|dc.description.abstract||Intestinal epithelial cells form important barriers that protect the body from biotic and abiotic or dietary stresses. Thus, maintaining the health and functionality of enterocytes, and their progenitors, is critically important to support barrier integrity and avoid entrance of non-nutrient substances that can lead to endotoxemia and inflammation. Dietary polyphenols have potential antioxidant and other bioactive effects on intestinal epithelial cells, and their possible role in improving mitochondrial function to provide sufficient energy for the cells to combat stressful conditions has not gained much attention.
In my thesis, Caco-2 intestinal epithelial cells exposed to mixed micelles (MM) was used as a model of high dietary fat consumption to induce cellular stress, and the molecular aspects of protection by anthocyanins and the polyphenol resveratrol were investigated.
Exposure of the Caco-2 cells to MM induced cytotoxicity, oxidative stress and mitochondrial dysfunction, and increased differentiated cell monolayer permeability. In protection against intracellular and mitochondrial generation of reactive oxygen species (ROS), an anthocyanin-rich bilberry extract (ARBE) was more effective than resveratrol, and also protected against differentiated cell monolayer permeability to a larger extent, whereas resveratrol only protected for a short time (Chapter 3). Resveratrol, however, protected more than ARBE against a MM-induced decrease in mitochondrial content and expression of mRNA for proteins related to mitochondrial biogenesis (such as PGC-1α, and TFAM), although ARBE protected against declines in mitochondrial function such as basal respiration, spare capacity and ATP production (Chapter 4). In investigations of a possible protective interactions of ARBE and resveratrol against MM-induced intracellular ROS, cytotoxicity and mitochondrial dysfunction, little evidence was found except a significantly greater protection by the combination against intracellular ROS at the lowest concentration (0.1 µM) (Chapter 5). Comparing pure anthocyanins (cyanidin and cyanidin-3-glucoside (C3G)) and their phenolic derivatives 2,4,6-trihydroxybenzaldehyde (THB) and protocatechuic acid (PCA), showed that PCA equally decreased intracellular ROS, and the derivatives acted stronger than the pure anthocyanins in reducing mitochondrial superoxide after 24 h MM challenge (Chapter 6). At shorter times (2-12 h), however, cyanidin, THB and PCA, but not the glycosides C3G or ARBE protected against MM-induced mitochondrial superoxide formation (Chapter 6).
In conclusion, different polyphenols were all able to protect against MM-induced oxidative stress in the in vitro Caco-2 cell model. In general, anthocyanins increased mitochondrial efficiency, that is higher ATP generation as well as lower ROS production, and resveratrol induced mitochondrial content. The effects of anthocyanins and resveratrol were not synergistic however, and some of the effects of the anthocyanins could be due to their phenolic metabolites/degradation products. Further studies investigating an in vivo model of protective effects of polyphenols in increased intestinal permeability due to high dietary fat consumption could enlighten our understanding of how these compounds contribute to health.||