OBJECTIVE: Endothelial progenitor cells (EPCs) have the ability to differentiate into mature endothelial cells. Inhibition of EPC proliferation and migration may be a new method for anti-tumor therapy. Medroxyproges-terone acetate (MPA) may act on tumor angio-genesis by impacting biological functions of EPCs. The aim of this work was to study the effect of different concentrations of MPA combined with 17β β-estradiol (17β β-E2) on proliferation , migration, and apoptosis of EPCs in vitro.

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... ALS AND METHODS: Proliferation tests (MTT analysis) and migration assay of EPCs, isolated from bone marrow of canine, were performed to detect their response to different concentrations of MPA combined with 17β β-E2 (1 × 10-8 mol/L). The growth curves were drawn every 24 h for 7 consecutive days. The cell cycle and apopto-sis of EPCs were analyzed by flow cytometry. RESULTS: 17β β-E2 (1 × 10-8 mol/L) increased EPC proliferation, while lower concentration of MPA (≤ 10-5 mol/L) partially inhibited it. The higher concentration of MPA (≥ 10-4 mol/L) combined with 17β β-E2 had a significant inhibitory effect on EPC growth, arresting it in the S phase. It also increased the apoptosis rate and damaged the migration ability of EPCs. CONCLUSIONS: Low concentration of MPA partially inhibited the function of 17β β-E2 that promotes the proliferation of EPCs. However, high concentration of MPA combined with 17β β-E2 inhibited a variety of biological functions of EPCs. So, the MPA has a bidirectional effect combined with 17β β-E2 on the cell biology of EPCs.