Biomedical subjects

Ze Zhang

Publications and source records attributed to Ze Zhang.

32 records · Page 2Linked to original sources

PubMed2004

A novel electrically conductive and biodegradable composite made of polypyrrole nanoparticles and polylactide.

A novel electrically conductive biodegradable composite material made of polypyrrole (PPy) nanoparticles and poly(d,l-lactide) (PDLLA) was prepared by emulsion polymerization of pyrrole in a PDLLA solution, followed by precipitation. The composite was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The electrical stability of the composite containing 5 wt% PPy was investigated in a cell culture environment for 1000 h with 100 mV DC applied voltage. Fibroblasts were cultured on the composite membranes and were stimulated with various DC currents. The PPy particles formed aggregations and constituted microdomains and networks embedded in the PDLLA. With the 1-17% increase in the PPy content, the conductivity of the composite increased by six orders of magnitude. The surface resistivity of the PPy/PDLLA membrane with 3% PPy was as low as 1x10(3) Omega/square. The electrical stability was significantly better in the PPy/PDLLA composite than in the PPy-coated polyester fabrics. For the composite with 5% PPy, the test membrane retained 80% and 42% of the initial conductivity in 100 and 400 h, respectively, following the addition of the MEM solution, compared to 5% and 0.1% for the PPy-coated polyester fabrics. Under 100 mV, a composite membrane 3.0x2.5x0.03cm3 in size and containing 5% PPy sustained a biologically meaningful electrical conductivity in a typical cell culture environment for 1000 h. The growth of fibroblasts was up regulated under the stimulation of medium range intensity of DC current.

Adult↗

PubMed2004

Pore size, tissue ingrowth, and endothelialization of small-diameter microporous polyurethane vascular prostheses.

Small-diameter microporous polyurethane vascular prostheses with an average pore size of between 5 and 30mum at the outer surfaces and 30mum at the luminal surface were prepared. Thirty-two PU and 8 expanded polytetrafluoroethylene (ePTFE) prostheses were implanted into the abdominal aorta of rats for periods ranging from 1 to 8 weeks. Harvested prostheses were analysed histologically and morphologically. The progress of endothelial-like cells and the extent of infiltration of perigraft tissues were quantified. All of the prostheses showed fast growth of endothelial-like cells in the second week, with the PU prostheses having an external pore size of 30mum producing the highest rate. It was also during the second week that perigraft tissue grew most significantly into the prosthetic structure. This coincident may suggest the importance of rapid tissue regeneration for the early endothelial healing. The role of the ingrowth perigraft tissues is likely to support and stabilize the neointima. The thickening of neointima was mainly located at the vicinity of the proximal anastomoses of some of the PU prostheses and was unrelated with the extent of perigraft tissue infiltration. In the PU prostheses, a complete lining of endothelial-like cells was achieved by the end of 4 weeks. Expanded PTFE prostheses displayed smooth, thin intima, very limited tissue ingrowth, and incomplete coverage of endothelial-like cells.

Animals↗

PubMed2004

Genomic background predicts the fate of duplicated genes: evidence from the yeast genome.

Gene duplication with subsequent divergence plays a central role in the acquisition of genes with novel function and complexity during the course of evolution. With reduced functional constraints or through positive selection, these duplicated genes may experience accelerated evolution. Under the model of subfunctionalization, loss of subfunctions leads to complementary acceleration at sites with two copies, and the difference in average rate between the sequences may not be obvious. On the other hand, the classical model of neofunctionalization predicts that the evolutionary rate in one of the two duplicates is accelerated. However, the classical model does not tell which of the duplicates experiences the acceleration in evolutionary rate. Here, we present evidence from the Saccharomyces cerevisiae genome that a duplicate located in a genomic region with a low-recombination rate is likely to evolve faster than a duplicate in an area of high recombination. This observation is consistent with population genetics theory that predicts that purifying selection is less effective in genomic regions of low recombination (Hill-Robertson effect). Together with previous studies, our results suggest the genomic background (e.g., local recombination rate) as a potential force to drive the divergence between nontandemly duplicated genes. This implies the importance of structure and complexity of genomes in the diversification of organisms via gene duplications.

