The chemistry and biology of nitroxide compounds

Synthesis of a novel adamantyl nitroxide derivative with potent anti-hepatoma activity in vitro and in vivo

In this study, a novel adamantyl nitroxide derivative was synthesized and its antitumor activities in vitro and in vivo were investigated. The adamantyl nitroxide derivative 4 displayed a potent anticancer activity against all the tested human hepatoma cells, especially with IC50 of 68.1 μM in Bel-7404 cells, compared to the positive control 5-FU (IC50=607.7 μM). The significant inhibition of cell growth was also observed in xenograft mouse model, with low toxicity. Compound 4 suppressed the cell migration and invasion, induced the G2/M phase arrest. Further mechanistic studies revealed that compound 4 induced cell death, which was accompanied with damaging mitochondria, increasing the generation of intracellular reactive oxygen species, cleavages of caspase-9 and caspase-3, as well as activations of Bax and Bcl-2. These results confirmed that adamantyl nitroxide derivative exhibited selective antitumor activities via mitochondrial apoptosis pathway in Bel-7404 cells, and would be a potential anticancer agent for liver cancer.

Nitroxide radicals as research tools: Elucidating the kinetics and mechanisms of catalase-like and "suicide inactivation" of metmyoglobin

BACKGROUND

Metmyoglobin (MbFe(III)) reaction with H(2)O(2) has been a subject of study over many years. H(2)O(2) alone promotes heme destruction frequently denoted "suicide inactivation," yet the mechanism underlying H(2)O(2) dismutation associated with MbFe(III) inactivation remains obscure.

METHODS

MbFe(III) reaction with excess H(2)O(2) in the absence and presence of the nitroxide was studied at pH 5.3-8.1 and 25°C by direct determination of reaction rate constants using rapid-mixing stopped-flow technique, by following H(2)O(2) depletion, O(2) evolution, spectral changes of the heme protein, and the fate of the nitroxide by EPR spectroscopy.

RESULTS

The rates of both H(2)O(2) dismutation and heme inactivation processes depend on [MbFe(III)], [H(2)O(2)] and pH. Yet the inactivation stoichiometry is independent of these variables and each MbFe(III) molecule catalyzes the dismutation of 50±10 H(2)O(2) molecules until it is inactivated. The nitroxide catalytically enhances the catalase-like activity of MbFe(III) while protecting the heme against inactivation. The rate-determining step in the absence and presence of the nitroxide is the reduction of MbFe(IV)O by H(2)O(2) and by nitroxide, respectively.

CONCLUSIONS

The nitroxide effects on H(2)O(2) dismutation catalyzed by MbFe(III) demonstrate that MbFe(IV)O reduction by H(2)O(2) is the rate-determining step of this process. The proposed mechanism, which adequately fits the pro-catalytic and protective effects of the nitroxide, implies the intermediacy of a compound I-H(2)O(2) adduct, which decomposes to a MbFe(IV)O and an inactivated heme at a ratio of 25:1.

GENERAL SIGNIFICANCE

The effects of nitroxides are instrumental in elucidating the mechanism underlying the catalysis and inactivation routes of heme proteins.

Expeditious dissolution dynamic nuclear polarization without glassing agents

The hyperpolarization of metabolic substrates at low temperature using dynamic nuclear polarization (DNP), followed by rapid dissolution and injection into an MRSI or NMR system, allows in vitro or in vivo observation and tracking of biochemical reactions and metabolites in real time. This article describes an elegant approach to sample preparation which is broadly applicable for the rapid polarization of aqueous small-molecule substrate solutions and obviates the need for glassing agents. We demonstrate its utility for solutions of sodium acetate, pyruvate and butyrate. The polarization behavior of substrates prepared using rapid freezing without glassing agents enabled a 1.5-3-fold time savings in polarization buildup, whilst removing the need for toxic glassing agents used as standard for dissolution DNP. The achievable polarization with fully aqueous substrate solutions was equal to that observed using standard approaches and glassing agents. Copyright © 2016 John Wiley & Sons, Ltd.

Dynamic nuclear polarization-magnetic resonance imaging at low ESR irradiation frequency for ascorbyl free radicals

Highly water-soluble ubiquinone-0 (CoQ₀) reacts with ascorbate monoanion (Asc) to mediate the production of ascorbyl free radicals (AFR). Using aqueous reaction mixture of CoQ₀ and Asc, we obtained positively enhanced dynamic nuclear polarization (DNP)-magnetic resonance (MR) images of the AFR at low frequency (ranging from 515 to 530 MHz) of electron spin resonance (ESR) irradiation. The shape of the determined DNP spectrum was similar to ESR absorption spectra with doublet spectral peaks. The relative locational relationship of spectral peaks in the DNP spectra between the AFR (520 and 525 MHz), ¹⁴N-labeled carbamoyl-PROXYL (¹⁴N-CmP) (526.5 MHz), and Oxo63 (522 MHz) was different from that in the X-band ESR spectra, but were similar to that in the 300-MHz ESR spectra. The ratio of DNP enhancement to radical concentration for the AFR was higher than those for ¹⁴N-CmP, Oxo63, and flavin semiquinone radicals. The spectroscopic DNP properties observed for the AFR were essentially the same as those for AFR mediated by pyrroloquinoline quinone. Moreover, we made a success of in vivo DNP-MR imaging of the CoQ₀-mediated AFR which was administered by the subcutaneous and oral injections as an imaging probe.

