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.

A Perspective on Reagent Diversity and Non-covalent Binding of Reactive Carbonyl Species (RCS) and Effector Reagents in Non-enzymatic Glycation (NEG): Mechanistic Considerations and Implications for Future Research

This perspective focuses on illustrating the underappreciated connections between reactive carbonyl species (RCS), initial binding in the nonenzymatic glycation (NEG) process, and nonenzymatic covalent protein modification (here termed NECPM). While glucose is the central species involved in NEG, recent studies indicate that the initially-bound glucose species in the NEG of human hemoglobin (HbA) and human serum albumin (HSA) are non-RCS ring-closed isomers. The ring-opened glucose, an RCS structure that reacts in the NEG process, is most likely generated from previously-bound ring-closed isomers undergoing concerted acid/base reactions while bound to protein. The generation of the glucose RCS can involve concomitantly-bound physiological species (e.g., inorganic phosphate, water, etc.); here termed effector reagents. Extant NEG schemes do not account for these recent findings. In addition, effector reagent reactions with glucose in the serum and erythrocyte cytosol can generate RCS (e.g., glyoxal, glyceraldehyde, etc.). Recent research has shown that these RCS covalently modify proteins in vivo via NECPM mechanisms. A general scheme that reflects both the reagent and mechanistic diversity that can lead to NEG and NECPM is presented here. A perspective that accounts for the relationships between RCS, NEG, and NECPM can facilitate the understanding of site selectivity, may help explain overall glycation rates, and may have implications for the clinical assessment/control of diabetes mellitus. In view of this perspective, concentrations of ribose, fructose, Pi, bicarbonate, counter ions, and the resulting RCS generated within intracellular and extracellular compartments may be of importance and of clinical relevance. Future research is also proposed.

The Role of Oxidative Stress in Diabetic Neuropathy: Generation of Free Radical Species in the Glycation Reaction and Gene Polymorphisms Encoding Antioxidant Enzymes to Genetic Susceptibility to Diabetic Neuropathy in Population of Type I Diabetic Patients

Diabetic neuropathy (DN) represents the main cause of morbidity and mortality among diabetic patients. Clinical data support the conclusion that the severity of DN is related to the frequency and duration of hyperglycemic periods. The presented experimental and clinical evidences propose that changes in cellular function resulting in oxidative stress act as a leading factor in the development and progression of DN. Hyperglycemia- and dyslipidemia-driven oxidative stress is a major contributor, enhanced by advanced glycation end product (AGE) formation and polyol pathway activation. There are several polymorphous pathways that lead to oxidative stress in the peripheral nervous system in chronic hyperglycemia. This article demonstrates the origin of oxidative stress derived from glycation reactions and genetic variations within the antioxidant genes which could be implicated in the pathogenesis of DN. In the diabetic state, unchecked superoxide accumulation and resultant increases in polyol pathway activity, AGEs accumulation, protein kinase C activity, and hexosamine flux trigger a feed-forward system of progressive cellular dysfunction. In nerve, this confluence of metabolic and vascular disturbances leads to impaired neural function and loss of neurotrophic support, and over the long term, can mediate apoptosis of neurons and Schwann cells, the glial cells of the peripheral nervous system. In this article, we consider AGE-mediated reactive oxygen species (ROS) generation as a pathogenesis factor in the development of DN. It is likely that oxidative modification of proteins and other biomolecules might be the consequence of local generation of superoxide on the interaction of the residues of L-lysine (and probably other amino acids) with α-ketoaldehydes. This phenomenon of non-enzymatic superoxide generation might be an element of autocatalytic intensification of pathophysiological action of carbonyl stress. Glyoxal and methylglyoxal formed during metabolic pathway are detoxified by the glyoxalase system with reduced glutathione as co-factor. The concentration of reduced glutathione may be decreased by oxidative stress and by decreased in situ glutathione reductase activity in diabetes mellitus. Genetic variations within the antioxidant genes therefore could be implicated in the pathogenesis of DN. In this work, the supporting data about the association between the -262T > C polymorphism of the catalase (CAT) gene and DN were shown. The -262TT genotype of the CAT gene was significantly associated with higher erythrocyte catalase activity in blood of DN patients compared to the -262CC genotype (17.8 ± 2.7 × 10(4) IU/g Hb vs. 13.5 ± 3.2 × 10(4) IU/g Hb, P = 0.0022). The role of these factors in the development of diabetic complications and the prospective prevention of DN by supplementation in formulations of transglycating imidazole-containing peptide-based antioxidants (non-hydrolyzed carnosine, carcinine, n-acetylcarcinine) scavenging ROS in the glycation reaction, modifying the activity of enzymic and non-enzymic antioxidant defenses that participate in metabolic processes with ability of controlling at transcriptional levels the differential expression of several genes encoding antioxidant enzymes inherent to DN in Type I Diabetic patients, now deserve investigation.

