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Biomedical subjects

K Williams

Publications and source records attributed to K Williams.

At least 19 recordsLinked to original sources
PubMed1995

Potent in vitro and in vivo inhibitors of platelet aggregation based upon the Arg-Gly-Asp sequence of fibrinogen. (Aminobenzamidino)succinyl (ABAS) series of orally active fibrinogen receptor antagonists.

Our initial orally active fibrinogen receptor antagonist benzamidinopentanoyl (BAP) series which was discovered through truncation of our i.v. antiplatelet agent (SC-52012) demonstrated modest oral activity in canine studies (ethyl [5-(4-amindinophenyl)pentanoyl]-3-amino-3-(3-pyridyl)propionate, 1e). Introduction of an amide bond adjacent to the benzamidine led to a novel series with an (aminobenzamidino)succinyl (ABAS) Arg-Gly surrogate that had improved in vitro potency (5-17 times) relative to the BAP series. Four ester prodrug/acid active metabolite pairs (2a/2e, 60a/60e, 62a/62e, 63a/63e) from the ABAS series which varied in their 3-substituent on the beta-amino ester "aspartate mimetic" were prepared in enantiomerically enriched form (> 95:5), and they were evaluated in canine studies for their ability to block collagen-induced aggregation in platelet-rich plasma, the elimination profile (t1/2 beta-phase), repeated oral dosing studies, and oral systemic availability. Of the four ester prodrug/acid active metabolite pairs, 2e/2a (SC-54684A/SC-54701A) has the most favorable properties in the above studies with an IC50 = 67 +/- 5 nM (dog platelet-rich plasma, collagen), t1/2 beta = 1.6 h (ester) and 6.5 h (acid), no adverse effects upon repeated dosing, and a drug oral systemic availability of 62% (area under curve (AUC) of acid 2a (drug) following ig administration of ester 2e (prodrug, 2.5 mg/kg) divided by AUC of acid 2a (drug) following i.v. administration of ester 2e (prodrug, 2.5 mg/kg) as determined by HPLRC). In further pharmacokinetic studies using nonlabeled 2e/2a, the oral systemic availability (ester 2e ig/ester 2e i.v.) of 2e was measured to be in the range of 44.7-53.0%. The more biologically relevant oral systemic availability (ester 2e ig/acid 2a i.v.) of 2e was found to be in the range of 22.0-26.4%. A pharmacophore model based on inhibitors from several different benzamidine classes including 2a (ABAS class) was developed using a combination of molecular modeling (MM2) and pharmacophore identification (APOLLO) methods.

Administration, Oral↗
PubMed1995

Pharmacological properties of recombinant N-methyl-D-aspartate (NMDA) receptors containing the epsilon 4 (NR2D) subunit.

The modulatory effects of spermine, histamine, and ifenprodil on recombinant N-methyl-D-aspartate (NMDA) receptors expressed from the NR1A and epsilon 4 (NR2D) subunits were studied by voltage-clamp recording in Xenopus oocytes. Spermine had no effect on responses to glutamate and glycine at NR1A/epsilon 4 receptors. None of the four previously described effects of spermine, all of which are seen at NR1A receptors and at NR1A/NR2B receptors, was seen at NR1A/epsilon 4 receptors. Similarly, NR1A/epsilon 4 receptors were insensitive to potentiation by histamine and to blockade by ifenprodil. The properties of NR1A/epsilon 4 receptors thus resemble those of NR1A/NR2C receptors and are markedly different from those of homomeric NR1A receptors. In heteromeric NR1A/epsilon 4 receptors the epsilon 4 subunit may alter properties associated with the NR1A subunit, as has been previously suggested for NR2A, NR2B, and NR2C subunits in NR1A/NR2 receptors.

Animals↗
PubMed1995

Preconditioning with a single short episode of global ischemia in the isolated working rat heart: effect on structure, mechanical function, and energy metabolism for various durations of sustained global ischemia.