Selective Imaging of Malignant Ascites in a Mouse Model of Peritoneal Metastasis Using in Vivo Dynamic Nuclear Polarization-Magnetic Resonance Imaging

The presence of malignant ascites in advanced cancer patients is associated with both a poor prognosis and quality of life with a risk of abdominal infection and sepsis. Contemporary noninvasive visualization methods such as ultrasound, computed tomography, and magnetic resonance imaging (MRI) often struggle to differentiate malignant ascites from surrounding tissues. This study aimed to determine the utility of selective H2O imaging in the abdominal cavity with a free radical probe and deuterium oxide (D2O) contrast agent using in vivo dynamic nuclear polarization-MRI (DNP-MRI). Phantom imaging experiments established a linear relationship between H2O volume and image intensity using in vivo DNP-MRI. Similar results were obtained when the radical-D2O probe was used to determine selective and spatial information on H2O in vivo, modeled by the injection of saline into the abdominal cavity of mice. To demonstrate the utility of this method for disease, malignant ascites in peritoneal metastasis animal model was selected as one of the typical examples. In vivo DNP-MRI of peritoneal metastasis animal model was performed 7-21 days after intraperitoneal injection of luciferase, stably expressing the human pancreatic carcinoma (SUIT-2). The image intensity with increasing malignant ascites was significantly increased at days 7, 16, and 21. This increase corresponded to in vivo tumor progression, as measured by bioluminescent imaging. These results suggest that H2O signal enhancement in DNP-MRI using radical-D2O contrast is positively associated with the progression of dissemination and could be a useful biomarker for malignant ascites with cancer metastasis.

Investigating the DMPO-formate spin trapping method for the study of paper iron gall ink corrosion

Reactive oxygen species evidenced in acidic iron gall inks are not hydroxyl radicals and are not linked to paper degradation.

Oxidative stress in oral diseases

Oxidative species, including reactive oxygen species (ROS), are components of normal cellular metabolism and are required for intracellular processes as varied as proliferation, signal transduction, and apoptosis. In the situation of chronic oxidative stress, however, ROS contribute to various pathophysiologies and are involved in multiple stages of carcinogenesis. In head and neck cancers specifically, many common risk factors contribute to carcinogenesis via ROS-based mechanisms, including tobacco, areca quid, alcohol, and viruses. Given their widespread influence on the process of carcinogenesis, ROS and their related pathways are attractive targets for intervention. The effects of radiation therapy, a central component of treatment for nearly all head and neck cancers, can also be altered via interfering with oxidative pathways. These pathways are also relevant to the development of many benign oral diseases. In this review, we outline how ROS contribute to pathophysiology with a focus toward head and neck cancers and benign oral diseases, describing potential targets and pathways for intervention that exploit the role of oxidative species in these pathologic processes.

Invariom approach to electron density studies of open-shell compounds: the case of an organic nitroxide radical

The study reports the successful modeling of electron density with invarioms for an open-shell compound, an organic nitroxide radical.

Tempol, a Membrane-Permeable Radical Scavenger, Exhibits Anti-Inflammatory and Cardioprotective Effects in the Cerulein-Induced Pancreatitis Rat Model

To date, it remains unclear whether mild form of acute pancreatitis (AP) may cause myocardial damage which may be asymptomatic for a long time. Pathogenesis of AP-related cardiac injury may be attributed in part to ROS/RNS overproduction. The aim of the present study was to evaluate the oxidative stress changes in both the pancreas and the heart and to estimate the protective effects of 1-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine (tempol) at the early phase of AP. Cerulein-induced AP led to the development of acute edematous pancreatitis with a significant decrease in the level of sulfhydryl (–SH) groups (oxidation marker) both in heart and in pancreatic tissues as well as a substantial increase in plasma creatine kinase isoenzyme (CK-MB) activity (marker of the heart muscle lesion) which confirmed the role of oxidative stress in the pathogenesis of cardiac damage. The tempol treatment significantly reduced the intensity of inflammation and oxidative damage and decreased the morphological evidence of pancreas injury at early AP stages. Moreover, it markedly attenuated AP-induced cardiac damage revealed by normalization of the –SH group levels and CK-MB activity. On the basis of these studies, it is possible to conclude that tempol has a profound protective effect against cardiac and pancreatic damage induced by AP.

