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1.  Bioanalytical techniques for detecting biomarkers of response to human asbestos exposure 
Bioanalysis  2015;7(9):1157-1173.
Asbestos exposure is known to cause lung cancer and mesothelioma and its health and economic impacts have been well documented. The exceptionally long latency periods of most asbestos-related diseases have hampered preventative and precautionary steps thus far. We aimed to summarize the state of knowledge on biomarkers of response to asbestos exposure. Asbestos is not present in human biological fluids; rather it is inhaled and trapped in lung tissue. Biomarkers of response, which reflect a change in biologic function in response to asbestos exposure, are analyzed. Several classes of molecules have been studied and evaluated for their potential utility as biomarkers of asbestos exposure. These studies range from small molecule oxidative stress biomarkers to proteins involved in immune responses.
PMCID: PMC4487641  PMID: 26039812
2.  8-Oxo-2′-Deoxyguanosine as a Biomarker of Tobacco Smoking-Induced Oxidative Stress 
Free radical biology & medicine  2012;53(3):610-617.
7,8-Dihydro-8-oxo-2′-deoxyguanosine (8-oxo-dGuo) is a useful biomarker of oxidative stress. However, its analysis can be challenging because 8-oxo-dGuo must be quantified in the presence of dGuo, without artifactual conversion to 8-oxo-dGuo. Urine is the ideal biological fluid for population studies, since it can be obtained non-invasively and it is less likely that artifactual oxidation of dGuo can occur because of the relatively low amounts that are present when compared with hydrolyzed DNA. Stable isotope dilution liquid chromatography/selected reaction monitoring-mass spectrometry (LC-SRM/MS) with [15N5]-8-oxo-dGuo as internal standard provided the highest possible specificity for 8-oxo-dGuo analysis. Furthermore, artifact formation was determined by addition of [13C1015N5]-dGuo and monitoring its conversion to [13C1015N5]-8-oxo-dGuo during the analytical procedure. 8-Oxo-dGuo concentrations were normalized for inter-individual differences in urine flow by analysis of creatinine using stable isotope dilution LC-SRM/MS. A significant increase in urinary 8-oxo-dGuo was observed in tobacco smokers when compared with non-smokers using either simple urinary concentrations or after normalization for creatinine excretion. The mean levels of 8-oxo-dGuo were 1.65 ng/mL and the levels normalized to creatinine were 1.72 μg/g creatinine. Therefore, stable isotope dilution LC-SRM/MS analysis of urinary 8-oxo-dGuo complements urinary isoprostane (isoP) analysis for assessing tobacco-smoking-induced oxidative stress. This method will be particularly useful for studies that employ polyunsaturated fatty acids, where reduction in arachidonic acid precursor could confound isoP measurements.
PMCID: PMC4283839  PMID: 22613262
stable isotope dilution; liquid chromatography-mass spectrometry; 8-oxo-dGuo; urine; oxidative DNA damage
3.  Metabolism of a Representative Oxygenated Polycyclic Aromatic Hydrocarbon (PAH) Phenanthrene-9,10-quinone in Human Hepatoma (HepG2) Cells 
Chemical Research in Toxicology  2014;27(5):852-863.
Exposure to polycyclic aromatic hydrocarbons (PAHs) in the food chain is the major human health hazard associated with the Deepwater Horizon oil spill. Phenanthrene is a representative PAH present in crude oil, and it undergoes biological transformation, photooxidation, and chemical oxidation to produce its signature oxygenated derivative, phenanthrene-9,10-quinone. We report the downstream metabolic fate of phenanthrene-9,10-quinone in HepG2 cells. The structures of the metabolites were identified by HPLC–UV–fluorescence detection and LC–MS/MS. O-mono-Glucuronosyl-phenanthrene-9,10-catechol was identified, as reported previously. A novel bis-conjugate, O-mono-methyl-O-mono-sulfonated-phenanthrene-9,10-catechol, was discovered for the first time, and evidence for both of its precursor mono conjugates was obtained. The identities of these four metabolites were unequivocally validated by comparison to authentic enzymatically synthesized standards. Evidence was also obtained for a minor metabolic pathway of phenanthrene-9,10-quinone involving bis-hydroxylation followed by O-mono-sulfonation. The identification of 9,10-catechol conjugates supports metabolic detoxification of phenanthrene-9,10-quinone through interception of redox cycling by UGT, COMT, and SULT isozymes and indicates the possible use of phenanthrene-9,10-catechol conjugates as biomarkers of human exposure to oxygenated PAH.
