Biomedical subjects

J B Thomas

Publications and source records attributed to J B Thomas.

At least 37 records · Page 2Linked to original sources

PubMed2000

4-[(8-Alkyl-8-azabicyclo[3.2.1]octyl-3-yl)-3-arylanilino]-N,N-diethylbenzamides: high affinity, selective ligands for the delta opioid receptor illustrate factors important to antagonist activity.

The tropane derived compounds, 4-[(8-alkyl-8-azabicyclo[3.2.1]octyl-3-yl)-3-arylanilino]-N,N-d iethylbenzamides (5a-d), were synthesized and found to have high affinity and selectivity for the delta receptor. Compounds 5a-d are structurally similar to the full agonist (-)-RTI-5989-54 (3); yet, efficacy studies for compounds in this series (5a-d) reveal greatly diminished agonist activity as well as antagonism not found in piperidine-based compounds like 3.

Benzamides↗

PubMed2000

Transcriptional mechanisms in the development of motor control.

Considerable progress has been made in understanding how combinatorially expressed transcription factors control the development of neuronal subtypes in the fly and vertebrate central nervous systems. The mode of action of many of these factors has been conserved from invertebrates to vertebrates throughout evolution, such as the formation and regulation of specific transcriptional complexes, the utilization of repressors for maintaining specificity, and the use of phosphorylation as an important means for transiently altering transcriptional activity.

Animals↗

PubMed2000

Chip is an essential cofactor for apterous in the regulation of axon guidance in Drosophila.

LIM-homeodomain transcription factors are expressed in subsets of neurons and are required for correct axon guidance and neurotransmitter identity. The LIM-homeodomain family member Apterous requires the LIM-binding protein Chip to execute patterned outgrowth of the Drosophila wing. To determine whether Chip is a general cofactor for diverse LIM-homeodomain functions in vivo, we studied its role in the embryonic nervous system. Loss-of-function Chip mutations cause defects in neurotransmitter production that mimic apterous and islet mutants. Chip is also required cell-autonomously by Apterous-expressing neurons for proper axon guidance, and requires both a homodimerization domain and a LIM interaction domain to function appropriately. Using a Chip/Apterous chimeric molecule lacking domains normally required for their interaction, we reconstituted the complex and rescued the axon guidance defects of apterous mutants, of Chip mutants and of embryos doubly mutant for both apterous and Chip. Our results indicate that Chip participates in a range of developmental programs controlled by LIM-homeodomain proteins and that a tetrameric complex comprising two Apterous molecules bridged by a Chip homodimer is the functional unit through which Apterous acts during neuronal differentiation.

Animals↗

PubMed2000

The evaluation of subatmospheric pressure and hyperbaric oxygen in ischemic full-thickness wound healing.

We evaluated the efficacy of subatmospheric pressure and hyperbaric oxygen (HBO) as adjuncts in the treatment of hypoxic full-thickness wounds in a rabbit model. We hypothesized that subatmospheric pressure and HBO independently are effective in improving wound healing in the ischemic wound model and that when they are used in combination there is an increased positive effect on wound healing. Using a standard ischemic wound model four full-thickness wounds were created on each ear of 41 male New Zealand white rabbits (N = 82 ears). On each rabbit one ear was dressed with the vacuum-assisted closure (VAC) device and connected to suction; the other was dressed identically without the suction and suction tubing. Twenty rabbits were treated with HBO daily for 10 days at 2.0 atmospheres absolute for 90 minutes plus descent and ascent times. Necropsy on all rabbits was performed on postoperative day 10. Four ischemic wound treatment groups were evaluated: Group 1 (N = 21) VAC dressing alone; Group 2 (N = 20) VAC dressing plus HBO; Group 3 (N = 21) VAC dressing to suction alone; and Group 4 (N = 20) VAC dressing to suction and HBO. Using light microscopy a veterinary pathologist blinded to treatment groups quantified peak granulation tissue, granulation tissue gap, and epithelialization tissue gap. Data were analyzed by analysis of variance with significance indicated by P < 0.05. Statistical significance was found in a comparison of VAC dressing to suction and VAC dressing alone for peak granulation tissue and granulation tissue gap both with and without use of HBO. VAC device use appears to increase the rate of healing in a rabbit ischemic wound model. HBO therapy did not significantly affect the rate of healing in this model.

