Regularities of Structure Formation in 30 mm Rods of Thermoelectric Material during Hot Extrusion

In this study, Ingots of (Bi, Sb)₂Te₃ thermoelectric material with p-type conductivity have been obtained by hot extrusion. The main regularities of hot extrusion of 30 mm rods have been analyzed with the aid of a mathematical simulation on the basis of the joint use of elastic-plastic body approximations. The phase composition, texture and microstructure of the (Bi, Sb)₂Te₃ solid solutions have been studied using X-ray diffraction and scanning electron microscopy. The thermoelectric properties have been studied using the Harman method. We show that extrusion through a 30 mm diameter die produces a homogeneous strain. The extruded specimens exhibit a fine-grained structure and a clear axial texture in which the cleavage planes are parallel to the extrusion axis. The quantity of defects in the grains of the (Bi, Sb)₂Te₃ thermoelectric material decreases with an increase in the extrusion rate. An increase in the extrusion temperature leads to a decrease in the Seebeck coefficient and an increase in the electrical conductivity. The specimens extruded at 450 °C and a 0.5 mm/min extrusion rate have the highest thermoelectric figure of merit (Z = 3.2 × 10⁻³ K⁻¹).     

Changes in activity of µ- and m-calpains and signs of neuroinflammation in the hippocampus and striatum of rats after single intraperitoneal injection of subseptic dose of endotoxin

Some mechanisms of neuronal degeneration in endotoxinemia are already well described, but need to be detailed. In this study, we tested the effect of a single intraperitoneal injection of a LPS sub-septic dose (1 mg/kg of animal weight) on calpain activity in the striatum and hippocampus. We showed, that in the hippocampus the day after LPS administration an increase in production of IL-1β and TNF-α mRNA, followed by elevated mRNA expression and activity of µ- and m-calpains without signs of microglia activation is observed. In striatal cells, the day after LPS injection an increase in expression of IL-1β, TNF-α, IBA-1, m-calpain and calpastatin mRNA is revealed, which only intensifies over time. The elicited changes are accompanied by a decrease in motor behavior, which can be considered as a sign of sickness behavior. In the hippocampus, 180 days after LPS administration expression of TNF-α, content and activity of µ-calpain are increased. In the striatum, elevation in expression of TNF-α, IBA-1, µ- and m-calpain mRNA, with hyperactivation of only m-calpain, is observed. Significantly reduced motor activity can be a consequence of LPS-induced neuronal death. A long-lasting endotoxin activates microglia that damage neurons via proinflammation cytokines and calpain hyperactivation. The endotoxin hypothesis of neurodegeneration is unproven, but if correct, then neurodegeneration may be reduced by decreasing endotoxin-induced neuroinflammation and m-calpain hyperactivation. Therefore, the drugs, that decrease endotoxin-induced neuroinflammation and differently inhibit µ- or m-calpain, can be used to prevent or reduce the severity of neurodegeneration.

     

Biomonitoring of aristolactam-DNA adducts in human tissues using ultra-performance liquid chromatography/ion-trap mass spectrometry

Aristolochic acids (AAs) are a structurally related family of nephrotoxic and carcinogenic nitrophenanthrene compounds found in Aristolochia herbaceous plants, many of which have been used worldwide for medicinal purposes. AAs have been implicated in the etiology of so-called Chinese herbs nephropathy and of Balkan endemic nephropathy. Both of these disease syndromes are associated with carcinomas of the upper urinary tract (UUC). 8-Methoxy-6-nitrophenanthro-[3,4-d]-1,3-dioxolo-5-carboxylic acid (AA-I) is a principal component of Aristolochia herbs. Following metabolic activation, AA-I reacts with DNA to form aristolactam (AL-I)-DNA adducts. We have developed a sensitive analytical method, using ultraperformance liquid chromatography-electrospray ionization/multistage mass spectrometry (UPLC-ESI/MS(n)) with a linear quadrupole ion-trap mass spectrometer, to measure 7-(deoxyadenosin-N(6)-yl) aristolactam I (dA-AL-I) and 7-(deoxyguanosin-N(2)-yl) aristolactam I (dG-AL-I) adducts. Using 10 μg of DNA for measurements, the lower limits of quantitation of dA-AL-I and dG-AL-I are, respectively, 0.3 and 1.0 adducts per 10(8) DNA bases. We have used UPLC-ESI/MS(n) to quantify AL-DNA adducts in tissues of rodents exposed to AA and in the renal cortex of patients with UUC who reside in Taiwan, where the incidence of this uncommon cancer is the highest reported for any country in the world. In human tissues, dA-AL-I was detected at levels ranging from 9 to 338 adducts per 10(8) DNA bases, whereas dG-AL-I was not found. We conclude that UPLC-ESI/MS(n) is a highly sensitive, specific and robust analytical method, positioned to supplant (32)P-postlabeling techniques currently used for biomonitoring of DNA adducts in human tissues. Importantly, UPLC-ESI/MS(n) could be used to document exposure to AA, the toxicant responsible for AA nephropathy and its associated UUC.     

