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David M Smith

Publications and source records attributed to David M Smith.

At least 37 records · Page 2Linked to original sources
PubMed2004

Firing properties of dopamine neurons in freely moving dopamine-deficient mice: effects of dopamine receptor activation and anesthesia.

To examine the regulation of midbrain dopamine neurons, recordings were obtained from single neurons of freely moving, genetically engineered dopamine-deficient (DD) mice. DD mice were tested without dopamine signaling (basal state) and with endogenous dopamine signaling (after L-dopa administration). In the basal state, when dopamine concentration in DD mice is <1% of that in control animals, the firing properties of midbrain dopamine neurons were remarkably similar among genotypes. However, L-dopa treatment, which restores dopamine and feeding and locomotor behavior in DD mice, profoundly inhibited the firing rate and bursting of dopamine neurons in DD mice. In addition, dopamine neurons in DD mice were hypersensitive to the dopamine receptor agonists quinpirole and SKF 81297. Anesthesia markedly reduced the firing rate of dopamine neurons in DD mice but did not significantly decrease the firing rate in control dopamine neurons. These data suggest that restoration of endogenous dopamine signaling activates hypersensitive long-loop feedback pathways that serve to limit dopamine release and underscore the importance of recording from awake animals.

Anesthesia↗
PubMed2004

Docking studies and model development of tea polyphenol proteasome inhibitors: applications to rational drug design.

Previously, we demonstrated that natural and synthetic ester bond-containing green tea polyphenols were potent and specific non-peptide proteasome inhibitors. However, the molecular mechanism of inhibition is currently unknown. Here, we report that inhibition of the chymotrypsin activity of the 20S proteasome by (-)-epigallocatechin-3-gallate (EGCG) is time-dependent and irreversible, implicating acylation of the beta5-subunit's catalytic N-terminal threonine (Thr 1). This knowledge is used, along with in silico docking experiments, to aid in the understanding of binding and inhibition. On the basis of these docking experiments, we propose that (-)-EGCG binds the chymotrypsin site in an orientation and conformation that is suitable for a nucleophilic attack by Thr 1. Consistently, the distance from the electrophilic carbonyl carbon of (-)-EGCG to the hydroxyl group of Thr 1 was measured as 3.18 A. Furthermore, the A ring of (-)-EGCG acts as a tyrosine mimic, binding to the hydrophobic S1 pocket of the beta5-subunit. In the process, the (-)-EGCG scissile bond may become strained, which could lower the activation energy for attack by the hydroxyl group of Thr 1. This model is validated by comparison of predicted and actual activities of several EGCG analogs, either naturally occurring, previously synthesized, or rationally synthesized.

Amides↗
PubMed2004

The precision and accuracy of templating the size of unicondylar knee arthroplasty.

In trauma and joint arthroplasty, preoperative templating is an important step that can help in the selection of implant size, position and alignment. Although the precision (reproducibility) of templating in unicondylar knee arthroplasty has been assessed previously, the accuracy has never been studied. Our aim is to assess the precision and accuracy of using the templating system for one commonly used unicondylar knee arthroplasty, ALPHANORM design (Alphanorm Medizintechnik, Germany). Eight observers used the templating system to estimate the size of the unicondylar knee prosthesis ALPHANORM in 29 randomly selected patients with osteoarthritis. The observers, who all were orthopaedic surgeons with two different levels of experience, worked independently and repeated their measurements 2 weeks later. All the patients subsequently underwent unicondylar knee replacements, and the actual size of the femur and tibia was assessed intra-operatively without any knowledge of the template sizes. Our results revealed a high level of intra-observer reproducibility. However, the inter-observer reproducibility and the accuracy all were poor.

Arthroplasty, Replacement, Knee↗
PubMed2004

Indocyanine green alters transepithelial electrical parameters of the distal colon.

