Gary Peltz

Stanford Medicine, Stanford, California, United States

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Publications (111)741.23 Total impact

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    ABSTRACT: Inter-species differences have limited the predictive utility of toxicology studies performed using animal species. A drug that could be a safe and effective treatment for humans could cause toxicity in animals, which could prevent it from being used in humans. We investigated whether the use of TK-NOG mice with humanized livers could prevent this unfortunate outcome (i.e. "rescue" a drug for use in humans). A high dose of furosemide is known to cause severe liver toxicity in mice, but is a safe and effective treatment for humans. We demonstrate that administration of a high dose of furosemide (200 mg/kg IP) causes extensive hepatotoxicity in control mice, but not in humanized TK-NOG mice. This inter-species difference is shown to result from a higher rate of production of the toxicity-causing metabolite by mouse liver. In this test case, humanized TK-NOG mouse studies indicate that humans could be safely treated with a high dose of furosemide. The American Society for Pharmacology and Experimental Therapeutics.
    Journal of Pharmacology and Experimental Therapeutics 05/2015; 354(1). DOI:10.1124/jpet.115.224493 · 3.86 Impact Factor
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    ABSTRACT: We know very little about the genetic factors affecting susceptibility to drug-induced central nervous system (CNS) toxicities, and this has limited our ability to optimally utilize existing drugs or to develop new drugs for CNS disorders. For example, haloperidol is a potent dopamine antagonist that is used to treat psychotic disorders, but 50% of treated patients develop characteristic extrapyramidal symptoms caused by haloperidol-induced toxicity (HIT), which limits its clinical utility. We do not have any information about the genetic factors affecting this drug-induced toxicity. HIT in humans is directly mirrored in a murine genetic model, where inbred mouse strains are differentially susceptible to HIT. Therefore, we genetically analyzed this murine model and performed a translational human genetic association study. A whole genome SNP database and computational genetic mapping were used to analyze the murine genetic model of HIT. Guided by the mouse genetic analysis, we demonstrate that genetic variation within an ABC-drug efflux transporter (Abcb5) affected susceptibility to HIT. In situ hybridization results reveal that Abcb5 is expressed in brain capillaries, and by cerebellar Purkinje cells. We also analyzed chromosome substitution strains, imaged haloperidol abundance in brain tissue sections and directly measured haloperidol (and its metabolite) levels in brain, and characterized Abcb5 knockout mice. Our results demonstrate that Abcb5 is part of the blood-brain barrier; it affects susceptibility to HIT by altering the brain concentration of haloperidol. Moreover, a genetic association study in a haloperidol-treated human cohort indicates that human ABCB5 alleles had a time-dependent effect on susceptibility to individual and combined measures of HIT. Abcb5 alleles are pharmacogenetic factors that affect susceptibility to HIT, but it is likely that additional pharmacogenetic susceptibility factors will be discovered. ABCB5 alleles alter susceptibility to HIT in mouse and humans. This discovery leads to a new model that (at least in part) explains inter-individual differences in susceptibility to a drug-induced CNS toxicity.
    PLoS Medicine 02/2015; 12(2):e1001782. DOI:10.1371/journal.pmed.1001782 · 14.00 Impact Factor
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    ABSTRACT: Due to the substantial inter-species differences in drug metabolism and drug disposition, drug-induced liver injury (DILI) in humans is often not predicted by studies performed in animal species. For example, a drug (bosentan) used to treat pulmonary artery hypertension caused unexpected cholestatic liver toxicity in humans, which was not predicted by pre-clinical toxicology studies in multiple animal species. Here, we demonstrate that TK-NOG mice with humanized livers have a humanized profile of biliary excretion of a test (cefmetazole) drug, which was shown by an in situ perfusion study to result from inter-species differences in the rate of biliary transport and in liver retention of this drug. We also found that readily detectable cholestatic liver injury develops in TK-NOG mice with humanized livers after one week of treatment with bosentan (160, 32 or 6 mg/kg/day PO), while liver toxicity did not develop in control mice after one month of treatment. The laboratory and histologic features of bosentan-induced liver toxicity in humanized mice mirrored that of human subjects. Since DILI has become a significant public health problem, drug safety could be improved if pre-clinical toxicology studies were performed using humanized TK-NOG. The American Society for Pharmacology and Experimental Therapeutics.
    Journal of Pharmacology and Experimental Therapeutics 11/2014; 352(2). DOI:10.1124/jpet.114.220798 · 3.86 Impact Factor
