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Biomedical subjects

David E Smith

Publications and source records attributed to David E Smith.

At least 19 recordsLinked to original sources
PubMed2006

PEPT1 enhances the uptake of gabapentin via trans-stimulation of b0,+ exchange.

PURPOSE: The aims of this study were (1) to determine whether amino acid and dipeptide loading can improve the effective permeability of gabapentin and (2) to characterize the underlying mechanism that is responsible for this interaction. MATERIALS AND METHODS: An in situ single-pass rat intestinal perfusion model was used to assess the effective permeability of gabapentin in rat, in the absence and presence of cellular loading by amino acid and dipeptide mixtures. RESULTS: Compared to gabapentin alone, cellular loading with amino acid and dipeptide mixtures significantly improved the effective permeability of gabapentin by 46-79% in jejunum and by 67-72% in ileum (p < or = 0.01). However, coperfusion of glycylsarcosine (i.e., PEPT1 substrate), methionine sulfoximine (i.e., glutamine synthase inhibitor), or lysine and arginine (i.e., b(0,+) substrates) with the amino acid and dipeptide mixtures compromised the intestinal uptake of gabapentin. CONCLUSIONS: These findings demonstrate, for the first time, a direct relationship between the PEPT1-mediated uptake of a dipeptide and the trans-stimulated uptake of gabapentin (an amino acid-like drug) through the transport system b(0,+).

Amines↗
PubMed2006

Molecular simulations of the pressure, temperature, and chemical potential dependencies of clay swelling.

A new method for the determination of clay swelling thermodynamics from computer simulation is discussed and evaluated. This method allows for the determination of temperature, pressure, and water chemical potential dependence of clay swelling from simulations at a single thermodynamic state point. The temperature dependence and pressure dependence of clay swelling are shown to be directly related to the composite system entropy and volume change, respectively, that accompany swelling. Expressions for the chemical potential dependence of clay swelling are used to determine constant pressure layer spacing and adsorption isotherms, quantities that are well suited for comparison with experimental measurements. This method is evaluated through grand isoshear ensemble simulations of Na-montmorillonite, a prototypical swelling clay. Approximations associated with all expressions are discussed with explicit calculations used to demonstrate their regimes of validity.

Journal Article↗
PubMed2006

PEPT2-mediated transport of 5-aminolevulinic acid and carnosine in astrocytes.

5-aminolevulinic acid (ALA) and carnosine have important physiological and pathophysiological roles in the CNS. Both are substrates for the proton-coupled oligopeptide transporter PEPT2. The purpose of the current study was to determine the importance of PEPT2 in the uptake of ALA and carnosine in rat and mouse (PEPT2+/+ and PEPT2-/-) cultured neonatal astrocytes. Although neonatal astrocytes are known to express PEPT2, its quantitative importance in the transport of these compounds is not known. [14C]ALA uptake in neonatal rat astrocytes was inhibited by dipeptides, an alpha-amino containing cephalosporin (which is a PEPT2 substrate) but was not affected by a non-amino containing cephalosporin (which is not a PEPT2 substrate). Uptake was pH sensitive as expected from a proton-coupled transporter and was saturable (Vmax=715+/-29 pmol/mg/min, Km=606+/-14 microM). [3H]Carnosine uptake in neonatal rat astrocytes was inhibited by dipeptides but not by histidine (a substrate for the peptide/histidine transporters PHT1 and PHT2) and also showed saturable transport (Vmax=447+/-23 pmol/mg/min, Km=43+/-5.5 microM). Neonatal astrocytes from PEPT2-/- mice had a 62% reduction in [14C]ALA uptake and a 92% reduction in [3H]carnosine uptake compared to PEPT2+/+ mice. These results demonstrate that PEPT2 is the primary transporter responsible for the astrocytic uptake of ALA and carnosine.

Aminolevulinic Acid↗
PubMed2006

Towards improved empirical isobase models of Holocene land uplift for mainland Scotland, UK.

