Biomedical subjects

Gary A Thompson

Publications and source records attributed to Gary A Thompson.

11 recordsLinked to original sources

PubMed2006

Simultaneous determination of dextromethorphan, dextrorphan, and guaifenesin in human plasma using semi-automated liquid/liquid extraction and gradient liquid chromatography tandem mass spectrometry.

A method for the simultaneous determination of dextromethorphan (DEX), dextrorphan (DET), and guaifenesin (GG) in human plasma was developed, validated, and applied to determine plasma concentrations of these compounds in samples from six clinical pharmacokinetic (PK) studies. Semi-automated liquid handling systems were used to perform the majority of the sample manipulation including liquid/liquid extraction (LLE) of the analytes from human plasma. Stable-isotope-labeled analogues were utilized as internal standards (ISTDs) for each analyte to facilitate accurate and precise quantification. Extracts were analyzed using gradient liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Use of semi-automated LLE with LC-MS/MS proved to be a very rugged and reliable approach for analysis of more than 6200 clinical study samples. The lower limit of quantification was validated at 0.010, 0.010, and 1.0 ng/mL of plasma for DEX, DET, and GG, respectively. Accuracy and precision of quality control (QC) samples for all three analytes met FDA Guidance criteria of +/-15% for average QC accuracy with coefficients of variation less than 15%. Data from the thorough evaluation of the method during development, validation, and application are presented to characterize selectivity, linearity, over-range sample analysis, accuracy, precision, autosampler carry-over, ruggedness, extraction efficiency, ionization suppression, and stability. Pharmacokinetic data are also provided to illustrate improvements in systemic drug and metabolite concentration-time profiles that were achieved by formulation optimization.

Administration, Oral↗

PubMed2006

Transcriptomics and functional genomics of plant defence induction by phloem-feeding insects.

The relationship between phloem-feeding insects (PFIs) and plants offers an intriguing example of a highly specialized biotic interaction. These insects have evolved to survive on a nutritionally imbalanced diet of phloem sap, and to minimize wound responses in their host plants. As a consequence, plant perception of and responses to PFIs differ from plant interactions with other insect-feeding guilds. Transcriptome-wide analyses of gene expression are currently being applied to characterize plant responses to PFIs in crop plants with race-specific innate resistance, as well as in compatible interactions with susceptible hosts. Recent studies indicate that PFIs induce transcriptional reprogramming in their host plants, and that plant responses to PFIs appear to be quantitatively and qualitatively different from responses to other insects or pathogens. Transcript profiling studies also suggest that PFIs induce cell wall modifications, reduce photosynthetic activity, manipulate source-sink relations, and modify secondary metabolism in their hosts, and many of these responses appear to occur within the phloem tissue. Plant responses to these insects appear to be regulated in part by the salicylate, jasmonate, and ethylene signalling pathways. As additional transcript profiling data become available, forward and reverse genetic approaches will be necessary to determine which changes in gene expression influence resistance or susceptibility to PFIs.

Animals↗

PubMed2005

Cucurbit phloem serpins are graft-transmissible and appear to be resistant to turnover in the sieve element-companion cell complex.

Serpins are unique inhibitors of serine proteases that are located in various plant tissues and organs. An orthologue of the pumpkin (Cucurbita maxima) phloem serpin CmPS-1 was amplified from cucumber (Cucumis sativus) RNA by RT-PCR, cloned, and designated as CsPS-1 (GenBank accession no. AJ866989). Alternative amino acid sequences in the reactive centre loop suggest distinct inhibitory specificity between CmPS-1 and CsPS-1. A difference in the electrophoretic mobility of these serpins was used in heterografts to establish that serpins are phloem-mobile. Immuno light microscopy revealed that the phloem serpins are localized exclusively to sieve elements (SE), while the phloem filament protein CmPP1, used as a reference, is localized to both SEs and companion cells (CCs). Similar to CmPS-1, CsPS-1 accumulates over time in phloem exudates, indicating that serpins differ from other phloem-mobile proteins whose concentrations appear to be stable in phloem exudates. These differences could reflect alternative mechanisms regulating protein turnover and/or inaccessibility of protein degradation. The functionality of the pore/plasmodesma units connecting SEs and CCs was tested with graft-transmitted CmPP1 as a transport marker. The occurrence of CmPP1 in the CCs of the Cucumis graft partner shows that translocated 88 kDa phloem filament protein monomers can symplasmically exit the SE and accumulate in the CC. By contrast, serial sections probed with the serpin antibody demonstrate that the 43 kDa serpin does not enter CCs. Collectively, these data indicate that CCs play a decisive role in homeostasis of exudate proteins; proteins not accessing the CCs accumulate in SEs and display a time-dependent increase in concentration.

Amino Acid Sequence↗

PubMed2005

Influence of coadministration on the pharmacokinetics of azimilide dihydrochloride and digoxin.

