Outcomes of Acute Ischemic Stroke Among Patients with Renal Cell Carcinoma: A Nationwide Analysis.

INTRODUCTION: Renal cell carcinoma (RCC) has been associated with an increased risk for acute ischemic stroke (AIS). As individuals with cancer who experience AIS tend to face higher mortality rates compared to AIS patients without cancer, recognizing the implications of RCC in AIS is crucial for identifying high-risk patients for major complications and directing management strategies. OBJECTIVE: To examine risk factors, interventions, and outcomes for patients with AIS stratified by their RCC diagnosis. METHODS: The National Inpatient Sample (NIS) database was queried for the period 2010-2019 using International Classification of Disease 10th Edition (ICD-10) codes for acute ischemic stroke and renal malignancies. We assessed demographic information, comorbidities, and clinical interventions between patients presenting with AIS, with and without renal malignancies. A logistic regression model was employed to further examine mortality outcomes. RESULTS: Among 1,609,817 patients identified with AIS, 2,068 (0.12%) had a concomitant diagnosis of RCC. AIS patients with RCC were older (72.09 yrs. vs. 70.9 yrs., p < 0.01), more often white (72.05% vs. 68.16%, p < 0.01), and had similar stroke severity scores. RCC patients received less tissue plasminogen activator (tPA; 4.98% vs. 6.2%, p = 0.02) but underwent endovascular mechanical thrombectomy (MT) at similar rates. RCC patients had more complications (p < 0.01) as well as longer hospital stays (8.19 days vs. 5.98 days, p < 0.01), and higher rates of mortality (11.27% vs. 5.63%, p < 0.01), when compared to their non-RCC counterparts. Propensity score-adjusted analysis largely confirmed these findings, with RCC being positively associated with in-hospital mortality (OR: 1.373, p < 0.01) and longer stays (OR: 2.591, p < 0.01). CONCLUSION: In addition to describing the demographics and clinical course of AIS patients diagnosed with RCC, our study underscores the substantial impact of RCC on AIS outcomes. Despite experiencing strokes of similar severity, AIS patients diagnosed with RCC are at a heightened risk of complications, including thromboembolic events and infections, leading to elevated in-hospital mortality rates and prolonged hospital stays.

SoxB1 transcription factors are essential for initiating and maintaining the neural plate border gene expression.

SoxB1 transcription factors (Sox2/3) are well known for their role in early neural fate specification in the embryo, but little is known about functional roles for SoxB1 factors in non-neural ectodermal cell types, such as the neural plate border (NPB). Using Xenopus laevis , we set out to determine if SoxB1 transcription factors have a regulatory function in NPB formation. Herein, we show that SoxB1 factors are necessary for NPB formation, and that prolonged SoxB1 factor activity blocks the transition from a NPB to a neural crest state. Using ChIP-seq we demonstrate that Sox3 is enriched upstream of NPB genes in early NPB cells and, surprisingly, in blastula stem cells. Depletion of SoxB1 factors in blastula stem cells results in downregulation of NPB genes. Finally, we identify Pou5f3 factors as a potential SoxB1 partners in regulating the formation of the NPB and show their combined activity is needed to maintain NPB gene expression. Together, these data identify a novel role for SoxB1 factors in the establishment and maintenance of the NPB, in part through partnership with Pou5f3 factors.

An open-source transparent microelectrode array.

Objective.The micro-electrode array (MEA) is a cell-culture surface with integrated electrodes used for assays of electrically excitable cells and tissues. MEAs have been a workhorse in the study of neurons and myocytes, owing to the scalability and millisecond temporal resolution of the technology. However, traditional MEAs are opaque, precluding inverted microscope access to modern genetically encoded optical sensors and effectors.Approach. To address this gap, transparent MEAs have been developed. However, for many labs, transparent MEAs remain out of reach due to the cost of commercially available products, and the complexity of custom fabrication. Here, we describe an open-source transparent MEA based on the OpenEphys platform (Siegleet al2017J. Neural Eng.14045003).Main results.We demonstrate the performance of this transparent MEA in a multiplexed electrical and optogenetic assay of primary rat hippocampal neurons.Significance.This open-source transparent MEA and recording platform is designed to be accessible, requiring minimal microelectrode fabrication or circuit design experience. We include low-noise connectors for seamless integration with the Intan Technologies headstage, and a mechanically stable adaptor conforming to the 24-well plate footprint for compatibility with most inverted microscopes.

