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Biomedical subjects

S C Chow

Publications and source records attributed to S C Chow.

At least 91 records · Page 5Linked to original sources
PubMed1990

Interleukin 1 inhibits T cell receptor-mediated apoptosis in immature thymocytes.

T cell receptor signaling has been implicated in an intrathymic process of cell selection in which potentially harmful autoreactive precursors are deleted before they emigrate to the periphery. Recent work has shown that immature thymocytes undergo apoptosis, or programmed cell death, upon stimulation via the T cell antigen receptor, and it has been suggested that this mechanism may mediate deletion of the self-reactive clones during T cell development. Here we report that the accessory cell-derived T cell growth hormone interleukin-1 prevents T cell receptor-mediated thymocyte apoptosis by a mechanism that appears to involve protein kinase C activation. This effect may be relevant to the positive signaling that spares the appropriate precursors during the generation of functional T lymphocytes.

Antibodies, Monoclonal↗
PubMed1990

Polyunsaturated free fatty acids stimulate an increase in cytosolic Ca2+ by mobilizing the inositol 1,4,5-trisphosphate-sensitive Ca2+ pool in T cells through a mechanism independent of phosphoinositide turnover.

Polyunsaturated free fatty acids (PUFAs) of both w-3 and w-6 series, induce a rapid increase of cytosolic free Ca2+ concentration ([Ca2+]i) in a leukemic T-cell line (JURKAT), measured by the fluorescent indicator fura-2. The early increase in [Ca2+]i was transient, falling to a sustained level which returned to base line after 10-15 min. In Ca2+-free medium, PUFAs still caused an early increase in [Ca2+]i but rapidly returned to basal. Depletion of endoplasmic reticular Ca2+ pool by addition of OKT3 (antibodies to CD3 of the T3-antigen receptor complex) to JURKAT cells (in Ca2+-free medium) abolished the PUFAs-mediated [Ca2+]i increase and vice versa. By using saponin-permeabilized JURKAT cells, the intracellular free Ca2+ released by PUFAs was found to be the non-mitochondrial, ATP-dependent sequestered Ca2+ pool which is sensitive to inositol 1,4,5-trisphosphate. However, PUFAs do not induce any apparent increase in inositol phosphates in JURKAT cells. No Ca2+ influx was detected in JURKAT cells when stimulated with PUFAs. A correlation was observed between both the carbon chain length and the number of double bonds with the ability to mobilize cytosolic free [Ca2+]i in the w-3 PUFAs. These results demonstrate that PUFAs stimulate the release of Ca2+ from the inositol 1,4,5-trisphosphate-sensitive Ca2+ pool in the endoplasmic reticulum of JURKAT cells via a mechanism independent of inositol lipid hydrolysis.

Benzofurans↗
PubMed1990

Outlier detection in bioavailability/bioequivalence studies.

This paper concerns techniques for detection of a potential outlier or extreme observation in a bioavailability/bioequivalence study. A bioavailability analysis that includes possible outlying values may affect the decision on bioequivalence. We consider a general crossover model that takes into account period and formulation effects. We derive two test procedures, the likelihood distance and the estimates distance, to detect potential outliers. We show that the two procedures relate to a chi-square distribution with three degrees of freedom. The main purpose of this paper is to exhibit and discuss these two general approaches of outliers detection in the context of a bioavailability/bioequivalence study. To illustrate these approaches, we use data from three-way crossover experiment in the pharmaceutical industry that concerned the comparison of the bioavailability of two test formulations and a standard (reference) formulation of a drug. This example demonstrates the influence of an outlying value in the study of bioequivalence.

Analysis of Variance↗
PubMed1990

NK cell-induced cytotoxicity is dependent on a Ca2+ increase in the target.

In previous work we showed that programmed cell death (PCD) in thymocytes is mediated by a sustained increase in cytosolic Ca2+ concentration, resulting in the activation of an endogenous endonuclease, DNA fragmentation, and cell death. In this study we investigated the roles of Ca2+ and DNA fragmentation in target cell killing by natural killer (NK) cells. The effector cells induced a rapid, sustained increase in cytosolic Ca2+ concentration in Jurkat target cells. Buffering the target cell cytosolic Ca2+ with the Ca2(+)-selective dye, quin-2, prevented target cell killing. Extensive DNA fragmentation was associated with killing in every target tested, and this response was also blocked by quin-2. The endonuclease inhibitor, aurintricarboxylic acid, inhibited both DNA fragmentation and killing without influencing the Ca2+ increase in target cells. Thus, it is concluded that NK cell killing depends on a Ca2+ increase and appears to involve endogenous endonuclease activation in target cells.

