PubMed Health⌕ Search

Biomedical subjects

F Li

Publications and source records attributed to F Li.

At least 37 records · Page 2Linked to original sources
PubMed2006

Bioactive hydrogel-filament scaffolds for nerve repair and regeneration.

The design of novel biomaterials is crucial for the advancement of tissue engineering in nerve regeneration. In this study we developed and evaluated novel biosynthetic scaffolds comprising collagen crosslinked with a terpolymer of poly(N-isopropylacrylamide) (PNiPAAm) as conduits for nerve growth. These collagen-terpolymer (collagen-TERP) scaffolds grafted with the laminin pentapeptide YIGSR were previously used as corneal substitutes in pigs and demonstrated enhanced nerve regeneration compared to allografts. The purpose of this project was to enhance neuronal growth on the collagen-TERP scaffolds through the incorporation of supporting fibers. Neuronal growth on these matrices was assessed in vitro using isolated dorsal root ganglia as a nerve source. Statistical significance was assessed using a one-way ANOVA. The incorporation of fibers into the collagen-TERP scaffolds produced a significant increase in neurite extension (p<0.05). The growth habit of the nerves varied with the type of fiber and included directional growth of the neurites along the surface of certain fiber types. Furthermore, the presence of fibers in the collagen-TERP scaffolds appeared to influence neurite morphology and function; neurites grown on fibers-incorporated collagen-TERP scaffolds expressed higher levels of Na channels compared to the scaffolds without fiber. Overall, our results suggest that incorporation of supporting fibers enhanced neurite outgrowth and that surface properties of the scaffold play an important role in promoting and guiding nerve regeneration. More importantly, this study demonstrates the potential value of tissue engineered collagen-TERP hybrid scaffolds as conduits in peripheral nerve repair.

Biocompatible Materials↗
PubMed2006

Promotion of angiogenesis in tissue engineering: developing multicellular matrices with multiple capacities.

One of the aims of tissue engineering is to be able to develop multi-tissue organs in the future. This requires the optimization of conditions for the differentiation of multiple cell types and maintenance of the differentiated phenotype within complex engineered tissues. The goal of this study was to develop prototype tissue engineered matrices to support the simultaneous growth of different cell types with a particular focus on the angiogenic process. We examined two different matrix compositions for the promotion of blood vessel and tube formation. A fibrin-based matrix with the addition of a combination of growth factors supported vascular growth and the invasion of inflammatory cells. Using this fibrin matrix, in combination with a collagen-based hydrogel, a simple in vitro model of the cornea with adjacent sclera was developed that was complete with innervation and vascular structures. In addition, we showed that collagen-based matrices were effective in delivering mononuclear endothelial progenitor cells to ischemic tissue in vivo, and allowing these cells to incorporate into vascular structures. It is anticipated that with further development, these matrices have potential for use as delivery matrices for cell transplantation and for in vitro study purposes of multiple cell types.

Acrylamides↗
PubMed2006

Winding through the WNT pathway during cellular development and demise.

In slightly over a period of twenty years, our comprehension of the cellular and molecular mechanisms that govern the Wnt signaling pathway continue to unfold. The Wnt proteins were initially implicated in viral carcinogenesis experiments associated with mammary tumors, but since this period investigations focusing on the Wnt pathways and their transmembrane receptors termed Frizzled have been advanced to demonstrate the critical nature of Wnt for the development of a variety of cell populations as well as the potential of the Wnt pathway to avert apoptotic injury. In particular, Wnt signaling plays a significant role in both the cardiovascular and nervous systems during embryonic cell patterning, proliferation, differentiation, and orientation. Furthermore, modulation of Wnt signaling under specific cellular influences can either promote or prevent the early and late stages of apoptotic cellular injury in neurons, endothelial cells, vascular smooth muscle cells, and cardiomyocytes. A number of downstream signal transduction pathways can mediate the biological response of the Wnt proteins that include Dishevelled, beta-catenin, intracellular calcium, protein kinase C, Akt, and glycogen synthase kinase-3beta. Interestingly, these cellular cascades of the Wnt-Frizzled pathways can participate in several neurodegenerative, vascular, and cardiac disorders and may be closely integrated with the function of trophic factors. Identification of the critical elements that modulate the Wnt-Frizzled signaling pathway should continue to unlock the potential of Wnt pathway for the development of new therapeutic options against neurodegenerative and vascular diseases.