Analysis of Variance↗

PubMed1999

Optically pure (-)-4-[(N-allyl-3-methyl-4-piperidinyl)phenyl-amino]-N,N-diethylbenzami de displays selective binding and full agonist activity for the delta opioid receptor.

The optical isomers of 4-[(N-allyl-3-methyl-4-piperidinyl)phenylamino]-N,N-diethylbenzamide+ ++ (3) have been prepared and tested in both binding and functional assays. The data show that (-)-3 is responsible for the delta opioid activity demonstrated by the racemic material. This compound displays a binding affinity of 5.5 nM for the delta opioid receptor as well as a 470-fold delta versus mu selectivity. Importantly, (-)-3 is a full agonist at the delta receptor in comparison with SNC-80 (2). Taken together, the data suggest that (-)-3 behaves more like the prototypical delta agonists, BW373U86 or SNC-80, and less like the peptidomimetic compound SL-3111 (5).

Benzamides↗

PubMed1999

Axon routing across the midline controlled by the Drosophila Derailed receptor.

In nervous systems with symmetry about the midline, many neurons project axons from one side to the other. Although several of the components controlling midline crossing have been identified, little is known about how axons choose the appropriate pathway when crossing. For example, in the Drosophila embryo axons cross the midline in one of two distinct tracts, the anterior or posterior commissure (AC or PC, respec tively). Here we show that the Derailed (Drl) receptor tyrosine kinase is expressed by neurons that project in the AC, and that in the absence of Drl such neurons often project abnormally into the PC. Conversely, misexpression of Drl in PC neurons forces them to cross in the AC. The behaviour of Drl-misexpressing neurons and the in vivo binding pattern of a soluble Drl receptor probe indicate that Drl acts as a guidance receptor for a repellent ligand present in the PC. Our results show that Drl is a novel component in the control of midline crossing.

Animals↗

PubMed1999

(+/-)-4-[(N-allyl-cis-3-methyl-4-piperidinyl)phenylamino]-N,N-diethylbenzamide displays selective binding for the delta opioid receptor.

Racemic 4-[(N-allyl-cis-3-methyl-4-piperidinyl)phenylamino]-N,N-diethylbenzam ide (3a) was synthesized and found to have good affinity and selectivity for the delta receptor. These compounds can be viewed as an analog of BW373U86 and SNC-80 where an internal piperazine nitrogen has been transposed with a benzylic carbon. Functionally, 3a behaves as an agonist at the delta receptor with no measurable stimulation of either the mu or kappa receptor subtypes and was found to be devoid of any measurable amount of antagonist activity for any opioid receptor. A comparison of 3a to SNC-80 and DPDPE in the [35S]GTPgammaS functional assay suggests that 3a may be more like the peptide DPDPE.

Benzamides↗

PubMed1999

Micronutrients Measurement Quality Assurance Program: helping participants use interlaboratory comparison exercise results to improve their long-term measurement performance.

Over the past decade, the Micronutrients Measurement Quality Assurance Program (M2QAP) at the National Institute of Standards and Technology (NIST) has administered nearly 40 interlaboratory comparison exercises devoted to fat-soluble vitamin-related analytes in human serum. While M2QAP studies have been used to help certify reference materials and to document the performance of analytical systems, the primary focus of the M2QAP has been, and remains, the improvement of among-participant measurement comparability for target analytes. Recent analysis of historical measurement performance indicated the most efficient mechanism for further improving measurement comparability among participants is the improvement of long-term (months to years) comparability within each laboratory. The summary reports for the M2QAP studies are being redesigned to provide more chemist-friendly analyses of participant performance, dissecting systematic and random components of measurement incomparability as functions of analyte level and time. This report documents the semantic and graphical tools developed to help interlaboratory-comparison-exercise participants interpret their own measurement performance.

