Antiplatelet drugs: mechanisms and risks of bleeding following cardiac operations

Antiplatelet Aggregation Properties of Cirsilineol: A Novel Inhibitor of Blood Coagulation Factor Xa

A small natural substance called cirsilineol (CSL), which was discovered in the plant Artemisia vestita, is lethal to many cancer cells and has antioxidant, anticancer, and antibacterial properties. Here, we investigated the underlying mechanisms of the antithrombotic action of CSL. We demonstrated that CSL has antithrombotic efficacy comparable to rivaroxaban, a direct blood coagulation factor Xa (FXa) inhibitor employed as a positive control, in inhibiting the enzymatic activity of FXa and the platelet aggregation induced by adenosine diphosphate (ADP) and U46619, a thromboxane A2 analog. The expression of P-selectin, the phosphorylation of myristoylated alanine-rich C kinase substrate by U46619 or ADP, and the activation of PAC-1 in platelets were inhibited by CSL. Nitric oxide production was increased by CSL in ADP- or U46619-treated human umbilical vein endothelial cells (HUVECs), although excessive endothelin-1 secretion was suppressed. CSL demonstrated strong anticoagulant and antithrombotic effects in a mouse model of arterial and pulmonary thrombosis. Our findings suggest that CSL is a potential pharmacological candidate for a novel class of anti-FXa and antiplatelet medications.

Inhibition of factor Xa activity, platelet aggregation, and experimentally induced thrombosis by Sparstolonin B

BACKGROUND

Sparstolonin B (SsnB) is an isocumarin compound extracted from medicinal plants such as Sparganium stoloniferum and Scirpus yagara with well documented anti-inflammatory activity. Here we examined if SsnB also possesses antithrombotic activity and the underlying mechanisms.

METHODS

Anti-thrombotic effects of SsnB were determined by measuring in vitro/ex vivo/in vivo clotting times, platelet aggregation assay, production and activity of factor Xa, nitric oxide, and expressions of relative proteins.

RESULTS

Treatment with SsnB prolonged the clotting time of human platelet-poor serum at concentrations comparable to the clinical anticoagulant rivaroxaban (as a positive control) and inhibited human platelet aggregation induced by adenosine diphosphate (ADP) or the thromboxane A2 analog U46619. SsnB also inhibited U46619-induced and ADP-induced phosphorylation of phospholipase C (PLC)γ2/protein kinase C (PKC) and intracellular calcium mobilization, both of which are required for platelet aggregation. In addition, SsnB inhibited expression of the cell adhesion factors P-selectin and PAC-1. SsnB increased production of the vasodilator nitric oxide and suppressed secretion of the vasoconstrictor endothelin-1 from ADP- or U46619-treated human umbilical vein endothelial cells. Further, SsnB reduced coagulation factor Xa (FXa) catalytic activity and production by endothelial cells as well as FXa-induced platelet aggregation.

CONCLUSION

Finally, SsnB injection reduced thrombus formation time, number, size, and related mortality in mouse models of thromboembolism. SsnB is a promising antithrombotic agent targeting both FXa and platelet aggregation pathways, which can overcome the side effects of existing antithrombotic agents.

Risk of perioperative coronary stent stenosis or occlusion in patients with previous percutaneous coronary intervention undergoing coronary artery bypass grafting surgery

OBJECTIVES

There is an ongoing discussion about how to treat coronary stents during bypass surgery: Should patent stents be left alone and the stented vessels be ungrafted, or should every stented coronary artery receive a bypass graft? This study aims to determine the relevance of perioperative stent stenosis or occlusion on postoperative outcomes up to 3 years postoperatively.

METHODS

Patients undergoing coronary artery bypass grafting surgery (CABG) (±concomitant procedures) with previous percutaneous coronary intervention from 4 centres were prospectively included in this observatory study between April 2015 and June 2017. A coronary angiography was conducted between the fifth and seventh postoperative days. The preoperative and postoperative angiograms were assessed in a core laboratory, assessing the patencies of coronary stents and bypass grafts. The core lab investigators were blinded to the patients' characteristics and perioperative course.

RESULTS

A total of 107 patients were included in the study. In the postoperative coronary angiography, 265 bypass grafts and 189 coronary stents were examined angiographically. Ninety-seven percent of preoperatively patent stents remained patent. New coronary stent stenoses were observed in 5 patients (4.7%). All 5 patients were asymptomatic and managed conservatively. Bypass stenoses were observed in 12 patients (11%), of whom were managed conservatively, 4 underwent percutaneous coronary intervention and 1 underwent redo-CABG. Two years postoperatively, 97% of patients were alive. Patients with new stent stenosis tended to have a better survival compared with patients with bypass stenosis (100% vs 73%; P = 0.09) up to 3 years postoperatively.

