Genetic structure of natural populations of Escherichia coli in wild hosts on different continents

Current knowledge of genotypic and phenotypic diversity in the species Escherichia coli is based almost entirely on strains recovered from humans or zoo animals. In this study, we analyzed a collection of 202 strains obtained from 81 mammalian species representing 39 families and 14 orders in Australia and the Americas, as well as several reference strains; we also included a strain from a reptile and 10 from different families of birds collected in Mexico. The strains were characterized genotypically by multilocus enzyme electrophoresis (MLEE) and phenotypically by patterns of sugar utilization, antibiotic resistance, and plasmid profile. MLEE analysis yielded an estimated genetic diversity (H) of 0.682 for 11 loci. The observed genetic diversity in this sample is the greatest yet reported for E. coli. However, this genetic diversity is not randomly distributed; geographic effects and host taxonomic group accounted for most of the genetic differentiation. The genetic relationship among the strains showed that they are more associated by origin and host order than is expected by chance. In a dendrogram, the ancestral cluster includes primarily strains from Australia and ECOR strains from groups B and C. The most differentiated E. coli in our analysis are strains from Mexican carnivores and strains from humans, including those in the ECOR group A. The kinds and numbers of sugars utilized by the strains varied by host taxonomic group and country of origin. Strains isolated from bats were found to exploit the greatest range of sugars, while those from primates utilized the fewest. Toxins are more frequent in strains from rodents from both continents than in any other taxonomic group. Strains from Mexican wild mammals were, on average, as resistant to antibiotics as strains from humans in cities. On average, the Australian strains presented a lower antibiotic resistance than the Mexican strains. However, strains recovered from hosts in cities carried significantly more plasmids than did strains isolated from wild mammals. Previous studies have shown that natural populations of E. coli harbor an extensive genetic diversity that is organized in a limited number of clones. However, knowledge of this worldwide bacterium has been limited. Here, we suggest that the strains from a wide range of wild hosts from different regions of the world are organized in an ecotypic structure where adaptation to the host plays an important role in the population structure.

Hierarchical analysis of linkage disequilibrium in Rhizobium populations: evidence for sex?

Many bacterial species exhibit strong linkage disequilibrium of their chromosomal genes, which apparently indicates restricted recombination between alleles at different loci. The extent to which restricted recombination reflects limited migration between geographically isolated populations versus infrequent mixis of genotypes within populations is more difficult to determine. We examined the genetic structure of Rhizobium leguminosarum biovar phaseoli populations associated with wild and cultivated beans (Phaseolus spp.) over several spatial scales, ranging from individual host plants to throughout the Western Hemisphere. We observed significant linkage disequilibrium at scales at least as small as a cultivated plot. However, the amount of disequilibrium was much greater among isolates collected throughout the Western Hemisphere than among isolates from one area of Mexico, even when disequilibrium was quantified using an index that scales for allelic diversity. This finding suggests that limited migration between populations contributes substantially to linkage disequilibrium in Rhizobium. We also compared the genetic structure for R. leguminosarum bv. phaseoli taken from a cultivated plot with that for Escherichia coli obtained from one human host in an earlier study. Even at this fine scale, linkage disequilibrium in E. coli was very near the theoretical maximum level, whereas it was much less extreme in the local population of Rhizobium. Thus, the genetic structure for R. leguminosarum bv. phaseoli does not exclude the possibility of frequent mixis within local populations.

Single-photon emission computed tomography with 99mTc-exametazime in unmedicated schizophrenic patients

We examined 20 actively psychotic unmedicated schizophrenic patients and 20 matched control subjects by using single-photon emission, computed tomography (SPECT) with 99mtechnetium-exametazime. Patients showed a hyperfrontal pattern of tracer uptake with significant relative increases in superior prefrontal cortex. This abnormality was less pronounced in patients with higher symptom scores for psychomotor poverty. In addition, patients showed associations between certain schizophrenic syndrome scores, such as psychomotor poverty, disorganization, and reality distortion, and tracer uptake to a number of cortical and subcortical brain regions. This syndrome-related pattern of tracer uptake was, at least in part, consistent with similar associations previously reported in chronically medicated schizophrenic patients. SPECT therefore provides a readily available method to examine the relationship between symptom pattern and regional brain metabolism in psychotic patients. Any observed patterns of association will depend on the current mental and medication status of the patients examined.

