Giorgis Isaac

Waters Corporation, Милфорд, Massachusetts, United States

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Publications (38)109.39 Total impact

  • G Isaac · J Yuk · D Patel · L Qiao · M Wrona · D Diehl · K Yu ·

    Planta Medica 11/2015; 81(16). DOI:10.1055/s-0035-1565314 · 2.15 Impact Factor
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    ABSTRACT: Controversy exists concerning the beneficial or harmful effects of the presence of ectopic calcification in the coronary arteries. Additionally, further elucidation of the exact pathophysiological mechanism is needed. In this study, we sought to identify metabolic markers of vascular calcification that could assist in understanding the disease, monitoring its progress and generating hypotheses describing its pathophysiology. Untargeted lipid profiling and complementary modeling strategies were employed to compare serum samples from patients with different levels of calcific coronary artery disease (CCAD) based on their calcium score (CS). Subsequently, patients were divided into three groups: no calcification (NC; CS=0; n=26), mild calcification (MC; CS:1-250; n=27) and severe (SC; CS>250; n=17). Phosphatidylcholine levels were found to be significantly altered in the disease states (p=0.001-0.04). Specifically, 18-carbon fatty acyl chain (FAC) phosphatidylcholines were detected in lower levels in the SC group, while 20:4 FAC lipid species were detected in higher concentrations. A statistical trend was observed with phosphatidylcholine lipids in the MC group, showing the same tendency as with the SC group. We also observed several sphingomyelin signals present at lower intensities in SC when compared with NC or MC groups (p=0.000001-0.01). This is the first lipid profiling study reported in CCAD. Our data demonstrate dysregulations of phosphatidylcholine lipid species, which suggest perturbations in fatty acid elongation/desaturation. The altered levels of the 18-carbon and 20:4 FAC lipids may be indicative of disturbed inflammation homeostasis. The marked sphingomyelin dysregulation in SC is consistent with profound apoptosis as a potential mechanism of CCAD. Copyright © 2015. Published by Elsevier Ireland Ltd.
    International journal of cardiology 10/2015; 197. DOI:10.1016/j.ijcard.2015.06.048 · 4.04 Impact Factor
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    ABSTRACT: Prostate cancer (PCa) is the most prevalent cancer amongst men and the second most common cause of cancer related-deaths in the USA. Prostate cancer is a heterogeneous disease ranging from indolent asymptomatic cases to very aggressive life threatening forms. The goal of this study was to identify differentially expressed metabolites and lipids in prostate cells with different tumorigenic phenotypes. We have used mass spectrometry metabolomic profiling, lipidomic profiling, bioinformatic and statistical methods to identify, quantify and characterize differentially regulated molecules in five prostate derived cell lines. We have identified potentially interesting species of different lipid subclasses including phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), glycerophosphoinositols (PIs) and other metabolites that are significantly upregulated in prostate cancer cells derived from distant metastatic sites. Transcriptomic and biochemical analysis of key enzymes that are involved in lipid metabolism demonstrate the significant upregulation of choline kinase alpha in the metastatic cells compared to the non-malignant and non-metastatic cells. This suggests that different de novo lipogenesis and other specific signal transduction pathways are activated in aggressive metastatic cells as compared to normal and non-metastatic cells.
    PLoS ONE 08/2015; 10(8):e0134206. DOI:10.1371/journal.pone.0134206 · 3.23 Impact Factor
  • D Narendrabhai Patel · L Qiao · J Yuk · G Isaac · K Yu ·

    Planta Medica 06/2015; 81(11). DOI:10.1055/s-0035-1556236 · 2.15 Impact Factor
  • K Yu · D Patel · L Qiao · G Isaac · J Traub · J Yuk ·

    Planta Medica 06/2015; 81(11). DOI:10.1055/s-0035-1556151 · 2.15 Impact Factor
  • V Shulaev · MD Jones · D Sturtevant · KD Chapman · G Isaac ·

