Dinitrosyl Iron Complexes Research Articles

Homeostatic nanomedicine: Protein S-nitrosylation dyshomeostasis dominated oncotherapy based on a tumor-microenvironment-activated nanoparticle

Nitric oxide (NO) holds promise as a therapeutic agent in oncotherapy, yet its efficacy is hindered by low bioavailability, concentration-dependency, and tumor resistance to nitrosative stress. To overcome these limitations, herein, we propose a novel strategy aimed at specifically breaking the protein S-nitrosylation homeostasis of tumors. An acid-responsive nanoplatform comprising amorphous iron / mesoporous silica (AMSP) is constructed to orchestrate synergistic anti-tumor effect of Fe2+ and NO. Activating by the tumor microenvironment, nanopores of AMSP facilitate the in-situ generation of dinitrosyl iron complexes, promoting the physiological stability of NO and protein S-nitrosylation via transnitrosylation. Moreover, the released Fe2+ accelerate reactive oxygen species accumulation in tumor cells, which not only derives stronger nitrating reagents, but also inhibits the denitrosylation reaction triggered by tumor-expressed reducing species. The multiple effects of AMSP induce excessive cellular S-nitrosylation, thereby guiding an untraditional apoptotic pathway, glyceraldehyde-3-phosphate dehydrogenase S-nitrosylation mediated nuclear translocation and protein degradation. Overall, our findings offer a new paradigm of homeostatic nanomedicine, potentially advancing oncotherapy modalities.

Mechanisms of the Formation and Function of Dinitrosyl Iron Complexes as a “Working Form” of Nitric Oxide in Living Organisms

It has been proposed that only the introduction of endogenous nitric oxide (NO) into dinitrosyl iron complexes (DNIC) or S-nitrosothiols (RS-NO) can ensure stabilization of NO that is critical for operating in an auto/paracrine manner as a regulator of biological processes in living organisms. Without this introduction, the majority of endogenous NO disappears due to aggressive intra/intercellular environment thereby eliminating it from metabolic processes. Administration of exogenous NO in human and animal organisms (the only possible route of administration is via inhalation when it is in the gaseous state) does not lead to formation of DNIC or RS-NO in blood or other tissues. Hence, the majority of exogenous NO during its inhalation is converted into nitrosonium cations (NO+), the emergence of which is evidenced by their conversion into RS-NO when various thiol-containing compounds are administered to animal blood concomitantly. In turn, RS-NO formation in those animals was manifested by hypotensive effect on them. NO molecule transformation into nitrosonium cations may also occur during DNIC formation induced by a disproportionation reaction of endogenous NO molecules binding with Fe2+ ions in pairs. Subsequent binding of Fe(NO)2 groups to thiol-containing ligands that occur during this reaction promotes formation of rather stable DNICs that act as donors of both neutral molecules of NO and nitrosonium cations (NO+) in living organisms. The transfer of NO and NO+ to targets for nitrosation reactions occurs by the interaction of low molecular DNICs with heme groups of heme-containing proteins (for example, guanylate cyclase) or thiol groups in low molecular or protein thiol-containing compounds. This paper presents different results of NO and NO+ transfer in living organisms disussing both positive, regulatory and negative, toxic effects of it.

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.

The influence of exogenous and endogenous nitric oxide on the human and animal body

It has been shown that the inhalation of gaseous NO (exogenous nitric oxide) leads to the formation of nitrosonium cations (NO+) in the circulating blood of humans and animals during the oxidation of NO, which can have a detrimental effect on pathogenic viruses and bacteria. When thiols enter the blood simultaneously with NO inhalation, they form S-nitrosothiols with NO+ and cause hypotensive effect in animals. The biological effect of endogenous NO, which is produced in cells and tissues with the participation of NO synthases in animals and humans, is mediated by the dinitrosyl iron complexes (DNIC) formed with thiol-containing ligands. As NO and NO+ donors, these complexes have a variety of regulatory and cytotoxic effects on the animal and human body. In particular, the NO+ released by DNIC was shown to suppress SARS-CoV-2 infection in Syrian hamsters.