Aminoquinolines↗
PubMed1990

A central role for phosphoinositide hydrolysis in activating the lytic mechanism of human natural killer cells.

Using neomycin, which inhibits phosphoinositide breakdown, cytotoxicity mediated by natural killer (NK) cells was suppressed in a dose-dependent manner, with complete inhibition at 16 mM. Generation of inositol phosphates in effector cells after target cell binding was inhibited in the presence of neomycin. The formation of effector to target cell conjugates was not affected. Neomycin-induced inhibition of NK killing was abolished when TPA was added to the cytotoxic assays. This reconstitution was dependent upon extracellular Ca2+. When the intracellular free Ca2+ level in effector cells was reduced from 73 +/- 11 nM to 43 +/- 3 nM (n = 4) using the Ca2+ indicator dye, Quin 2, NK killing was markedly reduced. Inhibiting the enzyme diacylglycerol (DG) kinase in effector cells with 10 microM R59022 (DG kinase inhibitor) potentiates NK killing, suggesting an increase in protein kinase C (PKC) activity due to accumulation of DG. The PKC inhibitor, H-7, suppressed NK killing in a concentration-dependent manner. These results demonstrate that phosphoinositide metabolism is an early event and its derived second messengers play a central role in activating the lytic mechanism of NK cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1989

Quantitation of DNA fragmentation using fiberglass filters.

Many types of physiological and toxicological cell killing are mediated by extensive DNA fragmentation. To date, most assays used to detect DNA fragmentation have relied on cumbersome techniques to separate intact chromatin from cleaved DNA. Here we describe a filtration assay for quantitation of DNA fragmentation. Fiberglass filtermats were used to separate intact chromatin from DNA fragments. Analysis of the separation showed that intact chromatin consistently remained on filters, while DNA fragments of all (random) sizes were consistently found in the filtrates. The assay was adaptable to different DNA detection procedures and generated results comparable to those obtained using established methods in standard model systems.

Animals↗
PubMed1989

Test for batch-to-batch variation in stability analysis.

We propose several statistical tests for batch-to-batch variation in the stability analysis of a drug product and present applications with data from new drug application stability and marketing stability analyses.

Drug Industry↗
PubMed1989

Suppression of growth in a leukemic T cell line by n-3 and n-6 polyunsaturated fatty acids.

Proliferation in a leukemic T cell line (Jurkat) was suppressed in a dose dependent manner by n-6 and n-3 polyunsaturated fatty acids (PUFA) added to the culture medium. At high concentrations, PUFA have a cytotoxic effect on Jurkat cells. The inhibitory effect of the PUFA was not due to production of prostaglandins, and lipid peroxidation was only partly responsible. In addition to production of peroxides and aldehydes, lipid peroxidation also reduced the plasmalogen levels in these cells. The antioxidant alpha-tocopherol blocked lipid peroxidation and restored the plasmalogen levels to normal. alpha-Tocopherol did not totally restore cell proliferation although the MDA-like products in these cultures (supplemented with PUFA) were reduced to control level. Cultures supplemented with n-6 PUFA seemed to respond better to alpha-tocopherol than n-3 PUFA. This suggests that n-6 PUFA may exert their growth inhibitory effect predominantly via lipid peroxidation while different mechanisms might be operating for the n-3 PUFA.

Arachidonic Acid↗
PubMed1988

Phosphoinositide breakdown and evidence for protein kinase C involvement during human NK killing.

Conjugation between human NK cells and susceptible target cells (K562 and Jurkat) leads to breakdown of inositol lipids in the effector cells but not when conjugated with resistant target cells. Extracellular Ca2+ is required for this activation. Sphingosine inhibits NK killing in both normal and IL-2-activated NK cells. Phorbol esters, TPA, and PDBU enhanced NK killing at low concentrations, where 4-alpha-PDIDE did not. The diacylglycerol derivative OAG increased NK cell killing and activated PKC from human lymphocytes. These results strongly suggest that phosphoinositide breakdown and activation of PKC is involved in NK killing.

