Mechanism of action of an antiallergic agent, amlexanox (AA-673), in inhibiting histamine release from mast cells. Acceleration of cAMP generation and inhibition of phosphodiesterase

Amlexanox markedly inhibits histamine release from rat mast cells. To clarify the mechanism of this inhibition, we investigated the effect of amlexanox on cAMP content, which, when increased, inhibits histamine release in rat peritoneal mast cells. At concentrations of 10(-8)-10(-6)M, amlexanox or isoproterenol increased the cAMP content of mast cells over that of control cells about 2-fold. When the mast cells were incubated with 10(-8), 10(-7) and 10(-6) M of amlexanox combined with 10(-7) M isoproterenol, the cAMP contents were synergistically increased 15-, 60- and 88-fold, respectively. 3-Isobutyl-1-methylxanthine (IBMX) at 10(-6)-10(-4) M increased the cAMP content 1.7-3.8-fold, and a combination of 10(-4) M IBMX and 10(-7) M isoproterenol synergistically increased the cAMP content 41-fold. A combination of amlexanox and IBMX synergistically increased the cAMP content 19-fold. The increase in cAMP content, when amlexanox and isoproterenol were combined, was transient; it peaked at 0.5 min after the drugs were administered, then decreased to 20-30% of the peak value about 2 min later. Pretreatment of mast cells with amlexanox reduced the effect of the combination of amlexanox and isoproterenol, indicating tachyphylaxis; pretreatment with IBMX had no such effect. The cAMP content of macrophages was also increased by amlexanox, but when combined with isoproterenol or PGE2, the effect was additive. Amlexanox inhibited cAMP phosphodiesterase in rat mast cells; its IC50 value was 1.4 X 10(-5) M, and its inhibitory activity was half that of IBMX.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition by amoxanox (AA-673) of the immunologically, leukotriene D4- or platelet-activating factor-stimulated bronchoconstriction in guinea pigs and rats

We studied the effects of amoxanox (AA-673) on allergic asthma and spasmogen-induced bronchoconstriction in guinea pigs and rats. Amoxanox given orally or parenterally inhibited allergic asthma mediated by IgE, IgG1, or heterologous IgG in guinea pigs and by IgE in rats. This compound also reduced leukotriene D4- and platelet-activating factor-induced bronchoconstriction in guinea pigs, strongly suggesting an antagonistic activity against slow reacting substance of anaphylaxis (SRS-A). Histamine- or acetylcholine-induced bronchoconstriction was not significantly affected by amoxanox. These antiasthmatic effects of amoxanox seem to be associated with an inhibition of the release of chemical mediators such as histamine and SRS-A and with an antagonism against SRS-A.     

Prevention of antigen-induced bronchoconstriction by lodoxamide ethyl,a new orally active antiallergic drug

Lodoxamide ethyl, an orally active drug with pharmacologic activity similar to that of cromolyn sodium, blocks passive cutaneous anaphylaxis (PCA) in rats and antigen-induced bronchoconstriction in guinea pigs and monkeys. Its effectiveness in preventing antigen-induced airway obstruction was studied in 12 asymptomatic asthmatic adults with immediate skin test sensitivity to ragweed, Alternaria, or animal dander. The dose required to reduce the forced expiratory volume in 1 sec (FEV₁) by 20% (PD₂₀) was determined by dosimeter bronchoprovocation challenge with the appropriate antigen. At 1-wk intervals each subject received either placebo or 1, 3, or 10 mg drug in a randomized, double-blind fashion 30 min prior to starting bronchoprovocation challenge. On average, 1 mg increased the PD₂₀ fivefold, 3 mg about sixfold, and 10 mg about 27-fold. Dose-related side effects began 10 min after drug and lasted up to 40 min. Thus the oral administration of lodoxamide ethyl was effective in preventing antigen-induced bronchoconstriction, and both the beneficial effects and side effects are dose related.     

