Abstract WP252: Tamoxifen Treatment Worsens Astrocyte Activation And Mitochondrial Stress From Oxygen Glucose Deprivation

Abstract

Introduction: Tamoxifen (TAM), a selective estrogen receptor modifier, is a first-line treatment option for hormone receptor positive breast cancer. TAM inhibits the downstream estrogen receptor signaling in tumor cells. Stroke risk is increased in women with low estrogen levels, such as early-onset menopause, and doubles in women after the age of 55, which corresponds with the average age of menopause. Women with breast cancer who were treated with tamoxifen had an increased risk for ischemic stroke (82%). Since stroke severity is associated with increased blood brain barrier (BBB) damage, we investigated the effects of tamoxifen on activation and mitochondrial stress in astrocytes, which is a cellular component of the BBB. Methods: Cultured female human astrocytes were treated with tamoxifen (1uM), 17ß-estradiol (10nM), or vehicle (DMSO) for 24 hours. Cells were separated into two groups: normoxic (21% O2, 25mM glucose) or oxygen and glucose deprivation (OGD) conditions 6 hours before analysis. ROS production was measured using the Cellular ROS Assay Kit (Red) and aquaporin-4 levels were visualized via immunocytochemistry. Mitochondrial function was assessed by using a Seahorse XFe96 Analyzer. Results: Tamoxifen treatment increased Aquaporin-4 protein levels (p <0.0001) in cultured astrocytes after OGD compared to both vehicle (DMSO) and 17ß-estradiol treatment. While there was no significant effect, tamoxifen treated cells showed a trend toward (p =0.0732) increased ROS production after OGD compared to vehicle. Additionally, tamoxifen reduced oxygen consumption rate (p =0.0197) and basal respiration under normoxic conditions in astrocytes when compared with DMSO or 17ß-estradiol treatment. Conclusions: Tamoxifen treatment altered the expression of a water channel protein and decreased the ability to respond to oxidative stress in astrocytes. Aquaporin-4, when localized to the astrocytic end feet, facilitates edema after stroke, and ischemic stroke by definition puts brain tissue under oxidative stress. Our findings suggest tamoxifen may increase edema, which is known to impair stroke recovery. These data suggest a mechanism by which breast cancer treatment may increase the risk for severe ischemic stroke. Supported by RFAG042189 to FS