The influence of coadministration on digoxin and azimilide pharmacokinetics/pharmacodynamics was assessed in a randomized, 3-way crossover study in 18 healthy men. Serial blood and urine samples were obtained for azimilide and digoxin quantitation. Treatment effects on pharmacokinetics were assessed using analysis of variance. The relationship between azimilide blood concentrations and QT(c) prolongation was characterized by an E(max) model. Effects of coadministration on pharmacodynamics were assessed using a mechanistic-based inhibition model. Azimilide pharmacokinetics was unaffected by digoxin, except for a 36% increase in CL(r) (P = .0325), with no change in CL(o). Digoxin pharmacokinetics was unaffected by azimilide, except for a 21% increase in C(max) (P = .0176) and a 10% increase in AUC(tau) (P = .0121). Digoxin coadministration increased the apparent EC(50) with no effect on E(max), consistent with competitive inhibition (K(i) = 0.899 ng/mL). The pharmacokinetic and pharmacodynamic changes observed upon coadministration were small and are not expected to be clinically important.

Adolescent↗

PubMed2004

Effect of mild and moderate hepatic impairment on azimilide pharmacokinetics following single dose oral administration.

Azimilide dihydrochloride (75-125 mg/day) is currently being developed for use in prolonging the time to recurrence of atrial fibrillation/flutter and for reducing the frequency of shocks in patients with an implantable cardioverting defibrillator. This study investigated the influence of mild and moderate hepatic impairment on azimilide pharmacokinetics. Six subjects each with mild and moderate hepatic impairment (Child-Pugh grades A and B, respectively) were age, weight, smoking status, and gender-matched to a healthy subject (total N = 24). Each subject was administered a single, oral dose of 100 mg azimilide dihydrochloride following an overnight fast. Blood/plasma and urine samples were collected up to 28 days and over 9 days, respectively, and analyzed using HPLC with MS/MS or UV detection. For azimilide, most parameters in subjects with mild to moderate hepatic impairment were within 25% of those observed in matched healthy subjects, with no statistically significant differences observed. For F-1292 (major metabolite in plasma), a significant decrease in AUC was observed in subjects with moderate hepatic impairment, secondary to an increase in renal clearance (CL(r)). Based on these results, no a priori dosage adjustment is required in subjects with mild to moderate hepatic impairment.

Administration, Oral↗

PubMed2004

Urinary excretion: does it accurately reflect relative differences in bioavailability/systemic exposure when renal clearance is nonlinear?

PURPOSE: The purpose of this study was to assess the influence of nonlinear renal clearance on the ability of urinary excretion data to accurately determine relative differences in systemic exposure and bioavailability. METHODS: Serum concentration and urinary excretion-time profiles were simulated assuming an open one-compartmental model with first-order absorption, linear nonrenal clearance, and either linear or nonlinear renal clearance (saturable secretion). Renal clearance comprised 5% or 95% of total clearance. Doses were varied over a 100-fold range (10-fold decrease/increase from the reference dose). Relative systemic exposures were based on the ratios of AUC and C(max) and the corresponding ratios of cumulative amount excreted in urine (A(e)) and the maximum urinary excretion rate. Relative bioavailability was based on the ratios of A(e) and the test to reference dose (D(ratio)). RESULTS: When renal clearance was linear and urinary excretion data were used to assess relative systemic exposure and relative bioavailability, no significant errors in accuracy were observed. However, when renal clearance was nonlinear, errors in the accuracy of estimation of relative bioavailability (Clr =5% only) and relative systemic exposure ranged from -53% to +125%; minimal error in accuracy existed in the estimation of relative bioavailability when Clr = 95% (-3% to +6%). CONCLUSIONS: Prior to the use of urinary excretion data to assess relative systemic exposure or bioavailability, the relationship between serum concentration and renal clearance should be established.

Algorithms↗

PubMed2004

Influence of ketoconazole on azimilide pharmacokinetics in healthy subjects.

AIM: To assess the influence of ketoconazole on azimilide pharmacokinetics. METHODS: A two-period randomized crossover study was conducted in healthy male and female subjects (19-45 years). Placebo or 200 mg ketoconazole were administered orally every 24 h for 29 days. On day 8, a single oral dose of 125 mg azimilide dihydrochloride was coadministered following an overnight fast. Blood samples were obtained prior to and for 22 days following azimilide dihydrochloride administration. The plasma protein binding of azimilide was also assessed at 6 h after dosing. RESULTS: Following ketoconazole administration, a 16% increase in azimilide AUC (90% confidence interval (CI) 112%, 120%), a 12% increase in C(max) (95% CI 107%, 116%), a 13% increase in t(1/2,z) (95% CI 107%, 120%) and a 14% decrease in CL(o) (95% CI 82%, 90%) were observed. CONCLUSIONS: The changes in azimilide pharmacokinetics following ketoconazole treatment are not clinically important since the 90% CI for the AUC fell within the prespecified range of 80-125%. Thus, no clinically important drug interactions are expected when azimilide dihydrochloride is coadministered with CYP3A4 inhibitors.

