Effects of Nitrosyl Iron Complexes with Thiol, Phosphate, and Thiosulfate Ligands on Hemoglobin.

Nitrosyl iron complexes are remarkably multifactorial pharmacological agents. These compounds have been proven to be particularly effective in treating cardiovascular and oncological diseases. We evaluated and compared the antioxidant activity of tetranitrosyl iron complexes (TNICs) with thiosulfate ligands and dinitrosyl iron complexes (DNICs) with glutathione (DNIC-GS) or phosphate (DNIC-PO4-) ligands in hemoglobin-containing systems. The studied effects included the production of free radical intermediates during hemoglobin (Hb) oxidation by tert-butyl hydroperoxide, oxidative modification of Hb, and antioxidant properties of nitrosyl iron complexes. Measuring luminol chemiluminescence revealed that the antioxidant effect of TNICs was higher compared to DNIC-PO4-. DNIC-GS either did not exhibit antioxidant activity or exerted prooxidant effects at certain concentrations, which might have resulted from thiyl radical formation. TNICs and DNIC-PO4- efficiently protected the Hb heme group from decomposition by organic hydroperoxides. DNIC-GS did not exert any protective effects on the heme group; however, it abolished oxoferrylHb generation. TNICs inhibited the formation of Hb multimeric forms more efficiently than DNICs. Thus, TNICs had more pronounced antioxidant activity than DNICs in Hb-containing systems.

JP4-039, a Mitochondria-Targeted Nitroxide, Mitigates the Effect of Apoptosis and Inflammatory Cell Migration in the Irradiated Mouse Retina.

We hypothesize that the injection of JP4-039, a mitochondria-targeted nitroxide, prior to irradiation of the mouse retina may decrease apoptosis and reduce neutrophil and macrophage migration into the retina. In our study, we aimed to examine the effects of JP4-039 in the mouse retina using fluorescent microscopy, a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, and flow cytometry. Forty-five mice and one eye per mouse were used. In Group 1, fluorescent microscopy was used to determine retinal uptake of 10 µL (0.004 mg/µL) of intravitreally injected BODIPY-labeled JP4-039 at 0, 15, and 60 min after injection. In Group 2, the TUNEL assay was performed to investigate the rate of apoptosis after irradiation in addition to JP4-039 injection, compared to controls. In Group 3, flow cytometry was used to determine the extent of inflammatory cell migration into the retina after irradiation in addition to JP4-039 injection, compared to controls. Maximal retinal uptake of JP4-039 was 15 min after intravitreal injection (p < 0.0001). JP4-039-treated eyes had lower levels of retinal apoptosis (35.8 ± 2.5%) than irradiated controls (49.0 ± 2.7%; p = 0.0066) and demonstrated reduced migration of N1 cells (30.7 ± 11.7% vs. 77.7 ± 5.3% controls; p = 0.004) and M1 cells (76.6 ± 4.2 vs. 88.1 ± 3.7% controls, p = 0.04). Pretreatment with intravitreally injected JP4-039 reduced apoptosis and inflammatory cell migration in the irradiated mouse retina, marking the first confirmed effect of this molecule in retinal tissue. Further studies may allow for safety profiling and potential use for patients with radiation retinopathy.

Activation of Transcription Factor Nrf2 in HeLa Cells under the Action of Nitrosyl Iron Complex with N-Ethylthiourea.

We studied the effect of an NO donor, nitrosyl iron complex with N-ethylthiourea, on Nrf2-dependent antioxidant system activation of tumor cells in vitro. The complex increased intracellular accumulation of Nrf2 transcription factor and induced its nuclear translocation. It was shown that both heme oxygenase-1 gene and protein expression increased significantly under the influence of the complex. Nrf2 activation was accompanied by a decrease in the intracellular accumulation of proinflammatory transcription factor NF-κB p65 subunit and expression of its target genes. The cytotoxic effect of N-ethylthiourea leads to induction of Nrf2/HO-1 antioxidant response and suppression of NF-κB-dependent processes in tumor cells.

