Preparation of PLGA nano inner ear drug delivery system and its transport mechanism in inner ears of rats

To explore the cytotoxicity of chitosan-modified ploy lactic-co-glycolic acid (CS-PLGA) drug-loaded nanoparticle (NP) and its role in the treatment of inner ear disease, the CS-PLGA NP loaded with Nile red (CS-PLGA-NR NP) was constructed, and the safety of its transport in the inner ear was explored. First, PLGA NPs with different particle sizes were prepared and modified with CS to obtain CS-PLGA-NR NPs. After the CS-PLGA-NR NP suspension was incubated with HEI-OC1 cells, cytotoxicity and cellular uptake were detected. Subsequently, the CS-PLGA-NR NP suspension was injected into SD rat binaural tympanum, and healthy rats were taken as control. Morphological differences in the hair cells morphology and tissue morphology in rat vestibular sensory area and cochlea sensory area were measured via immunohistochemical staining and HE staining. It was found that the shape of the prepared PLGA NP was relatively round and evenly distributed, and there was no adhesion. In addition, different NPs had similar infrared spectrum characteristics. Verified by X-ray photoelectron spectroscopy (XPS), CS-PLGA-NR NPs were successfully prepared. In vitro test results showed that the viability of HEI-OC1 cells after being incubated with 1–10 mg/mL CS-PLGA-NR NP was higher than 90%, and the cell uptake also increased with the increase of concentration of CS-PLGA-NR NP (within the range of 0–150 μg/mL). In vivo results showed that after CS-PLGA-NR NP treatment, the rat hair cells in vestibule and cochlea sensory areas were arranged regularly, without deficient. In addition, the morphology and size of rat vestibule and cochlea tissue cells were normal, and no inflammatory cells such as granulocytes appeared. In summary, the prepared CS-PLGA-NR NP had low cytotoxicity and favorable inner ear tissue biocompatibility.