4-Mercaptoimidazoles derived from the naturally occurring antioxidant ovothiols 2. Computational and experimental approach of the radical scavenging mechanism

Extraction, purification, structure, modification, and biological activity of traditional Chinese medicine polysaccharides: A review

Traditional Chinese medicines (TCM), as the unique natural resource, are rich in polysaccharides, polyphenols, proteins, amino acid, fats, vitamins, and other components. Hence, TCM have high medical and nutritional values. Polysaccharides are one of the most important active components in TCM. Growing reports have indicated that TCM polysaccharides (TCMPs) have various biological activities, such as antioxidant, anti-aging, immunomodulatory, hypoglycemic, hypolipidemic, anti-tumor, anti-inflammatory, and other activities. Hence, the research progresses and future prospects of TCMPs must be systematically reviewed to promote their better understanding. The aim of this review is to provide comprehensive and systematic recombinant information on the extraction, purification, structure, chemical modification, biological activities, and potential mechanism of TCMPs to support their therapeutic effects and health functions. The findings provide new valuable insights and theoretical basis for future research and development of TCMPs.

Characterization and antioxidant activity of pectin from Indonesian mangosteen (Garcinia mangostana L.) rind

Pectin, a natural polysaccharide, has gained increasing attention due to not only its biomaterial properties but also its biomedical activities. One of the abundant sources of pectin is mangosteen (Garcinia mangostana L.) rind. In this study, we characterized the pectin from Indonesian mangosteen rind extract and evaluated its antioxidant activity. Pectin was extracted in acid condition and evaluated its physicochemical properties by fourier transform infrared (FTIR), powder X-ray diffractometer (PXRD), water content, ash content, equivalent weight, methoxyl level and of galacturonic acid content. Furthermore, the antioxidant activity of pectin was also observed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. Pectin was successfully extracted from dry weight of Indonesian mangosten rind with yield about 1,16 ± 0,17%, fine powder, brownish and odorless. FTIR and PXRD results showed that pectin from mangosteen rind extract was amorphous and similar characteristic with a commercial pectin. The chemical properties of pectin such as water content, ash content, equivalent weight, methoxyl level and of galacturonic acid level were 9.85 ± 0.12%, 3.91 ± 0.17%, 6330.76 ± 220.43 g/mol, 2.86 ± 0.05% and 75.98 ± 0.88%, respectively. In addition, pectin showed an antioxidant activity with the IC₅₀ about 161.94 ± 31.57 ppm. These results suggest that pectin from Indonesian mangosteen rind has the potential properties as biopolymers for biomedical applications with a low-methylated pectin and a moderate antioxidant activity.

Ovothiol A is the Main Antioxidant in Fish Lens

Tissue protection from oxidative stress by antioxidants is of vital importance for cellular metabolism. The lens mostly consists of fiber cells lacking nuclei and organelles, having minimal metabolic activity; therefore, the defense of the lens tissue from the oxidative stress strongly relies on metabolites. Protein-free extracts from lenses and gills of freshwater fish, Sander lucioperca and Rutilus rutilus lacustris, were subjected to analysis using high-field 1H NMR spectroscopy and HPLC with optical and high-resolution mass spectrometric detection. It was found that the eye lenses of freshwater fish contain high concentrations of ovothiol A (OSH), i.e., one of the most powerful antioxidants exciting in nature. OSH was identified and quantified in millimolar concentrations. The concentration of OSH in the lens and gills depends on the fish genus and on the season. A possible mechanism of the reactive oxygen species deactivation in fish lenses is discussed. This work is the first to report on the presence of OSH in vertebrates. The presence of ovothiol in the fish tissue implies that it may be a significantly more common antioxidant in freshwater and marine animals than was previously thought.