Helicobacter pylori AlpA and AlpB bind host laminin and influence gastric inflammation in gerbils

Helicobacter pylori persistently colonizes humans, causing gastritis, ulcers, and gastric cancer. Adherence to the gastric epithelium has been shown to enhance inflammation, yet only a few H. pylori adhesins have been paired with targets in host tissue. The alpAB locus has been reported to encode adhesins involved in adherence to human gastric tissue. We report that abrogation of H. pylori AlpA and AlpB reduces binding of H. pylori to laminin while expression of plasmid-borne alpA or alpB confers laminin-binding ability to Escherichia coli. An H. pylori strain lacking only AlpB is also deficient in laminin binding. Thus, we conclude that both AlpA and AlpB contribute to H. pylori laminin binding. Contrary to expectations, the H. pylori SS1 mutant deficient in AlpA and AlpB causes more severe inflammation than the isogenic wild-type strain in gerbils. Identification of laminin as the target of AlpA and AlpB will facilitate future investigations of host-pathogen interactions occurring during H. pylori infection.     

Analysis of the Genome of the Escherichia coli O157:H7 2006 Spinach-Associated Outbreak Isolate Indicates Candidate Genes That May Enhance Virulence

In addition to causing diarrhea, Escherichia coli O157:H7 infection can lead to hemolytic-uremic syndrome (HUS), a severe disease characterized by hemolysis and renal failure. Differences in HUS frequency among E. coli O157:H7 outbreaks have been noted, but our understanding of bacterial factors that promote HUS is incomplete. In 2006, in an outbreak of E. coli O157:H7 caused by consumption of contaminated spinach, there was a notably high frequency of HUS. We sequenced the genome of the strain responsible (TW14359) with the goal of identifying candidate genetic factors that contribute to an enhanced ability to cause HUS. The TW14359 genome contains 70 kb of DNA segments not present in either of the two reference O157:H7 genomes. We identified seven putative virulence determinants, including two putative type III secretion system effector proteins, candidate genes that could result in increased pathogenicity or, alternatively, adaptation to plants, and an intact anaerobic nitric oxide reductase gene, norV. We surveyed 100 O157:H7 isolates for the presence of these putative virulence determinants. A norV deletion was found in over one-half of the strains surveyed and correlated strikingly with the absence of stx₁. The other putative virulence factors were found in 8 to 35% of the O157:H7 isolates surveyed, and their presence also correlated with the presence of norV and the absence of stx₁, indicating that the presence of norV may serve as a marker of a greater propensity for HUS, similar to the correlation between the absence of stx₁ and a propensity for HUS.Escherichia coli O157:H7 is a human pathogen that infects more than 73,000 North Americans per year (39). Although infection by this organism typically causes symptoms such as watery or bloody diarrhea, it may also lead to the development of hemolytic-uremic syndrome (HUS), an infection sequela characterized by hemolysis and renal failure that can result in long-lasting kidney damage. Variables that contribute to the development of HUS include host factors, such as age (51), and the genetic background of the enterohemorrhagic E. coli (EHEC) isolate. Currently, no effective prophylaxis exists for HUS (45). Antibiotic treatment of E. coli O157:H7 infections is contraindicated as it is associated with increased infection sequelae (45, 58).Humans become infected with EHEC by consuming contaminated food. EHEC are noninvasive pathogens that primarily colonize the human colon. Serotype O157:H7 is the predominant EHEC serotype in North America. The other commonly isolated EHEC serotypes include O26:H11, O103:H2, O111:NM, and O113:H21 (34). The systemic absorption of Shiga toxins produced by intestinal EHEC is thought to damage endothelial cells and to cause HUS (31). Shiga toxins are A-B-type toxins that inhibit protein synthesis. The genes encoding these potent toxins are borne on prophages that are related to phage λ. There are two main variants of Shiga toxin, Stx1 and Stx2. Stx2 is more cytotoxic than Stx1 in cell culture and animal models (27, 46, 48), and epidemiologic observations have revealed that the risk of developing HUS following an EHEC infection is heightened if the isolate produces Stx2 (4). Several variants of Stx2 exist, and Stx2c is the variant most commonly found in O157:H7 strains. Stx2 and Stx2c have the same biological function and possess identical A subunits and B subunits that share at least 97% identity (10).Although important for virulence, Stx2 does not appear to be the only EHEC factor that significantly influences whether patients infected with EHEC develop HUS. A comparison of statistics for several outbreaks caused by Stx2-producing O157:H7 strains showed that the rate of HUS can vary from less than 1% to 26% (23), indicating that strain-specific factors of stx₂-carrying O157:H7 strains are involved in determining clinical outcomes. To date, the most significant factor identified as a factor contributing to the variability is the presence of the stx₁ gene. O157:H7 strains that lack stx₁ but carry one or two stx₂ alleles are more likely to cause infections resulting in HUS (11, 35, 36).A comparison of the genome sequences of O157:H7 outbreak isolates that have resulted in different HUS rates may provide further insight into genetic factors that contribute to this severe sequela of EHEC infection. The genome sequences of two O157:H7 strains that caused low frequencies of HUS are available. The Sakai strain, the cause of the 1996 outbreak in Japan, caused ∼8,000 infections in people, the majority of whom were children, and the rate of HUS was 1.2% (32). In 1982, EDL933 caused the first diarrhea outbreak linked to the O157:H7 serotype and involved 44 individuals but no recorded HUS cases (41).Sakai shares 4.1 Mb of DNA with the commensal E. coli K-12 strain MG1655 and has 296 novel DNA segments more than 19 bp long, termed S-loops, that account for 1.39 Mb. EDL933 shares 4.1 Mb with E. coli K-12 strain MG1655 and has 177 unique sequence segments more than 50 bp long, termed O-islands, that account for 1.34 Mb (19). For both the Sakai and EDL933 genomes there is significant evidence of horizontal transfer due to the presence of numerous prophage-related elements and the pO157 virulence plasmid. The virulence factors carried on the O157:H7-specific DNA segments, as well as pO157, include stx₁, stx₂, the locus of enterocyte effacement (LEE), which confers the ability to cause attaching and effacing lesions on enterocytes and, notably, encodes a type III secretion system (TTSS) (22), at least 39 TTSS effectors encoded either on the LEE or at other chromosomal locations (49), numerous fimbrial and nonfimbrial adhesins, and more than one hemolysin (56).No genome sequence is available yet for an O157:H7 outbreak isolate that has caused an outbreak resulting in a significantly higher HUS rate. One O157:H7 isolate, TW14359, caused an outbreak associated with contaminated spinach that sickened 205 individuals in September and October of 2006. A total of 15% of the afflicted individuals developed HUS (5, 28). This rate is significantly higher than the average annual rate of 4.1% for O157:H7 cases that develop HUS (39). The relatively high percentage of adults, ∼8%, who developed HUS in the TW14359 outbreak also likely reflects the greater virulence of this strain (6). Furthermore, Manning et al. performed a phylogenetic analysis of TW14359 utilizing 96 single-nucleotide polymorphisms (SNPs) and demonstrated that this isolate belongs to a more virulent clade of O157:H7 strains (clade 8); the majority of these isolates lack stx₁ and carry stx₂ (28). A partial genome sequence consisting of 200 contigs of the TW14359 genome was also reported by Manning et al., which was found to contain stx₂ and stx_2c. While an analysis of these sequence data identified the genes of the two reference isolates that were also present in TW14359 and identified backbone SNPs, it did not provide a list of novel genetic features or provide assembled DNA segments containing repetitive DNA elements, such as phage-like elements. Here we describe the entire genome sequence of this isolate and, focusing on novel genetic material, identify potential genetic features of TW14359 that may promote this strain''s outstanding pathogenicity.     

