Protein oxidation and proteolysis by the nonradical oxidants singlet oxygen or peroxynitrite

Middle-age abolishes cardioprotection conferred by thioredoxin-1 in mice

Thioredoxin-1 (Trx1) has cardioprotective effects on ischemia/reperfusion (I/R) injury, although its role in ischemic postconditioning (PostC) in middle-aged mice is not understood. This study aimed to evaluate if combining two cardioprotective strategies, such as Trx1 overexpression and PostC, could exert a synergistic effect in reducing infarct size in middle-aged mice. Young or middle-aged wild-type mice (Wt), transgenic mice overexpressing Trx1, and dominant negative (DN-Trx1) mutant of Trx1 mice were used. Mice hearts were subjected to I/R or PostC protocol. Infarct size, hydrogen peroxide (H2O2) production, protein nitration, Trx1 activity, mitochondrial function, and Trx1, pAkt and pGSK3β expression were measured. PostC could not reduce infarct size even in the presence of Trx1 overexpression in middle-aged mice. This finding was accompanied by a lack of Akt and GSK3β phosphorylation, and Trx1 expression (in Wt group). Trx1 activity was diminished and H2O2 production and protein nitration were increased in middle-age. The respiratory control rate dropped after I/R in Wt-Young and PostC restored this value, but not in middle-aged groups. Our results showed that Trx1 plays a key role in the PostC protection mechanism in young but not middle-aged mice, even in the presence of Trx1 overexpression.

X-ray Activated Nanoplatforms for Deep Tissue Photodynamic Therapy

Photodynamic therapy (PDT), the use of light to excite photosensitive molecules whose electronic relaxation drives the production of highly cytotoxic reactive oxygen species (ROS), has proven an effective means of oncotherapy. However, its application has been severely constrained to superficial tissues and those readily accessed either endoscopically or laparoscopically, due to the intrinsic scattering and absorption of photons by intervening tissues. Recent advances in the design of nanoparticle-based X-ray scintillators and photosensitizers have enabled hybridization of these moieties into single nanocomposite particles. These nanoplatforms, when irradiated with diagnostic doses and energies of X-rays, produce large quantities of ROS and permit, for the first time, non-invasive deep tissue PDT of tumors with few of the therapeutic limitations or side effects of conventional PDT. In this review we examine the underlying principles and evolution of PDT: from its initial and still dominant use of light-activated, small molecule photosensitizers that passively accumulate in tumors, to its latest development of X-ray-activated, scintillator-photosensitizer hybrid nanoplatforms that actively target cancer biomarkers. Challenges and potential remedies for the clinical translation of these hybrid nanoplatforms and X-ray PDT are also presented.

Development of Novel Tetrapyrrole Structure Photosensitizers for Cancer Photodynamic Therapy

The effectiveness of photodynamic therapy (PDT) is based on the triad effects of photosensitizer (PS), molecular oxygen and visible light on malignant tumors. Such complex induces a multifactorial manner including reactive-oxygen-species-mediated damage and the killing of cells, vasculature damage of the tumor, and activation of the organism immunity. The effectiveness of PDT depends on the properties of photosensitizing drugs, their selectivity, enhanced photoproduction of reactive particles, absorption in the near infrared spectrum, and drug delivery strategies. Photosensitizers of the tetrapyrrole structure (porphyrins) are widely used in PDT because of their unique diagnostic and therapeutic functions. Nevertheless, the clinical use of the first-generation PS (sodium porfimer and hematoporphyrins) revealed difficulties, such as long-term skin photosensitivity, insufficient penetration into deep-seated tumors and incorrect localization to it. The second generation is based on different approaches of the synthesis and conjugation of porphyrin PS with biomolecules, which made it possible to approach the targeted PDT of tumors. Despite the fact that the development of the second-generation PS started about 30 years ago, these technologies are still in demand and are in intensive development, especially in the direction of improving the process of optimization split linkers responsive to input. Bioconjugation and encapsulation by targeting molecules are among the main strategies for developing of the PS synthesis. A targeted drug delivery system with the effect of increased permeability and retention by tumor cells is one of the ultimate goals of the synthesis of second-generation PS. This review presents porphyrin PS of various generations, discusses factors affecting cellular biodistribution and uptake, and indicates their role as diagnostic and therapeutic (theranostic) agents. New complexes based on porphyrin PS for photoimmunotherapy are presented, where specific antibodies are used that are chemically bound to PS, absorbing light from the near infrared part of the spectrum. Additionally, a two-photon photodynamic approach using third-generation photosensitizers for the treatment of tumors is discussed, which indicates the prospects for the further development of a promising method antitumor PDT.

FOXO transcription factors in antioxidant defense

Forkhead box, class O (FOXO) family proteins are widely expressed and highly conserved transcriptional regulators that modulate cellular fuel metabolism, stress resistance and cell death. FOXO target genes include genes encoding antioxidant proteins, thus likely contributing to the key role FOXOs play in the cellular response to oxidative stress and supporting the cellular strategies of antioxidant defense, that is, prevention (of the formation of reactive oxygen species), interception (of reactive species prior to their reaction with cellular components), repair (of damaged biomolecules), and adaptation (i.e., the stimulation of signaling pathways allowing for the expression of protective proteins). FOXOs themselves are regulated by redox processes at several levels, including expression of FOXO genes and enzymatic as well as nonenzymatic posttranslational modifications of FOXO proteins. The latter include modifications of FOXO cysteine residues. Here, an overview is provided on (i) the contribution of FOXO target genes to cellular antioxidative strategies, and (ii) on the impact of thiol homeostasis and thiol modification on FOXO activity.

