherogenicity of the LDL particle.

High intake of cholesterol results in less atherogenic low-density lipoprotein particles in men and women independent of response classification

The influence of a high-cholesterol diet on the atherogenicity of the low-density lipoprotein (LDL) particle was examined by measuring LDL peak diameter and composition, LDL susceptibility to oxidation, and the distribution of cholesterol between LDL subclasses. The crossover intervention randomly assigned 27 premenopausal women and 25 men (18 to 50 years) to an egg (640 mg/d additional dietary cholesterol) or placebo (0 mg/d additional dietary cholesterol) diet for 30 days, followed by a 3-week washout period. Subjects were classified as either hyperresponders (>2.5 mg/dL increase in plasma cholesterol for each 100 mg additional dietary cholesterol consumed) or hyporesponders to dietary cholesterol. Sex was found to have a significant effect on 3 of the parameters examined. LDL peak diameter was significantly larger ( P < .005) in females (26.78 ± 0.59 nm, n = 27) as compared with males (26.52 ± 0.49 nm, n = 25), regardless of response to dietary cholesterol. The LDL particles of the male participants also had a higher number of triglyceride (TG) and cholesteryl ester (CE) molecules ( P < .01); however, cholesterol ester transfer protein (CETP) activity was higher in females ( P < .05). Response classification also revealed significant differences in the determination of LDL subclasses. Independent of sex, the LDL-1 particle ( P < .05), which is considered to be less atherogenic, was predominant in hyperresponders and this finding was associated with increased cholesterol intake (interactive effect, P < .001). In addition, CETP and lecithin: cholesterol acyltransferase (LCAT) activities were higher in hyperresponders during the egg period (interactive effect, P < .05). Sex, response to cholesterol intake, and diet were not found to affect the susceptibility of LDL to oxidation ( P > 0.5). Because LDL peak diameter was not decreased and the larger LDL-1 subclass was greater in hyperresponders following egg intake, these data indicate that the consumption of a high-cholesterol diet does not negatively influence the atherogenicity of the LDL particle.

Relationship between low-density lipoprotein subclasses and asymptomatic atherosclerosis in subjects from the atherosclerosis risk in communities (ARIC) Study

Low-density lipoprotein (LDL) particle size has been associated with coronary heart disease, but an association between LDL size and preclinical atherosclerosis is less well established. Using gradient gel electrophoresis, large (A), intermediate (I) and small (B) LDL size subclasses were determined in 198 cases with asymptomatic carotid artery atherosclerosis (determined by B-mode ultrasonography) and 318 controls from the Atherosclerosis Risk in Communities (ARIC) Study. In Caucasians, a smaller LDL size was more prevalent in men and associated with a higher body mass index, hypertension prevalence, and plasma total- and LDL-cholesterol and triglycerides, but lower HDL-cholesterol. In African-Americans, a smaller LDL size was associated with higher triglycerides and lower HDL-cholesterol and hypertension prevalence. In Caucasians, Subclass B prevalence was 29.1% among cases and 14.8% among controls. The odds ratio (95% confidence interval) for Subclass B rather than Subclass A in Caucasian cases was 2.94 (1.67–5.17); the association remained significant after controlling for age, body mass index, smoking, and either plasma triglycerides or HDL-cholesterol. In African-Americans, however, there was no significant association between LDL subclass and case status. A predominance of smaller LDL particles is associated with asymptomatic carotid artery atherosclerosis in Caucasians, through mechanisms that remain to be elucidated.

High insulin levels and increased low-density lipoprotein oxidizability in pediatric patients with systemic lupus erythematosus.

