Plasmodium falciparum heterochromatin protein 1 binds to tri-methylated histone 3 lysine 9 and is linked to mutually exclusive expression of var genes

Increasing experimental evidence shows a prominent role of histone modifications in the coordinated control of gene expression in the human malaria parasite Plasmodium falciparum. The search for the histone-mark-reading machinery that translates histone modifications into biological processes, such as formation of heterochromatin and antigenic variation is of foremost importance. In this work, we identified the first member of a histone modification specific recognition protein, an orthologue of heterochromatin protein 1 (PfHP1). Analysis of the PfHP1 amino-acid sequence revealed the presence of the two characteristic HP1 domains: a chromodomain (CD) and a chromo shadow domain (CSD). Recombinant CD binds to di- and tri-methylated lysine 9 from histone H3, but not to unmodified or methylated histone H3 in lysine 4. PfHP1 is able to interact with itself to form dimers, underlying its potential role in aggregating nucleosomes to form heterochromatin. Antibodies raised against PfHP1 detect this molecule in foci at the perinuclear region. ChIP analysis using anti-PfHP1 shows that this protein is linked to heterochromatin of subtelomeric non-coding repeat regions and monoallelic expression of the major virulence var gene family. This is the first report implicating an HP1 protein in the control of antigenic variation of a protozoan parasite

S-allylmercaptocysteine scavenges hydroxyl radical and singlet oxygen in vitro and attenuates gentamicin-induced oxidative and nitrosative stress and renal damage in vivo

BACKGROUND: Oxidative and nitrosative stress have been involved in gentamicin-induced nephrotoxicity. The purpose of this work was to study the effect of S-allylmercaptocysteine, a garlic derived compound, on gentamicin-induced oxidative and nitrosative stress and nephrotoxicity. In addition, the in vitro reactive oxygen species scavenging properties of S-allylmercaptocysteine were studied. RESULTS: S-allylmercaptocysteine was able to scavenge hydroxyl radicals and singlet oxygen in vitro. In rats treated with gentamicin (70 mg/Kg body weight, subcutaneously, every 12 h, for 4 days), renal oxidative stress was made evident by the increase in protein carbonyl content and 4-hydroxy-2-nonenal, and the nitrosative stress was made evident by the increase in 3-nitrotyrosine. In addition, gentamicin-induced nephrotoxicity was evident by the: (1) decrease in creatinine clearance and in activity of circulating glutathione peroxidase, and (2) increase in urinary excretion of N-acetyl-β-D-glucosaminidase, and (3) necrosis of proximal tubular cells. Gentamicin-induced oxidative and nitrosative stress and nephrotoxicity were attenuated by S-allylmercaptocysteine treatment (100 mg/Kg body weight, intragastrically, 24 h before the first dose of gentamicin and 50 mg/Kg body weight, intragastrically, every 12 h, for 4 days along gentamicin-treatment). CONCLUSION: In conclusion, S-allylmercaptocysteine is able to scavenge hydroxyl radicals and singlet oxygen in vitro and to ameliorate the gentamicin-induced nephrotoxicity and oxidative and nitrosative stress in vivo

Viscoelastic properties of dispersed chitosan/xanthan hydrogels

In this work a gel was formed by complexation of two natural polyelectrolytes, chitosan and xanthan. Changes in the hydrogels rheological properties have been studied in terms of hydrogel concentration (7-10% w/w), chemical media used for the hydrogel dispersion, and 'test lag time'; i.e., the time between hydrogel dispersion in the chemical media and the start of the rheological test (up to 390 min). The viscoelastic properties of this polysaccharide system were characterized by oscillatory shear measurements under small-deformation conditions and the results show that chitosan/xanthan hydrogels behave like weak gels. The shear modulus increased almost linearly with frequency in the range studied (0.1-65 s-1). The effects of hydrogel concentration and dispersion medium have been related to electrostatic equilibrium and by the presence of counter-ions modifying the internal structure of the hydrogel. © 2006 Elsevier Ltd. All rights reserved

Dynamic rheological properties of concentrated chitosan soltions

A detailed analysis of the dynamic flow properties of chitosan in solution at different temperatures (25 - 45°C), chitosan concentration (0.5% - 2.0%), solvent type (acetic, lactic, and hydrochloric acid), and ionic strength (0 and 0.2M NaCl) has been undertaken. The storage modulus, G', loss modulus, G" and complex viscosity, ?* have been determined over a wide range of frequencies and the results are presented using master curves. For the conditions studied, at low frequencies chitosan solutions show a constant complex viscosity which decreases as frequency increases. Likewise, storage modulus, G' and loss modulus, G" increase as frequency increases with G" being always greater than G'(?' > ?") indicating that viscous effects are more important than elastic effects. For modelling the oscillatory-shear results we used the generalized Maxwell model. Two empirical equations were used to correlate the data: Cox-Merz rule for viscosity and Laun's rule for primary normal stress difference. Both relations were found to represent our data for the experimental conditions studied. Zapotitlán Appl. Rheol. 14 (2004)