Downregulation of PHLPP induced by endoplasmic reticulum stress promotes eIF2α phosphorylation and chemoresistance in colon cancer.

Aberrant activation of endoplasmic reticulum (ER) stress by extrinsic and intrinsic factors contributes to tumorigenesis and resistance to chemotherapies in various cancer types. Our previous studies have shown that the downregulation of PHLPP, a novel family of Ser/Thr protein phosphatases, promotes tumor initiation, and progression. Here we investigated the functional interaction between the ER stress and PHLPP expression in colon cancer. We found that induction of ER stress significantly decreased the expression of PHLPP proteins through a proteasome-dependent mechanism. Knockdown of PHLPP increased the phosphorylation of eIF2α as well as the expression of autophagy-associated genes downstream of the eIF2α/ATF4 signaling pathway. In addition, results from immunoprecipitation experiments showed that PHLPP interacted with eIF2α and this interaction was enhanced by ER stress. Functionally, knockdown of PHLPP improved cell survival under ER stress conditions, whereas overexpression of a degradation-resistant mutant PHLPP1 had the opposite effect. Taken together, our studies identified ER stress as a novel mechanism that triggers PHLPP downregulation; and PHLPP-loss promotes chemoresistance by upregulating the eIF2α/ATF4 signaling axis in colon cancer cells.

Inhibition of protein tyrosine phosphatase receptor type F suppresses Wnt signaling in colorectal cancer.

Wnt signaling dysregulation promotes tumorigenesis in colorectal cancer (CRC). We investigated the role of PTPRF, a receptor-type tyrosine phosphatase, in regulating Wnt signaling in CRC. Knockdown of PTPRF decreased cell proliferation in patient-derived primary colon cancer cells and established CRC cell lines. In addition, the rate of proliferation as well as colony formation ability were significantly decreased in tumor organoids grown in 3D, whereas the number of differentiated tumor organoids were markedly increased. Consistently, knockdown of PTPRF resulted in a decrease in the expression of genes associated with cancer stem cells downstream of Wnt/ß-catenin signaling. Treating PTPRF knockdown cells with GSK3 inhibitor rescued the expression of Wnt target genes suggesting that PTPRF functions upstream of the ß-catenin destruction complex. PTPRF was found to interact with LRP6 and silencing PTPRF largely decreased the activation of LRP6. Interestingly, this PTPRF-mediated activation of Wnt signaling was blocked in cells treated with clathrin endocytosis inhibitor. Furthermore, knockdown of PTPRF inhibited xenograft tumor growth in vivo and decreased the expression of Wnt target genes. Taken together, our studies identify a novel role of PTPRF as an oncogenic protein phosphatase in supporting the activation of Wnt signaling in CRC.

The mitochondrial retrograde signaling regulates Wnt signaling to promote tumorigenesis in colon cancer.

Cancer cells are known to upregulate aerobic glycolysis to promote growth, proliferation, and survival. However, the role of mitochondrial respiration in tumorigenesis remains elusive. Here we report that inhibition of mitochondrial function by silencing TFAM, a key transcription factor essential for mitochondrial DNA (mtDNA) replication and the transcription of mtDNA-encoded genes, markedly reduced tumor-initiating potential of colon cancer cells. Knockdown of TFAM significantly decreased mitochondrial respiration in colon cancer cells; however, the cellular levels of ATP remained largely unchanged as a result of increased glycolysis. This metabolic alteration rendered cancer cells highly susceptible to glucose deprivation. Interestingly, upregulation of glycolysis was independent of hypoxia-inducible factor-1 (HIF1) as TFAM knockdown cells fail to stabilize HIF1α under hypoxic conditions. Moreover, knockdown of TFAM results in decreased expression of genes-associated cancer stem cells downstream of Wnt/ß-catenin signaling. Metabolic analysis reveals that the level of α-ketoglutarate (α-KG) was significantly upregulated in TFAM knockout cells. Silencing of prolyl hydroxylase domain-containing protein 2 (PHD2), a α-KG-dependent dioxyenase, rescued the expression of target genes of both HIF1α and Wnt/ß-catenin. Furthermore, intestinal-specific knockout of TFAM prevents tumor formation in Apc-mutant mouse models of colon cancer. Taken together, our findings identify a novel role of mitochondria-mediated retrograde signaling in regulating Wnt signaling and tumor initiation in colon cancer.