Cadmium uptake by a human hepatic cell line (WRL-68 cells)

A hepatic human cell line (WRL-68 cells) was employed to investigate the uptake of the toxic heavy metal cadmium. Cd accumulation in WRL-68 cells is a time-, temperature- and concentration-dependent process. A rapid initial phase of uptake was followed by a second slower phase. The transport does not require energy and 55% of Cd transport occurs by temperature-insensitive processes, possibly by diffusion. The rest of Cd transport (45%) occurs by temperature-sensitive processes, probably ion channels and carriers, that involve interaction with sulfhydryl groups. The calcium channel blockers nifedipine and verapamil inhibit the uptake of cadmium, with an inhibition of 35% after 30 min incubation with 100 microM verapamil and 10 microM Cd. These data suggest that about one third of the Cd enters WRL-68 cells through the calcium channels. The toxic metals appear to use the transport pathways that exist for biologically essential metals. Our results in human hepatic cells are very similar to those reported in cultured rat hepatocytes. It appears that transport pathways available for Cd uptake are similar and independent of the species of hepatocyte origin. Moreover, the WRL-68 cell line seems to be an excellent in vitro model to study the mechanism of cell damage due to Cd.

Cadmium and mercury toxicity in a human fetal hepatic cell line (WRL-68 cells)

The toxic effects of cadmium (Cd) and mercury (Hg), as chloride salts, were studied using an hepatic human fetal cell line (WRL-68 cells). From viability curves and the proliferative capacity of the cell in the presence of the metal, three different cell treatments were chosen, (1) 0.5 microM of the metal chloride for 24 h (acute low dose treatment), (2) 0.5 microM of the metal chloride for 7 days (chronic treatment), and (3) 5 microM of the metal chloride for 24 h (acute high dose treatment). WRL-68 cells grown in the presence of Cd exhibited the same proliferative curve as control cells, whereas in the case of Hg, the cells increased their proliferative capacity. Both metals produced ultrastructural alterations in different degrees, mainly observed as mitochondrial and RER structural changes, depending of the treatment and concentration of the metal used. Cytotoxicity was assessed by measuring the release of lactate dehydrogenase from the cells. Acutely high dose-treated cells showed the highest value for this parameter, and Cd-treated cells presented higher lactate dehydrogenase release than the Hg-treated ones. Cell damage was also measured by alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) activities. Acute high dose Cd treatment caused the highest value of enzymatic release. Lipid peroxidation was significantly different with respect to control cells in chronic and acute high dose treatments with both metals. Metallothionein (MT) induction in response to Hg treatment was not detected. However, a dramatic induction of this protein occurred in Cd-treated cells. WRL-68 cells differentially respond to Cd and Hg making this hepatic fetal human cell line a useful tool in investigating the mechanism of toxicity of these heavy metals.

Genetic Structure of Rhizobium etli biovar phaseoli Associated with Wild and Cultivated Bean Plants ( Phaseolus vulgaris and Phaseolus coccineus ) in Morelos, Mexico

The genetic structure of Rhizobium etli biovar phaseoli was determined for five populations in three different locations in the state of Morelos, Mexico, by using starch gel electrophoresis for five to nine polymorphic loci. Two populations were sampled during two different years from nodules of cultivated and wild common bean plants ( Phaseolus vulgaris ). The three other populations were associated with wild runner beans ( P. coccineus ) and sampled during 1988. The Rhizobium populations differ genetically both among sites and among populations within the same site in different years, as shown by differences in allelic frequencies, genetic differentiation analysis, and differences in electrotypes. The total genetic diversity for the five populations during 1988 was H = 0.487; there were also high levels of genetic variation within each population. We found the highest linkage disequilibrium in a global analysis for all the populations. At a local scale, we also found significant linkage disequilibrium in two populations, although the distribution of the D′ suggest some recombination at a local scale. The other three rhizobium populations exhibit low linkage disequilibrium. A cluster analysis (UPGMA) of pairwise genetic distances showed that bacteria isolated from most wild Phaseolus spp. are grouped by population, whereas those obtained from cultivated P. vulgaris are very heterogeneous. The analysis of the genetic structure of Rhizobium strains may allow the identification of strains that are naturally well adapted to a wide range of different environments, which may be useful for agricultural purposes or as a starting point for developing improved Rhizobium strains.

