Fig 1.
Cross reactivity characterisation of anti-CS-6253 antibody.
Non denaturing gradient gel electrophoresis (4–20%) is used to separate CS-6253 complexes, apo A-I and apo E. CS-6253 was immunoblotted using antibody against human apo A-I, human apo E and against CS-6253. Normolipidemic human plasma was used as positive control. Molecular weight markers were revealed by Ponceau S. Left panel shows dose response relationship with an antibody directed against CS-6253. Middle panel shows anti-apo A-I antibody does not cross-react with CS-6253; similarly, right panel shows antibody against apo E does not react against CS-6253.
Fig 2.
Effect of CS-6253 treatment on cholesterol efflux.
A. Time-course activity of ABCA1-mediated cholesterol efflux to lipid-free CS-6253 (30 μg/ml) and apo A-I (10 μg/ml), using BHK cells expressing ABCA1, and control cells (unstimulated BHK-ABCA1 and BHK-mock cells). Cholesterol efflux from either ABCA1 cells or control cells to apo A-I (closed circles), and CS-6253 (closed triangles) was determined at the indicated time points. B. Dose dependent ABCA1 mediated cholesterol efflux in BHK-ABCA1 induced with mifepristone. Kinetic parameters for ABCA1-mediated cholesterol efflux from BHK-ABCA1 cells to apo A-I: Km = 4.53±0.67 μg/ml (0.15±0.02 μM), Vmax = 14.85±0.02% efflux/4h, and relative catalytic efficiency: Vmax/Km = 3.27. CS-6253: Km = 2.27±0.16 μg/ml (0.73±0.05 μM), Vmax = 15.25±0.05% efflux/4h, and relative catalytic efficiency: Vmax/Km = 6.71. ATI-5261: Km = 1.04 ± 0.16 μg/ml (0.37 ± 0.04 μM), Vmax = 14.48 ± 0.29% efflux/ h, and relative catalytic efficiency: Vmax/Km = 13.92. Apo E: Km = 10.30±2.84 μg/ml (0.21±0.05 μM), Vmax = 11.45±1.16% efflux/4h, and relative catalytic efficiency: Vmax/Km = 1.11. C. Ability of CS-6253 to stimulate cholesterol efflux from human macrophages THP-1. Foam cells were incubated with CS-6253 or apoA-I at equimolar ratio (0.96 μM) for 4h. Cholesterol efflux induced by CS-6253 and apoA-I were compared to control cells incubated alone. P<0.001 by Student’s t-test. D. Membrane ABCA1 levels assessment by Western blotting assays. ABCA1 was detected from THP-1 foam cells lysis at 4°C with lysis buffer containing 0.5% n-dodecylmaltoside in the presence of a protease inhibitor mixture followed by low speed centrifugation to remove cell debris. Protein concentration was determined by standard assay (Bio-Rad). The supernatants were then separated by SDS-PAGE (4–22.5%) in duplicate. After electrophoresis, ABCA1 was detected by an anti-ABCA1 antibody. GAPDH was used as loading control. E. Quantification of FC and CE in foam cells after interaction with CS-6253 and apoA-I. After a period of 4h cholesterol efflux, THP-1 foam cell lipids were extracted with hexane: isopropanol (3v/2v) as under ‘‘Material and Methods’. 3[H]-FC and 3[H]-CE were separated by TLC and located by exposure to iodine vapor, and were scraped off into liquid scintillating vials and assayed for radioactivity. Results are from a single experiment using triplicate wells and the mean (±SD) is presented. P<0.0001 versus control sample untreated THP-1 cells for cholesterol efflux. P<0.05 versus FC or CE in untreated cells, by Student’s t-test.
Fig 3.
Competitive binding of CS-6253 peptide to ABCA1 cells expressing ABCA1.