To examine low-density lipoprotein (LDL) size, LDL susceptibility to oxidation, and plasma insulin levels in children with systemic lupus erythematosus (SLE). Fifty-nine SLE patients and 59 healthy, age-matched control subjects were studied. LDL size was determined by gradient gel electrophoresis. LDL oxidizability was assessed by lag time for conjugated diene formation during copper incubation. Plasma levels of fasting insulin, glucose, lipids, lipoproteins, apolipoproteins B and A-I, and fatty acids were also measured. Compared with control subjects, SLE patients showed significantly higher plasma insulin levels and increased susceptibility of LDLs to oxidation. Patients with active disease were more likely than patients with inactive disease or control subjects to have the following lipid characteristics: small, dense LDL subclass, elevated total cholesterol levels, elevated LDL cholesterol levels, elevated triglyceride levels, and low levels of high-density lipoprotein cholesterol (HDL-C). Statistically significant direct correlations were observed between disease activity and triglyceride levels and between disease activity and lag time, whereas significant inverse correlations were found between disease activity and HDL-C levels and between disease activity and LDL size. Prednisone dosage explained only 15.6% of the variance in insulin levels. SLE patients have higher plasma insulin levels and increased LDL oxidizability compared with healthy control subjects. These abnormalities may contribute to the accelerated atherosclerosis observed in patients with SLE.

Effects on lipoprotein subclasses of combined expression of human hepatic lipase and human apoB in transgenic rabbits.

The effects of combined expression of human hepatic lipase (HL) and human apolipoprotein B (apoB) on low-density lipoprotein (LDL) subclasses were examined in rabbits, a species naturally deficient in HL activity. In apoB-transgenic rabbit plasma, >80% of the protein was found in the 1.006- to 1.050-g/mL fraction. Gradient gel electrophoresis (GGE) of this fraction revealed two distinct species, designated large and small LDL. A denser fraction (d=1.050 to 1.063 g/mL) contained small LDL as well as another discrete LDL subspecies, designated very small LDL. Expression of HL resulted in reductions in protein concentrations in the 1.006- to 1.050-g/mL density-gradient subfractions containing large (6.5+/-4.1 versus 32.6+/-12.0 mg/dL, P<0.005) and small LDL (59.6+/-17.4 versus 204.3+/-50.3 mg/dL, P<0.002). A concomitant small but not significant increase in protein concentration in the denser LDL fraction (48.0+/-28.2 versus 44.6+/-18.2 mg/dL) was due primarily to an increase in very small LDL (25.9+/-3.1 versus 9.6+/-5.4% of total LDL GGE densitometric area, P<0.002). These findings support a direct role for HL in regulating total plasma LDL concentrations as well as in the production of smaller, denser LDL from larger, more buoyant precursors.

Low-density lipoprotein subclass and its correlating factors in diabetics

Objectives Small dense LDL, low density lipoprotein (LDL) particles with small size and high density, is regarded as a significant risk factor for cardiovascular diseases. Diabetes mellitus is one of the conditions accompanied by increased small dense LDL. We analyzed LDL subclass in type 2 diabetics and normal controls with LipoPrint LDL System to investigate the LDL heterogeneity in diabetics and factors affecting it. Design and methods We selected 40 normal controls and 40 type 2 diabetics with fasting blood glucose level over 7.0 mmol/L and HbA1c level over 7%. LDL subclass was determined with LipoPrint LDL System. LipoPrint LDL System fractionates LDL into seven parts (LDL1-7) by size and LDL3 to LDL7 are defined as small-sized LDL. In addition we estimated ‘the percent of small-sized LDL over whole LDL’ and defined it as ‘small-sized LDL proportion’. Results Mean small-sized LDL proportion was significantly higher in diabetics (23.4%) than in controls (11.8%) ( p < 0.001) and small-sized LDL proportion showed positive correlation with blood levels of glucose, HbA1c, total cholesterol, triglyceride, and oxidized LDL and negative correlation with HDL cholesterol level in univariate analysis ( p < 0.001). Of these parameters, triglyceride, HbA1c, oxidized LDL were statistically significant variables contributing to the small-sized LDL proportion in stepwise multiple regression analysis. Conclusions We analyzed small-sized LDL proportion in type 2 diabetics and found that it was significantly increased in diabetics than control subjects and it was independently correlated with triglyceride, HbA1c, oxidized LDL in descending order, which are reflecting lipid metabolism, glycation, and oxidative stress, respectively.