Metadoxine prevents damage produced by ethanol and acetaldehyde in hepatocyte and hepatic stellate cells in culture

Metadoxine (pyridoxine-pyrrolidone carboxylate) has been reported to improve liver function tests in alcoholic patients. In the present work we have investigated the effect of metadoxine on some parameters of cellular damage in hepatocytes and hepatic stellate cells in culture treated with ethanol and acetaldehyde. HepG2 and CFSC-2G cells were treated with 50 mM ethanol or 175 microM acetaldehyde as initial concentration in the presence or absence of 10 microg ml(-1) of metadoxine. Twenty-four hours later reduced and oxidized glutathione content, lipid peroxidation damage, collagen secretion and IL-6, IL-8 and TNF- alpha secretion were determined. Our results suggest that metadoxine prevents glutathione depletion and the increase in lipid peroxidation damage caused by ethanol and acetaldehyde in HepG2 cells. In hepatic stellate cells, metadoxine prevents the increase in collagen and attenuated TNF- alpha secretion caused by acetaldehyde. Thus, metadoxine could be useful in preventing the damage produced in early stages of alcoholic liver disease as it prevents the redox imbalance of the hepatocytes and prevents TNF- alpha induction, one of the earliest events in hepatic damage.

Performance of serum-supplemented and serum-free media in IFNgamma Elispot Assays for human T cells

The choice of serum for supplementation of media for T cell assays and in particular, Elispot has been a major challenge for assay performance, standardization, optimization, and reproducibility. The Assay Working Group of the Cancer Vaccine Consortium (CVC-CRI) has recently identified the choice of serum to be the leading cause for variability and suboptimal performance in large international Elispot proficiency panels. Therefore, a serum task force was initiated to compare the performance of commercially available serum-free media to laboratories' own medium/serum combinations. The objective of this project was to investigate whether a serum-free medium exists that performs as well as lab-own serum/media combinations with regard to antigen-specific responses and background reactivity in Elispot. In this way, a straightforward solution could be provided to address the serum challenge. Eleven laboratories tested peripheral blood mononuclear cells (PBMC) from four donors for their reactivity against two peptide pools, following their own Standard Operating Procedure (SOP). Each laboratory performed five simultaneous experiments with the same SOP, the only difference between the experiments was the medium used. The five media were lab-own serum-supplemented medium, AIM-V, CTL, Optmizer, and X-Vivo. The serum task force results demonstrate compellingly that serum-free media perform as well as qualified medium/serum combinations, independent of the applied SOP. Recovery and viability of cells are largely unaffected by serum-free conditions even after overnight resting. Furthermore, one serum-free medium was identified that appears to enhance antigen-specific IFNgamma-secretion.

Cytokines, growth factors, and oxidative stress in HepG2 cells treated with ethanol, acetaldehyde, and LPS

Inflammatory mediators, including cytokines, growth factors, and reactive oxygen species, are associated with the pathology of chronic liver disease. In the liver, cytokine and growth factor secretion are usually associated with nonparenchymal cells, particularly Kupffer cells. In the present studies, the effect of 24 and 72 h administration of ethanol (50 mM). acetaldehyde (175 microM), and LPS (1 microg/ml) were studied on the expression and secretion of TNF-alpha, IL-1beta, IL-6, and TGF-beta3, lipid peroxidation damage and glutathion content in HepG2 cell cultures. A 24 h exposure to ethanol induced the expression of TNF-alpha and TGF-beta1, and the secretion of IL-1beta and TGF-beta1. With the same period of treatment, acetaldehyde markedly increased TNF-alpha expression, and stimulated IL-1beta secretion, while LPS exposure induced the expression of TNF-alpha, IL-6, and TGF-beta1, and the secretion of IL-1beta, IL-6, and TGF-beta1. A reduced in TNF-alpha response and TGF-beta1 expression were observed after 72 h exposure to ethanol. A 72 h acetaldehyde exposure decreased markedly TNF-alpha expression and stimulated a previously absent TGF-beta1 response. With the same time of exposure, LPS reduced slightly TGF-beta1 expression, and decreased its secretion. IL-1beta and IL-6 were not detected under 72 h exposure conditions. Lipid peroxidation damage was increased in all treatments, but higher values were found in 72 h treatments. Glutathion content diminished in all treatments. These findings suggest that HepG2 cells, independent of other cells such as Kupffer or macrophages, participate in a differential cytokine, growth factor and oxidative stress response, which differs according to the toxic agent and the time of exposure.