Nitroxides protect against peroxynitrite-induced nitration and oxidation

Nitroxides are promising compounds for prevention of undesired protein modifications. The aim of this study was to compare the efficiency of 11 nitroxides, derivatives of 2,2,6,6-tetramethylpiperidine-1-oxide (TEMPO) and 2,2,5,5-tetramethylpirrolidine-1-oxyl (PROXYL) in prevention of nitration and oxidation of model compounds and human serum albumin (HSA). Most nitroxides were very efficient in preventing loss of fluorescein fluorescence induced by peroxynitrite (PN) (IC50 in the nanomolar range) and preventing HSA nitration. The loss of fluorescein fluorescence was demonstrated to be due to nitration. Nitroxides were more effective in prevention nitration than oxidation reactions. They showed a concentration window for preventing dihydrorhodamine (DHR) 123 oxidation but exerted a prooxidant effect at both high and low concentrations. No prooxidant effect of nitroxides was seen in prevention of DHR123 oxidation induced by SIN-1. In all essays hydrophobic nitroxides (especially 4-nonylamido-TEMPO and 3-carbamolyl-dehydroPROXYL) showed the lowest efficiency. An exception was the prevention of thiol group oxidation by PN and SIN-1 where hydrophobic nitroxides were the most effective, apparently due to binding to the protein. Nitroxides showed low toxicity to MCF-7 cells. Most nitroxides, except for the most hydrophobic ones, protected cells from the cytotoxic action of SIN-1 and SIN-1-induced protein nitration. These results point to potential usefulness of nitroxides for prevention of PN-induced oxidation and, especially, nitration.

Redox imaging of skeletal muscle using in vivo DNP-MRI and its application to an animal model of local inflammation

Disorders of skeletal muscle are often associated with inflammation and alterations in redox status. A non-invasive technique that could localize and evaluate the severity of skeletal muscle inflammation based on its redox environment would be useful for disease identification and monitoring, and for the development of treatments; however, no such technique currently exists. We describe a method for redox imaging of skeletal muscle using dynamic nuclear polarization magnetic resonance imaging (DNP-MRI), and apply this method to an animal model of local inflammation. Female C57/BL6 mice received injections of 0.5% bupivacaine into their gastrocnemius muscles. Plasma biomarkers, myeloperoxidase activity, and histological sections were assessed at 4 and 24h after bupivacaine injection to measure the inflammatory response. In vivo DNP-MRI was performed with the nitroxyl radicals carbamoyl-PROXYL (cell permeable) and carboxy-PROXYL (cell impermeable) as molecular imaging probes at 4 and 24h after bupivacaine administration. The images obtained after carbamoyl-PROXYL administration were confirmed with the results of L-band EPR spectroscopy. The plasma biomarkers, myeloperoxidase activity, and histological findings indicated that bupivacaine injection caused acute muscle damage and inflammation. DNP-MRI images of mice treated with carbamoyl-PROXYL or carboxy-PROXYL at 4 and 24h after bupivacaine injection showed similar increases in image intensity and decay rate was significantly increased at 24h. In addition, reduction rates in individual mice at 4h and 24h showed faster trends with bupivacaine injection than in their contralateral sides by image-based analysis. These findings indicate that in vivo DNP-MRI with nitroxyl radicals can non-invasively detect changes in the focal redox status of muscle resulting from locally-induced inflammation.

COX inhibitors: a patent review (2011 - 2014)

INTRODUCTION

The COX enzymes play a central role in the biosynthetic pathway of important biological mediators called prostanoids. Differences in regulation of gene expression, stability of transcripts and proteins determine the different biological functions of COX-1 and COX-2. While the COX-1 gene has been considered to be a 'housekeeping' gene expressed in many tissues and cells, COX-2 gene is upregulated during inflammation, hypoxia and in many cancers.

AREAS COVERED

The first part of this review provides a survey of the development of both modified traditional NSAIDs (tNSAIDs) and COX inhibitors (coxibs) with reduced side effects for the treatment of inflammation and cancer. The second part deals with patents reporting several dual inhibitors characterized by the conjugation of a COX-inhibitor scaffold to a molecule able to modulate a different target. Finally, two patents on novel COX inhibitor scaffolds are reported.

EXPERT OPINION

The most interesting branch of research concerns the conjugation of a COX-inhibitor scaffold to a molecule able to modulate a different target, in order to either enhance anti-inflammatory activity or to act as a dual inhibitor. Among the described compounds, selenium-containing coxibs inhibiting COX-2 and Akt, in addition to the multi-target biphenyl derivatives as dual inhibitors of COX and fatty acid amide hydrolase, are the most promising ones.

Cyclic nitroxide radicals attenuate inflammation and Hyper-responsiveness in a mouse model of allergic asthma

The effects of stable cyclic nitroxide radicals have been extensively investigated both in vivo and in vitro demonstrating anti-inflammatory, radioprotective, anti-mutagenic, age-retardant, hypotensive, anti-cancer and anti-teratogenic activities. Yet, these stable radicals have not been evaluated in asthma and other airway inflammatory disorders. The present study investigated the effect of 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl (TPL) and 3-carbamoyl-proxyl (3-CP) in a mouse model of ovalbumin (OVA)-induced allergic asthma. Both 3-CP and TPL were non-toxic when administered either orally (1% w/w nitroxide-containing chow) or via intraperitoneal (IP) injection (∼300 mg/kg). Feeding the mice orally demonstrated that 3-CP was more effective than TPL in reducing inflammatory cell recruitment into the airway and in suppressing airway hyper-responsiveness (AHR) in OVA-challenged mice. To characterize the optimal time-window of intervention and mode of drug administration, 3-CP was given orally during allergen sensitization, during allergen challenge or during both sensitization and challenge stages, and via IP injection or intranasal instillation for 3 days during the challenge period. 3-CP given via all modes of delivery markedly inhibited OVA-induced airway inflammation, expression of cytokines, AHR and protein nitration of the lung tissue. Oral administration during the entire experiment was the most efficient delivery of 3-CP and was more effective than dexamethasone a potent corticosteroid used for asthma treatment. Under a similar administration regimen (IP injection before the OVA challenge), the effect of 3-CP was similar to that of dexamethasone and even greater on AHR and protein nitration. The protective effect of the nitroxides, which preferentially react with free radicals, in suppressing the increase of main asthmatic inflammatory markers substantiate the key role played by reactive oxygen and nitrogen species in the molecular mechanism of asthma. The present results demonstrate the therapeutic potential of nitroxides for the treatment of asthma.