Reactivity of Thiolate and Hydrosulfide with a Mononuclear {FeNO}7 Complex Featuring a Very High N-O Stretching Frequency.

Synthesis, characterization, electronic structure, and redox reactions of a mononuclear {FeNO}7 complex with a very high N-O stretching frequency in solution are presented. Nitrosylation of [(LKP)Fe(DMF)]2+ (1) (LKP = tris((1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methyl)amine) produced a five-coordinate {FeNO}7 complex, [(LKP)Fe(NO)]2+ (2). While complex 2 could accommodate an additional water molecule to generate a six-coordinate {FeNO}7 complex, [(LKP)Fe(NO)(H2O)]2+ (3), the coordinated H2O in 3 dissociates to generate 2 in solution. The molecular structure of 2 features a nearly linear Fe-N-O unit with an Fe-N distance of 1.744(4) Å, N-O distance of 1.162(5) Å, and <Fe-N-O angle of 178.3°, while that of 3 features a slightly bent Fe-N-O unit with an Fe-N distance of 1.750(5) Å, N-O distance of 1.157(6) Å, and <Fe-N-O angle of 173.3°. Complex 2 displays a very high N-O stretching frequency of 1844 cm-1 in dichloromethane and readily dissociates NO when dissolved in coordinating solvents such as acetonitrile or N,N-dimethylformamide. Investigation of the reduction of 2 by FTIR-SEC and EPR spectroscopy shows the generation of a {Fe(NO)2}9 species, and the results have been corroborated by electronic structure calculations. Furthermore, the reaction of 2 with bezenethiolate (PhS-) and hydrosulfide (HS-) allowed the unambiguous characterization of a dinitrosyl iron complex (DNIC), [Fe(SPh)2(NO)2]1-, and an unprecedented complex, [{(LKP)Fe(DMF)}2{Fe6S6(NO)6}]2+, featuring an iron-sulfur prismane dianion.

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.

Mechanistic and Kinetic Insights into Cellular Uptake of Biomimetic Dinitrosyl Iron Complexes and Intracellular Delivery of NO for Activation of Cytoprotective HO-1.

Dinitrosyl iron unit (DNIU), [Fe(NO)2], is a natural metallocofactor for biological storage, delivery, and metabolism of nitric oxide (NO). In the attempt to gain a biomimetic insight into the natural DNIU under biological system, in this study, synthetic dinitrosyl iron complexes (DNICs) [(NO)2Fe(μ-SCH2CH2COOH)2Fe(NO)2] (DNIC-COOH) and [(NO)2Fe(μ-SCH2CH2COOCH3)2Fe(NO)2] (DNIC-COOMe) were employed to investigate the structure-reactivity relationship of mechanism and kinetics for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective heme oxygenase (HO)-1. After rapid cellular uptake of dinuclear DNIC-COOMe through a thiol-mediated pathway (tmax = 0.5 h), intracellular assembly of mononuclear DNIC [(NO)2Fe(SR)(SCys)]n-/[(NO)2Fe(SR)(SCys-protein)]n- occurred, followed by O2-induced release of free NO (tmax = 1-2 h) or direct transfer of NO to soluble guanylate cyclase, which triggered the downstream HO-1. In contrast, steady kinetics for cellular uptake of DNIC-COOH via endocytosis (tmax = 2-8 h) and for intracellular release of NO (tmax = 4-6 h) reflected on the elevated activation of cytoprotective HO-1 (∼50-150-fold change at t = 3-10 h) and on the improved survival of DNIC-COOH-primed mesenchymal stem cell (MSC)/human corneal endothelial cell (HCEC) under stressed conditions. Consequently, this study unravels the bridging thiolate ligands in dinuclear DNIC-COOH/DNIC-COOMe as a switch to control the mechanism, kinetics, and efficacy for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective HO-1, which poses an implication on enhanced survival of postengrafted MSC for advancing the MSC-based regenerative medicine.

Electronic Structure and Transformation of Dinitrosyl Iron Complexes (DNICs) Regulated by Redox Non-Innocent Imino-Substituted Phenoxide Ligand.

