Search PubMed⌕ Search

Biomedical subjects

S U Kim

Publications and source records attributed to S U Kim.

At least 73 records · Page 4Linked to original sources
PubMed1999

Effects of ATP and elevated K+ on K+ currents and intracellular Ca2+ in human microglia.

We have used whole-cell patch-clamp recordings and calcium microfluorescence measurements to study the effects of ATP and elevated external K+ on properties of human microglia. The application of ATP (at 0.1 mM) led to the activation of a transient inward non-selective cationic current at a cell holding potential of -60 mV and a delayed, transient expression of an outward K+ current activated with depolarizing steps applied from holding level. The ATP response included an increase in inward K+ conductance and a depolarizing shift in reversal potential as determined using a voltage ramp waveform applied from -120 to -50 mV. Fura-2 microspectrofluorescence measurements showed intracellular calcium to be increased following the application of ATP. This response was characterized by an initial transient phase, which persisted in Ca2+-free media and was due to release of Ca2+ from intracellular storage sites. The response had a later plateau phase, consistent with Ca2+ influx. In addition, ATP-induced changes in intracellular Ca2+ exhibited prominent desensitization. Elevated external K+ (at 40 mM) increased inward K+ conductance and shifted the reversal potential in the depolarizing direction, with no effect on outward K+ current or the level of internal Ca2+. The results of these experiments show the differential responses of human microglia to ATP and elevated K+, two putative factors associated with neuronal damage in the central nervous system.

Adenosine Triphosphate↗
PubMed1999

Inhibition of chitin synthase II by catechins from stem bark of Taxus cuspidata.

Two flavonoids, (+/-)-catechin and (-)-epicatechin, were isolated from the stem bark of Taxus cuspidata by monitoring chitin synthase II inhibitory activity. The compounds inhibit chitin synthase II with an IC50 of 15 and 29 micrograms/ml, respectively and appear to be selective for chitin synthase II. They did not inhibit chitin synthase III.

Catechin↗
PubMed1999

Chitin synthase II inhibitory activity of ursolic acid, isolated from Crataegus pinnatifida.

Two triterpenoid compounds, ursolic acid and uvaol, were isolated from Crataegus pinnatifida Bunge leaves. Ursolic acid inhibits chitin synthase II from S. cerevisiae with an IC50 value of 0.84 microgram/ml and the inhibition appears to be selective for chitin synthase II, whereas uvaol has no inhibitory activity up to 280 micrograms/ml. Oleanolic acid, alpha-hederin hydrate, and betulic acid inhibited the chitin synthase II activity under the same conditions with an IC50 of 5.6, 64.3, and 98.7 micrograms/ml, respectively.

Chitin Synthase↗
PubMed1999

Modification of chitosan to improve its hypocholesterolemic capacity.

Cholestyramine is the most widely used bile acid sequestrant in the treatment of hypercholesterolemia. However, cholestyramine has unpleasant side effects as a consequence of its hydrophobic backbone. Therefore, high-capacity bile acid sequestering biopolymers with cationic chitosan derivatives were developed, because electrostatic interactions are important for binding with bile acid anions. Dialkylaminoalkylation and reductive amination of chitosan were done to add dialkylaminoalkyl and an additional free amino group at a hydroxyl site in the chitosan backbone respectively and the amino-derivatized chitosan derivatives were quaternized with methyl iodide to produce a cationic polyelectrolyte. The in vitro bile acid binding capacity of the chitosan derivatives in aqueous NaCl was measured by reversed-phase HPLC. The binding capacities of sodium glycocholate (a major bile acid) to chitosan, DEAE-chitosan, quaternized DEAE-chitosan, and cholestyramine were 1.42, 3.12, 4.06, and 2.78 mmol/g resin, respectively. With quaternized DEAE-chitosan, the bile acid binding capacity increased approximately 50% over that of cholestyramine. The bile acid binding capacity of dialkylaminoalkyl chitosan derivatives increased with the number of carbons in the alkyl groups, indicating that hydrophobic interaction is a secondary factor for the sequestration of bile acids.

Anion Exchange Resins↗
PubMed1999

Neurotoxicity of isoniazid and its metabolites in cultures of mouse dorsal root ganglion neurons and hybrid neuronal cell line.