Identification and human exposure prediction of two aldehyde oxidase-mediated metabolites of a methylquinoline-containing drug candidate.

1. Aldehyde oxidase (AO enzymes)-mediated oxidation predominantly occurs at a carbon atom adjacent to the nitrogen on aromatic azaheterocycles. In the current report, we identified that AO enzymes oxidation took place at both the C-2 and C-4 positions of the methylquinoline moiety of Compound A based on data from mass spectrometric analysis, AO enzymes "litmus" test, and comparison with authentic standards. 2. To assess the potential for inadequate coverage for these two AO enzyme-mediated metabolites in nonclinical safety studies, given concerns due to differences in AO enzymes expression between preclinical species and humans, the human circulating levels of the two AO enzyme-mediated metabolites were predicted prospectively using in vitro and in vivo models. Both formation clearance and elimination clearance of the two metabolites were predicted based on in vitro to in vivo correlation and comparison with in vivo data from rats. 3. The result showed that the 4-OH metabolite of Compound A would account for less than 3% of the total drug-related exposure in human plasma, while the exposure to the 2-oxo metabolite would be relatively high (∼70%). 4. The predicted human exposure levels for the two metabolites are in similar ranges as those observed in monkeys. These data taken together support the advancement to clinical development of Compound A.

Erbin Suppresses KSR1-Mediated RAS/RAF Signaling and Tumorigenesis in Colorectal Cancer.

Erbin belongs to the LAP (leucine-rich repeat and PDZ domain) family of scaffolding proteins that plays important roles in orchestrating cell signaling. Here, we show that Erbin functions as a tumor suppressor in colorectal cancer. Analysis of Erbin expression in colorectal cancer patient specimens revealed that Erbin was downregulated at both mRNA and protein levels in tumor tissues. Knockdown of Erbin disrupted epithelial cell polarity and increased cell proliferation in 3D culture. In addition, silencing Erbin resulted in increased amplitude and duration of signaling through Akt and RAS/RAF pathways. Erbin loss induced epithelial-mesenchymal transition, which coincided with a significant increase in cell migration and invasion. Erbin interacted with kinase suppressor of Ras 1 (KSR1) and displaced it from the RAF/MEK/ERK complex to prevent signal propagation. Furthermore, genetic deletion of Erbin in Apc knockout mice promoted tumorigenesis and significantly reduced survival. Tumor organoids derived from Erbin/Apc double knockout mice displayed increased tumor initiation potential and activation of Wnt signaling. Results from gene set enrichment analysis revealed that Erbin expression associated positively with the E-cadherin adherens junction pathway and negatively with Wnt signaling in human colorectal cancer. Taken together, our study identifies Erbin as a negative regulator of tumor initiation and progression by suppressing Akt and RAS/RAF signaling in vivoSignificance: These findings establish the scaffold protein Erbin as a negative regulator of EMT and tumorigenesis in colorectal cancer through direct suppression of Akt and RAS/RAF signaling. Cancer Res; 78(17); 4839-52. ©2018 AACR.

Downregulation of SREBP inhibits tumor growth and initiation by altering cellular metabolism in colon cancer.

Sterol regulatory element-binding proteins (SREBPs) belong to a family of transcription factors that regulate the expression of genes required for the synthesis of fatty acids and cholesterol. Three SREBP isoforms, SREBP1a, SREBP1c, and SREBP2, have been identified in mammalian cells. SREBP1a and SREBP1c are derived from a single gene through the use of alternative transcription start sites. Here we investigated the role of SREBP-mediated lipogenesis in regulating tumor growth and initiation in colon cancer. Knockdown of either SREBP1 or SREBP2 decreased levels of fatty acids as a result of decreased expression of SREBP target genes required for lipid biosynthesis in colon cancer cells. Bioenergetic analysis revealed that silencing SREBP1 or SREBP2 expression reduced the mitochondrial respiration, glycolysis, as well as fatty acid oxidation indicating an alteration in cellular metabolism. Consequently, the rate of cell proliferation and the ability of cancer cells to form tumor spheroids in suspension culture were significantly decreased. Similar results were obtained in colon cancer cells in which the proteolytic activation of SREBP was blocked. Importantly, knockdown of either SREBP1 or SREBP2 inhibited xenograft tumor growth in vivo and decreased the expression of genes associated with cancer stem cells. Taken together, our findings establish the molecular basis of SREBP-dependent metabolic regulation and provide a rationale for targeting lipid biosynthesis as a promising approach in colon cancer treatment.