The coupled NO-vibrational peaks [IR νNO 1775 s, 1716 vs, 1668 vs cm-1 (THF)] between two adjacent [Fe(NO)2] groups implicate the electron delocalization nature of the singly O-phenoxide-bridged dinuclear dinitrosyliron complex (DNIC) [Fe(NO)2(μ-ON2Me)Fe(NO)2] (1). Electronic interplay between [Fe(NO)2] units and [ON2Me]- ligand in DNIC 1 rationalizes that "hard" O-phenoxide moiety polarizes iron center(s) of [Fe(NO)2] unit(s) to enforce a "constrained" π-conjugation system acting as an electron reservoir to bestow the spin-frustrated {Fe(NO)2}9-{Fe(NO)2}9-[·ON2Me]2- electron configuration (Stotal = 1/2). This system plays a crucial role in facilitating the ligand-based redox interconversion, working in harmony to control the storage and redox-triggered transport of the [Fe(NO)2]10 unit, while preserving the {Fe(NO)2}9 core in DNICs {Fe(NO)2}9-[·ON2Me]2- [K-18-crown-6-ether)][(ON2Me)Fe(NO)2] (2) and {Fe(NO)2}9-[·ON2Me] [(ON2Me)Fe(NO)2][PF6] (3). Electrochemical studies suggest that the redox interconversion among [{Fe(NO)2}9-[·ON2Me]2-] DNIC 3 ↔ [{Fe(NO)2}9-[ON2Me]-] ↔ [{Fe(NO)2}9-[·ON2Me]] DNIC 2 are kinetically feasible, corroborated by the redox shuttle between O-bridged dimerized [(μ-ONMe)2Fe2(NO)4] (4) and [K-18-crown-6-ether)][(ONMe)Fe(NO)2] (5). In parallel with this finding, the electronic structures of [{Fe(NO)2}9-{Fe(NO)2}9-[·ON2Me]2-] DNIC 1, [{Fe(NO)2}9-[·ON2Me]2-] DNIC 2, [{Fe(NO)2}9-[·ON2Me]] DNIC 3, [{Fe(NO)2}9-[ONMe]-]2 DNIC 4, and [{Fe(NO)2}9-[·ONMe]2-] DNIC 5 are evidenced by EPR, SQUID, and Fe K-edge pre-edge analyses, respectively.

Insight into the relevance of dinitrosyl iron complex (DNIC) formation in the absence of thiols in aqueous media.

DNIC can be formed in aqueous media in the absence of thiols via mechanisms that depend exclusively on Fe(II) and NO. However, these reactions do not take place at intracellular concentrations of Fe(II) and NO, reinforcing the relevance of thiols to assist Fe(II) to Fe(I) reduction during DNIC formation in biological media.

Dinitrosyl Iron Complex-Derived Nanosized Zerovalent Iron (NZVI) as a Template for the Fe-Co Cracked NZVI: An Electrocatalyst for the Oxygen Evolution Reaction.

Nanosized zerovalent iron (NZVI) Fe@Fe3O4 with a core-shell structure derived from photocatalytic MeOH aqueous solution of dinitrosyl iron complex (DNIC) [(N3MDA)Fe(NO)2] (N3MDA = N,N-dimethyl-2-(((1-methyl-1H-imidazole-2-yl)methylene)amino)ethane-1-amine) (1-N3MDA), eosin Y, and triethylamine (TEA) is demonstrated. The NZVI Fe@Fe3O4 core shows a high percentage of zerovalent iron (Fe0 %) and is stabilized by a hydrophobic organic support formed through the photodegradation of eosin Y hybridized with the N3MDA ligand. In addition to its well-known reductive properties in wastewater treatment and groundwater remediation, NZVI demonstrates the ability to form heterostructures when it interacts with metal ions. In this research, Co2+ is employed as a model contaminant and reacted with NZVI Fe@Fe3O4 to result in the formation of a distinct Fe-Co heterostructure, cracked NZVI (CNZVI). The slight difference in the standard redox potentials between Fe2+ and Co2+, the magnetic properties of Co2+, and the absence of surface hydroxides of Fe@Fe3O4 enable NZVI to mildly reduce Co2+ and facilitate Co2+ penetration into the iron core. Taking advantage of the well-dispersed nature of CNZVI on an organic support, the reduction in particle size due to Co2+ penetration, and Fe-Co synergism, CNZVI is employed as a catalyst in the alkaline oxygen evolution reaction (OER). Remarkably, CNZVI exhibits a highly efficient OER performance, surpassing the benchmark IrO2 catalyst. These findings show the potential of using NZVI as a template for synthesizing highly efficient OER catalysts. Moreover, the study demonstrates the possibility of repurposing waste materials from water treatment as valuable resources for catalytic energy conversion, particularly in water oxidation processes.

