Ann L. Akeson

A fluorometric assay for the quantitation of cell adherence to endothelial cells

A rapid quantitative fluorometric assay was developed for analysis of leukocyte adherence to endothelial cells. In this method adherent monocyte and T cell lines are labeled with the fluorescent dye Calcein AM without affecting cell function. Following coincubation with endothelial cells and gentle washing to remove nonadhering cells, the relative fluorescence intensity of the adhering cells is determined with a fluorescence microtiter plate reader. Relative fluorescence intensity increases linearly with cell number over a wide range of concentrations. By comparison of fluorescence levels of adhering cells to a dilution series of labeled cells alone, the number of adhering cells can be determined. We compared this adherence assay with the 51Cr-labeling assay and found comparable adherence. However, we found the fluorescence assay to be more rapid as the use and special handling of radioactive material is eliminated. To monitor the reliability and reproducibility of this method, we followed the adherence of Calcein AM-labeled THP-1 cells, a human monocytic cell line, to human endothelial cells treated with interleukin-1.

Inhibition of IL-1β expression in THP-1 cells by probucol and tocopherol

Abstract The cytokine interleukin-1, IL-1, likely plays an important role in the early stages of atherogenesis. The possible action of probucol and tocopherol on the expression and secretion of IL-1β was investigated using the human monocytic leukemia cell line, THP-1. Both probucol and D-α-tocopherol inhibit the phorbol ester-induced release of IL-1β without altering differentiation. Analysis of IL-1β mRNA levels revealed that probucol and tocopherol had an inhibitory effect on the activation of expression of the IL-1β gene. The data suggest that the beneficial effects of probucol may be related to inhibition of IL-1 at an early phase of atherosclerotic plaque formation.

AF12198, a Novel Low Molecular Weight Antagonist, Selectively Binds the Human Type I Interleukin (IL)-1 Receptor and Blocks in Vivo Responses to IL-1

Interleukin-1 (IL-1) -α and -β are potent regulators of inflammatory responses. The naturally occurring interleukin-1 receptor antagonist (IL-1ra) is effective in vitro and in vivo in modulating biological responses to IL-1. We have previously reported the discovery of IL-1 antagonist peptides from the search of phage display libraries. Further characterization of this group of peptides has led to a 15-mer, AF12198, Ac-FEWTPGWYQJYALPL-NH2 (J represents the unnatural amino acid, 2-azetidine-1-carboxylic acid), with both in vitro and in vivo IL-1 antagonist activity. AF12198 selectively binds the human type I IL-1 receptor but not the human type II receptor or the murine type I receptor. In vitro, AF12198 inhibits IL-1-induced IL-8 production by human dermal fibroblasts with a half-maximal inhibition concentration or IC50 of 25 nM and IL-1-induced intercellular adhesion molecule-1 (ICAM-1) expression by endothelial cells with an IC50 of 9 nM. When given as an intravenous infusion to cynomolgus monkeys, AF12198 blocks ex vivo IL-1 induction of IL-6 and down modulates in vivo induction of IL-6. This is the first small molecule to show IL-1 receptor antagonist activity in vivo.

Human IL-1 receptor antagonist from Escherichia coli: Large-scale microbial growth and protein purification

Interleukin-1 receptor antagonist (IL-1ra) is a recently discovered cytokine which specifically inhibits IL-1 pro-inflammatory activities in various experimental conditions. In this work, the growth conditions of a recombinant E. coli strain which in laboratory studies expressed human IL-1ra mostly in insoluble form, have been optimized at the level of 6-1 bioreactors and then scaled up to a 50-1 process. As a result, a high amount (0.43 g l-1 of microbial culture) of soluble, active IL-1ra has been directly obtained in the large-scale cell lysate with no need for protein solubilization. Also, an efficient purification procedure has been developed for the soluble protein, based on cation exchange expanded bed adsorption directly followed by anion exchange chromatography. This process, which does not include any intermediate dialysis step or gradient elutions, can be easily scaled up to larger production volumes and is therefore well-suited for manufacturing. As a result of the overall optimization study, more than 12 g of pure IL-1ra have been obtained from a single 50-1 fermentation run, without any denaturation/renaturation process. The final product, whose identity and purity have been checked also by MALDI-TOF and ESI-MS, shows full biological activity both in cellular assays and in in vivo experiments with Cynomolgus monkeys.

