Jean-Francois Lontie

Apolipoproteins C-II and C-III metabolism in hypertriglyceridemic patients Effect of a drastic triglyceride reduction by combined diet restriction and fenofibrate administration

Four hypertriglyceridemic patients, who had received an equilibrated high calorie diet and no lipid lowering drug for 1 month, were injected intravenously with 125I-apo C-II and 131I-apo C-III labeled homologous lipoproteins. Plasma and urine radioactivity, lipid and apolipoprotein levels were followed at regular intervals for 15 days. At the end of this first kinetic study the patients were advised to adhere for 1 month to a more restricted diet, limited in fat, and were given additionally 300 mg fenofibrate daily. After this treatment, a new kinetic study involving intravenous injection (similar to the first one) was performed. The protocols of both studies were identical. Treatment (diet plus drug) (1) reduced total cholesterol by 26 +/- 8%, triglycerides by 56 +/- 15%, apo C-II by 36 +/- 14%, and apo C-III by 48 +/- 10%; (2) modified the distribution of radioactivity between lipoproteins proportionally to the change in their mass ratio (decrease in VLDL and increase in HDL); (3) changed the kinetics of both apoproteins by rising the fractional removal rate, shortening residence time and decreasing the synthesis rate of both apolipoproteins C-II and C-III. The treatment was, however, unable to reduce the synthesis rate of apo C-III to normal, suggesting a major role of the apoprotein overproduction in the triggering of hypertriglyceridemia.

Effect of simvastatin on receptor-dependent low density lipoprotein catabolism in normocholesterolemic human volunteers

Simvastatin, an inhibitor of HMG-CoA reductase was given to 7 normolipidemic healthy volunteers for 1 month at a dose of 20 mg/day. Measurements of turnover of low density lipoprotein apolipoprotein B (LDL-apo B) were determined before and after drug treatment using intravenous injection of 125I-labeled LDL and 131I-labeled cyclohexanedione-treated LDL to quantify the receptor pathway. In addition to a 13% increase in HDL cholesterol and apolipoprotein A-I concentrations, plasma cholesterol was reduced by 20%, LDL-cholesterol by 32%, and apolipoprotein B by 23%. Assuming a heterogeneous pool of LDL, the new model presented in the companion paper was built to calculate the contribution of the receptor-dependent and the receptor-independent pathways and the corresponding fractional catabolic rates. Simvastatin did not modify constantly the synthetic rate of LDL-apo B but increased the fractional catabolic rate of the receptor-dependent pathway and the contribution of this pathway in the catabolism. The fall in LDL plasma levels observed in normocholesterolemic subjects can be then entirely explained by an enhanced fractional removal of LDL from the circulation by the receptor route.

Metabolism of apolipoprotein C-III in normolipemic human subjects

Radioiodinated apolipoprotein C-III labeled either by the iodine monochloride procedure or by the Bolton-Hunter reagent were incubated in vitro with normal HDL. The labeled HDL-apo C-III, after ultracentrifugation and dialysis, was injected intravenously in 8 normolipidemic subjects. The label was followed in VLDL, IDL + LDL, HDL, d = 1.225 g/ml infranate as well as in total plasma and urine for the first time over a period of 2 weeks. Apolipoprotein C-III distributes readily between the different lipoprotein classes, only a small amount being present in the non-lipoprotein fraction. The percent distribution of apo C-III radioactivity and mass was found similar in VLDL, IDL and HDL using 3 different separation methods. Residence time in the whole system was 2.45 +/- 0.33 days. Fractional catabolic rates calculated from the urine/plasma radioactivity ratios or from the plasma curve were 0.731 +/- 0.096 and 0.767 +/- 0.125 pools/day. Synthetic rate was 2.28 +/- 0.32 mg/day/kg. The parameters seem not affected by the labeling procedure. The shapes of the plasma curve and of the urine/plasma ratio curve suggest a kinetic heterogeneity in the metabolism of apo C-III-containing particles.

