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

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.

Possible Involvement of Free Radicals in Lipopolysaccharide-Induced Labyrinthitis in the Guinea Pig: A Morphological and Functional Investigation

“…The formation of superoxide in the vestibular end organs after inoculation with LPS has been documented by the use of xanthine oxidase immunohistochemistry [11]. The present investigation, which confirmed a marked protective role of SOD against the action of LPS upon both the caloric responses and inner ear morphology, thus supports the view that reaction of NO with superoxide is indeed involved in ototoxicity.…”

“…10 9 M -1 W s -1 ) to form what is a highly oxidizing and cytotoxic molecular species, compared with NO or O 2 - [14]. In fact, formation of peroxynitrite in the LPS-inoculated vestibular organ is substantiated by the immunohistochemical study using a specific antinitrotyrosine antibody, which clearly demonstrated intense staining of the apical border of the sensory cells, of vestibular fluid transporting cells, and of ES epithelial cells [11]. Several forms of evidence revealed that nitrotyrosine was produced by peroxynitrite in a variety of proteins through a reaction catalyzed by heavy metals such as iron and copper [14].…”

“…We have demonstrated the production of NO, superoxide and peroxynitrite in the vestibular organs, together with a weakening of the caloric response, which could be prevented by L-NAME, a competitive inhibitor of NOS, SOD (an O -2 scavenger) or ebselen (a scavenger of peroxynitrite). It is therefore possible that enhanced production of both NO by NOS II and superoxide resulting in subsequent formation of peroxynitrite are probably important factors responsible for pathological damage to the vestibuli and removal of NO and/or superoxide, thus preventing the formation of peroxynitrite as well as the removal of peroxynitrite itself may be beneficial treatment to certain vestibular diseases [6,11].…”

Simultaneous Detection of Both Nitric Oxide and Reactive Oxygen Species in Guinea Pig Vestibular Sensory Cells

“…A considerable amount of evidence has recently accumulated suggesting that nitric oxide (NO) and its related reactive oxygen species (ROS) play a crucial role in certain inner ear disorders, such as acoustic trauma [1], labyrinthitis [2][3][4], aminoglycoside [5][6][7][8][9] and cisplatin ototoxicity [10], and endolymphatic hydrops [11]. The involvement of ROS and their importance in hair cell death caused by aminoglycosides is suggested by a number of studies that have demonstrated a prophylactic effect of antioxidants [6,7,12].…”

“…The other important free radical, NO, also plays an important part in inner ear toxicity. In the pathological condition, overproduction of NO, resulting in formation of peroxynitrite, can induce morphological and functional inner ear disorders [3,4,9].…”