title: Measuring In Vivo Free Radical Production by the Outer Retina.
abstract: OBJECTIVE
  Excessive and continuously produced free radicals in the outer retina are implicated in retinal aging and the pathogenesis of sight-threatening retinopathies, yet measuring outer retinal oxidative stress in vivo remains a challenge. Here, we test the hypothesis that continuously produced paramagnetic free radicals from the outer retina can be measured in vivo using high-resolution (22-μm axial resolution) 1/T1magnetic resonance imaging (MRI) without and with a confirmatory quench (quench-assisted MRI).
  
  
  METHODS
  Low-dose sodium iodate-treated and diabetic C57Bl6/J mice (and their controls), and rod-dominated (129S6) or cone-only R91W;Nrl-/- mice were studied. In dark-adapted groups, 1/T1 was mapped transretinally in vivo without or with (1) the antioxidant combination of methylene blue (MB) and α-lipoic acid (LPA), or (2) light exposure; in subgroups, retinal superoxide production was measured ex vivo (lucigenin).
  
  
  RESULTS
  In the sodium iodate model, retinal superoxide production and outer retina-specific 1/T1 values were both significantly greater than normal and corrected to baseline with MB+LPA therapy. Nondiabetic mice at two ages and 1.2-month diabetic mice (before the appearance of oxidative stress) had similar transretinal 1/T1 profiles. By 2.3 months of diabetes, only outer retinal 1/T1 values were significantly greater than normal and were corrected to baseline with MB+LPA therapy. In mice with healthy photoreceptors, a light quench caused 1/T1 of rods, but not cones, to significantly decrease from their values in the dark.
  
  
  CONCLUSIONS
  Quench-assisted MRI is a feasible method for noninvasively measuring normal and pathologic production of free radicals in photoreceptors/RPE in vivo.
authors.affiliation: Department of Anatomy and Cell Biology Wayne State University School of Medicine, Detroit, Michigan, United States 2Department of Ophthalmology, Wayne State University School of Medicine, Detroit, Michigan, United States.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Berkowitz
authors.affiliation: Department of Anatomy and Cell Biology Wayne State University School of Medicine, Detroit, Michigan, United States.
authors.forename: Bryce X
authors.initials: BX
authors.lastname: Bredell
authors.affiliation: Department of Anatomy and Cell Biology Wayne State University School of Medicine, Detroit, Michigan, United States.
authors.forename: Christopher
authors.initials: C
authors.lastname: Davis
authors.affiliation: Laboratory for Retinal Cell Biology, Department of Ophthalmology, University of Zurich, Switzerland.
authors.forename: Marijana
authors.initials: M
authors.lastname: Samardzija
authors.affiliation: Laboratory for Retinal Cell Biology, Department of Ophthalmology, University of Zurich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Grimm
authors.affiliation: Department of Anatomy and Cell Biology Wayne State University School of Medicine, Detroit, Michigan, United States.
authors.forename: Robin
authors.initials: R
authors.lastname: Roberts
mesh_terms: D000818:Animals; D003623:Dark Adaptation; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism* / Q000473:pathology; D005609:Free Radicals / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018384:Oxidative Stress; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism* / Q000473:pathology
chemical_list: D005609:Free Radicals