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Singh VK, Seed TM. Repurposing Pharmaceuticals Previously Approved by Regulatory Agencies to Medically Counter Injuries Arising Either Early or Late Following Radiation Exposure. Front Pharmacol 2021; 12:624844. [PMID: 34040517 PMCID: PMC8141805 DOI: 10.3389/fphar.2021.624844] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2020] [Accepted: 04/26/2021] [Indexed: 12/12/2022] Open
Abstract
The increasing risks of radiological or nuclear attacks or associated accidents have served to renew interest in developing radiation medical countermeasures. The development of prospective countermeasures and the subsequent gain of Food and Drug Administration (FDA) approval are invariably time consuming and expensive processes, especially in terms of generating essential human data. Due to the limited resources for drug development and the need for expedited drug approval, drug developers have turned, in part, to the strategy of repurposing agents for which safety and clinical data are already available. Approval of drugs that are already in clinical use for one indication and are being repurposed for another indication is inherently faster and more cost effective than for new agents that lack regulatory approval of any sort. There are four known growth factors which have been repurposed in the recent past as radiomitigators following the FDA Animal Rule: Neupogen, Neulasta, Leukine, and Nplate. These four drugs were in clinic for several decades for other indications and were repurposed. A large number of additional agents approved by various regulatory authorities for given indications are currently under investigation for dual use for acute radiation syndrome or for delayed pathological effects of acute radiation exposure. The process of drug repurposing, however, is not without its own set of challenges and limitations.
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Affiliation(s)
- Vijay K. Singh
- Division of Radioprotectants, Department of Pharmacology and Molecular Therapeutics, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD, United States
- Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, Bethesda, MD, United States
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Singh VK, Seed TM. Pharmacological management of ionizing radiation injuries: current and prospective agents and targeted organ systems. Expert Opin Pharmacother 2020; 21:317-337. [PMID: 31928256 PMCID: PMC6982586 DOI: 10.1080/14656566.2019.1702968] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 12/06/2019] [Indexed: 12/20/2022]
Abstract
Introduction: There is a limited array of currently available medicinals that are useful for either the prevention, mitigation or treatment of bodily injuries arising from ionizing radiation exposure.Area covered: In this brief article, the authors review those pharmacologic agents that either are currently being used to counter the injurious effects of radiation exposure, or those that show promise and are currently under development.Expert opinion: Although significant, but limited progress has been made in the development and fielding of safe and effective pharmacotherapeutics for select types of acute radiation-associated injuries, additional effort is needed to broaden the scope of drug development so that overall health risks associated with both short- and long-term injuries in various organ systems can be reduced and effectively managed. There are several promising radiation countermeasures that may gain regulatory approval from the government in the near future for use in clinical settings and in the aftermath of nuclear/radiological exposure contingencies.
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Affiliation(s)
- Vijay K. Singh
- Division of Radioprotectants, Department of Pharmacology and Molecular Therapeutics, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
- Armed Forces Radiobiology Research Institute, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Thomas M Seed
- Tech Micro Services, 4417 Maple Avenue, Bethesda, MD 20814, USA
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Sadowska-Bartosz I, Gajewska A, Skolimowski J, Szewczyk R, Bartosz G. Nitroxides protect against peroxynitrite-induced nitration and oxidation. Free Radic Biol Med 2015; 89:1165-75. [PMID: 26546694 DOI: 10.1016/j.freeradbiomed.2015.11.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Revised: 11/02/2015] [Accepted: 11/02/2015] [Indexed: 12/20/2022]
Abstract
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.
