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Flavonoids have been reported to exhibit prooxidant cytotoxicity against cancer cells, but the underlying mechanism is still poorly understood. Here we investigated the potential mechanism that p53-inducible gene 3 (PIG3), a NADPH:quinone oxidoreductase, mediated the prooxidant cytotoxicity of flavonoids on human hepatoma HepG2 cells. The results showed that flavonoids (apigenin, luteolin, kaempferol, and quercetin) inhibited the growth of HepG2 cells in a dosage- and time-dependent manner, and induced the morphological changes characteristic of apoptosis in HepG2 cells. We also found that expression of PIG3 was increased markedly in HepG2 cells treated with flavonoids at both mRNA and protein levels, which was accompanied by increased intracellular ROS production and a decreased mitochondrial membrane potential (ΔΨm). All these effects were largely reversed through knockdown of the PIG3 gene in HepG2 cells. Western blotting indicated that flavonoids increased cytochrome c release, upregulated the ratio of Bax/Bcl-2, and activated the caspases-9 and -3. Moreover, knockdown of PIG3 could reverse the changes of these apoptotic-related proteins. These results suggest that PIG3 plays an important role in regulating the prooxidant activity and apoptosis-inducing action of flavonoids on HepG2 cells though the ROS-triggered mitochondrial apoptotic pathway.

This updated meta-analysis was performed to clarify the relationship between phytoestrogens and prostate cancer risk. Twenty one case-control and two cohort studies were finally selected for this meta-analysis, totaling 11,346 cases and 140,177 controls. Analytical results showed that daidzein (OR = 0.85; 95% CI: 0.75-0.96), genistein (OR = 0.87; 95% CI: 0.78-0.98), and glycitein (OR = 0.89; 95% CI: 0.81-0.98) were associated with a reduction of prostate cancer risk, but total isoflavones (OR = 0.93; 95% CI: 0.84-1.04), equol (OR = 0.86; 95% CI: 0.66-1.14), total lignans (OROgna.05; 95% CI: 0.54-2.04), secoisolariciresinol (OR = 1.02; 95% CI: 0.83-1.24), matairesinol (OR = 0.91; 95% CI: 0.75-1.11), enterolactone (OR = 0.94; 95% CI: 0.73-1.20), and coumestrol (OR = 0.89; 95% CI: 0.76-1.06) were not. Sensitivity and publication bias analyses demonstrated that the pooled estimates were stable and reliable. The results support the notion that some phytoestrogens may have a role in decreasing the risk of prostate cancer. Additional large and well-designed cohort studies are needed to confirm these relationships.