Downregulation of nicotinic and muscarinic receptor function in rats after subchronic exposure to diazinon.

Diazinon (DZN) is an organophosphate insecticide which exerts its effect through the inhibition of acetylcholinesterase enzyme (AChE). In this work, we studied the development of tolerance to subchronic p.o. administration of DZN in rats, under both in vivo and in vitro conditions. A group of 20 rats (2 groups, n = 10) was administered p.o. the 1/10 of established LD50 DZN (namely 55.87 mg/kg bw) for 28 days. On the 14th and 28th day of study with isolated diaphragm and ileum, we examined the downregulation of nicotinic and muscarinic receptor function through Electrical Field Stimulation (EFS). Maximum contractility of the diaphragm was recorded on the 14th day of the study (25% higher compared to the non-treated rats), while on the 28th day the contractions almost did not differ from the values found in non-treated rats. EFS of isolated ileum on the 14th day of study caused significantly higher contractions compared to the non-treated rats, but after 28 days, ileum contractions decreased approximately to the level of contractions in non-treated rats. On the 14th study day, we also recorded increased amplitude of spontaneous ileum contractions, compared to non-treated rats. The application of increasing ACh concentrations caused dose-dependent ileum contractions, without statistically significant differences of median effective concentration (EC50) values in non-treated and treated rats. Tolerance to subchronic DZN administration develops due to various adaptation mechanisms, including the most important one-downregulation of nicotinic and muscarinic receptor function.

Cation-π interactions in high resolution protein-RNA complex crystal structures.

In this work, we have analyzed the influence of cation-π interactions to the stability of 59 high resolution protein-RNA complex crystal structures. The total number of Lys and Arg are similar in the dataset as well as the number of their interactions. On the other hand, the aromatic chains of purines are exhibiting more cation-π interactions than pyrimidines. 35% of the total interactions in the dataset are involved in the formation of multiple cation-π interactions. The multiple cation-π interactions have been conserved more than the single interactions. The analysis of the geometry of the cation-π interactions has revealed that the average distance (d) value falls into distinct ranges corresponding to the multiple (4.28 Å) and single (5.50 Å) cation-π interactions. The G-Arg pair has the strongest interaction energy of -3.68 kcal mol(-1) among all the possible pairs of amino acids and bases. Further, we found that the cation-π interactions due to five-membered rings of A and G are stronger than that with the atoms in six-membered rings. 8.7% stabilizing residues are involved in building cation-π interactions with the nucleic bases. There are three types of structural motifs significantly over-represented in protein-RNA interfaces: beta-turn-ir, niche-4r and st-staple. Tetraloops and kink-turns are the most abundant RNA motifs in protein-RNA interfaces. Amino acids deployed in the protein-RNA interfaces are deposited in helices, sheets and coils. Arg and Lys, involved in cation-π interactions, prefer to be in the solvent exposed surface. The results from this study might be used for structure-based prediction and as scaffolds for future protein-RNA complex design.

Effects of infection intensity with Strongyloides papillosus and albendazole treatment on development of oxidative/nitrosative stress in sheep.

The objective of this study was to estimate and evaluate oxidative/nitrosative stress parameters in sheep infected with Strongyloides papillosus and after antihelminthic treatment with albendazole (ABZ). This parasite, especially during development stages can seriously damage parenchaematous organs during migration within the host. The presence of parasites leads to increased productions of reactive oxygen species (ROS) and reactive nitrogen species (RNS). It is also well known that certain drugs can be very harmful for the delicate oxidant-antioxidant equilibrium, provoking oxidative stress during their biotransformation. ABZ is a broad spectrum antihelminthic drug, frequently used in veterinary medicine for therapy of parasitic infections. The current research was performed on female Württemberg sheep (n=48). The distribution of parasites in sheep was evaluated using the native smear coprological technique, by sedimentation and flotation methods, revealing the presence of S. papillosus. The degree of infection intensity per sheep was quantitatively established by the method of McMaster, the animals having been divided into three groups according to the intensity of infection; mild, moderate and high. The control group consisted of sheep negative to the parasites. After determining the type of parasite infection, the sheep were treated with ABZ, per orally, in single doses of 5mg/kg per body weight. Sampling of feces for parasitological and blood for biochemical assaying was performed on the 0 and 21st day after treatment with ABZ. The oxidative stress parameters were measured for catalase activity (CAT), the red cell membrane damage by level of malondialdehyde (MDA), while carbonyl and thiol plasma protein group concentrations were used as indicators of the degree of protein oxidative modification. The activity of Cu,Zn-superoxide dismutase (SOD) and relative distribution of lactate dehydrogenase (LDH(1)-LDH(5)) activity were determined electrophoretically. The distribution of LDH isoenzymes in sheep moderately and highly infected with S. papillosus revealed that the parasite induced damage to the myocardial (LDH(2)), lung (LDH(3)) and liver cells (LDH(5)) in infected animals, while ABZ treatment only damaged liver cells (LDH(5)). The MDA concentration revealed that lipid peroxidation increased both in the presence of parasites and the antihelminthic formulation tested (p<0.001) when compared to the control sheep, while the increase of carbonyl concentration (p<0.001), as well as the observed decrease of thiol concentration (p<0.001) indicated significant oxidative damage of plasma proteins in experimental sheep, when compared to the control animals. Our results indicate that S. papillosus induces oxidative/nitrosative stress in sheep. The antihelminthic treatment with ABZ further promotes the disbalance of oxidative-antioxidative equilibrium in all tested sheep.