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Biomedical subjects

S H Chen

Publications and source records attributed to S H Chen.

At least 91 records · Page 5Linked to original sources
PubMed2001

The outcome of failed free flaps in head and neck and extremity reconstruction: what is next in the reconstructive ladder?

The indications for free flaps have been more or less clarified; however, the course of reconstruction after the failure of a free flap remains undetermined. Is it better to insist on one's initial choice, or should surgeons downgrade their reconstructive goals? To establish a preliminary guideline, this study was designed to retrospectively analyze the outcome of failed free-tissue transfers performed in the authors hospital. Over the past 8 years (1990 through 1997), 3361 head and neck and extremity reconstructions were performed by free-tissue transfers, excluding toe transplantations. Among these reconstructions, 1235 flaps (36.7 percent) were transferred to the head and neck region, and 2126 flaps (63.3 percent) to the extremities. A total of 101 failures (3.0 percent total plus the partial failure rate) were encountered. Forty-two failures occurred in the head and neck region, and 59 in the extremities. Evaluation of the cases revealed that one of three following approaches to handling the failure was taken: (1) a second free-tissue transfer; (2) a regional flap transfer; or (3) conservative management with debridement, wound care, and subsequent closure by secondary intention, whether by local flaps or skin grafting. In the head and neck region, 17 second free flaps (40 percent) and 15 regional flaps (36 percent) were transferred to salvage the reconstruction, whereas conservative management was undertaken in the remaining 10 cases (24 percent). In the extremities, 37 failures were treated conservatively (63 percent) in addition to 17 second free flaps (29 percent) and three regional flaps (5 percent) used to salvage the failed reconstruction. Two cases underwent amputation (3 percent). The average time elapsed between the failure and second free-tissue transfer was 12 days (range, 2 to 60 days) in the head and neck region and 18 days (range, 2 to 56 days) in the extremities. In a total of 34 second free-tissue transfers at both localizations, there were only three failures (9 percent). However, in the head and neck region, seven of the regional flaps transferred (47 percent) and four cases that were conservatively treated (40 percent) either failed or developed complications that lengthened the reconstruction period because of additional procedures. Six other free-tissue transfers had to be performed to manage these complicated cases. Conservative management was quite successful in the extremities; most patients' wounds healed, although more than one skin-graft procedure was required in 10 patients (27 percent). In conclusion, a second free-tissue transfer is, in general, a relatively more reliable and more effective procedure for the treatment of flap failure in the head and neck region, as well as failed vascularized bone flaps in the reconstruction of the extremities. Conservative treatment may be a simple and valid alternative to second (free) flaps for soft-tissue coverage in extremities with partial and even total losses.

Extremities↗
PubMed2001

Traversal of Candida albicans across human blood-brain barrier in vitro.

Candida albicans is an opportunistic pathogen, which primarily affects neonates and immunocompromised individuals. The pathogen can invade the central nervous system, resulting in meningitis. At present, the pathogenesis of C. albicans meningitis is unclear. We used an in vitro model of the human blood-brain barrier to investigate the interaction(s) of C. albicans with human brain microvascular endothelial cells (BMEC). Binding of C. albicans to human BMEC was time and inoculum dependent. Invasion of C. albicans into human BMEC was demonstrated by using an enzyme-linked immunosorbent assay based on fluorescent staining of C. albicans with calcoflour. In contrast, avirulent Candida mutant strains and nonpathogenic yeast Saccharomyces cerevisiae were not able to bind and invade human BMEC. Morphological studies revealed that on association with human BMEC, C. albicans formed germ tubes and was able to bud intracellularly. Transmission electron microscopy showed various stages of C. albicans interactions with human BMEC, e.g., pseudopod-like structures on human BMEC membrane and intracellular vacuole-like structures retaining C. albicans. Of interest, C. albicans was able to bud and develop pseudohyphae inside human BMEC without apparent morphological changes of the host cells. In addition, C. albicans penetrates through human BMEC monolayers without a detectable change in transendothelial electrical resistance and inulin permeability. This is the first demonstration that C. albicans is able to adhere, invade, and transcytose across human BMEC without affecting monolayer integrity. A complete understanding of the interaction(s) of C. albicans with human BMEC should contribute to the understanding of the pathogenic mechanism(s) of C. albicans meningitis.

