Modification of allergen-induced airway obstruction and bronchial hyperresponsiveness in the allergic rabbit by theophylline aerosol

A current review on animal models of anti-asthmatic drugs screening

Asthma is a chronic inflammatory respiratory condition characterised by airway constriction, smooth muscle spasm, and severe morbidity. It affects around 300 million people globally, with children being especially vulnerable. Despite its worldwide effect, the invention of innovative asthma medicines has been slow over the last 5 decades, leaving significant unmet requirements in asthma care. Although intriguing medicines have demonstrated efficacy in animal models, many fail to fulfil safety and effectiveness requirements in human trials, highlighting the critical need for more predictive models that better transfer to human results. This comprehensive review investigates the mechanisms and efficacy of anti-asthmatic drugs using both genetic and conventional animal models. Both genetic and traditional models of anti-asthmatic agents, their characteristics, and their significance are summarized as: In-Vitro Animal Models: Histamine receptor assay, Cell Culture Method, WST Assay, Spasmolytic Activity of the Lungs of Guinea Pigs, Airway and Vascular Responses to an Isolated Lung, The Isolated Perfused Guinea Pig Trachea's Reactivity. In-Vivo Models: In vivo small animal models, Broncho Spasmolytic Activity in anaesthetized Guinea Pigs, Guinea Pigs Respiratory and Vascular Dysfunction Caused by Arachidonic Acid or platelet-activated factor (PAF), Guinea Pig Asphyxia Induced by Serotonin Aerosol and Anaphylactic Microshock, Guinea Pigs Under Anaesthesia: Histamine-Induced Bronchoconstriction, Microshock in Rabbits and Pneumotachography in Guinea Pigs, Guinea Pig Bronchial Hyperactivity, Guinea Pig Airway Microvascular Leakage, Mice With Inflammatory Airways. Conclusion: This review focusses on the benefits and limitations of current animal models in asthma research, emphasising the need for more sophisticated, predictive models to decrease translational failures. By critically evaluating these models, the review emphasises their importance in directing anti-asthmatic drug development and highlights the urgent need for innovation to bridge the gap between preclinical success and clinical efficacy.

Effects of inhaled aminophylline on airway constriction and inflammation in ovalbumin-sensitized guinea pigs

BACKGROUND

The systemic administration of theophylline is useful for asthma treatment. However its narrow therapeutic range makes it difficult to use. Little is known about its potential in inhalation therapy, particularly repeated inhalation.

OBJECTIVE

The purpose of this study is to investigate the therapeutic usefulness of inhaled aminophylline in an asthma model.

METHODS

The effects of pretreatment with inhaled aminophylline (25 mg/mL for 30 min/dose) on airway response and inflammation after an ovalbumin (OVA) challenge and airway hypersensitivity to acetylcholine (Ach) were evaluated using guinea pigs sensitized with OVA.

RESULTS

Aminophylline relaxed the ACh-induced contraction of tracheal smooth muscle in vitro in a concentration-dependent manner. Pretreatment with single-dose aminophylline inhalation suppressed OVA-induced airway constriction to the same extent as the intraperitoneal pretreatment with high-dose aminophylline (10-20 mg/kg). However, pretreatment with single-dose aminophylline inhalation did not suppress eosinophil infiltration into airways (neither bronchoalveolar lavage [BAL] fluid nor lung tissue) and did not suppress airway hyperreactivity to ACh, 24 h after OVA challenge. Repeated inhalation of aminophylline (twice daily for 7 days) suppressed the infiltration of eosinophils and suppressed airway hypersensitivity to ACh. In addition, high concentrations of aminophylline inhibited production of oxygen radicals by BAL cells.

CONCLUSION

Single-dose inhalation treatment with aminophylline has transient but relatively strong bronchodilating effects due to delivery of high doses into local airways. Repeated inhalation treatment suppressed airway inflammation and hypersensitivity induced by allergens. Therefore, inhaled aminophylline may be useful for asthma treatment.

Adenosine A1 receptor antagonist versus montelukast on airway reactivity and inflammation

Adenosine produces bronchoconstriction in allergic rabbits, primates, and humans by activating adenosine A(1) receptors. Previously, it is reported that a high dose of L-97-1, a water-soluble, small molecule adenosine A(1) receptor antagonist, blocks early and late allergic responses, and bronchial hyper-responsiveness to histamine in a hyper-responsive rabbit model of allergic asthma. Effects of a lower dose of L-97-1 are compared to montelukast, a cysteinyl leukotriene-1 receptor antagonist on early allergic response, late allergic response, bronchial hyper-responsiveness, and inflammatory cells in bronchoalveolar lavage (BAL) fluid following house dust mite administration. Rabbits received intraperitoneal injections of house dust mite extract within 24 h of birth followed by booster house dust mite injections. Hyper-responsive rabbits received aerosolized house dust mite (2500 allergen units), 1 h after intragastric administration of L-97-1 (1 mg/kg) or montelukast (0.15 mg/kg) and lung dynamic compliance was measured for 6 h. Lung dynamic compliance was significantly higher following L-97-1 at all time points and with montelukast at 60-300 min following house dust mite (P<0.05). L-97-1 blocks both early and late allergic responses. Montelukast blocks only the late allergic response. Both L-97-1 and montelukast significantly blocked bronchial hyper-responsiveness at 24 h (P<0.05). Both L-97-1 and montelukast significantly reduced BAL eosinophils at 6 h and neutrophils at 6 and 24 h (P<0.05). L-97-1 significantly reduced BAL lymphocytes at 6 and 24 h (P<0.05). Montelukast significantly reduced BAL macrophages at 6 and 24 h (P<0.05). By blocking both bronchoconstriction and airway inflammation, L-97-1 may be an effective oral anti-asthma treatment.