Antiatherothrombotic effects of nicotinic acid

Cardiovascular event reduction in hypercholesterolemic subjects appropriately emphasizes the prominent role of statin therapy; however, niacin (nicotinic acid) is also an effective lipid-altering agent that prevents atherosclerosis and reduces cardiovascular events. Niacin has multifarious lipoprotein and anti-atherothrombosis effects that improve endothelial function, reduce inflammation, increase plaque stability, and diminish thrombosis. Niacin reduces the atherogenicity of low-density lipoprotein (LDL) by changing the distribution of small LDL to large LDL subclass, and the susceptibility of LDL to oxidative modification. It is the most effective agent for increasing high-density lipoprotein cholesterol. Moreover, it favorably alters high-density lipoprotein composition, increasing apolipoprotein AI relative to apolipoprotein AII. Niacin reduces blood viscosity through a variety of mechanisms, thus improving blood flow and perfusion through stenotic segments of the vasculature. Finally, niacin has cardioprotective effects that may limit ischemia–reperfusion injury. By preserving glycolysis during periods of ischemia and improving subendocardial blood flow during reperfusion, niacin can improve the functional recovery of the myocardium.

Comparison of Low-Density Lipoprotein Size by Polyacrylamide Tube Gel Electrophoresis and Polyacrylamide Gradient Gel Electrophoresis

We evaluated a low-density lipoprotein (LDL) subfraction separation method using polyacrylamide tube gel electrophoresis (PTGE) and compared it with the reference method, polyacrylamide gradient gel electrophoresis (PGGE-REF). Excellent intra-assay and interassay coefficients of variation were obtained (<4%) for PTGE. For 102 subjects, LDL subclasses correlated most significantly with triglyceride (TG) level, high-density lipoprotein (HDL) cholesterol level, total cholesterol/HDL cholesterol ratio, and non-HDL cholesterol level (P < .05). The distribution of large LDL (76%) was predominant for subjects with low TG levels (<150 mg/dL [1.69 mmol/L]), while distribution of small LDL (79%) was predominant for subjects with high TG levels (>200 mg/dL [2.26 mmol/L]). Excellent agreement between the methods was observed (weighted kappa = 0.78). Of 51 samples classified as small, dense LDL by PGGE-REF, none were misclassified as large LDL and 4 as intermediate LDL by PTGE (92% concordance); of 44 samples classified as large LDL by PGGE-REF, 3 were misclassified as small and 7 as intermediate by PTGE (77% concordance). The PTGE method is precise and compares favorably with PGGE-REF. It has the advantage of being simple, less expensive, and more suitable for use in the clinical laboratory.

Hypercholesterolemia and Dyslipidemia: Issues for the Clinician.

The current state of the art in the diagnosis and treatment of lipoprotein disorders has progressed beyond the standard "lipid profile," which includes total low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol, along with fasting triglycerides. Incorporating aspects of the atherogenic lipoprotein profile (ALP) (ALP and LDL subclass distribution), HDL subclass distribution, apolipoprotein E isoforms, lipoprotein (a), homocysteine, and high-sensitivity C-reactive protein provides the clinician with the tools to create a more detailed, accurate, and personalized diagnosis of disorders contributing to coronary artery disease in their patients. Sophisticated laboratory tests are available to clinicians through technology transfer programs as exemplified by the Lawrence Berkeley National Laboratory/Berkeley HeartLab, Berkeley, CA, collaboration and allow clinicians access to research quality laboratory tools. This has significant clinical relevance because the presence of these disorders guides treatment that is specific to the disorder(s). Appropriate treatment has been shown to have significantly greater clinical benefit in patient subgroups exhibiting the disorder the therapy is most likely to correct. A single drug or lifestyle therapy plan is no longer appropriate for all patients. The treatment must match the individual disorder(s).

Comparison of effectiveness of statin monotherapy versus statin and niacin combination therapy in primary prevention and effects on calcified plaque burden