Indocyanine green (ICG) is used as a dye marker of the vascular space in gastroenterology, ophthalmology, neurology, and critical care medicine. It is widely regarded to be inert. We report, however, that ICG demonstrates effects on colonic transepithelial electrical parameters which could form a basis for a growing number of deleterious gastrointestinal and other clinical effects. Short-circuit current (Iscc), transepithelial conductance (gt), and transepithelial paracellular flux of 14C-D-mannitol were monitored across sheets of rat distal colon. Dye was introduced to mucosal or serosal tissue surfaces at a concentration similar to that used in vivo (10 microg/ml). ICG decreased Iscc by over 50% and gt by over 10%. Transepithelial mannitol flux was not altered. Dye was effective only from the serosal surface. Cyclic AMP-induced spiking of Iscc was not affected by ICG. Preincubation with amiloride or furosemide did not affect the action of the dye on gt or Iscc. ICG at in vivo dosages is clearly capable of inhibiting ion transport across colon epithelial tissue. The serosal site of action indicates activity on a basal-lateral transport system or diffusion into the cell only across the basal-lateral membrane followed by inhibition of a transporter from the intracellular side. ICG should not be considered inert in vivo. Leakage of ICG from the vascular space into the interstitial fluid space will likely result in tissue morbidity.

Animals↗
PubMed2004

Fornix lesions impair context-related cingulothalamic neuronal patterns and concurrent discrimination learning in rabbits (Oryctolagus cuniculus).

Cingulothalamic neurons develop topographic patterns of cue-elicited neuronal activity during discrimination learning. These patterns are context-related and are degraded by hippocampal lesions, suggesting that hippocampal modulation of cingulothalamic activity results in the expression of the patterns, which could promote the retrieval of context-appropriate responses and memories. This hypothesis was tested by training rabbits (Oryctolagus cuniculus) with fornix lesions concurrently on two discrimination tasks (approach and avoidance) in different contexts. Because the same conditioned stimuli were used for both tasks, contextual information was critical for overcoming intertask interference during concurrent task acquisition. The lesions degraded the topographic patterns and significantly impaired concurrent learning, suggesting that hippocampal-cingulothalamic interactions and the resulting topographic patterns are critical for processing contextual information needed to defeat interference.

Action Potentials↗
PubMed2004

Risk factors for nonelective hospitalization in frail and older adult, inner-city outpatients.

PURPOSE: In our study, we sought to improve the accuracy of predicting the risk of hospitalization and to identify older, inner-city patients who could be targeted for preventive interventions. DESIGN AND METHODS: Participants (56% were African American) in a randomized trial were from a primary care practice and included 1,041 patients living in the inner city who were either > or = 75 years of age or were > or = 50 years of age with severe disease. As a secondary analysis, we assessed patient characteristics at baseline involving five domains of health, including utilization and satisfaction. We followed participants for 12 months and recorded the occurrence of nonelective hospitalization within the study period. We developed a multivariate model using logistic regression to predict this outcome. RESULTS: The following patient characteristics independently predicted an increased risk for nonelective hospitalization: having the diagnosis of congestive heart failure, diabetes mellitus, or anemia; and having more medications prescribed, having a lower body mass index, and having more emergency department visits during the previous year. Better physical functioning reduced the risk of hospitalization. IMPLICATIONS: Moderate accuracy of a prediction model (0.73) was observed. In addition to focusing on patients with chronic disease, helping them maintain physical functioning may help reduce nonelective hospitalization.

Black or African American↗
PubMed2004

Cerebellar, prefrontal cortex, and thalamic volumes over two time points in adolescent-onset schizophrenia.

OBJECTIVE: Structural and functional studies implicate multiple brain lesions as a basis for a functional dysconnectivity underlying the cognitive and symptom profiles in schizophrenia. The aim of this study was to examine the hypothesis that early-onset schizophrenia is associated with structural abnormalities in the prefrontal cortex, thalamus, and cerebellum, compatible with a dysconnectivity syndrome. METHOD: Two magnetic resonance imaging scans of 16 patients and 16 normal comparison subjects were undertaken on average 2 to 3 years apart. The participants were all from a defined geographic area in the United Kingdom with a population of 2.5 million. RESULTS: In comparison to the normal adolescents, the schizophrenic subjects demonstrated low prefrontal cortex and thalamic volumes. The relatively large difference in prefrontal and thalamic volumes in these adolescents with schizophrenia implies a more severe disease process than in adult subjects. CONCLUSIONS: The thalamic and frontal lobe findings provide preliminary, supportive structural evidence for a neurodevelopmental basis for a dysconnectivity syndrome, although the cerebellar findings were inconclusive.

