An SOD-mimicry mechanism underlies the role of nitroxides in protecting papain from oxidative inactivation

Two faces of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) - An antioxidant or a toxin?

2,2,6,6-Tetramethylpiperidine-1-oxyl, commonly known as TEMPO, is one of the compounds called nitroxides that are used in the chemical industry for synthesis of many organic compounds as well as for electrodes in all-organic radical batteries. Additionally, TEMPO is a widely used antioxidant in scientific studies. Technological progress and simultaneous care for the environment leads to resorting to new industrial methods which require the use of compounds that have not been fully tested for their impact on living organisms. Therefore, TEMPO may be an environmental pollutant and its effect on living organisms is not fully understood. The aim of our study was to determine the influence of TEMPO on the physiology, chronological lifespan and wide transcription changes of a eukaryotic model organism, namely the Saccharomyces cerevisiae yeast. For this purpose, we used the BY4741 wild-type and isogenic mutants with a disorder in the response to oxidative stress (sod1Δ, sod2Δ, yap1Δ) and repair of DNA damage (rad52Δ). We showed that supplementation with TEMPO inhibited the cell growth rate of all analyzed strains while simultaneously slowing down the aging of post-mitotic cells in the yeast population. In addition, TEMPO-treated yeast cells manifested a significantly increased level of metabolism in the wild-type and sod2Δ strains. TEMPO also displayed genoprotective effect by reducing the number of DNA double-strand breaks in cells. Here, we are the first to show the widespread effect of TEMPO on yeast. In conclusion, we have shown that, contrary to the commonly accepted notion, TEMPO has also a toxic effect, especially on active mitotic cells. We hypothesize that translation impairment or ribosome biogenesis disorder is likely to be considered secondary effects of TEMPO toxicity related to cell cycle arrest. Therefore, despite the growing interest in the use of this compound in the chemical industry, its toxic effect on the environment, especially biosphere, should be taken into account.

Nitroxides Mitigate Neutrophil-Mediated Damage to the Myocardium after Experimental Myocardial Infarction in Rats

Reperfusion therapy increases survival post-acute myocardial infarction (AMI) while also stimulating secondary oxidant production and immune cell infiltration. Neutrophils accumulate within infarcted myocardium within 24 h post-AMI and release myeloperoxidase (MPO) that catalyses hypochlorous acid (HOCl) production while increasing oxidative stress and inflammation, thereby enhancing ventricular remodelling. Nitroxides inhibit MPO-mediated HOCl production, potentially ameliorating neutrophil-mediated damage. Aim: Assess the cardioprotective ability of nitroxide 4-methoxyTEMPO (4MetT) within the setting of AMI. Methods: Male Wistar rats were separated into 3 groups: SHAM, AMI/R, and AMI/R + 4MetT (15 mg/kg at surgery via oral gavage) and subjected to left descending coronary artery ligation for 30 min to generate an AMI, followed by reperfusion. One cohort of rats were sacrificed at 24 h post-reperfusion and another 28 days post-surgery (with 4MetT (15 mg/kg) administration twice daily). Results: 3-chlorotyrosine, a HOCl-specific damage marker, decreased within the heart of animals in the AMI/R + 4-MetT group 24 h post-AMI, indicating the drug inhibited MPO activity; however, there was no evident difference in either infarct size or myocardial scar size between the groups. Concurrently, MPO, NfκB, TNFα, and the oxidation marker malondialdehyde increased within the hearts, with 4-MetT only demonstrating a trend in decreasing MPO and TNF levels. Notably, 4MetT provided a significant improvement in cardiac function 28 days post-AMI, as assessed by echocardiography, indicating potential for 4-MetT as a treatment option, although the precise mechanism of action of the compound remains unclear.

Neutrophil-Mediated Cardiac Damage After Acute Myocardial Infarction: Significance of Defining a New Target Cell Type for Developing Cardioprotective Drugs

Significance: Acute myocardial infarction (AMI) is a leading cause of death worldwide. Post-AMI survival rates have increased with the introduction of angioplasty as a primary coronary intervention. However, reperfusion after angioplasty represents a clinical paradox, restoring blood flow to the ischemic myocardium while simultaneously inducing ion and metabolic imbalances that stimulate immune cell recruitment and activation, mitochondrial dysfunction and damaging oxidant production. Recent Advances: Preclinical data indicate that these metabolic imbalances contribute to subsequent heart failure through sustaining local recruitment of inflammatory leukocytes and oxidative stress, cardiomyocyte death, and coronary microvascular disturbances, which enhance adverse cardiac remodeling. Both left ventricular dysfunction and heart failure are strongly linked to inflammation and immune cell recruitment to the damaged myocardium. Critical Issues: Overall, therapeutic anti-inflammatory and antioxidant agents identified in preclinical trials have failed in clinical trials. Future Directions: The versatile neutrophil-derived heme enzyme, myeloperoxidase (MPO), is gaining attention as an important oxidative mediator of reperfusion injury, vascular dysfunction, adverse ventricular remodeling, and atrial fibrillation. Accordingly, there is interest in therapeutically targeting neutrophils and MPO activity in the setting of heart failure. Herein, we discuss the role of post-AMI inflammation linked to myocardial damage and heart failure, describe previous trials targeting inflammation and oxidative stress post-AMI, highlight the potential adverse impact of neutrophil and MPO, and detail therapeutic options available to target MPO clinically in AMI patients.

