Inhibition of cholesteryl ester transfer protein by substituted dithiobisnicotinic acid dimethyl ester: involvement Of a critical cysteine.

SC-71952, a substituted analog of dithiobisnicotinic acid dimethyl ester, was identified as a potent inhibitor of cholesteryl ester transfer protein (CETP). When tested in an in vitro assay, the concentration of SC-71952 required for half-maximal inhibition was 1 microm. The potency of SC-71952 was enhanced 200-fold by preincubation of the inhibitor with CETP, and was decreased 50-fold by treatment with dithiothreitol. Analogs of SC-71952 that did not contain a disulfide linkage were less potent, did not display time dependency, and were not affected by dithiothreitol treatment. Kinetic and biochemical characterization of the inhibitory process of CETP by SC-71952 suggested that the inhibitor initially binds rapidly and reversibly to a hydrophobic site on CETP. With time, the bound inhibitor irreversibly inactivates CETP, presumably by reacting with one of the free cysteines of CETP. Liquid chromatography/mass spectroscopy (LC/MS) analyses of tryptic digests of untreated or SC-71952-inactivated CETP was used to identify which cysteine(s) were potentially involved in the time-dependent, irreversible component of inactivation by the inhibitor. One disulfide bond, Cys143-Cys184, was unaffected by treatment with the inhibitor. Inactivation of CETP by SC-71952 correlated with a progressive decrease in the abundance of free Cys-13 and Cys-333. Conversion of Cys-13 to alanine had no effect on the rapid reversible component of inactivation by SC-71952. However, it abolished the time-dependent enhancement in potency seen with the inhibitor when using wild-type CETP. These data indicate that Cys-13 is critical for the irreversible inactivation of CETP by SC-71952 and provides support for the structural model that places Cys-13 near the neutral lipid-binding site of CETP.

Large-scale purification of myeloperoxidase from HL60 promyelocytic cells: characterization and comparison to human neutrophil myeloperoxidase.

A large-scale purification procedure was developed for the isolation of myeloperoxidase from HL60 promyelocytic cells in culture. Initial studies showed the bulk of peroxidase-positive myeloperoxidase activity to be located in the cetyltrimethylammonium bromide solubilized particulate fraction of cell homogenates. The myeloperoxidase was then chromatographically purified using concanavalin A followed by gel filtration. SDS-PAGE analysis of the final preparation showed the presence of only two proteins with molecular masses of approximately 55 and 15 kDa, corresponding to the large and small subunits of myeloperoxidase. These data, along with Reinheit Zahl (RZ) values (A(430)/A(280)) of greater than or equal to 0.72, indicate that the myeloperoxidase prepared by this method is apparently homogeneous. Preparations routinely yielded 12-20 mg of pure myeloperoxidase per 10 ml of cell pellet. The HL60 myeloperoxidase was shown to be indistinguishable from purified human neutrophil myeloperoxidase by size exclusion chromatography, analytical ultracentrifugation, SDS-PAGE, Western blot, and NH(2)-terminal sequence analysis. The activities of the two myeloperoxidase samples, as measured using either the tetramethylbenzidine or the taurine chloramine assay, were indistinguishable. Finally, both enzymes responded identically to dapsone and aminobenzoic acid hydrazide, known inhibitors of myeloperoxidase. A protocol is presented here for the rapid, large-scale purification of myeloperoxidase from cultured HL60 cells, as well as evidence for the interchangeability of this myeloperoxidase and that purified from human neutrophils.

Inhibition of cholesteryl ester transfer protein by apolipoproteins, lipopolysaccharides, and cholesteryl sulfate.

Cholesteryl ester transfer protein (CETP) mediates the exchange of cholesteryl esters and triglycerides between lipoproteins in the plasma. In studies dealing with the mechanism of CETP-mediated lipid transfer, we have examined the effects of several classes of biomolecules, including apolipoproteins and related synthetic peptides, cholesteryl sulfate, and lipopolysaccharides. In all cases, the molecules were inhibitory and their effects were associated with modifications of either HDL, LDL, or both. However, the probable mechanisms were distinct for each class of inhibitor. Inhibition of lipid transfer activity by apolipoprotein A-I was correlated with an increase in the apolipoprotein A-I content of HDL but not LDL, whereas the primary effect of cholesteryl sulfate was associated with modification of LDL, and only modest alteration of HDL. Lipopolysaccharides were found to modify the size and charge properties of both LDL and HDL over the same concentration ranges that affected CETP activity, but might also interact directly with CETP. It is suggested from the present studies that a variety of biomolecules that can interact with lipoproteins under natural or pathological situations have the potential to modify CETP activity, which in turn could affect normal lipoprotein composition and distribution.

