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.

Circular permutation of the granulocyte colony-stimulating factor receptor agonist domain of myelopoietin.

Myelopoietins (MPOs) are a family of engineered dual interleukin-3 (IL-3) and granulocyte colony-stimulating factor (G-CSF) receptor agonists that are superior in comparison to the single agonists in their ability to promote the growth and maturation of hematopoietic cells of the myeloid lineage. A series of MPO molecules were created which incorporated circularly permuted G-CSF (cpG-CSF) sequences with an IL-3 receptor (IL-3R) agonist moiety attached at locations that correspond to the loops that connect the helices of the G-CSF four-helix bundle structure. The cpG-CSF linkage sites (using the original sequence numbering) were residue 39, which is at the beginning of the first loop connecting helices 1 and 2; residue 97, which is in the turn connecting helices 2 and 3; and residues 126, 133, and 142, which are at the beginning, middle, and end, respectively, of the loop connecting helices 3 and 4. The N- and C-terminal helices of each cpG-CSF domain were constrained, either by direct linkage of the termini (L0) or by replacement of the amino-terminal 10-residue segment with a seven-residue linker composed of SGGSGGS (L1). All of the MPO molecules stimulated the proliferation of both IL-3-dependent (EC50 = 13-95 pM) and G-CSF-dependent (EC50 = 35-710 pM) cell lines. MPOs with the IL-3R agonist domain linked to cpG-CSFs in the first (residue 39) or second (residue 133) long overhand loops were found by CD spectroscopy to have helical contents similar to that expected for a protein comprised of two linked four-helix bundles. The MPOs retained the ability to bind to the IL-3R with affinities similar to that of the parental MPO. Using both a cell surface competitive binding assay and surface plasmon resonance detection of binding kinetics, the MPOs were found to bind to the G-CSF receptor with low nanomolar affinities, similar to that of G-CSF(S17). In a study of isolated cpG-CSF domains [Feng, Y., et al. (1999) Biochemistry 38, 4553-4563], domains with the L1 linker had lower G-CSF receptor-mediated proliferative activities and conformational stabilities than those which had the L0 linker. A similar trend was found for the MPOs in which the G-CSFR agonist activity is mostly a property of the cpG-CSF domain. Important exceptions were found in which the linkage to the IL-3R agonist domain either restored (e.g., attachment at residue 142) or further decreased (linkage at residue 39) the G-CSFR-mediated proliferative activity. MPO in which the IL-3R agonist domain is attached to the cpG-CSF(L1)[133/132] domain was shown to be more potent than the coaddition of the IL-3R agonist and G-CSF in stimulating the production of CFU-GM colonies in a human bone marrow-derived CD34+ colony-forming unit assay. Several MPOs also had decreased proinflammatory activity in a leukotriene C4 release assay using N-formyl-Met-Leu-Phe-primed human monocytes. It was found that circular permutation of the G-CSF domain can alter the ratio of G-CSFR:IL-3R agonist activities, demonstrating that it is a useful tool in engineering chimeric proteins with therapeutic potential.

Identification and characterization of rhesus macaque interleukin-8.

To establish a direct link between IL-8 and inflammation in vivo, we first isolated the gene encoding rhesus macaque IL-8. The open reading frame directs the translation of a 101 amino acid (aa) precursor, which is 94% identical to human IL-8. Rhesus IL-8 was expressed in bacteria and purified to homogeneity with ion-exchange chromatography. Pure rhesus IL-8 was biologically active as measured by its ability to bind specifically to either rhesus (Kd = 0.5 nM) or human (Kd = 2 nM) IL-8 receptors and to promote in vitro chemotaxis of rhesus (EC50 = 2 nM) or human neutrophils (EC50 = 4 nM). Moreover, a mouse monoclonal antibody, DM/C7, which neutralizes human IL-8 activity, also recognized and neutralized (IC50 = 0.5-3.0 microgram/ml) rhesus IL-8 in vitro. Systemic administration of DM/C7 completely inhibited the dermal inflammation of rhesus ears induced by the external application of phorbol myristoyl acetate. These observations reveal that rhesus IL-8 is structurally and functionally similar to human IL-8 and suggests that IL-8 plays a prominent role in a primate model of inflammation.

Interleukin 8 and mast cell-generated tumor necrosis factor-alpha in neutrophil recruitment.

In the reverse passive Arthus reaction in mouse skin and immune injury of mouse dermal basement membrane, neutrophil (PMN) infiltration in mast cell deficient WBB6F1-W/Wv (W/Wv) mice was only 40% of that in WBB6F1-(+)/+ (+/+) mice that had a normal mast cell repertoire. An anti-tumor necrosis factor-alpha (TNF-alpha) monoclonal antibody (mAb) decreased PMN infiltration by 35-80% in +/+ but not W/Wv mice. In addition, an anti-human interleukin-8 (IL-8) MAb, DM/C7, inhibited PMN infiltration of the skin induced by either intradermal administration of recombinant human IL-1 beta or immune complex deposition. In both models of immune complex injury, DM/C7 reduced PMN infiltration by 40-60% in +/+ mice but not W/Wv mice. PMN infiltration and the sensitivity of this infiltration to anti-TNF-alpha or DM/C7 MAb in W/Wv mice whose mast cell population had been restored was indistinguishable from the influx observed in +/+ mice. These data suggest that TNF-alpha, IL-8, and mast cells play a fundamental role in PMN recruitment following immune complex injury.

