Toxicity Evaluation of a Novel Magnetic Resonance Imaging Marker, CoCl2-N-Acetylcysteine, in Rats

Figure 1

Histopathological changes of skeletal muscle at the site of C4 (CoCl₂:NAC) injection. A volume of nine microliters of CoCl₂:NAC at various concentrations (0% CoCl2:NAC [control], 1% CoCl2:2% NAC [mid- or reference dose], and 10% CoCl2:2% NAC [high dose]) was injected intramuscular into the middle region of the left hind limb quadriceps femoris muscle of male Sprague-Dawley rats. Images of H&E stained tissue sections at 20x and 40x magnification. (a)–(c) Images show mild inflammation (arrow) in control animals (a) and acute degeneration and necrosis of myofibers with granulomatous inflammation at the site of intramuscular injection (arrows) in the mid- and high-dose groups ((b) and (c), respectively), at 48 hours after treatment. (d)–(f) Images show minimal edema with occasional degenerated myofibers (arrow) in control (d) and middose group (e) animals, which is associated with focal mild lymphohistiocytic inflammation (arrow) and myofiber regeneration in the high-dose group (f), at 28 days after treatment. (g)–(i) Images reveal presence of rare small foci of histiocytic inflammation (arrow) similar in control and treated groups of animals ((g), (h), and (i)), and areas of normally regenerated myofibers surrounded by minimal interstitial fibrosis in the mid- and high-dose groups ((h) and (i), respectively), at 63 days after treatment.

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