Macáková K

Antioxidant Effects of Coumarins Include Direct Radical Scavenging, Metal Chelation and Inhibition of ROS-Producing Enzymes

Coumarins represent a large group of 1,2-benzopyrone derivatives which have been identified in many natural sources and synthetized as well. Several studies have shown that their antioxidant capacity is not based only on direct scavenging of reactive oxygen and nitrogen species (RONS) but other mechanisms are also involved. These include: a) the chelation of transient metals iron and copper, which are known to catalyse the Fenton reaction; and b) the inhibition of RONS-producing enzymes (e.g. xanthine oxidase, myeloperoxidase and lipoxygenase), suggesting that mechanism(s) involved on cellular level are complex and synergistic. Moreover, many factors must be taken into account when analysing structure-antioxidant capacity relationships of coumarins due to different in vitro/in vivo methodological approaches. The structural features necessary for the direct RONS scavenging and metal chelation are apparently similar and the ideal structures are 6,7-dihydroxy- or 7,8-dihydroxycoumarins. However, the clinical outcome is unknown, because these coumarins are able to reduce copper and iron, and may thus paradoxically potentiate the Fenton chemistry. The similar structural features appear to be associated with inhibition of lipoxygenase, probably due to interference with iron in its active site. Contrarily, 6,7-dihydroxycoumarin seems to be the most active coumarin in the inhibition of xanthine oxidase while its derivative bearing the 4-methyl group or 7,8-dihydroxycoumarin are less active or inactive. In addition, coumarins may hinder the induction of inducible NO-synthase and cyclooxygenase- 2. Sparse data on inhibition of myeloperoxidase do not enable any clear conclusion, but some coumarins may block it.

Evaluation of the antioxidant activity of several naturally occurring coumarins and their synthesized analogues by "ferric reducing antioxidant power" assay.

Abstract Coumarins have attracted intense interest in recent years because of their diverse pharmacological properties. According to our continuing investigations of biological effects of several coumarins, the structure–antioxidant activity relationships (SARs) of six naturally occurring coumarins and their 16 synthesized analogues were established. For this purpose, the very reliable colorimetric assay (ferric reducing antioxidant power) modified to be used in 96-well microplates was used. This approach, which determines the reducing capacity of tested compounds directly, has previously been used for the determination of SARs of flavonoids, but has not been used for SAR determination of coumarins. It is known that the biological properties and consequently, therapeutic application of simple coumarins depends upon the pattern of substitution. It was established that 7,8-dihydroxy- and 6,7-dihydroxy-4-methylcoumarins have shown excellent ferric-reducing properties.

New antioxidant flavonoid isolated from Leuzea carthamoides

A new natural flavonoid patuletin 3′-β-xylofuranoside was isolated from Leuzea carthamoides leaves. The antioxidant activity of this compound was evaluated by the DPPH radical assay and ferric reducing antioxidant power (FRAP) assay, and the results were compared with those for trolox and quercetin. DPPH radical scavenging activity of the tested compounds was expressed by the parameter EC50: patuletin 3′-β-xylofuranoside (56.0 μM), trolox (27.8 μM), and quercetin (25.3 μM). The ferric reducing activity of the compounds was demonstrated as FRAP values at 4 and 60 min: patuletin 3′-β-xylofuranoside (28.4 μM, 35.8 μM), trolox (19.3 μM, 20.2 μM), and quercetin (54.3 μM, 79.9 μM). The structure/activity relationship of the flavonoid is also discussed. The results indicate significant antioxidant potency of patuletin 3′-β-xylofuranoside.

In vitro immunomodulatory activity, cytotoxicity and chemistry of some central European polypores

Abstract Context Some mushrooms of the order Polyporales are known for their immunomodulatory actions. Objective The objective of this study is to evaluate the in vitro phagocytic and cytotoxic effects of extracts from polyporales native to Central Europe. Materials and methods The effects of ethanol extracts from 27 polypore species on opsonized zymosan-induced phagocytosis of isolated human neutrophils were tested by a chemiluminescence method. Colon epithelial cell lines, Caco-2 and HT-29, were used for cytotoxicity assays, and extracts were chemically characterized in terms of total phenolic and β-glucan content. Results We observed phagocytosis or respiratory burst enhancing activity in 17 extracts, of which five species, namely Aurantiporus fissilis (Berk. & M.A. Curtis) H. Jahn ex Ryvarden, Trametes gibbosa (Pers.) Fr., Piptoporus betulinus (Bull.) P. Karst, Neolentinus lepideus (Fr.) Redhead & Ginns, Polyporus squamosus (Huds.) Fr., significantly increased phagocytosis in granulocytes by 205, 181, 158, 155 and 141%, respectively. The β-glucan content of the three most potent extracts was 58, 42 and 74 mg/g, respectively, and the polyphenol content was 155.6, 133.5 and 155.2 μmol of gallic acid equivalent/g, respectively. Some extracts showed cytotoxic activity, with higher cytotoxicity in Caco-2 than in HT-29 cells. Pycnoporus cinnabarinus (Jacq.) P. Karst. extract was cytotoxic to both cell lines, with IC50 values of 81 and 31 μg/mL, respectively. Discussion and conclusion The most promising extracts were from N. lepideus and Polyporus squamosus, which are edible species and may be considered safe. Our findings support their use as culinary preparations or food supplements for various immunological gut disorders.

Effect of novel 1-phenyl-3-methyl-4-acylpyrazolones on iron chelation and Fenton reaction.

Iron is an essential element in many physiological processes due to its ability to easily convert between two oxidation states Fe(III)/Fe(II). However, at a pathological state, unbound iron may promote the production of highly toxic hydroxyl radicals via Fenton reaction, particularly when it is present in the excess.Iron chelators forming tight complexes with iron may prevent this reaction. In this study, novel synthetic 1-phenyl-3-methyl-4-acyl-pyrazol-5-ones were analyzed for their iron-chelating properties at four pathophysiologically relevant pH conditions (4.5-7.5) as well as for their effects on iron-based Fenton reaction. For the former competitive ferrozine spectrophotometric assay and for the latter HPLC method using salicylic acid as the indicator of hydroxyl radical production were used. All of the tested acylpyrazolones were efficient ferric chelators, however, their ferrous-chelating properties were clearly dependent on an acyl substitution. Interestingly, several acylpyrazolones had ferrous-chelating properties superior to those of the standard iron chelator - deferoxamine. Of particular interest is H2QpyQ, i.e. 2,6-bis[4(1-phenyl-3-methylpyrazol-5-one)carbonyl]pyridine, whose ferrous-chelating properties were increasing while pH was decreasing. In spite of large differences in ferrous chelation, a majority of the tested acylpyrazolones were powerful inhibitors of Fenton reaction as deferoxamine. In conclusion, the novel 1-phenyl-3-methyl-4-acyl-pyrazol-5-ones are efficient iron chelators and H2QpyQ may represent a prototype of specific iron chelators designed for chelation at acidic conditions in particular.