Author: Samsu Udayana Nurdin Nurdin

Nurdin, Samsu Udayana Nurdin, 2013 EFFECT OF ANTIOXIDANT-DIETARY FIBER MIXTURES ON CANCER GROWTH IN COLORECTAL CANCER-INDUCED RATS, Flinders University, School of Biological Sciences

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Colorectal cancer (CRC) incidence is rising significantly in most Countries due to increasing prosperity. Epidemiological studies indicate that dietary fiber and antioxidants may protect against CRC. Dietary fiber is thought to suppress colorectal cancer growth via the production of short chain fatty acids (SCFA) in the colon, where specific compounds are produced via bacterial breakdown of the fiber. Colonic bacteria are also involved in antioxidant metabolism in the colon, and they can increase antioxidant bioavailability and activity. My research aimed to study the beneficial effect of different combinations of dietary fiber and antioxidant sources including dried green cincau extracts in the colon, these effects were examined in both in vitro and in vivo models of colon cancer. Green cincau (Premna oblongifolia Merr) is an Indonesia plant where the extract has high dietary fiber and antioxidant activity and was also tested in this thesis. SCFA significantly inhibited proliferation while inducing differentiation of Caco-2 cells irrespective of the media pH. Caspase 3 and 7 (key mediators in the extrinsic and intrinsic apoptotic pathway) activities were affected by both pH and SCFA, but there was no interaction between them. Caco 2 cells were less proliferated in low media pH as this condition induced cell apoptosis. Butyrate induced cell death was observed through both caspase3/7-dependent and -independent pathways as indicated by increased caspase 3/7 activity. Fermentation experiments using anaerobic batch cultures inoculated with human fecal slurries showed that soluble fiber (pectin and inulin) resulted in significantly higher SCFA production than that observed with insoluble (cellulose) fiber. In Caco-2 cells, inhibition of cell growth was dependent on the amount of SCFA generated during fermentation in particular butyrate. However, the effect of fermentation supernatant (FS) on cell differentiation and apoptosis was not able to be explained by the butyrate content, as high butyrate in the FS did not always promote differentiation and the apoptotic process. Apoptotic, necrotic and autophagic pathways might all be involved in cell death in response to FS treatment. The ability of the supernatant to modulate parameters of cell growth, differentiation and apoptosis was dependent on butyrate concentration and, possibly, unidentified compounds. Using the Azoxymethane (AOM)-induced rat model of CRC it was found that 0.1% epigallocatechin-3-gallate (EGCG) increased some individual SCFA concentrations (acetate and butyrate) in digesta when the dietary fiber source was cellulose (CE), and an opposite effect was observed when the dietary fiber source was pectin (PE). Pectin-EGCG combined induced cancer progression, characterized by an increase in total number of aberrant crypt foci (ACF), and also an increase in the proliferating cell nuclear antigen (PCNA) labelling index and PCNA positive cells. This effect was associated with increasing lipid peroxidation in the liver. The protective effect of antioxidant EGCG consumption against colon cancer development appears to be dependent on the type of the dietary fiber source in the diet and the mechanism particularly through the modification of antioxidant/prooxidant properties of the EGCG. The beneficial effect of individual dietary fibers does not automatically synergize with the positive effects of potential antioxidants, and their combined effect will depend on how they interact with the colon microbiota of the individual. Natural mixtures of dietary fiber and antioxidant sources (as found in fruits, vegetables and plant extracts) may exhibit protective effect against CRC, and utilization of these sources should consider the processing method such as the drying process to protect their potency. In conclusion the work presented in this thesis suggests that the consumption of fresh dietary fiber antioxidants sources may pose the greatest protection against CRC.

Keywords: Dietary fiber,antioxidant,CRC,pectin,EGCG,green cincau
Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2013
School: School of Biological Sciences
Supervisor: Associate Professor Catherine Abbott