Biomedical subjects

K Chen

Publications and source records attributed to K Chen.

At least 73 records · Page 4Linked to original sources

PubMed2001

Solitons in the one-dimensional forest fire model.

Fires in the one-dimensional Bak-Chen-Tang forest fire model propagate as solitons, resembling shocks in Burgers turbulence. The branching of solitons, creating new fires, is balanced by the pairwise annihilation of oppositely moving solitons. Two distinct, diverging length scales appear in the limit where the growth rate of trees, p, vanishes. The width of the solitons, w, diverges as a power law, 1/p, while the average distance between solitons diverges much faster as d approximately exp(pi2/12p).

Journal Article↗

PubMed2001

A facile and highly diastereoselective aziridination of chiral camphor n-enoylpyrazolidinones with n-aminophthalimide.

Reaction of various chiral camphor N-enoylpyrazolidinones 2a-g with N-aminophthalimide in the presence of lead tetraacetate in CH(2)Cl(2) proceed smoothly afford the corresponding N-phthalimidoaziridines (3a-e, 4f-g) with excellent material yields (86-95%) at room temperature in 5 min. High levels of diastereoselectivities (up to >95:5 dr) were obtained. The solvent effect was investigated, and the auxiliary can be easily recovered in high yields under mild reaction conditions.

Journal Article↗

PubMed2001

Biochemical effects of the monoamine neurotoxins DSP-4 and MDMA in specific brain regions of MAO-B-deficient mice.

Previous studies reported that drugs acting as monoamine oxidase (MAO)-B inhibitors prevented biochemical effects induced by the neurotoxins N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) and 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"). In this study, we administered DSP-4 (50 mg/kg) or MDMA (50 mg/kg x 2, 2 h apart) to MAO-B deficient mice. Monoamine content in various brain regions (cerebellum, frontal cortex, hippocampus, hypothalamus, striatum, substantia nigra) was assayed 1 week after neurotoxin administration. Injection of DSP-4 to wild-type mice caused a marked norepinephrine (NE) loss in specific brain regions. Unexpectedly, DSP-4 caused similar effects in MAO-B-deficient and in wild-type mice in all brain regions investigated. These results suggest that MAO-B is not involved in DSP-4 toxicity. In wild-types, the neurotoxin MDMA induced both serotonin (5HT) and dopamine (DA) depletion in specific brain areas. In MAO-B-deficient mice, 5HT depletion observed in wild-types did not occur. In contrast, MDMA produced a more pronounced DA loss in knockout mice compared with wild-types. The present findings, together with previous data obtained using selective enzyme inhibitors, suggest that MAO-B is not involved in the mechanism of action of DSP-4, whereas it plays opposite roles in MDMA-induced DA and 5HT depletions.

Animals↗

PubMed2001

c-Jun N-terminal kinase activation by hydrogen peroxide in endothelial cells involves SRC-dependent epidermal growth factor receptor transactivation.

The phenotypic properties of the endothelium are subject to modulation by oxidative stress, and the c-Jun N-terminal kinase (JNK) pathway is important in mediating cellular responses to stress, although activation of this pathway in endothelial cells has not been fully characterized. Therefore, we exposed endothelial cells to hydrogen peroxide (H(2)O(2)) and observed rapid activation of JNK within 15 min that involved phosphorylation of JNK and c-Jun and induction of AP-1 DNA binding activity. Inhibition of protein kinase C and phosphoinositide 3-kinase did not effect JNK activation. In contrast, the tyrosine kinase inhibitors, genistein, herbimycin A, and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) significantly attenuated H(2)O(2)-induced JNK activation as did endothelial cell adenoviral transfection with a dominant-negative form of Src, implicating Src as an upstream activator of JNK. Activation of JNK by H(2)O(2) was also inhibited by AG1478 and antisense oligonucleotides directed against the epidermal growth factor receptor (EGFR), implicating the EGFR in this process. Consistent with this observation, H(2)O(2) stimulated EGFR tyrosine phosphorylation and complex formation with Shc-Grb2 that was abolished by PP2, implicating Src in H(2)O(2)-induced EGFR activation. Tyrosine phosphorylation of the EGFR by H(2)O(2) did not involve receptor autophosphorylation at Tyr(1173) as assessed by an autophosphorylation-specific antibody. These data indicate that H(2)O(2)-induced JNK activation in endothelial cells involves the EGFR through an Src-dependent pathway that is distinct from EGFR ligand activation. These data represent one potential pathway for mediating oxidative stress-induced phenotypic changes in the endothelium.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Integrin-mediated mechanotransduction requires its dynamic interaction with specific extracellular matrix (ECM) ligands.

