Investigation of the role of bioactive compounds contained in the diet in molecular mechanisms related to oxidative stress and human health (Doctoral thesis)

Γερογιάννη, Παρασκευή

Mediterranean diet has been the subject of a large number of studies, particularly with regard to its role in human health. The present study started with the aim of evaluating the ability of extracts of three aromatic plants, sage, oregano and rosemary, to protect the cellular DNA, after exposure of cells to H2O2. The finding that aqueous extracts from these plants, as well as extracts from ethyl acetate, provided protection, led us to the isolation of some bioactive compounds and the investigation of their mechanisms of action. One of the investigated compounds was rosmarinic acid. It was observed that long-time incubations and high concentrations of rosmarinic acid, were required in order to be able to protect nuclear DNA. We hypothesized that rosmarinic acid due to its negative charge, can’t easily penetrate through cell membrane and act inside the cells. In order to neutralize its negative charge, we synthesized ester derivatives of rosmarinic acid which have higher lipophilicity. It was observed that their protective effects were much greater than that of the mother compound, rosmarinic acid. However, both esters examined, showed toxicity at high concentrations, in the absence of H2O2. Hypothesizing that this toxicity was due to the hydrolysis of esters within the cells of non – specific esterases, resulting in their accumulation in the cells, we then, chemically synthesized the corresponding amides of rosmarinic acid, which are not hydrolysed and subsequently are not entrapped inside the cells. It was observed that the amides had no toxicity in the absence of H2O2. Also, a strong correlation was observed between the capacity of binding intracellular redox active iron and the protective activity of these compounds. In conclusion, the above results demonstrate the importance of the esterification or amidation of phenolic acids in general, in order to be uptaken by the cells and act intracellularly. Thus, in order for a compound to be biologically active, it should: a) be able to be diffused into the cell interior and b) have the ability to bind the redox active iron ions. Then, we tried to evaluate the protective effects of extracts from industrially prepared functional dairy foods (cheese and yogurt), which were already enriched with extracts from aromatic plants and fruits. We concluded that the esters contained in the aromatic plant extracts and fruits extracts, are hydrolysed at the acid pH of the extraction of the dairy products and therefore, their constituents lose their protective capacity. In contrast, when the extraction is performed at neutral pH, ester hydrolysis is inhibited. In a final step, we turned our attention to in vivo actions of iron-binding compounds. In particular, we tried to evaluate the protection generated by two iron-binding pharmaceuticals, desferrioxamine and deferiprone, which have different lipophilicity and iron binding capacity, against reperfusion after a period of ischemia in liver. Initially, we observed that the protection of nuclear DNA in hepatic cells, in conditions of oxidative stress, was dramatically greater when the two compounds were combined, compared to that offered by each compound individually. To explain this effect, we hypothesized that deferiprone, being a more lipophilic compound, enters into the cells and binds redox active iron. Then, it transfers it out of the cell, delivering it to desferrioxamine, which has a much higher iron binding affinity. It is concluded that a plethora of components of the diet with specific chemical characteristics, can exert beneficial effects on many pathological conditions, contributing to the preservation of human health.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Επιστημών Υγείας. Τμήμα Ιατρικής
Subject classification: Οξειδωτικό στρες
Keywords: Οξειδωτικό στρες,Ελεύθερες ρίζες,Ροσμαρινικό οξύ,Παράγωγα ροσμαρινικού οξέος,Oxidative stress,Free radicals,Rosmarinic acid,Derivatives of rosmarinic acid,Cοmet assay
Appears in Collections:Διδακτορικές Διατριβές

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