The current understanding of the complex role of ROS in the organism and pathological sequelae of oxidative stress points to the necessity of comprehensive studies of antioxidant reactivities and interactions with cellular constituents. Studies of antioxidants performed within the COST B-35 action has concerned the search for new natural antioxidants, synthesis of new antioxidant compounds and evaluation and elucidation of mechanisms of action of both natural and synthetic antioxidants. Representative studies presented in the review concern antioxidant properties of various kinds of tea, the search for new antioxidants of herbal origin, modification of tocopherols and their use in combination with selenium and properties of two promising groups of synthetic antioxidants: derivatives of stobadine and derivatives of 1,4-dihydropyridine.

Although the term 'antioxidant' is used very frequently, there are problems with the definition of antioxidants and estimation of antioxidant activity. The distinction between antioxidant and antiradical activities is not always obvious. This minireview discusses critically the principles, advantages and limitations of the most frequently used methods of estimation of antiradical and antioxidant activities.

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Betulin is a principal component of birch bark and is known to possess a broad range of biological activities, including antiinflammatory, antiviral and anticancer actions. The present study was carried out in vitro to clarify the influence of betulin on melanocortin (MC) receptor-ergic signalling by using COS-7 cells transfected with corresponding human MC receptor DNA. The results showed that betulin binds to the human melanocortin MC1, three to five receptors with selectivity to the MC1 subtype (K(i) value 1.022 +/- 0.115 microM). Betulin binds to the MC receptors with the following potency order-MC > MC3 > MC5 > MC4. Betulin itself does not stimulate cAMP generation, however, it slightly antagonizes alpha-melanocyte-stimulating hormone (alpha-MSH)-induced cAMP accumulation in the mouse melanoma cell line B16-F1. As a water-insoluble substance, betulin was dissolved in DMSO therefore DMSO competition with the labelled ligand NDP-MSH for the binding to the MC receptors was tested in the identical experimental set-up. We found that DMSO competes for binding to all the MC receptor subtypes, at 20% concentration and above. Selectivity for one or another receptor subtype was not observed. We have demonstrated for the first time, the ability of the plant compound betulin to bind to the MC receptors. One may suggest MC receptor MC1 subtype as the essential target for the antimelanoma action of betulin and its structurally close molecules such as betulinic acid. Moreover, we have found a new non-peptide small molecule MC mimetic, that is betulin. Thus, we report a new chemical motif for the binding to the MC receptors that could be used as a template for the search of more selective MC mimetics.

Auf der Basis von Modellsystemen (thermische Autoxidation der Ester von ungesattigten Fettsauren) wurde die Antioxidationsaktivitat (AOA) der 3,5-Dicarbonylderivate des 2,6-Dirnethyl-1,4-dihydropyridins bewiesen. Bei den Verbindungen, die in Position 4 nicht substituiert sind, ist die AOA nicht linear abhkgig von der Konzentration der Verbindung und hat bei der Konzentration 7.5. MOM ihren Maximalwert.

The 1,4-dihydropyridine (I, 1,4-DHP) derivatives, especially compounds unsubstituted in position 4 (I, R'=H), show AOA in homogenous lipid systems (TIRZITIS et al. 1988;ABDALLA et al. 1999). IThe 2,6-dimethyl-3,5-diethoxycarbonyl-1,4-DHP (trade name Diludin) possesses considerable AOA in the stabilization of edible oils (KOUØIMSKÁ et al. 1993) and exhibits synergistic properties with antioxidants, such as α-tocopherol (TIRZITIS et al. 1983) and 2,6-bis(tert-butyl)-4-hydroxytoluene (BHT) (TIRZITIS & KIRULE 1999). Unfortunately the insufficient solubility of Diludin in lipids limits its practical application. This limitation demanded the synthesis and investigation of more lipophilic Diludin homologues.Most foods differ from refined oils and fats in that they are oil-in-water emulsions, where the aqueous phase contains hydrated proteins and carbohydrates (including dietary fibre), and on the other hand, also trace metals that catalyze oxidation. The 1,4-DHP has been less investigated in transition valence metal-ion catalyzed peroxidation. The aim of our study was to investigate the relationship between AOA and alkyl substituent (R) length in of increasing lipophilicity ranging from C 1 (methyl) to C 16 (hexadecyl) in the ester moiety of 1,4-DHP. This would help to choose the best compound for fat, oil and another lipid containing product stabilization studies.We used metal-ion (ferrous and copper) catalyzed phospholipid liposome peroxidation. Liposomes belong to very important lipid systems, present in most foods. The AOA of tested I was compared with AOA of Probucol™ and Trolox™, which belong to relatively polar antioxidants. The study of incorporation of 1,4-DHP into phosphatidylcholine liposomes was carried out as well. The results could be useful for the stabilization of non-homogenous lipid products (margarines, salad dressings, creams, etc.). Antioxidants with 1,4-dihydropyridine structure were investigated as a less harmful alternative to synthetic phenolic antioxidants in liposomes under conditions simulating food storage. The antioxidant activities (AOA) of 2,6-dimethyl-3,5-dialkoxycarbonyl-1,4-dihydropyridines possessing various side chain length alkyls (CH 3 -C 16 H 33 ) in ester moiety were tested in transition metalion catalyzed liposome peroxidation and compared with AOA of Trolox™ and Probucol™. The compounds with C 2 H 5 -C 4 H 9 residues in the 3,5-position ester moieties exert the most pronounced AOA. The AOA of tested compounds is associated with their ability to incorporate into liposomes. MATERIALS AND METHODS Phospholipid