Nitric Oxide and Immune Responses in Cancer: Searching for New Therapeutic Strategies

In recent years, there has been an increasing interest in understanding the mysterious functions of nitric oxide (NO) and how this pleiotropic signaling molecule contributes to tumorigenesis. This review attempts to expose and discuss the information available on the immunomodulatory role of NO in cancer and recent approaches to the role of NO donors in the area of immunotherapy. To address the goal, the following databases were searched to identify relevant literature concerning empirical evidence: The Cochrane Library, Pubmed, Medline, EMBASE from 1980 through March 2020. Valuable attempts have been made to develop distinctive NO-based cancer therapy. Although the data do not allow generalization, the evidence seems to indicate that low / moderate levels may favor tumorigenesis while higher levels would exert anti-tumor effects. In this sense, the use of NO donors could have an important therapeutic potential within immunotherapy, although there are still no clinical trials. The emerging understanding of NO-regulated immune responses in cancer may help unravel the recent features of this "double-edged sword" in cancer physiological and pathologic processes and its potential use as a therapeutic agent for cancer treatment. In short, in this review, we discuss the complex cellular mechanism in which NO, as a pleiotropic signaling molecule, participates in cancer pathophysiology. We also debate the dual role of NO in cancer and tumor progression, and clinical approaches for inducible nitric oxide synthase (iNOS) based therapy against cancer.

Investigating Dynamic Molecular Events in Melanoma Cell Nucleus During Photodynamic Therapy by SERS

Photodynamic therapy (PDT) involves the uptake of photosensitizers by cancer cells and the irradiation of a light with a specific wavelength to trigger a series of photochemical reactions based on the generation of reactive oxygen, leading to cancer cell death. PDT has been widely used in various fields of biomedicine. However, the molecular events of the cancer cell nucleus during the PDT process are still unclear. In this work, a nuclear-targeted gold nanorod Raman nanoprobe combined with surface-enhanced Raman scattering spectroscopy (SERS) was exploited to investigate the dynamic intranuclear molecular changes of B16 cells (a murine melanoma cell line) treated with a photosensitizer (Chlorin e6) and the specific light (650 nm). The SERS spectra of the cell nucleus during the PDT treatment were recorded in situ and the spectroscopic analysis of the dynamics of the nucleus uncovered two main events in the therapeutic process: the protein degradation and the DNA fragmentation. We expect that these findings are of vital significance in having a better understanding of the PDT mechanism acting on the cancer cell nucleus and can further help us to design and develop more effective therapeutic platforms and methods.

Natural Phytotherapeutic Antioxidants in the Treatment of Mercury Intoxication-A Review

Heavy metals taken into the organism can make the toxic effects on the metabolism in various ways. For example, they may interact with proteins to alter and inhibit their enzymatic and structural functions. Mercury is one of the toxic elements that are widely distributed in nature. Mercury toxicity poses a serious threat to human health. It is an element that causes oxidative stress to increase in individuals, leading to tissue damage. Oxidative stress is the result of the imbalance between the production of oxidative species and cellular antioxidant defense. Phytotherapy continues to play an important role in health care. Natural phytotherapeutic antioxidants, exhibit a broad sequence of biological impacts, including anti-oxidative stress, anti-aging, anti-toxicicity and anticancer. Many studies have also shown that the phytotherapeutic agents play an important role in the removal of mercury from the tissue and in reducing oxidative stress. Our goal in this review was to investigate alternative ways of extracting the mercury in the tissue.

Light treatments of nail fungal infections

Nail fungal infections are notoriously persistent and difficult to treat which can lead to severe health impacts, particularly in the immunocompromized. Current antifungal treatments, including systemic and topical drugs, are prolonged and do not effectively provide a complete cure. Severe side effects are also associated with systemic antifungals, such as hepatotoxicity. Light treatments of onychomycosis are an emerging therapy that has localized photodynamic, photothermal or photoablative action. These treatments have shown to be an effective alternative to traditional antifungal remedies with comparable or better cure rates achieved in shorter times and without systemic side effects. This report reviews significant clinical and experimental studies in the field, highlighting mechanisms of action and major effects related to light therapy; in particular, the impact of light on fungal genetics.

Organoiridium Photosensitizers Induce Specific Oxidative Attack on Proteins within Cancer Cells

Strongly luminescent iridium(III) complexes, [Ir(C,N)2 (S,S)]+ (1) and [Ir(C,N)2 (O,O)] (2), containing C,N (phenylquinoline), O,O (diketonate), or S,S (dithione) chelating ligands, have been characterized by X-ray crystallography and DFT calculations. Their long phosphorescence lifetimes in living cancer cells give rise to high quantum yields for the generation of 1 O2 , with large 2-photon absorption cross-sections. 2 is nontoxic to cells, but potently cytotoxic to cancer cells upon brief irradiation with low doses of visible light, and potent at sub-micromolar doses towards 3D multicellular tumor spheroids with 2-photon red light. Photoactivation causes oxidative damage to specific histidine residues in the key proteins in aldose reductase and heat-shock protein-70 within living cancer cells. The oxidative stress induced by iridium photosensitizers during photoactivation can increase the levels of enzymes involved in the glycolytic pathway.

