| 4971. |
- Yahyapour, Noushin, 1971
(author)
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Interactions between whole blood and biomaterial surfaces. With focus on the respiratory burst of adhering neutrophils as an early sign of cytotoxicity
- 2004
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Doctoral thesis (other academic/artistic)abstract
- Although a vast array of materials is used to augment or replace a natural function in the human body, many of them cause side-effects or may be rejected. The growing need for more biocompatible devices has been accompanied by an increase in new materials. For evaluation of such new materials, it is of importance to develop simple, rapid and sensitive in vitro models. Therefore, one aim of this thesis was to develop a model for estimating the toxicity of fluid materials, based on the degree of diminution of the respiratory burst activity of neutrophils. During the respiratory burst, oxygen is reduced by NADPH oxidase to reactive oxygen species. The effects of commercially used heat-sterilized peritoneal dialysis (PD) fluids on the respiratory burst response of titanium-adhering neutrophils were compared with the effects of filter-sterilized PD fluids. Filter-sterilized PD fluids lack the toxic components that develop during the commercial heat sterilization of PD fluids. The possibility of reducing the toxic effect of heat-sterilized PD fluids by addition of scavengers/antioxidants was also investigated.Bleeding and inflammation are the first steps in wound healing around biomaterials. Understanding each step of wound healing is of importance for understanding the whole process. Another aim of this thesis was therefore to study the interactions between whole blood and biomaterial surfaces. Blood cell adhesion to hydrophilic and hydrophobic glass surfaces was studied. The kinetics of formation of the three key proteins thrombin, kallikrein and complement C5b-9 on hydrophilic and hydrophobic glass and titanium surfaces was also investigated. Neutrophils adhering to titanium surfaces after whole blood exposure for 1 hour were found to be in a primarily activated state, since the expression of surface integrins was down-regulated and the expression of selectins was not detected. They also mounted a respiratory burst in the presence of stimulating agents. The respiratory burst response was attenuated in a time-dependent manner for neutrophils incubated in heat-sterilized PD fluids, while the response for neutrophils in a control buffer and in filter-sterilized PD fluids was not affected. The addition of glutathione to PD fluids improved the extracellular respiratory burst activity, whereas the intracellular activity was not affected.Thrombin and kallikrein were generated on hydrophilic and hydrophobic glass and titanium surfaces after a few seconds, and C5b-9 was detected after 32 minutes of blood exposure. Platelets were found on glass surfaces after a few seconds and were followed by neutrophils after 8 minutes, lymphocytes after 32 minutes and monocytes after 2 hours. Platelet adhesion was faster to hydrophobic glass. Activation of the coagulation cascade on titanium and glass was higher on the hydrophilic surfaces. C5b-9 coverage showed a different pattern on each surface and became denser with time.In conclusion, initial interactions at blood-material interfaces are dependent on both the type of material used and its surface properties. Furthermore, titanium-adhering neutrophils constitute a simple and sensitive model for cytotoxicity testing of fluid materials such as PD fluids.
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| 4972. |
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| 4973. |
- Yan, Yubin, 1965
(author)
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Semidiscrete Galerkin approximation for a linear stochastic parabolic partial differential equation driven by an additive noise
- 2004
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In: BIT. - 0006-3835 .- 1572-9125. ; 44:4, s. 829-847
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Journal article (peer-reviewed)abstract
- Abstract We study the semidiscrete Galerkin approximation of a stochastic parabolic partial differential equation forced by an additive space-time noise. The discretization in space is done by a piecewise linear finite element method. The space-time noise is approximated by using the generalized L2 projection operator. Optimal strong convergence error estimates in the L2 and norms with respect to the spatial variable are obtained. The proof is based on appropriate nonsmooth data error estimates for the corresponding deterministic parabolic problem. The error estimates are applicable in the multi-dimensional case.
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| 4974. |
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| 4975. |
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| 4976. |
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| 4977. |
- Yang, Xiao Lin, 1955, et al.