Evolution, Molecular↗

PubMed2004

Biocompatibility studies of the Anaconda stent-graft and observations of nitinol corrosion resistance.

PURPOSE: To validate the deployment, in vivo performance, biostability, and healing capacity of the Anaconda self-expanding endoprosthesis in a canine aortic aneurysm model. METHODS: Aneurysms were surgically created in 12 dogs by sewing a woven polyester patch onto the anterior side of the thoracic or abdominal aorta. Anaconda prostheses were implanted transfemorally for prescheduled periods (1 or 3 months). Aneurysm exclusion and stent-graft patency were monitored angiographically. Healing was assessed with histological analysis and scanning electron microscopy (SEM). Textile analysis determined the physical and chemical stability of the woven polyester material, while the biostability of the nitinol wires was evaluated with SEM and spectroscopy. RESULTS: All prostheses were intact at explantation. After 1 month, endothelial-like cells were migrating in a discontinuous manner both proximally and distally over the internal collagenous pannus at the device-host boundary. After 3 months, endothelialization had reached the midsections of the devices, with a thicker collagenous internal capsule. Patches of endothelial-like cells were sharing the luminal surface with thrombotic deposits. However, the wall of the device at the level of the aneurysm was generally poorly healed, with multiple thrombi scattered irregularly over the luminal surface. The polyester fabric was intact except for some filaments that were ruptured adjacent to the sutures and some abrasion caused by the nitinol wires. No evidence of corrosion was found on the nitinol stents. CONCLUSIONS: This Anaconda stent-graft has demonstrated its ability to exclude arterial aneurysms. The device used in this study was an experimental prototype, and the manufacturer has incorporated new immobilization features into the model for clinical use. The constituent materials appear to be suitable in terms of biocompatibility, biofunctionality, and short-term durability.

Alloys↗

PubMed2003

Genomic background drives the divergence of duplicated amylase genes at synonymous sites in Drosophila.

In some Drosophila species, there are two types of greatly diverged amylase (Amy) genes (Amy clusters 1 and 2), each encoding active amylase isozymes. Cluster 1 is located at the middle of its chromosomal arm, and the region has a normal local recombination rate. However, cluster 2 is near the centromere, and this region is known to have a reduced recombination rate. Although nonsynonymous substitutions follow a molecular clock, synonymous substitutions were accelerated in cluster 2 after gene duplications. This resulted in a higher GC content at the third codon position (GC3) and codon usage bias in cluster 1, and lower GC3 content and codon usage bias in the cluster 2. However, no systematic difference in GC content was observed in the first and second codon positions or the 3'-flanking regions. Therefore, differences in local recombination rate rather than mutation bias might explain the divergence at synonymous sites between the two Amy clusters within species (Hill-Robertson effect). Alternatively, the different patterns and levels of expression between the two clusters may imply that the reduced expression level in cluster 2 caused by chromatin potentiation decreased the codon bias. Both of these hypotheses imply the importance of the genomic background as a driving force of divergence between non-tandemly duplicated genes.

3' Flanking Region↗

PubMed2003

A biodegradable electrical bioconductor made of polypyrrole nanoparticle/poly(D,L-lactide) composite: A preliminary in vitro biostability study.