PMCID: PMC4028327  PMID: 24646012
As part of the Family Smoking Prevention and Tobacco Control Act, the United States Food and Drug Administration charged the Tobacco Products Scientific Advisory Committee with developing a report and recommendations regarding the effect of menthol in cigarettes on the public health. The purpose of this study was to examine smoking behaviors, biomarkers of exposure and subjective responses when switching from a novel menthol cigarette to a non-menthol cigarette to isolate the effect of menthol and to approximate the effect a menthol ban might have on smokers.
Thirty two adult smokers completed this 35-day randomized, open-label, laboratory study. After a 5-day baseline period, participants were randomized to the experimental group (n=22) where they would smoke menthol Camel Crush for 15 days followed by 15 days of non-menthol Camel Crush, or the control group (n=10) where they smoked their own brand cigarette across all periods. Participants attended study visits every five days and completed measures of smoking rate, smoking topography, biomarkers of exposure, and subjective responses.
Although total puff volume tended to increase when the experimental group switched from menthol to non-menthol (p=0.06), there were no corresponding increases in cigarette consumption or biomarkers of exposure (ps>0.1). Subjective ratings related to taste and smell decreased during the non-menthol period (ps<0.01), compared to the menthol.
Results suggest menthol has minimal impact on smoking behaviors, biomarkers of exposure and subjective ratings.
When controlling for all other cigarette design features, menthol in cigarettes had minimal effect on outcome measures.
PMCID: PMC3596436  PMID: 23334588
cigarette; menthol; smoking; nicotine; behavior
5.  Dietary Flaxseed in Non-Small Cell Lung Cancer Patients Receiving Chemoradiation 
The standard of care in Locally-Advanced Non-Small Cell Lung Cancer (LA-NSCLC) is chemotherapy and radiation; however, Radiation-Induced Lung Injury (RILI), which may be prevented by the anti-inflammatory and anti-oxidant properties of Flaxseed (FS), impedes its maximum benefit.
Materials and Methods
Patients with LA-NSCLC requiring definitive RT were randomized to one FS or control muffin daily from start to 2 weeks after RT. Blood and urine were collected to quantify plasma FS metabolites, Enterodione (ED) and Enterolactone (EL), and urinary oxidative stress biomarkers, 8, 12-iso-iPF2a-VI (isoprostane) and 8-oxo-7,8-dihydro-2′deoxyguanosine (8-oxo-dGuo). Tolerability was defined as consuming ≥ 75% of the intended muffins and no ≥ grade 3 gastrointestinal toxicities.
Fourteen patients (control,7; FS,7) were enrolled. The tolerability rates were 42.9 versus 71.4% (p=0.59) for FS and control, respectively. Mean percentages of intended number of muffins consumed were 37% versus 73% (p=0.12). ED and EL increased at onset of FS and decreased with discontinuation, confirming bioavailability. Isoprostane and 8-oxo-dGuo were detectable. There was a trend towards decreased rates of pneumonitis in FS.
This is the first study to report FS bioavailability and quantify oxidative stress markers in NSCLC patients. FS in the administered muffin formulation did not meet tolerability criteria. Given the promising mechanism of FS as a radioprotectant, further investigations should focus on the optimal method for administration of FS.
PMCID: PMC3932620  PMID: 24575360
Flaxseed; Lignan; Radiation; Isoprostane; 8-oxo dGuo; Non-small cell lung cancer; Radiation induced lung injury; RILI; Pneumonitis; Fibrosis; Esophagitis
6.  Stereospecific reduction of 5β-reduced steroids by human ketosteroid reductases of the AKR (aldo-keto reductase) superfamily: role of AKR1C1–AKR1C4 in the metabolism of testosterone and progesterone via the 5β-reductase pathway 
The Biochemical journal  2011;437(1):10.1042/BJ20101804.