T combination of a statin and niacin is increasingly being prescribed for treatment of combined lipid disorders, and has recently been shown to produce a dramatic decrease in clinical events and atherosclerosis progression, measured by quantitative coronary angiography in secondary prevention patients.1 This study was designed to determine whether calcified plaque progression, determined by electron beam tomography (EBT), differs in groups of primary prevention patients treated with statins alone compared with statin and niacin combination therapy. In addition, the correlations between the change in calcified plaque burden and changes in low-density lipoprotein (LDL) particle size and subgroups were evaluated. • • • One hundred sixty-two consecutive asymptomatic patients with EBT evidence for subclinical atherosclerosis, who were treated with a statin alone or in combination with niacin (Niaspan; Kos Pharmaceuticals, Miami, Florida) and underwent repeat EBT evaluation, comprised the patient population. This was an observational study; serial EBT evaluation and lipidlowering agents and doses employed were chosen by the treating physicians based on clinical considerations, and not according to criteria set by the investigators. All patients gave consent for their data to be used in subsequent analyses. No patient had a history of clinical coronary artery disease. Hypertension was defined as the current or recommended use of antihypertensive medications for blood pressure control. Smoking was defined as current tobacco usage, and diabetes was defined as the current or recommended use of diet or medication to decrease blood sugar. Family history of coronary artery disease was defined as established disease in first-degree male relatives 56 years of age or female relatives 66 years of age. Body mass index was calculated as weight (kilograms)/height (meters squared). Lipid measurements were obtained at the time of both EBT evaluations. EBT was performed using an Imatron C-150 scanner (GE/Imatron, South San Francisco, California) and previously described acquisition protocol.2 The coronary artery calcium score was calculated with the Agatston method.3 The calcium volume score, a parameter of plaque burden that is density independent, was calculated according to the method of Callister et al.4 The calcium percentile, an age and gender corrected index of plaque prematurity, was derived from the University of Illinois asymptomatic patient database. EBT studies done before and after treatment were reviewed side-by-side for comparability of analysis by an experienced observer (HSH), blinded to the treatment effects. Changes in coronary calcium and calcium volume scores were calculated on an absolute basis and as a percent change per year. To avoid skewing the data by large percentage changes in a few patients with lower scores, the percent change per year for the treated and untreated groups was calculated by dividing the mean annualized change by the mean baseline values for the groups as a whole, rather than by the mean of the percent change per year for each patient. Fasting plasma lipid and lipoprotein cholesterol concentrations were determined by the methods of the Lipid Research Clinics in all patients.5 In 53 patients treated with niacin, densitometric measurements of LDL subspecies were carried out using custom made, triple gradient (S3), 2% to 16% polyacrylamide gradient gel electrophoresis (S3GGE) of plasma samples (Berkeley HeartLab, Burlingame, California).6 LDL peak particle diameter was measured and LDL subclass distribution was determined in 3 large regions (I, IIa, IIb) and 4 small regions (IIIa, IIIb, IVa, IVb). LDL subclass pattern was classified based on LDL peak particle diameter, number and position of peaks, and From the Beth Israel Medical Center, New York, New York; and Kronos Longevity Research Institute, Phoenix, Arizona. Dr. Hecht’s address is: PO Box 450, 9 Woodland Road, Brookside, New Jersey 07926. E-mail: hhecht@aol.com. Manuscript received July 22, 2002; revised manuscript received and accepted September 20, 2002. TABLE 1 Patient Characteristics

Impact of statins on novel risk markers.

Long-and-short term trials with the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have demonstrated significant reductions in cardiovascular and cerebrovascular events in patients with and without preexisting heart disease. Beyond improving the lipid profile, statins have additional effects that may contribute to their overall clinical benefit. Statin treatment appears to reduce global risk profile by affecting both novel and established lipid, inflammatory, and morphologic markers including low-density lipoprotein subclasses, lipoprotein (a), markers of endothelial function, inflammatory mediators, intima-media thickening, and coronary calcification. Although statins may be regarded as a rather homogeneous drug class in terms of biological activity, some agents feature unique properties that have beneficial effects on selected important risk matters.

Influence of low molecular weight heparin compared to conventional heparin for anticoagulation during haemodialysis on low density lipoprotein subclasses.

