Characterization of modified low density lipoprotein subfractions by capillary isotachophoresis

Anion exchange HPLC isolation of high-density lipoprotein (HDL) and on-line estimation of proinflammatory HDL

Proinflammatory high-density lipoprotein (p-HDL) is a biomarker of cardiovascular disease. Sickle cell disease (SCD) is characterized by chronic states of oxidative stress that many consider to play a role in forming p-HDL. To measure p-HDL, apolipoprotein (apo) B containing lipoproteins are precipitated. Supernatant HDL is incubated with an oxidant/LDL or an oxidant alone and rates of HDL oxidation monitored with dichlorofluorescein (DCFH). Although apoB precipitation is convenient for isolating HDL, the resulting supernatant matrix likely influences HDL oxidation. To determine effects of supernatants on p-HDL measurements we purified HDL from plasma from SCD subjects by anion exchange (AE) chromatography, determined its rate of oxidation relative to supernatant HDL. SCD decreased total cholesterol but not triglycerides or HDL and increased cell-free (cf) hemoglobin (Hb) and xanthine oxidase (XO). HDL isolated by AE-HPLC had lower p-HDL levels than HDL in supernatants after apoB precipitation. XO+xanthine (X) and cf Hb accelerated purified HDL oxidation. Although the plate and AE-HPLC assays both showed p-HDL directly correlated with cf-Hb in SCD plasma, the plate assay yielded p-HDL data that was influenced more by cf-Hb than AE-HPLC generated p-HDL data. The AE-HPLC p-HDL assay reduces the influence of the supernatants and shows that SCD increases p-HDL.

Low-density lipoprotein oxidized to various degrees activates ERK1/2 through Lox-1

Although the standard procedure for preparing extensively oxidized low-density lipoprotein (Ox-LDL) is to incubate it with 10muM CuSO(4) at 37 degrees C for 24h, it is not well known how important the degree of oxidation of LDL is for inducing cell signaling. Since Lox-1 (an Ox-LDL receptor) contributes to cell proliferation through extracellular-signal-regulated kinase (ERK)1/2 activation and subsequently induces plaque growth, we analyzed ERK activity using LDL with various degrees of oxidation, from minimally Ox-LDL, which is mainly in human plasma, to extensively Ox-LDL using capillary electrophoresis (cITP). The cITP was a suitable tool for evaluating the degree of oxidation of LDL for analyzing the optimal conditions for the oxidation of LDL by CuSO(4) to obtain LDL that was oxidized to a degree comparable to that in human plasma. In addition, both minimally and extensively Ox-LDL induced similar levels of ERK1/2 activation through Lox-1 in human coronary artery smooth muscle cells. These results indicate that both minimally and extensively Ox-LDL may be important for the progression of plaque growth through Lox-1. Since most previous reports have provided data only using extensively Ox-LDL, a re-evaluation is needed to analyze several signals that use LDL which has been oxidized to various degrees.

Open Tubular Capillary Electrochromatography: Technique for Oxidation and Interaction Studies on Human Low-Density Lipoproteins

A novel, open tubular capillary electrochromatographic method was developed for the in vitro oxidation of low-density lipoprotein (LDL) particles. Low-density lipoprotein particles with molar mass of approximately 2.5 MDa yielded a stable stationary phase at temperatures 25 and 37 degrees C and at pH values from 3.2 to 7.4. The quality of the coatings was not influenced by variations in the LDL concentration in the coating solutions (within the range of 2-0.015 mg/mL) with the coating procedure used in the study. Radiolabeled LDL stationary phases and scanning electron microscopy, employed to shed light on the location and coating density of LDL particles on the inner surface of the capillary wall, confirmed the presence of an LDL monolayer and almost 100% coating efficiency (99 +/- 8%). In addition, the radioactivity measurements allowed estimation of the amount of LDL present in a single capillary coating. Capillaries coated with human LDL particles were submitted to different oxidative conditions by changing the concentration of the oxidant (CuSO4), oxidation time, pH value, and temperature. The oxidation procedure was followed with electroosmotic flow mobility, which served as an indicator of the increase in total negative charges of LDL coatings, and by asymmetrical field flow fractionation, which measured the changes in size of the lipoprotein particles. The results indicated that oxidation of LDL was progressing with increasing time, temperature, and concentration of the oxidant as expected. The oxidation process was faster around neutral pH values (pH 6.5-7.4) and inhibited at acidic pH values (pH 5.5 and lower).

