Platelet function normalization after a prasugrel loading-dose: time-dependent effect of platelet supplementation

BACKGROUND

Hemostatic benefits of platelet transfusions in thienopyridine-treated acute coronary syndrome (ACS) patients may be compromised by residual metabolite in circulation.

OBJECTIVES

To estimate the earliest time after a prasugrel loading-dose when added platelets are no longer inhibited by prasugrel's active metabolite.

METHODS

Baseline platelet reactivity of healthy subjects (n=25, 30 ± 5 years, 68% male) on ASA 325 mg was tested using maximum platelet aggregation (MPA, ADP 20 μm) and VerifyNow(®) P2Y12 and was followed by a 60 mg prasugrel loading-dose. At 2, 6, 12 and 24 h post-dose, fresh concentrated platelets from untreated donors were added ex-vivo to subjects' blood, raising platelet counts by 0% (control), 40%, 60% and 80%. To estimate the earliest time when prasugrel's active metabolite's inhibitory effect on the added platelets ceases, platelet function in supplemented samples was compared across time-points to identify the time when effect of supplementation on platelet function stabilized (i.e. the increase in platelet reactivity was statistically similar to that at the next time-point).

RESULTS

Supplemented samples showed concentration-dependent increases in platelet reactivity vs. respective controls by both MPA and VerifyNow(®) at all assessment time-points. For each supplementation level, platelet reactivity showed a sharp increase from 2 to 6 h but was stable (P=NS) between 6 and 12 h.

CONCLUSIONS

The earliest measured time when supplemented platelets were not inhibited by circulating active metabolite of prasugrel was 6 h after a prasugrel loading-dose. These findings may have important implications for prasugrel-treated ACS patients requiring platelet transfusions during surgery.

A novel anti-ischemic nitric oxide donor (LA419) reduces thrombogenesis in healthy human subjects

BACKGROUND

Platelet and endothelial production of nitric oxide (NO) is known to be impaired in coronary artery disease patients. Compounds that release NO (e.g. nitrates) have antiplatelet effects, but at supratherapeutic doses with hypotensive side effects.

OBJECTIVES

To investigate the antithrombotic effect on human blood of a novel NO donor (LA419) with known anti-ischemic properties but without hypotensive side effects and to compare with abciximab.

PATIENTS/METHODS

Healthy subjects (n = 8; 32 +/- 3 years) received daily aspirin starting three days prior to the study day. Treatments (LA419 10 and 20 microm, and abciximab 4 microm) were added ex vivo to non-anticoagulated blood, and the antithrombotic properties were assessed by measuring changes in thrombus size from pretreatment baseline in the Badimon perfusion chamber at low and high shear rates. Platelet surface adhesion using a Cone and Platelet Analyzer (CPA) and platelet fibrinogen-receptor activation with flow cytometry were also evaluated.

RESULTS

At low shear rates, LA419 displayed a reduction in thrombus area of 43% +/- 8% (10 microm) and 56% +/- 6% (20 microm), whereas at high shear rates the reductions were 44% +/- 3% (10 microm) and 62% +/- 6% (20 microm). Platelet surface adhesion with the CPA was also reduced. Abciximab exhibited a strong inhibitory effect on thrombus formation, platelet surface adhesion and fibrinogen receptor activation.

CONCLUSIONS

The novel NO donor, LA419, shows a strong antithrombotic effect in human blood, which is comparable to abciximab, especially under high shear rate conditions. Our observations suggest that the availability of an NO donor could prove beneficial in the prevention of thrombotic complications of cardiovascular disease. Further clinical studies are warranted.

Normalization of platelet reactivity in clopidogrel-treated subjects

BACKGROUND

Aspirin (ASA) + clopidogrel are commonly used in acute coronary syndrome (ACS), but persistent antiplatelet effects may complicate surgery.

METHODS AND RESULTS

To study the possibility of normalizing platelet reactivity after ASA + clopidogrel treatment, 11 healthy subjects received a 325-mg ASA + clopidogrel loading dose (300 or 600 mg dependent on study arm), followed by 81 mg of ASA + 75 mg of clopidogrel daily for 2 days. Platelet reactivity was assessed by light transmittance aggregometry (LTA) [challenged by adenosine diphosphate (ADP), arachidonic acid (AA), collagen, and thrombin receptor activating peptide (TRAP)] and flow cytometry for platelet activation by GPIIb/IIIa receptor exposure pretreatment, 4 and 72 h postload. To normalize platelet reactivity, increasing amounts of pooled platelets from five untreated volunteers [volunteers (V)-platelet-rich plasma (PRP)] were added ex vivo to the subject's PRP (S-PRP). At both 4 and 72 h, 40% and 50% V-PRP were needed to overcome platelet disaggregation in the 300 or 600 mg arms, respectively, after ADP challenge; an additional 10% V-PRP fully normalized aggregation. Recovery of function was linear with each incremental increase of V-PRP. ADP-induced GPIIb/IIIa activation showed the same pattern as LTA (r = 0.74). Forty percent V-PRP was required to normalize platelet function to AA, collagen, and TRAP.

