Effect of the PAF antagonists, CV-3988 and L-652,731 on the pulmonary and hematological responses to guinea pig anaphylaxis

Anaphylaxis: lessons from mouse models

Studies with mouse models demonstrate 2 pathways of systemic anaphylaxis: a classic pathway mediated by IgE, FcepsilonRI, mast cells, histamine, and platelet-activating factor (PAF) and an alternative pathway mediated by IgG, FcgammaRIII, macrophages, and PAF. The former pathway requires much less antigen and antibody than the latter. This is modified, however, by IgG antibodies that prevent IgE-mediated anaphylaxis by intercepting antigen before it binds to mast cell-associated IgE. Consequently, IgG antibodies block systemic anaphylaxis induced by small quantities of antigen but mediate systemic anaphylaxis induced by larger quantities. The importance of the alternative pathway in human subjects is unknown, but human IgG, IgG receptors, macrophages, mediators, and mediator receptors have appropriate properties to support this pathway if sufficient IgG and antigen are present. The severity of systemic anaphylaxis is increased by nitric oxide produced by the enzyme endothelial nitric oxide synthase and by the cytokines IL-4 and IL-13 and decreased by endogenous beta-adrenergic stimulation and receptors that contain ITIM that bind tyrosine phosphatases. Anaphylaxis is also suppressed by other receptors and ion channels that function through distinct mechanisms. Unlike systemic anaphylaxis, intestinal anaphylaxis (allergic diarrhea) is almost totally IgE and mast cell dependent and is mediated predominantly by PAF and serotonin. Some potent food allergens, including peanuts and tree nuts, can directly enhance anaphylaxis by stimulating an anaphylactoid response through the innate immune system. Results of these studies suggest novel prophylactic agents, including nonstimulatory anti-IgE mAbs, IL-4 receptor antagonists, PAF antagonists, and agents that cross-link FcepsilonRI or FcgammaRIII to an ITIM-containing inhibitory receptor.

The tripeptide FEG ameliorates systemic inflammatory responses to rat intestinal anaphylaxis

BACKGROUND

Food allergies are generally associated with gastrointestinal upset, but in many patients systemic reactions occur. However, the systemic effects of food allergies are poorly understood in experimental animals, which also offer the opportunity to explore the actions of anti-allergic drugs. The tripeptide D-phenylalanine-D-glutamate-Glycine (feG), which potentially alleviates the symptoms of systemic anaphylactic reactions, was tested to determine if it also reduced systemic inflammatory responses provoked by a gastric allergic reaction.

RESULTS

Optimal inhibition of intestinal anaphylaxis was obtained when 100 microg/kg of feG was given 20 min before the rats were challenged with antigen. The increase in total circulating neutrophils and accumulation of neutrophils in the heart, developing 3 h and 24 h, respectively, after antigen challenge were reduced by both feG and dexamethasone. Both anti-inflammatory agents reduced the increase in vascular permeability induced by antigen in the intestine and the peripheral skin (pinna), albeit with different time courses. Dexamethasone prevented increases in vascular permeability when given 12 h before antigen challenge, whereas feG was effective when given 20 min before ingestion of antigen. The tripeptide prevented the anaphylaxis induced up regulation of specific antibody binding of a cell adhesion molecule related to neutrophil activation, namely CD49d (alpha4 integrin).

CONCLUSIONS

Aside from showing that intestinal anaphylaxis produces significant systemic inflammatory responses in non-intestinal tissues, our results indicate that the tripeptide feG is a potent inhibitor of extra-gastrointestinal allergic reactions preventing both acute (30 min) and chronic (3 h or greater) inflammatory responses.

Effect of YM264 on the airway hyperresponsiveness and the late asthmatic response in a guinea pig model of asthma

We investigated the effects of YM264, a specific platelet-activating factor (PAF) antagonist, on the airway hyperresponsiveness (AH) and the late asthmatic response (LAR) of guinea pigs that were sensitized by exposure to aerosolized ovalbumin (OA). Respiratory resistance (Rrs) was determined by the oscillation technique. Airway responsiveness was evaluated by administering a dose of histamine at which the Rrs reached 200% of the baseline value (H200). Animals were administered 1 or 3 mg/kg of YM264 orally 30 min before and again at 3 h after exposure to OA. YM264 significantly suppressed AH 24 h after and 5 days after the exposure. YM264 also suppressed the development of the LAR and accumulation of eosinophils and neutrophils in the tracheal mucosa of guinea pigs. These observations suggest that PAF is involved in the AH and the development of the LAR in asthma. PAF antagonists may play a beneficial role in the treatment of asthma.

Inhibitory effects of a novel PAF antagonist E6123 on anaphylactic responses in passively and actively sensitized guinea pigs and passively sensitized mice

The effects of the platelet-activating factor (PAF) antagonist, E6123, on anaphylactic responses in guinea pigs and mice were investigated. E6123 inhibited i.v. antigen (Ag)- or inhaled Ag-induced bronchoconstriction in passively and actively sensitized guinea pigs after oral administration at 3 and 10 micrograms/kg, respectively. E6123 inhibited Ag inhalation-induced airway hyperreactivity in guinea pigs after oral administration at 30 micrograms/kg. E6123 protected mice from anaphylactic death with an ED50 value (p.o.) of 7 micrograms/kg. The inhibitory effects of E6123 described above were very potent compared to those of the PAF-antagonists WEB2347 and Y-24180. The present results suggest that E6123 may be beneficial for the treatment of asthma, a condition in which PAF is assumed to be involved.

