Aspirin response: Differences in serum thromboxane B2 levels between clinical studies

Abstract

Serum thromboxane B2 (TxB2) is a specific marker of platelet inhibition by aspirin. Yet, TxB2 levels differ by up to 10-fold between some aspirin-treated patient cohorts. This study aimed to identify factors responsible for differences in serum TxB2 between cohorts in the ADRIE study (n = 657) and the BOSTON study (n = 678) of aspirin-treated cardiovascular patients originally tested with different ELISA assays. TxB2 levels were assessed in representative subgroups of the two cohorts (34 samples in BOSTON and 39 in ADRIE) by both ELISAs, as well as liquid chromatography and tandem mass spectroscopy (MS). A multivariate analysis was performed on the whole cohort database to identify determinants of the difference of TxB2 levels between cohorts. There was no systematic bias between the original ELISA TxB2 values and the MS values and the median difference was small, 0.12 ng/ml, thus not explaining the difference between median TxB2 levels in the two study populations (7 and 0.6 ng/ml in the ADRIE and BOSTON studies, respectively). In the combined dataset of the ADRIE and BOSTON cohorts (n = 1342), body mass index, age, gender, aspirin dose, time from aspirin intake to blood draw, NSAID intake, platelet count and C-reactive protein were significantly associated with TxB2 levels. After adjustment for patient characteristics, the difference between cohorts did not decrease. Unexplained differences in serum TxB2 levels in different populations of aspirin-treated cardiovascular patients suggest that further studies are needed to confirm the role of serum TxB2 level as a prognostic factor or rather as a marker of therapeutic observance.

Patient-independent variables affecting the assessment of aspirin responsiveness by serum thromboxane measurement

“…A statistically-significant difference, albeit minimal (~6 %), is already observed after a delay of 5 min, while beyond 10 min, sTXB 2 values decay exponentially, rather than linearly, as shown in ▶ Figure 1. This pre-analytical bias seems quite relevant and is independent of the sensitivity and specificity of the analytical assay used to measure sTXB 2 . Our data showing a good agreement between our EIA and LC/MS-MS determinations (▶ Figure 2) are consistent with a previous similar comparison between an immunoenzymatic assay different from the one we used which was also compared to LC/MS-MS (15).…”

“…In fact, a simulated delay in starting 37 °C incubation, reduced the relative percentage of aspirin 'non-responders' by 22 % to 52 %, depending on the response threshold (▶ Figure 3). This might have contributed to some large discrepancies of sTXB 2 observed among different studies (15), as well as to different clinical characteristics of poorly-responsive populations (11,14).…”

“…Moreover, repeated measurements of sTXB 2 during the 24-hour (h) dosing interval have characterised some of the determinants of reduced aspirin responsiveness in selected clinical settings, such as type 2 diabetes (12) and essential thrombocythemia (13). However, a recent comparison of sTXB 2 levels in two large cohorts of aspirin-treated patients (11,14) showed up to 10-fold difference in median sTXB 2 levels between the two study populations (7 and 0.6 ng/ml in the ADRIE (14) and BOSTON (11) studies, respectively) that could not be explained by patient characteristics or analytical biases (15). However, the time interval from blood sampling to 37 °C incubation was not recorded in either study (15).…”

The Aspirin Regimens in Essential Thrombocythemia (ARES) phase II randomized trial design: Implementation of the serum thromboxane B2 assay as an evaluation tool of different aspirin dosing regimens in the clinical setting

“…However, a reproducible implementation of this procedure in multicenter studies might face practical hurdles, such as logistic delays between blood withdrawal from patients and access to a thermostatic bath, as well as the lack of appreciation of the time- and temperature-dependence of TXB 2 production during blood clotting. Consistent with this expectation, a comparison of serum TXB 2 values in two large, multicenter cohorts of aspirin-treated patients 45 , 46 showed up to 10-fold difference in median TXB 2 levels (7 and 0.6 ng/ml in the ADRIE 46 and BOSTON 45 studies, respectively) that could not be explained by patient characteristics or analytical biases 47 . Two recent in vitro studies showed that even a minor delay in starting 37 °C incubation can time-dependently underestimate serum TXB 2 levels 17 , 48 , and thus potentially account for variable aspirin responsiveness across studies and centers.…”

Regulation of inflammation by lipid mediators in oral diseases

“…Similarly, serum thromboxane levels are an indicator of platelet inhibition by aspirin and can thus be used for epidemiological studies on the effects of aspirin (Reny et al , ; Zantek et al , ). However, measurement methods for serum thromboxane need to be standardized to produce consistent results across studies (Brun et al , ).…”