A homogeneous assay to determine high-density lipoprotein subclass cholesterol in serum.

Existing methods to measure high-density lipoprotein cholesterol (HDL-C) subclasses (HDL2-C and HDL3-C) are complex and require proficiency, and thus there is a need for a convenient, homogeneous assay to determine HDL-C subclasses in serum. Here, cholesterol reactivities in lipoprotein fractions [HDL2, HDL3, low-density lipoprotein (LDL), and very-low-density lipoprotein (VLDL)] toward polyethylene glycol (PEG)-modified enzymes were determined in the presence of varying concentrations of dextran sulfate and magnesium nitrate. Particle sizes formed in the lipoprotein fractions were measured by dynamic light scattering. We optimized the concentrations of dextran sulfate and magnesium nitrate before assay with PEG-modified enzymes to provide selectivity for HDL3-C. On addition of dextran sulfate and magnesium nitrate, the sizes of particles of HDL2, LDL, and VLDL increased, but the size of HDL3 fraction particles remained constant, allowing only HDL3-C to participate in coupled reactions with the PEG-modified enzymes. In serum from both healthy volunteers and patients with type 2 diabetes, a good correlation was observed between the proposed assay and ultracentrifugation in the determination of HDL-C subclasses. The assay proposed here enables convenient and accurate determination of HDL-C subclasses in serum on a general automatic analyzer and enables low-cost routine diagnosis without preprocessing.

Lifestyle intervention enhances high-density lipoprotein function among patients with metabolic syndrome only at normal low-density lipoprotein cholesterol plasma levels.

BACKGROUND: Metabolic syndrome (MetS) is associated with altered lipoprotein metabolism and impairment in the functionality of small, dense high-density lipoprotein (HDL) particles secondary to compositional alterations. OBJECTIVE: The objective of this study was to investigate the capacity of a lifestyle program to improve the composition and antioxidative function (AOX) of small dense HDL3c in MetS. METHODS: Patients with MetS (n = 33) not taking lipid-lowering drugs were recruited to follow a 12-week educational program to reduce caloric intake and to increase physical activity. HDL subfractions were preparatively isolated by isopycnic density-gradient ultracentrifugation. AOX of HDL3c was assessed as its capacity to inhibit low-density lipoprotein oxidation induced by an azoinitiator. RESULTS: AOX of HDL3c was significantly improved (mean reduction in the propagation rate of low-density lipoprotein oxidation by HDL3c, -6.8%, P = .03) and systemic oxidative stress, assessed as plasma levels of 8-isoprostanes, tended to decrease in normocholesterolemic MetS patients (low-density lipoprotein cholesterol [LDL-C] < 130 mg/dL) but not in patients with elevated LDL-C levels and in the whole study population. In both the whole study population and the normocholesterolemic subgroup, lifestyle intervention resulted in a significant degree of normalization of HDL3c composition, (enrichment in apolipoprotein A-I and cholesteryl esters, depletion in triglycerides), which was more pronounced at LDL-C < 130 mg/dL. CONCLUSION: In patients with MetS, a lifestyle program improves AOX of small, dense HDL in subjects with normal LDL-C levels. Correction of HDL composition, involving partial normalization of apoA-I content and core lipid composition, 2 central features of the lipid hydroperoxide-inactivating capacity of HDL, may account for this effect.

Chemical modification of high density lipoprotein subfractions - HDL2 and HDL3 - after use of atorvastatin.

Regardless of its effect on the concentrations of serum cholesterol, statins exert pleiotropic effects, including the regulation of endothelial function, reduced oxidative stress and inflammation, as well as a slight improvement in the concentrations of high density lipoprotein (HDL). However, its role on the composition of HDL is not yet established. The aim of this study was to evaluate the composition of HDL subfractions, HDLsub>2 and HDL3, after 14 days of placebo and atorvastatin (10 mg/day) use in 30 asymptomatic volunteers. The serum parameters and the HDL subfractions compositions were determined using radiometric, nephelometric and biochemical enzymatic methods. We observed significant reductions of total cholesterol, low density lipoprotein (LDL) and apolipoprotein B-100 by 28%, 40% and 38%, respectively. The analyses of chemical composition of the subfractions revealed a lower lipid protein ratio in HDL2, suggesting enrichment in proteins, and also lower in HDL3, probably by an increase in the number of particles. Several mechanisms can be suggested for the effects observed after the use of atorvastatin, such as a possible action on the reverse cholesterol transport (decreased activity of hepatic lipase and increased phospholipid transfer protein, PLTP), which would explain the enrichment of HDL. The results suggest that statin use may be relevant in the primary prevention of atherosclerosis not only by its lowering effect on LDLcholesterol and its anti-inflammatory effect but also by beneficial changes in HDL subfractions.

Ezetimibe decreases serum amyloid A levels in HDL3 in hemodialysis patients.

AIM: The aim of this study was to investigate the effects of ezetimibe on high-density lipoprotein (HDL) subspecies and serum amyloid A (SAA), an apolipoprotein mainly bound and transported by HDL particles, in patients with end-stage renal disease (ERSD), a condition typically characterized by high SAA- and low HDL-cholesterol (C ) levels. METHODS: 26 ERSD patients receiving hemodialysis (HD) were given ezetimibe (10 mg/d) for 6 - 8 weeks. HDL3 was separated from serum by a single precipitation method established by our group. HDL2 was estimated by subtracting HDL3 from total HDL. Serum amyloid A (SAA) was measured by the ELISA method. RESULTS: Ezetimibe significantly reduced remnant-like particle (RLP)-C, low-density lipoprotein (LDL)-C, and apolipoprotein (apo) B without affecting triglyceride, HDL-C and LCAT activities. HDL2-C levels were lower and HDL3-C was substantially lower in the HD patients than in the controls. Ezetimibe increased HDL2-apoAI but decreased HDL3-apoAI without affecting serum apoAI or AII. HDL-SAA was 5-fold higher in the HD patients than in the controls (56 ± 49 vs. 12 ± 9 µg/ml). Ezetimibe decreased HDL-SAA by 43 % (to 32 ± 36 µg/ml), and this inhibitory effect was exclusively attributable to a 72% reduction in HDL3-SAA in response to the ezetimibe treatment. The reduction of HDL3-SAA was significantly associated with increased HDL2-apo AI and reduced HDL3-apo AI. CONCLUSIONS: Ezetimibe treatment decreased "inflammatory" (SAA-containing) HDL3, and may thus have restored the anti-atherogenic function of HDL particles in ESRD patients.

FT-IR spectroscopy of lipoproteins--a comparative study.

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