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Biomedical subjects

R A Lewis

Publications and source records attributed to R A Lewis.

At least 145 records · Page 8Linked to original sources
PubMed1993

Two metabolites of anticonvulsant U-54494A: their anticonvulsant activity and interaction with sodium channel.

U-54494A, 3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzamide, has been shown to be a potent and long-acting anticonvulsant without analgesic or sedative effects on intact animals. The persistence of anticonvulsant activity after a decline in its concentration in the brain implies the conversion of the parent drug into active metabolites. In this study, two major metabolites of U-54494A, U-83892E [cis-N-(2-aminocyclohexyl)-3,4-dichlorobenzamide] and U-83894A [cis-N-(2-methylaminocyclohexyl)-3,4-dichlorobenzamide], were identified. The synthetic metabolites displayed anticonvulsant activity against electric shock in experimental animals and blocked voltage-gated sodium channel in N1E-115 neuroblastoma cells in voltage- and use-dependent manner by interacting with the inactivated channels as well as with the channels in the resting state (like the parent compound). These observations may provide one explanation for the long duration of the anticonvulsant activity of the parent compound U-54494A and further underscore the importance of voltage-dependent sodium channels in neuronal excitability, especially during seizures.

Animals↗
PubMed1993

Negative-configuration electroretinogram in Oregon eye disease. Consistent phenotype in Xp21 deletion syndrome.

OBJECTIVE: To determine whether abnormal configurations on electroretinogram were a consistent finding in patients with Xp21 deletion and to characterize the associated ophthalmologic phenotype. DESIGN: Case series. SETTING: University hospitals and eye institutes. PATIENTS: Five patients with complex glycerol kinase deficiency (Duchenne-type or Becker's muscular dystrophy, glycerol kinase deficiency, and congenital adrenal hypoplasia) and demonstrated chromosomal deletions at Xp21. Control patients were matched by age. MAIN OUTCOME MEASURES: Clinical information was obtained from medical records. Complete ophthalmologic examinations were performed. Electroretinography was performed using a Ganzfeld technique and chloral hydrate sedation. RESULTS: We report the clinical features and abnormal configurations on electroretinograms of five patients with complex glycerol kinase deficiency, including follow-up studies on a previously described patient. The original patient had ocular hypopigmentation; four, strabismus; two, myopia; three, astigmatism; and one, symptomatic night blindness. All had negative configurations on scotopic electroretinograms showing a reduced-amplitude B wave in the dark-adapted state. CONCLUSIONS: Our original report suggested a diagnosis of Aland Island eye disease, which appears to be an incomplete form of congenital stationary night blindness. Linkage data place Aland Island eye disease and congenital stationary night blindness at Xp11, whereas our patients had deletions at Xp21. The phenotype reported here may represent the effects of a single gene defect or the compound effects of the Xp21 contiguous gene syndrome (complex glycerol kinase deficiency). The phenotype is referred to as Oregon eye disease.

Adolescent↗
PubMed1993

Two-dimensional time-resolved X-ray diffraction studies of live isometrically contracting frog sartorius muscle.

Results were obtained from contracting frog muscles by collecting high quality time-resolved, two-dimensional, X-ray diffraction patterns at the British Synchrotron Radiation Source (SERC, Daresbury, Laboratory). The structural transitions associated with isometric tension generation were recorded under conditions in which the three-dimensional order characteristic of the rest state is either present or absent. In both cases, new layer lines appear during tension generation, subsequent to changes from activation events in the thin filaments. Compared with the 'decorated' actin layer lines of the rigor state, the spacings of the new layer lines are similar whereas their intensities differ substantially. We conclude that in contracting muscle an actomyosin complex is formed whose structure is not like that in rigor, although it is possible that the interacting sites are the same. Transition from rest to plateau of tension is accompanied by approximately 1.6% increase in the axial spacing of the myosin layer lines. This is explained as arising from axial disposition of the interacting myosin heads in the actomyosin complex. Model calculations are presented which support this view. We argue that in a situation where an actomyosin complex is formed during contraction, one cannot describe the diffraction features as being either thick or thin filament based. Accordingly, the layer lines seen during tension generation are referred to as actomyosin layer lines. It is shown that these layer lines can be indexed as submultiples of a minimum axial repeat of approximately 218.7 nm. After lattice disorder effects are taken into account, the intensity increases on the 15th and 21st AM layer lines at spacings of approximately 14.58 and 10.4 nm respectively, show the same time course as tension rise. However, the time course of the intensity increase of the other actomyosin layer lines and of the spacing change (which is the same for both phenomena) shows a substantial lead over tension rise. These findings suggest that the actomyosin complex formed prior to tension rise is a non-tension-generating state and that this is followed by a transition of the complex to a tension-generating state. The intensity increase in the 15th actomyosin layer line, which parallels tension rise, can be accounted for assuming that in the tension-generating state the attached heads adopt (axially) a more perpendicular orientation with respect to the muscle axis than is seen at rest or in the non-tension-generating state. This suggests the existence of at least two structurally distinct interacting myosin head conformations.(ABSTRACT TRUNCATED AT 400 WORDS)

Actomyosin↗
PubMed1993

Genetic mapping of the X-linked dominant mutations striated (Str) and bare patches (Bpa) to a 600-kb region of the mouse X chromosome: implications for mapping human disorders in Xq28.