Interaction of the antiallergic agent AA-344 with biogenic amines and prostaglandins in production of cyclic AMP in rat mast cells

AA-344, which has been evidenced to inhibit selectively IgE-mediated allergic reactions, exhibited an inhibitory effect on cyclic AMP phosphodiesterase (PDase) in the homogenates of purified rat peritoneal mast cells (RMC). AA-344 showed synergistic effects with epinephrine, isoproterenol or prostaglandin E2 and F2 alpha in increasing cyclic AMP level in RMC: the combinations caused an increase in cyclic AMP 30-160 times as much as that caused by the respective agent alone. In the latter effect, AA-344 was at least 1,000 times as potent as theophylline. On the other hand, histamine or serotonin with or without AA-344 had no effect on the RMC cyclic AMP. These results obtained in vitro suggest that AA-344 may exert antiallergic action by increasing cyclic AMP via an interaction with epinephrine or prostaglandins which might be endogenously involved in regulation of a function of RMC in allergic reactions.     

Inhibitory effect of amlexanox (AA-673) on the immunological and non-immunological release of histamine or leukotrienes

The effect of amlexanox on the non-immunological or immunological release of histamine or leukotrienes (LTs) from passively sensitized human lung fragments and atopic human leukocytes was investigated and compared with those of AA-861, tranilast, azelastine and disodium cromoglycate. 1) Amlexanox at concentrations of 10(-7)-10(-4) M showed an inhibition of histamine, LTB4, LTC4, LTD4 and LTE4 release from passively sensitized human lung fragments in a concentration-dependent fashion. A selective and competitive inhibitor of the 5-lipoxygenase activity, AA-861 modestly affected the histamine release and potently suppressed the any LT release at 10(-7) and 10(-6) M. Antiallergic drugs, tranilast and disodium cromoglycate also suppressed these chemical mediator release, but the inhibition potency was somewhat weaker than that of amlexanox. 2) Ca ionophore A23187-induced release of LTB4 and LTC4 from atopic human leukocytes was slightly enhanced up to 10(-6) M of amlexanox. However, 10(-4) M of the drug strongly diminished both of LT release. From these results, it is suggested that amlexanox is a clinically effective drug for atopic diseases, especially allergic asthma and rhinitis.     

CP-123,369: A potent,orally active immunosuppressive agent

Inflammation Research -     

Mechanism of action of the nonlipophilic antiallergic drug eclazolast (REV 2871) in the inhibition of mediator release in a mast cell model

OBJECTIVE AND DESIGN: In this study, we compared eclazolast with other lipophilic antiallergic drugs, relating to effects on signal transduction pathways, leading to inhibition of exocytosis in a rat basophilic leukemia cell (RBL-2H3). MATERIALS AND METHODS: Effects of the drugs on mediator release (beta-hexosaminidase, arachidonic acid metabolites) after Fc(epsilon)RI activation in RBL-2H3 cell were quantified. Furthermore, effects of the drugs on cellular signalling (Ca2+ influx, intracellular Ca2+ concentration, inositol 1,4,5-trisphosphate (IP3) concentration) were assayed. Effects of the drugs on bilayer and cell membranes have been recorded. RESULTS: It is shown that eclazolast down-regulates IP3 levels. In contrast to lipophilic drugs, eclazolast does not affect artificial bilayers and erythrocyte membranes, and there is no effect on thapsigargin induced Ca2+ influx. The effect of eclazolast was highly dependent on the antigen concentration with which the cells were triggered. CONCLUSIONS: The mechanism of action of eclazolast is deviant from lipophilic antiallergic agents. It inhibits exocytosis by intracellularly affecting only direct Fc(epsilon)RI linked processes and not through inhibition of Ca2+ influx channels, as found for membrane disturbing lipophilic drugs.     

Mechanism of action of active elastase on pancreatic tissue

Acute pancreatitis developed 15 min after injection of 0.65 mg active elastase into the pancreatic duct. The histological changes in the gland tissue increased from the edematous form to necrotic pancreatitis with a hemorrhagic component, and with an increase in the dose of elastase injected up to 2.6 mg the elastic structures of the blood vessels were destroyed. The changes described above were accompanied by a decrease in the proelastase content in the pancreatic tissue and a decrease in the inhibitory power of the blood serum. The results are evidence of the important role of elastase in the pathogenesis of acute pancreatitis.     

