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Experimental data were summarized to assume that dinitrosyl iron complexes (DNICs) with thiol-containing ligands are an endogenous "working form" of the nitric oxide (NO) system in living organisms. DNICs can function as donors of both neutral NO molecules, which are responsible for positive regulatory effects of the NO system on various physiological and biochemical processes in humans and animals, and nitrosonium cations (NO^(+)), which are responsible mostly for negative cytotoxic activity of the system. Special attention is paid to the finding that DNICs, especially in combination with dithiocarbamate derivatives, suppress SARS-CoV-2 infection in Syrian hamsters.

The proposed in our studies mechanism of dinitrosyl iron complex (DNIC) formation through the main step of disproportionation of two NO molecules in complex with Fe2+ ion leads to emergence of the resonance structure of dinitrosyl-iron fragment of DNIC, [Fe2+(NO)(NO + )]. The latter allowed suggesting capacity of these complexes to function as donor of both neutral NO molecules as well as nitrosonium cations (NO + ), which has been demonstrated in experiments. Analysis of biological activity of DNICs with thiol-containing ligands presented in this review demonstrates that NO molecules and nitrosonium cations released from the complexes exert respectively positive (regulatory) and negative (cytotoxic) effects on living organisms. It has been suggested to use dithiocarbamate derivatives to enhance selective release of nitrosonium cations from DNIC in living organisms followed by simultaneous incorporation of the released NO molecules into the biologically non-active mononitrosyl iron complexes with dithiocarbamate derivatives.

We announce a call for contributions to a Special Issue of Biophysical Reviews associated with the VII Congress of Russian Biophysicists (to be held in Krasnodar, Russia, 17-23 April 2023). The Congress is the main biophysical meeting held within Russia and is organized every four years. The Congress will focus on both the physical principles and mechanisms of biological processes occurring at different levels of structural organization, from molecular to cellular to organism and to population levels. The Special Issue will accept reviews on topics from molecular biophysics, structure and dynamics of biopolymers, biophysics of the cell, energy transformation mechanisms, biophotonics, ecological biophysics, and medical biophysics, following the sections of the Congress. The VII Congress of Russian Biophysicists is supported by International Union of Pure and Applied Biophysics (IUPAB). Here we describe main topics and sections of the coming event, the paper types for the journal issue, and the key deadline dates., Competing Interests: Conflict of interestThe authors declare no competing interests., (© International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany, part of Springer Nature 2022.)

A method of treatment of a new coronavirus infection COVID-19 in patients undergoing high flow oxygenation is proposed and technically implemented; the method is based on high-dose inhalation of gaseous nitric oxide (NO) with the patient's spontaneous breathing. The results of the treatment of this disease demonstrating the high efficiency of the new method are presented. A possible mechanism of the blocking effect of high doses of inhaled nitric oxide on the replication of the SARS-CoV-2 virus is discussed; it is based on the formation of dinitrosyl iron complexes in the respiratory tract and lungs of COVID-19 patients with thiol-containing ligands acting as donors of NO and nitrosonium NO + cations in a living organism that have a cytotoxic effect on the SARS CoV-2 virus., Competing Interests: Conflict of interest. The author declares that she has no conflicts of interest., (© The Author(s) 2022, ISSN 0006-3509, Biophysics, 2022, Vol. 67, No. 6, pp. 1023–1032. © The Author(s), 2022. This article is an open access publication.Russian Text © The Author(s), 2022, published in Biofizika, 2022, Vol. 67, No. 6, pp. 1251–1261.)

