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Biomedical subjects

R M Lawrence

Publications and source records attributed to R M Lawrence.

At least 19 recordsLinked to original sources
PubMed1998

An MTP inhibitor that normalizes atherogenic lipoprotein levels in WHHL rabbits.

Patients with abetalipoproteinemia, a disease caused by defects in the microsomal triglyceride transfer protein (MTP), do not produce apolipoprotein B-containing lipoproteins. It was hypothesized that small molecule inhibitors of MTP would prevent the assembly and secretion of these atherogenic lipoproteins. To test this hypothesis, two compounds identified in a high-throughput screen for MTP inhibitors were used to direct the synthesis of a highly potent MTP inhibitor. This molecule (compound 9) inhibited the production of lipoprotein particles in rodent models and normalized plasma lipoprotein levels in Watanabe-heritable hyperlipidemic (WHHL) rabbits, which are a model for human homozygous familial hypercholesterolemia. These results suggest that compound 9, or derivatives thereof, has potential applications for the therapeutic lowering of atherogenic lipoprotein levels in humans.

Alanine Transaminase↗
PubMed1996

A continuous fluorometric assay for gamma-glutamyltranspeptidase.

The synthesis of gamma-glutamyl-7-amino-4-(trifluoromethyl)coumarin and its use as a substrate for gamma-glutamyltranspeptidase is described. The reaction product 7-amino-4-(trifluoromethyl)coumarin was fluorescent at neutral pH values and with excitation and emission wavelengths of 400 and 490 nm, respectively, concentration was linearly related to fluorescence over the range of 10 to 300 pmol/3 ml reaction mixture. At pH 8.4, the optimum for purified gamma-glutamyltranspeptidase, continuous fluorometric determination of enzyme activity with time could be carried out. This permitted accurate estimations to be made of initial reaction rates. Low levels of gamma-glutamyltranspeptidase activity could be shown in isolated rat hepatocytes (1 x 10(5) cells). Such activity could be inhibited by the addition acivicine (alpha-amino-3-chloro-5-isoxazoleacetic acid), suggesting the absence of peptidase-like activity. Following 2-week pretreatment of rats with the antiestrogen, tamoxifen, a fourfold increase in gamma-glutamyltranspeptidase activity was observed. The present method offers a convenient, sensitive method for the determination of gamma-glutamyltranspeptidase activity without the need for elaborate workup procedures.

Animals↗
PubMed1996

Synthesis and characterization of peptide adducts for use in monitoring human exposure to acrylonitrile and ethylene oxide.

Human exposure to ethylene oxide and acrylonitrile may be monitored by determination of the products that these electrophilic compounds form with the amino terminal of hemoglobin. The procedure involves a modified Edman degradation, using the reagent pentafluorophenyl isothiocyanate, which cleaves the adducted N-terminal amino acid from the protein chain as a substituted pentafluorophenyl thiohydantoin. This may then be quantitated using selected ion monitoring gas chromatography-mass spectrometry (GC-MS). To overcome problems arising from the lack of an ideal internal standard for this analysis, we have now synthesized adducts of ethylene oxide and acrylonitrile with the N-terminal tripeptide of the alpha-chain of human globin (Val-Leu-Ser). These adducts should behave analogously to the protein adduct in the Edman degradation. The adducts were characterized by nuclear magnetic resonance and fast atom bombardment and electrospray MS and tandem MS. Additionally, an analogous stable isotope-labeled standard was synthesized for the acrylonitrile adduct using a d8-labeled tripeptide. Quantitative calibration lines for analysis of the adducts have been established and the validity of the assays established by the detection of acrylonitrile adducts in the globin of acrylonitrile-exposed workers and of cigarette smokers.

Acrylonitrile↗
PubMed1996

Monitoring of exposure to acrylonitrile by determination of N-(2-cyanoethyl)valine at the N-terminal position of haemoglobin.

A selected ion monitoring gas chromatography-mass spectrometry (GC-MS) procedure was developed to determine the interaction product formed by acrylonitrile (ACN) with the N-terminal amino group in haemoglobin. The product, N-(2-cyanoethyl)valine (CEV), was analysed following its release from the protein by a modified Edman degradation procedure. Quantitation was achieved using N-(2-cyanoethyl)-[2H8]Val-Leu-Ser as internal standard. The limit of detection of the assay was 1 pmol CEV/g globin. A close to linear dose-response relationship was found for adduct formation in rats treated with ACN by gavage. On the basis of a linear extrapolation, a dose of 1 mg/kg body wt yielded 248 pmol CEV/g globin. Two groups of workers who were exposed to ACN contained 1984 +/- SD 2066 (n = 9) and 2276 +/- SD 1338 (n = 7) pmol CEV/g globin respectively. These values were highly significantly greater (P < 0.01 following a one-way analysis of variance with a logarithmic transformation of the data) than those in a group of control workers in the same factory (31.1 +/- SD 18.5 pmol CEV/g globin, n = 11). The concentrations of N-terminal CEV in globin samples from 13 smoking and 10 non-smoking mothers and from their newborns were determined. Adduct levels in the smokers averaged 217 +/- 85.1 pmol CEV/g globin, significantly higher than the levels in non-smokers, which were undetectable. Individual values in the mothers were very highly correlated with the levels in their babies (which averaged 99.5 +/- 53.8 pmol CEV/g globin), which demonstrates that transplacental transfer of ACN occurs. Significant correlations were also found between the number of cigarettes smoked per day by the mother and the CEV levels in both the mothers' and newborns' globin. There was, however, no correlation between the CEV levels and those of the ethylene oxide adduct N-(2-hydroxyethyl)valine in samples from either the mothers or babies.

