A docking model of human ribonucleotide reductase with flavin and phenosafranine

Ribonucleotide Reductase (RNR) is an enzyme responsible for the reduction of ribonucleotides to their corresponding Deoxyribonucleotides (DNA), which is a building block for DNA replication and repair mechanisms. The key role of RNR in DNA synthesis and control in cell growth has made this an important target for anticancer therapy. Increased RNR activity has been associated with malignant transformation and tumor cell growth. In recent years, several RNR inhibitors, including Triapine, Gemcitabine and GTI-2040, have entered the clinical trials. Our current work focuses on an attempted to dock this inhibitors Flavin and Phenosafranine to curtail the action of human RNR2. The docked inhibitor Flavin and Phenosafranine binds at the active site with THR176, which are essential for free radical formation. The inhibitor must be a radical scavenger to destroy the tyrosyl radical or iron metal scavenger. The iron or radical site of R2 protein can react with one-electron reductants, whereby the tyrosyl radical is converted to a normal tyrosine residue. However, compounds such as Flavin and Phenosafranine were used in most of the cases to reduce the radical activity. The docking study was performed for the crystal structure of human RNR with the radical scavengers Flavin and Phenosafranine to inhibit the human RNR2. This helps to understand the functional aspects and also aids in the development of novel inhibitors for the human RNR2.     

On the hydrophobicity of nitrogen dioxide: Could there be a “lens” effect for NO2 reaction kinetics?

Solvent “lens” effects for the reaction kinetics of NO₂ can be evaluated on the basis of published Henry’s law constants for nitrogen dioxide in various solvents. Water-to-organic solvent partition coefficients were derived from Henry’s law constants and used to assess the tendencies of NO₂ toward fleeing the aqueous environments and concentrating in biological hydrophobic media. It is concluded, based only on the estimated aqueous medium-to-cell membrane partition coefficient for NO₂, that such tendencies will be relatively small, and that they may account for an acceleration of chemical reactions in biological hydrophobic media with reaction kinetics that are first order on NO₂ by a factor of approximately 3 ± 1. Thus, kinetic effects due to mass action will be relatively small but it is also important to recognize that because NO₂ will tend to dissolve in cell membranes, reactions with cell membrane components will not be hindered by lack of physical solubility at these loci. In comparison to other gases, nitrogen dioxide is less hydrophobic than NO, O₂ and N₂.     

Estimation of antioxidant capacity against pathophysiologically relevant oxidants using Pyrogallol Red

Peroxynitrite and hypochlorite are oxidants relevant in many pathological situations. We propose a simple spectrophotometric assay to determine antioxidant capacity against hypochlorite and peroxynitrite based on protection against Pyrogallol Red decolorization. The assay can be performed on a microplate and requires minute amounts of material. Standard antioxidants show different reactivities for both oxidants. Antioxidant capacity of blood plasma (anticoagulated with EDTA) of healthy persons was found to be 559 ± 49 μmol/l and 11.6 ± 1.2 mmol/l of ascorbic acid equivalents for peroxynitrite and hypochlorite, respectively.     

Understanding the fate of peroxynitrite in plant cells--from physiology to pathophysiology

Peroxynitrite (ONOO⁻) is a potent oxidant and nitrating species, generated by the reaction of nitric oxide and superoxide in one of the most rapid reactions known in biology. It is widely accepted that an enhanced ONOO⁻ formation contributes to oxidative and nitrosative stress in various biological systems. However, an increasing number of studies have reported that ONOO⁻ cannot only be considered as a mediator of cellular dysfunction, but also behaves as a potent modulator of the redox regulation in various cell signal transduction pathways.Although the formation of ONOO⁻ has been demonstrated in vivo in plant cells, the relevance of this molecule during plant physiological responses is still far from being clarified. Admittedly, the detection of protein tyrosine nitration phenomena provides some justification to the speculations that ONOO is generated during various plant stress responses associated with pathophysiological mechanisms. On the other hand, it was found that ONOO⁻ itself is not as toxic for plant cells as it is for animal ones. Based on the concepts of the role played by ONOO⁻ in biological systems, this review is focused mainly on the search for potential functions of ONOO⁻ in plants. Moreover, it is also an attempt to stimulate a discussion on the significance of protein nitration as a paradigm in signal modulation, since the newest reports identified proteins associated with signal transduction cascades within the plant nitroproteome.     

