Reactions of sulfur-nitrosyl iron complexes of “g=2.03” family with hemoglobin (Hb): Kinetics of Hb–NO formation in aqueous solutions

The Influence of Cationic Nitrosyl Iron Complex with Penicillamine Ligands on Model Membranes, Membrane-Bound Enzymes and Lipid Peroxidation

This paper shows the biological effects of cationic binuclear tetranitrosyl iron complex with penicillamine ligands (TNIC-PA). Interaction with a model membrane was assessed using a fluorescent probes technique. Antioxidant activity was studied using a thiobarbituric acid reactive species assay (TBARS) and a chemiluminescence assay. The catalytic activity of monoamine oxidase (MAO) was determined by measuring liberation of ammonia. Antiglycation activity was determined fluometrically by thermal glycation of albumine by D-glucose. The higher values of Stern-Volmer constants (K_SV) obtained for the pyrene located in hydrophobic regions (3.9 × 10⁴ M^-1) compared to K_SV obtained for eosin Y located in the polar headgroup region (0.9 × 10⁴ M^-1) confirms that TNIC-PA molecules prefer to be located in the hydrophobic acyl chain region, close to the glycerol group of lipid molecules. TNIC-PA effectively inhibited the process of spontaneous lipid peroxidation, due to additive contributions from releasing NO and penicillamine ligand (IC50 = 21.4 µM) and quenched luminol chemiluminescence (IC50 = 3.6 μM). High activity of TNIC-PA in both tests allows us to assume a significant role of its radical-scavenging activity in the realization of antioxidant activity. It was shown that TNIC-PA (50-1000 μM) selectively inhibits the membrane-bound enzyme MAO-A, a major source of ROS in the heart. In addition, TNIC-PA is an effective inhibitor of non-enzymatic protein glycation. Thus, the evaluated biological effects of TNIC-PA open up the possibility of its practical application in chemotherapy for socially significant diseases, especially cardiovascular diseases.

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.

Dinitrosyl Iron Complexes with Thiol-Containing Ligands Can Suppress Viral Infections as Donors of the Nitrosonium Cation (Hypothesis)

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.

Influence of hemoglobin and albumin on the NO donation effect of tetranitrosyl iron complex with thiosulfate

The effects of deoxyhemoglobin (Hb) and albumin on the NO-donor activity of the anionic tetranitrosyl iron complex with thiosulfate ligands (1) were studied for the first time. It was shown that Hb significantly stabilizes complex 1; in its presence, NO generation from the complex proceeds at a noticeably slower rate. A similar effect is observed when complex 1 is bound to albumin, in which case complex 1 decomposes 27 times slower than in the absence of albumin in the solution. The observed effects provide a prolonged action of complex 1 as NO-donor, which may enhance its potential pharmacological efficacy.

Effect of albumin on the transformation of dinitrosyl iron complexes with thiourea ligands

BSA binds the Fe(NO)₂⁺ fragment of DNIC and multiple molecules of [Fe(SC(NH₂)₂)₂(NO)₂]⁺ that prolongs NO donation by this DNIC.

Fe in biosynthesis, translocation, and signal transduction of NO: toward bioinorganic engineering of dinitrosyl iron complexes into NO-delivery scaffolds for tissue engineering

The ubiquitous physiology of nitric oxide enables the bioinorganic engineering of [Fe(NO)₂]-containing and NO-delivery scaffolds for tissue engineering.

Effects of Nitrosyl Iron Complexes with Thiocarbamide and Its Aliphatic Derivatives on Activities of Ca2+-ATPase of Sarcoplasmic Reticulum and cGMP Phosphodiesterase

We studied the effects of water-soluble cationic dinitrosyl iron complexes with thiocarbamide and its aliphatic derivatives, new synthetic analogs of natural NO donors, active centers of nitrosyl [1Fe-2S]proteins, on activities of Ca²⁺-ATPase of sarcoplasmic reticulum and cGMP phosphodiesterase. Nitrosyl iron complexes [Fe(C₃N₂H₈S)Cl(NO)₂]⁰[Fe(NO)₂(C₃N₂H₈S)₂]⁺Cl^- (I), [Fe(SC(N(CH₃)₂)₂(NO)₂]Cl (II), [Fe(SC(NH₂)₂)₂(NO)₂Cl×H₂O (III), and [Fe(SC(NH₂)₂)₂(NO)₂]₂SO₄×H₂O (IV) in a concentration of 10^-4 M completely inhibited the transporting and hydrolytic functions of Ca²⁺-ATPase. In a concentration of 10^-5 M, they inhibited active Ca²⁺ transport by 57±6, 75±8, 80±8, and 85±9% and ATP hydrolysis by 0, 40±4, 48±5, and 38±4%, respectively. Complex II reversibly and noncompetitively inhibited the hydrolytic function of Ca²⁺-ATPase (Ki=1.7×10^-6 M). All the studied iron-sulphur complexes in a concentration of 10^-4 M inhibited cGMP phosphodiesterase function. These data suggest that the studied complexes can exhibit antimetastatic, antiaggregation, vasodilatatory, and antihypertensive activities.