Adolescent↗
PubMed2004

The pharmacology of adrenomedullin receptors and their relationship to CGRP receptors.

Adrenomedullin (AM) has two specific receptors formed by the calcitonin-receptor-like receptor (CL) and receptor activity-modifying protein (RAMP) 2 or 3. These are known as AM1 and AM2 receptors, respectively. In addition, AM has appreciable affinity for the CGRP1 receptor, composed of CL and RAMP1. The AM1 receptor has a high degree of selectivity for AM over CGRP and other peptides, and AM22-52 is an effective antagonist at this receptor. By contrast, the AM2 receptor shows less specificity for AM, having appreciable affinity for betaCGRP. Here, CGRP8-37 is either equipotent or more effective as an antagonist than AM22-52, depending on the species from which the receptor components are derived. Thus, under the appropriate circumstances it seems that betaCGRP might be able to activate both CGRP1 and AM2 receptors and AM could activate both AM1 and AM2 receptors as well as CGRP1 receptors. Current peptide antagonists are not sufficiently selective to discriminate between these three receptors. The CGRP-selectivity of RAMP1 and RAMP3 may be conferred by a putative disulfide bond from the N-terminus to the middle of the extracellular domain of these molecules. This is not present in RAMP2.

Animals↗
PubMed2003

Inhibition of the proteasome activity, a novel mechanism associated with the tumor cell apoptosis-inducing ability of genistein.

Epidemiological studies have suggested that increased soy consumption is associated with reduced cancer occurrence. Genistein, a soy isoflavone, has been reported to inhibit the growth of human tumor cells although the involved molecular mechanisms are not clearly defined. Here we report that genistein inhibits the proteasomal chymotrypsin-like activity in vitro and in vivo. Computational docking studies suggest that the interaction of genistein with the proteasomal beta 5 subunit is responsible for inhibition of the chymotrypsin-like activity. Inhibition of the proteasome by genistein in prostate cancer LNCaP and breast cancer MCF-7 cells is associated with accumulation of ubiquitinated proteins and three known proteasome target proteins, the cyclin-dependent kinase inhibitor p27(Kip1), inhibitor of nuclear factor-kappa B (I kappa B-alpha), and the pro-apoptotic protein Bax. Genistein-mediated proteasome inhibition was accompanied by induction of apoptosis in these solid tumor cells. Finally, genistein induced proteasome inhibition and apoptosis selectively in simian virus 40-transformed human fibroblasts, but not in their parental normal counterpart. Our results suggest that the proteasome is a potential target of genistein in human tumor cells and that inhibition of the proteasome activity by genistein might contribute to its cancer-preventive properties.

Antineoplastic Agents↗
PubMed2003

Overexpression of interleukin-2 receptor alpha in a human squamous cell carcinoma of the head and neck cell line is associated with increased proliferation, drug resistance, and transforming ability.