Active sex hormones such as testosterone and progesterone are metabolized to tetrahydrosteroids in the liver to terminate hormone action. One main metabolic pathway, the 5β-pathway, involves 5β-steroid reductase (AKR1D1, where AKR refers to the aldo-keto reductase superfamily), which catalyses the reduction of the 4-ene structure, and ketosteroid reductases (AKR1C1–AKR1C4), which catalyse the subsequent reduction of the 3-oxo group. The activities of the four human AKR1C enzymes on 5β-dihydrotestosterone, 5β-pregnane-3,20-dione and 20α-hydroxy-5β-pregnan-3-one, the intermediate 5β-dihydrosteroids on the 5β-pathway of testosterone and progesterone metabolism, were investigated. Product characterization by liquid chromatography–MS revealed that the reduction of the 3-oxo group of the three steroids predominantly favoured the formation of the corresponding 3α-hydroxy steroids. The stereochemistry was explained by molecular docking. Kinetic properties of the enzymes identified AKR1C4 as the major enzyme responsible for the hepatic formation of 5β-tetrahydrosteroid of testosterone, but indicated differential routes and roles of human AKR1C for the hepatic formation of 5β-tetrahydrosteroids of progesterone. Comparison of the kinetics of the AKR1C1–AKR1C4-catalysed reactions with those of AKR1D1 suggested that the three intermediate 5β-dihydrosteroids derived from testosterone and progesterone are unlikely to accumulate in liver, and that the identities and levels of 5β-reduced metabolites formed in peripheral tissues will be governed by the local expression of AKR1D1 and AKR1C1–AKR1C3.
PMCID: PMC3825703  PMID: 21521174
dihydrosteroid; hydroxysteroid dehydrogenases; liquid-chromatography–MS (LC–MS); steroid metabolism; tetrahydrosteroid
7.  Antioxidant protection by PECAM-targeted delivery of a novel NADPH-oxidase inhibitor to the endothelium in vitro and in vivo 
Oxidant stress caused by pathological elevation of reactive oxygen species (ROS) production in the endothelial cells lining the vascular lumen is an important component of many vascular and pulmonary disease conditions. NADPH oxidase (NOX) activated by pathological mediators including angiotensin and cytokines is a major source of endothelial ROS. In order to intercept this pathological pathway, we have encapsulated an indirect NOX inhibitor, MJ33, into immunoliposomes (Ab-MJ33/IL) targeted to endothelial marker platelet endothelial cell adhesion molecule (PECAM-1). Ab-MJ33/IL, but not control IgG-MJ33/IL specifically bound to endothelium and attenuated angiotensin-induced ROS production in vitro and in vivo. Additionally, Ab-MJ33/IL inhibited endothelial expression of the inflammatory marker vascular cell adhesion molecule (VCAM) in cells and animals challenged with the cytokine TNF. Furthermore, Ab-MJ33/IL alleviated pathological disruption of endothelial permeability barrier function in cells exposed to vascular endothelial growth factor (VEGF) and in the lungs of mice challenged with lipopolysaccharide (LPS). Of note, the latter beneficial effect has been achieved both by prophylactic and therapeutic injection of Ab-MJ33/IL in animals. Therefore, specific suppression of ROS production by NOX in endothelium, attainable by Ab-MJ33/IL targeting, may help deciphering mechanisms of vascular oxidative stress and inflammation, and potentially improve treatment of these conditions.
PMCID: PMC3495982  PMID: 22974832
8.  Bisphenol A Exposure Disrupts Genomic Imprinting in the Mouse 
PLoS Genetics  2013;9(4):e1003401.
Exposure to endocrine disruptors is associated with developmental defects. One compound of concern, to which humans are widely exposed, is bisphenol A (BPA). In model organisms, BPA exposure is linked to metabolic disorders, infertility, cancer, and behavior anomalies. Recently, BPA exposure has been linked to DNA methylation changes, indicating that epigenetic mechanisms may be relevant. We investigated effects of exposure on genomic imprinting in the mouse as imprinted genes are regulated by differential DNA methylation and aberrant imprinting disrupts fetal, placental, and postnatal development. Through allele-specific and quantitative real-time PCR analysis, we demonstrated that maternal BPA exposure during late stages of oocyte development and early stages of embryonic development significantly disrupted imprinted gene expression in embryonic day (E) 9.5 and 12.5 embryos and placentas. The affected genes included Snrpn, Ube3a, Igf2, Kcnq1ot1, Cdkn1c, and Ascl2; mutations and aberrant regulation of these genes are associated with imprinting disorders in humans. Furthermore, the majority of affected genes were expressed abnormally in the placenta. DNA methylation studies showed that BPA exposure significantly altered the methylation levels of differentially methylated regions (DMRs) including the Snrpn imprinting control region (ICR) and Igf2 DMR1. Moreover, exposure significantly reduced genome-wide methylation levels in the placenta, but not the embryo. Histological and immunohistochemical examinations revealed that these epigenetic defects were associated with abnormal placental development. In contrast to this early exposure paradigm, exposure outside of the epigenetic reprogramming window did not cause significant imprinting perturbations. Our data suggest that early exposure to common environmental compounds has the potential to disrupt fetal and postnatal health through epigenetic changes in the embryo and abnormal development of the placenta.