Effects of the antioxidants Trolox, Tiron and Tempol on neutrophil extracellular trap formation

Neutrophils can entrap and kill pathogens by releasing of neutrophil extracellular traps (NETs), in addition to their routine functions such as phagocytosis and degranulation. NETs consist of a DNA backbone supplemented by multiple bactericidal proteins from the nucleus, the cytoplasm and the granules. Neutrophils release NETs after their activation by a number of physiological and pharmacological stimuli. In addition to the antimicrobial function, NETs are involved in the pathogenesis of various autoimmune and inflammatory diseases. Since NET formation predominantly depends on the generation of reactive oxygen species (ROS), all substances that are capable of scavenging ROS or inhibiting the enzymes responsible for their synthesis should prevent ROS-associated NET release. The aim of this study was to test substances with an antioxidant activity, such as Trolox, Tiron, and Tempol, for their capacity to inhibit NET formation by primary human neutrophils in vitro. We revealed for the first time an inhibitory effect of Trolox on ROS-dependent NET release. We also established a suppressive effect of Tempol on NET formation that manifested itself in a wide range of concentrations. In this study, no inhibitory influence of Tiron on NET release was revealed. All tested substances exerted a significant dose-dependent antioxidative effect on ROS generation induced by phorbol 12-myristate 13-acetate (PMA). We suggest that the antioxidants Trolox and Tempol should be recommended for treating autoimmune and inflammatory diseases that implicate ROS-dependent NET release.

Radioprotective agents for radiation therapy: future trends

Only two radioprotective compounds, amifostine and palifermin, currently have the US FDA approval for use in radiation therapy. However, several agents have been reported that show therapeutic promise. Many of these agents are free radical scavengers/antioxidants. Superoxide dismutase and superoxide dismutase mimetics, nitroxides and dietary antioxidants are all being investigated. Recently, alternative strategies of drug development have been evolving, which focus on targeting the series of cellular insult recognition/repair responses initiated following radiation. These agents, which include cytokines/growth factors, angiotensin-converting enzyme inhibitors and apoptotic modulators, show promise of having significant impact on the mitigation of radiation injury. Herein, we review current literature on the development of radioprotectors with emphasis on compounds with proven or potential usefulness in radiation therapy.

Nanomedicine in the ROS-mediated pathophysiology: Applications and clinical advances

Reactive oxygen species (ROS) are important in regulating normal cell physiological functions, but when produced in excess lead to the augmented pathogenesis of various diseases. Among these, ischemia reperfusion injury, Alzheimer's disease and rheumatoid arthritis are particularly important. Since ROS can be counteracted by a variety of antioxidants, natural and synthetic antioxidants have been developed. However, due to the ubiquitous production of ROS in living systems, poor in vivo efficiency of these agents and lack of target specificity, the current clinical modalities to treat oxidative stress damage are limited. Advances in the developing field of nanomedicine have yielded nanoparticles that can prolong antioxidant activity, and target specificity of these agents. This article reviews recent advances in antioxidant nanoparticles and their applications to manage oxidative stress-mediated diseases.

FROM THE CLINICAL EDITOR

Production of reactive oxygen species (ROS) is a purely physiological process in many disease conditions. However, excessive and uncontrolled production will lead to oxidative stress and further tissue damage. Advances in nanomedicine have provided many novel strategies to try to combat and counteract ROS. In this review article, the authors comprehensively highlighted the current status and future developments in using nanotechnology for providing novel therapeutic options in this field.

Synthesis of a Novel Nitronyl Nitroxide Radical and Determination of its Protective Effects Against Infrasound-Induced Injury

