Intracellular iron, but not copper, plays a critical role in hydrogen peroxide-induced DNA damage

Exploiting the beneficial effects of Salvia officinalis L. extracts in human health and assessing their activity as potent functional regulators of food microbiota

Salvia officinalis L. has attracted scientific and industrial interest due to its pharmacological properties. However, its detailed phytochemical profile and its correlation with beneficial effects in the human microbiome and oxidative stress remained elusive. To unveil this, S. officinalis was collected from the region of Epirus and its molecular identity was verified with DNA barcoding. Phytochemical profile for both aqueous and ethanol-based extracts was determined by high-pressure liquid chromatography-tandem mass spectrometry and 103 phytochemicals were determined. The effect of S. officinalis extracts as functional regulators of food microbiota by stimulating the growth of Lacticaseibacillus rhamnosus strains and by suppressing evolution of pathogenic bacteria was verified. Furthermore, we recorded that both extracts exhibited a significant cellular protection against H2O2-induced DNA damage. Finally, both extracts exhibited strong inhibitory effect towards LDL oxidation. This study provides a comprehensive characterization of S. officinalis on its phytochemical components as also its potential impact in human microbiome and oxidative stress.

Redox modulation of oxidatively-induced DNA damage by ascorbate enhances both in vitro and ex-vivo DNA damage formation and cell death in melanoma cells

Elevated genomic instability in cancer cells suggests a possible model-scenario for their selective killing via the therapeutic delivery of well-defined levels of further DNA damage. To examine this scenario, this study investigated the potential for redox modulation of oxidatively-induced DNA damage by ascorbate in malignant melanoma (MM) cancer cells, to selectively enhance both DNA damage and MM cell killing. DNA damage was assessed by Comet and ɣH2AX assays, intracellular oxidising species by dichlorofluorescein fluorescence, a key antioxidant enzymatic defence by assessment of catalase activity and cell survival was determined by clonogenic assay. Comet revealed that MM cells had higher endogenous DNA damage levels than normal keratinocytes (HaCaT cells); this correlated MM cells having higher intracellular oxidising species and lower catalase activity, and ranked with MM cell melanin pigmentation. Comet also showed MM cells more sensitive towards the DNA damaging effects of exogenous H2O2, and that ascorbate further enhanced this H2O2-induced damage in MM cells; again, with MM cell sensitivity to induced damage ranking with degree of cell pigmentation. Furthermore, cell survival data indicated that ascorbate enhanced H2O2-induced clonogenic cell death selectively in MM cells whilst protecting HaCaT cells. Finally, we show that ascorbate serves to enhance the oxidising effects of the MM therapeutic drug Elesclomol in both established MM cells in vitro and primary cell cultures ex vivo. Together, these results suggest that ascorbate selectively enhances DNA damage and cell-killing in MM cells. This raises the option of incorporating ascorbate into clinical oxidative therapies to treat MM.

Ultrasound-Assisted Extraction of Taro Leaf Antioxidants Using Natural Deep Eutectic Solvents: An Eco-Friendly Strategy for the Valorization of Crop Residues

Colocasia esculenta L. leaves are considered a by-product of taro cultivation and are discarded as environmental waste, despite their valuable phenolic composition. Their valorization to obtain value-added substances for medicinal, food, and cosmetic applications is the aim of the current work. An ultrasound-assisted extraction was developed for the environmentally friendly and sustainable isolation of taro leaf antioxidants using natural deep eutectic solvents (NaDESs). Among the utilized solvents, the NaDES based on betaine and ethylene glycol provided the best extraction efficiencies in terms of polyphenolic content and antioxidant activity. Multi-response optimization suggested a solvent-to-solid ratio of 10 mL g-1, a processing time of 60 min, an extraction temperature of 60 °C, and a water content of 33.8% (w/w) as optimal extraction parameters. Leaf extract obtained under these optimum operational parameters demonstrated a strong radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (65.80 ± 0.87%), a high ferric reducing antioxidant power (126.62 ± 1.92 μmol TE g-1 sample), and significant protection against oxidative stress-induced DNA damage. The chromatographic characterization of the optimum extract revealed its richness in flavonoids (flavones and flavonols). The outcomes of the present study suggest that the proposed method could serve as a highly efficient and green alternative for the recovery of polyphenols from agricultural wastes.

Oxidative Stress-Induced Cellular Senescence: Is Labile Iron the Connecting Link?

Cellular senescence, a cell state characterized by a generally irreversible cell cycle arrest, is implicated in various physiological processes and a wide range of age-related pathologies. Oxidative stress, a condition caused by an imbalance between the production and the elimination of reactive oxygen species (ROS) in cells and tissues, is a common driver of cellular senescence. ROS encompass free radicals and other molecules formed as byproducts of oxygen metabolism, which exhibit varying chemical reactivity. A prerequisite for the generation of strong oxidizing ROS that can damage macromolecules and impair cellular function is the availability of labile (redox-active) iron, which catalyzes the formation of highly reactive free radicals. Targeting labile iron has been proven an effective strategy to counteract the adverse effects of ROS, but evidence concerning cellular senescence is sparse. In the present review article, we discuss aspects of oxidative stress-induced cellular senescence, with special attention to the potential implication of labile iron.

Multiscale Modeling Unravels the Influence of Biomembranes on the Photochemical Properties of Embedded Anti-Oxidative Polyphenolic and Phenanthroline Chelating Dyes

The embedding of caffeate methyl ester, the flavonoids luteolin and quercetin, and the o-phenanthroline and neocuproine in a liquid disordered lipid bilayer has been studied through extensive atomistic calculations. The location and the orientation of these bio-active antioxidants are explained and analyzed. While the two phenanthrolines strongly associate with the lipid tail region, the other three compounds are rather found among the head groups. The simulations showcase conformational changes of the flavonoids. Through the use of a hybrid quantum mechanics-molecular mechanics scheme and supported by a profound benchmarking of the electronic excited-state method for these compounds, the influence of the anisotropic environment on the compounds' optical properties is analyzed. Influences of surrounding water molecules and of the polar parts of the lipids on the transition dipole moments and excited-state dipole moments are weighted with respect to a change in conformation. The current study highlights the importance of the mapping of molecular interactions in model membranes and pinpoints properties, which can be biomedically used to discriminate and detect different lipid environments.