This study demonstrates a bacteriostatic effect of binuclear dinitrosyl iron complexes with glutathione on Escherichia coli TN300 cells. It has been quantified by the colony formation assay. The bacteriostatic effect exerted by these complexes increases considerably in the presence of diethyldithiocarbamate. Our results suggest that this effect is caused by the intense release of nitrosonium cations, NO + , from the complexes, which decompose under the action of diethyldithiocarbamate. A similar effect is observed when E. coli cells are treated with diethyldithiocarbamate 40 min after the addition of sodium nitrite or S -nitrosoglutathione. Notably, the level of dinitrosyl iron complexes observed in the bacterial cells due to the effects of sodium nitrite or S -nitrosoglutathione is almost the same as that obtained after treatment with glutathione-containing complexes. The bacteriostatic effects of the NO molecules released from nitrite or S -nitrosoglutathione during their brief interaction with bacteria were significantly smaller than the bacteriostatic effect of NO + . We deduce therefrom that the nitrosonium cations released from DNICs are responsible for the observed bacteriostatic effect of these complexes in E. coli cells., Competing Interests: Conflict of Interests. The authors declare that they have no conflicts of interest., (© Pleiades Publishing, Inc. 2022, ISSN 0006-3509, Biophysics, 2022, Vol. 67, No. 5, pp. 761–767. © Pleiades Publishing, Inc., 2022.Russian Text © The Author(s), 2022, published in Biofizika, 2022, Vol. 67, No. 5, pp. 942–950.)

The antiviral action of binuclear dinitrosyl iron complexes with glutathione along with diethyldithiocarbamate against the SARS-CoV-2 virus has been demonstrated on a Syrian hamster model after aerosol exposure of SARS-CoV-2-infected animals to the solutions of said compounds. EPR assays in analogous experiments on intact hamsters have demonstrated that the iron complexes and diethyldithiocarbamate are predominantly localized in lung tissues. These results have been compared with similar measurements on intact mice, which have shown the equal localization of these agents in both the lungs and liver. We assume that the release of the nitrosonium cations from the binuclear dinitrosyl iron complexes with glutathione occurs during their contact with diethyldithiocarbamate in the animal body. These cations caused S-nitrosation of host and viral cell proteases, leading to suppression of SARS-CoV-2 infection., Competing Interests: CONFLICT OF INTERESTThe authors declare that they have no conflicts of interest., (© The Author(s) 2022, ISSN 0006-3509, Biophysics, 2022, Vol. 67, No. 5, pp. 785–795. © The Author(s), 2022. This article is an open access publication.Russian Text © The Author(s), 2022, published in Biofizika, 2022, Vol. 67, No. 5, pp. 981–993.)

In this article we minutely discuss the so-called "oxidative" mechanism of mononuclear form of dinitrosyl iron complexes (M-DNICs) formations proposed by the author. M-DNICs are proposed to be formed from their building material-neutral NO molecules, Fe 2+ ions and anionic non-thiol (L - ) and thiol (RS - ) ligands based on the disproportionation reaction of NO molecules binding with divalent ion irons in pairs. Then a protonated form of nitroxyl anion (NO - ) appearing in the reaction is released from this group and a neutral NO molecule is included instead. As a result, M-DNICs are produced. Their resonance structure is described as [(L - ) 2 Fe 2+ (NO)(NO + )], in which nitrosyl ligands are represented by NO molecules and nitrosonium cations in equal proportions. Binding of hydroxyl ions with the latter causes conversion of these cations into nitrite anions at neutral pH values and therefore transformation of DNICs into the corresponding high-spin mononitrosyl iron complexes (MNICs) with the resonance structure described as [(L - ) 2 Fe 2+ (NO)]. In case of replacing L - by thiol-containing ligands, which are characterized by high π-donor activity, electron density transferred from sulfur atoms to iron-dinitrosyl groups neutralizes the positive charge on nitrosonium cations, which prevents their hydrolysis, ensuring relatively a high stability of the corresponding M-DNICs with the resonance structure [(RS - ) 2 Fe 2+ (NO, NO + )]. Therefore, M-DNICs with thiol-containing ligands, as well as their binuclear analogs (B-DNICs, respective resonance structure [(RS - ) 2 Fe 2+ 2 (NO, NO + ) 2 ]), can serve donors of both NO and NO + . Experiments with solutions of B-DNICs with glutathione or N-acetyl-L-cysteine (B-DNIC-GSH or B-DNIC-NAC) showed that these complexes release both NO and NO + in case of decomposition in the presence of acid or after oxidation of thiol-containing ligands in them. The level of released NO was measured via optical absorption intensity of NO in the gaseous phase, while the number of released nitrosonium cations was determined based on their inclusion in S-nitrosothiols or their conversion into nitrite anions. Biomedical research showed the ability of DNICs with thiol-containing ligands to be donors of NO and NO + and produce various biological effects on living organisms. At the same time, NO molecules released from DNICs usually have a positive and regulatory effect on organisms, while nitrosonium cations have a negative and cytotoxic effect.