Author Summary
BPA is a widely used compound to which humans are exposed, and recent studies have demonstrated the association between exposure and adverse developmental outcomes in both animal models and humans. Unfortunately, exact mechanisms of BPA–induced health abnormalities are unclear, and elucidation of these relevant biological pathways is critical for understanding the public health implication of exposure. Recently, increasing data have demonstrated the ability of BPA to induce changes in DNA methylation, suggesting that epigenetic mechanisms are relevant. In this work, we study effects of BPA exposure on expression and regulation of imprinted genes in the mouse. Imprinted genes are regulated by differential DNA methylation, and they play critical roles during fetal, placental, and postnatal development. We have found that fetal exposure to BPA at physiologically relevant doses alters expression and methylation status of imprinted genes in the mouse embryo and placenta, with the latter tissue exhibiting the more significant changes. Additionally, abnormal imprinting is associated with defective placental development. Our data demonstrate that BPA exposure may perturb fetal and postnatal health through epigenetic changes in the embryo as well as through alterations in placental development.
PMCID: PMC3616904  PMID: 23593014
9.  Effects of 21 days of varenicline versus placebo on smoking behaviors and urges among non-treatment seeking smokers 
Varenicline promotes smoking cessation and reduces urges to smoke. However, the mechanisms associated with these effects and their time course are not well characterized. One mechanism may be extinction, but the duration of the current dosing protocol may not be sufficient. We examined the effect of extended pre-treatment with varenicline on smoking behavior among 17 non-treatment seeking adult smokers. Using a within-subjects, double-blind, placebo-controlled crossover design, participants received standard dosing of varenicline for 21 days, followed by a 14-day washout period and 21 days of placebo; order counterbalanced. Cigarettes per day (CPD), smoking topography, smoking urges (QSU), and side effects were assessed every three days. Biomarkers (e.g. nicotine metabolites) were collected on days 1, 7, and 21. There was a significant drug by time interaction indicating a reduction in CPD during varenicline phase (between days 10–21), but no reduction during placebo. Varenicline also led to reductions in nicotine metabolites and urges to smoke. Among this sample of non-treatment seeking smokers, varenicline significantly reduced smoking behavior. Results have important treatment implications because changes in CPD and craving did not occur until after the typical one-week run-up period. This suggests that a longer duration of pre-treatment may be beneficial for some smokers.
PMCID: PMC3526838  PMID: 22695488
Cigarette smoking; varenicline; nicotine; positive reinforcement; smoking cessation
10.  Targeted Chiral Analysis of Bioactive Arachidonic Acid Metabolites Using Liquid-Chromatography-Mass Spectrometry 
Metabolites  2012;2(2):337-365.
A complex structurally diverse series of eicosanoids arises from the metabolism of arachidonic acid. The metabolic profile is further complicated by the enantioselectivity of eicosanoid formation and the variety of regioisomers that arise. In order to investigate the metabolism of arachidonic acid in vitro or in vivo, targeted methods are advantageous in order to distinguish between the complex isomeric mixtures that can arise by different metabolic pathways. Over the last several years this targeted approach has become more popular, although there are still relatively few examples where chiral targeted approaches have been employed to directly analyze complex enantiomeric mixtures. To efficiently conduct targeted eicosanoid analyses, LC separations are coupled with collision induced dissociation (CID) and tandem mass spectrometry (MS/MS). Product ion profiles are often diagnostic for particular regioisomers. The highest sensitivity that can be achieved involves the use of selected reaction monitoring/mass spectrometry (SRM/MS); whereas the highest specificity is obtained with an SRM transitions between an intense parent ion, which contains the intact molecule (M) and a structurally significant product ion. This review article provides an overview of arachidonic acid metabolism and targeted chiral methods that have been utilized for the analysis of the structurally diverse eicosanoids that arise.
