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.

Antiglycation and Antioxidant Effect of Nitroxyl towards Hemoglobin

Donors of nitroxyl and nitroxyl anion (HNO/NO⁻) are considered to be promising pharmacological treatments with a wide range of applications. Remarkable chemical properties allow nitroxyl to function as a classic antioxidant. We assume that HNO/NO⁻ can level down the non-enzymatic glycation of biomolecules. Since erythrocyte hemoglobin (Hb) is highly susceptible to non-enzymatic glycation, we studied the effect of a nitroxyl donor, Angeli’s salt, on Hb modification with methylglyoxal (MG) and organic peroxide―tert-butyl hydroperoxide (t-BOOH). Nitroxyl dose-dependently decreased the amount of protein carbonyls and advanced glycation end products (AGEs) that were formed in the case of Hb incubation with MG. Likewise, nitroxyl effectively protected Hb against oxidative modification with t-BOOH. It slowed down the destruction of heme, formation of carbonyl derivatives and inter-subunit cross-linking. The protective effect of nitroxyl on Hb in this system is primarily associated with nitrosylation of oxidized Hb and reduction of its ferryl form, which lowers the yield of free radical products. We suppose that the dual (antioxidant and antiglycation) effect of nitroxyl makes its application possible as part of an additional treatment strategy for oxidative and carbonyl stress-associated diseases.

Protective Effect of Dinitrosyl Iron Complexes Bound with Hemoglobin on Oxidative Modification by Peroxynitrite

Dinitrosyl iron complexes (DNICs) are a physiological form of nitric oxide (•NO) in an organism. They are able not only to deposit and transport •NO, but are also to act as antioxidant and antiradical agents. However, the mechanics of hemoglobin-bound DNICs (Hb-DNICs) protecting Hb against peroxynitrite-caused, mediated oxidative modification have not yet been scrutinized. Through EPR spectroscopy we show that Hb-DNICs are destroyed under the peroxynitrite action in a dose-dependent manner. At the same time, DNICs inhibit the oxidation of tryptophan and tyrosine residues and formation of carbonyl derivatives. They also prevent the formation of covalent crosslinks between Hb subunits and degradation of a heme group. These effects can arise from the oxoferryl heme form being reduced, and they can be connected with the ability of DNICs to directly intercept peroxynitrite and free radicals, which emerge due to its homolysis. These data show that DNICs may ensure protection from myocardial ischemia.

Expressed Soybean Leghemoglobin: Effect on Escherichia coli at Oxidative and Nitrosative Stress

Leghemoglobin (Lb) is an oxygen-binding plant hemoglobin of legume nodules, which participates in the symbiotic nitrogen fixation process. Another way to obtain Lb is its expression in bacteria, yeasts, or other organisms. This is promising for both obtaining Lb in the necessary quantity and scrutinizing it in model systems, e.g., its interaction with reactive oxygen (ROS) and nitrogen (RNS) species. The main goal of the work was to study how Lb expression affected the ability of Escherichia coli cells to tolerate oxidative and nitrosative stress. The bacterium E. coli with the embedded gene of soybean leghemoglobin a contains this protein in an active oxygenated state. The interaction of the expressed Lb with oxidative and nitrosative stress inducers (nitrosoglutathione, tert-butyl hydroperoxide, and benzylviologen) was studied by enzymatic methods and spectrophotometry. Lb formed NO complexes with heme-nitrosylLb or nonheme iron-dinitrosyl iron complexes (DNICs). The formation of Lb-bound DNICs was also detected by low-temperature electron paramagnetic resonance spectroscopy. Lb displayed peroxidase activity and catalyzed the reduction of organic peroxides. Despite this, E. coli-synthesized Lb were more sensitive to stress inducers. This might be due to the energy demand required by the Lb synthesis, as an alien protein consumes bacterial resources and thereby decreases adaptive potential of E. coli.

Anabolic/anticatabolic and adaptogenic effects of 24-epibrassinolide on Lupinus angustifolius: Causes and consequences