Adult↗

PubMed2004

Influence of azimilide on CYP2C19-mediated metabolism.

The purpose of this study was to assess the influence of multiple-dose oral administration of azimilide dihydrochloride on CYP2C19-mediated metabolism. A two-period, randomized crossover study was conducted in 40 healthy male subjects who were phenotyped as extensive CYP2C19 metabolizers. Oral doses of placebo or 125 mg of azimilide dihydrochloride were administered every 12 hours for 3 days, followed by every 24 hours for 5 days; 20 mg omeprazole was coadministered on Day 8. Blood or plasma samples were obtained over 24 hours and analyzed for azimilide or omeprazole/5-hydroxyomeprazole using high-performance liquid chromatography with tandem mass spectrometry. Data were analyzed using "noncompartmental" analysis. Azimilide blood concentrations observed in this study were similar to those previously observed at steady state in patients. Based on AUC(m)/AUC(p) for omeprazole, azimilide does not significantly inhibit CYP2C19-mediated metabolism (90% confidence interval [CI] = 104%-111%). For 5-hydroxyomeprazole, no significant changes in pharmacokinetics were observed. For omeprazole, a statistically significant decrease ( approximately 12%) was observed for AUC. However, this change was small and is not expected to be clinically important since the CI was contained within those used to establish bioequivalence. These results indicate that azimilide does not inhibit CYP2C19-mediated metabolism. Since this isozyme had the lowest in vitro IC(50) values for the cytochrome P450s most commonly involved with the metabolism of drugs (CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4), azimilide-related drug interactions mediated via these isozymes are not anticipated.

Adult↗

PubMed2003

Diversity of the superfamily of phloem lectins (phloem protein 2) in angiosperms.

Phloem protein 2 (PP2) is one of the most abundant and enigmatic proteins in the phloem sap. Although thought to be associated with structural P-protein, PP2 is translocated in the assimilate stream where its lectin activity or RNA-binding properties can exert effects over long distances. Analyzing the diversity of these proteins in vascular plants led to the identification of PP2-like genes in species from 17 angiosperm and gymnosperm genera. This wide distribution of PP2 genes in the plant kingdom indicates that they are ancient and common in vascular plants. Their presence in cereals and gymnosperms, both of which lack structural P-protein, also supports a wider role for these proteins. Within this superfamily, PP2 proteins have considerable size polymorphism. This is attributable to variability in the length of the amino terminus that extends from a highly conserved domain. The conserved PP2 domain was identified in the proteins encoded by six genes from several cucurbits, celery (Apium graveolens), and Arabidopsis that are specifically expressed in the sieve element-companion cell complex. The acquisition of additional modular domains in the amino-terminal extensions of other PP2-like proteins could reflect divergence from its phloem function.

Amino Acid Sequence↗

PubMed2002

Gene expression profiling of Arabidopsis thaliana in compatible plant-aphid interactions.

Phloem feeding involves unique biological interactions between the herbivore and its host plant. The economic importance of aphids, whiteflies, and other phloem-feeding insects as pests has prompted research to isolate sources of resistance to piercing-sucking insects in crops. However, little information exists about the molecular nature of plant sensitivity to phloem feeding. Recent discoveries involving elicitation by plant pathogens and chewing insects and limited studies on phloem feeders suggest that aphids are capable of inducing responses in plants broadly similar to those associated with pathogen infection and wounding. Our past work showed that compatible aphid feeding on leaves of Arabidopsis thaliana induces localized changes in levels of transcripts of genes that are also associated with infection, mechanical damage, chewing herbivory, or resource allocation shifts. We used microarray and macroarray gene expression analyses of infested plants to better define the response profile of A. thaliana to M. persicae feeding. The results suggest that genes involved in oxidative stress, calcium-dependent signaling, pathogenesis-related responses, and signaling are key components of this profile in plants infested for 72 or 96 h. The use of plant resistance to aphids in crops will benefit from a better understanding of induced responses. The establishment of links between insect elicitation, plant signaling associated with phloem feeding, and proximal resistance mechanisms is critical to further research progress in this area.

Animals↗

PubMed2002

Effect of severe renal impairment on the pharmacokinetics of azimilide following single dose oral administration.

AIMS: To assess the influence of severe renal impairment on azimilide pharmacokinetics. METHODS: A single oral dose of 125 mg azimilide dihydrochloride was administered to subjects with normal and severely impaired renal function. Blood and urine samples were collected for 22-28 and 10 days, respectively. RESULTS: Azimilide renal clearance decreased in subjects with renal impairment (mean 14 vs 4.8 ml h-1 kg-1, 95% confidence interval on the ratio 0.23, 0.50). However, no change in any other pharmacokinetic parameter including oral clearance (mean 109 vs 104 ml h-1 kg-1, 95% confidence interval on the ratio 0.67, 1.36) was observed. CONCLUSIONS: Since azimilide blood concentrations are essentially unaffected by renal function, an a priori dosage regimen adjustment is not required in patients with renal impairment.

Administration, Oral↗