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In vivo bioluminescence imaging of labile iron accumulation in a murine model of Acinetobacter baumannii infection

  1. Christopher J. Changa,g,h,3
  1. aDepartment of Chemistry, University of California, Berkeley, CA 94720;
  2. bDepartment of Pathology, Microbiology, and Immunology, Vanderbilt University Medical Center, Nashville, TN 37232;
  3. cDepartment of Pharmaceutical Chemistry, University of California, San Francisco, CA 94158;
  4. dMass Spectrometry Research Center, Vanderbilt University, Nashville, TN 37232;
  5. eDepartment of Biochemistry, Vanderbilt University, Nashville, TN 37232;
  6. fDepartment of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720;
  7. gDepartment of Molecular and Cell Biology, University of California, Berkeley, CA 94720;
  8. hHoward Hughes Medical Institute, University of California, Berkeley, CA 94720
  1. Edited by Harry B. Gray, California Institute of Technology, Pasadena, CA, and approved October 26, 2017 (received for review May 26, 2017)

Significance

Iron is a required metal nutrient for life, and its altered homeostasis is associated with a number of diseases. We present a bioluminescent reporter for visualizing iron pools in living animals, where iron-dependent uncaging of d-aminoluciferin enables sensitive and selective imaging of ferrous over ferric forms of iron in luciferase-expressing cell and mouse models. Application of this technology to a model of systemic bacterial infection reveals elevation of iron in infected tissues that accompany markers for increased iron acquisition and retention. These data establish the ability to assess iron status in living animals and provide a unique platform for studying its contributions to stages of health, aging, and disease.

Abstract

Iron is an essential metal for all organisms, yet disruption of its homeostasis, particularly in labile forms that can contribute to oxidative stress, is connected to diseases ranging from infection to cancer to neurodegeneration. Iron deficiency is also among the most common nutritional deficiencies worldwide. To advance studies of iron in healthy and disease states, we now report the synthesis and characterization of iron-caged luciferin-1 (ICL-1), a bioluminescent probe that enables longitudinal monitoring of labile iron pools (LIPs) in living animals. ICL-1 utilizes a bioinspired endoperoxide trigger to release d-aminoluciferin for selective reactivity-based detection of Fe2+ with metal and oxidation state specificity. The probe can detect physiological changes in labile Fe2+ levels in live cells and mice experiencing iron deficiency or overload. Application of ICL-1 in a model of systemic bacterial infection reveals increased iron accumulation in infected tissues that accompany transcriptional changes consistent with elevations in both iron acquisition and retention. The ability to assess iron status in living animals provides a powerful technology for studying the contributions of iron metabolism to physiology and pathology.

Footnotes

  • ?1A.T.A., M.C.H., and Z.R.L. contributed equally to this work.

  • ?2Present address: Department of Chemistry, University of California, Davis, CA 95616.

  • ?3To whom correspondence may be addressed. Email: eric.skaar{at}vanderbilt.edu or chrischang{at}berkeley.edu.
  • Author contributions: A.T.A., M.C.H., Z.R.L., M.N.V.W., A.R.R., E.P.S., and C.J.C. designed research; A.T.A., M.C.H., Z.R.L., M.N.V.W., and Y.Z. performed research; B.R.B., B.S., H.M.P., A.S., and A.R.R. contributed new reagents/analytic tools; A.T.A., M.C.H., and Z.R.L. analyzed data; and A.T.A., M.C.H., Z.R.L., and C.J.C. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.danielhellerman.com/lookup/suppl/doi:10.1073/pnas.1708747114/-/DCSupplemental.

Published under the PNAS license.

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