The aim of this study is to elucidate the role of integrins in transducing fluid shear stress into intracellular signals in vascular endothelial cells, a fundamental process in vascular biology. We demonstrated that shear stress activates specific integrins in endothelial cells plated on substrates containing the cognate extracellular matrix (ECM) ligands. The shear stress-induced mechanotransduction, as manifested by integrin-Shc association, was abolished when new integrin-ECM ligand interactions were prevented by either blocking the integrin-binding sites of ECM ligands or conjugating the integrins to immobilized antibodies. Our results indicate that the dynamic formation of new connections between integrins and their specific ECM ligands is critical in relaying the signals induced by shear stress to intracellular pathways.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Engineering of a mammalian cell line for reduction of lactate formation and high monoclonal antibody production.

Lactate and ammonia are the two major waste products formed during mammalian cell growth. Accumulation of these side products can have a negative effect on cell growth, and has drawn recent attention because of their inhibitory effects on the specific product synthesis rate. Our aim is to reduce lactate formation in the cell culture by genetically manipulating of the pathway of lactate synthesis with an aim to achieve high monoclonal antibody production. We have partially disrupted the LDH-A gene by homologous recombination in hybridoma cells (ATCC-CRL-1606). The cells that received the newly introduced DNA were selected by G418, and an LDH-deficient cell was identified by a screening method based on medium color changing in 96-well plates. A variant cell, LDH-neo21, was identified through this screening method and was characterized. The specific productivity of lactate by LDH-neo21 cells was 50% lower than that of parental cells. Intracellular LDH enzyme activity was significantly reduced. The cell growth was improved both in terms of cell density and cell viability. Total cell density potentially reached 5 x 10(6) cells/mL while the parental hybridoma cells had a cell density of 3.5 x 10(6) cells/mL, which represented a 30% increase. The antibody production of LDH-neo21 cells was threefold greater than that of parental cells during 5-day batch culture. Polymerase chain reaction (PCR) results showed that at least one copy of the LDH-A gene was disrupted in the LDH-neo21 cells. The variant of the hybridoma cell exhibited a significant advantage of reduced lactate formation in the cell culture with a high concentration of glucose, which led to a higher production of monoclonal antibody. 2001 John Wiley & Sons, Inc.

Ammonia↗

PubMed2001

Subtle radiographic findings of achondroplasia in patients with Crouzon syndrome with acanthosis nigricans due to an Ala391Glu substitution in FGFR3.

A unique type of craniofacial dysostosis, Crouzon syndrome with acanthosis nigricans (CAN), has been attributed to a specific substitution (Ala391Glu) in the fibroblast growth factor receptor 3 (FGFR3) gene. At birth, individuals with this disorder have craniosynostosis, ocular proptosis, midface hypoplasia, choanal atresia, hydrocephalus, and they experience the onset of acanthosis nigricans during childhood. We report three cases and compare the clinical characteristics of our cases with the previously reported cases of this disorder. Since the Ala391Glu substitution in FGFR3 is close to the substitutions in the transmembrane domain that result in achondroplasia, we carefully reviewed the skeletal findings in six patients. We identified subtle radiographic findings of achondroplasia in all six cases including narrow sacrosciatic notches, short vertebral bodies, lack of the normal increase in interpediculate distance from the upper lumbar vertebrae caudally, and broad, short metacarpals and phalanges. Even before acanthosis nigricans appears, the presence of choanal atresia and hydrocephalus in an individual with features of Crouzon syndrome should suggest the diagnosis of CAN, and subtle skeletal findings can lend further support to this diagnosis.

Acanthosis Nigricans↗

PubMed2001

Identification of incompletely processed potential carboxypeptidase E substrates from CpEfat/CpEfat mice.

In an attempt to identify peptides that may be involved in the obese phenotype observed in CpEfat/CpEfat mice (deficient in Carboxypeptidase E, CpE) samples from fourteen neuroendocrine tissues in wild-type and CpEfat/CpEfat mice were obtained. Peptides were purified from these tissues and potential CpE substrate peptides were enriched using an anhydrotrypsin column that captures peptides with basic C-termini. Bound peptides were subjected to tryptic digestion and followed by liquid chromatography-mass spectrometry analysis. The relative levels of CpEfat/CpEfat versus wild-type peptides were determined by comparison of the ion intensities. Peptide ions elevated in the CpEfat/CpEfat samples were identified by targeted liquid chromatography-tandem mass spectrometry. From those ions, 27 peptides derived from known neuropeptides (including CpE substrates) were identified, together with another 25 peptides from proteins not known to be components of the neuropeptide processing pathway. The known CpE substrates identified included the recently discovered proSAAS, granin-like neuroendocrine peptide precursor that inhibits prohormone processing. The approach demonstrated the feasibility of using an affinity-based method for identifying differences in specific classes of peptides between normal and mutant mice.