Intraphagosomal peroxynitrite as a macrophage-derived cytotoxin against internalized Trypanosoma cruzi: consequences for oxidative killing and role of microbial peroxiredoxins in infectivity

Macrophage-derived radicals generated by the NADPH oxidase complex and inducible nitric-oxide synthase (iNOS) participate in cytotoxic mechanisms against microorganisms. Nitric oxide (^•NO) plays a central role in the control of acute infection by Trypanosoma cruzi, the causative agent of Chagas disease, and we have proposed that much of its action relies on macrophage-derived peroxynitrite (ONOO⁻ + ONOOH) formation, a strong oxidant arising from the reaction of ^•NO with superoxide radical (O₂^˙̄). Herein, we have shown that internalization of T. cruzi trypomastigotes by macrophages triggers the assembly of the NADPH oxidase complex to yield O₂^˙̄ during a 60–90-min period. This does not interfere with IFN-γ-dependent iNOS induction and a sustained ^•NO production (∼24 h). The major mechanism for infection control via reactive species formation occurred when ^•NO and O₂^˙̄ were produced simultaneously, generating intraphagosomal peroxynitrite levels compatible with microbial killing. Moreover, biochemical and ultrastructural analysis confirmed cellular oxidative damage and morphological disruption in internalized parasites. Overexpression of cytosolic tryparedoxin peroxidase in T. cruzi neutralized macrophage-derived peroxynitrite-dependent cytotoxicity to parasites and favored the infection in an animal model. Collectively, the data provide, for the first time, direct support for the action of peroxynitrite as an intraphagosomal cytotoxin against pathogens and the premise that microbial peroxiredoxins facilitate infectivity via decomposition of macrophage-derived peroxynitrite.     

Design,synthesis and evaluation of rivastigmine and curcumin hybrids as site-activated multitarget-directed ligands for Alzheimer’s disease therapy

A series of novel 2-methoxy-phenyl dimethyl-carbamate derivatives were designed, synthesized and evaluated as site-activated MTDLs based on rivastigmine and curcumin. Most of them exhibited good to excellent AChE and BuChE inhibitory activities with sub-micromolar IC₅₀ values. Among all the compounds, 6a demonstrated the most potent AChE inhibition with IC₅₀ value of 0.097 μM, which is about 20-fold than that of rivastigmine. In addition, the three selected compounds 5a, 6a and 6e demonstrated inhibitory activity against Aβ self-aggregation similar to cucurmin in TEM assay, which is obviously different from the weak activity of rivastigmine. Moreover, the hydrolysate of 6a (compound 7) also showed potent ABTS⁺ scavenging and moderate copper ion chelating activity in vitro.     

Searching for a successful HDL-based treatment strategy

Despite strong evidence that HDL-cholesterol levels predict atherosclerotic events in a population, attempts at using an HDL-based treatment strategy have not yet been successful. Most of the efforts to date have focused on raising plasma HDL-cholesterol levels. This brief review focuses on a different strategy, which is based on the use of 18-amino acid apoA-I mimetic peptides. The story of these peptides spans decades and illustrates the remarkable complexity of HDL-based treatment strategies, but suggests that such a strategy may still be successful.     

Analysis of Abscisic Acid in the Brains of Rodents and Ruminants

The surface tension (σ) of batter prepared with one or two of the major ingredients of wheat flour, egg and sucrose was measured by the maximum bubble pressure method. The surface tension of the soft- and hard-wheat flour suspension decreased as the solid content of wheat flour was increased, finally reaching 48.2 and 52.7 dyn/cm, respectively. The surface tension of the wheat flour suspension was lower than that of its supernatant, which suggests that the precipitate reduced the surface tension. Gelatinization of the wheat flour suspension lowered its surface tension. The surface tension of the whole egg dispersion decreased markedly to about 53 dyn/cm as the solid concentration was increased from 0 to 1%, and remained almost constant as the concentration was increased further. This tendency was almost the same as that of the egg yolk dispersion. The surface tension of mixtures of two ingredients such as egg and wheat flour, and egg and sucrose was almost equal to that of the ingredient with the lower surface tension at the same concentration as in the mixture.     

Deleterious Activation of Poly(ADP-Ribose)Polymerase-1 in Brain after In Vivo Oxidative Stress

Oxidative stress has been shown to be implicated in the pathogenesis of central nervous system injuries such as cerebral ischemia and trauma, and chronic neurodegenerative diseases. In vitro studies show that oxidative stress, particularly peroxynitrite, could trigger DNA strand breaks, which lead to the activation of repairing enzymes including Poly(ADP-ribose) Polymerase-1 (PARP-1). As excessive activation of this enzyme induces cell death, we examined whether such a cascade also occurs in vivo in a model of oxidative stress in rat brain. For this purpose, the mitochondrial toxin malonate, which promotes free radical production, was infused into the left striatum of rats. Immunohistochemistry showed that 3-nitrotyrosine, an indicator of nitrosative stress, and poly(ADP-ribose), a marker of poly(ADP-ribose)polymerase-1 activation, were present as early as 1 h after malonate, and that they persisted for 24 h. The PARP inhibitor, 3-aminobenzamide, significantly reduced the lesion and inhibited PARP-1 activation induced by malonate. These results demonstrate that oxidative stress induced in vivo in the central nervous system leads to the activation of poly(ADP-ribose)polymerase-1, which contributes to neuronal cell death.