The aim of this study was to investigate the therapeutic effects of bioflavonoids hesperetin and isoliquiritigenin (falls in a group of citrus and chalcone respectively) in cultured HO-1 human melanoma cells. Bioflavonoids - a large group of phenolic substances are present in foods of plant origin, with higher concentration found in the colored exterior tissues such as peels, skin, and the outer layer of fruits and vegetables. The consumption of food containing high amount of bioflavonoids has been reported to lower the risk of various cancers.

We conducted cell proliferation and cell viability studies using trypan blue cell exclusion method, western blot analysis, DNA fragmentation using agrose gel electrophoresis in HO-1 melanoma cells treated with bioflavonoids ISL and hesperetin, alone and in combination. Our data shows that bioflavonoids significantly inhibited the growth of melanoma cells and promoted apoptosis, which was determine by observing a time-dependent increase in expression of the pro-apoptotic Bad gene and time-dependent decrease in anti-apoptotic Bcl-2 expression in cells treated from 24 to 72 hrs. Hesperetin shows gradual increase after 72 hrs while ISL show maximum expression of Bad after 48hrs. We confirmed the occurrence of apoptosis by performing DNA fragmentation experiments. The result shows a time-dependent progressive increase in DNA fragmentation, more prominent after 72hrs when treated with bioflavonoids.

In summary, these studies demonstrate that ISL and hesperetin alone and combination significantly inhibit cell proliferation of HO-1 cells by inducing apoptosis. Further studies are required to investigate the detailed mechanism of apoptosis in response to treatment of HO-1 cells with these flavonoids and other bioflavonoids mixture. There may be synergistic or antagonist effects when cells are treated with mixtures of flavonoids.