CONCLUSION

Our results suggest that the pre-operative transfusion of 10 platelet concentrate units (the equivalent of 40% V-PRP) after a 300-mg clopidogrel loading or 12.5 units (50% V-PRP) after a 600 mg loading may adequately reverse clopidogrel-induced platelet disaggregation to facilitate postoperative hemostasis. An additional 2.5 units fully normalized platelet function. The potential clinical implications of our observations could include shorter hospitalizations and reduced bleeding complications. But these observations should be fully explored in an in vivo clinical setting with clopidogrel-treated patients before and after surgery.

Links between inflammation and thrombogenicity in atherosclerosis

Plaque disruption and subsequent thrombus formation play a critical role in the clinical manifestations of atherothrombosis. Vulnerable lesions are characterized by the existence of core rich in lipid, macrophages and tissue factor (TF). Plaque disruption facilitates the interaction between flowing blood with the inner components (TF) of disrupted atherosclerotic lesions triggering the coagulation cascade. TF, thrombin, platelets, fibrin and inflammatory cells are involved in this process of acute thrombus formation. This pathologic process is significantly accelerated by several "cardiovascular risk factors" such as diabetes, smoking, dyslipemia, etc. We will review on the role of TF, plaque cell apoptosis and blood thrombogenicity acting as a thread of inflammatory and prothrombotic mediators. We will also review the role of activated platelets as source for pro-inflammatory cytokines and enunciation of thrombotic process. Overall, we will try to emphasize the most recent understanding of the concepts involved in the interaction between inflammation and coagulation within the setting of atherothrombotic disease.

The Role of High-Density Lipoprotein Cholesterol in the Prevention and Possible Treatment of Cardiovascular Diseases

Despite significant progress in the management of atherosclerosis and its resultant complications, cardiovascular disease remains the principal cause of death in the world. The National Cholesterol Education Project Adult Treatment Panel III (NCEP ATP III) recognizes low levels of high-density lipoprotein cholesterol (HDL) as a risk factor for coronary heart disease (CHD) and high levels of HDL as a risk-reducing factor; however, the elevation of HDL as a specific therapeutic target for the prevention and treatment of CHD has yet to be accepted on the same level as low-density lipoprotein (LDL)-reducing therapies. Current HDL elevators including nicotinic acid, fibric acid derivatives, peroxisome proliferator activated receptor (PPAR) agonists and statins also affect other lipid constituents which make interpretation of the clinical trials of these drugs difficult in teasing out the independent effect of HDL elevation. Ample laboratory investigation suggests that HDL elevation would reduce atherosclerotic burden through multiple independent mechanisms. In this review, we explore HDL biology, its potential mechanisms in the treatment of atherosclerotic disease, and promising new drugs with HDL-raising activity.

Real time magnetic resonance guided endomyocardial local delivery

OBJECTIVE

To investigate the feasibility of targeting various areas of left ventricle myocardium under real time magnetic resonance (MR) imaging with a customised injection catheter equipped with a miniaturised coil.

DESIGN

A needle injection catheter with a mounted resonant solenoid circuit (coil) at its tip was designed and constructed. A 1.5 T MR scanner with customised real time sequence combined with in-room scan running capabilities was used. With this system, various myocardial areas within the left ventricle were targeted and injected with a gadolinium-diethylenetriaminepentaacetic acid (DTPA) and Indian ink mixture.

RESULTS

Real time sequencing at 10 frames/s allowed clear visualisation of the moving catheter and its transit through the aorta into the ventricle, as well as targeting of all ventricle wall segments without further image enhancement techniques. All injections were visualised by real time MR imaging and verified by gross pathology.

CONCLUSION

The tracking device allowed real time in vivo visualisation of catheters in the aorta and left ventricle as well as precise targeting of myocardial areas. The use of this real time catheter tracking may enable precise and adequate delivery of agents for tissue regeneration.