Why gaseous nitric oxide inhalation does not influence on systemic arterial pressure in human and animal organisms?

The reason has been elucidated why gaseous nitric oxide inhalation does not produce hypotensive effect in human and animal organisms. The defect was completely removed when low molecular thiol solutions were added by intravenous pathway simultaneously with gaseous NO inhalation into the animals (rats). The proposition was made that gaseous NO molecules including through the lungs into the circulation of the blood are transformed as a result of one-electron mechanism oxidation into nitosonium cation (NO+) which are not capable of vasodilating and thereby hypotensive action on men and animals. NO+ cation binding with low molecular thiols results in the S-nitrosothiol (RS-NO) formation with following release of the nitrosyl component from the RS-NO in the form of neutral NO molecule characterized with hypotensive activity. The formation of another NO donor - dinitrosyl iron complexes with thiol-containing ligands did not occur in the animals. Hypotensive action observed in lungs could be determined by gaseous NO penetration trough external vascular wall followed by the activation of vasodilation and hypotensia inductor - guanylate cyclase enzyme immediately inside of vascular walls.

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.

DNIC is a Structure Providing Specificity of Physiological Effects of NO.

Metabolism of nitric oxide (NO) donors: dinitrosyl iron complexes (DNIC), nitrosothiols (RSNO), and nitroprusside was studied on a chick embryo model. The obtained results give reason to assume that DNIC constituting the main pool of nitroso compounds in the vast majority of tissues are NO donors immediately interacting with the physiological target of NO, and other NO donors can perform this function after their transformation into DNIC. NO is released from DNIC not spontaneously, but under a joint influence of a factor destroying the complex and a target having chemical affinity for NO. A similar mechanism is apparently implicated in NO passage through the cell membrane.

Dinityrosyl Iron Complexes with Thiol-Containing Ligands as a Functionally Active “Working Form” of Nitric Oxide System in Living Organisms: A Review

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.

Evaluation of NO Release Capability from Dinitrosyl Iron Complexes (DNIC) Containing Biomolecules as Ligands in Aqueous Media

Evaluation of NO Release Capability from Dinitrosyl Iron Complexes (DNIC) Containing Biomolecules as Ligands in Aqueous Media

Dinityrosyl Iron Complexes with Thiol-Containg Ligands as a Funcionally Active “Working Form” of Nitric Oxide System in Living Organisms

The experimental data are summarized which allow to suggest that dinitrosyl iron complexes (DNIC) with thiol-containing ligands can be considered as an endogenous “working form” of nitric oxide (NO) system in living organisms. The complexes can function as donors of both neutral NO molecules as well as nitrosonium cations (NO+) which exert respectively positive (regulatory) or negative (cytotoxic) effect on human and animal organisms. A special attention is paid to DNIC capacity to block (especially in combination with dithiocarbamate derivatives) coronavirus SARS-CoV-2 infection in Syrian hamsters.