Here we demonstrate that binuclear dinitrosyl iron complexes with thiol-containing ligands (glutathione and mercaptosuccinate, B-DNIC-GSH and B-DNIC-MS, respectively) exert cytotoxic effects on MCF7 human breast cancer cells. We showed that they are mediated by nitrosonium cations released from these complexes (NO + ). This finding is supported by the cytotoxic effect of both B-DNICs on MCF7 cells evidenced to retain or was even promoted in the presence of N-Methyl-D-glucamine dithiocarbamate (MGD). MGD recruits an iron nitrosyl group [Fe(NO)] from the iron-dinitrosyl fragment [Fe(NO) 2 ] of B-DNIC-MS forming stable mononitrosyl complexes of iron with MGD and releasing NO + cations from a [Fe(NO) 2 ] fragment.

It is shown that the inhalation of gaseous nitric oxide (gNO) or sprayed aqueous solutions of binuclear dinitrosyl iron complexes with glutathione or N -acetyl-L-cysteine by animals or humans provokes no perceptible hypotensive effects. Potentially, these procedures may be useful in COVID-19 treatment. The NO level in complexes with hemoglobin in blood decreases as the gNO concentration in the gas flow produced by the Plazon system increases from 100 to 2100 ppm, so that at 2000 ppm more than one-half of the gas can be incorporated into dinitrosyl complexes formed in tissues of the lungs and respiratory tract. Thus, the effect of gNO inhalation may be similar to that observed after administration of solutions of dinitrosyl iron complexes, namely, to the presence of dinitrosyl iron complexes with thiol-containing ligands in lung and airway tissues. With regard to the hypothesis posited earlier that these complexes can suppress coronavirus replication as donors of nitrosonium cations (Biophysics 65, 818, 2020), it is not inconceivable that administration of gNO or chemically synthesized dinitrosyl iron complexes with thiol-containing ligands may help treat COVID-19. In tests on the authors of this paper as volunteers, the tolerance concentration of gNO inhaled within 15 min was approximately 2000 ppm. In tests on rats that inhaled sprayed aqueous solutions of dinitrosyl iron complexes, their tolerance dose was approximately 0.4 mmol/kg body weight., Competing Interests: Conflict of Interests.The authors declare that they have no conflict of interest., (© Pleiades Publishing, Inc. 2021, ISSN 0006-3509, Biophysics, 2021, Vol. 66, No. 1, pp. 155–163. © Pleiades Publishing, Inc., 2021.Russian Text © The Author(s), 2021, published in Biofizika, 2021, Vol. 66, No. 1, pp. 183–194.)

The appropriateness of verification of the possible antiviral effect of dinitrosyl iron complexes with thiol-containing ligands as donors of nitrosonium cations (NO + ) is argued. There is reason to hope that treatment of the human respiratory tract and lungs with sprayed solutions of dinitrosyl iron complexes with glutathione or N-acetylcysteine (NAC) ​​as NO + donors during COVID-19 infection can initiate S-nitrosylation of cellular proteases and thereby suppress viral infection., Competing Interests: Conflict of Interest. The authors declare that they have no conflicts of interest., (© Pleiades Publishing, Inc. 2020.)

The present work provides theoretical and experimental foundations for the ability of dinitrosyl iron complexes (DNICs) with thiol - containing ligands to be not only the donors of neutral NO molecules, but also the donors of nitrosonium cations (NO + ) in living organisms ensuring S-nitrosation of various proteins and low-molecular-weight compounds. It is proposed that the emergence of those cations in DNICs is related to disproportionation reaction of NO molecules, initiated by their binding with Fe 2+ ions (two NO molecules per one ion). At the same time, possible hydrolysis of iron-bound nitrosonium cations is prevented by the electron density transition to nitrosonium cations from sulfur atoms of thiol-containing ligands, which are included in the coordination sphere of iron. It allows supposing that iron in iron-nitrosyl complexes of DNICs has a d 7 electronic configuration. This supposition is underpinned by experimental data revealing that a half of nitrosyl ligands are converted into S-nitrosothiols (RSNOs) when those complexes decompose, with the other half of those ligands released in the form of neutral NO molecules., (© Springer-Verlag GmbH Austria, part of Springer Nature 2020.)