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.

Carbonyl Stress in Bacteria: Causes and Consequences

Pathways of synthesis of the α-reactive carbonyl compound methylglyoxal (MG) in prokaryotes are described in this review. Accumulation of MG leads to development of carbonyl stress. Some pathways of MG formation are similar for both pro- and eukaryotes, but there are reactions specific for prokaryotes, e.g. the methylglyoxal synthase reaction. This reaction and the glyoxalase system constitute an alternative pathway of glucose catabolism - the MG shunt not associated with the synthesis of ATP. In violation of the regulation of metabolism, the cell uses MG shunt as well as other glycolysis shunting pathways and futile cycles enabling stabilization of its energetic status. MG was first examined as a biologically active metabolic factor participating in the formation of phenotypic polymorphism and hyperpersistent potential of bacterial populations. The study of carbonyl stress is interesting for evolutionary biology and can be useful for constructing highly effective producer strains.

Methylglyoxal as a scavenger for superoxide anion-radical

Methylglyoxal at a concentration of 5 mM caused a significant inhibition of superoxide anion radical (O2 (·-)) comparable to the effect of Tirone. In the process of O2 (·-) generation in the system of egg phosphatidylcholine liposome peroxidation induced by the azo-initiator AIBN, a marked inhibition of chemiluminescence in the presence of 100 mM methylglyoxal was found. At the same time, methylglyoxal did not inhibit free radical peroxidation of low-density lipoprotein particles, which indicates the absence of interaction with methylglyoxal alkoxyl and peroxyl polyenoic lipid radicals. These findings deepen information about the role of methylglyoxal in the regulation of free radical processes.

Aldehyde inhibition of antioxidant enzymes in the blood of diabetic patients

BACKGROUND

The aim of the present study was to examine the effect of aldehyde modification on antioxidant enzyme activity in diabetic patients.

METHODS

The activity of commercially available antioxidant enzymes (catalase, glutathione peroxidase [GPx], and Cu,Zn-superoxide dismutase [SOD]) was determined in vitro prior to and after aldehyde modification. The activity of erythrocyte Cu,Zn-SOD was assayed in blood drawn from healthy donors, diabetic patients with decompensated carbohydrate metabolism, and diabetic patients after glucose-lowering therapy.

RESULTS

In vitro aldehyde modification had no effect on catalase activity, but diminished GPx and Cu,Zn-SOD activity. In diabetic patients with decompensated carbohydrate metabolism, glucose-lowering therapy significantly increased Cu,Zn-SOD activity, the effect being especially pronounced after administration of metformin.

CONCLUSIONS

It is likely that metformin antagonizes the aldehyde-induced inhibition of erythrocyte Cu,Zn-SOD in diabetic patients more effectively than sulfonylurea drugs.

Patenting strategies, the authentication US fiscal methodology, discovery and development of imidazole-containing peptide compounds with free-radical scavenging and transglycating properties acting as targeted drug regulators and homeostatic agents with diverse therapeutic activities for pharmacy of diabetes and metabolic diseases

INTRODUCTION

Diabetes mellitus is the seventh-leading cause of death in the US and diabetic complications are interlaced with specific diverse microvascular and macrovascular pathologies resulting from hyperglycemia. The society should expand prowess and patenting of biotechnology to cure disease and complications.

AREAS COVERED

The work summarizes biological activities of patented carnosine mimetics resistant in formulations to enzymatic hydrolysis with human carnosinases that are acting as a universal form of antioxidant, deglycating and transglycating agents that inhibit sugar-mediated protein crosslinking, chelate or inactivate a number of transition metal ions (including ferrous and copper ions), possess lipid peroxidase type of activity and protection of antioxidant enzymes from inactivation. L-Carnosine released systemically from N-acetylcarnosine lubricant eye drops or from skeletal muscle during exercise is transported into hypothalamic tuberomammillary nucleus-histamine neurons and hydrolyzed. The resulting L-histidine is subsequently converted into histamine acting as metabolic fuel feeding for the hypothalamic histaminergic system. This mechanism is responsible for the effects of L-carnosine on autonomic neurotransmission and physiological function of pancreas, stimulating in vivo regeneration of insulin-producing β cells.

EXPERT OPINION

Therapeutic benefits for imidazole-containing antioxidants (nutraceutical non-hydrolyzed carnosine, carcinine, D-carnosine, ophthalmic prodrug N-acetylcarnosine, leucyl-histidylhydrazide and patented formulations thereof) are an essential part of diabetes treatment.