Blue light induced reactive oxygen species from flavin mononucleotide and flavin adenine dinucleotide on lethality of HeLa cells

Photodynamic therapy (PDT) is a safe and non-invasive treatment for cancers and microbial infections. Various photosensitizers and light sources have been developed for clinical cancer therapies. Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are the cofactor of enzymes and are used as photosensitizers in this study. Targeting hypoxia and light-triggering reactive oxygen species (ROS) are experimental strategies for poisoning tumor cells in vitro. HeLa cells are committed to apoptosis when treated with FMN or FAD and exposed to visible blue light (the maximum emitted wavelength of blue light is 462nm). Under blue light irradiation at 3.744J/cm² (=0.52mW/cm² irradiated for 2h), the minimal lethal dose is 3.125μM and the median lethal doses (LD₅₀) for FMN and FAD are 6.5μM and 7.2μM, respectively. Individual exposure to visible blue light irradiation or riboflavin photosensitizers does not produce cytotoxicity and no side effects are observed in this study. The western blotting results also show that an intrinsic apoptosis pathway is activated by the ROS during photolysis of riboflavin analogues. Blue light triggers the cytotoxicity of riboflavins on HeLa cells in vitro. Based on these results, this is a feasible and efficient of PDT with an intrinsic photosensitizer for cancer research.

Design features for optimization of tetrapyrrole macrocycles as antimicrobial and anticancer photosensitizers

Photodynamic therapy (PDT) uses non-toxic dyes called photosensitizers (PS) and harmless visible light that combine to form highly toxic reactive oxygen species that kill cells. Originally, a cancer therapy, PDT, now includes applications for infections. The most widely studied PS are tetrapyrrole macrocycles including porphyrins, chlorins, bacteriochlorins, and phthalocyanines. The present review covers the design features in PS that can work together to maximize the PDT activity for various disease targets. Photophysical and photochemical properties include the wavelength and size of the long-wavelength absorption peak (for good light penetration into tissue), the triplet quantum yield and lifetime, and the propensity to undergo type I (electron transfer) or type II (energy transfer) photochemical mechanisms. The central metal in the tetrapyrrole macrocycle has a strong influence on the PDT activity. Hydrophobicity and charge are important factors that govern interactions with various types of cells (cancer and microbial) in vitro and the pharmacokinetics and biodistribution in vivo. Hydrophobic structures tend to be water insoluble and require a drug delivery vehicle for maximal activity. Molecular asymmetry and amphiphilicity are also important for high activity. In vivo some structures possess the ability to selectively accumulate in tumors and to localize in the tumor microvasculature producing vascular shutdown after illumination.

Peroxynitrite: From interception to signaling

Peroxynitrite is a strong oxidant and nitrating species that mediates certain biological effects of superoxide and nitrogen monoxide. These biological effects include oxidative damage to proteins as well as the formation of 3-nitrotyrosyl moieties in proteins. As a consequence, such proteins may lose their activity, gain altered function, or become prone to proteolytic degradation - resulting in modulation of cellular protein turnover and in the modulation of signaling cascades. In analogy to hydrogen peroxide, peroxynitrite may be scavenged by selenoproteins like glutathione peroxidase-1 (GPx-1) or by selenocompounds with a GPx-like activity, such as ebselen; in further analogy to H2O2, peroxiredoxins have also been established as contributors to peroxynitrite reduction. This review covers three aspects of peroxynitrite biochemistry, (i) the interaction of selenocompounds/-proteins with peroxynitrite, (ii) peroxynitrite-induced modulation of cellular proteolysis, and (iii) peroxynitrite-induced modulation of cellular signaling.

In situ production of ROS in the skin by photodynamic therapy as a powerful tool in clinical dermatology

Photodynamic therapy (PDT) is a clinical modality of photochemotherapy based on the accumulation of a photosensitizer in target cells and subsequent irradiation of the tissue with light of adequate wavelength promoting reactive oxygen species (ROS) formation and cell death. PDT is used in several medical specialties as an organ-specific therapy for different entities. In this review we focus on the current dermatological procedure of PDT. In the most widely used PDT protocol in dermatology, ROS production occurs by accumulation of the endogenous photosensitizer protoporphyrin IX after treatment with the metabolic precursors 5-methylaminolevulinic acid (MAL) or 5-aminolevulinic acid (ALA). To date, current approved dermatological indications of PDT include actinic keratoses (AK), basal cell carcinoma (BCC) and in situ squamous cell carcinoma (SCC) also known as Bowen disease (BD). With regards to AKs, PDT can also treat the cancerization field carrying an oncogenic risk. In addition, an increasing number of pathologies, such as other skin cancers, infectious, inflammatory or pilosebaceous diseases are being considered as potentially treatable entities with PDT. Besides the known therapeutic properties of PDT, there is a modality used for skin rejuvenation and aesthetic purposes defined as photodynamic photorejuvenation. This technique enables the remodelling of collagen, which in turn prevents and treats photoaging stygmata. Finally we explore a new potential treatment field for PDT determined by the activation of follicular bulge stem cells caused by in situ ROS formation.

Non-monotonic dose-response effect of bisphenol A on rare minnow Gobiocypris rarus ovarian development

Bisphenol A (BPA) is widely spread in the environment, and can cause various reproductive disrupting effects on different organisms, including fish. Our previous published study showed that BPA has non-monotonic (inverted U-shaped) dose-response effect on rare minnow Gobiocypris rarus ovarian weight at different concentrations. To investigate the potential mechanism, we exposed female rare minnow to 1, 15 and 225 µg L(-1) BPA for 7 days in the present study. The levels of vitellogenin (Vtg), sex hormones, hydrogen peroxide (H2O2), glutathione (GSH) and triglyceride (TG) were measured. RNA-seq of ovary tissues was also performed. Result showed that Vtg, sex hormone and TG levels showed an inverted U-shaped increased response, while H2O2 and GSH levels showed a U-shaped inhibited response. RNA-seq data showed that many genes involved in lipid metabolism, oxidative stress, and proteolysis processes were altered. The change of Vtg, H2O2, GSH and TG levels was possibly related to the altered sex hormone levels. Sex hormone's direct effect, Vtg accumulation, TG accumulation and oxidative stress induced proteolysis may contribute to the change of ovary weight.