Physical and kinetic characterization of recombinant human cholesteryl ester transfer protein.

Cholesteryl ester transfer protein (CETP) mediates the exchange of triglycerides (TGs), cholesteryl esters (CEs) and phospholipids (PLs) between lipoproteins in the plasma. In order to better understand the lipid transfer process, we have used recombinant human CETP expressed in cultured mammalian cells, purified to homogeneity by immunoaffinity chromatography. Purified recombinant CETP had a weight-average relative molecular mass (MW) of 69561, determined by sedimentation equilibrium, and a specific absorption coefficient of 0.83 litre.g-1.cm-1. The corresponding hydrodynamic diameter (Dh) of the protein, determined by dynamic light scattering, was 14 nm, which is nearly twice the expected value for a spheroidal protein of this molecular mass. These data suggest that CETP has a non-spheroidal shape in solution. The secondary structure of CETP was estimated by CD to contain 32% alpha-helix, 35% beta-sheet, 17% turn and 16% random coil. Like the natural protein from plasma, the recombinant protein consisted of several glycoforms that could be only partially deglycosylated using N-glycosidase F. Organic extraction of CETP followed by TLC showed that CE, unesterified cholesterol (UC), PL, TG and fatty acids (FA) were associated with the pure protein. Quantitative analyses verified that each mol of CETP contained 1.0 mol of cholesterol, 0.5 mol of TG and 1.3 mol of PL. CETP mediated the transfer of CE, TG, PL, and UC between lipoproteins, or between protein-free liposomes. In dual-label transfer experiments, the transfer rates for CE or TG from HDL to LDL were found to be proportional to the initial concentrations of the respective ligands in the donor HDL particles. Kinetic analysis of CE transfer was consistent with a carrier mechanism, having a Km of 700 nM for LDL particles and of 2000 nM for HDL particles, and a kcat of 2 s-1. The Km values were thus in the low range of the normal physiological concentration for each substrate. The carrier mechanism was verified independently for CE, TG, PL and UC in 'half-reaction' experiments.

Inactivation of cholesteryl ester transfer protein by cysteine modification.

The present studies examine the effects of various cysteine-modifying reagents on human recombinant cholesteryl ester transfer protein (CETP) activity. Dithiothreitol or other reducing agents had no effect on CETP transfer activity. Alkylating agents, including iodoacetamide and N-ethyl maleimide, also did not affect transfer activity. However, incubation of CETP with hydrophobic thiol-modifying reagents such as p-chloromercuriphenylsulfonic acid (IC50 = 0.02 microM), 4,4'-dithiodipyridine (IC50 = 0.5 microM), or 4,4'-dithiobis (phenyl azide) (IC50 = 0.5 microM) resulted in complete, time-dependent inactivation of both the cholesteryl ester and triglyceride transfer activities. Inactivation could be prevented by including dithiothreitol in the incubation. Long chain fatty acyl coenzyme A compounds were also found to be effective CETP inhibitors. The extent of inhibition was time-dependent, and proportional to the chain length of the fatty acyl portion of the molecule. These results suggest that CETP contains an essential free cysteine that resides in a hydrophobic environment within the protein.

Free bone graft reconstruction of irradiated facial tissue: experimental effects of basic fibroblast growth factor stimulation.

A study was undertaken to evaluate the potential utility of basic fibroblast growth factor in the induction of angiogenesis and osseous healing in bone previously exposed to high doses of irradiation. Thirty New Zealand rabbits were evaluated by introducing basic fibroblast growth factor into irradiated mandibular resection sites either prior to or simultaneous with reconstruction by corticocancellous autografts harvested from the ilium. The fate of the free bone grafts was then evaluated at 90 days postoperatively by microangiographic, histologic, and fluorochrome bone-labeling techniques. Sequestration, necrosis, and failure to heal to recipient osseous margins was observed both clinically and histologically in all nontreated irradiated graft sites as well as those receiving simultaneous angiogenic stimulation at the time of graft placement. No fluorescent activity was seen in these graft groups. In the recipient sites pretreated with basic fibroblast growth factor prior to placement of the graft, healing and reestablishment of mandibular contour occurred in nearly 50 percent of the animals. Active bone formation was evident at cortical margins adjacent to the recipient sites but was absent in the more central cancellous regions of the grafts.

