8-nitroguanine, a product of nitrative DNA damage caused by reactive nitrogen species: formation, occurrence, and implications in inflammation and carcinogenesis

Comprehensive assessment of Zingiber sianginensis: Phytometabolomic analysis and its impact on oxidative stress biomarkers

In India, ginger is highly valued for cultural and medicinal purposes. Besides traditional uses, ginger has been proven for its efficacy in cancer, chemotherapy-induced nausea, bacterial infections, neuroinflammation, and oxidative stress. This study focuses on Zingiber sianginensis, a rare ginger species in the Siang region of Arunachal Pradesh, India. This study studied pharmacognostical evaluation, phytometabolomics analysis, and its effect on oxidative stress biomarkers. Microscopic and chemical tests were employed for pharmacognostical evaluation, revealing distinctive characteristics of Zingiber sianginensis, such as non-close collateral vascular bundles and unique cork layers. Chemical tests, including the phloroglucinol and hydrochloric acid test, differentiated Zingiber sianginensis from Zingiber officinale Roscoe. Phytometabolomics analysis, using Gas Chromatography-Mass Spectrometry (GC/MS) and Liquid Chromatography-Electrospray Ionisation-Quadrupole Time of Flight-Mass Spectrometry (LC-ESI-QTOF-MS/MS) techniques, identified a diverse range of metabolites in Zingiber sianginensis, including polyphenols, monoterpenoids, diterpenoids, sesquiterpenoids, and organic compounds. The LC-ESI-QTOF-MS/MS analysis revealed 158 compounds, verified through cross-referencing with established databases. Heavy metal analysis by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) confirmed that Zingiber sianginensis complies with safety standards, showing concentrations of heavy metals within acceptable limits. The isolation and characterization of compounds from Zingiber sianginensis identified natural products such as (R)-(-)- alpha-Curcumene (1), 1-Dehydro-[10]-gingerdione (2), 6-Shogaol (3), and 6-Gingerol (4). Quantification of 6-gingerol revealed that Zingiber sianginensis contains approximately twice the amount compared to Zingiber officinale Roscoe's, suggesting its potential as a source for higher 6-gingerol content. The hydroalcoholic extract of Zingiber sianginensis exhibited antioxidant properties, reducing oxidative stress biomarkers in human dermal fibroblast cells treated with rotenone. Allantoin and 3-bromotyrosine levels significantly decreased, indicating the extract's potential in combating oxidative stress-related disorders. Overall, this comprehensive study provides valuable insights into the pharmacognostical, phytometabolomic, and safety aspects of Zingiber sianginensis, highlighting its potential as a source of bioactive compounds with health benefits.

Role of Oxidative Stress and Inflammation in Doxorubicin-Induced Cardiotoxicity: A Brief Account

Cardiotoxicity is the main side effect of several chemotherapeutic drugs. Doxorubicin (Doxo) is one of the most used anthracyclines in the treatment of many tumors, but the development of acute and chronic cardiotoxicity limits its clinical usefulness. Different studies focused only on the effects of long-term Doxo administration, but recent data show that cardiomyocyte damage is an early event induced by Doxo after a single administration that can be followed by progressive functional decline, leading to overt heart failure. The knowledge of molecular mechanisms involved in the early stage of Doxo-induced cardiotoxicity is of paramount importance to treating and/or preventing it. This review aims to illustrate several mechanisms thought to underlie Doxo-induced cardiotoxicity, such as oxidative and nitrosative stress, inflammation, and mitochondrial dysfunction. Moreover, here we report data from both in vitro and in vivo studies indicating new therapeutic strategies to prevent Doxo-induced cardiotoxicity.

8-Aminopurines in the Cardiovascular and Renal Systems and Beyond

Screening of compounds comprising 8-substituted guanine revealed that 8-aminoguanosine and 8-aminoguanine cause diuresis/natriuresis/glucosuria, yet decrease potassium excretion. Subsequent investigations demonstrated that 8-aminoguanosine's effects are mediated by its metabolite 8-aminoguanine. The mechanism by which 8-aminoguanine causes diuresis/natriuresis/glucosuria involves inhibition of PNPase (purine nucleoside phosphorylase), which increases renal interstitial inosine levels. Additional evidence suggests that inosine, via indirect or direct adenosine A2B receptor activation, increases renal medullary blood flow which enhances renal excretory function. Likely, 8-aminoguanine has pleiotropic actions that also alter renal excretory function. Indeed, the antikaliuretic effects of 8-aminoguanine are independent of PNPase inhibition. 8-Aminoguanine is an endogenous molecule; nitrosative stress leads to production of biomolecules containing 8-nitroguanine moieties. Degradation of these biomolecules releases 8-nitroguanosine and 8-nitro-2'-deoxyguanosine which are converted to 8-aminoguanine. Also, guanosine and guanine per se may contribute to 8-aminoguanine formation. 8-Aminoinosine, 8-aminohypoxanthine, and 8-aminoxanthine likewise induce diuresis/natriuresis/glucosuria, yet do not reduce potassium excretion. Thus, there are several pharmacologically active 8-aminopurines with nuanced effects on renal excretory function. Chronic treatment with 8-aminoguanine attenuates hypertension in deoxycorticosterone/salt rats, prevents strokes, and increases lifespan in Dahl salt-sensitive rats on a high salt diet and attenuates the metabolic syndrome in rats; 8-aminoguanosine retards progression of pulmonary hypertension in rats and anemia and organ damage in sickle cell mice. 8-Aminoguanine reverses age-associated lower urinary tract dysfunction and retinal degeneration. 8-Aminopurines represent a new class of agents (and potentially endogenous factors) that have beneficial effects on the cardiovascular system and kidneys and may turn back the clock in age-associated diseases.

Functions of nitric oxide-mediated post-translational modifications under abiotic stress

Environmental conditions greatly impact plant growth and development. In the current context of both global climate change and land degradation, abiotic stresses usually lead to growth restriction limiting crop production. Plants have evolved to sense and respond to maximize adaptation and survival; therefore, understanding the mechanisms involved in the different converging signaling networks becomes critical for improving plant tolerance. In the last few years, several studies have shown the plant responses against drought and salinity, high and low temperatures, mechanical wounding, heavy metals, hypoxia, UV radiation, or ozone stresses. These threats lead the plant to coordinate a crosstalk among different pathways, highlighting the role of phytohormones and reactive oxygen and nitrogen species (RONS). In particular, plants sense these reactive species through post-translational modification (PTM) of macromolecules such as nucleic acids, proteins, and fatty acids, hence triggering antioxidant responses with molecular implications in the plant welfare. Here, this review compiles the state of the art about how plant systems sense and transduce this crosstalk through PTMs of biological molecules, highlighting the S-nitrosylation of protein targets. These molecular mechanisms finally impact at a physiological level facing the abiotic stressful traits that could lead to establishing molecular patterns underlying stress responses and adaptation strategies.

Role of oxidative stress and inflammation-related signaling pathways in doxorubicin-induced cardiomyopathy

Doxorubicin (DOX) is a powerful and commonly used chemotherapeutic drug, used alone or in combination in a variety of cancers, while it has been found to cause serious cardiac side effects in clinical application. More and more researchers are trying to explore the molecular mechanisms of DOX-induced cardiomyopathy (DIC), in which oxidative stress and inflammation are considered to play a significant role. This review summarizes signaling pathways related to oxidative stress and inflammation in DIC and compounds that exert cardioprotective effects by acting on relevant signaling pathways, including the role of Nrf2/Keap1/ARE, Sirt1/p66Shc, Sirt1/PPAR/PGC-1α signaling pathways and NOS, NOX, Fe²⁺ signaling in oxidative stress, as well as the role of NLRP3/caspase-1/GSDMD, HMGB1/TLR4/MAPKs/NF-κB, mTOR/TFEB/NF-κB pathways in DOX-induced inflammation. Hence, we attempt to explain the mechanisms of DIC in terms of oxidative stress and inflammation, and to provide a theoretical basis or new idea for further drug research on reducing DIC. Video Abstract.

Potential preventive markers in the intracerebral hemorrhage process are revealed by serum untargeted metabolomics in mice using hypertensive cerebral microbleeds

Hypertensive cerebral microbleeds (HCMB) may be the early stage of hypertensive intracerebral hemorrhage (HICH), which is a serious threat to health due to its high mortality and disability rates. The early clinical symptoms of HCMB may not be significant. Moreover, it is difficult to achieve early diagnosis and intervention for targeted prevention of HICH. Although hypertension (HTN) is a predisposition for HCMB, it remains unclear whether there is any difference between hypertensive patients with or without HCMB. Therefore, we carried out liquid chromatography-mass spectrometry (LC-MS) to analyze early biomarkers for HCMB in mice with hypertension and to lay the foundation for early prevention of HICH in hypertensive patients. In total, 18 C57 male mice were randomly divided into the HCMB (n = 6), HTN (n = 6), and control groups (CON, n = 6). Hematoxylin-eosin and diaminobenzidine staining were used to assess the reliability of the model. The metabolite expression level and sample category stability were tested using the displacement test of orthogonal partial least squares discriminant analysis (OPLS-DA). Significant differences in metabolites were screened out using variable importance in the projection (VIP > 1), which were determined using the OPLS-DA model and the P-value of the t-test (P < 0.05) combined with the nonparametric rank-sum test. With an area under the curve (AUC) > 0.85 and a P-value of 0.05, the receiver operating characteristic curve (ROC) was used to further screen the distinct metabolites of HCMB. Compared with the HTN and CON groups, the HCMB group had significantly higher blood pressure and lower average body weight (P < 0.05). Through untargeted LC-MS analysis, 93 distinct metabolites were identified in the HCMB (P < 0.05, VIP > 1) group. Among these potential biomarkers, six significantly decreased and eight significantly increased differential metabolites were found. Meanwhile, we found that the HCMB group had statistically distinct arginine and purine metabolism pathways (P < 0.05), and citrulline may be the most significant possible biomarker of HCMB (AUC > 0.85, P < 0.05). All of these potential biomarkers may serve as early biomarkers for HICH in hypertension.