Blood-Brain Barrier↗
PubMed2001

Syntheses and antitumor activities of potent inhibitors of ribonucleotide reductase: 3-amino-4-methylpyridine-2-carboxaldehyde-thiosemicarba-zone (3-AMP), 3-amino-pyridine-2-carboxaldehyde-thiosemicarbazone (3-AP) and its water-soluble prodrugs.

The reductive conversion of ribonucleotides to deoxyribonucleotides by ribonucleotide reductase (RR) is a crucial and rate-controlling step in the pathway leading to the biosynthesis of DNA, since deoxyribonucleotides are present in extremely low levels in mammalian cells. Mammalian ribonucleotide reductase (RR) is composed of two dissimilar proteins, often referred to as R(1), which contains polythiols and R(2), which contains non-heme iron and a free tyrosyl radical. Both the R(1) and R(2) subunits contribute to the active site of the enzyme. Currently, there are two broad classes of RR inhibitors. The first class includes nucleoside analogs which bind to the R1 subunit of the enzyme, several of which are in development. Among those, Gemcitabine and MDL 101,731 have demonstrated impressive efficacy against various solid tumors. Gemcitabine has now been approved for the treatment of pancreatic cancer and non-small cell lung cancer. The most promising second class of inhibitors of RR includes HCTs [alpha--(N)-heterocyclic carboxaldehyde thiosemicarbazones, e.g., 3-AP and 3-AMP], which exert enzyme inhibitory effect through high affinity binding with non-heme iron. Based on the clinical success achieved by Gemcitabine, it seems reasonable that a strong inhibitor of RR, which is essential for cellular replication, would be a useful addition to the existing therapeutic agents against cancer. In this chapter, we wish to report several highly efficient syntheses for both 3-AP and 3-AMP based upon palladium mediated Stille/Suzuki/Heck coupling reactions. Based upon the in vivo efficacy profile observed with these two agents, 3-AP was chosen over 3-AMP as the candidate for further optimization with the intention to improve its biological and pharmaceutical properties. In this vein, we have completed the synthesis of two water soluble phosphate containing prodrugs and one disulfide-linked prodrug of 3-AP. As expected, bioconversion study using either alkaline phosphatase or glutathione showed that these prodrugs were indeed converted to the parent 3-AP. When evaluated against the murine M-109 lung carcinoma as well as the B16-F10 murine melanoma xenograft models, the newly prepared phosphate prodrugs displayed improved efficacy and safety profiles than that found with the parent. More significantly, the ortho-phosphate prodrug 21 demonstrated impressive antitumor effect using once-a-day dosing regimen. In summary, the results disclosed herein demonstrated that some of 3-AP prodrugs prepared indeed demonstrated improved pharmaceutical, biological and toxicity profiles over the parent 3-AP. Efforts directed towards further optimization of 3-AP prodrugs as novel anticancer agents is clearly warranted.

Animals↗
PubMed2001

[The establishment of four cell lines from Colossoma brachypomum and their growth characteristics under various temperatures].

Four cell lines originated from embryo, caudal fin, anal fin and snout of Colossoma brachypomum were established, and subcultured for 70, 47, 45 and 40 passages to the present. The results of the experiment indicated that the four cell lines were fibroblast-like diploid cells, and the model number of their chromosome is 54. These cell lines could grow under temperature of 20-35 degrees C, and its optimum temperature was 27-30 degrees C. The cells grew slowly at 20 degrees C, stopped growth at 15 degrees C, and died below 10 degrees C. This indicated that the growth temperature of the these cell lines was coincident with that of fish. In addition, the attachment time, doubling time, mitotic index, passage survival rate and cell cycle were determined and compared.

Animals↗
PubMed2001

Relationship of duodenal ulcer recurrence to gastric metaplasia of the duodenal mucosa and duodenal bulb deformity.

