Free radical mediated interaction of ascorbic acid and ascorbate/Cu(II) with viral and plasmid DNAs

Ascorbic acid modulates the structure of the Pseudomonas aeruginosa virulence factor pyocyanin and ascorbic acid-furanone-30 combination facilitate biofilm disruption

The production of pyocyanin by Pseudomonas aeruginosa increases its virulence, fitness and biofilm formation. Pyocyanin is also a redox molecule and we hypothesize that ascorbic acid being an antioxidant will interact with pyocyanin. The main objective of this study was to investigate the potential interaction of ascorbic acid with pyocyanin, and also to investigate the impact of ascorbic acid in combination with Furanone-30 on quorum sensing and biofilm formation of P. aeruginosa. When incubated with ascorbic acid, hyperchromic and hypsochromic shifts in pyocyanin absorbance peaks at 385 nm and 695 nm were observed. In the presence of dehydroascorbic acid and citric acid, these shifts were absent, indicating that the intrinsic antioxidant property of ascorbic acid was probably essential in binding to pyocyanin. NMR spectroscopy showed shifts in ¹H NMR pyocyanin peaks between 8.2 to 5.8 ppm when incubated in the presence of ascorbic acid. Density Functional Theory (DFT) supported potential interactions between the -CH₂OH or -OH moieties of ascorbic acid with the -C=O moiety of pyocyanin. The pyocyanin-ascorbic acid complex impaired pyocyanin binding to DNA. Ascorbic acid combined with furanone-30 elevated quorum-sensing inhibition in P. aeruginosa, which was directly associated with significantly reduced P. aeruginosa virulence, adhesion, aggregation and biofilm formation and enhanced antibiotic-mediated bacterial killing. This study demonstrated that the antioxidant ascorbic acid directly binds to pyocyanin, modulates its structure and results in disruption of biofilm formation and associated tolerance to antibiotics.

Cellular Red-Ox system in health and disease: The latest update

Cells are continually exposed to reactive oxygen species (ROS) generated during cellular metabolism. Apoptosis, necrosis, and autophagy are biological processes involving a feedback cycle that causes ROS molecules to induce oxidative stress. To adapt to ROS exposure, living cells develop various defense mechanisms to neutralize and use ROS as a signaling molecule. The cellular redox networks combine signaling pathways that regulate cell metabolism, energy, cell survival, and cell death. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) are essential antioxidant enzymes that are required for scavenging ROS in various cell compartments and response to stressful situations. Among the non-enzymatic defenses, vitamin C, glutathione (GSH), polyphenols, carotenoids, vitamin E, etc., are also essential. This review article describes how ROS are produced as byproducts of oxidation/reduction (redox) processes and how the antioxidants defense system is directly or indirectly engaged in scavenging ROS. In addition, we used computational methods to determine the comparative profile of binding energies of several antioxidants with antioxidant enzymes. The computational analysis demonstrates that antioxidants with a high affinity for antioxidant enzymes regulate their structures.

Recent Advancements in Enhancing Antimicrobial Activity of Plant-Derived Polyphenols by Biochemical Means

Plants are a reservoir of phytochemicals, which are known to possess several beneficial health properties. Along with all the secondary metabolites, polyphenols have emerged as potential replacements for synthetic additives due to their lower toxicity and fewer side effects. However, controlling microbial growth using these preservatives requires very high doses of plant-derived compounds, which limits their use to only specific conditions. Their use at high concentrations leads to unavoidable changes in the organoleptic properties of foods. Therefore, the biochemical modification of natural preservatives can be a promising alternative to enhance the antimicrobial efficacy of plant-derived compounds/polyphenols. Amongst these modifications, low concentration of ascorbic acid (AA)–Cu (II), degradation products of ascorbic acid (DPAA), Maillard reaction products (MRPs), laccase–mediator (Lac–Med) and horse radish peroxidase (HRP)–H2O2 systems standout. This review reveals the importance of plant polyphenols, their role as antimicrobial agents, the mechanism of the biochemical methods and the ways these methods may be used in enhancing the antimicrobial potency of the plant polyphenols. Ultimately, this study may act as a base for the development of potent antimicrobial agents that may find their use in food applications.