A Crucial Role of Proteolysis in the Formation of Intracellular Dinitrosyl Iron Complexes.

Dinitrosyl iron complexes (DNICs) stabilize nitric oxide in cells and tissues and constitute an important form of its storage and transportation. DNICs may comprise low-molecular-weight ligands, e.g., thiols, imidazole groups in chemical compounds with low molecular weight (LMWDNICs), or high-molecular-weight ligands, e.g., peptides or proteins (HMWDNICs). The aim of this study was to investigate the role of low- and high-molecular-weight ligands in DNIC formation. Lysosomal and proteasomal proteolysis was inhibited by specific inhibitors. Experiments were conducted on human erythroid K562 cells and on K562 cells overexpressing a heavy chain of ferritin. Cell cultures were treated with •NO donor. DNIC formation was monitored by electron paramagnetic resonance. Pretreatment of cells with proteolysis inhibitors diminished the intensity and changed the shape of the DNIC-specific EPR signal in a treatment time-dependent manner. The level of DNIC formation was significantly influenced by the presence of protein degradation products. Interestingly, formation of HMWDNICs depended on the availability of LMWDNICs. The extent of glutathione involvement in the in vivo formation of DNICs is minor yet noticeable, aligning with our prior research findings.

The Cellular and Organismal Effects of Nitroxides and Nitroxide-Containing Nanoparticles.

Nitroxides are stable free radicals that have antioxidant properties. They react with many types of radicals, including alkyl and peroxyl radicals. They act as mimics of superoxide dismutase and stimulate the catalase activity of hemoproteins. In some situations, they may exhibit pro-oxidant activity, mainly due to the formation of oxoammonium cations as products of their oxidation. In this review, the cellular effects of nitroxides and their effects in animal experiments and clinical trials are discussed, including the beneficial effects in various pathological situations involving oxidative stress, protective effects against UV and ionizing radiation, and prolongation of the life span of cancer-prone mice. Nitroxides were used as active components of various types of nanoparticles. The application of these nanoparticles in cellular and animal experiments is also discussed.

Synthesis, antioxidant and neuroprotective analysis of diversely functionalized α-aryl-N-alkyl nitrones as potential agents for ischemic stroke therapy.

Herein, we report the synthesis, antioxidant and biological evaluation of 32 monosubstituted α-arylnitrones derived from α-phenyl-tert-butyl nitrone (PBN) in the search for neuroprotective compounds for ischemic stroke therapy, trying to elucidate the structural patterns responsible for their neuroprotective activity. Not surprisingly, the N-tert-butyl moiety plays beneficious role in comparison to other differently N-substituted nitrone groups. It seems that electron donor substituents at the ortho position and electron withdrawing substituents at the meta position of the aryl ring induce good neuroprotective activity. As a result, (Z)-N-tert-butyl-1-(2-hydroxyphenyl)methanimine oxide (21a) and (Z)-N-tert-butyl-1-(2-(prop-2-yn-1-yloxy)phenyl)methanimine oxide (24a) showed a significant increase in neuronal viability in an experimental ischemia model in primary neuronal cultures, and induced neuroprotection and improved neurodeficit score in an in vivo model of transient cerebral ischemia. These results showed that nitrones 21a and 24a are new effective small and readily available antioxidants, and suitable candidates for further structure optimization in the search for new phenyl-derived nitrones for the treatment of ischemic stroke and related diseases.

Effect of Low Concentration of Nitroxides on SH-SY5Y Cells Transfected with the Tau Protein.

