Comparison of different sandwich enzyme immunoassays for the quantitation of human apolipoproteins A-I and A-II

Effect of ALA-enriched food supply on cardiovascular risk factors in males

The outcome of a total dietary approach using a wide range of n-3 polyunsaturated fatty acids (PUFA) enriched food items on cardiovascular diseases called for further investigation. The study objective was to assess the effect of an ALA-enriched food supply on cardiovascular risk factors in healthy males. A dietary intervention (single-blind field trial with pre- and post-measurements) was performed with 59 healthy males in a Belgian prison. Over a period of 12 weeks they were supplied with an n-3 enriched diet (containing 6.5 g n-3 PUFA/day compared to 4 g n-3 PUFA/day in the standard diet) that was substituted for their regular diet, increasing mainly the alpha-linolenic acid intake (from 2.8 to around 5 g/day). The results indicated no impact on subjects waist circumference, weight and BMI or systolic blood pressure. In contrast, the diastolic blood pressure significantly decreased during the intervention period (from 74.6 +/- 8.2 to 71.7 +/- 10.1 mmHg; P < 0.02). Moreover, the HDL-cholesterol level increased in non-smoking participants (from 0.97 +/- 0.25 to 1.06 +/- 0.23 mmol/l; P < 0.03). In summary, the study demonstrated that enrichment of commonly eaten food items with n-3 fatty acids provides the opportunity to increase the n-3 fatty acid intake and to decrease the n-6/n-3 ratio which results in a decreasing diastolic blood pressure and an increase of HDL-cholesterol (in non-smokers).

Inclusion of 10% fish oil in mixed medium-chain triacylglycerol-long-chain triacylglycerol emulsions increases plasma triacylglycerol clearance and induces rapid eicosapentaenoic acid (20:5n-3) incorporation into blood cell phospholipids

BACKGROUND

Lipolysis of a fish oil (FO) emulsion is much slower than that of a soybean [long-chain triacylglycerol (LCT)] emulsion; in contrast, emulsions containing medium-chain triacylglycerol (MCT) are efficiently hydrolyzed by lipoprotein lipase.

OBJECTIVES

We questioned whether incorporating 10% FO in a mixed MCT-LCT emulsion would affect plasma triacylglycerol clearance and provide efficient delivery of n-3 polyunsaturated fatty acids to cells and tissues.

DESIGN

This prospective crossover study was conducted in 8 normolipidemic subjects with the use of the hypertriglyceridemic clamp model and compared plasma triacylglycerol clearance of a lipid emulsion (5:4:1) made of 50% MCT, 40% LCT, and 10% FO (wt:wt:wt) to a control (5:5) preparation with 50% MCT and 50% LCT. Subjects were daily infused for 5 h, over 4 consecutive days. Fatty acyl pattern was daily measured in plasma phospholipids as well as in leukocyte and platelet phospholipids.

RESULTS

Inclusion of 10% FO in mixed emulsion particles enhanced plasma clearance of infused triacylglycerols (18%; P < 0.0001). The faster elimination of the 5:4:1 emulsion appears related to an enhanced uptake of remnant particles rather than to faster intravascular lipolysis. Each infusion of 5:4:1 raised the eicosapentaenoic acid (C20:5n-3) concentration in blood cell phospholipids to reach a 7-fold enrichment in platelets and a >2-fold enrichment in leukocytes after 4 infusions. In contrast, the docosahexaenoic acid (C22:6n-3) concentration remained unchanged in blood cell phospholipids.

CONCLUSIONS

Infusion of a mixed emulsion with MCTs, soy LCTs, and FO is associated with efficient plasma triacylglycerol clearance and results in rapid incorporation of C20:5n-3 but not C22:6n-3 in leukocyte and platelet phospholipids.

Quantitative determination of humanized monoclonal antibody rhuMAb2H7 in cynomolgus monkey serum using a Generic Immunoglobulin Pharmacokinetic (GRIP) assay

Preclinical pharmacokinetic (PK) assays are important to help evaluate the safety and efficacy of a potential biotherapeutic before clinical studies. The assay typically requires a biotherapeutic-specific reagent to minimize matrix effects especially when the host species are non-human primates such as cynomolgus monkeys and the biotherapeutic is a humanized monoclonal antibody (MAb). Recombinant humanized mAb 2H7 (rhuMAb2H7) binds to the extracellular domain of CD20 that is expressed on B cells and results in B cell depletion. It is currently being evaluated for its therapeutic potential in rheumatoid arthritis (RA) in clinical studies. During the early development of rhuMAb2H7, a cynomolgus monkey PK assay was needed to help assess the pharmacokinetic parameters of rhuMAb2H7 in a pilot cynomolgus monkey study. However, development of a cynomolgus monkey PK assay was challenging due to lack of rhuMAb2H7-specific reagents. Here we describe an alternative method for detection of rhuMAb2H7 in cynomolgus monkey serum using polyclonal antibodies against human IgGs. This assay quantifies rhuMAb2H7 in 10% cynomolgus monkey serum with high sensitivity, accuracy, and precision. This assay successfully supported the rhuMAb2H7 development, and has the potential to be used to quantify other humanized MAb biotherapeutics in serum from a variety of non-human species.