BACKGROUND AND PURPOSE: This study investigated changes in the severity of gastric metaplasia (GM) of the duodenal mucosa before and after ulcer healing and Helicobacter pylori eradication. It also investigated whether deformity of the duodenal bulb affects the severity of GM and the likelihood of ulcer recurrence. METHODS: Eleven patients were consecutively enrolled in this study. They all had duodenal ulcer(s) and H. pylori infection, for which they had received anti-H. pylori triple therapy during the active ulcer stage, and had all undergone serial endoscopic examinations during both the active ulcer and scarring ulcer stages, and at 1 year after ulcer healing. Duodenal biopsies were obtained at each endoscopy to identify the severity of GM. Duodenal ulcers were divided into three types by bulbar shape and GM was classified into four grades of severity. RESULTS: All 11 patients had increased GM severity just after ulcer healing. The 1-year follow-up study revealed that the GM was unchanged in six of eight patients with grade 3 GM severity at the scarring stage, while in the other two it regressed to grade 1 or 2; these two patients suffered ulcer recurrence. A markedly deformed bulb (type III) was found in three patients, of whom two had ulcer recurrence. CONCLUSION: Two characteristic conditions were found in patients with duodenal ulcer recurrence after H. pylori eradication: a markedly deformed bulb with grade 3 GM at the scarring stage, and a change in GM from high to low grade at or around the previous ulcer site after ulcer healing.

Adult↗
PubMed2001

Endoscopic mucosal resection with a cap-fitted endoscope for early gastric carcinoma with focal submucosal invasion in a patient with decompensated liver cirrhosis.

Prognosis for patients with early gastric cancer who undergo gastric resection is far better than that for patients with advanced disease. However, patients with advanced liver cirrhosis may not be suitable for general anesthesia and major surgery. We used a less invasive endoscopic mucosal resection (EMR) with a cap-fitted endoscope to resect an early gastric cancer in a 58-year-old male with decompensated liver cirrhosis. Although postoperative pathology revealed that the tumor had focal invasion to the submucosa, the patient had an uneventful course and was well during 4 years' follow-up. This method may be effective for the treatment of early gastric cancer with focal submucosal invasion when patients are not suitable for major surgery.

Adenocarcinoma↗
PubMed2001

[The development of cerebral circulation analyzer].

In this paper a new cerebral circulation analyzer is introduced, inducing the main structure, the operating principle, the software program and its clinical applications. We can get the cerebrovascular hemodynamics indexes such as resistance, compensatorg blood flow etc., from the blood velocity, pressure waveform, and arterial diameter detected in carotid and vertebral arteries.

Algorithms↗
PubMed2000

Persistent elevated expression of cytokine transcripts in ganglia latently infected with herpes simplex virus in the absence of ganglionic replication or reactivation.

Infection of mouse trigeminal ganglia by herpes simplex virus induces cytokine expression that persists long after infectious virus or viral antigens become undetectable. To examine mechanisms underlying this phenomenon, we used a thymidine kinase mutant, dlsptk, which fails to replicate in ganglia and does not reactivate upon ganglionic explant. Using quantitative reverse transcriptase-polymerase chain reaction assays, we found that levels of interferon-gamma and tumor necrosis factor-alpha transcripts in dlsptk-infected ganglia were lower than those in wild type-infected ganglia, but were significantly (eight- to 10-fold) higher than those in mock-infected ganglia from Day 3 to Day 100 postinfection. We also studied latency-associated transcript (LAT) negative mutants that exhibit increased expression of productive cycle transcripts in ganglia. Ganglia infected with these mutants contained levels of cytokine transcripts similar to those in wild type-infected ganglia; any increases in viral antigen expression mediated by the LAT deletion were not accompanied by increased cytokine expression. Thus, neither viral replication, the ability to reactivate, nor LAT expression in ganglia is required for persistent elevated cytokine expression. The results provide indirect evidence that low-level expression of viral productive cycle genes in neurons can provide signals that elicit cytokine expression.

Animals↗
PubMed2000

Syntheses and antifungal activity of pseudomycin side-chain analogues. Part 1.