The electrical stability of a novel polypyrrole (PPy)/poly(D,L-lactide) (PDLLA) composite was studied in vitro and compared with that of PPy-coated polyester fabrics. Specimens were incubated in Ringer's solution at 37 degrees C for up to 8 weeks with or without the circulation of DC current under a constant 100 mV voltage. In situ current variation with incubation time was recorded. The AC volume electrical conductivity of the specimens before and after incubation in phosphate-buffered saline was recorded using a frequency analyzer. Water absorption and weight loss were monitored metrologically. Changes in the oxidation state of incubated PPy were analyzed with X-ray photoelectron spectroscopy. The morphological changes were observed with scanning electron microscopy, and the glass transition temperature of the PDLLA was investigated using differential scanning calorimetry. The PPy/PDLLA composite in Ringer's solution sustained a relatively stable conductivity up to 8 weeks after an initial period of "conditioning." The PPy-coated fabrics experienced a rapid loss of conductivity when subjected to electrical circulation and regained part of it when disconnected. The volume conductivity of the nonincubated PPy/PDLLA membrane behaved as a typical conductor in the low-frequency range. The mechanisms involved in the various electrical behaviours of the PPy/PDLLA composite and PPy-coated fabrics are discussed. In conclusion, the PPy/PDLLA composite was able to deliver a biologically significant electrical current in a simulated biological solution for up to 8 weeks and therefore may be considered as a first-generation synthetic biodegradable bioconductor.

Biocompatible Materials↗

PubMed2003

Liquid chromatographic/electrospray ionization mass spectrometric studies of proanthocyanidins in foods.

The proanthocyanidins in three foods (pinto beans, plums and cinnamon) were studied with electrospray ionization (ESI) mass spectrometry (MS) in the negative mode following separation by normal-phase high-performance liquid chromatography. The MS/MS analysis demonstrated that the major ions derived from heterocyclic ring fission and retro-Diels-Alder reaction of flavan-3-ol provided information about the hydroxylation pattern and type of interflavan bond. The connection sequence of the oligomers was identified through diagnostic ions derived from quinone methide (QM) cleavage of the interflavan bond. Novel heterogeneous B-type proanthocyanidins containing (epi)afzelechin as subunits were identified in pinto beans. Proanthocyanidins with interestingly different A-type linkages were identified in plums and cinnamon. In efforts aimed at extending the identification capacity of ESI-MS to polymers, we found that the polymeric procyanidins fragmented readily instead of forming multiply charged ions in the negative ESI mode. Fragmentation patterns were proposed based on our data obtained by ESI-MS/MS and ESI time-of-flight MS.

Chromatography, Liquid↗

PubMed2003

Phylogeny and the evolution of the Amylase multigenes in the Drosophila montium species subgroup.

To investigate the phylogenetic relationships and molecular evolution of alpha-amylase (Amy) genes in the Drosophila montium species subgroup, we constructed the phylogenetic tree of the Amy genes from 40 species from the montium subgroup. On our tree the sequences of the auraria, kikkawai, and jambulina complexes formed distinct tight clusters. However, there were a few inconsistencies between the clustering pattern of the sequences and taxonomic classification in the kikkawai and jambulina complexes. Sequences of species from other complexes (bocqueti, bakoue, nikananu, and serrata) often did not cluster with their respective taxonomic groups. This suggests that relationships among the Amy genes may be different from those among species due to their particular evolution. Alternatively, the current taxonomy of the investigated species is unreliable. Two types of divergent paralogous Amy genes, the so-called Amy1- and Amy3-type genes, previously identified in the D. kikkawai complex, were common in the montium subgroup, suggesting that the duplication event from which these genes originate is as ancient as the subgroup or it could even predate its differentiation. Thc Amy1-type genes were closer to the Amy genes of D. melanogaster and D. pseudoobscura than to the Amy3-type genes. In the Amy1-type genes, the loss of the ancestral intron occurred independently in the auraria complex and in several Afrotropical species. The GC content at synonymous third codon positions (GC3s) of the Amy1-type genes was higher than that of the Amy3-type genes. Furthermore, the Amy1-type genes had more biased codon usage than the Amy3-type genes. The correlations between GC3s and GC content in the introns (GCi) differed between these two Amy-type genes. These findings suggest that the evolutionary forces that have affected silent sites of the two Amy-type genes in the montium species subgroup may differ.