    Planta Medica 06/2015; 81(11). DOI:10.1055/s-0035-1556131 · 2.15 Impact Factor
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    ABSTRACT: Most lipids are best characterized by their fatty acids which may differ in (a) chain length, (b) degree of unsaturation, (c) configuration and position of the double bonds, and (d) the presence of other functionalities. Thus, a fast, simple, and quantitative analytical technique to determine naturally occurring free fatty acids (FFA) in different samples is very important. Just as for saponified acylglycerols, the determination of FFA's has generally been carried out by high resolution gas chromatography (HRGC). The use of an open tubular capillary column coupled with a flame ionization or mass spectrometric detector provides for both high resolution and quantification of FFA's but only after conversion of all free fatty acids to fatty acid methyl esters (FAME) or pentafluorobenzyl esters. Unfortunately, volatilization of labile ester derivatives of mono- and poly-unsaturated FFA's can cause both thermal degradation and isomerization of the fatty acid during HRGC. The employment of a second generation instrument (here referred to as UltraHigh Performance Supercritical Fluid Chromatograph, UHPSFC) with high precision for modified flow and repeated back pressure adjustment in conjunction with sub-2μm various bonded silica particles (coupled with evaporative light scattering, ELSD, and mass spectrometric, MS, detection) for separation and detection of the following mixtures is described: (a) 31 free fatty acids, (b) isomeric FFA's, and (c) lipophilic materials in two real world fish oil samples. Limits of detection for FFA's via UHPSFC/MS and UHPSFC/ELSD versus detection of FAME's via HRGC/MS are quantitatively compared. Copyright © 2015 Elsevier B.V. All rights reserved.
    Journal of Chromatography B 05/2015; 997. DOI:10.1016/j.jchromb.2015.05.031 · 2.73 Impact Factor
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  • Planta Medica 04/2015; 81(05). DOI:10.1055/s-0035-1545136 · 2.15 Impact Factor
  • L Qiao · J Huang · D Diehl · J Yuk · M Wrona · G Isaac · K Yu ·

    Planta Medica 04/2015; 81(05). DOI:10.1055/s-0035-1545133 · 2.15 Impact Factor
  • M Maziarz · M Wrona · G Isaac · SM McCarthy ·

    Planta Medica 04/2015; 81(05). DOI:10.1055/s-0035-1545135 · 2.15 Impact Factor
  • G Isaac · J Yuk · D Patel · L Qiao · M Wrona · D Diehl · K Yu ·