PMCID: PMC3901208  PMID: 24957514
arachidonic acid; eicosanoids; chiral liquid chromatography; tandem mass spectrometry; selected reaction monitoring; atmospheric pressure chemical ionization; electron capture; cyclooxygenase; lipoxygenase; cytochrome P-450
11.  A new liquid chromatography/mass spectrometry method for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in urine 
4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a carcinogenic nitrosamine produced upon curing tobacco. It is present in tobacco smoke and undergoes metabolism to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in the lungs. NNAL undergoes further uridine diphosphate glucuronosyltransferase (UGT)-mediated metabolism to give N- and O-glucuronide metabolites, which together with free (non-conjugated) NNAL are then excreted in the urine. The ability to conduct validated analyses of free and conjugated NNAL in human urine is important in order to assess inter-individual differences in lung cancer risk from exposure to cigarette smoke. The use of stable isotope dilution (SID) methodology in combination with liquid chromatography/multiple reaction monitoring/mass spectrometry (LC/MRM-MS) provides the highest bioanalytical specificity possible for such analyses. We describe a novel derivatization procedure, which results in the formation of a pre-ionized N-propyl-NNAL derivative. The increased LC/MS sensitivity arising from this derivative then makes it possible to analyze free NNAL in only 0.25 mL urine. This substantial reduction in urine volume when compared with other methods that have been developed will help preserve the limited amounts of stored urine samples that are available from on-going longitudinal biomarker studies. The new high sensitivity SID LC/MRM-MS assay was employed to determine free and conjugated NNAL concentrations in urine samples from 60 individual disease-free smokers. Effects of inter-individual differences in urinary creatinine clearance on NNAL concentrations were then assessed and three metabolizer phenotypes were identified in the 60 subjects from the ratio of urinary NNAL glucuronides/free NNAL. Poor metabolizers (PMs, 14 subjects) with a ratio of NNAL glucuronides/free NNAL <2 (mean = 1.3), intermediate metabolizers (IMs, 36 subjects) with a ratio between 2 and 5 (mean = 3.4), and extensive metabolizers (EMs, 10 subjects) with a ratio >5 (mean = 11.1).
PMCID: PMC3348551  PMID: 21154658
12.  Analysis of epoxyeicosatrienoic acids by chiral liquid chromatography/electron capture atmospheric pressure chemical ionization mass spectrometry using [13C]-analog internal standards 
The metabolism of arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) is thought to be mediated primarily by the cytochromes P450 (P450s) from the 2 family (2C9, 2C19, 2D6, and 2J2). In contrast, P450s of the 4 family are primarily involved in omega oxidation of AA (4A11 and 4A22). The ability to determine enantioselective formation of the regioisomeric EETs is important in order to establish their potential biological activities and to asses which P450 isoforms are involved in their formation. It has been extremely difficult to analyze individual EET enantiomers in biological fluids because they are present in only trace amounts and they are extremely difficult to separate from each other. In addition, the deuterium-labeled internal standards that are commonly used for stable isotope dilution liquid chromatography/mass spectrometry (LC/MS) analyses have different LC retention times when compared with the corresponding protium forms. Therefore, quantification by LC/MS-based methodology can be compromised by differential suppression of ionization of the closely eluting isomers. We report the preparation of [13C20]-EET analog internal standards and the use of a validated high-sensitivity chiral LC/electron capture atmospheric pressure chemical ionization (ECAPCI)-MS method for the trace analysis of endogenous EETs as their pentafluorobenzyl (PFB) ester derivatives. The assay was then used to show the exquisite enantioselectivity of P4502C19-, P4502D6-, P4501A1-, and P4501B1-mediated conversion of AA into EETs and to quantify the enantioselective formation of EETs produced by AA metabolism in a mouse epithelial hepatoma (Hepa) cell line.
PMCID: PMC3348553  PMID: 20972997
13.  Prediction of Postoperative Recurrence-Free Survival in Non-small Cell Lung Cancer by Using an Internationally Validated Gene Expression Model 
This study was performed to discover prognostic genomic markers associated with post-operative outcome of stage I-III non-small cell lung cancer (NSCLC) that are reproducible between geographically distant and demographically distinct patient populations.
Experimental design
American patients (n=27) were stratified on the basis of recurrence and microarray profiling of their tumors was performed to derive a training set of 44 genes. A larger Korean patient validation cohort (n=138) was also stratified by recurrence and screened for these genes. Four reproducible genes were identified and used to construct genomic and clinicogenomic Cox models for both cohorts.