Amylases↗

PubMed2003

Evolutionary history and mode of the amylase multigene family in Drosophila.

Previous studies indicate that the tandemly repeated members of the amylase (Amy) gene family evolved in a concerted manner in the melanogaster subgroup and in some other species. In this paper, we analyzed all of the 49 active and complete Amy gene sequences in Drosophila, mostly from subgenus Sophophora. Phylogenetic analysis indicated that the two types of diverged Amy genes in the Drosophila montium subgroup and Drosophila ananassae, which are located in distant chromosomal regions from each other, originated independently in different evolutionary lineages of the melanogaster group after the split of the obscura and melanogaster groups. One of the two clusters was lost after duplication in the melanogaster subgroup. Given the time, 24.9 mya, of divergence between the obscura and the melanogaster groups (Russo et al. 1995), the two duplication events were estimated to occur at about 13.96 +/- 1.93 and 12.38 +/- 1.76 mya in the montium subgroup and D. ananassae, respectively. An accelerated rate of amino acid changes was not observed in either lineage after these gene duplications. However, the G+C contents at the third codon positions (GC3) decreased significantly along one of the two Amy clusters both in the montium subgroup and in D. ananassae right after gene duplication. Furthermore, one of the two types of the Amy genes with a lower GC3 content has lost a specific regulatory element within the montium subgroup species and D. ananassae. While the tandemly repeated members evolved in a concerted manner, the two types of diverged Amy genes in Drosophila experienced frequent gene duplication, gene loss, and divergent evolution following the model of a birth-and-death process.

Amylases↗

PubMed2003

Partial conservation of LFY function between rice and Arabidopsis.

The LFY/FLO genes encode plant-specific transcription factors and play major roles in the reproductive transition as well as floral development. In this study, we reconstructed the phylogenetic tree of the 49 LFY/FLO homologs from various plant species. The tree clearly shows that the LFY/FLO genes from the eudicots and monocots formed the two monophyletic clusters with very high bootstrap probabilities, respectively. Furthermore, grass LFY/FLO genes have experienced significant acceleration of amino acid replacement rate compared with the eudicot homolog. To test whether grass LFY/FLO genes have a conserved function with those of eudicots, we introduced RFL, a rice LFY homolog, into the Arabidopsis lfy mutant. The RFL gene driven by LFY promoter partially rescued the lfy mutation, suggesting that the functions of LFY and RFL partly overlap. Interestingly, the RFL but not LFY, strongly activated the expression of AP1 and AG, the downstream targets of LFY, even in the vegetative tissues. The LFY::RFL transgenic Arabidopsis plants exhibited abnormal patterns of development such as leaf curling, bushy appearance and the transformation of ovules into carpels. All of the results indicate that both the partial conservation and divergence of LFY function between rice and Arabidopsis.

Amino Acid Sequence↗

PubMed2002

Biostability of electrically conductive polyester fabrics: an in vitro study.

The biostability of a series of polypyrrole (PPy)-coated polyester fabrics was investigated in an in vitro model. PPy-coated sample fabrics were incubated in saline at 37 degrees C for 1 and 2 weeks. After each period of incubation, the surface electrical resistivity of the sample fabrics was measured to monitor the changes caused by the incubation. Redoping was then performed by immersing the sample fabrics in a 1N HCl solution at room temperature for 30 min, which was followed by another measurement of the surface resistivity. The surface morphology of the sample fabrics was observed by scanning electron microscopy. The surface chemical composition of the fabrics and the oxidation of nitrogen in PPy were measured with X-ray photoelectron spectroscopy. The surface electrical resistivity of the PPy-coated fabrics was found to increase with the progress of incubation, which was mainly caused by dedoping and uptake of oxygen. This increase was nonlinear and accelerated with time. The surface resistivity of most of the samples was retained in the range of 10(3)-10(4) Omega/square after 1 week of incubation, which was considered suitable for short-term electrical stimulation applications. Physical deterioration represented by the cracking and delamination of the PPy coating was occasionally observed on the sample fabrics showing the most significant increase of resistivity. Further improvement of the stability of conductivity is highly desirable.