Here, I present the data testifying that the conversion of free radical NO molecules to nitrosonium ions (NO + ), which are necessary for the realization of one of NO biological effects (S-nitrosation), may occur in living organisms after binding NO molecules to loosely bound iron (Fe 2+ ions) with the subsequent mutual one-electron oxidation-reduction of NO molecules (their disproportionation). Inclusion of thiol-containing substances as iron ligands into this process prevents hydrolysis of NO + ions bound to iron thus providing the formation of stable dinitrosyl iron complexes (DNIC) with thiol ligands. Such complexes act in living organisms as donors of NO and NO + , providing stabilization and transfer of these agents via the autocrine and paracrine pathways. Without loosely bound iron (labile iron pool) and thiols participating in the DNIC formation, NO functioning as one of universal regulators of diverse metabolic processes would be impossible.

Hypochlorous acid (HOCl), one of the major precursors of free radicals in body cells and tissues, is endowed with strong prooxidant activity. In living systems, dinitrosyl iron complexes (DNIC) with glutathione ligands play the role of nitric oxide donors and possess a broad range of biological activities. At micromolar concentrations, DNIC effectively inhibit HOCl-induced lysis of red blood cells (RBCs) and manifest an ability to scavenge alkoxyl and alkylperoxyl radicals generated in the reaction of HOCl with tert -butyl hydroperoxide. DNIC proved to be more effective cytoprotective agents and organic free radical scavengers in comparison with reduced glutathione (GSH). At the same time, the kinetics of HOCl-induced oxidation of glutathione ligands in DNIC is slower than in the case of GSH. HOCl-induced oxidative conversions of thiolate ligands cause modification of DNIC, which manifests itself in inclusion of other ligands. It is suggested that the strong inhibiting effect of DNIC with glutathione on HOCl-induced lysis of RBCs is determined by their antioxidant and regulatory properties.

The possibility that binuclear dinitrosyl iron complexes with glutathione and cysteine (DNIC-GSН and B-DNIC-Cys) have a strong cytotoxic effect on the growth of endometrioid tumours (EMT) in rats with surgically induced experimental endometriosis established in our previous studies has been supported with experimental data. The increase in the DNIC-GSН or B-DNIC-Cys dose from 10 (in our previous studies) to 20 μmol/kg (after i/p administration to experimental rats) fully suppressed the growth of uterine tissues implanted onto the inner surface of the abdominal wall. At 2 μmol/kg DNIC-GSН, the median value of EMT volume increased from 0 to 15 mm 3 , while the mean size of EMT-from 55 to 77 mm 3 (data from EMT measurements in 10 experimental rats). After treatment of animals with B-DNIC with N-acetyl-L-cysteine (10 μmol/kg) known for its ability to penetrate easily through the cell membrane, the inhibiting effect on EMT growth diminished as could be evidenced from the transformation of ~30% of the implants into large-size EMT. Possible reasons for this phenomenon are discussed.

We have studied the effect of interactions between dinitrosyl iron complexes with thiol-containing ligands (DNIC-TL) and diglucamine salt of chlorine e6 (photoditazine, PD) on the rate of photosensitized oxidation of a model organic substrate - tryptophan - in the presence and absence of an amphiphilic polymer, Pluronic F127, as well as on the DNIC-TL and PD photostability. Using EPR and UV spectroscopy, we determined the rate constants for photodegradation of mono- and dinuclear DNIC-TL and PD, respectively. The presence of the photosensitizer and Pluronic F127 has been shown to have a negligible effect on the rate of photodestruction of mono- and dinuclear DNIC-TL, taking into account the changing DNIC-TL and PD concentrations in the photoexcitation conditions. At the same time, in the DNIC-TL presence, the rate of PD photodestruction increases, however, addition of Pluronic F127 leads to a decrease in the rate constant of PD photodestruction. The latter circumstance creates an opportunity for a simultaneous application of DNIC-TL and photodynamic therapy in the wound treatment without losing the PDT efficiency. Indeed, photodynamic therapy in combination with DNIC-TL facilitated skin wound healing in laboratory rats. As shown by a morphological study, application of the DNIC-TL-PD-F127 complex with the subsequent photoactivation was beneficial in reducing inflammation and stimulating regenerative processes., (Copyright © 2018. Published by Elsevier Inc.)