    Planta Medica 04/2015; 81(05). DOI:10.1055/s-0035-1545104 · 2.15 Impact Factor
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    ABSTRACT: The goal of the study was to quantify fatty acid ethyl esters (FAEE's) produced from two large batches of tobacco seed oil after trans-esterification by heating in ethanol with sulfuric acid catalyst. Purification of the combined ethyl ester reaction products by removing as much of the color and odor from the final product as possible was achieved via conventional column chromatography with amorphous silica and tandem elution of first hexane and then ethyl alcohol as the mobile phase. Gas chromatography was used to quantify specific FAEE's in the purified material. Recovery of pure FAEE's in batch #1 was near 87%; while, recovery of FAEE's in batch #2 was greater than 89% with mass yields greater than 400 g of ethyl esters per esterifica-tion trial. The FAEE's possessed no detectable aroma and only a slight yellow color after this chromatographic treatment. Supercritical fluid chromatography with a mobile phase of methanol/acetonitrile modified carbon dioxide and an octadecyl bonded silica stationary phase were used to characterize the purity of each batch of fatty acid ethyl ester product. No free fatty acids nor glycerol-related impurities were detected in the purified trans-esterified product.This is the first report describing the optimized trans-esterification of tobacco seed oil on a relatively large scale coupled with subsequent purification and isolation of the resultant ethyl esters. [Beitr. Tabak-forsch. Int. 26 (2015) 205–213] ZUSAMMENFASSUNG
    03/2015; 26(5):205. DOI:10.1515/cttr-2015-0008
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    ABSTRACT: Metabolic profiling studies aim towards global metabolome coverage of the examined biological systems. However, wide metabolome coverage has proven difficult to achieve, mostly due to the diverse physicochemical properties of small molecules, obligating analysts to seek multi-platform and multi-method approaches. Challenges are even greater when it comes to applications on tissue samples, where tissue lysis and metabolite extraction can induce significant systematic variation. We develop a pipeline for obtaining the aqueous and organic compounds from diseased arterial tissue using two consecutive extractions and followed by a different untargeted UPLC-MS analysis method, for each extract. Methods were rationally chosen and optimized to address the different physicochemical properties of each extract: hydrophilic interaction liquid chromatography (HILIC) for the aqueous extract and reversed-phase for the organic. This pipeline can be generic for tissue analysis as demonstrated by applications on different tissue types. The experimental set-up and fast turnaround time of the two methods contributed towards obtaining highly reproducible features with exceptional chromatographic performance (CV %< 0.5%), making this pipeline suitable for metabolic profiling applications. We structurally assigned 226 metabolites from a range of chemical classes (e.g. carnitines, α-amino acids, purines, pyrimidines, phospholipids, sphingolipids, free fatty acids and glycerolipids) which were mapped to their corresponding pathways, biological functions and known disease mechanisms. The combination of the two untargeted UPLC-MS methods showed high metabolite complementarity. We demonstrate the application of this pipeline to cardiovascular disease, where we show that the analyzed diseased groups (n=120) of arterial tissue could be distinguished based on their metabolic profiles.
    Analytical Chemistry 02/2015; 87(8). DOI:10.1021/ac503775m · 5.64 Impact Factor
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    ABSTRACT: Current optimum medical treatments have had limited success in the primary prevention of cardiovascular events underscoring the need for new pharmaceutical targets and enhanced understanding of mechanistic metabolic dysregulation. Here, we use a combination of novel metabolic profiling methodologies, based on ultra performance liquid chromatography coupled to mass spectrometry (UPLC-MS), followed by chemometric modeling, data integration and pathway mapping, to create a systems level metabolic atlas of atherogenesis. We apply this workflow to compare arterial tissue incorporating plaque lesions to intimal thickening tissue (immediate pre-plaque stage). We find changes in several metabolite species consistent with well-established pathways in atherosclerosis, such as the cholesterol, purine, pyrimidine, and ceramide pathways. We then illustrate differential levels of previously unassociated lipids to atherogenesis, namely phosphatidylethanolamine-ceramides (t-test p-values: 3.8x10(-6)-9.8x10(-12)). Most importantly, these molecules appear to be interfacing two pathways recognized for their involvement in atherosclerosis: ceramide and cholesterol. Furthermore, we show that β-oxidation intermediates (i.e. acylcarnitines) manifest a pattern indicating truncation of the process and overall dysregulation of fatty acid metabolism and mitochondrial dysfunction. We develop a metabolic framework which offers the ability of mapping significant statistical associations between detected biomarkers. These dysregulated molecules and consequent pathway modulations may provide novel targets for pharmacotherapeutic intervention.
    Journal of Proteome Research 01/2015; 14(3). DOI:10.1021/pr5009898 · 4.25 Impact Factor
