Atsushi Kurihara

Dexamethasone inhibits generation in inflammatory sites of the chemotactic activity attributable to leukotriene B4

Effects of dexamethasone on chemotactic activity to polymorphonuclear leukocytes (PMN) of a lipophilic fraction collected with the aid of octadecylsilyl silica cartridge from exudates of an allergic inflammation were investigated. The chemotactic activity of this fraction was attributable to leukotriene B4 fraction separated by means of a reversed phase high performance liquid chromatography. Local application of dexamethasone suppressed dose-dependently the chemotactic activity of the lipophilic fraction in parallel with the inhibition of PMN infiltration in the inflammatory sites.

Reduction by dexamethasone of chemotactic activity in inflammatory exudates.

Using an experimental model for allergic inflammation of the air pouch type in rats, the effects of dexamethasone and indomethacin on leukocyte infiltration and level of chemotactic activity in the inflammatory exudate were examined to clarify the mechanisms of anti-inflammatory effects of glucocorticoids. Both dexamethasone and indomethacin when locally administered inhibited leukocyte infiltration, while chemotactic activity of the exudate was reduced by dexamethasone only. Indomethacin failed to reduce the level of chemotactic activity. Suppression by dexamethasone of the level of chemotactic activity became evident prior to the decrease in the number of leukocytes in the inflammatory exudate. These results suggest that the anti-inflammatory steroids manifest their inhibitory effect on leukocyte infiltration by inhibiting the generation of chemotactic factors in the inflammatory site. Besides this, the possible production of some inhibitory factors by the steroids may be considered as an alternative mechanism.

Inhibitory effect of extracellular histidine on cobalt-induced HIF-1α expression

Cobalt chloride (CoCl(2)) can mimic hypoxia in inducing hypoxia-inducible factor 1 (HIF-1). Several cultured cells were examined for susceptibility to CoCl(2) in DMEM, MEM and RPMI 1640 medium. Here we report that HIF-1α expression of mammalian cells by CoCl(2) was largely dependent on the culture medium. HIF-1α protein and hypoxia response element (HRE)-dependent reporter activity were strongly induced in RPMI 1640 but not in DMEM in several cultured cells including MCF-7, a human breast cancer cell line. Analysis of causal nutrients has revealed that histidine, which is contained richer in DMEM, acts as the inhibitory nutrient for cobalt-induced HIF-1α expression of MCF-7 cells in DMEM. D-Histidine also inhibited the HIF-1α activity at the same level as L-histidine, suggesting that sequestration of free cobaltous ion by chelation with histidine was the cause of the inhibition. These results demonstrate that selection of the culture medium must be considered with caution in cell culture experiments using CoCl(2) as a hypoxia-mimetic reagent.

Chemotactic factor production by rat polymorphonuclear leukocytes: stimulation with opsonized zymosan particles and inhibition by dexamethasone.

Rat polymorphonuclear leukocytes exposed to opsonised zymosan particles in vitro instantaneously and continuously release a chemotactic factor in the medium. The activity of this factor was mainly attributed to leukotriene B4, based on the data with high performance liquid chromatography. Preincubation of the cells with an antiinflammatory steroid, dexamethasone, at a dose of 0.25 micrograms/ml caused suppression in generation of the chemotactic factor from the leukocytes in a time-dependent manner.

Effects of sematilide, a novel class III antiarrhythmic agent, on membrane currents in rabbit atrial myocytes

The effects of sematilide, a novel class III antiarrhythmic agent, on membrane currents were examined in single myocytes isolated from the rabbit left atrium, using the whole-cell voltage clamp technique. Application of 10, 30, 100 and 300 microM sematilide caused a concentration-dependent inhibition of the delayed rectifier K+ current (IC50 approx. 25 microM). The sematilide-sensitive current, which was recorded by means of a triangular voltage command, showed a strong inward rectification and had a peak at about -40 mV, suggesting that sematilide inhibits the rapidly activating delayed rectifier K+ current. The Ca2+-independent transient K+ and the inward rectifier K+ currents were not affected significantly by application of 100 microM sematilide. Moreover, voltage-dependent Na+ and Ca2+ currents were not affected significantly by 100 microM sematilide. These findings indicate that sematilide selectively blocks the rapidly activating delayed rectifier K+ current in atrial myocytes and provide evidence supporting the usefulness of the drug as a class III antiarrhythmic agent.

Correlation of Leukocyte Accumulation with Chemotactic Activity in the Exudate of an Allergic Air-Pouch Inflammation

Chemotactic activity at the site of an allergic air-pouch inflammation induced with azobenzene-arsonate-conjugated acetyl bovine serum albumin as an antigen was studied and a close correlation of the chemotactic activity with the intensity of leukocyte migration was demonstrated. In the period of vigorous leukocyte immigration into the fluid in the allergic air-pouch, chemotactic activity of the exudate was maintained at a high level, while no significant activity was detected after the number of leukocytes in the pouch fluid reached maximum.

Delayed-Type Hypersensitivity as Revealed on the Footpads of Mice to Azobenzenearsonate-Acetyl Bovine Serum Albumin

A strong delayed-type footpad reaction was established in mice using azobenzenearsonate-acetyl bovine serum albumin (ABA-AcBSA) as an antigen. Male ddY/S mice were sensitized by subcutaneous injection of 100 microliter of Freunds complete adjuvant - saline (1:1) emulsion containing 100 microgram of the antigen and challenged by subcutaneous injection of 2.5 microliter of Freunds incomplete adjuvant - saline (1:1) emulsion with 2.5 microgram antigen in the footpad on the 10th day after the sensitization. The analysis of the system which fulfilled criteria for delayed-type hypersensitivity with regard to kinetics, passive transfer and histology of the footpad reaction, and the effect of dexamethasone, indomethacin and quinacrine on the footpad reaction were described.