Brain-derived neurotrophic factor stimulates beta-amyloid gene promoter activity by a Ras-dependent/AP-1-independent mechanism in SH-SY5Y neuroblastoma cells

The beta-amyloid peptide, the major component of Alzheimer-associated plaques, derives from a larger beta-amyloid precursor protein (APP), that is expressed in both neural and non-neural cells. Overexpression of APP actively contributes to the development of senile plaques and is considered a risk factor for the disease. APP expression is regulated by a variety of cellular mediators, among them ligands of tyrosine kinase receptors. In this study, we present evidence that brain-derived neurotrophic factor (BDNF) modulates, in a dose- and time-dependent fashion, APP promoter activity in SH-SY5Y neuroblastoma cells transiently expressing the receptor TrkB. The APP promoter contains two potential AP-1 sites, and we examined whether or not protein kinase C (PKC) and the AP-1 sites of the promoter mediate the BDNF-induced stimulation of APP. Stimulation of APP promoter activity by BDNF was not affected by the PKC inhibitor bisindolylmaleimide, or by dominant negative mutants of the AP-1 components Fos and Jun, which, however, blocked the response to phorbol esters. These results suggest that activation of the APP promoter by BDNF is largely independent of PKC and AP-1. In contrast, activated Ras increased APP promoter activity in SH-SY5Y cells, and a dominant negative mutant of Ras abolished BDNF-mediated promoter stimulation. Taken together, our results suggest a mechanism that involves activation of the Ras/MAP kinase signaling pathway, and phosphorylation of as yet unidentified effectors which in turn can activate response elements within the APP promoter.

Glutamine potentiates TNF-alpha-induced tumor cytotoxicity

L-glutamine (Gln) sensitizes tumor cells to tumor necrosis factor (TNF)-alpha-induced cytotoxicity. The type and mechanism of cell death induced by TNF-alpha was studied in Ehrlich ascites tumor (EAT)-bearing mice fed a Gln-enriched diet (GED; where 30% of the total dietary nitrogen was from Gln). A high rate of Gln oxidation promotes a selective depletion of mitochondrial glutathione (mtGSH) content to approximately 58% of the level found in tumor mitochondria of mice fed a nutritionally complete elemental diet (standard diet, SD). The mechanism of mtGSH depletion involves a glutamate-induced inhibition of GSH transport from the cytosol into mitochondria. The increase in reactive oxygen intermediates (ROIs) production induced by TNF-alpha further depletes mtGSH to approximately 35% of control values, which associates with a decrease in the mitochondrial transmembrane potential (MMP), and elicits mitochondrial membrane permeabilization and release of cytochrome c. Mitochondrial membrane permeabilization was also found in intact tumor cells cultured with a Gln-enriched medium under conditions of buthionine sulfoximine (BSO)-induced selective GSH synthesis inhibition. Enforced expression of the bcl-2 gene in tumor cells could not avoid the glutamine- and TNF-alpha-induced cell death under conditions of mtGSH depletion. However, addition of GSH ester, which delivers free intracellular GSH and increases mtGSH levels, preserved cell viability. These findings show that glutamine oxidation and TNF-alpha, by causing a change in the glutathione redox status within tumor mitochondria, activates the molecular mechanism of apoptotic cell death.

Nuclear hormone receptors and gene expression

The nuclear hormone receptor superfamily includes receptors for thyroid and steroid hormones, retinoids and vitamin D, as well as different "orphan" receptors of unknown ligand. Ligands for some of these receptors have been recently identified, showing that products of lipid metabolism such as fatty acids, prostaglandins, or cholesterol derivatives can regulate gene expression by binding to nuclear receptors. Nuclear receptors act as ligand-inducible transcription factors by directly interacting as monomers, homodimers, or heterodimers with the retinoid X receptor with DNA response elements of target genes, as well as by "cross-talking" to other signaling pathways. The effects of nuclear receptors on transcription are mediated through recruitment of coregulators. A subset of receptors binds corepressor factors and actively represses target gene expression in the absence of ligand. Corepressors are found within multicomponent complexes that contain histone deacetylase activity. Deacetylation leads to chromatin compactation and transcriptional repression. Upon ligand binding, the receptors undergo a conformational change that allows the recruitment of multiple coactivator complexes. Some of these proteins are chromatin remodeling factors or possess histone acetylase activity, whereas others may interact directly with the basic transcriptional machinery. Recruitment of coactivator complexes to the target promoter causes chromatin decompactation and transcriptional activation. The characterization of corepressor and coactivator complexes, in concert with the identification of the specific interaction motifs in the receptors, has demonstrated the existence of a general molecular mechanism by which different receptors elicit their transcriptional responses in target genes.