BHK-ABCA1 cells were plated in 24-well plates and stimulated for 20 h. Cells were then incubated with 2 μg/ml of 125I-apo A-I for 2 h at 37°C with increasing molar concentrations relative to apo A-I of either CS-6253 peptide, ATI-5261, human apo E, and unlabelled apo A-I (0, 0.0035, 0.017, 0.035, 0.071, 0.17, 0.35, 1.79 μM). Cells were then washed rapidly three times with ice-cold PBS/BSA and then PBS alone. 125I-apo A-I cell associated was determined as described under “Experimental Procedures.” The values shown represent the mean ± S.D from triplicate wells. The 100% of control value measured in the absence of competitors was 0.21 ng of apo A-I /μg cell protein. Values of IC50 shown were determined using the Graph Pad Prism 6 software.
Fig 4.
Apo A-I (left panels) and CS-6253 (right panels) desorb phospholipids species from raft and nonraft domains.
BHK-ABCA1 cells were labeled with 3[H]choline for 48 h, followed by stimulation with mifepristone for 18–20h as described in “experimental procedures”. Cells were then incubated for 12h with apo A-I or CS-6253 (0.96 μM). After lipid extraction by Folch, 3[H]phosphatidyl choline (3[H]PC) (A and B), or 3[H]sphingomyelin (3[H]SM) (C and D) in each fraction was assessed for radioactivity. Radioactivity appearing in fractions corresponding to raft (1–5) and nonraft (6–10) material was pooled, and desorption of 3[H]PC (A and B inset) and 3[H]SM (C and D inset), from raft versus nonraft in the presence of apo A-I or CS-6253 was expressed as a percentage of control (100%, in the absence of acceptor). 3[H]PC and 3[H]SM distributions in sucrose gradient fractions after 12h incubation with apo A-I or CS-6253 were assessed by TLC respectively. Results shown are representative of three independent experiments. *P < 0.05 by Student's t-test.
Fig 5.
Time course ability of CS-6253 to generate nHDL-mimetic like particles.
(A and B): nHDL-CS-6253 and nHDL-apo A-I released to the medium at specific time points (45 min and 6 h) from BHK cells expressing ABCA1 were analyzed by 2D-PAGGE. Apo A-I was detected by polyclonal anti-apo A-I, CS-6253 peptides was detected by anti-CS-6253 and revealed by chemiluminescence. Molecular markers are indicated.
Fig 6.
Dynamics of transfer and redistribution of BHK-ABCA1 cell-derived cholesterol content of nHDL-CS-6253.
nHDL-CS-6253 particles were labelled with cell derived 3[H]cholesterol and incubated with normolipidemic plasma for various time periods at 37°C (1μg peptide: 10μg plasma apo A-I). A. Characterization of lipid particles released to the medium in the presence of CS-6253. 3[H]-cholesterol-labelled BHK cells expressing ABCA1 or not were incubated in the presence of 0.96 μM apo A-I (solid line) or CS-6253 (dashed line) for 45min at 37°C. Concentrated medium from cells was analysed by FPLC, and radioactivity associated with each fraction was determined. B. Transfer of total 3[H]cholesterol from 3[H]nHDL-CS-6253 to plasma lipoproteins. nHDL-CS-6253 or nHDL-apo A-I were generated after incubation (4h) of BHK cells expressing ABCA1 with increased doses of lipid free CS-6253 or apo A-I. Media cell culture containing 3[H]-nHDL-particles was incubated in human plasma for 1h, 37°C. After ApoB precipitation, fractions were dialysed and counted for radioactivity. Kinetic parameters for cholesterol transfer to apoB particles in plasma: nHDL-CS-6253 (439±0.20μM), Vmax (439± 19.74%cpm/μl) vs nHDL-apo A-I (0.37 ± 0.035), Vmax (517±24.45).C. Effects of ex vivo incubation of CS-6253 on plasma cholesterol lipoproteins. FPLC cholesterol profiles (OD 490 nm) of plasma apo A-I: peptide ratio (1:1) (dashed line) and plasma apo A-I: peptide ratios (1:0; i.e. apo A-I alone) (solid line) are obtained after 5 min incubation at 37°C. In all experiment counts were made in triplicate, (*P<0.05 by Student‘s t-test). For reference purposes, the inset shows an FPLC profile of normal plasma. D. Effect of ex vivo incubation of CS-6253 on plasma lipoproteins after separation by ND-PAGGE (5–35%) electrophoresis. CS-6253 (0.96 μM final dose) was incubated for 1h at 37°C with HDL, LDL or VLDL isolated by ultracentrifugation or with human plasma and then separated by electrophoresis at concentration of 1 mg/protein/mL. Gel is followed by Western blot analysis with anti-CS-6253 antibody. Internal control was run on the left of the gel and detected by Ponceau S.