Changes in plasma LDL and HDL composition in patients undergoing cardiac surgery

Changes of lipoprotein composition have been mainly reported in conditions of sepsis. This study characterized compositional changes in LDL and HDL during the acute phase response following cardiac surgery with cardiopulmonary bypass. Twenty-one patients undergoing cardiac surgery were included in this study. Blood samples were drawn before operation and on day 2 post-surgery. In parallel to plasma lipids and antioxidant status, lipoproteins were analyzed for lipid, apolipoprotein (apo), hydroperoxide and alpha-tocopherol content. Beyond decreases in lipid concentrations and antioxidant defenses, cardiac surgery induced substantial modifications in plasma lipoproteins. ApoB decrease in LDL fraction (-46%; P < 0.0001) reflected a marked reduction in the circulating particle number. LDL cholesteryl ester content relative to apoB concentration remained unchanged post-surgery while triglyceride (+113%; P < 0.001), free cholesterol (+22%; P < 0.05) and phospholipid (+23%; P < 0.025) were raised relative to apoB indicating increased particle size. In HDL, an abrupt rise of apoSAA (P < 0.05) was observed together with a decrease of apoA1 (-22%; P < 0.005). Cholesteryl ester content in HDL fraction decreased in parallel to apoA1 concentration while triglycerides, free cholesterol and phospholipids increased relative to apoA1. In contrast to unchanged alpha-tocopherol content, hydroperoxide content was increased in LDL and HDL. By comparison to sepsis, cardiac surgery induces a comparable reduction in circulating LDL but a more limited decrease in HDL particles. Furthermore, in contrast, cardiac surgery induces an increase in polar and non-polar lipids, as well as of particle size in both LDL and HDL.

Ghrelin interacts with human plasma lipoproteins

Ghrelin, a peptide hormone produced predominantly by the stomach, stimulates food intake and GH secretion. The Ser(3) residue of ghrelin is mainly modified by a n-octanoic acid. In the human bloodstream, ghrelin circulates in two forms: octanoylated and desacylated. We previously demonstrated that ghrelin is desoctanoylated in human serum by butyrylcholinesterase (EC 3.1.1.8) and other esterase(s), whereas in rat serum, only carboxylesterase (EC 3.1.1.1) is involved. The aims of this study were to determine the role of lipoprotein-associated enzymes in ghrelin desoctanoylation and the role of lipoproteins in the transport of circulating ghrelin. Our results show that ghrelin desoctanoylation mostly occurred in contact with low-density lipoproteins (LDLs) and lipoprotein-poor plasma subfractions. Butyrylcholinesterase and platelet-activating factor acetylhydrolase (EC 3.1.1.47) were responsible for the ghrelin hydrolytic activity of the lipoprotein-poor plasma and LDL subfractions, respectively. Moreover, we observed that ghrelin is associated with triglyceride-rich lipoproteins (TRLs), high-density lipoproteins (HDLs), very high-density lipoproteins (VHDLs), and to some extent LDLs. In conclusion, we report that the presence of the acyl group is necessary for ghrelin interaction with TRLs and LDLs but not HDLs and VHDLs. Ghrelin interacts via its N- and C-terminal parts with HDLs and VHDLs. This suggests that, whereas TRLs mostly transport acylated ghrelin, HDLs and VHDLs transport both ghrelin and des-acyl ghrelin.

Species-dependent serum interference in a sandwich ELISA for Apo2L/TRAIL

To support pre-clinical studies of Apo2L/TRAIL in rodents and non-human primates, a sandwich ELISA was developed using two mouse monoclonal anti-Apo2L/TRAIL antibodies. Mouse, rat, cynomolgus monkey, and chimpanzee serum at concentrations of > or =1% were found to interfere with accurate quantitation of Apo2L/TRAIL. Moreover, the characteristics of the serum interference for each species were different. In order to resolve the observed serum effect, studies were performed in which salts, detergents, and blocking proteins were added to the sample diluent, and optimized sample diluents that eliminated serum interference were developed for mouse, cynomolgus monkey, and chimpanzee serum. These buffers consisted of a base assay diluent (PBS/0.5% BSA/0.05% Tween-20/10 ppm ProClin 300) supplemented with: NaCl (mouse serum); NaCl, EDTA, CHAPS, bovine gamma globulin (BGG), and human IgG (cynomolgus monkey serum); and NaCl and EDTA (chimpanzee serum). Full characterization studies were performed for the "buffer" ELISA run in base assay diluent (intended for non-serum samples) as well as the assays optimized for mouse serum and cynomolgus monkey serum. Precision, accuracy, linearity, and specificity were found to be satisfactory. With the availability of a rabbit polyclonal antibody against Apo2L/TRAIL, a new pAb/mAb ELISA was developed. This assay was not only more sensitive by > or =6-fold, but it was also much less subject to serum interference.

