Minocycline attenuates streptomycin-induced cochlear hair cell death by inhibiting protein nitration and poly (ADP-ribose) polymerase activation

This study aimed to elucidate the protective effect of minocycline against streptomycin-induced damage of cochlear hair cells and its mechanism. Cochlear membranes were isolated from newborn Wistar rats and randomly divided into control, 500 μmol/L streptomycin, 100 μmol/L minocycline, and streptomycin and minocycline treatment groups. Hair cell survival was analyzed by detecting the expression of 3-nitrotyrosine (3-NT) in cochlear hair cells by immunofluorescence and an enzyme-linked immunosorbent assay. Expression of 3-NT and inducible nitric oxide synthase (iNOS), and poly (ADP-Ribose) polymerase (PARP) and caspase-3 activation were evaluated by western blotting. The results demonstrated hair cell loss at 24 h after streptomycin treatment. No change was found in supporting cells of the cochleae. Minocycline pretreatment improved hair cell survival and significantly reduced the expression of iNOS and 3-NT in cochlear tissues compared with the streptomycin treatment group. PARP and caspase-3 activation was increased in the streptomycin treatment group compared with the control group, and pretreatment with minocycline decreased cleaved PARP and activated caspase-3 expression. Minocycline protected cochlear hair cells from injury caused by streptomycin in vitro. The mechanism underlying the protective effect may be associated with the inhibition of excessive formation of nitric oxide, reduction of the nitration stress reaction, and inhibition of PARP and caspase-3 activation in cochlear hair cells. Combined minocycline therapy can be applied to patients requiring streptomycin treatment.