CONCLUSIONS

Perioperative coronary stent stenosis occurs rarely. It is safe to leave a patently stented coronary vessel without bypass grafting.

Novel factor Xa inhibitor, maslinic acid, with antiplatelet aggregation activity

As antithrombotic effects of maslinic acid (MA) have not yet been studied, MA-mediated downregulation of coagulation factor Xa (FXa) and platelet aggregation was studied. We show that MA inhibited the enzymatic activity of FXa and platelet aggregation, induced by adenosine diphosphate (ADP) and a thromboxane A₂ (TXA₂ ) analog, U46619 with a similar antithrombotic efficacy to rivaroxaban, a direct FXa inhibitor used as a positive control. Mechanistically, MA suppressed U46619- or ADP-induced phosphorylation of myristoylated alanine-rich C kinase substrate, and the expression of P-selectin, and activated PAC-1 in platelets. MA increased generation of nitric oxide, but downregulated excessive secretion of endothelin-1 in ADP- or U46619-treated human umbilical vein endothelial cells. In arterial and pulmonary thrombosis mouse model, MA showed prominent anticoagulant and antithrombotic effects. Our data suggest MA as a candidate molecule for a new class of drugs targeting anti-FXa and antiplatelet.

Bioactive peptides and proteins as alternative antiplatelet drugs

Antiplatelet drugs reduce the risks associated with atherothrombotic events and show various applications in diverse cardiovascular diseases including myocardial infarctions. Efficacy of the current antiplatelet medicines including aspirin, clopidogrel, prasugrel and ticagrelor, and the glycoprotein IIb/IIIa antagonists, are limited due to their increased risks of bleeding, and antiplatelet drug resistance. Hence, it is important to develop new effective antiplatelet drugs, with fewer side-effects. The vast repertoire of natural peptides can be explored towards this goal. Proteins and peptides derived from snake venoms and plants represent exciting candidates for the development of novel and potent antiplatelet agents. Consequently, this review discusses multiple peptides that have displayed antiplatelet aggregation activity in preclinical drug development stages. This review also describes the antiplatelet mechanisms of the peptides, emphasizing the signaling pathways intervened by them. Also, the hurdles encountered during the development of peptides into antiplatelet drugs have been listed. Finally, hitherto unexplored peptides with the potential to prevent platelet aggregation are explored.

Novel direct factor Xa inhibitory compounds from Tenebrio molitor with anti-platelet aggregation activity

Tenebrio molitor is an edible insect that has antimicrobial, anticancer, and antihypertensive effects. The aim of this study was to identify the unreported bioactive compounds from T. molitor larvae with inhibitory activities against factor Xa (FXa) and platelet aggregation. Isolated compounds were evaluated for their anti-FXa and anti-platelet aggregation properties by monitoring clotting time, platelet aggregation, FXa activity, and thrombus formation. A diketopiperazine (1, cyclo(_L-Pro-_L-Tyr)) and a phenylethanoid (2, N-acetyltyramine) were isolated and inhibited the catalytic activity of FXa in a mixed inhibition model and inhibited platelet aggregation induced by adenosine diphosphate (ADP) and U46619. They inhibited ADP- and U46619-induced phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) and the expression of P-selectin and PAC-1 in platelets. They also improved the production of nitric oxide and inhibited the oversecretion of endothelin-1 compared to that of the ADP- or U46619-treated group. In an animal model of arterial and pulmonary thrombosis, the isolated compounds showed enhanced antithrombotic effects. They also elicited anticoagulant effects in mice. Compounds 1-2 inhibited ADP-, collagen-, or U46619-induced platelet aggregation and showed similar anti-thrombotic efficacy to rivaroxaban, a positive control. Therefore, 1-2 could serve as candidates and provide scaffolds for the development of new anti-FXa and anti-platelet drugs.