Effect of Atorvastatin Therapy and Conversion to Tacrolimus on Hypercholesterolemia and Endothelial Dysfunction After Renal Transplantation

BACKGROUND

Hypercholesterolemia is a frequent complication in renal transplant patients treated with cyclosporine A (CsA). Whether it is preferable to treat hypercholesterolemia with statins or to switch patients from CsA to tacrolimus (TRL) has not been investigated.

METHODS

Twelve CsA-treated kidney transplant recipients with hypercholesterolemia were successively crossed over from CsA alone to: CsA plus atorvastatin; TRL alone; and TRL plus atorvastatin. Total cholesterol (C), Low density lipoprotein (LDL)-C, high density lipoprotein (HDL)-C, LDL and HDL alpha-tocopherol content, lag-time of LDL oxidation, plasma levels of oxidized LDL and the percentage of small dense LDL were assayed at the end of each treatment period. Endothelial function was assessed by high resolution ultrasound measurement of flow-mediated brachial artery vasodilatation (FMD).

RESULTS

Atorvastatin therapy was more efficient in reducing total cholesterol and LDL-C levels than conversion from CsA to TRL. Combining TRL with atorvastatin further reduced LDL-C levels as compared to TRL alone, but was no more efficient than the CsA-statin combination. Neither atorvastatin therapy nor conversion to TRL significantly changed the proportion of dense LDL, lipoprotein alpha-tocopherol contents or the lag time of LDL oxidation. Addition of atorvastatin to CsA increased FMD from 4.0+/-1.8% to 6.5+/-4.0% (P<0.05 vs. CsA). Conversion from CsA to TRL caused a slight improvement in FMD (5.1+/-2.1%, P<0.05 vs. CsA). Adding atorvastatin to TRL had no detectable effect on FMD (5.5+/-2.3%, P=NS vs. TRL).

CONCLUSIONS

Atorvastatin was more efficient in reducing total and LDL cholesterol levels of CsA-treated renal transplant patients than conversion to TRL and significantly improved endothelial dysfunction.

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 x 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.

Incubation of lipid emulsions with plasma lipoproteins modifies the fluidity of each particle

Lipid emulsions (LE) contain triglyceride (TG)-rich particles (TGRP) and phospholipid-rich particles (PLRP). Various lipid and protein exchanges take place during in vitro incubations of LE with lipoproteins. These composition changes affect physical properties of particles. The aim of this study was to determine the role of different LE particles and the effect of TG composition on physical modifications. Low density lipoproteins (LDL: 1.025 < d < 1.040 g/mL) or high density lipoproteins (HDL: 1.085 < d< 1.150 g/mL) were incubated with the following four LE or their TGRP or PLRP, which were manufactured with the same phospholipid emulsifier: long-chain triglycerides (LCT): 100% soybean oil; medium-chain triglycerides (MCT)/LCT (MCT/LCT, 5:5, w/w); FO (100% fish oil); and MLF541 (MCT/LCT/FO, 5:4:1, by wt). After incubation, modified LE particles and lipoproteins were analyzed by fluorescence polarization. Observed physical modifications were significant in emulsion particles (ordering effect) but not in lipoproteins and also were significant for TG composition effect. Since intact emulsion contained a large excess of TGRP over PLRP, it is not surprising that intact emulsion had the same behavior as TGRP alone, and that PLRP had the same physical characteristics as lipoproteins. TG loss and cholesterol and protein acquisitions by emulsion particles rigidify their envelope. The two emulsions containing FO were less ordered after incubation. In conclusion, incubation of LE with lipoproteins changes physical properties of each kind of particle, and TG composition of the emulsion affects emulsion particle changes but has no effect on LDL and HDL. These order modifications induce more effective exchanges between LE particles and lipoproteins and modify their metabolism; HDL changes may increase the reverse cholesterol transport.