Nerve growth factor modulates the expression and secretion of beta-amyloid precursor protein through different mechanisms in PC12 cells

The beta-amyloid protein, component of the senile plaques found in Alzheimer brains is proteolytically derived from the beta-amyloid precursor protein (APP), a larger membrane-associated protein that is expressed in both neural and non-neural cells. Overexpression of APP might be one of the mechanisms that more directly contributes to the development of Alzheimer's disease. The APP gene expression is regulated by a number of cellular mediators including nerve growth factor (NGF) and other ligands of tyrosine kinase receptors. We have previously described that NGF increases APP mRNA levels in PC12 cells. However, the molecular mechanisms and the precise signalling pathways that mediate its regulation are not yet well understood. In the present study we present evidence that NGF, and to a lesser extent fibroblast growth factor and epidermal growth factor, stimulate APP promoter activity in PC12 cells. This induction is mediated by DNA sequences located between the nucleotides - 307 and - 15, and involves activation of the Ras-MAP kinase signalling pathway. In contrast, we have also found that NGF-induced secretion of soluble fragments of APP into the culture medium is mediated by a Ras independent mechanism.

Unusual changing CT and MR appearance of an epithelial intracranial cyst

INTRODUCTION

Epithelial cysts are infrequent intracranial lesions and may content cilia and mucosecretant cells that may be responsible for the protein concentration within the contents and the variable radiological appearance on CT and MRI.

METHODS AND PATIENTS

We present a case of an extraaxial epithelial cyst with changing CT and MR characteristics.

RESULTS

The appearance of our cyst on CT or MRI changed with size and morphology. When CT studies showed an hypodense cyst, the lesion was large but when an hyperdense mass was present, the lesion was smaller. In the later situation MRI showed hyperintensity on T1-weighted images and hypointensity on T2-weighted images and the protein concentration of the cystic contents was high.

CONCLUSIONS

We believe that a relatively high protein concentration in our cyst was the major factor for the high attenuation on CT and the hyperintensity or hypointensity on T1- and T2-weighted images, respectively. We believe than these atypical imaging findings were caused by changes in the protein concentration within the cyst.

Synthesis and structure-activity relationships of benzophenone hydrazone derivatives with insecticidal activity

A broad range of benzophenone hydrazone derivatives was prepared and tested against selected chewing insect pests, allowing the analysis of structure-activity relationships. Good activity was found only when the aromatic rings were substituted at the 4-positions with an halogen atom and a triflate or perhaloalkoxy group. In contrast, a number of substituents on the hydrazone part led to active compounds, the best results being achieved with acyl-type substituents. The excellent laboratory and greenhouse activity of the best representatives was confirmed in semi-field trials against Spodoptera littoralis.

[False resistance to imipenem in gram negative bacilli with and automatized system]

BACKGROUND

The aim of this study was to evaluate the reliability of MIC values of imipenem against gramnegative rods obtained with the automated system WalkAway-98 (MicroScan, Dade, USA).

MATERIAL AND METHODS

One-hundred and seventy three consecutive clinical isolates of Gram-negative rods for which the MIC of imipenem were > or = 4 mg/l (Urine-Combo 6I panels, U6I) or > or = 8 mg/l (Neg-Combo 6I panels, N6I) were evaluated, including 104 non-fermenting gram-negative rods (NFGNR) and 69 enterobacteria. Panels were inoculated and read according to manufacturer's instructions. Microdilution, according to NCCLS guidelines, was used as the method of reference. MIC of imipenem determined by WalllAway-96 and microdilution differing > or = 2 dilution steps from those obtained with mirodilution were considered as discrepant results. Discrepancies in clinical categories were also evaluated by calculating three types of errors: very major (false susceptibility), major (false resistance) and minor (either susceptible or resistant by one method and intermediate by the other one).

RESULTS

The percentages of discrepancies in the MIC of imipenem determined with U6I panels were 74% and 84% for NFGNR and enterobacteria, respectively. No very major errors were detected. Major errors were observed for 6% and 12% of the strains with U6I panels in NFGNR and enterobacteria, respectively, and in 12% (NFGNR) and 50% (enterobacteria) with N61 panels. With U61 panels minor errors were observed in 11% and 25% of NFGNR and enterobacteria, respectively, while with N61 panels minor error were observed in 39% and 45% of both groups, respectively.