Animals↗
PubMed2006

Epigenetic transfer of metastatic activity by uptake of highly metastatic B16 melanoma cell-released exosomes.

AIM: To investigate potential role of highly metastatic BL6-10 tumor cell-released exosomes (EXO) in transfer of metastatic activity into poorly metastatic tumor cell line F1. METHODS: The highly metastatic B16 melanoma cell line (BL6-10) was generated in our laboratory. EXO from this cell line were isolated and amount of exosomal recovered proteins was measured using Bradford assay. For phenotypic analysis BL6-10 and F1 melanoma cells were stained with FITC-conjugated anti-MHC I (H-2K(b)), MHC II (Ia(b)) and Met 72 antibodies and analyzed by flow cytometry. C57BL/6 mice (8 per group) were injected (i. v.) with 0.5 x 10(6) F1, BL6-10 and F1(EXO) melanoma cells. Lungs were removed 4 weeks after tumor cell injection, fixed in 10% neutral buffered formaldehyde and embedded in paraffin for histological analysis. RESULTS: Data revealed that BL6-10 cells expressed metastasis marker (Met 72 tumor antigen), while F1 cells did not display this cell surface marker. All mice inoculated with BL6-10 melanoma cells had numerous lung tumor colonies, while mice injected with F1 tumor cells were free of lung metastatic colonies. BL6-10 tumor cells-released EXO also expressed Met 72 tumor antigen as BL6-10 tumor cells, but in less amount. F1 tumor cells can uptake EXO from BL6-10 tumor cells and express acquired exosomal Met 72 tumor antigen. CONCLUSION: The metastatic activity of highly metastatic BL6-10 tumor cells can be transferred to poorly metastatic F1 tumor cells by uptake of highly metastatic BL6-10 tumor-released EXO.

Animals↗
PubMed2006

Stimulative activity of Drynaria fortunei (Kunze) J. Sm. extracts and two of its flavonoids on the proliferation of osteoblastic like cells.

The osteoblastic activity of extracts of Drynaria fortunei (Kunze) J. Sm. rhizome was assayed in the UMR106 cell line cultured in vitro. An ethanol extract and its fractions were added to the cell culture at different concentrations. Osteoblastic proliferation stimulating activity was determined using the MTT method. The ethanol extract, and its ethyl acetate and n-butanol fractions exhibited stimulating activity. Two active constituents were isolated from n-butanol fraction by bioassay-directed isolation, and identified as naringin and neoeriocitrin. The latter is reported for the first time from this herbal medicine.

Cell Line↗
PubMed2006

Transcriptional and post-transcriptional controls of survivin in cancer cells: novel approaches for cancer treatment.

Survivin is a novel member of the inhibitor of apoptosis (IAP) protein family, and its aberrant expression in cancer cells has been shown to be associated with tumorigenesis, cancer progression, radiation/drug resistance and shorter patient survival. Survivin is also expressed in certain human adult tissues and cells, and has been shown to play a role in physiology. Interestingly, targeting survivin for cancer treatment did not show obvious toxicity to normal tissues and cells. This suggests that the mechanism for the regulation and function of survivin may actually be different in cancer cells as compared to normal cells. This review intends to summarize the most important information about the transcriptional and/or post-transcriptional controls of survivin in cancer cells. Further studies along this line may find essential interfaces for the development of novel approaches for cancer therapeutics.

Biomarkers, Tumor↗
PubMed2005

Animal virus replication and RNAi-mediated antiviral silencing in Caenorhabditis elegans.

