Dietary rice bran component γ-oryzanol inhibits tumor growth in tumor-bearing mice

Scope We investigated the effects of rice bran and components on tumor growth in mice. Methods and results Mice fed standard diets supplemented with rice bran, γ‐oryzanol, Ricetrienol®, ferulic acid, or phytic acid for 2 weeks were inoculated with CT‐26 colon cancer cells and fed the same diet for two additional weeks. Tumor mass was significantly lower in the γ‐oryzanol and less so in the phytic acid group. Tumor inhibition was associated with the following biomarkers: increases in cytolytic activity of splenic natural killer (NK) cells; partial restoration of nitric oxide production and phagocytosis in peritoneal macrophages increases in released the pro‐inflammatory cytokines tumor necrosis factor‐α, IL‐1β, and IL‐6 from macrophages; and reductions in the number of blood vessels inside the tumor. Pro‐angiogenic biomarkers vascular endothelial growth factor (VEGF), cyclooxygenase‐2 (COX‐2), and 5‐lipoxygenase‐5 (5‐LOX) were also significantly reduced in mRNA and protein expression by tumor genes. ELISA of tumor cells confirmed reduced expression of COX‐2 and 5‐LOX up to 30%. Reduced COX‐2 and 5‐LOX expression downregulated VEGF and inhibited neoangiogenesis inside the tumors. Conclusion Induction of NK activity, activation of macrophages, and inhibition of angiogenesis seem to contribute to the inhibitory mechanism of tumor regression by γ‐oryzanol.