Dietary flavonoid intake and risk of stomach and colorectal cancer

Stomach and colorectal cancers are common cancers and leading causes of cancer deaths.Because the alimentary tract can interact directly with dietary components,stomach and colorectal cancer may be closely related to dietary intake.We systematically searched published literature written in English via PubMed by searching for terms related to stomach and colorectal cancer risk and dietary flavonoids up to June 30,2012.Twenty-three studies out of 209 identified articles were finally selected for the analysis.Log point effect estimates and the corresponding standard errors were calculated using covariate-adjusted point effect estimates and 95%CIs from the selected studies.Total dietary flavonoid intake was not associated with a reduced risk of colorectal or stomach cancer [odds ratio(OR)(95%CI) = 1.00(0.90-1.11) and 1.07(0.70-1.61),respectively].Among flavonoid subclasses,the intake of flavonols,flavan-3-ols,anthocyanidins,and proanthocyanidins showed a significant inverse association with colorectal cancer risk [OR(95%CI) = 0.71(0.63-0.81),0.88(0.79-0.97),0.68(0.56-0.82),and 0.72(0.61-0.85),respectively].A significant association was found only between flavonols and stomach cancer risk based on a limited number of selected studies [OR(95%CI) = 0.68(0.46-0.99)].In the summary estimates from casecontrol studies,all flavonoid subclasses except flavones and flavanones were inversely associated with colorectal cancer risk,whereas neither total flavonoids nor any subclasses of flavonoids were associated with colorectal cancer risk in the summary estimates based on the cohort studies.The significant association between flavonoid subclasses and cancer risk might be closely related to bias derived from the case-control design.There was no clear evidence that dietary flavonoids are associated with reduced risk of stomach and colorectal cancer.

Identification and biosynthesis of plant papanridins,a group of novel oligomeric flavonoids

The discovery of novel flavonoids and elucidation of their biosynthesis are fundamental to understanding their roles in plants and their benefits for human and animal health.Here,we report a new pathway for polymerization of a group of novel oligomeric flavonoids in plants.We engineered red cells for discovering genes of interest involved in the flavonoid pathway and identified a gene encoding a novel flavanol polymerase(FP)localized in the central vacuole.FP catalyzes the polymerization of flavanols,such as epicatechin and catechin,to produce yellowish dimers or oligomers.Structural elucidation shows that these compounds feature a novel oligomeric flaven–flavan(FF)skeleton linked by interflavan–flaven and interflaven bonds,distinguishing them from proanthocyanidins and dehydrodicatechins.Detailed chemical and physical characterizations further confirmed the novel FFs as flavonoids.Mechanistic investigations demonstrated that FP polymerizes flavan-3-ols and flav-2-en-3-ol carbocation,forming dimeric or oligomeric flaven-4→8-flavans,which we term“papanridins.”Data from transgenic experiments,mutant analysis,metabolic profiling,and phylogenetic analyses show that the biosynthesis of papanridins is prevalent in cacao,grape,blueberry,corn,rice,Arabidopsis,and other species in the plant kingdom.In summary,our study discoveries a group of novel oligomeric flavonoids,namely papanridins,and reveals that a novel FP-mediated polymerization mechanism for the biosynthesis of papanridins in plants.