Calcium↗
PubMed1987

gamma-Aminobutyric acid receptor ionophore complexes: differential effects of deltamethrin, dichlorodiphenyltrichloroethane, and some novel insecticides in a rat brain membrane preparation.

The binding of [35S]t-butylbicyclophosphorothionate ([35S]TBPS), a gamma-aminobutyric acid (GABA)-activated chloride ionophore ligand; [3H]diazepam, a benzodiazepine agonist; and [3H]muscimol, a GABA receptor probe, were used to assess the effects at 100 microM of deltamethrin, dichlorodiphenyltrichloroethane (DDT), and three experimental insecticides--a DDT-pyrethroid hybrid, GH414 (cycloprothrin), and two DDT-analogues, GH266 and GH149 (EDO), on GABA receptor ionophore complexes in a rat brain membrane preparation. GH266 and GH149 were found to inhibit a greater percentage of [35S]TBPS binding than the same concentration of deltamethrin or DDT, although GH414 had little effect. GH266 and GH149 enhanced [3H]diazepam binding by nearly 200%, in contrast to the inhibitory effects of deltamethrin, DDT, and GH414. GH266 and GH149 also caused a dramatic enhancement of [3H]muscimol binding, 367 and 236% of control, respectively, whereas DDT and deltamethrin caused only a moderate enhancement. The effects of the insecticides on binding affinity and density were examined for each of the ligands. The results show a differential interaction of the insecticides on the various ligand binding sites.

Animals↗
PubMed1985

Differential modulation of gamma-aminobutyric acid receptors by caprolactam derivatives with central nervous system depressant or convulsant activity.

The effects of a series of caprolactam derivatives with central depressant, convulsant or muscle relaxant activity were investigated upon gamma-aminobutyric acid (GABA) receptor-ionophore binding to rat brain membranes using [3H]GABA, [3H]GABA, [3H]muscimol and [35S]-tert.-butylbicyclophophorothionate ([35S]TBPS) as ligands, and GABA responses in mouse spinal cord neurones in dissociated cell culture. Some caprolactams produced a picrotoxin-like chloride-dependent partial inhibition of muscimol binding and were potent inhibitors of TBPS binding. One compound that was further investigated (4,4,6,6-tetramethylhexahydro-2H-azepin-2-one), inhibited GABA responses and increased the frequency of paroxysmal depolarizations in cultured neurones. Other caprolactams enhanced muscimol binding and were relatively weak inhibitors of TBPS binding, and one (3,3-diallyl-6,6-dimethylhexahydro-2H-azepin-2,4-dione) was shown to enhance GABA responses and produced quiescence of activity in cultured neurones. There was a direct correlation between caprolactam effects on muscimol binding in the presence of chloride ions and their effects on TBPS binding suggesting a similar site of action for the caprolactams influencing the binding of these two ligands. For the two classes of caprolactams, with respect to inhibition or enhancement of muscimol binding, there appeared to be a relationship between in vitro effects and their convulsant or depressant activity in mice. Caprolactams may be useful low molecular weight probes for the study of GABA receptor-ionophore complexes.

Animals↗
PubMed1984

Pyrazolo[3,4-d]pyrimidines as adenosine antagonists.

A large number of nitrogen heterocycles structurally related to caffeine and theophylline have been tested for activity as adenosine antagonists. Preliminary screening, utilizing displacement of [3H]N6-phenylisopropyladenosine (PIA) binding to rat brain membranes, identified several pyrazolo[3,4-d]pyrimidines with potential antagonist activity. These were then tested for their ability to antagonize adenosine-stimulated adenylate cyclase of guinea-pig slices and to block adenosine receptors which mediate presynaptic inhibition of transmitter release from cholinergic nerves in guinea-pig ileum. Of several compounds found to have antagonist activity, one of these, 4,6-bis-alpha- carbamoylethylthio -1-phenylpyrazolo[3,4-d]pyrimidine ( DJB -KK) was approximately an order of magnitude more potent than theophylline in both tests. GTP greatly reduces the potency of purine agonists, but not antagonists, as inhibitors of [3H] PIA binding; the potency of the pyrazolo[3,4-d]pyrimidine compounds was not altered by GTP. The compounds have no significant activity against [3H]adenosine uptake or on the binding of ligands to muscarinic cholinergic, beta-adrenergic, GABA or L-glutamate receptors.