Data Display↗

PubMed1999

A LIM-homeodomain combinatorial code for motor-neuron pathway selection.

Different classes of vertebrate motor neuron that innervate distinct muscle targets express unique combinations of LIM-homeodomain transcription factors, suggesting that a combinatorial code of LIM-homeodomain proteins may underlie the control of motor-neuron pathway selection. Studies of LIM-homeodomain genes in mouse, Drosophila melanogaster and Caenorhabditis elegans have revealed functions of these genes in neuronal survival, axon guidance, neurotransmitter expression and neuronal function, but, to our knowledge, none of these studies have addressed the issue of a functional code. Here we study two members of this gene family in Drosophila, namely lim3, the homologue of the vertebrate Lhx3 and Lhx4 genes, and islet, the homologue of the vertebrate Isl1 and Is12 genes. We show that Drosophila lim3 is expressed by a specific subset of islet-expressing motor neurons and that mutating or misexpressing lim3 switches motor-neuron projections predictably. Our results provide evidence that lim3 and islet constitute a combinatorial code that generates distinct motor-neuron identities.

Amino Acid Sequence↗

PubMed1999

Isolation and characterization of Dek, a Drosophila eph receptor protein tyrosine kinase.

We have isolated a Drosophila receptor protein tyrosine kinase (RTK) of the Eph subfamily. Dek, for Drosophila Eph kinase, possesses all the domains characteristic of the Eph subfamily of RTKs and is equally similar in sequence to both the EphA and the EphB subclasses. Antibody staining and promoter fusions to axon-targeted reporters reveal that Dek is expressed by a large subset of developing embryonic interneurons and is targeted to their axons and growth cones at the time of axon pathfinding. Dek is also expressed by photoreceptor cells of third-instar larvae as they project axons into the optic brain lobe. Misexpression and overexpression of full-length Dek or kinase-inactive Dek do not grossly affect axon pathfinding.

Animals↗

PubMed1999

Vascular reconstruction utilizing artery from an amputated extremity: A case report.

Although infrainguinal arterial reconstruction is best performed with autologous tissue, reconstruction with vein in an infected field has been associated with vein graft disruption and hemorrhage. H.P., a 61-year-old man with peripheral vascular disease, was initially seen with an infected prosthetic right femoral-tibioperoneal artery bypass graft. Because of the presence of purulent drainage from the proximal and distal anastomotic regions and his comorbidities, a right through-knee guillotine amputation was performed, followed by graft excision and groin débridement. Right hip and thigh perfusion was preserved via arterial reconstruction by using a segment of endarterectomized popliteal artery, harvested from the amputated extremity. Arterial reconstruction with autologous tissue from an amputated extremity allowed us to balance our patient's overall risks with life and tissue preservation. This technique may be applied in the settings of lower extremity ischemia, trauma, or malignancy requiring concomitant arterial or venous reconstruction.

Amputation, Surgical↗

PubMed1999

Cell-type specific modular regulation of derailed in the Drosophila nervous system.

The derailed (drl) gene encodes a receptor tyrosine kinase (RTK) that governs aspects of axon guidance and muscle-epidermal interactions in the Drosophila embryo. To determine the types of neurons that express drl, we have examined a series of drl promoter fusions to axon-targeted reporters. We have identified enhancers that drive reporter expression in four distinct subtypes of embryonic neurons, all of which project axons in the anterior commissure of the developing nervous system. We also identified enhancers driving expression in the drl-expressing muscles and epidermal attachment cells. These enhancers define the classes of neurons projecting in the anterior commissure and can be used to precisely define axon pathfinding errors in drl and other mutants.