Metabolism of Apolipoprotein C-I in Normolipoproteinemic Human Subjects

Labeling of apolipoprotein C-I by the Bolton and Hunter reagent allowed a study of the kinetics of this peptide in normolipidemic human volunteers. After its intravenous injection the appearance of radioactivity of the labeled apoprotein was followed in plasma, lipoprotein fractions, and urine for 15 days. Apolipoprotein C-I was quickly associated with HDL and to a smaller extent with VLDL in in vitro and in vivo incubation. Kinetic parameters of apolipoprotein C-I were compared with those of apo A-I. Fractional catabolic rates are respectively 0.422 +/- 0.044 vs 0.240 +/- 0.003 pools/day, residence times through the whole system 3.24 +/- 0.27 vs 6.31 +/- 0.27 days and production rates 1.79 +/- 0.18 vs 13.2 +/- 2.1 mg/kg X day. Two explanations for these differences are proposed.

Modifications of plasma lipids, lipoproteins and apolipoproteins in advanced cancer patients treated with recombinant interleukin-2 and autologous lymphokine-activated killer cells

Intravenous injection of recombinant interleukin-2 (r-Met-hu-IL-2(Ala-125] and LAK cells induced dramatic changes of lipoproteins in 12 patients with advanced cancer. After r-IL-2 injection (1) total cholesterol was reduced by 47% as a mean, LDL-cholesterol by 62%, HDL-cholesterol by 77%; (2) the triglyceride/cholesterol ratio was greatly increased (352%); (3) apolipoproteins B, A-I and A-II showed a mean reduction of 26%, 55% and 51%, respectively; and (4) very low density lipoproteins relatively increased, and HDL were separated into two definite fractions (I and II). LAK cell administration accentuated all the above effects and in most patients, HDL-fraction I almost completely disappeared. An action on hepatic synthesis of acute phase proteins is pointed out by the increase in C-reactive protein and apolipoprotein S concentrations contrasting with an unexpected reduction of fibrinogen. Surprisingly the drastic changes caused by treatment were quickly and completely reversible.

The effect of combined fenofibrate and cholestyramine therapy on low-density lipoprotein kinetics in familial hypercholesterolemia patients

The effects of combined drug treatment (fenofibrate and cholestyramine) have been investigated in vivo by simultaneously determining total and receptor-independent LDL catabolism with 125I-labelled LDL and 131I-labelled LDL coupled with cyclohexanedione. Receptor-mediated catabolism of LDL determined as the difference between the turnover of 125I and 131I, was found to be reduced in heterozygotes with familial hypercholesterolemia. Treatment with combined fenofibrate and cholestyramine markedly stimulated both receptor-mediated (by more than 2-fold) and receptor-independent catabolism. LDL-Apo B and LDL-cholesterol levels were reduced by 38% and 36%, respectively. The combined treatment also reduced the absolute synthetic rate of LDL-Apo B (by 9%). The mechanisms responsible for these kinetic effects are discussed.

In vivo metabolism of apolipoprotein S in humans. Comparison with apolipoprotein A-I metabolism

125I-labelled apolipoprotein (Apo) S and 131I-labelled apolipoprotein A-I were injected i.v. into healthy volunteers. Blood samples and daily urine collections were drawn periodically for 15 days. Ninety-eight percent of 131I radioactivity and greater than 95% of 125I radioactivity were found in HDL after Superose gel chromatography of plasma. About 10% of each radioactivity was recovered in the d 1.250 infranate after one ultracentrifugation. Affinity chromatography on monoclonal anti-Apo A-I Sepharose column separates two lipoprotein particles containing Apo S, one retained with Apo A-I (42.5%) and the other eluting without Apo A-I (57.5%). Kinetic parameters were calculated according to exponential curve fitting. Mean transit time was about 7.0 days for both Apo A-I and Apo S. FCR of Apo S was 50% higher than FCR of Apo A-I. Synthetic rate of Apo S was about 150 times smaller than for Apo A-I. As heterogeneity of HDL-S was suggested by both the results of affinity chromatography and the urinary data, a compartmental model was built which fitted adequately all data. Part of the model is common to HDL-A-I and HDL-S.