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Affiliation(s)
- Izabela Sadowska-Bartosz
- Department of Biochemistry and Cell Biology, Faculty of Biology and Agriculture, University of Rzeszów, Rzeszów, Poland.
| | - Agnieszka Gajewska
- Department of Molecular Biophysics, Faculty of Biology and Environmental Protection, University of Łódź, Łódź, Poland
| | - Janusz Skolimowski
- Department of Organic Chemistry, Faculty of Chemistry, University of Łódź, Łódź, Poland
| | - Rafał Szewczyk
- Department of Industrial Microbiology and Biotechnology, Institute of Microbiology, Biotechnology and Immunology, Faculty of Biology and Environmental Protection, University of Łódź, Łódź, Poland
| | - Grzegorz Bartosz
- Department of Biochemistry and Cell Biology, Faculty of Biology and Agriculture, University of Rzeszów, Rzeszów, Poland; Department of Molecular Biophysics, Faculty of Biology and Environmental Protection, University of Łódź, Łódź, Poland
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Sadowska-Bartosz I, Galiniak S, Skolimowski J, Stefaniuk I, Bartosz G. Nitroxides prevent protein glycoxidationin vitro. Free Radic Res 2014; 49:113-21. [DOI: 10.3109/10715762.2014.982113] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Kuntić VS, Stanković MB, Vujić ZB, Brborić JS, Uskoković-Marković SM. Radioprotectors - the evergreen topic. Chem Biodivers 2014; 10:1791-803. [PMID: 24130023 DOI: 10.1002/cbdv.201300054] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2013] [Indexed: 11/08/2022]
Abstract
To protect organisms from ionizing radiation (IR), and to reduce morbidity or mortality, various agents, called radioprotectors, have been utilized. Because radiation-induced cellular damage is attributed primarily to the harmful effects of free radicals, molecules with radical-scavenging properties are particularly promising as radioprotectors. Early development of such agents focused on thiol synthetic compounds, known as WR protectors, but only amifostine (WR-2721) has been used in clinical trials as an officially approved radioprotector. Besides thiol compounds, various compounds with different chemical structure were investigated, but an ideal radioprotector has not been found yet. Plants and natural products have been evaluated as promising sources of radioprotectors because of their low toxicity, although they exhibit an inferior protection level compared to synthetic thiol compounds. Active plant constituents seem to exert the radioprotection through antioxidant and free radical-scavenging activities. Our research established that plants containing polyphenolic compounds (raspberry, blueberry, strawberry, grape, etc.) exhibit antioxidative activities and protect genetic material from IR.
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Affiliation(s)
- Vesna S Kuntić
- University of Belgrade - Faculty of Pharmacy, Vojvode Stepe 450, P.O. Box 146, 11221 Belgrade, Serbia (phone: +381-11-39-51-238; fax: +381-11-39-72-840)
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Jagetia GC, Venkatesha VA. Treatment of mice with stem bark extract ofAphanamixis polystachyareduces radiation-induced chromosome damage. Int J Radiat Biol 2009; 82:197-209. [PMID: 16638717 DOI: 10.1080/09553000600621413] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
PURPOSE Normal tissue radiosensitivity is the major limiting factor in radiotherapy of cancer. The use of phytochemicals may reduce the adverse effects of radiation in normal tissue. The effect of ethyl acetate fraction of Aphanamixis polystachya (EAP) was investigated on the radiation-induced chromosome damage in the bone marrow cells of Swiss albino mice exposed to various doses of gamma-radiation. MATERIALS AND METHODS The mice were divided into two groups, one group was exposed to 0, 1, 2, 3, 4 or 5 Gy of gamma-radiation, while another group received 7.5 mg/kg body weight (BW) of EAP 1 h before exposure to 0, 1, 2, 3, 4 or 5 Gy of gamma-radiation. Various asymmetrical chromosome aberrations were studied in the bone marrow cells of mice at 12, 24 or 48 h post-irradiation. To understand the mechanism of action of the free radical scavenging activity of 0, 5, 10, 20, 30, 40, 50, 60 or 70 microg/ml EAP, assays were carried out in vitro. RESULTS Irradiation of mice to different doses of gamma radiation caused a dose dependent elevation in the frequency of aberrant cells and chromosome aberrations like chromatid breaks, chromosome breaks, dicentrics, acentric fragments and total aberrations at all the post-irradiation times studied. The maximum asymmetrical aberrations were scored at 24 h post-irradiation except chromatid breaks that were highest at 12 h post-irradiation. A maximum number of polyploid and severely damaged cells (SDC) were recorded at 24 h post-irradiation in the SPS+irradiation group. Treatment of mice with 7.5 mg/kg BW of EAP before