(author)
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Evidence of impaired adipogenesis in insulin resistance
- 2004
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In: Biochem Biophys Res Commun. - : Elsevier BV. - 0006-291X. ; 317:4, s. 1045-51
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Journal article (peer-reviewed)abstract
- To elucidate the roles of adipose tissue and skeletal muscle in the early development of insulin resistance, we characterized gene expression profiles of isolated adipose cells and skeletal muscle of non-diabetic insulin-resistant first-degree relatives of type 2 diabetic patients using oligonucleotide microarrays. About 600 genes and expressed sequence tags, which displayed a gene expression pattern of cell proliferation, were differentially expressed in the adipose cells. The differentially expressed genes in the skeletal muscle were mostly related to the cellular signal transduction and transcriptional regulation. To verify the microarray findings, we studied expression of genes participating in adipogenesis. The expression of Wnt signaling genes, WNT1, FZD1, DVL1, GSK3beta, beta-catenin, and TCF1, and adipogenic transcription factors, C/EBPalpha and beta and delta, PPARgamma, and SREBP-1, was reduced in the adipose tissue. The expression of adipose-specific proteins related to terminal differentiation, such as adiponectin and aP2, was reduced both in the adipose tissue and in the adipose cells isolated from portions of the biopsies. The adipose cells were enlarged in the insulin-resistant relatives and the cell size inversely correlated with the expression of the Wnt signaling genes, adiponectin, and aP2. Our findings suggest that insulin resistance is associated with an impaired adipogenesis.
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| 4978. |
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| 4979. |
- Yao, Yiming, 1957, et al.
(author)
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Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part II: the nanotube film
- 2004
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In: Journal of Materials Science: Materials in Electronics. ; 15:9, s. 583-594
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Journal article (other academic/artistic)abstract
- Carbon nanotube films have been grown at 750° and 900 °C by thermal chemical vapor deposition (CVD) with acetylene (C2H2) and hydrogen on silicon (0 0 2) wafers supporting preformed (Fe,Si)3O4 particles. The reduction of the (Fe,Si)3O4 particles during CVD at 750 °C was accompanied by a disintegration leading to the formation of a high density of smaller (predominantly 5–15 nm) iron silicide (α1-Fe2Si) particles that catalyzed the growth of a dense and aligned multi-wall carbon nanotube film. The tubes did not contain any inclusions apart from the catalytic particles present in the bottom part of the film, and it was concluded that the nanotubes grew via a “base-growth” mechanism. CVD at 900 °C resulted in a random growth of predominantly multi-wall carbon nanotubes. The film contained an increased number of amorphous carbon, or graphite, clusters containing particles that had been carbonized, the larger ones to cementite, θ-Fe3C. Nanotubes were observed to grow from some of these clusters. Multi-wall carbon nanotube tips contained after CVD at 900 °C encapsulated θ-Fe3C, or in a few cases α- or γ-Fe, particles.
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| 4980. |
- Yazdanparast, P., et al.
(author)
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A thyroid hormone analogue, triiodothyroacetic acid, corrects corticosteroid-downregulated collagen synthesis
- 2004
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In: Thyroid. ; 14:5, s. 345-53
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Journal article (peer-reviewed)abstract
- The aim of this study was to compare the change in collagen synthesis between topical treatments with two doses of triiodothyroacetic acid (TRIAC), a thyroid hormone analogue, and placebo, after pretreatment with topical betamethasone 17-valerate (BM). Eighteen healthy volunteers were pretreated with BM on abdominal skin for 3 days, and were then treated for 14 days with a cream containing TRIAC (0.03% or 0.1%) or a placebo cream. Collagen production was assessed by quantifying the amino terminal propeptides of human type I and type III procollagen (PINP and PIIINP) in fluids from suction-induced blisters on the treated skin. Three days of treatment with BM led to an average reduction of PINP of 70% and of PIIINP of 50%. Seven days after treatment, the median increase in PINP was 230% (p = 0.03) in the Triac 0.03% group, 148% (p = 0.2) in the TRIAC 0.1% and 5% in the placebo group. The median increase in PINP in the skin area from the start of treatment to the end of treatment was 521% (p = 0.06) in the TRIAC 0.03% group, 339% (p = 0.2) in the TRIAC 0.1% group, and 55% in the placebo group (the p values are related to baseline). Seven days after treatment, the median increase in PIIINP was 24% (p = 0.6) in the Triac 0.03% group, 23% (p = 0.6) in the TRIAC 0.1% group, and -12% in the placebo group. The median increase in PIIINP in the skin area from the start of treatment to the end of treatment was 137% (p = 0.7) in the TRIAC 0.03% group, 230% (p = 0.9) in the TRIAC 0.1% group and 58% in the placebo group (the p values are related to baseline). Histologic examinations of sections from punch biopsies taken at the end of the treatment showed more thickened collagen fibers and increased density of PINP-producing dermal fibroblasts in the TRIAC groups compared to the placebo group. The result suggests a potential role for TRIAC-containing cream concomitant with anti-inflammatory topical treatment with potent glucocorticoids to prevent their suppressive activity on dermal collagen production.
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