We have described herein the syntheses of three novel series of aromatic ring containing pseudomycin side-chain analogues. Preliminary biological evaluations of these analogues clearly indicate that it is possible to synthesize rigid pseudomycin side-chain analogues without compromising in vitro antifungal activity.

Antifungal Agents↗
PubMed2000

Pressure-induced retention of the lysozyme on reversed-phase liquid chromatography.

This study investigated the effect of pressure on the retention behavior of a model protein, lysozyme, on octadecylsilica (C18) stationary phase under various equilibrium conditions. It is demonstrated that the retention time of the lysozyme was increased by as much as two to three times as the absolute pressure on the viewing window was increased from 23 to 318 bar. This pressure-induced retention was likely to be reversible and the corresponding volume change (deltaV = Vsta - Vmob) was found to be on the order of minus tens to hundreds of mL/mol. Moreover, the pressure-induced retention was also observed for a homologous series of hydrophobic poly-L-phenylalanine, which do not have the secondary structure, and the volume change was determined to be around minus 10 mL/mol per phenylalanine. Perturbations in solute ionization and conformational change are predicted to have a minor impact under the investigated conditions. It is believed that the pressure-induced shift of the equilibria regarding hydrophobic ad-desorption is the major cause of the observed increase of protein retention. About ten phenylalanine-equivalent residues on the lysozyme surface were involved in the hydrophobic association with the chromatographic ligands.

Chromatography, Liquid↗
PubMed2000

Cloned pigs produced by nuclear transfer from adult somatic cells.

Since the first report of live mammals produced by nuclear transfer from a cultured differentiated cell population in 1995 (ref. 1), successful development has been obtained in sheep, cattle, mice and goats using a variety of somatic cell types as nuclear donors. The methodology used for embryo reconstruction in each of these species is essentially similar: diploid donor nuclei have been transplanted into enucleated MII oocytes that are activated on, or after transfer. In sheep and goat pre-activated oocytes have also proved successful as cytoplast recipients. The reconstructed embryos are then cultured and selected embryos transferred to surrogate recipients for development to term. In pigs, nuclear transfer has been significantly less successful; a single piglet was reported after transfer of a blastomere nucleus from a four-cell embryo to an enucleated oocyte; however, no live offspring were obtained in studies using somatic cells such as diploid or mitotic fetal fibroblasts as nuclear donors. The development of embryos reconstructed by nuclear transfer is dependent upon a range of factors. Here we investigate some of these factors and report the successful production of cloned piglets from a cultured adult somatic cell population using a new nuclear transfer procedure.

Animals↗
PubMed2000

Cuneothalamic relay neurons are postsynaptic to glycine-immunoreactive terminals in the rat cuneate nucleus.

This study was aimed to clarify whether the cuneothalamic relay neurons (CTNs) in the rat cuneate nucleus contained glycine or whether the neurons were modulated directly by presynaptic glycine-IR terminals. For this purpose, retrograde transport of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) and immunoperoxidase labelling for glycine have been used to ascertain if the CTNs in the rat are glycine-immunoreactive (glycine-IR). Our results have shown that the WGA-HRP-labelled CTNs (mean area = 318 +/- 6.5 microm(2)) were not reactive for glycine. Glycine immunoreactivity, however, was localized in some small-sized neurons (mean area = 210 +/- 6.2 microm(2)) and axon terminals associated with the CTNs. The synaptic organization between the glycine-IR terminals and CTNs was further analyzed using anti-glycine postembedding immunogold labelling. By electron microscopy, the immunogold-labelled glycine-IR terminals containing pleomorphic synaptic vesicles formed symmetrical synaptic contacts with the dendrites, dendritic spines, and somata of CTNs. Quantitative estimation showed that the mean ratios of glycine-IR terminals to total terminals associated with the soma, proximal dendrites and distal dendrites of the CTN were 49.5, 45.2, and 45.8%, respectively. The higher incidence of glycine-IR terminals on the soma, however, was not significantly different from that of the proximal and distal dendrites. Notwithstanding the above, this study has shown a large number of glycine-IR terminals making direct synaptic contacts with CTNs, suggesting that glycine is one of the important neurotransmitters involved in postsynaptic inhibition on the cuneothalamic relay neurons to modulate incoming somatosensory information from forelimb areas in the rat.