Infrasound causes functional disorders and structural injury to the central nervous system. However, few anti-infrasound drugs exist, and they are inefficient. Nitronyl nitroxide radicals have been reported to be good antioxidants that act as superoxide dismutase mimics and directly react with reactive oxygen species, such as ·OH, H2O2, and O 2 (∙) -. Our previous research showed that the nitronyl nitroxide radical L-NNNBP has good protective effects against β-amyloid deposition and memory deficits in an AD rat model of APP/PS1. The objective of the present study was to find a new group of anti-infrasound drugs and determine the underlying pharmacological actions of nitronyl nitroxide radicals against infrasound-induced neuronal impairment in vivo. We synthesized a new stable nitronyl nitroxide radical, NRbt, and characterized its crystal structure. The results of the anti-oxidative damage effects of NRbt and the positive control drug tempol showed that they could significantly increase the SOD activity, CAT activity and GSH level and decrease the MDA level in rat hippocampi compared with infrasound exposure without pretreatment. Moreover, the ability of NRbt to regulate the activity or level of these biochemical markers was better than that of tempol. Our results showed that both NRbt and tempol significantly protected against the learning and memory impairments induced by infrasound exposure in a Morris water maze, but there were no significant differences in the path length or escape latency between the rats in the tempol group and the three NRbt groups (P > 0.05). In addition, the infrasound-induced neuronal apoptosis in rat hippocampi was significantly suppressed by NRbt and tempol. The results demonstrated that compared with the infrasound exposure group, the expression of Bcl-2 was up-regulated and the expressions of Bax and caspase-3 were down-regulated in rats pretreated with NRbt (40 mg/kg) or tempol (40 mg/kg). These results showed that the newly synthesized nitronyl nitroxide radical, NRbt, may be an effective anti-infrasound drug because of its capacity to inhibit the oxidative damage of free radicals induced by infrasound exposure.

Experimental demonstration of pH-dependent electrostatic catalysis of radical reactions

Fluorescence spectroscopy demonstrated pH-dependent electrostatic effects on the kinetics and thermodynamics of hydrogen atom transfer between 1-hydroxy-2,2,6,6-tetramethyl-4-piperidinecarboxylic acid and {2,2,6,6-tetramethyl-4-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-1-piperidinyl}oxidanyl radical in dichloromethane.

Time-dependent fluorescence spectroscopy has been used to demonstrate significant pH-dependent electrostatic effects on the kinetics and thermodynamics of hydrogen atom transfer between 1-hydroxy-2,2,6,6-tetramethyl-4-piperidinecarboxylic acid (4-CT-H) and the profluorescent nitroxide {2,2,6,6-tetramethyl-4-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-1-piperidinyl}oxidanyl radical (PFN) in dichloromethane. This pH switching does not occur when 4-CT-H is replaced with a structurally analogous hydroxylamine that lacks an acid-base group, or when the polarity of the solvent is increased. These findings validate our recent theoretical predictions that electrostatic stabilisation of delocalised radicals is of functional significance in low polarity environments.

Development of an oral nanotherapeutics using redox nanoparticles for treatment of colitis-associated colon cancer

Oral chemotherapy is the preferred treatment for colon cancer. However, this strategy faces many challenges, including instability in the gastrointestinal (GI) tract, insufficient bioavailability, low tumor targeting, and severe adverse effects. In this study, we designed a novel redox nanoparticle (RNP(O)) that is an ideal oral therapeutics for colitis-associated colon cancer treatment. RNP(O) possesses nitroxide radicals in the core, which act as reactive oxygen species (ROS) scavengers. Orally administered RNP(O) highly accumulated in colonic mucosa, and specifically internalized in cancer tissues, but less in normal tissues. Despite of long-term oral administration of RNP(O), no noticeable toxicities were observed in major organs of mice. Because RNP(O) effectively scavenged ROS, it significantly suppressed tumor growth after accumulation at tumor sites. Combination of RNP(O) with the conventional chemotherapy, irinotecan, led to remarkably improved therapeutic efficacy and effectively suppressed its adverse effects on GI tract. Therefore, RNP(O) is promising oral nanotherapeutics for cancer therapies.

The nitroxide radical TEMPOL prevents obesity, hyperlipidaemia, elevation of inflammatory cytokines, and modulates atherosclerotic plaque composition in apoE-/- mice

OBJECTIVE

The nitroxide compound TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl radical) has been shown to prevent obesity-induced changes in adipokines in cell and animal systems. In this study we investigated whether supplementation with TEMPOL inhibits inflammation and atherosclerosis in apoE-/- mice fed a high fat diet (HFD).

METHODS

ApoE-/- mice were fed for 12 weeks on standard chow diet or a high-fat diet. Half the mice were supplemented with 10 mg/g TEMPOL in their food. Plasma samples were analysed for triglycerides, cholesterol, low- and high-density lipoprotein cholesterol, inflammatory cytokines and markers (interleukin-6, IL-6; monocyte-chemotactic protein, MCP-1; myeloperoxidase, MPO; serum amyloid A, SAA; adiponectin; leptin). Plaques in the aortic sinus were analysed for area, and content of collagen, lipid, macrophages and smooth muscle cells.

RESULTS

High fat feeding resulted in marked increases in body mass and plasma lipid levels. Dietary TEMPOL decreased both parameters. In the high-fat-fed mice significant elevations in plasma lipid levels and the inflammatory markers IL-6, MCP-1, MPO, SAA were detected, along with an increase in leptin and a decrease in adiponectin. TEMPOL supplementation reversed these effects. When compared to HFD-fed mice, TEMPOL supplementation increased plaque collagen content, decreased lipid content and increased macrophage numbers.

CONCLUSIONS

These data indicate that in a well-established model of obesity-associated hyperlipidaemia and atherosclerosis, TEMPOL had a significant impact on body mass, atherosclerosis, hyperlipidaemia and inflammation. TEMPOL may therefore be of value in suppressing obesity, metabolic disorders and increasing atherosclerotic plaque stability.