Fast and biphasic 8-nitroguanine production from guanine and peroxynitrite

Guanine (Gua), among purines, is a preferred oxidation/nitration target because of its low one-electron redox potential. The reactive oxygen/nitrogen species peroxynitrite (ONOO^-), produced in vivo by the reaction between nitric oxide (^•NO) and superoxide radical (O₂^•‒), is responsible for several oxidative modifications in biomolecules, including nitration, nitrosation, oxidation, and peroxidation. In particular, the nitration of Gua, although detected, as well as its reaction kinetics have been seldom investigated. Thus, we studied the concentration- and temperature-dependent formation of 8-nitroguanine (8-NitroGua) in phosphate buffer (pH 7.40) using stopped-flow spectrophotometry. Traces showed a biexponential behavior, with best-fit rate constants: k_fast = 4.4 s^-1 and k_slow = 0.41 s^-1 (30 °C, 400 μM both Gua and ONOO^-). k_fast increased linearly with the concentration of both reactants whereas k_slow was concentration-independent. Linear regression analysis of k_fast as a function of Gua and ONOO^- concentration yielded values of 2.5-6.3 × 10³ M^-1s^-1 and 1.5-3.5 s^-1 for the second-order (slope) and first-order (ordinate) rate constants, respectively (30 °C). Since ONOO^- is a short-lived species, its decay kinetics was also taken into account for this analysis. The 8-NitroGua product was stable for at least 4 h, so no spontaneous denitration was observed. Stopped-flow assays using antioxidants and free-radical scavengers suggested a mixed direct/indirect reaction mechanism for 8-NitroGua formation. Gua nitration by ONOO^- was also observed in the presence of physiologically relevant CO₂ concentrations. The reaction product identity, its yield (∼4.2%, with 400 μM ONOO^- and 200 μM Gua), and the reaction mechanism were unequivocally determined by HPLC-MS/MS experiments. In conclusion, 8-NitroGua production at physiologic pH reached significant levels in a few hundred milliseconds, suggesting that the process might be kinetically relevant in vivo and can likely cause permanent nitrative damage to DNA bases.

8-Aminoinosine and 8-Aminohypoxanthine Inhibit Purine Nucleoside Phosphorylase and Exert Diuretic and Natriuretic Activity

8-Aminoguanine and 8-aminoguanosine (via metabolism to 8-aminoguanine) are endogenous 8-aminopurines that induce diuresis, natriuresis, and glucosuria by inhibiting purine nucleoside phosphorylase (PNPase); moreover, both 8-aminopurines cause antikaliuresis by other mechanisms. Because 8-aminoinosine and 8-aminohypoxanthine are structurally similar to 8-aminoguanosine and 8-aminoguanine, respectively, we sought to define their renal excretory effects. First, we compared the ability of 8-aminoguanine, 8-aminohypoxanthine, and 8-aminoinosine to inhibit recombinant PNPase. These compounds inhibited PNPase with a potency order of 8-aminoguanine > 8-aminohypoxanthine = 8-aminoinosine. Additional studies showed that 8-aminoinosine is a competitive substrate that is metabolized to a competitive PNPase inhibitor, namely 8-aminohypoxanthine. Administration of each 8-aminopurine (33.5 µmol/kg) reduced the guanine-to-guanosine and hypoxanthine-to-inosine ratios in urine, a finding confirming their ability to inhibit PNPase in vivo. All three 8-aminopurines induced diuresis, natriuresis, and glucosuria; however, the glucosuric effects of 8-aminohypoxanthine and 8-aminoinosine were less pronounced than those of 8-aminoguanine. Neither 8-aminohypoxanthine nor 8-aminoinosine altered potassium excretion, whereas 8-aminoguanine caused antikaliuresis. In vivo administration of 8-aminoinosine increased 8-aminohypoxanthine excretion, indicating that 8-aminohypoxanthine mediates, in part, the effects of 8-aminoinosine. Finally, 8-aminohypoxanthine was metabolized to 8-aminoxanthine by xanthine oxidase. Using ultraperformance liquid chromatography-tandem mass spectrometry, we identified 8-aminoinosine as an endogenous 8-aminopurine. In conclusion, 8-aminopurines have useful pharmacological profiles. To induce diuresis, natriuresis, glucosuria, and antikaliuresis, 8-aminoguanine (or its prodrug 8-aminoguanosine) would be preferred. If only diuresis and natriuresis, without marked glucosuria or antikaliuresis, is desired, 8-aminohypoxanthine or 8-aminoinosine might be useful. Finally, here we report the in vivo existence of another pharmacologically active 8-aminopurine, namely 8-aminoinosine. SIGNIFICANCE STATEMENT: Here, we report that a family of 8-aminopurines affects renal excretory function: effects that may be useful for treating multiple diseases including hypertension, heart failure, and chronic kidney disease. For diuresis and natriuresis accompanied by glucosuria and antikaliuresis, 8-aminoguanine (or its prodrug 8-aminoguanosine) would be useful; if only diuresis and natriuresis is called for, 8-aminohypoxanthine or 8-aminoinosine would be useful. Previously, we identified 8-aminoguanine and 8-aminoguanosine as endogenous 8-aminopurines; here, we extend the family of endogenous 8-aminopurines to include 8-aminoinosine.

TEB/POLQ plays dual roles in protecting Arabidopsis from NO-induced DNA damage

Nitric oxide (NO) is a key player in numerous physiological processes. Excessive NO induces DNA damage, but how plants respond to this damage remains unclear. We screened and identified an Arabidopsis NO hypersensitive mutant and found it to be allelic to TEBICHI/POLQ, encoding DNA polymerase θ. The teb mutant plants were preferentially sensitive to NO- and its derivative peroxynitrite-induced DNA damage and subsequent double-strand breaks (DSBs). Inactivation of TEB caused the accumulation of spontaneous DSBs largely attributed to endogenous NO and was synergistic to DSB repair pathway mutations with respect to growth. These effects were manifested in the presence of NO-inducing agents and relieved by NO scavengers. NO induced G2/M cell cycle arrest in the teb mutant, indicative of stalled replication forks. Genetic analyses indicate that Polθ is required for translesion DNA synthesis across NO-induced lesions, but not oxidation-induced lesions. Whole-genome sequencing revealed that Polθ bypasses NO-induced base adducts in an error-free manner and generates mutations characteristic of Polθ-mediated end joining. Our experimental data collectively suggests that Polθ plays dual roles in protecting plants from NO-induced DNA damage. Since Polθ is conserved in higher eukaryotes, mammalian Polθ may also be required for balancing NO physiological signaling and genotoxicity.

Biochemical Pathways of 8-Aminoguanine Production In Sprague-Dawley and Dahl Salt-Sensitive Rats

BACKGROUND

8-Aminoguanine exerts natriuretic and antihypertensive activity. Whether and how "free" 8-aminoguanine exists in vivo is unclear. Because 8-nitroguanosine is naturally occurring, we tested the hypothesis that 8-aminoguanine can arise from: pathway 1, 8-nitroguanosine→8-aminoguanosine→8-aminoguanine; and pathway 2, 8-nitroguanosine→8-nitroguanine→8-aminoguanine.

METHODS

8-Aminoguanine biosynthesis was explored in rats using renal microdialysis, mass spectrometry and enzyme kinetics.

RESULTS

In Sprague-Dawley rats, 8-nitroguanosine infusions increased kidney levels of 8-nitroguanine, 8-aminoguanosine and 8-aminoguanine; 8-nitroguanine infusions increased 8-aminoguanine. Purine nucleoside phosphorylase (PNPase) converted 8-nitroguanosine to 8-nitroguanine and 8-aminoguanosine to 8-aminoguanine. Forodesine (PNPase inhibitor) reduced metabolism of 8-nitroguanosine by pathway 2 and shunted metabolism of 8-nitroguanosine to 8-aminoguanosine. In Dahl salt-sensitive rats, 8-nitroguanosine infusions increased kidney levels of 8-nitroguanine, 8-aminoguanosine and 8-aminoguanine. These results indicate that both pathways 1 and 2 participate in the biosynthesis of 8-aminoguanine in Sprague-Dawley and Dahl rats. Endogenous 8-aminoguanine in kidneys and urine were elevated many-fold in Dahl, compared to Sprague-Dawley, rats. The increased levels of 8-aminoguanine in Dahl rats were not due to alterations in pathways 1 and 2 but were associated with increased urine levels of endogenous 8-nitroguanosine suggesting that the "upstream" production of 8-nitroguanosine was increased in Dahl rats. Dahl rats are known to have high levels of peroxynitrite, and peroxynitrite is known to nitrate guanosine in biomolecules. Here we confirm that a peroxynitrite donor increases kidney levels of 8-aminoguanine.