Striated (Str) and bare patches (Bpa) are X-irradiation-induced, X-linked dominant mouse mutations that are lethal prenatally in hemizygous males. To map the Str mutation, we generated a backcross involving Mus castaneus. Pedigree analysis of 193 affected female and normal male progeny from the cross places Str extremely close to DXMIT1 and favors a gene order of (Cf-9)-Ids-Gabra3-DXS1104h-(Str, DXMIT1)-F8a-DXPas8-DXBay6-DXMIT6 for the loci studied. This region of the mouse X Chromosome (Chr) is syntenic with proximal human Xq28. Based on the mode of inheritance and clinical phenotype, Str may be a homolog of human familial incontinentia pigmenti (IP2). Further refinement of our genetic mapping of bare patches positions that locus between DXS1104h and DXPas8 in the same region as Str, raising the possibility that Bpa and Str may be allelic or are due to mutations in overlapping contiguous genes.

Animals↗
PubMed1993

Automated perimetry and short wavelength sensitivity in patients with asymmetric intraocular pressures.

Automated visual field testing [white-on-white (W-on-W) perimetry] and perimetry of short wavelength sensitive mechanisms [blue-on-yellow (B-on-Y) perimetry] were conducted in both eyes of patients with large asymmetries in intraocular pressure (IOP) between eyes (average difference = 19.9 mm Hg). Overall visual field sensitivity was significantly (P < 0.05) depressed in the eyes with higher IOP by an average of 2.33 dB, in spite of the fact that all but two of the eyes with higher IOP demonstrated visual field sensitivities that were within normal limits. None of the eyes with lower IOP were outside of normal sensitivity limits. B-on-Y perimetry revealed similar findings, except that three of the fellow eyes with relatively lower IOP also demonstrated abnormalities. Our results are consistent with the hypothesis that the diffuse loss in visual field sensitivity in glaucoma is related to IOP. In addition, it appears that short wavelength sensitive mechanism may reveal early glaucomatous losses in patients with elevated IOP.

Adult↗
PubMed1993

The efficacy of brimonidine in decreasing elevations in intraocular pressure after laser trabeculoplasty.

PURPOSE: The authors explored the empirical dosing requirement for administration of an alpha 2-adrenoceptor agonist, brimonidine, and determined its efficacy in decreasing elevations in intraocular pressure (IOP) after 360 degrees argon laser trabeculoplasty (ALT). METHODS: This vehicle-controlled, double-masked, multicenter trial evaluated three dosing regimens of brimonidine. Two hundred thirty-two patients for whom 360 degrees ALT was indicated were randomized into one of four treatment groups: 0.5% brimonidine both before and after ALT; brimonidine before but vehicle after ALT; vehicle before but brimonidine after ALT; or vehicle at both times. RESULTS: During the first 3 hours after 360 degrees ALT, the overall incidence of IOP elevations of 5 mmHg or greater was 38% (23 of 60 eyes) in the group receiving vehicle only, and it ranged from 3% to 9% (2 of 62 to 5 of 53 eyes) in the groups receiving any brimonidine treatment. There was little difference in efficacy between the three dosing regimens of brimonidine. Brimonidine was well tolerated by the patients. CONCLUSION: Based on this large, controlled, multicenter study, 0.5% brimonidine was an effective agent for reducing elevations in IOP after 360 degrees ALT. Only one dose, administered either before or after 360 degrees ALT, was required.

Adrenergic alpha-Agonists↗
PubMed1993

Variability of expression in tuberous sclerosis.

We present three families in whom a diagnosis of tuberous sclerosis is difficult to secure and we review published reports about similar cases. Tuberous sclerosis has been reported to affect as many as 1 in 9400 subjects in the population. The manifestations of this disease vary not only between but also within families. Currently no reliable method of prenatal diagnosis is available. For these reasons, subjects known to be at 50% risk should be assessed scrupulously to clarify their status. These cases illustrate the difficulties in the clinical diagnosis of tuberous sclerosis and further reinforce the need for a molecular method of determining whether an at risk subject has the disease.

Adolescent↗
PubMed1993

Genetic heterogeneity among blue-cone monochromats.

