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Eric Yang

Publications and source records attributed to Eric Yang.

15 recordsLinked to original sources
PubMed2007

Bioinformatics analysis of the early inflammatory response in a rat thermal injury model.

BACKGROUND: Thermal injury is among the most severe forms of trauma and its effects are both local and systemic. Response to thermal injury includes cellular protection mechanisms, inflammation, hypermetabolism, prolonged catabolism, organ dysfunction and immuno-suppression. It has been hypothesized that gene expression patterns in the liver will change with severe burns, thus reflecting the role the liver plays in the response to burn injury. Characterizing the molecular fingerprint (i.e., expression profile) of the inflammatory response resulting from burns may help elucidate the activated mechanisms and suggest new therapeutic intervention. In this paper we propose a novel integrated framework for analyzing time-series transcriptional data, with emphasis on the burn-induced response within the context of the rat animal model. Our analysis robustly identifies critical expression motifs, indicative of the dynamic evolution of the inflammatory response and we further propose a putative reconstruction of the associated transcription factor activities. RESULTS: Implementation of our algorithm on data obtained from an animal (rat) burn injury study identified 281 genes corresponding to 4 unique profiles. Enrichment evaluation upon both gene ontologies and transcription factors, verifies the inflammation-specific character of the selections and the rationalization of the burn-induced inflammatory response. Conducting the transcription network reconstruction and analysis, we have identified transcription factors, including AHR, Octamer Binding Proteins, Kruppel-like Factors, and cell cycle regulators as being highly important to an organism's response to burn response. These transcription factors are notable due to their roles in pathways that play a part in the gross physiological response to burn such as changes in the immune response and inflammation. CONCLUSION: Our results indicate that our novel selection/classification algorithm has been successful in selecting out genes with play an important role in thermal injury. Additionally, we have demonstrated the value of an integrative approach in identifying possible points of intervention, namely the activation of certain transcription factors that govern the organism's response.

Algorithms↗
PubMed2006

Does a stable isotopically labeled internal standard always correct analyte response? A matrix effect study on a LC/MS/MS method for the determination of carvedilol enantiomers in human plasma.

A stable isotopically labeled (SIL) analogue is believed to be the most appropriate internal standard in a quantitative bioanalytical liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay. It is assumed that a SIL internal standard always compensates for variability in chemical derivatization, sample extraction and LC/MS/MS analysis due to its nearly identical chemical and physical properties to the unlabeled analyte. Hence, the analyte to internal standard peak area ratio should be constant despite any variations in sample processing or analysis. However, in our laboratories, a deuterium labeled internal standard of carvedilol demonstrated an unexpected behavior-the analyte to internal standard peak area ratio changed with two specific lots of commercially supplied human plasma. Several experiments, including dilution of the extract with LC mobile phase and post-column infusion of the carvedilol solution followed by the injection of extracted blank plasma, have indicated that a high level of matrix suppression affected the ionization of the carvedilol-S enantiomer and its deuterated internal standard differently in these two lots of plasma. For the first time, it was clearly demonstrated that a slight difference in retention time between the analyte and the SIL internal standard, caused by deuterium isotope effect, has resulted in a different degree of ion suppression between these two analogues. This difference was significant enough to change the analyte to internal standard peak area ratio and affect the accuracy of the method.

Adrenergic Antagonists↗
PubMed2006

Relation of preprocedural statin therapy to in-hospital procedural complications following percutaneous coronary interventions in patients with hyperlipidemia.