Biological Relevance of Free Radicals and Nitroxides

Nitroxides are stable, kinetically-persistent free radicals which have been successfully used in the study and intervention of oxidative stress, a critical issue pertaining to cellular health which results from an imbalance in the levels of damaging free radicals and redox-active species in the cellular environment. This review gives an overview of some of the biological processes that produce radicals and other reactive oxygen species with relevance to oxidative stress, and then discusses interactions of nitroxides with these species in terms of the use of nitroxides as redox-sensitive probes and redox-active therapeutic agents.

The effect of hyperoxia on reactive oxygen species (ROS) in rat petrosal ganglion neurons during development using organotypic slices

Hyperoxia, during development in rats, results in hypoxic chemosensitivity ablation, carotid body hypoplasia, and reduced chemoafferents. We hypothesized that hyperoxia increases reactive oxygen species (ROS) in cell bodies of chemoafferents. Organotypic slices of petrosal-nodose ganglia from rats at day of life (DOL) 5-6 and 17-18 were exposed to 8%, 21%, or 95% O(2) for 4 h in the presence or absence of the ROS-sensitive fluorescent indicator, CM-H(2)DCFDA, and propidium iodide was used to determine the relationship between cell death and oxygen tension. In tissue slices from DOL 5-6 rats, fluorescence intensity was 182.5 +/- 2.9 for hypoxia, 217.5 +/- 3.3 for normoxia, and 336.6 +/- 3.8 for hyperoxia, (mean +/- SEM, p < 0.001, ANOVA). Normoxia increased ROS levels by 19.2% from hypoxia (p < 0.01) with a further increase of 54.8% from normoxia to hyperoxia (p < 0.001). In tissue slices from DOL 17-18 rats, ROS levels increased with increasing oxygen tension but were less than in younger animals (p < 0.01, ANOVA). The antioxidants, NAC and TEMPO-9-AC, attenuated ROS levels and cell death. Electron microscopy demonstrated that hyperoxia damages the ultrastructure within petrosal ganglion neurons. Hyperoxic-induced increased levels of ROS in petrosal ganglion neurons may contribute to loss of hypoxic chemosensitivity during early postnatal development.

Amphiphilic amine-N-oxides with aliphatic alkyl chain act as efficient superoxide dismutase mimics, antioxidants and lipid peroxidation blockers in yeast

Amphiphilic 3-(alkanoylamino)propyldimethylamine-N-oxides with different length of the alkyl chain, i.e. different hydrophilic-lipophilic balance, act in micromolar concentrations as SOD mimics by lifting the inhibition of aerobic growth caused by SOD deletions in Saccharomyces cerevisiae. They also enhance the survival of sod mutants of S. cerevisiae exposed to the hydrophilic superoxide-generating prooxidant paraquat and the amphiphilic hydroperoxide-producing tert-butylhydroperoxide (TBHP), and largely prevent TBHP-induced peroxidation of isolated yeast plasma membrane lipids. Unlike the SOD-mimicking effect, the magnitude of these effects depends on the alkyl chain length of the amine-N-oxides, which incorporate into S. cerevisiae membranes, causing fluidity changes in both the hydrophilic surface part of the membrane and the membrane lipid matrix. Unlike wild-type strains, the membranes of sod mutants were found to contain polyunsaturated fatty acids; the sensitivity of the mutants to lipophilic pro-oxidants was found to increase with increasing content of these acids. sod mutants are useful in assessing pro- and antioxidant properties of different compounds.

Neuroprotection by the stable nitroxide 3-carbamoyl-proxyl during reperfusion in a rat model of transient focal ischemia

OBJECT

Nitroxides mimic superoxide dismutase (SOD) biochemically and may prevent free radical oxidative injury in settings in which endogenous SOD is overwhelmed. The authors have previously shown the efficacy of a nitroxide, Tempol, in reducing stroke infarct size. Of the nitroxides, 3-carbamoyl-proxyl (3-CP) is especially promising for clinical use, because it does not cause hypotension in animals. Its efficacy in brain ischemia, however, is untested. The goal of this study was to ascertain whether 3-CP would reduce brain damage in a rat ischemia-reperfusion model.

