The role of Nrf2 in the antigenotoxic potential of raspberry metabolites.

Abstract

Colorectal cancer (CRC) is the third most prevalent cancer worldwide; as it has an increasing incidence rate in westernised countries. This correlation has been attributed in part to poor diet. In contrast, individuals with high consumption of (poly)phenol rich foods such as fruit and vegetable have a reduced risk of CRC. Berries are a particularly rich source of (poly)phenols and in recent years have been associated with a range of anticancer activities. When consumed, these berries undergo a range of structural transformations as they are digested, which could alter their potential bioactivity. The aim of this thesis was to develop an ex-vivo model with which to produce physiologically relevant samples that represent the colonic contents post-raspberry consumption. Eleven post-berry ileal samples were collected following a human feeding study and subsequently in vitro fermented. The potential antigenotoxic activity of these samples was assessed in a model of normal colonic epithelium (CCD 841 CoN) and a cell model of colonic adenocarcinoma (HT29). The anticancer activity, previously demonstrated by crude berry extracts and isolated (poly)phenols, was retained following digestion. Both post-berry ileal samples and post-berry ileal fermentate samples decreased H2O2 induced DNA damage. Following this discovery, it was important to attempt to identify the mechanism by which this antigenotoxic activity occurs. There was sufficient previous evidence to suggest that (poly)phenolic compounds have the potential to induce the nuclear factor-erythroid 2-related factor 2 (Nrf2)/ antioxidant response element (ARE) pathway and this warranted further investigation. The post-berry IFF samples showed the ability to significantly induce the mRNA expression of Nrf2 and its downstream targets heme-oxygenase 1 (HO-1), N-acetyltransferase (NAT), NADPH quinine oxidoreductase 1 (NQO-1). In addition to these findings a novel raspberry seed derived triterpenoid was identified within the post-berry ileal fluid samples. This compound was present in the original raspberry seeds and survived in vivo digestion, it therefore was pertinent to assess its antigenotoxic capacity. As with the other raspberry metabolites investigated in this study, the triterpenoid rich fraction (TRF) significantly decreased H2O2 induced damage in CCD 841 CoN and HT29 cells, in conjunction with the up-regulation of HO-1 and NQO1.
In conclusion, this thesis has determined that the berry metabolites produced following in vivo digestion and in vitro fermentation retain the antigenotoxic activity previously demonstrated by crude berry extracts. This activity in maybe part due to the activation of the Nrf2/ARE pathway. These findings further expand our understanding of the role of berry metabolites as potential dietary anticarcinogenic agents.

Date of Award	Apr 2019
Original language	English
Sponsors	DEL
Supervisor	Chris Gill (Supervisor) & Nigel Ternan (Supervisor)