Abstract
Although laboratory data clearly suggest a role for oxidants (dioxygen and free radicals derived from dioxygen) in the pathogenesis of many age-related and degenerative diseases (such as arthrosis and arthritis), methods to image such species in vivo are still very limited. This methodological problem limits physiopathologic studies about the role of those species in vivo, the effects of their regulation using various drugs, and the evaluation of their levels for diagnosis of degenerative diseases. In vivo electron paramagnetic resonance (EPR) imaging and spectroscopy are unique, noninvasive methods used to specifically detect and quantify paramagnetic species. However, two problems limit their application: the anatomic location of the EPR image in the animal body and the relative instability of the EPR probes. Our aim is to use EPR imaging to obtain physiologic and pathologic information on the mouse knee joint. This article reports the first in vivo EPR image of a small tissue, the mouse knee joint, with good resolution (≈ 160 μm) after intra-articular injection of a triarylmethyl radical EPR probe. It was obtained by combining EPR and x-ray micro-computed tomography for the first time and by taking into account the disappearance kinetics of the EPR probe during image acquisition to reconstruct the image. This multidisciplinary approach opens the way to high-resolution EPR imaging and local metabolism studies of radical species in vivo in different physiologic and pathologic situations.
Highlights
IntroductionLaboratory data clearly suggest a role for oxidants (dioxygen and free radicals derived from dioxygen) in the pathogenesis of many age-related and degenerative diseases (such as arthrosis and arthritis), methods to image such species in vivo are still very limited
Laboratory data clearly suggest a role for oxidants in the pathogenesis of many age-related and degenerative diseases, methods to image such species in vivo are still very limited
To minimize the number of animals used in this study, all of the electron paramagnetic resonance (EPR) experiments and parameters were optimized on an EPR tube containing two plastic balls (2 mm diameter) in a 2 mM tris-(p-carboxyltetrathiaaryl)methyl radical (TAM) solution in phosphate buffer pH 7.4, providing an adequate model (1:1 scale) of the space between the tibia and the femur of the mouse knee joint (100–200 mm, for a volume ca 8 mL)
Summary
Laboratory data clearly suggest a role for oxidants (dioxygen and free radicals derived from dioxygen) in the pathogenesis of many age-related and degenerative diseases (such as arthrosis and arthritis), methods to image such species in vivo are still very limited. This article reports the first in vivo EPR image of a small tissue, the mouse knee joint, with good resolution (< 160 mm) after intra-articular injection of a triarylmethyl radical EPR probe It was obtained by combining EPR and x-ray micro–computed tomography for the first time and by taking into account the disappearance kinetics of the EPR probe during image acquisition to reconstruct the image. I N VIVO ELECTRON PARAMAGNETIC RESONANCE (EPR) IMAGING and spectroscopy[1] emerged during the 1990s These methods are regarded as unique and noninvasive approaches for locating, characterizing, and possibly quantifying paramagnetic species such as nitric oxide,[2] dioxygen,[3,4] and free radical species derived from dioxygen, ascorbic acid, or melanin[5] in living organisms.
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