The effect of an increase in inhaled allergen dose after terfenadine on the occurrence and magnitude of the late asthmatic response

Allergen dose dependency of the early- and late-phase cutaneous response in the cynomolgus monkey

BACKGROUND

Cutaneous administration of allergen provides a means to confirm an allergic status, investigate the pathogenesis of allergic diseases, and/or provide a mechanism to evaluate the benefit of new potential therapeutics.

OBJECTIVE

Studies were performed to characterize the allergen-induced cutaneous early- and late-phase response (EPR and LPR) in the cynomolgus monkey.

METHODS

Following intradermal injections of Ascaris suum allergen, the cutaneous weal and flare EPR was measured 15 min post-injection, and skin biopsies were collected at 8-24 h to determine the optimal time of LPR occurrence. Biopsies were analysed for epidermal and dermal inflammatory changes.

RESULTS

The EPR was dose related with a reproducible, measurable response at 1 : 10 000 and maximal at a 1 : 100 allergen dilution. In contrast, the threshold dose required for a reproducible LPR was much greater requiring a dilution of 6 : 100, suggesting independent mechanisms for the EPR and LPR. The LPR 20 h post-allergen injection induced an inflammatory response in the upper and deep dermis. The response was characterized by a moderate perivascular to diffuse inflammation consisting of mononuclear cells, neutrophils and eosinophils. Dexamethasone, while having no effect on the EPR, reduced dermal inflammation (upper dermis, P=0.004; deep dermis, P=0.03). Similarly, dermal eosinophilia was also reduced (upper dermis, P<0.001; deep dermis, P=0.02).

CONCLUSION

Collectively, the results indicate the dose dependency of the EPR and LPR. Furthermore, our observations indicate the value of the LPR response in the cynomolgus monkey to evaluate new therapeutics for the treatment of allergic diseases such as atopic dermatitis.

The allergen bronchoprovocation model: an important tool for the investigation of new asthma anti-inflammatory therapies

Allergen bronchoprovocation tests have been used for more than two decades in the investigation of respiratory allergic diseases such as asthma and rhinitis. These bronchial challenges are now well standardized and can offer key information on the therapeutic potential of new agents and on their anti-inflammatory effects on the airways. Both standard and low-dose allergen provocations are safe when performed by experienced investigators and do not lead to persistent worsening of asthma or change in airway function. The evaluation of new therapeutic agents by these methods can also provide important information on the mechanisms of development and persistence of airway diseases.

Inhibition of mediator and cytokine release from dispersed nasal polyp cells by terfenadine

The mechanism of action of H1-blockers requires elucidation because they may possess properties unrelated to the blockage of histamine at its receptor level. A study was performed with enzymatically dispersed cells obtained from nasal polyps to examine the effect of terfenadine (0.1-10 mumol) on the release of leukotrienes (LT) (LTC4/D4 and LTB4) after stimulation by anti-IgE, and on the spontaneous release of cytokines (granulocyte/macrophage-colony stimulating factor [GM-CSF] and tumor necrosis factor-alpha [TNF-alpha]) released from cells cultured for 6 h. Terfenadine inhibited significantly, and in a dose-dependent manner, the release of LTC4/D4, LTB4, TNF-alpha, and GM-CSF. IC50 values were determined for LTC4/D4 (8 mumol), LTB4 (9.9 mumol), TNF-alpha (6.1 mumol), and GM-CSF (4 mumol). Terfenadine was found to possess new antiallergic properties with a novel in vitro model which mimics more closely inflammatory cells of allergic rhinitis or asthma.

Bronchial biopsy evidence for leukocyte infiltration and upregulation of leukocyte-endothelial cell adhesion molecules 6 hours after local allergen challenge of sensitized asthmatic airways

We have examined the mucosal changes occurring in bronchial biopsies from six atopic asthmatics 5-6 h after local endobronchial allergen challenge and compared them with biopsies from saline-challenged segments from the same subjects at the same time point. All the subjects developed localized bronchoconstriction in the allergen-challenged segment and had a decrease in forced expiratory volume in 1 s (FEV1) (P < 0.01) and a decrease in their methacholine provocative concentration of agonist required to reduce FEV1 from baseline by 20% (P < 0.05) 24 h postchallenge. At 6 h we observed an increase in neutrophils (P = 0.03), eosinophils (P = 0.025), mast cells (P = 0.03), and CD3+ lymphocytes (P = 0.025), but not in CD4+ or CD8+ lymphocyte counts. We also detected an increase in endothelial intercellular adhesion molecule type 1 (P < 0.05) and E-selectin (P < 0.005), but not vascular cell adhesion molecule type 1 expression with a correlative increase in submucosal and epithelial LFA+ leucocytes (P < 0.01). Thus, in sensitized asthmatics, local endobronchial allergen instillation leads to an increased inflammatory cell infiltrate of the airway mucosa that involves upregulation of specific adhesion molecules expressed on the microvasculature.