It has been previously demonstrated that human carcinomas express interleukin-2 receptor (IL-2R) alpha, beta, and gamma chains. The beta and gamma chains of IL-2R have intermediate binding affinity for IL-2 and are responsible for the intracellular signaling cascades after IL-2 stimulation. IL-2Ralpha lacks the cytoplasmic domain, but is essential for increasing the IL-2-binding affinity of other receptors. Overexpression of IL-2Ralpha in tumor cells is associated with tumor progression and a poor patient prognosis. To define molecular mechanisms responsible for the effects associated with IL-2Ralpha expression, ex vivo experiments were performed with the squamous cell carcinoma head-and-neck cancer line, PCI-13, which was genetically engineered to overexpress the IL-2Ralpha chain. While IL-2Ralpha-overexpressing PCI-13 cells were capable of forming colonies in soft agar, PCI-13 cells transfected with the control vector or those expressing IL-2Rgamma did not. Consistently, IL-2Ralpha-expressing tumor cells proliferated more rapidly than the control or IL-2Rgamma+ cells, associated with increased levels of cyclins A and D1 and cyclin-dependent kinase (cdk(s)) 2 and 4 proteins. In addition, IL-2Ralpha-expressing cells were significantly more resistant to apoptosis induction by a tripeptidyl proteasome inhibitor (ALLN) and two chemotherapeutic drugs (VP-16 and taxol) than the control or IL-2Rgamma+ cells. Accompanying the drug resistance, high levels of anti-apoptotic Bcl-X(L) and Bcl-2 proteins were found in the mitochondria-containing fraction of IL-2Ralpha-expressing tumor cells. Treatment of IL-2Ralpha-expressing cells with a specific Janus kinase 3 (Jak3) inhibitor decreased expression of cyclin A, cyclin D1, Bcl-X(L), and Bcl-2 proteins. Finally, high levels of ubiquitinated proteins were detected in the proliferating IL-2Ralpha-expressing cells. Our data suggest that increased proliferation rates and decreased drug sensitivity of IL-2Ralpha-expressing tumor cells are responsible for the enhanced tumor aggressiveness and poor clinical prognosis of patients whose tumors express IL-2Ralpha.

Apoptosis↗
PubMed2003

Desensitisation of adrenomedullin and CGRP receptors.

Adrenomedullin (AM), a potent vasoactive peptide, is elevated in certain disease states such as sepsis. Its role as a physiologically relevant peptide has been confirmed with the advent of the homozygous lethal AM peptide knockout mouse. So far, there have been few and conflicting studies which examine the regulatory role of AM at the receptor level. In this article, we discuss the few studies that have been presented on the desensitisation of AM receptors and also present novel data on the desensitisation of endogenous AM receptors in Rat-2 fibroblasts.

Adrenomedullin↗
PubMed2003

Reliability of templating in estimating the size of uni-condylar knee arthroplasty.

The use of template systems has aided the preoperative selection of correct prosthetic size during routine arthroplasty. A similar system exists for unicondylar knee arthroplasty. Our goal is to assess the reliability of these templates for preoperatively predicting the correct prosthetic size in unicompartmental knee systems. Ten observers estimated the size of the unicondylar knee prosthesis required for 30 randomly selected patients with osteoarthritis. Estimation of the size was gauged using templates and instructions provided by the manufacturer. The observers worked independently and repeated their measurements 2 weeks later. Intraobserver and interobserver agreement was evaluated using the weighted kappa coefficient, and this revealed poor agreement regardless of the surgeon's experience. This shows that the present system lacks reliability and raises concerns about the place for preoperative radiological templating in unicompartmental knee arthroplasty.

Femur↗
PubMed2003

The role of the 8-18 helix of CGRP8-37 in mediating high affinity binding to CGRP receptors; coulombic and steric interactions.

1. The role of individual residues in the 8-18 helix of CGRP(8-37) in promoting high-affinity binding to CGRP(1) receptors expressed on rat L6 and human SK-N-MC cells has been examined. The relative potencies of various derivatives were estimated from their ability to inhibit the human alphaCGRP-mediated increase in cyclic AMP production and the binding of [(125)I]-human alphaCGRP. 2. Arg(11) and Arg(18) were replaced by serines to give [Ser(11,18)]CGRP(8-37). These bound with pKi values <6 to SK-N-MC cells and had apparent pA(2) values of 5.81+/-0.04 and 5.31+/-0.11 on SK-N-MC and L6 cells. CGRP(8-37) had a pKi of 8.22 on SK-N-MC cells and pK(b) values on the above cell lines of 8.95+/-0.04 and 8.76+/-0.04. 3. The arginines were replaced with glutamic acid residues. [Glu(11)]CGRP(8-37) had a pK(b) of 7.14+/-0.14 on SK-N-MC cells (pKi=7.05+/-0.05) and 6.99+/-0.08 on L6 cells. [Glu(18)]CGRP(8-37) had a pK(b) of 7.10+/-0.0.08 on SK-N-MC cells (pKi=6.91+/-0.23) and 7.12+/-0.09 on L6 cells. 4. Leu(12), Leu(15) and Leu(16) were replaced by benzoyl-phenylalanine (bpa) residues. On SK-N-MC cells, the apparent pA(2) values of [bpa(12)]-, [bpa(15)]- and [bpa(16)]CGRP(8-37) were respectively 7.43+/-0.23, 8.34+/-0.11 and 5.66+/-0.16 (pKi values of 7.14+/-0.17, 7.66+/-0.21 and <6): on L6 cells they were 7.96+/-0.36, 8.28+/-0.21 and 6.09+/-0.04 (all n=3). 5. It is concluded that the Arg(11) and Arg(18) are involved in specific electrostatic interactions with other residues, either on the CGRP(1) receptors or elsewhere on CGRP(8-37). Leu(16) is in a conformationally restricted site when CGRP(8-37) binds to CGRP(1) receptors, unlike Leu(12) and Leu(15).