CONCLUSION

8-Aminoguanine occurs naturally via two distinct pathways and kidney levels of 8-aminoguanine are increased in Dahl rats, likely due to increased production of 8-nitroguanosine, a by-product of peroxynitrite chemistry.

Integration of DNA Repair, Antigenic Variation, Cytoadhesion, and Chance in Babesia Survival: A Perspective

Apicomplexan parasites live in hostile environments in which they are challenged chemically and their hosts attempt in many ways to kill them. In response, the parasites have evolved multiple mechanisms that take advantage of these challenges to enhance their survival. Perhaps the most impressive example is the evolutionary co-option of DNA repair mechanisms by the parasites as a means to rapidly manipulate the structure, antigenicity, and expression of the products of specific multigene families. The purpose of variant proteins that mediate cytoadhesion has long been thought to be primarily the avoidance of splenic clearance. Based upon known biology, I present an alternative perspective in which it is survival of the oxidative environment within which Babesia spp. parasites live that has driven integration of DNA repair, antigenic variation, and cytoadhesion, and speculate on how genome organization affects that integration. This perspective has ramifications for the development of parasite control strategies.

Inflammatory pathways and cholangiocarcinoma risk mechanisms and prevention

Cholangiocarcinoma (CCA), a neoplasm burdened by a poor prognosis and currently lacking adequate therapeutic treatments, can originate at different levels of the biliary tree, in the intrahepatic, hilar, or extrahepatic area. The main risk factors for the development of CCA are the presence of chronic cholangiopathies of various etiology. To date, the most studied prodromal diseases of CCA are primary sclerosing cholangitis, Caroli's disease and fluke infestations, but other conditions, such as metabolic syndrome, nonalcoholic fatty liver disease and obesity, are emerging as associated with an increased risk of CCA development. In this review, we focused on the analysis of the pro-inflammatory mechanisms that induce the development of CCA and on the role of cells of the immune response in cholangiocarcinogenesis. In very recent times, these cellular mechanisms have been the subject of emerging studies aimed at verifying how the modulation of the inflammatory and immunological responses can have a therapeutic significance and how these can be used as therapeutic targets.

Plasma checkpoint protein 1 (Chk1) as a potential diagnostic biomarker for opisthorchiasis and cholangiocarcinoma

BACKGROUND

Patients infected with a parasite often develop opisthorchiasis viverrini, which often progresses into cholangiocarcinoma (CCA) due to the asymptomatic nature of the infection. Currently, there are no effective diagnostic methods for opisthorchiasis or cholangiocarcinoma.

OBJECTIVE

The aim of this study was to identify the host-responsive protein that can be developed as a diagnostic biomarker of opisthorchiasis and cholangiocarcinoma.

METHODS

Plasma samples were collected from non-OVCCA, OV, and CCA subjects, and the proteomes were investigated by LC-MS/MS. Venn diagrams and protein network prediction by STITCH were used to identify the potential biomarkers. The level of candidate protein, the plasma checkpoint protein 1 (Chk1), was measured by indirect enzyme-linked immunosorbent assay (ELISA).

RESULTS

Chk1 was present in the center of the protein network analysis in both the OV and CCA groups. In addition, the plasma Chk1 levels were significantly increased in both groups (P< 0.05). The sensitivity of the opisthorchiasis viverrini and cholangiocarcinoma was 59.38% and 65.62%, respectively, while the specificity of both was 85.71%.

CONCLUSION

Chk1 was identified by differential plasma proteomes and was increased in O. viverrini-infected and cholangiocarcinoma-derived plasma samples. Higher levels of plasma Chk1 levels may serve as a potential diagnostic biomarker for opisthorchiasis and cholangiocarcinoma.

Melatonin, Its Metabolites and Their Interference with Reactive Nitrogen Compounds

Melatonin and several of its metabolites are interfering with reactive nitrogen. With the notion of prevailing melatonin formation in tissues that exceeds by far the quantities in blood, metabolites come into focus that are poorly found in the circulation. Apart from their antioxidant actions, both melatonin and N¹-acetyl-5-methoxykynuramine (AMK) downregulate inducible and inhibit neuronal NO synthases, and additionally scavenge NO. However, the NO adduct of melatonin redonates NO, whereas AMK forms with NO a stable product. Many other melatonin metabolites formed in oxidative processes also contain nitrosylatable sites. Moreover, AMK readily scavenges products of the CO₂-adduct of peroxynitrite such as carbonate radicals and NO₂. Protein AMKylation seems to be involved in protective actions.

A Brief Overview of Oxidative Stress in Adipose Tissue with a Therapeutic Approach to Taking Antioxidant Supplements

One of the leading causes of obesity associated with oxidative stress (OS) is excessive consumption of nutrients, especially fast-foods, and a sedentary lifestyle, characterized by the ample accumulation of lipid in adipose tissue (AT). When the body needs energy, the lipid is broken down into glycerol (G) and free fatty acids (FFA) during the lipolysis process and transferred to various tissues in the body. Materials secreted from AT, especially adipocytokines (interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α)) and reactive oxygen species (ROS), are impressive in causing inflammation and OS of AT. There are several ways to improve obesity, but researchers have highly regarded the use of antioxidant supplements due to their neutralizing properties in removing ROS. In this review, we have examined the AT response to OS to antioxidant supplements focusing on animal studies. The results are inconsistent due to differences in the study duration and diversity in animals (strain, age, and sex). Therefore, there is a need for different studies, especially in humans.

Recent progress in the LC-MS/MS analysis of oxidative stress biomarkers

The presence of a dynamic and balanced equilibrium between the production of reactive oxygen (ROS) and nitrogen (RNS) species and the in-house antioxidant defense mechanisms is characteristic for a healthy body. During oxidative stress (OS), this balance is switched to increased production of ROS and RNS, exceeding the capacity of physiological antioxidant systems. This can cause damage to biological molecules, leading to loss of function and even cell death. Nowadays, there is increasing scientific and clinical interest in OS and the associated parameters to measure the degree of OS in biofluids. An increasing number of reports using LC-MS/MS methods for the analysis of OS biomarkers can be found. Since bioanalysis is usually complicated by matrix effects, various types of cleanup procedures are used to effectively separate the biomarkers from the matrix. This is an essential part of the analysis to prepare a reproducible and homogenous solution suitable for injection onto the column. The present review gives a summary of the chromatographic methods used for the determination of OS biomarkers in both urine and plasma, serum, and whole blood samples. The first part mainly describes the biological background of the different OS biomarkers, while the second part reports examples of chromatographic methods for the analysis of different metabolites connected with OS in biofluids, covering a period from 2015 till early 2020. The selected examples mainly include LC-MS/MS methods for isoprostanes, oxidized proteins, oxidized lipoproteins, and DNA/RNA biomarkers. The last part explains the clinical relevance of this review.

Nitric oxide: A radical molecule with potential biotechnological applications in fruit ripening

Nitric oxide (NO) is a short-life and free radical molecule involved in a wide range of cellular, physiological and stressful processes in higher plants. In recent years it has been observed that exogenous NO application can palliate adverse damages against abiotic and biotic stresses. Conversely, there is accumulating information indicating that endogenous NO participates significantly in the mechanism of modulation of the ripening in climacteric and non-climacteric fruits. Even more, when NO is exogenously applied, it can mediate beneficial effects during ripening and postharvest storage being one of the main effects the increase of antioxidant systems. Consequently, NO could be a promising biotechnological tool to improve crops through ameliorating nutritional indexes and to alleviate damages during fruit ripening and postharvest management. Thus, this approach should be complementary to previous strategies to allow preserving the quality and healthiness of fruits with a view of enhancing their added value. The present mini-review aims to provide an overview of NO biochemistry in plants and updated information on the relevance of NO in fruit ripening and postharvest stages with a view to its biotechnological applications.

Fatty Acid Mediators in the Tumor Microenvironment

Patients with cancer frequently overexpress inflammatory cytokines with an associated neutrophilia both of which may be downregulated by diets with high omega-3 polyunsaturated fatty acids (ω-3 PUFA). The anti-inflammatory activity of dietary ω-3 PUFA has been suggested to have anticancer properties and to improve survival of cancer patients. Currently, the majority of dietary research efforts do not differentiate between obesity and dietary fatty acid consumption as mediators of inflammatory cell expansion and tumor microenvironmental infiltration, initiation, and progression. In this chapter, we discuss the relationships between dietary lipids, inflammation, neoplasia and strategies to regulate these relationships. We posit that dietary composition, notably the ratio of ω-3 vs. ω-6 PUFA, regulates tumor initiation and progression and the frequency and sites of metastasis that, together, impact overall survival (OS). We focus on three broad topics: first, the role of dietary lipids in chronic inflammation and tumor initiation, progression, and regression; second, lipid mediators linking inflammation and cancer; and third, dietary lipid regulation of murine and human tumor initiation, progression, and metastasis.

