Development of preclinical models for testing antiasthma drugs.

The antiasthmatic agent, sodium cromoglycate, owes its discovery to a series of antigen challenge tests carried out during the 1960s by an asthmatic, Roger Altounyan, on himself. Until recently, research efforts to identify new antiasthma drugs have relied heavily on screening methods which involved passively-sensitised mast cells. In theory these tests, such as rat passive cutaneous anaphylaxis, appeared relevant and showed sodium cromoglycate to have a stabilising effect on the mast cell membrane. In practice no new drugs were discovered, since this type of activity in animal models was not predictive of antiasthmatic potential. A more relevant research programme has subsequently evolved, which attempts to approach more closely the conditions prevailing in the asthmatic lung. The use of a model of immune lung inflammation in macaque monkeys in conjunction with a model of bronchial hyper-reactivity in the dog has been successful in producing the new compound, nedocromil sodium, which is proving to be an effective addition to the drugs available for the treatment of inflammatory diseases of the airways.

The development of a new agent for the treatment of inflammatory/allergic conditions.

The search for new drugs for the treatment of reversible obstructive airways disease has been a major pursuit of the pharmaceutical industry for almost two decades. Little progress has been achieved. The acceptance that asthma is a multi-facetted disease state has led to the development of a new complex in vivo screen in the macaque monkey. This model is mediated through mast cells which stain positively with alcian blue/safranin. A new therapeutic agent, nedocromil sodium, was significantly more active than sodium cromoglycate in this primate model of airway disease. Extensive clinical trials have shown that this new agent is effective in the treatment of the reversible component of obstructive airways disease.

The ultrastructure of mucosal mast cells.

The two mast cell populations in the rat small intestine, mucosal mast cells (from the lamina propria) and connective tissue mast cells (from the submucosa), have differing staining characteristics. Differential staining techniques have also shown that these two mast cell populations exist widely in the rat, human and macaque monkey. Mucosal mast cells obtained from the rat ileum, the human jejunum (biopsy) and the macaque lung (by bronchoalveolar lavage) were examined by electron microscopy in an attempt to characterize this type of mast cell by its ultrastructural features. Although no common feature typified the cells from these three species, a number of individual features within each species were noted.

The effect of nedocromil sodium and sodium cromoglycate on antigen-induced bronchoconstriction in the Ascaris-sensitive monkey.

Nedocromil sodium inhibited the bronchoconstriction caused by antigen challenge in Ascaris-sensitive monkeys and in addition it prevented the release of histamine from mast cells lavaged from sensitive monkeys. Sodium cromoglycate was relatively inactive in both these systems. It is suggested that nedocromil sodium can stabilize both mucosal and connective tissue mast cells and may represent a new type of drug.

Ascaris-induced bronchoconstriction in primates experimentally infected with Ascaris suum ova.

Bronchial provocation with Ascaris allergen evoked bronchoconstriction in home-bred Macaca arctoides monkeys sensitized by experimental infection with embryonated Ascaris suum ova. Inhalation of Ascaris allergen by aerosol prior to infection produced no changes in lung function. In infected animals total lung resistance (RL) increased and dynamic lung compliance (Cdyn) decreased following Ascaris inhalation. The changes in lung function reached a peak, 2-5 min after allergen inhalation, lasted for approximately 30 min and were associated with increases in arterial plasma histamine levels and decreases in arterial Po2 levels. Reproducible changes in lung function were obtained when the monkeys were challenged at bi-weekly intervals and lung sensitivity to Ascaris was maintained for at least 6 months. Histamine produced similar changes in RL and Cdyn before and after infection. Ascaris-induced bronchoconstriction was reversed by the beta 2-stimulant, salbutamol, and was partially reversed by cholinergic blockade with atropine. The responses were not inhibited by antihistamines or sodium cromoglycate although a new anti-allergic agent, FPL 58668 (disodium salt), inhibited Ascaris-induced bronchoconstriction and the increase in plasma histamine levels seen after Ascaris inhalation. Ascaris-induced bronchoconstriction in experimentally infected monkeys provides an animal model demonstrating many of the characteristics of allergic asthma in man and does not require the use of wild-caught monkeys.

Laboratory infection of primates with Ascaris suum to provide a model of allergic bronchoconstriction.