Dynamic rheological properties of concentrated chitosan soltions

A detailed analysis of the dynamic flow properties of chitosan in solution at different temperatures (25 - 45°C), chitosan concentration (0.5% - 2.0%), solvent type (acetic, lactic, and hydrochloric acid), and ionic strength (0 and 0.2M NaCl) has been undertaken. The storage modulus, G', loss modulus, G" and complex viscosity, η* have been determined over a wide range of frequencies and the results are presented using master curves. For the conditions studied, at low frequencies chitosan solutions show a constant complex viscosity which decreases as frequency increases. Likewise, storage modulus, G' and loss modulus, G" increase as frequency increases with G" being always greater than G'(η' > η") indicating that viscous effects are more important than elastic effects. For modelling the oscillatory-shear results we used the generalized Maxwell model. Two empirical equations were used to correlate the data: Cox-Merz rule for viscosity and Laun's rule for primary normal stress difference. Both relations were found to represent our data for the experimental conditions studied. © Appl. Rheol. 14 (2004)

Effect of the weather conditions on the mechanical properties of an epoxy resin crosslinked with an aromatic amine

In this research work, we simulate the deterioration of a polymeric material caused by the sunlight, the humidity and the dew. The sunlight is simulated by lamps whose main range affects the polymers in such a way as to expose the material to condensation and heat. The change in the mechanical behavior of the polymer at different concentrations and times of exposure is observed

Polymer nanocomposites containing carbon nanotubes and miscible polymer blends based on poly[ethylene-co-(acrylic acid)]

This work presents the synthesis of polyacrylamide-gelatin (PAM-G) semi-interpenetrating hydrogels, as well as the study of the swelling capacity of this material at different pH's, and we report its Young modulus. The hydrogels were crosslinked with N,N-methylenebisacrylamide and synthesized at different acrylamide/gelatin weight relationship. It was observed that the swelling capacity of the hydrogels increases when the gelatin concentration is increased; while the Young modulus (at the swelling equilibrium) decreases lightly. Therefore, the gelatin has a small effect in the Young modulus, unlike its influence in the swelling ability. The swelling experiments reveal that the PAM-G hydrogels increase its swelling capacity in alkaline mediums because the presence of the hydrophobic functional groups (mainly COO-) in the gelatin structure. " 2009 Springer-Verlag.",,,,,,"10.1007/s00289-008-0037-4",,,"http://hdl.handle.net/20.500.12104/43698","http://www.scopus.com/inward/record.url?eid=2-s2.0-63449113247&partnerID=40&md5=0a7dd536d8c0138d8db4b464358f0de4",,,,,,"4",,"Polymer Bulletin",,"53

Microstructured polyacrylamide-co-chitosan/xanthan hydrogels

The synthesis of microstructured polyacrylamide-co-chitosan and polyacrylamida-co-chitosan/xanthan hydrogels with large swelling capacity and improved mechanical properties were studied. Crosslinked polyacrylamide particles of nanosize scale are made by inverse microemulsion polymerization. These particles are then dried and redispersed in an aqueous solution of acrylamide and polymerized in the presence of a crosslinking agent and chitosan solution with or without the presence of xanthan polysaccharide solution. The swelling capacity of these hydrogels are studied and compared with the results obtained with conventional polyacrylamide hydrogels

Microstructured polyacrylamide-co-chitosan/xanthan hydrogels

The synthesis of microstructured polyacrylamide-co-chitosan and polyacrylamida-co-chitosan/xanthan hydrogels with large swelling capacity and improved mechanical properties were studied. Crosslinked polyacrylamide particles of nanosize scale are made by inverse microemulsion polymerization. These particles are then dried and redispersed in an aqueous solution of acrylamide and polymerized in the presence of a crosslinking agent and chitosan solution with or without the presence of xanthan polysaccharide solution. The swelling capacity of these hydrogels are studied and compared with the results obtained with conventional polyacrylamide hydrogels

Polyacrylamide-gelatin polymeric networks: Effect of pH and gelatin concentration on the swelling kinetics and mechanical properties

This work presents the synthesis of polyacrylamide-gelatin (PAM-G) semi-interpenetrating hydrogels, as well as the study of the swelling capacity of this material at different pH's, and we report its Young modulus. The hydrogels were crosslinked with N,N-methylenebisacrylamide and synthesized at different acrylamide/gelatin weight relationship. It was observed that the swelling capacity of the hydrogels increases when the gelatin concentration is increased; while the Young modulus (at the swelling equilibrium) decreases lightly. Therefore, the gelatin has a small effect in the Young modulus, unlike its influence in the swelling ability. The swelling experiments reveal that the PAM-G hydrogels increase its swelling capacity in alkaline mediums because the presence of the hydrophobic functional groups (mainly COO-) in the gelatin structure. © 2009 Springer-Verlag