We investigated whether the observed protective effect of hyperlipidemia is stronger in patients who take statins and, if so, whether that effect is likely due to patient characteristics associated with statin use. In-hospital complications and long-term outcomes of patients with hyperlipidemia (cholesterol level > or = 240 mg/dl) undergoing percutaneous coronary interventions (PCI) on statins (group Ia, n = 2,052) and not on statins (group Ib, n = 1,650) were compared with 726 patients with lower cholesterol levels (group II). Despite a higher prevalence of co-morbidities and worse angiographic characteristics in patients with hyperlipidemia, patients in group Ia had significantly lower in-hospital mortality (0% vs 2% in the other 2 groups, p < 0.001), a lower increase in the postprocedure creatine kinase-MB fraction (14% vs 27% in group Ib and 28% in group II, p < 0.001), and fewer PCI complications (15% vs 30% in groups Ib and II, p < 0.001). After adjustment, patients in group Ia had a significant decrease in complications (odds ratio 0.72, 95% confidence interval 0.65 to 0.92, p = 0.009). In contrast, those in group Ib had outcomes similar to those of patients with lower cholesterol. After application of propensity analysis to adjust for the likelihood of receiving statins based on clinical, angiographic, and procedural characteristics, group Ia had fewer in-hospital complications (odds ratio 0.75, 95% confidence interval 0.62 to 0.90, p = 0.002) and lower in-hospital mortality (odds ratio 0.32, 95% confidence interval 0.12 to 0.84, p = 0.021). After successful PCI, overall survival after dismissal and survival free of myocardial infarction and target vessel revascularization were similar. In conclusion, hyperlipidemia per se is not associated with lower in-hospital complications after PCI. The benefit is largely limited to patients on statin treatment.

Aged↗
PubMed2006

Incorporation of a nanosplitter interface into an LC-MS-RD system to facilitate drug metabolism studies.

In the work reported here, a novel interface, the nanosplitter, is incorporated into the drug metabolism laboratory in order to enhance the analytical capabilities of detecting and identifying drug-related metabolites to support drug metabolism studies during the drug development process. When an existing LC-MS-radiometric detector (RD) system is coupled with this nanosplitter, the system becomes capable of performing dynamic microspray under a typical analytical LC method. With the superior MS sensitivity offered by this system, most of the analytical LC methods developed for metabolite profiling can then be easily adopted for metabolite identification work. The improvement of these analytical capabilities can streamline the entire process of the drug metabolism study. In the experiments presented here, the nanosplitter interface coupled with analytical HPLC systems (e.g. 4.6 x 250 mm column @ 1 ml/min) demonstrated significant increases in MS signal (2x to 40x peak area) when compared to the standard LC-MS interface for both in vitro and in vivo metabolism studies. Furthermore, this signal gain facilitated the MS detection of additional metabolites (observed in the radiometric trace) that were below the MS level of detection when using the standard interface.

Animals↗
PubMed2006

Presbycusic neuritic degeneration within the osseous spiral lamina.

OBJECTIVE: To describe a neglected anatomic variant occurring with presbycusis. STUDY DESIGN: Retrospective temporal bone histopathology study. METHODS: Quantitative analysis of peripheral hair cells, neurites, neurons, and the stria vascularis in temporal bones from individuals who had presbycusis. Fifty-three patients aged 65 years or older and with a down-sloping audiogram and clinical diagnosis of presbycusis were reviewed. Nine cases had normal hair and ganglion cell populations but reduced peripheral processes (neuritic presbycusis). These were compared with five normal-hearing controls on measurements of anterior middle and basal turn fiber bundle diameter and the ratio of basal to middle diameters. RESULTS: Thresholds at 4 and 8 kHz were significantly poorer in the neuritic presbycusis group than in the control group (p<or=0.004 and 0.05, respectively), as was speech discrimination score (p<or=0.028). The ratio of basal to middle turn diameters was significantly smaller in the neuritic presbycusis group (p<or=0.003). This effect was quite marked in that there was no overlap in ratios between the groups, with the maximum neuritic presbycusis group ratio smaller than the minimum control group ratio. There was a moderate negative correlation between ratio and threshold at 4 kHz (sigma=-0.49, p<or=0.075). CONCLUSION: Loss of peripheral neurites in the anterior basal cochlear segment is found in conjunction with presbycusis in temporal bones that have no other morphologic abnormalities. These cases can be identified by a gradual down-sloping audiogram in contrast to sensory (hair cell) presbycusis, which is characterized by a precipitous high tone loss.

Aged↗
PubMed2006

Feasibility of a pressure wire and single arterial puncture for assessing aortic valve area in patients with aortic stenosis.