The worm Caenorhabditis elegans is a model system for studying many aspects of biology, including host responses to bacterial pathogens, but it is not known to support replication of any virus. Plants and insects encode multiple Dicer enzymes that recognize distinct precursors of small RNAs and may act cooperatively. However, it is not known whether the single Dicer of worms and mammals is able to initiate the small RNA-guided RNA interference (RNAi) antiviral immunity as occurs in plants and insects. Here we show complete replication of the Flock house virus (FHV) bipartite, plus-strand RNA genome in C. elegans. We show that FHV replication in C. elegans triggers potent antiviral silencing that requires RDE-1, an Argonaute protein essential for RNAi mediated by small interfering RNAs (siRNAs) but not by microRNAs. This immunity system is capable of rapid virus clearance in the absence of FHV B2 protein, which acts as a broad-spectrum RNAi inhibitor upstream of rde-1 by targeting the siRNA precursor. This work establishes a C. elegans model for genetic studies of animal virus-host interactions and indicates that mammals might use a siRNA pathway as an antiviral response.

Animals↗
PubMed2005

Role of survivin and its splice variants in tumorigenesis.

Survivin, a unique member of the inhibitor of apoptosis (IAP) protein family, is highly expressed in cancer but is undetectable in nonproliferating normal adult tissues, suggesting a potential role in tumorigenesis. Differential splicing of survivin pre-mRNA results in three new survivin variants, survivin-DeltaEx3, survivin-2B, and survivin-3B. Loss of survivin-2B expression was found in the later stage of cancer development, while survivin and survivin-DeltaEx3 are not, suggesting a differential role of them in tumour development. In this minireview, the author intends to summarise and discuss the current data relevant to the role of survivin and its splicing variants in tumorigenesis, which may facilitate further investigation in this interesting area.

Animals↗
PubMed2005

Recruitment of multiple cell lines by collagen-synthetic copolymer matrices in corneal regeneration.

Collagen hydrogel matrices with high optical clarity have been developed from collagen I, cross-linked with a copolymer based on N-isopropylacrylamide, acrylic acid and acryloxysuccinimide. The controlled reaction of collagen amine groups with this copolymer under neutral pH and aqueous conditions gave robust, optically clear hydrogels and prevented the excessive collagen fibrillogenesis that can lead to collagen opacity. These sterile, non-cytotoxic hydrogels allowed epithelial cell overgrowth and both stromal cell and nerve neurite ingrowth from the host tissue. This regenerative ability appeared to result from the high glucose permeability, nanoporosity and the presence of cell adhesion factors, RGD in collagen and the laminin pentapeptide, YIGSR, grafted onto the copolymer. Under physiological conditions, optical clarity superior to the human cornea and tensile performance adequate for suturing were obtained from some formulations.

Animals↗
PubMed2005

Endothelin-1-induced proliferation of human endothelial cells depends on activation of K+ channels and Ca+ influx.

AIMS: Endothelin-1 (ET-1) promotes endothelial cell growth. Endothelial cell proliferation involves the activation of Ca2+-activated K+ channels. In this study, we investigated whether Ca2+-activated K+ channels with big conductance (BK(Ca)) contribute to endothelial cell proliferation induced by ET-1. METHODS: The patch-clamp technique was used to analyse BK(Ca) activity in endothelial cells derived from human umbilical cord veins (HUVEC). Endothelial proliferation was examined using cell counts and measuring [3H]-thymidine incorporation. Changes of intracellular Ca2+ levels were examined using fura-2 fluorescence imaging. RESULTS: Characteristic BK(Ca) were identified in cultured HUVEC. Continuous perfusion of HUVEC with 10 nmol L(-1) ET-1 caused a significant increase of BK(Ca) open-state probability (n = 14; P < 0.05; cell-attached patches). The ET(B)-receptor antagonist (BQ-788, 1 micromol L(-1)) blocked this effect. Stimulation with Et-1 (10 nmol L(-1)) significantly increased cell growth by 69% (n = 12; P < 0.05). In contrast, the combination of ET-1 (10 nmol L(-1)) and the highly specific BK(Ca) blocker iberiotoxin (IBX; 100 nmol L(-1)) did not cause a significant increase in endothelial cell growth. Ca2+ dependency of ET-1-induced proliferation was tested using the intracellular Ca2+-chelator BAPTA (10 micromol L(-1)). BAPTA abolished ET-1 induced proliferation (n = 12; P < 0.01). In addition, ET-1-induced HUVEC growth was significantly reduced, if cells were kept in a Ca2+-reduced solution (0.3 mmol L(-1)), or by the application of 2 aminoethoxdiphenyl borate (100 micromol L(-1)) which blocks hyperpolarization-induced Ca2+ entry (n = 12; P < 0.05). CONCLUSION: Activation of BK(Ca) by ET-1 requires ET(B)-receptor activation and induces a capacitative Ca2+ influx which plays an important role in ET-1-mediated endothelial cell proliferation.