Peroxynitrite induced signaling pathways in plant response to non-proteinogenic amino acids

Nitro/oxidative modifications of proteins and RNA nitration resulted from altered peroxynitrite generation are elements of the indirect mode of action of canavanine and meta-tyrosine in plants Environmental conditions and stresses, including supplementation with toxic compounds, are known to impair reactive oxygen (ROS) and reactive nitrogen species (RNS) homeostasis, leading to modification in production of oxidized and nitrated derivatives. The role of nitrated and/or oxidized biotargets differs depending on the stress factors and developmental stage of plants. Canavanine (CAN) and meta-tyrosine (m-Tyr) are non-proteinogenic amino acids (NPAAs). CAN, the structural analog of arginine, is found mostly in seeds of Fabaceae species, as a storage form of nitrogen. In mammalian cells, CAN is used as an anticancer agent due to its inhibitory action on nitric oxide synthesis. m-Tyr is a structural analogue of phenylalanine and an allelochemical found in root exudates of fescues. In animals, m-Tyr is recognized as a marker of oxidative stress. Supplementation of plants with CAN or m-Tyr modify ROS and RNS metabolism. Over the last few years of our research, we have collected the complex data on ROS and RNS metabolism in tomato (Solanum lycopersicum L.) plants exposed to CAN or m-Tyr. In addition, we have shown the level of nitrated RNA (8-Nitro-guanine) in roots of seedlings, stressed by the tested NPAAs. In this review, we describe the model of CAN and m-Tyr mode of action in plants based on modifications of signaling pathways induced by ROS/RNS with a special focus on peroxynitrite induced RNA and protein modifications.

Determination of levels of oxidative stress and nitrosative stress in patients with epilepsy

BACKGROUND

Epilepsy is one of the most common neurological diseases. The underlying pathophysiological mechanisms in epilepsy are still unknown. Oxidative stress is believed to be one of the factors involved in the pathogenesis of epileptogenesis. In various pathophysiological conditions, reactive nitrogen species (RNS) such as nitrogen and peroxynitrite are produced and these RNSs can bind to free nucleosides and nucleotides or to nucleosides and nucleotides existing in the DNA/RNA structure. 8-Nitroguanine (8-NG) is a typical DNA nucleobase product of nitrosative damage generated by RNS. It has been proposed that F2-isoprostanes, in particular 8-iso-Prostaglandin F2α (8-isoPGF2α), are specific, reliable and non-invasive biomarkers of lipid peroxidation in vivo. In the present study, we compared the levels of lipid oxidative stress biomarker 8-isoPGF2α and nitrosative stress DNA biomarker 8-NG in patients with epilepsy undergoing antiepileptic drug (AEDs) treatment and with those in healthy participants.

METHODS

The present study comprised 90 patients aged between 17 and 53 who were admitted to the Neurology Clinic of Cumhuriyet University and diagnosed with epilepsy. The patients were assigned into the intervention (n = 45) and control (n = 45) groups. Of the participants in the intervention group, 37.7% (n = 17) were treated with levetiracetam (LEV), 33.3% (n = 15) with valproic acid (VA) and 29% (n = 13) with carbamazepine. Serum 8-iso-PGF2α and 8-NG levels of the participants in the intervention and control groups were determined by ELISA.

RESULTS

There was no significant difference between the medication (LEV, VA, Carbamazepine) used by the participants and their 8-iso-PGF2α and 8-NG levels (p > 0.05). However, 8-iso-PGF2α and 8-NG were significantly higher in the participants in the intervention than in the participants in the control group (p < 0.001).

CONCLUSION

Our study demonstrated that there was an increase in oxidative and nitrosative stres markers in patients with epilepsy. There was no significant difference between the 8-iso-PGF2α and 8-NG levels of the participants taking three different AEDs.

Nitrated Nucleotides: New Players in Signaling Pathways of Reactive Nitrogen and Oxygen Species in Plants

Nitration of diverse biomolecules, including proteins, lipids and nucleic acid, by reactive nitrogen species represents one of the key mechanisms mediating nitric oxide (NO) biological activity across all types of organisms. 8-nitroguanosine 3'5'-cyclic monophosphate (8-nitro-cGMP) has been described as a unique electrophilic intermediate involved in intracellular redox signaling. In animal cells, 8-nitro-cGMP is formed from guanosine-5'-triphosphate by a combined action of reactive nitrogen (RNS) and oxygen species (ROS) and guanylate cyclase. As demonstrated originally in animal models, 8-nitro-cGMP shows certain biological activities closely resembling its analog cGMP; however, its regulatory functions are mediated mainly by its electrophilic properties and chemical interactions with protein thiols resulting in a novel protein post-translational modification termed S-guanylation. In Arabidopsis thaliana, 8-nitro-cGMP was reported to mediate NO-dependent signaling pathways controlling abscisic acid (ABA)-induced stomatal closure, however, its derivative 8-mercapto-cGMP (8-SH-cGMP) was later shown as the active component of hydrogen sulfide (H₂S)-mediated guard cell signaling. Here we present a survey of current knowledge on biosynthesis, metabolism and biological activities of nitrated nucleotides with special attention to described and proposed functions of 8-nitro-cGMP and its metabolites in plant physiology and stress responses.

8-Aminoguanine Induces Diuresis, Natriuresis, and Glucosuria by Inhibiting Purine Nucleoside Phosphorylase and Reduces Potassium Excretion by Inhibiting Rac1

Background 8-Aminoguanosine and 8-aminoguanine are K⁺-sparing natriuretics that increase glucose excretion. Most effects of 8-aminoguanosine are due to its metabolism to 8-aminoguanine. However, the mechanism by which 8-aminoguanine affects renal function is unknown and is the focus of this investigation. Methods and Results Because 8-aminoguanine has structural similarities with inhibitors of the epithelial sodium channel (ENaC), Na⁺/H⁺ exchangers, and adenosine A₁ receptors, we examined the effects of 8-aminoguanine on EN aC activity in mouse collecting duct cells, on intracellular pH of human proximal tubular epithelial cells, on responses to a selective A₁-receptor agonist in vivo, and on renal excretory function in A₁-receptor knockout rats. These experiments showed that 8-aminoguanine did not block EN aC, Na⁺/H⁺ exchangers, or A₁ receptors. Because Rac1 enhances activity of mineralocorticoid receptors and some guanosine analogues inhibit Rac1, we examined the effects of 8-aminoguanine on Rac1 activity in mouse collecting duct cells. Rac1 activity was significantly inhibited by 8-aminoguanine. Because in vitro 8-aminoguanine is a purine nucleoside phosphorylase ( PNP ase) inhibitor, we examined the effects of a natriuretic dose of 8-aminoguanine on urinary excretion of PNP ase substrates and products. 8-Aminoguanine increased and decreased, respectively, urinary excretion of PNP ase substrates and products. Next we compared in rats the renal effects of intravenous doses of 9-deazaguanine ( PNP ase inhibitor) versus 8-aminoguanine. 8-Aminoguanine and 9-deazaguanine induced similar increases in urinary Na⁺ and glucose excretion, yet only 8-aminoguanine reduced K⁺ excretion. Nsc23766 (Rac1 inhibitor) mimicked the effects of 8-aminoguanine on K⁺ excretion. Conclusions 8-Aminoguanine increases Na⁺ and glucose excretion by blocking PNP ase and decreases K⁺ excretion by inhibiting Rac1.

Mapping three guanine oxidation products along DNA following exposure to three types of reactive oxygen species

Reactive oxygen and nitrogen species generated during respiration, inflammation, and immune response can damage cellular DNA, contributing to aging, cancer, and neurodegeneration. The ability of oxidized DNA bases to interfere with DNA replication and transcription is strongly influenced by their chemical structures and locations within the genome. In the present work, we examined the influence of local DNA sequence context, DNA secondary structure, and oxidant identity on the efficiency and the chemistry of guanine oxidation in the context of the Kras protooncogene. A novel isotope labeling strategy developed in our laboratory was used to accurately map the formation of 2,2-diamino-4-[(2-deoxy-β-D-erythropentofuranosyl)amino]- 5(2 H)-oxazolone (Z), 8-oxo-7,8-dihydro-2'-deoxyguanosine (OG), and 8-nitroguanine (8-NO₂-G) lesions along DNA duplexes following photooxidation in the presence of riboflavin, treatment with nitrosoperoxycarbonate, and oxidation in the presence of hydroxyl radicals. Riboflavin-mediated photooxidation preferentially induced OG lesions at 5' guanines within GG repeats, while treatment with nitrosoperoxycarbonate targeted 3'-guanines within GG and AG dinucleotides. Little sequence selectivity was observed following hydroxyl radical-mediated oxidation. However, Z and 8-NO₂-G adducts were overproduced at duplex ends, irrespective of oxidant identity. Overall, our results indicate that the patterns of Z, OG, and 8-NO₂-G adduct formation in the genome are distinct and are influenced by oxidant identity and the secondary structure of DNA.