Animals↗

PubMed1999

The LIM homeodomain protein dLim1 defines a subclass of neurons within the embryonic ventral nerve cord of Drosophila.

Members of the LIM homeodomain family of transcription factors have been implicated in specifying cell identity in a range of species. In Drosophila three LIM homeobox genes, apterous, lim3 and isl, have been shown to control axon pathfinding of subsets of neurons within the embryo. Here we describe the isolation and characterization of another LIM homeobox gene in Drosophila termed dlim1, a homolog of the vertebrate Lim-1 gene. The sequence and expression of dLim1 is highly related to its vertebrate homologs. Within the Drosophila embryo, dLim1 is expressed in the head primordia, the brain lobes, and in distinct sets of motorneurons and interneurons within the ventral nerve cord. Comparatively in vertebrates, Lim-1 (Lhx1) along with Lim-3 (Lhx3), Gsh-4 (Lhx4), Isl-1 and Isl-2 are expressed in developing motorneurons along the spinal column, where their overlapping expression suggests a role for these genes in the establishment of specific motorneuron subtypes. dLim1 is absent from all cells expressing Isl, Lim3, and Apterous, indicating that these proteins function independently within the Drosophila embryo. To investigate the function of dlim1, we generated loss-of-function mutations within the locus. Our findings show that dlim1 is an essential gene that when mutated results in lethality near the larval-pupal boundary. In contrast to vertebrate Lim-1, dlim1 has no apparent role in anterior patterning of the Drosophila embryo. Our analysis shows that dlim1 has been evolutionarily conserved, however the Drosophila lim1 gene exhibits unique properties that distinguishes it from its vertebrate homologs.

Amino Acid Motifs↗

PubMed1999

Chip and apterous physically interact to form a functional complex during Drosophila development.

LIM homeodomain (LIM-HD) proteins play key roles in a variety of developmental processes throughout the animal kingdom. Here we show that the LIM-binding protein Chip acts as a cofactor for the Drosophila LIM-HD family member Apterous (Ap) in wing development. We define the domains of Chip required for LIM-HD binding and for homodimerization and show that mutant proteins deleted for these domains act in a dominant-negative fashion to disrupt Ap function. Our results support a model for multimeric complexes containing Chip and Ap in transcriptional regulation. This model is confirmed by the activity of a chimeric fusion between Chip and Ap that reconstitutes the complex and rescues the ap mutant phenotype.

Animals↗

PubMed1998

Identification of an opioid kappa receptor subtype-selective N-substituent for (+)-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine.

A three-component library of compounds was prepared in parallel using multiple simultaneous solution-phase synthetic methodology. The compounds were biased toward opioid receptor antagonist activity by incorporating (+)-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (a potent, nonselective opioid pure antagonist) as one of the monomers. The other two monomers, which included N-substituted or unsubstituted Boc-protected amino acids and a range of substituted aryl carboxylic acids, were selected to add chemical diversity. Screening of these compounds in competitive binding experiments with the kappa opioid receptor selective ligand [3H]U69,593 led to the discovery of a novel kappa opioid receptor selective ligand, N-¿(2'S)-[3-(4-hydroxyphenyl)propanamido]-3'-methylbutyl¿-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (8, RTI-5989-29). Additional structure-activity relationship studies suggested that 8 possesses lipophilic and hydrogen-bonding sites that are important to its opioid receptor potency and selectivity. These sites appear to exist predominantly within the kappa receptor since the selectivity arises from a 530-fold loss of affinity of 8 for the mu receptor and an 18-fold increase in affinity for the kappa receptor relative to the mu-selective ligand, (+)-N-[trans-4-phenyl-2-butenyl]-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (5a). The degree of selectivity observed in the radioligand binding experiments was not observed in the functional assay. According to its ability to inhibit agonist stimulated binding of [35S]GTPgammaS at all three opioid receptors, compound 8 behaves as a mu/kappa opioid receptor pure antagonist with negligible affinity for the delta receptor.

