Antithrombin Exerts a Cardioprotective Effect against Myocardial Ischemic/reperfusion Injury through Induction of Prostacyclin and Inhibition of NF-kappa B Signaling

Antithrombin (AT) is a plasma serpin inhibitor that regulates the proteolytic activity of procoagulant proteases of the clotting cascade. In addition to its anticoagulant activity, AT also possesses potent antiinflammatory and antiangiogenic properties. In this study, we investigated the antiinflammatory activity of wild-type AT (AT-WT) and a reactive center loop mutant of AT (AT-RCL) not capable of inhibiting thrombin in a mouse model of ischemia/reperfusion injury in which the left anterior descending coronary artery (LAD) was occluded and released then. The results demonstrate that AT markedly reduces the myocardial infarct size (p<0.05 vs. vehicle) by a mechanism that is independent of its anticoagulant activity. Thus, the AT-RCL mutant, lacking any detectable reactivity with thrombin, attenuated myocardial infarct size to the same extent as the AT-WT in the acute injury model. Further studies revealed that AT binds to vascular heparan sulfate proteoglycans via its heparin-binding domain to exert its protective activity as evidenced by the therapeutic AT-binding pentasaccharide fragment of heparin (fondaparinux) abrogating the cardioprotective activity of AT. We further demonstrate that AT up-regulates the production of prostacyclin in myocardial tissues (p<0.05 vs. vehicle) and inhibits the production of proinflammatory cytokines TNF-α and IL-6 (p<0.05 vs. vehicle) in vivo by attenuating the ischemia/reperfusion-induced JNK and NF-κB signaling pathways. These results suggest that AT, through its antiinflammatory signaling effect, may have therapeutic potential for reducing cardiac ischemia/reperfusion injury and that a normal cardioprotective activity for the AT-RCL variant renders it a superior drug candidate if bleeding becomes a concern in the treatment.