Anti-factor Xa activities of zingerone with anti-platelet aggregation activity

Zingerone (ZGR), a phenolic alkanone found in Zingiber officinale, has been reported to have various pharmacological activities such as anti-inflammatory, anti-apoptotic, and protecting myocardial infarction and irritable bowel disorder. The aim was to identify the unreported bioactive anti-factor Xa (FXa) and anti-platelet activities of ZGR. ZGR was evaluated for their anti-FXa and anti-platelet aggregation properties by monitoring clotting time, platelet aggregation, FXa activity and production, and thrombus formation. ZGR reduced activated partial thromboplastin time and it inhibited the catalytic activity of FXa toward its substrate S-2222 in a noncompetitive inhibition model and inhibited platelet aggregation induced by adenosine diphosphate (ADP) and U46619 (not thrombin). However, ZGR did not prolong bleeding time in mice, as shown by tail clipping. ZGR also inhibited ADP- and U46619- induced phosphorylation of myristolated alanine-rich C-kinase substrate (MARCKS) and the expressions of P-selectin and PAC-1 in platelets. In an animal model of arterial and pulmonary thrombosis, ZGR showed enhanced antithrombotic effects. ZGR also elicited anticoagulant effects in mice. Our results reveal that ZGR is an antithrombotic compound with both FXa inhibitory and anti-platelet aggregation activities. Collectively, these results show that ZGR could serve as candidates and provide scaffolds for the development of new anti-FXa and anti-platelet drugs.

Platelet sequestration and activation during GalTKO.hCD46 pig lung perfusion by human blood is primarily mediated by GPIb, GPIIb/IIIa, and von Willebrand Factor

BACKGROUND

Here, we ask whether platelet GPIb and GPIIb/IIIa receptors modulate platelet sequestration and activation during GalTKO.hCD46 pig lung xenograft perfusion.

METHODS

GalTKO.hCD46 transgenic pig lungs were perfused with heparinized fresh human blood. Results from perfusions in which αGPIb Fab (6B4, 10 mg/l blood, n = 6), αGPIIb/IIIa Fab (ReoPro, 3.5 mg/l blood, n = 6), or both drugs (n = 4) were administered to the perfusate were compared to two additional groups in which the donor pig received 1-desamino-8-d-arginine vasopressin (DDAVP), 3 μg/kg (to pre-deplete von Willebrand Factor (pVWF), the main GPIb ligand), with or without αGPIb (n = 6 each).

RESULTS

Platelet sequestration was significantly delayed in αGPIb, αGPIb+DDAVP, and αGPIb+αGPIIb/IIIa groups. Median lung "survival" was significantly longer (>240 vs. 162 min reference, p = 0.016), and platelet activation (as CD62P and βTG) were significantly inhibited, when pigs were pre-treated with DDAVP, with or without αGPIb Fab treatment. Pulmonary vascular resistance rise was not significantly attenuated in any group, and was associated with residual thromboxane and histamine elaboration.

CONCLUSIONS

The GPIb-VWF and GPIIb/IIIa axes play important roles in platelet sequestration and coagulation cascade activation during GalTKO.hCD46 lung xenograft injury. GPIb blockade significantly reduces platelet activation and delays platelet sequestration in this xenolung rejection model, an effect amplified by adding αGPIIb/IIIa blockade or depletion of VWF from pig lung.

Antithrombotic drugs: pharmacology and implications for dental practice

Appropriate preoperative assessment of the dental patient should always include an analysis of the patient's medications. This article reviews the actions and indications for the various categories of antithrombotic medications and considers actual risks for postoperative bleeding and potential interactions with drugs the dental provider might administer or prescribe.

Does Dual Antiplatelet Therapy Affect Blood Loss and Transfusion Requirements in Robotic-Assisted Coronary Artery Surgery?

Objective

Patients who present for coronary surgery often receive preoperative dual antiplatelet therapy with aspirin and a thienopyridine derivative (clopidogrel or prasugrel), especially after a recent acute coronary syndrome. Studies have shown that patients on aspirin and clopidogrel are at increased risk for perioperative bleeding and related events. We sought to examine the impact of dual antiplatelet therapy on bleeding and transfusion requirements in patients undergoing robotic-assisted minimally invasive coronary artery bypass grafting.

Methods

From January 2010 to November 2011, a total of 110 patients underwent robotic-assisted off-pump coronary surgery at our institution. All patients underwent robotic-assisted harvest of the left internal mammary artery from the chest wall. Some patients then underwent direct coronary anastomosis to the left anterior descending coronary artery via a left minithoracotomy, whereas others had a complete robotic endoscopic procedure within the closed chest. The patients were divided into two groups for outcome analysis on the basis of preoperative antiplatelet therapy: group 1 (either aspirin alone or no antiplatelet agents at all; n = 53) and group 2 (aspirin plus clopidogrel or prasugrel; n = 57).

Results

Perioperative chest tube drainage was not significantly different between the patient groups, irrespective of the preoperative antiplatelet agents used. Transfusion requirements and other morbidities were also similar in both groups of patients.

Conclusions

Preoperative dual antiplatelet therapy does not result in significantly increased bleeding or perioperative transfusion requirements. If clinically indicated, it is reasonable to continue preoperative combination antiplatelet therapy in patients undergoing robotic-assisted coronary surgery.