Nitroxides, stable synthetic free radicals, are promising antioxidants, showing many beneficial effects both at the cellular level and in animal studies. However, the cells are usually treated with high millimolar concentrations of nitroxides which are not relevant to the concentrations that could be attained in vivo. This paper aimed to examine the effects of low (≤10 µM) concentrations of three nitroxides, 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), 4-hydroxy-TEMPO (TEMPOL) and 4-amino-TEMPO (TEMPAMINE), in pure chemical systems and on SH-SY5Y cells transfected with the human tau protein (TAU cells), a model of chronic cellular oxidative stress, and transfected with the empty plasmid (EP cells). All nitroxides were active in antioxidant-activity tests except for the 2,2'-azinobis-(3-ethylbenzthiazolin-6-sulfonate) radical (ABTS•) decolorization assay and reduced Fe3+, inhibited autoxidation of adrenalin and pyrogallol and oxidation of dihydrorhodamine123 by 3-morpholino-sydnonimine SIN-1. TEMPO protected against fluorescein bleaching from hypochlorite, but TEMPAMINE enhanced the bleaching. Nitroxides showed no cytotoxicity and were reduced by the cells to non-paramagnetic derivatives. They decreased the level of reactive oxygen species, depleted glutathione, and increased mitochondrial-membrane potential in both types of cells, and increased lipid peroxidation in TAU cells. These results demonstrate that even at low micromolar concentrations nitroxides can affect the cellular redox equilibrium and other biochemical parameters.

Preserving Retinal Structure and Function with the Novel Nitroxide Antioxidant, DCTEIO.

Oxidative stress is a major contributor to progressive neurodegenerative disease and may be a key target for the development of novel preventative and therapeutic strategies. Nitroxides have been successfully utilised to study changes in redox status (biological probes) and modulate radical-induced oxidative stress. This study investigates the efficacy of DCTEIO (5,6-dicarboxy-1,1,3,3-tetraethyllisoindolin-2-yloxyl), a stable, kinetically-persistent, nitroxide-based antioxidant, as a retinal neuroprotectant. The preservation of retinal function following an acute ischaemic/reperfusion (I/R) insult in the presence of DCTEIO was quantified by electroretinography (ERG). Inflammatory responses in retinal glia were analysed by GFAP and IBA-1 immunohistochemistry, and retinal integrity assessed by histology. A nitroxide probe combined with flow cytometry provided a rapid technique to assess oxidative stress and the mitigation offered by antioxidant compounds in cultured 661W photoreceptor cells. DCTEIO protected the retina from I/R-induced damage, maintaining retinal function. Histological analysis showed preservation of retinal integrity with reduced disruption and disorganisation of the inner and outer nuclear layers. I/R injury upregulated GFAP expression, indicative of retinal stress, which was significantly blunted by DCTEIO. The number of 'activated' microglia, particularly in the outer retina, in response to cellular stress was also significantly reduced by DCTEIO, potentially suggesting reduced inflammasome activation and cell death. DCTEIO mitigated oxidative stress in 661W retinal cell cultures, in a dose-dependent fashion. Together these findings demonstrate the potential of DCTEIO as a neuroprotective therapeutic for degenerative diseases of the CNS that involve an ROS-mediated component, including those of the retina e.g. age-related macular degeneration and glaucoma.

Discovery of endogenous nitroxyl as a new redox player in Arabidopsis thaliana.

Nitroxyl (HNO) is the one-electron reduced and protonated congener of nitric oxide (•NO), owning a distinct chemical profile. Based on real-time detection, we demonstrate that HNO is endogenously formed in Arabidopsis. Senescence and hypoxia induce shifts in the redox balance, triggering HNO decay or formation mediated by non-enzymatic •NO/HNO interconversion with cellular reductants. The stimuli-dependent HNO generation supports or competes with •NO signalling, depending on the local redox environment.

Strategies targeting the NO pathway to counteract extra-pulmonary manifestations of COPD: A systematic review and meta-analysis.