PURPOSE: Preconditioning in the setting of global ischemia, using functional recovery during reperfusion as the endpoint, has recently been demonstrated in the isolated perfused rat heart. It has been suggested that its beneficial actions have a metabolic basis. The isolated rat heart has not been fully characterized with respect to the metabolic, functional, and structural changes associated with this phenomenon in the setting of global ischemia. The purpose of this study was to determine (1) the time course of protection conferred by a single episode (5 minutes) of preconditioning; (2) changes in tissue high energy phosphates, lactate, and glycogen levels at different time intervals; and (3) morphological appearance of the heart at the end of ischemia as well as after reperfusion. METHODS: Isolated perfused working rat hearts were used. Preconditioning consisted of a single episode of 5 minutes of global ischemia and 15 minutes of reperfusion. Preconditioned and non-preconditioned hearts were subjected to global ischemia of 20-35 minutes duration. Functional recovery, energy metabolism (high energy phosphates, lactate, and glycogen), and structural appearance were studied at different stages. RESULTS: The functional recovery of the preconditioned hearts was significantly higher than in the corresponding nonpreconditioned group during reperfusion for all durations of ischemia longer than 25 minutes. The degree of protection observed was less than reported previously. A minor degree of energy sparing was reflected by differences in the rate of depletion of glycogen and accumulation of tissue lactate during the sustained episode of ischemia. Semiquantitative light microscopy evaluation revealed that ischemia-induced structural damage was less in the preconditioned hearts, both at the end of the sustained ischemic episode as well as after reperfusion. CONCLUSIONS: A single episode of global ischemia successfully preconditions the isolated working rat heart. The protection elicited was demonstrated on a functional and structural level, and was accompanied by a small energy-sparing effect.

Animals↗
PubMed1995

A novel series of orally active antiplatelet agents.

A novel series of orally active fibrinogen receptor antagonists has been discovered through structural modification of our lead intravenous (iv) antiplatelet agent, 5-(4-amidinophenyl)pentanoyl-Asp-Phe 1 (SC-52012). The Asp-Phe amide bond was removed through truncation to a 3-substituted beta-amino acid aspartate mimetic which resulted in a tripeptide mimetic inhibitor of lower molecular weight (from 482 to the 330-390 g mol-1). The zwitterionic nature of the inhibitor was masked through the preparation of an ethyl ester prodrug. A lead compound from this series, 5-(4-amidinophenyl)pentanoyl-3-(3-pyridyl)propanoic acid 19a, was found to be a potent inhibitor of canine platelet aggregation in vitro (collagen, platelet rich plasma, PRP, IC50 = 270 nM). In further canine studies, oral administration of different ester pro-drugs of 19a at 10 mg kg-1 resulted in the following oral systemic activities: pivaloyloxymethyl ester derivative 19p (5.1 +/- 1.5% OSA), cyclohexyl ester derivative 19c (9.2 +/- 1.9% OSA), and ethyl ester derivative 19e (9.9 +/- 2.3% OSA).

Administration, Oral↗
PubMed1995

Expression of mRNAs encoding subunits of the NMDA receptor in developing rat brain.

Developmental changes in the levels of N-methyl-D-aspartate (NMDA) receptor subunit mRNAs were identified in rat brain using solution hybridization/RNase protection assays. Pronounced increases in the levels of mRNAs encoding NR1 and NR2A were seen in the cerebral cortex, hippocampus, and cerebellum between postnatal days 7 and 20. In cortex and hippocampus, the expression of NR2B mRNA was high in neonatal rats and remained relatively constant over time. In contrast, in cerebellum, the level of NR2B mRNA was highest at postnatal day 1 and declined to undetectable levels by postnatal day 28. NR2C mRNA was not detectable in cerebellum before postnatal day 11, after which it increased to reach adult levels by postnatal day 28. In cortex, the expression of NR2A and NR2B mRNAs corresponds to the previously described developmental profile of NMDA receptor subtypes having low and high affinities for ifenprodil, i.e., a delayed expression of NR2A correlating with the late expression of low-affinity ifenprodil sites. In cortex and hippocampus, the predominant splice variants of NR1 were those without the 5' insert and with or without both 3' inserts. In cerebellum, however, the major NR1 variants were those containing the 5' insert and lacking both 3' inserts. The results show that the expression of NR1 splice variants and NR2 subunits is differentially regulated in various brain regions during development. Changes in subunit expression are likely to underlie some of the changes in the functional and pharmacological properties of NMDA receptors that occur during development.

Aging↗
PubMed1995

Phase I evaluation of zalcitabine administered to human immunodeficiency virus-infected children.