exposure to 1-5 Gy of whole body gamma-radiation significantly reduced the frequencies of aberrant cells and chromosomal aberrations like acentric fragments, chromatid and chromosome breaks, centric rings, dicentrics and total aberrations at all post-irradiation scoring times (p<0.01). The EAP showed a concentration dependent scavenging of hydroxyl, superoxide, 2,2'-diphenyl-1-picryl hydrazyl (DPPH) radicals and the 2,2-azino-bis-3-ethyl benzothiazoline-6-sulphonic acid (ABTS) cation radicals in vitro. EAP treatment also reduced lipid peroxidation in bone marrow cells in a concentration dependent manner. CONCLUSION Our study demonstrates that EAP protects mouse bone marrow cells against radiation-induced chromosomal aberrations and this reduction in radiation-induced chromosome damage may be due to free radical scavenging and reduction in lipid peroxidation. The radioprotection by EAP is best comparable to that of protection demonstrated by the grape fruit flavonone, naringin, in our earlier studies in mouse bone marrow cells.
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Wilcox CS, Pearlman A. Chemistry and antihypertensive effects of tempol and other nitroxides. Pharmacol Rev 2009; 60:418-69. [PMID: 19112152 DOI: 10.1124/pr.108.000240] [Citation(s) in RCA: 280] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Nitroxides can undergo one- or two-electron reduction reactions to hydroxylamines or oxammonium cations, respectively, which themselves are interconvertible, thereby providing redox metabolic actions. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (tempol) is the most extensively studied nitroxide. It is a cell membrane-permeable amphilite that dismutates superoxide catalytically, facilitates hydrogen peroxide metabolism by catalase-like actions, and limits formation of toxic hydroxyl radicals produced by Fenton reactions. It is broadly effective in detoxifying these reactive oxygen species in cell and animal studies. When administered intravenously to hypertensive rodent models, tempol caused rapid and reversible dose-dependent reductions in blood pressure in 22 of 26 studies. This was accompanied by vasodilation, increased nitric oxide activity, reduced sympathetic nervous system activity at central and peripheral sites, and enhanced potassium channel conductance in blood vessels and neurons. When administered orally or by infusion over days or weeks to hypertensive rodent models, it reduced blood pressure in 59 of 68 studies. This was accompanied by correction of salt sensitivity and endothelial dysfunction and reduced agonist-evoked oxidative stress and contractility of blood vessels, reduced renal vascular resistance, and increased renal tissue oxygen tension. Thus, tempol is broadly effective in reducing blood pressure, whether given by acute intravenous injection or by prolonged administration, in a wide range of rodent models of hypertension.
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Affiliation(s)
- Christopher S Wilcox
- Division of Nephrology and Hypertension, Kidney and Vascular Disorder Center, Georgetown University, Washington, DC 20007, USA.
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Lewinska A, Wnuk M, Slota E, Bartosz G. The nitroxide antioxidant Tempol affects metal-induced cyto- and genotoxicity in human lymphocytes in vitro. MUTATION RESEARCH-GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2008; 649:7-14. [DOI: 10.1016/j.mrgentox.2007.07.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2007] [Revised: 06/04/2007] [Accepted: 07/12/2007] [Indexed: 01/06/2023]
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Soule BP, Hyodo F, Matsumoto KI, Simone NL, Cook JA, Krishna MC, Mitchell JB. Therapeutic and clinical applications of nitroxide compounds. Antioxid Redox Signal 2007; 9:1731-43. [PMID: 17665971 DOI: 10.1089/ars.2007.1722] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Nitroxide compounds have been used for many years as biophysical tools, but only during the past 15-20 years have the many interesting biochemical interactions been discovered and harnessed for therapeutic applications. By modifying oxidative stress and altering the redox status of tissues, nitroxides have the ability to interact with and alter many metabolic processes. This interaction can be exploited for therapeutic and research use, including protection against ionizing radiation, as probes in functional magnetic resonance imaging, cancer prevention and treatment, control of hypertension and weight, and protection from damage resulting from ischemia/reperfusion injury. Although much remains to be done, many applications have been well studied, and some are presently being tested in clinical trials. The therapeutic and research uses of nitroxides are reviewed here, with a focus on the progress from initial development to modern, state-of-the art trials.