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    ABSTRACT: Ondansetron is the drug of choice to prevent nausea in women undergoing cesarean surgery and can be used to prevent neonatal abstinence syndrome (NAS). Pharmacokinetics of ondansetron has not been characterized in pregnant women or in newborns. A nonlinear mixed-effects modeling approach was used to analyze plasma samples obtained from 20 non-pregnant and 40 pregnant women following single administration of 4 or 8 mg ondansetron, from umbilical cord blood at delivery, and from neonates after birth. The analysis indicates that: ondansetron disposition is not affected by pregnancy (p>0.05), but influenced by dose (p<0.05), and is characterized by rapid transplacental transfer and longer elimination half-life in neonates compared to their mother. A dosing regimen for prevention of NAS was designed based on the model. The regimen involves IV administration of 4 mg to the mothers shortly before cord clamping, or oral administration of 0.07 mg/kg (or equivalently 0.04 mg/kg IV) to neonates. This article is protected by copyright. All rights reserved.
    Clinical Pharmacology &#38 Therapeutics 11/2014; 97(2). DOI:10.1002/cpt.5 · 7.39 Impact Factor
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    ABSTRACT: Background Opioids are the cornerstone of treatment for moderate to severe pain, but chronic use leads to maladaptations that include: tolerance, dependence and opioid-induced hyperalgesia (OIH). These responses limit the utility of opioids, as well as our ability to control chronic pain. Despite decades of research, we have no therapies or proven strategies to overcome this problem. However, murine haplotype based computational genetic mapping and a SNP data base generated from analysis of whole-genome sequence data (whole-genome HBCGM), provides a hypothesis-free method for discovering novel genes affecting opioid maladaptive responses. Results Whole genome-HBCGM was used to analyze phenotypic data on morphine-induced tolerance, dependence and hyperalgesia obtained from 23 inbred strains. The robustness of the genetic mapping results was analyzed using strain subsets. In addition, the results of analyzing all of the opioid-related traits together were examined. To characterize the functional role of the leading candidate gene, we analyzed transgenic animals, mRNA and protein expression in behaviorally divergent mouse strains, and immunohistochemistry in spinal cord tissue. Our mapping procedure identified the allelic pattern within the netrin-1 receptor gene (Dcc) as most robustly associated with OIH, and it was also strongly associated with the combination of the other maladaptive opioid traits analyzed. Adult mice heterozygous for the Dcc gene had significantly less tendency to develop OIH, become tolerant or show evidence of dependence after chronic exposure to morphine. The difference in opiate responses was shown not to be due to basal or morphine-stimulated differences in the level of Dcc expression in spinal cord tissue, and was not associated with nociceptive neurochemical or anatomical alterations in the spinal cord or dorsal root ganglia in adult animals. Conclusions Whole-genome HBCGM is a powerful tool for identifying genes affecting biomedical traits such as opioid maladaptations. We demonstrate that Dcc affects tolerance, dependence and OIH after chronic opioid exposure, though not through simple differences in expression in the adult spinal cord. Electronic supplementary material The online version of this article (doi: 10.1186/1471-2164-15-345) contains supplementary material, which is available to authorized users.
    BMC Genomics 05/2014; 15(1):345. DOI:10.1186/1471-2164-15-345 · 4.04 Impact Factor
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    ABSTRACT: Seven of 15 clinical trial participants treated with a nucleoside analogue (fialuridine [FIAU]) developed acute liver failure. Five treated participants died, and two required a liver transplant. Preclinical toxicology studies in mice, rats, dogs, and primates did not provide any indication that FIAU would be hepatotoxic in humans. Therefore, we investigated whether FIAU-induced liver toxicity could be detected in chimeric TK-NOG mice with humanized livers. Control and chimeric TK-NOG mice with humanized livers were treated orally with FIAU 400, 100, 25, or 2.5 mg/kg/d. The response to drug treatment was evaluated by measuring plasma lactate and liver enzymes, by assessing liver histology, and by electron microscopy. After treatment with FIAU 400 mg/kg/d for 4 d, chimeric mice developed clinical and serologic evidence of liver failure and lactic acidosis. Analysis of liver tissue revealed steatosis in regions with human, but not mouse, hepatocytes. Electron micrographs revealed lipid and mitochondrial abnormalities in the human hepatocytes in FIAU-treated chimeric mice. Dose-dependent liver toxicity was detected in chimeric mice treated with FIAU 100, 25, or 2.5 mg/kg/d for 14 d. Liver toxicity did not develop in control mice that were treated with the same FIAU doses for 14 d. In contrast, treatment with another nucleotide analogue (sofosbuvir 440 or 44 mg/kg/d po) for 14 d, which did not cause liver toxicity in human trial participants, did not cause liver toxicity in mice with humanized livers. FIAU-induced liver toxicity could be readily detected using chimeric TK-NOG mice with humanized livers, even when the mice were treated with a FIAU dose that was only 10-fold above the dose used in human participants. The clinical features, laboratory abnormalities, liver histology, and ultra-structural changes observed in FIAU-treated chimeric mice mirrored those of FIAU-treated human participants. The use of chimeric mice in preclinical toxicology studies could improve the safety of candidate medications selected for testing in human participants. Please see later in the article for the Editors' Summary.
    PLoS Medicine 04/2014; 11(4):e1001628. DOI:10.1371/journal.pmed.1001628 · 14.00 Impact Factor