CONCLUSIONS

MIC of imipenem > or = 4 mg/l obtained with the WalkAway-96 system against gramnegative rods, particularly in the case of enterobacteria, should be confirmed with a reference susceptibility method.

Mitochondrial glutathione depletion by glutamine in growing tumor cells

The effect of L-glutamine (Gln) on mitochondrial glutathione (mtGSH) levels in tumor cells was studied in vivo in Ehrlich ascites tumor (EAT)-bearing mice. Tumor growth was similar in mice fed a Gln-enriched diet (GED; where 30% of the total dietary nitrogen was from Gln) or a nutritionally complete elemental diet (SD). As compared with non-tumor-bearing mice, tumor growth caused a decrease of blood Gln levels in mice fed an SD but not in those fed a GED. Tumor cells in mice fed a GED showed higher glutaminase and lower Gln synthetase activities than did cells isolated from mice fed an SD. Cytosolic glutamate concentration was 2-fold higher in tumor cells from mice fed a GED ( approximately 4 mM) than in those fed an SD. This increase in glutamate content inhibited GSH uptake by tumor mitochondria and led to a selective depletion of mitochondrial GSH (mtGSH) content (not found in mitochondria of normal cells such as lymphocytes or hepatocytes) to approximately 57% of the level found in tumor mitochondria of mice fed an SD. In tumor cells of mice fed a GED, 6-diazo-5-norleucine- or L-glutamate-gamma-hydrazine-induced inhibition of glutaminase activity decreased cytosolic glutamate content and restored GSH uptake by mitochondria to the rate found in EAT cells of mice fed an SD. The partial loss of mtGSH elicited by Gln did not affect generation of reactive oxygen intermediates (ROIs) or mitochondrial functions (e.g., intracellular peroxide levels, O(2)(-)(*) generation, mitochondrial membrane potential, mitochondrial size, adenosine triphosphate and adenosine diphosphate contents, and oxygen consumption were found similar in tumor cells isolated from mice fed an SD or a GED); however, mitochondrial production ROIs upon TNF-alpha stimulation was increased. Our results demonstrate that glutamate derived from glutamine promotes an inhibition of GSH transport into mitochondria, which may render tumor cells more susceptible to oxidative stress-induced mediators.

Intracellular penetration and activity of gemifloxacin in human polymorphonuclear leukocytes

The intracellular penetration and activity of gemifloxacin in human polymorphonuclear leukocytes (PMN) were evaluated. Gemifloxacin reached intracellular concentrations eight times higher than extracellular concentrations. The uptake was rapid, reversible, and nonsaturable and was affected by environmental temperature, cell viability, and membrane stimuli. At therapeutic extracellular concentrations, gemifloxacin showed intracellular activity against Staphylococcus aureus.

Absence of maternal-fetal transmission of human immunodeficiency virus type 1 to second-trimester fetuses

OBJECTIVE

The aim of this study was to evaluate the contribution of in utero infection to the vertical transmission of human immunodeficiency virus type 1 during the second trimester.

STUDY DESIGN

We examined fetal tissues from 21 second-trimester prostaglandin-induced abortions among human immunodeficiency virus type 1-infected women and compared the fetal vertical transmission rates with those among children born to human immunodeficiency virus-seropositive women. The presence of human immunodeficiency virus type 1 nucleic acid sequences was investigated with two different highly sensitive polymerase chain reaction techniques in tissue samples from the fetal thymus, lung, and brain.

RESULTS

No human immunodeficiency virus type 1 deoxyribonucleic acid was detected in any of the samples.

CONCLUSION

The absence of human immunodeficiency virus type 1 in all fetuses in our study is compatible with a low rate of maternal-fetal transmission during the second trimester of pregnancy.

Activities of imipenem and cephalosporins against clonally related strains of Escherichia coli hyperproducing chromosomal beta-lactamase and showing altered porin profiles

Forty clonally related clinical isolates of Escherichia coli from hospitalized patients were resistant to cefoxitin (MICs, >256 microg/ml) and ceftazidime (MICs, 32 to 256 microg/ml) and were intermediate or resistant to cefotaxime (MICs, 16 to 128 microg/ml) but susceptible to both cefepime (MICs, 0.5 to 2 microg/ml) and imipenem (MICs, 0.125 to 0.25 microg/ml). Resistance to beta-lactams was related to high-level production of AmpC beta-lactamase and loss of OmpF porin.