METHODS

The authors performed a blinded, dose-response study of the effect of different amounts of 3-CP (1, 10, and 100 mg/kg) on infarct size at 24 hours after focal ischemia and reperfusion. The 3-CP was given intravenously during reperfusion, which followed 1 hour of reversible ischemia induced by a thread placed intraluminally in the middle cerebral artery of rats. Brain infarcts, measured with 2,3,5-triphenyltetrazolium chloride staining in six 3-CP groups, were compared with those measured in controls (animals given an equal volume of saline). Edema-corrected infarct sizes (mean +/- standard deviation) were as follows: 146 +/- 64 mm3 in controls; 107 +/- 18 mm3 in rats given 1 mg/kg 3-CP; 40 +/- 20 mm3 in those given 10 mg/kg 3-CP; and 44 +/- 17 mm3 in those given 100 mg/kg 3-CP. A statistically significant reduction in infarct size was achieved in the 10- and 100-mg/kg 3-CP-treated groups (p < 0.01). A reduction in infarct size was also seen in the 1 mg/kg 3-CP-treated group, but this did not reach statistical significance. The authors observed no effects of 3-CP on blood pressure or brain temperature.

CONCLUSIONS

Given at reperfusion, 3-CP significantly decreases brain infarct size at doses of 10 and 100 mg/kg without causing hypotension. The authors found that 3-CP is well suited for further laboratory and clinical use in brain ischemia and reperfusion.

The pro-oxidative activity of SOD and nitroxide SOD mimics

Native Cu,Zn-SOD and synthetic SOD mimics sometimes demonstrate an apparently anomalous bell-shaped dose-response relationship when protecting various biological systems from oxidative stress. Several mechanisms have been proposed to account for such an effect, including: overproduction of H(2)O(2), peroxidative activity of SOD, and opposing roles played by O(2)(*-) in both initiation and termination of radical chain reactions. In the present study, ferrocyanide and thiols, which are susceptible to one-electron and two-electron oxidation, respectively, were subjected to a flux of superoxide in the presence and absence of SOD or SOD mimics. The results show that 1) either O(2)(*-)/HO(2)(*) or H(2)O(2) alone partially inactivates papain, whereas when combined they act synergistically; 2) nitroxide SOD mimics, but not SOD, exhibit a bell-shaped dose-response relationship in protecting papain from inactivation; 3) SOD, which at low dose inhibits superoxide-induced oxidation of ferrocyanide, loses its antioxidative effect as its concentration increases. These findings offer an additional explanation for the pro-oxidative activity of SOD and SOD mimics without invoking any dual activity of O(2)(*-) or a combined effect of SOD and H(2)O(2). The most significant outcome of an increase in SOD level is a decrease of [O(2)(*-)](steady state), rather than any notable elevation of [H(2)O(2)](steady state). As a result, the reaction kinetics of the high oxidation state of each catalyst is altered. In the presence of ultra-low [O(2)(*-)](steady state), the oxidized form of SOD [Cu(II),Zn-SOD] or SOD mimic (oxo-ammonium cation) does not react with O(2)(*-) but rather oxidizes the target molecule that it was supposed to have protected. Consequently, these catalysts exert an anti- or pro-oxidative effect depending on their concentration.

Induction of superoxide in glioma cell line U87 stimulated with lipopolysaccharide and interferon-gamma: ESR using a new flow-type quartz cell

The production of superoxide and nitric oxide induced in U87 glioma treated with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) was examined by electron spin resonance (ESR) spectroscopy using a newly designed flow-type quartz cuvette without detaching cells from the culture plate. ESR spectra of 2,2,6, 6-tetramethyl-4-hydroxy-1-piperidinyloxy (TEMPOL) with U87 cells on a quartz culture plate were measured at 15 min intervals. The signal intensity of TEMPOL decreased in the presence of U87 cells at the pseudo-first order rate. The signal decay was accelerated in the U87 cells treated with LPS/IFN-gamma for 24 h, and was suppressed in the presence of superoxide dismutase and catalase. By the spin-trapping method, nitric oxide from U87 cells pretreated with LPS/IFN-gamma for 24 h was measured by the ESR, but only a weak signal of nitric oxide adducts was detected. Further, the nitrite and nitrate levels in the medium did not increase for 24 h. By the ESR measurement of cells on culture plates without detachment stress, it was found that the production of superoxide was induced by LPS/IFN-gamma, but that of nitric oxide was not, in U87 glioma cells.

Antioxidants in the prevention of renal disease

In view of the role of oxidative processes in inflicting damage that leads to glomerulosclerosis and renal medullary interstitial fibrosis, more attention could be paid to the use of antioxidant food constituents and the usage of drugs with recognized antioxidant potential. In any case atherosclerosis is an important component of chronic renal diseases. There is a wide choice of foods and drugs that could confer benefit. Supplementation with vitamins E and C, use of soy protein diets and drinking green tea could be sufficient to confer remarkable improvements.