Regulation of hexose transport in aortic endothelial cells by vascular permeability factor and tumor necrosis factor-alpha, but not by insulin.

Vascular permeability factor (VPF) is mitogenic for bovine aortic endothelial (BAE) cells, whereas tumor necrosis factor (TNF) is cytostatic and was found to completely block the mitogenic response to VPF. In contrast to the apparently antagonistic mitogenic effects that these two factors elicit, chronic exposure of BAE cells to either VPF of TNF resulted in significant (about 3-fold) increases in the rates of hexose transport. The concentrations required for half-maximal stimulation were 2 ng/ml (40 pM) for TNF and 4 ng/ml (100 pM) for VPF. Exposure to both factors simultaneously resulted in a greater stimulation of transport (about 7-fold) than exposure to either factor alone. Northern blot analysis indicated that the amount of message for the GLUT-1/erythrocyte form of the glucose transporter was specifically increased by treatment with VPF (5-fold), TNF (25-fold), or to both cytokines together (35-fold). Expression of mRNAs for the insulin-sensitive muscle/adipose transporter (GLUT-4), brain/fetal skeletal muscle transporter (GLUT-3), or the hepatic transporter (GLUT-2) were not detected in either control or treated cells. Acute or chronic exposure to insulin (10(-9) to 10(-6) M) did not activate hexose transport in BAE cells. Thus, glucose transport in aortic endothelial cells can be up-regulated by either VPF, a growth stimulator, or by TNF, a growth inhibitor, but not by insulin. The additive effect of the two cytokines together may be important in the control of increased glucose metabolism at sites of inflammation.

Human vascular permeability factor. Isolation from U937 cells.

Human vascular permeability factor (hVPF) is a glycoprotein that promotes fluid and protein leakage from blood vessels. The function of hVPF is at present unknown, but the potent bioactivities of this protein suggest that it could act during inflammation, wound healing, and tumor angiogenesis. hVPF was purified from serum-free conditioned medium of the human histiocytic lymphoma cell line U937 as a disulfide-linked dimeric 40-kDa protein that promoted dermal blood vessel leakage in guinea pigs at a dose of 20 ng (3 x 10(-9) M) and promoted in vitro endothelial cell growth at concentrations as low as 50 PM. Multiple forms of hVPF with apparent pI values greater than 7.5 were resolved using pH gradient electrophoresis. Antibodies against guinea pig vascular permeability factor were found to cross-react with hVPF. The N-terminal amino acid sequence of hVPF was similar to, but not identical with, the N-terminal sequence of guinea pig vascular permeability factor.

Tumor vascular permeability factor stimulates endothelial cell growth and angiogenesis.

Vascular permeability factor (VPF) is an Mr 40-kD protein that has been purified from the conditioned medium of guinea pig line 10 tumor cells grown in vitro, and increases fluid permeability from blood vessels when injected intradermally. Addition of VPF to cultures of vascular endothelial cells in vitro unexpectedly stimulated cellular proliferation. VPF promoted the growth of new blood vessels when administered into healing rabbit bone grafts or rat corneas. The identity of the growth factor activity with VPF was established in four ways: (a) the molecular weight of the activity in preparative SDS-PAGE was the same as VPF (Mr approximately 40 kD); (b) multiple isoforms (pI greater than or equal to 8) for both VPF and the growth-promoting activity were observed; (c) a single, unique NH2-terminal amino acid sequence was obtained; (d) both growth factor and permeability-enhancing activities were immunoadsorbed using antipeptide IgG that recognized the amino terminus of VPF. Furthermore, 125I-VPF was shown to bind specifically and with high affinity to endothelial cells in vitro and could be chemically cross-linked to a high-molecular weight cell surface receptor, thus demonstrating a mechanism whereby VPF can interact directly with endothelial cells. Unlike other endothelial cell growth factors, VPF did not stimulate [3H]thymidine incorporation or promote growth of other cell types including mouse 3T3 fibroblasts or bovine smooth muscle cells. VPF, therefore, appears to be unique in its ability to specifically promote increased vascular permeability, endothelial cell growth, and angio-genesis.