Biomedical subjects

S Chi

Publications and source records attributed to S Chi.

At least 19 recordsLinked to original sources

PubMed2006

Regulatory effect of sulphatides on BKCa channels.

BACKGROUND AND PURPOSE: Sulphatides are sulphated glycosphingolipids expressed on the surface of many cell types, particularly neurones. Changes in sulphatide species or content have been associated with epilepsy and Alzheimer's disease. As the large conductance, calcium sensitive K(+) channel (BK(Ca)) are modulated by membrane lipids, the aim of the study was to explore possible effects of sulphatides on BK(Ca) channels. EXPERIMENTAL APPROACH: Using patch-clamp techniques, we studied effects of exogenous sulphatides on BK(Ca) channels expressed in Chinese hamster ovary cells. KEY RESULTS: Sulphatides reversibly increased the whole-cell current and the single channel open probability of BK(Ca) channels dose-dependently. The EC(50) value on the channel at +10 mV was 1.6 microM and the Hill coefficient was 2.5. In inside-out patches, sulphatides increased the single channel open probability from both intra- and extra-cellular faces of the membrane, but more effectively with external application. Furthermore, activation of the channels by sulphatides was independent of intracellular Ca(2+) concentration. Sulphatides also shifted the activation curve of the channels to less positive membrane potentials. Mutant BK(Ca) channels lacking a 59 aminoacid region important for amphipath activation (STREX) were less activated by the sulphatides. CONCLUSIONS AND IMPLICATIONS: Sulphatides are novel activators of BK(Ca) channels, independent of intracellular Ca(2+) or other signalling molecules but partly dependent on the STREX sequence of the channel protein. As changes of sulphatide content are associated with neuronal dysfunction, as in epilepsy and Alzheimer's disease, our results imply that these effects of sulphatides may play important pathophysiological roles in regulation of BK(Ca) channels.

Algorithms↗

PubMed2004

Molecular weight of chitosan influences antimicrobial activity in oil-in-water emulsions.

The objective of this study was to evaluate the antimicrobial efficiency of chitosans in oil-in-water emulsions. Model emulsions were prepared with 20% corn oil, 1.5% Tween 20, 1.5% Trypticase soy broth, 0.58% acetic acid, and chitosan polysaccharide or chitosan oligosaccharide in concentrations of 0, 0.1, 0.2, 0.5, and 0.7%. A control containing HCl was included to determine the role of acetic acid in the overall antibacterial activity. The pH of samples and controls was adjusted to 4.5. Emulsions were inoculated with Listeria monocytogenes (strains Scott A and 310) or Salmonella Typhimurium DT104 (strains 2486 and 2576) at a level of 10(7) CFU/ml. Inoculated emulsions were incubated at 10 and 25 degrees C for 4 days and analyzed for bacterial count every 24 h. Both tested Salmonella strains were more susceptible to acetic acid than Listeria. However, L. monocytogenes was more affected by chitosan than either Salmonella strain. During the storage at 25 degrees C, initial inoculum in the emulsions with 0.58% acetic acid and 0.1% chitosan polysaccharide was reduced to below the detection limits after 24, 48, 72, or 96 h for L. monocytogenes 310, Salmonella Typhimurium DT104 2576, Salmonella Typhimurium DT104 2486, or L. monocytogenes Scott A, respectively. Chitosan oligosaccharide was less effective against all tested bacteria and showed a concentration-dependent effect. The antimicrobial efficacy of chitosan was reduced at 10 degrees C, and reduction of microbial loads was delayed for approximately 24 h compared with 25 degrees C. Results suggest that addition of 0.1% chitosan polysaccharide would be sufficient to ensure the microbial safety of oil-in-water emulsions regardless of storage temperature.

Anti-Bacterial Agents↗

PubMed2002

The cellular matrix: a feature of tensile bearing dense soft connective tissues.

The term connective tissue encompasses a diverse group of tissues that reside in different environments and must support a spectrum of mechanical functions. Although the extracellular matrix of these tissues is well described, the cellular architecture of these tissues and its relationship to tissue function has only recently become the focus of study. It now appears that tensile-bearing dense connective tissues may be a specific class of connective tissues that display a common cellular organization characterized by fusiform cells with cytoplasmic projections and gap junctions. These cells with their cellular projections are organised into a complex 3-dimensional network leading to a physically, chemically and electrically connected cellular matrix. The cellular matrix may play essential roles in extracellular matrix formation, maintenance and remodelling, mechanotransduction and during injury and healing. Thus, it is likely that it is the interaction of both the extracellular matrix and cellular matrix that provides the basis for tissue function. Restoration of both these matrices, as well as their interaction must be the goal of strategies to repair these connective tissues damaged by either injury or disease.