Acrylonitrile↗
PubMed1996

Rapid oral desensitization to trimethoprim-sulfamethoxazole in infants and children.

BACKGROUND: Although trimethoprim-sulfamethoxazole is the preferred chemoprophylaxis against Pneumocystis carinii pneumonia, there are frequent IgE-mediated reactions among children infected with the human immunodeficiency virus (HIV). Oral desensitization allows more patients to receive chemoprophylaxis, but it has been studied in only a limited number of children. METHODS: We desensitized five children infected with the HIV using a rapid, 4-h oral protocol. RESULTS: Three children (including two infants) successfully completed desensitization and started maintenance therapy, but the other two experienced reactions that precluded further administration of trimethoprim-sulfamethoxazole. CONCLUSIONS: We conclude that a rapid, oral trimethoprim-sulfamethoxazole desensitization protocol is safe and, in some instances, effective among HIV-infected children and infants with a history of non-life-threatening, IgE-mediated reactions to trimethoprim-sulfamethoxazole.

AIDS-Related Opportunistic Infections↗
PubMed1995

1,1-Bisphosphonate squalene synthase inhibitors: interplay between the isoprenoid subunit and the diphosphate surrogate.

Inhibitors of squalene synthase have the potential to be superior cholesterol-lowering agents. We previously disclosed that lipophilic 1,1-bisphosphonates I are potent squalene synthase inhibitors and orally active cholesterol-lowering agents in animal models (Ciosek, C. P., Jr.; et al. J. Biol. Chem. 1993, 268, 24832-24837). In this paper, we describe modifications to the bisphosphonate moiety, in an attempt to reduce the number of acidic functions contained in these inhibitors. Replacing one of the acidic groups with a methyl (II, R2 = CH3) results in potent inhibitors when paired with a close mimic of the naturally occurring farnesyl moiety (R1 = farnesylethyl) but not when paired with the shorter isoprene surrogates (R1 = geranylethyl or 4-biphenylpropyl). In contrast, all three corresponding bisphosphonates I are potent squalene synthase inhibitors. Inhibitory potency is recovered with the shorter isoprene surrogates when R2 is CH2OH or CH2OCH3. It is proposed that these R2 groups serve as hydrogen bond acceptors with the active site of the enzyme. The properties of these compounds as cholesterol biosynthesis inhibitors in rats are described, and synthetic routes to these and related compounds are detailed.

Animals↗
PubMed1995

Application of thin-section low-dose chest CT (TSCT) in the management of pediatric AIDS.

The aim of this study was to evaluate the usefulness of thin-section low-dose computed tomography (TSCT) in the management of children with AIDS, as chest radiographs (CXR) often fail to adequately explain the patients' clinical status. We performed 54 noncontrast TSCTs on 32 children. The patients aged from 3 months to 14.6 years, were diagnosed as having bacterial pneumonia, lumphocytic interstitial pneumonitis (LIP), Pneumocystis carinii pneumonia (PCP), or Mycobacterium avium-intracellulare infection (MAI). The scans were correlated with the clinical diagnosis, T-lymphocyte-subset percentages, and p24-antigen levels. Subsegmental consolidations were seen in patients with LIP, PCP, and MAI, and as an isolated finding in those with only bacterial pneumonia. Ground-glass haziness was seen exclusively with acute PCP. Reticulonodular thickening was identified only in patients with LIP. Mosaic perfusion was seen with MAI, LIP, and pneumonia. The presence of adenopathy correlated with CD4+ T-cell subset percentages. The greatest value of CT in this study was in detecting new disease when chest films failed to correlate with a patient's clinical state, and in demonstrating acute/subacute disease in patients with severe baseline chest-film changes. Recurrent pneumonias may represent progression of "smoldering" disease, rather than true recurrent disease following complete clearing. Adenopathy with low CD4+ levels should suggest lymphoma or infection with MAI.

AIDS-Related Opportunistic Infections↗
PubMed1994

Feasibility of high-resolution, low-dose chest CT in evaluating the pediatric chest.

Thin-section, high-resolution (1.0/1.5 mm thick slices), low-dose chest CT scans were performed in 55 infants and children. The studies were carried out with 1- and 2-s scan (data acquisition) times using a high-resolution (bone) algorithm. Although there was some motion artifact, the studies provided valuable information for evaluating diffuse parenchymal lung disease. The thin slices provided finer detail and more diagnostic information than images representing thicker sections. Most studies were performed using between 40 and 80 mAs. It is estimated that the patients' radiation exposure was 20% that of conventional high-resolution CT (HRCT) and 57% that of routine chest CT. Diagnostic HRCT scans can be obtained in infants and young children without the need for suspended respiration or specialized ultrafast CT scanners.