In haemodialysis (HD) patients, low density lipoprotein (LDL) particle distribution is characterized by a higher proportion of more atherogenic dense LDL. Though clinical studies showed favourable effects of low molecular weight (LMW) heparin compared to standard heparin on triglycerides (TG) and cholesterol (CH) in HD patients with hypertriglyceridaemia, it is not known if LMW heparin influences LDL subfraction pattern. Thus, the aim of this pilot study was to investigate if a switch to LMW heparin influences LDL subfractions and apolipoproteins. Ten outpatients with fasting TG >230 mg/dl in the chronic HD programme on heparin for anticoagulation (AC) were switched to dalteparin (80 IU/kg body weight as a bolus). Blood samples were drawn for CH, TG, LDL-CH, HDL-CH, apolipoproteins (apo), very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), and LDL subclasses at the beginning and after 12 months of therapy. Lipoproteins were isolated by preparative ultracentrifugation. Total LDL were fractionated into six density classes by equilibrium density gradient ultracentrifugation [(density in kg/l): LDL-1 1.019-1.031, LDL-2 1.031-1.034, LDL-3 1.034-1.037, LDL-4 1.037-1.040, LDL-5 1.040-1.044, LDL-6 1.045-1.063]. CH and TG were determined enzymatically, apolipoproteins by turbidimetry. In eight patients suitable for evaluation cholesterol decreased from 241 to 202 (P<0.05) and TG from 557 to 278 mg/dl (P<0.01), whereas LDL-CH and HDL-CH did not change significantly. A 28.2% decrease of VLDL (P<0.01) and a 19.3% decrease of IDL (P<0.05) paralleled by a significant drop of apoB were observed. Buoyant LDL subclasses increased (LDL-2, +34.3% and LDL-3, +20.3%) whereas dense LDL (LDL-5, -13.4% and LDL-6, -33.1%) decreased (P<0.05 for LDL-6). The ratio of buoyant LDL to dense LDL increased from 0.46+/-0.28 to 0.72+/-0.33 (P<0.05). In hypertriglyceridaemic HD patients, dalteparin improved metabolism of TG-rich lipoproteins, increased buoyant LDL and decreased potentially atherogenic dense LDL. Preservation of lipoprotein lipase by LMW heparin may be a possible mechanism to explain our findings.

Mildly oxidized LDL particle subspecies are distinct in their capacity to induce apoptosis in endothelial cells: role of lipid hydroperoxides.

The risk of atherosclerosis is intimately related to the heterogeneity of low-density lipoprotein (LDL) particles. The potential relationship between oxidative modification of distinct LDL subspecies and induction of apoptosis in arterial wall cells is indeterminate. The capacity of light LDL3 versus dense LDL5 to induce cytotoxicity in endothelial cells as a function of the degree of copper-mediated oxidation was compared. Mildly oxidized LDL3 (oxLDL3) exerted potent cytotoxicity, which was intimately related to both the degree of oxidation and the oxLDL3 concentration based on either cholesterol content or particle number. In contrast, dense LDL5 particles exerted a minor effect on cell viability. Cells incubated with oxLDL3 exhibited apoptotic features, with cytoplasmic condensation, cell or nuclear fragmentation, and accumulation of DNA fragments. OxLDL3-induced apoptosis involved cytoplasmic release of cytochrome c, with a concomitant increase in caspase-3-like protease activity. OxLDL3 particles were uniquely distinct from oxLDL5 particles in their elevated content of lipid hydroperoxides. Hydroperoxide removal by NaBH4 markedly reduced oxLDL3-induced cytotoxicity, leading to an increase in cell viability. Lipid hydroperoxide content of oxidatively modified LDL subclasses is therefore a major determinant of the induction of apoptosis in endothelial cells. These data are highly relevant to atherogenic hypercholesterolemia, in which the LDL phenotype is dominated by elevated concentrations of light LDL3.

LDL particle size: Relation to risk factors and subclinical atherosclerosis measured by coronary calcium

The effect of ciprofibrate treatment on the atherogenic profile of low-density lipoprotein (LDL) subspecies in combined hyperlipidemia (CHL) has been investigated in six patients displaying elevated plasma triglyceride and cholesterol levels ( > 200 and > 250 mg/dl, respectively). The E2E2 phenotype was excluded; four patients possessed familial antecedents of premature coronary heart disease (CHD). Analysis of five LDL subclasses separated by isopycnic density gradient ultracentrifugation showed a predominance of dense LDL subspecies (LDL-4 and LDL-5, d 1.039–1.063 g/ml; 51% of total LDL mass) in the asymmetric LDL density profile characteristic of CHL patients at baseline. Ciprofibrate treatment (100 mg/day for 1 month) effected marked reductions in both total plasma LDL and apo B-100 levels ( ∼ 19% and ∼ 23%, respectively). Equally, the plasma profile of LDL subspecies was normalised to a significant degree as a result of preferential reduction in the elevated levels of both dense subspecies (LDL-4 and LDL-5; −43% and −54%, respectively; P < 0.03 and P < 0.06, respectively). The circulating concentrations of light LDL (LDL-1, d 1.019-1.023 g/ml) were also diminished significantly by ciprofibrate (−30%; P < 0.06). Furthermore, ciprofibrate not only effected reductions in the elevated triglyceride content of the hydrophobic core of all LDL subspecies but also normalised their common deficiency in free cholesterol. In addition, the abnormally small particle diameters of LDL-4 and −5 were increased to normal. Plasma levels of both apo B-100 and triglycerides were significantly and positively correlated with those of LDL-4 and LDL-5, suggesting not only that the degree of triglyceride elevation is intimately linked to the extent of shift in LDL subclass profile towards denser subspecies, but also that triglyceride reduction upon treatment strongly influences LDL-4 and LDL-5. In conclusion, our findings indicate that ciprofibrate treatment in combined hyperlipidemia results in marked reduction in plasma triglyceride levels (-33%), and that such reduction is intimately linked to normalisation of both the qualitative and quantitative features of the atherogenic LDL subspecies profile typical of this disorder.

