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Biomedical subjects

C Block

Publications and source records attributed to C Block.

At least 19 recordsLinked to original sources
PubMed2000

High rate of candidemia in patients sustaining injuries in a bomb blast at a marketplace: a possible environmental source.

In this study, a cluster of candidemia among patients sustaining injuries in a bomb blast at a marketplace was investigated by means of a multivariate analysis, a case-control study, and quantitative air sampling. Candidemia occurred in 7 (30%) of 21 patients (58% of those admitted to the intensive care unit [ICU]) between 4 and 16 days (mean, 12 days) after the injury and was the single most frequent cause of bloodstream infections. Inhalation injury was the strongest predictor for candidemia by multivariate analysis. Candidemia among the case patients occurred at a significantly higher rate than among comparable trauma patients injured in different urban settings, including a pedestrian mall (2 of 29; P=. 02), and among contemporary ICU control patients (1 of 40; P=.001). Air sampling revealed exclusive detection of Candida species and increased mold concentration in the market in comparison with the mall environment. These findings suggest a role for an exogenous, environmental source in the development of candidemia in some trauma patients.

Adolescent↗
PubMed2000

Phosphoinositide 3-kinase-dependent Ras activation by tauroursodesoxycholate in rat liver.

Ursodesoxycholic acid, widely used for the treatment of cholestatic liver disease, causes choleretic, anti-apoptotic and immunomodulatory effects. Here the effects on choleresis of its taurine conjugate tauroursodesoxycholate (TUDC), which is present in the enterohepatic circulation, were correlated with the activation of important elements of intracellular signal transduction in cultured rat hepatocytes and perfused rat liver. TUDC induced a time- and concentration-dependent activation of the small GTP-binding protein Ras and of phosphoinositide 3-kinase (PI 3-kinase) in cultured hepatocytes. Ras activation was dependent on PI 3-kinase activity, without the involvement of protein kinase C- and genistein-sensitive tyrosine kinases. Ras activation by TUDC was followed by an activation of the mitogen-activated protein kinases extracellular-signal-regulated kinase-1 (Erk-1) and Erk-2. In perfused rat liver, PI 3-kinase inhibitors largely abolished the stimulatory effect of TUDC on taurocholate excretion, suggesting an important role for a PI 3-kinase/Ras/Erk pathway in the choleretic effect of TUDC.

Animals↗
PubMed2000

Mitogenic signaling of Ras is regulated by differential interaction with Raf isozymes.

In the mitogenic signaling cascade interaction of Ras with Raf represents a critical step for the regulation of cell growth and differentiation. The major effector of Ras, the serine/threonine kinase Raf exists as three isoforms with different tissue distributions. We demonstrate that transient transfection of oncogenic Ha-Ras leads to a preferential activation of endogenous c-Raf-1 in HEK 293 cells as opposed to A-Raf. In vitro binding studies using purified Ras binding domains of Raf as well as in vivo bindings tests with full length molecules reveals significantly lower binding affinities of A-Raf to Ha-Ras as compared to other Raf isoforms. The Ras-binding interface of c-Raf differs from A-Raf by a conservative Arg to Lys exchange at residue 59 or 22 respectively. Mutational analysis reveals that this residue represents a point of isozyme discrimination: c-Raf-R59K binds Ha-Ras weaker than the wildtype, likewise A-Raf-K22R increases its affinity to Ha-Ras in vivo and in vitro. Differential binding affinities are reflected in downstream signaling. Immunecomplex kinase assays reveal that Ha-Ras mediated Raf activation is decreased for c-Raf-R59K and increased for A-Raf-K22R when compared to the respective wildtype forms. Thus our observations introduce a new level of isoform discrimination in Ras/Raf signaling as a functional consequence of a conservative amino acid exchange in the Ras binding domains.

Amino Acid Sequence↗
PubMed2000

Evaluation of chlorhexidine and povidone iodine activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis using a surface test.

Most published studies of the activity of biocides against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) have been based on suspension tests. This study was undertaken to provide information on the effect of chlorhexidine and povidone iodine on bacteria dried on to surfaces, a situation in which biocide activity is known to be reduced. The inactivation of MRSA (10 strains), methicillin-sensitive Staphylococcus aureus (MSSA, 10 strains), VRE (nine strains) and vancomycin-sensitive Enterococcus faecalis (VSE, 10 strains) by 0.5% aqueous chlorhexidine gluconate or 10% povidone iodine was evaluated by applying the European surface test method. Povidone iodine was equally active against resistant and sensitive strains of both species with microbicidal effects (ME), i.e. the log(10)concentration of micro-organisms compared with controls treated with distilled water, after 1.5 min of 3.14 and 3.49 for VRE and VSE respectively, and 3.47 and 3.78 for MRSA and MSSA. Chlorhexidine was equally active against VRE and VSE (ME 3.37 vs. 3. 56 after 7 min, respectively), but was significantly less active against MRSA as opposed to MSSA (ME 3.07 vs. 3.83 after 10 min, P= 0. 017).