A novel A1 adenosine receptor antagonist, L-97-1 [3-[2-(4-aminophenyl)-ethyl]-8-benzyl-7-{2-ethyl-(2-hydroxy-ethyl)-amino]-ethyl}-1-propyl-3,7-dihydro-purine-2,6-dione], reduces allergic responses to house dust mite in an allergic rabbit model of asthma

Adenosine, an important signaling molecule in asthma, produces bronchoconstriction in asthmatics. Adenosine produces bronchoconstriction in allergic rabbits, primates, and humans by activating A1 adenosine receptors (ARs). Effects of L-97-1 [3-[2-(4-aminophenyl)-ethyl]-8-benzyl-7-{2-ethyl-(2-hydroxyethyl)-amino]-ethyl}-1-propyl-3,7-dihydro-purine-2,6-dione] a water-soluble, small molecule A1 AR antagonist were investigated on early and late phase allergic responses (EAR and LAR) in a hyper-responsive rabbit model of asthma. Rabbits were made allergic by intraperitoneal injections of house dust mite [HDM; 312 allergen units (AU)] extract within 24 h of their birth. Booster HDM injections were given weekly for 1 month, biweekly for 4 months, and continued monthly thereafter. Hyperresponsiveness was monitored by measuring lung dynamic compliance (Cdyn), after histamine or adenosine aerosol challenge in allergic rabbits. Hyper-responsive rabbits were subjected to aerosol of HDM (2500 AU), 1 h after intragastric administration of L-97-1 (10 mg/kg) solution or an equivalent volume of saline. Cdyn was significantly higher after treatment with L-97-1 compared with untreated controls (p < 0.05 n = 5). Histamine PC30 was significantly higher (p < 0.05; n = 5) after L-97-1 at 24 h compared with histamine PC30 at 24 h after HDM. Adenosine PC30 was significantly higher at 15 min and 6 h after L-97-1 compared with control (p < 0.05; n = 5). L-97-1 showed strong affinity for human A1 ARs in radioligand binding studies and no inhibition toward human phosphodiesterase II, III, IV, and V enzymes. These data suggest that L-97-1 produces a significant reduction of histamine or adenosine-induced hyper-responsiveness and HDM-induced EAR and LAR in allergic rabbits by blocking A1 ARs and may be beneficial as an oral therapy for human asthma.

Different bronchial responsiveness to Ach between normal and OA-sensitized guinea pigs after acoustic stress: a role for adenosine

Noise-exposure makes non-sensitized guinea pigs hyporesponsive to Acetylcholine (Ach), while in Ovalbumin (OA)-sensitized guinea pigs the responsiveness to the cholinergic mediator is not modified by acoustic stress (Nieri et al., 1996). The occurrence of bronchial hyporesponsiveness after acoustic stress in non-sensitized guinea pigs was verified also with histamine, obtaining a result similar to that observed with Ach. Moreover, the role of adenosine as modulator of the bronchial responsiveness to Ach after noise-exposure was assessed both in normal and in sensitized guinea pigs. In non-sensitized noise-exposed guinea pigs, the hyporesponsiveness to Ach was abolished by pretreatment of the animals with the peripheral A1/A2 antagonist 8-p-(sulfophenyl)theophylline (8-pSPT, 3 mg/kg i.v.) or with the A2-selective blocker 3,7-dimethyl-1-propargylxanthine (DMPX, 80 microg/kg i.v.) but not with the A1-selective antagonist Xanthine Amine Congener (XAC, 0.1 mg/kg i.v.). In sensitized guinea pigs, pretreatment with theophylline (25 mg/kg i.v.) makes noise-exposed animals again hyporesponsive to Ach, while no effect was obtained with the selective A1 and A2 antagonists employed. Also enprofylline (10 mg/kg i.v.), a phosphodiesterase inhibitor more potent than theophylline, does not modify the responsiveness to Ach in sensitized noise-exposed guinea pigs. The overall data presented suggest the involvement of the peripheral purinergic system in the regulation of airway reactivity after the stressful condition and indicate an altered functionality of this system as a consequence of sensitization. Furthermore, noise-exposure makes it possible to reveal in guinea pigs an opposite influence by theophylline on airway responsiveness to Ach, in sensitized, with respect to normal, animals.

Intratracheal administration of phosphodiesterase III inhibitor attenuates bronchoconstriction in cats: a preliminary report

The effects of intratracheal administration of MKS 492, a selective phosphodiesterase (PDE) III inhibitor, were studied in five anesthetized bronchoconstricted cats. The animals were challenged by four repeated doses of intratracheal methacholine (67 micrograms/kg), and the degree of bronchoconstriction was assessed from increases in respiratory system resistance (Rrs). All animals demonstrated good bronchoconstrictive responses (i.e., 86-99% increases in Rrs) to methacholine without tachyphylaxis. On a separate day, the cats received the same four doses of methacholine after being pretreated with either intratracheal saline or three different doses of MKS 492 (0.17, 1.7, and 17 micrograms/kg). The increases in Rrs with 1.7 micrograms/kg [52.6 +/- 8.4% (SE)] and 17 micrograms/kg of MKS 492 (44.4 +/- 10.1%) were smaller than those with saline pretreatment (88.1 +/- 16.8%) (P < 0.05). There were no treatment-associated changes in mean arterial pressure or heart rate during administration of MKS 492. We conclude that intratracheal MKS 492 effectively reduced methacholine-induced bronchoconstriction in a dose-dependent fashion without substantial systemic effects. These preliminary results suggest that inhalation of isozyme-selective PDE inhibitors may deserve consideration for clinical trials provided that more extensive preclinical investigations justify such trials.