Connecting genomic patterns of local adaptation and niche suitability in teosintes

The central abundance hypothesis predicts that local adaptation is a function of the distance to the centre of a species' geographic range. To test this hypothesis, we gathered genomic diversity data from 49 populations, 646 individuals and 33,464 SNPs of two wild relatives of maize, the teosintes Zea mays ssp. parviglumis and Zea. mays. ssp. mexicana. We examined the association between the distance to their climatic and geographic centroids and the enrichment of SNPs bearing signals of adaptation. We identified candidate adaptive SNPs in each population by combining neutrality tests and cline analyses. By applying linear regression models, we found that the number of candidate SNPs is positively associated with niche suitability, while genetic diversity is reduced at the limits of the geographic distribution. Our results suggest that overall, populations located at the limit of the species' niches are adapting locally. We argue that local adaptation to this limit could initiate ecological speciation processes and facilitate adaptation to global change.

In vitro and occupational induction of sister-chromatid exchanges in human lymphocytes with furfuryl alcohol and furfural

Sister-chromatid exchanges (SCEs) in human lymphocytes were studied using the FPG technique in order to determine the cytogenetic effect of furfural and furfuryl alcohol. The induction of SCEs was also investigated in workers occupationally exposed to these solvents that are commonly used in the manufacture of furoic resins. The results obtained from the in vitro treatments show that furfural increased the number of SCEs, while furfuryl alcohol did not. In exposed workers, neither of these solvents increased the spontaneous frequency of SCEs per metaphase.

Uptake, cellular distribution and DNA damage produced by mercuric chloride in a human fetal hepatic cell line

A human hepatic cell line (WRL-68 cells) was employed to investigate the uptake of the toxic heavy metal mercury. Hg accumulation in WRL-68 cells is a time and concentration dependent process. A rapid initial phase of uptake was followed by a second slower phase. The transport does not require energy and at low HgCl2 concentrations (<50 microM) Hg transport occurs by temperature-insensitive processes. Subcellular distribution of Hg was: 48% in mitochondria, 38% in nucleus and only 8% in cytosolic fraction and 7% in microsomes. Little is known at the molecular level concerning the genotoxic effects following the acute exposure of eucaryotic cells to low concentrations of Hg. Our results showed that Hg induced DNA single-strand breaks or alkali labile sites using the single-cell gel electrophoresis assay (Comet assay). The percentage of damaged nucleus and the average length of DNA migration increased as metal concentration and time exposure increased. Lipid peroxidation, determined as malondialdehyde production in the presence of thiobarbituric acid, followed the same tendency, increased as HgCl2 concentration and time of exposure increased. DNA damage recovery took 8 h after partial metal removed with PBS-EGTA.

Epistatic effects of promoter and repressor functions of the Tn10 tetracycline-resistance operon of the fitness of Escherichia coli

We have been studying the effects of expression of plasmid-borne, Tn10-encoded, tetracycline resistance on the fitness of Escherichia coli K12. We previously demonstrated large reductions in fitness resulting from induced or constitutive expression of the resistance protein; however, any residual expression by the repressed operon was so slight that possession of an inducible resistance function imposed essentially no burden in the absence of antibiotic. Here, we demonstrate two distinct disadvantages for inducible genotypes relative to isogenic constitutive constructs. During the transition from antibiotic-free to antibiotic-containing media, the inducible genotype experiences a longer lag phase prior to growth. In the sustained presence of antibiotic, full induction of the resistance function in the inducible genotype is prevented by the continued action of its repressor. However, these disadvantages may be reduced by increasing the strength of the promoter for the resistance gene in the inducible genotype. Simultaneous consideration of the mode of gene regulation (i.e. constitutive or inducible) and the strength of the resistance-gene promoter (i.e. maximum level of expression) indicates an adaptive landscape with very strong epistasis and, perhaps, multiple fitness peaks.

