Ultrasound Microbubble-Facilitated Inner Ear Delivery of Gold Nanoparticles Involves Transient Disruption of the Tight Junction Barrier in the Round Window Membrane

Yi-Chun Lin; Cheng-Ping Shih; Hsin-Chien Chen; Ying-Liang Chou; Huey-Kang Sytwu; Mei-Cho Fang; Yuan-Yung Lin; Chao-Yin Kuo; Hsiao-Han Su; Chia-Lien Hung; Hang-Kang Chen; Chih-Hung Wang

doi:10.3389/fphar.2021.689032

Ultrasound Microbubble-Facilitated Inner Ear Delivery of Gold Nanoparticles Involves Transient Disruption of the Tight Junction Barrier in the Round Window Membrane

Front Pharmacol. 2021 Jun 28:12:689032. doi: 10.3389/fphar.2021.689032. eCollection 2021.

Authors

Yi-Chun Lin¹, Cheng-Ping Shih², Hsin-Chien Chen², Ying-Liang Chou^{2

3}, Huey-Kang Sytwu^{1

4}, Mei-Cho Fang⁵, Yuan-Yung Lin^{1

2}, Chao-Yin Kuo², Hsiao-Han Su², Chia-Lien Hung³, Hang-Kang Chen^{2

3}, Chih-Hung Wang^{1

2

3

4}

Affiliations

¹ National Defense Medical Center, Graduate Institute of Medical Sciences, Taipei, Taiwan.
² Department of Otolaryngology-Head and Neck Surgery, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan.
³ Department of Otorhinolaryngology, Taichung Armed Forces General Hospital, Taichung, Taiwan.
⁴ National Institute of Infectious Diseases and Vaccinology, National Health Research Institutes, Zhunan Town, Miaoli County, Taiwan.
⁵ Laboratory Animal Center, National Defense Medical Center, Taipei, Taiwan.

Abstract

The application of ultrasound microbubbles (USMBs) enhances the permeability of the round window membrane (RWM) and improves drug delivery to the inner ear. In this study, we investigated the efficiency of USMB-aided delivery of chitosan-coated gold nanoparticles (CS-AuNPs) and the mechanism of USMB-mediated enhancement of RMW permeability. We exposed mouse inner ears to USMBs at an intensity of 2 W/cm² and then filled the tympanic bulla with CS-AuNPs or fluorescein isothiocyanate-decorated CS-AuNPs (FITC-CS-AuNPs). The membrane uptake of FITC-CS-AuNPs and their depth of permeation into the three-layer structure of the RWM, with or without prior USMB treatment, were visualized by z-stack confocal laser scanning microscopy. Ultrastructural changes in the RWM due to USMB-mediated cavitation appeared as sunburn-like peeling and various degrees of depression in the RWM surface, with pore-like openings forming in the outer epithelium. This disruption of the outer epithelium was paralleled by a transient reduction in tight junction (TJ)-associated protein levels in the RWM and an enhanced delivery of FITC-CS-AuNPs into the RWM. Without prior USMB exposure, the treatment with CS-AuNPs also caused a noticeable reduction in TJ proteins of the RWM. Our findings indicated that the combined treatment with USMBs and CS-AuNPs represents a promising and efficient drug and gene delivery vehicle for a trans-RWM approach for inner ear therapy. The outer epithelial layer of the RWM plays a decisive role in controlling the transmembrane transport of substances such as CS-AuNPs following the administration of USMBs. Most importantly, the enhanced permeation of AuNPs involved the transient disruption of the TJ-created paracellular barrier in the outer epithelium of the RWM.

Keywords: drug delivery; gene expression; gold nanoparticle (AuNP); inner ear; permeability; round window membrane (RWM); tight junction; ultrasound microbubble (USMB).