Fig 7.
Dose dependent effects of pre-incubation of plasma with lipid free CS-6253, or nHDL-CS-6253 on ABCA1 cholesterol efflux.
A. Increased doses of lipid free CS-6253 or apo A-I were added to normolipidemic plasma and incubated for 1h at 37°C. A volume of 2.8% of HDL fractions isolated by PEG was used for the measurements of cholesterol efflux from BHK cells expressing ABCA1 and mock cells. Kinetic parameters for ABCA1-mediated cholesterol efflux from BHK expressing ABCA1 cells to apo A-I in plasma: Km = 0.03±0.008 μM, Vmax = 9.26±0.29% efflux/4h. CS-6253: Km = 0.20±0.05 μM, Vmax = 14.71±0.39% efflux/4h. Kinetic parameters for cholesterol efflux from BHK-mock cells to apo A-I in plasma: Km = 0.07±0.95 μM, Vmax = 0.30±0.15% efflux/6h. CS-6253: Km = 0.65±0.63 μM, Vmax = 0.84±0.17% efflux/4h. B. nHDL-CS-6253 and nHDL-apo A-I were generated as indicated above. nHDL particles were incubated in plasma for 1h at 37°C, and specific HDL fractions isolated by PEG were subjected to cholesterol efflux in 3[H]-radiolabelled BHK cells. Kinetic parameters for ABCA1-mediated cholesterol efflux from BHK expressing ABCA1 cells to nHDL-apo A-I in plasma: Km = 0.25±0.08 μM, Vmax = 15.73±2.14% efflux/4h. nHDL-CS-6253: Km = 0.32±0.15 μM, Vmax = 15.01±0.84% efflux/4h. C. Mobilization of cholesterol efflux of increasing concentrations of peptide: plasma apo A-I molar ratios: (1:0) (closed circles), (1:10) (upright closed triangles), and (1:1) (closed squares). (C inset). The double reciprocal-plot was used to calculate the apparent appKm of the efflux activity in peptide: plasma with indicated ratios. Kinetics values are as follows, molar ratio of plasma apo A-I: CS-6253 (1:0); appKm (28±0.07 μM). Molar ratio of plasma apo A-I: CS-6253 (1:1); appKm (4.17±0.47 μM). Molar ratio of plasma apo A-I: CS-6253 (1:10); appKm (0.71±0.46 μM). D. Lipid free CS-6253 was incubated with normolipidemic plasma, using peptide: apo A-I mole ratio of (1:1) for 5 min at 37°C versus plasma alone. Isolated HDL fractions by PEG were separated by 2D-PAGGE and HDL subpopulations were detected by apo A-I Western blot. Molecular size markers are shown. In all experiments, efflux of 3[H]cholesterol is shown as means ± SD of triplicate experiments.
Table 1.
Comparison of kinetic parameters for ABCA1-mediated cholesterol efflux (4h) from BHK cells in media cell culture and human plasma.
Data are presented as mean ± SD.
Fig 8.
Time dependent effects of incubation of lipid free CS-6253 with human plasma, on HDL subparticles.