Anti-Infective Agents, Local↗
PubMed1999

Thermodynamic and kinetic characterization of the interaction between the Ras binding domain of AF6 and members of the Ras subfamily.

Cellular signaling downstream of Ras is highly diversified and may involve many different effector molecules. A potential candidate is AF6 which was originally identified as a fusion to ALL-1 in acute myeloid leukemia. In the present work the interaction between Ras and AF6 is characterized and compared with other effectors. The binding characteristics are quite similar to Raf and RalGEF, i.e. nucleotide dissociation as well as GTPase-activating protein activity are inhibited, whereas the intrinsic GTPase activity of Ras is unperturbed by AF6 binding. Particularly, the dynamics of interaction are similar to Raf and RalGEF with a lifetime of the Ras. AF6 complex in the millisecond range. As probed by 31P NMR spectroscopy one of two major conformational states of Ras is stabilized by the interaction with AF6. Looking at the affinities of AF6 to a number of Ras mutants in the effector region, a specificity profile emerges distinct from that of other effector molecules. This finding may be useful in defining the biological function of AF6 by selectively switching off other pathways downstream of Ras using the appropriate effector mutant. Notably, among the Ras-related proteins AF6 binds most tightly to Rap1A which could imply a role of Rap1A in AF6 regulation.

Amino Acid Sequence↗
PubMed1999

Outbreak of bloodstream infections associated with dialysis machine waste ports in a hemodialysis facility.

Eight cases of gram-negative bloodstream infection without a clinically evident source occurred at a hemodialysis unit in Jerusalem between February and September 1997. All infections could be traced to three of the 13 dialysis machines in use. Epidemiological investigation, including pulsed-field gel electrophoretic characterization of organisms isolated from the patients and dialysis machines, implicated the Waste Handling Option system of the machines as the source of the infections. Discontinuation of the Waste Handling Option system use was associated with prompt cessation of the outbreak.

Adult↗
PubMed1999

Factors associated with pharyngeal carriage of Neisseria meningitidis among Israel Defense Force personnel at the end of their compulsory service.

In this 1 year cross-sectional study of personnel being discharged from compulsory military service, an available database of health-related information was used to examine the association of meningococcal carriage with socio-demographic factors. A representative, systematic sample of 1632 personnel was interviewed and had throat cultures taken. The overall meningococcal carriage rate was 16%. Serogroups B and Y accounted for 76% and 13% of the isolates respectively. In univariate analysis, carriage was associated with male gender (P < 0.0001), < 12 years school education (P = 0.002), smoking (P = 0.014), and service at a 'closed' base, reflecting greater interpersonal contact (P < 0.0001). In multivariate analysis, only service on a closed base and male gender retained significance. School education of < 12 years remained significant for females only. Variables not associated with carriage included number of siblings, intensity of smoking, and use of the contraceptive pill. In this setting, meningococcal carriage was associated with the type of base on which soldiers served; and smoking was not an independent risk factor for carriage.

Adult↗
PubMed1998

Sulindac sulfide inhibits Ras signaling.

The non-steroidal anti-inflammatory drug sulindac is used in cancer prevention and therapy, but the molecular aspects of its anti-tumor effect remain unresolved. In vivo the prodrug sulindac, is converted into the metabolite sulindac sulfide. We found that sulindac sulfide strongly inhibits Ras induced malignant transformation and Ras/Raf dependent transactivation. Sulindac sulfide decreases the Ras induced activation of its main effector, the c-Raf-1 kinase. In vitro sulindac sulfide directly binds to the Ras gene product p21ras in a non-covalent manner. Moreover, we can show that sulindac sulfide inhibits the interaction of p21ras with the p21ras binding domain of the Raf protein. In addition, sulindac sulfide can impair the nucleotide exchange on p21ras by CDC25 as well as the acceleration of the p21ras GTPase reaction by p120GAP. Due to its action at the most critical site in Ras signaling we propose sulindac sulfide as a lead compound in the search for novel anti-cancer drugs which directly inhibit Ras mediated cell proliferation and malignant transformation.

3T3 Cells↗
PubMed1998

Failure of mass antibiotic prophylaxis to control a prolonged outbreak of meningococcal disease in an Israeli village.

