Abstract 345: Syzygium Jambos: A Potential Therapeutic Approach to Treat the Vascular and Hematological Complications of Sickle Cell Disease

Abstract

Protein disulfide isomerase (PDI) is an oxidoreductase that mediates thiol/disulfide interchange reactions and has been reported to play a critical role in thrombus formation following vascular injury. PDI has also been shown to regulate leukocyte adherence to the endothelium and nitric oxide delivery. We recently reported that PDI is present at high levels and regulates erythrocyte homeostasis and Gardos Channel activity in humans with Sickle Cell Disease (SCD). Thus, PDI inhibition has been proposed as a promising therapeutic approach to ameliorate both the vascular and hematological complications of SCD. Syzygium jambos (S. jambos) is purported to have anti-inflammatory and antioxidant properties. However, the regulation of PDI activity by S. jambos has not been studied. We studied in vitro PDI activity in the presence of the S. jambos aqueous leaf extract using a PDI insulin turbidity assay. We observed significant reductions in PDI activity at 25 μg/mL (66.0 ± 9.7%, p<0.01, n=3), 50 μg/mL (83.3 ± 6.0%, p<0.01, n=3), and 100 μg/mL (91.6 ± 11.5%, p<0.01, n=3). S. jambos extract showed a dose-dependent anti-PDI activity with an IC50 of 14.40 μg/mL. We then tested the effects of S. jambos on endothelin-1 (ET-1)-stimulated PDI activity in human endothelial cells. Using a fluorescence based PDI activity assay, we observed that ET-1 increased PDI activity (1.7 ± 0.7 folds, n=3) that was dose-dependently blocked by S. jambos extract. In addition, we observed that ET-1 stimulated ex vivo human polymorphic nucleated (PMN) leukocyte migration toward the endothelial cells that was likewise dose-dependently blocked by S. jambos extract. (p<0.01, n=3). We also quantified the levels of reactive oxygen species (ROS) production in ET-1 treated endothelial cells. ET-1 stimulation significantly increased ROS levels [3 fold] when compared to vehicle treatment (p<0.05, n=3). S. jambos extract reduced ET-1 stimulated ROS to baseline levels (p<0.05, n=3). Our results suggest that S. Jambos may represent a novel pharmacological approach to treat complications of SCD.