Calcium↗
PubMed2005

Comparative analysis of the antibacterial effects of combined mouthrinses on Streptococcus mutans.

BACKGROUND/AIMS: Chlorhexidine has been proposed as a potent chemotherapeutic agent against oral bacteria. However, there are some inconsistent results regarding the usefulness of chlorhexidine mouthrinse as an antimicrobial for Streptococcus mutans. The purpose of this study was to investigate the effectiveness of combining oral rinses to reduce S. mutans levels in human saliva. METHODS: Sixteen healthy adult subjects were randomly assigned to one of four rinse groups using a 4-cell crossover design. The groups rinsed twice a day for 7 days with one of the following: 0.12% chlorhexidine (PerioGard), 1.5% hydrogen peroxide (Peroxyl), a combined chlorhexidine+hydrogen peroxide, or water (control). Every 5 weeks, each group initiated a different rinse. Saline wash samples were collected on days 7 and 21 for assessment of S. mutans and total streptococci. RESULTS: No significant differences were seen in S. mutans levels among the groups; however, the levels of total streptococci on day 7 samples were significantly lower in the chlorhexidine and chlorhexidine+hydrogen peroxide groups than in the hydrogen peroxide and control groups. There was no additional decrease seen in S. mutans or total streptococci levels in the group receiving chlorhexidine+hydrogen peroxide compared to chlorhexidine alone. CONCLUSIONS: Sample variation was high throughout the study, with a significant trend toward lower counts as the study progressed. Adding hydrogen peroxide to the chlorhexidine mouthrinse did not result in a further decrease in S. mutans levels.

Adult↗
PubMed2005

Prevalence of Type 2 diabetes in urban and rural Chinese populations in Qingdao, China.

AIMS: To determine the prevalence of diabetes in the Chinese adult population in rural and urban areas of Qingdao city. METHODS: A population-based cross-sectional study of diabetes was performed in 12 436 (5346 men) Chinese adults (20-74 years old) from 2001 to 2002. Fasting capillary whole blood glucose test (FCG) was performed in all participants and a 2-h 75-g oral glucose tolerance test in those with FCG > or = 6.1 mmol/l following initial screening. The 1999 World Health Organization diagnostic criteria for diabetes were used. RESULTS: The age-standardized prevalence of diabetes was 6.1% (4.1% for undiagnosed and 2.1% for previously known diabetes) in adults aged 20-74 years. Diabetes prevalence increased with age up to the oldest age group (70-74); in subjects over 50 years of age, the prevalence reached 10%. Men tended to have a higher prevalence of known diabetes than women, whereas the prevalence of undiagnosed diabetes was lower in men than in women (4.6% vs. 3.3%, d.f. = 1, P = 0.001). Diabetes was more prevalent in the urban than in the rural population (6.9% vs. 5.6%, d.f. = 1, P < 0.001). However, the proportion of undiagnosed diabetes was higher in the rural than in the urban areas (70.5% vs. 58.0%, d.f. = 1, P < 0.001). CONCLUSIONS: The prevalence of Type 2 diabetes in Qingdao city is moderately high, but much higher than reported in 1996. The large proportion of undiagnosed cases of diabetes indicates the lack of public awareness of diabetes and shortage of medical facilities. In view of the huge population in China, the results of this study emphasize the need to improve the early detection and prevention of diabetes in China to prevent the emerging diabetes epidemic.

Adult↗
PubMed2005

Human immunodeficiency virus type 1 subtype B ancestral envelope protein is functional and elicits neutralizing antibodies in rabbits similar to those elicited by a circulating subtype B envelope.