Molecular mechanism of the unusual biphasic effects of the natural compound hinokitiol on iron-induced cellular DNA damage

Hinokitiol is a natural monoterpene compound found in the heartwood of cupressaceous plants that have anticancer and anti-inflammatory properties. However, few studies have focused on its effect on iron-mediated cellular DNA damage. Here we show that hinokitiol exhibited unusual biphasic effects on iron-induced DNA damage in a molar ratio (hinokitiol/iron) dependent manner in HeLa cells. Under low ratios (<3:1), hinokitiol markedly enhanced DNA damage induced by Fe(II) or Fe(II)-H₂O₂; However, when the ratios increased over 3:1, the DNA damage was progressively inhibited. We found that the total cytoplasmic and nuclear iron concentration increased as the ratios of hinokitiol/iron increased. However, the cellular level of labile iron pool (LIP) only increased at ratios lower than 3, and the ROS generation is consistent with LIP change. Hinokitiol was found to interact with iron to form lipophilic hinokitiol-iron complexes with different stoichiometry and redox-activity by complementary applications of various analytical methods. Taken together, we propose that the enhancement of iron-induced cellular DNA damage by hinokitiol at low ratios (<3:1) was due to formation of lipophilic and redox-active iron complexes which facilitated cellular iron uptake and •OH production, while the inhibition at ratios higher than 3 was due to formation of redox-inactive iron complexes. These new findings will help us to design more effective drugs for the prevention and treatment of a series of iron-related diseases via regulating the two critical physicochemical factors (lipophilicity and redox activity of iron complexes) by simple natural compounds with iron-chelating properties.

Combined administration of membrane-permeable and impermeable iron-chelating drugs attenuates ischemia/reperfusion-induced hepatic injury

BACKGROUND

The underlying pathophysiological mechanisms of hepatic ischemia-reperfusion (I/R) injury have not been completely elucidated. However, it is well known that oxidative stress, caused by a burst of reactive oxygen species (ROS) production during the reperfusion phase, plays a crucial role. A growing body of evidence indicates that the intracellular availability of free iron represents a requirement for ROS-induced adverse effects, as iron catalyzes the generation of highly reactive free radicals. The aim of this study was to examine whether a combination of iron chelators with varying lipophilicity could offer enhanced protection against I/R by diminishing the conversion of weak oxidants, like H₂O₂, to extremely reactive ones such as hydroxyl radicals (HO^.).

METHODS

HepG2 cells (hepatocellular carcinoma cell line) were exposed to oxidative stress conditions after pre-treatment with the iron chelators desferrioxamine (DFO) and deferiprone (DFP) alone or in combination. Labile iron pool was estimated using the calcein-acetoxymethyl ester (calcein-AM) method and DNA damage with the comet assay. We subsequently used a rabbit model (male New Zealand white rabbits) of hepatic I/R-induced injury to investigate, by measuring biochemical (ALT, ALT, ALP, γGT) and histological parameters, whether this may be true for in vivo conditions.

RESULTS

The combination of a membrane-permeable iron chelator (DFP) with a strong membrane-impermeable one (DFO) raises the level of protection in both hepatic cell lines exposed to oxidative stress conditions and hepatic I/R rabbit model.

CONCLUSIONS

Our results show that combinations of iron chelators with selected lipophilicity and iron-binding properties may represent a valuable strategy to protect against tissue damage during reperfusion after a period of ischemia.

Role of Fe, Transferrin and Transferrin Receptor in Anti-Tumor Effect of Vitamin C

High-dose vitamin C (VC) exhibits anti-tumor effects, and the cytotoxicity of VC is correlated with oxidative stress. However, iron, as a redox metal, plays an important effect in redox cycling and free radical formation in cells. This study addresses the role of iron ion in the cytotoxicity of VC. We found that iron supplementation increases the anti-tumor effect of VC, which was influenced by the cellular iron uptake pathway-transferrin (TF)/transferrin receptor (TFR) system. The TFR expression of tumors can be assessed by ⁶⁸Ga-citrate PET imaging, and it would be helpful to screen out the tumor type which is more sensitive to VC combined with an iron supplementation treatment.

Neuroprotective Effect of Quercetin during Cerebral Ischemic Injury Involves Regulation of Essential Elements, Transition Metals, Cu/Zn Ratio, and Antioxidant Activity

Cerebral ischemia results in increased oxidative stress in the affected brain. Accumulating evidence suggests that quercetin possesses anti-oxidant and anti-inflammatory properties. The essential elements magnesium (Mg), zinc (Zn), selenium (Se), and transition metal iron (Fe), copper (Cu), and antioxidants superoxide dismutase (SOD) and catalase (CAT) are required for brain functions. This study investigates whether the neuroprotective effects of quercetin on the ipsilateral brain cortex involve altered levels of essential trace metals, the Cu/Zn ratio, and antioxidant activity. Rats were intraperitoneally administered quercetin (20 mg/kg) once daily for 10 days before ischemic surgery. Cerebral ischemia was induced by ligation of the right middle cerebral artery and the right common carotid artery for 1 h. The ipsilateral brain cortex was homogenized and the supernatant was collected for biochemical analysis. Results show that rats pretreated with quercetin before ischemia significantly increased Mg, Zn, Se, SOD, and CAT levels, while the malondialdehyde, Fe, Cu, and the Cu/Zn ratio clearly decreased as compared to the untreated ligation subject. Taken together, our findings suggest that the mechanisms underlying the neuroprotective effects of quercetin during cerebral ischemic injury involve the modulation of essential elements, transition metals, Cu/Zn ratio, and antioxidant activity.

Outcomes of Deferoxamine Action on H2O2-Induced Growth Inhibition and Senescence Progression of Human Endometrial Stem Cells

Mesenchymal stem cells (MSCs) are broadly applied in regenerative therapy to replace cells that are lost or impaired during disease. The low survival rate of MSCs after transplantation is one of the major limitations heavily influencing the success of the therapy. Unfavorable microenvironments with inflammation and oxidative stress in the damaged regions contribute to MSCs loss. Most of the strategies developed to overcome this obstacle are aimed to prevent stress-induced apoptosis, with little attention paid to senescence—another common stress reaction of MSCs. Here, we proposed the strategy to prevent oxidative stress-induced senescence of human endometrial stem cells (hMESCs) based on deferoxamine (DFO) application. DFO prevented DNA damage and stress-induced senescence of hMESCs, as evidenced by reduced levels of reactive oxygen species, lipofuscin, cyclin D1, decreased SA-β-Gal activity, and improved mitochondrial function. Additionally, DFO caused accumulation of HIF-1α, which may contribute to the survival of H₂O₂-treated cells. Importantly, cells that escaped senescence due to DFO preconditioning preserved all the properties of the initial hMESCs. Therefore, once protecting cells from oxidative damage, DFO did not alter further hMESCs functioning. The data obtained may become the important prerequisite for development of a new strategy in regenerative therapy based on MSCs preconditioning using DFO.