BACKGROUND: Determination of a transvalvular pressure gradient for measurement of aortic valve area (AVA) by hemodynamic cardiac catheterization usually requires 2 catheters and 2 arterial access sites. We assessed the feasibility of using a single arterial puncture and a 0.014 inch pressure wire for evaluation of aortic stenosis. METHODS: Eighteen patients (mean age, 76 years; 10 men) underwent hemodynamic catheterization for assessment of AVA. Cardiac output was determined by thermodilution (using a pulmonary artery catheter), and the transvalvular pressure gradient was obtained from simultaneous pressure recordings (using a pressure wire to measure left ventricular pressure and a 5 Fr catheter to measure ascending aortic pressure). RESULTS: This novel technique was technically feasible in all patients. Calibration of the pressure wire with the pressure of the fluid-filled catheter was possible and accurate in the left ventricle and aorta. The method required 36.4 +/- 9.6 minutes from injection of a local anesthetic to completion of AVA measurement; 53.3 +/- 18.6 minutes were required to finish all catheterization procedures, including coronary angiography. Measurements of AVA (mean, 1.01 +/- 0.43 cm2) and pressure gradients (mean, 27.5 +/- 10.5 mmHg) taken by a pressure wire were similar to measurements taken by Doppler echocardiography (1.07 +/- 0.58 cm2 and 32.9 +/- 12.1 mmHg, respectively); the correlation was significant (r = 0.856; p < 0.001, and r = 0.741; p < 0.001, respectively). CONCLUSIONS: Our findings suggest that a single arterial approach using a pressure wire is feasible, safe, accurate and rapid for the invasive assessment of aortic stenosis.

Aged↗
PubMed2005

Trapping 4-fluorobenzyl chloride in human plasma with chemical derivatization followed by quantitative bioanalysis using high-performance liquid chromatography/tandem mass spectrometry.

A quantitative bioanalytical method involving chemical derivatization, solid phase extraction (SPE) and high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) was developed for the determination of 4-fluorobenzyl chloride (4FBCl) in human plasma. 4FBCl is a volatile and reactive molecule that is very unstable in human plasma. In order to stabilize 4FBCl in plasma samples prior to storage, 4-dimethylaminopyridine (DMAP) was added, forming a stable quaternary amine salt derivative. A three-step weak cation-exchange SPE procedure was then employed to remove excess DMAP. The plasma extracts were analyzed by HPLC/MS/MS using a TurboIonspray interface and multiple reaction monitoring. Unlike 4FBCl, the quaternary amine derivative shows excellent sensitivity in electrospray mass spectrometry. The method was validated over a concentration range of 0.5-500 ng/mL using 45 microL of plasma. The maximum within-run and between-run precision observed in a three-run validation for quality control (QC) samples was 12.5 and 7.6%, respectively. The maximum percentage bias observed at all QC sample concentrations was 11.9%. The method has proven to be robust and compatible with high-throughput bioanalysis.

Benzyl Compounds↗
PubMed2005

A high-throughput liquid chromatography/tandem mass spectrometry method for screening glutathione conjugates using exact mass neutral loss acquisition.

Chemically reactive metabolites may cause hepatotoxicity and as a result liver failure or other adverse side reactions. Therefore, this is a vital topic of interest because early reactive metabolite screening may prevent compound failure at a later stage. In order to address this issue, a screening assay has been developed to detect the formation of reactive metabolites by using glutathione as a trapping reagent, which will allow us to search for phase I metabolites and also glutathiones during in vitro metabolite screening using liquid chromatography/tandem mass spectrometry (LC/MS/MS) with exact mass. Glutathione conjugations when fragmented by the mass spectrometer give a common loss corresponding to the pyroglutamic acid moiety, which can be monitored. Until recently, this work has been carried out with triple quadrupole technology using nominal mass. The advantage of the hybrid quadrupole time-of-flight mass spectrometer is the selectivity and sensitivity that can be achieved. Exact neutral loss detection is achieved via sequential low- and high-energy MS acquisitions. After detection of the loss of the pyroglutamic acid moiety, using a window of +/-20 mDa on the high-energy scan, MS/MS is carried out on the parent mass of interest to confirm the common neutral loss.