The Interplay of Ascorbic Acid with Quinones-Chelators—Influence on Lipid Peroxidation: Insight into Anticancer Activity

Ascorbic acid is a multifaceted compound that can perform both antioxidant and pro-oxidant activities in the redox reactions induced by transition metal ions, so its role in nature and especially in the human body is still the subject of debate. In the present study, we have examined the influence of ascorbic acid on lipid peroxidation in a model system that mimics the cell membrane, namely micelles of linoleic acid (LA), induced by chelate complexes of iron and copper ions with quinone-chelator 2-phenyl-4-(butylamino)-naphtholquinoline-7,12-dione (Q1). This quinone effectively generates reactive oxygen species and semiquinone radicals inside cancer cells via a cycling redox reaction. Here it was demonstrated that in the absence of quinone-chelator ascorbic acid significantly accelerates the lipid peroxidation induced by both Fe(II) and Cu(II) ions. It has been shown also that Q1 chelate complexes with Fe(II) and Cu(II) ions are redox active in the LA micelles oxidation. No effect of ascorbate was detected on the reactivity of chelate complex with Fe(II) ions. On the other hand, ascorbate performs pro-oxidant activity in Q1-Cu(II) complex induced reaction. We can conclude that ascorbate-driven redox cycling of Q1 may promote its anti-tumor activity.

Mechanistic Insights of Chelator Complexes with Essential Transition Metals: Antioxidant/Pro-Oxidant Activity and Applications in Medicine

The antioxidant/pro-oxidant activity of drugs and dietary molecules and their role in the maintenance of redox homeostasis, as well as the implications in health and different diseases, have not yet been fully evaluated. In particular, the redox activity and other interactions of drugs with essential redox metal ions, such as iron and copper, need further investigation. These metal ions are ubiquitous in human nutrition but also widely found in dietary supplements and appear to exert major effects on redox homeostasis in health, but also on many diseases of free radical pathology. In this context, the redox mechanistic insights of mainly three prototype groups of drugs, namely alpha-ketohydroxypyridines (alpha-hydroxypyridones), e.g., deferiprone, anthraquinones, e.g., doxorubicin and thiosemicarbazones, e.g., triapine and their metal complexes were examined; details of the mechanisms of their redox activity were reviewed, with emphasis on the biological implications and potential clinical applications, including anticancer activity. Furthermore, the redox properties of these three classes of chelators were compared to those of the iron chelating drugs and also to vitamin C, with an emphasis on their potential clinical interactions and future clinical application prospects in cancer, neurodegenerative and other diseases.

Antioxidant Activity of Deferasirox and Its Metal Complexes in Model Systems of Oxidative Damage: Comparison with Deferiprone

Deferasirox is an orally active, lipophilic iron chelating drug used on thousands of patients worldwide for the treatment of transfusional iron overload. The essential transition metals iron and copper are the primary catalysts of reactive oxygen species and oxidative damage in biological systems. The redox effects of deferasirox and its metal complexes with iron, copper and other metals are of pharmacological, toxicological, biological and physiological importance. Several molecular model systems of oxidative damage caused by iron and copper catalysis including the oxidation of ascorbic acid, the peroxidation of linoleic acid micelles and the oxidation of dihydropyridine have been investigated in the presence of deferasirox using UV-visible and NMR spectroscopy. Deferasirox has shown antioxidant activity in all three model systems, causing substantial reduction in the rate of oxidation and oxidative damage. Deferasirox showed the greatest antioxidant activity in the oxidation of ascorbic acid with the participation of iron ions and reduced the reaction rate by about a 100 times. Overall, deferasirox appears to have lower affinity for copper in comparison to iron. Comparative studies of the antioxidant activity of deferasirox and the hydrophilic oral iron chelating drug deferiprone in the peroxidation of linoleic acid micelles showed lower efficiency of deferasirox in comparison to deferiprone.

