Cytoprotective effect of taurine against hypochlorous acid toxicity to PC12 cells

Taurine has been shown to be an effective scavenger of hypochlorous acid (HOCl). The role of HOCl is well established in tissue damage associated with reperfusion injury mediated by neutrophils. The role of HOCl in CNS injury and inflammatory reactions has not been well established. Myeloperoxidase activity is present in the CNS and it has been associated with ischemic injury. The aim of the present study was to determine the cytotoxicity of HOCl in a neuronal cell line (PC12) and the ability of taurine to prevent or reverse neurotoxicity. PC12 cells were grown in 96 well plates at a plating density of approximately 100,000 cells per well. HOCl was made up fresh from NaOCl for each experiment and the concentration verified spectrophotometrically. PC12 cells were exposed to HOCl for 1 hour in phosphate-buffered saline. Taurine was added at the time of HOCl treatment and in some experiments a post-treatment with taurine was performed by adding 1 or 10 mM taurine to the culture media (RPMI 1640). The cells were allowed 24 hours to recover and viability was determined using a tetrazolium-based (MTT) assay. The first series of experiments evaluated the toxicity of HOCl and the efficacy of taurine to protect PC12 cells. HOCl at 50 microM reduced PC12 cell viability by 50% and 150 microM reduced viability to <25% of control levels. Taurine (0.5-20 mM) was tested for cytoprotection against 150 microM HOCl and PC12 cells treated with 0.5 mM taurine exhibited only a 20% reduction in viability compared to untreated controls. Taurine concentrations of 1 mM or higher provided nearly 100% protection against HOCl. A second study was performed comparing taurine to beta-alanine, glutathione and isethionic acid. HOCl (100 microM) reduced viability to 25 +/- 1% of controls and taurine, beta-alanine and glutathione at 1 mM provided nearly complete protection. In contrast, isethionic acid, which lacks an amino group, failed to provide protection. Taurine (1 or 10 mM) added after 50 microM HOCl treatment did not provide any protection and PC12 cell viability was reduced to <39% of controls. In contrast, if taurine (50 microM) was present during the HOCl treatment and 1 mM taurine was added after the treatment, PC12 cell viability was 80 +/- 5% of controls. A combination of 250 microM taurine during the HOCl treatment and 1 mM taurine post-treatment produced 100% protection. These results clearly show that taurine is an efficient scavenger of HOCl and can prevent neuronal damage caused by HOCl. Since myeloperoxidase expression in the CNS is increased by ischemia, one function of taurine released during an ischemic event may be to scavenge HOCl and provide neuroprotection.