Animals↗

PubMed1998

N-substituted octahydro-4a-(3-hydroxyphenyl)-10a-methyl-benzo[g]isoquinolines are opioid receptor pure antagonists.

N-Methyl- and N-phenylethyl-(+/-)-1,2,3,4,4a,5,10,10a- octahydro-4a-(3-hydroxyphenyl)-10a-methyl-benzo[g]isoquinolines (4 and 5, respectively) were found to be pure opioid antagonists. These compounds were shown to share many of the characteristics identified with the N-methyl- and N-phenylethyl trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine (1 and 2, respectively) including N-substituent mediated potency and a lack of N-substituent mediated antagonism. These data suggest that compounds 4 and 5 and the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines (1 and 2) may interact with opioid receptors similarly.

Animals↗

PubMed1998

N-Substituted 9beta-methyl-5-(3-hydroxyphenyl)morphans are opioid receptor pure antagonists.

The inhibition of radioligand binding and [35S]GTPgammaS functional assay data for N-methyl- and N-phenethyl-9beta-methyl-5-(3-hydroxyphenyl)morphans (5b and 5c) show that these compounds are pure antagonists at the micro, delta, and kappa opioid receptors. Since 5b and 5c have the 5-(3-hydroxyphenyl) group locked in a conformation comparable to an equatorial group of a piperidine chair conformation, this information provides very strong evidence that opioid antagonists can interact with opioid receptors in this conformation. In addition, it suggests that the trans-3, 4-dimethyl-4-(3-hydroxyphenyl)piperidine class of antagonist operates via a phenyl equatorial piperidine chair conformation. Importantly, the close relationship between the 4-(3-hydroxyphenyl)piperidines and 5-(3-hydroxyphenyl)morphan antagonists shows that the latter class of compound provides a rigid platform on which to build a novel series of opioid antagonists.

Animals↗

PubMed1998

Investigation of the N-substituent conformation governing potency and mu receptor subtype-selectivity in (+)-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine opioid antagonists.

A study of the binding site requirements associated with the N-substituent of (+)-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (4) derivatives was undertaken using a set of rigid vs flexible N-substituents. The study showed that compounds 7-9 bearing the trans-cinnamyl N-substituent most closely reproduced the potency at the opioid receptor of the flexible N-propylphenyl or N-propylcyclohexyl analogues previously reported. Neither the N-substituted cis-cinnamyl nor the cis-phenylcyclopropylmethyl compounds 10 and 11, respectively, showed high affinity for the opioid receptor. However, the N-trans-phenylcyclopropylmethyl compound 12 closely approximated the affinity of compounds 7-9. Additionally, we found that free rotation of the phenyl ring is necessary for high affinity binding and mu receptor subtype selectivity as the planar N-substituted thianaphthylmethyl and benzofuranylmethyl compounds 13 and 14 had significantly lower binding affinities. Altogether, these findings suggest that the high binding affinity, selectivity, and antagonist potency of N-propylphenyl or N-propylcyclohexyl analogues of (+)-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (4) are achieved via a conformation wherein the connecting chain of the N-substituents is extended away from piperidine nitrogen with the appended ring system rotated out-of-plane relative to the connecting chain atoms. This conformation is quite similar to that observed in the solid state for 5, as determined by single crystal X-ray analysis. Additionally, it was found that, unlike naltrexone, N-substituents bearing secondary carbons attached directly to the piperidine nitrogen of 4 suffer dramatic losses of potency vs analogues not substituted in this manner. Using a functional assay which measured stimulation or inhibition of [35S]GTP-gamma-S binding, we show that the trans-cinnamyl analogues of (+)-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (4) retain opioid pure antagonist activity and possess picomolar antagonist potency at the mu receptor.

Animals↗