Abstract Body: Introduction: Acute promyelocytic leukemia (APL) is associated with intracranial hemorrhage (ICH). Patients with APL have a dysregulated hemostatic system. However, mechanisms leading to local pathological changes in the brain that contribute to ICH have not been elucidated.
Hypothesis: We hypothesize that APL cell-derived neutrophil elastase (NE) disrupts the brain vascular endothelium leading to increased vascular permeability and ICH in APL.
Methods: Plasma samples were collected from 25 consecutive patients with APL, 9 (36%) of whom developed ICH. There were 13 males and 17 non-Hispanic White individuals with APL. The median age at diagnosis was 46 (range,19-83). Unbiased plasma proteomic analysis was performed using mass spectrometry. The level of plasma NE in human and mouse plasma was measured by ELISA. Brain vascular permeability was evaluated using Evans blue injection, edema was determined using magnetic resonance imaging (MRI), and brain vascular endothelium structure was examined using transmission electron microscopy (TEM) in APL mice. Sivelestat was used to inhibit NE in APL mice.
Results: Compared to those without ICH, patients who developed ICH had significantly higher plasma NE levels by mass spectrometry (Fig. 1A; 1.5-fold increase; P < 0.05). This increase in NE was confirmed by ELISA (Fig. 1B). In our mouse model, we observed spontaneous ICH in 4 of 15 (27%) mice. APL mice exhibited significantly increased brain vascular permeability compared with controls. Brain MRI revealed no differences in T1-weighted images, which enhances fat and hemoglobin (early bleeding), between control and APL mice. However, increased fluid signals were observed on T2-weighted images in 2 of 3 APL mice, suggesting brain edema (Fig.2). We also observed abnormal brain blood vessels and extravascular fibrin deposition in 2 of 4 APL mice. Plasma NE levels increased in APL mice in a time-dependent manner. Treatment of APL mice with NE inhibitor sivelestat significantly reduced brain vascular permeability.
Conclusions: We identified NE as a novel biomarker associated with ICH in patients with APL. NE was also increased in APL mice. These mice had increased brain vascular permeability that was reduced by inhibition of NE. Our data revealed a new mechanism of increased brain vascular permeability in APL.