Thienopyridine-linked thrombotic microangiopathy: association with endothelial cell apoptosis and activation of MAP kinase signalling cascades

The thienopyridine platelet antagonist ticlopidine is associated with development of thrombotic thrombocytopenic purpura (TTP) but the pathophysiology of this link is unclear. Severe deficiency of disintegrin and metalloproteinase with thrombospondin motif-13 (ADAMTS13), described in familial cases and a significant fraction of idiopathic TTP, has been reported in only a few ticlopidine-linked cases. As ticlopidine can disrupt production of extracellular matrix (ECM) components critical to microvascular endothelial cell (MVEC) integrity in vitro, we explored the hypotheses that ticlopidine and ticlopidine-linked TTP plasmas induce MVEC apoptosis in a manner similar to that of idiopathic TTP plasmas, and that ECM components and related mitogen-activated protein kinase (MAPK) signalling cascades may be involved in this process. Replicating the activity of plasmas from patients with idiopathic TTP, plasma from five ticlopidine-linked TTP patients induced apoptosis of primary human dermal, glomerular and hepatic MVEC, but had no effect on pulmonary MVEC or large vessel endothelial cells (EC). Pharmacological levels of ticlopidine initiated apoptosis with similar EC lineage restriction. In parallel, ticlopidine and plasmas from idiopathic and ticlopidine-TTP patients decreased transcripts for the ECM component thrombospondin-1 in MVEC, but not in large vessel EC. These changes were accompanied by prolonged induction of MAPKs extracellular signal-related kinase (ERK)-1/2 and p38 only in TTP susceptible MVEC. Induction of apoptosis by ticlopidine and TTP plasma was abrogated by inhibitors of ERK-1/2 and p38 phosphorylation. In conclusion, MVEC apoptosis related to altered ECM-MVEC interactions may be a key part of the pathology of ticlopidine-linked and idiopathic TTP.