Amino Acid Sequence↗

PubMed2001

Towards defining the urinary proteome using liquid chromatography-tandem mass spectrometry. I. Profiling an unfractionated tryptic digest.

The proteome of normal male urine from a commercial pooled source has been examined using direct liquid chromatography-tandem mass spectrometry (LC-MS/MS). The entire urinary protein mixture was denatured, reduced and enzymatically digested prior to LC-MS/MS analysis using a hybrid-quadrupole time-of-flight mass spectrometer (Q-TOF) to perform data-dependent ion selection and fragmentation. To fragment as many peptides as possible, the mixture was analyzed four separate times, with the mass spectrometer selecting ions for fragmentation from a subset of the entire mass range for each run. This approach requires only an autosampler on the HPLC for automation (i.e, unattended operation). Across these four analyses, 1.450 peptide MS/MS spectra were matched to 751 sequences to identify 124 gene products (proteins and translations of expressed sequence tags). Interestingly, the experimental time for these analyses was less than that required to run a single two-dimensional gel.

Amino Acid Sequence↗

PubMed2001

Effects of AGN 192024, a new ocular hypotensive agent, on aqueous dynamics.

PURPOSE: To determine the mechanism of intraocular pressure lowering for the Ocular Hypotensive Lipid, AGN 192024 (Allergan, Inc, Irvine, California). METHODS: Twenty-five normal human volunteers between the ages of 21 and 48 took part in a randomized, double-masked, placebo-controlled, paired-comparison study in which intraocular pressure, aqueous humor flow, and tonographic resistance to outflow were studied. Measurements of aqueous flow were made during the day and at night while subjects slept. Intraocular pressure was measured with the Goldmann tonometer, and resistance to outflow was measured by electronic recording Schiötz tonography. RESULTS: Intraocular pressure was decreased by 20% on day 3 in AGN 192024-treated eyes in comparison with placebo-treated eyes in normal subjects (P <.001). Aqueous humor flow was stimulated 13% during the day (P =.007) and 14% at night (P =.014) by the drug. Tonographic resistance to outflow was decreased 26% by AGN 192024 (P <.001), and apparent resistance to outflow (the ratio of intraocular pressure to aqueous flow) was decreased 31% (P <.001). Assuming that AGN 192024 does not cause prolonged lowering of episcleral venous pressure, the results show that pressure-insensitive outflow is enhanced by 50%, whereas tonographic facility of outflow (reciprocal of resistance) was enhanced 35%. CONCLUSIONS: AGN 192024 is an ocular hypotensive agent that works by enhancing both pressure-sensitive and pressure-insensitive aqueous humor outflow without diminishing aqueous humor formation.

Adult↗

PubMed2001

Brownian dynamics simulations of interaction between scorpion toxin Lq2 and potassium ion channel.

The association of the scorpion toxin Lq2 and a potassium ion (K(+)) channel has been studied using the Brownian dynamics (BD) simulation method. All of the 22 available structures of Lq2 in the Brookhaven Protein Data Bank (PDB) determined by NMR were considered during the simulation, which indicated that the conformation of Lq2 affects the binding between the two proteins significantly. Among the 22 structures of Lq2, only 4 structures dock in the binding site of the K(+) channel with a high probability and favorable electrostatic interactions. From the 4 candidates of the Lq2-K(+) channel binding models, we identified a good three-dimensional model of Lq2-K(+) channel complex through triplet contact analysis, electrostatic interaction energy estimation by BD simulation and structural refinement by molecular mechanics. Lq2 locates around the extracellular mouth of the K(+) channel and contacts the K(+) channel using its beta-sheet rather than its alpha-helix. Lys27, a conserved amino acid in the scorpion toxins, plugs the pore of the K(+) channel and forms three hydrogen bonds with the conserved residues Tyr78(A-C) and two hydrophobic contacts with Gly79 of the K(+) channel. In addition, eight hydrogen-bonds are formed between residues Arg25, Cys28, Lys31, Arg34 and Tyr36 of Lq2 and residues Pro55, Tyr78, Gly79, Asp80, and Tyr82 of K(+) channel. Many of them are formed by side chains of residues of Lq2 and backbone atoms of the K(+) channel. Thirteen hydrophobic contacts exist between residues Met29, Asn30, Lys31 and Tyr36 of Lq2 and residues Pro55, Ala58, Gly79, Asp80 and Tyr82 of the K(+) channel. These favorable interactions stabilize the association between the two proteins. These observations are in good agreement with the experimental results and can explain the binding phenomena between scorpion toxins and K(+) channels at the level of molecular structure. The consistency between the BD simulation and the experimental data indicates that our three-dimensional model of Lq2-K(+) channel complex is reasonable and can be used in further biological studies such as rational design of blocking agents of K(+) channels and mutagenesis in both toxins and K(+) channels.

