Abstract 3513: Induction of Apoptosis in Endothelial Progenitor Cells by the Adipokine Resistin

Abstract

Introduction: The risk for atherosclerosis is higher in patients with significant obesity and is partly mediated by higher circulating levels of detrimental adipokines released by the adipose tissue. One such adipokine is resistin, which increases endothelial dysfunction and inflammation. Little is known about its effect on endothelial progenitor cells (EPCs), which participate in endothelial repair and angiogenesis. We therefore studied the effects of resistin on apoptosis and oxidative stress in EPCs. Methods: Human EPCs were obtained from umbilical cord blood by culturing mononuclear cells and identifying highly proliferative endothelial colonies. Mature human aortic endothelial cells (HAECs) were obtained from Cambrex (Baltimore, MD). Cells were exposed to varying doses of resistin. Apoptosis was measured by caspase-3 activation using the EnzCheck Caspase-3 Assay Kit (Molecular Probes, OR). Since oxidative stress is a pro-apoptotic pathway, we quantified oxidative stress using the fluorescent dye Dichlorofluorescein. Values for apoptosis and oxidative stress are given as relative fluorescence units. Results: Even a low dose of resistin (10 ng/ml) induced apoptosis in EPCs (Baseline vs 10 ng/ml: 977 ± 100 vs 1112 ± 129, p=0.03). However, at 100 ng/ml resistin the effect was more pronounced (1337 ± 92, p=0.02). Interestingly, this pro-apoptotic effect of resistin could not be observed in mature HAECs (Baseline: 1160 ± 277 vs. Resistin 10ng/ml: 964 ± 160), even at 100 ng/ml (1168 ± 138). Resistin treatment also increased oxidative stress in EPCs, and the peak effect occurred at the dose of 50 ng/ml (Baseline: 2053 ± 237 vs. Resistin 50 ng/ml: 4261 ± 1262). Similar to the apoptosis resilience, mature endothelial cells did not increase oxidative stress with resistin. Conclusion: Circulating levels of resistin can range from 10 ng/ml to 25 ng/ml, in lean subjects while levels found in obesity range from 40 –100 ng/ml. Our data shows that resistin in this physiologic and pathophysiologic range can affect the survival EPCs. Progenitor cells also appear to be more vulnerable to resistin that mature cells. We believe these findings will lead to new insight into the detrimental effects of resistin on the vasculature and develop vasculoprotective therapies.