Ethanolic extract from Hemidesmus indicus (Linn) displays otoprotectant activities on organotypic cultures without interfering on gentamicin uptake

The ethanolic extract from Hemidesmus indicus (Linn) (Apocynaceae) (Hie) was studied for its otoprotective effects in ex vivo rat organotypic model of gentamicin (GM) toxicity. In organ of Corti organotypic cultures (OC), GM can induce a fast dose-dependent apoptosis of hair cells (HC), both external and internal. We found that, after coadministration of GM and Hie to organotypic cultures, the extract was able to significantly counteract this toxic effect on HC, at the concentration of 25 and 50 μg/ml. Interestingly, at these concentrations the extract was present in the cell medium at a concentration 1.6- and 3.3-fold lower than GM, suggesting its otoprotective activity could not merely due to an aspecific inhibition of GM entry. To support this hypothesis, we evaluated the amount of GM present in organotypic cultures after the coadministration of 1.5 mg/ml GM and Hie, and found no significant reduction of GM uptake in the presence of 100 μg/ml Hie. These data suggest the otoprotective action of Hie derives from specific inhibition of the apoptotic routine induced by GM treatment.