Mechanism of the effector function of adenosine in asthma and rhintis

Heparin attenuates symptoms and mast cell degranulation induced by AMP nasal provocation

BACKGROUND

Previous studies have shown that inhaled heparin attenuated the airway responses to allergen, exercise, and AMP bronchial provocation, possibly through an inhibition of mast cell activation.

OBJECTIVE

The aim of this study was to provide the evidence of in vivo inhibition of human mast cell activation by heparin in a noninvasive model.

METHODS

Nine atopic and 6 nonatopic subjects received placebo and unfractionated heparin sodium (5000 IU/mL) 15 minutes before an AMP nasal provocation in a double-blind crossover study design. The nasal lavage was collected from these subjects before or 3, 5, 15, or 30 minutes after the AMP nasal challenge, and concentrations of histamine and tryptase in the nasal lavage were measured.

RESULTS

AMP nasal provocation produced considerable sneezing and induced a transient increase in histamine and tryptase release, with peak values achieved at 3 to 5 minutes after the challenge in all atopic subjects. Compared with placebo, inhaled heparin significantly attenuated the release of histamine and tryptase induced by AMP challenge (P=.012 and.004, respectively). Moreover, the AMP-induced sneezing was also inhibited by pretreatment with heparin (P=.016). In nonatopic subjects, AMP did not induce a significant increase in histamine and tryptase release on placebo-treated or heparin-treated days.

CONCLUSION

These data suggest that AMP nasal provocation and AMP bronchial provocation cause mast cell mediator release in a similar fashion. In addition, the data support the hypothesis that inhaled heparin plays a protective role against AMP provocation by inhibition of mast cell activation.

An evaluation of short-term corticosteroid response in perennial allergic rhinitis using histamine and adenosine monophosphate nasal challenge

AIMS

To evaluate the role of AMP nasal challenge as a measure of short-term treatment response in patients receiving intranasal corticosteroids. Adenosine monophosphate (AMP) challenge has been shown to be a good inflammatory surrogate in the lower airways, but it has not been properly evaluated as a nasal challenge test.

METHODS

Fourteen patients with perennial allergic rhinitis (PAR) were randomized to receive 2 weeks treatment with placebo (PL) or 200 microg intranasal mometasone furoate (MF) once daily in a randomized single-blind crossover study. AMP (25-800 mg ml-1) and histamine (0.25-8 mg ml-1) nasal challenge testing were performed after each treatment period with 30% decrease in minimal cross-sectional area (MCA). Domiciliary symptom data were collected.

RESULTS

There was a significant (P < 0.05) improvement in PC30 MCA and nasal volume with AMP but not with histamine comparing MF vs PL. This amounted to a 2.8 (95% CI 1.5, 4.0) and 0.7 (95% CI -0.5, 1.9) doubling-dose change for AMP and histamine challenges, respectively. There were significant (P < 0.05) improvements in nasal symptoms and quality of life.

CONCLUSIONS

AMP nasal challenge using acoustic rhinometry may be a useful test to assess short-term treatment response in patient with PAR.

Induction of interleukin 8 release from the HMC-1 mast cell line: synergy between stem cell factor and activators of the adenosine A(2b) receptor

The HMC-1 mast cell line has both adenosine A(3) and A(2b) receptors on its surface, but only agonists of the A(2b) receptor are effective at releasing interleukin 8. Object of this study was to look for co-factors for adenosine A(2b) receptor activation. There was a powerful and statistically significant synergy for release of IL-8, both at the mRNA level (measured after 4 hr) and protein level (measured after 24 hr), between adenosine A(2b) receptor agonists and stem cell factor (SCF). Suitable concentrations for showing synergy were 100 ng/mL SCF and 3 microM 5'-N-ethylcarboxamidoadenosine (NECA). At these concentrations, the IL-8 released into the culture medium after SCF and NECA together was typically 3-5-fold greater in amount than the sum of the amounts of IL-8 released after exposure to the same concentrations of NECA and SCF separately. Since mast cells may be exposed to both adenosine and stem cell factor in the diseased lung, the synergy observed in this model system may have implications for asthma.

Adenosine A2B receptors: a novel therapeutic target in asthma?

Adenosine is an endogenous nucleoside that modulates many physiological processes. Its actions are mediated by interaction with specific cell membrane receptors. Four subtypes of adenosine receptor have been cloned: A1, A2A, A2B and A3. Significant advancement has been made in our understanding of the molecular pharmacology and physiological relevance of adenosine receptors but our knowledge of A2B receptors lags behind that of other receptor types. Only recently have potentially important functions been discovered for the A2B receptors, prompting a renewed interest in this receptor type. A2B receptors have been implicated in the regulation of vascular smooth muscle tone, cell growth, intestinal function and neurosecretion. In this review, Igor Feoktistov, Riccardo Polosa, Stephen Holgate and Italo Biaggioni focus on the role of A2B receptors in mast cell activation and the potential relevance of this action on asthma.

Purine derivatives in the study of allergic inflammation in respiratory diseases

Adenosine, a naturally occurring purine nucleoside, elicits dose-related bronchoconstriction in asthmatic subjects when administered by inhalation and it is recovered in increased amounts from the bronchial lavage fluid of subjects with active asthma when compared to normal controls. Although the mechanism by which adenosine mediates bronchoconstriction in asthmatic subjects is not clear, recent data indicate an important role for mast cell mediator release. We have recently shown that local airway challenge with adenosine in subjects with asthma and rhinitis provokes an increase in the levels of PGD2, histamine and tryptase. However, airway responsiveness and atopic status are the most important determinants of adenosine-induced responses, regardless of any increases in mast cell mediators in airway fluids. New discoveries suggest that the airway response to adenosine may be an index of mast cell priming and therefore may provide a useful tool to further explore the inflammatory processes in allergic asthma and rhinitis. Therefore adenosine provocation may gain increasing acceptance as an additional measure of disease activity in asthma and rhinitis.