Isoniazid (INH) is one of the anti-tuberculosis drugs widely prescribed for patients since the early 1950s. It is relatively nontoxic but some patients develop peripheral neuropathy attributed to a disturbance of vitamin B6 metabolism. Some isoniazid metabolites are hepatotoxic but little is known about their neurotoxic property. Isoniazid and its metabolites including acetylisoniazid, acetylhydrazine, diacetylhydrazine, isonicotinic acid and hydrazine were examined for their potential neurotoxic effects in cultured mouse dorsal root ganglion (DRG) neurons and mouse neuroblastoma x DRG neuron hybrid cell line N18D3. Isoniazid did not cause neurotoxicity at exposures up to 7 days. Hydrazine was found to be the most toxic metabolite with LC50 values of 2.7 mM and 0.3 mM after 7 days of exposure in DRG neurons and N18D3 hybrid neurons, respectively. Other metabolites including acetylisoniazid, acetylhydrazine, diacetylhydrazine and isonicotinic acid had moderate to minor neurotoxic effects on N18D3 hybrid neurons. Pyridoxine, which is used in clinical practice to prevent or ameliorate the isoniazid-induced neuropathy, did not consistently reverse the neurotoxicity of any of the metabolites in the cell cultures, but some interaction with hydrazine cannot be ruled out. Pyridoxine itself was found to be neurotoxic both in DRG neurons and N18D3 hybrid neurons, in agreement with human peripheral sensory neuropathy caused by prolonged overdosage. The enzymes catalase and superoxide dismutase and the antioxidant agent selenium showed some protection against hydrazine neurotoxicity, suggesting an involvement of the generation of reactive oxygen species in the pathogenesis of isoniazid neuropathy. Both mouse DRG neurons and N18D3 mouse hybrid neurons were shown to be useful culture systems for elucidating the neurotoxicity mechanisms of agents causing sensory neuropathies and general neurotoxic effects in the nervous system.

Animals↗
PubMed1998

Expression of complement C4 and C9 genes by human astrocytes.

Evidence exists that complement activation is involved in the pathogenesis of Alzheimer's disease (AD). It has been previously demonstrated that central nervous system (CNS) resident cells can synthesize complement proteins. Two key proteins in the complement pathway are the complement C4 and C9 proteins. Using reverse transcription-polymerase chain reaction, ELISA, immunocytochemical and immunoblot techniques, we showed that primary human astrocytes constitutively expressed complement C4 mRNA and protein, and that this was increased when cells were treated with interferon-gamma, but inhibited when cells were treated with interleukin-1beta (IL-1beta). C4 immunoreactivity could be localized to GFAP-positive astrocytes when protein secretion was inhibited. These results indicated that astrocytes could be a source of complement C4 in the human CNS. In addition it was shown that stimulated astrocytes could also express complement C9 mRNA, though C9 protein was not detectable in culture supernatants.

Astrocytes↗
PubMed1998

Cholinergic agonists increase intracellular Ca2+ in cultured human microglia.

Microglia are resident phagocytic cells in the central nervous system (CNS), and can be activated in response to various stimuli including neurotransmitters. Using fura-2 imaging, we investigated the effects of carbachol (CCh), a cholinergic agonist, on [Ca2+]i in cultured human microglia. Treatment of microglia with CCh (100 microM) produced a transient increase in [Ca2+]i, which was atropine-sensitive and was associated with release from intracellular Ca2+ stores. Successive applications of CCh showed a change in the amplitude of the [Ca2+]i signal consistent with desensitization. These results show that human microglia express functional muscarinic receptors and respond to cholinergic agonists. The rapid change of [Ca2+]i in microglia may serve as a second messenger to trigger downstream cascades which contribute to signalling pathways in CNS pathology.

Atropine↗
PubMed1998

Role of jasmonic acid in biotransformation of (--)-isopiperitenone in suspension cell culture of Mentha piperita.

The role of jasmonic acid was studied in biotransformation of (--)-isopiperitenone to (--)-7-hydroxyisopiperitenone using alpha suspension cells were treated with (--)-isopiperitenone, mRNA of a cytochrome P450 was induced in a similar time-course pattern as the biotransformation shown in a previous study (Park et al., 1997). The induction of P450 mRNA and the biotransformation of (--)-isopiperitenone were increased by methyl jasmonate, but decreased by salicylhydroxamic acid, and inhibitor of jasmonic acid synthesis. These results suggest that the biotransformation involves the induction of P450 which is mediated by jasmonic acid as a signaling molecule.

Acetates↗
PubMed1998

Enhanced biosynthesis of clavulanic acid in Streptomyces clavuligerus due to oxidative challenge by redox-cycling agents.

Streptomyces clavuligerus produces a clinically important beta-lactamase inhibitor, clavulanic acid. When several of the selected redox-cycling agents were treated, an increase in clavulanate production was observed. The stimulatory effect was seen when the reaction was fed with menadione, plumbagin and phenazine methosulfate (PMS), whereas feeding with methyl viologen had a negative effect. PMS exerted the strongest effect, enhancing the accumulation of clavulanic acid by 150%. Induction of superoxide dismutase upon the addition of PMS suggested an involvement of superoxide in the enhancing process. The stimulatory effect of PMS was offset by the addition of butylated hydroxyanisole, further supporting the involvement of the active oxygen. The enhanced production of clavulanic acid correlated well with the increased total activity of clavaminic acid synthase, a key enzyme in its biosynthesis, and the transcription of cas2, its coding gene. The results suggested that active oxygen species could enhance the biosynthesis of secondary metabolites through the transcriptional activation of the biosynthetic gene.