Uptake and intracellular activity of ofloxacin isomers in human phagocytic and non-phagocytic cells

The penetration and intracellular activity of ofloxacin and its isomers (levofloxacin and D-ofloxacin) into human polymorphonuclear leucocytes (PMN), human peritoneal macrophages (PMphi) and tissue cultured epithelial cells (McCoy) were evaluated. The cellular to extracellular concentration (C/E) values of the three fluoroquinolones were higher than 3.6 and 2.6 in PMN and PMphi, respectively. The C/E ratios in McCoy cells were lower than those in PMN, but still higher than 2.0. The uptake of ofloxacin and its isomers was rapid, non-saturable and reversible. All quinolones (extracellular concentrations: 2, 5 and 10 mg/l) produced a significant reduction of viable intraphagocytic Staphylococcus aureus in phagocytic cells. We concluded that ofloxacin and its isomers reach high intracellular concentrations in phagocytic and non phagocytic cells while remaining active in the former.

Relationship between outer membrane alterations and susceptibility to antimicrobial agents in isogenic strains of Klebsiella pneumoniae

The activities of beta-lactams, chloramphenicol, tetracycline, fluoroquinolones and aminoglycosides against Klebsiella pneumoniae C3 (O1:K66, producing porins OmpK35 and OmpK36) and a set of isogenic mutants derived from it lacking the O antigen of lipopolysaccharide (LPS), capsular K antigen, or one or both porins were determined. MICs remained within one dilution step in mutants deficient in antigen O, in capsule or in one of the two porins. No increases in the MICs of aminoglycosides, fluoroquinolones, tetracycline and chloramphenicol were observed for strains deficient in the two porins, but the MICs of ampicillin, cephalothin, cefoxitin, cefotaxime and ceftazidime for this type of mutant increased four- to >256-fold. The highest MICs of beta-lactams were obtained in a porin-deficient mutant expressing increased beta-lactamase activity. It is concluded that isolated outer membrane alterations in K. pneumoniae are not decisive factors in increasing resistance to antimicrobial agents, but porin loss co-operates with beta-actamase production to increase resistance to beta-lactams.

Mapping and fuzzy classification of macromolecular images using self-organizing neural networks

In this work the effectiveness of the fuzzy kohonen clustering network (FKCN) in the unsupervised classification of electron microscopic images of biological macromolecules is studied. The algorithm combines Kohonen's self-organizing feature maps (SOFM) and Fuzzy c-means (FCM) in order to obtain a powerful clustering technique with the best properties inherited from both. Exploratory data analysis using SOFM is also presented as a step previous to final clustering. Two different data sets obtained from the G40P helicase from B. Subtilis bacteriophage SPP1 have been used for testing the proposed method, one composed of 2458 rotational power spectra of individual images and the other composed by 338 images from the same macromolecule. Results of FKCN are compared with self-organizing feature maps (SOFM) and manual classification. Experimental results prove that this new technique is suitable for working with large, high-dimensional and noisy data sets and, thus, it is proposed to be used as a classification tool in electron microscopy.

In vitro adherence of Enterococcus faecalis and Enterococcus faecium to urinary catheters

The in vitro adherence of ten strains of Enterococcus faecalis and ten strains of Enterococcus faecium to siliconized latex urinary catheters and to silicone elastomer was evaluated. Bacterial suspensions (2.5x10(5) cfu/ml) in tryptic soy broth containing 0.5 cm segments from each type of catheter were incubated at 37 degrees C. At specified intervals, the segments were washed to remove nonadherent bacteria and sonicated for 1 min, and colony-forming units were quantified. Bacterial adherence occurred rapidly, reaching maximal peaks after 24 h of incubation. Enterococcus faecium adherence to both biomaterials was significantly lower than that of Enterococcus faecalis. No differences were observed between the two elastomers. Bacterial adherence was not related to bacterial surface hydrophobicity, hemolysin or gelatinase production.

[Heart arrest in cemented hip arthroplasty]

Hip arthroplasty is a common surgical intervention in our hospital practice, involving high perioperative risk related to patients age and multiple concomitant diseases. Hemodynamic complications described vary from slight hypotension during surgery to heart failure and sudden death, particularly if the operation involves a cemented femoral component. Because of the type of patients undergoing such operations (elderly patients, with osteoporosis and scarce cardiopulmonary reserve), the unclear origin of complications and the lack of consensus on what constitutes adequate monitoring during surgery, hip arthroplasty is problematic for the specialists involved. We report on five deaths during cemented hip arthroplasty; after reviewing the case history and autopsy report of one, we believe the events leading to death were triggered by massive pulmonary embolism.