Posttranslational protein modifications by reactive nitrogen and chlorine species and strategies for their prevention and elimination

Proteins are subject to various posttranslational modifications, some of them being undesired from the point of view of metabolic efficiency. Prevention of such modifications is expected to provide new means of therapy of diseases and decelerate the process of aging. In this review, modifications of proteins by reactive nitrogen species and reactive halogen species, is briefly presented and means of prevention of these modifications and their sequelae are discussed, including the denitrase activity and inhibitors of myeloperoxidase.

Mechanisms in photodynamic therapy: part one-photosensitizers, photochemistry and cellular localization

The use of non-toxic dyes or photosensitizers (PS) in combination with harmless visible light that is known as photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as a tumor therapy, some of its most successful applications are for non-malignant disease. In a series of three reviews we will discuss the mechanisms that operate in the field of PDT. Part one discusses the recent explosion in discovery and chemical synthesis of new PS. Some guidelines on how to choose an ideal PS for a particular application are presented. The photochemistry and photophysics of PS and the two pathways known as Type I (radicals and reactive oxygen species) and Type II (singlet oxygen) photochemical processes are discussed. To carry out PDT effectively in vivo, it is necessary to ensure sufficient light reaches all the diseased tissue. This involves understanding how light travels within various tissues and the relative effects of absorption and scattering. The fact that most of the PS are also fluorescent allows various optical imaging and monitoring strategies to be combined with PDT. The most important factor governing the outcome of PDT is how the PS interacts with cells in the target tissue or tumor, and the key aspect of this interaction is the subcellular localization of the PS. Examples of PS that localize in mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus and plasma membranes are given. Finally the use of 5-aminolevulinic acid as a natural precursor of the heme biosynthetic pathway, stimulates accumulation of the PS protoporphyrin IX is described.

Down-regulation of oxidative stress and COX-2 and iNOS expressions by dimethyl lithospermate in aged rat kidney

Oxidative stress has been proposed to be a major cause of aging and many age-related diseases. Peroxynitrite (ONOO(-)), formed from the reaction of superoxide ((•)O2 (-)) and nitric oxide (NO), is a cytotoxic species that can oxidize various cellular components, such as proteins, lipids, and DNA. The present study investigated whether dimethyl lithospermate (DML), isolated from Salvia miltiorrhiza, modulates age-related increases of ONOO(-), NO, and reactive species (RS) levels and expressions of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). For this study, 20-month-old rats were intraperitoneally injected with 5 or 10 mg/kg/day of DML, and 6-month-old rats were used as young control animals. Our results indicated that DML reduces ONOO(-) levels in a dose-dependent manner. The data also revealed that DML has significant inhibitory effects on NO metabolites and RS generation in a dose-dependent manner during aging. Furthermore, the results of Western blot analysis revealed that DML treatment reduces age-associated increases in COX-2 and iNOS expressions. Thus, this study found that DML caused the decrease of renal oxidative stress and COX-2 and iNOS expressions in aged rats. The significance of the present study is the finding of DML in its potential application against the aging process.

Evaluating the antioxidative activity of diselenide containing compounds in human blood

This study was designed to determine and compare the antioxidant effects of synthetic organoselenium compounds. In experimental trials three different diselenides were used: bis(2-hydroxyphenyl) diselenide, bis{[2-(4-hydroxybenzyl)imino]phenyl} diselenide and bis[2-(4-methylphenylsulfonylamino)phenyl] diselenide. The compounds were screened for antioxidant activities in human blood under oxidation stress conditions. Oxidative stress was induced in vitro in human blood platelet samples and in plasma by 0.1 mM peroxynitrite (ONOO(-)) or by Fe(2+). In experimental trials the levels of chosen oxidative stress markers (TBARS, O2(-), and protein carbonyl groups) were significantly decreased by the action of the tested compounds. The antioxidative properties and the changes in proteins and lipids in the presence of new synthesized selenoorganic compounds were studied in vitro and compared with activity of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one)--a classical antioxidant, well known as the most important glutathione peroxidase mimetic agent. Our results indicate that the tested diselenides have distinctly protective effects against oxidative alterations of biomolecules caused by ONOO(-) and Fe(2+) in blood platelets and in plasma. Therefore it seems that not only ebselen with a wide spectrum of therapeutic actions but also other organoselenium compounds can be considered in the future as active pharmacological agents.

CYP2E1-catalyzed alcohol metabolism: role of oxidant generation in interferon signaling, antigen presentation and autophagy

Cytochrome P450 2E1 (CYP2E1) is one of two major enzymes that catalyze ethanol oxidation in the liver. CYP2E1 is also unique because it is inducible, as its hepatic content rises after continuous (chronic) ethanol administration, thereby accelerating the rate of ethanol metabolism and affording greater tolerance to heavy alcohol consumption. However, the broad substrate specificity of CYP2E1 and its capacity to generate free radicals from alcohol and other hepatotoxins, places CYP2E1 as a central focus of not only liver toxicity, but also as an enzyme that regulates cytokine signaling, antigen presentation, and macromolecular degradation, all of which are crucial to liver cell function and viability. Here, we describe our own and other published work relevant to the importance of CYP2E1-catalyzed ethanol oxidation and how this catalysis affects the aforementioned cellular processes to produce liver injury.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