Caffeic Acid Phenyl Ester (CAPE) Protects against Iron-Mediated Cellular DNA Damage through Its Strong Iron-Binding Ability and High Lipophilicity

Caffeic acid phenethyl ester (CAPE) and its structurally-related caffeic acid (CA), ferulic acid (FA) and ethyl ferulate (EF) are constituents of honeybee propolis that have important pharmacological activities. This study found that CAPE—but not CA, FA, and EF—could effectively prevent cellular DNA damage induced by overloaded iron through decreasing the labile iron pool (LIP) levels in HeLa cells. Interestingly, CAPE was found to be more effective than CA in protecting against plasmid DNA damage induced by Fe(II)–H₂O₂ or Fe(III)–citrate–ascorbate-H₂O₂ via the inhibition of hydroxyl radical (•OH) production. We further provided more direct and unequivocal experimental evidences for the formation of inactive CAPE/CA–iron complexes. CAPE was found to have a stronger iron-binding ability and a much higher lipophilicity than CA. Taken together, we propose that the esterification of the carboxylic moiety with phenethyl significantly enhanced the iron-binding ability and lipophilicity of CAPE, which is also responsible for its potent protection against iron-mediated cellular DNA damage. A study on the iron coordination mechanism of such natural polyphenol antioxidants will help to design more effective antioxidants for the treatment and prevention of diseases caused by metal-induced oxidative stress, as well as help to understand the structure–activity relationships of these compounds.

Implication of Dietary Iron-Chelating Bioactive Compounds in Molecular Mechanisms of Oxidative Stress-Induced Cell Ageing

One of the prevailing perceptions regarding the ageing of cells and organisms is the intracellular gradual accumulation of oxidatively damaged macromolecules, leading to the decline of cell and organ function (free radical theory of ageing). This chemically undefined material known as "lipofuscin," "ceroid," or "age pigment" is mainly formed through unregulated and nonspecific oxidative modifications of cellular macromolecules that are induced by highly reactive free radicals. A necessary precondition for reactive free radical generation and lipofuscin formation is the intracellular availability of ferrous iron (Fe²⁺) ("labile iron"), catalyzing the conversion of weak oxidants such as peroxides, to extremely reactive ones like hydroxyl (HO^•) or alcoxyl (RO^•) radicals. If the oxidized materials remain unrepaired for extended periods of time, they can be further oxidized to generate ultimate over-oxidized products that are unable to be repaired, degraded, or exocytosed by the relevant cellular systems. Additionally, over-oxidized materials might inactivate cellular protection and repair mechanisms, thus allowing for futile cycles of increasingly rapid lipofuscin accumulation. In this review paper, we present evidence that the modulation of the labile iron pool distribution by nutritional or pharmacological means represents a hitherto unappreciated target for hampering lipofuscin accumulation and cellular ageing.

First Direct and Unequivocal Electron Spin Resonance Spin-Trapping Evidence for pH-Dependent Production of Hydroxyl Radicals from Sulfate Radicals

Recently, the sulfate radical (SO₄^•-) has been found to exhibit broad application prospects in various research fields such as chemical, biomedical, and environmental sciences. It has been suggested that SO₄^•- could be transformed into a more reactive hydroxyl radical (^•OH); however, no direct and unequivocal experimental evidence has been reported yet. In this study, using an electron spin resonance (ESR) secondary radical spin-trapping method coupled with the classic spin-trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and the typical ^•OH-scavenging agent dimethyl sulfoxide (DMSO), we found that ^•OH can be produced from three SO₄^•--generating systems from weakly acidic (pH = 5.5) to alkaline conditions (optimal at pH = 13.0), while SO₄^•- is the predominant radical species at pH < 5.5. A comparative study with three typical ^•OH-generating systems strongly supports the above conclusion. This is the first direct and unequivocal ESR spin-trapping evidence for ^•OH formation from SO₄^•- over a wide pH range, which is of great significance to understand and study the mechanism of many SO₄^•--related reactions and processes. This study also provides an effective and direct method for unequivocally distinguishing ^•OH from SO₄^•-.

Mechanism of synergistic DNA damage induced by caffeic acid phenethyl ester (CAPE) and Cu(II): Competitive binding between CAPE and DNA with Cu(II)/Cu(I)

Caffeic acid phenethyl ester (CAPE) is an active polyphenol of propolis from honeybee hives, and exhibits antioxidant and interesting pharmacological activities. However, in this study, we found that in the presence of Cu(II), CAPE exhibited pro-oxidative rather than antioxidant effect: synergistic DNA damage was induced by the combination of CAPE and Cu(II) together as measured by strand breakage in plasmid DNA and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation, which is dependent on the molar ratio of CAPE:Cu(II). Production of Cu(I) and H₂O₂ from the redox reaction between CAPE and Cu(II), and subsequent OH formation was found to be responsible for the synergistic DNA damage. DNA sequencing investigations provided more direct evidence that CAPE/Cu(II) caused preferential cleavage at guanine, thymine and cytosine residues. Interestingly, we found there are competitive binding between CAPE and DNA with Cu(II)/Cu(I), which changed the redox activity of Cu(II)/Cu(I), via complementary applications of different analytical methods. The observed DNA damage was mainly attributed to the formation of DNA-Cu(II)/Cu(I) complexes, which is still redox active and initiated the redox reaction near the binding site between copper and DNA. Based on these data, we proposed that the synergistic DNA damage induced by CAPE/Cu(II) might be due to the competitive binding between CAPE and DNA with Cu, and site-specific production of OH near the binding site of copper with DNA. Our findings may have broad biological implications for future research on the pro-oxidative effects of phenolic compounds in the presence of transition metals.

Metals and low dose IR: Molecular effects of combined exposures using HepG2 cells as a biological model

Uranium mining sites produce residues rich in metals and radionuclides, that may contaminate all environmental matrices, exposing human and non-human biota to low doses of ionizing radiation (LDIR) and to the chemical toxicity of several metals. To date, experimental and radio-epidemiological studies do not provide conclusive evidence of LDIR induced cancer. However, co-exposures (LDIR plus other contaminants), may increase the risks. To determine the potential for genotoxic effects in human cells induced by the exposure to LDIR plus metals, HEPG2 cells were exposed to different concentrations of a uranium mine effluent for 96 h. DNA damage was evaluated using the comet assay and changes in the expression of tumor suppressor and oncogenes were determined using qPCR. Results show that effluent concentrations higher than 5%, induce significant DNA damage. Also, a significant under-expression of ATM and TP53 genes and a significant overexpression of GADD45a gene was observed. Results show that the exposure to complex mixtures cannot be disregarded, as effects were detected at very low doses. This study highlights the need for further studies to clarify the risks of exposure to LDIR along with other stressors, to fully review the IR exposure risk limits established for human and non-human biota.