In January 1994 mass antibiotic prophylaxis was undertaken in the contiguous villages of Deir el-Asad and B'ine in northern Israel (combined population of 11600) in response to a prolonged outbreak of serogroup B meningococcal infection with an overall annual rate of 37.4 cases of infection per 100000 residents. The average case fatality rate in the villages was 23% compared with 11% in Israel during the same period. Neisseria meningitidis group B was identified in 9 of 13 (69%) cases. Seven of these were subtype P1.7,16. The persistence of the outbreak with its accompanying public reaction prompted the establishment of an intervention programme that included antibiotic prophylaxis for the whole community with monitoring for pharyngeal carriage of meningococci in a stratified sample of the population. The objectives were to achieve a reduction of carriage of the outbreak strain and to reduce morbidity and mortality. A total of 1036 pharyngeal swabs were taken 1 day before and 6 weeks after treatment. Antibiotic prophylaxis was administered in one dose: children under 5-years-old received ceftriaxone i.m.; all others received oral ciprofloxacin. Overall, 96% of the population received treatment. The carriage rate was 8.3% prior to treatment (three serogroup B:14:P1.7,16), and 1.3% afterwards (one serogroup B:14:P1.7,16). The intervention failed to eradicate carriage of the putative outbreak strain, or to reduce the incidence and fatality rates in the villages. The outbreak finally terminated in late 1996. Public health professionals should bear this experience in mind when faced with prolonged, localized, nonexplosive outbreaks of meningococcal disease associated with low carriage rates of the outbreak strain.

Adolescent↗
PubMed1998

Paroxetine treatment of trichotillomania in an adolescent.

The authors present a case report involving an adolescent with trichotillomania who was treated with paroxetine. A significant reduction in symptoms was apparent after two weeks of treatment. Dose was gradually increased to 30 mg of paroxetine per day, which was well tolerated without any significant adverse events. The authors discuss potential treatment implications of this case.

Adolescent↗
PubMed1998

Unreliability of disc diffusion test for screening for reduced penicillin susceptibility in Neisseria meningitidis.

The 2-U penicillin and microgram oxacillin discs proposed for screening meningococci for susceptibility to penicillin were evaluated by using MICs measured by the E test. The discs yielded unacceptably high frequencies of misclassification of susceptibility category and should be abandoned in favor of MIC estimations. An agreed breakpoint for reduced penicillin susceptibility in meningococci is needed for the E test.

Humans↗
PubMed1998

The RafC1 cysteine-rich domain contains multiple distinct regulatory epitopes which control Ras-dependent Raf activation.

Activation of c-Raf-1 (referred to as Raf) by Ras is a pivotal step in mitogenic signaling. Raf activation is initiated by binding of Ras to the regulatory N terminus of Raf. While Ras binding to residues 51 to 131 is well understood, the role of the RafC1 cysteine-rich domain comprising residues 139 to 184 has remained elusive. To resolve the function of the RafC1 domain, we have performed an exhaustive surface scanning mutagenesis. In our study, we defined a high-resolution map of multiple distinct functional epitopes within RafC1 that are required for both negative control of the kinase and the positive function of the protein. Activating mutations in three different epitopes enhanced Ras-dependent Raf activation, while only some of these mutations markedly increased Raf basal activity. One contiguous inhibitory epitope consisting of S177, T182, and M183 clearly contributed to Ras-Raf binding energy and represents the putative Ras binding site of the RafC1 domain. The effects of all RafC1 mutations on Ras binding and Raf activation were independent of Ras lipid modification. The inhibitory mutation L160A is localized to a position analogous to the phorbol ester binding site in the protein kinase C C1 domain, suggesting a function in cofactor binding. Complete inhibition of Ras-dependent Raf activation was achieved by combining mutations K144A and L160A, which clearly demonstrates an absolute requirement for correct RafC1 function in Ras-dependent Raf activation.

Amino Acid Sequence↗
PubMed1997

Discrimination of amino acids mediating Ras binding from noninteracting residues affecting raf activation by double mutant analysis.