Ubiquitin-proteasome pathway and cellular responses to oxidative stress

The ubiquitin-proteasome pathway (UPP) is the primary cytosolic proteolytic machinery for the selective degradation of various forms of damaged proteins. Thus, the UPP is an important protein quality control mechanism. In the canonical UPP, both ubiquitin and the 26S proteasome are involved. Substrate proteins of the canonical UPP are first tagged by multiple ubiquitin molecules and then degraded by the 26S proteasome. However, in noncanonical UPP, proteins can be degraded by the 26S or the 20S proteasome without being ubiquitinated. It is clear that a proteasome is responsible for selective degradation of oxidized proteins, but the extent to which ubiquitination is involved in this process remains a subject of debate. Whereas many publications suggest that the 20S proteasome degrades oxidized proteins independent of ubiquitin, there is also solid evidence indicating that ubiquitin and ubiquitination are involved in degradation of some forms of oxidized proteins. A fully functional UPP is required for cells to cope with oxidative stress and the activity of the UPP is also modulated by cellular redox status. Mild or transient oxidative stress up-regulates the ubiquitination system and proteasome activity in cells and tissues and transiently enhances intracellular proteolysis. Severe or sustained oxidative stress impairs the function of the UPP and decreases intracellular proteolysis. Both the ubiquitin-conjugating enzymes and the proteasome can be inactivated by sustained oxidative stress, especially the 26S proteasome. Differential susceptibilities of the ubiquitin-conjugating enzymes and the 26S proteasome to oxidative damage lead to an accumulation of ubiquitin conjugates in cells in response to mild oxidative stress. Thus, increased levels of ubiquitin conjugates in cells seem to be an indicator of mild oxidative stress.

Vitamin C inhibits NO-induced stabilization of HIF-1alpha in HUVECs

HIF-1alpha represents the oxygen-regulated sub-unit of the transcription factor HIF-1, which regulates the transcription of numerous genes involved in cellular response to hypoxia and oxidative stress. It is shown here that nitric oxide (NO) induces HIF-1alpha stabilization in human endothelial cells from umbilical cords (HUVECs) under normoxic conditions. HIF-1alpha protein was increased approximately 36-fold after incubation with 500 microM DETA-NO, which releases a steady state NO concentration of roughly one thousandth of the initial concentration of the donor. Loading of the cells with vitamin C counteracted NO-induced HIF-1alpha accumulation. Based on the observations that oxidative and nitrosative stress can influence the activity of the proteasomal system, which is responsible for the non-lysosomal degradation of proteins, among them HIF-1alpha, it was investigated whether NO-induced stabilization of HIF-1alpha might be due to reduced 20S proteasomal activity. This hypothesis could not be proved, because NO concentrations to inhibit 20S proteasomal activity were about one order of magnitude higher than that to inhibit HIF-1alpha degradation.

Visible light sensitized inactivation of MS-2 bacteriophage by a cationic amine-functionalized C60 derivative

Recently, we reported the successful synthesis of various hexakis C60 derivatives (i.e., C60 with six functional groups containing NH3+-, CO2H-, or OH-terminals) with enhanced stability in water for aqueous phase application (Lee et al., Environ. Sci. Technol. 2009, 43, pp 6604-6610). Among these newly synthesized C60 derivatives, the cationic hexakis C60 derivative with amine functionality, C60(CR2)6 (R=CO2(CH2)2NH3+CF3CO2-), was found to exhibit remarkable efficiency to inactivate Escherichia coli and MS-2 bacteriophage under UVA irradiation. Herein, we report that this amine-functionalized C60 derivative is also photoactive in response to visible light from both commercial fluorescence lamps and sunlight. Efficient production of 1O2, facile reaction of 1O2 with proteins in MS-2 phage capsid and electrostatic attraction between positively charged C60 derivative and negatively charged MS-2 phage collectively contributed to high efficiency of MS-2 phage inactivation in this photocatalytic disinfection system. The rate of 1O2 production was evaluated using a probe compound, furfuryl alcohol, and 1O2 CT (the product of 1O2 concentration and exposure time) required to achieve a target level of virus inactivation was quantitatively analyzed. The unique visible-light sensitized virucidal property makes this C60 derivative highly desirable for the development of sustainable disinfection strategies that do not require continuous chemical addition nor an external energy source other than ambient light.

Butein up-regulates the expression of the π class of glutathione S-transferase in rat primary hepatocytes through the ERK/AP-1 pathway

Induction of phase II enzymes is an important mechanism of chemoprevention. Here we compared the effects of chalcones on the expression of the π class of glutathione S-transferase (GSTP) in rat primary hepatocytes. Hepatocytes were treated with 10 or 25 μM of phloretin or butein for 24 h. Both butein and phloretin dose-dependently increased GSTP protein expression, and the induction potency of butein was stronger than that of phloretin. The increase in GSTP mRNA in cells treated with 25 μM of phloretin and butein was 107% and 211%, respectively (P < 0.05). Butein increased GST enzyme activity by 27% compared with that in the control cells (P < 0.05). In contrast, phloretin had no significant effect on GST enzyme activity. The pTA-luciferase reporter construct with the rat -2.7 kb GSTP promoter region was transiently transfected into Clone 9 liver cells, and the luciferase activity in butein-treated cells was 1.1-fold higher than that in control cells (P < 0.05). GSTP enhancer 1 (GPE1) deletion abolished the induction of reporter activity by butein. The phosphorylation of extracellular signal-regulated kinase (ERK), but not of c-Jun NH2-terminal kinase (JNK) and p38, was stimulated in the presence of butein. Pretreatment with PD98059, an ERK inhibitor, alleviated the increase in activator protein-1 (AP-1)-DNA binding activity and also the activation of GSTP protein expression by butein. Moreover, c-Jun is likely to bind to the GPE1. Silencing of ERK2 by siRNA gene knockdown reduced the butein-induced expression of GSTP. In conclusion, the increased GSTP expression by butein is likely related to the ERK-AP-1 pathway.