Four genomic markers, DBN1 (drebrin 1), CACNB3 (calcium channel beta 3), FLAD1 (PP591; flavin adenine dinucleotide synthetase), and CCND2 (cyclin D2), exhibited highly significant differential expression in recurrent tumors in the training set (P<0.001). In the validation set, DBN1, FLAD1 (PP591) and CACNB3 were significant by Cox univariate analysis (P≤0.035), whereas only DBN1 was significant by multivariate analysis. Genomic and clinicogenomic models for recurrence free survival (RFS) were equally effective for risk stratification of stage I-II or I-III patients (all models P<0.0001). For stage I-II or I-III patients, 5-y RFS of the low- and high-risk patients was ∼ 70 vs. 30% for both models. The genomic model for overall survival (OS) of stage I-III patients was improved by addition of pT and pN stage (P<0.0013 vs. 0.010).
A 4-gene prognostic model incorporating the multivariate marker DBN1 exhibits potential clinical utility for risk stratification of stage I-III NSCLC patients.
PMCID: PMC3086939  PMID: 21242119
NSCLC recurrence; DBN1; CACNB3; FLAD1; CCND2
14.  Nicotine exposure and metabolizer phenotypes from analysis of urinary nicotine and its 15 metabolites by LC–MS 
Bioanalysis  2011;3(7):745-761.
Smokers who inhale less deeply are exposed to lower amounts of the toxic substances present in tobacco smoke. In order to more rigorously assess tobacco smoke exposure, it is necessary to have an accurate method for quantifying nicotine and all of its known metabolites.
A stable-isotope dilution LC–MRM/MS assay has been developed for quantification of urinary nicotine and the 15 possible metabolites that could arise from known metabolic pathways. Nicotine, cotinine, trans-3′-hydroxy-cotinine, nicotine-N-oxide, cotinine-N-oxide, nornicotine, norcotinine and 4-hydroxy-4-(3-pyridyl)butanoic acid were quantified by direct analysis. The corresponding glucuronide metabolites were quantified after urine hydrolysis with β-glucuronidase.
Nicotine and all 15 nicotine metabolites were quantified by LC MRM/MS in most urine samples from 61 tobacco smokers. Urinary nicotine and metabolite concentrations ranged from 7.9 to 337.8 μM (mean 75.5 ± 67.8 μM). Three nicotine metabolizer phenotypes were established as reduced metabolizers (ratio < 8), normal metabolizers (ratio 8–30), and extensive metabolizers (ratio > 30). 4-hydroxy-4-(3-pyridyl)butanoic acid, which has not been quantified previously, was an abundant metabolite in all three phenotypes.
Using this assay it will now be possible to determine whether there are relationships between nicotine exposure and/or metabolizer phenotype with exposure to toxic substances that are present in tobacco smoke and/or to biological response biomarkers to tobacco smoking. This will help in identifying individuals at high risk for developing smoking-related diseases as well as those amenable to smoking cessation programs.
PMCID: PMC3134267  PMID: 21452992
15.  A 13-Oxo-9,10-epoxytridecenoate Phospholipid Analog of the Genotoxic 4,5-Epoxy-2E-decenal: Detection In Vivo, Chemical Synthesis, and Adduction with DNA 
Chemical research in toxicology  2010;23(3):516-527.