Anti-Bacterial Agents↗
PubMed1998

Engraftable human neural stem cells respond to developmental cues, replace neurons, and express foreign genes.

Stable clones of neural stem cells (NSCs) have been isolated from the human fetal telencephalon. These self-renewing clones give rise to all fundamental neural lineages in vitro. Following transplantation into germinal zones of the newborn mouse brain they participate in aspects of normal development, including migration along established migratory pathways to disseminated central nervous system regions, differentiation into multiple developmentally and regionally appropriate cell types, and nondisruptive interspersion with host progenitors and their progeny. These human NSCs can be genetically engineered and are capable of expressing foreign transgenes in vivo. Supporting their gene therapy potential, secretory products from NSCs can correct a prototypical genetic metabolic defect in neurons and glia in vitro. The human NSCs can also replace specific deficient neuronal populations. Cryopreservable human NSCs may be propagated by both epigenetic and genetic means that are comparably safe and effective. By analogy to rodent NSCs, these observations may allow the development of NSC transplantation for a range of disorders.

Animals↗
PubMed1998

Length of huntingtin and its polyglutamine tract influences localization and frequency of intracellular aggregates.

It is unclear how polyglutamine expansion is associated with the pathogenesis of Huntington disease (HD). Here, we provide evidence that polyglutamine expansion leads to the formation of large intracellular aggregates in vitro and in vivo. In vitro these huntingtin-containing aggregates disrupt normal cellular architecture and increase in frequency with polyglutamine length. Huntingtin truncated at nucleotide 1955, close to the caspase-3 cleavage site, forms perinuclear aggregates more readily than full-length huntingtin and increases the susceptibility of cells to death following apoptotic stimuli. Further truncation of huntingtin to nucleotide 436 results in both intranuclear and perinuclear aggregates. For a given protein size, increasing polyglutamine length is associated with increased cellular toxicity. Asymptomatic transgenic mice expressing full-length huntingtin with 138 polyglutamines form exclusively perinuclear aggregates in neurons. These data support the hypothesis that proteolytic cleavage of mutant huntingtin leads to the development of aggregates which compromise cell viability, and that their localization is influenced by protein length.

Animals↗
PubMed1998

Proliferation of human Schwann cells induced by neu differentiation factor isoforms.

Neu differentiation factor (NDF), a 44-kD polypeptide, is a member of the neuregulin family which also includes glial growth factor, heregulin and acetylcholine-receptor-inducing activity. Previous studies have demonstrated that NDF/glial growth factor/heregulin/acetylcholine-receptor-including activity are products of neurons and mediate proliferation, differentiation and gene expression in Schwann cells of experimental animals. In the present study, the efficacy of different isoforms of NDF in stimulating human Schwann cell proliferation is investigated in Schwann-cell-enriched cultures derived from fetal human dorsal root ganglia (15-20 weeks gestation). NDF isoforms examined include alpha1, alpha2, EGF-like domain alpha2 (EGFalpha2), alpha3, beta1, EGFbeta1, EGFbeta, beta2 and beta3. For the assessment of Schwann cell proliferation, double immunostaining using antibodies specific for S-100 protein and bromodeoxyuridine was used. While treatment of Schwann cells with NDF alpha isoforms (alpha1, alpha2, alpha3 and EGFalpha2) had little effect on Schwann cell proliferation, NDF beta isoforms (beta1, beta2, beta3, EGFbeta1 and EGFbeta) induced a greatly enhanced proliferation in Schwann cells. The proliferation index in unstimulated Schwann cells was 1.3 +/- 0.9%, whereas in Schwann cells treated with NDFbeta isoforms the proliferation index was 21.8 +/- 2.2%. The finding that the truncated beta isoforms such as EGFbeta1 and EGFbeta retain a mitogenic activity as potent as full-length beta isoform indicates that the C-terminal portion of the EGF-like domain is responsible for its receptor binding and subsequent biological activity.

Cell Division↗
PubMed1997

Neuronal differentiation of human neuroblastoma SH-SY5Y cells by gangliosides.

Exogenous administration of gangliosides induced neuronal differentiation with prominent neuritogenesis in human neuroblastoma SH-SY5Y cells in vitro. Neuritogenesis was characterized by ruffling of the cell membrane, the development of lamellipodia and filopodia, and the subsequent elongation and branching of the neurites ultrastructurally. Both axons and neurites were identified. Increased numbers of cell organelles in the neurites and cell bodies were noted. Nonsynaptic contacts and gap junctions formed between neurites or between each neurite and cell body. These findings could be implicated in histopathologic changes from neuroblastoma to ganglioneuroblastoma.

