Use of a composite Biomer-butyl rubber/Biomer material to prevent transdiaphragmatic water permeation during long-term, electrically-actuated left ventricular assist device (LVAD) pumping

The pumping diaphragm of the Texas Heart Institute (THI) E-Type ALVAD must perform the dual functions of providing a flexible blood interface and isolating the electrical actuator from adjacent fluids. Thus, protection is required against fluid leakage and moisture diffusion to prevent corrosion and damage to electrical actuator components. Average diffusion rates up to 1 ml per day through currently used elastomeric diaphragm materials have been measured during static in-vitro and in-vivo tests. To circumvent this problem, an improved pumping diaphragm has been recently developed for use with the electrically-actuated THI E-Type ALVAD. This trilaminar diaphragm consists of a composite Biomer and butyl rubber design. A.010 inch layer of butyl rubber (characterized by an extremely low diffusion rate for water, approximately 0 ml per day) is positioned between two Biomer layers (.020 and.010 inches in thickness). Initial invitro and in-vivo studies, in calves, indicate that this composite diaphragm provides an excellent barrier to water permeation, without sacrificing biocompatibility or structural integrity under conditions of chronic flexure.     

Factors influencing bacterial production of inducers of settlement behavior of larvae of the oysterCrassostrea gigas

Dissolved chemical inducers of settlement behavior of veliger larvae of the oysterCrassostrea gigas are found in supernatants of both pigmented species of bacteria (Alteromonas colwelliana, Vibrio cholerae strain HTX) as well as nonpigmented bacteria (Excherichia coli, Vibrio cholerae strain 596-B). Usually less than 10% of veligers exhibited settlement behavior in response to supernatants from the early bacterial growth phases, whereas 30–90% of larvae responded when exposed to supernatant from late-log and stationary phase cultures. Percentages of larvae exhibiting settlement behavior were inversely correlated with oxygen levels in the culture. Furthermore, the behavioral response decreased with pigment formation, suggesting that quantities of noxious compounds such as quinones may build up in the supernatants of cultures of pigmented bacteria. Tyrosinase, an enzyme that converts L-tyrosine to L-DOPA in the first step of melanogenesis, was detected both in the bacterial pellet and the supernatant during growth of the pigmented species. The enzyme is not required for the production of settlement inducer as the nonpigmented speciesE. coli andV. cholerae (596-B) also released inducer into the supernatant and had no detectable tyrosinase. The data suggest either that there is more than one inducer of settlement behavior found in bacterial supernatants or that the inducer is not L-DOPA or an L-DOPA-mimetic associated with the melanin biochemical pathway.     

Isolation and characterization of an adriamycin-resistant breast tumor cell line

Summary An adriamycin-resistant human breast tumor cell line MDA-A1 ^R was generated by step-wise selection in increasing concentrations of drug from the parent cell line MDA-MB-231. MDA-A1 ^R cells grow as loosely attached cell aggregates with a doubling time of 28–32 h; the MDA-MB-231 parent cell line grows as a standard monolayer culture with a 20-h doubling time. The MDA-A1 ^R cell line is highly resistant to adriamycin compared to the parent cell line, and is cross-resistant to velban and colchicine suggestive of a multidrug resistance (MDR) phenotype. MDA-A1 ^R cells exhibit reduced net adriamycin conent as compared to the parent cell line. The MDR-associated P-glycoprotein gene is amplified approximately 10-to 30-fold in MDA-A1 ^R cells. P-glycoprotein sequences are overexpressed in the resistant cells and are stable for up to 13 wk after drug removal. Moreover, MDA-A1 ^R cells show the presence of very high levels of P-glycoprotein. MDA-A1 ^R is thus an in vitro model system to study the mechanism of MDR in human breast cancer. This work was supported in part by grant C30195 from the National Institute of health, Bethesda, MD. Portion of this study appeared as a poster presentation at the Tissue Culture Association meeting, Las Vegas, 1988.     

