title: Caspase inhibition decreases both platelet phosphatidylserine exposure and aggregation: caspase inhibition of platelets.
abstract: Apoptosis of nucleated cells is regulated by caspases, a group of cysteine proteases, and is characterized by phosphatidylserine expression on the outer leaflet of the plasma membrane. Reports indicate that platelets contain caspases. However, the role of caspases in platelet function is not well understood. When platelets become activated, they express phosphatidylserine (PS) on the outer leaflet of the plasma membrane. In addition, platelets aggregate when activated. The aims of this study were to determine if caspase inhibition (using the pan-caspase inhibitor zVAD-fmk): (1) decreased PS expression and (2) decreased platelet aggregation following activation. Flow cytometry was used to determine PS expression and a platelet aggregometer was used to assess aggregation. We found that platelets treated with zVAD-fmk significantly decreased both A23187-induced PS exposure (total fluorescence index, TFI: A23187=791.42+/-174; zVAD+A23187=92.97+/-57, p<==0.05) and ADP-induced PS exposure (TFI: ADP=669.24+/-145, zVAD+ADP=174.6+/-151, p<==0.05). Further, treatment with zVAD-fmk significantly decreased ADP-induced platelet aggregation (%: untreated=80+/-1.5, zVAD treated=69+/-3.0, p<==0.05). These results indicate that caspases play a role in platelet activation, suggesting a unique physiologic role for these proteases.
authors.affiliation: College of Nursing and Department of Neurology, University of Arizona, Tucson, AZ 85724, USA. cohenz@smh.toronto.on.ca
authors.forename: Zoë
authors.initials: Z
authors.lastname: Cohen
authors.forename: Jonathan
authors.initials: J
authors.lastname: Wilson
authors.forename: Leslie
authors.initials: L
authors.lastname: Ritter
authors.forename: Paul
authors.initials: P
authors.lastname: McDonagh
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology*; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000502:physiology*; D061945:Caspase Inhibitors; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D008297:Male; D010718:Phosphatidylserines / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D010718:Phosphatidylserines; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone