Natural and natural-like polyphenol compounds: in vitro antioxidant activity and potential for therapeutic application.

Introduction: Phenols are a large family of natural and synthetic compounds with known antioxidant activity. The aim of this study was to perform in vitro screening of natural and natural-like phenol monomers and their C2-symmetric dimers (hydroxylated biphenyls) in order to identify those representatives whose pharmacophores have the strongest antioxidant and the lowest prooxidant activity. Material and methods: Antioxidative properties of 36 compounds (monomers and their C2-symmetric dimers) were evaluated in vitro. Different (red/ox) assays were used to measure their total oxidative potential (TOP), their total antioxidative capacity (TAC), the pro-oxidative-antioxidant balance (PAB) and total SH-group content (SHG) in a biologically relevant environment. The Pro-oxidative Score, Antioxidative Score and the Oxy Score were also calculated. Trolox, a water soluble analogue of α-tocopherol, was used as a positive control. Results: In an assay consisting of pooled human serum, 6 of the 36 compounds showed significant antioxidant activity (compounds 6, 7, 12, 13, 26, and 27), whereas 4 showed extremely weak antioxidant activity (compounds 2, 29, 30, and 31). Within the 36 compounds comprising zingerone, dehydrozingerone, aurone, chalcone, and magnolol derivatives, in both monomeric and dimeric forms, the 2 compounds that indicated the highest antioxidant activity were dehydrozingerone derivatives (compounds 6 and 12). Trolox's activity was found between the strong and weak antioxidant compounds analysed in our study. Conclusions: In this study selected dehydrozingerones were identified as good candidates for in-depth testing of their biological behaviour and for possible precursors for synthesis of novel polyphenolic molecules with potential therapeutic applications.

Antioxidant properties of novel curcumin analogues: A combined experimental and computational study.

The multi-target activity of curcumin makes it a promising pharmacological lead for structural modifications focused on the preparation of new better therapeutics with improved bioavailability. A possible modification is to "decompose" the parent curcumin structure into constituent units and to build up curcumin analogues with biphenyl structural moiety. The antioxidant properties of the so-called "monomers" (m1-m3) and "dimers" (d1-d3) are studied experimentally and computationally. Their protective effects as chain-breaking antioxidants are investigated for the individual compounds and in binary/ternary compositions with α-tocopherol (TOH) and ascorbyl palmitate (AscPH). All monomers manifest significant synergism up to 70% in mixtures with TOH. Synergistic effects are found for the ternary compositions of monomeric analogues upon addition to the binary mixture of standard antioxidants (TOH + AscPH). Dimers with biphenyl skeleton manifest a lower potential in compositions under lipid oxidation conditions. DFT computations provide a detailed insight into the structure and antiradical properties of the curcumin analogues and standard antioxidants. PRACTICAL APPLICATIONS: Bioactive compounds in the diet play a crucial role in the prevention of numerous diseases in whose pathogenesis oxidative stress is well known to be involved. Therefore, enhancement of the antioxidant status of the biological target is often helpful. Two of the monomers studied are considered leading agents in the treatment or prophylaxis of smooth muscle disorders and are useful in the maintenance of the normal gut function- as a calmative for the gut and to ease upset stomach. We hypothesized that the presence of a biphenyl scaffold in the parent molecular structure can enhance the biological activity. Equimolar mixtures of TOH with studied compounds have potential application in food chemistry and medicine. A composition comprising the active agent and additional components (strong conventional antioxidants) may be administered in foodstuffs, as a food supplement, beverage supplement, or as a pharmaceutical composition.

Hydroxylated biphenyl derivatives are positive modulators of human GABA(A) receptors.

A series of 7 hydroxylated biphenyl derivatives (1-7) were prepared to evaluate their ability to modulate the function of several ligand gated ion channel (LGIC) recombinant receptors expressed in Xenopus laevis oocytes. Compounds 1, 3, 4, 6 and 7 are natural occurring compounds whereas the synthesis of compounds 2 and 5 was previously reported (Delogu et al., 2004; Fabbri et al., 2007). None of the compounds tested were able to modify, the activity of the strychnine-sensitive glycine receptor, or the activity of nicotinic receptor. The function of the 5HT(3A) receptor was partially inhibited by all compounds tested, however this inhibition occurred at relatively high concentrations (100 µM). All compounds, with the exception of compound 6, potentiate the action of gamma-aminobutyric acid (GABA)-evoked Cl(-) currents in Xenopus laevis oocytes expressing recombinant human α(1)ß(2)γ(2L) GABA(A) receptors. Compounds 1, 2, 5 and 7 enhance the function of the GABA(A) receptor at concentrations higher than 3-10 µM. Compound 4 was the most efficacious. However, compound 3 was the most potent (EC(50) 0.8 µM). The potency of compound 3 in modulating the function of the GABA(A) receptor was comparable to that of diazepam, propofol or allopregnanolone. The enhancement of the GABA evoked Cl(-) currents by compound 3 was not affected by flumazenil. Compound 3 did not induce loss of the righting reflex in rats suggesting that it is not an anesthetic agent, however, its ability in protecting the animals from seizures induced by picrotoxin confirm that its action occurs through the GABA(A) receptor.