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Sebastian Mueller, Rebecca Dollinger, Sebastian Thaler, Johanna Hofmann, Martin Spitzer, Karl Bartz-Schmidt, Peter Szurman, Kai Januschowski; Investigating Retinal Toxicity of the Potentially Neuroprotective Substance Tempol. Invest. Ophthalmol. Vis. Sci. 2013;54(15):413.
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Tempol is a low weight antioxidant that can act as a superoxide dismutase thus preventing the production of radicals via oxidation of Fe(II). Oxidative stress tributes to apoptotic cell death, a main reason for retinal ganglion cell (RGC) degeneration in glaucoma. Tempol already showed neuroprotective effects in models of brain trauma, ischemic stroke and Parkinson’s disease. This study evaluated the retinal tolerance to different concentrations of tempol in a model of isolated and perfused bovine retina by measuring an electroretinogramm (ERG) and performing an MTT stationary toxicity assay on retinal gangion cell cultures.
For functionality testing bovine retinas were prepared and perfused with an oxygen saturated standard solution and the ERG was recorded until stable b-wave amplitudes were recorded. 0.5 mM, 1 mM, 2 mM or 5 mM tempol concentrations were tested for 45 minutes. To investigate the effects on photoreceptor function 1 mM asparate was added to obtain a-waves. ERG-recovery was monitored for 110 minutes. For cytotoxicity testing concentrations of 0.1 mM, 1 mM, 2.5 mM, 5mM, 10mM, 25mM, 40mM and 50mM tempol were tested on retinal ganglion cell lines (RGC 5).
While no toxic effects for a concentration of 0.5 mM and 1 mM tempol could be detected, starting from a concentration of 2 mM tempol, statistically significant effects on the b-wave amplitude were noted (48%, p= 0.007 for 2 mM). The a-wave amplitude remained stable even at higher concentrations of 10 mM. RGC 5 displayed a higher tolerance towards tempol with toxic effects starting at 50 mM (cell viability 86.46%, p<0.05).
Although the photoreceptors seem to display a tolerance to higher concentrations of tempol, higher doses than 1mM should be avoided.
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