Animals↗
PubMed2000

Gr-1+ myeloid cells derived from tumor-bearing mice inhibit primary T cell activation induced through CD3/CD28 costimulation.

Activation of T cells is a necessary step in the development of a specific antitumor immune response. In the present study, we evaluated the ability of Gr-1+ myeloid cells, derived from the bone marrow or spleen of tumor-bearing mice, to inhibit CD3/CD28-mediated T cell activation. Using flow cytometry, we found that growth of a murine colon carcinoma (MCA-26) induces a significant increase in the number of Gr-1+ and Gr-1+/Mac-1+ myeloid cells in both bone marrow and spleen of the tumor host. The proliferative response of T cells was dramatically decreased when naive T cells were activated by anti-CD3 and anti-CD28 Abs in the presence of a myeloid-enriched cell fraction derived from spleen or bone marrow of tumor-bearing mice vs the bone marrow of naive mice. Reversal of the inhibitory effect could be achieved by adding a combination of MnTBAP (manganese [III] tetrakis [4-benzoic acid]) porphyrin and l -NMMA (NG-monomethyl-l -arginine), a superoxide dismutase mimetic and inducible NO synthase inhibitor, respectively, or by depletion of the Gr-1-positive cells. IFN-gamma, which is endogenously produced by CD3/CD28-stimulated naive T cells, is involved in induction of the inhibitory activity of myeloid cells. Importantly, when T cells pre-activated with anti-CD3 Abs were used as responder cells, the bone marrow- or spleen-derived Gr-1+ myeloid cells were unable to suppress CD3/CD28-induced T cell proliferation. Our findings suggest that one mechanism by which an increased number of immune suppressive Gr-1+ cells can induce T cell unresponsiveness or immune tolerance in tumor hosts could be through peroxynitrite production upon primary T cell activation.

Animals↗
PubMed2000

Structure-activity relationships study at the 3'-N position of paclitaxel. Part 2: synthesis and biological evaluation of 3'-N-thiourea- and 3'-N-thiocarbamate-bearing paclitaxel analogues.

The syntheses and preliminary biological evaluation of 3'-N-thiocarbamate- and 3'-N-thiourea-bearing paclitaxel analogues, 4a-f and 5a-e, are described. 3'-N-thiocarbamates 4a-e were found to be more potent than paclitaxel in both the tubulin polymerization assay and the in vitro cytotoxicity assay. Several derivatives of this class such as 4c, 4d, and 4e also exhibited some in vivo activity.

Antineoplastic Agents, Phytogenic↗
PubMed2000

A novel immunocytolytic factor secreted by pancreatic adenocarcinoma.

BACKGROUND: We have observed a putative immunocytolytic factor secreted by several pancreatic adenocarcinoma cell lines that mediates a potent cytolytic effect on lymphocytes. We sought to investigate its mechanism of action and determine if it is Fas ligand (FasL)-mediated. MATERIALS AND METHODS: Coincubation assays with murine splenocytes and supernatants from various species of pancreatic adenocarcinoma cell lines were performed. The mechanism of lymphocytic cell death was evaluated by the TUNEL assay. Pancreatic adenocarcinoma supernatant was coincubated with Fas-sensitive Jurkat cells and Western blotting for FasL was performed. RESULTS: A marked reduction in the viability (%/control) of target splenocytes was observed after incubation with the conditioned media from hamster PAN-1 (14.7%), PC 1.0 (21.7%), Taka-1 p70 (12.4%), Taka-1 p79 (7.6%), murine PANCO2 (16.1%), and human Capan-1 (14.0%) pancreatic adenocarcinoma cell lines. FACS analysis demonstrated significant lymphoid apoptosis at 16 h. The cytolytic effect appeared to be specific for lymphocytes and was not observed with the conditioned media of other tumor cells or normal pancreatic ductal cells. Pancreatic adenocarcinoma supernatant had no killing effect on Jurkat cells compared with control supernatant of TC-248 cells (87% vs 15%) and immunoblotting did not demonstrate soluble FasL. CONCLUSIONS: These findings demonstrate that pancreatic adenocarcinoma cells secrete a potent cytolytic factor that induces apoptosis of lymphocytes and is not FasL-mediated.