Interference of BN 52021, an antagonist of PAF, with different forms of active anaphylaxis in the guinea-pig: importance of the booster injection

1. BN 52021, an antagonist of platelet activating factor (PAF), was inactive against bronchoconstriction in guinea-pigs sensitized with low amounts of ovalbumin (OA) injected twice, at a 14 day interval and challenged i.v. 7 days later. 2. Serum IgG titers increased for 7 weeks after the booster injection at day 14 and returned to low levels at day 96. 3. Administered by the intratracheal (i.t.) route at 1 mg, BN 52021 failed to inhibit bronchoconstriction induced by the i.t. administration of OA to guinea-pigs tested 7, 28, 56 and 84 days after the booster injection, even when the titers of circulating IgG had declined with time. BN 52021 was also inactive against bronchoconstriction in guinea-pigs boosted at day 98 and tested 7 days later and against contractions and thromboxane (Tx) B2 and histamine release induced by OA-challenged parenchymal lung strips from the boosted guinea-pigs. 4. Sensitized unboosted guinea-pigs displayed reduced IgG serum titers. Used 21 or 70 days after the sensitizing injection, they did develop bronchoconstriction upon the i.t. instillation of OA, which was blocked by BN 52021. The latter also inhibited OA-induced contractions of lung parenchymal strips from these unboosted guinea-pigs. 5. When boosted and non-boosted guinea-pigs received OA i.t. and bronchoalveolar lavage fluid was collected 10 min later, the number of eosinophils increased markedly in boosted, but not in non-boosted guinea-pigs. 6. The booster injection of antigen thus modifies the response of the lung and PAF appears to be relevant for antigen-induced bronchoconstriction in unboosted animals, but loses its major role following the booster injection.

The booster injection of antigen during active sensitization of guinea-pig modifies the anti-anaphylactic activity of the PAF antagonist WEB 2086

1. Serum IgG levels of sensitized guinea-pigs bled at various times after the booster injection were evaluated and its capacity to sensitize passively lung strips from normal guinea-pigs assessed. Following the booster injection, both serum IgG and the ability to sensitize passively lung strips increased during the first week and decreased slowly thereafter. 2. The PAF antagonist WEB 2086 (3 mg kg-1, i.v.) blocked the anaphylactic bronchoconstriction induced by intravenous administration of ovalbumin (1 mg kg-1) when guinea-pigs were challenged 2 and 4 days after the booster injection, but became ineffective when tested in guinea-pigs challenged 7, 28 and 56 days after the booster injection. 3. The ability of WEB 2086 to reduce anaphylactic bronchoconstriction of guinea-pigs challenged 2 and 4 days after the booster injection was unrelated to either the selective involvement of one type of immunoglobulin, low IgG titres in sera or a reduced sensitizing capacity. 4. The booster injection, which accounts for the loss of efficacy of WEB 2086 from the fourth day thereafter, probably operates as a PAF-independent inflammatory challenge. 5. The protocol for immunisation and the day of experiment after the booster injection determines the sensitivity of the anaphylactic bronchoconstriction to inhibition of PAF antagonists.

Prevention of non-specific airway hyperreactivity after allergen challenge in guinea-pigs by the PAF receptor antagonist SDZ 64-412

1. Allergen challenge by aerosol in sensitized guinea-pigs elicited non-specific airway hyperreactivity assessed by reactivity to i.v. histamine or acetylcholine. Airway hyperreactivity to histamine persisted for at least 48 h and was accompanied by pulmonary eosinophilia as determined by bronchoalveolar lavage cell analysis. 2. Airway hyperreactivity was independent of vagal reflex mechanisms since it was not abrogated by bilateral vagotomy. 3. The novel platelet-activating factor (PAF) receptor antagonist SDZ 64-412 inhibited the development of airway hyperreactivity, as measured 24 h after aerosol allergen challenge, when given as a single treatment orally 2 h before allergen challenge. The PAF receptor antagonist WEB 2086 as well as methylprednisolone and ketotifen also showed efficacy in preventing development of airway hyperreactivity. 4. Neither the two PAF antagonists nor ketotifen had any effect on bronchoalveolar lavage (BAL) eosinophil numbers. Methylprednisolone was the only substance which readily prevented eosinophil recruitment in addition to airway hyperreactivity. 5. We conclude that allergen-induced airway hyperreactivity in guinea-pigs is inhibited by prophylactic anti-asthma drugs and specific PAF receptor antagonists, thus demonstrating a pivotal role of PAF in this response. There was a lack of correlation between airway hyperreactivity and the presence of BAL eosinophils.

The emergence of potent and selective peptide leukotriene receptor antagonists

Leukotriene (LT) C4, LTD4 and LTE4 collectively comprise the constituents of slow reacting substance of anaphylaxis. Based on their well-documented physiology, and a substantial body of circumstantial evidence, it has been hypothesized that they may be etiologic in allergic diseases, including asthma. Using various chemical approaches, a variety of chemically distinct, highly potent and selective LT antagonists have been disclosed including SKF 104,353, ICI 198,615, L 660,711 and WY 48,252. All are, or will soon, enter clinical trials for asthma. These compounds should provide a viable test for the hypothesis that LTs are etiologic in asthma. The complexity of the disease suggests that clinical expectations for these compounds, or any single entity, should be moderate.