A new approach to modelling patterns of glacio-isostatic land uplift during the Holocene in mainland Scotland, UK, is described. The approach is based upon altitude measurements at the inner margin or locally highest point of raised estuarine surfaces dated by radiocarbon assay supported by microfossil analyses. 2,241 altitudes have been analysed by a technique new to studies of former sea-levels, Gaussian Trend Surface Analysis, and isobase models for four Holocene shorelines: the Holocene Storegga Slide tsunami shoreline, abandoned rapidly circa 7,900 sidereal years BP; the Main Postglacial shoreline, abandoned during circa 6,400-7,700 sidereal years BP; the Blairdrummond shoreline, abandoned during circa 4,500-5,800 sidereal years BP, and a speculative fourth shoreline, the Wigtown shoreline, abandoned during circa 1,520-3,700 sidereal years BP, are shown in a series of maps. The implications of the shoreline patterns for glaicio-isostasy in the area are discussed. It is maintained that the statistical technique used enables broad estimates to be made of near shore sea surface change.

Age Factors↗
PubMed2006

Two-way laser link over interplanetary distance.

Here we report timed observations with subnanosecond precision of short laser pulses at a distance of nearly 24 million kilometers between the Mercury Laser Altimeter (MLA) aboard the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft and the NASA Goddard Geophysical and Astronomical Observatory (GGAO). Forty MLA downlink observations and 90 uplink observations were obtained during observing sessions on 27 and 31 May 2005. Precise standard ground timing allowed a solution for spacecraft range, range rate, and acceleration, as well as clock bias. This experiment established a new distance record for laser detection and accomplished a two-way laser link at an interplanetary distance.

Journal Article↗
PubMed2005

Role of PEPT2 in glycylsarcosine transport in astrocyte and glioma cultures.

The aims of the current study were (1) to quantify the role of PEPT2 in the uptake of glycylsarcosine (GlySar) in cultured neonatal astrocytes and (2) to examine GlySar transport and PEPT2 expression in two glioma cell lines. The uptake of [(14)C]GlySar was measured in astrocytes cultured from neonatal mouse (PEPT2(+/+) and PEPT2(-/-)) and rat, as well as rat C6 and F98 glioma cells. PEPT2 expression was examined by reverse transcription-polymerase chain reaction (RT-PCR). Neonatal astrocytes from PEPT2(-/-) mice had a 94% reduction in [(14)C]GlySar uptake compared to wild type mice and there was no saturable transport. In PEPT2(+/+) mice, [(14)C]GlySar uptake was saturable (V(max) 58 +/- 12 pmol/mg/min, K(m) 107 +/- 46 microM, K(d) 0.043 +/- 0.004 microl/mg/min). In neonatal rat astrocytes, kinetic analysis also suggested that [(14)C]GlySar uptake was via a single transporter. The inhibitor profile and pH dependence of that transport process was consistent with PEPT2. In C6 and F98 glioma cells, [(14)C]GlySar uptake was markedly reduced ( approximately 96-98%) compared to that in neonatal astrocytes and this was reflected by an absence of PEPT2 mRNA expression. These results indicate that PEPT2 is the sole transporter involved in the uptake of GlySar into neonatal cultured astrocytes. However, PEPT2 mRNA appears to be absent from two glioma cell lines.

Animals↗
PubMed2005

PEPT2 (Slc15a2)-mediated unidirectional transport of cefadroxil from cerebrospinal fluid into choroid plexus.

Cefadroxil is a cephalosporin antibiotic used in the treatment of infection. However, cerebrospinal fluid (CSF) concentrations of cefadroxil and other aminocephalosporins are not adequate for the treatment of bacterial meningitis. To evaluate the relevance of PEPT2 in affecting the exposure of aminocephalosporins in brain, we investigated the transport properties of cefadroxil at the blood-CSF interface using primary-cultured epithelial cells and isolated whole tissues of choroid plexus. Our results indicated that cefadroxil was preferentially taken up from the apical as opposed to basal side of the monolayer (5-fold), and its apical uptake was stimulated by an inwardly directed proton gradient. The concentration-dependent apical uptake of cefadroxil was characterized by a high-affinity/low-capacity transport system (Km = 39.0 +/- 22.7 microM; Vmax = 22.9 +/- 6.6 pmol/mg/min) and a nonsaturable component (Kd = 0.15 +/- 0.01 microl/mg/min); in contrast, only a nonsaturable component was found for the basal uptake of cefadroxil (Kd = 0.14 +/- 0.01 microl/mg/min). The apical-to-basal transepithelial transport of 2 microM cefadroxil was greater than its basal-to-apical transport, but no differences were observed in directionality when 5 mM concentrations of cefadroxil were studied. Moreover, the cellular efflux of cefadroxil was not saturable in either direction (i.e., to apical or basal side). Finally, no differences were observed in the choroid plexus tissue efflux of 2 microM cefadroxil from wild-type and PEPT2 null mice. These findings demonstrate that PEPT2 has an important role in limiting the exposure of cefadroxil in CSF. Located at the apical membrane of choroid plexus epithelium, PEPT2 acts in a unidirectional (as opposed to bidirectional) manner in transporting cefadroxil from CSF into the cell.

