Defibrotide Inhibits Ca2+ Dependent Neutrophil Activation: Implications for its Pharmacological Activity in Vascular Disorders

Abstract

Defibrotide (DEF) is a polydeoxyribonucleotide agent provided with profibrinolytic and antithrombotic properties. Moreover, an antiischemic, cardi oprotective effect of the drug has recently been demonstrated in experimental animals. Increasing evidence exists of the important role played by neutrophils in the development of tissue damage during chronic and acute ischemia and in the early phases of reperfusion. In order to evaluate whether the overall cytoprotective effect of DEF could be based, at least in part, on a neutrophil- involving mechanism, the authors studied the in vitro effects of the drug on hu man neutrophil activation triggered by several specific stimuli.

The drug dose-dependently (10-100 μM) inhibited enzyme release, superoxide anion generation, and chemiluminescence induced in neutrophils by the chemoat tractant oligopeptide fMLP and by the divalent cation ionophores A23187 and ionomycin. The increase of extracellular calcium concentration from 0.5 to 2.0 mM antagonized the inhibitory effect of DEF. The use of the fluorescent probe Fura 2/AM led them to show that DEF is able to reduce the cytosolic free calci um increase following specific stimulation by affecting extracellular calcium en trance. Such a behavior resembles that of calcium-antagonistic drugs, thus suggesting that DEF works, at least in part, similarly to calcium entry blockers. Such an activity on cell calcium translocation could represent the underlying molecular mechanism of cytoprotection. Finally, the inhibitory action on neu trophil functions may play a role in tissue protection during ischemic injury.