Lipopolysaccharide-induced expression of reactive oxygen species and peroxynitrite in the guinea pig vestibular organ

A Two-Photon Fluorescent Probe for the Visual Detection of Peroxynitrite in Living Cells and Zebrafish

Peroxynitrite (ONOO−), as an important reactive oxygen species (ROS), holds great potential to react with a variety of biologically active substances, leading to the occurrence of various diseases such as cancer and neurodegenerative diseases. In this work, we developed a novel mitochondria-localized fluorescent probe, HDBT-ONOO−, which was designed as a mitochondria-targeting two-photon fluorescence probe based on 1,8-naphthylimide fluorophore and the reactive group of 4-(bromomethyl)-benzene boronic acid pinacol ester. More importantly, the probe exhibited good biocompatibility, sensitivity, and selectivity, enabling its successful application in imaging the generation of intracellular and extracellular ONOO−. Furthermore, exogenous and endogenous ONOO− products in live zebrafish were visualized. It is greatly expected that the designed probe can serve as a useful imaging tool for clarifying the distribution and pathophysiological functions of ONOO− in cells and zebrafish.

Antioxidant Activity and Probiotic Properties of Lactic Acid Bacteria

Oxidative stress, which can cause imbalance in the body by damaging cells and tissues, arises from the immoderate production of reactive oxygen species (ROS)/reactive nitrogen species (RNS). Therefore, external supplements having antioxidant activity are required for reducing oxidative stress. In our study, we investigated DPPH and ABTS radical scavenging ability, and the inhibition effect on the nitric oxide (NO) production of 15 food-derived bacterial strains in LPS-activated RAW264.7 cells. Among these LAB strains, eight strains with an excellent inhibition effect on NO production were selected through comparisons within the same genera. Moreover, the selected strains, including Leuconostoc mesenteroides MG860, Leu. citreum MG210, Pediococcus acidilactici MG5001, P. pentosaceus MG5078, Weissella cibaria MG5090, Levilactobacillus brevis MG5306, Latilactobacillus curvatus MG5020, and Latilactobacillus sakei MG5048 diminished the inducible nitric oxide synthase (iNOS)/cyclooxygenase-2 (COX-2) expression. In addition, the stability and adhesion ability of the eight LAB strains in the gastrointestinal tract were determined. In conclusion, the selected strains have potential as new probiotics with antioxidant effects.

Response of the inner ear to lipopolysaccharide introduced directly into scala media

In an attempt to develop an animal model of immune mediated Meniere's disease, we have injected lipopolysaccharide (LPS) directly into scala media of guinea pigs and monitored functional and morphological changes over a period of 6 weeks. Depending on the concentration of LPS, changes ranged from moderate-to-severe hearing loss and endolymphatic hydrops with minimal cellular infiltrate or fibrosis, to dense cellular infiltration that filled the scalae. Interestingly, higher concentrations of LPS not only induced severe cellular infiltration, hydrops, and hearing loss, but also a substantial enlargement of the endolymphatic duct and sac. Moreover, LPS injections into perilymph failed to induce hydrops, yet still resulted in cellular infiltration and fibrosis in the cochlea. This suggests that chronic hydrops resulting from an immune challenge of the cochlea may not be due to blockage of the endolymphatic duct and sac, restricting fluid absorption. Furthermore, injecting antigen into endolymph may produce chronic immune-mediated hydrops, and provide a more promising animal model of Meniere's, although animals did not display signs of vestibular dysfunction, and the hearing loss was relatively severe.

Effects of hydrogen peroxide on vestibular hair cells in the guinea pig: importance of cell membrane impairment preceding cell death

CONCLUSION

Our findings indicate that oxidative stress induces morphological changes in vestibular hair cells and subsequently leads to cell death after 2.5 h.

OBJECTIVES

The aim of this study was to confirm the direct effects of oxidative stress on vestibular hair cells.

MATERIALS AND METHODS

Vestibular hair cells isolated from guinea pigs were loaded with 1 or 10 mM H2O2, and morphological changes were observed. In addition, in a viability/cytotoxicity assay system, the numbers of dead cells in isolated cristae ampullares were counted 1, 3, and 5 h after loading with H2O2 or artificial perilymph (control).

RESULTS

Reactive oxygen, in the form of H2O2, directly affects the cell membrane of isolated vestibular hair cells and causes swelling of the cell body, bleb formation, and shortening of the neck region. Morphological changes occur within 30 min after loading with H2O2, but a significant increase in the number of dead cells is noted only after 3 h.

Simultaneous detection of both nitric oxide and reactive oxygen species in guinea pig vestibular sensory cells

Gentamicin-induced production of reactive oxygen species (ROS) and of nitric oxide (NO) in the vestibular end organs of the guinea pig was investigated by applying two new fluorescence indicators, 4,5-diaminofluorescein diacetate for direct detection of NO and dihydrotetramethylrosamine for ROS. The vestibular sensory cells produced both NO and ROS after exposure to gentamicin. A nonspecific inhibitor of NO synthase, L-NAME, inhibited the production of NO but did not appear to affect the production of ROS following exposure to gentamicin. In contrast, a radical scavenger, D-methionine, or the neurotrophin BDNF suppressed the production of ROS, in turn stimulating NO production. These findings could indicate that both NO and ROS play an important role in aminoglycoside ototoxicity.

Allopurinol attenuates endolymphatic hydrops in the guinea pig cochlea

Based on the hypothesis that Ca(2+) overload in the scala media may produce endolymphatic hydrops and generate free oxygen radicals (FOR), allopurinol, a xanthine oxidase inhibitor and free radical scavenger, was administered to guinea pigs after the surgical obliteration of the endolymphatic duct. Allopurinol was given intraperitoneally (50 mg/kg/day) for 15 days starting 1 day prior to the surgical blockage procedure. Measurements from histological serial sections of these temporal bones showed that the total volume of the scala media was significantly reduced (p = 0.007) compared with control hydropic ears. There was an indication of reduced incidence of atrophy in sensorineural structures and stria vascularis. These findings suggest that allopurinol may attenuate the development of endolymphatic hydrops and cell damage by preventing the formation of FOR or scavenging FOR. This study may lead to a new aspect of treatment for Menière's disease.

Lipopolysaccharide-induced expression of inducible nitric oxide synthase in the guinea pig organ of Corti

The purpose of the investigation was to ascertain whether inoculation of bacterial lipopolysaccharide (LPS) into the cochlea of the guinea pig could elicit formation of inducible nitric oxide synthase (iNOS). Immunohistochemical study revealed that immunoreactivity to iNOS was seen below outer hair cells representing nerve fibers and synaptic nerve endings. iNOS-staining could also be observed in phalangeal dendrites of Deiter's cells pointing to the cuticular membrane, Hensen's cells and on stria vascularis 48 h after inoculation with LPS. Immunohistochemical investigation with a specific anti-nitrotyrosine antibody also revealed intense immunoreactivity identical to that of iNOS, suggesting formation of peroxynitrite in the organ of Corti by the reaction of NO with O(2)(-). On the basis of these findings, it can be concluded that NO together with O(2)(-), which form the more reactive peroxynitrite, are the most important pathogenic agents in LPS-induced damage of cochlea in the guinea pig.