The interaction of protein structure, selection, and recombination on the evolution of the type-1 fimbrial major subunit (fimA) from Escherichia coli

Fimbrial adhesins allow bacteria to interact with and attach to their environment. The bacteria possibly benefit from these interactions, but all external structures including adhesins also allow bacteria to be identified by other organisms. Thus adhesion molecules might be under multiple forms of selection including selection to constrain functional interactions or evolve novel epitopes to avoid recognition. We address these issues by studying genetic diversity in the Escherichia coli type-1 fimbrial major subunit, fimA. Overall, sequence diversity in fimA is high (pi = 0.07) relative to that in other E. coli genes. High diversity is a function of positive diversifying selection, as detected by d(N)/d(S) ratios higher than 1.0, and amino acid residuces subject to diversifying selection are nonrandomly clustered on the exterior surface of the peptide. In addition, McDonald and Kreitman tests suggest that there has been historical but not current directional selection at fimA between E. coli and Salmonella. Finally, some regions of the fimA peptide appear to be under strong structural constraint within E. coli, particularly the interior regions of the molecule that is involved in subunit to subunit interaction. Recombination also plays a major role contributing to E. coli fimA allelic variation and estimates of recombination (2N(e)c) and mutation (2N(e)mu) are about the same. Recombination may act to separate the diverse evolutionary forces in different regions of the fimA peptide.

Effect of endotoxin pretreatment on hepatic stellate cell response to ethanol and acetaldehyde

BACKGROUND AND AIM

The role of endotoxin in alcohol-induced liver damage is well recognized. How pre-exposure to endotoxin might affect alcohol injury is not known. We herein studied the effect of endotoxin pretreatment on hepatic stellate cell (HSC) response to ethanol and acetaldehyde.

METHODS

Rat HSC (CFSC-2G) were exposed to media supplemented with 1 microg/mL lipopolysaccharide (LPS). This was followed by a 24 h exposure to media containing LPS plus 50 mmol/L ethanol or 175 micromol/L acetaldehyde. Lipid peroxidation, collagen, and tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6 and transforming growth factor (TGF)-beta1 secretion were determined at the end of both periods of exposure.

RESULTS

Lipopolysaccharide pretreatment did not modify lipid peroxidation induced by ethanol or acetaldehyde alone. Glutathione (GSH) content decreased to 4.2 +/- 0.5 and 16.3 +/- 0.8 nmol protein after exposure to ethanol or acetaldehyde alone, and decreased further with LPS pretreatment (2.4 +/- 0.2 and 2.7 +/- 0.3 nmol/mg protein, respectively). Oxidized GSH (GSSG) content increased in ethanol and acetaldehyde LPS-pretreated cells only. Collagen secretion increased to 988 +/- 82 and 1169 +/- 91 microg/10(6) cells after exposure to acetaldehyde or LPS alone. Lipopolysaccharide pretreatment enhanced collagen secretion significantly in both ethanol- and acetaldehyde-treated cells (969 +/- 56 and 1360 +/- 72 microg/10(6) cells, respectively). Interleukin-6 production increased to 288 +/- 48, 1195 +/- 86 and 247 +/- 35 pg/mL per 10(6) cells after ethanol, acetaldehyde and LPS exposure, and increased further with LPS pretreatment in ethanol-exposed cells (680 +/- 23 pg/mL 10(6) cells).

CONCLUSION

Lipopolysaccharide pretreatment of HSC adds to the damage produced by ethanol and acetaldehyde by diminishing GSH content and increasing GSSG content, collagen and IL-6 secretion.

Expression of some hepatocyte-like functional properties of WRL-68 cells in culture

Some morphologic and functional characteristics of an hepatic fetal human epithelial cell line (WRL-68 cells) were determined to validate the use of these cells as an in vitro hepatic model. WRL-68 cells have a morphologic structure similar to hepatocytes and hepatic primary cultures. They secrete alpha-feto protein and albumin and exhibit a cytokeratin pattern similar to other hepatic cultures. WRL-68 cells preserve the activity of some characteristic or specific liver enzymes or both used in clinical chemistry for the diagnosis of hepatic disorders, i.e. alanine amino transferase, aspartate amino transferase, gamma-glutamyl transpeptidase, and alkaline phosphatase.