Reactive carbonyl species in vivo: generation and dual biological effects

Reactive carbonyls are widespread species in living organisms and mainly known for their damaging effects. The most abundant reactive carbonyl species (RCS) are derived from oxidation of carbohydrates, lipids, and amino acids. Chemical modification of proteins, nucleic acids, and aminophospholipids by RCS results in cytotoxicity and mutagenicity. In addition to their direct toxicity, modification of biomolecules by RCS gives rise to a multitude of adducts and cross links that are increasingly implicated in aging and pathology of a wide range of human diseases. Understanding of the relationship between metabolism of RCS and the development of pathological disorders and diseases may help to develop effective approaches to prevent a number of disorders and diseases. On the other hand, constant persistence of RCS in cells suggests that they perform some useful role in living organisms. The most beneficial effects of RCS are their establishment as regulators of cell signal transduction and gene expression. Since RCS can modulate different biological processes, new tools are required to decipher the precise mechanisms underlying dual effects of RCS.

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.

Fructation in vivo: detrimental and protective effects of fructose

There is compelling evidence that long-term intake of excessive fructose can have deleterious side effects in different experimental models. However, the role of fructose in vivo remains controversial, since acute temporary application of fructose is found to protect yeast as well as animal tissues against exogenous oxidative stress. This review suggests the involvement of reactive carbonyl and oxygen species in both the cytotoxic and defensive effects of fructose. Potential mechanisms of the generation of reactive species by fructose in the nonenzymatic reactions, their implication in the detrimental and protective effects of fructose are discussed.

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.

[The influence of natural dicarbonils on the antioxidant enzymes activity in vitro and in vivo]

Natural dicarbonyls, which may be accumulated during oxidative stress in atherosclerosis (e.g. malondialdehyde) or carbonyl stress in diabetes mellitus (glyoxal and methylglyoxal) effectively inhibited the activities of commercial preparations of antioxidant enzymes: catalase, Cu, Zn-superoxide dismutase (Cu, Zn-SOD) and Se-contained glutathione peroxidase from human and bovine erythrocytes and also rat liver glutathione-S-transferase. After incubation of human erythrocytes with 10 mM of each investigated dicarbonyls the decrease of intracellular Cu, Zn-SOD was observed. The decreased activity of erythrocyte Cu, Zn-SOD was also detected in diabetic patients with carbohydrate metabolism disturbance but effective sugar-lowered therapy was accompanied by the increase of this enzyme activity. The increase of erythrocytes activity of Cu, Zn-SOD of diabetic patients theated with metformin (which may utilize methylglyoxal) was higher than in erythrocytase of diabetic patients subjected to traditional therapy.

The influence of glucose on the free radical peroxidation of low density lipoproteins in vitro and in vivo

It was shown that glucose in concentration 12.5-100 mM stimulated of Cu2+-mediated free radical peroxidation of low density lipoproteins (LDL) from human blood plasma. On the base investigation of kinetic parameters of LDL peroxidation it was stated that intensification of this process in the conditions of our experiments is caused by formation of free radical intermediates of glucose autoxidation during active oxygen species generation in the presence of metal ions with variable valence. It was found that glucose level normalization in the blood of patients with type 2 diabetes during therapy accompanied by significant decreasing of LDL oxidizing. During therapy with sugar-lowering drug metformin which utilizate methylglyoxal the LDL peroxidation from blood diabetes mellitus in vivo inhibited in more higher degree probably in consequence of decreasing of methylglyoxal-dependent generation of superoxide anion radicals as was shown by us early [Biochemistry (Moscow), 2007, 72: 1081-1090; Biochemistry (Moscow), 2009, 74: 461-466].

Formation of nitrogen-containing oligomers by methylglyoxal and amines in simulated evaporating cloud droplets

Reactions of methylglyoxal with amino acids, methylamine, and ammonium sulfate can take place in aqueous aerosol and evaporating cloud droplets. These processes are simulated by drying droplets and bulk solutions of these compounds (at low millimolar and 1 M concentrations, respectively) and analyzing the residuals by scanning mobility particle sizing, nuclear magnetic resonance, aerosol mass spectrometry (AMS), and electrospray ionization MS. The results are consistent with imine (but not diimine) formation on a time scale of seconds, followed by the formation of nitrogen-containing oligomers, methylimidazole, and dimethylimidazole products on a time scale of minutes to hours. Measured elemental ratios are consistent with imidazoles and oligomers being major reaction products, while effective aerosol densities suggest extensive reactions take place within minutes. These reactions may be a source of the light-absorbing, nitrogen-containing oligomers observed in urban and biomass-burning aerosol particles.