Hypertonic shrinking but not hypotonic swelling increases sodium concentration in rat brain synaptosomes

Neurotransmitter release is dependent on both calcium and sodium influx. Hypotonic swelling and hypertonic shrinking of neurons evokes calcium-independent exocytosis of neurotransmitters into the synaptic cleft. To date, there are not too much data available on relationship between extracellular osmolarity and sodium concentration in presynaptic endings. In the present study we investigated the effects of hypotonic swelling and hypertonic shrinking on sodium levels, as measured using fluorescent dyes SBFI-AM and Sodium Green in rat brain synaptosomes. Reduction of incubation medium osmolarity from 310 to 230 mOsm did not raise the intrasynaptosomal sodium concentration. An increase of osmolarity from 310 to 810 mOsm is accompanied by a dose-dependent elevation of sodium concentration from 8.1+/-0.5 to 46.5+/-2.8mM, respectively. This effect was insensitive to several channel inhibitors such as: tetrodotoxin, an inhibitor of voltage-gated sodium channels, bumetanide, an inhibitor of Na(+)/K(+)/2Cl(-) cotransport, gadolinium, an inhibitor of nonselective mechanosensitive channels, ruthenium red, an inhibitor of transient receptor potential channel and amiloride, an inhibitor of epithelial sodium channel/degenerin. Additionally, using the fluorescent dye BCECF-AM, we have shown that hypertonic shrinking caused a dose-dependent acidification of intrasynaptosomal cytosol, which suggests that the Na(+)/H(+) exchanger is not involved in the effect of increased osmolarity on cytosolic sodium levels. The increase in intrasynaptosomal sodium concentrations following increases in osmolarity is probably due to sodium influx through another sodium channels.