Core-shell hybrid upconversion nanoparticles carrying stable nitroxide radicals as potential multifunctional nanoprobes for upconversion luminescence and magnetic resonance dual-modality imaging

Nitroxide radicals, such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives, have recently been used as contrast agents for magnetic resonance imaging (MRI) and electron paramagnetic resonance imaging (EPRI). However, their rapid one-electron bioreduction to diamagnetic N-hydroxy species when administered intravenously has limited their use in in vivo applications. In this article, a new approach of silica coating for carrying stable radicals was proposed. A 4-carboxyl-TEMPO nitroxide radical was covalently linked with 3-aminopropyl-trimethoxysilane to produce a silanizing TEMPO radical. Utilizing a facile reaction based on the copolymerization of silanizing TEMPO radicals with tetraethyl orthosilicate in reverse microemulsion, a TEMPO radicals doped SiO2 nanostructure was synthesized and coated on the surface of NaYF4:Yb,Er/NaYF4 upconversion nanoparticles (UCNPs) to generate a novel multifunctional nanoprobe, PEGylated UCNP@TEMPO@SiO2 for upconversion luminescence (UCL) and magnetic resonance dual-modality imaging. The electron spin resonance (ESR) signals generated by the TEMPO@SiO2 show an enhanced reduction resistance property for a period of time of up to 1 h, even in the presence of 5 mM ascorbic acid. The longitudinal relaxivity of PEGylated UCNPs@TEMPO@SiO2 nanocomposites is about 10 times stronger than that for free TEMPO radicals. The core-shell NaYF4:Yb,Er/NaYF4 UCNPs synthesized by this modified user-friendly one-pot solvothermal strategy show a significant enhancement of UCL emission of up to 60 times more than the core NaYF4:Yb,Er. Furthermore, the PEGylated UCNP@TEMPO@SiO2 nanocomposites were further used as multifunctional nanoprobes to explore their performance in the UCL imaging of living cells and T1-weighted MRI in vitro and in vivo.

The redox-active nanomaterial toolbox for cancer therapy

Advances in nanomaterials science contributed in recent years to develop new devices and systems in the micro and nanoscale for improving the diagnosis and treatment of cancer. Substantial evidences associate cancer cells and tumor microenvironment with reactive oxygen species (ROS), while conventional cancer treatments and particularly radiotherapy, are often mediated by ROS increase. However, the poor selectivity and the toxicity of these therapies encourage researchers to focus efforts in order to enhance delivery and to decrease side effects. Thus, the development of redox-active nanomaterials is an interesting approach to improve selectivity and outcome of cancer treatments. Herein, we describe an overview of recent advances in redox nanomaterials in the context of current and emerging strategies for cancer therapy based on ROS modulation.

The antioxidant mechanism of nitroxide TEMPO: scavenging with glutathionyl radicals

A rhodamine-nitroxide probe (R-NO˙) was introduced to probe glutathionyl radicals (GS˙) with high sensitivity and selectivity.

Liponitroxides: EPR study and their efficacy as antioxidants in lipid membranes

Fighting lipid peroxidation on its own ground: the antioxidant activity of new synthesized lipid-functionalized nitroxides is maximized in the PUFA region and correlates with the nitroxide location within the lipid bilayer as found by EPR spectroscopy.

Development of silica-containing redox nanoparticles for medical applications

Silica-containing redox nanoparticles act as adsorbents for peritoneal dialysis and orally administrable drug carriers for the treatment of gastrointestinal inflammation.

Nitroxide-coated silver nanoparticles: synthesis, surface physicochemistry and antibacterial activity

We report the synthesis of well-defined silver nanoparticles with high antibacterial activity. Nitroxides on their surface may be oxidized under the influence of ROS to oxoammonium ions which are capable of interacting with bacterial membrane.

Synthesis and characterization of silica nanoparticles functionalized with multiple TEMPO groups and investigation on their oxidation activity

A series of novel silica nanoparticles functionalized with multiple TEMPO groups were synthesized using a novel, efficient and versatile protocol, and the catalytic activity of SN-g-(PGMA-TEMPO) was evaluated by the oxidation of benzylic alcohols.