Inhibition of lung inflammatory reactions in rats by an anti-human IL-8 antibody.

IL-8 belongs to the family of chemotactic cytokines and may play an important role in the inflammatory response. In the current studies, a murine mAb (DM/C7) to human rIL-8 was found to have protective effects in inflammatory lung injury in rats. DM/C7 was nonreactive with the rat cytokine-induced neutrophil chemoattractant peptide. In vivo, DM/C7 blocked the glycogen-induced accumulation of neutrophils in rats and was highly protective against lung and dermal vascular injury after deposition of IgG immune complexes. The latter model of injury has recently been shown to be E-selectin dependent. The protective effects of DM/C7 correlated with reduced tissue accumulation of neutrophils, as measured by myeloperoxidase content. DM/C7 reacted with an epitope expressed by TNF-alpha-stimulated rat pulmonary artery endothelial cells and with the pulmonary vascular endothelium after intrapulmonary deposition of IgG immune complexes. In the model of IgG immune complex-induced lung injury, the protective effects of DM/C7 were abolished by prior absorption of the antibody with human rIL-8. Polyclonal antibody to cytokine-induced neutrophil chemoattractant peptide failed to protect against IgG immune complex-induced vascular injury even though this antibody blocked the in vitro chemotactic activity of cytokine-induced neutrophil chemoattractant. In the model of rapidly developing lung injury due to systemic activation of C after infusion of cobra venom factor, DM/C7 was not protective. As well, in the neutrophil-independent model of IgA immune complex-induced lung injury, treatment with DM/C7 was not protective. These data indicate that in inflammatory lung injury that is linked to E-selectin-dependent recruitment of neutrophils in rats, antibody to human IL-8 also blocks recruitment of neutrophils and thereby affords protection against lung injury. The data suggest the presence of an IL-8-like product in this model of lung injury.

Polyamine spider toxins are potent un-competitive antagonists of rat cortex excitatory amino acid receptors.

We examined the effect of argiopine and argiopinine 3, low molecular weight polyamine venom components of the spider Argiope lobata, on rat cortical excitatory amino acid (EAA) receptors expressed in Xenopus oocytes. Responses to 100 microM N-methyl-D-aspartate (NMDA) with 10 microM glycine were blocked by both of the polyamine toxins in a dose-dependent manner. Both compounds had similar potencies against 100 microM kainate or 50 microM (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (L-AMPA). Oscillatory responses to 2 microM quisqualate were unaffected by either polyamine toxin. Increasing concentrations of either NMDA, kainate or AMPA were unable to overcome the antagonism by either spider toxin. We were able to demonstrate a use-dependent phenomenon similar to that of phencyclidine; neither polyamine toxin affected the NMDA, kainate or AMPA response without the presence of the respective agonist.

D-cycloserine acts as a partial agonist at the glycine modulatory site of the NMDA receptor expressed in Xenopus oocytes.

In the Xenopus oocyte preparation, D-cycloserine (DCS) had the profile of a partial agonist at the glycine modulatory site of the NMDA receptor. Maximal NMDA responses in the presence of DCS were only 40-50% of those in the presence of glycine. Glycine and D-serine were agonists at this site. The actions of DCS were competitively antagonized by HA-966, a known glycine antagonist.

Purification and partial characterization of a bovine epidermal growth factor-like polypeptide.

A heterologous radioreceptor assay was developed to follow the purification of an EGF-like polypeptide from bovine kidney. Purification of the growth factor was facilitated by the use of a novel affinity column using fixed A431 cells attached to sephadex beads. The mol. wt. of the purified EGF-LP was estimated to be 5480 from the amino acid composition. The purified EGF-like polypeptide stimulated the proliferation of bovine mammary epithelial cells and appeared to be equipotent to mouse EGF. Available evidence suggests that the purified molecule is distinct from bovine TGF-alpha.

Glycine antagonist action of 1-aminocyclobutane-1-carboxylate (ACBC) in Xenopus oocytes injected with rat brain mRNA.

ACBC has been reported to have the binding profile of an antagonist at the glycine site of the NMDA receptor. In Xenopus oocytes injected with rat brain mRNA, we have confirmed the antagonist action of ACBC on NMDA responses. ACBC and HA-966, a known glycine antagonist, blocked NMDA responses in a non-competitive manner and blocked the potentiation of NMDA responses by glycine in a competitive manner. We conclude that ACBC blocks NMDA responses via a competitive interaction at the glycine modulatory site.