Jennifer M Johnson

Emory University, Atlanta, GA, United States

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Publications (6)29.34 Total impact

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    ABSTRACT: Information-rich technologies have advanced personalized medicine, yet obstacles limit measurement of large numbers of chemicals in human samples. Current laboratory tests measure hundreds of chemicals based upon existing knowledge of exposures, metabolism and disease mechanisms. Practical issues of cost and throughput preclude measurement of thousands of chemicals. Additionally, individuals are genetically diverse and have different exposures and response characteristics; some have disease mechanisms that have not yet been elucidated. Consequently, methods are needed to detect unique metabolic characteristics without presumption of known pathways, exposures or disease mechanisms, i.e., using a top-down approach. In this report, we describe profiling of human plasma with liquid chromatography (LC) coupled to Fourier-transform mass spectrometry (FTMS). FTMS is a high-resolution mass spectrometer providing mass accuracy and resolution to discriminate thousands of m/z features, which are peaks defined by m/z, retention time and intensity. We demonstrate that LC-FTMS detects 2000 m/z features in 10 min. These features include known and unidentified chemicals with m/z between 85 and 850, most with <10% coefficient of variation. Comparison of metabolic profiles for 4 healthy individuals showed that 62% of the m/z features were common while 10% were unique and 770 discriminated the individuals. Because the simple one-step extraction and automated analysis is rapid and cost-effective, the approach is practical for personalized medicine. This provides a basis to rapidly characterize novel metabolic patterns which can be linked to genetics, environment and/or lifestyle.
    The Analyst 11/2010; 135(11):2864-70. · 4.23 Impact Factor
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    Tianwei Yu, Youngja Park, Jennifer M Johnson, Dean P Jones
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    ABSTRACT: Liquid chromatography-mass spectrometry (LC/MS) profiling is a promising approach for the quantification of metabolites from complex biological samples. Significant challenges exist in the analysis of LC/MS data, including noise reduction, feature identification/ quantification, feature alignment and computation efficiency. Here we present a set of algorithms for the processing of high-resolution LC/MS data. The major technical improvements include the adaptive tolerance level searching rather than hard cutoff or binning, the use of non-parametric methods to fine-tune intensity grouping, the use of run filter to better preserve weak signals and the model-based estimation of peak intensities for absolute quantification. The algorithms are implemented in an R package apLCMS, which can efficiently process large LC/ MS datasets. The R package apLCMS is available at www.sph.emory.edu/apLCMS. Supplementary data are available at Bioinformatics online.
    Bioinformatics 06/2009; 25(15):1930-6. · 5.47 Impact Factor
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    ABSTRACT: The steady-state redox potential of the cysteine/cystine couple in human plasma provides a measure of oxidative stress, yet available assays are limited by either specificity or speed of assay. The present study evaluated the use of LC-FTMS for identification based on accurate mass combined with quantification by stable isotopic dilution to rapidly determine cysteine and cystine concentration and cysteine/cystine steady-state redox potential in human plasma. A simple extraction procedure followed by a rapid LC separation eluted cysteine in 4 min and cystine in 1.5 min with simultaneous measurement of glutathione (GSH) and glutathione disulfide (GSSG). A study of five young (mean age=25.7) subjects and 5 older (mean age=67.8 y) subjects showed an increased oxidation with age. The analysis by LC-FTMS is suitable for high-throughput analysis of plasma cysteine, cystine and cysteine/cystine steady-state redox potential as clinical measures of oxidative stress.
    Clinica Chimica Acta 10/2008; 396(1-2):43-8. · 2.85 Impact Factor
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    ABSTRACT: Thioredoxin-2 (Trx2) is a multifunctional, mitochondria-specific protein, which inhibits cell death. The mitochondrial permeability transition (MPT) is a distinct mechanism for cell death activated by oxidants and linked to both necrotic and apoptotic morphologies. We studied mitochondria from Trx2 transgenic mice to determine whether Trx2 protects against oxidant-induced MPT. All experiments were performed in isolated mitochondria. Results showed that Trx2 protected against MPT induced by exogenously added peroxide. Unexpectedly, Trx2 also protected against the MPT induced by Ca(2+) in the absence of added peroxide. The results indicate that in addition to protecting against oxidative stress, Trx2 is an endogenous regulator of the MPT.
    Toxicological Sciences 07/2008; 105(1):44-50. · 4.33 Impact Factor
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    ABSTRACT: The effects of nuclear-localized oxidative stress on both nuclear antioxidant systems, and the processes that they regulate, are not clearly understood. Here, we targeted a hydrogen peroxide (H(2)O(2))-producing enzyme, D-amino acid oxidase (DAAO), to the nucleus (NLS-DAAO) and used this to generate H(2)O(2) in the nuclei of cells. On addition of N-acetyl-D-alanine (NADA), a substrate of DAAO, to NLS-DAAO-transfected HeLa cells, a twofold increase in ROS production relative to untreated, transfected control was observed. Staining of cellular thiols confirmed that NLS-DAAO-induced ROS selectively modified the nuclear thiol pool, whereas the cytoplasmic pool remained unchanged. Furthermore, NLS-DAAO/NADA-induced ROS caused significant oxidation of the nuclear GSH pool, as measured by nuclear protein S-glutathionylation (Pr-SSG), but under the same conditions, nuclear Trx1 redox state was not altered significantly. NF-kappaB reporter activity was diminished by NLS-DAAO/NADA-stimulated nuclear oxidation. We conclude that nuclear GSH is more susceptible to localized oxidation than is nuclear Trx1. Furthermore, the attenuation of NF-kappaB reporter activity in the absence of nuclear Trx1 oxidation suggests that critical nuclear redox proteins are subject to control by S-glutathionylation during oxidative stress in the nucleus.
    Antioxidants and Redox Signaling 08/2007; 9(7):807-16. · 7.19 Impact Factor
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    ABSTRACT: Little is known about the relative sensitivities of antioxidant systems in nuclei, mitochondria, and cytoplasm. The present study examined the oxidation of the thiol-dependent antioxidant systems in these subcellular compartments under conditions of limited energy supply of human colonic epithelial HT-29 cells induced by depletion of glucose (Glc) and glutamine (Gln) from the culture medium. Increased oxidation of dichlorofluoroscein (DCF) indicated an increased level of reactive oxygen species (ROS). Redox Western blot analysis showed oxidation of cytosolic thioredoxin-1 (Trx1) and mitochondrial thioredoxin-2 (Trx2) by 24 h, but little oxidation of nuclear Trx1. The Trx1 substrate, redox factor-1 (Ref-1), was also oxidized in cytosol but was reduced in nuclei. Protein S-glutathionylation (PrSSG), expressed as a ratio of protein thiol (PrSH), was also increased in the cytosol, while nuclear PrSSG/PrSH was not. Taken together, the data show that oxidative stress induced by depletion of Glc and Gln affects the redox states of proteins in the cytoplasm and mitochondria more than those in the nucleus. These results indicate that the nuclear compartment has better protection against oxidative stress than cytoplasm or mitochondria. These results further suggest that energy and/or substrate supply may contribute to sensitivity of mitochondrial and cytoplasmic systems to oxidative damage.
    Free Radical Biology and Medicine 03/2007; 42(3):363-70. · 5.27 Impact Factor

Publication Stats

141 Citations
29.34 Total Impact Points

Institutions

  • 2007–2010
    • Emory University
      • • Department of Internal Medicine
      • • Department of Biostatistics and Bioinformatics
      • • Division of Pulmonary, Allergy and Critical Care Medicine
      Atlanta, GA, United States