Radiation resistance of elastomeric O-rings in mixed neutron and gamma fields: Testing methodology and experimental results.

Materials and components employed in the presence of intense neutron and gamma fields are expected to absorb high dose levels that may induce deep modifications of their physical and mechanical properties, possibly causing loss of their function. A protocol for irradiating elastomeric materials in reactor mixed neutron and gamma fields and for testing the evolution of their main mechanical and physical properties with absorbed dose has been developed. Four elastomeric compounds used for vacuum O-rings, one fluoroelastomer polymer (FPM) based and three ethylene propylene diene monomer rubber (EPDM) based, presently available on the market have been selected for the test. One EPDM is rated as radiation resistant in gamma fields, while the other elastomers are general purpose products. Particular care has been devoted to dosimetry calculations, since absorbed dose in neutron fields, unlike pure gamma fields, is strongly dependent on the material composition and, in particular, on the hydrogen content. The products have been tested up to about 2 MGy absorbed dose. The FPM based elastomer, in spite of its lower dose absorption in fast neutron fields, features the largest variations of properties, with a dramatic increase in stiffness and brittleness. Out of the three EPDM based compounds, one shows large and rapid changes in the main mechanical properties, whereas the other two feature more stable behaviors. The performance of the EPDM rated as radiation resistant in pure gamma fields does not appear significantly better than that of the standard product. The predictive capability of the accelerated irradiation tests performed as well as the applicable concepts of threshold of radiation damage is discussed in view of the use of the examined products in the selective production of exotic species facility, now under construction at the Legnaro National Laboratories of the Italian Istituto Nazionale di Fisica Nucleare. It results that a careful account of dose rate effects and oxygen penetration in the material, both during test irradiations and in operating conditions, is needed to obtain reliable predictions.

Functional and structural effects of percutaneous edge-to-edge double-orifice repair under cardiac cycle in comparison with suture repair.

Percutaneous procedures for double-orifice mitral valve repair using the MitraClip device (clip) have been recently introduced as new treatment options as alternatives to medical management and open-heart surgery, especially for patients with high estimated operative risk. Similarly to the open-heart surgical technique, where suturing is used, the clip creates a double-orifice configuration that not only improves the closing function of the valve, but also significantly modifies its behaviour, particularly in the diastolic phase. While several clinical trials have been conducted, and are ongoing, in order to assess the safety and effectiveness of this technique, a deeper knowledge of the structural and functional effects on the valve, and of the cyclic loads transmitted to the clip itself, would allow a comparison with other repair techniques, and could serve as a foundation for possible further optimization of the clip design. The effects of the MitraClip device developed by Evalve Inc. were studied by means of a finite element model of the mitral valve, specifically developed to study the structural effects of the original, suture-based, edge-to-edge technique. A second model was developed in order to simulate the effects of a suture with similar extension from the leaflet edge in a direction to the annulus, in order to compare the two repair techniques. The mitral valve area and transvalvular pressure gradient predicted by the models for the clip and the suture are quite similar. Similar leaflet cyclic stresses, both in value and in location, were noted for the two mechanisms of linking the leaflets, while minor differences were found in the load transmitted to the suture and the clip, with slightly higher values for the clip. The model satisfactorily allowed functional parameters (valve area and transvalvular pressure gradient) and structural parameters (load, leaflet stress) to be determined. Overall, the structural effects of the clip and the suture are quite similar under the cyclic loading conditions imposed by the cardiac cycle.

Structural effects of an innovative surgical technique to repair heart valve defects.

The structural and functional effects of the "edge-to-edge" technique on the human mitral valve have been investigated, paying particular attention to the diastolic phase. An advanced finite element model of the valve has been developed, using a hyperelastic material schematization, suitable geometry and constraint conditions, and an effective fluidodynamic analysis. The edge-to-edge suture has been applied on this model and the diastolic phase has been simulated. The results of this calculation show that the operation increases the transvalvular pressure and the maximum stress in the leaflets, which reaches a level similar to that of the systolic phase. The influence of suture position and extension, and the mitral annulus dimension has also been investigated. The results indicate that a lateral location of the stitch is better than a central one, both regarding valve functionality (pressure level and mobility) and internal stresses level, that a longer suture worsens the valve functionality but reduces the stresses level, finally, that the dilatation of the mitral annulus does not affect the valve functionality but increases the stresses level.

