Determination of pKa values of benzoxa-, benzothia- and benzoselena-zolinone derivatives by capillary electrophoresis. Comparison with potentiometric titration and spectrometric data.

Acidity constants of benzoxa-, benzothia- and benzoselena-zolinone derivatives were determined by capillary electrophoresis, potentiometry and spectrophotometry experiments. These three analytical techniques gave pK(a) results that were in good agreement. A convenient, accurate and precise method for the determination of pK(a) was developed to measure changes in acidity constants induced by heteroatom or 6-benzoyl substituted derivatives. pK(a) values were determined simultaneously for two compounds characterized by different electrophoretic mobility (micro(e)) and pK(a) value and in the presence of an analogous neutral marker.

Measurement of apolipoprotein B concentration in plasma lipoproteins by combining selective precipitation and mass spectrometry.

The measurement of apolipoprotein B (apoB) in purified lipoproteins by immunological assays is subject to criticism because of denatured epitopes or immunoreactivity differences between purified lipoproteins and standard. Chemical methods have therefore been developed, such as the selective precipitation of apoB followed by quantification of the precipitate. In this study, we present the measurement of apoB concentration in lipoproteins purified by ultracentrifugation by combining isopropanol precipitation and gas chromatography/mass spectrometry. Very low density lipoprotein (VLDL; d < 1.006 g/mL); VLDL plus intermediate density lipoprotein (VLDL + IDL; d < 1.019 g/mL); and VLDL, IDL, and low density lipoprotein (VLDL + IDL + LDL; d < 1.063 g/mL) were purified by ultracentrifugation. Apolipoprotein B-100 was selectively precipitated by isopropanol. The leucine content of the pellet was then determined by gas chromatography/mass spectrometry, using norleucine as internal standard. Knowledge of the number of leucine molecules in one apoB-100 molecule makes it possible to calculate the plasma concentration of apoB in the various lipoprotein fractions. ApoB in IDL (d 1.006-1.019 g/mL) and LDL (d 1.019-1.063 g/mL) were then determined by subtracting VLDL-apoB from apoB in lipoproteins d < 1.019 and apoB in lipoproteins d < 1.019 g/mL from apoB in lipoproteins d < 1.063 g/mL, respectively. The isopropanol precipitate was verified as pure apoB (>97%) in lipoprotein fractions isolated from normo- and hyperlipidemic plasma and the method appeared reproducible. The combination of isopropanol precipitation and the GC/MS method appears therefore to be a precise and reliable method for kinetic and epidemiological studies.

Metabolism of apolipoproteins AI and AII in subjects carrying similar apoAI mutations, apoAI Milano and apoAI Paris.

ApoAI Milano (AI(M)) and apoAI Paris (AI(P)) are mutant forms of apoAI in which cysteine is substituted for arginine at residues 173 and 151 respectively leading to the formation of homodimers and heterodimers with apoAII. Heterozygous subjects with these mutants are characterized by low levels of plasma HDL cholesterol and apoAI. The present study analyzed the metabolism of the different complexes of apoAI in three subjects, two AI(M) and one AI(P), using a primed-constant infusion of trideuterated leucine. In AI(M) carriers, the mutant form was almost equally distributed in AI(M) dimer, AI(M):AII heterodimer and the monomer, whereas, in the AI(P) subject, the mutant apoAI was essentially in the apoAI(P):AII complex. Normal apoAI was low in the AI(M) subjects (20 and 16 mg/dl) but very low in the AI(P) subject (0.3 mg/dl). In the AI(M) subjects, the low levels of apoAI were due to a rapid catabolism with a normal synthetic rate. However, the apoAI kinetics were heterogeneous with a rapid catabolism of the AI(M):AII complex (FCR of 0.430 and 0.401 day(-1)) and the AI(M) monomer (FCR of 0.570 and 0.406 day(-1)) whereas the AI(M) dimer was catabolized slowly (FCR of 0.114 and 0. 118 day(-1)). In contrast, AI(P) was catabolized relatively slowly with a FCR of 0.263, 0.182 and 0.258 day(-1) for AI(P) homodimer, apoAI(P):AII heterodimer and AI(P) monomer. In the three subjects, normal apoAI was catabolized quickly, with an FCR of 0.805 and 0.601 day(-1) in AI(M) carriers and 0.526 day(-1) in the AI(P) carrier. Therefore, the low level of apoAI in the AI(P) carrier is caused by a low production rate of apoAI, particularly of normal apoAI. In conclusion, apoAI is kinetically heterogeneous in AI(M) and in AI(P) subjects. Moreover, the two mutations lead to significant differences in the kinetic behavior of mutant apoAI depending on its inclusion in its complexes.