Animals↗
PubMed2003

Pattern of recruitment of immunoregulatory antigen-presenting cells in malignant melanoma.

The mechanism by which the immune system of a tumor-bearing host acquires tolerance toward tumor antigens is still elusive. Antigen-presenting cells (APCs) are critical regulators of the decision between immune response and tolerance. APCs that express the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) have been found to inhibit T-cell responses both in vitro and in vivo. We hypothesized that malignant tumors exploit this mechanism by recruiting IDO-expressing APCs to the tumor-draining lymph nodes. To test this hypothesis, archival tissues and records of 26 cases of lymph node dissection for invasive cutaneous melanoma were obtained. IDO immunohistochemistry was performed on 14 cutaneous tumors and 328 regional lymph nodes. Abnormal accumulations of IDO-positive cells with a monocytoid or plasmacytoid morphology were identified in the perisinusoidal regions of draining lymph nodes in 45% of nodes studied. Recruitment of IDO-positive cells was seen in nodes with and without malignancy. We hypothesize that these IDO-positive APCs may contribute mechanistically to acquired tolerance to tumor antigens. Immunostaining of tumor-draining lymph nodes for abnormal accumulation of IDO-expressing cells might thus constitute an adverse prognostic factor and could contribute to the decision process and the appropriate care of patients with this deadly disease.

Adult↗
PubMed2003

Suicidal asphyxiation by using pure helium gas: case report, review, and discussion of the influence of the internet.

Suffocation by inhaled gases has been reported involving a variety of gases. We report a case of suicidal asphyxiation by forced replacement of oxygen with helium by using a complex homemade mask. In this case, a young woman researched suicide on the Internet and found an advocated method of suicide using helium. To our knowledge, there is only 1 previously reported case of suicidal asphyxia by using helium.

Adult↗
PubMed2003

Interruption of tumor cell cycle progression through proteasome inhibition: implications for cancer therapy.

The ubiquitin/proteasome-dependent protein degradation pathway plays an essential role in both up-regulation of cell proliferation and down-regulation of cell death in human cancer cells. The idea that proteasome function is required for tumor cell survival has prompted the design, synthesis and evaluation of various pharmacological proteasome inhibitors. Both in vitro and in vivo experimental and clinical results have demonstrated the potential use of proteasome inhibitors as novel anticancer drugs.

Animals↗
PubMed2002

Understanding the mechanism of action of B12-dependent ethanolamine ammonia-lyase: synergistic interactions at play.

Ab initio molecular orbital calculations are used to examine the mechanism of action of B(12)-dependent ethanolamine ammonia-lyase involving the conversion of 2-aminoethanol to acetaldehyde plus ammonia. We attempt to elucidate the mechanism by which the enzyme facilitates this reaction through interactions between active-site residues and the substrate. Our calculations suggest a preferred pathway involving a 1,2-shift in the associated radical and also suggest that interactions between the enzyme and the migrating group of the substrate that afford an almost fully protonated migrating group will lead to the most efficient catalysis. However, this criterion on its own is insufficient to fully understand the rearrangement. Additional synergistic interactions between the spectator hydroxyl group in the substrate and active-site residues on the enzyme are required to lower the barrier height to a value consistent with experimental observations.

Cobamides↗