Algorithms↗
PubMed2005

Cyanide trapping of iminium ion reactive intermediates followed by detection and structure identification using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Secondary and tertiary alicyclic amines are widely found in pharmaceuticals and environmental compounds. The formation of iminium ions as reactive intermediates in the metabolic activation of alicyclic amines has previously been investigated in radiometric assays where radiolabeled cyanide is typically employed. In this paper, we report a relatively high throughput LC-MS/MS method for the detection of the nonradiolabeled cyanide adduct formed in rat or human liver microsomal incubations via constant neutral loss scan followed by structural characterization using product ion scan on a triple quadrupole mass spectrometer. A total of 14 alicyclic amine compounds were investigated with the cyanide trapping LC-MS/MS screen and also with the glutathione (GSH) trapping screen, a well-established and commonly employed technique for reactive metabolite screening. Our results are found to be in general agreement with the previous metabolism reports for these compounds, demonstrating the effectiveness, speed, and simplicity of the cyanide trapping LC-MS/MS method to study the iminium ion intermediates from alicyclic amines and its complementarities to GSH trapping method for reactive metabolite screenings.

Amines↗
PubMed2004

Stereoselective analysis of carvedilol in human plasma using HPLC/MS/MS after chiral derivatization.

A relatively high-throughput high-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) method using a chiral derivatization reagent was developed for the quantitative determination of carvedilol enantiomers in human plasma. S-carvedilol and R-carvedilol are extracted from human plasma by protein precipitation using acetonitrile containing racemic [(2)H(5)]-carvedilol as an internal standard. Extracts are then derivatized with 2,3,4,6-tetra-O-acetyl-beta-glucopyranosyl isothiocyanate (GITC) and analysed using HPLC-MS/MS with a TurboIonspray (TIS) interface and selected reaction monitoring. Using 150microL of plasma, the method was validated over a concentration range of 0.2-200ng/mL. The maximum within-run precision observed in a three run quality control was 8.2% for S-carvedilol and 6.7% for R-carvedilol, respectively. The maximum percentage bias observed at all quality control sample concentrations was 9.4% for S-carvedilol and 11.6% for R-carvedilol, respectively. The HPLC-MS/MS method was also compared with a previously developed high-performance LC/fluorescence method by analysing 25 samples containing racemic carvedilol. Based on results obtained, these two methods were found to be equivalent. However, compared with LC/fluorescence method, HPLC-MS/MS method is more sensitive, uses less plasma, and also employs a less time-consuming sample preparation process.

Carbazoles↗
PubMed2004

Improved liquid chromatography-mass spectrometry performance in quantitative analysis using a nanosplitter interface.

Several pairs of analytes in plasma were investigated to demonstrate the successful utility of a novel interface in quantitative bioanalytical LC-MS and LC-MS/MS. Recently in our laboratory, an interface (the nanosplitter) was developed that allows the coupling of normal-bore liquid chromatography with microelectrospray mass spectrometry. The post-column concentric split minimizes turbulence and is shown to produce significant gains in the mass spectrometric signal. This configuration of the splitter allows sampling of the center portion of the parabolic HPLC plug, which maintains chromatographic integrity while producing high split ratios and effectively conserving nearly 99.9% of the sample. When utilizing a Finnigan mass spectrometer (with a heated capillary interface design), the signal gain with the nanosplitter ranged from 5 to 16 times the peak area obtained using the conventional interface without splitting. The linearity of the nanosplitter and conventional interface are shown to be comparable for all analytes tested. The nanosplitter was also fitted to a Sciex mass spectrometer and the results were compared to those from turbo ionspray. While in this case no significant signal improvement was observed, when normalized to the actual analyte mass introduced into the MS, the mass sensitivity was still increased 270-fold. The variations in signal gain utilizing the nanosplitter on instruments from different manufacturers reflect the inherent differences in the source designs while confirming the benefits of coupling high flow LC separations with low flow mass spectrometric detection.

Chromatography, Liquid↗
PubMed2004

High-throughput liquid chromatography-tandem mass spectrometry determination of bupropion and its metabolites in human, mouse and rat plasma using a monolithic column.