Adenocarcinoma↗
PubMed2000

Immunomodulatory gene therapy with interleukin 12 and 4-1BB ligand: long- term remission of liver metastases in a mouse model.

BACKGROUND: The success of immunomodulatory cancer therapy is frequently hampered by the transient nature of the antitumor immune response. We have shown previously in a mouse model that interleukin 12 (IL-12) generates a strong natural killer (NK) cell-mediated antitumor response and reduces liver metastases induced by a colon carcinoma cell line. However, only a small percentage of the treated animals developed the cytotoxic T-lymphocytic response required for a long-term systemic antitumor immunity. 4-1BB is a co-stimulatory molecule expressed on the surface of activated T cells. Interaction of 4-1BB with its natural ligand (4-1BBL) has been shown to amplify T-cell (especially CD8+)-mediated immunity. In this study, we investigated the effects of adenovirus-mediated gene therapy delivering both IL-12 and 4-1BBL genes on mice with hepatic metastases induced by colon cancer cells. METHODS: Syngeneic BALB/c mice received intrahepatic injection of poorly immunogenic MCA26 colon cancer cells. Various combinations of replication-defective adenoviruses expressing IL-12 and 4-1BBL genes were injected into the established liver tumors. Changes in tumor size and animal survival were then monitored. All statistical tests were two-sided. RESULTS: The long-term survival rate of mice treated with the combination of IL-12 and 4-1BBL was significantly improved over that of animals in the control group (P =.0001). In vivo depletion of NK cells or CD8+ T cells completely abolished the long-term survival advantage of the IL-12 plus 4-1BBL-treated animals (P<.002). Moreover, the systemic immunity induced by this combination treatment protected these animals against a subcutaneous challenge with parental MCA26 cells. CONCLUSION: Adenovirus-mediated transfer of IL-12 and 4-1BBL genes directly into liver tumors resulted in tumor regression that required both NK and CD8+ T cells and generated a potent, long-lasting antitumor immunity.

4-1BB Ligand↗
PubMed2000

Ras/MEK/ERK Up-regulation of the fibroblast KCa channel FIK is a common mechanism for basic fibroblast growth factor and transforming growth factor-beta suppression of myogenesis.

The 10T1/2-MRF4 fibroblast/myogenic cell system was used to address the following interrelated questions: whether distinct signaling pathways underlie myogenic inhibition by basic fibroblast growth factor (bFGF) and transforming growth factor (TGF)-beta; which of these pathways also up-regulates the fibroblast intermediate conductance calcium-activated potassium channel, FIK, a positive regulator of cell proliferation; and whether FIK up-regulation underlies some or all myogenic inhibitory signaling events. The results show that myogenic inhibition in 10T1/2-MRF4 cells, by both bFGF and TGF-beta, requires activation of the Ras/mitogen-activated protein (MAP) kinase/MAP kinase-ERK kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway, and resultant FIK up-regulation. We show that FIK is instrumental in MEK-dependent suppression of acetylcholine receptor channel expression but that MEK activation and FIK up-regulation are not essential to suppression of myosin heavy chain and myotube formation. These data indicate that Ras/MEK/ERK induction of FIK is pivotal to regulation of certain myogenic events by both receptor tyrosine kinases and TGF-beta receptor, and this is also the first demonstration of chronic FIK up-regulation by the TGF-beta receptor family. Furthermore, the results define the physiologic signaling requirements for growth factor-stimulated FIK up-regulation, whereas previous work has concentrated on constitutive FIK up-regulation in cells stably transfected with oncoprotein signaling molecules. This study, together with earlier work showing that FIK positively regulates cell proliferation, establishes this member of the IK channel family as a multifunctional, growth factor-regulated signaling molecule.

Animals↗