The clinical symptoms of chronic obstructive pulmonary disease (COPD) disease are accompanied by severely debilitating extra-pulmonary manifestations, including vascular dysfunction and hypertension. This systematic review evaluated the current evidence for several therapeutic interventions, targeting the nitric oxide (NO) pathway on hemodynamics and, secondarily, exercise capacity in patients with COPD. A comprehensive search on COPD and NO donors was performed on online databases. Of 934 initially found manuscripts, 27 were included in the review, and 16 in the meta-analysis. The analysis indicated inconsistent effects of dietary nitrate supplementation on exercise tolerance in COPD patients. Dietary nitrate supplementation decreased systolic (-3.7 ± 4.3 mmHg; p = 0.10) and diastolic blood pressure (BP; -2.6 ± 3.2 mmHg; p = 0.05) compared with placebo. When restricted to acute studies, a clinically relevant BP lowering effect of nitrate supplementation during diastole was observed (-4.7 ± 3.2 mmHg; n = 5; p = 0.05). In contrast, inhaled NO (iNO) at doses <20 ppm (+9.2 ± 11.3 mmHg) and 25-40 ppm (-5±2 mmHg) resulted in inconsistent effects on PaO2 (p = 0.48). Data on the effect of iNO on exercise capacity were too limited and inconsistent, but preliminary evidence suggests a possible benefit of iNO on pulmonary vascular resistance during exercise in severe COPD patients. Overall, the effects of acute dietary nitrate supplementation on BP may be of clinical relevance as an adjunct therapy and deserve further investigation in large sample size studies of COPD patients with and without cardiovascular comorbidities. iNO exerted inconsistent physiological effects, with the use of high doses posing safety risks.

Cardioprotective actions of nitroxyl donor Angeli's salt are preserved in the diabetic heart and vasculature in the face of nitric oxide resistance.

BACKGROUND AND PURPOSE: The risk of fatal cardiovascular events is increased in patients with type 2 diabetes mellitus (T2DM). A major contributor to poor prognosis is impaired nitric oxide (NO•) signalling at the level of tissue responsiveness, termed NO• resistance. This study aimed to determine if T2DM promotes NO• resistance in the heart and vasculature and whether tissue responsiveness to nitroxyl (HNO) is affected. EXPERIMENTAL APPROACH: At 8 weeks of age, male Sprague-Dawley rats commenced a high-fat diet. After 2 weeks, the rats received low-dose streptozotocin (two intraperitoneal injections, 35 mg·kg-1 , over two consecutive days) and continued on the same diet. Twelve weeks later, isolated hearts were Langendorff-perfused to assess responses to the NO• donor diethylamine NONOate (DEA/NO) and the HNO donor Angeli's salt. Isolated mesenteric arteries were utilised to measure vascular responsiveness to the NO• donors sodium nitroprusside (SNP) and DEA/NO, and the HNO donor Angeli's salt. KEY RESULTS: Inotropic, lusitropic and coronary vasodilator responses to DEA/NO were impaired in T2DM hearts, whereas responses to Angeli's salt were preserved or enhanced. Vasorelaxation to Angeli's salt was augmented in T2DM mesenteric arteries, which were hyporesponsive to the relaxant effects of SNP and DEA/NO. CONCLUSION AND IMPLICATIONS: This is the first evidence that inotropic and lusitropic responses are preserved, and NO• resistance in the coronary and mesenteric vasculature is circumvented, by the HNO donor Angeli's salt in T2DM. These findings highlight the cardiovascular therapeutic potential of HNO donors, especially in emergencies such as acute ischaemia or heart failure.

Nucleobase-Derived Nitrones: Synthesis and Antioxidant and Neuroprotective Activities in an In Vitro Model of Ischemia-Reperfusion.