Deferasirox protects against hydrogen peroxide-induced cell apoptosis by inhibiting ubiquitination and degradation of p21WAF1/CIP1

Deferasirox (DFX) is an iron chelator approved for the treatment of iron overload diseases. However, the role of DFX in oxidative stress-induced cell apoptosis and the exact molecular mechanisms underlying these processes remain poorly understood and require further investigation. In this study, we found that DFX rendered resistant to H₂O₂-induced apoptosis in HEK293T cells, reduced the intracellular levels of the labile iron pool (LIP) and oxidative stress induced by H₂O₂. Furthermore, DFX inhibited the ubiquitination and degradation of the cyclin-dependent kinase inhibitor p21^WAF1/CIP1 (p21) via modulation of the interaction of p21 with SCF-Skp2. DFX also showed the inhibition effect on the activation of c-Jun N-terminal kinase (JNK), pro-caspase-3 and related mitochondrial apoptosis pathway induced by H₂O₂. These results provide novel insights into the molecular mechanism underpinning iron-mediated oxidative stress and apoptosis, and they may represent a promising target for therapeutic interventions in related pathological conditions.

Polyamine Catabolism in Acute Kidney Injury

Acute kidney injury (AKI) refers to an abrupt decrease in kidney function. It affects approximately 7% of all hospitalized patients and almost 35% of intensive care patients. Mortality from acute kidney injury remains high, particularly in critically ill patients, where it can be more than 50%. The primary causes of AKI include ischemia/reperfusion (I/R), sepsis, or nephrotoxicity; however, AKI patients may present with a complicated etiology where many of the aforementioned conditions co-exist. Multiple bio-markers associated with renal damage, as well as metabolic and signal transduction pathways that are involved in the mediation of renal dysfunction have been identified as a result of the examination of models, patient samples, and clinical data of AKI of disparate etiologies. These discoveries have enhanced our ability to diagnose AKIs and to begin to elucidate the mechanisms involved in their pathogenesis. Studies in our laboratory revealed that the expression and activity of spermine/spermidine N1-acetyltransferase (SAT1), the rate-limiting enzyme in polyamine back conversion, were enhanced in kidneys of rats after I/R injury. Additional studies revealed that the expression of spermine oxidase (SMOX), another critical enzyme in polyamine catabolism, is also elevated in the kidney and other organs subjected to I/R, septic, toxic, and traumatic injuries. The maladaptive role of polyamine catabolism in the mediation of AKI and other injuries has been clearly demonstrated. This review will examine the biochemical and mechanistic basis of tissue damage brought about by enhanced polyamine degradation and discuss the potential of therapeutic interventions that target polyamine catabolic enzymes or their byproducts for the treatment of AKI.

Mechanism of the Formation of Electronically Excited Species by Oxidative Metabolic Processes: Role of Reactive Oxygen Species

It is well known that biological systems, such as microorganisms, plants, and animals, including human beings, form spontaneous electronically excited species through oxidative metabolic processes. Though the mechanism responsible for the formation of electronically excited species is still not clearly understood, several lines of evidence suggest that reactive oxygen species (ROS) are involved in the formation of electronically excited species. This review attempts to describe the role of ROS in the formation of electronically excited species during oxidative metabolic processes. Briefly, the oxidation of biomolecules, such as lipids, proteins, and nucleic acids by ROS initiates a cascade of reactions that leads to the formation of triplet excited carbonyls formed by the decomposition of cyclic (1,2-dioxetane) and linear (tetroxide) high-energy intermediates. When chromophores are in proximity to triplet excited carbonyls, the triplet-singlet and triplet-triplet energy transfers from triplet excited carbonyls to chromophores result in the formation of singlet and triplet excited chromophores, respectively. Alternatively, when molecular oxygen is present, the triplet-singlet energy transfer from triplet excited carbonyls to molecular oxygen initiates the formation of singlet oxygen. Understanding the mechanism of the formation of electronically excited species allows us to use electronically excited species as a marker for oxidative metabolic processes in cells.

Myricetin-induced oxidative stress suppresses murine T lymphocyte activation

A number of polyphenolic compounds present in fruits and vegetables have the capacity to modulate immune responses; however, the impact of the common plant-derived flavonoid myricetin on T lymphocyte function has not been investigated. We show that myricetin inhibited mouse T lymphocyte activation by bead-immobilized anti-CD3 and anti-CD28 monoclonal antibodies, as indicated by a dose-dependent reduction in cell proliferation and decreased synthesis of interferon-γ, interleukin (IL)-2, IL-4, and IL-17 associated with different T helper cell subsets. This effect was attributed to myricetin-induced reactive oxygen species (ROS) since myricetin caused hydrogen peroxide (H₂ O₂ ) to accumulate in cell-free culture medium and H₂ O₂ inhibited T cell proliferation and cytokine synthesis. In addition, the antioxidant N-acetyl cysteine restored the ability of myricetin-treated T lymphocytes to proliferate in response to a mitogenic stimulus. The presence of dendritic cells or bone marrow-derived macrophages negated the inhibitory effect of myricetin on T cell activation, and H₂ O₂ in T cell cultures that were treated with exogenous H₂ O₂ was reduced when antigen-presenting cells were also present. These findings suggest that antioxidant molecules produced by dendritic cells and macrophages protected T cells from myricetin-induced oxidative stress, and underscore the importance of considering immune cell interactions when evaluating the immunomodulatory activity of ROS-generating phytochemicals.

Myricetin-induced apoptosis of triple-negative breast cancer cells is mediated by the iron-dependent generation of reactive oxygen species from hydrogen peroxide

Myricetin is a dietary phytochemical with anticancer activity; however, the effect of myricetin on breast cancer cells remains unclear. Here, we show that myricetin inhibited the growth of triple-negative breast cancer (TNBC) cells but was less inhibitory for normal cells. The effect of myricetin was comparable to epigallocatechin gallate and doxorubicin, and greater than resveratrol and cisplatin. Myricetin-treated TNBC cells showed evidence of early and late apoptosis/necrosis, which was associated with intracellular reactive oxygen species (ROS) accumulation, extracellular regulated kinase 1/2 and p38 mitogen-activated protein kinase activation, mitochondrial membrane destabilization and cytochrome c release, and double-strand DNA breaks. The antioxidant N-acetyl-cysteine protected myricetin-treated TNBC cells from cytotoxicity due to DNA damage. Myricetin also induced hydrogen peroxide (H₂O₂) production in cell-free culture medium, as well as in the presence of TNBC cells and normal cells. In addition, deferiprone-mediated inhibition of intracellular ROS generation via the iron-dependent Fenton reaction and inhibition of extracellular ROS accumulation with superoxide dismutase plus catalase prevented myricetin-induced cytotoxicity in TNBC cell cultures. We conclude that the cytotoxic effect of myricetin on TNBC cells was due to oxidative stress initiated by extracellular H₂O₂ formed by autoxidation of myricetin, leading to intracellular ROS production via the Fenton reaction.

