Antioxidants and natural anti-cancer agents in the large bowel and the influence of intestinal microbial fermentation.

Epidemiological studies of colorectal cancer, in particular time trends in migrant and religious groups, indicate that environmental factors might be of importance in determining the incidence of disease in a given population. Of the possible environmental factors implicated in cancer of the large bowel, diet has been the focus of attention. One such component is dietary fibre but results of epidemiological and laboratory studies considering dietary fibre are rather contradictory, and the assumption that high consumption of vegetables and fruit is protective against colorectal cancer may be better supported by the literature than most of the other dietary fibre hypotheses. This study has involved an entirely new approach and investigated the issue that antioxidants and other associated compounds contained within the vegetable cell matrix are the key anticarcinogenic factor, rather than the dietary fibre per se. Preliminary studies involved the development of a chemostat designed to simulate bacterial interactions that occur in the large bowel using porcine faeces and dissolved oxygen at concentrations within the range detected in the large bowel. This demonstrated the effects of antioxidants and oxygen on intestinal bacteria using enumeration techniques. In those bacteria unable to dispose of reactive oxygen species (ROS) (anaerobes) a protective effect was found for Beta-carotene (P<0.01) with oxygen, but there was NSD in the growth of aerobes. Beta-carotene mitigated the detrimental effects of increased H2O2 production associated with exposure to oxygen. H2O2 production decreased after the addition of Beta-carotene such that the lowest concentrations were obtained after 5 h (P=0.004) and then increased until a stable phase was maintained after 3 d. Beta-carotene did not affect the growth of anaerobes under anaerobic conditions, nor aerobes with or without oxygen. Further study involved pig animal models and demonstrated that differences in plasma and colonic DNA damage could not be explained by changes in bacterial populations. Ingestion of raw or cooked broccoli did not significantly affect vitamin C, alpha-tocopherol or retinol concentrations in plasma. Consumption of broccoli did, however, provide greater protection than cooked broccoli and control diets in terms of gross DNA damage as determined by the comet assay in frozen colonocytes (P<0.001). Although this study has not established the specific components that confer protection, this thesis has built on data obtained previously and would seem to reinforce dietary guidelines that increased consumption of fruit and vegetables is a desirable goal.

Grantor dc:publisher.institution

Robert Gordon University

Year dc:date.issued

2000

Author dc:creator

• Kemble, R.J.T.

Advisor dc:contributor.advisor

• B. Ratcliffe and K. Hillman

• Epidemiological studies
• Colorectal Cancer
• Environmental factors
• Antioxidants
• Anticarcinogenic
• Dietary guidelines
• Broccoli

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:2807423
https://doi.org/10.48526/rgu-wt-2807423

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:2807423