A Computational Investigation of the Binding of the Selenium Analogues of Ergothioneine and Ovothiol to Cu(I) and Cu(II) and the Effect of Binding on the Redox Potential of the Cu(II)/Cu(I) Redox Couple

The complexes formed from the binding of ovoselenol (OSeH) and ergoseloneine (ESeH) to Cu(II) and Cu(I) have been investigated with DFT methods. From the calculated thermodynamics, the binding of OSeH and ESeH to Cu(II) and Cu(I) ions increases the reduction potential for the Cu(II)/Cu(I) redox couple. The calculated reduction potentials for the Cu(II)(OSe)2/Cu(I)(OSeH)3+ and Cu(II)(ESe)2/Cu(I)(ESeH)3+ redox couples were found to be 1.15 V and 1.24 V in a dilute aqueous solution. By combining the half reactions for the oxidation of OSeH to the diselenide OSeSeO with the reduction of Cu(II)(OSe)2 to Cu(I)(OSeH)3+, the calculated EMF was 0.90 V. For the oxidation of ESeH to the diselenide ESeSeE with the concomitant reduction of Cu(II)(ESe)2 to Cu(I)(ESeH)3+, the calculated EMF was 0.67 V. Thus, for both systems, the reduction of Cu(II) to Cu(I) with concomitant formation of either diselenide is thermodynamically favourable, and it is expected that both OSeH and ESeH are suitable for the protection against copper induced oxidative damage. As a result, the inhibition of the recycling of Cu(I) to Cu(II) is thermodynamically favourable in the presence of OSeH and ESeH.

Regenerable Thiophenolic Radical-Trapping Antioxidants

Diphenyl disulfides carrying alkyltelluro groups in the o-, m-, and p-positions were prepared using ortho-lithiation and lithium halogen exchange reactions. The novel antioxidants showed only minimal inhibitory effect on the azo-initiated peroxidation of linoleic acid in chlorobenzene until reduced to the corresponding thiophenols by tris(2-carboxyethyl)phosphine (TCEP). The best in situ generated thiophenol (from 7c) under these conditions quenched peroxyl radicals more efficiently than α-tocopherol with an almost 3-fold increase in inhibition time.

The complete microspeciation of ovothiol A disulfide: a hexabasic symmetric biomolecule

The site-specific acid-base properties of ovothiol A disulfide (OvSSOv), the smallest hexabasic multifunctional biomolecule with complex interdependent moieties, were studied with (1)H NMR-pH and potentiometric titrations. The unprecedented complexity of the protonation microequilibria could be overcome by taking into account the mirror-image molecular symmetry, synthesizing and studying auxiliary model compounds and developing a custom-tailored evaluation method. The amino, imidazole, and carboxylate moieties are quantified in terms of 192 microscopic protonation constants and 64 microspecies, 96 and 36 of which are chemically different ones, respectively. Nine pairwise interactivity parameters also characterize the OvSSOv-proton system at the level of molecular subunits. These data allow understanding and influencing the co-dependent acid-base and redox properties of the highly complex OvSH-OvSSOv and related thiol-disulfide systems, which provide protection against oxidative stress. This work is the first complete microspeciation of a hexabasic molecule.

Ovothiol isolated from sea urchin oocytes induces autophagy in the Hep-G2 cell line

Ovothiols are histidine-derived thiols isolated from sea urchin eggs, where they play a key role in the protection of cells toward the oxidative burst associated with fertilization by controlling the cellular redox balance and recycling oxidized glutathione. In this study, we show that treatment of a human liver carcinoma cell line, Hep-G2, with ovothiol A, isolated from Paracentrotus lividus oocytes, results in a decrease of cell proliferation in a dose-dependent manner. The activation of an autophagic process is revealed by phase contrast and fluorescence microscopy, together with the expression of the specific autophagic molecular markers, LC3 II and Beclin-1. The effect of ovothiol is not due to its antioxidant capacity or to hydrogen peroxide generation. The concentration of ovothiol A in the culture media, as monitored by HPLC analysis, decreased by about 24% within 30 min from treatment. The proliferation of normal human embryonic lung cells is not affected by ovothiol A. These results hint at ovothiol as a promising bioactive molecule from marine organisms able to inhibit cell proliferation in cancer cells.

