Clinical Inhibition of the Seven-Transmembrane Thrombin Receptor (PAR1) by Intravenous Aprotinin During Cardiothoracic Surgery

Abstract

Background-Protease-activated receptor-1 (PAR1) is the principal thrombin receptor in the vasculature, and antagonists against this receptor are in preclinical trials. Aprotinin, already approved for clinical use to reduce transfusion requirements in cardiopulmonary bypass (CPB) surgery, has been shown to inhibit PAR1 activation in vitro. Here, we exploit CPB as a model for thrombin generation in humans to examine whether aprotinin can inhibit platelet PAR1 activation clinically. Methods and Results-PAR1 expression and function on platelets was examined in coronary artery bypass grafting (CABG) patients randomized into 2 groups: (1) those receiving saline infusion during CPB (nϭ17) and (2) those receiving aprotinin (2ϫ10 6 kallikrein inhibitor units [KIU] in pump prime, 2ϫ10 6 KIU loading dose, followed by 0.5ϫ10 6 KIU/h [nϭ13]). Platelets in the saline group showed loss of PAR1-specific function at 2 hours after CPB, but this was preserved in the aprotinin group (PϽ0.001). These effects were most likely targeted at PAR1 receptor cleavage, because (1) the level of thrombin generated during CPB did not vary significantly between groups, (2) expression of SPAN12, which detects only uncleaved PAR1 receptors, was preserved in the aprotinin but not the placebo group (PϽ0.05), and (3) supporting evidence in vitro showed reduced thrombin-induced PAR1 cleavage (PϽ0.001) and platelet aggregation (PϽ0.001) in the presence of aprotinin. Conclusions-This study demonstrates that platelet PAR1 activation by thrombin can be inhibited by aprotinin. Our results extend the clinical mechanism of action of aprotinin and provide the first proof of principle that PAR1 can be inhibited clinically. This has implications beyond cardiac surgery for the development of therapeutic PAR1 blockade.

The effect of aprotinin on activated protein C‐mediated downregulation of endogenous thrombin generation

“…Although aprotinin is a poor inhibitor of thrombin (K i ¼ 61 lmol/l) (Pintigny & Dachary-Prigent, 1992), it reduced the peak TG in a dose-dependent manner (but was not statistically significant) in both normal (Figs 1 and 2) and PC-depleted plasma samples (Fig 3). This is consistent with other reports (Poullis et al, 2000;Day et al, 2004;Khan et al, 2005). Thus, aprotinin-mediated reduction in thrombin activity may result in inhibition of APC generation as reported with thrombin inhibitors (Linder et al, 1999).…”

Aprotinina preserva plaquetas em crianças com cardiopatia congênita acianogênica operadas com circulação extracorpórea?

“…This finding is consistent with the institutions of great experience using Aprotinin in heart surgery [4,9,12]. The most common causes of bleeding after CPB include platelet dysfunction and hyperfibrinolysis [1], considering that the former is more important [12], and likely to exacerbation of thrombocytopenia, typical of CPB with hemodilution, by the adhesion and consumption in the cardiopulmonary bypass circuit and the platelet effects of heparin [13]. In this study, Aprotinin preserved quantitatively the circulating platelets, whereas the Control group developed with thrombocytopenia from the start of CPB until the end of the study in order to corroborate the findings of Masiak et al [6] and Royston et al [14].…”

Plasmin Overcomes Resistance to Prostaglandin E2 in Fibrotic Lung Fibroblasts by Reorganizing Protein Kinase A Signaling

“…In some experiments, cells received additional pretreatment with PAR-1 antagonist FLLRN (500 M), the HGF receptor c-Met kinase inhibitor PHA-66575 (0.1 M), or anti-c-Met blocking Ab (20 g/ml) 30 min prior to Plg ϩ uPA addition. In previous papers, these concentrations for FLLRN (19), PHA-66575 (20), and c-Met blocking Ab (17) were established as effective. In some experiments, PKA inhibitors KT5720 (100 nM) or PKI (10 M) were added 30 min prior to Plg ϩ uPA addition or 4 h before PGE 2 addition, respectively.…”