Lipopolysaccharide-Induced Expression of Reactive Oxygen Species and Peroxynitrite in the Guinea Pig Vestibular Organ

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Abstract
The purpose of this study was to investigate the occurrence of reactive oxygen species and peroxynitrite in the vestibular organ of the guinea pig following inoculation with bacterial lipopolysaccharide (LPS). The animals were injected transtympanically with 1 mg of LPS 24 h after the intraperitoneal injection of 0.1 mg LPS. Forty-eight hours after the inoculation, varying degrees of degeneration of the vestibular end organs were observed. Immunohistochemical study revealed immunoreactivity to xanthine oxidase (which generates O–2) in the vestibular organ after inoculation with LPS. Immunohistochemical investigation with a specific antinitrotyrosine antibody also showed intense staining of sensory epithelium, fluid transporting cells and the endolymphatic sac, suggesting formation of peroxynitrite in the vestibular organ through the reaction of NO with O–2. On the basis of these data, it can be concluded that NO together with O–2, which form more reactive peroxynitrite, may be the most important pathogenic agents in LPS-induced labyrinthitis in the guinea pig.