Cytoprotective Effects of Dinitrosyl Iron Complexes on Viability of Human Fibroblasts and Cardiomyocytes

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.

Dietary nitrate accelerates the healing of infected skin wounds in mice by increasing microvascular density

As skin injuries resulting from acute trauma, burns, and chronic diseases present significant challenges to healthcare systems worldwide, the promotion of skin wound healing remains an unmet therapeutic area. Dietary nitrate serves as a crucial pathway for the production of nitric oxide, which plays various physiological roles in the body, including vasodilation, increased blood flow, and antioxidant activity. However, the impact of dietary nitrate on skin wound healing remains uncertain. This study aimed to investigate the role of dietary nitrate in infected skin wound healing using a mouse model. We created a full-thickness wound infection model in mice and examine the effects of dietary nitrate (0.5 mmol/kg/d and 1 mmol/kg/d) on wound healing. The results demonstrated that dietary nitrate significantly increased serum nitrate and nitrite levels, leading to accelerated wound healing by increasing microvascular density, promoting collagen deposition and re-epithelialization. Moreover, nitrate supplementation exhibited a certain degree of reduction in inflammatory factors within the body. Our study also found that 1 mmol/kg/d nitrate has a more effective therapeutic effect and can increase blood perfusion and expedite the formation of new blood vessels, thereby promoting skin wound healing. These results indicate that dietary nitrate presents a novel therapeutic approach for infected skin wound healing.

Histidine-Bound Dinitrosyl Iron Complexes: Antioxidant and Antiradical Properties

Dinitrosyl iron complexes (DNICs) are important physiological derivatives of nitric oxide. These complexes have a wide range of biological activities, with antioxidant and antiradical ones being of particular interest and importance. We studied the interaction between DNICs associated with the dipeptide L-carnosine or serum albumin and prooxidants under conditions mimicking oxidative stress. The ligands of these DNICs were histidine residues of carnosine or His39 and Cys34 in bovine serum albumin. Carnosine-bound DNICs reduced the level of piperazine free radicals in the reaction system containing tert-butyl hydroperoxide (t-BOOH), bivalent iron ions, a nitroxyl anion donor (Angeli's salt), and HEPES buffer. The ability of carnosine DNICs to intercept organic free radicals produced from t-BOOH decay could lead to this effect. In addition, carnosine DNICs reacted with the superoxide anion radical (O2•-) formed in the xanthine/xanthine oxidase enzymatic system. They also reduced the oxoferryl form of the heme group formed in the reaction of myoglobin with t-BOOH. DNICs associated with serum albumin were found to be rapidly destroyed in a model system containing metmyoglobin and t-BOOH. At the same time, these protein DNICs inhibited the t-BOOH-induced oxidative degradation of coenzymes Q9 and Q10 in rat myocardial homogenate. The possible mechanisms of the antioxidant and antiradical action of the DNICs studied and their role in the metabolism of reactive oxygen and nitrogen species are discussed.

Inflammation, dysregulated iron metabolism, and cardiovascular disease

Iron is an essential trace element associated with both pathologic deficiency and toxic overload. Thus, systemic and cell iron metabolism are highly controlled processes regulated by protein expression and localization, as well as turnover, through the action of cytokines and iron status. Iron metabolism in the heart is challenging because both iron overload and deficiency are associated with cardiac disease. Also associated with cardiovascular disease is inflammation, as many cardiac diseases are caused by or include an inflammatory component. In addition, iron metabolism and inflammation are closely linked. Hepcidin, the master regulator of systemic iron metabolism, is induced by the cytokine IL-6 and as such is among the acute phase proteins secreted by the liver as part of the inflammatory response. In an inflammatory state, systemic iron homeostasis is dysregulated, commonly resulting in hypoferremia, or low serum iron. Less well characterized is cardiac iron metabolism in general, and even less is known about how inflammation impacts heart iron handling. This review highlights what is known with respect to iron metabolism in the heart. Expression of iron metabolism-related proteins and processes of iron uptake and efflux in these cell types are outlined. Evidence for the strong co-morbid relationship between inflammation and cardiac disease is also reviewed. Known connections between inflammatory processes and iron metabolism in the heart are discussed with the goal of linking inflammation and iron metabolism in this tissue, a connection that has been relatively under-appreciated as a component of heart function in an inflammatory state. Therapeutic options connecting inflammation and iron balance are emphasized, with the main goal of this review being to bring attention to alterations in iron balance as a component of inflammatory diseases of the cardiovascular system.