Analysis of Lipoproteins by Microchip Electrophoresis with High Speed and High Reproducibility

A method for the fast analysis of lipoproteins by microchip electrophoresis with light-emitting diode confocal fluorescence detection has been developed. Lipoproteins labeled with BODIPY FL C(5)-ceramide are found to strongly adsorb on the bare surface of a poly(methyl methacrylate) (PMMA) microchip. Sodium dodecyl sulfate and cetyltrimethylammonium bromide were therefore utilized to alter lipoproteins and channel surface to make them bear the same type of charge. After modification, the peak shape of lipoproteins was greatly improved, demonstrating lipoprotein adsorption on a PMMA chip dramatically reduced due to electrostatic repulsion. In addition, polymers were added into the running buffer to suppress electroosmotic flow and to serve as a sieving matrix. As a result, lipoprotein separation was manipulated by both electrophoretic mobilities and particle sizes. Various separation parameters including surfactant concentration, buffer pH, and polymer concentration as well as on-line concentration were investigated systematically. Under optimal conditions, two baseline separations of standard lipoproteins including high-density lipoprotein, low-density lipoprotein, and very low-density lipoprotein were achieved with different selectivity. This method affords high separation speed (within 100 s) and high reproducibility. The intraassay and interassay RSDs of lipoprotein migration times were in the range of 0.90-1.9%, indicating this method is highly reliable.

Tendon xanthomas in familial hypercholesterolemia are associated with a differential inflammatory response of macrophages to oxidized LDL

Tendon xanthomas (TX) are pathognomonic lipid deposits commonly found in familial hypercholesterolemia (FH) patients. The aim of this study was to determine whether macrophages from FH patients with TX (TX+) have higher predisposition to foam cells formation after oxidized LDL (oxLDL) overload than those from FH patients without TX (TX-), and if their differential gene expression profile could explain these different phenotypes. Total RNA pools from macrophages from FH patients TX+ and TX- were analyzed using Affymetrix oligonucleotide arrays to evaluate the gene expression profile in presence and absence of oxLDL. Also, the intracellular lipid content was measured by fluorescence flow cytometry. Results of these studies suggest that macrophages from FH subjects TX+ compared to those TX- have a differential response to oxLDL, since they show higher intracellular cholesterol ester accumulation and a differential gene expression profile. The gene array data were validated by relative quantitative real-time RT-PCR and quantitative ELISA in culture media and plasma samples. FH subjects TX+ showed increased plasma tryptase, TNF-alpha, IL-8 and IL-6 concentrations. We propose that TX formation are associated with higher intracellular lipid content, and higher inflammatory response of macrophages in response to oxLDL.

Charge-based heterogeneity of human plasma lipoproteins at hypertriglyceridemia: capillary isotachophoresis study

To reveal the metabolic links between and within pools of pro-atherogenic triglyceride(TG)-rich lipoproteins and anti-atherogenic high density lipoproteins (HDL), the changes in lipoprotein profile at hypertriglyceridemia were analyzed by capillary isotachophoresis. Plasma samples from patients with apoE3/3 phenotype were stained with a fluorescent probe NBD-C6-ceramide and lipoproteins resolved into six H-, one (V+I) and four L-components which belong to HDL, very low and intermediate density (VLDL+IDL) and low density lipoproteins (LDL), respectively. The expected correlation between the relative size of the combined fractions and lipid and apolipoprotein values was obtained confirming the validity of the approach. The new findings were obtained as follows. (1) The fast L-component correlated inversely with HDL-cholesterol (Chol), while intermediate and slow H-components correlated inversely with plasma and LDL-Chol and apoB. (2) The content of intermediate and slow H-components increased within H-pool and decreased relative TG-rich lipoproteins as hypertriglyceridemia rose due to the impairment of triglyceride hydrolysis by lipoprotein lipase within TG-rich particles. (3) A predictive value of the ratios of fast to slow H-components as an indicator of lecithin:cholesterol acyltransferase activity was demonstrated which tended to decrease at hypertriglyceridemia. (4) The L1/L2 ratio may be considered as an indicator of the accumulation of small dense LDL, which is a feature of clinically manifested atherogenic B-pattern. The competition between H(DL) and L(DL) particles for hepatic lipase and significant contribution of apoE to functional deficiency of H(DL) particles at hypertriglyceridemia are suggested.

Capillary electrophoresis and its application in the clinical laboratory

Over the past 10 years, capillary electrophoresis (CE) is an analytical tool that has shown great promise in replacing many conventional clinical laboratory methods, especially electrophoresis and high performance liquid chromatography (HPLC). The main attraction of CE was that it was fast, used small amounts of sample and reagents, and was extremely versatile, being able to separate large and small analytes, both neutral and charged. Because of this versatility, numerous methods for clinically relevant analytes have been developed. However, with the exception of the molecular diagnostic and forensic laboratories CE has not had a major impact. A possible reason is that CE is still perceived as requiring above-average technical expertise, precluding its use in a laboratory workforce that is less technically adept. With the introduction of multicapillary instruments that are more automated, less technique-dependent, in addition to the availability of commercial and cost effective test kit methods, CE may yet be accepted as a instrument routinely used in the clinical laboratories. Thus, this review will focus on the areas where CE shows the most potential to have the greatest impact on the clinical laboratory. These include analysis of proteins found in serum, urine, CSF and body fluids, immunosubstraction electrophoresis, hemoglobin variants, lipoproteins, carbohydrate-deficient transferrin (CDT), forensic and therapeutic drug screening, and molecular diagnostics.