Platelet aggregation unchanged by lipoprotein-associated phospholipase A₂ inhibition: results from an in vitro study and two randomized phase I trials

Bonnie C Shaddinger, Yanmei Xu, James H Roger, Colin H Macphee, Malcolm Handel, Charlotte A Baidoo, Mindy Magee, John J Lepore, Dennis L Sprecher, Bonnie C Shaddinger, Yanmei Xu, James H Roger, Colin H Macphee, Malcolm Handel, Charlotte A Baidoo, Mindy Magee, John J Lepore, Dennis L Sprecher

Abstract

Background: We explored the theorized upregulation of platelet-activating factor (PAF)- mediated biologic responses following lipoprotein-associated phospholipase A2 (Lp-PLA2) inhibition using human platelet aggregation studies in an in vitro experiment and in 2 clinical trials.

Methods and results: Full platelet aggregation concentration response curves were generated in vitro to several platelet agonists in human plasma samples pretreated with rilapladib (selective Lp-PLA2 inhibitor) or vehicle. This was followed by a randomized, double-blind crossover study in healthy adult men (n = 26) employing a single-agonist dose assay of platelet aggregation, after treatment of subjects with 250 mg oral rilapladib or placebo once daily for 14 days. This study was followed by a second randomized, double-blind parallel-group trial in healthy adult men (n = 58) also treated with 250 mg oral rilapladib or placebo once daily for 14 days using a full range of 10 collagen concentrations (0-10 µg/ml) for characterizing EC50 values for platelet aggregation for each subject. Both clinical studies were conducted at the GlaxoSmithKline Medicines Research Unit in the Prince of Wales Hospital, Sydney, Australia. EC50 values derived from multiple agonist concentrations were compared and no pro-aggregant signals were observed during exposure to rilapladib in any of these platelet studies, despite Lp-PLA2 inhibition exceeding 90%. An increase in collagen-mediated aggregation was observed 3 weeks post drug termination in the crossover study (15.4% vs baseline; 95% confidence interval [CI], 3.9-27.0), which was not observed during the treatment phase and was not observed in the parallel-group study employing a more robust EC50 examination.

Conclusions: Lp-PLA2 inhibition does not enhance platelet aggregation.

Trial registration: 1) Study 1: ClinicalTrials.gov NCT01745458 2) Study 2: ClinicalTrials.gov NCT00387257.

Conflict of interest statement

Competing Interests: BCS, YX, JHR, CHM, CAB, MM, JJL, and DLS disclose that they are full-time employees of GlaxoSmithKline. MH was a full-time employee of GlaxoSmithKline at the time this study was completed and is currently employed by Janssen-Cilag Pty Ltd. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

Figures

Figure 1. Flow diagram depicting (A) single…
Figure 1. Flow diagram depicting (A) single agonist-dose and (B) Emax model.
Figure 2. In vitro platelet aggregation results…
Figure 2. In vitro platelet aggregation results of (A) ADP, (B) collagen, and (C) PAF. ADP, adenosine diphosphate; PAF, platelet-activating factor.
Figure 3. Concentration response curves for collagen-induced…
Figure 3. Concentration response curves for collagen-induced platelet aggregation 14 days post-dosing (treatment A = rilapladib, treatment B = placebo).

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Source: PubMed

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