Trying to Solve the Puzzle of the Interaction of Ascorbic Acid and Iron: Redox, Chelation and Therapeutic Implications

Iron and ascorbic acid (vitamin C) are essential nutrients for the normal growth and development of humans, and their deficiency can result in serious diseases. Their interaction is of nutritional, physiological, pharmacological and toxicological interest, with major implications in health and disease. Millions of people are using pharmaceutical and nutraceutical preparations of these two nutrients, including ferrous ascorbate for the treatment of iron deficiency anaemia and ascorbate combination with deferoxamine for increasing iron excretion in iron overload. The main function and use of vitamin C is its antioxidant activity against reactive oxygen species, which are implicated in many diseases of free radical pathology, including biomolecular-, cellular- and tissue damage-related diseases, as well as cancer and ageing. Ascorbic acid and its metabolites, including the ascorbate anion and oxalate, have metal binding capacity and bind iron, copper and other metals. The biological roles of ascorbate as a vitamin are affected by metal complexation, in particular following binding with iron and copper. Ascorbate forms a complex with Fe³⁺ followed by reduction to Fe²⁺, which may potentiate free radical production. The biological and clinical activities of iron, ascorbate and the ascorbate–iron complex can also be affected by many nutrients and pharmaceutical preparations. Optimal therapeutic strategies of improved efficacy and lower toxicity could be designed for the use of ascorbate, iron and the iron–ascorbate complex in different clinical conditions based on their absorption, distribution, metabolism, excretion, toxicity (ADMET), pharmacokinetic, redox and other properties. Similar strategies could also be designed in relation to their interactions with food components and pharmaceuticals, as well as in relation to other aspects concerning personalized medicine.

Redox Interactions of Vitamin C and Iron: Inhibition of the Pro-Oxidant Activity by Deferiprone

Ascorbic acid (AscH₂) is one of the most important vitamins found in the human diet, with many biological functions including antioxidant, chelating, and coenzyme activities. Ascorbic acid is also widely used in medical practice especially for increasing iron absorption and as an adjuvant therapeutic in iron chelation therapy, but its mode of action and implications in iron metabolism and toxicity are not yet clear. In this study, we used UV–Vis spectrophotometry, NMR spectroscopy, and EPR spin trapping spectroscopy to investigate the antioxidant/pro-oxidant effects of ascorbic acid in reactions involving iron and the iron chelator deferiprone (L1). The experiments were carried out in a weak acidic (pH from 3 to 5) and neutral (pH 7.4) medium. Ascorbic acid exhibits predominantly pro-oxidant activity by reducing Fe³⁺ to Fe²⁺, followed by the formation of dehydroascorbic acid. As a result, ascorbic acid accelerates the redox cycle Fe³⁺ ↔ Fe²⁺ in the Fenton reaction, which leads to a significant increase in the yield of toxic hydroxyl radicals. The analysis of the experimental data suggests that despite a much lower stability constant of the iron–ascorbate complex compared to the FeL1₃ complex, ascorbic acid at high concentrations is able to substitute L1 in the FeL1₃ chelate complex resulting in the formation of mixed L1₂AscFe complex. This mixed chelate complex is redox stable at neutral pH = 7.4, but decomposes at pH = 4–5 during several minutes at sub-millimolar concentrations of ascorbic acid. The proposed mechanisms play a significant role in understanding the mechanism of action, pharmacological, therapeutic, and toxic effects of the interaction of ascorbic acid, iron, and L1.

Liposomal integration method for assessing antioxidative activity of water insoluble compounds towards biologically relevant free radicals: example of avarol

The liposomal integration method, in conjunction with electron paramagnetic resonance (EPR) spectroscopy, has been presented for the investigation of antioxidant activity of selected water-insoluble compound towards biologically relevant free radicals. This method was applied to avarol, a sesquiterpenoid hydroquinone isolated from the marine sponge Dysidea avara. The antioxidant activity of water-insoluble avarol towards ^•OH, O₂^•- and NO^• radicals was attained by its incorporation into the DPPC liposomes bilayer, and towards ascorbyl radicals in the organic solvent. Avarol's activity towards ^•OH, O₂^•-, NO^• and ascorbyl radicals was 86.2%, 50.9%, 23.6% and 61.8%, respectively, showing its significant radical scavenging potential.

A facile hydroxylation of arylboronic acids mediated by sodium ascorbate

A mild and selective method for the synthesis of phenols has been described.

Bovine Colostrum Whey Protein Hydrolysate Inhibits Cell DNA Damage and LDL Oxidation In Vitro

Whey protein isolated from bovine colostrums collected on the second day postpartum was two-stage hydrolyzed by alcalase and flavourzyme [...].