Chlorides↗

PubMed2002

Tissue reaction to polypyrrole-coated polyester fabrics: an in vivo study in rats.

Electrically conductive polypyrrole is very attractive for tissue engineering because of its potential to modulate cellular activities through electrical stimulation. However, its in vivo behaviors have not been fully studied. This paper investigates the in vivo biocompatibility and biostability of PPy-coated polyester fabrics. Three PPy-coated fabrics were prepared using phosphonylation (PPy-Phos), plasma activation (PPy-Plas), and plasma activation plus heparin treatment (PPy-Plas-HE). Virgin and fluoropassivated fabrics (F-PET) were controls. The specimens were implanted subcutaneously in the back of rats for 3-90 days, then harvested and processed for enzymatic, histological, and morphological analyses. A noninvasive MRI method was used to continuously monitor the inflammation. The level of acid and alkaline phosphatase showed a similar or a less intensive cellular reaction by the PPy-coated fabrics, when compared to the controls. Histology supported the enzymatic results and showed a fast collagen infiltration at 28 days for the PPy-Phos fabric. MRI reported an overall decrease of inflammation over time, with the PPy-coated fabrics showing a similar or mild inflammation in contrast to the non-coated fabrics. PPy clusters and excessive PPy laminary coating on the PPy-Plas and PPy-Plas-HE were lost with the implantation. This experiment suggests a similar in vivo biocompatibility of the PPy-coated and noncoated polyester fabrics and the importance of achieving a thin, uniform PPy coating.

Acid Phosphatase↗

PubMed2002

Codon bias differentiates between the duplicated amylase loci following gene duplication in Drosophila.

We examined the pattern of synonymous substitutions in the duplicated Amylase (Amy) genes (called the Amy1- and Amy3-type genes, respectively) in the Drosophila montium species subgroup. The GC content at the third synonymous codon sites of the Amy1-type genes was higher than that of the Amy3-type genes, while the GC content in the 5'-flanking region was the same in both genes. This suggests that the difference in the GC content at third synonymous sites between the duplicated genes is not due to the temporal or regional changes in mutation bias. We inferred the direction of synonymous substitutions along branches of a phylogeny. In most lineages, there were more synonymous substitutions from G/C (G or C) to A/T (A or T) than from A/T to G/C. However, in one lineage leading to the Amy1-type genes, which is immediately after gene duplication but before speciation of the montium species, synonymous substitutions from A/T to G/C were predominant. According to a simple model of synonymous DNA evolution in which major codons are selectively advantageous within each codon family, we estimated the selection intensity for specific lineages in a phylogeny on the basis of inferred patterns of synonymous substitutions. Our result suggested that the difference in GC content at synonymous sites between the two Amy-type genes was due to the change of selection intensity immediately after gene duplication but before speciation of the montium species.

Amylases↗

PubMedDate not supplied

Phylogenetic analysis of Nosema antheraeae (Microsporidia) isolated from Chinese oak silkworm, Antheraea pernyi.

The microsporidian Nosema antheraeae is a pathogen that infects the Chinese oak silkworm, Antheraea pernyi. We sequenced the complete small subunit (SSU) rRNA gene and the internal transcribed spacer (ITS) of N. antheraeae, and compared the SSU rRNA sequences in other microsporidia. The results indicated that Nosema species, including N. antheraeae, formed two distinct clades, consistent with previous observations. Furthermore, N. antheraeae is clustered with N. bombycis with high bootstrap support. The organization of the rRNA gene of N. antheraeae is LSU-ITS1-SSU-ITS2-5S, also following a pattern similar to the Nosema type species, N. bombycis. Thus, N. antheraeae is a Nosema species and has a close relationship to N. bombycis.

Animals↗