D-4F, an apolipoprotein A-I mimetic, suppresses IL-4 induced macrophage alternative activation and pro-fibrotic TGF-β1 expression.

We reported that D-4F, an apolipoprotein A-I (Apo A-I) mimetic polypeptide with 18 d-amino acids, suppressed IL-4 induced macrophage alternative activation and TGF-β1 expression in phorbol 12-myristate 13-acetate (PMA) treated human acute monocytic leukemia cells (THP-1). Macrophage alternative activation, TGF-β1 and epithelial-mesenchymal transition (EMT) are intensively involved in pulmonary fibrosis. Recent studies demonstrated that Apo A-I resolved established pulmonary fibrotic nodules, and D-4F inhibited TGF-β1 induced EMT in alveolar cells. Therefore, this study evaluated the effects of D-4F on IL-4 induced macrophage alternative activation and TGF-β1 expression. THP-1 cells were simulated with PMA (100 ng/mL) for 48 h and treated with medium control, IL-4 (20 ng/mL) alone, or IL-4 (20 ng/mL) in the presence of D-4F (1, 5, and 10 μg/mL) for 24 and 48 h. Flow cytometry, RT-PCR and ELISA evaluations were performed to investigate the subsequent effects of D-4F. Compared to stimulation with IL-4 alone, 1, 5, and 10 μg/mL of D-4F reduced alternative activation by 45.38%, 59.98%, and 60.10%, increased TNF-α mRNA levels by 8%, 11%, and 16% and decreased TGF-β1 mRNA levels by 21%, 37%, and 39%, respectively (all  ≤ 0.05). In addition, TNF-α protein levels increased from 388 pg/mL (IL-4 alone) to 429, 475, and 487 pg/mL (1, 5, and 10 μg/mL D-4F), while TGF-β1 protein levels dropped from 27.01 pg/mL (IL-4 alone) to 19.15, 12.27, and 10.47 pg/mL (1, 5, and 10 μg/mL D-4F). D-4F suppressed IL-4 induced macrophage alternative activation and pro-fibrotic TGF-β1 expression.