Therapy of wounds and inflammatory diseases with NO-containing gas flows (NO-CGF) has proved to be effective in a longterm clinical practice. Plasma-chemical generation of nitric oxide occurs from atmospheric air in Plason device. For the purpose of modification and improvement of NO-therapy, effects of various physicochemical parameters of the NO-CGF on inflammatory and reparative processes in wounds were studied. Treatment of planar full-thickness skin wounds in laboratory rats was analyzed with morphological, immunohistochemical, morphometric and statistical methods. The study showed that the Plason device and the experimental device, which differs from Plason by the NO-CGF temperature, significantly reduce inflammatory and enhance regenerative processes in the wounds. The NO-CGF with an ambient temperature generated by the experimental device has noticeably facilitated the wound healing in direct ration to a nitric oxide content and flow velocity at the area of application. Temperature did not affect the course of wound healing process. The development of a new device for NO-therapy may be of use for both physicians and patients., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The overview demonstrates how the use of only one physico-chemical approach, viz., the electron paramagnetic resonance method, allowed detection and identification of dinitrosyl iron complexes with thiol-containing ligands in various animal and bacterial cells. These complexes are formed in biological objects in the paramagnetic (electron paramagnetic resonance-active) mononuclear and diamagnetic (electron paramagnetic resonance-silent) binuclear forms and control the activity of nitrogen monoxide, one of the most universal regulators of metabolic processes in the organism. The analysis of electronic and spatial structures of dinitrosyl iron complex sheds additional light on the mechanism whereby dinitrosyl iron complex with thiol-containing ligands function in human and animal cells as donors of nitrogen monoxide and its ionized form, viz., nitrosonium ions (NO + ).

This work is aimed at exhaustive and detailed study of chemical, physical and physico-chemical characteristics of NO-containing gas flow (NO-CGF) generated by a plasma-chemical generator of Plason device, which has been used in medical practice for more than 15 years for effectively healing wound and inflammatory conditions with exogenous nitric oxide (NO-therapy). Data was obtained on spatial structure of the gas flow, and values of its local parameters in axial and radial directions, such as nitric oxide content, velocity, temperature and mass flow density of nitric oxide, providing altogether the effectiveness of treatment by the exogenous NO-therapy method, were determined experimentally and by computations. It was demonstrated that plasma-chemical synthesis of NO from atmospheric air in a low direct current (DC) arc provides a high mass flow of nitric oxide at the level of 1.6-1.8 mg/s, while in the area of impact of NO-CGF on the biological tissue, on its axis, NO content is 400-600 ppm, flow velocity about 5 m/s, nitric oxide mass flow density 0.25-0.40 mg/(s·cm 2 ), temperature 40-60 °C. Tendencies were determined for designing new devices for further experimental biological and medical research in the field of NO-therapy: lowering the temperature of NO-CGF to ambient temperature will enable variation, in experiments, of the affecting flow parameters in a wide range up to their maximum values: NO content up to 2000 ppm, velocity up to 20 m/s, nitric oxide mass flow density up to 2.5 mg/(s·cm 2 )., (Copyright © 2017. Published by Elsevier Inc.)

Two approaches to the synthesis of dinitrosyl iron complexes (DNIC) with glutathione and l-cysteine in aqueous solutions based on the use of gaseous NO and appropriate S-nitrosothiols, viz., S-nitrosoglutathione (GS-NO) or S-nitrosocysteine (Cys-NO), respectively, are considered. A schematic representation of a vacuum unit for generation and accumulation of gaseous NO purified from the NO 2 admixture and its application for obtaining aqueous solutions of DNIC in a Thunberg apparatus is given. To achieve this, a solution of bivalent iron in distilled water is loaded into the upper chamber of the Thunberg apparatus, while the thiol solution in an appropriate buffer (рН 7.4) is loaded into its lower chamber. Further steps, which include degassing, addition of gaseous NO, shaking of both solutions and formation of the Fe 2+ -thiol mixture, culminate in the synthesis of DNIC. The second approach consists in a stepwise addition of Fe 2+ salts and nitrite to aqueous solutions of glutathione or cysteine. In the presence of Fe 2+ and after the increase in рН to the physiological level, GS-NO or Cys-NO generated at acid media (pH < 4) are converted into DNIC with glutathione or cysteine. Noteworthy, irrespective of the procedure used for their synthesis DNIC with glutathione manifest much higher stability than DNIC with cysteine. The pattern of spin density distribution in iron-dinitrosyl fragments of DNIC characterized by the d 7 electronic configuration of the iron atom and described by the formula Fe + (NO + ) 2 is unique in that it provides a plausible explanation for the ability of DNIC to generate NO and nitrosonium ions (NO + ) and the peculiar characteristics of the EPR signal of their mononuclear form (M-DNIC)., (Copyright © 2017. Published by Elsevier Inc.)