Animals↗
PubMed2005

Monitoring the quality of medical news reporting: early experience with media doctor.

OBJECTIVE: To analyse the reviews of medical news articles posted on media doctor, a medical news-story monitoring website. DESIGN AND SETTING: A descriptive summary of operating the media doctor website between 1 February and 1 September 2004. MAIN OUTCOME MEASURES: Consensus scores for 10 assessment criteria for the medical intervention described in the article (novelty, availability in Australia, alternative treatment options given, evidence of "disease mongering", objective supportive evidence given, quantification of benefits, coverage of harms, coverage of costs, independent sources of information, and excessive reliance on a press release); cumulative article rating scores for major media outlets. RESULTS: 104 news articles were featured on media doctor in the study period. Both online and print media scored poorly, although the print media were superior: mean total scores 56.1% satisfactory for print and 40.1% for online; percentage points difference 15.9 (95% CI, 8.3-23.6). The greatest differences were seen for the use of independent information sources, quantification of benefits and coverage of potential harms. CONCLUSIONS: Australian lay news reporting of medical advances, particularly by the online news services, is poor. This might improve if journals and researchers became more active in communicating with the press and the public.

Australia↗
PubMed2005

Glycyl-L-glutamine disposition in rat choroid plexus epithelial cells in primary culture: role of PEPT2.

PURPOSE: The purpose of this research was to determine the polarity and directionality of the PEPT2-mediated uptake and transepithelial transport of the neuropeptide glycyl-L-glutamine (GlyGln) in choroid plexus. METHODS: The transport kinetics of [3H]GlyGln was studied in neonatal rat choroid plexus epithelial cells in primary culture grown on laminin-coated Transwell filter inserts. Using a bicarbonate artificial cerebrospinal fluid (CSF) buffer (pH 7.4) at 37 degrees C, GlyGln studies were performed as a function of time, substrate concentration, and the presence of potential inhibitors (at 1 mM). RESULTS: GlyGln (2 microM) accumulation was about three to four times greater when introduced from the apical (CSF-facing) as opposed to the basal (blood-facing) side of the cell monolayer, and transepithelial transport was about two times greater in the apical-to-basal direction. The apical uptake of radiolabeled GlyGln (2 microM) was inhibited significantly by dipeptides (i.e., unlabeled GlyGln and cysteinylglycine) and some neuropeptides (i.e., carnosine, N-acetylaspartylglutamate, kyotorphin), but was unaffected by amino acids (i.e., glycine, glutamine) as well as by [D-Arg2]-kyotorphin and glutathione. The concentration-dependent apical uptake of GlyGln (2-1000 microM) was characterized by a high-affinity process (i.e., Vmax of 72 pmol/mg/min; Km of 136 microM), consistent with the properties of PEPT2. The intracellular hydrolysis of GlyGln was extensive, however, with only 40% of the dipeptide remaining intact after 1 h. CONCLUSIONS: The results demonstrate that PEPT2 plays an important role in regulating the apical uptake of GlyGln at the blood-CSF interface. Once inside the cell, GlyGln is rapidly degraded to its constitutive amino acids for further processing.

Animals↗
PubMed2005

Role and relevance of peptide transporter 2 (PEPT2) in the kidney and choroid plexus: in vivo studies with glycylsarcosine in wild-type and PEPT2 knockout mice.