Allergen extracts. Standardization of preparations for bronchial provocation tests. A position paper. (EAACI Sub-committee on Bronchial Provocation Tests)

Standardization of allergen provocation tests of the airways requires standardization of each of the steps involved, including standardization of the extracts used. The value of international standards is emphasized and so is the determination of a clinically relevant potency. The allergen extracts used for bronchial provocation tests must be compared with qualitatively and quantitatively clinically relevant standards using complementary immunochemical and biological methods. Ideally the same extracts should be used for diagnosis (skin test, specific IgE determinations, provocations) and treatment (immunotherapy). The importance of the biological compared with the non-biological methods is that the biological methods are established in allergenic patients in order to select a clinically relevant potency of the allergen in question, and this potency ought to be confirmed in clinical trials. Once established the biological potency of an in-house preparation can be reproduced by supplementary in vitro methods. Very few commercial allergen preparations are available which fulfil the above-mentioned criteria.

Modulation of eicosanoid and histamine release from human dispersed lung cells by terfenadine

Terfenadine is an H1-blocker that may have antiallergic properties. A study was carried out to examine the ability of terfenadine to inhibit the release of histamine and arachidonic-acid-derived mediators from human lung cells. Cells were dispersed from fresh human lung tissue obtained from four accident victims whose hearts were donated for transplantation and four lung cancer resections. Cells were dispersed by enzymatic digestion with type XIV protease and chymopapain, and this resulted in a cell population containing approximately 5% mast cells. The remaining cells were mainly macrophages. The cells were challenged with anti-IgE at a 1/1000 dilution. Cells were challenged without terfenadine and after a preincubation of 0.1, 1, and 10 mumol terfenadine. The release of PGD2 and LTC4/D4 was assessed with an EIA. Histamine was assayed by RIA with a monoclonal antibody against acylated histamine. A release of both eicosanoids and histamine was observed in all experiments. An inhibition of eicosanoids was observed at both 1 and 10 mumol terfenadine (median percentage of inhibition of PGD2: 38.00 +/- 15.65 and 56.00 +/- 13.12; median percentage of inhibition of LTC4/D4: 37.5 +/- 19.80 and 52.5 +/- 26.8). On the other hand, histamine release was not blocked by terfenadine. Terfenadine inhibits, in a dose-dependent manner, the release of eicosanoids after challenge of dispersed lung cells by anti-IgE, and this effect may have some clinical relevance.

Airway inflammation, bronchial reactivity and asthma

Asthma is a common disease of children the basis of which is a state of chronic immunological inflammation which causes bronchial hyperreactivity and renders the patient liable to develop widespread airways obstruction in response to a variety of stimuli. In many instances it is likely that the immunological inflammation results from ongoing antigenic stimuli with the release of chemical mediators responsible for short term bronchospasm and cytokines responsible for the ongoing inflammatory process. Other insults can apparently result in very similar immunological events in asthmatics, particularly viral infections and a similar process can be initiated in children without asthma, including those with chronic bacterial infections of the lungs. There are differences in the bronchial hyperreactivity of asthma and other diseases which suggest that in the asthmatic the mast cell is either different structurally or functionally and this renders the patient susceptible to exercise induced asthma in addition to the bronchial hyperreactivity to chemical mediators common to a number of diseases with hyperreactivity. There is good evidence of direct genetic control of atopy and the large majority of children with asthma are atopic but there is no direct genetic link between atopy and asthma and twin studies strongly suggest the existence of a 'permissive' asthma gene which will allow the disease to develop if there is an appropriate external trigger. The only drugs which have been shown to significantly reduce bronchial reactivity are the corticosteroids with a lesser effect noted for sodium cromoglycate and nedocromil. Inhaled corticosteroids can reverse the immunologic inflammatory process and reduce bronchial reactivity, sometimes to normal levels, but on stopping treatment the patient reverts back to the asthmatic state. At the present time it appears that controlled longterm inhaled corticosteroid therapy is the most rational treatment for significant perennial childhood asthma.