Light-Stimulated Generation of Free Radicals by Quinones-Chelators

The role of metal ions in the mechanism of light-stimulated redox activity of potential anticancer agent 2-phenyl-4-(butylamino)naphtha[2,3-h]quinoline-7,12-dione (Qc) has been studied by CIDNP (chemically induced dynamic nuclear polarization) and EPR methods. The photo-induced oxidation of NADH and its synthetic analog – substituted dihydropyridine (DHP) – by quinone Qc was used as a model. The Qc capability of producing chelating complexes with divalent metal ions of Fe, Zn and Ca was studied quantitatively by optical absorption spectroscopy. A significant decrease of electrochemical reduction potential of Qc (ΔE=0.4−0.6 eV for ACN and ACN/PBS solutions) in chelating complexes and in protonated form of Qc was observed. A pronounced increase in efficiency of DHP oxidation in chelating complexes with Zn2+ and Ca2+ ions compared with free Qc was demonstrated. The yields of free radicals, including reactive oxygen species (ROS) and reaction products, were a few times higher than those in the absence of metal ions. Application of such chelating compounds to enhance ROS generation looks very promising for anti-cancer therapy, including the photodynamic therapy.

The Inhibition Effect of Cell DNA Oxidative Damage and LDL Oxidation by Bovine Colostrums

In the present study, we investigated the effect of bovine colostrums on inhibition of DNA oxidative damage and low density lipoprotein (LDL) oxidation in vitro. Results showed that whey and skimmed milk exhibited not only higher inhibitory activities of oxidative damage of deoxyribose but also an inhibitory effect on the breakdown of supercoiled DNA into open circular DNA and linear DNA. The quantities of 8-OH-2'-dG formed under whey, caseins and skimmed milk treatment were 0.24, 0.24 and 1.24 μg/mL, respectively. The quantity of malondialdehyde formed through LDL oxidation induced by copprous ion was significantly decreased as colostrums protein solutions were added, in which whey and caseins led to a more significant decrease than skimmed milk. The formation of conjugated dienes could be inhibited by treatment with colostrums protein solutions. Whey exhibited the longest lag time of conjugated dienes formation among the colostrums proteins. The lag time of the whey was 2.33 times that of the control. From the results of foregoing, the bovine colostrums protein has potential value in the inhibition of DNA oxidation damage and LDL oxidation.

Phenazine virulence factor binding to extracellular DNA is important for Pseudomonas aeruginosa biofilm formation

Bacterial resistance to conventional antibiotics necessitates the identification of novel leads for infection control. Interference with extracellular phenomena, such as quorum sensing, extracellular DNA integrity and redox active metabolite release, represents a new frontier to control human pathogens such as Pseudomonas aeruginosa and hence reduce mortality. Here we reveal that the extracellular redox active virulence factor pyocyanin produced by P. aeruginosa binds directly to the deoxyribose-phosphate backbone of DNA and intercalates with DNA nitrogenous base pair regions. Binding results in local perturbations of the DNA double helix structure and enhanced electron transfer along the nucleic acid polymer. Pyocyanin binding to DNA also increases DNA solution viscosity. In contrast, antioxidants interacting with DNA and pyocyanin decrease DNA solution viscosity. Biofilms deficient in pyocyanin production and biofilms lacking extracellular DNA show similar architecture indicating the interaction is important in P. aeruginosa biofilm formation.

Investigation of ascorbate-Cu (II) induced cleavage of DNA by scanning tunneling microscopy

Scanning Tunneling Microscopy (STM) was used for the investigation of oxidative DNA damage. A PCR amplified fragment of human beta-globin gene was used as a model for time dependent cleavage reaction by ascorbate and copper. Cleavage reactions were carried out in a medium containing 0.5 microgram/20 microliters DNA, 20 nM Tris-HC1 pH, 7.8 and ascorbate-Cu (II) in the final concentrations of 1 mM and 30 microM, respectively. The mixtures were incubated at 37 degrees C for 5, 15 and 30 min. For STM studies, 3 pg/5 microliters DNA samples were deposited on the gold coated mica and dried in a water flow vacuum drier. The STM was operated in air at atmospheric pressure with a tip-to-substrate bias of 100 mV and tunneling currents of < 10 pA. Etched tips of Pt/Ir wires were used in a constant current mode. The degradated DNA structure can be distinguished from the intact DNA and the sizes of the degradation products can be identified in the STM micrographs. The size of fragments decreased from approximately 3000 A to 34 A in ascorbate-Cu (II) medium, after 30 min of incubation.