Herein, we report the synthesis, antioxidant, and neuroprotective properties of some nucleobase-derived nitrones named 9a-i. The neuroprotective properties of nitrones, 9a-i, were measured against an oxygen-glucose-deprivation in vitro ischemia model using human neuroblastoma SH-SY5Y cells. Our results indicate that nitrones, 9a-i, have better neuroprotective and antioxidant properties than α-phenyl-N-tert-butylnitrone (PBN) and are similar to N-acetyl-L-cysteine (NAC), a well-known antioxidant and neuroprotective agent. The nitrones with the highest neuroprotective capacity were those containing purine nucleobases (nitrones 9f, g, B = adenine, theophylline), followed by nitrones with pyrimidine nucleobases with H or F substituents at the C5 position (nitrones 9a, c). All of these possess EC50 values in the range of 1-6 µM and maximal activities higher than 100%. However, the introduction of a methyl substituent (nitrone 9b, B = thymine) or hard halogen substituents such as Br and Cl (nitrones 9d, e, B = 5-Br and 5-Cl uracil, respectively) worsens the neuroprotective activity of the nitrone with uracil as the nucleobase (9a). The effects on overall metabolic cell capacity were confirmed by results on the high anti-necrotic (EC50's ≈ 2-4 µM) and antioxidant (EC50's ≈ 0.4-3.5 µM) activities of these compounds on superoxide radical production. In general, all tested nitrones were excellent inhibitors of superoxide radical production in cultured neuroblastoma cells, as well as potent hydroxyl radical scavengers that inhibit in vitro lipid peroxidation, particularly, 9c, f, g, presenting the highest lipoxygenase inhibitory activity among the tested nitrones. Finally, the introduction of two nitrone groups at 9a and 9d (bis-nitronas 9g, i) did not show better neuroprotective effects than their precursor mono-nitrones. These results led us to propose nitrones containing purine (9f, g) and pyrimidine (9a, c) nucleobases as potential therapeutic agents for the treatment of cerebral ischemia and/or neurodegenerative diseases, leading us to further investigate their effects using in vivo models of these pathologies.

Inorganic nitrate supplementation and blood flow restricted exercise tolerance in post-menopausal women.

Exercise tolerance appears to benefit most from dietary nitrate (NO3-) supplementation when muscle oxygen (O2) availability is low. Using a double-blind, randomized cross-over design, we tested the hypothesis that acute NO3- supplementation would improve blood flow restricted exercise duration in post-menopausal women, a population with reduced endogenous nitric oxide bioavailability. Thirteen women (57-76 yr) performed rhythmic isometric handgrip contractions (10% MVC, 30 per min) during progressive forearm blood flow restriction (upper arm cuff gradually inflated 20 mmHg each min) on three study visits, with 7-10 days between visits. Approximately one week following the first (familiarization) visit, participants consumed 140 ml of NO3- concentrated (9.7 mmol, 0.6 gm NO3-) or NO3-depleted beetroot juice (placebo) on separate days (≥7 days apart), with handgrip exercise beginning 100 min post-consumption. Handgrip force recordings were analyzed to determine if NO3- supplementation enhanced force development as blood flow restriction progressed. Nitrate supplementation increased plasma NO3- (16.2-fold) and NO2- (4.2-fold) and time to volitional fatigue (61.8 ± 56.5 s longer duration vs. placebo visit; p = 0.03). Nitrate supplementation increased the rate of force development as forearm muscle ischemia progressed (p = 0.023 between 50 and 75% of time to fatigue) with non-significant effects thereafter (p = 0.052). No effects of nitrate supplementation were observed for mean duration of contraction or relaxation rates (all p > 0.150). These results suggest that acute NO3- supplementation prolongs time-to-fatigue and speeds grip force development during progressive forearm muscle ischemia in postmenopausal women.

Nitroxyl Delivered by Angeli's Salt Causes Short-Lasting Activation Followed by Long-Lasting Deactivation of Meningeal Afferents in Models of Headache Generation.