The complete microspeciation of ovothiol A, the smallest octafarious antioxidant biomolecule

Ovothiol A, a small biomolecule with highly potent antioxidant capacity, and three newly synthesized derivatives were studied by (1)H NMR, (15)N NMR, UV-pH titrations, and a customized evaluation method. The omni-interactive imidazole, amino, carboxylate, and thiolate moieties of ovothiol A are quantified in terms of 32 microscopic protonation constants, the relative concentrations of 16 microspecies, 6 pairwise interactivity parameters, and 8 protonation shifts. The highest and lowest imidazole basicities differ by a record-breaking five orders of magnitude, and the predominant thiolate protonation constant is by far the smallest known thiolate logK value. The latter provides an indication as to why ovothiol A occurs naturally under deep-water circumstances only. Since thiolate basicities are in correlation with thiol-disulfide redox potentials, the eight different, fine-tunable thiolate basicities offer versatile and highly specific antioxidant capacities within one single molecular skeleton. This work is the first complete microspeciation of a tetrabasic, nonsymmetrical natural compound.

Model iron-oxo species and the oxidation of imidazole: insights into the mechanism of OvoA and EgtB?

A density functional theory cluster and first-principles quantum and statistical mechanics approach have been used to investigate the ability of iron-oxygen intermediates to oxidize a histidine cosubstrate, which may then allow for the possible formation of 2- and 5-histidylcysteine sulfoxide, respectively. Namely, the ability of ferric superoxo (Fe(III)O(2)(•-)), Fe(IV)═O, and ferrous peroxysulfur (Fe(III)OOS) complexes to oxidize the imidazole of histidine via an electron transfer (ET) or a proton-coupled electron transfer (PCET) was considered. While the high-valent mononuclear Fe(IV)═O species is generally considered the ultimate biooxidant, the free energies for its reduction (via ET or PCET) suggest that it is unable to directly oxidize histidine's imidazole. Instead, only the ferrous peroxysulfur complexes are sufficiently powerful enough oxidants to generate a histidyl-derived radical via a PCET process. Furthermore, while this process preferably forms a HisN(δ)(-H)(•) radical, several such oxidants are also suggested to be capable of generating the higher-energy HisC(δ)(-H)(•) and HisC(ε)(-H)(•) radicals. Importantly, the present results suggest that formation of the sulfoxide-containing products (seen in both OvoA and EgtB) is a consequence of the reduction of a powerful Fe(III)OOS oxidant via a PCET.

Component analysis and free radicals scavenging activity of Cicer arietinum L. husk pectin

A pectin (CAP) was extracted from the husk of Cicer arietinum L. Monosaccharide analysis of CAP revealed the dominance of galacturonic acid and smaller amounts of galactose, arabinose, rhamnose, glucose, xylose and mannose. Viscosimetric analysis showed that the intrinsic viscosity ([η]) and the molecular weight (MW) of CAP were 296 mL/g and 105 kDa, respectively. The degree of esterification (DE = 10%) was determined by FTIR spectroscopy. CAP exhibited a dose-dependent free radical scavenging activity, as shown by its DPPH radical inhibition. At 1.0 mg/mL CAP exhibited a scavenging rate of 29% on DPPH radicals. The evaluation of antioxidant activity suggested that CAP had good potential for DPPH radical scavenging activity and should be explored as a novel potential antioxidant.

Antiradical and antioxidant activities of alkaloids isolated from Mahonia aquifolium. Structural aspects

The antioxidant activities of three alkaloids isolated from Mahonia aquifolium--berberine, jatrorrhizine, and magnoflorine--were studied with respect to their structural aspects, particularly the presence and the position of -OH groups, steric conditions of unpaired electron delocalization and parameters of lipophilicity and hydration energy. The antiradical activities of the compounds tested were evaluated as the reactivities toward free stable alpha,alpha'-diphenyl-beta-picrylhydrazyl radical (DPPH). The antioxidant features of the alkaloids tested were investigated in heterogeneous membrane system of DOPC liposomes stressed by peroxidative damage induced by AAPH azoinitiator. Both alkaloids bearing free phenolic groups--jatrorrhizine and magnoflorine--showed better activities in both systems used than berberine not bearing any readily abstractable hydrogen on its skeleton. The former two showed antiperoxidative efficiency in DOPC liposomal membrane comparable to that of an effective scavenger of peroxyl radicals--stobadine-and higher than that of Trolox. We conclude that the favorable antioxidant features of the hydroxylated alkaloids are most probably ensured by the combination of reasonably high antiradical reactivity with high lipophilicity, however, the solvation process was found to markedly interfere with these beneficial effects.