Inhibitors of oxidation and matrix metalloproteinases, floridoside, and D-isofloridoside from marine red alga Laurencia undulata

In the exploration of abundant marine biological resources, edible red alga Laurencia undulata led to two bioactive isolates: floridoside (1) and D-isofloridoside (2). For the first time, the antioxidant properties of both derivatives (1 and 2) were characterized via free radical scavenging using the ESR technique, reactive oxygen species (ROS) inhibition, membrane protein oxidation, myeloperoxidase (MPO) inhibition, gene expression levels of glutathione (GSH) and superoxide dismutase (SOD), and protein expression of MMP-2 and MMP-9. The results demonstrate that floridoside and D-isofloridoside possess significant antioxidant capacity and are potential inhibitors of MMP-2 and MMP-9. These results clarified that these components may be responsible for the relative activities of crude extract from this genus, which is used as folk medicine. Furthermore, the structure-activity relationships were also suggested. Both isomers could be effective candidates for applications in food and pharmaceutical fields as natural marine antioxidants.

The proteasome is an integral part of solar ultraviolet a radiation-induced gene expression

Solar ultraviolet (UV) A radiation is a well known trigger of signaling responses in human skin fibroblasts. One important consequence of this stress response is the increased expression of matrix metalloproteinase-1 (MMP-1), which causes extracellular protein degradation and thereby contributes to photoaging of human skin. In the present study we identify the proteasome as an integral part of the UVA-induced, intracellular signaling cascade in human dermal fibroblasts. UVA-induced singlet oxygen formation was accompanied by protein oxidation, the cross-linking of oxidized proteins, and an inhibition of the proteasomal system. This proteasomal inhibition subsequently led to an accumulation of c-Jun and phosphorylated c-Jun and activation of activator protein-1, i.e. transcription factors known to control MMP-1 expression. Increased transcription factor activation was also observed if the proteasome was inhibited by cross-linked proteins or lactacystin, indicating a general mechanism. Most importantly, inhibition of the proteasome was of functional relevance for UVA-induced MMP-1 expression, because overexpression of the proteasome or the protein repair enzyme methionine sulfoxide reductase prevented the UVA-induced induction of MMP-1. These studies show that an environmentally relevant stimulus can trigger a signaling pathway, which links intracellular and extracellular protein degradation. They also identify the proteasome as an integral part of the UVA stress response.

Hesperetin: A Potent Antioxidant Against Peroxynitrite

Peroxynitrite (ONOO-) is a reactive oxidant formed from superoxide (*O2(-)) and nitric oxide (*NO), that can oxidize several cellular components, including essential protein, non-protein thiols, DNA, low-density lipoproteins (LDL), and membrane phospholipids. ONOO- has contributed to the pathogenesis of diseases such as stroke, heart disease, Alzheimer's disease, and atherosclerosis. Because of the lack of endogenous enzymes to thwart ONOO- activation, developing a specific ONOO- scavenger is remarkably important. In this study, the ability of hesperetin (3',5,7-trihydroxy-4-methoxyflavanone) to scavenge ONOO- and to protect cells against ONOO- and ROS was investigated. The data gained show that hesperetin can efficiently scavenge authentic ONOO- . In spectrophotometric analysis, the data revealed that hesperetin led to declined ONOO- -mediated nitration of tyrosine through electron donation. Hesperetin exhibited significant inhibition on the nitration of bovine serum albumin (BSA) by ONOO- in a dose-dependent manner. Hesperetin also manifested cytoprotection from cell damage induced by ONOO- and ROS. The present study suggests that hesperetin is a powerful ONOO- scavenger and promotes cellular defense activity in the protection against ONOO- involved diseases.

Validation of an in vitro model for assessment of androstenedione hepatotoxicity using the rat liver cell line clone-9

Androstenedione, a naturally occurring steroid hormone, has been used to enhance athletic performance. Little is known, however, about its hepatotoxicity. Clone-9 cells, a non-transformed epithelial cell line that was originally isolated from normal liver of a 4-week old Sprague-Dawley rat, were used as an in vitro model to assess the hepatotoxic potential of androstenedione. The cultures were treated with androstenedione for 24 h at 37 degrees C in 5% CO(2) at concentrations of 0-100 microg ml(-1). After the treatment period, the cells and the culture supernatants were assayed for markers of cytotoxicity which included: release of liver enzymes, cell viability, cellular double-stranded DNA content, oxidative stress, steatosis, cellular ATP content, caspase-3 activity, the mitochondrial permeability transition and induction of cytochrome P450 activity. Significant concentration-dependent differences from control were observed in some endpoints at medium concentrations of 10 microg ml(-1) and above. These in vitro findings were compared with comparable endpoints obtained from an in vivo study of androstenedione toxicity in female Sprague-Dawley rats. Of the eight endpoints that could be compared between the two studies, only three (lipid accumulation, ATP depletion and P450 activity) appeared to be concordant. This suggests that, under the experimental conditions used, the clone-9 cells were not a good model for androstenedione hepatotoxicity.

Protein carbonyls and antioxidant defenses in corkwing wrasse (Symphodus melops) from a heavy metal polluted and a PAH polluted site

The use of fish in environmental monitoring has become increasingly important in recent years as anthropogenic substances, many of which function as prooxidants, are accumulating in aquatic environments. We have measured a battery of antioxidant defenses as a measure of oxidative status, as well as protein carbonylation as a measure of oxidative damage, in corkwing wrasse (Symphodus melops) captured near a disused copper mine, where water and sediment are contaminated with heavy metals, and an aluminum smelter, a site contaminated with PAHs. Results were compared to two different reference sites. Fish at the heavy metal site had lower glucose-6-phosphate dehydrogenase activity and elevated protein carbonyls (1.8 times) compared to fish from the reference site. At the PAH site, EROD was increased 2-fold, while total glutathione and methemoglobin reductase concentration, were decreased. No differences were seen in protein carbonyl levels at the PAH site. Measures of both antioxidant defenses and oxidative damage should be used when assessing effects of xenobiotics on oxidative stress in fish species.