[The activity of eight fluoroquinolones versus biolayers of Escherichia coli and Pseudomonas aeruginosa in siliconized latex urinary catheters]

OBJECTIVE

To evaluate the in vitro activity of eight fluoroquinolones against Escherichia coli and Pseudomonas aeruginosa biofilms on siliconized latex urinary catheters.

MATERIAL AND METHODS

The MICs and MBCs of norfloxacin, ciprofloxacin, ofloxacin, levofloxacin, clinafloxacin, sparfloxacin, trovafloxacin, and moxifloxacin for two strains of E. coli (CBR-3 and CBR-4) and two strains of P. aeruginosa (HUS-3 and PBR-2) were determined according to the NCCLS guidelines. The susceptibility of bacteria attached to siliconized latex catheters to fluoroquinolones was also evaluated. Catheter segments containing 6 or 24 hours old biofilms were used as inocula for the studies of antimicrobial activity against bacterial biofilms.

RESULTS

MICs of ciprofloxacin for planktonic and attached bacteria were equal. MICs values for the others fluoroquinolones increased two or more times when bacterial biofilms were used as inocula, except for ofloxacin and E. coli CBR-4, trovafloxacin and E. coli CBR-3, and levofloxacin and trovafloxacin and P. aeruginosa PBR-4; in these cases the MIC values for planktonic and attached bacteria were similar. When bacteria attached to siliconized latex were used as inocula, MBCs values increased 8-> 4,096-fold for all the fluoroquinolones evaluated.

CONCLUSIONS

E. coli and P. aeruginosa biofilms on siliconized latex were more resistant to the bactericidal activity of fluoroquinolones than planktonic bacteria.

Roles of beta-lactamases and porins in activities of carbapenems and cephalosporins against Klebsiella pneumoniae

Two clinical isolates of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae were noted to be less susceptible than expected to imipenem. Both were missing outer membrane proteins that serve as channels for antibiotic entry. The role of beta-lactamase in resistance was investigated by eliminating the original ESBL and introducing plasmids encoding various ESBLs and AmpC beta-lactamase types, by studying the effect of an increased inoculum, and by evaluating interactions with beta-lactamase inhibitors. The contribution of porin deficiency was investigated by restoring a functional ompK36 gene on a plasmid. Plasmids encoding AmpC-type beta-lactamases provided resistance to imipenem (up to 64 microg/ml) and meropenem (up to 16 microg/ml) in strains deficient in porins. Carbapenem resistance showed little inoculum effect, was not affected by clavulanate but was blocked by BRL 42715, and was diminished if OmpK36 porin was restored. Plasmids encoding TEM- and SHV-type ESBLs conferred resistance to cefepime and cefpirome, as well as to earlier oxyimino-beta-lactams. This resistance was magnified with an increased inoculum, was blocked by clavulanate, and was also lowered by OmpK36 porin restoration. In addition, SHV-2 beta-lactamase had a small effect on carbapenem resistance (imipenem MIC, 4 microg/ml, increasing to 16 microg/ml with a higher inoculum) when porins were absent. In K. pneumoniae porin loss can thus augment resistance provided either by TEM- or SHV-type ESBLs or by plasmid-mediated AmpC enzymes to include the latest oxyimino-beta-lactams and carbapenems.

Substrate binding and catalysis by ribonuclease P from cyanobacteria and Escherichia coli are affected differently by the 3' terminal CCA in tRNA precursors

We have studied the effect of the 3' terminal CCA sequence in precursors of tRNAs on catalysis by the RNase P RNA or the holoenzyme from the cyanobacterium Synechocystis sp. PCC 6803 in a completely homologous system. We have found that the absence of the 3' terminal CCA is not detrimental to activity, which is in sharp contrast to what is known in other bacterial systems. We have found that this is also true in other cyanobacteria. This situation correlates with the anomalous structure of the J15/16 loop in cyanobacteria, which is an important loop in the CCA interaction in Escherichia coli RNase P, and with the fact that cyanobacteria do not code the CCA sequence in the genome but add it posttranscriptionally. Modification of nucleotides 330-332 in the J15/16 loop of Synechocystis RNase P RNA from GGU to CCA has a modest effect on kcat for CCA-containing substrates and has no effect on cleavage-site selection. We have developed a direct physical assay of the interaction between RNase P RNA and its substrate, which was immobilized on a filter, and we have determined that Synechocystis RNase P RNA binds with better affinity the substrate lacking CCA than the substrate containing it. Our results indicate a mode of substrate binding in RNase P from cyanobacteria that is different from binding in other eubacteria and in which the 3' terminal CCA is not involved.