Animals↗

PubMed2001

Neuroblastic and Schwannian stromal cells of neuroblastoma are derived from a tumoral progenitor cell.

The coexistence of neuroblastic and Schwannian stromal (SS) cells in differentiating neuroblastoma (NB), and derivation of Schwannian-like cells from neuroblastic clones in vitro, were accepted previously as evidence of a common pluripotent tumor stem line. This paradigm was challenged when SS cells were suggested to be reactive in nature. The advent of microdissection techniques, PCR-based allelic analysis, and in situ fluorescent cytometry made possible the analysis of pure cell populations in fresh surgical specimens, allowing unequivocal determination of clonal origins of various cell subtypes. To overcome the complexity and heterogeneity of three-dimensional tissue structure, we used: (a) Laser-Capture Microdissection to obtain histologically homogeneous cell subtype populations for allelotype analysis at chromosomes 1p36, 11q23, 14q32, and 17q and study of MYCN copy number; (b) multiparametric analysis by Laser-Scanning Cytometry of morphology, DNA content, and immunophenotype of intact cells from touch imprints; and (c) bicolor fluorescence in situ hybridization on touch imprints from manually microdissected neuroblast and stroma-rich areas. Histologically distinct SS and neuroblastic cells isolated by Laser-Capture Microdissection had the same genetic composition in 27 of 28 NB analyzed by allelic imbalance and gene copy number. In all 20 cases studied by Laser-Scanning Cytometry, SS cells identified by morphology and S-100 immunostaining had identical DNA content and GD2-staining pattern as their neuroblastic counterparts. In 7 cases, fluorescence in situ hybridization demonstrated the same chromosomal makeup for SS and neuroblastic cells. These results provide unequivocal evidence that neuroblastic and SS cells in NB are derived from genetically identical neoplastic cells and support the classical paradigm that NB arises from tumoral cells capable of development along multiple lineages.

Adolescent↗

PubMed2000

Proteasome inhibitors induce cytochrome c-caspase-3-like protease-mediated apoptosis in cultured cortical neurons.

The ubiquitin-proteasome protein degradation pathway is crucial in controlling intracellular levels of a variety of short-lived proteins and maintaining cellular growth and metabolism. In a previous study, we showed the accumulation of conjugated ubiquitin in CA1 neurons of the gerbil after 5 min of forebrain ischemia (; ). The accumulation of conjugated ubiquitin may reflect proteasome malfunction. In the present study, we investigated the effects of proteasome inhibitors on primary neuronal cultures to determine whether proteasomal malfunction induces neuronal death. When carbobenzoxy-Leu-Leu-Leu-aldehyde or lactacystin, two different types of proteasome inhibitors, were separately used to suppress proteasome activity, we observed induction of apoptotic neuronal cell death in both cases. During the apoptotic process, mitochondrial membrane potential was disrupted, cytochrome-c was released from mitochondria into the cytosol, and caspase-3-like proteases were activated. Apoptosis was inhibited by pretreatment with acetyl-aspartyl-glutamyl-valyl-aspart-1-aldehyde or overexpression of Bcl-x/(L). These results demonstrated that suppression of proteasome function induces neuronal apoptosis via the release of cytochrome c from mitochondria and activation of caspase-3-like proteases.

Animals↗

PubMed2000

Axially symmetric on-axis flat-top beam.

A synthesis method for arbitrary on-axis intensity distributions from axially symmetric fields is developed in the paraxial approximation. As an important consequence, a new pseudo-nondiffracting beam, the axially symmetric on-axis flat-top beam (AFTB), is given by an integral transform form. This AFTB is completely determined by three simple parameters: the central spatial frequency S(c), the on-axis flat-top length L, and the on-axis central position z(c). When LS(c) >> 1, this AFTB can give a nearly flat-top intensity distribution on the propagation axis. In particular, this AFTB approaches the nondiffracting zero-order Bessel J0 beam when L--> infinity. It is revealed that the superposition of multiple AFTB fields can give multiple on-axis flat-top intensity regions when some appropriate conditions are satisfied.

Models, Theoretical↗

PubMed1999

High level calcineurin activity predisposes neuronal cells to apoptosis.

Calcineurin is a Ca(2+)/calmodulin-dependent protein phosphatase that is abundantly expressed in several specific areas of the brain, which are exceptionally vulnerable to stroke, epilepsy, and neurodegenerative diseases. In this study, we assessed the effects of high level activity of calcineurin on neuronal cells. Virus-mediated high level constitutive activity of calcineurin rendered neuronal cells susceptible to apoptosis induced by serum reduction or by a brief exposure to calcium ionophore. Adenovirus-mediated, high level forced activity of calcineurin induced cytochrome c/caspase-3-dependent apoptosis in neurons. Preincubation with the calcineurin inhibitors cyclosporin A and FK506 reduced susceptibility to apoptosis. High level constitutive expression of Bcl-2 or CrmA or incubation with a specific caspase-3 inhibitor inhibited the calcineurin-induced apoptosis. These data indicate that high level constitutive activity of calcineurin predisposes neuronal cells to cytochrome c/caspase-3 dependent apoptosis even under sublethal conditions.

Adenoviruses, Human↗

PubMed1999

Total syntheses of (+/-)-preussomerins G and I.

[formula: see text] Preussomerins G and I (2 and 3) have been synthesized for the first time. The key reaction in the synthesis is a possibly biomimetic tautomerization reaction depicted in Scheme 3 and the foregoing graphic. The driving force for this interesting rearrangement is primarily derived from the increase in resonance energy associated with converting a naphthalene ring into two isolated benzene rings.

Ascomycota↗

PubMed1999

Neuregulin stimulates myogenic differentiation in an autocrine manner.

During myogenesis, mononucleated myoblasts form multinucleated myotubes by membrane fusion. Efficiency of this intercellular process can be maximized by a simultaneous progress, with a time window, of other neighboring myoblasts in the differentiation program. This phenomenon has been described as the community effect. It proposes the existence of a molecule that acts as a differentiation-inducing signal to a group of identical cells. Here, we show that neuregulin is a strong candidate for this molecule in myoblast differentiation. The expression of neuregulin increased rapidly but transiently at early stage of differentiation of rat L6 cells. Neuregulin showed a potent differentiation-promoting activity in membrane fusion and expression of myosin heavy chain. The antibodies raised against neuregulin and its cognate receptor ErbB3, which were capable of neutralizing the signal pathway, inhibited myotube formation and expression of myosin heavy chain in both L6 cells and primary rat myoblasts. The progress of differentiation was mostly halted after the expression of myogenin and cell cycle arrest. These results suggest that the activation of an autocrine signaling of neuregulin may provide a basic mechanism for the community effect observed in the differentiation of the embryonic muscle cells.

Animals↗

PubMed1999

Oncogenic Ras triggers cell suicide through the activation of a caspase-independent cell death program in human cancer cells.

To prevent neoplasia, cells of multicellular organisms activate cellular disposal programs such as apoptosis in response to deregulated oncogene expression, making the suppression of such programs an essential step for potentially neoplastic cells to become established as clinically relevant tumors. Since the mutation of ras proto-oncogenes, the most frequently mutated proto-oncogenes in human tumors, is very rare in some tumor types such as glioblastomas and gastric cancers, we hypothesized that mutated ras genes might activate a cell death program that cannot be overcome by these tumor types. Here we show that the expression of oncogenically mutated ras gene induces cellular degeneration accompanied by cytoplasmic vacuoles in human glioma and gastric cancer cell lines. Cells dying as a result of oncogenic Ras expression had relatively well-preserved nuclei that were negative for TUNEL staining. An immunocytochemical analysis demonstrated that the cytoplasmic vacuoles are derived mainly from lysosomes. This oncogenic Ras-induced cell death occurred in the absence of caspase activation, and was not inhibited by the overexpression of anti-apoptotic Bcl-2 protein. These observations suggested that oncogenic Ras-induced cell death is most consistent with a type of programmed cell death designated 'type 2 physiological cell death' or 'autophagic degeneration', and that this cell death is regulated by a molecular mechanism distinct from that of apoptosis. Our findings suggest a possible role for this non-apoptotic cell death in the prevention of neoplasia, and the activation of the non-apoptotic cell death program may become a potential cancer therapy complementing apoptosis-based therapies. In addition, the approach used in this study may be a valuable way to find genetically-regulated cell suicide programs that cannot be overcome by particular tumor types.

Brain Neoplasms↗

PubMed1999

State-level variation in Medicare spending.