Lipophilic ester and amide derivatives of rosmarinic acid protect cells against H2O2-induced DNA damage and apoptosis: The potential role of intracellular accumulation and labile iron chelation

Phenolic acids represent abundant components contained in human diet. However, the negative charge in their carboxylic group limits their capacity to diffuse through biological membranes, thus hindering their access to cell interior. In order to promote the diffusion of rosmarinic acid through biological membranes, we synthesized several lipophilic ester- and amide-derivatives of this compound and evaluated their capacity to prevent H2O2-induced DNA damage and apoptosis in cultured human cells. Esterification of the carboxylic moiety with lipophilic groups strongly enhanced the capacity of rosmarinic acid to protect cells. On the other hand, the amide-derivatives were somewhat less effective but exerted less cytotoxicity at high concentrations. Cell uptake experiments, using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS), illustrated different levels of intracellular accumulation among the ester- and amide-derivatives, with the first being more effectively accumulated, probably due to their extensive hydrolysis inside the cells. In conclusion, these results highlight the hitherto unrecognized fundamental importance of derivatization of diet-derived phenolic acids to unveil their biological potential.

Association of textile industry effluent with mutagenicity and its toxic health implications upon acute and sub-chronic exposure

Complex industrial discharges pose certain risks to the ecosystem. This study was aimed at identifying acute and sub-chronic toxicological effects of the textile industry wastewater. The textile wastewater was evaluated for the metals and organic pollutants by atomic absorption spectrophotometer and GC-MS respectively. In vitro genotoxicity and mutagenicity were assessed by Comet assay in peripheral lymphocytes isolated from Ovis aries and Ames test in Salmonella typhimurium strains TA-100 and 102 respectively. Physiological and behavioral changes along with systemic toxicity were determined in Rattus norvegicus albinus following acute and sub-chronic exposure. High amount of heavy metals such as Cr, Pb, Hg, As, and Cd were detected in textile wastewater. Organic pollutants such as 25-deacetoxy cucurbitacin-b, E-14-Hexadecenal, 11-Tricosene, and phthalates were also found. In vitro genotoxicity assessment in lymphocytes showed statistically significant DNA damaging potential of textile wastewater. Textile wastewater also showed significantly higher (p˂ 0.05) mutagenic potential in Salmonella TA-100 and TA-102 strains than sodium azide and 2-amino anthracycline. Acute exposure of textile wastewater to Rattus norvegicus was associated with several physiological changes and behavioral symptoms. Sub-chronic exposure of textile wastewater in Rattus norvegicus instigated the degeneration and necrosis of epithelial cells in renal tubules, hydropic degeneration and necrosis of hepatocytes, peri-bronchiolar infiltration and emphysema of the alveoli, and the degradation of myocardial cells. This study concludes that the textile wastewater may cause genotoxicity and mutagenicity, result in physiological and behavioral changes upon acute exposure, and inflict various pathological lesions upon sub-chronic exposure.

Kastle-Meyer blood test reagents are deleterious to DNA

The Kastle-Meyer (KM) test is a quick and easy chemical test for blood used in forensic analyses. Two practical variations of this test are the KM-rub (indirect) test and the more sensitive KM-direct test, the latter of which is performed by applying reagents directly to a suspected blood stain. This study found that sodium hydroxide present in the KM reagents eliminated the potential to generate a DNA profile when applied directly to small quantities of blood. A modified approach to the KM-rub test that increases its sensitivity is presented as a method to replace destructive KM-direct testing.

Phosphate scouting by root tips

Chemistry assigns phosphate (Pi) dominant roles in metabolism; however, it also renders the macronutrient a genuinely limiting factor of plant productivity. Pi bioavailability is restricted by low Pi mobility in soil and antagonized by metallic toxicities, which force roots to actively seek and selectively acquire the vital element. During the past few years, a first conceptual outline has emerged of the sensory mechanisms at root tips, which monitor external Pi and transmit the edaphic cue to inform root development. This review highlights new aspects of the Pi acquisition strategy of Arabidopsis roots, as well as a framework of local Pi sensing in the context of antagonistic interactions between Pi and its major associated metallic cations, Fe³⁺ and Al³⁺.

Activation of endoplasmic reticulum stress response by enhanced polyamine catabolism is important in the mediation of cisplatin-induced acute kidney injury

Cisplatin-induced nephrotoxicity limits its use in many cancer patients. The expression of enzymes involved in polyamine catabolism, spermidine/spermine N1-acetyltransferase (SSAT) and spermine oxidase (SMOX) increase in the kidneys of mice treated with cisplatin. We hypothesized that enhanced polyamine catabolism contributes to tissue damage in cisplatin acute kidney injury (AKI). Using gene knockout and chemical inhibitors, the role of polyamine catabolism in cisplatin AKI was examined. Deficiency of SSAT, SMOX or neutralization of the toxic products of polyamine degradation, H2O2 and aminopropanal, significantly diminished the severity of cisplatin AKI. In vitro studies demonstrated that the induction of SSAT and elevated polyamine catabolism in cells increases the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) and enhances the expression of binding immunoglobulin protein BiP/GRP78) and CCAAT-enhancer-binding protein homologous protein (CHOP/GADD153). The increased expression of these endoplasmic reticulum stress response (ERSR) markers was accompanied by the activation of caspase-3. These results suggest that enhanced polyamine degradation in cisplatin AKI may lead to tubular damage through the induction of ERSR and the consequent onset of apoptosis. In support of the above, we show that the ablation of the SSAT or SMOX gene, as well as the neutralization of polyamine catabolism products modulate the onset of ERSR (e.g. lower BiP and CHOP) and apoptosis (e.g. reduced activated caspase-3). These studies indicate that enhanced polyamine catabolism and its toxic products are important mediators of ERSR and critical to the pathogenesis of cisplatin AKI.

Simplified qPCR method for detecting excessive mtDNA damage induced by exogenous factors

Damage to mitochondrial DNA (mtDNA) is a meaningful biomarker for evaluating genotoxicity of drugs and environmental toxins. Existing PCR methods utilize long mtDNA fragments (∼8-10kb), which complicates detecting exact sites of mtDNA damage. To identify the mtDNA regions most susceptible to damage, we have developed and validated a set of primers to amplify ∼2kb long fragments, while covering over 95% of mouse mtDNA. We have modified the detection method by greatly increasing the enrichment of mtDNA, which allows us solving the problem of non-specific primer annealing to nuclear DNA. To validate our approach, we have determined the most damage-susceptible mtDNA regions in mice treated in vivo and in vitro with rotenone and H₂O₂. The GTGR-sequence-enriched mtDNA segments located in the D-loop region were found to be especially susceptible to damage. Further, we demonstrate that H₂O₂-induced mtDNA damage facilitates the relaxation of mtDNA supercoiled conformation, making the sequences with minimal damage more accessible to DNA polymerase, which, in turn, results in a decrease in threshold cycle value. Overall, our modified PCR method is simpler and more selective to the specific sites of damage in mtDNA.