Immunoreactive hephaestin and ferroxidase activity are present in the cytosolic fraction of rat enterocytes

Discovered over a decade ago, hephaestin (Heph) has been implicated as a ferroxidase (FOX) vital for intestinal iron absorption. Stringent structural or kinetic data derived from purified, native protein is however lacking, leading to the hypothesis that an alternate, undiscovered form of Heph could exist in mammalian enterocytes. This possibility was tested using laboratory rodent and cell culture models. Cytosolic and membrane fractions were obtained from rat enterocytes and purity of the fractions was assessed. Western blot analyses revealed Heph in cytosol obtained by three different methods, ruling out the possibility of a method-induced artifact being the major contributor to this observation. Absence of two different membrane-proteins, ferroportin 1 and Menke's copper ATPase in cytosol, and the absence of lipids in representative cytosolic samples tested by thin layer chromatography, eliminated significant membrane contamination of cytosol. Further, immunohisto- and immunocyto-chemical analyses identified Heph in rat enterocytes and in two intestinal epithelial cell lines, IEC-6 and Caco-2, intracellularly. Additionally, cytosolic Heph increased upon iron-deprivation but more important, decreased significantly upon copper-deprivation, mimicking the response of membrane-bound Heph. Moreover, FOX activity was present in rat cytosol, and was partly inhibited by anti-Heph antibody. Finally, lack of immunodetectable ceruloplasmin (Cp) by western blot precluded Cp as an underlying cause of this activity. These data demonstrate that rat enterocytes contain a soluble/cytosolic form of Heph possibly contributing to the observed FOX activity.     

A cooperative virulence plasmid imposes a high fitness cost under conditions that induce pathogenesis

Harbouring a plasmid often imposes a fitness cost on the bacterial host. Motivated by implications for public health, the majority of studies on plasmid cost are focused on elements that impart antibiotic resistance. Plasmids, however, can provide a wide range of ecologically important phenotypes to their bacterial hosts-such as virulence, specialized catabolism and metal resistance. The Agrobacterium tumefaciens tumour-inducing (Ti) plasmid confers both the ability to infect dicotyledonous plants and to catabolize the metabolites that plants produce as a result of being infected. We demonstrate that this virulence and catabolic plasmid imposes a measurable fitness cost on host cells under resource-limiting, but not resource replete, environmental conditions. Additionally, we show that the expression of Ti-plasmid-borne pathogenesis genes necessary to initiate cooperative pathogenesis is extremely costly to the host cell. The benefits of agrobacterial pathogenesis stem from the catabolism of public goods produced by infected host plants. Thus, the virulence-plasmid-dependent costs we demonstrate constitute costs of cooperation typically associated with the ability to garner the benefits of cooperation. Interestingly, genotypes that harbour derived opine catabolic plasmids minimize this trade-off, and are thus able to freeload upon the pathogenesis initiated by other individuals.     

A plant fiber reinforced polymer composite prepared by a twin-screw extruder

Polypropylene (PP) composites reinforced using a novel plant fiber, sunflower hull sanding dust (SHSD), were prepared using a twin-screw extruder. Thermal and mechanical properties of the SHSD/PP composites were characterized and compared to an organically modified clay (organo-clay)/PP composite. Differential scanning calorimetry (DSC) analysis showed that the crystallization temperature and the degree of crystallinity of PP exhibited changes with addition of SHSD and organo-clay. Mechanical properties of the PP were enhanced with the addition of SHSDs. Both the flexural strength and flexural modulus of the PP composites containing 5% (w/w) SHSD were comparable to that of the 5% (w/w) organo-clay reinforced PP. Scanning electron microscope (SEM) observation showed that no obvious agglomeration of SHSD existed in the PP matrix. Compared to the neat PP and organo-clay/PP, the SHSD/PP composites exhibited a relatively decreasing rate of thermal degradation with increase in temperature. Experimental results suggest that SHSD, as a sunflower processing byproduct, may find promising applications in composite materials.     

Efficiency clustering for low-density microarrays and its application to QPCR

Background  

Pathway-targeted or low-density arrays are used more and more frequently in biomedical research, particularly those arrays that are based on quantitative real-time PCR. Typical QPCR arrays contain 96-1024 primer pairs or probes, and they bring with it the promise of being able to reliably measure differences in target levels without the need to establish absolute standard curves for each and every target. To achieve reliable quantification all primer pairs or array probes must perform with the same efficiency.