Lipid and apolipoprotein changes after orthotopic liver transplantation for end-stage liver diseases

Orthotopic liver transplantation was performed in 37 patients with different endstage liver diseases. Changes in lipid and apolipoprotein concentrations were followed daily from day 1 to 20 after surgery and regularly thereafter until 12 months. When the acute effects of surgery had cleared away, there was a sharp drop in HDL-C, apo A-I and A-II from day 1 to 5, a stabilization at their lowest values from day 5 to 15 and then a progressive rise. Contrasting with this drop, triglycerides, apo B, C-II and C-III increased from day 1 to 5 with variable concentrations thereafter. Apo SAA considerably increased early after surgery and remained significantly higher than normal in most patients after 12 months. All other parameters returned to normal from 3 to 6 months after transplant. The mechanism leading to these lipid and apolipoprotein changes are discussed with respect to the distant effect of infusions, re-alimentation, immunosuppressive therapy and lipoprotein metabolism. The apolipoprotein concentrations appear very useful indicators of functional liver recovery.

Alterations in lipoprotein density classes in infantile visceral leishmaniasis: presence of apolipoprotein SAA

This study describes the alterations in the plasma lipoproteins from nine young Tunisian children with active visceral Leishmaniasis. The plasma lipid profile from affected patients was characterized by a marked hypertriglyceridaemia associated with reduced levels of total and high density lipoprotein (HDL)-cholesterol and a significant increase in the plasma ratio of unesterified to total cholesterol. Quantitative determination of plasma apolipoproteins revealed significantly decreased levels of all measured apolipoproteins, especially of apolipoproteins A-I and A-II, with the exception of apolipoprotein E, the levels of which were markedly increased. Moreover, at least two isoforms of the apolipoprotein serum amyloid A (SAA), an acute phase protein, were detected in all patients' plasma using two-dimensional electrophoresis. Immunochemical evidence was presented that apolipoproteins E and SAA, although both primarily associated with apolipoprotein A- (A-I and A-II) as well as with apolipoprotein B-containing lipoproteins, could occur as LP-E and LP-SAA subspecies, devoid of apolipoproteins A and B. However, it should be pointed out that LP-SAA particles were found in HDL2 from only two patients whereas the abnormal LP-E particles were detected in LDL and HDL2 from all investigated patients. The polydispersity and heterogeneity of patients' HDL3 were assessed by electron microscopy. It was further suggested that the profound changes in the lipoprotein metabolism of these young patients may be due to the increased hepatic synthesis of apolipoprotein SAA and/or to their altered immune function during active visceral Leishmaniasis.

Enzyme-linked immunosorbent assay to measure apolipoproteins AI and B secreted by a human hepatic carcinoma cell line (Hep G2)

We describe an enzyme-linked immunosorbent assay (ELISA) to measure apolipoproteins AI and B secreted by Hep G2 cells and in cell homogenates. These assays utilize commercially available polyclonal antibodies, affinity-purified to improve their specificity, thereby achieving a dramatic increase in the sensitivity of the assay. These affinity-purified antibodies were also more sensitive than a series of monoclonal antibodies tested. We achieved a sensitivity of 0.4 ng in the apo AI assay, and a sensitivity of 5 ng in the apo B assay. By these methods, we measured secretion rates by Hep G2 cells of 358 +/- 41 ng/mg cell protein/hr for apo B and 137 +/- 8 ng/mg cell protein/hr for apo AI. These assays also allowed the measurement of intracellular apolipoproteins and thus can be used to facilitate investigations of human lipoprotein metabolism in cell culture systems.

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.

Characterization of anti-apolipoprotein A-I monoclonal antibodies and their use in the measurement of apolipoprotein A-I by a two-site enzyme immunoassay

Six monoclonal antibodies raised against pure apo A-I or high density lipoprotein were characterized for epitope specificity by enzyme and radioimmunoassays, immunodiffusion and affinity chromatography. The six antibodies were classified into three groups according to the region of apo A-I they reacted with. The antibody VI10H, from group II, appeared to recognize a region fully exposed on native HDL-apo A-I, whereas group I comprised antibodies specific for a partially masked region. Group III comprised only one antibody. Use of the non-ionic detergent Tween 20 in the immunoassays permitted antibodies from the three groups to react with their respective epitope on native HDL-apo A-I. An antibody from group I (V4F) was chosen as the first antibody and VI10H, the antibody showing the highest affinity, was chosen for the anti-A-I-peroxidase conjugate in a two-site enzyme immunoassay.

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.

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.

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.

Non-competitive enzyme-linked immunosorbent assay for human apolipoprotein SAA or S

Purified antibodies against human apolipoprotein S were used to measure apo S levels in human plasma by a sandwich ELISA technique. The method developed was highly sensitive and specific. A reliable calibration of a plasma standard was obtained by reassociating the purified protein with plasma HDL. A significant correlation (r = 0.69) was found between plasma apo S and CRP values. This correlation coefficient reached 0.97 when the plasma samples were selected according to additional clinical and laboratory criteria.

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.