Increased Platelet Activation in Cystic Fibrosis: A Role for cAMP/Adenylate Cyclase But Not for Mead Acid or Platelet CFTR

Abstract number: P0361

Linden¹ MD, O'Sullivan¹ BP, Frelinger III, AL¹ , Barnard¹ MR, Spencer-Manzon¹ M, Laposata² M, Michelson¹ AD

¹¹University of Massachusetts, Worcester, MA, USA ¹¹University of Massachusetts, Worcester, MA, USA ²²Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA

Cystic fibrosis (CF) is caused by a mutation of the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). Because there is an excessive host inflammatory response, and increased 11-dehydro-thromboxane B₂ in CF patients, we examined the role of platelet function in the thrombo-inflammatory response of CF patients. Circulating platelets in CF patients were more activated than normal donors, as determined by monocyte-platelet aggregates (25.6% and 10.8% respectively, n= 18, P < 0.05) and neutrophil-platelet aggregates (11.5% and 6.1% respectively, n= 18, P < 0.05). CF plasma caused activation of normal and CF platelets – demonstrating a role of CF plasma in platelet activation. However, activation was greater in CF platelets compared to normal platelets when treated with CF plasma – demonstrating a role for an intrinsic platelet mechanism. Furthermore, washed CF platelets also showed increased reactivity to agonists in the absence of CF plasma. CF platelet hyperreactivity was incompletely inhibited by PGE₁, suggesting increased cyclic AMP/adenylate cyclase as an intrinsic mechanism of increase platelet activity in CF. However, as demonstrated by Western blotting and RT-PCR, there was neither CFTR nor CFTR-specific mRNA in normal platelets. In CF platelets, there was an increase in Mead acid (20:3 n-9), a metabolite of which enhances platelet activation. However in vitro spiking of plasma with 20:3 n-9 at concentrations seen in CF did not promote platelet activation. In summary, CF patients have an increase in circulating activated platelets and platelet reactivity, as determined by monocyte-platelet aggregation and neutrophil-platelet aggregation. This increased platelet activation in CF is the result of both a plasma factor(s) and an intrinsic platelet mechanism via cAMP/adenylate cyclase, but not via increased Mead acid or platelet CFTR. Our findings may account, at least in part, for the reported beneficial effects of ibuprofen in CF.