It has been established that treatment of mice with sodium nitrite, S-nitrosoglutathione and the water-soluble nitroglycerine derivative isosorbide dinitrate (ISDN) as NO donors initiates in vivo synthesis of significant amounts of EPR-silent binuclear dinitrosyl iron complexes (B-DNIC) with thiol-containing ligands in the liver and other tissues of experimental mice. This effect is especially apparent if NO donors are administered to mice simultaneously with the Fe 2+ -citrate complex. Similar results were obtained in experiments on isolated liver and other mouse tissues treated with gaseous NО in vitro and during stimulation of endogenous NO synthesis in the presence of inducible NO synthase. B-DNIC appeared in mouse tissues after in vitro treatment of tissue samples with an aqueous solution of diethyldithiocarbamate (DETC), which resulted in the transfer of iron-mononitrosyl fragments from B-DNIC to the thiocarbonyl group of DETC and the formation of EPR-detectable mononitrosyl iron complexes (MNIC) with DETC. EPR-Active MNIC with N-methyl-d-glucamine dithiocarbamate (MGD) were synthesized in a similar way. MNIC-MGD were also formed in the reaction of water-soluble MGD-Fe 2+ complexes with sodium nitrite, S-nitrosoglutathione and ISDN., (Copyright © 2016. Published by Elsevier Inc.)

Subcutaneous injection of Oxacom with glutathione-bound dinitrosyl iron complex as the active principle produced a slower drop of mean BP and longer accumulation of protein-bound dinitrosyl iron complexes in whole blood and tissues than intravenous injection of this drug, while durations of hypotensive effect in both cases were practically identical. In contrast to intravenous injection of the drug, its subcutaneous administration was not characterized by a high concentration of protein-bound dinitrosyl iron complexes in the blood at the onset of experiment; in addition, accumulation of these NO forms in the lungs was more pronounced after subcutaneous injection than after intravenous one.

The material presented herein is an overview of the results obtained by our research team during the many years' study of biological activities and occurrence of dinitrosyl iron complexes (DNIC) with thiol-containing ligands in human and animal organisms. With regard to their dose dependence and vast diversity of biological activities, DNIC are similar to the system of endogenous NO, one of the most universal regulators of biological processes. The role of biologically active components in DNIC is played by their iron-dinitrosyl fragments, [Fe(NO)2], endowed with the ability to generate neutral NO molecules and nitrosonium ions (NO(+)). Their release is effected by heme-and thiol-containing proteins, which fulfill the function of biological targets and acceptors of NO and NO(+). Beneficial regulatory effects of DNIC on physiological and metabolic processes are numerous and diverse and include, among other things, lowering of arterial pressure and accelerated healing of skin wounds. In the course of fast decomposition of their Fe(NO)2 fragments (e.g., in the presence of iron chelators), DNIC produce adverse (cytotoxic) effects, which can best be exemplified by their ability to suppress the development of experimental endometriosis in animals. In animal tissues, DNIC with thiol-containing ligands are predominantly represented by the binuclear form, which, contrary to mononuclear DNIC detectable by the 2.03 signal, is EPR-silent. The ample body of evidence on biological activities and occurrence of DNIC gained so far clearly demonstrates that in human and animal organisms DNIC with thiol-containing ligands represent a "working form" of the system of endogenous NO responsible for its accumulation and stabilization in animal tissues as well as its further transfer to its biological targets., (Copyright © 2016 Elsevier Inc. All rights reserved.)

