Low-dose curcumin treatment increases OEC proliferation.

<p>(A–D). Increased proliferation of OECs was observed after treatment with 0.5 µM curcumin (B) or 0.5 µM curcumin combined with G5 supplement (D); cells appeared to have longer processes and formed a net-like structure. Cells treated with higher concentrations of curcumin (C) displayed a more flattened morphology (arrows) and the number of cells was lower compared to the control (A). Scale bar = 100 µm in A–D. (E–F) Quantification of the proliferation rate in MTS assays. (E) After two days in culture 0.5 µM curcumin with or without G5, and G5 supplement alone had significantly higher proliferation compared to control treatment. Higher doses of curcumin (10, 20 µM) showed a significant decrease in OEC proliferation compared to control treatment p<0.05 (*), p<0.001 (**). After four days in culture, 1 µM curcumin, 0.5 µM curcumin with G5, and G5 supplement alone significantly increased OEC proliferation; whereas 10 µM and 20 µM curcumin decreased proliferation compared to control treatment (F). p<0.05(*), p<0.001(**), one way ANOVA post-hoc Tukey test. (G) ERK (PD98059) and p38 kinase (SB203580) inhibitors blocked curcumin-induced proliferation of OECs p<0.05 (*); p<0.01 (**) compared with control; p<0.01 (##) compared with cultures treated with curcumin alone; (n = 30–36 cells per treatment). Values are expressed as mean ± s.e. of triplicates. Low-dose curcumin induced transient-activation of ERK and p38 MAP kinases in OEC cells (H). Whole cell extracts (40 µg for p–p38 and 20 µg for p-ERKs) from OECs treated with and without curcumin (0.5 µM) for the indicated time periods were subjected to western blot analysis using antibodies against phospo-ERK1/2 and phospo-p38. Data represent the mean of three independent experiments ± s.e. Statistical significance was determined by Student’s t-test p<0.05 (*). Levels of β-tubulin were used as loading control.