Lupinus angustifolius L. is a legume culture known as a source of valuable feed protein and the N₂-fixator for improving soil fertility. However, its low ecological resistance does not allow for a stable yield of the crop. Earlier, we have shown that steroid phytohormone 24-epibrassinolide (EBR) increases the tolerance of lupine to chlorine ions by activating the protective proteins in ripening seeds (such as proteinase inhibitors that prevent protein breakdown) and lectins. Here we investigated the effect of EBR on the functional status of the N₂-fixing system in root nodules, protein synthesis in ripening seeds and the resistance of lupine plants to various pathogens. It was found that EBR enhanced the nodulation process, N₂-fixing activity of nitrogenase and the accumulation of poly-β-hydroxybutirate in the bacteroides, increased the leghemoglobin content in the nodules as well as the metabolic activity of bacteroides. According to data on the inclusion of ¹⁴C-leucine in maturing seed proteins, EBR increased the accumulation of protein in them against the background of a short-term decrease in protein synthesis and its subsequent regeneration to the control level. Gradual inhibition of protein synthesis, characteristic of other legumes, was observed in control variants of lupine. EBR increased lupine resistance to phytopathogenic fungi of Colletotrichum genus and insects of Noctuidae and Scarabaeidae families. We concluded that a more complete implementation of the potential productivity and sustainability of lupine under the action of EBR was achieved due to the anabolic/anti-catabolic effect on the N₂ fixation system in root nodules, as well as on protein synthesis in ripening seeds.

New dinitrosyl iron complexes bound with physiologically active dipeptide carnosine

Dinitrosyl iron complexes (DNICs) are physiological NO derivatives and account for many NO functions in biology. Polyfunctional dipeptide carnosine (beta-alanyl-L-histidine) is considered to be a very promising pharmacological agent. It was shown that in the system containing carnosine, iron ions and Angeli's salt, a new type of DNICs bound with carnosine as ligand {(carnosine)₂-Fe-(NO)₂}, was formed. We studied how the carbonyl compound methylglyoxal influenced this process. Carnosine-bound DNICs appear to be one of the cell's adaptation mechanisms when the amount of reactive carbonyl compounds increases at hyperglycemia. These complexes can also participate in signal and regulatory ways of NO and can act as protectors at oxidative and carbonyl stress conditions.

Formation of nitri- and nitrosylhemoglobin in systems modeling the Maillard reaction

BACKGROUND

Nitric oxide (NO) and its metabolites can nitrosylate hemoglobin (Hb) through the heme iron. Nitrihemoglobin (nitriHb) can be formed as result of porphyrin vinyl group modification with nitrite. However, in those with diabetes the non-enzymatic glycation of Hb amino acids residues (the Maillard reaction) can take place. The objectives of this study were to investigate effects of the Maillard reaction on the interaction of methemoglobin (metHb) with S-nitrosoglutathione (GSNO) and nitrite.

METHODS

Nitrosylhemoglobin production was registered using increasing optical density at 572 nm and compared with 592 nm, and with EPR spectroscopy. Formation of nitriHb was determined using an absorbance band of reduced hemochromogen (582 nm) in the alkaline pyridine solution. Accumulation of fluorescent advanced glycation end-products of Hb was measured through increasing of fluorescence at 385-395 nm (excitation λ=320 nm).

RESULTS

We determined that NO metabolites such as GSNO and nitrite at physiological pH values and aerobic conditions caused modification of metHb porphyrin vinyl groups with nitriHb formation. It was ascertained that this formation was inhibited by superoxide dismutase. In microaerobic conditions metHb was nitrosylated under the action of GSNO or GSNO with methylglyoxal. Nitrite nitrosylated metHb only in the presence of methylglyoxal. It was shown that GSNO inhibited accumulation of fluorescent products which formed during Hb glycation with methylglyoxal.

CONCLUSIONS

The assumption was made that intermediates of the Hb glycation reaction play an important role both in vinyl group nitration and in heme iron nitrosylation. Oxygen content in reaction medium is an important factor influencing these processes. These effects can play an important role in pathogenesis of the diseases connected with carbonyl, oxidative and nitrosative stresses.

Interaction of S-nitrosoglutathione with methemoglobin under conditions of modeling carbonyl stress

The Maillard reaction is the key process in protein modification during pathologies connected with carbonyl stress. It was shown in system modeling that Maillard reaction interaction of L-lysine (L-lys) with methylglyoxal (MG) led to the formation of compounds reducing methemoglobin (metHb). Under the above conditions and in the presence of S-nitrosoglutathione (GSNO), metHb nitrosylation took place. Processes of metHb reduction and nitrosylation had the lag phase that was dependent on the presence of oxygen (O2) in the reaction mixture. Oxygen interacting with organic free radicals of the Maillard reaction inhibited hemoglobin (Hb) reduction and hence Hb nitrosylation during the first minutes of the reaction. It was also shown that the yield of organic free-radical intermediates of the L-lys with MG was increased in the presence of GSNO and metHb. All effects described could be a result of the formation of active red-ox GSNO derivates in the Maillard reaction. These derivates are probably mediators of one-electron oxidation of dialkylimine by MG. Anion radicals of S-nitrosothiols can function as such mediators.