Molecular modeling and in vitro reactivation study between the oxime BI-6 and acetylcholinesterase inhibited by different nerve agents

Nerve agents are organophosphates acting as potent inhibitors of acetylcholinesterase (AChE), the enzyme responsible for the hydrolysis of acetylcholine and, consequently, the termination of the transmission of nerve impulses. The inhibition of AChE by an organophosphate can be reversed by a nucleophilic agent able to dephosphorylate a serine residue in the active site of AChE. In this sense, the oximes are compounds capable of removing the nerve agent and reactivate the enzyme. Here, we have applied a methodology involving theoretical docking and Quantum Mechanics/Molecular Mechanics, using the softwares Molegro^® and Spartan^®, to evaluate the kinetic constants of reactivation and the interactions of the oxime BI-6 with AChE inhibited by different organophosphorus compounds in comparison to in vitro data. Results confirm that this method is suitable for the prediction of kinetic and thermodynamic parameters of oximes, which may be useful in the design and selection of new and more effective oximes.     

The mechanism of the photochromic transformation of spirorhodamines

We investigate the equilibrium, kinetics, and mechanism of the photochromic transformation of a series of amido spirorhodamine compounds-differing in the nature of the substituents of the amido group and in the rhodamine chromophore-in ethanol at room temperature in the presence of trifluoroacetic acid. A proton participates in the equilibrium between the spiro form and the open rhodamine form. The relaxation times in the dark or under continuous irradiation show a linear dependence on the proton concentration. The slopes of these plots show a linear free energy relation with the equilibrium constant of the transformation. A mechanism involving reversible reaction steps between four states: the two thermodynamically stable isomers, a protonated spiro form, and a deprotonated open form, can account for the kinetic observations in the dark and under irradiation.     

Butane-2,3-dionethiosemicarbazone: an oxime with antioxidant properties

Oximes are compounds generally used to reverse the acetylcholinesterase (AChE) inhibition caused by organophosphates (OPs). The aim of this study was to examine the capacity of the butane-2,3-dionethiosemicarbazone oxime to scavenge different forms of reactive species (RS) in vitro, as well as counteract their formation. The potential antioxidant and toxic activity of the oxime was assayed both in vitro and ex vivo. The obtained results indicate a significant hydrogen peroxide (H₂O₂), nitric oxide (NO) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity at 0.275, 0.5 and 5 μM of oxime, respectively (p ≤ 0.05). The oxime exhibited a powerful inhibitory effect on dihydroxybenzoate formation (25 μM) (p ≤ 0.05) and also decreased deoxyribose degradation induced by Fe²⁺ and via Fenton reaction (0.44 and 0.66 mM, respectively) (p ≤ 0.05). The oxime showed a significant inhibitory effect on σ-phenantroline reaction with Fe²⁺ (0.4 mM) suggesting a possible interaction between the oxime and iron. A significant decrease in the basal and pro-oxidant-induced lipid peroxidation in brain, liver, and kidney of mice was observed both in vitro and ex vivo (p ≤ 0.05). In addition, in our ex vivo experiments the oxime did not depict any significant changes in thiol levels of liver, kidney and brain as well as did not modify the δ-aminolevulinate dehydratase (δ-ALA-D) activity in these tissues. Taken together our results indicate an in vitro and ex vivo antioxidant activity of the oxime possibly due to its scavenging activity toward different RS and a significant iron interaction.     

Characterization of the sexual pattern of Parastacus varicosus (Crustacea: Decapoda: Parastacidae)

Abstract. Freshwater crayfishes of the genus Parastacus are intersex, i.e., show characteristics of both sexes in the same individual; also, intersexuality has been documented in hermaphroditic species. The aim of this study was to analyze the gonads of Parastacus varicosus , characterizing its sexual pattern. The animals were collected at Cova do Touro, Gravataí, Rio Grande do Sul, Brazil. Three sexual forms were identified: intersex females, intersex males, and transitional specimens showing an ovotestes gonad that could only be identified by means of histological analysis. All specimens had two pairs of gonopores and gonoducts. The oviduct had a wider diameter in females, whereas in males the vasa deferentia were more developed. Gonads were composed of two parallel structures located in the cephalothorax. Female gonads were classified into three stages. The presence of transitional specimens may indicate that sex change occurs, with protandric hermaphroditism, as observed in other species of Parastacus . Because previous studies had demonstrated that P. varicosus is a gonochoristic species in a population from Uruguay, the present study addressed the possibility that the sexual pattern depends on differences in environmental factors among populations. To improve understanding of evolution of hermaphroditism in these crustaceans, their reproductive dynamics should be studied, including identification of the factors stimulating male and female functions.     