(A, B, C and D). Lipid free CS-6253 was incubated with normolipidemic plasma, using peptide: apo A-I molar ratio of (10:1) and (0:1 i.e. no peptide) for (5 min, 1h, 2h, and 4h) at 37°C. HDL subpopulations were detected by an anti-apo A-I antibody. E and F Samples were then PEG precipitated to remove apoB-containing lipoproteins and separated by 2D-PAGGE. HDL subfractions were detected by an antibody against CS-6253. Molecular size markers are shown.
Fig 9.
Time dependent effects of incubation of lipid free CS-6253 with human plasma, on HDL subparticles.
(A, B, C). Radiolabeled Lipid free apoA-I was prepared as indicated in “Material and Methods”. 125I-lipid free apoA-I in incubated with normolipidemic plasma, using molar ratio (10 μg Lipid free apoA-I or peptide: 1 μg plasma apoA-I) at 37°C for increasing time for (5 min, 1h, 2h, and 4h) at 37°C. Samples were separated by 2D-PAGGE, and 125I-apoA-I was detected by autoradiography. Lipid-free 125I-apoA-I (C) incubated in PBS for 4 h at 37°C is shown as controls. Molecular size markers are shown.
Fig 10.
Uptake of cholesterol to hepatic cells expressing SR-BI from plasma containing HDL-CS-6253 or HDL-apo A-I.
A. Fu5AH liver hepatoma cells expression of SR-BI transporter ability. Fu5AH cells were grown as described in Experimental procedures, cells were lysed at 4°C with (20mM Tris, 5mM EDTA, and 5 mM EGTA; pH 7.5) containing 0.5% n-dodecylmaltoside. The suspension was subjected for further lysis in the presence of protease inhibitor mixture followed by low speed centrifugation to remove insoluble material. Protein concentration was determined by standard assay (Bio-Rad). Cells were separated by SDS-PAGE (4–22.5%), and immunoblotted using antibodies against human SR-BI, ABCG1 and ABCA1. Cells lysate from BHK cells expressing ABCG1 and ABCG1 was used as positive control. Molecular weight (Bio-Rad) is shown on the left of the gel. B and C. Radiolabelled nHDL-CS-6253 or nHDL-apoA-I particles were generated after incubation of J774 cells with lipid free CS-6253 or apo A-I at increased concentrations as showed in experimental procedures. nHDL particles with CS-6253 or apoA-I were then incubated in plasma to induce lipidation. Cholesterol uptake by SR-BI Fu5AH cells was determined by incubation for 6h with 20% apoB depleted plasma as described in experimental procedures. BLT-1 was used to specifically inhibit SR-BI. The values shown represent the mean ± S.D from triplicate wells.
Fig 11.
A proposed in-vitro model for lipid free CS-6253 lipidation and remodelling in RCT pathway.
1). ABCA1 interaction: a. ABCA1 oligomerization, b. Binding to ABCA-1. 2). Lipid efflux process: a. PM microdomains lipid desorption, b. ABCA1 and ABCG1 induction of lipid efflux and nHDL-CS-6253 formation, 3–4) HDL-CS-6253 remodelling by LCAT/PLTP in plasma, 5) generation of mature HDL-CS-6253, 6) Cholesterol uptake by liver via SR-BI, and 7) lipid transfer to both apoB-containing particles and the plasma HDL resident pool. 8) Although the mechanisms underlying this process is presently ambiguous, it is possible that nHDL-CS-6253 remodelling may lead to loss or ‘shedding’ of CS-6253 from HDL-CS-6253 in plasma as they are actively delipidated of phospholipids by PLTP to yield lipid poor apo A-I precursor of RCT activation. 9) Alternatively lipid free CS-6253 associates with αHDL-apo A-I species leading to preβ1-apo A-I formation, that can also close the loop and initiate again RCT. 10) in this process, the peptide transfer cholesterol to apoB particles, and 11) cholesterol is delivered to liver by the LDLR.