The effect of 7-year infancy-onset dietary intervention on serum LDL and HDL cholesterol subclasses in healthy children: The prospective, randomised strip study

The oxidation of lipoproteins is thought to be an important early step in atherogenesis. The measurement of lipid peroxidation in low-density lipoprotein (LDL) challenged with Cu2+ has become a widespread test to determine the “susceptibility” of LDL to oxidation. The determination of lag time to oxidation is thought to be a measure of the total antioxidant capacity of the LDL. However, we and others have failed to observe any correlation between lag time and the LDL content of its major lipid antioxidant, α-tocopherol. In fact, several studies now suggest a pro-oxidant role for tocopherol under some conditions of LDL oxidation. In the present study we sought to determine if there was a relationship between Cu2+ reduction by LDL and kinetic parameters of LDL oxidation. LDL (0.3 mmol/l cholesterol, ∼0.1 mg protein/ml) was incubated at 30°C with 2 μM Cu2+ and the formation of conjugated dienes measured over a 4-h period. Using neocuproine, an indicator molecule that specifically complexes Cu+ but not Cu2+, the reduction of Cu2+ by LDL was monitored. The final Cu concentration in these assays was 100 μM and neocuproine 750 μM. Cu+ formation was measured by absorbance at 454 nm. A strong negative correlation was observed between copper reduction by LDL and lag time to oxidation (r = −0.66, p < .005, n = 16). Further experiments showed that (1) LDL was able to reduce Cu2+ to Cu+ in a time and concentration-dependent manner; (2) blocking of free —SH groups on LDL apoprotein B by preincubation with dithionitrobenzoic acid (DTNB) had no significant effect on the rate and extent of Cu2+ reduction; (3) consumption of tocopherol in LDL undergoing oxidation with Cu was very rapid (rate = 6 × 10−10 M s−1). When Cu+ formed during incubation with LDL was complexed with neocuproine, there was significant inhibition of LDL oxidation, as indicated by lipid peroxide formation and mobility on agarose gel electrophoresis. Surprisingly, tocopherol consumption was even more rapid in the presence of neocuproine, consistent with a shift in Cu2+/ Cu+ equilibrium and faster reduction of Cu2+ by α-tocopherol. These results indicate that under these conditions tocopherol is a major reducing agent in LDL, converting Cu2+ to Cu+, and therefore, may play an important role in promoting LDL oxidation. However, there was no correlation between LDL tocopherol content and reduction of Cu2+. Examination of the time course of Cu2+ reduction in tocopherol enriched and depleted LDL indicates that tocopherol may determine Cu reduction at early time points but that the eventual capacity of LDL to reduce Cu may depend on more complex interactions between tocopherol and other LDL components.