Reversible dissociation and ligand-glutathione exchange reaction in binuclear cationic tetranitrosyl iron complex with penicillamine

This paper describes a comparative study of the decomposition of two nitrosyl iron complexes (NICs) with penicillamine thiolic ligands [Fe₂(SC₅H₁₁NO₂)₂(NO)₄]SO₄·5H₂O (I) and glutathione- (GSH-) ligands [Fe₂(SC₁₀H₁₇N₃O₆)₂(NO)₄]SO₄·2H₂O (II), which spontaneously evolve to NO in aqueous medium. NO formation was measured by a sensor electrode and by spectrophotometric methods by measuring the formation of a hemoglobin- (Hb-) NO complex. The NO evolution reaction rate from (I)  k₁ = (4.6 ± 0.1)·10⁻³ s⁻¹ and the elimination rate constant of the penicillamine ligand k₂ = (1.8 ± 0.2)·10⁻³ s⁻¹ at 25°C in 0.05 M phosphate buffer,  pH 7.0, was calculated using kinetic modeling based on the experimental data. Both reactions are reversible. Spectrophotometry and mass-spectrometry methods have firmly shown that the penicillamine ligand is exchanged for GS⁻ during decomposition of 1.5·10⁻⁴ M (I) in the presence of 10⁻³ M GSH, with 76% yield in 24 h. As has been established, such behaviour is caused by the resistance of (II) to decomposition due to the higher affinity of iron to GSH in the complex. The discovered reaction may impede S-glutathionylation of the essential enzyme systems in the presence of (I) and is important for metabolism of NIC, connected with its antitumor activity.

Exchange of cysteamine, thiol ligand in binuclear cationic tetranitrosyl iron complex, for glutathione

This paper describes the comparative study of the decomposition of two iron nitrosyl complexes (NICs) with a cysteamine thiolate ligand {Fe₂[S(CH₂)₂NH₃]₂(NO)₄}SO₄·2.5H₂O (I) and a glutathione (GSH)-ligand, [Fe₂(SC₁₀H₁₇N₃O₆)₂(NO)₄]SO₄·2H₂O (II), which spontaneously evolve NO in aqueous medium.

Electronic and spatial structures of water-soluble dinitrosyl iron complexes with thiol-containing ligands underlying their ability to act as nitric oxide and nitrosonium ion donors

The ability of mononuclear dinitrosyl iron commplexes (M-DNICs) with thiolate ligands to act as NO donors and to trigger S-nitrosation of thiols can be explain only in the paradigm of the model of the [Fe(+)(NO(+))(2)] core ({Fe(NO)(2)}(7) according to the Enemark-Feltham classification). Similarly, the {(RS(-))(2)Fe(+)(NO(+))(2)}(+) structure describing the distribution of unpaired electron density in M-DNIC corresponds to the low-spin (S = 1/2) state with a d(7) electron configuration of the iron atom and predominant localization of the unpaired electron on MO(d(z2)) and the square planar structure of M-DNIC. On the other side, the formation of molecular orbitals of M-DNIC including orbitals of the iron atom, thiolate and nitrosyl ligands results in a transfer of electron density from sulfur atoms to the iron atom and nitrosyl ligands. Under these conditions, the positive charge on the nitrosyl ligands diminishes appreciably, the interaction of the ligands with hydroxyl ions or with thiols slows down and the hydrolysis of nitrosyl ligands and the S-nitrosating effect of the latter are not manifested. Most probably, the S-nitrosating effect of nitrosyl ligands is a result of weak binding of thiolate ligands to the iron atom under conditions favoring destabilization of M-DNIC.

Nitrosyl iron complexes--synthesis, structure and biology

Nitrosyl complexes of iron are formed in living species in the presence of nitric oxide. They are considered a form in which NO can be stored and stabilized within a living cell. Upon entering a topic in bioinorganic chemistry the researcher faces a wide spectrum of issues concerning synthetic methods, the structure and chemical properties of the complex on the one hand, and its biological implications on the other. The aim of this review is to present the newest knowledge on nitrosyl iron complexes, summarizing the issues that are important for understanding the nature of nitrosyl iron complexes, their possible interactions, behavior in vitro and in vivo, handling of the preparations etc. in response to the growing interest in these compounds. Herein we focus mostly on the dinitrosyl iron complexes (DNICs) due to their prevailing occurrence in NO-treated biological samples. This article reviews recent knowledge on the structure, chemical properties and biological action of DNICs and some mononitrosyls of heme proteins. Synthetic methods are also briefly reviewed.

A study of NO trafficking from dinitrosyl-iron complexes to the recombinant E. coli transcriptional factor SoxR

SoxR is a transcriptional factor in Escherichia coli that induces the expression of SoxS to initiate the production of enzymes in response to oxidative stress. In addition to superoxide, SoxR is also sensitive to cellular NO to produce a protein-bound dinitrosyl-iron complex (DNIC) with a characteristic electron paramagnetic resonance (EPR) signal at g(av)=2.03. Toward developing a strategy for NO sensing based on this property of SoxR, we have overexpressed and purified the recombinant His-tagged SoxR protein. Upon treatment of the purified protein under anaerobic conditions with (1) NO solution, (2) S-nitrosothiol (RSNO), and (3) chemically synthesized low molecular weight DNICs (LMW-DNICs), we have observed enhancement of the EPR signal at g(av)=2.03 from the protein-bound DNICs over time, reflecting the redistribution of NO from the NO solution, RSNO and LMW-DNICs to the SoxR. We have exploited this NO exchange to investigate the kinetics and mechanisms of release and delivery of NO from various LMW-DNICs to an isopropyl-beta-D-thiogalactopyranoside-dependent SoxR expressed in E. coli cells. These experiments revealed that the NO from RSNO and LMW-DNICs could cross the biological membrane and enter the cytoplasm of the cell to form the SoxR protein-bound DNIC complex. For comparison, we have also studied the direct NO transfer from the LMW-DNICs to the SoxR protein in buffer. The NO transfer was found to be rapid. From the kinetic data derived, we showed that LMW-DNICs with bidentate thiolate ligands displayed greater stability in aqueous solution but exhibited more facile NO delivery to cytoplasmic SoxR in whole cells.