Mechanism of action of physical antioxidants in lipoprotein oxidation

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PhD thesis (EN)

2008 (EN)
Μελέτη των μηχανισμών δράσης φυσικών αντιοξειδωτικών στην οξείδωση των λιποπρωτεϊνών
Mechanism of action of physical antioxidants in lipoprotein oxidation

Φεσληκίδης, Θεοχάρης Ε.

The aim of this study was to analyze the mechanism by which flavonoids actas antioxidants in lipoproteins and to correlate their antioxidant potency with their structure. In order to extract the most accurate results possible, we chose to study different flavonoids with similar structure from three different flavonoid subclasses. In order to study the mechanism of oxidation, LDL oxidation was made with Cu+2, a cation that is supposedly chelating with flavonoids and AAPH a free racidal generator. Finding the exact position and the species of the chemical substitute can determine the antioxidant potency of the flavonoid and the formation of chelate compounds with transition metals, and can lead to selection or synthesis of flavonoids with bigger antioxidant potency and lesser side effects. To serve our needs, we tried 14 flavonoids that belonged to flavanol, flavonol and isoflavone subsegments. The standards by which the choice of the flavonoids was made, was to have little differences between them, a hydroxyl group for instance, or the position of a hydroxyl group, or to be esterified with gallic acid. Then they were separated according to their subclass. The results of LDL of oxidation, by means of Cu+2 and AAPH, using the first subclass of antioxidants, catechins, showed that this particular subclass had the best antioxidant effect on LDL. More specifically, epicatechin gallate and epigallocatechin gallate, exhibited the biggest lag time of all flavonoids. After these came epicatechin, catechin and epigallocatechin. The results of the second flavonoid subclass, flavonols had medium antioxidant effect on LDL oxidation. The flavonols with the best antioxidant were myricetin and quercetin. After these were morin, kaempferol and galangine. The third flavonoid subclass shows the weakest antioxidant capacity of all. Only luteolin had adequate antioxidant capacity. Geraldol, chrysin and acacetin showed weak antioxidant potency. This study showed thal all flavonoids had antioxidant effects, major or minor. Flavonoids that had two hydroxyl groups in ortho-position in B ring or in gallic ester ring had the biggest antioxidant effect. This occurred possibly because they bind in these positions transition metals, such as Cu+2 ion. Another function of thisortho-position can be that from these hydroxyl groups it is easier to detach ahydrogen atom because stable intermediates are formed, thus enhancing theinantioxidant capacity. It was also noted that in B rings that had three consecutive hydroxyl substitutes, the antioxidant activity was smaller related to these rings that had two substitutes. In flavonols, a new chelate bond can be formed among the C-2 ketone group and C-3 hydroxyl group to increase the antioxidant capacity. Finally, it was noted that hydrophile flavonoids had bigger antioxidant capacity
Σκοπός της διατριβής αυτής ήταν η μελέτη του μηχανισμού της αντιοξειδωτικής δράσης που παρουσιάζουν τα φλαβονοειδή στις λιποπρωτεΐνες και η συσχέτιση της αντιοξειδωτικής δράσης με τη δομή τους. Η εύρεση των θέσεων και του είδους των υποκαταστατών που καθορίζουν την αντιοξειδωτική δράση των φλαβονοειδών και το σχηματισμό χηλικών ενώσεων με μεταβατικά μέταλλα, μπορεί να οδηγήσει στην επιλογή ή στη σύνθεση φλαβονοειδών που να παρουσιάζουν πολύ μεγάλη αντιοξειδωτική δράση με ελάχιστες παρενέργειες. Για την εξαγωγή όσο το δυνατό πιο ασφαλών συμπερασμάτων, επιλέχθηκαν και μελετήθηκαν φλαβονοειδή με παρόμοια δομή από τρεις υποομάδες των φλαβονοειδών. Για το σκοπό αυτό μελετήθηκαν 14 φλαβονοειδή, τα οποία ανήκουν στις υποκατηγορίες των φλαβανολών, φλαβονολών και ισοφλαβονών. Η επιλογή των φλαβονοειδών έγινε με κριτήριο τη δομή τους. Επιλέχθηκαν φλαβονοειδή που να έχουν μικρές διαφορές μεταξύ τους, στη θέση ή στον αριθμό των υδροξυλομάδων στο μοριό τους, ή να είναι εστεροποιημένα με γαλλικό οξύ, για να φανεί η αντιοξειδωτική συμπεριφορά του γαλλικού υποκαταστάτη. Στη συνέχεια, χωρίστηκαν σε τρεις ομάδες ανάλογα με την υποκατηγορία στην οποία ανήκαν. Για τη μελέτη του μηχανισμού δράσης των αντιοξειδωτικών χρησιμοποιείται ο φασματοσκοπικός έλεγχος της οξείδωσης των LDL στα 234nm ή με Cu2+ ή με την αζωένωση 2,2΄-azobis (2-amidino-propane) dihydochloride (ΑΑΡΗ), που ουσιαστικά είναι μία «γεννήτρια» παραγωγής ελευθέρων ριζών

PhD Thesis / Διδακτορική Διατριβή


Αριστοτέλειο Πανεπιστήμιο Θεσσαλονίκης (EL)
Aristotle University of Thessaloniki (EN)



Αριστοτέλειο Πανεπιστήμιο Θεσσαλονίκης, Σχολή Επιστημών Υγείας, Τμήμα Ιατρικής

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