The anti-tumor activity of the binuclear form of dinitrosyl iron complexes with glutathione against Lewis lung carcinoma, found earlier upon intraperitoneal administration of the complexes, was also observed when this preparation was injected subcutaneously. A 100 μM/kg subcutaneous dose of the complex being used daily (as calculated per one iron atom in binuclear dinitrosyl iron complexes) for 10 or 15 days, inhibited the tumor growth by 43%. The effect was observed during the first two weeks after tumor transplantation. After that, the tumors began to grow at the rate equal to or even higher than that one for control animals. The mean survival time for treated mice exceeded the control values by 30%. Binuclear dinitrosyl iron complexes administered intraperitoneally was also effective against Ca-755 adenocarcinoma. However, in this case the mean survival time for treated animals increased only by 7%. The anti-tumor activity of S-nitrosoglutathione against Lewis lung carcinoma growth inhibition by 70% and Ca-755 adenocarcinoma growth inhibition by 90% was also shown. However, unlike binuclear dinitrosyl iron complexes the anti-tumor effect of S-nitrosoglutathione decreased when a daily dose of the compound increased (from 200 to 400 μM/kg) The initial anti-tumor effect of binuclear dinitrosyl iron complexes and S-nitrosoglutathione is suggested to be due to NO released from both compounds. A subsequent suppression of the effect is determined by the development of anti-nitrosative and anti-oxidant defense systems in tumors.

Earlier it has been found that the hypotensive drug Oxacom containing binuclear dinitrosyl iron complexes (B-DNIC) with glutathione can effectively decrease, as a nitric monooxide (NO) donor, the mean arterial pressure (МАР) in rats upon intravenous bolus injection in the form of an aqueous solution (Chazov et al., 2012). The aim of this study was to investigate the hypotensive effects of Oxacom administered to experimental rats by intravenous, intramuscular, subcutaneous, intraperitoneal, intragastric, rectal routes.MAP and heart rate (HR) were measured with the help of arterial catheters equipped with tensometric sensors. Oxacom was administered to rats at the dose of 2.0 μmole of B-DNIC/kg. The concentration of paramagnetic mononuclear protein-bound DNIC (М-DNIC) formed in the blood and tissues of various internal organs of the rat was determined by the EPR method. Upon subcutaneous, intramuscular or intraperitoneal administration of Oxacom, the maximum amplitude of the МАР decrease varies from 30% to 70%, respectively, in comparison with the corresponding parameter for the intravenously injected Oxacom. Another difference is the lack of the fast phase in the initial stage of the МАР decrease and the longer persistence of protein-bound M-DNIC formed in the circulating blood after intramuscular, subcutaneous or intraperitoneal administration of Oxacom. Thus, the NO donor Oxacom exerts pronounced hypotensive effects on rats not only upon intravenous, but also upon intramuscular, subcutaneous or intraperitoneal administration., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Composites of a collagen matrix and dinitrosyl iron complexes with glutathione (DNIC-GS) (in a dose of 4.0 μmoles per item) in the form of spongy sheets (DNIC-Col) were prepared and then topically applied in rat excisional full-thickness skin wound model. The effects of DNIC-Col were studied in comparison with spontaneously healing wounds (SpWH) and wounds treated with collagen sponges (Col) without DNIC-GS. The composites induced statistically and clinically significant acceleration of complete wound closure (21±1 day versus 23±1 day and 26±1 day for DNIC-Col, Col and SpWH, respectively). Histological examination of wound tissues on days 4, 14, 18 and 21 after surgery demonstrated that this improvement was supported by enhanced growth, maturation and fibrous transformation of granulation tissue and earlier epithelization of the injured area in rats treated with DNIC-Col composites benchmarked against Col and SpWH. It is suggested that the positive effect of the new pharmaceutical material on wound healing is based on the release of NO from decomposing DNIC. This effect is believed to be potentiated by the synergy of DNIC and collagen., (Copyright © 2015. Published by Elsevier B.V.)