Theoretically, Medicare provides one standard benefit package to all enrollees. But because of State-level variations in populations, service supply, and local practice patterns, national policy changes may have unequal impacts on access and service utilization. Across-the-board policy changes may create hardships in one area while appropriately discouraging use in another area. In this article, the authors describe State-level variations in Medicare enrollees, their insurance coverage, 1995 Medicare and beneficiary spending patterns in aggregate, per capita, and by service, and certain spending patterns for dually eligible beneficiaries. These data are useful for considering the State-level effects of payment reform.

Accounting↗

PubMed1998

Calbindin-D28k buffers intracellular calcium and promotes resistance to degeneration in PC12 cells.

The calcium-binding protein calbindin-D28k (CB) has been hypothesized to function, in part, as a neuroprotective protein. CB is localized within nerve cells that are often less vulnerable to degeneration in patients with Alzheimer's disease and Parkinson's disease, and cells containing CB can buffer intracellular calcium concentrations ([Ca2+]i). The present study was designed to directly test the hypothesis that CB can protect cells from degeneration by reducing [Ca2+]i. PC12 cells, transfected to express different levels of CB, were found to be significantly less vulnerable to degeneration caused by serum withdrawal, glutamate, and the neurotoxin 1-methyl-4-phenylpyridinium (MPP+). However, CB did not protect cells from degeneration caused by the calcium ionophore A23187. CB-transfected cells exhibited reduced elevations in [Ca2+]i following treatment with bradykinin, or ATP compared to non-CB-containing cells. These data indicate that CB can protect cells from degeneration caused by certain conditions, and it reduces elevations in [Ca2+]i caused by influx from extracellular sources.

1-Methyl-4-phenylpyridinium↗

PubMed1997

Caspase-dependent apoptosis of COS-7 cells induced by Bax overexpression: differential effects of Bcl-2 and Bcl-xL on Bax-induced caspase activation and apoptosis.

Bcl-2 family proteins and ICE/CED-3 family proteases (caspases) are regarded as the basic regulators of apoptotic cell death. They are evolutionarily conserved and implicated in a variety of apoptosis. However, the precise mechanism by which these two families interact to regulate cell death is not yet known. In this study, we found that the overexpression of the Bcl-2 family member Bax induced apoptotic cell death in COS-7 cells through the activation of CPP32 (caspase-3)-like proteases that cleaved the DEVD tetrapeptide. This apoptotic cell death was suppressed by the viral proteins CrmA and p35, as well as by the chemically synthesized caspase inhibitors Z-Asp-CH2-DCB and zVAD-fmk. We also found that the Bax-induced apoptosis of COS-7 cells was suppressed by Bcl-xL and Bcl-2, though both Bcl-xL and Bcl-2 similarly prevented etoposide-induced apoptosis in COS-7 cells. In addition, Bcl-xL inhibited the activation of caspase-3-like proteases accompanying Bax-induced COS-7 cell death but Bcl-2 did not. These results indicate that the caspase activation is essential for Bax-induced apoptosis, and that the ability of Bcl-2 and Bcl-xL to prevent the Bax-induced caspase activation and apoptosis in COS-7 cells could be differentially regulated. Our results also suggest that Bcl-2 family proteins function upstream of caspase activation and control apoptosis through the regulation of caspase activity.

Animals↗

PubMed1997

Pim-1 kinase stimulates c-Myc-mediated death signaling upstream of caspase-3 (CPP32)-like protease activation.

Pim-1 oncoprotein is a serine/threonine kinase that can closely cooperate with c-Myc in lymphomagenesis, as does Bcl-2. Although the molecular mechanism of this cooperative transformation remains unknown, it is speculated that, similar to Bcl-2, Pim-1 contributes to transformation by inhibiting apoptosis. In this study, therefore, we examined the effect of Pim-1 expression on c-Myc-mediated apoptosis of Rat-1 fibroblasts triggered by serum deprivation. Our results showed that, rather than inhibiting apoptosis, Pim-1 expression stimulated c-Myc-mediated apoptosis in Rat-1 fibroblasts. Pim-1 stimulated c-Myc-mediated apoptosis through an enhancement of the c-Myc-mediated activation of caspase-3 (CPP32)-like proteases, since the suppression of this activity by a specific caspase inhibitor abolished the apoptosis stimulation by Pim-1. A kinase-defective Pim-1 mutant failed to stimulate c-Myc-mediated apoptosis, and Pim-1 expression alone in the absence of c-Myc overexpression did not induce apoptosis of serum-deprived Rat-1 cells, indicating that the kinase activity of Pim-1 and the activated c-Myc signaling pathway were required for apoptosis stimulation by Pim-1. Together, these results suggest that Pim-1 oncoprotein stimulates as a serine/threonine kinase the death signaling elicited by c-Myc at a step upstream of caspase-3-like protease activation in Rat-1 fibroblasts. Our results also suggest that Pim-1 kinase might function cooperatively with c-Myc through the phosphorylation of a factor(s) which regulates the common signaling pathway involved in c-Myc-mediated apoptosis and transformation.