Weeds as Alternative Hosts of the Citrus, Coffee, and Plum Strains of Xylella fastidiosa in Brazil

In Brazil, Xylella fastidiosa is present in citrus (Citrus sinensis), coffee (Coffea arabica), and plum (Prunus sp.) crops, causing the citrus variegated chlorosis (CVC), coffee leaf scorch (CLS), and plum leaf scald (PLS). Also present in these crops and infesting weeds, which ultimately could serve as sources of inoculum for the cultivated trees, are diverse populations of xylem-feeding leafhopper vectors. In order to assess host range of X. fastidiosa among weeds and to better understand their role in epidemics, field surveys, mechanical inoculations, and insect transmission tests were conducted. Polymerase chain reaction (PCR) and culture plating were used to detect the pathogen from plant tissues. X. fastidiosa was detected in 10 out of 23 species of the weed plants sampled in two citrus groves affected by CVC. None of the weed plants showed external symptoms. In the greenhouse, the average percentages of infection on plants mechanically inoculated with the CVC, CLS, and PLS strains of X. fastidiosa were, respectively, 25, 10, 0 in Medicago sativa; 70, 45, 20 in Echinochloa crus-galli; 45, 30, 0 in Brachiaria decumbens; 72, 70, 40 in Brachiaria plantaginea; 13, 10, 0 in Digitaria horizontalis; 31, 30, 0 in Solanum americanum; and 17, 0, 0 in Bidens pilosa. Symptoms were observed only in S. americanum and citrus and only when inoculated with the CVC strain. In insect transmission tests, the grass leafhopper Ferrariana trivittata was first caged on citrus plants showing CVC symptoms and then on healthy citrus and on the four most common weeds. No plants tested positive by PCR or culture, or showed symptoms for at least 4 months after inoculation. The amount of X. fastidiosa cells that may accumulate in weeds inoculated by leafhoppers is probably under insect acquisition thresholds, a factor that would limit their importance to the CVC epidemics, as studies on spatial distribution of diseased citrus trees over time indicate.

Zinc pretreatment prevents hepatic stellate cells from cadmium-produced oxidative damage

Pretreatment with zinc produces tolerance to several cadmium toxic effects. This study was performed to further elucidate the mechanism of zinc-induced tolerance to cadmium cytotoxicity in a rat hepatic stellate cell line (CFSC-2G). Twenty four hours after seeding, cells were treated with 60 micromol/L ZnCl2 for 24 h. Following zinc pretreatment, cells were exposed to 3 micromol/L and 5 micromol/L CdCl2 for an additional 24 h. The toxicity of cadmium was significantly reduced in the zinc-pretreated cells. Zinc pretreatment produced a decrease in lipid peroxidation damage of cadmium-treated cells. Glutathione cell content diminished 33% and 43% as a result of 3 micromol/L and 5 micromol/ L CdCl2 treatment, respectively. Cell pretreatment with zinc recovered glutathione content at control cells level. Catalase and glutathione peroxidase activities were also recovered to control values with zinc pretreatment. Cadmium (5 micromol/L) was able to induce 39% the expression of alpha1 collagen (I) gene after 1 h treatment, while zinc pretreatment prevented this cadmium profibrogenic effect. We also examined the production of heat shock protein 70 (Hsp70) as a cellular response to oxidative stress produced by cadmium. By Western blot analysis, a 1.3 and 3 times increment in Hsp70, with 3 micromol/L and 5 micromol/L CdCl2 treatment, respectively, was observed. Zinc pretreatment prevented the production of Hsp70. Metallothionein-II (MT-II) gene expression was induced by cadmium, but the induction was unaffected with zinc pretreatment. These data suggest that zinc-induced protection against the cytotoxicity of cadmium in stellate cells may be related to the maintenance of normal redox balance inside the cell.

Pentoxifylline diminished acetaldehyde-induced collagen production in hepatic stellate cells by decreasing interleukin-6 expression

The effect of pentoxifylline (PTX), a methylxanthine derivative, on collagen induction and secretion and on the production of mRNA of two fibrogenic cytokines: interleukin-6 and transforming growth factor-beta(1) (IL-6 and TGF-beta(1)) in a rat hepatic stellate cell line (CFSC-2G) exposed to acetaldehyde was studied. CFSC-2G cells were treated with 175 microM acetaldehyde for 24h. The cells were then exposed to a medium containing 200 microM PTX. Collagen secretion, increased 2.6 times in acetaldehyde treated cells. Cells exposed to acetaldehyde and treated with PTX diminished collagen secretion to control values and decreased alpha(1)(I) collagen mRNA by 15%. Reverse transcriptase-polymerase chain reaction (RT-PCR) assays of TGF-beta(1) mRNA showed no variation in different experimental conditions. However, PTX induced a decrease of 32% in IL-6 mRNA in acetaldehyde-treated cells. CFSC-2G cells treated with anti-IL-6 monoclonal antibody, 15min before acetaldehyde was added, did not present an increase in alpha(1)(I) collagen mRNA. These results show that PTX inhibits the expression of alpha(1)(I) collagen via the inhibition of IL-6 in acetaldehyde treated cells. The effect herein reported on IL-6 and alpha(1)(I) collagen mRNA adds to the previously described effect of PTX, which could be useful in the fibrogenic process induced by acetaldehyde.

