Early Intravascular Events Are Associated with Development of Acute Respiratory Distress Syndrome. A Substudy of the LIPS-A Clinical Trial

Abstract

Rationale: Acute respiratory distress syndrome (ARDS) is a devastating illness with limited therapeutic options. A better understanding of early biochemical and immunological events in ARDS could inform the development of new preventive and treatment strategies.

Objectives: To determine select peripheral blood lipid mediator and leukocyte responses in patients at risk for ARDS.

Methods: Patients at risk for ARDS were randomized as part of a multicenter, double-blind clinical trial of aspirin versus placebo (the LIPS-A [Lung Injury Prevention Study with Aspirin] trial; NCT01504867). Plasma thromboxane B2 (TXB2), aspirin-triggered lipoxin A4 (15-epi-LXA4, ATL), and peripheral blood leukocyte number and activation were determined on enrollment and after treatment with either aspirin or placebo.

Measurements and main results: Thirty-three of 367 subjects (9.0%) developed ARDS after randomization. Baseline ATL levels, total monocyte counts, intermediate monocyte counts, and monocyte-platelet aggregates were associated with the development of ARDS. Peripheral blood neutrophil count and monocyte-platelet aggregates significantly decreased over time. Of note, nine subjects developed ARDS after randomization yet before study drug initiation, including seven subjects assigned to aspirin treatment. Subjects without ARDS at the time of first dose demonstrated a lower incidence of ARDS with aspirin treatment. Compared with placebo, aspirin significantly decreased TXB2 and increased the ATL/TXB2 ratio.

Conclusions: Biomarkers of intravascular monocyte activation in at-risk patients were associated with development of ARDS. The potential clinical benefit of early aspirin for prevention of ARDS remains uncertain. Together, results of the biochemical and immunological analyses provide a window into the early pathogenesis of human ARDS and represent potential vascular biomarkers of ARDS risk. Clinical trial registered with www.clinicaltrials.gov (NCT01504867).

Keywords: ARDS; monocyte-platelet aggregates; aspirin; lipoxin; thromboxane..

Figures

Figure 1.

Timeline of cohort and acute respiratory distress syndrome (ARDS) incidence. (A) ARDS development compared with time of randomization and first dose of study drug (placebo or loading dose of aspirin) for all subjects with flow cytometry or lipid mediator results. ARDS was adjudicated using modified Berlin criteria (see Methods). The latest of the qualifying criteria defined the time of ARDS development. (B) ARDS incidence after study drug loading dose.

Figure 2.

Baseline plasma aspirin-triggered lipoxin A4 (ATL) and thromboxane B2 (TXB2) levels before the development of acute respiratory distress syndrome (ARDS). The distribution of plasma (A) ATL, (B) TXB2, and (C) ATL/TXB2 at baseline in subjects who developed ARDS more than 12 hours after baseline draw versus those who never developed ARDS is shown. Insets: receiver operating characteristic curves for prediction of ARDS. Area under the curve and 95% confidence interval calculated using the Delong method and the Mann-Whitney test for differences between ARDS and no-ARDS group at baseline are provided. AUC = area under the curve; No-ARDS = did not develop ARDS.

Figure 3.

Baseline whole-blood leukocyte counts and activation before the development of acute respiratory distress syndrome (ARDS). The distribution of (A) neutrophil counts, (B) neutrophil–platelet aggregates, (C) neutrophil CD11b surface expression, (D) monocyte counts, (E) monocyte–platelet aggregates, (F) monocyte CD11b surface expression, (G) intermediate monocyte counts, and (H) intermediate monocyte–platelet aggregates in whole blood of subjects who developed ARDS more than 12 hours after baseline draw versus those who never developed ARDS is shown. Insets: Receiver operating characteristic curve for prediction of ARDS. Area under the curve and 95% confidence interval calculated using the Delong method and the Mann-Whitney test for differences between ARDS and no-ARDS group at baseline are provided. Percent (%) parent in B, E, and H refers to total neutrophils, total monocytes, and intermediate monocytes, respectively. AUC = area under the curve; IntMo = intermediate monocyte; IntMo-PA = intermediate monocyte–platelet aggregates; MFI = mean fluorescence intensity; Mo = monocyte; Mo-PA = monocyte–platelet aggregates; Ne = neutrophil; Ne-PA = neutrophil–platelet aggregates; No-ARDS = did not develop ARDS.

Figure 4.

Aspirin and draw-time effect on plasma aspirin-triggered lipoxin A4 (ATL) and thromboxane B2 (TXB2). Plasma (A) TXB2, (B) ATL, and (C) ATL/TXB2 levels at baseline and after (Day 1 and Day 3) aspirin or placebo are shown. The inset shows linear mixed-effects model results for effect of treatment arm, time, and treatment × time interactions. P values listed below each draw time are for the between-group comparison at that draw based on the model estimates. Error bars for 90% Wald confidence intervals are shown. Units for ATL and TXB2 are ng/ml.

Figure 5.

Whole-blood leukocyte counts and activation. Whole-blood (A) neutrophil count, (B) neutrophil–platelet aggregates, (C) neutrophil CD11b surface expression, (D) monocyte count, (E) monocyte–platelet aggregates, and (F) monocyte CD11b surface expression at baseline and after (Day 1 and Day 3) aspirin or placebo are shown. The inset shows linear mixed-effects model results for effect of treatment arm, time, and treatment × time interactions. P values listed below each draw time are for the between-group comparison at that draw based on the model estimates. Error bars for 90% Wald confidence intervals are shown. Percent (%) parent in B and E refers to total neutrophils and monocytes, respectively. MFI = mean fluorescence intensity; Mo = monocyte; Mo-PA = monocyte–platelet aggregates; Ne = neutrophil; Ne-PA = neutrophil–platelet aggregates.

Figure 6.

Plasma lipid mediators and peripheral blood leukocyte responses correlogram. A Spearman correlation matrix between plasma lipids aspirin-triggered lipoxin A4 (ATL) and thromboxane B2 (TXB2) and whole-blood leukocyte markers in all samples is shown. Under the diagonal list of parameters, Spearman correlation values are shown for each pair of intersecting parameters. Above the diagonal, the correlations are represented as pie charts, with a full pie representing a correlation of +1.0 or −1.0. Color scale (right bar) shows Spearman correlation values >0 as blue and <0 as red. Percent (%) parent refers to total neutrophils (Ne) and monocytes (Mo). MFI = median fluorescence intensity; Mo-PA = monocyte–platelet aggregates; Ne-PA = neutrophil–platelet aggregates.