An orally active formulation of angiotensin-(1-7) produces an antithrombotic effect

INTRODUCTION AND OBJECTIVE:

The heptapeptide angiotensin-(1-7) is a component of the renin-angiotensin system, which promotes many beneficial cardiovascular effects, including antithrombotic activity. We have recently shown that the antithrombotic effect of angiotensin-(1-7) involves receptor Mas-mediated NO-release from platelets. Here, we describe an orally active formulation based on angiotensin-(1-7) inclusion in cyclodextrin [Ang-(1-7)- CyD] as an antithrombotic agent. Cyclodextrins are pharmaceutical tools that are used to enhance drug stability, absorption across biological barriers and gastric protection.

METHOD:

To test the antithrombotic effect of Ang-(1-7)-CyD, thrombus formation was induced in the abdominal vena cava of spontaneously hypertensive rats that were pretreated either acutely or chronically with Ang-(1-7)-CyD. Male Mas-knockout and wild-type mice were used to verify the role of the Mas receptor on the effect of Ang-(1-7)-CyD.

RESULTS:

Acute or chronic oral treatment with Ang-(1-7)-CyD promoted an antithrombotic effect (measured by thrombus weight; all values are, respectively, untreated vs. treated animals) in spontaneously hypertensive rats (acute: 2.86 ± 0.43 mg vs. 1.14 ± 0.40 mg; chronic: 4.27 ± 1.03 mg vs. 1.39 ± 0.68 mg). This effect was abolished in Mas-knockout mice (thrombus weight in Mas wild-type: 0.76 ± 0.10 mg vs. 0.37 ± 0.02 mg; thrombus weight in Mas-knockout: 0.96 ± 0.11 mg vs. 0.87 ± 0.14 mg). Furthermore, the antithrombotic effect of Ang-(1-7)-CyD was associated with an increase in the plasma level of Angiotensin-(1-7).

CONCLUSION:

These results show for the first time that the oral formulation Ang-(1-7)-CyD has biological activity and produces a Mas-dependent antithrombotic effect.     

Cilomilast,an orally active phosphodiesterase 4 inhibitor for the treatment of COPD

Cilomilast is a highly selective, orally active phosphodiesterase (PDE)4 inhibitor currently under evaluation for the treatment of chronic obstructive pulmonary disease (COPD). PDE4 is the predominant cyclic AMP-degrading enzyme in various inflammatory cells such as eosinophils, neutrophils, macrophages, T-cells and monocytes. As a second-generation PDE4 inhibitor, cilomilast demonstrates a markedly improved side-effect profile over the prototype rolipram. In humans, cilomilast is rapidly absorbed after oral administration and is almost completely bioavailable with nearly no first-pass hepatic metabolism. Cilomilast has been shown to be well tolerated in both short- and long-term studies in doses of up to 15 mg twice daily. Phase II and III studies demonstrated improvements in lung function and quality of life in patients with COPD. Significant reduction was observed in subepithelial neutrophil, CD68⁺ monocyte and CD8⁺ lymphocyte densities in bronchial biopsies of COPD patients following administration of cilomilast for 12 weeks. As there are no pharmacokinetic interactions between cilomilast and commonly prescribed drugs such as theophylline, salbutamol, erythromycin and corticosteroids, or with smoking, it can be assumed that no dose adjustments will be required in patients with COPD. Cilomilast is thus a promising substance for use in the anti-inflammatory treatment of COPD.     