In the present work, a high-throughput LC/MS/MS method using a Chromolith RP-18 (50 mm x 4.6 mm) monolithic column was developed and partially validated for the determination of bupropion (BUP), an anti-depressant drug, and its metabolites, hydroxybupropion and threo-hydrobupropion (TB), in human, mouse, and rat plasma. A modern integrated liquid chromatograph and an LC/MS/MS system with a TurboIonSpray (TIS) interface were used for the positive electrospray selected reaction monitoring (SRM) LC/MS analyses. Spiked control plasma calibration standards and quality control (QC) samples were extracted by semi-automated 96-well liquid-liquid extraction (LLE) using ethyl acetate. A mobile phase consisting of 8mM ammonium acetate-acetonitrile (55:45, v/v) delivered isocratically at 5 ml/min, and split post-column to 2 ml/min directed to the TIS, provided the optimum conditions for the chromatographic separation of bupropion and its metabolites within 23s. The isotope-labeled D(6)-bupropion and D(6)-hydroxybupropion were used as internal standards. The method was linear over a concentration range of 0.25-200 ng/ml (bupropion and threo-hydrobupropion), and 1.25-1000 ng/ml (hydroxybupropion). The intra- and inter-day assay accuracy and precision were within 15% for all analytes in each of the biological matrices. The monolithic column performance as a function of column backpressure, peak asymmetry, and retention time reproducibility was adequately maintained over 864 extracted plasma injections.

Animals↗
PubMed2004

Epstein-Barr virus-encoded dUTPase modulates immune function and induces sickness behavior in mice.

Epstein-Barr virus (EBV) is the causative agent of infectious mononucleosis (IM). In addition, latent infections with EBV are associated with nasopharyngeal carcinoma (NPC) and Burkitt's Lymphoma (BL). Antibodies to several EBV-encoded early antigens (EA) are often observed in patients with NPC and BL, however, the role of EBV-encoded proteins in the etiology of these and other EBV-associated diseases is not completely understood. The EA complex encodes for at least six different viral enzymes including deoxyuridine triphosphate nucleotidohydrolase (dUTPase). dUTPase has recently been shown to modulate activation of human peripheral blood mononuclear cells in vitro (unpublished data). Therefore, these studies were designed to test whether dUTPase would modulate immune function in an in vivo model. Mice were injected with purified EBV dUTPase, and baseline immune function and sickness behaviors were measured. EBV dUTPase treatment inhibited replication of mitogen-stimulated lymphocytes obtained from treated mice. These lymphocytes were also less able to synthesize interferon-gamma after re-stimulation. In addition, treatment with dUTPase induced sickness behaviors. For example, as compared to control animals, dUTPase-treated animals lost body mass, had elevated body temperature, and displayed diminished locomotor activity. These data suggest that individual viral proteins may play a role in the pathophysiology of EBV associated disease.

Animals↗
PubMed2004

Steady-state brain concentrations of antihistamines in rats: interplay of membrane permeability, P-glycoprotein efflux and plasma protein binding.

The purpose of this study was to measure the in vivo brain distribution of antihistamines and assess the influence of in vitro permeability, P-glycoprotein (Pgp) efflux, and plasma protein binding. Six antihistamines (acrivastine, chlorpheniramine, diphenhydramine doxylamine, fexofenadine, terfenadine) were selected based on previously reported in vitro permeability and Pgp efflux properties and dosed intravenously to steady-state plasma concentrations of 2-10 micromol/l in rats. Plasma and brain concentrations were measured by LC/MS/MS, and protein binding determined by ultrafiltration. Doxylamine, diphenhydramine and chlorpheniramine had brain-to-plasma concentration ratios of 4.34 +/- 1.26, 18.4 +/- 2.35 and 34.0 +/- 9.02, respectively. These drugs had high passive membrane permeability (>310 nm/s), moderate protein binding (71-84%) and were not Pgp substrates; features that yield high CNS penetration. In contrast, acrivastine and fexofenadine had low brain-to-plasma ratios of 0.072 +/- 0.014 and 0.018 + 0.002, consistent with low passive membrane permeability for both compounds (16.2 and 66 nm/s, respectively) and Pgp efflux. Finally, terfenadine had a brain-to-plasma ratio of 2.21 +/- 1.00 even though it underwent Pgp-mediated efflux (in vitro ratio = 2.88). Terfenadine's high passive permeability (285 nm/s) overcame the Pgp-mediated efflux to yield brain-to-plasma ratio >1. The brain-to-unbound plasma ratio was 22-fold higher suggesting that protein binding (96.3% bound) limited terfenadine's brain distribution. In conclusion, passive membrane permeability, Pgp-mediated efflux and/or high plasma protein binding influence the in vivo brain distribution of antihistamine drugs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