The strategic localization of peptide transporter 2 (PEPT2), a proton-coupled oligopeptide transporter, to the apical membrane of epithelial cells in the kidney and choroid plexus suggests that it plays an important role in the disposition of peptides/mimetics in the body. Therefore, the in vivo significance of PEPT2 was investigated in wild-type and PEPT2 null mice following an i.v. bolus dose (0.05 micromol/g body weight) of [14C]glycylsarcosine (GlySar). In PEPT2 null mice, the clearance (total and renal) of GlySar was markedly increased (2-fold), resulting in concomitantly lower systemic concentrations. In addition, renal reabsorption was almost abolished, and GlySar was eliminated by glomerular filtration. Of the 46% of GlySar reabsorbed in wild-type mice, PEPT2 accounted for 86% and PEPT1 accounted for 14% of reabsorbed substrate. Analysis of GlySar uptake in kidney sections revealed that PEPT2 was primarily localized in the outer medullary region. Wild-type mice also had greater choroid plexus concentrations of GlySar and a 5-fold greater choroid plexus/cerebrospinal fluid (CSF) ratio as compared with null mice at 60 min. Null mice exhibited a greater CSF/blood ratio at 60 min (0.9 versus 0.2) and area under the curve (AUC)(CSF)/AUC(blood) ratio over 60 min (0.45 versus 0.12), indicating that PEPT2 significantly reduces the exposure of GlySar in CSF. Our in vivo results demonstrate that PEPT2 is the predominant peptide transporter in kidney and that it acts as an efflux transporter in choroid plexus. Thus, PEPT2 may have profound effects on the sensitivity and/or toxicity of peptides and peptide-like drugs.

Animals↗
PubMed2005

Determination of WR-1065 in human blood by high-performance liquid chromatography following fluorescent derivatization by a maleimide reagent ThioGlo3.

In order to improve the sensitivity and stability of human blood samples containing WR-1065 (i.e., active metabolite of the cytoprotective agent amifostine), a high-performance liquid chromatographic method was developed and validated using fluorescent derivatization with ThioGlo3. Using a sample volume of only 100 microl, the method was specific, sensitive (limit of quantitation=10 nM in deproteinized blood or 20 nM in whole blood), accurate (error < or = 3.2%) and reproducible (CV < or = 8.7%). In addition, the stability of WR-1065 in deproteinized and derivatized blood samples was assured for at least four weeks at -20 degrees C. This method should be particularly valuable in translating the kinetic-dynamic relationship of WR-1065 in preclinical models to that in cancer patients.

Amifostine↗
PubMed2005

[11C]Glycylsarcosine: synthesis and in vivo evaluation as a PET tracer of PepT2 transporter function in kidney of PepT2 null and wild-type mice.

[11C]Glycylsarcosine (Gly-Sar) was synthesized as a potential radiotracer to investigate the localization and in vivo function of the peptide transporter PepT2 in mouse kidney. Its C-11 labeled diketopiperazine derivative, [11C]cyclo(Gly-Sar) [1-methylpiperazine-2,5-dione], was also evaluated as a potential tracer. [11C]Gly-Sar exhibited rapid initial uptake into kidneys with slow clearance from the medulla, consistent with uptake and retention of the radiotracer through the actions of PepT2. In contrast, the corresponding cyclized dipeptide [11C]cyclo(Gly-Sar) showed rapid clearance and accumulation only in the renal pelvis region. Involvement of PepT2 in reabsorption and delayed clearance of [11C]Gly-Sar was confirmed using the PepT2 knockout mouse, where rapid renal elimination of [11C]Gly-Sar and the absence of radioactivity in medulla were observed. This study demonstrates using in vivo imaging technique that PepT2 is primarily responsible for renal tubular active reabsorption of Gly-Sar, and provides a new tool for studying tubular peptide reabsorption and clearance.

Animals↗
PubMed2005

Pharmacokinetics, safety, and tolerability of a depot formulation of naltrexone in alcoholics: an open-label trial.