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    ABSTRACT: We developed a novel method for differentiating adipocyte-derived stem cells (ASCs) into hepatocyte-like cells (iHeps). ASCs are cultured as spherical cellular aggregates and are then induced by culture in chemically defined media for a short time period to differentiate into spherical culture iHeps (SCi-Heps). SCi-Heps have many of the in vitro functional properties of mature hepatocytes, and they can stably reconstitute functioning human liver in vivo in a murine model system. Implantation studies demonstrate that SCi-Heps have a very low malignant potential. All human liver regenerative procedures, including ultrasound-guided direct liver implantation, are scalable and appropriate for human clinical use. These methods can be used to achieve the major promise of regenerative medicine. It may now be possible to regenerate human liver using autologous stem cells obtained from a readily accessible tissue.
    Cell Transplantation 10/2013; 23(12). DOI:10.3727/096368913X673432 · 3.57 Impact Factor
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    ABSTRACT: Metabolomic profiling is a promising methodology of identifying candidate biomarkers for disease detection and monitoring. Although lung cancer is among the leading causes of cancer-related mortality worldwide, the lung tumor metabolome has not been fully characterized. We utilized a targeted metabolomic approach to analyze discrete groups of related metabolites. We adopted a dansyl [5-(dimethylamino)-1-naphthalene sulfonamide] derivatization with liquid chromatography/mass spectrometry (LC/MS) to analyze changes of metabolites from paired tumor and normal lung tissues. Identification of dansylated dipeptides was confirmed with synthetic standards. A systematic analysis of retention times was required to reliably identify isobaric dipeptides. We validated our findings in a separate sample cohort. We produced a database of the LC retention times and MS/MS spectra of 361 dansyl dipeptides. Interpretation of the spectra is presented. Using this standard data, we identified a total of 279 dipeptides in lung tumor tissue. The abundance of 90 dipeptides was selectively increased in lung tumor tissue compared to normal tissue. In a second set of validation tissues, 12 dipeptides were selectively increased. A systematic evaluation of certain metabolite classes in lung tumors may identify promising disease-specific metabolites. Our database of all possible dipeptides will facilitate ongoing translational applications of metabolomic profiling as it relates to lung cancer. Copyright © 2013 John Wiley & Sons, Ltd.
    Rapid Communications in Mass Spectrometry 09/2013; 27(18):2091-8. DOI:10.1002/rcm.6656 · 2.64 Impact Factor
  • Min Ren · Peng Li · Ming Zheng · Gary Peltz · Warren J. Leonard
    Annual Joint Conference of the International-Cytokine-Society and the; 09/2013
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    ABSTRACT: CRPS is a painful, debilitating, and often-chronic condition characterized by various sensory, motor, and vascular disturbances. Despite many years of study, current treatments are limited by our understanding of the underlying mechanisms. Little is known on the molecular level concerning changes in gene expression supporting the nociceptive sensitization commonly observed in CRPS limbs, or how those changes might evolve over time. We used a well-characterized mouse tibial fracture/cast immobilization model of CRPS to study molecular, vascular and nociceptive changes. We observed that the acute (3 weeks after fracture) and chronic (7 weeks after fracture) phases of CRPS-like changes in our model were accompanied by unique alterations in spinal gene expression corresponding to distinct canonical pathways. For the acute phase, top regulated pathways were: chemokine signaling, glycogen degradation, and cAMP-mediated signaling; while for the chronic phase, the associated pathways were: coagulation system, granzyme A signaling, and aryl hydrocarbon receptor signaling. We then focused on the role of CcL2, a chemokine that we showed to be upregulated at the mRNA and protein levels in spinal cord tissue in our model. We confirmed its association with the nociceptive sensitization displayed in this model by demonstrating that the spinal but not peripheral administration of a CCR2 antagonist (RS504393) in CRPS animals could decrease mechanical allodynia. The spinal administration of CcL2 itself resulted in mechanical allodynia in control mice. Our data provide a global look at the transcriptional changes in the spinal cord that accompany the acute and chronic phases of CRPS as modeled in mice. Furthermore, it follows up on one of the top-regulated genes coding for CcL2 and validates its role in regulating nociception in the fracture/cast model of CRPS.
    Molecular Pain 08/2013; 9(1):40. DOI:10.1186/1744-8069-9-40 · 3.53 Impact Factor

Publication Stats

4k Citations
741.23 Total Impact Points

Institutions

  • 2010–2015
    • Stanford Medicine
      • Department of Anesthesia
      Stanford, California, United States
  • 2006–2014
    • Stanford University
      • Department of Anesthesia
      Palo Alto, California, United States
  • 2011
    • St. Jude Children's Research Hospital
      • Department of Infectious Diseases
      Memphis, Tennessee, United States
    • Duke University Medical Center
      • Department of Medicine
      Durham, North Carolina, United States
  • 2007
    • The University of Tokyo
      Tōkyō, Japan
  • 2005
    • Roche
      • Genetics and Genomics
      Basel, BS, Switzerland
  • 2004
    • Washington University in St. Louis
      • Department of Medicine
      San Luis, Missouri, United States
  • 2001
    • Oregon Health and Science University
      Portland, Oregon, United States
  • 1990–1992
    • Palo Alto Institute for Research and Education
      Palo Alto, California, United States