Spx mediates oxidative stress regulation of the methionine sulfoxide reductases operon in Bacillus subtilis

Background

All aerobically grown living cells are exposed to oxidative damage by reactive oxygen species (ROS). A major damage by ROS to proteins is caused by covalent modifications of methionine residues giving methionine sulfoxide (Met-SO). Methionine sulfoxide reductases are enzymes able to regenerate methionine and restore protein function after oxidative damage.

Results

We characterized the methionine sulfoxide reductase genes msrA and msrB in Bacillus subtilis, forming an operon transcribed from a single sigma A-dependent promoter. The msrAB operon was specifically induced by oxidative stress caused by paraquat (PQ) but not by H₂O₂. Spx, a global oxidative stress regulator in B. subtilis, is primarily responsible for this PQ-specific induction of msrAB expression. In support of this finding, an spx deletion mutant is extremely sensitive to PQ, and increased expression of msrA was identified in a clpX mutant in which Spx accumulated. However, the Spx effect was also visible under conditions where the protein did not accumulate (PQ treatment), suggesting a specific molecular effect at the level of the Spx protein. Indeed, the CXXC motif of Spx was found essential for its function in the PQ-specific induction of msrAB expression. PQ caused a modification of Spx requiring at least one of the cysteines of the CXXC motif of Spx. The PQ modified form of Spx showed a dynamic change in vivo.

Conclusion

The Spx mediated PQ-specific regulation pathway of the msrAB operon in B. subtilis is reported. Our results suggest that PQ induced the expression of msrAB partially through an oxidation on Spx via modification of its CXXC motif.

Proteasome activation by hepatitis C core protein is reversed by ethanol-induced oxidative stress

BACKGROUND & AIMS

The proteasome is a major cellular proteinase. Its activity is modulated by cellular oxidants. Hepatitis C core protein and ethanol exposure both cause enhanced oxidant generation. The aim was to investigate whether core protein, by its ability to generate oxidants, alters proteasome activity and whether these alterations are further affected by ethanol exposure.

METHODS

These interactions were examined in Huh-7 cell lines that expressed inducible HCV core protein and/or constitutive cytochrome P450 2E1 (CYP2E1) and as purified components in a cell-free system. Chymotrypsin-like proteasome activity was measured fluorometrically.

RESULTS

Proteasome activity in core-positive 191-20 cells was 20% higher than that in core-negative cells and was enhanced 3-fold in CYP2E1-expressing L14 cells. Exposure of core-positive cells to glutathione ethyl ester, catalase, or the CYP2E1 inhibitor diallyl sulfide partially reversed the elevation of proteasome activity in core-positive cells, whereas ethanol exposure suppressed proteasome activity. The results indicate that proteasome activity was up-regulated by low levels of core-induced oxidative stress but down-regulated by high levels of ethanol-elicited stress. These findings were partially mimicked in a cell-free system. Addition of core protein enhanced the peptidase activity of purified 20S proteasome containing the proteasome activator PA28 and was further potentiated by addition of liver mitochondrial and/or microsome fractions. However, proteasome activation was significantly attenuated when fractions were obtained from ethanol-fed animals.

CONCLUSIONS

HCV core protein interacts with PA28, mitochondrial, and endoplasmic reticulum proteins to cause low levels of oxidant stress and proteasome activation, which is dampened during ethanol metabolism when oxidant generation is higher.

Assay of 3-nitrotyrosine in tissues and body fluids by liquid chromatography with tandem mass spectrometric detection

3-Nitrotyrosine (3-NT) is a marker of protein nitration in physiological systems. It is present as 3-nitrotyrosine residues in proteins of tissue, extracellular matrix, plasma, and other body fluids and food. It is also present in body fluids and some beverages as free nitrotyrosine and is excreted in urine with the major urinary metabolite 3-nitro-4-hydroxyphenylacetic acid. Quantitation of 3-nitrotyrosine requires tandem mass spectrometry for specific detection. The method developed to determine 3-nitrotyrosine (along with protein glycation and oxidation adducts in a quantitative screening assay) by liquid chromatography with tandem mass spectrometric detection is described. The 3-NT residue contents of plasma protein, hemoglobin, lipoproteins, and cerebrospinal fluid protein and the concentrations of free 3-nitrotyrosine in plasma, urine, and cerebrospinal fluid are given. Changes of 3-nitrotyrosine residue and free 3-nitrotyrosine in diabetes, cirrhosis, acute and chronic renal failure, and neurological disorders, including Alzheimer's disease, are presented and compared with independent estimates.

Modulation of the expression of the pi class of glutathione S-transferase by Andrographis paniculata extracts and andrographolide

Andrographis paniculata (Ap) is a commonly used herb for traditional medicine in many Southeast Asian countries. In the present study, we investigated the effect of Ap on the expression of the pi class of glutathione S-transferase (GSTP) in rat primary hepatocytes. Hepatocytes were treated with 25 or 50 microg/mL of ethanol or ethyl acetate extracts of Ap (ApEE or ApEAE) or 10 or 20 microM andrographolide, which is the major active diterpene lactone of Ap, for 48 h. ApEE, ApEAE, and andrographolide dose-dependently induced GSTP protein and mRNA expression. In a GST activity assay, GST activity was significantly higher in cells treated with the maximum concentrations of ApEE, ApEAE, and andrographolide than in control cells (P<0.05). The pTA-2713 luciferase reporter construct containing rat GSTP enhancer 1 (GPE1) was transiently transfected into Clone 9 liver cells. Cells treated with ApEE, ApEAE, and andrographolide showed a dose-dependent increase in luciferase activity. GPE1 deletion abolished the induction efficiency of Ap. Also, the induction of GSTP expression by Ap was inhibited by wortmannin, which is an inhibitor of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. These results indicate that ApEE, ApEAE, and andrographolide induce GSTP expression. This induction is likely related to the PI3K/Akt pathway, and GPE1, an enhancer element in GSTP promoter, is essential for the induction.