Targeting Oxidatively Induced DNA Damage Response in Cancer: Opportunities for Novel Cancer Therapies

Cancer is a death cause in economically developed countries that results growing also in developing countries. Improved outcome through targeted interventions faces the scarce selectivity of the therapies and the development of resistance to them that compromise the therapeutic effects. Genomic instability is a typical cancer hallmark due to DNA damage by genetic mutations, reactive oxygen and nitrogen species, ionizing radiation, and chemotherapeutic agents. DNA lesions can induce and/or support various diseases, including cancer. The DNA damage response (DDR) is a crucial signaling-transduction network that promotes cell cycle arrest or cell death to repair DNA lesions. DDR dysregulation favors tumor growth as downregulated or defective DDR generates genomic instability, while upregulated DDR may confer treatment resistance. Redox homeostasis deeply and capillary affects DDR as ROS activate/inhibit proteins and enzymes integral to DDR both in healthy and cancer cells, although by different routes. DDR regulation through modulating ROS homeostasis is under investigation as anticancer opportunity, also in combination with other treatments since ROS affect DDR differently in the patients during cancer development and treatment. Here, we highlight ROS-sensitive proteins whose regulation in oxidatively induced DDR might allow for selective strategies against cancer that are better tailored to the patients.

Sensitive Detection of 8-Nitroguanine in DNA by Chemical Derivatization Coupled with Online Solid-Phase Extraction LC-MS/MS

8-Nitroguanine (8-nitroG) is a major mutagenic nucleobase lesion generated by peroxynitrite during inflammation and has been used as a potential biomarker to evaluate inflammation-related carcinogenesis. Here, we present an online solid-phase extraction (SPE) LC-MS/MS method with 6-methoxy-2-naphthyl glyoxal hydrate (MTNG) derivatization for a sensitive and precise measurement of 8-nitroG in DNA. Derivatization optimization revealed that an excess of MTNG is required to achieve complete derivatization in DNA hydrolysates (MTNG: 8-nitroG molar ratio of 3740:1). The use of online SPE effectively avoided ion-source contamination from derivatization reagent by washing away all unreacted MTNG before column chromatography and the ionization process in mass spectrometry. With the use of isotope-labeled internal standard, the detection limit was as low as 0.015 nM. Inter- and intraday imprecision was <5.0%. This method was compared to a previous direct LC-MS/MS method without derivatization. The comparison showed an excellent fit and consistency, suggesting that the present method has satisfactory effectiveness and reliability for 8-nitroG analysis. This method was further applied to determine the 8-nitroG in human urine. 8-NitroG was not detectable using LC-MS/MS with derivatization, whereas a significant false-positive signal was detected without derivatization. It highlights the use of MTNG derivatization in 8-nitroG analysis for increasing the method specificity.

Reactive nitrogen species (RNS)-resistant microbes: adaptation and medical implications

Nitrosative stress results from an increase in reactive nitrogen species (RNS) within the cell. Though the RNS - nitric oxide (·NO) and peroxynitrite (ONOO-) - play pivotal physiological roles, at elevated concentrations, these moieties can be poisonous to both prokaryotic and eukaryotic cells alike due to their capacity to disrupt a variety of essential biological processes. Numerous microbes are known to adapt to nitrosative stress by elaborating intricate strategies aimed at neutralizing RNS. In this review, we will discuss both the enzymatic systems dedicated to the elimination of RNS as well as the metabolic networks that are tailored to generate RNS-detoxifying metabolites - α-keto-acids. The latter has been demonstrated to nullify RNS via non-enzymatic decarboxylation resulting in the production of a carboxylic acid, many of which are potent signaling molecules. Furthermore, as aerobic energy production is severely impeded during nitrosative stress, alternative ATP-generating modules will be explored. To that end, a holistic understanding of the molecular adaptation to nitrosative stress, reinforces the notion that neutralization of toxicants necessitates significant metabolic reconfiguration to facilitate cell survival. As the alarming rise in antimicrobial resistant pathogens continues unabated, this review will also discuss the potential for developing therapies that target the alternative ATP-generating machinery of bacteria.

Elevation in and persistence of multiple urinary biomarkers indicative of oxidative DNA stress and inflammation: Toxicological implications of maleic acid consumption using a rat model

Maleic acid (MA), an intermediate reagent used in many industrial products, instigated public health concerns in Taiwan when it was used to adulterate an array of starch-based delicacies to improve texture and storage time. Established studies reported that exposure to high concentrations of MA induce renal injury; little is known whether oxidative stress is induced at a relative low dose. This study aims to investigate the effect of oral single dose exposure of MA on the status of oxidative stress and inflammation. Single dose of MA at 0, 6 and 60 mg/kg (control, low- and high-dose groups, respectively) were orally administered to adult male and female rats. Urine samples were collected and analyzed to measure 8-hydroxy-2’-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F_2α (8-IsoPGF_2α), 8-nitroguanine (8-NO₂Gua) and N-acetyl-S-(tetrahydro-5-hydroxy-2-pentyl-3-furanyl)-L-cysteine (HNE-MA) using LC-MS/MS. Results revealed that oral consumption of MA induced oxidative DNA damage and lipid peroxidation, as demonstrated by the statistically significant increases in urinary levels of 8-NO₂Gua, 8-OHdG, and 8-isoPGF_2α, in high-dosed male rats within 12 h of oral gavage (p < 0.05). Additionally, increases in concentration of these biomarkers persist for days after consumption; male rats appear to be more sensitive to oxidative burden compared to their counterparts. The aforementioned findings could help elucidate the mechanisms through which nephrotoxicity occur.

8-Nitro-cGMP: A Novel Protein-Reactive cNMP and Its Emerging Roles in Autophagy

Nitric oxide (NO) raises the intracellular 3',5'-cyclic guanosine monophosphate (cGMP) level through the activation of soluble guanylate cyclase and, in the presence of reactive oxygen species (ROS), reacts with biomolecules to produce nitrated cGMP derivatives. 8-Nitro-cGMP was the first endogenous cGMP derivative discovered in mammalian cells (2007) and was later found in plant cells. Among the six nitrogen atoms in this molecule, the one in the nitro group (NO₂) comes from NO. This chapter asserts that this newly found cGMP is undoubtedly one of the major physiological cNMPs. Multiple studies suggest that its intracellular abundance might exceed that of unmodified cGMP. The characteristic chemical feature of 8-nitro-cGMP is its ability to modify proteinous cysteine residues via a stable sulfide bond. In this posttranslational modification, the nitro group is detached from the guanine base. This modification, termed "protein S-guanylation," is known to regulate the physiological functions of several important proteins. Furthermore, 8-nitro-cGMP participates in the regulation of autophagy. For example, in antibacterial autophagy (xenophagy), S-guanylation accumulates around invading bacterial cells and functions as a "tag" for subsequent clearance of the organism via ubiquitin modifications. This finding suggests the existence of a system for recognizing the cGMP structure on proteins. Autophagy induction by 8-nitro-cGMP is mechanistically distinct from the well-described starvation-induced autophagy and is independent of the action of mTOR, the master regulator of canonical autophagy.

8-Aminoguanosine Exerts Diuretic, Natriuretic, and Glucosuric Activity via Conversion to 8-Aminoguanine, Yet Has Direct Antikaliuretic Effects

8-Aminoguanosine induces diuresis, natriuresis, glucosuria, and antikaliuresis. These effects could be mediated via 8-aminoguanosine's metabolism to 8-aminoguanine. In this study, we tested this hypothesis in anesthetized rats. First, we demonstrated that at 55- to 85-minutes post-i.v. administration, 8-aminoguanosine and 8-aminoguanine (33.5 µmol/kg) significantly increased urine volume [ml/30 min: 8-aminoguanosine from 0.3 ± 0.1 to 0.9 ± 0.1 (mean ± S.E.M.; n = 7); 8-aminoguanine from 0.3 ± 0.1 to 1.5 ± 0.2 (n = 8)], sodium excretion (µmol/30 min: 8-aminoguanosine from 12 ± 5 to 109 ± 21; 8-aminoguanine from 18 ± 8 to 216 ± 31), and glucose excretion (µg/30 min: 8-aminoguanosine from 18 ± 3 to 159 ± 41; 8-aminoguanine from 17 ± 3 to 298 ± 65). Both compounds significantly decreased potassium excretion (µmol/30 min: 8-aminoguanosine from 62 ± 7 to 39 ± 9; 8-aminoguanine from 61 ± 10 to 34 ± 6). Next, we administered 8-aminoguanosine and 8-aminoguanine i.v. (33.5 µmol/kg) and measured renal interstitial (microdialysis probes) 8-aminoguanosine and 8-aminoguanine. The i.v. administration of 8-aminoguanosine and 8-aminoguanine similarly increased renal medullary interstitial levels of 8-aminoguanine [nanograms per milliliter; 8-aminoguanosine from 4 ± 1 to 1025 ± 393 (n = 6), and 8-aminoguanine from 2 ± 1 to 1069 ± 407 (n = 6)]. Finally, we determine the diuretic, natriuretic, glucosuric, and antikaliuretic effects of intrarenal artery infusions of 8-aminoguanosine and 8-aminoguanine (0.1, 0.3, and 1 µmol/kg/min). 8-Aminoguanine increased urine volume and sodium and glucose excretion by the ipsilateral kidney, yet had only mild effects at the highest dose in the contralateral kidney. Intrarenal infusions of 8-aminoguanosine did not induce diuresis, natriuresis, or glucosuria in either the ipsilateral or contralateral kidney, yet decreased potassium excretion in the ipsilateral kidney. Together these data confirm that the diuretic, natriuretic, and glucosuric effects of 8-aminoguanosine are not direct, but require metabolism to 8-aminoguanine. However, 8-aminoguanosine has direct antikaliuretic effects.