Moderate red wine consumption in healthy volunteers reduced plasma clearance of apolipoprotein AII.

BACKGROUND: The mechanisms of the positive relationship between alcohol intake and plasma concentration of high-density lipoprotein (HDL) are still unclear. The present study shows the metabolism modifications of apolipoprotein (apo) AI and apoAII in normolipidaemic healthy volunteers after a period of moderate red wine consumption. DESIGN: Five non-smoking male subjects were studied at the end of two consecutive 4-week periods, one without alcohol and the other with an intake of 50 g per day of alcohol, in random order. The metabolic parameters of apoAI and apoAII in HDL were determined after endogenous labelling using amino acid labelled with stable isotope. Cholesterol, triacylglycerols, HDL-cholesterol, apoAI, apoAII, LpAI, LpAI:AII were determined in plasma at the end of the two study periods. RESULTS: Cholesterol and triacylglycerols did not vary significantly during the two periods, whereas HDL-cholesterol increased from 43.8 to 50.0 mg dL-1 (P < 0.05). ApoAI and apoAII increased significantly (20% and 60% respectively) after the diet was supplemented with alcohol. LpAI:AII increased from 73.8 to 101.6 mg dL-1 (+32%) (P < 0.05), whereas alcohol had no effect on the concentration of LpAI. The alcohol treatment did not significantly alter the metabolism of apoAI. Conversely, the fractional catabolic rate of apoAII decreased significantly by 21% (P < 0.05) with alcohol, whereas the production rate of apoAII tended to increase by 18% (P = 0.08). CONCLUSION: The decrease in the fractional catabolic rate of apoAII could lead to an accumulation of apoAII-containing lipoproteins in plasma and account for the dramatic increase in LpAI:AII observed in the plasma of subjects consuming alcohol.

Fish-eye disease: structural and in vivo metabolic abnormalities of high-density lipoproteins.

Fish-eye disease (FED) in humans is characterized by corneal opacities and markedly decreased plasma concentrations of high-density lipoprotein (HDL) cholesterol, apolipoprotein (apo) AI, and apo All, but no tendency to precocious atherosclerosis is present. To elucidate this paradox, the structure of HDL, the potential of serum to promote cholesterol efflux from cultured cells, and the in vivo metabolism of HDL were examined in a 53-year-old woman with a FED syndrome in association with a markedly decreased lecithin:cholesterol acyltransferase (LCAT) activity in HDL due to a mutation of the LCAT gene (Arg158 --> Cys). HDLs isolated by ultracentrifugation were small and enriched in unesterified cholesterol and phospholipids at the expense of cholesteryl esters and proteins. The apolipoprotein content showed an enrichment in apo E and apo AIV, whereas apo AI and apo All were dramatically reduced. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting using specific antibodies showed that the apo E was free or covalently bound to apo All. These particles analyzed by electron microscopy were small and round lipoproteins with a size similar to the smallest fraction of normal HDL3. The potential capacity of the serum to promote efflux from the cells was approximately 40% of control serum levels, but FED HDLs were as efficient as control HDLs in promoting cholesterol efflux from cells. To assess the metabolism of HDL apolipoproteins, in vivo apolipoprotein kinetic studies were performed using endogenous labeling techniques in the patient with FED and three control subjects. All subjects were administered D3-labeled leucine by primed constant infusion for up to 10 hours. The fractional synthetic rates (FSRs) of apo AI and apo All in the patient were 0.674 and 0.594 per day, clearly higher than in controls, 0.210 +/- 0.053 and 0.148 +/- 0.014 per day for apo AI and apo All, respectively. Apo AI and apo All production rates in the patient with FED were normal, 11.32 and 2.62 mg/kg x d, respectively, as compared with those in normal subjects, 11.45 +/- 1.23 and 2.68 +/- 0.17 mg/kg x d. These data established that hypoalphalipoproteinemia in FED was caused by marked hypercatabolism of apo AI and apo All. This hypercatabolism could be the consequence of structural abnormalities due to the selective LCAT deficiency. In conclusion, two steps of reverse cholesterol transport, cholesterol efflux and apo-HDL metabolism, appeared particularly efficient. This efficiency could participate in the absence of premature atherosclerosis in FED patients as regards the low HDL level.