Structural identification of imatinib cyanide adducts by mass spectrometry and elucidation of bioactivation pathway.

RATIONALE: Recent publications have reported that imatinib forms cyanide and methoxylamine adducts in vitro but without detail structural identification. The current work reports the identification of seven cyanide adducts that elucidate the bioactivation pathways and may provide hints for observed clinical adverse effects of the drug. METHODS: Imatinib was incubated with human liver microsomal proteins in the presence of a NADPH-regeneration system and the trapping agents reduced GSH, potassium cyanide and methoxylamine. Samples were analyzed by high-performance liquid chromatography (HPLC) coupled with a LTQ-Orbitrap data collection system. Chemical structures were determined and/or postulated based on data-dependent high-resolution tandem mass spectrometric (MS(n)) exact mass measurements in both positive and negative scan modes, as well as in combination with hydrogen-deuterium exchange (HDX). RESULTS: GSH and methoxylamine conjugates were either not detected or were in insufficient quantities for characterization. However, seven cyanide conjugates were identified, indicating that the piperazine and p-toluidine partial structures in imatinib can become bioactivated and subsequently trapped by the nucleophile cyanide ion. The reactive intermediates were postulated as imine and imine-carbonyl conjugate (α,ß-unsaturated) structures on the piperazine ring, and imine-methide on the p-toluidine partial structure. CONCLUSIONS: Chemical structures of seven cyanide adducts of imatinib have been identified or proposed based on high-resolution MS/MS data. Mechanisms for the formation of the conjugates were also proposed. The findings may help to understand the mechanism of hepatotoxicity of imatinib in humans.

Boronic acid-containing proteasome inhibitors: alert to potential pharmaceutical bioactivation.

Medicinal chemists try to avoid certain organic functional groups, summarized in an ever-growing list, in order to avoid the potential bioactivation to reactive metabolites. To add to that alert list, we report herein that boronic acid-containing compound structures, such as those found in proteasome inhibitors bortezomib and ixazomib, can become bioactivated to chemically reactive imine amide metabolites. Test compounds, ixazomib and bortezomib, were incubated in vitro using human liver fractions containing cytosol and microsomes (S9) under conventional conditions in the presence of GSH. Metabolites were then analyzed using LC-MS(n) with or without online hydrogen-deuterium exchange (HDX) liquid chromatography coupled with an LTQ-Orbitrap. The exact mass measurements of both the precursor and product ions were acquired through data dependent acquisition and compared with theoretical values of proposed fragment ions. Upon deboronation catalyzed by cytochrome P450 enzymes, both test compounds formed imine amide metabolites that were identified by high resolution exact mass measurements in both normal aqueous and HDX HPLC-MS analysis. GSH conjugates were also identified and were postulated as nucleophilic addition of GSH to the imine amide metabolites. All mass spectrometric and HDX measurements of these GSH conjugates proved that the GSH unit was added to the carbon atom of the imine amide partial structure, hence demonstrating the electrophilic property of these imine amide metabolites. The awareness of the formation of electrophilic imine amide metabolites from boronic acid-containing compounds, where the boron atom is bonded to a carbon atom adjacent to an amide nitrogen, should help in drug candidate design and optimization with regard to avoiding potential bioactivation.

Update on hydrocodone metabolites in rats and dogs aided with a semi-automatic software for metabolite identification Mass-MetaSite.

