UBC Theses and Dissertations
Coffee constituents and modulation of antioxidant status in Caco-2 cells Liu, Yazheng
Coffee contains biologically active components which may affect chronic disease risk. These biologically active components include caffeine, cafestol and kahweol, and antioxidants such as chlorogenic acids and Maillard reaction products (MRPs) that are generated during roasting. Although MRPs are regarded as being the most abundant group of antioxidants present in coffee, the mechanism underlying the antioxidant effects of coffee MRPs in both in vitro and in biological systems has yet to be elucidated. In this study, the in vitro antioxidant properties of roasted and non-roasted coffee extracts (Coffea arabica L.) were tested using oxygen radical absorbance capacity (ORAC), Trolox equivalent antioxidant capacity (TEAC) and reducing power assays. MRPs were shown to be the prevailing antioxidants in roasted coffee extracts. The mechanisms of the antioxidant action associated with coffee MRPs involve the hydrogen atom transfer (HAT) mechanism and the single electron transfer (SET) mechanism. The biological effects of MRPs derived from coffee extracts on the enzymatic antioxidant defense in human colon adenocarcinoma Caco-2 cells were also investigated. No induction of antioxidant enzyme activities of catalase, glutathione peroxidase, glutathione reductase and superoxide dismutase were observed in Caco-2 cells after exposure to coffee MRPs, except for an increased glutathione peroxidase activity after 24 h exposure. In contrast, significantly decreased activities of catalase and glutathione peroxidase, and a reduced glutathione content were observed in Caco-2 cells after treatment with coffee MRPs (p<0.05). The antioxidant gene expression profile in Caco-2 cells after coffee treatment was further investigated using a Real-Time Polymerase Chain Reaction (PCR) array technology. Results demonstrated that roasted coffee extracts induced the expression of specific antioxidant response element (ARE)-driven genes in Caco-2 cells, thus enhancing cellular endogenous defense systems. This is the first report of the molecular mechanism underlying the antioxidant effect of coffee in Caco-2 cells. Hydrogen peroxide generated in the cell culture system as a consequence of coffee exposure, may serve as a signaling molecule that is involved in the gene regulatory effect associated with coffee extracts.
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