Identification of a specific receptor for interleukin-1 in vascular smooth muscle cells: regulation by interleukin-1 and interleukin-6

A fluorescently labeled ligand was utilized to establish the existence of an interleukin-1 (IL-1) receptor in vascular smooth muscle. The binding of the phycoerythrin-labeled IL-1 beta to the murine T cell line, EL-4, was examined as a positive control. The phycoerythrin-labeled IL-1 beta identified a specific IL-1 receptor in the EL-4 cells. Vascular smooth muscle cells were also positively stained by the fluorescent ligand. The binding of phycoerythrin-labeled IL-1 beta to these cells was saturable and reversed by 100-fold excess unlabeled IL-1 beta. Incubation of the vascular smooth muscle cells with IL-1 beta (25 ng/ml) or IL-6 (250 ng/ml) for 18 h increased and decreased, respectively, the percentage of cells positively stained by phycoerythrin-labeled IL-1 beta which suggests these cytokines regulate IL-1 receptor expression in these cells. These data indicate a specific receptor for IL-1 exists in vascular smooth muscle cells.

CRYSTALS OF SOLUBLE INTERLEUKIN-1 RECEPTOR COMPLEXED WITH ITS NATURAL ANTAGONIST REVEAL A 1:1 RECEPTOR-LIGAND COMPLEX

Interleukin‐1 is a cytokine involved in the acute phase response against infection and injury. We obtained crystals of a complex of soluble, recombinant human interleukin‐1 receptor and recombinant human interleukin‐1 receptor antagonist, a naturally occurring antagonist. The crystals are suitable for X‐ray analysis and diffract to 2.7 Å resolution. Solvent content calculations indicate that the crystals contain one receptor and one antagonist molecule per asymmetric unit. Other receptor to antagonist ratios are highly unlikely. These results suggest that the interleukin‐1 antagonist binds a single receptor molecule and does not cause receptor aggregation.

Application of conformationally restricted peptidomimetics to modeling the bound conformation of peptide antagonists with the IL-1 receptor

A collection of complementary peptide caricatures that closely mimic low-energy (presumably highly populated) conformations of amino acids of interest would constitute a valuable tool set to study the interactions of small peptide ligands with their biological targets. Our general strategy for the design, synthesis and application of peptidomimetics is presented. An illustration of how structural information from mimetics combined with cutting edge biophysical data can be used to derive a model for the bound conformation of an 11-mer peptide antagonist with the IL-1 receptor is given.

An ex vivo method for studying inflammation in cynomolgus monkeys: Analysis of interleukin-1 receptor antagonist

Nonhuman primates have been used as models for testing the role of interleukin-1 (IL-1) in inflammatory diseases, including endotoxemia. The objective of this investigation was to develop a reproducible and rapid method for in vivo evaluation of IL-1 antagonists using cynomolgus monkeys. IL-1 alone can induce many of the symptoms of endotoxemia in monkeys including fever, loss of appetite, and lethargy, however, test animals are slow to recover and may become desensitized to IL-1. We have developed an ex vivo method using whole blood for analysis of IL-1 antagonists administered in vivo to the monkeys and report here results for the naturally occurring IL-1 receptor antagonist, IL-1ra. In this procedure, animals are given an i.v. infusion of IL-1ra, and blood samples are taken preinfusion and during the infusion. The samples are incubated with or without IL-1 beta and the subsequent ex vivo induction of IL-6 determined. This allows analysis of the effects of in vivo pharmacodynamics on the efficacy of antagonists without exposing the test animals to IL-1. In this ex vivo protocol, each animal serves as its own control, eliminating from the assessment the large animal to animal variation observed with in vivo responses. By testing various doses, we estimate that 50% inhibition of IL-1 induced IL-6 can be achieved with an infusion of IL-1ra at 5 micrograms/kg/15 min. This method allows simple and efficient analysis of inhibitors and antagonists of IL-1 and, potentially, other effectors.