1. There has been a lack of in vivo metabolite profiling update of hydrocodone since the original report on species differences was published in 1978. As such, the mechanism for its analgesic activity in different species has been ambiguous. To address safety concern from regulatory agencies, hydrocodone metabolite profiles in rats and dogs are updated herein aided by a newly developed software, Mass-MetaSite. 2. Samples collected from rats and dogs dosed orally with hydrocodone were analyzed with reversed phase liquid chromatography coupled with LTQ-Orbitrap. The exact mass measurement data collected with data-dependent acquisition methodology were analyzed both traditionally, using Xcalibur Qual Browser and MetWorks, and by Mass-MetaSite. 3. Profiling of hydrocodone metabolites in rat and dog plasma reflected previously reported species differences in circulating metabolites. While hydrocodone mainly underwent O-demethylation and ketone reduction in rats forming hydromorphone and reduced hydromorphone, which were then subsequently cleared via glucuronide conjugation, hydrocodone in dogs was cleared predominantly by N-demethylation and N-oxidation. 4. Given the success ratio of metabolite detection offered by Mass-MetaSite, the software will be able to aid chemists in early identification of drug metabolites from complex biomatrices.

Identification of imine or enamine drug metabolites using online hydrogen/deuterium exchange and exact mass measurements.

RATIONALE: Drug metabolites that have imine or enamine partial structures cause extra mass-to-charge (m/z) increases in online hydrogen/deuterium exchange (HDX) in addition to hydroxyl or amine protons. Online HDX and exact mass measurement were used herein to characterize this extra increase property, and to further confirm proposed metabolite structures. METHODS: Metabolites of two proprietary compounds as well as two commercially available compounds were analyzed using aqueous and HDX liquid chromatography coupled with an LTQ-Orbitrap. The exact mass measurements of both the precursor ions and product ions were acquired through data-dependent acquisition and compared with theoretical values of proposed fragment ions. RESULTS: Analysis of exact mass measurements of metabolite product ions under both normal aqueous and HDX conditions led to the identification of the isoxazole ring opening of compound C-1, and a double-bond formation on the methylpyrrolidine ring of compound C-2 during biotransformation. In both cases, imine or enamine structures formed in the metabolites caused extra m/z increases upon HDX that contributed confirmatory information to the structure identification. The compound 3,3-diphenyl-2-ethyl-1-pyrroline also demonstrated that the methylene protons adjacent to the imine were exchanged during online HDX. CONCLUSIONS: The exchangeability of methylene protons adjacent to imine or enamine moieties proved to be useful to narrow down or even pinpoint the metabolism sites of parent drugs when high-resolution exact mass measurement and online HDX were used.

Two-injection workflow for a liquid chromatography/LTQ-Orbitrap system to complete in vivo biotransformation characterization: demonstration with buspirone metabolite identification.

The relatively high background matrix in in vivo samples typically poses difficulties in drug metabolite identification, and causes repeated analytical runs on unit resolution liquid chromatography/mass spectrometry (LC/MS) systems before the completion of biotransformation characterization. Ballpark parameter settings for the LTQ-Orbitrap are reported herein that enable complete in vivo metabolite identification within two HPLC/MS injections on the hybrid LTQ-Orbitrap data collection system. By setting the FT survey full scan at 60K resolution to trigger five dependent LTQ MS(2) scans, and proper parameters of Repeat Duration, Exclusion Duration and Repeat Count for the first run (exploratory), the Orbitrap achieved the optimal parallel data acquisition capability and collected maximum number of product ion scans. Biotransformation knowledge based prediction played the key role in exact mass ion extraction and multiple mass defect filtration when the initial data was processed. Meanwhile, product ion extraction and neutral loss extraction of the initial dependent data provided additional bonus in identifying metabolites. With updated parent mass list and the data-dependent setting to let only the ions on the parent mass list trigger dependent scans, the second run (confirmatory) ensures that all precursor ions of identified metabolites trigger not only dependent product ion scans, but also at or close to the highest concentration of the eluted metabolite peaks. This workflow has been developed for metabolite identification of in vivo or ADME studies, of which the samples typically contain a high level of complex matrix. However, due to the proprietary nature of the in vivo studies, this workflow is presented herein with in vitro buspirone sample incubated with human liver microsomes (HLM). The major HLM-mediated biotransformation on buspirone was identified as oxidation or hydroxylation since five mono- (+16 Da), seven di- (+32 Da) and at least three tri-oxygenated (+48 Da) metabolites were identified. Besides the metabolites 1-pyrimidinylpiperazine (1-PP) and hydroxylated 1-PP that formed by N-dealkylation, a new metabolite M308 was identified as the result of a second N-dealkylation of the pyrimidine unit. Two new metabolites containing the 8-butyl-8-azaspiro[4,5]decane-7,9-dione partial structure, M240 and M254, were also identified that were formed apparently due to the first N-dealkylation of the 1-PP moiety.