It has been shown that dinitrosyl iron complexes with thiol-containing ligands, bound with modified bovine serum albumin with high amount of thiol groups, appeared in baker yeast or in animal tissues in the presence of exogenous or endogenous nitric oxide, respectively, are represented predominantly by EPR-silent binuclear form. This form can be transformed into EPR-active mononuclear form of dinitrosyl iron complexes with an increase in pH to basic values, into EPR-active form of mononuclear iron nitrosyl complexes in case of bielectronic recovery of the binuclear form of dinitrosyl iron complexes or under the action of dithiocarbamate derivatives. The latter induced the transformation of dinitrosyl iron complexes into EPR-active mononitrosyl iron complexes with dithiocarbamates. A significant amount of binuclear dinitrosyl iron complexes with thiol-containing ligands in living systems and identical biological activity of these complexes and endogenous nitric oxide systems allow of considering endogenous binuclear dinitrosyl iron complexes as a "working form" of endogenous nitric oxide recognized now as a universal regulator of biological processes.

Using atomic emission spectrometry and EPR analysis metal-ligand homeostasis (MLH) has been studied in epidermal cells of 954 liquidators of the Chernobyl accident and 947 healthy individuals. A possible association of the redox status with the quantitative changes in the MLH, which could be used as discriminators of oxidative/nitrosative stress, attracts special interest. Characteristic features of oxidative stress mainly related to electrogenic metals (Ca, K, Na), were found not only among the liquidators examined, but also in some healthy individuals (18.1%); this suggests the presence of oxidative/nitrosative stress of non-radiation origin. Correlation between intracellular production of nitric oxide (NO) with quantitative changes in the electrogenic metals may indicate the possible involvement of NO in the generation of an electric potential of the cell.

The dynamics of oxidative metabolism in healthy people's blood (n = 30) under the influence of gaseous nitric oxide and dinitrosyl iron complexes is explored. In all blood samples we studied lipid peroxidation intensity and malonic dialdehyde in plasma and erythrocytes, plasma antioxidant potential and activity of superoxide dismutase. During our investigations it was possible for the first time to identify the peculiarities in the responses of pro- and antioxidant blood systems in vitro to the treatment with nitrogen monoxide as the free. radical and its storage form (as a component of dinitrosyl iron complexes). So, a pronounced prooxidant effect for the gas flow from the "Plazon" apparatus moderately decreases when a tenfold dilution of a NO-containing mixture is made. Gas flow from the experimental NO-generator causes minimal prooxidant action, and injection of water solution of dinitrosyl iron complexes in blood specimens leads to an antioxidant action, as limitation of lipoperoxidation processes in plasma and stimulation of superoxide dismutase in erythrocytes.

Effective accumulation of binuclear dinitrosyl iron complexes with glutathione was shown after a subcutaneous para lymphatic injection of an aqueous solution of a dinitrosyl-iron complex into animal lung tissue at a single-dose of 2 micromoles per kilogram two times a day with a 2-h interval. Two hours later after the administration was repeated the concentration of these complexes was 16 micromoles per kilogram of tissue dropping down for the last two hours to 7 micromoles per kilogram of tissue. At one dose injection of binuclear dinitrosyl iron complexes with glutathione their concentration in 2 and 4 hours was two times lower than in the previous experiments. Presumably at the obtained concentration of dinitrosyl iron complexes a bactericidal effect in lungs can be observed against mycobacterium tuberculosis and rapidly proliferating lung tumors.

The inhibitory action of binuclear dinitrosyl iron complexes with glutathione on the growth of implanted solid tumor in BDF1 mice bearing Lewis lung carcinoma cells was found. The effect was induced by intraperitoneal injection of the binuclear dinitrosyl iron complexes to mice at a dose of 200 μM/kg daily on days 1-5 and 7-11. At the binuclear dinitrosyl iron complexes: free glutathione ratios of 1:1; and 1:10 in solutions, the inhibitory effect of the DNICs reached the level of 70% and 85%, respectively. When B-DNICs were not further infused, intensive tumor growth, a more rapid rate of tumor growth than control, was observed. The selective accumulation of DNICs as well as iron nitrosyl complexes of heme-containing proteins in tumors were detected by EPR method. The latter were found also in the tumors in control animals. Tumor growth delay in course of B-DNIC administration to the mice is supposed to be due to the elaboration of anti-nitrosative defense in tumor tissue in response to the action of NO released from B-DNIC.