Comparative Studies on Dicholesteroyl Diselenide and Diphenyl Diselenide as Antioxidant Agents and their Effect on the Activities of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript> ATPase and <Emphasis Type="Italic">δ</Emphasis>-Aminolevulinic acid Dehydratase in the Rat Brain

The present study sought to evaluate the effect of a newly synthesized selenium compound, dicholesteroyl diselenide (DCDS) and diphenyl diselenide (DPDS) on the activities of delta-aminolevulinate dehydratase and Na⁺/K⁺-ATPase in the rat brain. The glutathione peroxidase mimetic activity of the two compounds as well as their ability to oxidize mono- and di- thiols were also evaluated. The antioxidant effects were tested by measuring the ability of the compounds to inhibit the formation of thiobarbituric acid reactive species and also their ability to inhibit the formation of protein carbonyls. The results show that DPDS exhibited a higher glutathione peroxidase mimetic activity as well as increased ability to oxidize di-thiols than DCDS. In addition, while DPDS inhibited the formation of thiobarbituric acid reactive species and protein carbonyls, DCDS exhibited a prooxidant effect in all the concentration range (20–167 μM) tested. Also the activities of cerebral delta-aminolevulinate dehydratase and Na⁺/K⁺ ATPase were significantly inhibited by DPDS but not by DCDS. In addition, the present results suggested that the inhibition of Na⁺/K⁺ ATPase by organodiselenides, possibly involves the modification of the thiol group at the ATP binding site of the enzyme. In conclusion, the results of the present investigation indicated that the non-selenium moiety of the organochalcogens can have a profound effect on their antioxidant activity and also in their reactivity towards SH groups from low-molecular weight molecules and from brain proteins.     

Biogeography and priority areas for the conservation of bats in the Brazilian Cerrado

In this study, we describe the distribution pattern of bat species and select priority areas for the conservation of the Cerrado based on a systematic planning approach. We estimated species richness and calculated the total beta diversity based on Sørensen’s dissimilarity index (βsor). We estimated the species turnover using Simpson’s dissimilarity index (βsim). We then evaluated the nesting (βsne) by the difference between the dissimilarity indices (βsor and βsim). Based on this analysis, we identified the priority areas for the conservation of bats in the Cerrado based on the zonation approach. We found that the species richness and beta diversity of bats in the Cerrado are concentrated primarily in the central and northern portions of the biome. We also discovered that the conservation units of the Cerrado are ineffective for the protection of species with a restricted distribution (≤ 150 grid cells), such as Vampyrum spectrum, for which we propose the creation of new conservation units that better cover the diversity patterns observed in the present study. By conserving this diversity, we will also be protecting local habitats, which will in turn enable the survival of a wide range of species, and provide the ecosystems with the capacity to respond adequately to future changes in the environment.     

Interactions of cantharidin-like inhibitors with human protein phosphatase-5 in a Mg<Superscript>2+</Superscript> system: molecular dynamics and quantum calculations

The serine/threonine protein phosphatase type 5 (PP5) is a promising target for designing new antitumor drugs. This enzyme is a member of the PPP phosphatases gene family, which catalyzes a dephosphorylation reaction: a regulatory process in the signal transduction pathway that controls various biological processes. The aim of this work is to study and compare the inhibition of PP5 by ten cantharidin-like inhibitors in order to bring about contributions relevant to the better comprehension of their inhibitory activity. In this theoretical investigation, we used molecular dynamics techniques to understand the role of key interactions that occur in the protein active site; QM calculations were employed to study the interaction mode of these inhibitors in the enzyme. In addition, atoms in molecules (AIM) calculations were carried out to characterize the chemical bonds among the atoms involved and investigate the orbital interactions with their respective energy values. The obtained results suggest that the Arg275, Asn303, His304, His352, Arg400, His427, Glu428, Val429, Tyr451, and Phe446 residues favorably contribute to the interactions between inhibitors and PP5. However, the Asp271 and Asp244 amino acid residues do not favor such interactions for some inhibitors. Through the QM calculations, we can suggest that the reactional energy of the coordination mechanism of these inhibitors in the PP5 active site is quite important and is responsible for the inhibitory activity. The AIM technique employed in this work was essential to get a better comprehension of the transition states acquired from the mechanism simulation. This work offers insights of how cantharidin-like inhibitors interact with human PP5, potentially allowing the design of more specific and even less cytotoxic drugs for cancer treatments.

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Graphical Abstract Interactions of cantharidin-like inhibitors with human protein phosphatase-5 in a Mg²⁺ system

     

A biochemical and toxicological study with diethyl 2-phenyl-2-tellurophenyl vinylphosphonate in a sub-chronic intraperitoneal treatment in mice

Diethyl-2-phenyl-2-tellurophenyl vinylphosphonate (DPTVP) is an organotellurium compound with low toxicity after subcutaneous administration in mice. This study evaluated possible in vivo and ex vivo toxicological effects of daily injections of DPTVP for 12 days in mice, using the intraperitoneal administration. This route potentially increases the pharmacokinetics of absorption, distribution, metabolism and toxicity of DPTVP. Treatment with DPTVP (0, 30, 50, 75, 100, 250, 350 or 500 micromol/kg) were not associated with mortality or body weight loss. Nevertheless, the liver and liver-to-body weight ratio increased in groups treated with 350 and 500 micromol/kg of DPTVP. However, plasmatic aspartate and alanine aminotransferase activities (classical markers of hepatotoxicity) were not increased after diethyl-2-phenyl-2-tellurophenyl vinylphosphonate administration. Hepatic, renal and cerebral thiobarbituric acid reactive substances (TBARS), delta-ALA-D activity and Vitamin C levels were not modified after DPTVP treatment. Renal and hepatic superoxide dismutase (SOD) and catalase (CAT) were unchanged after DPTVP treatment. Conversely, SOD activity significantly increased in brain in groups treated with 50, 75, 100 and 500 micromol/kg of DPTVP treated groups. Our findings corroborates that brain is a potential target for organochalcogen action. The absence of severe overt signs of toxicity after sub-chronic exposure to DPTVP reinforces the necessity for more detailed pharmacological studies concerning this new organotellurium compound.