Targeting reactive nitrogen species suppresses hereditary pancreatic cancer

Germline mutation of BRCA2 induces hereditary pancreatic cancer. However, how BRCA2 mutation specifically induces pancreatic tumorigenesis remains elusive. Here, we have examined a mouse model of Brca2-deficiency-induced pancreatic tumors and found that excessive reactive nitrogen species (RNS), such as nitrite, are generated in precancerous pancreases, which induce massive DNA damage, including DNA double-strand breaks. RNS-induced DNA lesions cause genomic instability in the absence of Brca2. Moreover, with the treatment of antioxidant tempol to suppress RNS, not only are DNA lesions significantly reduced, but also the onset of pancreatic cancer is delayed. Thus, this study demonstrates that excess RNS are a nongenetic driving force for Brca2-deficiency-induced pancreatic tumors. Suppression of RNS could be an important strategy for pancreatic cancer prevention.

Comprehensive analysis of the formation and stability of peroxynitrite-derived 8-nitroguanine by LC-MS/MS: Strategy for the quantitative analysis of cellular 8-nitroguanine

Peroxynitrite is a major oxidizing and nitrating biological agent formed at sites of inflammation. Peroxynitrite can cause DNA damage and is thought to contribute to inflammation-related carcinogenesis. This study describes a sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the direct determination of peroxynitrite-derived 8-nitroguanine (8-nitroGua) in DNA hydrolysates. This method exhibited a sensitive detection limit of 3 fmol and inter- and intraday imprecision of <10% and was applied to systemically examine the formation and stability of peroxynitrite-derived 8-nitroGua in different DNA substrates under various conditions. The 8-nitroGua formation was maximal at pH 8. The formation rate of 8-nitroGua in different DNA substrates decreased in the order of monodeoxynucleoside>single-stranded DNA>double-stranded DNA. A stability test revealed that the half-life for the depurination of 8-nitroGua from DNA was short and affected by both the temperature and DNA structure. When present in monodeoxynucleoside, the half-life of 8-nitroGua was estimated to be ~6min at 25°C and 2.3h at ~0°C. In single-stranded DNA, the half-life varied from 1.6h at 37°C to 533h at -20°C, whereas the half-life increased from 2.4h at 37°C to 1115h at -20°C in double-stranded DNA. We demonstrated that the measurement of 8-nitroGua in isolated DNA is not practicable because 8-nitroGua is unstable and lost during DNA extraction from cell. Therefore, we suggest that directly detecting cellular 8-nitroGua following nuclear membrane lysis is an alternative measure of the nitrative damage of nucleic acids, accounting for both DNA and RNA lesions within cells.

Design, Synthesis, and Evaluation of Diazeniumdiolate-Based DNA Cross-Linking Agents Activatable by Glutathione S-Transferase

A novel class of O²-(2,4-dinitrophenyl)-1-[N,N-bis(2-substituted ethyl)amino]diazen-1-ium-1,2-diolates 4-6 were designed, synthesized, and biologically evaluated. The most active compound 6 caused significant DNA damage by releasing N,N-bis(2-TsO ethyl)amine and two molecules of nitric oxide (NO) after activation by GST/GSH in cancer cells, being more cytotoxic against three cancer cell lines than a well-known diazeniumdiolate-based anticancer agent JS-K, suggesting that the strategy has potential to extend to other O²-derived diazeniumdiolates to improve anticancer activity.

8-Aminoguanosine and 8-Aminoguanine Exert Diuretic, Natriuretic, Glucosuric, and Antihypertensive Activity

In vivo, guanine moieties in DNA, RNA, guanine nucleotides, or guanosine or guanine per se can undergo nitration (for example, by peroxynitrite) or hydroxylation (for example, by superoxide anion) on position 8 of the purine ring. Subsequent catabolism of these modified biomolecules leads to the production of a diverse group of 8-nitro, 8-amino, and 8-hydroxy guanosine and guanine compounds. Indeed, studies suggest the in vivo existence of 8-nitroguanosine, 8-nitroguanine, 8-aminoguanosine, 8-aminoguanine, 8-hydroxyguanosine, 8-hydroxy-2'-deoxyguanosine, and 8-hydroxyguanine. Since a multitude of these compounds exist in vivo, and since the renal effects of 8-substituted guanosine and guanine compounds are entirely unknown, we examined the effects of guanosine, guanine, 8-nitroguanosine, 8-nitroguanine, 8-hydroxyguanosine, 8-hydroxyguanine, 8-hydroxy-2'-deoxyguanosine, 8-aminoguanosine, and 8-aminoguanine (33.5 µmol/kg/min; intravenous infusion for 115 minutes) on excretion of sodium, potassium, and glucose in rats. Guanosine, 8-nitroguanosine, and 8-hydroxy-2'-deoxyguanosine had minimal natriuretic activity. Guanine, 8-nitroguanine, 8-hydroxyguanosine, and 8-hydroxyguanine had moderate natriuretic activity (increased sodium excretion by 9.4-, 7.8-, 7.1-, and 8.6-fold, respectively). In comparison with all other compounds, 8-aminoguanosine and 8-aminoguanine were highly efficacious and increased sodium excretion by 26.6- and 17.2-fold, respectively, exceeding that of a matched dose of amiloride (13.6-fold increase). 8-Aminoguanosine and 8-aminoguanine also increased glucose excretion by 12.1- and 12.2-fold, respectively, and decreased potassium excretion by 69.1 and 71.0%, respectively. Long-term radiotelemetry studies demonstrated that oral 8-aminoguanosine and 8-aminoguanine (5 mg/kg/day) suppressed deoxycorticosterone/salt-induced hypertension. These experiments demonstrate that some naturally occurring 8-substitued guanosine and guanine compounds, particularly 8-aminoguanosine and 8-aminoguanine, are potent and efficacious potassium-sparing diuretics/natriuretics that may represent a novel class of antihypertensive diuretics.

Analysis of Chlorination, Nitration, and Nitrosylation of Tyrosine and Oxidation of Methionine and Cysteine in Hemoglobin from Type 2 Diabetes Mellitus Patients by Nanoflow Liquid Chromatography Tandem Mass Spectrometry

The post-translational modification (PTM) of proteins by endogenous reactive chlorine, nitrogen, and oxygen species is implicated in certain pathological conditions, including diabetes mellitus. Evidence showed that the extents of modifications on a number of proteins are elevated in diabetic patients. Measuring modification on hemoglobin has been used to monitor the extent of exposure. This study develops an assay for simultaneous quantification of the extent of chlorination, nitration, and oxidation in human hemoglobin and to examine whether the level of any of these modifications is higher in poorly controlled type 2 diabetic mellitus patients. This mass spectrometry-based assay used the bottom-up proteomic strategy. Due to the low amount of endogenous modification, we first characterized the sites of chlorination at tyrosine in hypochlorous acid-treated hemoglobin by an accurate mass spectrometer. The extents of chlorination, nitration, and oxidation of a total of 12 sites and types of modifications in hemoglobin were measured by nanoflow liquid chromatography-nanospray ionization tandem mass spectrometry under the selected reaction monitoring mode. Relative quantification of these PTMs in hemoglobin extracted from blood samples shows that the extents of chlorination at α-Tyr-24, nitration at α-Tyr-42, and oxidation at the three methionine residues are significantly higher in diabetic patients (n = 19) than in nondiabetic individuals (n = 18). After excluding the factor of smoking, chlorination at α-Tyr-24, nitration at α-Tyr-42, and oxidation at the three methionine residues are significantly higher in the nonsmoking diabetic patients (n = 12) than in normal nonsmoking subjects (n = 11). Multiple regression analysis performed on the combined effect of age, body-mass index (BMI), and HbA1c showed that the diabetes factor HbA1c contributes significantly to the extent of chlorination at α-Tyr-24 in nonsmokers. In addition, age contributes to oxidation at α-Met-32 significantly in all subjects and in nonsmokers. These results suggest the potential of using chlorination at α-Tyr-24-containing peptide to evaluate protein damage in nonsmoking type 2 diabetes mellitus.

Entacapone is an Antioxidant More Potent than Vitamin C and Vitamin E for Scavenging of Hypochlorous Acid and Peroxynitrite, and the Inhibition of Oxidative Stress-Induced Cell Death

Background

Entacapone (ENT), a clinical drug for the treatment of Parkinson’s disease, has been shown to have antioxidant effects, but little is known about its antioxidant mechanisms. The objective of the current study was to determine the antioxidant activity of ENT against different species of oxidants and compared it with that of vitamin C and vitamin E. We also determined the effect of ENT on oxidative stress-induced cell death in human umbilical vein endothelial cells (HUVECs).

