Effect of resveratrol and β-sitosterol in combination on reactive oxygen species and prostaglandin release by PC-3 cells

The objective of this project was to identify some possible mechanisms by which two common phytochemicals, resveratrol and β-sitosterol, inhibit the growth of human prostate cancer PC-3 cells. These mechanisms include the effect of the phytochemicals on apoptosis, cell cycle progression, prostaglandin synthesis and the production of reactive oxygen species (ROS). Prostaglandins have been known to play a role in regulating cell growth and apoptosis. PC-3 cells were supplemented with 50 μM resveratrol or 16 μM β-sitosterol alone or in combination for up to 5 days. Phytochemical supplementation resulted in inhibition in cell growth. β-Sitosterol was more potent than resveratrol and the combination of the two resulted in greater inhibition than supplementation with either alone. Long-term supplementation with resveratrol or β-sitosterol elevated basal prostaglandin release but β-sitosterol was much more potent than resveratrol in this regard. β-Sitosterol was more effective than resveratrol in inducing apoptosis and the combination had an intermediate effect after 1 day of supplementation. Cells supplemented with resveratrol were arrested at the G₁ phase and at the G₂/M phase in the case of β-sitosterol while the combination resulted in cell arrest at the two phases of the cell cycle. β-Sitosterol increased ROS production while resveratrol decreased ROS production. The combination of the two phytochemicals resulted in an intermediate level of ROS. The observed changes in prostaglandin levels and ROS production by these two phytochemicals may suggest their mediation in the growth inhibition. The reduction in ROS level and increase by resveratrol supplementation in PC-3 cells reflects the antioxidant properties of resveratrol. It was concluded that these phytochemicals may induce the inhibition of tumor growth by stimulating apoptosis and arresting cells at different locations in the cell cycle and the mechanism may involve alterations in ROS and prostaglandin production.