Lluís Juliá

Effect of new antioxidant cysteinyl-flavanol conjugates on skin cancer cells

Novel catechin derivatives obtained from grape procyanidins and l‐cysteine scavenge free radicals by hydrogen atom donation, rather than electron transfer, and reduce cell viability in A375 and M21 melanoma cells. In particular, 4β‐(S‐cysteinyl)epicatechin 3‐O‐gallate has a free radical scavenging capacity as strong as that of tea (−)‐epigallocatechin gallate and causes a significant S‐phase cell‐cycle arrest in both cell lines at doses higher than 100 μM. The other cysteinyl compounds do not affect normal cell cycle distribution. The gallate derivative also induces apoptosis in melanoma cells more strongly than the other derivatives and the parent (−)‐epicatechin do. The gallate compound seems to trigger nuclear condensation and fragmentation, which is confirmed by DNA laddering. Interestingly, they do not induce apoptosis in keratinocytes (HaCaT).

Electron‐transfer capacity of catechin derivatives and influence on the cell cycle and apoptosis in HT29 cells

Galloylated and nongalloylated catechin conjugates with cysteine derivatives have been synthesized and evaluated for their capacity to scavenge free radicals and to influence crucial functions (cell cycle, apoptosis) in HT29 colon carcinoma cells. We show that the nonphenolic part of the molecule modified the capacity of catechins to donate hydrogen atoms and to transfer electrons to free radicals. Nongalloylated derivatives did not significantly influence either the cell cycle or apoptosis. Among the galloylated species, 4β‐[S‐(O‐ethyl‐cysteinyl)]epicatechin 3‐O‐gallate, which showed a high electron‐transfer capacity (5 e– per molecule), arrested the cell cycle and induced apoptosis as expected for galloylated catechins such as tea (–)‐epigallocatechin 3‐O‐gallate. 4β‐[S‐(N‐Acetyl‐O‐methyl‐cysteinyl)]epicatechin 3‐O‐gallate, which showed the highest hydrogen‐donating capacity (10 H per molecule) while keeping the electron‐transfer capacity low (2.9 e– per molecule), did not trigger any significant apoptosis. The gallate moiety did not appear to be sufficient for the pro‐apoptotic effect of the catechin derivatives in HT29 cells. Instead, a high electron‐transfer capacity is more likely to be behind this effect. The use of stable radicals sensitive exclusively to electron transfer may help to design molecules with either preventive scavenging action (high hydrogen donation, low electron transfer) or therapeutic pro‐apoptotic activity (high electron transfer).

Tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical: a new stable coloured magnetic species as a chemosensor for natural polyphenols

We report the synthesis, electron paramagnetic resonance and electrochemical properties of a novel stable radical of the TTM series. Its strong electron acceptor ability has been tested with (-)-epicatechin, a natural polyphenolic antioxidant.

Punicalagin and catechins contain polyphenolic substructures that influence cell viability and can be monitored by radical chemosensors sensitive to electron transfer.

Plant polyphenols may be free radical scavengers or generators, depending on their nature and concentration. This dual effect, mediated by electron transfer reactions, may contribute to their influence on cell viability. This study used two stable radicals (tris(2,3,5,6-tetrachloro-4-nitrophenyl)methyl (TNPTM) and tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl (HNTTM)) sensitive only to electron transfer reduction reactions to monitor the redox properties of polyphenols (punicalagin and catechins) that contain phenolic hydroxyls with different reducing capacities. The use of the two radicals reveals that punicalagins substructures consisting of gallate esters linked together by carbon-carbon (C-C) bonds are more reactive than simple gallates and less reactive than the pyrogallol moiety of green tea catechins. The most reactive hydroxyls, detected by TNPTM, are present in the compounds that affect HT-29 cell viability the most. TNPTM reacts with C-C-linked gallates and pyrogallol and provides a convenient way to detect potentially beneficial polyphenols from natural sources.

The Effect of Convolvulus arvensis Dried Extract as a Potential Antioxidant in Food Models

In this study, the antioxidant activity of the Convolvulus arvensis Linn (CA) ethanol extract has been evaluated by different ways. The antioxidant activity of the extract assessed by 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical cation, the oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP) was 1.62 mmol Trolox equivalents (TE)/g DW, 1.71 mmol TE/g DW and 2.11 mmol TE/g DW, respectively. CA ethanol extract exhibited scavenging activity against the methoxy radical initiated by the Fenton reaction and measured by Electron Paramagnetic Resonance (EPR). The antioxidant effects of lyophilised CA measured in beef patties containing 0.1% and 0.3% (w/w) CA stored in modified atmosphere packaging (MAP) (80% O2 and 20% CO2) was determined. A preliminary study of gelatine based film containing CA showed a strong antioxidant effect in preventing the degradation of lipid in muscle food. Thus, the present results indicate that CA extract can be used as a natural food antioxidant.

Selective control of the radical-scavenging activity of poly(phenols) in aqueous media in terms of their electron-donor properties, using a stable organic radical as chemical sensor

The tri-potassium salt of tris(2,3,5,6-tetrachloro-4-hydroxysulphonylphenyl)methyl radical, 3K(+) TSPTM(3-), is a good chemical sensor of the radical-scavenging activity of poly(phenols) in aqueous media. Its water solubility and its stability at all pH values facilitates the study of the influence of the pH of the medium on the activity of poly(phenols). The radical-scavenging activity of three flavonoids of the catechol and pyrogallol type and the activity of catechol, pyrogallol and methyl gallate at pH values 7 and 8 which are close to physiological pH value (7.4) have been measured. This radical species reacts exclusively by an electron transfer mechanism against the reducing poly(phenols). Therefore, the experiments to determine the radical-scavenging activity of poly(phenols) with 3K(+) TSPTM(3-) are related to their ionization potentials (IP). As IP is a function of the pH of the medium, the electron donor ability of a poly(phenol) depends on the acidity or basicity of the fluid in question. The radical-scavenging activity of poly(phenols) 1-6 is higher at pH 8 than at pH 7. 3K(+) TSPTM(3-) is able to discriminate between catecholic and pyrogallolic moieties of poly(phenols) in water solutions by taking measurements at different pH values. By adjusting the pH of the medium 3K(+) TSPTM(3-) will easily detect those moieties (e.g. pyrogallol) most prone to elicit prooxidant effects.

EPR/spin-trapping study of free radical intermediates in the photolysis of trifluoromethyl ketones with initiators.

Photolysis of trifluoromethyl ketones (TFMKs) 1a–1e versus the non‐fluorinated ketones 2a–2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2‐methyl‐2‐nitrosopropane (MNP) and 2,4,6‐tri‐tert‐butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t‐butylperoxide, short‐chain TFMKs, such as 1,1,1‐trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long‐chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one α‐methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a γ‐hydrogen to the carbonyl group. Copyright

A tri(potassium sulfonate) derivative of perchlorotriphenylmethyl radical (PTM) as a stable water soluble radical-scavenger of the hydroxyl radical more powerful than 5,5-dimethyl-1-pyrroline-N-oxide

The tripotassium salt of tris(2,3,5,6-tetrachloro-4-hydroxysulfonylphenyl)methyl radical (3 K+ TSPTM3−) reacts in water with hydroxyl radical very fast with a rate constant (k = 2.4 × 1011 M−1 s−1) much higher than that of the reaction of hydroxyl radical with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) (k = 3.4 × 109 M−1 s−1). The reaction affects the radical character of the molecule and is monitored by electron paramagnetic resonance (EPR). The hydroxyl radical scavenging is established by the characterization of the resulting water-soluble product as the dipotassium salt of 4-[bis(2,3,5,6-tetrachloro-4-hydroxysulfonylphenyl)methylene]-2,3,5,6-tetrachlorocyclohexa-2,5-dien-1-one (2).

High electron transfer capacity of thio-derivatives of tea catechins measured using a water soluble stable free radical and their effects on colon cancer cells

The antiradical capacity of cysteamine- and cysteine-flavan-3-ol derivatives of green tea catechins bearing the pyrogallol moiety was evaluated using two stable triphenylmethyl radicals, the tri-potassium salt of a tris(4-hydroxysulfonyltetrachlorophenyl)methyl radical (K3TSPTM) and a tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical (HNTTM), as chemosensors in a buffer solution at pH 7 and in the CHCl3–MeOH mixture (2:1, v/v), respectively. The different results obtained using HNTTM or K3TSPTM lie in the chemical nature of these radicals and, therefore, in their reduction potentials, and in the solvent used in the experiments. The K3TSPTM radical was selectively sensitive to the pyrogallol moiety in water like TNPTM was in organic solvents, and as a chemosensor is closer to the biological processes by using aqueous media as solvent. The new radical is a useful tool to detect highly reactive phenolic positions that are also the most biologically active as shown by the results on the viability and apoptosis of the colon adenocarcinoma cell line HT-29.

An EPR analysis of β-dimerization in α-blocked pyrroles in oxidant conditions

Electron paramagnetic resonance (EPR) analysis of neutral and acidic solutions of 2,5‐dimethyl‐1‐phenylpyrrol (1) and meta‐, para‐, and ortho‐bis(2,5‐dimethylpyrrol‐1‐yl)benzenes (4–6) in the presence of Tl(III) trifluoroacetate as oxidant reveals the poor stability of their generated monomeric radical cations which dimerize through C(β)C(β) bond formation. EPR spectra of the monomeric radical cations 4•+, 5•+, and 6•+ coincide with that of 1•+, suggesting that the unpaired electron in these charged species is confined in one of the pyrrolic rings. The very twisted angles between pyrrolic and phenyl planes due to steric hindrance in the X‐ray analysis of the molecular structure of 4 confirm the absence of extended conjugation in the π‐system. Copyright