Increased prostaglandin E2 concentrations and cyclooxygenase-2 expression in asthmatic subjects with sputum eosinophilia.
BACKGROUND
Prostaglandin E2 (PGE2) is known to be produced within human airways, but it is not clear whether in airway diseases it can play a deleterious or a beneficial role. Recently it has been reported that PGE2 can enhance eosinophil survival in vitro.


OBJECTIVE
To evaluate whether the concentrations of PGE2 in asthmatic airways correlate with the number of eosinophils and can be responsible for eosinophil-enhanced survival and to identify the cyclooxygenase isoform contributing to the synthesis of PGE2 by cells present in asthmatic airways.


METHODS
Reversed-phase high-performance liquid chromatography and/or specific radioimmunoassay was used to measure PGE2 concentrations in induced sputum supernatants from 14 control and 30 asthmatic subjects. Correlations between concentrations of PGE2 and the number of eosinophils in induced sputum were evaluated. Expression of cyclooxygenase-2 (COX-2) in induced sputum cells was determined by immunocytochemistry, and the effect of COX-2 inhibition on PGE2 production was evaluated with the use of radiolabeled arachidonic acid. The effects on eosinophil apoptosis by PGE2 or induced sputum supernatants were studied by using peripheral blood eosinophils obtained by negative immunomagnetic selection.


RESULTS
PGE2 concentrations resulted in elevated samples from asthmatic subjects and directly correlated with the percentage of eosinophils and the concentrations of eosinophilic cationic protein. Immunostaining for COX-2 showed enhanced expression in macrophages of asthmatic subjects when compared with control subjects, and the use of a specific COX-2 inhibitor provided evidence that PGE2 synthesis was the result of COX-2 enzymatic activity in asthma-induced sputum cells. Supernatant from induced sputum of asthmatic subjects with high eosinophil counts caused a decreased apoptosis of peripheral blood eosinophils when compared with control subjects, and immunoprecipitation of PGE2 significantly reverted this phenomenon, suggesting that PGE2 was present in biologically relevant concentrations in induced sputum.


CONCLUSIONS
The results obtained suggest that COX-2 expression in alveolar macrophages from asthmatic subjects may contribute to enhanced eosinophil survival through an increased PGE2 production.
Profita
Mirella
M
Institute of Lung Pathophysiology, Italian National Research Council, Palermo, Italy.
Sala
Angelo
A
Bonanno
Anna
A
Riccobono
Loredana
L
Siena
Liboria
L
Melis
Mario R
MR
Di Giorgi
Rossana
R
Mirabella
Franco
F
Gjomarkaj
Mark
M
Bonsignore
Giovanni
G
Vignola
Antonio M
AM
D000328:Adult; D017209:Apoptosis / Q000187:drug effects; D001249:Asthma / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology; D001798:Blood Proteins / Q000032:analysis; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000032:analysis* / Q000096:biosynthesis / Q000494:pharmacology; D047091:Eosinophil Granule Proteins; D004802:Eosinophilia / Q000473:pathology*; D004804:Eosinophils; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000032:analysis*; D007958:Leukocyte Count; D008297:Male; D008565:Membrane Proteins; D008875:Middle Aged; D009994:Osmolar Concentration; D011451:Prostaglandin-Endoperoxide Synthases / Q000032:analysis*; D012260:Ribonucleases / Q000032:analysis; D013183:Sputum / Q000737:chemistry* / Q000166:cytology* / Q000378:metabolism
D001798:Blood Proteins; D047091:Eosinophil Granule Proteins; D007527:Isoenzymes; D008565:Membrane Proteins; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D012260:Ribonucleases; D015232:Dinoprostone