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    ABSTRACT: Ultrahigh performance supercritical fluid chromatography (UHPSFC) in combination with sub-2μm particles and either diode array ultraviolet (UV), evaporative light scattering, (ELSD), or mass spectrometric (MS) detection has been shown to be a valuable technique for the determination of acylglycerols in soybean, corn, sesame, and tobacco seed oils. Excellent resolution on an un-endcapped single C18 column (3.0mm×150mm) with a mobile phase gradient of acetonitrile and carbon dioxide in as little as 10min served greatly as an improvement on first generation packed column SFC instrumentation. Unlike high resolution gas chromatography and high performance liquid chromatography with mass spectrometric detection, UHPSFC/MS was determined to be a superior analytical tool for both separation and detection of mono-, di-, and tri-acylglycerols as well as free glycerol itself in biodiesel without derivatization. Baseline separation of residual tri-, di-, and mono-acylglycerols alongside glycerol at 0.05% (w/w) was easily obtained employing packed column SFC. The new analytical methodology was applied to both commercial B100 biodiesel (i.e. fatty acid methyl esters) derived from vegetable oil and to an "in-house" synthetic biodiesel (i.e. fatty acid ethyl esters) derived from tobacco seed oil and ethanol both before and after purification via column chromatography on bare silica. Copyright © 2015 Elsevier B.V. All rights reserved.
    Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 01/2015; 983-984C:94-100. DOI:10.1016/j.jchromb.2014.12.012 · 2.73 Impact Factor
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    ABSTRACT: Roman and German chamomile are widely used throughout the world. Chamomiles contain a wide variety of active constituents including sesquiterpene lactones. Various extraction techniques were performed on these two types of chamomile. A packed-column supercritical fluid chromatography-mass spectrometry method was designed for the identification of sesquiterpenes and other constituents from chamomile extracts with no derivatization step prior to analysis. Mass spectrometry detection was achieved by using electrospray ionization. All of the compounds of interest were separated within 15 min. The chamomile extracts were analyzed and compared for similarities and distinct differences. Multivariate statistical analysis including principal component analysis and orthogonal partial least squares-discriminant analysis (OPLS-DA) were used to differentiate between the chamomile samples. German chamomile samples confirmed the presence of cis- and trans-tonghaosu, chrysosplenols, apigenin diglucoside whereas Roman chamomile samples confirmed the presence of apigenin, nobilin, 1,10-epioxynobilin, and hydroxyisonobilin.
    Analytica Chimica Acta 06/2014; 847. DOI:10.1016/j.aca.2014.06.031 · 4.51 Impact Factor
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    ABSTRACT: An ultra-performance liquid chromatography method for the separation of different lipid molecular species and lipid isomers using a stationary phase incorporating charged surface hybrid technology is described. The resulting enhanced separation possibilities of the method are demonstrated using standards and human plasma extracts. Lipids are extracted from human plasma samples with the Bligh and Dyer method. Separation of lipids was achieved on a 100 x 2.1 mm ID CSH C18 column using gradient elution with aqueous/acetonitrile /isopropanol mobile phases containing 10mM ammonium formate/0.1% formic acid buffers at a flow rate of 0.4 mL/min. A UPLC run time of 20 min was routinely used and additionally a shorter method with a 10 min runtime is described. The method shows extremely stable retention times when human plasma extracts and a variety of bio-fluids or tissues are analysed (Intra-assay RSD <0.385% and <0.451% for 20 and 10 min gradient respectively (n=5), Inter-assay RSD <0.673% and <0.763% for 20 and 10 min gradient respectively (n=30). The UPLC system was coupled to a hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometer, equipped with a travelling wave ion-mobility cell. Besides demonstrating the separation for different lipids using the chromatographic method we additionally demonstrate the use of the IM-MS platform for the structural elucidation of lipids. The method can now be used to elucidate structures of a wide variety of lipids in biological samples of different matrices.
    The Journal of Lipid Research 06/2014; 55(8). DOI:10.1194/jlr.D047795 · 4.42 Impact Factor
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    ABSTRACT: Ultra high resolution SFC-MS (on sub-2μm particles) coupled to mass spectrometry has been evaluated for the metabolic profiling of rat and dog bile. The selectivity of the SFC separation differed from that seen in previous reversed-phase UPLC-MS studies on bile, with the order of elution for analytes such as e.g., the bile acids showing many differences. The chromatography system showed excellent stability, reproducibility and robustness with relative standard deviation of less than 1% for retention time obtained over the course of the analysis. SFC showed excellent chromatographic performance with chromatographic peak widths in the order of 3s at the base of the peak. The use of supercritical fluid carbon dioxide as a mobile phase solvent also reduced the overall consumption of organic solvent by a factor of 3 and also reduced the overall analysis time by a factor of 30% compared to reversed-phase gradient LC. SFC-MS appear complementary to RPLC for the metabolic profiling of complex samples such as bile.
    Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 04/2014; 966. DOI:10.1016/j.jchromb.2014.04.017 · 2.73 Impact Factor

Publication Stats

460 Citations
109.39 Total Impact Points


  • 2014-2015
    • Waters Corporation
      Милфорд, Massachusetts, United States
  • 2012
    • Purdue University
      • Department of Biological Sciences
      West Lafayette, IN, United States
  • 2011-2012
    • Pacific Northwest National Laboratory
      • Biological Sciences Division
      Ричленд, Washington, United States
  • 2007-2012
    • Kansas State University
      • Department of Biology
      Kansas, United States