Complete profiling and characterization of in vitro nefazodone metabolites using two different tandem mass spectrometric platforms.

This paper describes the complete profiling and characterization of in vitro metabolites of the antidepressant agent nefazodone (NEF) generated by human liver microsome (HLM). Two new metabolic pathways (biotransformation) for NEF have been discovered by the characterization of three new metabolites, including two new metabolites (M24, M25) formed due to the N-dealkylation reaction that occurred between the triazolone and propyl units, and one new metabolite (M26) formed due to the O-dearylation reaction that occurred on the phenoxyethyl unit. These metabolites were initially detected by a 4000 Q-Trap instrument and then confirmed by exact mass measurement using an LTQ-Orbitrap. Both instruments proved to be capable of providing complete in vitro metabolite information in a single liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis, although each had its advantages and disadvantages. One noticeable disadvantage of the 4000 Q-Trap was the reduced quality of isotopic pattern in the enhanced mass scan (EMS) spectrum when it was used as survey scan to trigger multiple dependent product ion scans. The problem was especially exacerbated for minor metabolites with low signal intensity. On the other hand, the LTQ-Orbitrap maintained excellent isotopic pattern when used as a full scan survey scan. Twenty-six metabolites were detected and identified. The formation of these new metabolites was also confirmed by analyzing duplicate incubations at different time points.

Metabolite profiling of [14C]hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in Yucatan miniature pigs.

The study reported herein examined the metabolism of 14C-labeled hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) resulting from a single oral gavage of 5 ml/kg to male and female Yucatan miniature pigs (43 mg/kg, 56 microCi/kg in 0.5% carboxymethylcellulose in water). Blood, urine, and feces were collected at selected times of 1, 6, 12, and 24 h postdose. At 24 h postdose, liver samples were collected. Blood, plasma, liver, and excreta were analyzed for total RDX-derived radioactivity and metabolites were identified. Urine was the major route of elimination of 14C-RDX-derived radioactivity in both males and females. Relatively low levels of radioactivity were found in gastrointestinal contents and in feces, suggesting nearly complete absorption of 14C-RDX following an oral dose. Analysis of urine by liquid chromatography-mass spectrometry (LC/MS) identified quantifiable levels of two ring-cleavage metabolites, 4-nitro-2,4-diazabutanal and 4-nitro-2,4-diaza-butanamide, as well as parent RDX. The 4-nitro-2,4-diazabutanal, was seen in earlier studies of aerobic metabolism of RDX. The 4-nitro-2,4-diaza-butanamide, an amide, was not previously reported but was tentatively identified in this study. Analysis by a more sensitive method (LC/MS/MS) also showed trace amounts of the RDX metabolites 1-nitroso-3,5-dinitro-1,3,5-triazacyclohexane (MNX) (in both male and female urine) and 1-nitro-3,5-dinitroso-1,3,5-triazacyclohexane (DNX) (in male urine). Analysis of plasma by LC/MS/MS also revealed quantifiable levels of RDX and trace levels of MNX, DNX, and 1,3,5-trinitroso-1,3,5-triazacyclohexane (TNX). None of the liver extracts showed quantifiable levels of RDX or any identifiable metabolites. Most of the radioactivity was in the form of water-soluble high-molecular-weight compounds. RDX when given orally to pigs was rapidly metabolized by loss of two nitro groups followed by ring cleavage.

'N-in-one' strategy for metabolite identification using a liquid chromatography/hybrid triple quadrupole linear ion trap instrument using multiple dependent product ion scans triggered with full mass scan.