The contribution of residues outside the Ras binding domain of Raf (RafRBD) to Ras-Raf interaction and Ras-dependent Raf activation has remained unresolved. Here, we utilize a double mutant approach to identify complementary interacting amino acids that are involved in Ras-Raf interaction and activation. Biochemical analysis demonstrates that Raf-Arg59 and Raf-Arg67 from RafRBD are interacting residues complementary to Ras-Glu37 located in the Ras effector region. Raf-Arg59 and Raf-Arg67 also mediate interaction with Ras-Glu37 in Ras-dependent Raf activation. The characteristics observed here can be used as criteria for a role of residues from other regions of Raf in Ras-Raf interaction and activation. We developed a quantitative two-hybrid system as a tool to investigate the effect of point mutations on protein-protein interactions that elude biochemical analysis of bacterially expressed proteins. This assay shows that Raf-Ser257 in the RafCR2 domain does not contribute to Ras-Raf interaction and that the Raf-S257L mutation does not restore Raf binding to Ras-E37G. Yet, Raf-S257L displays high constitutive kinase activity and further activation by Ras-G12V/E37G is still impaired as compared with activation by Ras-G12V. This strongly suggests that the RafCR2 domain is an independent domain involved in the control of Raf activity and a common mechanism for constitutively activating mutants may be the interference with the inactive ground state of the kinase.

Amino Acid Substitution↗
PubMed1997

Ras-binding domains: predicting function versus folding.

Ras interacts with a number of effector molecules to achieve its prolific signalling. Based on iterative sequence profile and motif searches of databases a novel family of Ras-binding domains was recently identified (Ponting and Benjamin, Trends Biochem. Sci. 21: 422-425, 1996). Among them the rat unconventional myosin and Rho-GTPase-activating protein myr 5 was predicted to contain a Ras-binding domain at its N-terminus. Here we report that direct binding experiments between the proposed Ras-binding domain of myr 5 and Ras failed to demonstrate any interaction. Molecular modelling suggests that this domain in myr 5 adopts a similar folding topology as the Ras-binding domain of Raf kinase. However, unlike the Ras-binding domain of Raf kinase, the myr 5 domain lacks the positive surface charges necessary for binding the negatively charged Ras contact site. This result exemplifies the functional diversity of similar structures and suggests that the identified Ras-binding motif does not reliably predict Ras-binding domains.

Animals↗
PubMed1997

Double-blind vaccine-controlled randomised efficacy trial of an investigational Shigella sonnei conjugate vaccine in young adults.

BACKGROUND: The aim of this double-blind randomised vaccine-controlled trial was to assess the efficacy of a conjugate vaccine composed of Shigella sonnei O-specific polysaccharide bound to Pseudomonas aeruginosa recombinant exoprotein A (S sonnei-rEPA) and of an oral, live-attenuated Escherichia coli/S flexneri 2a (EcSf2a-2) hybrid vaccine among military recruits in Israel at high risk of exposure to Shigella spp. We report here our preliminary findings on the efficacy of S sonnei-rEPA; we have not documented sufficient cases to assess the efficacy of EcSf2a-2. METHODS: Between April, 1993, and August, 1994, male Israeli Military recruits aged 18-22 years were asked to take part in our study. We enrolled 1446 soldiers from seven separate field sites (groups A-G). Soldiers were randomly allocated one injection of S sonnei-rEPA and four doses of oral placebo (n = 576), four oral doses of EcSf2a-2 and one injection of saline placebo (n = 580), or one injection of meningococcal tetravalent control vaccine and four doses of oral placebo (n = 290). Because there were no cases of S flexneri 2a, the EcSf2a-2 and meningococcal vaccines were the control group. We defined S sonnei shigellosis as diarrhoea with a positive faecal culture for S sonnei. Each group of soldiers was followed up for 2.5-7.0 months. The primary endpoint was protective efficacy of S sonnei-rEPA against S sonnei shigellosis. FINDINGS: Cases of culture-proven S sonnei shigellosis occurred in four groups of soldiers (groups A-D), which comprised 787 volunteers (312 received S sonnei-rEPA, 316 received EcSf2a-2, and 159 received meningococcal control vaccine). In groups A-C, cases of shigellosis occurred 70-155 days after vaccination, whereas in group D cases occurred after 1-17 days. In groups A-C, the attack rate of shigellosis was 2.2% in recipients of S sonnei-rEPA compared with 8.6% in controls (protective efficacy 74% [95% CI 28-100], p = 0.006). S sonnei-rEPA also showed significant protection against shigellosis in group D (43% [4-82], p = 0.039). Prevaccination and postvaccination ELISA measurements of antibody to S sonnei lipopolysaccharide among recipients of S sonnei-rEPA showed that the vaccinees who developed S sonnei shigellosis had significantly lower serum IgG and IgA responses to the homologous lipopolysaccharide than those who did not (p = < 0.05). INTERPRETATION: One injection of S sonnei-rEPA confers type-specific protection against S sonnei shigellosis. The high antibody concentration induced by the conjugate vaccine in volunteers who did not develop shigellosis suggests that there is an association between serum antibody titre and protection.

Adolescent↗