Adenosine↗
PubMed1984

Interaction of purines and related compounds with photoaffinity-labelled benzodiazepine receptors in rat brain membranes.

The interaction of purine-receptor agonists and antagonists with [3H]Ro15-1788 binding sites in rat brain membranes was examined before and after UV-photoaffinity labelling of a proportion of the sites with flunitrazepam. Whereas photoaffinity labelling of the receptors reduced benzodiazepine agonist affinity but not benzodiazepine antagonist affinity, the IC50S of adenosine-receptor agonists, partial agonists and antagonists were unaltered by the conformational changes in the benzodiazepine receptors which are thought to be induced by the photolabelling process. The affinity of dipyridamole, a potent adenosine uptake blocker and potent displacer of [3H]diazepam binding, was drastically reduced by photolabelling.

Affinity Labels↗
PubMed1983

Pyrazolo [3,4-d] pyrimidines, a new class of adenosine antagonists.

A variety of nitrogen heterocycles structurally related to caffeine and theophylline have been tested for activity as adenosine receptor antagonists. Preliminary screening, utilizing displacement of [3H]N6-phenylisopropyladenosine binding to rat brain membrane A1-adenosine receptors, identified several pyrazolo[3,4-d]pyrimidines with potential antagonist activity. These were then tested for their ability to antagonize the adenosine-stimulated adenylate cyclase system of guinea-pig brain slices. One of these, 4,6-bis-alpha-carbamoylethylthio-1-phenylpyrazolo[3,4-d]pyrimidine (DJB-KK), was over an order of magnitude more potent than theophylline in blocking adenosine-stimulated increases in cyclic AMP levels.

Adenosine↗
PubMed1983

Interactions of the anticonvulsant carbamazepine with adenosine receptors. 2. Pharmacological studies.

The interactions of carbamazepine with adenosine receptors were studied in two pharmacological systems. In the isolated guinea pig ileum, several adenosine agonists and carbamazepine potently inhibited nicotine-stimulated and electrically stimulated contractions in a manner sensitive to the adenosine antagonist theophylline. High concentrations of carbamazepine were able to reduce the inhibition of electrically stimulated contractions by the adenosine agonist l-methylisoguanosine. The ability of theophylline to reduce the anticonvulsant efficacy of several drugs against pentylenetetrazole-induced seizures in mice was investigated. Theophylline pretreatment failed to alter anticonvulsant protection by trimethadione and sodium valproate, but significantly decreased the anticonvulsant effects of carbamazepine and phenobarbital. These results suggest that carbamazepine may exert some of its anti-convulsant effects by acting as a partial agonist at adenosine receptors.

Animals↗
PubMed1982

Contrasting regulation by GABA of the displacement of benzodiazepine antagonist binding by benzodiazepine agonists and purines.

Gaba increases the potency of the benzodiazepines chlordiazepoxide, clonazepam, diazepam, nitrazepam and oxazepam, and the triazolopyridazine CL 218,872 in displacing specific binding of the benzodiazepine antagonist [3H]Ro 15-1788. In contrast, the potencies of the purines 1-methyl- and 1-ethylisoguanosine for benzodiazepine antagonist binding sites were decreased by GABA, while the potencies of inosine, hypoxanthine, 6-dimethylaminopurine, and the non-benzodiazepine anxiolytic, zopiclone, were unaltered by GABA. The results suggest that the purines and 'classical' benzodiazepine agonists may bind to different conformations or populations of receptors.

Animals↗
PubMed1981

A new screen for anti-inflammatory agents. Estimation of rat serum acute phase alpha2-macroglobulin levels using an electroimmunoassay.

Induction of alpha2-macroglobulin acute phase protein in rats by the injection of turpentine revealed strain and sex differences in the amounts of this protein detected in sera by rocket immunoelectrophoresis. Studies in vivo with a wide variety of drugs showed that non-steroidal anti-inflammatory drugs (NSAID) such as aspirin, indomethacin and BW 755C as well as colchicine, clofibrate and clozic, inhibited serum concentrations of the acute phase protein 48 h after turpentine injection. The procedure used offers a new and convenient screen for assessing NSAIDs and the method may be of value as a screen for new clozic-like compounds with anti-rheumatic activity. The possibility that the NSAIDs are inhibiting a humoral factor initiated by the inflammatory stimulus and that the humoral factor is a metabolite of arachidonic acid is discussed.

Animals↗