The safety, tolerability, and pharmacokinetics of zalcitabine (ddC) in a single oral dose (0.02 mg/kg) was evaluated in 23 mildly symptomatic human immunodeficiency virus-infected children (mean age, 4.2 years). After administration of ddC, blood samples were obtained at 0.5, 1, 1.5, 2, 4, 6, and 8 h for analysis. The drug was well tolerated and no side effects were noted. Plasma ddC levels were determined by ion spray liquid chromatography/tandem mass spectrometry. ddC was rapidly absorbed, with a mean maximum plasma concentration of 9.3 ng/mL (range, 3.2-14.1) attained within a mean of 1 h (range, 0.5-2.0). Mean elimination half-life was 1.4 h (range, 1.0-3.5), mean area under the plasma concentration-time curve was 25 ng.h/mL (range, 11-37), and mean total body clearance was 14.6 mL/min/kg (range, 8.9-30.6). Plasma concentrations were lower and the half-life shorter in these children than in adults given comparable doses, suggesting that ddC may be cleared more rapidly in children than adults.

Adult↗
PubMed1995

Estimating blood alcohol from urinary alcohol at autopsy.

Urine alcohol concentration (UAC) and blood alcohol concentration (BAC) measured by gas chromatography were available from 435 medicolegal autopsies. Simple linear regression with BAC as outcome variable and UAC as predictor variable (range, 3-587 mg%) gave the regression equation BAC = -5.6 + 0.811UAC with 95% prediction interval +/- 0.026 square root of [9465804 + (UAC-213.3)2] and 99% prediction interval +/- 0.034 square root of [9465804 + (UAC-213.3)2]. The standard error of the slope was 0.013 and the 95% confidence interval for the slope 0.785-0.837. In practice, a BAC of 80 mg% is predicted with 95% certainty by a UAC of 204 mg% and similarly a BAC of 150% by a UAC of 291 mg%. The prediction interval is too wide to be helpful in the assessment of an individual case fatality. The UAC is useful in corroborating but not in predicting BAC.

Alcoholic Intoxication↗
PubMed1995

Diagnosis and treatment of acute myocardial infarction.

Rapid diagnosis and treatment of myocardial infarction are essential for maximizing patient survival. Recent advances in early detection of creatine kinase myocardial band isoforms and other chemical markers, as well as increased use of echocardiography, magnetic resonance imaging, and nuclear imaging, have enhanced the diagnostic capabilities for providers caring for a patient suspected of myocardial infarction. In management of myocardial infarction, the focus continues to be primarily on using thrombolytics, percutaneous transluminal coronary angioplasty, and coronary bypass surgery. In addition, an array of pharmacologic agents aimed at reducing cardiac muscle damage, alleviating reperfusion injuries, and preventing thrombus formation are undergoing clinical trials. These agents may hold promise for the future treatment of myocardial infarction.

Angioplasty, Balloon, Coronary↗
PubMed1995

Immortalization and characterization of rat microglial cells.

Microglial cell lines from rat brain were established by transfer of a temperature sensitive simian virus 40 large tumour antigen by means of a retrovirus. Four weeks after infection, colonies were generated in the presence of neomycin and granulocyte-macrophage colony stimulating factor (GM-CSF), and subsequently subcloned. Both bulk cell lines and clones proliferate actively at 33 degrees C, whereas the rate of division was significantly decreased at 39 degrees C when the large T antigen is non-functional. At 39 degrees C, these cells take on the microglial phenotype as demonstrated by immunoreactivity to ED-1 (an intracellular antigen), OX-42 (complement type 3 receptor), W3/25 (CD4 homologue), OX-6 (MHC class II antigen) and OX-18 (MHC class I antigen). These cells are capable of active phagocytosis and retain these properties for 10-15 passages. Long-term culture of these lines and clones, greater than 15 passages, displayed a gradual down-regulation of all cell surface specific antigens that were not rescued by lipopolysaccharide (LPS), interferon-gamma (gamma-IFN), GM-CSF or colony-stimulating factor-1 (CSF-1). The expression of the SV-40 large T antigen was unaffected. These results demonstrate the feasibility of immortalizing short-term cell lines with the SV-40 large T antigen for their use in the characterization of microglial properties.