Positive (Regulatory) and Negative (Cytotoxic) Effects of Dinitrosyl Iron Complexes on Living Organisms

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.

Effect of solvents and glutathione on the decomposition of the nitrosyl iron complex with N-ethylthiourea ligands: An experimental and theoretical study

Dinitrosyl iron complexes (DNICs) are a depot and potential source of free NO in organisms. Their synthetic analog, N-ethylthiourea DNIC [Fe(SC(NH₂)(NHC₂H₅))₂(NO)₂]⁺Cl^-∙[Fe(SC(NH₂)(NHC₂H₅))Cl(NO)₂]⁰ (complex 1), as cardioprotective and cytostatic agent is a promising prodrug for the treatment of socially relevant diseases. In this work, transformation mechanism of complex 1 has been studied in anaerobic aqueous solution (pH = 7.0), DMSO, and ethanol. It was shown that the solvent has a significant effect on the decomposition of complex. According to EPR-spectroscopy, only cationic part of complex is found upon its dissolution in water; only neutral part is retained in DMSO, and both fragments are present in ethanol. Effective generation of NO occurs in an aqueous solution. The structures of the decomposition products were proposed for all solvents, their UV-spectra and rate constants were calculated. From the experimental and theoretical data obtained, it follows that complex 1 is most stable in DMSO. Solutions of complex in a DMSO-water mixture can be used to improve its bioavailability in further in vitro and in vivo studies. Also, we have analyzed its interaction with glutathione (GSH), which can participate in the metabolism of this compound. This study shows that complex 1 reacts with GSH to form a new binuclear DNIC with two GS^--ligands. It was found that the resulting complex is a more prolonged NO-donor than the initial one: k = 6.1∙10^-3·s^-1 in buffer, k = 6.4∙10^-5 s^-1 with GSH. This reaction may prevent S-glutathionylation of the essential enzyme systems and is important for metabolism of complex, associated with its antitumor activity.

Albumin as a prospective carrier of the nitrosyl iron complex with thiourea and thiosulfate ligands under aerobic conditions

High-molecular-weight dinitrosyl iron complexes (DNICs) are formed in living systems and are a stable depot of nitrogen monoxide (NO). In this work, using experimental and theoretical methods, we investigated the interaction of their synthetic analog, a promising cardiotropic complex of the composition [Fe(SC(NH₂)₂)₂(NO)₂]₂[Fe₂(S₂O₃)₂(NO)₄], with bovine serum albumin (BSA) in aqueous aerobic solutions. We suggested that, under these conditions, the decomposition product of the initial complex with oxygen, the [Fe(NO)(NO₂)]⁺ fragment, can bind in the hydrophobic pocket of the protein. As a result of this interaction, high-molecular-weight Fe(Cys34)(His39)(NO)(NO₂) is formed. The binding constant of the complex with protein measured by the quenching of intrinsic fluorescence of BSA is 7.2 × 10⁵ M^-1. According to EPR and UV-spectroscopy data, the interaction of the complex with the protein leads to its significant stabilization. In addition to coordination binding, the studied complex can be adsorbed onto the protein surface due to weak intermolecular interactions, resulting in the prolonged generation of NO.

Role of GSH and Iron-Sulfur Glutaredoxins in Iron Metabolism-Review

Glutathione (GSH) was initially identified and characterized for its redox properties and later for its contributions to detoxification reactions. Over the past decade, however, the essential contributions of glutathione to cellular iron metabolism have come more and more into focus. GSH is indispensable in mitochondrial iron-sulfur (FeS) cluster biosynthesis, primarily by co-ligating FeS clusters as a cofactor of the CGFS-type (class II) glutaredoxins (Grxs). GSH is required for the export of the yet to be defined FeS precursor from the mitochondria to the cytosol. In the cytosol, it is an essential cofactor, again of the multi-domain CGFS-type Grxs, master players in cellular iron and FeS trafficking. In this review, we summarize the recent advances and progress in this field. The most urgent open questions are discussed, such as the role of GSH in the export of FeS precursors from mitochondria, the physiological roles of the CGFS-type Grx interactions with BolA-like proteins and the cluster transfer between Grxs and recipient proteins.