The reaction of glutathione-derived dinitrosyl iron complex and superoxide radical anion - the detection and quantitation of peroxynitrite

The reaction of glutathione-derived dinitrosyl iron complex and superoxide radical anion - the detection and quantitation of peroxynitrite

The Effect of Peroxynitrite and tert-Butyl Hydroperoxide on Thiol Ligands of Dinitrosyl Iron Complexes

The Effect of Peroxynitrite and tert-Butyl Hydroperoxide on Thiol Ligands of Dinitrosyl Iron Complexes

Ligand Control of Dinitrosyl Iron Complexes for Selective Superoxide-Mediated Nitric Oxide Monooxygenation and Superoxide-Dioxygen Interconversion.

Through nitrosylation of [Fe-S] proteins, or the chelatable iron pool, a dinitrosyl iron unit (DNIU) [Fe(NO)2] embedded in the form of low-molecular-weight/protein-bound dinitrosyl iron complexes (DNICs) was discovered as a metallocofactor assembled under inflammatory conditions with elevated levels of nitric oxide (NO) and superoxide (O2-). In an attempt to gain biomimetic insights into the unexplored transformations of the DNIU under inflammation, we investigated the reactivity toward O2- by a series of DNICs [(NO)2Fe(μ-MePyr)2Fe(NO)2] (1) and [(NO)2Fe(μ-SEt)2Fe(NO)2] (3). During the superoxide-induced conversion of DNIC 1 into DNIC [(K-18-crown-6-ether)2(NO2)][Fe(μ-MePyr)4(μ-O)2(Fe(NO)2)4] (2-K-crown) and a [Fe3+(MePyr)x(NO2)y(O)z]n adduct, stoichiometric NO monooxygenation yielding NO2- occurs without the transient formation of peroxynitrite-derived •OH/•NO2 species. To study the isoelectronic reaction of O2(g) and one-electron-reduced DNIC 1, a DNIC featuring an electronically localized {Fe(NO)2}9-{Fe(NO)2}10 electronic structure, [K-18-crown-6-ether][(NO)2Fe(μ-MePyr)2Fe(NO)2] (1-red), was successfully synthesized and characterized. Oxygenation of DNIC 1-red leads to the similar assembly of DNIC 2-K-crown, of which the electronic structure is best described as paramagnetic with weak antiferromagnetic coupling among the four S = 1/2 {FeIII(NO-)2}9 units and S = 5/2 Fe3+ center. In contrast to DNICs 1 and 1-red, DNICs 3 and [K-18-crown-6-ether][(NO)2Fe(μ-SEt)2Fe(NO)2] (3-red) display a reversible equilibrium of "3 + O2- ⇋ 3-red + O2(g)", which is ascribed to the covalent [Fe(μ-SEt)2Fe] core and redox-active [Fe(NO)2] unit. Based on this study, the supporting/bridging ligands in dinuclear DNIC 1/3 (or 1-red/3-red) control the selective monooxygenation of NO and redox interconversion between O2- and O2 during reaction with O2- (or O2).

Effect of Peroxynitrite and &lt;i&gt;tert&lt;/i&gt;-Butyl Hydroperoxide on Thiol Ligands of Dinitrosyl Iron Complexes

Low molecular weight dinitrosyl iron complexes (DNICs) with thiol-containing ligands are a physiological form for deposit and transport of nitric oxide (NO) in the organism, herewith DNICs can exhibit antioxidant and antiradical properties. It was that DNICs containing cysteine, glutathione and lipoic acid as ligands, decreased the rate of dihydrodamine oxidation by peroxynitrite formed during 3-morpholinononymine decomposition. Thiol (sulfhydryl) ligands are present in DNICs in the form of thiolate anions (R-S−), which protects these groups from oxidation by peroxynitrite. When tert-butyl peroxide was used as an oxidizer at low concentration, the protective effect of DNICs on their SH-groups was observed for complexes with lipoic acid (LA-DNIC) and with glutathione (GS-DNIC). LA-DNIC was more resistant to oxidizing agents and more effective peroxynitrite trap than other DNICs. DNICs associated with bovine serum albumin had a negligible protective effect on cysteine residue during oxidation by peroxynitrite and tert-butyl hydroperoxide. The obtained results allow us to consider low molecular weight DNICs with thiol ligands as peroxynitrite traps and thiol residues protectors in proteins.