Antihypertensive effect of mitochondria-targeted proxyl nitroxides

Superoxide (O2-•) has been implicated in the pathogenesis of many human diseases including hypertension. Mitochondria-targeted superoxide scavenger mitoTEMPO reduces blood pressure; however, the structure–functional relationships in antihypertensive effect of mitochondria-targeted nitroxides remain unclear. The nitroxides are known to undergo bioreduction into hydroxylamine derivatives which reacts with O2-• with much lower rate. The nitroxides of pyrrolidine series (proxyls) are much more resistant to bioreduction compared to TEMPOL derivatives suggesting that mitochondria-targeted proxyls can be effective antioxidants with antihypertensive activity. In this work we have designed and studied two new pyrrolidine mitochondria targeted nitroxides: 3-[2-(triphenyphosphonio)acetamido]- and 3-[2-(triphenyphosphonio) acetamidomethyl]-2,2,5,5-tetramethylpyrrolidine-1-oxyl (mCP2) and (mCP1). These new mitochondria targeted nitroxides have 3- to 7-fold lower rate constants of the reaction with O2-• compared with mitoTEMPO; however, the cellular bioreduction of mCP1 and mCP2 was 3- and 2-fold slower. As a consequence incubation with cells afforded much higher intracellular concentration of mCP1 and mCP2 nitroxides compared to mitoTEMPO nitroxide. This has compensated for the difference in the rate of O2-• scavenging and all nitroxides similarly protected mitochondrial respiration in H₂O₂ treated endothelial cells. Treatment of hypertensive mice with mCP1 and mCP2 (1.4 mg/kg/day) after onset of angiotensin II-induced hypertension significantly reduced blood pressure to 133±5 mmHg and 129±6 mmHg compared to 163±5 mmHg in mice infused with angiotensin II alone. mCP1 and mCP2 reduced vascular O2-• and prevented decrease of endothelial nitric oxide production. These data indicate that resistance to bioreduction play significant role in antioxidant activity of nitroxides. Studies of nitroxide analogs such as mCP1 and mCP2 may help in optimization of chemical structure of mitochondria-targeted nitroxides for improved efficacy and pharmacokinetics of these drugs in treatment of hypertension and many other conditions including atherosclerosis, diabetes and degenerative neurological disorders in which mitochondrial oxidative stress seems to play a role.

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Nitroxides bioreduction into hydroxylamine can reduce their antioxidant properties.

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Mitochondria-targeted proxyls are more resistant to bioreduction vs mitoTEMPO.

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Intracellular concentration of mCP1 and mCP2 nitroxides is higher vs mitoTEMPO.

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mCP1 and mCP2 diminished vascular superoxide and reduced hypertension.

Mitochondria-targeted ROS scavenger improves post-ischemic recovery of cardiac function and attenuates mitochondrial abnormalities in aged rats

Mitochondria-generated reactive oxygen species (ROS) play a crucial role in the pathogenesis of aging and age-associated diseases. In this study, we evaluated the effects of XJB-5-131 (XJB), a mitochondria-targeted ROS and electron scavenger, on cardiac resistance to ischemia-reperfusion (IR)-induced oxidative stress in aged rats. Male adult (5-month old, n=17) and aged (29-month old, n=19) Fischer Brown Norway (F344/BN) rats were randomly assigned to the following groups: adult (A), adult+XJB (AX), aged (O), and aged+XJB (OX). XJB was administered 3 times per week (3mg/kg body weight, IP) for four weeks. At the end of the treatment period, cardiac function was continuously monitored in excised hearts using the Langendorff technique for 30 min, followed by 20 min of global ischemia, and 60-min reperfusion. XJB improved post-ischemic recovery of aged hearts, as evidenced by greater left ventricular developed-pressures and rate-pressure products than the untreated, aged-matched group. The state 3 respiration rates at complexes I, II and IV of mitochondria isolated from XJB-treated aged hearts were 57% (P<0.05), 25% (P<0.05) and 28% (P<0.05), respectively, higher than controls. Ca(2+)-induced swelling, an indicator of permeability transition pore opening, was reduced in the mitochondria of XJB-treated aged rats. In addition, XJB significantly attenuated the H2O2-induced depolarization of the mitochondrial inner membrane as well as the total and mitochondrial ROS levels in cultured cardiomyocytes. This study underlines the importance of mitochondrial ROS in aging-induced cardiac dysfunction and suggests that targeting mitochondrial ROS may be an effective therapeutic approach to protect the aged heart against IR injury.

Altering the response to radiation: sensitizers and protectors

A number of agents are used clinically to enhance the efficacy of radiotherapy today, many of which are cytotoxic chemotherapies. Agents that enhance radiation induced tumor cell killing or protect normal tissues from the deleterious effects of ionizing radiation are collectively termed radiation modifiers. A significant effort in radiobiological research is geared towards describing and testing radiation modifiers with the intent of enhancing the therapeutic effects of radiation while minimizing normal tissue toxicity. In this review, we discuss the characteristics of these agents, the testing required to translate these agents into clinical trials, and highlight some challenges in these efforts.

Design and synthesis of novel spin-labeled camptothecin derivatives as potent cytotoxic agents

In our continuing search for natural product-based spin-labeled antitumor drugs, 20 novel spin-labeled camptothecin derivatives were synthesized via a Cu-catalyzed one pot reaction and evaluated for cytotoxicity against four human tumor cell lines (A-549, MDA-MB-231, KB, and KBvin). Eighteen of the target compounds (9a, 9b, 9d-9k, 9m-9t) exhibited significant in vitro antiproliferative activity against these four tested tumor cell lines. Compounds 9e and 9j (IC50 0.057 and 0.072μM, respectively) displayed the greatest cytotoxicity against the multidrug-resistant (MDR) KBvin cell line and merit further development into preclinical and clinical drug candidates for treating cancer including MDR phenotype.