The role of TRPA1 receptor channels in meningeal nociception underlying the generation of headaches is still unclear. Activating as well as inhibitory effects of TRPA1 agonists have been reported in animal models of headache. The aim of the present study was to clarify the effect of the TRPA1 agonist nitroxyl (HNO) delivered by Angeli's salt in two rodent models of meningeal nociception. Single fibre recordings were performed using half-skull preparations of mice (C57BL/6) in vitro. Angeli's salt solution (AS, 300 µM) caused short-lasting vigorous increases in neuronal activity of primary meningeal afferents, followed by deactivation and desensitisation. These effects were similar in TRPA1 knockout and even more pronounced in TRPA1/TRPV1 double-knockout mice in comparison to wild-type mice. The activity of spinal trigeminal neurons with afferent input from the dura mater was recorded in vivo in anesthetised rats. AS (300 µM) or the TRPA1 agonist acrolein (100 and 300 µM) was applied to the exposed dura mater. AS caused no significant changes in spontaneous activity, while the mechanically evoked activity was reduced after acrolein application. These results do not confirm the assumption that activation of trigeminal TRPA1 receptor channels triggers the generation of headaches or contributes to its aggravation. Instead, there is evidence that TRPA1 activation may have an inhibitory function in the nociceptive trigeminal system.

Expanding the spectrum of polydopamine antioxidant activity by nitroxide conjugation.

Polydopamine (PDA) materials are important due to their unique physicochemical properties and their potential as chemopreventive agents for diseases connected with oxidative stress. Although PDA has been suggested to display antioxidant activity, its efficacy is controversial and its mechanism of action is still unclear. Herein, we report that accurately purified PDA nanoparticles in water at pH 7.4 are unable to quench alkylperoxyls (ROO˙), which are the radicals responsible for the propagation of lipid peroxidation, despite PDA reacting with the model DPPH˙ and ABTS˙+ radicals. PDA nanoparticles prepared by copolymerization of dopamine with the dialkyl nitroxide 4-NH2TEMPO show instead good antioxidant activity, thanks to the ROO˙ trapping ability of the nitroxide. Theoretical calculations performed on a quinone-catechol dimer, reproducing the structural motive of PDA, indicate a reactivity with ROO˙ similar to catechol. These results suggest that PDA nanoparticles have an "onion-like" structure, with a catechol-rich core, which can be reached only by DPPH˙ and ABTS˙+, and a surface mainly represented by quinones. The importance of assessing the antioxidant activity by inhibited autoxidation studies is also discussed.

Cell Culture Characterization of Prooxidative Chain-Transfer Agents as Novel Cytostatic Drugs.

Prooxidative therapy is a well-established concept in infectiology and parasitology, in which prooxidative drugs like artemisinin and metronidazole play a pivotal clinical role. Theoretical considerations and earlier studies have indicated that prooxidative therapy might also represent a promising strategy in oncology. Here, we have investigated a novel class of prooxidative drugs, namely chain-transfer agents, as cytostatic agents in a series of human tumor cell lines in vitro. We have found that different chain-transfer agents of the lipophilic thiol class (like dodecane-1-thiol) elicited half-maximal effective concentrations in the low micromolar range in SY5Y cells (human neuroblastoma), Hela cells (human cervical carcinoma), HEK293 cells (immortalized human kidney), MCF7 cells (human breast carcinoma), and C2C12 cells (mouse myoblast). In contrast, HepG2 cells (human hepatocellular carcinoma) were resistant to toxicity, presumably through their high detoxification capacity for thiol groups. Cytotoxicity was undiminished by hypoxic culture conditions, but substantially lowered after cellular differentiation. Compared to four disparate, clinically used reference compounds in vitro (doxorubicin, actinomycin D, 5-fluorouracil, and hydroxyurea), chain-transfer agents emerged as comparably potent on a molar basis and on a maximum-effect basis. Our results indicate that chain-transfer agents possess a promising baseline profile as cytostatic drugs and should be explored further for anti-tumor chemotherapy.

Synthesis and Biological Evaluation of Cyclic Analogues from Nitrone LQB-278: A New Potential Antileukemia Compound.

