Transcranial Doppler ultrasound signals associated with prosthetic heart valves: an in vitro study

The application of transcranial Doppler (TCD) ultrasonography to asymptomatic prosthetic heart valve patients can result in detection of localized bursts of high intensity signals, similar to those caused by the passage of emboli. The origin of these signals is not known. In order to investigate this phenomenon in a simplified, more controllable environment, a TCD machine was used to record flow downstream from mechanical prosthetic heart valves in a mock circulatory loop. The model, which uses a saline solution seeded with silk particles (< 15 micrometers) as the circulatory fluid, recreates the principal hydrodynamic characteristics of the left heart and systemic circulation. Reproducibility of the system was established through repeated testing of a Monostrut valve. Three different mechanical valve types, (Monostrut, Medtronic Hall, St. Jude Medical) were tested over a range of simulated cardiac outputs, and the effect of valve size was investigated with four Omniscience tilting disc valves (21, 23, 25 and 29 mm). Average energy of the reflected Doppler signal was used to quantify the amount of high intensity Doppler signal, QTCD. TCD signals recorded in vitro were visually and aurally similar to those found in prosthetic heart valve patients. All valve types generated exponentially more QTCD with increasing simulated cardiac output. Differences amongst valve types were only significant at higher flow outputs, with the Monostrut valve producing the greatest QTCD. Larger valves consistently generated greater QTCD than smaller valves. In conclusion, TCD signals found in prosthetic heart valve patients can be reproduced, at least qualitatively, using a mock circulatory loop which does not incorporate the formed elements of blood.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification and characterization of genus-specific epitopes of Serpulina species using monoclonal antibodies

Four murine monoclonal antibodies (mAbs) designated as C9E8, A10, G12, and G8 which recognized both Serpulina hyodysenteriae and S. innocens were produced and characterized. The mAbs reacted with whole cell antigens in ELISA, indirect immunofluorescence and immunoblot assays. The mAbs did not show any cross reactivity in rapid dot ELISA or immunoblot assay with Leptospira icterohemorrhagiae, Campylobacter jejuni and Escherichia coli. Treatment of whole cell suspension with proteinase K and sodium periodate indicated that the reacting epitopes of the mAbs were protein in nature. The genus-specific antigens were identified as heat-stable proteins with molecular weight in the range of 26 to 45 kDa. Immunofluorescence and immunogold labelling studies showed that the antibody-binding epitopes were exposed on the outer-surface of the spirochaetal cell wall. The mAbs inhibited growth of reference strains of both S. hyodysenteriae and S. innocens in vitro but failed to cause agglutination. The detection of spirochaetal forms directly in fecal smears or paraffin-embeded tissue sections from experimentally infected pigs indicated that such mAbs were potentially useful for the diagnosis of swine spirochaetosis. This is the first report of mAbs identifying and characterizing common antigens of porcine Serpulina.     

Etoposide: four decades of development of a topoisomerase II inhibitor

Podophyllin-containing materials have been used as folk medicines for centuries. In the 1950s, scientists began a search to identify a more effective podophyllotoxin derivative. These efforts eventually resulted in the development of a new class of antineoplastic agents which target the DNA unwinding enzyme, topoisomerase II. The history of the development of one of the first identified topoisomerase II inhibitors, etoposide, is reviewed in this paper. Critical developments in etoposide's mechanism of action, pharmacology and administration schedule are summarised. The clinical benefits of the recently marketed etoposide prodrug, etoposide phosphate (Etopophos) are also detailed. The current status of other clinically approved anticancer agents which target topoisomerase II is briefly reviewed.     

An abrupt transition in colony founding behaviour in the ant Messor pergandei

Transitions in behaviour across a continuous distribution of organisms can provide valuable information on how variation in behaviour is maintained. We used analyses developed for interspecific hybrid zones to examine geographic variation in colony founding strategy in the desert seed-harvester ant, Messor pergandei. Newly mated females initiate new colonies either alone (haplometrosis) or cooperatively with other foundresses (pleometrosis). The incidence of these founding strategies were surveyed across the species' range and found to occur in geographically distinct regions joined by a narrow transition zone. Foundresses collected from haplometrotic sites were more likely to display aggression and found solitary nests than foundresses from pleometrotic sites, suggesting that geographical variation in metrosis is due to genotypic divergence. Foundresses from transitional sites were generally not aggressive and tended to co-found nests in the laboratory, yet rarely formed associations in the field. Such an abrupt shift in behaviour indicates that variation in colony founding strategy is maintained by selection rather than the result of secondary contact of neutral characters. Level of aggression displays a wider cline than founding strategy and is likely under selection only when accompanied by active strategy preference. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.     

