Aim: 

There is evidence that melatonin enhances apoptosis in tumor cells, but the apoptotic mechanisms of melatonin on human hepatocarcinoma are still not understood. In the present study we investigated the potential proapoptotic effects by melatonin on HepG2 cells.

Methods: 

HepG2 hepatocarcinoma cells were grown in supplemented Dulbecco's modified Eagle's medium, and confluent cells were treated with melatonin (1,000 mM) at different times (2-10 days). Caspase-3, 8 and 9 activities were measured by a fluorometric assay. Moreover, different markers of the intrinsic and the extrinsic pathways of apoptosis were analyzed by western blot.

Results: 

Treatment with melatonin resulted in a marked increase of caspase-3 activity (236%-362% vs control), and substantial PARP proteolysis was documented by the detection of the characteristic 85-kDa fragment (350%-450% from control), indicating that cells were undergoing apoptosis. Different markers of the intrinsic pathway of apoptosis were analyzed and our data indicate that Bax (129%-156% vs control) and cytochrome c (124-150% vs control) protein content were significantly elevated by melatonin. This effect was accompanied by a significant increase in caspase-9 activity (260-470% vs control). When the extrinsic pathway was analyzed we observed that melatonin treatment resulted in a significantly increased caspase-8 activity (232–439% vs control), but not significant change was detected on FasL expression.

Conclusion: 

Melatonin is able to induce apoptosis on HepG2 hepatocarcinoma cells. In the light of these findings, it is possible that melatonin might be useful as adjuvant in hepatocarcinoma therapy, but further studies are necessary.