Wild-caught non-human primates are naturally sensitive to Ascaris antigen and provide a useful model for studying atopic asthma. The present study was carried out to determine the effect of experimentally infecting home-bred macaques with the nematode Ascaris suum and hence provide an alternative for the naturally occurring model. Following oral infection with the parasite the animals developed a blood eosinophilia and specific antibodies to purified Ascaris antigen. These antibodies appeared to be of the IgE class as they could be detected by a radiometric assay using a radiolabelled antibody to human IgE. However, on further investigation, using the passive cutaneous anaphylaxis test, two classes of antibody were found, a heat labile (56 degrees C) and a heat stable antibody. Lung lavage cells taken from monkeys infected with Ascaris suum were shown to include cells morphologically characteristic of mast cells and released histamine when challenged in vitro with Ascaris antigen. Hence this model of immediate hypersensitivity provides a simple alternative to the less accessible natural model.

The activity of an anti-allergic compound, proxicromil, on models of immunity and inflammation.

A tricyclic chromone, proxicromil (sodium 6,7,8,9-tetrahydro-5-hydroxy-4-oxo-10-propyl-naphtho (2,3-b) pyran-2-carboxylate), has been tested for activity against certain immunological and inflammatory reactions. When given parenterally it suppressed the development of delayed hypersensitivity reactions in sensitized mice and guinea-pigs but did not affect the rejection of skin allografts in mice. The compound had no activity against certain in vitro correlates of delayed hypersensitivity reactions (lymphocyte transformation and lymphokine activity), but did have an inhibitory effect on lymphokine (MIF) productions at 10(-4) M but not at 10(-5) M. Proxicromil was also found to be active in non-immunologically mediated models of inflammation and in models having an immunological component which are known to be sensitive to non-steroidal anti-inflammatory drugs (adjuvant arthritis, reversed passive Arthus reaction). The activity of this compound was enhanced when administered in arachis oil when compared to its activity in saline. Proxicromil has not direct activity on the development of immune responsiveness but appear to suppress the expression of delayed hypersensitivity and immune complex mediated hypersensitivity reactions by virtue and its anti-inflammatory properties. This activity is not associated with inhibition of cyclo-oxygenase.

Role of bronchial irritant receptors in asthma.

Sulphur dioxide inhaled at low concentration had no detectable effect on forced expiratory volume in one second in non-asthmatic atopic controls, but it induced asthma and increased bronchial reactivity in nine symptomless atopic and non-atopic asthmatic patients. This increased reactivity was inhibited by sodium cromoglycate (SCG) and partly inhibited by atropine. This suggests that SCG, in addition to its ability to stabilise mast cells, may also act on bronchial irritant receptors or directly on smooth muscle in asthmatic patients.

Anaphylactic bronchoconstriction in rats immunized with antigen-coated latex particles.

Studies have been carried out on the immunization of rats with antigen-coated latex particles. These studies confirmed that a significant lung blood eosinophilia is induced by a repeat intravenous injection of antigen-coated latex particles. Rats treated with antigen-coated latex particles also become sensitive to antigen such that on antigen challenge the animals show bronchoconstriction. Studies show that the bronchoconstriction is specific for antigen, but is unlikely to be mediated by tissue-fixing antibodies. Experiments comparing different immunization schedules involving latex particles indicate a strong association between the level of eosinophilia and degree of antigen-induced bronchoconstriction. These studies suggest that eosinophils may contribute to the anaphylactic bronchoconstriction.

New orally effective chromosome derivatives for the treatment of asthma.

Two new chromone derivatives have been identified which possess oral anti-allergic activity in the rat PCA model of immediate hypersensitivity. They may have a wider spectrum of anti-allergic activity than disodium cromoglycate (SCG) since they are effective in in vitro tests involving sensitized basophils, in which SCG is inactive. Both compounds, when given orally, provide relief from experimental and clinical asthma in man.

[Effect of cromoglicinic acid on the degranulation of mast cells (author's transl)]. / Zur Wirkung der Cromoglicinsäure auf die Degranulation von Mastzellen

An interference microscopic method is described which allows quantitative measurements of the inhibiting effect of the di-sodium salt of 1,3-bis(3-carboxy-chroman-5-yl-oxy)-2-hydroxypropand (cromoglicinic acid; Intal; DSCG) on the degranulation of mast cells in vitro induced by polymixin B and Compound 48/80. The specific degranulation inhibiting effect of DSCG is increased in the presence of Ca++ and Mg++ ions.