Thrombin receptor-related hemostatic defect after cardiopulmonary bypass

Changes in MicroRNA Expression Level of Circulating Platelets Contribute to Platelet Defect After Cardiopulmonary Bypass

OBJECTIVES

Platelet defect mechanisms after cardiopulmonary bypass remain unclear. Our hypothesis microRNA expressions in circulating platelets significantly change between pre and post cardiopulmonary bypass, and consequent messenger RNA and protein expression level alterations cause postcardiopulmonary bypass platelet defect.

DESIGN

Single-center prospective observational study.

SETTING

Operating room of Kyoto Prefectural University of Medicine.

PATIENTS

Twenty-five adult patients scheduled for elective cardiac surgeries under cardiopulmonary bypass.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In the initial phase, changes in microRNA expression between pre and post cardiopulmonary bypass underwent next generation sequencing analysis (10 patients). Based on the results, we focused on changes in mir-10b and mir-96, which regulate glycoprotein 1b and vesicle-associated membrane protein 8, respectively, and followed them until messenger RNA and protein syntheses (15 patients) using quantitative polymerase chain reaction and Western blotting. Seven microRNAs including mir-10b and mir-96 exhibited significant differences in the initial phase. In the subsequent phase, mir-10b-5p and mir-96-5p overexpressions were confirmed, and glycoprotein 1b and vesicle-associated membrane protein 8 messenger RNA levels were significantly decreased after cardiopulmonary bypass: fold differences (95% CI): mir-10b-5p: 1.35 (1.05-2.85), p value equals to 0.01; mir-96-5p: 1.59 (1.06-2.13), p value equals to 0.03; glycoprotein 1b messenger RNA: 0.46 (0.32-0.60), p value of less than 0.001; and vesicle-associated membrane protein messenger RNA: 0.70 (0.56-0.84), p value of less than 0.001. Glycoprotein 1b and vesicle-associated membrane protein 8 were also significantly decreased after cardiopulmonary bypass: glycoprotein 1b: 82.6% (71.3-93.8%), p value equals to 0.005; vesicle-associated membrane protein 8: 79.0% (70.7-82.3%), p value of less than 0.001.

CONCLUSIONS

Expressions of several microRNAs in circulating platelets significantly changed between pre and post cardiopulmonary bypass. Overexpressions of mir-10b and mir-96 decreased glycoprotein 1b and vesicle-associated membrane protein 8 messenger RNA as well as protein, possibly causing platelet defect after cardiopulmonary bypass.

Aprotinin counteracts heparin-induced inhibition of platelet contractile force

BACKGROUND

Aprotinin interferes with heparin binding to platelets and decreases blood loss during cardiopulmonary bypass (CPB). Heparin abolishes platelet force during CPB, and the extent of platelet force recovery after protamine administration appears to correlate with blood loss. This study assessed the effect of aprotinin on heparin suppression of platelet force.

METHODS

Platelet force was measured using the Hemodyne Hemostasis Analyzer. Clots were formed from platelet-rich plasma (PRP) by the addition of batroxobin and 10 mM CaCl(2). Clotting conditions included pH 7.4, ionic strength 0.15 M, fibrinogen level 1 mg/ml and 75,000 platelets/microl.

RESULTS

After 1200 s of clotting, force was reduced from 7110+/-1190 to 450+/-450 dyn by 0.2 U/ml of heparin. Platelet force in aprotinin [20 microg/ml (140 KIU/ml)] containing PRP was not suppressed by heparin addition (7480+/-2410 dyn). Aprotinin [40 microg/ml (280 KIU/ml)] addition to previously heparinized plasma counteracted heparin force suppression. Aprotinin (40 microg/ml) increased platelet force from 5630 to 11,138+/-562 in PRP devoid of heparin. Aprotinin did not affect thrombin activity, fibrin structure, platelet aggregation or secretion.

CONCLUSIONS

Aprotinin counteracts heparin suppression of platelet force and enhances platelet force in the absence of heparin. Aprotinin-heparin-platelet interactions may help explain aprotinin's ability to reduce blood loss during CPB.

The platelet thrombin receptor and postoperative bleeding

BACKGROUND

We hypothesized that small amounts of thrombin desensitize the platelet thrombin receptor during cardiopulmonary bypass (CPB), resulting in postoperative platelet dysfunction and bleeding.

METHODS

Seventy-nine patients were entered into a study designed to measure changes in platelet thrombin receptor function during CPB and to correlate them to postoperative bleeding. In addition to measurements of clinical blood loss, platelet function tests of aggregation, activation, and cell-cell adhesion were used. The thrombin receptor agonist peptide (TRAP) was used to activate the platelets. Flow cytometry was used to measure various platelet surface markers and platelet-white cell interactions during CPB.

RESULTS

Compared with preoperative values, both aggregometry and flow cytometry measured a significant reduction of TRAP-induced activation immediately and up to 24 hours after CPB. The response of other activating agents returned to normal by 24 hours. Postoperatively, 8 of 79 patients required excessive blood transfusion (> or = 10 units of blood products) and had significantly decreased TRAP-induced aggregation response.

CONCLUSIONS

Our results show that (1) platelet activation, aggregation, and adhesion to leukocytes induced by TRAP are reduced after CPB, (2) decreased thrombin receptor responsiveness is associated with excessive postoperative blood loss, and (3) because the aggregation and activation responses are different for TRAP and thrombin, there may be a second thrombin receptor on platelets that is protected from damage during CPB. These results imply that prevention of the CPB-induced effects on the thrombin receptor will lessen postoperative morbidity associated with blood transfusion.