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The development of drug resistance in the treatment of cancer remains a major problem.

1. Human total HDL (high-density lipoprotein), HDL2 and HDL3 were labelled in vitro by incubation with lipoprotein-deficient serum (LPDS) which contained either [3H]cholesteryl oleate or [14C]cholesterol under different conditions. The lipoproteins were then subfractionated by heparin-Sepharose column chromatography, and three subfractions (A, B and C) were successively eluted from each preparation of HDL, HDL2 and HDL3. When the labelling was done at 37 degrees C for 17 h, the subfractions were homogeneously labelled with [3H]cholesteryl oleate. However, when it was performed for only 30 min at 4 degrees C, the subfractions showed marked differences in the 3H specific radioactivity, which was much higher in the C fractions than in the others. 2. 3H-labelled HDL2 and HDL3 subfractions behaved differently under the precipitant action of heparin-Mn2+; fraction C (the richest in apolipoprotein E) produced the largest amount of radioactive and chemical precipitate. More 3H radioactivity, but not the cholesterol, was precipitated from HDL2 or HDL3 by the reagent, demonstrating that 3H-labelled HDL2 and HDL3 behave like their fraction C, which becomes labelled to the highest specific radioactivity despite having the smallest mass. 3. The incubation of 3H-labelled HDL subfractions with human LPDS and very-low-density lipoprotein (VLDL) at 37 degrees C increased the quantity of 3H radioactivity that was precipitated, in proportion to the amount of VLDL present in the media. These changes were attributable to the action of cholesterol ester transfer protein, since they did not occur at 4 degrees C or when human LPDS was replaced with rat LPDS. 4. Kinetics of the transfer of HDL [3H]cholesteryl oleate to VLDL showed a greater apparent Vmax for fractions A than for fractions B from either HDL2 or HDL3, whereas the apparent Km values were very similar, which suggest that this transfer process is influenced by the apoprotein composition of the donor lipoprotein.

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We describe a simple iminunoturbidimetric method for quantifying lipoprotein(a) in serum based on latex-enhanced particle agglutination technology. Carboxylated latex particles (diameter 240 nm) covalently coated with F(ab')2 fragments of anti-lipoprotein(a) antibodies are incubated with the sample for 5 min at 37 °C, and the resulting agglutination is quantified by measuring the change of turbidity produced at 700 nm. The assay is rapid, precise and fully automated on the Hitachi 911 analyser. The assay range is about 0.03-0.9 g/1. Average analytical recovery was 97-8%. Precision (CV) ranged from 1.9 to 3.1% at different lipoprotein(a) values. There was no interference from bilirubin, Intfalipid®, haemoglobin, plasminogen or apolipoprotein B. Comparisons with a latex nephelometric assay carried out on the Behring nephelometer analyser, and with three commercially available methods, a radioimmunoassay and two ELISA assays, gave good correlations (r > 0.95), although a large among-method variation in lipoprotein(a) values was found. We conclude that the proposed latex turbidimetric immunoassay method is suitable for routine use in clinical laboratories.These findings generated the need for a serum lipoprotein(a) assay in the clinical chemistry laboratory. Various quantitative immunological assays for lipoprotein(a) determination, including electrophoretic techniques (10), radial immunodiffusion (11), enzyme immunoassays (12), and radio immunoassays (13) have been developed. However, these procedures generally require specialized reagents and equipment, long reaction times, and multiple washing steps, and they are not easily automated. Recently, in an effort to overcome these problems several automated fluid-phase immunoprecipitation procedures have been described (14,15).In this study, we present a turbidimetric method which uses particle-enhanced immunoassay technology and is carried out on a last generation clinical chemistry analyser. This turbidimetric method has the advantage of being precise, rapid, easy to perform, and suffers no interference from apolipoprotein B, plasminogen, or from endogenous lipids, haemoglobin, or bilirubin. Here we describe the characteristics and performance of the method. AntibodyRabbit polyclonal antiserum directed against human lipoprotein(a) was manufactured by Dakopatts A/S (Glostrup, Denmark). It showed no cross-reaction with apolipoprotein B or plasminogen and was stored at 4°C. (Lot No. 012, 3.7 g/1 of protein.)Eur.