Anthocyanins are potent antioxidants in model systems but do not reduce endogenous oxidative DNA damage in human colon cells

Anthocyanins are common colored plant flavonoids, occurring as glycosides o f the respective anthocyanidin-chromophores. Like other flavonoids, anthocy anidins are also expected to have antioxidative and antimutagenic propertie s in vivo. although only few data are available. To gain more knowledge on possible protective mechanisms in mammalian cells, we have compared their e xtracellular and intracellular antioxidative potential in vitro and in huma n colon tumor cells. We used Aronia melanocarpa Elliot anthocyanin (AA) con centrates, fractions thereof, concentrates from Elderberry, Macqui, and Tin torera fruits, as well as pure compounds. In vitro, antioxidative propertie s of the samples were studied with the ferric reducing ability assay (FRA a ssay). As a measure of intracellular oxidative/antioxidative effects, H2O2- induced strand breaks as well as oxidized DNA bases were determined in huma n tumor HT29 clone 19A cells using a microgelelectrophoresis assay (comet t est). Major results were that isolated compounds (aglycons and glycosides) and complex plant samples are powerful antioxidants in vitro. In fact their activities by far exceeded those of Trolox and vitamin C in the FRA assay. Also, H2O2-induced DNA strand breaks were reduced in cells treated with th e complex plant extracts. In contrast, endogenous generation of oxidized DN A bases was not prevented. In summary, the intracellular steady state of ox idized DNA bases is not altered by anthocyanins or anthocyanidins. This fin ding raises questions with respect to the cancer preventive potential of an thocyanidins within specific tissues, such as the colon. Extracellularly, h owever, the compounds are potent antioxidants. This points to their potenti al for providing systemic protection in vivo, e.g., by scavenging oxidants in the blood stream and in the colon. Notably, both aglycons and glycosides have equally strong antioxidant activity.