L-cysteine attenuates peroxynitrite-elicited cytotoxicity to spiral ganglion neurons: possible relation to hearing loss

Abstract

Objectives: The purpose of this work was to investigate whether L-cysteine was able to protect spiral ganglion neurons (SGNs) against peroxynitrite (ONOO⁻)-elicited toxicity.

Methods: The rat SGNs were isolated and cultured in this work. Cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The morphological changes were examined under inverted phase contrast microscope. Cells underwent apoptosis were determined by TdT-mediated dUTP nick end labeling (TUNEL) assay. Intracellular glutathione (GSH) content, superoxide dismutase (SOD) activity and malonaldehyde (MDA) level were detected by biochemical methods. Laser scanning confocal microscope was employed to analyze cytosolic Ca²⁺ concentration.

Results: Results showed that ONOO⁻ reduced the cell viability of SGNs in a time- and dose-dependent manner. ONOO⁻-triggered cell damage was further confirmed via apoptotic pathway rather than necrosis. Pretreatment with L-cysteine (5 mM) for 12 hours could almost completely rescue SGNs from ONOO⁻-induced damage. The decrease in intracellular GSH content and SOD activity, as well as the increase in MDA level induced by ONOO⁻ were correspondingly antagonized by the administration of L-cysteine. Furthermore, L-cysteine can significantly inhibit elevation of Ca²⁺ concentration induced by ONOO⁻.

Discussion: Our findings indicate that L-cysteine protects SGNs from ONOO⁻-induced damage via enhancing the antioxidative activity and, suppressing the lipid peroxidation as well as the release of cytosolic Ca²⁺, thereby indicating that oxidation resistance was useful to prevent audiological diseases initiated by oxidative stress.

Keywords:

• Glutathione
• Peroxynitrite
• Piral ganglion cells
• Superoxide dismutase