In vitro aspirin resistance detected by PFA‐100^TM closure time: pivotal role of plasma von Willebrand factor

Abstract

SummaryThe in vitro closure time (CT), determined by the Platelet Function Analyzer (PFA-100 TM ), is used to monitor patients treated with aspirin. A relatively high percentage of in vitro aspirin resistance was reported despite an adequate inhibition of platelet response to arachidonic acid and we investigated whether high plasma levels of von Willebrand factor ristocetin cofactor activity (vWF:RCo) may contribute to this profile. Platelet aggregation test, CT [collagen adrenaline (CEPI-CT) and collagen adenosine 5¢-diphosphate (ADP) (CADP-CT)], and vWF:RCo levels were evaluated in 55 consecutive patients receiving aspirin (75-250 mg/d) versus 32 untreated control subjects. All the aspirin-treated patients showed platelet aggregation responses that reflected the aspirin intake. However, CT data analysis enabled aspirin good-responder (GR) and aspirin bad-responder (BR) patients to be identified. All GR group subjects (n ¼ 27), had a CEPI-CT and a CADP-CT longer than 300 s and 96 s respectively. The BR group (n ¼ 28) had CEPI-CT values below 200 s and all CADP-CT were in the normal range (77 ± 19 s). Interestingly, the BR plasma vWF:RCo levels were significantly higher (159 ± 43%) than those of the GR group (121 ± 34%) (P < 0AE01), which were similar to control values (114 ± 31%). A negative correlation between vWF:RCo and CT values was established. We demonstrate that in vitro aspirin-resistance, revealed by PFA-100 TM CT prolongation failure, is correlated to increased plasmatic vWF:RCo levels, reinforcing its particular importance in PFA-100 TM cartridges performance.

Aspirin and Clopidogrel

“…As a matter of fact, Chakroun et al recently showed that high plasma VWF levels are the main determinant of short PFA-100 closure time in patients with cardiovascular disease on aspirin treatment, 61 and Watala et al demonstrated that VWF interaction with GPIb and GPIIb/IIIa is the major determinant of PFA-100 closure time, whereas other platelet receptors and mechanisms leading to platelet aggregation are of minor significance. 63 These findings explain the relatively high prevalence of short PFA-100 closure time in patients on aspirin treatment for cardiovascular or cerebrovascular disease, 42,43,[57][58][59][60][61][62] because these patients tend to have higher than normal levels of plasma VWF. Therefore, because aspirin does not inhibit the major determinants of the PFA-100 closure time, it appears that the PFA-100 system is not an adequate method to measure platelet inhibition by aspirin.…”

“…This could easily account for the high percentage of subjects with short closure time despite being on aspirin treatment. 42,43,[57][58][59][60][61][62] Because the PFA-100 system studies platelet function under flow conditions that are characterized by high shear, plasma VWF is a major determinant of closure time. As a matter of fact, Chakroun et al recently showed that high plasma VWF levels are the main determinant of short PFA-100 closure time in patients with cardiovascular disease on aspirin treatment, 61 and Watala et al demonstrated that VWF interaction with GPIb and GPIIb/IIIa is the major determinant of PFA-100 closure time, whereas other platelet receptors and mechanisms leading to platelet aggregation are of minor significance.…”

“…42,43,[57][58][59][60][61][62] Because the PFA-100 system studies platelet function under flow conditions that are characterized by high shear, plasma VWF is a major determinant of closure time. As a matter of fact, Chakroun et al recently showed that high plasma VWF levels are the main determinant of short PFA-100 closure time in patients with cardiovascular disease on aspirin treatment, 61 and Watala et al demonstrated that VWF interaction with GPIb and GPIIb/IIIa is the major determinant of PFA-100 closure time, whereas other platelet receptors and mechanisms leading to platelet aggregation are of minor significance. 63 These findings explain the relatively high prevalence of short PFA-100 closure time in patients on aspirin treatment for cardiovascular or cerebrovascular disease, 42,43,[57][58][59][60][61][62] because these patients tend to have higher than normal levels of plasma VWF.…”

“…The mechanisms responsible for insufficient platelet function inhibition during aspirin therapy should be looked for among the several aforementioned variables that affect the platelet function tests that have been used: increased sensitivity to ADP-induced GPIIb/IIIa activation, 71 increased responsiveness to collagen, 47 high plasma levels of VWF, 61 GPIIb/IIIa polymorphisms, 72 among others. In addition, the role of a nonenzymatic, oxidation-dependent pathway for the synthesis of the arachidonic acid derivatives isoprostanes, which exhibit potent proaggergatory activity, should also be considered.…”

Platelet functional implications of glycoprotein Ibα polymorphisms in African Americans

“…One of the drawbacks is the use of PFA-100 TM testing to assess thrombotic risk because of the fact that it is particularly sensitive to vWF levels [29] and functional testing may be altered if vWF levels are different in the patients studied. Other methods that may provide additional information include ex vivo reperfusion studies, receptor density measurements, and ristocetin induced platelet aggregation however in a previous study, ristocetin induced platelet agglutination was not affected by the HPA-2b polymorphism [7].…”