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Affiliation(s)
- Benjamin P Soule
- Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892, USA.
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Soule BP, Hyodo F, Matsumoto KI, Simone NL, Cook JA, Krishna MC, Mitchell JB. The chemistry and biology of nitroxide compounds. Free Radic Biol Med 2007; 42:1632-50. [PMID: 17462532 PMCID: PMC1991293 DOI: 10.1016/j.freeradbiomed.2007.02.030] [Citation(s) in RCA: 381] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2006] [Revised: 02/21/2007] [Accepted: 02/27/2007] [Indexed: 02/04/2023]
Abstract
Cyclic nitroxides are a diverse group range of stable free radicals that have unique antioxidant properties. Because of their ability to interact with free radicals, they have been used for many years as biophysical tools. During the past 15-20 years, however, many interesting biochemical interactions have been discovered and harnessed for therapeutic applications. Biologically relevant effects of nitroxides have been described, including their ability to degrade superoxide and peroxide, inhibit Fenton reactions, and undergo radical-radical recombination. Cellular studies defined the activity of nitroxides in vitro. By modifying oxidative stress and altering the redox status of tissues, nitroxides have been found to interact with and alter many metabolic processes. These interactions can be exploited for therapeutic and research use, including protection against ionizing radiation, as probes in functional magnetic resonance imaging, cancer prevention and treatment, control of hypertension and weight, and protection from damage resulting from ischemia/reperfusion injury. Although much remains to be done, many applications have been well studied and some are currently being tested in clinical trials. The therapeutic and research uses of nitroxide compounds are reviewed here with a focus on the progress from initial development to modern trials.
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Affiliation(s)
- Benjamin P Soule
- Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
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Klingler W, Kreja L, Nothdurft W, Selig C. Influence of different radioprotective compounds on radiotolerance and cell cycle distribution of human progenitor cells of granulocytopoiesis in vitro. Br J Haematol 2002; 119:244-54. [PMID: 12358931 DOI: 10.1046/j.1365-2141.2002.03795.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Ficoll-separated mononuclear cells (MNC) of cryopreserved human bone marrow were incubated with isotoxic doses of diltiazem, N-acetylcysteine (NAC), glycopolysaccharide extract of spirulina platensis (SPE), tempol, thiopental, WR2721 and WR1065. After irradiation with a single dose of 0.73 Gy, survival of granulocyte/macrophage colony-forming cells (GM-CFC) was determined at d 10-14, using an agar culture system. Diltiazem, NAC, tempol and WR1065 significantly improved radiotolerance with protection factors (PF) between 1.21 and 1.36 (n = 5, P < 0.05) at 0.73 Gy (PF-0.73 Gy). The survival curves of diltiazem (D0 = 0.88 Gy, n = 1.00), NAC (D0 = 0.92 Gy, n = 1.10), tempol (D0 = 0.99 Gy, n = 1.10), WR1065 (D0 = 0.89 Gy, n = 1.16) and control (D0 = 0.78 Gy, n = 1.00) over 0.36-2.91 Gy showed a significant radioprotective effect for D0 only for tempol (P = 0.018) and for the extrapolation number 'n' only in the case of NAC (P = 0.023). Cell cycle analysis of the CD34+ cell subpopulation (control-0 h: G1 = 82.7%, S = 13.7%, G2/M = 3.6%) revealed that all compounds with a significant PF-0.73 Gy also caused a significant increase in CD34+ cells in S phase up to 48 h. Within the first 24 h, only NAC (26.7 +/- 4.1%), tempol (14.3 +/- 1.0%) and possibly WR1065 (15.5 +/- 1.6%) had higher fractions of CD34+ S-phase cells compared with controls. This observation and the improvement of GM-CFC cloning efficiency indicated that only NAC was able to recruit progenitor cells in the cell cycle, whereas tempol and WR1065 possibly inhibited cell cycle progression by S and G2/M arrest. Of the radioprotectors tested, NAC, tempol and WR1065 may be suitable to support, alone or combined with cytokine therapy, accelerated haematopoietic recovery after irradiation.
