OBJECTIVETo study the effect of melatonin (MLT) in in vitro apoptosis of hepatocarcinoma cells and its mechanism.

METHODSThe apoptotic cells, bcl-2 and bax were detected through immunocytochemical method (ICC) and Tolt-mediated x-duTP nick end labeling (TUNEL). Computer image analysis system was used to quantify the expression of bcl-2 and bax by detecting the absorbance value of positive products. Apoptosis index (AI) was used to quantify the number of apoptotic cells.

RESULTSIn vitro, AI increase was both concentration- and time-dependent through TUNEL. During the same duration, AI of medium dose group was higher than that of low dose and control group (P < 0.05); AI of high dose, medium dose and 5-Fu group were higher than those of low dose and control group (P < 0.01), however, there was no significant difference between the low dose and control group (P > 0.05). At the same dose, in high dose, medium dose and 5-Fu group, the change of AI showed significant difference from 24 to 36 hours (P < 0.05). The expression of bcl-2 was down-regulated as the MLT increased, and there was significant difference between the low dose and control group (P < 0.01). But, the expression of bax was up-regulated as the dose of MLT increased, showing significant difference between the high dose and control groups (P < 0.01). As time went on, the expression of bcl-2 was decreased and in every group, with the change in absorbance value of bcl-2 significantly different from 24 to 36 hours (P < 0.05), whereas that of bax remained almost unchanged. The ratio of bax/bcl-2 was increased with the increase in the concentration of MLT.

CONCLUSIONMelatonin may induce apoptosis in the hepatocarcinoma cells which is concentration- and time-dependent, in which bcl-2 and bax are involved.