Adolescent↗
PubMed1994

The role of flexible bronchoscopy in children with AIDS: an update of the New York University experience.

The clinical courses of children with acquired immunodeficiency syndrome (AIDS) who underwent diagnostic flexible bronchoscopy at Bellevue Hospital from 1987-1992 were reviewed to determine the value of the procedure in patient management. Twenty-eight children (age 13 days to 12 years) underwent 31 bronchoscopies for indications including respiratory distress, fever and abnormal chest radiograph. Procedures were well tolerated. Complications were limited to transient hypoxia and epistaxis. Although 58% of bronchoscopies yielded a diagnosis (Pneumocystis carinii, Streptococcus viridans, Pseudomonas aeruginosa, Cytomegalovirus, atypical mycobacterium, giant cell pneumonia, and mechanical obstruction), empiric medical therapy was altered in only 16% of cases. Bronchoscopic diagnoses are correlated with Centers for Disease Control (CDC) classification, immune status, treatment and outcome.

AIDS-Related Opportunistic Infections↗
PubMed1993

Lipophilic 1,1-bisphosphonates are potent squalene synthase inhibitors and orally active cholesterol lowering agents in vivo.

Squalene synthase catalyzes the reductive dimerization of two molecules of farnesyl diphosphate to form squalene at the final branchpoint of the cholesterol biosynthetic pathway. We report herein that isoprenyl 1,1-bisphosphonates and related analogs are potent inhibitors of rat microsomal squalene synthase (I50 = 0.7-32 nM). In addition, members of this family are potent inhibitors of cholesterol biosynthesis in rats on intravenous and oral dosing, as well as cholesterol lowering agents in rats and hamsters. Significant inhibition of cholesterol biosynthesis in rats by lovastatin occurs with a concomitant inhibition of dolichol and coenzyme-Q9 synthesis. In contrast, bisphosphonate 4 has no effect on dolichol and coenzyme-Q9 biosynthesis in rats under conditions where cholesterol biosynthesis is > 90% inhibited.

Administration, Oral↗
PubMed1990

Expression of the cloned gene for enterotoxin STb of Escherichia coli.

This study involved the construction of hybrid plasmids to produce heat-stable enterotoxin type II of Escherichia coli (STb). The translation of the open reading frame for the STb gene estA was demonstrated in several ways. Studies using in vivo labeling with [35S]cysteine demonstrated a radiolabeled protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the expected molecular weight of 5,000 for toxin STb. Insertion of translational or transcriptional termination signals into the BglII site of the estA gene blocked the expression of estA. The estA gene was cloned into high-expression vector pKC30 downstream from the strong pL promoter. Northern (RNA) blotting assays revealed a 10- to 20-fold increase in mRNA produced by strain C600F(pKC30STb) over other STb-producing strains, compared with little or no increase in enterotoxin activity demonstrated by bioassay. The estA gene, with its own promoter and Shine-Delgarno region and a portion of the sequence for the signal peptide deleted, was also inserted under the control of the tac promoter. Even after induction of the tac promoter by addition of isopropyl-beta-D-thiogalactopyranoside, no biologic enterotoxin activity could be identified. Neutralizing antibodies to STb were produced in rabbits by using either a purified OmpF-STb-beta-galactosidase fusion protein or a 19-amino-acid synthetic STb peptide coupled to keyhole limpet hemocyanin.

Animals↗
PubMed1989

Stereocontrolled synthesis of peptide bond isosteres.

Absolute stereochemical control is employed in the synthesis of isosteres for dipeptide subunits (1; see Fig. 1) in which the amide linkage has been replaced by a trans carbon-carbon double bond. The synthesis affords access to the four stereoisomers of 1 in which R and R' = CH3, including the isostere for D-alanine-D-alanine (D-Ala-D-Ala), 2.

Amino Acid Sequence↗
PubMed1989

Diagnostic flexible bronchoscopy in human immunodeficiency virus (HIV)-positive children.

Twelve children with laboratory evidence of human immunodeficiency virus (HIV) infection underwent diagnostic flexible bronchoscopy with washings or bronchoalveolar lavage at Bellevue Hospital Center from October 1987 to April 1989. The patients included 7 boys and 5 girls ranging from age 3.5 months to 10 years 5 months. Indications for bronchoscopy included respiratory distress with or without focal changes on chest radiograph in 11 patients, and persistent but asymptomatic right middle lobe collapse in one child. The etiology of pneumonia was diagnosed in 7 children and included Pneumocystis carinii, (PCP) (17%), Streptococcus viridans (17%), mechanical obstruction (17%) and cytomegalovirus (CMV) (8%). Bronchoscopy was non-diagnostic in 5 cases. Techniques for maximal yield of information using flexible bronchoscopy in HIV-positive children are discussed.

Bronchoalveolar Lavage Fluid↗