Dexamethasone inhibits the antigen-induced contractile activity and release of inflammatory mediators in isolated guinea pig lung tissue

Effect of premedications in a murine model of asparaginase hypersensitivity

A murine model was developed that recapitulates key features of clinical hypersensitivity to Escherichia coli asparaginase. Sensitized mice developed high levels of anti-asparaginase IgG antibodies and had immediate hypersensitivity reactions to asparaginase upon challenge. Sensitized mice had complete inhibition of plasma asparaginase activity (P = 4.2 × 10(-13)) and elevated levels of mouse mast cell protease 1 (P = 6.1 × 10(-3)) compared with nonsensitized mice. We investigated the influence of pretreatment with triprolidine, cimetidine, the platelet activating factor (PAF) receptor antagonist CV-6209 [2-(2-acetyl-6-methoxy-3,9-dioxo-4,8-dioxa-2,10-diazaoctacos-1-yl)-1-ethyl-pyridinium chloride], or dexamethasone on the severity of asparaginase-induced allergies. Combining triprolidine and CV-6209 was best for mitigating asparaginase-induced hypersensitivity compared with nonpretreated, sensitized mice (P = 1.2 × 10(-5)). However, pretreatment with oral dexamethasone was the only agent capable of mitigating the severity of the hypersensitivity (P = 0.03) and partially restoring asparaginase activity (P = 8.3 × 10(-4)). To rescue asparaginase activity in sensitized mice without requiring dexamethasone, a 5-fold greater dose of asparaginase was needed to restore enzyme activity to a similar concentration as in nonsensitized mice. Our results suggest a role of histamine and PAF in asparaginase-induced allergies and indicate that mast cell-derived proteases released during asparaginase allergy may be a useful marker of clinical hypersensitivity.

Using guinea pigs in studies relevant to asthma and COPD

The guinea pig has been the most commonly used small animal species in preclinical studies related to asthma and COPD. The primary advantages of the guinea pig are the similar potencies and efficacies of agonists and antagonists in human and guinea pig airways and the many similarities in physiological processes, especially airway autonomic control and the response to allergen. The primary disadvantages to using guinea pigs are the lack of transgenic methods, limited numbers of guinea pig strains for comparative studies and a prominent axon reflex that is unlikely to be present in human airways. These attributes and various models developed in guinea pigs are discussed.

Effects of dexamethasone and cyclosporin A on the accumulation of eosinophils in acute cutaneous inflammation in the guinea-pig

1. Eosinophils are thought to play an important role in the pathophysiology of allergic diseases and pharmacological suppression of their recruitment is considered to be of therapeutic benefit. In the present study we have assessed and compared the effects of treatment with dexamethasone and cyclosporin A on the accumulation of 111In-labelled eosinophils and local oedema formation in sites of acute inflammation in guinea-pig skin. 2. When injected locally 150 min prior to i.d. administration of antigen in a passive cutaneous anaphylactic (PCA) reaction, dexamethasone (10(-9) to 3 x 10(-7) mol per site) dose-dependently inhibited oedema formation by up to 50%. Similarly, oedema formation induced by PAF and lipopolysaccharide (LPS), but not by zymosan-activated plasma (ZAP), was significantly inhibited by dexamethasone. In contrast, 111In-eosinophil accumulation measured in response to i.d. injection of PAF, LPS and ZAP or in the PCA reaction was not altered. 3. Systemic treatment with dexamethasone (4 mg kg-1, i.v., 150 min pretreatment period) inhibited both oedema formation and 111In-eosinophil accumulation induced by PAF, ZAP, LPS and in the PCA reaction. 4. The effects of i.d. injection of cyclohexamide (2 x 10(-7) mol per site) on 111In-eosinophil accumulation and oedema formation induced by PAF, ZAP or in a PCA reaction were evaluated in order to assess the dependency of these responses on protein synthesis. Cycloheximide had no effect on the responses measured. In contrast, 111In-eosinophil accumulation, but oedema formation, induced by LPS was inhibited by 30%. 5. Acute (10 mg kg-1, i.v., 15 min pretreatment) or prolonged (10 mg kg-1, s.c. daily for 3 days) systemic treatment with cyclosporin A had no effect on 111In-eosinophil accumulation or oedema formation induced by PAF, ZAP, LPS or in the PCA reaction. 6. In conclusion, we demonstrate preferential inhibitory effects of dexamethasone on 111In-eosinophil accumulation according to its site of administration. In addition we show that dexamethasone inhibits protein synthesis-independent acute inflammation in guinea-pig skin. Finally, our results do not support the concept that eosinophils are an important cellular site of action for the inhibitory effects of cyclosporin A in a guinea-pig model of allergic inflammation.