Cell Differentiation↗
PubMed1997

Ion channels of human microglia in culture.

Macroscopic and microscopic currents have been recorded using human microglia isolated from fetal human brains (12-20 weeks gestation). Within a period of two days following plating of cells, inward K+ currents were small (mean amplitude of 0.3 nA at -100 mV) and outward K+ currents were not observed. For periods in excess of five days after adherence to substrate, an inactivating outward K+ current, sensitive to 4-aminopyridine, was expressed. A slowly rising current, blocked by tetraethylammonium, was also evident in a small population of human microglia. This current was activated with cell depolarization positive to +10 mV and had properties similar to those recently described for a proton current in mouse cells. In early adherent cells (days 1 or 2 after plating), treatment of microglia with interferon-gamma led to the expression of outward K+ current which was lacking in the absence of the treatment. In excised, inside-out patches, two high conductance channels were identified. A calcium-dependent K+ channel (unitary conductance of 106 pS with physiological levels of K+ across the patch) had an open probability of 0.5 with internal Ca2+ at 7 microM and the patch potential at 0 mV. In addition, an anion channel (unitary conductance of 280 pS) was transiently activated with depolarizing or hyperpolarizing steps applied from 0 mV. Characterization of the macroscopic and unitary properties of currents in microglia will have relevance to a description of putative cell functions in the human CNS. In particular, modification of cell electrophysiological properties by various activating stimuli may contribute to signalling processes in CNS pathology.

Anions↗
PubMed1997

Role of extracellular signal-regulated protein kinases 1 and 2 in oligodendroglial process extension.

The relationship between extracellular signal-regulated protein kinase (ERK) activation and process extension in cultured bovine oligodendrocytes (OLGs) was investigated. Process extension was induced through the exposure of cultured OLGs to phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C (PKC), for various intervals. During the isolation of these OLGs from bovine brain, the original processes were lost. Therefore, any reinitiation of process extension via PMA stimulation was easily discemible through morphological monitoring. It was found that exposure of OLGs to PMA for 10 min was enough to induce OLG process extension 24-72 h later. Furthermore, this extension was still evident at least 1 week after the initial PMA stimulation, indicating that OLGs do not need continuous PKC activation to sustain process extension. Control and PMA-stimulated OLGs were also subjected to immunocytochemistry using an anti-ERK antibody selective for the mitogen-activated protein kinases p42 Erk2 (ERK2) and p44 Erk1 (ERK1) isoforms. ERK immunoreactivity in the nucleus was evident after PMA stimulation of OLGs but not in control OLGs. In parallel experiments, the control and PMA-stimulated OLGs were purified by Mono Q fractionation and subjected to ERK phosphotransferase assays using [gamma-32P]ATP and either myelin basic protein (MBP) or a synthetic peptide substrate based on the Thr97 phosphorylation site in MBP. These assays indicated that in PMA-treated OLGs, ERK activation was at least 12-fold higher than in control OLGs. Anti-ERK and anti-phosphotyrosine western blots of the assay fractions verified an enhanced phosphorylation of ERK1 and ERK2 in PMA-treated fractions relative to control fractions. When OLGs were pretreated for 15 min with the ERK kinase (MEK) inhibitor PD 098059 before PMA stimulation, they exhibited a 67% decrease in ERK activation as compared with cells treated with PMA alone. Furthermore, these MEK inhibitor-pretreated cells were still viable but showed no process extensions up to 1 week later. Therefore, we propose that a threshold level of ERK activity is required for the initiation of OLG process extension.

Animals↗
PubMed1997

Tissue culture model of Krabbe's disease: psychosine cytotoxicity in rat oligodendrocyte culture.

Krabbe's disease (globoid cell leukodystrophy) is a progressive cerebral degenerative disease of infancy characterized by severe myelin loss and the presence of globoid bodies in the white matter. Previous studies have suggested that psychosine is the causative agent for the pathogenesis of Krabbe's disease. In the present study, we investigated psychosine-induced injury and cell death of oligodendrocytes in enriched cultures of oligodendrocytes prepared from 3-week-old rat brain. The psychosine concentration sufficient to induce 50% cell death in oligodendrocytes was 30 micrograms/ml in the medium containing serum and 10 micrograms/ml in the serum-free medium. When oligodendrocytes were exposed to psychosine in the presence of phorbol esters, insulin, insulin-like growth factor I (IGF-I), demethylsulfoxide, or serum albumin, the survival of oligodendrocytes was greatly increased. These results indicate that psychosine cytotoxicity against oligodendrocytes is blocked by phorbol esters, insulin, and IGF-I through activation of protein kinase-C, by dimethylsulfoxide through activation of beta-galactosidase, and by albumin through its binding to psychosine.

Albumins↗