Lipoprotein subclasses and coronary artery calcium in postmenopausal women from the healthy women study

Lipoprotein subclass levels may improve the prediction of cardiovascular disease (CAD) in individuals beyond the risk assessment provided by conventional enzymatically determined lipid levels. The objective of this study was to evaluate the associations between nuclear magnetic resonance (NMR) spectroscopy–determined lipoprotein subclasses and coronary calcification in postmenopausal women, and to determine whether the associations were independent of conventional lipid measures. Coronary artery calcification (CAC) was measured by electron beam computed tomography, and lipoprotein subclasses were determined by NMR spectroscopy (Liposcience, Inc., Raleigh, NC), in 286 healthy women (mean age = 61.7), at 8 years postmenopause. CAC was analyzed as categories 0, 1 to 99, and ≥100. The mean CAC was 53 (range, 0 to 1,175), and 54% of the women had 0 scores. Large high-density lipoprotein (HDL) was inversely associated with CAC category, but small HDL was not. All very low-density lipoprotein (VLDL) subclasses—small, medium, and large—were positively associated with CAC (p <0.01). Small low-density lipoprotein (LDL) was positively associated with CAC (p <0.01), but medium and large LDL were not. Smaller LDL particle size (p <0.01) and higher levels of LDL particles (p <0.001) were associated with higher CAC category. In separate ordinal logistic regression models, small LDL, LDL particles, and large VLDL were each positively associated (p <0.05) with higher CAC after adjustment for age, systolic blood pressure (SBP), current smoking, and conventional measures of LDL cholesterol, HDL cholesterol, and triglycerides. These results suggest that the measurement of lipoprotein subclasses may improve the prediction of CAD in postmenopausal women beyond that provided by the conventional lipid panel and CAD risk factors.

Abnormalities in uremic lipoprotein metabolism and its impact on cardiovascular disease

Patients with end-stage renal disease (ESRD) suffer from a secondary form of complex dyslipidemia consisting of both quantitative and qualitative abnormalities in serum lipoproteins resulting from alterations in lipoprotein metabolism and composition. The prominant features of uremic dyslipidemia are an increase in serum triglyceride levels (due to elevated very low density lipoprotein [VLDL]-remnants and intermediate-density lipoprotein [IDL]) and low high-density lipoprotein (HDL) cholesterol. Low-density lipoprotein (LDL) cholesterol often is normal, but the cholesterol may originate from the atherogenic small and dense LDL subclass (sdLDL). The apolipoprotein B (apoB)-containing part of the lipoprotein may undergo modifications (enzymatic- and advanced glycation end-product [AGE]-peptide modification, oxidation, or glycosilation). Modifications contribute to impaired LDL receptor-mediated clearance from plasma and promote prolonged circulation. While LDL particles undergo a vicious cycle of accumulation and modification, reverse cholesterol transport is also impaired due to low lecithin:cholesterol acyltransferase (LCAT) and paraoxonase activity. Therefore, discoid HDL particles are structurally altered and hepatic cholesterol clearance is limited. The composition of HDL may also be altered during states of inflammation. The contribution of this complex and atherogenic form of dyslipidemia to cardiovascular disease in patients with renal disease is unclear at present. Most studies are negative in demonstrating the predictive power of serum lipids for the development of cardiovascular disease. This is most likely due to interference with deteriorating aspects of the activated acute-phase response. Nevertheless, patients with renal disease belong to a very high cardiovascular risk group and dyslipidemia should most likely be subjected to sufficient lipid-lowering therapy in most patients. Because it is also still unclear whether we have available therapies with sufficient impact on LDL size, remnant lipoprotein-lowering, and restoration of HDL function, we urgently need the results from large scale intervention trials such as the 4D-trial and the CHORUS study. © 2001 by the National Kidney Foundation, Inc.

Dietary and genetic effects on low-density lipoprotein heterogeneity.

We have tested whether differences in distribution and dietary responsiveness of low-density lipoprotein (LDL) subclasses contribute to the variability in the magnitude of LDL-cholesterol reduction induced by diets low in total and saturated fat and high in carbohydrate. Our studies have focused on a common, genetically influenced metabolic profile, characterized by a predominance of small, dense LDL particles (subclass pattern B), that is associated with a two- to threefold increase in risk for coronary artery disease. We have found that healthy normolipidemic individuals with this trait show a greater reduction in LDL cholesterol and particle number in response to low-fat, high-carbohydrate diets than do unaffected individuals (subclass pattern A). Moreover, such diets result in reduced LDL particle size, with induction of pattern B in a substantial proportion of pattern A men. Recent studies have indicated that this response is under genetic influence. Future identification of the specific genes involved may lead to improved targeting of dietary therapies aimed at reducing cardiovascular disease risk.