Caspase inhibition decreases human platelet activation

Abstract

Apoptosis utilizes three groups of proteins: death receptors, the Bcl-2 family, and caspases. Recent observations indicate that platelets contain caspases. However, the role of caspases in platelet function remains unclear. There is limited research on the role of caspases on platelet adhesion proteins such as P-selectin or the GPIIb/IIIa complex, which are expressed on the cell surface during activation. The aim of this study was to investigate if caspase inhibition attenuated P-selectin and GPIIb/IIIa expression on activated platelets. Using blood from healthy volunteers, we found that pre-treatment with zVAD-fmk, a broad spectrum caspase inhibitor, significantly attenuated P-selectin expression on ADP and PAF stimulated platelets, measured by flow cytometry. Alone, zVAD-fmk did not affect expression of P-selectin compared to control. Activation with ADP significantly increased P-selectin expression (p ≤ 0.05). In samples pretreated with 20 μM zVAD-fmk and then stimulated with ADP, there was significant attenuation of P-selectin expression (p ≤ 0.03). We found a modest attenuation of GPIIb/IIIa expression in caspase inhibited platelets when they were stimulated with PAF, but not ADP. We have previously demonstrated in a rodent model, that there is a decrease in aggregation when platelets were treated in vitro with zVAD-fmk. These data suggest that caspases may play a role in platelet activation. This novel finding may lead to the development of improved agents to limit platelet activation. Supported by T32NRO7958, NIH HLB 58859, NIH NINR 05028.