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Affiliation(s)
- Werner Klingler
- Department of Anaesthesiology, Institute for Occupational, Social and Environmental Medicine, University of Ulm, Ulm, Germany
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Poggi MM, Coleman CN, Mitchell JB. Sensitizers and protectors of radiation and chemotherapy. Curr Probl Cancer 2001; 25:334-411. [PMID: 11740469 DOI: 10.1067/mcn.2001.120122] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- M M Poggi
- Radiation Oncology Sciences Program, National Cancer Institute, Bethesda, Maryland, USA
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Abstract
Nitroxide stable free radicals exhibit varied chemical and biological properties. Their biological applications have been greatly expanded over the past few years. Not only have they been shown to exhibit potent antioxidant and radioprotective properties, but also they can serve as in vivo functional imaging probes that non-invasively report on the oxygen status and redox properties of tissue, which may have utility in clinical biomedical research.
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Affiliation(s)
- J B Mitchell
- Radiation Biology Branch, National Cancer Institute, Bethesda, Maryland 20892, USA.
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Abstract
Because of the increasing interest in the use of nitroxide radicals as antioxidants and probes for various applications in biological systems, the question of their toxicity is of paramount importance. Cytotoxicity and mutagenicity studies have been extensively performed with the commercially available aliphatic nitroxides, and the general outcome is that these compounds are nonmutagenic and relatively noncytotoxic. In this study, the cytotoxicity and genotoxicity of a new class of aromatic nitroxides that we have synthesized (i.e., indolinonic and quinolinic nitroxides), whose antioxidant activity has been established in both chemical and biological systems, were evaluated and compared with those of two commercial nitroxides and with that of butylated hydroxytoluene (BHT). The mutagenicity assay was performed using Salmonella typhimurium tester strains TA98, TA100, and TA102, chosen on the basis of their ability to detect various types of mutations and their sensitivity to oxidative damage. None of the compounds tested were found to be mutagenic. The colony-forming assay (CFA) using Chinese hamster ovary (CHO) AS52 cells was employed for determining the cytotoxicity of the test compounds. On comparing the effective dose that inhibits the CFA by 50% (IC(50)), most of the compounds tested on an equal molar concentration basis were less toxic than BHT. Therefore, the overall results obtained correlate well with the data reported in the literature on the toxicity of aliphatic nitroxides and lend support to the possible use of these compounds as therapeutic antioxidants.