In vivo effect of simvastatin on lipoprotein cholesteryl ester metabolism in normocholesterolemic volunteers

A kinetic study on lipoprotein cholesteryl ester metabolism was carried out in 4 normolipidemic volunteers before and after treatment with simvastatin. They received LDL labelled with 3H-cholesteryl linoleate. A lipoprotein cholesteryl ester model was developed that fit the radioactivity in LDL, HDL and VLDL cholesteryl ester during 24 hours following injection. Before treatment, the model is consistent with previously reported data. Moreover our results suggest that, in normal fasting subjects, the efflux of plasma cholesteryl ester is almost exclusively derived from LDL. Administration of drug decreased LDL cholesteryl ester concentration by 35%. After treatment, the rate constant concerning LDL catabolism was increased by 25% and the model required the existence of a direct removal of VLDL cholesteryl ester (40% of total VLDL turnover). Our results suggest that the reduction in the LDL cholesteryl ester concentration induced by treatment with simvastatin is due to an increase in the uptake of LDL and LDL precursors (VLDL, VLDL remnants) by LDL receptors.

Plasma lipids, lipoproteins and apolipoproteins in two kindreds of hypobetalipoproteinemia

Plasma lipids and apolipoproteins were quantified in two kindreds of hypobetalipoproteinemia. All affected members were asymptomatic but showed a decrease of 75% in apolipoprotein B and of 69% in LDL-cholesterol. There were no major changes in apo A-I and A-II but all affected family members had reduced levels of apo C-II (by 58%) and C-III (by 59%) without significant decrease in apo C-I and no specific decrease of apo C-III1. Apolipoprotein E is decreased in SDS-PAGE. The plasma level and phenotype of Lp(a) are not affected by HBL, suggesting that a catabolic rather than a synthetic mechanism is responsible for the disease. As shown by density gradient ultracentrifugation, HDL2 particles that contain essentially apolipoprotein A-I, cholesterol and phospholipids represent in affected subjects the major part of HDL. Due to the net reduction of apolipoprotein B-containing particles (VLDL and LDL) as acceptors of lipids in HBL, there is an accumulation of large particles rich in cholesteryl esters.

LDL binding to lipid emulsion particles: effects of incubation duration, temperature, and addition of plasma subfractions.

Lipid emulsions used in parenteral nutrition interact with lipoproteins leading to exchanges of lipids and acquisition of several apolipoproteins (apo). It has been previously observed that, during in vitro incubation of emulsions with purified LDL, a variable fraction of LDL binds to TG-rich emulsion particles. The purpose of this study was to better characterize such an interaction. Two emulsions containing 20% soybean oil (Endolipid®, B. Braun AG, Melsungen, Germany) or fish oil were incubated with LDL, either alone or in the presence of various plasma subfractions, for different durations and at different temperatures. The fraction named M-LE (containing TG-rich particles modified after incubation) was separated by ultracentrifugation or gel filtration chromatography, and the apoB content was measured as an index of LDL binding to TG-rich emulsion particles. The formation of such complexes was visualized by freeze-fracture electron microscopy. LDL binding was not influenced by the method used for M-LE isolation. Binding occurred quickly, did not increase with prolonged incubation, was inversely related to increasing incubation or ultracentrifugation temperature, and withstood 40 h of ultracentrifugation at 163,000×g. The presence of glycerol or excess phospholipids in the emulsion did not markedly affect the formation of the complexes. In contrast, adding very small amounts of lipoprotein-poor plasma (d>1.210 g/mL) or HDL markedly reduced the process, and albumin had no effect. The TG composition of the emulsion influenced the binding of LDL to TG-rich particles, since more apoB was found in M-LE from fish oil than from soybean oil emulsion.