Abstract WMP116: Thromboembolism in Atrial Fibrillation: Relationship to Leukocyte Gene Expression

Background: Atrial fibrillation (AF) is an important cause of stroke, for which anticoagulation provides substantial benefit. However, not all patients with AF will have a stroke. There remains uncertainty regarding factors that promote thromboembolism and stroke in patients with AF. In this study we examined differences in blood cell gene expression unique to AF in acute stroke to better understand factors important to atrial fibrillation thromboembolism in human stroke.

Methods: Gene expression in blood was compared in acute stroke patients with AF to non-AF stroke and to controls without stroke. Blood was collected in PAXgene tubes, and leukocyte/platelet gene expression was measured by Affymetrix microarray. Differentially expressed genes were identified using ANOVA adjusted for age, sex and batch.

Results: In the 184 patients studied, 40 were acute strokes with AF, 143 had non-AF acute stroke, and 116 were non-stroke controls. There were 43 genes unique to AF in patients with stroke, and 69 genes associated AF that were shared between AF stroke and controls (FDR<0.05, fold change>|1.5|). Functional analysis indicate acute stroke AF genes are associated with changes in the hematological system including blood cell rheology and leukocyte activation. In contrast non-stroke AF genes are associated cardiac hypertrophy and blood vessel injury.

Conclusions: AF has differences in blood cell gene expression in acute stroke that may relate to risk of thromboembolism. Acute stroke patients with AF display changes in blood cell rheology and leukocyte activation; whereas non-stroke AF patients have changes in cardiac hypertrophy and vascular injury. These differences are important to understanding blood cell contribution to thrombus formation and stroke risk in patients with AF. Further study is required to assess the relationship of these gene changes to stroke risk and response to anticoagulation in patients with AF.

Abstract WP535: Differential Immune Activation in Patients With Acute Ischemic Stroke and Admission Blood Pressure Greater Than 185/110 mm Hg

Background: A blood pressure > 185/110 mm Hg is associated with increased risk of tPA related hemorrhagic transformation (HT). Stroke guidelines recommend blood pressure >185/110 mm Hg be lowered before tPA treatment. How high blood pressure increases blood-brain barrier disruption and risk of hemorrhagic transformation remains poorly understood. We evaluated peripheral leukocyte activation in stroke patients in relation to elevated blood pressure and their potential contribution to blood-brain barrier disruption.

Methods: Blood samples from acute ischemic stroke patients were collected within 3 hours of stroke onset, prior to treatment with thrombolytic. Patients were grouped by BP >185/110 mm Hg (n=19) and BP <185/110 mm Hg (n=46). Total blood RNA was assessed by whole genome microarray and differential gene expression analyzed by ANCOVA. Functional analysis of identified genes was performed. Correlation analysis was conducted to identify genes correlated with systolic blood pressure.

Results: Strokes with admission BP >185/110 mm Hg had 231 genes differentially expressed compared to strokes with BP <185/110 mm Hg (p <0.05, fold change ≥|1.2|). Key genes and pathways associated with BP>185/110 mm Hg included downregulation of caveolin-1 and upregulation of matrix metalloproteinases (MMPs). Several of these genes, including MMP-21, linearly correlated with increasing systolic blood pressure (r=0.25, p = 0.02).

Conclusions: A blood pressure >185/110 mm Hg is associated with differential immune activation in patients with acute ischemic stroke, including caveolin-1 and matrix metalloproteinases. These differences may contribute to blood-brain barrier disruption and risk of hemorrhagic transformation in acute stroke patients with blood pressure >185/110 mm Hg. Whether modulating immune activation could reduce blood-brain barrier disruption and risk of HT requires further study.