Differential release of prostaglandins by organ cultures of human fetal trachea and lung

Human fetal lung at 16-19 weeks gestation has a partially differentiated epithelium, and in organ culture, distal airsacs dilate and the epithelium autodifferentiates to type I and II pneumatocytes, processes regulated by endogenous prostaglandin PGE2. Human fetal trachea, at the same gestation, has a terminally differentiated mucociliary epithelium but after 4-6 d in organ culture, develops squamous metaplasia. Tracheal cultures restricted to 3 d have normal phase-contrast and light microscopy appearances and immunohistochemical reactivities (epithelium: cytokeratin 7,8,18; glutathione S-transferase pi-isozyme; epithelial membrane antigen and mesenchyme; desmin; vimentin). In human fetal trachea organ cultures, the predominant prostaglandins released are 6-keto-PGF1 alpha, PGF2 alpha, and PGE2, a pattern similar to that previously described for human adult trachea and lung. In fetal lung cultures, 13,14-dihydro-15-keto-PGF2 alpha is the major prostaglandin released with lesser amounts of 13,14-dihydro-15-keto-PFG2 alpha,PGF2 alpha,PGE2, and 6-keto-PGF1 alpha. Human fetal lung in vitro has the competence to self-differentiate, as early as 12 weeks gestation and presence of high levels in fetal lung of the inactive metabolite 13,14-dihydro-15-keto-PGE2 relative to PGE2 suggests that active prostaglandin catabolism may be one of the mechanisms to retard this stage of maturation in vivo by limiting PGE2 availability. Surprisingly, the profile of prostaglandins released from fetal lung organ culture does not change to that of a mature lung with terminal differentiation of the epithelium, and this may indicate differences in the expression of key prostaglandin-metabolizing enzymes in developing human fetal lung in culture and with in utero ontogeny.

Arachidonic acid metabolites and glucocorticoid regulatory mechanism in cultured porcine tracheal smooth muscle cells

To elucidate the signal transduction system in the production of prostaglandin E2 (PGE2) by porcine tracheal smooth muscle cells in culture (PTSMC), we examined the pattern of arachidonic acid metabolites released from PTSMC and the relationship between bradykinin-stimulated rises in intracellular calcium concentration ([Ca2+]i) and PGE2 production by PTSMC. We next examined the effect of dexamethasone on these parameters. Bradykinin induced a dose-dependent increase in both the rise in [Ca2+]i and PGE2 production by PTSMC. The increase in [Ca2+]i paralleled an increase in PGE2 production. High-performance liquid chromatography (HPLC) revealed that dexamethasone-treated PTSMC were suppressed to release arachidonic acid metabolites such as PGE2 and prostaglandin F2 alpha (PGF2 alpha). Incubation of PTSMC with 10(-6)M dexamethasone for 24 h significantly suppressed both the rise in [Ca2+]i and PGE2 production by PTSMC in response to bradykinin, and also significantly suppressed bradykinin-stimulated release of radioactivity from PTSMC prelabeled with 3H-labeled arachidonic acid (3H-AA). When PTSMC pretreated with dexamethasone were incubated with 170 nM prostaglandin H2 (PGH2) or 20 microM arachidonic acid; PTSMC synthesized less PGE2 than control PTSMC. Results suggest that bradykinin stimulates PTSMC to produce PGE2 via the signal transduction system including Ca2+, and dexamethasone appeared to suppress PGE2 production by reducing the activity of cytosolic phospholipase A2 (cPLA2) and PGE2 synthase. However, we failed to demonstrate the suppression of the activity of cyclooxygenase in PTSMC by dexamethasone. Since the elevation of [Ca2+]i is necessary for the contraction of airway smooth muscles, dexamethasone seems to reduce the contraction of airway smooth muscles by suppressing the rise in [Ca2+]i and the release of arachidonic acid metabolites. Reduced production of arachidonic acid metabolites may also contribute to improvement in the bronchial inflammation.

Pharmacological characterization of mediators and vagal influence in the acute allergic bronchoconstriction in guinea pigs

The allergic bronchoconstriction in guinea pigs has been attributed mainly to the release of mast cell mediators. Histamine has been involved in the first minutes of the anaphylactic reaction and new-formed compounds in the subsequent response. In this asthma model the vagal influence has been sparsely investigated. In the present work we evaluated the pharmacological modification of the acute allergic bronchoconstrictor response in guinea pigs sensitized to ovalbumin through aerosol exposure. Pyrilamine (20 micrograms/kg), diethylcarbamazine (a lipoxygenase inhibitor, 10 mg/kg) and dexamethasone (4 mg/kg) each reduced the antigen-induced bronchoconstriction throughout the 30 min studied. Indomethacin (3.1 mg/kg) did not modify the response to the antigen. Atropine (2 mg/kg) plus bilateral vagotomy also diminished this response from 5 min onward. On the other hand, from 5 min ahead pyrilamine-resistant bronchoconstriction was partially inhibited by dexamethasone, and it was almost completely blocked during all of the response when atropine plus bilateral vagotomy were added to dexamethasone. Dipyridamole (an inhibitor of the adenosine uptake, 0.4 mg/kg) enhanced the bronchoconstriction, though this was significant only in the 2-5 min time-interval of the response. These results suggest that histamine and vagal influence play an important role in the whole response to antigen, that other mediators, probably leukotrienes, participate in this response from 5 min onward, and that adenosine could exert a potentiation effect on this response.