Animals↗
PubMed1995

[Keratomileusis with a lamellar microkeratome and the excimer laser].

In a combined prospective study with E. Arnott's department, intrastromal excimer keratomileusis on the lenticle stroma was performed in 15 eyes of 15 patients (follow-up 6 months). The primary keratectomy was performed using the lamellar automatic rotating microkeratome, followed by refractive modification by the excimer laser on the excised corneal discs. For the laser ablation, a repetition rate of 10 Hz and a fluence on the corneal plane of 180 mJ/cm2 was used. Following surgery, all treated eyes were subjected to guttae of Maxitrol q.i.d. for 12 weeks. Excimer laser intrastromal keratomileusis effectively combines corneal microsurgery and photoablation. The predictability of the refractive correction is better than with the other surgical keratomileusis techniques.

Adult↗
PubMed1995

Hypertension in pregnancy.

Hypertension occurs in 7% to 10% of pregnancies. It is associated with increased risk of maternal and fetal complications. Early diagnosis in the office by careful attention to signs and symptoms could result in adequate management. Delivery provides the only care for this disease process. Recently, low-dose acetylsalicylic acid has been used in high-risk situations to prevent the development of preeclampsia.

Antihypertensive Agents↗
PubMed1995

Antagonist properties of polyamines and bis(ethyl)polyamines at N-methyl-D-aspartate receptors.

The polyamine spermine has both stimulatory and inhibitory effects on N-methyl-D-aspartate (NMDA) receptors. At recombinant NMDA receptors, effects of spermine are dependent on the subunit composition of the receptor. In the present work we have used voltage-clamp recording to examine the effects of polyamines and bis(ethyl)polyamines on recombinant NMDA receptors expressed in Xenopus oocytes. The compounds that were studied include several bis(ethyl)polyamines that may be clinically useful as antitumor agents. A number of pentaamines and bis(ethyl)pentaamines were found to act as potent voltage-dependent antagonists at heteromeric NR1A/NR2A and NR1A/NR2B receptors, but not at NR1A/NR2C receptors. Antagonism was more pronounced in oocytes voltage-clamped at -80 mV than at -20 mV. Some polyamine analogs also potentiated responses to glutamate at NR1A/NR2B receptors at membrane potentials of -20 to +40 mV, but this effect required higher concentrations of polyamines than did inhibition seen at hyperpolarized membrane potentials. At NR1A/NR2A receptors the block seen with pentaamines and bis(ethyl)pentaamines, but not with spermine or bis(ethyl)spermine, was maximal at a membrane potential of -100 mV and was relieved at more negative as well as at more positive membrane potentials. This suggests that the mechanism of inhibition of NMDA receptors by pentaamines is different from that of spermine. Pentaamines may permeate the ion channel of NMDA receptors at very hyperpolarized membrane potentials and may be useful for studying the structural properties of NMDA receptor channels.

Animals↗
PubMed1994

The NADH dehydrogenase subunit 7 gene is interrupted by four group II introns in the wheat mitochondrial genome.

We have characterized a wheat mitochondrial gene, designated nad7, capable of encoding a 394-amino acid subunit of the respiratory chain NADH dehydrogenase complex. It contains four introns possessing group II features and their positions differ from those in both the liverwort mitochondrial nad7 pseudogene and the nuclear gene encoding the homologous 49 kDa subunit of complex I in Neurospora. The derived amino acid sequence of the wheat nad7 gene is strongly conserved relative to its nuclear or organellar counterparts in other organisms. C-to-U type RNA editing, which is observed at 32 positions within the coding region of wheat nad7 transcripts, strengthens protein sequence similarity. RNA editing is also predicted to improve base-pairing within the domain V/VI regions of all four introns.

Amino Acid Sequence↗
PubMed1994

Activation of adult human derived microglia by myelin phagocytosis in vitro.