This paper describes a new strategy that utilizes the fast trap mode scan of the hybrid triple quadrupole linear ion trap (QqQ(LIT)) for the identification of drug metabolites. The strategy uses information-dependent acquisition (IDA) where the enhanced mass scan (EMS), the trap mode full scan, was used as the survey scan to trigger multiple dependent enhanced product ion scans (EPI), the trap mode product ion scans. The single data file collected with this approach not only includes full scan data (the survey), but also product ion spectra rich in structural information. By extracting characteristic product ions from the dependent EPI chromatograms, we can provide nearly complete information for in vitro metabolites that otherwise would have to be obtained by multiple precursor ion scan (prec) and constant neutral loss (NL) analysis. This approach effectively overcomes the disadvantages of traditional prec and NL scans, namely the slow quadrupole scan speed, and possible mass shift. Using nefazodone (NEF) as the model compound, we demonstrated the effectiveness of this strategy by identifying 22 phase I metabolites in a single liquid chromatography/tandem mass spectrometry (LC/MS/MS) run. In addition to the metabolites reported previously in the literature, seven new metabolites were identified and their chemical structures are proposed. The oxidative dechlorination biotransformation was also discovered which was not reported in previous literature for NEF. The strategy was further evaluated and worked well for the fast discovery setting when a ballistic gradient elution was used, as well as for a simulated in vivo setting when the incubated sample (phase I metabolites) was spiked to control human plasma extract and control human urine.

Advantages of using tetrahydrofuran-water as mobile phases in the quantitation of cyclosporin A in monkey and rat plasma by liquid chromatography-tandem mass spectrometry.

A new analytical method is described here for the quantitation of anti-inflammatory drug cyclosporin A (CyA) in monkey and rat plasma. The method used tetrahydrofuran (THF)-water mobile phases to elute the analyte and internal standard, cyclosporin C (CyC). The gradient mobile phase program successfully eluted CyA into a sharp peak and therefore improved resolution between the analyte and possible interfering materials compared with previously reported analytical approaches, where CyA was eluted as a broad peak due to the rapid conversion between different conformers. The sharp peak resulted from this method facilitated the quantitative calculation as multiple smoothing and large number of bunching factors were not necessary. The chromatography in the new method was performed at 30 degrees C instead of 65-70 degrees C as reported previously. Other advantages of the method included simple and fast sample extraction-protein precipitation, direct injection of the extraction supernatant to column for analysis, and elimination of evaporation and reconstitution steps, which were needed in solid phase extraction or liquid-liquid extraction reported before. This method is amenable to high-throughput analysis with a total chromatographic run time of 3 min. This approach has been verified as sensitive, linear (0.977-4000 ng/mL), accurate and precise for the quantitation of CyA in monkey and rat plasma. However, compared with the usage of conventional mobile phases, the only drawback of this approach was the reduced detection response from the mass spectrometer that was possibly caused by poor desolvation in the ionization source. This is the first report to demonstrate the advantages of using THF-water mobile phases to elute CyA in liquid chromatography.

Determination of S-phenylmercapturic acid in human urine using an automated sample extraction and fast liquid chromatography-tandem mass spectrometric method.

S-phenylmercapturic acid is widely accepted as a specific biomarker for the evaluation of benzene exposure. Here, we describe a fast, specific and sensitive high-performance liquid achromatography coupled with tandem mass spectrometry (LC-MS/MS) method that has been developed and validated for the determination of S-phenylmercapturic acid in human urine. Isotope-labeled S-phenylmercapturic acid-d5 was used as internal standard to improve the method ruggedness. The fully automated solid-phase extraction method on a 96-well Oasis MAX (mix-mode anion exchange) plate was employed to clean up the urine samples before analysis. The rapid LC-MS/MS analysis of extracted samples was achieved on a Genesis C18 column with a run time of only 3 min. Negative electrospray ionization with multiple reaction monitoring (ESI-MRM) mode was used to detect S-phenylmercapturic acid (m/z 238 --> 109) and S-phenylmercapturic acid -d5 (m/z 243 --> 114). The method fulfils all the standard requirements of method validation. The calibration curve was linear within the concentration range 0.400-200 ng/mL. The method performed accurately and precisely in validation with <7.5% relative error and <6.5% relative standard deviation of quality control samples. The method efficacy was also verified by the analysis of urine samples from 12 smokers and 12 non-smokers. With the fully automated sample cleanup procedure and the fast LC-MS/MS analysis, a sample analysis throughput of 384 samples per day could be achieved.