Toxicity, accumulation, and trophic transfer of chemically and biologically synthesized nano zero valent iron in a two species freshwater food chain

The impact of bio-remediation agent nZVI on environment is still inadequately understood, especially on aquatic food web. The study presented here has therefore considered both chemical (CS) and biological (BS) synthetic origins of nZVI and their effects on both algae and daphnia. The study is unique in its attempt to explore the possibility of trophic transfer from algae to its immediate higher niche (daphnia as the model). An equal weightage of the effects of both CS and BS nZVI on algae and daphnia has been explored here; hence it allows us to compare the capping of nZVI on toxicity. To examine the causes of observed lethality- ROS generation, effects on the activity of oxidative enzymes, membrane damage and biouptake of nZVI was analysed. The overall outcome of CS and BS nZVI on lethality was significantly different in algae and daphnia, where daphnia demonstrated relatively higher sensitivity against CS nZVI. Algae demonstrated considerable differences in CS and BS nZVI toxicity only at higher concentration. This study did not show a probable biomagnification and trophic transfer from algae to daphnia under the experimental conditions even at the highest exposure concentration. The study instigates the importance of trophic transfer to understand the possible biomagnification of nZVI among organisms of different trophic levels and eventually the consequences on environment.

An Exceptionally Facile Two-Step Structural Isomerization and Detoxication via a Water-Assisted Double Lossen Rearrangement

N-hydroxyphthalimide (NHPI), which is best known as an organocatalyst for efficient C-H activation, has been found to be oxidized by quinoid compounds to its corresponding catalytically active nitroxide-radical. Here, we found that NHPI can be isomerized into isatoic anhydride by an unusually facile two-step method using tetrachloro-1,4-benzoquinone (TCBQ, p-chloranil), accompanied by a two-step hydrolytic dechlorination of highly toxic TCBQ into the much less toxic dihydroxylation product, 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid). Interestingly, through the complementary application of oxygen-18 isotope-labeling, HPLC combined with electrospray ionization quadrupole time-of-flight and high resolution Fourier transform ion cyclotron resonance mass spectrometric studies, we determined that water was the source and origin of oxygen for isatoic anhydride. Based on these data, we proposed that nucleophilic attack with a subsequent water-assisted Lossen rearrangement coupled with rapid intramolecular addition and cyclization in two consecutive steps was responsible for this unusual structural isomerization of NHPI and concurrent hydroxylation/detoxication of TCBQ. This is the first report of an exceptionally facile double-isomerization of NHPI via an unprecedented water-assisted double-Lossen rearrangement under normal physiological conditions. Our findings may have broad implications for future research on hydroxamic acids and polyhalogenated quinoid carcinogens, two important classes of compounds of major chemical and biological interest.

Intracellular labile iron determines H2O2-induced apoptotic signaling via sustained activation of ASK1/JNK-p38 axis

Hydrogen peroxide (H2O2) acts as a second messenger in signal transduction participating in several redox regulated pathways, including cytokine and growth factor stimulated signals. However, the exact molecular mechanisms underlying these processes remain poorly understood and require further investigation. In this work, using Jurkat T lymphoma cells and primary human umbilical vein endothelial cells, it was observed that changes in intracellular "labile iron" were able to modulate signal transduction in H2O2-induced apoptosis. Chelation of intracellular labile iron by desferrioxamine rendered cells resistant to H2O2-induced apoptosis. In order to identify the exact points of iron action, we investigated selected steps in H2O2-mediated apoptotic pathway, focusing on mitogen activated protein kinases (MAPKs) JNK, p38 and ERK. It was observed that spatiotemporal changes in intracellular labile iron, induced by H2O2, influenced the oxidation pattern of the upstream MAP3K ASK1 and promoted the sustained activation of JNK-p38 axis in a defined time-dependent context. Moreover, we indicate that H2O2 induced spatiotemporal changes in intracellular labile iron, at least in part, by triggering the destabilization of lysosomal compartments, promoting a concomitant early response in proteins of iron homeostasis. These results raise the possibility that iron-mediated oxidation of distinct proteins may be implicated in redox signaling processes. Since labile iron can be pharmacologically modified in vivo, it may represent a promising target for therapeutic interventions in related pathological conditions.

Effect of zero valent iron nanoparticles to Eisenia fetida in three soil types

In this study, the influence of soil types on the effect of the commercial form of C-nZVI on tissue concentrations, cellular component, reproduction outcome in Eisenia fetida, and the soil health was investigated. C-nZVI at concentration level of 3 g kg(-1) soil showed no effect on the survival of E. fetida in the three soil types. However, varying effects such as concentration-dependent increase in tissue iron concentration, lipid peroxidation, and damage to DNA molecules by C-nZVI were observed. C-nZVI at an exposure concentration of 60 mg kg(-1) soil induced oxidative stress in E. fetida. Tissue Fe concentration appeared correlated to the DNA damage. Oxidative stress and DNA damage may explain the toxicity mechanisms of nZVI to E. fetida. Graphical Abstract Reactive oxygen species induced by nZVI.

Simultaneous Real-Time Monitoring of Oxygen Consumption and Hydrogen Peroxide Production in Cells Using Our Newly Developed Chip-Type Biosensor Device

All living organisms bear its defense mechanism. Immune cells during invasion by foreign body undergoes phagocytosis during which monocyte and neutrophil produces reactive oxygen species (ROS). The ROS generated in animal cells are known to be involved in several diseases and ailments, when generated in excess. Therefore, if the ROS generated in cells can be measured and analyzed precisely, it can be employed in immune function evaluation and disease detection. The aim of the current study is to introduce our newly developed chip-type biosensor device with high specificity and sensitivity. It comprises of counter electrode and working electrodes I and II. The counter electrode is a platinum plate while the working electrodes I and II are platinum microelectrode and osmium-horseradish peroxidase modified gold electrode, respectively which acts as oxygen and hydrogen peroxide (H₂O₂) detection sensors. Simultaneous measurement of oxygen consumption and H₂O₂ generation were measured in animal cells under the effect of exogenous addition of differentiation inducer, phorbol 12-myristate 13-acetate. The results obtained showed considerable changes in reduction currents in the absence and presence of inducer. Our newly developed chip-type biosensor device is claimed to be a useful tool for real-time monitoring of the respiratory activity and precise detection of H₂O₂ in cells. It can thus be widely applied in biomedical research and in clinical trials being an advancement over other H₂O₂ detection techniques.

Synergistic Application of Black Tea Extracts and Lactic Acid Bacteria in Protecting Human Colonocytes against Oxidative Damage

In view of the potential of lactic acid bacteria (LAB) to enhance the antioxidant activity of food products, this work explored the effectiveness of LAB fermented black tea samples in alleviating H2O2-induced oxidative stress in human colonocytes. The antioxidant capacity of tea samples was evaluated in terms of cyto-protectiveness, mitochondria membrane potential (Δψm)-stabilizing activity, ROS-inhibitory effect, and antioxidant enzyme-modulating activity. The effect on oxidative DNA damage and repair was studied in CCD 841 by comet assay. Results showed that the protective effect of tea pretreatment was more pronounced in normal cells (CCD 841) than in carcinomas (Caco-2), and fermented samples were invariably more effective. Higher cell viability and Δψm were maintained and ROS production was markedly inhibited with tea pretreatment. The fermented tea samples also remarkably stimulated DNA repair, resulting in fewer strand breaks and oxidative lesions. Our study implied that LAB fermentation may be an efficient way to enhance the antioxidative effectiveness of black tea flavonoid-enriched foods.