BACKGROUND/AIM: A new set of LQB-nitrones and analogues was synthesized to evaluate anticancer activity based on the substitution of the terpenyl moiety of the antileukemic compound LQB-278 by the conformationally restricted cinnamyl ether. MATERIALS AND METHODS: A structure-activity relationship study was performed in vitro on Jurkat cells to screen the antileukemic activity of LQB-nitrones and analogues and elucidate the mechanisms of action of the most active derivatives. RESULTS: The cynamyl ramification and its ortho position aldehyde substitution improved the antileukemic activity. Three compounds showed an in vitro antiproliferative action, but only 5b induced apoptosis. Analysis of the molecular mechanisms showed increased expression of the cell cycle inhibitor p21CIP1/WAF1/Sdi1, caspase 3, Fas receptor, and Bax/Bcl-2 ratio. CONCLUSION: The cinnamyl derivative 5b (LQB-461) presented higher antileukemic effects than the prototype terpenyl nitrone, inducing Jurkat cell death by activating both extrinsic and intrinsic pathways of apoptosis. Therefore, this compound is a new promising candidate drug against leukemia.

The potent radioprotective agents: Novel nitronyl nitroxide radical spin-labeled resveratrol derivatives.

It is commonly known that radiotherapy is still a key modality for treatment of cancer. Though this effect is desirable during radiotherapy, it leads to radiotoxicity on normal healthy cells. In the present research, we designed, synthesized and analyzed a series of nitronyl nitroxide radical (NITR) spin-labeled resveratrol (RES) derivatives. The cytotoxicity of the newly synthesized substances was tested on Jurkat T cells. The derivatives were studied as reactive oxygen species (ROS) scavenger to protect ionizing radiation of Jurkat T cells upon 6 Gy X-irradiation. The experimental results revealed that compound 2 and 3 could significantly alleviate the damage of Jurkat T cells, as evidenced by decreasing ROS production and restoring the cell apoptosis. Further mechanism investigations indicated that the radioprotective effects of the novel derivatives were largely associated with modulating the expression of apoptotic proteins including cIAP-1, cIAP-2, cytochrome c, caspase-3 and caspase-9. Based on the experimental result, we disclosed that the novel NITR spin-labeled RES derivatives exhibit the potential to be used as the novel radioprotective candidates to ameliorate the injury induced by ionizing radiation.

Putative Role of Ligands of DNIC in the Physiological Action of the Complex.

In a relatively isolated system of avian embryo, the metabolism of NO, a component of the dinitrosyl iron complexes (DNIC), the main NO donor in most tissues, depends on the ligands that make up the complex. This fact corroborates the earlier hypothesis that these ligands perform a regulatory function in NO metabolism. It is also shown that nitrite injected into the embryo is not oxidized to nitrate like NO in DNIC, but is accumulated outside the amniotic sac. Normally, nitrite is present in an embryo in trace amounts. These facts suggest that NO in the embryo is transferred from the donor molecule to a target in the embryo tissues further transformed with minimum oxidation to nitrite.

Effects of albumin-bound nitrosyl iron complex with thiosulfate ligands on lipid peroxidation and activities of mitochondrial enzymes in vitro.

Nitric oxide (NO) mediates diverse physiological processes in living organisms. Small molecular NO donors usually lack stability and have a short half-life in human tissues, limiting the therapeutic application. The anionic tetranitrosyl iron complex with thiosulfate ligands (TNIC) is one of the most promising NO donors. This study shows that bovine serum albumin (BSA) can effectively stabilize the TNIC complex under aerobic (physiological) conditions, which contributes to its prolonged action as NO donor. Our results demonstrated that TNIC-BSA inhibits formation of TBARS - standard biomarker for the lipid peroxidation induced oxidative stress. Also, it was found that TNIC-BSA inhibits the catalytic activity of mitochondrial membrane-bound enzymes: cytochrome c oxidase and monoamine oxidase A. Together, these results demonstrate that, stabilization of TNIC with BSA opens up the possibility of its practical application in chemotherapy of socially significant diseases.