Anthocyanins suppress the cleavable complex formation by irinotecan and diminish its DNA-strand-breaking activity in the colon of Wistar rats.

In the present study, the question was addressed whether anthocyanins interfere with the topoisomerase I poison irinotecan in vivo. In vivo complexes of enzyme to DNA bioassay was used to detect irinotecan-induced stabilization of topoisomerase I/DNA complexes and single cell gel electrophoresis to determine DNA-strand-break induction in the colon of male Wistar rats. Furthermore, analysis of anthocyanin concentrations in rat plasma and rat colon was included in the testing, demonstrating that anthocyanins reach the colon and the concentrations do not differ between rats that only received anthocyanins and the anthocyanin/irinotecan group. Blackberry extract was found to significantly reduce irinotecan-mediated topoisomerase I/DNA cleavable complex formation. Overall, anthocyanins did not notably increase cleavable complex formation. However, a significant increase of DNA damage was shown after a single dose of irinotecan as well as the single compounds cyanidin (cy) and cyanidin-3-glucoside (cy-3-g). Furthermore, a significant reduction of irinotecan-induced DNA-strand breaks after a pretreatment with cy, cy-3-g and blackberry extract was observed. Thus, the question arises whether anthocyanin-rich preparations might interfere with chemotherapy or whether, due to low systemic bioavailability, the preparations might provide protective potential in the gastrointestinal tract.

Anthocyanin-rich blackberry extract suppresses the DNA-damaging properties of topoisomerase I and II poisons in colon carcinoma cells.

In the present study, we addressed the question whether cyanidin-3-glucoside (C3G) or complex C3G-rich blackberry extracts affect human topoisomerases with special emphasis on the contribution of the potential degradation products phloroglucinol aldehyde (PGA) and protocatechuic acid (PCA). In HT29 colon carcinoma cells a C3G-rich blackberry extract suppressed camptothecin- (CPT-) or doxorubicin- (DOX-) induced stabilization of the covalent DNA-topoisomerase intermediate, thus antagonizing the effects of these classical topoisomerase poisons on DNA integrity. As a single compound, C3G (100 µM) decreased the DNA-damaging effects of CPT as well, but did not significantly affect those induced by DOX. At the highest applied concentration (100 µM), cyanidin protected DNA from CPT- and DOX-induced damage. Earlier reports on DNA-damaging properties of cyanidin were found to result most likely from the formation of hydrogen peroxide as an artifact in the cell culture medium when the incubation was performed in the absence of catalase. The suppression of hydrogen peroxide accumulation, achieved by the addition of catalase, demonstrated that cyanidin does not exhibit DNA-damaging properties in HT29 cells (up to 100 µM). The observed effects on topoisomerase interference and DNA protection against CPT or DOX were clearly limited to the parent compound and were not observed for the potential cyanidin degradation products PGA and PCA.

Limited stability in cell culture medium and hydrogen peroxide formation affect the growth inhibitory properties of delphinidin and its degradation product gallic acid.

In the present study we investigated the stability of anthocyanidins under cell culture conditions and addressed the question whether degradation products might contribute to the cellular effects assigned to the parent compounds. Substantial degradation was found already after 30 min, measured by HPLC/DAD. However, the decrease of detectable anthocyanidins exceeded by far the formation of the respective phenolic acids. From the formed phenolic acids only gallic acid (GA) exhibited growth inhibitory properties. However, also GA was found to be degraded rapidly. Furthermore, the incubation with delphinidin (DEL) or GA resulted in a substantial formation of hydrogen peroxide. The suppression of hydrogen peroxide accumulation by catalase modified significantly the growth inhibitory effects of DEL and GA, indicating that hydrogen peroxide formation might generate experimental artefacts. In summary, the results show that the phenolic acids formed by the degradation of cyanidin (CY), pelargonidin (PG), peonidin (PN) and malvidin (MV) do not contribute to the growth inhibitory effect of the parent compound. The degradation of DEL generates a phenolic acid with substantial growth inhibitory properties (GA). However, taken into account the small proportion of generated GA and its lacking stability, the contribution of GA to the growth inhibitory properties of DEL might be limited.