Implication of a central cysteine residue and the HHCC domain of Moloney murine leukemia virus integrase protein in functional multimerization.

Moloney murine leukemia virus (M-MuLV) IN-IN protein interactions important for catalysis of strand transfer and unimolecular and bimolecular disintegration reactions were investigated by using a panel of chemically modified M-MuLV IN proteins. Functional complementation of an HHCC-deleted protein (Ndelta105) by an independent HHCC domain (Cdelta232) was severely compromised by NEM modification of either subunit. Productive Ndelta105 IN-DNA interactions with a disintegration substrate lacking a long terminal repeat 5'-single-stranded tail also required complementation by a functional HHCC domain. Virus encoding the C209A M-MuLV IN mutation exhibited delayed virion production and replication kinetics.

AMD3100, a small molecule inhibitor of HIV-1 entry via the CXCR4 co-receptor.

The bicyclam AMD3100 (formula weight 830) blocks HIV-1 entry and membrane fusion via the CXCR4 co-receptor, but not via CCR5. AMD3100 prevents monoclonal antibody 12G5 from binding to CXCR4, but has no effect on binding of monoclonal antibody 2D7 to CCR5. It also inhibits binding of the CXC-chemokine, SDF-1alpha, to CXCR4 and subsequent signal transduction, but does not itself cause signaling and has no effect on RANTES signaling via CCR5. Thus, AMD3100 prevents CXCR4 functioning as both a HIV-1 co-receptor and a CXC-chemokine receptor. Development of small molecule inhibitors of HIV-1 entry is feasible.

Functional domains of Moloney murine leukemia virus integrase defined by mutation and complementation analysis.

Retroviral integrases perform two catalytic steps, 3' processing and strand transfer, that result in the stable insertion of the retroviral DNA into the host genome. Mutant M-MuLV integrases were constructed to define the functional domains important for 3' processing, strand transfer, and disintegration by in vitro assays. N-terminal mutants had no detectable 3' processing activity, and only one mutant which lacks the HHCC domain, Ndelta105, had strand transfer activity. Strand transfer mediated by Ndelta105 showed preference for one site in the target DNA. Disintegration activity of N-terminal mutants decreased only minimally. In contrast, all C-terminal mutants truncated by more than 28 amino acids had no integration or disintegration activity. Activity on a single-strand disintegration substrate did not require a functional HHCC domain but did require most of the C-terminal region. Complementation analysis found that the HHCC region alone was able to function in trans to a promoter containing only the DD(35)E and C-terminal regions and to enhance integration site selection. Increasing the reducing conditions or adding the HHCC domain to Ndelta105 reaction mixtures restored the wild-type strand transfer activity and range of target sites. The reducing agent affected Cys-209 in the DD(35)E region. The presence of C-209 was required for complementation of Ndelta105 by the HHCC region.

Coordinated disintegration reactions mediated by Moloney murine leukemia virus integrase.

The protein-DNA and protein-protein interactions important for function of the integrase (IN) protein of Moloney murine leukemia virus (M-MuLV) were investigated by using a coordinated-disintegration assay. A panel of M-MuLV IN mutants and substrate alterations highlighted distinctions between the intermolecular and intramolecular reactions of coordinated disintegration. Mispairing of the crossbone single-strand region and altered long terminal repeat (LTR) positioning affected the intermolecular, but not the intramolecular, reactions of coordinated disintegration. Partial components of the crossbone substrate were coordinated by M-MuLV IN, indicating a reliance on both LTR and target DNA determinants for substrate assembly. The intramolecular reaction was dependent on the presence of either the HHCC domain or a crossbone LTR 5' single-stranded tail. An M-MuLV IN mutant without the HHCC domain (Ndelta105) catalyzed reduced levels of double disintegration but not single disintegration. A separately purified HHCC domain protein (Cdelta232) stimulated double disintegration mediated by Ndelta105, suggesting a role of the N-terminal HHCC domain in stable IN-IN and IN-DNA interactions. Significantly, crossbone substrates lacking the LTR 5' tails were not recognized by the fingerless Ndelta105 protein. Collectively, these data suggest similar roles of the HHCC domain and 5' LTR tail in substrate recognition and modulation of IN activity.