Animals↗

PubMed1997

Risk of nodal metastases at laparoscopic pelvic lymphadenectomy using PSA, Gleason score, and clinical stage in men with localized prostate cancer.

Laparoscopic pelvic lymph node dissection (LPLND) is a low-morbidity procedure used to stage prostate cancer accurately prior to definitive local therapy. To better select patients for LPLND, we reviewed the clinical features of 120 patients with clinically localized prostate cancer who underwent LPLND to define significant risk factors for nodal metastases. The age ranged from 43 to 79 years (mean 68). Serum prostate specific antigen (PSA) concentration ranged from 1.3 to 329 ng/mL, Gleason score ranged from 2 to 9, and clinical stage ranged from T1b to T3c. Nodal metastases were discovered in 15 patients (13%). Among men with a Gleason score > or = 7, 21% had nodal metastases (P = 0.004). A serum PSA > 20 ng/mL and clinical stage T1b, T2b, or greater also were statistically significant predictors of lymph node metastases (20% and 19%, respectively). In multivariate analysis, Gleason score significantly predicted nodal metastases when controlling for all other clinical measures. Therefore, LPLND is indicated for any patient with a Gleason score > or = 7, PSA > 20 ng/mL, and advanced clinical T stage, independently or in combination.

Age Factors↗

PubMed1996

Calbindin-D28K in the nucleus of nerve growth factor-treated PC12 cells.

Calbindin-D28K (CB) is a calcium-binding protein found within a subset of neurons, which has been proposed to buffer intracellular calcium and to protect cells from calcium-induced neurodegeneration. The rat pheochromocytoma PC12 cell line has been an invaluable tool for studying neuronal development and characterizing the molecular actions of nerve growth factor (NGF). Using Western and RNAse protection analyses and immunocytochemical and cell fractionation techniques, we now report that NGF induces the expression of CB not only in the cytoplasm and neurites, but also within the nuclei of PC12 cells. These data indicate that PC12 cells can serve as a useful model system in which to study the functions of CB and the role of nuclear CB.

Animals↗

PubMed1995

Calcium supplementation during pregnancy for reducing pregnancy induced hypertension.

Pregnancy induced hypertension (PIH) is a common complication in pregnancy and prenatal stage. Because the direct and indirect relationship between low calcium intake and many diseases, such as rachitis, young age myopia and hypertension, calcium supplementation has been a hot topic among nutritionists. Randomized trials of calcium supplementation during pregnancy were conducted in 212 healthy primipara. They were divided into 4 groups and gave 120mg, 240mg, 1g or 2g of calcium daily from 20 to 28 wks of gestation up to delivery respectively. As a result, the incidence of PIH was 8.9%, 7.5%, 8% and 4% respectively in these groups. The control group (106 pregnant women) who did not receive calcium gave an incidence of 18%. Supplementation of 2g of calcium daily showed significant results in lowering the incidence of PIH (P < 0.05) without any adverse effects. In 1992 calcium supplementation was widely used in antenatal-clinic. 200 cases with intake of 2g calcium were compared with corresponding non-calcium supplementation cases, and the incidence of PIH was 7.5% and 16.5% (P < 0.005) respectively. Mediating parathyroid hormone and renin activity are thought to be the effect of calcium on decreasing the incidence of PIH.

Calcium↗

PubMed1995

[Apoptosis of mouse MS-2 fibrosarcoma cells induced by photodynamic therapy with LDL-administered zinc-phthalocyanine].

Photodynamic destruction of MS-2 fibrosarcoma cells in mice induced by LDL-administered Zinc-phthalocyanine and red light irradiation was studied by electron microscopy. The pronounced structural changes such as chromatin condensation, disappearance of nuclear pores, karyopyknosis, karyorrhexis, leakage of chromatin aggregates, autophagocytosis, bleb formation on the cell surface, cytoplasmic vacuolization and cell fragmentation suggest that the tumor cell death was induced by apoptosis. However, its exact mechanism and regulating pathways remain to be further investigated.

Animals↗