Ab initio studies of the properties of intracellular thiols ergothioneine and ovothiol

Intracellular naturally occurring aromatic thiols such as ergothioneine and the ovothiols have been shown to play a variety of roles in cellular function. A detailed ab initio electronic structure analysis of these thiols is reported evaluating the thermodynamics of the reactions of these intracellular thiols with alkyl thiols, HO*, H2O2, ascorbate and their disulfides.

Design, synthesis and glutathione peroxidase-Like properties of ovothiol-Derived diselenides

Eleven imidazole diselenides derived from the naturally occurring family of antioxidants, the ovothiols, were synthetised by cyclisation of selenoamides with trimethylsilyltrifluoromethanesulfonate or refluxing of cyanoamines in a selenium/sodium borohydride mixture. These compounds were assayed for their glutathione peroxidase-like (GSH Px-like) activity and their capacity to be reduced by glutathione. The most active molecules of the series were 4 times more potent in the GSH Px-like test than the widely known reference compound, ebselen. This catalytic activity was mediated by the formation of the antioxidant selenol intermediate upon partial but significant exchange reaction with glutathione.

Structural aspects of antioxidant activity of substituted pyridoindoles

Stobadine and its two structural analogues, dehydrostobadine and N-acetylated stobadine were used to examine how structural alteration in the close proximity of the indolic nitrogen would influence the antioxidant activity of the substituted pyridoindoles. The compounds were tested for their efficiency to scavenge stable free radicals of alpha,alpha'-diphenyl-beta-picrylhydrazyl as well as for their ability to prevent 2,2'-azobis-(2-amidinopropane)hydrochloride induced peroxidation of dioleoyl phosphatidylcholine liposomes. The results proved that the substituted pyridoindoles can act as potent scavengers of peroxyl radicals both in aqueous and lipid phases, the antioxidant activity being comparable with that of Trolox. Structural changes in the proximity of the indolic nitrogen were found crucial for the radical scavenging efficiency: aromatisation of the pyridoindole skeleton in dehydrostobadine lowered the antioxidant activity, while acetylation of the indolic nitrogen completely abolished the ability to scavenge peroxyl radicals. The results are in agreement with the notion that the antioxidant activity of stobadine and of the related pyridoindoles may be mediated via the indolic nitrogen centre. When stobadine and Trolox were present simultaneously in liposomal incubations, Trolox spared stobadine in a dose-dependent manner; a direct interaction of Trolox with stobadinyl radical appears to be a plausible explanation with possible consequences for the antioxidant capacity of stobadine under in vivo conditions, where re-cycling of stobadine by vitamin E might occur.

Antioxidant actions of ovothiol-derived 4-mercaptoimidazoles: glutathione peroxidase activity and protection against peroxynitrite-induced damage

4-Mercaptoimidazoles derived from the naturally occurring antioxidants, ovothiols, were tested for their glutathione peroxidase-like (GSH Px-like) activity and protection against peroxynitrite-induced damage. All the thiol compounds displayed similar significant GSH Px-like activities, which are however weaker than that of the reference compound, ebselen. The inhibitions of the peroxynitrite-dependent oxidation of Evans blue dye and dihydrorhodamine 123 showed that the thiol compounds substituted on position 5 of the imidazole ring were nearly as effective as ebselen while the C-2 substituted ones were less effective. Both assays corroborate the large superiority of mercaptoimidazoles over glutathione as inhibitors of peroxynitrite-dependent oxidation.