Material/Methods

The total antioxidant activities of ENT, vitamin C and vitamin E were determined with a standard DPPH-scavenging assay. Specific assays to determine ENT’s scavenging activity on hypochlorous acid (HOCl), peroxynitrite (ONOO⁻), and hydrogen peroxide (H₂O₂), and the chelating effect on Fe(II) were used. H₂O₂-induced cell death in HUVECs was determined with the MTT assay.

Results

ENT (10 and 20 μM) scavenged 60% and 83% of DPPH activity, respectively. These percentages were greater than those resulting from using the same concentrations of vitamin C and vitamin E. ENT’s HOCl-scavenging activity was concentration-dependent and 8 to 20 times stronger than those of vitamin C and vitamin E. ENT’s ONOO⁻-scavenging activity was 8% to 30% stronger than that of vitamin C. However, ENT, vitamin C, and vitamin E were not able to directly scavenge H₂O₂, and did not show any chelating effect on Fe(II). Importantly ENT, but not vitamin C or vitamin E, inhibited H₂O₂-induced cell death in HUVECs.

Conclusions

ENT is an antioxidant that can scavenge toxic HOCl and ONOO⁻ species and inhibit oxidative stress-induced cell death more effectively than vitamin C and vitamin E. ENT may have new clinical applications as an antioxidant in the treatment of ROS-induced diseases including cardiovascular disease, cancer, and neurodegenerative diseases.

Investigation on oxidative stress of nitric oxide synthase interacting protein from Clonorchis sinensis

Numerous evidences indicate that excretory-secretory products (ESPs) from liver flukes trigger the generation of free radicals that are associated with the initial pathophysiological responses in host cells. In this study, we first constructed a Clonorchis sinensis (C. sinensis, Cs)-infected BALB/c mouse model and examined relative results respectively at 3, 5, 7, and 9 weeks postinfection (p.i.). Quantitative reverse transcription (RT)-PCR indicated that the transcriptional level of both endothelial nitric oxide synthase (eNOS) and superoxide dismutase (SOD) gradually decreased with lastingness of infection, while the transcriptional level of inducible NOS (iNOS) significantly increased. The level of malondialdehyde (MDA) in sera of infected mouse significantly increased versus the healthy control group. These results showed that the liver of C. sinensis-infected mouse was in a state with elevated levels of oxidation stress. Previously, C. sinensis NOS interacting protein coding gene (named CsNOSIP) has been isolated and recombinant CsNOSIP (rCsNOSIP) has been expressed in Escherichia coli, which has been confirmed to be a component present in CsESPs and confirmed to play important roles in immune regulation of the host. In the present paper, we investigated the effects of rCsNOSIP on the lipopolysaccharide (LPS)-induced activated RAW264.7, a murine macrophage cell line. We found that endotoxin-free rCsNOSIP significantly promoted the levels of nitric oxide (NO) and reactive oxygen species (ROS) after pretreated with rCsNOSIP, while the level of SOD decreased. Furthermore, rCsNOSIP could also increase the level of lipid peroxidation MDA. Taken together, these results suggested that CsNOSIP was a key molecule which was involved in the production of nitric oxide (NO) and its reactive intermediates, and played an important role in oxidative stress during C. sinensis infection.

The role of inflammation in sarcoma

Sarcomas encompass a heterogenous group of tumors with diverse pathologically and clinically overlapping features. It is a rarely curable disease, and their management requires a multidisciplinary team approach. Chronic inflammation has emerged as one of the hallmarks of tumors including sarcomas. Classical inflammation-associated sarcomas comprise the inflammatory malignant fibrous histiocytoma and Kaposi sarcoma. The identification of specific chromosomal translocations and important intracellular signaling pathways such as Ras/Raf/MAPK, insulin-like growth factor, PI3K/AKT/mTOR, sonic hedgehog and Notch together with the increasing knowledge of angiogenesis has led to development of targeted therapies that aim to interrupt these pathways. Innovative agents like oncolytic viruses opened the way to design new therapeutic options with encouraging findings. Preclinical evidence also highlights the therapeutic potential of anti-inflammatory nutraceuticals as they can inhibit multiple pathways while being less toxic. This chapter gives an overview of actual therapeutic standards, newest evidence-based studies and exciting options for targeted therapies in sarcomas.

Oxidative stress and neurodegenerative disorders

Living cells continually generate reactive oxygen species (ROS) through the respiratory chain during energetic metabolism. ROS at low or moderate concentration can play important physiological roles. However, an excessive amount of ROS under oxidative stress would be extremely deleterious. The central nervous system (CNS) is particularly vulnerable to oxidative stress due to its high oxygen consumption, weakly antioxidative systems and the terminal-differentiation characteristic of neurons. Thus, oxidative stress elicits various neurodegenerative diseases. In addition, chemotherapy could result in severe side effects on the CNS and peripheral nervous system (PNS) of cancer patients, and a growing body of evidence demonstrates the involvement of ROS in drug-induced neurotoxicities as well. Therefore, development of antioxidants as neuroprotective drugs is a potentially beneficial strategy for clinical therapy. In this review, we summarize the source, balance maintenance and physiologic functions of ROS, oxidative stress and its toxic mechanisms underlying a number of neurodegenerative diseases, and the possible involvement of ROS in chemotherapy-induced toxicity to the CNS and PNS. We ultimately assess the value for antioxidants as neuroprotective drugs and provide our comments on the unmet needs.

redox Signaling by 8-nitro-cyclic guanosine monophosphate: nitric oxide- and reactive oxygen species-derived electrophilic messenger

SIGNIFICANCE

Emerging evidence has revealed that nitric oxide (NO)- and reactive oxygen species (ROS)-derived electrophiles formed in cells mediate signal transduction for responses to oxidative stress.

RECENT ADVANCES

The cyclic nucleotide with a nitrated guanine moiety-8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP)-first identified in 2007 as a second messenger for NO and ROS-has certain unique properties that its parental cGMP lacks. For example, it can react with particular protein Cys thiols because of its electrophilicity and can cause unique post-translational modifications of redox-sensor proteins such as Keap1 and H-Ras.

CRITICAL ISSUES

Site-specific S-guanylation of Keap1 at Cys434 induced NO- and ROS-mediated adaptive responses to oxidative stress. H-Ras Cys184 S-guanylation was recently found to be involved in activation of mitogen-activated protein kinase cascades as manifested by cellular senescence and heart failure in mouse cardiac hypertrophy models. The latest finding related to the concept of electrophile-based redox signaling is a potent regulatory function of endogenously produced hydrogen sulfide for redox signaling via 8-nitro-cGMP.

FUTURE DIRECTIONS

Electrophile modification of 8-nitro-cGMP, as a second messenger for NO and ROS, by hydrogen sulfide (i.e., electrophile sulfhydration) can most likely effect physiological regulation of cellular redox signaling. Continued investigation of the precise function of cellular hydrogen sulfide that may control electrophile-dependent redox cellular signaling, most typically via 8-nitro-cGMP formation, may provide novel insights into the molecular mechanisms of oxidative stress responses, oxidative stress-related pathology and disease control, and development of therapeutics for various diseases.

Targeting nitric oxide signaling with nNOS inhibitors as a novel strategy for the therapy and prevention of human melanoma

AIMS

Our previous studies have shown that nitric oxide (NO) plays an important role in increasing the invasion and proliferation of human melanoma cells, suggesting that targeting NO signaling may facilitate therapy and prevention. Neuronal nitric oxide synthase (nNOS) is present in melanocytes, a cell type that originates from the neural crest. The aims of this study were to determine the role of nNOS in melanoma progression and the potential antitumor effects of novel synthesized nNOS inhibitors.

RESULTS

In vitro studies demonstrated abundant expression of nNOS in melanoma compared to melanocytes, which was inducible by ultraviolet radiation and was associated with increased NO generation. nNOS was also detected in melanoma biopsies that increased with disease stage. Knockdown of nNOS in melanoma cells diminished L-arginine-induced NO production; the metastatic capacity was also reduced as well as the levels of MMP-1, Bcl-2, JunD, and APE/Ref-1. Similar inhibition of NO and invasion potential was observed utilizing novel, highly selective nNOS inhibitors. In three-dimensional human skin reconstructs, the nNOS inhibitor cpd8 effectively reversed the melanoma overgrowth stimulated by NO stress.

INNOVATION

Our work lays the foundation for development of clinical "drug-like" nNOS inhibitors as a new and promising strategy for the chemoprevention of early melanoma progression and the inhibition of secondary melanoma in high-risk individuals.

CONCLUSION

Based on our observations, we propose that nNOS in melanoma results in constitutive overproduction of NO, which stimulates proliferation and increases invasion potential, leading to subsequent development of metastases.