Nitrogen fixation in microbial mat and stromatolite communities from Cuatro Cienegas, Mexico

Nitrogen fixation (nitrogenase activity, NA) of a microbial mat and a living stromatolite from Cuatro Cienegas, Mexico, was examined over spring, summer, and winter of 2004. The goal of the study was to characterize the diazotrophic community through molecular analysis of the nifH gene and using inhibitors of sulfate reduction and oxygenic and anoxygenic photosynthesis. We also evaluated the role of ultraviolet radiation on the diazotrophic activity of the microbial communities. Both microbial communities showed patterns of NA with maximum rates during the day that decreased significantly with 3-3,4-dichlorophenyl-1',1'-dimethylurea, suggesting the potential importance of heterocystous cyanobacteria. There is also evidence of NA by sulfur-reducing bacteria in both microbial communities suggested by the negative effect exerted by the addition of sodium molybdate. Elimination of infrared and ultraviolet radiation had no effect on NA. Both microbial communities had nifH sequences that related to group I, including cyanobacteria and purple sulfur and nonsulfur bacteria, as well as group II nitrogenases, including sulfur reducing and green sulfur bacteria.

Methodological considerations in measurement of the P300 component of the auditory oddball ERP in schizophrenia

Twenty-three schizophrenic patients and 26 age-matched control subjects were studied using the P300 recorded during the auditory oddball task, with counting. Our aim was to assess the most suitable method of measurement and analysis of P300 amplitude and latency for use in clinical studies of schizophrenia. The effect of high-pass filtering, peak definition method and recording electrode site were all investigated. We have developed a technique, based on a least-mean-squares approximation to data, which seems particularly well suited to dealing with multi-peak P300 complexes. We have also investigated the spectral composition of the P300 and have found some evidence to support a proposed 2-frequency model of the P300 complex.

Apical hard-tissue deposition in adult teeth of monkeys with use of calcium hydroxide

The periapical tissues of adult teeth of monkeys were examined histologically after root canal treatment with calcium hydroxide. Healing, as evidenced by complete apical closure with a hard tissue bridge and an inflammation-free periodontal ligament, occurred more frequently where canals were instrumented 1 mm short of the apex. Overinstrumented canals exhibited a significantly decreased incidence of apical closure.

Effect of cadmium on calcium transport in a human fetal hepatic cell line (WRL-68 cells)

Toxic metals appear to use the transport pathways that exist for biologically essential metals. Calcium uptake in cells occurs through specific membrane channels. Since cadmium inhibits calcium uptake, this study was carried on to elucidate the mechanism of Cd interference with calcium transport using the fetal hepatic cell line WRL-68 as an in vitro model. Ca accumulation by WRL-68 cells presented an initial rapid phase, followed by a sustained phase of slower accumulation over a 60 min period. A concentration of 50 microM CdCl2 produced 39% inhibition of the uptake of CaCl2 (100 microM), while 100 microM nifedipine or verapamil decreased Ca accumulation by 35 and 63%, respectively. All Cd concentrations tested produced significant decrease in Ca uptake in a concentration-dependent manner at 1 min and thereafter, although with 10 microM CdCl2 no significant difference was found after 30 min of incubation. From the Lineweaver-Burk plot, we found that Cd exerted a competitive inhibition on Ca uptake, since there was no significant effect on the Vmax but an increased K(m). A second order rate constant of Cd inactivation of 0.061 mM-1.s-1 was determined from the course of Ca uptake during Cd inhibition. SH groups seemed to play an essential role in Ca inhibition uptake by Cd because the inhibition of Ca accumulation by 50 microM Cd was practically reversed after the addition of dithiothreitol.

The effect of the filling material in the tissue reactions following apical plugging of the root canal with dentin chips. A histologic study in monkeys' teeth

The object of the present work was to observe whether the root canal filling material has some influence in the periapical healing process after apical plugging with dentin chips. Monkeys' teeth were filled with nine different filling materials in use today. Ninety days after the treatment, the histologic data showed no differences in the results with the nine materials studied. This fact suggests that the filling material does not influence the healing process when the plug is present.