In vivo imaging of tumor physiological, metabolic, and redox changes in response to the anti-angiogenic agent sunitinib: longitudinal assessment to identify transient vascular renormalization

AIMS

The tumor microenvironment is characterized by a highly reducing redox status, a low pH, and hypoxia. Anti-angiogenic therapies for solid tumors frequently function in two steps: the transient normalization of structurally and functionally aberrant tumor blood vessels with increased blood perfusion, followed by the pruning of tumor blood vessels and the resultant cessation of nutrients and oxygen delivery required for tumor growth. Conventional anatomic or vascular imaging is impractical or insufficient to distinguish between the two steps of tumor response to anti-angiogenic therapies. Here, we investigated whether the noninvasive imaging of the tumor redox state and energy metabolism could be used to characterize anti-angiogenic drug-induced transient vascular normalization.

RESULTS

Daily treatment of squamous cell carcinoma (SCCVII) tumor-bearing mice with the multi-tyrosine kinase inhibitor sunitinib resulted in a rapid decrease in tumor microvessel density and the suppression of tumor growth. Tumor pO2 imaging by electron paramagnetic resonance imaging showed a transient increase in tumor oxygenation after 2-4 days of sunitinib treatment, implying improved tumor perfusion. During this window of vascular normalization, magnetic resonance imaging of the redox status using an exogenously administered nitroxide probe and hyperpolarized (13)C MRI of the metabolic flux of pyruvate/lactate couple revealed an oxidative shift in tumor redox status.

INNOVATION

Redox-sensitive metabolic couples can serve as noninvasive surrogate markers to identify the vascular normalization window in tumors with imaging techniques.

CONCLUSION

A multimodal imaging approach to characterize physiological, metabolic, and redox changes in tumors is useful to distinguish between the different stages of anti-angiogenic treatment.

Reactive oxygen species-scavenging nanomedicines for the treatment of oxidative stress injuries

This Progress Report describes a development of two types of reactive oxygen species (ROS)-scavenging nanomedicines for the treatment of oxidative stress injuries, referred to as pH-sensitive redox nanoparticle (RNP(N) ) and pH-insensitive redox nanoparticle (RNP(O) ), which are prepared by self-assembling amphiphilic block copolymers possessing nitroxide radicals as a side chain of hydrophobic segment via amine and ether linkages, respectively. Due to a protonation of amino groups in hydrophobic core, RNP(N) disintegrates in low pH environments such as ischemic, inflamed, and tumor tissues, resulting in increased ROS-scavenging activity because of the exposed nitroxide radicals from the core. Utilizing pH-responsiveness of RNP(N) , it shows remarkable therapeutic effects on oxidative stress injuries such as renal and cerebral ischemia-reperfusion injuries after intravenous administration. Moreover, RNP(N) shows an enhancement of the activity of anticancer drugs by suppression of activation of transcription factors in tumor due to the ROS scavenging. On the other hand, orally administered RNP(O) has notable characteristics such as preferential accumulation in mucosa and inflamed area of gastrointestinal tract and no uptake into blood stream. Based on these characters, RNP(O) shows a remarkable therapeutic effect for the gastrointestinal inflammation without any adverse effects. Thus, ROS-scavenging nanomedicines have therapeutic efficacy in numerous oxidative stress diseases.

Selective protection of zidovudine-induced DNA-damage by the antioxidants WR-1065 and tempol

The cytokinesis-block micronucleus cytome (CBMN) assay, introduced by Fenech, was used to demonstrate different types of DNA damage in MOLT-3 human lymphoblastoid cells exposed to 10 μM zidovudine (AZT). In addition, we explored the cytoprotective potential of two antioxidants, WR-1065 and Tempol, to decrease AZT-induced genotoxicity. Binucleated cells, arrested by Cytochalasin B (Cyt B), were evaluated for micronuclei (MN), caused by DNA damage or chromosomal loss, and chromatin nucleoplasmic bridges (NPBs), caused by telomere attrition. Additionally, nuclear buds (NBUDs), caused by amplified DNA, and apoptotic and necrotic (A/N) cells were scored. We hypothesized that AZT exposure would increase the frequency of genotoxic end points, and that the antioxidants Tempol and WR-1065 would protect against AZT-induced genotoxicity. MOLT-3 cells were exposed to 0 or 10 µM AZT for a total of 76 hr. After the first 24 hr, 0 or 5 µM WR-1065 and/or 0 or 200 µM Tempol were added for the remainder of the experiment. For the last 28 hr (of 76 hr), Cyt B was added to arrest replication after one cell division, leaving a predominance of binucleated cells. The nuclear division index (NDI) was similar for all treatment groups, indicating that the exposures did not alter cell viability. MOLT-3 cells exposed to AZT alone had significant (P < 0.05) increases in MN and NBs, compared to unexposed cells. Both Tempol and WR-1065 protected against AZT-induced MN formation (P < 0.003 for both), and WR-1065, but not Tempol, reduced the levels of A/N (P = 0.041). In cells exposed to AZT/Tempol there were significantly reduced levels of NBUDs, compared to cells exposed to AZT alone (P = 0.015). Cells exposed to AZT/WR-1065 showed reduced levels of NPBs, compared to cells exposed to AZT alone (P = 0.037). Thus WR-1065 and Tempol protected MOLT-3 cells against specific types of AZT-induced DNA damage.