Tucum-Do-Cerrado (Bactris setosa Mart.) Consumption Modulates Iron Homeostasis and Prevents Iron-Induced Oxidative Stress in the Rat Liver

This study investigated the effect of tucum-do-cerrado consumption in the oxidative status of iron-supplemented rats. Four groups of rats were treated: Control (AIN-93G), Tuc (AIN-93G added of tucum-do-cerrado), Fe (AIN-93G iron-enriched), or TucFe (AIN-93G with tucum-do-cerrado and iron-enriched) diet, for 30 days. Iron-enriched diet increased serum, liver, spleen, and intestine iron levels; transferrin saturation; liver lipid oxidation; mRNA levels of hepatic Hamp and Bmp6, and Nrf2 in the intestine. Tucum-do-cerrado consumption reduced spleen lipid and protein oxidation; mRNA levels of hepatic Hamp and Ftl, and increased serum antioxidant capacity and hepatic mRNA levels of Bmp6, Hmox1, Nqo1, and Nrf2. TucFe diet consumption abrogated the liver Hamp iron-induced up-regulation, prevented intestinal iron accumulation; hepatic lipid peroxidation; splenic protein damage, and the increase of catalase, glutathione reductase, and glutathione peroxidase activity in some tissues. These results suggest that tucum-do-cerrado protects tissues against oxidative damage, by reducing iron availability in liver and consequently inhibiting liver Hamp expression.

Effects of pyrrolidine dithiocarbamate on proliferation and nuclear factor-κB activity in autosomal dominant polycystic kidney disease cells

BACKGROUND

Pyrrolidine dithiocarbamate (PDTC) reduces renal cyst growth in a rodent model of polycystic kidney disease (PKD) but the mechanism of action is not clear. Here, we investigated the hypothesis that PDTC reduces the proliferation of cystic epithelial cells in vitro in a nuclear factor (NF)-κB-dependent manner.

METHODS

Immortalized autosomal dominant PKD (ADPKD) cells that are heterozygous (WT9-7) and homozygous (WT-9-12) for a truncating Pkd1 mutation, and immortalized normal human tubular cells (HK-2), were exposed to NF-κB-inducing agents with or without PDTC. Cell proliferation and apoptosis were assessed by bromodeoxyuridine assay and Annexin V flow cytometry, respectively. NF-κB activity was assessed by luciferase reporter assay and western blotting for nuclear p65, p50, and RelB subunits and cytoplasmic phosphorylated-IκBα.

RESULTS

Serum-induced proliferation was similar in all cell lines over 72 h. PDTC demonstrated anti-proliferative effects that were delayed in ADPKD cells compared to HK-2. Basal NF-κB-dependent luciferase reporter activity was lower in ADPKD cells compared to normal cells. Classical NF-κB stimulants, lipopolysaccharide (LPS) and tumor necrosis factor (TNF)-α, increased NF-κB luciferase activity in HK-2, whereas in PKD cell lines, NF-κB activity was only induced by TNF-α. However, neither stimulant altered proliferation in any cell line. PDTC reduced TNF-α-stimulated NF-κB activity in HK-2 only.

CONCLUSIONS

PDTC reduced proliferation in ADPKD cells but did not consistently alter NF-κB activation, suggesting that other signalling pathways are likely to be involved in its ability to attenuate renal cyst growth in vivo.

Enhanced Inactivation of Escherichia coli and MS2 Coliphage by Cupric Ion in the Presence of Hydroxylamine: Dual Microbicidal Effects

The inactivation of Escherichia coli and MS2 coliphage by Cu(II) is found to be significantly enhanced in the presence of hydroxylamine (HA). The addition of a small amount of HA (i.e., 5-20 μM) increased the inactivation efficacies of E. coli and MS2 coliphage by 5- to 100-fold, depending on the conditions. Dual effects were anticipated to enhance the biocidal activity of Cu(II) by the addition of HA, viz. (i) the accelerated reduction of Cu(II) into Cu(I) (a stronger biocide) and (ii) the production of reactive oxidants from the reaction of Cu(I) with dissolved oxygen (evidenced by the oxidative transformation of methanol into formaldehyde). Deaeration enhanced the inactivation of E. coli but slightly decreased the inactivation efficacy of MS2 coliphage. The addition of 10 μM hydrogen peroxide (H2O2) greatly enhanced the MS2 inactivation, whereas the same concentration of H2O2 did not significantly affect the inactivation efficacy of E. coli Observations collectively indicate that different biocidal actions lead to the inactivation of E. coli and MS2 coliphage. The toxicity of Cu(I) is dominantly responsible for the E. coli inactivation. However, for the MS2 coliphage inactivation, the oxidative damage induced by reactive oxidants is as important as the effect of Cu(I).

Iron-induced reactive oxygen species mediate transporter DMT1 endocytosis and iron uptake in intestinal epithelial cells

Recent evidence shows that iron induces the endocytosis of the iron transporter dimetal transporter 1 (DMT1) during intestinal absorption. We, and others, have proposed that iron-induced DMT1 internalization underlies the mucosal block phenomena, a regulatory response that downregulates intestinal iron uptake after a large oral dose of iron. In this work, we investigated the participation of reactive oxygen species (ROS) in the establishment of this response. By means of selective surface protein biotinylation of polarized Caco-2 cells, we determined the kinetics of DMT1 internalization from the apical membrane after an iron challenge. The initial decrease in DMT1 levels in the apical membrane induced by iron was followed at later times by increased levels of DMT1. Addition of Fe(2+), but not of Cd(2+), Zn(2+), Cu(2+), or Cu(1+), induced the production of intracellular ROS, as detected by 2',7'-dichlorofluorescein (DCF) fluorescence. Preincubation with the antioxidant N-acetyl-l-cysteine (NAC) resulted in increased DMT1 at the apical membrane before and after addition of iron. Similarly, preincubation with the hydroxyl radical scavenger dimethyl sulfoxide (DMSO) resulted in the enhanced presence of DMT1 at the apical membrane. The decrease of DMT1 levels at the apical membrane induced by iron was associated with decreased iron uptake rates. A kinetic mathematical model based on operational rate constants of DMT1 endocytosis and exocytosis is proposed. The model qualitatively captures the experimental observations and accurately describes the effect of iron, NAC, and DMSO on the apical distribution of DMT1. Taken together, our data suggest that iron uptake induces the production of ROS, which modify DMT1 endocytic cycling, thus changing the iron transport activity at the apical membrane.