Thirty-three unrelated subjects with blue-cone monochromacy or closely related variants of blue-cone monochromacy were examined for rearrangements in the tandem array of genes encoding the red- and green-cone pigments. In 24 subjects, eight genotypes were found that would be predicted to eliminate the function of all of the genes within the array. As observed in an earlier study, the rearrangements involve either deletion of a locus control region adjacent to the gene array or loss of function via homologous recombination and point mutation. One inactivating mutation, Cys203-to-Arg, was found in 15 probands who carry single genes and in both visual pigment genes in one subject whose array has two genes. This mutation was also found in at least one of the visual pigment genes in 1 subject whose array has multiple genes and in 2 of 321 control subjects, suggesting that preexisting Cys203-to-Arg mutations constitute a reservoir of chromosomes that are predisposed to generate blue-cone-monochromat genotypes by unequal homologous recombination and/or gene conversion. Two other point mutations were identified: (a) Arg247-to-Ter in one subject with a single red-pigment gene and (b) Pro307-to-Leu in one subject with a single 5' red-3' green hybrid gene. The observed heterogeneity of genotypes points to the existence of multiple one- and two-step mutational pathways to blue-cone monochromacy.

Base Sequence↗
PubMed1992

Inhibition of RNA polymerase by captan at both DNA and substrate binding sites.

RNA synthesis carried out in vitro by Escherichia coli RNA polymerase was inhibited irreversibly by captan when T7 DNA was used as template. An earlier report and this one show that captan blocks the DNA binding site on the enzyme. Herein, it is also revealed that captan acts at the nucleoside triphosphate (NTP) binding site, and kinetic relationships of the action of captan at the two sites are detailed. The inhibition by captan via the DNA binding site of the enzyme was confirmed by kinetic studies and it was further shown that [14C]captan bound to the beta' subunit of RNA polymerase. This subunit contains the DNA binding site. Competitive-like inhibition by captan versus UTP led to the conclusion that captan also blocked the NTP binding site. In support of this conclusion, [14C]captan was observed to bind to the beta subunit which contains the NTP binding site. Whereas, preincubation of RNA polymerase with both DNA and NTPs prevented captan inhibition, preincubation with either DNA or NTPs alone was insufficient to protect the enzyme from the action of captan. Furthermore, the interaction of [14C]captan with the beta and beta' subunits was not prevented by a similar preincubation. Captan also bound, to a lesser extent, to the alpha and sigma subunits. Therefore, captan binding appears to involve interaction with RNA polymerase at sites in addition to those for DNA and NTP; however, this action does not inhibit the polymerase activity.

Bacterial Proteins↗
PubMed1992

Drug design by machine learning: the use of inductive logic programming to model the structure-activity relationships of trimethoprim analogues binding to dihydrofolate reductase.

The machine learning program GOLEM from the field of inductive logic programming was applied to the drug design problem of modeling structure-activity relationships. The training data for the program were 44 trimethoprim analogues and their observed inhibition of Escherichia coli dihydrofolate reductase. A further 11 compounds were used as unseen test data. GOLEM obtained rules that were statistically more accurate on the training data and also better on the test data than a Hansch linear regression model. Importantly machine learning yields understandable rules that characterized the chemistry of favored inhibitors in terms of polarity, flexibility, and hydrogen-bonding character. These rules agree with the stereochemistry of the interaction observed crystallographically.

Artificial Intelligence↗
PubMed1992

The Lowe's oculocerebrorenal syndrome gene encodes a protein highly homologous to inositol polyphosphate-5-phosphatase.

Lowe's oculocerebrorenal syndrome (OCRL) is a human X-linked developmental disorder of unknown pathogenesis and has a pleiotropic phenotype affecting the lens, brain and kidneys. The OCRL locus has been mapped to Xq25-q26 by linkage and by finding de novo X; autosome translocations at Xq25-q26 in two unrelated females with OCRL. Here we use yeast artificial chromosomes with inserts that span the X chromosomal breakpoint from a female OCRL patient in order to isolate complementary DNAs for a gene that is interrupted by the translocation. We show that the transcript is absent in both female OCRL patients with X; autosome translocations and that it is absent or abnormally sized in 9 of 13 unrelated male OCRL patients with no detectable genomic rearrangement. The open reading frame encodes a new protein with 71% similarity to human inositol polyphosphate-5-phosphatase. Our results suggest that OCRL may be an inborn error of inositol phosphate metabolism.

Amino Acid Sequence↗
PubMed1992

Isolation of a candidate gene for choroideremia.

