Thienopyridines: effects on cultured endothelial cells

Area of Science:

• Endothelial cell biology
• Pharmacology
• Cardiovascular research

Background:

• Endothelial cells play a crucial role in regulating vascular tone and platelet aggregation.
• Thienopyridines are antiplatelet agents widely used in cardiovascular disease management.
• The in vitro effects of thienopyridines on endothelial cells, particularly regarding vasodilator release, require further elucidation.

Purpose of the Study:

• To investigate the effects of ticlopidine and clopidogrel on nitric oxide (NO) and prostacyclin (PGI2) generation in cultured endothelial cells.
• To examine the role of intracellular calcium ([Ca2+]i) in mediating these endothelial responses.
• To compare the effects of thienopyridines with a known calcium ionophore.

Main Methods:

• Cultured human umbilical vein endothelial cells (HUVEC) and bovine aorta endothelial cells (BAEC) were treated with ticlopidine, clopidogrel, or calcium ionophore A 23187.
• Nitrite generation (a marker of NO production) and 6-keto-PGF1alpha release (a marker of PGI2 production) were measured.
• Intracellular calcium levels ([Ca2+]i) were monitored using fluorescence microscopy.
• Cell viability was assessed after treatment.

Main Results:

• Ticlopidine and clopidogrel significantly increased nitrite and 6-keto-PGF1alpha generation in HUVEC and BAEC.
• Calcium ionophore A 23187 also stimulated NO and PGI2 release, with a more rapid onset than ticlopidine.
• Both ticlopidine and clopidogrel caused a rise in [Ca2+]i, although the effect was less pronounced and slower compared to A 23187.
• Aspirin pretreatment inhibited the ticlopidine-induced increase in 6-keto-PGF1alpha release.
• Cell viability was not affected by the tested concentrations of thienopyridines or A 23187.

Conclusions:

• Thienopyridines, including ticlopidine and clopidogrel, directly stimulate the release of NO and PGI2 from cultured endothelial cells in vitro.
• These effects are independent of their known ex vivo anti-platelet activity.
• A rise in intracellular calcium ([Ca2+]i) may be involved in mediating the endothelial actions of thienopyridines, though this mechanism requires further confirmation.