Curcumin induces human glioma cell apoptosis via alteration of expression of cyclooxygenase-2 and activation of Caspase

Objective To study the mechanism of curcumin inducing U251 human glioma cell apoptosis. Methods U251 glioma cells were treated with 20-100 μmol/L curcumin for 24 h and the growth inhibition rate was measured by methyl thiazol tetrazolium (MTT) method. MTT method was used to measure the effects of Caspase inhibitors on curcumin-induced apoptosis. The mitochondrial membrane potential (MMP) and the apoptosis of glioma cells were investigated by flow cytometer. The glioma cells with apoptosis were observed under an electron microscope. The inhibition of cyclooxygenase-2 (COX-2) protein was observed by confocal microscope. The activity of Caspase-3 was measured by spectrofluorometry. Results The study shows the U251 glioma cells growing can be inhibited by curcumin with different concentration (20-100 μmol/L) and different time (6-24 h). The cell growing inhibition ratio changes from (26.23±3.31)% to (89.02±2.13)% in time-concentration dependence. Statistics analysis shows P=0.007 in this research. The apoptosis of glioma cells induced by curcumin can be observed by flow cytometer. The ratio of apoptosis changes from (16.35±1.72)% to (52.91±2.18)% (P=0.005). Curcumin decreased the MMP. At the same time the protein levels of COX-2 in U251 glioma cells decreased and the activity of Caspase-3 increased significantly. The apoptosis of glioma cells were partially reversed by Caspase inhibitors and the cell growing inhibition ratio with different time (15, 20, 25, 30 h) changes from 85.23% to 36.52 %, 59.86%, 48.39% (P=0.006). The cell growing inhibition ratio with the Caspase-8 inhibitor changes from 85.23% to 68.32% (P=0.004). Conclusion Apoptosis could be induced by curcumin in glioma cells via alteration of expression of COX-2 and activation of casepase. The decreases in the mitochondrial membrane potential in glioma cells treated with curcumin take part in the process of cell apoptosis. Key words: Curcumin; Apoptosis; Glioma; Mitochondrial membrance potential