Often guided by analogy with non phospholipid products from oxidative cleavage of polyunsaturated fatty acids (PUFAs), we previously identified a variety of biologically active oxidatively truncated phospholipids. Previously, 4,5-epoxy-2(E)-decenal (4,5-EDE)1 was found to be produced by oxidative cleavage of 13-(S)-hydroperoxy-9,11-(Z,E)-octadeca-dienoic acid (13-HPODE). 4,5-EDE reacts with deoxy-adenosine (dAdo) and deoxy-guanosine (dGuo) to form mutagenic etheno derivatives. We hypothesized that a functionally similar and potentially mutagenic compound, i.e., 13-oxo-9,10-epoxytridecenoic acid (OETA) would be generated from 9-HPODE through an analogous fragmentation. We expected that an ester of 2-lysophosphatidylcoline (PC), OETA-PC, would be produced by oxidative cleavage of 9-HPODE-PC in biological membranes. An efficient, unambiguous total synthesis of trans-OETA-PC was first executed to provide a standard that could facilitate the identification of this phospholipid epoxyalkenal that was shown to be produced during oxidation of the linoleic acid ester of 2-lysoPC. Finally, trans-OETA-PC was detected in a lipid extract from rat retina. The identity of the naturally occurring oxidatively truncated phospholipid was further confirmed by derivatization with methoxylamine that produced characteristic mono and bis adducts. The average amount of trans-OETA-PC in rat retina, 0.33 pmol, is relatively low, compared to other oxidatively truncated PCs, e.g., the 4-hydroxy-7-oxohept-5-enoic acid PC ester (HOHA-PC, 2.5 pmol) or the 4-keto-7-oxohept-5-enoic acid PC ester (KOHA-PC, 1.7 pmol), derived from the docosahexaenoic acid ester of 2-lysoPC. This, most likely, is because docosahexaenoate PCs are particularly abundant in the retina compared to the linoleate PC ester precursor of OETA-PC. As predicted by analogy with 4,5-EDE, OETA-PC reacts with dAdo and dGuo, as well as with DNA, to form mutagenic etheno-adducts.
PMCID: PMC2848942  PMID: 20131875
Phosphatidylcholine; trans-OETA-PC; oxPC; PUFA-PC; MPO; UV; Cu(II); LC-MS/MS; ESI; lipid oxidation; retina
16.  Stable Isotope Labeling by Essential Nutrients in Cell Culture for Preparation of Labeled Coenzyme A and Its Thioesters 
Analytical Chemistry  2011;83(4):1363-1369.
Stable isotope dilution mass spectrometry (MS) represents the gold standard for quantification of endogenously formed cellular metabolites. Although coenzyme A (CoA) and acyl-CoA thioester derivatives are central players in numerous metabolic pathways, the lack of a commercially available isotopically labeled CoA limits the development of rigorous MS-based methods. In this study, we adapted stable isotope labeling by amino acids in cell culture (SILAC) methodology to biosynthetically generate stable isotope labeled CoA and thioester analogues for use as internal standards in liquid chromatography/multiple reaction monitoring mass spectrometry (LC/MRM-MS) assays. This was accomplished by incubating murine hepatocytes (Hepa 1c1c7) in media in which pantothenate (a precursor of CoA) was replaced with [13C315N1]-pantothenate. Efficient incorporation into various CoA species was optimized to >99% [13C315N1]-pantothenate after three passages of the murine cells in culture. Charcoal−dextran-stripped fetal bovine serum (FBS) was found to be more efficient for serum supplementation than dialyzed or undialyzed FBS, due to lower contaminating unlabeled pantothenate content. Stable isotope labeled CoA species were extracted and utilized as internal standards for CoA thioester analysis in cell culture models. This methodology of stable isotope labeling by essential nutrients in cell culture (SILEC) can serve as a paradigm for using vitamins and other essential nutrients to generate stable isotope standards that cannot be readily synthesized.
PMCID: PMC3048769  PMID: 21268609
17.  Targeted quantitative analysis of eicosanoid lipids in biological samples using liquid chromatography-tandem mass spectrometry 
The eicosanoids are a large family of arachidonic acid oxidation products that contain twenty carbon atoms. Cyclooxygenase (COX)-derived eicosanoids have important roles as autacoids involved in the regulation of cardiovascular function and tumor progression. Lipoxygenase (LO)-derived eicosanoids have been implicated as important mediators of inflammation, asthma, cardiovascular disease and cancer. Cytochrome P-450 (P450)-derived eicosanoids are both vasodilators and vasoconstrictors. There is intense interest in the analysis of reactive oxygen species (ROS)-derived isoprostanes (isoPs) because of their utility as biomarkers of oxidative stress. Enzymatic pathways of eicosanoid formation are regioselective and enantioselective, whereas ROS-mediated eicosanoid formation proceeds with no stereoselectivity. Many of the eicosanoids are also present in only pM concentrations in biological fluids. This presents a formidable analytical challenge because methodology is required that can separate enantiomers and diastereomers with high sensitivity and specificity. However, the discovery of atmospheric pressure ionization (API)/MS methodology of electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and electron capture (EC) APCI has revolutionized our ability to analyze endogenous eicosanoids. LC separations of eicosanoids can now be readily coupled with API ionization, collision induced dissociation (CID) and tandem MS (MS/MS). This makes it possible to efficiently conduct targeted eicosanoid analyses using LC-multiple reaction motoring (MRM)/MS. Several examples of targeted eicosanoid lipid analysis using conventional LC-ESI/MS have been discussed and some new data on the analysis of eicosanoids using chiral LC-ECAPCI/MS has been presented.