Cross-linking of signal transducer and activator of transcription 3--a molecular marker for the photodynamic reaction in cells and tumors

PURPOSE

Photodynamic therapy (PDT) depends on the delivery of a photosensitizer to the target tissue that, under light exposure, produces singlet oxygen and other reactive oxygen species, which in turn cause the death of the treated cell. This study establishes a quantitative marker for the photoreaction that will predict the outcome of PDT.

EXPERIMENTAL DESIGN

Cells in tissue culture, murine s.c. tumors, and endobronchial carcinomas in patients were treated with PDT, and the noncleavable cross-linking of the latent signal transducer and activator of transcription 3 (STAT3) was determined.

RESULTS

Murine and human cancer cell lines reacted to PDT by an immediate covalent cross-linking of STAT3 to homodimeric and other complexes. The magnitude of this effect was strictly a function of the PDT reaction that is determined by the photosensitizer concentration and light dose. The cross-link reaction of STAT3 was proportional to the subsequent cytotoxic outcome of PDT. An equivalent photoreaction as detected in vitro occurred in tumors treated in situ with PDT. The light dose-dependent STAT3 cross-linking indicated the relative effectiveness of PDT as a function of the distance of the tissue to the treating laser light source. Absence of cross-links correlated with treatment failure.

CONCLUSIONS

The data suggest that the relative amount of cross-linked STAT3 predicts the probability for beneficial outcome, whereas absence of cross-links predicts treatment failure. Determination of STAT3 cross-links after PDT might be clinically useful for early assessment of PDT response.

Inactivation of cysteine and serine proteases by singlet oxygen

The reaction of singlet oxygen with individual proteins is less well understood than that with other biological molecules. The inhibition of caspase 3 by singlet oxygen appears to involve the modification of a catalytic cysteine residue, since the reactivity of the sulfhydryl with alkylating agents decreased after singlet oxygen treatment. In addition to three cysteine proteases, two serine proteases were also found to be inhibited by singlet oxygen with a similar dose dependency, while an aspartate protease and a metalloprotease were not affected. The carbonyl content of these enzymes was elevated as the result of treatment with singlet oxygen. The catalytic center in serine proteases and cysteine proteases, in which catalytic reactions are based on similar mechanisms involving nucleophilic catalysis assisted by histidine as a general acid/base, can be expected to be modified by singlet oxygen and undergo inactivation.

Nitrotyrosine and protein carbonyls are equally distributed in HT22 cells after nitrosative stress

The generation of reactive oxygen and nitrogen species is an inevitable result of cellular metabolism and environmental influence. Such oxidation processes are always combined with the formation of various protein oxidation products. Environmental oxidants might either be activated inside the cell or act by themselves. Therefore, differences in the localization of oxidant formation might change the major compartment of oxidant action. Therefore, we employed NO donors (SNOC, DETA/NO, and Spe/NO) alone or in combination with the redox-cycling bipyridinium compound paraquat, the superoxide- and NO-releasing compound SIN-1, the relatively more lipophilic oxidants tert-butyl and cumene hydroperoxide, and peroxynitrite itself to test the ability of these compounds to generate oxidized and nitrated proteins in various cellular compartments. Combined treatment with oxidants and nitrating compounds led to the formation of protein carbonyls and nitrotyrosine with a severalfold higher concentration in the cytosol, compared to the nucleus. In fluorescence microscopy studies, the resulting protein modifications show a similar distribution of oxidized proteins and nitrotyrosine with highest concentrations in the perinuclear area. Studying the time- and concentration-dependent formation and degradation of protein carbonyls and nitrated proteins large similarities could be measured. Therefore, it can be concluded that formation, localization, and kinetics of protein carbonyl and nitrotyrosine formation parallel each other depending on the stress-inducing agent.

Binding of aflatoxins to the 20S proteasome: effects on enzyme functionality and implications for oxidative stress and apoptosis

Aflatoxins (AF) are contaminants of improperly stored foods; they are potent genotoxic and carcinogenic compounds, exerting their effects through damage to DNA. They can also induce mutations that increase oxidative damage. The goal of this study was to evaluate the possibility that a third mechanism could be involved in the carcinogenic action of aflatoxins, namely, direct binding to key enzymes involved in the regulatory pathways of the cell cycle, thereby modulating enzyme functionality. The 20S constitutive and immunoproteasome peptidase and proteolytic activities were assayed in the presence of aflatoxins B1, G1 and M1. All three toxins activated multiple peptidase activities of the proteasome. Aflatoxin (AF) M1 was the most potent activator of proteasome activity, while the constitutive 20S proteasome was specifically stimulated by AFG1. Furthermore, the effects of AFB1 on cultured hepatoma cells were investigated and the various proteasomal activities determined with cell lysates were differently affected. Taking into account the key role of the proteasome in cellular defense against oxidative stress, the carbonyl group content and the activities of antioxidant enzymes in cell lysates were analyzed. The proapoptotic effect of AFB1 was also investigated by measuring caspase-3 activity and cellular levels of p27 and IkappaBalpha.