CGS 26529: The biological profile of a novel,orally active 5-lipoxygenase inhibitor with an extended duration of action

Inflammation Research -     

A controlled study on the preventive effect of ketotifen, an antiallergic agent, on methacholine-induced bronchoconstriction in asthmatics

We studied the preventive effect of ketotifen, an oral drug with antianaphylactic and antihistaminic properties on methacholine-induced bronchoconstriction in controlled cross-over experiments in twenty-six adult patients with extrinsic asthma. Both a single dose of 1 mg ketotifen and 4 weeks treatment of ketotifen, 1 mg twice daily, failed to reduce the methacholine-induced drop in peak expiratory flow. The spirometric findings remained unchanged during ketotifen treatment. There was no difference between treatments with ketotifen and placebo with regard to the patients assessment of the severity of asthma or airway sensitivity to tobacco smoke, fumes or dusts, or exercise. The results suggest that treatment during 4 weeks with ketotifen does not reduce unspecific broncial hyperreactivity in patients with extrinsic asthma.     

Lotifazole (F 1686), a non-steroidal anti-inflammatory agent with an unusual pharmacological spectrum

Lotifazole (F 1686) — 4-phenyl-2-(2, 2, 2-trichloroethoxycarboxamido) thiazole — has a range of antiinflammatory activities in animals that differs from the activities of classic non-steroidal drugs. It reduces carrageenin-induced oedema in rats, UV-induced erythema in guinea pigs, and Arthus pleurisies in rats only at high doses. It does not affect Freund's-adjuvant polyarthritis, and it only slightly affects passive skin anaphylaxis in rats and anaphylactic shock in guinea pigs. Lotifazole does not greatly inhibit prostaglandin synthesis.However, at low doses and after various conditions of treatment, F 1686 reduces PPD- andBordetella- pertussis-induced delayed-hypersensitivity pleurisy in guinea pigs and rats, respectively, and contact hypersensitivity reactions to picryl chloride and oxazolone in mice. Its action on the two models of delayed-hypersensitivity pleurisy is reflected in a decrease of the pleural exudate and of the number of mononuclear cells in the focus of inflammation. At active doses, Lotifazole does not cause changes in the differential leukocyte count in normal animals. It appears, furthermore, to be a T-lymphocyte stimulant.Preliminary results were presented at the First International Conference on Immunopharmacology, Brighton, 29 July-1 August 1980.     

Mechanism of action of aldosterone on active sodium transport across toad skin

Epithelium of the abdominal skin of the toad,Bufo marinus, has been studied by microelectrode impalement. Using an electrical equivalent circuit model, effective EMF's and specific conductances of the apical and basolateral membrane could be calculated. The skin was divided into 2 fragments for incubation in the presence, or not, of aldosterone (0.1 M). After incubation overnight, sodium transport by the hormone-treated piece was increased 2.7-fold on average, compared to the untreated control. Concomitantly, conductance of the apical border increased more than 3-fold. Furthermore, mean conductance and electromotive force at the basolateral border increased by 80% and by 10%, respectively. Whether the latter changes merely represent delayed adaptation to increased apical conductance, cannot be settled from the data available.     

The discovery and development of zileuton: an orally active 5-lipoxygenase inhibitor.

The enzyme 5-lipoxygenase is a key target in the effort to discover drugs which inhibit the pathophysiology associated with the formation of leukotrienes. The research efforts of these laboratories have focused on the discovery of direct enzyme inhibitors of 5-lipoxygenase. In particular, compounds with hydroxamate or N-hydroxyurea functionalities have proven to be potent inhibitors of leukotriene biosynthesis in vitro and more importantly in vivo. One of these compounds, zileuton (N-(1-benzo-[b]-thien-2-ylethyl)-N-hydroxyurea) has been shown recently to be an effective leukotriene inhibitor in man. The critical approaches and breakthroughs in the discovery and development of zileuton are described. In addition, some recent results with zileuton in animals and man are detailed.     

新型免疫抑制剂霉酚酸酯的作用机理及临床作用

霉酚酸酯(mycophenolatemofetil，MMF)是一种新型、高效免疫抑制剂，主要通过非竞争性、可逆性抑制嘌呤从头合成途径的限速酶次黄嘌呤单核苷酸脱氢酶(IMPDH)，强烈抑制T、B淋巴细胞增殖发挥免疫抑制作用。由于MMF选择性作用于淋巴细胞，副作用较少，因而在器官移植、骨髓移植及自身免疫性疾病的治疗中得到越来越广泛的应用。