BACKGROUND: Naltrexone is an effective medication for treatment of alcohol dependence, but its efficacy is limited by lack of adherence to the oral dosage form. A long-acting depot formulation of naltrexone may increase adherence. METHODS: A single site, 6-week open label study was conducted with 16 alcohol dependent subjects each receiving 300 mg of Naltrexone Depot by intramuscular injection. The main outcomes were safety and tolerability of the Naltrexone Depot formulation, blood levels of naltrexone and its main metabolite 6-beta naltrexol, and self-reported alcohol use. All subjects received weekly individual counseling sessions. RESULTS: The medication was well tolerated with 88% of subjects completing the 6-week trial. The most common side effect experienced was injection site complications. There were no serious adverse events. Subjects had naltrexone and 6-beta-naltrexol concentrations throughout the trial with mean values ranging from 0.58 ng/mL to 2.04 ng/mL and 1.51 ng/mL to 5.52 ng/mL, respectively, at each sampling time following administration. Compared to baseline, subjects had significantly reduced number of drinks per day, heavy drinking days and proportion of drinking days. CONCLUSION: Naltrexone Depot is safe and well tolerated in alcoholics and these findings support the further investigation of its utility in larger double-blind placebo controlled trials.

Adolescent↗
PubMed2005

New perspectives on ancient Mars.

Mars was most active during its first billion years. The core, mantle, and crust formed within approximately 50 million years of solar system formation. A magnetic dynamo in a convecting fluid core magnetized the crust, and the global field shielded a more massive early atmosphere against solar wind stripping. The Tharsis province became a focus for volcanism, deformation, and outgassing of water and carbon dioxide in quantities possibly sufficient to induce episodes of climate warming. Surficial and near-surface water contributed to regionally extensive erosion, sediment transport, and chemical alteration. Deep hydrothermal circulation accelerated crustal cooling, preserved variations in crustal thickness, and modified patterns of crustal magnetization.

Atmosphere↗
PubMed2005

Can drug design inhibit abuse?

A recent federal report indicates that prescription drug abuse is now the second leading category of illicit drug use, following marijuana use. Control strategies typically focus on reducing the diversion of prescription drugs from legitimate sources. The proliferation of unregulated Internet sources, however, has rendered control strategies less effective. This study examines a new approach that focuses on reducing abusability through the use of abuse-resistant drug designs. Drugs with and without such designs are compared and abuse levels assessed using multiple sources. In every instance, drugs employing abuse-resistant designs were found to have significantly lower levels of abuse than comparator drugs without such designs.

Clinical Pharmacy Information Systems↗
PubMed2004

Peptide and peptide analog transport systems at the blood-CSF barrier.

In addition to being the main source of cerebrospinal fluid (CSF) secretion, the choroid plexuses are involved in the supply and distribution of peptides to brain, the removal of toxic metabolites, the excretion of xenobiotics, and the delivery of drugs as an alternative route to the blood-brain barrier (BBB). The discovery of proton-coupled oligopeptide transporters in choroid plexus has generated considerable interest regarding their physiologic role at the blood-cerebrospinal fluid interface and their potential for peptide/antagonist pharmacotherapy in the central nervous system. Many of the same factors that affect the disposition of naturally occurring peptides in brain will also affect the disposition of exogenously delivered peptide or peptidomimetic drugs. Therefore, this review addresses three main areas: (1) choroid plexus structure, physiology, and barrier function in relation to peptide transport; (2) polypeptide transport and secretion mechanisms into cerebrospinal fluid; and (3) molecular physiology, expression, and functional activity of proton-coupled oligopeptide transporters in choroid plexus.

Animals↗
PubMed2004

Memory impairment in aged primates is associated with focal death of cortical neurons and atrophy of subcortical neurons.

Mechanisms of cognitive decline with aging remain primarily unknown. We determined whether localized cell loss occurred in brain regions associated with age-related cognitive decline in primates. On a task requiring the prefrontal cortex, aged monkeys were impaired in maintaining representations in working memory. Stereological quantification in area 8A, a prefrontal region associated with working memory, demonstrated a significant 32 +/- 11% reduction in the number of Nissl-stained neurons compared with young monkeys. Furthermore, the number of immunolabeled cholinergic neurons projecting to this region of cortex from the nucleus basalis was also reduced by 50 +/- 6%. In contrast, neuronal number was strikingly preserved in an adjoining prefrontal cortical region also associated with working memory, area 46, and in the component of the nucleus basalis projecting to this region. These findings demonstrate extensive but highly localized loss of neocortical neurons in aged, cognitively impaired monkeys that likely contributes to cognitive decline. Cell degeneration, when present, extends transneuronally.

Aging↗