Role of labile iron in the toxicity of pharmacological ascorbate

Pharmacological ascorbate has been shown to induce toxicity in a wide range of cancer cell lines. Pharmacological ascorbate in animal models has shown promise for use in cancer treatment. At pharmacological concentrations the oxidation of ascorbate produces a high flux of H2O2 via the formation of ascorbate radical (Asc(•-)). The rate of oxidation of ascorbate is principally a function of the level of catalytically active metals. Iron in cell culture media contributes significantly to the rate of H2O2 generation. We hypothesized that increasing intracellular iron would enhance ascorbate-induced cytotoxicity and that iron chelators could modulate the catalytic efficiency with respect to ascorbate oxidation. Treatment of cells with the iron-chelators deferoxamine (DFO) or dipyridyl (DPD) in the presence of 2mM ascorbate decreased the flux of H2O2 generated by pharmacological ascorbate and reversed ascorbate-induced toxicity. Conversely, increasing the level of intracellular iron by preincubating cells with Fe-hydroxyquinoline (HQ) increased ascorbate toxicity and decreased clonogenic survival. These findings indicate that redox metal metals, e.g., Fe(3+)/Fe(2+), have an important role in ascorbate-induced cytotoxicity. Approaches that increase catalytic iron could potentially enhance the cytotoxicity of pharmacological ascorbate in vivo.

The formation of electronically excited species in the human multiple myeloma cell suspension

In this study, evidence is provided on the formation of electronically excited species in human multiple myeloma cells U266 in the growth medium exposed to hydrogen peroxide (H2O2). Two-dimensional imaging of ultra-weak photon emission using highly sensitive charge coupled device camera revealed that the addition of H2O2 to cell suspension caused the formation of triplet excited carbonyls (3)(R = O)*. The kinetics of (3)(R = O)* formation in the real time, as measured by one-dimensional ultra-weak photon emission using low-noise photomultiplier, showed immediate enhancement followed by a slow decay. In parallel to the formation of (3)(R = O)*, the formation of singlet oxygen ((1)O2) in U266 cells caused by the addition of H2O2 was visualized by the imaging of (1)O2 using the green fluorescence of singlet oxygen sensor green detected by confocal laser scanning microscopy. Additionally, the formation of (1)O2 after the addition of H2O2 to cell suspension was detected by electron paramagnetic resonance spin-trapping spectroscopy using 2,2,6,6-tetramethyl-4-piperidone. Presented results indicate that the addition of H2O2 to cell suspension results in the formation of (3)(R = O)* and (1)O2 in U266 cell suspension. The contribution of the cell-free medium to the formation of electronically excited species was discussed.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Cytotoxicity and apoptosis induction by nanoscale talc particles from two different geographical regions in human lung epithelial cells

We have characterized the physicochemical properties of nanotalc particles from two different geographical regions and examined their toxicity mechanisms in human lung epithelial (A549) cells. Indigenous nanotalc (IN) of Indian origin and commercial nanotalc (CN) of American origin were used in this study. Physicochemical properties of nanotalc particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), Brunauer-Emmet-Teller (BET), and dynamic light scattering (DLS). Results showed that both IN and CN particles significantly induce cytotoxicity and alteration in cell cycle phases. Both IN and CN particles were found to induce oxidative stress indicated by induction of reactive oxygen species (ROS), lipid peroxidation, and depletion of antioxidant levels. DNA fragmentation and caspase-3 enzyme activation due to IN and CN particles exposure were also observed. We further showed that after iron chelation, IN and CN particles produce significantly less cytotoxicity, oxidative stress, and genotoxicity to A549 cells as compared with nonchelated particles. In conclusion, this study demonstrated that redox active iron plays significant role in the toxicity of IN and CN particles, which may be mediated through ROS generation and oxidative stress.

Metal-mediated DNA damage and cell death: mechanisms, detection methods, and cellular consequences

Metal ions cause various types of DNA damage by multiple mechanisms, and this damage is a primary cause of cell death and disease.

Oxidative DNA damage and mammary cell proliferation by alcohol-derived salsolinol

Drinking alcohol is a risk factor for breast cancer. Salsolinol (SAL) is endogenously formed by a condensation reaction of dopamine with acetaldehyde, a major ethanol metabolite, and SAL is detected in blood and urine after alcohol intake. We investigated the possibility that SAL can participate in tumor initiation and promotion by causing DNA damage and cell proliferation, leading to alcohol-associated mammary carcinogenesis. SAL caused oxidative DNA damage including 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), in the presence of transition metal ions, such as Cu(II) and Fe(III)EDTA. Inhibitory effects of scavengers on SAL-induced DNA damage and the electron spin resonance study indicated the involvement of H₂O₂, which is generated via the SAL radical. Experiments on scavengers and site specificity of DNA damage suggested ·OH generation via a Fenton reaction and copper-peroxide complexes in the presence of Fe(III)EDTA and Cu(II), respectively. SAL significantly increased 8-oxodG formation in normal mammary epithelial MCF-10A cells. In addition, SAL induced cell proliferation in estrogen receptor (ER)-negative MCF-10A cells, and the proliferation was inhibited by an antioxidant N-acetylcysteine and an epidermal growth factor receptor (EGFR) inhibitor AG1478, suggesting that reactive oxygen species may participate in the proliferation of MCF-10A cells via EGFR activation. Furthermore, SAL induced proliferation in estrogen-sensitive breast cancer MCF-7 cells, and a surface plasmon resonance sensor revealed that SAL significantly increased the binding activity of ERα to the estrogen response element but not ERβ. In conclusion, SAL-induced DNA damage and cell proliferation may play a role in tumor initiation and promotion of multistage mammary carcinogenesis in relation to drinking alcohol.

Potent DNA damage by polyhalogenated quinones and H₂O₂ via a metal-independent and Intercalation-enhanced oxidation mechanism

Polyhalogenated quinones are a class of carcinogenic intermediates. We found recently that the highly reactive and biologically/environmentally important ·OH can be produced by polyhalogenated quinones and H₂O₂ independent of transition metal ions. However, it is not clear whether this unusual metal-independent ·OH producing system can induce potent oxidative DNA damage. Here we show that TCBQ and H₂O₂ can induce oxidative damage to both dG and dsDNA; but surprisingly, it was more efficient to induce oxidative damage in dsDNA than in dG. We found that this is probably due to its strong intercalating ability to dsDNA through competitive intercalation assays. The intercalation of TCBQ in dsDNA may lead to ·OH generation more adjacent to DNA. This is the first report that polyhalogenated quinoid carcinogens and H₂O₂ can induce potent DNA damage via a metal-independent and intercalation-enhanced oxidation mechanism, which may partly explain their potential genotoxicity, mutagenesis, and carcinogenicity.