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Affiliation(s)
- E Damiani
- Dipartimento di Scienze dei Materiali e della Terra, Università, Ancona, Italy
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Kuppusamy P, Wang P, Shankar RA, Ma L, Trimble CE, Hsia CJ, Zweier JL. In vivo topical EPR spectroscopy and imaging of nitroxide free radicals and polynitroxyl-albumin. Magn Reson Med 1998; 40:806-11. [PMID: 9840823 DOI: 10.1002/mrm.1910400604] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Piperidine nitroxides have considerable clinical potential, both as antioxidant therapeutic compounds and contrast agents in magnetic resonance imaging. However, their development has thus far been limited by their rapid bioreduction in vivo. Recently, it was reported that polynitroxyl albumin (PNA) can reverse the bioreduction of the reduced 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (Tempol) in the rat heart, enabling the performance of high resolution EPR imaging for prolonged time (Kuppusamy et al., Biochemistry 35, 7051-7057 (1996)). In this report, the efficacy of PNA in maintaining Tempol concentrations in vivo in mice was demonstrated, using L-band (1.25 GHz) EPR spectroscopy and imaging. The EPR signal of intravenous Tempol had a half-life of 1.0+/-0.2 min and became undetectable within 6 min. Subcutaneous Tempol, however, decayed at a slower rate (half-life, 5.0+/-0.5 min) suggesting that Tempol had been bioreduced to the corresponding hydroxylamine form, Tempol-H. Subcutaneously injected PNA restored 20% of the Tempol signal in the vicinity of the PNA deposit. In vivo topical EPR imaging demonstrated that the Tempol signal was restored at the site of PNA injection, but not at locations remote from the PNA injection site. The ability of PNA to maintain Tempol in its paramagnetic state in vivo should enable a wide range of therapeutic and diagnostic applications of piperidinyl nitroxides.
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Affiliation(s)
- P Kuppusamy
- Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
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Offer T, Mohsen M, Samuni A. An SOD-mimicry mechanism underlies the role of nitroxides in protecting papain from oxidative inactivation. Free Radic Biol Med 1998; 25:832-8. [PMID: 9823549 DOI: 10.1016/s0891-5849(98)00162-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Nitroxide stable free radicals have previously been found to afford protection in various biological systems against diverse types of oxidative stress, including, ischemia/reperfusion, hyperoxia, mechanical trauma, toxic xenobiotics, ionizing radiation, gastric and colonic irritants or strong oxidants. Dismutation of superoxide has originally been suggested to be one of the mechanisms that underlie the anti-oxidant effect of nitroxides. However, no direct evidence has been found, so far, to support this assumption. In the present study, superoxide and H2O2, generated enzymatically, were used to directly inactivate papain, a sulfhydryl enzyme, in vitro. The rate of papain inactivation served to assess the damage. The reaction mixtures contained a chelate in order to prevent the effect of adventitious redox-active metal ions, pre-empt the Fenton reaction and avoid hydroxyl-induced damage. Catalase or SOD alone partially protected the papain from inactivation. The protective effect of nitroxides resembled that of SOD in several aspects: a) nitroxides provided partial protection; b) the protective effect of nitroxides did not increase with the elevation of their concentration (above 0.5 mM); c) the combined addition of SOD and the nitroxide did not provide greater protection than that demonstrated by nitroxides or SOD separately; d) the effects of catalase with the nitroxide were additive; e) the nitroxide, like SOD itself, did not protect papain from H2O2-induced inactivation; f) the nitroxide was found not to be consumed in the course of the reaction but rather to be recycled. The results indicate that: (a) the main species responsible for the papain inactivation in a system in which the effect of transition metals is pre-empted, are O2-. and H2O2; (b) nitroxides inhibit the oxidative damage by removing superoxide not stoichiometrically, but rather catalytically as SOD-mimics; (c) nitroxides do not afford protection when the oxidative damage is induced directly by H2O2 (and not mediated by redox-active metals).
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Affiliation(s)
- T Offer
- Department of Molecular Biology, Faculty of Medicine, The Hebrew University, Jerusalem, Israel
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VARANDA EA, TAVARES DC. RADIOPROTECTION: MECHANISMS AND RADIOPROTECTIVE AGENTS INCLUDING HONEYBEE VENOM. ACTA ACUST UNITED AC 1998. [DOI: 10.1590/s0104-79301998000100002] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- E. A. VARANDA
- São Paulo State University; UNESP, São Paulo State University, Botucatu, SP, Brazil
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A 1H, 13C and 15N NMR study of oxidation and reduction products of 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxyl. J Mol Struct 1997. [DOI: 10.1016/s0022-2860(96)09730-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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