Curcumin regulation of glioma cell proliferation and apoptosis through Wnt/β-catenin signaling pathway: an experimental study

Objective To investigate the effects of curcumin on glioma cell proliferation and apoptosis through Wnt/β-catenin signaling pathway. Methods The research objects were the human glioblastoma U251 cell lines. The experiment was divided into either a blank control group or a curcumin experiment group (the experiment concentrations were 10 μmol/L and 20 μmol/L respectively). The cell toxicity test was used to study cellular toxic effect of curcumin on U251 glioma. Four methyl thiazolyl tetrazolium (MTT) assay was used to observe the cell proliferative capacity; the caspase-3 activity assay and flow cytometry (FCM) test were used to detect cell apoptosis; flow cytometry was used detect the cell cycle; real-time quantitative PCR, Western-blotting, and immunofluorescence assay were used to detect the expression levels of intracellular β-catenin and c-myc. The luciferase assay was used to detect the changes of Wnt/β-catenin signaling pathway activity after the effects of curcumin. Results With the increased effect concentration of curcumin, the cytotoxicity of U251 glioma cells enhanced. In the curcumin experimental group, when the concentrations were 5, 10, 20, and 40 μmol/L, the cells activities were 88.55%±2.35%, 62.78%±3.35%, 35.17%±2.05%, and 7.47%±1.92%, respectively (P<0.05), and the effect of proliferation inhibition enhanced obviously. IC50 of the measured curcumin effect for 24 h was 16.32 μmol/L, therefore, the concentrations of 10 μmol/L and 20 μmol/L in the curcumin experimental group were chosen; the relative activities of caspase-3 in the experimental group (10 μmol/L and 20 μmol/L) were 3.64%±1.49% and 5.41%±0.36% respectively. Compared with the control group 0.91%±0.62%, the activities enhanced significantly (P<0.05). After flow cytometry was used to detect the curcumin effects for 48 h, the U87 apoptotic rates of the experimental group were 14.7%±2.21% and 35.6%±1.37% respectively. Compared with the apoptotic rate of the control group (0.5%±0.67%), there was significant difference (P<0.05). The detection of curcumin with the flow cytometry could block the cell cycle to the G2/M phase. The G2/M phases of the control group and the curcumin experiment group (10 μmol/L and 20 μmol/L) were 7.52%±3.84%, 16.28%±2.73%, and 25.47%±5.61%, respctively P<0.05); After curcumin acting on gliomas, the mRNA level of β-catenin was decreased. The test results of fluorescence quantitative PCR were 93.87%±5.73%, 68.83%±7.67%, and 47.46%±8.52%, respectively (P<0.05); and there were significant differences. Westen blotting showed that the expression levels of β-catenin and c-myc protein were decreased. Immunofluorescence assay found that curcumin suppressed β-catenin into the cell nuclei and reduced the formation of its compound at the same time. Luciferase experiment showed that the activity of Wnt/β-catenin signaling pathway was inhibited obviously after curcumin acting on glioma cells (P<0.01). Conclusion Curcumin may inhibit glioma cell proliferation and promote apoptosis by downreglating Wnt/β-catenin signaling pathway. Key words: Glioma; Curcumin; Wnt/β-catenin signaling pathway; Proliferation; Apoptosis