PMCID: PMC2745066  PMID: 19345647
Liquid chromatography-mass spectrometry; Lipids; Fatty acids; Electrospray ionization; Electron capture atmospheric pressure chemical ionization; Hydroxyeicosatetraenoic acids; Isoprostanes; Stable isotopes
18.  20-HETE Mediates Ozone-Induced, Neutrophil-Independent Airway Hyper-Responsiveness in Mice 
PLoS ONE  2010;5(4):e10235.
Ozone, a pollutant known to induce airway hyper-responsiveness (AHR), increases morbidity and mortality in patients with obstructive airway diseases and asthma. We postulate oxidized lipids mediate in vivo ozone-induced AHR in murine airways.
Methodology/Principal Findings
Male BALB/c mice were exposed to ozone (3 or 6 ppm) or filtered air (controls) for 2 h. Precision cut lung slices (PCLS; 250 µm thickness) containing an intrapulmonary airway (∼0.01 mm2 lumen area) were prepared immediately after exposure or 16 h later. After 24 h, airways were contracted to carbachol (CCh). Log EC50 and Emax values were then calculated by measuring the airway lumen area with respect to baseline. In parallel studies, dexamethasone (2.5 mg/kg), or 1-aminobenzotriazol (ABT) (50 mg/kg) were given intraperitoneal injection to naïve mice 18 h prior to ozone exposure. Indomethacin (10 mg/kg) was administered 2 h prior. Cell counts, cytokine levels and liquid chromatography-mass spectrometry (LC-MS) for lipid analysis were assessed in bronchoalveolar lavage (BAL) fluid from ozone exposed and control mice. Ozone acutely induced AHR to CCh. Dexamethasone or indomethacin had little effect on the ozone-induced AHR; while, ABT, a cytochrome P450 inhibitor, markedly attenuated airway sensitivity. BAL fluid from ozone exposed animals, which did not contain an increase in neutrophils or interleukin (IL)-6 levels, increased airway sensitivity following in vitro incubation with a naïve PCLS. In parallel, significant increases in oxidized lipids were also identified using LC-MS with increases of 20-HETE that were decreased following ABT treatment.
These data show that ozone acutely induces AHR to CCh independent of inflammation and is insensitive to steroid treatment or cyclooxygenase (COX) inhibition. BAL fluid from ozone exposed mice mimicked the effects of in vivo ozone exposure that were associated with marked increases in oxidized lipids. 20-HETE plays a pivotal role in mediating acute ozone-induced AHR.
PMCID: PMC2857875  PMID: 20422032
19.  Secondhand smoke inhibits both Cl- and K+ conductances in normal human bronchial epithelial cells 
Respiratory Research  2009;10(1):120.
Secondhand smoke (SHS) exposure is an independent risk factor for asthma, rhinosinusitis, and more severe respiratory tract infections in children and adults. Impaired mucociliary clearance with subsequent mucus retention contributes to the pathophysiology of each of these diseases, suggesting that altered epithelial salt and water transport may play an etiological role. To test the hypothesis that SHS would alter epithelial ion transport, we designed a system for in vitro exposure of mature, well-differentiated human bronchial epithelial cells to SHS. We show that SHS exposure inhibits cAMP-stimulated, bumetanide-sensitive anion secretion by 25 to 40% in a time-dependent fashion in these cells. Increasing the amount of carbon monoxide to 100 ppm from 5 ppm did not increase the amount of inhibition, and filtering SHS reduced inhibition significantly. It was determined that SHS inhibited cAMP-dependent apical membrane chloride conductance by 25% and Ba2+-sensitive basolateral membrane potassium conductance by 50%. These data confirm previous findings that cigarette smoke inhibits chloride secretion in a novel model of smoke exposure designed to mimic SHS exposure. They also extend previous findings to demonstrate an effect on basolateral K+ conductance. Therefore, pharmacological agents that increase either apical membrane chloride conductance or basolateral membrane potassium conductance might be of therapeutic benefit in patients with diseases related to SHS exposure.
PMCID: PMC2792224  PMID: 19943936

Results 1-19 (19)