Amino Acid Sequence↗

PubMed2001

Oxytocinergic neurotransmission at the hippocampus in the central neural regulation of penile erection in the rat.

OBJECTIVES: To investigate whether there is an oxytocinergic neurotransmission at the hippocampus involved in the central regulation of penile erection in the rat. METHODS: Male adult Sprague-Dawley (n = 27) rats anesthetized with pentobarbital were used. A 26-gauge needle was inserted into the corpus cavernosum to measure the intracavernous pressure (ICP) and the systemic and mean arterial pressure and heart rate simultaneously. The following studies were performed: stereotaxic delivery of oxytocin acetate (3 pmol/100 nL) into the hippocampus; microinjection of a mixture of [d(CH(2))(5)-Tyr(Me)(2)-Orn(8)]-vasotocin (3 pmol/100 nL) and oxytocin (3 pmol/100 nL) into the hippocampus; injection of saline into the hippocampus; and intracavernous injection of oxytocin (3 pmol/100 microL). The ICP and hemodynamic parameters were monitored after each administration of the experimental agents. RESULTS: After administration of oxytocin into the hippocampus, a significant increase in the ICP occurred from resting (8.8 +/- 1.7 mm Hg) to a peak at 49.6 +/- 12.5 mm Hg and persisted for 18.6 +/- 9.4 minutes after an onset latency of 500.0 +/- 389.7 seconds. However, no change in the ICP occurred after administration of [d(CH(2))(5)-Tyr(Me)(2)-Orn(8)]-vasotocin plus oxytocin into the hippocampus. In addition, no elevation of ICP occurred after administration of saline to the hippocampus or after intracavernous injection of oxytocin. CONCLUSIONS: The results demonstrate that administration of oxytocin into the hippocampus induces penile erection in the rat. However, concomitant administration of oxytocin and its antagonist was ineffective in eliciting penile erection. These observations suggest that oxytocinergic neurotransmission at the hippocampus may be involved in the central neural regulation of the penile erection in the rat.

Animals↗

PubMed2001

Comparison of once- or twice-daily bimatoprost with twice-daily timolol in patients with elevated IOP : a 3-month clinical trial.

OBJECTIVE: To compare the safety, tolerability, and efficacy of bimatoprost 0.03% instilled once daily or twice daily with timolol 0.5% twice daily. DESIGN: Multicenter, 3-month, randomized, double-masked, interventional comparison trial. PARTICIPANTS: Patients diagnosed with ocular hypertension or glaucoma (n = 596). INTERVENTION: Patients received bimatoprost 0.03% ophthalmic solution once daily (8 PM, with vehicle control at 8 AM), bimatoprost 0.03% twice daily (8 AM; 8 PM), or timolol 0.5% twice daily (8 AM; 8 PM) in an uneven 2:2:1 randomization. Scheduled visits were at prestudy, baseline (day 0), weeks 2 and 6, and month 3. Intraocular pressure (IOP) was measured at 8 AM (predose), 10 AM, and 4 PM. MAIN OUTCOME MEASURES: The primary outcome measure was reduction in IOP in the eye with higher IOP at baseline. Secondary outcome measures included safety variables (adverse events, ophthalmoscopy, biomicroscopy, iris pigmentation, laser-flare meter, visual acuity, visual fields, heart rate, blood pressure, blood chemistry, hematology, and urinalysis). RESULTS: At month 3, the mean reduction in IOP from baseline at 8 AM was 9.16 mmHg (35.2%) with bimatoprost once daily, 7.78 mmHg (30.4%) with bimatoprost twice daily, and 6.74 mmHg (26.2%) with timolol twice daily. At all follow-up visits, mean IOP reductions were significantly greater in the bimatoprost once daily group than in the timolol group at each time point (8 AM, 10 AM, and 4 PM; P < 0.001). Twice-daily dosing of bimatoprost also provided significantly greater mean reductions in IOP than timolol at most time points but was not as effective as once-daily dosing. Bimatoprost was associated with significantly more hyperemia and eyelash growth than timolol, whereas timolol was associated with significantly more burning and stinging sensation in eyes. Overall, bimatoprost was well tolerated with few discontinuations because of adverse events. CONCLUSIONS: Bimatoprost 0.03% once daily was safe and statistically superior to timolol 0.5% twice daily in lowering IOP in patients with ocular hypertension or glaucoma. Bimatoprost given once daily consistently provided IOP reductions approximately 2 to 3 mmHg greater than those provided by timolol. Once-daily dosing of bimatoprost, 0.03%, demonstrated greater IOP-lowering effect and better ocular tolerability than twice-daily dosing.