Choroideremia is an X chromosome-linked retinal dystrophy of unknown pathogenesis. We have isolated cDNAs from a human retinal library with a genomic probe located at the X chromosomal breakpoint in a female with choroideremia and an X;13 translocation. This cDNA spans the breakpoint in the X;13 translocation female and is deleted in males who have choroideremia as part of a complex phenotype including mental retardation and deafness. However, this cDNA detects no alterations in the DNA of 34 males with isolated choroideremia. Nonetheless, the cDNA does detect reduced or absent levels of mRNA in three-quarters of male patients with an apparently intact gene. These data support the hypothesis that this cDNA represents the gene in which mutations cause choroideremia.

Amino Acid Sequence↗
PubMed1992

Mycophenolic acid inhibits the degranulation of rat peritoneal mast cells.

The effect of mycophenolic acid (MPA), a potent inhibitor of inosine monophosphate dehydrogenase, on the degranulation of rat peritoneal mast cells (RMC) was studied. RMC were pretreated for 48 hr with 0.1-10 microM MPA before the cells were sensitized with IgE and triggered with specific Ag. The net amount of [3H]5-HT released from granules was decreased by 44 and 32% with 1 and 10 microM MPA treatment, respectively. MPA inhibition of degranulation was completely reversed by the addition of 30 microM guanosine to the incubation medium. There was no difference in the apparent number or affinity of IgE binding sites between control and MPA-treated RMC. MPA pretreatment also had no effect on the IgE receptor-mediated production of PGD2 in RMC. These results suggest that depletion of intracellular GTP pools by MPA can disrupt the signaling between the IgE receptor and the secretory granules and that, under these same conditions, the release and metabolism of arachidonic acid are unaffected.

Animals↗
PubMed1992

Automated site-directed drug design: a method for the generation of general three-dimensional molecular graphs.

A new algorithm for creating diverse, irregular and physically reasonable three-dimensional linear atomic chains is described. The linear chains of atoms, or molecular graphs, are generated by solving a series of trigonometric equations within geometric constraints for a given set of atom types. The nature and number of the chains that are produced can be controlled by changing the palette of atom types, so that a chemist user could generate template suggestions that are synthetically relevant to a drug design project. Testing has shown that the method is sufficiently robust to be used in a general context. The molecular graphs could serve as useful structural templates for joining up regions in an active site where a ligand might interact strongly with the receptor. This paper is concerned with the description and proof of the methodology. The approach will form part of a larger structural tool kit for helping chemists to design novel ligands for a specified site.

Algorithms↗
PubMed1992

Automated site-directed drug design using molecular lattices.

Receptor-based drug design is predicated on the knowledge of the structure of a target receptor and the principles of molecule recognition. The objective is to produce a wide diversity of structures that are sterically and electrostatically complementary to a specified receptor site. Many drug-receptor interactions are controlled by a few key receptor groups. This observation leads to a design approach in which one focuses on chemical fragments that putatively interact with the key receptor groups. There then remains the difficult task of joining the fragments into molecular structures that match the spatial patterns of recognition forces in the receptor site. In this paper, we describe a new modeling program, BUILDER, that combines database searching techniques and structure generation algorithms within an interactive graphics modeling environment (MidasPlus). A novel tool for process communication (delegate) is introduced and examples of its use are given. To demonstrate the functionality of the package and its ability to produce novel structures, we examine the active site of HIV-1 protease.

Algorithms↗
PubMed1992

Linkage studies of Usher syndrome type 1: exclusion results from the Usher syndrome consortium.

Usher Syndrome Type 1 is an autosomal recessive disease characterized by profound congenital hearing impairement and vestibular dysfunction followed by the onset of retinitis pigmentosa in childhood or early adolescence. Members of the Usher Syndrome Consortium, whose objective is to locate and isolate the genes for Usher syndrome, have pooled linkage data from 36 families with 111 affected individuals. We report the analysis of 206 blood group, protein, and DNA marker polymorphisms. No evidence of linkage heterogeneity among families was found for any of the markers studied; the negative lod scores exclude the locus for this disease from about 39% of the genome. Our results indicate the regions of the genome to which our continuing efforts should be directed.

Chromosome Mapping↗
PubMed1992

Modelling the structure and function of enzymes by machine learning.

A machine learning program, GOLEM, has been applied to two problems: (1) the prediction of protein secondary structure from sequence and (2) modelling a quantitative structure-activity relationship in drug design. GOLEM takes as input observations and combines them with background knowledge of chemistry to yield rules expressed as stereochemical principles for prediction. The secondary structure prediction was explored on the alpha/alpha class of proteins; on an unrelated test set it yielded 81% accuracy. The rules from GOLEM defined patterns of residues forming alpha-helices. The system studied for drug design was the activities of trimethoprim analogues binding to E. coli dihydrofolate reductase. The GOLEM rules were a better model than standard regression approaches. More importantly, these rules described the chemical properties of the enzyme-binding site that were in broad agreement with the crystallographic structure.

Amino Acid Sequence↗