1α,25-Dihydroxyvitamin D3 reduces several types of UV-induced DNA damage and contributes to photoprotection

Vitamin D production requires UVB. In turn, we have shown that vitamin D compounds reduce UV-induced damage, including inflammation, sunburn, thymine dimers, the most frequent type of cyclobutane pyrimidine dimer, immunosuppression, and photocarcinogenesis. Our previous studies have shown most of the photoprotective effects by 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) occurred through the nongenomic pathway because similar protection was seen with an analog, 1α,25-dihydroxylumistrol3 (JN), which has little ability to alter gene expression and also because a nongenomic antagonist of 1,25(OH)2D3 abolished protection. In the current study, we tested whether this photoprotective effect would extend to other types of DNA damage, and whether this could be demonstrated in human ex vivo skin, as this model would be suited to pre-clinical testing of topical formulations for photoprotection. In particular, using skin explants, we examined a time course for thymine dimers (TDs), the most abundant DNA photolesion, as well as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which is a mutagenic DNA base lesion arising from UV-induced oxidative stress, and 8-nitroguanosine (8-NG). Nitric oxide products, known markers for chronic inflammation and carcinogenesis, are also induced by UV. This study showed that 1,25(OH)2D3 significantly reduced TD and 8-NG as early as 30min post UV, and 8-oxodG at 3h post UV, confirming the photoprotective effect of 1,25(OH)2D3 against DNA photoproducts in human skin explants. At least in part, the mechanism of photoprotection by 1,25(OH)2D3 is likely to be through the reduction of reactive nitrogen species and the subsequent reduction in oxidative and nitrosative damage. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

1α,25 dihydroxyvitamin D3 enhances cellular defences against UV-induced oxidative and other forms of DNA damage in skin

DNA damage induced by ultraviolet radiation is the key initiator for skin carcinogenesis since mutations may arise from the photoproducts and it also contributes to photoimmune suppression. The active vitamin D hormone, 1α,25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) reduces thymine dimers, the major photoproduct found in human skin after UV exposure, and suppresses the accumulation of nitric oxide derivatives that lead to more toxic reactive nitrogen species (RNS). We examined whether other forms of DNA damage are reduced by 1,25(OH)(2)D(3), and hypothesized that photoprotection by 1,25(OH)(2)D(3) is, in part, due to the suppression of various forms of promutagenic DNA damage, including thymine dimers, through a reduction of genotoxic RNS. Different forms of UV-induced DNA damage were investigated in irradiated skin cells treated with or without 1,25(OH)(2)D(3), or inhibitors of metabolism and inducible nitric oxide synthase. Keratinocytes were also treated with nitric oxide donors in the absence of UV light. DNA damage was assessed by comet assay incorporating site specific DNA repair endonucleases, and by immunohistochemistry using antibodies to thymine dimers or 8-oxo-7,8-dihydro-2'-deoxyguanosine, and quantified by image analysis. Strand breaks in T4 endonuclease V, endonuclease IV and human 8-oxoguanine DNA glycosylase digests increased more than 2-fold in UV irradiated human keratinocytes, and were reduced by 1,25(OH)(2)D(3) treatment after UV exposure, and also by low temperature, sodium azide and an inhibitor of inducible nitric oxide synthase. Conversely, nitric oxide donors induced all three types of DNA damage in the absence of UV. We present data to show that 1,25(OH)(2)D(3) protects skin cells from at least three forms of UV-induced DNA damage, and provide further evidence to support the proposal that a reduction in RNS by 1,25(OH)(2)D(3) is a likely mechanism for its photoprotective effect against oxidative and nitrative DNA damage, as well as cyclobutane pyrimidine dimers.

Formation, signaling functions, and metabolisms of nitrated cyclic nucleotide

8-Nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) is a unique derivative of guanosine 3',5'-cyclic monophosphate (cGMP) formed in mammalian and plant cells in response to production of nitric oxide and reactive oxygen species. 8-Nitro-cGMP possesses signaling activity inherited from parental cGMP, including induction of vasorelaxation through activation of cGMP-dependent protein kinase. On the other hand, 8-nitro-cGMP mediates cellular signaling that is not observed for native cGMP, e.g., it behaves as an electrophile and reacts with protein sulfhydryls, which results in cGMP adduction to protein sulfhydryls (protein S-guanylation). Several proteins have been identified as targets for endogenous protein S-guanylation, including Kelch-like ECH-associated protein 1 (Keap1), H-Ras, and mitochondrial heat shock proteins. 8-Nitro-cGMP signaling via protein S-guanylation of those proteins may have evolved to convey adaptive cellular stress responses. 8-Nitro-cGMP may not undergo conventional cGMP metabolism because of its resistance to phosphodiesterases. Hydrogen sulfide has recently been identified as a potent regulator for metabolisms of electrophiles including 8-nitro-cGMP, through sulfhydration of electrophiles, e.g., leading to the formation of 8-SH-cGMP. Better understanding of the molecular basis for the formation, signaling functions, and metabolisms of 8-nitro-cGMP would be useful for the development of new diagnostic approaches and treatment of diseases related to oxidative stress and redox metabolisms.

Teaching the basics of redox biology to medical and graduate students: Oxidants, antioxidants and disease mechanisms

This article provides a succinct but limited overview of the protective and deleterious effects of reactive oxygen and nitrogen species in a clinical context. Reactive oxygen species include superoxide, hydrogen peroxide, single oxygen and lipid peroxides. Reactive nitrogen species include species derived from nitric oxide. This review gives a brief overview of the reaction chemistry of these species, the role of various enzymes involved in the generation and detoxification of these species in disease mechanisms and drug toxicity and the protective role of dietary antioxidants. I hope that the graphical review will be helpful for teaching both the first year medical and graduate students in the U.S. and abroad the fundamentals of reactive oxygen and nitrogen species in redox biology and clinical medicine.

Chemoprevention of gastrointestinal cancer: the reality and the dream

Despite substantial progress in screening, early diagnosis, and the development of noninvasive technology, gastrointestinal (GI) cancer remains a major cause of cancer-associated mortality. Chemoprevention is thought to be a realistic approach for reducing the global burden of GI cancer, and efforts have been made to search for chemopreventive agents that suppress acid reflux, GI inflammation and the eradication of Helicobacter pylori. Thus, proton pump inhibitors, statins, monoclonal antibodies targeting tumor necrosis factor-alpha, and nonsteroidal anti-inflammatory agents have been investigated for their potential to prevent GI cancer. Besides the development of these synthetic agents, a wide variety of the natural products present in a plant-based diet, which are commonly called phytoceuticals, have also sparked hope for the chemoprevention of GI cancer. To perform successful searches of chemopreventive agents for GI cancer, it is of the utmost importance to understand the factors contributing to GI carcinogenesis. Emerging evidence has highlighted the role of chronic inflammation in inducing genomic instability and telomere shortening and affecting polyamine metabolism and DNA repair, which may help in the search for new chemopreventive agents for GI cancer.

Vitamin D and death by sunshine

Exposure to sunlight is the major cause of skin cancer. Ultraviolet radiation (UV) from the sun causes damage to DNA by direct absorption and can cause skin cell death. UV also causes production of reactive oxygen species that may interact with DNA to indirectly cause oxidative DNA damage. UV increases accumulation of p53 in skin cells, which upregulates repair genes but promotes death of irreparably damaged cells. A benefit of sunlight is vitamin D, which is formed following exposure of 7-dehydrocholesterol in skin cells to UV. The relatively inert vitamin D is metabolized to various biologically active compounds, including 1,25-dihydroxyvitamin D3. Therapeutic use of vitamin D compounds has proven beneficial in several cancer types, but more recently these compounds have been shown to prevent UV-induced cell death and DNA damage in human skin cells. Here, we discuss the effects of vitamin D compounds in skin cells that have been exposed to UV. Specifically, we examine the various signaling pathways involved in the vitamin D-induced protection of skin cells from UV.

Novel vitamin D compounds and skin cancer prevention

As skin cancer is one of the most costly health issues in many countries, particularly in Australia, the possibility that vitamin D compounds might contribute to prevention of this disease is becoming increasingly more attractive to researchers and health communities. In this article, important epidemiologic, mechanistic and experimental data supporting the chemopreventive potential of several vitamin D-related compounds are explored. Evidence of photoprotection by the active hormone, 1α,25dihydroxyvitamin D3, as well as a derivative of an over-irradiation product, lumisterol, a fluorinated analog and bufalin, a potential vitamin D-like compound, are provided. The aim of this article is to understand how vitamin D compounds contribute to UV adaptation and potentially, skin cancer prevention.

Whole-genome reconstruction and mutational signatures in gastric cancer

Background

Gastric cancer is the second highest cause of global cancer mortality. To explore the complete repertoire of somatic alterations in gastric cancer, we combined massively parallel short read and DNA paired-end tag sequencing to present the first whole-genome analysis of two gastric adenocarcinomas, one with chromosomal instability and the other with microsatellite instability.

Results

Integrative analysis and de novo assemblies revealed the architecture of a wild-type KRAS amplification, a common driver event in gastric cancer. We discovered three distinct mutational signatures in gastric cancer - against a genome-wide backdrop of oxidative and microsatellite instability-related mutational signatures, we identified the first exome-specific mutational signature. Further characterization of the impact of these signatures by combining sequencing data from 40 complete gastric cancer exomes and targeted screening of an additional 94 independent gastric tumors uncovered ACVR2A, RPL22 and LMAN1 as recurrently mutated genes in microsatellite instability-positive gastric cancer and PAPPA as a recurrently mutated gene in TP53 wild-type gastric cancer.

Conclusions

These results highlight how whole-genome cancer sequencing can uncover information relevant to tissue-specific carcinogenesis that would otherwise be missed from exome-sequencing data.