The present study was designed to determine the extent to which cultured glial cells phagocytose normal central nervous system (CNS) myelin and CNS myelin opsonized with serum or purified antibody against myelin basic protein (MBP). Glial cells studied were mixed cultures (consisting of astrocytes, microglia, and oligodendrocytes) and enriched microglia established from adult human brain specimens and enriched astrocytes from fetal human brain. A human monocytic cell line, THP-1, was included as a control. Uptake of 125I-labelled myelin was followed over a 24 hr time period. An assay of oxidative burst (30 min) and cytokine bioassays measuring IL-1, IL-6, and tumor necrosis factor (TNF) production (6-48 hr) were used to investigate short- and long-term activation of phagocytosing cells. Maximum myelin uptake by phagocytosing glial cells occurred within 12-24 hr following myelin incubation. Opsonization of myelin prior to the phagocytosis assay resulted in greater myelin uptake by mixed glial cell cultures, microglia, and THP-1 cells over that of nontreated myelin. The magnitude of myelin phagocytosis by astrocytes was considerably lower than microglia and THP-1, and was not affected by myelin opsonization. Within 30 min of myelin phagocytosis, microglia and THP-1 cells underwent oxidative burst; opsonization of myelin by purified anti-MBP IgG and heat-inactivated serum enhanced the microglial oxidative burst activity. Production of IL-1, TNF, and most markedly IL-6 by microglia was increased following 12-24 hr of myelin ingestion. Our data demonstrate that myelin phagocytosis by adult human-derived microglia occurs in vitro, is augmented when myelin is opsonized, and results in the activation of microglia as assessed by oxidative burst and cytokine production.

Adult↗
PubMed1994

Activation of a novel serine/threonine kinase that phosphorylates c-Fos upon stimulation of T and B lymphocytes via antigen and cytokine receptors.

Ligation of Ag receptors in T and B lymphocytes initiates signal transduction cascades which alter the expression of genes that regulate cellular proliferation and differentiation. The transmission of signals from the membrane to the nucleus is mediated principally through the action of protein tyrosine and serine/threonine kinases. We have identified and characterized a novel serine/threonine kinase that phosphorylated the proto-oncogene product, c-Fos, and is termed Fos kinase. Fos kinase was rapidly activated after ligation of the CD3 and CD2 receptors in Jurkat and normal human T lymphocytes and in response to IL-6 and anti-IgM in the human B cell lines AF10 and Ramos, respectively. The phorbol ester, PMA, was also a potent inducer of Fos kinase activity in all of the above populations, suggesting that PKC plays a role in the regulation of this enzyme. Fos kinase phosphorylates c-Fos at a site near the C-terminus, as well as a peptide derived from this region (residues 359-370, RKGSSSNEPSSD), and Fos peptide competitively inhibited c-Fos phosphorylation. Fos kinase was shown to be distinct from other identified serine/threonine kinases, including protein kinase A, protein kinase C, casein kinase II, MAP kinases, p70S6K and p90RSK. Fos kinase was purified by anion exchange chromatography and exhibited an apparent M(r) = 65,000 and isoelectric point = 6.1. Fos kinase may play a role in transcriptional regulation through its capacity to phosphorylate c-Fos at a site required for expression of the transcriptional transrepressive activity of this molecule. Moreover, its rapid activation suggests it may have a wider role within signal transduction cascades in lymphocytes.

Amino Acid Sequence↗
PubMed1994

Self peptides isolated from MHC glycoproteins of non-obese diabetic mice.

The non-obese diabetic (NOD) mouse spontaneously develops an insulin-dependent diabetes mellitus that resembles human type I diabetes. This disease can be transferred by purified T cells or cloned T cell lines, implicating an autoimmune T cell attack on the pancreatic beta cells of the islets of Langerhans. As all T cell responses involve recognition of peptides bound to MHC molecules displayed at the cell surface, we have examined self peptides binding to the MHC molecules on spleen cells of the NOD mouse. Peptides eluted from the MHC class I molecule Kd have sequences that conform to known motifs for peptides binding this molecule in other strains of mice. The NOD mouse expresses the unique MHC class II molecule I-Ag7. Peptides eluted from I-Ag7 have sequences that implicate an acidic residue in the C terminus of the peptide as important for binding. The role of this residue in binding has been confirmed by direct peptide-binding analysis. This C-terminal acidic amino acid may interact with an arginine residue in the MHC class II alpha-chain that is exposed when beta-chain residue 57 is mutated to serine, or to the unique beta-chain residue histidine 56. These data may provide valuable insights into the nature of autoantigenic peptides presented by NOD mouse MHC molecules by defining the nature of I-Ag7-peptide binding.

Amino Acid Sequence↗