Influence of substrate structure on disintegration activity of Moloney murine leukemia virus integrase.

The disintegration activity of Moloney murine leukemia virus (M-MuLV) integrase (IN) was investigated through structural and sequence modifications of a Y substrate that resembles an integration intermediate. The Y substrates, constructed from individual oligonucleotides, contain a single viral long terminal repeat (LTR) joined to a nicked target DNA. Truncation of the double-stranded LTR sequences distal to the conserved 5'-CA-3' dinucleotide progressively diminished disintegration activity. M-MuLV IN was also able to catalyze disintegration of a heterologous double-stranded LTR sequence. Significantly, the activity of M-MuLV IN on single-stranded LTR Y substrates was more dependent on the sequence and length of the LTR strand than that reported for human immunodeficiency virus type 1 (HIV-1) IN. Modifications introduced at the Y-substrate junction demonstrated that the 3'-hydroxyl group at the terminus of the target strand was necessary for efficient joining of the target DNA strands. The presence of a 2'-hydroxyl group at the 3' end of the target strand, as well as a single-nucleotide gap at the LTR-target junction, reduced disintegration activity. The absence of hydroxyl groups on the terminal nucleotide abolished joining of the target strands. The results presented here suggest that M-MuLV IN disintegration activity is dependent on substantially different LTR sequence requirements than those reported for HIV-1 IN and may be mediated primarily through a structural recognition event.

Characterization of the forward and reverse integration reactions of the Moloney murine leukemia virus integrase protein purified from Escherichia coli.

The forward and reverse reactions for integration were characterized for the Moloney murine leukemia virus integrase (M-MuLV IN) protein. The M-MuLV IN was recombinantly produced in Escherichia coli, and was purified to greater than 90% homogeneity by a one-step affinity purification scheme. M-MuLV IN was highly active for integration as measured by in vitro cleavage and strand transfer assays. Furthermore, the integration of a model viral substrate into lambda concatamers by IN correctly produced the flanking 4-base pair duplications characteristic of M-MuLV IN. The reverse reaction of integration, disintegration, was also catalyzed by the recombinant M-MuLV IN. Two products were generated, a 3'-recessed long terminal repeat and a ligated target DNA, from a model integration-intermediate substrate in the presence of M-MuLV IN. The requirements and optimal conditions for maximal integration and disintegration activity for M-MuLV IN were determined. The forward and reverse reactions required different concentrations of manganese ion and reductant. Salt was also titrated for the forward and reverse reactions. Sodium chloride inhibited integration, but had little affect on disintegration. Low concentrations of potassium chloride enhanced integration, but had no affect on disintegration. The dinucleotide cleavage, strand transfer, and the disintegration reactions each had a unique pH profile of activity.

Personality and duodenal ulcer response to antisecretory treatment.

Two groups of duodenal ulcer (DU) patients, responders and nonresponders, have been compared in order to verify if psychological factors are linked to relapse. Responders are defined as those patients who on endoscopy did not present proven relapse during treatment with maintenance doses of antisecretory drugs (cimetidine 400 mg/day, ranitidine 150 mg/day, pirenzepine 50 mg/day) for a period of 12 months after healing of the lesion. Nonresponders were all patients presenting with at least one relapse during treatment with antisecretory drugs. One hundred and twelve DU patients (81 responders, 31 nonresponders) were examined with the Cattell 16 Personality Factors Questionnaire (16PF) form C. There were no significant differences between the two groups for age, sex, duration of illness and type of drug treatment. The 16 PF scores of responders and nonresponders were not statistically different except in the case of factor E (dominance), in which the nonresponder subjects scored higher than responder subjects (p less than 0.01). However, when the significance level was corrected for the number of variables involved, the above finding is not considered to be meaningful.

Personality pattern of patients with chronic gastric ulcer: a case control study.

Personality factors are thought to play a role in peptic ulcer disease. In this study the psychological profiles of chronic gastric ulcer (GU) patients (n = 28) were compared to matched controls (n = 28) using the Cattell Sixteen Personality Factor Questionnaire Form C. GU patients were characterized by traits of anxiety, dependence, introspection, trustfulness and adaptability. These findings are discussed in the light of the literature on personality and peptic ulcer disease.