Adult↗

PubMed2001

Antitumor agents 210. Synthesis and evaluation of taxoid-epipodophyllotoxin conjugates as novel cytotoxic agents.

Five compounds composed of a taxoid (paclitaxel or cephalomannine) and a 4'-O-demethyl epipodophyllotoxin derivative joined by an imine linkage were prepared and evaluated as cytotoxic agents and inhibitors of mammalian DNA topoisomerase II. Compounds 12 and 14-16 exhibited comparable or better activity than the unconjugated epipodophyllotoxin derivatives in most tumor cell lines, and 12, 15, and 16 also showed enhanced activity against paclitaxel-resistant cells. Compound 13, which contains an epipodophyllotoxin moiety at both the taxoid 2' and 7 positions, did not stimulate protein-DNA breaks, but was 2-fold more potent than 12 and 15 and comparable to GL-331 in the topo II inhibitory assay.

Antineoplastic Agents↗

PubMed2001

Three new sesquiterpene glycosides from Dendrobium nobile with immunomodulatory activity.

Dendroside A (1) and dendronobilosides A and B (2 and 3), three new sesquiterpene glycosides, have been isolated from the stems of Dendrobium nobile, a plant used in Chinese traditional medicine. Their structures and stereochemistry were determined as 10beta,12,14-trihydroxyalloaromadendrane 14-O-beta-D-glucopyranoside (1), 10,12-dihydroxypicrotoxane 10,12-di-O-beta-D-glucopyranoside (2), and 6alpha,10,12-trihydroxypicrotoxane 10-O-beta-D-glucopyranoside (3), respectively, on the basis of spectroscopic and chemical methods. Quantum chemistry calculations were used in support of the structural determination of 1. Compounds 1 and 2 were found to stimulate the proliferation of murine T and B lymphocytes in vitro, while compound 3 showed inhibitory activity in this same assay.

Adjuvants, Immunologic↗

PubMed2001

Network dynamics and cell physiology.

Complex assemblies of interacting proteins carry out most of the interesting jobs in a cell, such as metabolism, DNA synthesis, movement and information processing. These physiological properties play out as a subtle molecular dance, choreographed by underlying regulatory networks. To understand this dance, a new breed of theoretical molecular biologists reproduces these networks in computers and in the mathematical language of dynamical systems.

CDC2 Protein Kinase↗

PubMed2001

Persistently modified h-channels after complex febrile seizures convert the seizure-induced enhancement of inhibition to hyperexcitability.

Febrile seizures are the most common type of developmental seizures, affecting up to 5% of children. Experimental complex febrile seizures involving the immature rat hippocampus led to a persistent lowering of seizure threshold despite an upregulation of inhibition. Here we provide a mechanistic resolution to this paradox by showing that, in the hippocampus of rats that had febrile seizures, the long-lasting enhancement of the widely expressed intrinsic membrane conductance Ih converts the potentiated synaptic inhibition to hyperexcitability in a frequency-dependent manner. The altered gain of this molecular inhibition-excitation converter reveals a new mechanism for controlling the balance of excitation-inhibition in the limbic system. In addition, here we show for the first time that h-channels are modified in a human neurological disease paradigm.

Animals↗

PubMed2001

Solution structure of a viral DNA repair polymerase.

DNA polymerase X (Pol X) from the African swine fever virus (ASFV) specifically binds intermediates in the single-nucleotide base-excision repair process, an activity indicative of repair function. In addition, Pol X catalyzes DNA polymerization with low nucleotide-insertion fidelity. The structural mechanisms by which DNA polymerases confer high or low fidelity in DNA polymerization remain to be elucidated. The three-dimensional structure of Pol X has been determined. Unlike other DNA polymerases, Pol X is formed from only a palm and a C-terminal subdomain. Pol X has a novel palm subdomain fold, containing a positively charged helix at the DNA binding surface. Purine deoxynucleoside triphosphate (dNTP) substrates bind between the palm and C-terminal subdomain, at a dNTP-binding helix, and induce a unique conformation in Pol X. The purine dNTP-bound conformation and high binding affinity for dGTP-Mg(2+) of Pol X may contribute to its low fidelity.

African Swine Fever Virus↗