Human immunodeficiency virus type 1 (HIV-1) is a difficult target for vaccine development, in part because of its ever-expanding genetic diversity and attendant capacity to escape immunologic recognition. Vaccine efficacy might be improved by maximizing immunogen antigenic similarity to viruses likely to be encountered by vaccinees. To this end, we designed a prototype HIV-1 envelope vaccine using a deduced ancestral state for the env gene. The ancestral state reconstruction method was shown to be >95% accurate by computer simulation and 99.8% accurate when estimating the known inoculum used in an experimental infection study in rhesus macaques. Furthermore, the deduced ancestor gene differed from the set of sequences used to derive the ancestor by an average of 12.3%, while these latter sequences were an average of 17.3% different from each other. A full-length ancestral subtype B HIV-1 env gene was constructed and shown to produce a glycoprotein of 160 kDa that bound and fused with cells expressing the HIV-1 coreceptor CCR5. This Env was also functional in a virus pseudotype assay. When either gp160- or gp140-expressing plasmids and recombinant gp120 were used to immunize rabbits in a DNA prime-protein boost regimen, the artificial gene induced immunoglobulin G antibodies capable of weakly neutralizing heterologous primary HIV-1 strains. The results were similar for rabbits immunized in parallel with a natural isolate, HIV-1 SF162. Further design efforts to better present conserved neutralization determinants are warranted.

AIDS Vaccines↗
PubMed2005

Activating Akt and the brain's resources to drive cellular survival and prevent inflammatory injury.

Protein kinase B, also known as Akt, is a serine/threonine kinase and plays a critical role in the modulation of cell development, growth, and survival. Interestingly, Akt is ubiquitously expressed throughout the body, but its expression in the nervous system is substantially up-regulated during cellular stress, suggesting a more expansive role for Akt in the nervous system that may involve cellular protection. In this regard, a body of recent work has identified a robust capacity for Akt and its downstream substrates to foster both neuronal and vascular survival during apoptotic injury. Cell survival by Akt is driven by the modulation of both intrinsic cellular pathways that oversee genomic DNA integrity and extrinsic mechanisms that control inflammatory microglial activation. A series of distinct pathways are regulated by Akt that include the Forkhead family of transcription factors, GSK-3 beta, beta-catenin, c-Jun, CREB, Bad, IKK, and p53. Culminating below these substrates of Akt are the control of caspase mediated pathways that promote genomic integrity as well as prevent inflammatory cell demise. With further levels of progress in defining the cellular role of Akt, the attractiveness of Akt as a vital and broad cytoprotectant for both neuronal and vascular cell populations should continue to escalate.

Animals↗
PubMed2005

Optimization and characterization of chitosan-coated alginate microcapsules containing albumin.

In order to obtain small microcapsules with high protein encapsulation efficiency and extended release characteristics various processing factors were studied. Bovine serum albumin-loaded alginate microcapsules were prepared by an emulsion method and further incubated in chitosan. Many process factors were tested including the concentration and molecular weight of alginate, the concentration and pH of chitosan, and surfactants, etc. Microcapsules were achieved with diameters less than 2 microm, high encapsulation efficiency (> 80%) and high loading rate (> 10% w/w). The results also showed that the initial BSA amount of 20%-30% loaded alginate microcapsules coated with 0.2%-0.5% chitosan solutions at pH 4 by the two-stage procedure present the best sustained releasing characteristics.

2-Propanol↗
PubMed2005

Integrated airlift bioreactor system for on-site small wastewater treatment.

An integrated airlift bioreactor system was developed, which mainly consists of a multi-stage loop reactor and a gas-liquid-solid separation baffle and possesses dual functions as bioreactor and settler. This integrated system was used for on-site treatment of industrial glycol wastewater in lab-scale. The strategy of gradually increasing practical wastewater concentration while maintaining the co-substrate glucose wastewater concentration helped to accelerate the microbial acclimation process. Investigation of microbial acclimation, operation parameters evaluation and microbial observation has demonstrated the economical and technical feasibility of this integrated airlift bioreactor system for on-site small industrial wastewater treatment.

Bacteria↗