Monocular enucleation prevents retinal ganglion-cell loss following neonatal visual cortex damage in cats

Studies were conducted to assess the utility of free solution capillary electrophoresis (CE) for monitoring the effects of selected excipients on the thermal denaturation of a model protein (Ribonuclease A, RNase A) at low pH. Thermal denaturation/unfolding experiments were conducted via temperature-controlled CE using a run buffer of 20 mM citric acid in the pH range of 2.3-3.1, with a marker peptide incorporated to correct for temperature-induced changes in endoosmotic flow. The effects of selected excipients on the thermal unfolding of RNase A were then evaluated by adding either sorbitol, sucrose, polyethylene glycol 400 (PEG 400) or 2-methyl-2,4-pentanediol (MPD) to the electrophoretic run buffer (pH 2.3). Confirmatory denaturation experiments were conducted under the same solution conditions using circular dichroism (CD) spectropolarimetry. Using temperature-controlled CE, an increase in solution pH from 2.3 to 2.7 and 3.1 resulted in an increase in transition temperatures of RNase A by approximately 8 and 13 degrees C, respectively. Similar shifts in transition temperatures were observed when thermal denaturation transitions were monitored by far-UV CD. Sorbitol (0.55-1.1 M) and sucrose (0.55 M) each shifted the denaturation transition temperatures of RNase A to higher values, whereas PEG 400 and MPD had minimal effect on the unfolding transition midpoint at the concentrations evaluated (0.55 M for each). The observed changes in the transition temperatures for RNase A as a function of pH and selected excipients were similar when measured by either CE or far-UV CD. These results support the utility of CE for monitoring the effects of neutral excipients on the thermal denaturation of a model protein under selected conditions. The widespread utility of the technique may be limited by the narrow temperature range of most commercial CE instruments and the need to use extreme pH conditions to monitor the complete denaturation transition.     

Inversin, a novel gene in the vertebrate left-right axis pathway, is partially deleted in the inv mouse

A DNA fragment containing the recA gene of Gluconobacter oxydans was isolated and further characterized for its nucleotide sequence and ability to functionally complement various recA mutations. When expressed in an Escherichia coli recA host, the G. oxydans recA protein could efficiently function in homologous recombination and DNA damage repair. The recA gene's nucleotide sequence analysis revealed a protein of 344 amino acids with a molecular mass of 38 kDa. We observed an E. coli-like LexA repressor-binding site in the G. oxydans recA gene promoter region, suggesting that a LexA-like mediated response system may exist in G. oxydans. The expression of G. oxydans recA in E. coli RR1, a recA+ strain, surprisingly caused a remarkable reduction of the host wild-type recA gene function, whereas the expression of both Serratia marcescens recA and Pseudomonas aeruginosa recA gene caused only a slight inhibitory effect on function of the host wild-type recA gene product. Compared with the E. coli RecA protein, the identity of the amino acid sequence of G. oxydans RecA protein is much lower than those RecA proteins of both S. marcescens and Pseudomonas aeruginosa. This result suggests that the expression of another wild-type RecA could interfere with host wild-type recA gene's function, and the extent of such an interference is possibly correlated to the identity of the amino acid sequence between the two classes of RecA protein.     

Mechanisms of expression of pyruvate dehydrogenase deficiency caused by an E1alpha subunit mutation

OBJECTIVE: To characterize the biochemical mechanisms of expression of the pyruvate dehydrogenase (PDH) E1alpha subunit exon 10 R302C missense mutation. BACKGROUND: Mutations in the X-linked E1alpha subunit gene are responsible for most cases of PDH deficiency, an important cause of neurodevelopmental defects and neurodegeneration with primary lactic acidemia. Although the disease shows extreme allelic heterogeneity, the R302C mutation has been defined in several unrelated cases. METHODS: Cell lines expressing selectively either the mutant or wild-type E1alpha alleles against identical genetic backgrounds were generated from the fibroblasts of a female heterozygous for the R302C mutation. Enzyme activity, mRNA, polypeptide expression, and turnover were studied in each. RESULTS: The residual PDH activity was below measurable levels in the cell line (B5) expressing only the mutant allele and normal in the wild-type polypeptide expressing (A10) cell line, confirming that the R302C mutation alone is sufficient to cause a severe PDH deficiency. The mutant polypeptide was less stable than the wild-type polypeptide, but the steady-state level of the mutant E1alpha protein was reduced only two- to threefold. CONCLUSIONS: The primary mechanism of expression of the R302C mutation must be limitation of catalytic efficiency. We speculate that catalysis may be inhibited in the mutant polypeptide because conformational changes are induced near serine 300, a residue that is particularly important as a regulatory phosphorylation site in the wild-type polypeptide.     

Clinical applications of anticancer drugs targeted to topoisomerase II

Agents which 'poison' the enzyme topoisomerase II, have proven to be useful drugs for cancer treatment. Six antineoplastic drugs, which target topoisomerase II (doxorubicin, daunorubicin, idarubicin, mitoxantrone, etoposide and teniposide) are currently approved for clinical use in the United States. In this paper, the strategies and goals of cancer chemotherapy are summarized for the non-clinician. The use, pharmacology and toxicity of each of the six currently approved topoisomerase II inhibiting agents are reviewed.     

Fibular shortening in poliomyelitis

We have determined the nucleotide and encoded amino acid sequences of the capsid, membrane precursor, membrane, envelope, and nonstructural NS1 protein genes of a dengue-2 virus (D2-04) isolated from a patient in Hainan, China. The sequenced region contains a gene organization similar to that of other flaviviruses. The overall amino acid sequence similarity between D2-04 and other dengue-2 viruses is greater than 92%, whereas that between D2-04 and members of the other dengue serotypes is about 65%.