Bronchial allergen challenge: dose versus concentration

This study was designed to investigate if two equivalent doses of allergen administered by different dosing regimes--two breaths and 10 breaths of each concentration--would result in the same magnitude of the early and late asthmatic response. Fifteen patients with extrinsic allergic asthma were challenged twice with either two or 10 breaths of twofold increasing allergen concentrations. The challenge was continued until a 20% decrease in FEV1 had been achieved. A non-cumulative PC20FEV1 allergen was derived, and the cumulative dose of allergen given was similarly derived. In order to assess the reproducibility of the challenge, seven patients were challenged twice with two-breath regime. The mean value of allergen PC20 obtained by the two-breath regime was 4.1 fold (95% CI: 2.3-7.1 fold) greater than those obtained by the 10-breath regime (P less than 0.05), whereas the difference was 1.4 fold (95% CI: -3.3-0.5 fold) for the cumulative dose (P greater than 0.05). A statistically significant larger magnitude of the early asthmatic response, as determined by the maximum per cent fall in FEV1, and late asthmatic response determined by the maximum per cent fall in peak expiratory flow domiciliary recorded during the following 24 hr after challenge, was observed in favour of the 10-breath regime compared to the two-breath regime (mean difference 6%, 95% CI: 0.6-11%). The reproducibility of the provocation test was acceptable (+/- 1.8 two-fold concentration difference). These results confirm the 'equivalent dose hypothesis', and demonstrates that dosage rather than concentration appears to determine the early and late asthmatic response after bronchial allergen challenge.

The effect of a beta 2-adrenergic agonist and a histamine H1-receptor antagonist on the late asthmatic response to inhaled antigen

In this double-blind, randomized, cross-over trial, the role of histamine and the possible protective effect of a beta 2-adrenergic agonist in the later asthmatic response to inhaled antigen was investigated in nine atopic asthmatic patients. On four study days, 2-4 weeks apart, patients were given either: placebo; salbutamol aerosol 400 micrograms before and 200 micrograms 2-hourly after challenge; oral terfenadine 120 mg 2 h before and 10 h after challenge; and, on the final day, lung function was monitored without medication or antigen challenge. A nebuliser-dosimeter system was used to deliver a predetermined, single dose of antigen aerosol. Response was assessed by specific airways conductance (SGAW) measured in a body plethysmograph; FEV1 and PEFR were measured with a Pocket Spirometer. All measurements were made for 10 h in the clinic and then the patients continued to record PEFR and FEV1 at home for at least 2 more hours. Similar findings were obtained with all three lung function parameters. After challenge, the early response (ER) was small when compared with the late response (LR). All patients had a definite LR on the placebo day when FEV1 was compared with 'no challenge day'. Neither drugs had much effect on the small ER. The LR was not altered by terfenadine but was very significantly attenuated by salbutamol; the mean maximum fall in FEV1 during LR being 31, 29 and 12% after placebo, terfenadine and salbutamol, respectively. It is unlikely that histamine plays an important role in the LR to inhaled antigen but beta 2-adrenergic stimulants can attenuate LR, probably by directly preventing bronchial smooth muscle constriction and also by stabilising bronchial mast cells.

Late airway response increases at repeat allergen challenge

The relationship between the immediate and late responses to repeated inhalations of allergen was studied. Sixteen male atopic asthmatics were challenged twice with an interval of 2 weeks. Forced expiratory volume in 1 s (FEV1) was measured serially over an 8-hour period after challenge. The method of provocation used implied that only slight differences between the immediate responses on the two provocation days were observed. However, differences in the late responses were demonstrated. Thus, the maximum percent change in FEV1 at the first and second provocation differed significantly in the late (P less than 0.01), but not in the immediate phase. The increase in maximal late response was greater than the small change in maximal immediate response (P less than 0.05). Further, the FEV1 values from 4 to 8 h post-challenge were in each recording significantly lower on the second day suggesting a more pronounced late bronchial response to repeat challenge. The results suggest that after one challenge specific airway reactivity, i.e., reactivity to allergen, at a subsequent rechallenge is increased in the late phase. This late phase hyperreactivity seems to persist for at least 2 weeks after allergen provocation.