Oleuropein Reduces Prdx1 Expression, Cell Proliferation and Viability in K562 Human Leukemia Cells

Oleuropein is one of the two main phenolic compounds derived from olive leaves.Numerous studies have found that the polyphenols contained in olive leaves possess strong antioxidant properties, and increase apoptosis in many types of cancer cells, suggesting its possible efficacy as an anti-cancer treatment.The purpose of this study was to examine the effects of oleuropein extract on cell growth and viability of the K562 human leukemia cell line.It was first demonstrated that cells treated with 200 or 400 μg/mL oleuropein exhibited a significant reduction in cell number and viability after four days, as compared to ethanol-treated controls.Cells treated with 200 μg/mL oleuropein showed approximately 90% reduction in cell density and viability after four days of treatment, while the 400 μg/mL concentration resulted in 100% toxicity by the fourth day.It was also found that a two-fold elevation in LDH release within 24 hours of treatment with 200 μg/mL oleuropein, confirming cytotoxicity.Examination of caspase-1 activity revealed an increase in apoptosis within 24 hours.To begin to explore a mechanism of action, we examined the effect of oleuropein on expression of the Peroxiredoxin (Prdx) family of antioxidant proteins.A concentration of 200 μg/mL oleuropein reduced Prdx1 expression by about 50% after eight and twenty-four hours.This study reveals new data on the specific effects of oleuropein on K562 cells, and the regulation of Prdx1 as a possible mechanism of action.Together with previous reports, this research provides further insight into our understanding of natural products as anti-cancer agents.