Apple polyphenols modulate antioxidant defense in human colon cancer cells

B24

Diets rich in fruits and vegetables are associated with a lower risk of tumour incidence in the intestine and other sites. This is mainly attributed to high amounts of secondary plant constituents such as polyphenols, which display a spectrum of bioactive effects, including prevention from ROS (reactive oxygen species)-mediated DNA damage, mutations and cell death. We investigated the modulation of antioxidant response element (ARE) dependent gene expression, poly-(ADP-ribosyl)-transferase (PARP1) transcription (real time TaqMan PCR) and DNA damage (comet assay) in the human colon cell lines Caco-2 and HT-29 by polyphenolic apple juice extracts (AE05: from different cider apple varieties; BA: from cider apple “Bohnapfel”). Selected phenolic constituents (chlorogenic acid, ChA; caffeic acid, CA) were also studied. Incubation with both AEs (50/ 100 µg/ml) as well as with ChA and CA (10/ 30 µM) resulted in a decrease of γ-glutamylcystein-ligase (γ-GCL), gastrointestinal glutathione peroxidase and glutathione reductase transcription in Caco-2 cells; in HT-29 cells, however, γ-GCL transcription was distinctly elevated by AE05 and CA. PARP1 mRNA transcription was significantly depleted down to 40% of DMSO control by BA (6h, 50/ 100 µg/ml) in HT-29 cells; AE05 (50/ 100 µg/ml) and ChA (30µM) caused a moderate PARP1 inhibition and CA (30 µM) was inhibitory in both cell lines. In Caco-2 cells, with both extracts/ components slight modulation of PARP1 transcription was observed; menadione induced DNA-damage was slightly decreased after 24h incubation with AE05 and BA (10 µg/ ml).
 >Taken together, the apple juice extracts and ChA show a distinct potential to deplete PARP1 transcription, to diminish oxidative DNA-damage and partially elevate γ-GCL transcription in human colon cell lines. The results suggest that apple polyphenols can prevent oxidative cell damage by inhibiting excessive PARP1 gene expression; ChA, the major constituent of both extracts might well contribute to the effects observed with the AEs. Other extract constituents, however, might also account for the protection against ROS-mediated DNA and cell damage. Supported by Federal Ministry of Education and Research (BMBF), grant no. 01EA0501 and federal state of Rhineland-Palatinate (project A4, ,,intestinal health and nutrition “)