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Uncoupled regulation of leukotriene C 4 synthase in platelets from aspirin‐intolerant asthmatics and healthy volunteers after aspirin treatment
Author(s) -
Tornhamre S.,
Ehnhage A.,
Kölbeck K. G.,
Edenius C.,
Lindgren J. Å.
Publication year - 2002
Publication title -
clinical and experimental allergy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.462
H-Index - 154
eISSN - 1365-2222
pISSN - 0954-7894
DOI - 10.1046/j.1365-2222.2002.01531.x
Subject(s) - aspirin , platelet , arachidonic acid , leukotriene c4 , leukotriene , chemistry , thromboxane a synthase , pharmacology , atp synthase , medicine , thromboxane , endocrinology , biochemistry , asthma , enzyme
SummaryBackground We have reported that thromboxane A 2 induces suppression of leukotriene (LT) C 4 synthase activity in human platelets. Aim In the present study, we describe a mechanism whereby aspirin treatment can lead to increased formation of LTC 4 , which is a potent bronchoconstrictor and inflammatory mediator. This mechanism is also demonstrated to be present in platelets from aspirin‐intolerant asthmatics (AIA). Methods The effect of arachidonic acid or platelet agonists on LTC 4 synthase activity was investigated in platelets obtained from healthy volunteers, aspirin‐intolerant asthmatics or aspirin‐tolerant asthmatics after in vivo treatment or in vitro pre‐incubation with aspirin. Results Incubation of normal platelets with arachidonic acid or collagen provoked approximately 50% reduction of platelet LTC 4 synthase activity, as determined by the conversion of LTA 4 to LTC 4 . However, the inhibitory effect of arachidonic acid or collagen was not observed after oral administration of aspirin prior to collection of the platelets. Arachidonic acid‐induced inhibition of LTC 4 synthase activity was totally abolished in platelets collected from peripheral blood already 30 min after aspirin ingestion but was fully restored in platelets collected 3 to 7 days after the administration of aspirin. Treatment of platelet suspensions with aspirin in vitro dose‐dependently counteracted the suppressive effect of arachidonic acid on LTC 4 formation, with total reversal at approximately 40 µ m . In contrast, the major aspirin metabolite, salicylic acid did not alter arachidonic acid‐induced reduction of LTC 4 synthase activity. Similarly, LTC 4 synthase activity in platelets from AIA and aspirin‐tolerant asthmatics (ATA) was reduced by approximately 50% after pre‐treatment with arachidonic acid in vitro . Again the inhibitory effect was abolished when platelets were pre‐incubated in the presence of aspirin. Conclusion The results indicate that oral aspirin administration can lead to uncoupling of thromboxane A 2 ‐dependent negative feedback mechanisms, which may normally restrict the production of cysteinyl leukotrienes. This mechanism can be of potential interest in aspirin‐induced asthma.